Highly ionic conductive composite membrane electrolyte with vertically aligned structure and radial gradient copolymer for high-performance solid-state lithium metal batteries

Abstract

Solid-state polymer electrolytes are crucial for advancing solid-state lithium-metal batteries owing to their flexibility, excellent manufacturability, and strong interfacial compatibility. However, their widespread applications are hindered by low ionic conductivity at room temperature and lithium dendrite growth. Herein, we report a novel solid-state composite membrane electrolyte design that combines the vertically aligned channel structure and copolymer with a radial gradient composition. Within the vertically aligned channels, the composition of poly(vinyl ethylene carbonate-co-poly(ethylene glycol) diacrylate) (P(VEC-PEGDA) varies in a gradient along the radial direction: from the center to the wall of vertically aligned channels, the proportion of vinyl ethylene carbonate (VEC) in the copolymer decreases, while the proportion of poly(ethylene glycol) diacrylate (PEGDA) increases accordingly. It can be functionally divided into a mechanical-reinforcement layer and a fast-ion-conducting layer. The resulting solid-state composite membrane electrolyte achieves a high critical current density of 1.2 mA cm⁻² and high ionic conductivity of 2.03 mS cm⁻¹ at room temperature. Employing this composite membrane electrolyte, a Li//Li symmetric cell exhibits stable cycling for over 1850 h at 0.2 mA cm⁻²/0.2 mA h cm⁻², and a Li//LiFePO₄ (LFP) battery maintains 77.3% capacity retention at 2 C after 300 cycles. Our work provides insight into the rational design of safer and more efficient solid-state batteries through electrolyte structural engineering.