In Situ Observation of Lithium Ion Migration in Lithium Battery Using ToF-ERD

Abstract

  The lithium (Li) concentrations for both of Au/LiCoO₂/Li_1.4Al_0.4Ge_0.7Ti_0.9P₃O₁₂(LATP) positive electrode side and Pt/LATP negative one in Au/LiCoO₂/LATP/Pt (thickness: approximately 14 nm/88 nm/150 μm/10 nm) all-solid-state Li⁺ ion secondary batteries were in situ measured under applying various voltages in a vacuum using the high-energy time-of-flight elastic recoil detection (ToF-ERD) technique with 9.0-MeV Cu¹⁰⁺ ion-probe beams. The ToF-ERD spectra significantly revealed that the Li concentration in the LiCoO₂ positive electrode decreased with an increase in the charged voltages from 1.71 to 2.04 V and the Li concentration in LiCoO₂ around the LiCoO₂/LATP interface became approximately twice higher than that around the Au/LiCoO₂ interface at charged voltages above 1.8 V. The gradient of Li concentration leaded to Li deficiency, which was called as space charge layers, in the LATP region of approximately 150 ± 10 nm from the LiCoO₂/LATP interface. In addition, the Li concentration in the LATP region of approximately 240 ± 10 nm from the LATP/Pt interface increased with an increase in the charged voltages from 1.65 to 2.05 V. Therefore, it could be concluded that the Li migration from the LiCoO₂ positive electrode to the LATP negative one in the battery was dynamically observed under the various charges using the ToF-ERD technique with the reliable depth resolution in approximately a ten of nm scale.