Tin–Graphite Composite as a High-Capacity Anode for All-Solid-State Li-Ion Batteries

The use of composites instead of pure metals as negative electrodes is an alternative strategy for making all-solid-state lithium-ion batteries (Li-SSBs) more viable. This study reports on the properties of a composite electrode (Sn/Graphite) consisting of nanosized Sn (17 wt %) and graphite (83 wt %). The theoretical capacity of this material is 478 mAh g_{(Sn/Graphite)}^–1. When mixed with Li₃PS₄ (LPS) as a solid electrolyte (SE), an areal capacity of 1.75 mAh cm^–2 (active mass loading of 3.8 mg cm^–2) is obtained, which can be increased up to 3.0 mAh cm^–2 for 7.6 mg cm^–2. At 0.02 mA cm^–2, the Sn/Graphite electrode delivers a gravimetric capacity of 470 mAh g_{(Sn/Graphite)}^–1, i.e., close to its theoretical value. At 0.1 mA cm^–2, the capacity is 330 mAh g^–1 (second cycle) but drops to 84 mAh g^–1 after 100 cycles. Solid-state nuclear magnetic resonance spectroscopy (ssNMR) and X-ray photoelectron spectroscopy (XPS) are used to investigate the stability of the solid electrolyte for this cell configuration. Optimization of the electrode is explored by varying the electrode loading between 3.8 and 7.6 mg cm^–2 and the SE content between 0 and 65%. For electrodes without any SE, gravimetric capacities (mAh g_{(Sn/Graphite)}^–1) and areal capacities (mAh cm^–2) are lower compared to electrodes with SE; however, their volumetric capacity is higher. This emphasizes the need to optimize the composition of electrodes for SSBs.