Sodium Phytate Cross-Linked Polyacrylic Acid as Multifunctional Aqueous Binder Stabilizes LiNi0.8Co0.1Mn0.1O2 to 4.6 V

Abstract

Nickel-rich layered oxides are promising candidates for next-generation lithium-ion batteries. However, nickel-rich cathodes largely suffer from poor cyclability due to interfacial instability and intergranular cracking, particularly under high voltages and elevated temperatures. Herein, a multifunctional binder (PAA–PN) derived from the cross-linking of sodium phytate (PN) and poly(acrylic acid) (PAA) was designed to stabilize the LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) working under a cutoff voltage of 4.6 V. The PAA–PN promotes the formation of dual protective layers, consisting of an outer stable cathode electrolyte interface and an inner thin rock-salt phase on the NCM811 surface, effectively mitigating electrolyte decomposition, transition-metal dissolution, and phase-fatigue issues. Additionally, the robust elastic PAA–PN cross-linking network and chelation of PAA–PN with the NCM811 surface effectively inhibit intergranular cracking. Benefiting from these multifunctional advantages, NCM811 cathodes with PAA–PN binder achieve capacity retention of 95.1% (25 °C) and 84.7% (45 °C) after 100 cycles at 4.6 V, respectively.