How Do Impurities in Electrolytes Affect the Electrochemical Performance of Oxides in Lithium-Ion Batteries?

The recovery and treatment of spent LIBs has already been studied extensively. On one hand, the hydrometallurgical recovery of cathode materials has aroused widespread attention because of its low energy consumption and benefit to the environment. On another hand, the purification of the materials reclaimed from spent batteries is a challenging process with high probability that, later, some remaining impurities such as transition metal carbonates and sulfates could be released into the electrolyte. In this way the impurity content will have a serious impact on the final performance of the battery. To this point different electrochemical and analytical measurements were conducted to elucidate the effects of impurities in the electrolyte formulation, specifically Li, Mn, Co, Ni, and Al carbonates, sulfates, and acetates. The base LP30 electrolyte was intentionally contaminated with a maximum concentration of selected impurity to study the effects of the contaminated electrolyte on the electrode. Different combinations and varieties were explored correspondingly. Test setups were based on both, NMC811 in half cells (vs. Li) and symmetrical Li||Li cells, and the influence of contaminations was thus exploited on the Li counter electrode and on the NMC811 in Li||NMC811 configuration. A number of standard and advanced electrochemical test techniques such as CC-CV, electrochemical impedance, rate capability tests, GITT, and CV was applied for a fully understanding of the electrochemical characteristics of standard cathode active materials such as NMC811 when electrolytes with (artificially downgraded) low purity levels are present. The presentation will focus on discussion of results regarding the presence of transition metals Ni, Co, and Mn as impurities in the electrolyte which showed a significant impact on the electrochemical performance of the tested cells. When the concentration of the impurities increases, both the overpotentials at the cathode and the rate of capacity decay during cycling increase as well. The data shown will be very helpful for the researchers to understand the impact of impurities on the performance of oxide-based LIB cathode materials.