Functioning mechanism of AlF3 coating on the Li- and Mn-rich cathode materials
Li- and Mn-rich (LMR) material is a very promising cathode for lithium ion batteries because of their high theoretical energy density (~900 Wh kg-1) and low cost. However, their poor long-term cycling stability, voltage fade, and low rate capability are significant barriers hindered their practical applications. Surface coating, e.g. AlF3 coating, can significantly improve the capacity retention and enhance the rate capability. However, the fundamental mechanism of this improvement and the microstructural evolution related to the surface coating is still not well understood. Here, we report systematic studies of the microstructural changes of uncoated and AlF3-coated materials before and after cycling using aberration-corrected scanning/transmission electron microscopy and electron energy loss spectroscopy. The results reveal that surface coating can reduce the oxidation of electrolyte at high voltage, thus suppressing the accumulation of SEI layer on electrode particle surface. Surface coating also enhances structural stability of the surface region (especially the electrochemically transformed spinel-like phase), and protects the electrode from severe etching/corrosion by the acidic species in the electrolyte, therefore limiting the degradation of the material. Moreover, surface coating can alleviate the undesirable voltage fade by minimize layered-spinel phase transformation in the bulk region of the materials. These fundamental findings may also be widely applied to explain the functioning mechanism of other surface coatings used in a broad range of electrode materials.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1188951
- Report Number(s):
- PNNL-SA-102894; 48106; VT1201000
- Journal Information:
- Chemistry of Materials, 26(22):6320-6327, Journal Name: Chemistry of Materials, 26(22):6320-6327
- Country of Publication:
- United States
- Language:
- English
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