Negative electrode for secondary battery, and secondary battery

Abstract

To provide a secondary battery capable of having excellent battery characteristics.SOLUTION: A secondary battery includes a positive electrode, a negative electrode including a negative electrode active material that stores and releases an electrode reactive material, and an electrolyte solution. The negative electrode active material includes metal silicate. The metal silicate includes a metal element, silicon, and oxygen as the constituent elements. The metal element is at least one kind of alkaline earth metal elements, alkali metal elements, transition metal elements, and amphoteric metal elements (however, the constituent elements of the electrode reactive material are excluded). The negative electrode active material includes a central part, a surface part existing outside the central part, and an intermediate part existing between the central part and the surface part. In a cross section of the negative electrode active material, when the ratio among the cross-sectional area of the central part, the cross-sectional area of the intermediate part, and the cross-sectional area of the surface part is 1:3:5, the present amount of the metal element in the intermediate part is larger than that of the metal element in the central part, and the present amount of the metal element in the surface part is larger than that of the metal element in the intermediate part.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[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] For example, there is an increasing demand for higher capacity and better cycle characteristics, and an active material with a higher capacity than conventional negative electrode active materials is now required.

[0004] To solve these problems, for example, negative electrode active material particles have been disclosed that have a structure in which silicon nanoparticles are dispersed in silicon oxide (see, for example, Patent Document 1). However, such negative electrode active material particles experience a Li (lithium) trapping phenomenon due to oxygen, which reduces the amount of Li that can be released during discharge (known as "Li loss"). Furthermore, significant expansion during charging causes cracks in the negative electrode active material particles. These cracks promote a reaction with the electrolyte, resulting in a deterioration of cycle characteristics.

[0005] Furthermore, a technology has been disclosed in which magnesium is introduced into negative electrode active material particles in order to achieve even higher capacity and improved cycle characteristics. The introduction of magnesium can suppress the occurrence of Li loss and cracking of negative electrode active material particles during charging. Specifically, a silicon composite oxide for use as a negative electrode material in lithium secondary batteries contains Si clusters and magnesium silicate formed around the Si clusters. The magnesium silicate contains Mg x SiO y(0.5≦x≦2 and 2.5≦y≦4) (see, for example, Patent Document 2). The negative electrode active material contains a lithium silicon-containing oxide, and magnesium is present in the surface layer of the lithium silicon-containing oxide (see, for example, Patent Document 3). However, the introduction of magnesium into the negative electrode active material particles may result in a decrease in discharge capacity. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2001-185127 [Patent Document 2] Special Publication No. 2022-530780 [Patent Document 3] International Publication No. 2022 / 059340 Brochure Summary of the Invention [Problem to be solved by 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 there is room for improvement.

[0008] There is a demand for a negative electrode for a secondary battery and a secondary battery that can provide excellent battery characteristics. [Means for solving the problem]

[0009] According to one embodiment of the present disclosure, a secondary battery negative electrode includes a negative electrode active material that occludes and releases an electrode reactant. The negative electrode active material includes a metal silicate, which includes a metal element, silicon, and oxygen as constituent elements. The metal element is at least one of an alkaline earth metal element, an alkali metal element, a transition metal element, and an amphoteric metal element (excluding the constituent elements of the electrode reactant). The negative electrode active material includes a central portion that includes the metal silicate, a surface portion that is located outside the central portion and includes the metal silicate, and an intermediate portion that is located between the central portion and the surface portion and includes the metal silicate. When the ratio of the cross-sectional areas of the central portion, the intermediate portion, and the surface portion in a cross section of the negative electrode active material is 1:3:5, the amount of metal element present in the intermediate portion is greater than the amount of metal element present in the central portion, and the amount of metal element present in the surface portion is greater than the amount of metal element present in the intermediate portion.

[0010] 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.

[0011] Here, the classification of the cross section of the negative electrode active material is performed by observing the cross section of the negative electrode active material using an electron microscope and then processing the image using the electron microscope photograph obtained by the observation. As a result, the cross section of the negative electrode active material is classified into a center portion, an intermediate portion, and a surface portion. The details of the classification procedure for the cross section of the negative electrode active material will be described later.

[0012] The amount of metal elements present in the negative electrode active material is measured by analyzing a cross section of the negative electrode active material using elemental analysis. This allows the amount of metal elements present in the surface portion, the amount of metal elements present in the intermediate portion, and the amount of metal elements present in the central portion to be measured. Details of the measurement procedure for the amount of metal elements present in the negative electrode active material will be described later. [Effects of the Invention]

[0013] According to the negative electrode for a secondary battery or the secondary battery of one embodiment of the present technology, the negative electrode active material contains metal silicate, and when a cross section of the negative electrode active material is divided into a center portion, an intermediate portion, and a surface portion, the amount of metal elements present in the negative electrode active material satisfies the relationship: amount of metal elements present in the surface portion > amount of metal elements present in the intermediate portion > amount of metal elements present in the center portion, and therefore excellent battery characteristics can be obtained.

[0014] 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. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view illustrating a configuration of a negative electrode for a secondary battery according to an embodiment of the present technology. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing the configuration of the negative electrode active material. [Figure 3] FIG. 3 is an enlarged cross-sectional view showing another configuration of the negative electrode active material. [Figure 4] FIG. 4 is a cross-sectional view showing the configuration of an apparatus for producing a negative electrode active material. [Figure 5] FIG. 5 is a cross-sectional view showing the structure of the negative electrode active material produced using the production apparatus shown in FIG. [Figure 6] FIG. 6 is a cross-sectional view illustrating a manufacturing process of the negative electrode active material. [Figure 7] FIG. 7 is a cross-sectional view illustrating the manufacturing process of the negative electrode active material following FIG. [Figure 8] FIG. 8 is a cross-sectional view illustrating a configuration of a secondary battery according to an embodiment of the present technology. [Figure 9] FIG. 9 is an enlarged cross-sectional view showing the configuration of the battery element shown in FIG. [Figure 10] FIG. 10 is a cross-sectional view showing the structure of a test secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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 batteries 1-1. Overall structure 1-2. Detailed composition of negative electrode active material 1-3.Operation 1-4. Manufacturing method 1-5. Action and effects 2. Secondary battery 2-1.Configuration 2-2.Operation 2-3. Manufacturing method 2-4. Action and effects 3. Variations 4. Uses of secondary batteries

[0017] <1. Negative electrode for secondary batteries> First, a negative electrode for a secondary battery (hereinafter simply referred to as "negative electrode") according to one embodiment of the present technology will be described.

[0018] 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.

[0019] The negative electrode absorbs and releases an electrode reactant during an electrode reaction. The type of electrode reactant is not particularly limited, but specifically, it is a light metal such as an alkali metal or alkaline earth metal. Specific examples of alkali metals include lithium, sodium, and potassium, and specific examples of alkaline earth metals include magnesium and calcium.

[0020] 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.

[0021] <1-1. Overall structure> Fig. 1 shows a cross-sectional structure of an example of a negative electrode, a negative electrode 1. As shown in Fig. 1, this negative electrode 1 includes a negative electrode current collector 1A and a negative electrode active material layer 1B. However, the negative electrode current collector 1A may be omitted.

[0022] [Negative electrode current collector] The negative electrode current collector 1A is a conductive member that supports the negative electrode active material layer 1B. The negative electrode current collector 1A contains one or more conductive materials such as metal materials, and a specific example of the conductive material is copper. Here, the negative electrode current collector 1A has a pair of surfaces on which the negative electrode active material layer 1B is provided.

[0023] The surface of the negative electrode current collector 1A on which the negative electrode active material layer 1B is provided is preferably roughened. This is because the adhesion of the negative electrode active material layer 1B to the negative electrode current collector 1A is improved by utilizing the so-called anchor effect. The roughening method is not particularly limited, but specifically, it is a method of forming fine particles on the surface of a metal foil using an electrolytic treatment. In this electrolytic treatment, fine particles are formed on the surface of the metal foil using an electrolytic method in an electrolytic bath, so that unevenness is provided on the surface of the metal foil.

[0024] [Negative electrode active material layer] The negative electrode active material layer 1B is provided on the surface of the negative electrode current collector 1A and contains a negative electrode active material. However, the negative electrode active material layer 1B may further contain one or both of a negative electrode binder and a negative electrode conductive agent. The method for forming the negative electrode active material layer 1B is not particularly limited, but specifically may be any one or more of a coating method, a vapor phase method, a liquid phase method, a thermal spraying method, and a firing method (sintering method).

[0025] Here, the negative electrode active material layer 1B is provided on both sides of the negative electrode current collector 1A, but the negative electrode active material layer 1B may be provided on only one side of the negative electrode current collector 1A.

[0026] (Negative electrode active material) The negative electrode active material is a plurality of particulate substances that absorb and release lithium, an electrode reactant. This negative electrode active material contains one or more metal silicates. Metal silicates have excellent lithium absorption capacity, which allows for high energy density. Furthermore, metal silicates have excellent physical durability during electrode reactions, which prevents damage to the negative electrode active material and reduces the surface reactivity of the negative electrode active material.

[0027] This metal silicate contains a metal element, silicon, and oxygen as constituent elements, and the metal element is at least one of an alkaline earth metal element, an alkali metal element, a transition metal element, and an amphoteric metal element (excluding the constituent elements of the electrode reactant).

[0028] That is, the metal element may contain only alkaline earth metal elements, only alkali metal elements, only transition metal elements, only amphoteric metal elements, or a combination of these metals. It may contain both alkaline earth metal elements and alkali metal elements. In this case, the number of types of alkaline earth metal elements may be one or more. Similarly, the number of types of alkali metal elements may be one or more. Similarly, the number of types of transition metal elements may be one or more. Similarly, the number of types of amphoteric metal elements may be one or more.

[0029] Specific examples of alkaline earth metals include magnesium and calcium, and specific examples of alkali metals include lithium, sodium and potassium.

[0030] However, the constituent elements of the electrode reactant are excluded from the metal elements that are constituent elements of the metal silicate described here, and therefore lithium, which is a constituent element of the electrode reactant, is excluded from the metal elements.

[0031] The reason why the negative electrode active material contains a metal silicate is that, as will be described later, by optimizing the distribution of the metal element in the negative electrode active material, the reactivity near the surface of the negative electrode active material is reduced, and the lithium storage and release properties near the center of the negative electrode active material are improved. Details of the specific structure of the negative electrode active material regarding the distribution of this metal element will be described later.

[0032] (The first metal silicate, the second metal silicate, the third metal silicate, the fourth metal silicate, and the fifth metal silicate) The composition of the metal silicon oxide is not particularly limited as long as it contains a metal element, silicon, and oxygen as constituent elements.

[0033] Specifically, the metal silicate contains any one or two or more of the first metal silicate, the second metal silicate, the third metal silicate, the fourth metal silicate, and the fifth metal silicate.

[0034] That is, the metal silicate may contain only any one of the first metal silicate, the second metal silicate, and the third metal silicate, or may contain two or more of the first metal silicate, the second metal silicate, and the third metal silicate.

[0035] The first metal silicate is a compound represented by the formula (1). The type of the first metal silicate may be only one type or two or more types.

[0036] M1 a Si b O c ···(1) (M1 is at least one of alkaline earth metal elements. a satisfies 0 < a < 4. b satisfies 0 < b < 5. c satisfies 0 < c < 7.)

[0037] This first metal silicate is a compound containing an alkaline earth metal element, silicon, and oxygen as constituent elements, as shown in formula (1). Specific examples of the first metal silicon oxide are MgSiO3, Mg2SiO4, Mg2Si2O6, BeSiO3, Be2SiO4, CaSiO3, Ca2SiO4, Ca2SiO4, Ca3SiO5, Ca2SiO4, CaSiO3, SrSiO3, Sr2SiO4, BaSiO3, Ba2SiO4, etc.

[0038] The second metal silicate is a compound represented by formula (2). The type of the second metal silicate may be only one type or two or more types.

[0039] M2 d Si e O f ···(2) (M2 is at least one of the alkali metal elements. d satisfies 1 < d < 7. e satisfies 2 < e < 5. f satisfies 2 < f < 10.)

[0040] This second metal silicate is a compound containing an alkali metal element, silicon, and oxygen as constituent elements, as shown in formula (2). Specific examples of the second metal silicate are Li2SiO3, Li2Si2O5, Li6Si2O7, Li4SiO4, Na2SiO3, Na4SiO4, Na2Si2O5, Na2Si4O9, K2SiO3, Rb2SiO3 etc.

[0041] The third metal silicate is a compound represented by formula (3). The type of the third metal silicate may be only one type or two or more types.

[0042] M3 g Si[[ID=3​​​​​​

[0043] This third metal silicate is a compound containing a transition metal element, silicon, and oxygen as constituent elements, as shown in formula (3). Specific examples of the third metal silicate include Fe2SiO4, FeSiO4, Cu2SiO4, Ni2SiO4, Co2SiO3, Mn2SiO4, ZrSiO4, etc.

[0044] The fourth metal silicate is a compound represented by formula (4). The type of the fourth metal silicate may be only one kind or two or more kinds.

[0045] M4 j M5 k Si l O m ···(4) (M4 is at least one of the alkali metal elements. M5 is at least one of the alkali metals, alkaline earth metal elements, transition metals, and amphoteric metals. j satisfies 0 < j < 3. k satisfies 0 < k < 3. l satisfies 0 < l < 4. m satisfies 2 < m < 7.)

[0046] This fourth metal silicate is a compound containing an alkali metal element, at least one of an alkaline earth metal element, a transition metal element, and an amphoteric metal element, silicon, and oxygen as constituent elements, as shown in formula (4). Specific examples of the fourth metal silicate include Li2MgSiO4, Na2MgSiO4, K2MgSiO4, Li2CaSiO4, Na2CaSiO4, Na2CaSiO4, LiAlSi2O6, NaAlSi2O6, etc.

[0047] The fifth metal silicate is a compound represented by formula (5). The type of the fifth metal silicate may be only one kind or two or more kinds. M6 n M7 o Si p O q ···(5) (M6 is at least one of alkaline earth metal elements. M7 is at least one of transition metals and amphoteric metals. n satisfies 0 < n < 4. o satisfies 0 < o < 3. p satisfies 0 < p < 4. q satisfies 2 < q < 7.)

[0048] This fifth metal silicate is a compound containing an alkaline earth metal element, at least one of an alkaline earth metal element, a transition metal element, and an amphoteric metal element, silicon, and oxygen as constituent elements, as shown in formula (5). Specific examples of the fifth metal silicate are CaMgSiO4, Ca2MgSi2O6, Ca2MnSi2O6, Ca2ZnSi2O6, Ca2FeSi2O6, MnMgSi2O6, and the like.

[0049] Among them, it is preferable that the metal silicate contains the first metal silicate. This is because the reactivity near the surface of the negative electrode active material is sufficiently reduced, and the lithium insertion / extraction property near the center of the negative electrode active material is sufficiently improved. <000029​​​​​​​​​​​The content of the metal element in the negative electrode active material is not particularly limited. In particular, the abundance ratio, which is the ratio of the metal element content to the sum of the metal element content (mol), silicon content (mol), and oxygen content (mol), is preferably 1 mol% to 20 mol%. This is because an optimal abundance ratio sufficiently reduces the reactivity near the surface of the negative electrode active material and sufficiently improves the lithium absorption / desorption properties near the center of the negative electrode active material. This metal content ratio (%) is calculated based on the formula: Metal content ratio = [metal element content / (metal element content + silicon content + oxygen content)] × 100.

[0052] The procedure for calculating this metal content ratio is as follows: In the following, a case where the negative electrode active material layer 1B contains a negative electrode binder and a negative electrode conductive agent in addition to the negative electrode active material will be described.

[0053] First, the negative electrode 1 is placed in a solvent. This solvent is either a non-aqueous solvent or an aqueous solvent capable of dissolving the negative electrode binder. A specific example of a non-aqueous solvent is NMP (N-methylpyrrolidone). A specific example of an aqueous solvent is water. As a result, the negative electrode binder is dissolved in the solvent, and a solution containing the dissolved negative electrode binder is obtained.

[0054] The solution is then filtered. This yields a filtrate containing the dissolved negative electrode binder, and a filtrate separated from the filtrate. This filtrate contains a mixture of the negative electrode current collector 1A, the negative electrode active material, and the negative electrode conductive agent that were not dissolved in the solvent. The negative electrode current collector 1A is then removed from the mixture, yielding a mixture of the negative electrode active material and the negative electrode conductive agent.

[0055] Subsequently, the mixture is separated using a separator such as a centrifugal separator, and the negative electrode active material is recovered from the mixture.

[0056] Next, the negative electrode active material is analyzed using one or more of composition analysis methods such as inductively coupled plasma (ICP) emission spectroscopy and ratio-dispersive infrared absorption spectroscopy, thereby measuring the metal element content (mol), silicon content (mol), and oxygen content (mol).

[0057] Finally, the metal content is calculated using the above-mentioned formula based on the metal element content, silicon content, and oxygen content.

[0058] (oxygen silicon ratio) The mixing ratio of silicon to oxygen in the negative electrode active material is not particularly limited. In particular, the oxygen-silicon ratio, which is the ratio of the oxygen content (mol) to the silicon content (mol), is preferably 0.80 to 1.30. This is because an optimized oxygen-silicon ratio sufficiently reduces the reactivity near the surface of the negative electrode active material and sufficiently improves the lithium absorption / desorption properties near the center of the negative electrode active material. This oxygen-silicon ratio is calculated based on the formula: oxygen-silicon ratio = oxygen content / silicon content.

[0059] When calculating this oxygen-silicon ratio, the silicon content and the oxygen content are each measured by, for example, non-dispersive infrared absorption spectroscopy, and then the oxygen-silicon ratio is calculated using the above-mentioned formula.

[0060] (crystallite size) The crystalline state of the negative electrode active material is not particularly limited. In particular, the crystallite size of the Si(220) crystal plane is preferably 30 nm or less. This is because the optimized crystallite size sufficiently reduces the reactivity near the surface of the negative electrode active material and sufficiently improves the lithium absorption / desorption property near the center of the negative electrode active material. Note that the crystallite size of the Si(220) crystal plane may be 0 nm. In other words, the silicon may be amorphous.

[0061] This crystallite size can be measured by analyzing the negative electrode active material using any one or two or more of the crystal structure analysis methods such as X-ray diffraction method (XRD).

[0062] (Median diameter) Since the negative electrode active material is in the form of a plurality of particles, the negative electrode active material layer 1B contains a plurality of particulate negative electrode active materials. In this case, the average particle diameter of the plurality of particulate negative electrode active materials is not particularly limited. Among them, the median diameter of the plurality of particulate negative electrode active materials is preferably 0.1 μm to 50 μm, particularly preferably 3 μm to 15 μm. This is because when the median diameter is optimized, the reactivity near the surface of the negative electrode active material is sufficiently reduced, and the lithium intercalation and deintercalation properties near the center of the negative electrode active material are sufficiently improved.

[0063] This median diameter can be measured, for example, by analyzing a plurality of negative electrode active materials using a laser diffraction particle size distribution measuring device.

[0064] (Elemental silicon and silicon oxide) In addition, the negative electrode active material preferably further contains one or both of elemental silicon and silicon oxide. This is because the reactivity near the surface of the negative electrode active material is further reduced, and the lithium intercalation and deintercalation properties near the center of the negative electrode active material are further improved.

[0065] Since elemental silicon simply means a general elemental silicon, the elemental silicon may contain trace amounts of impurities. That is, the purity of elemental silicon is not necessarily limited to 100%.

[0066] Silicon oxide is a compound containing silicon and oxygen as constituent elements, and more specifically, it is a compound represented by the formula (6). SiO x ···(6) (x satisfies

[0067] The value of x is not particularly limited as long as it is within the above-mentioned range. In particular, x preferably satisfies 0.5≦x≦1.5. This is because the reactivity near the surface of the negative electrode active material is further reduced and the lithium absorption / desorption property near the center of the negative electrode active material is further improved.

[0068] (Negative electrode binder) The negative electrode binder contains one or more of materials such as synthetic rubber and polymer compounds. Specific examples of synthetic rubber include styrene-butadiene rubber, fluorine-containing rubber, and ethylene-propylene-diene. Specific examples of polymer compounds include polyvinylidene fluoride, polyimide, polyamide, carboxymethyl cellulose or its metal salt, polyacrylic acid, or its metal salt.

[0069] (negative electrode conductive agent) The negative electrode conductive agent contains one or more conductive materials such as carbon materials, metal materials, and conductive polymer compounds, and specific examples of the carbon materials include graphite, carbon black, acetylene black, carbon nanotubes, carbon nanofibers, and ketjen black.

[0070] (Other materials) The negative electrode active material layer 1B may further contain one or more of the other materials.

[0071] The type of the other material is not particularly limited, but specifically, it is another negative electrode active material. The other negative electrode active material is a carbon material, and specific examples of the carbon material include graphitizable carbon, non-graphitizable carbon, and graphite. This graphite may be natural graphite, artificial graphite, or both.

[0072] When negative electrode active material layer 1B further contains a carbon material as another negative electrode active material, damage to negative electrode active material layer 1B is suppressed while the battery capacity of a secondary battery using negative electrode 1 is ensured.

[0073] Specifically, a negative electrode active material containing silicon as a constituent element (metal silicon oxide) has the advantage of a high theoretical capacity, but has the drawback of being prone to severe expansion and contraction during charging and discharging of a secondary battery using the negative electrode 1. On the other hand, other negative electrode active materials (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 charging and discharging of a secondary battery using the negative electrode 1. Therefore, by using a metal silicon material and a carbon material in combination, a high theoretical capacity can be obtained while suppressing expansion and contraction of the negative electrode active material layer 1B during charging and discharging. As a result, as described above, damage to the negative electrode active material layer 1B is suppressed while maintaining the battery capacity.

[0074] The trends described here for metal silicates also apply to elemental silicon and silicon oxides, because elemental silicon and silicon oxides each contain silicon as a constituent element, just like metal silicates.

[0075] <1-2. Detailed composition of negative electrode active material> As described above, this negative electrode active material contains a metal silicate. Within the negative electrode active material, the metal element is dispersed over a wide range from the surface to the center of the negative electrode active material. Therefore, the metal element is not present in only a limited area within the negative electrode active material, but is present throughout the entire area within the negative electrode active material.

[0076] In this case, the distribution of the metal silicate inside the negative electrode active material, that is, the state of existence of the metal element inside the negative electrode active material, is optimized to be in a predetermined state.

[0077] [Distribution of metal elements] Specifically, the amount of metal elements present in the negative electrode active material decreases in the direction from the surface toward the center of the negative electrode active material. That is, within the negative electrode active material, metal silicates are widely dispersed throughout the entire region, but the amount of dispersed metal silicates decreases in the direction from the surface toward the center of the negative electrode active material. As a result, the amount of metal elements present, which are constituent elements of the metal silicates, decreases in the direction from the surface toward the center of the negative electrode active material.

[0078] The amount of the metal element may decrease continuously in the direction from the surface of the negative electrode active material 2 toward the center of the negative electrode active material 2, or may decrease intermittently in the direction from the surface of the negative electrode active material 2 toward the center of the negative electrode active material 2. Of course, a region in which the amount of the metal element decreases continuously and a region in which the amount of the metal element decreases intermittently may coexist in the direction from the surface of the negative electrode active material 2 toward the center of the negative electrode active material 2. Note that the gradient of the decrease in the amount of the metal element in the direction from the surface of the negative electrode active material 2 toward the center of the negative electrode active material 2 may be constant, or may not be constant but may change one or more times along the way.

[0079] (Specified relationship regarding the abundance of metallic elements) More specifically, when the abundance of a metal element decreases in the direction from the surface of the negative electrode active material toward the center of the negative electrode active material, a predetermined relationship is established regarding the abundance of the metal element.

[0080] Fig. 2 shows an enlarged cross-sectional configuration of the negative electrode active material 2. In Fig. 2, for simplicity of illustration, the cross-sectional shape of the negative electrode active material 2 is shown as a circle. Note that the cross-sectional shape of the negative electrode active material 2 is not particularly limited, and may be any one or more of any shapes, not limited to a circle.

[0081] 2, the cross section of the negative electrode active material 2 is divided into three mutually different and adjacent regions: a central region 2A, an intermediate region 2B, and a surface region 2C.

[0082] Here, "classifying the cross section of the negative electrode active material 2" does not mean separating the negative electrode active material 2 from each other so as to obtain a central portion 2A, an intermediate portion 2B, and a surface portion 2C that are separated from each other, but means dividing the cross section of the negative electrode active material 2 so as to identify three different regions, namely the central portion 2A, the intermediate portion 2B, and the surface portion 2C.

[0083] The central portion 2A is the innermost region of the negative electrode active material 2 and contains metal silicon oxide. The surface portion 2C is the outermost region of the negative electrode active material 2 and contains metal silicon oxide. The intermediate portion 2B is a region located between the central portion 2A and the surface portion 2C and adjacent to both the central portion 2A and the surface portion 2C, and contains metal silicon oxide. As a result, the intermediate portion 2B is located outside the central portion 2A, and the surface portion 2C is located outside the intermediate portion 2B.

[0084] The reason why the central portion 2A, the intermediate portion 2B, and the surface portion 2C each contain metal silicon oxide is that, as described above, metal elements are present within the negative electrode active material 2 over a wide range from near the surface of the negative electrode active material 2 to near the center of the negative electrode active material 2.

[0085] The central portion 2A, the intermediate portion 2B and the surface portion 2C are specified according to their cross-sectional areas.

[0086] 2, the cross-sectional areas SA, SB, and SC of the negative electrode active material 2 are set so that the cross-sectional area SA of the central portion 2A, the cross-sectional area SB of the intermediate portion 2B, and the cross-sectional area SC of the surface portion 2C are 1:3:5, thereby setting the central portion 2A, the intermediate portion 2B, and the surface portion 2C. Here, it is assumed that the outer surfaces of the central portion 2A, the intermediate portion 2B, and the surface portion 2C are each the surface of a sphere, and the ratio of the radius of the central portion 2A, the radius of the intermediate portion 2B, and the radius of the surface portion 2C is 1:2:3.

[0087] In this case, as described above, the central portion 2A, the intermediate portion 2B, and the surface portion 2C each contain metal silicate, and the amount of metal elements present inside the negative electrode active material 2 decreases in the direction from near the surface of the negative electrode active material 2 toward near the center of the negative electrode active material 2.

[0088] Therefore, the abundance CC of the metal element in the surface portion 2C is greater than the abundance CB of the metal element in the intermediate portion 2B, and the abundance CB of the metal element in the intermediate portion 2B is greater than the abundance CA of the metal element in the central portion 2A. That is, the abundances CA, CB, and CC of the metal elements in the negative electrode active material 2 satisfy the appropriate relationship CC>CB>CA.

[0089] The reason why the abundances CA, CB, and CC have an appropriate relationship (CC>CB>CA) is that, for the reasons described above, the distribution of metal elements inside the negative electrode active material 2 is optimized, which reduces reactivity near the surface of the negative electrode active material 2 and improves lithium absorption / desorption near the center of the negative electrode active material 2. As a result, in a secondary battery using the negative electrode 1, the decomposition reaction of the electrolyte is suppressed and the battery capacity is increased.

[0090] Specifically, when a metal silicate is used as the negative electrode active material 2, the metal silicate contains a metal element as a constituent element, and therefore the physical durability is improved near the surface of the negative electrode active material 2. As a result, in a secondary battery using the negative electrode 1, damage to the negative electrode active material 2 due to expansion and contraction during charge and discharge is suppressed, and the formation of new surfaces of the highly reactive negative electrode active material 2 is suppressed. Therefore, the reactivity of the negative electrode active material 2 is reduced, and the decomposition reaction of the electrolyte near the surface of the negative electrode active material 2 is suppressed. In this case, the formation of a coating due to the decomposition reaction of the electrolyte during charge and discharge is also suppressed, and an increase in the electrical resistance of the negative electrode active material 2 is also suppressed.

[0091] Furthermore, when a metal silicon oxide is used as the negative electrode active material 2, a high-resistance coating derived from the metal silicate is formed during charge and discharge in a secondary battery using the negative electrode 1, and this coating is used to electrochemically protect the surface of the negative electrode active material 2. This reduces the reactivity of the negative electrode active material 2, further suppressing the decomposition reaction of the electrolyte on the surface of the negative electrode active material 2.

[0092] However, if the amount of metal element present in the metal silicate becomes excessive, the lithium absorption / desorption property decreases near the center of the negative electrode active material 2. As a result, in a secondary battery using the negative electrode 1, the discharge capacity per weight of the negative electrode active material 2 decreases, and the battery capacity decreases.

[0093] For these reasons, depending on the amount of metal element present in the metal silicate, a trade-off occurs between the suppression of the decomposition reaction of the electrolyte and the improvement of the lithium absorption / desorption properties, in that an improvement in one property results in a deterioration of the other property.

[0094] Specifically, when the amount of metal element present in the metal silicate is reduced, the amount of metal element present near the surface of the negative electrode active material 2 is reduced, and the amount of metal element present near the center of the negative electrode active material 2 is also reduced.

[0095] In this case, the amount of metal elements present near the center of the negative electrode active material 2 decreases, improving lithium absorption / desorption. On the other hand, the amount of metal elements present near the surface of the negative electrode active material 2 decreases, reducing physical durability. As a result, in a secondary battery using the negative electrode 1, the battery capacity increases, but the decomposition reaction of the electrolyte is accelerated, creating a trade-off.

[0096] Furthermore, when the amount of metal element present in the metal silicate is increased, the amount of metal element present near the surface of the negative electrode active material 2 increases, and the amount of metal element present near the center of the negative electrode active material 2 also increases.

[0097] In this case, the amount of metal elements increases near the surface of the negative electrode active material 2, improving physical durability. On the other hand, the amount of metal elements increases near the center of the negative electrode active material 2, reducing lithium absorption / desorption. As a result, in a secondary battery using the negative electrode 1, the decomposition reaction of the electrolyte is suppressed, but the battery capacity decreases, resulting in a trade-off.

[0098] In contrast, since the abundance of metal elements decreases in the direction from the surface of the negative electrode active material 2 toward the center of the negative electrode active material 2, when the appropriate relationship (CC>CB>CA) is established between the abundances CA, CB, and CC, the abundance of metal elements increases near the surface of the negative electrode active material 2 and decreases near the center of the negative electrode active material 2.

[0099] In this case, the amount of metal elements increases near the surface of the negative electrode active material 2, improving physical durability. Moreover, the amount of metal elements decreases near the center of the negative electrode active material 2, improving lithium absorption / desorption. As a result, in a secondary battery using the negative electrode 1, the above-mentioned trade-off relationship is overcome, suppressing the decomposition reaction of the electrolyte and increasing the battery capacity.

[0100] In this case, in particular, since the metal element is present throughout the entire area inside the negative electrode active material 2, damage to the negative electrode active material 2 is more effectively suppressed, unlike when the metal element is present only in a partial area inside the negative electrode active material 2.

[0101] Specifically, when a metal element is present only in a partial region inside the negative electrode active material 2, an interface is formed between the region where the metal element is present and the region where the metal element is not present. As a result, in a secondary battery using the negative electrode 1, when the negative electrode active material 2 expands and contracts during charge and discharge, damage to the negative electrode active material 2 originating from the interface is accelerated.

[0102] In contrast, when the metal element is present throughout the entire interior of the negative electrode active material 2, there is no interface between the region where the metal element is present and the region where the metal element is not present. As a result, in a secondary battery using the negative electrode 1, even if the negative electrode active material 2 expands and contracts during charge and discharge, cracks in the negative electrode active material 2 originating from the interface are suppressed.

[0103] (Classification procedure for cross sections of negative electrode active materials) The procedure for classifying the cross section of the negative electrode active material 2 into the central portion 2A, the intermediate portion 2B, and the surface portion 2C is as described below. The following describes the case where the negative electrode active material layer 1B contains a negative electrode binder and a negative electrode conductive agent in addition to the negative electrode active material.

[0104] First, the negative electrode active material is recovered from the negative electrode 1 by the same procedure as that used for calculating the metal content ratio described above.

[0105] Next, a cutting tool such as a microtome or an ion mill is used to cut the negative electrode active material 2, thereby exposing a cross section of the negative electrode active material 2. Next, the cross section of the negative electrode active material 2 is observed using one or more types of electron microscopes such as a scanning electron microscope, thereby obtaining an electron microscope photograph that is an observation result of the cross section of the negative electrode active material 2.

[0106] Next, based on the electron microscope photograph, the cross-sectional areas of a plurality of regions of the negative electrode active material 2 are calculated using image processing.

[0107] In this case, the cross-sectional area of ​​the negative electrode active material 2 defined by the outer edge of the cross section of the negative electrode active material 2 is calculated based on the outer edge.

[0108] Next, the entire outer edge of the cross section of the negative electrode active material 2 is moved inward by a predetermined distance (movement distance), and the cross section of the negative electrode active material 2 is image-processed so that the size of the cross section after the movement of the outer edge is slightly smaller than the size of the cross section before the movement of the outer edge.

[0109] In this way, the cross-sectional area of ​​the negative electrode active material 2 defined by the outer edge after the movement is calculated. In addition, the cross-sectional area of ​​the peripheral region of the negative electrode active material 2 defined by the outer edge after the movement is calculated by subtracting the cross-sectional area of ​​the negative electrode active material 2 defined by the outer edge after the movement from the cross-sectional area of ​​the negative electrode active material 2 defined by the outer edge before the movement. This peripheral region of the negative electrode active material 2 defined by the outer edge after the movement is a so-called ring-shaped region.

[0110] The moving distance is not particularly limited and can be set arbitrarily. For example, the moving distance is 0.8 μm. In this case, the shorter the moving distance, the easier it is to classify the cross section of the negative electrode active material 2 into the central portion 2A, the intermediate portion 2B, and the surface portion 2C with high accuracy.

[0111] Next, the entire outer edge of the cross section of the negative electrode active material 2 is further moved inward, and then the process of calculating the cross-sectional area of ​​the negative electrode active material 2 defined by the moved outer edge and the cross-sectional area of ​​the peripheral region of the negative electrode active material 2 defined by the moved outer edge is repeated multiple times. This allows the cross-sectional areas of multiple negative electrode active materials 2 to be obtained, as well as the cross-sectional areas of multiple peripheral regions.

[0112] The number of times that the calculations of the cross-sectional area of ​​the negative electrode active material 2 and the cross-sectional area of ​​the peripheral region are repeated is not particularly limited and can be set arbitrarily. In this case, the more times the calculations are repeated, the easier it is to classify the cross section of the negative electrode active material 2 into the central portion 2A, the intermediate portion 2B, and the surface portion 2C with high accuracy.

[0113] Finally, by repeatedly calculating the cross-sectional area of ​​the negative electrode active material 2 and the cross-sectional area of ​​the surrounding region, the cross-sectional areas of multiple regions of the negative electrode active material 2 are calculated using image processing, and then the cross-sectional area of ​​the inner region located on the inside of the negative electrode active material 2, the cross-sectional area of ​​the outer region located on the outside of the negative electrode active material 2, and the cross-sectional area of ​​the intermediate region located between the inner region and the outer region are calculated.

[0114] The cross-sectional area of ​​the inner region is the sum of the cross-sectional area of ​​the negative electrode active material 2 defined when the outer edge is moved to the end and the cross-sectional area of ​​one or more peripheral regions located outside the negative electrode active material 2. The cross-sectional area of ​​the outer region is the sum of the cross-sectional areas of one or more peripheral regions located outside the negative electrode active material 2. The cross-sectional area of ​​the intermediate region is the sum of the cross-sectional areas of one or more peripheral regions located between the inner region and the outer region.

[0115] In this case, the cross-sectional area of ​​the inner region, the cross-sectional area of ​​the intermediate region, and the number of cross-sectional areas of the outer region are adjusted so that the sum of the cross-sectional areas of the inner region, the intermediate region, and the outer region is 1:3:5.

[0116] As a result, the inner region becomes a central portion 2A having a cross-sectional area SA. The intermediate region becomes a middle portion 2B having a cross-sectional area SB. The outer region becomes a surface portion 2C having a cross-sectional area SC. Therefore, the central portion 2A, middle portion 2B, and surface portion 2C are each identified according to the cross-sectional areas SA, SB, and SC, and the cross section of the negative electrode active material 2 is classified into the central portion 2A, middle portion 2B, and surface portion 2C.

[0117] (Procedure for measuring the abundance of metal elements) When measuring the abundances CA, CB, and CC of metal elements, the negative electrode active material 2 is recovered from the negative electrode 1 using the same procedure as that used to calculate the metal content ratio described above, and the cross section of the negative electrode active material 2 is exposed. Then, the cross section of the negative electrode active material 2 is analyzed using one or more elemental analysis methods such as energy dispersive X-ray analysis (EDX).

[0118] In this case, the amount of abundance CA is measured by analyzing the central portion 2A, the amount of abundance CB is measured by analyzing the intermediate portion 2B, and the amount of abundance CC is measured by analyzing the surface portion 2C.

[0119] As a result, the amounts CA, CB, and CC of abundance are obtained, and the relationship between the amounts CA, CB, and CC of abundance can be identified.

[0120] (Reason for classifying cross sections of negative electrode active materials) The cross section of the negative electrode active material 2 is classified into three types of regions (a central portion 2A, an intermediate portion 2B, and a surface portion 2C) in order to enable subsequent confirmation with high accuracy that the amount of metal elements present inside the negative electrode active material 2 decreases in the direction from the surface of the negative electrode active material 2 toward the center of the negative electrode active material 2.

[0121] More specifically, consider a case where the cross section of the negative electrode active material 2 is separated into two regions (an inner region and an outer region). The outer region is located outside the inner region.

[0122] Even in this case, if the amount of metal element present in the inner portion is measured and the amount of metal element present in the outer portion is measured, and the amount of metal element present in the inner portion is found to be less than the amount of metal element present in the outer portion, it can be considered that the amount of metal element present in the direction from the surface of the negative electrode active material 2 toward the center of the negative electrode active material 2 is decreasing.

[0123] However, there are concerns when comparing the abundances of metal elements in only two regions.

[0124] Specifically, even if the amount of metal element present in the inner portion and the amount of metal element present in the outer portion are essentially intended to be the same, if the metal element is unevenly dispersed within the negative electrode active material 2 due to some factor, the amount of metal element present in the outer portion may unintentionally be greater than the amount of metal element present in the inner portion. In this case, the amount of metal element present in the outer portion may accidentally be greater than the amount of metal element present in the inner portion, even if there is no active intention to make the amount of metal element present in the outer portion greater than the amount of metal element present in the inner portion.

[0125] In contrast to this, when the cross section of the negative electrode active material 2 is divided into three types of regions (central portion 2A, intermediate portion 2B, and surface portion 2C), the abundance of metal elements in the three types of regions is compared.

[0126] In this case, unlike when the cross section of the negative electrode active material 2 is divided into two types of regions (an inner portion and an outer portion), the possibility that the abundance CA becomes larger than the abundance CB unintentionally and that the abundance CB becomes larger than the abundance CA decreases. This is because, unless there is a positive intention to make the abundance CC larger than the abundance CB and to make the abundance CB larger than the abundance CA, the above-described appropriate relationship (CC>CB>CA) regarding the abundances CA, CB, and CC cannot substantially be established.

[0127] Therefore, by classifying the cross section of the negative electrode active material 2 into three types of regions (central region 2A, intermediate region 2B, and surface region 2C), it becomes possible to confirm afterwards with high accuracy that the content of metal elements decreases in the direction from the surface of the negative electrode active material 2 toward the center of the negative electrode active material 2.

[0128] [Coating] FIG. 3 is an enlarged view of another cross-sectional configuration of the negative electrode active material 2, and corresponds to FIG.

[0129] As shown in FIG. 3, the negative electrode active material layer 1B further includes a coating 3 provided on the surface of the negative electrode active material 2, and therefore the coating 3 may cover the surface of the negative electrode active material 2.

[0130] The coating 3 may cover the entire surface of the negative electrode active material 2, or may cover only a portion of the surface of the negative electrode active material 2. When the coating 3 covers only a portion of the surface of the negative electrode active material 2, a plurality of coatings 3 may be provided on the surface of the negative electrode active material 2, the coatings 3 being spaced apart from one another.

[0131] Specifically, the coating 3 contains a conductive material, more specifically, a carbon material, because this improves the conductivity of the negative electrode active material 2. The method for forming the coating 3 will be described in detail later.

[0132] <1-3. Operation> In this negative electrode 1, during the electrode reaction, lithium is absorbed in an ionic state in the negative electrode active material contained in the negative electrode active material layer 1B, and lithium is released in an ionic state from the negative electrode active material.

[0133] <1-4. Manufacturing method> The negative electrode 1 is manufactured using the example procedure described below.

[0134] Here, the procedure for producing the negative electrode active material 2 shown in FIGS. 2 and 3 will be described first, and then the procedure for producing the negative electrode 1 using the negative electrode active material 2 will be described.

[0135] The negative electrode active material 2 is manufactured using a predetermined manufacturing apparatus. Therefore, when describing the manufacturing procedure of the negative electrode active material 2, the configuration of the manufacturing apparatus will be described first, and then the manufacturing procedure of the negative electrode active material 2 using the manufacturing apparatus will be described.

[0136] [Configuration of negative electrode active material manufacturing equipment] 4 shows a cross-sectional configuration of a manufacturing apparatus 100, which is an example of a manufacturing apparatus for the negative electrode active material 2. FIG. 5 shows a cross-sectional configuration of the negative electrode active material 2 manufactured using the manufacturing apparatus 100 shown in FIG.

[0137] The manufacturing apparatus 100 shown in Fig. 4 is used to manufacture the anode active material 2 shown in Fig. 5. In this case, raw material particles 2X are used as a starting material, and a deposited film 2Y is formed on the surface of the raw material particles 2X, thereby forming the anode active material 2 including the raw material particles 2X and the deposited film 2Y.

[0138] In particular, since a plurality of raw material particles 2X are used in the manufacturing apparatus 100, a plurality of negative electrode active materials 2 are formed. The following describes the case where a plurality of negative electrode active materials 2 are formed using the manufacturing apparatus 100.

[0139] Specifically, as shown in FIG. 4, manufacturing apparatus 100 includes a rotation section 110, a storage section 120, a first deposition section 130, and a second deposition section 140.

[0140] Although not shown here, the manufacturing apparatus 100 is placed inside a vacuum container whose degree of vacuum is adjustable, so that the manufacturing apparatus 100 can manufacture the negative electrode active material 2 in a vacuum environment.

[0141] (rotating part) The rotating part 110 is a cylindrical member having a through hole 110K, and holds a plurality of raw material particles 2X during deposition of the deposited film 2Y. The rotating part 110 is rotatable about a rotation axis P, and has an inner wall surface 110M for holding the plurality of raw material particles 2X during rotation. The rotation axis P is an imaginary axis extending in the penetrating direction of the rotating part 110.

[0142] (storage area) The storage section 120 is a box-shaped member that stores a plurality of raw material particles 2X. The storage section 120 is spaced apart from the inner wall surface 110M and disposed in close proximity to the inner wall surface 110M. The storage section 120 also includes a stirring mechanism for stirring the plurality of raw material particles 2X. A portion of the storage section 120 that faces the inner wall surface 110M can be opened and closed. This allows the storage section 120 to store a plurality of raw material particles 2X in a closed state and to release a plurality of raw material particles 2X toward the inner wall surface 110M in an open state.

[0143] (1st vapor deposition section) The first vapor deposition unit 130 is a vapor deposition source that forms the deposited film 2Y using a vapor deposition method, and includes a first raw material and a heating mechanism. The first vapor deposition unit 130 is disposed inside the through-hole 110K. The first vapor deposition unit 130 is spaced apart from the inner wall surface 110M and disposed close to the inner wall surface 110M. The heating mechanism of the first vapor deposition unit 130 heats the first raw material during the formation of the deposited film 2Y, thereby generating a vapor deposition gas (vapor deposition gas G1 shown in FIG. 7, which will be described later).

[0144] Here, as described above, since the manufacturing apparatus 100 is disposed inside a vacuum chamber, the first vapor deposition section 130 performs the vapor deposition process using a vacuum vapor deposition method.

[0145] The type of the first raw material is different from the type of the second raw material, which will be described later. Specifically, the first raw material contains one or both of elemental silicon and silicon oxide.

[0146] (Second evaporation section) The second vapor deposition unit 140 is another vapor deposition source that forms the deposited film 2Y using a vapor deposition method, and includes a second raw material and a heating mechanism. The second vapor deposition unit 140 is disposed inside the through-hole 110K, and here, is disposed adjacent to and in close proximity to the first vapor deposition unit 130. The second vapor deposition unit 140 is spaced apart from the inner wall surface 110M, but is also disposed in close proximity to the inner wall surface 110M. The heating mechanism of the second vapor deposition unit 140 heats the second raw material during the formation of the deposited film 2Y, thereby generating a vapor deposition gas (vapor deposition gas G2 shown in FIG. 7, which will be described later).

[0147] Here, as described above, since the manufacturing apparatus 100 is disposed inside the vacuum chamber, the second vapor deposition section 140 performs the vapor deposition process using the vacuum vapor deposition method.

[0148] The type of the second raw material is different from the type of the first raw material. Specifically, the second raw material contains a metallic material that is a supply source of a metallic element, and the metallic material is an elemental metal or the like.

[0149] In particular, the heating mechanism of the second deposition unit 140 can change the heating temperature of the second raw material when forming the deposition film 2Y, and therefore the second deposition unit 140 can change the amount of deposition gas G2 generated when forming the deposition film 2Y. Specifically, the heating mechanism increases the heating temperature when forming the deposition film 2Y, and therefore the second deposition unit 140 increases the amount of deposition gas G2 generated.

[0150] (others) The manufacturing apparatus 100 may also include one or more of the other components, such as a power supply, a control device, and a rotation mechanism.

[0151] The power supply supplies power to components such as the control device, the rotation mechanism, the rotation unit 110, the first deposition unit 130, and the second deposition unit 140. The control device is a device that controls the overall operation of the manufacturing apparatus 100, and includes a central processing unit (CPU) and the like. The rotation mechanism is a mechanism that rotates the rotation unit 110, and includes a motor and the like.

[0152] [Manufacturing procedure for negative electrode active material] 6 and 7 each show a cross-sectional configuration corresponding to FIG. 4 in order to explain the manufacturing process of the negative electrode active material 2. Hereinafter, the manufacturing procedure of the negative electrode active material 2 will be described while explaining the operation of the manufacturing apparatus 100 with reference to FIGS. 4 and 5 as well as FIGS. 6 and 7.

[0153] Before the start of production of the negative electrode active material 2, the rotating part 110 is not yet rotating, so the rotating part 110 is stationary, and the storage part 120 is blocked, so multiple raw material particles 2X are stored in the storage part 120.

[0154] There is no particular limitation on the type (composition) of the raw material particles 2X. Specifically, the raw material particles 2X may contain only elemental silicon, or may contain elemental silicon and silicon oxide.

[0155] When a plurality of negative electrode active materials 2 are manufactured using the manufacturing apparatus 100, first, the pressure inside the vacuum container is reduced to create a vacuum environment inside the through-hole 110K. The pressure of the vacuum environment is not particularly limited and can be set arbitrarily.

[0156] 6, the rotating part 110 rotates in a rotation direction R around the rotation axis P. Here, the rotating part 110 rotates clockwise.

[0157] The rotation speed of the rotating part 110 is not particularly limited and can be set arbitrarily as long as the inner wall surface 110M can hold a plurality of raw material particles 2X by utilizing the centrifugal force generated in response to the rotation of the rotating part 110. As an example, the rotation speed of the rotating part 110 is 150 rpm.

[0158] Next, the storage section 120 opens while the inner wall surface 110M holds the plurality of raw material particles 2X in accordance with the rotation of the rotating section 110. As a result, the plurality of raw material particles 2X are released from the storage section 120 toward the inner wall surface 110M, as shown in FIG.

[0159] In this case, the inner wall surface 110M moves relative to the storage section 120 in accordance with the rotation of the rotating section 110, and thus a plurality of raw material particles 2X are sequentially supplied to the entire inner wall surface 110M. Moreover, the plurality of raw material particles 2X are pressed against the inner wall surface 110M by utilizing centrifugal force generated in accordance with the rotation of the rotating section 110, and thus the plurality of raw material particles 2X are held on the inner wall surface 110M. As a result, the entire inner wall surface 110M holds the plurality of raw material particles 2X.

[0160] Finally, in a state where the entire inner wall surface 110M holds a plurality of raw material particles 2X, the first vapor deposition section 130 and the second vapor deposition section 140 each perform a vapor deposition process as shown in FIG.

[0161] Specifically, the first deposition unit 130 heats the first raw material to emit a deposition gas G1 toward the raw material particles 2X held by the inner wall surface 110M. The heating temperature of the first raw material is not particularly limited as long as the first raw material can be gasified, and can be set arbitrarily. In this case, when the rotating unit 110 rotates, each of the raw material particles 2X rotates while being held by the inner wall surface 110M, and the deposition gas G1 is emitted onto the entire surface of each of the raw material particles 2X.

[0162] The second deposition unit 140 heats the second raw material to emit a deposition gas G2 onto the raw material particles 2X held by the inner wall surface 110M. The heating temperature of the second raw material is not particularly limited as long as it is a temperature at which the second raw material can be gasified, and can be set arbitrarily. In this case, as described above, each of the raw material particles 2X rotates while being held by the inner wall surface 110M, and the deposition gas G2 is emitted onto the entire surface of each of the raw material particles 2X.

[0163] As a result, the deposition gases G1 and G2 are released onto the surfaces of the plurality of raw material particles 2X, and the first raw material and the second raw material are deposited onto the surfaces of the plurality of raw material particles 2X, respectively.

[0164] 5, a deposited film 2Y is formed on the surface of each of the raw material particles 2X. This deposited film 2Y contains both the first raw material and the second raw material, and therefore contains one or both of elemental silicon and silicon oxide, as well as a metal element.

[0165] In particular, in the second deposition unit 140, the heating temperature of the second raw material is increased as the deposition process progresses. The rate at which the heating temperature is increased is not particularly limited and can be set arbitrarily. In this case, the amount of deposition gas G2 released increases as the deposition process progresses, and the amount of metal elements contained in the deposited film 2Y also increases. As a result, the content of metal elements in the deposited film 2Y increases in the direction from the raw material particles 2X to the deposited film 2Y, and conversely, decreases in the direction from the deposited film 2Y to the raw material particles 2X.

[0166] As a result, a plurality of negative electrode active materials 2 including raw material particles 2X and deposited films 2Y are completed as shown in FIG.

[0167] When producing the plurality of negative electrode active materials 2, the median diameter of the plurality of raw material particles 2X can be set arbitrarily, and the amount (thickness) of the deposited film 2Y formed can be set arbitrarily.

[0168] However, when the raw material particles 2X do not contain metal silicate, it is preferable to adjust one or both of the median diameter of the multiple raw material particles 2X and the amount of deposited film 2Y formed so that not only the intermediate portion 2B and the surface portion 2C but also the center portion 2A contains metal silicate, as shown in Figure 2.

[0169] In this case, first, the median diameter of the plurality of raw material particles 2X may be made sufficiently small so that the central portion 2A includes not only the raw material particles 2X but also a portion of the deposited film 2Y. Second, the amount of deposited film 2Y formed may be made sufficiently large so that the central portion 2A includes not only the raw material particles 2X but also a portion of the deposited film 2Y. Third, the median diameter of the plurality of raw material particles 2X may be made sufficiently small and the amount of deposited film 2Y formed may be made sufficiently large so that the central portion 2A includes not only the raw material particles 2X but also a portion of the deposited film 2Y.

[0170] As a result, not only the intermediate portion 2B and the surface portion 2C but also the center portion 2A contains a metal silicon compound, and the amounts of CA, CB, and CC present satisfy the above-mentioned appropriate relationship (CC>CB>CA).

[0171] After the negative electrode active material 2 is produced, a coating 3 may be formed on the surface of the negative electrode active material 2, as shown in Fig. 3. In this case, a heating device such as a tubular electric furnace is used, and a carbon source such as methane is used as a raw material. The thickness of the coating 3 is not particularly limited and can be set arbitrarily.

[0172] [Negative electrode manufacturing procedure] First, a plurality of negative electrode active materials 2, a negative electrode binder, and a negative electrode conductive agent are mixed together to form a negative electrode mixture.

[0173] 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. Finally, the negative electrode mixture slurry is applied to the surface of the negative electrode current collector 1A to form the negative electrode active material layer 1B.

[0174] Thereafter, the negative electrode active material layer 1B may be compression-molded using a compression device such as a roll press, etc. In this case, the negative electrode active material layer 1B may be heated, and the compression molding may be repeated multiple times.

[0175] As a result, the negative electrode active material layer 1B is formed on the surface of the negative electrode current collector 1A, and the negative electrode 1 is completed.

[0176] <1-5. Actions and Effects> According to this negative electrode 1, the negative electrode active material 2 contains metal silicate, and when the cross section of the negative electrode active material 2 is divided into a central portion 2A, an intermediate portion 2B, and a surface portion 2C, the amounts CA, CB, and CC have an appropriate relationship of CC>CB>CA.

[0177] In this case, as described above, the distribution of metal elements is optimized inside the negative electrode active material 2. This reduces the reactivity near the surface of the negative electrode active material 2, and improves the lithium absorption / desorption property near the center of the negative electrode active material 2. Therefore, in a secondary battery using the negative electrode 1, the decomposition reaction of the electrolyte is suppressed and the battery capacity is increased, making it possible to realize a secondary battery with excellent battery characteristics.

[0178] In particular, if the metal silicate contains one or more of the first metal silicate, the second metal silicate, and the third metal silicate, the reactivity is sufficiently reduced near the surface of the negative electrode active material 2, and the lithium absorption / desorption property is sufficiently improved near the center of the negative electrode active material 2, thereby achieving a greater effect.

[0179] In this case, if the metal silicate contains the first metal silicate, an even greater effect can be obtained because the reactivity near the surface of the negative electrode active material 2 is sufficiently reduced and the lithium absorption / desorption property near the center of the negative electrode active material 2 is sufficiently improved. Furthermore, if the first metal silicate contains magnesium as an alkaline earth metal element, the reactivity near the surface of the negative electrode active material 2 is further reduced and the lithium absorption / desorption property near the center of the negative electrode active material 2 is further improved, thereby achieving a significantly greater effect. That's why.

[0180] Furthermore, if the metal content of the metal element in the metal silicate is 1% to 20%, the reactivity is sufficiently reduced near the surface of the negative electrode active material 2, and the lithium absorption / desorption property is sufficiently improved near the center of the negative electrode active material 2, thereby achieving a greater effect.

[0181] Furthermore, if the oxygen-silicon ratio in the metal silicate is 0.80 to 1.30, the reactivity is sufficiently reduced near the surface of the negative electrode active material 2, and the lithium absorption / desorption property is sufficiently improved near the center of the negative electrode active material 2, thereby achieving a greater effect.

[0182] Furthermore, if the crystallite size of the Si(220) crystal plane in the metal silicate is 30 nm or less, the reactivity near the surface of the negative electrode active material 2 is sufficiently reduced, and the lithium absorption / desorption property near the center of the negative electrode active material 2 is sufficiently improved, thereby achieving a greater effect.

[0183] Furthermore, if the negative electrode 1 contains a plurality of negative electrode active materials 2 and the median diameter of the plurality of negative electrode active materials 2 is 0.1 μm to 50 μm, the reactivity is sufficiently reduced near the surface of the negative electrode active materials 2, and the lithium absorption / desorption property is sufficiently improved near the center of the negative electrode active materials 2, thereby achieving a greater effect.

[0184] Furthermore, if the negative electrode active material 2 further contains elemental silicon and silicon oxide, the reactivity in the vicinity of the surface of the negative electrode active material 2 is further reduced, and the lithium absorption / desorption property in the vicinity of the center of the negative electrode active material 2 is further improved, thereby achieving a greater effect.

[0185] In this case, if x satisfies 0.5≦x≦1.5 in formula (4) representing the structure of silicon oxide, the reactivity in the vicinity of the surface of the negative electrode active material 2 is further reduced, and the lithium absorption / desorption property in the vicinity of the center of the negative electrode active material 2 is further improved, thereby achieving significantly high effects.

[0186] <2. Secondary battery> Next, a secondary battery according to an embodiment of the present technology to which the above-described negative electrode 1 is applied will be described.

[0187] The secondary battery described here is a secondary battery that obtains battery capacity by utilizing the absorption and desorption of an electrode reactant, and includes a positive electrode, a negative electrode, and an electrolyte. Hereinafter, 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 secondary battery (or lithium ion secondary battery). In this secondary battery, lithium is absorbed and desorbed in an ionic state.

[0188] 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 lithium from being deposited on the surface of the negative electrode during charging.

[0189] <2-1.Configuration> Fig. 8 shows a cross-sectional structure of a secondary battery, and Fig. 9 shows a cross-sectional structure of the battery element 20 shown in Fig. 8.

[0190] 8 and 9, this secondary battery includes a battery can 11, a pair of insulating plates 12 and 13, a battery element 20, a positive electrode lead 25, and a negative electrode lead 26. The secondary battery described here is a cylindrical secondary battery in which the battery element 20 is housed in the cylindrical battery can 11.

[0191] [Battery can] As shown in FIG. 8, the battery can 11 is a component that mainly houses the battery element 20. This battery can 11 has one open end and the other closed end, and therefore has a hollow structure. The battery can 11 contains one or more metal materials such as iron, aluminum, iron alloys, and aluminum alloys. The surface of the battery can 11 may be plated with a metal material such as nickel.

[0192] The battery lid 14, safety valve mechanism 15, and PTC element 16 are crimped to one open end of the battery can 11 via a gasket 17. This seals the battery can 11 with the battery lid 14. Here, the battery lid 14 contains the same material as the material from which the battery can 11 is formed. The PTC element 16 is a thermosensitive resistor. The safety valve mechanism 15 and the PTC element 16 are disposed inside the battery lid 14, and the safety valve mechanism 15 is electrically connected to the battery lid 14 via the PTC element 16. The gasket 17 contains an insulating material, and the surface of the gasket 17 may be coated with asphalt or the like.

[0193] In the safety valve mechanism 15, when the internal pressure of the battery can 11 reaches a certain level due to factors such as an internal short circuit or external heating, the disk plate 15A reverses, cutting off the electrical connection between the battery lid 14 and the battery element 20. To prevent abnormal heat generation due to a large current, the electrical resistance of the PTC element 16 increases as the temperature rises.

[0194] [Insulating plate] 8, the insulating plates 12 and 13 are arranged to face each other with the battery element 20 interposed therebetween. As a result, the battery element 20 is sandwiched between the insulating plates 12 and 13.

[0195] [Battery element] As shown in FIGS. 8 and 9, the battery element 20 is a so-called power generating element, and includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown).

[0196] This battery element 20 is a so-called wound electrode body, and therefore the positive electrode 21 and the negative electrode 22 are wound while facing each other with a separator 23 interposed therebetween. A center pin 24 is inserted into a space 20S provided at the center of the winding of the battery element 20. However, the center pin 24 may be omitted.

[0197] (positive electrode) 8 and 9, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B. However, the positive electrode current collector 21A may be omitted.

[0198] 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.

[0199] The positive electrode active material layer 21B contains one or more types of positive electrode active materials that absorb and release 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.

[0200] Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A. However, the positive electrode active material layer 21B may be 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.

[0201] 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 contain one or more other elements as constituent elements. The type of other element is not particularly limited as long as it is an element other than lithium and transition metal elements, 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.

[0202] Specific examples of oxides are LiNiO2, LiCoO2, LiCo 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2 and LiMn2O4. Specific examples of phosphate compounds include LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0203] The positive electrode binder contains one or more of the following materials: synthetic rubber, polymer compound, etc. Specific examples of synthetic rubber include styrene-butadiene rubber, fluorine-containing rubber, and ethylene-propylene-diene. Specific examples of polymer compounds include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

[0204] The positive electrode conductive agent contains one or more conductive materials such as carbon materials, metal materials, and conductive polymer compounds, and specific examples of the carbon materials include graphite, carbon black, acetylene black, and ketjen black.

[0205] (Negative electrode) As shown in FIGS. 8 and 9, the negative electrode 22 has a configuration similar to that of the negative electrode 1.

[0206] Specifically, the anode 22 includes an anode current collector 22A and an anode active material layer 22B. The configuration of the anode current collector 22A is the same as that of the anode current collector 1A, and the configuration of the anode active material layer 22B is the same as that of the anode active material layer 1B. Here, the anode active material layer 22B is provided on both sides of the anode current collector 22A. However, the anode active material layer 22B may be provided on only one side of the anode current collector 22A, on the side where the anode 22 faces the positive electrode 21.

[0207] (separator) 8 and 9, separator 23 is an insulating porous film interposed between positive electrode 21 and negative electrode 22, and allows lithium to pass through in an ionic state while preventing a short circuit caused by contact between positive electrode 21 and negative electrode 22. Separator 23 contains a polymer compound such as polyethylene.

[0208] (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.

[0209] The solvent contains one or more types of non-aqueous solvents (organic solvents). An electrolyte containing a non-aqueous solvent is a so-called non-aqueous electrolyte.

[0210] The non-aqueous solvent is an ester, an ether, or the like, more specifically, a carbonate ester compound, a carboxylic acid ester compound, a lactone compound, or the like, because it improves the dissociation of the electrolyte salt and the mobility of ions.

[0211] 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.

[0212] 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.

[0213] The lactone compound is a lactone, etc. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

[0214] The ethers may be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, or the like.

[0215] The non-aqueous solvent may be an unsaturated cyclic carbonate, a fluorinated cyclic carbonate, a sulfonate, a phosphate, an acid anhydride, a nitrile compound, an isocyanate compound, or the like, because the electrochemical stability of the electrolyte solution is improved.

[0216] 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.

[0217] The electrolyte salt contains one or more types of light metal salts such as lithium salts.

[0218] Specific examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium trifluoromethanesulfonate (LiCFSO), lithium bis(fluorosulfonyl)imide (LiN(FSO)), lithium bis(trifluoromethanesulfonyl)imide (LiN(CFSO)), lithium tris(trifluoromethanesulfonyl)methide (LiC(CFSO)), lithium bis(oxalato)borate (LiB(CO)), lithium monofluorophosphate (LiPFO), and lithium difluorophosphate (LiPFO). These salts are used because they can provide high battery capacities.

[0219] 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.

[0220] [Positive and negative leads] 8, the positive electrode lead 25 is connected to the positive electrode current collector 21A and contains a conductive material such as aluminum. The positive electrode lead 25 is electrically connected to the battery lid 14 via the safety valve mechanism 15.

[0221] 8, the negative electrode lead 26 is connected to the negative electrode current collector 22A and contains a conductive material such as nickel. The negative electrode lead 26 is electrically connected to the battery can 11.

[0222] <2-2. Operation> The secondary battery operates as follows during charging and discharging.

[0223] 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 charging and discharging, lithium is absorbed and released in an ionic state.

[0224] <2-3. Manufacturing method> When manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are fabricated and the electrolyte solution is prepared according to the procedure described below as an example, and then the secondary battery is assembled and subjected to a stabilization process after assembly.

[0225] [Preparation of positive electrode] First, a cathode active material, a cathode binder, and a cathode conductive agent are mixed together to form a cathode mixture. Next, the cathode mixture is poured into a solvent to prepare a paste-like cathode mixture slurry. This solvent may be an aqueous solvent or an organic solvent. Finally, the cathode mixture slurry is applied to both surfaces of the cathode current collector 21A to form the cathode active material layer 21B. The cathode active material layer 21B may then be compression-molded using a compression device such as a roll press. In this case, the cathode active material layer 21B may be heated, or the compression molding may be repeated multiple times. This results in the formation of the cathode active material layer 21B on both surfaces of the cathode current collector 21A, thereby producing the cathode 21.

[0226] [Preparation of negative electrode] Using the same procedure as that for producing the negative electrode 1 described above, the negative electrode active material layers 22B are formed on both sides of the negative electrode current collector 22A, thereby producing the negative electrode 22.

[0227] [Preparation of electrolyte] An electrolyte salt is added to a solvent, whereby the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing an electrolytic solution.

[0228] [Secondary battery assembly] First, a positive electrode lead 25 is connected to the positive electrode current collector 21A of the positive electrode 21 using a joining method such as welding, and a negative electrode lead 26 is connected to the negative electrode current collector 22A of the negative electrode 22 using a joining method such as welding.

[0229] Next, the positive electrode 21 and the negative electrode 22 are stacked together 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) having a space 20S. This wound body has the same configuration 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. Next, a center pin 24 is inserted into the space 20S.

[0230] Next, with the wound body sandwiched between insulating plates 12 and 13, the wound body and insulating plates 12 and 13 are housed in battery can 11. In this case, the positive electrode lead 25 is connected to safety valve mechanism 15 using a joining method such as welding, and the negative electrode lead 26 is connected to battery can 11 using a joining method such as welding. Next, an electrolyte solution is injected into battery can 11, thereby impregnating the wound body with the electrolyte. As a result, the positive electrode 21, the negative electrode 22, and the separator 23 are each impregnated with the electrolyte solution, and battery element 20 is produced.

[0231] Finally, the battery lid 14, the safety valve mechanism 15, and the PTC element 16 are housed in the battery can 11, and then the battery can 11 is crimped with the gasket 17 interposed therebetween.

[0232] As a result, the battery lid 14, the safety valve mechanism 15, and the PTC element 16 are fixed to the battery can 11, and the battery element 20 is sealed in the battery can 11, thereby assembling a secondary battery.

[0233] [Stabilization process for secondary batteries after assembly] The assembled secondary battery is charged and discharged. The charging and discharging conditions, such as the ambient temperature, the number of charging and discharging cycles (number of cycles), and the charging and discharging conditions, can be set arbitrarily. This forms a coating on the surface of each of the positive electrode 21 and the negative electrode 22, electrochemically stabilizing the state of the battery element 20. This completes the secondary battery.

[0234] <2-4. Actions and Effects> In this secondary battery, the negative electrode 22 has the same configuration as the negative electrode 1. Therefore, for the reasons described above, the decomposition reaction of the electrolyte is suppressed and the battery capacity is increased, thereby obtaining excellent battery characteristics.

[0235] In particular, if the secondary battery is a lithium secondary battery, a sufficient battery capacity can be stably obtained by utilizing the absorption and desorption of lithium, and therefore a greater effect can be obtained.

[0236] Other functions and effects of the secondary battery are the same as those of the negative electrode 1.

[0237] <3. Modifications> The configuration of the secondary battery can be modified as appropriate, as described below, although the series of modifications described below may be combined with each other.

[0238] [Variation 1] A porous film separator 23 was used. However, although not specifically shown here, a laminated separator including a polymer compound layer may also be used.

[0239] 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 of the battery element 20. This suppresses miswinding of the positive electrode 21, the negative electrode 22, and the separator, thereby suppressing swelling of the secondary battery even if a decomposition reaction of the electrolyte occurs. The polymer compound layer includes polyvinylidene fluoride or the like. This is because polyvinylidene fluoride has excellent physical strength and is electrochemically stable.

[0240] One or both of the porous film and the polymer compound layer may contain one or more types of insulating particles. This is because the insulating particles dissipate heat when the secondary battery generates heat, improving the safety (heat resistance) of the secondary battery. The insulating particles contain one or more types of 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.

[0241] When a laminated separator is produced, a precursor solution containing a polymer compound and an organic solvent is prepared, and then the precursor solution is applied to one or both sides of a porous film. In this case, the precursor solution may contain a plurality of insulating particles.

[0242] Even when this laminated separator is used, the same effect can be obtained because lithium can move in an ionic state between the positive electrode 21 and the negative electrode 22. In this case, as described above, swelling of the secondary battery is further suppressed, and therefore a greater effect can be obtained.

[0243] [Variation 2] An electrolyte solution, which is a liquid electrolyte, was used, but although not specifically shown here, an electrolyte layer, which is a gel electrolyte, may also be used.

[0244] In a battery element 20 using an electrolyte layer, a positive electrode 21 and a negative electrode 22 are wound facing each other with a separator 23 and an 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.

[0245] 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.

[0246] 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, leakage of the electrolyte solution is prevented as described above, and therefore a greater effect can be obtained.

[0247] <4. Uses of secondary batteries> Finally, the uses (application examples) of the secondary battery will be described.

[0248] The use of the secondary battery is not particularly limited. The secondary battery used as a power source may be a main power source or an auxiliary power source in electronic devices, electric vehicles, etc. 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 that is used in place of the main power source or a power source that can be switched from the main power source.

[0249] 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.

[0250] The battery pack may include 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 includes 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. [Example]

[0251] An embodiment of the present technology will be described.

[0252] <Examples 1 to 24 and Comparative Examples 1 to 3> As will be described below, negative electrode active materials were prepared, and secondary batteries were prepared using the negative electrode active materials, and the battery characteristics of the secondary batteries were then evaluated.

[0253] [Preparation of negative electrode active material] Here, a plurality of negative electrode active materials 2 were produced using the production apparatus 100 shown in FIG.

[0254] As the raw material particles 2X, 10 kg of powdered silicon compound (SiO) was used. The median diameter of the powdered silicon compound was 1 μm. As the first raw material, 100 kg of a mixture of powdered elemental silicon (Si, purity = 99.9%) and powdered silicon oxide (SiO) was used. In this case, the mixing ratio (molar ratio) of elemental silicon to silicon oxide was 50:50. As the second raw material, 100 kg of elemental magnesium (Mg, purity = 99.9%) was used.

[0255] When producing a plurality of negative electrode active materials 2, first, the pressure inside the through-hole 110K was reduced (pressure = 0.1 torr (= approximately 13.3322 Pa)), and then the rotating part 110 was rotated clockwise (rotation speed = 150 rpm) around the rotation axis P. Subsequently, while the rotating part 110 was rotating, a plurality of raw material particles 2X were released from the storage part 120 toward the inner wall surface 110M.

[0256] Next, in a state in which a plurality of raw material particles 2X were held by inner wall surface 110M using centrifugal force, deposition processes were performed using first deposition unit 130 and second deposition unit 140. In this case, the heating temperature of the first raw material in first deposition unit 130 was set to 1450°C. In second deposition unit 140, the heating temperature of the second raw material was increased to 650°C, and after 5 hours, the heating temperature was increased to 700°C, and after another 5 hours, the heating temperature was increased to 750°C.

[0257] As a result, a deposited film 2Y was formed on the surfaces of the plurality of raw material particles 2X, thereby producing a plurality of negative electrode active materials 2. In this case, as described above, the heating temperature was increased in the second vapor deposition section 140, and therefore the amount of metal elements present decreased in the direction from the surface of the negative electrode active material 2 toward the center of the negative electrode active material 2.

[0258] Finally, a plurality of negative electrode active materials 2 were placed inside the tubular electric furnace. After that, methane gas and argon gas were supplied into the tubular electric furnace (supply rate = 1 L / min (= 1 dm 3The plurality of negative electrode active materials 2 were stirred while being heated (heating temperature = 1000°C, heating time = 1 hour) at a rate of 1 / min. As a result, a coating 3 containing a carbon material was formed on the surface of each of the plurality of negative electrode active materials 2.

[0259] Thus, a plurality of negative electrode active materials 2 provided with the coating 3 were completed (Examples 1 to 20). The negative electrode active material 2 was made of a metal silicate (first metal silicate) containing Mg a SiO b (specifically, at least one of MgSiO3 and Mg2SiO4), as well as elemental silicon and silicon oxides.

[0260] In the following, for the sake of simplicity, the plurality of negative electrode active materials 2 provided with the coating 3 will be simply referred to as "plural negative electrode active materials 2," and the negative electrode active material 2 provided with the coating 3 will be simply referred to as "negative electrode active material 2."

[0261] When a plurality of negative electrode active materials 2 were produced, the compositions of the plurality of negative electrode active materials 2 were varied as shown in Tables 1 and 2.

[0262] Specifically, the abundance ratio (mol%) and oxygen-silicon ratio were changed by varying conditions such as the amount of the second raw material used and the heating temperature. After the completion of the plurality of negative electrode active materials 2, the plurality of negative electrode active materials 2 were further heated, and the crystallite size (nm) was changed by varying the heating temperature. The median diameter (μm) was changed by varying the amount of deposition film 2Y formed by changing the deposition time of each of the first deposition unit 130 and the second deposition unit 140.

[0263] After multiple negative electrode active materials 2 were completed, the amounts of abundance CA, CB, and CC were calculated, and the relationship between the amounts of abundance CA, CB, and CC was investigated. The results shown in the "Relationship between amounts of abundance (CA, CB, CC)" column in Tables 1 and 2 were obtained. "CC>CB>CA" indicates that the amount of abundance CC was greater than the amount of abundance CB, and that the amount of abundance CB was greater than the amount of abundance CA. The calculation procedures for the amounts of abundance CA, CB, and CC were as described above.

[0264] For comparison, a plurality of negative electrode active materials 2 were produced in the same manner except that only the first vapor deposition unit 130 was used without the second vapor deposition unit 140 (Comparative Example 1).

[0265] For comparison, a plurality of negative electrode active materials 2 were prepared by the same procedure except that the heating temperature of the second raw material was not increased (Comparative Example 2). In this case, the "abundance relationship (CA, CB, CC)" was "CC = CB = CA", and therefore the abundances CA, CB, and CC were all the same.

[0266] [Secondary battery production] Here, a test secondary battery was fabricated to simply evaluate the battery characteristics. Figure 10 shows the cross-sectional structure of the test secondary battery, which is a coin-type lithium metal secondary battery.

[0267] Below, the configuration of the test secondary battery will be explained, and then the procedure for fabricating the test secondary battery will be explained.

[0268] (Configuration of test secondary battery) As shown in FIG. 10, this test secondary battery includes a test electrode 31, a counter electrode 32, a separator 33, an exterior cup 34, an exterior can 35, a gasket 36, and an electrolyte (not shown).

[0269] The test electrode 31 is housed in a vessel-shaped exterior cup 34, and the counter electrode 32 is housed in a vessel-shaped exterior can 35. The test electrode 31 and the counter electrode 32 are stacked together with a separator 33 interposed therebetween, and the test electrode 31, the counter electrode 32, and the separator 33 are each impregnated with an electrolyte. The exterior cup 34 is housed in an exterior can 35, and the exterior cup 34 and the exterior can 35 are crimped together with a gasket 36. As a result, the test electrode 31, the counter electrode 32, and the separator 33 are sealed inside the exterior cup 34 and the exterior can 35.

[0270] (Procedure for producing secondary batteries for testing) The procedure for producing the test secondary battery is as follows: Hereinafter, the above-mentioned plurality of negative electrode active materials 2 will be simply referred to as "negative electrode active materials."

[0271] (Preparation of test electrodes) First, 9.6 g of the negative electrode active material, 1.2 g of a negative electrode binder (polyacrylamide), and 1.2 g of a negative electrode conductive agent (carbon black) were mixed together to prepare a negative electrode mixture.

[0272] Next, a plastic container (capacity = 150 ml (= 150 cm 3 38 g of a solvent (ion-exchanged water, an aqueous solvent) was added to the mixture, and the negative electrode mixture was then added to the solvent. The solvent was then stirred using a planetary mixer (stirring speed: 2000 rpm, stirring time: 5 minutes) to prepare a negative electrode mixture slurry.

[0273] Next, the negative electrode mixture slurry was applied to one side of a negative electrode current collector (copper foil, thickness = 10 μm) using a coating device, and then the negative electrode mixture slurry was dried (drying temperature = 100 °C, drying time = 10 minutes) to form a negative electrode active material layer, which was then compression-molded using a press.

[0274] Finally, the negative electrode current collector on which the negative electrode active material layer was formed was punched out into a disk shape (diameter = 15 mm), thereby producing test electrode 31.

[0275] (Preparation of counter electrode) A lithium metal plate was punched into a disk shape (diameter = 16 μm), thereby producing a counter electrode 32.

[0276] (Preparation of Electrolyte) An electrolyte salt (lithium hexafluorophosphate) was added to the solvent, and the solvent was then stirred.

[0277] The solvent used was a mixture of ethylene carbonate, a cyclic carbonate, dimethyl carbonate, a chain carbonate, and monofluoroethylene carbonate, a fluorinated cyclic carbonate, in a mass ratio of 40:50:10 (cyclic carbonate:chain carbonate:fluorinated cyclic carbonate).

[0278] In this case, the content of the electrolyte salt in the electrolyte solution was 1 mol / kg relative to the solvent.

[0279] (Assembling a secondary battery for testing) First, the test electrode 31 was placed in an outer cup 34, and the counter electrode 32 was placed in an outer can 35. Next, the test electrode 31 placed in the outer cup 34 and the counter electrode 32 placed in the outer can 35 were stacked together with a separator 33 (polyethylene, thickness = 20 μm) impregnated with an electrolyte interposed therebetween. In this case, the test electrode 31 was positioned so that the negative electrode active material layer formed on one side of the negative electrode current collector faced the counter electrode 32 with the separator 33 interposed between them. Finally, with the test electrode 31 and the counter electrode 32 stacked together with the separator 33 interposed between them, the outer cup 34 and the outer can 35 were crimped together with a gasket 36 (resin material, thickness = 500 μm). As a result, the test electrode 31 and the counter electrode 32 were sealed inside the outer cup 34 and the outer can 35, and a test secondary battery was completed.

[0280] [Evaluation of battery characteristics] The battery characteristics, including capacity characteristics, initial charge / discharge characteristics, and cycle characteristics, were evaluated, and the results shown in Tables 1 and 2 were obtained.

[0281] [Capacitance characteristics] To evaluate the capacity characteristics, the secondary battery was charged and discharged in a room temperature environment (temperature = 23 ° C.) to measure the discharge capacity (mAh). Then, the discharge capacity was divided by the weight (g) of the negative electrode active material to calculate the battery capacity (mAh / g), which is an index for evaluating the capacity characteristics.

[0282] During charging, the current is 0.2mA / cm 2 The battery was charged at a constant current density of 0.2 mA / cm until the voltage reached 0 V, and then charged at a constant voltage of 0 V until the current reached 0.04 mA. 2 The battery was discharged at a constant current density of 0.1 V until the voltage reached 1.5 V.

[0283] [Initial charge / discharge characteristics] When evaluating the initial charge / discharge characteristics, the secondary battery was first charged in a room temperature environment (temperature = 23°C) to measure the charge capacity (mAh). Next, the secondary battery was discharged in the same environment to measure the discharge capacity (mAh). 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 / charge capacity) × 100. The conditions for charging and discharging were the same as those for evaluating the capacity characteristics.

[0284] [Cycle characteristics] To evaluate cycle characteristics, the secondary battery was first charged and discharged in a room temperature environment (temperature = 23°C) to measure the discharge capacity (mAh) at the first cycle. Next, in the same environment, charge and discharge were repeated until the total number of cycles reached 400, and the discharge capacity (mAh) at the 400th cycle was measured. 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 the 400th cycle / discharge capacity at the first cycle) × 100.

[0285] During charging, the current is 0.5mA / cm2 The battery was charged at a constant current density of 0.5 mA / cm until the voltage reached 0 V, and then charged at a constant voltage of 0 V until the current reached 0.05 mA. 2 The battery was discharged at a constant current density of 0.1 V until the voltage reached 1.5 V.

[0286] [Table 1]

[0287] [Table 2]

[0288] [Consideration] As shown in Tables 1 and 2, the battery capacity, initial efficiency, and capacity retention rate each varied depending on the composition of the negative electrode active material.

[0289] Specifically, when the negative electrode active material did not contain metal silicate (Comparative Example 1), both the initial efficiency and the capacity retention rate decreased.

[0290] Furthermore, even if the negative electrode active material contained metal silicate, when the appropriate relationship (CC>CB>CA) was not established for the amounts CA, CB, and CC present (as in Comparative Examples 2 and 3), the battery capacity, initial efficiency, and capacity retention rate all decreased.

[0291] In contrast, when the negative electrode active material contained metal silicate and the amounts CA, CB, and CC had an appropriate relationship (CC>CB>CA) (Examples 1 to 24), the battery capacity, initial efficiency, and capacity retention rate all increased.

[0292] In particular, when the appropriate relationships were established for the abundances CA, CB, and CC, a series of trends were obtained, as explained below.

[0293] First, when the metal silicate is the first metal silicate and the first metal silicate contains magnesium as an alkaline earth metal element, a high battery capacity, a high initial efficiency, and a high capacity retention rate are obtained.

[0294] Although the experimental results are not specifically described here, when a second metal silicate or a third metal silicate was used instead of the first metal silicate, the same tendency as when the first metal silicate was used was observed.

[0295] Secondly, when the content was 1 mol % to 20 mol %, the capacity retention rate increased while satisfying the battery capacity and initial efficiency.

[0296] Thirdly, when the oxygen / silicon ratio was 0.80 to 1.30, the battery capacity and initial efficiency were satisfied, and the capacity retention rate was further increased.

[0297] Fourth, when the crystallite size was 30 nm or less, the battery capacity and initial efficiency were satisfied, and the capacity retention rate was further increased.

[0298] Fifth, when the median diameter was 0.1 μm to 50 μm, the battery capacity and initial efficiency capacity retention rate were further increased.

[0299] Sixth, when the negative electrode active material contained elemental silicon and silicon oxide together with metal silicate, high battery capacity, high initial efficiency, and high capacity retention were obtained.

[0300] [summary] From the results shown in Tables 1 and 2, when the negative electrode active material 2 contains metal silicate and the cross section of the negative electrode active material 2 is divided into a central portion 2A, a middle portion 2B, and a surface portion 2C, if the amounts CA, CB, and CC have an appropriate relationship (CC>CB>CA), a high battery capacity, a high initial efficiency, and a high capacity retention rate are obtained. Therefore, the capacity characteristics, initial charge / discharge characteristics, and cycle characteristics are all improved, resulting in excellent battery characteristics.

[0301] 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.

[0302] Specifically, the battery structure of the secondary battery has been described as being cylindrical and coin-shaped. However, the battery structure of the secondary battery is not particularly limited, and may be a laminate film type, a square type, a button type, or the like.

[0303] 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.

[0304] 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.

[0305] 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.

[0306] The present technology can also be configured as follows. <1> A positive electrode and a negative electrode including a negative electrode active material that occludes and releases an electrode reactant; Electrolyte and Equipped with the negative electrode active material contains a metal silicate, The metal silicate contains a metal element, silicon, and oxygen as constituent elements, The metal element is at least one of an alkaline earth metal element, an alkali metal element, a transition metal element, and an amphoteric metal element (however, excluding the constituent elements of the electrode reactant). The negative electrode active material includes a central portion containing the metal silicate, a surface portion located outside the central portion and containing the metal silicate, and an intermediate portion located between the central portion and the surface portion and containing the metal silicate. When the ratio of the cross-sectional area of the central portion, the cross-sectional area of the intermediate portion, and the cross-sectional area of the surface portion in the cross-section of the negative electrode active material is 1:3:5, The abundance of the metal element in the intermediate portion is greater than the abundance of the metal element in the central portion, The abundance of the metal element in the surface portion is greater than the abundance of the metal element in the intermediate portion. Secondary battery. <2> The metal silicon oxide includes at least one of a first metal silicon oxide represented by formula (1), a second metal silicon oxide represented by formula (2), a third metal silicon oxide represented by formula (3), a fourth metal silicon oxide represented by formula (4), and a fifth metal silicon oxide represented by formula (5). The secondary battery according to <1> above. M1 a SiO b ···(1) (M1 is at least one of alkaline earth metal elements. a satisfies 0 < a < 2. b satisfies 0 < b < 4.) M2 c SiO d ···(2) (M2 is at least one of alkali metal elements. c satisfies 0 < c < 4. d satisfies 0 < d < 4.) M3 e SiO g ···(3) (M3 is at least one of transition metal elements. e satisfies 0 < e < 2. f satisfies 0 < f < 4. g satisfies 0 < g < 4.) M4 j M5 k Si l O m ···(4) (M4 is at least one of alkali metal elements. M5 is at least one of an alkali metal element, an alkaline earth metal element, a transition metal element, and an amphoteric metal element.) M6 n M7 o Si p O q ···(5) (M6 is at least one of alkaline earth metal elements. M7 is at least one of an alkali metal element, an alkaline earth metal element, a transition metal element, and an amphoteric metal element.) <3> The metal silicon oxide contains the first metal silicon oxide. The secondary battery according to <2> above. <4> The alkaline earth metal element includes magnesium. The secondary battery according to <3> above. <5> In the negative electrode active material, the ratio of the content of the metal element to the sum of the content of the metal element, the content of the silicon, and the content of the oxygen is 1 mol% or more and 20 mol% or less. The secondary battery according to any one of <1> to <4> above. <6> In the negative electrode active material, the ratio of the content of the oxygen to the content of the silicon is 0.80 or more and 1.30 or less. The secondary battery according to any one of <1> to <5> above.​​​​​​​​​The negative electrode contains a plurality of particulate negative electrode active materials, The median diameter of the plurality of particulate negative electrode active materials is 0.1 μm or more and 50 μm or less, The secondary battery according to any one of <1> to <7> above. <9> The negative electrode active material further contains elemental silicon and a silicon oxide represented by formula (6), The secondary battery according to any one of <1> to <8> above. SiO x ···(6) (x satisfies 0 < x ≦ 2.) <�10> x satisfies 0.5 ≦ x ≦ 1.5, The secondary battery according to <9> above. <11> The negative electrode further contains a film provided on the surface of the negative electrode active material, The film contains a carbon material, The secondary battery according to any one of <1> to <10> above. <12> It is a lithium secondary battery, The secondary battery according to any one of <1> to <11> above. <13> It contains a negative electrode active material that occludes and releases an electrode reactant, The negative electrode active material contains a metal silicate, The metal silicate contains a metal element, silicon, and oxygen as constituent elements, The metal element is at least one of an alkaline earth metal element, an alkali metal element, a transition metal element, and an amphoteric metal element (however, excluding the constituent elements of the electrode reactant), The negative electrode active material includes a central portion containing the metal silicate, a surface portion located outside the central portion and containing the metal silicate, and an intermediate portion located between the central portion and the surface portion and containing the metal silicate, When the ratio of the cross-sectional area of the central portion, the cross-sectional area of the intermediate portion, and the cross-sectional area of the surface portion of the negative electrode active material is 1:3:5 in the cross-section of the negative electrode active material, the amount of the metal element present in the intermediate portion is greater than the amount of the metal element present in the central portion, the amount of the metal element present in the surface portion is greater than the amount of the metal element present in the intermediate portion; Negative electrode for secondary batteries. [Explanation of symbols]

[0307] 1,22...Negative electrode, 2...Negative electrode active material, 2A...Central part, 2B...Intermediate part, 2C...Surface part, 3...Coating, 21...Positive electrode.

Claims

1. A positive electrode and a negative electrode including a negative electrode active material that occludes and releases an electrode reactant; Electrolyte and Equipped with the negative electrode active material contains a metal silicate, The metal silicate contains a metal element, silicon, and oxygen as constituent elements, the metal element is at least one of an alkaline earth metal element, an alkali metal element, a transition metal element, and an amphoteric metal element (excluding the constituent elements of the electrode reactant); the negative electrode active material includes a central portion containing the metal silicate, a surface portion located outside the central portion and containing the metal silicate, and an intermediate portion located between the central portion and the surface portion and containing the metal silicate; When the ratio of the cross-sectional area of ​​the center portion to the cross-sectional area of ​​the intermediate portion to the cross-sectional area of ​​the surface portion in the cross section of the negative electrode active material is 1:3:5, the amount of the metal element present in the intermediate portion is greater than the amount of the metal element present in the central portion, the amount of the metal element present in the surface portion is greater than the amount of the metal element present in the intermediate portion; Secondary battery.

2. The metal silicon oxide comprises at least one of a first metal silicon oxide represented by formula (1), a second metal silicon oxide represented by formula (2), a third metal silicon oxide represented by formula (3), a fourth metal silicon oxide represented by formula (4), and a fifth metal silicon oxide represented by formula (5). The secondary battery according to claim 1 . M1 a SiO b ・・・(1) (M1 is at least one alkaline earth metal element. a satisfies 0<a<2. b satisfies 0<b<4.) 12 c SiO d ・・・(2) (M2 is at least one alkali metal element. c satisfies 0<c<4. d satisfies 0<d<4.) 53 e SiO g ・・・(3) (M3 is at least one transition metal element. e satisfies 0<e<2. f satisfies 0<f<4. g satisfies 0<g<4.) M4 j M5 k Yes l O m ・・・(4) (M4 is at least one of alkali metal elements. M5 is at least one of alkali metal elements, alkaline earth metal elements, transition metal elements, and amphoteric metal elements.) M6 n M7 o Si p O q ・・・(5) (M6 is at least one of alkaline earth metal elements. M7 is at least one of alkaline earth metal elements, transition metal elements, and amphoteric metal elements.

3. The metal silicon oxide includes the first metal silicon oxide. The secondary battery according to claim 2 .

4. The alkaline earth metal element includes magnesium. The secondary battery according to claim 3 .

5. In the negative electrode active material, a ratio of the content of the metal element to the sum of the content of the metal element, the content of the silicon, and the content of the oxygen is 1 mol % or more and 20 mol % or less. The secondary battery according to claim 1 .

6. In the negative electrode active material, the ratio of the oxygen content to the silicon content is 0.80 or more and 1.30 or less. The secondary battery according to claim 1 .

7. In the negative electrode active material, the crystallite size of the Si (220) crystal plane is 30 nm or less. The secondary battery according to claim 1 .

8. the negative electrode includes a plurality of particles of the negative electrode active material, The median diameter of the plurality of particles of the negative electrode active material is 0.1 μm or more and 50 μm or less. The secondary battery according to claim 1 .

9. The negative electrode active material further contains elemental silicon and a silicon oxide represented by formula (6): The secondary battery according to claim 1 . Yes x ・・・(6) (x satisfies 0<x≦2.)

10. The x satisfies 0.5≦x≦1.5, The secondary battery according to claim 9.

11. the negative electrode further includes a coating provided on a surface of the negative electrode active material, The coating includes a carbon material. The secondary battery according to claim 1 .

12. It is a lithium secondary battery, The secondary battery according to claim 1 .

13. a negative electrode active material that occludes and releases an electrode reactant, the negative electrode active material contains a metal silicate, The metal silicate contains a metal element, silicon, and oxygen as constituent elements, the metal element is at least one of an alkaline earth metal element, an alkali metal element, a transition metal element, and an amphoteric metal element (excluding the constituent elements of the electrode reactant); the negative electrode active material includes a central portion containing the metal silicate, a surface portion located outside the central portion and containing the metal silicate, and an intermediate portion located between the central portion and the surface portion and containing the metal silicate; When the ratio of the cross-sectional area of ​​the center portion to the cross-sectional area of ​​the intermediate portion to the cross-sectional area of ​​the surface portion in the cross section of the negative electrode active material is 1:3:5, the amount of the metal element present in the intermediate portion is greater than the amount of the metal element present in the central portion, the amount of the metal element present in the surface portion is greater than the amount of the metal element present in the intermediate portion; Negative electrode for secondary batteries.

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