Negative electrode for secondary battery, and secondary battery

Abstract

The secondary battery includes a positive electrode, a negative electrode, and an electrolyte solution. The negative electrode includes a plurality of first negative electrode active material particles and a plurality of second negative electrode active material particles. The first negative electrode active material particles contain an oxide of silicon, and the second negative electrode active material particles contain at least one of a monomer of silicon and an alloy of silicon. In the observation result of the cross section of the negative electrode using an electron microscope, the median diameter of the plurality of first negative electrode active material particles is 5-8 [mu] m, and the median diameter of the plurality of second negative electrode active material particles is 0.12-1.2 [mu] m. The ratio of the median diameter of the plurality of first negative electrode active material particles to the median diameter of the plurality of second negative electrode active material particles is from 5 to 50 (inclusive), and the ratio of the total area of the plurality of first negative electrode active material particles to the total area of the plurality of second negative electrode active material particles is from 0.6 to 0.9 (inclusive).

Description

Technical Field

[0001] The present technology relates to a negative electrode for a secondary battery and a secondary battery. Background Art

[0002] As various electronic devices such as mobile phones are becoming more popular, secondary batteries are being developed as small, lightweight power sources with high energy density. The secondary battery includes a positive electrode, a negative electrode (negative electrode for secondary batteries), and an electrolyte, and various studies have been conducted on the structure of the secondary battery.

[0003] Specifically, the negative electrode includes first active material particles and second active material particles (for example, see Patent Document 1). The first active material particles include silicon or a silicon alloy, and the second active material particles include silicon oxide (SiO x (x=0.5~1.5)).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2015-232921 Summary of the invention

[0007] Although various studies have been conducted on the configuration of secondary batteries, the battery characteristics of the secondary batteries are still insufficient, and thus there is room for improvement.

[0008] A negative electrode for a secondary battery and a secondary battery that can provide excellent battery characteristics are desired.

[0009] A negative electrode for a secondary battery of one embodiment of the present technology includes a plurality of first negative electrode active material particles and a plurality of second negative electrode active material particles. The first negative electrode active material particles include silicon oxide, and the second negative electrode active material particles include at least one of silicon monomer and silicon alloy. In the observation results of the cross section using an electron microscope, the median diameter of the plurality of first negative electrode active material particles is greater than 5 μm and less than 8 μm, the median diameter of the plurality of second negative electrode active material particles is greater than 0.12 μm and less than 1.2 μm, the ratio of the median diameter of the plurality of first negative electrode active material particles to the median diameter of the plurality of second negative electrode active material particles is greater than 5 and less than 50, and the ratio of the total area of ​​the plurality of first negative electrode active material particles to the total area of ​​the plurality of second negative electrode active material particles is greater than 0.6 and less than 0.9.

[0010] A secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolyte solution. The negative electrode has the same configuration as that of the negative electrode for a secondary battery according to the embodiment of the present technology described above.

[0011] As described above, the following four constituent conditions are determined based on the observation results of the cross section of the negative electrode using an electron microscope. The details of the determination procedure of the four constituent conditions will be described below.

[0012] (1) Range of median diameter of the plurality of first negative electrode active material particles

[0013] (2) Range of median diameter of the plurality of second negative electrode active material particles

[0014] (3) Range of the ratio of the median diameter of the plurality of first negative electrode active material particles to the median diameter of the plurality of second negative electrode active material particles

[0015] (4) Range of the ratio of the total area of ​​the plurality of first negative electrode active material particles to the total area of ​​the plurality of second negative electrode active material particles

[0016] According to an embodiment of the present technology, a negative electrode for a secondary battery or a secondary battery, the negative electrode for a secondary battery comprises a plurality of first negative electrode active material particles and a plurality of second negative electrode active material particles, the first negative electrode active material particles comprise silicon oxide, the second negative electrode active material particles comprise at least one of silicon monomer and silicon alloy, and the above-mentioned four constituent conditions are satisfied, so that excellent battery characteristics can be obtained.

[0017] It should be noted that the effects of the present technology are not necessarily limited to the effects described here, and may be any of a series of effects related to the present technology described later. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a cross-sectional view showing the structure of a negative electrode for a secondary battery in one embodiment of the present technology.

[0019] Figure 2 Yes means Figure 1 2 is a cross-sectional view showing the structure of each of a plurality of first negative electrode active material particles and a plurality of second negative electrode active material particles.

[0020] Figure 3 It is a perspective view showing the structure of a secondary battery in one embodiment of the present technology.

[0021] Figure 4 Yes means Figure 3 A cross-sectional view showing the structure of a battery element.

[0022] Figure 5 It is a block diagram showing the configuration of an application example of a secondary battery.

[0023] Figure 6 It is a cross-sectional view showing the structure of a secondary battery used for testing. DETAILED DESCRIPTION

[0024] Hereinafter, one embodiment of the present technology will be described in detail with reference to the drawings. It should be noted that the order of the description is as follows.

[0025] 1. Negative electrode for secondary batteries

[0026] 1-1. Composition

[0027] 1-2. Action

[0028] 1-3. Manufacturing method

[0029] 1-4. Function and effect

[0030] 2. Secondary battery

[0031] 2-1. Composition

[0032] 2-2. Action

[0033] 2-3. Manufacturing method

[0034] 2-4. Actions and effects

[0035] 3. Modifications

[0036] 4. Uses of secondary batteries

[0037] <1. Negative electrode for secondary battery>

[0038] First, a negative electrode for a secondary battery (hereinafter simply referred to as “negative electrode”) according to an embodiment of the present technology will be described.

[0039] The negative electrode described here is used for a secondary battery as an electrochemical device. In addition, the negative electrode can also be used for other electrochemical devices other than secondary batteries. Specific examples of other electrochemical devices are primary batteries and capacitors.

[0040] The negative electrode inserts and extracts the electrode reaction substance during the operation of the electrochemical device (electrode reaction). The type of the electrode reaction substance is not particularly limited, and specifically, it is a light metal such as an alkali metal and an alkaline earth metal. Specific examples of alkali metals are lithium, sodium, and potassium, and specific examples of alkaline earth metals are beryllium, magnesium, and calcium.

[0041] Hereinafter, the case where the electrode reaction substance is lithium is taken as an example. Therefore, in the negative electrode, lithium is inserted and released in an ionic state during the electrode reaction.

[0042] <1-1. Structure>

[0043] Figure 1 A cross-sectional configuration of a negative electrode 100 as an example of a negative electrode is shown, and Figure 2 Shows Figure 1The illustrated cross-sectional structures of the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 .

[0044] like Figure 1 As shown, the negative electrode 100 includes a negative electrode current collector 110 and a negative electrode active material layer 120 .

[0045] [Negative electrode current collector]

[0046] like Figure 1 As shown, the negative electrode current collector 110 is a conductive support member that supports the negative electrode active material layer 120, and has a pair of surfaces (upper surface and lower surface) provided with the negative electrode active material layer 120. The negative electrode current collector 110 includes any one or two or more conductive materials such as metal materials, and a specific example of the conductive material is copper.

[0047] The surface of the negative electrode current collector 110 is preferably roughened by electrolysis because the adhesion of the negative electrode active material layer 120 to the negative electrode current collector 110 can be improved by utilizing a so-called anchor effect.

[0048] In addition, the negative electrode current collector 110 may be omitted. In other words, the negative electrode 100 may include only the negative electrode active material layer 120 .

[0049] [Negative Electrode Active Material Layer]

[0050] like Figure 1 As shown, the negative electrode active material layer 120 is a layer for inserting and extracting lithium and is provided on one surface (upper surface or lower surface) of the negative electrode current collector 110. Alternatively, the negative electrode active material layer 120 may be provided on both surfaces (upper surface and lower surface) of the negative electrode current collector 110.

[0051] The negative electrode active material layer 120 includes two types of negative electrode active materials in particle form. Figure 2 As shown, the negative electrode active material layer 120 includes a plurality of first negative electrode active material particles 121 and a plurality of second negative electrode active material particles 122. The plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 are mixed with each other inside the negative electrode active material layer 120. Most of the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 are dispersed, but some of the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 sometimes aggregate with each other.

[0052] In addition, Figure 2In order to simplify the content of the figure, the cross-sectional shape of the first negative electrode active material particle 121 is a circle. However, since the cross-sectional shape of the first negative electrode active material particle 121 is not particularly limited, it is not limited to a circle, and may also be a shape other than the circle. Of course, the cross-sectional shape of each of the plurality of first negative electrode active material particles 121 is not limited to one, and may also be two or more.

[0053] Here, the contents described about the cross-sectional shape of the first negative electrode active material particle 121 are also applicable to the cross-sectional shape of the second negative electrode active material particle 122. Figure 2 In the embodiment, the cross-sectional shape of the second negative electrode active material particle 122 is a circle. However, the cross-sectional shape of the second negative electrode active material particle 122 is not particularly limited and may be a shape other than a circle.

[0054] (First Negative Electrode Active Material Particles)

[0055] The plurality of first negative electrode active material particles 121 have a relatively large median diameter, more specifically, a median diameter larger than the median diameter of the plurality of second negative electrode active material particles 122 .

[0056] The median diameter of the plurality of first negative electrode active material particles 121 described here is a so-called D50 (μm). Hereinafter, the median diameter of the plurality of first negative electrode active material particles 121 is referred to as “median diameter MD1”.

[0057] The first negative electrode active material particles 121 include one or more of silicon oxides. This is because the discharge capacity of a secondary battery using the negative electrode 100 is unlikely to decrease even if charge and discharge are repeated.

[0058] The type of silicon oxide is not particularly limited. Among them, the silicon oxide preferably contains any one or two or more of the compounds represented by formula (1). This is because the irreversible capacity is sufficiently reduced.

[0059] SiO x … (1)

[0060] (x satisfies 0.5<x<1.2.)

[0061] It should be noted that the detailed structure (four structural conditions) of the plurality of first negative electrode active material particles 121 will be described below.

[0062] (Second Negative Electrode Active Material Particles)

[0063] The plurality of second negative electrode active material particles 122 have a relatively small median diameter, and more specifically, have a median diameter smaller than the median diameter of the plurality of first negative electrode active material particles 121 .

[0064] The median diameter of the second negative electrode active material particles 122 described here is the so-called D50 (μm), similar to the median diameter of the first negative electrode active material particles 121. Hereinafter, the median diameter of the second negative electrode active material particles 122 is referred to as “median diameter MD2”.

[0065] The second negative electrode active material particle 122 includes any one or more of a silicon monomer and a silicon alloy. This is because a high energy density can be obtained. The second negative electrode active material particle 122 may include only a silicon monomer, or only a silicon alloy, or both a silicon monomer and a silicon alloy. In the case where the second negative electrode active material particle 122 includes a silicon alloy, the type of the silicon alloy may be one or more than two.

[0066] Silicon monomer refers to general silicon monomer. Therefore, silicon monomer may contain a small amount of impurities. That is, the purity of silicon monomer is not necessarily limited to 100%.

[0067] The type of silicon alloy is not particularly limited. Specifically, the silicon alloy contains any one or two or more of metal elements such as tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium as constituent elements other than silicon.

[0068] A specific example of a silicon alloy is SiB 4 、SiB 6 Mg 2 Si、Ni 2 Si、TiSi 2 、MoSi 2 、CoSi 2 、NiSi 2 、CaSi 2 ,CrSi 2 , Cu 5 Si、FeSi 2 、MnSi 2 、NbSi 2 、TaSi 2 、VSi 2 , WSi 2 、ZnSi 2 and SiC, etc. In addition, the composition of the silicon alloy exemplified here (mixing ratio of silicon and metal elements) can be changed arbitrarily.

[0069] It should be noted that the detailed structure (four structural conditions) of the plurality of second negative electrode active material particles 122 will be described below.

[0070] (Other materials)

[0071] It should be noted that the negative electrode active material layer 120 may also include any one or two or more of other materials.

[0072] The other material is a negative electrode binder, which includes any one or more of materials such as synthetic rubber and polymer compounds. Specific examples of synthetic rubber are styrene-butadiene rubber, fluorine rubber, and EPDM rubber. Specific examples of polymer compounds are polyvinylidene fluoride, polyimide, polyacrylic acid, and carboxymethyl cellulose.

[0073] In addition, the other material is a negative electrode conductive agent, which includes any one or more conductive materials such as carbon materials, metal materials, and conductive polymer compounds. Specific examples of carbon materials include graphite, carbon black, acetylene black, and Ketjen black.

[0074] In addition, the other material is a third negative electrode active material in a plurality of granular forms (a plurality of third negative electrode active material particles), and the third negative electrode active material particles contain any one or two or more of the carbon materials. When lithium is inserted and released, the crystal structure of the carbon material hardly changes, so a high energy density can be obtained stably. In addition, since the carbon material also functions as a negative electrode conductive agent, the conductivity of the negative electrode active material layer 120 is improved.

[0075] Specific examples of carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite. The graphite may be natural graphite, artificial graphite, or both. The interplanar spacing of the (002) plane of non-graphitizable carbon is not particularly limited, and is specifically 0.37 nm or more. The interplanar spacing of the (002) plane of graphite is not particularly limited, and is specifically 0.34 nm or less.

[0076] In addition, specific examples of carbon materials are pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound sintered bodies, activated carbon, and carbon black. The cokes include pitch coke, needle coke, and petroleum coke. The organic polymer compound sintered body is a sintered product obtained by sintering (carbonizing) polymer compounds such as phenolic resin and furan resin at an appropriate temperature. In addition, the carbon material can be low-crystalline carbon obtained by heat treatment at a temperature below about 1000°C, or it can be amorphous carbon. The shape of the carbon material is not particularly limited, and specifically, it is any one or more of fibrous, spherical, granular, and flaky.

[0077] When the negative electrode active material layer 120 includes a plurality of first negative electrode active material particles 121, a plurality of second negative electrode active material particles 122, and a plurality of third negative electrode active material particles, in particular, during the electrode reaction of a secondary battery using the negative electrode 100 (during charging and discharging), the damage and falling off of the negative electrode active material layer 120 can be suppressed while ensuring the battery capacity.

[0078] In detail, silicon-containing materials (silicon oxides, silicon monomers, and silicon alloys) have the advantage of high theoretical capacity, but have the risk of rapid expansion and contraction during charge and discharge. On the other hand, carbon materials have the risk of low theoretical capacity, but have the advantage of being difficult to expand and contract during charge and discharge. Therefore, by using silicon-containing materials and carbon materials in combination, it is possible to suppress the expansion and contraction of the negative electrode active material layer 120 during charge and discharge while obtaining a high theoretical capacity. As a result, as described above, it is possible to suppress the damage and shedding of the negative electrode active material layer 120 while ensuring the battery capacity.

[0079] [Detailed composition]

[0080] Here, the detailed structure of each of the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 will be described.

[0081] (4 types of constituent conditions)

[0082] The configurations of the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 satisfy predetermined conditions. Specifically, in the observation result of the cross section of the negative electrode 100 using an electron microscope, the following four configuration conditions are satisfied.

[0083] Hereinafter, a procedure for obtaining the observation result of the cross section of the negative electrode 100 using an electron microscope will be described, and then the four conditions will be described in detail.

[0084] When the cross-section of the negative electrode 100 is observed using an electron microscope, the negative electrode 100 is Figure 1 The negative electrode 100 is cut in the vertical direction (in the vertical direction) to expose the cross section of the negative electrode 100. Thus, the cross section of the negative electrode active material layer 120 including the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 is exposed.

[0085] Thereafter, the cross section of the negative electrode active material layer 120 is observed using an electron microscope to obtain the observation result of the cross section (electron microscope photograph). Figure 2As shown, a state where a plurality of first negative electrode active material particles 121 and a plurality of second negative electrode active material particles 122 coexist is observed. The type of electron microscope is not particularly limited, and specifically, any one or more of a scanning electron microscope and a transmission electron microscope, etc., is used. Thus, the observation result of the cross section of the negative electrode 100 using the electron microscope is obtained.

[0086] The cutting method and cutting conditions of the negative electrode 100 are not particularly limited, and the observation conditions of the cross section of the negative electrode 100 are not particularly limited. Specifically, when the negative electrode 100 is cut, an ion milling device is used as a cutting device, and the conditions during cutting are set to acceleration voltage = 6 kV, discharge voltage = 1.5 kV, and cutting time = 3 hours. When observing the cross section of the negative electrode 100, the conditions during observation are set to observation magnification = 2000 times to 5000 times, and acceleration voltage = 3 kV.

[0087] As a first condition, the median diameter MD1 is within a predetermined range. Specifically, the median diameter MD1 is 5 μm to 8 μm. The value of the median diameter MD1 is a value obtained by rounding off the third decimal place.

[0088] As the second condition, the median diameter MD2 is within a predetermined range. Specifically, the median diameter MD2 is 0.12 μm to 1.2 μm. The value of the median diameter MD2 is a value obtained by rounding off the third decimal place.

[0089] As a third condition, the ratio of the median diameter MD1 to the median diameter MD2 (particle diameter ratio RD) is within a predetermined range. Specifically, the particle diameter ratio RD (= MD1 / MD2) is 5 to 50. The value of the particle diameter ratio RD is a value obtained by rounding off the third decimal place.

[0090] As a fourth condition, the ratio (area ratio RS) of the total area S1 of the plurality of first negative electrode active material particles 121 to the total area S2 of the plurality of second negative electrode active material particles 122 is within a predetermined range. Specifically, the area ratio RS (= S1 / S2) is 0.6 to 0.9. The value of the area ratio RS is a value obtained by rounding off the value to the second decimal place.

[0091] It should be noted that the area ratio RS is an index representing the mixing ratio of the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 based on the abundance of the plurality of first negative electrode active material particles 121 and the abundance of the plurality of second negative electrode active material particles 122 .

[0092] The reason why the above four constituent conditions are satisfied is that, unlike the case where the four constituent conditions are not satisfied, the relationship between the median diameter MD1 and the median diameter MD2 is optimized, and the mixing ratio of the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 is also optimized. As a result, in a secondary battery using the negative electrode 100, a sufficient discharge capacity can be obtained from the initial charge and discharge, and even if charge and discharge are repeated thereafter, the discharge capacity is unlikely to decrease.

[0093] In particular, regarding the particle diameter ratio RD (=5 to 50) as the third condition, there is a tendency as described below.

[0094] When the particle diameter ratio RD is less than 5, the difference between the median diameter MD1 and the median diameter MD2 is too small, so it is difficult to arrange the plurality of first negative electrode active material particles 121 to cover the surface of the second negative electrode active material particles 122. As a result, it is difficult to obtain a sufficient discharge capacity from the initial charge and discharge, and the discharge capacity is likely to decrease if charge and discharge are repeated thereafter.

[0095] On the other hand, when the particle diameter ratio RD is greater than 50, the difference between the median diameter MD1 and the median diameter MD2 is too large, so it is difficult to arrange the plurality of first negative electrode active material particles 121 to cover the surface of the second negative electrode active material particles 122, as in the case where the particle diameter ratio RD is less than 5. Therefore, since the coverage of the plurality of first negative electrode active material particles 121 on the surface of the second negative electrode active material particles 122 is insufficient, it is difficult to obtain a sufficient discharge capacity from the initial charge and discharge, and if charge and discharge are repeated thereafter, the discharge capacity is likely to decrease.

[0096] Among them, the particle diameter ratio RD is preferably 10 to 30. This is because since the particle diameter ratio RD is more appropriate, sufficient discharge capacity is easily obtained from the initial charge and discharge, and the discharge capacity is unlikely to decrease further even if charge and discharge are repeated thereafter.

[0097] (Element distribution)

[0098] It should be noted that the element distribution on the surface of the first negative electrode active material particle 121 is not particularly limited. Among them, in the analysis result of the surface of the first negative electrode active material particle 121 using X-ray photoelectron spectroscopy (XPS), the ratio of the amount of carbon E2 to the amount of all elements E1 (carbon ratio RE=E2 / E1) is preferably less than 1%. This is because the covering layer containing carbon as a constituent element is almost not provided on the surface of the first negative electrode active material particle 121, so the covering layer almost does not cover the surface of the first negative electrode active material particle 121. The value of the carbon ratio RE is a value after rounding off the value of the second decimal place.

[0099] Here, all elements are all kinds of elements detected in the surface analysis of the first negative electrode active material particles 121 using XPS, including carbon. Therefore, the carbon ratio RE is an indicator showing how much carbon exists on the surface of the first negative electrode active material particles 121.

[0100] (Calculation steps and determination steps)

[0101] When calculating the median diameter MD1, first, identify a plurality of first negative electrode active material particles 121 in an electron microscope photograph. Next, select any 300 first negative electrode active material particles 121 from the plurality of first negative electrode active material particles 121, and then measure the particle size (μm) of each of the 300 first negative electrode active material particles 121. In this case, the particle size can be measured manually, or it can be measured mechanically using any image processing software. It should be noted that when the particle size is different depending on the measurement direction, the maximum value of the particle size is selected. Finally, the median diameter MD1 is calculated based on the number (=300) and the measurement results of multiple particle sizes.

[0102] The procedure for calculating the median diameter MD2 is the same as the procedure for calculating the median diameter MD1 described above, except that the focus is on the plurality of second negative electrode active material particles 122 instead of the plurality of first negative electrode active material particles 121 .

[0103] When calculating the particle diameter ratio RD, after calculating the median diameters MD1 and MD2 by the above-mentioned steps, the particle diameter ratio RD is calculated using a calculation formula of the particle diameter ratio RD (= MD1 / MD2).

[0104] When investigating the area ratio RS, first, 300 first negative electrode active material particles 121 are randomly selected from the plurality of first negative electrode active material particles 121 in the electron microscope photograph. Next, the area (μm) of each of the 300 first negative electrode active material particles 121 is measured. 2 ), and then add up the 300 areas to calculate the total area S1 (μm 2 ). That is, the total area S1 is the sum of the areas of the 300 first negative electrode active material particles 121 .

[0105] Next, the total area S2 (μm 2 ). That is, the total area S2 is the sum of the areas of the 300 second negative electrode active material particles 122 .

[0106] Finally, the area ratio RS is calculated using the calculation formula of area ratio RS (= S1 / S2).

[0107] The steps of calculating the carbon ratio RE are as follows: Hereinafter, the description will be made on the case where the negative electrode active material layer 120 includes a plurality of first negative electrode active material particles 121 and a plurality of second negative electrode active material particles 122 , a negative electrode binder, and a negative electrode conductor.

[0108] First, the negative electrode 100 is disassembled to collect a plurality of first negative electrode active material particles 121 .

[0109] In this case, after the negative electrode current collector 110 is peeled off from the negative electrode active material layer 120, the negative electrode active material layer 120 is put into a solvent. The solvent is any one of an aqueous solvent and an organic solvent that can dissolve the negative electrode binder. A specific example of a non-aqueous solvent is water, etc., and a specific example of an organic solvent is N-methyl-2-pyrrolidone, etc. In this case, the negative electrode binder is dissolved, while a plurality of first negative electrode active material particles 121, a plurality of second negative electrode active material particles 122, and a negative electrode conductive agent are not dissolved. Thus, since the negative electrode binder is dissolved and removed, a mixture of a plurality of first negative electrode active material particles 121 and a plurality of second negative electrode active material particles 122 is recovered.

[0110] Next, the mixture is put into a sieve having a plurality of holes, and a plurality of first negative electrode active material particles 121 are screened from the mixture. In this case, the size of the plurality of holes is set so that the plurality of first negative electrode active material particles 121 can pass through and the plurality of second negative electrode active material particles 122 and the negative electrode conductive agent cannot pass through. Thus, the plurality of first negative electrode active material particles 121 pass through the holes, whereas the plurality of second negative electrode active material particles 122 and the negative electrode conductive agent do not pass through the holes. Therefore, the plurality of first negative electrode active material particles 121 are separated from the plurality of second negative electrode active material particles 122 and the negative electrode conductive agent.

[0111] Next, the surface of the first negative electrode active material particle 121 is analyzed using XPS to measure the abundance of a series of elements. Thus, the abundance E1 of all elements is calculated, and the abundance E2 of carbon is calculated.

[0112] Finally, the carbon ratio RE is calculated using the calculation formula of carbon ratio RE=(E2 / E1)×100.

[0113] <1-2. Action>

[0114] The negative electrode 100 operates as follows during the electrode reaction.

[0115] In the negative electrode active material layer 120, lithium is inserted into the first negative electrode active material particles 121 and the second negative electrode active material particles 122 in an ionic state. In addition, in the negative electrode active material layer 120, lithium is removed from the first negative electrode active material particles 121 and the second negative electrode active material particles 122 in an ionic state.

[0116] <1-3. Manufacturing method>

[0117] The negative electrode 100 is manufactured through an exemplary process described below.

[0118] First, a plurality of first negative electrode active material particles 121 , a plurality of second negative electrode active material particles 122 , a negative electrode binder, and a negative electrode conductive agent are mixed with each other to prepare a negative electrode mixture.

[0119] In this case, the median diameters MD1 and MD2 are adjusted to satisfy the first condition and the second condition, respectively. Specifically, by using a plurality of first negative electrode active material particles 121 that satisfy the first condition regarding the median diameter MD1 and using a plurality of second negative electrode active material particles 122 that satisfy the second condition regarding the median diameter MD2, the third condition regarding the particle size ratio RD is satisfied.

[0120] In addition, the mixing ratio of the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 is adjusted so that the fourth condition is satisfied with respect to the area ratio RS.

[0121] Next, the negative electrode mixture is added to a solvent to prepare a paste-like negative electrode mixture slurry. The solvent may be an aqueous solvent or an organic solvent.

[0122] Finally, the negative electrode active material layer 120 is formed by coating the negative electrode mixture slurry on one side of the negative electrode current collector 110. Thereafter, the negative electrode active material layer 120 may be compression-molded using a roll press or the like. In this case, the negative electrode active material layer 120 may be heated, or compression molding may be repeated multiple times.

[0123] Thus, the negative electrode active material layer 120 is formed on the negative electrode current collector 110 , and the negative electrode 100 is completed.

[0124] <1-4. Functions and effects>

[0125] According to the negative electrode 100 , the negative electrode 100 includes a plurality of first negative electrode active material particles 121 and a plurality of second negative electrode active material particles 122 . The first negative electrode active material particles 121 include silicon oxide, and the second negative electrode active material particles 122 include either or both of silicon alone and silicon alloy.

[0126] In addition, the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 satisfy the above four constituent conditions. Specifically, the median diameter MD1 is 5 μm to 8 μm (first condition). The median diameter MD2 is 0.12 μm to 1.2 μm (second condition). The particle diameter ratio RD is 5 to 50 (third condition). The area ratio RS is 0.6 to 0.9 (fourth condition).

[0127] In this case, as described above, the relationship between the median diameters MD1 and MD2 is optimized, and the mixing ratio of the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 is also optimized. As a result, in a secondary battery using the negative electrode 100, sufficient discharge capacity can be obtained from the initial charge and discharge, and the discharge capacity is unlikely to decrease even if charge and discharge are repeated thereafter. Therefore, the use of the negative electrode 100 can realize a secondary battery with excellent battery characteristics.

[0128] In particular, when the particle diameter ratio RD is 10 to 30, sufficient discharge capacity is easily obtained from the initial charge and discharge, and even if charge and discharge are repeated thereafter, the discharge capacity is unlikely to decrease further, so that a higher effect can be obtained.

[0129] Furthermore, when the silicon oxide contains the compound represented by formula (1), the irreversible capacity is sufficiently reduced, and thus a higher effect can be obtained.

[0130] On the other hand, if the carbon ratio RE is less than 1%, the surface of the first negative electrode active material particle 121 is hardly covered with carbon, so a higher effect can be obtained.

[0131] In addition, if the negative electrode 100 further includes a plurality of third negative electrode active material particles, and the third negative electrode active material particles include carbon material, then when the secondary battery using the negative electrode 100 is charged and discharged, the damage and shedding of the negative electrode active material layer 120 can be suppressed while ensuring the battery capacity, thereby achieving a higher effect.

[0132] <2. Secondary batteries>

[0133] Next, a secondary battery according to an embodiment of the present technology to which the negative electrode 100 is applied will be described.

[0134] The secondary battery described here is a secondary battery that can obtain battery capacity by inserting and extracting electrode reaction materials, and includes a positive electrode, a negative electrode, and an electrolyte.

[0135] The charge capacity of the negative electrode is preferably greater than the discharge capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is preferably greater than the electrochemical capacity per unit area of ​​the positive electrode. This is to prevent the electrode reaction material from precipitating on the surface of the negative electrode during charging.

[0136] In the following, as described above, the case where the electrode reaction material is lithium is taken as an example. A secondary battery that obtains battery capacity by inserting and extracting lithium is a so-called lithium ion secondary battery. In this lithium ion secondary battery, lithium is inserted and extracted in an ionic state.

[0137] <2-1. Structure>

[0138] Figure 3 The three-dimensional structure of the secondary battery is shown. Figure 4 Shows Figure 3 The cross-sectional structure of the battery element 20 shown in FIG. Figure 4 , a state in which the outer film 10 and the battery element 20 are separated from each other is shown, and a cross section of the battery element 20 along the XZ plane is shown by a dotted line.

[0139] like Figure 3 as well as Figure 4 As shown, the secondary battery includes an outer film 10 , a battery element 20 , a positive electrode lead 31 , a negative electrode lead 32 , and sealing films 41 , 42 .

[0140] As described above, the secondary battery described here uses the outer packaging film 10 having flexibility or elasticity as an outer packaging member for accommodating the battery element 20, and is therefore a so-called laminated film type secondary battery.

[0141] [Outer packaging film]

[0142] like Figure 3 As shown, the outer film 10 has a bag-like structure which is sealed in a state of accommodating the battery element 20. Thus, the outer film 10 accommodates the positive electrode 21, the negative electrode 22, the separator 23 and the electrolyte solution which will be described later.

[0143] Here, the outer film 10 is a single film-shaped member, and is folded in a folding direction F. The outer film 10 is provided with a recessed portion 10U (so-called deep-drawn portion) for accommodating the battery element 20 .

[0144] Specifically, the outer packaging film 10 is a three-layer laminated film in which a welding layer, a metal layer, and a surface protection layer are sequentially stacked from the inside. When the outer packaging film 10 is folded, the outer peripheral edges of the mutually opposed welding layers are welded to each other. The welding layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

[0145] The structure (number of layers) of the outer film 10 is not particularly limited, and may be one layer, two layers, or four or more layers.

[0146] [Battery components]

[0147] The battery element 20 is housed in the outer packaging film 10. The battery element 20 is a so-called power generation element, and Figure 3 as well as Figure 4 As shown, it includes a positive electrode 21, a negative electrode 22, a separator 23 and an electrolyte (not shown).

[0148] Here, the battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 are opposed to each other with the separator 23 interposed therebetween, and are wound around a winding axis P as the center. Figure 3 It can be seen that the winding axis P is a virtual axis extending in the Y-axis direction.

[0149] The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the battery element 20 has a flat three-dimensional shape, the cross section of the battery element 20 intersecting the winding axis P (cross section along the XZ plane) is a flat shape defined by the major axis J1 and the minor axis J2.

[0150] The major axis J1 is an imaginary axis extending in the X-axis direction, and has a length greater than that of the minor axis J2. The minor axis J2 is an imaginary axis extending in the Z-axis direction intersecting the X-axis direction, and has a length less than that of the major axis J1. Here, the three-dimensional shape of the battery element 20 is a flat cylindrical shape, and therefore the cross-sectional shape of the battery element 20 is a flat, substantially elliptical shape.

[0151] (positive electrode)

[0152] like Figure 4 As shown, the positive electrode 21 includes a positive electrode collector 21A and a positive electrode active material layer 21B.

[0153] The positive electrode current collector 21A has a pair of surfaces provided with a positive electrode active material layer 21B. The positive electrode current collector 21A is made of a conductive material such as a metal material, and a specific example of the conductive material is aluminum.

[0154] The positive electrode active material layer 21B includes any one or more of the positive electrode active materials capable of inserting and removing lithium. In addition, the positive electrode active material layer 21B may further include any one or more of other materials such as a positive electrode binder and a positive electrode conductive agent. The method for forming the positive electrode active material layer 21B is not particularly limited, and specifically, it is a coating method or the like.

[0155] Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode collector 21A, so the positive electrode 21 includes two positive electrode active material layers 21B. Alternatively, the positive electrode active material layer 21B may be provided only on one side of the positive electrode collector 21A on the side opposite to the negative electrode 22 of the positive electrode 21, so the positive electrode 21 includes only one positive electrode active material layer 21B.

[0156] The type of positive electrode active material is not particularly limited, specifically, it is a lithium-containing compound, etc. The lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements, and may further contain one or more other elements as constituent elements. The types of other elements are not particularly limited, specifically, they are elements belonging to Group 2 to Group 15 in the long-period periodic table. The type of lithium-containing compound is not particularly limited, specifically, it is an oxide, a phosphate compound, a silicate compound, a boric acid compound, etc.

[0157] A specific example of an oxide is LiNiO 2 、LiCoO 2 、LiCo 0.98 Al 0.01 Mg 0.01 O 2 、LiNi 0.5 Co 0.2 Mn 0.3 O 2 and LiMn 2 O 4 etc. A specific example of the phosphoric acid compound is LiFePO 4 、LiMnPO 4 and LiFe 0.5 Mn 0.5 PO 4 wait.

[0158] The details of the positive electrode binder and the positive electrode conductive agent are the same as the details of the negative electrode binder and the negative electrode conductive agent described above.

[0159] (negative electrode)

[0160] The negative electrode 22 has the same configuration as that of the negative electrode 100. Figure 4 As shown, the negative electrode 22 includes a negative electrode collector 22A and a negative electrode active material layer 22B. The configurations of the negative electrode collector 22A and the negative electrode active material layer 22B are the same as the configurations of the negative electrode collector 110 and the negative electrode active material layer 120 .

[0161] Here, the negative electrode active material layer 22B is provided on both surfaces of the negative electrode collector 22A. Alternatively, the negative electrode active material layer 22B may be provided on only one surface of the negative electrode collector 22A.

[0162] (Diaphragm)

[0163] like Figure 4As shown, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and allows lithium to pass therethrough in an ionic state while preventing a short circuit caused by contact between the positive electrode 21 and the negative electrode 22. The separator 23 includes a polymer compound such as polyethylene.

[0164] (Electrolyte)

[0165] The electrolyte solution is a liquid electrolyte, and is impregnated into each of the positive electrode 21, the negative electrode 22, and the separator 23. The electrolyte solution contains a solvent and an electrolyte salt.

[0166] The solvent includes one or more of non-aqueous solvents (organic solvents), and the electrolyte solution including the non-aqueous solvent is a so-called non-aqueous electrolyte solution.

[0167] The non-aqueous solvent is an ester or an ether, and more specifically, is one or more of a carbonate compound, a carboxylate compound, a lactone compound, etc. This is because the dissociation property of the electrolyte salt and the ion mobility are improved.

[0168] The carbonate-based compounds are cyclic carbonates and chain carbonates. Specific examples of cyclic carbonates are ethylene carbonate and propylene carbonate, and specific examples of chain carbonates are dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0169] The carboxylate ester compound is a chain carboxylate, etc. Specific examples of the chain carboxylate are ethyl acetate, ethyl propionate, propyl propionate, ethyl trimethylacetate, and the like.

[0170] The lactone compound is lactone, etc. Specific examples of lactone are γ-butyrolactone and γ-valerolactone.

[0171] It should be noted that the ether may also be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, and the like.

[0172] The nonaqueous solvent is any one or more of unsaturated cyclic carbonate, fluorinated cyclic carbonate, sulfonic acid ester, phosphoric acid ester, acid anhydride, nitrile compound and isocyanate compound, etc. This is also because the dissociation property and ion mobility of the electrolyte salt are improved.

[0173] Specific examples of unsaturated cyclic carbonates are vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate. Specific examples of fluorinated cyclic carbonates are monofluoroethylene carbonate and difluoroethylene carbonate. Specific examples of sulfonic acid esters are propane sultone and propene sultone. Specific examples of phosphates are trimethyl phosphate and triethyl phosphate. Specific examples of anhydrides are succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of nitrile compounds are succinonitrile. Specific examples of isocyanate compounds are hexamethylene diisocyanate.

[0174] Of course, the composition of the non-aqueous solvent is not particularly limited as long as it contains any one or two or more of the above-mentioned series of non-aqueous solvents, and can be set arbitrarily.

[0175] The electrolyte salt includes one or two or more of light metal salts such as lithium salts.

[0176] A specific example of a lithium salt is lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 )、Lithium bis(fluorosulfonyl)imide(LiN(FSO 2 ) 2 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 ) 2 ), lithium tris(trifluoromethanesulfonyl) methylide (LiC(CF 3 SO 2 ) 3 ), lithium bis(oxalate)borate (LiB(C 2 O 4 ) 2 ), lithium monofluorophosphate (Li 2 PFO 3 ) and lithium difluorophosphate (LiPF 2 O 2 ) etc. This is because a high battery capacity can be obtained.

[0177] The content of the electrolyte salt is not particularly limited, but is specifically 0.3 mol / kg to 3.0 mol / kg relative to the solvent, because high ion conductivity can be obtained.

[0178] [Positive lead]

[0179] like Figure 3 as well as Figure 4As shown, the positive electrode lead 31 is a positive electrode wiring connected to the positive electrode collector 21A of the positive electrode 21, and is led out to the outside of the outer film 10. The positive electrode lead 31 includes a conductive material such as a metal material, and a specific example of the conductive material is aluminum, etc. It should be noted that the shape of the positive electrode lead 31 is any one of a thin plate shape, a mesh shape, etc.

[0180] [Negative lead]

[0181] like Figure 3 as well as Figure 4 As shown, the negative electrode lead 32 is a negative electrode wiring connected to the negative electrode collector 22A of the negative electrode 22, and is led out to the outside of the outer film 10. Here, the lead-out direction of the negative electrode lead 32 is the same as the lead-out direction of the positive electrode lead 31. The negative electrode lead 32 contains a conductive material such as a metal material, and a specific example of the conductive material is copper. It should be noted that the details of the shape of the negative electrode lead 32 are the same as the details of the shape of the positive electrode lead 31.

[0182] [Sealing film]

[0183] The sealing film 41 is inserted between the outer film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the outer film 10 and the negative electrode lead 32. In addition, one or both of the sealing films 41 and 42 may be omitted.

[0184] The sealing film 41 is a sealing member that prevents outside air and the like from intruding into the interior of the outer film 10. The sealing film 41 contains a polymer compound such as polyolefin that has close adhesion to the positive electrode lead 31, and a specific example of the polymer compound is polypropylene and the like.

[0185] The sealing film 42 has the same configuration as the sealing film 41 except that the sealing film 42 is a sealing member having close contact with the negative electrode lead 32. That is, the sealing film 42 includes a polymer compound such as polyolefin having close contact with the negative electrode lead 32.

[0186] <2-2. Action>

[0187] This secondary battery operates as follows during charge and discharge.

[0188] During charge, in the battery element 20, lithium is extracted from the positive electrode 21, and the lithium is inserted into the negative electrode 22 via the electrolyte. On the other hand, during discharge, in the battery element 20, lithium is extracted from the negative electrode 22, and the lithium is inserted into the positive electrode 21 via the electrolyte. During discharge and charge, lithium is inserted and extracted in an ionic state.

[0189] <2-3. Manufacturing method>

[0190] When manufacturing a secondary battery, after the positive electrode 21 and the negative electrode 22 are respectively produced and the electrolyte is prepared by the steps of an example described below, the secondary battery is assembled using the positive electrode 21, the negative electrode 22 and the electrolyte, and the assembled secondary battery is subjected to stabilization treatment.

[0191] [Production of positive electrode]

[0192] First, the positive electrode active material, the positive electrode binder and the positive electrode conductive agent are mixed with each other to form a positive electrode mixture. Next, the positive electrode mixture is added to the solvent to prepare a paste-like positive electrode mixture slurry. The solvent can be an aqueous solvent or an organic solvent. Finally, the positive electrode mixture slurry is applied to both sides of the positive electrode collector 21A to form a positive electrode active material layer 21B. Thereafter, the positive electrode active material layer 21B can be compression molded using a roller press or the like. In this case, the positive electrode active material layer 21B can be heated, or the compression molding can be repeated multiple times. Thus, the positive electrode active material layer 21B is formed on both sides of the positive electrode collector 21A, thereby producing the positive electrode 21.

[0193] [Production of negative electrode]

[0194] The negative electrode 22 is produced by the same steps as those for producing the negative electrode 100. In this case, the negative electrode active material layers 22B are formed on both surfaces of the negative electrode current collector 22A.

[0195] [Preparation of electrolyte]

[0196] The electrolyte salt is added to the solvent so that the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing an electrolytic solution.

[0197] [Assembly of secondary battery]

[0198] First, the positive electrode lead 31 is connected to the positive electrode collector 21A of the positive electrode 21 using a joining method such as welding, and the negative electrode lead 32 is connected to the negative electrode collector 22A of the negative electrode 22 using a joining method such as welding. Next, the positive electrode lead 31 is connected to the positive electrode collector 21A of the positive electrode 21 using a joining method such as welding, and the negative electrode lead 32 is connected to the negative electrode collector 22A of the negative electrode 22 using a joining method such as welding.

[0199] Next, the positive electrode 21 and the negative electrode 22 are stacked on each other with the separator 23 interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound to produce a wound body (not shown). Next, the wound body is pressed using a press or the like, thereby forming the wound body into a flat shape. The wound body after forming has the same structure as the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with an electrolyte.

[0200] Next, after the roll is stored in the recessed portion 10U, the outer packaging film 10 (welding layer / metal layer / surface protection layer) is folded so that the outer packaging films 10 face each other. Next, the outer peripheral edge portions of the two sides of the mutually facing welding layers are bonded to each other using an adhesive method such as a heat welding method, so that the roll is stored in the bag-shaped outer packaging film 10.

[0201] Finally, after the electrolyte is injected into the bag-shaped outer packaging film 10, the outer peripheral edge portions of the remaining one side of the mutually opposed welded layers are bonded to each other using a bonding method such as a heat welding method. In this case, the sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32.

[0202] Thus, the electrolyte solution is impregnated into the wound body, and the battery element 20 as a wound electrode body is formed. Thus, the battery element 20 is sealed inside the bag-shaped outer film 10, and a secondary battery is assembled.

[0203] [Stabilization of secondary batteries]

[0204] The assembled secondary battery is charged and discharged. Various conditions such as the ambient temperature, the number of charge and discharge cycles, and the charge and discharge conditions can be set arbitrarily. As a result, the positive electrode 21 and the negative electrode 22 are electrochemically stable, and the secondary battery is completed.

[0205] <2-4. Functions and effects>

[0206] According to this secondary battery, the negative electrode 22 has the same configuration as the negative electrode 100. Therefore, for the reasons described above, sufficient discharge capacity can be obtained from the initial charge and discharge, and the discharge capacity is unlikely to decrease even if charge and discharge are repeated thereafter, thereby achieving excellent battery characteristics.

[0207] In particular, if the secondary battery is a lithium ion secondary battery, a sufficient battery capacity can be stably obtained by inserting and extracting lithium, and thus a higher effect can be obtained.

[0208] <3. Modifications>

[0209] As described below, the configuration of the secondary battery described above can be appropriately changed. In addition, a series of modified examples described below can also be combined with each other.

[0210] [Modification 1]

[0211] The separator 23 which is a porous film is used. However, although not specifically shown in the figure, a laminated separator including a polymer compound layer may also be used.

[0212] Specifically, the laminated separator includes a porous film having a pair of surfaces and a polymer compound layer disposed on one or both surfaces of the porous film. This is because the adhesion of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, so the positional deviation (winding deviation) of the battery element 20 can be suppressed. Thus, even if side reactions such as decomposition reactions of the electrolyte occur, the expansion of the secondary battery can be suppressed. The polymer compound layer includes polymer compounds such as polyvinylidene fluoride. This is because excellent physical strength and excellent electrochemical stability can be obtained with respect to the polymer compound layer.

[0213] It should be noted that one or both of the porous film and the polymer compound layer may contain a plurality of insulating particles. This is because the plurality of insulating particles promote heat dissipation when the secondary battery is heated, so the safety (heat resistance) of the secondary battery is improved. The plurality of insulating particles include any one or more of insulating materials such as inorganic materials and resin materials. Specific examples of inorganic materials are aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of resin materials are acrylic resins and styrene resins.

[0214] When a laminated separator is produced, a precursor solution containing a polymer compound and a solvent is prepared, and then the precursor solution is applied to one or both sides of a porous membrane. In this case, a plurality of insulating particles may be added to the precursor solution as required.

[0215] When the laminated separator is used, the same effect can be obtained because lithium ions can move between the positive electrode 21 and the negative electrode 22. In this case, in particular, as described above, the safety of the secondary battery is improved, so a higher effect can be obtained.

[0216] [Modification 2]

[0217] An electrolyte solution is used as a liquid electrolyte. However, although not specifically shown here, an electrolyte layer as a gel electrolyte may also be used.

[0218] In the battery element 20 using the electrolyte layer, positive electrodes 21 and negative electrodes 22 are alternately stacked via separators 23 and electrolyte layers. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and between the negative electrode 22 and the separator 23.

[0219] Specifically, the electrolyte layer includes an electrolyte and a polymer compound, and the electrolyte is maintained by the polymer compound. This is because leakage of the electrolyte can be prevented. The electrolyte is composed as described above. The polymer compound includes polyvinylidene fluoride, etc. When forming the electrolyte layer, a precursor solution including an electrolyte, a polymer compound and a solvent is prepared, and then the precursor solution is coated on one or both sides of each of the positive electrode 21 and the negative electrode 22.

[0220] When the electrolyte layer is used, lithium ions can also move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, so the same effect can be obtained. In this case, in particular, as described above, since leakage of the electrolyte can be prevented, a higher effect can be obtained.

[0221] <4. Applications of secondary batteries>

[0222] The purpose (application example) of the secondary battery is not particularly limited. In electronic devices and electric vehicles, the secondary battery used as a power source can be a main power source or an auxiliary power source. The main power source is the power source that is used preferentially, regardless of the presence or absence of other power sources. The auxiliary power source can be a power source that is used instead of the main power source, or a power source that is switched from the main power source.

[0223] Specific examples of the use of secondary batteries are as follows: electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, stereo headphones, portable radios, and portable information terminals; storage devices such as backup power supplies and memory cards; power tools such as electric drills and electric saws; battery packs mounted on electronic devices, etc.; medical electronic devices such as pacemakers and hearing aids; electric vehicles such as electric vehicles (including hybrid vehicles); power storage systems such as household or industrial battery systems that store electricity in advance in case of emergencies. In these uses, one secondary battery or multiple secondary batteries can be used.

[0224] The battery pack may use a single cell or a battery pack. An electric vehicle is a vehicle that uses a secondary battery as a driving power source, or a hybrid vehicle that also has other driving sources besides the secondary battery. In a home power storage system, the power stored in the secondary battery as a power storage source can be used to use home electrical products, etc.

[0225] Here, an example of application of the secondary battery will be described in detail. The configuration of the application example described below is just an example and can be appropriately changed.

[0226] Figure 5 The module structure of the battery pack is shown. The battery pack described here is a battery pack using one secondary battery (so-called soft pack), and is installed in electronic devices such as smartphones.

[0227] like Figure 5 As shown in FIG. 1 , the battery pack includes a power source 71 and a circuit board 72 . The circuit board 72 is connected to the power source 71 and includes a positive electrode terminal 73 , a negative electrode terminal 74 , and a temperature detection terminal 75 .

[0228] The power source 71 includes a secondary battery. In the secondary battery, the positive lead is connected to the positive terminal 73, and the negative lead is connected to the negative terminal 74. The power source 71 can be connected to the outside via the positive terminal 73 and the negative terminal 74, so that charging and discharging are possible. The circuit substrate 72 includes a control unit 76, a switch 77, a thermistor element (PTC element) 78, and a temperature detection unit 79. In addition, the PTC element 78 can also be omitted.

[0229] The control unit 76 includes a central processing unit (CPU) and a memory, etc., and controls the operation of the entire battery pack. The control unit 76 detects and controls the use state of the power source 71 as needed.

[0230] It should be noted that when the voltage of the power source 71 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control unit 76 cuts off the switch 77 so that the charging current does not flow through the current path of the power source 71. The overcharge detection voltage is not particularly limited, but is specifically 4.20V±0.05V, and the overdischarge detection voltage is not particularly limited, but is specifically 2.40V±0.1V.

[0231] The switch 77 includes a charge control switch, a discharge control switch, a charge diode, a discharge diode, etc., and switches the connection between the power supply 71 and the external device according to the instruction of the control unit 76. The switch 77 includes a field effect transistor (MOSFET) using a metal oxide semiconductor, etc., and the charge and discharge current is detected based on the on-resistance of the switch 77.

[0232] The temperature detection unit 79 includes a temperature detection element such as a thermistor. The temperature detection unit 79 measures the temperature of the power supply 71 using the temperature detection terminal 75, and outputs the temperature measurement result to the control unit 76. The temperature measurement result measured by the temperature detection unit 79 is used for the control unit 76 to perform charge and discharge control when abnormal heating occurs and to perform correction processing when the control unit 76 calculates the remaining capacity.

[0233] Example

[0234] Embodiments of the present technology will be described.

[0235] <Examples 1 to 21 and Comparative Examples 1 to 13>

[0236] As described below, after the secondary battery was manufactured, the battery characteristics of the secondary battery were evaluated.

[0237] [Manufacturing of Secondary Batteries]

[0238] Here, as an evaluation of battery characteristics, a secondary battery for testing was produced for simple evaluation. Figure 6 The cross-sectional structure of a secondary battery (coin-type lithium ion secondary battery) used for the test is shown.

[0239] like Figure 6 As shown, the secondary battery includes a test electrode 61, a counter electrode 62, a separator 63, an outer cup 64, an outer can 65, a gasket 66, and an electrolyte (not shown). Here, the test electrode 61 corresponds to the negative electrode, and the counter electrode 62 corresponds to the positive electrode.

[0240] The test electrode 61 is housed in an outer packaging cup 64, and the counter electrode 62 is housed in an outer packaging can 65. The test electrode 61 and the counter electrode 62 are stacked on each other via a separator 63, and the electrolyte is impregnated in the test electrode 61, the counter electrode 62, and the separator 63, respectively. Since the outer packaging cup 64 and the outer packaging can 65 are riveted to each other via a gasket 66, the test electrode 61, the counter electrode 62, and the separator 63 are sealed by the outer packaging cup 64 and the outer packaging can 65.

[0241] (Fabrication of the test electrode (negative electrode))

[0242] When preparing the test electrode 61, first, 80 parts by mass of the negative electrode active material, 10 parts by mass of the negative electrode binder (polyacrylic acid), and 10 parts by mass of the negative electrode conductive agent (carbon black) are mixed with each other to prepare a negative electrode mixture. As the negative electrode active material, a plurality of first negative electrode active material particles 121 (silicon oxide (SiO) as silicon oxide) and a plurality of second negative electrode active material particles 122 (silicon monomer (Si) or silicon-iron-nickel alloy (SiFeNi) as silicon alloy) are used. In this case, both silicon monomer and silicon alloy are used as needed.

[0243] Next, the negative electrode mixture is put into the solvent (pure water as an aqueous solvent), and then the aqueous solvent is kneaded using a self-revolving mixer. Thus, since the negative electrode mixture is dispersed in the aqueous solvent, a paste-like negative electrode mixture slurry is prepared. Next, the negative electrode mixture slurry is applied to a single surface of the negative electrode collector 22A (copper foil with a thickness of 12 μm) using a coating device, and then the negative electrode mixture slurry is dried, thereby forming a negative electrode active material layer 22B. In this case, the negative electrode mixture slurry is dried by heating (drying temperature = 120°C), and then the negative electrode mixture slurry is vacuum dried. Finally, the negative electrode active material layer 22B is compression-molded using a roller press. Thus, the negative electrode active material layer 22B is formed on a single surface of the negative electrode collector 22A, thereby producing a test pole 61.

[0244] (Fabrication of Counter Electrode)

[0245] As described above, in order to use the secondary battery for testing ( Figure 6 A simple evaluation of battery characteristics was performed using a coin-shaped lithium-ion secondary battery as shown, using a lithium metal plate as the counter electrode 62.

[0246] (Preparation of electrolyte)

[0247] An electrolyte salt (lithium hexafluorophosphate (LiPF 6 )), and then the solvent was stirred. In this case, the mixing ratio (weight ratio) of the solvent was 50:50, and the content of the electrolyte salt was 1 mol / l (=1 mol / dm 3 ). Thus, an electrolyte solution was prepared.

[0248] (Assembly of secondary batteries)

[0249] First, the test electrode 61 is housed in the outer packaging cup 64, and the counter electrode 62 is housed in the outer packaging can 65. Next, the test electrode 61 housed in the outer packaging cup 64 and the counter electrode 62 housed in the outer packaging can 65 are stacked on each other via a separator 63 (microporous polyethylene film with a thickness of 25 μm) impregnated with an electrolyte. In this case, the negative electrode active material layer 22B and the counter electrode 62 are placed opposite to each other via the separator 63. Finally, in a state where the test electrode 61 and the counter electrode 62 are stacked on each other via the separator 63, the outer packaging cup 64 and the packaging can 65 are riveted to each other via the gasket 66. As a result, the test electrode 61 and the counter electrode 62 are sealed by the outer packaging cup 64 and the outer packaging can 65, thereby assembling a secondary battery.

[0250] (Stabilization of secondary batteries)

[0251] The secondary battery was charged and discharged for one cycle at room temperature (temperature = 23°C). During charging, constant current charging was performed at a current of 0.1C until the voltage reached 0.02V, and then constant voltage charging was performed at the voltage of 0.02V until the current reached 0.025C. During discharge, constant current discharge was performed at a current of 0.1C until the voltage reached 1.5V. 0.1C refers to the current value that completely discharges the battery capacity (theoretical capacity) within 10 hours, and 0.025C refers to the current value that completely discharges the battery capacity within 40 hours.

[0252] As a result, the states of the test electrode 61 and the counter electrode 62 are electrochemically stabilized, and the secondary battery is completed.

[0253] (Median diameter MD1, MD2, size relationship, particle size ratio RD, area ratio RS and carbon ratio RE)

[0254] After the secondary battery was completed, it was disassembled to recover the test electrode 61 , and then the median diameters MD1 and MD2 (μm), size relationship, particle diameter ratio RD, and area ratio RS were investigated. The results are shown in Tables 1 to 3.

[0255] Here, "Size Relationship" shows the size relationship between median diameters MD1 and MD2. "Large" in the "Size Relationship" column means that median diameter MD1 is larger than median diameter MD2. On the other hand, "Small" in the "Size Relationship" column means that median diameter MD1 is smaller than median diameter MD2.

[0256] It should be noted that when the test electrode 61 is produced, the surface of the first negative electrode active material particle 121 is not subjected to carbon coating. Therefore, after the test electrode 61 is recovered from the secondary battery, the surface of the first negative electrode active material particle 121 is analyzed using XPS, and the result shows that the carbon ratio RE is less than 1%.

[0257] The calculation procedure and determination procedure of the median diameters MD1 and MD2 (μm), the size relationship, the particle diameter ratio RD, the area ratio RS, and the carbon ratio RE are as described above.

[0258] [Evaluation of battery characteristics]

[0259] As battery characteristics, initial charge and discharge characteristics and cycle characteristics were evaluated, and the results shown in Tables 1 to 3 were obtained.

[0260] (Initial charge and discharge characteristics)

[0261] Initially, the charge capacity (charge capacity of the first cycle) was measured by charging the secondary battery in a room temperature environment (temperature = 23°C). Next, the discharge capacity (discharge capacity of the first cycle) was measured by discharging the secondary battery in the same environment. Finally, the initial efficiency, which is an indicator for evaluating the initial charge and discharge characteristics, was calculated based on the calculation formula of initial efficiency (%) = (discharge capacity of the first cycle / discharge capacity of the first cycle) × 100. The charge and discharge conditions were the same as those when the secondary battery was stabilized.

[0262] It should be noted that the values ​​of the primary efficiency shown in Table 1 are values ​​standardized by taking the value of the primary efficiency in Comparative Example 2 as 1. The values ​​of the primary efficiency shown in Table 2 are values ​​standardized by taking the value of the primary efficiency in Comparative Example 7 as 1. The values ​​of the primary efficiency shown in Table 3 are values ​​standardized by taking the value of the primary efficiency in Comparative Example 11 as 1.

[0263] (Cyclic characteristics)

[0264] First, the discharge capacity (discharge capacity of the first cycle) was measured by charging and discharging the secondary battery in a room temperature environment (temperature = 23° C.) The charging and discharging conditions were the same as those for stabilizing the secondary battery.

[0265] Next, the secondary battery was repeatedly charged and discharged in the same environment until the total number of cycles reached 100, and the discharge capacity (discharge capacity at the 100th cycle) was measured. The charge and discharge conditions were the same as those for stabilizing the secondary battery, except that the current during charge and the current during discharge were changed to 0.7 C, respectively.

[0266] Finally, based on the calculation formula: capacity retention rate (%)=(discharge capacity at the 100th cycle / discharge capacity at the 1st cycle)×100, the capacity retention rate, which is an index for evaluating the cycle characteristics, was calculated.

[0267] It should be noted that the values ​​of the capacity maintenance rates shown in Table 1 are values ​​standardized by taking the value of the capacity maintenance rate in Comparative Example 2 as 1. The values ​​of the capacity maintenance rates shown in Table 2 are values ​​standardized by taking the value of the capacity maintenance rate in Comparative Example 7 as 1. The values ​​of the capacity maintenance rates shown in Table 3 are values ​​standardized by taking the value of the capacity maintenance rate in Comparative Example 11 as 1.

[0268] [Table 1]

[0269]

[0270] [Table 2]

[0271]

[0272] [Table 3]

[0273]

[0274] [Investigation]

[0275] As shown in Tables 1 to 3, the initial efficiency and the capacity retention rate vary greatly depending on the configuration of the test electrode 61 .

[0276] Specifically, when the following four structural conditions were satisfied (Examples 1 to 21), a high primary efficiency was obtained and a high capacity retention rate was also obtained compared to when the four structural conditions were not satisfied (Comparative Examples 1 to 13).

[0277] Median diameter MD1 = 5μm~8μm

[0278] Median diameter MD2 = 0.12μm ~ 1.2μm

[0279] Particle size ratio RD = 5~50

[0280] Area ratio RS = 0.6 ~ 0.9

[0281] In particular, when the four constituent conditions are met (Examples 1 to 21), the following trends are obtained. First, high initial efficiency and high capacity retention rate are obtained regardless of the material of the second negative electrode active material particles 122. In this case, the same trend is obtained even if either a silicon monomer or a silicon alloy is used, and the same trend is obtained even if a silicon monomer and a silicon alloy are used in combination. Second, if the particle size ratio RD is 10 to 30, a high capacity retention rate is obtained while maintaining a high initial efficiency.

[0282] [Summarize]

[0283] According to the results shown in Tables 1 to 3, when the test electrode 61 includes a plurality of first negative electrode active material particles 121 and a plurality of second negative electrode active material particles 122, the first negative electrode active material particles 121 include silicon oxide, and the second negative electrode active material particles 122 include either or both of silicon monomer and silicon alloy, and the above four constituent conditions are satisfied, a high initial efficiency is obtained and a high capacity retention rate is obtained. Therefore, since both the initial charge and discharge characteristics and the cycle characteristics are improved, excellent battery characteristics are obtained in the secondary battery.

[0284] As mentioned above, although the present technology has been described by taking one embodiment and an example, the configuration of the present technology is not limited to the configuration described in one embodiment and an example, and various modifications are possible.

[0285] Specifically, the battery structure of the secondary battery is described as a laminated film type and a coin type, but since the battery structure of the secondary battery is not particularly limited, it may be a cylindrical type, a square type, a button type, or the like.

[0286] In addition, the case where the element structure of the battery element is a winding type is described. However, the element structure of the battery element is not particularly limited, and thus may be a stacked type, a repeatedly folded type, etc. In the stacked type, the positive electrode and the negative electrode are alternately stacked with a separator, and in the repeatedly folded type, the positive electrode and the negative electrode are folded into a Z shape with the separator interposed therebetween.

[0287] In addition, although the case where the electrode reaction material is lithium is described, the electrode reaction material is not particularly limited. Specifically, as described above, the electrode reaction material can be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium and calcium. In addition, the electrode reaction material can also be other light metals such as aluminum.

[0288] The effects described in this specification are merely examples, and therefore the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects can also be obtained with respect to the present technology.

[0289] It should be noted that the present technology can also adopt the following configurations.

[0290] <1> A secondary battery,

[0291] It has a positive electrode, a negative electrode and an electrolyte.

[0292] The negative electrode includes a plurality of first negative electrode active material particles and a plurality of second negative electrode active material particles.

[0293] The first negative electrode active material particles include silicon oxide,

[0294] The second negative electrode active material particles include at least one of silicon alone and silicon alloy.

[0295] In the observation result of the cross section of the said negative electrode using an electron microscope,

[0296] The median diameter of the plurality of first negative electrode active material particles is 5 μm or more and 8 μm or less,

[0297] The median diameter of the plurality of second negative electrode active material particles is 0.12 μm or more and 1.2 μm or less,

[0298] The ratio of the median diameter of the plurality of first negative electrode active material particles to the median diameter of the plurality of second negative electrode active material particles is 5 or more and 50 or less,

[0299] A ratio of a total area of ​​the plurality of first negative electrode active material particles to a total area of ​​the plurality of second negative electrode active material particles is greater than or equal to 0.6 and less than or equal to 0.9.

[0300] <2> The secondary battery according to <1>,

[0301] A ratio of a median diameter of the plurality of first negative electrode active material particles to a median diameter of the plurality of second negative electrode active material particles is 10 or more and 30 or less.

[0302] <3> The secondary battery according to <1> or <2>,

[0303] The silicon oxide includes a compound represented by formula (1).

[0304] SiO x … (1)

[0305] (x satisfies 0.5<x<1.2.)

[0306] <4> The secondary battery according to any one of <1> to <3>,

[0307] In the analysis result of the surface of the first negative electrode active material particle using X-ray photoelectron spectroscopy, the ratio of the amount of the carbon to the amount of all elements including carbon was less than 1%.

[0308] <5> The secondary battery according to any one of <1> to <4>,

[0309] The negative electrode further comprises a plurality of third negative electrode active material particles,

[0310] The third negative electrode active material particles include a carbon material.

[0311] <6> The secondary battery according to any one of <1> to <5>

[0312] It is a lithium-ion secondary battery.

[0313] <7> A negative electrode for a secondary battery,

[0314] comprising a plurality of first negative electrode active material particles and a plurality of second negative electrode active material particles,

[0315] The first negative electrode active material particles include silicon oxide,

[0316] The second negative electrode active material particles include at least one of silicon alone and silicon alloy.

[0317] In the observation results of the cross section using an electron microscope,

[0318] The median diameter of the plurality of first negative electrode active material particles is 5 μm or more and 8 μm or less,

[0319] The median diameter of the plurality of second negative electrode active material particles is 0.12 μm or more and 1.2 μm or less,

[0320] The ratio of the median diameter of the plurality of first negative electrode active material particles to the median diameter of the plurality of second negative electrode active material particles is 5 or more and 50 or less,

[0321] A ratio of a total area of ​​the plurality of first negative electrode active material particles to a total area of ​​the plurality of second negative electrode active material particles is greater than or equal to 0.6 and less than or equal to 0.9.

Claims

1. A secondary battery, It has a positive electrode, a negative electrode and an electrolyte. The negative electrode includes a plurality of first negative electrode active material particles and a plurality of second negative electrode active material particles. The first negative electrode active material particles include silicon oxide, The second negative electrode active material particles include at least one of silicon alone and silicon alloy. In the observation result of the cross section of the said negative electrode using an electron microscope, The median diameter of the plurality of first negative electrode active material particles is 5 μm or more and 8 μm or less, The median diameter of the plurality of second negative electrode active material particles is 0.12 μm or more and 1.2 μm or less, The ratio of the median diameter of the plurality of first negative electrode active material particles to the median diameter of the plurality of second negative electrode active material particles is 5 or more and 50 or less, A ratio of a total area of ​​the plurality of first negative electrode active material particles to a total area of ​​the plurality of second negative electrode active material particles is greater than or equal to 0.6 and less than or equal to 0.

9.

2. The secondary battery according to claim 1, wherein A ratio of a median diameter of the plurality of first negative electrode active material particles to a median diameter of the plurality of second negative electrode active material particles is 10 or more and 30 or less.

3. The secondary battery according to claim 1 or 2, wherein: The silicon oxide includes a compound represented by formula (1), Not. x …(1) Wherein, x satisfies 0.5<x<1.

2.

4. The secondary battery according to any one of claims 1 to 3, wherein In the analysis result of the surface of the first negative electrode active material particle using X-ray photoelectron spectroscopy, the ratio of the amount of the carbon to the amount of all elements including carbon was less than 1%.

5. The secondary battery according to any one of claims 1 to 4, wherein The negative electrode further comprises a plurality of third negative electrode active material particles, The third negative electrode active material particles include a carbon material.

6. The secondary battery according to any one of claims 1 to 5, The secondary battery is a lithium ion secondary battery.

7. A negative electrode for a secondary battery, comprising a plurality of first negative electrode active material particles and a plurality of second negative electrode active material particles, The first negative electrode active material particles include silicon oxide, The second negative electrode active material particles include at least one of silicon alone and silicon alloy. In the observation results of the cross section using an electron microscope, The median diameter of the plurality of first negative electrode active material particles is 5 μm or more and 8 μm or less, The median diameter of the plurality of second negative electrode active material particles is 0.12 μm or more and 1.2 μm or less, The ratio of the median diameter of the plurality of first negative electrode active material particles to the median diameter of the plurality of second negative electrode active material particles is 5 or more and 50 or less, A ratio of a total area of ​​the plurality of first negative electrode active material particles to a total area of ​​the plurality of second negative electrode active material particles is greater than or equal to 0.6 and less than or equal to 0.9.

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