Kim Jongjung, Adiraju Venkata A K, Rodrigo Nuwanthi, Hoffmann Jennifer, Payne Martin, Lucht Brett L
Department of Chemistry, University of Rhode Island, Kingston, Rhode Island 02881, United States.
Gotion, Independence, Ohio 44131, United States.
ACS Appl Mater Interfaces. 2021 May 19;13(19):22351-22360. doi: 10.1021/acsami.1c02572. Epub 2021 May 4.
The beneficial role of lithium bis(trimethylsilyl) phosphate (LiTMSP), which may act as a novel bifunctional additive for high-voltage LiNiMnO (LNMO)/graphite cells, has been investigated. LiTMSP is synthesized by heating tris(trimethylsilyl) phosphate with lithium -butoxide. The cycle performance of LNMO/graphite cells at 45 °C significantly improved upon incorporation of LiTMSP (0.5 wt %). Nuclear magnetic resonance analysis suggests that the trimethylsilyl (TMS) group in LiTMSP can react with hydrogen fluoride (HF), which is generated through the hydrolysis of lithium hexafluorophosphate (LiPF) by residual water in an electrolyte solution or water generated via oxidative electrolyte decomposition reactions to form TMS fluoride. Inhibition of HF leads to a decrease in the concentration of transition-metal ion-dissolution (Ni and Mn) from the LNMO electrode, as determined by inductively coupled plasma mass spectrometry. In addition, the generation of the superior passivating surface film derived by LiTMSP on the graphite electrode, suppressing further electrolyte reductive decomposition as well as deterioration/reformation caused by migrated transition metal ions, is supported by a combination of chronoamperometry, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. Furthermore, a LiTMSP-derived surface film has better lithium ion conductivity with a decrease in resistance of the graphite electrode, as confirmed by electrochemical impedance spectroscopy, leading to improvement in the rate performance of LNMO/graphite cells. The HF-scavenging and film-forming effects of LiTMPS are responsible for the less polarization of LNMO/graphite cells enabling improved cycle performance at 45 °C.
双（三甲基硅基）磷酸锂（LiTMSP）作为一种新型的双功能添加剂，可用于高压LiNiMnO（LNMO）/石墨电池，其有益作用已得到研究。LiTMSP是通过将三（三甲基硅基）磷酸酯与丁醇锂加热合成的。在45℃下，加入LiTMSP（0.5 wt%）后，LNMO/石墨电池的循环性能显著提高。核磁共振分析表明，LiTMSP中的三甲基硅基（TMS）基团可与氟化氢（HF）反应，HF是由电解质溶液中的残留水或氧化电解质分解反应产生的水水解六氟磷酸锂（LiPF）生成的，反应生成三甲基硅基氟化物。电感耦合等离子体质谱分析表明，抑制HF可降低LNMO电极中过渡金属离子（Ni和Mn）的溶解浓度。此外，计时电流法、X射线光电子能谱和场发射扫描电子显微镜的综合分析表明，LiTMSP在石墨电极上形成了优异的钝化表面膜，抑制了电解质的进一步还原分解以及迁移的过渡金属离子引起的劣化/再形成。此外，电化学阻抗谱证实，LiTMSP衍生的表面膜具有更好的锂离子传导性，石墨电极的电阻降低，从而提高了LNMO/石墨电池的倍率性能。LiTMPS的HF清除和成膜作用导致LNMO/石墨电池的极化减小，从而在45℃下提高了循环性能。
