A well-designed water-soluble binder enlightening the 5 V-class LiNi_0.5Mn_1.5O₄ cathodes

Spinel LiNi_0.5Mn_1.5O₄ (LNMO) is one of the most promising cathode materials for high-energy density lithium batteries owing to its high reversible capacity and high operating voltage. However, LNMO-based lithium batteries have poor cycling performance due to the decomposition of liquid electrolytes and dissolution of transition metal (e.g. Mn and Ni) ions at high operating voltages. Herein, poly(methyl vinyl ether-alt-lithium maleic acid) (P(MVE-LMA)) is presented as an excellent aqueous binder for the first time to tackle the abovementioned issues, in which the lithium carboxylic motifs of P(MVE-LMA) deliver superior adhesion and cohesion capabilities and interact with transition metal cations to inhibit their dissolution from cathodes, whereas its ether motifs can adsorb on the carbon particle surface to render excellent distribution of carbon black. As a result, a 5 V-class LNMO/Li battery fabricated employing the P(MVE-LMA) binder exhibited better electrochemical performance (e.g., cycling life, cell impedance and rate capability) when compared with the battery with the traditional polyvinylidene fluoride (PVDF) binder. A more thorough investigation clearly elucidated that the enhanced battery performance of the P(MVE-LMA) binder could be attributed to the generation of a favorable cathode electrolyte interphase (CEI) layer, in turn favorably suppressing the oxidative decomposition of electrolytes and stabilizing the lattice structure of LNMO upon cycling.