Operando X-Ray CT Analysis of Composite Electrode in All-Solid-State Battery Using Silicon Anode

Abstract

As a next-generation rechargeable battery, all-solid-state battery is expected for used in practical applications, in which electrolyte solution of the current lithium-ion battery is replaced with a solid electrolyte. To further increase the capacity of all-solid-state batteries, silicon is used as the anode active material forming an alloy with lithium. However, in the charge and discharge reaction using silicon anode, poor cycle capability due to the volume change of the silicon alloying reaction has been known. Many reports are limited to the analysis of the volume change of the whole electrode, and there are few reports on the quantitative analysis of the volume change of the silicon active material itself. In this study, X-ray computed tomography (X-ray CT) was used to analyze the expansion and contraction of silicon-active materials in all-solid-state battery. X-ray CT analysis can provide the contacted state information between electrode active materials and solid electrolytes [1]. By operando X-ray CT analysis, the expansion and contraction behavior of silicon particles during charging and discharging on the electrode was studied.Nb-coated LiNi1/3Co1/3Mn1/3O2(NCM), Li10GeP2S12(LGPS), acetylene black (AB) mixed at a weight ratio of 1:1:0.2 were used as the cathode composite. Silicon, LGPS, AB mixed at a weight ratio of 1:1:0.1 were used as the anode composite. All-solid-state battery, Si | LGPS | NCM was assembled in a cylinder with an inner diameter 1 mm. The cell was brought into SPring-8 BL20XU beamline, and the operando X-ray CT measurement was carried out. From the obtained X-ray CT images, the three-dimensional analysis of silicon particles was performed.Mean expansion coefficients of silicon‐particles traced during charging and discharging were calculated. The expansion of silicon particles by charging (lithiation) and the contraction of silicon particles by discharging (delithiation) are confirmed. Furthermore, the volume expansion rate of the silicon particles after the charging is average exceeded 300%. After discharge, silicon shrinkage is observed with delithiation, but the solid electrolyte cannot follow the volume change, and the silicon/solid electrolyte interface is broken. However, the contact is not completely failed, maintaining the partial contact between silicon and the electrolyte.[1] Y. Sakka, H. Yamashige, A. Watanabe, A. Takeuchi, M. Uesugi, K. Uesugi and Y. Orikasa, J. Mater. Chem. A, 10 16602–16609 (2022).Acknowledgement: This work was partially supported by the New Energy and Industrial Technology Development Organization (NEDO), JPNP20004.