Negative electrode active material and method for manufacturing the same

Abstract

This invention provides a negative electrode active material, which is a negative electrode active material having negative electrode active material particles. The negative electrode active material particles comprise a porous carbon structure, within which amorphous low-valent nano-silicon oxide is dispersed. The low-valent nano-silicon oxide comprises SiOx, wherein x < 1.0. At least a portion of the surface layer of the low-valent nano-silicon oxide exposed to the surface of the porous carbon structure is coated with a condensation reaction product of at least one of an organopolysiloxane and an organosilicon oligomer, having at least one of a silanol group and an alkoxy group directly bonded to a silicon atom. Thus, a negative electrode active material that can improve battery cycle characteristics and increase capacity is provided.

Description

Technical Field

[0001] This invention relates to a negative electrode active material and its manufacturing method. Background Technology

[0002] In recent years, small electronic devices, such as mobile terminals, have become widely used, creating an urgent need for further miniaturization, weight reduction, and lifespan extension. In response to this market demand, a small, lightweight rechargeable battery capable of achieving high energy density is being developed. This rechargeable battery is not limited to applications in small electronic devices; its application in large electronic devices such as automobiles and in energy storage systems such as buildings is also under research.

[0003] Among them, lithium-ion secondary batteries are highly anticipated because they are small, easy to achieve high capacity, and can also achieve higher energy density than lead-acid and nickel-cadmium batteries.

[0004] The aforementioned lithium-ion secondary battery, in addition to having a positive electrode, a negative electrode, and a separator, also has an electrolyte. The negative electrode contains negative electrode active materials related to the charge and discharge reaction.

[0005] Carbon-based active materials are widely used as negative electrode active materials; however, recent market demands require further increases in battery capacity. To improve battery capacity, silicon is being researched as a negative electrode active material. This is because silicon's theoretical capacity (4199 mAh / g) is more than 10 times greater than graphite's (372 mAh / g), thus a significant increase in battery capacity is expected. The development of silicon materials as negative electrode active materials is not limited to elemental silicon; research is also being conducted on compounds such as alloys and oxides. Furthermore, regarding the shape of the active material, for carbon-based active materials, both standard coated types and integral types directly deposited on the current collector have been studied.

[0006] However, if silicon is used as the main raw material for the negative electrode active material, the active material will expand and contract during charging and discharging, making it prone to cracking primarily near the surface. Furthermore, ionic substances will form inside the active material, further contributing to its fragility. If the surface of the active material cracks, a new surface will be created, increasing the reaction area. At this point, the electrolyte will decompose on the new surface, forming a film of electrolyte decomposition products, thus consuming the electrolyte. Therefore, the cycle performance is prone to decline.

[0007] To date, various studies have been conducted on negative electrode active materials and electrode structures for lithium-ion secondary batteries, with silicon as the main material, in order to improve the initial efficiency and cycle characteristics of batteries.

[0008] Specifically, to achieve good cycle characteristics and high safety, a vapor-phase method is used to simultaneously deposit silicon and amorphous silicon dioxide (see, for example, Patent Document 1). Furthermore, to obtain high battery capacity and safety, a carbon material (electron-conducting material) is placed on the surface of the silicon oxide particles (see, for example, Patent Document 2). Further, 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 (see, for example, Patent Document 3). Moreover, to enhance cycle characteristics, the silicon active material contains oxygen, forming an average oxygen content of 40 at% or less, with a higher oxygen content near the current collector (see, for example, Patent Document 4).

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

[0010] Furthermore, to improve cycling characteristics, silicon oxide is used, and a graphite coating is formed on its surface, thereby imparting conductivity (see, for example, Patent Document 10). In Patent Document 10, regarding the shift value obtained from the Raman spectrum associated with the graphite coating, at 1330 cm⁻¹... -1 and 1580cm -1 A broad peak appears at this point, and the intensity of both is greater than that of I. 1330 / I 1580 1.5 < I 1330 / I 1580 <3. Furthermore, in order to achieve high battery capacity and improve cycle characteristics, a particle having a silicon microcrystalline phase dispersed in silicon dioxide is used (see, for example, Patent Document 11). In addition, in order to improve overcharge and over-discharge characteristics, a silicon oxide with the atomic ratio of silicon to oxygen controlled at 1:y (0 < y < 2) is used (see, for example, Patent Document 12).

[0011] Furthermore, regarding lithium-ion secondary batteries using silicon oxide, Hitachi Maxell began shipping square secondary batteries for smartphones using nano-silicon composites in June 2010 (see, for example, Non-Patent Literature 1). The silicon oxide proposed by Hohl is Si... 0+ ~Si 4+ The composite material exhibits various oxidation states (Non-Patent Document 2). Furthermore, Kapaklis proposed a disproportionation structure that separates silicon oxide into Si and SiO2 by applying a thermal load (Non-Patent Document 3).

[0012] Miyachi et al. focused on Si and SiO2 participating in charge and discharge in silicon oxide with a disproportionated structure (Non-Patent Document 4), while Yamada et al. proposed the following reaction formula between silicon oxide and Li (Non-Patent Document 5). 2SiO(Si+SiO2)+6.85Li + +6.85e - →1.4Li 3.75 Si + 0.4Li → 4SiO4 + 0.2SiO2 In the reaction formula, Si and SiO2, which constitute silicon oxide, react with Li to separate into Li silicide and Li silicate, as well as some unreacted SiO2.

[0013] The Li silicate formed here generally refers to an irreversible, stable substance that does not release Li once formed. The capacity per unit mass calculated based on the reaction formula has a value close to the experimental value, and is therefore considered to be a reaction mechanism involving silicon oxides. Kim et al. used... 7 Li-MAS-NMR or 29 Si-MAS-NMR analysis identified irreversible components associated with the charging and discharging of silicon oxides, and Li silicate as Li4SiO4 (Non-Patent Document 6).

[0014] The irreversible capacity is the biggest drawback of silicon oxides and needs to be improved. To address this, Kim et al. used a Li pre-doping method to pre-form Li silicates, creating a negative electrode that significantly improves initial efficiency during battery fabrication and is durable enough for practical use (Non-Patent Document 7). Furthermore, a method for improving irreversible capacity was proposed that does not involve Li doping the electrode but rather processing the powder (Patent Document 13).

[0015] On the other hand, the price of Li metal used in Li doping varies greatly depending on market conditions, posing numerous problems when used for industrial applications. To address this, CVD-Si-C, which uses silane gas in porous carbon to generate nano-silicon internally, can achieve an energy density higher than that of Li-doped SiO (Patent Documents 14, 15). Existing technical documents

[0016] Patent documents Patent Document 1: Japanese Patent Application Publication No. 2001-185127 Patent Document 2: Japanese Patent Application Publication No. 2002-042806 Patent Document 3: Japanese Patent Application Publication No. 2006-164954 Patent Document 4: Japanese Patent Application Publication No. 2006-114454 Patent Document 5: Japanese Patent Application Publication No. 2009-070825 Patent Document 6: Japanese Patent Application Publication No. 2008-282819 Patent Document 7: Japanese Patent Application Publication No. 2008-251369 Patent Document 8: Japanese Patent Application Publication No. 2008-177346 Patent Document 9: Japanese Patent Application Publication No. 2007-234255 Patent Document 10: Japanese Patent Application Publication No. 2009-212074 Patent Document 11: Japanese Patent Application Publication No. 2009-205950 Patent Document 12: Japanese Patent Application Publication No. 06-325765 Patent Document 13: Japanese Patent Application Publication No. 2015-156355 Patent Document 14: US Patent No. 10608254 Patent Document 15: US Patent No. 1,116,5054 Non-patent literature

[0017] Non-patent document 1: Battery Manufacturers Association official paper "でんち" dated May 1, 2011, page 10 Non-Patent Literature 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-patent literature 3: V. Kapaklis, J. Non-Crystalline Solids, 354 (2008) 612 Non-patent literature 4: Mariko Miyachi, Hironori Yamamoto, and Hidemasa Kawai, J. Electrochem. Soc. 2007, volume 154, issue 4, A376-A380 Non-patent literature 5: M. Yamada, A. Inaba, A. Ueda, K. Matsumoto, T. Iwasaki, T. Ohzuku, J. Electrochem. Soc., 159, A1630 (2012) Non-patent literature 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 forefront of development of automotive batteries, pages 96~111, published by Seiko, released on November 27, 2020 Summary of the Invention (a) Technical problems to be solved

[0018] As mentioned above, in recent years, small electronic devices, such as mobile terminals, have continuously improved in performance and functionality, necessitating increased capacity in their main power source, lithium-ion secondary batteries. As one approach to address this problem, it is desirable to develop a lithium-ion secondary battery that incorporates a silicon-based negative electrode.

[0019] Furthermore, it is expected that the initial charge-discharge characteristics and cycle characteristics of lithium-ion secondary batteries using silicon materials will be nearly identical to those of lithium-ion secondary batteries using carbon-based active materials. To address this, silicon oxide modified by Li intercalation and partial deintercalation has been used as the negative electrode active material to improve cycle characteristics and initial charge-discharge characteristics. Recently, however, lithium silicates, primarily composed of silicon oxide and pre-containing Li, have begun to appear on the market, mitigating the drawback of silicon oxides, namely irreversible capacity. Even when a battery is prototyped using Li-SiO-C (Non-Patent Document 8), which uses Li in silicon oxide, to completely replace the carbon negative electrode material, the capacity improvement compared to batteries using carbon negative electrodes only reaches the latter half of 20%. This means that considering the increasing performance of small electronic devices (5G, etc.) and the increased driving range of electric vehicles, further increases in battery capacity are needed.

[0020] In response, although CVD-Si-C with lower irreversible capacity has been developed, it is known that high-speed charging performance and battery cycle characteristics are insufficient due to the reaction between Si and electrolyte.

[0021] The present invention was made in view of the above-mentioned problems, and its object is to provide a negative electrode active material that can improve battery cycle characteristics and increase capacity. (II) Technical Solution

[0022] To solve the above-mentioned technical problems, the present invention provides a negative electrode active material, which is a negative electrode active material having negative electrode active material particles. The negative electrode active material particles contain a porous carbon structure, and amorphous low-valence nano-silicon oxide is dispersed inside the porous carbon structure. The low-valence nano-silicon oxide contains SiOx, wherein x < 1.0. At least a portion of the surface layer of the low-valence nano-silicon oxide exposed to the surface of the porous carbon structure is coated with a condensation reaction product of at least one of organopolysiloxane and organosilicon oligomer having at least one of silanol group and alkoxy group directly bonded to silicon atom.

[0023] The negative electrode active material of this invention contains amorphous low-valence nano-silicon oxide dispersed within a porous carbon structure. Therefore, the presence of the porous carbon structure mitigates the adverse effects caused by the expansion of the internal low-valence nano-silicon oxide. Furthermore, in conventional SiO, Si... 4+While it would become an irreversible component, the negative electrode active material of the present invention contains various states of SiOx (x < 1.0), thus maintaining a lower irreversible capacity than conventional SiO. Furthermore, the Si-O bonds can suppress electrolyte decomposition, thereby reducing the SEI (Solid Electrolyte Interphase) deposited on the surface. In addition, at least a portion of the surface layer of the low-valent nano-silicon oxide exposed to the porous carbon structure is coated with a condensation reactant of at least one of an organopolysiloxane and an organosilicon oligomer having at least one of a silanol group and an alkoxy group directly bonded to a silicon atom, thereby suppressing electrolyte decomposition. As a result, excessive electrolyte decomposition can be suppressed, and the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved.

[0024] Furthermore, the organopolysiloxane preferably has structural units represented by the following general formula (1) and groups represented by the following general formula (2) directly bonded to silicon atoms. R 1 -SiO 3 / 2 (1) (In general formula (1), R) 1 (This refers to alkyl groups with 1 to 3 carbon atoms that have been substituted or not substituted) -OR 2 (2) (In general formula (2), R) 2 (representing a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms, whether substituted or unsubstituted).

[0025] By using such organopolysiloxane condensation reactants to coat at least a portion of the surface layer of low-valence nano-silicon oxides exposed on the surface of porous carbon structures, electrolyte decomposition can be effectively suppressed and cycle characteristics can be improved.

[0026] Furthermore, the organosilicon oligomer preferably has structural units represented by the following general formula (3) and groups represented by the following general formula (4) directly bonded to silicon atoms. R 3 SiO 2 / 2 (OR 4 (3) (In general formula (3), R) 3 Each independently represents an alkyl group having 1 to 3 carbon atoms, whether substituted or unsubstituted, R 4 Each of the following can be independently represented as a hydrogen atom or an alkyl group having 1 to 6 substituted or unsubstituted carbon atoms. -OR 5 (4) (In general formula (4), R) 5(representing a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms, whether substituted or unsubstituted).

[0027] By using the condensation reactants of such organosilicon oligomers to coat at least a portion of the surface layer of low-valence nano-silicon oxide exposed to the surface of the porous carbon structure, it is possible to reliably suppress electrolyte decomposition and improve cycle characteristics.

[0028] Furthermore, it is preferred that the thickness of the condensation reactant is 0.1 nm or more and 10 nm or less.

[0029] A condensation reactant of this thickness can better suppress electrolyte decomposition and further improve cycle characteristics.

[0030] Furthermore, the low-valent nano-silicon oxide is preferably in a composite state of 0, 1, and 2 valences.

[0031] Thus, by making the low-valent nano-silicon oxide essentially a composite state of 0, 1, and 2 valences, it is possible to achieve even lower irreversible capacity.

[0032] Furthermore, the x-axis of the low-valence nano-silicon oxide dispersed in the porous carbon structure preferably increases from the center of the porous carbon structure toward the surface.

[0033] Thus, in this invention, because low-valence nano-silicon oxides are dispersed in the porous carbon structure, during manufacturing, it is easy to increase x from the center of the porous carbon structure towards the surface (increasing the oxygen composition ratio). Since the silicon oxidation ratio is larger at the surface, electrolyte decomposition is more effectively suppressed, while the silicon oxidation ratio is smaller inside the active material, thus further improving battery capacity.

[0034] Furthermore, it is preferable that the grain size of the 0-valent Si constituting the low-valent nano-silicon oxide, as determined by the peaks obtained from X-ray diffraction measurements of the negative electrode active material particles and calculated using the Scherrer formula, is in the range of 1 nm to 5 nm.

[0035] The preferred anode active material particles are those with a grain size of 0-valent Si that is substantially amorphous.

[0036] Furthermore, the porous carbon structure is predominantly type I in the IUPAC classification, with a surface area of ​​1400 m². 2 / g or more, pore volume of 1cm 3 / g or more.

[0037] Because porous carbon structures possess this IUPAC classification, surface area, and pore volume, it is possible to fabricate anode active materials containing large quantities and high efficiency of low-valent nano-silicon oxides. In particular, the type I structure in the IUPAC classification can smoothly undergo post-deposition Si-O bond formation.

[0038] Furthermore, the present invention provides a method for manufacturing a negative electrode active material, which is a method for manufacturing a negative electrode active material having negative electrode active material particles. The method for manufacturing this negative electrode active material is characterized by the following steps: Steps for preparing porous carbon structures; The step of allowing silane gas to flow into the porous carbon structure under heating, thereby depositing silicon into the interior of the porous carbon structure; The step of cooling the material obtained by depositing silicon inside the porous carbon structure to below 50°C; After cooling, while maintaining the temperature of the material obtained by depositing silicon inside the porous carbon structure below 50°C, oxygen diluted with nitrogen is introduced into the material obtained by depositing silicon inside the porous carbon structure, thereby transforming at least a portion of the silicon into low-valence nano-silicon oxide. The step of coating at least a portion of the surface layer of the low-valent nano-silicon oxide with a condensation reaction product having at least one of a silanol group and an alkoxy group directly bonded to a silicon atom, or an organopolysiloxane and an organosilicon oligomer.

[0039] If such a method is used to manufacture the negative electrode active material, it is possible to easily and efficiently manufacture a negative electrode active material, which, as described above, disperses amorphous low-valence nano-silicon oxides inside a porous carbon structure, and at least a portion of the surface layer of the low-valence nano-silicon oxides is coated with a condensation reaction product of at least one of organopolysiloxanes and organosilicon oligomers having at least one of silanol groups and alkoxy groups directly bonded to silicon atoms.

[0040] Furthermore, preferably, a condensation reactant is formed on at least a portion of the surface layer of the low-valent nano-silicon oxide by hydrolysis and dehydration condensation of at least one of the organopolysiloxane and organosilicon oligomer, thereby coating at least a portion of the surface layer of the low-valent nano-silicon oxide.

[0041] By using the hydrolysis and dehydration condensation of at least one of such organopolysiloxanes and organosilicon oligomers, condensation reactants can be easily formed on the surface of low-valent nano-silicon oxides.

[0042] In addition, a catalytic amount of condensation catalyst is preferably added to hydrolyze and dehydrate at least one of the organopolysiloxane and organosilicon oligomer.

[0043] By adding such a catalytic amount of condensation catalyst, it becomes easier to hydrolyze and dehydrate at least one of the organopolysiloxanes and organosilicon oligomers. (III) Beneficial Effects

[0044] The negative electrode active material of the present invention disperses amorphous low-valence nano-silicon oxide within a porous carbon structure. Due to the presence of the porous carbon structure, the adverse effects of expansion of the internal low-valence nano-silicon oxide are mitigated. Since it contains SiOx and x < 1.0, a lower irreversible capacity than conventional SiO can be maintained. Furthermore, since the Si-O bonds suppress electrolyte decomposition, the SEI deposited on the surface layer can be reduced. Moreover, by coating at least a portion of the surface layer of the low-valence nano-silicon oxide exposed to the porous carbon structure with a condensation reactant of at least one of an organopolysiloxane and an organosilicon oligomer having at least one silanol group and an alkoxy group directly bonded to a silicon atom, electrolyte decomposition can be suppressed. As a result, excessive electrolyte decomposition can be suppressed, and the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved.

[0045] Furthermore, the method for manufacturing the negative electrode active material of the present invention can easily and efficiently manufacture a negative electrode active material in which amorphous low-valence nano-silicon oxide is dispersed inside a porous carbon structure, and at least a portion of the surface layer of the low-valence nano-silicon oxide is coated with a condensation reaction product of at least one of organopolysiloxane and organosilicon oligomer having at least one of silanol group and alkoxy group directly bonded to silicon atom. Attached Figure Description

[0046] Figure 1 A cross-sectional view showing the structure of a negative electrode containing the negative electrode active material of the present invention. Figure 2 An exploded view showing a structural example (laminated film type) of a lithium-ion secondary battery containing the negative electrode active material of the present invention. Figure 3 A flowchart illustrating an example of a method for manufacturing the negative electrode active material of the present invention. Figure 4 A graph illustrating the changes in the depth direction of the negative electrode active material in the O1s region as measured by XPS in Example 1. Figure 5 The X-ray diffraction spectra are those of Examples 1, 2, 10, and 11. Detailed Implementation

[0047] The following describes embodiments of the present invention, but the present invention is not limited thereto.

[0048] As mentioned earlier, as one method to increase the capacity of lithium-ion secondary batteries, an investigation was conducted on using a negative electrode made of low-cost nano-silicon oxide as the main material within a carbon structure as the negative electrode for lithium-ion secondary batteries. It is expected that lithium-ion secondary batteries using this active material will exhibit nearly the same battery characteristics as lithium-ion secondary batteries using carbon-based active materials, while also achieving higher battery capacity.

[0049] In order to obtain a negative electrode active material that can achieve high cycle characteristics when used as the negative electrode of a secondary battery, while simultaneously improving the initial charge-discharge characteristics and increasing the battery capacity, the inventors of this application have repeatedly conducted in-depth research, thus completing this invention.

[0050] In particular, the CVD-Si-C disclosed in Patent Documents 14 and 15 suffers from excessive reaction with the electrolyte. In this invention, to suppress this reaction with the electrolyte, the Si portion is transformed into a Si-O phase, and the siloxane bonds unique to silicon oxide are used. This not only significantly suppresses the reaction and decomposition of the electrolyte, but also demonstrates good Li acceptability in the Si-O material with siloxane bonds, thus developing a negative electrode active material that ensures high-speed charging. Furthermore, a negative electrode active material has been developed that, in addition to using the SiOx phase to suppress the electrolyte decomposition reaction, also utilizes a condensation reaction product containing at least one of a silanol group and an alkoxy group directly bonded to silicon atoms, and at least one of an organopolysiloxane and an organosilicon oligomer, to coat at least a portion of the surface layer of low-valence nano-silicon oxide exposed to the surface of the porous carbon structure, thereby further suppressing electrolyte decomposition.

[0051] [The negative electrode active material of the present invention] The negative electrode active material of the present invention is a negative electrode active material having negative electrode active material particles, characterized in that the negative electrode active material particles comprise a porous carbon structure, and amorphous low-valence nano-silicon oxide is dispersed inside the porous carbon structure. The low-valence nano-silicon oxide comprises SiOx, wherein x < 1.0, and at least a portion of the surface layer of the low-valence nano-silicon oxide exposed to the surface of the porous carbon structure is coated with a condensation reaction product of at least one of organopolysiloxane and organosilicon oligomer having at least one of silanol group and alkoxy group directly bonded to silicon atom.

[0052] This negative electrode active material, due to the dispersion of amorphous low-valence nano-silicon oxides within a porous carbon structure, mitigates the adverse effects caused by the expansion of these internal low-valence nano-silicon oxides through the presence of the porous carbon structure. Furthermore, conventional SiO, Si... 4+While the components are irreversible, the negative electrode active material of the present invention, due to the inclusion of various states of SiOx (x < 1.0), can maintain a lower irreversible capacity than that of SiO. Furthermore, since the Si-O bonds can suppress electrolyte decomposition, the amount of SEI (Solid Electrolyte Interphase) deposited on the surface can be reduced. Moreover, by coating at least a portion of the surface portion of the low-valence nano-silicon oxide exposed to the porous carbon structure with a condensation reactant of at least one of an organopolysiloxane and an organosilicon oligomer having at least one silanol group and an alkoxy group directly bonded to silicon atoms, electrolyte decomposition can be suppressed. As a result, excessive electrolyte decomposition can be suppressed and the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved.

[0053] In other words, to suppress the decomposition reaction of insufficient electrolyte in CVD-Si-C generated from conventional silane gas, the negative electrode active material of the present invention is a Si-Ox-formed material having siloxane bonds in the Si phase. However, since tetravalent Si constituting SiO becomes an irreversible component, by producing SiOx with a valence of divalent or lower, the irreversible capacity is larger than that of silicon alone, but the irreversible capacity is maintained at a lower level than that of conventional SiO. Furthermore, since the Si-O bonds can suppress electrolyte decomposition, the SEI (Solid Electrolyte Interphase) deposited on the surface of CVD-Si-C can be reduced. The main part of this material involved in charge and discharge is low-valence nano-silicon oxide; therefore, it can be defined as CVD-SiOx-C relative to CVD-Si-C. The active material produced in this way can maintain the cycle characteristics of the battery while simultaneously possessing high energy density and fast charging performance. Furthermore, by coating at least a portion of the surface layer of the low-valent nano-silicon oxide exposed to the surface of the porous carbon structure with a condensation reactant of at least one of an organopolysiloxane and an organosilicon oligomer having at least one silanol group and an alkoxy group directly bonded to silicon atoms, the decomposition of the electrolyte can be suppressed. As a result, excessive decomposition of the electrolyte can be suppressed and the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved.

[0054] When using organopolysiloxanes, it is preferable to have structural units represented by the following general formula (1) and groups represented by the following general formula (2) that are directly bonded to silicon atoms. R 1 -SiO 3 / 2 (1) (In general formula (1), R) 1 (This refers to alkyl groups with 1 to 3 carbon atoms that have been substituted or not substituted) -OR 2 (2) (In general formula (2), R) 2 (representing a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms, whether substituted or unsubstituted).

[0055] By using such organopolysiloxane condensation reactants to coat at least a portion of the surface layer of low-valence nano-silicon oxides exposed on the surface of porous carbon structures, electrolyte decomposition can be effectively suppressed and cycle characteristics can be improved.

[0056] Additionally, although not limited, KR-220L (containing silanol groups and CH3-SiO2) can be used as a specific example of an organopolysiloxane. 3 / 2 Methyl polysiloxane as the structural unit, manufactured by Shin-Etsu Chemical Industry Co., Ltd.

[0057] Furthermore, when using organosilicon oligomers, the organosilicon oligomers preferably have structural units represented by the following general formula (3) and groups represented by the following general formula (4) directly bonded to silicon atoms. R 3 SiO 2 / 2 (OR 4 (3) (In general formula (3), R) 3 Each independently represents an alkyl group having 1 to 3 carbon atoms, whether substituted or unsubstituted, R 4 Each can independently represent a hydrogen atom, or an alkyl group having 1 to 6 substituted or unsubstituted carbon atoms. -OR 5 (4) (In general formula (4), R) 5 (representing a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms, whether substituted or unsubstituted).

[0058] By using the condensation reactants of such organosilicon oligomers to coat at least a portion of the surface layer of low-valence nano-silicon oxide exposed to the surface of the porous carbon structure, electrolyte decomposition can be effectively suppressed and cycle characteristics can be improved.

[0059] Furthermore, although not limited, as a specific example of an organosilicon oligomer, X-40-9225 (having a methoxy group directly bonded to a silicon atom and CH3SiO) can be used. 2 / 2 (OCH3) is an organosilicon oligomer, manufactured by Shin-Etsu Chemical Industry Co., Ltd.

[0060] The grain size of low-cost nanocrystalline silicon oxides can be confirmed using TEM-EDX. The conditions are set as follows: double-section processing of the negative electrode active material is performed using a focused ion beam (FIB) apparatus without exposure to the atmosphere. The FIB apparatus is a SIINT XVision200DB, with an accelerating voltage of 30 kV. TEM observation is performed using a FEI Tecnai G2F20 with an accelerating voltage of 200 kV, and EDX is performed using an EDAX r-TEM with an accelerating voltage of 200 kV.

[0061] If the particle size of the low-valent silicon nano-oxide increases, it becomes difficult to form Si-O bonds. As described later, in the method for manufacturing the negative electrode active material of the present invention, specifically during the process of decomposing SiH4 to produce amorphous Si, Si-O bonds are intentionally formed by reacting with oxygen. Therefore, if the particle size is large, oxygen penetration is poor, and for example, an O concentration distribution may occur in the low-valent silicon oxide phase, leading to SiO2ization. Furthermore, at this time, the interior of the phase may become Si, similar to the CVD-Si-C described above. In addition, a portion of the interior of the low-valent silicon nano-oxide grains may also contain amorphous Si with zero valence, and low crystallinity is desirable. If crystallinity is reduced, the irreversible capacity increases, but there is the advantage of improved Li acceptability. Conversely, if crystallinity is high, the electrolyte decomposition reaction characteristic of Si is promoted, thus deteriorating the cycle characteristics.

[0062] Furthermore, it is preferred that the thickness of the condensation reactant is 0.1 nm or more and 10 nm or less.

[0063] If the condensation reactant is of such thickness, it can better suppress the decomposition of the electrolyte and further improve the cycle characteristics.

[0064] Furthermore, preferably, in the negative electrode active material of the present invention, the low-valent nano-silicon oxide is essentially a composite state of 0-valent, 1-valent, and 2-valent.

[0065] Thus, by making the low-valent nano-silicon oxide essentially a composite state of 0, 1, and 2 valences, it is possible to achieve even lower irreversible capacity.

[0066] The negative electrode active material of the present invention has a low-valent nano-silicon oxide phase inside the porous carbon material. For the silicon to oxygen ratio constituting this low-valent silicide, it is preferable to include SiOx with x < 1.0, and more preferably x ≤ 0.7. The lower limit of x is not particularly limited, but for example, it can be set to 0 < x. Furthermore, the low-valent nano-silicon oxide is mainly composed of compounds with valences of 1 to 2, and the low-valent nano-silicon oxide phase existing inside the porous material may also include a microcrystalline phase of Si with valence of 0.

[0067] The valence of low-cost nano-silicon oxides can be quantitatively determined using NMR (nuclear magnetic resonance) and XPS (X-ray photoelectron spectroscopy).

[0068] NMR measurements can be performed, for example, under the following conditions. 29 Si MAS NMR (Magic Angle Rotation Nuclear Magnetic Resonance) • Apparatus: 700 NMR spectrometer manufactured by Bruker • Probe: 4mm HR-MAS rotor 50μL • Sample rotation speed: 10kHz • Measured ambient temperature: 25℃

[0069] XPS measurements can be performed, for example, under the following conditions. XPS • Apparatus: X-ray photoelectron spectrometer • X-ray source: Monochromatic Al Kα rays • X-ray spot diameter: 100µm Argon (Ar) ion gun sputtering conditions: 0.5kV, 2mm×2mm

[0070] In the negative electrode active material of the present invention, it is preferable that the grain size of 0-valent Si constituting low-valent nano-silicon oxide, as determined by the peaks obtained from X-ray diffraction measurements of the negative electrode active material particles and calculated using the Scherrer equation, is in the range of 1 nm to 5 nm. Thus, negative electrode active material particles with such a grain size of 0-valent Si having a substantially amorphous structure are preferred.

[0071] Grain size calculations using XRD can be performed, for example, under the following conditions. For broad peaks, the calculations can be performed using analysis software like TOPAS, for example, under the following conditions. XRD measurement • Device: D2 PHASER manufactured by Bruker X-ray source: Cu • Diverging slit: 0.5° • Incident side Sola slit: 4° • Solar slit on the light-receiving side: 4° Calculation of grain size • Analysis software: DIFFRAC, TOPAS • Analysis method: Peak fitting method • Emission Profile: Cu Ka5.lam • Function: FP (First Principle) function • Refinement Option: Select "Calculate Error" and "Use Extrapolation"

[0072] Furthermore, preferably, in the negative electrode active material of the present invention, the x-value of the low-valent nano-silicon oxide dispersed in the porous carbon structure increases from the center of the porous carbon structure towards the surface. In the present invention, since low-valent nano-silicon oxide is dispersed in the porous carbon structure, it is easy to produce a material in which x-value increases from the center of the porous carbon structure towards the surface (the oxygen composition ratio increases) during manufacturing. Because the silicon oxidation ratio is larger at the surface, electrolyte decomposition is more effectively suppressed, and because the silicon oxidation ratio is smaller inside the active material, battery capacity can be further improved.

[0073] Negative electrode for non-aqueous electrolyte secondary batteries Next, the structure of a negative electrode (hereinafter also referred to as "negative electrode") for a non-aqueous electrolyte secondary battery containing the negative electrode active material of the present invention will be described.

[0074] [Structure of the negative electrode] Figure 1 A cross-sectional view showing the negative electrode containing the negative electrode active material of the present invention. For example... Figure 1 As shown, the negative electrode 10 has a structure with a negative electrode active material layer 12 on the negative electrode current collector 11. The negative electrode active material layer 12 may be disposed on both sides of the negative electrode current collector 11 or only on 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 absent.

[0075] [Negative current collector] The negative current collector 11 is a highly conductive material and is composed of a substance with excellent mechanical strength. Examples of conductive materials suitable for use in the negative current collector 11 include copper (Cu) and nickel (Ni). Preferably, this conductive material does not form an intermetallic compound with lithium (Li).

[0076] The negative electrode current collector 11 preferably contains carbon (C) and sulfur (S) in addition to the main elements. This is because it increases the physical strength of the negative electrode current collector. In particular, when the current collector has an active material layer that expands during charging, the inclusion of these elements helps to suppress deformation of the electrode containing the current collector. While the content of these elements is not particularly limited, it is preferable that each element is present in amounts of 100 ppm by mass or less. This is because a higher deformation suppression effect can be obtained. This deformation suppression effect further improves cycle characteristics.

[0077] Furthermore, the surface of the negative current collector 11 is preferably roughened, with a desired ten-point average roughness Rz of 1.5 μm or more and 5 μm or less. The roughened negative current collector is, for example, a metal foil that has undergone electrolytic treatment, embossing treatment, or chemical etching treatment.

[0078] [Negative electrode active material layer] In addition to silicon-based active material particles, the negative electrode active material layer 12 may also contain various other negative electrode active materials such as carbon-based active materials. Furthermore, in terms of battery design, it may also contain other materials such as thickeners (also known as "binders" or "adhesives") and conductive additives.

[0079] [Negative electrode active material and manufacturing method of negative electrode] Next, an example of the negative electrode active material of the non-aqueous electrolyte secondary battery of the present invention and a method for manufacturing a negative electrode using the negative electrode active material will be described.

[0080] First, a method for manufacturing the negative electrode active material contained in the negative electrode will be described. 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. This method is characterized by comprising the following steps: a step of preparing a porous carbon structure; a step of introducing silane gas into the porous carbon structure under heating, thereby depositing silicon into the interior of the porous carbon structure; a step of cooling the material obtained by depositing silicon into the interior of the porous carbon structure to below 50°C; a step of, after cooling, introducing oxygen diluted with nitrogen into the material obtained by depositing silicon into the interior of the porous carbon structure while adjusting the temperature of the material obtained by depositing silicon into the interior of the porous carbon structure to be maintained below 50°C, thereby changing at least a portion of the silicon into low-valent nano-silicon oxide; and a step of coating at least a portion of the surface layer of the low-valent nano-silicon oxide with a condensation reaction product having at least one of a silanol group and an alkoxy group directly bonded to a silicon atom, and at least one of an organopolysiloxane and an organosilicon oligomer.

[0081] Reference Figure 3 Steps S1 to S5 describe each step of the method for manufacturing the negative electrode active material.

[0082] First, a porous carbon structure is prepared (step S1). The porous carbon structure prepared here preferably has carbon-carbon double bonds in at least a portion.

[0083] Furthermore, the porous carbon structure prepared here is preferably of type I in the IUPAC classification and has a surface area of ​​1400 m². 2 / g or more, pore volume of 1cm 3 / g or more. By setting the classification, surface area, and pore volume according to IUPAC standards, silicon deposition can be performed in larger quantities and more efficiently. The upper limit for the surface area is not specifically limited; for example, it can be set to 3000m². 2 / g or less. Furthermore, there is no specific upper limit on the pore volume; for example, it can be set to 5cm. 3 / g or less. Furthermore, the determination methods described below can be used for IUPAC classification, surface area, and pore volume. • Specific surface area / pore size distribution was determined using a static volumetric method based on gas adsorption, employing the Tristar II Plus from Shimadzu Corporation. The conditions are shown below. • Gas used: Nitrogen • Environment: Under liquid nitrogen • Pressure operating range: P / P0 • Adsorption 0~0.998 • Desorption 0.998~0.10 • Pretreatment at 200℃ for 1 hour

[0084] Next, silane gas is flowed into the porous carbon structure prepared in step S1 under heating, thereby depositing silicon from the silane gas into the interior of the porous carbon structure (step S2).

[0085] Furthermore, it is preferable to place the porous carbon structure in a vacuum container and evacuate it after step S1 and before step S2. The vacuum level can be maintained up to, for example, approximately -100 kPa, but is not limited to this. Additionally, it is preferable to restore the pressure using nitrogen after evacuation and then heat it to approximately 350-450°C using an external heater while nitrogen is flowing. This heating can be set for 5 minutes to 1 hour. By performing this vacuuming and preheating in the presence of nitrogen, nucleation for silicon deposition in step S2 and removal of hydrogen and water adhering to the porous carbon structure can be achieved, thus enabling more reliable silicon deposition in step S2.

[0086] The silicon deposition in step S2 can be performed, for example, by introducing silane gas at a temperature of around 400°C to 500°C. The deposition time can be set, for example, to 30 minutes to 10 hours.

[0087] Next, the material obtained by depositing silicon inside the porous carbon structure is cooled to below 50°C (step S3). In this step, cooling is preferably performed, for example, while nitrogen gas is flowing through it. In this cooling, for example, it is possible to cool to room temperature. In addition, there is no particular limitation on the more specific lower limit of the cooling temperature, but it can be set to, for example, 25°C or higher.

[0088] After the aforementioned cooling (step S3), the material obtained by depositing silicon into the porous carbon structure is then kept at a temperature below 50°C. Oxygen diluted with nitrogen is introduced into the material, thereby transforming at least a portion of the silicon into low-valence nano-silicon oxide (step S4). This step enables the formation of Si-O bonds. Furthermore, it is more preferable to maintain the temperature at 35°C or below.

[0089] Oxygen dilution using nitrogen can be set to, for example, 5 to 50 times, preferably 10 to 30 times. This dilution can typically be set to 20 times.

[0090] Furthermore, in step S4, if the internal temperature rises and exceeds 50°C, silicon dioxide will be generated in a portion of the material, which is undesirable as a negative electrode active material. Therefore, in step S4, it is necessary to adjust the temperature of the material to be maintained below 50°C. Additionally, the material temperature in step S4 is preferably set to 25°C or higher, more preferably 30°C or higher, to facilitate the oxidation reaction and thus promote the formation of Si-O bonds.

[0091] The oxidation time (the flow time of nitrogen-diluted oxygen) in step S4 can be set to, for example, 30 minutes or more and 5 hours or less, preferably 1 hour or more and 3 hours or less. Furthermore, after the nitrogen-diluted oxygen is flowed, the flow can be switched to nitrogen, followed by further cooling. The flow of nitrogen alone can be set to, for example, 30 minutes or more and 2 hours or less.

[0092] In the oxidation process described above, which utilizes a flow of oxygen diluted with nitrogen, it is preferable to adjust the process such that the x-value of the low-valence nano-silicon oxide dispersed in the porous carbon structure increases from the center of the porous carbon structure towards the surface. Furthermore, in the porous carbon structure, the pore structure tends to have a large cross-sectional area on the particle surface, and this cross-sectional area gradually decreases towards the interior of the particle. Therefore, as shown in this invention, by performing oxidation using a flow of oxygen diluted with nitrogen, it is easy to naturally cause x to gradually increase from the center of the porous carbon structure towards the surface.

[0093] Following step S4, at least a portion of the surface layer of the low-valent nano-silica oxide is then coated with a condensation reaction product of at least one of an organopolysiloxane and an organosilicon oligomer having at least one of a silanol group and an alkoxy group directly bonded to a silicon atom (step S5).

[0094] Preferably, a condensation reactant is formed on at least a portion of the surface layer of the low-valent nano-silicon oxide by hydrolysis and dehydration condensation of at least one of the organopolysiloxane and organosilicon oligomer, thereby coating at least a portion of the surface layer of the low-valent nano-silicon oxide.

[0095] By using the hydrolysis and dehydration condensation of at least one of such organopolysiloxanes and organosilicon oligomers, condensation reactants can be easily formed on the surface of low-valent nano-silicon oxides.

[0096] In addition, a catalytic amount of condensation catalyst is preferably added to hydrolyze and dehydrate at least one of the organopolysiloxane and organosilicon oligomer.

[0097] By adding such a catalytic amount of condensation catalyst, it becomes easier to hydrolyze and dehydrate at least one of the organopolysiloxanes and organosilicon oligomers.

[0098] In addition, although there is no limitation, as a specific example of a condensation catalyst, DX-9740 (aluminum-based condensation catalyst, manufactured by Shin-Etsu Chemical Co., Ltd.) can be used.

[0099] Then, the material is removed from the storage container. Through the above process, the following negative electrode active material can be produced: amorphous low-valence nano-silicon oxide is dispersed inside the porous carbon structure, and at least a portion of the surface of the low-valence nano-silicon oxide is coated with a condensation reaction product of at least one of organopolysiloxane and organosilicon oligomer having at least one of silanol group and alkoxy group directly bonded to silicon atom.

[0100] When manufacturing the negative electrode active material in the above manner, it is preferable to adjust the amount of silicon deposition and the degree of oxidation so that the proportion of porous carbon structures in the overall negative electrode active material particles is more than 38% by mass and less than 63% by mass.

[0101] Lithium-ion secondary batteries Next, as a specific example of a non-aqueous electrolyte secondary battery using the negative electrode active material of the present invention, a laminated film type lithium-ion secondary battery will be described.

[0102] [Structure of laminated film type lithium-ion secondary battery] Figure 2 The laminated lithium-ion secondary battery 30 shown primarily houses a wound electrode body 31 within a sheet-like packaging component 35. The wound electrode body 31 has a separator between the positive and negative electrodes and is wound in place. Alternatively, there may be a case where a separator is present between the positive and negative electrodes, and a laminated structure is also included. In either electrode body configuration, 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 periphery of the electrode body is protected by protective tape.

[0103] The positive lead 32 and the negative lead 33 are led out in one direction, for example, from the inside of the packaging member 35 to the outside. The positive lead 32 is formed of a conductive material such as aluminum, and the negative lead 33 is formed of a conductive material such as nickel or copper.

[0104] The packaging component 35 is, for example, a laminated film formed by sequentially stacking a weld layer, a metal layer, and a surface protective layer. In this laminated film, the outer peripheral edges of the weld layers of the two films are bonded together using welding or adhesives, with the weld layer facing the electrode body 31. The weld portion is, for example, a polyethylene or polypropylene film, and the metal portion is, for example, aluminum foil. The protective layer is, for example, nylon.

[0105] A sealing membrane 34 is embedded between the packaging component 35 and the positive and negative leads to prevent the intrusion of external gases. The material is, for example, polyethylene, polypropylene, or polyolefin resin.

[0106] Positive electrode, for example, with Figure 1 Similarly, the negative electrode 10 has a layer of positive active material on both sides or one side of the positive current collector.

[0107] The positive current collector is formed, for example, from a conductive material such as aluminum.

[0108] The positive electrode active material layer includes one or more positive electrode materials capable of absorbing, storing, and releasing lithium ions, and may also include other materials such as positive electrode binders, positive electrode conductive additives, and dispersants, depending on the design. In this case, the relevant details of the positive electrode binders and positive electrode conductive additives are, for example, the same as those of the negative electrode binders and negative electrode conductive additives already described.

[0109] Lithium-containing compounds are preferred as cathode materials. Examples of such lithium-containing compounds include composite oxides composed of lithium and transition metal elements, or phosphate compounds containing lithium and transition metal elements. Among these cathode materials, compounds containing at least one of nickel, iron, manganese, and cobalt are preferred. Their chemical formulas are, for example, derived from Li x M1O2 or Li y M2PO4 represents the formula. In the formula, M1 and M2 represent at least one or more transition metal elements. The values ​​of x and y vary depending on the battery's charge and discharge state, but are generally expressed as 0.05≤x≤1.10 and 0.05≤y≤1.10.

[0110] As a composite oxide containing lithium and a transition metal element, examples include lithium-cobalt composite oxide (Li₂O₃). x CoO2), lithium nickel composite oxide (Li x NiO2), lithium nickel cobalt composite oxides, etc. Examples of lithium nickel cobalt composite oxides include lithium nickel cobalt aluminum composite oxide (NCA) or lithium nickel cobalt manganese composite oxide (NCM).

[0111] Examples of phosphoric acid compounds containing lithium and transition metal elements include lithium iron phosphate (LiFePO4) and lithium iron manganese phosphate (LiFe). 1-u Mn u PO4 (0 < u < 1), etc. Using these cathode materials can achieve high battery capacity and excellent cycle characteristics.

[0112] [negative electrode] The negative electrode has the same characteristics as the above. Figure 1 The lithium-ion secondary battery uses the same structure as the negative electrode 10, for example, having negative electrode active material layers on both sides of the current collector. Preferably, the negative electrode charging capacity is greater than the capacity obtained by the positive electrode active material (as the battery charging capacity). This suppresses the deposition of lithium metal on the negative electrode.

[0113] The positive electrode active material layer is disposed locally on both sides of the positive electrode current collector, and similarly, the negative electrode active material layer is disposed locally on both sides of the negative electrode current collector. For example, the negative electrode active material layer disposed on the negative electrode current collector may have regions where there is no opposing positive electrode active material layer. This is for the purpose of a stable battery design.

[0114] The regions where the negative electrode active material layer and the positive electrode active material layer are not opposite each other are almost unaffected by charging and discharging. Therefore, the state of the negative electrode active material layer remains as it was just formed, thus allowing for reproducible and accurate study of the composition of the negative electrode active material regardless of whether charging or discharging occurs.

[0115] [Septum] The separator isolates the positive and negative electrodes, preventing short circuits caused by contact between the two electrodes and allowing lithium ions to pass through. This separator is, for example, formed of a porous membrane made of synthetic resin or ceramic, and may also have a laminated structure consisting of two or more porous membranes. Examples of synthetic resins include polytetrafluoroethylene, polypropylene, and polyethylene.

[0116] Electrolyte At least a portion of the active material layer or the membrane is impregnated with a liquid electrolyte (electrolyte). The electrolyte contains electrolyte salts dissolved in a solvent and may also contain other materials such as additives.

[0117] Non-aqueous solvents can be used as solvents. Examples of non-aqueous solvents include ethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, or tetrahydrofuran. Ideally, at least one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate should be used because better properties can be obtained. Furthermore, combining high-viscosity solvents such as ethylene carbonate and propylene carbonate with low-viscosity solvents such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate can yield even better properties because the dissociation and ion mobility of the electrolyte salt are increased.

[0118] When using alloy-based negative electrodes, it is particularly desirable to include at least one of halochain carbonates or halocyclic carbonates as a solvent. This allows a stable coating to form on the surface of the negative electrode active material during charging and discharging, especially during charging. Here, halochain carbonates refer to chain carbonates having a halogen as a constituent element (at least one hydrogen atom is replaced by a halogen). Furthermore, halocyclic carbonates refer to cyclic carbonates having a halogen as a constituent element (i.e., at least one hydrogen atom is replaced by a halogen).

[0119] There are no particular restrictions on the type of halogen, but fluorine is preferred. This is because it forms a superior coating compared to other halogens. Furthermore, a higher number of halogens is generally better, as it results in a more stable coating and reduces electrolyte decomposition reactions.

[0120] Examples of halogenated chain carbonates include fluoromethyl carbonate and difluoromethyl carbonate. Examples of halogenated cyclic carbonates include 4-fluoro-1,3-dioxolane-2-one and 4,5-difluoro-1,3-dioxolane-2-one.

[0121] As a solvent additive, unsaturated carbon-bonded cyclic carbonates are preferred. This is because, during charging and discharging, a stable coating forms on the negative electrode surface, thereby suppressing the decomposition reaction of the electrolyte. Examples of unsaturated carbon-bonded cyclic carbonates include vinylene carbonate or ethylene ethylene carbonate.

[0122] Furthermore, sulfonyl lactones (cyclic sulfonates) are preferably included as solvent additives. This is because they increase the chemical stability of the battery. Examples of sulfonyl lactones include propane sulfonyl lactone and propene sulfonyl lactone.

[0123] Furthermore, the solvent preferably includes an acid anhydride. This is because it increases the chemical stability of the electrolyte. Examples of acid anhydrides include propane disulfonic acid anhydride.

[0124] Electrolyte salts can contain one or more light metal salts, such as lithium salts. Examples of lithium salts include lithium hexafluorophosphate (LiPF6) and lithium tetrafluoroborate (LiBF4).

[0125] The electrolyte salt content is preferably 0.5 mol / kg or more and 2.5 mol / kg or less relative to the solvent. This is because it allows for high ionic conductivity. Example

[0126] The following examples and comparative examples illustrate the present invention in more detail, but the present invention is not limited to these examples. (Example 1)

[0127] The negative electrode active material is prepared through the following steps, and then further processed. Figure 2 The laminated film type lithium-ion secondary battery 30 is shown.

[0128] The negative electrode active material is manufactured as follows. First, a material with a surface area (BET specific surface area) of 2433 m² is prepared. 2 / g, pore volume 1.34cm 3 Porous carbon material (porous carbon structure) with a particle size (D50) of 11 μm and classified as Type I by IUPAC was placed in a vacuum container and evacuated to -90 kPa. The pressure was then restored using nitrogen, and the material was heated to 400°C using an external heater while nitrogen flow was maintained. After 30 minutes of heating, the temperature was increased to 415°C, and silane gas was introduced and deposited for 4 hours. Then, the material was cooled to room temperature while nitrogen flow was maintained. After the temperature dropped to 25°C, oxygen diluted 20 times with nitrogen was introduced, and the material temperature was adjusted to below 50°C to allow Si-O bond formation. Nitrogen containing oxygen was then introduced for 2 hours, and when the material temperature reached below 30°C, nitrogen was switched back to nitrogen and allowed to flow for 60 minutes. Finally, 2.0% by mass of KR-220L (containing silanol groups and CH3-SiO2) was dissolved in the porous carbon material in the container. 3 / 2 Methyl polysiloxane (manufactured by Shin-Etsu Chemical Co., Ltd.) as the structural unit was heated to 400°C for 2 hours under nitrogen flow. After cooling to room temperature, the material was removed from the storage container and used as the negative electrode active material.

[0129] The methyl polysiloxane used here, KR-220L, is the R in the general formula (1) of the above-mentioned organopolysiloxane structural unit. 1 Let it be an alkyl (methyl: CH3-) methyl polysiloxane with 1 carbon atom.

[0130] In addition, a structural unit refers to the smallest unit that describes the chemical structure of a polymer chain, excluding end groups and junctions; it is also called a repeating unit.

[0131] [Making the negative electrode] The negative electrode active material (containing CVD-SiOx-C active material), graphite, conductive additive 1 (carbon nanotubes, CNT), conductive additive 2 (carbon microparticles with a median particle size of about 50 nm), sodium polyacrylate, and carboxymethyl cellulose (hereinafter referred to as CMC) prepared in the above manner are mixed in a dry mass ratio of 9.3:83.7:1:1:4:1 and then diluted with pure water to prepare a negative electrode slurry.

[0132] 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 a concentration of 70 ppm by mass, respectively. Finally, a negative electrode slurry was coated onto the negative electrode current collector and dried at 100°C in a vacuum atmosphere for 1 hour. The deposition amount of the negative electrode active material layer per unit area (also known as the areal density) on one side of the dried negative electrode was 7.0 mg / cm³. 2 .

[0133] [Assembly of the experimental button battery] Next, ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed, and the electrolyte salt (lithium hexafluorophosphate: LiPF6) was dissolved to prepare the electrolyte. At this point, the solvent composition was set at a volume ratio of EC:DMC = 30:70, and the electrolyte salt content was set at 1 mol / kg relative to the solvent. 1.0% by mass of vinylene carbonate (VC) and 2.0% by mass of fluoroethylene carbonate (FEC) were added as additives.

[0134] Next, the button cell is assembled as follows. First, a 1mm thick Li foil is punched to a diameter of 16mm and then attached to the aluminum cladding layer.

[0135] Next, the previously obtained negative electrode was punched to a diameter of 15mm, so that it was positioned opposite the Li foil attached to the aluminum cladding layer through the separator. After injecting electrolyte, a 2032 button cell was manufactured.

[0136] [Initial efficiency measurement] The initial efficiency was determined under the following conditions. First, the button cell used for the initial efficiency test was charged at a rate equivalent to 0.03C in CCCV (constant current constant voltage) mode (initial charge). CV was set to 0V and the cutoff current was set to 0.04mA. Next, the discharge rate was set to 0.03C and the discharge cutoff voltage was set to 1.2V, and CC (constant current) discharge was performed (initial discharge).

[0137] When studying the initial charge and discharge characteristics, the initial efficiency (sometimes referred to as initial efficiency below) is calculated. The initial efficiency is calculated using the formula: Initial efficiency (%) = (Initial discharge capacity / Initial charge capacity) × 100.

[0138] [Manufacturing and Evaluation of Lithium-ion Secondary Batteries] Based on the initial data obtained, the positive electrode was designed with a negative electrode utilization rate of 95%. The utilization rate was calculated based on the capacities of the positive and negative electrodes obtained from the counter electrode Li, using the following formula. Utilization rate = (positive electrode capacity - negative electrode loss) / (negative electrode capacity - negative electrode loss) × 100 Based on this design, various lithium-ion secondary batteries (such as) were manufactured in the embodiments and comparative examples. Figure 2 (The lithium-ion secondary battery shown). Battery evaluation was performed on each lithium-ion secondary battery of the examples and comparative examples.

[0139] The cycle characteristics were studied as follows. First, to stabilize the battery, two charge-discharge cycles were performed at 0.2C in an atmosphere at 25°C, and the discharge capacity of the second cycle was measured. The battery cycle characteristics were calculated based on the discharge capacity of the third cycle, and the battery test was terminated after 1000 cycles. Charge and discharge were performed at 0.7C and 0.5C. The charging voltage was set to 4.3V, the discharge cutoff voltage to 2.5V, and the charging cutoff rate to 0.07C.

[0140] The thickness of the condensation reactants in KR-220L was investigated by disassembling the battery after the cycle test and then using TEM to observe the porous carbon structure in the negative electrode active material particles.

[0141] The results of each measurement are shown in Table 1. Comparative Example 1, Comparative Example 2, and Examples 2-15 described below are also shown in Table 1.

[0142] [Table 1]

[0143] (Comparative Example 1) The following steps were not performed: adding acetone containing 2.0% by mass of KR-220L to the porous carbon material and heating at 400°C for 2 hours under nitrogen flow. Otherwise, the negative electrode active material was manufactured using the same method as in Example 1. The obtained negative electrode active material was evaluated using the same method as in Example 1.

[0144] The negative electrode active material of Comparative Example 1 exhibits deteriorated cycling characteristics because the low-valence nano-silicon oxide exposed on the surface of the porous carbon structure is not coated by the condensation reactants of KR-220L.

[0145] (Comparative Example 2) Prepare a porous carbon structure identical to that in Example 1. Then, using silane gas under the same conditions as in Example 1, form amorphous silicon from the surface of the porous carbon structure particles to near the center at 415°C. This state contains Si-H bonds, thus undergoing Si-Si formation, requiring the temperature to be increased to 435°C to stabilize the Si-Si. Then, cool to room temperature under flowing nitrogen. Next, add acetone containing 2.0% by mass of KR-220L to the porous carbon material in a container, and heat at 400°C for 2 hours under flowing nitrogen. After cooling to room temperature, remove the sample while exposed to the atmosphere. Using this method, it is possible to prepare materials (different from those of this invention) without low-valent silicon oxide compounds. The obtained negative electrode active material was evaluated using the same method as in Example 1.

[0146] Since the negative electrode active material of Comparative Example 2 does not contain low-valent silicon oxide compounds, although it has high capacity and initial efficiency, it also has high reactivity with the electrolyte, which deteriorates the battery cycle characteristics.

[0147] (Examples 2-3) Except for changing the starting material used to form the condensation reactant (at least one of a silanol group and an alkoxy group directly bonded to a silicon atom, an organopolysiloxane, and an organosilicon oligomer) as shown in Table 1 above, the negative electrode active material was manufactured using the same method as in Example 1. The obtained negative electrode active material was evaluated using the same method as in Example 1.

[0148] Additionally, X-40-9225 listed in Table 1 is a methoxy group directly bonded to silicon atoms and uses CH3SiO 2 / 2 Organosilicon oligomers with (OCH3) as the structural unit (manufactured by Shin-Etsu Chemical Industry Co., Ltd.).

[0149] The organosilicon oligomer X-40-9225 used here is the organosilicon oligomer whose structural unit R is derived from the general formula (3) of the above organosilicon oligomer. 3 R 4 The organosilicon oligomer is defined as an alkyl group (methyl: CH3-) with one carbon atom. Furthermore, the methoxy group (CH3O-) directly bonded to the silicon atom can transfer the R in the general formula (4) of the aforementioned organosilicon oligomer. 5 It is represented as an alkyl group with 1 carbon atom (methyl: CH3-).

[0150] (Example 4) In addition to adding acetone containing 2.0% by mass of KR-220L dissolved in it to the porous carbon material, acetone containing 0.020% by mass of DX-9740 (an aluminum-based condensation catalyst, manufactured by Shin-Etsu Chemical Industry Co., Ltd.) dissolved in it was also added to the porous carbon material. Otherwise, the negative electrode active material was manufactured using the same method as in Example 1. The obtained negative electrode active material was evaluated using the same method as in Example 1.

[0151] (Examples 5 and 6) Except for changing the amounts of the starting materials (at least one of silanol groups and alkoxy groups directly bonded to silicon atoms, at least one of organopolysiloxanes and organosilicon oligomers) and the condensation catalyst used to form the condensation reactants as shown in Table 1 above, the negative electrode active material was manufactured using the same method as in Example 4. The obtained negative electrode active material was evaluated using the same method as in Example 1.

[0152] In the negative electrode active materials of Examples 1-6, at least a portion of the surface layer of the low-valence nano-silicon oxide exposed to the surface of the porous carbon structure is coated with condensation reactants, thus inhibiting its reactivity with the electrolyte. Therefore, the cycling characteristics of Examples 1-6 are superior to those of Comparative Example 1.

[0153] (Examples 7-9) Except for changing the amount of KR-200L as shown in Table 1 above, the negative electrode active material was manufactured using the same method as in Example 1. The obtained negative electrode active material was evaluated using the same method as in Example 1.

[0154] (Examples 10-12) Except for changing the amount of X-40-9225 as shown in Table 1 above, the negative electrode active material was manufactured using the same method as in Example 2. The obtained negative electrode active material was evaluated using the same method as in Example 1.

[0155] Compared to Comparative Examples 1 and 2, the cycling characteristics of Examples 9 and 12 were significantly improved. This result shows that even when the thickness of the condensation reactant exceeds 10 nm, the cycling characteristics remain improved. On the other hand, the cycling characteristics of Example 9 were worse than those of Examples 1, 7, and 8, and the cycling characteristics of Example 12 were worse than those of Examples 5, 10, and 11. Based on these results, it can be considered that the ideal thickness of the condensation reactant is 10 nm or less.

[0156] (Example 13) The negative electrode active material was fabricated by changing the conditions as follows, relative to the same porous carbon structure as in Example 1. First, the temperature was raised to 415°C, allowing silane gas to flow in and deposit for 4 hours. Then, the temperature was increased to allow Si... 0+The material was grown to the desired grain size and then cooled to room temperature while flowing nitrogen. After lowering the temperature to 25°C, oxygen diluted 20 times with nitrogen was introduced and adjusted to bring the material temperature below 50°C, thereby forming Si-O bonds. Next, nitrogen containing oxygen was flowed in for 2 hours, and at a point when the material temperature fell below 30°C, nitrogen was switched to flow for 60 minutes. Then, acetone containing 2.0% by mass of KR-220L was added to the porous carbon material in a container, and the mixture was heated at 400°C for 2 hours under flowing nitrogen. After cooling to room temperature, the material was removed from the container as the negative electrode active material. The obtained negative electrode active material was evaluated using the same method as in Example 1.

[0157] The cycling characteristics of Example 13 were improved compared to Comparative Example 1, but worse than those of Example 1. Specifically, compared to Example 1, Example 13 had a larger grain size and slightly lower cycling characteristics (retention rate after 1000 cycles in Table 1). This result indicates that a smaller grain size is preferred. Among these, smaller grain sizes are closer to an amorphous structure, therefore it is believed that the closer the negative electrode active material is to an amorphous structure, the better the cycling characteristics are.

[0158] (Examples 14 and 15) Except for the changes to the initially prepared porous carbon structure as shown in Table 1 above, the negative electrode active material was manufactured using the same method as in Example 1. The obtained negative electrode active material was evaluated using the same method as in Example 1.

[0159] The cycling characteristics of Examples 14 and 15 were improved compared to Comparative Example 1, but worse than those of Example 1. Based on these results, it can be considered that a pore volume of 1 cm³ for the porous carbon structure is more ideal. 3 / g or more, BET specific surface area is 1400m² 2 Those with a weight of 6g or more are classified as Type I by IUPAC.

[0160] Figure 4 The changes in the depth direction of the O1s region are shown in the XPS measurements of the negative electrode active material in Example 1. Figure 4 It can be seen that the O1s peak decreases in depth from the surface, and the oxygen concentration decreases from the surface to the deeper layers.

[0161] Figure 5 The X-ray diffraction spectra of Examples 1, 2, 10, and 11 are shown. In all these spectra, a peak appears near 2θ = 28°, and the grain size of silicon was calculated based on this peak. The other examples and comparative examples are similar.

[0162] This manual includes the following solutions. (1): A negative electrode active material, which is a negative electrode active material having negative electrode active material particles, characterized in that, The negative electrode active material particles contain porous carbon structures. Amorphous, low-valence nano-silicon oxides are dispersed within the porous carbon structure. The low-cost nano-silicon oxide comprises SiOx, where x < 1.0. At least a portion of the surface layer of the low-valence nano-silicon oxide exposed to the surface of the porous carbon structure is coated with a condensation reactant of at least one of organopolysiloxane and organosilicon oligomer having at least one of silanol group and alkoxy group directly bonded to silicon atom. (2): The negative electrode active material as described in (1) above, wherein the organopolysiloxane has a structural unit represented by the following general formula (1) and a group represented by the following general formula (2) directly bonded to silicon atoms. R 1 -SiO 3 / 2 (1) (In general formula (1), R) 1 (This refers to alkyl groups with 1 to 3 carbon atoms that have been substituted or not substituted) -OR 2 (2) (In general formula (2), R) 2 (representing a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms, whether substituted or unsubstituted). (3): The negative electrode active material as described in (1) or (2) above, wherein the organosilicon oligomer has a structural unit represented by the following general formula (3) and a group represented by the following general formula (4) directly bonded to silicon atoms. R 3 SiO 2 / 2 (OR 4 (3) (In general formula (3), R) 3 Each independently represents an alkyl group having 1 to 3 carbon atoms, whether substituted or unsubstituted, R 4 Each of the following can be independently represented as a hydrogen atom or an alkyl group having 1 to 6 substituted or unsubstituted carbon atoms. -OR 5 (4) (In general formula (4), R) 5 (representing a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms, whether substituted or unsubstituted). (4): The negative electrode active material as described in any one of (1) to (3) above, wherein the thickness of the condensation reactant is 0.1 nm or more and 10 nm or less. (5): The negative electrode active material as described in any one of (1) to (4) above, wherein the low-valent nano silicon oxide is essentially a composite state of 0-valent, 1-valent and 2-valent. (6): The negative electrode active material as described in any one of (1) to (5) above, wherein the x of the low-valence nano-silicon oxide dispersed in the porous carbon structure increases from the center of the porous carbon structure toward the surface. (7): The negative electrode active material as described in any one of (1) to (6) above, wherein the grain size of the 0-valent Si constituting the low-valent nano-silicon oxide, as determined by measuring the particles of the negative electrode active material by X-ray diffraction and calculated using the Scherrer formula, is in the range of 1 nm to 5 nm. (8): The negative electrode active material as described in any one of (1) to (7) above, wherein the porous carbon structure is mainly of type I in the IUPAC classification and has a surface area of ​​1400 m². 2 / g or more, pore volume of 1cm 3 / g or more. (9): A method for manufacturing a negative electrode active material, which is a method for manufacturing a negative electrode active material having negative electrode active material particles, the manufacturing method being characterized by comprising the following steps: Steps for preparing porous carbon structures; The step of allowing silane gas to flow into the porous carbon structure under heating, thereby depositing silicon into the interior of the porous carbon structure; The step of cooling the material obtained by depositing silicon inside the porous carbon structure to below 50°C; After cooling, while maintaining the temperature of the material obtained by depositing silicon inside the porous carbon structure below 50°C, oxygen diluted with nitrogen is introduced into the material obtained by depositing silicon inside the porous carbon structure, thereby transforming at least a portion of the silicon into low-valence nano-silicon oxide. The step of coating at least a portion of the surface layer of the low-valent nano-silicon oxide with a condensation reaction product having at least one of a silanol group and an alkoxy group directly bonded to a silicon atom, or an organopolysiloxane and an organosilicon oligomer. (10): The method for manufacturing the negative electrode active material as described in (9) above, wherein at least a portion of the surface layer of the low-valent nano-silicon oxide is formed by hydrolysis and dehydration condensation of at least one of the organopolysiloxane and organosilicon oligomer, thereby coating at least a portion of the surface layer of the low-valent nano-silicon oxide. (11): The method for manufacturing the negative electrode active material as described in (9) or (10) above, wherein a catalytic amount of condensation catalyst is added to hydrolyze and dehydrate at least one of the organopolysiloxane and organosilicon oligomer.

[0163] Furthermore, this invention is not limited to the above embodiments. The above embodiments are illustrative examples, and any technical solutions having a substantially identical structure and achieving the same effect as the technical concept described in the claims of this invention are included within the scope of protection of this invention.

Claims

1. A negative electrode active material, which is a negative electrode active material having negative electrode active material particles, characterized in that, The negative electrode active material particles contain porous carbon structures. Amorphous, low-valence nano-silicon oxides are dispersed within the porous carbon structure. The low-cost nano-silicon oxide comprises SiOx, where x < 1.

0. At least a portion of the surface layer of the low-valence nano-silicon oxide exposed to the surface of the porous carbon structure is coated with a condensation reactant of at least one of organopolysiloxane and organosilicon oligomer having at least one of silanol group and alkoxy group directly bonded to silicon atom.

2. The negative electrode active material according to claim 1, characterized in that, The organopolysiloxane has structural units represented by the following general formula (1) and groups represented by the following general formula (2) directly bonded to silicon atoms. R 1 -SiO 3 / 2 (1) In general formula (1), R 1 This indicates alkyl groups with 1 to 3 carbon atoms, whether substituted or unsubstituted. -OR 2 (2) In general formula (2), R 2 It refers to an alkyl group having 1 to 6 hydrogen atoms, or substituted or unsubstituted carbon atoms.

3. The negative electrode active material according to claim 1, characterized in that, The organosilicon oligomer has structural units represented by the following general formula (3) and groups represented by the following general formula (4) directly bonded to silicon atoms. R 3 SiO 2 / 2 (OR 4 ) (3) In general formula (3), R 3 Each independently represents an alkyl group having 1 to 3 carbon atoms, whether substituted or unsubstituted, R 4 Each of these can independently represent a hydrogen atom, or an alkyl group having 1 to 6 substituted or unsubstituted carbon atoms. -OR 5 (4) In general formula (4), R 5 It refers to an alkyl group having 1 to 6 hydrogen atoms, or substituted or unsubstituted carbon atoms.

4. The negative electrode active material according to claim 1, characterized in that, The thickness of the condensation reactant is greater than 0.1 nm and less than 10 nm.

5. The negative electrode active material according to claim 1, characterized in that, The low-valent nano-silicon oxide is essentially a composite state of 0, 1, and 2 valences.

6. The negative electrode active material according to claim 1, characterized in that, The x-value of the low-valence nano-silicon oxide dispersed in the porous carbon structure increases from the center of the porous carbon structure toward the surface.

7. The negative electrode active material according to claim 1, characterized in that, The grain size of the 0-valent Si constituting the low-valent nano-silicon oxide, as determined by the peaks obtained from X-ray diffraction measurements of the negative electrode active material particles and calculated using the Scherrer equation, is in the range of 1 nm to 5 nm.

8. The negative electrode active material according to claim 1, characterized in that, The porous carbon structure is predominantly type I in the IUPAC classification, with a surface area of ​​1400 m². 2 / g or more, pore volume of 1cm 3 / g or more.

9. A method for manufacturing a negative electrode active material, comprising the steps of manufacturing negative electrode active material particles: Steps for preparing porous carbon structures; The step of allowing silane gas to flow into the porous carbon structure under heating, thereby depositing silicon into the interior of the porous carbon structure; The step of cooling the material obtained by depositing silicon inside the porous carbon structure to below 50°C; After cooling, while maintaining the temperature of the material obtained by depositing silicon inside the porous carbon structure below 50°C, oxygen diluted with nitrogen is introduced into the material obtained by depositing silicon inside the porous carbon structure, thereby transforming at least a portion of the silicon into low-valence nano-silicon oxide; and The step of coating at least a portion of the surface layer of the low-valent nano-silicon oxide with a condensation reaction product having at least one of a silanol group and an alkoxy group directly bonded to a silicon atom, or an organopolysiloxane and an organosilicon oligomer.

10. The method for manufacturing the negative electrode active material according to claim 9, characterized in that, By hydrolysis and dehydration condensation of at least one of the organopolysiloxane and organosilicon oligomer, a condensation reactant is formed on at least a portion of the surface layer of the low-valent nano-silicon oxide, thereby coating at least a portion of the surface layer of the low-valent nano-silicon oxide.

11. The method for manufacturing the negative electrode active material according to claim 10, characterized in that, Adding a catalytic amount of condensation catalyst causes at least one of the organopolysiloxane and organosilicon oligomer to undergo hydrolysis and dehydration condensation.

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