Entropy-Tuned Layered Oxide Cathodes for Potassium-Ion Batteries.

The manganese-based layered oxides as a promising cathode material for potassium ion batteries (PIBs) have attracted considerable interest owing to their simple synthesis, high specific capacity, and low cost. However, due to the irreversible phase transition and the Jahn-Teller distortion of the Mn 3+ , its application in potassium ion batteries is limited, leading to slow potassium ion kinetics and severe capacity attenuation. Here, entropy-tuning by changing the content of cathode material composition is proposed to address the above challenges. Compared to low and high entropy variants of K 0.45 Mn x Co (1- x )/4 Mg (1- x )/4 Cu (1- x )/4 Ti (1- x )/4 O 2 , where x = 0.8, 0.6, and 0.4, the medium entropy K 0.45 Mn 0.6 Co 0.1 Mg 0.1 Cu 0.1 Ti 0.1 O 2 shows more balanced electrochemical properties in the PIBs. Benefiting from entropy-tuned suppression of the Jahn-Teller distortion of the Mn 3+ , the K 0.45 Mn 0.6 Co 0.1 Mg 0.1 Cu 0.1 Ti 0.1 O 2 can achieve a high K + ion transport rate and alleviated volume variation while retaining high specific capacity. Accordingly, the medium entropy K 0.45 Mn 0.6 Co 0.1 Mg 0.1 Cu 0.1 Ti 0.1 O 2 cathode in the full cell exhibits a high capacity of 100 mAh g -1 at 50 mA g -1 , delivers superior rate capability (65.8 mAh g -1 at 500 mA g -1 ) and cycling stability (67.8 mAh g -1 after 350 cycles at 100 mA g -1 ). The entropy-tuning strategy is expected to open new avenues in designing PIB cathode materials and beyond.