Article
Submicron-Sized Nb-Doped Lithium Garnet for High
Ionic Conductivity Solid Electrolyte and Performance
of Quasi-Solid-State Lithium Battery

Yan Ji 1, Cankai Zhou 1, Feng Lin 1, Bingjing Li 1, Feifan Yang 1, Huali Zhu 2
Zhaoyong Chen 1,*
1 College of Materials Science and Engineering, Changsha University of Science and Technology,

, Junfei Duan 1 and

Changsha 410114, China; jueﬂy@stu.csust.edu.cn (Y.J.); zhoucankai@stu.csust.edu.cn (C.Z.);
18216359528@163.com (F.L.); krystalbingjingli@163.com (B.L.); yﬀ_0413@126.com (F.Y.);
junfei_duan@csust.edu.cn (J.D.)

2 College of Physics and Electronic Science, Changsha University of Science and Technology, Changsha 410114,

China; juliezhu2005@126.com

* Correspondence: chenzhaoyongcioc@126.com

Received: 23 December 2019; Accepted: 20 January 2020; Published: 24 January 2020

Abstract: The garnet Li7La3Zr2O12 (LLZO) has been widely investigated because of its high
conductivity, wide electrochemical window, and chemical stability with regards to lithium metal.
However, the usual preparation process of LLZO requires high-temperature sintering for a long time
and a lot of mother powder to compensate for lithium evaporation.
In this study submicron
Li6.6La3Zr1.6Nb0.4O12 (LLZNO) powder—which has a stable cubic phase and high sintering
activity—was prepared using the conventional solid-state reaction and the attrition milling process,
and Li stoichiometric LLZNO ceramics were obtained by sintering this powder—which is diﬃcult
to control under high sintering temperatures and when sintered for a long time—at a relatively
low temperature or for a short amount of time. The particle-size distribution, phase structure,
microstructure, distribution of elements, total ionic conductivity, relative density, and activation
energy of the submicron LLZNO powder and the LLZNO ceramics were tested and analyzed using
laser diﬀraction particle-size analyzer (LD), X-Ray Diﬀraction (XRD), Scanning Electron Microscope
(SEM), Electrochemical Impedance Spectroscopy (EIS), and the Archimedean method. The total ionic
−1, the activation energy
conductivity of samples sintered at 1200
was 0.311 eV, and the relative density was 87.3%. When the samples were sintered at 1150
C for
60 min the total ionic conductivity was 3.49 × 10
−1, the activation energy was 0.316 eV, and
the relative density was 90.4%. At the same time, quasi-solid-state batteries were assembled with
LiMn2O4 as the positive electrode and submicron LLZNO powder as the solid-state electrolyte. After
50 cycles, the discharge speciﬁc capacity was 105.5 mAh/g and the columbic eﬃciency was above 95%.

C for 30 min was 5.09 × 10

−4 S·cm

−4 S·cm

◦

◦

Keywords:
solid-state batteries

solid-state electrolyte;

submicron powder; garnet;

lithium-ion conductivity;

1. Introduction

Currently, lithium-ion batteries are widely used in electric vehicles (EVs), hybrid electric vehicles
(HEVs), computers, smart grids, wearable devices, etc. [1]. Traditional lithium-ion batteries have organic
liquid electrolytes which easily burn and explode under abusive conditions. In addition, with the
development of modern society, lithium-ion batteries have gradually moved toward high speciﬁc energy.
Researchers have studied cathode materials, such as LiCoO2, LiMn2O4, LiFePO4, LiNi0.6Co0.2Mn0.2O2,
LiNi0.8Co0.1Mn0.1O2, LiNi0.8Co0.15Al0.05O2, and xLi2MnO3·(1− x)LiMO2, to increase the energy density

Materials 2020, 13, 560; doi:10.3390/ma13030560

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of lithium-ion batteries [2–8]. The energy density can be improved by increasing the charging voltage,
which will lead to serious side reactions and safety issues. In order to solve the safety problem of
lithium-ion batteries, researchers have turned their attention to all-solid-state lithium batteries, which
use inorganic electrolytes. The non-ﬂammability, long cycling life and wide electrochemical window
of all-solid-state lithium batteries are considered to provide the high safety and high energy density of
the next-generation energy storage systems [9,10].

−3 S·cm

A solid electrolyte is an important component of all-solid-state batteries. It can not only be used
as a lithium ionic conductor, substituting for a liquid organic electrolyte, but also can be used to block
direct contact between the positive and negative electrodes, like a separator [11]. Solid electrolytes
generally contain Li3N, LiPON, perovskite, LISICON, NASICON, garnet, etc. [12–17]. Some of these
−1). However, some issues still exist, such as
solid electrolytes have high ionic conductivity (~10
instability in an ambient atmosphere (Li10GeP2S12, LGPS) and the metal cation being easily reduced
by lithium (such as Ti4+ in LixLa2/3 -x/3TiO3, LLTO) [18,19]. The cubic garnet LLZO was discovered
by Murugan et al. [17] in 2007 and attracted world-wide attention for its advantages, e.g., the simple
−1) at room temperature, high electrochemical
preparation process, high ionic conductivity (~10
window (0~6 V vs. Li/Li+), and electrochemical stability of lithium metal. On the other hand, LLZO
also has some defects, such as an unstable cubic phase and a low density of ceramics [20,21]. Moreover,
a mass of LLZO mother powder is needed to compensate for lithium loss when sintering at high
temperatures [21,22]. Many solutions have been adopted to solve the above issues. For example,
Al, Ga, Fe, Ta, Nb, W, Y, and Sb doping were used to stabilize the cubic phase [23–30]; hot pressing
sintering, plasma sintering, and microwave sintering were adopted to improve the relative density and
sintering additives [31–33]; and Y2O3, Al2O3, B2O3, CaO, MgO, Li3PO4, and Li4SiO4 were investigated
to reduce the grain-boundary resistance [34–40]. Usually, in order to evaluate the electrochemical
performance, LLZO was used as solid electrolyte in all-solid-state batteries [41–43].

−3 S·cm

In this study, submicron LLZNO powder with a stable cubic phase was synthesized using
the conventional solid-state reaction and prepared by the attrition milling process. The submicron
LLZNO powder had a high sintering activity, which promoted the sintering process, reduced the
sintering temperature and time, and reduced the loss of Li during high-temperature sintering. All these
characteristics favored lithium stoichiometry and ionic conductivity. Furthermore, LLZNO ceramics
were obtained without mother powder while sintering under reduced temperature and time.
The particles-size distribution, phase structure, microtopography, total ionic conductivity, relative
density, and activation energy were characterized and analyzed. The quasi-solid-state lithium batteries
with LiMn2O4 as the positive electrode and submicron LLZNO powder as the solid electrolyte were
assembled and the electrochemical performance are tested and analyzed.

2. Materials and Methods

2.1. The Synthesis of LLZNO Powder and Ceramics

A process ﬂow chart of the preparation of submicron LLZNO powder and the sintering of LLZNO
ceramics is showed in Figure 1. LLZNO powder was synthesized by the conventional solid-state
reaction [44]. Lithium hydroxide monohydrate (LiOH·H2O, 98%, Xilong Scientiﬁc Co., Ltd., Shantou,
China), lanthanum oxide (La2O3, 99.99%, Shanghai Aladdin Bio-Chem Technology Co., Ltd., Shanghai,
China), zirconia (ZrO2, 99%, Shanghai Aladdin Bio-Chem Technology Co., Ltd., Shanghai, China), and
niobium oxide (Nb2O5, 99.99%, Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) were used
as the raw materials and 10 wt% excess of LiOH·H2O was added to compensate for the lithium loss in
the high-temperature calcination and sintering process. Yttrium stabilized zirconia (YSZ, 4~8 mm in
diameter) and isopropanol (IPA) were used as the ball-grinding medium. The ratio of raw material
to grinding balls was 1:5 and the mixed raw material powder was wet-ball ground at 800 rpm in the
planetary ball mill for 6 h. The mixture was dried at 70
C for 12 h in
an alumina crucible with ambient air to obtain the cubic-phase LLZNO powder. LLZNO slurry was
attrition milled (Shanghai ROOT mechanical and electrical equipment Co., Ltd., Shanghai, China, 0.7 L

C for 14 h, then calcined at 950

◦

◦

Materials 2020, 13, 560

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volume, 70% ﬁlling rate) at 1000 rpm for 2 h, taking YSZ (0.4 mm in diameter) and IPA as the grinding
medium, and the solid-liquid ratio was 1:5. The LLZNO slurry was dried at 70
C for 14 h to obtain
submicron LLZNO powder, from which green pellets (mass of 3 g, 19 mm in diameter and a thickness
of about 4 mm) were pressed at 200 MPa under a cold uniaxial press. After that, the green pellets were
sintered in a muﬄe furnace (Changsha Yuandong Electric Furnace Factory) without mother powder at
1100–1200
C for 30–360 min and then cooled down naturally. At the same time, the green pellets were
put on a platinum wire and placed in a crucible of MgO with the lid on to prevent impurity migration
and a large amount of volatilization of lithium during the process of high-temperature sintering.
For further testing, LLZNO ceramic pellets were polished with 400 and 1000 mesh sandpaper.

◦

◦

Figure 1. Process ﬂow chart for the preparation of submicron Li6.6La3Zr1.6Nb0.4O12 (LLZNO) powder
and the sintering of LLZNO ceramics.

2.2. Fabrication of Composite Cathodes and Assembly of Quasi-Solid-State Batteries

In order to test the electrochemical performance of submicron LLZNO powder, we prepared a
composite cathode and assembled quasi-solid-state batteries. The composite cathode consisted of a
LiMn2O4 positive electrode layer and a submicron LLZNO electrolyte layer. The positive electrode was
fabricated by coating the slurry of a mixture containing LiMn2O4 powder, submicron LLZNO powder,
acetylene black (Shanghai Hersbit Chemical Co., Ltd., Shanghai, China), and polyvinylidene diﬂuoride
(PVDF, FR905, Shanghai San ai fu New Material Technology Co., Ltd., Shanghai, China), with a weight
ratio of 7:2:1:1, onto circular aluminum foils (thickness of 20 µm, Shenzhen Kejingstar Technology Ltd.,
Shenzhen, China) as the current collector, and the positive material loading was 1.66 mg/cm2. Then the
composite cathode was fabricated by coating the slurry of a mixture containing submicron LLZNO
powder and Polyvinylidene Fluoride (PVDF) with a weight ratio of 9:1 onto the positive electrode
layer. The composite cathode was punched into disks with 18 mm diameters after compacted by a
roller press (Shenzhen Kejingstar Technology Ltd., Shenzhen, China), and the density of composite
cathode was about 2.5 g/cm3. Quasi-solid-state batteries were assembled with two electrode coin
cells (type CR-2025) in a glove box ﬁlled with argon and with lithium metal foil (15 mm in diameter
and 1 mm thick, Shenzhen Kejingstar Technology Ltd., Shenzhen, China) as the negative current
collector. In addition, 20 µL of a liquid organic electrolyte (1 M LiPF6 dissolved in ethyl carbonate (EC)
and dimethyl carbonate (DMC) with a ratio of 1:1, CAPCHEM, Shenzhen, China [45]) was added to
improve the contact and reduce the interface impedance between the submicron LLZNO electrolyte
layer and the anode/cathode [46,47]. Compared with lithium-ion batteries, the added amount of liquid
organic electrolyte was small [48,49].

Materials 2020, 13, 560

2.3. Characterization

4 of 11

◦

◦

C with steps of 5

X-ray diﬀraction (XRD, Cu-Kα radiation, λ = 1.542 Å, Bruker D8 ADVANCE, Bruker AXS GmbH,
Karlsruhe, Germany) was used to determine the phase of the ceramics pellets at room temperature
C/min. Jade Software was used to match and analyze the phase of
within 10–60
the sample. The relative density of ceramics was measured by Archimedes’ method and deionized
water was used as the immersion medium. Meanwhile, the theoretical density of LLZNO, calculated
by the Jade Software, was 5.20 g/cm3, and the relative density was the measured density divided
by the theoretical density. The particle size and distribution of the powder were determined by
the laser diﬀraction particle-size test method (LD, Mastersizer 3000, Malvern Instruments Limited,
Malvern, UK), and the relative density, refractive index, and absorption rate of the LLZNO powder was
5.20 g/cm3, 1.4, and 0.1, respectively. The microtopography of the submicron LLZNO powder and cross
section of the ceramic pellets was observed by scanning electron microscope (SEM, TESCAN MIRA3
LMU, TESCAN Orsay Holding, a. s., Brno, Czech Republic). Energy dispersive spectrometer (Oxford
X-ray Max20, Oxford Instruments plc, Oxford, UK) mapping was used to characterize the distribution
of each element in the cross section of the ceramic pellets. The total lithium ion conductivity of the
ceramic pellets was measured by an Electrochemical Impedance Spectroscopy (EIS, Gamry Reference
600+, Gamry Instruments, Warminster, PA, USA) within a temperature range of 25–80
C, within
the frequency of 10 Hz–5 MHz, and with an AC amplitude of 40 mV. The blocking electrode was
uniformly coated by a thin silver layer on both sides of the ceramic pellets. The activation energy of
C and calculated based on the
the ceramic pellets was measured within a temperature range of 25–80
Arrhenius equation [16]. The quasi-solid-state batteries were tested under the battery charge-discharge
◦
tester (BTS-5V3A, Neware Technology Co., Ltd., Shenzhen, China) at 25
C, and current density was
0.02 mA/cm2.

◦

◦

3. Results and Discussions

The XRD pattern of the LLZNO powder is shown in Figure 2b and was identiﬁed as cubic phase
(PDF 63-0174). The LD result and SEM image of the LLZNO powder after the attrition milling process,
which demonstrated a submicron powder, are showed in Figure 2a and Table 1. The D(10), D(50),
D(90), and primary particle size of the submicron LLZNO powder were 0.43 µm, 0.59 µm, 0.812 µm,
and about 0.1 µm, respectively. The value of D(3,2) (0.575 µm) is similar to that of D(4,3) (0.607 µm),
which indicates that the prepared powder had a uniform particle-size distribution. In addition, the
powder also had a higher speciﬁc surface area (2007 m2/kg), which means that the powder had a high
sintering activity, which can promote crystal growth and the rapid densiﬁcation of ceramics in the
sintering process.

Figure 2. (a) Particle-size distribution of the LLZNO powder after being attrition milled 2 h at 1000 rpm
and its SEM image and (b) XRD pattern of the LLZNO powder.

Materials 2020, 13, 560

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Table 1. Laser particle-size test results of submicron-scale LLZNO powder.

Preparation
Condition

Attrition milled
2 h @ 1000 rpm

D10 (µm)

D50 (µm)

D90 (µm)

D(3,2) (µm) D(4,3) (µm)

Speciﬁc Surface
Area (m2/kg)

0.430

0.590

0.812

0.575

0.607

2007

◦

The XRD patterns of the LLZNO ceramic samples are showed in Figure 3. The phases of all the
prepared ceramic samples were identiﬁed as cubic phases (PDF 63-0174). The crystal parameters of the
C × 60 min
diﬀerent samples are showed in Table 2. The XRD patterns of the samples sintered at 1200
C × 360 min (SL5) showed a few impure phase peaks, mainly belonging to LiNbO3
(SL1) and at 1100
(PDF 82-0459) and Li7NbO6 (PDF 29-0816), and due to the decomposition from the high sintering
activity of the LLZNO after having been sintered for too long at a high temperature. Moreover, these
impure phases decreased the total ionic conductivity of LLZNO ceramics by increasing the resistance
of the grain boundary.

◦

Figure 3. XRD patterns of the LLZNO ceramics with diﬀerent sintering conditions.

◦

AC impedance plots and the enlargement of the LLZNO ceramic pellets under diﬀerent sintering
conditions are showed in Figure 4a, b. The ﬁtting curve of the sample sintered at 1200
C for 30 min
(SL2) is showed in Figure 4c, and it consists of a quasi-semicircle at high frequency and a long diﬀusion
tail at low frequency. The equivalent circuit model Rb(RgbQgb)(RelQel), in which Rb, Rgb, and Rel are
resistances originating from the bulk, grain boundaries, and Ag electrodes, is used to ﬁt the plots and
is shown in Figure 4d. The total ionic conductivity of the ceramics is mainly decided by Rb plus Rgb.
The total ionic conductivity and relative density of the LLZNO ceramic pellets are showed in Figure 4e
and Table 2. The highest total ionic conductivity (5.09 × 10
−1) of the LLZNO ceramic pellets
C × 30 min), and its
was obtained when sintered at a high temperature and for a short time (SL2, 1200
relative density is 87.3%. This indicates that high-performance LLZNO ceramics are obtained when
sintered at high temperatures only for short sintering times. However, the total ionic conductivity
and relative density of ceramic pellets decreased and impure phases occurred when the sintering
−4 S·cm
C. The lowest total ionic conductivity (0.35 × 10
−1) and
time was prolonged at 1100 and 1200
◦
C for 360 min
relative density (83.4%) were obtained when the ceramic pellets were sintered at 1100

−4 S·cm

◦

◦

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◦

−1) and a higher relative density
C × 60 min) were obtained when sintered for 60 min from 1100 to
C, and this result indicates that, in this study, increasing the sintering temperature too much was

(SL5). Meanwhile, a higher total ionic conductivity (3.49 × 10
(90.3%) of ceramic pellets (SL3, 1150
1200
disadvantageous for obtaining LLZNO ceramics with good performance.
◦

−4 S·cm

◦

Table 2. Sintering condition, cell parameter, total ionic conductivity at 25
relative density of LLZNO ceramics.

C, activation energy, and

Sample
Name
SL−1
SL−2
SL−3
SL−4
SL−5

Sintering
Condition
C × 60 min
◦
1200
C × 30 min
◦
1200
C × 60 min
◦
1150
C × 60 min
◦
1100
C × 360 min
◦
1100

Cell Parameter

(Å)

12.8952
12.8953
12.9028
12.8916
12.8870

Total Ionic Conductivity
(10−4 S·cm−1), 25

C

◦

1.58
5.09
3.49
0.51
0.35

Activation
Energy (eV)

0.315
0.311
0.316
0.319
0.328

Relative
Density
86.7%
87.3%
90.4%
90.3%
83.4%

Arrhenius plots and the linear ﬁtting curve are showed in Figure 5a. The activation energy
of ceramics samples is showed in Figure 5b and Table 2, and their values are within the range of
0.31–0.33 eV. This indicates that there was no obvious eﬀect on the activation energy of the ceramics
when the green pellets prepared from the submicron LLZNO powder were sintered. The variation
tendency of the activation energy was similar to the total ionic conductivity, and the lowest and the
C × 360 min).
highest activation energy was 0.311 eV (SL2, 1200

C × 30 min) and 0.328 eV (SL5, 1100

◦

◦

◦

Figure 4. (a, b) AC impedance plots of the LLZNO ceramics with diﬀerent sintering conditions at
C; (d) equivalent circuit to ﬁt the curves.
25
(e) Total conductivity and relative density of the LLZNO ceramics.

C; (c) AC impedance plots and ﬁtting curve of SL2 at 25

◦

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Figure 5.
LLZNO ceramics.

(a) Arrhenius plots and ﬁtting results and (b) the activation energy of diﬀerent

◦

◦

◦

◦

C for 60 min, Figure 6c), and ﬁnally, all grains were about 200 µm (SL1, 1200

SEM images of cross sections of the LLZNO ceramics, which were sintered under diﬀerent
conditions, are showed in Figure 6a–e. We found that the grain size of the ceramics that were sintered
for 60 min within a temperature range of 1100 to 1200
C gradually increased from 1~5 µm (SL4,
C for 60 min, Figure 6d). A few of the grains were 5 µm and most of the grains were 100~200 µm
1100
(SL3, 1150
C for 60 min,
Figure 6a). Here, we found a mass of abnormal growth grains (AGGs) [50], as shown in Figure 6a,c,e,
and a mass of pores were distributed in the AGGs. Meanwhile, the total ionic conductivity was
lower when the AGGs were bigger. This was due to the submicron LLZNO powder having a high
sintering activity, which made the crystal grain of the LLZNO ceramics have a high speciﬁc surface
energy during the high-temperature sintering process, and promoted rapid grain growth and ceramic
densiﬁcation in the sintering process. For the above reasons, the growth rate of the grains was higher
than the migration rate of the pores at the grain boundaries when the sintering temperature was higher
and the sintering time was longer and the pores could not be discharged from the grain boundaries and
ﬁnally stay on the inside of the AGGs. As a result, the bulk impedance of the crystal grains increased,
and the total ion conductivity was reduced. However, although the submicron LLZNO powder had
high sintering activity, the growth of grains could not be entirely promoted in a shorter sintering time
and at a lower temperature. Therefore, a mass of grains which stayed in the initial state are shown in
C × 60 min), and this was disadvantageous for lithium-ionic conduction due
Figure 6d (SL4, 1100
to the incomplete surface of the LLZNO grains after the attrition milling process. Eventually, the
ceramic pellets showed a lower total ionic conductivity (0.51 × 10
−1). A cross-sectional SEM
image of the sample sintered at 1200
C for 30 min (SL2) is showed in Figure 6b. It was found that
the grains grew uniformly (~4 µm), their surfaces were smooth without pores, and they bond tightly
with other grains. A highest ionic conductivity of 5.09 × 10
−1 was obtained, which indicates
that the submicron LLZNO powder had a higher sintering activity and high total ionic conductivity
LLZNO ceramic pellets could be obtained by sintered at a high temperature for only a short time.
At the same time, the LLZNO ceramic pellets which had a higher total ionic conductivity could also be
also obtained when the sintering temperature was properly reduced.

−4 S·cm

−4 S·cm

◦

◦

◦

Figure 6f shows the SEM image and its EDS mapping, including La, Zr, and Nb in the cross section
C× 30 min (SL2). The cross section of the sample exhibits a transgranular
of the LLZNO ceramic of 1200
fracture and an intergranular fracture, and the elements of La, Zr, and Nb are relatively uniformly
distributed, which indicates that the Nb element was successfully incorporated into the LLZO lattice.
This is also veriﬁed by the XRD result. However, the non-uniform distribution of Zr, La, and Nb exists
in the central part of the EDS mapping. This indicates that during high-temperature sintering element
segregation and depletion occurred due to the diﬀerent migration rates of the elements.

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Figure 6. (a–e) SEM images of the cross-sectional microstructures of the ceramics that were sintered by
diﬀerent particles sizes under diﬀerent sintering conditions and (f) EDS mapping of LLZNO ceramics
section sintered at 1200

C for 30 min.

◦

◦

The speciﬁc capacity and coulombic eﬃciency of quasi-solid-state batteries with LiMn2O4 as
the positive electrode after 50 cycles of a galvanostatic charge-discharge test at 25
C are showed in
Figure 7a. The 1st, 2nd, 10th, 20th, and 50th galvanostatic charge-discharge curves of quasi-solid-state
batteries are showed in Figure 7b. The quasi-solid-state batteries showed good cycling performance at
a current density of 0.02 mA/cm2 and a voltage within 3.0–4.3 V. The ﬁrst discharge speciﬁc capacity
was 106.4 mAh/g and the coulomb eﬃciency was 93.23%. The 2nd, 10th, 20th, and 50th discharge
speciﬁc capacities were 106.8 mAh/g, 105.3 mAh/g, 106.9 mAh/g, and 105.5 mAh/g, respectively. After
50 cycles of the galvanostatic charge-discharge test, the coulomb eﬃciency was maintained at about
95% and the capacity retention rate was 99.15%. The capacity of the batteries increased in the early
stage of the galvanostatic charge-discharge test, which may be caused by the activation of positive
material. This indicates that submicron LLZNO powder can be used in quasi-solid-state batteries,
and that the speciﬁc capacity and the cycling stability of quasi-solid-state batteries are relatively good.
Here, the electrochemical performance of quasi-solid-state batteries using submicron LLZNO powder
is only discussed, and further research will be carried out in the future.

(a) Speciﬁc capacity and coulombic eﬃciency and (b) the 1st, 2nd, 10th, 20th, and
Figure 7.
50th galvanostatic charge-discharge curves of quasi-solid-state batteries with LiMn2O4 as the
positive electrode.

Materials 2020, 13, 560

4. Conclusions

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In this study, we synthesized Nb-doped stabilized cubic-phase LLZO powder using the
conventional solid-state reaction and prepared submicron LLZNO powder using the attrition milling
process. Electrolyte ceramics prepared using submicron LLZNO powder can be sintered without
mother powder, which reduces the sintering temperature and shortens the sintering time. After being
◦
C for 60 min, the total ionic conductivity, relative density, and activation energy was
sintered at 1150
3.49 × 10
−4 S·cm
−1, 90.4%, and 0.316 eV, respectively. When sintered at 1200
C for 30 min, we obtained
the highest total ionic conductivity of 5.09 × 10
−1, the relative density was 87.3%, and the
smallest activation energy was 0.311 eV. For the quasi-solid-state batteries assembled with submicron
LLZNO powder, the capacity retention rate was 99.15% and the speciﬁc capacity was 105.5 mAh/g after
50 cycles at room temperature with a current density of 0.02 mA/cm2. Therefore, we have presented a
simple method to reduce the waste of raw materials and energy used when sintering LLZO ceramics.
At the same time, the prepared submicron LLZO powder can also be applied in quasi-solid-state
batteries, with a good electrochemical performance.

−4 S·cm

◦

Author Contributions: Methodology and conceptualization, Z.C., Y.J., and C.Z.; resources, Z.C. and H.Z.; data
curation, Y.J., C.Z., F.L., B.L., and F.Y.; writing—original draft preparation, Y.J.; writing—review and editing,
Y.J. and J.D.; funding acquisition, Z.C. and H.Z. All authors have read and agreed to the published version of
the manuscript.
Funding: This work was supported by the National Natural Science Foundation of China (No. 51874048),
the National Science Foundation for Young Scientists of China (No. 51604042), the Research Foundation of
Education Bureau of Hunan Province (No. 19A003), the Scientiﬁc Research Fund of Changsha Science and
Technology Bureau (No. kq1901100), and the Postgraduate Innovative Test Program of Hunan Province.
Conﬂicts of Interest: The authors declare no conﬂict of interest.

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