実験報告書様式（一般利用課題・成果公開利用）

MLF Experimental Report

提出日 Date of Report
July 24, 2012

課題番号 Project No.

装置責任者 Name of responsible person

2012A0044

Yasuhiro Miyake

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Diffusive behavior of garnet-type compounds II

D1

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Jun Sugiyama

May 14, 2012 - May 20, 2012

所属 Affiliation
Toyota Central Research and Development Laboratories, Inc.
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.
Garnet-type compounds, LixLa3Zrx-5Nb7-xO12 with x=6.3, 6.5, and 6.85.
A 2g powder sample was pressed in a disc with 27 mm diameter and 1 mm thickness, and then the disc
was packed in a gold O-ring sealed titanium cell.

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

In order to fabricate an all solid-state lithium-ion battery for improving safety and volumetric energy
density, a solid electrolyte is unambiguously one of the key materials, because only the electrolyte is ina liquid state among the components for the present Li-ion batteries. Recently, a novel garnet-type
compound, Li6.75La3Zr1.75Nb0.25O12 [see Fig. 1], was found to exhibit the highest Li-ion conductivity(σLi=10-3 S/cm at ambient temperature) [1,2] among several oxide electrolytes. Note that this σLi is lower
only by one order of magnitude than σLi for the present liquid electrolyte, and is almost comparable toσLi for a gel electrolyte [3].
Here, the chemical formula of the garnet-type compound is represented by LixLa3Zrx-5Nb7-xO12, and σLi
is known to depend on x; i.e. the σLi(x) curve exhibits a maximum at x=6.75 [see Fig. 2(a)] [1,2], forreasons currently unknown. In order for clarifying the reason why x=6.75 is an optimal composition, we
have attempted to investigate the diffusive nature of LixLa3Zrx-5Nb7-xO12 by µ+SR.
According to ZF- and LF-µ+SR measurements on the present (x=6.5 and 6.85) and previous (x=5, 6,6.75, and 7) samples in the T range between 100 and 400 K, the field fluctuation rate (n) at 300 K isfound to change with x. Assuming that n corresponds to the jump rate of the Li+ ions between theneighboring sites, as for LixCoO2 [4], we obtain1

2. 実験方法及び結果（つづき） Experimental method and results (continued)
a diffusion coefficient of Li+ ions (DLi) as afunction of x [see Fig. 2(b)].
Since all the six samples are a goodinsulator, DLi and σLi is connected by asimple Nernst-Einstein formula;DLi = σLiRT/(F2z2),
where R is the gas constant, F is theFaraday's constant, and z is the number
density of mobile Li+ ions. In other words, wecan estimate the change in z with x from therelationship between (σLi/DLi)0.5 and x [seeFig. 2(b)]. This implies that not DLi but z isFig.1: The crystal structure of Li6.75La3Zr1.75Nb0.25O12

the predominant parameter to determine σLidetermined by neutron.

for LixLa3Zrx-5Nb7-xO12. The present result
also suggests a novel µ+SR power todetermine the mobile carrier concentration inREFERENCES[1] S. Ohta et al., J. Power Sources 196,402cm /s)-12

and/or hole concentration in solids.

60

DLi (10measurements for estimating an electron

80[2] S. Ohta et al., J. Power Sources 202, 332(2012).

DLi
σLi

0.60.3

20053342 (2011).

0.9(a)σLi (10-3 S/cm)

ionic-conducting materials, as in the Hall

05.5
66.5
7x in LixLa3Zr(x-5)Nb(7-x)O126000(2011).
[4] J. Sugiyama et al., Phys. Rev. Lett. 103,147601 (2009).
[5] R. J. Borg et al., An Introduction to Solid(σLi /DLi )0.5

[3] N. Kamaya et al., Nature Mater. 10, 682

4000
2000(b)State Diffusion, (Academic Press, San

05Diego, 1988).

5.5
66.5
7x in LixLa3Zr(x-5)Nb(7-x)O12

Fig. 2: The x dependences of (a) DLi and σLi and (b)(σLi/DLi)0.5

for

LixLa3Zrx-5Nb7-xO12.

In

the2012experiment, two more data at x=6.5 and 6.85 areadded. Although we also measured the x=6.3 sample,
we were unable to evaluate its DLi from the hopping
rate due to the absence of a detailed structural data.

2