Understanding the enhancement effect of boron doping on the electrochemical performance of single-crystalline Ni-rich cathode materials

Surface structure regulation toward anionic redox activation of Li1.20Mn0.533Ni0.133Co0.133O2 cathodes with high initial coulombic efficiency

Li-rich layered oxides cathodes (LLOs) as the promising next-generation cathode materials can provide ultrahigh capacity and energy density due to their distinctive anionic redox chemistry. Unfortunately, severe interfacial side reactions, surface structural degradation and sluggish Li+ kinetics have resulted in low initial coulombic efficiency (ICE), capacity decay and poor rate performance, restricting their practical applications for high-energy-density lithium-ion batteries. Herein, Surface structure regulation strategy used as surface modified agent is proposed to activate the anionic redox chemistry via ammonium tungstate treatment. Experimental results showcase that dual coating layer spinel-like structure LiMn2O4 and Li2WO4 have been successfully constructed on the surface of LLOs. The surface spinel-like structure providing 3 D Li+ diffusion channels together with fast-ion conductive layer decrease the interfacial Li+ diffusion barrier and boost the fasting Li+ kinetics. In addition, the in-situ reconstruction layer can further alleviate the interfacial side reactions and reinforce the surface structural stability. As a result, the ICE of modified LLOs can be precisely increased from 74.71 % to 107.42 % with the adjustment of ammonium tungstate usage. Moreover, it delivers a high reversible capacity of 279.5 mAh/g at 0.1 C, as well as excellent rate capability with capacity of 147.2 mAh/g at 5 C. This work provides a significant reference for designing high-energy-density LLOs via surface structure regulation strategy.

Two birds with one stone: One-pot concurrent Ta-doping and -coating on Ni-rich LiNi0.92Co0.04Mn0.04O2 cathode materials with fiber-type microstructure and Li+-conducting layer formation

A novel scalable Taylor-Couette reactor (TCR) synthesis method was employed to prepare Ta-modified LiNi0.92Co0.04Mn0.04O2 (T-NCM92) with different Ta contents. Through experiments and density functional theory (DFT) calculations, the phase and microstructure of Ta-modified NCM92 were analyzed, showing that Ta provides a bifunctional (doping and coating at one time) effect on LiNi0.92Co0.04Mn0.04O2 cathode material through a one-step synthesis process via a controlling suitable amount of Ta and Li-salt. Ta doping allows the tailoring of the microstructure, orientation, and morphology of the primary NCM92 particles, resulting in a needle-like shape with fine structures that considerably enhance Li+ ion diffusion and electrochemical charge/discharge stability. The Ta-based surface-coating layer effectively prevented microcrack formation and inhibited electrolyte decomposition and surface-side reactions during cycling, thereby significantly improving the electrochemical performance and long-term cycling stability of NCM92 cathodes. Our as-prepared NCM92 modified with 0.2 mol% Ta (i.e., T2-NCM92) exhibits outstanding cyclability, retaining 84.5 % capacity at 4.3 V, 78.3 % at 4.5 V, and 67.6 % at 45 ℃ after 200 cycles at 1C. Even under high-rate conditions (10C), T2-NCM92 demonstrated a remarkable capacity retention of 66.9 % after 100 cycles, with an initial discharge capacity of 157.6 mAh g-1. Thus, the Ta modification of Ni-rich NCM92 materials is a promising option for optimizing NCM cathode materials and enabling their use in real-world electric vehicle (EV) applications.

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.

Advancements and Challenges in High-Capacity Ni-Rich Cathode Materials for Lithium-Ion Batteries

Nowadays, lithium-ion batteries are undoubtedly known as the most promising rechargeable batteries. However, these batteries face some big challenges, like not having enough energy and not lasting long enough, that should be addressed. Ternary Ni-rich Li[NixCoyMnz]O2 and Li[NixCoyAlz]O2 cathode materials stand as the ideal candidate for a cathode active material to achieve high capacity and energy density, low manufacturing cost, and high operating voltage. However, capacity gain from Ni enrichment is nullified by the concurrent fast capacity fading because of issues such as gas evolution, microcracks propagation and pulverization, phase transition, electrolyte decomposition, cation mixing, and dissolution of transition metals at high operating voltage, which hinders their commercialization. In order to tackle these problems, researchers conducted many strategies, including elemental doping, surface coating, and particle engineering. This review paper mainly talks about origins of problems and their mechanisms leading to electrochemical performance deterioration for Ni-rich cathode materials and modification approaches to address the problems.

A new high-valence cation pillar within the Li layer of compositionally optimized Ni-rich LiNi0.9Co0.1O2 with improved structural stability for Li-ion battery

Elevating the nickel (Ni) content within layered cathodes constitutes a straightforward and effective approach to enhance the energy density of lithium-ion batteries (LIBs). However, the phase transition from H2 to H3 introduces substantial alterations in lattice volume, leading to structural degradation and diminished electrochemical performance. This study employs density functional theory (DFT) calculations to determine that the formation energy for Nb5+ occupied at Li 3b sites is lower compared to that of Ni 3a and Co 3a sites, yet higher than that of Mn 3a sites. This suggests a preference for Nb5+ doping within the Li layer of Mn-free cathodes. Motivated by these DFT results, we show the viability of high-valence Nb5+ as a stable pillar in the compositionally optimized binary oxide LiNi0.9Co0.1O2. The inclusion of this Nb5+ pillar in the Li layer of Ni/Co-based oxide significantly enhances the reversibility of the H2-H3 redox couple and mitigates microcrack formation in polycrystalline cathodes. As a result, the Nb-doped Ni/Co-based cathode exhibits an extended cycling lifespan, elevated rate capability, and increased thermal stability compared to the undoped. This investigation achieves precise control over doping sites by optimizing the chemical composition of Ni-rich cathodes and provides novel insights into advancing their electrochemical performance for high-energy LIBs.

Challenges and approaches of single-crystal Ni-rich layered cathodes in lithium batteries

High energy density and high safety are incompatible with each other in a lithium battery, which challenges today's energy storage and power applications. Ni-rich layered transition metal oxides (NMCs) have been identified as the primary cathode candidate for powering next-generation electric vehicles and have been extensively studied in the last two decades, leading to the fast growth of their market share, including both polycrystalline and single-crystal NMC cathodes. Single-crystal NMCs appear to be superior to polycrystalline NMCs, especially at low Ni content (≤60%). However, Ni-rich single-crystal NMC cathodes experience even faster capacity decay than polycrystalline NMC cathodes, rendering them unsuitable for practical application. Accordingly, this work will systematically review the attenuation mechanism of single-crystal NMCs and generate fresh insights into valuable research pathways. This perspective will provide a direction for the development of Ni-rich single-crystal NMC cathodes.

In Situ Polymerization Anchoring Effect Enhancing the Structural Stability and Electrochemical Performance of the LiNi0.8Co0.1Mn0.1O2 Cathode Material

LiNi_xCo_yMn_1-x-yO₂ (NCM) is identified as the most classical cathode material on account of its outstanding specific capacity, moderate price, and high safety. However, the surface stability of the high nickel cathode material is poor, which is extremely sensitive to air. Herein, we discover that the electron donor functional groups of organic polymers can form a stable coordination anchoring effect with nickel atoms in the cathode material that can provide an empty orbit through electron transfer, which not only enhances the mutual interface stability between the polymer coating and NCM but also greatly inhibits the decomposition of metal ions in the deintercalation/intercalation process. Density functional theory calculations and first principles reveal that there are coordination bonds and charge transfers between poly(3,4-ethylenedioxythiophene) (PEDOT) and NCM. Consequently, the modified material displayed excellent cyclic stability, with a capacity retention of 91.93% at 1 C after 100 cycles and a rate property of 143.8 mA h g^-1 at 5 C. Moreover, structural analysis indicated that the enhanced cycling stability resulted from the suppression of irreversible phase transitions of PEDOT-coated NCM. This unique mechanism provides a thought for organic coating and surface modification of NCM materials.

Enhanced microstructure stability of LiNi0.8Co0.1Mn0.1O2 cathode with negative thermal expansion shell for long-life battery

With high specific energy density, Ni-rich layered LiNi_0.8Co_0.1Mn_0.1O₂ (NCM) material has become one promising cathode candidate for advanced lithium-ion batteries (LIBs). However, severe capacity fading induced by microstructure degradation and deteriorated interfacial Li⁺ transportation upon repeated cycling makes the commercial application of NCM cathode in dilemma. To address these issues, LiAlSiO₄ (LASO), one unique negative thermal expansion (NTE) composite with high ionic conductivity, is utilized as a coating layer to improve the electrochemical performances of NCM material. Various characterizations demonstrate that LASO modification can endow NCM cathode with significantly enhanced long-term cyclability, through reinforcing the reversibility of phase transition and restraining lattice expansion, as well as depressing microcrack generation during repeated delithiation-lithiation processes. The electrochemical results indicate that LASO-modified NCM cathode can deliver an excellent rate capability of 136 mAh g^-1 at a high current rate of 10 C (1800 mA g^-1), larger than that of the pristine cathode (118 mAh g^-1), especially higher capacity retention of 85.4% concerning the pristine NCM cathode (65.7%) over 500 cycles under 0.2 C. This work provides a feasible strategy to ameliorate the interfacial Li⁺ diffusion and suppress the microstructure degradation of NCM material during long-term cycling, which can effectively promote the practical application of Ni-rich cathode in high-performance LIBs.

Single-Crystalline Cathodes for Advanced Li-Ion Batteries: Progress and Challenges

Single-crystalline cathodes are the most promising candidates for high-energy-density lithium-ion batteries (LIBs). Compared to their polycrystalline counterparts, single-crystalline cathodes have advantages over liquid-electrolyte-based LIBs in terms of cycle life, structural stability, thermal stability, safety, and storage but also have a potential application in solid-state LIBs. In this review, the development history and recent progress of single-crystalline cathodes are reviewed, focusing on properties, synthesis, challenges, solutions, and characterization. Synthesis of single-crystalline cathodes usually involves preparing precursors and subsequent calcination, which are summarized in the details. In the following sections, the development issues of single-crystalline cathodes, including kinetic limitations, interfacial side reactions, safety issues, reversible planar gliding and micro-cracking, and particle size distribution and agglomeration, are systematically analyzed, followed by current solutions and characterization techniques. Finally, this review is concluded with proposed research thrusts for the future development of single-crystalline cathodes.

A Molten-Salt Method to Synthesize Ultrahigh-Nickel Single-Crystalline LiNi0.92 Co0.06 Mn0.02 O2 with Superior Electrochemical Performance as Cathode Material for Lithium-Ion Batteries

Ni-rich layered oxides have been intensively considered as promising cathode materials for next-generation Li-ion batteries. Nevertheless, the performance degradation caused by intergranular cracks and electrode/electrolyte interface parasitic reactions restricts their further application. Compared with secondary particles, single-crystal (SC) materials have better mechanical integrity and cycling stability. However, the preparation of ultrahigh-nickel layered SC cathode still remains a serious challenge. Herein, a novel LiOH-LiNO₃ -H₃ BO₃ molten-salt method is proposed to synthesize SC LiNi_0.92 Co_0.06 Mn_0.02 O₂ with considerable crystallinity and uniformity. The critical impacts of calcination temperature and boric acid on the microstructure and electrochemical property of Ni-rich layered oxides are systematically investigated. The results show that the crystal growth is promoted and the stability of crystal structure is improved by this synthesis method. In particular, the optimal electrode demonstrates a superior initial discharge capacity of 214.8 mAh g^-1 with a high capacity retention of 86.3% over 300 cycles as tested by pouch-type full cells at 45 ºC. This work not only prepares an ultrahigh-nickel layered CS cathode with superior electrochemical performances, but also provides a feasible method for the synthesis of other CS layered cathode materials.

Face-lifting the surface of LiNi0.8Co0.15Al0.05O2cathode via Y(PO3)3to form anin situtriple composite Li-ion conductor coating layer with the enhanced electrochemical performance

Due to the assets such as adequate discharge capacity and rational cost, LiNi_0.8Co_0.15Al_0.05O₂(NCA), a high-nickel ternary layered oxide, is regarded to be a favorable cathode contender for lithium-ion batteries. However, the superior commercial application is restricted by the surface residual alkaline lithium salt (LiOH or/and Li₂CO₃) of nickel-rich cathode materials, which will expedite the disintegration of the structure and the engendering of gas (CO₂). Therefore, in this paper, we devise and fabricate a Y(PO₃)₃modified LiNi_0.8Co_0.15Al_0.05O₂(NCA), intending to optimize the surface residual alkaline lithium salt (antecedent deportation of H₂O and CO₂) while forming anin situtriple composite Li-ion conductor coating (Y(PO₃)₃-Li₃PO₄-YPO₄) to enhance the electrochemical behavior. Under this method, the 2 mol% Y(PO₃)₃modified NCA electrode reveals exceptional rate capability (5 C/156.3 mAh g^-1) and extraordinary cycle stability after 200 cycles (2 C/88.3%), whereas the original sample is only 5 C/123.1 mAh g^-1and 2 C/71.2% after 200 cycles. Conspicuously, even under the draconian circumstances of the high temperature and the high rate at 55 °C/1 C, the 2 mol% Y(PO₃)₃modified NCA electrode sustains a high reversible capacity, with an admirable capacity retention rate of 89.4% after 100 cycles. These contented results signify that the surface remodeling tactic presents a viable scheme for ameliorating high-nickel materials' performance and appropriateness.

The influence of water in electrodes on the solid electrolyte interphase film of micro lithium-ion batteries for the wireless headphone

During the production of micro lithium-ion batteries (LIBs), which are widely used in wireless headphones and other small portable devices, numerous factors can affect their quality, among which the content of water plays a crucial role. In this work, the influence of water in electrodes on the performances of micro LIBs is studied deeply. When the content of water increases, both the rate performance and the cycling performance of the batteries fade. The discharge capacity retention of the battery from high water content sample group H (group H) is 81.81% after 350 cycles at 2C, while that of the battery from low water content sample group L (group L) is 89.89% under the same condition. As for the rate performance, the discharge capacity of group H is only 58.66% of group L at 5C. To take a step further, it is mainly because an overgrowth of the solid electrolyte interphase film happen with the growth of water content. Accordingly, excess lithium ions are consumed and the porous structure of the anode is destroyed. Considering the results above, we believe that this work can offer a theory foundation to carry out the failure analysis of micro batteries.