A Phosphorofluoridate-Based Multifunctional Electrolyte Additive Enables Long Cycling of High-Energy Lithium-Ion Batteries

Abstract

Ni-rich layered oxides are regarded as key componentsfor realizingpost Li-ion batteries (LIBs). However, high-valence Ni, which actsas an oxidant in deeply delithiated states, aggravates the oxidationof the electrolyte at the cathode, causing cell impedance to increase.Additionally, the leaching of transition metal (TM) ions from Ni-richcathodes by acidic compounds such as Bronsted-acidic HF producedthrough LiPF6 hydrolysis aggravates the structural instabilityof the cathode and renders the electrode-electrolyte interfaceunstable. Herein, we present a multifunctional electrolyte additive,bis(trimethylsilyl) phosphorofluoridate (BTSPFA), to attain enhancedinterfacial stability of graphite anodes and Ni-rich cathodes in Li-ioncells. BTSPFA eliminates the corrosive HF molecules by cleaving silylether bonds and enables the formation of a polar P-O- and P-F-enrichedcathode electrolyte interface (CEI) on the Ni-rich cathode. It alsopromotes the creation of a solid electrolyte interphase composed ofinorganic-rich species, which suppresses the reduction of the electrolyteduring battery operation. The synergistic effect of the HF scavengingability of BTSPFA and the stable BTSPFA-promoted CEI effectively suppressesthe TM leaching from the Ni-rich cathode while also preventing unwantedTM deposition on the anode. LiNi0.8Co0.1Mn0.1O2/graphite full cells with 1 wt % BTSPFA exhibitedan enhanced discharge capacity retention of 79.8% after 500 cyclesat 1C and 45 & DEG;C. These unique features of BTSPFA are useful forresolving the interfacial deterioration issue of high-capacity Ni-richcathodes paired with graphite anodes.