Highly stable energy-storage performance of donor-acceptor co-doped TiO₂ films

Energy-storage films that remain stable at high temperatures and frequencies are crucial for various applications. In this study, we demonstrated that donor-acceptor co-doped simple oxide TiO₂ films, viz. V⁵⁺-Cr³⁺ co-doped TiO₂ [(V_0.5Cr_0.5)_xTi_1-xO₂] films, can exhibit highly stable energy-storage performance. The co-doped TiO₂ films exhibited high breakdown strength and polarization owing to the local polarization induced by the V⁵⁺-Cr³⁺ ionic pairs. The energy-storage density of the (V_0.5Cr_0.5)_0.02Ti_0.98O₂ film was approximately 48.93 J/cm³ at room temperature, which is approximately 195 times higher than that of the pure TiO₂ film (0.25 J/cm³). In addition, the (V_0.5Cr_0.5)_0.02Ti_0.98O₂ film exhibited excellent temperature stability from 303 K to 403 K, frequency stability from 0.5 kHz to 7.5 kHz, and fatigue durability over 10⁷ charge-discharge cycles. The proposed strategy can effectively improve the stable energy-storage performance of lead-free donor-acceptor co-doped TiO₂ films, which are in high demand in various applications.