Toward higher-power Li-ion batteries: Unravelling kinetics and thermodynamics of MoNb12O33 vs. NMC622

Wadsley-Roth niobates are promising anode materials for high-power lithium-ion batteries. The kinetics and thermodynamics of Li-ion transport in MoNb₁₂O33 (MNO) electrodes were investigated, and its performance in high-power cells alongside a LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622) cathode were optimised. Electrodes and cells were designed with an areal capacity of 1.2 ± 0.2 mAh cm², 90 wt% active material, and a negative-to-positive capacity ratio of ∼1.2. Galvanostatic intermittent titration techniques and electrochemical impedance spectroscopy (EIS) were employed to elucidate kinetic and thermodynamic electrochemical parameters. MNO exhibited an exchange current density of ∼0.012–0.021 mA cm⁻² and high lithium diffusion coefficients of ∼10⁻⁹ cm² s⁻¹ at 50 % state of charge (SOC) and 25 °C. Lithiation and delithiation rate tests in MNO||Li and NMC622||MNO cell configurations at 15 °C and 0 °C highlighted the exceptional rate performance. Rapid charging of full cells was achieved at all tested temperatures, with charging times of 3 min–75 % state of charge at 25 °C, 6 min at 15 °C, and 30 min at 0 °C. Notably, a 6-min charge (10C rate) at 0 °C still provided 50 % of the initial capacity. EIS at various SOC levels indicated the formation of an unstable or reversible solid electrolyte interphase (SEI) layer on the MNO anode at 70–100 % SOC.