Characterization of Tin Phosphide Films for All-Solid-State Battery Anode Fabricated By Aerosol Deposition

Abstract

Aerosol deposition (AD) method has many advantages compared to the conventional film deposition process [1]. This method uses impact consolidation at room temperature between raw ceramic particles and substrate during aerosolized powders crash onto the substrate. The film formed by AD has relatively dense structure made of nanocrystalline particles and its structural and physical properties is similar to base powder material. This feature is attractive for the fabrication of oxide-based solid state batteries, because various electrode layers can be formed on solid electrolyte without any thermal treatment [2-4]. In order to achieve higher energy density of the all-solid-state battery, the use of both cathode and anode materials with high capacity are required. Tin phosphide Sn4P3 is one of the high capacity anode materials for lithium ion batteries, with the thoretical lithium storage capacity of 1256 mAh g-1 [5]. In lithium insertion process, Sn4P3 forms Sn and Li3P and Li3P would act as a matrix suppressing the volume change during alloying reaction and keep the electrode particles mechanically connected together. Moreover, Li3P has good ionic conductivity so that self-formation of a good ionic conduction matrix is formed in the electrode in lithium insertion process. Therefore, Sn4P3 is considered to be attractive candidate for anode with high capacity of all-solid-state lithium-ion batteries. In this study, we fabricated Sn4P3 film electrode by AD on both SUS316L plate and garnet-type Ta-doped Li7La3Zr2O12 (LLZTO) solid electrolyte and electrical and electrochemical properties of the films were investigated. Ball-milled Sn4P3 powder with the size of 0.5-1 µm was used as raw material for Sn4P3 film fabrication. The powders were aerosolized with N2 carrier gas at flow rate of 10-20 L/min and splayed through the nozzle onto SUS316L plate or LLZTO sintered pellet fixed on X-Y stage in vacuumed deposition chamber to form Sn4P3 film. From XRD measurement, the diffraction peaks for Sn4P3 were clearly confirmed in as-deposited films by AD and other impurity phases were not observed. Sn4P3 films have relatively dense structure composed of deformed and fractured particles via impact consolidation. Electronic conductivity of Sn4P3 film by AD is in the range of 10-3-10-2 S cm-1 at room temperature, which is slightly lower than pressed Sn4P3 powders. Li metal foil was attached on the other end face of LLZTO pellet with AD Sn4P3 film to consist all-solid-state cell sample. Galvanostatic testing for Sn4P3/LLZTO/Li was carried out at 0-2.5 V, 0.07 mA cm-2 (corresponding to 200 mA g-1) and 100ºC. As a result, reversible charge and discharge reaction in Sn4P3/LLZTO/Li solid-state cell was demonstrated, with an initial reversible capacity of 800 mAh g-1. Influence of controlling the cell voltage range on the cycling stability for Sn4P3/LLZTO/Li solid-state cell will be discussed.This work was partly supported by JSPS KAKENHI Grant numbers 16K06218 and 16KK0127.