Negative electrode active material for non-aqueous electrolyte secondary batteries, negative electrode for non-aqueous electrolyte secondary batteries, and non-aqueous electrolyte secondary battery

Abstract

The present invention provides a negative electrode active material for a non-aqueous electrolyte secondary battery, the negative electrode active material containing a silicon-based material, and the area-based particle size distribution of the negative electrode active material for a non-aqueous electrolyte secondary battery has two or more peaks including a first peak and a second peak.

Description

Technical Field

[0001] The present invention relates to a negative electrode active material for a non-aqueous electrolyte secondary battery, a negative electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

[0002] This application claims the priority of Japanese Application No. 2023-045578 filed on March 22, 2023, and incorporates by reference all the disclosures in the above-mentioned Japanese application. Background Art

[0003] Patent Document 1 discloses a hollow silicon-based particle containing silicon (Si) or silicon oxide (SiO x , 0 < x < 2) particles having a hollow core portion inside, and the size of the hollow core portion is 5 nm to 45 μm.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-530342. Summary of the Invention

[0007] The negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention contains a silicon-based material,

[0008] The particle size distribution of the negative electrode active material for a non-aqueous electrolyte secondary battery based on area has two or more peaks including a first peak and a second peak. Brief Description of the Drawings

[0009] Figure 1 It is an explanatory diagram of the particle size distribution of the negative electrode active material for a non-aqueous electrolyte according to one embodiment of the present invention.

[0010] Figure 2 It is an explanatory diagram of the negative electrode for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention.

[0011] Figure 3 It is an explanatory diagram of the non-aqueous electrolyte secondary battery according to one embodiment of the present invention. Detailed Description of the Invention

[0012] [Problems to be Solved by the Invention]

[0013] As a power source for portable terminals such as smartphones and electric vehicles, non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are widely used. Further performance improvement is required for non-aqueous electrolyte secondary batteries, and various studies have been conducted on constituent members.

[0014] For example, as the negative electrode active material of a non-aqueous electrolyte secondary battery, carbon-based materials such as graphite have been used. However, higher battery capacity is required for non-aqueous electrolyte secondary batteries. Therefore, as disclosed in Patent Document 1 and the like, silicon-based materials have attracted attention as the negative electrode active material of non-aqueous electrolyte secondary batteries.

[0015] However, it is known that when a silicon-based material is applied to a non-aqueous electrolyte secondary battery, the battery capacity decreases during repeated charge and discharge. Therefore, a negative electrode active material for a non-aqueous electrolyte secondary battery is required, which, when applied to a non-aqueous electrolyte secondary battery, enables high battery capacity and has excellent retention rate of battery capacity, i.e., capacity retention rate, during repeated charge and discharge.

[0016] Therefore, an object of the present invention is to provide a negative electrode active material for a non-aqueous electrolyte secondary battery, which has excellent battery capacity and capacity retention rate when applied to a non-aqueous electrolyte secondary battery.

[0017] [Effects of the Present Invention]

[0018] According to the present invention, it is possible to provide a negative electrode active material for a non-aqueous electrolyte secondary battery, which has excellent battery capacity and capacity retention rate when applied to a non-aqueous electrolyte secondary battery.

[0019] Hereinafter, the embodiments for implementation will be described.

[0020] [Description of Embodiments of the Present Invention]

[0021] First, the embodiments of the present invention will be listed and described. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description thereof will not be repeated.

[0022] (1) The negative electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention contains a silicon-based material.

[0023] The particle size distribution of the negative electrode active material for a non-aqueous electrolyte secondary battery based on area has two or more peaks including a first peak and a second peak.

[0024] The negative electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention, by containing a silicon-based material, can form a non-aqueous electrolyte secondary battery with a high battery capacity when applied to a non-aqueous electrolyte secondary battery as compared with the case of using a carbon-based material. (Hereinafter, the negative electrode active material for a non-aqueous electrolyte secondary battery will also be referred to as "negative electrode active material". In addition, the non-aqueous electrolyte secondary battery will also be referred to as "secondary battery").

[0025] In the case of a negative electrode active material having two or more peaks in the particle size distribution based on area, it is considered that the relatively large-sized negative electrode active material contained has the effect of improving the contact with the current collector. Therefore, when applied to a secondary battery, the battery capacity can be increased.

[0026] In addition, it is considered that by including a relatively large-sized negative electrode active material, the relatively small-sized negative electrode active material can be supported to form a path for lithium ions to pass between the negative electrode active materials. Therefore, by including a relatively large-sized negative electrode active material, even if the addition amounts of the conductive assistant and the binder are suppressed, the proportion of the negative electrode active material contributing to charge and discharge can be increased, and the form of the negative electrode can be easily maintained. As a result, it is considered that the battery capacity can be increased.

[0027] The relatively small-sized negative electrode active material contained in the negative electrode active material of one embodiment of the present invention can suppress the pulverization of the relatively small-sized negative electrode active material itself during repeated charge and discharge. Furthermore, it is considered that the relatively small-sized negative electrode active material contained in the negative electrode active material of one embodiment of the present invention can absorb the volume change of the relatively large-sized negative electrode active material and suppress the pulverization of the relatively large-sized negative electrode active material. Therefore, it is considered that by including a relatively small-sized negative electrode active material, the capacity retention rate can be increased when applied to a secondary battery.

[0028] As described above, regarding the negative electrode active material of one embodiment of the present invention, it is considered that the relatively small-sized negative electrode active material corresponding to each peak and the relatively large-sized negative electrode active material cooperate with each other by the negative electrode active material having two or more peaks in the particle size distribution based on area. Therefore, it is considered that when the negative electrode active material of one embodiment of the present invention is applied to a secondary battery, the battery capacity and the capacity retention rate can be increased.

[0029] (2) In the above (1), the top of the first peak may be in the range of 10 nm or more and 500 nm or less in particle size,

[0030] The top of the second peak may be in the range of 0.5 μm or more and 50 μm or less in particle size.

[0031] Regarding the top of the first peak, by being in the range of 10 nm or more and 500 nm or less in particle size, when the negative electrode active material of one embodiment of the present invention is applied to a secondary battery and repeatedly charged and discharged, pulverization can be suppressed and the capacity retention rate can be increased.

[0032] Regarding the top of the second peak, by being in the range of 0.5 μm or more and 50 μm or less in particle size, when the negative electrode active material of one embodiment of the present invention is applied to a secondary battery, the battery capacity can be increased.

[0033] (3) In the above (1) or (2), the difference between the particle size at the top of the first peak and the particle size at the top of the second peak may be 500 nm or more.

[0034] By making the difference between the particle size at the top of the first peak and the particle size at the top of the second peak 500 nm or more, the negative electrode active material of one embodiment of the present invention will contain two or more negative electrode active materials with sufficiently different particle sizes. Therefore, for the negative electrode active material of one embodiment of the present invention, by making the difference between the particle size at the top of the first peak and the particle size at the top of the second peak 500 nm or more, the battery capacity and the capacity retention rate can be particularly improved.

[0035] (4) In any one of the above (1) to (3), the ratio of the area of the second peak to the area of the first peak may be 0.1 or more and 5.0 or less.

[0036] The ratio of the area of the second peak to the area of the first peak means the ratio of the frequency based on the area of the negative electrode active material corresponding to the second peak contained in the negative electrode active material to the frequency based on the area of the negative electrode active material corresponding to the first peak.

[0037] Moreover, by making the ratio of the area of the second peak to the area of the first peak 0.1 or more, the proportion of the negative electrode active material with a relatively large particle size in the negative electrode active material can be sufficiently ensured, and the battery capacity can be particularly improved.

[0038] In addition, by making the ratio of the area of the second peak to the area of the first peak 5.0 or less, the proportion of the negative electrode active material with a relatively small particle size in the negative electrode active material can be sufficiently ensured, and the capacity retention rate can be particularly improved.

[0039] (5) The negative electrode for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes a current collector and a negative electrode composite material supported on the current collector.

[0040] The negative electrode composite material includes the negative electrode active material for a non-aqueous electrolyte secondary battery according to any one of (1) to (4), a conductive assistant, and a binder.

[0041] According to the negative electrode active material of one embodiment of the present invention, when applied to a secondary battery, a secondary battery with excellent battery capacity and capacity retention rate can be manufactured. Therefore, for the negative electrode for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention (hereinafter also referred to as "negative electrode") containing the negative electrode active material of one embodiment of the present invention, when applied to a secondary battery, a secondary battery with high capacity and excellent capacity retention rate can also be manufactured.

[0042] (6) In the above (5), the current collector may be a porous metal.

[0043] By using porous metal for the current collector, the durability of the negative electrode can be improved, and the negative electrode active material can be arranged at a high density on the negative electrode. Therefore, in the case of being used for a secondary battery, the battery capacity and the capacity retention rate can be particularly improved.

[0044] (7) The non-aqueous electrolyte secondary battery according to one embodiment of the present invention has the negative electrode for the non-aqueous electrolyte secondary battery described in the above (5) or (6).

[0045] The secondary battery according to one embodiment of the present invention has the negative electrode for the non-aqueous electrolyte secondary battery according to one embodiment of the present invention. Therefore, it can be a secondary battery excellent in battery capacity and capacity retention rate.

[0046] [Details of Embodiments of the Present Invention]

[0047] Hereinafter, specific examples of the negative electrode active material for the non-aqueous electrolyte secondary battery, the negative electrode for the non-aqueous electrolyte secondary battery, and the non-aqueous electrolyte secondary battery according to one embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described with reference to the drawings. In addition, the present invention is not limited to these examples, but is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0048] In this specification, as in the case of the first peak and the second peak, numbers such as the first and the second may sometimes be added to the name in order to clarify the indicated content and avoid confusion, and do not indicate a priority order or the like. Therefore, when there is no confusion, it is also possible to omit adding numbers such as the first and the second and simply describe it as a peak or the like.

[0049] [Negative Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery]

[0050] The negative electrode active material for the non-aqueous electrolyte secondary battery according to the present embodiment contains a silicon-based material, and the particle size distribution based on area has two or more peaks including a first peak and a second peak. In this specification, it may sometimes be simply described as the particle size distribution, and unless otherwise specified, the particle size distribution refers to the particle size distribution based on area.

[0051] (1) Regarding the silicon-based material

[0052] The negative electrode active material according to the present embodiment can contain a silicon-based material. By containing a silicon-based material, the negative electrode active material according to the present embodiment can be made into a secondary battery with a high battery capacity when applied to a non-aqueous electrolyte secondary battery as compared with the case of using a carbon-based material.

[0053] As the silicon-based material contained in the negative electrode active material according to the present embodiment, one or more selected from silicon monomer, silicon alloy, silicon oxide, silicon compound, etc. can be used.

[0054] The silicon monomer may be one or more selected from crystalline silicon and amorphous silicon, and the purity may be 95% by mass or more.

[0055] Silicon alloy refers to an alloy of silicon and other metal elements, and as the metal element, one or more selected from aluminum (Al), magnesium (Mg), lanthanum (La), silver (Ag), tin (Sn), titanium (Ti), yttrium (Y), chromium (Cr), nickel (Ni), zirconium (Zr), vanadium (V), niobium (Nb), molybdenum (Mo), etc. The alloy may be a complete solid solution alloy, a eutectic alloy, a hypoeutectic alloy, a hypereutectic alloy, a peritectic alloy, etc.

[0056] Silicon oxide refers to silicon oxide or a composite composed of silicon monomer and silicon oxide (SiO2). The element ratio of silicon (Si) to oxygen (O) is 1 to 1.7 or less for oxygen.

[0057] Silicon compounds are substances formed by chemical bonding of silicon with two or more other elements.

[0058] As the silicon-based material, for example, silicon alone can be used as described above.

[0059] The negative electrode active material of this embodiment may contain carbon-based materials (graphite, hard carbon, soft carbon, etc.) in addition to silicon-based materials. In the case where the negative electrode active material of this embodiment contains carbon-based materials in addition to silicon-based materials, it may be a mixture of silicon-based materials and carbon-based materials, or a material formed by a composite of silicon-based materials and carbon-based materials. In addition, the negative electrode active material of this embodiment may also be composed only of silicon-based materials.

[0060] The shape of the silicon-based material is not particularly limited, and may be spherical, elliptical, polyhedral, ribbon-shaped, fibrous, flaky, ring-shaped, or hollow powder. These may be single particles or granules.

[0061] (2) Particle size distribution

[0062] The inventors of the present invention have studied a non-aqueous electrolyte secondary battery negative electrode active material having excellent battery capacity and capacity retention rate when applied to a secondary battery. In addition, in this specification, battery capacity refers to initial discharge capacity. In addition, capacity retention rate refers to the retention rate of discharge capacity when repeatedly charging and discharging.

[0063] The research focused on silicon-based materials that can be expected to have high capacity. In addition, the relationship between the particle size of silicon-based materials and the characteristics when used in secondary batteries was studied. In addition, the particle size was determined based on the most frequent particle size in the area-based particle size distribution obtained by electron microscope observation, i.e., the mode diameter.

[0064] According to the research of the inventors of the present invention, it has been confirmed that in the case of manufacturing a secondary battery using a silicon-based material with a relatively large particle size as the negative electrode active material, the battery capacity can be increased. However, regarding this secondary battery, it has been confirmed that if charge and discharge are repeated, the negative electrode active material is pulverized, and the battery capacity decreases, that is, the capacity retention rate decreases.

[0065] In contrast, in the case of manufacturing a secondary battery using a silicon-based material with a relatively small particle size as the negative electrode active material, the volume change of the negative electrode active material during repeated charge and discharge can be suppressed. Therefore, it has been confirmed that the pulverization of the negative electrode active material can be suppressed, and the decrease in the capacity retention rate can be suppressed.

[0066] However, in the case of a secondary battery using a silicon-based material with a relatively small particle size as the negative electrode active material, it has been confirmed that the battery capacity is lower than that in the case of using a silicon-based material with a relatively large particle size as the negative electrode active material. As a reason for this, it is speculated that when manufacturing the negative electrode, the negative electrode active material is supported on the current collector, but since the particle size of the negative electrode active material is relatively small, the bite on the current collector becomes weaker compared to the case of a relatively large particle size, and the contact between the current collector and the negative electrode active material deteriorates.

[0067] In addition, in the case of a secondary battery using a silicon-based material with a relatively small particle size for the negative electrode active material, in order to make the battery capacity sufficiently large, compared with the case of using a silicon-based material with a relatively large particle size for the negative electrode active material, it is necessary to increase the addition amount of the conductive assistant when manufacturing the negative electrode. It is considered that this is because only the negative electrode active material within a certain range from the conductive assistant contributes to charge and discharge. Furthermore, in the case of manufacturing a secondary battery using a silicon-based material with a relatively small particle size for the negative electrode active material, compared with the case of using a silicon-based material with a relatively large particle size for the negative electrode active material, the specific surface area of the negative electrode active material increases. Therefore, in the case of manufacturing a secondary battery using a silicon-based material with a relatively small particle size for the negative electrode active material, in order to maintain the shape of the negative electrode, compared with the case of using a silicon-based material with a relatively large particle size for the negative electrode active material, it is necessary to increase the addition amount of the binder.

[0068] However, if the addition amounts of the conductive assistant and the binder are increased, the proportion of the components that do not contribute to charge and discharge in the negative electrode composite material becomes higher, and as a result, the battery capacity per unit volume and weight of the secondary battery decreases.

[0069] As described above, in the case of manufacturing a secondary battery using a silicon-based material for the negative electrode active material, it has been confirmed that the case of using a silicon-based material with a relatively large particle size and the case of using a relatively small particle size each have advantages. However, it has been confirmed that a secondary battery with both excellent battery capacity and capacity retention rate cannot be achieved.

[0070] Therefore, the inventors of the present invention conducted further research. As a result, it was confirmed that when a negative electrode active material having a particle size distribution with two or more peaks is applied to a secondary battery, a secondary battery excellent in battery capacity and capacity retention rate can be obtained. Therefore, the negative electrode active material of the present embodiment is as follows Figure 1 shown, the particle size distribution 10 can have a first peak 11 and a second peak 12. The negative electrode active material having a particle size distribution with two or more peaks as the negative electrode active material of the present embodiment means a negative electrode active material containing two or more negative electrode active materials having different particle diameters and particle size distributions corresponding to each peak.

[0071] It is considered that when a negative electrode active material having a particle size distribution with two or more peaks is produced, the relatively large-diameter negative electrode active material contained therein has the effect of improving the contact with the current collector. Therefore, when applied to a secondary battery, the battery capacity can be increased.

[0072] In addition, it is considered that by including a relatively large-diameter negative electrode active material, the relatively small-diameter negative electrode active material can be supported, and a path for lithium ions to pass between the negative electrode active materials can be formed. Therefore, by including a relatively large-diameter negative electrode active material, even if the addition amounts of the conductive assistant and the binder are suppressed, the proportion of the negative electrode active material contributing to charge and discharge can be increased, and the shape of the negative electrode can be easily maintained. As a result, it is considered that the battery capacity can be increased.

[0073] The relatively small-diameter negative electrode active material contained in the negative electrode active material of the present embodiment can suppress the pulverization of the relatively small-diameter negative electrode active material itself during repeated charge and discharge. Furthermore, it is considered that the relatively small-diameter negative electrode active material contained in the negative electrode active material of the present embodiment can absorb the volume change of the relatively large-diameter negative electrode active material and suppress the pulverization of the relatively large-diameter negative electrode active material. Therefore, it is considered that by including a relatively small-diameter negative electrode active material, when applied to a secondary battery, the capacity retention rate can be increased.

[0074] As described above, regarding the negative electrode active material of the present embodiment, it is considered that by producing a negative electrode active material having a particle size distribution with two or more peaks, the relatively small-diameter negative electrode active material corresponding to each peak and the relatively large-diameter negative electrode active material act synergistically. Therefore, it is considered that when the negative electrode active material of the present embodiment is applied to a secondary battery, the battery capacity and the capacity retention rate can be increased.

[0075] The method for measuring the particle size distribution of the negative electrode active material of the present embodiment is not particularly limited. For example, first, the cross-sections of a plurality of particles can be observed with a scanning electron microscope or the like, and the equivalent circle diameter obtained from the area of the cross-section of the particle can be used as the particle diameter of each particle. Then, as the particle size distribution of the negative electrode active material of the present embodiment, a particle size distribution based on area can be used, and the particle size distribution based on area is created using the particle diameters of the obtained particles.

[0076] In the case of observing the cross-sections of a plurality of particles with a scanning electron microscope (SEM), first, the particles of the negative electrode active material to be evaluated are embedded in a resin. Then, after the resin is cured, it is cut along the plane passing through the particles in the resin with a microtome or the like, or mechanical polishing and polishing using a cross-section polisher are performed to produce a specimen with the cross-section of the particles exposed. Next, the produced specimen is observed with a scanning electron microscope. At this time, the number of fields of view and magnification are selected so that a total of 1000 or more and 100000 or less particles can be observed. The cross-sectional area of each particle portion can be obtained by image processing from the obtained observation images, the equivalent circle diameter can be calculated, and the particle size distribution can be created. The particle size distribution can be created using the particle diameters of all the particles for which the equivalent circle diameter has been observed and calculated.

[0077] In addition, in the case of obtaining the particle size distribution by observing the negative electrode active material used in the negative electrode with a scanning electron microscope, the negative electrode can be embedded in a resin, and after the resin is cured, it is cut with a microtome or the like, or mechanical polishing and polishing using a cross-section polisher are performed. Through the above operations, a specimen with the cross-section of the negative electrode active material particles exposed can be produced. Except for the above aspects, the particle size distribution can be measured by the same steps.

[0078] In addition, the particle size distribution of the negative electrode active material of the present embodiment may have two or more peaks including a first peak and a second peak related to the silicon-based material. Therefore, when the negative electrode active material also contains materials other than the silicon-based material, for example, when performing cross-section observation with a scanning electron microscope, particles of the silicon-based material can be selected and evaluated by EDS or the like. EDS is an abbreviation for Energy Dispersive X-ray Spectroscopy, and is sometimes also referred to as EDX or the like.

[0079] (3) Regarding the first peak and the second peak of the particle size distribution

[0080] (3-1) Regarding the peak position

[0081] In the particle size distribution 10 of the negative electrode active material of the present embodiment, the top 11A of the first peak 11 may be within the range of 10 nm or more and 500 nm or less in particle diameter (see Figure 1 ). Further, the top 12A of the second peak 12 may be within the range of 0.5 μm or more and 50 μm or less.

[0082] The top of the peak means the point where a straight line parallel to the horizontal axis of the particle size distribution is drawn in contact with the peak at a single point. Thus, in the case of the particle size distribution 10 shown in Figure 1 , the point where the first peak 11 contacts the straight line L1 passing through the maximum value of the first peak and contacting the first peak 11 at a single point becomes the top 11A of the first peak. Further, the point where the second peak 12 contacts the straight line L2 passing through the maximum value of the second peak and contacting the second peak 12 at a single point becomes the top 12A of the second peak.

[0083] For the top 11A of the first peak 11, by being within the range of 10 nm or more and 500 nm or less in particle diameter, when the negative electrode active material of the present embodiment is applied to a secondary battery and charged and discharged repeatedly, pulverization can be suppressed and the capacity retention rate can be improved. For the top 11A of the first peak 11, by being within the range of 50 nm or more and 300 nm or less in particle diameter, the capacity retention rate can be further improved.

[0084] For the top 12A of the second peak 12, by being within the range of 0.5 μm or more and 50 μm or less in particle diameter, when the negative electrode active material of the present embodiment is applied to a secondary battery, the battery capacity can be increased. For the top 12A of the second peak 12, by being within the range of 1 μm or more and 10 μm or less in particle diameter, the effect of increasing the battery capacity is particularly excellent.

[0085] There is no particular limitation on the difference D between the particle diameter of the top 11A of the first peak 11 and the particle diameter of the top 12A of the second peak 12, and the difference D between the particle diameter of the top 11A of the first peak 11 and the particle diameter of the top 12A of the second peak 12 may be 500 nm or more.

[0086] The difference D between the particle diameter of the top 11A of the first peak 11 and the particle diameter of the top 12A of the second peak 12 is a value obtained by subtracting the particle diameter of the top 11A of the first peak 11 from the particle diameter of the top 12A of the second peak 12.

[0087] By making the difference D between the particle size of the top 11A of the first peak 11 and the particle size of the top 12A of the second peak 12 be 500 nm or more, the negative electrode active material of the present embodiment contains two or more types of negative electrode active materials with sufficiently different particle sizes. Therefore, for the negative electrode active material of the present embodiment, by making the difference D between the particle size of the top 11A of the first peak 11 and the particle size of the top 12A of the second peak 12 be 500 nm or more, the battery capacity and the capacity retention rate can be particularly improved.

[0088] There is no particular limitation on the upper limit value of the difference D between the particle size of the top 11A of the first peak 11 and the particle size of the top 12A of the second peak 12, and it can be, for example, 2000 nm or less. That is, the difference D between the particle size of the top 11A of the first peak 11 and the particle size of the top 12A of the second peak 12 can be 500 nm or more and 2000 nm or less.

[0089] The negative electrode active material of the present embodiment can also have three or more peaks in the particle size distribution. In this case, any two of the three or more peaks can be set as the first peak and the second peak, and the above range can also be satisfied.

[0090] (3-2) Regarding the area ratio of the peaks

[0091] In the particle size distribution of the negative electrode active material of the present embodiment, the ratio of the area of the second peak 12 to the area of the first peak 11 can be 0.1 or more and 5.0 or less.

[0092] Let the area of the first peak 11 be S1 and the area of the second peak 12 be S2. In this case, the ratio R of the area of the second peak 12 to the area of the first peak 11 can be calculated by the following formula (1).

[0093] R = S2÷S1…(1)

[0094] The ratio R of the area of the second peak 12 to the area of the first peak 11 means the ratio of the frequency based on the area of the negative electrode active material corresponding to the second peak 12 contained in the negative electrode active material of the present embodiment to the frequency based on the area of the negative electrode active material corresponding to the first peak 11.

[0095] Moreover, by making the ratio of the area of the second peak 12 to the area of the first peak 11 be 0.1 or more, the proportion of the negative electrode active material with a relatively large particle size in the negative electrode active material can be sufficiently ensured, and the battery capacity can be particularly improved.

[0096] In addition, by making the ratio of the area of the second peak 12 to the area of the first peak 11 be 5.0 or less, the proportion of the negative electrode active material with a relatively small particle size in the negative electrode active material can be sufficiently ensured, and the capacity retention rate can be particularly improved.

[0097] In particular, from the viewpoint of improving battery capacity and capacity retention rate, in the particle size distribution of the negative electrode active material of the present embodiment, the ratio of the area of the second peak 12 to the area of the first peak 11 can be 0.3 or more and 1.5 or less.

[0098] (4) Method for manufacturing negative electrode active material for non-aqueous electrolyte secondary battery

[0099] The method for manufacturing the negative electrode active material of the present embodiment is not particularly limited, and it can be prepared and manufactured in such a way that the particle size distribution has two or more peaks including a first peak and a second peak.

[0100] The method for manufacturing the negative electrode active material of the present embodiment can have, for example, a mixing step of mixing a first negative electrode active material and a second negative electrode active material having different particle size distribution characteristics prepared in advance.

[0101] In the mixing step, the method of mixing the first negative electrode active material and the second negative electrode active material is not particularly limited, and they can be mixed in such a way that the particle form of the first negative electrode active material is not damaged and the particle form of the second negative electrode active material is not damaged.

[0102] After the mixing step, sieving or the like can also be performed as needed to further adjust the particle size distribution.

[0103] [Negative electrode for non-aqueous electrolyte secondary battery]

[0104] Figure 2 The figure shows a schematic view showing an enlarged part of the negative electrode for non-aqueous electrolyte secondary battery of the present embodiment (hereinafter, also referred to as "negative electrode"). In Figure 2 the figure, an example is shown in which the negative electrode composite material 25 is disposed only in a part of the pores 211, but the negative electrode composite material 25 can also be disposed in all the pores 211.

[0105] As Figure 2 shown, the negative electrode 20 of the present embodiment can include a current collector 21 and a negative electrode composite material 25 supported on the current collector 21.

[0106] The negative electrode active material according to one aspect of the present invention, when applied to a secondary battery, can be made into a secondary battery having excellent battery capacity and capacity retention rate. Therefore, for the negative electrode of the present embodiment including the negative electrode active material according to one aspect of the present invention, when applied to a secondary battery, a secondary battery having high capacity and excellent capacity retention rate can also be made.

[0107] (1) Regarding the components and materials of the negative electrode

[0108] The components and materials of the negative electrode of the present embodiment will be described.

[0109] (1-1) Current collector

[0110] As the current collector 21, any material can be used as long as it can support the negative electrode composite material 25 and has conductivity, and there is no particular limitation. As the current collector 21, for example, porous metal can be used. By using porous metal for the current collector 21, the durability of the negative electrode 20 can be improved, and the negative electrode active material can be arranged at a high density in the negative electrode 20. Therefore, in the case of being used for a secondary battery, the battery capacity and the capacity retention rate can be particularly improved. When porous metal is used for the current collector 21, for example, Figure 2 as shown, the negative electrode composite material 25 can be supported in the pores 211 of the porous metal.

[0111] As the porous metal, one or more selected from metal mesh, woven fabric, non-woven fabric, embossed body, punched body, expanded body, foam body, etc. can be used. As the porous metal, a foam metal body can also be used. In particular, as the porous metal, a foam metal body having a three-dimensional grid structure with continuous pores can also be used, and for example, Celmet (registered trademark) (manufactured by Sumitomo Electric Industries, Ltd.) can be used.

[0112] As the material of the current collector 21, as long as it has electron conductivity and can conduct electricity to the supported negative electrode composite material, there is no particular limitation. As the material of the current collector 21, for example, one selected from the group of conductive metals such as aluminum, aluminum alloy, nickel, nickel-chromium alloy, iron, copper, titanium, chromium, gold, molybdenum, tungsten, tantalum, platinum, ruthenium, rhodium, etc. can be used. In addition, as the material of the current collector 21, a conductive alloy containing two or more selected from the above group of conductive metals, etc. can also be used. As the conductive alloy, for example, stainless steels such as SUS304, SUS316, SUS316L, YUS270, etc. can be cited.

[0113] As the material of the current collector 21, a multi-layer structure of dissimilar metals having a first layer of iron and a second layer of copper and nickel covering the first layer can also be used.

[0114] As the material of the current collector 21, nickel or nickel alloy can also be used because of its excellent electron conductivity and reducibility resistance.

[0115] (1-2) Negative electrode composite material

[0116] The negative electrode composite material 25 can contain the negative electrode active material 22, the conductive assistant 23, and the binder 24 of one embodiment of the present invention.

[0117] The negative electrode active material 22 can contain the first negative electrode active material 221 and the second negative electrode active material 222 which are negative electrode active materials with different particle sizes.

[0118] (Conductive additive)

[0119] As the conductive additive 23, there is no particular limitation as long as it has electron conductivity, and metals, carbon materials, conductive polymers, conductive glass, etc. can be used. Specifically, as the conductive additive 23, one or more selected from, for example, acetylene black, Ketjen black (registered trademark), furnace black, thermal black, lamp black, channel black, roller black, disc black, carbon black, carbon fiber, carbon nanotube, carbon nano horn, graphite, graphene, glassy carbon, amorphous carbon, etc. can be used.

[0120] (Binder)

[0121] There is also no particular limitation for the binder 24. Specifically, one or more selected from, for example, the following substances can be used: polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, aramid, acrylic polymer, styrene-butadiene rubber (SBR), ethylene-vinyl acetate copolymer (EVA), styrene-ethylene-butene-styrene copolymer (SEBS), carboxymethyl cellulose (CMC), xanthan gum, polyvinyl alcohol (PVA), ethylene-vinyl alcohol, polyvinyl butyral (PVB), ethylene-vinyl alcohol, polyethylene (PE), polypropylene (PP), polyacrylic acid, lithium polyacrylate, sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, methyl polyacrylate, ethyl polyacrylate, acrylamide polyacrylate, polyacrylate, epoxy resin, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), nylon, vinyl chloride, silicone rubber, nitrile rubber, cyanoacrylate, urea-formaldehyde resin, melamine resin, phenolic resin, latex, polyurethane, silylated polyurethane, nitrocellulose, dextrin, polyvinylpyrrolidone, vinyl acetate, polystyrene, allyl chloride, resorcinol resin, polyaromatic, modified silicon, methacrylic resin, polybutene, butyl rubber, 2-acrylic acid, cyanoacrylic acid, methyl methacrylate, glycidyl methacrylate, acrylic oligomer, 2-hydroxyethyl acrylate, alginic acid, starch, raw lacquer, sucrose, gelatin, casein, cellulose nanofiber and other organic materials.

[0122] In addition to the above-mentioned organic materials, the binder 24 can also contain inorganic materials. Specific examples of the inorganic materials include, for example, silicate-based, phosphate-based, sol-based, cement-based materials, etc. One or more materials selected from the following can be used: lithium silicate, sodium silicate, potassium silicate, cesium silicate, guanidine silicate, ammonium silicate, fluorosilicate, borate, lithium aluminate, sodium aluminate, potassium aluminate, aluminosilicate, lithium aluminate, sodium aluminate, potassium aluminate, polyaluminum chloride, polyaluminum sulfate, polyaluminum silicate sulfate, aluminum sulfate, aluminum nitrate, ammonium alum, lithium alum, sodium alum, potassium alum, chromium alum, iron alum, manganese alum, ammonium nickel sulfate, diatomaceous earth, Polyzirconoxane, Polytantaloxane, mullite, fumed silica, silica sol, colloidal silica, fumed silica, alumina sol, colloidal alumina, fumed alumina, zirconia sol, colloidal zirconia, fumed zirconia, magnesia sol, colloidal magnesia, fumed magnesia, calcium oxide sol, colloidal calcium oxide, fumed calcium oxide, titanium dioxide sol, colloidal titanium dioxide, fumed titanium dioxide, zeolite, silicoaluminophosphate zeolite, sepiolite, montmorillonite, kaolin, soapstone, aluminum phosphate salt, magnesium phosphate salt, calcium phosphate salt, iron phosphate salt, copper phosphate salt, zinc phosphate salt, titanium phosphate salt, manganese phosphate salt, barium phosphate salt, tin phosphate salt, low melting point glass, stucco, gypsum, magnesia cement, litharge cement, Portland cement, blast furnace cement, fly ash cement, silica cement, phosphate cement, concrete, solid electrolyte, etc.

[0123] The content ratios of the negative electrode active material 22, the conductive assistant 23, and the binder 24 contained in the negative electrode composite material 25 are not particularly limited and can be selected according to the required battery characteristics and the like.

[0124] For the negative electrode composite material 25, when the total content ratio of the negative electrode active material 22, the conductive assistant 23, and the binder 24 is set to 100% by mass, for example, the content ratio of the conductive assistant 23 can be 0% or more and 25.0% by mass or less, or it can be 5.0% by mass or more and 20.0% by mass or less. By setting the content of the conductive assistant 23 to 0% or more and 25.0% by mass or less, the conductivity can be improved without reducing the negative electrode capacity density.

[0125] Regarding the negative electrode composite material 25, when the total of the content ratios of the negative electrode active material 22, the conductive assistant 23, and the binder 24 is set to 100% by mass, for example, the content ratio of the binder 24 can be 0.1% by mass or more and 60.0% by mass or less, or it can be 0.5% by mass or more and 30.0% by mass or less. By setting the content ratio of the binder 24 to 0.1% by mass or more and 60.0% by mass or less, the mechanical strength of the negative electrode can be improved without reducing the negative electrode capacity density. Therefore, the capacity retention rate can also be improved.

[0126] (2) Regarding the manufacturing method of the negative electrode

[0127] The manufacturing method of the negative electrode of the present embodiment is not particularly limited, and it can be manufactured by coating the negative electrode composite material 25 on the current collector 21 and loading it.

[0128] The manufacturing method of the negative electrode of the present embodiment can have, for example, the following negative electrode composite material preparation process and loading process.

[0129] In the negative electrode composite material preparation process, the negative electrode active material 22, the conductive assistant 23, and the binder 24 can be mixed to prepare the negative electrode composite material 25.

[0130] In the loading process, after filling and coating the negative electrode composite material 25 on the current collector 21 and drying, a thickness adjustment process can be performed, whereby the negative electrode composite material 25 is loaded on the current collector 21 to manufacture the negative electrode.

[0131] After the loading process, coating of a coating agent, heat treatment, etc. can also be performed as needed.

[0132] [Non-aqueous electrolyte secondary battery]

[0133] The secondary battery of the present embodiment can have a negative electrode of one aspect of the present invention.

[0134] The secondary battery 30 of the present embodiment, in addition to having the negative electrode 20, can also have a positive electrode 31, a separator 32, an electrolyte, etc. as the positive electrode for a non-aqueous electrolyte secondary battery.

[0135] For example, as Figure 3 shown, the secondary battery 30 of the present embodiment can have a structure including an electrode laminate, in which the positive electrode 31, the separator 32, and the negative electrode 20 are laminated. It is also possible to impregnate an electrolyte (not shown) in the electrode laminate.

[0136] The electrode laminate can be disposed in a container 33 such as a laminate, and can be configured as follows: a positive terminal 34 and a negative terminal 35 that are led out of the container 33 are respectively connected to the positive electrode 31 and the negative electrode 20, and can be connected to other components.

[0137] The secondary battery 30 of this embodiment has the negative electrode 20 of one aspect of the present invention. Therefore, it is possible to obtain a secondary battery having excellent battery capacity and capacity retention rate.

[0138] Each component of the secondary battery 30 of this embodiment will be described.

[0139] (1) Positive electrode

[0140] The positive electrode 31 can be any positive electrode that can be used in a secondary battery, and there is no particular limitation. The positive electrode 31 can contain, for example, a current collector and a positive electrode composite material supported on the current collector. The positive electrode composite material can contain, for example, a positive electrode active material, a conductive additive, and a binder.

[0141] Hereinafter, the positive electrode active material, the conductive additive, and the binder will be described.

[0142] (Positive electrode active material)

[0143] As the positive electrode active material, as long as it is a positive electrode active material commonly used in a non-aqueous electrolyte secondary battery, there is no particular limitation. For example, positive electrode active materials such as alkali metal transition metal oxide-based, vanadium-based, sulfur-based, solid solution systems (lithium-excess system, sodium-excess system, potassium-excess system), carbon-based, and organic compound-based can be used.

[0144] (Conductive additive)

[0145] As the conductive additive, the same materials as those described for the conductive additive in the negative electrode can be used, so the description is omitted. In addition, regarding the content ratio of the conductive additive, except for replacing the negative electrode active material with the positive electrode active material, it is the same as that described for the negative electrode active material, so the description is omitted.

[0146] (Binder)

[0147] As the binder, for example, one or more selected from organic materials such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), hexafluoropropylene, tetrafluoroethylene, polyacrylic acid, and alginic acid can be used.

[0148] In addition to containing the above organic materials, the binder can also contain inorganic materials. As the inorganic materials, specifically, for example, silicate-based, phosphate-based, sol-based, and cement-based materials can be mentioned.

[0149] (Current collector)

[0150] As the current collector that can be used in the positive electrode, as long as it is a material having electronic conductivity and capable of energizing the positive electrode active material it holds, there is no particular limitation.

[0151] As the material of the current collector, one kind selected from the group of conductive substances such as carbon, titanium, chromium, nickel, copper, molybdenum, ruthenium, rhodium, tantalum, tungsten, osmium, iridium, platinum, gold, aluminum, etc. can be used. In addition, as the material of the current collector, conductive alloys containing two or more kinds selected from the above group of conductive substances can also be used. Examples of the conductive alloy include stainless steel, aluminum-iron alloy, etc.

[0152] As the material of the current collector, for example, a structure of dissimilar metals having a first layer of iron and a second layer of aluminum covering the first layer; or a structure of dissimilar elements having a first layer of aluminum and a second layer of carbon covering the first layer can also be used.

[0153] As the material of the current collector, from the viewpoint of selecting a material with high electron conductivity and high stability in the electrolyte, one or more kinds selected from carbon, titanium, chromium, gold, aluminum, stainless steel, etc. can be used. Furthermore, from the viewpoints of oxidation resistance and material cost, as the material of the current collector, one or more kinds selected from carbon, aluminum, stainless steel, etc. can also be used. As the material of the current collector, aluminum or aluminum alloy coated with carbon, stainless steel coated with carbon, etc. can also be used.

[0154] The shape of the current collector that can be used in the positive electrode is not particularly limited, and one or more kinds selected from linear, rod-shaped, plate-shaped, foil-shaped, porous, etc. can be used. Especially from the aspect of being able to improve the packing density, the shape of the current collector can be porous. Among the porous ones, examples include nets, woven fabrics, non-woven fabrics, embossed bodies, punched bodies, expanded bodies, or foamed bodies, etc. The porous metal body described for the current collector of the negative electrode can also be used for the current collector of the positive electrode.

[0155] (2)Separator

[0156] As the separator, there is no particular limitation, and the separators commonly used in non-aqueous electrolyte secondary batteries can be used. For example, polyethylene porous membranes, polypropylene porous membranes, glass non-woven fabrics, aramid non-woven fabrics, polyimide porous membranes, polyolefin porous membranes, etc. can be used as the separator.

[0157] (3)Electrolyte

[0158] For the electrolyte, there is also no particular limitation, and the electrolytes commonly used in secondary batteries can be used. Examples of the electrolyte include electrolytic solutions dissolved in solvents, gel electrolytes, solid electrolytes, ionic liquids, or molten salts. An electrolytic solution refers to a state where an electrolyte is dissolved in a solvent.

[0159] In the case where the secondary battery is a lithium-ion secondary battery, as the electrolyte, it is necessary to contain lithium ions as carriers for electron conduction. Therefore, as the electrolyte salt used in the electrolyte, as long as it is an electrolyte salt used in a lithium-ion secondary battery, there is no particular limitation, and for example, a lithium salt can be used. As the lithium salt, one or more selected from lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO4), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium bis(pentafluoroethanesulfonyl)imide (LiN(SO2C2F5)2), lithium bis(oxalato)borate (LiBC4O8), etc. can be used.

[0160] There is also no particular limitation on the solvent of the electrolyte, and at least one selected from, for example, the following substances can be used: propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (GBL), methyl-γ-butyrolactone, dimethoxymethane (DMM), dimethoxyethane (DME), vinylene carbonate (VC), vinyl ethylene carbonate (EVC), fluoroethylene carbonate (FEC), ethylene sulfite (ES).

[0161] In addition, there is no particular limitation on the concentration of the electrolyte solution, which is the concentration of the salt in the solvent. For example, it can be 0.1 mol / L or more and 3.0 mol / L or less, or it can be 0.8 mol / L or more and 2.0 mol / L or less.

[0162] Ionic liquids and molten salts are classified into pyridine-based, alicyclic amine-based, aliphatic amine-based, etc. according to the type of cation. By selecting the type of anion combined with it, various ionic liquids or molten salts can be synthesized.

[0163] Examples of the cation include ammonium-based such as imidazolium salts and pyridinium salts; phosphonium-based ions; inorganic-based ions, etc. Examples of the anions used include halogen-based such as bromide ions and trifluoromethylsulfonates; boron-based such as tetraphenylborate; phosphorus-based such as hexafluorophosphate, etc.

[0164] Ionic liquids and molten salts can be obtained, for example, by combining cations such as imidazolium with Br - , Cl - , BF4 - , PF6 - , (CF3SO2)2N - , CF3SO3 - , FeCl4 -It is obtained by a well-known synthesis method composed of the following anionic combinations. As long as it is an ionic liquid or a molten salt, it can function as an electrolyte even without adding an electrolyte.

[0165] Solid electrolytes are classified into sulfide-based, oxide-based, hydride-based, organic polymer-based, etc. Most of them are amorphous or crystalline substances composed of a salt as a carrier and an inorganic derivative. It is less likely to leak like an electrolyte.

[0166] Examples

[0167] Hereinafter, specific examples will be given for illustration, but the present invention is not limited to these examples.

[0168] (Evaluation method)

[0169] First, the evaluation methods for the negative electrode active material and the secondary battery produced in the following experimental examples will be described.

[0170] (1) Evaluation of the negative electrode active material

[0171] (1-1) Particle size distribution

[0172] A plurality of particles of the negative electrode active material to be evaluated are embedded in a resin. After the resin is cured, it is cut along the plane passing through the particles in the resin, and the cross-section is polished with a cross-section polishing machine to produce a specimen with the cross-section of the particles exposed. Then, the produced specimen is observed with a scanning electron microscope. At this time, the number of fields of view and magnification are selected so that a total of 3000 to 20000 particles can be observed.

[0173] Based on the obtained observation images, the cross-sectional area of each particle part is obtained by image processing, the equivalent circle diameter is calculated, and the particle size distribution is made with the frequency based on the area on the vertical axis. The particle size distribution is made using the particle diameters of all the observed particles.

[0174] In the obtained particle size distribution, a peak is determined with the range between the minimum value and the next minimum value as one peak. Then, the number of peaks, the particle diameter at the top of the first peak, the particle diameter at the top of the second peak, the difference between the particle diameter at the top of the first peak and the particle diameter at the top of the second peak, and the ratio of the area of the second peak to the area of the first peak are obtained. These evaluation results are shown in Table 2.

[0175] (2) Secondary battery

[0176] (2-1) Fabrication of the secondary battery

[0177] (Fabrication of the negative electrode)

[0178] The negative electrode composite material produced in the following experimental examples was coated on a nickel porous metal as a current collector. Then, it was dried and thickness-adjusted to produce a negative electrode.

[0179] (Fabrication of the positive electrode)

[0180] As the positive electrode active material, lithium cobalt oxide (LiCoO₂) was prepared. Then, 95% by mass of the positive electrode active material, 3% by mass of carbon black as a conductive aid, and 2% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed, and the resulting mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode composite material slurry.

[0181] The positive electrode composite material slurry was coated on an aluminum foil as a current collector and dried in a vacuum at 140 °C for 12 hours. Then, the thickness was adjusted by a roll press so that the density of the composite material became 3.3 g / cm 3 to fabricate a positive electrode.

[0182] (Fabrication of the secondary battery)

[0183] As a separator, a polyethylene microporous membrane with a thickness of 25 μm was prepared and cut into a size of 500 mm in length × 450 mm in width. Then, as Figure 3 shown in the secondary battery 30, the positive electrode 31, the separator 32, and the negative electrode 20 were laminated to fabricate an electrode laminate.

[0184] After that, the positive electrode terminal 34 and the negative electrode terminal 35 were joined to the current collecting regions of the positive electrode 31 and the negative electrode 20 by ultrasonic welding. The electrode laminate with the joined terminals was inserted into a container 33 formed by heat-sealing an aluminum laminate and processing it into a bag shape to fabricate a laminated battery cell.

[0185] As the electrolyte, LiPF₆ was dissolved in a solvent obtained by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 3:4:3 so as to be 1.0 mol / L, and 1 wt% of vinylene carbonate was further added to this solution to prepare an electrolyte. Then, the electrolyte was injected into the laminated battery cell to fabricate the secondary battery 30 as a lithium-ion secondary battery.

[0186] (2-2) Evaluation of the characteristics of the secondary battery

[0187] For the fabricated secondary battery, the estimated capacity of the positive electrode at a temperature of 25 °C was calculated based on the amount of the active material of the negative electrode active material. Then, based on the calculated estimated capacity, the current value capable of discharging for 20 hours (0.05C) was determined.

[0188] (Energy density)

[0189] For the secondary battery using the negative electrode composite material prepared in each experimental example, it is charged at a constant current of 0.05C to 4.1V, charged at a constant voltage of 4.1V for 1 hour, and then discharged at a constant current of 0.05C to 3.1V. The capacity based on the mass of the negative electrode active material during the above constant current discharge is defined as the rated capacity (mAh / g). On the other hand, in the charge-discharge curve during the constant current discharge, the voltage at the capacity of 1 / 2 of the rated capacity is defined as the average voltage (V), and the energy density (Wh / kg) is calculated by the following formula (A).

[0190] Energy density (Wh / kg) = Rated capacity (mAh / g) × Average voltage (V) × Mass of negative electrode active material (g) ÷ Battery cell weight (kg)…(A)

[0191] In addition, here, the battery cell weight is the sum of the masses of the positive electrode, negative electrode, and separator constituting a single battery cell. Furthermore, the sum of the volumes of the positive electrode, negative electrode, and separator constituting a single battery cell is defined as the battery cell volume (L), and the energy density relative to the battery volume is also calculated by the following formula (B).

[0192] Energy density (Wh / L) = Energy density (Wh / kg) × Battery cell weight (kg) ÷ Battery cell volume (L)…(B)

[0193] The energy density calculated by formula (A) and the energy density calculated by formula (B) are respectively shown in the "per unit mass" and "per unit volume" columns of the "energy density" column in Table 1.

[0194] (Internal resistance)

[0195] Next, at a temperature of 25°C, it is charged at 0.05C for 2.5 hours so that the state of charge (SOC: State Of Charge) becomes 50% of the above-rated capacity.

[0196] Next, for the operation of discharging for 10 seconds at a specified current value and measuring the voltage at this time, and then charging a capacity equivalent to the discharge amount at 0.05C, the specified current value is changed from 0.5C in increments of 0.5C each time to 3.0C, and the above operation is repeated. Then, the current value is plotted on the horizontal axis and the voltage corresponding to each current value is plotted on the vertical axis, and the slope of the straight line obtained at this time is taken as the internal resistance. The evaluation results are shown in the "internal resistance" column of Table 1.

[0197] (Initial discharge capacity, capacity retention rate)

[0198] For the cycle life test, the test environment temperature is set to 25°C, the current density is set to 0.05C-rate, and the cut-off potential is set to 3.1V to 4.1V, and 10 cycles are implemented.

[0199] The discharge capacity before the start of the cycle and the discharge capacity after 10 cycles were measured, and the capacity retention rate, which is the ratio of the discharge capacity after 10 cycles to the initial discharge capacity as the discharge capacity before the start of the cycle, was calculated. The evaluation results are shown in the columns of "Initial Discharge Capacity" and "Capacity Retention Rate" in Table 1, respectively.

[0200] (Experimental Conditions)

[0201] Hereinafter, the manufacturing conditions of the negative electrode active material and the negative electrode composite material in the experimental examples will be described. Experimental Examples 1 to 4 are comparative examples, and Experimental Examples 5 to 7 are examples.

[0202] [Experimental Example 1]

[0203] As the first silicon powder, silicon powder with the highest frequency of occurrence in the particle size distribution based on area obtained by cross-sectional observation using an electron microscope and having a particle diameter of 1.26 μm was prepared as the negative electrode active material.

[0204] The evaluation results for the negative electrode active material are shown in Table 2.

[0205] Then, the first silicon powder was mixed with a conductive additive and a binder at the ratio shown in Table 1 to prepare a negative electrode composite material and a secondary battery, and evaluation was carried out. The evaluation results are shown in Table 1.

[0206] [Experimental Examples 2, 3, 4]

[0207] As the second silicon powder, silicon powder with the highest frequency of occurrence in the particle size distribution based on area obtained by cross-sectional observation using an electron microscope and having a particle diameter of 79 nm was prepared as the negative electrode active material.

[0208] The evaluation results for the negative electrode active material are shown in Table 2.

[0209] Then, the second silicon powder was mixed with a conductive additive and a binder at the ratio shown in Table 1 to prepare a negative electrode composite material and a secondary battery, and evaluation was carried out. The evaluation results are shown in Table 1.

[0210] [Experimental Examples 5, 6, 7]

[0211] The first silicon powder and the second silicon powder were mixed at the ratio shown in Table 1 as the negative electrode active material.

[0212] The evaluation results for the negative electrode active material are shown in Table 2.

[0213] Then, the negative electrode active material containing the first silicon powder and the second silicon powder is mixed with a conductive additive and a binder at the ratios shown in Table 1 to fabricate a negative electrode composite material and a secondary battery, and evaluations are performed. The evaluation results are shown in Table 1.

[0214] [Table 1]

[0215]

[0216] [Table 2]

[0217]

[0218] From the results shown in Table 1 and Table 2, it can be confirmed that in the secondary batteries using the negative electrode active materials of Experimental Examples 5, 6, and 7 having two peaks in the particle size distribution, the initial discharge capacity and the capacity retention rate are high.

[0219] Description of Reference Numerals

[0220] 10: Particle size distribution;

[0221] 11: First peak;

[0222] 11A: Top of the first peak;

[0223] 12: Second peak;

[0224] 12A: Top of the second peak;

[0225] L1, L2: Straight lines;

[0226] D: Difference in particle diameter between the top of the first peak and the top of the second peak;

[0227] 20: Negative electrode for non-aqueous electrolyte secondary battery;

[0228] 21: Current collector;

[0229] 211: Pores;

[0230] 22: Negative electrode active material;

[0231] 221: First negative electrode active material;

[0232] 222: Second negative electrode active material;

[0233] 23: Conductive additive;

[0234] 24: Binder;

[0235] 25: Negative electrode composite material;

[0236] 30: Non-aqueous electrolyte secondary battery;

[0237] 31: Positive electrode;

[0238] 32: Spacer;

[0239] 33: Container;

[0240] 34: Positive terminal;

[0241] 35: Negative terminal.

Claims

1. A negative electrode active material for a non-aqueous electrolyte secondary battery, which contains a silicon-based material, The particle size distribution based on the area of the negative electrode active material for the non-aqueous electrolyte secondary battery has two or more peaks including a first peak and a second peak.

2. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, The top of the first peak is within the range of a particle size of 10 nm or more and 500 nm or less, The top of the second peak is within the range of a particle size of 0.5 μm or more and 50 μm or less.

3. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The difference between the particle size at the top of the first peak and the particle size at the top of the second peak is 500 nm or more.

4. The negative electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, The ratio of the area of the second peak to the area of the first peak is 0.1 or more and 5.0 or less.

5. A negative electrode for a non-aqueous electrolyte secondary battery, which contains a current collector and a negative electrode composite material supported on the current collector, The negative electrode composite material contains the negative electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, a conductive assistant, and a binder.

6. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 5, wherein, The current collector is a porous metal.

7. A non-aqueous electrolyte secondary battery, which has the negative electrode for a non-aqueous electrolyte secondary battery according to claim 5 or 6.

Images