Lithium-Metal Batteries with Ternary Cathode-Supported NASICON-Type Composite Solid Electrolytes Enabling High-Rate Capability and Excellent Cyclic Performance

This study aimed to investigate the robust design of composite solid electrolytes (CSEs) for high-performance lithium-metal batteries by incorporating metal-doped Li1.5Al0.5Ti1.5(PO4)3 (LATP) powders into a soft polymer matrix with a lithium salt. These batteries utilize ternary LiNi0.5Co0.2Mn0.3O2 (NCM523) materials as the cathode. LATP powders were modified via doping with various bimetallic ions (Co, Cu, and Sn) and synthesized through the sol–gel method followed by thermal calcination, serving as highly ionic conductors in the CSEs. Li symmetric cells with Sn-LATP electrolytes demonstrated stable cycling for up to 600 cycles without short circuits. The Li-metal batteries with Sn- doped LATP powder CSEs exhibited exceptional electrochemical stability across a wide voltage range of 2.8–4.3 V vs Li/Li+. The battery with the Sn-LATP CSE achieved notable performance, with capacity retentions of 94.5% (0.5C), 87.3% (1C), 72.5% (2C), and 57.1% (3C) relative to its capacity at 0.1C. The inclusion of Sn-LATP powders in the CSEs enhanced both high-rate capability and cyclic stability compared to other LATP variants. The Sn-LATP-containing CSE exhibited a lithium diffusion coefficient and ionic conductivity of up to 2.89 × 10–10 cm2 s–1 and 4.24 × 10–4 S cm–1, respectively, approximately 70.5 and 17.1 times higher those of the pristine PVDF-HFP sample. Notably, the Li-metal battery with Sn-LATP CSE maintained superior cyclic performance with excellent Coulombic efficiency (>99.3%) over 300 cycles. At a high power density (902 W kg–1), the NCM523||Sn-LATP||Li battery achieved an impressive energy density of approximately 230 W kg–1. The higher electronegativity of Sn (∼1.96) compared to Co and Cu played a critical role in stabilizing the NASICON framework, especially during extended cycling, while the robust Li–Sn bonding further enhanced performance. These results underscore the potential of Sn-LATP fillers to enhance high-performance solid-state electrolytes, enabling improved energy and power densities with stable cycling in Li-metal batteries.