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

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.