Lithium-philic organic polymer@mixed-phase TiO2 core-shell nanospheres for high-rate and long-cyclic performance in liquid/solid-state lithium-ion batteries

To address the issues of slow capacity activation and poor stability faced by organic polymer electrodes, this study, proposed a synergistic lithium storage effect derived from modified polydopamine sphere by mixed-phase TiO₂ shell of anatase TiO₂, rutile TiO₂, and TiO₂(B), synthesizing polydopamine@mixed-phase TiO₂ (PDA@mp-TiO₂) core-shell nanospheres. The in-situ growth of mixed-phase TiO₂ grains induces the partial oxidation of hydroxyl groups in polydopamine to quinone groups, making the C=O groups and benzene rings more active for lithium storage and thus improving the reversible capacity. The coordination between mixed-phase TiO₂ and polydopamine reduces the spatial hindrance effect among polydopamine long chains, endowing extra stable channels for rapid adsorption and diffusion of lithium ion. Moreover, the mixed-phase TiO₂ shell intercepts side reactions between organic groups of the electrolyte and polydopamine without affecting electron-ion transport, promotes the formation of a fluorine-rich inorganic SEI layer, improving the long-term cycling stability of the PDA@mp-TiO₂ electrode. In the liquid lithium-ion batteries, the PDA@mp-TiO₂ electrode exhibits an unprecedented reversible capacity at low current densities. Furthermore, the PDA@mp-TiO₂ demonstrates an ultra high-rate long cyclic life. As the anode for solid-state lithium-ion batteries, PDA@mp-TiO₂ also achieves up to 90 % capacity retention under high current densities.