JP2013073680A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with both of a shut-down effect and an input/output characteristic at a high rate.SOLUTION: The nonaqueous electrolyte secondary battery comprises a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode active material layer containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The negative electrode active material layer contains 0.15 mass% to 2.0 mass% resin having a melting point in a temperature range of 105°C-135°C. The separator contains a layer formed of a resin having a melting point in a range of 105°C-135°C.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. In the present specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged, such as a lithium ion battery or a nickel metal hydride battery. In the present specification, the “lithium ion battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of electrons accompanying the lithium ions between the positive and negative electrodes. Further, in this specification, the “active material” can reversibly occlude and release (typically insertion and removal) chemical species (for example, lithium ions in a lithium ion battery) that become charge carriers in a secondary battery. A substance.

Non-aqueous electrolyte secondary batteries represented by lithium ion batteries are becoming increasingly important as power sources for vehicles or as power sources for personal computers and portable terminals. In particular, a lithium ion battery that is lightweight and obtains a high energy density is expected to be preferably used as a high-output power source mounted on a vehicle.
In this non-aqueous electrolyte secondary battery, the separator interposed between the positive electrode and the negative electrode prevents short circuit due to contact between the positive electrode and the negative electrode for the purpose of ensuring the safety of the battery and the device in which the battery is mounted. Has a role to prevent (short-circuit prevention function). In addition to this short-circuit prevention function, when the inside of the battery reaches a certain temperature range (typically, the melting point or softening point of the separator), the resistance is increased by blocking the ion conduction path. And it has the function (shutdown function) which stops charging / discharging by this resistance increase, and prevents the thermal runaway of a battery. In general separators, the melting point of a resin such as polyolefin, which is a constituent material, is a shutdown temperature, and when this temperature is reached, the fine pores of the separator are blocked by melting or softening, and the resistance is increased. It is.

Regarding such a non-aqueous electrolyte secondary battery, for example, Patent Document 1 discloses that a negative electrode contains a polymer compound having a melting point of 90 to 130 ° C. and a heat of fusion of 30 J / g or more as a heat absorbing material. A proposed configuration has been proposed. It has been disclosed that, by such a configuration, even if the battery is short-circuited and Joule heat is generated, it is possible to suppress the heat absorption material from absorbing heat as the heat of melting of the heat absorbing material and increasing the battery temperature.
Further, Patent Document 2 proposes a lithium ion battery having a configuration in which a heat absorbing agent having a melting point of 65 ° C. or higher and lower than 100 ° C. and an endothermic heat absorption is added to any of a positive electrode, a negative electrode, and a separator. . According to such a configuration, it is disclosed that even when abnormal heat generation in the battery is large, the entire separator is shut down reliably.

Japanese Patent Laid-Open No. 10-064548 JP 2009-238705 A

  By the way, since the lithium ion battery can realize a high input / output density and a high energy density, enhancement of a large-sized battery as an in-vehicle power source for EV and PHEV in particular is strongly desired. However, such a large battery is inferior in heat dissipation of the battery because of its high energy density structure. Therefore, even when the temperature inside the battery suddenly increases due to overcharge or the like, it is required to ensure safety without causing thermal runaway.

The non-aqueous electrolyte secondary battery disclosed herein includes a positive electrode including a positive electrode active material layer including a positive electrode active material, a negative electrode including a negative electrode active material layer including a negative electrode active material, and the positive electrode and the negative electrode. And a non-aqueous electrolyte.
Here, the negative electrode active material layer contains the resin A having a melting point in the temperature range of 105 ° C. to 135 ° C. in a proportion of 0.15% by mass to 2.0% by mass. The separator contains a resin B having a melting point in the range of 105 ° C to 135 ° C.
According to such configuration, the reaction resistance of the non-aqueous electrolyte secondary battery is kept low, and the effect of preventing battery thermal runaway (shutdown effect) when the non-aqueous electrolyte secondary battery abnormally generates heat due to some abnormality Can be obtained.

  In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the resins A and B can be polyethylene. Polyethylene can easily adjust the melting point to a desired value within a temperature range of, for example, 105 ° C. to 135 ° C. by adjusting the molecular weight, molecular structure, density, etc., and is easily available and processed. . And the cost is relatively low. Therefore, it can be said that this is a desirable material for the resins A and B disclosed herein.

  When the separator has a multilayer structure, the resin B may form an inner layer in the multilayer structure. In this case, the separator can maintain the form of the separator without melting the outer layer even if the inner layer made of the resin B is melted by the shutdown. For this reason, it is avoided that a short circuit arises between a positive electrode and a negative electrode also at the time of shutdown.

  In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the positive electrode active material may contain a lithium transition metal oxide as a main component. The non-aqueous electrolyte secondary battery disclosed herein includes such a lithium transition metal oxide as a main component as a positive electrode active material, and thus has good characteristics as described above while having characteristics such as high energy density. It also has a shutdown characteristic. Therefore, a large-sized secondary battery with high safety is realized.

  Further, as described above, the non-aqueous electrolyte secondary battery disclosed herein has excellent shutdown characteristics without greatly impairing the original battery performance, and has improved safety performance and reliability. Therefore, it is particularly suitable as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) that requires input / output characteristics at a high rate, and a vehicle (for example, an automobile) equipped with this non-aqueous electrolyte secondary battery. Can be provided.

FIG. 1 is a perspective view schematically showing an overall configuration of a lithium ion battery according to an embodiment of the present invention. 2 is a cross-sectional view showing a II-II cross section in FIG. FIG. 3 is a schematic view of a wound electrode body. FIG. 4 is a schematic diagram showing a vehicle equipped with a lithium ion battery according to an embodiment of the present invention. FIG. 5 is a typical diagram of a Cole-Cole plot (Nyquist plot). FIG. 6 is a graph in which DC resistance is evaluated for Sample 1 to Sample 4. FIG. 7 shows the total weight (mg / cm ² ) of PE (resins A and B) contained in the negative electrode active material layer and the separator, and the test cell was constructed by exposing the negative electrode active material layer and the separator to a high temperature atmosphere. It is a graph which shows the relationship with the direct current | flow resistance (mohm) in the case. FIG. 8 shows the proportion (mass%) of PE (resin A) contained in the negative electrode active material layer and the reaction at −30 ° C. when the test cell was constructed without exposing the negative electrode active material layer and the separator to a high temperature atmosphere. It is a graph which shows the relationship with resistance (mohm). FIG. 9 is a graph showing the relationship between the resistance values of the test cells of Examples and Comparative Examples and the melting point of polyethylene.

  First, as a typical embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the present invention will be described by taking a structure of a lithium ion battery as an example. Thereafter, a lithium ion battery according to an embodiment of the present invention will be described with reference to such structural examples as appropriate. In addition, the same code | symbol is attached | subjected suitably to the member and site | part which show the same effect | action. Moreover, each drawing is drawn typically and does not necessarily reflect the real thing. Each drawing shows only an example and does not limit the present invention unless otherwise specified.

≪Lithium-ion battery structure≫
FIG. 1 is a perspective view showing the appearance of the lithium ion battery 100. FIG. 2 is a II-II cross-sectional view of the lithium ion battery 100 in FIG. As shown in FIG. 2, the lithium ion battery 100 includes a wound electrode body 200 and a battery case 300. FIG. 3 is a schematic diagram for explaining the configuration of the wound electrode body 200.
As shown in FIG. 3, the wound electrode body 200 includes a positive electrode sheet 220, a negative electrode sheet 240, and two separators 262 and 264. The positive electrode sheet 220, the negative electrode sheet 240, and the separators 262 and 264 are respectively strip-shaped sheet materials.

  In the lithium ion battery 100 disclosed herein, the positive electrode (positive electrode sheet 220) includes a positive electrode active material layer 223 containing a positive electrode active material (not shown) on the surface of a strip-shaped positive electrode current collector 221. The negative electrode (negative electrode sheet 240) includes a negative electrode active material layer 243 containing a negative electrode active material (not shown) on the surface of a strip-shaped negative electrode current collector 241. Separators 262 and 264 are interposed between the positive electrode and the negative electrode. Here, the negative electrode active material layer 243 contains 0.15% by mass to 2.0% by mass of the resin A having a melting point in the temperature range of 105 ° C. to 135 ° C. Moreover, the separators 262 and 264 have a resin B having a melting point in the range of 105 ° C to 135 ° C. Hereinafter, the lithium ion battery 100 will be described in more detail.

≪Positive electrode (positive electrode sheet) ≫
As the positive electrode current collector 221 of the positive electrode sheet 220, a metal foil suitable for the positive electrode can be suitably used. For example, a rod-like body, a plate-like body, a foil-like body, a net-like body or the like mainly composed of aluminum, nickel, titanium, stainless steel, or the like can be used. In this example, specifically, a strip-shaped aluminum foil having a thickness of about 15 μm is used for the positive electrode current collector 221. An uncoated portion 222 is set on the positive electrode current collector 221 along one edge portion in the width direction. In the illustrated example, the positive electrode active material layer 223 is held on both surfaces of the positive electrode current collector 221 except for the uncoated portion 222 set on the positive electrode current collector 221 as shown in FIG.

≪Positive electrode active material layer≫
The positive electrode active material layer 223 can be formed by applying a positive electrode active material layer forming paste containing a positive electrode active material to the positive electrode current collector 221. That is, for example, a positive electrode active material layer forming paste in which a positive electrode active material, a conductive material, and a binder are dispersed in an appropriate solvent is prepared. The prepared paste is applied to the positive electrode current collector 221, dried, and then compressed (pressed) to form the positive electrode active material layer 223. Although it does not specifically limit, the usage-amount of the electrically conductive material with respect to 100 mass parts of positive electrode active materials can be 1-20 mass parts (preferably 5-15 mass parts), for example. Moreover, the usage-amount of a binder with respect to 100 mass parts of positive electrode active materials can be 0.5-10 mass parts, for example. Note that a known method can be applied as a method of forming the positive electrode active material layer 223, and the detailed description thereof is omitted here because the invention is not characterized.

≪Positive electrode active material≫
As the positive electrode active material, various materials that can be used as the positive electrode active material of a non-aqueous electrolyte secondary battery (typically, a lithium ion battery) can be used without any particular limitation. Examples of the positive electrode active material include LiNiCoMnO ₂ (lithium nickel cobalt manganese composite oxide; so-called ternary system), LiNiO ₂ (lithium nickelate), LiCoO ₂ (lithium cobaltate), LiMn ₂ O ₄ (manganese) Acid lithium), LiFePO ₄ (lithium iron phosphate), LiMnO ₃ and their solid solutions, and so on. Here, LiMn ₂ O ₄ has, for example, a spinel structure. LiNiO ₂ or LiCoO ₂ has a layered rock salt structure. For example, LiFePO ₄ has an olivine structure. Additional modes such as the particle size of these materials and coating with a carbon film can be appropriately selected according to desired characteristics.

The invention disclosed herein is particularly effective when realized as a large capacity lithium ion battery. As the positive electrode active material, for example, the positive electrode of a large capacity lithium ion battery is used. A lithium transition metal oxide represented by the general formula: LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , which has been studied for use as an active material, can be contained as a main component. In the invention disclosed herein, “containing as a main component” means containing 50% by mass or more, and typically 70% by mass or more, more preferably 90% by mass or more. .

≪Conductive material≫
As the conductive material, for example, various carbon blacks (for example, acetylene black, oil furnace black, graphitized carbon black, carbon black, graphite, ketjen black), and carbon powder such as graphite powder can be used. These may be used alone or in combination of two or more.

≪Binder≫
In addition, the binder has a function of binding each particle of the positive electrode active material and the conductive material included in the positive electrode active material layer 223 or binding these particles and the positive electrode current collector 221. As such a binder, a polymer that can be dissolved or dispersed in a solvent to be used can be used. For example, in a positive electrode active material layer forming paste using an aqueous solvent, a cellulose polymer (carboxymethyl cellulose (CMC), hydroxypropylmethyl cellulose (HPMC), etc.), a fluorine resin (eg, polyvinyl alcohol (PVA), polytetra Fluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP, etc.), rubbers (vinyl acetate copolymer, styrene butadiene copolymer (SBR), acrylic acid-modified SBR resin (SBR latex) A water-soluble or water-dispersible polymer such as In the positive electrode active material layer forming paste using a non-aqueous solvent, a polymer (polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), or the like) can be preferably used.

≪Solvent, thickener≫
As the solvent, any of an aqueous solvent and a non-aqueous solvent can be used. A suitable example of the non-aqueous solvent is N-methyl-2-pyrrolidone (NMP). The polymer material exemplified as the binder may be used for the purpose of exhibiting functions as a thickener and other additives of the positive electrode active material layer forming paste in addition to the function as a binder.

  The mass ratio of the positive electrode active material to the entire positive electrode active material layer is preferably about 50% by mass or more (typically 50 to 95% by mass), and usually about 70 to 95% by mass (for example, 75 to 90%). (Mass%) is more preferable. The proportion of the conductive material in the entire positive electrode active material layer can be, for example, about 2 to 20% by mass, and is usually preferably about 2 to 15% by mass. In the composition using a binder, the ratio of the binder to the whole positive electrode active material layer forming paste can be, for example, about 1 to 10% by mass, and usually about 2 to 5% by mass is preferable.

≪Negative electrode≫
As shown in FIG. 3, the negative electrode sheet 240 includes a negative electrode active material layer 243 containing a negative electrode active material (not shown) on the surface of a strip-shaped negative electrode current collector 241. For the negative electrode current collector 241, a metal foil suitable for the negative electrode can be suitably used. For example, a rod-like body, a plate-like body, a foil-like body, a net-like body or the like mainly composed of copper, nickel, titanium, stainless steel, or the like can be used. In this example, specifically, the negative electrode current collector 241 is made of a strip-shaped copper foil having a predetermined width and a thickness of about 10 μm. In such a negative electrode current collector 241, an uncoated portion 242 is set along one edge portion in the width direction. The negative electrode active material layer 243 is formed on both surfaces of the negative electrode current collector 241 except for the uncoated portion 242 set on the negative electrode current collector 241.

<< Negative Electrode Active Material Layer 243 >>
The negative electrode active material layer 243 disclosed herein includes a negative electrode active material and a resin A having a melting point in a temperature range of 105 ° C. to 135 ° C. In this embodiment, the negative electrode active material layer 243 contains negative electrode active material particles as the negative electrode active material, the resin A, a thickener, a binder, and the like.

≪Negative electrode active material≫
As the negative electrode active material, one type or two or more types of materials conventionally used in lithium ion batteries can be used without any particular limitation. For example, a particulate carbon material (carbon particles) including a graphite structure (layered structure) at least in part. More specifically, the negative electrode active material is, for example, natural graphite, natural graphite coated with an amorphous carbon material, graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon ( Soft carbon) or a carbon material combining these may be used. Further, for example, a metal compound (preferably a metal oxide) containing Si, Ge, Sn, Pb, Al, Ga, In, As, Sb, Bi, or the like as a constituent metal element may be used. It has also been proposed to use LTO (lithium titanate) as the negative electrode active material particles. Moreover, about the negative electrode active material which consists of metal compounds, the surface of a metal compound may fully be coat | covered with a carbon film, for example, and you may use as a granular material excellent in electroconductivity. In this case, the negative electrode active material layer may not contain a conductive material, or the content of the conductive material may be reduced as compared with the conventional case. The additional aspect of these negative electrode active materials and forms, such as a particle size, can be suitably selected according to a desired characteristic.

≪Binder≫
For the binder of the negative electrode active material layer 243, the polymer material exemplified as the binder of the positive electrode active material layer 223 can be used. The negative electrode active material layer 243 is prepared, for example, by preparing a paste for forming a negative electrode active material layer in which the above-described negative electrode active material particles and a binder are mixed in a paste (slurry) with a solvent, and applied to the negative electrode current collector 241. It is formed by drying and rolling. In the negative electrode active material layer 243, the negative electrode active material particles and the negative electrode active material particles and the negative electrode current collector are bonded together by a binder. In the negative electrode active material layer 243 thus formed, voids are formed between the negative electrode active material particles so that the electrolyte solution can penetrate.

≪Solvent, thickener, conductive material≫
As the solvent, any of an aqueous solvent and a non-aqueous solvent used in the positive electrode active material layer 223 can be used. A suitable example of the non-aqueous solvent is N-methyl-2-pyrrolidone (NMP). The polymer material exemplified as the binder of the positive electrode active material layer 223 is used for the purpose of exhibiting a function as a thickener and other additives of the negative electrode active material layer forming paste in addition to the function as a binder. It can happen.
Although not particularly limited, the negative electrode active material layer 243 may include a conductive material. In this case, the usage-amount of the electrically conductive material with respect to 100 mass parts of negative electrode active materials to be used shall be about 1-30 mass parts (preferably, about 2-20 mass parts, for example, about 5-10 mass parts). it can. Moreover, the usage-amount of a binder with respect to 100 mass parts of negative electrode active materials can be 0.5-10 mass parts, for example.

<Resin A contained in negative electrode active material layer>
As described above, the negative electrode active material layer 243 contains the resin A having a melting point of 105 ° C. to 135 ° C. The resin A can be used without particular limitation as long as its melting point is 105 ° C. to 135 ° C. When the temperature of the negative electrode active material layer 243 increases, the resin A melts and closes the gaps in the negative electrode active material layer 243. This restricts the movement of lithium ions in the negative electrode active material layer 243 and limits the battery reaction (shutdown in the negative electrode active material layer 243).
Note that if the melting point of the resin A is lower than 105 ° C., the DC resistance (IV resistance) of the lithium ion battery is high because the resin A melts in the drying step when forming the negative electrode active material layer 243. There is a case. On the other hand, when the melting point of the resin A is higher than 135 ° C., melting is delayed when the temperature of the negative electrode active material layer 243 becomes abnormally high, so that the shutdown function in the negative electrode active material layer 243 is deteriorated.

  As the resin A, for example, a resin having a desired melting point and various characteristics can be appropriately selected from polyolefin resins. As such a resin A, it is preferable to use polyethylene (PE) which is comparatively easy to adjust the melting point and easily available. For example, the density of polyethylene varies depending on the molecular weight and molecular structure, and the melting point can be controlled to a desired temperature by adjusting the density. Further, such a resin is preferably blended in the negative electrode active material layer 243 so as to be approximately 0.15% by mass to 2.0% by mass.

  Even if the content of the resin A in the negative electrode active material layer 243 is less than 0.15% by mass, the effect of increasing the resistance during high-temperature heating can be obtained. The effect is dramatically improved. In addition, when the content of the resin A is too large in the negative electrode active material layer 243, the reaction resistance of the lithium ion battery 100 increases. For example, when the content of the resin A in the negative electrode active material layer 243 is more than 3.0% by mass, the reaction resistance of the lithium ion battery 100 is significantly deteriorated in a low temperature environment of about −30 ° C. In the lithium ion battery 100 for automobile use, it is desirable to keep the reaction resistance in such a low temperature environment low. For this reason, the content of the resin A in the negative electrode active material layer 243 is preferably about 2.0 mass% or less. Thereby, the reaction resistance of the lithium ion battery 100 can be kept low.

<< Separators 262, 264 >>
As shown in FIG. 2 or 3, the separators 262 and 264 are members that insulate the positive electrode sheet 220 and the negative electrode sheet 240 and allow the electrolyte to move. Therefore, typically, a separator can be made into a porous body, a nonwoven fabric, a cloth-like body, etc. having fine pores that can move lithium ions. Moreover, the material which comprises a separator will not be specifically limited if this requirement is satisfy | filled. As such a material, for example, a material having desired characteristics can be selected from polyolefins. Specific examples include resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide.

  In the example illustrated in FIG. 2, the separators 262 and 264 are band-shaped (sheet-shaped) members, and the width b1 of the negative electrode active material layer 243 is slightly wider than the width a1 of the positive electrode active material layer 223. Furthermore, the widths c1 and c2 of the separators 262 and 264 are slightly wider than the width b1 of the negative electrode active material layer 243 (c1, c2> b1> a1). The negative electrode active material layer 243 is opposed so as to cover the positive electrode active material layer 223, and the separators 262 and 264 are interposed between the negative electrode active material layer 243 and the positive electrode active material layer 223. The material layer 243 is overlaid so as to cover it.

  The separators 262 and 264 contain a resin B having a melting point in the range of 105 ° C to 135 ° C. The melting point of the material constituting the separator excluding the resin B is set higher than that of the resin B. Accordingly, the lithium ion battery 100 generates heat due to some factor, and when the temperature of the separators 262 and 264 reaches the melting point of the resin B, the resin B contained in the separators 262 and 264 is melted. The melted resin B closes the fine pores of the separators 262 and 264 and shuts off (shuts down) the ion conduction path of lithium ions that are charge carriers. Therefore, for example, abnormal heating of the battery can be prevented.

  Note that the melting point of the resin B contained in the separators 262 and 264 and the melting point of the resin A contained in the negative electrode active material layer 243 are set to substantially the same temperature range. The melting points of the resin A and the resin B can be determined independently. For example, the melting point of the resin A included in the negative electrode active material layer 243 and the melting point of the resin B included in the separators 262 and 264 may be the same. Further, the melting point of the resin A included in the negative electrode active material layer 243 may be higher than the melting point of the resin B included in the separators 262 and 264. Conversely, the melting point of the resin A included in the negative electrode active material layer 243 may be lower than the melting point of the resin B included in the separators 262 and 264.

  As the resin B included in the separators 262 and 264, the same resin as the resin A included in the negative electrode active material layer 243 can be used. Further, the resin A included in the negative electrode active material layer 243 and the resin B included in the separators 262 and 264 may be different resins. For example, the resins A and B are preferably polyethylene from the viewpoints of adjustment of the melting point and easy acquisition and handling.

  In this embodiment, although not shown, the separators 262 and 264 have a multilayer structure, and the resin B forms an inner layer in the multilayer structure. Here, the multilayer structure means a laminated structure of two or more layers, and can typically be three or more layers. For example, when the separators 262 and 264 have a three-layer structure, a sheet material made of a porous polyolefin resin having a large number of minute holes (for example, polypropylene (PP)) is used as an outer layer, and a melting point is 105 ° C. to 135 ° C. A layer made of resin B (for example, polyethylene (PE)) may be used as an inner layer (PP / PE / PP). The separators 262 and 264 may have a two-layer structure. For example, a polypropylene porous sheet may be used as a base material, and a polyethylene porous sheet may be stacked.

  In this case, when the lithium ion battery 100 generates heat, an inner layer (for example, polyethylene (PE)) made of a low melting point resin is melted in the separators 262 and 264. Even when the inner layer melts, the outer layer (for example, polypropylene (PP)) remains without being melted, so that the separators 262 and 264 can maintain their shapes. And since an internal layer melt | dissolves and the shutdown by the separators 262 and 264 advances, the heat_generation | fever of the lithium ion battery 100 accompanying a battery reaction can be suppressed, and the danger of the further temperature rise can be reduced.

  On the other hand, the separators 262 and 264 replace the sheet-like member with, for example, an insulating particle layer formed on the surface of the positive electrode active material layer 223 or the negative electrode active material layer 243 and the above-described low layer. You may comprise by making the layer (or sheet | seat) of particle | grains consisting of melting | fusing point resin into an internal layer. Here, as the particles having insulating properties, inorganic fillers having insulating properties (for example, fillers such as metal oxides and metal hydroxides) or resin particles having insulating properties (for example, particles such as polyethylene and polypropylene) ). In this case, a resin B having a melting point of 105 ° C. to 135 ° C. may be included in the insulating particle layer (separator). Further, for example, a layer of resin B having a melting point of 105 ° C. to 135 ° C. may be stacked on a layer (separator) of particles having insulating properties.

≪Battery case 300≫
In the example shown in FIG. 1, the battery case 300 is a so-called rectangular battery case, and includes a container body 320 and a lid 340. The container main body 320 has a bottomed rectangular tube shape and is a flat box-shaped container having one side surface (upper surface) opened. The lid 340 is a member that is attached to the opening (opening on the upper surface) of the container body 320 and closes the opening.

  In an in-vehicle secondary battery, it is desired to improve the weight energy efficiency (battery capacity per unit weight) in order to improve the fuel efficiency of the vehicle. For this reason, in this embodiment, lightweight metals, such as aluminum and an aluminum alloy, are employ | adopted for the container main body 320 and the cover body 340 which comprise the battery case 300. FIG. Thereby, the weight energy efficiency can be improved.

  The battery case 300 has a flat rectangular internal space as a space for accommodating the wound electrode body 200. Further, as shown in FIG. 2, the flat internal space of the battery case 300 is slightly wider than the wound electrode body 200. In this embodiment, the battery case 300 includes a bottomed rectangular tubular container body 320 and a lid 340 that closes the opening of the container body 320. A positive electrode terminal 420 and a negative electrode terminal 440 are attached to the lid 340 of the battery case 300. The positive electrode terminal 420 and the negative electrode terminal 440 pass through the battery case 300 (lid 340) and come out of the battery case 300. The lid 340 is provided with a liquid injection hole and a safety valve (not shown).

  As shown in FIG. 3, the wound electrode body 200 includes a positive electrode sheet 220 on which a positive electrode active material layer 223 is formed and a negative electrode sheet 240 on which a negative electrode active material layer 243 is formed. The electrode body 200 obtained by overlapping with 262 and 264 and winding around the winding axis WL is pressed and bent flatly in one direction orthogonal to the axis. In the example shown in FIG. 3, the uncoated portion 222 of the positive electrode current collector 221 and the uncoated portion 242 of the negative electrode current collector 241 are exposed in a substantially elliptical cross section on both sides of the separators 262 and 264, respectively. Yes. In this embodiment, the uncoated portions 222 and 242 in the minor axis direction of the substantially ellipse are brought near the center of the ellipse, and are welded and electrically joined to the tip portions of the positive electrode terminal 420 and the negative electrode terminal 440, respectively. . At this time, for example, ultrasonic welding is used for welding the positive electrode terminal 420 and the positive electrode current collector 221 due to the difference in materials. Further, for example, resistance welding is used for welding the negative electrode terminal 440 and the negative electrode current collector 241.

  The wound electrode body 200 is attached to the electrode terminals 420 and 440 fixed to the lid body 340 in a state where the wound electrode body 200 is pressed and bent flat. As shown in FIG. 2, the wound electrode body 200 is accommodated in the flat internal space of the container body 320 in a posture in which the wound shaft WL is lying sideways. The container body 320 is closed by the lid 340 after the wound electrode body 200 is accommodated. The joint between the lid 340 and the container main body 320 is sealed by welding, for example, by laser welding. Thus, in this example, the wound electrode body 200 is positioned in the battery case 300 by the electrode terminals 420 and 440 fixed to the lid 340 (battery case 300).

≪Electrolytic solution≫
Thereafter, an electrolytic solution is injected into the battery case 300 from a liquid injection hole (not shown) provided in the lid 340. As the electrolytic solution, a so-called nonaqueous electrolytic solution containing a nonaqueous solvent and a lithium salt soluble in the solvent without using water as a solvent is preferably used. Such a non-aqueous electrolyte may be a solid (gel) to which a polymer is added.
As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones and lactones can be used. For example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, Generally lithium ion batteries such as 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone, etc. One kind or two or more kinds selected from non-aqueous solvents known as those that can be used in the electrolyte can be used.

Lithium salts include LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiClO _4, etc., one or more selected from various lithium salts known to be capable of functioning as a supporting electrolyte in the electrolyte of a lithium ion battery can be used. The concentration of the lithium salt is not particularly limited, and can be the same as, for example, the electrolyte used in a conventional lithium ion battery. Usually, a non-aqueous electrolyte containing a supporting electrolyte (lithium salt) at a concentration of about 0.1 mol / L to 5 mol / L (for example, about 0.8 mol / L to 1.5 mol / L) is preferably used. it can.
In this example, an electrolytic solution in which LiPF ₆ is contained at a concentration of about 1 mol / liter in a mixed solvent of ethylene carbonate and diethyl carbonate (for example, a mixed solvent having a volume ratio of about 1: 1) is used. Yes. Thereafter, a metal sealing cap is attached to the injection hole (for example, by welding) to seal the battery case 300. The electrolytic solution is not limited to the electrolytic solution exemplified here. For example, non-aqueous electrolytes conventionally used for lithium ion batteries can be used as appropriate.

  In the lithium ion battery 100 having the above-described configuration, for example, the temperature of the electrode (here, the negative electrode (the negative electrode sheet 240)) may begin to rise abnormally during overcharging or the like. In this case, when the melting point of the resin A contained in the negative electrode active material layer 243 is reached, the resin A covers the surface of the negative electrode active material particles, thereby increasing the resistance. Further, the gap in the negative electrode active material layer 243 is closed, and movement of the electrolytic solution is restricted. Thereby, the battery reaction in the negative electrode active material layer 243 can be shut down.

  Therefore, it is possible to prevent the battery from being defective due to the negative electrode (negative electrode sheet 240). In the case of a large battery or the like, the temperature in the lithium ion battery 100 can rise slowly while the resin A melts in the negative electrode. In this case, in the lithium ion battery 100, the separators 262 and 264 contain the resin B having a melting point in the temperature range of 105 ° C. to 135 ° C. For this reason, when the temperature of the separators 262 and 264 reaches the melting point of the resin B, the resin B melts and closes the fine pores of the separators 262 and 264. Thereby, the ion conduction between the positive electrode (positive electrode sheet 220) and the negative electrode (negative electrode sheet 240) can be shut down. Therefore, it is possible to prevent occurrence of problems in the lithium ion battery 100 in the separators 262 and 264 as well.

  Further, the increase in resistance in the negative electrode (negative electrode sheet 240) and the separators 262 and 264 is larger than the total increase in resistance when each of them is shut down alone. That is, according to the lithium ion battery 100, the negative electrode active material layer 243 and the separators 262 and 264 include the resins A and B having melting points in the temperature range of 105 ° C. to 135 ° C., respectively. In this case, a higher shutdown effect is obtained as compared with the case where the negative electrode active material layer 243 or the separators 262 and 264 includes a resin having a melting point in the temperature range of 105 ° C. to 135 ° C. Needless to say, the effect is synergistically enhanced by shutting down both the negative electrode active material layer 243 and the separators 262 and 264. Therefore, the lithium ion battery 100 with further improved safety and reliability is realized.

  Furthermore, in this embodiment, the negative electrode active material layer 243 and the separators 262 and 264 include resins A and B having melting points in the temperature range of 105 ° C. to 135 ° C., respectively. Then, the negative electrode active material layer 243 and the separators 262 and 264 are both shut down, and the effect is synergistically enhanced. Therefore, in order to obtain the same effect, when either the negative electrode active material layer 243 or the separators 262 and 264 contains a resin having a melting point in the temperature range of 105 ° C. to 135 ° C. In comparison, the amount of the resins A and B used can be reduced. Thereby, the high shutdown performance at the time of abnormal heat generation can be ensured while keeping the direct current resistance of the lithium ion battery 100 low.

FIG. 4 is a schematic cross-sectional view showing a vehicle equipped with a lithium ion battery 100 according to an embodiment. The lithium ion battery 100 described above can have a performance suitable as a battery mounted on the vehicle 1 by using not only a single battery but also an assembled battery 1000 or the like in which a plurality of lithium ion batteries are connected and combined. Further, a metal oxide such as SiO _x can be employed as the negative electrode active material, and higher capacity can be realized.

  Hereinafter, an evaluation test for evaluating a nonaqueous electrolyte secondary battery according to an embodiment of the present invention will be described.

<Preparation of test cell>
A test cell (here, a laminate type cell) was constructed as follows.

<Preparation of negative electrode active material layer forming paste>
That is, a negative electrode active material layer forming paste was prepared for producing a negative electrode of a test cell. As the paste, two types of pastes were prepared: a paste (A) not containing the polyethylene resin as the resin A and a paste (B) containing the polyethylene resin as the resin A.
That is, the paste (A) has a mass ratio of 98: 1: 1 (graphite as a negative electrode active material), carboxymethyl cellulose (CMC) as a binder, and styrene-butadiene block copolymer (SBR) as a binder. A negative electrode active material: CMC: SBR = 98: 1: 1) was prepared by mixing with ion-exchanged water.

  In the paste (B), polyethylene resin particles (PE) having a melting point of 130 ° C. and an average particle size of 20 μm, which are the resin A, were added to the paste (A). That is, the paste (B) has a mass ratio of graphite as the negative electrode active material, carboxymethyl cellulose (CMC) as the binder, styrene butadiene block copolymer (SBR) as the binder, and PE as the resin A. It was prepared by mixing with ion-exchanged water so as to be 98: 1: 1: 1 (negative electrode active material: CMC: SBR: resin A = 98: 1: 1: 1).

<Creation of negative electrode>
These pastes (A) and (B) were applied to both sides of a copper foil (thickness 10 μm) as a negative electrode current collector and dried. After drying, it is stretched into a sheet shape by a roller press and formed into a thickness of 100 μm, and punched out so that the negative electrode active material layer becomes a square of about 5.0 cm × 5.0 cm, and the negative electrode (negative electrode sheet) (A) And (B). At this time, the amount of paste (A) and (B) applied to the negative electrode current collector is (resin A) per unit area of the negative electrode current collector after the pastes (A) and (B) are dried. Except) The negative electrode active material layer is set to 13 mg / cm ² . Thus, the negative electrode sheet (A) provided with the negative electrode active material layer which does not contain resin A and the negative electrode sheet (B) provided with the negative electrode active material layer containing resin A were prepared here.

<Preparation of positive electrode>
Next, when forming the positive electrode active material layer in the positive electrode, a positive electrode active material layer forming paste was prepared. The paste includes a ternary lithium transition metal oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) as a positive electrode active material, acetylene black (AB) as a conductive material, and a binder as a binder. Polyvinylidene fluoride (PVDF) was prepared by mixing with ion-exchanged water so that the mass ratio of these materials was 91: 6: 3. Next, the positive electrode active material layer forming paste was applied to both sides of an aluminum foil (thickness 15 μm) as a positive electrode current collector and dried. After drying, the sheet is stretched into a sheet with a roller press to form a thickness of 110 μm, and the positive electrode active material layer is punched out so as to be a square of about 4.8 cm × 4.8 cm, and the surface of the positive electrode current collector A positive electrode (positive electrode sheet) having a positive electrode active material layer was prepared. At this time, the amount of the positive electrode active material layer forming paste applied to the positive electrode current collector was 25 mg of the positive electrode active material layer per unit area of the positive electrode current collector after the positive electrode active material layer forming paste was dried. / Cm ² .

<Separator>
Two types of separators were prepared: a separator (C) having a single layer structure of polypropylene (PP) and a separator (D) having a three layer structure of PP / PE / PP. That is, the separator (C) was made of polypropylene (PP) having a melting point of 170 ° C., and a porous sheet having a thickness of 25 μm was used. The separator (D) has a total thickness of 25 μm, and has a three-layer structure (PP / PE / PP) of polypropylene (PP) having a melting point of 170 ° C. and polyethylene (PE) having a melting point of 130 ° C. A sheet was used. The separator (D) contains 35% by mass of PE.

<Assembly of test cell>
A test laminate type cell (lithium ion battery) was constructed using the negative electrode prepared above, a positive electrode, and a separator. That is, a positive electrode sheet and a negative electrode sheet were laminated with a separator interposed therebetween to produce an electrode body. Then, the electrode body was housed in a laminated bag-shaped battery container together with the non-aqueous electrolyte and sealed to construct a test cell. As a non-aqueous electrolyte, a 1: 4: 3 (volume ratio) mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) was used, and 1 mol / L LiPF ₆ (as a lithium salt) ( A solution in which LPFO) was dissolved was used.

  In the test, if necessary, the negative electrodes (A) and (B) and the separators (C) and (D) prepared above were placed in a high-temperature atmosphere (here, the resin A contained in the negative electrode active material layer) And an atmosphere in which the resin B contained in the separator can be melted) for a predetermined time, and in the same manner as described above, a test laminate cell (lithium ion battery) was constructed. As a result, a test cell simulating a state in which the battery is abnormally heated and exposed to a high temperature can be obtained.

≪Samples 1 to 4≫
Here, the sample 1 uses a negative electrode (A) provided with a negative electrode active material layer not containing the resin A, and a separator (C) having a single layer structure of polypropylene (PP).
Sample 2 uses a negative electrode (A) having a negative electrode active material layer not containing resin A, and a separator (D) having a three-layer structure of PP / PE / PP.
Sample 3 uses a negative electrode (B) having a negative electrode active material layer containing resin A and a separator (C) having a single layer structure of polypropylene (PP).
Sample 4 uses a negative electrode (B) having a negative electrode active material layer containing resin A, and a separator (D) having a three-layer structure of PP / PE / PP.

  Samples 1-4 were exposed to the negative electrodes (A) and (B) prepared above and separators (C) and (D) in an atmosphere of 130 ° C. for 1 minute, and the battery heated abnormally to a high temperature. A test cell simulating the exposed state is obtained.

Here, the DC resistance was measured for the test cells of Samples 1 to 4 described above. Here, the DC resistance was measured based on the AC impedance measurement method. FIG. 5 is a diagram illustrating a typical example of a Cole-Cole plot (Nyquist plot) in the AC impedance measurement method. As shown in FIG. 5, the DC resistance (Rsol) and the reaction resistance (Rct) can be calculated based on the Cole-Cole plot obtained by equivalent circuit fitting in the AC impedance measurement method. Here, the reaction resistance (Rct) can be obtained by the following equation.
Rct = (Rsol + Rct) −Rsol

<DC resistance>
Such measurement and calculation of direct current resistance (Rsol) and reaction resistance (Rct) can be carried out using a commercially available apparatus programmed in advance. An example of such an apparatus is an electrochemical impedance measuring apparatus manufactured by Solartron. Here, in a temperature environment of 25 ° C., complex impedance measurement is performed in a frequency range of 10 ⁻³ Hz to 10 ⁴ Hz based on a test cell adjusted to SOC 40% (charged state of about 40% of the rated capacity). I did it. Then, as shown in FIG. 5, the DC resistance (Rsol) obtained by the equivalent circuit fitting of the Nyquist plot was defined as “DC resistance”.

<Reaction resistance at −30 ° C.>
Further, as will be described later, “reaction resistance at −30 ° C.” is also evaluated. In this case, in a temperature environment of −30 ° C., complex impedance measurement is performed in a frequency range of 10 ⁻³ Hz to 10 ⁴ Hz based on a test cell adjusted to SOC 40% (a charged state of approximately 40% of the rated capacity). Was done. Then, as shown in FIG. 5, the reaction resistance (Rct) obtained by the equivalent circuit fitting of the Nyquist plot was defined as “reaction resistance at −30 ° C.”.

  FIG. 6 is a graph in which DC resistance is evaluated for Sample 1 to Sample 4. As shown in FIG. 6, the direct current resistance of sample 4 is significantly improved as compared with samples 1 to 3. That is, in samples 1 to 4, the negative electrodes (A) and (B) prepared above and the separators (C) and (D) were exposed to an atmosphere of 130 ° C. for 1 minute, and the battery heated abnormally to a high temperature. A test cell simulating the exposed state is obtained. In this case, in the sample 4, since the negative electrode active material layer contains the resin A and the separator contains the resin B, the direct current resistance is dramatically improved by the action of the resins A and B. It is considered a thing.

  Specifically, Sample 1 does not contain PE at all in the negative electrode and the separator. For this reason, in Sample 1, a result showing almost the same DC resistance (less than 100 mΩ) was obtained whether the sample was exposed to high temperature or not.

  Sample 2 includes a separator (D) having PE as an inner layer. In sample 2, PE (resin B) in the separator is melted by being exposed to a high temperature. For this reason, the ion conduction path was interrupted (limited) between the positive electrode and the negative electrode, and the resistance increased to less than 300 mΩ.

  Sample 3 includes a negative electrode (B) containing PE. In Sample 3, PE (resin A) in the negative electrode active material layer is melted by being exposed to a high temperature. For this reason, the resistance increased to a little less than 200 mΩ, and although it was inferior to the sample 2, a shutdown effect was obtained.

  Sample 4 includes both a negative electrode (B) containing PE and a separator (D) having PE in the inner layer. In sample 4, the negative electrode active material layer and the PE (resin A, resin B) in the separator are melted by being exposed to a high temperature. For this reason, the resistance increased significantly to over 600 mΩ. Furthermore, the increase in resistance of sample 4 is much larger than the sum of the increase in resistance of sample 2 and sample 3. For this reason, it is considered that a larger shutdown effect can be obtained by a synergistic effect by melting the negative electrode active material layer and the PE (resin A, resin B) in the separator. As a result, as in sample 4, in the form including the negative electrode active material layer and the PE (resin A, resin B) in the separator, even when the lithium ion battery abnormally generates heat, the DC resistance is sufficiently increased, The battery reaction is quickly suppressed.

≪Sample 5 to Sample 25≫
Next, samples 5 to 25 will be described. Samples 5 to 25 are test cells in which the amount of the resin A in the negative electrode active material layer and the amount of the resin B in the separator are changed. Table 1 shows the weight (mg / cm ² ) and the ratio (mass%) of PE (resin A) contained in the negative electrode active material layer and the weight of PE (resin B) contained in the separator for samples 5 to 25 ( mg / cm ² ), the total weight (mg / cm ² ) of PE (resins A and B) contained in the negative electrode active material layer and the separator, the negative electrode active material layer and the separator are exposed to a high temperature atmosphere to construct a test cell DC resistance (mΩ), and reaction resistance (mΩ) at −30 ° C. when a test cell is constructed without exposing the negative electrode active material layer and the separator to a high temperature atmosphere are shown.

FIG. 7 shows the total weight (mg / cm ² ) of PE (resins A and B) contained in the negative electrode active material layers and separators of Samples 5 to 25 shown in Table 1, and the high temperature of the negative electrode active material layers and separators. The graph shows the relationship with DC resistance (mΩ) when a test cell is constructed in an atmosphere. In addition, a line indicated as “PE 0.15 mass%” in FIG. 7 indicates three samples (7, 7) in which the proportion (mass%) of PE (resin A) contained in the negative electrode active material layer is 0.15 mass%. 14, 21). As shown in FIG. 7, when the total weight (mg / cm ² ) of PE (resins A and B) contained in the negative electrode active material layer and the separator is approximately the same, the PE ( When the proportion (mass%) of the resin A) is increased, the direct current resistance (mΩ) is increased when the negative electrode active material layer and the separator are exposed to a high temperature atmosphere to construct a test cell. In particular, if the ratio (mass%) of PE (resin A) in the negative electrode active material layer is about 0.15 mass% or more, the ratio (mass%) of PE (resin A) in the negative electrode active material layer is about. The direct current resistance (mΩ) is surely higher than in the case of less than 0.15% by mass.

For example, Samples 5 and 6 have a total weight (mg / cm ² ) of PE (resins A and B) of 0.25 (mg / cm ² ) and 0.261 (mg / cm ² ), respectively, and The ratio (mass%) of PE (resin A) is 0 (mass%) and 0.10 (mass%). In this case, the DC resistance was 216.5 (mΩ) and 254.3 (mΩ). In contrast, Samples 7 and 8 have a total weight (mg / cm ² ) of PE (resins A and B) of 0.266 (mg / cm ² ) and 0.271 (mg / cm ² ), respectively. And the proportion (mass%) of PE (resin A) is about 0.15 (mass%) and 0.2 (mass%). In this case, the DC resistance was 474.2 (mΩ) and 504.2 (mΩ).

As shown in Table 1 and FIG. 7, when the total weight (mg / cm ² ) of PE (resins A and B) contained in the negative electrode active material layer and the separator is approximately the same, the negative electrode active material layer When the ratio (mass%) of PE (resin A) contained is less than 0.15 (mass%), it is about 0.15 (mass%) to 2.0 (mass%). The DC resistance can be greatly improved.

  FIG. 8 shows the proportion of PE (resin A) contained in the negative electrode active material layer (mass%) and the test cell for samples 5 to 25 without exposing the negative electrode active material layer and the separator to a high temperature atmosphere. The relationship with the reaction resistance (mΩ) at −30 ° C. is shown. As shown in FIG. 8, when the ratio of PE (resin A) contained in the negative electrode active material layer is about 2.0 (mass%) or less, the reaction resistance (mΩ) of the test cell at −30 ° C. ) Is suppressed to less than about 650 (mΩ). On the other hand, when the proportion of PE (resin A) contained in the negative electrode active material layer increases to about 3.0 (mass%), the reaction resistance (mΩ) at −30 ° C. of the test cell is 800 ( mΩ). Thus, when the proportion of PE (resin A) contained in the negative electrode active material layer becomes too large, the reaction resistance of the battery, particularly in a low temperature environment, increases. For this reason, it is desirable that the ratio of PE (resin A) contained in the negative electrode active material layer is kept low to some extent. For example, the ratio of PE (resin A) contained in the negative electrode active material layer is preferably about 2.0 (% by mass) or less.

  In FIG. 9, a negative electrode sheet (B) provided with a negative electrode active material layer containing resin A and a separator (D) having a three-layer structure of PP / PE / PP are used. However, for PE (resin A) contained in the negative electrode active material layer and PE (resin B) contained in the separator, five types having a melting point between 94 ° C. and 135 ° C. were prepared. Furthermore, two types of cases where the ratio of PE (resin A) contained in each of the negative electrode active material layers is 0.5 (mass%) and 2.0 (mass%) are prepared, A total of 10 negative electrodes (negative electrode sheets) were prepared. And the cell for a test was created using each negative electrode sheet | seat, and IV resistance (DC resistance) in each 25 degreeC was measured. Here, the negative electrode before assembling the cell and the separator were not exposed to the high temperature atmosphere.

  FIG. 9 is a graph showing the relationship between the melting points of resins A and B and the DC resistance at 25 ° C. for these 10 test cells. As shown in FIG. 9, when the ratio (mass%) of PE (resin A) contained in the negative electrode active material layer is about the same, the melting points of the resins A and B contained in the negative electrode active material layer and the separator Is less than 100 ° C., the IV resistance (DC resistance) at 25 ° C. is high. On the other hand, when the melting points of the resins A and B contained in the negative electrode active material layer and the separator are 105 ° C. or higher, IV resistance (DC resistance) at 25 ° C. can be kept low.

  In this regard, the present inventor puts PE (resin A) contained in the negative electrode active material layer into a high-temperature dry atmosphere in the drying step when forming the negative electrode active material layer. At this time, when the melting point of PE (resin A) contained in the negative electrode active material layer is as low as about 100 ° C., PE (resin A) contained in the negative electrode active material layer is slightly dissolved. It is considered that the melted PE (resin A) adheres to the surface of the negative electrode active material and becomes a factor that increases the IV resistance (DC resistance) at 25 ° C. of the evaluation cell. Thus, it is preferable that melting | fusing point (especially melting | fusing point of resin A contained in a negative electrode active material layer) of resin A and B contained in the negative electrode active material layer and the separator is about 105 degreeC or more.

  Considering the above evaluation, for example, as shown in FIG. 3, a lithium ion battery 100 (nonaqueous electrolyte secondary battery) includes a positive electrode sheet 220 (positive electrode) including a positive electrode active material layer 223 containing a positive electrode active material, And a negative electrode sheet 240 (negative electrode) including a negative electrode active material layer 243 containing a negative electrode active material, separators 262 and 264 interposed between the positive electrode sheet 220 and the negative electrode sheet 240, and a non-aqueous electrolyte. In this case, the negative electrode active material layer preferably contains a resin A having a melting point in the temperature range of 105 ° C. to 135 ° C. in a proportion of 0.15% by mass to 2.0% by mass. Moreover, the separator is good to contain resin B which has melting | fusing point in the range of 105 to 135 degreeC. Furthermore, in this case, the amount of PE (resin A) contained in the negative electrode active material layer is preferably 0.15% by mass or more and 2% by mass or less. According to such configuration, the reaction resistance of the non-aqueous electrolyte secondary battery is kept low, and the effect of preventing battery thermal runaway (shutdown effect) when the non-aqueous electrolyte secondary battery abnormally generates heat due to some abnormality Can be obtained.

  As described above, the present invention has been described with reference to the preferred embodiments. However, such description is not a limitation, and various modifications can be made.

  As described above, the lithium ion battery according to an embodiment of the present invention exhibits a very high resistance when the battery abnormally generates heat, and exhibits an excellent shutdown effect without greatly impairing the original battery performance. Therefore, it is particularly suitable for use as a non-aqueous electrolyte secondary battery (typically, a secondary battery for a vehicle driving power source of a hybrid vehicle (including a plug-in hybrid vehicle)) that requires input / output characteristics at a high rate. can do. In this case, for example, as shown in FIG. 4, as a vehicle driving battery for driving a motor (electric motor) of a vehicle 1 such as an automobile in the form of an assembled battery 1000 in which a plurality of lithium ion batteries 100 are connected and combined. It can be suitably used.

DESCRIPTION OF SYMBOLS 1 Vehicle 100 Lithium ion battery 200 Winding electrode body 220 Positive electrode sheet 221 Positive electrode current collector 222 Uncoated part 223 Positive electrode active material layer 240 Negative electrode sheet 241 Negative electrode current collector 242 Uncoated part 243 Negative electrode active material layer 262, 264 Separator 300 Battery case 320 Container body 340 Cover body 420 Positive electrode terminal 440 Negative electrode terminal 1000 Battery pack WL Winding shaft

Claims (5)

A positive electrode including a positive electrode active material layer including a positive electrode active material; a negative electrode including a negative electrode active material layer including a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte.
The negative electrode active material layer includes 0.15% by mass to 2.0% by mass of a resin A having a melting point in a temperature range of 105 ° C. to 135 ° C.,
The separator is a nonaqueous electrolyte secondary battery including a resin B having a melting point in a range of 105 ° C to 135 ° C.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the resin A and the resin B are polyethylene.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the separator has a multilayer structure, and the resin B forms an inner layer in the multilayer structure.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material contains a lithium transition metal oxide as a main component.   The vehicle provided with the nonaqueous electrolyte secondary battery as described in any one of Claims 1-4.

Images