Enhancing ionic conductivity and electrochemical stability via an ultrathin coating for interfacial side reaction suppression

Abstract

Introducing plastic crystals and garnet solid-state electrolyte fillers into poly(vinylidene fluorideco-trifluoroethylene-co-chlorotrifluoroethylene) (PVTC) polymer electrolytes represents an effective strategy to enhance ionic conductivity. However, a strong coordination interaction exists between the nitrile groups in plastic crystals like succinonitrile (SN) and the La atoms in garnet electrolytes, which can lead to polymerization of the nitrile groups. This polymerization disrupts the rapid ion exchange and migration at the interface. To address this issue, we propose an interface modification strategy, in which a poly(vinylene carbonate) (PVCA) nanolayer is pre-coated on the garnet surface via free radical polymerization to prevent side reactions between the garnet and SN. Experimental characterization and theoretical calculations reveal that PVCA strongly interacts with Li⁺, facilitating the dissociation of lithium salts. Moreover, the plasticizing effect of SN reduces the crystallinity of the overall polymer matrix, thereby promoting fast lithium-ion transport. Consequently, the resulting composite solid electrolyte exhibits high ionic conductivity (5.1 × 10⁻⁴ S cm⁻¹) and a high oxidation potential (4.9 V vs. Li⁺/Li). Notably, the electrolyte remains stable in contact with lithium metal for over 1600 h. More importantly, Li‖LiFePO₄ full cells assembled with this solid electrolyte demonstrate negligible loss of specific capacity after 300 cycles at 0.5C, while Li|LiNi_0.6Co_0.2Mn_0.2O₂ full cells retain 80.7% of their reversible capacity after 150 cycles at 0.2C.