Cathode for secondary batteries and secondary battery

Abstract

To provide a secondary battery capable of obtaining excellent battery characteristics.SOLUTION: A secondary battery comprises a cathode including a cathode active material layer, an anode and an electrolyte. The cathode active material layer includes a plurality of cathode active material particles, and each of the particles includes a center part containing an olivine type phosphate compound and a coated part provided on a surface of the center part. The olivine type phosphate compound contains manganese and iron as constituent elements and when a sum of a content of manganese and a content of iron in the olivine type phosphate compound is defined as 100 pts. mol, the content of manganese is 50 pts. mol or more to 90 pts. mol or less. The center part includes secondary particles obtained by granulating a plurality of primary particles. A first median diameter relating to the plurality of primary particles is 0.01 μm or more to 0.5 μm or less, and a second median diameter relating to the plurality of secondary particles is 1 μm or more to 20 μm or less. The coated part includes a nitrile group. A rate of porosity of the cathode active material layer is 20% or more to 40% or less.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] Due to the widespread use of various electronic devices such as mobile phones, the development of secondary batteries is underway as a power source that is small and lightweight and can obtain a high energy density. This secondary battery includes a negative electrode and an electrolyte together with a positive electrode that is a positive electrode for a secondary battery, and various studies have been made on the configuration of the secondary battery.

[0003] Specifically, in a lithium-ion secondary battery, olivine iron as a positive electrode active material and acrylonitrile as a positive electrode binder are used, and the particle diameter of the positive electrode active material, the particle diameter and mixing amount of the positive electrode binder, and the positive electrode porosity are defined (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Although various studies have been made on the configuration of secondary batteries, the battery characteristics of the secondary batteries are not yet sufficient, so there is room for improvement.

[0006] A positive electrode for a secondary battery and a secondary battery capable of obtaining excellent battery characteristics are desired.

Means for Solving the Problems

[0007] The positive electrode for a secondary battery according to an embodiment of the present technology includes a positive electrode active material layer. The positive electrode active material layer contains a plurality of positive electrode active material particles, and each of the plurality of positive electrode active material particles includes a central portion containing an olivine-type phosphate compound and a coating portion provided on the surface of the central portion. The olivine-type phosphate compound contains manganese and iron as constituent elements, and when the sum of the content of manganese in the olivine-type phosphate compound and the content of iron in the olivine-type phosphate compound is 100 mol parts, the content of manganese in the olivine-type phosphate compound is 50 mol parts or more and 90 mol parts or less. The central portion is secondary particles formed by granulating a plurality of primary particles, the first median diameter of the plurality of primary particles is 0.01 μm or more and 0.5 μm or less, and the second median diameter of the plurality of secondary particles is 1 μm or more and 20 μm or less. The coating portion contains a nitrile group. The porosity of the positive electrode active material layer is 20% or more and 40% or less.

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

Advantages of the Invention

[0009] According to the positive electrode for a secondary battery or the secondary battery according to an embodiment of the present technology, each of the plurality of positive electrode active material particles includes a central portion and a coating portion, the central portion contains an olivine-type phosphate compound, the content of manganese in the olivine-type phosphate compound is 50 mol parts or more and 90 mol parts or less, the first median diameter is 0.01 μm or more and 0.5 μm or less, the second median diameter is 1 μm or more and 20 μm or less, the coating portion contains a nitrile group, and the porosity of the positive electrode active material layer is 20% or more and 40% or less. Therefore, excellent battery characteristics can be obtained.

[0010] Note that the effects of the present technology are not necessarily limited to the effects described here, and may be any of a series of effects related to the present technology described later.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0012] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The order of description is as follows. 1. Positive electrode for secondary battery 1-1. Structure 1-2. Operation 1-3. Manufacturing method 1-4. Action and effect 2. Secondary battery 2-1. Structure 2-2. Operation 2-3. Manufacturing method 2-4. Action and effect 3. Modification example 4. Applications of secondary batteries

[0013] <1. Positive electrode for secondary battery> First, the positive electrode for a secondary battery (hereinafter simply referred to as "positive electrode") according to an embodiment of the present technology will be described.

[0014] The positive electrode described herein is used in a secondary battery, which is an electrochemical device. However, the positive electrode may be used in other electrochemical devices other than secondary batteries. The types of other electrochemical devices are not particularly limited, but specifically include primary batteries and capacitors, etc.

[0015] This positive electrode stores and releases electrode reactants during the operation of the electrochemical device, in other words, during the electrode reaction of the positive electrode. The types of electrode reactants are not particularly limited, but specifically include light metals such as alkali metals and alkaline earth metals. Specific examples of alkali metals include lithium, sodium, potassium, etc., and specific examples of alkaline earth metals include beryllium, magnesium, calcium, etc.

[0016] Hereinafter, the case where the electrode reactant is lithium will be taken as an example. Accordingly, in the positive electrode, lithium is stored and released in an ionic state during the electrode reaction.

[0017] <1-1. Configuration> FIG. 1 shows a cross-sectional configuration of a positive electrode 100, which is an example of the positive electrode in an embodiment of the present technology. FIG. 2 shows a cross-sectional configuration of the positive electrode active material particles 110. FIG. 3 shows another cross-sectional configuration of the positive electrode 1000.

[0018] As shown in FIG. 1, this positive electrode 100 includes a positive electrode active material layer 100B. Here, the positive electrode 100 further includes a positive electrode current collector 100A that supports the positive electrode active material layer 100B. However, the positive electrode current collector 100A may be omitted.

[0019] [Positive Electrode Current Collector] As shown in FIG. 1, the positive electrode current collector 100A is a conductive member that supports the positive electrode active material layer 100B. Here, the positive electrode current collector 100A has a pair of surfaces on which the positive electrode active material layer 100B is provided. This positive electrode current collector 100A contains a conductive material such as a metal material, and specific examples of the conductive material include aluminum, etc.

[0020] [Positive Electrode Active Material Layer] Here, as shown in FIG. 1, the positive electrode active material layer 100B is provided on one side of the positive electrode current collector 100A. However, the positive electrode active material layer 100B may be provided on both sides of the positive electrode current collector 100A.

[0021] This positive electrode active material layer 100B contains a positive electrode active material. However, the positive electrode active material layer 100B may further contain any one or two or more of other materials such as a positive electrode binder and a positive electrode conductive agent.

[0022] (Positive electrode active material) Specifically, as shown in FIG. 2, the positive electrode active material layer 100B contains a plurality of positive electrode active material particles 110 which are a plurality of particulate positive electrode active materials that occlude and release lithium. Each of the plurality of positive electrode active material particles 100 includes a central portion 110X and a coating portion 110Y.

[0023] However, in FIG. 2, only one of the plurality of positive electrode active material particles 110 is shown, and the cross-sectional shape of the positive electrode active material particle 100 is made circular in order to simplify the illustration.

[0024] (Central portion) The central portion 110X is a portion that occludes and releases lithium, and contains any one or two or more of olivine-type phosphates. This olivine-type phosphate compound is a phosphate compound having an olivine-type crystal structure.

[0025] The reason why the central portion 110X contains an olivine-type phosphate compound is that since the crystal structure of the olivine-type phosphate compound is strong and stable, the release of oxygen from the olivine-type phosphate compound during the electrode reaction is suppressed. As a result, lithium is stably occluded and released in the central portion 110X, so that the electrode reaction proceeds stably. Therefore, in the secondary battery provided with the positive electrode 100, a stable battery capacity can be obtained and the safety is improved.

[0026] Here, as described above, since the electrode reactant is lithium, the olivine-type phosphate compound contains lithium as a constituent element together with phosphorus and oxygen. In this case, the olivine-type phosphate compound further contains manganese and iron as constituent elements.

[0027] The content of manganese in the olivine-type phosphate compound is within a predetermined range. Specifically, when the sum of the content of manganese in the olivine-type phosphate compound and the content of iron in the olivine-type phosphate compound is 100 mole parts, the content of manganese in the olivine-type phosphate compound is 50 to 90 mole parts. This is because the electronic conductivity of the olivine-type phosphate compound is improved. As a result, both the improvement of the electronic conductivity of the plurality of positive electrode active material particles 110 and the stabilization of the operating potential and battery capacity in the secondary battery using the positive electrode 100 are achieved.

[0028] More specifically, the olivine-type phosphate compound contains any one or two or more of the compounds represented by the formula (1).

[0029] LiMn x Fe 1-x PO4···(1) (x satisfies 0.5 to 0.9.)

[0030] Specific examples of the olivine-type phosphate compound are LiMn 0.5 Fe 0.5 PO4, LiMn 0.7 Fe 0.3 PO4, and LiMn 0.9 Fe 0.1 PO4 and the like.

[0031] In addition, in order to confirm whether the central portion 110X contains an olivine-type phosphate compound, the central portion 110X is analyzed using an analysis method such as X-ray diffraction method (XDR). Further, in order to confirm whether the olivine-type phosphate compound contains manganese and iron as constituent elements, the central portion 110X is analyzed using an analysis method such as inductively coupled plasma (ICP) emission spectroscopic analysis method.

[0032] (Median diameter) In particular, the central portion 110X is a granulated body, and more specifically, it is a secondary particle formed by granulating a plurality of primary particles. Here, since the plurality of primary particles are aggregated with each other, the secondary particle that is the central portion 110X is an aggregate of the plurality of primary particles.

[0033] As described above, the positive electrode active material layer 100B contains a plurality of positive electrode active material particles 110. Therefore, the positive electrode active material layer 100B contains a plurality of central portions 110X.

[0034] The reason why the central portion 110X is a granulated body is that the conductivity of the positive electrode active material layer 100B is improved.

[0035] Specifically, the olivine-type phosphate compound essentially has low electron conductivity. Therefore, in order to improve the conductivity of the olivine-type phosphate compound, it is preferable that the olivine-type phosphate compound has a plurality of minute particle structures. Thus, it is preferable to use, as secondary particles, granulated bodies of the plurality of primary particles by granulating the plurality of primary particles.

[0036] As a result, the plurality of secondary particles are likely to come into contact with each other, so that the electron conductivity between the plurality of secondary particles is improved, and the plurality of primary particles are likely to come into contact with each other, so that the electron conductivity between the primary particles is also improved. Therefore, the conductivity is improved inside the positive electrode active material particles 110, and the conductivity between the plurality of positive electrode active material particles 110 is also improved, so that the conductivity of the positive electrode active material layer 100B is improved.

[0037] Specifically, the median diameter MD1, which is the first median diameter of the plurality of primary particles, is 0.01 μm to 0.5 μm. This is because the plurality of primary particles are likely to come into contact with each other, so that the electron conductivity between the plurality of primary particles is improved.

[0038] Among them, the median diameter MD1 is preferably 0.1 μm to 0.3 m. This is because when a plurality of primary particles are more likely to come into contact with each other, the electron conductivity between the plurality of primary particles is further improved.

[0039] Also, the median diameter MD2, which is the second median diameter of a plurality of secondary particles, is 1 μm to 20 μm. This is because when a plurality of secondary particles are more likely to come into contact with each other, the electron conductivity between the plurality of secondary particles is improved.

[0040] Among them, the median diameter MD2 is 5 μm to 15 μm. This is because when a plurality of secondary particles are more likely to come into contact with each other, the electron conductivity between the plurality of secondary particles is further improved.

[0041] The procedure for measuring the median diameter MD2 is as described below. Here, a case where the positive electrode active material layer 100B contains a plurality of positive electrode active material particles 110, a positive electrode binder, and a positive electrode conductive agent will be described.

[0042] To measure the median diameter MD2, a plurality of positive electrode active material particles 110 are analyzed using a particle size measuring device. As this particle size measuring device, it is possible to use a laser diffraction / scattering type particle size distribution measuring device LA-960 manufactured by Horiba, Ltd.

[0043] More specifically, when measuring the median diameter MD2, first, after putting the positive electrode 100 into a solvent, the solvent is stirred to peel the positive electrode active material layer 100B from the positive electrode current collector 100A. The type of the solvent is not particularly limited as long as it can dissolve the positive electrode binder. As a result, since the positive electrode binder is dissolved and removed, a plurality of positive electrode active material particles 110 and the positive electrode conductive agent, which are solid components, are recovered.

[0044] Subsequently, after introducing the solid content into the solvent, the solid content in the solvent is centrifuged using a centrifuge. The type of the solvent is not particularly limited as long as it can disperse the plurality of positive electrode active material particles 110 and the positive electrode conductive agent. As a result, since the plurality of positive electrode active material particles 110 are separated from the positive electrode conductive agent, the plurality of positive electrode active material particles 110 are recovered.

[0045] Finally, the median diameter MD2 is measured by analyzing the plurality of positive electrode active material particles 110 using a particle size measuring device.

[0046] The procedure for measuring the median diameter MD1 is as described below.

[0047] First, the positive electrode 100 is cut using a cutting instrument such as a microtome to expose the cross-section of the positive electrode active material layer 100B.

[0048] Subsequently, the cross-section of the positive electrode active material layer 100B is observed (observation magnification = 10,000 times) using a scanning electron microscope (SEM). As a result, since the plurality of positive electrode active material particles 110 contained in the positive electrode active material layer 100B are observed, the plurality of primary particles forming each of the plurality of secondary particles which are the plurality of central portions 110X are observed.

[0049] Subsequently, after selecting any 50 primary particles from among the plurality of primary particles that allow the entire contour (outer edge) to be observed, the particle size of each of the 50 primary particles is measured. This particle size is the diameter of the major axis (the maximum value of the diameter in the direction of the major axis) when the primary particle includes a major axis and a minor axis. Finally, the median diameter MD1 is obtained by calculating the average value of the 50 particle sizes.

[0050] (Coating portion) Since the coating portion 110Y is provided on the surface of the central portion 110X, it is a portion that protects the surface of the central portion 110X.

[0051] This coating portion 110Y may be provided over the entire surface of the central portion 110X, or may be provided only on a part of the surface of the central portion 110Y. When the coating portion 110Y is provided only on a part of the surface of the central portion 110Y, a plurality of coating portions 110Y spaced apart from each other may be provided on the surface of the central portion 110X.

[0052] In particular, the coating portion 110Y contains a nitrile group. The number of nitrile groups is not particularly limited, and thus may be only one or two or more.

[0053] Specifically, as will be described later, in the step of forming the positive electrode active material layer 100B, a part of the positive electrode binder containing a nitrile group adheres to the surface of the central portion 110X, and thus the coating portion 110Y is formed using a part of the positive electrode binder. In this case, since the positive electrode binder and the central portion 110X are mixed with each other, the positive electrode binder does not exist near the central portion 110X. On the other hand, due to the step of forming the positive electrode active material layer 100B, a part of the positive electrode binder preferentially adheres to the surface of the central portion 110X, and thus the coating portion 110Y is formed using the preferential adhesion of a part of the positive electrode binder.

[0054] Details of the procedure for forming the coating portion 110Y using the step of forming the positive electrode active material layer 100B will be described later.

[0055] As described above, since this coating portion 110Y is formed using a positive electrode binder, the configuration of the coating portion 110Y is the same as that of the positive electrode binder. Specifically, since the coating portion 110Y contains a nitrile group, it contains any one or two or more of nitrile group-containing polymer compounds that are polymer compounds containing a nitrile group. This nitrile group-containing polymer compound may be a homopolymer obtained by polymerizing one type of monomer, a copolymer obtained by polymerizing two or more types of monomers, or both.

[0056] Specific examples of the homopolymer include polyacrylonitrile and the like. Specific examples of the copolymer include acrylonitrile-butadiene copolymer, acrylonitrile-ethylhexyl acrylate copolymer, and the like.

[0057] A coating portion 110Y is provided on the surface of the central portion 110X. The reason why the coating portion 110Y contains a nitrile group is that the surface of the highly reactive central portion 110X is electrochemically protected by using the coating portion 110Y. Thereby, even when using the central portion 110X having high reactivity, the occurrence of side reactions on the surface of the central portion 110X during the electrode reaction is suppressed. In this case, in particular, in a secondary battery using the positive electrode 100, the occurrence of the decomposition reaction of the electrolytic solution during charge and discharge is suppressed.

[0058] (Procedure for confirming the coating portion) The procedure for confirming that the coating portion 110Y is provided on the surface of the central portion 110X is as described below.

[0059] First, by cutting the positive electrode 100 by ion milling, the cross section of the positive electrode active material layer 100B is exposed.

[0060] Subsequently, by performing negative ion analysis on the cross section of the positive electrode active material layer 100B using time-of-flight secondary ion mass spectrometry (TOF-SIMS), a first mapping based on oxygen ions (O - ) and a second mapping based on nitrile ions (CN - ) are obtained.

[0061] The first mapping is the result of two-dimensionally displaying the detection amount of oxygen ions, and the existence range of the oxygen ions is displayed in color. This first mapping is used to specify the existence range of the central portion 110X containing the olivine-type phosphate compound by specifying the existence range of the olivine-type phosphate compound containing oxygen as a constituent element.

[0062] The second mapping is the result of two-dimensionally displaying the value obtained by excluding the detected amount of nitrile ions from the detected amounts of all ions, and the range where the nitrile ions are present is displayed in color. This second mapping is used to identify the range where the coating portion 110Y containing the nitrile group-containing polymer compound is present by identifying the range where the nitrile group-containing polymer compound containing a nitrile group is present.

[0063] In the second mapping, the reason for using the value obtained by excluding the detected amount of nitrile ions from the detected amounts of all ions without using the detected amount of nitrile ions is to eliminate the gradient of the detected amount of ions caused by the inclination of the sample.

[0064] In this case, as the analyzer, the time-of-flight secondary ion mass spectrometer "TOF-SIMS5" manufactured by IONTOF is used. Regarding the analysis conditions, the primary ion is Bi 3+ and the acceleration voltage of the ion gun is 25 keV, the analysis mode is Burst Alignment, the current of the irradiated ions (measurement with a pulsed beam) is 0.03 pA, the pulse frequency is 10 kHz, the mass range is 1 amu to 80 amu, and the scanning range is 130 μm × 130 μm. Also, before measurement, the measurement location is sputtered with Ar + ions or the like.

[0065] Subsequently, based on the first mapping, the range where the central portion 110X is present is identified. In this first mapping, the range where the central portion 110X is present is the range defined by the outer edge of a substantially spherical shape.

[0066] Subsequently, based on the second mapping, the range where the coating portion 110Y is present is identified. In this second mapping, the range where the coating portion 110Y is present is the range defined by the outer edge of a substantially ring shape or a substantially arc shape.

[0067] Of course, when the coating portion 110Y is not formed, the range where the coating portion 110Y is present is not identified in the second mapping, so the range where the coating portion 110Y is present is not visually recognized.

[0068] Finally, based on the first mapping and the second mapping, it is confirmed whether the coating portion 110Y exists on the surface of the central portion 110X.

[0069] Specifically, the existence range of the central portion 110X specified in the first mapping is compared with the existence range of the coating portion 110Y specified in the second mapping. As a result, when the existence range of the central portion 110X and the existence range of the coating portion 110Y are in contact with each other, it is determined that the coating portion 110Y is provided on the surface of the central portion 110X.

[0070] On the other hand, as a result of comparing the existence range of the central portion 110X specified in the first mapping with the existence range of the coating portion 110Y specified in the second mapping, when the existence range of the central portion 110X and the existence range of the coating portion 110Y are not in contact with each other, it is determined that the coating portion 110Y is not provided on the surface of the central portion 110X.

[0071] Here, the number of times of confirming that the coating portion 110Y is provided on the surface of the central portion 110X is not particularly limited, so it may be only once or two or more times. If the number of times is two or more, the accuracy in confirming that the coating portion 110Y is provided on the surface of the central portion 110X is improved as compared with the case where the number of times is only once.

[0072] However, as described above, since the coating portion 110Y is formed due to the formation process of the characteristic positive electrode active material layer 100B described later, it cannot be formed without using the formation process of the characteristic positive electrode active material layer 100B. For this reason, even if the number of times of confirming that the coating portion 110Y is provided on the surface of the central portion 110X is only once, the accuracy in confirming that the coating portion 110Y is provided on the surface of the central portion 110X is ensured.

[0073] (Total formation amount ratio of coating portion) Here, as described above, in the step of forming the positive electrode active material layer 100B, a coating portion 110Y is formed by a part of the positive electrode binder preferentially adhering to the surface of the central portion 110X. As a result, the formation amount of the coating portion 110Y on the surface of the central portion 110X is less likely to be unevenly distributed inside the positive electrode active material layer 100B, so that it is likely to be evenly distributed inside the positive electrode active material layer 100B.

[0074] Specifically, since the positive electrode 100 includes the positive electrode current collector 100A, when the positive electrode active material layer 100B is supported by the positive electrode current collector 100A, as shown in FIG. 3, the positive electrode active material layer 100B is divided with reference to the position of the positive electrode current collector 100A.

[0075] In this case, in the direction in which the positive electrode current collector 100A and the positive electrode active material layer 100B face each other, that is, in the thickness direction of the positive electrode active material layer 100B (the vertical direction in FIG. 3), the positive electrode active material layer 100B is bisected. As a result, the positive electrode active material layer 100B is divided into a lower positive electrode active material layer 100B1 that is the first positive electrode active material layer and an upper positive electrode active material layer 100B2 that is the second positive electrode active material layer. The lower positive electrode active material layer 100B1 is a portion located closer to the positive electrode current collector 100A than the upper positive electrode active material layer 100B2, and the upper positive electrode active material layer 100B2 is a portion located farther from the positive electrode current collector 100A than the lower positive electrode active material layer 100B1.

[0076] Here, consider the total formation amount R1 of the plurality of coating portions 110Y inside the lower positive electrode active material layer 100B1 and the total formation amount R2 of the plurality of coating portions 110Y inside the upper positive electrode active material layer 100B2.

[0077] As a result, the total formation amount ratio R, which is the ratio of the total formation amount R2 to the total formation amount R1, is not particularly limited, but preferably is 0.6 to 1.4. This is because the distribution of the plurality of coating portions 110Y is substantially uniform inside the positive electrode active material layer 100B, so that lithium is likely to be occluded and released substantially uniformly.

[0078] Specifically, when the total formation ratio R is less than 0.6 and when the total formation ratio R is greater than 1.4, the value of the total formation ratio R deviates significantly from 1.0. In this case, since the difference between the total formation amounts R1 and R2 becomes large, segregation of the coating portion 110Y is likely to occur inside the positive electrode active material layer 100B. As a result, the abundance of the plurality of coating portions 110Y becomes non-uniform inside the positive electrode active material layer 100B, making it difficult for the electrode reaction to proceed uniformly.

[0079] On the other hand, when the total formation ratio R is between 0.6 and 1.4, the value of the total formation ratio R approaches 1.0. In this case, since the difference between the total formation amounts R1 and R2 becomes small, segregation of the coating portion 110Y is less likely to occur inside the positive electrode active material layer 100B. As a result, the abundance of the coating portion 110Y becomes almost uniform inside the positive electrode active material layer 100B, making it easier for the electrode reaction to proceed uniformly.

[0080] The procedure for calculating this total formation ratio R is as described below.

[0081] First, by analyzing the cross-section of the lower positive electrode active material layer 100B1 using TOF-SIMS, mapping based on nitrile ions is obtained, and the total formation amount R1 is measured based on this mapping.

[0082] Subsequently, by analyzing the cross-section of the upper positive electrode active material layer 100B2 using TOF-SIMS, mapping based on nitrile ions is obtained, and the total formation amount R2 is measured based on this mapping.

[0083] The details of the analyzer and analysis conditions during the analysis using TOF-SIMS are as described above.

[0084] Finally, the total formation ratio R is calculated based on the formula: total formation ratio R (%) = (total formation amount R2 / total formation amount R1) × 100.

[0085] (Porosity) The positive electrode active material layer 100B has a plurality of voids. These plurality of voids are spaces within the positive electrode active material layer 100B where components such as a plurality of positive electrode active material particles 110 do not exist.

[0086] The porosity P of the positive electrode active material layer 100B is 20% to 40%. This is because the flexibility of the positive electrode 100 is improved, and thus damage to the positive electrode 100 during the electrode reaction is suppressed. Specific examples of damage to the positive electrode 100 include the occurrence of cracks. In addition, in a secondary battery using the positive electrode 100, since the amount of a plurality of voids in the positive electrode active material layer 100B is ensured, the impregnation property of the electrolyte solution with respect to the positive electrode active material layer 100B is ensured.

[0087] Among them, the porosity P is preferably 25% to 35%. This is because the flexibility of the positive electrode 100 is further improved, and thus damage to the positive electrode 100 during the electrode reaction is further suppressed.

[0088] When measuring the porosity P, the positive electrode 100 is analyzed using the mercury intrusion method. In this case, a mercury porosimeter AutoPore 9500 series manufactured by Micromeritics is used as the analysis device. The analysis conditions are such that the surface tension of mercury = 485 mN / m, the contact angle = 130°, and the relationship between the pore diameter and pressure of a plurality of voids is approximated by 180 / pressure = pore diameter.

[0089] (Positive electrode binder) The positive electrode binder is a material that binds particles such as a plurality of positive electrode active material particles to each other. Also, as described above, the positive electrode binder is a material for forming the coating portion 110Y in the formation process of the positive electrode active material layer 100B.

[0090] As described above, this positive electrode binder contains any one or two or more of nitrile group-containing polymer compounds. The details regarding the nitrile group-containing polymer compounds are as described above.

[0091] Here, even after the formation of the positive electrode active material layer 100B, that is, after the formation of the coating portion 110Y, the positive electrode active material layer 100B contains a nitrile group-containing polymer compound that is a positive electrode binder. Thereby, in the formation process of the positive electrode active material layer 100B, a part of the positive electrode binder is consumed to form the coating portion 110Y, but the rest of the positive electrode binder remains in the positive electrode active material layer 100B, so the rest of the positive electrode binder performs its original binding function.

[0092] However, the positive electrode binder may further contain any one or two or more of other materials. The other materials include any one or two or more of materials such as synthetic rubber and polymer compounds, and the nitrile group-containing polymer compound is excluded from the polymer compounds described here. Specific examples of the synthetic rubber are styrene-butadiene rubber, fluorine rubber, and ethylene propylene diene, etc. Specific examples of the polymer compound are polyvinylidene fluoride, polyimide, and carboxymethyl cellulose, etc.

[0093] (Positive electrode conductive agent) The positive electrode conductive agent is a material that improves the conductivity of the positive electrode active material layer 100B, and contains any one or two or more of conductive materials such as carbon materials, metal materials, and conductive polymer compounds. Specific examples of the carbon material are graphite, carbon black, acetylene black, and ketjen black, etc.

[0094] <1-2. Operation> In this positive electrode 100, during the electrode reaction, lithium is released from the positive electrode active material layer 100B in an ionic state, and at the same time, lithium is occluded in the positive electrode active material layer 100B in an ionic state.

[0095] <1-3. Manufacturing method> This positive electrode 100 is manufactured using the procedure of an example described below.

[0096] First, prepare a plurality of primary particles containing an olivine-type phosphate compound. In this case, adjust the median diameter MD1 so as to be within the above-described range.

[0097] Subsequently, granulate the plurality of primary particles to form a plurality of secondary particles. As a result, a plurality of central portions 110X which are a plurality of secondary particles containing an olivine-type phosphate compound are obtained. Adjust the median diameter MD2 so as to be within the above-described range. The granulation is performed, for example, by spray drying. For example, a spray drying apparatus "MDP-050" manufactured by GF Corporation can be used. However, the granulation method is not particularly limited.

[0098] Subsequently, prepare a dispersion liquid by adding a dispersant (carboxymethyl cellulose) to a solvent (aqueous solvent). The type of the aqueous solvent is not particularly limited, but specifically, it is pure water or the like. The concentration of the dispersant is not particularly limited, but specifically, it can be 1.3% with respect to 100% of the positive electrode active material.

[0099] Subsequently, pre-treat the plurality of central portions 110X using the dispersion liquid by adding the plurality of central portions 110X to the dispersion liquid. In this case, the dispersion liquid into which the plurality of central portions 110X are added may be stirred.

[0100] By this pre-treatment, the dispersant preferentially adheres to each of the plurality of central portions 110X, and thus a base film containing the dispersant is formed on the surface of each of the plurality of central portions 110X. This base film is a film to which a part of the positive electrode binder preferentially adheres in a subsequent process, and the thickness of the base film is extremely thin.

[0101] Subsequently, obtain a positive electrode mixture by mixing the plurality of pre-treated central portions 110X, a positive electrode binder containing a nitrile group-containing polymer compound, and a positive electrode conductive agent with each other.

[0102] Subsequently, prepare a positive electrode mixture slurry by adding the positive electrode mixture to a solvent (aqueous solvent).

[0103] In this case, since the base film is formed on the surface of the central portion 110X, a part of the positive electrode binder preferentially adheres to the surface of the central portion 110X. As a result, a nitrile-containing polymer compound forms a film on the surface of the central portion 110X, and thus a coating portion 110Y is formed on the surface of the central portion 110X. This coating portion 110Y contains a nitrile group derived from the nitrile-containing polymer compound. Thereby, a plurality of positive electrode active material particles 110 including the central portion 110X and the coating portion 110Y are formed.

[0104] Note that, as described above, the thickness of the base film is extremely thin, and the base film has extremely high reactivity with the nitrile group-containing polymer compound. Therefore, it is difficult to directly confirm the presence of the base film after the formation of the coating portion 110Y.

[0105] However, as described in the procedure for confirming that the coating portion 110Y is provided on the surface of the central portion 110X described above, the coating portion 110Y is not formed without using the base film. Therefore, the fact that the coating portion 110Y is formed on the surface of the central portion 110X means that the base film was formed on the surface of the central portion 110Y. Thus, based on the fact that the coating portion 110Y is formed on the surface of the central portion 110X, it is possible to indirectly confirm the presence of the base film.

[0106] Specifically, in the step of forming the positive electrode active material layer 100B, even when a positive electrode binder containing a nitrile group-containing polymer compound is used, if the pretreatment of a plurality of central portions 110X using a dispersion liquid containing a dispersant is not performed, the base film is not formed on the surface of each of the plurality of central portions 110X.

[0107] In this case, although the nitrile group-containing polymer compound may happen to approach the surface of the central portion 110X, the nitrile group-containing polymer compound does not form a film while preferentially adhering to the surface of the central portion 110X. As a result, when checking whether the coating portion 110Y is provided on the surface of the central portion 110X, since the existence range of the central portion 110X and the existence range of the coating portion 110Y do not touch each other, it is determined that the coating portion 110Y is not provided on the surface of the central portion 110X.

[0108] On the other hand, in the step of forming the positive electrode active material layer 100B, when a positive electrode binder containing a nitrile group-containing polymer compound is used and a pretreatment of a plurality of central portions 110X is performed using a dispersion liquid containing a dispersant, a base film is formed on the surface of each of the plurality of central portions 110X.

[0109] In this case, the nitrile group-containing polymer compound does not happen to approach the surface of the central portion 110X, and the nitrile group-containing polymer compound forms a film while preferentially adhering to the surface of the central portion 110X. As a result, when checking whether the coating portion 110Y is provided on the surface of the central portion 110X, since the existence range of the central portion 110X and the existence range of the coating portion 110Y touch each other, it is determined that the coating portion 110Y is provided on the surface of the central portion 110X.

[0110] Subsequently, the positive electrode active material layer 100B is formed by applying a positive electrode mixture slurry on one side of the positive electrode current collector 100A.

[0111] Finally, the positive electrode active material layer 100B is compression-molded using a compression device such as a roll press. In this case, the positive electrode active material layer 100B may be heated, or the compression molding may be repeated a plurality of times. Further, the compression conditions such as the press pressure and the press time are adjusted so that the porosity P is within the above-described range.

[0112] As a result, since the positive electrode active material layer 100B is formed on one side of the positive electrode current collector 100A, the positive electrode 100 is completed.

[0113] <1-4. Function and Effect> According to this positive electrode 100, each of the plurality of positive electrode active material particles 110 includes a central portion 110X and a coating portion 110. The central portion 110X contains an olivine-type phosphate compound. The manganese content in the olivine-type phosphate compound is 50 to 90 mol parts. The central portion 110X is a granulated body, the median diameter MD1 is 0.01 μm to 0.5 μm, the median diameter MD2 is 1 μm to 20 μm, the coating portion 110Y contains a nitrile group, and the porosity P is 20% to 40%.

[0114] In this case, as described above, a series of operations described below can be obtained.

[0115] First, the central portion 110X contains an olivine-type phosphate compound. In this case, the release of oxygen from the central portion 110X during the electrode reaction is suppressed. As a result, lithium is stably occluded and released in the positive electrode active material layer 100B, so that the electrode reaction proceeds stably.

[0116] Second, the central portion 110X is a granulated body, the median diameter MD1 is 0.01 μm to 0.5 μm, and the median diameter MD2 is 1 μm to 20 μm. In this case, since the plurality of primary particles are likely to contact each other, the electron conductivity between the plurality of primary particles is improved. Also, since the plurality of secondary particles are likely to contact each other, the electron conductivity between the plurality of secondary particles is improved. Thereby, even when using an olivine-type phosphate compound having inherently low electron conductivity, the conductivity of the positive electrode active material layer 100B is improved.

[0117] Third, the coating portion 110Y contains a nitrile group. As a result, the surface of the central portion 110X having high reactivity is electrochemically protected by using the coating portion 110Y. Therefore, even when using the central portion 110X having high reactivity, the occurrence of side reactions on the surface of the central portion 110X during the electrode reaction is suppressed.

[0118] Fourth, the porosity P is 20% to 40%. In this case, the impregnation property of the electrolytic solution with respect to the positive electrode active material layer 100B is ensured, and the flexibility of the positive electrode 100 is improved. Thereby, a stable electrode reaction is ensured, and breakage of the positive electrode 100 during the electrode reaction is suppressed.

[0119] From these facts, in the secondary battery including the positive electrode 100, while ensuring the stable progress of the electrode reaction, the physical durability of the positive electrode 100 is improved, and the operation stability of the secondary battery is improved, so that excellent battery characteristics can be obtained.

[0120] In particular, if the median diameter MD1 is 0.1 μm to 0.3 μm, the median diameter MD2 is 5 μm to 15 μm, and the porosity P is 25% to 35%, the conductivity of the positive electrode active material layer 100B is further improved, and while the impregnation property of the electrolytic solution with respect to the positive electrode active material layer 100B is ensured, the flexibility of the positive electrode 100 is further improved, so that a higher effect can be obtained.

[0121] Further, if the positive electrode active material layer 100B is a positive electrode binder and the positive electrode binder contains a nitrile group, it becomes easier to form the coating portion 110Y using the positive electrode binder, so that a higher effect can be obtained. In this case, if the positive electrode binder contains polyacrylonitrile, the coating portion 110Y is more likely to be sufficiently formed, so that an even higher effect can be obtained.

[0122] Further, if the total formation ratio R is 0.6 to 1.4, the distribution of the plurality of coating portions 110Y inside the positive electrode active material layer 100B becomes substantially uniform, so that segregation of the coating portion 110Y is less likely to occur. Therefore, lithium is likely to be occluded and released substantially uniformly inside the positive electrode active material layer 100B, so that a higher effect can be obtained.

[0123] <2. Secondary Battery> Next, a secondary battery according to an embodiment of the present technology to which the positive electrode 100 is applied will be described.

[0124] The secondary battery described herein is a secondary battery that obtains battery capacity by utilizing the occlusion and release of electrode reactants, and includes an electrolytic solution together with a positive electrode and a negative electrode. Hereinafter, as described above, the case where the electrode reactant is lithium will be taken as an example. A secondary battery that obtains battery capacity by utilizing the occlusion and release of lithium is a so-called lithium secondary battery (or lithium ion secondary battery). In this lithium ion secondary battery, lithium is occluded and released in an ionic state.

[0125] Note that the charging capacity of the negative electrode is preferably larger than the discharging 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 depositing on the surface of the negative electrode during charging.

[0126] <2-1. Configuration> FIG. 4 shows a cross-sectional configuration of a secondary battery that is an example of the secondary battery according to an embodiment of the present technology. FIG. 5 shows a cross-sectional configuration of the battery element 20 shown in FIG. 4.

[0127] As shown in FIGS. 4 and 5, 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 herein is a cylindrical secondary battery in which the battery element 20 is housed in a cylindrical battery can 11.

[0128] [Battery Can] The battery can 11 is a member that houses the battery element 20 and the like. Since this battery can 11 has an open end portion and a closed other end portion, it has a hollow structure. Further, the battery can 11 contains any one or two or more of metal materials such as iron, aluminum, iron alloy, and aluminum alloy. Note that the surface of the battery can 11 may be plated with a metal material such as nickel.

[0129] At one open end of the battery can 11, a battery lid 14, a safety valve mechanism 15, and a PTC element 16 which is a thermal resistance element are clamped via a gasket 17. Thereby, the battery can 11 is sealed by the battery lid 14. Here, the battery lid 14 contains the same material as the forming material of the battery can 11. The safety valve mechanism 15 and the PTC element 16 are provided 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 asphalt or the like may be applied to the surface of the gasket 17.

[0130] In the safety valve mechanism 15, when the internal pressure of the battery can 11 reaches a certain level or more due to factors such as internal short circuit and external heating, the disk plate 15A is inverted, so the electrical connection between the battery lid 14 and the battery element 20 is disconnected. In order to prevent abnormal heat generation caused by a large current, the electrical resistance of the PTC element 16 increases in response to an increase in temperature.

[0131] [Insulating plate] The insulating plates 12, 13 are arranged so as to face each other via the battery element 20. Thereby, the battery element 20 is sandwiched between the insulating plates 12, 13.

[0132] [Battery element] The battery element 20 is a so-called power generation element and includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolytic solution (not shown).

[0133] Since this battery element 20 is a so-called wound electrode body, the positive electrode 21 and the negative electrode 22 are wound while facing each other via the separator 23. A center pin 24 is inserted into a space 20S provided at the winding center of the battery element 20. However, the center pin 24 may be omitted.

[0134] (Positive electrode) The positive electrode 21 has the same configuration as the configuration of the positive electrode 100.

[0135] Specifically, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B. The configuration of the positive electrode current collector 21A is the same as that of the positive electrode current collector 100A, and the configuration of the positive electrode active material layer 21B is the same as that of the positive electrode active material layer 100B. 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 only on one side of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22.

[0136] (Negative electrode) The negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

[0137] The negative electrode current collector 22A has a pair of surfaces on which the negative electrode active material layer 22B is provided. The negative electrode current collector 22A contains a conductive material such as a metal material, and specific examples of the conductive material include copper and the like.

[0138] The negative electrode active material layer 22B contains any one or two or more of negative electrode active materials that occlude and release lithium. However, the negative electrode active material layer 22B may further contain any one or two or more of other materials such as a negative electrode binder and a negative electrode conductive agent. The method for forming the negative electrode active material layer 22B is not particularly limited, but specifically, it is any one or two or more of a coating method, a vapor phase method, a liquid phase method, a spraying method, and a firing method (sintering method).

[0139] Here, the negative electrode active material layer 22B is provided on both sides of the negative electrode current collector 22A. However, the negative electrode active material layer 22B may be provided only on one side of the negative electrode current collector 22A on the side where the negative electrode 22 faces the positive electrode 21.

[0140] The type of the negative electrode active material is not particularly limited, but specifically, it is a carbon material, a metal-based material, and the like. This is because a high energy density can be obtained.

[0141] Specific examples of the carbon material include graphitizable carbon, non-graphitizable carbon, and graphite. This graphite may be natural graphite or artificial graphite.

[0142] The metal-based material is a material containing, as constituent elements, any one or two or more of metal elements and metalloid elements that can form an alloy with lithium. Specific examples of the metal elements and metalloid elements include silicon and tin. This metal-based material may be a single substance, an alloy, a compound, a mixture of two or more of them, or a material containing two or more phases of them. However, since the single substance may contain any amount of impurities, the purity of the single substance is not necessarily limited to 100%. Specific examples of the metal-based material are TiSi2 and SiO x (0 < x ≤ 2 or 0.2 < x < 1.4), etc.

[0143] The negative electrode binder contains any one or two or more of materials such as synthetic rubber and polymer compounds. Specific examples of the synthetic rubber include styrene-butadiene rubber, fluorine rubber, and ethylene propylene diene. Specific examples of the polymer compound include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

[0144] The negative electrode conductive agent contains any one or two or more of conductive materials such as carbon materials, metal materials, and conductive polymer compounds. Specific examples of the carbon materials include graphite, carbon black, acetylene black, and ketjen black.

[0145] (Separator) The separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and allows lithium to pass in an ionic state while preventing a short circuit caused by contact between the positive electrode 21 and the negative electrode 22. This separator 23 contains a polymer compound such as polyethylene.

[0146] (Electrolyte) The electrolyte is a liquid electrolyte and is impregnated in each of the positive electrode 21, the negative electrode 22, and the separator 23. This electrolyte contains a solvent and an electrolyte salt.

[0147] The solvent contains any one or two or more of non-aqueous solvents (organic solvents), and the electrolyte containing the non-aqueous solvent is a so-called non-aqueous electrolyte.

[0148] These non-aqueous solvents are esters, ethers, etc. More specifically, they are carbonate-based compounds, carboxylic acid ester-based compounds, lactone-based compounds, etc. This is because the dissociation of the electrolyte salt and the mobility of ions are improved.

[0149] The carbonate-based compounds are cyclic carbonates and chain carbonates. Specific examples of the cyclic carbonate are ethylene carbonate, propylene carbonate, etc., and specific examples of the chain carbonate are dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc.

[0150] The carboxylic acid ester-based compounds are chain carboxylic acid esters, etc. Specific examples of the chain carboxylic acid ester are ethyl acetate, ethyl propionate, propyl propionate, ethyl trimethylacetate, etc.

[0151] The lactone-based compounds are lactones, etc. Specific examples of the lactone are γ-butyrolactone, γ-valerolactone, etc.

[0152] In addition, the ethers may be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, etc.

[0153] Also, the non-aqueous solvents are unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonic acid esters, phosphoric acid esters, acid anhydrides, nitrile compounds, isocyanate compounds, etc. This is because the electrochemical stability of the electrolyte is improved.

[0154] Specific examples of the unsaturated cyclic carbonate include vinylene carbonate, vinyl ethylene carbonate, and methylene ethylene carbonate. Specific examples of the fluorinated cyclic carbonate include ethylene monofluorocarbonate and ethylene difluorocarbonate. Specific examples of the sulfonic acid ester include propane sultone and propene sultone. Specific examples of the phosphate ester include trimethyl phosphate and triethyl phosphate. Specific examples of the acid anhydride include succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of the nitrile compound include succinonitrile. Specific examples of the isocyanate compound include hexamethylene diisocyanate.

[0155] The electrolyte salt contains any one or two or more of light metal salts such as lithium salts.

[0156] Specific examples of the lithium salt include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF3SO2)3), lithium bis(oxalato)borate (LiB(C2O4)2), lithium monofluorophosphate (Li2PFO3), and lithium difluorophosphate (LiPF2O2). This is because a high battery capacity can be obtained.

[0157] The content of the electrolyte salt is not particularly limited, but specifically, it is 0.3 mol / kg to 3.0 mol / kg with respect to the solvent. This is because high ionic conductivity can be obtained.

[0158] [Positive electrode lead and negative electrode lead] 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.

[0159] The negative electrode lead 26 is connected to the negative electrode current collector 22A and contains a conductive material such as nickel. This negative electrode lead 26 is electrically connected to the battery can 11.

[0160] <2-2. Operation> The secondary battery operates as follows during charge and discharge.

[0161] During charging, in the battery element 20, lithium is released from the positive electrode 21 and the lithium is occluded in the negative electrode 22 through the electrolyte. On the other hand, during discharging, in the battery element 20, lithium is released from the negative electrode 22 and the lithium is occluded in the positive electrode 21 through the electrolyte. During charging and discharging, lithium is occluded and released in an ionic state.

[0162] <2-3. Manufacturing method> When manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are produced using the procedure of an example described below, the electrolyte is prepared, and then the secondary battery is assembled and a stabilization treatment of the assembled secondary battery is performed.

[0163] [Production of positive electrode] The positive electrode 21 is produced by forming the positive electrode active material layer 21B on both sides of the positive electrode current collector 21A using the same procedure as the production procedure of the positive electrode 100 described above.

[0164] [Production of negative electrode] First, a paste-like negative electrode mixture slurry is prepared by introducing a mixture (negative electrode mixture) in which a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent are mixed with each other into a solvent. This solvent may be an aqueous solvent or an organic solvent. Subsequently, a negative electrode active material layer 22B is formed by applying the negative electrode mixture slurry to both surfaces of the negative electrode current collector 22A. Finally, the negative electrode active material layer 22B may be compression-molded using a compression device such as a roll press. In this case, the negative electrode active material layer 22B may be heated, or the compression molding may be repeated a plurality of times. Thereby, since the negative electrode active material layers 22B are formed on both surfaces of the negative electrode current collector 22A, the negative electrode 22 is produced.

[0165] [Preparation of Electrolyte Solution] An electrolyte salt is introduced into a solvent. Thereby, since the electrolyte salt is dispersed or dissolved in the solvent, the electrolyte solution is prepared.

[0166] [Assembly of Secondary Battery] 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 a welding method, 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 a welding method.

[0167] Subsequently, after laminating the positive electrode 21 and the negative electrode 22 with each other via the separator 23, a wound body (not shown) having a space 20S is produced by winding the positive electrode 21, the negative electrode 22, and the separator 23. This wound body has the same configuration as that of the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with the electrolyte solution. Subsequently, a center pin 24 is inserted into the space 20S of the wound body.

[0168] Subsequently, with the wound body sandwiched by the insulating plates 12 and 13, the wound body and the insulating plates 12 and 13 are housed in the battery can 11. In this case, the positive electrode lead 25 is connected to the safety valve mechanism 15 using a joining method such as a welding method, and the negative electrode lead 26 is connected to the battery can 11 using a joining method such as a welding method. Subsequently, an electrolytic solution is injected into the battery can 11 to impregnate the wound body with the electrolytic solution. As a result, since each of the positive electrode 21, the negative electrode 22, and the separator 23 is impregnated with the electrolytic solution, the battery element 20 is produced.

[0169] Finally, after housing the battery lid 14, the safety valve mechanism 15, and the PTC element 16 in the battery can 11, the battery can 11 is clamped via the gasket 17.

[0170] 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 enclosed in the battery can 11, so that the secondary battery is assembled.

[0171] [Stabilization treatment of the secondary battery after assembly] The assembled secondary battery is charged and discharged. The charge and discharge conditions such as the environmental temperature, the number of charge and discharge cycles, and the charge and discharge conditions can be arbitrarily set. As a result, a film is formed on the surfaces of the positive electrode 21 and the negative electrode 22, so that the state of the battery element 20 is electrochemically stabilized. Thus, the secondary battery is completed.

[0172] [2-4. Actions and effects] According to this secondary battery, the positive electrode 21 has the same configuration as that of the positive electrode 100. Therefore, for the reasons described above, while ensuring the stable progress of the charge and discharge reaction, the physical durability of the positive electrode 21 is improved and the operation stability of the secondary battery is improved, so that excellent battery characteristics can be obtained.

[0173] In particular, if the secondary battery is a lithium secondary battery, a sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium, so that a higher effect can be obtained.

[0174] Note that other operations and effects related to the secondary battery are the same as those related to the positive electrode 100.

[0175] <3. Modification Example> As described below, the configuration of the secondary battery described above can be appropriately changed. However, a series of modification examples described below may be combined with each other.

[0176] [Modification Example 1] In the step of forming the positive electrode active material layer 100B when the positive electrode binder contains a nitrile group-containing polymer compound, a part of the nitrile group-containing polymer compound is consumed to form the coating portion 110Y, but the rest of the nitrile group-containing polymer compound remains in the positive electrode active material layer 100B, so that the rest of the nitrile group-containing polymer compound functions as a binder.

[0177] However, in the step of forming the positive electrode active material layer 100B when the positive electrode binder contains other materials together with the nitrile group-containing polymer compound, all of the nitrile group-containing polymer compound is consumed to form the coating portion 110Y, so that the nitrile group-containing polymer compound does not have to remain in the positive electrode active material layer 100B. Even in this case, the coating portion 110Y is formed and other materials function as a binder, so that the same effect can be obtained.

[0178] [Modification Example 2] The separator 23 which is a porous membrane was used. However, although not specifically illustrated here, a laminated separator may be used.

[0179] Specifically, the laminated separator includes a porous membrane and a polymer compound layer. This porous membrane has a pair of surfaces, and the polymer compound layer is provided on one or both surfaces of the porous membrane. This is because the adhesion of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, and thus the winding displacement of each of the positive electrode 21, the negative electrode 22, and the separator 23 is suppressed. As a result, even if a decomposition reaction of the electrolytic solution occurs, swelling of the secondary battery is suppressed. The polymer compound layer contains a polymer compound such as polyvinylidene fluoride. This is because polyvinylidene fluoride has excellent physical strength and is electrochemically stable.

[0180] Note that one or both of the porous membrane and the polymer compound layer may contain a plurality of insulating particles. This is because when the secondary battery generates heat, the plurality of insulating particles promote heat dissipation, thereby improving the safety (heat resistance) of the secondary battery. The plurality of insulating particles include any one or two or more of insulating materials such as inorganic materials and resin materials. Specific examples of the inorganic material include aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of the resin material include acrylic resin and styrene resin.

[0181] When manufacturing the laminated separator, after preparing a precursor solution containing a polymer compound and a solvent, the precursor solution is applied to one or both surfaces of the porous membrane. In this case, if necessary, a plurality of insulating particles may be added to the precursor solution.

[0182] Even when this laminated separator is used, since lithium can move between the positive electrode 21 and the negative electrode 22, the same effect can be obtained. In this case, in particular, as described above, since the safety of the secondary battery is improved, a higher effect can be obtained.

[0183] [Modification Example 3] An electrolyte solution, which is a liquid electrolyte, was used. However, although not specifically illustrated here, an electrolyte layer, which is a gel electrolyte, may also be used.

[0184] In the battery element 20 using the electrolyte layer, the positive electrode 21 and the negative electrode 22 are wound while facing each other through the separator 23 and the electrolyte layer. This electrolyte layer is interposed between the positive electrode 21 and the separator 23 and also between the negative electrode 22 and the separator 23.

[0185] Specifically, the electrolyte layer contains a polymer compound together with the electrolyte solution, and the electrolyte solution is retained by the polymer compound. This is because leakage of the electrolyte solution is prevented. The composition of the electrolyte solution is as described above. The polymer compound includes polyvinylidene fluoride and the like. When forming the electrolyte layer, a precursor solution containing the electrolyte solution, the polymer compound, and a solvent is prepared, and then the precursor solution is applied to one side or both sides of each of the positive electrode 21 and the negative electrode 22.

[0186] Even when this electrolyte layer is used, since lithium can move between the positive electrode 21 and the negative electrode 22 through the electrolyte layer, the same effect can be obtained. In this case, in particular, as described above, since leakage of the electrolyte solution is prevented, a higher effect can be obtained.

[0187] <4. Applications of the secondary battery> The applications (application examples) of the secondary battery are 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, and the like. The main power source is a power source that is preferentially used regardless of the presence or absence of other power sources. The auxiliary power source may be a power source used in place of the main power source or a power source that can be switched from the main power source.

[0188] Specific examples of the uses of secondary batteries are as follows. Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals. Storage devices such as backup power supplies and memory cards. Electric tools such as electric drills and electric saws. Battery packs mounted on electronic devices and the like. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles (including hybrid vehicles). Power storage systems such as household or industrial battery systems that store power for emergencies and the like. In these applications, one secondary battery may be used, or a plurality of secondary batteries may be used.

[0189] The battery pack may use a single cell or a battery pack. An electric vehicle is a vehicle that runs using a secondary battery as a driving power source, and may also be a hybrid vehicle that is provided with other driving sources in addition to the secondary battery. In a household power storage system, household electrical appliances and the like can be used by utilizing the power stored in the secondary battery that is the power storage source.

Examples

[0190] The embodiments of the present technology will be described.

[0191] <Examples 1 to 21 and Comparative Examples 1 to 8> As described below, after manufacturing the secondary battery, the battery characteristics of the secondary battery were evaluated.

[0192] [Manufacture of secondary battery] Here, in order to simply evaluate the battery characteristics, a test secondary battery described later was manufactured. Below, after explaining the configuration of the test secondary battery, the manufacturing procedure of the test secondary battery will be explained.

[0193] (Configuration of secondary battery) FIG. 6 shows a cross-sectional configuration of a secondary battery for testing, and the secondary battery for testing is a so-called coin-type lithium ion secondary battery. Hereinafter, the secondary battery for testing is also simply referred to as "secondary battery".

[0194] As shown in FIG. 6, this secondary battery includes a test electrode 61, a counter electrode 62, a separator 63, an outer case 64, an outer can 65, a gasket 66, and an electrolytic solution (not shown).

[0195] The test electrode 61 is housed in the outer case 64, and the counter electrode 62 is housed in the outer can 65. The test electrode 61 and the counter electrode 62 are laminated on each other with the separator 63 therebetween, and the electrolytic solution is impregnated into each of the test electrode 61, the counter electrode 62, and the separator 63. Since the outer case 64 and the outer can 65 are clamped to each other via the gasket 66, the test electrode 61, the counter electrode 62, and the separator 63 are enclosed by the outer case 64 and the outer can 65.

[0196] (Manufacturing procedure of secondary battery) The secondary battery shown in FIG. 6 was manufactured using the procedure described below.

[0197] (Manufacture of test electrode) When manufacturing the test electrode 61, first, a plurality of primary particles containing an olivine-type phosphate compound were prepared. In this case, as the olivine-type phosphate compound, LiMn 0.5 Fe 0.5 PO4 (manganese content = 50 mol parts), LiMn 0.7 Fe 0.3 PO4 (manganese content = 70 mol parts), and LiMn 0.9 Fe 0.1 PO4 (manganese content = 90 mol parts) were used. When the median diameter MD1 (μm) was examined after the completion of the secondary battery, the results shown in Tables 1 to 3 were obtained.

[0198] Subsequently, a plurality of primary particles were granulated to form a plurality of central portions which are a plurality of secondary particles. As a result, a plurality of central portions containing an olivine-type phosphate compound were obtained. When the median diameter MD2 (μm) was examined after the completion of the secondary battery, the results shown in Tables 1 to 3 were obtained.

[0199] Subsequently, a dispersant (carboxymethyl cellulose) was added to a solvent (pure water which is an aqueous solvent), and then the solvent was stirred to prepare a dispersion (concentration = 55%).

[0200] Subsequently, a plurality of central portions were added to the dispersion, and then the dispersion was stirred to pretreat the plurality of central portions using the dispersion. By this pretreatment, a base film containing a dispersant was formed on the surface of each of the plurality of central portions.

[0201] Subsequently, 100 parts by mass of the pretreated plurality of central portions, 3.0 parts by mass of a positive electrode binder (polyacrylonitrile (PAN)-ethylhexyl acrylate copolymer which is a nitrile group-containing polymer compound), and 2.0 parts by mass of a positive electrode conductive agent (carbon black) were mixed with each other to obtain a positive electrode mixture.

[0202] Subsequently, the positive electrode mixture was added to a solvent (pure water which is an aqueous solvent), and then the solvent was stirred to prepare a positive electrode mixture slurry. As a result, a part of the nitrile group-containing polymer compound which is a positive electrode binder preferentially adhered to the surface of each of the plurality of central portions, so that a coating portion containing a nitrile group was formed. Thus, a plurality of positive electrode active material particles including the central portion and the coating portion were obtained.

[0203] Subsequently, after applying the positive electrode mixture slurry to one side of the positive electrode current collector (aluminum foil, thickness = 12 μm) using a coating device, the positive electrode mixture slurry was dried to form a positive electrode active material layer. When the total formation ratio R (%) was examined after the completion of the secondary battery, the results shown in Tables 1 to 3 were obtained. Note that the total formation ratio R (%) can be adjusted by changing the air supply temperature and air supply volume when drying the positive electrode mixture slurry.

[0204] Subsequently, the positive electrode active material layer was compression-molded using a press machine. In this case, the porosity P (%) was adjusted by changing conditions such as the press pressure and press time. When the porosity P was examined after the completion of the secondary battery, the results shown in Tables 1 to 3 were obtained.

[0205] Finally, the positive electrode current collector with the positive electrode active material layer formed thereon was punched out to be disk-shaped (diameter = 16.5 mm). Thereby, the test electrode 61 was fabricated.

[0206] Note that for comparison, the test electrode 61 was fabricated using the same procedure except that a plurality of primary particles were used as they were without granulation. When the median diameter MD1 (μm) was examined after the completion of the secondary battery, the results shown in Table 2 were obtained.

[0207] (Fabrication of the counter electrode) A lithium metal plate was punched out to be disk-shaped (diameter = 17 mm). Thereby, the counter electrode 62 was obtained.

[0208] (Preparation of the electrolyte) After adding an electrolyte salt (LiPF6) to a solvent (ethylene carbonate which is a cyclic carbonate ester and diethyl carbonate which is a chain carbonate ester), the solvent was stirred. In this case, the mixing ratio (weight ratio) of the solvents was ethylene carbonate:diethyl carbonate = 30:70, and the content of the electrolyte salt in the electrolyte was 1 mol / kg with respect to the solvent. Thereby, the electrolyte was prepared.

[0209] (Assembly of the secondary battery) First, the test electrode 61 was accommodated in the exterior cup 64, and the counter electrode 62 was accommodated in the exterior can 65. Subsequently, through the separator 63 (micro-porous polyethylene film, thickness = 20 μm, diameter = 17.5 mm) impregnated with the electrolytic solution, the test electrode 61 accommodated in the exterior cup 64 and the counter electrode 62 accommodated in the exterior can 65 were laminated on each other. In this case, the positive electrode active material layer and the counter electrode 62 were opposed to each other through the separator 63.

[0210] Subsequently, in a state where the test electrode 61 and the counter electrode 62 were laminated on each other through the separator 63, the exterior cup 64 and the exterior can 65 were clamped to each other through the gasket 66. As a result, since the test electrode 61 and the counter electrode 62 were sealed by the exterior cup 64 and the exterior can 65, the secondary battery was assembled.

[0211] Finally, the assembled secondary battery was left standing (standing time = 10 hours). As a result, the secondary battery was completed.

[0212] [Evaluation of Battery Characteristics] When evaluating the physical durability and operation stability as battery characteristics, the results shown in Tables 1 to 3 were obtained. Here, using the procedure described below, the adhesion and flexibility of the test electrode 61 were evaluated as physical durability, and the load characteristics and cycle characteristics of the secondary battery were evaluated as operation stability.

[0213] (Adhesion) First, the test electrode 61 was recovered by disassembling the secondary battery. Subsequently, after washing the test electrode 61 with a solvent for washing (pure water), the test electrode 61 was dried.

[0214] Subsequently, in a normal temperature environment (temperature = 23 °C), after mounting the test electrode 61 on a peeling tester, a 180° peel test was performed using the peeling tester. As a result, since the positive electrode current collector was peeled from the positive electrode active material layer, the peel strength (mN / mm), which is an index for evaluating the adhesion, was measured.

[0215] Finally, the adhesion was determined based on the peel strength. Specifically, when the peel strength was 20 mN / mm or more, it was determined as "A". When the peel strength was 10 mN / m or more and less than 20 mN / m, it was determined as "B". When the peel strength was less than 10 mN / m, it was determined as "C".

[0216] (Flexibility) First, the test electrode 61 was recovered from the secondary battery using the same procedure as when evaluating the adhesion, and then the test electrode 61 was washed.

[0217] Subsequently, in a normal temperature environment, the test electrode 61 was wound around the surface of an iron metal rod (diameter = 4 mm) to bend the test electrode 61, and then the bent test electrode 61 was left standing (standing time = 10 minutes). Subsequently, by visually checking the state of the test electrode 61, the state of the positive electrode active material layer, which is an index for evaluating flexibility, was observed.

[0218] Finally, the flexibility was determined based on the state of the positive electrode active material layer. Specifically, when no abnormality occurred in the positive electrode active material layer, it was determined as "A". When the positive electrode active material layer did not break, but there were minute cracks in the positive electrode active material layer, it was determined as "B". When a serious abnormality occurred in the positive electrode active material layer, it was determined as "C". The abnormalities in the positive electrode active material layer described here are cracks, breakages, and detachments, etc.

[0219] (Load characteristics) First, in a normal temperature environment, the secondary battery was charged and discharged for 1 cycle to measure the discharge capacity (discharge capacity of the first cycle).

[0220] During charging, constant current charging was performed at a current of 0.2C until the voltage reached 3.8V, and then constant voltage charging was performed at the voltage of 3.8V until the current reached 0.05C. During discharging, constant current discharging was performed at a current of 0.2C until the voltage reached 2.0V. 0.2C is the current value that can discharge the battery capacity (theoretical capacity) in 5 hours, and 0.05C is the current value that can discharge the battery capacity in 20 hours.

[0221] Subsequently, the secondary battery was charged and discharged once in the same environment, and the discharge capacity (the discharge capacity at the second cycle) was measured.

[0222] The charge-discharge conditions were the same as those in the first cycle, except that the current during discharge was changed from 0.2C to 2C. 2C is the current value at which the battery capacity can be completely discharged in 0.5 hours.

[0223] Subsequently, based on the calculation formula of load retention rate (%) = (discharge capacity at the second cycle / discharge capacity at the first cycle) × 100, the load retention rate, which is an index for evaluating load characteristics, was calculated.

[0224] Finally, the load characteristics were determined based on the load retention rate. Specifically, when the load retention rate was 90% or more, it was determined as "A". When the load retention rate was 80% or more and less than 90%, it was determined as "B". When the load retention rate was less than 80%, it was determined as "C".

[0225] (Cycle characteristics) First, the secondary battery was charged and discharged once in a normal temperature environment, and the discharge capacity (the discharge capacity at the first cycle) was measured. Subsequently, the secondary battery was repeatedly charged and discharged in the same environment until the total number of cycles reached 100 cycles, and the discharge capacity (the discharge capacity at the 100th cycle) was measured. The charge-discharge conditions were the same as those in the first cycle when evaluating the load characteristics.

[0226] Subsequently, based on the calculation formula of cycle retention rate (%) = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100, the cycle retention rate, which is an index for evaluating cycle characteristics, was calculated.

[0227] Finally, the cycle characteristics were determined based on the cycle retention rate. Specifically, when the cycle retention rate was 90% or more, it was determined as "A". When the cycle retention rate was 80% or more and less than 90%, it was determined as "B". When the cycle retention rate was less than 80%, it was determined as "C".

[0228] (Comprehensive Evaluation) Here, after obtaining the determination results of adhesiveness and flexibility respectively, and the determination results of load characteristics and cycle characteristics respectively, the battery characteristics were comprehensively evaluated based on these four types of determination results.

[0229] Specifically, when any one of the four types of determination results was C, the comprehensive evaluation was set as "C". When none of the four types of determination results was C, but any one of the four types of determination results was B, the comprehensive evaluation was set as "B". When all of the four types of determination results were A, the comprehensive evaluation was determined as "A".

[0230] [Table 1]

[0231] [Table 2]

[0232] [Table 3]

[0233] [Discussion] As shown in Tables 1 to 3, the comprehensive evaluation regarding the four types of evaluation results (adhesiveness, flexibility, load characteristics, and cycle characteristics) varied according to the configuration of the test electrode 61.

[0234] Specifically, each of the plurality of positive electrode active material particles includes a central portion and a coating portion. The central portion contains an olivine-type phosphate compound, and the content of manganese in the olivine-type phosphate compound is 50 to 90 mol parts. The central portion is a granulated body with a median diameter MD1 of 0.01 μm to 0.5 μm and a median diameter MD2 of 1 μm to 20 μm. The coating portion contains a nitrile group, and when appropriate conditions such as a porosity P of 20% to 40% are satisfied (Examples 1 to 21), all of the adhesion, flexibility, load characteristics, and cycle characteristics are improved, resulting in an overall evaluation of B or higher.

[0235] On the other hand, when the above-described appropriate conditions are not satisfied (Comparative Examples 1 to 8), any one of the adhesion, flexibility, load characteristics, and cycle characteristics deteriorates, resulting in an overall evaluation of C. In this case, in particular, when a plurality of primary particles are used as they are without granulation (Comparative Example 8), the cycle characteristics deteriorate significantly.

[0236] In addition, when the above-described appropriate conditions are satisfied (Examples 1 to 21), a series of tendencies described below were obtained.

[0237] First, when the median diameter MD1 is 0.1 μm to 3 μm, each of the adhesion, load characteristics, and cycle characteristics is further improved.

[0238] Second, when the median diameter MD2 is 5 μm to 15 μm, each of the adhesion, load characteristics, and cycle characteristics is further improved.

[0239] Third, when the porosity P is 25% to 35%, each of the flexibility, load characteristics, and cycle characteristics is further improved.

[0240] Fourth, when the coating portion contains polyacrylonitrile, which is a nitrile group-containing polymer compound, all of the adhesion, flexibility, load characteristics, and cycle characteristics are sufficiently improved.

[0241] Fifthly, when the total formation ratio R is 0.6 to 1.4, all of the adhesion, flexibility, load characteristics, and cycle characteristics are sufficiently improved.

[0242] [Summary] From the results shown in Table 1 and Table 2, each of the plurality of positive electrode active material particles includes a central portion and a coating portion, the central portion contains an olivine-type phosphate compound, and the content of manganese in the olivine-type phosphate compound is 50 to 90 mol parts. The central portion is a granule, the median diameter MD1 is 0.01 μm to 0.5 μm, the median diameter MD2 is 1 μm to 20 μm, the coating portion contains a nitrile group, and when the porosity P is 20% to 40%, all of the adhesion, flexibility, load characteristics, and cycle characteristics are improved, so excellent battery characteristics are obtained.

[0243] As described above, the present technology has been described with reference to one embodiment and examples. However, the configuration of the present technology is not limited to the configuration described in one embodiment and examples, and thus can be variously modified.

[0244] Specifically, the case where the battery structure of the secondary battery is cylindrical and coin-shaped has been described. However, since the battery structure of the secondary battery is not particularly limited, it may be a laminate film type, square type, button type, or the like.

[0245] Also, the case where the element structure of the battery element is a wound type has been described. However, since the element structure of the battery element is not particularly limited, it may be a stacked type, a ninety-nine-fold type, or the like. In this stacked type, the positive electrode and the negative electrode are stacked on each other, and in the ninety-nine-fold type, the positive electrode and the negative electrode are folded in a zigzag manner.

[0246] Furthermore, although the electrode reactant has been described in the case where it is lithium, the electrode reactant is not particularly limited. Specifically, the electrode reactant may be other alkali metals such as sodium and potassium as described above, or alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be other light metals such as aluminum.

[0247] The effects described in this specification are merely examples, and thus 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.

[0248] Note that the present technology may also adopt the following configuration. <1> A positive electrode including a positive electrode active material layer, A negative electrode, An electrolytic solution And comprising The positive electrode active material layer includes a plurality of positive electrode active material particles, Each of the plurality of positive electrode active material particles A central portion containing an olivine-type phosphate compound, And a coating portion provided on the surface of the central portion And comprising The olivine-type phosphate compound contains manganese and iron as constituent elements, When the sum of the content of manganese in the olivine-type phosphate compound and the content of iron in the olivine-type phosphate compound is 100 mol parts, the content of manganese in the olivine-type phosphate compound is 50 mol parts or more and 90 mol parts or less, The central portion is secondary particles formed by granulating a plurality of primary particles, The first median diameter of the plurality of primary particles is 0.01 μm or more and 0.5 μm or less, The second median diameter of the plurality of secondary particles is 1 μm or more and 20 μm or less, The coating portion contains a nitrile group, The porosity of the positive electrode active material layer is 20% or more and 40% or less. Secondary battery. <2> The first median diameter is 0.1 μm or more and 0.3 μm or less, The second median diameter is 5 μm or more and 15 μm or less, The porosity is 25% or more and 35% or less. The secondary battery according to <1>. <3> The positive electrode active material layer further contains a positive electrode binder, The positive electrode binder contains a nitrile group. The secondary battery according to <1> or <2>. <4> The positive electrode binder contains at least one of polyacrylonitrile and acrylonitrile-ethylhexyl acrylate copolymer. The secondary battery according to <3>. <5> The positive electrode further includes a positive electrode current collector that supports the positive electrode active material layer, When the positive electrode active material layer is bisected into a first positive electrode active material layer located closer to the positive electrode current collector and a second positive electrode active material layer located farther from the positive electrode in the thickness direction of the positive electrode active material layer, The ratio of the total formation amount of the plurality of coating portions inside the second positive electrode active material layer to the total formation amount of the plurality of coating portions inside the first positive electrode active material layer is 0.6 or more and 1.4 or less. The secondary battery according to any one of <1> to <4>. <6> It is a lithium secondary battery. The secondary battery according to any one of <1> to <5>. <7> Comprising a positive electrode active material layer, The positive electrode active material layer contains a plurality of positive electrode active material particles, Each of the plurality of positive electrode active material particles, A central portion containing an olivine-type phosphate compound, And a coating portion provided on the surface of the central portion And includes, The olivine-type phosphate compound contains manganese and iron as constituent elements, When the sum of the content of manganese in the olivine-type phosphate compound and the content of iron in the olivine-type phosphate compound is 100 mole parts, the content of manganese in the olivine-type phosphate compound is 50 mole parts or more and 90 mole parts or less, The central portion is secondary particles formed by granulating a plurality of primary particles, The first median diameter of the plurality of primary particles is 0.01 μm or more and 0.5 μm or less, The second median diameter of the plurality of secondary particles is 1 μm or more and 20 μm or less, The coating portion contains a nitrile group, The porosity of the positive electrode active material layer is 20% or more and 40% or less. Positive electrode for a secondary battery.

Explanation of reference numerals

[0249] 21,100... positive electrode, 21A,100A... positive electrode current collector, 21B,100B... positive electrode active material layer, 22... negative electrode, 100B1... lower layer positive electrode active material layer, 100B2... upper layer positive electrode active material layer, 110... positive electrode active material particles, 110X... central portion, 110Y... coating portion.

Claims

1. a positive electrode including a positive electrode active material layer, a negative electrode, and an electrolytic solution are provided, the positive electrode active material layer includes a plurality of positive electrode active material particles, each of the plurality of positive electrode active material particles includes a central portion containing an olivine-type phosphate compound, and a coating portion provided on the surface of the central portion and includes, the olivine-type phosphate compound contains manganese and iron as constituent elements, when the sum of the content of manganese in the olivine-type phosphate compound and the content of iron in the olivine-type phosphate compound is 100 mol parts, the content of manganese in the olivine-type phosphate compound is 50 mol parts or more and 90 mol parts or less, the central portion is secondary particles formed by granulating a plurality of primary particles, a first median diameter of the plurality of primary particles is 0.01 μm or more and 0.5 μm or less, a second median diameter of the plurality of secondary particles is 1 μm or more and 20 μm or less, the coating portion contains a nitrile group, a porosity of the positive electrode active material layer is 20% or more and 40% or less, a secondary battery.

2. the first median diameter is 0.1 μm or more and 0.3 μm or less, the second median diameter is 5 μm or more and 15 μm or less, the porosity is 25% or more and 35% or less, the secondary battery according to Claim 1.

3. the positive electrode active material layer further includes a positive electrode binder, the positive electrode binder contains a nitrile group, the secondary battery according to Claim 1.

4. the positive electrode binder contains at least one of polyacrylonitrile and an acrylonitrile-ethylhexyl acrylate copolymer, the secondary battery according to Claim 3.

5. the positive electrode further includes a positive electrode current collector that supports the positive electrode active material layer, when the positive electrode active material layer is bisected into a first positive electrode active material layer located on the side closer to the positive electrode current collector and a second positive electrode active material layer located on the side farther from the positive electrode in the thickness direction of the positive electrode active material layer, a ratio of the total formation amount of the plurality of coating portions inside the second positive electrode active material layer to the total formation amount of the plurality of coating portions inside the first positive electrode active material layer is 0.6 or more and 1.4 or less, the secondary battery according to Claim 1.

6. a lithium secondary battery, the secondary battery according to Claim 1.

7. including a positive electrode active material layer, the positive electrode active material layer includes a plurality of positive electrode active material particles, each of the plurality of positive electrode active material particles includes a central portion containing an olivine-type phosphate compound, and a coating portion provided on the surface of the central portion including the olivine-type phosphate compound contains manganese and iron as constituent elements, when the sum of the content of the manganese in the olivine-type phosphate compound and the content of the iron in the olivine-type phosphate compound is 100 mole parts, the content of the manganese in the olivine-type phosphate compound is 50 mole parts or more and 90 mole parts or less, the central portion is secondary particles formed by granulating a plurality of primary particles, the first median diameter of the plurality of primary particles is 0.01 μm or more and 0.5 μm or less, the second median diameter of the plurality of secondary particles is 1 μm or more and 20 μm or less, the coating portion contains a nitrile group, the porosity of the positive electrode active material layer is 20% or more and 40% or less, a positive electrode for a secondary battery.

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