Stabilizing Ca-ion batteries with a 7000-cycle lifespan and superior rate capability by a superlattice-like vanadium heterostructure

Calcium-ion batteries (CIBs) by their strong competitiveness in cost and capacities have been considered as a desirable electrochemical energy technology. Nonetheless, the large ion radius and high charge density of Ca²⁺ lead to sluggish electrochemical reaction kinetics and structural collapse of electrode materials. Herein, we construct a superlattice-like poly 3,4-ethylenedioxythiophene−V₂O₅ (P–V₂O₅) heterostructure using an in situ self-assembly strategy and employ it as a CIB cathode. In the heterostructure, the inserted poly 3,4-ethylenedioxythiophene enlarges the interlayer of V₂O₅, exposing abundant active sites for efficient Ca²⁺ absorption and transport; meanwhile, it serves as an ‘interlayer linker’ between neighboring layers, which alleviates the volume change of V₂O₅ during Ca²⁺ insertion/extraction processes. Under the synergistic effect of these factors, the P–V₂O₅ electrode exhibits a longer life span and greater rate capability than pristine V₂O₅. Specifically, the electrode delivers a significant capacity of 157.2 mAh/g at 1 A/g and excellent cycle stability over a long period of 7000 cycles at a high current density of 20 A/g. Furthermore, it has a superior rate capability of 129.0 mAh/g even at 30 A/g. Electrochemical mechanism studies reveal that the insertion/extraction of Ca²⁺ in P–V₂O₅ is highly reversible, accompanied by the interlayer contraction/expansion.