Roles of Trimethyl Borate in Constructing an Interphase on Li Anode: Angel or Demon?

Abstract

Although coupling a lithium metal anode with a Ni-rich layer cathode is a promising approach for high-energy lithium metal batteries, both electrodes are plagued by their intrinsic unstable interfaces which trigger electrolyte decomposition, lithium dendritic growth, and transition metal dissolution during cycling. Making use of electrolyte additives is one of the most effective solutions to address this issue. In this paper, we explore the roles of trimethyl borate (TMB)─a common film-forming additive to protect high-nickel-ratio ternary cathodes─in suppressing lithium dendrite growth. It is found that, on the one hand, the borate-containing solid electrolyte interphase (SEI) derived from the decomposition of TMB facilitates Li+ transport, homogenizing the deposition of Li ions. On the other hand, TMB as an anion receptor provokes LiPF6 decomposition, prompting the formation of SEI with superfluous LiF. As a result, it is imperative to raise awareness of this double-edge additive when using it to be immune to lithium dendrite and cathodic degradation.