Strain-mediated lattice stabilization and suppressed manganese dissolution in α-MnO2 for advanced calcium storage

Iron doping regulates lattice strain to stabilize the manganese dioxide framework. • Modifying the local structure suppresses manganese dissolution during cycling. • Strain modulation accelerates calcium storage kinetics and improves robustness. • The optimized cathode delivers high capacity and long cycle life. Calcium-ion batteries (CIBs) have attracted increasing attention owing to the natural abundance and potentially low cost of calcium resources. However, practical CIBs cathodes are broadly hindered by sluggish Ca 2+ diffusion, large polarization, and structural instability upon repeated (de)intercalation. Among Mn-based candidates, α-MnO 2 exhibits a low Ca 2+ diffusion barrier, yet its structure suffers irreversible damage during Ca 2+ insertion/extraction. Herein, we propose a Fe-doping strategy to reconstruct the tunnel skeleton of Mn octahedra in α-MnO 2 , which toughens the lattice and regulates its electronic properties, thereby inhibiting the Jahn-Teller effect and preventing Mn dissolution. The strategic incorporation of Fe induces targeted lattice strain, maintaining the long-range skeletal integrity while precisely modifying short-range local distortions. This strain-driven regulation significantly expedites Ca 2+ transport, yielding a diffusion coefficient of 1.24 × 10 −9  cm 2  s −1 , which is the highest recorded value among Mn-based CIB cathodes. Consequently, the optimized Fe-doped α-MnO 2 delivers high rate performance, achieving capacities of 201, 161, 145, 132, and 111 mAh g −1 at 0.1, 0.2, 0.3, 0.5, and 1.0 A g −1 , respectively. Furthermore, it exhibits a long-term cycle life by retaining 74 mAh g −1 after 3000 cycles at 1 A g −1 , providing a rational design paradigm for advanced Mn-based cathodes in CIBs.