Negative electrode active material and method for producing the same

Abstract

To provide a negative electrode active material that can increase capacity while maintaining battery characteristics. [Solution] A negative electrode active material having negative electrode active material particles, wherein the negative electrode active material particles include a porous carbon structure which is a matrix material, the porous carbon structure has a structure in which some of the pores formed inside communicate with other pores, amorphous low-valence nanosilicon compounds are dispersed inside the porous carbon structure, Si-C bonds exist in at least a portion of the low-valence nanosilicon compounds, and the porous carbon structure and the low-valence nanosilicon compounds are detachably bonded to each other.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode active material and a method for producing the same. [Background technology]

[0002] In recent years, small electronic devices such as mobile terminals have become widespread, and there is a strong demand for further miniaturization, weight reduction, and longer lifespan. In response to these market demands, development is progressing on secondary batteries that are particularly small, lightweight, and capable of achieving high energy density. These secondary batteries are being considered not only for small electronic devices but also for large electronic devices such as automobiles, and for power storage systems such as those found in homes.

[0003] Among these, lithium-ion secondary batteries are highly anticipated because they are easy to miniaturize and increase capacity, and they can achieve a higher energy density than lead-acid batteries and nickel-cadmium batteries.

[0004] The lithium-ion secondary battery described above comprises an electrolyte along with a positive electrode, a negative electrode, and a separator, and the negative electrode contains a negative electrode active material that is involved in the charge and discharge reaction.

[0005] While carbon-based active materials are widely used as negative electrode active materials, recent market demands require further improvements in battery capacity. To improve battery capacity, the use of silicon as a negative electrode active material is being considered. This is because the theoretical capacity of silicon (4199 mAh / g) is more than 10 times greater than that of graphite (372 mAh / g), thus promising a significant increase in battery capacity. Development of silicon materials as negative electrode active materials involves not only pure silicon but also compounds such as alloys and oxides. Furthermore, the shape of the active material is being considered, ranging from the standard coated type for carbon-based active materials to an integrated type directly deposited on the current collector.

[0006] However, when silicon is used as the main raw material for the negative electrode active material, the negative electrode active material expands and contracts during charging and discharging, making it prone to cracking, mainly near the surface of the negative electrode active material. In addition, ionic substances are generated inside the active material, making the negative electrode active material more susceptible to cracking. When the surface of the negative electrode active material cracks, a new surface is created, increasing the reaction area of ​​the active material. At this time, a decomposition reaction of the electrolyte occurs on the new surface, and a film of electrolyte decomposition products is formed on the new surface, thus consuming the electrolyte. As a result, the cycle characteristics tend to deteriorate.

[0007] To date, various studies have been conducted on negative electrode active materials and electrode configurations for lithium-ion secondary batteries, primarily using silica materials, in order to improve the initial efficiency and cycle characteristics of batteries.

[0008] Specifically, to obtain good cycle characteristics and high safety, silicon and amorphous silicon dioxide are deposited simultaneously using a vapor phase method (see, for example, Patent Document 1). In addition, to obtain high battery capacity and safety, a carbon material (electron conductive material) is provided on the surface of the silicon oxide particles (see, for example, Patent Document 2). Furthermore, in order to improve cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is prepared, and an active material layer with a high oxygen ratio near the current collector is formed (see, for example, Patent Document 3). In addition, in order to improve cycle characteristics, oxygen is incorporated into the silicon active material, and it is formed so that the average oxygen content is 40 at% or less, and the oxygen content is higher near the current collector (see, for example, Patent Document 4).

[0009] Furthermore, to improve the initial charge-discharge efficiency, Si phase, SiO2, M y A nanocomposite containing a metal oxide is used (see, for example, Patent Document 5). In addition, to improve the cycle characteristics, SiO x(0.8 ≤ x ≤ 1.5, particle size range = 1 μm to 50 μm) is mixed with a carbon material and fired at high temperature (see, for example, Patent Document 6). Further, in order to improve cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is set to 0.1 to 1.2, and the active material is controlled within a range where the difference between the maximum value and the minimum value of the molar ratio near the interface between the active material and the current collector is 0.4 or less (see, for example, Patent Document 7). Further, in order to improve the battery load characteristics, a metal oxide containing lithium is used (see, for example, Patent Document 8). Further, in order to improve cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface layer of the silicon material (see, for example, Patent Document 9).

[0010] Further, in order to improve cycle characteristics, silicon oxide is used, and conductivity is imparted by forming a graphite film on its surface layer (see, for example, Patent Document 10). In Patent Document 10, regarding the shift value obtained from the Raman spectrum of the graphite film, broad peaks appear at 1330 cm -1 and 1580 cm -1 , and the intensity ratio I 1330 / I 1580 is such that 1.5 < I 1330 / I 1580 < 3. Further, in order to improve high battery capacity and cycle characteristics, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used (see, for example, Patent Document 11). Further, in order to improve overcharge and overdischarge characteristics, a silicon oxide in which the atomic ratio of silicon to oxygen is controlled to 1:y (0 < y < 2) is used (see, for example, Patent Document 12).

[0011] Further, a lithium ion secondary battery using silicon oxide was shipped by Hitachi Maxell in June 2010 as a rectangular secondary battery for smartphones that adopted a nanosilicon composite (see, for example, Non-Patent Document 1). The silicon oxide proposed by Hohl is a composite material of Si 0+ ~Si 4+ and has various oxidation states (Non-Patent Document 2). Further, Kapaklis has proposed a disproportionation structure that is divided into Si and SiO2 by applying a heat load to silicon oxide (Non-Patent Document 3).

[0012] Miyachi et al. have focused on Si and SiO2 that contribute to charge and discharge among silicon oxides having disproportionated structures (Non-Patent Document 4), and Yamada et al. have proposed the following reaction formula between silicon oxide and Li (Non-Patent Document 5). 2SiO(Si + SiO2) + 6.85Li + + 6.85e - → 1.4Li 3.75 Si + 0.4Li4SiO4+ 0.2SiO2 In the reaction formula, Si and SiO2 constituting the silicon oxide react with Li and are divided into Li silicide, Li silicate, and a part of unreacted SiO2.

[0013] The Li silicate generated here is irreversible and is generally said to be a stable substance that does not release Li after once formed. The capacity per mass calculated from this reaction formula has a value close to the experimental value and is recognized as the reaction mechanism of silicon oxide. Kim et al. have identified the irreversible component associated with the charge and discharge of silicon oxide, Li silicate as Li4SiO4, 7 using Li-MAS-NMR and 29 Si-MAS-NMR (Non-Patent Document 6).

[0014] This irreversible capacity is the most disadvantageous part of silicon oxide and improvement is required. Therefore, Kim et al. have used the Li pre-doping method to form Li silicate in advance, significantly improving the initial efficiency as a battery and producing a negative electrode that can withstand actual use (Non-Patent Document 7). In addition, a method of treating powder instead of doping the electrode with Li has also been proposed, realizing improvement of the irreversible capacity (Patent Document 13).

[0015] On the other hand, the Li metal used for Li doping has extremely large upper and lower limits of price depending on the market situation, and there are many problems when considered as industrialization. Therefore, by using silane gas in porous carbon and generating nano-silicon inside, CVD-Si-C can achieve a higher energy density than Li-doped SiO (Patent Documents 14 and 15).

[0016] Also, paying attention to the problem that an excessive amount of silicon is deposited on the surface due to the small pore diameter of the porous carbon material, resulting in an increase in the electrical resistivity, in order to reduce the electrical resistivity, composite particles that do not contain SiC (silicon carbide) or have an extremely low SiC content have been proposed (Patent Document 16).

Prior Art Documents

Patent Documents

[0017]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

Patent Document 11

Patent Document 12

Patent Document 13

Patent Document 十四

Patent Document 15

[0018] [Non-licensed Document 1] Battery Industry Association Official Paper "Denchi", May 1, 2013, page 10 [Non-licensed Document 2] A. Hohl, T. Wieder, PA van Aken, TE Weirich, G. Denninger, M. Vidal, S. Oswald, C. Deneke, J. Mayer, and H. Fuess : J. Non-Cryst. Solids, 320, (2003), 255. [Non-licensed Document 3] V. Kapaklis, J. Non-Crystalline Solids, 354 (2008) 612 [Non-licensed Document 4] Mariko Miyachi, Hironori Yamamoto, and Hidemasa Kawai, J. Electrochem. Soc. 2007 volume 154, issue 4, A376-A380 [Non-licensed Document 5] M. Yamada, A. Inaba, A. Ueda, K. Matsumoto, T. Iwasaki, T. Ohzuku, J. Electrochem. Soc., 159, A1630 (2012) [Non-licensed Document 6] Taeahn Kim, Sangjin Park, and Seung M. Oh, J. Electrochem. Soc. volume 154, (2007), A1112-A1117. [Non-licensed Document 7] Hye Jin Kim, Sunghun Choi, Seung Jong Lee, Myung Won Seo, Jae Goo Lee, Erhan Deniz, Yong Ju Lee, Eun Kyung Kim, and Jang Wook Choi,. Nano Lett. 2016, 16, 282-288. [Non-Patent Document 8] The Cutting Edge of Automotive Lithium-ion Battery Development, pp. 96-111, CMC Publishing, November 27, 2020. [Overview of the Initiative] [Problems that the invention aims to solve]

[0019] As mentioned above, in recent years, small electronic devices such as mobile terminals have become more high-performance and multi-functional, and there is a need for increased battery capacity in the lithium-ion secondary batteries that are their main power source. One way to solve this problem is to develop a lithium-ion secondary battery in which the negative electrode is made mainly of silica material.

[0020] Furthermore, lithium-ion secondary batteries using silica materials are desired to have initial charge-discharge characteristics and cycle characteristics close to those of lithium-ion secondary batteries using carbon-based active materials. Therefore, cycle characteristics and initial charge-discharge characteristics have been improved by using silicon oxide modified by insertion and partial desorption of Li as the negative electrode active material. Recently, by mainly using silicon oxide and pre-containing Li to produce Li silicate, the irreversible capacity, which is a disadvantage of silicon oxide, has been reduced, and such products have actually begun to be marketed. Even when a battery using this silicon oxide with Li, Li-SiO-C (Non-Patent Literature 8), is prototyped and 100% replaced with carbon negative electrode material, the capacity improvement compared to carbon negative electrode material is limited to the high 20% range. This means that further improvements in battery capacity are required when considering the high performance of small electronic devices (5G, etc.) and the increased driving range of electric vehicles.

[0021] Therefore, CVD-Si-C, which has a low irreversible capacity, was developed, but it has been found that its fast charging capability and battery cycle characteristics are insufficient due to the reaction between Si and the electrolyte.

[0022] Furthermore, Li-Si compounds generally have a problem where the electrolyte decomposes each time a new surface is created during repeated charging and discharging.

[0023] The present invention has been made in view of the above-mentioned problems, and aims to provide a negative electrode active material that can increase capacity while maintaining battery characteristics. [Means for solving the problem]

[0024] To solve the above problems, the present invention provides a negative electrode active material having negative electrode active material particles, wherein the negative electrode active material particles include a porous carbon structure as a base material, the porous carbon structure has a structure in which some of the pores formed inside communicate with other pores, amorphous low-valence nanosilicon compounds are dispersed inside the porous carbon structure, Si-C bonds exist at least in part of the interface between the porous carbon structure and the low-valence nanosilicon compounds, and the porous carbon structure and the low-valence nanosilicon compounds are peelably bonded.

[0025] The negative electrode active material of the present invention has amorphous low-valence nanosilicon oxide dispersed inside a porous carbon structure. Therefore, the presence of the porous carbon structure reduces the adverse effects of expansion of the internal low-valence nanosilicon oxide. Furthermore, the presence of Si-C bonds in at least a portion of the negative electrode active material particles stabilizes the structure and improves water resistance. Additionally, some of the internally formed pores communicate with other pores, and the porous carbon structure and the low-valence nanosilicon compound are detachably bonded, significantly improving the diffusivity of Li. As a result, batteries using negative electrode active materials with these properties can exhibit good battery characteristics.

[0026] In this case, it is preferable that the low-valence nanosilicon oxide in the range of 50 nm from the surface of the negative electrode active material particles has a different structure from the Si phase structure in the bulk portion deeper than 50 nm from the surface of the negative electrode active material particles.

[0027] This structure allows for even more effective improvement of water resistance.

[0028] Furthermore, it is preferable that the low-valent nanosilicon oxide is substantially in a composite state of 0, 1, 2, and 3 valent states.

[0029] By using such silicon oxides, it is possible to maintain a lower irreversible capacity than that of general SiO.

[0030] Furthermore, the pore diameter of the pores in the porous carbon structure has discontinuous changes, and it is preferable that, when measuring the pore diameter distribution using the BJH method with nitrogen gas, the relationship between the pore volume A of micropores with a diameter of 1.8 to 2 nm, the pore volume B of mesopores with a diameter of 10.0 to 22.0 nm, the pore volume C of mesopores with a diameter of 25.0 nm to 42.0 nm, and the pore volume D of macropores with a diameter of 50.0 nm to 102 nm is such that the ratio B / A is 0.03 or higher, the ratio C / A is 0.01 or higher, and the ratio D / A is 0.01 or higher.

[0031] This type of pore size distribution increases the probability of silane decomposition, which in turn allows for an increase in the amount of silicon packed into the pores. As a result, it leads to an improvement in battery capacity.

[0032] Furthermore, it is preferable that the negative electrode active material particles have a carbon layer separate from the porous carbon matrix on part or all of their surface, and that a C=O or CO bond is formed at the interface.

[0033] Having C=O or CO bonds strengthens the adhesion of the carbon layer. Therefore, a robust structure can be achieved, for example, maintaining integrity even when subjected to high-speed shear during slurry preparation.

[0034] Furthermore, the grain size of zero-valent Si constituting the low-valent nanosilicon oxide, calculated using Scherrer's formula from the peaks measured by X-ray diffraction of the negative electrode active material particles, is preferably in the range of 0.8 nm to 5 nm. In addition, the low-valent nanosilicon oxide of the negative electrode active material particles is preferably substantially amorphous.

[0035] Furthermore, the total amount of oxygen contained in the negative electrode active material particles is preferably in the range of 0.3 wt% or more and 8 wt% or less.

[0036] This amount of oxygen allows for a higher battery capacity.

[0037] Furthermore, the present invention relates to a method for producing a negative electrode active material having negative electrode active material particles, comprising the steps of: preparing a porous carbon structure as a base material; incorporating OH groups into the active sites contained in the porous carbon structure; placing the porous carbon structure in a heating container; heating the porous carbon structure in the heating container and placing it under a gas flow, confirming that carbon monoxide gas or carbon dioxide gas originating from oxygen atoms contained in the active sites is detected in the exhaust process under the heating; and, while the carbon monoxide gas or carbon dioxide gas originating from oxygen atoms is detected in the exhaust process, introducing monosilane gas into the heating container. The present invention provides a method for producing a negative electrode active material, comprising the steps of: flowing a gas through a positive pressure atmosphere of 25 kPa to 80 kPa to decompose monosilane gas, thereby depositing silicon oxide containing dangling bonds, and depositing silicon oxide partially bonded to the oxygen atoms of the porous carbon inside the porous carbon structure; oxidizing at least a portion of the Si contained in the silicon oxide present on the surface layer of the porous carbon in a reduced pressure atmosphere; and depositing a carbon layer at 600°C or below using a hydrocarbon gas after the oxidation.

[0038] With this method of producing a negative electrode active material, as described above, an anode active material containing a low-valence nanosilicon oxide with a controlled phase structure, in which amorphous low-valence nanosilicon oxide is dispersed inside a porous carbon structure, Si-C bonds exist, and the porous carbon structure and the low-valence nanosilicon compound are detachably bonded, can be produced simply and efficiently.

[0039] In this case, when forming the low-valent nanosilicon compound by the decomposition of the monosilane gas, the monosilane gas can undergo a reaction via silylene through a single-molecule thermal decomposition reaction in the gas phase.

[0040] The above-mentioned negative electrode active material can be manufactured using this principle. [Effects of the Invention]

[0041] The negative electrode active material of the present invention has amorphous low-valence nanosilicon oxide dispersed inside a porous carbon structure. The presence of the porous carbon structure reduces the adverse effects of expansion of the internal low-valence nanosilicon oxide. Furthermore, the presence of Si-C bonds in at least a portion of the negative electrode active material particles stabilizes the structure and improves water resistance. Additionally, some of the internally formed pores communicate with other pores, and the porous carbon structure and the low-valence nanosilicon compound are detachably bonded, allowing for the formation of soft silicon without a scaffold structure. Moreover, the interior of the silicon compound thus deposited exhibits high Li diffusivity, significantly improving Li diffusion. As a result, batteries using negative electrode active materials with these properties can exhibit excellent battery characteristics.

[0042] Furthermore, the present invention provides a simple and efficient method for producing a negative electrode active material in which amorphous low-valence nanosilicon oxide is dispersed inside a porous carbon structure, Si-C bonds exist, and the phase structure of the low-valence nanosilicon oxide is controlled, and the porous carbon structure and the low-valence nanosilicon compound are detachably bonded. [Brief explanation of the drawing]

[0043] [Figure 1] This is a cross-sectional view showing the configuration of a negative electrode containing the negative electrode active material of the present invention. [Figure 2] This is an exploded view showing an example of the configuration (laminated film type) of a lithium-ion secondary battery containing the negative electrode active material of the present invention. [Figure 3] This is a flowchart illustrating an example of a method for producing the negative electrode active material of the present invention. [Modes for carrying out the invention]

[0044] The following describes embodiments of the present invention, but the present invention is not limited thereto.

[0045] As mentioned above, one method for increasing the battery capacity of lithium-ion secondary batteries is to use a negative electrode made primarily of low-valence nanosilicon oxide in a carbon structure. A lithium-ion secondary battery using this active material is desired to exhibit battery characteristics close to those of lithium-ion secondary batteries using carbon-based active materials, while also achieving a high battery capacity.

[0046] Therefore, the present inventors diligently conducted research to obtain a negative electrode active material that, when used as the negative electrode of a secondary battery, can improve initial charge-discharge characteristics while obtaining high cycle characteristics and increasing battery capacity, leading to the present invention.

[0047] The anode active material of the present invention is an anode active material having anode active material particles, wherein the anode active material particles include a porous carbon structure which is a matrix material, the porous carbon structure has a structure in which some of the pores formed inside communicate with other pores, amorphous low-valence nanosilicon compounds are dispersed inside the porous carbon structure, Si-C bonds exist at least in part of the interface between the porous carbon structure and the low-valence nanosilicon compounds, and the porous carbon structure and the low-valence nanosilicon compounds are peelably bonded.

[0048] A manufacturing method for producing such a negative electrode active material will be described later.

[0049] [The negative electrode active material of the present invention] First, the anode active material of the present invention will be described. Since the above anode active material has amorphous low-valence nanosilicon oxide dispersed inside a porous carbon structure, the presence of the porous carbon structure can reduce the adverse effects caused by the expansion of the low-valence nanosilicon oxide inside.

[0050] Furthermore, the presence of Si-C bonds in at least a portion of the negative electrode active material particles stabilizes the structure and improves water resistance. As a result, batteries using negative electrode active materials with these properties can have good battery performance. In addition, some of the pores formed internally have a structure that communicates with other pores, and the porous carbon structure and the low-valence nanosilicon compound are detachably bonded, thereby forming soft silicon without a scaffold structure. Moreover, the interior of the silicon compound deposited in this way has high Li diffusion, so the diffusion of Li can be greatly improved. As a result, batteries using negative electrode active materials with these properties can have good battery performance. Note that "detachable" means that the porous carbon and the low-valence silicon oxide are not strongly bonded by chemical bonds or the like, and are in a state where they can be detached (separated). In other words, this indicates that the low-valence silicon oxide is deposited in the pores of the porous carbon structure without forming a scaffold structure.

[0051] Also, common SiO is Si 4+ Although the silicon-O bond is an irreversible component, the negative electrode active material of the present invention contains amorphous low-valence nanosilicon oxide, thus maintaining a lower irreversible capacity than SiO. Furthermore, the Si-O bond can suppress the decomposition of the electrolyte, making it possible to reduce the SEI (Solid Electrolyte Interphase) deposited on the surface. In this invention, it is sufficient that the amorphous low-valence nanosilicon oxide is dispersed inside a porous carbon structure, and some of the nanosilicon oxide may be crystalline.

[0052] As described later, the negative electrode active material of the present invention can be manufactured as a Si-Ox material with siloxane bonds in the Si phase, in order to suppress the electrolyte decomposition reaction, which is insufficient for CVD-Si-C produced from general silane gas. The purpose of intentionally creating Si-O bonds is that while Si-Si bonds promote the decomposition of the electrolyte, Si-O bonds react with the electrolyte more slowly than Si-Si bonds. Furthermore, since Si-O bonds can suppress the decomposition of the electrolyte, it is possible to reduce the SEI deposited on the surface layer of CVD-Si-C. As a result, the battery cycle characteristics are improved. In addition, grain boundaries in grains with Si-Si bonds reduce Li diffusion, while Si-O bonds allow for good Li diffusion, improving fast charging performance. Since the main part of the material of the present invention that contributes to charging and discharging is a low-valence nanosilicon oxide, it can be defined as CVD-SiOx-C in contrast to CVD-Si-C. Thus, the manufactured active material can have high energy density and fast charging performance while maintaining the battery cycle characteristics.

[0053] Furthermore, in the negative electrode active material of the present invention, the presence of low-valence nanosilicon oxides and Si-C bonds can be measured by the following measurement method.

[0054] First, the negative electrode active material particles 29In the spectrum obtained from Si-MAS-NMR, it is preferable that a peak originating from Si-C bonds is obtained in the range of 0 to -30 ppm, and a peak originating from Si or low-valent Si oxide is obtained near -40 to 80 ppm. The presence of these peaks can more reliably indicate the presence of Si-C bonds and low-valent nanosilicon oxides.

[0055] Furthermore, in the anode active material of the present invention, it is preferable that the low-valence nanosilicon oxide in the range of 50 nm from the surface of the anode active material particles has a different structure from the Si phase structure in the bulk portion deeper than 50 nm from the surface of the anode active material particles. Such different phases of low-valence nanosilicon oxide can be identified by XANES measurement. Specifically, the total electron yield (TEY) method obtained from the XANES Si-k edge spectrum shows the surface layer up to 50 nm, and the X-ray fluorescence (PFY) method can detect information about the bulk interior of about 5 μm.

[0056] Furthermore, XANES (X-ray Absorption Near-Edge Structure) measurements can be performed, for example, under the following conditions. • Aichi Synchrotron Radiation Center, using BL6N1 line • Samples were prepared in an Ar atmosphere, airless, stored in a transfer vessel, and connected to the BL6N1 line for measurement under the following conditions. • Acceleration energy: 1.2 GeV • Accumulated current value: 300mA • Monochromatization conditions: White X-rays from a bending magnet are monochromatized using a two-crystal spectrometer and used for measurement. • Light focusing conditions: Light focusing in both vertical and horizontal directions using a Ni-coated bent cylindrical mirror. • Upstream slit opening: 10.0 mm horizontally x 3.0 mm vertically • Beam size: 2.0mm horizontally x 1.0mm vertically • Incidence angle to the sample: 45 degrees (incidence angle 45 degrees), so fluorescence yield can be measured simultaneously. • Energy calibration: Calibration of the peak position at the SK end of K2SO4 to 2481.70 eV. • Measurement method: Total electron yield method by measuring sample current, X-ray fluorescence ·I0 measurement method: XANES measurement Au-mesh Cu-mesh during EXAFS measurement

[0057] Furthermore, in the anode active material of the present invention, it is preferable that the low-valence nanosilicon oxide is substantially in a composite state of 0, 1, 2, and 3 valencies. Since the tetravalent Si that constitutes SiO is an irreversible component, in the anode active material of the present invention, it is preferable that the low-valence nanosilicon oxide is substantially in a composite state of 0, 1, 2, and 3 valencies, as described above. In particular, it is preferable that the low-valence nanosilicon oxide is substantially dominated by 1 to 2 valencies. By making SiOx of 2 valency or less dominant, the irreversible capacity is larger than that of silicon alone, but the irreversible capacity can be maintained at a lower level than that of general SiO.

[0058] Furthermore, in the negative electrode active material of the present invention, it is preferable that the negative electrode active material particles have a carbon layer separate from the porous carbon matrix on part or all of their surface, and that the interface between the carbon layer separate from the porous carbon matrix and the low-valence nanosilicon oxide has a C=O or CO bond. Having such a C=O or CO bond can strengthen the adhesion of the carbon layer.

[0059] In the anode active material of the present invention, the grain size of zero-valent Si constituting the low-valence nanosilicon oxide, calculated using Scherrer's formula from peaks measured by X-ray diffraction of the anode active material particles, is preferably in the range of 0.8 nm to 5 nm. Such a grain size of zero-valent Si, which is substantially amorphous, is preferred.

[0060] Crystallite size can be calculated using XRD under the following conditions, for example. For broad peaks, the analysis can be performed using the TOPAS software under the following conditions, for example. XRD measurement • Equipment: Bruker D2 PHASER ·X-ray source:Cu • Divergence slit: 0.5° • Incident solar angle: 4° • Solar receiving side: 4° Calculation of crystallite size • Analysis software: DIFFRAC.TOPAS • Analysis method: Peak fitting method · Emission Profile: CuKa5.lam • Function: FP (First Principle) function • Refinement Option: Select "Caluculate Error" and "Use Extrapolation".

[0061] The valency of low-valency nanosilicon oxides can be quantified using NMR (nuclear magnetic resonance) and XPS (X-ray photoelectron spectroscopy).

[0062] NMR measurements for determining the valence of low-valence nanosilicon oxides can be performed, for example, under the following conditions. 29 Si MAS NMR (Magic Angle Rotation Nuclear Magnetic Resonance) • Equipment: Bruker 700NMR spectrometer, • Probe: 4mm HR-MAS rotor, 50μL • Sample rotation speed: 10 kHz, ·Measurement environment temperature: 25℃

[0063] XPS can be measured under the following conditions, for example. XPS ·Equipment: X-ray photoelectron spectrometer, • X-ray source: Monochromatic Al Kα rays, • X-ray spot diameter: 100 μm Ar ion gun sputtering conditions: 0.5kV 2mm x 2mm.

[0064] Furthermore, in the negative electrode active material of the present invention, the amount of oxygen contained in the total negative electrode active material particles is preferably in the range of 0.3 wt% or more and 8 wt% or less. Within this range of oxygen content, it is possible to prevent excessive formation of Si-C bonds during CVD of hydrocarbons such as acetylene, which would reduce the battery capacity, due to insufficient oxygen content, and to prevent irreversible capacity reduction due to excessive oxygen content.

[0065] Furthermore, in the negative electrode active material of the present invention, it is preferable that the pore diameter of the pores in the porous carbon structure has the following characteristics. First, the pore diameter distribution has a discontinuous change. Also, in pore diameter distribution measurement by the BJH method using nitrogen gas, it is preferable that the ratio B / A of the pore volume A of micropores with a diameter of 1.8 to 2 nm, the pore volume B of mesopores with a diameter of 10.0 to 22.0 nm, the pore volume C of mesopores with a diameter of 25.0 nm to 42.0 nm, and the pore volume D of macropores with a diameter of 50.0 nm to 102 nm is 0.03 or higher, the ratio C / A is 0.01 or higher, and the ratio D / A is 0.01 or higher.

[0066] This type of pore size distribution increases the probability of silane decomposition, which in turn allows for an increase in the amount of silicon packed into the pores. As a result, it leads to an improvement in battery capacity.

[0067] <Non-aqueous electrolyte secondary battery negative electrode> Next, the configuration of the negative electrode for a non-aqueous electrolyte secondary battery (hereinafter also referred to as "negative electrode") containing the negative electrode active material of the present invention will be described.

[0068] [Composition of the negative electrode] Figure 1 shows a cross-sectional view of a negative electrode containing the negative electrode active material of the present invention. As shown in Figure 1, the negative electrode 10 has a negative electrode active material layer 12 on a negative electrode current collector 11. This negative electrode active material layer 12 may be provided on both sides of the negative electrode current collector 11, or on only one side. Furthermore, in the negative electrode of the non-aqueous electrolyte secondary battery of the present invention, the negative electrode current collector 11 may be omitted.

[0069] [Negative electrode current collector] The negative electrode current collector 11 is made of a material that has excellent conductivity and high mechanical strength. Examples of conductive materials that can be used for the negative electrode current collector 11 include copper (Cu) and nickel (Ni). It is preferable that this conductive material does not form intermetallic compounds with lithium (Li).

[0070] The negative electrode current collector 11 preferably contains carbon (C) and sulfur (S) in addition to the main element. This is because it improves the physical strength of the negative electrode current collector. In particular, if the active material layer expands during charging, the presence of the above elements in the current collector has the effect of suppressing electrode deformation, including the current collector. The content of the above elements is not particularly limited, but it is preferable that each be 100 ppm by mass or less. This is because a higher deformation suppression effect can be obtained. Such deformation suppression effect can further improve cycle characteristics.

[0071] Furthermore, the surface of the negative electrode current collector 11 is preferably roughened, and more preferably, the ten-point average surface roughness Rz is 1.5 μm or more and 5 μm or less. The roughened negative electrode current collector is, for example, a metal foil that has been electrolytically treated, embossed, or chemically etched.

[0072] [Negative electrode active material layer] The negative electrode active material layer 12 may contain multiple types of negative electrode active materials, such as carbon-based active materials, in addition to the silicon-based active material particles of the present invention. Furthermore, for battery design purposes, it may also contain other materials such as thickeners (also called "binding agents" or "binders") and conductive additives.

[0073] [Method for manufacturing negative electrode active material and negative electrode] Next, an example of a negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention and a method for manufacturing a negative electrode using the same will be described.

[0074] First, the method for producing the negative electrode active material contained in the negative electrode will be described. The method for producing the negative electrode active material of the present invention is a method for producing a negative electrode active material having negative electrode active material particles, comprising the steps of: preparing a porous carbon structure which is a base material; including OH groups in the active sites contained in the porous carbon structure; placing the porous carbon structure in a heating container; heating the porous carbon structure in the heating container and placing it under a gas flow, and confirming that carbon monoxide gas or carbon dioxide gas originating from oxygen atoms contained in the active sites is detected in the exhaust process under the heating; and in a state in which carbon monoxide gas or carbon dioxide gas originating from oxygen atoms is detected in the exhaust process, the heating container is filled with mono A method for producing a negative electrode active material, comprising the steps of: flowing silane gas to decompose monosilane gas in a positive pressure atmosphere of 25 kPa to 80 kPa to deposit silicon oxide containing dangling bonds, thereby depositing silicon oxide partially bonded to the oxygen atoms of the porous carbon inside the porous carbon structure; oxidizing at least a portion of the Si contained in the silicon oxide present on the surface layer of the porous carbon in a reduced pressure atmosphere; and depositing a carbon layer at 600°C or below using hydrocarbon gas after the oxidation.

[0075] Conventionally, particles with silicon deposited inside porous carbon (Si-C), as commonly known, are produced using a fluidized bed tank, under a heated atmosphere, by injecting silane gas and a carrier gas from the bottom to deposit silicon inside the porous carbon. This is followed by an oxidation process, and then carbon coating using hydrocarbon gas or coal tar pitch.

[0076] In this case, with such conventional methods, the Si produced by the reaction of silane gas will have at least a portion of Si-H bonds and will be deposited in a Si-Si state. Furthermore, the material obtained in the oxidation process will be SiO2, so Si 0+ and Si 4+The composite material is formed within porous carbon. SiO2 is present in the outermost layer, and general SiC can be produced by carbon coating CVD with hydrocarbon gas on top of it. Furthermore, heat treatment for stabilization (reducing Si-H) results in Si 0+ and Si 4+ This process involves a disproportionation reaction that leads to separation. Furthermore, since Si-C crystals are formed when treated at high temperatures of 500 degrees Celsius or higher with hydrocarbon gas, it is common practice to reduce Si-H at lower temperatures.

[0077] In contrast, the present invention utilizes the active sites of porous carbon to incorporate OH groups into the porous carbon structure. When heat treatment is performed in this state, CO is detected in the exhaust gas. Normally, CO gas does not come out when completely dried, but by reacting it with silane gas in a pressurized atmosphere while the exhaust gas contains a large amount of CO, silane decomposition products are deposited on the porous carbon as low-valent oxides. At this time, since CO gas continues to come out from inside the porous pores, it is important to use a hydrogen carrier in a pressurized atmosphere to allow the silane gas to penetrate to the interior.

[0078] While typical fluidized beds experience a pressure drop of around 10 kPa, the reaction of this invention is known to gradually begin from around 25 kPa. Low-valent silicon oxides have high Li diffusivity. Generally, compounds of Si and Li contain Li 15 While Si4 is produced, it exhibits ionic properties and reduced diffusivity, whereas low-valent oxides can reduce the formation of ionic substances.

[0079] In particular, typical silane decomposition reactions, such as those used in semiconductors (polysilicon), primarily involve adsorption-based thermal decomposition, requiring thermal energy of approximately 400°C.

[0080] However, by controlling the pressure inside the tank to a positive level, silane is introduced into the pores, and the generation of silylene-containing radicals increases. This distorts the molecular structure and lowers the activation energy, resulting in a faster reaction rate and enabling low-temperature decomposition. Furthermore, during decomposition, oxygen components attached to the porous carbon are incorporated, allowing for the formation of Si-O bonds.

[0081] Since the amount of radicals generated is approximately proportional to the square of the silane concentration, Si is formed more significantly inside the pores in a pressurized atmosphere. When CO gas is present at this time, low-valence Si portions are formed. Furthermore, compared to adsorption pyrolysis, the silicon does not adhere strongly to the porous carbon, and after at least one charge-discharge cycle, it becomes fluid enough that silicon can be extracted from the pore surface. This helps to improve the diffusivity of Li.

[0082] Furthermore, by increasing the pressure during silicon oxide deposition and reaction, it becomes possible to create a large number of dangling bonds. These dangling bonds are highly reactive and can be carbonized at a temperature lower than the typical decomposition temperature of hydrocarbon gases (in this case, acetylene gas). At this time, some of the Si forms Si-C bonds, which not only stabilizes the structure but also significantly improves water resistance. However, since Si-C bonds deactivate Si, it is not possible to form many of them. Therefore, before introducing the hydrocarbon gas, the Si-H portion of the outermost layer is converted to a monovalent to trivalent Si oxide compound, and then reacted with the hydrocarbon gas to suppress the formation of Si-C crystals. At this time, if oxidation is performed to the extent that SiO2 is formed, Si is also produced simultaneously, and this Si portion will form Si-C crystals. Incidentally, the Si inside the bulk material is Si 0+ While this is dominant, low-valent oxides derived from CO gas are also present.

[0083] In this invention, by introducing silane gas into the pores of porous carbon under a pressurized environment ranging from 25 kPa to 80 kPa, it becomes possible to deposit silicon oxide deep into the pores. In this case, the reaction rate tends to be slower compared to conventional methods, but productivity does not deteriorate excessively as long as the pressurized range is 80 kPa or less. As a result, silicon oxide with a sufficiently low true density compared to activated carbon can be deposited, and a negative electrode active material with sufficient capacity as negative electrode active material particles can be obtained.

[0084] To increase the pressure, the internal pressure is adjusted by controlling the silane flow rate and the opening of the exhaust valve. Fluidized tanks are generally around 10 kPa, but pressure control becomes difficult above 25 kPa. Therefore, in addition to adjusting the valve opening as described above, a vent valve is also provided. For example, if the reaction is to be carried out at 50 kPa, the vent valve operates in the 50 + 5 kPa range to adjust the internal pressure. From a productivity standpoint, this significantly worsens the process, but by using this method, it becomes possible to distribute the gas to even the smallest details.

[0085] Furthermore, by reacting the porous carbon with silane gas while the OH groups are present in the pores, a CO-Si moiety is formed. This O-Si bond exhibits excellent Li diffusion properties, which can improve rapid charging capabilities. Moreover, even when heat is applied during subsequent CVD with hydrocarbon gas, Si crystallization is difficult, and the amorphous state can be maintained.

[0086] Furthermore, by increasing the pressure during silicon oxide deposition and reaction, it becomes possible to create a large number of dangling bonds. These dangling bonds are highly reactive and can be carbonized at temperatures lower than the typical decomposition temperature of hydrocarbon gases (e.g., below 530°C).

[0087] Specifically, the process involves depositing silicon oxide containing dangling bonds, and then, after depositing the silicon oxide, depositing a carbon layer using hydrocarbon gas.

[0088] Furthermore, by heat-treating the OH groups, CO gas can be detected on the exhaust gas side. After removing the moisture contained in the porous carbon, silane gas is introduced, but CO gas continues to be emitted at that time, and it is important to introduce the silane gas and allow the reaction to proceed in that state. If silane gas is introduced without gas detection, O-Si is difficult to form. Also, after the silane decomposition reaction, it is in a very active state, and if oxygen is introduced in that state, it will become SiO2 (tetravalent), so the low-valence state cannot be maintained. Therefore, in this invention, as described above, it is necessary to start flowing monosilane gas into the heating container when carbon monoxide gas or carbon dioxide gas derived from oxygen atoms is detected in the exhaust process, and to deposit silicon oxide by decomposing the silane gas in a positive pressure atmosphere of 25 kPa to 80 kPa.

[0089] The carbon CVD coating deposited on the silicon compound near the surface uses some of the oxygen component of silicon to produce C=O or CO compounds. At this time, it is thought that compounds similar to Si-OC are produced, which strengthens the adhesion of the carbon layer, thus maintaining integrity even when high-speed shear is applied during slurry preparation.

[0090] With this method of producing a negative electrode active material, as described above, an anode active material containing a low-valence nanosilicon oxide with a controlled phase structure, in which amorphous low-valence nanosilicon oxide is dispersed inside a porous carbon structure, Si-C bonds exist, and the porous carbon structure and the low-valence nanosilicon compound are detachably bonded, can be produced simply and efficiently.

[0091] Each step in the method for producing the negative electrode active material will be explained with reference to steps S1 to S7 in Figure 3.

[0092] First, prepare the porous carbon structure that will serve as the base material (Step S1). The porous carbon structure prepared here is predominantly Type I according to the IUPAC classification, and its surface area is 1400 m². 2 / g or more, pore volume 1cm³ 3It is preferable that the value is 1 / g or more. By using such IUPAC classification, surface area, and pore volume, silicon can be deposited more efficiently in larger quantities. Furthermore, the following measurement methods can be used for IUPAC classification, surface area, and pore volume. The specific surface area / pore size distribution will be measured using a constant-volume method based on gas adsorption with Shimadzu Tristar II Plus. The conditions are as follows: • Gas used: Nitrogen • Environment: Under liquid nitrogen • Pressure operating range: P / P0 Adsorption 0~0.998 Detachable 0.998~0.10 Pre-treatment: Vacuum, 200°C, 1 hour The porous carbon that can be used in this invention is of biological origin, resin origin, or petroleum origin, with biological or resin origin being preferred.

[0093] Next, OH groups are added to the active sites contained in the porous carbon structure prepared in step S1 (step S2). In this step, OH groups can be added to the active sites contained in the porous carbon structure by exposing it to air (a gas containing moisture).

[0094] The active sites within the porous carbon structure are generated through activation treatment. As described later, the presence of these active sites can be confirmed by the fact that, after OH group treatment and subsequent heat treatment, they are released into the exhaust gas as carbon dioxide and carbon monoxide.

[0095] Next, the porous carbon structure is placed in the heating container (step S3). Note that step S2 may be performed after step S3. That is, after placing the porous carbon structure in the heating container, OH groups may be added to the active sites contained in the porous carbon structure.

[0096] Next, the porous carbon structure is heated in a heating container and placed under a gas flow, and it is confirmed that carbon monoxide gas or carbon dioxide gas originating from oxygen atoms contained in the active sites is detected in the exhaust process under this heating (step S4).

[0097] Step S4 can be carried out more specifically as follows, but is not limited to these methods. First, a porous carbon structure is placed in a reaction vessel and heated to approximately 150°C while nitrogen gas is flowed through it. At the same time, a trap is installed in the exhaust gas section to ensure that no moisture is completely discharged. Simultaneously, a gas detector is used to check the CO or CO2 gas concentration. Typically, the gas concentration when no moisture is released is approximately 8000 ppm.

[0098] Next, step S5 is performed under conditions in which carbon monoxide gas or carbon dioxide gas derived from oxygen atoms is detected in the exhaust process. In this state, monosilane gas is introduced into the heating vessel and the silane gas is decomposed in a positive pressure atmosphere of 25 kPa to 80 kPa. This causes silicon oxide to be deposited inside the porous carbon structure. At this time, silicon oxide that is partially bonded to the oxygen atoms present in the porous carbon is deposited.

[0099] Step S5 can be carried out more specifically as follows, but is not limited to these methods. First, the heating container is heated to 450-500°C. When the internal temperature reaches 350°C, silane gas is introduced from the bottom to deposit silicon inside the porous carbon. At this time, it is preferable to estimate the pore volume of the porous carbon in advance from pore distribution measurement and flow an amount of silane equal to the pore volume / 0.9 ⇒ controlling the reaction rate to 90%. Also, at this time, although the internal pressure of the container is variable, it is averaged to be in the range of 25kPa to 80kPa. Deposition at a pressure exceeding 80kPa may result in a denser film, but considering the durability of the device, it is stopped at 80kPa. This silicon deposition can be carried out, for example, by flowing monosilane gas at around 400°C to 500°C. The deposition time can be, for example, 30 minutes to 10 hours.

[0100] Next, at least a portion of the Si contained in the silicon oxide present on the surface layer of the porous carbon is oxidized (step S6).

[0101] Step S6 can be carried out more specifically as follows, but is not limited to these methods. After the reaction in step S5, the temperature of the material is lowered to room temperature, and oxygen diluted with nitrogen is introduced to increase the weight of the oxygen by about 0.5 wt%. At this time, it is important to stir the powder with a stirring bar and allow it to heat slowly. Rapid oxidation will result in SiO2 formation, which will degrade the properties.

[0102] This oxidation process allows the low-valence nanosilicon oxide contained in the bulk region, which is deeper than 50 nm from the surface of the negative electrode active material particles (bulk low-valence nanosilicon oxide), and the low-valence nanosilicon oxide contained in the surface region, which is deeper than 50 nm from the surface of the negative electrode active material particles (surface low-valence nanosilicon oxide), to form a negative electrode active material structure having different Si phase structures.

[0103] Next, after oxidation, a carbon layer is deposited using hydrocarbon gas at a temperature of 600°C or lower (step S7). After the reaction in step S6, when the internal temperature has decreased to a low temperature (e.g., 530-600°C) under a nitrogen atmosphere, acetylene gas is introduced to form a surface carbon film. The process can be carried out at a pressure of 10,000 Pa for 8 hours.

[0104] The obtained material was analyzed by XRD, and the crystallite size of Si was calculated using Scherrer's equation, which typically yielded a value of 0.8 nm. However, this is a calculated result, and the material is considered substantially amorphous. At this time, the reaction is carried out under reduced pressure to allow acetylene gas to permeate the Si filling the pores. By reacting the Si-H bonds that did not reach a low-valence oxidation state with the Si-C bonds, a stable material is obtained.

[0105] Furthermore, the oxidation process in step S6 described above is preferably carried out in a reduced-pressure atmosphere. This oxidation process promotes oxidation of the parts closer to the surface. While the bulk interior utilizes the oxygen components contained in porous carbon, the parts closer to the surface have less oxygen and therefore need to be supplemented from the outside.

[0106] Furthermore, some of the Si-O compound formed in the oxidation step S6 is further compounded during the C-CVD process in step S7 (confirmed by XPS), thereby improving the adhesion between the carbon film and the Si portion.

[0107] <Lithium-ion rechargeable battery> Next, as a specific example of a non-aqueous electrolyte secondary battery using the negative electrode active material of the present invention described above, a laminate film type lithium-ion secondary battery will be explained.

[0108] [Configuration of a laminate film type rechargeable battery] The laminate film type lithium-ion secondary battery 30 shown in Figure 2 mainly consists of a wound electrode body 31 housed inside a sheet-like outer casing member 35. This wound electrode body 31 has a separator between the positive and negative electrodes and is wound around them. There are also cases where a laminate is housed inside with a separator between the positive and negative electrodes. In both electrode bodies, a positive electrode lead 32 is attached to the positive electrode and a negative electrode lead 33 is attached to the negative electrode. The outermost part of the electrode body is protected by protective tape.

[0109] The positive and negative electrode leads 32 and 33 are led out in one direction, for example, from the inside to the outside of the outer casing member 35. The positive electrode lead 32 is made of a conductive material such as aluminum, and the negative electrode lead 33 is made of a conductive material such as nickel or copper.

[0110] The exterior component 35 is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order. In this laminate film, the outer edges of the fusion layers of two films are fused together or bonded together with an adhesive so that the fusion layer faces the electrode body 31. The fusion part is, for example, a film such as polyethylene or polypropylene, and the metal part is, for example, aluminum foil. The protective layer is, for example, nylon.

[0111] An adhesive film 34 is inserted between the outer casing member 35 and the positive and negative electrode leads to prevent outside air from entering. This material can be, for example, polyethylene, polypropylene, or polyolefin resin.

[0112] The positive electrode, for example, has a positive electrode active material layer on both sides or one side of the positive electrode current collector, similar to the negative electrode 10 in Figure 1.

[0113] The positive electrode current collector is formed from a conductive material such as aluminum.

[0114] The positive electrode active material layer contains one or more positive electrode materials capable of intercalating and deintercalating lithium ions, and may also contain other materials such as positive electrode binders, positive electrode conductive additives, and dispersants, depending on the design. In this case, the details regarding the positive electrode binder and positive electrode conductive additive are the same as those for the negative electrode binder and negative electrode conductive additive already described, for example.

[0115] Lithium-containing compounds are preferred as the cathode material. Examples of lithium-containing compounds include composite oxides composed of lithium and transition metal elements, or phosphoric acid compounds having lithium and transition metal elements. Among these cathode materials, compounds containing at least one of nickel, iron, manganese, and cobalt are preferred. Examples of these chemical formulas include Li x M1O2 or Li y It is represented as M2PO4. In the formula, M1 and M2 represent at least one transition metal element. The values ​​of x and y vary depending on the battery charge and discharge state, but are generally given by 0.05 ≤ x ≤ 1.10 and 0.05 ≤ y ≤ 1.10.

[0116] Examples of the composite oxide having lithium and a transition metal element include, for example, lithium cobalt composite oxide (Li x CoO2), lithium nickel composite oxide (Li x NiO2), lithium nickel cobalt composite oxide, and the like. Examples of the lithium nickel cobalt composite oxide include lithium nickel cobalt aluminum composite oxide (NCA), lithium nickel cobalt manganese composite oxide (NCM), and the like.

[0117] Examples of the phosphate compound having lithium and a transition metal element include, for example, lithium iron phosphate compound (LiFePO4) or lithium iron manganese phosphate compound (LiFe 1-u Mn u PO4 (0 < u < 1)), and the like. By using these positive electrode materials, a high battery capacity can be obtained, and excellent cycle characteristics can also be obtained.

[0118] [Negative electrode] The negative electrode has the same configuration as the negative electrode 10 for the lithium ion secondary battery shown in FIG. 1 described above. For example, negative electrode active material layers are provided on both sides of the current collector. It is preferable that the negative electrode charging capacity is larger than the electric capacity (charging capacity as a battery) obtained from the positive electrode active material agent. Thereby, precipitation of lithium metal on the negative electrode can be suppressed.

[0119] The positive electrode active material layer is provided on a part of both sides of the positive electrode current collector, and similarly, the negative electrode active material layer is also provided on a part of both sides of the negative electrode current collector. In this case, for example, the negative electrode active material layer provided on the negative electrode current collector is provided with a region where the opposing positive electrode active material layer does not exist. This is for performing a stable battery design.

[0120] In the region where the above negative electrode active material layer and positive electrode active material layer do not face each other, it is hardly affected by charge and discharge. Therefore, the state of the negative electrode active material layer is maintained as it is immediately after formation, and thereby the composition of the negative electrode active material and the like can be accurately examined with good reproducibility without depending on the presence or absence of charge and discharge.

[0121] [Separator] A separator separates the positive and negative electrodes, preventing current short circuits caused by contact between the two electrodes while allowing lithium ions to pass through. This separator is formed from a porous membrane made of, for example, synthetic resin or ceramic, and may have a laminated structure in which two or more porous membranes are stacked. Examples of synthetic resins include polytetrafluoroethylene, polypropylene, and polyethylene.

[0122] [Electrolyte] At least a portion of the active material layer, or the separator, is impregnated with a liquid electrolyte. This electrolyte contains an electrolyte salt dissolved in a solvent and may also contain other materials such as additives.

[0123] For example, non-aqueous solvents can be used as solvents. Examples of non-aqueous solvents include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, 1,2-dimethoxyethane, or tetrahydrofuran. Among these, it is desirable to use at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, or ethylmethyl carbonate, as this will yield better properties. In this case, even more advantageous properties can be obtained by combining high-viscosity solvents such as ethylene carbonate and propylene carbonate with low-viscosity solvents such as dimethyl carbonate, ethylmethyl carbonate, and diethyl carbonate. This is because the dissociability and ion mobility of the electrolyte salt are improved.

[0124] When using an alloy-based negative electrode, it is particularly desirable to include at least one of the following as a solvent: a halogenated linear carbonate ester or a halogenated cyclic carbonate ester. This allows for the formation of a stable film on the surface of the negative electrode active material during charging and discharging, especially during charging. Here, a halogenated linear carbonate ester is a linear carbonate ester having halogen as a constituent element (at least one hydrogen atom is substituted by halogen). A halogenated cyclic carbonate ester is a cyclic carbonate ester having halogen as a constituent element (i.e., at least one hydrogen atom is substituted by halogen).

[0125] While there are no particular limitations on the type of halogen, fluorine is preferred because it forms a better quality film than other halogens. Furthermore, a higher number of halogens is desirable because it results in a more stable film and reduces the decomposition reaction of the electrolyte.

[0126] Examples of halogenated chain carbonate esters include fluoromethylmethyl carbonate and difluoromethylmethyl carbonate. Examples of halogenated cyclic carbonate esters include 4-fluoro-1,3-dioxolan-2-one and 4,5-difluoro-1,3-dioxolan-2-one.

[0127] It is preferable that the solvent additive contains an unsaturated carbon-bonded cyclic carbonate ester. This is because a stable film is formed on the negative electrode surface during charging and discharging, which suppresses the decomposition reaction of the electrolyte. Examples of unsaturated carbon-bonded cyclic carbonate esters include vinylene carbonate or vinylethylene carbonate.

[0128] Furthermore, it is preferable to include a sultone (cyclic sulfonic acid ester) as a solvent additive, as this improves the chemical stability of the battery. Examples of sultones include propanesultone and propenesultone.

[0129] Furthermore, the solvent preferably contains an acid anhydride, as this improves the chemical stability of the electrolyte. Examples of acid anhydrides include propanedisulfonic acid anhydride.

[0130] The electrolyte salt may contain one or more light metal salts, such as lithium salts. Examples of lithium salts include lithium hexafluoride phosphate (LiPF6) and lithium tetrafluoroborate (LiBF4).

[0131] The electrolyte salt content is preferably 0.5 mol / kg to 2.5 mol / kg relative to the solvent, because this allows for high ionic conductivity. [Examples]

[0132] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the examples and comparative examples, a negative electrode active material was prepared by the following procedure, and then a laminate film type lithium-ion secondary battery 30 shown in Figure 2 was prepared.

[0133] (Comparative Example 1) The negative electrode active material was manufactured as follows: First, porous carbon was activated, with a surface area (BET specific surface area) of 1940 m². 2 / g, pore volume 1.00 cm³ 3A porous carbon material (porous carbon structure) with a particle size (D50) of 7.5 μm was prepared. Next, this porous carbon material was placed in air to impregnate it with OH groups. This porous carbon material was placed in a vacuum container, purged with nitrogen, and heated to 400°C using an external heater while nitrogen flowed through it. At this time, CO gas and CO2 gas were not detected (below the detection limit). With carbon monoxide gas and carbon dioxide gas not detected during the exhaust process, monosilane gas was started to flow into the heating container. Furthermore, with OH groups contained in the pores of the porous carbon, silane gas was flowed while controlling the pressure inside the container to 10 kPa to deposit silicon. During drying before the silane reaction, with CO gas not detected (below the detection limit), the silane decomposition reaction (adsorption thermal decomposition reaction of silane) was carried out (400°C) to form amorphous silicon inside the bulk material.

[0134] The reaction was completed when the pore volume was filled to 98%, and then the mixture was cooled to room temperature. Subsequently, oxygen diluted with nitrogen (1% concentration) was flowed over the mixture for 48 hours to perform a slow oxidation treatment. At this time, if the oxygen concentration is high, an exothermic reaction occurs with the highly reactive powder, not only forming SiO2 but also transforming it into a high-BET material. After this, the internal temperature was heated to 500°C in a nitrogen atmosphere, and acetylene gas was introduced at 10,000 Pa for 8 hours to form a surface carbon film. This suppresses Si-C formation.

[0135] [Calculation of crystallite size] The crystallite size of the negative electrode active material particles was calculated by XRD measurement using the Bruker D2 PHASER mentioned above.

[0136] [Measurement of different phases of low-valence nanosilicon oxides] XANES measurements revealed that the low-valence nanosilicon oxide in the bulk portion and the low-valence nanosilicon oxide in the surface portion of the negative electrode active material particles have different Si phase structures. Specifically, total electron yield (TEY) obtained from the XANES Si-k edge spectrum shows the surface portion up to 50 nm, while X-ray fluorescence (PFY) detects information about the bulk interior of approximately 5 μm.

[0137] [Measurement of the number of dangling bonds in silicon] The number of dangling bonds in silicon was measured using ESR.

[0138] [Fabrication of the negative electrode] The negative electrode active material (active material containing CVD-SiOx-C), graphite, conductive additive 1 (carbon nanotubes, CNT), conductive additive 2 (carbon fine particles with a median diameter of approximately 50 nm), sodium polyacrylate, and carboxymethylcellulose (hereinafter referred to as CMC) prepared as described above were mixed in a dry mass ratio of 9.3:83.7:1:1:4:1, and then diluted with pure water to obtain a negative electrode mixture slurry.

[0139] Furthermore, a 15 μm thick electrolytic copper foil was used as the negative electrode current collector. This electrolytic copper foil contained carbon and sulfur at concentrations of 70 ppm by mass each. Finally, the negative electrode mixture slurry was applied to the negative electrode current collector and dried in a vacuum atmosphere at 100°C for 1 hour. After drying, the amount of negative electrode active material deposited per unit area on one side of the negative electrode (also called area density) was 7.0 mg / cm³. 2 That was the case.

[0140] [Assembly of a coin cell battery for testing] Next, the solvents ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed, and then the electrolyte salt (lithium hexafluoride phosphate: LiPF6) was dissolved to prepare the electrolyte. In this case, the solvent composition was set to a volume ratio of EC:DMC = 30:70, and the electrolyte salt content was 1 mol / kg relative to the solvent. As additives, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were added in amounts of 1.0% by mass and 2.0% by mass, respectively.

[0141] Next, the coin cell was assembled as follows: First, a 1mm thick lithium foil was punched out to a diameter of 16mm and attached to the aluminum cladding.

[0142] Next, the negative electrode obtained earlier was punched out to a diameter of 15 mm, and this was placed opposite a Li foil attached to an aluminum cladding via a separator. After injecting the electrolyte, a 2032 coin cell was fabricated.

[0143] [Initial Efficiency Measurement] The initial efficiency was measured under the following conditions. First, the coin cell battery prepared for the initial efficiency test was charged in CCCV mode with a charge rate equivalent to 0.03C (initial charge). The CV was 0V and the termination current was 0.04mA. Next, CC discharge (initial discharge) was performed with a discharge rate of 0.03C and a discharge termination voltage of 1.2V.

[0144] When investigating the initial charge-discharge characteristics, the initial efficiency (sometimes referred to as initial efficiency below) was calculated. The initial efficiency was calculated using the formula: Initial Efficiency (%) = (Initial Discharge Capacity / Initial Charge Capacity) × 100.

[0145] [Manufacturing and evaluation of lithium-ion secondary batteries] Based on the initial data obtained, the cathode was designed so that the utilization rate of the negative electrode was 95%. The utilization rate was calculated from the capacities of the positive and negative electrodes obtained with the counter electrode Li, based on the following formula. Utilization rate = (Positive electrode capacity - Negative electrode loss) / (Negative electrode capacity - Negative electrode loss) × 100 Based on this design, lithium-ion secondary batteries (as shown in Figure 2) for both the examples and comparative examples were manufactured. Battery evaluation was performed on each of the lithium-ion secondary batteries for both the examples and comparative examples.

[0146] The cycle characteristics were investigated as follows: First, to stabilize the battery, two charge-discharge cycles were performed at 0.2C in a 25°C atmosphere, and the discharge capacity of the second cycle was measured. The battery cycle characteristics were calculated from the discharge capacity of the third cycle, and the battery test was stopped at 1000 cycles. Charging was performed at 0.7C and discharging at 0.5C. The charging voltage was 4.3V, the discharge termination voltage was 2.5V, and the charge termination rate was 0.07C.

[0147] The results of each measurement are shown in Tables 1 and 2. Tables 1 and 2 also include the examples and comparative examples described later.

[0148] [Table 1]

[0149] [Table 2]

[0150] (Comparative Example 2) Comparative Example 2 involved silicon deposition using a silane monomolecule pyrolysis reaction, compared to Comparative Example 1. The decomposition temperature was 375°C. The oxidation process was the same as in Comparative Example 1, but the silicon grains formed by adsorption pyrolysis were of lower density, allowing for the generation of some low-valent Si during the oxidation process.

[0151] (Example 1) The procedure was the same as in Comparative Example 2, except that the reaction pressure was changed to 50 kPa, and the silane decomposition reaction was carried out with approximately 7500 ppm of CO gas detected during drying before the silane reaction. In this case, the decomposition reaction can be carried out in the range of 350 to 375°C, which is lower than the temperature of the silane decomposition reaction. This is because by controlling the pressure inside the tank to positive pressure, silane is introduced into the pores, and the production of silylene increases, the molecular structure is distorted, the activation energy is lowered, the reaction rate is increased, low-temperature decomposition is achieved, and oxygen components attached to porous carbon are incorporated during decomposition, forming Si-O bonds. After the reaction, the temperature is returned to room temperature, oxygen gas at a concentration of 1% in nitrogen is used, the pressure is reduced to -95 kPa, and then diluted oxygen gas is introduced until the pressure reaches -10 kPa. The amount of gas consumed is estimated from the amount of gas introduced, and this is repeated until the roughly planned weight increase is reached.

[0152] In Example 1, the Si layer on the outermost surface was made slightly oxygen-rich. Subsequently, when CVD was performed at 580°C (Example 1) using acetylene gas, some oxygen was exchanged at the interface between the oxygen-rich layer and the carbon layer, and C=O or CO bonds were formed, ensuring adhesion. Furthermore, the acetylene CVD was carried out under a reduced pressure of 10,000 Pa, allowing impregnation into the porous carbon to enable the reaction. The reaction breaks the bonds in the formed Si-H moieties and creates Si-C bonds. This suppresses the generation of hydrogen gas during slurry formation. Higher CVD temperatures result in the formation of more Si-C bonds. Because a low-valence oxidation state is formed on the surface, excessive Si-C bonds are not generated.

[0153] Furthermore, the silicon portion of the surface is in a low-valent oxidation state, Si 0+ It is almost completely absent, which is significantly different from the bulk structure. Water (more precisely, OH) is present in the surface layer. - By preventing the presence of substances that react with ), the stability of the slurry is also improved. In the bulk, Si 0+ While this is dominant, low-valence states are common.

[0154] By oxidizing without converting to SiO2, excessive Si-C conversion during acetylene CVD can be suppressed. Furthermore, Si-C is electrochemically stable, and when exposed Si comes into contact with the electrolyte during charging, it has the effect of suppressing excessive decomposition of the electrolyte, which ultimately contributes to cycle maintenance.

[0155] In single-molecule pyrolysis, silylene molecules bond together within the pores, expanding and generating silicon grains based on active sites on the inner wall of the porous carbon. Unlike adsorption pyrolysis, this low adhesion and unstable conditions between the porous carbon and silicon significantly increase the diffusivity of Li. Furthermore, while Si precipitates on the surface of the porous carbon in adsorption pyrolysis, single-molecule pyrolysis decomposes only the interior. This is evident when dQdV is obtained from the charge-discharge curve. Due to the low adhesion, TEM analysis after charge-discharge shows that when an electron beam is applied, Si near the surface is pulled by the binder and detaches from the particle surface. In other words, in Example 1, it can be seen that the porous carbon structure and the low-valence nanosilicon compound are bonded in a detachable manner.

[0156] In Example 1, an activation treatment is performed on porous carbon to increase the size of the same pore by two in the mesopores and one in the macropores. The activation treatment can be adjusted by varying the water vapor density, temperature, and pressure. In addition to acting as a buffer tank, the increased size of the same pores helps to form a connected pore structure. General porous carbon has a branched structure that extends deep into the material, but when these branched pores connect (also called recombining), the paths for silicon, i.e., the diffusion paths for Li, can be increased, and the acceptance of Li can be greatly improved. Furthermore, because the paths are connected, it is possible to increase the probability of silane decomposition, which leads to an increase in the amount of silicon packed in the material. The state of pore connection (recombination) can be analyzed using the atom probe method and visualized as an equisurface concentration of Si. The size of the same pore can be calculated from the nitrogen adsorption method using the BJH analysis method.

[0157] Furthermore, acetylene CVD is carried out under reduced pressure of 10,000 Pa, allowing for penetration into the porous carbon and enabling the reaction. The reaction breaks the Si-H bonds in the formed Si-C bonds. This suppresses the generation of hydrogen gas during slurry formation. Higher CVD temperatures result in the formation of more Si-C bonds.

[0158] Furthermore, the silicon portion of the surface is in a low-valent oxidation state, Si 0+It is almost completely absent, which is significantly different from the bulk structure. Water (more precisely, OH) is present in the surface layer. - By preventing the presence of substances that react with ), the stability of the slurry is also improved.

[0159] (Examples 2-6) In Examples 2-6, the same manufacturing method as in Example 1 was used, except that heat treatment was performed after oxidation treatment to crystallize some of the Si. The aim was to reduce the Si-H bond, but no significant reduction was observed. The Si-H bond was confirmed by CP / MAS-NMR. As crystallinity increases, the acceptance of Li deteriorates, and the battery characteristics deteriorate slightly. However, considering that the handling of the powder improves after raising the temperature, crystallites of 5 nm or less are desirable. The best battery characteristics are obtained when the material is substantially amorphous (0.8 nm is calculated using Scherrer's formula and is considered substantially amorphous).

[0160] (Examples 7-11) Examples 7-11 used the same manufacturing method as in Example 1, but with a different oxidation level. When the oxygen level was low, more Si-C bonds tended to form during acetylene CVD, slightly reducing the battery capacity. An oxidation level of 0.3 wt% or higher was considered sufficient to prevent a significant drop in capacity. Furthermore, too much oxygen caused SiO2 to begin forming, indicating an optimal range for oxygen levels.

[0161] (Examples 12-14) In Examples 12-14, the same manufacturing method as in Example 1 was used, except that the pressure during silane gas introduction was changed. If the pressure during silane gas introduction is low, the silane gas cannot reach the depths of the pores, creating voids. As a result, silicon cannot be filled to that extent, and the battery capacity decreases. Furthermore, silicon decomposed and deposited in a pressurized atmosphere can form a denser silicon structure because the generation of silylene-containing radicals increases in proportion to the square of the pressure.

[0162] Furthermore, to increase the pressure, the internal pressure is adjusted by controlling the silane flow rate and the opening of the exhaust valve. Fluidized tanks are generally around 10 kPa, but pressure control becomes difficult above 30 kPa. Therefore, in addition to adjusting the valve opening as described above, a vent valve is also provided. For example, if the reaction is to be carried out at 50 kPa, the vent valve operates in the 50 + 5 kPa range to adjust the internal pressure. From a productivity standpoint, this significantly worsens the process, but by using this method, it becomes possible to distribute the gas to even the smallest details.

[0163] (Example 15) When performing acetylene CVD, if a diffusion layer is not intentionally created by heating at a low temperature of 500 degrees Celsius for one hour and then increasing the temperature to 580 degrees Celsius, the battery's cycle characteristics will be slightly reduced.

[0164] (Examples 16, 17, Comparative Example 3) The manufacturing method was the same as in Example 1, except that the degree of activation treatment of the prepared porous carbon was reduced. The degree of activation treatment decreased in the order of Example 1, Example 16, Example 17, and Comparative Example 3. In Comparative Example 3, the porous carbon structure was a branched structure and did not have a connected structure. As the buffer tank portion decreases in the order of Example 1, Example 16, Example 17, and Comparative Example 3, the recombination of pores also decreases. Ultimately, a branched structure (Comparative Example 3) is formed, resulting in a decrease in battery performance. Reducing the pressure during water vapor activation results in a branched activation treatment.

[0165] This specification includes the following embodiments: [1]: A negative electrode active material having negative electrode active material particles, wherein the negative electrode active material particles include a structure of porous carbon which is a matrix material, the porous carbon structure has a structure in which some of the pores formed inside communicate with other pores, amorphous low-valence nanosilicon compounds are dispersed inside the porous carbon structure, Si-C bonds exist in at least a portion of the low-valence nanosilicon compounds, and the porous carbon structure and the low-valence nanosilicon compounds are detachably bonded. [2]: The anode active material of [1] wherein the low-valence nanosilicon oxide in the range of 50 nm from the surface of the anode active material particles has a different structure from the phase structure of Si in the bulk portion deeper than 50 nm from the surface of the anode active material particles. [3]: The low-valence nanosilicon oxide is substantially a composite state of 0, 1, 2, and 3 valencies, as described in [1] or [2] above. [4]: The pore diameter of the pores in the porous carbon structure has discontinuous changes, and the negative electrode active material of any of the above [1] to [3] is such that, when the pore diameter distribution is measured by the BJH method using nitrogen gas, the relationship between the pore volume A of micropores with a diameter of 1.8 to 2 nm, the pore volume B of mesopores with a diameter of 10.0 to 22.0 nm, the pore volume C of mesopores with a diameter of 25.0 nm to 42.0 nm, and the pore volume D of macropores with a diameter of 50.0 nm to 102 nm is such that the ratio B / A is 0.03 or more, the ratio C / A is 0.01 or more, and the ratio D / A is 0.01 or more. [5]: The negative electrode active material particles have a carbon layer separate from the porous carbon matrix on part or all of their surface, and the interface is formed of C=O or CO bonds, as described in any of the negative electrode active materials described in [1] to [4] above. [6]: Any of the negative electrode active materials [1] to [5] above, wherein the grain size of zero-valent Si constituting the low-valent nanosilicon oxide, calculated using Scherrer's formula from the peaks measured by X-ray diffraction of the negative electrode active material particles, is in the range of 0.8 nm to 5 nm. [7]: The anode active material of the anode active material particles wherein the low-valence nanosilicon oxide is substantially amorphous, as described in [6] above. [8]: Any of the negative electrode active materials described in [1] to [7] above, wherein the total amount of oxygen contained in the negative electrode active material particles is in the range of 0.3 wt% or more and 8 wt% or less. [9]: A method for producing a negative electrode active material having negative electrode active material particles, comprising the steps of: preparing a porous carbon structure which is a base material; incorporating OH groups into the active sites contained in the porous carbon structure; placing the porous carbon structure in a heating container; heating the porous carbon structure in the heating container and placing it under a gas flow, confirming that under the heating, carbon monoxide gas or carbon dioxide gas originating from oxygen atoms contained in the active sites is detected in the exhaust process; and introducing monosilane gas into the heating container while the carbon monoxide gas or carbon dioxide gas originating from oxygen atoms is detected in the exhaust process. A method for producing a negative electrode active material, comprising the steps of: flowing a monosilane gas through a positive pressure atmosphere of 25 kPa to 80 kPa to decompose the gas, thereby depositing silicon oxide containing dangling bonds, and depositing silicon oxide partially bonded to the oxygen atoms of the porous carbon inside the porous carbon structure; oxidizing at least a portion of the Si contained in the silicon oxide present on the surface layer of the porous carbon in a reduced pressure atmosphere; and depositing a carbon layer at 600°C or below using a hydrocarbon gas after the oxidation.

[10] : A method for producing the negative electrode active material of [9], wherein when the low-valence nanosilicon compound is formed by the decomposition of the monosilane gas, the monosilane gas reacts via silylene by a monomolecule thermal decomposition reaction in the gas phase.

[0166] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of Symbols]

[0167] 10...Negative electrode, 11...Negative electrode current collector, 12...Negative electrode active material layer, 30...Lithium-ion secondary battery (laminated film type), 31...Electrode body, 32... Positive lead (positive aluminum lead), 33... Negative electrode lead (negative electrode nickel lead), 34...Adhesive film, 35...Exterior components.

Claims

1. A negative electrode active material having negative electrode active material particles, The negative electrode active material particles include a porous carbon structure which is the base material. The porous carbon structure has a structure in which some of the pores formed inside communicate with other pores. Amorphous low-valence nanosilicon compounds are dispersed within the porous carbon structure. At least a portion of the low-valence nanosilicon compound contains Si-C bonds, A negative electrode active material characterized in that the porous carbon structure and the low-valence nanosilicon compound are detachably bonded together.

2. The negative electrode active material according to claim 1, characterized in that the low-valence nanosilicon compound in the range of 50 nm from the surface of the negative electrode active material particles has a different structure from the Si phase structure in the bulk portion deeper than 50 nm from the surface of the negative electrode active material particles.

3. The negative electrode active material according to claim 1, characterized in that the low-valence nanosilicon compound is substantially in a composite state of zero, mono, di, and tri valencies.

4. The pore size of the pores in the porous carbon structure exhibits discontinuous changes, and the pore size distribution was measured using the BJH method with nitrogen gas. The pore volume A of a micropore with a diameter of 1.8 to 2 nm, The pore volume B of a mesopore with a diameter of 10.0 to 22.0 nm, The pore volume C of mesopores with a diameter of 25.0 nm or more and 42.0 nm or less, The pore volume D of macropores with a diameter of 50.0 nm to 102 nm and The relationship is The ratio B / A is 0.03 or higher. The ratio C / A is 0.01 or higher. The negative electrode active material according to claim 1, characterized in that the ratio D / A is 0.01 or greater.

5. The negative electrode active material according to claim 1, wherein part or all of the surface of the negative electrode active material particles has a carbon layer separate from the porous carbon that is the base material, and a C=O or C-O bond is formed at the interface.

6. The negative electrode active material according to claim 1, characterized in that the grain size of zero-valent Si constituting the low-valent nanosilicon compound, calculated using Scherrer's formula from the peaks measured by X-ray diffraction of the negative electrode active material particles, is in the range of 0.8 nm to 5 nm.

7. The negative electrode active material according to claim 6, characterized in that the low-valence nanosilicon compound of the negative electrode active material particles is substantially amorphous.

8. The negative electrode active material according to claim 1, characterized in that the total amount of oxygen contained in the negative electrode active material particles is in the range of 0.3 wt% or more and 8 wt% or less.

9. A method for producing a negative electrode active material having negative electrode active material particles, The steps include preparing a porous carbon structure as the base material, The steps include: adding OH groups to the active sites contained in the porous carbon structure; The steps include: placing the porous carbon structure inside a heating container; The steps include: heating the porous carbon structure in the heating container and placing it under a gas flow, and confirming that carbon monoxide gas or carbon dioxide gas originating from oxygen atoms contained in the active site is detected in the exhaust process under heating conditions; The steps include: flowing monosilane gas into the heating container while carbon monoxide gas or carbon dioxide gas derived from the oxygen atoms is detected in the exhaust process, and decomposing the monosilane gas in a positive pressure atmosphere of 25 kPa to 80 kPa, thereby depositing the low-valence nanosilicon compound containing dangling bonds, and depositing the low-valence nanosilicon compound partially bonded to the oxygen atoms of the porous carbon inside the porous carbon structure; The process involves oxidizing at least a portion of the Si contained in the low-valent nanosilicon compound present on the surface of the porous carbon in a reduced-pressure atmosphere, The process involves the following steps: depositing a carbon layer at a temperature of 600°C or lower using hydrocarbon gas after the oxidation; A method for producing a negative electrode active material, characterized by producing a negative electrode active material containing the negative electrode active material.

10. The method for producing a negative electrode active material according to claim 9, characterized in that when the low-valence nanosilicon compound is formed by the decomposition of the monosilane gas, the monosilane gas undergoes a reaction via silylene by a single-molecule thermal decomposition reaction in the gas phase.

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