부산대학교 도서관

Two cut-off voltage ranges, 0.5-2.7 V and 0.5-3.7 V, outside the theoretical electrochemical stability window of Li3PS4, were applied to analyze the chemo-mechanical stability due to the redox of Li3PS4 sulfide solid electrolytes in a full cell of a Li13Si4 / Li3PS4 / S+Li3PS4+C structure. In the voltage range of 0.5-3.7 V, a micro-short circuit was generated because of dendritic lithium growth on the surface of the anode due to the irreversibility of the redox of Li3PS4, thereby causing capacity loss. This was expressed through unstable charge-discharge behavior and voltage noise. Therefore, this study introduced a composite anode structure of an anode-active material and a solid electrolyte in which a (de)lithiated region is artificially widened to suppress degradation due to a redox of Li3SP4. First, a Li13Si4+Li3PS4 composite anode structure was applied instead of the Li13Si4 anode structure, and a Li13Si4+Li3N+LiF composite anode structure was additionally applied by introducing a Li3N+LiF composite electrolyte with sufficiently high ion conductivity and the effect of suppressing lithium dendrite in consideration of the characteristics of Li3PS4 unstable lithium.A three-electrode system was introduced to investigate the voltage noise under a charging condition of 0.5-3.7 V. In the voltage range of 0.5-2.7 V, the full cells to which the two composite anode structures were applied stably cycled and exhibited reversible charge-discharge behavior. This indicates that there is a practical stability window for each cell condition. On the other hand, in the voltage range of 0.5-3.7 V, it was found through EIS measurement that oxidative decomposition products were generated by the redox of Li3PS4 inside the cathode in the case of a full cell to which the two composite anode structures were applied. However, these full cells showed reversible charge-discharge behavior without unstable voltage noise compared to the full cell where the anode was made with only Li13Si4. When the composite anode structures are applied compared to an anode formed only of Li13Si4, (de)lithiation is uniformly performed in the anode layer, and it is visually confirmed that lithium ions are uniformly distributed throughout the anode layer through TOF-SIMS measurement. Through a two-electrode long-term cycle test, stable cycle and reversible charge-discharge behavior were observed without voltage noise for 150 cycles in the cell to which the Li13Si4+Li3PS4 composite anode is applied and for 96 cycles in the cell to which the Li13Si4+Li3N+LiF composite anode is applied at a voltage range of 0.5-3.7 V.This study showed that dendritic lithium growth due to irreversible redox of Li3PS4 was suppressed as compared with lithium alloy anode by applying a composite lithium alloy anode with a solid electrolyte, and observed that a practical stability window was widened through structural changes of the lithium alloy anode.