Synthesis Towards TiO₂/Graphene Nanocomposites to Enhance the Energy Storage Capability and Stability of Sodium-Ion Batteries

Lithium-ion batteries (LIB) are widely used for powering electric vehicles, cell phone devices, and stationary energy storage because of their long cycle life and high energy density. However, due to the limited availability and high cost of lithium and lithium-ion storage materials, the demand is raising concerning the use of other materials to store energy. Sodium-ion batteries (SIB) could be used to replace LIBs because of the low cost of sodium and its virtually unlimited availability [1]. However, the drawbacks of SIBs are Lower energy density compared to LIBs, and the larger Na⁺ ion radius of (1.02 Å) compared to Li⁺ (0.76Å), leading to an immediate structure change during Na⁺ insertion and extraction that may cause gradual capacity fade. Suitable combinations of cathode and anode materials can provide similar energy densities of SIBs and some types of LIBs. Regarding the anode, developing long-term stable, environmentally friendly, and abundant active materials is of particular interest. Titanium dioxide (TiO₂) has been selected because it is low-cost and non-toxic and features a moderate sodium insertion/extraction voltage (∼0.7 V vs. Na/Na⁺), which efficiently avoids sodium plating on the anode and provides a suitable working voltage when coupled with a cathode material [2]. However, TiO₂ has poor ionic and electronic conductivity limiting its performance and practical capacity. Therefore, integrating ultrafine TiO₂ into a highly conductive and stable graphene matrix achieves exceptional rate capacity and durability [3]. Herein, we report a facile and direct self-assembly method of TiO₂/graphene nanocomposites with a controllable graphene loading to enhance the capacity and stability performance of TiO₂-based materials. The TiO₂/graphene with a graphene loading of 20 and 30 wt. % was tested as an anode in SIBs. With the outstanding conductivity enhancement and synergetic effect between TiO₂ nanoparticles and graphene sheets, the nanocomposites exhibited excellent electrochemical performance with a higher reversible capacity of 281 mAh g^-1 at 0.1C as compared to pristine TiO₂ (155 mAh g^-1) at the same rate. In addition, the nanocomposites could deliver a high reversible capacity of 154 mAh g^-1 after 500 cycles at 10 C and a high average rate capability performance of 158 mAh g^-1 up to 20 C. Overall. The formation of TiO₂/graphene composites prevents the agglomeration of the nanoparticles and provides a high specific surface area, thus leading to an increase in the electrochemical activity of the anode materials. In addition, different in-situ and ex-situ techniques were used to study the mechanism of sodium storage in an anode structure. The synthesized route of the nanomaterials and their outstanding performance provide a new strategy to synthesize advanced nanomaterials for Na-ion batteries applications.<br/><br/><br/><br/><b>References</b><br/><br/>1. D. Karabelli, S. Singh, S. Kiemel, J. Koller, A. Konarov, F. Stubhan, R. Miehe, M. Weeber, Z. Bakenov, K. P. Birke, Sodium-Based Batteries: In Search of the Best Compromise Between Sustainability and Maximization of Electric Performance, Frontiers in Energy Research <b>8,</b> 605129 (2020).<br/>2. J.-Y. Hwang, S.-T. Myung, Y.-K. Sun, Sodium-ion batteries: present and future, Chemical Society Reviews <b>46,</b> 3529-3614 (2017).<br/>3. J. Wang, J. Li, X. He, X. Zhang, B. Yan, X. Hou, L. Du, T. Placke, M. Winter, J. Li, A three-dimensional TiO₂-Graphene architecture with superior Li ion and Na ion storage performance, Journal of Power Sources <b>461,</b> 228129 (2020).