An aliovalent-substituted inorganic-open-framework anode for high-performance potassium-ion batteries

Potassium-ion batteries have drawn great attention owing to the abundant and low-cost potassium resources. However, the lack of highly reversible K+-storage electrodes remains a key concern, due to the large size of K+ ions. Inorganic-open-framework KTiOPO4-type (KTP) anodes are promising K+-hosts, due to their large interstitial vacancies allowing fast and reversible insertion of K+ ions with low structural evolution. Here, we report a new member in the KTP family, K0.63Cr0.56Ti0.55OPO4 (KCTP), with partial aliovalent substitution. The KCTP exhibits a high specific capacity of 123.4 mAh/g and achieves stable cycle life, over 135 days with 98% capacity retention at 10 mA/g and up to 9.9 months with 81% retention at 20 mA/g. The K+-storage process involves biphasic reaction and solid-solution reaction, with a minor volume change of only 8.06%. This work demonstrates that inorganic open frameworks with aliovalent substitution may open a promising way to design high-performance potassium-ion batteries.