Rationally designing electrolyte additives for highly improving cyclability of LiNi0.5Mn1.5O4/Graphite cells

Abstract

High voltage is necessary for high energy lithium-ion batteries but difficult to achieve because of the highly deteriorated cyclability of the batteries. A novel strategy is developed to extend cyclability of a high voltage lithium-ion battery, LiNi0.5Mn1.5O4/Graphite (LNMO/Graphite) cell, which emphasizes a rational design of an electrolyte additive that can effectively construct protective interphases on anode and cathode and highly eliminate the effect of hydrogen fluoride (HF). 5-Trifluoromethylpyridine-trimethyl lithium borate (LTFMP-TMB), is synthesized, featuring with multi-functionalities. Its anion TFMP-TMB− tends to be enriched on cathode and can be preferentially oxidized yielding TMB and radical TFMP.. Both TMB and radical TFMP. can combine HF and thus eliminate the detrimental effect of HF on cathode, while the TMB dragged on cathode thus takes a preferential oxidation and constructs a protective cathode interphase. On the other hand, LTFMP-TMB is preferentially reduced on anode and constructs a protective anode interphase. Consequently, a small amount of LTFMP-TMB (0.2%) in 1.0 M LiPF6 in EC/DEC/EMC (3/2/5, wt%) results in a highly improved cyclability of LNMO/Graphite cell, with the capacity retention enhanced from 52% to 80% after 150 cycles at 0.5 C between 3.5 and 4.8 V. The as-developed strategy provides a model of designing electrolyte additives for improving cyclability of high voltage batteries.