実験報告書様式（一般利用課題・成果公開利用）（ ※本報告書は英語で記述してください。ただし、産業利用課題として採択されている方は日本語で記述していただいても結構です。 ）Experimental Report

承認日 Date of Approval
承認者 Approver
提出日 Date of Report

課題番号 Project No.

装置責任者 Name of Instrument scientist

2015A0272

山﨑 大

実験課題名 Title of experiment
Bias-voltage-dependent depth profile measurement of Liconcentration at electrolyte/electrode interfaces
実験責任者名 Name of principal investigator

装置名 Name of Instrument/（BL No.）

Taro Hitosugi

BL-17
実施日 Date of ExperimentMar. 3rd, 2016 – Mar. 7th 2016

所属 Affiliation
Tohoku University
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.
Our purpose is to measure distribution of Li ions in a solid
electrolyte under applied voltage. For this purpose, we prepared asolid electrolyte sandwiched with metal electrodes. Amorphous
Li1+x+yAlx(Ti,Ge)2-xSiyP3-yO12 (LICGC) is selected as a model solidelectrolyte. Chromium (Cr) electrodes, with thickness of 50 nm,
were deposited on both sides of the mirror polished 20 mm × 20 mm
× 0.18 mm LICGC substrate by using DC magnetron sputtering. AFig. 1 A schematic of sample. Chromium isdeposited on both sides of a Li1+x+yAlx(Ti,Ge)2xSiyP3-yO12 (LICGC) surface.

schematic of the sample is shown in Fig. 1.

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.

Distribution of Li ions in solid electrolytes is key information for revealing the mechanism of all-solid-state
Li-ion battery operations. However, few studies have reported the Li-ion distribution in solid electrolytes.
Recently, we have succeeded in unveiling the distribution of Li ions at electrode/electrolyte interfaces undervoltage application､using Rutherford backward scattering (RBS) and nuclear reaction analysis (NRA) methods.
The results clearly show that, when 5 V is applied to a positive electrode, a Li composition decreases for morethan 40% within 8 m from the positive-electrode/electrolyte interface （Fig. 2）. This is quite surprising because
it is widely believed that the Li-ion-density depression layer, namely, space-charge layer, is a nano-meter scalein solid electrolytes. Although the distribution of Li ions in micrometer scale became clear, investigations of thedepletion of Li in a nano-meter scale at the interface is still unsatisfactory. To answer this question, we carriedout neutron reflectivity measurements of LICGC solid electrolyte with applying various voltages. The conceptof this study is summarized in Fig. 3.

2. 実験方法及び結果（つづき） Experimental method and results (continued)
Using neutron reflectivity measurements, we tried to determine
the depth profile of the density of Li-ions in a LICGC solid electrolyte.
Neutron reflectivity is measured in-situ under applying 0, +2.5, +5, 2.5 and -5 V to the top Cr electrode. AC impedance spectra (SL-150,Biologic) were also obtained before and after the neutron reflectivity
measurements, to compare the insights from electrochemicalmeasurements and the actual Li-ion distributions.
The reflectivity profiles at 0, +5 and -5 V are compared in Fig. 4.
The circles show the experimental profiles and the solid lines are
simulation results. The profiles show clear difference depending onFig. 2 Li-ion distribution measured using
Rutherford backward scattering and nuclear
reaction analysis. The measured sample is
Li1+xGe2-yAlyP3O12 sandwiched with Nielectrode. A voltage of 5 V is applied to theone side of Ni electrode.

voltages, especially in the region of large scattering vector.
The scattering length density (SLD) profiles used for the simulatedlines in Fig. 4 are shown in Fig. 5. The SLD profile at +5 V is larger
than that at 0 V in deep region over 50 nm. These results can beinterpreted as following. The difference in SLD between +5 V and 0 V
is according to the difference in Li-ion compositions because active ionsin LICGC is only Li. Since the SLD value of Li is quite small (about 9), the SLD value is increased when the Li composition is decreased.
Hence, the result at +5 V indicates that the Li composition aroundFig. 3 Concept of this study. Lithium-ion
distribution
nearelectrode/electrolyte
interface is measured.

positive electrode/electrolyte interface is decreased. The decrease ofLi composition is consistent with the RBS and NRA result in Fig. 2.
Here, we note that there is no steep peak of SLD value in the profile
at +5 V; this means that there is no abrupt change of Li density near
the positive electrode/electrolyte interface.
In contrast to the SLD profile at +5V, the SLD profile at -5 V issmaller than that at 0 V in the deep region over 50 nm. This is because
the Li ions concentrate around negative-electrode/electrolyteinterface. At 0 to 50 nm, the SLD value is very small because Li

Fig. 4 Neutron reflectivity obtained at 0 V(green), 5 V (red) and -5 V (blue). Circles areexperimental data and lines are simulation
results.

appears on top side of negative Cr electrode by applying -5 V; aphenomenon well known as “Li stripping” reactions [1]. These results
show that the SLD values have a good correspondence with profiles
obtained using RBS and NRA (Fig. 2). Furthermore, the results indicatethat there is no abrupt change in SLD value in nm scale. Therefore, weconclude that there is no steep Li depression or accumulation aroundthe electrode/electrolyte interfaces.
Toconclude,

theRBS,

NRA and neutronreflectivity

measurements revealed that the density of Li-ions in solid electrolyteschanges in m scale, depending on applied voltages.
[1] F. Sagane, et al., J. Pow. Soucrces, 225 (2013) 245-250.

Fig. 5 SLD depth profile at 5 V (red), 0 V(green) and -5 V (blue) used for thesimulation in Fig. 4.