Characterization of Lithium Vanadate Film Electrode Formed on Garnet-Type Oxide Solid Electrolyte by Aerosol Deposition
Authors: Inada Ryoji , Okuno Kohei , Kito Shunsuke , Tsukahara Kohei , Tojo Tomohiro , Sakurai Yoji 
Published: February 2020

Aerosol deposition (AD) method has many advantages compared to the conventional film deposition process such as sputtering deposition and pulsed laser deposition [1]. This method uses room temperature impact consolidation (RTIC) between raw ceramic powders and substrate during aerosolized powders crash onto the substrate. The film formed by AD method has 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 an electrode layer can be formed on solid electrolyte without any thermal treatment [2, 3]. In this study, we fabricated lithium vanadate LiV3O8 (LVO) film electrode by AD on both SUS316L plate and garnet-type Ta doped Li7La3Zr2O12 (LLZT) solid electrolyte as substrates.
Ball-milled LVO powder with the size of 0.5-2 µm was used as raw material for LVO film fabrication. The powders were aerosolized with N2 carrier gas at flow rate of 20L/min and splayed through the nozzle onto SUS316L plate or LLZT pellet fixed on X-Y stage in vacuumed deposition chamber to form LVO film. Crystal phase and microstructure of LVO film was investigated by XRD, FE-SEM and EDX. In addition, two-electrode coin cell was constituted using LVO film on SUS316L plate as working electrode, Li metal foil as counter one and 1 mol/L LiPF6-EC:DMC(1:1v/v%) electrolyte to measure the electrochemical properties of film electrode at 25ºC. On the other hand, for LVO film on LLZT pellet, Li metal foil was attached on the other end face of LLZT pellet to consist all-solid-state cell. Electrochemical properties for LVO/LLZT/Li cell were measured at 50 and 100ºC.
From XRD measurement results, diffraction peaks for LVO were clearly confirmed in films formed by AD and other impurity phases were not observed, while the diffraction peaks become broader than raw powders. From SEM observation, LVO films have highly dense structure composed of deformed and fractured LVO particles via impact consolidation, and their thicknesses were in the range of 2.5-10 μm depending on the deposition times. In the cell with liquid organic electrolyte, LVO film with the thickness of 2.5 μm showed initial discharge capacity around 300 mAh/g, which is close to the theoretical capacity of LVO with V5+/V4+ redox couple. Capacity retention of LVO film electrode in liquid electrolyte is approximately 80% after 30 cycles.
LVO film with the thickness of 5 µm formed on LLZT pellet has also dense structure and pores were not observed at LVO/LLZT interface. From AC impedance measurment, charge transfer resistance at LVO/LLZT interface is estimated to be around 103 Ωcm2 at room temperature range, which is much higher than at Li/LLZT interface (= 50 Ωcm2). Reversible charge and discharge reaction in LVO/LLZT/Li all-solid-state cell was demonstrated successfully and the specific capacites were 100 and 290 mAh g-1 at 50 and 100ºC, respectively. Good reversibility of electrode reaction indicates strong adhesion between LVO film electrode formed via impact consolidation and LLZT.
This work was partly supported by JSPS KAKENHI Grant numbers 16K06218 and 16KK0127, and Research Foundation for the Electro-technology of Chubu (R-28241).

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[1] J. Akedo, Journal of the American Ceramic Society 89, 1834-1839, 2006.
[2] T. Kato, S. Iwasaki, Y. Ishii, M. Motoyama, W.C. West, Y. Yamamoto, Y. Iriyama, Journal of Power Sources 303, 65-72, 2016.
[3] R. Inada, S. Yasuda, M. Tojo, K. Tsuritani, T. Tojo, Y. Sakurai, Frontiers in Energy Research 4, 28, 2016.

Figure 1