Surface Modification of NaCrO2 Positive Electrode Material for Sodium-Ion-Batteries

Abstract

Sodium-ion batteries are potential successors of lithium-ion batteries, due to the abundance of sodium resources, which leads to up to 30% cost reduction when the two systems are compared directly[1]. While the cost advantage is high the performance of sodium ion batteries still needs improvement if they are to replace their lithium counterparts in many areas. Stability and performance are big areas which need to be improved.The volatile (H2AlOtBu)2-precursor can be used to create a coating of HAlO on metal surfaces at 270°C from the gas phase via chemical vapor deposition. It has also been used to coat Li1+x(Ni0.85Co0.10Mn0.05)1-x positive electrode material for lithium ion batteries in an autoclave at 180°C, resulting in a LiAlO2 layer and improving cycling stability.[2],[3]In this work the same coating procedure was applied to the NaCrO2 positive electrode material resulting in a similar coating and improving the performance of the material in electrochemical tests in half cells. The coating received has been shown to be a mix of different aluminium compounds resulting in an artificial cathode electrolyte interface. Electrochemical testing shows that the capacity of the treated material is higher than the capacity of the pristine one from the first cycle and it shows increased cycling stability. These improvements can be attributed to a lower resistance of the coated compared to the pristine material as shown by electrochemical impedance spectroscopy.Overall the coating procedure is simple and the required amount of 0.3 weight percent of precursor material compared to the positive electrode material is very small for a big effect on electrochemical performance.[1] D.Larcher, J-M. Tarascon, Nat. Chem, 2014, 7, 19-25[2] M. Veith, S. Faber, H. Wolfanger, V. Huch, Chem. Ber. 1996, 129, 381.[3] A. Martens, C. Bolli, A. Hoffmann, C. Erk, T. Ludwig, M. El Kazzi, U. Bredde-mann, P. Novák, I. Krossing, J. Electrochem. Soc. 2020, 167, 70510.