Negative electrode active material, method for producing negative electrode active material, and battery

Abstract

A negative electrode active material according to the present disclosure comprises composite particles 10 which include a carbon phase 1 and silicon particles 2 dispersed in the carbon phase 1, wherein in a solid-state 29Si-NMR spectrum, the area ratio of a peak A having a peak top in the range of a -30 ppm to -7.5 ppm chemical shift to the total area of all detected peaks is more than 7.6%.

Description

Negative electrode active material, method for manufacturing negative electrode active material, and battery

[0001] This disclosure relates to a negative electrode active material, a method for producing a negative electrode active material, and a battery.

[0002] In recent years, secondary batteries such as lithium-ion batteries have been widely used in applications requiring high capacity, such as automotive and energy storage. The electrodes that make up such batteries have a significant impact on their performance. For this reason, various studies have been conducted on electrodes.

[0003] It is known that silicon (Si)-containing negative electrode active materials are effective in increasing the capacity of batteries. However, negative electrode active materials containing Si undergo large volume changes with charging and discharging, so repeated charging and discharging can break the conductive path with the surrounding active material, resulting in capacity degradation with each charge-discharge cycle. Therefore, Patent Documents 1 and 2 propose negative electrode active materials containing Si that can improve cycle characteristics. Specifically, Patent Documents 1 and 2 propose negative electrode active materials that include composite particles in which silicon is attached to the pores of a carbon material having predetermined pores.

[0004] Patent No. 6451320 Patent No. 7405249

[0005] As described above, conventional negative electrode active materials have room for improvement in terms of battery charge-discharge cycle characteristics.

[0006] Therefore, this disclosure provides a technology that can improve the charge-discharge cycle characteristics of batteries using a negative electrode active material containing Si.

[0007] This disclosure comprises a composite particle comprising a carbon phase and silicon particles dispersed in the carbon phase, and is solid 29 The present invention provides a negative electrode active material in which, in a Si-NMR spectrum, the area ratio of peak A, whose peak top is within the range of chemical shift -30 ppm or more and -7.5 ppm or less, to the total area of ​​all detected peaks, exceeds 7.6%.

[0008] The negative electrode active material of this disclosure can improve the charge-discharge cycle characteristics of a battery.

[0009] Figure 1 is a cross-sectional view showing the schematic configuration of composite particles contained in the negative electrode active material according to Embodiment 1. Figure 2 is a cross-sectional view showing the schematic configuration of a modified example of the composite particles contained in the negative electrode active material according to Embodiment 1. Figure 3 is a flowchart showing an example of a method for manufacturing the negative electrode active material according to Embodiment 1. Figure 4 is a cross-sectional view showing the schematic configuration of a battery according to Embodiment 2.

[0010] The embodiments of this disclosure will be described in detail below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0011] (Embodiment 1) The negative electrode active material according to Embodiment 1 comprises composite particles. Figure 1 is a cross-sectional view showing the schematic configuration of the composite particles 10 comprising the negative electrode active material according to Embodiment 1. The composite particles 10 are particles comprising a carbon phase 1 and silicon particles 2 dispersed in the carbon phase 1. Solid in the negative electrode active material according to Embodiment 1 29 In the Si-NMR spectrum, the area ratio of peak A, whose peak top is within the chemical shift range of -30 ppm or more and -7.5 ppm or less, to the total area of ​​all detected peaks exceeds 7.6%.

[0012] In the negative electrode active material according to Embodiment 1, since the silicon particles 2 are dispersed within the carbon phase 1, the expansion of the silicon particles 2 during charging is mitigated by the carbon phase 1. In other words, the negative electrode active material according to Embodiment 1 has a configuration comprising a composite particle 10 that includes the carbon phase 1 and the silicon particles 2 dispersed within the carbon phase 1, thereby minimizing expansion due to charging.

[0013] The negative electrode active material in Embodiment 1 is a solid, as described above. 29 In the Si-NMR spectrum, the area ratio of peak A, whose peak top is within the chemical shift range of -30 ppm or more and -7.5 ppm or less, to the total area of ​​all detected peaks, is greater than 7.6%. Here, solid 29In the Si-NMR spectrum, peak A, whose peak top is within the range of chemical shift -30 ppm or more and -7.5 ppm or less, is presumed to be a peak originating from SiO2C2. In a negative electrode active material comprising composite particles 10 containing a carbon phase 1 and silicon particles 2 dispersed in the carbon phase 1, it is presumed that O-Si-C bonding can occur near the interface between the carbon phase 1 and the silicon particles 2. Therefore, it is considered that the silicon particles 2 are fixed to the carbon phase 1 by O-Si-C bonding, and that the expansion of the negative electrode active material due to the expansion of the silicon particles 2 during charging can be further suppressed. In the negative electrode active material according to Embodiment 1, the area ratio of peak A, which is presumed to be a peak originating from SiO2C2, exceeds 7.6%, thus further suppressing expansion during charging. Therefore, the negative electrode active material according to Embodiment 1 can further suppress cracks and fractures in the composite particles 10 due to stress associated with the expansion and contraction of the silicon particles 2 during charging and discharging, thereby improving the charge-discharge cycle characteristics of the battery.

[0014] In this specification, solid 29 The standard for chemical shift in Si-NMR spectra is tetramethylsilane as an external standard (0 ppm).

[0015] Solid negative electrode active material according to Embodiment 1 29 In the Si-NMR spectrum, the area ratio of peak A may be 10% or more. This further suppresses the expansion of the negative electrode active material during charging according to Embodiment 1. Therefore, the negative electrode active material according to Embodiment 1 can further improve the charge-discharge cycle characteristics of the battery. In order to further suppress the expansion during charging and improve the charge-discharge cycle characteristics, the area ratio of peak A may be 12% or more.

[0016] Solid negative electrode active material according to Embodiment 1 29In the Si-NMR spectrum, the area ratio of peak A may be 50% or less. This allows the negative electrode active material according to Embodiment 1 to suppress the capacity reduction caused by the bonding of Si in the silicon particles 2 with C in the carbon phase 1, thereby ensuring sufficient capacity. To improve capacity, the area ratio of peak A may be 40% or less, or 35% or less.

[0017] In the negative electrode active material according to Embodiment 1, it is desirable that the full width at half maximum (FWHM) of the diffraction peaks originating from the Si(111) plane, which appear in the range of diffraction angle 2θ between 28.0° and 28.7° in the X-ray diffraction pattern obtained by X-ray diffraction measurement of the negative electrode active material using Cu-Kα rays, be 1.8° or more. By setting the FWHM of the diffraction peaks originating from the Si(111) plane to 1.8° or more, the negative electrode active material according to Embodiment 1 can suppress the crystallinity of the silicon particles 2 from becoming too high, thereby further improving the charge-discharge cycle characteristics of the battery. To further improve the charge-discharge cycle characteristics of the battery, the FWHM of the diffraction peaks originating from the Si(111) plane may be 2.0° or more, or 3.0° or more. Furthermore, diffraction peaks originating from the Si(111) plane that appear in the range of diffraction angle 2θ between 28.0° and 28.7° are, for example, X-ray diffraction peaks where the peak top with the highest intensity is observed within the diffraction angle 2θ range of 28.0° and 28.7°.

[0018] In the negative electrode active material according to Embodiment 1, it is desirable that the full width at half maximum (FWHM) of the diffraction peaks originating from the Si(111) plane, which appear in the range of diffraction angle 2θ between 28.0° and 28.7° in the X-ray diffraction pattern obtained by X-ray diffraction measurement of the negative electrode active material using Cu-Kα rays, be 7.0° or less. By setting the FWHM of the diffraction peaks originating from the Si(111) plane to 7.0° or less, the negative electrode active material according to Embodiment 1 can further improve the charge / discharge efficiency and rate characteristics of the battery. The FWHM of the diffraction peaks originating from the Si(111) plane may be 5.0° or less.

[0019] The X-ray diffraction pattern of the composite particles 10 can be obtained by X-ray diffraction measurement by the θ-2θ method using Cu-Kα rays having wavelengths of 1.5405 Å and 1.5444 Å, that is, wavelengths of 0.15405 nm and 0.15444 nm.

[0020] In this specification, a peak is a mountain-shaped portion where the value of the signal-to-noise ratio (that is, the ratio of the signal S to the background noise N) is 1.3 or more and the full width at half maximum is 10° or less.

[0021] The diffraction angle of a peak in the X-ray diffraction pattern is defined as the angle indicating the maximum intensity of a mountain-shaped portion where the value of the signal-to-noise ratio is 1.3 or more and the full width at half maximum is 10° or less. The full width at half maximum is the width represented by the difference between two diffraction angles at which the intensity becomes half of the maximum intensity I MAX when the maximum intensity of the X-ray diffraction peak is taken as I MAX and becomes half of the value of I.

[0022] Hereinafter, each component of the negative electrode active material according to Embodiment 1 will be described more specifically.

[0023] The carbon phase 1 is a matrix containing carbon and includes, for example, a carbonaceous material. The carbonaceous material is not particularly limited as long as it is a carbon material capable of occluding lithium ions. The carbonaceous material may be amorphous. The carbon phase 1 may be composed of an amorphous carbonaceous material. The carbonaceous material is, for example, a material derived from pitch, amorphous carbon, carbon black, a material derived from an organic polymer, or the like. The pitch is, for example, coal pitch or petroleum pitch, and the coal pitch is, for example, coal tar pitch. Thereby, the electrical connection between the silicon particles 2 in the negative electrode active material and the electrical connection between the silicon particles 2 and the carbonaceous material can be more stabilized. The carbon phase 1 may contain a plurality of types of carbonaceous materials.

[0024] As described above, the composite particles 10 in the negative electrode active material according to Embodiment 1 have a configuration in which silicon particles 2 are dispersed in a carbon phase 1. The composite particles 10 may also have a configuration in which, for example, the carbon phase 1 is a porous carbon skeleton, and the silicon particles 2 are present in the pores of the porous carbon skeleton. A negative electrode active material having composite particles 10 with such a configuration can be manufactured, for example, by depositing silicon particles in the pores of a porous carbon skeleton by chemical vapor deposition (CVD). Details of the method for manufacturing a negative electrode active material using the CVD method will be described later.

[0025] The ratio of silicon (Si) in the composite particle 10 may be 40% by mass or more and 80% by mass or less, 45% by mass or more and 75% by mass or less, or 50% by mass or more and 70% by mass or less.

[0026] The ratio of Si in the composite particle 10 can be measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0027] The silicon particles 2 may be formed in a phase of elemental Si, or they may contain other elements to improve electronic conductivity, for example. If the silicon particles 2 contain elements other than Si, the state of the other elements in the silicon particles 2 is not particularly limited; for example, the other elements may be located inside the silicon particles 2 or on the surface of the silicon particles 2. The other elements may be contained in the silicon particles 2 in any form, such as atoms, elements, or compounds. Examples of other elements include Ge, Al, Ni, P, B, Sb, etc.

[0028] The silicon particles 2 may include crystalline silicon. If the silicon particles 2 include elements other than Si, they may also include crystalline silicon in which atoms of the other elements are in solid solution. The silicon particles 2 may be composed of, for example, multiple crystallites. The crystallite size of the silicon particles 2 may be 10 nm or less, 5 nm or less, or 2 nm or less. According to the above, the volume change due to the expansion and contraction of the silicon particles 2 accompanying charging and discharging can be reduced, and the improvement effect on cycle characteristics becomes more pronounced. The crystallite size of the silicon particles 2 is calculated from the full width at half maximum of the diffraction peak originating from the Si(111) plane in the X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα rays, using Scherrer's formula.

[0029] The lower limit of the crystallite size of the silicon particles 2 is not particularly limited, but one example is 1 nm. A suitable example of the crystallite size of the silicon phase 13 may be 1 nm or more and 5 nm or less. When the crystallite size of the silicon particles 2 is 1 nm or more, for example, the surface area of ​​the silicon particles 2 can be kept small, making it less likely for the silicon particles 2 to deteriorate with irreversible capacitance to occur. When the crystallite size is 5 nm or less, the expansion and contraction of the silicon particles 2 can be made more uniform, and the stress generated in the composite particles 10 is effectively relieved.

[0030] The average particle size of the composite particle 10 may be 1 μm or more and 20 μm or less, or 1 μm or more and 10 μm or less. The average particle size of the composite particle 10 refers to the particle size at which the volume integrated value in the particle size distribution measured by laser diffraction scattering method becomes 50% (hereinafter referred to as "volume-based D50"). For the measuring device, for example, the "MT3000II" manufactured by Microtrac-Bell Co., Ltd. is used, and the measurement is performed using, for example, water as the dispersion medium.

[0031] Figure 2 is a cross-sectional view showing a schematic configuration of a modified example of the composite particles contained in the negative electrode active material according to Embodiment 1. The modified example of the negative electrode active material shown in Figure 2 further comprises a coating layer 3 that covers the surface of the carbon phase 1, and the coating layer 3 contains carbon.

[0032] The composite particle 20 shown in FIG. 2 has a coating layer 3 on its surface. The coating layer 3 covers at least a part of the surface of the particle formed of the carbon phase 1 and the silicon particle 2 (hereinafter, also referred to as “parent particle”).

[0033] The coating layer 3 is composed of, for example, a carbonaceous material. Examples of the carbonaceous material include those described above for the carbon phase 1. The carbonaceous material contained in the coating layer 3 may be the same material as the carbonaceous material contained in the carbon phase 1. The coating layer 3 may be composed of a carbonaceous material made from a pitch-derived material. By having the coating layer 3 containing a conductive carbon material on the surface, the composite particle 20 can enhance its conductivity.

[0034] The thickness of the coating layer 3 is preferably thin enough not to substantially affect the average particle diameter of the composite particle 20. From the viewpoints of ensuring conductivity and the diffusibility of ions contributing to charge and discharge, the thickness of the coating layer 3 may be 0.1 nm or more and 10 nm or less, or may be 5 nm or less. The thickness of the coating layer 3 can be measured, for example, by observing the cross section of the negative electrode active material using SEM.

[0035] The composite particle contained in the negative electrode active material according to Embodiment 1 may not have the coating layer 3 like the composite particle 10 shown in FIG. 1. That is, the composite particle may consist only of the parent particle.

[0036] The negative electrode active material according to Embodiment 1 may further contain other components in addition to the above-described components. The composite particle 10 may contain other components at a ratio of more than 0 mass% and 10 mass% or less, or may contain other components at a ratio of more than 0 mass% and 5 mass% or less, or may contain other components at a ratio of more than 0 mass% and 1 mass% or less, or may contain other components at a ratio of more than 0 mass% and 0.1 mass% or less.

[0037] (Method for producing negative electrode active material) An example of a method for producing negative electrode active material according to Embodiment 1 will be described. Figure 3 is a flowchart of an example of a method for producing negative electrode active material according to Embodiment 1. As shown in Figure 3, an example of a method for producing negative electrode active material according to Embodiment 1 includes: (I) preparing a porous carbon skeleton (S1), and (II) using a silicon precursor gas as a raw material gas and precipitating silicon particles in the pores of the porous carbon skeleton by CVD at a temperature exceeding 500°C and not exceeding 700°C (S2).

[0038] According to the above manufacturing method, the composite particle comprises silicon particles dispersed in a carbon phase, and is solid 29 In the Si-NMR spectrum, a negative electrode active material can be produced in which the area ratio of peak A, whose peak top is within the range of chemical shift -30 ppm or more and -7.5 ppm or less, relative to the total area of ​​all detected peaks, exceeds 7.6%. In (II) above, by setting the temperature for depositing silicon particles in the pores of the porous carbon skeleton by the CVD method to over 500°C and 700°C or less, it is considered that O-Si-C bonds are effectively formed at the interface between the porous carbon skeleton and the silicon particles. As a result, solid 29 It is thought that the area ratio of peak A in the Si-NMR spectrum can be made to exceed 7.6%.

[0039] When producing a negative electrode active material that includes composite particles 20 further comprising a coating layer 3 covering the surface of the carbon phase 1, the method for producing the negative electrode active material may further include a step (III) of forming the coating layer 3 after step (II) above.

[0040] The following details each step.

[0041] (Step (I)) A porous carbon skeleton is prepared. The porous skeleton has a structure corresponding to carbon phase 1. Therefore, the carbon materials described as materials for carbon phase 1 can be used.

[0042] A porous carbon skeleton may be fabricated. For example, carbonizable organic materials and polymer materials can be used as carbon sources. Examples of carbonizable organic materials include plant biomass containing lignocellulosic materials (such as coconut shells and wood), coal, and fossil carbon sources. Examples of polymer materials include phenolic resins, pitch, melamine, polystyrene, polyvinyl alcohol (PVA), and polyvinylpyrrolidone (PVP).

[0043] First, the carbon source is thermally decomposed and carbonized at a predetermined temperature. Subsequently, a chemical activation process or gas activation may be performed to adjust the pore size of the porous carbon skeleton. For example, the pore volume and pore size (pore diameter) of the carbon material obtained by thermal decomposition can be adjusted by contacting it with water vapor, CO, CO2, KOH, etc., at a temperature of, for example, 600°C or higher and 1200°C or lower.

[0044] The pore volume of a porous carbon skeleton is, for example, 0.5 cm³. 3 / g or more and 3.1cm 3 It may be less than / g. The pore volume of the porous carbon skeleton can be measured, for example, by the nitrogen adsorption amount measurement method (BET method).

[0045] The pores contained in the porous carbon skeleton may have a diameter of, for example, 0.4 nm or more and 100 nm or less. The diameter of the pores contained in the porous carbon skeleton can be measured, for example, by the nitrogen adsorption measurement method (BJH method).

[0046] (Step (II)) Silicon precursor gases used as raw material gases for the deposition of silicon particles by the CVD method include, for example, dichlorosilane, trichlorosilane, disilane, silane, and trisilane. At a temperature exceeding 500°C and below 700°C, O-Si-C bonds are effectively formed at the interface between the porous carbon skeleton and the silicon particles, resulting in a solid. 29 To efficiently obtain a negative electrode active material with an area ratio of peak A exceeding 7.6% in the Si-NMR spectrum, it is desirable that the precursor gas contains dichlorosilane gas.

[0047] When a gas containing Cl, such as dichlorosilane gas, is used, the resulting negative electrode active material may further contain Cl. That is, the negative electrode active material according to Embodiment 1 may contain Cl. Cl analysis is performed, for example, using energy-dispersive X-ray (EDX). Specifically, elemental mapping analysis by EDX is performed from the backscattered electron image of the cross-section of the negative electrode active material in which the cross-section of the composite particles is exposed. The area containing Cl is calculated using image analysis software. The observation magnification is, for example, 2,000 to 20,000 times. When measuring from the state of the battery, 10 composite particles with a maximum particle diameter of 5 μm or more are randomly selected from the cross-sectional image of the backscattered electron image of the negative electrode mixture layer containing the negative electrode active material, and elemental mapping analysis by EDX is performed for each. If it is confirmed that Cl is contained in at least one particle, the negative electrode active material is determined to contain Cl.

[0048] In (II) above, silicon particles may be deposited in the pores of the porous carbon skeleton by CVD at a temperature of 530°C or higher and 650°C or lower. In (II) above, by setting the temperature for depositing silicon particles in the pores of the porous carbon skeleton by CVD to 530°C or higher and 650°C or lower, a solid 29 The area ratio of peak A in the Si-NMR spectrum can be increased, for example, to 10% or more. This makes it possible to manufacture a negative electrode active material that further suppresses expansion during charging and improves the charge-discharge cycle characteristics of the battery.

[0049] In (II) above, the temperature for depositing silicon particles in the pores of the porous carbon skeleton by the CVD method may be 550°C or higher and 600°C or lower.

[0050] In (II) above, the temperature for depositing silicon particles in the pores of the porous carbon skeleton by the CVD method may be less than 600°C. This makes it possible to set the full width at half maximum of the diffraction peak originating from the Si(111) plane of the resulting negative electrode active material to 1.8° or more. Therefore, it is possible to produce a negative electrode active material that can further improve the charge-discharge cycle characteristics of the battery by suppressing excessive crystallinity of the silicon particles 2.

[0051] In (II) above, for example, porous carbon skeleton powder is placed in a reaction vessel and oxygen is removed by flowing an inert gas (e.g., Ar gas). The reaction vessel is heated to a reaction temperature above 500°C and below 700°C. For example, while flowing dichlorosilane gas diluted with Ar at a predetermined flow rate, the porous carbon skeleton powder is stirred with a blade inside the vessel, and the reaction for Si deposition is carried out by adjusting the time required to precipitate the target mass of Si.

[0052] (Step (III)) At least a portion of the surface of the mother particles obtained in Step (II) may be coated with a conductive material to form a coating layer 3. The conductive material is preferably electrochemically stable, and a conductive carbon material is preferred. As a method for coating at least a portion of the surface of the mother particles with a conductive carbon material, a CVD method using hydrocarbon gases such as acetylene and methane as raw materials can be mentioned. Another example is a method in which coal pitch, petroleum pitch, phenolic resin, etc. are mixed with the mother particles and heated to carbonize them. The mixture of mother particles and raw materials for the conductive carbon material such as coal pitch, petroleum pitch, and phenolic resin is heated, for example, in an inert atmosphere (for example, an atmosphere such as argon or nitrogen) at a temperature of 500°C or higher and 950°C or lower. Carbon black may also be attached to the surface of the mother particles. In this way, composite particles 10 or composite particles 20 are obtained.

[0053] Subsequently, the obtained composite particles 10 or composite particles 20 may be subjected to further heat treatment at a temperature of 500°C or higher and 950°C or lower in order to grow the internal composition.

[0054] (Embodiment 2) The battery according to Embodiment 2 comprises a negative electrode, a positive electrode, and an electrolyte. The negative electrode contains the negative electrode active material according to Embodiment 1. With this configuration, the battery according to Embodiment 2 can suppress the expansion of the negative electrode due to charging and improve the charge-discharge cycle characteristics.

[0055] Figure 4 is a schematic longitudinal cross-sectional view showing an example of a battery according to Embodiment 2. The battery 100 is a cylindrical battery comprising a cylindrical battery case, a wound electrode group 54, and an electrolyte (not shown). The electrode group 54 is housed within the battery case and is in contact with the electrolyte.

[0056] The battery case consists of a case body 55, which is a bottomed cylindrical metal container, and a sealing body 56 that seals the opening of the case body 55. A gasket 67 is placed between the case body 55 and the sealing body 56. The gasket 67 ensures that the battery case is airtight. Inside the case body 55, insulating plates 57 and 58 are placed at both ends of the electrode group 54 in the winding axis direction, respectively.

[0057] The case body 55 has, for example, a stepped portion 61. The stepped portion 61 may be formed by partially pressing the side wall of the case body 55 from the outside. The stepped portion 61 may be formed in an annular shape on the side wall of the case body 55 along the circumferential direction of a virtual circle defined by the case body 55. In this case, the sealing body 56 is supported, for example, by the opening side surface of the stepped portion 61.

[0058] The sealing body 56 comprises a filter 62, a lower valve body 63, an insulating member 64, an upper valve body 65, and a cap 66. In the sealing body 56, these members are stacked in this order. The sealing body 56 is installed in the opening of the case body 55 such that the cap 66 is located on the outside of the case body 55 and the filter 62 is located on the inside of the case body 55.

[0059] Each of the above-mentioned components constituting the sealing body 56 is, for example, disc-shaped or ring-shaped. Except for the insulating member 64, each of the above-mentioned components is electrically connected to one another.

[0060] The electrode group 54 includes a positive electrode 51, a separator 52, and a negative electrode 53. The positive electrode 51, the separator 52, and the negative electrode 53 are all strip-shaped. The width direction of the strip-shaped positive electrode 51 and negative electrode 53 is, for example, parallel to the winding axis of the electrode group 54. The separator 52 is positioned between the positive electrode 51 and the negative electrode 53. The positive electrode 51 and the negative electrode 53 are wound in a spiral shape with the separator 52 interposed between them.

[0061] When observing a cross-section of the battery 100 in a direction perpendicular to the winding axis of the electrode group 54, the positive electrode 51 and the negative electrode 53 are alternately stacked in the radial direction of a virtual circle defined by the case body 55, with a separator 52 interposed between them.

[0062] The positive electrode 51 is electrically connected to the cap 66, which also serves as the positive electrode terminal, via a positive electrode lead 59. One end of the positive electrode lead 59 is connected, for example, near the center of the positive electrode 51 in the longitudinal direction. The positive electrode lead 59 extends from the positive electrode 51 to the filter 62 through a through hole formed in the insulating plate 57. The other end of the positive electrode lead 59 is welded, for example, to the side of the filter 62 facing the electrode group 54.

[0063] The negative electrode 53 is electrically connected to the case body 55, which also serves as the negative electrode terminal, via a negative electrode lead 60. One end of the negative electrode lead 60 is connected, for example, to the end of the negative electrode 53 in the longitudinal direction. The other end of the negative electrode lead 60 is welded, for example, to the inner bottom surface of the case body 55.

[0064] The components of battery 100 will be described in detail below.

[0065] The positive electrode 51 includes a material having the property of intercalating and releasing metal ions (e.g., lithium ions). The positive electrode 51 includes, for example, a positive electrode active material. The positive electrode 51 comprises, for example, a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector.

[0066] As the positive electrode current collector, a sheet or film made of a metallic material such as aluminum, stainless steel, titanium, or their alloys can be used. Aluminum and its alloys are suitable as materials for positive electrode current collectors because they are inexpensive and easy to make into thin films. The sheet or film may be porous or non-porous. Metal foil, metal mesh, etc., can be used as the sheet or film. A carbon material such as carbon may be coated on the surface of the positive electrode current collector as a conductive auxiliary material.

[0067] The positive electrode mixture layer contains a positive electrode active material. The positive electrode active material may be a material that has the ability to intercept and release metal ions (e.g., lithium ions). As the positive electrode active material, lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, transition metal oxynitrides, etc., can be used. In particular, when lithium-containing transition metal oxides or lithium-containing transition metal phosphates are used as the positive electrode active material, the manufacturing cost of the battery can be reduced and the average discharge voltage can be increased. Examples of lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

[0068] The positive electrode mixture layer may optionally contain a conductive additive, an ion conductor, and a binder.

[0069] A binder is used to improve the bonding properties of the materials constituting the electrodes. Examples of binders include polymer materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethylcellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide. At least one of these binders can be used.

[0070] Conductive additives and ionic conductors are used to reduce electrode resistance. Examples of conductive additives include carbon materials and conductive polymer compounds. Examples of carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of conductive polymer compounds include polyaniline, polypyrrole, and polythiophene. At least one of these conductive additives can be used. Examples of ionic conductors include gel electrolytes such as polymethyl methacrylate and polymethyl methacrylate, organic solid electrolytes such as polyethylene oxide, and Li7La3Zr2O 12 Examples include inorganic solid electrolytes. At least one of these ion conductors can be used.

[0071] The negative electrode 53 includes a negative electrode active material according to Embodiment 1. The negative electrode 53 comprises, for example, a negative electrode current collector and a negative electrode mixture layer supported on the surface of the negative electrode current collector.

[0072] The negative electrode current collector is a foil made of a metallic material such as stainless steel, nickel, nickel alloy, copper, or copper alloy.

[0073] The negative electrode mixture layer contains the negative electrode active material according to Embodiment 1. The negative electrode mixture layer may optionally contain other materials such as conductive additives, ion conductors, and binders. The materials described above for the positive electrode mixture layer can also be used as conductive additives, ion conductors, and binders for the negative electrode mixture layer.

[0074] The electrolyte solution used as the electrolyte may contain a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolyte solution may be, for example, 0.5 mol / liter or more and 2 mol / liter or less. By controlling the lithium salt concentration within the above range, an electrolyte solution with excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0075] As non-aqueous solvents, cyclic carbonate esters, linear carbonate esters, cyclic ethers, linear ethers, nitriles, amides, etc., may be used. One of these solvents may be used, or two or more may be used in combination.

[0076] Examples of lithium salts that can be used include lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. One of these electrolyte salts may be used, or two or more may be used in combination.

[0077] Typically, it is desirable to interpose a separator between the positive and negative electrodes. The separator 52 has high ion permeability and appropriate mechanical strength and insulating properties. As the separator 52, a microporous thin film, woven fabric, and nonwoven fabric can be used. As the material of the separator 52, for example, a polymer can be used. The polymer may be polyolefin such as polypropylene and polyethylene.

[0078] In the battery according to Embodiment 2, the electrolyte may be impregnated into a polymer provided as a separator, for example. That is, the battery according to Embodiment 2 may have a structure in which both the electrolyte and the polymer are used in combination.

[0079] The battery according to Embodiment 2 may further contain a solid electrolyte as the electrolyte. That is, the battery of this disclosure may have a hybrid structure in which an electrolyte and a solid electrolyte are used in combination. Examples of solid electrolyte materials are halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, or organic polymer solid electrolytes. In this disclosure, "halide solid electrolyte" means a solid electrolyte in which a halogen element is the main component of the anions. "Sulfide solid electrolyte" means a solid electrolyte in which sulfur is the main component of the anions. "Oxide solid electrolyte" means a solid electrolyte in which oxygen is the main component of the anions. The main component of the anions means the anion with the largest amount of substance among all the anions that make up the solid electrolyte.

[0080] As an example of the structure of the battery according to Embodiment 2, Figure 4 describes a configuration example, namely a cylindrical non-aqueous electrolyte secondary battery in which a wound-type electrode group, in which the positive and negative electrodes are wound around a separator, and an electrolyte are housed in an outer casing. However, the battery according to this disclosure is not limited to this configuration example. The battery according to Embodiment 2 may take any form, such as prismatic, coin-type, button-type, laminate-type, etc. Furthermore, as the electrode group in the battery according to Embodiment 2, other forms of electrode groups may be used instead of the wound-type electrode group, such as an electrode group in which the positive and negative electrodes are stacked with a separator.

[0081] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0082] (Technology 1) A composite particle comprising a carbon phase and silicon particles dispersed in the carbon phase, and a solid 29 A negative electrode active material in which, in the Si-NMR spectrum, the area ratio of peak A, whose peak top is within the range of chemical shift -30 ppm or more and -7.5 ppm or less, to the total area of ​​all detected peaks, exceeds 7.6%.

[0083] With this configuration, the negative electrode active material of Technology 1 can improve the charge-discharge cycle characteristics of the battery.

[0084] (Technology 2) The negative electrode active material according to Technology 1, wherein the area ratio of peak A is 10% or more.

[0085] This configuration allows the negative electrode active material of Technology 2 to further improve the charge-discharge cycle characteristics of the battery.

[0086] (Technology 3) The negative electrode active material according to Technology 1 or 2, wherein the area ratio of peak A is 50% or less.

[0087] This configuration allows the negative electrode active material of technology 3 to ensure sufficient battery capacity.

[0088] (Technical 4) The negative electrode active material according to any one of Technical 1 to 3, wherein in the X-ray diffraction pattern obtained by X-ray diffraction measurement of the negative electrode active material using Cu-Kα rays, the full width at half maximum of the diffraction peaks originating from the Si(111) plane that appear in the range of diffraction angle 2θ value of 28.0° or more and 28.7° or less is 1.8° or more.

[0089] This configuration allows the negative electrode active material of technology 4 to further improve the charge-discharge cycle characteristics of the battery.

[0090] (Technical 5) The negative electrode active material according to Technical 4, wherein the full width at half maximum is 7.0° or less.

[0091] This configuration allows the negative electrode active material of technology 5 to further improve the charge-discharge cycle characteristics of the battery.

[0092] (Technical 6) A negative electrode active material according to any one of Technical 1 to 5, further comprising Cl.

[0093] This configuration allows the negative electrode active material of technology 6 to further improve the charge-discharge cycle characteristics of the battery.

[0094] (Technical 7) A method for producing a negative electrode active material, comprising: (I) preparing a porous carbon skeleton; and (II) using a silicon precursor gas as a raw material gas and precipitating silicon particles in the pores of the porous carbon skeleton by chemical vapor deposition at a temperature exceeding 500°C and not exceeding 700°C.

[0095] This manufacturing method makes it possible to produce a negative electrode active material that can improve the charge-discharge cycle characteristics of a battery.

[0096] (Technical 8) A method for producing a negative electrode active material according to Technical 7, wherein, in (II) above, silicon particles are deposited in the pores of the porous carbon skeleton by chemical vapor deposition at a temperature of 530°C or higher and 650°C or lower.

[0097] This manufacturing method makes it possible to produce a negative electrode active material that can further improve the charge-discharge cycle characteristics of a battery.

[0098] (Technical 9) A method for producing a negative electrode active material according to Technical 7 or 8, wherein the precursor gas contains dichlorosilane gas.

[0099] This manufacturing method makes it possible to produce a negative electrode active material that can further improve the charge-discharge cycle characteristics of a battery.

[0100] (Technical 10) A battery comprising a negative electrode containing a negative electrode active material described in any one of Technical 1 to 6, a positive electrode, and an electrolyte.

[0101] This configuration allows the battery of technology 10 to improve its charge-discharge cycle characteristics.

[0102] The present disclosure will be described in more detail below with reference to examples. The following examples are merely illustrative and not limited to any one aspect.

[0103] [Preparation of Composite Particles] (Example 1) First, a porous carbon skeleton was prepared. A phenolic resin was used as the carbon source and was thermally decomposed at 900°C to obtain carbon. The obtained carbon was brought into contact with water vapor at 1000°C to adjust the pore size. The resulting porous carbon skeleton was 0.9 cm 3 The pores had a pore volume of 0.4 nm or more and a pore diameter of 60 nm or less.

[0104] Next, 10 g of the obtained porous carbon skeleton powder was placed in a quartz cylindrical reaction vessel with an inner diameter of 50 mm, and oxygen was removed by flowing inert gas (Ar) through the vessel. The reaction vessel was heated to 550°C. At this time, dichlorosilane gas diluted with Ar was diffused at 5 v / v%. The porous carbon skeleton powder was stirred with a feather inside the reaction vessel and reacted for 1.5 hours to precipitate silicon particles. The mass of precipitated Si was 13.2 g. As a result, a mother particle formed from the carbon phase and silicon particles was obtained.

[0105] As described above, the composite particles of Example 1 were obtained. Furthermore, the presence of Cl was confirmed when the cross-section of the composite particles was analyzed by SEM-EDX.

[0106] (Example 2) Composite particles were prepared in the same manner as in Example 1, except that the temperature for precipitation of silicon particles was changed from 550°C to 560°C and the reaction time was set to 55 minutes. The amount of Si deposited was 12.6 g. Furthermore, the presence of Cl was confirmed when the cross-section of the composite particles was analyzed by SEM-EDX.

[0107] (Example 3) Composite particles were prepared in the same manner as in Example 1, except that the temperature for precipitation of silicon particles was changed from 550°C to 580°C and the reaction time was set to 36 minutes. The amount of Si deposited was 13.7 g. Furthermore, the presence of Cl was confirmed when the cross-section of the composite particles was analyzed by SEM-EDX.

[0108] (Example 4) Composite particles were prepared in the same manner as in Example 1, except that the temperature for precipitation of silicon particles was changed from 550°C to 600°C and the reaction time was set to 20 minutes. The amount of Si deposited was 13.8 g. Furthermore, the presence of Cl was confirmed when the cross-section of the composite particles was analyzed by SEM-EDX.

[0109] (Comparative Example 1) Composite particles were prepared in the same manner as in Example 1, except that the temperature for precipitation of silicon particles was changed from 550°C to 500°C and the reaction time was set to 6 hours. The amount of Si deposited was 13.0 g.

[0110] [NMR] For the composite particles of Examples 1 to 4 and Comparative Example 1, solid 29 Si-NMR measurements were performed. The area ratio of peak A, whose peak top is within the chemical shift range of -30 ppm or greater and -7.5 ppm or less, to the total area of ​​all detected peaks was determined. The results are shown in Table 1. Below, solid 29 The measurement conditions and waveform separation method for Si-NMR measurement are shown below. (Measurement conditions) Measurement device: JEOL Solid State Nuclear Magnetic Resonance Spectrometer (JNM-ECA600) Probe: 8 mm CPMAS MAS: 6.0 kHz Pulse: Single pulse method Observation width: 500 ppm Observation center: Near 0 ppm Signal acquisition time: 3600 sec Number of integrations: 28 Sample amount: 500 mg (Waveform separation) The measurement data from the device was corrected for phase rotation using JEOL Delta v6.1 software, and waveform separation was performed using IGOR v9.0.5.1 fitting software. Three peaks were introduced at initial values ​​of around -80 ppm, -55 ppm, and -10 ppm, and peak fitting was performed with a Lorentzian shape to separate the waveforms.

[0111] [X-ray Diffraction] X-ray diffraction patterns of the composite particles of Examples 1 to 4 and Comparative Example 1 were obtained by powder X-ray diffraction measurement. An X-ray diffractometer (RIGAKU, MiniFlex 600) was used for the measurement. Cu-Kα rays (wavelengths 1.5405 Å and 1.5444 Å) were used as the X-ray source. The full width at half maximum of the diffraction peaks originating from the Si(111) plane was determined using the obtained X-ray diffraction patterns. The results are shown in Table 1.

[0112] [Battery Fabrication] Using the composite particles of Examples 1 to 4 and Comparative Example 1, evaluation cells for Examples 1 to 4 and Comparative Example 1 were fabricated as follows.

[0113] (Preparation of the negative electrode) A mixture of composite particles and graphite was used as the negative electrode active material, mixed in a mass ratio of 20:80. The negative electrode active material, sodium carboxymethylcellulose (CMCNa), styrene-butadiene rubber (SBR), and lithium polyacrylate were mixed in a mass ratio of negative electrode active material:CMCNa:SBR:lithium polyacrylate = 96.5:1:1.5:1. Water was added to the mixture, and it was stirred using a mixer to prepare the negative electrode slurry. Next, 1 m was applied to the surface of the copper foil. 2 The negative electrode slurry is applied so that the mass of the negative electrode mixture per unit is 190 g. After the coating is dried, it is rolled out and a density of 1.5 g / cm³ is applied to both sides of the copper foil. 3 A negative electrode was fabricated with a negative electrode mixture layer formed thereon.

[0114] The negative electrode was cut into a 20mm x 20mm shape with a 5mm x 5mm protrusion, and the negative electrode mixture layer was peeled off the protrusion to expose the copper foil. Then, a negative electrode tab lead was connected to the exposed copper foil, and a predetermined area around the outer circumference of the negative electrode tab lead was covered with an insulating film.

[0115] (Preparation of the counter electrode) Tabs were made by welding small pieces of Ni mesh to the ends. The tabs were cut to the required size, and the mesh portion was pressed onto a 300 μm thick lithium metal foil to create the counter electrode.

[0116] (Preparation of non-aqueous electrolyte) A non-aqueous electrolyte was prepared by dissolving LiPF6 in a mixed solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC = 4:1:15. The LiPF6 concentration was 1.3 mol / L.

[0117] (Cell Fabrication) Using the above-mentioned negative electrode and two counter electrodes, an evaluation cell for negative electrode regulation was fabricated as follows. The cell was fabricated in a dry air atmosphere with a dew point of -60°C or lower. An electrode group was fabricated by sandwiching the negative electrode between a pair of counter electrodes and facing the negative electrode mixture layer and lithium metal foil via a separator. Next, a rectangular piece of Al laminate film was folded in half, and the two ends on the long side were heat-sealed to form a cylinder. Then, the fabricated electrode group was inserted into the cylinder from one of the short sides of the Al laminate film, and the end face of the Al laminate film and the insulating film of each tab lead were aligned and heat-sealed. Next, 0.3 cm of electrolyte was poured from the unheat-sealed short side of the cylinder. 3 The solution was injected. After injection, the cells were left to stand for 3 minutes under reduced pressure of 0.02 MPa, and then returned to atmospheric pressure. This process was repeated twice to impregnate the negative electrode mixture layer with a non-aqueous electrolyte. Finally, the end face of the cylindrical Al laminate film on the injected side was heat-sealed under reduced pressure to obtain an evaluation cell.

[0118] [Battery Evaluation] (Charge-Discharge Cycle Characteristics) The charge-discharge cycle characteristics (capacity retention rate) of the evaluation cells for Examples 1 to 4 and Comparative Example 1 were evaluated as follows. The evaluation results are shown in Table 1.

[0119] Under an ambient temperature of 25°C, constant current charging was performed at a current of 0.1C until the voltage reached 1.0V. Subsequently, constant current discharge was performed at a current of 0.1C until the cell voltage reached 0.005V. This allowed for the evaluation of the initial charge capacity of the evaluation cells in Examples 1 to 4 and Comparative Example 1. The above charge-discharge process was performed for 300 cycles, with one cycle being considered as one unit, and the capacity retention rate was calculated using the following formula: Capacity retention rate [%] = (Discharge capacity at 300th cycle / Discharge capacity at 1st cycle) × 100

[0120] (Measurement of the expansion rate of the negative electrode during charging) For the negative electrodes of Examples 1 to 4 and Comparative Example 1, the expansion rate during charging was determined by the following method. The evaluation cell was disassembled after charging, and the negative electrode was removed. The thickness of the negative electrode in the charged state (fully charged state) (T) and the thickness of the negative electrode in the discharged state (completely discharged state) (T0) were determined. The rate of increase in thickness of the negative electrode in the charged state relative to the thickness of the negative electrode in the discharged state (T × 100 / T0 - 100) was calculated and expressed as the expansion rate of the negative electrode during charging (%). The results are shown in Table 1.

[0121]

[0122] As shown in Table 1, solid 29 The negative electrodes using the negative electrode active materials of Examples 1 to 4, in which the area ratio of peak A in the Si-NMR spectrum exceeded 7.6%, exhibited a lower expansion rate during charging compared to the negative electrode using the negative electrode active material of Comparative Example 1, in which the area ratio of peak A was 7.6% or less. Furthermore, batteries equipped with negative electrodes using the negative electrode active materials of Examples 1 to 4 showed improved charge-discharge cycle characteristics compared to batteries equipped with the negative electrode using the negative electrode active material of Comparative Example 1.

[0123] The negative electrode active materials of Examples 1 to 3, which had a Si full width at half maximum (FWHM) of 1.8° or more, showed improved charge-discharge cycle characteristics compared to the negative electrode active material of Example 4, which had a Si FWHM of less than 1.8°.

[0124] From the above, it has been confirmed that the charge-discharge cycle characteristics of a battery can be improved by using the negative electrode active material of this disclosure.

[0125] The technology disclosed herein can be used in batteries such as lithium-ion secondary batteries.

Claims

Carbon phase and, Silicon particles dispersed in the carbon phase, Composite particles comprising, solid 29 In the Si-NMR spectrum, the area ratio of peak A, whose peak top is within the chemical shift range of -30 ppm or more and -7.5 ppm or less, to the total area of ​​all detected peaks exceeds 7.6%. Negative electrode active material. 　 The area ratio of the aforementioned peak A is 10% or more. The negative electrode active material according to claim 1. 　 The area ratio of the aforementioned peak A is 50% or less. The negative electrode active material according to claim 1. 　 In the X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα rays of the negative electrode active material, the full width at half maximum of the diffraction peaks originating from the Si(111) plane that appear in the range of diffraction angle 2θ of 28.0° or more and 28.7° or less is 1.8° or more. The negative electrode active material according to claim 1. 　 The aforementioned full width at half maximum is 7.0° or less. The negative electrode active material according to claim 4. 　 Further containing Cl, The negative electrode active material according to claim 1. (I) Preparing a porous carbon skeleton, and (II) Using a silicon precursor gas as a raw material gas, silicon particles are deposited in the pores of the porous carbon skeleton by chemical vapor deposition at a temperature exceeding 500°C and not exceeding 700°C. A method for producing a negative electrode active material, including the material itself. 　 In (II) above, the silicon particles are deposited in the pores of the porous carbon skeleton by chemical vapor deposition at a temperature of 530°C or higher and 650°C or lower. A method for producing a negative electrode active material according to claim 7. 　 The aforementioned precursor gas includes dichlorosilane gas. A method for producing a negative electrode active material according to claim 7. 　 A negative electrode comprising the negative electrode active material according to any one of claims 1 to 6, Positive electrode and, Electrolytes, A battery equipped with a battery.

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