Materials Sciences and Applications, 2013, 4, 246-249
http://dx.doi.org/10.4236/msa.2013.44030 Published Online April 2013 (http://www.scirp.org/journal/msa)

Synthesis, Characterization and Charge-Discharge
Properties of Layer-Structure Lithium Zinc Borate,
LiZnBO3
Isao Tsuyumoto, Akihiro Kihara
Department of Applied Chemistry, College of Bioscience and Chemistry, Kanazawa Institute of Technology Ishikawa, Ishikawa,Japan.
Email: tsuyu@neptune.kanazawa-it.ac.jp
Received January 15th, 2013; revised February 17th, 2013; accepted March 20th, 2013
Copyright © 2013 Isao Tsuyumoto, Akihiro Kihara. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

ABSTRACT
Layer-Structure lithium zinc borate, LiZnBO3, is prepared by a solid state reaction of LiOH·H2O, ZnO, and H3BO3 at
1000˚C for 10 h. Highly preferred orientation and a layer-structure are observed in the powder XRD patterns and theSEM images, respectively. The Rietveld analysis indicates a monoclinic unit cell with space group C2/c, and the lattice
parameters are refined as a = 8.827 Å, b = 5.078 Å, c = 6.171 Å, and β = 118.86˚. LiZnBO3 shows the capacity of 17mAh/g between 1.3 V and 4.3 V (vs. Li/Li+) larger than ZnO.
Keywords: Oxide; Borate; Lithium; Zinc; X-Ray Diffraction; Battery

1. Introduction
Lithium metal phosphates (LiMPO4), lithium metal silicates (Li2MSiO4) and lithium metal borates (LiMBO3)
have attracted considerable interest as cathode materialsof lithium ion battery [1]. LiFePO4 with olivine structure
showed the reversible extraction and insertion of lithium
at 3.5 V (vs. Li) [2], and this material has been already
put to practical use by some lithium ion battery manufacturers. Analogs of LiFePO4 have been explored extensively by many researchers, and the charge-discharge
properties have been reported for lithium metal phosphates such as LiMnPO4, LiCoPO4 [3-5], lithium metal
silicates such as Li2FeSiO4 [6-9], and lithium metal borates such as LiMnBO3, LiFeBO3 [10-15]. Polyanionswith strong covalent bonds such as PO34 , SiO 44  , BO33
raise transition metal redox energies through inductive
effect and stabilize the structure, thereby providing highperformance and chemical safety.
LiZnBO3 was first reported by Lehman and Shadow,and its preparation and characterization have been reported by a number of researchers [16-20]. In the ternary
system of Li2O-ZnO-B2O3, two polymorphs of LiZnBO3
have been reported: one prepared by solid state reaction(α-LiZnBO3) and the other from hydrothermal synthesis
Copyright © 2013 SciRes.

(β-LiZnBO3). Zinc-containing borates have been investigated aiming at the application to nonlinear optics andferroelectrics, and the earlier reports describe the preparation of single crystals and structure analysis with a view
to non-centrosymmetry. The crystal structure of αLiZnBO3 is composed of ZnO4 tetrahedra and BO3 triangles by sharing O vertices and affords three-dimensional
open channels that are occupied by lithium ions [20]. In
spite of the attractive framework structure of LiZnBO3,
there have been no reports on the lithium deinsertion/insertion properties of LiZnBO3. In this study, we
successfully synthesized a layer-structure lithium zincborate, α-LiZnBO3, by a conventional solid state reaction,and investigated its crystal structure, morphology, andlithium deinsertion/insertion properties.

2. Experimental
2.1. Synthesis
α-LiZnBO3 was synthesized from a stoichiometric mixture of lithium hydroxide, zinc oxide, and boric acid, i.e.,
2.10 g LiOH·H2O, 4.07 g ZnO, and 3.09 g H3BO3. The
mixture was placed in an alumina boat and heated in air
at 1000˚C for 10 h to yield a white powder product. Inearlier reports, polycrystalline LiZnBO3 has been obMSA

Synthesis, Characterization and Charge-Discharge Properties of Layer-Structure Lithium Zinc Borate, LiZnBO3247

tained by heating the stoichiometric mixture of ZnO andLiBO2 at 1000˚C for 12 h. After preliminary heating at620˚C for 1 h [19] or by heating the stoichiometric mixture of Li2CO3, ZnO, and H3BO3 for 750˚C for 24 h [18],whereas single plate-like crystal of α-LiZnBO3 has beenobtained in a lithium borate matrix by heating the mixtureof Li2CO3, ZnO, and H3BO3 with excess amount ofLi2B4O7 at 830˚C [20]. In this study, LiOH·H2O was usedas the starting material instead of Li2CO3, and the heating
temperature was set at 1000˚C because the thermogravimetry and differential thermal analysis (DTA/TG, DTG50, Shimadzu, Tokyo, Japan) of the starting mixture in air
showed a broad exothermic peak above around 750˚C.

2.2. Characterization
The powder X-ray diffraction (XRD) patterns were measured with a diffractometer (XD-D1, Shimadzu, Tokyo,Japan) using graphite-monochromatized Cu Kα radiation
at 30 kV and 20 mA. The crystalline parameters wererefined by the Rietveld method using the RIETAN-2000
program [21]. Impurity peaks were excluded in the refinement. The morphology of α-LiZnBO3 was observed
by a scanning electron microscope (SEM, JSM-5610,JEOL, Tokyo, Japan). Each sample was ground with acetylene black and polytetrafluoroethylene (PTFE) binder
into paste at a weight ratio of 84:4:12, and the paste mixture was pressed onto a nickel mesh for the lithium deinsertion/insertion measurements. The Ag/Ag+ electrode for
non-aqueous solvent (RE-7, ALS Corporation Ltd., Tokyo, Japan) was used as a reference electrode, and naturalgraphite as a counter electrode. A 1 M LiClO4 EC/DEC
solution (EC:DEC = 1:1 in volume) was used as an electrolyte. The lithium deinsertion/insertion measurements
were carried out in the galvanostatic mode in the range
between x = 0 and x = 0.5, where x is the Li content per
formula unit, i.e., x in Li1−xZnBO3. The electrochemicalcapacity of samples (mAh/g) was evaluated using theweight of the active materials.

3. Results and Discussion
White powder products were obtained by the solid state
reaction at 1000˚C for 10 h. The powder XRD pattern ofthe product and the structure refinement result are shownin Figure 1. The crystal structure was refined on the basisof monoclinic symmetry with space group C2/c similarly
to α-LiZnBO3 in the earlier work [20], except for some
impurity peaks. In the XRD measurements, the powder
sample was solidified using glue to make each planerandomly oriented, because without the sample pretreatment with the glue the strongest (002) reflection was
more than twenty times greater than the second strongest reflection due to the preferred orientation. This suggested that plate-like crystallites were formed by aniCopyright © 2013 SciRes.

Figure 1. The observed XRD pattern (Iobs) of the LiZnBO3
and the pattern refined by the Rietveld method (Icalc), alongwith the calculated Bragg position and the residual error(Iobs-Icalc).

sotropic crystal growth and the samples were prone toorient along the a-b plane. Structure parameters and selected interatomic distances are summarized in Tables 1
and 2, respectively, and view of the crystal structure ofLiZnBO3 is shown in Figure 2. The lattice parametersand monoclinic angle were calculated as a = 8.827 Å, b =5.078 Å, c = 6.171 Å, and β = 118.86˚. In this structure,
two ZnO4 tetrahedra are linked together by edge- sharing(two O1 atoms) to form a Zn2O6 dimer, and the Zn2O6
dimer is linked to the six other Zn2O6 dimers by sharing
oxygen vertices to form a three-dimensional framework.
Boron atoms are located at the triangular void surroundedby three oxygen vertices to form BO3 triangles. Lithium
atoms are located in the three-dimensional channels surrounded by Zn2O6 dimers and BO3 triangles. In this study
the O2 atom was located at 8f site with occupancy of 0.5,
while it was located at 4e site (0, y, 1/4) with occupancyof 1.0 in the earlier work [20]. The two O2 atoms witheach occupancy of 0.5 were refined at extremely close
two positions at the vertex of ZnO4 tetrahedron, as shownin Figure 2, indicating the two possibilities of ZnO4 tetrahedron shape. Such arbitrary property is probable inview of the occupancy of 0.5 for Zn1. In Figure 3, SEM
images show secondary particles formed by aggregationof plate-like crystallites, and the crystallites are considered to be stacked perpendicular to the a-b plane. Thepresent sample showed a lamellar structure consisting ofplate-like crystallites stacked perpendicular to the a-bplane. This may be advantageous to lithium deinsertion/insertion because open channels in the crystallites
are facing the electrolyte with large area. The conductivity of the powder compact of the present LiZnBO3 estimated from the diameter of the semicircle in the cole-coleplot was 2.12 × 10−9 Scm−1. It is much smaller than
LiFeBO3, 1.52 × 10−4 Scm−1 [12], and as small as
LiFePO 4, 2.2 × 10 −9 Scm −1 [23]. The low electricMSA

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Synthesis, Characterization and Charge-Discharge Properties of Layer-Structure Lithium Zinc Borate, LiZnBO3

Table 1. Structure parameters of LiZnBO3 obtained byheating at 1000˚C for 10 h. System: monoclinic. Space group:C2/c (No. 15), a = 8.827 Å, b = 5.078 Å, c = 6.171 Å, β =118.86˚, z = 4.
AtomSitexyz

Occupancy

Li18f

0.310 (4)0.603 (4)0.797 (4)

0.50

Zn1

8f

0.3223 (7)0.567 (2)0.6965 (9)

0.50

B1

4e

0.00

0.408 (4)

0.25

1.0

O1

8f

0.167 (1)0.543 (4)0.295 (2)

1.0O2

8f

0.03 (2)0.172 (2)0.318 (2)0.50

Figure 3. The SEM image of the layer-structure LiZnBO3.
The plane facing upward is the a-b plane.

Table 2. Selected interatomic distances (Å) of LiZnBO3.
Selected atom

Distance (Å)

Selected atom

Distance (Å)

Li1-O1

1.46 (4)

Li1-O11.93 (3)

Li1-O22.13 (3)

Li1-O22.31 (3)Li1-O22.36 (3)Zn1-O11.84 (1)Zn1-O1

1.98 (2)Zn1-O1

2.18 (1)Zn1-O2

1.85 (2)Zn1-O2

1.99 (2)B1-O1

1.52 (1)B1-O2

1.25 (9)Figure 4. The charge-discharge curves of the LiZnBO3 forfirst three cycles at rate of 20.3 mA/g.

Figure 2. The crystal structure of the LiZnBO3 projectedalong b-axis (upper) and c-axis (lower) visualized by
VESTA3 [22]. Half-filled and fully-filled circles mean theoccupancies of 0.50 and 1.0, respectively.

conductivity and/or lithium diffusivity suggests the necessity to give conductivity to LiZnBO3 by treatment
with carbon in order to improve the electrochemical
Copyright © 2013 SciRes.

performance.
Figure 4 shows the typical charge and discharge curvesof LiZnBO3 at charge/discharge rate of 20.3 mA/g. The
first charge curve deviated from the second and thirdones, indicating that the solid electrolyte interface (SEI)
was formed at the cathode/electrolyte interface during thefirst charge process. The capacity between 1.3 V and 4.3V (vs. Li/Li+) was 17 mAh/g, and the charge/discharge
curves showed almost the same behavior for different
charge/discharge rates from 2.03 mA/g to 203 mA/g. It
should be noted that our comparative experiments usingZnO as an active material did not show such charge/discharge behavior. This is probably because LiZnBO3 acted
as an electric double layer capacitor (EDLC) and electriccharge was accumulated at the interfacial region between
the electrolyte and LiZnBO3 powder. The layer structureof LiZnBO3 was advantageous for EDLC over ZnO. Thefaradaic redox reaction of LiZnBO3 was not observed as
opposed to the cases of LiFeBO3 and LiMnBO3 [10-15],
indicating that divalent zinc was not oxidized to trivalentzinc in LiZnBO3 as well as in ZnO.

4. Conclusion
Lithium zinc borate, LiZnBO3, prepared by the solid state
reaction showed a layer-structure in the SEM images.
MSA

Synthesis, Characterization and Charge-Discharge Properties of Layer-Structure Lithium Zinc Borate, LiZnBO3

The XRD patterns well fitted to a monoclinic unit cellwith space group C2/c, and the lattice parameters wererefined as a = 8.827 Å, b = 5.078 Å, c = 6.171 Å, and β =118.86˚. LiZnBO3 showed the capacity of 17 mAh/g between 1.3 V and 4.3 V (vs. Li/Li+) larger than ZnO. Thecapacity was due to the EDLC between the electrolyte
and LiZnBO3 powder.

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