Proceedings of International Forum for Green Asia 2019
5th International Exchange and Innovation Conference on Engineering & Sciences (IEICES 2019)

GA01 / P13
Single-phase All-solid-state Batteries using NASICON-type Oxide Materials
1Akira Nishio1, Atsushi Inoishi2, Shigeto Okada2
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 2 Institute for Materials Chemistry andEngineering, Kyushu University
Email: akira.nishio.924@s.kyushu-u.ac.jp

Abstract: All-sold-state batteries have been expected as the next-generation secondary battery due to its high reliabilityand safety. However, the difficulty for the commercialization is the interfacial resistance between electrode and electrolyte
which is larger than the bulk ionic conductivity of the electrolyte. “Single-phase all-solid-state batteries” are adopted asa new concept in order to reduce the interface resistance between the electrodes and the electrolyte, compared to theconventional all-solid-state batteries which have clearly several components (i.e. electrolyte part and electrode parts).
Single-phase all-solid-state batteries are made of a single material which plays a role of the electrode and the electrolyte.
Here, we demonstrate the properties for single-phase all-solid-state batteries we reported so far.
Keywords: single-phase, all-solid-state battery, solid electrolyte, NASICON
1. INTRODUCTION
All-solid-state batteries have been recently expected forthe next-generation energy storage devise since its solid
electrolyte based on thio-LISICON family or glassy
oxide material has demonstrated almost the same ionic
conductivity (10-2 ~ 10-3 S cm-1) to the liquid electrolyte.
However, the interfacial resistance between electrodeand electrolyte, which is almost one-order larger than thebulk resistance of solid electrolyte itself, is the biggest
problem to commercialize the all-solid-state alkali-ion
battery. The interfacial resistance is caused by the side
reaction during the calcination, the space-charge layer,
the mismatch of impedance and the insufficient contact
between electrodes and electrolyte.
One of the essential solutions for eliminating theinterfacial resistance is to use the same material for thesolid electrolyte and electrodes. The concept of thebattery consisting of a single-material, Li10GeP2S12(sulfide-based high ionic conductor), was first reported
by Han et al [1], and it demonstrated significantly low
interfacial resistance between electrode and electrolyte.
However, sulfide is unfavorable for handling in the air
because it reacts with water and generates H2S gas whichis indeed toxic. Therefore, we tried to convert the sulfidebased materials to the oxide-based materials. Among theoxide-based materials, NASICON (NA-ion Super Ionic
CONductor)-type materials (Fig. 1) are known for theirhigh ionic conductivity and large bottle-neck structure
based on the corner-sharing framework. In addition, it iswell known that NASICON is also suitable structure forintercalation host. Such advantages of NASICON-typematerials realized the oxide-based single-phase all-solidstate batteries [2-5]. Table 1 shows the NASICON-typesingle-phase all-solid-state alkali-ion batteries reported
by our group. Among them, we demonstrate the superior
performances properties such as the high rate capability
and the high operating voltage recently found in
Li1.5Cr0.5Ti0.5(PO4)3.

battery have the role of the solid-electrolyte andelectrodes. In order to realize rapid charge/discharge rate,
the conductivity of the solid-electrolyte had better to be
as large as possible. In this research, NASICON oxidematerials are focused as the materials for the single-phaseall-solid-state battery because they have high ionic
conductivity due to its large bottle-neck structure basedon the corner-sharing framework.
For the electrode function, NASICON materials areappropriate because they contain transition metals in thecrystal structure. Moreover, the insertion/elimination
reaction only occurs without any structure change in thecharge/discharge process, so the cyclability can be
expected. In addition, NASICON materials demonstrate
the high redox potential due to an inductive effect causedby its poly-anionic structure.
For these reasons, we focused on NASICON materials as
the main materials of the single-phase all-solid-statebatteries.

Fig. 1. Crystal structure of NASICON-type compounds.
2.2 Methods
The NASICON materials were synthesized byconventional solid phase methods. The materials
containing vanadium were calcined under Ar + 5%H2 inorder to avoid the oxidation; and others were calcined
under air. The samples were pelletized and annealed in

2. MATERIALS and METHODS
2.1 Materials selection
The materials must be satisfied 2 conditions; first is highionic conductivity and second is to include transition
metals. The materials of a single-phase all-solid-state-1-

each appropriate temperature. For arranging as same
thickness, the pellets were polished at 0.8 - 0.7 mm.
The X-ray diffraction (XRD) measurements (Cu Ka)
were conducted using a Rigaku MiniFlex600
diffractometer. The scanning electron microscopy (SEM)
analysis was performed using a JEOL JSM-6340F
microscope. A thin platinum layer was sputtered on bothsides of a sample pellet as a current collector. The cell
was finally sealed into an HS cell (Hohsen Corp.) in an
Ar-filled glove box.
The electrochemical charge/discharge measurements
were performed using the galvanostatic method with acharge/discharge cycle instrument (BTS2400W, Nagano
Electric Co.). The AC impedance measurements wereexecuted under open-circuit conditions using animpedance analyzer over the frequency range from 1
MHz to 0.1 Hz.

Fig. 3. SEM images of (a) Li1.5Cr0.5Ti1.5(PO4)3 and(b)Li1.5Cr0.5Ti1.5(PO4)3+Li3BO3 pellets.
Table 1. Typical NASICON-type all-solid-state alkaliion batteries.

3. RESULTS and DISCUSSION
Figure 2 shows the Arrhenius plots which is thetemperature dependence of the electrical conductivity ofalkali-ion NASICON-type materials. For these,
Li1.5Cr0.5Ti1.5(PO4)3 demonstrated the highest electric
conductivity of 2×10-4 S cm-1 at 298 K. Furthermore,
addition of Li3BO3 into Li1.5Cr0.5Ti1.5(PO4)3 ledenhancing the electric conductivity as shown in Fig. 2
because Li3BO3 worked as flux to fill the voids of
Li1.5Cr0.5Ti1.5(PO4)3 due to its lower melting point thanthose of NASICON materials [6]. SEM images in Fig.
3(a) and 3(b) visibly indicate that the Li3BO3 additive
Li1.5Cr0.5Ti1.5(PO4)3 pellet has higher density than theLi1.5Cr0.5Ti1.5(PO4)3 pellet.

NASICON-typematerials

Electricalconductivity(S cm-2)

Current
density(mA cm-2)

OperatingvoltageNa2.6V1.6Zr0.4(PO4)3 [2]

5×10-6< 0.015

1.8 V

Li3V1.6Al0.4(PO4)3 [3]

6×10-6< 0.0151.7 V

Li1.5Cr0.5Ti1.5(PO4)3 [4]2×10-40.1

2.2 V

Ag1.5Cr0.5Ti1.5(PO4)3 [5]5×10-50.1

0.9 V

REFERENCES[1] F. Han, T. Gao, Y. Zhu, K. J. Gaskell, C. Wang, A
Battery Made from a Single Material, Adv. Mater., 27(2015) 3437.
[2] A. Inoishi, T. Omuta, Y. Yoshioka, E. Kobayashi, A.
Kitajou, S. Okada, A Single-phase, All-solid-state
Sodium Battery Using Na3−xV2−xZrx(PO4)3 as the
Cathode, Anode, and Electrolyte, Adv. Mater.
Interfaces, 4 (2017) 1600942.
[3] A. Inoishi, T. Omuta, Y. Yoshioka, E. Kobayashi, A.
Kitajou, S. Okada, Single-phase All-solid-state
Lithium -ion Battery Using Li3V2(PO4)3 as the
Cathode, Anode, and Electrolyte, ChemistrySelect, 2(2017) 7925.
[4] A. Inoishi, A. Nishio, Y. Yoshioka, A. Kitajou, S.
Okada, A Single-Phase All-solid-state Lithium
Battery Based on Li1.5Cr0.5Ti1.5(PO4)3 for High Rate
Capability and Low Temperature Operation, Chem.
Commun., 54 (2018) 3178.
[5] A. Inoishi, A. Nishio, A. Kitajou, S. Okada, Singlephase All-solid-state Silver Battery Using
Ag1.5Cr0.5Ti1.5(PO4)3 as Anode, Cathode, andElectrolyte, ChemistrySelect, 3 (2018) 9965.
[6] A. Nishio, A. Inoishi, A. Kitajou, S. Okada, Effect of
Li3BO3 Addition to NASICON-type Single-phaseAll-solid-state Lithium Battery Based on
Li1.5Cr0.5Ti1.5(PO4)3, J. Ceram. Soc. Jpn, 127 (2019)18.

Fig. 2. Temperature dependence of the electricalconductivity of alkali-ion NASICON-type materials.
Table 1 shows the electric conductivity and the operating
voltage with each current density for the NASICON-typeall-solid-state alkali-ion battery cells. In the presentation,
we will introduce the more detailed properties such as
charge/discharge profiles and its electrode reaction.

-2-