Improvement of the Anode Properties of Lithium-Ion Batteries for SiO x with a Third Element.

Silicon oxide (SiO x ) has been placed into practical use as an anode active material for next-generation Li-ion batteries because it has a higher theoretical capacity than graphite anodes. However, the synthesis method is typically vapor deposition, which is expensive, and the poor electron conductivity of SiO x restricts high performance. In this study, we prepared M/SiO x active materials consisting of SiO x and a third element (M = Al, B, Sn) using a low-cost mechanical milling (MM) method and investigated their electrode properties as Li-ion battery anodes. Also, the authors added a third element to improve the conductivity of the SiO2 matrix. Al, B, and Sn were selected as elements that do not form a compound with Si, exist as a simple substance, and can be dispersed in SiO2. As a result, we confirmed that SiO x has a nanostructure of nanocrystalline Si dispersed in an amorphous-like SiO2 matrix and that the third element M exists not in the nanocrystalline Si but in the SiO2 matrix. The electron conductivity of SiO x was improved by the addition of B and Sn. However, it was not improved by the addition of Al. This is because Al2O3 was formed in the insulator due to the oxidization of Al. The charge-discharge cycle tests revealed that the cycle life was improved from 170 cycles to 330 or 360 cycles with the addition of B or Sn, respectively. The improvement in electron conductivity is assumed to make it possible for SiO2 to react with Li ions more uniformly and form a structure that can avoid the concentration of stress due to the volume changes of Si, thereby suppressing the electrode disintegration.

Introduction

Lithium-ion batteries have been used in many types of devices, such as power supplies for laptop computers, because they are lighter and have a higher energy density than other secondary batteries. In recent years, owing to the demands of the higher performance of portable electronic devices and the electrification of automobiles, there has been a strong demand for energy densities higher than those exhibited by conventional materials. Therefore, it is necessary to further increase the capacities of the cathode and anode materials.

Currently, graphite is used as the anode material, and its initial capacity reversibility has reached 90% or higher. In addition, it has excellent cycle properties because the volume change during charge–discharge is small. However, its theoretical capacity is only 372 mA h g–1, and it is not expected to exceed this theoretical capacity.

Therefore, Si is an attractive active material as an anode for lithium-ion batteries because it is the same group 14 element as graphite and repeatedly alloyed and dealloyed reversibly with lithium ions. Si is an indispensable material for increasing capacity because it has a theoretical capacity (3600 mA h g–1) that is nearly 10 times that of graphite. However, the smooth redox reaction of alloying and dealloying with lithium ions cannot be performed because the electron conductivity of Si is low, and the diffusion of lithium ions is slow. Additionally, it causes a large volumetric change of approximately 380% during lithiation and delithiation, and the stress generated at that time causes cracks in the Si particles, causing the particles to fall out of the current collector. As a result, a rapid capacity decrease occurs because the contact between the active material, surrounding Si particles, and conductive material is interrupted, the Si particles are electrically isolated, and they are not involved in the subsequent charge–discharge reaction.

To address this problem, various approaches have been carried out.[1−20] For example, it has been reported that the yield stress exceeds the stress generated during charging by setting the Si crystallite size to 10 nm or less so that the cracking of Si particles is suppressed and the cycle properties are improved. In addition, it has been reported that the cracking of Si particles can be suppressed and the cycle properties can be improved by reducing the Si particle size to 150 nm or less.[21]

As a result of such various developments, in recent years, SiO has been installed in the anode material for Li-ion batteries of electric vehicles because it enables a longer driving range. SiO has a higher capacity than the current graphite. SiO is a mixed phase consisting of Si and SiO2. Our group has previously revealed that SiO is an amorphous material composed of a three-dimensional SiO4 tetrahedral network similar to silica (SiO2) glass and metallic Si clusters and that the Si clusters are finely dispersed in the SiO4 matrices.[22] Therefore, the SiO2 matrix is considered to exhibit better cycle properties than Si alone by relaxing the stress due to volume expansion during charge and discharge of Si.[23]

However, the capacity reduction of SiO during the charge–discharge cycle is remarkable compared to that of graphite. It is suggested that this is because the reaction with lithium ions is localized due to the poor electron conductivity of SiO and then the active material phase cracks, eventually leading to electrode collapse. Therefore, SiO used in the anode material of electric vehicles is also utilized as an anode material composed of a mixture with graphite. In the future, it is expected that the mixing ratio of SiO to graphite tends to increase because further increases in the driving range and extension of battery life are required. Therefore, it is necessary to improve the anode properties of SiO.

The main efforts to improve the anode properties of SiO have involved improving Si particles and imparting conductivity. Meanwhile, there are no reports that focus on the improvement of the properties of a SiO2 amorphous matrix with a third element. Therefore, the authors developed a new approach to improve the anode properties of SiO by improving the poor electron conductivity of the SiO2 matrix.

Figure shows a schematic illustration of the SiO structure designed by the authors in this study.[22] Conventional SiO has a structure of cluster-shaped Si dispersed in a SiO2 matrix having a SiO4 tetrahedral network structure. However, SiO2 itself is an insulator, and its electron conductivity is quite poor at 10–18 S cm–1. Therefore, the third element M (Al, B, Sn) was added to the SiO4 tetrahedral network structure. This is expected to improve the poor electron conductivity of the SiO2 matrix and promote the uniform reaction of lithium ions in the SiO electrode. Therefore, the authors thought that the damage to the electrodes was relatively small and the electrode collapse could be suppressed because the stress due to the volume expansion of Si was difficult to concentrate during charging and discharging.

Figure 1

Schematic illustration of the target SiO structure.

Conventional SiO is manufactured by mixing Si and SiO2, heating then cooling the mixture, precipitating the generated SiO gas, and precipitating fine Si through a disproportionation reaction (2SiO → Si + SiO2).[24] However, it is extremely difficult to control the proportion of Si because the boiling point of Si (3538 K) is much higher than that of SiO (2153 K). In addition, it is difficult to precisely add other elements with different boiling points. Therefore, the authors adopted the mechanical milling method because it enables the addition of materials without going through the gas phase. In this study, we evaluated the charge–discharge properties of the anode for a lithium-ion secondary battery of an electrode made of M/SiO prepared using the mechanical milling method and investigated the effect of the addition of the third element M on the anode properties.

Results and Discussion

Observation of Powder Shape

Figure shows the scanning electron microscopy (SEM) images of SiO and M/SiO powders prepared using the mechanical milling method. In each case, secondary particles with a size of approximately 5 μm were observed. The secondary particles showed irregular shapes. Therefore, it can be considered that the influence of the third element on the size and shape of the secondary particles was small. Subsequently, the shapes of the primary particles could not be clearly confirmed. Therefore, the primary particles are expected to have mixed on a scale smaller than several hundred nanometers.

Figure 2

SEM images of milled SiO and M/SiO (M = Al, B, Sn).

Structural Analysis of Powder

There was concern that each raw material powder would react or that the third element would dissolve in Si because of the high energy when the balls collide with each other in the powder prepared using mechanical milling. First, we checked whether the prepared material had a target structure (Figure ). It has a structure of cluster-shaped Si dispersed in a SiO2 matrix in which the third element (Al, B, Sn) is dispersed.

Figure a shows the X-ray diffraction (XRD) patterns of the SiO and M/SiO powders prepared using mechanical milling. The Si diffraction peaks of (111), (220), and (311) were observed for all of the powders. The crystallite size of these Si was calculated from the Scherrer equation and was found to be approximately 8–12 nm. In contrast, the diffraction peak of SiO2 did not appear. This is probably because SiO2 became amorphous-like owing to the high-energy milling of the mechanical milling.

Figure 3

X-ray diffraction patterns of milled SiO and M/SiO (M = Al, B, Sn) powders in the diffraction angle ranges of (a) 20–60° and (b) 25–32°.

Regarding the third element, the diffraction peaks of elemental substances, derivative compounds, oxides, etc. were not confirmed. First, we investigated the Si diffraction peak of (111) at approximately 28° that the third element was not dissolved in Si to disperse the third element in the SiO2 matrix. Figure b shows the X-ray diffraction pattern in the range of 25–32° of SiO and M/SiO (M = Al, B, Sn) powders. If the third element is dissolved in Si, the crystal lattice of Si should expand or contract and the diffraction peak should shift to the low- or high-angle side.[25] However, by comparing the powder with and without the addition of the third element, it was found that the position of the Si diffraction peak (111) at approximately 28° did not change at all. Thus, it is considered that the third element was not dissolved in Si, but it became amorphous and existed in the SiO2 matrix as intended.

From these results, it was confirmed that the powder with the third element prepared using mechanical milling was composed of amorphous-like SiO2 and nanocrystalline Si, and the third element was not present in Si.

Furthermore, the structures of the prepared powders were analyzed. Figure a shows a low-magnification bright-field image of the edge of the SiO particles using transmission electron microscopy. It is considered that the black spot-like part in the particle is Si and the gray area is SiO2. It was found that Si and SiO2 were finely pulverized after the mechanical milling treatment and Si formed a structure dispersed in the SiO2 matrix. Figure b shows a high-magnification bright-field image and electron diffraction of a SiO powder using transmission electron microscopy. Most of the gray areas, except the black spots, showed a halo pattern. It was considered that the areas were amorphous Si oxide because energy-dispersive X-ray spectroscopy (EDS) analysis of the part revealed that Si comprised 78 wt %, while O comprised 22 wt %. On the other hand, the black spot-like part of the red dashed line part (1) was confirmed to be elemental Si using electron diffraction. It was also found that the size of the Si microcrystals was approximately 10 nm. These results support the structure in which fine Si is dispersed in an amorphous SiO2 matrix, as predicted based on XRD results.

Figure 4

Transmission electron microscopy (TEM) images of a milled SiO particle at (a) low magnification and (b) high magnification, and (c) Al/SiO and (d) Sn/SiO particles at high magnification.

Similarly, we found that the black spot-like part of red dashed line parts (2) and (3) of the powders with third elements Al (Figure c) and Sn (Figure d) was elemental Si using electron diffraction and had a size of approximately 10 nm. Meanwhile, there was a difference in the amorphous SiO2 matrix, which was confirmed in the SiO particles. EDS analysis of these areas revealed compositions of Si 73 wt %, O 24 wt %, and Al 1.8 wt % for the Al/SiO powder, and Si 72 wt %, O 23 wt %, and Sn 2.1 wt % for the Sn/SiO powder. Therefore, it is highly possible that the added third element is dispersed in the amorphous SiO2 matrix.

The distribution of the third element was confirmed from the bright-field image and the EDS mapping images of Al, B, and Sn of the M/SiO particles in Figure . In the case of the powder with Al or Sn, elemental Al and Sn in microcrystals, such as Si, that were confirmed in Figure b–d were not confirmed, and it was found that Al and Sn were uniformly dispersed throughout the powder. Meanwhile, with respect to the powder with B, B was dispersed throughout the powder, but some large particles of approximately 1 μm were confirmed. It is presumed that the mechanical milling power was insufficient under the same mechanical milling conditions because B (Mohs hardness 9.5) is harder than Al (Mohs hardness 2.9) and Sn (Mohs hardness 1.8).

Figure 5

TEM images and EDS mappings of milled (a) Al/SiO, (b) B/SiO, and (c) Sn/SiO particles.

Figure shows the measurement results of the electrical resistivity of the pressed M/SiO powder. It was confirmed that the addition of B or Sn improved the electron conductivity by nearly an order of magnitude compared to the powder without the addition of the third element. On the other hand, the electron conductivity of the powder with Al did not improve because the electrical resistivity was equivalent to that of SiO.

Figure 6

Electrical conductivity of milled SiO and M/SiO (M = Al, B, Sn) powders under compression.

The reaction Gibbs energies (ΔrG°) of Al2O3, B2O3, and SnO2 are −594.61, 181.25, and 340.93 kJ mol–1, respectively.

In the case of the powder with B and Sn, ΔrG° was a positive value, and it can be found that the presence of SiO2 was more stable than that of B2O3 and SnO2. Meanwhile, in the case of the powder with Al, ΔrG° was negative, and it can be found that the presence of Al2O3 was thermodynamically more stable than SiO2. Therefore, it is presumed that Al2O3, which is an insulator, was formed because the oxidation reaction proceeded during sample preparation.

From these results, it is inferred that B and Sn[26] may have been dissolved in the SiO2 matrix during the mechanical milling method.

Charge–Discharge Properties

Figure shows the dependence of the discharge capacity of M/SiO (M = Al, B, Sn) electrodes on the cycle number in 1 M lithium bis(trifluoromethanesulfonyl)amide (LiTFSA)/propylene carbonate (PC) solution with a charge capacity limit of 1000 mA h g(Si)−1. For comparison, the SiO and Si electrodes were also evaluated. The Si alone electrode caused a rapid capacity decay after 100 cycles. Meanwhile, for the SiO electrode, the capacity decay was suppressed until 170 cycles. Subsequently, in the case of the Al/SiO electrode, the cycle properties were equivalent to those of the SiO electrode, and the electrode performance did not improve. However, it was found that electrodes with B and Sn can achieve a longer cycle life of 150 cycles or more. It is presumed that the addition of B and Sn improved the current-collecting property of the electrodes because it improved the electron conductivity of SiO by approximately 1 order of magnitude.

Figure 7

Dependence of the discharge capacity of M/SiO (M = Al, B, Sn) electrodes on cycle number in 1 M LiTFSA/PC solution with a charge capacity limit of 1000 mA h g(Si)−1 (the result of Si alone electrode is also shown).

To determine the reason for the improvement of the electrode properties as described above, an active material consisting only of a matrix was prepared and the electrode reaction was investigated. In addition, in the M/SiO2 samples, the reactivity with lithium ions due to the addition of the third element was investigated. In other words, to investigate how much lithium ions are occluded, we decided to conduct a test to examine the amount of lithium ions reacted without capacity regulation. Figure a shows the dependence of the discharge capacity of SiO2 and M/SiO2 (M = Al, B, Sn) electrodes on cycle number in 1 M LiTFSA/PC at 0.38 A g–1. The temperature and potential range for testing were set to 303 K and 0.005–2.000 V vs Li+/Li, respectively. It was found that the electrodes with B and Sn showed higher capacities than those of SiO2 without the addition of the third element. Originally, SiO2 hardly reacted with Li ions and did not exhibit Li storage properties. However, it has recently been reported that, when SiO2 becomes amorphous, the reactionproceeds, and it is possible to form silicon and lithium silicate (Li2Si2O5), due to lithium-ion activity.[27] The authors confirmed from Figures and 4 that SiO2 is amorphous. In addition, the charge–discharge curves and dQ/dV curves after 10 cycles were newly investigated for SiO2 and M/SiO2 (M = Al, B, Sn) electrodes. As a result, it was found that the Si single-phase peak was observed even though these were matrix-only electrodes. In particular, it appears clearly near 0.5 V on the discharge side. This also suggests that reaction is progressing. Therefore, in this study, it is considered that SiO2, which became amorphous after mechanical milling, showed charge–discharge capacity. Furthermore, it is considered that the electrode with B and Sn showed higher capacity than the SiO2 electrode because the reactivity with the lithium ions in the matrix was improved by the solid dissolution of B and Sn in the SiO2 matrix and the uniform dispersion of B and Sn (Figure b). Meanwhile, it is considered that Al was oxidized and formed amorphous Al2O3, and it is dispersed in SiO2 because the electron conductivity of Al/SiO is equivalent to that of SiO. Therefore, it is presumed that the capacity of the Al/SiO2 electrode did not increase because the reactivity with lithium ions could not be improved and reaction was not promoted.

Figure 8

Dependence of the (a) discharge capacity of SiO2 and M/SiO2 (M = Al, B, Sn) electrodes on cycle number in 1 M LiTFSA/PC at 0.38 A g–1. The temperature and potential range for the testing were set to 303 K and 0.005–2.000 V vs Li+/Li, respectively. (b) Schematic illustration of SiO2 and M/SiO2 (M = B, Sn) reaction with Li ions.

From these results, we consider the mechanism of extending the life of the cycle properties by adding B and Sn to SiO. Figure shows a schematic illustration of the M/SiO (M = B, Sn) performance improvement mechanism. Si exhibits the following two-step lithium alloying reaction during charging.[28−31] If reaction progresses, the electrode will collapse because the volume change (380%) due to the formation of Li3.75Si in reaction is larger than the volume change (240%) due to the formation of Li2.00Si in reaction (“a” in a-Si and a-Li2.00Si means amorphous, and “c” in c-Li3.75Si means crystalline).

Figure 9

Schematic illustration of the M/SiO (M = B, Sn) performance improvement mechanism.

In the case of a charge capacity limit of 1000 mA h g–1, it is considered that lithium alloying of Si occurs locally because the electrodes without the addition of the third element or with the addition of Al have low reactivity with lithium ions in the SiO2 matrix. As a result, Li3.75Si, which has a large volume change, was formed, which is thought to have caused electrode collapse and capacitance decline. Meanwhile, in the case of the electrode with B or Sn, the electron conductivity was improved, and the lithium-ion reactivity of the SiO2 matrix was increased. Thus, Si in the entire active material phase can easily react with lithium ions more uniformly. Therefore, it was possible to suppress the formation of Li2.00Si, which has a small volume change. Therefore, it is considered that the electrode with B or Sn improved the cycle properties because the stress due to the volume expansion of Si was difficult to concentrate during charging, and the damage to the electrodes was relatively small and the electrode collapse could be suppressed.

Conclusions

In this study, we prepared an active material (M/SiO) with a third element (M = Al, B, Sn) in SiO using a mechanical milling method and investigated the anode properties of Li-ion batteries. We confirmed that the structure of SiO consists of nanocrystalline Si dispersed in an amorphous-like SiO2 matrix, and a third element is present in the SiO2 matrix but not in the nanocrystalline Si. The electron conductivities of B/SiO and Sn/SiO were higher than that of SiO. Meanwhile, the electron conductivity of Al/SiO was not higher than that of SiO. This is because Al2O3 was formed in the insulator due to the oxidization of Al. In the cycle properties test conducted with a charge (Li storage) capacity limit of 1000 mA h g–1, it was found that the cycle life was improved from 170 cycles to 330 or 360 cycles in the powder with B or Sn, respectively. When SiO2 becomes amorphous, the reaction 5SiO2 + 4Li+ + 4e– → 2Li2Si2O5 + Si (1) proceeds, and it is possible to form silicon and lithium silicate (Li2Si2O5), due to lithium-ion activity. The electron conductivity was improved because they were present in the matrix and B or Sn was dispersed in the SiO2 matrix. Therefore, it is considered that this is because SiO2 reacts uniformly with lithium ions due to the improvement of electron conductivity so that the stress due to the volume change of Si is difficult to concentrate and the destruction of the electrode is reduced.

Experimental Section

Sample Preparation

Preparation of SiO and M/SiO (M = Al, B, Sn) Powder

Normal Si powder was prepared using a mass-produced gas-atomizing device. A flake-shaped Si raw material (purity 98.7%) of approximately 10–20 mm was placed in a crucible with pores of φ2.5 mm at the bottom of the crucible and heated and melted in a dry argon gas atmosphere using a high-frequency induction melting furnace. The molten metal was then discharged at 1823 K. N2 gas was sprayed on the molten metal at the part directly below the pores, and it was solidified at a cooling rate of approximately 100–2 K s–1. As a result, a gas-atomized Si powder was obtained. This powder was classified using a sieve with an opening of 300 μm.

To prepare the SiO powder, a mixture of the above-mentioned gas-atomized Si powder and commercially available SiO2 powder (Kojundo Chemical Lab. Co. Ltd., purity 99.9%) was placed in an austenite-based stainless steel vessel together with high-carbon chromium-bearing steel (C 1%, Cr 1%) balls (φ19 mm) with a Si:SiO2 weight ratio of 54:46. The amount of each powder was 32.4 g for the Si powder and 27.6 g for the SiO2 powder. The weight of each ball was 12 kg. The weight ratio of the active material to the balls was 1:200.

To prepare the M/SiO powder, a mixture of gas-atomized Si powder and commercially available SiO2 powder and the third element M (Al: purity 99.9%, Kojundo Chemical Lab. Co. Ltd., B: purity 99.9%, Kojundo Chemical Lab. Co. Ltd., Sn: purity 99.0%, Kojundo Chemical Lab. Co. Ltd.) was placed in an austenite-based stainless steel vessel together with high-carbon chromium-bearing steel balls with a Si:SiO2:M weight ratio of 52:45:3. The amount of each powder was 31.4 g for Si powder and 26.8 g for SiO2 powder and 1.8 g for M (Al, B, Sn) powder. The weight of each ball was 12 kg.

These vessels were sealed, the interior was evacuated to a pressure of 0.1 MPa, and dry argon gas was sealed through gas replacement. The vessel was set in a vibrating ball mill device (MB-1 type manufactured by Chuo Kakohki Co. Ltd.). After 50.4 ks of mechanical milling treatment under the specified conditions (amplitude: ± 4 mm, frequency: 1200 rpm), the number of balls was increased, the weight ratio of the active materials to the balls was 1:300, and the mechanical milling was repeated for 50.4 ks.

The obtained mechanical milling powder was adjusted to a particle size of 10 μm or less due to collisions between powders in a 0.7 MPa N2 gas stream using a jet mill device (Co-Jet manufactured by SEISHIN ENTERPRISE Co. Ltd.) to crush the agglomerated powder. The target powder was obtained using this process.

Preparation of M/SiO2 and SiO2 Powder

For comparison, the same powder preparation was performed by adding only SiO2 and the third element M, without adding the gas-atomized Si powder. Consequently, the change in the properties (reactivity with lithium ions) of the SiO2 matrix due to the presence of the third element M was investigated.

Commercially available SiO2 powder was weighed and placed in a zirconia vessel filled with φ5 mm zirconia balls. Additionally, SiO2 powder and the third element powder (Al powder: purity 99.9% FUJIFILM Wako Pure Chemical Corporation, B powder: purity 99.0% FUJIFILM Wako Pure Chemical Corporation, Sn powder: purity 99.9%, 325 mesh RARE METALLIC Co., Ltd.) were placed in a zirconia vessel together with φ5 mm zirconia balls with a SiO2:M weight ratio of 94:6 (powder: 1.5 g, ball: 100 g).

The vessel was then sealed and set in the Premium Line planetary ball mill device (PL-7 type). Each powder was subjected to a mechanical milling treatment (SiO2: 7.2 ks, Al/SiO2: 14.4 ks, B/SiO2: 7.2 ks, Sn/SiO2: 7.2 ks) at 380 rpm to obtain the target powder.

Analysis of the Obtained Sample

The Si crystallite sizes of the prepared SiO and M/SiO powders were measured using X-ray diffraction (XRD, RINT-2500, Rigaku Corporation, Cu Kα, 50 kV, 200 mA, 4° min–1, 20–60°).

The morphologies of the powders were observed using a scanning electron microscope (JSM-6490LV, 5 kV, JEOL Ltd.). In addition, the prepared powders were attached to conductive tape for observation.

The size and dispersibility of nanocrystalline Si and the third elements were observed using a transmission electron microscope (JEM-F200, 200 kV, JEOL Ltd.). The preparation of the observation samples is described below. First, the prepared powder was embedded in a conductive thermosetting resin. Subsequently, a carbon-protective film was deposited on the sample surface. Finally, these samples were cut to a size of approximately 10 μm × 10 μm × thickness 100 nm using a high-performance focused ion beam device (MI4050, Mo mesh; Hitachi High-Tech Corporation) and used as an observation sample.

The electron conductivity of the obtained powder was evaluated using a powder resistivity measuring unit (MCP-PD51, Nittoseiko Analytech Co. Ltd., four-probe device). Approximately 3 g of the prepared powder was placed in a sample holder of φ10 mm and compressed to a maximum of 64 MPa to measure the volumetric electron conductivity.

Electrode Fabrication

SiO, M/SiO powder, SiO2, and M/SiO2 powder were each mixed with acetylene black, carboxymethyl cellulose, and styrene-butadiene rubber at a weight ratio of 70:15:10:5 using a kneading machine. These were then applied on a Cu foil with a coating amount of approximately 1.0 mg cm–2 to obtain a mixture electrode.

Cell Assembly and Charge–Discharge Tests

For the charge–discharge test, a 2032-type coin was constructed, composed of the above electrode as the working electrode, a Li metal sheet as the counter electrode, and a glass fiber filter as the separator. Lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) dissolved in propylene carbonate (PC) was used at the concentration of 1 M. Cell assembly and electrolyte preparation were conducted in an Ar-filled glovebox (Miwa MFG, DBO-2.5LNKP-TS) with an oxygen content less than 1 ppm and dew point below 173 K. Also, the authors want to show that this material can be used in cold climates. Therefore, it is evaluated on a PC (MP 223 K), which has a lower melting point than EC (MP 311 K) and is hard to freeze.

Regarding the SiO and M/SiO electrodes, galvanostatic charge–discharge cycling tests were performed using an electrochemical measurement system in the potential range of 0.005–2.000 V vs Li+/Li. In addition, the current density and measurement temperature were set to 1.60–1.93 A g–1 (1C) and 303 K, respectively. Electrochemical measurements were performed with a charge limit of 1000 mA h g–1. In this study, we considered it to be a mixture of Si and SiO2 and treated SiO2 as being inactive with lithium ions. The theoretical capacitance was calculated assuming that only Si reacted with lithium ions. The maximum alloying composition in this case was calculated to be Li15Si4. In this case, the theoretical capacity of each powder was calculated to be 1931 mA h g–1 for SiO, 1890 mA h g–1 for Al/SiO, 1860 mA h g–1 for B/SiO, and 1890 mA h g–1 for Sn/SiO. Regarding SiO2 and M/SiO2 electrodes, galvanostatic charge–discharge tests were performed with a potential range of 0.005–2.000 V vs Li+/Li, a current density of 0.38 A g–1, and a measurement temperature of 303 K.