三(三甲基硅烷)类添加剂助力5 V镍锰酸锂电池实用化

基于LiNi_0.5Mn_1.5O₄的5 V电池尚未实现实际应用，解决这一问题的关键在于电解液调控和电极界面优化。我们系统性研究了三（三甲基硅烷）硼酸酯（TMSB）和三（三甲基硅烷）亚磷酸酯（TMSPi）作为常规碳酸乙烯酯（EC）-LiPF₆基电解液添加剂在LiNi_0.5Mn_1.5O₄电池体系中的应用。结合理论计算、物理化学表征以及电化学手段分析了三（三甲基硅烷）类添加剂在高压电解液中的作用机制。研究发现，TMSB和TMSPi均可以通过优化电极/电解液界面来提高LiNi_0.5Mn_1.5O₄循环稳定性和库仑效率。TMSB中缺电子B可与阴离子相互作用，稳定PF₆^-，抑制LiNi_0.5Mn_1.5O₄正极阻抗的持续增加。TMSPi具有更高的最高占据分子轨道（HOMO）能级，可在更低电位下钝化高压正极，提高LiNi_0.5Mn_1.5O₄放电电压平台和放电容量。此外，TMSPi还可通过亲核反应参与石墨界面组分优化，改善负极循环性能。石墨LiNi_0.5Mn_1.5O₄软包电池在含1% TMSPi电解液中1C循环100次后的容量保持率为88.9%，优于基础电解液（60.5%）和含1% TMSB的电解液（77.4%）。

Tris(trimethylsilyl)-Based Additives Enables Practical 5 V LiNi0.5Mn1.5O4 Batteries

LiNi_0.5Mn_1.5O₄ cathode materials have been considered promising candidates for high energy density Li-ion batteries due to their high operation potential. However, to develop 5 V LiNi_0.5Mn_1.5O₄-based batteries, practical electrolytes with high electrochemical stability are yet to be realized. In this work, tris(trimethylsilyl)-based additives, including tris(trimethylsilyl) borate (TMSB) and tris(trimethylsilyl) phosphite (TMSPi), were selected as electrolyte additives for typical ethylene carbonate (EC)-LiPF₆ based electrolyte to develop practical LiNi_0.5Mn_1.5O₄-based batteries. Combining theoretical calculations, physicochemical characterization, and electrochemical measurements, we found that both TMSB and TMSPi can improve the Coulombic efficiency and cycling stability of 5 V LiNi_0.5Mn_1.5O₄-based cells. Specifically, TMSB can act as the stabilizer for PF₆^- due to its electron deficiency nature, thereby suppressing the increase of cell impedance. In addition, thanks to its high highest occupied molecule orbital (HOMO) energy level, TMSPi can be preferentially oxidized on the surface of charged LiNi_0.5Mn_1.5O₄ electrodes, resulting in a decent rate capacity and high discharge platform. In addition, TMSPi is conducive to the formation of robust solid electrolyte interphase (SEI) on graphite anode through the nucleophilic attack, resulting in enhanced cycle performance. As a result, GraphiteLiNi_0.5Mn_1.5O₄ pouch cells with TMSPi-containing electrolyte displayed capacity retention of 88.9% after 100 cycles at 1C, superior to that in the blank (60.5%) and TMSB-containing (77.4%) electrolytes.