Targeted trifunctional regulation via bimetal-oxide hollow spheres boosts PVDF-HFP-based polymer-in-salt electrolyte for stable solid-state lithium metal batteries

Abstract

Poly(vinylidene fluoride) (PVDF)-based polymer-in-salt electrolytes (PISEs) emerge as highly promising candidates for solid-state lithium metal batteries (SSLMBs). However, challenges such as inhomogeneous Li⁺ flux, a low Li⁺ transference number ($t_{L{i}^{+}}$), and unstable solid electrolyte interphase (SEI) significantly compromise compatibility with lithium metal, severely hindering their practical application. Herein, tailored CuWO₄ hollow spheres are strategically introduced as trifunctional regulator to achieve PVDF-based PISEs (PCW-6) with markedly enhanced lithium metal compatibility. The nucleation-regulating effect reduces spherulite dimensions, forming a dense electrolyte with superior mechanical strength, while isotropic spherical fillers enable continuous and uniform ion transport channels. Additionally, the interaction between CuWO₄ and anions facilitates Li⁺ dissociation, resulting in a high $t_{L{i}^{+}}$ (0.68). Moreover, the interfacial phase-regulating function of Cu²⁺ within CuWO₄ induces the formation of an SEI featuring a Cu-containing, LiF-rich inner layer and an organic-dominated outer layer, thereby fostering uniform deposition and bolstering mechanical robustness. Based on these advantages, the Li||Cu cell exhibits excellent plating/stripping reversibility. The Li||Li symmetric cell achieves stable cycling for 1100 h with low polarization voltage (∼75 mV), accompanied by an even and dense deposition morphology. Furthermore, the LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622)||Li cell showcases superior rate capability and stable cycling performance, maintaining 80% capacity retention after 400 cycles at 1 C. This work offers valuable insights into the rational design of functional fillers, laying a solid foundation for the development of lithium-metal-compatible polymer electrolytes toward high-performance SSLMBs.