Na+ and Zr4+ co-doped Li4Ti5O12 as anode materials with superior electrochemical performance for lithium ion batteries

Article abstract of DOI:10.1039/c6ra16717a

Na⁺ and Zr⁴⁺ co-doped lithium titanates with the formula Li_4-xNa_xTi_5-xZr_xO₁₂ (x = 0, 0.01, 0.03, 0.05, 0.10, 0.15 and 0.20) were successfully synthesized via a solid-state reaction in air. XRD analysis indicates that Na⁺ and Zr⁴⁺ co-doping does not change the spinel structure of Li₄Ti₅O₁₂ and the lattice parameter slightly increases with the enhancement of doping amount. Smaller particle size and larger BET surface areas are obtained for Na⁺ and Zr⁴⁺ co-doped Li₄Ti₅O₁₂ samples. The four-point probe method and electrochemical impedance spectroscopy (EIS) results demonstrate that the Na⁺ and Zr⁴⁺ co-doped Li₄Ti₅O₁₂ samples possess higher electrical conductivity and smaller charge transfer resistance compared with undoped Li₄Ti₅O₁₂, resulting in improved electrochemical performance. Particularly, Li_3.97Na_0.03Ti_4.97Zr_0.03O₁₂ exhibits the best rate capability and cycling stability. Even at 20C, it delivers a discharge capacity of 140 mA h g^-1, and after 100 cycles at 10C, 97.7% of its initial capacity is retained.

Full text of DOI:10.1039/c6ra16717a

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+
4+
Na and Zr co-doped Li Ti O as anode materials
4
5 12
with superior electrochemical performance for
lithium ion batteries
Cite this: RSC Adv., 2016, 6, 90455
ab
c
abd
Jianning Ding,*abe Haiyan Wang,f
Peng Lu, Xiaobing Huang,* Yurong Ren,*
c
c
c
Shibiao Zhou, Yuandao Chen and Xiang Ding
+
4+
Na and Zr co-doped lithium titanates with the formula Li4ꢀxNa
0
x
Ti5ꢀxZr
x
O
12 (x ¼ 0, 0.01, 0.03, 0.05, 0.10,
+
.15 and 0.20) were successfully synthesized via a solid-state reaction in air. XRD analysis indicates that Na
4+
and Zr co-doping does not change the spinel structure of Li
4 5
Ti O12 and the lattice parameter slightly
increases with the enhancement of doping amount. Smaller particle size and larger BET surface areas are
+
4+
obtained for Na and Zr
electrochemical impedance spectroscopy (EIS) results demonstrate that the Na and Zr co-doped
Li Ti 12 samples possess higher electrical conductivity and smaller charge transfer resistance compared
with undoped Li Ti resulting in improved electrochemical performance. Particularly,
12 exhibits the best rate capability and cycling stability. Even at 20C, it delivers
4 5
co-doped Li Ti O12 samples. The four-point probe method and
+
4+
Received 29th June 2016
Accepted 12th September 2016
4
5
O
4
5 12
O ,
DOI: 10.1039/c6ra16717a
Li3.97Na0.03Ti4.97Zr0.03
O
ꢀ1
www.rsc.org/advances
a discharge capacity of 140 mA h g , and after 100 cycles at 10C, 97.7% of its initial capacity is retained.
+
Li/Li ), and excellent structural and thermodynamic stability
1
. Introduction
during cycling. Li
Among the current energy storage systems, the lithium-ion insertion during discharge, resulting in a structural transition
battery (LIB) has received intense attention from both the from spinel-LTO to rock-salt phase Li Ti 12 with its zero-strain
academic community and industry as the power source in hybrid characteristics. Unfortunately, the low electronic conductivity
4 5
Ti O12 (LTO) can accommodate lithium
O
5
7
4,5
ꢀ
13
ꢀ1
electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), (ca. 10
S cm ) results in the poor electrochemical perfor-
1
and full electric vehicles (EVs) due to its high energy density. As mance of LTO, preventing them from being commercially
6
we know, graphite is used as an anode in commercial LIBs, used. To overcome the kinetic problems of LTO, researchers
nevertheless, crucial safety concerns exist in connection with the have taken various approaches, such as decreasing its particle
7
graphite anode, which are attributed to its low operating size, coating it with conductive material and doping it with
+
8
+
9
2+ 10
2+ 11
potential. Metallic lithium will easily give rise to dendrites on the transition metal non-metal ions (Li , Na , Mg , Zn ,
2
+
12
3+ 13
3+ 14
3+ 15
4+ 16
4+ 17 5+ 18
5+ 19
6+ 20
ꢀ
surface of the lithium metal because of the low potential, espe- Ca , Al , Cr , La , Zr , Ru , V , Ta , W ,
F
ꢀ
cially at high rates. Therefore, it is important to nd advanced (ref. 21) and Br (ref. 22)) in the Li, Ti or O sites.
+
materials with an excellent rate and a better safety capability
In this research, we found that the radius of Na (113 pm) is
+
4+
2,3
which are critical components for the next generation of LIBs.
Spinel lithium titanate (Li Ti O ) has received considerable than Ti (60.5 pm).
larger than Li (73 pm) and the radius of Zr (80 pm) is larger
4
+
9,23
The doping of Na–Zr will enlarge the
4
5 12
attention as a potential candidate for lithium-ion batteries due lattice parameters of the LTO, and enlarged lattice parameters
to its high lithium ion insertion potential at around 1.55 V (vs. are benecial for fast lithium-ion transfer resulting in
11
improving the electrochemical performance of LTO. Accord-
ing to the literature, doping ions with the same valence into the
corresponding Li and Ti sites can distort its spinel crystal
a
School of Materials Science and Engineering, Jiangsu Collaborative Innovation Center
of Photovoltaic Science and Engineering, Changzhou University, Changzhou 213164,
China. E-mail: ryrchem@163.com; ryrchem@cczu.edu.cn
1
structure to affect its electrochemical performances. At the
b
same time, few kinds of metal ion can greatly improve the
Jiangsu Province Cultivation Base for State Key Laboratory of Photovoltaic Science
and Technology, Changzhou University, Changzhou 213164, China
electrochemical performance of LTO, which Na and Zr ions are
c
+
College of Chemistry and Chemical Engineering, Hunan University of Arts and two of them. More importantly, both doping Na in Li site and
Science, Changde 415000, China. E-mail: hxb220170@yahoo.com
4+
doping Zr in Ti site singly have been proved that the electro-
d
Jiangnan Graphene Research Institute, Changzhou 213164, China
chemical performances of LTO can be highly enhanced based
on the reports. So we tried Na and Zr co-doped to LTO naturally.
Surprisingly, the results of the electrochemical performances
have been highly enhanced because of the so-called ‘synergic
e
Micro/Nano Science and Technology Center, Jiangsu University, Zhenjiang 212013,
China
f
College of Chemistry and Chemical Engineering, Central South University, Changsha
4
10083, China
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effect’. However, the mechanism of co-doping is not clear until not shi to a lower angels when x > 0.10, and the appearance of
+
4+
now, and needs more research. Whereas, Na and Zr co-doped the impurity phase in XRD can demonstrate that more dopants
LTO has not been investigated as far as we know. For compar- cannot enter the lattice cell. All the results shows that the
ison, the pristine LTO without doping was also synthesized.
addition of CH COONa and ZrO(NO ) $xH O cannot hinder the
3 3 2 2
+
4+
formation of spinel LTO and the Na and Zr have successfully
entered the lattice of spinel LTO. The enlarged lattice parame-
ters is benecial for fast lithium-ion transfer without lattice
2. Experimental
Li4ꢀxNa
compounds were prepared by a conventional solid-state reac-
tion process using Li CO (Aladdin, AR), TiO (Aladdin, AR), and
CH COONa (Aladdin, AR) and ZrO(NO $xH O (Aladdin, AR) as
x
Ti5ꢀxZr
x
O12 (x ¼ 0, 0.01, 0.03, 0.05, 0.10, 0.15 and 0.20) stability damaged.
2
3
2
3
3
)
2
2
raw materials. The quality proportion between agate ball and
ꢁ
total sample is 1 : 15. The obtained slurry was dried at 70 C for
2
hours in a vacuum oven. The as-prepared powder was heated
ꢁ
in a muffle furnace at 750 C for 8 hours to obtain the nal LTO.
X-ray diffraction (XRD) data were examined by X-ray diffrac-
1
tometer (DX-2700, Dandong Haoyuan) utilizing a Cu-Ka source.
Morphological studies were conducted by scanning electron
microscope (SEM, JSM-6510LA) and transmission electron
microscopy (TEM, JEOL JEM-2100F). X-ray photoelectron spec-
troscopy (XPS) measurement was performed on a K-Alpha 1063
spectrometer. The BET surface area of the samples was detected
ꢁ
by nitrogen adsorption–desorption at ꢀ196 C using a Builder
SSA-4200 apparatus. Four-point probe method (RTS-9, Guangz-
hou) was employed to measure the electronic conductivity.
Working electrodes were constructed by mixing the active
material, Super-P carbon and LA-132 in the weight ratio of
Fig. 1 XRD patterns of as-obtained LTO samples.
8
5 : 10 : 5. Water was used as solvent. The slurry was cast onto
ꢁ
Al foil using the doctor-blade technique and dried at 100 C for
10 h in a vacuum oven. Finally, CR2032 coin-type cells were
assembled in an argon-lled glove box, using lithium foil as the
ꢀ1
counter electrode, Celgard 2400 as the separator, and 1 mol L
LiPF dissolved in a mixture of EC, DEC, DMC with a volume
6
ratio of 1 : 1 : 1 as the electrolyte. Galvanostatic charge and
discharge measurements were performed in a potential range of
ꢁ
1
–3 V at 25 C. The AC impedance data were recorded in the
ꢀ
2
5
frequency range 10 Hz to 10 Hz using CHI600E electro-
chemical station (Shanghai Chenhua).
3. Results and discussion
Fig. 1 presents the XRD patterns of the pristine and Na–Zr co-
doped LTO. The diffraction peaks of Li4ꢀxNa Ti5ꢀxZr 12 (x ¼
, 0.01, 0.03, 0.05, 0.10, 0.15 and 0.20) compounds in Fig. 1
x
x
O
0
Fig. 2 The enlarged peak of (111) planes of the samples.
coincide with the cubic spinel structure (JCPDS no. 49-0207)
without obvious impurity. However, there are few weak peaks
corresponding to the impurity phase in the Li4 Na Ti Zr O
ꢀx
x
5ꢀx
x
12
Table 1 Lattice parameters of Li Na Ti Zr O (x ¼ 0, 0.01, 0.03
4ꢀx
x
5ꢀx
x
12
(
x ¼ 0.15 and 0.20) samples (* for ZrO
2 2
peaks, # for Na
O peaks), and 0.05) samples
indicating that few Na and Zr ions do not enter the crystal
lattice. The reason may be that the great difference of ionic
radius between Na and Li, or Zr and Ti. The enlarged peak of
3
˚
˚
Sample
Li Ti
a/A
V/A
4
5
O
12
8.3629
8.3675
8.3722
8.3764
8.3812
8.3812
8.3812
584.89
585.85
586.84
587.73
588.73
588.73
588.73
(111) planes of the samples in the Fig. 2 shows that the peaks of Li3.99Na0.01Ti4.99Zr0.01O12
the Na–Zr co-doped LTO shied to smaller angles and indicated Li3.97Na0.03Ti4.97Zr0.03
O
O
O
O
O
12
12
12
12
12
Li3.95Na0.05Ti4.95Zr0.05
an enlarged lattice parameter of the LTO according to the Bragg
Li3.90Na0.10Ti4.90Zr0.10
equation and the precise lattice parameters are listed in the
Li3.95Na0.01Ti4.95Zr0.05
Table 1. Clearly, the lattice parameters become larger and larger
Li3.95Na0.01Ti4.95Zr0.05
with the addition of dopants, when x < 0.10. The (111) planes do
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The XPS spectrum of Li3.97Na0.03Ti4.97Zr0.03
O
12 contains the LTO. Specially, one peak centered on 1071.2 eV, and two broad
Li 1s, Na 1s, C 1s, O 1s and Zr 3d peaks (Fig. 3). The carbon peak peaks centered on 182.24 and 184.29 eV are well in accordance
may be caused by the carbon oxides in the air. No other peaks with the characteristic peaks of Na 1s, Zr 3d and Zr 3d3/2 of
5
/2
4
+
were detected, indicating the high purity of the Na–Zr co-doped Zr in Li3.97Na0.03Ti4.97Zr0.03O . The characteristic peaks of Li
12
1
s, Ti 2p and O 1s can be found in Li3.97Na0.03Ti4.97Zr0.03
O12 as
well. Combined with XRD results, all the evidence demon-
strated that the Li3.97Na0.03Ti4.97Zr0.03O12 composite has been
synthesized successfully.
Fig. 4 shows the SEM pictures of Li4ꢀxNa
.01, 0.03 and 0.05) compounds. It is apparent that the
x
Ti5ꢀxZr
x
O
12 (x ¼ 0,
0
morphologies of four samples are similar. All the samples are
well crystallized with a uniform and narrow size distribution in
the range of 200–300 nm. BET analysis was carried out to get
further information of the specic surface area change caused
by the doping process. The corresponding BET surface areas of
2
the Li4ꢀxNa
g
x
Ti5ꢀxZr
x
O
12 (x ¼ 0, 0.01, 0.03 and 0.05) are 8.856 m
ꢀ
1
2
ꢀ1
2 2 ꢀ1
ꢀ1
, 10.611 m g , 10.863 m g and 10.869 m g , respec-
tively. According to the experimental results, the values of the
BET have a slight increase, which may be caused by the increase
of particle surface roughness or the decrease of the diameter of
crystal particle. In fact, the increase of specic surface area can
increase the contact areas of LTO and the electrolyte, resulting
in the enhancement of electrochemical performance of Na–Zr
7,24
co-doped LTO.
To investigate the effect of Na–Zr co-doping on the rate
performance of the samples, Li4 Na Ti Zr O (x ¼ 0, 0.01,
ꢀx
x
5ꢀx
x 12
0.03 and 0.05) were tested at various charge–discharge current
densities from 0.5C to 20C between 1 and 3 V. The results are
shown in Fig. 5. Clearly, the margins of discharge capacity
between Li3.97Na0.03Ti4.97Zr0.03O12 and the other samples
become more and more obvious with increasing the current
densities. For example, at 0.5C, 5C and 10C the discharge
ꢀ
1
capacity of Li3.97Na0.03Ti4.97Zr0.03O12 retains 174 mA h g , 152.7
ꢀ
1
ꢀ1
mA h g and 140.7 mA h g , respectively, while those of
Li Ti O , Li3.99Na Ti4.99Zr0.01O12 and Li3.95Na0.05Ti4.95Zr0.05
-
4
5
12
0.01
ꢀ
1
ꢀ1
ꢀ1
O
g
are 157.6 mA h g , 111.5 mA h g , 80 mA h g ; 170.7 mA h
2
1
ꢀ
1
ꢀ1
ꢀ1
ꢀ1
, 145.8 mA h g , 138.1 mA h g and 173.5 mA h g , 150.9
ꢀ1
ꢀ1
mA h g , 142.5 mA h g at the same rates, respectively. These
results indicate that the Na–Zr co-doping could improve the
capacity and rate capability of the LTO. The above results
demonstrate that Li3.97Na0.03Ti4.97Zr0.03O12 exhibits the best
rate performance. As evidenced in four-point results, electronic
conductivity of the Li4 Na Ti Zr O (x ¼ 0, 0.01, 0.03 and
ꢀx
x
5ꢀx
x 12
0.05) can be improved when the dopants are increased.
Furthermore, the larger specic surface area is obtained with
the increasing of dopants, providing more active sites for the
electrochemical reaction and reducing path for the electron
25
migration naturally.
Therefore, Li3.97Na0.03Ti4.97Zr0.03
O
12
exhibits the better rate performance than Li
4
Ti
5
O
12, Li3.99-
Na0.01Ti4.99Zr0.01O12 and Li3.95Na0.05Ti4.95Zr0.05O12 for its
enhancements of electronic and intrinsic ionic conductivity.
Fig. 6 shows the rst charge and discharge curves: (A)
Li
From Fig. 6, it can been observed that the Li
12 electrodes both have a discharge plateau at
about 1.5 V between 1 V and 3 V respectively, which indicates
that the discharge specic capacities of the two electrodes are
4
Ti
5
O
12 and (B) Li3.97Na0.03Ti4.97Zr0.03
O
12 at different rates.
4
Ti 12 and Li3.97
5
O
-
Fig. 3 XPS survey spectra of Li3.97Na0.03Ti4.97Zr0.03
high-resolution XPS spectra of Na 1s for Li3.97Na0.03Ti4.97Zr0.03
and typical high-resolution XPS spectra of Zr 3d for Li3.97Na0.03Ti4.97
Zr0.03 12 (C).
O
12 (A), typical
Na0.03Ti4.97Zr0.03
O
O12 (B)
-
O
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Fig. 4 SEM pictures of Li4ꢀxNa
x
Ti5ꢀxZr
x
O12 samples: (A) x ¼ 0, (B) x ¼ 0.01, (C) x ¼ 0.03, and (D) x ¼ 0.05.
4
+
Zr co-doping did not change the electrochemical reaction
process. In addition, the charge plateaus elevate and the
discharge plateaus decrease for both samples with current
density increasing, suggesting that the higher polarization at
high current densities.
Fig. 7 shows the cycling performance of Li4ꢀxNa
x ¼ 0, 0.01, 0.03 and 0.05) at 10C. Aer 100 cycles, the capacity
retention ratio of Li4ꢀxNa Ti5ꢀxZr 12 (x ¼ 0, 0.01, 0.03 and
.05) are 89.2%, 96.9%, 97.7% and 96.2%, respectively. As
x
Ti5ꢀxZr
x 12
O
(
x
x
O
0
shown in Fig. 7, the charge and discharge efficiency of the
Li3.97Na0.03Ti4.97Zr0.03O12 is also better than that of others. It
can be clearly seen from the results that too low or too high
dopants in the samples do not lead to highest discharge
capacity and the best cycle performance. Additionally, the
electronic conductivity measured by four-point probe method
provides evidence for the above results and the parameters
obtained are shown in Table 2. The conductivity of co-doped
LTO is much higher than that of LTO. Clearly, the more
dopants were added, the larger value of electronic conductivity
became. The improvement of the cycle performance may partly
correspond to the enhancement of the electronic conductivity.
However, the more dopants were added, the more conductive
Fig. 5 Cycling performance of Li4ꢀxNa
x
Ti5ꢀxZr
x
O
12 (x ¼ 0, 0.01, 0.03
and 0.05) at various rates.
the result of the electrochemical reaction processes. Also, the
charge and discharge curves of Li3.97Na0.03Ti4.97Zr0.03 are
O
12
+
similar in shape with that of Li Ti O , suggesting that Na and
4
5 12
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Fig. 7 Cyclic performance of Li4ꢀxNa
x
x
Ti5ꢀxZr O
12 (x ¼ 0, 0.01, 0.03
and 0.05) at 10C.
Table 2 Electronic conductivity for Li4ꢀxNa
.03 and 0.05)
x
Ti5ꢀxZr
x
O12 (x ¼ 0, 0.01,
0
ꢀ1
Samples
Electronic conductivity (S cm )
ꢀ5
ꢀ3
ꢀ3
ꢀ3
ꢀ3
ꢀ3
ꢀ2
x ¼ 0
9.80 ꢂ 10
6.13 ꢂ 10
6.23 ꢂ 10
6.82 ꢂ 10
7.11 ꢂ 10
9.07 ꢂ 10
1.76 ꢂ 10
x ¼ 0.01
x ¼ 0.03
x ¼ 0.05
x ¼ 0.10
x ¼ 0.15
x ¼ 0.20
4 5
Fig. 6 The first charge and discharge curves for Li Ti O12 (A) and
Li3.97Na0.03Ti4.97Zr0.03O12 (B) at various rates.
voltage drop for the kinetics limitation, thereby leading to
27
deterioration in the electrochemical performance. Appro-
+
4+
priate amount of Na and Zr doped in LTO is favorable for
reducing the electrodes polarization, but that a higher amount
of doping is disadvantageous. Moreover, the slope in the low
frequency region for co-doped LTO is slightly greater than that
the LTO will become. The battery performance was not better,
which may be because the dopants may hinder the Li inser-
tion to the lattice of LTO. The above results suggest that LTO by
doping Na and Zr elements is favorable to improve the elec-
trical conductivity and ionic conductivity, resulting superior
rate properties.
+
To understand the improved electrochemical performance
of Na–Zr co-doping LTO, electrochemical impedance spectros-
copy (EIS) is evaluated, and the typical Nyquist impedance plots
are described in Fig. 8. Each spectrum consists of a depressed
semicircle at high frequency and a straight line at low
0
0
frequency. An intercept at the Z axis in the high frequency
corresponds to the ohmic resistance (R ), which represents the
e
resistance of the electrolyte and electrode. The high frequency
semicircle is related to the charge transfer resistance (R ), while
ct
the straight line in the lower frequency is attributed to the
26
lithium-ion diffusion in LTO. All the parameters obtained
from EIS are shown in Table 3. As seen from Fig. 8 and Table 3,
Li3.97Na0.03Ti4.97Zr0.03O12 exhibits a much smaller Rct (1002 U)
than that of bare LTO (1919 U). According to previous report,
the effect of Rct can be ignored at a low current density, whereas
at a high current density, the Rct is mainly responsible for the
Fig. 8 Nyquist plots of Li4ꢀxNa
.05).
x x
Ti5ꢀxZr O12 (x ¼ 0, 0.01, 0.03 and
0
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Table 3 Impedance parameters of Li4ꢀxNa
x
Ti5ꢀxZr
x
O
12 (x ¼ 0, 0.01, shown in Fig. 9. All the parameters obtained and calculated
0
.03 and 0.05)
from EIS are summarized in Table 3. It can be seen from that
ꢀ1/2
2
ꢀ1
the D of LTO doped with Na and Zr is larger by 20 times than
that without Na and Zr, and Li3.97Na0.03Ti4.97Zr0.03O12 exhibits
the smaller charge transfer resistance than that of the LTO. It
can be conrmed that the decrease of charge transfer resistance
is benecial to the kinetic behaviors during charge/discharge
process. This indicates Na and Zr co-doping is favorable to
improve the conductivity of LTO, leading to the improved rate
performance and cycle performance, and these results corre-
spond with the cycling performance and the polarization shown
in the charge–discharge curve.
Samples
R
e
(U)
R
ct (U)
s (U s
)
D (cm s
)
ꢀ
ꢀ
ꢀ
ꢀ
15
14
13
14
x ¼ 0
10.8
6.2
4.7
4.9
1919
1528
1002
1122
2175
1269
530
7.88 ꢂ 10
2.31 ꢂ 10
1.33 ꢂ 10
3.14 ꢂ 10
x ¼ 0.01
x ¼ 0.03
x ¼ 0.05
1089
Table 4 compares the result of the current study with the rate
capabilities taken from the literature for Na-doped LTO and Zr-
doped LTO in a potential range of 1–3 V. The electrochemical
performance of Li3.97Na0.03Ti4.97Zr0.03O12 obtained in this work
is considered highly comparable or even much better than
those of the others, implying that both of the two doping
elements have strong impact on the electrochemical perfor-
mance of LTO, appropriate Na–Zr doping is an effective method
to improve the rate capability and cycling stability of LTO.
4. Conclusions
In summary, cubic spinel Li4 Na Ti Zr O (x ¼ 0, 0.01, 0.03
ꢀx
x
5ꢀx
x 12
and 0.05) samples were successfully synthesized by means of
solid phase method. The structure and electrochemical
performance of Na–Zr co-doped LTO were investigated. Na–Zr
doping does not change the crystal structure of LTO. A certain
amount of Mg–Zr doping increases the specic capacity
signicantly, as well as the rate capability of LTO. The two
doping elements contribute to improvement of the electro-
ꢀ
1/2
Fig. 9 The relationship curve between Zre and u
frequency.
in the low
of LTO, which could demonstrate that lithium ions diffusion
can be easier than that in LTO.
The lithium ion diffusion coefficient could be calculated
from the low frequency plots according to the following
+
chemical property of LTO by the this mechanism: the larger Na
+
4+
4+
28–30
into Li and the larger Zr into Ti exaggerate the lattice
parameters of LTO indicating faster electron transfer kinetics.
According to the four probe results, the electronic conductivity
equation:
2
2
2 4 4 2 2
D ¼ R T /2A n F C s
(1)
has been enhanced greatly at the same time. Sample Li3.97
where R is the gas constant, T is the absolute temperature, A is Na0.03Ti4.97Zr0.03 12, particle size of 200–300 nm in diameter,
the surface area of the cathode, n is the number of electrons per has the best rate performance with a large capacity of 148.9 mA
-
O
ꢀ
1
ꢀ1
molecule during oxidation, F is the Faraday constant, C is the h g at 10C, while Li
Ti O12 only possesses 111.5 mA h g , and
4
5
concentration of lithium ion, and s is the Warburg factor which aer 100 cycles at 10C, 97.7% of its initial capacity is retained.
3
1,32
is relative with Zre:
The superior electrochemical performance can be attributed to
the exaggeration of lattice parameters indicating faster electron
(2) transfer kinetics and reduced charge transfer resistance in the
ꢀ
D L
+ R + su
1/2
Z
re ¼ R
+
4+
electrode due to the Na and Zr co-doping. This strategy could
pave a new way for LTO and other electrode materials to achieve
the signicant improvement of electrochemical properties.
where u is frequency. The relationships between Zre and the
reciprocal square root of frequency in the low frequency are
Table 4 Comparison of rate performance of the Li4ꢀxNa
x
x 4 5 12
Ti5ꢀxZr O12 with Na-doped and Zr-doped Li Ti O
Reaction temperature
( C)/holding time (h)
Particle diameter
(nm)
Charge/discharge
current
Discharge capacity
ꢁ
ꢀ1
Sample
(mA h g
)
Reference
Li3.9Na0.1Ti
5
O
12
0.01Ti
12
Li3.97Na0.03Ti4.97Zr0.03
850/24
800/10
800/10
750/8
400–600
300–400
300–400
200–300
5C
133 (1–3 V)
56 (1–3 V)
132 (1–3 V)
148.9 (1–3 V)
9
33
25
Li3.98Na0.01
K
5
O
12
10C
10C
10C
Li
4
Ti4.9Zr0.1
O
O
12
Current study
90460 | RSC Adv., 2016, 6, 90455–90461
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Paper
RSC Advances
1
2 Q. Zhang, C. Zhang, B. Li, S. Kang, X. Li and Y. Wang,
Electrochim. Acta, 2013, 98, 146–152.
Acknowledgements
This project was nancially supported by the National Nature 13 H. Zhao, Y. Li, Z. Zhu, J. Lin, Z. Tian and R. Wang,
Science Foundation of China (No. 21576030, 51304077 and
Electrochim. Acta, 2008, 53, 7079–7083.
1574090), the Hunan Provincial Natural Science Foundation of 14 Y. K. Sun, D. J. Jung, Y. S. Lee and K. S. Nahm, J. Power
5
China (No. 13JJ4100 and 2016JJ2092), the Construct Program of
Sources, 2004, 125, 242–245.
the Key Discipline in Hunan Province of China (Applied 15 Y.-J. Bai, C. Gong, Y.-X. Qi, N. Lun and J. Feng, J. Mater.
Chemistry), the Opening Project of Material Corrosion and
Chem., 2012, 22, 19054.
Protection Key Laboratory of Sichuan Province of China 16 Z. Wang, Z. Wang, W. Peng, H. Guo and X. Li, Ceram. Int.,
2014CL03 and 2014CL15), the Six Talents Peak Project of
2014, 40, 10053–10059.
Jiangsu Province of China (XNY-002), the Natural Science 17 C.-Y. Lin, Y.-R. Jhan and J.-G. Duh, J. Alloys Compd., 2011,
Foundation of the Jiangsu Higher Education Institutions of
509, 6965–6968.
China (No. 15KJA150002) and also sponsored by the Priority 18 T.-F. Yi, J. Shu, Y.-R. Zhu, X.-D. Zhu, C.-B. Yue, A.-N. Zhou
(
Academic Program Development of Jiangsu Higher Education
Institutions.
and R.-S. Zhu, Electrochim. Acta, 2009, 54, 7464–7470.
19 J. Wolfenstine and J. L. Allen, J. Power Sources, 2008, 180,
582–585.
2
2
0 Q. Zhang, H. Lu, H. Zhong, X. Yan, C. Ouyang and L. Zhang,
J. Mater. Chem. A, 2015, 3, 13706–13716.
1 S. Huang, Z. Wen, Z. Gu and X. Zhu, Electrochim. Acta, 2005,
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RSC Adv., 2016, 6, 90455–90461 | 90461