K + Induced Phase Transformation of Layered Titanium Disulfide Boosts Ultrafast Potassium‐Ion Storage

Abstract Potassium dual‐ion batteries (K‐DIBs) have invoked considerable interest owing to their high safety and power density. However, achieving high‐rate and good cyclability anodes for K‐DIBs is still a grand challenge. Herein, layered TiS 2 is proposed as an attractive anode for K‐DIBs, which achieves a discharge capacity of 91.0 mA h g −1 while being discharged/charged to 2000 cycles in half cells. Interestingly, such a stable capacity is attributed to the mechanism of the K + induced phase transformation. In situ characterizations and first principles calculations reveal that the inserted K + acts as pillar between the Ti‐S layers producing the thermodynamically stable K 0.25 TiS 2 phase eventually. The robust K 0.25 TiS 2 phase shows enlarged interlayer space, enhanced electronic conductivity, and lower diffusion barrier that enable highly stable and fast storage of K + . Moreover, a novel K‐DIB based on TiS 2 anode and mesocarbon microbead cathode is reported for the first time. The K‐DIB achieves a reversible capacity of 75.6 mA h g −1 at 100 mA g −1 and excellent cyclability with 85.8% capacity retention over 1000 discharge/charge at 5000 mA g −1 . Such mechanistic research provides new insights into the reaction process of layered sulfides/selenides and will facilitate their application in safe and high‐power K‐DIBs.