Negative electrode active material, manufacturing method for the same, negative electrode mixture, and secondary battery

Abstract

To provide a negative electrode active material capable of suppressing volume changes in the negative electrode active material, thereby improving the cycle characteristics of a battery, and capable of suppressing expansion of the negative electrode active material at the time of initial charging, a manufacturing method for the same, a negative electrode mixture containing such a negative electrode active material, and a secondary battery containing such a negative electrode mixture.SOLUTION: A negative electrode active material 10 has a composite material including a carbon material 11 and a tin alloy 12. The tin alloy in the negative electrode active material is an alloy including tin and a metal selected from at least one of cobalt, iron, copper, and nickel. The carbon material content is 10 mass% or more and 30 mass% or less. The half-width of the tin alloy in the XRD spectrum is 0.3° or more. The negative electrode active material has voids 14 of 0.5 volume % or more and 40 volume % or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a negative electrode active material and a method for producing the same, a negative electrode mixture, and a secondary battery. [Background technology]

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

[0003] However, it is known that when silicon or tin is used as the negative electrode active material, volume change occurs in the negative electrode active material with charging and discharging of the battery, which deteriorates the cycle characteristics of the battery. In order to suppress this volume change, a technique for forming voids (pores) in the negative electrode active material has been developed, as disclosed in Patent Documents 3 and 4. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2004 / 100291 [Patent Document 2] International Publication No. 2004 / 100293 [Patent Document 3] International Publication No. 2013 / 146658 [Patent Document 4] JP 2011-249173 A Summary of the Invention [Problem to be solved by the invention]

[0005] There is room for improvement in suppressing the volume change of the negative electrode active material.

[0006] The present disclosure has an object to provide a negative electrode active material that can suppress a volume change of a negative electrode active material, thereby improving the cycle characteristics of a battery and / or suppressing the expansion of the negative electrode active material during initial charging, a method for producing the same, a negative electrode composite including such a negative electrode active material, and a secondary battery containing such a negative electrode composite. [Means for solving the problem]

[0007] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> A composite material including 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 content of the carbon material is 10% by mass or more and 30% by mass or less, The half-width of the tin alloy in the XRD spectrum is 0.3° or more; and The material has voids of 0.5% by volume or more and 40% by volume or less. Negative electrode active material. <Aspect 2> Further comprising silicon carbide and silicon metal; The content of the metal silicon is 0.1% by mass or more and 15% by mass or less, and The ratio of the peak intensity of the silicon carbide to the peak intensity of the metal silicon in an XRD spectrum is 1.0 or more; 2. The negative electrode active material of embodiment 1. <Aspect 3> 3. The negative electrode active material of embodiment 1 or 2, further comprising silicon oxide. <Aspect 4> A negative electrode mixture comprising the negative electrode active material according to any one of aspects 1 to 3. <Aspect 5> A negative electrode active material layer is provided, and The negative electrode active material layer contains the negative electrode mixture according to aspect 4. Secondary battery. Aspect 6 A method for producing the negative electrode active material according to any one of aspects 1 to 3, comprising the steps of: mixing the carbon material, the tin, and the metal by a mechanical alloying method to obtain the composite material; mixing the composite material, metal silicon and / or silicon oxide by a mechanical alloying method 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 silicon metal and / or silicon oxide, thereby forming the pores. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a negative electrode active material and a manufacturing method thereof that can suppress a volume change of the negative electrode active material, thereby improving the cycle characteristics of the battery and / or suppressing the expansion of the negative electrode active material during the first charge, a negative electrode composite including such a negative electrode active material, and a secondary battery containing such a negative electrode composite. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing an example of a process for producing a negative electrode active material according to the present disclosure ((a) composite material production process, (b) negative electrode active material precursor production process, (c) pore formation process). [Diagram 2] FIG. 2 is a schematic cross-sectional view showing an example of a secondary battery according to the present disclosure. [Diagram 3] FIG. 3 is a cross-sectional SEM image of the negative electrode active material of the present disclosure for the secondary battery of Example 1-2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the present disclosure.

[0011] 《Negative electrode active material》 First, the negative electrode active material according to the first embodiment of the present disclosure will be described. The negative electrode active material of the present disclosure has a composite material containing a carbon material and a tin alloy. The tin alloy in the negative electrode active material of the present disclosure is an alloy containing tin and at least one metal selected from cobalt, iron, copper, and nickel, the content of the carbon material is 10% by mass or more and 30% by mass or less, and the half width of the tin alloy in the XRD spectrum is 0.3° or more. The negative electrode active material of the present disclosure has pores of 0.5% by volume or more and 40% by volume or less.

[0012] The present inventors have discovered that in a negative electrode active material having a composite material containing a carbon material and a specified tin alloy, not only can pores be formed, but also the content of the carbon material and the volume of the pores can be set within specified ranges, and further the half-width of the tin alloy can be set to a specified value or more, thereby improving the cycle characteristics of the battery.

[0013] The reason for this is presumed to be as follows, without intending to be bound by any theory.

[0014] That is, in the negative electrode active material of the present disclosure, the tin alloy can react with lithium ions, sodium ions, etc., and thereby function as a negative electrode active material. In addition, the negative electrode active material of the present disclosure contains a predetermined amount of carbon material, which increases the half-width of the tin alloy in the XRD spectrum, that is, the tin alloy can be made low crystalline or amorphous. In this way, it is believed that the negative electrode active material of the present disclosure contains a tin alloy and can make the tin alloy low crystalline or amorphous, thereby smoothly occluding and desorbing lithium into the tin alloy and suppressing the reaction between the tin alloy and the electrolyte. In addition, when the negative electrode active material of the present disclosure is used together with an electrolyte, the negative electrode active material of the present disclosure contains a carbon material, which suppresses contact between the electrolyte and the tin alloy, thereby suppressing undesirable reactions between them.

[0015] In addition to the above, in the negative electrode active material of the present disclosure, since the volume ratio of the vacancies is within a predetermined range, the negative electrode active material as a whole can suppress the expansion and contraction even when the tin alloy expands and contracts due to the absorption and release of lithium ions, etc. Therefore, according to the negative electrode active material of the present disclosure, the negative electrode active material is less likely to crack even when charging and discharging, and as a result, it is believed that the cycle characteristics can be improved.

[0016] <Composite materials> The negative electrode active material of the present disclosure comprises a composite material including a carbon material and a tin alloy.

[0017] (Carbon materials) The composite material includes a carbon material. As described above, the composite material includes a carbon material, so that the crystallinity of the negative electrode active material can be reduced, thereby improving the cycle characteristics of the battery. In the present disclosure, the carbon material may be amorphous, and in this case, the carbon material may not be involved in the charging and discharging of the battery.

[0018] The carbon material content is 10% by mass or more and 30% by mass or less. The carbon material content 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.

[0019] The content of the carbon material in the negative electrode active material can be quantified, for example, by a combustion method using a carbon-sulfur analyzer (CS analyzer).

[0020] (Tin alloy) The composite material includes a tin alloy. The tin alloy has a function of absorbing and desorbing diffusible ions such as lithium ions and sodium ions, and therefore participates in the charging and discharging of the battery. The tin alloy undergoes a volume change during charging and discharging.

[0021] The tin alloy is an alloy containing tin and at least one metal selected from cobalt, iron, copper, and nickel. The cycle characteristics are improved by forming an alloy with tin and these metals.

[0022] The half-width of the tin alloy in the XRD spectrum is 0.3° or more. This half-width may 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 may be 10.0° or less, 8.0° or less, 6.0° or less, or 5.0° or less. The XRD spectrum may be, for example, a diffraction peak obtained by X-ray diffraction using CuKα rays as the specific X-rays and a sweep speed of 1° / min. The half-width of the tin alloy in the XRD spectrum can be evaluated by the half-width of the peak near 2θ=45°. The half-width of the tin alloy in the XRD spectrum can be evaluated in a discharged state, that is, in a state in which lithium ions or the like are not inserted.

[0023] <Vacancy> The negative electrode active material of the present disclosure has pores of 0.5 volume % or more and 40 volume % or less. The volume ratio of the pores in the negative electrode active material may be 1.0 volume % or more, 1.5 volume % or more, 2.0 volume % or more, 3.0 volume % or more, 4.0 volume % or more, 5.0 volume % or more, 6.0 volume % or more, 7.0 volume % or more, 8.0 volume % or more, or 9.0 volume % or more, and may be 35 volume % or less, 30 volume % or less, 25 volume % or less, 20 volume % or less, 15 volume % or less, or 10 volume % or less. When the negative electrode active material has pores at such a ratio, the volume change of the tin alloy accompanying the charging and discharging of the battery can be mitigated.

[0024] The average diameter of the pores may be 1.0 μm or less. The average diameter of the pores may be 0.1 μm or more, or 0.2 μm or more, and may be 0.8 μm or less, 0.6 μm or less, or 0.4 μm or less.

[0025] The volume ratio and average diameter of the pores can be measured, for example, by mercury intrusion porosimetry.

[0026] <Silicon carbide and silicon metal> The negative electrode active material of the present disclosure may further contain silicon carbide and metal silicon, in which case the content of metal silicon may be 0.1 mass% or more and 15 mass% or less, and the ratio of the peak intensity of silicon carbide to the peak intensity of metal silicon in the XRD spectrum may be 1.0 or more. By adopting such a configuration, the cycle characteristics of the battery are further improved. The reason for this, without intending to be bound by any theory, is believed to be that a certain amount of silicon carbide can contribute to suppressing the reaction between the negative electrode active material and the electrolyte.

[0027] In the present disclosure, "further containing silicon carbide and metal silicon" means that both silicon carbide and metal silicon are contained in an amount detectable by a predetermined measurement method. Specifically, for silicon carbide, for example, when it can be observed as a peak in an XRD spectrum, the negative electrode active material can be deemed to contain silicon carbide, and for metal silicon, for example, when it can be detected by energy dispersive X-ray fluorescence spectroscopy (EDX) and high frequency inductively coupled plasma (ICP) optical emission spectroscopy, the negative electrode active material can be deemed to contain metal silicon.

[0028] When the negative electrode active material of the present disclosure further contains silicon carbide and silicon metal, the content of the silicon metal may be 1.0 mass% or more, 2.0 mass% or more, 3.0 mass% or more, 4.0 mass% or more, or 4.5 mass% or more, and may be 10 mass% or less, 8.0 mass% or less, 7.0 mass% or less, or 6.5 mass% or less.

[0029] The ratio of the peak intensity of silicon carbide to the peak intensity of silicon metal 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 more, and may be 15 or less, 10 or less, 8.0 or less, or 7.0 or less.

[0030] The content of silicon carbide (SiC) and metal silicon (Si) can be measured, for example, by X-ray diffraction (XRD). Specifically, for example, the peak intensity value at 70°±0.5 in the XRD measurement result is taken as the background, and the value of SiC can be obtained by subtracting the background from the maximum value at 35.2-35.7°. Similarly, the value of Si can be obtained by subtracting the background from the maximum value at 47.5-48.0°. The value of SiC divided by the value of Si can be obtained as the SiC / Si peak intensity ratio.

[0031] <Silicon oxide> The negative electrode active material of the present disclosure may further include silicon oxide.

[0032] The method for detecting silicon oxide is not particularly limited. For example, when silicon oxide can be detected by infrared absorption method, acid dissolution, and ICP-AES method, the negative electrode active material can be determined to contain silicon oxide.

[0033] In the context of the present disclosure, "silicon oxide" refers specifically to silicon dioxide (SiO 2 ) may be the case.

[0034] <<Method for producing negative electrode active material>> The method of the present disclosure for producing 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 preparation step), mixing the composite material and metallic silicon by mechanical alloying to obtain a negative electrode active material precursor (negative electrode active material precursor preparation step), and contacting the negative electrode active material precursor with an alkaline aqueous solution to dissolve the metallic silicon, thereby forming pores (pore formation step).

[0035] A schematic diagram of the composite material obtained in the composite material preparation step is shown in Fig. 1(a), a schematic diagram of the negative electrode active material precursor obtained in the negative electrode active material precursor preparation step is shown in Fig. 1(b), and a schematic diagram of the negative electrode active material 10 obtained in the pore formation step is shown in Fig. 1(c). In Fig. 1, 11 indicates a carbon material, 12 indicates a tin alloy, 13 indicates metallic silicon, and 14 indicates pores.

[0036] <Composite material manufacturing process> The method of the present disclosure involves mixing a carbon material, a metal, and tin by a mechanical alloying process to obtain a composite material.

[0037] With respect to the methods of the present disclosure, the composition of the tin alloy can be adjusted by adjusting the amount of metal and tin used.

[0038] The mechanical alloying method may be, for example, a method in which the raw material is treated in an inert gas atmosphere with a ball mill at a predetermined rotation speed for a predetermined time. For example, the half-width of the tin alloy, the volume ratio of the voids, etc. can be adjusted by controlling the rotation speed and treatment time during the treatment in this step.

[0039] <Negative electrode active material precursor preparation process> The method of the present disclosure includes mixing the composite material and silicon metal and / or silicon oxide by a mechanical alloying method to obtain a negative electrode active material precursor.

[0040] For the mechanical alloying method, the above description in the composite material preparation process can be referred to. For example, by controlling the rotation speed and treatment time during this process, the volume ratio and average diameter of the pores, as well as the contents of silicon carbide and metal silicon contained in the negative electrode active material, can be adjusted.

[0041] <Vacancy formation process> The method of the present disclosure includes contacting a negative electrode active material precursor with an alkaline aqueous solution to dissolve silicon metal and / or silicon oxide, thereby forming pores.

[0042] The method of contacting the negative electrode active material precursor with the alkaline aqueous solution includes, for example, immersing the negative electrode active material precursor in the alkaline aqueous solution and stirring the solution. By controlling the immersion and stirring time in this step, the content of silicon carbide and metal silicon contained in the negative electrode active material can be controlled.

[0043] In the pore forming step, when metallic silicon is used as the component to be eluted by contacting with an alkaline aqueous solution, it becomes easy to produce a negative electrode active material further containing silicon carbide and metallic silicon.

[0044] In the pore forming step, silicon oxide may be used as a component to be dissolved by contacting with an alkaline aqueous solution. Silicon oxide is easily dissolved in an alkaline aqueous solution, and therefore easily forms pores in the negative electrode active material. 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 further contains silicon oxide, silicon oxide does not react with lithium, and therefore the decrease in battery capacity can be suppressed.

[0045] In the pore-forming step, pores can also be formed in the negative electrode active material by using a component other than metallic silicon that dissolves when contacted with an alkaline aqueous solution. Examples of such components include aluminum.

[0046] 《Negative electrode mixture》 The negative electrode mixture of the present disclosure includes the negative electrode active material of the present disclosure, and optionally includes a conductive additive and a binder. When the secondary battery of the present disclosure is a solid-state battery, the negative electrode mixture of the present disclosure optionally includes a solid electrolyte.

[0047] <Negative electrode active material> For the negative electrode active material, reference can be made to the above description regarding the negative electrode active material of the present disclosure.

[0048] <Conductive assistant, binder and solid electrolyte> The conductive assistant, binder and solid electrolyte may be any of those commonly used in secondary batteries.

[0049] 《Secondary battery》 2, the secondary battery 100 of the present disclosure has an anode active material layer 120, and the anode active material layer contains the anode composite of the present disclosure. The secondary battery of the present disclosure may have an anode current collector 110, an anode active material layer 120 containing the anode composite of the present disclosure, a separator 130, a cathode active material layer 140, and a cathode current collector 150.

[0050] The secondary battery of the present disclosure may be a liquid battery containing an electrolytic solution as an electrolyte layer, or may be a solid battery having a solid electrolyte layer as an electrolyte layer. The electrolyte layer in the liquid battery may be a separator impregnated with an electrolytic solution. The solid electrolyte layer in the solid battery may have the function of a separator. The battery of the present disclosure may be a liquid battery containing an electrolytic solution as an electrolyte layer. In this disclosure, the term "solid battery" means a battery that uses at least a solid electrolyte as an electrolyte, and therefore the solid battery may use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. The solid battery of the present disclosure may also be an all-solid-state battery, i.e., a battery that uses only a solid electrolyte as an electrolyte.

[0051] Examples of the secondary battery include a lithium ion battery and a sodium ion battery.

[0052] <Negative electrode current collector> The negative electrode current collector may be made of a known metal that can be used as a negative electrode current collector for secondary batteries.

[0053] <Negative electrode active material layer> The negative electrode active material layer includes the negative electrode mixture of the present disclosure. For the negative electrode mixture of the present disclosure, reference can be made to the above description of the negative electrode mixture of the present disclosure.

[0054] <Separator> As the separator, a separator known to be used in secondary batteries may be used.

[0055] When the secondary battery of the present disclosure is a liquid battery, the separator may be impregnated with an electrolyte solution to form an electrolyte layer. The electrolyte solution may be any known electrolyte solution used in secondary batteries.

[0056] When the secondary battery of the present disclosure 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, the above description of the negative electrode mixture of the present disclosure can be referred to.

[0057] <Cathode active material layer> The positive electrode active material layer includes a positive electrode active material, and optionally includes a conductive assistant and a binder. When the secondary battery of the present disclosure is a solid-state battery, the positive electrode active material layer of the present disclosure optionally includes a solid electrolyte.

[0058] As the positive electrode active material, any known positive electrode active material for use in secondary batteries may be used.

[0059] For the conductive assistant, binder, and solid electrolyte, reference can be made to the above descriptions regarding the negative electrode mixture of the present disclosure.

[0060] <Positive electrode current collector> The positive electrode current collector may be made of a known metal that can be used as a positive electrode current collector for a secondary battery. EXAMPLES

[0061] Example 1 <Production of negative electrode active material> (Composite material manufacturing process) The raw materials consisting of carbon material, tin, and metal elements that form an alloy with tin were weighed out to achieve the desired composition ratio. The total mass of the raw materials was 10 g. 400 g of SUS balls and the weighed raw materials were placed in a 500 mL chrome steel container, and the container was sealed after replacing with argon (Ar) gas. The mechanical alloying process was carried out at a rotation speed of 250 rpm for 20 hours. A composite material was thus obtained.

[0062] (Negative electrode active material precursor preparation process) After weighing a predetermined amount of metal silicon, it was put into the above-mentioned container, replaced with Ar gas, sealed, and treated by mechanical alloying at a rotation speed of 250 rpm for 1 hour. After the treatment, the material in the container was collected and classified with a mesh with an opening of 53 μm, and the powder that passed through the mesh was collected. This resulted in a negative electrode active material precursor.

[0063] (Vacancy formation process) The obtained negative electrode active material precursor was contacted with an alkaline aqueous solution to dissolve the metallic silicon. Specifically, 5 g of the negative electrode active material precursor was immersed in 500 mL of 2M NaOH solution for 1 hour while stirring, and then suction filtered. After washing with 5 L of ion-exchanged water and filtering, it was vacuum dried at room temperature. As a result, a powdered negative electrode active material was obtained.

[0064] Example 1-1 <Manufacture of secondary batteries> The negative electrode active material of Production Example 1 / acetylene black (AB) / polyvinylidene fluoride (PVdF) was weighed out in a mass ratio of 80 / 15 / 5, and dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry. This slurry was applied onto a copper (Cu) current collector foil, pressed, and then vacuum-dried overnight at 120°C to obtain a test electrode. Metallic lithium (Li) foil was used as the counter electrode. 1M LiPF6 in EC / DMC / FEC was used as the electrolyte. This produced the electrochemical measurement coin cell (CR2032) of Example 1-1.

[0065] Example 2-1 The negative electrode active material of Production Example 1 was weighed out in a mass ratio of 80 / 10 / 10, and dispersed in NMP to prepare a slurry. This slurry was applied onto an aluminum (Al) current collector foil, pressed, and then vacuum-dried overnight at 120°C to obtain a test electrode. Metallic sodium (Na) foil was used as the counter electrode. 1M NaPF6 in PC was used as the electrolyte. This produced the electrochemical measurement coin cell (CR2032) of Example 2-1.

[0066] "evaluation" <Confirmation of the composition of tin alloy> The amounts of tin and metal elements that form alloys with tin were quantified using energy dispersive X-ray fluorescence spectroscopy (EDX) and inductively coupled plasma (ICP) optical emission spectroscopy, and the composition of the tin alloy was confirmed.

[0067] 〈Quantitative determination of carbon content〉 The amount of carbon in the negative electrode active material was quantified using a carbon-sulfur analyzer (CS analyzer) by the combustion method.

[0068] <Measurement of half-value width of tin alloy> The half-width of the tin alloy was measured by X-ray diffraction (XRD). The XRD spectrum was a diffraction peak obtained by X-ray diffraction at a scanning speed of 1° / min using CuKα radiation as the specific X-ray.

[0069] <Volume ratio and average diameter of pores> The volume ratio and average diameter of pores in the negative electrode active material were measured by mercury intrusion porosimetry.

[0070] <Capacity maintenance rate> The capacity retention rate was measured for each reaction species by the following method.

[0071] (Lithium-ion battery) The voltage range was 0.05V-2.0V and the rate was 0.1C. The capacity retention rate was calculated by taking the initial Lithium removal capacity as the denominator and the capacity at the time of Lithium removal reaction after 10 cycles of charge and discharge as the numerator. The evaluation was performed in a thermostatic chamber at 25℃.

[0072] (Sodium ion battery) The voltage range was 0.05V-1.5V and the rate was 0.1C. The capacity retention rate was calculated by taking the capacity at the first sodium removal reaction as the denominator and the capacity at the sodium removal reaction after 8 cycles of charging and discharging as the numerator. The evaluation was performed in a thermostatic chamber at 25°C.

[0073] Examples 1-2 to 1-12 and 2-2 to 8-2, and Comparative Examples 1-1 to 8-1 The batteries of each example were fabricated and evaluated in the same manner as in Examples 1-1 and 2-1, except that the tin alloy composition, carbon content, half-width of the tin alloy, and volume ratio and average diameter of the voids were changed as shown in Tables 1 to 8.

[0074] "result" Tables 1 to 8 show the tin alloy composition, carbon content, half-width of the tin alloy, volume ratio and average diameter of the pores, and capacity retention rate.

[0075] [Table 1]

[0076] [Table 2]

[0077] As shown in Tables 1 and 2, the comparative batteries in which no pores were formed had a smaller capacity retention rate than the batteries of the examples.

[0078] [Table 3]

[0079] [Table 4]

[0080] As shown in Tables 3 and 4, the batteries of the comparative examples, which had carbon contents outside the range of the present disclosure, had smaller capacity retention rates than the batteries of the examples.

[0081] [Table 5]

[0082] [Table 6]

[0083] As shown in Tables 5 and 6, the batteries of the comparative examples in which the half-width of the tin alloy was outside the range of the present disclosure had smaller capacity retention rates than the batteries of the examples.

[0084] [Table 7]

[0085] [Table 8]

[0086] As shown in Tables 7 and 8, the batteries of Comparative Examples, in which the pore volume ratio was outside the range of the present disclosure, had smaller capacity retention rates than the batteries of Examples.

[0087] A cross-sectional SEM image of the negative electrode active material of the battery of Example 1-2 is shown in Fig. 3. As shown in Fig. 3, it was confirmed that pores were formed in the negative electrode active material.

[0088] Example 2 A negative electrode active material was prepared in the same manner as in Production Example 1, except that in the composite material preparation step, the total mass of the raw materials was 15 g and the treatment was performed by mechanical alloying at a rotation speed of 275 rpm for 22 hours, in the negative electrode active material precursor preparation step, the treatment was performed by mechanical alloying at a rotation speed of 280 rpm for 3 hours, and the immersion and stirring time in the pore formation step was 3 hours.

[0089] Examples 9-1 and 10-1 Batteries of Examples 9-1 and 10-1 were produced in the same manner as in Examples 1-1 and 2-1, except that the negative electrode active material of Production Example 2 was used. Note that Examples 1-1 and 9-1 correspond to each other, and Examples 2-1 and 10-1 correspond to each other.

[0090] "evaluation" <Quantitative Determination of Silicon Carbide and Metallic Silicon> The content of silicon carbide (SiC) and metal silicon (Si) was quantified by X-ray diffraction (XRD). Specifically, the peak intensity value at 70°±0.5 in the XRD measurement results was used as the background, and the value of SiC was obtained by subtracting the background from the maximum value at 35.2-35.7°. Similarly, the value of Si was obtained by subtracting the background from the maximum value at 47.5-48.0°. The value of SiC divided by the value of Si was used as the SiC / Si peak intensity ratio.

[0091] Other evaluations were carried out in the same manner as above.

[0092] Examples 9-2 to 9-12 and 10-2 to 18-3, and Comparative Examples 9-1 to 18-1 The batteries of each example were produced and evaluated in the same manner as in Examples 9-1 and 10-1, except that the tin alloy composition, carbon content, Si content, SiC / Si peak intensity ratio, half-width of the tin alloy, and void volume ratio were changed as shown in Tables 9 to 18.

[0093] "result" Tables 9 to 18 show the tin alloy composition, carbon content, Si content, SiC / Si peak intensity ratio, half-width of the tin alloy, void volume ratio, and capacity retention rate.

[0094] [Table 9]

[0095] As shown in Table 9, when the negative electrode active material further contained silicon carbide and silicon metal, the comparative example batteries having SiC / Si peak intensity ratios outside the range of the present disclosure had smaller capacity retention rates than the example batteries.

[0096] [Table 10]

[0097] As shown in Table 10, even when the negative electrode active material further contained silicon carbide and silicon metal, the comparative example batteries in which no pores were formed had smaller capacity retention rates than the example batteries.

[0098] [Table 11]

[0099] [Table 12]

[0100] As shown in Tables 11 and 12, even when the negative electrode active material further contained silicon carbide and silicon metal, the comparative example batteries, whose carbon content was outside the range of the present disclosure, had smaller capacity retention rates than the example batteries.

[0101] [Table 13]

[0102] [Table 14]

[0103] As shown in Tables 13 and 14, even when the negative electrode active material further contained silicon carbide and silicon metal, the batteries of the comparative examples in which the half-width of the tin alloy was outside the range of the present disclosure had smaller capacity retention rates than the batteries of the examples.

[0104] [Table 15]

[0105] [Table 16]

[0106] As shown in Tables 15 and 16, even when the negative electrode active material further contained silicon carbide and silicon metal, the batteries of the comparative examples, in which the volume ratio of pores was outside the range of the present disclosure, had smaller capacity retention rates than the batteries of the examples.

[0107] [Table 17]

[0108] [Table 18]

[0109] As shown in Tables 17 and 18, when the negative electrode active material further contained silicon carbide and silicon metal, the comparative example batteries having SiC / Si peak intensity ratios outside the range of the present disclosure had smaller capacity retention rates than the example batteries.

[0110] Example 3 <Production of negative electrode active material> (Composite material manufacturing process) 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 by mechanical alloying was carried out at a rotation speed of 250 rpm for 28 hours.

[0111] (Negative electrode active material precursor preparation process) Silicon oxide (SiO 2 A negative electrode active material precursor was obtained in the same manner as in Production Example 1, except that a rotating shaft was used, and the treatment was carried out by the mechanical alloying method at a rotation speed of 250 rpm for 2 hours.

[0112] (Vacancy formation process) The obtained negative electrode active material precursor is contacted with an alkaline aqueous solution to form SiO 2Specifically, 3 g of the negative electrode active material precursor was immersed in 250 mL of 2M NaOH solution for 4 hours while stirring. After washing with 3 L of ion-exchanged water and filtering, the mixture was vacuum-dried at room temperature. As a result, a powdered negative electrode active material was obtained.

[0113] Example 19-1 The negative electrode active material of Production Example 3 was weighed out at a mass ratio of 80 / 15 / 5, and dispersed in NMP to prepare a slurry. The obtained slurry was applied to a copper (Cu) current collector foil, pressed, and then vacuum-dried at 120°C overnight to obtain a negative electrode laminate as a test electrode. The positive electrode active material was weighed out at a weight ratio of 85 / 10 / 5, and dispersed in NMP to prepare a slurry. The obtained slurry was applied to an Al current collector foil, pressed, and then vacuum-dried at 120°C overnight to obtain a positive electrode laminate as a test electrode. Each laminate was opposed to each other via a polypropylene separator, and these were impregnated with an electrolyte and sealed to prepare an evaluation cell. In addition, in the evaluation cell as a lithium ion battery, nickel cobalt manganese oxide (NCM) was used as the positive electrode active material, and 1M LiPF was used as the electrolyte. 6 In the evaluation cell for the sodium ion battery, nickel iron manganese (NiFeMn) oxide was used as the positive electrode active material and 1M NaPF 6 in EC / DEC was used.

[0114] "evaluation" <Increase in confining pressure> The evaluation was performed in a thermostatic chamber at 25°C, with a voltage range of 4.2-2.5V and a rate of 0.1C. A load cell (KYOWA, LCX-A-10KN) was inserted during charging and discharging, and charging was started at an initial pressure of 1MPa. The increase in the binding pressure during the initial charging was divided by the charging capacity to calculate the increase in the binding pressure per capacity. The increase in the binding pressure refers to the amount of expansion of the negative electrode active material. The results are shown in Table 19.

[0115] Other evaluations were carried out in the same manner as above.

[0116] In this example, the carbon concentration before and after dissolution was measured using HORIBA's EMIA-20E, and the amount of SiO in the negative electrode active material was calculated from the change in the ratio of the carbon amount by infrared absorption method. 2 was confirmed to be included.

[0117] Examples 19-2 to 19-5, Comparative Examples 19-1 to 19-5, and Reference Example 19-1 Except for changing the composition, carbon content, half width of the tin alloy, and volume ratio of the voids as shown in Table 19, the batteries of each example were fabricated and evaluated in the same manner as in Example 19-1.

[0118] The confining pressure increase for each of the above examples is shown in Table 19. In Table 19, the confining pressure increase for the examples is shown as a relative value when the confining pressure increase for the comparative example with the corresponding composition is set to 100.

[0119] In these examples, the carbon concentration before and after dissolution was measured using an EMIA-20E manufactured by HORIBA, and the amount of SiO in the negative electrode active material was calculated based on the change in the ratio of the carbon amount by infrared absorption method. 2 was confirmed to be included.

[0120] [Table 19]

[0121] As shown in Table 19, in the batteries of the examples in which the carbon content, half-width of the tin alloy, and void volume ratio were within the ranges of the present disclosure, the increase in confining pressure, i.e., the expansion of the negative electrode active material, was small.

[0122] Examples 20-1 to 20-4 In particular, except that the volume ratio of the pores was changed as shown in Table 20, the batteries of each example were fabricated in the same manner as in Example 19-1 and evaluated.

[0123] The confining pressure increase for each of the above examples is shown in Table 20. In Table 20, the confining pressure increase for each example is shown as a relative value when the confining pressure increase for Comparative Example 19-1 is set to 100.

[0124] [Table 20]

[0125] As shown in Table 20, in the batteries of the examples in which the pore volume ratio was within the range of the present disclosure, the increase in confining pressure, that is, the amount of expansion of the negative electrode active material, was small. [Explanation of symbols]

[0126] 10 Negative electrode active material 11 Carbon Materials 12 Tin alloy 13 Silicon metal 14 Vacancies 100 Secondary battery 110 Negative electrode current collector 120 Negative electrode active material layer 130 Separator 140 Cathode active material layer 150 Positive electrode current collector

Claims

1. A composite material including 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 content of the carbon material is 10% by mass or more and 30% by mass or less, The half width of the tin alloy in the XRD spectrum is 0.3° or more; and The porous material has pores of 0.5% by volume or more and 40% by volume or less. Negative electrode active material.

2. Further comprising silicon carbide and silicon metal; The content of the metal silicon is 0.1% by mass or more and 15% by 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; The negative electrode active material according to claim 1 .

3. The negative electrode active material of claim 1 , further comprising silicon oxide.

4. A negative electrode mixture comprising the negative electrode active material according to any one of claims 1 to 3.

5. A negative electrode active material layer is provided, and The negative electrode active material layer contains the negative electrode mixture according to claim 4. Secondary battery.

6. A method for producing the negative electrode active material according to any one of claims 1 to 3, comprising the following steps: mixing the carbon material, the tin, and the metal by a mechanical alloying method to obtain the composite material; mixing the composite material, metal silicon and / or silicon oxide by a mechanical alloying method 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 silicon metal and / or silicon oxide, thereby forming the pores.

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