Negative electrode for secondary battery and secondary battery

Abstract

This secondary battery comprises a positive electrode, a negative electrode, and an electrolytic 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 each include silicon oxide, and the second negative electrode active material particles each include at least one of a silicon element and a silicon alloy. In observation results of a 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 μm to 8 μm, the median diameter of the plurality of second negative electrode active material particles is 0.12 μm to 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 5 to 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 0.6 to 0.9.

Description

Negative electrode for secondary battery and secondary battery

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

[0002] Due to the widespread use of various electronic devices such as mobile phones, secondary batteries have been developed as small, lightweight power sources that can provide high energy density. These secondary batteries contain a positive electrode, a negative electrode (secondary battery negative electrode), and an electrolyte solution, and various studies have been conducted on the configuration of these secondary batteries.

[0003] Specifically, the negative electrode includes first active material particles and second active material particles (see, for example, 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 to 1.5)

[0004] JP 2015-232921 A

[0005] Although various studies have been conducted on the configuration of secondary batteries, the battery characteristics of the secondary batteries are still insufficient and there is room for improvement.

[0006] There is a demand for a negative electrode for a secondary battery and a secondary battery that can provide excellent battery characteristics.

[0007] According to one embodiment of the present disclosure, a secondary battery 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 an oxide of silicon, and the second negative electrode active material particles include at least one of elemental silicon and an alloy of silicon. Cross-sectional observation using an electron microscope reveals that the first negative electrode active material particles have a median diameter of 5 μm to 8 μm, the second negative electrode active material particles have a median diameter of 0.12 μm to 1.2 μm, the ratio of the median diameter of the first negative electrode active material particles to the median diameter of the second negative electrode active material particles is 5 to 50, and the ratio of the total area of ​​the first negative electrode active material particles to the total area of ​​the second negative electrode active material particles is 0.6 to 0.9.

[0008] A secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolyte solution, and the negative electrode has a configuration similar to that of the negative electrode for a secondary battery according to the embodiment of the present technology described above.

[0009] As described above, the following four types of configuration conditions are identified based on the results of observation of a cross section of the negative electrode using an electron microscope. The details of the procedure for identifying these four types of configuration conditions will be described later. (1) Range of median diameters of the plurality of first negative electrode active material particles (2) Range of median diameters of the plurality of second negative electrode active material particles (3) Range of ratios of median diameters of the plurality of first negative electrode active material particles to the median diameters of the plurality of second negative electrode active material particles (4) Range of ratios 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

[0010] According to the negative electrode for a secondary battery or the secondary battery of one embodiment of the present technology, the negative electrode for a secondary battery 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 an oxide of silicon, and the second negative electrode active material particles include at least one of elemental silicon and an alloy of silicon, and since the above-mentioned four configuration conditions are satisfied, excellent battery characteristics can be obtained.

[0011] Note that the effects of the present technology are not necessarily limited to the effects described here, but may be any of a series of effects related to the present technology described below.

[0012] Fig. 4 is a cross-sectional view showing the configuration of a negative electrode for a secondary battery in an embodiment of the present technology. Fig. 5 is a cross-sectional view showing the configuration of each of a plurality of first negative electrode active material particles and a plurality of second negative electrode active material particles shown in Fig. 1. Fig. 6 is a perspective view showing the configuration of a secondary battery in an embodiment of the present technology. Fig. 7 is a cross-sectional view showing the configuration of the battery element shown in Fig. 3. Fig. 8 is a block diagram showing the configuration of an application example of a secondary battery. Fig. 9 is a cross-sectional view showing the configuration of a test secondary battery.

[0013] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The description will be made in the following order: 1. Negative electrode for secondary battery 1-1. Configuration 1-2. Operation 1-3. Manufacturing method 1-4. Action and effect 2. Secondary battery 2-1. Configuration 2-2. Operation 2-3. Manufacturing method 2-4. Action and effect 3. Modification 4. Use of secondary battery

[0014] 1. Negative electrode for secondary battery First, a negative electrode for secondary battery (hereinafter simply referred to as "negative electrode") according to one embodiment of the present technology will be described.

[0015] The negative electrode described here is used in a secondary battery, which is an electrochemical device. However, the negative electrode may also be used in electrochemical devices other than secondary batteries. Specific examples of other electrochemical devices include primary batteries and capacitors.

[0016] The negative electrode absorbs and releases an electrode reactant during operation of the electrochemical device (during electrode reaction). The type of electrode reactant is not particularly limited, but specifically includes light metals such as alkali metals and alkaline earth metals. Specific examples of alkali metals include lithium, sodium, and potassium, and specific examples of alkaline earth metals include beryllium, magnesium, and calcium.

[0017] In the following, an example will be given in which the electrode reactant is lithium, whereby lithium is absorbed and released in an ionic state at the negative electrode during the electrode reaction.

[0018] <1-1. Structure> FIG. 1 shows a cross-sectional structure of a negative electrode 100, which is an example of a negative electrode, and FIG. 2 shows a cross-sectional structure of each of a plurality of first negative electrode active material particles 121 and a plurality of second negative electrode active material particles 122 shown in FIG. 1 .

[0019] As shown in FIG. 1, the negative electrode 100 includes a negative electrode current collector 110 and a negative electrode active material layer 120 .

[0020] 1, 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 and lower surfaces) on which the negative electrode active material layer 120 is provided. The negative electrode current collector 110 contains one or more types of conductive materials such as metal materials, and a specific example of the conductive material is copper.

[0021] 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 is improved by utilizing the so-called anchor effect.

[0022] However, the negative electrode current collector 110 may be omitted. That is, the negative electrode 100 may include only the negative electrode active material layer 120.

[0023] 1 , the negative electrode active material layer 120 is a layer that absorbs and releases lithium, and is provided on one surface (upper surface or lower surface) of the negative electrode current collector 110. However, 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.

[0024] The negative electrode active material layer 120 contains two types of particulate negative electrode active material. Specifically, as shown in FIG. 2 , the negative electrode active material layer 120 contains 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 together 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 may be agglomerated together.

[0025] 2, in order to simplify the illustration, the cross-sectional shape of the first negative electrode active material particles 121 is shown as a circle. However, the cross-sectional shape of the first negative electrode active material particles 121 is not particularly limited, and may be a shape other than a 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 type, and may be two or more types.

[0026] The same applies to the cross-sectional shape of the second negative electrode active material particles 122 as described above with respect to the cross-sectional shape of the first negative electrode active material particles 121. That is, although the cross-sectional shape of the second negative electrode active material particles 122 is circular in Fig. 2, the cross-sectional shape of the second negative electrode active material particles 122 is not particularly limited and may be a shape other than circular.

[0027] (First Negative Electrode Active Material Particles) The 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 second negative electrode active material particles 122 .

[0028] The median diameter of the plurality of first negative electrode active material particles 121 described here is so-called D50 (μm). Hereinafter, the median diameter of the plurality of first negative electrode active material particles 121 will be referred to as the "median diameter MD1."

[0029] The first negative electrode active material particles 121 contain one or more types of oxides of silicon because in a secondary battery using the negative electrode 100, the discharge capacity is less likely to decrease even with repeated charge and discharge.

[0030] The type of silicon oxide is not particularly limited. Among them, it is preferable that the silicon oxide contains one or more of the compounds represented by formula (1), because the irreversible capacity is sufficiently reduced.

[0031] SiO x ... (1) (x satisfies 0.5<x<1.2)

[0032] The detailed configurations (four types of configuration conditions) of the plurality of first negative electrode active material particles 121 will be described later.

[0033] (Second Negative Electrode Active Material Particles) The second negative electrode active material particles 122 have a relatively small median diameter, more specifically, a median diameter smaller than the median diameter of the first negative electrode active material particles 121 .

[0034] The median diameter of the plurality of second negative electrode active material particles 122 described here is so-called D50 (μm), similar to the median diameter of the plurality of first negative electrode active material particles 121. Hereinafter, the median diameter of the plurality of second negative electrode active material particles 122 will be referred to as the "median diameter MD2."

[0035] The second negative electrode active material particles 122 contain one or more types of silicon elemental material and silicon alloys. This is because a high energy density can be obtained. The second negative electrode active material particles 122 may contain only silicon elemental material, only silicon alloys, or both silicon elemental material and silicon alloys. When the second negative electrode active material particles 122 contain a silicon alloy, the type of silicon alloy may be only one type or two or more types.

[0036] The term "silicon element" refers to a general silicon element. Therefore, the silicon element may contain trace amounts of impurities. In other words, the purity of the silicon element is not necessarily limited to 100%.

[0037] The type of silicon alloy is not particularly limited. Specifically, the silicon alloy contains, as a constituent element other than silicon, one or more of metal elements such as tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium.

[0038] Specific examples of silicon alloys include 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. However, the composition of the silicon alloy exemplified here (the mixing ratio of silicon and metal elements) can be changed as desired.

[0039] The detailed configurations (four types of configuration conditions) of the plurality of second negative electrode active material particles 122 will be described later.

[0040] (Other Materials) The negative electrode active material layer 120 may further contain one or more of the other materials.

[0041] The other material is a negative electrode binder, which includes one or more of synthetic rubbers and polymer compounds. Specific examples of synthetic rubbers include styrene-butadiene rubbers, fluorine-containing rubbers, and ethylene-propylene-diene. Specific examples of polymer compounds include polyvinylidene fluoride, polyimide, polyacrylic acid, and carboxymethyl cellulose.

[0042] The other material is a negative electrode conductive agent, which contains one or more conductive materials such as a carbon material, a metal material, and a conductive polymer compound. Specific examples of the carbon material include graphite, carbon black, acetylene black, and ketjen black.

[0043] Furthermore, the other material is a plurality of particulate third anode active materials (a plurality of third anode active material particles), and the third anode active material particles contain one or more types of carbon materials. Since the crystal structure of the carbon material hardly changes during lithium absorption and desorption, a high energy density can be stably obtained. In addition, the carbon material also functions as an anode conductive agent, thereby improving the conductivity of the anode active material layer 120.

[0044] 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, but is specifically 0.37 nm or more. The interplanar spacing of the (002) plane of graphite is not particularly limited, but is specifically 0.34 nm or less.

[0045] Specific examples of carbon materials include pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound calcined bodies, activated carbon, and carbon blacks. Examples of cokes include pitch coke, needle coke, and petroleum coke. Organic polymer compound calcined bodies are calcined (carbonized) polymer compounds such as phenolic resins and furan resins at an appropriate temperature. Alternatively, the carbon material may be low-crystalline carbon heat-treated at a temperature of approximately 1000°C or less, or amorphous carbon. The shape of the carbon material is not particularly limited, but may be one or more of the following: fibrous, spherical, granular, and flaky.

[0046] When the negative electrode active material layer 120 contains a plurality of third negative electrode active material particles together with a plurality of first negative electrode active material particles 121 and a plurality of second negative electrode active material particles 122, damage and falling off of the negative electrode active material layer 120 are suppressed while the battery capacity is guaranteed, particularly during the electrode reaction (charging and discharging) of a secondary battery using the negative electrode 100.

[0047] Specifically, silicon-containing materials (silicon oxides, silicon elemental elements, and silicon alloys) have the advantage of high theoretical capacity, but have the drawback of being prone to severe expansion and contraction during charge and discharge. On the other hand, carbon materials have the drawback of being prone to low theoretical capacity, but have the advantage of being less prone to expansion and contraction during charge and discharge. Therefore, by using a silicon-containing material in combination with a carbon material, a high theoretical capacity can be obtained while suppressing expansion and contraction of the negative electrode active material layer 120 during charge and discharge. As a result, as described above, damage and detachment of the negative electrode active material layer 120 are suppressed while ensuring the battery capacity.

[0048] [Detailed Configuration] Here, the detailed configuration 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.

[0049] (Four Types of Configuration Conditions) Predetermined conditions are satisfied with respect to the configurations of the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122. Specifically, the results of observation of a cross section of the negative electrode 100 using an electron microscope show that the following four types of configuration conditions are satisfied.

[0050] Below, the procedure for obtaining the observation results of the cross section of the negative electrode 100 using an electron microscope will be described, and then the four types of conditions will be described in detail.

[0051] When obtaining the results of observation of the cross section of the negative electrode 100 using an electron microscope, the negative electrode 100 is cut in the thickness direction (the vertical direction in FIG. 1 ) to expose the cross section of the negative electrode 100. This exposes the cross section of the negative electrode active material layer 120 containing a plurality of first negative electrode active material particles 121 and a plurality of second negative electrode active material particles 122.

[0052] Thereafter, a cross section of the negative electrode active material layer 120 is observed using an electron microscope to obtain an observation result (electron microscope photograph) of the cross section. As a result, a state in which a plurality of first negative electrode active material particles 121 and a plurality of second negative electrode active material particles 122 coexist is observed, as shown in FIG. 2 . The type of electron microscope is not particularly limited, but specifically, it is any one or more types of a scanning electron microscope, a transmission electron microscope, or the like. As a result, an observation result of the cross section of the negative electrode 100 using the electron microscope is obtained.

[0053] The cutting method and cutting conditions for the negative electrode 100 are not particularly limited, and the conditions for observing the cross section of the negative electrode 100 are not particularly limited. Specifically, when cutting the negative electrode 100, an ion milling device is used as the cutting device, and the cutting conditions are an acceleration voltage of 6 kV, a discharge voltage of 1.5 kV, and a cutting time of 3 hours. When observing the cross section of the negative electrode 100, the observation conditions are an observation magnification of 2000 to 5000 times and an acceleration voltage of 3 kV.

[0054] The first condition is that the median diameter MD1 is within a predetermined range. Specifically, the median diameter MD1 is 5 μm to 8 μm. The value of this median diameter MD1 is rounded to two decimal places.

[0055] The second condition is that 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 this median diameter MD2 is rounded to two decimal places.

[0056] The third condition is that the ratio of the median diameter MD1 to the median diameter MD2 (grain size ratio RD) is within a predetermined range. Specifically, the grain size ratio RD (= MD1 / MD2) is 5 to 50. The value of this grain size ratio RD is rounded to two decimal places.

[0057] 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 this area ratio RS is rounded to one decimal place.

[0058] The area ratio RS is an index that represents 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.

[0059] The reason why the above four types of configuration conditions are satisfied is that, unlike when the four types of configuration conditions are not satisfied, the relationship between the median diameter MD1 and the median diameter MD2 is optimized, and the mixing ratio between the plurality of first anode active material particles 121 and the plurality of second anode active material particles 122 is also optimized. As a result, in a secondary battery using anode 100, sufficient discharge capacity can be obtained from the first charge / discharge, and the discharge capacity is less likely to decrease even when the battery is subsequently charged / discharged repeatedly.

[0060] In particular, the third condition, the particle size ratio RD (=5 to 50), has the following tendency, which will be explained below.

[0061] When the particle size ratio RD is smaller than 5, the difference between the median diameter MD1 and the median diameter MD2 is too small, making it difficult for the plurality of first negative electrode active material particles 121 to be arranged so as to cover the surfaces of the second negative electrode active material particles 122. This makes it difficult to obtain a sufficient discharge capacity from the first charge / discharge, and the discharge capacity is likely to decrease when the charge / discharge is repeated thereafter.

[0062] On the other hand, when the particle size ratio RD is greater than 50, the difference between the median diameter MD1 and the median diameter MD2 is too large, and therefore, similar to the above-described case where the particle size ratio RD is less than 5, it becomes difficult for the plurality of first negative electrode active material particles 121 to be arranged so as to cover the surfaces of the second negative electrode active material particles 122. As a result, the amount of coverage of the surfaces of the second negative electrode active material particles 122 by the plurality of first negative electrode active material particles 121 becomes insufficient, making it difficult to obtain a sufficient discharge capacity from the first charge / discharge, and the discharge capacity is likely to decrease when charge / discharge is repeated thereafter.

[0063] In particular, the particle size ratio RD is preferably 10 to 30. This is because the particle size ratio RD is more optimized, making it easier to obtain a sufficient discharge capacity from the first charge / discharge, and also making it more difficult for the discharge capacity to decrease even after repeated charge / discharge.

[0064] (Element Distribution) The element distribution on the surface of the first negative electrode active material particle 121 is not particularly limited. In particular, in the results of analyzing the surface of the first negative electrode active material particle 121 using X-ray photoelectron spectroscopy (XPS), it is preferable that the ratio of the amount of carbon present E2 to the amount of all elements present E1 (carbon ratio RE = E2 / E1) is less than 1%. This is because a coating layer containing carbon as a constituent element is hardly provided on the surface of the first negative electrode active material particle 121, and therefore the coating layer hardly covers the surface of the first negative electrode active material particle 121. The value of this carbon ratio RE is rounded to one decimal place.

[0065] Here, the term "total elements" refers to all types of elements detected in the surface analysis of the first negative electrode active material particles 121 using XPS, including carbon. Thus, the carbon fraction RE is an index representing the amount of carbon present on the surface of the first negative electrode active material particles 121.

[0066] (Calculation Procedure and Identification Procedure) When calculating the median diameter MD1, first, a plurality of first negative electrode active material particles 121 are identified in an electron microscope photograph. Next, 300 first negative electrode active material particles 121 are arbitrarily selected from the plurality of first negative electrode active material particles 121, and the particle diameter (μm) of each of the 300 first negative electrode active material particles 121 is measured. In this case, the particle diameter may be measured manually or mechanically using any image processing software. Note that, if the particle diameter varies depending on the measurement direction, the maximum particle diameter is selected. Finally, the median diameter MD1 is calculated based on the number (= 300 particles) and the measurement results of the plurality of particle diameters.

[0067] The procedure for calculating the median diameter MD2 is the same as the procedure for calculating the median diameter MD1 described above, except that attention is focused on a plurality of second negative electrode active material particles 122 instead of a plurality of first negative electrode active material particles 121.

[0068] When calculating the particle size ratio RD, the median diameters MD1 and MD2 are calculated using the procedure described above, and then the particle size ratio RD is calculated using the formula RD (= MD1 / MD2).

[0069] When examining the area ratio RS, first, 300 first negative electrode active material particles 121 are arbitrarily selected from the plurality of first negative electrode active material particles 121 in the electron microscope photograph. Then, the area (μm 2 ) and then add up the areas of the 300 particles to obtain 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.

[0070] Next, the total area S2 (μm ) is calculated by the same procedure as the procedure for calculating the total area S1 described above, except that attention is focused on the plurality of second negative electrode active material particles 122 instead of the plurality of first negative electrode active material particles 121. 2 That is, the total area S2 is the sum of the areas of the 300 second negative electrode active material particles 122.

[0071] Finally, the area ratio RS (=S1 / S2) is calculated using the calculation formula.

[0072] The procedure for calculating the carbon ratio RE is as follows. The following describes a case where the anode active material layer 120 contains a plurality of first anode active material particles 121 and a plurality of second anode active material particles 122, as well as a anode binder and anode conductor.

[0073] First, the negative electrode 100 is disassembled to recover a plurality of first negative electrode active material particles 121 .

[0074] In this case, the negative electrode current collector 110 is peeled from the negative electrode active material layer 120, and then the negative electrode active material layer 120 is placed in a solvent. This solvent is either an aqueous solvent or an organic solvent that can dissolve the negative electrode binder. A specific example of a non-aqueous solvent is water, and a specific example of an organic solvent is N-methyl-2-pyrrolidone. In this case, the negative electrode binder is dissolved, but the plurality of first negative electrode active material particles 121, the plurality of second negative electrode active material particles 122, and the negative electrode conductor are not dissolved. As a result, the negative electrode binder is dissolved and removed, and a mixture of the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 is recovered.

[0075] Next, the mixture is poured into a sieve having a plurality of holes to separate the plurality of first anode active material particles 121 from the mixture. In this case, the size of the plurality of holes is set so that the plurality of first anode active material particles 121 can pass through but the plurality of second anode active material particles 122 and the anode conductive agent cannot. As a result, the plurality of first anode active material particles 121 pass through the holes, while the plurality of second anode active material particles 122 and the anode conductive agent do not. Therefore, the plurality of first anode active material particles 121 are separated from the plurality of second anode active material particles 122 and the anode conductive agent.

[0076] Next, the abundances of a series of elements are measured by performing a surface analysis of the first negative electrode active material particles 121 using XPS, thereby calculating the abundance E1 of all elements and the abundance E2 of carbon.

[0077] Finally, the carbon ratio RE is calculated using the formula: carbon ratio RE=(E2 / E1)×100.

[0078] <1-2. Operation> This negative electrode 100 operates as follows during the electrode reaction.

[0079] In the anode active material layer 120, lithium is absorbed in an ionic state into each of the plurality of first anode active material particles 121 and the plurality of second anode active material particles 122. In the anode active material layer 120, lithium is released in an ionic state from each of the plurality of first anode active material particles 121 and the plurality of second anode active material particles 122.

[0080] <1-3. Manufacturing Method> The negative electrode 100 is manufactured by the following example procedure.

[0081] 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 together to form a negative electrode mixture.

[0082] In this case, the median diameters MD1 and MD2 are each adjusted so that the first and second conditions are satisfied. Specifically, by using a plurality of first negative electrode active material particles 121 whose median diameter MD1 satisfies the first condition and a plurality of second negative electrode active material particles 122 whose median diameter MD2 satisfies the second condition, the third condition is satisfied with respect to the particle size ratio RD.

[0083] Furthermore, the mixing ratio of the plurality of first negative electrode active material particles 121 to the plurality of second negative electrode active material particles 122 is adjusted so that the fourth condition regarding the area ratio RS is satisfied.

[0084] Next, the negative electrode mixture is poured into a solvent to prepare a paste-like negative electrode mixture slurry. This solvent may be an aqueous solvent or an organic solvent.

[0085] Finally, the negative electrode mixture slurry is applied to one surface of the negative electrode current collector 110 to form the negative electrode active material layer 120. After this, 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 the compression molding may be repeated multiple times.

[0086] As a result, the negative electrode active material layer 120 is formed on the negative electrode current collector 110, and the negative electrode 100 is completed.

[0087] <1-4. Actions and Effects> According to this 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 including an oxide of silicon, and the second negative electrode active material particles 122 including either or both of elemental silicon and an alloy of silicon.

[0088] Furthermore, the plurality of first negative electrode active material particles 121 and the plurality of second negative electrode active material particles 122 satisfy the four configuration conditions described above. 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 size ratio RD is 5 to 50 (third condition). The area ratio RS is 0.6 to 0.9 (fourth condition).

[0089] In this case, as described above, the relationship between the median diameters MD1 and MD2 is optimized, and the mixture ratio of the plurality of first anode active material particles 121 and the plurality of second anode active material particles 122 is also optimized. As a result, in a secondary battery using the anode 100, sufficient discharge capacity can be obtained from the first charge / discharge, and the discharge capacity is less likely to decrease even with repeated charge / discharge thereafter. Therefore, a secondary battery with excellent battery characteristics can be realized using the anode 100.

[0090] In particular, if the particle size ratio RD is 10 to 30, a sufficient discharge capacity is likely to be obtained from the first charge / discharge, and the discharge capacity is less likely to decrease even after repeated charge / discharge, thereby achieving a greater effect.

[0091] Furthermore, if the oxide of silicon contains the compound represented by formula (1), the irreversible capacity is sufficiently reduced, and therefore a higher effect can be obtained.

[0092] Furthermore, if the carbon ratio RE is less than 1%, the surfaces of the first negative electrode active material particles 121 are hardly covered with carbon, and therefore a higher effect can be obtained.

[0093] Furthermore, if the negative electrode 100 further contains a plurality of third negative electrode active material particles, and the third negative electrode active material particles contain a carbon material, the battery capacity is guaranteed during charging and discharging of a secondary battery using the negative electrode 100, while damage and detachment of the negative electrode active material layer 120 are suppressed, thereby achieving a greater effect.

[0094] 2. Secondary Battery Next, a secondary battery according to an embodiment of the present technology to which the negative electrode 100 is applied will be described.

[0095] The secondary battery described here is a secondary battery that obtains battery capacity by utilizing the absorption and desorption of electrode reactants, and is equipped with a positive electrode, a negative electrode, and an electrolyte.

[0096] The charge capacity of the negative electrode is preferably larger than the discharge capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is preferably larger than the electrochemical capacity per unit area of ​​the positive electrode. This is to prevent deposition of electrode reactants on the surface of the negative electrode during charging.

[0097] In the following, as described above, an example will be given in which the electrode reactant is lithium. A secondary battery that obtains battery capacity by utilizing the absorption and desorption of lithium is a so-called lithium ion secondary battery. In this lithium ion secondary battery, lithium is absorbed and desorbed in the ionic state.

[0098] <2-1. Configuration> Fig. 3 shows a perspective configuration of a secondary battery, and Fig. 4 shows a cross-sectional configuration of the battery element 20 shown in Fig. 3. However, Fig. 4 shows a state in which the exterior film 10 and the battery element 20 are separated from each other, and also shows a cross section of the battery element 20 along the XZ plane by a dashed line.

[0099] As shown in FIGS. 3 and 4, this secondary battery includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and .

[0100] The secondary battery described here is a so-called laminate film type secondary battery, since it uses the flexible or pliable exterior film 10 as an exterior member for housing the battery element 20, as described above.

[0101] 3, the exterior film 10 has a bag-like structure that is sealed when the battery element 20 is housed therein. As a result, the exterior film 10 houses a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte solution, which will be described later.

[0102] Here, the exterior film 10 is a single film-like member that is folded in a folding direction F. The exterior film 10 is provided with a recessed portion 10U (a so-called deep drawn portion) for accommodating the battery element 20.

[0103] Specifically, the exterior film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside out, and when the exterior film 10 is folded, the outer peripheral edges of the opposing fusion layers are fused to each other. The fusion 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.

[0104] However, the configuration (number of layers) of the exterior film 10 is not particularly limited, and may be one layer, two layers, or four or more layers.

[0105] [Battery Element] The battery element 20 is housed in an exterior film 10. The battery element 20 is a so-called power generating element, and as shown in Figures 3 and 4, includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown).

[0106] Here, battery element 20 is a so-called wound electrode body. That is, positive electrode 21 and negative electrode 22 are wound around winding axis P while facing each other with separator 23 interposed therebetween. As is clear from FIG. 3 , winding axis P is a virtual axis extending in the Y-axis direction.

[0107] There are no particular limitations on the three-dimensional shape of battery element 20. Here, battery element 20 has a flat three-dimensional shape, and therefore the shape of a cross section (cross section along the XZ plane) of battery element 20 intersecting winding axis P is a flat shape defined by major axis J1 and minor axis J2.

[0108] 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 flattened cylinder, and therefore the cross-sectional shape of the battery element 20 is a flattened, approximately elliptical shape.

[0109] (Positive Electrode) As shown in FIG. 4, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B.

[0110] The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. The positive electrode current collector 21A contains a conductive material such as a metal material, and a specific example of the conductive material is aluminum.

[0111] The positive electrode active material layer 21B contains one or more types of positive electrode active materials capable of absorbing and releasing lithium. However, the positive electrode active material layer 21B may further contain one or more types 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, but specifically includes a coating method.

[0112] Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A, and therefore the positive electrode 21 includes two positive electrode active material layers 21B. However, since the positive electrode active material layer 21B is provided on only one side of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22, the positive electrode 21 may include only one positive electrode active material layer 21B.

[0113] The type of positive electrode active material is not particularly limited, but specifically includes a lithium-containing compound. This lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements, and may further include one or more other elements as constituent elements. The type of other elements is not particularly limited, but specifically includes elements belonging to Groups 2 to 15 of the long period periodic table. The type of lithium-containing compound is not particularly limited, but specifically includes oxides, phosphate compounds, silicate compounds, borate compounds, etc.

[0114] A specific example of the 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 Specific examples of phosphate compounds include LiFePO 4 , LiMnPO 4 and LiFe 0.5 Mn 0.5 P.O. 4 And so on.

[0115] 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.

[0116] (Negative Electrode) The negative electrode 22 has a configuration similar to that of the negative electrode 100. That is, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B, as shown in Fig. 4. The configurations of the negative electrode current collector 22A and the negative electrode active material layer 22B are similar to the configurations of the negative electrode current collector 110 and the negative electrode active material layer 120, respectively.

[0117] Here, the anode active material layer 22B is provided on both sides of the anode current collector 22A, but the anode active material layer 22B may be provided on only one side of the anode current collector 22A.

[0118] 4, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and allows lithium to pass through in an ionic state while preventing the occurrence of a short circuit due to contact between the positive electrode 21 and the negative electrode 22. The separator 23 contains a polymer compound such as polyethylene.

[0119] (Electrolyte) The electrolyte is a liquid electrolyte, and is impregnated into each of the positive electrode 21, the negative electrode 22, and the separator 23. The electrolyte contains a solvent and an electrolyte salt.

[0120] The solvent contains one or more types of non-aqueous solvents (organic solvents), and the electrolyte containing the non-aqueous solvent is a so-called non-aqueous electrolyte.

[0121] The non-aqueous solvent is an ester, an ether, or the like, and more specifically, is one or more of a carbonate ester compound, a carboxylic acid ester compound, and a lactone compound, because the dissociation of the electrolyte salt and the mobility of ions are improved.

[0122] The carbonate ester compounds include cyclic carbonate esters and chain carbonate esters. Specific examples of the cyclic carbonate esters include ethylene carbonate and propylene carbonate, and specific examples of the chain carbonate esters include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0123] The carboxylic acid ester compound is a chain carboxylic acid ester, etc. Specific examples of the chain carboxylic acid ester include ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethylacetate.

[0124] The lactone compound is lactone, etc. Specific examples of lactone include γ-butyrolactone and γ-valerolactone.

[0125] The ethers may be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, or the like.

[0126] The nonaqueous solvent is one or more of unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonates, phosphates, acid anhydrides, nitrile compounds, isocyanate compounds, etc. This is because the dissociation of the electrolyte salt and the mobility of ions are similarly improved.

[0127] Specific examples of unsaturated cyclic carbonates include vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate. Specific examples of fluorinated cyclic carbonates include monofluoroethylene carbonate and difluoroethylene carbonate. Specific examples of sulfonic acid esters include propane sultone and propene sultone. Specific examples of phosphate esters include trimethyl phosphate and triethyl phosphate. Specific examples of acid anhydrides include succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of nitrile compounds include succinonitrile. Specific examples of isocyanate compounds include hexamethylene diisocyanate.

[0128] Of course, the composition of the non-aqueous solvent is not particularly limited as long as it contains one or more of the non-aqueous solvents described above, and can be set arbitrarily.

[0129] The electrolyte salt contains one or more types of light metal salts such as lithium salts.

[0130] A specific example of the 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)methide (LiC(CF 3 SO 2 ) 3 ), lithium bis(oxalato)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.

[0131] The content of the electrolyte salt is not particularly limited, but specifically, it is 0.3 mol / kg to 3.0 mol / kg relative to the solvent, because high ionic conductivity can be obtained.

[0132] 3 and 4, the positive electrode lead 31 is a positive electrode wiring connected to the positive electrode current collector 21A of the positive electrode 21, and is led out of the exterior film 10. The positive electrode lead 31 contains a conductive material such as a metal material, and a specific example of the conductive material is aluminum. The positive electrode lead 31 has a shape such as a thin plate or a mesh.

[0133] [Negative Electrode Lead] As shown in Figures 3 and 4 , the negative electrode lead 32 is a negative electrode wiring connected to the negative electrode current collector 22A of the negative electrode 22, and is led out of the exterior 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. This negative electrode lead 32 contains a conductive material such as a metal material, and a specific example of the conductive material is copper. Note that the details regarding the shape of the negative electrode lead 32 are the same as the details regarding the shape of the positive electrode lead 31.

[0134] [Sealing Film] The sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

[0135] The sealing film 41 is a sealing member that prevents outside air and the like from entering the inside of the exterior film 10. This sealing film 41 contains a polymer compound such as polyolefin that has adhesiveness to the positive electrode lead 31, and a specific example of the polymer compound is polypropylene.

[0136] The configuration of the sealing film 42 is the same as the configuration of the sealing film 41, except that the sealing film 42 is a sealing member that has adhesiveness to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin that has adhesiveness to the negative electrode lead 32.

[0137] <2-2. Operation> This secondary battery operates as follows during charging and discharging.

[0138] During charging, lithium is released from the positive electrode 21 of the battery element 20 and is absorbed into the negative electrode 22 via the electrolyte. During discharging, lithium is released from the negative electrode 22 of the battery element 20 and is absorbed into the positive electrode 21 via the electrolyte. During both discharging and charging, lithium is absorbed and released in an ionic state.

[0139] <2-3. Manufacturing Method> When manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are each produced and an electrolytic solution is prepared according to the procedure described below as an example. Thereafter, the positive electrode 21, the negative electrode 22, and the electrolytic solution are used to assemble a secondary battery, and a stabilization process is performed on the assembled secondary battery.

[0140] [Fabrication of Positive Electrode] First, a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent are mixed together to form a positive electrode mixture. Next, the positive electrode mixture is poured into a solvent to prepare a paste-like positive electrode mixture slurry. This solvent may be an aqueous solvent or an organic solvent. Finally, the positive electrode mixture slurry is applied to both surfaces of the positive electrode current collector 21A to form the positive electrode active material layer 21B. Thereafter, the positive electrode active material layer 21B may be compression-molded using a roll press or the like. In this case, the positive electrode active material layer 21B may be heated, or the compression molding may be repeated multiple times. As a result, the positive electrode active material layer 21B is formed on both surfaces of the positive electrode current collector 21A, thereby fabricating the positive electrode 21.

[0141] [Fabrication of Negative Electrode] The negative electrode 22 is fabricated by the same procedure as that for fabricating 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.

[0142] [Preparation of Electrolyte Solution] An electrolyte salt is added to a solvent, whereby the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing an electrolyte solution.

[0143] [Assembly of Secondary Battery] First, the positive electrode lead 31 is connected to the positive electrode current 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 current 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 current 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 current collector 22A of the negative electrode 22 using a joining method such as welding.

[0144] Next, the positive electrode 21 and the negative electrode 22 are stacked one on top of the other with the separator 23 interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound together to produce a wound body (not shown). Next, the wound body is pressed using a press or the like to form a flat shape. The wound body after this formation has a configuration similar to that of the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with an electrolyte solution.

[0145] Next, after the roll is housed inside the recess 10U, the exterior film 10 (fusion layer / metal layer / surface protection layer) is folded to face each other. Next, the outer peripheral edges of two sides of the facing fusion layers are joined together using an adhesive method such as heat fusion, thereby housing the roll inside the bag-shaped exterior film 10.

[0146] Finally, after injecting the electrolyte solution into the bag-shaped exterior film 10, the outer peripheral edges of the remaining sides of the opposing fusion layers are joined together using an adhesive method such as heat fusion. In this case, a sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32.

[0147] As a result, the wound body is impregnated with the electrolyte, forming the wound electrode body, which is the battery element 20. The battery element 20 is then sealed inside the bag-shaped exterior film 10, and the secondary battery is assembled.

[0148] [Stabilization of Secondary Battery] The assembled secondary battery is charged and discharged. Various conditions, such as the ambient temperature, the number of charge / discharge cycles (number of cycles), and the charge / discharge conditions, can be set as desired. This electrochemically stabilizes the states of the positive electrode 21 and the negative electrode 22, thereby completing the secondary battery.

[0149] <2-4. Actions and Effects> In this secondary battery, the negative electrode 22 has a configuration similar to that of the negative electrode 100. Therefore, for the reasons described above, a sufficient discharge capacity can be obtained from the first charge / discharge, and the discharge capacity is less likely to decrease even after repeated charge / discharge, thereby achieving excellent battery characteristics.

[0150] In particular, if the secondary battery is a lithium ion secondary battery, a sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium, and therefore a greater effect can be obtained.

[0151] 3. Modifications The configuration of the secondary battery described above can be modified as appropriate, as described below. However, the series of modifications described below may be combined with each other.

[0152] [Modification 1] A porous film separator 23 is used. However, although not specifically shown here, a laminated separator including a polymer compound layer may also be used.

[0153] Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer provided on one or both surfaces of the porous membrane. This is because the separator improves adhesion to each of the positive electrode 21 and the negative electrode 22, thereby suppressing misalignment (winding misalignment) of the battery element 20. This suppresses swelling of the secondary battery even if a side reaction, such as a decomposition reaction of the electrolyte, occurs. The polymer compound layer includes a polymer compound such as polyvinylidene fluoride. This is because the polymer compound layer provides excellent physical strength and excellent electrochemical stability.

[0154] 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 promotes heat dissipation when the secondary battery generates heat, thereby improving the safety (heat resistance) of the secondary battery. The plurality of insulating particles contain one or more insulating materials, such as inorganic materials and resin materials. Specific examples of inorganic materials include aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of resin materials include acrylic resin and styrene resin.

[0155] 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 film. In this case, multiple insulating particles may be added to the precursor solution as needed.

[0156] Even when this laminated separator is used, the same effect can be obtained because lithium ions are able to move between the positive electrode 21 and the negative electrode 22. In this case, as described above, the safety of the secondary battery is particularly improved, and therefore, even greater effects can be obtained.

[0157] [Modification 2] An electrolytic solution that is a liquid electrolyte is used. However, although not specifically shown here, an electrolyte layer that is a gel electrolyte may also be used.

[0158] In the battery element 20 using the electrolyte layer, the positive electrode 21 and the negative electrode 22 are alternately stacked with the separator 23 and the electrolyte layer interposed therebetween. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and also between the negative electrode 22 and the separator 23.

[0159] Specifically, the electrolyte layer contains a polymer compound together with an electrolytic solution, and the electrolytic solution is held by the polymer compound. This is because leakage of the electrolytic solution is prevented. The composition of the electrolytic solution is as described above. The polymer compound contains polyvinylidene fluoride, etc. When forming the electrolyte layer, a precursor solution containing the electrolytic solution, the polymer compound, and a solvent is prepared, and then the precursor solution is applied to one or both surfaces of each of the positive electrode 21 and the negative electrode 22.

[0160] Even when this electrolyte layer is used, the same effect can be obtained because lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer. In this case, particularly, as described above, leakage of the electrolyte solution is prevented, so that a greater effect can be obtained.

[0161] 4. Uses of Secondary Batteries There are no particular limitations on the uses (application examples) of secondary batteries. Secondary batteries used as power sources may be the main power source or auxiliary power source in electronic devices, electric vehicles, and the like. The main power source is a power source that is used preferentially regardless of the presence or absence of other power sources. The auxiliary power source may be a power source used in place of the main power source or a power source that can be switched from the main power source.

[0162] Specific examples of uses for secondary batteries are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, headphone stereos, portable radios, and portable information terminals; Storage devices such as backup power supplies and memory cards; Power tools such as power drills and power saws; Battery packs installed in electronic devices; Medical electronic devices such as pacemakers and hearing aids; Electric vehicles such as electric cars (including hybrid cars); Power storage systems such as home or industrial battery systems that store power in preparation for emergencies, etc. In these uses, one secondary battery may be used, or multiple secondary batteries may be used.

[0163] The battery pack may use a single cell or a battery pack. The electric vehicle is a vehicle that runs on a secondary battery as a driving power source, and may be a hybrid vehicle that also has a driving source other than the secondary battery. In a home power storage system, power stored in a secondary battery, which is a power storage source, can be used to power home electrical appliances, etc.

[0164] Here, an example of an application of the secondary battery will be specifically described. The configuration of the application described below is merely an example and can be modified as appropriate.

[0165] Fig. 5 shows the block configuration of a battery pack. The battery pack described here is a battery pack (a so-called soft pack) that uses one secondary battery, and is installed in electronic devices such as smartphones.

[0166] 5, the battery pack includes a power supply 71 and a circuit board 72. The circuit board 72 is connected to the power supply 71 and includes a positive terminal 73, a negative terminal 74, and a temperature detection terminal 75.

[0167] The power source 71 includes one secondary battery. The positive electrode lead of this secondary battery is connected to a positive electrode terminal 73, and the negative electrode lead is connected to a negative electrode terminal 74. The power source 71 can be connected to the outside via the positive electrode terminal 73 and the negative electrode terminal 74, and is therefore capable of charging and discharging. The circuit board 72 includes a control unit 76, a switch 77, a thermosensitive resistor (PTC element) 78, and a temperature detection unit 79. However, the PTC element 78 may be omitted.

[0168] The control unit 76 includes a central processing unit (CPU) and memory, and controls the operation of the entire battery pack. The control unit 76 detects and controls the usage state of the power source 71 as necessary.

[0169] When the voltage of the power supply 71 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control unit 76 turns off the switch 77 to prevent the charging current from flowing through the current path of the power supply 71. The overcharge detection voltage is not particularly limited, but specifically, it is 4.20 V±0.05 V, and the overdischarge detection voltage is not particularly limited, but specifically, it is 2.40 V±0.1 V.

[0170] Switch 77 includes a charge control switch, a discharge control switch, a charge diode, a discharge diode, etc., and switches between the connection and disconnection of power supply 71 and an external device in response to instructions from control unit 76. Switch 77 includes a metal oxide semiconductor field effect transistor (MOSFET), etc., and the charge / discharge current is detected based on the ON resistance of switch 77.

[0171] 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 when the control unit 76 controls charging and discharging in the event of abnormal heat generation, and when the control unit 76 performs correction processing when calculating the remaining capacity.

[0172] An embodiment of the present technology will be described.

[0173] Examples 1 to 21 and Comparative Examples 1 to 13 As will be described below, secondary batteries were manufactured, and then the battery characteristics of the secondary batteries were evaluated.

[0174] [Manufacture of Secondary Battery] Here, a test secondary battery was manufactured to perform a simple evaluation of battery characteristics. Fig. 6 shows the cross-sectional structure of the test secondary battery (coin-type lithium ion secondary battery).

[0175] 6, this secondary battery includes a test electrode 61, a counter electrode 62, a separator 63, an exterior cup 64, an exterior 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.

[0176] The test electrode 61 is housed in an exterior cup 64, and the counter electrode 62 is housed in an exterior can 65. The test electrode 61 and the counter electrode 62 are stacked together with a separator 63 interposed therebetween, and the test electrode 61, the counter electrode 62, and the separator 63 are each impregnated with an electrolyte. The exterior cup 64 and the exterior can 65 are crimped together with a gasket 66, so that the test electrode 61, the counter electrode 62, and the separator 63 are sealed by the exterior cup 64 and the exterior can 65.

[0177] (Preparation of Test Electrode (Negative Electrode)) When preparing the test electrode 61, first, 80 parts by mass of the negative electrode active material, 10 parts by mass of a negative electrode binder (polyacrylic acid), and 10 parts by mass of a negative electrode conductive agent (carbon black) were mixed together 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) which is an oxide of silicon) and a plurality of second negative electrode active material particles 122 (silicon elemental element (Si) or silicon-iron-nickel alloy (SiFeNi) which is a silicon alloy) were used. In this case, silicon elemental element and a silicon alloy were used in combination as necessary.

[0178] Next, the negative electrode mixture was added to a solvent (pure water, an aqueous solvent), and the aqueous solvent was kneaded using a planetary mixer. This dispersed the negative electrode mixture in the aqueous solvent, preparing a paste-like negative electrode mixture slurry. Next, using a coating device, the negative electrode mixture slurry was applied to one side of the negative electrode current collector 22A (copper foil with a thickness of 12 μm), and then the negative electrode mixture slurry was dried to form the negative electrode active material layer 22B. In this case, the negative electrode mixture slurry was heated and dried (drying temperature = 120°C), and then vacuum-dried. Finally, the negative electrode active material layer 22B was compression-molded using a roll press. This resulted in the formation of the negative electrode active material layer 22B on one side of the negative electrode current collector 22A, resulting in the production of the test electrode 61.

[0179] (Fabrication of Counter Electrode) As described above, in order to perform a simple evaluation of battery characteristics using a test secondary battery (coin-type lithium ion secondary battery shown in FIG. 6), a lithium metal plate was used as the counter electrode 62.

[0180] (Preparation of Electrolyte Solution) A solvent (ethylene carbonate, which is a cyclic carbonate ester, and ethyl methyl carbonate, which is a chain carbonate ester) was dissolved in an electrolyte salt (lithium hexafluorophosphate (LiPF 6 In this case, the mixing ratio (weight ratio) of the solvents was set to 50:50, and the content of the electrolyte salt was set to 1 mol / L (=1 mol / dm 3 ) Thus, the electrolyte solution was prepared.

[0181] (Assembly of Secondary Battery) First, the test electrode 61 was housed in an exterior cup 64, and the counter electrode 62 was housed in an exterior can 65. Next, the test electrode 61 housed in the exterior cup 64 and the counter electrode 62 housed in the exterior can 65 were stacked together with a separator 63 (a microporous polyethylene film with a thickness of 25 μm) impregnated with an electrolyte solution interposed therebetween. In this case, the negative electrode active material layer 22B and the counter electrode 62 faced each other with the separator 63 interposed therebetween. Finally, with the test electrode 61 and the counter electrode 62 stacked together with the separator 63 interposed therebetween, the exterior cup 64 and the exterior can 65 were crimped together with the gasket 66. As a result, the test electrode 61 and the counter electrode 62 were enclosed by the exterior cup 64 and the exterior can 65, and a secondary battery was assembled.

[0182] (Stabilization of Secondary Battery) The secondary battery was subjected to one cycle of charge and discharge in a room temperature environment (temperature = 23°C). During charging, the battery was charged at a constant current of 0.1 C until the voltage reached 0.02 V, and then charged at a constant voltage of 0.02 V until the current reached 0.025 C. During discharging, the battery was discharged at a constant current of 0.1 C until the voltage reached 1.5 V. 0.1 C is the current value at which the battery capacity (theoretical capacity) is fully discharged in 10 hours, and 0.025 C is the current value at which the battery capacity is fully discharged in 40 hours.

[0183] As a result, the test electrode 61 and the counter electrode 62 were electrochemically stabilized, and the secondary battery was completed.

[0184] (Median diameters MD1, MD2, size relationship, particle size ratio RD, area ratio RS and carbon proportion RE) After the secondary battery was completed, the secondary battery was disassembled to recover the test electrode 61, and the median diameters MD1, MD2 (μm), size relationship, particle size ratio RD and area ratio RS were investigated. The results are shown in Tables 1 to 3.

[0185] Here, "size relationship" refers to the size relationship between the median diameters MD1 and MD2. "Large" in the "size relationship" column means that the median diameter MD1 is larger than the median diameter MD2. On the other hand, "small" in the "size relationship" column means that the median diameter MD1 is smaller than the median diameter MD2.

[0186] When producing the test electrode 61, no treatment was performed to coat the surfaces of the first negative electrode active material particles 121 with carbon. As a result, after recovering the test electrode 61 from the secondary battery, a surface analysis of the first negative electrode active material particles 121 was performed using XPS, and the carbon ratio RE was found to be less than 1%.

[0187] The calculation procedures and determination procedures for the median diameters MD1 and MD2 (μm), the magnitude relationship, the particle size ratio RD, the area ratio RS, and the carbon proportion RE are as described above.

[0188] [Evaluation of Battery Characteristics] When the initial charge / discharge characteristics and cycle characteristics were evaluated as the battery characteristics, the results shown in Tables 1 to 3 were obtained.

[0189] (Initial Charge-Discharge Characteristics) First, the charge capacity (charge capacity at the first cycle) was measured by charging the secondary battery in a room temperature environment (temperature = 23°C). Next, the discharge capacity (discharge capacity at the first cycle) was measured by discharging the secondary battery in the same environment. Finally, the initial efficiency, which is an index for evaluating the initial charge-discharge characteristics, was calculated based on the formula: initial efficiency (%) = (discharge capacity at the first cycle / discharge capacity at the first cycle) × 100. The charge-discharge conditions were the same as those during stabilization of the secondary battery.

[0190] The initial efficiency values ​​shown in Table 1 are normalized values ​​with the initial efficiency value in Comparative Example 2 set to 1. The initial efficiency values ​​shown in Table 2 are normalized values ​​with the initial efficiency value in Comparative Example 7 set to 1. The initial efficiency values ​​shown in Table 3 are normalized values ​​with the initial efficiency value in Comparative Example 11 set to 1.

[0191] (Cycle Characteristics) First, the discharge capacity (discharge capacity at the first cycle) was measured by charging and discharging the secondary battery in a room temperature environment (temperature = 23°C). The charge and discharge conditions were the same as those during stabilization of the secondary battery.

[0192] Subsequently, the discharge capacity (discharge capacity at the 100th cycle) was measured by repeatedly charging and discharging the secondary battery in the same environment until the total number of cycles reached 100. The charge and discharge conditions were the same as those used during stabilization of the secondary battery, except that the charge current and discharge current were both changed to 0.7 C.

[0193] Finally, the capacity retention rate, which is an index for evaluating cycle characteristics, was calculated based on the formula: capacity retention rate (%)=(discharge capacity at 100th cycle / discharge capacity at 1st cycle)×100.

[0194] The values ​​of the capacity retention ratios shown in Table 1 are normalized values ​​with the value of the capacity retention ratio in Comparative Example 2 set to 1. The values ​​of the capacity retention ratios shown in Table 2 are normalized values ​​with the value of the capacity retention ratio in Comparative Example 7 set to 1. The values ​​of the capacity retention ratios shown in Table 3 are normalized values ​​with the value of the capacity retention ratio in Comparative Example 11 set to 1.

[0195]

[0196]

[0197]

[0198] [Discussion] As shown in Tables 1 to 3, the initial efficiency and capacity retention rate each varied greatly depending on the configuration of the test electrode 61.

[0199] Specifically, when the following four types of configuration conditions were satisfied (Examples 1 to 21), a higher initial efficiency and a higher capacity retention rate were obtained compared to when the four types of configuration conditions were not satisfied (Comparative Examples 1 to 13).

[0200] Median diameter MD1=5μm~8μm Median diameter MD2=0.12μm~1.2μm Particle size ratio RD=5~50 Area ratio RS=0.6~0.9

[0201] In particular, when four types of configuration conditions were satisfied (Examples 1 to 21), the following trends were obtained. First, high initial efficiency and high capacity retention were obtained regardless of the material of the second negative electrode active material particles 122. In this case, similar trends were obtained when either silicon alone or a silicon alloy was used, and also when silicon alone and a silicon alloy were used in combination. Second, when the particle size ratio RD was 10 to 30, a high capacity retention was obtained while maintaining a high initial efficiency.

[0202] [Summary] From the results shown in Tables 1 to 3, when the test electrode 61 contained a plurality of first anode active material particles 121 and a plurality of second anode active material particles 122, the first anode active material particles 121 contained an oxide of silicon, and the second anode active material particles 122 contained either or both of elemental silicon and a silicon alloy, and the four configuration conditions described above were satisfied, high initial efficiency and high capacity retention were obtained. Therefore, both the initial charge / discharge characteristics and the cycle characteristics were improved, and excellent battery characteristics were obtained in the secondary battery.

[0203] The present technology has been described above with reference to an embodiment and examples. However, the configuration of the present technology is not limited to the configuration described in the embodiment and examples, and can be modified in various ways.

[0204] Specifically, the battery structure of the secondary battery has been described as being a laminate film type and a coin type. However, the battery structure of the secondary battery is not particularly limited, and may be a cylindrical type, a square type, a button type, or the like.

[0205] The battery element has been described as having a wound structure. However, the structure of the battery element is not particularly limited, and may be a stacked structure or a zigzag structure. In the stacked structure, positive and negative electrodes are alternately stacked with a separator interposed therebetween, while in the zigzag structure, the positive and negative electrodes are folded in a zigzag pattern while facing each other with the separator interposed therebetween.

[0206] Furthermore, although the electrode reactant is lithium in the above description, the electrode reactant is not particularly limited. Specifically, as described above, the electrode reactant may be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be other light metals such as aluminum.

[0207] The effects described in this specification are merely examples, and the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

[0208] The present technology may also be configured as follows: <1> A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein 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 an oxide of silicon, and the second negative electrode active material particles include at least one of elemental silicon and an alloy of silicon, and wherein observation of a cross section of the negative electrode using an electron microscope reveals that 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, a 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, and a 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 0.6 or more and 0.9 or less. <2> The secondary battery according to <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 equal to or greater than 10 and equal to or less than 30. <3> The secondary battery according to <1> or <2>, wherein the oxide of silicon includes a compound represented by formula (1): SiO x ... (1) (x satisfies 0.5<x<1.2). <4> The secondary battery according to any one of <1> to <3>, wherein, in a result of analysis of the surface of the first negative electrode active material particle using X-ray photoelectron spectroscopy, the proportion of the amount of carbon present to the amount of all elements present, including carbon, is less than 1%. <5> The secondary battery according to any one of <1> to <4>, wherein the negative electrode further includes a plurality of third negative electrode active material particles, and the third negative electrode active material particles include a carbon material. <6> The secondary battery according to any one of <1> to <5>, which 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, wherein the first negative electrode active material particles comprise an oxide of silicon; and the second negative electrode active material particles comprise at least one of elemental silicon and an alloy of silicon, and wherein, when observed in 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, a 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, and 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 0.6 or more and 0.9 or less.

Claims

1. A secondary battery comprising a positive electrode, a negative electrode, and an electrolytic solution, wherein the negative electrode contains 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, the second negative electrode active material particles contain at least one of elemental 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 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, 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 0.6 or more and 0.9 or less. A secondary battery.

2. 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 10 or more and 30 or less. The secondary battery according to Claim 1.

3. The oxide of silicon contains a compound represented by the formula (1). The secondary battery according to Claim 1 or Claim 2. SiO x ・・・(1) (x satisfies 0.5 < x < 1.2.)

4. In the analysis result of the surface of the first negative electrode active material particles using X-ray photoelectron spectroscopy, the ratio of the abundance of carbon to the abundance of all elements containing carbon is less than 1%. The secondary battery according to Claim 1 or Claim 2.

5. The negative electrode further contains a plurality of third negative electrode active material particles, the third negative electrode active material particles contain a carbon material. The secondary battery according to Claim 1 or Claim 2.

6. A lithium ion secondary battery. The secondary battery according to Claim 1 or Claim 2.

7. A negative electrode containing a plurality of first negative electrode active material particles and a plurality of second negative electrode active material particles, wherein the first negative electrode active material particles contain an oxide of silicon, the second negative electrode active material particles contain at least one of elemental silicon and an alloy of silicon, in the observation result 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, 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 0.6 or more and 0.9 or less. Negative electrode for secondary battery.