Hin und zurück – die Entwicklung von LiNiO 2 als Kathodenaktivmaterial

Origin and Regulation of Interface Fusion during Synthesis of Single-Crystal Ni-Rich Cathodes

Interface fusion plays a key role in constructing Ni-based single-crystal cathodes, and is governed by the atomic migration related to kinetics. However, the interfacial atom migration path and its control factors are lack of clearly understanding. Herein, we systematically probe the solid-state synthesis mechanism of single-crystal LiNi_0.92 Co_0.04 Mn_0.04 O₂ , including the effects of precursor size, Li/transition metal (TM) ratio and sintering temperature on the structure. Multi-dimensional analysis unravels that thermodynamics drives interface atoms migration through intermediate state (i.e., cation mixing phase) to induce grain boundary fusion. Moreover, we demonstrate that smaller precursor size (<6 μm), lager Li/TM ratio (>1.0) and higher temperature (≥810 °C) are conducive to promote the growth of the intermediate state due to reaction kinetics enhancement, and ultimately strengthen the atomic migration-induced interface fusion.

Long-Range Cationic Disordering Induces two Distinct Degradation Pathways in Co-Free Ni-Rich Layered Cathodes

Ni-rich layered oxides are one of the most attractive cathode materials in high-energy-density lithium-ion batteries, their degradation mechanisms are still not completely elucidated. Herein, we report a strong dependence of degradation pathways on the long-range cationic disordering of Co-free Ni-rich Li_1-m (Ni_0.94 Al_0.06 )_1+m O₂ (NA). Interestingly, a disordered layered phase with lattice mismatch can be easily formed in the near-surface region of NA particles with very low cation disorder (NA-LCD, m≤0.06) over electrochemical cycling, while the layered structure is basically maintained in the core of particles forming a "core-shell" structure. Such surface reconstruction triggers a rapid capacity decay during the first 100 cycles between 2.7 and 4.3 V at 1 C or 3 C. On the contrary, the local lattice distortions are gradually accumulated throughout the whole NA particles with higher degrees of cation disorder (NA-HCD, 0.06≤m≤0.15) that lead to a slow capacity decay upon cycling.

In situ Interweaved Binder Framework Mitigating the Structural and Interphasial Degradations of High-nickel Cathodes in Lithium-ion Batteries

The practical viability of high-nickel layered oxide cathodes is compromised by the interphasial and structural degradations. Herein, we demonstrate that by applying an in situ interweaved binder, the cycling stability of high-nickel cathodes can be significantly improved. Specifically, the results show that the resilient binder network immobilizes the transition-metal ions, suppresses electrolyte oxidative decomposition, and mitigates cathode particles pulverization, thus resulting in suppressed cathode-to-anode chemical crossover and ameliorated chemistry and architecture of electrode-electrolyte interphases. Pouch full cells with high-mass-loading LiNi_0.8 Mn_0.1 Co_0.1 O₂ cathodes achieve 0.02 % capacity decay per cycle at 1 C rate over 1 000 deep cycles at 4.4 V (vs. graphite). This work demonstrates a rational structural and compositional design strategy of polymer binders to mitigate the structural and interphasial degradations of high-Ni cathodes in lithium-ion batteries.

Activating Lattice Oxygen in Layered Lithium Oxides through Cation Vacancies for Enhanced Urea Electrolysis

Despite the fact that high-valent nickel-based oxides exhibit promising catalytic activity for the urea oxidation reaction (UOR), the fundamental questions concerning the origin of the high performance and the structure-activity correlations remain to be elucidated. Here, we unveil the underlying enhanced mechanism of UOR by employing a series of prepared cation-vacancy controllable LiNiO₂ (LNO) model catalysts. Impressively, the optimized layered LNO-2 exhibits an extremely low overpotential at 10 mA cm^-2 along with excellent stability after the 160 h test. Operando characterisations combined with the theoretical analysis reveal the activated lattice oxygen in layered LiNiO₂ with moderate cation vacancies triggers charge disproportion of the Ni site to form Ni⁴⁺ species, facilitating deprotonation in a lattice oxygen involved catalytic process.

Synergistic Effects of Surface Coating and Bulk Doping in Ni-Rich Lithium Nickel Cobalt Manganese Oxide Cathode Materials for High-Energy Lithium Ion Batteries

Ni-rich layered oxide cathodes are promising candidates to satisfy the increasing energy demand of lithium-ion batteries for automotive applications. Thermal and cycling stability issues originating from increasing Ni contents are addressed by mitigation strategies such as elemental bulk substitution ("doping") and surface coating. Although both approaches separately benefit the cycling stability, there are only few reports investigating the combination of two of such approaches. Herein, the combination of Zr as common dopant in commercial materials with effective Li₂ WO₄ and WO₃ coatings was investigated with special focus on the impact of different material processing conditions on structural parameters and electrochemical performance in nickel-cobalt-manganese (NCM) || graphite cells. Results indicated that the Zr⁴⁺ dopant diffusing to the surface during annealing improved the electrochemical performance compared to samples without additional coatings. This work emphasizes the importance to not only investigate the effect of individual dopants or coatings but also the influences between both.

Micron-Sized Monodisperse Particle LiNi0.6Co0.2Mn0.2O2 Derived by Oxalate Solvothermal Process Combined with Calcination as Cathode Material for Lithium-Ion Batteries

Ni-rich cathode LiNi_xCo_yMn_1-x-yO₂ (NCM, x ≥ 0.5) materials are promising cathodes for lithium-ion batteries due to their high energy density and low cost. However, several issues, such as their complex preparation and electrochemical instability have hindered their commercial application. Herein, a simple solvothermal method combined with calcination was employed to synthesize LiNi_0.6Co_0.2Mn_0.2O₂ with micron-sized monodisperse particles, and the influence of the sintering temperature on the structures, morphologies, and electrochemical properties was investigated. The material sintered at 800 °C formed micron-sized particles with monodisperse characteristics, and a well-order layered structure. When charged–discharged in the voltage range of 2.8–4.3 V, it delivered an initial discharge capacity of 175.5 mAh g⁻¹ with a Coulombic efficiency of 80.3% at 0.1 C, and a superior discharge capacity of 135.4 mAh g⁻¹ with a capacity retention of 84.4% after 100 cycles at 1 C. The reliable electrochemical performance is probably attributable to the micron-sized monodisperse particles, which ensured stable crystal structure and fewer side reactions. This work is expected to provide a facile approach to preparing monodisperse particles of different scales, and improve the performance of Ni-rich NCM or other cathode materials for lithium-ion batteries.

Li-Rich Li2 [Ni0.8 Co0.1 Mn0.1 ]O2 for Anode-Free Lithium Metal Batteries

Anode-free lithium metal batteries can maximize the energy density at the cell level. However, without the Li compensation from the anode side, it faces much more challenging to achieve a long cycling life with a competitive energy density than Li metal-based batteries. Here, we prolong the lifespan of an anode-free Li metal battery by introducing Li-rich Li₂ [Ni_0.8 Co_0.1 Mn_0.1 ]O₂ into the cathode as a Li-ions extender. The Li₂ [Ni_0.8 Co_0.1 Mn_0.1 ]O₂ can release a large amount of Li-ions during the first charging process to supplement the Li loss in the anode, then convert into NCM811, thus extending the lifespan of the battery without the introduction of inactive elements. By the benefit of Li-rich cathode and high reversibility of Li metal on Cu foil, the anode-free pouch cells enable to achieve 447 Wh kg^-1 energy density and 84 % capacity retention after 100 cycles in the condition of limited electrolyte addition (E/C ratio of 2 g Ah^-1 ).

Phase Transformation Behavior and Stability of LiNiO2 Cathode Material for Li-Ion Batteries Obtained from In Situ Gas Analysis and Operando X-Ray Diffraction

Ni-rich layered oxide cathode materials, in particular the end member LiNiO₂ , suffer from drawbacks such as high surface reactivity and severe structural changes during de-/lithiation, leading to accelerated degradation and limiting practical implementation of these otherwise highly promising electrode materials in Li-ion batteries. Among all known phase transformations occurring in LiNiO₂ , the one from the H2 phase to the H3 phase at high state of charge is believed to have the most detrimental impact on the material's stability. In this work, the multistep phase transformation process and associated effects are analyzed by galvanostatic cycling, operando X-ray diffraction, and in situ pressure and gas analysis. The combined results provide thorough insights into the structural changes and how they affect the stability of LiNiO₂ . During the H2-H3 transformation, the most significant change occurs in the c-lattice parameter, resulting in large mechanical stress in LiNiO₂ . As for electrochemical stability, it suffers strongly in the H3 region. Oxygen evolution is observed not only during charge but also during discharge and found to be correlated with the presence of the H2 and H3 phases. Taken together, the experimental data improve the understanding of the degradation processes and the inherent instability of LiNiO₂ in Li-ion cells when operated above around 75 % state of charge.