First-Principles Calculations, Electrochemical and X-ray Absorption Studies of Li-Ni-PO4 Surface-Treated xLi2MnO3 (1 x)LiMO2 (M = Mn, Ni, Co) Electrodes for Li-Ion Batteries
- Northwestern University, Evanston
- Argonne National Laboratory (ANL)
It has been previously hypothesized that the enhanced rate capability of Li-Ni-PO{sub 4}-treated xLi{sub 2}MnO{sub 3} {center_dot} (1-x)LiMO{sub 2} positive electrodes (M = Mn, Ni, Co) in Li-ion batteries might be associated with a defect Ni-doped Li{sub 3}PO{sub 4} surface structure [i.e., Li{sub 3-2y}Ni{sub y}PO{sub 4} (0 < y < 1)], thereby promoting fast Li{sup +}-ion conduction at the xLi{sub 2}MnO{sub 3} {center_dot} (1-x)LiMO{sub 2} particle surface. In this paper, the solubility of divalent metals (Fe, Mn, Ni, Mg) in {gamma}-Li{sub 3}PO{sub 4} is predicted with the first-principles GGA+U method in an effort to understand the enhanced rate capability. The predicted solubility (x) is extremely small; this finding is consistent with experimental evidence: 1) X-ray diffraction data obtained from Li-Ni-PO{sub 4}-treated xLi{sub 2}MnO{sub 3} {center_dot} (1-x)LiMO{sub 2} electrodes that show that, after annealing at 550 C, a Li{sub 3}PO{sub 4}-like structure forms as a second phase at the electrode particle surface, and 2) X-ray absorption spectroscopy, which indicate that the nickel ions are accommodated in the transition metal layers of the Li{sub 2}MnO{sub 3} component during the annealing process. However, electrochemical studies of Li{sub 3-2y}Ni{sub y}PO{sub 4}-treated xLi{sub 2}MnO{sub 3} {center_dot} (1-x)LiMO{sub 2} electrodes indicate that their rate capability increases as a function of y over the range y = 0 (Li{sub 3}PO{sub 4}) to y = 1 (LiNiPO{sub 4}), strongly suggesting that, at some level, the nickel ions play a role in reducing electrochemical impedance and increasing electrode stability at the electrode particle surface.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 1049183
- Journal Information:
- Journal of the Electrochemical Society, Vol. 159, Issue 2; ISSN 0013-4651
- Country of Publication:
- United States
- Language:
- English
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