Self-Standing All-Solid-State Lithium Battery Prepared By Electrochemical in-Situ Electrode Growth Method
Authors: Sugiura Yu , Motoyama Munekazu , Iriyama Yasutoshi 
Published: February 2020

Introduction

All-solid-state rechargeable lithium battery (SSB) is one of the candidates for next generation rechargeable batteries. A crucial problem to improve the performance of the SSB will be the reduction of charge-transfer resistance at electrode/solid-electrolyte interface. Here, we focused on partial conversion of solid electrolyte [e.g. Li1.3Al0.3Ti1.7(PO4)3 (LATP)] into electrode active material via electrochemical irreversible Li+ insertion reaction into the LATP, that is, electrode active material grows in-situ from the LATP by electrochemical process. Charge transfer resistance at in-situ formed electrode/LATP is small probably because of well-connected interface without any mutual diffusion layer [1]. However, the growth amount of the in-situ formed electrode was extremely small at room temperature and the growth area was limited only around the LATP/current collector interface. This problem will arise from less electronic conductivity of the in-situ formed electrode material.
In this work, in-situ formed electrodes were grown at higher temperatures. These conditions are supposed to be effective to increase the growth amount of in-situ formed electrode because the electronic conductivity increases at higher temperatures. This study focuses on the temperature dependency on the thickness of in-situ formed electrode in the LATP.

Experimental

A mirror-polished-Li+-conductive-glass-ceramic (LATP; manufactured by OHARA Inc.) sheet with a thickness of 150 µm was used as the solid electrolyte. Lithium phosphorus oxynitride glass electrolyte (LiPON) was deposited on one side of a LATP sheet by RF magnetron sputtering. Thin film of Li was deposited on the LiPON film by vacuum evaporation. The opposite side of the LATP sheet was covered with Au film with a thickness of 100 nm. Eventually, a Li/LiPON/LATP/Au multilayer was fabricated, where electrode area of Au was 0.64 cm2. Electrochemical properties of the resultant cells were measured by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge-discharge measurements.

Results and Discussion

The Li/LiPON/LATP/Au cell delivered a couple of redox peaks at 2.35 V (vs. Li+/Li) in the CV measurements between 3.0 V and 1.5 V as shown in Fig. 1, which was in good agreement with the past work [1]. Initial discharge capacity at 25°C was 45 mC cm-2, which increased with increasing the reaction temperature. At 100°C, the capacity attained to 1250 mC cm-2, ca. 27 times larger value than that at 25°C. This result suggests that the in-situ formed electrode grow deeply inside the LATP sheet at higher temperatures. The growth distance of in-situ formed electrode from the current collector (Au) was ca. 700 nm at room temperature [2]. Thus, the in-situ formed electrode can grow few tens of micron meters from the interface at higher temperatures. To clarify this point, we used thinner LATP sheet (20 μm) alternatively and examined same measurements. At 70°C, all the LATP sheet exchanged to the in-situ formed electrode material though some of cracks were also observed. Electrochemical properties of those batteries will be discussed in the poster session.

Reference

1. Y. Amiki, F. Sagane, K. Yamamoto, T. Hirayama, M. Sudoh, M. Motoyama, and Y. Iriyama, J. Power Sources,
241,583 (2013).
2. K. Yamamoto, Y. Iriyama, T. Asaka, T. Hirayama, H. Fujita, K. Nonaka, K. Miyahara, Y. Sugita and Z. Ogumi, Electrochem. Comm., 20, 113 (2012).

Figure 1