New Organic Complex for Lithium Layered Oxide Modification: Ultra-thin Coating, High-Voltage and Safety Performances

Abstract

Surface modification of cathode (e.g., lithium layered oxide, NCM) has become ever more important in lithium-ion batteries, particularly for pursuing higher energy densities and safety at high voltage. This is because structural degradation of cathode can be mitigated significantly. Herein, an organic complex is introduced for metal phosphates (e.g., AlPO4) modification through a new film-forming process in non-aqueous solution. This general strategy overcomes the challenge of non-uniform coating in current precipitation method, then opens a new avenue towards ultra-thin surface modification on molecular scale. As one of examples, as-prepared AlPO4-coated NCM exhibits much improved structural and electrochemical stability; meanwhile, thermal runaway can be suppressed significantly in over-charged cell using the modified NCM, demonstrating higher and reliable safety features. The great improvements benefit from the uniform and ultrathin AlPO4 coating, which inhibits the collapse and conversion of layered structure to spinel especially to rock salt structure at high-voltage conditions, as confirmed by HRTEM and EELS.