Abstract
In LIBs, the metallic contaminants in the cathode are ionized and dissolve into the electrolyte during charging due to the oxidation-reduction potential, and the dissolved cations move and deposit on the anode as metal by the reduction. It is known that the repetition of this phenomenon causes the formation of needle-like metals resulting in the penetration through the separator and it may cause internal short circuit besides capacity degradation. Since slight voltage-drop occurs in the initial stage of this phenomenon, the defective batteries can be eliminated in the aging process. On the other hand, internal short circuit by metallic contaminant in all-solid-state batteries (ASSBs) has not been investigated well. In order to confirm this phenomenon in ASSBs, contaminant metals (Al, Cu, Fe, Ni, SUS) particles were intentionally added to the cathode and the cycle tests were carried out at 60℃. In the tests, internal short-circuit was detected only with the battery containing the Cu contaminant at 15 cycles. The location of short-circuit in the battery was visualized by magnetic imaging for the elucidation of the mechanism, then the battery was disassembled and the chemical state of Cu was measured by XAFS. It was found that Cu was present mainly as CuS in the solid electrolyte (SE) layer and the anode at the spot of short-circuit as well as the cathode, while CuS, having the structure of covellite in nature, is conductive.1 Thus, the short-circuit probably took place by the connection of the cathode and the anode via CuS through the SE layer. The movement of Cu in the battery during charging and discharging was monitored by in-situ SEM-EDX. After charging, Cu in the cathode moved to the SE layer whose Cu density decreased after the discharging, suggesting that Cu moves as cations.AcknowledgmentsThis study was carried out in SOLiD-EV project supported by NEDO (New Energy and Industrial Technology Development Organization).
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