Prelithiation Activates Li(Ni0.5Mn0.3Co0.2)O2 for High Capacity and Excellent Cycling Stability

Critical Review of Emerging Pre-metallization Technologies for Rechargeable Metal-Ion Batteries

Low Coulombic efficiency, low-capacity retention, and short cycle life are the primary challenges faced by various metal-ion batteries due to the loss of corresponding active metal. Practically, these issues can be significantly ameliorated by compensating for the loss of active metals using pre-metallization techniques. Herein, the state-of-the-art development in various pr-emetallization techniques is summarized. First, the origin of pre-metallization is elaborated and the Coulombic efficiency of different battery materials is compared. Second, different pre-metallization strategies, including direct physical contact, chemical strategies, electrochemical method, overmetallized approach, and the use of electrode additives are summarized. Third, the impact of pre-metallization on batteries, along with its role in improving Coulombic efficiency is discussed. Fourth, the various characterization techniques required for mechanistic studies in this field are outlined, from laboratory-level experiments to large scientific device. Finally, the current challenges and future opportunities of pre-metallization technology in improving Coulombic efficiency and cycle stability for various metal-ion batteries are discussed. In particular, the positive influence of pre-metallization reagents is emphasized in the anode-free battery systems. It is envisioned that this review will inspire the development of high-performance energy storage systems via the effective pre-metallization technologies.

Sulfur is a New High-Performance Additive toward High-Voltage LiNi0.5Co0.2Mn0.3O2 Cathode: Tiny Amount, Huge Impact

Increasing working voltage of cathode has been identified as one of the most promising strategies to increase energy density of the lithium-ion batteries. It is of crucial importance to suppress side reactions and control the formation of a cathode electrolyte interface (CEI) on the cathode surface in a high voltage range. In this work, sulfur is utilized to increase the working voltage of LiNi_0.5Co_0.2Mn_0.3O₂(NCM 523) to 4.5 V as demonstrated by both the NCM523/Li half-cell and NCM 523/graphite full cell. When a tiny amount of sulfur (0.1 mg mL^-1) is added to the blank electrolyte of ethylene carbonate (EC) and dimethyl carbonate (DMC) (3:7 by volume), the cycling stability and rate performance are greatly improved in the NCM523/Li half-cell. The capacity retention over 200 cycles at 170 mA g^-1 (1.0 C) is increased from 61.2 to 82.0%. The capacity at a high current density of 850 mA g^-1 (5.0 C) is increased from 92 mAh g^-1 to 120 mAh g^-1. Because the addition of sulfur also enhances the performance of the Li/graphite half-cell, improved performance is demonstrated by the NCM 523/graphite full cell as well. The mechanism is interpreted based on various characterizations. It is revealed that the preferential oxidation of sulfur at the cathode surface suppress decomposition of electrolyte solvent. Because only a tiny amount of sulfur is added into the electrolyte solution, excessive decomposition of sulfur is avoided, leading to improved electrochemical performance.

Ultrafast solid-liquid intercalation enabled by targeted microwave energy delivery

In chemical reactions, the breaking and formation of chemical bonds usually need external energy to overcome the activation barriers. Conventional energy delivery transfers energy from heating sources via various media, hence losing efficiency and inducing side reactions. In contrast, microwave (MW) heating is known to be highly energy efficient through dipole interaction with polar media, but how exactly it transmits energy to initiate chemical reactions has been unknown. Here, we report a rigorous determination of energy delivery mechanisms underlying MW-enabled rapid hydrothermal synthesis, by monitoring the structure and temperature of all the involved components as solid-liquid intercalation reaction occurs using in situ synchrotron techniques. We reveal a hitherto unknown direct energy transmission between MW irradiation source and the targeted reactants, leading to greatly reduced energy waste, and so the ultrafast kinetics at low temperature. These findings open up new horizons for designing material synthesis reactions of high efficiency and precision.

Nanoscale battery cathode materials induce DNA damage in bacteria

The increasing use of nanoscale lithium nickel manganese cobalt oxide (Li x Ni y Mn z Co1-y-z O2, NMC) as a cathode material in lithium-ion batteries poses risk to the environment. Learning toxicity mechanisms on molecular levels is critical to promote proactive risk assessment of these complex nanomaterials and inform their sustainable development. We focused on DNA damage as a toxicity mechanism and profiled in depth chemical and biological changes linked to DNA damage in two environmentally relevant bacteria upon nano-NMC exposure. DNA damage occurred in both bacteria, characterized by double-strand breakage and increased levels of many putative chemical modifications on bacterial DNA bases related to direct oxidative stress and lipid peroxidation, measured by cutting-edge DNA adductomic techniques. Chemical probes indicated elevated intracellular reactive oxygen species and transition metal ions, in agreement with DNA adductomics and gene expression analysis. By integrating multi-dimensional datasets from chemical and biological measurements, we present rich mechanistic insights on nano-NMC-induced DNA damage in bacteria, providing targets for biomarkers in the risk assessment of reactive materials that may be extrapolated to other nano-bio interactions.

Reaction Mechanisms of Layered Lithium-Rich Cathode Materials for High-Energy Lithium-Ion Batteries

Layered lithium-rich cathode materials have attracted extensive interest owing to their high theoretical specific capacity (320-350 mA h g^-1 ). However, poor cycling stability and sluggish reaction kinetics inhibit their practical applications. After many years of quiescence, interest in layered lithium-rich cathode materials is expected to revive in answer to our increasing dependence on high-energy-density lithium-ion batteries. Herein, we review recent research progress and in-depth descriptions of the structure characterization and reaction mechanisms of layered lithium-rich manganese-based cathode materials. In particular, we comprehensively summarize the proposed reaction mechanisms of both the cationic redox reaction of transition-metal ions and the anionic redox reaction of oxygen species. Finally, we discuss opportunities and challenges facing the future development of lithium-rich cathode materials for next-generation lithium-ion batteries.

Harnessing the surface structure to enable high-performance cathode materials for lithium-ion batteries

The impact of surface structure and interface reconstruction on the electrochemical performances of lithium-ion battery cathode materials is summarized.

Presodiation Strategies and Their Effect on Electrode-Electrolyte Interphases for High-Performance Electrodes for Sodium-Ion Batteries

Most active materials for sodium-ion batteries suffer from the problem of low-energy efficiency in the first cycle because of the loss of active sodium ions consumed for the formation of a solid electrolyte interface. To make up for the lost sodium ion, presodiation treatments have been applied, which are effective ways to mitigate the low initial efficiency. Here, we developed a direct-contact method to achieve the presodiation for cathode and anode electrodes and demonstrated the enhanced Coulombic efficiency of the first cycle with improved cyclability and reversible capacity. Moreover, we proved the formation of a thick passivation layer at the cathode-electrolyte interface during the presodiation process; this contributes to the improved cycle stability by preventing the dissolution of the active material and its deposition on the anode surface. The direct-contact method is a simple and cost-effective way to complete presodiation, and this simple process will be widely applicable for practical battery manufacturing.

Boosting High Energy Density Lithium-Ion Storage via the Rational Design of an FeS-Incorporated Sulfurized Polyacrylonitrile Fiber Hybrid Cathode

In order to satisfy the escalating energy demands, it is inevitable to improve the energy density of current Li-ion batteries. As the development of high-capacity cathode materials is of paramount significance compared to anode materials, here we have designed for the first time a unique synergistic hybrid cathode material with enhanced specific capacity, incorporating cost-effective iron sulfide (FeS) nanoparticles in a sulfurized polyacrylonitrile (SPAN) nanofiber matrix through a rational in situ synthesis strategy. Previous reports on FeS cathodes are scarce and consist of an amorphous carbon matrix to accommodate the volume changes encountered during the cycling process. However, this inactive buffering matrix eventually increases the weight of the cell, reducing the overall energy density. By the rational design of this hybrid composite cathode, we ensure that the presence of covalently bonded sulfur in SPAN guarantees high sulfur utilization, while effectively buffering the volume changes in FeS. Meanwhile, FeS can compensate for the conductivity issues in the SPAN, thereby realizing a synergistically driven dual-active cathode material improving the overall energy density of the composite. Simultaneous in situ generation of FeS nanoparticles within the SPAN fiber matrix was carried out via electrospinning followed by a one-step heating procedure. The developed hybrid cathode material displays enhanced lithium-ion storage, retaining 688.6 mA h g_{(FeS@SPAN composite)}^-1 at the end of 500 cycles at 1 A g^-1 even within a narrow voltage range of 1-3.0 V. A high discharge energy density > 900 W h kg_{(FeS@SPAN composite)}^-1, much higher than the theoretical energy density of the commercial LiCoO₂ cathode, was also achieved, revealing the promising prospects of this hybrid cathode material for high energy density applications.

In Situ Chelating Synthesis of Hierarchical LiNi1/3 Co1/3 Mn1/3 O2 Polyhedron Assemblies with Ultralong Cycle Life for Li-Ion Batteries

Layered lithium transition-metal oxides, with large capacity and high discharge platform, are promising cathode materials for Li-ion batteries. However, their high-rate cycling stability still remains a large challenge. Herein, hierarchical LiNi_1/3 Co_1/3 Mn_1/3 O₂ polyhedron assemblies are obtained through in situ chelation of transition metal ions (Ni²⁺ , Co²⁺ , and Mn²⁺ ) with amide groups uniformly distributed along the backbone of modified polyacrylonitrile chains to achieve intimate mixing at the atomic level. The assemblies exhibit outstanding electrochemical performances: superior rate capability, high volumetric energy density, and especially ultralong high-rate cyclability, due to the superiority of unique hierarchical structures. The polyhedrons with exposed active crystal facets provide more channels for Li⁺ diffusion, and meso/macropores serve as access shortcuts for fast migration of electrolytes, Li⁺ and electrons. The strategy proposed in this work can be extended to fabricate other mixed transition metal-based materials for advanced batteries.

Feasibility of Cathode Surface Coating Technology for High-Energy Lithium-ion and Beyond-Lithium-ion Batteries

Cathode material degradation during cycling is one of the key obstacles to upgrading lithium-ion and beyond-lithium-ion batteries for high-energy and varied-temperature applications. Herein, we highlight recent progress in material surface-coating as the foremost solution to resist the surface phase-transitions and cracking in cathode particles in mono-valent (Li, Na, K) and multi-valent (Mg, Ca, Al) ion batteries under high-voltage and varied-temperature conditions. Importantly, we shed light on the future of materials surface-coating technology with possible research directions. In this regard, we provide our viewpoint on a novel hybrid surface-coating strategy, which has been successfully evaluated in LiCoO₂ -based-Li-ion cells under adverse conditions with industrial specifications for customer-demanding applications. The proposed coating strategy includes a first surface-coating of the as-prepared cathode powders (by sol-gel) and then an ultra-thin ceramic-oxide coating on their electrodes (by atomic-layer deposition). What makes it appealing for industry applications is that such a coating strategy can effectively maintain the integrity of materials under electro-mechanical stress, at the cathode particle and electrode- levels. Furthermore, it leads to improved energy-density and voltage retention at 4.55 V and 45 °C with highly loaded electrodes (≈24 mg.cm^-2 ). Finally, the development of this coating technology for beyond-lithium-ion batteries could be a major research challenge, but one that is viable.

Synthetic Control of Kinetic Reaction Pathway and Cationic Ordering in High-Ni Layered Oxide Cathodes

Nickel-rich layered transition metal oxides, LiNi_1-x (MnCo)_x O₂ (1-x ≥ 0.5), are appealing candidates for cathodes in next-generation lithium-ion batteries (LIBs) for electric vehicles and other large-scale applications, due to their high capacity and low cost. However, synthetic control of the structural ordering in such a complex quaternary system has been a great challenge, especially in the presence of high Ni content. Herein, synthesis reactions for preparing layered LiNi_0.7 Mn_0.15 Co_0.15 O₂ (NMC71515) by solid-state methods are investigated through a combination of time-resolved in situ high-energy X-ray diffraction and absorption spectroscopy measurements. The real-time observation reveals a strong temperature dependence of the kinetics of cationic ordering in NMC71515 as a result of thermal-driven oxidation of transition metals and lithium/oxygen loss that concomitantly occur during heat treatment. Through synthetic control of the kinetic reaction pathway, a layered NMC71515 with low cationic disordering and a high reversible capacity is prepared in air. The findings may help to pave the way for designing high-Ni layered oxide cathodes for LIBs.

Explore the Effects of Microstructural Defects on Voltage Fade of Li- and Mn-Rich Cathodes

Li- and Mn-rich (LMR) cathode materials have been considered as promising candidates for energy storage applications due to high energy density. However, these materials suffer from a serious problem of voltage fade. Oxygen loss and the layered-to-spinel phase transition are two major contributors of such voltage fade. In this paper, using a combination of X-ray diffraction (XRD), pair distribution function (PDF), X-ray absorption (XAS) techniques, and aberration-corrected scanning transmission electron microscopy (STEM), we studied the effects of micro structural defects, especially the grain boundaries, on the oxygen loss and layered-to-spinel phase transition through prelithiation of a model compound Li₂Ru_0.5Mn_0.5O₃. It is found that the nanosized micro structural defects, especially the large amount of grain boundaries created by the prelithiation can greatly accelerate the oxygen loss and voltage fade. Defects (such as nanosized grain boundaries) and oxygen release form a positive feedback loop, promote each other during cycling, and accelerate the two major voltage fade contributors: the transition metal reduction and layered-to-spinel phase transition. These results clearly demonstrate the important relationships among the oxygen loss, microstructural defects and voltage fade. The importance of maintaining good crystallinity and protecting the surface of LMR material are also suggested.

Aligned Li+ Tunnels in Core-Shell Li(NixMnyCoz)O2@LiFePO4 Enhances Its High Voltage Cycling Stability as Li-ion Battery Cathode

Layered transition-metal oxides (Li[Ni_xMn_yCo_z]O₂, NMC, or NMCxyz) due to their poor stability when cycled at a high operating voltage (>4.5 V) have limited their practical applications in industry. Earlier researches have identified Mn(II)-dissolution and some parasitic reactions between NMC surface and electrolyte, especially when NMC is charged to a high potential, as primarily factors responsible for the fading. In our previous work, we have achieved a capacity of NMC active material close to theoretical value and optimized its cycling performance by a depolarized carbon nanotubes (CNTs) network and an unique "pre-lithiation process" that generates an in situ organic coating (∼40 nm) to prevent Mn(II) dissolution and minimize the parasitic reactions. Unfortunately, this organic coating is not durable enough during a long-term cycling when the cathode operates at a high potential (>4.5 V). This work attempts to improve the surface protection of the NMC532 particles by applying an active inorganic coating consisting of nanosized- and crystal-orientated LiFePO₄ (LFP) (about 50 nm, exposed (010) face) to generate a core-shell nanostructure of Li(Ni_xMn_yCo_z)O₂@LiFePO₄. Transmission electron microscopy (TEM) and etching X-ray photoelectron spectroscopy have confirmed an intimate contact coating (about 50 nm) between the original structure of NMC and LFP single-particle with atomic interdiffusion at the core-shell interface, and an array of interconnected aligned Li⁺ tunnels are observed at the interface by cross-sectional high-resolution TEM, which were formed by ball-milling and then strictly controlling the temperature below 100 °C. Batteries based on this modified NMC cathode material show a high reversible capacity when cycled between 3.0 and 4.6 V during a long-term cycling.

Countering the Segregation of Transition-Metal Ions in LiMn1/3 Co1/3 Ni1/3 O2 Cathode for Ultralong Life and High-Energy Li-Ion Batteries

High-voltage layered lithium transition-metal oxides are very promising cathodes for high-energy Li-ion batteries. However, these materials often suffer from a fast degradation of cycling stability due to structural evolutions. It seriously impedes the large-scale application of layered lithium transition-metal oxides. In this work, an ultralong life LiMn1/3 Co1/3 Ni1/3 O2 microspherical cathode is prepared by constructing an Mn-rich surface. Its capacity retention ratio at 700 mA g(-1) is as large as 92.9% after 600 cycles. The energy dispersive X-ray maps of electrodes after numerous cycles demonstrate that the ultralong life of the as-prepared cathode is attributed to the mitigation of TM-ions segregation. Additionally, it is discovered that layered lithium transition-metal oxide cathodes with an Mn-rich surface can mitigate the segregation of TM ions and the corrosion of active materials. This study provides a new strategy to counter the segregation of TM ions in layered lithium transition-metal oxides and will help to the design and development of high-energy cathodes with ultralong life.

Persistent State-of-Charge Heterogeneity in Relaxed, Partially Charged Li1- x Ni1/3 Co1/3 Mn1/3 O2 Secondary Particles

Ex situ transmission X-ray microscopy reveals micrometer-scale state-of-charge heterogeneity in solid-solution Li1- x Ni1/3 Co1/3 Mn1/3 O2 secondary particles even after extensive relaxation. The heterogeneity generates overcharged domains at the cutoff voltage, which may accelerate capacity fading and increase impedance with extended cycling. It is proposed that optimized secondary structures can minimize the state-of-charge heterogeneity by mitigating the buildup of nonuniform internal stresses associated with volume changes during charge.

Pre-Lithiation of Li(Ni1-x-yMnxCoy)O2 Materials Enabling Enhancement of Performance for Li-Ion Battery

Transition metal oxide materials Li(NixMnyCoz)O2 (NMCxyz) based on layered structure are potential cathode candidates for automotive Li-ion batteries because of their high specific capacities and operating potentials. However, the actual usable capacity, cycling stability, and first-cycle Coulombic efficiency remain far from practical. Previously, we reported a combined strategy consisting of depolarization with embedded carbon nanotube (CNT) and activation through pre-lithiation of the NMC host, which significantly improved the reversible capacity and cycling stability of NMC532-based material. In the present work we attempt to understand how pre-lithiation leads to these improvements on an atomic level with experimental investigation and ab initio calculations. By lithiating a series of NMC materials with varying chemical compositions prepared via a conventional approach, we identified the Ni in the NMC lattice as the component responsible for accommodating a double-layered Li structure. Specifically, much better improvements in the cycling stability and capacity can be achieved with the NMC lattices populated with Ni(3+) than those populated with only Ni(2+). Using the XRD we also found that the emergence of a double-layer Li structure is not only reversible during the pre-lithiation and the following delithiation, but also stable against elevated temperatures up to 320 °C. These new findings regarding the mechanism of pre-lithiation as well as how it affects the reversibility and stability of NMC-based cathode materials prepared by the conventional slurry approach will promote the possibility of their application in the future battery industry.

Core–shell nano-FeS2@N-doped graphene as an advanced cathode material for rechargeable Li-ion batteries

Based on an electrochemical mechanistic analysis, core–shell nano-FeS₂@N-graphene is significant because it has a very high reversible specific energy. This is much higher than other commercial Li-ion cell cathodes at different specific powers.

Enhancing the High-Voltage Cycling Performance of LiNi(0.5)Mn(0.3)Co(0.2)O2 by Retarding Its Interfacial Reaction with an Electrolyte by Atomic-Layer-Deposited Al2O3

High-voltage (>4.3 V) operation of LiNi(x)Mn(y)Co(z)O2 (NMC; 0 ≤ x, y, z < 1) for high capacity has become a new challenge for next-generation lithium-ion batteries because of the rapid capacity degradation over cycling. In this work, we investigate the performance of LiNi(0.5)Mn(0.3)Co(0.2)O2 (NMC532) electrodes with and without an atomic-layer-deposited (ALD) Al2O3 layer for charging/discharging in the range from 3.0 to 4.5 V (high voltage). The results of the electrochemical measurements show that the cells with ALD Al2O3-coated NMC532 electrodes have much enhanced cycling stability. The mechanism was investigated by using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and electrochemical methods. We find that the ultrathin ALD Al2O3 film can reduce the interface resistance of lithium-ion diffusion and enhance the surface stability of NMC532 by retarding the reactions at NMC532/electrolyte interfaces for preventing the formation of a new microstructure rock-salt phase NiO around the NMC532 surfaces.