Enabling stability at a high working voltage of a P2-Na0.85Li0.17Ni0.21Mn0.64O2 sodium-ion battery cathode via utilization of succinic anhydride as an electrolyte additive

The practical implementation of P2-Na0.85Li0.17Ni0.21Mn0.64O2 as sodium-ion battery cathode has been hampered by problems of self-discharge and poor cycling stability caused by electrolyte oxidation. Here, we developed an electrolyte formulation that makes use of succinic anhydride as a key additive to alleviate these drawbacks. The composition of the electrolyte was optimized and the so-optimized electrolyte enables a safe performance of the cathode in a 2-4.2 V vs. Na+/Na electrochemical window. Electrochemical studies including electrochemical impedance spectroscopy and microscopy studies showed that succinic anhydride favours the formation of a cathode electrolyte interface that protects the cathode against electrolyte oxidation. As compared to the electrodes tested in the succinic anhydride-free electrolyte, self-discharge processes were substantially reduced and cycling stability (up to 100 cycles, 2-fold improvement) and Coulombic efficiency were improved. More remarkable was the improvement on power density performance. The cathode tested in the optimized electrolyte performed up to the high current density of 5.78C delivering a high power of 1.88 kW kg−1, whereas the cathode tested in the SA-free electrolyte faded readily at 1.77C. Equally, the cathode showed a much more stable average voltage of 3.17-2.89 V vs. Na+/Na, over such a wider range of operating current rates. The cathode delivered a maximum energy density of 377 Wh kg−1. Importantly, SA also aided in preventing corrosion of aluminum current collectors in the electrochemical window of interest.