Insight into wide temperature electrolyte based on lithiumdifluoro(oxalate)borate for high voltage lithium-ion batteries

Spinel LiNi0.5Mn1.5O4 (LNMO) cathode with high voltage plateau at around 4.7 V (vs. Li/Li+) has attracted great attention. However, the lack of suitable electrolyte hinders its application. Although lithium difluoro(oxalate)borate (LiODFB)-based electrolyte has been proved to be suitable for high voltage electrolyte, traditional LiODFB-based electrolyte has poor low and high temperature performance. Therefore, we confirm that lithium difluorophosphate (LiPO2F2, LiDFP) as LiODFB-based electrolyte additive and dimethyl sulfite (DMS) as co-solvent significantly improve electrochemical performance of LNMO/Graphite full batteries at low and high temperature. Various physical and electrochemical techniques are used to investigate the effect of four electrolytes. The effect on cathode is mainly attributed to priority oxidation decomposition of LiDFP. The formed interface film can inhibit the dissolution of Mn2+, thereby improving the high temperature electrochemical performance. The effect on anode is that the interface film formed by LiODFB prevents continuous reduction of solvents and additive. The enhanced low temperature performance is due to the significantly increased ionic conductivity of DMS-containing electrolytes at low temperature. Besides, the formed of the cathode electrolyte interphase (CEI) membrane with low impedance by LiDFP can improve the kinetics of cathode/electrolyte interface, therefore enhancing the low and high temperature performance of LNMO/Graphite full cells.