Negative electrode active material and method for manufacturing the same

Abstract

To provide a negative electrode active material that can increase a capacity while maintaining battery characteristics.SOLUTION: There is provided a negative electrode active material having negative electrode active material particles. The negative electrode active material particles each include a porous carbon structure. An amorphous low valence nano silicon oxide is dispersed inside the porous carbon structure. The low valence nano silicon oxide includes each state of SiOx:(x<1.0), and at least a part of a surface layer portion of the low valence nano silicon oxide exposed on a surface of the porous carbon structure is coated with a decomposition product and / or a polymerization product of an organosilicon compound that is represented by the following general formula (1): Si(R1)l(R2)m(R3)4-l-m (1) (In the general formula (1), R1 represents an alkyl group having 1 to 20 carbon atoms, R2 represents an alkenyl group having 2 to 20 carbon atoms, and R3 represents an alkynyl group having 2 to 20 carbon atoms. In addition, l and m each independently represent an integer of 0 to 4.).SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In recent years, small electronic devices typified by mobile terminals have become widely popular, and further miniaturization, weight reduction, and long life are strongly demanded. In response to such market demands, the development of secondary batteries that are particularly small, lightweight, and capable of obtaining a high energy density has been promoted. The application of this secondary battery is not limited to small electronic devices, but is also being studied for large electronic devices typified by automobiles and power storage systems typified by houses.

[0003] Among them, lithium ion secondary batteries are easy to miniaturize and increase in capacity, and can obtain a higher energy density than lead batteries and nickel cadmium batteries, so they are highly expected.

[0004] The above lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution together with a separator, and the negative electrode contains a negative electrode active material involved in the charge and discharge reaction.

[0005] As this negative electrode active material, carbon-based active materials are widely used, while further improvement in battery capacity is required from recent market demands. In order to improve the battery capacity, the use of silicon as a negative electrode active material has been studied. This is because the theoretical capacity of silicon (4199 mAh / g) is more than 10 times larger than the theoretical capacity of graphite (372 mAh / g), so a significant improvement in battery capacity can be expected. The development of silicon materials as negative electrode active materials is being studied not only for elemental silicon but also for compounds typified by alloys and oxides. In addition, the shape of the active material has been studied from the standard coating type for carbon-based active materials to an integrated type that is 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 charge and discharge, so it is likely to crack mainly near the surface layer of the negative electrode active material. In addition, ionic substances are generated inside the active material, making the negative electrode active material prone to cracking. When the surface layer of the negative electrode active material cracks, a new surface is thereby generated, increasing the reaction area of the active material. At this time, the decomposition reaction of the electrolyte occurs on the new surface, and a film that is a decomposition product of the electrolyte is formed on the new surface, consuming the electrolyte. For this reason, the cycle characteristics are likely to deteriorate.

[0007] So far, various studies have been conducted on the negative electrode active material materials and electrode configurations for lithium-ion secondary batteries mainly composed of silicon materials in order to improve the initial battery efficiency and cycle characteristics.

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

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

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

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

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

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

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

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

Prior Art Documents

Patent Documents

[0016]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

Patent Document 11

Patent Document 12

Patent Document 13

Patent Document 14

Patent Document 15

Non - Patent Documents

[0017]

Non - Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

Non-Patent Document 8

Summary of the Invention

Problems to be Solved by the Invention

[0018] As described above, in recent years, small electronic devices typified by mobile terminals have been made more high-performance and multifunctional, and there is a demand for an increase in the battery capacity of lithium-ion secondary batteries, which are their main power sources. As one method for solving this problem, the development of a lithium-ion secondary battery having a negative electrode made mainly of a silicon material is desired.

[0019] In addition, a lithium-ion secondary battery using a silicon material is desired to have initial charge / discharge characteristics and cycle characteristics that are almost equivalent to those of a lithium-ion secondary battery using a carbon-based active material. Therefore, by using a silicon oxide modified by insertion and partial desorption of Li as a negative electrode active material, the cycle characteristics and the initial charge / discharge characteristics have been improved. These days, by mainly using silicon oxide and pre-containing Li to form Li silicate, the irreversible capacity, which is a demerit of silicon oxide, has been reduced, and it has actually started to be put on the market. Even when a battery was prototyped by replacing 100% of the carbon negative electrode material with Li-SiO-C (Non-Patent Document 8) using Li in this silicon oxide, the capacity improvement only reached the latter half of the 20% range compared to the carbon negative electrode material. This means that further improvement in battery capacity is required in consideration of the higher performance of small electronic devices (such as 5G) and the increased driving range of electric vehicles.

[0020] Therefore, CVD-Si-C with little irreversible capacity has been developed, but it has been found that due to the reaction between Si and the electrolytic solution, the fast charging performance and the battery cycle characteristics are insufficient.

[0021] The present invention has been made in view of the above problems, and an object thereof is to provide a negative electrode active material capable of increasing the capacity while maintaining battery characteristics.

Means for Solving the Problems

[0022] In order 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, and amorphous low-valence nanosilicon oxide is dispersed inside the porous carbon structure. The low-valence nanosilicon oxide includes each state of SiOx where x < 1.0, and at least a part of the surface layer portion of the low-valence nanosilicon oxide exposed on the surface of the porous carbon structure is represented by the following general formula (1). Si(R 1 ) l (R 2 ) m (R 3 ) 4-l-m (1) (In general formula (1), R 1 is an alkyl group having 1 to 20 carbon atoms, R 2 is an alkenyl group having 2 to 20 carbon atoms, and R 3 is an alkynyl group having 2 to 20 carbon atoms. Also, l and m each independently represent an integer of 0 to 4.) The negative electrode active material is characterized in that it is coated with a decomposition product and / or polymer of an organosilicon compound represented by the formula.

[0023] Since the negative electrode active material of the present invention has amorphous low-valence nanosilicon oxide dispersed inside the porous carbon structure, the adverse effect due to the expansion of the internal low-valence nanosilicon oxide can be reduced by the presence of the porous carbon structure. Also, in general SiO, Si 4+ becomes an irreversible component, but in the negative electrode active material of the present invention, since it includes each state of SiOx where x < 1.0, an irreversible capacity lower than that of general SiO can be maintained. Also, since the Si-O bond can suppress the decomposition of the electrolyte, it is possible to reduce the SEI (Solid Electrolyte Interphase) deposited on the surface layer portion. Further, by coating the active sites of the above nanosilicon oxide with a decomposition product and / or polymer of an organosilicon compound, the reactivity between the negative electrode active material and the electrolyte can be reduced, and as a result, the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved.

[0024] In this case, it is preferable that the organosilicon compound in the general formula (1) is represented by l = 0 to 3, and particularly preferably by l = 0.

[0025] Thus, when the organosilicon compound in the general formula (1) is represented by l = 0 to 3, and particularly preferably by l = 0, the reactivity between the negative electrode active material and the electrolytic solution can be more effectively reduced.

[0026] Further, it is preferable that the decomposition products and / or polymers of the organosilicon compound coated on the surface of the porous carbon structure contain polyethylene or polyacetylene.

[0027] Thus, by including polyethylene or polyacetylene in the decomposition products and / or polymers of the organosilicon compound, the reactivity with the electrolytic solution can be more effectively suppressed.

[0028] Further, it is preferable that the decomposition products and / or polymers of the organosilicon compound coated on the surface of the porous carbon structure contain silicon.

[0029] Thus, by including silicon in the decomposition products and / or polymers of the organosilicon compound, the reactivity with the electrolytic solution can be more effectively suppressed.

[0030] Further, it is preferable that the thickness of the decomposition products and / or polymers of the organosilicon compound is 10 nm or less.

[0031] Such a thickness is preferable for improving the cycle characteristics.

[0032] Further, it is preferable that the surface of the porous carbon structure is coated in a mesh shape by the decomposition products and / or polymers of the organosilicon compound.

[0033] Such a coating mode is preferable for improving the cycle characteristics.

[0034] Further, it is preferable that the low-valence nanosilicon oxide is in a substantially composite state of 0 valence, 1 valence, and 2 valence.

[0035] In this way, since the low-valence nanosilicon oxide is in a substantially composite state of 0 valence, 1 valence, and 2 valence, a lower irreversible capacity can be achieved.

[0036] Further, the grain size of 0-valent Si constituting the low-valence nanosilicon oxide, calculated using Scherrer's formula from the peaks measured by X-ray diffraction measurement of the negative electrode active material particles, is preferably in the range of 1 nm to 5 nm.

[0037] Those having such a grain size of 0-valent Si with a substantially amorphous structure are preferable.

[0038] Further, the structure of the porous carbon is predominantly of type I in the IUPAC classification, and its surface area is 1400 m 2 / g or more, and the pore volume is 1 cm 2 / g or more.

[0039] Since the structure of the porous carbon has such an IUPAC classification, surface area, and pore volume, a negative electrode active material containing a larger amount of low-valence nanosilicon oxide efficiently can be obtained. In particular, the type I structure in the IUPAC classification enables smooth formation of Si-O bonds after deposition.

[0040] Further, the low-valence nanosilicon oxide dispersed in the structure of the porous carbon can be such that x increases from the center to the surface layer of the structure of the porous carbon.

[0041] In the present invention, in order to disperse a low-valence nanosilicon oxide in a porous carbon structure, it is likely that from the center to the surface layer of the porous carbon structure during production, x increases (the oxygen composition ratio increases). Since the oxidation ratio of silicon is large on the surface, the decomposition of the electrolyte can be more effectively suppressed, while since the oxidation ratio of silicon is small inside the active material, the battery capacity can be further increased.

[0042] Further, the present invention is a method for producing a negative electrode active material having negative electrode active material particles, the method including the steps of: preparing a porous carbon structure; flowing monosilane gas under heating to the porous carbon structure to deposit silicon inside the porous carbon structure; cooling the material having silicon deposited inside the porous carbon structure to 50°C or lower; after the cooling, introducing oxygen diluted with nitrogen gas into the material having silicon deposited inside the porous carbon structure while adjusting the temperature of the material having silicon deposited inside the porous carbon structure to maintain 50°C or lower, to change at least a part of the silicon into a low-valence nanosilicon oxide by an oxidation reaction; and after the oxidation reaction, the low-valence nanosilicon oxide and the following general formula (1) Si(R 1 ) l (R 2 ) m (R 3 ) 4-l-m (1) (In the general formula (1), R 1 is an alkyl group having 1 to 20 carbon atoms, R 2 is an alkenyl group having 2 to 20 carbon atoms, and R 3 is an alkynyl group having 2 to 20 carbon atoms. Also, l and m each independently represent an integer of 0 to 4.) A step of bringing the organosilicon compound represented by the formula into contact at 100 to 1000 °C, and amorphous low-valence nanosilicon oxide is dispersed inside the structure of the porous carbon, and at least a part of the surface layer portion of the low-valence nanosilicon oxide exposed on the surface of the structure of the porous carbon is coated with a decomposition product and / or a polymer of the organosilicon compound, and a method for producing a negative electrode active material is provided.

[0043] According to such a method for producing a negative electrode active material, as described above, amorphous low-valence nanosilicon oxide is dispersed inside the structure of the porous carbon, and at least a part of the surface layer portion of the low-valence nanosilicon oxide is coated with a decomposition product and / or a polymer of the organosilicon compound, and a negative electrode active material can be produced simply and efficiently.

Advantages of the Invention

[0044] Since the negative electrode active material of the present invention has amorphous low-valence nanosilicon oxide dispersed inside the structure of the porous carbon, the adverse effects due to expansion can be reduced when the internal low-valence nanosilicon oxide expands due to the presence of the structure of the porous carbon. Also, although general SiO becomes an irreversible component with Si 4+ In the negative electrode active material of the present invention, since each state of SiOx: x < 1.0 is included, an irreversible capacity lower than that of general SiO can be maintained. Also, since the Si-O bond can suppress the decomposition of the electrolyte solution, it is possible to reduce the SEI (Solid Electrolyte Interphase) deposited on the surface layer portion. Further, by coating the active site of the nanosilicon oxide with a decomposition product and / or a polymer of the organosilicon compound, the reactivity between the negative electrode active material and the electrolyte solution can be reduced, and as a result, the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved.

[0045] In addition, 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 nanosilicon oxide is dispersed inside the structure of the porous carbon, and at least a part of the surface layer portion of the low-valence nanosilicon oxide is coated with a decomposition product and / or polymer of an organosilicon compound.

Brief Description of Drawings

[0046]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0047] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.

[0048] As described above, as one method for increasing the battery capacity of a lithium-ion secondary battery, using a negative electrode in which a low-valence nanosilicon oxide is used as a main material in a carbon structure as the negative electrode of a lithium-ion secondary battery has been considered. A lithium-ion secondary battery using this active material is desired to have a high battery capacity while showing battery characteristics almost equivalent to those of a lithium-ion secondary battery using a carbon-based active material.

[0049] Therefore, the present inventors have intensively studied to obtain a negative electrode active material that can improve the initial charge-discharge characteristics and increase the battery capacity while obtaining high cycle characteristics when used as the negative electrode of a secondary battery, and have arrived at the present invention.

[0050] In particular, in the case of CVD-Si-C as disclosed in Patent Documents 14 and 15, there has been a problem that the reaction with the electrolyte is too large. In the present invention, in order to suppress such a reaction with the electrolyte, the Si part is converted into a Si-O phase, and by using the siloxane bond peculiar to silicon oxide, not only is the reaction decomposition of the electrolyte significantly suppressed, but also the Si-O material having a siloxane bond has good Li acceptability, so that a negative electrode active material capable of ensuring high-speed charging has been developed.

[0051] [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, wherein the negative electrode active material particles include a structure of porous carbon, and amorphous low-valence nanosilicon oxide is dispersed inside the structure of the porous carbon. The low-valence nanosilicon oxide includes each state of SiOx: x < 1.0, and at least a part of the surface layer portion of the low-valence nanosilicon oxide exposed on the surface of the structure of the porous carbon has the following general formula (1) Si(R 1 ) l (R 2 ) m (R 3 ) 4-l-m (1) (In the general formula (1), R 1 is an alkyl group having 1 to 20 carbon atoms, R 2 is an alkenyl group having 2 to 20 carbon atoms, and R 3 is an alkynyl group having 2 to 20 carbon atoms. Also, l and m each independently represent an integer of 0 to 4.) It is a negative electrode active material characterized by being coated with a decomposition product and / or polymer of an organosilicon compound represented by

[0052] Such a negative electrode active material has amorphous low-valence nanosilicon oxide dispersed inside the structure of porous carbon. Therefore, due to the presence of the structure of porous carbon, the adverse effect due to the expansion of the internal low-valence nanosilicon oxide can be reduced. Also, general SiO is Si 4+Although it becomes an irreversible component, in the negative electrode active material of the present invention, since it includes each state of SiOx: x < 1.0, an irreversible capacity lower than that of general SiO can be maintained. Further, since the Si - O bond can suppress the decomposition of the electrolytic solution, it becomes possible to reduce the SEI (Solid Electrolyte Interphase) deposited on the surface layer portion. In the present invention, it suffices that amorphous low - valence nanosilicon oxide is dispersed inside the structure of porous carbon, and a part of the nanosilicon oxide may have crystallinity.

[0053] As described later, the negative electrode active material of the present invention can be manufactured as Si - Ox having a siloxane bond in the Si phase in order to suppress the decomposition reaction of the electrolytic solution, which is insufficient in CVD - Si - C generated from general silane gas. The purpose of intentionally creating the Si - O bond is that while the Si - Si bond promotes the decomposition of the electrolytic solution, the Si - O bond results in a milder reaction with the electrolytic solution compared to Si - Si. Further, since the Si - O bond can suppress the decomposition of the electrolytic solution, it becomes possible to reduce the SEI deposited on the surface layer portion of CVD - Si - C. As a result, the battery cycle characteristics are improved. In addition, the grain boundaries of the grains having Si - Si bonds lower the Li diffusivity, while the Si - O bond has good Li diffusivity and improves the high - speed chargeability. Since the main site contributing to the main charge and discharge of the material of the present invention is low - valence nanosilicon oxide, it can be defined as CVD - SiOx - C with respect to CVD - Si - C. Thus, the prepared active material can have high energy density and high - speed chargeability while maintaining the cycle characteristics of the battery.

[0054] Further, in the negative electrode active material of the present invention, at least a part of the surface layer portion of the low - valence nanosilicon oxide exposed on the surface of the structure of porous carbon is coated with a decomposition product and / or polymer of an organosilicon compound. This organosilicon compound is an organosilicon compound represented by the following general formula (1). Si(R 1 ) l (R 2 ) m (R 3 )4-l-m (1) (In general formula (1), R 1 is an alkyl group having 1 to 20 carbon atoms, R 2 is an alkenyl group having 2 to 20 carbon atoms, and R 3 is an alkynyl group having 2 to 20 carbon atoms. Also, l and m each independently represent an integer of 0 to 4.)

[0055] In general formula (1), R 1 is an alkyl group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 4 carbon atoms.)

[0056] R 1 Specific examples of the alkyl group of R include linear alkyl groups such as methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group; branched alkyl groups such as isopropyl group, isobutyl group, sec-butyl group, tert-butyl group, isopentyl group, neopentyl group, isohexyl group, isoheptyl group, isooctyl group, tert-octyl group, isononyl group, isodecyl group, isoundecyl group.)

[0057] Among these, from the viewpoint of ensuring the thermal decomposability of the organosilicon compound, a methyl group, an ethyl group, and an n-propyl group are preferable.)

[0058] In general formula (1), R 2 is an alkenyl group having 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms, more preferably 2 to 5 carbon atoms.)

[0059] R 2Specific examples of the alkenyl group include linear alkenyl groups such as vinyl group, 1-propenyl group, 1-butenyl group, 1-pentenyl group, 1-hexenyl group, 1-heptenyl group, 1-octenyl group, 1-nonenyl group, 1-decenyl group, 1-undecenyl group, 1-dodecenyl group; and branched alkenyl groups such as isopropenyl group, 1-methyl-1-propenyl group, 2-methyl-1-propenyl group, 1-methyl-1-butenyl group, 2-methyl-1-butenyl group, 3-methyl-1-butenyl group, isohexenyl group, isoheptenyl group, isooctenyl group, isononyl group, isodecenyl group, isoundecyl group.

[0060] Among these, from the viewpoint of ensuring the thermal decomposability of the organosilicon compound, vinyl group and 1-propenyl group are preferred.

[0061] In general formula (1), R 3 represents an alkynyl group having 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms, more preferably 2 to 5 carbon atoms.

[0062] R 3 Specific examples of the alkynyl group include linear alkynyl groups such as ethynyl group, 1-propynyl group, 1-butynyl group, 1-n-pentynyl group, 1-n-hexynyl group, 1-n-heptynyl group, 1-n-octynyl group, 1-n-nonynyl group, 1-n-decynyl group, 1-n-undecynyl group, 1-n-dodecynyl group; and branched alkynyl groups such as 3-methyl-1-butynyl group, 3,3-dimethyl-1-butynyl group, 3-methyl-1-pentynyl group, 4-methyl-1-pentynyl group, 3,3-dimethyl-1-pentynyl group, 3,4-methyl-1-pentynyl group, 4,4-dimethyl-1-pentynyl group.

[0063] Among these, from the viewpoint of ensuring the thermal decomposability of the organosilicon compound, ethynyl group, 1-propynyl group, and 1-butynyl group are preferred.

[0064] In general formula (1), l and m each independently represent an integer from 0 to 4. From the viewpoint of ensuring the thermal decomposability of the organosilicon compound, in general formula (1), it is preferable that l represents from 0 to 3 and n represents from 1 to 4.

[0065] Specific examples of the organosilicon compound represented by general formula (1) include tetramethylsilane, trimethylvinylsilane, dimethyldivinylsilane, methyltrivinylsilane, tetravinylsilane, trimethylethynylsilane, diethynyldimethylsilane, methyltriethynylsilane, tetraethynylsilane, ethynyltrivinylsilane, diethynyldivinylsilane, triethynylvinylsilane, ethynyldimethylvinylsilane, trimethyl(1-propenyl)silane, dimethyldi(1-propenyl)silane, methyltri(1-propenyl)silane, tetra(1-propenyl)silane, trimethyl(1-propynyl)silane, dimethyldi(1-propynyl)silane, methyltri(1-propynyl)silane, tetra(1-propynyl)silane, trimethyl(1-butynyl)silane, dimethyldi(1-butynyl)silane, methyltri(1-butynyl)silane, tetra(1-butynyl)silane, and the like.

[0066] By coating the active site of the above nano silicon oxide with the decomposition product and / or polymer of the organosilicon compound, the reactivity between the negative electrode active material and the electrolyte can be reduced, and as a result, the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved.

[0067] The decomposition product and polymer of the organosilicon compound of the present invention identify the original organosilicon compound, which is due to the difficulty in identifying the state of the compound after decomposition and polymerization. The organosilicon compound in the state before decomposition and polymerization can be easily identified by the above formula (1).

[0068] In addition, since tetravalent Si that constitutes SiO becomes an irreversible component, in the negative electrode active material of the present invention, it is preferable that the low-valence nanosilicon oxide is in a substantially composite state of 0 valence, 1 valence, and 2 valence. In particular, it is preferable that this low-valence nanosilicon oxide is substantially dominated by 1 to 2 valence. By making SiOx of 2 valence or less dominant, although the irreversible capacity is larger than that of silicon alone, an irreversible capacity lower than that of general SiO can be maintained.

[0069] Regarding the organosilicon compound that becomes a decomposition product or polymer, which is a coating on the negative electrode active material particles of the negative electrode active material of the present invention, in the general formula (1) above, it is preferable that l is represented by 0 to 3. That is, those having an alkenyl group or an alkynyl group as essential in the organosilicon compound are preferable. Furthermore, it is more preferable that it is represented by l = 0. That is, it is preferable that the organosilicon compound does not have an alkyl group and has one or both of an alkenyl group and an alkynyl group. By coating with a decomposition product and / or polymer of such an organosilicon compound, the reactivity with the electrolytic solution can be suppressed more effectively.

[0070] In addition, in the negative electrode active material particles of the negative electrode active material of the present invention, it is preferable that the decomposition product and / or polymer of the organosilicon compound coated on the surface of the porous carbon structure contains polyethylene or polyacetylene. In this way, by including polyethylene or polyacetylene in the decomposition product and / or polymer of the organosilicon compound, the reactivity with the electrolytic solution can be suppressed more effectively.

[0071] In addition, in the negative electrode active material particles of the negative electrode active material of the present invention, it is preferable that the decomposition product and / or polymer of the organosilicon compound coated on the surface of the porous carbon structure contains silicon. In this way, by including silicon in the decomposition product and / or polymer of the organosilicon compound, the reactivity with the electrolytic solution can be suppressed more effectively.

[0072] Further, in the negative electrode active material particles of the negative electrode active material of the present invention, it is preferable that the thickness of the decomposition product and / or polymer of the organosilicon compound is 10 nm or less. Such a thickness is preferable for improving the cycle characteristics.

[0073] Further, in the negative electrode active material particles of the negative electrode active material of the present invention, it is preferable that the surface of the porous carbon structure is covered in a mesh shape by the decomposition product and / or polymer of the organosilicon compound. Such a coating mode is preferable for improving the cycle characteristics.

[0074] In the negative electrode active material of the present invention, the grain size of Si of zero valence constituting the low-valence nano silicon oxide calculated using the Scherrer equation from the peak measured by X-ray diffraction measurement of the negative electrode active material particles is preferably in the range of 1 nm to 5 nm. Those having such a grain size of zero-valent Si having a substantially amorphous structure are preferable.

[0075] The calculation of the crystallite size by XRD can be performed, for example, under the following conditions. For broad peaks, it can be performed, for example, under the following conditions using the analysis software TOPAS. XRD measurement · Apparatus: D2 PHASER manufactured by Bruker · X-ray source: Cu · Divergence slit: 0.5° · Incident side Soller: 4° · Receiving side Soller: 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”

[0076] The valence of the low-valence nanosilicon oxide can be quantified by NMR (nuclear magnetic resonance) and XPS (X-ray photoelectron spectroscopy).

[0077] When measuring the valence of the low-valence nanosilicon oxide, the NMR measurement can be carried out under the following conditions, for example. 29 Si MAS NMR (magic angle spinning nuclear magnetic resonance) · Apparatus: 700 NMR spectrometer manufactured by Bruker, · Probe: 4 mm HR-MAS rotor 50 μL, · Sample rotation speed: 10 kHz, · Measurement ambient temperature: 25 °C

[0078] The XPS measurement can be carried out under the following conditions, for example. XPS · Apparatus: X-ray photoelectron spectrometer, · X-ray source: Monochromatized Al Kα ray, · X-ray spot diameter: 100 μm, · Ar ion gun sputtering conditions: 0.5 kV 2 mm × 2 mm.

[0079] In addition, in the negative electrode active material of the present invention, it is preferable that the low-valence nanosilicon oxide dispersed in the porous carbon structure increases from the center to the surface layer of the porous carbon structure as x increases. In the present invention, since the low-valence nanosilicon oxide is dispersed in the porous carbon structure, it tends to increase from the center to the surface layer of the porous carbon structure during production (the oxygen composition ratio increases). Since the oxidation ratio of silicon is large on the surface, the decomposition of the electrolyte can be more effectively suppressed, and since the oxidation ratio of silicon is small inside the active material, the battery capacity can be further increased.

[0080] <Negative electrode for non-aqueous electrolyte secondary battery> 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.

[0081] [Configuration of negative electrode] Figure 1 shows a cross-sectional view of a negative electrode including the negative electrode active material of the present invention. As shown in Figure 1, the negative electrode 10 is configured to have 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 or only on one side of the negative electrode current collector 11. Further, in the negative electrode of the non-aqueous electrolyte secondary battery of the present invention, the negative electrode current collector 11 may be absent.

[0082] [Negative electrode current collector] The negative electrode current collector 11 is made of an excellent conductive material and has mechanical strength. Examples of the conductive material that can be used for the negative electrode current collector 11 include copper (Cu) and nickel (Ni). This conductive material is preferably a material that does not form an intermetallic compound with lithium (Li).

[0083] The negative electrode current collector 11 preferably contains carbon (C) and sulfur (S) in addition to the main element. This is to improve the physical strength of the negative electrode current collector. In particular, when there is an active material layer that expands during charging, if the current collector contains the above elements, there is an effect of suppressing electrode deformation including the current collector. The content of the above-mentioned contained elements is not particularly limited, but among them, it is preferably 100 mass ppm or less respectively. This is because a higher deformation suppression effect can be obtained. Due to such a deformation suppression effect, the cycle characteristics can be further improved.

[0084] Also, the surface of the negative electrode current collector 11 is preferably roughened. Desirably, the ten-point average roughness Rz of the surface 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.

[0085] [Negative electrode active material layer] The negative electrode active material layer 12 may contain a plurality of types of negative electrode active materials such as a carbon-based active material in addition to the silicon-based active material particles of the present invention. Further, for battery design, it may also contain other materials such as a thickening agent (also referred to as a "binder" or "adhesive") and a conductive aid.

[0086] [Negative Electrode Active Material and Method for Manufacturing Negative Electrode] Subsequently, 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 same will be described.

[0087] 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, the method including: preparing a porous carbon structure; flowing monosilane gas under heating to the porous carbon structure to deposit silicon inside the porous carbon structure; cooling the material having silicon deposited inside the porous carbon structure to 50°C or lower; introducing oxygen diluted with nitrogen gas into the material having silicon deposited inside the porous carbon structure in a state where the temperature of the material having silicon deposited inside the porous carbon structure is adjusted to maintain 50°C or lower after cooling, to change at least a part of the silicon into a low-valence nanosilicon oxide by an oxidation reaction; and after the oxidation reaction, bringing the low-valence nanosilicon oxide into contact with an organosilicon compound represented by the following general formula (1) Si(R 1 ) l (R 2 ) m (R 3 ) 4-l-m (1) (In the general formula (1), R 1 is an alkyl group having 1 to 20 carbon atoms, R 2 is an alkenyl group having 2 to 20 carbon atoms, and R 3 is an alkynyl group having 2 to 20 carbon atoms. Also, l and m each independently represent an integer of 0 to 4.) at 100 to 1000°C, and manufacturing a negative electrode active material in which amorphous low-valence nanosilicon oxide is dispersed inside the porous carbon structure and at least a part of the surface layer portion of the low-valence nanosilicon oxide exposed on the surface of the porous carbon structure is covered with a decomposition product and / or polymer of the organosilicon compound.

[0088] In the method for manufacturing such a negative electrode active material, as described above, amorphous low-valence nanosilicon oxide is dispersed inside the structure of the porous carbon, and at least a part of the surface layer portion of the low-valence nanosilicon oxide is coated with a decomposition product and / or polymer of an organosilicon compound, so that the negative electrode active material can be easily and efficiently manufactured.

[0089] Referring to Steps S1 to S5 in FIG. 5, each step of the method for manufacturing the negative electrode active material will be described.

[0090] First, a structure of porous carbon is prepared (Step S1). The structure of porous carbon prepared here preferably has carbon-carbon double bonds at least in part. Further, the structure of porous carbon prepared here is dominated by Type I in the IUPAC classification, and its surface area is 1400 m 2 / g or more, and the pore volume is preferably 1 cm 3 / g or more. By setting such classification according to the IUPAC classification, surface area, and pore volume, more silicon can be deposited efficiently in a larger amount. Further, for the IUPAC classification, surface area, and pore volume, the following measurement methods can be used. · Using a Shimadzu TriStar II Plus, measure the specific surface area / pore distribution by the constant volume method based on the gas adsorption method. The conditions are as follows. · Gas used: Nitrogen · Environment: Under liquid nitrogen · Pressure operation range: P / P0 · Adsorption 0 to 0.998 · Desorption 0.998 to 0.10 · Pretreatment Vacuum 200 °C 1 hour

[0091] Next, by flowing monosilane gas under heating to the structure of porous carbon prepared in Step S1, silicon is deposited inside the structure of porous carbon (Step S2).

[0092] Note that after step S1 and before step S2, it is preferable to store the porous carbon structure in a vacuum vessel and perform evacuation. The degree of vacuum can be, for example, up to about -100 kPa, but is not limited thereto. Further, after evacuation, it is preferable to repressurize with nitrogen and heat using an external heater to about 350 to 450 °C with nitrogen flowing. This heating can be performed for 5 minutes to 1 hour. By performing such preheating under evacuation and 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 performed, so that silicon deposition in step S2 can be performed more reliably.

[0093] The silicon deposition in step S2 can be performed, for example, by flowing monosilane gas at about 400 °C to 500 °C. The deposition time can be, for example, 30 minutes to 10 hours.

[0094] Next, the material in which silicon has been deposited inside the porous carbon structure is cooled to 50 °C or lower (step S3). In this step, it is preferable to cool, for example, while flowing nitrogen gas. In this cooling, for example, it can be cooled to room temperature.

[0095] After the above cooling (step S3), next, while adjusting the temperature of the material in which silicon has been deposited inside the porous carbon structure to maintain 50 °C or lower, oxygen diluted with nitrogen gas is introduced into the material in which silicon has been deposited inside the porous carbon structure, whereby at least a part of the silicon is changed to a low-valence nanosilicon oxide (step S4). By this step, an Si-O bond can be formed. Note that the temperature to be maintained here is more preferably 35 °C or lower.

[0096] The dilution of oxygen with nitrogen can be, for example, 5 to 50 times, preferably 10 to 30 times. This dilution ratio can typically be 20 times.

[0097] Also, in this step S4, when the internal temperature rises and exceeds 50°C, a part of silicon dioxide is generated, which is not preferable as the negative electrode active material. Therefore, in this step S4, it is necessary to adjust so that the temperature of the material is maintained at 50°C or lower. Further, the material temperature in step S4 is preferably, for example, 25°C or higher, more preferably 30°C or higher, in order to facilitate the progress of the oxidation reaction and the formation of Si-O bonds.

[0098] The oxidation time (flow time of oxygen diluted with nitrogen gas) in this step S4 can be, for example, 30 minutes or more and 5 hours or less, preferably 1 hour or more and 3 hours or less. Further, after the flow of oxygen diluted with nitrogen gas, it is also possible to switch to the flow of nitrogen gas and further cool. The flow of only nitrogen gas can be, for example, 30 minutes or more and 2 hours or less.

[0099] In the oxidation by the flow of oxygen diluted with the above nitrogen gas, it is preferable to adjust so that the low-valence nanosilicon oxide dispersed in the porous carbon structure increases from the center to the surface layer of the porous carbon structure as x increases. In the porous carbon structure, the pore structure tends to have a larger cross-sectional area on the particle surface and a smaller cross-sectional area toward the particle interior. Therefore, by performing oxidation by the flow of oxygen diluted with nitrogen gas as in the present invention, it easily increases from the center to the surface layer of the porous carbon structure so that x increases.

[0100] Next, after performing the oxidation reaction in step S4, the low-valence nanosilicon oxide and an organosilicon compound represented by the following general formula (1) are brought into contact at 100 to 1000°C (step S5). Si(R 1 ) l (R 2 ) m (R 3 ) 4-l-m (1) (In the general formula (1), R 1 is an alkyl group having 1 to 20 carbon atoms, and R 2 is an alkenyl group having 2 to 20 carbon atoms, and R3 is an alkynyl group having 2 to 20 carbon atoms. Also, l and m each independently represent an integer of 0 to 4.)

[0101] The contact in this step S5 can be carried out, for example, by mixing the organosilicon compound represented by the general formula (1) and the porous carbon structure in which the low-valence nano silicon oxide is dispersed in the same storage container as in step S4, and then heating. However, it is not limited to this as long as the contact between the two is carried out and the coating by the decomposition product and / or polymer of the organosilicon compound is carried out.)

[0102] Thereafter, the material is taken out from the storage container. By the above steps, amorphous low-valence nano silicon oxide is dispersed inside the porous carbon structure, and at least a part of the surface layer of the low-valence nano silicon oxide exposed on the surface of the porous carbon structure is coated with the decomposition product and / or polymer of the organosilicon compound, and a negative electrode active material can be produced.)

[0103] <Lithium Ion Secondary 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 described.)

[0104] [Configuration of Laminate Film Type Secondary Battery] The laminate film type lithium ion secondary battery 30 shown in FIG. 2 mainly has a wound electrode body 31 housed inside a sheet-like exterior member 35. This wound electrode body 31 has a separator between the positive electrode and the negative electrode and is wound. There is also a case where a separator is provided between the positive electrode and the negative electrode and a laminate is housed. 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 peripheral portion of the electrode body is protected by a protective tape.)

[0105] The positive and negative electrode leads 32 and 33 are led out in one direction from the inside to the outside of the exterior member 35, for example. The positive electrode lead 32 is formed of a conductive material such as aluminum, for example, and the negative electrode lead 33 is formed of a conductive material such as nickel or copper, for example.

[0106] The exterior member 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 peripheral edges of the fusion layers of the two films are fused or bonded together with an adhesive or the like so that the fusion layer faces the electrode body 31. The fusion part is a film such as polyethylene or polypropylene, for example, and the metal part is aluminum foil or the like. The protective layer is nylon or the like, for example.

[0107] A close-contact film 34 is inserted between the exterior member 35 and the positive and negative electrode leads to prevent the intrusion of outside air. This material is, for example, polyethylene, polypropylene, or a polyolefin resin.

[0108] The positive electrode has a positive electrode active material layer on both sides or one side of the positive electrode current collector, for example, in the same manner as the negative electrode 10 in FIG. 1.

[0109] The positive electrode current collector is formed of a conductive material such as aluminum, for example.

[0110] The positive electrode active material layer contains any one or two or more kinds of positive electrode materials capable of occluding and releasing lithium ions, and may contain other materials such as a positive electrode binder, a positive electrode conductive aid, and a dispersant according to the design. In this case, the details regarding the positive electrode binder and the positive electrode conductive aid are the same as those of the negative electrode binder and the negative electrode conductive aid already described, for example.

[0111] As the positive electrode material, a lithium-containing compound is desirable. Examples of this lithium-containing compound include a composite oxide composed of lithium and a transition metal element, or a phosphate compound having lithium and a transition metal element. Among these positive electrode materials, a compound having at least one of nickel, iron, manganese, and cobalt is preferable. As these chemical formulas, for example, Lix M1O2 or Li y It is represented by M2PO4. In the formula, M1 and M2 represent at least one or more transition metal elements. The values of x and y represent different values depending on the charge and discharge state of the battery, but generally are represented by 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

[0112] 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), and lithium nickel cobalt composite oxide. Examples of the lithium nickel cobalt composite oxide include, for example, lithium nickel cobalt aluminum composite oxide (NCA) and lithium nickel cobalt manganese composite oxide (NCM).

[0113] 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)), etc. By using these positive electrode materials, a high battery capacity can be obtained and excellent cycle characteristics can also be obtained.

[0114] [Negative electrode] The negative electrode has the same configuration as the negative electrode 10 for the lithium ion secondary battery shown in FIG. 1 described above. For example, the negative electrode has negative electrode active material layers on both sides of the current collector. It is preferable that the negative electrode charging capacity is larger than the electric capacity (charging capacity as a battery) obtained from the positive electrode active material agent. Thereby, precipitation of lithium metal on the negative electrode can be suppressed.

[0115] The positive electrode active material layer is provided on a part of both sides of the positive electrode current collector, and similarly, the negative electrode active material layer is also provided on a part of both sides of the negative electrode current collector. In this case, for example, the negative electrode active material layer provided on the negative electrode current collector is provided with a region where there is no opposing positive electrode active material layer. This is for performing a stable battery design.

[0116] In a region where the above-mentioned negative electrode active material layer and positive electrode active material layer do not face each other, it is hardly affected by charge and discharge. Therefore, the state of the negative electrode active material layer is maintained as it is immediately after formation, and thus the composition of the negative electrode active material and the like can be accurately investigated with good reproducibility without depending on the presence or absence of charge and discharge.

[0117] [Separator] The separator separates the positive electrode and the negative electrode, allows lithium ions to pass through while preventing current short-circuit due to contact between the two electrodes. This separator is formed of, for example, a porous membrane made of a synthetic resin or a ceramic, and may have a laminated structure in which two or more porous membranes are laminated. Examples of the synthetic resin include polytetrafluoroethylene, polypropylene, polyethylene, and the like.

[0118] [Electrolyte] 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.

[0119] As the solvent, for example, a non-aqueous solvent can be used. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, or tetrahydrofuran. Among these, it is desirable to use at least one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and 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 and ion mobility of the electrolyte salt are improved.

[0120] When using an alloy-based negative electrode, it is particularly desirable that the solvent contains at least one of a halogenated chain carbonate ester or a halogenated cyclic carbonate ester. Thereby, during charge and discharge, particularly during charging, a stable film is formed on the surface of the negative electrode active material. Here, the halogenated chain carbonate ester is a chain carbonate ester having a halogen as a constituent element (at least one hydrogen is substituted by a halogen). Further, the halogenated cyclic carbonate ester is a cyclic carbonate ester having a halogen as a constituent element (that is, at least one hydrogen is substituted by a halogen).

[0121] The type of halogen is not particularly limited, but fluorine is preferred. This is because it forms a better-quality film than other halogens. Also, the larger the number of halogens, the more desirable. This is because the resulting film is more stable and the decomposition reaction of the electrolyte is reduced.

[0122] Examples of the halogenated chain carbonate ester include fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, etc. Examples of the halogenated cyclic carbonate ester include 4-fluoro-1,3-dioxolan-2-one, 4,5-difluoro-1,3-dioxolan-2-one, etc.

[0123] As a solvent additive, it is preferable to contain an unsaturated carbon-bonded cyclic carbonate ester. This is because a stable film is formed on the surface of the negative electrode during charge and discharge, and the decomposition reaction of the electrolyte can be suppressed. Examples of the unsaturated carbon-bonded cyclic carbonate ester include vinylene carbonate or vinyl ethylene carbonate, etc.

[0124] Also, as a solvent additive, it is preferable to contain sultone (cyclic sulfonic acid ester). This is because the chemical stability of the battery is improved. Examples of sultone include propane sultone, propene sultone.

[0125] Furthermore, the solvent preferably contains an acid anhydride, because the chemical stability of the electrolyte solution is improved. Examples of the acid anhydride include propane disulfonic anhydride.

[0126] The electrolyte salt can contain, for example, any one or more of light metal salts such as lithium salts. Examples of the lithium salt include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and the like.

[0127] The content of the electrolyte salt is preferably 0.5 mol / kg or more and 2.5 mol / kg or less with respect to the solvent, because high ionic conductivity can be obtained.

Examples

[0128] Hereinafter, the present invention will be described more specifically by showing examples and comparative examples of the present invention, but the present invention is not limited to these examples.

[0129] (Example 1) A negative electrode active material was produced by the following procedure, and further, a laminate film type lithium ion secondary battery 30 shown in FIG. 2 was produced.

[0130] A negative electrode active material was produced as follows. First, the surface area (BET specific surface area) was 2483 m 2 / g, and the pore volume was 1.35 cm 3 / g, a porous carbon material (porous carbon structure) with a particle size (D50) = 11 μm and an IUPAC classification of type I was prepared. This porous carbon material was stored in a vacuum vessel and evacuated to -90 kPa. Next, it was repressurized with nitrogen and heated to 400 °C using an external heater while nitrogen was flowing. After 30 minutes of heating, the temperature was raised to 415 °C, monosilane gas was flowed, and deposition was carried out for 4 hours. Then, it was cooled to room temperature while flowing nitrogen gas. After the temperature was lowered to 25 °C, oxygen diluted 20-fold with nitrogen was introduced, and the material temperature was adjusted to be 50 °C or lower to form Si-O bonds. Next, nitrogen containing oxygen was flowed for 2 hours, and when the material temperature reached 30 °C or lower, it was switched to nitrogen gas and flowed for 60 minutes. Subsequently, 1.0 [mass%] of trimethylvinylsilane (TMVS) was added to the porous carbon material in the storage container and heated at 400 °C for 2 hours. After cooling to room temperature, the material was taken out from the storage container and used as a negative electrode active material.

[0131] [Fabrication of negative electrode] The negative electrode active material (active material containing CVD-SiOx-C) prepared as described above, graphite, conductive assistant 1 (carbon nanotube, CNT), conductive assistant 2 (carbon fine particles with a median diameter of about 50 nm), sodium polyacrylate, and carboxymethyl cellulose (hereinafter referred to as CMC) were mixed at a dry mass ratio of 9.3:83.7:1:1:4:1, and then diluted with pure water to obtain a negative electrode binder slurry.

[0132] Also, as the negative electrode current collector, an electrolytic copper foil with a thickness of 15 μm was used. This electrolytic copper foil contained carbon and sulfur at concentrations of 70 mass ppm, respectively. Finally, the negative electrode binder slurry was applied to the negative electrode current collector and dried in a vacuum atmosphere at 100 °C for 1 hour. The deposition amount (also referred to as areal density) of the negative electrode active material layer per unit area on one side of the dried negative electrode was 7.0 mg / cm 2 was.

[0133] [Assembly of coin cell for testing] Next, after mixing the solvents ethylene carbonate (EC) and dimethyl carbonate (DMC), the electrolyte salt (lithium hexafluorophosphate: LiPF6) was dissolved to prepare an electrolyte solution. In this case, the composition of the solvent was EC:DMC = 30:70 by volume ratio, and the content of the electrolyte salt was 1 mol / kg with respect 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.

[0134] Next, a coin cell was assembled as follows. First, a Li foil with a thickness of 1 mm was punched out to a diameter of 16 mm and attached to an aluminum clad.

[0135] Next, the previously obtained negative electrode was punched out to a diameter of 15 mm, and this was placed facing the Li foil attached to the aluminum clad through a separator. After injecting the electrolyte solution, a 2032 coin cell was fabricated.

[0136] [Measurement of Initial Efficiency] The initial efficiency was measured under the following conditions. First, for the fabricated coin cell for initial efficiency test, the charge rate was made equivalent to 0.03C, and charging (initial charge) was performed in the CCCV mode. The CV was 0V and the termination current was 0.04 mA. Next, the discharge rate was similarly set to 0.03C, and CC discharge (initial discharge) was performed with the discharge termination voltage set to 1.2V.

[0137] When examining the initial charge-discharge characteristics, the initial efficiency (sometimes also referred to as the initial efficiency below) was calculated. The initial efficiency was calculated from the formula Initial efficiency (%) = (Initial discharge capacity / Initial charge capacity) × 100.

[0138] [Manufacture and Battery Evaluation of Lithium-Ion Secondary Battery] Based on the obtained initial data, the positive electrode was designed so that the utilization rate of the negative electrode would be 95%. The utilization rate was calculated based on the following formula from the capacities of the positive and negative electrodes obtained with the counter electrode Li. Utilization rate = (Positive electrode capacity - Negative electrode loss) / (Negative electrode capacity - Negative electrode loss) × 100 Based on this design, lithium-ion secondary batteries (lithium-ion secondary batteries as shown in Fig. 2) of each of the examples and comparative examples were manufactured. Battery evaluations were performed on the lithium-ion secondary batteries of each of the examples and comparative examples.

[0139] Regarding the cycle characteristics, they were examined as follows. First, for battery stabilization, charge and discharge were performed at 0.2C for 2 cycles in an atmosphere of 25°C, 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. Charge and discharge were performed at a charge of 0.7C and a discharge of 0.5C. The charge voltage was 4.3V, the discharge cut-off voltage was 2.5V, and the charge cut-off rate was 0.07C.

[0140] The thickness of the decomposition product and / or polymer was examined by observing the structure of the porous carbon in the negative electrode active material particles with TEM.

[0141] The film shape of the decomposition product and / or polymer was examined by observing the structure of the porous carbon in the negative electrode active material particles with SEM-EDX.

[0142] The results of each measurement are shown in Table 1. In Table 1, Comparative Examples 1 and 2 and Examples 2 to 12, which will be described later, are also shown together.

[0143]

Table 1

[0144] (Comparative Example 1) The negative electrode active material was produced in the same manner as in Example 1, except that the steps of adding 1.0 [mass%] of trimethylvinylsilane (TMVS) to the porous carbon material and heating at 400°C for 2 hours were not performed. The obtained negative electrode active material was evaluated in the same manner as in Example 1.

[0145] The negative electrode active material of Comparative Example 1 had poor cycle characteristics because the low-valence nanosilicon oxide exposed on the surface of the porous carbon structure was not coated with the decomposition product and / or polymer of the organosilicon compound.

[0146] (Comparative Example 2) A porous carbon structure similar to that of Example 1 was prepared. Thereafter, under the same conditions as in Example 1, using monosilane gas, amorphous silicon was formed at 415 °C from the surface layer of the porous carbon structure particles to a position close to the central part. In this state, since Si-H bonds are included, in order to form Si-Si, the temperature was raised to 435 °C to stabilize Si-Si. Subsequently, 1.0 [mass%] of trimethylvinylsilane (TMVS) was added to the porous carbon material in the storage container, and it was heated at 400 °C for 2 hours. After cooling to room temperature, it was cooled to normal temperature, and the sample was taken out with the atmosphere open. By using this method, (different from the present invention) a material without a low-valence silicon oxide compound can be prototyped. The obtained negative electrode active material was evaluated in the same manner as in Example 1.

[0147] Since the negative electrode active material of Comparative Example 2 has no low-valence silicon oxide compound, the capacity and initial Coulomb efficiency are high, but the reactivity with the electrolyte is high, and the battery cycle characteristics deteriorate.

[0148] (Examples 2 to 4) The negative electrode active material was produced in the same manner as in Example 1, except that the amount of trimethylvinylsilane (TMVS) used was changed as shown in Table 1 above. The obtained negative electrode active material was evaluated in the same manner as in Example 1.

[0149] (Example 5) The negative electrode active material was produced in the same manner as in Example 1, except that trimethylvinylsilane (TMVS) was changed to tetravinylsilane (TVSI). The obtained negative electrode active material was evaluated in the same manner as in Example 1.

[0150] (Example 6) The negative electrode active material was produced in the same manner as in Example 1, except that trimethylvinylsilane (TMVS) was changed to triethynylvinylsilane (TEVS). The obtained negative electrode active material was evaluated in the same manner as in Example 1.

[0151] (Example 7) The negative electrode active material was produced in the same manner as in Example 1, except that trimethylvinylsilane (TMVS) was changed to tetramethylsilane (TMSI). The obtained negative electrode active material was evaluated in the same manner as in Example 1.

[0152] In the negative electrode active materials of Examples 1 to 6, at least a part of the surface layer portion of the low-valence number nanosilicon oxide exposed on the surface of the porous carbon structure is coated with a decomposition product and / or polymer of an organosilicon compound containing polyethylene or polyacetylene, and the reactivity with the electrolytic solution is suppressed. Therefore, the cycle characteristics of Examples 1 to 6 are superior to those of Comparative Example 1.

[0153] In the negative electrode active materials of Examples 1 to 7, at least a part of the surface layer portion of the low-valence number nanosilicon oxide exposed on the surface of the porous carbon structure is coated with a decomposition product and / or polymer of an organosilicon compound containing silicon, and the reactivity with the electrolytic solution is suppressed. Therefore, the cycle characteristics of Examples 1 to 7 are superior to those of Comparative Example 1.

[0154] (Example 8) The negative electrode active material was produced in the same manner as in Example 1, except that the amount of trimethylvinylsilane (TMVS) used was changed as shown in Table 1 above. The obtained negative electrode active material was evaluated in the same manner as in Example 1.

[0155] The cycle characteristics of Example 8 are improved compared to Comparative Example 1. From this result, it can be seen that even when the thickness of the decomposition product and / or polymer exceeds 10 nm, the cycle characteristics are improved. On the other hand, the cycle characteristics of Example 8 are worse than those of Examples 1 to 4. From this result, it is considered desirable that the thickness of the decomposition product and / or polymer is 10 nm or less.

[0156] (Example 9) The negative electrode active material was produced in the same manner as in Example 1, except that 1.0 [mass%] of trimethylvinylsilane (TMVS) was added to the porous carbon material in a storage container and heated at 600 °C for 2 hours. The obtained negative electrode active material was evaluated in the same manner as in Example 1.

[0157] The cycle characteristics of Example 9 are improved compared to Comparative Example 1. From this result, it can be seen that even when the surface of the porous carbon structure is coated in an island shape with the decomposition products and / or polymers of the silicon compound, the cycle characteristics are improved. On the other hand, the cycle characteristics of Example 9 are worse than those of Example 1. From this result, it is considered desirable that the surface of the porous carbon structure be coated in a mesh shape with the decomposition products and / or polymers of the silicon compound.

[0158] (Example 10) For the same porous carbon structure as in Example 1, the conditions were changed as follows to produce a negative electrode active material. First, the temperature was raised to 415 °C, monosilane gas was passed, and deposition was carried out for 4 hours. Then, the temperature was raised to grow the grain size of Si 0+ . After that, it was cooled to room temperature while flowing nitrogen gas. After the temperature was lowered to 25 °C, oxygen diluted 20 times with nitrogen was introduced, and the material temperature was adjusted to 50 °C or lower to form Si-O bonds. Next, nitrogen containing oxygen was flowed for 2 hours, and when the material temperature reached 30 °C or lower, it was switched to nitrogen gas and flowed for 60 minutes. Subsequently, 1.0 [mass%] of trimethylvinylsilane (TMVS) was added to the porous carbon material in the storage container and heated at 400 °C for 2 hours. After cooling to room temperature, the material was taken out from the storage container to obtain a negative electrode active material. The obtained negative electrode active material was evaluated in the same manner as in Example 1.

[0159] From the results of Example 10, the closer to an amorphous structure, the more the cycle characteristics are improved.

[0160] (Examples 11, 12) The negative electrode active material was produced in the same manner as in Example 1, except that the porous carbon structure prepared first was changed as shown in Table 1 above. The obtained negative electrode active material was evaluated in the same manner as in Example 1.

[0161] From the results of Examples 11 and 12, the pore volume is 1 cm 31400 m² / g or more BET specific surface area 2 1400 m² / g or more, and the IUPAC classification is preferably type I

[0162] Fig. 3 shows the change in the depth direction measurement of the O1s region in the XPS measurement of the negative electrode active material in Example 1. As can be seen from Fig. 3, the O1s peak becomes smaller in the depth direction from the surface, and it can be seen that the oxygen concentration decreases from the surface toward the deep layer side

[0163] Fig. 4 shows the X-ray diffraction spectra of Examples 1, 2, 10, and 11. Peaks were observed in the vicinity of 2θ = 28° for all of these, and the crystallite size of silicon was calculated from this peak. The same applies to other examples and comparative examples

[0164] This specification includes the following aspects [1]: A negative electrode active material having negative electrode active material particles The negative electrode active material particles include a structure of porous carbon Amorphous low-valence nanosilicon oxide is dispersed inside the structure of the porous carbon The low-valence nanosilicon oxide includes each state where SiOx: x < 1.0 At least a part of the surface layer portion of the low-valence nanosilicon oxide exposed on the surface of the structure of the porous carbon is represented by the following general formula (1) Si(R 1 ) l (R 2 ) m (R 3 ) 4-l-m (1) (In general formula (1), R 1 is an alkyl group having 1 to 20 carbon atoms, R 2 is an alkenyl group having 2 to 20 carbon atoms, and R 3 is an alkynyl group having 2 to 20 carbon atoms. Also, l and m each independently represent an integer of 0 to 4.) The negative electrode active material is characterized in that it is coated with a decomposition product and / or polymer of an organosilicon compound represented by the formula [2]: The negative electrode active material according to the above [1], wherein the organosilicon compound is represented by l = 0 to 3 in the general formula (1). [3]: The negative electrode active material according to the above [2], wherein the organosilicon compound is represented by l = 0 in the general formula (1). [4]: The negative electrode active material according to any one of the above [1] to [3], wherein the decomposition product and / or polymer of the organosilicon compound coated on the surface of the porous carbon structure contains polyethylene or polyacetylene. [5]: The negative electrode active material according to any one of the above [1] to [4], wherein the decomposition product and / or polymer of the organosilicon compound coated on the surface of the porous carbon structure contains silicon. [6]: The negative electrode active material according to any one of the above [1] to [5], wherein the thickness of the decomposition product and / or polymer of the organosilicon compound is 10 nm or less. [7]: The negative electrode active material according to any one of the above [1] to [6], wherein the surface of the porous carbon structure is coated in a mesh shape by the decomposition product and / or polymer of the organosilicon compound. [8]: The negative electrode active material according to any one of the above [1] to [7], wherein the low-valence nanosilicon oxide is substantially in a composite state of 0 valence, 1 valence, and 2 valence. [9]: The negative electrode active material according to any one of the above [1] to [8], wherein the grain size of 0-valent Si constituting the low-valence nanosilicon oxide, calculated using Scherrer's formula from the peaks measured by X-ray diffraction measurement of the negative electrode active material particles, is in the range of 1 nm to 5 nm.

[10] : The porous carbon structure is predominantly of type I in the IUPAC classification, and its surface area is 1400 m 2 / g or more, and the pore volume is 1 cm 2 / g or more. The negative electrode active material according to any one of the above [1] to [9].

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

[10] , wherein the low-valence nanosilicon oxide dispersed in the porous carbon structure increases from the center to the surface layer of the porous carbon structure as x increases.

[12] : A method for producing a negative electrode active material having negative electrode active material particles, comprising: preparing a porous carbon structure; flowing monosilane gas over the porous carbon structure under heating to deposit silicon inside the porous carbon structure; cooling the material having silicon deposited inside the porous carbon structure to 50°C or lower; after cooling, introducing oxygen diluted with nitrogen gas into the material having silicon deposited inside the porous carbon structure while adjusting to maintain the temperature of the material having silicon deposited inside the porous carbon structure at 50°C or lower, to change at least a part of the silicon into a low-valence nanosilicon oxide by an oxidation reaction; after the oxidation reaction, contacting the low-valence nanosilicon oxide with an organosilicon compound represented by the following general formula (1) Si(R 1 ) l (R 2 ) m (R 3 ) 4-l-m (1) (In general formula (1), R 1 is an alkyl group having 1 to 20 carbon atoms, R 2 is an alkenyl group having 2 to 20 carbon atoms, and R 3 is an alkynyl group having 2 to 20 carbon atoms. Also, l and m each independently represent an integer of 0 to 4.) at 100 to 1000°C; and A method for producing a negative electrode active material, characterized in that an amorphous low-valence nanosilicon oxide is dispersed inside the porous carbon structure, and at least a part of the surface layer portion of the low-valence nanosilicon oxide exposed on the surface of the porous carbon structure is coated with a decomposition product and / or polymer of the organosilicon compound.

[0165] Note that the present invention is not limited to the above-described embodiments. The above-described embodiments are examples, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same operational effects is included in the technical scope of the present invention.

Explanation of Reference Numerals

[0166] 10... negative electrode, 11... negative electrode current collector, 12... negative electrode active material layer 30... lithium ion secondary battery (laminate film type), 31... electrode body 32... positive electrode lead (positive electrode aluminum lead) 33... negative electrode lead (negative electrode nickel lead) 34... adhesion film, 35... exterior member

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 is dispersed inside the porous carbon structure, The low valence nano silicon oxide includes each state of SiOx: x < 1.0, At least a part of the surface layer of the low-valence nanosilicon oxide exposed on the surface of the porous carbon structure is represented by the following general formula (1): Si(R １ ) ｌ (R ２ ) ｍ (R ３ ) ４－ｌ－ｍ (1) (In general formula (1), R １ is an alkyl group having 1 to 20 carbon atoms; R ２ is an alkenyl group having 2 to 20 carbon atoms, R ３ is an alkynyl group having 2 to 20 carbon atoms. Furthermore, l and m each independently represent an integer of 0 to 4.

1. A negative electrode active material comprising an organosilicon compound represented by the formula:

2. 2. The negative electrode active material according to claim 1, wherein the organosilicon compound is one represented by general formula (1) in which l=0 to 3.

3. 3. The negative electrode active material according to claim 2, wherein the organosilicon compound is one represented by the general formula (1) where l=0.

4. 2. The negative electrode active material according to claim 1, wherein the decomposition product and / or polymerization product of the organosilicon compound coating the surface of the porous carbon structure contains polyethylene or polyacetylene.

5. 2. The negative electrode active material according to claim 1, wherein the decomposition product and / or the polymer product of the organosilicon compound that coats the surface of the porous carbon structure contains silicon.

6. 2. The negative electrode active material according to claim 1, wherein the decomposition product and / or the polymer product of the organosilicon compound has a thickness of 10 nm or less.

7. 2. The negative electrode active material according to claim 1, wherein a surface of the porous carbon structure is covered in a mesh-like manner with a decomposition product and / or a polymer product of the organosilicon compound.

8. The negative electrode active material according to claim 1 , wherein the low valence nanosilicon oxide is substantially in a composite state of zero valence, monovalence and divalence.

9. The grain size of zero-valent Si constituting the low-valent nanosilicon oxide calculated using the Scherrer formula from the peak measured by X-ray diffraction measurement of the negative electrode active material particles is in the range of 1 nm to 5 nm. The negative electrode active material according to claim 1.

10. The porous carbon structure is predominantly Type I in the IUPAC classification and has a surface area of ​​1400 m ２ / g or more, pore volume is 1 cm ２ 2. The negative electrode active material according to claim 1, wherein the molecular weight of the negative electrode active material is 1 / g or more.

11. The negative electrode active material according to claim 1, characterized in that the low valence nanosilicon oxide dispersed in the porous carbon structure has x increasing from the center of the porous carbon structure to the surface layer.

12. A method for producing a negative electrode active material having negative electrode active material particles, comprising: Providing a porous carbon structure; depositing silicon inside the porous carbon structure by flowing monosilane gas through the porous carbon structure under heating; Cooling the material with silicon deposited inside the porous carbon structure to below 50° C.; After the cooling, while adjusting the temperature of the material in which silicon is deposited inside the porous carbon structure to be kept at 50° C. or less, oxygen diluted with nitrogen gas is introduced into the material in which silicon is deposited inside the porous carbon structure, thereby converting at least a part of the silicon into low-valence nanosilicon oxide by an oxidation reaction; After the oxidation reaction, the low valence nanosilicon oxide and the following general formula (1) Si(R １ ) ｌ (R ２ ) ｍ (R ３ ) ４－ｌ－ｍ (1) (In general formula (1), R １ is an alkyl group having 1 to 20 carbon atoms; R ２ is an alkenyl group having 2 to 20 carbon atoms, R ３ is an alkynyl group having 2 to 20 carbon atoms. Furthermore, l and m each independently represent an integer of 0 to 4. at 100 to 1000° C.; a porous carbon structure having a porous carbon structure on which an amorphous low-valence nano-silicon oxide is dispersed, and at least a portion of the surface layer of the low-valence nano-silicon oxide exposed on the surface of the porous carbon structure is covered with a decomposition product and / or a polymerization product of an organosilicon compound.

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