pH-Dependent Phosphates Conformal Coating Enabling 5.0 V Graphite Cathodes Over 10,000 Cycles via Reinforced Mechanical Strength and Optimized Interphase.

Abstract

Dual-ion batteries (DIBs) composed of a graphite cathode and a lithium anode are promising candidates for high-energy and high-power energy storage systems. However, graphite cathode undergoes rapid failure during the extended cycling and rapid charge/discharge mainly because of its structural breakdown and drastic resistance rise of cathode/electrolyte interphase (CEI) arising from the violent electrolyte decomposition at high voltage (4.5-5.0 V). Unlike the mainstream CEI modification strategy solely solving the problem of electrolyte decomposition, this work proposes a bifunctional CEI construction strategy that not only inhibits the electrolyte decomposition but also enhances the mechanical stability of graphite cathodes. Three pH-variable phosphates (LiH₂PO₄, Li₂HPO₄ and Li₃PO₄) are artificially coated on the surface of natural graphite (NG) particles through a green and low-cost wet coating route. The acidic LiH₂PO₄ coating not only effectively suppresses the electrolyte decomposition through the formation of a conformal coating layer, but also considerably enhances the mechanical strength of NG cathode via a strong bonding between LiH₂PO₄ and binder. The underlying mechanisms are elucidated through both theoretical calculations and empirical experiments. The optimized NG cathode is able to withstand fast charge/discharge at 60 C and exhibits exceptional capacity retention of 80.7% after 10,000 cycles 2 C.