Negative electrode active material, method for producing same, negative electrode composite material, and secondary battery

Abstract

The invention relates to a negative electrode active material, a method for producing the same, a negative electrode composite material, and a secondary battery. Provided are: a negative electrode active material capable of suppressing a change in volume of the negative electrode active material, improving cycle characteristics of a battery, and / or suppressing expansion of the negative electrode active material during initial charging; and a method for producing the negative electrode active material. A negative electrode composite material containing such a negative electrode active material; and a secondary battery containing such a negative electrode composite material. This negative electrode active material (10) has a composite material containing a carbon material (11) and a tin alloy (12). The tin alloy in the negative electrode active material of the present invention is an alloy containing tin and at least one metal selected from the group consisting of cobalt, iron, copper and nickel, the content of the carbon material is 10-30 mass%, and the half-peak width of the tin alloy in the XRD spectrum is 0.3 DEG or more. This negative electrode active material has a hole (14) in an amount of 0.5-40% by volume (inclusive).

Description

Technical Field

[0001] The invention relates to a negative electrode active material and a method for producing the same, a negative electrode composite material and a secondary battery. Background Art

[0002] As disclosed in Patent Documents 1 and 2, negative electrode materials containing an element capable of forming an alloy such as an intermetallic compound with lithium and a carbon material are known in order to improve the cycle characteristics of a battery.

[0003] However, it is known that when silicon and tin are used as negative electrode active materials, the volume of the negative electrode active material changes with the charge and discharge of the battery, thereby deteriorating the cycle characteristics of the battery. In order to suppress this volume change, as disclosed in Patent Documents 3 and 4, a technology for forming gaps (holes) in the negative electrode active material has been developed.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2004 / 100291

[0007] Patent Document 2: International Publication No. 2004 / 100293

[0008] Patent Document 3: International Publication No. 2013 / 146658

[0009] Patent Document 4: Japanese Patent Application Publication No. 2011-249173 Summary of the invention

[0010] Problems to be solved by the invention

[0011] There is room for improvement in suppressing the volume change of the negative electrode active material.

[0012] The object of the present invention is to provide a negative electrode active material and a method for manufacturing the negative electrode active material, a negative electrode composite material containing such a negative electrode active material, and a secondary battery containing such a negative electrode composite material, which can suppress the volume change of the negative electrode active material and thus improve the cycle characteristics of the battery and / or can suppress the expansion of the negative electrode active material during the initial charge.

[0013] Methods used to solve problems

[0014] The inventors of the present application have discovered that the above-mentioned problems can be solved by the following means.

[0015] <Method 1>

[0016] A negative electrode active material comprises a composite material containing a carbon material and a tin alloy,

[0017] The tin alloy is an alloy containing tin and at least one metal selected from cobalt, iron, copper and nickel.

[0018] The content of the carbon material is 10 mass % or more and 30 mass % or less,

[0019] The half-peak width of the tin alloy in the XRD spectrum is 0.3° or more, and

[0020] The negative electrode active material has 0.5 volume % or more and 40 volume % or less of holes.

[0021] <Method 2>

[0022] The negative electrode active material according to embodiment 1, further comprising silicon carbide and metallic silicon.

[0023] The content of the metal silicon is 0.1 mass % or more and 15 mass % or less, and

[0024] The ratio of the peak intensity of the silicon carbide to the peak intensity of the metal silicon in the XRD spectrum is 1.0 or more.

[0025] <Method 3>

[0026] The negative electrode active material according to aspect 1 or 2, further comprising silicon oxide.

[0027] <Method 4>

[0028] A negative electrode composite material comprising the negative electrode active material according to any one of aspects 1 to 3.

[0029] <Method 5>

[0030] A secondary battery comprises a negative electrode active material layer, wherein the negative electrode active material layer contains the negative electrode composite material according to embodiment 4.

[0031] <Method 6>

[0032] The method for producing a negative electrode active material according to any one of Embodiments 1 to 3 comprises the following steps:

[0033] The carbon material, the tin and the metal are mixed by mechanical alloying to obtain the composite material;

[0034] The composite material and metal silicon and / or silicon oxide are mixed by mechanical alloying to obtain a negative electrode active material precursor;

[0035] The negative electrode active material precursor is brought into contact with an alkaline aqueous solution to dissolve the metal silicon and / or silicon oxide, thereby forming the holes.

[0036] Effects of the Invention

[0037] According to the present invention, there can be provided a negative electrode active material which can suppress the volume change of the negative electrode active material and thus improve the cycle characteristics of the battery and / or can suppress the expansion of the negative electrode active material during initial charging, a negative electrode composite material containing such a negative electrode active material, and a secondary battery containing such a negative electrode composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram showing an example of the production process of the negative electrode active material of the present invention ((a) composite material production step, (b) negative electrode active material precursor production step, (c) hole formation step).

[0039] Figure 2 This is a schematic cross-sectional view showing an example of the secondary battery of the present invention.

[0040] Figure 3 This is a cross-sectional SEM image of the negative electrode active material of the present invention in the secondary battery of Example 1-2. DETAILED DESCRIPTION

[0041] Hereinafter, embodiments of the present invention will be described in detail. It should be noted that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the disclosed gist.

[0042] 《Negative electrode active material》

[0043] First, the negative electrode active material of the first embodiment of the present invention is described. The negative electrode active material of the present invention has a composite material containing a carbon material and a tin alloy. The tin alloy in the negative electrode active material of the present invention is an alloy containing tin and at least one metal selected from cobalt, iron, copper and nickel, the content of the carbon material is more than 10% by mass and less than 30% by mass, and the half-peak width of the tin alloy in the XRD spectrum is more than 0.3°. The negative electrode active material of the present invention has more than 0.5% by volume and less than 40% by volume of holes.

[0044] The inventors of the present application have discovered that in a negative electrode active material having a composite material containing a carbon material and a specified tin alloy, not only are holes formed, but the content of the carbon material and the volume of the holes are also within a specified range, and the half-peak width of the tin alloy is further made above a specified value, thereby improving the cycle characteristics of the battery.

[0045] The reason for this is presumed to be as follows, although not intending to be bound by any theory.

[0046] That is, in the negative electrode active material of the present invention, the tin alloy can react with lithium ions, sodium ions, etc., thereby functioning as a negative electrode active material. In addition, the negative electrode active material of the present invention contains a predetermined amount of carbon material, thereby enabling the half-peak width of the tin alloy in the XRD spectrum to become larger, that is, enabling the tin alloy to be low-crystalline or amorphous. It is considered that the negative electrode active material of the present invention contains a tin alloy and enables the tin alloy to be low-crystalline or amorphous, thereby, lithium can be smoothly absorbed and released in the tin alloy, and the reaction of the tin alloy with the electrolyte can be suppressed. In addition, when the negative electrode active material of the present invention is used together with an electrolyte, the negative electrode active material of the present invention contains a carbon material, thereby enabling the contact between the electrolyte and the tin alloy to be suppressed, thereby enabling the unpreferable reaction between them to be suppressed.

[0047] In addition to the above, in the negative electrode active material of the present invention, the volume ratio of the hole is within a specified range, thereby, even in the case where the expansion and contraction of the tin alloy is generated due to the absorption and release of lithium ions, the expansion and contraction of the negative electrode active material as a whole can be suppressed. Therefore, it is believed that according to the negative electrode active material of the present invention, the negative electrode active material is not easy to break even during charge and discharge, and as a result, the cycle characteristics can be improved.

[0048] <Composite Materials>

[0049] The negative electrode active material of the present invention has a composite material containing a carbon material and a tin alloy.

[0050] (Carbon material)

[0051] The composite material contains a carbon material. As described above, by making the composite material contain a carbon material, the crystallinity of the negative electrode active material can be reduced, thereby improving the cycle characteristics of the battery. It should be noted that, with respect to the present invention, the carbon material may be amorphous, in which case the carbon material may not participate in the charging and discharging of the battery.

[0052] The content of the carbon material is 10% by mass or more and 30% by mass or less. The content of the carbon material may be 11% by mass or more, 12% by mass or more, 13% by mass or more, 14% by mass or more, 15% by mass or more, or 16% by mass or more, and may be 28% by mass or less, 26% by mass or less, 24% by mass or less, 22% by mass or less, or 20% by mass or less.

[0053] The content of the carbon material in the negative electrode active material can be quantified by, for example, a combustion method using a carbon sulfur analyzer (CS analyzer).

[0054] (Tin alloy)

[0055] The composite material contains a tin alloy. The tin alloy has the function of absorbing and releasing diffuse ions such as lithium ions and sodium ions, and therefore participates in the charging and discharging of the battery. The tin alloy undergoes volume changes with charging and discharging.

[0056] The tin alloy is an alloy containing tin and at least one metal selected from cobalt, iron, copper, and nickel. Tin forms an alloy with these metals, thereby improving the cycle characteristics.

[0057] The half-peak width of the tin alloy in the XRD spectrum is 0.3° or more. The half-peak width can be 0.5° or more, 0.7° or more, 1.0° or more, 1.5° or more, 2.0° or more, or 3.0° or more, and can be 10.0° or less, 8.0° or less, 6.0° or less, or 5.0° or less. The XRD spectrum can be, for example, a diffraction peak obtained by X-ray diffraction using CuKα rays as characteristic X-rays and setting the scanning speed to 1° / minute. It should be noted that, with respect to the half-peak width of the tin alloy in the XRD spectrum, the half-peak width of the peak near 2θ=45° can be evaluated. In addition, the half-peak width of the tin alloy in the XRD spectrum can be evaluated in a discharged state, that is, in a state where lithium ions are not inserted.

[0058] <Hole>

[0059] The negative electrode active material of the present invention has a hole of more than 0.5 volume % and less than 40 volume %. The ratio of the volume of the hole in the negative electrode active material can be more than 1.0 volume %, more than 1.5 volume %, more than 2.0 volume %, more than 3.0 volume %, more than 4.0 volume %, more than 5.0 volume %, more than 6.0 volume %, more than 7.0 volume %, more than 8.0 volume % or more than 9.0 volume %, and can be less than 35 volume %, less than 30 volume %, less than 25 volume %, less than 20 volume %, less than 15 volume % or less than 10 volume %. The negative electrode active material has holes in such a ratio, thereby, it is possible to ease the volume change of the tin alloy accompanying the charge and discharge of the battery.

[0060] The average diameter of the holes may be 1.0 μm or less, 0.1 μm or more, or 0.2 μm or more, or 0.8 μm or less, 0.6 μm or less, or 0.4 μm or less.

[0061] The volume ratio and average diameter of the voids can be measured, for example, by mercury porosimetry.

[0062] <Silicon Carbide and Metallic Silicon>

[0063] The negative electrode active material of the present invention may also contain silicon carbide and metallic silicon. In this case, the content of metallic silicon may be 0.1% by mass or more and 15% by mass or less, and the ratio of the peak intensity of silicon carbide in the XRD spectrum to the peak intensity of metallic silicon may be 1.0 or more. By setting such a configuration, the cycle characteristics of the battery are further improved. As a reason for this, although it is not intended to be bound by any theory, it is believed that a predetermined amount of silicon carbide can help suppress the reaction of the negative electrode active material with the electrolyte.

[0064] It should be noted that, with respect to the present invention, "also containing silicon carbide and metallic silicon" means containing both silicon carbide and metallic silicon in an amount that can be detected by a prescribed determination method. Specifically, with respect to silicon carbide, for example, when it can be observed in the form of a peak in an XRD spectrum, the negative electrode active material may contain silicon carbide, and with respect to metallic silicon, for example, when it can be detected by energy dispersive X-ray fluorescence spectrometry (EDX) and high-frequency inductively coupled plasma (ICP) emission spectrometry, the negative electrode active material may contain metallic silicon.

[0065] When the negative electrode active material of the present invention also contains silicon carbide and metallic silicon, the content of metallic silicon can be more than 1.0 mass %, more than 2.0 mass %, more than 3.0 mass %, more than 4.0 mass % or more than 4.5 mass %, and can be less than 10 mass %, less than 8.0 mass %, less than 7.0 mass % or less than 6.5 mass %.

[0066] The ratio of the peak intensity of silicon carbide to the peak intensity of metallic silicon in the XRD spectrum may be 2.0 or more, 3.0 or more, 4.0 or more, 5.0 or more, or 5.5 or less, or 15 or less, 10 or less, 8.0 or less, or 7.0 or less.

[0067] The content of silicon carbide (SiC) and metallic silicon (Si) can be measured, for example, by X-ray diffraction (XRD). Specifically, for example, the peak intensity value of 70°±0.5 in the XRD measurement result can be used as the background, and the value obtained by subtracting the background from the maximum value of 35.2-35.7° can be used as the value of SiC. Similarly, the value obtained by subtracting the background from the maximum value of 47.5-48.0° can be used as the value of Si. The value obtained by dividing the value of SiC by the value of Si can be used as the SiC / Si peak intensity ratio.

[0068] <Silicon Oxide>

[0069] The negative electrode active material of the present invention may further contain silicon oxide.

[0070] The method for detecting silicon oxide is not particularly limited. For example, when silicon oxide can be detected by infrared absorption, acid dissolution, and ICP-AES, the negative electrode active material may contain silicon oxide.

[0071] In relation to the present invention, "silicon oxide" may in particular be silicon dioxide (SiO2).

[0072] 《Method for producing negative electrode active material》

[0073] The method of the present invention for manufacturing a negative electrode active material includes the following steps: mixing a carbon material, tin and a metal by mechanical alloying to obtain a composite material (composite material manufacturing step); mixing the composite material and metallic silicon by mechanical alloying to obtain a negative electrode active material precursor (negative electrode active material precursor manufacturing step); contacting the negative electrode active material precursor with an alkaline aqueous solution to dissolve the metallic silicon, thereby forming holes (hole forming step).

[0074] The schematic diagram of the composite material obtained in the composite material production process is shown in Figure 1 In (a), a schematic diagram of the negative electrode active material precursor obtained in the negative electrode active material precursor preparation step is shown. Figure 1 (b) shows a schematic diagram of the negative electrode active material 10 obtained in the hole forming step. Figure 1 (c). It should be noted that Figure 1 11 represents a carbon material, 12 represents a tin alloy, 13 represents metal silicon, and 14 represents a hole.

[0075] <Composite material production process>

[0076] The method of the present invention includes a step of mixing a carbon material, a metal and tin by a mechanical alloying method to obtain a composite material.

[0077] In the method of the present invention, the composition of the tin alloy can be adjusted by adjusting the amounts of the metal and tin used.

[0078] As a mechanical alloying method, for example, the following method can be cited: in an inert gas atmosphere, the raw material is treated by a ball mill at a predetermined rotation speed for a predetermined time. For example, by controlling the rotation speed and processing time during the processing in this step, the half-peak width of the tin alloy, the ratio of the volume of the pores, etc. can be adjusted.

[0079] <Negative electrode active material precursor preparation process>

[0080] The method of the present invention includes the step of mixing a composite material and metal silicon and / or silicon oxide by mechanical alloying to obtain a negative electrode active material precursor.

[0081] As a mechanical alloying method, the above-mentioned description in the composite material production process can be referred to. For example, by controlling the rotation speed and processing time during the processing in this process, the volume ratio and average diameter of the holes, and the content of silicon carbide and metallic silicon contained in the negative electrode active material can be adjusted.

[0082] <Hole Formation Process>

[0083] The method of the present invention includes the step of bringing a negative electrode active material precursor into contact with an alkaline aqueous solution to dissolve metal silicon and / or silicon oxide, thereby forming holes.

[0084] As a method for contacting the negative electrode active material precursor with the alkaline aqueous solution, for example, a method of immersing the negative electrode active material precursor in the alkaline aqueous solution and stirring it can be cited. By controlling the immersion and stirring time in this step, the content of silicon carbide and metallic silicon contained in the negative electrode active material can be controlled.

[0085] When metallic silicon is used as a component that is eluted in contact with an alkaline aqueous solution in the pore forming step, it is easy to produce a negative electrode active material that also contains silicon carbide and metallic silicon.

[0086] Silicon oxide can be used as a component that dissolves in contact with an alkaline aqueous solution in the hole formation process. Silicon oxide easily dissolves into an alkaline aqueous solution, so it is easy to form holes in the negative electrode active material. In addition, even if silicon oxide is not completely dissolved and remains in the negative electrode active material, that is, even if the negative electrode active material still contains silicon oxide, since silicon oxide does not react with lithium, it is possible to suppress the reduction of battery capacity.

[0087] It should be noted that in the hole forming step, holes can also be formed in the negative electrode active material by using a component other than metal silicon that is dissolved by contact with an alkaline aqueous solution. Examples of such a component include aluminum and the like.

[0088] 《Negative Electrode Composite Materials》

[0089] The negative electrode composite material of the present invention contains the negative electrode active material of the present invention, and optionally contains a conductive aid and a binder. When the secondary battery of the present invention is a solid-state battery, the negative electrode composite material of the present invention optionally contains a solid electrolyte.

[0090] <Negative Electrode Active Material>

[0091] Regarding the negative electrode active material, reference can be made to the above description regarding the negative electrode active material of the present invention.

[0092] <Conductive additives, binders and solid electrolytes>

[0093] The conductive auxiliary agent, the binder, and the solid electrolyte may be those commonly used in secondary batteries.

[0094] Secondary Batteries

[0095] like Figure 2 As shown, the secondary battery 100 of the present invention has a negative electrode active material layer 120, and the negative electrode active material layer includes the negative electrode composite material of the present invention. The secondary battery of the present invention may have a negative electrode collector 110, a negative electrode active material layer 120 including the negative electrode composite material of the present invention, a separator 130, a positive electrode active material layer 140 and a positive electrode collector 150.

[0096] The secondary battery of the present invention may be a liquid battery containing an electrolyte as an electrolyte layer, or may be a solid-state battery having a solid electrolyte layer as an electrolyte layer. The electrolyte layer in the liquid battery may be an electrolyte layer formed by immersing a diaphragm in an electrolyte. The solid electrolyte layer in the solid-state battery may have the function of a diaphragm. The battery of the present invention may in particular be a liquid battery containing an electrolyte as an electrolyte layer. It should be noted that, with respect to the present invention, "solid-state battery" refers to a battery that uses at least a solid electrolyte as an electrolyte, and therefore, a solid-state battery may also use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. In addition, the solid-state battery of the present invention may also be an all-solid-state battery, that is, a battery that uses only a solid electrolyte as an electrolyte.

[0097] Examples of the secondary battery include lithium ion batteries and sodium ion batteries.

[0098] <Negative Electrode Collector>

[0099] The negative electrode current collector may be made of a known metal or the like that can be used as a negative electrode current collector for a secondary battery.

[0100] <Negative Electrode Active Material Layer>

[0101] The negative electrode active material layer includes the negative electrode composite material of the present invention. With regard to the negative electrode composite material of the present invention, reference can be made to the above description of the negative electrode composite material of the present invention.

[0102] <Diaphragm>

[0103] As the separator, a separator known as a separator used in a secondary battery can be used.

[0104] When the secondary battery of the present invention is a liquid battery, the electrolyte layer can be formed by impregnating the separator with an electrolyte solution. The electrolyte solution can be a known electrolyte solution used in secondary batteries.

[0105] When the secondary battery of the present invention is a solid-state battery, the solid electrolyte layer can function as a separator. The solid electrolyte layer includes a solid electrolyte. For the solid electrolyte, reference can be made to the above description of the negative electrode composite material of the present invention.

[0106] <Positive Electrode Active Material Layer>

[0107] The positive electrode active material layer contains a positive electrode active material, and optionally contains a conductive auxiliary agent and a binder. In the case where the secondary battery of the present invention is a solid-state battery, the positive electrode active material layer of the present invention optionally contains a solid electrolyte.

[0108] As the positive electrode active material, a known positive electrode active material used in a secondary battery can be used.

[0109] Regarding the conductive auxiliary agent, the binder and the solid electrolyte, reference may be made to the above description regarding the negative electrode composite material of the present invention.

[0110] <Positive Electrode Collector>

[0111] The positive electrode current collector may be made of a known metal or the like that can be used as a positive electrode current collector for a secondary battery.

[0112] Example

[0113] 《Manufacturing Example 1》

[0114] <Manufacturing of Negative Electrode Active Material>

[0115] (Composite material production process)

[0116] The raw material consisting of carbon material, tin and the metal element forming an alloy with tin is weighed in a way that becomes the target composition ratio. The total mass of the raw material is 10g. Into a 500mL container made of chrome steel, 400g of SUS balls and the weighed raw materials are put into, and after replacement with argon (Ar) gas, it is sealed and processed based on the mechanical alloying method for 20 hours at a rotation speed of 250rpm. Thus, a composite material is obtained.

[0117] (Negative electrode active material precursor preparation process)

[0118] After measuring a predetermined amount of metallic silicon, the metal was put into the above container, replaced with Ar gas, and sealed, and treated at a speed of 250 rpm for 1 hour based on the mechanical alloying method. After the treatment, the material in the container was recovered and classified with a mesh with a mesh of 53 μm, and the powder that passed through the mesh was recovered. Thus, a negative electrode active material precursor was obtained.

[0119] (Cavity Formation Process)

[0120] The obtained negative electrode active material precursor was brought into contact with an alkaline aqueous solution to dissolve the metal silicon. Specifically, 5 g of the negative electrode active material precursor was immersed in 500 mL of a 2M NaOH solution for 1 hour while stirring, and then filtered. After washing and filtering with 5 L of ion exchange water, vacuum drying was performed at room temperature. Thus, a powdered negative electrode active material was obtained.

[0121] 《Example 1-1》

[0122] <Manufacturing of Secondary Battery>

[0123] The negative electrode active material / acetylene black (AB) / polyvinylidene fluoride (PVdF) of Manufacturing Example 1 were weighed in a mass ratio of 80 / 15 / 5, and they were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry. The slurry was coated on a copper (Cu) collector foil, pressed, and vacuum dried at 120°C overnight to form a test electrode. As a counter electrode, a metal lithium (Li) foil was used. As an electrolyte, 1M LiPF6 in EC / DMC / FEC was used. Thus, the electrochemical measurement button cell (CR2032) of Example 1-1 was prepared.

[0124] 《Example 2-1》

[0125] The negative electrode active material / AB / PVdF of Manufacturing Example 1 was weighed in a mass ratio of 80 / 10 / 10 and dispersed in NMP to prepare a slurry. The slurry was coated on an aluminum (Al) collector foil, pressed, and vacuum dried at 120°C overnight to prepare a test electrode. As a counter electrode, a metal sodium (Na) foil was used. 1M NaPF6 in PC was used as the electrolyte. Thus, the electrochemical measurement button cell (CR2032) of Example 2-1 was prepared.

[0126] "evaluate"

[0127] <Confirmation of the composition of the tin alloy>

[0128] The amounts of tin and metal elements forming an alloy with tin were quantified by energy dispersive X-ray fluorescence spectrometry (EDX) and high-frequency inductively coupled plasma (ICP) emission spectrometry to confirm the composition of the tin alloy.

[0129] <Quantification of Carbon Amount>

[0130] The amount of carbon in the negative electrode active material was quantitatively determined using a carbon sulfur analyzer (CS analyzer) by a combustion method.

[0131] <Measurement of Half Peak Width of Tin Alloy>

[0132] The half-value width of the tin alloy was measured by X-ray diffraction (XRD). The XRD spectrum was set to a diffraction peak obtained by X-ray diffraction using CuKα rays as characteristic X-rays and a scanning speed of 1° / min.

[0133] <Volume Ratio and Average Diameter of Holes>

[0134] The volume ratio and average diameter of the holes in the negative electrode active material were measured by mercury porosimetry.

[0135] <Capacity maintenance rate>

[0136] The capacity maintenance rate was measured for each reaction species by the following method.

[0137] (Lithium-ion battery)

[0138] The evaluation was performed at a voltage range of 0.05V-2.0V and a rate of 0.1C. The initial Li removal capacity was used as the denominator, and the capacity during the Li removal reaction after 10 cycles of charge and discharge was used as the numerator to calculate the capacity retention rate. It should be noted that the evaluation was performed in a constant temperature chamber at 25°C.

[0139] (Sodium-ion battery)

[0140] The evaluation was performed at a voltage range of 0.05V-1.5V and a rate of 0.1C. The capacity during the initial Na removal reaction was used as the denominator, and the capacity during the Na removal reaction after 8 cycles of charge and discharge was used as the numerator to calculate the capacity retention rate. It should be noted that the evaluation was performed in a thermostatic chamber at 25°C.

[0141] 《Examples 1-2 to 1-12 and 2-2 to 8-2 and Comparative Examples 1-1 to 8-1》

[0142] Batteries of each example were prepared and evaluated in the same manner as in Examples 1-1 and 2-1 except that the tin alloy composition, carbon content, half-value width of the tin alloy, and the ratio of the volume of holes and the average diameter were changed as described in Tables 1 to 8.

[0143] "result"

[0144] Tables 1 to 8 show the tin alloy composition, carbon content, half-value width of the tin alloy, the ratio and average diameter of the volume of the voids, and the capacity retention rate.

[0145]

[0146]

[0147] As shown in Tables 1 and 2, the battery of the comparative example in which holes were not formed had a lower capacity retention rate than the battery of the example.

[0148]

[0149]

[0150] As shown in Tables 3 and 4, the batteries of the comparative examples having carbon contents outside the range of the present invention have a smaller capacity retention rate than the batteries of the examples.

[0151]

[0152]

[0153] As shown in Tables 5 and 6, the batteries of the comparative examples in which the half-value width of the tin alloy was outside the range of the present invention had a smaller capacity retention rate than the batteries of the examples.

[0154]

[0155]

[0156] As shown in Tables 7 and 8, the batteries of the comparative examples in which the ratio of the volume of the holes was outside the range of the present invention had a smaller capacity retention rate than the batteries of the examples.

[0157] It should be noted that the cross-sectional SEM image of the negative electrode active material of the battery of Example 1-2 is shown in Figure 3 In. Figure 3 As shown, it was confirmed that holes were formed in the negative electrode active material.

[0158] 《Manufacturing Example 2》

[0159] In the composite material production process, the total mass of the raw materials was set to 15 g, and the treatment was carried out based on the mechanical alloying method at a rotation speed of 275 rpm for 22 hours. In the negative electrode active material precursor production process, the treatment was carried out based on the mechanical alloying method at a rotation speed of 280 rpm for 3 hours, and the immersion and stirring time in the hole formation process was set to 3 hours. Except for this, the negative electrode active material was produced in the same manner as in Production Example 1.

[0160] 《Examples 9-1 and 10-1》

[0161] Batteries of Examples 9-1 and 10-1 were prepared in the same manner as Examples 1-1 and 2-1 except that the negative electrode active material of Preparation Example 2 was used. It should be noted that Example 1-1 corresponds to Example 9-1, and Example 2-1 corresponds to Example 10-1, respectively.

[0162] "evaluate"

[0163] <Quantification of Silicon Carbide and Metallic Silicon>

[0164] The contents of silicon carbide (SiC) and metallic silicon (Si) were quantified by X-ray diffraction (XRD). Specifically, the peak intensity value of 70°±0.5 in the XRD measurement result was used as the background, and the value obtained by subtracting the background from the maximum value of 35.2-35.7° was used as the value of SiC. Similarly, the value obtained by subtracting the background from the maximum value of 47.5-48.0° was used as the value of Si. The value obtained by dividing the value of SiC by the value of Si was used as the SiC / Si peak intensity ratio.

[0165] The other evaluations were carried out in the same manner as above.

[0166] 《Examples 9-2 to 9-12 and 10-2 to 18-3 and Comparative Examples 9-1 to 18-1》

[0167] The tin alloy composition, carbon content, Si content, SiC / Si peak intensity ratio, half-peak width of the tin alloy and the ratio of the volume of the holes were changed as described in Tables 9 to 18, and the batteries of each example were prepared and evaluated in the same manner as in Examples 9-1 and 10-1.

[0168] "result"

[0169] Tables 9 to 18 show the tin alloy composition, carbon content, Si content, SiC / Si peak intensity ratio, half-peak width of the tin alloy, ratio of the volume of voids, and capacity retention rate.

[0170]

[0171] As shown in Table 9, when the negative electrode active material further contains silicon carbide and metallic silicon, the battery of the comparative example having the SiC / Si peak intensity ratio outside the range of the present invention has a smaller capacity retention rate than the battery of the example.

[0172]

[0173] As shown in Table 10, when the negative electrode active material further contained silicon carbide and metallic silicon, the capacity retention rate of the battery of the comparative example in which no holes were formed was smaller than that of the battery of the example.

[0174]

[0175]

[0176] As shown in Tables 11 and 12, when the negative electrode active material further contains silicon carbide and metallic silicon, the capacity retention rate of the battery of the comparative example having a carbon content outside the range of the present invention is smaller than that of the battery of the example.

[0177]

[0178]

[0179] As shown in Tables 13 and 14, when the negative electrode active material further contained silicon carbide and metallic silicon, the capacity retention rate of the battery of the comparative example in which the half width of the peak of the tin alloy was outside the range of the present invention was smaller than that of the battery of the example.

[0180]

[0181]

[0182] As shown in Tables 15 and 16, when the negative electrode active material further contains silicon carbide and metallic silicon, the capacity retention rate of the battery of the comparative example in which the volume ratio of the holes is outside the range of the present invention is smaller than that of the battery of the example.

[0183]

[0184]

[0185] As shown in Tables 17 and 18, when the negative electrode active material further contains silicon carbide and metallic silicon, the capacity retention rate of the battery of the comparative example having the SiC / Si peak intensity ratio outside the range of the present invention is smaller than that of the battery of the example.

[0186] 《Manufacturing Example 3》

[0187] <Manufacturing of Negative Electrode Active Material>

[0188] (Composite material production process)

[0189] A composite material was obtained in the same manner as in Production Example 1 except that the total mass of the raw materials was 15 g and the treatment was performed by mechanical alloying at a rotation speed of 250 rpm for 28 hours.

[0190] (Negative electrode active material precursor preparation process)

[0191] A negative electrode active material precursor was obtained in the same manner as in Production Example 1 except that silicon oxide (SiO 2 ) was used instead of metallic silicon and the treatment was performed by mechanical alloying at a rotation speed of 250 rpm for 2 hours.

[0192] (Cavity Formation Process)

[0193] The obtained negative electrode active material precursor was brought into contact with an alkaline aqueous solution to dissolve SiO2. Specifically, 3 g of the negative electrode active material precursor was immersed in 250 mL of a 2M NaOH solution for 4 hours while stirring. The mixture was then washed with 3 L of ion exchange water and filtered, and then vacuum dried at room temperature. Thus, a powdered negative electrode active material was obtained.

[0194] 《Example 19-1》

[0195] The mass ratio of the negative electrode active material / AB / PVdF=80 / 15 / 5 of Manufacturing Example 3 was weighed and dispersed in NMP to prepare a slurry. The obtained slurry was coated on a copper (Cu) collector foil, pressed, and vacuum dried at 120°C overnight to obtain a negative electrode laminate as a test electrode. The positive electrode active material / AB / PVdF=85 / 10 / 5 was weighed and dispersed in NMP to prepare a slurry. The obtained slurry was coated on an Al collector foil, pressed, and vacuum dried at 120°C overnight to obtain a positive electrode laminate as a test electrode. The laminates were placed opposite each other through a polypropylene separator, and they were impregnated in an electrolyte for sealing to prepare an evaluation battery. It should be noted that in the evaluation battery as a lithium-ion battery, nickel cobalt manganese oxide (NCM) was used as the positive electrode active material, and 1M LiPF6 in EC / DMC / FEC was used as the electrolyte. In the evaluation cell as a sodium ion battery, nickel iron manganese (NiFeMn) oxide was used as the positive electrode active material, and 1 M NaPF6 in EC / DEC was used as the electrolyte.

[0196] "evaluate"

[0197] <Increase in restraint pressure>

[0198] The evaluation was carried out in a thermostatic chamber at 25°C at a voltage range of 4.2-2.5V and a rate of 0.1C. A force sensor (LCX-A-10KN manufactured by KYOWA) was clamped during charge and discharge, and charging was started with an initial pressure of 1MPa. The increase in constraint pressure per unit capacity was calculated by dividing the increase in constraint pressure during initial charge by the charge capacity. It should be noted that the increase in constraint pressure refers to the amount of expansion of the negative electrode active material. The results are shown in Table 19.

[0199] The other evaluations were carried out in the same manner as above.

[0200] In this example, the carbon concentration before and after dissolution was determined by infrared absorption using EMIA-20E manufactured by HORIBA Corporation, and the presence of SiO 2 in the negative electrode active material was confirmed from the change in the ratio of the carbon amount.

[0201] 《Examples 19-2 to 19-5, Comparative Examples 19-1 to 19-5 and Reference Example 19-1》

[0202] The batteries of each example were prepared and evaluated in the same manner as in Example 19-1 except that the composition, carbon content, half-value width of the tin alloy, and ratio of the volume of the pores were changed as described in Table 19.

[0203] The restraint pressure increase of each example is shown in Table 19. In Table 19, the restraint pressure increase of the example is shown as a relative value when the restraint pressure increase of the comparative example with the corresponding composition is set to 100.

[0204] In addition, in these examples, the carbon concentration before and after dissolution was also confirmed by infrared absorption method using EMIA-20E manufactured by HORIBA Corporation based on the change in the ratio of the carbon amount to confirm that SiO 2 was contained in the negative electrode active material.

[0205]

[0206] As shown in Table 19, for the batteries of Examples in which the carbon content, the half-width of the tin alloy, and the ratio of the volume of the holes were within the range of the present invention, the increase in the restraint pressure, that is, the amount of expansion of the negative electrode active material was small.

[0207] 《Examples 20-1 to 20-4》

[0208] In particular, except that the ratio of the volume of the holes was changed as shown in Table 20, the same procedure as in Example 19-1 was carried out to prepare and evaluate batteries of each example.

[0209] The restraint pressure increase of each example is shown in Table 20. In Table 20, the restraint pressure increase of the example is shown as a relative value when the restraint pressure increase of Comparative Example 19-1 is set to 100.

[0210]

[0211] As shown in Table 20, in the batteries of Examples in which the ratio of the volume of the holes was within the range of the present invention, the increase in the restraint pressure, that is, the amount of expansion of the negative electrode active material was small.

[0212] Explanation of symbols

[0213] 10 Negative electrode active material

[0214] 11 Carbon Materials

[0215] 12 Tin alloy

[0216] 13 Metallic Silicon

[0217] 14 Hole

[0218] 100 Secondary batteries

[0219] 110 Negative electrode collector

[0220] 120 Negative electrode active material layer

[0221] 130 Diaphragm

[0222] 140 positive electrode active material layer

[0223] 150 Positive electrode collector

Claims

1. A negative electrode active material comprising a composite material containing a carbon material and a tin alloy, The tin alloy is an alloy containing tin and at least one metal selected from cobalt, iron, copper and nickel, The carbon material content is 10 mass % or more and 30 mass % or less, The half-peak width of the tin alloy in the XRD spectrum is greater than 0.3°, and The negative electrode active material has 0.5 volume % or more and 40 volume % or less of holes.

2. The negative electrode active material according to claim 1, wherein It also contains silicon carbide and metallic silicon. The content of the metal silicon is 0.1 mass % or more and 15 mass % or less, and The ratio of the peak intensity of the silicon carbide to the peak intensity of the metal silicon in the XRD spectrum is 1.0 or more.

3. The negative electrode active material according to claim 1, wherein It also contains silicon oxide. 4 . A negative electrode composite material comprising the negative electrode active material according to claim 1 . 5 . A secondary battery comprising a negative electrode active material layer, wherein the negative electrode active material layer comprises the negative electrode composite material according to claim 4 .

6. The method for producing a negative electrode active material according to any one of claims 1 to 3, comprising the following steps: The carbon material, the tin and the metal are mixed by mechanical alloying to obtain the composite material; The composite material and metal silicon and / or silicon oxide are mixed by mechanical alloying to obtain a negative electrode active material precursor; The negative electrode active material precursor is brought into contact with an alkaline aqueous solution to dissolve the metal silicon and / or silicon oxide, thereby forming the holes.

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