Electrolyte Engineering on Performance Enhancement of NiCo₂ S₄ Anode for Sodium Storage

NiCo₂ S₄ is an attractive anode for sodium-ion batteries (SIBs) due to its high capacity and excellent redox reversibility. Practical deployment of NiCo₂ S₄ electrode in SIBs, however, is still hindered by the inferior capacity and unsatisfactory cycling performance, which result from the mismatch between the electrolyte chemistry and electrode. Herein, a functional electrolyte containing 1.0 m NaCF₃ SO₃ in diethylene glycol dimethyl ether (DEGDME) (1.0 m NaCF₃ SO₃ -DEGDME) is developed, which can be readily used for NiCo₂ S₄ anode with high initial coulomb efficiency (96.2%), enhanced cycling performance, and boosted capacities (341.7 mA h g^-1 after 250 continuous cycles at the current density of 200 mA g^-1 ). The electrochemical tests and related phase characterization combined with density functional theory (DFT) calculation indicate the ether-based electrolyte is more suitable for the NiCo₂ S₄ anode in SIBs due to the formation of a stable electrode-electrolyte interface. Additionally, the importance of the voltage window is also demonstrated to further optimize the electrochemical performance of the NiCo₂ S₄ electrode. The formation of sulfide intermediates during charging and discharging is predicted by combining DFT and verified by in situ XRD and HRTEM. The findings indicate that electrolyte engineering would be an effective way of performance enhancement for sulfides in practical SIBs.