Negative electrode active material and method for manufacturing the same

Abstract

To provide a negative electrode active material which can increase the capacity while maintaining the battery characteristic.SOLUTION: The present invention relates to a negative electrode active material having negative electrode active material particles, the negative electrode active material particles including a structure of porous carbon. Amorphous low-valence nano-silicon oxides are dispersed in the inside of a structure of the porous carbon. When the negative electrode active material particles are measured by solid body 29Si-CP / MAS-NMR, the largest value exists in the range of -81 to -95 ppm.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

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

[0003] Among them, lithium-ion secondary batteries are highly expected because they can be easily miniaturized and have a high capacity, and can obtain a higher energy density than lead batteries and nickel-cadmium batteries.

[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 charge and discharge reactions.

[0005] As this negative electrode active material, carbon-based active materials are widely used. On the other hand, further improvement of battery capacity is required from recent market demands. In order to improve the battery capacity, 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. Development of silicon materials as negative electrode active materials has been 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 with silicon materials as the main 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, in order to improve the first charge-discharge efficiency, a nano-composite containing an Si phase, SiO 2 , M y O metal oxide is used (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 a high temperature (see, for example, Patent Document 6). Further, in order to improve cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is set to 0.1 to 1.2, and the active material is controlled within a range where the difference between the maximum value and the minimum value of the molar ratio near the interface between the active material and the current collector is 0.4 or less (see, for example, Patent Document 7). Further, in order to improve the battery load characteristics, a metal oxide containing lithium is used (see, for example, Patent Document 8). Further, in order to improve cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface layer of the silicon material (see, for example, Patent Document 9).

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

[0011] Further, 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 material of Si 0+ ~Si 4+ and has various oxidation states (Non-Patent Document 2). Further, Kapaklis proposed a disproportionation structure in which silicon oxide is divided into Si and SiO 2 by applying a heat load to the silicon oxide (Non-Patent Document 3).

[0012] Miyachi et al. have reported that the Si and SiO oxides that contribute to charging and discharging among the silicon oxides with disproportionated structures are 2 (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+SiO 2 ) + 6.85Li + + 6.85e - → 1.4Li 3.75 Si + 0.4Li 4 SiO 4 + 0.2SiO 2 In the reaction formula, silicon oxide consists of Si and SiO 2 reacts with Li to produce Li silicide, Li silicate, and some unreacted SiO 2 Divided into two.

[0013] The Li silicate formed here is irreversible, and it is generally said to be a stable substance that does not release Li once it is formed. The capacity per mass calculated from this reaction formula is close to the experimental value, and is recognized as the reaction mechanism of silicon oxide. Kim et al. have reported that the irreversible component Li silicate that accompanies the charge and discharge of silicon oxide is Li 4 SiO 4 As, 7 Li-MAS-NMR and 29 The identification was carried out using Si-MAS-NMR (Non-Patent Document 6).

[0014] This irreversible capacity is the weakest point of silicon oxide, and there is a need to improve it. Kim et al. have used a Li pre-doping method to form Li silicate in advance, significantly improving the initial efficiency of the battery and producing a negative electrode that can withstand practical use (Non-Patent Document 7). They also proposed a method of treating the powder rather than a method of doping the electrode with Li, and have achieved an improvement in the irreversible capacity (Patent Document 13).

[0015] On the one hand, the Li metal used for Li doping has extremely volatile upper and lower price limits according to market conditions, and there are many problems when considered as industrialization. Therefore, by using silane gas in porous carbon to generate nanosilicon inside, CVD-Si-C 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 Document

[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 promoted to have higher performance and more functions, and the lithium-ion secondary battery, which is their main power source, is required to increase its battery capacity. As one method to solve this problem, the development of a lithium-ion secondary battery composed of a negative electrode using a silicon material as the main material is desired.

[0019] In addition, lithium-ion secondary batteries using silicon materials are desired to have initial charge-discharge characteristics and cycle characteristics that are almost equivalent to those of lithium-ion secondary batteries using carbon-based active materials. Therefore, by using silicon oxide modified by the insertion and partial desorption of Li as the 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 generate 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 this silicon oxide with Li, 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 when considering the higher performance (such as 5G) of small electronic devices and the increased driving range of electric vehicles.

[0020] Therefore, CVD-Si-C with a small irreversible capacity has been developed, but it has been found that the high-rate chargeability and battery cycle characteristics are insufficient due to the reaction between Si and the electrolyte solution.

[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 structure of porous carbon, and an amorphous low-valence nano silicon oxide is dispersed inside the structure of the porous carbon, and the negative electrode active material particles are solid 29 A negative electrode active material is provided, which has a maximum value in the range of -81 to -95 ppm when measured by Si-CP / MAS-NMR.

[0023] Since the negative electrode active material of the present invention has an amorphous low-valence nano silicon oxide dispersed inside the structure of the porous carbon, the adverse effect due to the expansion of the internal low-valence nano silicon oxide can be reduced by the presence of the structure of the porous carbon. Also, solid 29 Negative electrode active material particles having a maximum value in the range of -81 to -95 ppm when measured by Si-CP / MAS-NMR are negative electrode active material particles sufficiently containing an SiOSi structure, so that an irreversible capacity lower than that of general SiO can be maintained. In addition, 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.

[0024] In this case, it is preferable that the negative electrode active material particles have an SiOSi structure in which oxygen is bonded to Si radicals.

[0025] In this way, by having a SiOSi structure in which oxygen is bonded to a Si radical, decomposition of the electrolyte can be effectively suppressed.

[0026] The low valence nano silicon oxide is preferably substantially in a complex state of 0 valence, 1 valence and 2 valences. In this case, it is preferable that the low valence nano silicon oxide is substantially predominantly in a valence of 1 to 2.

[0027] In this way, the low valence nano silicon oxide is substantially in a composite state of zero valence, monovalence and divalence, and further, the mono- to di-valence is substantially predominant, so that a lower irreversible capacity can be achieved.

[0028] In addition, the low valence nano silicon oxide includes each state of SiOx:x<1.0, and the low valence nano silicon oxide preferably has an average particle size of 35 nm or less as determined by image processing of a cross-sectional TEM image.

[0029] General SiO is Si 4+ is an irreversible component, but by including each state of SiOx:x<1.0 in this way, it is possible to maintain a lower irreversible capacity than general SiO. In addition, since the particle size of the low-valence nano silicon oxide (particle size obtained by image processing of the cross-sectional TEM image of the low-valence nano silicon oxide) is an average of 35 nm or less, it is easy to assume that the Si-O bond is appropriately formed.

[0030] Furthermore, the low valence nano silicon oxide dispersed in the porous carbon structure may have x increasing from the center to the surface layer of the porous carbon structure.

[0031] Thus, 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.

[0032] The low-valence nanosilicon oxide dispersed in the porous carbon structure covers the surface layer of the porous carbon structure, and the film thickness thereof can be 5 nm or less.

[0033] Thus, in the negative electrode active material of the present invention, the surface layer of the porous carbon structure can also be covered with a low-valence nanosilicon oxide. In that case, if the film thickness is 5 nm or less, the adverse effect of surface Si can be reduced.

[0034] Moreover, the ratio of the porous carbon structure in the entire negative electrode active material particles is preferably 45% by mass or more and 64% by mass or less.

[0035] With such a ratio, it is possible to effectively achieve both ensuring the battery capacity and alleviating the volume change of the low-valence nanosilicon oxide due to the porous carbon structure.

[0036] Moreover, the grain size of zero-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 zero-valent Si, which is substantially an amorphous structure, are preferred.

[0038] Moreover, the negative electrode active material particles preferably have a G / D ratio obtained from Raman spectrum in the range of 0.85 to 1.15 and an Si / G ratio of 0.25 or more and 0.45 or less.

[0039] If the G / D ratio is within the above range, it is neither too hard nor too soft. If it is within the above range, cracking during pressing and cracking due to volume changes during Li storage by low-valence nanosilicon can be prevented. Also, if the Si / G ratio is within the above range, the area of the low-valence nanosilicon oxide part visible on the particle surface layer is more appropriate. If it is within the above range, high-rate chargeability can be ensured while suppressing deterioration.

[0040] Also, the structure of the porous carbon is predominantly of type I in the IUPAC classification, and its surface area is 1300 m 2 / g or more, and the pore volume is preferably 0.85 cm 3 / g or more.

[0041] Since the structure of the porous carbon has such IUPAC classification, surface area, and pore volume, it can be used as a negative electrode active material that efficiently contains a larger amount of low-valence nanosilicon oxide. In particular, the type I structure in the IUPAC classification enables smooth formation of Si-O bonds after deposition.

[0042] The present invention also relates to a method for manufacturing a negative electrode active material having negative electrode active material particles, comprising the steps of preparing a structure of porous carbon, flowing monosilane gas under heating to the structure of porous carbon to deposit silicon inside the structure of porous carbon, cooling the material having silicon deposited inside the structure of porous carbon to 50°C or lower, and introducing oxygen diluted with nitrogen gas into the material having silicon deposited inside the structure of porous carbon while maintaining the temperature of the material having silicon deposited inside the structure of porous carbon at 50°C or lower after cooling, thereby changing at least a part of the silicon into low-valence nanosilicon oxide, whereby negative electrode active material particles in which amorphous low-valence nanosilicon oxide is dispersed inside the structure of porous carbon, and the negative electrode active material particles are solid 29Provided is a method for producing a negative electrode active material, which comprises producing a material having a maximum value in the range of -81 to -95 ppm when measured by Si-CP / MAS-NMR.

[0043] Further, the present invention is a method for producing a negative electrode active material having negative electrode active material particles, which comprises the steps of preparing a structure of porous carbon, flowing monosilane gas under heating to the structure of porous carbon to deposit silicon inside the structure of porous carbon, cooling the material having silicon deposited inside the structure of porous carbon to 50°C or lower, and introducing oxygen diluted with nitrogen gas into the material having silicon deposited inside the structure of porous carbon in a state where the temperature of the material having silicon deposited inside the structure of porous carbon is adjusted to maintain 50°C or lower after the cooling, thereby changing at least a part of the silicon into a low-valence nanosilicon oxide. Thereby, negative electrode active material particles in which amorphous low-valence nanosilicon oxide is dispersed are produced inside the structure of porous carbon, and from the produced negative electrode active material particles, a solid 29 Provided is a method for producing a negative electrode active material, which comprises selecting a material having a maximum value in the range of -81 to -95 ppm when measured by Si-CP / MAS-NMR, and producing a negative electrode active material using the selected negative electrode active material particles.

[0044] According to such a method for producing a negative electrode active material, as described above, a negative electrode active material in which amorphous low-valence nanosilicon oxide sufficiently containing an SiOSi structure is dispersed can be easily and efficiently produced inside the structure of porous carbon.

Advantages of the Invention

[0045] Since the negative electrode active material of the present invention has amorphous low-valence nanosilicon oxide dispersed inside the structure of 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 porous carbon. Also, a solid 29When measured by Si-CP / MAS-NMR, the negative electrode active material particles having a maximum value in the range of -81 to -95 ppm are negative electrode active material particles sufficiently containing a SiOSi structure, so that an irreversible capacity lower than that of general SiO can be maintained. In addition, since the Si-O bond can suppress the decomposition of the electrolyte, it is possible to reduce the SEI deposited on the surface layer portion. As a result, the negative electrode using the negative electrode active material of the present invention can achieve high initial efficiency, high capacity, high input characteristics, and high cycle characteristics.

[0046] In addition, the method for producing the negative electrode active material of the present invention can easily and efficiently produce a negative electrode active material in which amorphous low-valence nanosilicon oxide sufficiently containing a SiOSi structure is dispersed inside the structure of the porous carbon.

Brief Description of Drawings

[0047]

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Figure 9

Modes for Carrying Out the Invention

[0048] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.

[0049] As described above, as one method for increasing the battery capacity of a lithium-ion secondary battery, it has been considered to use, as the negative electrode of a lithium-ion secondary battery, a negative electrode in which a low-valence nanosilicon oxide is used as a main material in a carbon structure. A lithium-ion secondary battery using this active material is desired to have a high battery capacity while exhibiting battery characteristics almost equivalent to those of a lithium-ion secondary battery using a carbon-based active material.

[0050] Therefore, the present inventors have conducted intensive studies 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 reached the present invention.

[0051] In particular, in CVD-Si-C as disclosed in Patent Documents 14 and 15, a problem was that the reaction with the electrolytic solution was too large. In the present invention, in order to suppress such a reaction with the electrolytic solution, the Si part is converted into a Si-O phase, and by using a siloxane bond peculiar to silicon oxide, not only the reaction decomposition of the electrolytic solution is significantly suppressed, but also the Si-O material having a siloxane bond has good Li acceptability, so a negative electrode active material that can ensure high-speed charging has been developed.

[0052] [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, 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. When measured by solid 29 Si-CP / MAS-NMR, it is a negative electrode active material characterized by having a maximum value in the range of -81 to -95 ppm.

[0053] Such a negative electrode active material has an amorphous low-valence nano silicon oxide dispersed inside a porous carbon structure. Therefore, due to the presence of the porous carbon structure, the adverse effects caused by the expansion of the internal low-valence nano silicon oxide can be reduced. Also, solid 29 When measured by solid Si-CP / MAS-NMR, the negative electrode active material particles having a maximum value in the range of -81 to -95 ppm are negative electrode active material particles sufficiently containing a SiOSi structure. Therefore, an irreversible capacity lower than that of general SiO can be maintained. Also, since the Si-O bond can suppress the decomposition of the electrolytic solution, it is possible to reduce the SEI deposited on the surface layer portion. In the present invention, it is only necessary that an amorphous low-valence nano silicon oxide is dispersed inside a porous carbon structure, and a part of the nano silicon oxide may have crystallinity.

[0054] Solid Si-CP / MAS-NMR used for measuring the characteristics of the negative electrode active material of the present invention will be described. As is well known, CP / MAS is an abbreviation for Cross Polarization Magic Angle Spinning. Solid 29 Si-CP / MAS-NMR is a solid NMR measurement method that combines cross polarization (CP) and magic angle spinning (MAS). The MAS method without using cross polarization (CP) is a method of directly 29 exciting and detecting Si nuclei. On the other hand, CP / MAS is a method of 29 exciting H nuclei, then 1 transferring magnetization to Si nuclei, and detecting only the magnetically transferred 29 Si nuclei. Therefore, Si nuclei without 29 H nuclei that cause magnetization transfer in the vicinity are not detected. As a result, Si nuclei having Si-H groups, Si-OH groups, and Si-O groups are magnetically transferred with a high probability and thus detected with high sensitivity. On the other hand, portions having only Si-Si bonds or only SiO 1 bonds are not detected. Since solid 29 Si-CP / MAS-NMR is such a measurement method, it becomes a selective detection method. Such solid 2 Si-CP / MAS-NMR is such a measurement method. 29 Therefore, it is a selective detection method. Such solid 29When measuring the negative electrode active material particles in which amorphous low-valence nanosilicon oxide is dispersed inside the structure of porous carbon by Si-CP / MAS-NMR, if the maximum value is in the range of -81 to -95 ppm, it can be said that the SiOSi structure is sufficiently contained.

[0055] Thus, the negative electrode active material particles of the present invention can have a SiOSi structure in which oxygen is bonded to Si radicals.

[0056] Solid 29 The Si-CP / MAS-NMR measurement can be performed, for example, under the following conditions. Solid 29 Si-CP / MAS-NMR Measurement Conditions · Apparatus: Bruker AVANCE700 · Detector: 4mmφ CPMS solid probe · Rotor: Made of 4mmφ zirconia · Cap: Made of KEL-F · 29 Si resonance frequency: 139.1 MHz · Pulse sequence: CP / MAS · Contact time: 5 ms · Delay time: 5.0 sec · MAS speed: 9 kHz · Number of integrations: 16000 times · Measurement temperature: Room temperature · Chemical shift external standard: Hexamethylcyclotrisiloxane -9.66 ppm

[0057] As described below, the negative electrode active material of the present invention can be produced as a Si-Ox oxidized material having a siloxane bond in the Si phase in order to suppress the decomposition reaction of the electrolytic solution, which is insufficient for CVD-Si-C generated from general silane gas. The purpose of intentionally creating an Si-O bond is that while an Si-Si bond promotes the decomposition of the electrolytic solution, an Si-O bond results in a gentler reaction with the electrolytic solution compared to Si-Si. In addition, 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, while the grain boundaries of grains having an Si-Si bond reduce Li diffusivity, an Si-O bond has good Li diffusivity and improves high-rate chargeability. Since the main site contributing to charge and discharge of the material of the present invention is a low-valence nanosilicon oxide, it can be defined as CVD-SiOx-C with respect to CVD-Si-C. Thus, the produced active material can have high energy density and high-rate chargeability while maintaining the cycle characteristics of the battery.

[0058] In addition, since tetravalent Si constituting 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 substantially in a 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 predominantly having SiOx with a valence of 2 or less, although the irreversible capacity is larger than that of silicon alone, an irreversible capacity lower than that of general SiO can be maintained.

[0059] In addition, in the negative electrode active material of the present invention, it is preferable that the low-valence nanosilicon oxide includes each state of SiOx: x < 1.0. Further, it is preferable that the low-valence nanosilicon oxide has an average particle size of 35 nm or less obtained by image processing in a cross-sectional TEM image. General SiO is Si 4+becomes an irreversible component. By including each state of SiOx:x < 1.0 in this way, an irreversible capacity lower than that of general SiO can be maintained. Further, since the particle size of the low-valence nanosilicon oxide (the particle size obtained by image processing in the cross-sectional TEM image of the low-valence nanosilicon oxide) is 35 nm or less on average, it is easy to assume that Si-O bonds are appropriately formed.

[0060] The grain size of the low-valence nanosilicon oxide can be confirmed by TEM-EDX. The conditions at this time can be as follows. The negative electrode active material is processed into a cross-section in a non-atmospheric exposure state by a focused ion beam processing apparatus (FIB). The FIB processing apparatus is XVision200DB manufactured by SIINT, and the acceleration voltage is 30 kV. The TEM observation is TecnaiG2F20 manufactured by FEI, the acceleration voltage is 200 kV, and the EDX is r-TEM manufactured by EDAX, and the acceleration voltage is 200 kV.

[0061] In the present invention, as described above, the low-valence nanosilicon oxide preferably has grains of substantially 35 nm or less and contains a monovalent to divalent oxidation compound as a structure. The Si-O bond can suppress the decomposition of the electrolytic solution. Also, the diffusivity of Li is high, making it suitable for high-speed charging. When the grain size becomes larger than 35 nm, it is more difficult to form Si-O bonds than in the case of 35 nm or less. For example, when only the grain surface layer is oxidized to form SiO 2 it tends to become a resistance component, making it difficult to ensure high-speed charging performance.

[0062] When the particle size of the low-valence nanosilicon oxide increases, it becomes more difficult to form Si-O bonds. As will be described later, in the method for manufacturing the negative electrode active material of the present invention, specifically, during the process of decomposing SiH 4 to produce amorphous Si, it reacts with oxygen intentionally to produce Si-O bonds. Therefore, when the particle size is large, the invasiveness of oxygen is poor. For example, a concentration distribution of O occurs in the low-valence silicon oxide phase, and SiO 2It may be reduced. Or at that time, the inside of the phase may be in the state of Si like the above-mentioned CVD-Si-C. Also, inside this low-valence nanosilicon oxide grain, there is also a part of amorphous Si with a valence of 0, and it is desirable that the crystallinity is lower. When the crystallinity is lowered, the irreversible capacity increases, but there is an advantage that the Li acceptance property is improved. When the crystallinity is high, the electrolyte decomposition reaction peculiar to Si is promoted, so the cycle characteristics deteriorate.

[0063] In the negative electrode active material of the present invention, the grain size of Si with a valence of 0 that constitutes 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. Those having such a grain size of Si with a valence of 0 having a substantially amorphous structure are preferred.

[0064] 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”

[0065] The valence of the low-valence nanosilicon oxide can be quantified by NMR (nuclear magnetic resonance) and XPS (X-ray photoelectron spectroscopy).

[0066] The NMR measurement for measuring the valence of low-valence nanosilicon oxide can be performed, for example, under the following conditions. 29 Si MAS NMR (Magic Angle Spinning Nuclear Magnetic Resonance) · Apparatus: Bruker 700 NMR spectrometer, · Probe: 4 mm HR-MAS rotor 50 μL, · Sample rotation speed: 10 kHz, · Measurement ambient temperature: 25 °C

[0067] The XPS measurement can be performed, for example, under the following conditions. 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.

[0068] 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, in order to disperse low-valence nanosilicon oxide 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.

[0069] In addition, in the negative electrode active material of the present invention, the low-valence nanosilicon oxide dispersed in the porous carbon structure covers the surface layer of the porous carbon structure, and the film thickness can be 5 nm or less. In the negative electrode active material of the present invention, it is desirable that there is less Si part in the outermost layer. However, since Si forms a natural oxide film, the outermost layer of the Si part is SiO 2It is in this state. When the thickness of the low-valence number nano silicon oxide is sufficiently thin, such as 5 nm or less, since the oxide film covers the upper layer portion, there are few remaining portions as Si, the adverse effects are suppressed, and good cycle characteristics can be maintained.

[0070] Further, in the negative electrode active material of the present invention, the negative electrode active material particles preferably have a G / D ratio obtained by Raman spectrum in the range of 0.85 to 1.15 and an Si / G ratio of 0.25 or more and 0.45 or less. The G / D ratio is the ratio of the G-band peak intensity IG, which is the intensity of the peak derived from the G band by Raman spectroscopic analysis, to the D-band peak intensity ID, which is the intensity of the peak derived from the D band. The Si / G ratio is the intensity ratio of the Si peak intensity ISi, which is the intensity of the peak derived from Si by Raman spectroscopic analysis, to the G-band peak intensity IG, which is the intensity of the peak derived from the G band.

[0071] If the carbon particles are too hard, they will crack during pressing, but if they are too soft, they will crack due to the expansion when silicon occludes Li. Therefore, there is an optimal range. Also, if the area of the low-valence number silicon oxide part visible on the particle surface layer is large, the reaction area with the electrolyte is large and it is relatively easy to deteriorate quickly, but if it is small, the Li acceptance location becomes small and the high-rate chargeability deteriorates. As an index indicating these, there is an optimal value for the Si / G ratio. That is, if the G / D ratio is within the above range, it is neither too hard nor too soft. If it is within the above range, it is possible to prevent cracking during pressing and cracking due to volume change during Li occlusion by low-valence number nano silicon. Also, if the Si / G ratio is within the above range, the area of the low-valence number nano silicon oxide part visible on the particle surface layer is more appropriate. If it is within the above range, it is possible to ensure high-rate chargeability while suppressing deterioration.

[0072] <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.

[0073] [Configuration of negative electrode] Figure 1 shows a cross-sectional view of the 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 the 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. Furthermore, in the negative electrode of the non-aqueous electrolyte secondary battery of the present invention, the negative electrode current collector 11 may not be provided.

[0074] [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).

[0075] The negative electrode current collector 11 preferably contains carbon (C) and sulfur (S) in addition to the main elements. 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. Such a deformation suppression effect can further improve the cycle characteristics.

[0076] 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.

[0077] [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 carbon-based active materials in addition to the silicon-based active material particles of the present invention. Furthermore, 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.

[0078] [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.

[0079] 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, and includes a step of preparing a porous carbon structure, and flowing monosilane gas under heating to the porous carbon structure, thereby depositing silicon inside the porous carbon structure; a step of cooling the material having silicon deposited inside the porous carbon structure to 50°C or lower; and a step of 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, thereby changing at least a part of the silicon into a low-valence nanosilicon oxide. As a result, negative electrode active material particles in which amorphous low-valence nanosilicon oxide is dispersed inside the porous carbon structure, and the negative electrode active material particles are solid 29 A method for manufacturing a negative electrode active material, characterized in that when measured by Si-CP / MAS-NMR, it has a maximum value in the range of -81 to -95 ppm.

[0080] Further, the method for manufacturing a negative electrode active material of the present invention is a method for manufacturing a negative electrode active material having negative electrode active material particles, and includes a step of preparing a porous carbon structure, and flowing monosilane gas over the porous carbon structure under heating to deposit silicon inside the porous carbon structure, a step of cooling the material having silicon deposited inside the porous carbon structure to 50°C or lower, and 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, thereby changing at least a part of the silicon into a low-valence nanosilicon oxide. Thereby, negative electrode active material particles in which amorphous low-valence nanosilicon oxide is dispersed are produced inside the porous carbon structure, and from the produced negative electrode active material particles, a solid 29 When measured by Si-CP / MAS-NMR, those having a maximum value in the range of -81 to -95 ppm are selected, and a method for manufacturing a negative electrode active material may be characterized by manufacturing a negative electrode active material using the selected negative electrode active material particles.

[0081] First, with reference to steps S11 to S14 in FIG. 8, each step of an example of the method for manufacturing a negative electrode active material will be described.

[0082] First, a porous carbon structure is prepared (step S11). The porous carbon structure prepared here preferably has a carbon-carbon double bond at least in part. Further, the porous carbon structure prepared here is predominantly of type I in the IUPAC classification, and its surface area is 1300 m 2 / g or more, and the pore volume is preferably 0.85 cm 3 / g or more. By setting such classification according to the IUPAC classification, surface area, and pore volume, more efficient deposition of silicon can be achieved in a larger amount. Further, for the IUPAC classification, surface area, and pore volume, the following measurement methods can be used. · The specific surface area / pore size distribution is measured by the constant volume method based on the gas adsorption method using Shimadzu TriStar II Plus. The conditions are as follows. · Gas used: Nitrogen · Environment: Under liquid nitrogen · Pressure operating range: P / P0 · Adsorption 0 to 0.998 · Desorption 0.998 to 0.10 · Pretreatment Vacuum 200 °C for 1 hour

[0083] Next, silicon is deposited inside the porous carbon structure prepared in step S11 by flowing monosilane gas under heating (step S12).

[0084] Note that after step S11 and before step S12, 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 to about 350 to 450 °C using an external heater while flowing nitrogen. This heating can be performed for 5 minutes to 1 hour. By performing such preheating in the presence of evacuation and nitrogen, nucleation for silicon deposition in step S12 and removal of hydrogen and water adhering to the porous carbon structure can be performed, so that silicon deposition in step S12 can be performed more reliably.

[0085] The silicon deposition in step S12 can be performed, for example, by flowing monosilane gas at about 400 to 500 °C. The deposition time can be, for example, 30 minutes to 10 hours.

[0086] Next, the material with silicon deposited inside the porous carbon structure is cooled to 50 °C or lower (step S13). 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.

[0087] After the above cooling (step S13), next, with the temperature of the material with silicon deposited inside the porous carbon structure adjusted to maintain 50°C or lower, oxygen diluted with nitrogen gas is introduced into the material with silicon deposited inside the porous carbon structure, thereby changing at least a part of the silicon into a low-valence nano silicon oxide (step S14). 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.

[0088] 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.

[0089] Also, in this step S14, if the internal temperature rises and exceeds 50°C, silicon dioxide is partially generated, which is not preferable as the negative electrode active material. Therefore, in this step S14, it is necessary to adjust the temperature of the material to maintain 50°C or lower. Further, the material temperature in step S14 is preferably, for example, 25°C or higher, more preferably 30°C or higher, to facilitate the oxidation reaction and the formation of Si—O bonds.

[0090] The oxidation time (flow time of oxygen diluted with nitrogen gas) in this step S14 can be, for example, 30 minutes or longer and 5 hours or shorter, preferably 1 hour or longer and 3 hours or shorter. Further, after the flow of oxygen diluted with nitrogen gas, the flow can be switched to the flow of nitrogen gas for further cooling. The flow of only nitrogen gas can be, for example, 30 minutes or longer and 2 hours or shorter.

[0091] In the oxidation by the flow of oxygen diluted with the nitrogen gas, it is preferable that the low-valence nano silicon oxide dispersed in the porous carbon structure adjusts so that x increases from the center to the surface layer of the porous carbon structure. In the porous carbon structure, the pore structure tends to have a large cross-sectional area on the particle surface and a small 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 naturally becomes easier for x to increase from the center to the surface layer of the porous carbon structure.

[0092] Thereafter, the material is taken out from the storage container. Through the above steps, negative electrode active material particles in which amorphous low-valence nano silicon oxide is dispersed can be produced inside the porous carbon structure. In the above steps, the production conditions are appropriately adjusted for the negative electrode active material particles to be solid 29 When measured by Si-CP / MAS-NMR, those having a maximum value in the range of -81 to -95 ppm can be produced.

[0093] When manufacturing the negative electrode active material produced in this way, it is preferable to adjust the deposition amount of silicon and the degree of oxidation so that the ratio of the porous carbon structure in the entire negative electrode active material particles is 45% by mass or more and 64% by mass or less.

[0094] Next, with reference to steps S21 to S25 in FIG. 9, each step of another example of the method for manufacturing a negative electrode active material will be described.

[0095] Steps S21 to S23 are substantially the same as steps S11 to S13 above.

[0096] After cooling in step S23 similar to step S13, next, with the temperature of the material with silicon deposited inside the porous carbon structure adjusted to maintain 50°C or lower, oxygen diluted with nitrogen gas is introduced into the material with silicon deposited inside the porous carbon structure to change at least a part of the silicon into low-valence nanosilicon oxide (step S24). 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.

[0097] Next, from the negative electrode active material particles produced in step S24, solid 29 When measured by Si-CP / MAS-NMR, those having a maximum value in the range of -81 to -95 ppm are selected (step S25). This selection can be performed by actually measuring the sample by solid 29 Si-CP / MAS-NMR. Furthermore, a negative electrode active material can be manufactured using the negative electrode active material particles selected in step S25.

[0098] <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 laminated film type lithium ion secondary battery will be described.

[0099] [Configuration of laminated film type secondary battery] The laminated 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 either electrode body, 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.

[0100] 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.

[0101] 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 protection layer is nylon or the like, for example.

[0102] 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.

[0103] 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.

[0104] The positive electrode current collector is formed of a conductive material such as aluminum, for example.

[0105] 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.

[0106] 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 M 1 O 2 or Li y M 2 PO 4 It is represented by. In the formula, M 1 , M 2 represents at least one transition metal element. The values of x and y represent different values depending on the charge and discharge state of the battery, but are generally represented by 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

[0107] Examples of the composite oxide having lithium and a transition metal element include lithium cobalt composite oxide (Li x CoO 2 ), lithium nickel composite oxide (Li x NiO 2 ), etc. Examples of the lithium nickel cobalt composite oxide include lithium nickel cobalt aluminum composite oxide (NCA), lithium nickel cobalt manganese composite oxide (NCM), etc.

[0108] Examples of the phosphate compound having lithium and a transition metal element include lithium iron phosphate compound (LiFePO 4 ) or lithium iron manganese phosphate compound (LiFe 1-u Mn u PO 4 (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.

[0109] [Negative electrode] The negative electrode has the same configuration as the negative electrode 10 for the lithium ion secondary battery shown in FIG. 1 above. For example, it has a negative electrode active material layer on both sides of the current collector. It is preferable that the negative electrode charging capacity is larger than the electric capacity obtained from the positive electrode active material agent (charging capacity as a battery). Thereby, the precipitation of lithium metal on the negative electrode can be suppressed.

[0110] The positive electrode active material layer is provided on a part of both sides of the positive electrode current collector, and similarly, the negative electrode active material layer is provided on a part of both sides of the negative electrode current collector. In this case, for example, the negative electrode active material layer provided on the negative electrode current collector is provided with a region where there is no opposing positive electrode active material layer. This is for performing a stable battery design.

[0111] In the region where the above negative electrode active material layer and positive electrode active material layer do not face each other, it is hardly affected by charge and discharge. Therefore, the state of the negative electrode active material layer is maintained as it is immediately after formation, and thereby, the composition of the negative electrode active material and the like can be accurately investigated with good reproducibility without depending on the presence or absence of charge and discharge.

[0112] [Separator] The separator separates the positive electrode and the negative electrode, prevents current short - circuit due to contact between the two electrodes, and allows lithium ions to pass through. This separator is formed of, for example, a porous membrane made of a synthetic resin or 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.

[0113] [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.

[0114] 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, tetrahydrofuran, and the like. 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 properties can be obtained. In this case, by combining a high-viscosity solvent such as ethylene carbonate or propylene carbonate with a low-viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate, more excellent properties can be obtained. This is because the dissociation property and ion mobility of the electrolyte salt are improved.

[0115] 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). Also, 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).

[0116] 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 solution is reduced.

[0117] Examples of the halogenated chain carbonate ester include fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, and the like. Examples of the halogenated cyclic carbonate ester include 4-fluoro-1,3-dioxolan-2-one, 4,5-difluoro-1,3-dioxolan-2-one, and the like.

[0118] As the solvent additive, it is preferable to contain an unsaturated carbon-bonded cyclic carbonate. 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 electrolytic solution can be suppressed. Examples of the unsaturated carbon-bonded cyclic carbonate include vinylene carbonate or vinyl ethylene carbonate.

[0119] Also, as the 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 and propene sultone.

[0120] Furthermore, the solvent preferably contains an acid anhydride. This is because the chemical stability of the electrolytic solution is improved. Examples of the acid anhydride include propane disulfonic anhydride.

[0121] 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 (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), etc.

[0122] 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. This is because high ionic conductivity can be obtained.

Examples

[0123] 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.

[0124] (Example 1) According to the following procedure, a negative electrode active material was prepared, and further, a laminated film type lithium ion secondary battery 30 shown in FIG. 2 was prepared.

[0125] The negative electrode active material was manufactured as follows. First, the surface area (BET specific surface area) was 1940 m 2 / g, and the pore volume was 1.00 cm3 / g, particle size (D50) = 11 μm, a porous carbon material (porous carbon structure) of IUPAC classification type I was prepared. This porous carbon material was stored in a vacuum container 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 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, and then the material was taken out from the storage container to obtain a negative electrode active material.

[0126] [Measurement of negative electrode active material] For the negative electrode active material prepared as described above, TEM-EDX, XRD analysis, NMR analysis (solid 29 Si-MAS-NMR and solid 29 Si-CP / MAS-NMR), and Raman spectroscopic analysis were performed.

[0127] [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 mixture slurry.

[0128] 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 ppm by mass, respectively. Finally, the negative electrode mixture slurry was applied to the negative electrode current collector and dried in a vacuum atmosphere at 100 °C for 1 hour. 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.

[0129] [Assembly of Coin Cells for Testing] Next, after mixing the solvents ethylene carbonate (EC) and dimethyl carbonate (DMC), the electrolyte salt (lithium hexafluorophosphate: LiPF 6 ) 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.

[0130] 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.

[0131] 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.

[0132] [Measurement of Initial Efficiency] The initial efficiency was measured under the following conditions. First, for the fabricated coin cell for initial efficiency testing, the charging rate was set to be equivalent to 0.03C, and charging (first charge) was performed in the CCCV mode. The CV was 0V and the termination current was 0.04 mA. Next, the discharging rate was similarly set to 0.03C, and CC discharging (first discharge) was performed with the discharge termination voltage set to 1.2V.

[0133] When examining the initial charge-discharge characteristics, the initial efficiency (which may also be referred to as the initial efficiency hereinafter) was calculated. The initial efficiency was calculated from the formula: Initial efficiency (%) = (First discharge capacity / First charge capacity) × 100.

[0134] [Manufacture and Battery Evaluation of Lithium-Ion Secondary Batteries] 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.

[0135] The cycle characteristics 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 cycle numbers. Charge and discharge were performed at a charge rate of 0.7C and a discharge rate 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. Also, for the high-rate charge characteristics, the battery cycle characteristics were calculated from the discharge capacity of the third cycle, and the battery test was stopped at 500 cycle numbers. Charge and discharge were performed at a charge rate of 4C and a discharge rate of 0.5C. The charge cut-off voltage was 4.3V, the discharge cut-off voltage was 2.5V, and the charge cut-off rate was 0.07C.

[0136] The results of each measurement are shown in Table 1. In Table 1, Comparative Example 1 and Examples 2 to 20, which will be described later, are also shown together.

[0137]

Table 1

[0138] Regarding the negative electrode active material particles of the negative electrode active material of Example 1 29 The Si-MAS-NMR spectrum is shown in Fig. 3, 29 The Si-CP / MAS-NMR spectrum is shown in Fig. 4. In addition, the NMR spectra of Examples 13, 19, 20, and Comparative Example 1, which will be described later, are shown in Figs. 3 and 4. Also, the cross-sectional TEM photograph of the negative electrode active material of Example 1 is shown in Fig. 5.

[0139] In Example 1, the oxidation process was performed as described above to provide Si-H groups, Si-OH groups, and Si-O groups. Among these, there are particularly many Si-O groups and many SiOSi structures. As a result, the Li diffusivity inside the bulk was improved, the high-rate charging characteristics were good, and it was possible to achieve 4C charging without problems.

[0140] (Comparative Example 1) A porous carbon structure similar to that of Example 1 was prepared. Then, under the same conditions as in Example 1, amorphous silicon was formed from the surface layer to a location near the center of the porous carbon structure particles at 415 °C using SiH 4 gas. In this state, since Si-H bonds are included, the temperature was raised to 435 °C to stabilize Si-Si in order to Si-Si. Then, it was cooled to room temperature and the sample was taken out with the atmosphere released. By using this method, (different from the present invention) a material without a low-valence silicon oxide compound can be prototyped. Various measurements were performed in the same manner as in Example 1 and are shown in Table 1. The capacity and initial Coulomb efficiency were high, but the reactivity with the electrolyte was high, the battery cycle characteristics deteriorated, and particularly the high-rate chargeability resulted in Li deposition.

[0141] The difference between Comparative Example 1 and Example 1 is that there are many Si-Si bonds and few SiOSi structures (refer to CP / MAS-NMR in Fig. 4, with a peak top at -80 ppm). In Comparative Example 1, since the oxidation process is not performed, it is not affected by Si-H groups, Si-OH groups, and Si-O groups, and the CP / MAS-NMR (Fig. 4) and MAS-NMR spectrum (Fig. 3) are almost the same. In this state in Comparative Example 1, the Li diffusion inside the bulk deteriorates and Li deposition occurs. Although there are no problems with characteristics other than high-rate chargeability, since the characteristic required in applications such as EV (Electric Vehicle) is high-rate charging, it is essential.

[0142] (Examples 2 to 4) The oxidation method was changed from Example 1. For example, when reducing the degree of oxidation, oxygen diluted more with nitrogen was introduced to suppress the rise in the internal temperature. When increasing the degree of oxidation, the oxygen concentration was increased and oxidized in the range of 50 °C or less at the upper limit. Solid 29The Si-CP / MAS-NMR spectrum shifts to the low magnetic field side when the oxygen content is low and to the high magnetic field side when the oxygen content is high. When oxidized until the shift exceeds -95 ppm, it was not possible to maintain the low valence state and obtain a sample that could be evaluated in a battery. Therefore, in Examples 2 to 4, the range was set to -81 to -95 ppm. Among these, when the oxidation amount was relatively small (Example 2), the SiOSi structure decreased, and the fast charging performance deteriorated slightly compared to Example 1.

[0143] (Examples 5 to 7) The porous carbon was changed, and silicon was deposited inside the structure. As a result, the size of the particle diameter obtained by image processing in the cross-sectional TEM image of the low valence nano silicon oxide was changed. From the viewpoint of fast charging performance, it is more preferable that the particle diameter of this low valence nano silicon oxide is 35 nm or less on average.

[0144] (Examples 8 to 9, 17) This is an example in which the ratio of the carbon active material in the negative electrode was increased. As a result, the capacity simply decreases. Since it is preferable to have a capacity of 1800 mAh / g or more, the amount of carbon is also important. In addition, a cross-sectional TEM photograph of the negative electrode active material of Example 9 is shown in FIG. 6.

[0145] (Examples 10 to 14) 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 flowed, and deposition was carried out for 4 hours. Then, the temperature was raised to grow the grain size of Si. In this way, the crystal grain size (grain size) of Si present in the low valence nano silicon oxide was changed. When the crystal grain size of Si increases, the Si / Si grain boundaries also increase, the Li diffusivity decreases, and the fast charging characteristics deteriorate compared to Example 1. Therefore, it is better that the grain size of zero-valent Si is small, and it is preferably 5 nm or less. 0+ of 0+ of 0+ When the crystal grain size of increases, the Li diffusivity decreases, and the fast charging characteristics deteriorate compared to Example 1. Therefore, it is better that the grain size of zero-valent Si is small, and it is preferably 5 nm or less.

[0146] (Examples 15 to 16) The porous carbon was changed, and the G / D ratio of the carbon active material was changed. When the G / D ratio increases, the cycle characteristics deteriorate relatively. However, within the speculated range, it is speculated that when G is large, structural destruction occurs and direct contact with the electrolyte due to the exposure of the Si part may occur. Therefore, the G / D ratio is preferably 0.85 to 1.15.

[0147] (Examples 18 to 20) As the structure of the porous carbon to be prepared first, as shown in Table 1, a negative electrode active material was produced in the same manner as in Example 1 except that those having different characteristics (such as pore diameter) were used. Also, the same evaluation as in Example 1 was performed. From the results of Examples 18 to 20, by increasing the surface area and pore volume, the capacity of the active material can be simply increased. Considering the balance of capacity and efficiency, etc., the pore volume is 0.85 cm 3 / g or more, and the BET specific surface area is 1300 m 2 / g or more, and the IUPAC classification is preferably type I. Also, a cross-sectional TEM photograph of the negative electrode active material of Example 19 is shown in FIG. 7.

[0148] (Examples 21 to 24) A negative electrode active material was produced in the same manner as in Example 1, but the following changes were made. After incorporating low-valence nanosilicon oxide into the porous carbon, the exhaust side valve of the reaction vessel was closed, and a mixed gas of silane gas / nitrogen gas was sealed until the internal pressure reached 0.01 to 0.05 MPa. At this time, by changing from hydrogen gas to nitrogen gas, it becomes difficult for silane gas to penetrate into the remaining pore portions. In that state, the temperature was raised by 20 °C, and the silane gas remaining in the reaction vessel was deposited as silicon on the surface of the porous carbon. Then, it was cooled, and the same procedure as in Example 1 was performed. Also, the same evaluation as in Example 1 was performed. The results are shown in Table 2. In Table 2, the thickness of the low-valence nanosilicon oxide covering the surface layer of the structure of the porous carbon is shown as the "thickness of surface-exposed Si". In Examples 21 to 24, as described above, the same oxidation procedure as in other examples was followed. Due to this oxidation, the outermost layer becomes an SiO 2 component, and the low-valence silicon oxide comes to exist between the porous carbon and the SiO 2 layer.

[0149]

Table 2

[0150] As can be seen from Table 2, the effects of the present invention were obtained in Examples 21 to 24. In particular, the cycle characteristics were good in Examples 21 to 23.

[0151] This specification includes the following aspects. [1]: A negative electrode active material having negative electrode active material particles, wherein the negative electrode active material particles include a structure of porous carbon, and amorphous low-valence nanosilicon oxide is dispersed inside the structure of the porous carbon, and when the negative electrode active material particles are measured by solid 29 Si-CP / MAS-NMR, it has a maximum value in the range of -81 to -95 ppm. A negative electrode active material characterized by this. [2]: The negative electrode active material according to [1] above, wherein the negative electrode active material particles have a SiOSi structure in which oxygen is bonded to Si radicals. [3]: The negative electrode active material according to [1] or [2] above, wherein the low-valence nanosilicon oxide is substantially in a composite state of 0 valence, 1 valence, and 2 valence. [4]: The negative electrode active material according to [3] above, wherein the low-valence nanosilicon oxide is substantially dominated by 1 to 2 valences. [5]: The low-valence nanosilicon oxide includes each state of SiOx: x < 1.0, and the negative electrode active material according to any one of [1] to [4] above, wherein the particle size of the low-valence nanosilicon oxide obtained by image processing in a cross-sectional TEM image is 35 nm or less on average. [6]: The negative electrode active material according to any one of [1] to [5] above, wherein the low-valence nanosilicon oxide dispersed in the structure of the porous carbon increases in x from the center to the surface layer of the structure of the porous carbon. [7]: The low-valence nano silicon oxide dispersed in the porous carbon structure covers the surface layer of the porous carbon structure, and the film thickness is 5 nm or less, which is the negative electrode active material according to any one of [1] to [6] above. [8]: The ratio of the porous carbon structure in the whole negative electrode active material particles is 45% by mass or more and 64% by mass or less, which is the negative electrode active material according to any one of [1] to [7] above. [9]: The grain size of Si with a valence of 0 constituting the low-valence nano silicon 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, which is the negative electrode active material according to any one of [1] to [8] above.

[10] : The negative electrode active material particles have a G / D ratio obtained from Raman spectrum in the range of 0.85 to 1.15 and an Si / G ratio of 0.25 or more and 0.45 or less, which is the negative electrode active material according to any one of [1] to [9] above.

[11] : The porous carbon structure is mainly of type I in the IUPAC classification, and its surface area is 1300 m 2 / g or more, and the pore volume is 0.85 cm 3 / g or more, which is the negative electrode active material according to any one of [1] to

[10] above.

[12] : A method for manufacturing a negative electrode active material having negative electrode active material particles, The step of preparing a porous carbon structure, The step of depositing silicon inside the porous carbon structure by flowing monosilane gas under heating on the porous carbon structure, The step of cooling the material with silicon deposited inside the porous carbon structure to 50 °C or lower, After the cooling, while adjusting to maintain the temperature of the material with silicon deposited inside the porous carbon structure at 50 °C or lower, oxygen diluted with nitrogen gas is introduced into the material with silicon deposited inside the porous carbon structure to change at least a part of the silicon into low-valence nano silicon oxide having, thereby, within the structure of the porous carbon, negative electrode active material particles in which amorphous low-valence nanosilicon oxide is dispersed, and solidifying the negative electrode active material particles 29 A method for producing a negative electrode active material, characterized by producing one having a maximum value in the range of -81 to -95 ppm when measured by Si-CP / MAS-NMR.

[13] : A method for producing a negative electrode active material having negative electrode active material particles, preparing a structure of porous carbon; depositing silicon inside the structure of the porous carbon by flowing monosilane gas under heating with respect to the structure of the porous carbon; cooling the material having silicon deposited inside the structure of the porous carbon to 50°C or lower; after the cooling, introducing oxygen diluted with nitrogen gas into the material having silicon deposited inside the structure of the porous carbon while adjusting so that the temperature of the material having silicon deposited inside the structure of the porous carbon is maintained at 50°C or lower, thereby changing at least a part of the silicon into low-valence nanosilicon oxide; having, thereby, producing negative electrode active material particles in which amorphous low-valence nanosilicon oxide is dispersed inside the structure of the porous carbon, selecting, from the produced negative electrode active material particles, those having a maximum value in the range of -81 to -95 ppm when measured by solid 29 Si-CP / MAS-NMR; and producing a negative electrode active material using the selected negative electrode active material particles. A method for producing a negative electrode active material characterized by the above.

[0152] Note that the present invention is not limited to the above-described embodiment. The above-described embodiment is an example, and any configuration having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same operational effects is included in the technical scope of the present invention.

Explanation of Reference Numerals

[0153] 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…Adhesive 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 negative electrode active material particles are solidified ２９ A negative electrode active material characterized in that, when measured by Si-CP / MAS-NMR, it has a maximum value in the range of -81 to -95 ppm.

2. 2. The negative electrode active material according to claim 1, wherein the negative electrode active material particles have a SiOSi structure in which oxygen is bonded to a Si radical.

3. 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.

4. The negative electrode active material according to claim 3, wherein the low-valence nanosilicon oxide is substantially predominantly monovalent or divalent.

5. The low valence nano silicon oxide includes each state of SiOx: x < 1.0, 2 . The negative electrode active material according to claim 1 , wherein the low valence nanosilicon oxide has an average particle size of 35 nm or less as determined by image processing of a cross-sectional TEM image.

6. 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.

7. The negative electrode active material according to claim 1, characterized in that the low valence nanosilicon oxide dispersed in the porous carbon structure covers the surface layer of the porous carbon structure, and the film thickness thereof is 5 nm or less.

8. 2 . The negative electrode active material according to claim 1 , wherein the proportion of the porous carbon structure in the entire negative electrode active material particles is 45% by mass or more and 64% by mass or less.

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 negative electrode active material according to claim 1, characterized in that the negative electrode active material particles have a G / D ratio obtained by Raman spectroscopy in the range of 0.85 to 1.15 and a Si / G ratio of 0.25 or more and 0.45 or less.

11. The porous carbon structure is predominantly Type I in the IUPAC classification and has a surface area of ​​1300 m ２ / g or more, pore volume is 0.85 cm ３ 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.

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 nano-silicon oxide. Thus, the negative electrode active material particles are formed by dispersing amorphous low-valence nano-silicon oxide inside the porous carbon structure, and the negative electrode active material particles are solidified. ２９ A method for producing a negative electrode active material, characterized in that a maximum value is produced in the range of -81 to -95 ppm when measured by Si-CP / MAS-NMR.

13. 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 nano-silicon oxide. Thus, a negative electrode active material particle having an amorphous low valence nano silicon oxide dispersed therein is produced, From the produced negative electrode active material particles, a solid ２９ Select those having a maximum value in the range of -81 to -95 ppm when measured by Si-CP / MAS-NMR, The method for producing a negative electrode active material comprises producing a negative electrode active material using the selected negative electrode active material particles.

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