Secondary battery

Abstract

A secondary battery in which a first electrode and a second electrode are stacked with a separator interposed therebetween, the first electrode having a belt-shaped current collector and a mixture layer disposed on the current collector, the first electrode having an edge portion including one end portion in the width direction, and a main body portion other than the edge portion, the separator has a porous base material layer and a protective layer, the protective layer contains resin particles and covers the porous base material layer, and when the separator is divided into a first region facing the main body and a second region facing the edge portion, the protective layer contains the resin particles and covers the porous base material layer, and when the separator is divided into a first region facing the main body and a second region facing the edge portion, the first region and the second region face each other. The exposed area A1 of each resin particle exposed on the surface of the diaphragm in the first region is larger than the exposed area A2 of each resin particle exposed on the surface of the diaphragm in the second region.

Description

Technical Field

[0001] This disclosure relates to secondary batteries. Background Technology

[0002] In recent years, non-aqueous electrolyte secondary batteries, which have positive and negative electrodes arranged opposite each other with a separator, have been widely adopted as high-output, high-energy-density secondary batteries.

[0003] For example, Patent Document 1 proposes a scheme of "a non-aqueous electrolyte secondary battery having an electrode body formed by overlapping a positive electrode and a negative electrode separated by a separator, wherein at least one surface of the separator is formed with a porous layer having inorganic filler and binder, and the surface of the porous layer is formed with unevenness, wherein the maximum height difference of the unevenness is 0.2μm to 1.7μm".

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Re-evaluation No. 2011 / 158335 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The positive or negative electrode can be configured with an exposed portion (non-fusible portion) of the current collector, without an adhesive layer, for connection to the lead tab. This exposed portion can be located at one end in the width direction (short side direction). In this case, if the positive and negative electrodes overlap with a diaphragm in between, a height difference is created at the boundary between the exposed portion and the adhesive layer, thereby compressing the diaphragm. Under compression, the diaphragm becomes prone to rupture.

[0009] Methods for solving problems

[0010] One aspect of this disclosure relates to a secondary battery having a first electrode, a second electrode, an electrolyte, and a separator, wherein the first electrode and the second electrode overlap each other across the separator, the first electrode having a strip-shaped current collector and an agent layer disposed on the current collector, the first electrode having an edge portion including one end in the width direction and a main body portion other than the edge portion, the edge portion having an exposed portion on the surface of the current collector where the agent layer is not formed, the separator having a porous substrate layer and a protective layer, the protective layer being composed of resin particles and covering the porous substrate layer, wherein when the separator is divided in the width direction into a first region opposite to the main body portion and a second region opposite to the edge portion, the exposed area A1 of each resin particle 1 exposed on the surface of the separator in the first region is greater than the exposed area A2 of each resin particle exposed on the surface of the separator in the second region.

[0011] Invention Effects

[0012] According to this disclosure, in a secondary battery using a wound electrode assembly, when there is an exposed portion of a current collector without an adhesive layer at the edge of the electrode, the rupture of the separator can be suppressed.

[0013] Although novel features of the invention are described in the appended claims, both the structure and content of the invention, as well as other objects and features of the invention, can be better understood by taking into account the following detailed description in conjunction with the accompanying drawings. Attached Figure Description

[0014] [ Figure 1 [This is a cross-sectional schematic diagram of a secondary battery, representing one example of an implementation method.]

[0015] [ Figure 2 [Illustration] is a planar schematic diagram of the positive electrode, which is an example of an implementation method.

[0016] [ Figure 3 [This is a plan view of a diaphragm, one example of an implementation method.]

[0017] [ Figure 4 [Illustrative image] Figure 2 The positive electrode shown is Figure 3 The diagram shows a cross-sectional view of the diaphragm when it overlaps. Detailed Implementation

[0018] The following describes embodiments of this disclosure by way of example; however, this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials are sometimes shown, but other numerical values ​​and materials can be used as long as the effects of this disclosure are achieved. In this specification, the description of "numerical value A to numerical value B" includes both numerical value A and numerical value B, and can be interpreted as "numerical value A or higher and numerical value B or lower". In the following description, when examples are given of lower and upper limits for numerical values ​​relating to specific physical properties, conditions, etc., any combination of any of the example lower limits and any of the example upper limits can be arbitrarily combined, as long as the lower limit is not higher than the upper limit.

[0019] Furthermore, this disclosure includes combinations of matters recited in any two or more claims selected from the plurality of claims in the appended claims. That is, matters recited in any two or more claims selected from the plurality of claims in the appended claims can be combined, provided there is no technical contradiction.

[0020] Secondary batteries include non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries, lithium metal secondary batteries, and solid-state batteries containing gel electrolytes or solid electrolytes. That is, secondary batteries can be liquid secondary batteries containing an electrolyte solution, or all-solid-state secondary batteries containing a solid electrolyte.

[0021] One embodiment of the secondary battery disclosed herein includes a first electrode, a second electrode, an electrolyte, and a separator. The first electrode and the second electrode are overlapped together with the separator in between. The secondary battery may have a wound electrode assembly formed by winding the first electrode and the second electrode with the separator in between. The wound electrode assembly is cylindrical in shape, for example, it may be cylindrical. The configuration of the electrode assembly is not limited to this, and it may also have a stacked electrode assembly formed by stacking a positive electrode and a negative electrode with the separator in between.

[0022] Of the first electrode and the second electrode, at least the first electrode has a strip-shaped current collector and an adhesive layer disposed on the current collector. The first electrode has an edge portion including one end in the width direction and a main body portion other than the edge portion. The edge portion has an exposed portion (the portion where the adhesive layer is not formed) where the current collector is exposed on its surface. Multiple exposed portions may be formed at intervals along the length direction.

[0023] A height difference is formed at the boundary between the exposed portion and the compound layer. During charging and discharging, the electrode expands, and with this expansion, the diaphragm is subjected to pressure. At this time, the diaphragm is compressed at the portion in contact with the height difference, thus making the diaphragm prone to rupture.

[0024] In addition, the exposed portion is where the lead tabs are installed and the protective tape used to protect them is located, and a height difference is formed between the exposed portion and the lead tabs or protective tape. Therefore, the height difference formed by the lead tabs or protective tape can also cause the diaphragm to be compressed, making it more prone to breakage.

[0025] The diaphragm has a porous substrate layer and a protective layer. The protective layer is constructed containing resin particles and covers the porous substrate layer. The protective layer is more flexible than the porous substrate layer and has the function of mitigating pressure on the diaphragm. At elevation differences, the protective layer is compressed, thus preventing compression of the porous substrate layer. This helps to prevent diaphragm rupture.

[0026] Here, the diaphragm is divided into a first region opposite to the main body and a second region opposite to the edge in the width direction. At this time, the exposed area A1 of each resin particle exposed on the surface of the diaphragm in the first region is greater than the exposed area A2 of each resin particle exposed on the surface of the diaphragm in the second region (A1 > A2).

[0027] The second region, opposite to the edge, includes the region opposite to the lead tabs (and protective tape). Typically, the lead tabs (and protective tape) are thicker than the adhesive layer, so the height difference formed by the lead tabs or protective tape is also greater than the height difference formed by the adhesive layer. In this case, by making the exposed area A of each resin particle exposed on the surface of the diaphragm greater in the first region than in the second region, diaphragm breakage can be further suppressed.

[0028] Regarding the exposed area A of each resin particle on the surface of the diaphragm, without the heat-resistant layer described later, it is equal to the covered area of ​​each resin particle of the coated current collector. The larger the average size of the resin particles (the larger the average particle size), the larger the exposed area A becomes. The resin particles form protrusions protruding from the surface of the diaphragm. When the exposed area A is large, the height of the protrusions also increases due to the large particle size. The fact that the exposed area A1 in the first region is greater than the exposed area A2 in the second region means that the height h1 of the protrusions of the resin particles in the first region is higher than the height h2 of the protrusions of the resin particles in the second region.

[0029] As described above, the total thickness H of the lead tabs and protective tape opposite to the second region L Typically, the thickness H of the mixture layer opposite to the first region is greater. M Thickness (H) L >H M Therefore, when the diaphragm overlaps with the first electrode, the maximum electrode thickness is different in the main body and the edge portion. As a result, the diaphragm is subjected to compressive force and bends near the boundary between the main body and the area where the lead tabs are provided in the edge portion, making it easy to bend.

[0030] However, by making h1 > h2, the sum H of the thickness of the compound layer in the main body and the height of the protrusions of the resin particles in the first region can be reduced. M +h1 and the total of the thickness of the lead tabs and protective tape in the edge portion and the height of the protrusions of the resin particles in the second region H L The difference between +h2. As a result, the difference in the total thickness of the electrode and the diaphragm between the first region and the second region becomes smaller. When the diaphragm and the electrode are overlapped, the bending of the diaphragm at the boundary between the first region and the second region can be suppressed, thereby suppressing the rupture of the diaphragm.

[0031] In addition to resin particles, the protective layer of the separator can also include a heat-resistant layer containing inorganic particles. This heat-resistant layer imparts heat resistance to the separator, improving the safety of the secondary battery. The thickness of the heat-resistant layer can be greater than 0.1 μm and less than 10 μm.

[0032] In the protective layer with a heat-resistant layer, resin particles are dispersed within the heat-resistant layer. The thickness of the heat-resistant layer can be less than the average particle size of the resin particles. In this case, for each resin particle, at least a portion of each resin particle protrudes from the heat-resistant layer and is exposed on the surface of the diaphragm, forming a protrusion. The exposed area of ​​the protrusion corresponds to the aforementioned exposed area A of each resin particle.

[0033] Regarding the protrusion height (height of the protrusion) of the resin particles protruding from the surface of the separator, in the first region, it is, for example, 0.1 μm or more and 10 μm or less. The protrusion height of the resin particles can be obtained by taking a scanning electron microscope (SEM) image of a cross-section of the separator taken from the secondary battery using the method described later. For multiple (e.g., more than 100) resin particles, the height of the protrusions protruding from the surface of the separator is determined by image analysis, and the average height of the protrusions is taken as the protrusion height of the resin particles.

[0034] When the protective layer does not have a heat-resistant layer, the protrusion height of the resin particles is equal to the average particle size. When the protective layer has a heat-resistant layer, the protrusion height of the resin particles is approximately equal to the average particle size minus the thickness of the heat-resistant layer. The average particle size and the thickness of the heat-resistant layer can be determined through image analysis, thus deriving the protrusion height.

[0035] In region 2, the protrusion height (height h2) of the resin particles protruding from the diaphragm surface is less than the protrusion height (height h1) of the resin particles protruding from the diaphragm surface in region 1. Regarding the protrusion height of the resin particles in region 2, the thickness of the lead tabs and protective tape, as well as the thickness of the adhesive layer, can be considered, with the difference (h1-h2) between the protrusion heights of the resin particles in region 1 and region 2 approximately equal to the aforementioned H. L With H M The difference (H) L -H M This is determined in the way of ).

[0036] The exposed area A1 in region 1 is, for example, 1 μm. 2 Above and 80μm 2 The exposed area A1 can be 3.5 μm. 2 Above and 80μm 2 Below, 50μm 2 Above and 80μm 2 Below, or 50μm 2 Above and 71μm 2In this case, if the ratio A1 / A2 of the exposed area A1 in the first region to the exposed area A2 in the second region is 1.5 or more and 4 or less, the effect of suppressing membrane rupture is significant, and therefore preferred.

[0037] The exposed areas A1 and A2 can be determined as follows: by taking scanning electron microscope (SEM) images (hereinafter referred to as "SEM images") of the surface of the separator removed from the secondary battery, and performing image processing on the SEM images. For example, SEM observations are taken at magnification of 500x to 3000x for a measurement area of ​​100μm × 100μm. The separator can be removed from a fully charged secondary battery or from a discharged secondary battery. The separator removed from the secondary battery can be cleaned with dimethyl carbonate (DMC) and dried before measurement.

[0038] In the SEM image, the area occupied by each resin particle is taken as the exposed area of ​​the resin particle. For each resin particle, the exposed area is calculated through image processing. The average exposed area of ​​the resin particles in the measurement area is calculated as the exposed area A of each resin particle. In image analysis, the SEM image is binarized with resin particles represented as black (or white) and the rest as white (or black).

[0039] The exposed area A1 can be obtained by selecting a 100μm × 100μm measurement area in the first region and calculating the exposed area A of each resin particle using the method described above. Similarly, the exposed area A2 can be obtained by selecting a 100μm × 100μm measurement area in the second region and calculating the exposed area A of each resin particle using the method described above.

[0040] The constituent elements of the secondary battery constituting the embodiments of this disclosure will be described in detail below. Furthermore, the following description uses the first electrode having the aforementioned main body and edge portion as the positive electrode. However, the present invention is not limited thereto, and the first electrode may be the negative electrode. Both the positive and negative electrodes may be electrodes having the aforementioned main body and edge portion.

[0041] [positive electrode]

[0042] The positive electrode has a strip-shaped positive current collector and a positive electrode flux layer disposed on the positive current collector. The positive electrode flux layer may be in the form of a film. The positive electrode has a positive current collector and a positive electrode flux layer formed (or supported) on a portion of the surface of the positive current collector. Specifically, the positive electrode has a positive electrode edge portion including one end in the short side direction of the positive electrode, and a positive electrode body portion other than the positive electrode edge portion. The positive electrode edge portion has exposed portions of a plurality of positive current collectors disposed at intervals along the long side direction of the positive current collector. The portion of the exposed portion of the positive current collector from one end in the short side direction to the positive electrode body portion does not have a positive electrode flux layer.

[0043] The positive electrode flux layer is composed of a positive electrode flux. Since the positive electrode flux contains a positive electrode active material as an essential component, the positive electrode flux layer can also be called the positive electrode active material layer. The positive electrode flux layer can be supported on one or both surfaces of the positive electrode current collector.

[0044] The cathode compound contains a positive electrode active material as an essential component, and may also include binders, conductive additives, thickeners, etc., as optional components. The positive electrode active material can be a material capable of reversibly absorbing and releasing lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides. Representative examples of lithium-containing transition metal oxides include rock salt-type lithium cobalt oxide and lithium nickel oxide, which have a layered crystalline structure.

[0045] The positive electrode additive layer can be formed, for example, by coating a positive electrode slurry containing particles of the essential positive electrode active material and any other components (binder, conductive additive, etc.) in a dispersion medium onto the surface of the positive electrode current collector and then drying it. The dried coating can be calendered as needed. The positive electrode additive layer can be formed on one or both surfaces of the positive electrode current collector. N-methylpyrrolidone (NMP) or similar materials can be used as the dispersion medium for the positive electrode slurry.

[0046] As a positive electrode active material, composite oxides containing lithium and transition metals such as Ni, Co, and Mn can be used, for example. Li can be cited as an example. a CoO2, Li a NiO2, Li a MnO2, Li a Co b Ni 1-b O2, Li a Co b M 1-b O c Li a Ni 1-b M b O c Li a Mn2O4, Li a Mn2-b M b O4, LiMPO4, Li2MPO4F (M is selected from at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B). Where 0 < a ≤ 1.2, 0 < b ≤ 0.9, and 2.0 ≤ c ≤ 2.3. Furthermore, the value of 'a', representing the molar ratio of lithium, increases or decreases with charging and discharging.

[0047] Among them, Li is preferred. a Ni b Me 1-b Lithium-nickel composite oxide represented by O2 (where M is at least one selected from Mn, Co, and Al, 0 < a ≤ 1.2, 0.3 ≤ b < 1.) is preferred. From the viewpoint of high capacity, it is more preferable to satisfy 0.85 ≤ b < 1. From the viewpoint of the stability of the crystal structure, Li containing Co and Al as M is even more preferred. a Ni b Co c Al d O2 (0<a≦1.2, 0.85≦b<1, 0<c<0.15, 0<d≦0.1, b+c+d=1).

[0048] Examples of resin materials that can be used as adhesives include, for example, fluoropolymers such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF); polyolefin resins such as polyethylene and polypropylene; polyamide resins such as aromatic amide resins; polyimide resins such as polyimide and polyamide-imide; acrylic resins such as polyacrylic acid, polymethyl acrylate, and ethylene-acrylic acid copolymer; vinyl resins such as polyacrylonitrile and polyvinyl acetate; polyvinylpyrrolidone; and polyethersulfone. One type of adhesive can be used alone, or two or more can be used in combination.

[0049] Examples of conductive additives include carbon materials such as graphite, carbon black such as acetylene black, and carbon fibers (carbon nanotubes (CNTs) and other carbon fibers besides CNTs). A single conductive additive can be used alone, or two or more can be used in combination.

[0050] As the positive current collector, non-porous conductive substrates (such as metal foils) or porous conductive substrates (such as meshes, nets, perforated sheets, etc.) can be used. Examples of materials for the positive current collector include stainless steel, aluminum, aluminum alloys, and titanium. The thickness of the positive current collector is not particularly limited, but is preferably 1–50 μm, more preferably 5–20 μm.

[0051] [negative electrode]

[0052] The negative electrode has a strip-shaped negative electrode current collector. The negative electrode may have a negative electrode current collector and a negative electrode additive layer or a negative electrode active material layer formed (or supported) on the entire surface of the negative electrode current collector, or on a portion thereof. The negative electrode additive layer or negative electrode active material layer may be in the form of a film. The negative electrode additive layer or negative electrode active material layer may be supported on one or both surfaces of the negative electrode current collector.

[0053] The negative electrode additive layer can be composed of a negative electrode additive. The negative electrode active material layer can be composed of either a negative electrode additive or a negative electrode active material. Since the negative electrode additive contains a negative electrode active material as an essential component, the negative electrode additive layer can also be called the negative electrode active material layer. The negative electrode active material is a material capable of reversibly absorbing and releasing lithium ions; it can be lithium metal or a lithium alloy. The negative electrode active material layer, composed of substances other than the negative electrode additive, can be composed of at least one material selected from lithium metal and lithium alloys. The negative electrode additive layer or the negative electrode active material layer can be supported on one or both surfaces of the negative electrode current collector.

[0054] The negative electrode mixture contains a negative electrode active material as an essential component, and may also contain binders, conductive additives, tackifiers, etc., as optional components. Such a negative electrode mixture layer can be formed, for example, by coating a negative electrode slurry containing particles of the negative electrode active material (the essential component) and the optional negative electrode mixture in a dispersion medium onto the surface of the negative electrode current collector and then drying it. The dried coating film can be calendered as needed.

[0055] In the case where the negative electrode has a negative electrode flux layer, the negative electrode flux layer may contain an alloying material. This alloying material contains a phase capable of reversibly forming an alloy with lithium. For example, the phase capable of reversibly forming an alloy with lithium can be silicon (silicon phase). Such a phase undergoes very large expansion and contraction due to charging and discharging. The content of the alloying material in the negative electrode flux layer at the negative electrode edge can be greater than that in the negative electrode body. Therefore, it is easy to make the negative electrode expansion rate at the negative electrode edge greater than that in the negative electrode body.

[0056] The range of alloy materials includes Si-containing materials, Sn-containing materials, Si-Sn alloys, and Sn alloys. Among them, Si-containing materials have high capacity and are therefore suitable for use as negative electrode active materials. Si-containing materials contain a silicon phase. Silicon can reversibly form alloys with lithium. Si-containing materials are capable of reversibly absorbing and releasing lithium ions.

[0057] Silicon-containing materials can be composite particles containing a silicon phase and a matrix phase with dispersed silicon phase. The matrix phase can be composed of a material with lithium-ion conductivity. For example, the matrix phase may contain at least one selected from silicon oxide and carbon phases.

[0058] The silicon oxide phase contains Si and O, and may further contain a third element other than Si and O. The silicon oxide phase can be composed of SiO2, lithium silicate, or both.

[0059] The composite particles of silicon-containing materials (composite particles containing a silicon phase and a matrix phase containing a dispersed silicon phase) can be, for example, any of the following (a) to (c) forms.

[0060] (a) The first composite particle containing a silicon phase and a dispersed silicon phase of silicon dioxide (SiO2) phase.

[0061] (b) A second composite particle containing a silicon phase and a dispersed silicon phase of lithium silicate.

[0062] (c) A third composite particle containing a silicon phase and a carbon phase of dispersed silicon phase.

[0063] The first composite particle (containing a silicon dioxide (SiO2) phase and a silicon phase dispersed within the silicon dioxide (SiO2) phase) exhibits superior stability and minimal volume change in silicon-containing materials. This high stability is attributed to the small particle size of the silicon phase (or silicon particles) dispersed within the silicon dioxide phase, which hinders deep charging. While the silicon dioxide phase has numerous irreversible lithium-ion doping sites, it tends to exhibit increased irreversible capacity in silicon-containing materials; however, this increase is accompanied by high structural stability and effective suppression of volume changes.

[0064] The first composite particle can be synthesized, for example, by heating a raw silicon oxide in a non-oxidizing atmosphere to carry out a disproportionation reaction. During the disproportionation reaction, silicon microparticles can be uniformly generated within a silicon dioxide phase. The average particle size of the silicon microparticles generated by the disproportionation reaction is, for example, less than 100 nm, and can be 5 nm to 50 nm. For example, 95 to 100% by mass of the matrix phase of the first composite particle can be composed of silicon dioxide. The overall composition of the first composite particle can be based on the general formula SiO₂. x (0 < x < 2, preferably 0.5 ≦ x ≦ 1.5) indicates.

[0065] The silicon phase content in the first composite particle can be, for example, 20% to 60% by mass.

[0066] The second composite particle (containing a lithium silicate phase and a silicon phase dispersed within the lithium silicate phase) excels in silicon-containing materials due to its low irreversible capacity. Excellent charge-discharge efficiency can be achieved when using the second composite particle, especially during the initial stages of charge-discharge.

[0067] In addition to Li, Si, and O, the lithium silicate phase may contain at least one element selected from Group 1 (excluding Li) and Group 2 elements of the long-period periodic table as a third element. Examples of Group 1 and Group 2 elements include K, Na, Mg, Ca, Sr, and Ba. The lithium silicate phase may further contain Al, B, La, P, Zr, Ti, Fe, Cr, Ni, Mn, Cu, Mo, and Zn.

[0068] In the lithium silicate phase, the ratio of O atoms to Si atoms (O / Si) is, for example, greater than 2 and less than 4. This is advantageous in terms of stability and lithium-ion conductivity. The O / Si ratio can be greater than 2 and less than 3. In the lithium silicate phase, the ratio of Li atoms to Si atoms (Li / Si) is, for example, greater than 0 and less than 4.

[0069] The composition of lithium silicate can be derived from the general formula Li 2z SiO 2＋z (0 < z < 2) indicates that, from the viewpoint of the stability, ease of preparation and lithium-ion conductivity of lithium silicate, z preferably satisfies 0 < z < 1, and more preferably satisfies z = 1 / 2.

[0070] The second composite particles can be obtained, for example, by mixing lithium silicate with silicon, pulverizing and stirring the mixture using a mixer such as a ball mill, and then sintering the mixture under pressure in an inactive atmosphere. Alternatively, the mixture can be sintered, and the sintered body can be pulverized to obtain the second composite particles.

[0071] The silicon phase content in the second composite particle can be, for example, above 35% by mass and below 80% by mass. The silicon phase content in the second composite particle can be varied arbitrarily, so the design of high-capacity anodes is easy.

[0072] The third composite particle (containing a carbon phase and a silicon phase dispersed within the carbon phase) is superior in silicon-containing materials in terms of low irreversible capacity. Furthermore, the carbon phase can exhibit capacity through a Faraday reaction with lithium ions, which is advantageous for increasing capacity in silicon-containing materials.

[0073] The carbon phase can contain crystalline carbon (graphite) or amorphous carbon with low crystallinity (i.e., non-crystalline carbon). Amorphous carbon can be, for example, difficult-to-graphitize carbon, easy-to-graphitize carbon, or other amorphous carbon.

[0074] The third composite particles can be obtained, for example, by mixing a carbon source with raw silicon, pulverizing and stirring the mixture using a mixer such as a ball mill, and then sintering the mixture in an inactive atmosphere. Alternatively, the mixture can be sintered, and the sintered body can be pulverized to obtain the third composite particles.

[0075] As a carbon source, sugars, water-soluble resins, etc., can be used. For example, carboxymethyl cellulose (CMC), polyvinylpyrrolidone, cellulose, sucrose, etc., can be used as carbon sources. When mixing the carbon source with the raw material silicon, the carbon source and the raw material silicon can be dispersed in a dispersion medium of liquid organic matter such as alcohol.

[0076] The silicon phase content in the third composite particle can be, for example, above 40% by mass and below 80% by mass. The silicon phase content in the third composite particle can be varied arbitrarily, so the design of high-capacity anodes is easy.

[0077] The average particle size of the silicon phase (or silicon particles) in the second or third composite particles is, for example, greater than 100 nm and less than 500 nm, or less than 400 nm, or less than 200 nm. By giving the silicon phase such a large average particle size, it is easy to increase the capacity of these composite particles.

[0078] The silicon phase dispersed within the matrix phase of the second or third composite particle can be composed of multiple crystallites. The crystallite size can be, for example, less than 30 nm or less than 25 nm. In this case, the volume change caused by the expansion and contraction of the silicon phase during charging and discharging can be minimized. The crystallite size is not particularly limited; for example, it can be greater than 5 μm or greater than 10 nm.

[0079] The crystallite size of the silicon phase can be calculated from the half-width at half-maximum (WHM) of the diffraction peaks attributable to the Si (111) plane in the X-ray diffraction (XRD) pattern of the silicon phase using the Scherrer formula.

[0080] The average particle size of the first, second, and third composite materials can be, for example, 2 μm to 10 μm or 4 μm to 7 μm. This facilitates the mitigation of stress caused by volume changes in the silicon phase that occur during charging and discharging.

[0081] The average particle size refers to the particle size at which the cumulative volume value in a particle size distribution measured by laser diffraction scattering is 50% (volume average particle size). The measuring apparatus can be, for example, the "LA-750" manufactured by Horiba Corporation. The average particle size of carbon materials (such as graphite) can also be measured in the same way.

[0082] The silicon phase content in the first, second, and third composite materials can be determined, for example, by Si-NMR.

[0083] The average particle size of the silicon phase in composite materials 1, 2, and 3 can be determined by cross-sectional SEM (scanning electron microscopy) images of the composite particles. Specifically, the average particle size of the silicon phase can be calculated by averaging the maximum diameters of any 100 silicon particles.

[0084] The negative electrode mixture layer may contain a mixture of particles selected from at least one of the first composite particles, the second composite particles, and the third composite particles, and particles of materials other than such composite particles.

[0085] Materials other than Si-containing materials are preferred, including carbon materials, spinel-type lithium titanium oxide, and spinel-type lithium manganese oxide. Among these, carbon materials are preferred. Carbon materials can be graphite, easily graphitized carbon (soft carbon), or difficult-to-graphitize carbon (hard carbon). Graphite, which exhibits excellent charge-discharge stability and low irreversible capacity, is particularly preferred.

[0086] Graphite refers to carbon materials whose (002) plane spacing d002, as determined by X-ray diffraction, is, for example, 0.340 nm or less. In addition, the crystallite size Lc(002) of graphite, as determined by X-ray diffraction, can be, for example, 5 nm or more, 5 nm or more and 300 nm or less, or 10 nm or more and 200 nm or less.

[0087] The average particle size of graphite is, for example, greater than 1 μm and less than 30 μm.

[0088] When graphite and silicon-containing materials are used in combination, the proportion of silicon-containing materials in the negative electrode active material (the sum of graphite and silicon-containing materials) is, for example, 1% or more by mass and 20% or less by mass, 3% or more by mass and 15% or less by mass, or 3% or more by mass and 10% or less by mass. In this case, it is easy to achieve a good balance between improved cycle characteristics and high capacity.

[0089] Examples of adhesives include resin materials such as fluoropolymers like polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF); polyolefin resins like polyethylene and polypropylene; polyamide resins like aromatic amide resins; polyimide resins like polyimide and polyamide-imide; acrylic resins like polyacrylic acid, polymethyl acrylate, and ethylene-acrylic acid copolymers; vinyl resins like polyacrylonitrile and polyvinyl acetate; polyvinylpyrrolidone; polyethersulfone; and rubber-like materials like styrene-butadiene copolymer rubber (SBR). Adhesives can be used alone or in combination of two or more types.

[0090] Examples of conductive additives include carbon-based materials such as acetylene black, carbon fibers (carbon nanotubes (CNTs), and carbon fibers other than CNTs), metal fibers, and metal powders such as aluminum. A single conductive additive can be used, or two or more can be used in combination.

[0091] Examples of thickeners include carboxymethyl cellulose (CMC) and its modified forms (including salts such as Na salt), cellulose derivatives such as methyl cellulose (cellulose ethers, etc.), and saponifications of polymers containing vinyl acetate units such as polyvinyl alcohol. A single thickener can be used alone, or in combination of two or more.

[0092] As the negative current collector, non-porous conductive substrates (such as metal foil) or porous conductive substrates (such as mesh, net, perforated sheet, etc.) can be used. Examples of materials for the negative current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys. The thickness of the negative current collector is not particularly limited, but is preferably 1–50 μm, more preferably 5–20 μm.

[0093] [Septum]

[0094] A membrane exists between the positive and negative electrodes. The membrane has high ion permeability, moderate mechanical strength, and insulation properties. Microporous membranes, woven fabrics, non-woven fabrics, etc., can be used as membranes.

[0095] The diaphragm has a porous substrate layer and a protective layer. The protective layer contains resin particles. The protective layer can be disposed on one side or both sides of the porous substrate layer. The protective layer can be disposed on at least one side of the diaphragm, on the side opposite to the first electrode (here, the positive electrode).

[0096] Porous substrate layers can be, for example, porous sheets with ion permeability and insulation properties. Specifically, examples include microporous films, woven fabrics, and nonwoven fabrics. The materials for porous substrate layers are not particularly limited, and examples include, for instance, polyethylene, polypropylene, copolymers of polyethylene and α-olefins, acrylic resins, polystyrene, polyester, cellulose, polyimide, polyphenylene sulfide, polyetheretherketone, and fluoropolymers.

[0097] As resin particles, known polymers capable of being used as adhesives can be used, for example. As monomer units constituting the resin particles (polymer), examples include aromatic vinyl monomer units, (meth)acrylate monomer units, fluorinated monomer units, etc. Furthermore, in this disclosure, "(meth)acrylate" means acrylic acid and / or methacrylic acid. Additionally, "resin particles (polymer) containing monomer units" means that the polymer obtained using that monomer contains repeating units derived from the monomer.

[0098] Examples of aromatic vinyl monomers capable of forming aromatic vinyl monomer units are not particularly limited, and can be listed as styrene, α-methylstyrene, styrene sulfonic acid, butoxystyrene, vinylnaphthalene, etc. Examples of (meth)acrylate monomers capable of forming (meth)acrylate monomer units include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate and tert-butyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, and other alkyl acrylates; and methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate and tert-butyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, and other alkyl methacrylates.

[0099] In addition, there are no particular limitations on the examples of fluorinated monomers that can form fluorinated monomer units, such as vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, trifluorochloroethylene, fluoroethylene, perfluoroalkyl chain vinyl ethers, etc.

[0100] In addition to the monomer units mentioned above, the resin particles may contain crosslinking monomer units. Here, a crosslinking monomer unit refers to a monomer capable of forming a crosslinked structure during or after polymerization by heating or irradiation with energy rays. Examples of monomers capable of forming crosslinking monomer units include, for example, polyfunctional monomers having two or more polymerization-reactive groups. Examples of such polyfunctional monomers include, for example, divinyl methacrylate, divinylbenzene, and other divinyl compounds; di(meth)acrylate compounds such as diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, and 1,3-butanediol diacrylate; tri(meth)acrylate compounds such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate; and olefinically unsaturated monomers containing epoxy groups such as allyl glycidyl ether and glycidyl methacrylate; etc.

[0101] Resin particles can be prepared by polymerizing a monomer composition containing the aforementioned monomers, for example, in an aqueous solvent such as water. Furthermore, the polymerization method is not particularly limited; for example, it can be suspension polymerization, emulsion polymerization, coagulation polymerization, pulverization, etc. Additionally, any polymerization reaction, such as free radical polymerization or living free radical polymerization, can be used.

[0102] In the monomer composition used to prepare resin particles, chain transfer agents, polymerization regulators, polymerization retarders, reactive flow agents, fillers, flame retardants, anti-aging agents, colorants and other compounding agents can be added in any amount.

[0103] The protective layer can have a heat-resistant layer containing inorganic particles. In this case, the resin particles are dispersed in the heat-resistant layer. The average particle size (D50) of the resin particles can be greater than the thickness of the heat-resistant layer. In this case, resin particles with an average particle size (D50) larger than the thickness of the heat-resistant layer form protrusions from the surface of the heat-resistant layer.

[0104] The average particle size (D50) of the resin particles also depends on the thickness of the heat-resistant layer, and is preferably in the range of 1 μm to 10 μm. In this specification, D50 refers to the particle size at which the cumulative frequency in the volumetric particle size distribution reaches 50% from the smaller particle size side, also known as the median particle size. The particle size distribution of inorganic particles can be measured using a laser diffraction-type particle size distribution measuring device (e.g., the "LA-750" manufactured by Horiba Corporation).

[0105] Inorganic particles contained in the heat-resistant layer can include, for example, metal oxide particles, metal nitride particles, metal fluoride particles, and metal carbide particles.

[0106] Examples of metal oxide particles include, for example, aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, and manganese oxide. Examples of metal nitride particles include, for example, titanium nitride, boron nitride, aluminum nitride, magnesium nitride, and silicon nitride. Examples of metal fluoride particles include, for example, aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, and barium fluoride. Examples of metal carbide particles include, for example, silicon carbide, boron carbide, titanium carbide, and tungsten carbide.

[0107] Inorganic particles can also be zeolites (M 2 / n Porous aluminosilicates such as O・Al2O3・xSiO2・yH2O, where M is a metallic element, n is the valence of M, x≧2, y≧0, and talc (Mg3Si4O) are also mentioned. 10 Layered silicates such as (OH)2, barium titanate (BaTiO3), strontium titanate (SrTiO3), and other minerals. In addition, they can be used alone or in combination of two or more.

[0108] The average particle size (D50) of the inorganic particles is preferably in the range of 0.1 μm to 1.0 μm.

[0109] The content of inorganic particles in the heat-resistant layer, relative to the total mass of the heat-resistant layer, is preferably in the range of 15% to 85% by mass, and more preferably in the range of 30% to 60% by mass.

[0110] The thickness of the heat-resistant layer is preferably less than the thickness of the porous substrate layer, for example, 0.5 μm to 5 μm.

[0111] The heat-resistant layer preferably also contains an adhesive. The adhesive functions to bond the inorganic particles together with each other, and to the porous substrate layer. Examples of adhesive particles include fluorinated resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or its salts, and polyvinyl alcohol (PVA). One or more of these can be used individually. The content of the adhesive in the heat-resistant layer, relative to the total mass of the heat-resistant layer, is preferably 0.5 to 10% by mass, more preferably 1 to 5% by mass.

[0112] The content of resin particles dispersed in the heat-resistant layer, for example, from the perspective of ensuring good adhesion of the diaphragm, is preferably in the range of 1% to 15% by mass relative to the total mass of the heat-resistant layer, and more preferably in the range of 3% to 7% by mass.

[0113] The protrusions formed by resin particles, for example, from the perspective of ensuring good adhesion of the diaphragm, preferably have 10 to 35 protrusions in the range of 100 μm × 100 μm when viewed from above the surface of the functional layer, more preferably 15 to 30 protrusions.

[0114] A diaphragm having a protective layer containing resin particles can be made, for example, by mixing resin particles, water as a dispersion medium, and other components (inorganic particles, heat-resistant resin, adhesive, etc.) as needed to prepare a slurry composition for the protective layer, and then coating the protective layer slurry onto a porous substrate layer and allowing it to dry.

[0115] [Electrolytes]

[0116] The electrolyte can be a liquid electrolyte (electrolyte), a gel electrolyte, or a solid electrolyte. A liquid electrolyte is, for example, an electrolyte containing a non-aqueous solvent and a salt dissolved in the non-aqueous solvent. The concentration of the salt in the electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolyte may contain known additives.

[0117] Gel electrolytes contain salts and a matrix polymer, or salts, a non-aqueous solvent, and a matrix polymer. As a matrix polymer, for example, a polymer material that gels by absorbing a non-aqueous solvent can be used. Examples of polymer materials include fluoropolymers, acrylic resins, polyether resins, and polyethylene oxide.

[0118] As a solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) can be used.

[0119] For example, liquid non-aqueous electrolytes can be prepared by dissolving a salt in a non-aqueous solvent. The salt is an electrolyte salt that dissociates ions in the electrolyte, and may contain, for example, lithium salts. Various additives may be included in the electrolyte. Electrolytes are typically used directly as liquids, but they can also be used in states that restrict flowability, such as with gelling agents.

[0120] As a non-aqueous solvent, examples include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC) and ethylene carbonate (EC). Cyclic carbonates with unsaturated bonds, such as vinylene carbonate (VC), can also be used. Cyclic carbonates with fluorine atoms, such as fluoroethylene carbonate (FEC), can also be used. Examples of chain carbonates include dimethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. One non-aqueous solvent can be used alone, or two or more can be used in combination.

[0121] Examples of lithium salts include, for example, LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, and LiB. 10 Cl 10Examples of lithium salts include lower aliphatic carboxylic acids such as lithium, LiCl, LiBr, LiI, borates, and imide salts. Examples of borates include lithium bis(1,2-benzenediol(2-)-O,O')borate, lithium bis(2,3-naphthodinol(2-)-O,O')borate, lithium bis(2,2'-biphenyldiphenol(2-)-O,O')borate, and lithium bis(5-fluoro-2-phenol-1-benzenesulfonic acid-O,O')borate. Examples of imide salts include lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium trifluoromethanesulfonylnonafluorobutyrylimide (LiN(CF3SO2)(C4F9SO2)), and lithium bis(pentafluoroethanesulfonyl)imide (LiN(C2F5SO2)2). Lithium salts can be used alone or in combination of two or more. The concentration of lithium salts in non-aqueous electrolytes is, for example, 0.5 mol / L or higher and 2 mol / L or lower.

[0122] As an example of a secondary battery structure, one can exemplify a configuration where the positive and negative electrodes, wound together with a separator, are housed together with the electrolyte in an outer casing. However, this is not a limitation; other electrode configurations can also be used. For instance, a stacked electrode configuration can be formed by layering the positive and negative electrodes with a separator. The shape of the secondary battery is also not limited; it can be cylindrical, square, coin-shaped, button-shaped, or stacked, among other shapes.

[0123] The following detailed description of an example of a secondary battery according to an embodiment of the present disclosure is provided with reference to the accompanying drawings. The constituent elements of the secondary battery of the example described below can be those described above. The constituent elements of the secondary battery of the example described below can be modified based on the above description. Furthermore, the matters described below can also be applied to the above-described embodiments. In the constituent elements of the secondary battery of the example described below, constituent elements that are not essential to the secondary battery of the present disclosure can be omitted. Additionally, the figures shown below are schematic diagrams and do not accurately reflect the shape and number of actual components.

[0124] Figure 1 This is a cross-sectional schematic diagram of a secondary battery 10, which is an example of this embodiment. Figure 2 This is a planar schematic diagram of the positive electrode, which is an example of this embodiment. Figure 3 This is a planar schematic diagram of a diaphragm, which is an example of this embodiment. Figure 4 It is an illustrative representation of what will be Figure 2 The positive electrode shown Figure 3 The diagram shows a cross-sectional view of the diaphragm and the negative electrode when they overlap.

[0125] The secondary battery 10 can be, for example, a lithium-ion secondary battery or a lithium secondary battery (lithium metal secondary battery). Figure 1As shown, the secondary battery 10 has a non-polar casing 11, a wound electrode assembly 14, multiple positive leads 112 made of conductors, a positive terminal 16 made of conductors, an end face current collector 19 made of conductors, a negative current collector 22 made of conductors, and a sealing plate 23.

[0126] The outer casing 11 is formed at one end ( Figure 1 The lower end of the outer casing 11 is a bottomed cylindrical shape with an opening. The outer casing 11 is made of metal. The bottom of the outer casing 11 ( Figure 1 A through hole 12 is formed in the center of the upper end of the casing 11 for inserting the positive terminal 16. The casing 11 houses the electrode assembly 14 and an electrolyte (not shown). A recess 13 is formed near the opening in the casing 11, recessed radially inward towards the casing 11.

[0127] The electrode assembly 14 has a positive electrode 110 and a negative electrode 120. The electrode assembly 14 is a wound electrode assembly formed by winding the positive electrode 110 and the negative electrode 120 together with a diaphragm (not shown). The electrode assembly 14 is generally cylindrical in shape.

[0128] One end of each of the plurality of positive leads 112 is connected to the exposed portion 113b of the positive current collector at the positive edge portion 113 of the positive electrode 110. The other end of the plurality of positive leads 112 is configured to extend from one end face of the electrode group 14.

[0129] Multiple positive leads 112 overlap each other and are connected to the positive terminal 16 by soldering. In this embodiment, the number of positive leads 112 is eight, but it is not limited to this. Furthermore, Figure 1 Only 4 of the 8 positive leads 112 are shown in the diagram.

[0130] The materials of each positive lead 112 are, for example, stainless steel, aluminum, aluminum alloy, nickel, nickel alloy, etc.

[0131] An insulating member 24 is disposed between the electrode assembly 14 and the bottom of the housing 11 to electrically insulate the two. The insulating member 24 is made of, for example, insulating resin. The insulating member 24 can be mounted on the bottom of the housing 11.

[0132] The positive terminal 16 is positioned on the opposite side of the electrode assembly 14, separated by multiple positive leads 112. The positive terminal 16 is inserted into a through hole 12 at the bottom of the housing 11, penetrating the bottom of the housing 11. The positive terminal 16 is made of metal and can be secured with rivets or similar fasteners. The positive terminal 16 is insulated from the housing 11 by a positive washer 26 made of insulating material. An insulating plate 25 is disposed between the positive terminal 16 and the electrode assembly 14 to electrically insulate them from each other.

[0133] The positive terminal 16 has a first terminal component 17 extending inside and outside the housing 11, and a circular plate-shaped second terminal component 18 that is engaged with the first terminal component 17 and exposed to the outside of the housing 11. The first terminal component 17 has a circular plate-shaped first portion 17a, a hollow cylindrical second portion 17b continuously formed with the first portion 17a and inserted into the through hole 12, and a third portion 17c extending radially outward from the end of the second portion 17b and engaged with the second terminal component 18. The first terminal component 17 is welded to a plurality of positive electrode leads 112 by a laser beam irradiated from the first terminal component 17 in the first portion 17a in a direction toward the electrode assembly 14. Therefore, the positive terminal 16 is electrically connected to the positive electrode 110 via a plurality of positive electrode leads 112 and functions as the external positive terminal of the secondary battery 10. The first terminal component 17 is an example of a terminal component.

[0134] At least one of the positive leads 112 that is closest to the electrode group 14 (of the plurality of positive leads 112) Figure 1 The lowermost positive lead 112 has a folded portion 112a formed by folding a portion of the positive lead 112 (specifically, a portion of the front end side) and forming a portion of the laser mark LM generated by the laser. The folded portion 112a is disposed on the opposite side of the electrode group 14 through the insulating plate 25.

[0135] The end face current collector 19 is made of metal. The shape of the end face current collector 19 is not particularly limited; for example, it can be roughly cross-shaped. The end face current collector 19 is electrically connected to the negative terminal 120 of the electrode group 14.

[0136] The negative current collector 22 is electrically connected to the end face current collector 19 via a metal connecting plate 21 (e.g., which may be formed in a ring shape). Therefore, the negative current collector 22 is electrically connected to the negative electrode 120. The negative current collector 22 and the connecting plate 21 can be welded together (e.g., laser welding). The connecting plate 21 and the end face current collector 19 can be welded together (e.g., laser welding). Alternatively, the negative current collector 22 can be directly connected to the end face current collector 19. In this case, the connecting plate 21 is not required. The negative current collector 22 has one or more injection holes 22a for injecting electrolyte into the housing 11. The negative current collector 22 is welded to the aforementioned recess 13 of the housing 11 at its outer edge (e.g., laser welding). Therefore, the housing 11 is electrically connected to the negative electrode 120 via the negative current collector 22, etc.

[0137] The sealing plate 23 seals the opening of the outer casing 11. The sealing plate 23 is made of metal and is generally circular. The sealing plate 23 is insulated from the outer casing 11 by a negative electrode washer 27. In this embodiment, the sealing plate 23 is not electrically connected to either the positive electrode 110 or the negative electrode 120 of the electrode assembly 14, but this is not a limitation. The sealing plate 23 has an explosion-proof mechanism (not shown) that activates when the internal pressure of the outer casing 11 exceeds a predetermined value.

[0138] Figure 2 The positive electrode 110 shown depicts its state before being wound into electrode assembly 14. Figure 2 In the diagram, arrow Y1 indicates the winding direction of the positive electrode 110 during the fabrication of electrode assembly 14, and is the direction of the long side of the positive electrode 110. Additionally, in... Figure 2 In the diagram, arrow Y2, which is perpendicular to arrow Y1, is the winding axis direction of the positive electrode 110 (i.e., the winding axis direction of the electrode group 14), and is the direction of the short side of the positive electrode 110.

[0139] like Figure 2 As shown, the positive electrode 110 has a positive electrode edge portion (second region) 113 including one end 110a in the short side direction of the positive electrode 110, and a positive electrode main body portion 114 excluding the positive electrode edge portion 113. The positive electrode main body portion 114 is the region extending from the positive electrode central end 113a of the positive electrode edge portion 113 to the other end 110b in the short side direction of the positive electrode 110. The ratio of the width (length in the short side direction) of the positive electrode edge portion 113 to the width (length in the short side direction) of the positive electrode main body portion 114 is in the range of 1:15 to 3:4 or 1:12 to 1:7.

[0140] The positive electrode edge portion 113 of the positive electrode 110 has an exposed portion 113b of the positive electrode current collector without a positive electrode flux layer and a first positive electrode flux portion 113c of the positive electrode current collector with a positive electrode flux layer. Additionally, the positive electrode body portion 114 has a second positive electrode flux portion 114c of the positive electrode current collector with a positive electrode flux layer.

[0141] The exposed portion 113b of the positive current collector is provided at multiple locations (e.g., 8 locations) along the long side direction of the positive current collector. The exposed portion 113b does not have a positive electrode binder layer from one end 110a of the short side direction of the positive electrode 110 to the positive electrode body portion 114.

[0142] The length of the exposed portion 113b at each position of the positive current collector in the long side direction of the positive current collector can be 1% to 10% of the length of the long side direction of the positive current collector, and the total length of the exposed portions 113b of all positive current collectors in the long side direction of the positive current collector can be 5% to 30% or 8% to 20% of the length of the long side direction of the positive current collector.

[0143] The spacing between the exposed portions 113b of adjacent positive current collectors is preferably as equal as possible. For example, if the length of the positive current collector is set to L and the number of exposed portions 113b of the positive current collector is set to n, then the spacing between the exposed portions 113b of adjacent positive current collectors can be 0.8×L / n to 1.2×L / n.

[0144] Each exposed portion 113b of the positive current collector is connected to a sheet-like positive lead 112. Multiple positive leads 112 are bundled together and connected to the first portion 17a of the first terminal component 17. Additionally, although not in... Figure 2 As shown, however, the connection portion between the positive lead 112 and the exposed portion 113b can be protected by covering it with protective tape.

[0145] The other end of the negative electrode 120, in the short side direction, has an exposed portion of the negative electrode current collector without a negative electrode binder layer, similar to the positive electrode 110. This exposed portion of the negative electrode current collector is formed along the long side direction. Therefore, the exposed portion of the negative electrode current collector is exposed at the other end face of the electrode assembly 14. However, as... Figure 1 As shown, the exposed portion of the negative current collector is connected to the end face current collector plate 19, for example, by laser welding, instead of via a separately provided negative lead.

[0146] like Figure 3 As shown, the diaphragm 130 is divided into a first region 131 and a second region 132 with a certain position along its short side (width direction) as the boundary. The second region 132 is included in the region opposite to the positive electrode edge 113 when the electrode assembly 14 is formed, but does not include the region opposite to the positive electrode body 114. The first region 131 is the portion of the diaphragm 130 other than the second region 132, and includes the region opposite to the positive electrode body 114.

[0147] Resin particles 135 (135A, 135B) are exposed on the surface of the diaphragm 130. On the other hand, the exposed area of ​​resin particles 135A exposed in the first region 131 of the diaphragm 130 is greater than the exposed area of ​​resin particles 135B exposed in the second region 132.

[0148] like Figure 4 As shown in the cross-sectional view, the diaphragm 130 has a porous substrate layer 133 and a protective layer 134 covering the porous substrate layer 133. The protective layer 134 has resin particles 135 (135A, 135B) and a heat-resistant layer 136 containing inorganic particles. The average particle size of the resin particles 135A and 135B is larger than the thickness of the heat-resistant layer 136, so a portion of each resin particle 135A and 135B is exposed from the heat-resistant layer 136, thereby forming protrusions on the surface of the diaphragm 130.

[0149] The average particle size of resin particle 135A is larger than that of resin particle 135B. Therefore, the height h1 of the protrusion formed by resin particle 135A is greater than the height h2 of the protrusion formed by resin particle 135B. In addition, the exposed area of ​​resin particle 135A is greater than that of resin particle 135B.

[0150] If compressive stress is applied to the diaphragm through charging and discharging, resin particles 135A can contact the second positive electrode compound portion 114c formed on the positive electrode body portion 114, and at least a portion of resin particles 135B can contact the positive electrode lead 112 disposed on the positive electrode edge portion 113 or the protective tape 115 covering the positive electrode lead 112. In the positive electrode edge portion 113, the thickness H of the positive electrode lead 112 and the protective tape 115 is... L The thickness H is greater than that of the second positive electrode compound portion 114c in the positive electrode body portion 114. M However, the protrusion height h2 of resin particle 135B is less than the protrusion height h1 of resin particle 135A, therefore, as Figure 4 As shown, the total thickness when the separator is overlapped with the positive electrode can be kept approximately constant between the positive electrode body portion 114 and the positive electrode edge portion 113. Therefore, even when compressive stress is applied to the separator, bending or folding of the porous substrate layer 133 can be suppressed, and rupture of the separator 130 can be suppressed.

[0151] (Postscript)

[0152] The following technology is disclosed through the above description.

[0153] (Technology 1)

[0154] A secondary battery comprising a first electrode, a second electrode, an electrolyte, and a separator.

[0155] The first electrode and the second electrode overlap each other through the diaphragm.

[0156] The first electrode has a strip-shaped current collector and an agent layer disposed on the current collector.

[0157] The first electrode has an edge portion including one end in the width direction and a main body portion other than the edge portion. The edge portion has an exposed portion where the current collector is exposed because the agent layer is not formed on the surface of the current collector.

[0158] The membrane has a porous substrate layer and a protective layer, the protective layer being constructed containing resin particles and covering the porous substrate layer.

[0159] When the diaphragm is divided into two regions in the width direction, a first region opposite to the main body and a second region opposite to the edge,

[0160] In the first region, the exposed area A1 of each resin particle exposed on the surface of the diaphragm is greater than the exposed area A2 of each resin particle exposed on the surface of the diaphragm in the second region.

[0161] (Technology 2)

[0162] As described in Technique 1, the exposed area A1 is 1 μm. 2 Above and 80μm 2 the following,

[0163] The ratio of the exposed area A1 to the exposed area A2, A1 / A2, is 1.5 or more and 4 or less.

[0164] (Technology 3)

[0165] As described in technique 1 or 2, the secondary battery has a heat-resistant layer containing inorganic particles in its protective layer.

[0166] The resin particles are dispersed in the heat-resistant layer.

[0167] At least a portion of the resin particles protrude from the heat-resistant layer and are exposed on the surface of the diaphragm, thereby forming protrusions.

[0168] (Technology 4)

[0169] In the secondary battery as described in Technique 3, the protrusion height of the resin particles exposed in the first region of the separator is 0.1 μm or more and 10 μm or less.

[0170] (Technology 5)

[0171] In any one of the secondary batteries described in technical fields 1 to 4, the first electrode is the positive electrode.

[0172] The present invention will be specifically described below based on embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0173] <Example 1>

[0174] [The production of the positive electrode]

[0175] A suitable amount of N-methylpyrrolidone (NMP) is added to the positive electrode mixture to prepare a positive electrode slurry. The positive electrode mixture uses a mixture of lithium-containing composite oxide as the positive electrode active material, carbon black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder. The lithium-containing composite oxide uses LiNi 0.8 Co 0.1 Mn 0.1 In the positive electrode mixture, the mass ratio of lithium-containing composite oxide to carbon black to PVDF is 98:1:1.

[0176] A positive electrode slurry is coated on both sides of an aluminum foil serving as the positive current collector. The coating is dried and then calendered to form a positive electrode additive layer. Figure 2 The positive electrode is shown. Specifically, a positive electrode paste is applied at intervals along the long side of the positive electrode current collector at a predetermined thickness on one end of the aluminum foil in the short side direction, and then dried and calendered to form a positive electrode edge portion having a first positive electrode mixture portion. Additionally, a positive electrode paste is applied at a predetermined thickness on the positive electrode current collector other than the positive electrode edge portion, and then dried and calendered to form a positive electrode main body portion having a second positive electrode mixture portion. Furthermore, both the first and second positive electrode mixture portions are calendered simultaneously. Exposed portions of the positive electrode current collector in the positive electrode edge portion are provided at eight locations, and a positive electrode lead is installed at each exposed portion. The width of the positive electrode edge portion is set to 1 / 5 of the width of the positive electrode main body portion.

[0177] [Making the negative electrode]

[0178] Add an appropriate amount of water to the negative electrode mixture to prepare a negative electrode slurry. The negative electrode mixture uses SiO₂ as the active material for the negative electrode. x A mixture of graphite (x = 1.0) as the negative electrode active material, styrene-butadiene copolymer rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the tackifier. In the negative electrode mixture, the negative electrode active material (SiO₂) x The total mass ratio of SiO₂ (total with graphite) to SBR and CMC is 98:1:1. x The mass ratio of graphite to graphite is 5:95.

[0179] A negative electrode paste is coated on both sides of a copper foil serving as the negative electrode current collector, and the coating is dried. The coating is then rolled using rollers and cut to the specified electrode size to create a negative electrode with a negative electrode paste layer formed on both sides of the negative electrode current collector. However, a portion of the negative electrode current collector at the other end in the short side direction is left exposed.

[0180] [Septum fabrication]

[0181] Prepare a porous polyethylene substrate with a thickness of 12 μm. Mix α-Al2O3 powder (inorganic particles) with an average particle size (D50) of 0.8 μm, acrylic resin particles made from a copolymer of 2-ethylhexyl acrylate and styrene, and acrylic binder (adhesive) at a solid content mass ratio of 100:6:5. Then add an appropriate amount of water at a solid content concentration of 10% by mass to prepare a slurry for the protective layer.

[0182] Regarding the protective layer slurry, several types of slurries with different average particle sizes (D50) of the acrylic resin particles contained in the slurry are prepared. That is, a first protective layer slurry containing a first acrylic resin particle and a second protective layer slurry containing a second acrylic resin particle with an average particle size different from that of the first acrylic resin particle are prepared.

[0183] A first protective layer slurry is applied to a first region on one side of a porous substrate using a microgravure coating machine. Then, a second protective layer slurry is applied to a second region on the same side of the porous substrate using the same microgravure coating machine. The first region is the region opposite to the positive electrode body when forming the electrode assembly. The second region is the region opposite to the positive electrode edge when forming the electrode assembly.

[0184] The coating film, coated with the first protective layer slurry and the second protective layer slurry, is heated and dried in an oven at 50°C for 4 hours to produce a diaphragm having a heat-resistant layer and resin particles dispersed within the heat-resistant layer on one side of a porous substrate. The heat-resistant layer is formed with a thickness of 2 μm in both the first and second regions.

[0185] The surface of the protective layer of the diaphragm was observed using a scanning electron microscope, revealing multiple protrusions of the aforementioned resin particles extending from the heat-resistant layer. The exposed area of ​​the protrusion of each resin particle in each region of the first and second regions was calculated using the aforementioned method.

[0186] [Electrolyte Modulation]

[0187] Ethylene carbonate (VC) was added to a non-aqueous solvent prepared by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:3 volume ratio to dissolve LiPF6 and prepare an electrolyte. The VC content relative to the total electrolyte was 5% by mass. The concentration of LiPF6 in the electrolyte was 1.5 mol / L.

[0188] [Making a Secondary Battery]

[0189] In an inactive atmosphere, the positive and negative electrodes are wound together with a membrane (a microporous membrane made of polyethylene) in between to form an electrode assembly. The electrodes are overlapped such that the edge of the positive electrode is positioned on one end face of the electrode assembly, and the exposed portion of the negative electrode current collector is positioned on the other end face. The positive electrode and the membrane are overlapped such that the side of the membrane with the protective layer faces the positive electrode, with the first region overlapping the positive electrode body and the second region overlapping the edge of the positive electrode. The electrode assembly and electrolyte are then used to fabricate... Figure 1 The image shows a cylindrical lithium-ion secondary battery.

[0190] Multiple positive leads are bundled together and electrically connected to the first part of the first terminal component.

[0191] The exposed portion of the negative current collector is connected to the end face current collector plate by laser welding, and the end face current collector plate is electrically connected to the negative current collector plate via a connecting plate.

[0192] [evaluate]

[0193] Secondary batteries for each embodiment and comparative example were fabricated and subjected to constant current charging at 0.2C at 25°C. Constant voltage charging was then performed until the battery voltage reached 4.2V, at which point the charging current reached 0.02C. After a 10-minute pause, constant current discharging at 0.2C was performed until the battery voltage reached 2.5V. This charge-discharge cycle was repeated 100 times.

[0194] Observe the separator removed from the secondary battery after the charge-discharge test to confirm the state of the compression marks near the boundary between region 1 and region 2.

[0195] <Examples 2-5, Comparative Examples 1 and 2>

[0196] In Examples 2-5 and Comparative Example 2, the average particle size of the first acrylic resin particles and / or the average particle size of the second acrylic resin particles were made different from those in Example 1, and the slurry for the first protective layer and the slurry for the second protective layer were prepared. The other procedures were the same as in Example 1 to prepare the separator, and the separator was used to manufacture a lithium-ion secondary battery.

[0197] In Comparative Example 1, a protective layer without acrylic resin particles was coated onto the entire surface of one side of a porous substrate with a slurry. The coating was then heated and dried in an oven at 50°C for 4 hours to form a separator with a 2 μm thick protective layer (heat-resistant layer) without acrylic resin particles on one side of the porous substrate. The separator was then used to manufacture a lithium-ion secondary battery.

[0198] The evaluation results are shown in Table 1. In Table 1, secondary batteries A1 to A5 correspond to Examples 1 to 5, respectively. Secondary batteries B1 and B2 correspond to Comparative Examples 1 and 2. In Table 1, the exposed area A1 of each resin particle 1 in the first region, the exposed area A2 of each resin particle 1 in the second region, and the ratio A1 / A2 of the exposed area A1 to the exposed area A2 are shown as evaluation results in each battery.

[0199] Compression marks are evaluated by visually observing the condition of the diaphragm near the boundary between Region 1 and Region 2. The greater the compression of the diaphragm, the deeper the compression mark. First, the compression mark is classified into "deep" and "shallow" levels based on whether the discoloration of the diaphragm can be visually confirmed. Furthermore, based on the thickness of the porous substrate in the compression mark, "deep" is further divided into "very deep" and "slightly deep" levels, and "shallow" is divided into "very shallow" and "slightly shallow" levels, for a total of four levels for evaluation.

[0200]

[0201] As shown in Table 1, when the exposed area A1 is greater than the exposed area A2, the compression mark is shallow and can suppress the rupture of the diaphragm.

[0202] Industrial utilization potential

[0203] The secondary battery disclosed herein is useful in the main power source of mobile communication devices, portable electronic devices, electric vehicles, etc.

[0204] While preferred embodiments of the present invention have been described, the invention should not be construed as limited to such a disclosure. Various modifications and alterations are readily apparent to those skilled in the art upon reading the foregoing disclosure. Therefore, the scope of the appended claims should be interpreted as including all modifications and alterations without departing from the essential spirit and scope of the invention.

[0205] Explanation of reference numerals in the attached figures

[0206] 10: Secondary batteries

[0207] 11: Outer shell

[0208] 12: Through hole

[0209] 13: concave part

[0210] 14: Electrode assembly

[0211] 16: Positive extreme

[0212] 17: Terminal Component 1 (Terminal Component)

[0213] 17a: Part 1

[0214] 17b: Part 2

[0215] 17c: Part 3

[0216] 18: Second terminal component

[0217] 19: End face current collector

[0218] 21: Connecting plate

[0219] 22: Negative current collector

[0220] 22a: Injection Hole

[0221] 23: Sealing board

[0222] 24: Insulating components

[0223] 25: Insulation board

[0224] 26: Positive electrode washer

[0225] 27: Negative electrode washer

[0226] LM: Laser Mark

[0227] 110: Positive electrode

[0228] 110a one end

[0229] 110b other end

[0230] 112 positive lead

[0231] 112a: Folding section

[0232] 113 Positive electrode edge

[0233] 113a Positive Electrode Central End

[0234] 113b Positive Current Collector Exposed Section

[0235] 113c First Positive Electrode Mixture Section

[0236] 114 Positive Electrode Main Body

[0237] 114c Second Positive Electrode Mixture Section

[0238] 115 protective tape

[0239] 120: Negative electrode

[0240] 130: Diaphragm

[0241] 131 Area 1

[0242] 132 Area 2

[0243] 133 porous substrate layer

[0244] 134 protective layer

[0245] 135, 135A, 135B resin particles

[0246] 136 heat-resistant layer

Claims

1. A secondary battery comprising a first electrode, a second electrode, an electrolyte, and a separator. The first electrode and the second electrode overlap each other through the diaphragm. The first electrode has a strip-shaped current collector and an agent layer disposed on the current collector. The first electrode has an edge portion including one end in the width direction and a main body portion other than the edge portion. The edge portion has an exposed portion where the current collector is exposed because the agent layer is not formed on the surface of the current collector. The membrane has a porous substrate layer and a protective layer, the protective layer being constructed containing resin particles and covering the porous substrate layer. When the diaphragm is divided into two regions in the width direction, a first region opposite to the main body and a second region opposite to the edge, In the first region, the exposed area A1 of each resin particle exposed on the surface of the diaphragm is greater than the exposed area A2 of each resin particle exposed on the surface of the diaphragm in the second region.

2. The secondary battery as described in claim 1, wherein the exposed area A1 is 1 μm. 2 Above and 80μm 2 the following, The ratio of the exposed area A1 to the exposed area A2, A1 / A2, is 1.5 or more and 4 or less.

3. The secondary battery as described in claim 1 or 2, wherein the protective layer has a heat-resistant layer containing inorganic particles. The resin particles are dispersed in the heat-resistant layer. At least a portion of the resin particles protrude from the heat-resistant layer and are exposed on the surface of the diaphragm, thereby forming protrusions.

4. The secondary battery of claim 3, wherein the protrusion height of the resin particles exposed in the first region of the separator is 0.1 μm or more and 10 μm or less.

5. The secondary battery as described in claim 1 or 2, wherein the first electrode is the positive electrode.

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