X-Ray CT Measurement and Performance Evaluation of All Solid-State Lithium-Ion Battery with Sn Anode

Abstract

Stannum (Sn) is investigated as a high-capacity anode for all-solid-state Lithium-Ion batteries. It is focused much attention because of its high theoretical capacity (990 mAh/g), which is much higher lithium storage capacity than that of graphite (372 mAh/g). However, poor cycling stability and coulombic efficiency hinder their practical use in Li-ion batteries. These drawbacks mainly result from the huge volume change of Sn (255% when 4.25 Li is inserted per a Sn), leading to a loss of electric contact, pulverization, and cracking. Therefore, it can be considered that there is a deep relationship between electrode structure and performance.In this study, to elucidate the relationship between electrode structure and performance of all-solid-state battery using Sn as the anode active material we compare the Sn anode with Sn weight ratio of 50wt% and 70wt%. The Sn anode structure is measured with in-situ X-ray CT measurement and the three-dimensional structure is compared to the electrode performance.To prepare the composite electrode, 5:5 and 7:3 (Sn : SE) weight ratio of Sn powder (38 um) and Li6PS5Cl were mixed by agate mortar and pestle. Anode half cells were then assembled and within 1 mm diameter polyetheretherketone (PEEK) cell dies at 400 MPa, and cells were cycled at a constant stress of 100 MPa In-situ X-ray CT with Molybdenum (Mo) target X-ray（nano3DX, Rigaku）was used to determine the structure of the composite electrode at a voxel size of 1.24 µm. And electrode performances were evaluated by potentiogalvanostat in the current of 0.05C.Figure 1 shows the X-ray CT images of the Sn anode with different Sn weight ratio ((a) 50 wt%, (b) 70 wt%). Sn regions are shown by blue and solid electrolyte (SE) regions are shown by yellow. Table.1 shows the electrode structure parameters calculated from the X-ray CT images shown in fig.1. The discharge capacity of Sn anode is dramatically increased by increasing in the Sn weight ratio (95 to 403 mAh/g). The tortuosity of SE network is increased with the increase in Sn weight ratio (1.43 to 2.15), which has a negative influence on the lithium-ion transportation in anode. It is considered that resistance of the SE network is increased with the increase of Sn weight ratio. Moreover, the contact specific surface area between SE and Sn is increased with the increase of Sn weight ratio (94.9×103 to 117×103 m2/m3). This increase of specific surface area of contact is corresponding to the decrease of interface resistance between SE and Sn in anode. The growth of discharge capacity can be derived from the decrease of interface resistance with the increase in specific surface area of contact between SE and Sn. Moreover, we also measured the expansion and contraction of the active material during charging and discharging, but the structural changes were not enough to explain the above performance differences.From the mentioned above, it can be said that as the Sn weight ratio increases, the resistance of the SE network is increased with the increase of tortuosity, but the interface resistance decreases due to the increase in the specific surface area of contact between SE and Sn, which leads to increase of electrode performance.This work is supported by JKA foundation (2020-1155). Figure 1