Addressing Bottlenecks to Achieve High‐Energy Sodium‐Ion Cells Using Tin Anodes

ABSTRACT Sodium‐ion batteries (NIBs), as a complementary energy storage device for Li‐ion batteries, are swiftly making their way into high‐power applications market. However, further progress in NIBs requires high energy density. This requires a shift from commonly used hard carbon (HC) anodes to alloy anodes such as Bi, Sn, Sb, etc., while overcoming the problems these materials pose, with regard to volume changes and interfacial reactivity. Although ether‐ and glyme‐based electrolytes mitigate anode reactivity, their poor oxidative stability limits compatibility with high‐voltage cathodes such as Na ₃ V ₂ (PO ₄ ) ₂ F ₃ (NVPF). Here, we identify glyme oxidation by‐products and detail their cross‐talk–induced poisoning in NVPF|Sn‐HC cells using operando, ex situ, and post‐mortem (electro)chemical characterizations. Based on these insights, we explore mitigation strategies (i) by reducing the Sn‐poisoning via protective SnO coating and (ii) arresting the cross‐talk phenomenon using a chemical trap such as Na‐metal, Na ₁₅ Sn _4, or Na _x C between the separators. Both approaches improve cell performance, albeit not fully suppressing electrolyte oxidation, with later enabling to reach near 100% capacity retention over 200 cycles at C/5, also giving some hope for achieving anode‐free Na‐ion cells. Although still present some shortcomings, these strategies offer promising directions for materials design, cell engineering, and electrolyte development toward high‐energy sodium‐ion batteries.