Compensation for K+ loss of K-doped Na0.7MnO2 by K+ supply source for high-performance sodium-ion batteries

K 0.5 MnO 2 @Na 0.7 MnO 2 composite is prepared by a KCl@Na 2 CO 3 molten salt. • Electrochemically induced conversion of KMO@NMO into K-doped NMO is achieved. • K doping enhances structural stability of NMO and facilitates Na + migration. • KMO as K + supply source compensates K + loss in NMO upon cycling. • KMO@NMO shows high capacity retention after 800 cycles. P2-type layered Na 0.7 MnO 2 is regarded as a promising cathode material for sodium-ion batteries due to its high specific capacity. However, Mn 3+ -induced Jahn-Teller distortion and Mn 2+ dissolution result in the structural instability of Na 0.7 MnO 2 , thereby restricting its large-scale application. In this study, a K 0.5 MnO 2 @Na 0.7 MnO 2 composite is prepared by a molten salt method and used as a cathode. In particular, partial K + in K 0.5 MnO 2 substitutes for the Na + sites in Na 0.7 MnO 2 during the charge-discharge process, which decreases the Mn 3+ /Mn 4+ ratio and provides wide Na + channels, achieving fast reaction kinetics and long-term cycling stability. The persistent K 0.5 MnO 2 throughout the entire testing process works as a robust K + supply source and compensates for the K + loss of K-doped Na 0.7 MnO 2 during cyclic tests. Consequently, the cathode shows a high discharge capacity of 148 mA h g −1 at 0.04 A g −1 and outstanding cycling stability, with a capacity retention of 69% after 800 cycles at 0.5 A g −1 . This research provides important references for designing high-performance layered cathode materials in sodium-ion batteries. Download: Download high-res image (135KB) Download: Download full-size image