Boron-Containing Ternary Electrolyte for Excellent Li-Ion Transference and Stabilization of LiNMC-Based Cells

Abstract

In traditional carbonate electrolytes, lithium mobility is limited owing to the strong solvation effect between lithium ions and solvent sheaths. As a result, the lithium-ion transference number (t_Li⁺) is lower than 0.5 (mostly between 0.2 and 0.4), which indicates that anion transference is dominant in electrolyte’s charge conduction. In order to enhance lithium mobility in electrolytes, a low-polarity organic boron compound, mesityldimethoxyborane (MDMB), was added to conventional carbonate electrolytes to increase lithium-ion mobility. Two electrolyte systems with different MDMB ratios exhibited high t_Li⁺ as 0.93 for 111 (EC:DEC:MDMB = 1:1:1, volume ratio) and 0.86 for 112 (EC:DEC:MDMB = 1:1:2). Moreover, the stability of LiNMC cathodic half-cell was also improved by using 111 and 112 which form robust B-rich CEI. The activation energy for lithiation and resistance of CEI were decreased by MDMB. The durability of LiNMC cathodic half-cell was enhanced substantially under 1C CCCV mode. Cells with 111 and 112 electrolyte systems underwent more than twice as many cycles as conventional electrolytes.