Positive electrode for secondary battery, and secondary battery

Abstract

The secondary battery includes a positive electrode, a negative electrode, and an electrolyte solution. The positive electrode includes a positive electrode current collector and a positive electrode active material layer supported by the positive electrode current collector. The positive electrode active material layer contains a plurality of holding particles containing anatase-type titanium oxide, and a plurality of positive electrode active material particles containing a sulfur-containing material. The plurality of holding particles form a porous structure by being directly bonded to each other, and the porous structure is directly bonded to the positive electrode current collector. The plurality of positive electrode active material particles are held by each of the plurality of holding particles, and the average particle diameter of the plurality of holding particles is 100 nm or less.

Description

Technical Field

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

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

[0003] Specifically, a porous body formed of titanium nitride nanoparticles, a porous nonwoven fabric, conductive titanium oxide nanoparticles, or oxygen-reduced titanium oxide (TiO 2-x ) is used as a positive electrode (for example, refer to Patent Documents 1 to 4).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application No. 2020-529102

[0007] Patent Document 2: Japanese Patent Application Publication No. 2011-198550

[0008] Patent Document 3: Japanese Patent Application No. 2020-534239

[0009] Patent Document 4: Japanese Patent Application No. 2018-526793 Summary of the invention

[0010] Although various studies have been conducted on the structure of secondary batteries, the battery characteristics of the secondary batteries are still insufficient, and thus there is room for improvement.

[0011] It is desirable to provide a positive electrode for a secondary battery and a secondary battery having excellent battery characteristics.

[0012] A secondary battery positive electrode of one embodiment of the present technology includes a positive electrode collector and a positive electrode active material layer supported by the positive electrode collector. The positive electrode active material layer includes a plurality of retaining particles containing anatase-type titanium oxide, and a plurality of positive electrode active material particles containing a sulfur-containing material. The plurality of retaining particles form a porous structure by directly bonding to each other, and the porous structure is directly connected to the positive electrode collector. The plurality of positive electrode active material particles are each retained by a plurality of retaining particles, and the average particle size of the plurality of retaining particles is less than 100 nm.

[0013] In addition, a secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolyte solution. The positive electrode has the same structure as the positive electrode for a secondary battery according to the embodiment of the present technology described above.

[0014] Here, the "average particle size of the plurality of retained particles" is calculated based on the observation result (electron microscope photo) by observing the cross section of the positive electrode active material layer using an electron microscope. The definition of this "average particle size", that is, the details of the calculation procedure of the average particle size based on the electron microscope photo, will be described below.

[0015] According to one embodiment of the present technology, a positive electrode for a secondary battery or a secondary battery, the positive electrode for a secondary battery includes a positive electrode collector and a positive electrode active material layer, the positive electrode active material layer contains a plurality of retaining particles and a plurality of positive electrode active material particles, the plurality of retaining particles contain rutile-type titanium oxide, the plurality of positive electrode active material particles contain sulfur-containing materials, the plurality of retaining particles form a porous structure by directly bonding to each other, the porous structure is directly connected to the positive electrode collector, the plurality of positive electrode active material particles are respectively retained by the plurality of retaining particles, the average particle size of the plurality of retaining particles is less than 100 nm, so excellent battery characteristics can be obtained.

[0016] It should be noted that the effects of the present technology are not necessarily limited to the effects described here, and may be any of a series of effects related to the present technology described later. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a cross-sectional view showing the structure of a positive electrode for a secondary battery in one embodiment of the present invention.

[0018] Figure 2 It is a magnified representation Figure 1 A cross-sectional view of a portion of a positive electrode for a secondary battery shown.

[0019] Figure 3 Yes means Figure 1 Schematic diagram of an electron microscope photograph of a cross section of a positive electrode for a secondary battery shown.

[0020] Figure 4 It is a perspective view showing the structure of a secondary battery in one embodiment of the present technology.

[0021] Figure 5 Yes means Figure 4 A cross-sectional view of the structure of a battery element is shown.

[0022] Figure 6 It is a cross-sectional view showing the structure of a secondary battery used for testing. DETAILED DESCRIPTION

[0023] Below, while referring to the attached Figure 1 One embodiment of the present technology will be described in detail. It should be noted that the order of description is as follows.

[0024] 1. Positive electrode for secondary batteries

[0025] 1-1. Structure

[0026] 1-2. Action

[0027] 1-3. Manufacturing method

[0028] 1-4. Function and effect

[0029] 2. Secondary battery

[0030] 2-1. Structure

[0031] 2-2. Action

[0032] 2-3. Manufacturing method

[0033] 2-4. Actions and effects

[0034] 3. Modifications

[0035] 4. Uses of secondary batteries

[0036] <1. Positive electrode for secondary batteries>

[0037] First, a positive electrode for a secondary battery (hereinafter simply referred to as a “positive electrode”) according to an embodiment of the present technology will be described.

[0038] The positive electrode described here is used for a secondary battery as an electrochemical device. In addition, the positive electrode can also be used for other electrochemical devices other than secondary batteries. Specific examples of other electrochemical devices are primary batteries and capacitors.

[0039] The positive electrode operates by utilizing the electrochemical reaction of the sulfur-containing material in the electrochemical device. In a secondary battery using the positive electrode, the sulfur-containing material is electrochemically oxidized during discharge and electrochemically reduced during charge. It should be noted that the details of the sulfur-containing material will be described below.

[0040] <1-1. Structure>

[0041] Figure 1 A cross-sectional structure of a positive electrode 100 is shown as an example of a positive electrode. Figure 2 Zoomed in Figure 1 A cross-sectional structure of a portion of the positive electrode 100 is shown. Figure 3 Schematically shows Figure 1 An electron microscope photograph 200 of a cross section of a positive electrode 100 is shown.

[0042] like Figure 1 As shown, the positive electrode 100 includes a positive electrode current collector 110 and a positive electrode active material layer 120 .

[0043] [Positive electrode collector]

[0044] like Figure 1 As shown, the positive electrode current collector 110 is a conductive supporting member that supports the positive electrode active material layer 120 , and has a pair of surfaces (upper surface and lower surface) on which the positive electrode active material layer 120 is provided.

[0045] The positive electrode current collector 110 includes any one or two or more conductive materials such as metal materials. Specific examples of the conductive material include titanium, aluminum, titanium alloys, and aluminum alloys.

[0046] [Positive electrode active material layer]

[0047] like Figure 1 As shown, the positive electrode active material layer 120 is a place (layer) where the sulfur-containing material undergoes an electrochemical reaction, and is supported by the positive electrode current collector 110. The positive electrode active material layer 120 includes a positive electrode active material containing a sulfur-containing material and a retainer that retains the positive electrode active material. In addition, the positive electrode active material layer 120 may also include any one or more of other materials such as a positive electrode binder and a positive electrode conductive agent.

[0048] Here, the positive electrode active material layer 120 is provided on both surfaces (upper surface and lower surface) of the positive electrode current collector 110 . Alternatively, the positive electrode active material layer 120 may be provided on only one surface (upper surface or lower surface) of the positive electrode current collector 110 .

[0049] In particular, Figure 1 as well as Figure 2 As shown, the positive electrode active material layer 120 includes two types of particles. The first type of particles are the plurality of retaining particles 121 forming the retaining body (porous structure 124 described later), and the second type of particles are the plurality of positive electrode active material particles 122 which are the plurality of particle-shaped positive electrode active materials.

[0050] (Multiple Retained Particles)

[0051] The holding particle 121 contains anatase-type titanium oxide (TiO 2 ). That is, the titanium oxide contained in the holding particle 121 has an anatase-type crystal structure. The holding particle 121 described here is not a secondary particle which is an aggregate of a plurality of primary particles, but a primary particle thereof.

[0052] For example, anatase-type titanium oxide contains any one or two or more of the compounds represented by formula (1).

[0053] TiOw … (1)

[0054] (w satisfies 1.85≤w≤2.15.)

[0055] It should be noted that anatase titanium oxide may also contain any one or more of the dopants. The dopant is an element doped in anatase titanium oxide, and the type of the dopant is not particularly limited as long as it is an element that can be doped in anatase titanium oxide. Regarding the type of dopant, in order to improve the conductivity of the porous structure 124 as a retainer and promote the formation of the porous structure 124, it can be appropriately selected. Specific examples of dopants are Nb, Ta, Fe, Zr, La, As, P and B. In addition, from a cost point of view, anatase titanium oxide that does not contain a dopant is preferred over anatase titanium oxide that contains a dopant.

[0056] The reason why the retaining particles 121 contain anatase titanium oxide is that the electrochemical reaction of the plurality of positive electrode active material particles 122 (sulfur-containing material) in the positive electrode active material layer 120 is more likely to proceed stably than when the retaining particles 121 contain rutile or brookite titanium oxide.

[0057] Specifically, anatase titanium oxide has the property of easily promoting the electrochemical reaction of the sulfur-containing material compared to rutile or brookite titanium oxide. Therefore, compared to the retaining particles 121 containing rutile or brookite titanium oxide, the retaining particles 121 containing anatase titanium oxide easily make the electrochemical reaction of the sulfur-containing material proceed stably.

[0058] The plurality of holding particles 121 are directly bonded to each other to form a porous structure 124. Thus, the positive electrode active material layer 120 includes a porous structure 124 in which a plurality of primary particles, namely, a plurality of holding particles 121 are directly bonded to each other, and the porous structure 124 has a plurality of gaps (pores 123).

[0059] Specifically, the positive electrode active material layer 120 includes a sintered body of a plurality of retaining particles 121 formed by a sintering method, and the sintered body is the retaining body (porous structure 124) described above. Thus, in the interior of the positive electrode active material layer 120, as described above, the plurality of retaining particles 121 are directly bonded to each other. Details of the method for forming the positive electrode active material layer 120 using the sintering method will be described below.

[0060] As described above, the “direct bonding to each other” means that the porous structure 124 is a sintered body of the plurality of retaining particles 121. That is, the plurality of retaining particles 121 are not indirectly bonded to each other via a binder, but are directly bonded to each other without the binder, in order to form the porous structure 124. In addition, the plurality of retaining particles 121 are not indirectly bonded to each other via a conductive agent in order to form the porous structure 124, and are electrically connected to each other via the conductive agent, but are directly bonded to each other without the conductive agent in order to form the porous structure 124, and are electrically connected to each other without the conductive agent.

[0061] The positive electrode active material layer 120 includes a porous structure 124 as a sintered body of a plurality of retaining particles 121 because the plurality of retaining particles 121 are physically and electrically connected to each other. As a result, the energy density per unit volume of the positive electrode active material layer 120 is increased, and the electronic conductivity between the plurality of retaining particles 121 is improved. Therefore, in the positive electrode 100, the resistance can be reduced while ensuring the energy density, so a high discharge capacity can be obtained in a secondary battery using the positive electrode 100.

[0062] The porous structure 124 is directly connected to the positive electrode current collector 110 . Thus, the plurality of holding particles 121 are not only directly joined to each other to form the porous structure 124 , but also a part of the plurality of holding particles 121 forming the porous structure 124 is directly connected to the positive electrode current collector 110 .

[0063] “Directly connected to each other” means that a part of the plurality of holding particles 121 is not indirectly connected to the positive electrode collector 110 via a binder or a conductive agent, but a part of the plurality of holding particles 121 is directly connected to the positive electrode collector 110 without a binder or a conductive agent.

[0064] According to the above, if Figure 1 As shown in FIG. 1 , a plurality of holding particles 121 are directly bonded to each other, thereby forming a porous structure 124 as a skeleton of the positive electrode active material layer 120. In this case, as shown in FIG. Figure 2 As shown in FIG. 1 , the holding particles 121 hold a plurality of positive electrode active material particles 122. That is, each of the plurality of holding particles 121 holds a plurality of positive electrode active material particles 122. Figure 2 In order to simplify the illustration, only one holding particle 121 is shown.

[0065] Here, the average particle size AS of the plurality of retaining particles 121 forming the porous structure 124 becomes sufficiently small, specifically, less than 100 nm. That is, the value of the average particle size AS is a so-called nanometer-level value, so the retaining particles 121 are so-called nanoparticles. This is because the energy density per unit weight of the positive electrode active material layer 120 is increased, and the movement path (multiple pores 123) of the sulfur-containing material is easily formed inside the positive electrode active material layer 120. As a result, the electrochemical reaction of the plurality of positive electrode active material particles 122 (sulfur-containing material) can be promoted on the surface of the retaining particles 121, so the electrochemical reaction is easy to proceed stably. Therefore, the battery capacity of the secondary battery using the positive electrode 100 is increased.

[0066] The average particle size AS is preferably 30 nm or less. This is because the electrochemical reaction of the plurality of positive electrode active material particles 122 (sulfur-containing material) can be further promoted on the surface of the retaining particle 121. In addition, this is because the energy density per unit weight of the positive electrode active material layer 120 is further improved, and it is easier to form a plurality of pores 123 inside the positive electrode active material layer 120.

[0067] It should be noted that the lower limit of the average particle diameter AS is not particularly limited. Specifically, the average particle diameter AS is preferably 7 nm or more. This is because it is easy to stably form a plurality of holding particles 121.

[0068] The procedure for calculating the average particle size AS is as follows: To calculate the average particle size AS, an electron microscope photograph 200 is used.

[0069] Specifically, first, by Figure 1 The positive electrode 100 is cut in the vertical direction (in the vertical direction) to expose the cross section of the positive electrode 100. In this case, the positive electrode 100 is cut by using a cutting device such as an ion milling device to expose the cross section of the positive electrode active material layer 120. It should be noted that as the ion milling device, an ion milling device ArBlade (registered trademark) 5000 manufactured by Hitachi High-tech Co., Ltd. can be used.

[0070] Next, the cross section of the positive electrode active material layer 120 is observed using an electron microscope, thereby obtaining an electron microscope photograph 200. The type of electron microscope is not particularly limited, and specifically, it is any one or more of a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The observation conditions are not particularly limited, and specifically, the acceleration voltage = 5.0 kV, and the magnification = 150,000 times.

[0071] In the electron microscope photograph 200, as Figure 3As shown in FIG. 1 , since the plurality of retaining particles 121 are directly bonded to each other, a porous structure 124 having a plurality of pores 123 can be observed. Figure 3 In order to simplify the illustration, the planar shape of each of the plurality of holding particles 121 is set to be a rectangle, and the illustration of the plurality of positive electrode active material particles 122 is omitted.

[0072] Next, 50 arbitrary held particles 121 are selected from the plurality of held particles 121 identified in the electron microscope photograph 200 , and the particle size S (maximum outer diameter) of each of the 50 held particles 121 is measured. Thus, 50 particle sizes S are obtained.

[0073] When selecting 50 retaining particles 121, the retaining particle 121 that is closest to the front is selected from the multiple retaining particles 121 that overlap with each other. That is, since it overlaps with one or more other retaining particles 121, the retaining particle 121 (121Y) whose entire outer edge cannot be seen is not selected. On the other hand, since it does not overlap with one or more other retaining particles 121, the retaining particle 121 (121X) whose entire outer edge can be seen is selected. Figure 3 In FIG. 1 , several holding particles 121X that are selected are shaded.

[0074] Finally, the average value of 50 particle sizes S is calculated and the average value is taken as the average particle size AS.

[0075] It should be noted that a series of constituent conditions for the positive electrode active material layer 120 can be set arbitrarily. This series of constituent conditions is the volume density (g / cm 3 ), specific surface area (m 2 / g) and void ratio (%), etc.

[0076] (Multiple positive electrode active material particles)

[0077] like Figure 1 as well as Figure 2 As shown in FIG. 1 , the plurality of positive electrode active material particles 122 are held by the plurality of holding particles 121 . Here, the plurality of positive electrode active material particles 122 are adsorbed on the surface of the plurality of holding particles 121 . Figure 1 In the figure, illustration of the plurality of positive electrode active material particles 122 is omitted.

[0078] The plurality of positive electrode active material particles 122 are held by the plurality of holding particles 121 because the electrochemical reaction of the plurality of positive electrode active material particles 122 can be sufficiently and stably performed on the surface of the holding particles 121. Thus, in a secondary battery using the positive electrode 100, sufficient battery capacity can be stably obtained.

[0079] As described above, the positive electrode active material particles 122 include any one or two or more of the sulfur-containing materials. The sulfur-containing material is a general term for materials containing sulfur as a constituent element. That is, the sulfur-containing material may be a single substance of sulfur (hereinafter referred to as "single sulfur"), a sulfur alloy, a sulfur compound, a mixture of two or more thereof, or a material containing one or more phases thereof.

[0080] In addition, the "simple substance" described here refers to a general simple substance, and thus the simple substance may contain a trace amount of impurities. That is, the purity of the simple substance is not necessarily limited to 100%.

[0081] It should be noted that the sulfur compound may also contain a salt. The salt contains an anion containing sulfur as a constituent element (hereinafter referred to as a "sulfur-containing anion") and an arbitrary cation. The type of cation is not particularly limited, and among them, cations that undergo electrochemical reactions in a secondary battery using the positive electrode 100 are preferred. This is because the energy density is improved.

[0082] Specifically, the cation is a cation of a light metal such as an alkali metal and an alkaline earth metal. Specific examples of the alkali metal are lithium, sodium, and potassium, and specific examples of the alkaline earth metal are beryllium, magnesium, and calcium.

[0083] Specific examples of sulfur-containing materials include elemental sulfur, alkali metal sulfides, alkaline earth metal sulfides, alkali metal polysulfides, and alkaline earth metal polysulfides. Among them, the sulfur-containing material preferably contains alkali metal polysulfides, and more preferably contains lithium polysulfides. This is because the electrochemical reaction of the plurality of positive electrode active material particles 122 is easy to proceed fully. Specific examples of lithium polysulfides include lithium sulfide (Li2S8) and the like.

[0084] The sulfur-containing anions contain polysulfide ions (S n x- ), the ranges of n and x are not particularly limited. Specifically, n preferably satisfies 2≤n≤20, and more preferably satisfies 2<n≤12. x preferably satisfies 0<x≤2, and more preferably is 2.

[0085] (Positive electrode binder)

[0086] The positive electrode binder contains any one or two or more of synthetic rubber and polymer compounds, etc. Specific examples of the synthetic rubber are styrene-butadiene rubber, etc., and specific examples of the polymer compound are polyethylene glycol, polyvinylidene fluoride, and polyimide, etc.

[0087] (Positive electrode conductive agent)

[0088] The positive electrode conductive agent includes any one or two or more conductive materials such as carbon materials, metal materials and conductive polymer compounds. Specific examples of the carbon material include graphite, carbon black, acetylene black and Ketjen black.

[0089] <1-2. Action>

[0090] The positive electrode 100 operates as follows.

[0091] During the electrode reaction (during the discharge of the secondary battery using the positive electrode 100 and the electrolyte solution described later), in the positive electrode active material layer 120, the plurality of positive electrode active material particles 122 (sulfur-containing material) are electrochemically reduced on the surfaces of the plurality of retaining particles 121. In this case, if the sulfur-containing material contains highly soluble sulfur-containing anions, a salt containing the sulfur-containing anions may be eluted from the plurality of retaining particles 121 into the electrolyte solution.

[0092] In addition, during the electrode reaction (when charging the secondary battery using the positive electrode 100 and the electrolyte solution described later), in the positive electrode active material layer 120, on the surface of the plurality of holding particles 121, the plurality of positive electrode active material particles 122 (sulfur-containing material) are electrochemically oxidized. In this case, if the sulfur-containing material contains sulfur-containing anions having high solubility, the salt containing the sulfur-containing anions contained in the electrolyte solution is electrochemically oxidized. Therefore, the salt may be precipitated on the surface of the plurality of holding particles 121 to form part or all of the plurality of positive electrode active material particles 122.

[0093] For example, when the sulfur-containing material is elemental sulfur (S8), an electrochemical reaction represented by equation (2) occurs.

[0094] n / 8S8+x e- =S n x- … (2)

[0095] (Where n satisfies 2≤n≤20, and x satisfies 0<x≤2.)

[0096] As can be seen from formula (2), elemental sulfur becomes polysulfide ions due to being reduced during discharge, and becomes elemental sulfur due to being oxidized during charge. It should be noted that during discharge, since the positive electrode active material particles 122 are reduced, elemental sulfur becomes a salt containing polysulfide ions, but part or all of the salt can also be dissolved by the electrolyte. In addition, during charge, the salt containing polysulfide ions as the positive electrode active material particles 122 can be oxidized, and the salt containing polysulfide ions dissolved in the electrolyte can also be oxidized, so that part or all of the multiple positive electrode active material particles 122 can be formed.

[0097] <1-3. Manufacturing method>

[0098] The positive electrode 100 is manufactured by an exemplary process described below.

[0099] First, a plurality of retaining particles 121 (anatase-type titanium oxide), a positive electrode binder, and a solvent are mixed with each other to obtain a paste. In this case, a plurality of retaining particles 121 having an average particle size AS of 100 nm or less are used. The type of solvent is not particularly limited, and specifically, it is an aqueous solvent such as water, and a paste using an aqueous solvent as the solvent is a so-called aqueous paste. It should be noted that the composition (mixing ratio) of the paste can be set arbitrarily.

[0100] Next, the paste is applied to both surfaces of the positive electrode current collector 110 to form a coating film, and then the positive electrode current collector 110 with the coating film formed thereon is pressed. The pressing conditions can be set arbitrarily. Thus, the coating film is pressed onto both surfaces of the positive electrode current collector 110.

[0101] Next, the positive electrode current collector 110 formed with the coating film is fired in the atmosphere. The firing conditions such as the firing temperature and the firing time can be set arbitrarily. In this case, the firing conditions are adjusted so that the plurality of retaining particles 121 containing anatase-type titanium oxide are directly bonded to each other while maintaining the primary particles. For example, the maximum temperature during firing is 500°C to 1200°C. It should be noted that the environmental conditions during firing are not particularly limited, so the firing process can be performed in an oxygen atmosphere.

[0102] During the calcination process, the positive electrode binder is degreased by calcination. As a result, the plurality of retaining particles 121 are directly bonded to each other, thereby forming a porous structure 124 having a plurality of pores 123. In this case, a portion of the porous structure 124, that is, a portion of the plurality of retaining particles 121, is directly connected to the positive electrode collector 110.

[0103] Next, a sulfur-containing material is added to a solvent, and the solvent is then stirred to prepare a sulfur-containing solution. The type of solvent is not particularly limited, and specifically, an organic solvent or the like is used.

[0104] Finally, the positive electrode current collector 110 having the porous structure 124 is immersed in a sulfur-containing solution, and then the positive electrode current collector 110 having the porous structure 124 is taken out from the sulfur-containing solution and dried. The immersion conditions such as the immersion time can be set arbitrarily. Thus, the plurality of positive electrode active material particles 122 (sulfur-containing material) are each held by the plurality of holding particles 121.

[0105] Thus, the positive electrode active material layer 120 including the plurality of holding particles 121 (porous structure 124 ) and the plurality of positive electrode active material particles 122 is formed, and the positive electrode 100 is completed.

[0106] It should be noted that a method other than the method of firing the coating film containing the positive electrode binder described above may be used to produce the positive electrode 100. As long as the porous structure 124 can be formed by firing, the production steps of the positive electrode 100 may be changed as appropriate.

[0107] Specifically, the plurality of retaining particles 121 may be stamped without using a positive electrode binder, and then the plurality of retaining particles 121 may be fired. Alternatively, a dispersion in which the plurality of retaining particles 121 are dispersed may be applied to both sides of the positive electrode current collector 110, and the dispersion may be dried, and then the positive electrode current collector 110 coated with the dispersion may be fired.

[0108] <1-4. Functions and effects>

[0109] According to the positive electrode 100, the positive electrode 100 includes a positive electrode collector 110 and a positive electrode active material layer 120, and the positive electrode active material layer 120 includes a plurality of retaining particles 121 (anatase-type titanium oxide) and a plurality of positive electrode active material particles 122 (sulfur-containing material). The positive electrode active material layer 120 includes a porous structure 124, which is formed by direct bonding of a plurality of retaining particles 121 to each other and is directly connected to the positive electrode collector 110. The plurality of positive electrode active material particles 122 are respectively retained by the plurality of retaining particles 121, and the average particle size AS of the plurality of retaining particles 121 is 100 nm or less.

[0110] In this case, as described above, a series of effects described below can be obtained.

[0111] First, since the positive electrode active material layer 120 includes a porous structure 124 as a sintered body of a plurality of retaining particles 121, the plurality of retaining particles 121 are physically and electrically connected to each other. In this case, the energy density of the positive electrode active material layer 120 is increased, and the electronic conductivity between the plurality of retaining particles 121 is improved. Thus, the resistance can be reduced while ensuring the energy density.

[0112] Second, since the holding particles 121 contain anatase-type titanium oxide, the electrochemical reaction of the plurality of positive electrode active material particles 122 (sulfur-containing material) in the positive electrode active material layer 120 tends to proceed stably.

[0113] Third, since the average particle size AS of the plurality of holding particles 121 is 100 nm or less, the energy density per unit weight of the positive electrode active material layer 120 is improved, and migration paths (the plurality of pores 123 ) of the sulfur-containing material are easily formed inside the positive electrode active material layer 120 .

[0114] As described above, the electrochemical reaction of the sulfur-containing material is facilitated in the positive electrode 100. Furthermore, the positive electrode 100 including the porous structure 124 can be easily manufactured using a conventional calcination method. Therefore, a sufficient discharge capacity can be easily and stably obtained during charge and discharge, and thus a secondary battery having excellent battery characteristics can be realized using the positive electrode 100.

[0115] In particular, if the average particle size AS is less than 30 nm, the sulfur-containing material can more easily move inside the positive electrode active material layer 120, the energy density per unit weight of the positive electrode active material layer 120 is further improved, and the movement path (multiple pores 123) of the sulfur-containing material can be more easily formed inside the positive electrode active material layer 120, so that a higher effect can be obtained.

[0116] In addition, if the sulfur-containing material includes an alkali metal polysulfide, the electrochemical reaction of the sulfur-containing material is easy to proceed sufficiently, so that a higher effect can be obtained. In this case, if the alkali metal polysulfide includes a lithium polysulfide, the electrochemical reaction of the plurality of positive electrode active material particles 122 is easier to proceed, so that a higher effect can be obtained.

[0117] <2. Secondary batteries>

[0118] Next, a secondary battery according to an embodiment of the present technology to which the positive electrode 100 is applied will be described.

[0119] The secondary battery described here is a secondary battery that can obtain battery capacity by utilizing an electrochemical reaction of electrode reaction substances, and includes a positive electrode, a negative electrode, and an electrolyte.

[0120] In the negative electrode, the capacity is obtained by utilizing the electrochemical reaction of the cations contained in the electrolyte. In this case, it is preferred to utilize the electrochemical reaction of the cations that can form salts with the sulfur-containing anions. This is because the energy density of the secondary battery is improved. The negative electrode active material in this case is a material that can electrochemically react with the cations that can form salts with the sulfur-containing anions.

[0121] Specifically, the cation is an ion of a light metal such as an alkali metal and an alkaline earth metal. Specific examples of the alkali metal are lithium, sodium, and potassium, and specific examples of the alkaline earth metal are beryllium, magnesium, and calcium.

[0122] In this case, the negative electrode active material includes one or both of an alkali metal material and an alkaline earth metal material. The alkali metal material is a material containing an alkali metal element as a constituent element, and the alkaline earth metal material is a material containing an alkaline earth metal element as a constituent element. In addition, the alkali metal element and the alkaline earth metal material may each be of only one type, or may be of two or more types. In addition, the alkali metal material and the alkaline earth metal material may each be a simple substance, an alloy, a compound, or two or more types thereof. It should be noted that the meaning of a simple substance is as described above.

[0123] Hereinafter, the case where the cation is a lithium ion is taken as an example. A secondary battery that obtains capacity by inserting and extracting lithium in a negative electrode is a so-called lithium-sulfur secondary battery.

[0124] <2-1. Structure>

[0125] Figure 4 shows the three-dimensional structure of the secondary battery, and Figure 5 Shows Figure 4 The cross-sectional structure of the battery element 20 shown in FIG. Figure 4 , a state in which the outer film 10 and the battery element 20 are separated from each other is shown, and a cross section of the battery element 20 along the XZ plane is shown by a dotted line.

[0126] like Figure 4 as well as Figure 5 As shown, the secondary battery includes an outer film 10 , a battery element 20 , a positive electrode lead 31 , a negative electrode lead 32 , and sealing films 41 , 42 .

[0127] As described above, the secondary battery described here uses the outer packaging film 10 having flexibility or elasticity as an outer packaging member for accommodating the battery element 20, and is therefore a so-called laminated film type secondary battery.

[0128] [Outer packaging film]

[0129] like Figure 4 As shown, the outer film 10 has a bag-like structure which is sealed in a state of accommodating the battery element 20. Thus, the outer film 10 accommodates the positive electrode 21, the negative electrode 22, the separator 23 and the electrolyte solution which will be described later.

[0130] Here, the outer film 10 is a single film-shaped member, and is folded in a folding direction F. The outer film 10 is provided with a recessed portion 10U (so-called deep-drawn portion) for accommodating the battery element 20 .

[0131] Specifically, the outer packaging film 10 is a three-layer laminated film in which a welding layer, a metal layer, and a surface protection layer are sequentially stacked from the inside. When the outer packaging film 10 is folded, the outer peripheral edges of the mutually opposed welding layers are welded to each other. The welding layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

[0132] The structure (number of layers) of the outer film 10 is not particularly limited, and may be one layer, two layers, or four or more layers.

[0133] [Battery components]

[0134] The battery element 20 is housed in the outer packaging film 10. The battery element 20 is a so-called power generation element, and Figure 4 as well as Figure 5 As shown, it includes a positive electrode 21, a negative electrode 22, a separator 23 and an electrolyte (not shown).

[0135] Here, the battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 are opposed to each other with the separator 23 interposed therebetween, and are wound around a winding axis P as the center. Figure 4 It can be seen that the winding axis P is a virtual axis extending in the Y-axis direction.

[0136] The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the battery element 20 has a flat three-dimensional shape, the cross section of the battery element 20 intersecting the winding axis P (cross section along the XZ plane) is a flat shape defined by the major axis J1 and the minor axis J2.

[0137] The major axis J1 is an imaginary axis extending in the X-axis direction, and has a length greater than that of the minor axis J2. The minor axis J2 is an imaginary axis extending in the Z-axis direction intersecting the X-axis direction, and has a length less than that of the major axis J1. Here, the three-dimensional shape of the battery element 20 is a flat cylindrical shape, and therefore the cross-sectional shape of the battery element 20 is a flat, substantially elliptical shape.

[0138] (positive electrode)

[0139] The positive electrode 21 has the same structure as that of the positive electrode 100. Figure 5 As shown, the positive electrode 21 includes a positive electrode collector 21A and a positive electrode active material layer 21B. The structures of the positive electrode collector 21A and the positive electrode active material layer 21B are the same as the structures of the positive electrode collector 110 and the positive electrode active material layer 120 .

[0140] (negative electrode)

[0141] like Figure 5As shown, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

[0142] The negative electrode current collector 22A has a pair of surfaces provided with the negative electrode active material layer 22B. The negative electrode current collector 22A includes a conductive material such as a metal material, and a specific example of the conductive material is copper.

[0143] The negative electrode active material layer 22B includes any one or more of negative electrode active materials capable of inserting and removing lithium. In addition, the negative electrode active material layer 22B may also include any one 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, and specifically, it is any one or more of a coating method, a gas phase method, a liquid phase method, a thermal spraying method, and a sintering method (sintering method).

[0144] Here, the negative electrode active material layer 22B is provided on both surfaces of the negative electrode collector 22A. Alternatively, the negative electrode active material layer 22B may be provided only on one surface of the negative electrode collector 22A on the side of the negative electrode 22 facing the positive electrode 21 .

[0145] The type of negative electrode active material is not particularly limited, and specifically, it is a carbon material, a metal material, and metallic lithium (so-called lithium single substance), etc. This is because a high energy density can be obtained. It should be noted that the meaning of single substance is as described above.

[0146] The type of carbon material is not particularly limited, specifically, it is difficult graphitization carbon, easy graphitization carbon, graphite (natural graphite and artificial graphite), pyrolytic carbon, coke, glassy carbon, organic polymer compound sintered body, carbon fiber and activated carbon, etc. The coke includes pitch coke, needle coke and petroleum coke, etc. The organic polymer compound sintered body is a material that carbonizes the polymer compound by sintering polymer compounds such as phenolic resin and furan resin at an appropriate temperature. In addition, a part of the organic polymer compound sintered body is sometimes also classified as difficult graphitization carbon or easy graphitization carbon.

[0147] The change in the crystalline structure of the carbon material during charge and discharge is very small, so it is preferred in terms of obtaining a high charge and discharge capacity, and it is also preferred in terms of obtaining good cycle characteristics. In particular, graphite is preferred in terms of having a large electrochemical equivalent and being able to obtain a high energy density. In addition, difficult-graphitizable carbon is preferred in terms of being able to obtain excellent cycle characteristics. In addition, carbon materials with low charge and discharge potentials, more specifically carbon materials with charge and discharge potentials close to that of lithium metal, are preferred in terms of easily achieving high energy density of secondary batteries.

[0148] Metal-based materials are materials containing any one or more of metal elements and semi-metal elements that can form alloys with lithium as constituent elements. Specific examples of the metal elements and semi-metal elements are magnesium, boron, aluminum, titanium, gallium, indium, silicon, germanium, tin, lead, bismuth, cadmium, silver, zinc, hafnium, zirconium, yttrium, palladium and platinum.

[0149] The metal-based material can be crystalline or amorphous. More specifically, the metal-based material can be a simple substance, an alloy, a compound, a mixture of two or more thereof, or a material containing two or more phases thereof. It should be noted that the meaning of a simple substance is as described above. An alloy can be not only a material containing two or more metal elements as constituent elements, but also a material containing one or more metal elements and one or more semi-metal elements as constituent elements. In addition, an alloy can contain one or more non-metallic elements as constituent elements. The structure of the alloy is not particularly limited, and specifically, it can be a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or a coexistence of two or more thereof.

[0150] Among them, the metal-based material preferably contains a metal element or a semi-metal element of Group 4B in the short-period periodic table as a constituent element, and more preferably contains one or both of silicon and tin as a constituent element, because a sufficiently high energy density can be obtained.

[0151] As the element other than silicon, the alloy of silicon contains any one or two or more of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, niobium, molybdenum, aluminum, phosphorus, gallium, and chromium as constituent elements. As the element other than tin, the alloy of tin contains any one or two or more of silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, niobium, molybdenum, aluminum, phosphorus, gallium, and chromium as constituent elements.

[0152] The silicon compound and the tin compound each contain any one or two or more of oxygen and carbon as constituent elements. It should be noted that the silicon compound and the tin compound each contain any one or two or more of the series of elements described for the silicon alloy as constituent elements.

[0153] In particular, when the metal material contains tin as a constituent element, the metal material is preferably a material containing cobalt, tin and carbon as constituent elements and having low crystallinity or amorphousness, because a sufficiently high energy density can be obtained.

[0154] In addition, the negative electrode active material can be a metal oxide or a polymer compound that can embed and deintercalate lithium. The type of metal oxide is not particularly limited, and specifically, it is lithium titanium oxide, iron oxide, ruthenium oxide, and molybdenum oxide. A specific example of the lithium titanium oxide is lithium titanate (Li4Ti5O 12 ) etc., and specific examples of the polymer compound are polyacetylene, polyaniline and polypyrrole etc.

[0155] The details about the negative electrode binder are the same as those about the positive electrode binder, and the details about the negative electrode conductive agent are the same as those about the positive electrode conductive agent.

[0156] (Diaphragm)

[0157] like Figure 5 As shown, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and allows lithium to pass therethrough in an ionic state while preventing a short circuit caused by contact between the positive electrode 21 and the negative electrode 22. The separator 23 includes a polymer compound such as polyethylene.

[0158] (Electrolyte)

[0159] The electrolyte solution is a liquid electrolyte, and is impregnated into each of the positive electrode 21, the negative electrode 22, and the separator 23. The electrolyte solution contains a solvent and an electrolyte salt.

[0160] The solvent includes one or more of non-aqueous solvents (organic solvents), and the electrolyte solution including the non-aqueous solvent is a so-called non-aqueous electrolyte solution.

[0161] The non-aqueous solvent is an ester or an ether, and more specifically, is one or more of a carbonate compound, a carboxylate compound, a lactone compound, etc. This is because the dissociation property of the electrolyte salt and the ion mobility are improved.

[0162] The carbonate-based compounds are cyclic carbonates and chain carbonates. Specific examples of cyclic carbonates are ethylene carbonate and propylene carbonate, and specific examples of chain carbonates are dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0163] The carboxylate ester compound is a chain carboxylate, etc. Specific examples of the chain carboxylate are ethyl acetate, ethyl propionate, propyl propionate, ethyl trimethylacetate, and the like.

[0164] The lactone compound is lactone, etc. Specific examples of lactone are γ-butyrolactone and γ-valerolactone.

[0165] It should be noted that the ether may also be tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, etc. In addition, the ether may also be a compound represented by formula (3). The compound is a linear ether having an ethyleneoxy structural unit as a repeating unit, and specific examples of the compound are 1,2-dimethoxyethane, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0166]

[0167] (R1 and R2 are each an alkyl group having 1 to 10 carbon atoms. n is an integer of 1 to 10.)

[0168] The nonaqueous solvent is any one or more of unsaturated cyclic carbonate, fluorinated cyclic carbonate, sulfonic acid ester, phosphoric acid ester, acid anhydride, nitrile compound and isocyanate compound, etc. This is also because the dissociation property and ion mobility of the electrolyte salt are improved.

[0169] Specific examples of unsaturated cyclic carbonates are vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate. Specific examples of fluorinated cyclic carbonates are monofluoroethylene carbonate and difluoroethylene carbonate. Specific examples of sulfonic acid esters are propane sultone and propene sultone. Specific examples of phosphates are trimethyl phosphate and triethyl phosphate. Specific examples of anhydrides are succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of nitrile compounds are succinonitrile. Specific examples of isocyanate compounds are hexamethylene diisocyanate.

[0170] The electrolyte salt includes one or two or more of light metal salts such as lithium salts.

[0171] Specific examples of lithium salts are 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)methylide (LiC(CF3SO2)3), lithium bis(oxalate)borate (LiB(C2O4)2), lithium monofluorophosphate (Li2PFO3), lithium difluorophosphate (LiPF2O2), and lithium nitrate (LiNO3). This is because a high battery capacity can be obtained.

[0172] The content of the electrolyte salt is not particularly limited, but is specifically 0.3 mol / kg to 3.0 mol / kg relative to the solvent, because high ion conductivity can be obtained.

[0173] [Positive lead]

[0174] like Figure 4 as well as Figure 5 As shown, the positive electrode lead 31 is a positive electrode wiring connected to the positive electrode collector 21A of the positive electrode 21, and is led out to the outside of the outer film 10. The positive electrode lead 31 includes a conductive material such as a metal material, and a specific example of the conductive material is aluminum, etc. It should be noted that the shape of the positive electrode lead 31 is any one of a thin plate shape and a mesh shape.

[0175] [Negative lead]

[0176] like Figure 4 as well as Figure 5 As shown, the negative electrode lead 32 is a negative electrode wiring connected to the negative electrode 22, and is led out to the outside of the outer film 10. Here, the lead direction of the negative electrode lead 32 is the same as the lead direction of the positive electrode lead 31. The negative electrode lead 32 contains a conductive material such as a metal material, and a specific example of the conductive material is copper. It should be noted that the details of the shape of the negative electrode lead 32 are the same as the details of the shape of the positive electrode lead 31.

[0177] [Sealing film]

[0178] like Figure 4 As shown, the sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31. Figure 4 As shown, the sealing film 42 is inserted between the outer film 10 and the negative electrode lead 32. In addition, one or both of the sealing films 41 and 42 may be omitted.

[0179] The sealing film 41 is a sealing member that prevents outside air and the like from intruding into the interior of the outer film 10. The sealing film 41 contains a polymer compound such as polyolefin that has close adhesion to the positive electrode lead 31, and a specific example of the polymer compound is polypropylene and the like.

[0180] The sealing film 42 has the same structure as the sealing film 41 except that the sealing film 42 is a sealing member having close contact with the negative electrode lead 32. That is, the sealing film 42 includes a polymer compound such as polyolefin having close contact with the negative electrode lead 32.

[0181] <2-2. Action>

[0182] This secondary battery operates as follows during charge and discharge.

[0183] During charge, in the battery element 20, lithium is extracted from the positive electrode 21, and the lithium is inserted into the negative electrode 22 via the electrolyte. On the other hand, during discharge, in the battery element 20, lithium is extracted from the negative electrode 22, and the lithium is inserted into the positive electrode 21 via the electrolyte. During discharge and charge, lithium is inserted and extracted in an ionic state.

[0184] <2-3. Manufacturing method>

[0185] When manufacturing a secondary battery, after preparing the positive electrode 21 and the negative electrode 22 and preparing the electrolyte solution through the steps of an example described below, the secondary battery is assembled using the positive electrode 21, the negative electrode 22 and the electrolyte solution, and the assembled secondary battery is subjected to a stabilization treatment.

[0186] [Production of positive electrode]

[0187] The positive electrode 21 is produced by the same steps as those for producing the positive electrode 100. In this case, the positive electrode active material layers 21B are formed on both surfaces of the positive electrode current collector 21A.

[0188] [Production of negative electrode]

[0189] First, the negative electrode active material, the negative electrode binder and the negative electrode conductive agent are mixed with each other to form a negative electrode mixture. Next, a paste-like negative electrode mixture slurry is prepared by adding the negative electrode mixture to a solvent. The solvent can be an aqueous solvent or an organic solvent. Finally, the negative electrode mixture slurry is applied to both sides of the negative electrode collector 22A to form a negative electrode active material layer 22B. In addition, the negative electrode active material layer 22B can also be compression molded using a roller press or the like. In this case, the negative electrode active material layer 22B can be heated, or compression molding can be repeated multiple times. Thus, the negative electrode active material layer 22B is formed on both sides of the negative electrode collector 22A, thereby forming the negative electrode 22.

[0190] [Preparation of electrolyte]

[0191] The electrolyte salt is added to the solvent. Thus, the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing an electrolytic solution.

[0192] [Assembly of secondary battery]

[0193] First, the positive electrode lead 31 is connected to the positive electrode collector 21A of the positive electrode 21 by a joining method such as welding, and the negative electrode lead 32 is connected to the negative electrode collector 22A of the negative electrode 22 by a joining method such as welding.

[0194] Next, the positive electrode 21 and the negative electrode 22 are stacked with the separator 23 interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound to produce a wound body (not shown). Next, the wound body is pressed using a press or the like, thereby forming the wound body into a flat shape. The wound body after forming has the same structure as the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with an electrolyte.

[0195] Next, after the roll is stored in the recessed portion 10U, the outer packaging film 10 (welding layer / metal layer / surface protection layer) is folded so that the outer packaging films 10 face each other. Next, the outer peripheral edge portions of the two sides of the mutually facing welding layers are bonded to each other using an adhesive method such as a heat welding method, so that the roll is stored in the bag-shaped outer packaging film 10.

[0196] Finally, after the electrolyte is injected into the bag-shaped outer packaging film 10, the outer peripheral edge portions of the remaining one side of the mutually opposed welded layers are bonded to each other using a bonding method such as a heat welding method. In this case, the sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32.

[0197] Thus, the electrolyte solution is impregnated into the wound body, and the battery element 20 as a wound electrode body is formed. Thus, the battery element 20 is sealed inside the bag-shaped outer film 10, and the secondary battery is completed.

[0198] <2-4. Functions and effects>

[0199] According to this secondary battery, the positive electrode 21 has the same structure as that of the positive electrode 100. Therefore, it is easy to stably obtain a sufficient discharge capacity during charge and discharge for the above-mentioned reasons, and thus it is possible to obtain excellent battery characteristics.

[0200] In particular, if the secondary battery is a lithium-sulfur secondary battery, a sufficient battery capacity can be stably obtained by inserting and releasing lithium, and thus a higher effect can be obtained.

[0201] <3. Modifications>

[0202] As described below, the structure of the secondary battery can be appropriately changed. In addition, the series of modified examples described below can also be combined with each other.

[0203] [Modification 1]

[0204] In the above-mentioned positive electrode 100, the sulfur-containing material includes an alkali metal polysulfide, and the alkali metal polysulfide includes a lithium polysulfide. However, the alkali metal polysulfide may include a sodium polysulfide.

[0205] A secondary battery including a positive electrode 21 to which the positive electrode 100 is applied and a negative electrode 22 , in which a capacity can be obtained by intercalation and deintercalation of sodium in the negative electrode 22 , is a so-called sodium-sulfur secondary battery.

[0206] The structure of the sodium-sulfur secondary battery is the same as that of the lithium-sulfur secondary battery described above, except for the contents described below. The type of negative electrode active material is not particularly limited, and specifically includes carbon materials and metallic sodium (so-called single substance of sodium). It should be noted that the meaning of single substance is as described above. The electrolyte salt of the electrolyte solution includes any one or more of the sodium salts. Specific examples of the sodium salts are sodium salts corresponding to the specific examples of the lithium salts described above, etc.

[0207] In this case, it is easy to stably obtain a sufficient discharge capacity during charge and discharge of the secondary battery, and thus the same effect can be obtained.

[0208] [Modification 2]

[0209] In the above-mentioned positive electrode 100, the case where the sulfur-containing material includes polysulfide of an alkali metal is exemplified. However, the sulfur-containing material may include polysulfide of an alkaline earth metal, more specifically, may include polysulfide of magnesium.

[0210] A secondary battery including a positive electrode 21 to which the positive electrode 100 is applied and a negative electrode 22 , in which the capacity is obtained by intercalation and deintercalation of magnesium in the negative electrode 22 , is a so-called magnesium-sulfur secondary battery.

[0211] The structure of this magnesium-sulfur secondary battery is the same as that of the above-mentioned lithium-sulfur secondary battery except for the following details.

[0212] The type of negative electrode active material is not particularly limited, and specifically includes magnesium-based materials and the like. The magnesium-based material is a material containing magnesium as a constituent element, and may be a simple substance of magnesium, a magnesium alloy, a magnesium compound, a mixture of two or more thereof, or a material containing two or more phases thereof. It should be noted that the meaning of simple substance is as described above. The type of metal element (except magnesium) contained as a constituent element in the magnesium alloy is not particularly limited, and therefore can be selected arbitrarily. Magnesium compounds contain any one or more of non-metallic elements such as carbon, oxygen, sulfur, and halogens as constituent elements, and specific examples of the halogens are fluorine, chlorine, bromine, and iodine.

[0213] The electrolyte salt of the electrolyte solution includes one or more of the magnesium salts. The type of the magnesium salt is not particularly limited. When the electrolyte salt includes the magnesium salt, the solvent of the electrolyte solution preferably includes an ether (straight-chain ether) represented by formula (3). This is because the electrolyte salt is easily and stably dissolved in the solvent.

[0214] Specifically, the magnesium salt is a magnesium salt represented by formula (4).

[0215] MgX n … (4)

[0216] (X is a monovalent or divalent anion. n is 1 or 2.)

[0217] When X represented by formula (4) is a halogen ion, the magnesium salt is a so-called halogen metal salt. Specific examples of halogen are F, Cl, Br, and I.

[0218] Of course, X may also be an ion other than a halogen ion. Specific examples of magnesium salts when X is an ion other than a halogen ion are magnesium perchlorate (Mg(ClO4)2), magnesium nitrate (Mg(NO3)2), magnesium sulfate (MgSO4), magnesium acetate (Mg(CH3COO)2), magnesium trifluoroacetate (Mg(CF3COO)2), magnesium tetrafluoroborate (Mg(BF4)2), magnesium tetraphenylborate (Mg[B(C6H5)4]2), magnesium hexafluorophosphate (Mg(PF6)2), magnesium hexafluoroarsenate (Mg(AsF6)2), magnesium salt of perfluoroalkylsulfonic acid (Mg(RfSO3)2), magnesium salt of perfluoroalkylsulfonyl imide (Mg(Rf2SO2)2N)2), magnesium salt of hexaalkyldisilane (Mg[N(SiR3)2]), Mg[B(OCH(CRff3)2)4]2, etc. It should be noted that Rf is a perfluoroalkyl group and R is an alkyl group. In addition, the 48 Rffs are either H or F, and at least one of the 48 Rffs is F.

[0219] Among them, the magnesium salt preferably includes one or both of a halogen-based magnesium salt and an imide-based magnesium salt. This is because the energy density is further improved. In this case, the magnesium salt may include only one of a halogen-based magnesium salt and an imide-based magnesium salt, or the magnesium salt may include both a halogen-based magnesium salt and an imide-based magnesium salt.

[0220] The halogen magnesium salt is a magnesium salt in which X in formula (4) is a halogen ion. Specific examples of the halogen magnesium salt are magnesium fluoride (MgF2), magnesium chloride (MgCl2), magnesium bromide (MgBr2) and magnesium iodide (MgI2). Among them, the halogen magnesium salt is preferably magnesium chloride. This is because a sufficiently high energy density can be obtained.

[0221] The imide magnesium salt is a magnesium salt having an imide-type molecular structure, preferably a magnesium salt having a sulfonimide-type molecular structure. This is because a higher energy density can be obtained. In particular, if the imide magnesium salt and the halogen magnesium salt are used together, a higher energy density can be obtained.

[0222] Specific examples of imide magnesium salts are the above-mentioned magnesium salts of perfluoroalkylsulfonyl imide. In the structural formula of the magnesium salt of perfluoroalkylsulfonyl imide (Mg(Rf2SO2)2N), the number of carbon atoms of the perfluoroalkyl group (Rf) may be 1 to 10, 1 to 8, 1 to 6, 1 to 4, 1 to 3, or 1 or 2. Specific examples of magnesium salts of perfluoroalkylsulfonyl imide are magnesium bis(trifluoromethanesulfonyl)imide (Mg(CF3SO2)2N). In particular, if magnesium bis(trifluoromethanesulfonyl)imide and magnesium chloride are used in combination, a higher energy density can be obtained.

[0223] In this case, it is easy to stably obtain a sufficient discharge capacity during charge and discharge of the secondary battery, and thus the same effect can be obtained.

[0224] [Variation 3]

[0225] exist Figure 5 In the embodiment, the separator 23 which is a porous film is used. However, although not specifically shown here, a laminated separator including a polymer compound layer may be used instead of the separator 23 which is a porous film.

[0226] Specifically, the laminated separator includes a porous film having a pair of faces and a polymer compound layer arranged on one or both sides of the porous film. This is because the adhesion of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, so the positional deviation of the battery element 20, that is, the winding deviation of each of the positive electrode 21, the negative electrode 22 and the separator can be suppressed. Thus, even if a decomposition reaction of the electrolyte occurs, the expansion of the secondary battery can be suppressed. The polymer compound layer includes a polymer compound such as polyvinylidene fluoride. This is because polymer compounds such as polyvinylidene fluoride have excellent physical strength and are electrochemically stable.

[0227] It should be noted that one or both of the porous film and the polymer compound layer may contain a plurality of insulating particles. This is because the plurality of insulating particles dissipate heat when the secondary battery is heated, so the safety (heat resistance) of the secondary battery is improved. The plurality of insulating particles include any one or more of insulating materials such as inorganic particles and resin particles. The inorganic particles are aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. The resin particles are acrylic resins and styrene resins.

[0228] When a laminated separator is produced, a precursor solution containing a polymer compound and an organic solvent is prepared, and then the precursor solution is applied to one or both surfaces of a porous membrane. In this case, a plurality of insulating particles may be contained in the precursor solution.

[0229] When the laminated separator is used, the same effect can be obtained because lithium can move in an ion state between the positive electrode 21 and the negative electrode 22. In this case, in particular, as described above, since the positional displacement of the battery element 20 can be suppressed, the expansion of the secondary battery can be further suppressed, so that a higher effect can be obtained.

[0230] [Variation 4]

[0231] exist Figure 5 In the embodiment, an electrolyte solution as a liquid electrolyte is used. However, although not specifically shown here, an electrolyte layer as a gel electrolyte may be used instead of the electrolyte solution.

[0232] In the battery element 20 using the electrolyte layer, the positive electrode 21 and the negative electrode 22 are stacked on each other via the separator 23 and the electrolyte layer, and the positive electrode 21, the negative electrode 22, the separator 23 and the electrolyte layer are wound. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and between the negative electrode 22 and the separator 23.

[0233] Specifically, the electrolyte layer includes an electrolyte and a polymer compound, and the electrolyte is maintained by the polymer compound. This is because leakage of the electrolyte can be suppressed. The electrolyte is composed as described above. The polymer compound includes polyvinylidene fluoride, etc. When forming the electrolyte layer, a precursor solution including an electrolyte, a polymer compound, and an organic solvent is prepared, and then the precursor solution is coated on one or both sides of the positive electrode 21 and the negative electrode 22.

[0234] When the electrolyte layer is used, lithium can also move between the positive electrode 21 and the negative electrode 22 in an ionic state through the electrolyte layer, so the same effect can be obtained. In this case, in particular, as described above, since leakage of the electrolyte can be suppressed, a higher effect can be obtained.

[0235] <4. Applications of secondary batteries>

[0236] The purpose (application example) of the secondary battery is not particularly limited. The secondary battery used as a power source can be the main power source of electronic equipment and electric vehicles, etc., or it can be an auxiliary power source. The main power source is the power source that is used first, regardless of the presence or absence of other power sources. The auxiliary power source can be a power source that is used instead of the main power source, or a power source that is switched from the main power source.

[0237] Specific examples of the uses of secondary batteries are as follows. Electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, stereo headphones, portable radios, and portable information terminals. Storage devices such as backup power supplies and memory cards. Power tools such as electric drills and electric saws. Battery packs mounted on electronic devices, etc. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric vehicles (including hybrid vehicles). Power storage systems such as household or industrial battery systems that store electricity in advance in case of emergencies. In these uses, one secondary battery or multiple secondary batteries can be used.

[0238] The battery pack may use a single cell or a battery pack. An electric vehicle is a vehicle that uses a secondary battery as a driving power source to operate (drive), or a hybrid vehicle that also has other driving sources besides the secondary battery. In a home power storage system, the power stored in the secondary battery as a power storage source can be used to use home electrical products, etc.

[0239] Of course, the secondary battery may be used for other purposes besides the series of uses exemplified here.

[0240] Example

[0241] Embodiments of the present technology will be described.

[0242] <Examples 1 to 4 and Comparative Examples 1 to 3>

[0243] As described below, after the secondary battery was produced, the battery characteristics of the secondary battery were evaluated.

[0244] [Manufacturing of Secondary Batteries]

[0245] Through the steps described below, a secondary battery was manufactured.

[0246] Here, as an evaluation of battery characteristics, a secondary battery for testing was produced for simple evaluation. Figure 6 The cross-sectional structure of a secondary battery (a coin-type lithium-sulfur secondary battery) used for the test is shown.

[0247] like Figure 6 As shown, the secondary battery includes a test electrode 61, a counter electrode 62, a separator 63, an outer cup 64, an outer can 65, a gasket 66, and an electrolyte (not shown). Here, the test electrode 61 corresponds to the positive electrode, and the counter electrode 62 corresponds to the negative electrode.

[0248] The test electrode 61 is housed in an outer packaging cup 64, and the counter electrode 62 is housed in an outer packaging can 65. The test electrode 61 and the counter electrode 62 are stacked on each other via a separator 63, and the electrolyte is impregnated in the test electrode 61, the counter electrode 62, and the separator 63, respectively. Since the outer packaging cup 64 and the outer packaging can 65 are riveted to each other via a gasket 66, the test electrode 61, the counter electrode 62, and the separator 63 are sealed by the outer packaging cup 64 and the outer packaging can 65.

[0249] (Production of test pole)

[0250] In the case of manufacturing the test electrode 61, a calcination method was used. Specifically, first, a plurality of retaining particles 121 (anatase-type titanium oxide (anatase-type TiO2) or anatase-type titanium oxide (anatase-type TiO2 (boron-doped)) doped with 4 mol% of a dopant (boron) relative to titanium), a positive electrode binder (polyethylene glycol) and an aqueous solvent (water) were mixed with each other to obtain an aqueous paste. In this case, the mixing ratio (weight ratio) was set to a plurality of retaining particles 121: positive electrode binder = 90:10.

[0251] Next, the aqueous paste was applied to one side of the positive electrode current collector 110 (titanium foil with a thickness of 20 μm) to form a coating film. Next, the positive electrode current collector 110 with the coating film formed thereon was pressed using a roll press to press the coating film onto the positive electrode current collector 110 .

[0252] Next, the positive electrode current collector 110 with the coating film formed thereon was fired in the air (firing temperature = 750° C., firing time = 1 hour). As a result, the positive electrode binder was degreased, and the plurality of holding particles 121 were sintered to form a porous structure 124 .

[0253] Next, the positive electrode current collector 110 having the porous structure 124 formed thereon was punched out into a disk shape (diameter=15 mm).

[0254] Next, a sulfur-containing material (lithium sulfide (Li2S8) as a lithium polysulfide) was added to a solvent (1,2-dimethoxyethane), and the solvent was stirred to prepare a sulfur-containing solution. In this case, the concentration of the sulfur-containing solution was set to 200 mmol / l (=200 mmol / dm 3 ).

[0255] Finally, the positive electrode current collector 110 having the porous structure 124 was immersed in a sulfur-containing solution (immersion time = 1 hour), and then the positive electrode current collector 110 having the porous structure 124 was taken out from the sulfur-containing solution and dried. Thus, the plurality of positive electrode active material particles 122 (sulfur-containing material) were each held by the plurality of holding particles 121, thereby manufacturing a test electrode 61.

[0256] For comparison, a test electrode 61 was produced by the same procedure except that rutile titanium oxide (rutile TiO 2 ) was used instead of anatase titanium oxide as the material (forming material) of the plurality of holding particles 121 .

[0257] In addition, for comparison, a test pole 61 was made by substantially the same steps except that a carbon material (ketjen black) was used instead of anatase-type titanium oxide as the forming material (material) of the plurality of retaining particles 121. In this case, a coating method was used as a method for making the test pole 61. Specifically, a positive electrode active material (carbon material), a positive electrode binder (styrene-butadiene rubber) and a dispersant (carboxymethyl cellulose) were added to a solvent (a mixture of water as an aqueous solvent and ethanol as an organic solvent), thereby preparing a paste-like mixture slurry. In addition, the mixture slurry was applied to a single surface of the positive electrode collector 110, thereby drying the mixture slurry.

[0258] The column "Porous structure" in Table 1 shows whether the porous structure 124 is formed. "Formed" means that the porous structure 124 is formed because a sintered body that holds the plurality of particles 121 is formed. "Not formed" means that the porous structure 124 is not formed because a sintered body that holds the plurality of particles 121 is not formed.

[0259] (Fabrication of Counter Electrode)

[0260] An alkali metal (lithium metal plate) serving as a negative electrode active material was punched out into a disk shape (diameter = 16 mm). Thus, a counter electrode 62 was obtained.

[0261] (Preparation of electrolyte)

[0262] Electrolyte salt (lithium bis(trifluoromethanesulfonyl)imide) (LiN(CF3SO2)2) and lithium nitrate (LiNO3) are added to a solvent (1,2-dimethoxyethane as an ether), and then the solvent is stirred. In this case, the content of the electrolyte salt (lithium bis(trifluoromethanesulfonyl)imide) is 1 mol / l (=1 mol / dm 3 ), and the content of the electrolyte salt (lithium nitrate) relative to the solvent is 1 mol / l (=1 mol / dm 3 ). Thus, an electrolyte solution was prepared.

[0263] (Assembly of secondary batteries)

[0264] First, the test electrode 61 is housed in the outer packaging cup 64, and the counter electrode 62 is housed in the outer packaging can 65. Next, the test electrode 61 housed in the outer packaging cup 64 and the counter electrode 62 housed in the outer packaging can 65 are stacked on each other via a separator 63 (glass fiber separator with a thickness of 200 μm) impregnated with an electrolyte. In this case, the test electrode 61 is arranged in such a way that the positive electrode active material layer 120 is opposite to the counter electrode 62 via the separator 63. Finally, in a state where the test electrode 61 and the counter electrode 62 are stacked on each other via the separator 63, the outer packaging cup 64 and the packaging can 65 are riveted to each other via the gasket 66. Thus, the test electrode 61 and the counter electrode 62 are sealed in the outer packaging cup 64 and the outer packaging can 65, thereby completing the secondary battery.

[0265] After the secondary battery is completed, the secondary battery is disassembled to recover the test electrode 61. Using the test electrode 61, the average particle size AS (nm) of the plurality of holding particles 121 is calculated through the above-mentioned steps. The calculation results of the average particle size AS are shown in Table 1.

[0266] [Evaluation of battery characteristics]

[0267] As battery characteristics, initial charge and discharge characteristics and battery capacity characteristics were evaluated, and the results shown in Table 1 were obtained.

[0268] (Initial charge and discharge characteristics)

[0269] First, the charge capacity (mAh) and discharge capacity (mAh) of the secondary battery were measured using cyclic voltammetry at room temperature (temperature = 25°C). In this case, the scan rate = 0.01mV / sec, and the current (mA) was measured while scanning the potential (V) in the range of 1.9V to 2.8V, thereby obtaining the correlation between the potential and the current (cyclic voltammogram).

[0270] Next, the cyclic voltammogram is divided into a discharge region (a region where the current is negative) and a charge region (a region where the current is positive). Thus, the discharge capacity is calculated by integrating the current in the discharge region with time, and the charge capacity is calculated by integrating the current in the charge region with time.

[0271] Finally, the initial efficiency, which is an indicator for evaluating the initial charge and discharge characteristics, was calculated based on the calculation formula of initial efficiency (%) = charge capacity (mAh) / discharge capacity (mAh).

[0272] (Battery capacity characteristics)

[0273] After the above-mentioned discharge capacity (mAh) is measured, first, the secondary battery is disassembled to recover the test electrode 61, and the positive electrode current collector 110 is peeled off from the positive electrode active material layer 120. Next, the positive electrode active material layer 120 is added to an organic solvent (1,2-dimethoxyethane), the organic solvent is stirred, and then the organic solvent is filtered. As a result, since the plurality of positive electrode active material particles 122 are dissolved in the organic solvent, a filtrate as a non-dissolved component is recovered. The filtrate contains a porous structure 124 (a plurality of retaining particles 121).

[0274] Next, the surface area (m 2 ). In this case, as a surface area measuring device, a fully automatic specific surface area measuring device Macsorb (registered trademark) manufactured by Mountech Co., Ltd. was used. In addition, the porous structure 124 was degassed (heating temperature = 200° C. and heating time = 30 minutes), and then the surface area was measured using the BET method (nitrogen gas).

[0275] Finally, based on the basic capacity (mAh / m 2 ) = discharge capacity (mAh) / surface area (m 2 ) is used to calculate the basic capacity, which is an indicator for evaluating battery capacity characteristics.

[0276] [Table 1]

[0277]

[0278] [Investigation]

[0279] As shown in Table 1, the primary efficiency and the basic capacity vary greatly depending on the structure of the test electrode 61 .

[0280] Specifically, in the case where the material of the particles 121 is rutile titanium oxide and the porous structure 124 is formed (Comparative Example 2), the primary efficiency is significantly reduced and the basic capacity is also significantly reduced.

[0281] In addition, when the material of the holding particle 121 is a carbon material (ketjen black) and the porous structure 124 is not formed (Comparative Example 3), the primary efficiency is significantly increased, but the basic capacity is significantly reduced.

[0282] On the other hand, when the material of the particles 121 is anatase-type titanium oxide and a porous structure 124 is formed (Examples 1 to 4 and Comparative Example 1), the primary efficiency and the basic capacity vary depending on the average particle size AS.

[0283] When the average particle size AS is larger than 100 nm (Comparative Example 1), since the charge and discharge reaction does not proceed, the initial efficiency and the basic capacity cannot be calculated separately.

[0284] However, when the average particle size AS is 100 nm or less (Examples 1 to 3), the charge and discharge reactions proceed, so the primary efficiency and the basic capacity can be calculated separately. In this case, the primary efficiency increases significantly, and the basic capacity also increases significantly.

[0285] In particular, when the average particle size AS is 100 nm or less (Examples 1 to 3), if the average particle size AS is 30 nm or less, more specifically, 7 nm to 30 μm, the primary efficiency is further increased and the basic capacity is also further increased.

[0286] In addition, when boron-doped anatase titanium oxide is used as the material for retaining particles 121 (Example 4), the basic capacity can be further increased while maintaining significantly high primary efficiency, compared to the case of using anatase titanium oxide not doped with boron (Example 2).

[0287] [Summarize]

[0288] As shown in Table 1, the positive electrode 100 includes a positive electrode collector 110 and a positive electrode active material layer 120, the positive electrode active material layer 120 includes a plurality of retaining particles 121 (anatase-type titanium oxide) and a plurality of positive electrode active material particles 122 (sulfur-containing material), the positive electrode active material layer 120 includes a porous structure 124, the porous structure 124 is formed by direct bonding of a plurality of retaining particles 121 to each other, and is directly connected to the positive electrode collector 110, the plurality of positive electrode active material particles 122 are respectively retained by a plurality of retaining particles 121, and if the average particle size AS of the plurality of retaining particles 121 is 100 nm or less, a high initial efficiency can be obtained, and a high basic capacity can also be obtained. Therefore, since both the initial charge and discharge characteristics and the battery capacity characteristics are improved, excellent battery characteristics can be obtained in the secondary battery.

[0289] In the above, the structure of the secondary battery of the present technology has been described by taking one embodiment and one example. However, the structure of the secondary battery of the present technology is not limited to the structure described in one embodiment and one example, and various modifications are possible.

[0290] Specifically, the battery structure of the secondary battery is described as a laminated film type and a coin type, but since the battery structure of the secondary battery is not particularly limited, it may be a cylindrical type, a square type, a button type, or the like.

[0291] In addition, the case where the element structure of the battery element is a winding type is described. However, the element structure of the battery element is not particularly limited, and thus may be a stacked type, a repeatedly folded type, etc. In the stacked type, the positive electrode and the negative electrode are stacked on each other, and in the repeatedly folded type, the positive electrode and the negative electrode are folded into a Z shape.

[0292] The effects described in this specification are merely examples, and therefore the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects can also be obtained with respect to the present technology.

[0293] It should be noted that the present technology can also adopt the following structures.

[0294] <1> A secondary battery comprising a positive electrode, a negative electrode and an electrolyte,

[0295] The positive electrode comprises:

[0296] a positive electrode current collector; and

[0297] a positive electrode active material layer supported by the positive electrode current collector,

[0298] The positive electrode active material layer comprises:

[0299] a plurality of retaining particles containing anatase-type titanium oxide; and

[0300] A plurality of positive electrode active material particles containing a sulfur-containing material,

[0301] The plurality of retaining particles are directly bonded to each other to form a porous structure.

[0302] The porous structure is directly connected to the positive electrode collector.

[0303] The plurality of positive electrode active material particles are held by the plurality of holding particles, respectively.

[0304] The average particle size of the plurality of holding particles is 100 nm or less.

[0305] <2> The secondary battery according to <1>,

[0306] The average particle size is 30 nm or less.

[0307] <3> The secondary battery according to <1> or <2>,

[0308] The sulfur-containing material includes polysulfides of alkali metals.

[0309] <4> The secondary battery according to <3>,

[0310] The alkali metal polysulfide includes lithium polysulfide.

[0311] <5> The secondary battery according to any one of <1> to <4>,

[0312] The secondary battery is a lithium-sulfur secondary battery.

[0313] <6> A positive electrode for a secondary battery, comprising:

[0314] a positive electrode current collector; and

[0315] a positive electrode active material layer supported by the positive electrode current collector,

[0316] The positive electrode active material layer comprises:

[0317] a plurality of retaining particles containing anatase-type titanium oxide; and

[0318] A plurality of positive electrode active material particles containing a sulfur-containing material,

[0319] The plurality of retaining particles are directly bonded to each other to form a porous structure.

[0320] The porous structure is directly connected to the positive electrode collector.

[0321] The plurality of positive electrode active material particles are held by the plurality of holding particles, respectively.

[0322] The average particle size of the plurality of holding particles is 100 nm or less.

Claims

1. A secondary battery comprising a positive electrode, a negative electrode and an electrolyte, The positive electrode comprises: a positive electrode current collector; and a positive electrode active material layer supported by the positive electrode current collector, The positive electrode active material layer comprises: A plurality of retaining particles containing anatase-type titanium oxide; and A plurality of positive electrode active material particles containing a sulfur-containing material, The plurality of retaining particles are directly bonded to each other to form a porous structure. The porous structure is directly connected to the positive electrode collector. The plurality of positive electrode active material particles are held by the plurality of holding particles, respectively. The average particle size of the plurality of holding particles is 100 nm or less.

2. The secondary battery according to claim 1, wherein The average particle size is 30 nm or less.

3. The secondary battery according to claim 1 or 2, wherein: The sulfur-containing material includes polysulfides of alkali metals.

4. The secondary battery according to claim 3, wherein The alkali metal polysulfide includes lithium polysulfide.

5. The secondary battery according to any one of claims 1 to 4, wherein The secondary battery is a lithium-sulfur secondary battery.

6. A positive electrode for a secondary battery, comprising: a positive electrode current collector; and a positive electrode active material layer supported by the positive electrode current collector, The positive electrode active material layer comprises: A plurality of retaining particles containing anatase-type titanium oxide; and A plurality of positive electrode active material particles containing a sulfur-containing material, The plurality of retaining particles are directly bonded to each other to form a porous structure. The porous structure is directly connected to the positive electrode collector. The plurality of positive electrode active material particles are held by the plurality of holding particles, respectively. The average particle size of the plurality of holding particles is 100 nm or less.

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