Halloysite nanotube-based semi-solid electrolytes with weak electrostatic interaction for ultra-stable lithium metal batteries.

Semi-solid electrolytes integrate the merits of liquid and solid-state electrolytes, yet their skeleton materials are commonly costly and hard to scale up. Herein, a low-cost, eco-friendly semi-solid electrolyte is developed using natural halloysite nanotubes (HNTs) as the skeleton and poly (vinylidene fluoride) (PVDF) as the binder. The hollow tubular structure of HNTs enables efficient liquid encapsulation, constructs continuous ion-conduction pathways, while the asymmetric surface charges enable dual regulation via weak electrostatic interactions: the outer Si-O-Si surface interacts with Li+ to weaken Li+-PC and Li+-TFSI- coordination, and the inner Al-OH cavity exerts a weak attraction on TFSI-. This dual interaction helps attenuates the Li+-TFSI- coulombic attraction, facilitating ion migration. The resulting semi-solid electrolyte (SSE) exhibits a high ionic conductivity of 0.84 mS cm-1 and a Li+ transference number of 0.67at 30 °C. The Li||Li symmetric cell can operate stably for over 3700 h at 0.3 mA cm-2 and Li||LiFePO4 full battery achieve 90.5% capacity retention after 1400 cycles at 1C, 79.4% after 2700 cycles at 2C, and nearly 100% after 1000 cycles at 5C. It suggests that the natural HNTs are a promising scalable skeleton for high-performance semi-solid electrolytes in lithium metal batteries.