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ArticleTitle

Lithium Ion Secondary Cell Prepared by a Printing Procedure, and Its Application to All-Solid-State Inorganic
Lithium Ion Cells

Article Sub-Title
Article CopyRight

TMS(This will be the copyright line in the final PDF)

Journal Name

Journal of Electronic Materials

Corresponding Author

Family Name

Mori

Particle
Given Name

Ryohei

SuffixDivision

Schedule

Organization

Fuji Pigment Co. Ltd.

Address

2-23-2 Obana, 666-0015, Kawanishi, Hyogo Prefecture, Japan

Emailmoriryohei@fuji-pigment.co.jp

Received

12 February 2013

RevisedAccepted

15 January 2014

Abstract

We have developed a straightforward printing method for preparation of a lithium secondary cell.
LiCo1/3Ni1/3Mn1/3O2 and Li4Ti5O12 viscous printable pastes were used for the cathode and anode, respectively.
Electrochemical measurement was used to characterize the capacitance of each cell, and field-emission
scanning electron microscopy and particle size measurements were used to characterize particle size andmorphology. These film electrodes functioned stably both in a standard liquid electrolyte and in an Li2SiO3
solid electrolyte, although the capacitance of the all-solid-state cell was significantly lower than that of thecell containing liquid electrolyte. When liquid electrolyte was used, the capacity decreased by 36% after 50
cycles. However, the capacity of 0.2 mA h/g remained almost the same even after 50 charge–discharge cycles,
demonstrating the stability and strength of the all-solid-state lithium ion cell. It was also found that the cell
resistance mostly arose from the electrode/electrolyte interface and not from the bulk electrolyte. Additionof a sol–gel to the solid electrolyte printable paste improved cell performance.

Keywords (separated by '-')

Lithium ion cell - all-solid-state - sol–gel - thin film

Footnote Information

Journal: 11664
Article: 3039

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Please check and confirm the usage of term squige
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In the sentence “Although the choice of electrolyte...
electrode/electrolyte material.” we have deleted “andmorphology of the electrode/electrolyte material”
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Journal of ELECTRONIC MATERIALS

DOI: 10.1007/s11664-014-3039-z
Ó 2014 TMS

12F

RYOHEI MORI1,2

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1.—Fuji Pigment Co. Ltd., 2-23-2 Obana, Kawanishi, Hyogo Prefecture 666-0015, Japan.
2.—e-mail: moriryohei@fuji-pigment.co.jp

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We have developed a straightforward printing method for preparation of alithium secondary cell. LiCo1/3Ni1/3Mn1/3O2 and Li4Ti5O12 viscous printable
pastes were used for the cathode and anode, respectively. Electrochemicalmeasurement was used to characterize the capacitance of each cell, and fieldemission scanning electron microscopy and particle size measurements wereused to characterize particle size and morphology. These film electrodes
functioned stably both in a standard liquid electrolyte and in an Li2SiO3 solid
electrolyte, although the capacitance of the all-solid-state cell was significantly
lower than that of the cell containing liquid electrolyte. When liquid electrolyte was used, the capacity decreased by 36% after 50 cycles. However, thecapacity of 0.2 mA h/g remained almost the same even after 50 charge–discharge cycles, demonstrating the stability and strength of the all-solid-statelithium ion cell. It was also found that the cell resistance mostly arose from theelectrode/electrolyte interface and not from the bulk electrolyte. Addition of asol–gel to the solid electrolyte printable paste improved cell performance.

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Key words: Lithium ion cell, all-solid-state, sol–gel, thin film

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INTRODUCTION

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Lithium ion cells are widely used as power sources for a variety of mobile electronic devices.1–3 In
recent years, the demand for large lithium ion cells
for use in electric vehicles (EVs), hybrid electricvehicles (HEVs) in particular, has grown substantially, necessitating improvements in the safety oflithium ion cells. Current commercially-available
cells use primarily liquid electrolytes containing
organic solvent, which limit the safety and reliability of the cells. Exchanging the flammable liquid
electrolytes for non-flammable solid electrolytes has
been shown to drastically improve the performanceand robustness of lithium ion cells, and all-solidstate lithium secondary cells are expected to be thepreferred design for use in EVs and HEVs.
As a result of this high demand, several
approaches to preparing all-solid-state cells havebeen developed,4–9 including use of such techniques

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Lithium Ion Secondary Cell Prepared by a Printing Procedure,and Its Application to All-Solid-State Inorganic Lithium Ion Cells

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3(Received February 12, 2013; accepted January 15, 2014)

as radio-frequency (RF) sputtering and laser ablation. Another option is a bulk type cell constructedfrom solid electrolyte and electrode powder. Polymer electrolytes are also good candidates for use inall-solid-state cells, and have been proved to function well with good stability.8,9 Among inorganic
electrolyte materials, sulfide-based glassy materials
are favored as solid electrolytes for bulk-type allsolid-state cells, because of their advantages overcrystalline solid electrolytes.10–12 However, sulfides
are unsuitable for practical use because of theirinstability—they react with ambient moisture andemit hydrogen sulfide.
In this respect, inorganic oxide materials are now
regarded as the best candidates for use as solid
electrolytes in lithium ion cells, because their stability to air and humidity results in great flexibility
in their development for practical uses and implementation in industrial manufacturing processes.
Several all-solid-state thin film cells with inorganic
electrolytes have already been reported. Lithium
phosphorus oxynitride (LiPON) has excellent cycling
performance at room temperature.13,14 Sodium (Na)Journal : 11664_JEM

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Mori

Table I. Comparison of this study with related studies
Battery type

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Active material for the lithium ion cell cathode(LiCo1/3Ni1/3Mn1/3O2) was purchased from Tanaka
Chemical (Fukui, Japan). Lithium titanate (Li4Ti5O12) was purchased from Ishihara Sangyo (Osaka, Japan). Lithium silicate (Li2SiO3) powder,tetraethoxysilane (TEOS), lithium nitrate (LiNO3),
phosphoric acid (H3PO4), and nitric acid (HNO3)
were purchased from Wako Chemical (Osaka,
Japan). Terpineol (a-a-4-trimethyl cyclohex-3-ene-1methanol) was purchased from Arakawa Chemical
Industries (Osaka, Japan). The dispersant polyoxyethylene sorbitan tristearate, was purchased from
Kao Corporation (Japan).
The appropriate amount of electrode or solid
electrolyte powder was dissolved in terpineol, with
polyoxyethylene sorbitan tristearate as dispersant.
Ethyl cellulose (MW 20,000; Wako Chemical) was

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added as binder and to increase the viscosity of thedispersion liquid for the squige printing technique.
The viscous pastes for the electrode and electrolyte
were made by combining 21 g electrode or solid
electrolyte powder with 2 g dispersant and 47 g
terpineol. These were then dispersed for 30 min byuse of a stirring machine rotating at 3500 rpm.
Ethyl cellulose (3 g) was added to 45 g sol slurry
and the mixture was then stirred for an additional
30 min at 2000 rpm to completely dissolve the ethyl
cellulose.
Tetraethoxysilane (TEOS), LiNO3, H3PO4, water,and HNO3 were combined in the molar ratio
1:7:7:1:0.1 to form a sol–gel phase. To suit the scale ofour experiment, we combined 5.2 g TEOS, 12.075 g
LiNO3, 17.15 g H3PO4, 0.1575 g HNO3, and 0.45 g
water, and mixed them with 50 g ethanol. The mixture was added to the solid electrolyte printable paste
before printing in a weight ratio of 1:1 (sol–gel solution-to-printable paste). The resulting viscous paste
was deposited on to an aluminium plate substrate bysquige printing. The film was heat treated at 600°C
for 30 min then cooled to room temperature. For allsolid-state lithium ion cell preparation, LiCo1/3Ni1/
3Mn1/3O2 was coated on to an aluminium plate, followed by a coat of Li2SiO3 paste, and a final coat of
Li4Ti5O12 paste, with heat treatments at each step.
For electrochemical measurements of the lithium ion
cell containing liquid electrolyte, an electrolyte composed of 1.25 M LiClO4 in 3:1 v/v ethylene carbonate–propylene carbonate was used. For all-solid-statelithium ion cell electrochemical measurements, copper adhesive tape was placed on top of the Li4Ti5O12
layer to create an electrical contact. Cell performancewas evaluated galvanostatically by use of a charge
and discharge apparatus (SP-150; Bio Logics,
France). Cut off potential was determined from 2.2 V
to 0 V. Electrochemical impedance spectroscopy was
conducted from 1 MHz to 100 mHz with a 10 mV
amplitude. All electrochemical measurements wereconducted under ambient conditions. To determine
morphology, the films were imaged by use of fieldemission scanning electron microscopy (FESEM;
JSM-6700F; Jeol, Tokyo, Japan). The sizes of thedispersed particles were measured by use of a
Microtrac particle-size analyzer (Nanotrac TM 150;
Nikkiso, Japan); to perform this measurement, theparticle dispersion sample was aspirated from the

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super ionic conductor (NASICON)-type Li-ion conducting electrolyte consisting of Li2O–Al2O3–SiO2–
P2O5–TiO2 has also received much attention becauseof its high Li-ion conductivity of 10 4–10 3 S cm 1at room temperature.15,16 Our work and related
studies are compared in Table I.
Although the choice of electrolyte material is ofgreat importance, lithium ion cell performance isalso affected by electrode and solid electrolyte morphology, including particle size. Controlling particle
size and morphology is critical to obtaining highperformance lithium ion cells. One method for controlling particle size is an industrial dispersion
procedure, which is particularly effective for inorganic materials. In general, particles tend to form
aggregates when mixed with liquid, because of vander Waals forces. However, use of an appropriate
chemical which adheres to the surface of the particles can disperse the aggregates into small individual particles, as a result of acid–base interactions or
three-dimensional repulsive forces.17
In this study, we prepared printable viscous
pastes for both electrode and electrolyte to make anall-solid-state lithium ion cell by use of a simple
printing procedure. In addition, we investigated theeffect on lithium ion cell performance of mixing a
sol–gel solution with the solid electrolyte printable
paste.

Author Proof

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1–3
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10–12
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This study

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LIB with liquid electrolyte
All-solid-state LIB (RF sputtering, laser ablation)
All-solid-state LIB (polymer electrolyte)
All-solid-state LIB (sulfide-based materials)
All-solid-state LIB (oxide material, LIPON type)All-solid-state LIB (oxide material, NASICON type)All-solid-state LIB (oxide material, printing preparation)

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Fig. 1. Charge–discharge curve of the lithium ion cell made with
LiCo1/3Ni1/3Mn1/3O2 and Li4Ti5O12 containing a liquid electrolyte.

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Figure 1 shows the discharge curve for the lithium ion cell made with LiCo1/3Ni1/3Mn1/3O2 andLi4Ti5O12 thin films prepared by a printing procedure. The current density was measured at a constant rate of 20 lA/cm2. These materials werechosen for the electrodes because of their stability to
air and moisture, meaning that both can be prepared and handled under ambient conditions. In
addition, it was not necessary to use a fluoridecontaining organic solvent that could emit HF byreaction with the ambient atmosphere, because Li
metal was not used as an anode. The differences
between the electrochemical properties of LiCo1/
3Ni1/3Mn1/3O2 and Li4Ti5O12 and those of Li metal
are well understood.18–21 For intercalation cells
made without any metallic lithium, intermediate
voltages were related to the difference between thepositive (LiCo1/3Ni1/3Mn1/3O2: 3.6 V) and negative(Li4Ti5O12: 1.6 V) electrode potentials. The electrochemical charge–discharge curves for LiCo1/3Ni1/
3Mn1/3O2/Li4Ti5O12 at a current density of 20 lA/
cm2 in EC–PC electrolyte indicated that Li wasde-intercalated from Li1 xCo1/3Ni1/3Mn1/3O2 andstably inserted into Li1+xTi5O12. Unlike metallic
lithium cells, rocking chairs have no excess Li ineither the anode or cathode, so they tolerate
repeated discharges to 0 V.22 Despite this robustness, the capacity decreased from 60 mAh/g to40 mAh/g after 50 cycles, reflecting a 36% lossof reversibility. Hence, on repeated cycling, extraction and insertion of Li ions into the structure of
LiCo1/3Ni1/3Mn1/3O2/Li4Ti5O12 was not reversible. It
is difficult to fully explain this irreversibility; it is,however, evident that the LiCo1/3Ni1/3Mn1/3O2 andLi4Ti5O12 cell can be used as a rechargeable cell if
the capacity is improved.
Figure 2a shows the discharge curve of the allsolid-state lithium ion cell containing Li2SiO3 solid
electrolyte between the negative and positive electrodes. Measurements of current density were performed at a constant rate of 2 nA/cm2, a much lower
rate than that used for the cell containing a liquid
electrolyte. This is because of the low current
available, which may have been caused by inadequate interfacial contact between the electrode andsolid electrolyte. In addition, within the solid electrolyte, the available current decreased substantially because of high resistance. Please note that
because of a limitation of the experimental equipment used, the applied current could not be controlled below approximately one nanoampere(<1 nA), so the discharge curve declined steeply.

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suspension and quickly injected into a solvent solution. The crystalline phase of the solid electrolyte
prepared by use of a sol–gel was evaluated by x-ray
diffractometry (XRD; RINT 2500 x-ray diffractometer; Rigaku, Tokyo, Japan) using Cu Ka radiation andoperated at 40 kV and 50 mA.

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Lithium Ion Secondary Cell Prepared by a Printing Procedure, and Its Application to All-Solid-State
Inorganic Lithium Ion Cells

Fig. 2. Charge–discharge curve of the all-solid-state lithium ion cell.
(a) Lithium ion cell composed of an LiCo1/3Ni1/3Mn1/3O2/Li2SiO3/Li4Ti5O12 thin film. (b) Lithium ion cell composed of an LiCo1/3Ni1/3Mn1/
3O2/Li2SiO3/Li4Ti5O12 thin film with a sol–gel phase introduced into
the Li2SiO3 layer.

This is true for Fig. 2b also. Furthermore, themeasured capacitance was substantially lower thanthat for sulfide-based all-solid-state lithium ion
cells.10–12 We suggest that oxide particles are morerigid than sulfide particles, and this increases theresistance at particle boundaries because of the lackof particle contact to facilitate Li ion conduction.
However, the capacity remained at approximately
4 lAh/g even after 50 charge–discharge cycles,

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Mori

Figure 3a is a photograph of the all-solid-statethin film lithium ion cell. The cell was prepared on a
25 mm 9 35 mm aluminium board by use of a simple printing procedure. The size of the electrode andelectrolyte thin films can be easily changed bymodifying the squige or screen-printing methods,
both of which can be readily used for industrial
manufacture. Figures 3b–d show SEM images of
the Li4Ti5O12, Li2SiO3, and LiCo1/3Ni1/3Mn1/3O2

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indicative of the stability and strength of the allsolid-state lithium ion cell. The cell voltage wasalmost identical to the value obtained when theliquid electrolyte was used. Li2SiO3 was chosenbecause it was readily available for industrial use ina printable paste preparation. Although Li4SiO4 is awell-known lithium ion conductor, an Li4SiO4 solid
thin film could not be prepared on LiCo1/3Ni1/3Mn1/3O2
because of film cracking.

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Fig. 3. (a) Photograph of the all-solid-state lithium ion cell prepared in this study. SEM image of (b) the Li4Ti5O12 thin film, (c) the Li2SiO3 thin film,and (d) the LiCo1/3Ni1/3Mn1/3O2 thin film. (e) Cross-sectional image of LiCo1/3Ni1/3Mn1/3O2/Li2SiO3/Li4Ti5O12 thin film.

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Fig. 4. Cross-sectional SEM image of all-solid-state lithium ion cellcomposed of an LiCo1/3Ni1/3Mn1/3O2/Li2SiO3/Li4Ti5O12 thin film witha sol–gel-phase introduced into the Li2SiO3 layer.

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were 5.56 9 10 6 S cm 1 for the Li2SiO3 film and2.08 9 10 5 S cm 1 for the Li2SiO3 + sol–gel phasefilm. These are slightly higher than those obtained
previously.26 The Li2SiO3 film in the previous study
was prepared by PLD, so the conductivity may differ
because of the different method of film preparation.
Figure 6a shows the Nyquist plot for the preparedlithium ion cell. A magnified version of the Nyquist
plot is also shown for the lithium ion cell containing
liquid electrolyte. Figures 6b and c show thededuced electrical circuits for the lithium ion cellswith liquid and solid electrolyte, respectively. For
the lithium ion cell with liquid electrolyte, high andmiddle-range frequency was observed; this originated from the contributions of electrolyte resistance, charge-transfer resistance, and double-layer
capacitance at the electrolyte/electrode interface. At
low frequency the beginning of Warburg slope line isapparent; this represents the semi-infinite diffusionof Li-ions in the electrodes.25 For the lithium ion cellwith solid electrolyte, on the other hand, one large
semi-circle consisting of bulk electrolyte resistance,
charge transfer resistance, and double layer capacitance at the electrolyte/electrode interface wasobserved. Cell conductivity, estimated from measured cell area and sample film thickness, was3.51 9 10 9 S cm 1 for the cell with lithium silicate
solid electrolyte and 4.32 9 10 9 S cm 1 after
introduction of sol–gel phase into the electrolyte.
Comparison with the results in Fig. 5, reveals thatthe resistance of all the solid-state lithium ion cells
prepared in this study mostly arises from the electrolyte/electrode interface and not from electrolyte
film resistance. Thus, this large semi-circle isthought to arise predominantly from the chargetransfer resistance at the electrolyte/electrodeinterface rather than from the contribution of bulk
conductivity. Nagao et al.12 also reported that cell
resistance at the electrode/electrolyte interface is

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thin film surfaces, confirming that the particle sizes
ranged between 100 nm and 200 nm for the Li4Ti5O12 and Li2SiO3 films. Conversely, much larger(1 lm to 2 lm) flake-like particles were observed
for the LiCo1/3Ni1/3Mn1/3O2 electrode. Lu et al.23
indicated that active material porosity in the electrode film is critical for determining cell capacitance. There should be some correlation among
particle structure, size, film porosity, and film
strength; these relationships require further study
to enable development of better cells. Figure 3eshows the cross-sectional image of the LiCo1/3Ni1/
3Mn1/3O2/Li2SiO3/Li4Ti5O12 thin film. The lines that
distinguish one layer from another are visible, confirming successful coating of the three layers on topof each other.
Figure 2b shows the charge–discharge curve of
the cell prepared by mixing Li2SiO3 solid electrolyte
printable paste with sol–gel solution before heat
treatment. The current density was measured at aconstant rate of 10 nA/cm2. Initial capacitance was0.2 mAh/g and did not decrease even after 50
charge–discharge cycles, indicating that introduction of the sol–gel into the printable paste improved
cell performance, including film capacitance. Our
results clearly show that the solid electrolyte Li2SiO3 can be interchanged with liquid electrolyte toobtain the same cell voltage. Some previous studies
suggest that the capacitance of lithium ion cells may
be further improved by coating the surface of theactive material with silica or lithium silicate.24,25 It
should be noted here that the charge–discharge
experimental results obtained from the all-solidstate lithium ion cells in this study were stable todifferent air temperature (5–35°C) and humidity(30–70%) conditions.
Figure 4 shows an SEM image of a cross-sectionof an all-solid-state lithium ion cell prepared fromthe printable paste when sol–gel solution wasadded. The central region is composed of Li2SiO3particles mixed with sol–gel. If this is comparedwith the cross-section shown in Fig. 3e, no obvious
difference is apparent with regard to particle shapeor size. No clear difference in the morphology wasobserved for the sol–gel-containing film even on
inspection with SEM, and the capacity was
improved. This is likely to be because the particle
boundary neck was coated with solid electrolytecomposed of the sol–gel phase, reducing the resistance both within the solid electrolyte and at theelectrolyte/electrode interface. Liet al. et al.24 andMei et al.25 have also reported that SEM did notreveal any clear differences among samples containing silica or lithium silicate, although thesematerials improved cell capacitance owing toenhanced Li-ion conductivity.
The Nyquist plot of the Li2SiO3 film prepared in thisstudy is shown in Fig. 5. Film conductivities were
estimated from the measured area and sample film
thickness, which was determined from SEM crosssectional images (Figs. 3 and 4). The conductivities

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Fig. 5. Nyquist plots of Li2SiO3 films prepared in this study: (a) Li2SiO3 film; (b) Li2SiO3 film + sol gel phase. The insets are the crosssectional SEM images of the measured films.

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expected to be much larger than the bulk resistance,
especially for solid oxide-based electrolyte. Thisimplies cell capacitance could be improved by optimizing the interface. As presented in Figs. 5b and6a, although the conductivity enhancement as aresult of introducing the sol–gel phase was small,the capacitance was improved. Nagao et al.12 compared the capacitance of an all-solid-state lithium
ion cell with that of a cell containing bare lithium
titanate and pulverized lithium titanate; they foundthat although there was no clear difference between
the impedance of the cells, the lithium ion cell containing pulverized lithium titanate particles had
improved capacitance, owing to shortening of the
Li-ion diffusion path. Similarly, it is possible that bymodifying the lithium silicate solid electrolyte with
sol–gel, the Li-ion diffusion path was shortened,
resulting in improved cell capacitance even though
the impedance and estimated conductivity were notsubstantially improved. Nan et al. introduced sol–gel silica into lithium lanthanum titanium oxide(LLTO) solid electrolyte and found that it enhanced
ionic transport. They confirmed that lithium silicate
was formed when tetraethoxysilane (TEOS) was
introduced and demonstrated that lithium silicate
was present mostly at grain boundaries, and not on
the particle surface. In lithium ion conductive electrolytes in general, Li+ ions are depleted at the grainboundaries owing to evaporation of Li+ ions during

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Fig. 6. (a) Nyquist plot of the lithium ion cell prepared in this study.
The inset shows the Nyquist plot for the lithium ion cell containing
liquid electrolyte. m: liquid electrolyte, d: solid electrolyte: +: solid
electrolyte and sol gel phase. (b) Equivalent electrical circuit for thelithium ion cell with liquid electrolyte. (c) Equivalent electrical circuit
for the lithium ion cell with solid electrolyte.

the sintering process. However, Mei et al. 25 concluded that, as a result of formation of lithium silicate at grain boundaries, the Li-ion diffusion paths
were formed predominantly at grain boundaries,
giving rise to enhanced Li-ion conductivity. Similar
results obtained by us suggest that the sol–gel
phase mixed with lithium silicate was also present
largely at grain boundaries and had the same effectof improving the Li ion transport.
Figure 7 shows the particle size distribution of
the dispersion samples. The D0.5 values obtained for
Li4Ti5O12, Li2SiO3, and LiCo1/3Ni1/3Mn1/3O2 were0.76, 0.54, and 0.92 lm, respectively, which arelarger than the individual particle sizes confirmed
by SEM, especially for Li4Ti5O12 and Li2SiO3. To
measure the particle size, the suspension was
diluted in a measurement cell, meaning that thechemical composition of the solution measured was
different from that of the original solution and did
not contain adequate dispersant. Therefore, someparticles agglomerated, leading to the detection oflarger particle sizes than were present in the original suspension. Even so, the particle size distribution for LiCo1/3Ni1/3Mn1/3O2 was larger than thoseobserved for Li2SiO3 and Li4Ti5O12, in reasonableagreement with the observations made by SEM.

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Lithium Ion Secondary Cell Prepared by a Printing Procedure, and Its Application to All-Solid-State
Inorganic Lithium Ion Cells

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Author Proof

Fig. 8. X-ray diffraction pattern of the sol–gel phase prepared in thisstudy.

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CONCLUSION

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Lithium ion cell electrode material and solid
electrolyte were prepared as viscous printable
pastes, and films were prepared by a squige methodwith post-heat treatment at 600°C. It was foundthat the prepared thin-film electrode, used as alithium ion-cell electrode, was stable under ambientconditions when a liquid electrolyte was used. An
all-solid-state lithium ion cell composed of an LiCo1/
3Ni1/3Mn1/3O2/Li2SiO3/Li4Ti5O12 film structure wasprepared with Li2SiO3 solid-electrolyte film between
the cathode and anode layers. SEM observation
confirmed that the three layers were lying on top of
the bottom layer. The measured capacitance was

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solid electrolyte and at the electrode/electrolyte
interface, thus reducing resistivity.29–32 However,
Li4SiO4 was not observed, although the Li3PO4
phase has the potential to be a good lithium ion
conductor. Smaihi et al.33 reported the preparationof Li4SiO4–Li3PO4 by a sol–gel method and characterized the conductivity of Li4 xSi1 xPxO4 at
x = 0 0.6, concluding that the best conductancewas obtained at x = 0.6. Also by using a sol–gel
method, Li et al.24 and Mei et al.25 demonstrated
that coated silica and lithium silicate were present
as amorphous, not crystalline, phases. We observedthat the phosphate-based crystalline phase wasmore dominant than the silica-based crystalline
phase, even though the molar ratio of the sol–gel
solution was the same as that used to prepare the
Li4SiO4–Li3PO4 phase (7:1:1 = Li:Si:P). This isprobably because the volatile TEOS in the sol–gel
solution evaporated, causing the sintered phase to
become more phosphate-rich.
However, introduction of sol–gel into the electrolyte improved the lithium ion cell capacitance. The
sol–gel solution composition and preparation stillrequire optimization to further improve cell performance. Other solid electrolytes, for example LIPON,
NASICON, or LLTO are also good candidates forsolid electrolytes, and can be used in this all-solidstate lithium ion cell system.

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These results suggest that the particle dispersion
method used in this study effectively controlled
particle size in the prepared solid thin films.
Determining the optimum particle size for all-solidstate lithium ion cells is the next step in thisresearch.
X-ray diffraction analysis of the sol–gel phase isshown in Fig. 8. The lithium ion conductance of
Li4SiO4–Li3PO4 is known to be higher than that of
Li2SiO3.27,28 By using a sol–gel method we
attempted to prepare an Li4SiO4–Li3PO4 phase.
This was expected to act as an ion-conductive inorganic glue, as explained at Fig. 5 section, within the

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Fig. 7. Particle size distribution of the dispersion samples preparedin this study. The D0.5 values of (a) Li4Ti5O12, (b) Li2SiO3, and(c) LiCo1/3Ni1/3Mn1/3O2 were 0.76, 0.54, and 0.92 lm, respectively.

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ACKNOWLEDGEMENTS

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The author wishes to express his thanks to
Dr Sadayoshi Mori and Kazuo Sakai for helpful
discussions.

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lower than that of a lithium ion cell with liquid
electrolyte, because of the high resistance of thesolid electrolyte and the electrolyte/electrode interface. We also found that cell resistance mostly arosefrom the electrode/electrolyte interface and not frombulk electrolyte. Cell capacitance did not decrease
even after 50 charge–discharge cycles. It was also
found that all-solid-state lithium ion-cell capacitance was improved by introducing a sol–gel solution into the solid electrolyte viscous printable
paste. This is probably because the particle grainboundaries were coated with the sol–gel solution,
reducing the resistance within the solid electrolyte
and at the electrolyte/electrode interface.

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