Anode Properties of Sb-Based Alloy Electrodes for K-Ion Batteries in an Ionic-Liquid Electrolyte

Maintaining the sustainability of society demands the strategic use of multipurpose rechargeable batteries. One promising option is K-ion batteries (KIBs), which are suitable as large stationary storage batteries and store renewable energy because of their abundant K resources. Herein, the anode properties of different binary antimonide (MSbx; M: metal) electrodes were investigated for KIBs in an ionic-liquid electrolyte. The results indicated that although Sb and SnSb electrodes exhibited a high initial reversible capacity, their cycle stability was poor. In contrast, rare-earth antimonide (LaSb, SmSb, and YSb) electrodes showed extremely long cycle stability over 500 cycles with a capacity approximately one-third that of the Sb electrode. Interestingly, rare-earth antimonides possess seamless alloying and dealloying with K without undergoing phase separation into rare-earth and Sb phases. Additionally, other MSbx electrodes, such as FeSb2, FeSb, and AlSb, exhibited relatively higher reversible capacity and cycle stability when M was K-inactive. These electrodes possessed moderate Mohs hardness and low electrical resistance and caused MSbx phase separation into M and Sb phases. Notably, the stiff M phase effectively withstood the compressive stress produced by Sb and provided a supporting skeleton. Our study will provide insight into the physicochemical properties of M alloyed with Sb to achieve excellent cycle stability in KIBs and reveal that the same active material demonstrated different anode properties than Na-ion batteries.