Host–Guest Inversion Engineering Induced Superionic Composite Solid Electrolytes for High-Rate Solid-State Alkali Metal Batteries
Xiong Xiong Liu, Long Pan, Haotian Zhang, Pengcheng Yuan, Mufan Cao, Yaping Wang, Zeyuan Xu, Min Gao, Zheng Ming Sun
Abstract
Abstract Composite solid electrolytes (CSEs) are promising for solid-state Li metal batteries but suffer from inferior room-temperature ionic conductivity due to sluggish ion transport and high cost due to expensive active ceramic fillers. Here, a host–guest inversion engineering strategy is proposed to develop superionic CSEs using cost-effective SiO 2 nanoparticles as passive ceramic hosts and poly(vinylidene fluoride-hexafluoropropylene) (PVH) microspheres as polymer guests, forming an unprecedented “polymer guest-in-ceramic host” (i.e., PVH-in-SiO 2 ) architecture differing from the traditional “ceramic guest-in-polymer host”. The PVH-in-SiO 2 exhibits excellent Li-salt dissociation, achieving high-concentration free Li + . Owing to the low diffusion energy barriers and high diffusion coefficient, the free Li + is thermodynamically and kinetically favorable to migrate to and transport at the SiO 2 /PVH interfaces. Consequently, the PVH-in-SiO 2 delivers an exceptional ionic conductivity of 1.32 × 10 −3 S cm −1 at 25 °C (vs . typically 10 −5 –10 −4 S cm −1 using high-cost active ceramics), achieved under an ultralow residual solvent content of 2.9 wt% (vs . 8–15 wt% in other CSEs). Additionally, PVH-in-SiO 2 is electrochemically stable with Li anode and various cathodes. Therefore, the PVH-in-SiO 2 demonstrates excellent high-rate cyclability in LiFePO 4 |Li full cells (92.9% capacity-retention at 3C after 300 cycles under 25 °C) and outstanding stability with high-mass-loading LiFePO 4 (9.2 mg cm −1 ) and high-voltage NCM622 (147.1 mAh g −1 ). Furthermore, we verify the versatility of the host–guest inversion engineering strategy by fabricating Na-ion and K-ion-based PVH-in-SiO 2 CSEs with similarly excellent promotions in ionic conductivity. Our strategy offers a simple, low-cost approach to fabricating superionic CSEs for large-scale application of solid-state Li metal batteries and beyond.