Preparation and electrochemical properties of binary SixSb immiscible alloy for lithium ion batteries

Article abstract of DOI:10.1016/j.jallcom.2014.05.034

The novel binary Si_xSb immiscible alloy was synthesized using chemical reduction-mechanical alloying methods and first investigated as possible anodes for lithium ion batteries. The microstructures, morphologies and electrochemical properties were investigated utilizing X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), constant-current charge/discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Results showed that tiny Si particles were dispersed homogeneously in Sb active matrix. Cyclic voltammetry results indicated that the Li⁺-transport rates were significantly enhanced in the Si _xSb immiscible alloy. Results also showed that the Si_0.8Sb exhibited the best cyclability with a reversible capacity of 596.4 mAh g ^-1 after 50 cycles. The cyclability can be improved by restricting either the upper or lower cutoff voltage, which can control the lithiation/delithiation degree and prevented the powdering and shredding of the active materials after Li⁺ trapped into electrode materials.

Full text of DOI:10.1016/j.jallcom.2014.05.034

Accepted Manuscript
Preparation and Electrochemical properties of binary Si x Sb immiscible alloy
for lithium ion batteries
Jingwei Wang, Yang Wang, Peixin Zhang, Dongyun Zhang, Xiangzhong Ren
PII:
S0925-8388(14)01100-1
DOI:
http://dx.doi.org/10.1016/j.jallcom.2014.05.034
JALCOM 31223
Reference:
To appear in:
Received Date:
Revised Date:
Accepted Date:
28 March 2014
30 April 2014
5 May 2014
Please cite this article as: J. Wang, Y. Wang, P. Zhang, D. Zhang, X. Ren, Preparation and Electrochemical properties
of binary Si Sb immiscible alloy for lithium ion batteries, (2014), doi: http://dx.doi.org/10.1016/j.jallcom.
x
2014.05.034
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Preparation and Electrochemical properties of binary Si Sb immiscible alloy
x
for lithium ion batteries
Jingwei Wang, Yang Wang, Peixin Zhang*, Dongyun Zhang, Xiangzhong Ren*
( School of Chemistry and Chemical Engineering, Shenzhen University, Shenzhen 518060, PR China )
Abstract: The novel binary SixSb immiscible alloy was synthesized using chemical reduction-mechanical alloying
methods and first investigated as possible anodes for lithium ion batteries. The microstructures, morphologies and
electrochemical properties were investigated utilizing X-ray diffraction (XRD), field-emission scanning electron
microscopy (FE-SEM), constant-current charge/discharge tests, cyclic voltammetry and electrochemical impedance
spectroscopy (EIS). Results showed that tiny Si particles were dispersed homogeneously in Sb active matrix. Cyclic
voltammetry results indicated that the Li+-transport rates were significantly enhanced in the SixSb immiscible alloy.
Results also showed that the Si0.8Sb exhibited the best cycleability with a reversible capacity of 596.4 mAh·g-1 after
50 cycles. The cycleability can be improved by restricting either the upper or lower cutoff voltage, which can control
the lithiation/delithiation degree and prevented the powdering and shredding of the active materials after Li+ trapped
into electrode materials.
Key words: lithium ion batteries; SixSb immiscible alloy; electrochemical properties; cycle performance
1. Introduction
Due to their high energy capacity (4212 mAh·g-1), high storage, low voltage platform and environmental
compatibility, Si-based alloys have been widely investigated as the promising anode materials for lithium ion
batteries. However, the practical application was limited by the short cycle performance. Hence, simultaneously
improving the cycle performance and maintaining a high capacity of Si-based anode materials have been intensely
studied in recent years [1]. Cycle performance of Si-based anode materials has been primarily improved via the
following three ways: (1) Preparation of Si-based composite materials [2, 3]. (2) Synthesis of Si-based alloy [4, 5]. (3)
Preparation of amorphous silicon materials [6, 7]. Researches of Si-based anode materials were mainly focused on
Si-M binary system, where M can represent as the inert metals such as Ni [8], Fe [9], Mn [10], V [11] and Zr [12],
which can merely serve as support substrate for the electrode structure. In the other hand, M also can represent as
* Corresponding author: Peixin Zhang, Tel & Fax: 86-755-26558134, Email: pxzhang@szu.edu.cn, Xiangzhong Ren, Email:
renxz409@163.com

active metals like Sn [13], Ag [14], Zn [15], Al [16] and Ge [17], which are active to Li+ at different voltages. The
volume expansion of different elements occurs at different voltages, alleviating the internal stress generated during
the lithium process and improving the cycleability. The SiAg electrode prepared by milling for 50h shows good
cyclability with little fades over the first 50 cycles. It exhibited a stable capacity of ~280mAh·g-1, suggesting that the
cyclability is prompted by alloying Ag with Si [18]. Nevertheless, Sn is lithiated from 0.66 to 0.38 V, while Si is
approximately lithiated at 0.45 V except in the first cycle [17]. When the voltage was below 0.45 V, both Si and Sn
reacted with Li+, generating large volume expansion that could not be effectively relieved. Thus the cycle
performance can not be apparently improved [13].
Studies indicate that cycle performance of the active/active alloy system was yieldingly improved by making
lithiation products buffering matrices for each other at different potentials [19-22]. Researches also have reported the
electrochemical behavior of the complex immiscible alloy system with microcrystalline one kind of particles
dispersed homogeneously in another active matrix revealed superior cycleability [23-28]. Compared with other
Si-based alloys, SixSb immiscible alloy system exhibits superior capacity and good cycle performance. Si-Sb is an
immiscible alloy system that has no intermetallic and solid solution phase. But the components in system were
refined into nanoscale and dispersed homogeneously, forming a nanophase composite structure [23-26]. Few reports
have discussed the binary immiscible systems in which both of the elements are active to Li+.
2. Experimental
2.1. Preparation and characterization
Nano-sized SiSbx immiscible alloy powders were synthesized by chemical reduction-MA method in our studies.
To produce SiSbx immiscible alloy powders, a 0.1 M aqueous solution of SbCl3 within a chelating agent of trisodium
citrate dehydrate and a 0.2 M aqueous solution of NaBH4 (pH> 12) were prepared. The use of excess NaBH4 served
to ensure a complete reduction of metal ions. All reagents used were of analytical quality. After the completely
dissolve of SbCl3, the reduction reaction was carried out by first adding 100 ml SbCl3 (0.1 M) solution drop wise to a
NaBH4 solution immediately with vigorous magnetic stirring at room temperature and 30 min stirring after the drop
wise. In order to get a better microstructure, the reduced powders were aged in a water bath with a constant
temperature of 80 for 5 h. The solution was then filtered, and the product was washed thoroughly using distilled
water and ethanol. And then high-energy ball milling was used for the MA. The elemental Si and Sb powders were
mixed at a given ratio and loaded into a 100 ml stainless steel vial. The milling was performed under argon with
anhydrous ethanol as the solvent. All processes before milling were conducted inside an argon-filled glove box, and
the vial was sealed with an elastomer O-ring. After milling for 15 h, the product was dried at 120 for 10 h under
vacuum. Finally, sift the products, which have different molar ratios, with a 200-mesh sieve and then store them in an

Ar-filled glove box. The phases of the as-obtained powders were identified using a D8ADVANCE X-ray diffraction
(XRD) instrument. The microstructure and morphology of the particles were observed using field-emission scanning
electron microscopy (FE-SEM) on a Hitachi Limited S-3400N instrument.
2.2. Assembling and testing
To evaluate their electrochemical characteristics, the electrodes were prepared by mixing 70 wt% active
materials, 10 wt% acetylene black and 20 wt% polyvinylidene fluoride (PVDF) binder in 1-methy1-2-pyrrolidinone
(NMP) to form slurry, which was then spread onto a copper grid. After coating, the film was dried at 120° for 10 h
under vacuum. After pressing the films on a manual-tableting machine, the flakes were annealed in a pipe electric
furnace at 230° (removed them when temperature was below 50° ).
The electrochemical studies were performed on coin cells assembled in an argon-filled glove box; the cells were
composed of a metallic lithium foil as the counter electrode, 1 M LiPF6 in ethylene carbonate (EC)-dimethyl
carbonate (DMC) (1:1 v/v) as the electrodes, Celegard 2004 as the separator and the synthesized immiscible alloy as
the working electrode. The cycling tests were carried out using a CT2001A battery tester between 0 V and 2.0 V (vs.
Li) under a constant current density of 0.05 mA cm-2 under 25 , unless otherwise noted. The cyclic voltammetry and
electrochemical spectroscopy (EIS) tests were performed using a CHI660A electrochemical testing system in the
range of 0-2.0 V (vs. Li) at a scan rate of 0.05 mV·s-1 with a frequency of 0.01~105 Hz and amplitude of 5 mV. In
addition, the electrochemical properties of the immiscible alloy anode materials were performed within the
temperature range of -25-50
.
3. Results and discussion
3.1. Structure and morphology
Figure 1 shows the XRD patterns of SixSb immiscible alloy anode materials obtained using chemical
reduction-MA method. The diffraction peaks of a series Si-Sb are attributed to Si and Sb phases. There is no apparent
shift of Si and Sb peaks meaning that there is no obvious dissolution of Si to Sb or vice versa. The peaks
characteristic of SixSb immiscible alloy are enhanced with the increasing Si contents, stating that an appropriate
addition of Si contributes to the formation of SixSb immiscible alloy anode material.
The FE-SEM images of Si0.8Sb immiscible alloy anode materials are showed in Figure 2. As schematically
depicted in Fig. 2a, the sample is formed by tiny irregular particles and the particles aggregated into homogenous
secondary particles, which are uniformly distributed without distinct agglomeration. The back-scattered image of
Si0.8Sb provided in Fig. 2b shows that Si and Sb are integrated without an apparent distinction in phases, generating a
minimal difference in the atomic number/composition contrast. According to the EDX analysis and the element

mapping of Si0.8Sb in Figure 2c, the immiscible alloy are consisted of Si (43.72 at.%) and Sb (56.28 at.%) in the
scanning area, i.e., Si (16.21 wt%) and Sb (83.79 wt%), which are closely to theoretical values.
From Figure 1 and Figure 2, we can get the conclusion that there are no traditional intermetallic compounds but
a stable novel immiscible alloy system composed of simple Si and Sb substances formed in our studies. Moreover,
most Si is cladded by Sb, allowing small quantities of uncoated Si exposed on the surface.
3.2. Electrochemical behaviors of SixSb immiscible alloy anode materials
3.2.1. Electrochemical properties versus Si contents in Si Sb immiscible alloy anodes
x
Figure 3 depicts the cycle performance versus silicon content, providing a direct evidence of the good lithium
storage performance due to the proper silicon contents. When the x values are 0.6, 0.8, 1.0, 1.2, 1.4, the initial
discharge capacities of SixSb are 1194.1, 1288.4, 1229.5, 1385.3 and 1092.5 mAh·g-1, maintaining 556.5, 596.4, 526,
522 and 519.7 mAh·g-1 after 50 cycles, respectively. Especially when silicon contents are 0.6 and 0.8, the anodes
mainfest better cycle capacities, which slightly exceed to their theoretical values. The silicon oxides and antimony
oxides generated during the synthetic procedures irreversibly reacts with Li+, thereby artificially lower the initial
charge-discharge efficiency. Studies have shown that the 100-200 nm CuO film formed on the surface of current
collector also devotes to the irreversible capacity[29, 30]. When the silicon contents are 1, 1.2 and 1.4, the discharge
capacities are lower than the theoretical ones. The volume changes severely along with silicon content, and the
massive shredding materials block transmissions for electronic and lithium ions. It follows that the
lithiation/delithiation process is impeded and the specific discharge capacities reduced. In conclusion, the cycle
stability can be improved by controlling the silicon contents. The Si0.8Sb immiscible alloy shows the highest capacity
(3.5 times of graphite-based carbonaceous materials) and possesses reversible capacity retention of 58.82% after 50
cycles.
Figure 4 presents the electrochemical impedances of SixSb (x=0.6, 0.8, 1, 1.2, 1.4) and the representative fitting
lines before cycles. The arc in the high-frequency intercept represents the contact resistance at the open voltage
without lithium insertion, charge transfer and lithium-ion diffusion. As schematically depicted in the figure, the whole
tendencies of lines show insignificant changes with increasing silicon contents except the gradually increasing radius.
Typically, the resistance Re is used as the electrolyte impedance. And Qg is used as the diffusive resistance and Qcf,
Rcf as the contact resistances, analogously. All equivalent circuits are well fitted and displayed in Table 1. Results
indicate that the electrolyte resistances of SixSb (x=0.6, 0.8, 1, 1.2, 1.4) are 4.49, 4.68, 4.72, 4.75 and 4.79 Ω, the
contact resistances are 132.6, 138.5, 142.3, 163.7 and 171.2 Ω, and the diffusion resistances are 0.002638, 0.002743,
0.002896, 0.003569 and 0.003646 F, respectively, showing that the resistances of the immiscible alloy system is
enhanced by silicon. As the silicon contents increase, the material could not be fully infiltrated by electrolyte due to

the aggregation of part active particles, thus leading to increasing of Re. And the formation of the appropriate porous
structure is prevented by excessive silicon. Concurrently, the Qcf and Rcf drastically increase.
3.2.2. Cycle performance of Si0.8Sb immiscible alloy anodes under various temperatures
Both capacity and cycleability are osculating related to temperature. Figure 5 shows the cycle performance of
Si0.8Sb anode materials under different temperatures (−25 , 0 , 25 and 50 ). When temperature is −25
,
Si0.8Sb anodes exhibit good cycle performance with an initial discharge capacity of 862.7 mAh·g-1 and a mildly
capacity decay. The initial specific discharge capacity of Si0.8Sb is 1075.3 mAh·g-1 and reduces to 525.6 mAh·g-1
after 50 cycles at 0 , illustrating an improved cycle performance. The Si0.8Sb anode also possesses a favorable cycle
performance and a high discharge capacity at 25
and 50 , with an initial discharge capacities of 1288.4,
1303.8 mAhg-1 and 596.4, 532.5 mAh·g-1 after 50 cycles, respectively, showing that Si0.8Sb performs well under
either high or low temperatures. In summary, temperature doesn’t apparently affect the mechanism and the lithiation
degree of the anode materials. And meanwhile, the temperature has a slight effect on the intrinsic physical and
chemical properties.
Figure 6 reveals the EIS and part of the fitting curves of Si0.8Sb anodes materials at different temperatures over
the open voltage. As indicated in the image, the reaction rate is affected by temperature and the electrolyte viscosity.
The reaction rate and ions conduction rate increases with temperature, which in some ways promotes the conductivity
and reduces the electrolyte and contact impedance. Conversely, the impedance is enhanced when the temperature
declined. Table 2 lists the fitted impedance parameters before cycles, from which we can conclude that the contact
resistance is affected by the temperature. However, when it comes to the immiscible SixSb system, the lithiation
products of Si and Sb can serve as buffering matrices for each other and substantially remits the volume expansion,
maintained the electrode structure and Li+ transmissions. Hence, the immiscible alloy anodes display good
electrochemical properties under varying temperatures.
3.2.3. Cycle performance of the Si0.8Sb immiscible alloy anode over different operating voltages
Researches demonstrate that the lithiation/delithiation degree is greatly correlated with the operating voltage.
The electrochemical properties can be improved by controlling either the upper or lower cutoff voltages, which can
reduce the depth of lithium insertion/extraction, relieve the volume expansion, restrain the destruction of the inner
stress and ultimately boost the lithiation efficiency. Figure 7 shows the cycle performance of the Si0.8Sb immiscible
alloy anode over different operating voltages. The initial specific discharge capacity reduces while the cycle
performance and the coulomb efficiency enhance along with an increased cutoff voltage. When the cutoff voltages
are 0, 0.03, 0.05 and 0.07 V, the initial discharge capacities are 1288.4, 1203.5, 1199.6 and 1094.9 mAh·g-1,
respectively. The irreversible capacities are 286.5, 218.3, 246 and 213.6 mAh·g-1 and the discharge capacities are

596.4, 619.4, 585.2 and 575.1 mAh·g-1, with reversible capacity retentions of 58.82, 62.3, 60.96 and 64.70%. When
the cutoff voltage increases, the initial discharge capacity reduces and the cycle stability is enhanced. The Si0.8Sb
anode exhibits a higher capacity for deep lithiation in the first cycle when the cutoff voltage is 0 V. However, the
volume expansion causes powdering and shredding of the internal particles, which destroys the structure of the
electrode and the buffering matrix. Consequently, the initial discharge capacity reduces rapidly and the irreversible
capacity retention is the lowest one after 50 cycles. When the lower cutoff voltage is 0.03 V, Si0.8Sb performs a
slightly low initial discharge capacity after 50 cycles, it remains higher capacity than that of 0 V. The irreversible
phase transition of silicon from crystalline to amorphous is weakened and the depth of the lithiation recedes, which
adds active particles in subsequent cycles, resulting in improved electrochemical properties. Capacities of Si0.8Sb
discharge to 0.05 V and 0.07 V are lower than that of 0.03 V. Although the higher cutoff voltage helps to reduce the
volume expansion, the capacity loss is apparent in the lithiation depth.
3.3 Lithium intercalation characteristics
The initial charge–discharge curves of the SixSb anodes over an operating voltage from 2.0 V to 0 V are given in
Figure 8. The similar trends of the curves indicate that the silicon contents don’t influence the lithiation/delithiation
mechanisms. The initial discharge curves are divided into four parts with two main discharge platforms and some
narrow discharge platforms. An irreversible phase transition of the Si occurs at 0.2 V during the initial lithium
insertion, which converts Si from crystallized into amorphous state. More specifically, the crystal structure of Si is
destroyed by the mechanical-chemical strength, which also reduces the irreversible phase transition and the
irreversible capacity during the initial lithiation procedure. Due to its high capacity and semiconductor properties, Si
exhibits a serious polarization phenomenon that could cause severe voltage hysteresis. The immiscible Si-Sb alloy
can apparently promotes the electronic and ionic conductivity of the Si-based materials.
Theoretically, the lithiation product of silicon is mainly Li22Si5 [34]. Given the tremendous volume expansion
(which can reach 300%) [35], the electrode structure lose efficacy because of the shredding of active particles and the
collapse of the electrode structure. As a result, the capacity drops dramatically for the reason that active particles lose
electrical contact with each other. However, lithiation of Sb occurs at 0.8 V and Si can effectively relieve the strain of
volume expansion. When voltage decreases below 0.4 V, the volume expansion generated by lithiation of Si is
buffered by SbLi3 in reverse. Hence, the different lithiation voltage makes the active materials convert into buffering
matrices for each other, and thus improve the cycle performance and the electrochemical properties.
Figure 9 exhibits similar cyclic voltammetry curves of SixSb immiscible alloy anodes, which shows no
relationship between silicon content and reaction mechanism. And it is similar applied to the redox voltage and the
reversibility. However, the volume expansion and internal fracture increase with silicon content, resulting in

shredding of active particles and the destruction of the anode structure. Thus the Li+ transmissions decrease and the
electrochemical properties get worse. For the cathodic scan, a series of weak reduction peaks, which don’t appear in
subsequent cycles, are observed from 1.55 to 0.8 V in the first cycle, denoting several irreversible reduction reactions.
Given the alloying mechanism and the annealing process, the irreversible reduction reaction is proposed as follows:
xLi+ + e- + (Sb2O3, SnO) surface→Li2O + (Sb, Sn)
[19, 36]. The CuO film generated in the open air is easily
surface
converted to Cu2O [29, 30], which is irreversibly lithiated under an inert gas and contributes to the irreversible
capacity. Except that, the curve also contains the decomposition of the electrolyte and formation of SEI film. A sharp
peak appears between 1 .0 V and 0.7 V, corresponding to the lithiation of SiSb to form Li3Sb alloy: SixSb + 3 Li+ + 3e-
→ Li3Sb + xSi. A series of peaks appears above 0.48 V corresponds to the lithiation of both the native and extruded Si,
such as Li0-1.7Si, Li1.71-2.33Si, Li2.33-3.25Si and Li3.75-4.2Si [31-33]. A strong reduction peak is observed from 0.1 to 0 V in
the first cycle and appeared weak and asymmetrical in subsequent cycles, exhibiting an irreversible phase transition
from the crystalline to amorphous state. For the anodic scan, three sharp oxidation peaks are noted at 0.46, 1.07 and
1.38 V (vs. Li/Li+), which migrate in the subsequent cycles with a stable peak strength correspond to the extraction of
Li+. The CV curves of Si0.8Sb anode material show the highest peak current and lowest oxidation/reduction current
loss, suggesting better electrochemical properties.
Figure 10 shows a comparison between impedance response and the representative fitting curves of SixSb after
the initial cycle. Radiuses of the half-arc in high frequency area before cycles are absolutely bigger than the radius
after cycles, which are mainly owing to the generation of LixSb and LixSi alloys on the surface during the first cycle.
The generated alloys blocks the transmission channels for the Li+, leading to increased impedance and decreased
conductivity. During the delithiation process, alloys decomposing (also called de-alloying) bring about a recovery of
the porous structure and a strengthening of the conductivity, which then reduce the internal impedance. Figure 11
illustrates the EIS of SixSb immiscible alloy anode materials. The internal impedance is enhanced along with the
cycles. These results are mainly attributed to the collapse of the porous structure and the blocked transmission
channels after continuous powdering and shredding of the active materials. The shredded powders covered on the
surface, prevented the Li+ from trapping into the active materials and then produce an increased interfacial resistance.
Ultimately, the total impedance is improved after several cycles.
4. Conclusions
The novel SixSb immiscible alloy anode materials were synthesized through a chemical reduction-MA method.
The materials exhibit a superior capacity and good cycle stability under different temperatures.
The silicon content affected the capacity a lot. Either the theoretical or actual capacities were low with a low
silicon content. In contrast, the volume expansion and internal stress increased with silicon contents, which destroyed

the anode structure and shredded the active particles, thereby impeding the ion transmission channels. When the
silicon content was 0.8, the anodes exhibited the best electrochemical property and cycleability, with a specific
capacity of 596.4 mAh·g-1 after 50 cycles. The cycle stability was improved by restricting the voltage ranges to
0.03-2.0V. The powdering and shredding of the anode materials after lithium ions trapping into the active electrode
materials were artificially restricted.
The contact resistance had tremendous influences on the capacity. In the immiscible SixSb system, the lithiation
products LixSi and LixSb served as buffering matrices for each other and thus substantially reduced the volume
expansion, maintained the electrode structure and reduced the variation in the contact resistance. Therefore, the
immiscible alloy anodes exhibit good electrochemical properties at different temperatures.
Acknowledgments
This work was financially supported by the National Natural Science Foundation of China (Grant#51374146,
50874074), Shenzhen Government’s Plan of Science and Technology (Grant #JCYJ20120613173950029,
JCYJ20130329113849606) and Open Research Fund of Shenzhen Key Laboratory of Functional Polymer (Grant #
FP20130002).

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Figure captions
Figure 1. XRD patterns of SixSb immiscible alloy materials
Figure 2. Images of (a) FE-SEM; (b) back-scattered image; (c) energy spectrum analysis and element mapping of
Si0.8Sb immiscible alloy materials (Si: red; Sb: blue)
Figure 3. Cycle performance of SixSb immiscible alloy anodes
Figure 4. EIS of SixSb immiscible alloy anodes over the open voltage before cycles
Figure 5. Cycle performance of Si0.8Sb immiscible alloy anodes under different temperatures
Figure 6. EIS of Si0.8Sb immiscible alloy anodes under different temperatures
Figure 7. Cycle performance of Si0.8Sb immiscible alloy anodes over different operating voltages
Figure 8. Initial charge–discharge curves of SixSb immiscible alloy anodes
Figure 9. CV curves of (a) Si0.6Sb; (b) Si0.8Sb; (c) SiSb; (d) Si1.2Sb and (e) Si1.4Sb immiscible alloy anodes
Figure 10. EIS of SixSb immiscible alloy anodes after the initial cycle
Figure 11. EIS of Si0.8Sb immiscible alloy anodes after different cycles

Fig. 1 XRD patterns of SixSb immiscible alloy materials
(a)
(b)
(c)
Element
Si
Weight%
16.21
Atomic%
43.72
Sb
83.79
56.28
Totals
100.00
100.00
Fig. 2 Images of (a) FE-SEM; (b) back-scattered image; (c) energy and element mapping spectrum
of Si0.8Sb immiscible alloy materials (Si: red; Sb: blue)

Fig. 3 Cycle performance of SixSb immiscible alloy anodes
Fig. 4 EIS of SixSb immiscible alloy anodes over the open voltage before cycles

Fig. 5 Cycle performance of Si0.8Sb immiscible alloy anodes under different temperatures
Fig. 6 EIS of Si0.8Sb immiscible alloy anodes under different temperatures

Fig. 7 Cycle performance of Si0.8Sb immiscible alloy anodes over different operating voltages
Fig. 8 Initial charge–discharge curves of SixSb immiscible alloy anodes

Fig. 9 CV curves of (a) Si0.6Sb; (b) Si0.8Sb;
(c) SiSb; (d) Si1.2Sb and (e) Si1.4Sb immiscible alloy anodes

Fig. 10 EIS of SixSb immiscible alloy anodes after the initial cycle
Fig. 11 EIS of Si0.8Sb immiscible alloy anodes after different cycles

Tables
Table 1
Impedance parameters of SixSb immiscible alloy anode prior to cycles
SixSb
Si0.6Sb
Si0.8Sb
SiSb
Rs /Ω
4.49
4.68
4.72
4.75
4.79
Rcf /Ω
132.6
138.5
142.3
163.7
171.2
Qg /F
0.002638
0.002743
0.002896
0.003569
0.003646
Si1.2Sb
Si1.4Sb
Table 2
Impedance parameters of Si0.8Sb immiscible alloy anode at various temperatures without cycles
T /℃
50
Rs /Ω
4.26
4.68
4.89
5.06
Rcf /Ω
112.6
138.5
145.8
156.7
Qg /F
0.002237
0.002728
0.003043
0.003765
25
0
−25

Hightlights:
1. The SixSb immiscible alloy was synthesized by chemical reduction-mechanical alloying methods.
2. The Si0.8Sb anodes exhibit the best electrochemical and cycle performances.
3. The volume expansion can be whittled by making lithiation products buffering matrices for each other.
4. The lithiation and delithiation reaction mechanism are investigated.