Metal-ion-crosstalk-suppressing gel polymer electrolytes for high-voltage Li-ion batteries

Abstract

High voltage operation (>4.5 V versus Li/Li+) of nickel-rich layered oxides (LiNi<inf>x</inf>Co<inf>y</inf>Mn<inf>z</inf>O<inf>2</inf> or NCM with x + y + z = 1, x ≥ 0.6) benefits from high energy densities but suffers from instability issues caused by overoxidation of transition metals (TMs). High-valent and therefore highly reactive nickel ions (Ni4+) resulting from overoxidation bring about reductive electrolyte decomposition. The reduced Ni2+ is prone to dissolution, resultantly facilitating capacity degradation. To address the challenge, we employed polymer with functional groups designed to coordinate Ni4+ on NCM (surface-ion coordination) and chelate Ni2+ dissolved from NCM (dissolved-ion chelation). Cyanoethyl poly(vinyl alcohol) (PVA-CN) was modified with 2-pyrrolidone-5-carboxylate and succinimidyl carbonate moieties (Pyrd-PVA-CN and SC-PVA-CN, respectively). The gel polymer electrolytes (GPEs) successfully improved high-voltage operation at 4.55 V<inf>cell</inf> compared to liquid-electrolyte. Their coordinating moieties stabilized the NMC811 surface, suppressing Li/Ni mixing in the cathode and TM crosstalk from the cathode to the anode. © 2025 Elsevier B.V.