物理化学学报(Wuli Huaxue Xuebao)
Acta Phys. -Chim. Sin. 2014, 30 (5), 866-872
866
[Article]
May
www.whxb.pku.edu.cn
doi: 10.3866/PKU.WHXB201403041
真空辅助法合成 Fe3(PO4)2∙8H2O 及对 LiFePO4/C 结构、形貌和电化学
性能的影响
任建新 1
胡有坤 1
郭孝东 1,*
(1 四川大学化学工程学院, 成都 610065;
摘 要:
唐
2
艳1
钟本和 1
刘
恒2
四川大学材料科学与工程学院, 成都 610065)
采 用 了 一 种 真 空 辅 助 沉 淀 法 制 备 Fe3(PO4)2 ∙8H2O, 并 以 此 进 一 步 合 成 粒 径 尺 寸 在 400 nm 左 右
LiFePO4 颗粒. 研究了 Fe3(PO4)2∙8H2O 对于磷酸铁锂的形貌、结构、电化学性能的影响. X 射线衍射(XRD)结果
表明, 真空辅助制备的 Fe3(PO4)2∙8H2O 具有高纯度, 以此制备的 LiFePO4 具有高结晶度和纯度. 扫描电子显微
镜(SEM)结果表明, 真空辅助制备的 Fe3(PO4)2∙8H2O 具有未完全发育的颗粒, 以此制备的 LiFePO4 均匀无硬团
聚. 透射电子显微镜(TEM)结果显示真空辅助制备的 LiFePO4 包覆一层均匀的碳. 真空制备的 LiFePO4 显示了
优异的电化学性能, 在 1C、10C、20C 倍率下的容量分别为 140、113、100 mAh∙g-1. 真空制备的 LiFePO4 的循环
伏安曲线显示了小的极化电压和尖锐的氧化峰. 充放电平台曲线表明真空对 LiFePO4 高倍率性能起到重要作
用. 电化学阻抗谱(EIS)计算结果显示, 真空和非真空制备的 LiFePO4 的锂离子扩散系数分别为 1.42×10-13 和
4.22×10-14 cm2∙s-1, 说明真空辅助能够提高 LiFePO4 的扩散系数.
关键词: Fe3(PO4)2∙8H2O;
中图分类号:
LiFePO4/C; 真空辅助; 沉淀; 高倍率
O646
Vacuum-Assisted Synthesis of Fe3(PO4)2∙8H2O and Its Influence on
Structure, Morphology and Electrochemical Performance of LiFePO4/C
REN Jian-Xin1
HU You-Kun1
GUO Xiao-Dong1,*
ZHONG Ben-He1
LIU Heng2
TANG Yan1
(1College of Chemical Engineering, Sichuan University, Chengdu 610065, P. R. China;
College of Materials Science and Engineering, Sichuan University, Chengdu 610065, P. R. China)
2
Abstract: A vacuum-assisted precipitation method was used to synthesize Fe3(PO4)2∙8H2O (FP). The FP was
then used to synthesize carbon-coated LiFePO4 (LFP/C) particles. The influence of FP on the structure,
morphology, and electrochemical performance of LFP was investigated. The X-ray diffraction (XRD) patterns
and molar ratio of Fe to P showed that the FP which was produced using a vacuum-assisted method was of
high purity and gave highly crystalline, impurity-free LFP. Scanning electron microscopy (SEM) showed that
the FP contained undeveloped particles. The undeveloped FP results in uniform LFP/C particles, without
agglomeration. Transmission electron microscopy (TEM) showed that the LFP particles were coated with a
homogeneous carbon layer. The LFP/C showed excellent discharge capacities of 140, 113, and 100 mAh∙g-1 at
1C, 10C, and 20C rates, respectively. The cyclic voltammograms (CVs) of LFP showed a low polarization voltage
and sharp redox peaks. The charge-discharge platform curves showed that LFP had an excellent high-rate
capability. Electrochemical impedance spectroscopy (EIS) tests showed that the lithium-ion diffusion coefficients
of LFP/C produced with and without vacuum assistance were 1.42×10-13 and 4.22×10-14 cm2∙s-1, respectively,
Received: December 16, 2013; Revised: March 4, 2014; Published on Web: March 4, 2014.
∗
Corresponding author. Email: [email protected]; Tel: +86-28-85406702.
The project was supported by the Fund for Young Scientists of Sichuan University, China (2011SCU11081) and Research Fund for the Doctoral
Program of Higher Education, Ministry of Education of China (20120181120103).
四川大学青年基金(2011SCU11081)及教育部高校博士学科点科研基金(20120181120103)资助项目
© Editorial office of Acta Physico-Chimica Sinica
No.5
REN Jian-Xin et al.: Vacuum-Assisted Synthesis of Fe3(PO4)2∙8H2O and Its Influence on LiFePO4/C
867
proving that vacuum assistance can improve the diffusion coefficients of LFP/C.
Key Words: Fe3(PO4)2∙8H2O; LiFePO4/C; Vacuum-assistance; Precipitation;
1
Introduction
Since Padhi et al.1 first reported that LiFePO4 could insert
and extract Li ions reversibly, LiFePO4 has been considered as
one of the most potential and most challenged cathode materials because of its particular advantages such as nontoxicity, superior capacity retention, good thermal stability, remarkable
tolerance to overcharge and discharge, excellent safety, and potentially low cost. However, olivine LiFePO4 has a low electronic conductivity (~10-9 S∙cm-1) and a low lithium ion diffusion coefficient (~1.8 × 10- 14 cm2 ∙ s- 1),2,3 which prevent it from
being used in large scales. In recent years, numerous attempts
have been made to overcome the limitations, such as metal
doping,4,5 coating with the electronically conductive like carbon and metal oxide,6 reducing the particle size,7-10 controlling
the particle morphology.11 Furthermore, various synthesis methods have been developed to prepare LiFePO4 materials, involving solid-state reactions,12,13 polyol process,14 sol-gel process,15-17 hydrothermal synthesis,18,19 microwave synthesis,20 solvothermal
synthesis21-23 and co-precipitation.24-26
Among all the methods, solid-state reactions, hydrothermal
synthesis and co-precipitation have realized the industrial production. Solid- state reaction requires long time and high processing temperature, which make it a power-wasting method.
Hydrothermal synthesis can achieve an excellent electrochemical performance, however, hydrothermal synthesis demands
high temperature, high pressure, and excess lithium resource
(it is decided by the solubility- product constant of Fe3(PO4)2 ∙
8H 2O and Li3PO 4), which increase the cost and energy-consumption. Compared with the other two methods, co-precipitation can overcome most of the limitations. Nevertheless, it still
demands excess lithium resource. Most important of all, co-precipitation usually results in a precursor of nonstoichiometric
composition for the oxidation of Fe2 + in the synthesis process
of precursor. Thus, the precursor of nonstoichiometric composition will form impurities after calcination. The impurities
could be clearly observed from the X- ray diffraction (XRD)
pattern and are harmful for the cathode materials. Park24 and
Arnold25 et al. synthesized LiFePO4/C under the protection of
N2 flow by co- precipitation method, but some impurities such
as Li3PO4 was introduced. Franger et al.26 tried to synthesize
LiFePO4/C by co-precipitation method, but phosphide was formed
in the material.
In this paper, a vacuum-assisted precipitation method has been introduced to synthesize Fe3(PO4)2 ∙8H2O, which can prevent the oxidation of Fe2 + and reducing the impurities effectively. Then, the
LiFePO4/C was synthesized with the prepared Fe3(PO4)2 ∙ 8H2O,
Li3PO4 and carbon source. The influence of Fe3(PO4)2 ∙8H2O on the
LiFePO4 was investigated. The properties of the two LiFePO4/C
samples are characterized by XRD, transmission electron mi-
High rate
croscope (TEM), electrochemical impedance spectroscopy
(EIS), charge- discharge test, and cyclic voltammogram (CV) in
the following sections.
2
Experimental
2.1 Preparation of materials
The Fe3(PO4)2 ∙ 8H2O powders of stoichiometric ratio were
synthesized by using precipitation method, with FeSO4 ∙ 7H2O
(AR, 99%), NH4H2PO4 (AR, 99%), and NH3 ∙H2O (AR, 25%28%) as raw materials, according to the following reaction:
3FeSO4+2NH4H2PO4+4NH3+8H2O=
Fe3(PO4)2∙8H2O↓ +3(NH4)2SO4
An appropriate amount of NH3 ∙H2O was used to control the
pH value. The reactor was controlled at a vacuum degree of
0.095 MPa and the react temperature was maintained at the
boiling point of the solution (about 45 °C). Then, the prepared
Fe3(PO4)2 ∙ 8H2O powders and analytical grade Li3PO4 (99% )
with mole ratio of n(Fe3(PO4)2 ∙ 8H2O):n(Li3PO4) =1:1 and the
stearic acid which acted as the carbon source were mixed together. The precursor was obtained through ball milling the
mixture for several minutes. The LiFePO4/C composites were
obtained after the precursor was sintered at 600 °C for 4 h in a
tubular furnace under an argon flow. The LiFePO4/C composite
was synthesized by the Fe3(PO4)2 ∙8H2O without vacuum-assisted
through the same procedure for comparison. The Fe3(PO4)2 ∙
8H2O with and without vacuum- assisted was labeled as FP- A
and FP-B, respectively. The corresponding LiFePO4/C was labeled as LFP-A and LFP-B, respectively.
2.2 Characterization and measurement
Thermogravimetric-differential scanning calorimetry (TGDSC) analysis of the precursor was measured by NETZSCH
STA 449C device in the temperature range of 30 to 800 °C at
the heating rate of 10 °C ∙min-1 under an N2 flow of 20 mL∙min-1.
The Fe and P percentage compositions of Fe3(PO4)2∙8H2O are determined by a chemical analysis method of titanium trichloridepotassium dichromate titration and quimociac gravimetric
method respectively. The residual carbon content of the material was tested by CS-902 analytical device. The crystalline structure of material was analyzed by X- ray diffraction (XRD, D/
max-rB, Rigaku, Cu Kα radiation) (λ=0.15046 nm, operated at
40 kV and 40 mA from 10° to 70° at a scanning speed of 0.5 (°)∙
min- 1). The morphology of the samples was observed by scanning electron microscopy (SEM, SPA400 Seiko Instruments).
The micro-structure of samples was characterized by transmission electron microscope (JEM-2100, Japan). The cyclic
voltammetry test and electrochemical impedance spectroscopy
were performed on a CHI660B electrochemical workstation.
The electrochemical performance of the prepared materials
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Acta Phys. -Chim. Sin. 2014
was tested by constant current charge-discharge method. The
cathode was prepared by mixing the active materials with acetylene black and polyvinylidene fluoride (PVDF) in a mass ratio of 80:13:7. The mixture was spread onto Al foils. Then, the
foils were pressed at 10 MPa after drying for 24 h at 120 ° C.
The cells were assembled in an argon filled glove box with lithium metal as anode and Celgard 2400 film as separator. The
electrolytes were 1 mol∙L-1 LiPF6 dissolved in ethylenecarbonate (EC) and dimethyl carbonate (DMC) (VEC:VDMC=1:1). The
cells were galvanostatically charged and discharged at room
temperature between 2.5 and 4.3 V.
3
Results and discussion
3.1 TG-DSC curves of LiFePO4/C precursor
TG-DSC curves are carried out to optimize the calcination
temperature for the precursors. Fig.1 shows the TG-DSC curves
of LFP- A precursor from 30 to 800 ° C. Over the temperature
ranges from 30 to 600 ° C, the TG curve shows continuous
mass-loss about 30% and no mass-loss after 600 °C. According
to the mass-loss curve, the mass-loss can be sketchily divided
into three steps. The observed initial mass- loss from 25 to
100 °C is attributed to the evaporation of the free-water in the
samples. The second step from 100 to 250 ° C may be caused
by the elimination of crystal water of Fe3(PO4)2 ∙8H2O and the
volatilization of the stearic acid from the system. In this step,
several endothermic peaks appear in the DSC curve, which indicate that the elimination of crystal water of Fe3(PO4)2 ∙ 8H2O
molecules is step by step. The last mass-loss from 250 to 600 °C
corresponds to carbonization of stearic acid. A broad exothermic peak appears in the DSC curve, indicating it a time- continuing process. The small peak around 600 ° C could correspond to crystallization of LiFePO4. Based on the TG-DSC analysis results, the calcination temperature of the precursor is determined to be 600 °C.
3.2
Vol.30
1186) very well. No obvious impurities are detected from the
patterns of FP-A. The mole ratio of Fe to P in the FP-A is measured to be 1.498 (theoretical value is 1.5), which indicates that
the FP- A is of highly purified. However, some impurities can
be detected from the patterns of FP-B. The mole ratio of Fe to
P in the FP- B is measured to be 1.484. This can be attributed
that the boiling solution can provide the reactant of FP-A more
contact time and contact region, which make it possible to
transform the hydroxides into Fe3(PO4)2 ∙8H2O gradually under
the vacuum.
Fig.2b shows the XRD patterns of the LiFePO4 samples. The
LFP-A and LFP-B are well crystallized for the sharp peaks in
the XRD patterns. All the peaks in Fig.2b can be indexed as
olivine- type LiFePO4 with a Pnma space group (JCPDS card
No. 81-1173). The spectra of LFP-A agree well with LiFePO4
standard card, no impurity phase is detected. The refined parameters of the LFP- A are a=1.0337 nm, b=0.6010 nm, c=
0.4691 nm, which are well consistent with the LiFePO4 standard card (a=1.0332 nm, b=0.6010 nm, c=0.4692 nm). However, the LFP-B shows an obviously decreased value of a=1.0316
nm, b=0.5995 nm, c=0.4685 nm and impurities are analyzed as
Fe2P2O7 and Li4P2O7 by Jade 5.0. It is obvious that the Fe2P2O7
and Li4P2O7 should result from the impurities of FP-B.
3.3
Morphology of Fe3(PO4)2∙8H2O and LiFePO4/C
samples
XRD of the Fe3(PO4)2∙8H2O and LiFePO4/C
samples
Fig.2a shows the XRD patterns of the Fe3(PO4)2 ∙8H2O samples. The two XRD patterns show a good crystallinity and
match the Fe3(PO4)2 ∙8H2O standard peak (JCPDS card No.75-
Fig.1 TG and DSC curves of LiFePO4/C precursor
Fig.2 XRD patterns of (a) FP-A, FP-B and (b) LFP-A, LFP-B
No.5
REN Jian-Xin et al.: Vacuum-Assisted Synthesis of Fe3(PO4)2∙8H2O and Its Influence on LiFePO4/C
Fig.3(a, b) shows the SEM images of Fe3(PO4)2 ∙ 8H2O. The
FP-A and FP-B are both composed of flower-like particles.
The flower- like particles are piled up by uniform sheets from
different angles. However, the flower-like particles of FP-B are
remarkably bigger than the particles of FP-A. Moreover, the
FP-A contains many fragments with size of less than 1 μm.
Fig.3(c, d) shows the SEM images of LiFePO4/C samples.
The LFP-A consists of bar-like particles and their average particle-sizes are around 400 nm, with uniform particle size distribution and no obvious hard agglomeration. Moreover, the second particles are composed of many small primary particles. In
contrast, the LFP- B presents irregular shapes and has a large
particle distribution, from 500 nm to 5 μm, with a serious hard
agglomeration.
Comparing the SEM images of Fe3(PO4)2 ∙8H2O and LiFePO4/
C, it is obvious that the morphology of Fe3(PO4)2 ∙ 8H2O has a
great influence on the morphology of LiFePO4. As we known,
aging is helpful to the growth of crystal, so it is difficult for the
Fe3(PO4)2 ∙ 8H2O to grow in boiling solution. The fragment of
FP- A is likely to be the undeveloped Fe3(PO4)2 ∙ 8H2O, which
can be proved by the low crystallinity in XRD patterns. What
is more, the FP-A with undeveloped fragments is helpful for
mixing with Li3PO4 and stearic acid. Thus, it reduces the hard
agglomeration during calcinations.
3.4
Micro-structure analysis of the LiFePO4/C
samples
In order to investigate the carbon coating of LFP- A, TEM,
high-resolution TEM (HRTEM), and selected area electron diffraction (SAED) are further performed. As shown in Fig.4(a,
b), it reveals that the LFP-A consists of many irregular shaped
869
particles with the size about 50 nm. Fig.4c shows the HRTEM
image taken from an individual LFP-A particle, it can be seen
that the lattice fringes appeared clearly, indicating that the sample is well-crystallized. The observed lattice fringes with a
spacing of 0.301 nm corresponding to the (020) planes clearly
confirm the orthorhombic LiFePO4 structure, which agrees
well with the results of XRD. Meanwhile, a homogeneous
amorphous phase carbon layer with a thickness of around 1.3
nm covered on the surface of primary particles is observed distinctly. This means that the stearic acid could be uniformly
mixed with Fe3(PO4)2∙8H2O to ensure residual carbon distributed homogenously on the surface of LFP- A. Fig.4d shows the
SAED spot pattern of the LFP-A, which indicates that the particles are single crystal.
3.5 Electrochemical test
Fig.5 shows the typical charge-discharge platform curves of
electrode materials at various rates in a potential range from
2.5 and 4.3 V. The potential difference between charge and discharge plateau curves reflects the extent of polarization. Larger
polarization occurs with the current density increasing, which
has been proved by intervals between different rates as shown
in Fig.5. This phenomenon can be found more obviously in
LFP-B, that is to say, the more serious polarization happens in
LFP-B, which causes the worse rate performance. Both of platform curves at each rate have only one flat plateau around 3.4
V, corresponding to the redox reaction between LiFePO4 and
FePO4. The discharge curve of LFP-A is flatter and less polarization than that of LFP-B, especially at high rate, demonstrating a good electrochemical stability for LFP-A.
Fig.6 shows the specific capacities of the two LiFePO4 sam-
Fig.3 SEM images of Fe3(PO4)2∙8H2O and LiFePO4/C
(a) FP-A; (b) FP-B; (c) LFP-A; (d) LFP-B
Fig.4 TEM (a, b) and HRTEM (c) images and SAED pattern (d) of LFP-A
870
Acta Phys. -Chim. Sin. 2014
Vol.30
the LFP- A displayed better specific capacity at all rates than
LFP- B. The discharge capacities are up to 140, 113, and 100
mAh∙g-1 at 1C, 10C, and 20C rates, with capacity retention ratios of 82.4%, 66.5%, and 58.8%, respectively. What is more,
the LFP-A delivers a discharge capacity of 158 mAh∙g-1 when
the rate returns to 0.1C (0.1C-recycle in Fig.6) again after cycles at 20C, but LFP-B delivers an obvious decreasing specific
capacity of 146 mAh∙g-1 at 0.1C, only 92.4% of the initial discharge capacity.
Combined the analysis results of XRD, SEM, and TEM, it
can be a better understanding of the great difference in electrochemical performance. Firstly, the LFP-A consists of many primary particles about 50 nm without hard agglomeration. This
structure is not only suit for the access of electrolyte, but also
can short the length of diffuse path largely. Secondly, the impurities dispersing in LiFePO4/C particles can elongate the diffusion path and increase charge transfer resistance. Besides, impurities can affect the reversibility of the lithium extraction/insertion reactions, because the LFP- B does not return to initial
capacity after cycles at 20C. Overall, the vacuum-assisted could
improve the electrochemical performance to a large extent.
Fig.5
Charge-discharge curves of LFP-A and LFP-B
ples at various rates from 0.1C to 20C. The first discharging capacities for LFP-A and LFP-B are 123.6 and 126.8 mAh∙g- 1,
respectively, which indicates that the materials undergo an activating process. It can be clearly observed that specific capacity
of LFP-B is strongly influenced by the discharge rate. The LFPB delivers a good specific capacity of 158 mAh ∙ g- 1 at 0.1C
rate. While the capability decreased quickly at high rate, only
40 and 25 mAh∙g-1 remained at 10C and 20C rates, respectively. Compared with LFP- B, LFP-A shows the adjacent discharge capacity of 158 and 151 mAh∙g- 1 at the low rate (0.1C
and 0.2C), respectively. With the increasing of discharge rate,
Fig.6 Cycle performance of LFP-A and LFP-B at different
discharge rates
3.6 Cyclic voltammogram test
Fig.7 shows the cyclic voltammogram curves of the two
samples in the potential range from 2.5 to 4.3 V at a scan rate
of 0.1 mV∙s- 1. Both of the two samples exhibits sharp oxidation (around 3.5 V) and reduction (around 3.3 V) peaks, consistent with a two- phase reaction at about 3.4 V (versus Li/Li + ).
No other peak is observed, evidencing the absence of electroactive impurities. The LFP-A displays an unchanged redox
peak potential after 20 cycles except for a little weaker in intensity, confirming the outstanding reversibility of the lithium extraction/insertion reactions. The sample B shows a shifted redox peak after 10 cycles, indicating a change in the structure.
The polarization voltages from Fig.7 are 0.2 and 0.3 V for LFPA and LFP- B, respectively. This result is consistent with the
electrochemical performance shown in Fig.5.
3.7 Electrochemical impedance spectroscopy
Fig.8 represents the Nyquist curves of all the samples and an
Fig.7
Cyclic voltammogram curves for LFP-A and LFP-B
REN Jian-Xin et al.: Vacuum-Assisted Synthesis of Fe3(PO4)2∙8H2O and Its Influence on LiFePO4/C
No.5
871
ions are also listed in Table 1. The diffusion coefficients are
1.42×10-13 and 4.22×10-14 cm2∙s-1 for LFP-A and LFP-B respectively, which are little higher than the reported value29 (1.39 ×
10- 13 cm2 ∙s- 1 for LiFePO4/C at room temperature). The higher
diffusion coefficient of the LFP-A can be ascribed to the shorter length of diffuse path dependent on the secondary morphology. It is well known that the higher diffusion coefficient of the
material means a faster extraction of the lithium ions. Thus, the
faster extraction of lithium iron can reduce the accumulation of
electron, which leads to a less polarization and more excellent
electrochemical performance talked above.
Fig.8
Impedance spectra for LFP-A and LFP-B samples and
an equivalent circuit (inset)
equivalent circuit fitted by ZView2.0. All the Nyquist curves
combine an intercept at high frequency, followed by a semicircle in high-middle frequency region and straight line in low frequency region. The intercept at high frequency represents the
Ohmic resistance (Re) of electrode and electrolyte. According
to the recent studies,27,28 the high frequency region of the semicircle is likely related to the contact resistance (R0) between
particles and current collector and the double-layer capacitance
(C0) of the metal substrate/electrolyte interface. The low frequency region of the semicircle represents the charge transfer
resistance (R1) and capacitance of the double layer created at
the particle/electrolyte interface (C1). The oblique line represents the Warburg impedance (ZW), reflecting the solid- state
diffusion of lithium ion in material particle.
Table 1 gives a summary of fitting results for the two samples. The value of relative deviations is very small, indicating
the fitting results are believable. The ohmic resistances (Re in
Table 1) are almost the same for the LFP- A and LFP- B. The
contact resistances (R1 in Table 1) are 26.84 and 24.21 Ω for
the LFP-A and LFP-B, respectively. This can be expected because they were both pressed at the pressure of 10 MPa. The
charge transfer resistance of LFP-B is larger than that of LFPA. It is more likely to be related to the impurities of the LFP-B.
The diffusion coefficients of lithium ions can be calculated by
the formula as follows:
DLi=R2T2/(2A2n4F4c2σ2)
where, T is the absolute temperature, R is the gas constant, n is
the number of charge transfer, A is the surface area of cathode,
F is the Faraday constant, c is the concentration of lithium
ions, σ is the Warburg constant which can be calculated by the
linear fitting results of frequency and impedance from the EIS
data. The calculated results of diffusion coefficients of lithium
4
The Fe3(PO4)2 ∙8H2O of stoichiometric ratio was synthesized
by a fast, easy, and effective precipitation method. The LiFePO4/C
cathode material of typical olivine structure was synthesized
by the Fe3(PO4)2 ∙8H2O. The vacuum-assisted LiFePO4/C material shows less agglomeration and more excellent electrochemical performance than the one without vacuum-assisted. The average particle size of LFP-A is about 400 nm with a narrow distribution. The carbon coated on the particle surface with thickness of 1.3 nm with a homogeneous distribution. The specific
discharge capacities have been reached 158, 151, 140, 113 and
100 mAh∙g-1 at 0.1C, 0.2C, 1C, 10C, and 20C rates, respectively. Besides, the excellent electrochemical performance is also
step-forward demonstrated by CV and EIS measurements. Therefore, the vacuum- assisted precipitation is indeed a promising
way to synthesize the LiFePO4/C.
References
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Fitting results of equivalent circuit from Nyquist curves
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Sample
Re/Ω
R0/Ω
R1/Ω
Chi-Squared
σ
LFP-A
3.618
26.84
15.47
0.0007773
43.25
LFP-B
3.522
24.21
27.80
0.0299640
79.45
DLi/(cm2∙s-1)
1.42×10-13
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