Charge/discharge cycling of Li_1+x(Ni_0.6Co_0.2Mn_0.2)_1−xO₂ primary particles performed in a liquid microcell for transmission electron microscopy studies

Abstract Ni-rich layered oxides are promising positive electrodes for fulfillment of government and industry targets for lithium-ion-battery-operated electric mobility purposes. Apart from ongoing research focusing on their design and material production, advanced characterization techniques can provide valuable insights on their stabilization by monitoring in situ the degradation mechanisms. Herein, we use liquid-phase transmission electron microscopy to examine the effects of electrochemical stimuli on Ni-rich oxide cathodes by introducing an optimized micro-scale battery configuration. Ball-milled Li_1+x(Ni_0.6Co_0.2Mn_0.2)_1−xO₂ (NCM622) particles were cycled against a delithiated LiFePO₄ anode and the effects of different cycling methods were investigated. We show that commonly used cyclic voltammetry measurements at high scan rates cannot be used to simulate battery operation in situ due to geometry limitations of the cell that inhibits Li ion transport. However, using galvanostatic charge/discharge cycling and introducing a pause every 10 cycles for a total of 50 cycles results in degradation in the form of Mn and Co ion dissolution from the first 20 nm of the surface. Our results suggest that although performing battery cycling using liquid cell electron microscopy may differ from the case of coin cells, by tuning the electrochemical profiles used similar degradation mechanisms can be attained.