Effect of prelithiation with passivated lithium metal powder on passivation films on high-energy NMC-811 and SiCx electrodes

The effect of prelithiation using passivated lithium metal powder (PLMP) pressed onto SiCx anodes is reported for NMC-811k SiCx cells with high energy mass loadings. The effect of prelithiation degree and storage time after cell assembly on the formation and growth of the solid electrolyte interphase (SEI) was elucidated by impedance spectroscopy (EIS) and operando solid-state 7Li nuclear magnetic resonance (NMR) spectroscopy, which allowed determining the optimal storage period for the prelithiated cells. The galvanostatic intermittent titration technique (GITT) was used to compare apparent Li thorn diffusion co-efficients in prelithiated and non-prelithiated SiCx electrodes. Furthermore, we show that the electro-chemical performance of NMC-811k SiCx cells can be dramatically improved by prelithiation using PLMP. In particular, cycle life at 80% state of health (SoH) is almost tripled, increasing from 80 to 228 cycles. Moreover, X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray (EDX) analysis show that the composition of the cathode electrolyte interphase (CEI) is also markedly modified compared with non-prelithiated reference cells. In particular, the amount of LixPFyOz species is reduced as prelithiation using PLMP promotes a more effective SEI layer on the SiCx electrode, richer in LiF and Li3PO4, and richer in organic components that probably also contribute to the enhanced cycling stability.& COPY; 2023 Elsevier Ltd. All rights reserved.