双盐镁电池CoS2正极材料的电化学性能研究

镁金属电池因为镁金属负极的高体积比容量(3833 mAh/cm³)和高安全性而日益受到关注。然而, Mg²⁺引起的极化效应抑制了Mg²⁺在固相中的扩散, 限制了镁金属电池的比容量。锂镁双盐电解液利用Li⁺代替Mg²⁺驱动正极反应, 能够绕开Mg²⁺在固相中扩散缓慢的问题。本工作研究了过渡金属硫化物CoS₂在不同锂镁混合电解液中的电化学性能, 并分析了锂盐浓度和充放电电压区间对其转换反应和循环稳定性的影响。添加锂盐的策略提高了CoS₂基镁金属电池的转换反应动力学, 当充电电位提高至2.75 V时, Mg-CoS₂电池在LiCl-APC电解液中的循环稳定性得到显著提高, 在循环150次后, 其比容量仍能维持在275 mAh/g, 远高于在2.0 V截止电压条件下的33 mAh/g。电池容量衰减与CoS₂正极在2.0 V充电电位下Co₃S₄的不可逆生成有关, 其长期循环中伴随的Co和S元素溶解加剧了容量的不可逆损失。本工作为过渡金属硫族化合物在转换反应型镁电池中的应用提供了一种激活策略。

CoS2 as Cathode Material for Magnesium Batteries with Dual-salt Electrolytes

Magnesium metal batteries (MMBs) have attracted increasing attention due to the high volume specific capacity (3833 mAh/cm³) and high safety of Mg metal anode. Nevertheless, the high polarization effect induced by Mg²⁺ inhibits its diffusion in solid phase and therefore limits the specific capacity of MMBs. Li⁺/Mg²⁺ dual-salt electrolyte has been proposed to circumvent the sluggish diffusion of Mg²⁺ in solid phase, which enables Li⁺ to replace Mg²⁺ to drive the cathode reaction. In this work, the electrochemical performance of CoS₂ as conversion cathode of MMBs is studied based on different Li⁺/Mg²⁺ dual-salt electrolytes, and the effects of Li-salt concentration and discharge-charge voltage range on cycling stability are analyzed. The strategy of Li-salt additive remarkably promotes the conversion kinetics of CoS₂ based MMBs. By developing charge voltage to 2.75 V, the cycling stability of Mg-CoS₂ cell in LiCl-APC electrolyte is significantly enhanced. Its specific capacity can be maintained at 275 mAh/g after 150 cycles, which is much higher than that (33 mAh/g) under the protocol of 2.0 V charge voltage. It is found that the capacity degradation of MMBs is related to the irreversible reaction of CoS₂ and generation of Co₃S₄ at the charge potential of 2.0 V. And the dissolution of Co and S elements from active species aggravates the irreversible loss of capacity. This study provides an electrochemical activation solution to the development of transition metal sulfides in conversion type MMBs.