Borate-Coated Co-Free LiNi0.5Mn1.5O4: Enhanced Performance and Stability for High-Power-Density Libs

Abstract

Cobalt free LiNi0.5Mn1.5O4 (LNMO), also known as high-voltage spinel, has emerged as a promising cathode material for high energy-density and high power-density lithium-ion batteries (LIBs), making it a viable candidate for applications in large-scale energy storage systems (ESS) and transportation (1-5). Despite its potential, LNMO faces challenges, such as rapid capacity degradation and the formation of an unstable cathode electrolyte interphase (CEI), which have impeded its commercialization(4-5). To address these issues, we present a cost-effective and scalable approach involving the application of a borate-based surface coating to LNMO (borate-LNMO). In this study, we systematically applied varying amounts of borate coating to LNMO and assessed their electrochemical performance in both half- and full-cell configurations. Initial optimization of the coating amount revealed that borate-LNMO materials exhibited superior rate capability, and enhanced stability when compared to bare LNMO. Float testing demonstrated a stable LNMO/electrolyte interface for borate-LNMO materials, in contrast to the continuous increase in leakage (parasitic current) observed with bare LNMO over time. Furthermore, borate-LNMO materials exhibited superior cycling performance in full-cell setups, both at ambient (25℃) and elevated (45℃) temperatures. This enhanced performance can be attributed to the formation of relatively stable CEI and SEI interphases, resulting in reduced electrolyte decomposition, lower transition metal dissolution at the LNMO/electrolyte interface, and minimized cross-talk between the cathode and anode. Post-mortem SEM analysis of the cycled graphite anodes revealed a thicker and denser SEI in bare LNMO cells, whereas borate-LNMO cells exhibited a thinner and porous SEI. These findings suggest that borate-coated LNMO could be a promising solution for cost-effective and high-power LIBs.