Synergy in multiphase Nb-W-Ni-O anodes for Li-ion batteries

Anode materials like Li 4 Ti 5 O 12 and TiNb 2 O 7 hold high promise to deliver safe batteries for key applications such as medical devices and large vehicles, including tractors and buses. As high energy densities are required, thorough explorations of Nb-based anodes are underway, with the limitation of Nb being mitigated by other elements to provide stability during cycling. The addition of Ni has previously been shown to improve the rate performance of niobium oxide, and as such, we explore the entire Nb-W-Ni-O system to determine the extent to which Ni can improve the Nb-W-O pseudobinary materials. Interestingly, no single-phase material exists with all three metals. Instead, complex coexistence is seen, which includes multiple three-phase regions that transform during cooling. The best electrochemistry at room temperature is seen in materials with 10 % Ni, where the Ni exists in small particles of NiWO 4 or NiNb 2 O 6 , depending on where we are in the phase diagram. It is synergy between the Nb-W-O and Ni-containing phases that leads to the highest capacities at room temperature. This demonstrates that complex phase coexistence can play important roles in governing battery performance.