JP6586169B2 - Secondary battery - Google Patents

Description

  The present invention relates to a secondary battery.

  In recent years, as a power source of an electric vehicle or the like, a lithium ion secondary battery having a high energy density provided with a wound electrode group produced by winding a separator between a positive electrode and a negative electrode and winding them. Development is underway. In addition, while achieving higher energy, compatibility with safety is required. As a background art of this technical field, Patent Document 1 discloses that a protective layer made of organic particles and inorganic particles is provided on at least one electrode of a sealed battery, and the organic particles in the protective layer are melted when abnormal heat is generated. A technology that improves safety by providing a shutdown function that closes holes is published.

JP 2010-225545 A

  However, in the technique of Patent Document 1, since organic particles having a melting temperature in the range of 100 to 200 ° C. are used for the protective layer, for example, the inside through a foreign object due to penetration of the battery or crushing by a sharp metal such as a nail. In the case of an abnormal heat generation state above the shutdown temperature due to a short circuit or the like, the organic particles in the protective layer melt and shrink (shrink). A separator is interposed between the positive electrode and the negative electrode, but when the separator having a shutdown function made of polyethylene is used, the separator is also melted and shrinks. Therefore, both the separator and the protective layer may flow out between the positive electrode and the negative electrode, and the positive electrode and the negative electrode may be in direct contact with each other to cause a secondary short circuit.

  The present invention has been made in view of the above problems, and its purpose is to provide a protective layer between the positive electrode and the negative electrode even when the secondary battery falls into a high temperature state, so that the positive electrode and the negative electrode It is intended to provide a secondary battery that can avoid the secondary short circuit between them and improve safety.

  In order to solve the above problems, for example, the configuration described in the claims is adopted. The present invention includes a plurality of means for solving the above problems. To give one example, the secondary battery includes an electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween. Has a negative electrode mixture layer and a negative electrode protective layer provided on the surface of the negative electrode mixture layer, and the negative electrode protective layer has an inorganic filler, a resin filler, and a binder. The melting point is higher than the melting point of the separator.

  According to the present invention, since the negative electrode protective layer provided on the surface of the negative electrode mixture layer has an inorganic filler, a resin filler having a melting point higher than that of the separator, and a binder, abnormal heat generation above the melting point of the separator. Sometimes, the resin filler of the protective layer softens and develops adhesive strength, binds the inorganic filler, and can suppress the outflow of the protective layer. Therefore, even if the separator shrinks due to heat, the protective layer can suppress a secondary short circuit between the positive electrode and the negative electrode. Therefore, a highly safe battery can be provided. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

The external appearance perspective view of a square secondary battery. The disassembled perspective view of a square secondary battery. The perspective view of a winding group. The figure explaining the structure of a positive electrode. The figure explaining the structure of a negative electrode. Sectional drawing of the winding group in a present Example. The cross-sectional image figure which shows an example of a negative electrode protective layer. The cross-sectional image figure which shows the other example of a negative electrode protective layer.

  The present invention provides an inorganic filler and a resin filler that have ionic conductivity on the negative electrode active material layer and avoid direct contact between the positive electrode uncoated portion and the negative electrode coated portion due to separator contraction when abnormal heat is generated due to an internal short circuit or the like. The present invention relates to a sealed secondary battery including a layer made of

  Embodiments of the present invention will be described below with reference to the drawings. In the following examples, the case where the present invention is applied to a prismatic lithium ion secondary battery having a flat wound electrode group will be described. However, the present invention is limited to the configurations of these examples. For example, the present invention can also be applied to secondary batteries having other types of electrode groups such as a stacked type in which a plurality of positive electrodes and negative electrodes are alternately stacked.

[Example 1]
FIG. 1 is an external perspective view of a prismatic secondary battery, and FIG. 2 is an exploded perspective view of the prismatic secondary battery.
The prismatic secondary battery 100 includes a battery can 1 and a battery lid 6. The battery can 1 has a side surface and a bottom surface 1d having a pair of opposed wide side surfaces 1b having a relatively large area and a pair of opposed narrow side surfaces 1c having a relatively small area, and an opening 1a above the side surface 1d. Have

  A wound group 3 is accommodated in the battery can 1, and an opening 1 a of the battery can 1 is sealed by a battery lid 6. The battery lid 6 is a substantially rectangular flat plate that closes the opening 1 a and is welded to the battery can 1 to form a battery container in cooperation with the battery can 1. The battery lid 6 is provided with a positive external terminal 14 and a negative external terminal 12. The wound group 3 is charged through the positive external terminal 14 and the negative external terminal 12, and power is supplied to the external load.

  The battery cover 6 is integrally provided with a gas discharge valve 10, and when the pressure in the battery container rises to a preset value or more, the gas discharge valve 10 is opened and gas is discharged from the inside, so that the inside of the battery container The pressure of is reduced. Thereby, the safety of the prismatic secondary battery 100 is ensured.

  In the battery can 1, a wound group 3 is accommodated in an insulating protective film 2. Since the wound group 3 is wound in a flat shape, the wound group 3 has a pair of curved surface portions facing each other and having a semicircular cross section, and a flat surface portion formed continuously between the pair of curved surface portions. ing. The winding group 3 is inserted into the battery can 1 from one curved surface portion side so that the winding axis direction is along the lateral width direction of the battery can 1, and the other curved surface portion side is disposed on the opening 1a side.

  The positive electrode metal foil exposed portion 34 b of the wound group 3 is electrically connected to the positive electrode external terminal 14 provided on the battery lid 6 via the positive electrode current collector plate 44. Further, the negative electrode metal foil exposed portion 32 b of the wound group 3 is electrically connected to the negative electrode external terminal 12 provided on the battery lid 6 via the negative electrode current collector plate 24. Thereby, electric power is supplied from the winding group 3 to the external load via the positive electrode current collecting plate 44 and the negative electrode current collecting plate 24, and externally supplied to the wound group 3 via the positive electrode current collecting plate 44 and the negative electrode current collecting plate 24. The generated power is supplied and charged.

  In order to electrically insulate the positive electrode current collector plate 44 and the negative electrode current collector plate 24, and the positive electrode external terminal 14 and the negative electrode external terminal 12 from the battery lid 6, a gasket 5 and an insulating plate 7 are provided on the battery lid 6. It has been. Examples of the material for forming the positive electrode external terminal 14 and the positive electrode current collector plate 44 include an aluminum alloy, and examples of the material for forming the negative electrode external terminal 12 and the negative electrode current collector plate 24 include a copper alloy. Examples of the material for forming the insulating plate 7 and the gasket 5 include resin materials having insulating properties such as polybutylene terephthalate, polyphenylene sulfide, and perfluoroalkoxy fluororesin.

The battery lid 6 is provided with a liquid injection port 9 for injecting the electrolytic solution into the battery container. The liquid injection port 9 is injected by the liquid injection plug 11 after the electrolytic solution is injected into the battery container. Sealed. The liquid injection plug 11 is joined to the battery lid 6 by laser welding to seal the liquid injection port 9 and seal the rectangular secondary battery 100. For example, a nonaqueous electrolytic solution in which a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ) is dissolved in an organic carbonate-based organic solvent such as ethylene carbonate is used as the electrolytic solution injected into the battery container. Can do.

  The positive electrode connecting portion 14 a and the negative electrode connecting portion 12 a have a cylindrical shape that protrudes from the lower surface of the positive electrode external terminal 14 and the negative electrode external terminal 12 and can be inserted into the positive electrode side through hole 46 and the negative electrode side through hole 26 of the battery lid 6. Have. The positive electrode connecting portion 14 a and the negative electrode connecting portion 12 a penetrate the battery lid 6 and are more inside the battery can 1 than the positive electrode current collector plate 44, the positive electrode current collector plate base 41 of the negative electrode current collector plate 24, and the negative electrode current collector plate base 21. The positive electrode external terminal 14, the negative electrode external terminal 12, the positive electrode current collector plate 44, and the negative electrode current collector plate 24 are integrally fixed to the battery lid 6. A gasket 5 is interposed between the positive electrode external terminal 14 and the negative electrode external terminal 12 and the battery cover 6, and an insulating plate is interposed between the positive electrode current collector plate 44, the negative electrode current collector plate 24 and the battery cover 6. 7 is interposed.

  The positive electrode current collector plate 44 and the negative electrode current collector plate 24 are a rectangular plate-shaped positive electrode current collector plate base 41, a negative electrode current collector plate base 21, and a positive electrode current collector plate base 41 that are arranged to face the lower surface of the battery lid 6. The negative electrode current collector plate base 21 is bent at the side end and extends toward the bottom surface along the wide surface of the battery can 1, and the positive electrode metal foil exposed portion 34 b and the negative electrode metal foil exposed portion of the wound group 3. It has the positive electrode side connection end part 42 and the negative electrode side connection end part 22 which are connected in the state which overlapped facing 32b. The positive electrode current collector plate base 41 and the negative electrode current collector plate base 21 are respectively formed with a positive electrode side opening hole 43 and a negative electrode side opening hole 23 through which the positive electrode connection part 14a and the negative electrode connection part 12a are inserted.

FIG. 3 is an exploded perspective view showing a state in which a part of the wound group is developed.
The winding group 3 is configured by winding the negative electrode 32 and the positive electrode 34 in a flat shape with separators 33 and 35 interposed therebetween. In the winding group 3, the outermost electrode is the negative electrode 32, and the separators 33 and 35 are wound outside thereof. The separators 33 and 35 have a role of insulating between the positive electrode 34 and the negative electrode 32. The separators 33 and 35 are provided with a plurality of fine holes through which the electrolytic solution can pass.

  The negative electrode mixture layer 32a of the negative electrode 32 (see FIG. 5B) is larger in the width direction than the positive electrode mixture layer 34a of the positive electrode 34, and the positive electrode mixture layer 34a is always the negative electrode mixture layer 32a. It is configured to be sandwiched between them. The positive electrode metal foil exposed portion 34b and the negative electrode metal foil exposed portion 32b are respectively bundled at a plane portion and connected to the positive electrode current collector plate 44 and the negative electrode current collector plate 24 by welding or the like.

  Although the separators 33 and 35 are wider than the negative electrode mixture layer 32a in the width direction, the separators 33 and 35 are wound at positions where the metal foil surface at the end is exposed at the positive metal foil exposed portion 34b and the negative metal foil exposed portion 32b. , It does not hinder bundled welding. Moreover, it is also possible to arrange | position an axial center in the innermost periphery of the winding group 3 as needed. As the shaft core, for example, a material obtained by winding a resin sheet having higher bending rigidity than any of the positive electrode metal foil, the negative electrode metal foil, and the separators 33 and 35 can be used.

  In this embodiment, polyolefin separators are used as the separators 33 and 35. Specifically, a polyolefin multilayer separator made of polypropylene (melting point: about 130 ° C.) and polyethylene (melting point: about 100 ° C.) is used. Using. The configuration of the separator is not limited to the polyolefin-based multilayer separator, but may be a single-layer separator made of polypropylene or polyethylene or a heat-resistant separator made of aramid.

  Moreover, it is good also as a structure which has the heat resistant coating layer which consists of an inorganic filler in the at least single side | surface of a separator. As this inorganic filler, the same inorganic filler as the negative electrode protective layer 32c can be used. The desired place of the present invention is that the melting point of the resin filler mixed in the negative electrode protective layer 32c disposed in the negative electrode 32 described later is higher than that of the separator. In addition, it is preferable that the separator also has a shutdown function from the viewpoint of improving safety.

  4A and 4B are diagrams for explaining the configuration of the positive electrode in this example. FIG. 4A is a front view showing a part of the positive electrode, and FIG. It is A sectional view.

  The positive electrode 34 has a positive electrode mixture layer 34a in which a positive electrode mixture is applied to both surfaces of a positive electrode metal foil that is a positive electrode current collector, and a positive electrode mixture is provided at one end in the width direction of the positive electrode metal foil. An exposed positive metal foil exposed portion 34b is provided. The positive electrode metal foil exposed portion 34b is a region where the metal surface of the positive electrode metal foil is exposed, and is wound so as to be disposed at one position in the winding axis direction.

As for the positive electrode 34, 10 parts by weight of flaky graphite as a conductive material and 10 parts by weight of PVDF as a binder are added to 100 parts by weight of lithium manganate (chemical formula LiMn ₂ O ₄ ) as a positive electrode active material. Then, NMP was added as a dispersion solvent and kneaded to prepare a slurry-like positive electrode mixture. This slurry-like positive electrode mixture was applied on both sides of an aluminum foil (positive metal foil) having a thickness of 20 μm, leaving a positive metal foil exposed portion 34b (positive electrode uncoated portion) as a welded portion. Then, the positive electrode 34 with a thickness of 90 μm of the positive electrode mixture layer 34a not including the aluminum foil was obtained through drying, pressing, and cutting processes.

  Further, in this example, the case where lithium manganate is used as the positive electrode active material is exemplified, but other lithium manganate having a spinel crystal structure or a lithium manganese composite oxide or layered in which a part is substituted or doped with a metal element A lithium cobalt oxide or lithium titanate having a crystal structure, or a lithium-metal composite oxide obtained by substituting or doping a part thereof with a metal element may be used.

  In this example, PVDF was used as the binder in the positive electrode mixture, but polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene butadiene rubber, and polysulfide rubber. Polymers such as nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, and acrylic resins, and mixtures thereof can be used.

  5A and 5B are diagrams illustrating the configuration of the negative electrode. FIG. 5A is a front view showing a part of the negative electrode, and FIG. 5B is a cross-sectional view taken along line AA in FIG. FIG.

  The negative electrode 32 is provided on the surface of a negative electrode mixture layer 32a provided by applying a negative electrode mixture containing a negative electrode active material on both surfaces of a negative electrode metal foil which is a negative electrode current collector, and the surface of the negative electrode mixture layer 32a. Negative electrode protective layer 32c. And the negative electrode metal foil exposure part 32b in which the negative mix is not apply | coated is formed in the edge part of the width direction other side of negative electrode metal foil. The negative electrode metal foil exposed portion 32b is a region where the metal surface of the negative electrode metal foil is exposed, and is wound so as to be disposed at the position on the other side in the winding axis direction.

Regarding the negative electrode 32, 1 part by weight of styrene butadiene rubber (hereinafter referred to as SBR) is added as a binder to 100 parts by weight of graphite powder as a negative electrode active material, and carboxymethyl cellulose (CMC) as a thickener. Was added thereto, and H ₂ O was added thereto as a dispersion solvent and kneaded to prepare a negative electrode mixture. The negative electrode mixture was applied to both sides of a 10 μm thick copper foil (negative electrode metal foil) leaving the negative electrode metal foil exposed portion 32b (negative electrode uncoated portion) as a welded portion, dried and pressed, and then protected for negative electrode The slurry of the layer 32c was apply | coated on the negative mix layer 32a, and the negative electrode 32 with a thickness of 70 micrometers of the negative electrode active material application part which does not contain copper foil was obtained through the cutting process.

  In the present embodiment, the negative electrode mixture is applied, dried and pressed, and then the slurry for the negative electrode protective layer 32c is applied onto the negative electrode mixture layer 32a. However, the present invention is not limited to this. For example, after applying the slurry of the negative electrode protective layer 32c simultaneously with the negative electrode mixture, the negative electrode 32 may be produced by pressing and cutting.

In this embodiment, the case where graphite is used as the negative electrode active material is exemplified, but the present invention is not limited to this. Natural graphite capable of inserting and removing lithium ions, various artificial graphite materials, coke, etc. Carbonaceous materials, amorphous carbon, compounds such as Si and Sn (for example, SiO, TiSi ₂ etc.), or composite materials thereof may be used, and the particle shape may be scale-like, spherical, fibrous, massive, etc. There is no particular limitation.

Moreover, although illustrated about the case where SBR is used as a binder of the coating part in a negative electrode, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, polysulfide Polymers such as rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, and acrylic resins, and mixtures thereof can be used. Further, while an example has been shown where H _{2 O} is used as a dispersion solvent for the coated portion of the negative electrode, not limited thereto, it may be used such as polyvinylidene fluoride (NMP) solvent.

FIG. 6 is a cross-sectional view of the wound group in the first embodiment.
The negative electrode 32 has a negative electrode mixture layer 32a facing the positive electrode mixture layer 34a and wider than the positive electrode mixture layer 34a. The negative electrode protective layer 32c has a width that covers the negative electrode mixture layer 32a, and has a size that covers the negative electrode mixture layer 32a so that the negative electrode mixture layer 32a is not exposed particularly at a portion facing the positive electrode metal foil exposed portion 34b via the separator. Is a requirement.

  Next, the negative electrode protective layer 32c in the present embodiment will be described with reference to a cross-sectional image diagram of the negative electrode protective layer 32c in FIG. In addition, the cross-sectional image figure of FIG. 7 is the structure which imaged Example 1-2 mentioned later.

The negative electrode protective layer 32c is a mixture of an inorganic filler 32c1 and a resin filler 32c2 having a melting point higher than that of the separator as a protective material, SBR as a binder 32c3, and CMC (not shown) as a thickener. And including. H ₂ O is added to these mixtures as a dispersion solvent and kneaded to produce a slurry-like mixture, which is applied to the desired location, dried, and evaporated to a thickness of about 5 μm. A negative electrode protective layer 32c having the same was formed. In the present embodiment, the case where SBR is included as the binder of the negative electrode protective layer 32c and CMC is included as the thickener is exemplified, but the present invention is not limited thereto, and PVDF or acrylic is used as the binder. NMP may be used as a solvent.

The inorganic filler 32c1 is, for example, at least iron oxide, silica (SiO ₂ ), alumina (Al ₂ O ₃ ), boehmite (Al ₂ O ₃ hydrate), titanium oxide (TiO ₂ ), or barium titanate (BaTiO ₂ ). Have one. In this example, boehmite was used for the inorganic filler 32c1, and a battery in which the presence or absence of the resin filler, the material, and the composition ratio were changed was manufactured and the effect was verified. As a verification of the effect, in order to simulate a severe internal short-circuit outside the range normally used, a nail penetration test was conducted in which the battery was completely penetrated with a SUS nail having a diameter of 3 mm. The set SOC was set in increments of 5%, and the highest SOC that did not lead to smoke or ignition in the nail penetration test was used as an effect index.

  The mechanism of heat generation by the nail penetration test is not clear, but as an example of a hypothesis, the penetration portion by the nail penetration is not only indirect short circuit through the nail, but also by the electrode breakage by the nail, the positive electrode 34 It is considered that a part of the negative electrode 32 and a part of the negative electrode 32 are in contact and directly short-circuited. In general, the greater the area of the part that is directly short-circuited, and the higher the SOC, the greater the amount of heat generated during the short-circuit. These heat generations promote the shrinkage of the separators 33 and 35, and reduce the binding force of the binder (SBR) 32c3 constituting the negative electrode protective layer 32c.

  Due to the structure of the wound group 3, the separators 33 and 35 are shrunk, and the binding force of the binding material 32c3 of the constituent material of the negative electrode protection layer 32c becomes insufficient, and the resin filler 32c2 of the negative electrode protection layer 32c is melted. If it flows out between the positive electrode 34 and the negative electrode 32, the positive electrode metal foil exposed portion 34b and the negative electrode mixture layer 32a come into contact with each other, a secondary short circuit occurs, and eventually, ignition and smoke are caused. Is considered.

  Here, if the negative electrode protective layer 32c can maintain sufficient insulation, a short circuit due to contact between the positive electrode 34 and the negative electrode 32 due to nail penetration breakage can be avoided, and heat generation can be suppressed. In addition, since the heat generation is higher in the high SOC state, the separators 33 and 35 are likely to shrink. However, if the insulating property of the negative electrode protective layer 32c is sufficient, the positive metal foil exposed portion 34b and the negative electrode 32 A secondary short circuit can be avoided and safety can be ensured.

  What the present invention desires is to ensure sufficient insulation during abnormal heat generation. The mechanism will be described with reference to FIG. 7. The binder (SBR in this embodiment) 32c3 of the negative electrode protective layer 32c is: In the case of an abnormal heat generation state, the function as a binder is decreased by melting, but at the same time, the resin filler 32c2 is softened to exhibit tackiness and exhibit a function as a second adhesive. In addition, the movement of the inorganic filler 32c1 is suppressed, and at the same time, the pores are closed and the insulating properties are improved. Therefore, a secondary short circuit in which the positive electrode 34 and the negative electrode 32 are directly short-circuited can be avoided, and safety can be improved.

  Table 1 shows examples and comparative examples in which the composition of the negative electrode protective layer 32c was studied and the effects thereof. For comparison of effects, Comparative Example 1-1 shown in Table 1 was prepared without the negative electrode protective layer 32c shown in FIGS. 5 and 6, and Comparative Example 1-2 was a resin applied to the negative electrode protective layer 32c. The filler 32c2 was not mixed and it was produced using only the inorganic filler 32c1 and the binder 32c3. In addition, polyethylene (PE) having a melting point substantially equal to that of the separators 33 and 35 is used for the resin filler of the comparative example, and polyphenylene sulfide (PPS) having a melting point higher than that of the separators 33 and 35 is used for the resin filler of the example. The effect was confirmed using. A spherical inorganic filler having an aspect ratio of 2 or less was used. And the measurement of the particle size was performed using the particle size distribution measuring apparatus by a laser diffraction / scattering method.

  From the results shown in Table 1, when Comparative Example 1-1 and Comparative Example 1-2 were compared, Comparative Example 1-2 did not reach ignition / smoke up to a higher SOC, so the negative electrode protective layer 32c was disposed. The safety improvement effect by was confirmed.

  Next, compared with Comparative Example 1-2, Comparative Examples 1-3 to 1-5 were equivalent or lower, and no improvement effect was observed. In Comparative Examples 1-3 to 1-5, in addition to the resin filler being mixed, the amount of the inorganic filler was substantially reduced, and the resin filler and the binder were at substantially the same temperature as the melting point of the separator. Therefore, the resin filler and the binder of the protective layer are melted at the same time as the separator, and the inorganic filler fixed by the resin filler and the binder becomes movable, and a part of the negative electrode protective layer 32c is formed. It is thought that it flowed out and became thin and was in a state where sufficient insulation was not obtained.

  Next, when Comparative Examples 1-2 to 1-5 and Examples 1-1 to 1-3 are compared, all of Examples 1-1 to 1-3 have an increase in the maximum SOC and safety. The improvement effect was seen. In Examples 1-1 to 1-3, although the inorganic filler 32c1 is substantially reduced by mixing the resin filler 32c2, the heat resistance temperature of the resin filler 32c2 is high, so that the insulating property can be maintained. In addition, the resin filler 32c2 is softened by heat generation and develops an adhesive force, binds the inorganic filler 32c1 with a certain binding force, and exhibits a function as a second binding material. This is thought to be due to the suppression of movement, resulting in increased insulation.

  When Examples 1-1 to 1-3 were compared, the level (Example 1-2) in which the mixing ratio of the inorganic filler 32c1 and the resin filler 32c2 was 3: 1 was most effective. This is presumed that Example 1-2 had a sufficient amount of the inorganic filler 32c1 that can ensure insulation, and that it was an appropriate amount to serve as the second binder by the resin filler 32c2. The

  Next, when Example 2-1 and Example 1-2 were compared, Example 2-1 was more effective, and safety at high SOC (95%) could be ensured. In Example 2-1, the particle size of the resin filler 32c2 and the particle size of the inorganic filler 32c1 are made different from each other to mix particles of two types of particle sizes, whereby the density of the negative electrode protection layer 32c is mixed. This is thought to be due to an increase in insulation and improved insulation. Then, by making the particle size of the resin filler 32c2 smaller than the particle size of the inorganic filler 32c1, the number of contacts where the inorganic filler 32c1 and the resin filler 32c2 are in contact with each other can be increased. In addition to the effect of suppressing the movement of the inorganic filler 32c1 by binding the inorganic filler 32c1 more firmly when functioning as a binder, the voids of the negative electrode protective layer 32c are formed by melting the resin filler 32c2. It was estimated that the insulation was further improved.

  Next, when Example 3-1 and Example 2-1 were compared, Example 3-1 was more effective, and safety at the maximum SOC (100%) could be ensured. In Example 3-1, as shown in the image diagram of FIG. 8, the particle shape of the resin filler 32c2 is spherical, whereas the particle shape of the inorganic filler 32c1 is a plate shape. As a result, it was speculated that the number of contacts was further increased to suppress the movement of the inorganic filler 32c1 and the safety was improved. The plate-like inorganic filler 32c1 has an aspect ratio of 5 or more, and in the present embodiment, a filler having a ratio of 5 to 15 was used. And the measurement of the particle size was performed using the particle size distribution measuring apparatus by a laser diffraction / scattering method.

Table 2 shows the results of the nail penetration test when the material of the inorganic filler 32c1 is changed with respect to Example 3-1. In Example 3-1, boehmite (Al ₂ O ₃ hydrate) was used as the material of the inorganic filler 32c1, whereas alumina (Al ₂ O ₃ ) was used in Example 4-1, and in Example 4-2. silica (SiO _2), the titanium oxide in example 4-3 (TiO _2), in example 4-4, was used barium titanate (BaTiO _2).

  From the results in Table 2, it was confirmed that this test was effective without depending on the material of the inorganic filler 32c1.

  Table 3 shows the results of a nail penetration test when separators 33 and 35 in which inorganic filler (alumina) 32c1 is applied to separators 33 and 35 are used in Example 3-1. In addition, the secondary battery was produced so that the coating layer of the separators 33 and 35 might be arrange | positioned at the positive electrode side.

  From the results shown in Table 3, Example 5-1 had the same maximum SOC as Example 3-1 but the highest temperature reached. This is because the coated layers of the separators 33 and 35 generally have an effect of suppressing the thermal contraction of the separators 33 and 35, so that the contraction of the separators 33 and 35 around the nail is suppressed, and the break due to the nail is short-circuited. It is considered that the maximum temperature reached has decreased due to the decrease in. Therefore, higher safety can be expected by combining the coated separator with improved heat resistance and this example.

  According to the present invention, the protective layer 32c is mixed with the resin filler 32c2 having a melting point higher than that of the separators 33 and 35 and the binder 32c3 of the protective layer 32c. The function as the binder is exhibited to suppress the movement of the inorganic filler 32c1. Accordingly, even if the separators 33 and 35 are shrunk, the secondary short circuit between the positive electrode 34 and the negative electrode 32 can be avoided by the protective layer 32c, and safety can be improved.

  In the above-described embodiment, the case where the protective layer 32c is formed by mixing the inorganic filler 32c1 and the resin filler 32c2 has been described. However, at least a part of the inorganic filler 32c1 is made of a resin such as PPS constituting the resin filler 32c2. A coated material or a resin in which the resin constituting the resin filler 32c2 is supported on the inorganic filler 32c1 may be used, and the effect of improving the safety can be obtained similarly.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. Furthermore, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Battery can 3 Winding group 6 Battery cover 10 Gas discharge valve 12 Negative electrode external terminal 14 Positive electrode external terminal 32 Negative electrode 32a Negative electrode mixture layer 32b Negative electrode metal foil exposed part 32c Negative electrode protective layer 32c1 Inorganic filler 32c2 Resin filler 32c3 Binder 33, 35 Separator 34 Positive electrode 34a Positive electrode mixture layer 34b Positive metal foil exposed portion 100 Square secondary battery (secondary battery)

Claims (4)

A secondary battery having an electrode group in which a positive electrode and a negative electrode are laminated via a separator,
The negative electrode has a negative electrode mixture layer and a negative electrode protective layer provided on the surface of the negative electrode mixture layer,
The negative electrode protective layer has an inorganic filler, a resin filler, and a binder.
The melting point of the resin filler, rather higher than the melting point of the separator,
The resin filler has a particle size smaller than the inorganic filler,
The secondary battery , wherein the resin filler contains polyphenylene sulfide . The secondary battery according to claim 1 , wherein the inorganic filler is a plate-like particle, and the resin filler is a spherical particle. The inorganic filler is iron oxide, silica _(SiO 2), alumina _{(Al 2 O} 3), boehmite _(Al 2 _{O 3} hydrate), titanium oxide _(TiO 2), either at least barium titanate (BaTiO ₂₎ The secondary battery according to claim 1 , comprising the single material. The secondary battery according to claim 1 , wherein the separator includes a coating layer, and the coating layer includes an inorganic filler.

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