Probing the Electrochemical Role of Na2CO3 as Surface Residual on LiNi0.6Co0.2Mn0.2O2

Abstract

Lithium bearing compounds like LiOH and Li2CO3 are important raw materials for manufacturing of lithium-ion batteries. The chemical tolerance level of battery grade raw materials towards impurities will eventually determine the complexity and cost of the manufacturing process for raw materials. Sodium bearing compounds are a class of major impurities for lithium compounds extracted from the brine. In this work, the electrochemical role of surface residual Na2CO3 was systematically investigated using LiNi0.6Co0.2Mn0.2O2 as the model cathode material. As a demonstration, different amount of Na2CO3 was deposited on the surface of LiNi0.6Co0.2Mn0.2O2 for determination of the tolerance level towards Na2CO3. It was found that excessive amount of Na2CO3 (>10,000 ppm of Na+) substantially accelerated the parasitic reactions between the delithiated cathode and the electrolyte, leading to accelerated capacity fading of the cathode material. It was also found that low concentration Na2CO3 (≤1,000 ppm of Na+) had marginal impact on the electrochemical performance of the cathode primarily due to the existing background Li2CO3 impurity inherited from the synthesis and storage of the cathode material.