Degradation Mechanisms and Mitigation Strategies of Nickel-Rich NMC-Based Lithium-Ion Batteries

Mechanical Homogenization Promoting Dual-Directional Upcycling of Layered Oxide Cathodes

Upcycling is regarded as a sustainable and promising recycling solution for spent lithium-ion batteries (LIBs). However, current upcycling strategies such as converting Ni-lean to Ni-rich cathodes struggle to change the composition of the spent cathodes to meet the diverse market demands. In addition, the commonly employed molten-salts method requires tens of hours of high-temperature treatment, restricting its sustainability. Herein, this study reports an efficient, flexible dual-directional upcycling strategy to upcycle a broad family of layered oxide cathodes into fresh LiNixCoyMnzO2 (NCM) cathodes with tailored Ni-contents-either increased or decreased-in just 4 h via mechanical homogenization pretreatment. This study confirms that the bulk diffusion of transition metals (TMs) is the rate-determining step in the resynthesis process, and the mechanical homogenization can shorten the diffusion pathway of TMs, thus reducing the sintering duration effectively. The as-upcycled NCM cathodes can deliver electrochemical performance on par with commercial counterparts. Notably, a systematic technoeconomic analysis shows that upcycling spent LiCoO2 into NCM622 can yield a profit up to 35 US$/kg, 30% higher than the conventional acid-leaching resynthesis approach. This work provides an energy-saving, widely adaptable, flexible, and cost-efficient method for regenerating spent cathode materials, paving the way for the sustainable recycling of LIBs.

Operando Measurement of Transition Metal Deposition in a NMC Li-Ion Battery Using Laboratory Confocal Micro-X-ray Fluorescence Spectroscopy

The degradation of batteries has very different causes depending on the material and operation modes. However, most of these causes are associated with changes in one or more interfaces, in particular through depositions and their potential chemical changes under operating conditions. Over the last decade operando investigations have therefore become increasingly state-of-the-art, elemental analysis of full cell systems, though, is still missing due to a lack of depth resolved methods. Using laboratory confocal micro-X-ray fluorescence spectroscopy the analysis of a Li-ion battery coin cell during 10600 cycles are presented. It is shown that the confocal setup enables to differentiate between the nickel-manganese-cobalt-oxide (NMC) cathode with high levels of transition metal concentration and a possible deposition of traces of Mn, Ni, Co in the underlying layers. This allows for spatially resolved insights in operando without changing the layer stack, nor electrode area. This paper is the first to demonstrate the non-destructive and quantitative elemental analysis of battery interfaces under operating conditions. This quantitative analysis is the prerequisite for the determination of absolute transport and conversion rates, without which the transition from empirical research to a focused development of batteries will not succeed.

Structural Analysis of Deeply Charged Li(Ni0.95Co0.04Al0.01)O2 Cathode for Li-Ion Battery

LiNi0.95Co0.04Al0.01O2 (NCA95) is charged up to 4.6 V to study its structural stability at a highly delithiated state using transmission electron microscopy (TEM). The TEM analysis shows that the localized depletion of Li ions near the surface triggers the transition from the H3 phase to the H4 phase with the H4 phase with the O1 stacking appearing as a series of stacking faults even at 4.4 V. The H3→H4 transition appears irreversible and leads to the initial capacity loss. In addition, intraparticle cracks are observed when charged above 4.3 V. These intraparticle microcracks, unlike interparticle cracks that become sealed upon Li-uptake, likely remain during deintercalation, compromising the mechanical stability of the cathode and lead to fast deterioration of the cycling stability. The TEM analysis of the overcharged NCA95 cathode suggests a clear limit above which the cathode can be cycled without significant capacity loss. Introducing doping elements that promote the migration of Ni2+ ions into the Li layer would hinder the H3→H4 transition and help suppress the intraparticle cracks.

Enable Superior Performance of Solvent-Free Electrode With Ultra-High Loading Through Designed Conductive Binder

Compared to the traditional slurry-coating process, the solvent-free manufacturing process holds significant potential due to its advantages, including economic viability, thick electrodes, and avoidance of organic solvents. However, the currently dominant solvent-free process suffers from poor mechanical properties and electrochemical instability. Herein, a conductive binder (M@EP), composed of multi-walled carbon nanotubes (MWNT) and epoxy resin-based binders (EP), is designed and synthesized. The functional integration of the conductive agent and binder facilitates the formation of a 3D percolation network, significantly enhancing the conductivity of electrode. The abundant ether oxygen groups and nitrogen elements in EP promote the transmission of Li+ ions. Consequently, the dry electrodes exhibit outstanding cycling performance and rate capability. Furthermore, the combined enhancement of electronic and ionic conductivity enables the manufacturing of high-loading dry electrodes (HDEs-M@EP). The HDEs-M@EP (485 µm) have a maximum areal mass loading of 110.88 mg cm-2, and the corresponding areal capacity reaches 20.19 mAh cm-2. Finally, the structural design of M@EP facilitates an innovative method for the rapid recycling and reuse of spent batteries. It greatly simplifies the traditional procedure and enables the recycling of all types of electrode materials, offering new insights for future large-scale industrial recycling methods and green recycling systems.

Dynamic Lithium Transport Pathway via Crack Formation in Phase-Separating Battery Particles

Nanoscale cracks within battery particles are ubiquitously induced during battery cycling. Tracking the origin of nanocrack formation and its subsequent propagation remains challenging, although it is crucial for the cycle life and kinetics of batteries. Moreover, it is even more challenging to understand how such nanocracks influence lithium (de)insertion pathways and local strain fields within battery particles. In this study, we utilized operando scanning transmission X-ray microscopy on individual LiFePO4 (LFP) particles to visualize the relationship between lithium (de)insertion pathways and crack formation and propagation. We first demonstrate the generation mechanism of nanocracks occurs when the lithium insertion pathway at the edge of fresh LFP particles induces strong tensile stress in the middle of the particle. Then, we directly observe the nanocrack propagation mechanism, where the freshly exposed surface near the crack activates a fast lithium (de)insertion pathway, completely altering the internal stress fields near the nanocrack. Once the nanocrack transforms the dynamic lithium pathway and distribution, the delithiation process induces crack-opening tensile stress, while the lithiation process generates crack-closing compressive stress. 3D phase-field simulations support these observations, showing how dynamic lithium distribution shapes stress fields. Our findings reveal a recursive chemo-mechanical loop involving lithium (de)insertion pathways, internal stress fields, and crack development.

An emerging frontier of battery innovation: tackling lattice rotation in single-crystalline cathodes

Due to a lack of spatially resolved characterization studies on statistical and individual particle microstructure at multiple scales, a knowledge gap exists in understanding the mechanistic link between rapid performance failure and atomic-scale structure degradation in single-crystalline Ni-rich battery cathodes. In a recent publication in Science, Huang et al. developed a multi-crystal rocking curve technique (combining X-ray and electron microscopy to capture both statistical and individual lattice distortions), which enables multiscale observations and further proves that the accumulation of the unrecoverable lattice rotation in cathodes upon repeated cycling exacerbates mechanical failure and electrochemical decay. The elucidation of failure mechanisms in single-crystalline cathodes offers valuable insights into the development of long-lasting and high-energy-density cathodes in next-generation batteries, encompassing strategies to mitigate lattice rotation and enhance lattice structure tolerance against lattice distortion within individual particles.

Advancements in Chemical Vapor Deposited Carbon Films for Secondary Battery Applications

Carbon films, synthesized via chemical vapor deposition (CVD), have gained significant attention in secondary battery applications, where stability and capacity are required to be improved for next-generation electronic devices and electric vehicles. Beyond the inherent properties of carbon films, such as high electrical conductivity, mechanical strength, chemical stability, and flexibility, the CVD method provides a high degree of freedom in designing the carbon films in battery applications, enabling conformal coating with structure engineering for modification of its electrical and mechanical properties. In this review, the CVD-grown carbon films are highlighted in the secondary battery applications, enabling them to overcome critical issues, such as volume expansion, sluggish kinetics, and unstable interfaces. To deeply understand the CVD-grown carbon films, such as graphene and amorphous carbon, a comprehensive overview of the CVD process is also provided, focusing on growth mechanisms, control of 3D morphology, and doping techniques. In addition, a broad range of applications are introduced for carbon films in battery components, including their use in cathodes, anodes, and current collectors, as well as their potential in advanced battery systems, such as lithium-sulfur and all-solid-state batteries. This review proposes future directions for optimizing carbon films to achieve practical applications in next-generation energy storage devices.

Combinatorial ab initio calculations and core spectroscopy unravel the electronic structure of nickel cobalt manganese oxide

The rising interest in complex oxides for energy storage applications calls for the development of efficient computational schemes that enable exploring the vast configurational space of these materials to guide and complement experiments. In this work, we adopt a high-throughput screening method based on density-functional theory to investigate the electronic-structure fingerprints of a specific stoichiometry of lithiated manganese-cobalt-nickel oxide, [Formula: see text], which are relevant for the identification of the material in X-ray spectroscopy experiments. After creating the candidate structures in an automated fashion, we inspect their structural characteristics and electronic properties focusing specifically on the Ni and O contributions to the density of states. To do so, we exploit data analysis schemes that provide us with a metric to classify the considered structures according to the properties of interest, including the oxidation state. Comparison with X-ray absorption spectroscopy measurements confirms the robustness of the developed computational approach and reveals the most likely composition of the probed sample.

Kosmotropic aqueous processing solution for green lithium battery cathode manufacturing

The global pursuit of carbon neutrality is driving efforts toward environmentally friendly aqueous electrode manufacturing. However, the inherent chemical reactivity of water with cathode materials remains a challenge to achieving this goal. Here, we design a class of aqueous processing solutions based on the kosmotropic effect. Ion hydration shells in the kosmotropic solutions are restructured to form an ordered state of anion-water clusters and to stabilize local hydration structure adjacent to cathode materials. Consequently, interfacial side reactions and structural degradation of Ni-rich cathode materials are mitigated. The kosmotropic solution-processed LiNi0.8Co0.1Mn0.1O2 cathode achieve high specific and areal capacities (≥ 205 mAh g-1 and ≥ 3.7 mAh cm-2) together with stable cyclability, which are comparable to those of commercial N-methyl-2-pyrrolidone (NMP)-processed cathodes. Techno-economic analysis demonstrates that this kosmotropic solution approach reduces energy consumption in battery manufacturing by 46% compared to the NMP-based process, highlighting its practical and sustainable viability.

High Areal Loading Silicon Nanoparticle-Based Lithium-Ion Batteries

Interfacial mechanical stability between silicon (Si) and the current collector is crucial when high areal-loading of Si is demanded as intense stress develops at the interface due to its extreme volume alteration during the lithiation-delithiation process. Therefore, we propose using a thin, rough, porous, and highly conductive carbon nanotube network (CNT-N) as a buffer layer between the Si and current collector that provides abundant anchor sites for Si nanoparticles. The strong and elastic CNT-N, which is not involved directly in the lithiation process, reduces stress at interfaces between the Si and CNT-N and the CNT-N and current collector. We successfully fabricated a Si anode and NMC cathode with areal loadings of 6.13 mg cm-2 (7.65 mA h cm-2 at 1 mA cm-2) and ∼80 mg cm-2 (∼17 mA h cm-2 at 1 mA cm-2), respectively. Besides, a full cell composed of the Si anode (WSi+CNTs = 6.13 mg cm-2) and NMC cathode (WNMC = 35 mg cm-2) at 1 mA cm-2 exhibited an initial Coulombic efficiency (ICE) and capacity of 85.1% and 7.14 mA h cm-2, respectively. Despite the cell's continuous capacity fade (∼4 mA h cm-2 at 100th cycle), the bilayer design may pave the way for achieving high areal-loading Si-based anodes for high-energy-density lithium-ion batteries.

Electrochemo-Mechanical Degradation and Failure of Active Particles in High Energy Density Batteries: A Review

Failure of the active particles is inherently electrochemo-mechanics dominated. This review comprehensively examines the electrochemo-mechanical degradation and failure mechanisms of active particles in high-energy density lithium-ion batteries. The study delves into the growth of passivating layers, such as the solid electrolyte interphase (SEI), and their impact on battery performance. It highlights the role of elevated temperatures in accelerating degradation reactions, such as the dissolution of transition metals and the formation of new SEI layers, leading to capacity fade and increased internal resistance. The review also discusses the mechanical degradation of electrode materials, including the fracture of active particles and the impact of stress on electrode performance. Advanced characterization techniques, such as cryogenic scanning transmission electron microscopy and 3D tomography, are explored to provide insights into the structural and chemical evolution of battery materials. By addressing the interplay between chemical, mechanical, and thermal factors, this review aims to provide guidelines for the chemistry development, material selection, structural design as well as recycling of next-generation batteries with high safety, durability, and high energy density.

Formation Cycle Control for Enhanced Structural Stability of Ni-Rich LiNixCoyMn1-x-yO2 Cathodes

Nickel-rich NCM cathode materials promise lithium-ion batteries with a high energy density. However, an increased Ni fraction in the cathode leads to complex phase transformations with electrode-electrolyte side reactions, which cause rapid capacity fading. Here, we show that an initial formation cycle at 0.1 C with a higher cutoff voltage (≥4.35 V) increases the stability of Ni-rich NCM (LiNi0.88Co0.08Mn0.04O2) particles during cycling at 1 C. We unveil that the formation of intragranular nanovoids is directly associated with the initial formation cycle at a lower charging cutoff voltage when oxygen vacancies are introduced at the Ni-rich NCM particle surface, due to irreversible electrolyte decomposition at the cathode-electrolyte interface. Nanovoid evolution of the Ni-rich NCM particles after 50 cycles increases the NiO-like rock salt phase; it results in intragranular cracks, which cause structural instability via heterogeneous phase distribution. This work demonstrates the importance of controlling Ni-rich NCM surface chemistry from the initial formation cycle to achieve better cycling stability.

Integrated Oxygen-Constraining Strategy for Ni-Rich Layered Oxide Cathodes

Surface engineering is sought to stabilize nickel-rich layered oxide cathodes in high-energy-density lithium-ion batteries, which suffer from severe surface oxygen loss and rapid structure degradation, especially during deep delithiation at high voltages or high temperatures. Here, we propose a well-designed oxygen-constraining strategy to address the crisis of oxygen evolution. By integrating a La, Fe gradient diffusion layer and a LaFeO3 coating into the Ni-rich layered particles, along with incorporating an antioxidant binder into the electrodes, three progressive lines of defense are constructed: immobilizing the lattice oxygen at the subsurface, blocking the released oxygen at the interface, and capturing the residual singlet oxygen on the external surface. As a result, effective surface passivation, mitigated bulk and surface degradation, suppressed side reactions, and enhanced electrochemical performance are achieved, far beyond conventional single surface modification. The Ni-rich layered oxide cathodes with integrated oxygen-constraining modifications demonstrate impressive cycling stability in both half-cells and full cells, achieving stable long-term cycling even at a high cutoff voltage of 4.7 V and a high temperature of 45 °C. This work provides a multilevel oxygen-constraining strategy, which can be extended to various layered oxide cathodes involving oxygen release challenges, providing an effective path for the development of high-energy-density lithium-ion batteries.

Effects of catholyte aging on high-nickel NMC cathodes in sulfide all-solid-state batteries

Sulfide solid-state electrolytes (SSEs) in all-solid-state batteries (SSBs) are recognized for their high ionic conductivity and inherent safety. The LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode offers a high thermodynamic potential of approximately 3.8 V vs. Li/Li+ and a theoretical specific capacity of 200 mA h g-1. However, the practical utilization of NMC811 in sulfide SSBs faces significant interfacial challenges. The oxidation instability of sulfide solid electrolytes against NMC811 and the formation of the cathode electrolyte interphase (CEI) during cycling lead to degradation and reduced cell performance. Volumetric changes in NMC during lithiation and de-lithiation can also cause detachment from sulfide electrolytes or internal particle cracking. Despite extensive galvanostatic cycling studies to address the issues, the calendar life of sulfide SSBs remains poorly understood. Here, we systematically studied the effects of four different catholytes on the calendar aging of LiNbO3 (LNO)-coated NMC811, including Li6PS5Cl (LPSCl), Li3InCl6-Li6PS5Cl (LIC-LPSCl), Li3YCl6-Li6PS5Cl (LYC-LPSCl), and Li10GeP2S12 (LGPS). Our results indicate that LPSCl provides optimal capacity retention when stored at high state-of-charge (SOC) at room temperature, but the LIC-LPSCl cathode shows significant capacity degradation and chemical incompatibility. We also established an effective electrochemical calendar aging testing protocol to simulate daily usage, enabling quick inference of the calendar life of SSBs. This new testing approach accelerates materials selection strategies for high-nickel NMC composite cathodes in sulfide SSBs.

Bio-Inspired Core-Shell Structured Electrode Particles with Protective Mechanisms for Lithium-Ion Batteries

Lithium-ion batteries (LIBs), as predominant energy storage devices, are applied to electric vehicles, which is an effective way to achieve carbon neutrality. However, the major obstructions to their applications are two dilemmas: enhanced cyclic life and thermal stability. Taking advantage of bio-inspired core-shell structures to optimize the self-protective mechanisms of the mercantile electrode particles, LIBs can improve electrochemical performance and thermal stability simultaneously. The favorable core-shell structures suppress volume expansion to stabilize electrode-electrolyte interfaces (EEIs), mitigate direct contact between the electrode material and electrolyte, and promote electrical connectivity. They possess wide operating temperatures, high-voltage resistance, and inhibit short circuits. During cycling, the cathode and anode generate a cathode-electrolyte interface (CEI) and a solid-electrolyte interface (SEI), respectively. Applying multitudinous coating approaches can generate multifarious bio-inspired core-shell structured electrode particles, which is helpful for the generation of the EEIs, self-healing the surface cracks, and maintaining the structural integrities of electrodes. The protected shells act as barriers to minimize unwanted side reactions and enhance thermal stability. These in-depth understandings of the bio-inspired evolution for electrode particles can inspire further enhancements in LIB lifetime and thermal safety, especially for bio-inspired core-shell structured electrodes possessing high-performance protective mechanisms.

Revealing the impact of CO2 exposure during calcination on the physicochemical and electrochemical properties of LiNi0.8Co0.1Mn0.1O2

The synthesis atmosphere plays a fundamental role in determining the physicochemical properties and electrochemical performance of NMC811 cathode materials used in lithium-ion batteries. This study investigates the effect of carbonate impurities generated during synthesis by comparing three distinct samples: NMC811 calcined in ambient air, NMC811 calcined in synthetic air to mitigate carbonate formation, and NMC811 initially calcined in ambient air followed by annealing in synthetic air to eliminate carbonate species. Physicochemical characterization through XRD, SEM, FTIR, and TGA techniques revealed noticeable differences in the structural and chemical properties among the samples. Electrochemical assessments conducted via coin-cell testing demonstrate superior performance for materials synthesized in synthetic air, exhibiting an enhanced discharge capacity of 145.4 ± 4.8 mA h g-1 compared to materials synthesized in normal air (109.4 ± 4.3 mA h g-1) at C/10. More importantly, sample annealing in synthetic air after air calcination partially recovers the electrochemical performance of the cathode (142.1 ± 4.6 mA h g-1 at C/10) and this is related to the elimination of carbonate species from the ceramic powder. These findings highlight the importance of controlling synthesis conditions, particularly the atmosphere, to tailor the properties of NMC811 cathode materials for optimal lithium-ion battery performance.

A Case Study of an Energy Barrier in Li-Ion Battery Cathode Material Using DFT and Post-HF Approaches

With the ever-increasing interest toward energy storage materials, an accurate understanding of the underlying physicochemical processes becomes mandatory for enabling accurate and predictive simulations. In this study, we apply multilevel quantum chemical calculations on a benchmark material commonly adopted as a cathode in Lithium batteries, Li0.5Co0.5+3Ni0.5+4O2. We estimate the Lithium hopping barrier, a key quantity for the estimate of Li diffusion coefficient, at different levels: Hartree-Fock (HF), density functional theory (DFT), periodic local Møller-Plesset perturbation theory of second order, complemented with a coupled cluster correction evaluated using an embedded-fragment approach. The post-HF methods were used here not only for benchmarking the key quantities themselves but also for assessing the accuracy of different functionals and probing the influence of the long-range and static correlation. For the given system and quantity in question, we observe that obtained results do not significantly vary across different DFT functionals or post-HF methods, which is rather uncommon. Such an agreement between the employed methods suggests that static correlation, even if prominent in this system, cancels out in the studied energy differences. In fact, the values of the T1 diagnostics, which test the reliability of the single-reference description, do vary from one fragment to another. But for certain fragments they are fairly small and of similar magnitude, indicating the applicability of such fragments for the correction. Our best estimate of the reaction barrier is about 0.85 eV.

Cracking Mechanism and Inhibition Strategies of Polycrystalline NCM Electrode Particles

Developing a high-energy-density cathode material (LiNi1-x-yCoxMnyO2, NCM) for lithium-ion batteries is crucial to the electric vehicle and energy storage industries. However, the continuous insertion/extraction of Li+ generates diffusion-induced stress, causing NCM particles to crack or even pulverize, leading to battery capacity loss and limiting its wider commercial application. Current experimental studies are primarily postmortem examinations, and it is difficult to capture the particle cracking evolution. Simulation studies frequently ignore or simplify anisotropic volume contraction, demonstrating an insufficient understanding of the cracking mechanism of NCM polycrystalline particles, and cracking prevention strategies still need improvement. Therefore, we develop an anisotropic polycrystalline fracture phase-field model (AP-FPFM) that focuses on the anisotropic volume contraction of primary particles and precisely generates grain boundary distribution, coupling with Li+ diffusion, mechanical stress, and particle cracking. We employ AP-FPFM to demonstrate the behavior and mechanism of NCM polycrystalline particle cracking and illustrate the necessity and importance of anisotropic volume contraction to understand particle cracking. Furthermore, we explore the effects of average primary particle size, secondary particle size, and core-shell structure modulation on crack initiation and propagation and propose strategies to inhibit or migrate NCM polycrystalline particle cracking. This work provides theoretical support for revealing the cracking mechanism of anisotropic polycrystalline NCM particles and supplying optimization strategies to suppress particle cracking and improve the mechanical stability.

Electrolyte-Enabled High-Voltage Operation of a Low-Nickel, Low-Cobalt Layered Oxide Cathode for High Energy Density Lithium-Ion Batteries

The lithium-ion battery industry acknowledges the need to reduce expensive metals, such as cobalt and nickel, due to supply chain challenges. However, doing so can drastically reduce the overall battery energy density, attenuating the driving range for electric vehicles. Cycling to higher voltages can increase the capacity and energy density but will consequently exacerbate cell degradation due to the instability at high voltages. Herein, an advanced localized high-concentration electrolyte (LHCE) is utilized to enable long-term cycling of a low-Ni, low-Co layered oxide cathode LiNi0.60Mn0.31Co0.07Al0.02O2 (NMCA) in full cells with graphite or graphite-silicon anodes at 4.5 V (≈4.6 vs Li+/Li). NMCA cells with the LHCE deliver a high initial capacity of 194 mA h g-1 at C/10 rate along with 73% capacity retention after 400 cycles compared to 49% retention in a baseline carbonate electrolyte. This is facilitated by reduced impedance growth, active material loss, and gas evolution with the NMCA cathode. These improvements are attributed to the formation of robust, inorganic-rich interphase layers on both the cathode and anode throughout cycling, which are induced by a favorable salt decomposition in the LHCE. This study demonstrates the efficacy of electrolytes toward facilitating the operation of high-energy-density, long-life, and cost-effective cathodes.

Adsorptive Shield Derived Cathode Electrolyte Interphase Formation with Impregnation on LiNi0.8Mn0.1Co0.1O2 Cathode: A Mechanism-Guiding-Experiment Study

Lithium difluoro(oxalate) borate (LiDFOB) contributes actively to cathode-electrolyte interface (CEI) formation, particularly safeguarding high-voltage cathode materials. However, LiNixCozMnyO2-based batteries benefit from the LiDFOB and its derived CEI only with appropriate electrolyte design while a comprehensive understanding of the underlying interfacial mechanisms remains limited, which makes the rational design challenging. By performing ab initio calculations, the CEI evolution on the LiNi0.8Co0.1Mn0.1O2 has been investigated. The findings demonstrate that LiDFOB readily adheres to the cathode via semidissociative configuration, which elevates the Li deintercalation voltage and remains stable in solvent. Electrochemical processes are responsible for the subsequent cleavage of B-F and B-O bonds, while the B-F bond cleavage leading to LiF formation is dominant in the presence of adequate Li+ with a substantial Li intercalation energy. Thus, impregnation is established as an effective method to regulate the conversion channel for efficient CEI formation, which not only safeguards the cathode's structure but also counters electrolyte decomposition. Consequently, in comparison to utilizing LiDFOB as an electrolyte additive, employing LiDFOB impregnation in the NCM811/Li cell yields significantly improved cycling stability for over 2000 h.

Nonsolvating Fluoroaromatic Cosolvent Enabled Long-Term Cycling of High-Voltage Lithium-Ion Batteries with Organosulfur Electrolytes

The structure-activity relationships of nonsolvating cosolvents for organosulfur-based electrolyte systems were revealed. The performance of nonsolvating dilutant fluorobenzene (FB) was compared to various fluorinated ether dilutants in high-voltage electrolytes containing a concentration of 1.2 M LiPF6 dissolved in fluoroethylene carbonate (FEC), ethyl methyl sulfone (EMS), and the dilutant. In a high-voltage and high-loading LiNi0.8Mn0.1Co0.1O2 (NMC811) full cell configuration, the organosulfur-based electrolyte containing FB dilutant enabled superior electrochemical performance compared to the electrolytes using other nonsolvating fluorinated ether formulations. Moreover, the FB-containing electrolyte exhibited the highest ionic conductivity and lowest viscosity among all organosulfur-based electrolytes containing nonsolvating dilutant. These improvements are attributed to the enhanced physical properties of electrolyte and lithium-ion mobility. Furthermore, by employing first-principles simulations, the observed suppression of side reactions at high voltage is linked to FB's lower reactivity toward singlet dioxygen, which is likely produced at the NMC interface. Overall, FB is considered an excellent diluent that does not impede cell operation by mass decomposition at the cathode.

Construction of Hierarchical Conductive Networks for LiNi0.8Mn0.1Co0.1O2 Cathode toward Stable Cycling at High Areal Mass Loadings

Realizing high-performance thick electrodes is considered as a practical strategy to promote the energy density of lithium-ion batteries. However, establishing effective transport pathways for both lithium-ions and electrons in a thick electrode is very challenging. This study develops a hierarchical conductive network structure for constructing high-performance NMC811 (LiNi0.8Mn0.1Co0.1O2) cathode toward stable cycling at high areal mass loadings. The hierarchical conductive networks are composed of a Li+/e- mixed conducting interface (lithium polyacrylate/hydroxyl-functionalized multiwalled carbon nanotubes) on NMC811 particles, and a segregated network of single-walled carbon nanotubes in the electrode, without any additional binders or carbon black. Such strategy endows the NMC811 cathode (up to 250 µm and 50 mg cm-2) with low porosity/tortuosity, ultrahigh Li+/e- conductivities and excellent mechanical property at low carbon nanotube content (1.8 wt%). It significantly improves the electrochemical reaction homogeneity along the electrode depth, meanwhile effectively inhibits the side reactions at the electrode/electrolyte interface and cracks in the NMC particles during cycling. This work emphasizes the crucial role of the electronic/ionic cooperative transportation in the performance deterioration of thick cathodes, and provide guidance for architecture optimization and performance improvement of thick electrodes toward practical applications, not just for the NMC811 cathode.

Path ahead: Tackling the Challenge of Computationally Estimating Lithium Diffusion in Cathode Materials

In the roadmap toward designing new and improved materials for Lithium ion batteries, the ability to estimate the diffusion coefficient of Li atoms in electrodes, and eventually solid-state electrolytes, is key. Nevertheless, as of today, accurate prediction through computational tools remains challenging. Its experimental measurement does not appear to be much easier. In this work, we devise a computational protocol for the determination of the Li-migration energy barrier and diffusion coefficient, focusing on a common cathode material such as LiNiO2, which represents a prototype of the widely adopted NMC (LiNi1-x-y Mn x Co y O2) class of materials. Different methodologies are exploited, combining ab initio metadynamics, path sampling, and density functional theory. Furthermore, we propose a novel, fast, and simple 1D approximation for the estimation of the effective frequency. The outlined computational protocol aims to be generally applicable to Lithium diffusion in other materials and components for batteries, including anodes and solid electrolytes.

Vibrationally-resolved RIXS reveals OH-group formation in oxygen redox active Li-ion battery cathodes

Vibrationally-resolved resonant inelastic X-ray scattering (VR-RIXS) at the O K-edge is emerging as a powerful tool for identifying embedded molecules in lithium-ion battery cathodes. Here, we investigate two known oxygen redox-active cathode materials: the commercial LixNi0.90Co0.05Al0.05O2 (NCA) used in electric vehicles and the high-capacity cathode material Li1.2Ni0.13Co0.13Mn0.54O2 (LRNMC) for next-generation Li-ion batteries. We report the detection of a novel vibrational RIXS signature for Li-ion battery cathodes appearing in the O K pre-peak above 533 eV that we attribute to OH-groups. We discuss likely locations and pathways for OH-group formation and accumulation throughout the active cathode material. Initial-cycle behaviour for LRNMC shows that OH-signal strength correlates with the cathodes state of charge, though reversibility is incomplete. The OH-group RIXS signal strength in long-term cycled NCA is retained. Thus, VR-RIXS offers a path for gaining new insights to oxygen reactions in battery materials.

Advancing Lithium-Ion Batteries' Electrochemical Performance: Ultrathin Alumina Coating on Li(Ni0.8Co0.1Mn0.1)O2 Cathode Materials

Ni-rich Li(NixCoyMnz)O2 (x ≥ 0.8)-layered oxide materials are highly promising as cathode materials for high-energy-density lithium-ion batteries in electric and hybrid vehicles. However, their tendency to undergo side reactions with electrolytes and their structural instability during cyclic lithiation/delithiation impairs their electrochemical cycling performance, posing challenges for large-scale applications. This paper explores the application of an Al2O3 coating using an atomic layer deposition (ALD) system on Ni-enriched Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) cathode material. Characterization techniques, including X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, were used to assess the impact of alumina coating on the morphology and crystal structure of NCM811. The results confirmed that an ultrathin Al2O3 coating was achieved without altering the microstructure and lattice structure of NCM811. The alumina-coated NCM811 exhibited improved cycling stability and capacity retention in the voltage range of 2.8-4.5 V at a 1 C rate. Specifically, the capacity retention of the modified NCM811 was 5%, 9.11%, and 11.28% higher than the pristine material at operating voltages of 4.3, 4.4, and 4.5 V, respectively. This enhanced performance is attributed to reduced electrode-electrolyte interaction, leading to fewer side reactions and improved structural stability. Thus, NCM811@Al2O3 with this coating process emerges as a highly attractive candidate for high-capacity lithium-ion battery cathode materials.

Comprehensive Study of Ti and Ta Co-Doping in Ni-Rich Cathode Material LiNi0.8Mn0.1Co0.1O2 Towards Improving the Electrochemical Performance

Layered Ni-rich oxides (LiNi1-x-yCoxMnyO2) cathode materials are of current interest in high-energy-demanding applications, such as electric vehicles because of high discharge capacity and high intercalation potential. Here, the effect of co-doping a small amount of Ti and Ta on the crystal structure, morphology, and electrochemical properties of high Ni-rich cathode material LiNi0.8Mn0.1Co0.1-x-yTixTayO2 (0.0≤x+y≤0.2) was systematically investigated. This work demonstrates that an optimum level of Ti and Ta doping is beneficial towards enhancing electrochemical performance. The optimal Ti4+ and Ta5+ co-doped cathode LiNi0.8Mn0.1Co0.09Ti0.005Ta0.005O2 exhibits a superior initial discharge capacity of 161.1 mAh g-1 at 1 C, and excellent capacity retention of 87.1 % after 250 cycles, compared to the pristine sample that exhibits only 59.8 % capacity retention. Moreover, the lithium-ion diffusion coefficients for the co-doped cathode after the 3rd and 50th cycles are 9.9×10-10 cm2 s-1 and 9.3×10-10 cm2 s-1 respectively, which is higher than that of the pristine cathode (3.3×10-10 cm2 s-1 and 2.5×10-10 cm2 s-1 respectively). Based on these studies, we conclude that Ti and Ta co-doping enhances structural stability by mitigating irreversible phase transformation, improving Li-ion kinetics by expanding interlayer spacing, and nanosizing primary particles, thereby stabilizing high-nickel cathode materials and significantly enhancing cyclability.

Bio-Inspired Electrodes with Rational Spatiotemporal Management for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are currently the predominant energy storage power source. However, the urgent issues of enhancing electrochemical performance, prolonging lifetime, preventing thermal runaway-caused fires, and intelligent application are obstacles to their applications. Herein, bio-inspired electrodes owning spatiotemporal management of self-healing, fast ion transport, fire-extinguishing, thermoresponsive switching, recycling, and flexibility are overviewed comprehensively, showing great promising potentials in practical application due to the significantly enhanced durability and thermal safety of LIBs. Taking advantage of the self-healing core-shell structures, binders, capsules, or liquid metal alloys, these electrodes can maintain the mechanical integrity during the lithiation-delithiation cycling. After the incorporation of fire-extinguishing binders, current collectors, or capsules, flame retardants can be released spatiotemporally during thermal runaway to ensure safety. Thermoresponsive switching electrodes are also constructed though adding thermally responsive components, which can rapidly switch LIB off under abnormal conditions and resume their functions quickly when normal operating conditions return. Finally, the challenges of bio-inspired electrode designs are presented to optimize the spatiotemporal management of LIBs. It is anticipated that the proposed electrodes with spatiotemporal management will not only promote industrial application, but also strengthen the fundamental research of bionics in energy storage.

Strong Oxidizing Molten Salts for Strengthening Structural Restoration Enabling Direct Regeneration of Spent Layered Cathode

As a mainstream technology for recycling spent lithium-ion batteries, direct regeneration is rapidly developed due to its high efficiency and green characteristics. However, efficient reuse of spent LiNixCoyMn1- x - yO2 cathode is still a significant challenge, as the rock salt/spinel phase on the surface hinders the Li replenishment and phase transformation to the layered structure. In this work, the fundamental understanding of the repair mechanism is confirmed that the oxidizing atmosphere is the crucial factor that can greatly improve the rate and degree of phase restoration. Particularly, a ternary-component molten salt system (LiOH-Li2CO3-LiNO3) is proposed for direct regeneration of LiNi0.5Co0.2Mn0.3O2 (NCM523), which can in situ generate the strong oxidizing intermediate of superoxide radicals. Additionally, it shows a liquid-like reaction environment at a lower temperature to acceclerate the transport rate of superoxide-ions. Therefore, the synergistic effect of LiOH-Li2CO3-LiNO3 system can strengthen the full restoration of rock salt/spinel phases and achieve the complete Li-supplement. As anticipated, the regenerated NCM523 delivers a high cycling stability with a retention of 91.7% after 100 cycles, which is even competitive with the commercial NCM523. This strategy provides a facile approach for the complete recovery of layer structure cathode, demonstrating a unique perspective for the direct regeneration of spent lithium-ion batteries.

Stabilizing High-Voltage Performance of Nickel-Rich Cathodes via Facile Solvothermally Synthesized Niobium-Doped Strontium Titanate

Ni-rich layered ternary cathodes are promising candidates thanks to their low toxic Co-content and high energy density (∼800 Wh/kg). However, a critical challenge in developing Ni-rich cathodes is to improve cyclic stability, especially under high voltage (>4.3 V), which directly affects the performance and lifespan of the battery. In this study, niobium-doped strontium titanate (Nb-STO) is successfully synthesized via a facile solvothermal method and used as a surface modification layer onto the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode. The results exhibited that the Nb-STO modification significantly improved the cycling stability of the cathode material even under high-voltage (4.5 V) operational conditions. In particular, the best sample in our work could provide a high discharge capacity of ∼190 mAh/g after 100 cycles under 1 C with capacity retention over 84% in the voltage range of 3.0-4.5 V, superior to the pristine NCM811 (∼61%) and pure STO modified STO-811-600 (∼76%) samples under the same conditions. The improved electrochemical performance and stability of NCM811 under high voltage should be attributed to not only preventing the dissolution of the transition metals, further reducing the electrolyte's degradation by the end of charge, but also alleviating the internal resistance growth from uncontrollable cathode-electrolyte interface (CEI) evolution. These findings suggest that the as-synthesized STO with an optimized Nb-doping ratio could be a promising candidate for stabilizing Ni-rich cathode materials to facilitate the widespread commercialization of Ni-rich cathodes in modern LIBs.

Microstructures of layered Ni-rich cathodes for lithium-ion batteries

Millions of electric vehicles (EVs) on the road are powered by lithium-ion batteries (LIBs) based on nickel-rich layered oxide (NRLO) cathodes, and they suffer from a limited driving range and safety concerns. Increasing the Ni content is a key way to boost the energy densities of LIBs and alleviate the EV range anxiety, which are, however, compromised by the rapid performance fading. One unique challenge lies in the worsening of the microstructural stability with a rising Ni-content in the cathode. In this review, we focus on the latest advances in the understanding of NLRO microstructures, particularly the microstructural degradation mechanisms, state-of-the-art stabilization strategies, and advanced characterization methods. We first elaborate on the fundamental mechanisms underlying the microstructural failures of NRLOs, including anisotropic lattice evolution, microcracking, and surface degradation, as a result of which other degradation processes, such as electrolyte decomposition and transition metal dissolution, can be severely aggravated. Afterwards, we discuss representative stabilization strategies, including the surface treatment and construction of radial concentration gradients in polycrystalline secondary particles, the fabrication of rod-shaped primary particles, and the development of single-crystal NRLO cathodes. We then introduce emerging microstructural characterization techniques, especially for identification of the particle orientation, dynamic changes, and elemental distributions in NRLO microstructures. Finally, we provide perspectives on the remaining challenges and opportunities for the development of stable NRLO cathodes for the zero-carbon future.

Hybrid Density Functional Theory Comparison of Oxygen Release and Solvent Decomposition Kinetics on LixNiO2 Surfaces

High-nickel-content layered oxides are among the most promising electric vehicle battery cathode materials. However, their interfacial reactivity with electrolytes and tendency toward oxygen release (possibly yielding reactive 1O2) remain degradation concerns. Elucidating the most relevant (i.e., fastest) interfacial degradation mechanism will facilitate future mitigation strategies. We apply screened hybrid density functional (HSE06) calculations to compare the reaction kinetics of LixNiO2 surfaces with ethylene carbonate (EC) with those of O2 release. On both the (001) and (104) facets, EC oxidative decomposition exhibits lower activation energies than O2 release. Our calculations, coupled with previously computed liquid-phase reaction rates of 1O2 with EC, strongly question the role of "reactive 1O2" species in electrolyte oxidative degradation. The possible role of other oxygen species is discussed. To deal with the challenges of modeling LixNiO2 surface reactivity, we emphasize a "local structure" approach instead of pursuing the global energy minimum.

Revealing the Nanoscopic Corrosive Degradation Mechanism of Nickel-Rich Layered Oxide Cathodes at Low State-of-Charge Levels: Corrosion Cracking and Pitting

Ni-rich layered oxides have received significant attention as promising cathode materials for Li-ion batteries due to their high reversible capacity. However, intergranular and intragranular cracks form at high state-of-charge (SOC) levels exceeding 4.2 V (vs. Li/Li+), representing a prominent failure mechanism of Ni-rich layered oxides. The nanoscale crack formation at high SOC levels is attributed to a significant volume change resulting from a phase transition between the H2 and H3 phases. Herein, in contrast to the electrochemical crack formation at high SOC levels, another mechanism of chemical crack and pit formation on a nanoscale is directly evidenced in fully lithiated Ni-rich layered oxides (low SOC levels). This mechanism is associated with intergranular stress corrosion cracking, driven by chemical corrosion at elevated temperatures. The nanoscopic chemical corrosion behavior of Ni-rich layered oxides during aging at elevated temperatures is investigated using high-resolution transmission electron microscopy, revealing that microcracks can develop through two distinct mechanisms: electrochemical cycling and chemical corrosion. Notably, chemical corrosion cracks can occur even in a fully discharged state (low SOC levels), whereas electrochemical cracks are observed only at high SOC levels. This finding provides a comprehensive understanding of the complex failure mechanisms of Ni-rich layered oxides and provides an opportunity to improve their electrochemical performance.

The Influence of Cathode Degradation Products on the Anode Interface in Lithium-Ion Batteries

Degradation of cathode materials in lithium-ion batteries results in the presence of transition metal ions in the electrolyte, and these ions are known to play a major role in capacity fade and cell failure. Yet, while it is known that transition metal ions migrate from the metal oxide cathode and deposit on the graphite anode, their specific influence on anode reactions and structures, such as the solid electrolyte interphase (SEI), is still quite poorly understood due to the complexity in studying this interface in operational cells. In this work we combine operando electrochemical atomic force microscopy (EC-AFM), electrochemical quartz crystal microbalance (EQCM), and electrochemical impedance spectroscopy (EIS) measurements to probe the influence of a range of transition metal ions on the morphological, mechanical, chemical, and electrical properties of the SEI. By adding representative concentrations of Ni2+, Mn2+, and Co2+ ions into a commercially relevant battery electrolyte, the impacts of each on the formation and stability of the anode interface layer is revealed; all are shown to pose a threat to battery performance and stability. Mn2+, in particular, is shown to induce a thick, soft, and unstable SEI layer, which is known to cause severe degradation of batteries, while Co2+ and Ni2+ significantly impact interfacial conductivity. When transition metal ions are mixed, SEI degradation is amplified, suggesting a synergistic effect on the cell stability. Hence, by uncovering the roles these cathode degradation products play in operational batteries, we have provided a foundation upon which strategies to mitigate or eliminate these degradation products can be developed.

Why the Synthesis Affects Performance of Layered Transition Metal Oxide Cathode Materials for Li-Ion Batteries

The limited cyclability of high-specific-energy layered transition metal oxide (LiTMO2) cathode materials poses a significant challenge to the industrialization of batteries incorporating these materials. This limitation can be attributed to various factors, with the intrinsic behavior of the crystal structure during the cycle process being a key contributor. These factors include phase transition induced cracks, reduced Li active sites due to Li/Ni mixing, and slower Li+ migration. In addition, the presence of synthesis-induced heterogeneous phases and lattice defects cannot be disregarded as they also contribute to the degradation in performance. Therefore, gaining a profound understanding of the intricate relationship among material synthesis, structure, and performance is imperative for the development of LiTMO2. This paper highlights the pivotal role of structural play in LiTMO2 materials and provides a comprehensive overview of how various control factors influence the specific pathways of structural evolution during the synthesis process. In addition, it summarizes the scientific challenges associated with diverse modification approaches currently employed to address the cyclic failure of materials. The overarching goal is to provide readers with profound insights into the study of LiTMO2.

Optimized In Situ Doping Strategy Stabling Single-Crystal Ultrahigh-Nickel Layered Cathode Materials

Single-crystal Ni-rich cathodes offer promising prospects in mitigating intergranular microcracks and side reaction issues commonly encountered in conventional polycrystalline cathodes. However, the utilization of micrometer-sized single-crystal particles has raised concerns about sluggish Li+ diffusion kinetics and unfavorable structural degradation, particularly in high Ni content cathodes. Herein, we present an innovative in situ doping strategy to regulate the dominant growth of characteristic planes in the single-crystal precursor, leading to enhanced mechanical properties and effectively tackling the challenges posed by ultrahigh-nickel layered cathodes. Compared with the traditional dry-doping method, our in situ doping approach possesses a more homogeneous and consistent modifying effect from the inside out, ensuring the uniform distribution of doping ions with large radius (Nb, Zr, W, etc). This mitigates the generally unsatisfactory substitution effect, thereby minimizing undesirable coating layers induced by different solubilities during the calcination process. Additionally, the uniformly dispersed ions from this in situ doping are beneficial for alleviating the two-phase coexistence of H2/H3 and optimizing the Li+ concentration gradient during cycling, thus inhibiting the formation of intragranular cracks and interfacial deterioration. Consequently, the in situ doped cathodes demonstrate exceptional cycle retention and rate performance under various harsh testing conditions. Our optimized in situ doping strategy not only expands the application prospects of elemental doping but also offers a promising research direction for developing high-energy-density single-crystal cathodes with extended lifetime.

Chiral Molecular Coating of a LiNiCoMnO2 Cathode for High-Rate Capability Lithium-Ion Batteries

The growing demand for energy has increased the need for battery storage, with lithium-ion batteries being widely used. Among those, nickel-rich layered lithium transition metal oxides [LiNi1-x-yCoxMnyO2 NCM (1 - x - y > 0.5)] are some of the promising cathode materials due to their high specific capacities and working voltages. In this study, we demonstrate that a thin, simple coating of polyalanine chiral molecules improves the performance of Ni-rich cathodes. The chiral organic coating of the active material enhances the discharge capacity and rate capability. Specifically, NCM811 and NCM622 electrodes coated with chiral molecules exhibit lower voltage hysteresis and better rate performance, with a capacity improvement of >10% at a 4 C discharge rate and an average improvement of 6%. We relate these results to the chirally induced spin selectivity effect that enables us to reduce the resistance of the electrode interface and to reduce dramatically the overpotential needed for the chemical process by aligning the electron spins.

Exploring the Role of an Electrolyte Additive in Suppressing Surface Reconstruction of a Ni-Rich NMC Cathode at Ultrahigh Voltage via Enhanced In Situ and Operando Characterization Methods

Vinylene carbonate (VC) is a widely used electrolyte additive in lithium-ion batteries for enhanced solid electrolyte interphase formation on the anode side. However, the cathode electrolyte interphase (CEI) formation with VC has received a lot less attention. This study presents a comprehensive investigation employing advanced in situ/operando-based Raman and X-ray absorption spectroscopy (XAS) to explore the effect of electrolyte composition on the CEI formation and suppression of surface reconstruction of LixNiyMnzCo1-y-zO2 (NMC) cathodes. A novel chemical pathway via VC polymerization is proposed based on experimental results. In situ Raman spectra revealed a new peak at 995 cm-1, indicating the presence of C-O semi-carbonates resulting from the radical polymerization of VC. Operando Raman analysis unveiled the formation of NiO at 490 cm-1 in the baseline system under ultrahigh voltage (up to 5.2 V). However, this peak was conspicuously absent in the VC electrolyte, signifying the effectiveness of VC in suppressing surface reconstruction. Further investigation was carried out utilizing in situ XAS compared X-ray absorption near edge structure spectra from cells of 3 and 20 cycles in both electrolytes at different operating voltages. The observed shift at the Ni K-edge confirmed a more substantial reduction of Ni in the baseline electrolyte compared to that in the VC electrolyte, thus indicating less CEI protection in the former. A sophisticated extended X-ray absorption fine structure analysis quantitatively confirmed the effective suppression of rock-salt formation with the VC electrolyte during the charging process, consistent with the operando Raman results. The in situ XAS results thus provided additional support for the key findings of this study, establishing the crucial role of VC polymerization in enhancing CEI stability and mitigating surface reconstruction on NMC cathodes. This work clarifies the relationship between the enhanced CEI layer and NMC degradation and inspires rational electrolyte design for long-cycling NMC cathodes.

Diagnosis of high-Ni NCA/Gr-Si cells before rapid capacity drop by monitoring the heterogeneous degradation

Understanding the degradation of lithium-ion batteries is of utmost significance for preventing unexpected capacity drops and addressing safety concerns. The manner in which batteries degrade during operation has a notable influence on their subsequent cycle performance. In particular, the rapid capacity drop related to the spatial heterogeneity of the anode degradation highlights the necessity of a health indicator for an accurate battery diagnosis. A novel health indicator established in this study, the Dominant degradation factors among Negative and Positive electrodes (DNP) scores, enables clear identification of degraded states despite comparable capacity levels. Specifically, batteries with heterogeneous anode degradation exhibited negative scores and the aggravation of the cycle performance. It is anticipated that this health indicator can provide a distinct evaluation of batteries based on their degraded states, supporting onboard battery management and the efficient allocation of resources for the battery reuse industry.

Structurally robust lithium-rich layered oxides for high-energy and long-lasting cathodes

O2-type lithium-rich layered oxides, known for mitigating irreversible transition metal migration and voltage decay, provide suitable framework for exploring the inherent properties of oxygen redox. Here, we present a series of O2-type lithium-rich layered oxides exhibiting minimal structural disordering and stable voltage retention even with high anionic redox participation based on the nominal composition. Notably, we observe a distinct asymmetric lattice breathing phenomenon within the layered framework driven by excessive oxygen redox, which includes substantial particle-level mechanical stress and the microcracks formation during cycling. This chemo-mechanical degradation can be effectively mitigated by balancing the anionic and cationic redox capabilities, securing both high discharge voltage (~ 3.43 V vs. Li/Li+) and capacity (~ 200 mAh g-1) over extended cycles. The observed correlation between the oxygen redox capability and the structural evolution of the layered framework suggests the distinct intrinsic capacity fading mechanism that differs from the previously proposed voltage fading mode.

The role of oxygen in automotive grade lithium-ion battery cathodes: an atomistic survey of ageing

The rising demand for high-performance lithium-ion batteries, pivotal to electric transportation, hinges on key materials like the Ni-rich layered oxide LiNixCoyAlzO2 (NCA) used in cathodes. The present study investigates the redox mechanisms, with particular focus on the role of oxygen in commercial NCA electrodes, both fresh and aged under various conditions (aged cells have performed >900 cycles until a cathode capacity retention of ∼80%). Our findings reveal that oxygen participates in charge compensation during NCA delithiation, both through changes in transition metal (TM)-O bond hybridization and formation of partially reversible O2, the latter occurs already below 3.8 V vs. Li/Li+. Aged NCA material undergoes more significant changes in TM-O bond hybridization when cycling above 50% SoC, while reversible O2 formation is maintained. Nickel is found to be redox active throughout the entire delithiation and shows a more classical oxidation state change during cycling with smaller changes in the Ni-O hybridization. By contrast, Co redox activity relies on a stronger change in Co-O hybridization, with only smaller Co oxidation state changes. The Ni-O bond displays an almost twice as large change in its bond length on cycling as the Co-O bond. The Ni-O6 octahedra are similar in size to the Co-O6 octahedra in the delithiated state, but are larger in the lithiated state, a size difference that increases with battery ageing. These contrasting redox activities are reflected directly in structural changes. The NCA material exhibits the formation of nanopores upon ageing, and a possible connection to oxygen redox activity is discussed. The difference in interaction of Ni and Co with oxygen provides a key understanding of the mechanism and the electrochemical instability of Ni-rich layered transition metal oxide electrodes. Our research specifically highlights the significance of the role of oxygen in the electrochemical performance of electric-vehicle-grade NCA electrodes, offering important insights for the creation of next-generation long-lived lithium-ion batteries.

High Voltage Cycling Stability of LiF-Coated NMC811 Electrode

The development of LiNi0.8Mn0.1Co0.1O2 (NMC811) as a cathode material for high-energy-density lithium-ion batteries (LIBs) intends to address the driving limitations of electric vehicles. However, the commercialization of this technology has been hindered by poor cycling stability at high cutoff voltages. The potential instability and drastic capacity fade stem from irreversible parasitic side reactions at the electrode-electrolyte interface. To address these issues, a stable nanoscale lithium fluoride (LiF) coating is deposited on the NMC811 electrode via atomic layer deposition. The nanoscale LiF coating diminishes the direct contact between NMC811 and the electrolyte, suppressing the detrimental parasitic reactions. LiF-NMC811 delivers cycling stability superior to uncoated NMC811 with high cutoff voltage for half-cell (3.0-4.6 V vs Li/Li+) and full-cell (2.8-4.5 V vs graphite) configurations. The structural, morphological, and chemical analyses of the electrodes after cycling show that capacity decline fundamentally arises from the electrode-electrolyte interface growth, irreversible phase transformation, transition metal dissolution and crossover, and particle cracking. Overall, this work demonstrates that LiF is an effective electrode coating for high-voltage cycling without compromising rate performance, even at high discharge rates. The findings of this work highlight the need to stabilize the electrode-electrolyte interface to fully utilize the high-capacity performance of NMC811.

Protonation Stimulates the Layered to Rock Salt Phase Transition of Ni-Rich Sodium Cathodes

Protonation of oxide cathodes triggers surface transition metal dissolution and accelerates the performance degradation of Li-ion batteries. While strategies are developed to improve cathode material surface stability, little is known about the effects of protonation on bulk phase transitions in these cathode materials or their sodium-ion battery counterparts. Here, using NaNiO2 in electrolytes with different proton-generating levels as model systems, a holistic picture of the effect of incorporated protons is presented. Protonation of lattice oxygens stimulate transition metal migration to the alkaline layer and accelerates layered-rock-salt phase transition, which leads to bulk structure disintegration and anisotropic surface reconstruction layers formation. A cathode that undergoes severe protonation reactions attains a porous architecture corresponding to its multifold performance fade. This work reveals that interactions between electrolyte and cathode that result in protonation can dominate the structural reversibility/stability of bulk cathodes, and the insight sheds light for the development of future batteries.

Dual-modification of Ni-rich cathode materials through strontium titanate coating and thermal treatment

Ni-rich layered structure ternary oxides, such as LiNi0.8Co0.1Mn0.1O2 (NCM811), are promising cathode materials for high-energy lithium-ion batteries (LIBs). However, a trade-off between high capacity and long cycle life still obstructs the commercialization of Ni-rich cathodes in modern LIBs. Herein, a facile dual modification approach for improving the electrochemical performance of NCM811 was enabled by a typical perovskite oxide: strontium titanate (SrTiO3). With a suitable thermal treatment, the modified cathode exhibited an outstanding electrochemical performance that could deliver a high discharge capacity of 188.5 mAh/g after 200 cycles under 1C with a capacity retention of 90%. The SrTiO3 (STO) protective layer can effectively suppress the side reaction between the NCM811 and the electrolyte. In the meantime, the pillar effect provided by interfacial Ti doping could effectively reduce the Li+/Ni2+ mixing ratio on the NCM811 surface and offer more efficient Li+ migration between the cathode and the coating layer after post-thermal treatment (≥600 °C). This dual modification strategy not only significantly improves the structural stability of Ni-rich layered structure but also enhances the electrochemical kinetics via increasing diffusion rate of Li+. The electrochemical measurement results further disclosed that the 3 wt% STO coated NCM811 with 600 °C annealing exhibits the best performance compared with other control samples, suggesting an appropriate temperature range for STO coated NCM811 cathode is critical for maintaining a stable structure for the whole system. This work may offer an effective option to enhance the electrochemical performance of Ni-rich cathodes for high-performance LIBs.

Effects of cathode loadings and anode protection on the performance of lithium metal batteries

While lithium-ion batteries (LIBs) are approaching their energy limits, lithium metal batteries (LMBs) are undergoing intensive investigation for higher energy density. Coupling LiNi0.8Mn0.1Co0.1O2(NMC811) cathode with lithium (Li) metal anode, the resultant Li||NMC811 LMBs are among the most promising technologies for future transportation electrification, which have the potential to realize an energy density two times higher than that of state-of-the-art LIBs. To maximize their energy density, the Li||NMC811 LMBs are preferred to have their cathode loading as high as possible while their Li anode as thin as possible. To this end, we investigated the effects of different cathode active material loadings (2-14 mg cm-2) on the performance of the Li||NMC811 LMBs. Our study revealed that the cathode loadings have remarkably affected the cell performance, in terms of capacity retention and sustainable capacity. Cells with high cathode loadings are more liable to fade in capacity, due to more severe formation of the CEI and more sluggish ion transport. In this study, we also verified that the protection of the Li anode is significant for achieving better cell performance. In this regard, our newly developed Li-containing glycerol (LiGL) via molecular layer deposition (MLD) is promising to help boost the cell performance, which was controllably deposited on the Li anode.

Low-cost BPO4 In Situ Synthetic Li3 PO4 Coating and B/P-Doping to Boost 4.8 V Cyclability for Sulfide-Based All-Solid-State Lithium Batteries

Structural damage of Ni-rich layered oxide cathodes such as LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) and serious interfacial side reactions and physical contact failures with sulfide electrolytes (SEs) are the main obstacles restricting ≥4.6 V high-voltage cyclability of all-solid-state lithium batteries (ASSLBs). To tackle this constraint, here, a modified NCM811 with Li3 PO4 coating and B/P co-doping using inexpensive BPO4 as raw materials via the one-step in situ synthesis process is presented. Phosphates have good electrochemical stability and contain the same anion (O2- ) and cation (P5+ ) as in cathode and SEs, respectively, thus Li3 PO4 coating precludes interfacial anion exchange, lessening side reactivity. Based on the high bond energy of B─O and P─O, the lattice O and crystal texture of NCM811 can be stabilized by B3+ /P5+ co-doping, thereby suppressing microcracks during high-voltage cycling. Therefore, when tested in combination with Li─In anode and Li6 PS5 Cl solid electrolytes (LPSCl), the modified NCM811 exhibits extraordinary performance, with 200.36 mAh g-1 initial discharge capacity (4.6 V), cycling 2300 cycles with decay rate as low as 0.01% per cycle (1C), and 208.26 mAh g-1 initial discharge capacity (4.8 V), cycling 1986 cycles with 0.02% per cycle decay rate. Simultaneously, it also has remarkable electrochemical abilities at both -20 °C and 60 °C.

Design of Nb5+-doped high-nickel layered ternary cathode material and its structure stability

LiNi0.8Co0.1Mn0.1O2(NCM811) is one of the most promising cathode materials for high-energy lithium-ion batteries, but there are still problems such as rapid capacity decay during charge and discharge and poor cycle performance. Elemental doping can significantly improve the electrochemical performance of high nickel ternary cathode materials. In this work, Nb5+-doped NCM811 cathode material was successfully synthesized. The results show that Nb5+doping helps to increase the interlayer spacing of the lithium layer, electron transport, and structural stability, thereby significantly improving the conductivity of Li+. At a high voltage of 4.6 V, the initial discharge specific capacity of 1% Nb5+-doped NCM811 cathode material at 0.1 C is 222.3 mAh·g-1, and the capacity retention rate after 100 cycles at 1 C is 92.03%, which is far more than the capacity retention rate of NCM811 under the same conditions (74.30%). First-principles calculations prove that 1% Nb5+-doped NCM811 cathode material shows the highest electronic conductivity and Nb5+doping will not change the lattice structure, demonstrating the effectiveness of the proposed strategy.

State-of-charge of individual active material particles in lithium ion batteries: a perspective of analytical techniques and their capabilities

The state-of-charge (SOC) is an essential parameter for battery management systems to reflect and monitor the remaining capacity of individual battery cells. In addition to its application at the cell level, the SOC also plays an important role in the investigation of redox processes of cathode active materials (CAMs) in lithium ion batteries (LIBs) during electrochemical cycling. These processes can be influenced by a large variety of factors such as active material properties, inhomogeneities of the electrode, degradation phenomena and the charge/discharge protocol during cycling. Consequently, non-uniform redox reactions can occur, resulting in charge heterogeneities of the active material. This heterogeneity can translate into accelerated aging of the CAM and a reduction in reversible capacity of the battery cell, since the active material is not fully utilized. To understand and monitor the SOC heterogeneity at the mesoscale, a wide range of techniques have been implemented in the past. In this perspective an overview of current state-of-the-art techniques to evaluate charge heterogeneities of CAMs in LIBs is presented. Therefore, techniques which utilize synchrotron radiation like X-ray absorption near-edge structure (XANES) and transmission X-ray spectroscopy (TXM) are presented as well as Raman spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Next to these established techniques, classification single particle inductively coupled plasma optical emission spectroscopy (CL-SP-ICP-OES) as a new approach is also discussed in this perspective. For these techniques, the areas of application, advantages as well as drawbacks are highlighted and discussed.

Fluorinated High-Voltage Electrolytes To Stabilize Nickel-Rich Lithium Batteries

As state-of-the-art (SOA) lithium-ion (Li-ion) batteries approach their specific energy limit (∼250 Wh kg-1), layer-structured, nickel-rich (Ni-rich) lithium transition metal oxide-based cathode materials, e.g., LiNi0.8Mn0.1Co0.1O2 (NMC811), have attracted great interest owing to their practical high specific capacities (>200 mAhg-1). Coupled with their high average discharge voltages (∼4 V vs Li/Li+), Ni-rich cathode-based lithium batteries possess a great potential to achieve much higher specific energies (>350 Wh kg-1 at the cell level) than the SOA Li-ion counterparts. In addition, Ni-rich oxides are low-cost battery cathode materials due to their low cobalt contents. However, Ni-rich cathode-based lithium batteries suffer quick capacity degradations upon cycling, particularly at high upper cutoff voltages (e.g., ≥4.5 V vs Li/Li+), due to crystal structure changes of the active cathode materials and parasitic side reactions at the electrolyte/electrode interfaces. In this study, a fluorinated-solvent-based, high-voltage stable electrolyte (HVE), i.e., 1 M Li bis(trifluoromethanesulfonyl)imide (LiTFSI) in fluoroethylene carbonate (FEC), bis(2,2,2-trifluoroethyl) carbonate (FDEC), and methyl (2,2,2-trifluoroethyl) carbonate (FEMC) with Li difluoro(oxalate)borate (LiDFOB) additive, was formulated and evaluated in Li/NMC811 battery cells. To the best of our knowledge, this class of electrolyte has not been investigated for Ni-rich cathode-based lithium batteries. Li/NMC811 cells with HVE exhibited a superior long-term cycle performance stability, maintaining ∼80% capacity after ∼500 cycles at a high cutoff voltage of 4.5 V (vs Li/Li+) than a baseline carbonate-solvent-based electrolyte (BE). The superior cycle stability of the Li/NMC811 cells is attributed to the inherently high-voltage stability of HVE, supported by the physical and electrochemical analyses. This conclusion is supported by our density functional theory (DFT) modeling where HVE shows a less tendency of deprotonation/oxidation than BE, leading to the observed cycle stability. The findings in this study are important to help tackle the technical challenges facing Ni-rich cathode-based lithium batteries to realize their high energy density potentials with a long cycle life.