Aquatic Environment Breaks the Size Confinement of the TiO₂ Anodes in Aqueous Batteries

The particle size of TiO₂ anodes is commonly believed to have a negative impact on their mechanical properties. As submicron-sized TiO₂ exhibits low surface energy, which reduces yield strength and leads to mechanical fracture during the two-phase lithium storage mechanism, it is excluded from traditional nonaqueous lithium-ion batteries. In this study, we discovered that TiO₂ demonstrates an independent size effect in an aqueous environment, mitigating the mechanical fracture associated with submicron-sized TiO₂. Our studies reveal that water molecules strongly interact with submicron TiO₂ materials, increasing the surface energy in aqueous electrolytes in a unique manner. This enhancement makes submicron TiO₂ more resilient during the lithiation and de-lithiation reactions. Additionally, the transition from nano to submicron TiO₂ facilitates the inhibition of hydrogen evolution reactions (HER) in aqueous batteries and enhances the performance of electrode coatings. Consequently, submicron TiO₂ exhibits superior electrochemical performance in aqueous batteries, with an Ah-level pouch battery achieving an energy density of 66 Wh kg^-1 (217 Wh L^-1) and demonstrating excellent cycling stability of over 1200 cycles. Our work has successfully addressed the size limitations of the TiO₂ anodes, offering an innovative perspective on micro-sized electrode materials previously considered unsuitable for battery use.