Abstract
The cycling performance of nickel-rich lithium nickel cobalt manganese oxide (NMC) electrodes in Li-ion batteries (LIBs) partially depends on the control of the kinetics of degradation processes that result in impedance rise. The impedance contribution from surface film formation at the NMC/electrolyte interfaces is highly dependent on the initial chemical composition and the structure of the NMC surfaces. Through comparison of film quantity and electrochemical performance of composite electrodes made of pristine- and surface treated-NMC materials, we are able to demonstrate that a simple surface treatment suppressed the subsequent film formation and reduced impedance rise of the Li/NMC half-cells during cycling. Detailed modelling of factors affecting cell impedance provide further insights to index individual interphase resistance, highlighting the underlying positive effects of the proposed surface treatment, and demonstrating the importance of homogeneous, electronically conducting matrices throughout the composite electrode.
Highlights
Ni-rich LiNixMnyCozO2 (NMC) (x > y, z) electrode materials hold great promise as next-generation high-voltage, high-capacity positive electrodes in lithium ion batteries (LIBs)
The electrochemical performance of the composite electrodes pre pared from pristine NMC and the pre-treated NMC 532 powders was evaluated at ca. 0.5 C-rate between 2 - 4.7 V and 2–4.5 V
We demonstrated that a simple pre-treatment of NMC powder in 1 M LiPF6 EC:dimethyl carbonate (DEC) (1:2 vol) electrolyte at 60 ◦C helps improve long-term electrochemical performance of NMC composite electrodes
Summary
Ni-rich LiNixMnyCozO2 (NMC) (x > y, z) electrode materials hold great promise as next-generation high-voltage, high-capacity positive electrodes in lithium ion batteries (LIBs). It is important to assess the root cause and impact of such changes, in an attempt to separate out from other degradation processes that may occur in parallel As it is demonstrated by the strict level of quality control of materials and manufacturing in commercial cells, the combinatory effect of these many seemingly small differences can significantly improve (or impede) long-term cycling performance. The treatment used in the presented work is at higher temperature (60 ◦C vs room tempera ture) and for longer duration (240 vs 30 h) compared to the work in the previous study by Lin et al The more aggressive treatment presented here simulates the elevated temperatures in the electrolyte wetting and formation procedure for commercial LIB cells; allowing us to investigate how such treatment changes the NMC electrode/electrolyte interface and its influence on the cell degradation. We demonstrate that the sur face pre-treatment of NMC in the electrolyte at elevated temperatures has a positive effect on the subsequent electrode impedance and long-term electrochemical performance
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