This study investigates the development of tailored electrolyte formulations for commercial sodium-ion batteries (NIBs) with layered oxide cathodes and hard carbon anodes. The electrolyte plays a central role in improving key performance indicators (KPIs). By adjusting the electrolyte, material degradation and sodium plating are to be minimized while ensuring compatibility with existing patents. The aim is to enhance the performance of NIBs through new additives and improve their safety and lifespan.
The cathode material was characterized in detail to develop tailored electrolytes. Additionally, patent and literature analyses were conducted to identify relevant electrolyte components. Various formulations were electrochemically characterized and evaluated based on KPIs such as efficiency, cost, safety, and lifespan.
The patent and literature analysis identified NaPF₆, NaFSI, and NaTFSI as relevant conductive salts, carbonates as solvents, and additives analogous to lithium-ion technology. The cathode material identified was the NFM334-type layered oxide, Na0,96Ca0,04[Ni0,24Fe0,30Mn0,37Zn0,09]O2, which exists in the O3 phase. During cycling (1 C, 4.0 V, 40 °C), sodium plating and gas generation occurred due to the dissolution of transition metal ions. Degradation of the material occurred due to a phase transition during charge and discharge, resulting in the release of transition metal ions into solution, which were detected on the anode via ICP-OES and SEM/EDX. An optimized electrolyte formulation with a novel additive led to a 30 % increase in lifespan, suppressed sodium plating, and reduced gas generation by 25 % compared to a commercial state-of-the-art electrolyte. The conductivity of the optimized electrolyte at 40 °C was measured to be 9.4 mS/cm. Benchmarking against known additives such as VC (vinylene carbonate), FEC (fluoroethylene carbonate), TMSB (trimethyl(silyl)borate), and PS (1,3-propanesultone) demonstrated that the optimized formulation with the novel additive offers enhanced safety and lifespan without toxic components.
The iterative optimization of the electrolyte identified an additive that significantly improves the safety and lifespan of NIBs by suppressing sodium plating and reducing gas generation. A comparison of the KPIs indicates that this additive serves as a safety additive and a non-toxic alternative to traditional, potentially harmful additives.