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

Abstract

AbstractA 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 K2Ti6O13 nanowires with different diameters. K2Ti6O13 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 K2Ti6O13 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.