Performance and Stability Improvement of Layered NCM Lithium-Ion Batteries at High Voltage by a Microporous Al2O3 Sol-Gel Coating

A Promising Solid-State Synthesis of LiMn1- yFeyPO4 Cathode for Lithium-ion Batteries

LiMn1-yFeyPO4 (LMFP) is a significant and cost-effective cathode material for Li-ion batteries, with a higher working voltage than LiFePO4 (LFP) and improved safety features compared to layered oxide cathodes. However, its commercial application faces challenges due to a need for a synthesis process to overcome the low Li-ion diffusion kinetics and complex phase transitions. Herein, a solid-state synthesis process using LFP and nano LiMn0.7Fe0.3PO4 (MF73) is proposed. The larger LFP acts as a structural framework fused with nano-MF73, preserving the morphology and high performance of LFP. These results demonstrate that the solid-state reaction occurs quickly, even at a low sintering temperature of 500 °C, and completes at 700 °C. However, contrary to the expectations, the larger LFP particles disappeared and fused into the nano-MF73 particles, revealing that Fe ions diffuse more easily than Mn ions in the olivine framework. This discovery provides valuable insights into understanding ion diffusion in LMFP. Notably, the obtained LMFP can still deliver an initial capacity of 142.3 mAh g-1, and the phase separation during the electrochemical process is significantly suppressed, resulting in good cycling stability (91.1% capacity retention after 300 cycles). These findings offer a promising approach for synthesizing LMFP with improved performance and stability.

Ni-rich lithium nickel manganese cobalt oxide cathode materials: A review on the synthesis methods and their electrochemical performances

The demand for lithium-ion batteries (LIBs) has skyrocketed due to the fast-growing global electric vehicle (EV) market. The Ni-rich cathode materials are considered the most relevant next-generation positive-electrode materials for LIBs as they offer low cost and high energy density materials. However, by increasing Ni content in the cathode materials, the materials suffer from poor cycle ability, rate capability and thermal stability. Therefore, this review article focuses on recent advances in the controlled synthesis of lithium nickel manganese cobalt oxide (NMC). This work highlights the advantages and challenges associated with each synthesis method that has been used to produce Ni-rich materials. The crystallography and morphology obtained are discussed, as the performance of LIBs is highly dependent on these properties. To address the drawbacks of Ni-rich cathode materials, certain modifications such as ion doping, and surface coating have been pursued. The correlation between the synthesized and modified NMC materials with their electrochemical performances is summarized. Several gaps, challenges and guidelines are elucidated here in order to provide insights for facilitating research in high-performance cathode for lithium-ion batteries. Factors that govern the formation of nickel-rich layered cathode such as pH, reaction and calcination temperatures have been outlined and discussed.

Fabrication of modern lithium ion batteries by 3D inkjet printing: opportunities and challenges

Inkjet printing (IJP) is a prospective additive manufacturing technology that enables the rapid and precise deposition of thin films or patterns. It offers numerous advantages over other thin-film manufacturing processes, including cost-effectiveness, ease of use, reduced waste material, and scalability. The key advantage of this technique is the ability of the fabrication of complex patterns with very high precision. The IJP gives the possibility of building three-dimensional (3D) structures on the microscale, which is beneficial for modern Li-Ion batteries (LIBs) and All-Solid-State Li-Ion Batteries (ASSLIBs). In contrast to typical laminated composite electrodes manufactured by tape casting and calendaring, 3D electrode design allows the electrolyte to penetrate through the electrode volume, increasing the surface-to-volume ratio and reducing ion diffusion paths. Thus, 3D electrodes/electrolyte structures are one of the most promising strategies for producing next-generation lithium-ion batteries with enhanced electrochemical performance. Although in the literature review, the IJP is frequently reported as a future perspective for the fabrication of 3D electrodes/electrolytes structures for LIBs, only a few works focus on this subject. In this review, we summarize the previous studies devoted to the topic and discuss different bottlenecks and challenges limiting further development.

Electrochemical Performance of Layer-Structured Ni0.8Co0.1Mn0.1O2 Cathode Active Materials Synthesized by Carbonate Co-Precipitation

The layered Ni-rich NiCoMn (NCM)-based cathode active material Li[Ni_xCo_(1-x)/2Mn_(1-x)/2]O₂ (x ≥ 0.6) has the advantages of high energy density and price competitiveness over an LiCoO₂-based material. Additionally, NCM is beneficial in terms of its increasing reversible discharge capacity with the increase in Ni content; however, stable electrochemical performance has not been readily achieved because of the cation mixing that occurs during its synthesis. In this study, various layer-structured Li_1.0[Ni_0.8Co_0.1Mn_0.1]O₂ materials were synthesized, and their electrochemical performances were investigated. A NiCoMnCO₃ precursor, prepared using carbonate co-precipitation with Li₂CO₃ as the lithium source and having a sintering temperature of 850 °C, sintering time of 25 h, and metal to Li molar ratio of 1.00-1.05 were found to be the optimal parameters/conditions for the preparation of Li_1.0[Ni_0.8Co_0.1Mn_0.1]O₂. The material exhibited a discharge capacity of 160 mAhg^-1 and capacity recovery rate of 95.56% (from a 5.0-0.1 C-rate).

Interfacial Model Deciphering High-Voltage Electrolytes for High Energy Density, High Safety, and Fast-Charging Lithium-Ion Batteries

High-voltage lithium-ion batteries (LIBs) enabled by high-voltage electrolytes can effectively boost energy density and power density, which are critical requirements to achieve long travel distances, fast-charging, and reliable safety performance for electric vehicles. However, operating these batteries beyond the typical conditions of LIBs (4.3 V vs Li/Li⁺ ) leads to severe electrolyte decomposition, while interfacial side reactions remain elusive. These critical issues have become a bottleneck for developing electrolytes for applications in extreme conditions. Herein, an additive-free electrolyte is presented that affords high stability at high voltage (4.5 V vs Li/Li⁺ ), lithium-dendrite-free features upon fast-charging operations (e.g., 162 mAh g^-1 at 3 C), and superior long-term battery performance at low temperature. More importantly, a new solvation structure-related interfacial model is presented, incorporating molecular-scale interactions between the lithium-ion, anion, and solvents at the electrolyte-electrode interfaces to help interpret battery performance. This report is a pioneering study that explores the dynamic mutual-interaction interfacial behaviors on the lithium layered oxide cathode and graphite anode simultaneously in the battery. This interfacial model enables new insights into electrode performances that differ from the known solid electrolyte interphase approach to be revealed, and sets new guidelines for the design of versatile electrolytes for metal-ion batteries.

Constructing a High-Energy and Durable Single-Crystal NCM811 Cathode for All-Solid-State Batteries by a Surface Engineering Strategy

Single-crystal LiNi_0.8Co_0.1Mn_0.1O₂ (S-NCM811) with an electrochemomechanically compliant microstructure has attracted great attention in all-solid-state batteries (ASSBs) for its superior electrochemical performance compared to the polycrystalline counterpart. However, the undesired side reactions on the cathode/solid-state electrolyte (SSE) interface causes inferior capacity and rate capability than lithium-ion batteries, limiting the practical application of S-NCM811 in the ASSB technology. Herein, it shows that S-NCM811 delivers a high capacity (205 mAh g^-1, 0.1C) with outstanding rate capability (175 mAh g^-1 at 0.3C and 116 mAh g^-1 at 1C) in ASSBs by the coating of a nano-lithium niobium oxide (LNO) layer via the atomic layer deposition technique combined with optimized post-annealing treatment. The working mechanism is verified as the nano-LNO layer effectively suppresses the decomposition of sulfide SSE and stabilizes the cathode/SSE interface. The post-annealing of the LNO layer at 400 °C improves the coating uniformity, eliminates the residual lithium salts, and leads to small impedance increasing and less electrochemical polarization during cycling compared with pristine materials. This work highlights the critical role of the post-annealed nano-LNO layer in the applications of a high-nickel cathode and offers some new insights into the designing of high-performance cathode materials for ASSBs.

Unraveling the New Role of Metal-Organic Frameworks in Designing Silicon Hollow Nanocages for High-Energy Lithium-Ion Batteries

Metal-organic framework (MOF)-derived materials are attracting considerable attention because of the moldability in compositions and structures, enabling greater performances in diverse applications. However, the nanostructural control of multicomponent MOF-based complexes remains challenging due to the complexity of reaction mechanisms. Herein, we present a surface-induced self-nucleation-growth mechanism for the zeolitic imidazolate framework (ZIF) to prepare a new type of ZIF-8@SiO₂ polyhedral nanoparticles. We discover that the Zn hydroxide moieties (Zn-OH) within ZIF-8 can trigger the hydrolysis of tetraethyl orthosilicate effectively on the ZIF-8 surface precisely, avoiding the formation of free orthosilicic acid (Si(OH)₄) successfully. This is a pioneering work to elucidate the importance of MOF surface properties for preparing multicomponent materials. Then, a novel well-dispersed silicon hollow nanocage (H-Si@C) modified by the carbon was prepared after removal of the ZIF-8 and magnesiothermic reduction. The as-prepared H-Si@C demonstrates an overwhelmingly high lithium storage capability and extraordinary stability in lithium-ion batteries (LIBs), particularly the impressive performances when it was matched with the LiNi_0.6Co_0.2Mn_0.2O₂ cathode in a full cell. The MOF surface-induced self-nucleation-growth strategy is useful for preparing more multifunctional materials, while the study of lithium storage performances of the H-Si@C material is practical for LIB applications.

Future Material Developments for Electric Vehicle Battery Cells Answering Growing Demands from an End-User Perspective

Nowadays, batteries for electric vehicles are expected to have a high energy density, allow fast charging and maintain long cycle life, while providing affordable traction, and complying with stringent safety and environmental standards. Extensive research on novel materials at cell level is hence needed for the continuous improvement of the batteries coupled towards achieving these requirements. This article firstly delves into future developments in electric vehicles from a technology perspective, and the perspective of changing end-user demands. After these end-user needs are defined, their translation into future battery requirements is described. A detailed review of expected material developments follows, to address these dynamic and changing needs. Developments on anodes, cathodes, electrolyte and cell level will be discussed. Finally, a special section will discuss the safety aspects with these increasing end-user demands and how to overcome these issues.

An SiOx anode strengthened by the self-catalytic growth of carbon nanotubes

Modification using carbon nanotubes (CNTs) is one of the most important strategies to boost the performance of materials in various applications, among which the CNT-modified silicon-based anodes have gained considerable attention in lithium-ion batteries (LIBs) due to their improved conductivity and cycle stability. However, the realization of a close-knit CNT coating on silicon (Si) through an efficient and cost-effective approach remains challenging. Herein, a new in situ self-catalytic method by acetylene treatment is presented, in which, CNTs can be directly grown and knitted on the SiO_x particles to construct a conductive additive-free SiO_x@CNT anode. The in situ grown CNTs can not only enhance electric conductivity and alleviate the volume effect of SiO_x effectively, but also mitigate the electrolyte decomposition with improved coulombic efficiency. As a result, an extremely high capacity of 1012 mA h g^-1, long lifespan over 500 cycles at a current density of 2 A g^-1 as well as a good performance in full LIBs with a working potential of about 3.4 V (vs. nickel-rich cathode) were obtained. The rationally constructed SiO_x@CNTs with easy synthesis and high throughput will hopefully promote LIBs with energy density above 300 W h kg^-1. This study opens a new avenue to prepare CNT-decorated functional materials and brings the SiO_x-based anode one step closer to practical applications.

Exploiting the Degradation Mechanism of NCM523 ∥ Graphite Lithium-Ion Full Cells Operated at High Voltage

Layered oxides, particularly including Li[Nix Coy Mnz ]O2 (NCMxyz) materials, such as NCM523, are the most promising cathode materials for high-energy lithium-ion batteries (LIBs). One major strategy to increase the energy density of LIBs is to expand the cell voltage (>4.3 V). However, high-voltage NCM ∥ graphite full cells typically suffer from drastic capacity fading, often referred to as "rollover" failure. In this study, the underlying degradation mechanisms responsible for failure of NCM523 ∥ graphite full cells operated at 4.5 V are unraveled by a comprehensive study including the variation of different electrode and cell parameters. It is found that the "rollover" failure after around 50 cycles can be attributed to severe solid electrolyte interphase growth, owing to formation of thick deposits at the graphite anode surface through deposition of transition metals migrating from the cathode to the anode. These deposits induce the formation of Li metal dendrites, which, in the worst cases, result in a "rollover" failure owing to the generation of (micro-) short circuits. Finally, approaches to overcome this dramatic failure mechanism are presented, for example, by use of single-crystal NCM523 materials, showing no "rollover" failure even after 200 cycles. The suppression of cross-talk phenomena in high-voltage LIB cells is of utmost importance for achieving high cycling stability.

In Situ Monitoring of Thermally Induced Effects in Nickel-Rich Layered Oxide Cathode Materials at the Atomic Level

The thermal stability of cathode active materials (CAMs) is of major importance for the safety of lithium-ion batteries (LIBs). A thorough understanding of how commercially viable layered oxide CAMs behave at the atomic length scale upon heating is indispensable for the further development of LIBs. Here, structural changes of Li(Ni_0.85Co_0.15Mn_0.05)O₂ (NCM851005) at elevated temperatures are studied by in situ aberration-corrected scanning transmission electron microscopy (AC-STEM). Heating NCM851005 inside the microscope under vacuum conditions enables us to observe phase transitions and other structural changes at high spatial resolutions. This has been primarily possible by establishing low-dose electron beam conditions in STEM. Specific focus is put on the evolution of inherent nanopore defects found in the primary grains, which are believed to play an important role in LIB degradation. The onset temperature of structural changes is found to be ∼175 °C, resulting in phase transformation from a layered to a rock-salt-like structure, especially at the internal interfaces, and increasing intragrain inhomogeneity. The reducing environment and heat application lead to the formation and subsequent densification of {003}- and {014}-type facets. In the light of these results, postsynthesis electrode drying processes applied under reducing environment and heat, for example, in the preparation of solid-state batteries, should be re-examined carefully.

Research Progress on the Surface of High-Nickel Nickel-Cobalt-Manganese Ternary Cathode Materials: A Mini Review

To address increasingly prominent energy problems, lithium-ion batteries have been widely developed. The high-nickel type nickel–cobalt–manganese (NCM) ternary cathode material has attracted attention because of its high energy density, but it has problems such as cation mixing. To address these issues, it is necessary to start from the surface and interface of the cathode material, explore the mechanism underlying the material's structural change and the occurrence of side reactions, and propose corresponding optimization schemes. This article reviews the defects caused by cation mixing and energy bands in high-nickel NCM ternary cathode materials. This review discusses the reasons why the core-shell structure has become an optimized high-nickel ternary cathode material in recent years and the research progress of core-shell materials. The synthesis method of high-nickel NCM ternary cathode material is summarized. A good theoretical basis for future experimental exploration is provided.

Enhanced electrochemical performance of lithia/Li2RuO3 cathode by adding tris(trimethylsilyl)borate as electrolyte additive

In this study, we used tris(trimethylsilyl)borate (TMSB) as an electrolyte additive and analysed its effect on the electrochemical performance of lithia-based (Lithia/Li₂RuO₃) cathodes. Our investigation revealed that the addition of TMSB modified the interfacial reactions between a lithia-based cathode and an electrolyte composed of the carbonate solvents and the LiPF₆ salt. The decomposition of the LiPF₆ salt and the formation of Li₂CO₃ and -CO₂ was successfully reduced through the use of TMSB as an electrolyte additive. It is inferred that the protective layer derived from the TMSB suppressed the undesirable side reaction associated with the electrolyte and superoxides (O^- or O^0.5-) formed in the cathode structure during the charging process. This led to the reduction of superoxide loss through side reactions, which contributed to the increased available capacity of the Lithia/Li₂RuO₃ cathode with the addition of TMSB. The suppression of undesirable side reactions also decreased the thickness of the interfacial layer, reducing the impedance value of the cells and stabilising the cyclic performance of the lithia-based cathode. This confirmed that the addition of TMSB was an effective approach for the improvement of the electrochemical performance of cells containing lithia-based cathodes.

Effect of Vinylethylene Carbonate and Fluoroethylene Carbonate Electrolyte Additives on the Performance of Lithia-Based Cathodes

Nanolithia-based materials are promising lithium-ion battery cathodes owing to their high capacity, low overpotential, and stable cyclic performance. Their properties are highly dependent on the structure and composition of the catalysts, which play a role in activating the lithia to participate in the electrochemical redox reaction. However, the use of electrolyte additives can be an efficient approach to improve properties of the lithia-based cathodes. In this work, vinylethylene carbonate (VEC) and fluoroethylene carbonate (FEC) were introduced as electrolyte additives in cells containing lithia-based cathode (lithia/(Ir, Li₂IrO₃) nanocomposite). The use of additives enhanced the electrochemical performance of the lithia-based cathodes, including the rate capability and cyclic performance. Especially, their available capacity increased without modifying the cathodes. Results of X-ray photoelectron spectroscopy (XPS) analysis confirmed that the additives form interface layers at the cathode surface, which contain Li₂CO₃, more carbon reactants, and more LiF than the interface layer formed with the pristine electrolyte. The Li₂CO₃ and carbon reactants may improve rate capability by facilitating Li⁺ transport, and LiF may stabilize the Li₂O₂ (and/or LiO₂) produced by the oxygen redox reaction with lithia. Therefore, the additive-enhanced electrochemical performance of the cell is attributed to the effects of the interface layer derived from additive decomposition during cycling.