Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 14, Issue 1, Pages 543-556Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.1c16296
Keywords
LiCoPO4 5 V cathode material for Li ion batteries; LiCo2P3O10; MoO3; electronic structure; SPES and XANES; DFT calculations
Funding
- German Science Foundation (DFG) [CH566/4-1]
- EU-H2020 research and innovation programme [654360]
- EPFL in Lausanne (Switzerland) [360]
- Swiss Supercomputing center CSCS (Piz Daint) [s836]
- Italian supercomputing center CINECA through the ISCRA project Bat-Mat of the University of Pavia
- EUROFEL project (RoadMap Esfri)
- European Research Council (ERC) Horizon 2020 Program [805359-FOXON]
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The study demonstrated that the 5V LiCoPO4-LiCo2P3O10 thin-film cathode material coated with MOO layer exhibits high stability and does not undergo chemical reactions with the liquid electrolyte. Additionally, external electrolyte oxidation and internal electrolyte oxidation are the mechanisms leading to chemical reactions.
The intrinsic stability of the 5 V LiCoPO4-LiCo2P3O10 thin-film (carbon-free) cathode material coated with MOO, thin layer is studied using a comprehensive synchrotron electron spectroscopy in situ approach combined with first-principle calculations. The atomic-molecular level study demonstrates fully reversible electronic properties of the cathode after the first electrochemical cycle. The polyanionic oxide is not involved in chemical reactions with the tluoroethylene-containing liquid electrolyte even when charged to 5.1 V vs Li+/Li. The high stability of the cathode is explained on the basis of the developed energy level model. In contrast, the chemical composition of the cathode-electrolyte interface evolves continuously by involving MoO3 in the decomposition reaction with consequent leaching of oxide from the surface. The proposed mechanisms of chemical reactions are attributed to external electrolyte oxidation via charge transfer from the relevant electron level to the MoO3 valence band state and internal electrolyte oxidation via proton transfer to the solvents. This study provides a deeper insight into the development of both a doping strategy to enhance the electronic conductivity of high-voltage cathode materials and an efficient surface coating against unfavorable interfacial chemical reactions.
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