Potassium-ion batteries (KIBs) are promising electrochemical energy storage systems because of their low cost and high energy density. However, practical exploitation of KIBs is hampered by the lack of high-performance cathode materials. Here we report a potassium manganese hexacyanoferrate (K₂Mn[Fe(CN)₆]) material, with a negligible content of defects and water, for efficient high-voltage K-ion storage. When tested in combination with a K metal anode, the K₂Mn[Fe(CN)₆]-based electrode enables a cell specific energy of 609.7 Wh kg⁻¹ and 80% capacity retention after 7800 cycles. Moreover, a K-ion full-cell consisting of graphite and K₂Mn[Fe(CN)₆] as anode and cathode active materials, respectively, demonstrates a specific energy of 331.5 Wh kg⁻¹, remarkable rate capability, and negligible capacity decay for 300 cycles. The remarkable electrochemical energy storage performances of the K₂Mn[Fe(CN)₆] material are attributed to its stable frameworks that benefit from the defect-free structure.

Shear-coupled grain boundary (GB) migration is of general significance in the deformation of nanocrystalline and polycrystalline materials, but comprehensive understanding of the migration mechanism at the atomic scale remains largely lacking. Here, we systematically investigate the atomistic migration of Σ11(113) coherent GBs in gold bicrystals using a state-of-art in situ shear testing technique combined with molecular dynamic simulations. We show that shear-coupled GB migration can be realised by the lateral motion of layer-by-layer nucleated GB disconnections, where both single-layer and double-layer disconnections have important contributions to the GB migration through their frequent composition and decomposition. We further demonstrate that the disconnection-mediated GB migration is fully reversible in shear loading cycles. Such disconnection-mediated GB migration should represent a general deformation phenomenon in GBs with different structures in polycrystalline and nanocrystalline materials, where the triple junctions can act as effective nucleation sites of GB disconnections.