JP5839233B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. Specifically, the present invention relates to a lithium ion secondary battery and other non-aqueous electrolyte secondary batteries that can be applied to a vehicle-mounted power source.

  In recent years, secondary batteries such as lithium ion secondary batteries and nickel metal hydride batteries have become increasingly important as power sources mounted on vehicles using electricity as power sources, or power sources mounted on personal computers, portable terminals, and other electrical products. Yes. In particular, lithium ion secondary batteries and other non-aqueous electrolyte secondary batteries that are lightweight and obtain high energy density are expected to be preferably used as high-output power sources for mounting on vehicles. In such a non-aqueous electrolyte secondary battery, when the charging process is performed, for example, when the battery to be charged is a defective battery, or when the charging device breaks down and malfunctions, the battery has a current higher than normal. If supplied, the battery may fall into an overcharged state, causing a problem. Therefore, in order to prevent such a problem, an overcharge state is detected based on battery temperature, battery internal pressure, etc., and a mechanism that cuts off current when an overcharge state is detected (current interrupt mechanism: CID: Current Interrupt Device) is provided. The provided battery is adopted.

  In the secondary battery provided with the above-described CID, a gas generating agent such as cyclohexylbenzene (CHB) or biphenyl (BP) having an oxidation potential lower than that of the nonaqueous solvent of the electrolyte is included in the electrolyte. Yes. The gas generating agent reacts to generate gas before the electrolyte is decomposed when the battery is overcharged. Utilizing this, the amount of increase in battery pressure and the rate of increase when the battery is overcharged is increased, and the CID is activated at an appropriate timing against overcharge to prevent the occurrence of problems due to overcharge. ing. Patent document 1 is mentioned as literature which is equipped with CID and has disclosed the secondary battery which contains a gas generating agent in nonaqueous electrolyte.

  The above-described secondary battery includes a positive electrode and a negative electrode, and a basic configuration is that a separator composed of a porous layer is disposed between them. In this type of secondary battery, Patent Document 2 discloses a separator in which a porous layer mainly composed of inorganic particles having a predetermined specific surface area is formed on both surfaces of a polyolefin-based porous layer. Further, Patent Document 3 discloses the porosity of the composite material layer constituting the positive and negative electrodes and the porosity of the separator.

JP 2006-324235 A JP 2011-65849 A JP 2007-220454 A

  The present invention relates to an improvement in a non-aqueous electrolyte secondary battery that includes a CID and includes a gas generating agent in the non-aqueous electrolyte. The object of the present invention is to maintain the battery characteristics at a high level and to be in an overcharged state. And providing a non-aqueous electrolyte secondary battery capable of operating the CID at an appropriate timing.

  In order to achieve the above object, the present invention provides a non-aqueous electrolyte secondary battery including a current interrupting mechanism that operates when the internal pressure of the battery case increases. In this non-aqueous electrolyte secondary battery, the non-aqueous electrolyte contained in the non-aqueous electrolyte secondary battery contains a gas generating agent, and different pores are formed between the positive electrode and the negative electrode constituting the non-aqueous electrolyte secondary battery. At least two porous layers having a degree are arranged, and among the at least two porous layers, the porosity of the porous layer A arranged at a position facing the positive electrode is arranged on the negative electrode side. It is larger than the porosity of the porous layer B.

The gas generating agent present in the secondary battery equipped with CID emits electrons on the positive electrode side to become radical cations when overcharged. This radical cation further reacts (typically, the radical cations are polymerized with each other), and a large amount of H ⁺ is generated at that time. The generated H ⁺ moves in the electrode body and is reduced on the surface of the negative electrode to generate hydrogen gas (H ₂ ). However, the radical cation may move to the negative electrode side and be reduced without remaining on the positive electrode side. This reaction is called a gas generant shuttle reaction. When the shuttle reaction occurs, the amount of radical cations remaining on the positive electrode side decreases, so that there is a possibility that a reaction that generates a large amount of H ⁺ (typically, polymerization of radical cations) is not sufficiently performed. Therefore, in the present invention, the porous layer A having a high porosity is employed as a porous layer disposed at a position facing the positive electrode among two or more porous layers disposed between the positive electrode and the negative electrode. . Thereby, a larger amount of the gas generating agent contained in the non-aqueous electrolyte is supplied to the positive electrode side. The porous space of the porous layer A can also serve as a space for keeping radical cations necessary for gas generation on the positive electrode side. Therefore, the amount of radical cations existing on the positive electrode side when overcharged is increased. Furthermore, since the porous layer B disposed on the negative electrode side has a relatively low porosity, it prevents the radical cation from moving from the positive electrode side to the negative electrode side. That is, the shuttle reaction is suppressed. As a result, the tendency for radical cations to remain on the positive electrode side increases, and the amount of gas generated when an overcharged state is reached increases. The shuttle reaction is considered to be promoted in a high temperature environment where the diffusibility of radical cations and the like is improved. Generation can be realized. As a result, the amount of gas generant used (added amount) can be kept to the minimum necessary, resulting in a decrease in battery characteristics (typically an increase in battery resistance) caused by excessive gas generant. Can be suppressed. Therefore, according to the present invention, there is provided a nonaqueous electrolyte secondary battery capable of operating the CID at an appropriate timing when the battery is overcharged while maintaining the battery characteristics at a high level.

  In a preferred aspect of the nonaqueous electrolyte secondary battery disclosed herein, the at least two porous layers are composed of the porous layer A and the porous layer B. By making the porous layer into two layers of the porous layer A and the porous layer B, the amount of gas generated can be increased without inhibiting the ion passage of lithium ions.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the porosity of the porous layer A is 55% or more, and the porosity of the porous layer B is 50% or less. By setting the porosity of the porous layer A to 55% or more, it becomes possible to keep more radical cations on the positive electrode side. By setting the porosity of the porous layer B to 50% or less, the shuttle reaction in which radical cations move from the positive electrode side to the negative electrode side can be more effectively suppressed.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, one of the porous layer A and the porous layer B is a resin layer, and the other is a filler layer. Alternatively, both the porous layer A and the porous layer B may be resin layers.

  In a preferred aspect of the nonaqueous electrolyte secondary battery disclosed herein, the porosity of the porous layer A is larger than the porosity of the positive electrode mixture layer constituting the positive electrode. As a result, the amount of the gas generating agent decomposed on the positive electrode surface increases, and the amount of gas generated increases.

  Moreover, according to this invention, a vehicle provided with one of the nonaqueous electrolyte secondary batteries disclosed here is provided. Such a nonaqueous electrolyte secondary battery can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile equipped with an electric motor such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle.

It is a figure which shows typically the structure of the lithium ion secondary battery which concerns on one Embodiment. It is a figure which shows typically the structure of the winding electrode body of FIG. It is a figure which expands and shows a part of cross section of the structural example between the positive / negative electrodes of FIG. It is a figure corresponding to FIG. 3, Comprising: It is a schematic cross section which shows the other structural example. It is a figure corresponding to FIG. 3, Comprising: It is a schematic cross section which shows the other structural example. It is a figure corresponding to FIG. 3, Comprising: It is a schematic cross section which shows the other structural example. It is a figure corresponding to FIG. 3, Comprising: It is a schematic cross section which shows the other structural example. It is a side view which shows typically the vehicle (automobile) provided with the lithium ion secondary battery which concerns on one Embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than matters specifically mentioned in the present specification and matters necessary for the implementation of the present invention (for example, a configuration and a manufacturing method of an electrode body including a positive electrode and a negative electrode, a configuration and a manufacturing method of a separator and an electrolytic solution) The general shape and the like related to the construction of the battery, such as the shape of the battery (case), can be understood as the design items of those skilled in the art based on the prior art in this field.

  As a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, a lithium ion secondary battery will be described as an example. However, the application target of the present invention is not intended to be limited to such a battery. Absent. For example, the present invention can be applied to a non-aqueous electrolyte secondary battery using a metal ion other than lithium ion (for example, sodium ion) as a charge carrier. In the present specification, “secondary battery” generally refers to a battery that can be repeatedly charged and discharged. In addition to a storage battery such as a lithium ion secondary battery (that is, a chemical battery), a capacitor such as an electric double layer capacitor (that is, a physical battery). Battery). Further, in the present specification, the “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of charges accompanying the lithium ions between the positive and negative electrodes.

  As shown in FIG. 1, the lithium ion secondary battery 100 has a configuration in which a wound electrode body 80 is accommodated in a flat rectangular parallelepiped battery case 50 together with a nonaqueous electrolytic solution 25. The battery case 50 includes a flat box-shaped case main body 52 having an opening on the upper surface, and a lid 54 that closes the opening. The wound electrode body 80 is sealed by closing the opening of the case body 52 with the lid body 54. With this configuration, the lithium ion secondary battery 100 is constructed as a so-called sealed battery having a structure in which the inside of the battery case 50 is sealed.

  A positive electrode terminal 70 and a negative electrode terminal 72 are provided on the upper surface (lid 54) of the battery case 50. The positive electrode terminal 70 is electrically connected to a positive electrode current collector plate 74 attached to an end in the width direction of the positive electrode (positive electrode sheet) 10. The negative electrode terminal 72 is electrically connected to a negative electrode current collector plate 76 attached to the end of the negative electrode (negative electrode sheet) 20 in the width direction.

  In the battery case 50, a CID 30 that is operated by an increase in the internal pressure of the battery case 50 is provided. The CID 30 is provided between the positive electrode terminal 70 fixed to the lid body 54 and the wound electrode body 80. When the internal pressure of the battery case 50 increases and reaches a predetermined pressure, the CID 30 reaches the positive electrode 10. The conductive path is configured to be electrically disconnected.

  The CID 30 includes a deformed metal plate 32 and a connection metal plate 34 joined to the deformed metal plate 32. The deformed metal plate 32 has an arch-shaped curved portion 33 having a central portion curved downward. The peripheral portion of the curved portion 33 is connected to the lower surface of the positive electrode terminal 70 via the current collecting lead terminal 35. Further, a part (tip) of the curved portion 33 of the deformed metal plate 32 is joined to the upper surface of the connection metal plate 34 at a joint point 36. A positive electrode current collector plate 74 is joined to the lower surface (back surface) of the connection metal plate 34, and the positive electrode current collector plate 74 is connected to the positive electrode 10 of the wound electrode body 80. In this way, a conductive path from the positive electrode terminal 70 to the positive electrode 10 is formed.

  The CID 30 includes an insulating case 38 made of plastic. The material of the insulating case is not limited to plastic, and any material having insulating properties and airtightness may be used. The insulating case 38 is provided so as to surround the deformed metal plate 32. An opening for fitting the curved portion 33 of the deformed metal plate 32 is formed in the insulating case 38, and the curved portion 33 of the deformed metal plate 32 is fitted into the opening to seal the opening. doing. As a result, since the inside of the insulating case 38 is kept in a sealed state, the internal pressure of the battery case 50 does not act on the upper surface side of the sealed curved portion 33. On the other hand, the internal pressure of the battery case 50 acts on the lower surface of the curved portion 33 outside the insulating case 38. In the CID 30 having such a configuration, when the internal pressure of the battery case 50 is increased due to the overcharge current, the internal pressure acts to push the curved portion 33 curved downward of the deformed metal plate 32 upward. This action (force) increases as the internal pressure of the battery case 50 increases. When the internal pressure of the battery case 50 exceeds the set pressure, the curved portion 33 is turned upside down and deformed so as to bend upward. Due to the deformation of the curved portion 33, the joint point 36 between the deformed metal plate 32 and the connection metal plate 34 is cut. As a result, the conductive path is electrically disconnected and the current is interrupted.

  In this embodiment, the CID 30 is such that the deformed metal plate 32 disposed above is deformed, but is not limited thereto. When the internal pressure of the battery case rises, it is not the first member (the member disposed at the position of the deformed metal plate 32 of the present embodiment) disposed above but the second member (the member of the present embodiment) disposed below. The member arranged at the position of the connecting metal plate 34) may be deformed and separated from the other to electrically disconnect the conductive path, and both the first member and the second member It may be deformed. The CID as described above may be provided not only on the positive terminal side but also on the negative terminal side. In addition, the CID electrically disconnects a conductive path that conducts at least one of the positive and negative electrodes and an external terminal (positive electrode terminal or negative electrode terminal) exposed to the outside of the battery case when the internal pressure of the battery case increases. What is necessary is just to be comprised, and it is not limited to a specific shape and structure. Furthermore, CID is not limited to what performs the mechanical cutting | disconnection accompanied with a deformation | transformation of the 1st member mentioned above and / or the 2nd member. For example, it may be a CID provided with an external circuit that detects the internal pressure of the battery case with a sensor and interrupts the charging current when the internal pressure detected by the sensor exceeds a set pressure.

  FIG. 2 is a diagram schematically showing the configuration of the wound electrode body of FIG. 1, and shows a long sheet structure (electrode sheet) in the previous stage of constructing the wound electrode body 80. As shown in FIG. 2, the wound electrode body 80 includes a positive electrode 10 and a negative electrode 20. The positive electrode 10 and the negative electrode 20 have a configuration in which they are wound flatly via two separators 40A and 40B. Each of the positive electrode 10, the negative electrode 20, and the separators 40A and 40B has a long sheet shape. The positive electrode (positive electrode sheet) 10 and the negative electrode (negative electrode sheet) 20 are overlapped via separators 40A and 40B, thereby forming a laminate. In other words, the laminate is laminated in the order of the positive electrode sheet 10, the separator 40B, the negative electrode sheet 20, and the separator 40A. The wound electrode body 80 is formed in a flat shape by winding the laminated body in the longitudinal direction and further crushing the rolled body from the side surface direction so as to be ablated. The electrode body is not limited to a wound electrode body. Appropriate shapes and configurations can be appropriately employed depending on the shape and purpose of the battery.

  The positive electrode sheet 10 includes a positive electrode current collector 12 and a positive electrode mixture layer 14 formed on at least one surface (typically both surfaces) of the positive electrode current collector 12. Similarly to the case of the positive electrode, the negative electrode sheet 20 includes a negative electrode current collector 22 and a negative electrode mixture layer 24 formed on at least one surface (typically both surfaces) of the negative electrode current collector 22.

As shown in FIG. 3, the separator 40A is composed of a porous resin layer 41 (porous layer B). A porous filler layer 42 (porous layer A) is formed on the surface of the separator 40A on the positive electrode 10 side. The filler layer 42 is formed over the entire surface of the separator 40A, that is, over the entire length direction (winding direction) and width direction of the separator 40A. Thus, the resin layer 41 is disposed on the negative electrode 20 side in relation to the filler layer 42, and the filler layer 42 is disposed at a position facing the positive electrode 10 (typically, the positive electrode mixture layer). The porosity of the filler layer 42 is larger than the porosity of the resin layer 41. Accordingly, the resin layer 41 having a relatively low porosity suppresses the radical cation of the gas generating agent from moving from the positive electrode 10 side to the negative electrode 20 side, thereby suppressing the shuttle reaction. Further, a large amount of radical cations can remain in the filler layer 42 on the positive electrode 10 side having a relatively large porosity. As a result, a large amount of H ⁺ is generated on the positive electrode 10 side in an overcharged state, and as a result, the amount of gas generated increases. The separator is not limited to a single-layer structure, and may have a multilayer structure of two or more layers. A typical example is a separator 40A having a three-layer structure in which a resin layer 41A, a resin layer 41B, and a resin layer 41C as shown in FIG. 4 are sequentially laminated. Since the configuration of separator 40B is basically the same as that of separator 40A, the description will not be repeated.

  In this embodiment, the separators 40A and 40B are composed of a filler layer 42 disposed at a position facing the positive electrode 10 and a resin layer 41 disposed on the negative electrode 20 side from the filler layer 42. However, it is not limited to this. At least two porous layers are arranged between the positive and negative electrodes, and the porosity of the porous layer A arranged at a position facing the positive electrode is the porosity of the porous layer B arranged on the negative electrode side. Any larger one is acceptable. For example, as shown in FIG. 5, a separator 40 composed of a resin layer 41 (porous layer A) disposed at a position facing the positive electrode 10, and a filler layer 43 (porous) disposed on the negative electrode 20 side from the resin layer 41. Layer B) may be disposed between the positive and negative electrodes as a porous layer. In this configuration, the porosity of the resin layer 41 is larger than the porosity of the filler layer 43. Alternatively, for example, as shown in FIG. 6, a separator 40 made of a resin layer 41A (porous layer A), 41B (porous layer B) in which a heat-resistant layer such as a filler layer is not formed is used as a porous layer between positive and negative electrodes. The structure arrange | positioned may be sufficient. In this case, the porosity of the resin layer 41A arranged at a position facing the positive electrode 10 is larger than the porosity of the resin layer 41B arranged on the negative electrode 20 side from the resin layer 41A. Further, when the separator is composed of a resin layer having a multilayer structure of three or more layers, typically, when the separator 40 having a three-layer structure as shown in FIG. 7 is disposed between the positive and negative electrodes as a porous layer, the positive electrode The porosity of the resin layer 41A (porous layer A) disposed at a position opposite to the resin layer 10 is such that at least one of the resin layers 41B and 41C (porous layer B) disposed on the negative electrode 20 side from the resin layer 41A is porous. Greater than degree. Preferably, the porosity of the resin layer 41A is larger than the average value of the porosity of the resin layers 41B and 41C (more preferably, the porosity of each of the resin layers 41B and 41C).

  Moreover, when the filler layer is formed in the surface of a positive electrode (typically positive mix layer), this filler layer can become the porous layer A arrange | positioned in the position facing a positive electrode. The porosity of the filler layer is that of the porous layer B (typically a resin layer constituting the separator and a filler layer formed on the surface of the separator and / or the negative electrode) disposed on the negative electrode side of the filler layer. Greater than porosity. Furthermore, when the filler layer is formed in the surface of a negative electrode (typically negative electrode compound material layer), this filler layer can become the porous layer B arrange | positioned at the negative electrode side. The porosity of such a filler layer is smaller than the porosity of porous layer A (typically a resin layer constituting a separator or a filler layer formed on the surface of the positive electrode) disposed at a position facing the positive electrode. In such an embodiment, the separator may be composed of a single layer resin layer.

  Next, each component which comprises the above-mentioned lithium ion secondary battery is demonstrated. As a positive electrode current collector constituting a positive electrode (typically a positive electrode sheet) of a lithium ion secondary battery, a conductive member made of a metal having good conductivity is preferably used. For example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector can be different depending on the shape of the battery and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. The thickness of the positive electrode current collector is not particularly limited, and can be, for example, 5 μm to 30 μm. In addition to the positive electrode active material, the positive electrode mixture layer can contain additives such as a conductive material and a binder (binder) as necessary.

As the positive electrode active material, lithium transition metal composite oxide containing lithium (Li) and at least one transition metal element (preferably at least one of nickel (Ni), cobalt (Co) and manganese (Mn)) Is mentioned. Examples of the composite oxide include so-called binary lithium transition metal composite oxides containing one kind of the transition metal element, so-called binary lithium transition metal composite oxides containing two kinds of the transition metal elements, and transition metal elements. Examples thereof include ternary lithium transition metal composite oxides containing Ni, Co, and Mn as constituent elements, and solid solution lithium-excess transition metal composite oxides. These can be used alone or in combination of two or more. As the positive electrode active material, the general formula is LiMAO ₄ (where M is at least one metal element selected from the group consisting of Fe, Co, Ni and Mn, and A is P, Si, S and A polyanionic compound represented by the following formula is also preferably used: an element selected from the group consisting of V. Among these, a ternary lithium transition metal composite oxide containing Ni, Co, and Mn as transition metal elements as constituent elements is preferable. As a typical example of such a ternary lithium transition metal composite oxide, a general formula:
Li (Li _a Ni _x Co _y Mn _z ) O ₂
(A, x, y, and z in the previous formula are real numbers satisfying a + x + y + z = 1).

  The positive electrode active material includes aluminum (Al), chromium (Cr), vanadium (V), magnesium (Mg), calcium (Ca), titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo ), Copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La), tungsten (W), and cerium (Ce). Alternatively, two or more metal elements may be further added. The addition amount (blending amount) of these metal elements is not particularly limited, but is 0.01% by mass to 5% by mass (for example, 0.05% by mass to 2% by mass, typically 0.1% by mass to 0.00%). 8 mass%) is appropriate.

  The proportion of the positive electrode active material in the positive electrode mixture layer is more than about 50% by mass, and preferably about 70% to 97% by mass (for example, 75% to 95% by mass).

  As the conductive material, a conductive powder material such as carbon powder or carbon fiber is preferably used. As the carbon powder, various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder are preferable. Also, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives can be used singly or as a mixture of two or more. . Examples of the binder include various polymer materials. For example, when the positive electrode mixture layer is formed using an aqueous composition (a composition using water or a mixed solvent containing water as a main component as a dispersion medium of active material particles), water-soluble or water-dispersible These polymer materials can be preferably used as the binder. Examples of water-soluble or water-dispersible polymer materials include cellulose polymers such as carboxymethyl cellulose (CMC); polyvinyl alcohol (PVA); fluorine resins such as polytetrafluoroethylene (PTFE); vinyl acetate polymers; styrene butadiene rubber Rubbers such as (SBR) and acrylic acid-modified SBR resin (SBR latex); Alternatively, when the positive electrode mixture layer is formed using a solvent-based composition (a composition in which the dispersion medium of active material particles is mainly an organic solvent), polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC) Polymer materials such as vinyl halide resins such as polyethylene oxide, polyalkylene oxide such as polyethylene oxide (PEO), and the like can be used. Such a binder may be used alone or in combination of two or more. In addition, the polymer material illustrated above may be used as a thickener and other additives in the composition for forming a positive electrode mixture layer, in addition to being used as a binder.

  Although the ratio of these additives in the positive electrode mixture layer is not particularly limited, the ratio of the conductive material is about 1 to 20 parts by mass (eg, 2 to 10 parts by mass, for example, with respect to 100 parts by mass of the positive electrode active material, (Typically 3 to 7 parts by mass) is preferable. The ratio of the binder is about 0.8 parts by mass to 10 parts by mass (for example, 1 part by mass to 7 parts by mass, typically 2 parts by mass to 5 parts by mass) with respect to 100 parts by mass of the positive electrode active material. It is preferable.

The basis weight per unit area of the positive electrode mixture layer on the positive electrode current collector (the coating amount in terms of solid content of the composition for forming the positive electrode mixture layer) is not particularly limited, but a sufficient conductive path From the viewpoint of securing (conductive path), it is 3 mg / cm ² or more (for example, 6 mg / cm ² or more, typically 12 mg / cm ² or more) per side of the positive electrode current collector, and 45 mg / cm ² or less (for example, 28 mg / cm ² or less, typically 18 mg / cm ² or less). The density of the positive electrode mixture layer is not particularly limited, but is 1.0 g / cm ^{3 to} 3.8 g / cm ³ (for example, 1.5 g / cm ^{3 to} 3.5 g / cm ³ , typically 2.0 g / cm 3). ^{3 to} 3.0 g / cm ³ ).

The porosity of the positive electrode mixture layer is not particularly limited, but is preferably 20% or more (for example, 25% or more, typically 35% or more) from the viewpoint of increasing the decomposition amount of the gas generating agent. The porosity is preferably about 60% or less (for example, 55% or less, typically 50% or less). The porosity of the positive electrode mixture layer can be calculated by the following method. The apparent volume occupied by the positive electrode mixture layer of the unit area (surface area) is V1 [cm ³ ], and the mass of the positive electrode mixture layer of the unit area is W [g]. At this time, the positive electrode sheet is cut into a predetermined area to obtain a sample, the mass of the positive electrode sheet is measured, and the mass of the positive electrode current collector having the predetermined area is subtracted from the mass of the sample to thereby obtain the positive electrode mixture layer having the predetermined area. The mass of is calculated. The mass W [g] of the positive electrode mixture layer can be calculated by converting the mass of the positive electrode mixture layer thus calculated per unit area. The ratio between the mass W and the true density ρ [g / cm ³ ] of the material constituting the positive electrode mixture layer, that is, W / ρ is V0. In addition, V0 is the volume which the compact of the positive electrode composite material layer component of mass W occupies. The porosity of the positive electrode mixture layer can be calculated from [(V1-V0) / V1] × 100. The porosity of the positive electrode mixture layer can be adjusted by the constituent components, the blending ratio thereof, the application method, the drying method, the compression method, and the like.

  As the negative electrode current collector constituting the negative electrode (typically, the negative electrode sheet), a conductive member made of a metal having good conductivity is preferably used as in the conventional lithium ion secondary battery. For example, copper or an alloy containing copper as a main component can be used. The shape of the negative electrode current collector can be different depending on the shape of the battery and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. The thickness of the negative electrode current collector is not particularly limited, and can be, for example, 5 μm to 30 μm.

  The negative electrode mixture layer includes a negative electrode active material capable of inserting and extracting lithium ions serving as charge carriers. There is no restriction | limiting in particular in a composition and a shape of a negative electrode active material, The 1 type (s) or 2 or more types of the material conventionally used for a lithium ion secondary battery can be used. Examples of such a negative electrode active material include carbon materials generally used in lithium ion secondary batteries. Typical examples of such a carbon material include graphite carbon (graphite) and amorphous carbon. A particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least partially is preferably used. Of these, the use of a carbon material mainly composed of natural graphite is preferred. Such natural graphite may be obtained by spheroidizing flaky graphite. Alternatively, a carbonaceous powder having a graphite surface coated with amorphous carbon may be used. In addition, as the negative electrode active material, it is also possible to use oxides such as lithium titanate, simple substances such as silicon materials and tin materials, alloys, compounds, and composite materials using the above materials in combination. The proportion of the negative electrode active material in the negative electrode mixture layer is suitably about 90% to 99% by mass (for example, 95% to 99% by mass, typically 97% to 99% by mass). .

  In addition to the negative electrode active material, the negative electrode mixture layer needs one or more binders, thickeners, and other additives that can be blended in the negative electrode mixture layer of a general lithium ion secondary battery. Depending on the content. Examples of the binder include various polymer materials. For example, what can be contained in the positive electrode mixture layer can be preferably used for an aqueous composition or a solvent-based composition. In addition to being used as a binder, such a binder may be used as a thickener or other additive in a composition for forming a negative electrode mixture layer. The ratio of these additives in the negative electrode mixture layer is not particularly limited, but is approximately 0.8% by mass to 10% by mass (for example, approximately 1% by mass to 5% by mass, typically 1% by mass to 3% by mass). It can be.

The basis weight per unit area of the negative electrode composite material layer on the negative electrode current collector (the coating amount in terms of solid content of the composition for forming the negative electrode composite material layer) is not particularly limited, but sufficient conductive paths From the viewpoint of securing (conductive path), it is 2 mg / cm ² or more (for example, 5 mg / cm ² or more, typically 8 mg / cm ² or more) per side of the negative electrode current collector, and 40 mg / cm ² or less (for example, 22 mg / cm ² or less, typically 14 mg / cm ² or less). The density of the negative electrode mixture layer is not particularly limited, but is 1.0 g / cm ^{3 to} 3.0 g / cm ³ (for example, 1.2 g / cm ^{3 to} 2.0 g / cm ³ , typically 1.3 g / cm 3). ^{3 to} 1.5 g / cm ³ ).

  The separator (separator sheet) disposed so as to separate the positive electrode and the negative electrode may be a member that insulates the positive electrode mixture layer and the negative electrode mixture layer and allows the electrolyte to move. Preferable examples of the separator include those having a single layer structure or a multilayer structure composed of two or more resin layers. As resin which comprises a resin layer, polyolefin resin, such as polyethylene (PE) and a polypropylene (PP), can be used conveniently, for example.

  As the resin layer constituting the separator, for example, a uniaxially stretched or biaxially stretched porous resin film can be suitably used. Among these, a porous resin film uniaxially stretched in the longitudinal direction is particularly preferable because it has an appropriate strength and has little heat shrinkage in the width direction. When a separator having a uniaxially stretched porous resin film is used, thermal contraction in the longitudinal direction can be suppressed in a mode in which the separator is wound together with a long sheet-like positive electrode and negative electrode. Therefore, the porous resin film uniaxially stretched in the longitudinal direction is particularly suitable as one element of the separator constituting such a wound electrode body.

The porosity of the separator is not particularly limited, but is preferably 20% or more (for example, 30% or more, typically 35% or more) from the viewpoint of improving nonaqueous electrolyte retention and ion permeability. The porosity is about 60% or less (for example, 55% or less, typically 50% or less) from the viewpoint of easily adjusting the elongation of the separator to a suitable range and obtaining strength that does not cause film breakage. Preferably there is. The porosity of the separator can be calculated by the following method. The apparent volume occupied by the separator of the unit area (surface area) is V1 [cm ³ ], and the mass of the unit area separator is W [g]. The ratio between the mass W and the true density ρ [g / cm ³ ] of the resin material constituting the separator, that is, W / ρ is V0. Note that V0 is a volume occupied by a dense body of resin material having a mass W. The porosity of the separator can be calculated from [(V1-V0) / V1] × 100. The porosity of the separator can be adjusted by the material of the resin layer, the stretching strength, and the like.

  Although the thickness of a separator is not specifically limited, About 5 micrometers-30 micrometers (for example, 10 micrometers-30 micrometers, typically 15 micrometers-25 micrometers) are preferable. When the thickness of the separator is within the above range, the separator has better ion permeability and film breakage is less likely to occur.

  Moreover, it is preferable that at least one of the filler layers is provided on at least one of the separator and the positive electrode and the negative electrode. Such a filler layer may be mainly composed of an inorganic filler (for example, a filler such as a metal oxide or a metal hydroxide) or an organic filler (for example, resin particles such as polyethylene or polypropylene).

  The filler as the main component of the filler layer may be either an organic filler or an inorganic filler, but it is preferable to use an inorganic filler in consideration of dispersibility and stability. Examples of the inorganic filler include, but are not limited to, aluminum compounds such as boehmite and alumina, inorganic oxides such as magnesia, silica, titania, zirconia, and iron oxide, inorganic nitrides such as aluminum nitride, carbonates such as magnesium carbonate, Mineral materials such as sulfates such as barium sulfate, chlorides such as magnesium chloride, fluorides such as barium fluoride, covalent crystals such as silicon, talc, clay, mica, montmorillonite, zeolite, apatite, kaolin and mullite Or these artificial products etc. may be sufficient. These can be used alone or in combination of two or more. Aluminum compounds, magnesia, silica, titania, and zirconia are preferred for reasons of excellent heat resistance and cycle characteristics, and boehmite, alumina, and magnesia are particularly preferred.

The form of the filler is not particularly limited, and may be, for example, a particle shape, a fiber shape, a plate shape (flake shape), or the like. The average particle diameter of the filler is not particularly limited, but is suitably 0.1 μm to 15 μm (for example, 0.1 μm to 5 μm, typically 0.2 μm to 1.5 μm) in consideration of dispersibility and the like. . As the average particle diameter of the filler, a median diameter (average particle diameter D ₅₀ : 50% volume average particle diameter) that can be derived from the particle size distribution measured based on a particle size distribution measuring apparatus based on a laser scattering / diffraction method can be employed. .

  The filler layer also preferably contains a binder. When the filler layer forming composition is an aqueous solvent, a water-dispersible or water-soluble polymer can be used as a binder. Examples of the water-dispersible or water-soluble polymer include acrylic resins. Examples of acrylic resins include (meth) acrylic acid ester monomers such as methyl methacrylate, 2-ethylhexyl acrylate and butyl acrylate, carboxyl group-containing monomers such as acrylic acid and methacrylic acid, amide group-containing monomers such as acrylamide and methacrylamide, A homopolymer obtained by polymerizing monomers such as hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate in one kind is preferably used. Or the copolymer which superposed | polymerized 2 or more types of the said monomer may be sufficient. Further, a mixture of two or more of the above homopolymers and copolymers may be used. In addition to the acrylic resin described above, styrene butadiene rubber (SBR), acrylic acid-modified SBR resin (SBR latex), rubber such as gum arabic; polyolefin resin such as polyethylene (PE); carboxymethyl cellulose (CMC), etc. Cellulose polymers of the following: polyvinyl alcohol (PVA); fluorine resins such as polytetrafluoroethylene (PTFE); vinyl acetate polymers; polyalkylene oxides such as polyethylene oxide (PEO); These polymers can be used alone or in combination of two or more. Of these, acrylic resins, SBR, and polyolefin resins are preferable. These water-based binders are preferable in that they do not react and cure with moisture in the air, and thus can easily adjust the extensibility of the filler layer (for example, without performing moisture management during production).

  When the filler layer forming composition is a solvent-based solvent, a polymer that can be dispersed or dissolved in the solvent-based solvent can be used as the binder. Examples of the polymer that is dispersed or dissolved in the solvent-based solvent include vinyl halide resins such as polyvinylidene fluoride (PVDF). As the polyvinylidene fluoride, a homopolymer of vinylidene fluoride is preferably used. The polyvinylidene fluoride may be a copolymer of a vinyl monomer copolymerizable with vinylidene fluoride. Examples of vinyl monomers copolymerizable with vinylidene fluoride include hexafluoropropylene, tetrafluoroethylene, and ethylene trichloride fluoride. Alternatively, polytetrafluoroethylene (PTFE), polyacrylonitrile, polymethyl methacrylate, or the like is preferably used as a polymer that is dispersed or dissolved in a solvent-based solvent. These may be used alone or in combination of two or more. These solvent-based binders are preferable in that the extensibility of the porous filler layer can be suitably improved. However, since the solvent-based binder can be cured by reacting with moisture in the atmosphere, it is necessary to perform moisture management during production.

The form of the binder is not particularly limited, and a particulate (powdered) form may be used as it is, or a solution or emulsion prepared may be used. Two or more binders may be used in different forms. When the particulate binder is used, the average particle diameter (the above-mentioned average particle diameter D ₅₀ ) is, for example, about 0.09 μm to 0.15 μm. In addition, the said binder may be used in order to exhibit the function as a thickener other additives of the composition for filler layer formation besides the function as a binder.

  The ratio of the filler (preferably inorganic filler) in the entire filler layer is not particularly limited, but is approximately 90% by mass or more (for example, 92% by mass to 99.5% by mass, typically 95% by mass to 99% by mass). Preferably there is. When the filler layer contains an additive such as a binder or a thickener, the proportion of the additive in the porous filler layer is about 10% by mass or less (for example, 0.5% to 8% by mass, typical In particular, the content is preferably 1% by mass to 5% by mass. When the proportion of the filler, if necessary, the binder and other additive components is within the above range, the anchoring property of the filler layer and the strength (shape retention) of the filler layer itself are improved. Moreover, it tends to be easy to adjust the porosity of the filler layer within a favorable range. Furthermore, when forming a filler layer on a separator, it is easy to adjust the intensity | strength and elongation rate of a separator to a suitable range.

  The porosity of the filler layer is not particularly limited, but is preferably 40% or more (for example, 45% or more, typically 50% or more) from the viewpoint of improving nonaqueous electrolyte retention and ion permeability. The porosity is preferably 75% or less (for example, 70% or less, typically 65% or less) from the viewpoint of suppressing heat shrinkage and obtaining a strength that does not cause defects such as cracks or peeling. . The porosity of the filler layer can be calculated by the same method as the calculation of the separator porosity. In that case, the mass W of the filler layer can be measured as follows. That is, the separator, the positive electrode, or the negative electrode on which the filler layer is formed are cut out to a predetermined area to obtain a sample, and the mass is measured. Next, the mass of the filler layer having the predetermined area is calculated by subtracting the mass of the separator, positive electrode or negative electrode having the predetermined area from the mass of the sample. The mass W [g] of the filler layer can be calculated by converting the mass of the filler layer thus calculated per unit area. The porosity of the filler layer can be adjusted by the constituent components, the blending ratio thereof, the application method, the drying method, and the like.

  The thickness of the filler layer is not particularly limited, but is more preferably about 1 μm to 12 μm (for example, 2 μm to 10 μm, typically 3 μm to 8 μm). When the thickness of the filler layer is within the above range, the short-circuit prevention effect and the nonaqueous electrolyte retention are improved. When providing a filler layer on a separator, it is easy to adjust the strength and elongation of the separator to a suitable range. The thickness of the filler layer can be obtained by image analysis of an image taken with a scanning electron microscope (SEM).

  Both the separator and filler layer described above are porous layers, which can be disposed between the positive and negative electrodes. Of these porous layers, the porosity of the porous layer A disposed at a position facing the positive electrode is larger than the porosity of the porous layer B disposed on the negative electrode side. Said separator (typically each resin layer which comprises a separator) and filler layer may apply to either the porous layer A or the porous layer B by the arrangement | positioning relationship. When the filler layer is not formed and only the separator exists as the porous layer between the positive and negative electrodes, each layer of the resin layer constituting the separator can correspond to either the porous layer A or the porous layer B. One of the porous layer A and the porous layer B is preferably a resin layer.

The porosity of the porous layer A arranged at a position facing the positive electrode is preferably 5% or more larger than the porosity of the porous layer B arranged on the negative electrode side from the porous layer A, and preferably 10% or more (for example, 15% or more) is more preferable. As a result, radical cations of the gas generating agent remain on the positive electrode side, and a large amount of H ⁺ is generated on the positive electrode side in an overcharged state, increasing the amount of gas generated. From the viewpoint of suitably realizing such a configuration, the porosity of the porous layer A is preferably 35% or more (for example, 45% or more, typically 55% or more). The porosity of the porous layer B is preferably 50% or less (for example, 45% or less, typically 40% or less).

Further, the porosity of the porous layer A is preferably larger than the porosity of the positive electrode mixture layer facing the porous layer A. As a result, the amount of the gas generating agent that decomposes on the positive electrode surface increases, and a large amount of H ⁺ can be expected to be generated. Therefore, the porosity of the porous layer A is preferably 5% or more (typically 10% or more) larger than the porosity of the positive electrode mixture layer. However, if the difference between the porosity of the porous layer A and the porosity of the positive electrode mixture layer becomes too large, the porosity of the positive electrode mixture layer becomes relatively small, and the amount of decomposition of the gas generating agent decreases, There is a risk that the amount of gas generation will decrease. Therefore, the difference between the porosity of the porous layer A and the porosity of the positive electrode mixture layer is preferably within a range of 20% or less (typically 15% or less).

  The electrode body constructed using the above materials is preferably a wound electrode body in which a positive electrode and a negative electrode are wound. The wound electrode body tends to reduce the heat dissipation of the central portion due to winding, and tends to be in a high temperature state on the winding center side when it is overcharged. Since the shuttle reaction of the gas generating agent is likely to occur in a high temperature environment, it can be considered that a decrease in the amount of gas generated due to the shuttle reaction is likely to occur on the winding center side of the wound electrode body. By applying the configuration of the present invention to a wound electrode body having such a tendency, it is possible to suitably suppress a decrease in the amount of gas generated.

  As the non-aqueous solvent and the supporting salt constituting the non-aqueous electrolyte injected into the lithium ion secondary battery, those conventionally used for lithium ion secondary batteries can be used without particular limitation. Such a non-aqueous electrolyte is typically an electrolytic solution having a composition in which a supporting salt is contained in a suitable non-aqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2- Diethoxyethane, tetrahydrofuran, 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 These may be used alone or in combination of two or more. Of these, a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) is preferable.

Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _3. One or more of lithium compounds (lithium salts) such as LiI can be used. The concentration of the supporting salt is not particularly limited, but is approximately 0.1 mol / L to 5 mol / L (for example, 0.5 mol / L to 3 mol / L, typically 0.8 mol / L to 1.5 mol / L). Concentration.

The non-aqueous electrolyte can also include a gas generant. Here, the gas generating agent is a compound that can be dissolved or dispersed in the non-aqueous electrolyte, reacts when the battery is overcharged, and gasses before the decomposition of the non-aqueous solvent contained in the non-aqueous electrolyte. Refers to a compound that generates Among these, a gas generating agent that generates hydrogen gas is preferable. Such a gas generating agent is not oxidized at the operating voltage of the battery, but reacts (oxidizes) prior to oxidative decomposition of the nonaqueous solvent of the nonaqueous electrolyte when the battery is overcharged. Therefore, the oxidation potential (oxidation start potential) of the gas generating agent is higher than the upper limit potential of the positive electrode corresponding to the maximum operating voltage. Moreover, it is lower than the oxidation potential (oxidation start potential) of the nonaqueous solvent of the nonaqueous electrolyte. From the above viewpoint, the oxidation potential (vsLi / Li ⁺ ) of the gas generating agent is 0.1 V or higher (for example, 0.2 V or higher, typically 0.3 V or higher) from the upper limit potential (vsLi / Li ⁺ ) of the positive electrode. High is preferred. Moreover, it is preferable that it is 0.1 V or more (for example, 0.2 V or more, typically 0.3 V or more) lower than the oxidation potential (vsLi / Li ⁺ ) of the nonaqueous solvent. For example, in the case of a secondary battery in which the upper limit potential of the positive electrode is 4.2 V or less (typically 4.0 V to 4.2 V), the preferable range of the oxidation potential of the gas generating agent is 4.3 V or more (for example, 4 0.4V or more, typically 4.5V or more) and 5.0V or less (for example, 4.9V or less, typically 4.8V or less).

  Preferable examples of the gas generating agent include branched alkylbenzenes, cycloalkylbenzenes, biphenyls, terphenyls, diphenyl ethers, and dibenzofurans. Examples of the branched alkylbenzenes include branched alkylbenzenes having a branched alkyl group having 3 to 6 carbon atoms, and halides (typically fluorides) of branched alkylbenzenes. Specific examples of branched alkylbenzenes include branched alkylbenzenes such as cumene, diisopropylbenzene, t-butylbenzene, t-dibutylbenzene, t-amylbenzene, and t-diamilbenzene. Examples of the cycloalkylbenzenes include cycloalkylbenzene having a cycloalkyl group having 3 to 6 carbon atoms, and alkyl having at least one hydrogen atom bonded to a carbon atom constituting the cycloalkylbenzene having a linear or branched chain structure. Examples thereof include alkylated cycloalkylbenzene substituted with a group and / or a halogen atom (typically a fluorine atom), and a halide (typically a fluoride) of cycloalkylbenzene. As for carbon number of a linear or branched alkyl group, 1-6 pieces (for example, 3 pieces or 4 pieces) are preferable. Specific examples of the cycloalkylbenzenes include cycloalkylbenzenes such as cyclopentylbenzene and cyclohexylbenzene (CHB), alkylated cycloalkylbenzenes such as t-butylcyclohexylbenzene, and partial fluorides of cycloalkylbenzenes such as cyclohexylfluorobenzene. Biphenyls include biphenyl (BP) and at least one of hydrogen atoms bonded to carbon atoms constituting BP is a linear or branched alkyl group and / or halogen atom (typically a fluorine atom). And alkylbiphenyl substituted with a halide of biphenyl (typically fluoride). Specific examples of biphenyls include BP, alkyl biphenyls such as propyl biphenyl and t-butyl biphenyl, partial phenyls such as 2-fluorobiphenyl, 2,2′-difluorobiphenyl and 4,4′-difluorobiphenyl. A compound. Terphenyls, diphenyl ethers, dibenzofurans include terphenyl, diphenyl ether, dibenzofuran, and each of which at least one hydrogen atom bonded to the carbon atom constituting them is substituted with a linear or branched alkyl group Alkylates (alkylated terphenyls, alkylated diphenyl ethers, alkylated dibenzofurans) and / or terphenyl, diphenyl ether, dibenzofuran halides (typically fluorides) substituted with halogen atoms (typically fluorine atoms) Is mentioned. Terphenyl may be a partial hydride of terphenyl in which a hydrogen atom is added to a part thereof. These can be used alone or in combination of two or more. Of these, branched alkylbenzenes, cycloalkylbenzenes, biphenyls and diphenyl ethers are preferable, cycloalkylbenzenes (typically CHB) and biphenyls (typically BP) are more preferable, and cycloalkylbenzenes (typically In particular, the combined use of CHB) and biphenyls (typically BP) is particularly preferred.

  The amount (addition amount) of the gas generating agent is about 0.1 to 10% by mass (for example, 0.5 to 7% by mass, typically 1 to 5% by mass) in the non-aqueous electrolyte. ) Is preferable.

  The size (typically battery capacity) of the lithium ion secondary battery constructed in this way is not particularly limited. However, when the electrode body is configured as a wound electrode body, as described above, the winding center side tends to be in a high temperature state in which the shuttle reaction of the gas generating agent easily occurs when the overcharged state occurs. By applying the configuration of the present invention to a relatively large secondary battery having a rated capacity (design capacity) of 5 Ah or more (for example, 10 Ah or more, typically 20 Ah or more), the above shuttle reaction is more effectively suppressed. Can be expected to do.

  Such a lithium ion secondary battery can be used for various applications, but can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Therefore, as schematically shown in FIG. 8, the present invention provides a vehicle 1 (typically an automobile, in particular,) that includes a lithium ion secondary battery 100 (typically, a battery pack formed by connecting a plurality of batteries in series) as a power source. Vehicles equipped with electric motors such as hybrid vehicles, electric vehicles, and fuel cell vehicles).

  Next, some examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

<Example 1>
[Preparation of positive electrode sheet]
Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ powder as a positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder, these materials Was mixed with N-methyl-2-pyrrolidone (NMP) so that the mass ratio was 91: 6: 3 to prepare a paste-like composition for forming a positive electrode mixture layer. This composition was uniformly applied to both sides of a long sheet-like aluminum foil (positive electrode current collector: thickness 15 μm) so that the total application amount was 30 mg / cm ² (based on solid content), and dried. Then, the sheet-like positive electrode (positive electrode sheet) was produced by compressing. The density of the positive electrode mixture layer was 2.8 g / cm ³ . The porosity of the positive electrode mixture layer was 35%.

[Preparation of negative electrode sheet]
Natural graphite powder as the negative electrode active material, styrene-butadiene copolymer (SBR) as the binder, and carboxymethyl cellulose (CMC) as the thickener, the mass ratio of these materials becomes 98: 1: 1. Thus, the paste-like composition for forming a negative electrode mixture layer was prepared by mixing with ion-exchanged water. The composition is uniformly applied to a long sheet-like copper foil (thickness: 14 μm) so that the coating amount is 17 mg / cm ² (based on solid content), dried, and then compressed. A negative electrode (negative electrode sheet) was produced. The density of the negative electrode mixture layer was 1.4 g / cm ³ .

[Production of separator with filler layer]
As a base material for forming the filler layer, a long sheet separator (thickness: 20 μm, porosity: 40%) having a three-layer structure made of polypropylene / polyethylene / polypropylene was prepared. The filler layer was formed as follows. By mixing alumina as a filler, acrylic binder as a binder, and CMC as a thickener with ion-exchanged water so that the mass ratio thereof is 96.7: 2.6: 0.7 A paste-like composition was prepared. Mixing was performed using an ultrasonic disperser “CLEAMIX” manufactured by M Technique Co., Ltd. for 5 minutes at 15000 rpm and for 15 minutes at 20000 rpm. The obtained composition was applied to one side of the separator and dried at 70 ° C. In this way, a separator having a filler layer formed on one side was obtained. The thickness of the filler layer was 5 μm and the porosity was 55%.

[Construction of lithium ion secondary battery]
The positive electrode sheet and the negative electrode sheet produced as described above were each cut to have a 3.5 cm square and having a tab, the composite material layer of the tab portion was peeled off, and a lead with a seal was attached. Two negative electrode sheets were superposed on one positive electrode sheet. The separator with filler layer was sandwiched between a positive electrode sheet and a negative electrode sheet to produce an electrode body. At this time, it arrange | positioned so that the filler layer of a separator might oppose a positive electrode sheet. This electrode body was accommodated in a bag made of an aluminum laminate film, and a non-aqueous electrolyte was poured into the bag. As the non-aqueous electrolyte, a 3: 4: 3 (volume ratio) mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) was used, and about 1 mol / L LiPF ₆ as a supporting salt. Then, an electrolytic solution containing 1% cyclohexylbenzene (CHB) and 1% biphenyl (BP) was used. While the bag was evacuated, the aluminum laminate film and the seal portion attached to the lead were heat welded. Furthermore, the laminated type lithium ion secondary battery of the state which pinched | interposed using the restraint board and clip of two sheets of SUS (Steel Use Stainless), and restrained the composite-material layer part was produced.

<Example 2 to Example 7>
A laminated lithium ion secondary battery was produced in the same manner as in Example 1 except that the porosity of the filler layer, the porosity of the separator, and the porosity of the positive electrode mixture layer were varied as shown in Table 1.

[Gas generation measurement]
Each lithium ion secondary battery produced was charged to 4.1 V at a 1C rate in an environment of 25 ° C., and charged at a constant voltage (CV) until the current reached 0.1 C when the voltage reached 4.1 V. Went. And it discharged to 3V at 1C. After this charge / discharge was repeated three times, an overcharge test described below was performed. First, the restraint plate of SUS was removed with SOC (State of Charge) 100%, submerged in a beaker filled with water, and its volume (A0) was measured. At this time, it adjusted with tweezers so that a battery might not touch a beaker. The battery was taken out from the beaker and sandwiched again with a SUS restraining plate, and then overcharged in an environment of 25 ° C. and an environment of 60 ° C. until the SOC reached 140% at a 1C rate. Note that SOC 100% means charging to 4.1V at 1C rate, and CV charging is performed until the current reaches 0.1C when 4.1V is reached, and SOC 0% is discharged to 3V at 1C. Defined as state. The restraint plate of SUS was removed with SOC 140%, and the beaker filled with water was submerged, and the volume (A1) was measured. At this time, similarly to the above, adjustment was made with tweezers so that the battery did not touch the beaker. A1-A0 obtained above was defined as the gas generation amount (volume), and this was divided by the battery capacity to obtain the gas generation amount (cc / Ah) (mL / Ah) during overcharge. The results are shown in Table 1.

  As shown in Table 1, the lithium ion secondary batteries of Examples 1 to 4 in which the porosity of the filler layer (porous layer A) is larger than the porosity of the separator (porous layer B) are gases at 25 ° C. The generation amount was 60 cc / Ah or more, and the gas generation amount at 60 ° C. was 42 cc / Ah or more. On the other hand, in Examples 5 to 7, where the porosity of the filler layer (porous layer A) is smaller than the porosity of the separator (porous layer B), the gas generation rate at 25 ° C. is 55 cc / Ah or less, and 60 ° C. The amount of gas generated was 27 cc / Ah or less. From these results, the content of the gas generating agent is the same by disposing the highly porous porous layer A at a position facing the positive electrode and disposing the low porous layer B on the negative electrode side. Nevertheless, it can be seen that the amount of gas generation can be increased. The reason is presumed as follows. That is, when the radical cation of the gas generating agent moves to the negative electrode side, the porous layer B has a low porosity, so that the amount of movement to the negative electrode side is near the boundary between the porous layer A and the porous layer B. Decays rapidly. This attenuation is accompanied by energy loss, and as a result of effectively suppressing the shuttle reaction, a large amount of radical cations necessary for gas generation remain on the positive electrode side, which is considered to have contributed to an increase in gas generation amount. In addition, the effect of increasing the amount of gas generated was particularly remarkable under a high temperature environment of 60 ° C. This is considered because the above shuttle reaction is easily promoted in a high temperature environment.

Moreover, when Example 1 is compared with Example 2, the amount of gas generation is increasing in Example 2 where the porosity of the positive electrode mixture layer is large. This is thought to be because the amount of decomposition of the gas generating agent increased in the vicinity of the positive electrode in the vicinity of the positive electrode due to the high porosity of the positive electrode mixture layer, and a sufficient amount of H ⁺ required for gas generation was generated. It is done. Further, comparing Example 2 and Example 3, the amount of gas generation at 60 ° C. is increased in Example 3, where the difference in porosity between porous layer A and porous layer B is larger. From this result, it is considered that the shuttle reaction can be more effectively suppressed when the difference in porosity between the porous layer A and the porous layer B is larger.

  As described above, according to the present invention, the amount of gas generated can be increased when an overcharged state is reached. Therefore, it is possible to keep the amount of the gas generating agent added to the minimum necessary, and it is possible to suppress a decrease in battery characteristics (typically an increase in battery resistance) due to the excessive inclusion of the gas generating agent. Therefore, according to the present invention, the CID can be operated at an appropriate timing when the battery is overcharged while maintaining the battery characteristics at a high level.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The invention disclosed herein can include various modifications and alterations of the specific examples described above.

1 Automobile (vehicle)
10 Positive electrode sheet (positive electrode)
12 Positive electrode current collector 14 Positive electrode mixture layer 20 Negative electrode sheet (negative electrode)
22 Negative electrode current collector 24 Negative electrode composite material layer 25 Non-aqueous electrolyte 30 CID
32 Deformed metal plate 33 Curved portion 34 Connection metal plate 35 Current collecting lead terminal 36 Joint point 38 Insulating case 40, 40A, 40B Separator 41 Resin layer 41A, 41B, 41C Resin layer 42 Filler layer 43 Filler layer 50 Battery case 52 Case body 54 Lid 70 Positive electrode terminal 72 Negative electrode terminal 74 Positive electrode current collector plate 76 Negative electrode current collector plate 100 Lithium ion secondary battery

Claims (2)

A non-aqueous electrolyte secondary battery having a current interruption mechanism that operates when the internal pressure of the battery case increases,
The nonaqueous electrolyte contained in the nonaqueous electrolyte secondary battery contains a gas generating agent,
Between the positive electrode and the negative electrode constituting the nonaqueous electrolyte secondary battery, a filler layer as the porous layer A and a separator composed of the porous layer B are disposed,
The porosity of the porous layer A is 55% or more, the porosity of the porous layer B is 50% or less,
The porous layer A is disposed at a position facing the positive electrode,
The porosity of the porous layer A is larger than the porosity of the porous layer B and larger than the porosity of the positive electrode mixture layer constituting the positive electrode, and the porosity of the porous layer A and the positive electrode A nonaqueous electrolyte secondary battery in which the difference from the porosity of the composite layer is within 15%. A vehicle comprising the nonaqueous electrolyte secondary battery according to claim 1 .

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