Secondary batteries

Abstract

To realize a rechargeable battery with high safety. [Solution] The disclosed secondary battery includes a first electrode, a second electrode, and a separator interposed between the first electrode and the second electrode. Either the first electrode or the second electrode is the positive electrode and the other is the negative electrode. The first electrode includes a first electrode active material layer, the first electrode active material layer includes a first electrode active material and a first flame retardant containing halogen atoms. The separator includes a second flame retardant.

Description

[Technical Field]

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

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, offer high power output and high energy density. Therefore, they are used in small consumer applications, power storage devices, and as power sources for electric vehicles.

[0003] Various materials have been proposed as negative electrode active materials for non-aqueous electrolyte secondary batteries. As negative electrode active materials with high energy density, silicon compounds that alloy with lithium (e.g., silicon oxide) or silicon particles have been conventionally proposed (see, for example, Patent Document 1).

[0004] Patent Document 2 proposes a composite electrode plate for a lithium-ion battery, characterized in that it includes a battery electrode plate and a functional coating layer composited on the surface of the battery electrode plate, wherein the functional coating layer is manufactured from a functional substance and a bonding agent, the functional substance is one or more selected from phosphorus-containing compounds, nitrogen-containing compounds and inorganic silicon compounds, and the battery electrode plate is the positive electrode and / or negative electrode of the battery. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2010-212228 [Patent Document 2] Special Publication No. 2017-534138 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In recent years, the demand for higher energy density in non-aqueous electrolyte secondary batteries has been increasing. When increasing the energy density of non-aqueous electrolyte secondary batteries, high-level safety measures for the batteries in abnormal situations are required.

Means for Solving the Problems

[0007] One aspect according to the present disclosure relates to a secondary battery. The secondary battery includes a first electrode, a second electrode, and a separator interposed between the first electrode and the second electrode. The first electrode includes a first electrode active material layer. The first electrode active material layer includes a first electrode active material and a first flame retardant containing a halogen atom. The separator includes a second flame retardant.

Effects of the Invention

[0008] According to the present disclosure, a secondary battery having high safety can be realized. The novel features of the present invention are described in the appended claims. However, the present invention will be better understood with reference to the following detailed description in conjunction with the drawings, with respect to both the structure and the content, as well as other objects and features of the present invention.

Brief Description of the Drawings

[0009] [Figure 1] It is a schematic perspective view of a part of a secondary battery according to an embodiment of the present disclosure with a notch. [Figure 2] It is a schematic cross-sectional view showing a part of an electrode group of a secondary battery according to an embodiment of the present disclosure in an enlarged manner. [Figure 3] It is a schematic cross-sectional view showing a part of an electrode group of a secondary battery according to an embodiment of the present disclosure in an enlarged manner.

Modes for Carrying Out the Invention

[0010] Examples of embodiments according to the present disclosure will be described below. In the following, examples of embodiments according to the present disclosure will be described, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values and materials may be exemplified, but other numerical values and other materials may be applied as long as the effects of the present disclosure can be obtained. In this specification, when referring to "the range from numerical value A to numerical value B", the range includes numerical value A and numerical value B.

[0011] (Secondary battery) The secondary battery according to this embodiment includes a first electrode, a second electrode, and a separator interposed between the first electrode and the second electrode. The first electrode is either the positive electrode or the negative electrode in the secondary battery. The second electrode is the other of the positive electrode and the negative electrode in the secondary battery. The first electrode may be the positive electrode and the second electrode may be the negative electrode, or the first electrode may be the negative electrode and the second electrode may be the positive electrode.

[0012] The first electrode includes a first electrode active material layer. The first electrode active material layer contains a first electrode active material. The second electrode usually includes a second electrode active material layer. The second electrode active material layer usually contains a second electrode active material. When the first electrode is the positive electrode, the first electrode active material layer is the positive electrode active material layer, the second electrode active material layer is the negative electrode active material layer, the first electrode active material is the positive electrode active material, and the second electrode active material is the negative electrode active material. When the first electrode is the negative electrode, the first electrode active material layer is the negative electrode active material layer, the second electrode active material layer is the positive electrode active material layer, the first electrode active material is the negative electrode active material, and the second electrode active material is the positive electrode active material. The positive electrode active material layer is usually disposed on the surface of the positive electrode current collector. The negative electrode active material layer is usually disposed on the surface of the negative electrode current collector.

[0013] The first electrode active material layer further contains a first flame retardant containing a halogen atom. In other words, at least one of the positive electrode active material layer and the negative electrode active material layer, which are the first electrode active material layer, contains the first flame retardant. The separator also contains a flame retardant (second flame retardant).

[0014] The inventors of this application have found that by adding a specific flame retardant to the first electrode (positive or negative electrode) and the separator, it is possible to suppress the rise in battery temperature during abnormal conditions without significantly degrading battery performance. This disclosure is based on these new findings.

[0015] In the following, the first flame retardant contained in the first electrode active material layer may be referred to as "flame retardant (R1)," and the second flame retardant contained in the separator may be referred to as "flame retardant (R2)."

[0016] (First flame retardant (R1)) The first flame retardant (R1) contained in the first electrode active material layer exhibits a flame-retardant effect by releasing halogen atoms at high temperatures. Therefore, a secondary battery containing the first flame retardant (R1) can suppress excessive heat generation during abnormal conditions.

[0017] In the initial stages of an exothermic reaction, the negative electrode, which has a larger reaction area than the positive electrode, reacts preferentially with the electrolyte, generating H radicals. These H radicals then repeatedly react with other products, which is thought to accelerate the exothermic reaction. For example, O generated from the positive electrode active material. 2- The reaction between O2 and H radicals promotes exothermic reaction. However, by placing a flame retardant (R1) containing halogen atoms inside the negative electrode, the flame retardant (R1) deactivates the H radicals, suppressing the exothermic reaction. Similarly, by placing a flame retardant (R1) containing halogen atoms inside the positive electrode, the flame retardant (R1) deactivates the H radicals from the negative electrode, suppressing the exothermic reaction. Therefore, by placing a flame retardant (R1) containing halogen atoms in at least one of the positive and negative electrodes, exothermic reaction can be suppressed.

[0018] The flame retardant (R1) may satisfy at least one of the following conditions (1) and (2). However, it is preferable that the flame retardant (R1) satisfies both of the following conditions (1) and (2). (1) The flame retardant (R1) contains a cyclic structure to which halogen atoms are bonded. The cyclic structure may or may not be an aromatic ring. In this case, all halogen atoms may be bonded to the cyclic structure, or only some halogen atoms may be bonded to the cyclic structure. A structure in which halogen atoms are bonded to a cyclic structure is preferred because it makes it easier to increase the halogen atom content. (2) The proportion of halogen atoms in the flame retardant (R1) is 45% by mass or more. This proportion may be 60% by mass or more (for example, 70% by mass or more). There is no particular upper limit, but it may be 95% by mass or less (for example, 90% by mass or less). These lower and upper limits can be combined arbitrarily.

[0019] The structural formula of ethylene-1,2-bispentabromophenyl, an example of a flame retardant (R1), is shown below. The molecular weight of ethylene-1,2-bispentabromophenyl is 971.2, and it contains 10 bromine atoms (atomic weight: 79.9). Therefore, the proportion of halogen atoms in ethylene-1,2-bispentabromophenyl is 100 × 10 × 79.9 / 971.2 = 82.3% by mass.

[0020] [ka]

[0021] There are no particular limitations on the halogen atom, but preferred examples of halogen atoms include bromine (Br), fluorine (F), and chlorine (Cl). The halogen atom may be bromine and / or fluorine, or simply bromine, as it can be expected to have a flame-retardant effect from the initial stages of abnormal heat generation.

[0022] Because such a flame retardant (R1) containing halogen atoms has a higher specific gravity than conventionally used phosphorus-based flame retardants, its volume can be reduced relative to its added weight. This allows for the addition of a sufficient amount of flame retardant while maintaining a high amount of active material, thus enabling the maintenance of a high capacity. Due to its high specific gravity, it is preferable that the flame retardant (R1) contains bromine (Br). Furthermore, the more halogen atoms bonded to the flame retardant (R1), the better. The specific gravity of the flame retardant (R1) can be easily increased by the bonding of halogen atoms to a cyclic structure. The specific gravity of the flame retardant (R1) may be, for example, 2.7 or higher, and is preferably 3.0 or higher.

[0023] The flame retardant (R1) preferably does not contain moisture-generating moieties and / or hydrophilic groups in the compound structure. In this case, moisture is less likely to enter the battery during the secondary battery manufacturing process, enabling the realization of a highly reliable secondary battery. Examples of moisture-generating moieties include hydroxyl groups (-OH), carboxyl groups (-COOH), carbonyl groups (-CO-), and oxoacid groups such as sulfo groups and phosphate groups. Examples of hydrophilic groups include the above functional groups as well as amino groups.

[0024] Furthermore, when using a negative electrode active material containing silicon (Si), a flame retardant (R1) may be included in the negative electrode active material layer. In this case, the halogen atoms contained in the flame retardant (R1) react with Si, forming a stable film on the surface of the negative electrode active material. This allows for the maintenance of high cycle characteristics and the expectation of high durability.

[0025] The flame retardant (R1) may release halogen atoms at temperatures above 180°C (e.g., above 250°C). If the flame retardant releases halogen atoms at relatively low temperatures, the release of halogen atoms under normal circumstances may degrade the battery's performance. Therefore, it is preferable that the flame retardant (R1) does not substantially release halogen atoms at temperatures below 180°C.

[0026] Flame retardant (R1) is ethylene-1,2-bispentabromophenyl, ethylenebistetrabromophthalimide, tetrabromobisphenol A, hexabromocyclododecane, 2,4,6-tribromophenol, 1,6,7,8,9,14,15,16,17,17,18,18-dodecachloropentacyclo(12.2.1.1 6,9 .0 2,13 .0 5,10 ) may be at least one selected from the group consisting of octadeca-7,15-diene (trade name: dechloran plus) and tris(2,2,2-trifluoroethyl) phosphate. These flame retardants (R1) may be commercially available or may be synthesized by known synthetic methods.

[0027] When the mass ratio of the first electrode active material to the flame retardant (R1) in the first electrode active material layer is expressed as first electrode active material:flame retardant (R1) = 100:a, a may be greater than 0 and less than 15. This configuration can enhance safety without significantly reducing battery capacity. The value of a may be 0.1 or greater, 0.3 or greater, 0.5 or greater, or 1.0 or greater. The value of a may be less than 10, 5.0 or less, 3.0 or less, or 2.0 or less. These lower and upper limits can be combined arbitrarily as long as they do not contradict each other. For example, the value of a may be in the range of 0.1 or greater and less than 7 (for example, the range of 0.1 or greater and less than 4.5, the range of 0.1 to 3.0, the range of 0.1 to 2.0, the range of 0.1 to 1.0, the range of 0.5 to 2.0, the range of 0.5 to 1.0). The proportion of flame retardant (R1) in the first electrode active material layer can be determined by elemental analysis such as EDS on a cross-section of the first electrode active material layer.

[0028] (Second flame retardant (R2)) The second flame retardant (R2) contained in the separator has a flame-retardant effect similar to that of the flame retardant (R1), and also has the effect of suppressing excessive heat generation in the event of a malfunction in the secondary battery. By being included in the separator, the second flame retardant (R2) can suppress both the exothermic reaction that occurs at the positive electrode and the exothermic reaction that occurs at the negative electrode. When combined with the flame retardant (R1), the exothermic reaction that occurs at both the positive and negative electrodes of the secondary battery is significantly suppressed, and excessive heat generation and ignition in the event of a malfunction are effectively suppressed.

[0029] The flame retardant (R2) preferably contains at least one selected from the group consisting of cyclic compounds and phosphoric acid compounds, in which halogen atoms are bonded to a cyclic structure and the proportion of halogen atoms in the flame retardant (R2) is 45% by mass or more.

[0030] As the flame retardant (R2), a flame retardant containing halogen atoms, similar to that of flame retardant (R1), can be used. The flame retardant (R2) may include a cyclic structure in which halogen atoms are bonded, and may contain a cyclic compound in which halogen atoms account for 45% by mass or more of the flame retardant (R2). Examples of cyclic compounds include the compounds listed in the example of flame retardant (R1) above. However, in this case, the flame retardant (R2) may be the same cyclic compound as the flame retardant (R1), or it may contain a different cyclic compound from the flame retardant (R1).

[0031] A phosphate compound may be used as the flame retardant (R2). The phosphate compound is preferably one that transforms from a solid phase to a liquid phase or undergoes thermal decomposition. Such a phosphate compound may transform from a solid phase to a liquid phase in response to heat generation during an abnormal secondary battery operation, flowing across the surface of the separator's substrate layer, or it may expand across the substrate layer through thermal decomposition, forming a coating that covers the substrate layer. Since the coating functions as a resistive component, the amount of short-circuit current flowing between the positive and negative electrodes during an abnormal operation is suppressed, and as a result, the rise in battery temperature is also suppressed. The temperature at which the phosphate compound transforms from a solid phase to a liquid phase or undergoes thermal decomposition may be 180°C or higher. For example, the temperature at which the phosphate compound transforms from a solid phase to a liquid phase or undergoes thermal decomposition is in the range of 180°C to 1000°C, preferably 180°C to 900°C, and more preferably 180°C to 600°C.

[0032] Examples of phosphate compounds include metal phosphate salts such as lithium phosphate, sodium phosphate, potassium phosphate, calcium phosphate, magnesium phosphate, and aluminum phosphate; condensed phosphates such as ammonium polyphosphate, sodium tripolyphosphate, and melamine polyphosphate; and phosphate esters such as trimethylphosphate and triphenyl phosphate. In particular, it is preferable that the phosphate compound includes at least one selected from the group consisting of melamine polyphosphate, ammonium polyphosphate, and sodium tripolyphosphate.

[0033] As the flame retardant (R2), a mixture of the above-mentioned cyclic compound having a cyclic structure to which halogen atoms are bonded and a phosphoric acid compound may be used.

[0034] The flame retardant (R2) may be contained in the substrate layer of the separator, or in the surface layer facing the positive or negative electrode of the separator. When the flame retardant (R2) is included in the surface layer of the separator, the separator has a laminated structure comprising a base layer and a flame retardant layer containing the flame retardant (R2). In this case, the base layer may or may not contain the flame retardant (R2). The flame retardant (R2) may be included in both the base layer and the flame retardant layer. The flame retardant layer may be formed on only one side of the surface layer of the separator facing the positive or negative electrode, or it may be formed on both sides of the separator so that both the positive and negative electrodes face the flame retardant layer.

[0035] The flame retardant layer may be placed at least on the surface facing the second electrode of the separator. That is, if the positive electrode active material layer contains a flame retardant (R1), the flame retardant layer may be placed at least on the surface facing the negative electrode of the separator. On the other hand, if the negative electrode active material layer contains a flame retardant (R1), the flame retardant layer may be placed at least on the surface facing the positive electrode of the separator. In this case, the flame retardant layer containing a flame retardant (R2) enhances the effect of suppressing the exothermic reaction that occurs at the second electrode. Meanwhile, the exothermic reaction that occurs at the first electrode is sufficiently suppressed because the first electrode active material layer contains a flame retardant (R1). Therefore, the exothermic reactions that occur at both the positive and negative electrodes of the secondary battery can be efficiently suppressed, and excessive heat generation in abnormal situations can be effectively suppressed.

[0036] In the flame retardant layer, the flame retardant (R2) may exist in the form of aggregates formed by the aggregation of flame retardant (R2) particles, or in the form of aggregates formed by the aggregation of flame retardant (R2) particles via a binder. The flame retardant layer may partially cover the surface of the base layer, or it may cover almost the entire surface of the base layer. The coverage rate (based on area) of the flame retardant layer on the surface of the base layer may be 10% or more, or 20% or more, and preferably 30% or more, in order to suppress the rise in battery temperature during abnormal conditions. From the viewpoint of suppressing the rise in battery resistance, the coverage rate of the flame retardant layer on the surface of the base layer may be 90% or less, 80% or less, or 65% or less.

[0037] The coverage rate of the flame retardant layer on the surface of the base material layer may be 10% to 90%, 20% to 90%, 30% to 90%, 30% to 80%, or 30% to 65%.

[0038] The coverage rate of the flame retardant layer can be determined by performing elemental mapping of the separator surface using SEM-EDX (Energy Dispersive X-ray spectrometry) or the like. For example, by elemental mapping the flame retardant (R2) particles and the substrate layer, the coverage rate of the flame retardant layer on the surface of the substrate layer can be calculated.

[0039] In the flame retardant layer, the content of the flame retardant (R2) in the total flame retardant layer may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more. The content of the flame retardant (R2) in the total flame retardant layer may be 100% by mass or less, or 95% by mass or less. These lower and upper limits can be combined arbitrarily as long as they do not contradict each other. The proportion of the flame retardant (R2) in the flame retardant layer can be determined by elemental analysis such as EDS on a cross-section of the flame retardant layer.

[0040] The average particle size of the flame retardant (R2) particles in the flame retardant layer (or, if forming aggregates, the average particle size of the primary particles constituting the aggregate) may be 0.01 μm to 5 μm or 0.2 μm to 1 μm. The average particle size of the flame retardant (R2) is determined as follows: First, 20 flame retardant (R2) particles are randomly selected from the SEM image of the separator surface. Next, the grain boundaries of the 20 selected particles are observed to determine the particle shape, and the major axis of each of the 20 particles is determined. The average value of these values ​​is taken as the average particle size of the flame retardant (R2) particles.

[0041] The average thickness of the flame retardant layer is preferably 0.5 μm or more, and more preferably 1 μm or more, or 3 μm or more, in order to suppress the rise in battery temperature during abnormal conditions. The thickness of the flame retardant layer is preferably 4 μm or less in order to suppress the rise in battery resistance. These lower and upper limits can be combined arbitrarily as long as there is no contradiction. Note that the average thickness of the flame retardant layer is the average thickness considering the area on the surface of the base layer that is not covered by the flame retardant layer as having a thickness of 0 μm when the coverage rate is less than 100%, and is determined from the SEM image of the separator cross-section.

[0042] The flame retardant layer of the separator may contain a binder in addition to the flame retardant (R2). The inclusion of a binder in the flame retardant layer enhances the bonding between the flame retardant (R2) particles and the bonding of the flame retardant (R2) to the substrate layer. In other words, the flame retardant layer can be made to adhere closely to the substrate layer. The flame retardant layer can be formed by depositing a mixture containing at least flame retardant (R2) particles and a binder onto the surface of the substrate layer. The mixture may be a slurry containing flame retardant (R2) particles, a binder, and a solvent (dispersion medium). The flame retardant layer can be formed by spraying, dropping, or coating the slurry onto the surface of the substrate layer and allowing it to dry. The coverage and thickness of the flame retardant layer can be controlled by adjusting the amount of solvent relative to the amount of flame retardant (R2) particles in the slurry and / or the amount of slurry applied.

[0043] The binder is not particularly limited, but examples include polyvinylidene fluoride (PVdF), ethylene dimethacrylate, allyl methacrylate, t-dodecyl mercaptan, α-methylstyrene dimer, and methacrylic acid. The flame retardant layer may contain particles other than the flame retardant (R2) and binder. Examples of other particles include inorganic particles such as alumina, boehmite, and titania. These inorganic particles contribute to improving the heat resistance of the separator.

[0044] The base material (base layer) of the separator is made of porous sheets such as woven fabrics, nonwoven fabrics, or microporous membranes. Woven and nonwoven fabrics are primarily composed of fibers, with, for example, more than 60% by mass of the base layer being made up of fibers. Fibers such as glass fibers, polymer fibers, and pulp fibers can be used. Nonwoven fabrics are sheets formed by intertwining fibers without weaving. Woven and nonwoven fabrics may also contain components other than fibers, such as acid-resistant inorganic powders and polymers as binders. To incorporate a flame retardant (R2) into a woven or nonwoven fabric, for example, the flame retardant (R2) can be attached to fibers, and these fibers can be intertwined. This allows for the creation of a base layer containing the flame retardant (R2).

[0045] A microporous membrane is a porous sheet mainly composed of resin other than fiber components. When a microporous membrane is used as the substrate layer of a separator, the substrate layer containing a flame retardant (R2) can be manufactured as follows: A pore-forming agent is added to a synthetic resin mixed with flame retardant (R2) in a mass ratio of 0.5 to 50 parts resin, and the mixture is stretched at a temperature of approximately 100°C. The porosity of the microporous membrane is preferably 35 to 50%, and the pore size is preferably 1 μm or less. Fine flame retardant particles are uniformly arranged within the microporous membrane. Microporous membranes are preferably mainly composed of polymer components. Polyolefins such as polyethylene and polypropylene are preferred as polymer components. Other inorganic particles other than the flame retardant (R2) may be included in the composition. Examples of inorganic particles include ceramic particles such as silica, alumina, and titania.

[0046] The substrate layer may be a single layer or may have a laminated structure of multiple layers with different compositions. The thickness of the substrate layer is not particularly limited, but is, for example, in the range of 3 μm to 20 μm.

[0047] Below, an example of a secondary battery according to this embodiment and examples of its components will be described in detail. Note that known components may be used for components that are not characteristic of this disclosure. The secondary battery includes, for example, an outer casing (battery case), and a positive electrode, a negative electrode, an electrolyte, and a separator arranged inside the outer casing. The separator is positioned between the positive electrode and the negative electrode.

[0048] The shape of the rechargeable battery is not limited and may be cylindrical, rectangular, coin-shaped, button-shaped, etc. The battery case is selected according to the shape of the rechargeable battery. The rechargeable battery may be a non-aqueous electrolyte rechargeable battery.

[0049] [Negative electrode] The negative electrode includes a negative electrode active material layer and optionally further includes a negative electrode current collector. The negative electrode active material layer includes the negative electrode active material and essential components, and may include optional components such as binders, conductive materials, and thickeners. Known materials can be used as binders, conductive materials, and thickeners. The negative electrode active material layer may also contain a flame retardant (R1).

[0050] The negative electrode active material layer can be formed by dispersing the negative electrode active material layer material in a dispersion medium to create a negative electrode slurry, applying it to the surface of the negative electrode current collector to form a coating, and then drying the coating. The dried coating may be rolled if necessary. Examples of dispersion media include water, alcohol, ether, N-methyl-2-pyrrolidone (NMP), or mixed solvents thereof. The ratio of components in the negative electrode active material layer can be adjusted by changing the mixing ratio of the negative electrode active material materials. The negative electrode active material layer may be formed on only one surface of the negative electrode current collector, or on both surfaces.

[0051] The negative electrode active material can be at least one selected from materials that electrochemically intercalate and release lithium ions, lithium metals, and lithium alloys. Examples of electrochemically intercalating and releasing lithium ions include carbon materials and alloying materials. Examples of carbon materials include graphite, easily graphitizable carbon (soft carbon), and poorly graphitizable carbon (hard carbon). Among these, graphite is preferred because it has excellent charge-discharge stability and low irreversible capacity. Examples of alloying materials include those containing at least one metal that can form alloys with lithium, such as silicon, tin, silicon alloys, tin alloys, and silicon compounds. Silicon oxide and tin oxide, which are formed by bonding these with oxygen, may also be used.

[0052] As alloy materials containing silicon, for example, a silicon composite material can be used, which consists of a lithium-ion conductive phase and silicon particles dispersed in the lithium-ion conductive phase. As the lithium-ion conductive phase, for example, a silicon oxide phase, a silicate phase, and / or a carbon phase can be used. The main component of the silicon oxide phase (e.g., 95-100% by mass) may be silicon dioxide. Among these, a composite material composed of a silicate phase and silicon particles dispersed in the silicate phase is preferred because it has high capacity and low irreversible capacity.

[0053] The silicate phase may include, for example, at least one element selected from the group consisting of Group 1 and Group 2 elements of the long-period periodic table. Examples of Group 1 and Group 2 elements of the long-period periodic table include lithium (Li), potassium (K), sodium (Na), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Other elements that may be included include aluminum (Al), boron (B), lanthanum (La), phosphorus (P), zirconium (Zr), and titanium (Ti). Among these, a lithium-containing silicate phase (hereinafter also referred to as the lithium silicate phase) is preferred because it has a small irreversible capacity and high initial charge-discharge efficiency.

[0054] The lithium silicate phase may be any oxide phase containing lithium (Li), silicon (Si), and oxygen (O), and may also contain other elements. The atomic ratio of O to Si in the lithium silicate phase, O / Si, is, for example, greater than 2 and less than 4. Preferably, O / Si is greater than 2 and less than 3. The atomic ratio of Li: Li / Si is, for example, greater than 0 and less than 4. The lithium silicate phase is given by the formula: Li 2z SiO 2+zIt may have a composition represented by (0 < z < 2). It is preferable that z satisfies the relationship of 0 < z < 1, and more preferably z = 1 / 2. Examples of elements other than Li, Si, and O that may be contained in the lithium silicate phase include iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), aluminum (Al), and the like.

[0055] The carbon phase can be composed of, for example, low-crystalline amorphous carbon (i.e., amorphous carbon). The amorphous carbon may be, for example, hard carbon, soft carbon, or others.

[0056] As the negative electrode current collector, a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh body, a net body, a punching sheet, etc.) is used. Examples of the material of the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, copper alloy, and the like.

[0057] [Positive Electrode] The positive electrode includes a positive electrode active material layer. Typically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer (positive electrode binder layer) formed on the surface of the positive electrode current collector. The positive electrode active material layer can be formed by applying a positive electrode slurry in which a positive electrode binder containing a positive electrode active material is dispersed in a dispersion medium onto the surface of the positive electrode current collector and drying it. The dried coating film may be rolled if necessary. The positive electrode binder contains a positive electrode active material as an essential component and may contain, as optional components, a binder, a conductive agent, and the like. The positive electrode active material layer may contain a flame retardant (R1).

[0058] As the positive electrode active material, a lithium composite metal oxide can be used. Examples of the lithium composite metal oxide include, for example, Li 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 Ni1-b M b O c Li a Mn2O4, Li a Mn 2-b M b O 4、 LiGPO 4、 Li2GPO4F is one example. Here, M is at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. G includes at least one transition element (for example, at least one selected from the group consisting of Mn, Fe, Co, and Ni). Here, 0≦a≦1.2, 0≦b≦0.9, and 2.0≦c≦2.3. Note that the value of a, which indicates the molar ratio of lithium, increases or decreases with charging and discharging.

[0059] The same binders and conductive agents as those exemplified for the negative electrode can be used. Graphite such as natural graphite or artificial graphite may be used as the conductive agent.

[0060] Carbon nanotubes may be used as a conductive agent in the positive electrode active material layer. Carbon nanotubes have an extremely large aspect ratio (ratio of length to diameter). Therefore, even a small amount of carbon nanotubes exhibits high conductivity. By adding carbon nanotubes to the positive electrode active material layer, the resistance of the battery can be reduced, and degradation due to repeated charging and discharging can be suppressed. Furthermore, by using carbon nanotubes as a conductive material, it is possible to increase the proportion of positive electrode active material in the positive electrode active material layer. Therefore, secondary batteries can be made to have higher capacity.

[0061] On the other hand, secondary batteries with carbon nanotubes added to the positive electrode active material layer are more prone to abnormal events involving heat generation, such as internal short circuits, compared to secondary batteries with the same amount of conductive material such as acetylene black added. However, the inclusion of a flame retardant (R1) in the positive electrode active material layer suppresses the rise in battery temperature during abnormal events. As a result, high battery performance and safety can be achieved simultaneously. Carbon nanotubes may be single-walled, double-walled, or multi-walled. Single-walled carbon nanotubes are preferred because a large effect can be obtained with a small amount. Carbon nanotubes with a diameter of 5 nm or less contain a large amount of single-walled carbon nanotubes. Single-walled carbon nanotubes may make up 50% or more of the total carbon nanotube mass.

[0062] The carbon nanotube content in the positive electrode active material layer may be 0.01% by mass or more, 0.3% by mass or more, or 0.1% by mass or more, from the standpoint of reducing battery resistance. On the other hand, from the standpoint of achieving high capacity and suppressing the rise in battery temperature during abnormal conditions, the carbon nanotube content may be 10% by mass or less, 3% by mass or less, or 1% by mass or less. These lower and upper limits can be combined arbitrarily as long as they do not contradict each other.

[0063] The proportion of positive electrode active material in the positive electrode active material layer can be determined from a sample obtained by removing only the positive electrode active material layer from a discharged secondary battery. Specifically, first, the discharged secondary battery is disassembled and the positive electrode is removed. Next, the positive electrode is washed with an organic solvent, then vacuum-dried, and a sample is obtained by peeling off only the positive electrode active material layer. By performing thermal analysis such as TG-DTA on this sample, the ratio of binder components and conductive material components other than the positive electrode active material can be calculated. If the binder components and conductive material components contain multiple types of carbon materials, the proportion of carbon nanotubes among them can be calculated by performing micro-Raman spectroscopy on a cross-section of the positive electrode active material layer.

[0064] The outer diameter and length of carbon nanotubes can be determined by image analysis using a scanning electron microscope (SEM). For example, the length can be determined by arbitrarily selecting several carbon nanotubes (e.g., 100 to 1000), measuring their length and diameter, and averaging them. The outer diameter of a carbon nanotube (in the case of a multi-wall carbon nanotube, the diameter of the outermost tube) is not limited to this, but may be in the range of 0.001 to 0.05 μm. The length of a carbon nanotube is not limited to this, but may be 0.5 μm or longer from the viewpoint of ensuring electron conduction in the positive electrode active material layer. Considering that the particle size of the positive electrode active material is generally between 1 μm and 20 μm, the length of the carbon nanotube may be of a similar length. That is, the length of a carbon nanotube may be, for example, between 1 μm and 20 μm.

[0065] Examples of carbon nanotubes include carbon nanofibers. Since various types of carbon nanotubes are commercially available, commercially available ones may be used. Alternatively, carbon nanotubes may be synthesized using known synthesis methods.

[0066] The shape and thickness of the positive electrode current collector can be selected from the same shapes and ranges as those for the negative electrode current collector. Examples of materials for the positive electrode current collector include stainless steel, aluminum, aluminum alloy, and titanium.

[0067] [Electrolyte] The electrolyte can be an electrolyte solution containing a solvent and a solute dissolved in the solvent. The solute is an electrolyte salt that undergoes ion dissociation in the electrolyte solution. The solute may include, for example, a lithium salt. Components of the electrolyte solution other than the solvent and solute are additives. Various additives may be included in the electrolyte solution.

[0068] Non-aqueous solvents are used as solvents. Examples of non-aqueous solvents include cyclic carbonate esters, linear carbonate esters, cyclic carboxylic acid esters, and linear carboxylic acid esters. Examples of cyclic carbonate esters include propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC). Examples of linear carbonate esters include diethyl 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 linear carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP). Non-aqueous solvents may be used individually or in combination of two or more.

[0069] Other non-aqueous solvents include cyclic ethers, linear ethers, nitriles such as acetonitrile, and amides such as dimethylformamide.

[0070] Examples of lithium salts include lithium salts of chlorine-containing acids (LiClO4, LiAlCl4, LiB 10 Cl 10 Lithium salts of fluorine-containing acids (such as LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts of fluorine-containing acid imides (such as LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), lithium halides (such as LiCl, LiBr, LiI, etc.) can be used. Lithium salts may be used individually or in combination of two or more types.

[0071] The lithium salt concentration in the electrolyte may be between 1 mol / liter and 2 mol / liter, or between 1 mol / liter and 1.5 mol / liter. By controlling the lithium salt concentration within the above range, an electrolyte with excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0072] The electrolyte may contain other known additives. Examples of additives include 1,3-propanesalton, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene.

[0073] [Separator] A separator is placed between the positive and negative electrodes. The separator can be made of a material containing a flame retardant (R2), with high ion permeability, and possessing appropriate mechanical strength and insulation properties. As mentioned above, microporous thin films, woven fabrics, nonwoven fabrics, etc., can be used as the separator. Examples of separator materials include polyethylene, polypropylene, polyolefins such as copolymers of polyethylene and α-olefin, acrylic resin, polystyrene, polyester, and cellulose.

[0074] An example of a secondary battery includes an outer casing, an electrode group housed within the casing, and a non-aqueous electrolyte. The structure of the electrode group is not particularly limited. One example of an electrode group is formed by winding the positive electrode, negative electrode, and separator together, with a separator placed between them. Another example of an electrode group is formed by stacking the positive electrode, negative electrode, and separator such that a separator is placed between them. The form of the secondary battery is not limited and may be cylindrical, prismatic, coin-shaped, button-shaped, laminate-shaped, etc.

[0075] There are no particular limitations on the method of manufacturing the secondary battery; known manufacturing methods may be applied, or known manufacturing methods may be modified and applied.

[0076] Examples of embodiments relating to this disclosure will be specifically described below with reference to the drawings. The components of the examples described below can be the components described above. Furthermore, the examples described below can be modified based on the above description. In addition, the matters described below may be applied to the embodiments described above. Furthermore, in the embodiments described below, components that are not essential to the secondary battery relating to this disclosure may be omitted.

[0077] Figure 1 is a schematic perspective view showing a portion of a rectangular secondary battery according to one embodiment of the present disclosure. The secondary battery 1 shown in Figure 1 includes a bottomed rectangular battery case 11, an electrode group 10 and an electrolyte (not shown) housed within the battery case 11. The electrode group 10 includes a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator interposed between them to prevent direct contact. The electrode group 10 is formed by winding the negative electrode, positive electrode, and separator around a flat core and then removing the core.

[0078] One end of the negative electrode lead 15 is attached to the negative electrode current collector of the negative electrode by welding or the like. One end of the positive electrode lead 14 is attached to the positive electrode current collector of the positive electrode by welding or the like. The other end of the negative electrode lead 15 is electrically connected to the negative electrode terminal 13 provided on the sealing plate 12. A gasket 16 is placed between the sealing plate 12 and the negative electrode terminal 13 to insulate them. The other end of the positive electrode lead 14 is connected to the sealing plate 12 and electrically connected to the battery case 11, which also serves as the positive electrode terminal. A resin frame 18 is placed on top of the electrode group 10. The frame 18 isolates the electrode group 10 from the sealing plate 12 and also isolates the negative electrode lead 15 from the battery case 11. The opening of the battery case 11 is sealed by the sealing plate 12. An injection hole 17a is formed in the sealing plate 12. The electrolyte is injected into the battery case 11 through the injection port 17a. After that, the injection port 17a is sealed by the seal 17.

[0079] Figure 2 is a schematic cross-sectional view showing an enlarged portion of the electrode group 10. In Figure 2, the positive electrode 3 comprises a positive electrode current collector 30 and a positive electrode active material layer 31. The positive electrode active material layer 31 contains a positive electrode active material and a flame retardant (R1) (neither of which are shown). The positive electrode 3 faces the separator 4. The separator 4 comprises a base layer 41 and a flame retardant layer 42. The flame retardant layer 42 contains a flame retardant (R2) and is located on the surface of the separator 4 that does not face the positive electrode 3. In the example in Figure 2, the flame retardant layer 42 is located on the surface of the base layer 41 so as to face the negative electrode 2.

[0080] Figure 3 is a schematic cross-sectional view showing an enlarged portion of the electrode group 10, and unlike the electrode group 10 in Figure 2, it shows an example in which the flame retardant layer 42 is arranged on the surface of the base layer 41 so as to face the positive electrode 3. In Figure 3, the negative electrode 2 has a negative electrode current collector 20 and a negative electrode active material layer 21. The negative electrode active material layer 21 contains a negative electrode active material and a flame retardant (R1) (neither of which are shown). The negative electrode 2 faces the separator 4. The separator 4 has a base layer 41 and a flame retardant layer 42. The flame retardant layer 42 contains a flame retardant (R2) and is arranged on the surface of the separator 4 facing the positive electrode 3.

[0081] In both Figure 2 and Figure 3, the flame retardant layer 42 may be arranged on both sides of the base layer 41 so as to face both the positive and negative electrodes. The base layer 41 may also contain a flame retardant (R2). [Examples]

[0082] The secondary battery relating to this disclosure will be described in more detail by reference to examples.

[0083] ≪Batteries A1~A9, C1~C5≫ In this embodiment, multiple secondary batteries (non-aqueous electrolyte secondary batteries) were fabricated and evaluated using the following procedure.

[0084] [Fabrication of the negative electrode] For the negative electrode active material, a mixture of silicon composite material and graphite was used, with a mass ratio of silicon composite material:graphite = 5:95. The negative electrode slurry was prepared by mixing the negative electrode active material with sodium carboxymethylcellulose (CMC-Na), styrene-butadiene rubber (SBR), water, and, if necessary, a flame retardant (R1) in a predetermined mass ratio. Next, a coating film was formed by applying the negative electrode slurry to the surface of the copper foil (negative electrode current collector). After drying the coating film, it was rolled to form negative electrode active material layers on both sides of the copper foil.

[0085] [Fabrication of the positive electrode] As the positive electrode active material, LiNi 0.88 Co 0.09 Al 0.03 O2 was used. A positive electrode slurry was prepared by mixing the positive electrode active material, polyvinylidene fluoride, N-methyl-2-pyrrolidone (NMP), acetylene black, and, if necessary, a flame retardant (R1) in a predetermined mass ratio.

[0086] Next, a positive electrode slurry was applied to the surface of the aluminum foil (positive electrode current collector) to form a coating. After drying the coating, it was rolled to form positive electrode mixture layers on both sides of the aluminum foil.

[0087] [Separator fabrication] A porous polyethylene sheet containing a flame retardant (R2) was prepared using the method described below to obtain separator S1. The thickness of separator S1 was 15 μm.

[0088] Using two types of polyethylene with different molecular weights as the resin, a porosity-forming agent was added to a synthetic resin prepared by mixing the resin with a flame retardant (R2) in a mass ratio of 100:10, and then stretching the mixture at 90°C to obtain separator S1. The porosity of separator S1 was 40%.

[0089] In addition, a porous polyethylene sheet (separator) S0 (thickness 15 μm) without flame retardant (R2) was prepared. The porosity of separator S0 was 42%.

[0090] A slurry for the flame retardant layer was prepared by mixing a flame retardant (R2), polyvinylidene fluoride (PVdF), and N-methyl-2-pyrrolidone (NMP) in a predetermined mass ratio. The obtained slurry was applied to one surface of a porous sheet S0 and dried to form a flame retardant layer. In this way, a separator S2 having a flame retardant layer containing the flame retardant (R2) on its surface was obtained. The coverage rate of the flame retardant layer was 40%.

[0091] [Preparation of electrolyte solution] An electrolyte was prepared by adding LiPF6 as a lithium salt to a mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7. The concentration of LiPF6 in the non-aqueous electrolyte was 1.3 mol / liter.

[0092] [Manufacturing of secondary batteries] Lead tabs were attached to each electrode. Next, the positive and negative electrodes were wound in a spiral pattern via a separator so that the leads were located on the outermost edge. The electrode group was thus fabricated. Next, the electrode group was inserted into an outer casing made of laminate film with aluminum foil as a barrier layer and vacuum dried. Then, a non-aqueous electrolyte was injected into the outer casing and the opening of the casing was sealed. In this way, a secondary battery was obtained.

[0093] In this embodiment, the flame retardant (R1) was not added to the negative electrode slurry, but was added to the positive electrode slurry. Multiple secondary batteries (batteries A1-A9, C1-C5) were prepared by changing the content of the flame retardant (R1) in the positive electrode active material layer, the structure of the separator, and the type and content of the flame retardant (R2) in the separator. As the flame retardant (R1) in the positive electrode active material layer, ethylene-1,2-bispentabromophenyl (SAYTEX®-8010, manufactured by Albemarle Japan Co., Ltd.), a cyclic compound having a cyclic structure with a halogen atom bonded to it, was used. The ratio of the substances in the positive electrode active material layer was changed by changing their mixing ratio when preparing the positive electrode slurry. As the flame retardant (R2) in the separator, ethylene-1,2-bispentabromophenyl and / or ammonium polyphosphate as a phosphoric acid compound was used, and was blended into the substrate layer or flame retardant layer of the separator to achieve a predetermined content ratio.

[0094] For batteries A1 to A3, a secondary battery was fabricated using separator S1. In batteries A4 to A9, a secondary battery was fabricated using separator S2. However, in batteries A4 to A6, when fabricating the electrode group, the positive and negative electrodes were wound in a spiral pattern with the separator S2 so that the flame retardant layer of separator S2 faced the positive electrode. In batteries A7 to A9, when fabricating the electrode group, the positive and negative electrodes were wound in a spiral pattern with the separator S2 so that the flame retardant layer of separator S2 faced the negative electrode.

[0095] Battery C1 is a comparative example, and no flame retardant (R1) was added to the positive electrode active material layer. In addition, a porous sheet S0 without flame retardant (R2) was used as the separator. In battery C2, a flame retardant (R1) was added to the positive electrode active material layer, but a porous sheet S0 without a flame retardant (R2) was used as a separator. In batteries C3 to C5, the positive electrode active material layer did not contain a flame retardant (R1), while separator S1 or S2 containing a flame retardant (R2) was used.

[0096] The following evaluations were performed on the fabricated secondary batteries. (1) Nail penetration test (a) The battery was charged at a constant current of 0.5C in an environment of 25℃ until the battery voltage reached 4.2V, and then continued to be charged at a constant voltage until the current value reached 0.02C. (b) In a 25°C environment, the tip of a round nail (2.7 mm in diameter) was brought into contact with the center of the battery charged in (a), and it was driven in at a speed of 1 mm / second. The driving of the round nail was stopped immediately after detecting a voltage drop in the battery due to an internal short circuit. After the battery was short-circuited by a round nail, the short-circuit current (I) and the battery voltage (V) were measured for one second. The amount of heat generated in one second was then calculated by integrating the product of the current (I) and voltage (V) over time.

[0097] Table 1 shows some of the battery manufacturing conditions and evaluation results. In Table 1, the flame retardant (R1) content represents the mass of flame retardant (R1) (ethylene-1,2-bispentabromophenyl) when the mass of the positive electrode active material in the positive electrode active material layer is set to 100. The flame retardant (R2) content represents the mass of ethylene-1,2-bispentabromophenyl and ammonium polyphosphate contained in the separator, respectively, when the mass of the separator resin is set to 100. In Table 1, the location of the flame retardant (R2) means that if it is "in the substrate," the flame retardant (R2) is added to the substrate layer; if it is "opposite the positive electrode," the flame retardant layer is located on the surface of the substrate layer opposite the positive electrode; and if it is "opposite the negative electrode," the flame retardant layer is located on the surface of the substrate layer opposite the negative electrode. In the case of "opposite the positive electrode" or "opposite the negative electrode," the thickness (average film thickness) of the flame retardant layer is also shown.

[0098] [Table 1]

[0099] Table 1 shows that batteries A1 to A9, which contain a flame retardant (R1) in the positive electrode active material layer and a flame retardant (R2) in the separator, can reduce the amount of heat generated during the nail penetration test.

[0100] Battery C1, which does not contain flame retardants, generates a large amount of heat. Smoke was observed in battery C1 when a nail was driven into it. No smoke was observed in batteries A1 through A9.

[0101] A comparison of batteries A1 to A9 shows that in areas where the flame retardant (R2) is present within the separator, batteries A1 to A3, where the flame retardant (R2) is added to the base material, exhibit a significant decrease in heat generation. When the material and content of the flame retardant (R2) are the same, the heat generation tends to decrease in the following order: batteries A1 to A3 with the flame retardant (R2) added to the base material, batteries A7 to A9 where the flame retardant layer containing the flame retardant (R2) faces the negative electrode, and batteries A4 to A6 where the flame retardant layer containing the flame retardant (R2) faces the positive electrode.

[0102] Furthermore, as shown in batteries A3, A6, and A9, when a cyclic compound having a cyclic structure with a halogen atom bonded to it was combined with a phosphoric acid compound as the flame retardant (R2), the amount of heat generated decreased significantly.

[0103] ≪Batteries B1~B9, C6~C10≫ In this embodiment, the flame retardant (R1) was not added to the positive electrode slurry, but was added to the negative electrode slurry. Multiple secondary batteries (batteries B1-B9, C6-C10) were prepared by changing the content of the flame retardant (R1) in the negative electrode active material layer, the structure of the separator, and the type and content of the flame retardant (R2) contained in the separator. As the flame retardant (R1) contained in the negative electrode active material layer, ethylene-1,2-bispentabromophenyl (SAYTEX®-8010, manufactured by Albemarle Japan Co., Ltd.), a cyclic compound having a cyclic structure with a halogen atom bonded to it, was used. The ratio of the substances in the negative electrode active material layer was changed by changing their mixing ratio when preparing the negative electrode slurry. As the flame retardant (R2) contained in the separator, ethylene-1,2-bispentabromophenyl and / or ammonium polyphosphate as a phosphoric acid compound was used, and was blended into the substrate layer or flame retardant layer of the separator to achieve a predetermined content ratio.

[0104] For all other aspects, the same procedures as for secondary batteries A1-A9 and C1-C5 were followed, and multiple secondary batteries (non-aqueous electrolyte secondary batteries) were fabricated and evaluated in the same manner.

[0105] For batteries B1 to B3, a secondary battery was fabricated using separator S1. In batteries B4 to B9, a secondary battery was fabricated using separator S2. However, in batteries B4 to B6, when fabricating the electrode group, the positive and negative electrodes were wound in a spiral pattern with the separator S2 so that the flame retardant layer of separator S2 faced the positive electrode. In batteries B7 to B9, when fabricating the electrode group, the positive and negative electrodes were wound in a spiral pattern with the separator S2 so that the flame retardant layer of separator S2 faced the negative electrode.

[0106] Battery C6 is a comparative example, and no flame retardant (R1) was added to the negative electrode active material layer. In addition, a porous sheet S0 without flame retardant (R2) was used as a separator. In battery C7, a flame retardant (R1) was added to the negative electrode active material layer, but a porous sheet S0 without a flame retardant (R2) was used as a separator. In batteries C8 to C10, the negative electrode active material layer did not contain a flame retardant (R1), while separator S1 or S2 containing a flame retardant (R2) was used.

[0107] Some of the battery manufacturing conditions and evaluation results are shown in Table 2. In Table 2, the flame retardant (R1) content represents the mass of flame retardant (R1) (ethylene-1,2-bispentabromophenyl) when the mass of the negative electrode active material in the negative electrode active material layer is set to 100. The flame retardant (R2) content represents the mass of ethylene-1,2-bispentabromophenyl and ammonium polyphosphate contained in the separator, respectively, when the mass of the separator resin is set to 100. In Table 2, the location of the flame retardant (R2) means that if it is "in the substrate," the flame retardant (R2) is added to the substrate layer; if it is "opposite the positive electrode," the flame retardant layer is located on the surface of the substrate layer opposite the positive electrode; and if it is "opposite the negative electrode," the flame retardant layer is located on the surface of the substrate layer opposite the negative electrode. In the case of "opposite the positive electrode" or "opposite the negative electrode," the thickness (average film thickness) of the flame retardant layer is also shown.

[0108] [Table 2]

[0109] Table 2 shows that batteries B1 to B9, which contain a flame retardant (R1) in the negative electrode active material layer and a flame retardant (R2) in the separator, can reduce the amount of heat generated during the nail penetration test.

[0110] A comparison of batteries B1 to B9 shows that in areas where the flame retardant (R2) is present within the separator, batteries B1 to B3, in which the flame retardant (R2) is added to the base material, exhibit a significant decrease in heat generation. When the material and content of the flame retardant (R2) are the same, the heat generation tends to decrease in the following order: batteries B1 to B3, in which the flame retardant (R2) is added to the base material; batteries B4 to B6, in which the flame retardant layer containing the flame retardant (R2) faces the positive electrode; and batteries B7 to B9, in which the flame retardant layer containing the flame retardant (R2) faces the negative electrode.

[0111] Furthermore, as shown in batteries B3, B6, and B9, when a cyclic compound having a cyclic structure to which halogen atoms are bonded was combined with a phosphoric acid compound as the flame retardant (R2), the amount of heat generated decreased significantly. [Industrial applicability]

[0112] This disclosure can be used in secondary batteries. Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention. [Explanation of symbols]

[0113] 1: Non-aqueous electrolyte secondary battery, 2: Negative electrode, 3: Positive electrode, 4: Separator, 10: Electrode group, 11: Battery case, 12: Sealing plate, 13: Negative electrode terminal, 14: Positive electrode lead, 15: Negative electrode lead, 16: Gasket, 17: Sealing plug, 17a: Injection hole, 18: Frame, 20: Negative electrode current collector, 21: Negative electrode active material layer, 30: Positive electrode current collector, 31: Positive electrode active material layer, 41: Base layer, 42: Flame retardant layer

Claims

1. It includes a first electrode, a second electrode, and a separator interposed between the first electrode and the second electrode, The first electrode includes a first electrode active material layer, The first electrode active material layer comprises a first electrode active material and a first flame retardant containing halogen atoms. The first flame retardant includes a cyclic structure to which the halogen atoms are bonded, The proportion of the halogen atoms in the first flame retardant is 60% by mass or more. The separator contains a second flame retardant, The second flame retardant comprises at least one selected from the group consisting of a cyclic compound having a cyclic structure to which halogen atoms are bonded, wherein the proportion of halogen atoms in the cyclic compound is 45% by mass or more, and a phosphoric acid compound.

2. The secondary battery according to claim 1, wherein the first flame retardant releases the halogen atoms at a temperature of 180°C or higher.

3. The first flame retardant is ethylene-1,2-bispentabromophenyl, ethylenebistetrabromophthalimide, hexabromocyclododecane, 2,4,6-tribromophenol, and 1,6,7,8,9,14,15,16,17,17,18,18-dodecachloropentacyclo(12.2.1.1 ６，９ . 0 ２，１３ . 0 ５，１０ The secondary battery according to claim 1 or 2, wherein the secondary battery is at least one selected from the group consisting of octadeca-7,15-diene.

4. The secondary battery according to any one of claims 1 to 3, wherein the second flame retardant is contained in the substrate layer of the separator.

5. The secondary battery according to any one of claims 1 to 4, wherein the surface layer of one or both sides of the separator includes a flame retardant layer containing the second flame retardant.

6. The secondary battery according to claim 5, wherein the flame retardant layer is disposed at least on the surface layer of the separator facing the second electrode.

7. The secondary battery according to claim 5 or 6, wherein the average thickness of the flame retardant layer is 0.5 μm to 4 μm.

8. The second flame retardant comprises the phosphoric acid compound, The secondary battery according to any one of claims 1 to 7, wherein the phosphate compound comprises at least one selected from the group consisting of melamine polyphosphate, ammonium polyphosphate, and sodium tripolyphosphate.

9. The second flame retardant is ethylene-1,2-bispentabromophenyl, ethylenebistetrabromophthalimide, tetrabromobisphenol A, hexabromocyclododecane, 2,4,6-tribromophenol, 1,6,7,8,9,14,15,16,17,17,18,18-dodecachloropentacyclo(12.2.1.1 ６，９ . 0 ２，１３ . 0 ５，１０ The secondary battery according to any one of claims 1 to 8, wherein the battery is at least one selected from the group consisting of octadeca-7,15-diene and tris(2,2,2-trifluoroethyl) phosphate.

10. The secondary battery according to any one of claims 1 to 9, wherein the first electrode is a positive electrode and the second electrode is a negative electrode.

11. The secondary battery according to any one of claims 1 to 9, wherein the first electrode is a negative electrode and the second electrode is a positive electrode.

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