Electrochemical activity regulating by strain control to achieve high-performance potassium-ion-based dual-ion battery

Potassium dual ion batteries (K-DIBs) are attractive candidates for grid-scale energy storage. However, the poor rate capability/cycle stability and low energy density seriously impede their practical implementation. Herein, a method to realize electrochemical activity tuning for K-ion storage by regulating the interlayered strain of hydrogen titanate is proposed. Volume expansion, caused by the alloying reaction between Na+ and pre -imbedded Sn-ions in hydrogen titanate, triggers the widening of interlayer spacing and partial distortion of Ti-O slabs, and lattice tension of 24% is observed in the designed anode. Revealed by DFT and BVLS calculations, fully Na+ insertion between Ti-O layers would generate strong Coulomb repulsion with K+, increasing the diffusion barrier of K+. Partial Na+ removal could reduce the Coulomb repulsion and the Na-activated anode with 2/3 Na insertion per formula unit delivers the lowest percolation energies for K+ migration. Moreover, Na-based SEI with organics dominated on the outer layer and inorganics on the inner layer is more uniform and thinner than that of K-based SEI. These merits result in a 322% improvement in potassium storage performance. When used as an additive-free anode for K-DIBs, the K-DIBs can deliver a reversible capacity of 96 mAh g-1 and work stably for 2000 cycles.