Modified Lithium Borate Buffer Layer for Cathode/Sulfide Electrolyte Interface Stabilization

Abstract

<p>All-solid-state rechargeable batteries, using nonflammable sulfide-based solid electrolytes, address lithium-ion battery safety issues while enhancing energy density and operating temperature range. However, the electrochemical stability limitations of sulfide electrolytes present challenges to the interface stability, particularly with oxide-based cathodes. The application of a stable coating layer is known to be effective for stabilizing the cathode/sulfide electrolyte interface. In particular, lithium borate is a promising coating material owing to its cost-effectiveness and efficiency in controlling interfacial reactions. However, lithium borate exhibits oxide characteristics, leading to a difference in the chemical potential of Li<italic>⁺</italic> compared to sulfide electrolytes. This discrepancy results in an uneven distribution of Li<italic>⁺</italic> ions at the interface, which hinders Li-ion migration during charge and discharge cycles. To address this issue, a lithium borate-coating layer was modified with sulfur via a gaseous reaction involving sulfur. Sulfur-modified lithium borate is expected to reduce the chemical potential difference of Li<italic>⁺</italic> and enhance the electrochemical properties. To confirm the effectiveness of sulfur modification, the electrochemical properties of coated and pristine samples were compared via various analysis tools. The results confirmed that sulfur modification can further improve the effect of lithium borate coating in enhancing the rate capability and cyclic performance of a battery. Additionally, it was observed that sulfur modification further reduces interfacial resistance and considerably improves the control of side reactions.</p>