High-voltage deprotonation of layered-type materials as a newly identified cause of electrode degradation

Further development of electrochemical devices and electric vehicles requires advanced secondary batteries with higher energy density, longer lifetime and enhanced thermal safety. Increasing the cell operating voltage is one of the realistic strategies to extend the energy density, but it is inevitably accompanied by irreversible structural changes and mechanical failure of the electrode materials and continuous parasitic reactions within the electrode-electrolyte interface resulting in capacity fading and subsequent battery failure along with safety issues. Herein, we report deprotonation of layered-type materials at high voltages (>4.5 V vs. Li/Li+) as a newly identified cause of electrode degradation, which has not been addressed previously. Electrochemical analysis and diagnostics combined with advanced characterization studies and computational simulations were employed to understand deprotonation mechanisms and investigate the effect of the deprotonation process on the electrode during high voltage operation. We demonstrated that protons act as charge carriers in lithium (Li)-free materials through the deprotonation process during the initial charging. In addition, this study shows that the deprotonation process is dependent upon transition metals and accordingly deteriorates the electrode by changing its structure and electrochemical properties.