Carbon particles for negative electrode, carbon-silicon composite material for negative electrode, negative electrode active material, and battery

Abstract

Carbon particles for a negative electrode according to the present disclosure are porous and have a pore volume of 1.0 cm 3 / g or more, contain at least one element selected from the group consisting of Na, K, Ca, Sr, and Ba, and the content of the at least one element is 0.003 mass% or more. The carbon particles for a negative electrode according to the present disclosure are suitable for efficient precipitation of silicon on the particles.

Description

Carbon particles for negative electrodes, carbon-silicon composite materials for negative electrodes, negative electrode active materials, and batteries

[0001] This disclosure relates to carbon particles for negative electrodes, carbon-silicon composite materials for negative electrodes, negative electrode active materials, and batteries.

[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-containing negative electrode active materials are effective in increasing the capacity of batteries. However, silicon-containing negative electrode active materials undergo large volume changes with charging and discharging, so repeated charging and discharging can break the conductive path with surrounding active materials, resulting in capacity degradation with charge-discharge cycles. Therefore, Patent Document 1 proposes a silicon-containing negative electrode active material that can improve cycle stability. Specifically, Patent Document 1 proposes silicon-carbon composite particles in which the concentration of alkali metals or alkaline earth metals and the pH are within a predetermined range. The composite particles of Patent Document 1 are formed by precipitating silicon on porous carbon particles.

[0004] Japanese Patent Publication No. 2024-503167

[0005] Patent Document 1 does not address the efficient deposition of silicon onto carbon particles.

[0006] Therefore, this disclosure provides carbon particles for a negative electrode that are suitable for efficient silicon deposition onto the particles.

[0007] This disclosure is porous and 1.0 cm 3 The present invention provides carbon particles for negative electrodes, having a pore volume of 0.003% by mass or more, containing at least one element selected from the group consisting of Na, K, Ca, Sr, and Ba, and having a content of at least one element of 0.003% by mass or more.

[0008] The carbon particles of this disclosure are carbon particles for use as a negative electrode and are suitable for efficient silicon deposition onto the particles.

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

[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 carbon particles according to Embodiment 1 are porous and 1.0 cm 3 The particles have a pore volume of 1 / g or more and contain at least one element selected from the group consisting of Na, K, Ca, Sr, and Ba (hereinafter referred to as "element A"). The content of element A in the carbon particles according to Embodiment 1 is 0.003% by mass or more. The carbon particles according to Embodiment 1 are particles for a negative electrode. A negative electrode is typically the negative electrode of a battery.

[0012] In the carbon particles according to Embodiment 1, efficient silicon precipitation, typically an increase in the amount of silicon precipitated, can be achieved. According to the inventors' studies, 1.0 cm 3 The fact that carbon particles have a pore volume of 1 / g or more corresponds to the presence of a relatively large amount of space in the carbon particles where silicon can be deposited. Furthermore, element A belongs to the alkali metal or alkaline earth metal elements and may have catalytic activity for reactions that precipitate silicon particles, such as the thermal decomposition reaction of precursor gases. To increase the amount of silicon deposited, 1.0 cm 3 It is presumed that both a pore volume of 0.003% by mass or more and an element A content of 0.003% by mass or more work synergistically.

[0013] The content of element A in the carbon particles may be 0.004% by mass or more, 0.005% by mass or more, 0.007% by mass or more, 0.009% by mass or more, 0.01% by mass or more, 0.012% by mass or more, 0.014% by mass or more, 0.015% by mass or more, 0.017% by mass or more, 0.019% by mass or more, and even 0.02% by mass or more. The upper limit of the content is, for example, 1.0% by mass or less, and may be 0.9% by mass or less, 0.7% by mass or less, 0.5% by mass or less, 0.4% by mass or less, 0.3% by mass or less, 0.2% by mass or less, 0.1% by mass or less, 0.09% by mass or less, 0.07% by mass or less, 0.05% by mass or less, 0.04% by mass or less, 0.03% by mass or less, and even 0.02% by mass or less.

[0014] The content of element A in carbon particles can be determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). Semi-quantitative analysis may also be used for determination.

[0015] Element A may contain at least one element selected from the group consisting of Na, K, and Ca, or at least two elements selected from the group consisting of Na, K, and Ca. Element A may contain at least one element selected from the group consisting of Na and K, or at least one element selected from the group consisting of K and Ca. Element A may contain K. Carbon particles may contain one or more elements A. Carbon particles containing two or more elements A may contain K or Ca as the element A with the highest content, or may contain K. When carbon particles contain two or more elements A, the content of element A in the carbon particles is the sum (total amount) of the content of each element A contained. In carbon particles containing two or more elements A, the content of the element A with the highest content may be 0.003 mass% or more. Furthermore, at least one selected from the upper and lower limits of the content of the element A with the highest content may be within the above-mentioned ranges as the upper limit of the content of element A in carbon particles.

[0016] The pore volume of carbon particles is 1.1 cm 3 / g or more, 1.2cm 3 / g or more, 1.3cm 3 / g or more, 1.4cm 3above 1.5 cm / g 3 above 1.6 cm / g 3 above 1.8 cm / g 3 above 2.0 cm / g 3 above 2.2 cm / g 3 above 2.4 cm / g 3 above 2.5 cm / g 3 above 2.6 cm / g 3 above 2.7 cm / g or more. The upper limit of the pore volume may be, for example, 4.0 cm 3 / g or less, and may be 3.9 cm 3 / g or less, 3.7 cm 3 / g or less, 3.5 cm 3 / g or less, 3.4 cm 3 / g or less, 3.2 cm 3 / g or less, 3.1 cm 3 / g or less, and further may be 3.0 cm 3 / g or less. 3 / g or less may also be acceptable.

[0017] The pore volume of the carbon particles can be determined, for example, by nitrogen adsorption measurement (BET method).

[0018] The carbon particles according to Embodiment 1 are porous, and more specifically, have a porous skeleton. The skeleton of the carbon particles is a matrix containing carbon. The carbon particles contain, for example, a carbonaceous material. The carbonaceous material may be a material capable of occluding lithium ions. This aspect is suitable for use as a negative electrode active material of a carbon-silicon composite material in which silicon is deposited. The carbonaceous material may be amorphous. The carbon particles 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, etc. The pitch is, for example, coal pitch or petroleum pitch, and the coal pitch is, for example, coal tar pitch. The carbon particles may contain a plurality of types of carbonaceous materials.

[0019] The average particle diameter of carbon particles may be 1 μm or more and 100 μm or less, 1 μm or more and 75 μm or less, 1 μm or more and 50 μm or less, 1 μm or more and 25 μm or less, 1 μm or more and 20 μm or less, or even 1 μm or more and 10 μm or less. The average particle diameter of carbon particles can be determined by analyzing the observed image of carbon particles using a scanning electron microscope (SEM). However, the analysis should be performed on at least 10 carbon particles, and the average value should be taken as the average particle diameter.

[0020] [Embodiment 2] Figure 1 is a cross-sectional view showing the schematic configuration of a carbon-silicon composite material 10 according to Embodiment 2. The carbon-silicon composite material 10 includes carbon particles 1 according to Embodiment 1 and silicon particles 2 dispersed inside the carbon particles 1. The silicon particles 2 are typically located inside the pores of the carbon particles 1. The carbon-silicon composite material 10 is usually a particle, or in other words, usually a carbon-silicon composite particle. The carbon-silicon composite material 10 is suitable for use as a component of a battery, for example, as a negative electrode active material. In the carbon-silicon composite material 10, since the silicon particles 2 are dispersed inside the carbon particles 1, the expansion of the silicon particles 2 during charging is mitigated by the carbon particles 1. That is, the carbon-silicon composite material 10, with its configuration including carbon particles 1 and silicon particles 2 dispersed inside the carbon particles 1, is suitable for suppressing expansion during charging. Depending on the pore size and other pore conditions of carbon particle 1, silicon particles 2 may be observed to be deposited in layers inside the pores.

[0021] The proportion of silicon in the carbon-silicon composite material 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. The proportion of silicon in the carbon-silicon composite material 10 can be determined by ICP-AES.

[0022] The silicon particles 2 may be formed in the phase of elemental silicon. The silicon particles 2 may further contain other elements besides silicon. Containing other elements may contribute to improving the electron conductivity. When the silicon particles 2 contain other elements besides silicon, 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, simple substances, compounds, etc. Examples of the other elements include Ge, Al, Ni, P, B, Sb, etc.

[0023] The silicon particles 2 may contain crystalline silicon. When the silicon particles 2 contain other elements besides silicon, crystalline silicon in which atoms of the other elements are solid-dissolved may be contained. The silicon particles 2 may be composed of, for example, a plurality of crystallites. The crystallite size of the silicon particles 2 may be 10 nm or less, 5 nm or less, or 2 nm or less. The above aspect is particularly suitable for reducing the volume change due to the expansion and contraction of the silicon particles 2 accompanying charge and discharge. The crystallite size of the silicon particles 2 can be calculated from the half-value width of the diffraction peak derived from the Si(111) plane in the X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα rays according to Scherrer's formula.

[0024] The lower limit value of the crystallite size of the silicon particles 2 is not particularly limited, but as an example, it is 1 nm. An example of a suitable crystallite size of the silicon particles 2 may be 1 nm or more and 5 nm or less. The crystallite size of the silicon particles 2 being 1 nm or more can, for example, contribute to suppressing the deterioration of the silicon particles 2 accompanied by the generation of irreversible capacity by keeping the surface area of the silicon particles 2 small. The crystallite size being 5 nm or less can contribute to equalizing the expansion and contraction of the silicon particles 2, thereby effectively relaxing the stress generated in the carbon-silicon composite material 10.

[0025] The silicon particles 2 may be nanoparticles. The average particle diameter of the silicon particles 2 may be 50 nm or more and 300 nm or less, may be 100 nm or more and 200 nm or less, or may be 100 nm or more and 150 nm or less. The average particle diameter of the silicon particles 2 can be specified by analyzing the observation image of the carbon-silicon composite material 10 by SEM. However, the analysis is performed on the observation image in which the cross-section of the silicon particles 2 is exposed. The maximum major axis is evaluated for at least 10 silicon particles 2, and the average thereof is taken as the average particle diameter.

[0026] The average particle diameter of the carbon-silicon composite material 10 may be 1 μm or more and 20 μm or less, or may be 1 μm or more and 10 μm or less. The average particle diameter of the carbon-silicon composite material 10 can be specified in the same manner as, for example, the average particle diameter of the carbon particles 1.

[0027] The pH of the carbon-silicon composite material 10 may be less than 7.5, may be 7.2 or less, 7 or less, 6.7 or less, 6.5 or less, 6.2 or less, or even 6 or less. The pH of the carbon-silicon composite material 10 can be specified in accordance with Method A defined in ASTM D1512.

[0028] FIG. 2 is a cross-sectional view showing a schematic configuration of a modified example of the carbon-silicon composite material according to Embodiment 2. The modified example shown in FIG. 2 further includes a coating layer 3 that covers the surface of the carbon particles 1. The coating layer 3 may contain carbon. The configuration of the carbon-silicon composite material 20 shown in FIG. 2 may be the same as the configuration of the carbon-silicon composite material 10 shown in FIG. 1 except for including the coating layer 3. Redundant descriptions are omitted.

[0029] The carbon-silicon composite material 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 carbon-silicon composite material 20 (hereinafter, also referred to as "mother material") including the carbon particles 1 and the silicon particles 2. The mother material is usually a particle.

[0030] The coating layer 3 is composed of, for example, a carbonaceous material. Examples of carbonaceous materials include those described above for the carbon particles 1. The carbonaceous material contained in the coating layer 3 may be the same material as the carbonaceous material contained in the carbon particles 1. The coating layer 3 may also be composed of a carbonaceous material made from pitch-derived material. A carbon-silicon composite material 20 having a coating layer 3 containing a conductive carbon material on its surface is suitable for enhancing conductivity.

[0031] The thickness of the coating layer 3 is preferably thin enough not to substantially affect the average particle size of the silicon-carbon composite material 20. From the viewpoint of ensuring conductivity and ion diffusion that contributes to charging and discharging, the thickness of the coating layer 3 may be 0.1 nm or more and 10 nm or less, or 5 nm or less. The thickness of the coating layer 3 can be measured, for example, by cross-sectional observation of the silicon-carbon composite material 20 using a scanning electron microscope (SEM).

[0032] The silicon-carbon composite material according to Embodiment 2 does not necessarily have a coating layer 3, as shown in Figure 1. In other words, the silicon-carbon composite material may consist only of the matrix material.

[0033] The silicon-carbon composite material according to Embodiment 2 may further contain other components in addition to the components described above. The silicon-carbon composite material 10 may contain the other components in a proportion of more than 0% by mass and 10% by mass or less, more than 0% by mass and 5% by mass or less, more than 0% by mass and 1% by mass or less, or more than 0% by mass and 0.1% by mass or less.

[0034] (Method for manufacturing carbon-silicon composite material) An example of a method for manufacturing a carbon-silicon composite material according to Embodiment 2 will be described. Figure 3 is a flowchart showing an example of a method for manufacturing a carbon-silicon composite material according to Embodiment 2. As shown in Figure 3, an example of a method for manufacturing a carbon-silicon composite material according to Embodiment 2 is: (I) porous and 1.0 cm 3 (S1) Preparing carbon particles having a pore volume of / g and containing element A in a content of 0.003% by mass or more; and (II) Depositing silicon particles into the pores of the carbon particles by chemical vapor deposition (CVD) using a precursor gas containing silicon as a raw material gas (S2).

[0035] When manufacturing a carbon-silicon composite material 20 further comprising a coating layer 3 that covers the surface of carbon particles 1, the method for manufacturing the carbon-silicon composite material may include a step (III) of forming the coating layer 3 after step (II) above.

[0036] The following details each step.

[0037] (Step (I)) Porous carbon particles are prepared. However, 1.0 cm 3 Carbon particles are prepared having a pore volume of 1 / g and containing element A in a desired content of 0.003% by mass or more. Examples of element A, including preferred embodiments, are as described above. Examples of the types of carbon particles to be prepared are the same as those described above.

[0038] The carbon particles to be prepared may be made by carbonizing a carbon-containing material (carbon source). 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).

[0039] An example of carbon particle production by carbonization is described below. First, a carbon source is thermally decomposed at a predetermined temperature to induce carbonization. Subsequently, a chemical activation process or gas activation may be performed to adjust the pore size of the carbon particles. 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.

[0040] The pores contained in the prepared carbon particles may have a diameter of, for example, 0.4 nm or more and 100 nm or less. The pore diameter can be measured, for example, by a nitrogen adsorption measurement method (BJH method).

[0041] (Process (II)) The precursor gas used as a raw material gas for the deposition of silicon particles by the CVD method contains silicon. Examples of precursor gases include monosilane, disilane, trisilane, dichlorosilane, and trichlorosilane.

[0042] When a gas containing chlorine, such as dichlorosilane gas, is used, the resulting silicon carbon composite material may further contain chlorine. That is, the silicon carbon composite material according to Embodiment 2 may contain chlorine. Chlorine analysis can be 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 composite material. The area containing chlorine can be calculated using image analysis software. The observation magnification is, for example, 2,000 to 20,000 times. When evaluating from the state of the battery, 10 composite materials with a maximum diameter of 5 μm or more are randomly selected from the cross-sectional image of the backscattered electron image of the negative electrode composite layer containing the negative electrode active material, and elemental mapping analysis by EDX is performed on each. If it is confirmed that chlorine is contained in at least one composite material, the silicon carbon composite material can be determined to contain chlorine.

[0043] In step (II), silicon particles may be precipitated into the pores of carbon particles by CVD at a temperature of 400°C or higher and 700°C or lower. The temperature may be 450°C or higher and 700°C or lower, 500°C or higher and 650°C or lower, 530°C or higher and 650°C or lower, or 530°C or higher and less than 600°C.

[0044] In step (II), for example, carbon particles are 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 of, for example, 400°C or higher and 700°C or lower. For example, dichlorosilane gas diluted with Ar is flowed at a predetermined flow rate while stirring the carbon particles with a blade inside the vessel to adjust the time required to precipitate the target mass of silicon. In this way, the reaction for silicon particle precipitation is carried out.

[0045] (Step (III)) At least a portion of the surface of the base material 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 desirable. As a method for coating at least a portion of the surface of the base material 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 base material and heated to carbonize it. The mixture of the base material and the raw material of the conductive carbon material such as coal pitch, petroleum pitch, and phenolic resin is heated in an inert atmosphere (for example, an atmosphere such as argon or nitrogen) at a temperature of 400°C or higher and 950°C or lower. Carbon black may also be attached to the surface of the base material. In this way, a carbon-silicon composite material 10 or a carbon-silicon composite material 20 is obtained.

[0046] Subsequently, the obtained carbon-silicon composite material 10 or carbon-silicon composite material 20 may be subjected to further heat treatment at a temperature of 400°C or higher and 950°C or lower to promote growth of its internal composition.

[0047] The method for producing the carbon-silicon composite material according to Embodiment 2 is not limited to the above example.

[0048] [Embodiment 3] The negative electrode active material according to Embodiment 3 includes the carbon-silicon composite material according to Embodiment 2. The negative electrode active material according to Embodiment 3 may also include materials other than the carbon-silicon composite material according to Embodiment 2. For materials other than the carbon-silicon composite material, materials known as negative electrode active materials may be used. An example of a material other than the carbon-silicon composite material is a carbon material such as graphite. The main component of the negative electrode active material according to Embodiment 3 may be the carbon-silicon composite material according to Embodiment 2, or a material other than the carbon-silicon composite material. In this specification, the main component means the component with the largest content. The content of the main component may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, and even 99% by mass or more.

[0049] [Embodiment 4] The battery according to Embodiment 4 comprises a negative electrode, a positive electrode, and an electrolyte. The negative electrode contains the negative electrode active material according to Embodiment 3. With this configuration, the battery according to Embodiment 4 can be in a state suitable for suppressing the expansion of the negative electrode due to charging.

[0050] Figure 4 is a schematic longitudinal cross-sectional view showing an example of a battery according to Embodiment 4. 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 inside the battery case and is in contact with the electrolyte.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] The components of battery 100 will be described in detail below.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] The positive electrode mixture layer may optionally contain a conductive additive, an ion conductor, and a binder.

[0064] 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.

[0065] 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.

[0066] The negative electrode 53 includes a carbon-silicon composite material according to Embodiment 2. In other words, the negative electrode 53 may include a negative electrode active material according to Embodiment 3. 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.

[0067] The negative electrode current collector is a foil made of a metallic material such as stainless steel, nickel, nickel alloy, copper, or copper alloy.

[0068] The negative electrode mixture layer contains the carbon-silicon composite material according to Embodiment 2. In other words, the negative electrode mixture layer may also contain the negative electrode active material according to Embodiment 3. 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] In the battery according to Embodiment 4, the electrolyte may be impregnated into a polymer provided as a separator, for example. That is, the battery according to Embodiment 4 may have a structure in which both the electrolyte and the polymer are used in combination.

[0074] The battery according to Embodiment 4 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.

[0075] As an example of the structure of the battery according to Embodiment 4, Figure 4 describes a configuration example, namely a cylindrical non-aqueous electrolyte secondary battery in which a wound electrode group, in which a positive electrode and a negative electrode 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 4 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 4, other forms of electrode groups may be used instead of the wound electrode group, such as an electrode group in which a positive electrode and a negative electrode are stacked with a separator.

[0076] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0077] (Technology 1) Porous, 1.0 cm 3 Carbon particles for negative electrodes having a pore volume of 1 / g or more, containing at least one element selected from the group consisting of Na, K, Ca, Sr, and Ba, and having a content of 0.003% by mass or more of the at least one element.

[0078] (Technology 2) Carbon particles according to Technology 1, wherein the content of at least one of the elements is 0.005% by mass or more.

[0079] (Technology 3) Carbon particles according to Technology 1 or 2, wherein the content of at least one element is 0.1% by mass or less.

[0080] (Technical 4) Carbon particles according to any one of Technical 1 to 3, wherein at least one of the elements is K.

[0081] (Technology 5) 1.5cm 3 Carbon particles according to any one of the technologies 1 to 4, having a pore volume of 1 / g or more.

[0082] (Technology 6) 2.0cm 3 Carbon particles according to any one of the technologies described in 1 to 5, having a pore volume of 1 / g or more.

[0083] (Technical 7) Carbon particles according to any one of Technical 1 to 6, having an average particle diameter of 1 μm or more and 100 μm or less.

[0084] (Technical 8) A carbon-silicon composite material for a negative electrode, comprising carbon particles as described in any one of Technical 1 to 7, and silicon particles dispersed inside the carbon particles.

[0085] (Technical 9) A negative electrode active material comprising the carbon-silicon composite material described in Technical 8.

[0086] (Technical 10) A battery comprising a negative electrode containing the negative electrode active material described in Technical 9, a positive electrode, and an electrolyte.

[0087] 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.

[0088] <Example 1> The total content of element A (at least one selected from the group consisting of Na, K, Ca, Sr, and Ba) is 0.0031% by mass, and 1.10 cm 3 Porous carbon particles with a pore volume of 1 / g were prepared. The content of element A in the prepared carbon particles was determined by semi-quantitative analysis using ICP-AES (the same method is used in subsequent examples). The pore volume of the prepared carbon particles was determined by the nitrogen adsorption method (BET method) (the same method is used in subsequent examples).

[0089] Next, 0.05 g of the prepared carbon particles were placed in a quartz cylindrical tubular furnace with an inner diameter of 50 mm using a glass boat, and the atmosphere inside the furnace was replaced with nitrogen by flowing nitrogen through it. Then, after stopping the inflow of nitrogen, the furnace temperature was raised to 540°C while simultaneously flowing dichlorosilane gas at a flow rate of 3 sccm and hydrogen at a flow rate of 10 sccm into the furnace as silicon precursor gases, and the decomposition reaction of the silicon precursor gases was carried out for 80 minutes. As a result, silicon particles were deposited inside the carbon particles, and the carbon-silicon composite material of Example 1 was obtained.

[0090] The ratio of silicon mass to total mass of the obtained carbon-silicon composite material was evaluated by thermomass (TG) measurement (the evaluation method is the same in subsequent examples). Based on the above ratio, the mass of silicon precipitated per gram of carbon was calculated to be 1.04 g.

[0091] <Example 2> The total amount of element A is 0.11% by mass, and 1.16 cm 3 A carbon-silicon composite material of Example 2 was obtained in the same manner as in Example 1, except that porous carbon particles having a pore volume of 1 / g were prepared and used. In the carbon-silicon composite material of Example 2, the mass of silicon precipitated per gram of carbon was 1.11 g.

[0092] <Example 3> The total amount of element A is 0.0056% by mass, and 1.23 cm 3 A carbon-silicon composite material of Example 3 was obtained in the same manner as in Example 1, except that porous carbon particles having a pore volume of 1 / g were prepared and used. In the carbon-silicon composite material of Example 3, the mass of silicon precipitated per gram of carbon was 1.16 g.

[0093] <Example 4> The total amount of element A is 0.13% by mass, and 1.69 cm 3 A carbon-silicon composite material of Example 4 was obtained in the same manner as in Example 1, except that porous carbon particles having a pore volume of 1 / g were prepared and used. In the carbon-silicon composite material of Example 4, the mass of silicon precipitated per gram of carbon was 1.22 g.

[0094] <Example 5> The total amount of element A is 0.020% by mass, and 2.78 cm3 A carbon-silicon composite material of Example 5 was obtained in the same manner as in Example 1, except that porous carbon particles having a pore volume of 1 / g were prepared and used. In the carbon-silicon composite material of Example 5, the mass of silicon precipitated per gram of carbon was 1.94 g.

[0095] <Example 6> The total amount of element A is 0.020% by mass, and 2.83 cm 3 A carbon-silicon composite material of Example 6 was obtained in the same manner as in Example 1, except that porous carbon particles having a pore volume of 1 / g were prepared and used. In the carbon-silicon composite material of Example 6, the mass of silicon precipitated per gram of carbon was 1.97 g.

[0096] <Comparative Example 1> The total amount of element A is 0.0003% by mass, and 1.09 cm 3 A carbon-silicon composite material of Comparative Example 1 was obtained in the same manner as in Example 1, except that porous carbon particles having a pore volume of 1 / g were prepared and used. In the carbon-silicon composite material of Comparative Example 1, the mass of silicon precipitated per gram of carbon was 0.78 g.

[0097] <Comparative Example 2> The total amount of element A is 0.0020% by mass, and 1.89 cm 3 A carbon-silicon composite material of Comparative Example 2 was obtained in the same manner as in Example 1, except that porous carbon particles having a pore volume of 1 / g were prepared and used. In the carbon-silicon composite material of Comparative Example 2, the mass of silicon precipitated per gram of carbon was 0.73 g.

[0098] <Comparative Example 3> The total amount of element A is 0.0043% by mass, and 0.72 cm 3 A carbon-silicon composite material of Comparative Example 3 was obtained in the same manner as in Example 1, except that porous carbon particles having a pore volume of 1 / g were prepared and used. In the carbon-silicon composite material of Comparative Example 3, the mass of silicon precipitated per gram of carbon was 0.96 g.

[0099] <Comparative Example 4> The total amount of element A is 1.0% by mass, and 0.60 cm 3A carbon-silicon composite material of Comparative Example 4 was obtained in the same manner as in Example 1, except that porous carbon particles having a pore volume of 1 / g were prepared and used. In the carbon-silicon composite material of Comparative Example 4, the mass of silicon precipitated per gram of carbon was 0.84 g.

[0100] The results of the examples and comparative examples are summarized in Table 1. Table 1 also shows the content of each element A in the carbon particles, including Na, K, Ca, Sr, and Ba.

[0101]

[0102] As shown in Table 1, the total amount of element A is 0.003% by mass or more, and the pore volume is 1.0 cm³. 3 In the carbon particles of the example that satisfied both / g, ​​the amount of silicon precipitated per gram of carbon increased compared to the carbon particles of the comparative example that did not satisfy at least one of the group selected from the group consisting of element A content and pore volume.

[0103] From the above, it has been confirmed that the carbon particles of this disclosure are suitable for increasing the amount of silicon precipitated on the particles.

[0104] The technology disclosed herein can be used in batteries such as lithium-ion secondary batteries.

Claims

1. Porous, 1.0 cm 3 Carbon particles for negative electrodes having a pore volume of 1 / g or more, containing at least one element selected from the group consisting of Na, K, Ca, Sr, and Ba, and having a content of 0.003% by mass or more of the at least one element.

2. The carbon particles according to claim 1, wherein the content of at least one of the elements is 0.005% by mass or more.

3. The carbon particles according to claim 1, wherein the content of at least one of the elements is 0.1% by mass or less.

4. The carbon particle according to claim 1, wherein at least one of the elements includes K.

5. 1.5 cm 3 Carbon particles according to claim 1, having a pore volume of 1g or more.

6. 2.0 cm 3 Carbon particles according to claim 1, having a pore volume of 1g or more.

7. Carbon particles according to claim 1, having an average particle diameter of 1 μm or more and 100 μm or less.

8. A carbon-silicon composite material for a negative electrode, comprising carbon particles according to any one of claims 1 to 7 and silicon particles dispersed inside the carbon particles.

9. A negative electrode active material comprising the carbon-silicon composite material described in claim 8.

10. A battery comprising a negative electrode containing the negative electrode active material described in claim 9, a positive electrode, and an electrolyte.

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