Negative electrode active material and method for producing the same

Abstract

The present invention provides a negative electrode active material that can improve cycle characteristics while maintaining high battery capacity. [Solution] A negative electrode active material having negative electrode active material particles, wherein the negative electrode active material particles include a porous carbon structure, amorphous low-valence nanosilicon oxide dispersed inside it, and a carbon-based coating layer covering a part of the surface, the low-valence nanosilicon oxide having Si-C bonds with the porous carbon structure, and the porous carbon structure having a true density of 2.20~2.55 g / cm³ 3 Pore ​​volume 1.00~1.25 cm³ by BET method 3 / g, pore volume 0.5~0.75 cm³ by BJH method 3 It contains particle A at a density of / g, and furthermore, its true density is 2.50~2.90 g / cm³. 3 Pore ​​volume 1.15-1.30 cm³ by BET method 3 / g, pore volume 0.75~0.9 cm³ by BJH method 3 A negative electrode active material in which the weight ratio of particle B to particle A is within the range of 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B.

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. 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. Furthermore, in order to improve cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is fabricated, and an active material layer with a high oxygen ratio near the current collector is formed. In addition, 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.

[0009] Furthermore, to improve the initial charge-discharge efficiency, Si phase, SiO2, M y It uses nanocomposites containing metal oxides. 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. Also, to improve the 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 and minimum values of the molar ratio near the interface of the active material and the current collector is 0.4 or less. Also, to improve the battery load characteristics, a metal oxide containing lithium is used. Also, to improve the cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface layer of the silicon material.

[0010] Also, to improve the cycle characteristics, silicon oxide is used, and conductivity is imparted by forming a graphite film on its surface layer. Regarding the shift value obtained from the RAMAN spectrum of the graphite film, at 1330 cm -1 and 1580 cm -1 broad peaks appear, and their intensity ratio I 1330 / I 1580 is such that 1.5 < I 1330 / I 1580 < 3. Also, to improve the high battery capacity and cycle characteristics, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used. Also, to improve the overcharge and over-discharge characteristics, a silicon oxide in which the atomic ratio of silicon to oxygen is controlled to 1:y (0 < y < 2) is used.

[0011] Also, the lithium-ion secondary battery using silicon oxide was the shipment start of a rectangular secondary battery for smartphones that Hitachi Maxell adopted a nanosilicon composite in June 2010 (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). Also, Kapaklis has proposed a disproportionation structure that is divided into Si and SiO2 by applying a heat load to the silicon oxide (Non-Patent Document 3).

[0012] Miyachi et al. have focused on Si and SiO2, which contribute to charging and discharging among silicon oxides having a disproportionate structure (Non-Patent Literature 4), and Yamada et al. have proposed the following reaction equation between silicon oxide and Li (Non-Patent Literature 5). 2SiO(Si+SiO2) + 6.85Li + + 6.85e - → 1.4Li 3.75 Si + 0.4Li4SiO4 + 0.2SiO2 In the reaction equation, the silicon oxide is composed of Si and SiO2, which react with Li to form Li silicide, Li silicate, and some unreacted SiO2.

[0013] The Li silicate produced here is irreversible and is generally considered a stable substance that does not release Li once formed. The volume per unit mass calculated from this reaction equation is close to experimental values ​​and is recognized as a reaction mechanism for silicon oxides. Kim et al. referred to the irreversible component of silicon oxide charging and discharging, Li silicate, as Li4SiO4. 7 Li-MAS-NMR and 29 Identification is performed using Si-MAS-NMR (Non-Patent Document 6).

[0014] This irreversible capacity is the weakest point of silicon oxides, and improvement is needed. Therefore, Kim et al. have used a Li pre-doping method, which involves forming Li silicate in advance, to significantly improve the initial efficiency of the battery and create a negative electrode that can withstand practical use (Non-Patent Literature 7). They have also proposed a method of treating the powder rather than doping the electrode with Li, thereby achieving improvement in irreversible capacity.

[0015] On the other hand, the price of Li metal used for Li-doping fluctuates wildly depending on market conditions, presenting many challenges when considered for industrialization. Therefore, CVD-Si-C, which uses silane gas on porous carbon to generate nanosilicon inside, has been able to achieve a higher energy density than Li-doped SiO (Patent Documents 1 and 2).

[0016] Furthermore, focusing on the problem that the small pore size of porous carbon materials leads to the deposition of an excess amount of silicon (Si) on the surface, resulting in high electrical resistivity, composite particles that do not contain SiC (silicon carbide) or have an extremely low SiC content have been proposed to reduce electrical resistivity (Patent Document 3).

[0017] Furthermore, SiC, as commonly referred to, is produced by using a fluidized bed tank, injecting silane gas and carrier gas from the bottom in a heated atmosphere, depositing silicon inside porous carbon, and then performing a carbon coating using hydrocarbon gas or coal tar pitch after an oxidation process. At this time, adsorption thermal decomposition is likely to occur at least 400°C (effectively 450-500°C) (Patent Documents 4 and 5).

[0018] In this case, Si-O bonds exist in the outermost layer, and general SiC can be produced by performing carbon coating CVD with hydrocarbon gas on the upper part. However, if there are not enough Si-O bonds, Si-C crystals are formed, which is said to reduce battery capacity (Patent Documents 6 and 7).

[0019] Furthermore, in the oxidation process, it is believed that by performing the oxidation treatment using dry air with a low dew point (specifically -40°C), the silicon oxide reacts with the dangling bonds but does not react with the Si-H bonds (Non-Patent Documents 9 and 10).

[0020] Furthermore, while many Si-C compounds have a polydimethylsiloxane structure, some also possess Si-H bonds. It has been reported that Si-H bonds detach at around 450°C (Non-Patent Literature 11). [Prior art documents] [Patent Documents]

[0021] [Patent Document 1] U.S. Patent No. 10,608,254 [Patent Document 2] U.S. Patent No. 11,165,054 [License 3] WO2024 / 142699 [License 4] U.S. Patent No. 10,454,103 [Patent Document 5] U.S. Patent No. 10,714,744 [License 6] WO2024 / 161756 [License 7] U.S. Patent No. 12,046,744 [Non-licensed literature]

[0022] [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-Patent 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. [Non-Patent Document 9] Vacuum, Vol. 33, No. 11, 1990, pp. 854-860: Deactivation of Si single crystal surfaces by hydrogen termination. [Non-Patent Document 10] Surface Science Vol.19, No.3, pp.173-178, 1998 Theory of the oxidative process on Si surfaces [Non-Patent Document 11] C. Michael Greenlief, Michael Armstrong, “Hydrogen desorption from Si: How does this relate to film growth?” (J. Vac. Sci. Technol. B, Vol. 13, No. 4, Jul / Aug 1995) [Overview of the Initiative] [Problems that the invention aims to solve]

[0023] 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.

[0024] 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 prototype battery using this silicon oxide with Li, Li-SiO-C (Non-Patent Literature 8), is fabricated to replace 100% of the carbon negative electrode material, the capacity improvement compared to the 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.

[0025] 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.

[0026] The present invention has been made in view of the above-mentioned problems, and aims to provide a negative electrode active material that can improve cycle characteristics while maintaining high battery capacity. [Means for solving the problem]

[0027] 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, amorphous low-valence nanosilicon oxide dispersed inside the porous carbon structure, and a carbon-based coating layer covering at least a portion of the surface, the low-valence nanosilicon oxide having a Si-C bond with the porous carbon structure, and the porous carbon structure having a true density of 2.20 to 2.55 g / cm³ 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains at least / g of particle A, and furthermore, has a true density of 2.50-2.90 g / cm³. 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3 The present invention provides a negative electrode active material characterized in that the weight ratio of particle B to particle A in units of / g is in the range of 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B.

[0028] The negative electrode active material of the present invention contains low-valence nanosilicon oxide, which reduces the generation of ionic substances and enhances the diffusivity of Li. Furthermore, because the low-valence nanosilicon oxide has Si-C bonds, the internal Si-C bonds have a strong bond with the Si in the surface layer, which suppresses the electronic breakup of the Si portion during charging and discharging, resulting in a stable structure. For this reason, it is electrochemically stable during charging and discharging, and decomposition during charging and discharging is less likely to occur.

[0029] Next, the porous carbon structure has a true density of 2.20-2.55 g / cm³. 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3It contains particle A at a concentration of / g. This indicates that it is sufficiently carbonized. As a result, the amount of undegraded compounds is reduced, preventing Li from being trapped, suppressing the increase in irreversible capacity, and improving efficiency. In addition, the increase in electronically conductive aromatic compounds improves electronic conductivity and thus improves cycle characteristics.

[0030] Furthermore, the true density is 2.50-2.90 g / cm³ 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3 The weight ratio of particle B to particle A per gram is within the range of 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B. The large pore volume of particle B can increase the amount of silicon-based compound deposited, leading to an increase in capacity when used in a battery. Furthermore, by not having too much particle B, the increase in the specific surface area of ​​the negative electrode active material itself can be suppressed, preventing deterioration of cycle characteristics.

[0031] As a result, it is possible to provide a negative electrode active material that can improve cycle characteristics while maintaining high battery capacity and high initial efficiency.

[0032] Furthermore, it is preferable that particle A has a carbon-carbon unsaturated bond and a bond derived from an aromatic ester, and particle B has a carbon-carbon single bond and a bond derived from an ether system.

[0033] If particle A and particle B have such a bond, they become a suitable negative electrode active material capable of improving cycle characteristics while maintaining high battery capacity.

[0034] Furthermore, it is preferable that the particle size distribution of particle A is D10=3~9μm, D50=5~16μm, and D90=10~25μm, and the particle size distribution of particle B is D10=0.2~3μm, D50=1~5μm, and D90=3~6μm.

[0035] If particles A and B have this particle size distribution, they become a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0036] Furthermore, the porous carbon structure is found in the 1100 cm⁻¹ spectrum obtained from Raman spectroscopy analysis. -1 More than 1200cm -1 It is preferable that the peaks are within the following range.

[0037] A negative electrode active material with such a spectrum has pores of an appropriate size within the porous carbon structure, allowing gas to easily reach the pores. As a result, it becomes a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0038] Furthermore, the peaks in the spectrum obtained from the Raman spectroscopy analysis are peaks originating from C=O bonds or CO bonds, and it is preferable that the porous carbon structure contains at least one of C=O bonds or CO bonds.

[0039] If a material contains C=O or CO bonds internally, for example, when it reacts with silane gas, a CO-Si moiety is formed. This O-Si bond exhibits excellent Li diffusion properties, which can improve fast charging capabilities. As a result, it becomes a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0040] Furthermore, in the spectrum obtained from Raman spectroscopy, it is preferable that the porous carbon structure has a G / D ratio of less than 1.0 (ratio of peaks originating from the G band to peaks originating from the D band) and a 2D / D ratio of less than 0.1 (ratio of peaks originating from the 2D band to peaks originating from the D band), while the negative electrode active material particles have a D / G ratio of 0.9 to 1.25.

[0041] Thus, if the G / D ratio of the porous carbon structure is less than 1.0, the 2D / D ratio is less than 0.1, and the D / G ratio of the negative electrode active material particles is between 0.9 and 1.25, it becomes a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity. In particular, a large D-band peak suppresses side reactions with the electrolyte, improving the retention rate and initial efficiency, but reducing Li diffusion. Also, a large G improves Li diffusion and the 4C cycle, but side reactions with the electrolyte occur, reducing the retention rate and efficiency. The range of D / G ratio that provides a good overall balance is between 0.9 and 1.25.

[0042] Here, the D / G ratio is an index used to evaluate crystallinity in Raman spectroscopy, and the G band (1500-1660 cm⁻¹) -1 ) and D-band (1300~1460cm) -1 This represents the intensity ratio of (D / G), and a smaller D / G ratio indicates better crystallinity. The peak of the 2D band is approximately 2650 cm⁻¹. -1 It is observed at [location].

[0043] Raman spectroscopy can be performed, for example, under the following conditions. • Device: HORIBA XploRA Plus • Laser wavelength: 532nm

[0044] Furthermore, in the spectrum obtained from Raman spectroscopy, it is preferable that the negative electrode active material particles have a D / G ratio of 0.9 or higher and 1.0 or lower.

[0045] Such negative electrode active material particles with a D / G ratio are suitable for the negative electrode active material of the present invention.

[0046] Furthermore, it is preferable that the porous carbon structure of the negative electrode active material particles has a pore PD50 of 2 nm or more and 3 nm or less, as analyzed by the BJH method.

[0047] Porous carbon having such a PD50 pore size is suitable for the structure of the negative electrode active material particles of the present invention.

[0048] Furthermore, it is preferable that active sites exist within the pores of the porous carbon structure, and that some of these active sites are modified with OH groups and COOH groups.

[0049] Such a configuration results in a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity. First, if the active sites inside the pores of the porous carbon structure are modified with OH groups, then, for example, a reaction with silane gas will easily disperse silane decomposition products as amorphous low-valence nanosilicon oxides inside the porous carbon structure. Second, if the active sites inside the pores of the porous carbon structure are modified with COOH groups, then, for example, a reaction with silane gas will partially transform not only the low-valence nanosilicon oxides but also compounds having Si-C bonds. Therefore, it is easy and preferable for the negative electrode active material to have the desired low-valence nanosilicon oxides and Si-C bonds.

[0050] Furthermore, it is preferable that the low-valence nanosilicon oxide is substantially in a composite state of zero, mono, di, tri, and tetravalent states, with the tetravalent state containing dimethylsiloxane.

[0051] In this composite state, in addition to achieving a lower irreversible capacity, by adjusting the distribution of zero-valent to tetravalent elements, it is possible to more effectively realize the absorption and desorption of Li by low-valent nanosilicon oxides. In particular, if the tetravalent element contains dimethylsiloxane, it becomes a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0052] Furthermore, it is preferable that the low-valence nanosilicon oxide is deposited in a state where it is in a separate phase from the porous carbon structure, that a portion of it is precipitated via oxygen, and that it has amorphous Si-C bonds at the interface with the carbon-based coating layer.

[0053] Having such amorphous Si-C bonds not only stabilizes the structure but also significantly improves water resistance. What is needed here is Si-C bonding, which is different from crystalline SiC in the semiconductor field. As a result, it becomes a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0054] 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.

[0055] Such materials with a grain size of zero-valent Si, which is essentially an amorphous structure, are preferred. If the grain size is too large (if the amount of zero-valent Si increases and crystallization progresses too much), the true density increases, which improves discharge capacity and initial efficiency but deteriorates cycle characteristics. This can be prevented and a balance can be achieved. As a result, it becomes a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0056] Furthermore, it is preferable that the low-valent nanosilicon oxide is substantially amorphous.

[0057] Such substantially amorphous materials are preferred.

[0058] Furthermore, in order to solve the above problems, the present invention provides a method for producing a negative electrode active material having negative electrode active material particles, comprising the step of preparing a porous carbon structure, wherein the porous carbon structure has a true density of 2.20 to 2.55 g / cm³ 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains at least / g of particle A, and furthermore, has a true density of 2.50-2.90 g / cm³. 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method3 A method for producing a negative electrode active material is provided, comprising the steps of: setting the weight ratio of particle B per g to particle A to satisfy 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B; including OH groups and COOH groups in the active sites contained in the porous carbon structure; flowing monosilane gas to deposit silicon oxide bonded to oxygen atoms inside the porous carbon structure, wherein the silicon oxide contains dangling bonds; after the step of depositing the silicon oxide, oxidizing at least a portion of the silicon present on the surface layer of the negative electrode active material in a reduced-pressure atmosphere; and after the step of oxidation in a reduced-pressure atmosphere, depositing a carbon-based coating layer at 530-600°C using hydrocarbon gas.

[0059] In the present invention's method for producing the negative electrode active material, the porous carbon structure has a true density of 2.20 to 2.55 g / cm³. 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains particle A at a concentration of / g. This indicates that it is sufficiently carbonized. As a result, the amount of undegraded compounds is reduced, preventing Li from being trapped, suppressing the increase in irreversible capacity, and improving efficiency. In addition, the increase in electronically conductive aromatic compounds improves electronic conductivity and thus improves cycle characteristics.

[0060] Furthermore, the true density is 2.50-2.90 g / cm³ 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3The weight ratio of particle B to particle A per gram is such that 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B. The large pore volume of particle B increases the amount of silicon-based compound deposited, leading to an increase in capacity when used in a battery. Furthermore, by not having too much particle B, the increase in the specific surface area of ​​the negative electrode active material itself is suppressed, preventing deterioration of cycle characteristics.

[0061] As a result, it is possible to provide a method for manufacturing a negative electrode active material that can improve cycle characteristics while maintaining high battery capacity and high initial efficiency.

[0062] Furthermore, in the step of depositing the silicon oxide, it is preferable to decompose the monosilane gas in a pressurized atmosphere of 30 kPaG to 190 kPaG. In this specification, gauge pressure is denoted as PaG and absolute pressure as PaA.

[0063] By decomposing monosilane gas in such a pressurized atmosphere, the monosilane gas can penetrate deep into the pores, allowing silicon oxide to be deposited deep within the pores. This enables more efficient decomposition of monosilane gas on the inner surface of the pores. In particular, monosilane readily undergoes monomolecular thermal decomposition (gas-phase thermal decomposition) at low temperatures, resulting in a more fluid state compared to adsorption thermal decomposition, thus improving the diffusibility of Li. Furthermore, the high pressure during the reaction allows for the formation of many dangling bonds, which are highly reactive and can be carbonized at a lower temperature than the typical decomposition temperature of hydrocarbon gases (e.g., acetylene gas) used in the next step (the step of depositing a carbon-based coating layer). As a result, the cycle characteristics are improved. In addition, the smooth acetylene decomposition improves conductivity. Consequently, the acceptance of Li is significantly improved, providing a suitable method for producing a negative electrode active material that can improve cycle characteristics while maintaining high battery capacity. [Effects of the Invention]

[0064] The negative electrode active material of the present invention, firstly, contains low-valence nanosilicon oxide, which reduces the generation of ionic substances and enhances the diffusivity of Li. Furthermore, because the low-valence nanosilicon oxide has Si-C bonds, the internal Si-C bonds have a strong bond with the Si in the surface layer, which suppresses the electronic breakup of the Si portion during charging and discharging, resulting in a stable structure. For this reason, it is electrochemically stable during charging and discharging, and decomposition during charging and discharging is less likely to occur.

[0065] Next, the porous carbon structure has a true density of 2.20-2.55 g / cm³. 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains particle A at a concentration of / g. This indicates that it is sufficiently carbonized. As a result, the amount of undegraded compounds is reduced, preventing Li from being trapped, suppressing the increase in irreversible capacity, and improving efficiency. In addition, the increase in electronically conductive aromatic compounds improves electronic conductivity and thus improves cycle characteristics.

[0066] Furthermore, the true density is 2.50-2.90 g / cm³ 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3 The weight ratio of particle B to particle A per gram is within the range of 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B. The large pore volume of particle B can increase the amount of silicon-based compound deposited, leading to an increase in capacity when used in a battery. Furthermore, by not having too much particle B, the increase in the specific surface area of ​​the negative electrode active material itself can be suppressed, preventing deterioration of cycle characteristics.

[0067] As a result, it is possible to provide a negative electrode active material that can improve cycle characteristics while maintaining high battery capacity and high initial efficiency.

[0068] According to the method for producing the negative electrode active material of the present invention, the porous carbon structure has a true density of 2.20 to 2.55 g / cm³. 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains particle A at a concentration of / g. This indicates that it is sufficiently carbonized. As a result, the amount of undegraded compounds is reduced, preventing Li from being trapped, suppressing the increase in irreversible capacity, and improving efficiency. In addition, the increase in electronically conductive aromatic compounds improves electronic conductivity and thus improves cycle characteristics.

[0069] Furthermore, the true density is 2.50-2.90 g / cm³ 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3 The weight ratio of particle B to particle A per gram is set to a range where 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B. The large pore volume of particle B can increase the amount of silicon-based compound deposited, leading to an increase in capacity when used in a battery. Furthermore, by not having too much particle B, the increase in the specific surface area of ​​the negative electrode active material itself can be suppressed, preventing deterioration of cycle characteristics.

[0070] As a result, it is possible to provide a method for manufacturing a negative electrode active material that can improve cycle characteristics while maintaining high battery capacity and high initial efficiency. [Brief explanation of the drawing]

[0071] [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. [Figure 4] These are the C1s spectra of the XPS from Examples 1-1 and 1-2. [Figure 5] These are the O1s spectra of the XPS from Examples 1-1 and 1-2. [Figure 6] This is the Raman spectroscopy spectrum of the porous carbon structure of Example 1-1. [Figure 7] This is an enlarged view of the Raman spectroscopy spectrum of the porous carbon structure of Example 1-1. [Figure 8] This is a characteristic diagram of the ESR before CVD in Example 1-1. [Figure 9] This is a characteristic diagram of the ESR after CVD in Example 1-1. [Figure 10] This is a characteristic diagram of the amount of dangling bond before and after CVD in Example 1-1. [Modes for carrying out the invention]

[0072] The following describes embodiments of the present invention, but the present invention is not limited thereto.

[0073] 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.

[0074] Therefore, the inventors diligently conducted research to obtain a negative electrode active material that can improve cycle characteristics while maintaining high battery capacity when used as the negative electrode of a secondary battery.

[0075] In particular, regarding the porous carbon structure contained in the negative electrode active material particles, the true density is 2.20~2.55 g / cm³. 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3We discovered that if the material contains particles of a certain density ( / g), it is possible to improve cycle characteristics while maintaining high battery capacity, thus completing the present invention.

[0076] In other words, the present invention relates to a negative electrode active material having negative electrode active material particles, wherein the negative electrode active material particles include a porous carbon structure, amorphous low-valence nanosilicon oxide dispersed inside the porous carbon structure, and a carbon-based coating layer covering at least a portion of the surface, the low-valence nanosilicon oxide having Si-C bonds with the porous carbon structure, and the porous carbon structure having a true density of 2.20 to 2.55 g / cm³ 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains at least / g of particle A, and furthermore, has a true density of 2.50-2.90 g / cm³. 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3 The negative electrode active material is characterized in that the weight ratio of particle B to particle A in units of / g is in the range of 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B.

[0077] Furthermore, the present invention relates to a method for producing a negative electrode active material having negative electrode active material particles, comprising the step of preparing a porous carbon structure, wherein the porous carbon structure has a true density of 2.20 to 2.55 g / cm³ 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains at least / g of particle A, and furthermore, has a true density of 2.50-2.90 g / cm³. 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3A method for producing a negative electrode active material, comprising the steps of: setting the weight ratio of particle B to particle A in units of / g to satisfy 0≦mb / ma<0.45, where ma is the weight of particle A and mb is the weight of particle B; including OH groups and COOH groups in the active sites contained in the porous carbon structure; flowing monosilane gas to deposit silicon oxide bonded to oxygen atoms inside the porous carbon structure, wherein the silicon oxide contains dangling bonds; after the step of depositing the silicon oxide, oxidizing at least a portion of the silicon present on the surface layer of the negative electrode active material in a reduced-pressure atmosphere; and after the step of oxidation in a reduced-pressure atmosphere, depositing a carbon-based coating layer at 530~600°C using hydrocarbon gas.

[0078] The following will provide a detailed explanation with reference to the drawings.

[0079] Figure 1 is a cross-sectional view of the negative electrode containing the negative electrode active material of the present invention, and Figure 2 is an example of the configuration of a lithium-ion secondary battery (laminated film type) containing the negative electrode active material of the present invention. Details of Figures 1 and 2 will be described later.

[0080] [The negative electrode active material of the present invention] The present invention relates to a negative electrode active material having negative electrode active material particles, wherein the negative electrode active material particles include a porous carbon structure, amorphous low-valence nanosilicon oxide dispersed inside the porous carbon structure, and a carbon-based coating layer covering at least a portion of the surface, the low-valence nanosilicon oxide having Si-C bonds with the porous carbon structure, and the porous carbon structure having a true density of 2.20 to 2.55 g / cm³ 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains at least / g of particle A, and furthermore, has a true density of 2.50-2.90 g / cm³. 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3The negative electrode active material is characterized in that the weight ratio of particle B to particle A in units of / g is within the range of 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B.

[0081] The negative electrode active material of the present invention contains low-valence nanosilicon oxide, which reduces the generation of ionic substances and enhances the diffusivity of Li. Furthermore, because the low-valence nanosilicon oxide has Si-C bonds, the internal Si-C bonds have a strong bond with the Si in the surface layer, which suppresses the electronic breakup of the Si portion during charging and discharging, resulting in a stable structure. For this reason, it is electrochemically stable during charging and discharging, and decomposition during charging and discharging is less likely to occur.

[0082] Next, the porous carbon structure has a true density of 2.20-2.55 g / cm³. 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains particle A at a concentration of / g. This indicates that it is sufficiently carbonized. As a result, the amount of undegraded compounds is reduced, preventing Li from being trapped, suppressing the increase in irreversible capacity, and improving efficiency. In addition, the increase in electronically conductive aromatic compounds improves electronic conductivity and thus improves cycle characteristics.

[0083] Furthermore, the true density is 2.50-2.90 g / cm³ 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3 The weight ratio of particle B to particle A per gram is within the range of 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B. The large pore volume of particle B can increase the amount of silicon-based compound deposited, leading to an increase in capacity when used in a battery. Furthermore, by not having too much particle B, the increase in the specific surface area of ​​the negative electrode active material itself can be suppressed, preventing deterioration of cycle characteristics.

[0084] As a result, it is possible to provide a negative electrode active material that can improve cycle characteristics while maintaining high battery capacity and high initial efficiency.

[0085] Furthermore, although not particularly limited, it is preferable that particle A has a carbon-carbon unsaturated bond and a bond derived from an aromatic ester, and particle B has a carbon-carbon single bond and a bond derived from an ether system.

[0086] If particle A and particle B have such a bond, they become a suitable negative electrode active material capable of improving cycle characteristics while maintaining high battery capacity.

[0087] Furthermore, although not particularly limited, it is preferable that the particle size distribution of particle A is D10=3~9μm, D50=5~16μm, D90=10~25μm, and the particle size distribution of particle B is D10=0.2~3μm, D50=1~5μm, D90=3~6μm.

[0088] If particles A and B have this particle size distribution, they become a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0089] Furthermore, although not particularly limited, porous carbon structures are defined by the 1100 cm⁻¹ spectrum obtained from Raman spectroscopy. -1 More than 1200cm -1 It is preferable that the peaks are within the following range.

[0090] A negative electrode active material with such a spectrum has pores of an appropriate size within the porous carbon structure, allowing gas to easily reach the pores. As a result, it becomes a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0091] Furthermore, although not particularly limited, the peaks in the spectrum obtained from Raman spectroscopy are preferably peaks originating from C=O bonds or CO bonds, and the porous carbon structure preferably contains at least one of C=O bonds or CO bonds.

[0092] If a material contains C=O or CO bonds internally, for example, when it reacts with silane gas, a CO-Si moiety is formed. This O-Si bond exhibits excellent Li diffusion properties, which can improve fast charging capabilities. As a result, it becomes a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0093] Furthermore, although not particularly limited, in the spectrum obtained from Raman spectroscopy, the porous carbon structure preferably has a G / D ratio of less than 1.0 (ratio of peaks originating from the G band to peaks originating from the D band) and a 2D / D ratio of less than 0.1 (ratio of peaks originating from the 2D band to peaks originating from the D band), and the negative electrode active material particles preferably have a D / G ratio of 0.9 to 1.25.

[0094] Thus, if the G / D ratio of the porous carbon structure is less than 1.0, the 2D / D ratio is less than 0.1, and the D / G ratio of the negative electrode active material particles is between 0.9 and 1.25, it becomes a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity. In particular, a large D-band peak suppresses side reactions with the electrolyte, improving the retention rate and initial efficiency, but reducing Li diffusion. Also, a large G improves Li diffusion and the 4C cycle, but side reactions with the electrolyte occur, reducing the retention rate and efficiency. The optimal D / G ratio range for overall balance is 0.9 to 1.25.

[0095] Here, the D / G ratio is an index used to evaluate crystallinity in Raman spectroscopy, and the G band (1500-1660 cm⁻¹) -1 ) and D-band (1300~1460cm) -1This represents the intensity ratio of (D / G), and a smaller D / G ratio indicates better crystallinity. The peak of the 2D band is approximately 2650 cm⁻¹. -1 It is observed at [location].

[0096] Furthermore, although not particularly limited, it is preferable that the negative electrode active material particles have a D / G ratio of 0.9 or more and 1.0 or less in the spectrum obtained from Raman spectroscopy.

[0097] Such negative electrode active material particles with a D / G ratio are suitable for the negative electrode active material of the present invention.

[0098] Furthermore, although not particularly limited, the porous carbon structure of the negative electrode active material particles is preferably such that the PD50 of the pores, as analyzed by the BJH method, is 2 nm or more and 3 nm or less.

[0099] Porous carbon having such a PD50 pore size is suitable for the structure of the negative electrode active material particles of the present invention.

[0100] Furthermore, although not particularly limited, it is preferable that active sites exist within the pores of the porous carbon structure, and that some of the active sites are modified with OH groups and COOH groups.

[0101] Such a configuration results in a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity. First, if the active sites inside the pores of the porous carbon structure are modified with OH groups, then, for example, a reaction with silane gas will easily disperse silane decomposition products as amorphous low-valence nanosilicon oxides inside the porous carbon structure. Second, if the active sites inside the pores of the porous carbon structure are modified with COOH groups, then, for example, a reaction with silane gas will partially transform not only the low-valence nanosilicon oxides but also compounds having Si-C bonds. Therefore, it is easy and preferable for the negative electrode active material to have the desired low-valence nanosilicon oxides and Si-C bonds.

[0102] Furthermore, although not particularly limited, the low-valence nanosilicon oxide is preferably in a composite state of substantially zero-valence, mono-valence, di-valence, tri-valence, and tetra-valence, with the tetra-valence portion preferably containing dimethylsiloxane.

[0103] In this composite state, in addition to achieving a lower irreversible capacity, by adjusting the distribution of zero-valent to tetravalent elements, it is possible to more effectively realize the absorption and desorption of Li by low-valent nanosilicon oxides. In particular, if the tetravalent element contains dimethylsiloxane, it becomes a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0104] The valency of low-valency nanosilicon oxides can be quantified using NMR (nuclear magnetic resonance) and XPS (X-ray photoelectron spectroscopy).

[0105] NMR (nuclear magnetic resonance) measurements 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℃

[0106] 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.

[0107] Furthermore, although not particularly limited, it is preferable that the low-valence nanosilicon oxide is deposited in a state where its phase is separated from the porous carbon structure, that some of it is precipitated via oxygen, and that it has amorphous Si-C bonds at the interface with the carbon-based coating layer.

[0108] Having such amorphous Si-C bonds not only stabilizes the structure but also significantly improves water resistance. What is needed here is Si-C bonding, which is different from crystalline SiC in the semiconductor field. As a result, it becomes a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0109] Furthermore, although not particularly limited, 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.

[0110] Such materials with a grain size of zero-valent Si, which is essentially an amorphous structure, are preferred. If the grain size is too large (if the amount of zero-valent Si increases and crystallization progresses too much), the true density increases, which improves discharge capacity and initial efficiency but deteriorates cycle characteristics. This can be prevented and a balance can be achieved. As a result, it becomes a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0111] The grain size of low-valent nanosilicon oxides can be confirmed by TEM-EDX. The conditions for this can be as follows: The negative electrode active material is processed on both sides using a focused ion beam (FIB) system in an air-free environment. The FIB system used is a SIINT XVision200DB with an acceleration voltage of 30kV. TEM observation is performed using an FEI TecnaiG2F20 with an acceleration voltage of 200kV, and EDX is performed using an EDAX r-TEM with an acceleration voltage of 200kV.

[0112] 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".

[0113] Furthermore, although not particularly limited, it is preferable that the low-valent nanosilicon oxide is substantially amorphous.

[0114] Such substantially amorphous materials are preferred.

[0115] Furthermore, the negative electrode active material of the present invention may also include a silicon-cored carbon composite within a porous carbon structure, and this carbon composite may contain at least one of carbon black, acetylene black, and carbon nanotubes.

[0116] Furthermore, porous carbon can be derived from bio-based, resin-based, or petroleum-based sources, with bio-based or resin-based sources being preferred.

[0117] <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.

[0118] [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.

[0119] [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).

[0120] 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.

[0121] 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.

[0122] [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 silicon-based active material particles. Furthermore, for battery design purposes, it may also contain other materials such as thickeners (also called "binding agents" or "binders") and conductive additives.

[0123] [Negative electrode active material of the present invention and method for manufacturing negative electrode] Subsequently, an example of the negative electrode active material of the present invention and a method for manufacturing a negative electrode using the same will be described.

[0124] First, a method for manufacturing the negative electrode active material contained in the negative electrode will be described.

[0125] The method for manufacturing the negative electrode active material of the present invention is a method for manufacturing a negative electrode active material having negative electrode active material particles, and includes a step of preparing a porous carbon structure, wherein the porous carbon structure has a true density of 2.20 to 2.55 g / cm 3 , a pore volume of 1.00 to 1.25 cm 3 / g by the BET method, and a pore volume of 0.5 to 0.75 cm 3 / g by the BJH method, and at least includes particle A, and further has a true density of 2.50 to 2.90 g / cm 3 , a pore volume of 1.15 to 1.30 cm 3 / g by the BET method, and a pore volume of 0.75 to 0.9 cm 3 / g by the BJH method, and the weight ratio of particle A to particle B satisfies 0 ≦ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B; a step of including OH groups and COOH groups at the active sites contained in the porous carbon structure; a step of flowing monosilane gas to deposit silicon oxide bonded to oxygen atoms inside the porous carbon structure, wherein the silicon oxide is in a state containing dangling bonds; a step of oxidizing at least a part of the silicon present in the surface layer portion of the negative electrode active material in a reduced pressure atmosphere after the step of depositing the silicon oxide; and a step of depositing a carbon-based coating layer at 530 to 600 °C using hydrocarbon gas after the step of oxidizing in a reduced pressure atmosphere. The method for manufacturing a negative electrode active material is characterized by including these steps.

[0126] According to the method for manufacturing the negative electrode active material of the present invention, the porous carbon structure has a true density of 2.20 to 2.55 g / cm 3 , a pore volume of 1.00 to 1.25 cm 3 / g by the BET method, and a pore volume of 0.5 to 0.75 cm 3It contains particle A at a concentration of / g. This indicates that it is sufficiently carbonized. As a result, the amount of undegraded compounds is reduced, preventing Li from being trapped, suppressing the increase in irreversible capacity, and improving efficiency. In addition, the increase in electronically conductive aromatic compounds improves electronic conductivity and thus improves cycle characteristics.

[0127] Furthermore, the true density is 2.50-2.90 g / cm³ 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3 The weight ratio of particle B to particle A per gram is set to a range where 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B. The large pore volume of particle B can increase the amount of silicon-based compound deposited, leading to an increase in capacity when used in a battery. Furthermore, by not having too much particle B, the increase in the specific surface area of ​​the negative electrode active material itself can be suppressed, preventing deterioration of cycle characteristics.

[0128] As a result, it is possible to provide a method for manufacturing a negative electrode active material that can improve cycle characteristics while maintaining high battery capacity and high initial efficiency.

[0129] Furthermore, although not particularly limited, the step of depositing silicon oxide is preferably carried out by decomposing monosilane gas in a pressurized atmosphere of 30 kPaG to 190 kPaG. In this specification, gauge pressure is denoted as PaG and absolute pressure as PaA.

[0130] By decomposing monosilane gas in such a pressurized atmosphere, the monosilane gas can penetrate deep into the pores, allowing silicon oxide to be deposited deep within the pores. This enables more efficient decomposition of monosilane gas on the inner surface of the pores. In particular, monosilane readily undergoes monomolecular thermal decomposition (gas-phase thermal decomposition) at low temperatures, resulting in a more fluid state compared to adsorption thermal decomposition, thus improving the diffusibility of Li. Furthermore, the high pressure during the reaction allows for the formation of many dangling bonds, which are highly reactive and can be carbonized at a lower temperature than the typical decomposition temperature of hydrocarbon gases (e.g., acetylene gas) used in the next step (the step of depositing a carbon-based coating layer). As a result, the cycle characteristics are improved. In addition, the smooth acetylene decomposition improves conductivity. Consequently, the acceptance of Li is significantly improved, providing a suitable method for producing a negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0131] Here, we will explain the manufacturing process of SiC. Generally speaking, SiC is produced by using a fluidized bed tank, injecting silane gas and carrier gas from the bottom in a heated atmosphere, depositing silicon inside porous carbon, and then performing an oxidation process, followed by carbon coating using hydrocarbon gas or coal tar pitch.

[0132] In this case, with this method, the silicon (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.

[0133] Furthermore, adsorption thermal decomposition is more likely to occur at temperatures of at least 400°C (effectively 450-500°C) (Patent Documents 4 and 5), and the resulting silicon, although amorphous, has a coordination number greater than 3.3.

[0134] The coordination number is calculated by taking an EXAFS scan using the 6N line at the Aichi Synchrotron Radiation Center, which is capable of performing XANES and EXAFS measurements as shown below, and then fitting the image using Feff (a theoretical calculation software for XAFS based on multiple scattering theory).

[0135] 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 airless environment under an Ar atmosphere, 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

[0136] Furthermore, the substance obtained in the oxidation process is SiO2, so Si 0+ and Si 4+ The composite material is formed within porous carbon.

[0137] In this case, Si-O bonds exist in the outermost layer, and general SiC can be produced by performing carbon coating CVD with hydrocarbon gas on the upper part. However, if there are not enough Si-O bonds, Si-C crystals will form, reducing the battery capacity (Patent Documents 6 and 7).

[0138] In the method for producing the negative electrode active material of the present invention, the active sites of the porous carbon structure are utilized to incorporate acidic groups such as carboxyl groups (COOH groups). These acidic groups can react with silane gas to partially transform not only into complex oxides but also into compounds having Si-C bonds.

[0139] Furthermore, OH groups are incorporated into the porous carbon structure.

[0140] When heat treatment is performed in this state, CO or CO2 is detected in the exhaust gas. Normally, when completely dried, no CO gas is emitted, but by reacting silane gas in a pressurized atmosphere while the exhaust gas contains a large amount of CO and CO2, silane decomposition products are deposited on the porous carbon structure as low-valence nanosilicon oxides. At this time, since CO and CO2 gases continue to be emitted from inside the pores of the porous carbon structure, it is important to use a hydrogen carrier in a pressurized atmosphere to allow the silane gas to penetrate to the interior. In a typical fluidized bed, the pressure drop is about 10 kPaG, but it has been found that this reaction gradually starts from about 25 kPaG. In this specification, gauge pressure is denoted as PaG and absolute pressure as PaA.

[0141] Furthermore, although not specifically limited, by introducing silane gas into the pores under a pressure range of 30 kPaG to 190 kPaG (gauge pressure), it becomes possible to deposit silicon oxide deep within the pores. This has been shown to allow for more efficient decomposition of the silane gas on the inner surface of the pores.

[0142] Furthermore, when porous carbon containing C=O or CO bonds is reacted with silane gas, a CO-Si moiety is formed. This O-Si bond exhibits excellent Li diffusion properties, which can improve rapid charging capabilities. The presence of this C=O or CO bond is evident in the Raman spectrum at 1100 cm⁻¹. -1 More than 1200cm -1 This can be confirmed by the presence of peaks (shoulders) within the following range.

[0143] At this time, CO-Si moieties can also be generated by reacting porous carbon with silane gas while the pores contain OH groups and COOH groups. Furthermore, when heat is applied during subsequent CVD with hydrocarbon gas, Si crystallization is difficult, and the amorphous state can be maintained.

[0144] Furthermore, low-valent nanosilicon oxides deposited on porous carbon structures exhibit high Li diffusivity. Generally, compounds of Si and Li are Li 15 While Si4 is generated, it exhibits ionic properties and reduces diffusivity. In contrast, the low-valence nanosilicon oxide obtained by the method for producing the negative electrode active material of the present invention can reduce the generation of ionic substances.

[0145] Furthermore, it has been found that low-valence nanosilicon oxides with Si-C bonds are electrochemically stable during charging and discharging, and are less prone to decomposition during these processes.

[0146] Next, typical silane decomposition reactions, such as those used in semiconductors (polysilicon), primarily involve adsorption-based thermal decomposition, requiring thermal energy of approximately 400 degrees Celsius or higher.

[0147] However, in a pressurized region, for example, by impregnating the silane gas inside the pores and leaving active sites on the porous carbon, in a state where CO and CO2 gas coexist, monosilane undergoes single-molecule thermal decomposition (gas-phase thermal decomposition) in the gas phase at low temperatures below 380°C, producing silylene, and then hydrogen is removed as a single atom, ultimately forming silicon. Incidentally, even when estimated using the Boltzmann factor, decomposition does not occur below 380°C. In this temperature range, there exists a reaction pathway where the energy barrier allowing hydrogen detachment is irreversible, or where the equilibrium is heavily skewed towards the product side.

[0148] For example, in a pressurized atmosphere, monosilane and silylene mixed with hydrogen inside the pores are thought to have a lower activation energy, leading to a single-molecule thermal decomposition (gas-phase thermal decomposition) reaction. Furthermore, the dangling bonds present in porous carbon are also thought to contribute to the decomposition.

[0149] Furthermore, by mixing hydrogen or an inert gas into the silane and controlling the reaction of silylene returning to silane and the frequency of contact with dangling bonds, strain is generated during decomposition, making it possible to control the coordination number to 3.3 or less.

[0150] In particular, when the coordination number falls below 3, the form of Si that reacts with Li has a high theoretical capacity. 22 Si5 can be achieved.

[0151] In general, silicon reacts with lithium to produce a reaction product of lithium. 15 It is Si4, Li 15 The theoretical capacity of Si4 is Li 22 It has a lower pH than Si5 and exhibits ionic properties.

[0152] Furthermore, silicon deposited by gas-phase thermal decomposition and increased reaction pressure does not adhere as strongly to porous carbon as silicon deposited by adsorption thermal decomposition. After at least one charge-discharge cycle, it becomes fluid enough to allow extraction of silicon from the pore surface. This helps to improve the diffusivity of Li.

[0153] Furthermore, increasing the pressure during silicon oxide deposition and reaction makes it possible to create a larger number of dangling bonds.

[0154] These dangling bonds and Si-H bonds are highly reactive, allowing for carbonization at temperatures lower than the typical decomposition temperature of hydrocarbon gases (in this case, acetylene gas). (At the same temperature, generally only tar components are produced.)

[0155] Furthermore, at this stage, some of the Si possesses Si-C bonds, which not only stabilize the structure but also significantly improve water resistance. What is needed here is a Si-C bond, which is different from crystalline SiC in the semiconductor field.

[0156] However, since Si-C bonds cannot be formed in large quantities because they deactivate Si, the formation of Si-C crystals can be suppressed by converting the Si-H portion of the outermost layer to a low-valence silicon oxide (monovalent to trivalent) before introducing the hydrocarbon gas, and then reacting it with the hydrocarbon gas. At this time, a tetravalent state also exists because it has a dimethylsiloxane structure.

[0157] Incidentally, silicon oxides with Si-C bonds produced using hydrocarbon gases and silicon oxides with Si-C bonds derived from porous carbon structures have the same structure.

[0158] The decomposition reaction of hydrocarbon gases is not particularly limited, but it is preferable to carry it out in a reduced pressure atmosphere of 10,000 PaA or less. The carbon components decomposed under these conditions contain many dangling bonds and form CH bond states on the outermost layer. When forming a slurry for use in a battery, these bonds create repulsive forces with the binder, making it possible to ensure a stable dispersion state for a long period of time.

[0159] <An example of each step in the manufacturing method of the negative electrode active material> Referring to Figure 3, an example of each step in the method for producing the negative electrode active material will be explained.

[0160] The present invention relates to a method for producing a negative electrode active material, comprising the step of preparing a porous carbon structure, wherein the porous carbon structure has a true density of 2.20 to 2.55 g / cm³. 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains at least / g of particle A, and furthermore, has a true density of 2.50-2.90 g / cm³. 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3 Step S1: The weight ratio of particle B to particle A per gram is set to a range satisfying 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B. Step S2: The active sites contained in the porous carbon structure contain OH groups and COOH groups. Step S3: Monosilane gas is flowed to deposit silicon oxide bonded to oxygen atoms inside the porous carbon structure, wherein the silicon oxide contains dangling bonds. Step S4: After the step of depositing silicon oxide, at least a portion of the silicon present on the surface of the negative electrode active material is oxidized in a reduced-pressure atmosphere. Step S5: After the step of oxidation in a reduced-pressure atmosphere, a carbon-based coating layer is deposited at 530-600°C using hydrocarbon gas.

[0161] (Step S1) A step of preparing a porous carbon structure, wherein the porous carbon structure has a true density of 2.20 to 2.55 g / cm³. 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains at least / g of particle A, and furthermore, has a true density of 2.50-2.90 g / cm³. 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3This step involves setting the weight ratio of particle B to particle A (at a rate of / g) to a range that satisfies 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B.

[0162] Here, we will explain porous carbon, specifically conventional porous carbon a and the porous carbon b of the present invention.

[0163] [Porous carbon a] First, a 10 μm phenolic resin is heat-treated at 600°C for 1 hour under vacuum. At this time, the true density after activation can be adjusted by using other resins or bio-derived carbon sources instead of phenolic resin as the raw material. Next, potassium hydroxide and carbide are mixed in a 5:1 ratio and activated at 820°C. After the activation treatment, the potassium is deactivated with water, then hydrochloric acid (9) and oxalic acid (1) are added to adjust the pH to 7. After filtration, rinse with water. The extracted porous carbon is dried at 60°C under vacuum.

[0164] [Porous carbon b] First, charcoal is produced by heat treatment at 600°C for 1 hour under vacuum. Next, the material is ground to a median diameter of 10 μm. At this stage, the particles are separated and collected into those collected by the cyclone and those collected by the bag filter. The collected particles are designated as particle A and particle B. At this time, the true density of particle A and particle B can be adjusted by the carbon source used as the raw material, as described above.

[0165] For example, in the case of phenolic resin, where the primary particle size can be adjusted, particle A has a true density derived from the phenolic resin, while particle B depends on the small amount of binder component that held the primary particles together. In the case of bio-derived materials, which are uniform and do not have a primary particle size, the difference in true density between particle A and particle B is smaller compared to that of phenolic resin.

[0166] Here, the true density can be measured using, for example, a dry automatic densimeter manufactured by Micromerities.

[0167] Furthermore, the porous carbon structure of the present invention has a true density of 2.20 to 2.55 g / cm³. 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It must contain particles of / g, and the above particle A can be applied.

[0168] Here, pore volume can be measured using both the BET method and the BJH method, for example, with a Shimadzu TriStar. In particular, the Shimadzu TriStar II Plus can measure specific surface area / pore distribution etc. using a constant volume method based on gas adsorption. It can be used under the following conditions as an example. • 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

[0169] The porous carbon structure of the present invention further has a true density of 2.50 to 2.90 g / cm³. 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3 It may contain particles of / g, and the above particle B can be applied.

[0170] Particle A can be used alone, or an appropriate amount of particle B can be mixed in to form porous carbon. Increasing the content of particle B, which has a large pore volume, can increase the amount of silicon-based compounds deposited, leading to an increase in battery capacity. However, it also increases the specific surface area of ​​the negative electrode active material itself, which can worsen cycle characteristics. Therefore, it is necessary to control the amount of particle B so that it does not become too high compared to particle A. Specifically, the weight ratio of particle B to particle A should be within the range of 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B.

[0171] Furthermore, although not particularly limited, it is preferable that particle A has a carbon-carbon unsaturated bond and a bond derived from an aromatic ester, and particle B has a carbon-carbon single bond and a bond derived from an ether system.

[0172] If particle A and particle B have such a bond, they become a suitable negative electrode active material capable of improving cycle characteristics while maintaining high battery capacity.

[0173] The identification of surface bond species in porous carbon can be confirmed by XPS analysis of C1s and O1s. In C1s, carbon-carbon unsaturated bonds show a peak around 284.2 eV, while single bonds show a peak around 284.6 eV. In O1s, aromatic esters and ethers show peaks around 531.8-532.8 eV and 532.8 eV, respectively.

[0174] Furthermore, the types of bonds can be adjusted by controlling the temperature conditions during charcoal production. For example, increasing the temperature promotes carbonization, which increases the number of unsaturated bonds. However, if the temperature is too high, the CO bonds will break, so proper temperature control is desirable.

[0175] Furthermore, the difference between particle A and particle B is also evident in their particle size distribution. While not particularly limited, it is preferable that the particle size distribution of particle A is D10=3~9μm, D50=5~16μm, and D90=10~25μm, and the particle size distribution of particle B is D10=0.2~3μm, D50=1~5μm, and D90=3~6μm.

[0176] If particles A and B have this particle size distribution, they become a suitable negative electrode active material that can improve cycle characteristics while maintaining high battery capacity.

[0177] Here, the particle size distribution can be measured using a particle size distribution measuring device.

[0178] The subsequent activation treatment and subsequent steps are carried out in the same manner as described above for porous carbon a.

[0179] (Step S2) This step involves incorporating OH groups and COOH groups into the active sites contained within the porous carbon structure.

[0180] Porous carbon is placed in a reaction vessel and heated to 100°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 and CO2 gas concentrations. The gas concentration when no moisture is released should be approximately 7000-8000 ppm.

[0181] If some of the active sites within the pores of a porous carbon structure are modified with OH groups and COOH groups, it becomes a suitable negative electrode active material capable of improving cycle characteristics while maintaining high battery capacity. First, if the active sites within the pores of the porous carbon structure are modified with OH groups, then, for example, the reaction with silane gas in step S3 easily disperses silane decomposition products as amorphous low-valence nanosilicon oxides within the porous carbon structure. Second, if the active sites within the pores of the porous carbon structure are modified with COOH groups, then, for example, the reaction with silane gas partially transforms not only into low-valence nanosilicon oxides but also into compounds having Si-C bonds. Therefore, it is easy and preferable for the negative electrode active material to have the desired low-valence nanosilicon oxides and Si-C bonds.

[0182] (Step S3) The step involves flowing monosilane gas to deposit silicon oxide bonded to oxygen atoms inside a porous carbon structure, wherein the silicon oxide contains dangling bonds.

[0183] The container is heated. When the internal temperature reaches 370°C, silane gas is introduced from the bottom to deposit silicon inside the porous carbon. (The pore volume of the porous carbon is estimated in advance from pore distribution measurement, and an amount of silane equal to the pore volume / 0.9 is flowed in ⇒ the reaction rate is controlled to 90%.) At this time, it is preferable that the deposition takes place at a temperature below the decomposition temperature of the silane gas (350°C or higher, 400°C or lower).

[0184] At this time, although the pressure inside the container is variable, it is preferable to average it out to a range of 30 kPaG to 190 kPaG. Deposition at pressures above 190 kPaG may result in a denser film, but considering the durability of the equipment, it is stopped at 190 kPaG (in reality, it is variable and has been confirmed to rise up to a maximum of 195 kPaG). At this point, hydrogen gas equal to the amount of silane is flowed from the side for the purpose of stirring the powder.

[0185] After the reaction, the material temperature is lowered to room temperature, and under reduced pressure, nitrogen is introduced to form a nitrogen layer on the exposed surfaces, including the inside of the pores. Next, oxygen diluted with nitrogen is introduced to increase the weight of the oxygen by approximately 0.3 wt% (the moisture content of the introduced air is 100 ppm).

[0186] During this process, it is important to stir the powder and allow it to cool slowly. Rapid oxidation leads to the conversion to SiO2, which degrades its properties. Therefore, pre-pressurizing with nitrogen helps to create a nitrogen adsorption layer, which suppresses rapid oxidation.

[0187] (Step S4) The step involves depositing silicon oxide, followed by oxidizing at least a portion of the silicon present on the surface of the negative electrode active material in a reduced-pressure atmosphere.

[0188] Normally, the oxidation atmosphere is maintained at atmospheric pressure to reduced pressure, and by controlling the sample temperature to below 50°C as an exothermic reaction, low-valence nanosilicon oxide can be formed. In this case, including the oxygen derived from the O component adsorbed inside the porous carbon structure, an oxygen content of approximately 1 wt% can be achieved in the entire negative electrode active material.

[0189] Here, the actual oxidation process is carried out in a reduced-pressure atmosphere. Once in the FV state and after repressurizing with nitrogen, it is depressurized to -20 kPaG, and nitrogen containing oxygen is introduced up to -5 kPaG or almost normal pressure. When oxygen is consumed, it enters a reduced-pressure state. This promotes the oxidation of the part near the surface layer, and the bulk interior uses the oxygen component of the carbon described in step S1. Since the amount of oxygen in the part near the surface layer is small, it is necessary to add it from the outside.

[0190] Part of the Si-O compound formed at this time forms a compound in part during C-CVD performed in step S5 (which can be confirmed by XPS), thereby enhancing the adhesion between the carbon-based coating layer formed in step S5 and the Si part.

[0191] (Step S5) This is a step of depositing a carbon-based coating layer at 530 - 600 °C using a hydrocarbon gas.

[0192] Heat the internal temperature to 530 - 600 °C in a nitrogen atmosphere, introduce acetylene gas, and form a carbon-based coating layer on the surface. Perform a treatment at 8000 PaA for 9 hours. The obtained material was analyzed by XRD, and as a result of calculating the crystallite size of Si using the Scherrer equation, it is 0.8 nm, but this is the result of calculation and is considered to be substantially amorphous. (Here, the standard acetylene reaction temperature is set at 600 °C.)

[0193] At this time, by carrying out the reaction in a reduced-pressure atmosphere, acetylene gas is allowed to spread to the Si filled inside the pores. Here, by reacting with the Si-H bond that did not reach the low valence oxidation state to obtain a Si-C bond, a stable material is obtained.

[0194] As described above in steps S1 to S5, a negative electrode active material having negative electrode active material particles is provided, wherein the negative electrode active material particles include a porous carbon structure, amorphous low-valence nanosilicon oxide dispersed inside the porous carbon structure, and a carbon-based coating layer covering at least a portion of the surface, the low-valence nanosilicon oxide has Si-C bonds with the porous carbon structure, and the porous carbon structure has a true density of 2.20 to 2.55 g / cm³. 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains at least / g of particle A, and furthermore, has a true density of 2.50-2.90 g / cm³. 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3 A negative electrode active material can be manufactured characterized in that the weight ratio of particle B to particle A per gram is in the range of 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B.

[0195] According to the method for producing the negative electrode active material of the present invention, the porous carbon structure has a true density of 2.20 to 2.55 g / cm³. 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3 It contains particle A at a concentration of / g. This indicates that it is sufficiently carbonized. As a result, the amount of undegraded compounds is reduced, preventing Li from being trapped, suppressing the increase in irreversible capacity, and improving efficiency. In addition, the increase in electronically conductive aromatic compounds improves electronic conductivity and thus improves cycle characteristics.

[0196] Furthermore, the true density is 2.50-2.90 g / cm³ 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3The weight ratio of particle B to particle A per gram is set to a range where 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B. The large pore volume of particle B can increase the amount of silicon-based compound deposited, leading to an increase in capacity when used in a battery. Furthermore, by not having too much particle B, the increase in the specific surface area of ​​the negative electrode active material itself can be suppressed, preventing deterioration of cycle characteristics.

[0197] As a result, it is possible to provide a method for manufacturing a negative electrode active material that can improve cycle characteristics while maintaining high battery capacity and high initial efficiency.

[0198] <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.

[0199] [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.

[0200] 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.

[0201] 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.

[0202] 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.

[0203] 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.

[0204] The positive electrode current collector is formed from a conductive material such as aluminum.

[0205] 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.

[0206] 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.

[0207] 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.

[0208] 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 cathode materials, a high battery capacity can be obtained, and excellent cycle characteristics can also be obtained.

[0209] [Negative electrode] The negative electrode has the same configuration as the negative electrode 10 for a lithium-ion secondary battery in FIG. 1 described above. For example, the negative electrode has negative electrode active material layers on both sides of a 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.

[0210] 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 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 has a region where the opposing positive electrode active material layer does not exist. This is for performing a stable battery design.

[0211] In a region where the negative electrode active material layer and the 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.

[0212] [Separator] The separator isolates the positive electrode and the negative electrode, prevents current short - circuit due to contact between the two electrodes, and allows lithium ions to pass through. This separator is formed of, for example, a porous membrane made of synthetic resin or ceramic, and may have a laminated structure in which two or more porous membranes are laminated. Examples of synthetic resins include polytetrafluoroethylene, polypropylene, polyethylene, etc.

[0213] [Electrolyte solution] At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolyte solution). This electrolyte solution has an electrolyte salt dissolved in a solvent and may contain other materials such as additives.

[0214] As the solvent, for example, a non - aqueous solvent can be used. Examples of non - aqueous solvents include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2 - dimethoxyethane or tetrahydrofuran, etc. Among these, it is desirable to use at least one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate. This is because better characteristics can be obtained. Also in this case, by combining a high - viscosity solvent such as ethylene carbonate and propylene carbonate with a low - viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, more excellent characteristics can be obtained. This is because the dissociation property of the electrolyte salt and the ion mobility are improved.

[0215] 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).

[0216] 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.

[0217] 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.

[0218] 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.

[0219] 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.

[0220] 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.

[0221] 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).

[0222] 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]

[0223] The present invention will be described more specifically below with reference to examples and comparative examples of the present invention, but the present invention is not limited to these examples. Furthermore, to avoid redundancy, explanations of the steps of the above-mentioned <Example of each step in the method for producing the negative electrode active material> and Figure 3 may be omitted.

[0224] First, the negative electrode active materials for the following examples and comparative examples were prepared, and a laminate film type lithium-ion secondary battery 30, as shown in Figure 2, was fabricated using each of these negative electrode active materials.

[0225] In this case, as a specification common to both the examples and comparative examples, unless otherwise specified, the above <Example of each step in the method for producing the negative electrode active material> shall be followed, and furthermore, the above [porous carbon b] shall be used for the porous carbon in step S1 as the standard step.

[0226] (Comparative Example 1-1) In the standard steps, the heat treatment temperature in step S1 was increased to 1000°C to increase the true density of the porous carbon.

[0227] [Measurement of negative electrode active material] The negative electrode active material prepared as described above was subjected to measurements such as infrared spectroscopy, Raman spectroscopy, XAFS, and ESR as needed.

[0228] [Fabrication of the negative electrode] The negative electrode active material prepared as described above, graphite, conductive additive 1 (carbon nanotubes, CNTs), conductive additive 2 (carbon nanoparticles with a median diameter of approximately 50 nm), sodium polyacrylate, and carboxymethylcellulose (hereinafter referred to as CMC) 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.

[0229] 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.

[0230] [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.

[0231] 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.

[0232] 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.

[0233] [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 1.0V.

[0234] 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.

[0235] [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.

[0236] 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.

[0237] The types of silicon-cored carbon composites were investigated by observing the porous carbon structure in the negative electrode active material particles using a scanning electron microscope (SEM).

[0238] The results of each measurement are shown in Tables 1 and 2. Tables 1 and 2 also include information on Comparative Example 1-2 and Examples 1-1 to 11-4, which are described later.

[0239] [Table 1]

[0240] [Table 2]

[0241] Comparative Example 1-1 increased the true density of porous carbon by raising the heat treatment temperature in step S1 of the standard steps to 1000°C. As a result, the true density of both particle A and particle B increased. However, the pore volume was small, and the overall battery characteristics were poor.

[0242] (Comparative Example 1-2) The difference from Comparative Example 1-1 is that the heat treatment temperature in step S1 was lowered to 500°C, reducing the true density of the porous carbon. As a result, the true densities of both particle A and particle B also decreased. Furthermore, the pore volume was smaller. When this was used in a battery, a decrease in initial efficiency was observed compared to Comparative Example 1-1. It is thought that a large amount of irreversible components remain due to the low density of the porous carbon.

[0243] (Example 1-1) Porous carbon was fabricated using phenolic resin as the raw material. The difference from Comparative Example 1-1 was that the standard steps were followed, and the temperature for depositing the carbon-based coating layer in step S5 was set to 600°C. The porous carbon at this time had a true density of 2.44 g / cm³. 3 BET pore volume 1.12 cm³ 3 / g, BJH pore volume 0.61 cm³ 3 Particle A with a D50 of 7.4 μm and a true density of 2.85 g / cm³ 3 BET pore volume 1.20 cm³ 3 / g, BJH pore volume 0.77cm³ 3Particle B, with a D50 of 2.2 μm and a weight of / g, was mixed in a 95:5 ratio (mb / ma = 0.05) and used. Batteries using this technology exhibited excellent battery characteristics. Example 1-1 showed better results than Comparative Examples 1-1 and 1-2 in terms of efficiency, single-unit capacity, and cycle characteristics.

[0244] (Examples 1-2) The difference from Example 1-1 is that porous carbon was fabricated using bio-derived coconut shells as the raw material. The porous carbon in this case had a true density of 2.50 g / cm³. 3 BET pore volume 1.21 cm³ 3 / g, BJH pore volume 0.66 cm³ 3 Particle A with a D50 of 8.4 μm and a true density of 2.51 g / cm³ 3 BET pore volume 1.21 cm³ 3 / g, BJH pore volume 0.76 cm³ 3 Particle B, with a D50 of 2.2 μm and a weight of / g, was mixed in a 95:5 ratio (mb / ma = 0.05) and used. Batteries using this technology exhibited excellent battery characteristics. Examples 1-2 showed even better results than Example 1-1 in terms of efficiency, single-unit capacity, and cycle characteristics.

[0245] (Examples 2-1 to 2-7) The difference from Example 1-1 is that the particle size distribution of particle A was adjusted by adjusting the grinding conditions of the porous carbon. When the D50 of the negative electrode active material (particle A) decreased, the surface reaction increased and the initial efficiency tended to deteriorate. On the other hand, when the D50 increased, the surface reaction was suppressed, improving the initial efficiency and the cycle characteristics also tended to improve.

[0246] (Examples 2-8 to 2-14) The difference from Example 1-1 is that the particle size distribution of particle B was adjusted by adjusting the grinding conditions of the porous carbon. Similar to particle A (Examples 2-1 to 2-7), particle B also showed a tendency for the battery characteristics to improve as D50 increased.

[0247] (Examples 3-1 to 3-4, Comparative Example 3-1) The difference from Example 1-1 is that the mb / ma ratio was adjusted. As the proportion of particles B with large pore volume increased, i.e., as the mb / ma ratio increased, the surface reaction rate increased, and a tendency was observed for all battery characteristics to deteriorate slightly. From these results, an mb / ma ratio of less than 0.45 is desirable. Furthermore, the best characteristics were obtained when the mb / ma ratio was 0 (i.e., particle B was absent, and only particle A was present). From a battery performance perspective, using only particle A is best, but this would mean not using particle B. Therefore, considering productivity, it is acceptable to use particle B in appropriate amounts, within the range where the battery performance is acceptable.

[0248] (Example 4-1) The difference from Example 1-1 is that in step S2, after drying the porous carbon in a nitrogen atmosphere to remove moisture, the exhaust gas was analyzed, and the process proceeded to step S3 with the introduction of silane gas for the reaction. Subsequently, acetylene CVD treatment was performed in step S5, but the deposition rate was about 1 / 5 of that in Example 1-1. This is thought to be because the number of active sites decreased (the number of dangling bonds decreased), making it difficult for acetylene to decompose. Furthermore, analysis of the Si-kedge using XAFS revealed that it was a composite of zero-valent and tetra-valent components. This suggests that the Si-O bond was reduced as a result of removing the oxygen component from the porous carbon, or that the Si incorporated oxygen when exposed to the atmosphere after deposition, becoming partly SiO2. Example 4-1 was slightly worse than Example 1-1 in terms of efficiency, single unit capacity, and cycle characteristics. Therefore, the standard steps of Example 1-1 are preferable.

[0249] (Examples 5-1 to 5-6) The difference from Example 1-1 is that the pressure of the acetylene CVD in step S5 was adjusted. Lowering the pressure reduced the CVD rate, increased the density of the carbon film, and decreased the D / G ratio. On the other hand, increasing the pressure increased the D / G ratio. A D / G ratio in the range of 0.9 to 1.25 is preferable for a good balance of cycle retention rate, capacity, and initial efficiency.

[0250] (Examples 6-1 to 6-4: Phenolic resin), (Examples 6-5 to 6-8: Biologically derived coconut shell) The difference between Examples 1-1 and 1-2 is that the pressure during monosilane gas introduction in step S3 was changed. Generally, lower pressure during monosilane gas introduction makes it more difficult for the silane gas to reach deep into the pores, leading to more void formation. This, in turn, prevents sufficient silicon filling, resulting in a tendency for battery capacity to decrease. Furthermore, silicon decomposed and deposited in a pressurized atmosphere contains abundant dangling bonds, but the amount of dangling bonds tends to decrease at lower pressures. Therefore, to ensure sufficient dangling bonds, it is desirable to avoid excessively low pressure. Dangling bonds are highly reactive, allowing for the decomposition of carbon at low temperatures during subsequent carbon CVD. Specifically, while acetylene gas CVD typically requires temperatures of around 650°C under a reduced pressure atmosphere of 10,000 PaG, the presence of a large amount of dangling bonds accelerates acetylene decomposition, enabling decomposition at temperatures below 600°C. This improves cycle characteristics. Furthermore, the smoother acetylene decomposition improves conductivity. As a result, lithium acceptance is significantly improved. Therefore, it is preferable not to lower the pressure during monosilane gas introduction in step S3 below 30 kPaG.

[0251] (Examples 8-1~2) The difference between Examples 1-1 and 1-2 is that the sample was held at 580°C for 6 hours before introducing acetylene gas in step S5, reducing the number of dangling bonds. After heat treatment was performed within a range where Si crystallization did not progress, and then CVD treatment was carried out, the number of Si-C bonds was reduced to 1 / 10 (calculated from peak intensity). Although the same experiment was performed multiple times, the degree of reduction was not stable, making quantitative evaluation difficult, but it is certain that the reduction was significant. Si-C bonds can be confirmed using EXAFS or FT-IR (infrared spectroscopy), but in this case, they were confirmed using the isodiametric structure function and peak intensity of EXAFS. Si-C bonds have the effect of improving particle hardness, and we believe that the hardness decreased because the number of Si-C bonds was significantly reduced. As a result, while Examples 8-1 and 8-2 showed high initial efficiency, they tended to exhibit a slight deterioration in cycle characteristics.

[0252] (Examples 9-1 to 9-5: Phenolic resin), (Examples 9-6 to 9-10: Biologically derived coconut shell) The difference between Examples 1-1 and 1-2 is that, before flowing acetylene gas in step S5, heat treatment was performed in the range of 600-670°C to crystallize some of the deposited silicon. After that, the temperature was lowered and acetylene CVD was performed. The crystallization of silicon here means that the amount of silicon with zero valence increases. As a result, while battery capacity and initial efficiency improved, there was a tendency for cycle characteristics to deteriorate. Considering this, the crystallinity of Si (Si in the table) 0+ It is desirable to reduce the grain size to 5 nm or less.

[0253] (Examples 10-1 to 10-4) The difference from Example 1-1 lies in the D / G ratio of the negative electrode active material particles. Here, carbon derived from the G peak has high conductivity but lacks density. Carbon derived from the D peak has lower conductivity but achieves density. In terms of cycle characteristics, the key is how to suppress excessive decomposition of the electrolyte, and higher conductivity is preferable. Conversely, in terms of suppressing gas generation in the slurry, the key is how to densely cover the surface, and higher density is preferable. Considering these factors, it is desirable to select a D / G ratio that is in a region where both conductivity and density are good.

[0254] In terms of cycle characteristics ("1000 Cy maintenance rate" in Table 1), Examples 10-1 and 10-4 show a slight decrease compared to Examples 1-1 and 10-2 and 10-3. Therefore, it is preferable to set the D / G ratio to be between 0.9 and 1.1 so as to include the D / G ratios of Examples 1-1 and 10-2 and 10-3, while excluding the D / G ratios of 0.88 and 1.25 for Examples 10-1 and 10-4.

[0255] Furthermore, from the perspective of suppressing gas generation, the time until gas generation occurred in the slurry was measured for Examples 1-1 and 10-1 to 10-4, and this is listed on the far right of Table 2. Considering the suppression of gas generation, it is more preferable to set the D / G ratio to be between 0.9 and 1.0, including the D / G ratios of Examples 10-2 and 10-3, which showed no gas generation even after more than 168 hours, but excluding the D / G ratios of Examples 1-1 and 10-1 and 10-4.

[0256] (Examples 11-1 to 11-4) In Examples 11-1 to 11-4, the conditions for the activation treatment of the carbide were adjusted. Lowering the temperature and pressure during the activation treatment can increase the proportion of micropores. Conversely, lowering only the temperature and thus the activation rate can decrease the proportion of micropores.

[0257] Comparing Examples 11-1 to 11-4, Examples 11-2 and 11-3 showed better cycle characteristics ("1000 Cy maintenance rate" in Table 1), and the PD50 of the pores analyzed by the BJH method in these examples (second column from the right in Table 2) was between 2 nm and 3 nm. Therefore, it is preferable that the PD50 of the pores analyzed by the BJH method be between 2 nm and 3 nm.

[0258] The following provides further details about the embodiment using drawings.

[0259] Figure 4 shows the C1s spectra of XPS from Examples 1-1 and 1-2, and Figure 5 shows the O1s spectra of XPS from Examples 1-1 and 1-2. In Figures 4 and 5, "resin" refers to the phenolic resin from Example 1-1, and therefore [resin, particle A] and [resin, particle B] refer to particles A and B from Example 1-1. Also, in Figures 4 and 5, "organism" refers to coconut shell derived from an organism from Example 1-2, and therefore [organism, particle A] and [organism, particle B] refer to particles A and B from Example 1-2.

[0260] First, in Figure 4, under C1s, peaks are observed around 284.2 eV for the carbon-carbon unsaturated bonds in particle A of Examples 1-1 and 1-2, and around 284.6 eV for the single bonds in particle B. Furthermore, in Figure 5, under O1s, peaks are observed around 531.8-532.8 eV for the bonds originating from aromatic esters in particle A of Examples 1-1 and 1-2, and around 532.8 eV for the bonds originating from ether systems in particle B.

[0261] Therefore, it is considered that in Examples 1-1 and 1-2, the binding of particle A and particle B in this manner enabled the improvement of cycle characteristics while maintaining high battery capacity.

[0262] Figures 6 and 7 show the Raman spectroscopy spectra of the porous carbon structure of Example 1-1, with Figure 7 being an enlarged view of Figure 6 with the horizontal axis reversed.

[0263] Raman spectroscopy can be performed, for example, under the following conditions. • Device: HORIBA XploRA Plus • Laser wavelength: 532nm

[0264] First, from Figure 7, we see 1150cm -1 It can be seen that it has a peak (shoulder).

[0265] With a negative electrode active material having a spectrum like that of Example 1-1, the pores inside the porous carbon structure are of an appropriate size, allowing gas to easily reach the inside of the pores. As a result, it is believed that Example 1-1 was able to improve cycle characteristics while maintaining a high battery capacity.

[0266] Next, from Figure 6, we can see the carbon-derived D band (1300-1460 cm⁻¹). -1 The peak of the strait is approximately 1330 cm. -1 G-band (1500~1660cm) -1 The peak of the strait is approximately 1590 cm. -1 The peak of the 2D band is approximately 2650 cm. -1 These can be seen in each of them.

[0267] Referring to Tables 1 and 2, it is considered preferable that, in the spectra obtained from Raman spectroscopy, the porous carbon structure has a G / D ratio (ratio of peaks originating from the G band to peaks originating from the D band) of less than 1.0, a 2D / D ratio (ratio of peaks originating from the 2D band to peaks originating from the D band) of less than 0.1, and furthermore, the D / G ratio of the negative electrode active material particles (D / G ratio after CVD in Table 1) is 0.9 or greater and 1.25 or less.

[0268] In Example 1-1, the G / D ratio of the porous carbon structure was less than 1.0, the 2D / D ratio was less than 0.1, and the D / G ratio of the negative electrode active material particles was between 0.9 and 1.25, which is thought to have improved cycle characteristics while maintaining high battery capacity. In particular, negative electrode active material particles with a D / G ratio of 1.0 or higher are thought to have good Li acceptance on the surface of the negative electrode active material, improving cycle characteristics during fast charging.

[0269] Figures 8 and 9 are characteristic ESR diagrams of Example 1-1 before and after CVD. In particular, Figure 8 shows dangling voids of Si (2.0026 in the figure) and dangling bonds of carbon material (2.004 in the figure).

[0270] This document summarizes the measurement conditions for ESR (Electron Spin Resonance). • Equipment: Elexses E580 (manufactured by BRUKER) • Attached device: ESR900 cryostat (manufactured by OXFORD) • Main conditions [Narrow area] [Wide area] Measurement temperature 10K Same as left Central magnetic field around 3345G (same as above) Magnetic field sweep width 200G 1000G Modulation 100kHz, 2G (same as above) Microwave 9.38GHz, 0.68μW (same as above) Sweeping time: 83.89s × 2 times, 167.77s × 4 times Time constant 327.68ms (same as above) Number of data points: 1024 points, 2048 points Cavity Super-High Q (Same as above)

[0271] Figure 10 is a characteristic diagram of the amount of dangling bond before and after CVD in Example 1-1. It was confirmed that there is a large amount of Si dangling bond (however, this is for reference only, as it includes C dangling bond after CVD).

[0272] This specification includes the following embodiments: [1]: A negative electrode active material having negative electrode active material particles, The negative electrode active material particles include a porous carbon structure, amorphous low-valence nanosilicon oxide dispersed inside the porous carbon structure, and a carbon-based coating layer covering at least a portion of the surface. The low-valence nanosilicon oxide has a Si-C bond with the porous carbon structure, The porous carbon structure is True density is 2.20-2.55 g / cm³ 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3Contains at least particle A in / g, Furthermore, the true density is 2.50-2.90 g / cm³ 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3 A negative electrode active material characterized in that the weight ratio of particle B to particle A in units of / g is in the range of 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B. [2]: The particle A has a carbon-carbon unsaturated bond and a bond derived from an aromatic ester, The negative electrode active material of [1] above, characterized in that the particle B has a carbon-carbon single bond and a bond derived from an ether system. [3]: The particle size distribution of particle A is D10 = 3 to 9 μm, D50 = 5 to 16 μm, and D90 = 10 to 25 μm. The negative electrode active material according to [1] or [2] above, characterized in that the particle size distribution of particle B is D10 = 0.2 to 3 μm, D50 = 1 to 5 μm, and D90 = 3 to 6 μm. [4]: The porous carbon structure is found in the 1100 cm spectrum obtained from Raman spectroscopy. -1 More than 1200cm -1 The negative electrode active material of any of the above [1] to [3] is characterized by having peaks in the following ranges. [5]: The negative electrode active material according to [4], characterized in that the peaks in the spectrum obtained from the Raman spectroscopy analysis are peaks originating from C=O bonds or CO bonds, and the porous carbon structure contains at least one of C=O bonds and CO bonds. [6]: In the spectrum obtained from Raman spectroscopy, The porous carbon structure has a G / D ratio, which is the ratio of peaks originating from the G band to peaks originating from the D band, of less than 1.0, and a 2D / D ratio, which is the ratio of peaks originating from the 2D band to peaks originating from the D band, of less than 0.1. The negative electrode active material particles are characterized by having a D / G ratio of 0.9 or more and 1.25 or less, as described in any of the above [1] to [5] negative electrode active materials. [7]: The negative electrode active material according to any of the above [1] to [6], characterized in that, in the spectrum obtained from Raman spectroscopy, the negative electrode active material particles have a D / G ratio of 0.9 or more and 1.0 or less. [8]: The anode active material of any of the above [1] to [7], characterized in that the porous carbon structure of the anode active material particles has a pore PD50 of 2 nm or more and 3 nm or less, as analyzed by the BJH method. [9]: A negative electrode active material according to any of the above [1] to [8], characterized in that active sites exist inside the pores of the porous carbon structure, and some of the active sites are modified with OH groups and COOH groups.

[10] : The negative electrode active material of any of the above [1] to [9], characterized in that the low-valence nanosilicon oxide is substantially a composite state of 0-valence, 1-valence, 2-valence, 3-valence, and 4-valence, the 4-valence state contains dimethylsiloxane.

[11] : The negative electrode active material of any of the above [1] to

[10] , characterized in that the low-valence nanosilicon oxide is deposited in a state where it is in a phase separate from the porous carbon structure, a portion of which is precipitated via oxygen, and further having amorphous Si-C bonds at the interface with the carbon-based coating layer.

[12] : The negative electrode active material according to any of the above [1] to

[11] , characterized in that 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.

[13] : The negative electrode active material of any of the above [1] to

[12] , characterized in that the low-valence nanosilicon oxide is substantially amorphous.

[14] : A method for producing a negative electrode active material having negative electrode active material particles, A step of preparing a porous carbon structure, wherein the porous carbon structure is True density is 2.20-2.55 g / cm³ 3 , pore volume of 1.00~1.25 cm³ by BET method 3 / g, pore volume of 0.5~0.75 cm³ by BJH method 3Contains at least particle A in / g, Furthermore, the true density is 2.50-2.90 g / cm³ 3 The pore volume measured by the BET method was 1.15–1.30 cm³. 3 / g, pore volume of 0.75-0.9 cm³ by BJH method 3 The steps include: setting the weight ratio of particle B to particle A at a rate of / g to satisfy the range of 0≦mb / ma<0.45, where ma is the weight of particle A and mb is the weight of particle B; The steps include: providing OH groups and COOH groups to the active sites contained in the porous carbon structure; A step of flowing monosilane gas to deposit silicon oxide bonded to oxygen atoms inside the porous carbon structure, wherein the silicon oxide contains dangling bonds, Following the step of depositing the silicon oxide, the step of oxidizing at least a portion of the silicon present on the surface of the negative electrode active material in a reduced-pressure atmosphere, Following the step of oxidation in a reduced-pressure atmosphere, the process involves depositing a carbon-based coating layer at 530-600°C using hydrocarbon gas. A method for producing a negative electrode active material, characterized by containing the following:

[15] : The method for producing the negative electrode active material according to

[14] , characterized in that the step of depositing the silicon oxide is to decompose the monosilane gas in a pressurized atmosphere of 30 kPaG to 190 kPaG.

[0273] 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]

[0274] 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. S1, S2, S3, S4, S5... Steps.

Claims

1. A negative electrode active material having negative electrode active material particles, The negative electrode active material particles include a porous carbon structure, amorphous low-valence nanosilicon oxide dispersed inside the porous carbon structure, and a carbon-based coating layer covering at least a portion of the surface. The low-valence nanosilicon oxide has a Si-C bond with the porous carbon structure, The porous carbon structure is True density is 2.20–2.55 g / cm³ ３ , pore volume by BET method is 1.00 to 1.25 cm ３ / g, pore volume of 0.5–0.75 cm³ by BJH method ３ It contains at least particle A in a quantity of / g, Furthermore, the true density is 2.50–2.90 g / cm³ ３ The pore volume measured by the BET method is 1.15–1.30 cm³. ３ / g, pore volume of 0.75–0.9 cm³ by BJH method ３ A negative electrode active material characterized in that the weight ratio of particle B to particle A at a rate of / g is in the range of 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B.

2. The particle A has a carbon-carbon unsaturated bond and a bond derived from an aromatic ester, The negative electrode active material according to claim 1, characterized in that the particle B has a carbon-carbon single bond and a bond derived from an ether system.

3. The particle size distribution of particle A is D10 = 3 to 9 μm, D50 = 5 to 16 μm, and D90 = 10 to 25 μm. The negative electrode active material according to claim 1, characterized in that the particle size distribution of the particle B is D10 = 0.2 to 3 μm, D50 = 1 to 5 μm, and D90 = 3 to 6 μm.

4. The porous carbon structure is found in the 1100 cm⁻¹ spectrum obtained from Raman spectroscopy. －１ More than 1200cm －１ The negative electrode active material according to claim 1, characterized in that it has peaks within the following range.

5. The negative electrode active material according to claim 4, characterized in that the peaks in the spectrum obtained from the Raman spectroscopy analysis are peaks originating from C=O bonds or C-O bonds, and the porous carbon structure contains at least one of C=O bonds or C-O bonds.

6. In the spectrum obtained from Raman spectroscopy, The porous carbon structure has a G / D ratio, which is the ratio of peaks originating from the G band to peaks originating from the D band, of less than 1.0, and a 2D / D ratio, which is the ratio of peaks originating from the 2D band to peaks originating from the D band, of less than 0.

1. The negative electrode active material according to claim 1, characterized in that the negative electrode active material particles have a D / G ratio of 0.9 or more and 1.25 or less.

7. The negative electrode active material according to claim 1, characterized in that, in the spectrum obtained from Raman spectroscopy, the negative electrode active material particles have a D / G ratio of 0.9 or more and 1.0 or less.

8. The anode active material according to claim 1, characterized in that the porous carbon structure of the anode active material particles has a pore PD50 of 2 nm or more and 3 nm or less, as analyzed by the BJH method.

9. The negative electrode active material according to claim 1, characterized in that active sites exist inside the pores of the porous carbon structure, and some of the active sites are modified with OH groups and COOH groups.

10. The negative electrode active material according to claim 1, characterized in that the low-valence nanosilicon oxide is substantially in a composite state of zero, mono, di, tri, and tetravalent states, and the tetravalent state contains dimethylsiloxane.

11. The negative electrode active material according to claim 1, characterized in that the low-valence nanosilicon oxide is deposited in a phase separated from the porous carbon structure, a portion of which is precipitated via oxygen, and further having amorphous Si-C bonds at the interface with the carbon-based coating layer.

12. The negative electrode active material according to claim 1, characterized in that 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.

13. The negative electrode active material according to claim 1, characterized in that the low-valence nanosilicon oxide is substantially amorphous.

14. A method for producing a negative electrode active material having negative electrode active material particles, A step of preparing a porous carbon structure, wherein the porous carbon structure is The true density is 2.20 to 2.55 g / cm ３ , the pore volume by the BET method is 1.00 to 1.25 cm ３ / g, and the particle A having a pore volume by the BJH method of 0.5 to 0.75 cm ３ / g, at least contains, Furthermore, the true density is 2.50–2.90 g / cm³ ３ The pore volume measured by the BET method is 1.15–1.30 cm³. ３ / g, pore volume of 0.75–0.9 cm³ by BJH method ３ The step of setting the weight ratio of particle B to particle A at / g to a range satisfying 0 ≤ mb / ma < 0.45, where ma is the weight of particle A and mb is the weight of particle B, The steps include: providing OH groups and COOH groups to the active sites contained in the porous carbon structure; A step of flowing monosilane gas to deposit silicon oxide bonded to oxygen atoms inside the porous carbon structure, wherein the silicon oxide contains dangling bonds, Following the step of depositing the silicon oxide, the step of oxidizing at least a portion of the silicon present on the surface of the negative electrode active material in a reduced-pressure atmosphere, Following the step of oxidation in a reduced-pressure atmosphere, the process involves depositing a carbon-based coating layer at 530-600°C using hydrocarbon gas. A method for producing a negative electrode active material, characterized by containing the following:

15. The method for producing a negative electrode active material according to claim 14, characterized in that the step of depositing the silicon oxide involves decomposing the monosilane gas in a pressurized atmosphere of 30 kPaG to 190 kPaG.

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