The advancement of high charging cut-off voltage stands as a crucial avenue to enhance the energy density of LiCoO (LCO). However, LCO faces severe interface and bulk phase issues at high voltage (≥ 4.6 V), resulting in poor cycling stability. In this study, we reconstruct the surface structure of LCO based on the interdiffusion reaction between LCO and MgF in a high-temperature sintering process. Specifically, this interdiffusion reaction yields an ultra-thin LiF coating layer, artificially reinforcing the chemical structure of the cathode-electrolyte interphase (CEI) during cycling. This LiF-rich CEI not only effectively protects the surface structure of LCO, but also facilitates the lithium-ion diffusion. Furthermore, the diffusion of F and Mg into the LCO lattice significantly strengthens the structure, which inhibits unfavorable phase transitions from the O3 phase to the H1–3 phase at high voltage. Consequently, such modified LCO with concurrently enhanced interface and bulk structure exhibits outstanding long-term cycling performance within 3.0–4.6 V at 1 C, achieving a capacity retention of 84.9 % after 1000 cycles. Meanwhile, it also demonstrates excellent high-temperature performance, with a capacity retention of 85.0 % after 200 cycles under 45 °C.

中文翻译：

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高压LiCoO2相互扩散反应梯度氟化工程


高充电截止电压的进步是提高LiCoO（LCO）能量密度的重要途径。然而，LCO 在高电压（≥ 4.6 V）下面临严重的界面和体相问题，导致循环稳定性差。在本研究中，我们基于高温烧结过程中 LCO 和 MgF 之间的相互扩散反应重建了 LCO 的表面结构。具体来说，这种相互扩散反应会产生超薄的 LiF 涂层，在循环过程中人为地增强阴极电解质界面 (CEI) 的化学结构。这种富含LiF的CEI不仅有效保护了LCO的表面结构，而且有利于锂离子的扩散。此外，F和Mg扩散到LCO晶格中显着强化了结构，抑制了高电压下从O3相到H1-3相的不利相变。因此，这种同时增强界面和体结构的改性LCO在1C、3.0-4.6V范围内表现出出色的长期循环性能，1000次循环后容量保持率为84.9%。同时，它还表现出优异的高温性能，45℃下循环200次后容量保持率为85.0%。