Boosting Potassium Storage Capacity Based on Stress‐Induced Size‐Dependent Solid‐Solution Behavior

Abstract A prerequisite for successful development of a K‐ion battery anode based on solid‐solution behavior is to improve its potassium storage capacity. Increasing the solid‐solution domain by decreasing the particle size offers a promising strategy for enhancing the potassium storage capabilities of insertion anode materials. Extended solid‐solution composition range in nanostructured particles is mainly due to the existence of a coherency strain that suppresses phase separation upon intercalation. Here, the intercalation stress effect in size‐dependent solid‐solution behavior is explored by insertion of K + into K 2 Ti 6 O 13 nanowires with different diameters. K 2 Ti 6 O 13 nanowires with small average diameter of ≈5.5 nm deliver a large initial reversible depotassiated capacity of ≈120 mAh g −1 (deinsertion of ≈2.5 K + ) at 0.2 C. The remarkably high reversible depotassiated capacity is mainly ascribed to the decrease of the incoherent interface upon potassiation. The direct observation of enrichment of intragranular particles in potassiated K 2 Ti 6 O 13 nanowires with average diameter of ≈38 nm provides evidence of strain‐accommodating misfits or dislocations in solid‐solution intercalation compounds. This work offers a promising route to utilize coherency strain energy for K‐ion batteries with improved specific capacity and alleviated irreversible capacity loss.