Extraction of Performance Factors for Clay-Type-Solid-State Batteries Based on Electrochemical Evaluation
Authors: Suzuki Keigo , Ichikawa Takaaki , Okanishi Kento , Mogi Rintaro , Seki Shiro 
Published: December 2024

Extraction of performance factors for clay-type-solid-state batteries based on electrochemical evaluation.

Keigo Suzuki, Takaaki Ichikawa, Kento Okanishi, Rintaro Mogi, and Shiro Seki (Kogakuin Univ.)

Introduction

Performance development of Li-ion batteries (LIBs) has been desired due to high energy density, and is also expected to the engineering issues, such as huge mass loading of electrode sheet. To realize high-performance LIB with high energy density, clay-type solid-state batteries (CSSBs) with the composite electrode included electrolyte are attracting attention. CSSBs are easily prepared thick electrodes without adding a binder, and therefore, expected to increase energy density. In this study, we applied AC impedance measurements for clay into CSSBs to evaluate the factors for high-performance in the conduction pathways of electrode clay of high-performance with variations in electrolyte composition using the highly concentrated electrolyte with a wide potential window and a high Li-ion transference number1.

Experimental method

The clay electrode was prepared by using LiFePO4 (LFP) as the positive active material, acetylene black (AB) as the conductive additive, and (LiTFSA+4EC) as the electrolyte. LFP: AB was weighed to a weight ratio of 94.25:5.75, mixed in a mortar for 20 min, and then the electrolyte was added to the weight ratio of (100-x)(LFP+AB):x (LiTFSA+4EC) (x=0~100). Positive electrode clay was prepared after mixing for 10 min using a paste mixer. After that, the positive electrode clay was filled into the cell with [SUS | Positive electrode clay | SUS] and the AC impedance spectrum of the positive electrode clay was measured. The AC impedance measurements were conducted under constant temperature conditions of 30 ℃ with an amplitude of 100 mV and a frequency range of 200 kHz to 50 mHz. Temperature under temperature dependences were also evaluated for conditions of between -10 ℃ and 80 ℃ with an amplitude of 100 mV and a frequency range of 500 kHz to 50 mHz2.

Result and Discussion

Fig. 1 shows typical Nyquist plots of [SUS | Positive electrode clay | SUS] cells positive electrode clay for each electrolyte composition at 30 wt%. At 10 wt% electrolyte composition, resistance component (R
E) attributed to the electronic conduction was only observed at low frequencies. In contrast, the resistance component (R
I) attributed to the ionic conduction was observed at high frequencies at 80 wt% electrolyte composition. At 50 wt% electrolyte composition, two resistance components were observed on both the high and low frequencies, and considered to be resistance components desired to the electric composite electrode and ionic electrolyte components.

Fig. 2 shows the temperature dependence of resistance changes for the 30 wt% electrolyte composition of the positive electrode clay. Electric conduction generally involves electrons being scattered by lattice vibrations and increases resistance with temperature. On the other hand, for ionic conduction, the mobility of ions always increases with temperature. On the low-frequency side, the increasing trend of resistance with temperature was observed, while on the high-frequency side, the opposite trend was also confirmed. In these results, we defined that R
I corresponds to the high-frequency side and R
E corresponds to the low-frequency side, respectively.

Fig. 3 shows the Nyquist plots of [SUS | Positive electrode clay | SUS] cells (A) is an overview of Nyquist plots of [SUS | Positive electrode clay | SUS] cells, (B) and (C) are enlarged figures of (A). To analyze resistance components for electrode clay, obtained R
E and R
I were calculated and plotted against the percentage of the electrolyte composition.

Fig. 4 shows the relationship between R
E and R
I of positive electrode clay for electrolyte composition. Only R
E was observed in the region of (a) (electrolyte composition 0 ~ 20 wt%), and also only R
I was observed in the composition region of (c) (electrolyte composition 70 ~ 100 wt%). In contrast, both R
E and R
I were observed in the region of (b) (electrolyte composition 30 ~ 60 wt%). In the composition region (a), only continuous electron conduction paths in the clay electrode should be formed. Also, in the composition region (c), only ionic conduction paths should be formed. On the other hand, in the composition region (b) was considered that both continuous electric and ionic conduction paths into the clay electrodes are provided by AB and LiTFSA+4EC electrolyte. In addition, in the composition region (b) was confirmed both electron conduction and ionic conduction coexist conditions, the smallest values of R
E and R
I at 30 wt%, suggesting that the optimal composition condition of positive electrode clay.

(1) Y. Yamada, A. Yamada, J.Electrochem.Soc.,162, A2406-A2423 (2015).

(2) R. Motoyoshi, et al., ACS Appl. Mater. Interfaces, 14, 45403−45413 (2022).

Figure 1