A thin, uniform, and highly stable protective layer tailored using tris(trimethylsilyl) phosphite (TMSP) with a high tendency to donate electrons is formed on the Li-rich layered cathode, Li1.17Ni0.17Mn0.5Co0.17O2. This approach inhibits severe electrolyte decomposition at high operating voltages during cycling and dramatically improves the interfacial stability of the cathode. The TMSP additive in the LiPF6-based electrolyte is found to preferentially eliminate HF, which promotes the dissolution of metal ions from the cathode. Our investigation revealed that the TMSP-derived surface layer can overcome the significant capacity fading of the Li-rich cathode by structural instability ascribed to an irreversible phase transformation from layered to spinel-like structures. Moreover, the superior rate capability of the Li-rich cathode is achieved because the TMSP-originated surface layer allows facile charge transport at high C rates for the lithiation process.

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Lithium bis(oxalato)borate (LiBOB) is utilized as an oxidative additive to prevent the unwanted electrolyte decomposition on the surface of Li 1.17 Ni 0.17 Mn 0.5 Co 0.17 O 2 cathodes. Our investigation reveals that the LiBOB additive forms a protective layer on the cathode surface and effectively mitigates severe oxidative decomposition of LiPF 6 -based electrolytes. Noticeable improvements in the cycling stability and rate capability of Li 1.17 Ni 0.17 Mn 0.5 Co 0.17 O 2 cathodes are achieved in the LiBOB-added electrolyte. After 100 cycles at 60 • C, the discharge capacity retention of the Li 1.17 Ni 0.17 Mn 0.5 Co 0.17 O 2 cathode was 28.6% in the reference electrolyte, whereas the LiBOB-containing electrolyte maintained 77.6% of its initial discharge capacity. Moreover, the Li 1.17 Ni 0.17 Mn 0.5 Co 0.17 O 2 cathode with LiBOB additive delivered a superior discharge capacity of 115 mAh g −1 at a high rate of 2 C compared with the reference electrolyte. The OCV of a full cell charged in the reference electrolyte drastically decreased from 4.22 V to 3.52 V during storage at 60 • C, whereas a full cell charged in the LiBOB-added electrolyte exhibited superior retention of the OCV. . [1][2][3][4] Because a large reversible capacity of lithium-rich cathodes is attained with the condition of charging to the voltage range of 4.6-4.8 V at the first charge, 1 the oxidative decomposition of LiPF 6 /carbonate-based electrolytes occurring above 4.5 V vs. Li/Li + is inevitable. 5,6 The anodic limit of current electrolytes is not high enough to prevent such side reactions, which results in the formation of a resistive surface film on the cathode and continuous electrolyte decomposition at high voltages. Therefore, these undesired reactions limit the practical application of lithium-rich cathode materials. From this viewpoint, the formation of surface films through the use of oxidative additives in the electrolytes is thought to be one of the most effective strategies to stabilize the cathode-electrolyte interface in lithium-ion batteries (LIBs). 7,8 Recently, many research groups have reported the effect of electrolyte additives preventing significant electrolyte decomposition at lithium-rich cathodes that are operated above 4.5 V.9-13 Tri(hexafluoro-iso-propyl)phosphate (HFiP) was proposed as a oxidative additive (OA) to improve the cycling performance of the lithium-rich cathode Li 8 These authors also reported that the salt-type additive, LiFOB, can serve as a bi-functional additive, modifying the cathode and anode interfaces, in a subsequent paper.14 In addition, it has been reported that a LiFOB-lithium bis(oxalato)borate (LiBOB) combination leads to an improvement in the electrochemical performances of graphite/Li 1.2 Mn 0.55 Ni 0.15 Co 0.1 O 2 full cells 30• C. Lu et al. reported that the LiFOB additive improved the cycling stability of graphite/xLi 2 MnO 3 · (1-x)LiMO 2 full cells at room temperature. 4 These authors mentioned that the LiFOB-originated solid electrolyte interphase (SEI) on the anode effectively ...