Secondary batteries

Abstract

This disclosed secondary battery comprises a first electrode, a second electrode, and a separator disposed between the first electrode and the second electrode. Either the first electrode or the second electrode is a positive electrode and the other is a negative electrode. The first electrode contains a first electrode active substance layer, and the first electrode active substance layer contains a first electrode active substance and a first fireproofing agent containing halogen atoms. The separator contains a second fireproofing agent.

Description

[Technical Field]

[0001] The present disclosure relates to secondary batteries. [Background technology]

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

[0003] Various materials have been proposed for use as negative electrode active materials in non-aqueous electrolyte secondary batteries. As negative electrode active materials with high energy density, silicon compounds (e.g., silicon oxide) that are alloyed with lithium and silicon particles have been 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, the functional coating layer being made of a functional substance and a binder, the functional substance being one or more selected from a phosphorus-containing compound, a nitrogen-containing compound, and an inorganic silicon compound, and the battery electrode plate being a battery positive electrode and / or a battery negative electrode." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-212228 [Patent Document 2] Special Publication No. 2017-534138 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been an increasing demand for higher energy densities of non-aqueous electrolyte secondary batteries. Increasing the energy density of non-aqueous electrolyte secondary batteries requires a high level of safety measures for the batteries in the event of an abnormality. [Means for solving the problem]

[0007] One aspect of the present disclosure relates to a secondary battery including a first electrode, a second electrode, and a separator interposed between the first electrode and the second electrode, the first electrode including a first electrode active material layer, the first electrode active material layer including a first electrode active material and a first flame retardant including a halogen atom, and the separator including a second flame retardant. [Effects of the Invention]

[0008] According to the present disclosure, a highly safe secondary battery can be realized. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic perspective view of a secondary battery according to an embodiment of the present disclosure, with a portion cut away; [Figure 2] FIG. 2 is a schematic cross-sectional view showing an enlarged portion of an electrode group of a secondary battery according to an embodiment of the present disclosure. [Figure 3] FIG. 2 is a schematic cross-sectional view showing an enlarged portion of an electrode group of a secondary battery according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] Examples of embodiments according to the present disclosure will be described below. Note that, although examples of embodiments according to the present disclosure will be described below, 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 a "range between numerical value A and numerical value B" is mentioned, 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 and second electrodes. The first electrode is either a positive electrode or a negative electrode in the secondary battery. The second electrode is the other of the positive and negative electrodes in the secondary battery. The first electrode may be a positive electrode and the second electrode may be a negative electrode, or the first electrode may be a negative electrode and the second electrode may be a positive electrode.

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

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

[0014] The present inventors have discovered that adding a specific flame retardant to the first electrode (positive or negative electrode) and the separator can suppress the rise in battery temperature during abnormal conditions without significantly degrading battery performance. The present disclosure is based on these new findings.

[0015] Hereinafter, 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, and therefore, a secondary battery containing the first flame retardant (R1) can suppress excessive heat generation in abnormal conditions.

[0017] In the early stage of the exothermic reaction, the negative electrode, which has a larger reaction area than the positive electrode, reacts preferentially with the electrolyte, generating H radicals, which then react repeatedly with other products, promoting heat generation. For example, O generated from the positive electrode active material 2- The reaction of O2 and / or H radicals promotes heat generation. However, by disposing a flame retardant (R1) containing halogen atoms inside the negative electrode, the flame retardant (R1) deactivates the H radicals, suppressing the exothermic reaction. On the other hand, by disposing 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 disposing a flame retardant (R1) containing halogen atoms in at least one of the positive electrode and the negative electrode, heat generation 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 a halogen atom is bonded. The cyclic structure may or may not be an aromatic ring. In this case, all of the halogen atoms may be bonded to the cyclic structure, or only some of the 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 is easy to increase the content of halogen atoms. (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 is preferably 95% by mass or less (for example, 90% by mass or less). below These lower and upper limits can be combined in any way.

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

[0020] [ka]

[0021] Although the halogen atom is not particularly limited, preferred examples of the halogen atom include bromine (Br), fluorine (F), and chlorine (Cl). The halogen atom may be bromine and / or fluorine, or may be bromine, since a flame retardant effect can be expected from the early stage of abnormal heat generation.

[0022] Such halogen-containing flame retardants (R1) have a higher specific gravity than conventionally used phosphorus-based flame retardants, allowing for a smaller volume relative to the added weight. This allows for a high active material loading while adding a sufficient amount of flame retardant, thereby maintaining a high capacity. In terms of their high specific gravity, the flame retardant (R1) preferably 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 bonding halogen atoms to the cyclic structure. The specific gravity of the flame retardant (R1) may be, for example, 2.7 or more, and preferably 3.0 or more.

[0023] It is preferable that the flame retardant (R1) does not contain a moiety that generates moisture and / or a hydrophilic group in its compound structure. In this case, moisture is less likely to be mixed into the battery during the manufacturing process of the secondary battery, and a highly reliable secondary battery can be realized. Examples of moieties that generate moisture include a hydroxyl group (-OH), a carboxyl group (-COOH), a carbonyl group (-CO-), and an oxo acid group such as a sulfo group or a phosphate group. Examples of hydrophilic groups include the above functional groups as well as an amino group.

[0024] Furthermore, even when using a negative electrode active material containing silicon (Si), a flame retardant (R1) may be contained in the negative electrode active material layer. In this case, the halogen atoms contained in the flame retardant (R1) react with Si to form a stable coating on the surface of the negative electrode active material. This allows high cycle characteristics to be maintained and high durability can be expected.

[0025] The flame retardant (R1) may release halogen atoms at temperatures of 180°C or higher (e.g., 250°C or higher). If the flame retardant releases halogen atoms at relatively low temperatures, the halogen atoms may be released under normal conditions, resulting in a deterioration in battery performance. Therefore, it is preferable that the flame retardant (R1) does not substantially release halogen atoms at temperatures below 180°C.

[0026] The flame retardant (R1) may be at least one selected from the group consisting of 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(12.2.1.16,9.02,13.05,10)octadeca-7,15-diene (trade name: Dechlorane Plus), and tris(2,2,2-trifluoroethyl)phosphate. These flame retardants (R1) may be commercially available. Alternatively, the flame retardant (R1) may be synthesized using known synthesis 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 improve 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 arbitrarily combined as long as there is no contradiction. For example, the value of a may be in the range of 0.1 or greater and less than 7 (e.g., in 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, or the range of 0.5 to 1.0). The proportion of the 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 the flame retardant (R1), and has the effect of suppressing excessive heat generation in the event of an abnormality in the secondary battery. When contained in the separator, the second flame retardant (R2) can suppress both the exothermic reaction occurring in the positive electrode and the exothermic reaction occurring in the negative electrode. When combined with the flame retardant (R1), the exothermic reaction occurring in both the positive and negative electrodes of the secondary battery is significantly suppressed, effectively suppressing excessive heat generation and fire in the event of an abnormality.

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

[0030] The flame retardant (R2) may be a halogen-containing flame retardant similar to the flame retardant (R1). The flame retardant (R2) may include a cyclic compound containing a cyclic structure to which halogen atoms are bonded, with the proportion of halogen atoms in the flame retardant (R2) being 45% by mass or more. Examples of the cyclic compound include the compounds listed above as examples of the flame retardant (R1). However, in this case, the flame retardant (R2) may be the same cyclic compound as the flame retardant (R1), or may include a cyclic compound different from the flame retardant (R1).

[0031] A phosphate compound may be used as the flame retardant (R2). The phosphate compound is preferably a compound that transforms from a solid phase to a liquid phase or thermally decomposes. When the secondary battery generates heat during an abnormality, such a phosphate compound transforms from a solid phase to a liquid phase and flows on the surface of the separator substrate layer, or extends on the surface of the substrate layer through thermal decomposition, forming a coating that covers the surface of the substrate layer. The coating functions as a resistance component, which is thought to suppress the amount of short-circuit current flowing between the positive and negative electrodes during an abnormality, thereby suppressing the increase in battery temperature. The temperature at which the phosphate compound transforms from a solid phase to a liquid phase or thermally decomposes may be 180°C or higher. The temperature at which the phosphate compound transforms from a solid phase to a liquid phase or thermally decomposes is, for example, 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 the phosphate compound include metal phosphates 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 trimethyl phosphate and triphenyl phosphate. Of these, the phosphate compound preferably 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 of the separator facing the positive electrode or negative electrode. When the flame retardant (R2) is contained in the surface layer of the separator, the separator has a laminated structure including a substrate layer and a flame retardant layer containing the flame retardant (R2). In this case, the substrate layer may or may not contain the flame retardant (R2). The flame retardant (R2) may be contained in both the substrate layer and the flame retardant layer. The flame retardant layer may be formed on only one surface of the separator facing the positive electrode or the negative electrode, or may be formed on both surfaces of the separator so that both the positive electrode and the negative electrode face the flame retardant layer.

[0035] The flame retardant layer may be disposed at least on the surface layer of the separator facing the second electrode. That is, when the positive electrode active material layer contains the flame retardant (R1), the flame retardant layer may be disposed at least on the surface layer of the separator facing the negative electrode. On the other hand, when the negative electrode active material layer contains the flame retardant (R1), the flame retardant layer may be disposed at least on the surface layer of the separator facing the positive electrode. In this case, the flame retardant layer containing the flame retardant (R2) enhances the effect of suppressing the exothermic reaction occurring in the second electrode. On the other hand, the exothermic reaction occurring in the first electrode is sufficiently suppressed by the first electrode active material layer containing the flame retardant (R1). Therefore, the exothermic reaction occurring in 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 an aggregate in which particles of the flame retardant (R2) aggregate together, or in the form of an aggregate in which particles of the flame retardant (R2) aggregate together via a binder. The flame retardant layer may partially cover the surface of the substrate layer, or the flame retardant layer may cover almost the entire surface of the substrate layer. The coverage (area basis) of the flame retardant layer with respect to the surface of the substrate layer may be 10% or more, or 20% or more, and preferably 30% or more, from the viewpoint of suppressing an increase in battery temperature under abnormal conditions. The coverage of the flame retardant layer with respect to the surface of the substrate layer may be 90% or less, 80% or less, or 65% or less, from the viewpoint of suppressing an increase in battery resistance.

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

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

[0039] In the flame retardant layer, the content of the flame retardant (R2) in the entire 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 entire 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 there is no contradiction. The proportion of the flame retardant (R2) in the flame retardant layer can be determined by elemental analysis such as EDS of a cross section of the flame retardant layer.

[0040] The average particle size of the flame retardant (R2) particles in the flame retardant layer (when forming an aggregate, the average particle size of the primary particles forming 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 particles of the flame retardant (R2) are randomly selected from an SEM image of the separator surface. Next, the grain boundaries of the selected 20 particles are observed, and the outer shapes of the particles are identified. The major axis of each of the 20 particles is then determined, and the average value thereof 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, more preferably 1 μm or more or 3 μm or more, in order to suppress an increase in battery temperature under abnormal conditions. The thickness of the flame retardant layer is preferably 4 μm or less in order to suppress an increase in battery resistance. These lower and upper limits can be combined arbitrarily as long as there is no contradiction. Note that when the coverage rate is less than 100%, the average thickness of the flame retardant layer is the average thickness considering the area on the surface of the substrate layer that is not covered with the flame retardant layer as having a thickness of 0 μm, and is determined from an SEM image of the cross section of the separator.

[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 can enhance the adhesion between the flame retardant (R2) particles and the adhesion of the flame retardant (R2) to the substrate layer. That is, the flame retardant layer can be tightly attached to the substrate layer. The flame retardant layer can be formed by depositing a mixture containing at least particles of the flame retardant (R2) and a binder on the surface of the substrate layer. The mixture may be a slurry containing particles of the flame retardant (R2), a binder, and a solvent (dispersion medium). The flame retardant layer can be formed by spraying, dripping, or applying the slurry to the surface of the substrate layer and drying it. The coverage and thickness of the flame retardant layer can be controlled by adjusting the amount of solvent and / or the amount of slurry applied relative to the amount of flame retardant (R2) particles in the slurry.

[0043] The binder is not particularly limited, but examples thereof 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 the 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 substrate portion (substrate layer) of the separator is made of a porous sheet such as a woven fabric, a nonwoven fabric, or a microporous membrane. Woven fabrics and nonwoven fabrics are primarily composed of fibers, and for example, 60% by mass or more of the substrate layer is made of fibers. Examples of fibers that can be used include glass fibers, polymer fibers, and pulp fibers. Nonwoven fabrics are sheets in which fibers are intertwined without being woven. Woven fabrics and nonwoven fabrics may contain components other than fibers, such as acid-resistant inorganic powders and polymers as binders. To incorporate the flame retardant (R2) into woven fabrics or nonwoven fabrics, for example, the flame retardant (R2) may be attached to fibers and the fibers to which the flame retardant (R2) is attached may be intertwined. This allows the production of a substrate 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 produced as follows: A pore-forming agent is added to a synthetic resin in which the flame retardant (R2) is mixed in a mass ratio of 0.5 to 50 parts by weight to 100 parts by weight of resin, and the mixture is stretched at a temperature of about 100°C. The porosity of the microporous membrane is preferably about 35 to 50%, and the pore size is preferably 1 μm or less. Fine flame retardant particles are uniformly distributed within the microporous membrane. The microporous membrane is preferably composed mainly of a polymer component. The polymer component is preferably a polyolefin such as polyethylene or polypropylene. The composition may contain inorganic particles other than the flame retardant (R2). Examples of inorganic particles include ceramic particles such as silica, alumina, and titania.

[0046] The substrate layer may have a single layer structure or a laminate 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] An example of a secondary battery according to this embodiment and examples of its components are described in detail below. Note that known components may be applied to components that are not characteristic of the present disclosure. The secondary battery includes, for example, an exterior body (battery case), and a positive electrode, a negative electrode, an electrolyte, and a separator disposed within the exterior body. The separator is disposed between the positive electrode and the negative electrode.

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

[0049] [Negative electrode] The negative electrode includes a negative electrode active material layer and, if necessary, further includes a negative electrode current collector. The negative electrode active material layer includes a negative electrode active material as an essential component, and may include optional components such as a binder, a conductive material, and a thickener. Known materials can be used as the binder, conductive material, and thickener. The negative electrode active material layer may also include a flame retardant (R1).

[0050] The negative electrode active material layer can be formed by applying a negative electrode slurry, in which the materials for the negative electrode active material layer are dispersed in a dispersion medium, to the surface of the negative electrode current collector to form a coating film, and then drying the coating film. The dried coating film may be rolled if necessary. Examples of dispersion media include water, alcohol, ether, N-methyl-2-pyrrolidone (NMP), and 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 absorb and release lithium ions, lithium metal, and lithium alloys. Examples of materials that electrochemically absorb and release lithium ions include carbon materials and alloy-based materials. Examples of carbon materials include graphite, easily graphitized carbon (soft carbon), and hardly graphitized carbon (hard carbon). Of these, graphite is preferred because of its excellent charge / discharge stability and low irreversible capacity. Examples of alloy-based materials include those containing at least one metal that can form an alloy with lithium, such as silicon, tin, silicon alloys, tin alloys, and silicon compounds. Silicon oxides and tin oxides formed by bonding these with oxygen may also be used.

[0052] Examples of alloy materials containing silicon include a lithium ion conductive phase and a silicon composite material in which silicon particles are dispersed in the lithium ion conductive phase. Examples of the lithium ion conductive phase include a silicon oxide phase, a silicate phase, and / or a carbon phase. The main component of the silicon oxide phase (e.g., 95 to 100% by mass) may be silicon dioxide. Among these, composite materials composed of a silicate phase and silicon particles dispersed in the silicate phase are preferred because of their high capacity and low irreversible capacity.

[0053] The silicate phase may contain, for example, at least one element selected from the group consisting of Group 1 and Group 2 elements of the long periodic table. Examples of Group 1 elements of the long periodic table and Group 2 elements of the long 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 silicate phase containing lithium (hereinafter also referred to as a lithium silicate phase) is preferred because of its small irreversible capacity and high initial charge / discharge efficiency.

[0054] The lithium silicate phase may be an oxide phase containing lithium (Li), silicon (Si), and oxygen (O), and may 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 in the lithium silicate phase, Li / Si, is, for example, greater than 0 and less than 4. The lithium silicate phase has 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 included 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, poorly crystalline amorphous carbon (i.e., amorphous carbon). The amorphous carbon may be, for example, hard carbon, soft carbon, or the like.

[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 mixture 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 mixture 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 mixture contains a positive electrode active material as an essential component and may contain a binder, a conductive agent, and the like as optional components. 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 an 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 a 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. The value a, which indicates the molar ratio of lithium, increases or decreases during charge and discharge.

[0059] The binder and conductive agent may be the same as those exemplified for the negative electrode. As the conductive agent, graphite such as natural graphite or artificial graphite may be used.

[0060] Carbon nanotubes may be used as the conductive agent contained in the positive electrode active material layer. The aspect ratio of carbon nanotubes (ratio of length to diameter) is extremely large. Therefore, even a small amount of carbon nanotubes exhibits high conductivity. Adding carbon nanotubes to the positive electrode active material layer reduces the resistance of the battery and suppresses deterioration due to repeated charging and discharging. Furthermore, using carbon nanotubes as a conductive agent makes it possible to increase the proportion of positive electrode active material in the positive electrode active material layer. Therefore, the secondary battery can have a high capacity.

[0061] On the other hand, secondary batteries containing carbon nanotubes in the positive electrode active material layer are more susceptible to abnormal events accompanied by heat generation, such as internal short circuits, compared to secondary batteries containing the same amount of conductive material, such as acetylene black. However, the inclusion of a flame retardant (R1) in the positive electrode active material layer can suppress the rise in battery temperature during abnormal conditions. As a result, high battery performance and safety can be achieved at the same time. Carbon nanotubes may be single-walled, double-walled, or multi-walled. Single-walled carbon nanotubes are preferred because they can achieve significant effects 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 account for 50% or more by mass of the total carbon nanotubes.

[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 in order to reduce battery resistance. On the other hand, the carbon nanotube content may be 10% by mass or less, 3% by mass or less, or 1% by mass or less in order to achieve high capacity and suppress an increase in battery temperature in the event of an abnormality. These lower and upper limits can be combined arbitrarily as long as there is no contradiction.

[0063] The proportion of the positive electrode active material in the positive electrode active material layer is 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 to remove the positive electrode. Next, the positive electrode is washed with an organic solvent and further vacuum-dried, and then only the positive electrode active material layer is peeled off to obtain a sample. By performing thermal analysis such as TG-DTA on the sample, the proportion of the binder component and conductive material component other than the positive electrode active material can be calculated. When the binder component and conductive material component contain multiple types of carbon materials, the proportion of carbon nanotubes among them can be calculated by performing microscopic 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 measuring the length and diameter of a number of randomly selected carbon nanotubes (e.g., approximately 100 to 1000), averaging the measured values. The outer diameter of the carbon nanotubes (in the case of multi-walled carbon nanotubes, the diameter of the outermost tube) is not limited to, but may be in the range of 0.001 to 0.05 μm. The length of the carbon nanotubes is not limited to, but may be 0.5 μm or more to ensure electronic conduction in the positive electrode active material layer. Considering that the particle diameter of the positive electrode active material is generally 1 μm to 20 μm, the length of the carbon nanotubes may be approximately the same. That is, the length of the carbon nanotubes may be, for example, 1 μm to 20 μm.

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

[0066] The shape and thickness of the positive electrode current collector can be selected from the shape and range corresponding to those of the negative electrode current collector. Examples of the material of the positive electrode current collector include stainless steel, aluminum, aluminum alloy, and titanium.

[0067] [Electrolyte] The electrolyte may be an electrolytic solution containing a solvent and a solute dissolved in the solvent. The solute is an electrolyte salt that ionically dissociates in the electrolytic solution. The solute may include, for example, a lithium salt. Components of the electrolytic solution other than the solvent and the solute are additives. The electrolytic solution may contain various additives.

[0068] A non-aqueous solvent is used as the solvent. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of the cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC). Examples of the chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of the cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of the chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP). One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0069] Other examples of the non-aqueous solvent include cyclic ethers, chain 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 etc.), lithium salts of fluorine-containing acids (LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts of fluorine-containing acid imides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), lithium halides (LiCl, LiBr, LiI, etc.), etc., can be used. One type of lithium salt may be used alone, or two or more types may be used in combination.

[0071] The concentration of the lithium salt in the electrolyte may be 1 mol / L or more and 2 mol / L or less, or 1 mol / L or more and 1.5 mol / L or less. By controlling the lithium salt concentration within the above range, an electrolyte having 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, such as 1,3-propane sultone, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene.

[0073] [Separator] A separator is disposed between the positive electrode and the negative electrode. The separator may be a material containing a flame retardant (R2), having high ion permeability, and having adequate mechanical strength and insulating properties. As described above, the separator may be made of a microporous thin film, woven fabric, nonwoven fabric, or the like. Examples of separator materials include polyolefins such as polyethylene, polypropylene, and copolymers of polyethylene and α-olefins, acrylic resins, polystyrene, polyester, and cellulose.

[0074] An example of a secondary battery includes an exterior body, an electrode group housed in the exterior body, and a non-aqueous electrolyte. There are no particular limitations on the structure of the electrode group. One example of an electrode group is formed by winding a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. Another example of an electrode group is formed by stacking a positive electrode, a negative electrode, and a separator so that the separator is disposed between the positive electrode and the negative electrode. There are no limitations on the shape of the secondary battery, and it may be cylindrical, prismatic, coin-shaped, button-shaped, laminate-shaped, or the like.

[0075] There is no particular limitation on the method for manufacturing the secondary battery, and a known manufacturing method may be applied, or a known manufacturing method may be applied with at least a part thereof modified.

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

[0077] Fig. 1 is a schematic perspective view, with a portion cut away, of a prismatic secondary battery according to one embodiment of the present disclosure. The secondary battery 1 shown in Fig. 1 includes a bottomed prismatic battery case 11, and 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-plate-shaped winding core and then removing the winding core.

[0078] One end of a negative electrode lead 15 is attached to the negative electrode current collector of the negative electrode by welding or the like. One end of a 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 a negative electrode terminal 13 provided on the sealing plate 12. A gasket 16 is disposed between the sealing plate 12 and the negative electrode terminal 13 to insulate them from each other. The other end of the positive electrode lead 14 is connected to the sealing plate 12 and is electrically connected to the battery case 11, which also serves as the positive electrode terminal. A resin frame 18 is disposed above the electrode group 10. The frame 18 separates the electrode group 10 from the sealing plate 12 and also separates the negative electrode lead 15 from the battery case 11. The opening of the battery case 11 is sealed with the sealing plate 12. The sealing plate 12 has a liquid injection hole 17a formed therein. The electrolyte is injected into the battery case 11 through the injection hole 17a. The injection hole 17a is then closed with the seal 17.

[0079] FIG. 2 is a schematic cross-sectional view showing an enlarged portion of the electrode group 10. In FIG. 2, the positive electrode 3 has 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) (both not shown). The positive electrode 3 faces the separator 4. The separator 4 has a substrate layer 41 and a flame retardant layer 42. The flame retardant layer 42 contains a flame retardant (R2) and is disposed on a surface layer of the separator 4 that does not face the positive electrode 3. In the example of FIG. 2, the flame retardant layer 42 is disposed on the surface of the substrate layer 41 so as to face the negative electrode 2.

[0080] FIG. 3 is a schematic cross-sectional view showing an enlarged portion of an electrode group 10. Unlike the electrode group 10 of FIG. 2, this electrode group 10 shows an example in which a flame retardant layer 42 is disposed on the surface of a substrate layer 41 so as to face the positive electrode 3. In FIG. 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) (both not shown). The negative electrode 2 faces a separator 4. The separator 4 has a substrate layer 41 and a flame retardant layer 42. The flame retardant layer 42 contains a flame retardant (R2) and is disposed on the surface layer of the separator 4 facing the positive electrode 3.

[0081] 2 and 3, the flame retardant layer 42 may be disposed on both sides of the substrate layer 41 so as to face both the positive electrode and the negative electrode. The substrate layer 41 may also contain a flame retardant (R2). [Example]

[0082] The secondary battery according to the present disclosure will be described in further detail with reference to examples.

[0083] ≪Batteries A1~A9, C1~C5≫ In this example, a plurality of secondary batteries (nonaqueous electrolyte secondary batteries) were fabricated and evaluated in the following manner.

[0084] [Preparation of negative electrode] The negative electrode active material was a mixture of silicon composite material and graphite in a mass ratio of silicon composite material:graphite = 5:95. The negative electrode active material, carboxymethyl cellulose sodium (CMC-Na), styrene-butadiene rubber (SBR), water, and optionally a flame retardant (R1) were mixed in a predetermined mass ratio to prepare a negative electrode slurry. The negative electrode slurry was then applied to the surface of copper foil (negative electrode current collector) to form a coating. The coating was dried and then rolled to form negative electrode active material layers on both sides of the copper foil.

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

[0086] Next, the positive electrode slurry was applied to the surface of an aluminum foil (positive electrode current collector) to form a coating film, which was then dried and rolled to form a positive electrode mixture layer on both sides of the aluminum foil.

[0087] [Separator fabrication] A porous polyethylene sheet containing flame retardant (R2) as a base material was prepared by the following method to obtain separator S1. The thickness of separator S1 was 15 μm.

[0088] Two types of polyethylene with different molecular weights were used as the resin, and a pore-forming agent was added to the synthetic resin, which was mixed with a flame retardant (R2) in a mass ratio of 100:10. The separator S1 was obtained by stretching this at 90°C. The porosity of the separator S1 was 40%.

[0089] Also, a porous polyethylene sheet (separator) S0 (thickness: 15 μm) containing no flame retardant (R2) was prepared. The porosity of the separator S0 was 42%.

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

[0091] [Preparation of electrolyte] An electrolyte solution 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 solution was 1.3 mol / L.

[0092] [Secondary battery production] A lead tab was attached to each electrode. Next, the positive electrode and negative electrode were spirally wound with the separator interposed between them so that the lead was located at the outermost periphery. In this way, an electrode group was produced. Next, the electrode group was inserted into an outer casing made of a laminate film with an aluminum foil barrier layer, and vacuum dried. Next, a nonaqueous electrolyte solution was injected into the outer casing, and the opening of the outer casing was sealed. In this way, a secondary battery was obtained.

[0093] In this example, no flame retardant (R1) was added to the negative electrode slurry, but the flame retardant (R1) was added to the positive electrode slurry. Several secondary batteries (batteries A1 to A9, C1 to C5) were fabricated by varying the content of the flame retardant (R1) in the positive electrode active material layer, the separator structure, and the type and content of the flame retardant (R2) in the separator. The flame retardant (R1) in the positive electrode active material layer was ethylene-1,2-bispentabromophenyl (SAYTEX®-8010, manufactured by Albemarle Japan Co., Ltd.), a cyclic compound having a ring structure with halogen atoms bonded to it. The ratio of materials in the positive electrode active material layer was varied by changing the mixing ratio when preparing the positive electrode slurry. The flame retardant (R2) in the separator was ethylene-1,2-bispentabromophenyl and / or ammonium polyphosphate as a phosphate compound, and these were blended into the separator substrate layer or flame retardant layer to achieve a predetermined content ratio.

[0094] In the batteries A1 to A3, the separator S1 was used to fabricate the secondary batteries. For batteries A4 to A9, secondary batteries were fabricated using separator S2. However, for batteries A4 to A6, when fabricating the electrode assembly, the positive electrode and negative electrode were spirally wound with the separator interposed between them so that the flame retardant layer of separator S2 faced the positive electrode. For batteries A7 to A9, when fabricating the electrode assembly, the positive electrode and negative electrode were spirally wound with the separator interposed between them so that the flame retardant layer of separator S2 faced the negative electrode.

[0095] Battery C1 is a comparative example. positive electrode No flame retardant (R1) was added to the active material layer, and a porous sheet S0 containing no flame retardant (R2) was used as the separator. For battery C2, positive electrode A flame retardant (R1) was added to the active material layer, but a porous sheet S0 containing no flame retardant (R2) was used as the separator. For batteries C3 to C5, positive electrode Separator S1 or S2 was used in which no flame retardant (R1) was added to the active material layer, but which contained a flame retardant (R2).

[0096] The fabricated secondary batteries were evaluated as follows. (1) Nail penetration test (a) In an environment of 25°C, the battery was charged at a constant current of 0.5C 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 an environment of 25°C, the tip of a round nail (diameter 2.7 mm) was brought into contact with the center of the battery charged in (a) and pierced at a speed of 1 mm / sec. Immediately after detecting a drop in battery voltage due to an internal short circuit, the nail was stopped from piercing. After the battery was short-circuited by the round nail, the short-circuit current value I and the battery voltage V were measured for one second. The heat generation amount for one second was calculated by integrating the product (power) of the current value I and the voltage V over time.

[0097] Table 1 shows some of the battery fabrication conditions and evaluation results. In Table 1, the content of flame retardant (R1) indicates 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 taken as 100. The content of flame retardant (R2) indicates the mass of ethylene-1,2-bispentabromophenyl and ammonium polyphosphate contained in the separator when the mass of the separator resin is taken as 100. In Table 1, the location of flame retardant (R2) is indicated as follows: "in the substrate" means that the flame retardant (R2) is added to the substrate layer; "facing the positive electrode" means that the flame retardant layer is disposed on the surface of the substrate layer facing the positive electrode; and "facing the negative electrode" means that the flame retardant layer is disposed on the surface of the substrate layer facing the negative electrode. When "facing the positive electrode" or "facing the negative electrode" is used, the thickness (average film thickness) of the flame retardant layer is also shown.

[0098] [Table 1]

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

[0100] Battery C1, which does not contain a flame retardant, generates a large amount of heat. Battery C1 emitted smoke when a nail was inserted into it. Batteries A1 to A9 did not emit smoke.

[0101] A comparison of batteries A1 to A9 reveals that, in the locations of the separator where flame retardant (R2) is contained, batteries A1 to A3, in which flame retardant (R2) is incorporated into the substrate, show a significant decrease in heat generation. When the material and content of flame retardant (R2) are the same, the heat generation tends to decrease in the following order: batteries A1 to A3, in which flame retardant (R2) is incorporated into the substrate; batteries A7 to A9, in which a flame retardant layer containing flame retardant (R2) faces the negative electrode; and batteries A4 to A6, in which a flame retardant layer containing 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 to which halogen atoms are bonded and a phosphate compound were combined as the flame retardant (R2), the calorific value was significantly reduced.

[0103] ≪Batteries B1~B9, C6~C10≫ In this example, no flame retardant (R1) was added to the positive electrode slurry, but a flame retardant (R1) was added to the negative electrode slurry. Several secondary batteries (Batteries B1 to B9, C6 to C10) were fabricated by varying the content of the flame retardant (R1) in the negative electrode active material layer, the separator structure, and the type and content of the flame retardant (R2) in the separator. The flame retardant (R1) in the negative electrode active material layer was ethylene-1,2-bispentabromophenyl (SAYTEX®-8010, manufactured by Albemarle Japan Co., Ltd.), a cyclic compound having a ring structure with halogen atoms bonded to it. The ratio of materials in the negative electrode active material layer was varied by changing the mixing ratio when preparing the negative electrode slurry. The flame retardant (R2) in the separator was ethylene-1,2-bispentabromophenyl and / or ammonium polyphosphate as a phosphate compound, and these were blended into the separator substrate layer or flame retardant layer to achieve a predetermined content ratio.

[0104] Other than this, a plurality of secondary batteries (nonaqueous electrolyte secondary batteries) were fabricated in the same manner as secondary batteries A1 to A9 and C1 to C5, and were similarly evaluated.

[0105] For batteries B1 to B3, the separator S1 was used to fabricate secondary batteries. For batteries B4 to B9, secondary batteries were fabricated using separator S2. However, for batteries B4 to B6, when fabricating the electrode assembly, the positive electrode and negative electrode were spirally wound with the separator interposed between them so that the flame retardant layer of separator S2 faced the positive electrode. For batteries B7 to B9, when fabricating the electrode assembly, the positive electrode and negative electrode were spirally wound with the separator interposed between them so that the flame retardant layer of separator S2 faced the negative electrode.

[0106] Battery C6 is a comparative example in which no flame retardant (R1) was added to the negative electrode active material layer, and porous sheet S0 containing no flame retardant (R2) was used as the separator. In the battery C7, a flame retardant (R1) was added to the negative electrode active material layer, but a porous sheet S0 containing no flame retardant (R2) was used as the separator. In the batteries C8 to C10, no flame retardant (R1) was added to the negative electrode active material layer, but the separator S1 or S2 containing the flame retardant (R2) was used.

[0107] Table 2 shows some of the battery fabrication conditions and evaluation results. In Table 2, the content of flame retardant (R1) indicates 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 taken as 100. The content of flame retardant (R2) indicates the mass of ethylene-1,2-bispentabromophenyl and ammonium polyphosphate contained in the separator when the mass of the separator resin is taken as 100. In Table 2, the location of flame retardant (R2) is indicated as follows: "in the substrate" means that the flame retardant (R2) is added to the substrate layer; "facing the positive electrode" means that the flame retardant layer is disposed on the surface of the substrate layer facing the positive electrode; and "facing the negative electrode" means that the flame retardant layer is disposed on the surface of the substrate layer facing the negative electrode. When "facing the positive electrode" or "facing the negative electrode" is used, the thickness (average film thickness) of the flame retardant layer is also shown.

[0108] [Table 2]

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

[0110] A comparison of batteries B1 to B9 reveals that, in the locations of the separator where flame retardant (R2) is contained, batteries B1 to B3, in which flame retardant (R2) is incorporated into the substrate, show a significant decrease in heat generation. When the material and content of flame retardant (R2) are the same, the heat generation tends to decrease in the following order: batteries B1 to B3, in which flame retardant (R2) is incorporated into the substrate; batteries B4 to B6, in which a flame retardant layer containing flame retardant (R2) faces the positive electrode; and batteries B7 to B9, in which a flame retardant layer containing 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 and a phosphate compound were combined as the flame retardant (R2), the calorific value was significantly reduced. [Industrial Applicability]

[0112] The present disclosure can be used in secondary batteries. While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart 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: liquid 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: substrate layer, 42: flame retardant layer

Claims

1. 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; the second flame retardant includes at least one selected from the group consisting of a cyclic compound containing a cyclic structure to which a halogen atom is bonded, and a phosphoric acid compound, wherein the proportion of the halogen atoms in the second flame retardant is 45 mass% or more; the second flame retardant comprises the phosphate compound; The secondary battery, wherein the phosphate compound includes at least one selected from the group consisting of melamine polyphosphate, ammonium polyphosphate, and sodium tripolyphosphate.

2. the first flame retardant includes a cyclic structure to which the halogen atom is bonded, The secondary battery according to claim 1 , wherein the proportion of the halogen atoms in the first flame retardant is 45 mass % or more.

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

4. The first flame retardant is ethylene-1,2-bispentabromophenyl, ethylene bis(ethylene glycol) Tetrabromophthalimide, 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 4. The secondary battery according to claim 1, wherein the anionic surfactant is at least one selected from the group consisting of octadeca-7,15-diene, and tris(2,2,2-trifluoroethyl)phosphate.

5. 5. The secondary battery according to claim 1, wherein the second flame retardant is contained in a base material layer of the separator.

6. 6. The secondary battery according to claim 1, wherein a surface layer on one or both sides of the separator includes a flame retardant layer containing the second flame retardant.

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

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

9. 9. The secondary battery according to claim 1, wherein the first electrode is a positive electrode and the second electrode is a negative electrode.

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

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