Competitive Ion Coordination in Gel Polymer Electrolytes Enables Decoupling of Mechanical Strength and Ionic Conductivity

Gel polymer electrolytes (GPEs) show great potential for lithium-metal batteries, but balancing high ionic conductivity with robust mechanical properties remains challenging. In this study, a competitive coordination strategy is proposed to address this issue by incorporating highly polar succinonitrile (SN) into a poly(methyl methacrylate-co-methacrylamide) (PMAm) matrix. The strong Li⁺ affinity of SN enables effective displacement of lithium ions from polymer hydrogen-bonding sites, maintaining the polymer's structural integrity while enhancing mechanical strength. Additionally, the hydrogen bonding between polymer chains compresses the polymer matrix, inducing molecular aggregation that creates fast diffusion pathways for Li⁺ and promotes anion participation in the solvation shell, facilitating the formation of a stable, inorganic-rich solid electrolyte interphase (SEI). As a result, the resulting PMAm-SN GPE exhibits excellent toughness (24.8 MJ m^-3), high ionic conductivity (2.8 mS cm^-1 at 25 °C) and high Li⁺ transference number of 0.76. When paired with a LiNi_0.6Co_0.2Mn_0.2O₂ cathode, the GPE demonstrates a 90% capacity retention after 500 cycles at 4.3 V. A practical 5 Ah Li/LiNi_0.8Co_0.1Mn_0.1O₂ pouch cell delivers 456 Wh kg^-1 energy density and demonstrates outstanding safety under thermal and mechanical abuse, showcasing the potential of this GPE for practical applications.