JP2019071185A - Lithium ion secondary battery - Google Patents

Abstract

To provide a novel technique for satisfactorily discharging decomposition gas to outside an electrode body in a lithium ion secondary battery which uses lithium carbonate serving as an overcharging inhibitor.SOLUTION: A lithium ion secondary battery comprises: a container 8; a positive electrode 1, a separator 2, a negative electrode 3 and an electrolyte solution 4 which are enclosed in the container 8; and a pressure-sensitive safety mechanism 55 which operates in response to the rise in internal pressure in the container 8. The positive electrode 1 has: a positive electrode current collector 10; and a positive electrode active material layer 15 including a positive electrode active material and lithium carbonate, and provided on the positive electrode current collector 10. The negative electrode 3 has: a negative electrode current collector 30; and a negative electrode active material layer 35 including a negative electrode active material, and provided on the negative electrode current collector 30. A porous layer 18 is provided on each of the separator 2 and the negative electrode active material layer 35.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a lithium ion secondary battery, and more particularly to a lithium ion secondary battery using an overcharge inhibitor.

  In the lithium ion secondary battery, although the lithium ion secondary battery is in a fully charged state, there is a problem related to so-called overcharging, in which charging proceeds. When the lithium ion secondary battery is overcharged, the components of the lithium ion secondary battery such as the positive electrode, the negative electrode, the electrolyte solution, and the separator are decomposed or degraded, resulting in excessive heat generation, or the positive and negative electrodes. It may lead to a short circuit.

  As a method of suppressing overcharging of a lithium ion secondary battery, it has been proposed to add an overcharge inhibitor to the electrolytic solution. For example, Patent Document 1 describes that a technique is known in which at least one of biphenyl, cyclohexylbenzene, and diphenyl ether is added to an electrolytic solution.

By the way, according to Patent Document 1, the above-mentioned overcharge preventing agent is decomposed at a relatively low potential, and when using a battery containing the above overcharge preventing agent at a high voltage, a conventional battery can be used. It is also described that the overcharge preventing agent may be decomposed even during use.
And in the said patent document 1, the decomposition start voltage of lithium carbonate is a high voltage compared with said each overcharge inhibiting agent, and the said lithium carbonate is suitable as an overcharge inhibiting agent of the battery used by high electric potential. Is described.

JP, 2016-192338, A

  Lithium carbonate as an overcharge inhibitor is decomposed to generate carbon dioxide gas and oxygen gas when the voltage at the time of charging of the lithium ion secondary battery becomes equal to or higher than the decomposition initiation voltage of lithium carbonate. When the internal pressure of the container of the lithium ion secondary battery is increased by these decomposition gases generated by the decomposition of lithium carbonate, the pressure-sensitive safety mechanism operates to stop the charge of the lithium ion secondary battery.

  Although also described in the above-mentioned Patent Document 1, lithium carbonate as an overcharge inhibitor is used in the positive electrode active material layer of a lithium ion secondary battery. Therefore, a decomposition gas is generated in the positive electrode active material layer at the time of overcharging of the lithium ion secondary battery. In order to quickly operate the pressure-sensitive safety mechanism during overcharge, the decomposition gas generated in the positive electrode active material layer is quickly discharged to the outside of the electrode assembly composed of the positive electrode, the negative electrode and the separator, It is preferable to quickly increase the internal pressure of the battery container.

In Patent Document 1, the packing density of the positive electrode active material layer (referred to as a positive electrode active material mixture layer in Patent Document 1) is set to 2.2 to 2.9 g / cm ³ in consideration of discharge of decomposition gas, and The porosity of the positive electrode active material layer has been proposed to be 30 to 40%. That is, in Patent Document 1, it is considered that the positive electrode active material layer is used as a flow path for the decomposition gas by making the positive electrode active material layer not dense as much.

  However, in recent years, it is desired to further increase the capacity of the battery, and even in the lithium ion secondary battery, in order to realize the high capacity, it is required to make the positive electrode active material layer and the negative electrode active material layer dense. It is done. This requirement is contrary to the technique of Patent Document 1 described above that the positive electrode active material layer is not so dense.

  The present invention has been made in view of the above circumstances, and it is a novel that can discharge the decomposition gas to the outside of the electrode assembly well in a lithium ion secondary battery using lithium carbonate which is an overcharge inhibitor. Aim to provide various technologies.

The lithium ion secondary battery of the present invention which solves the above problems is
A container, a positive electrode contained in the container, a separator, a negative electrode, an electrolyte, and a pressure-sensitive safety mechanism that operates in response to an increase in the internal pressure of the container;
The positive electrode includes a positive electrode current collector, and a positive electrode active material layer including a positive electrode active material and lithium carbonate and provided on the positive electrode current collector.
The negative electrode includes a negative electrode current collector, and a negative electrode active material layer including a negative electrode active material and provided on the negative electrode current collector.
It is a lithium ion secondary battery in which each porous layer is provided on the said separator and the said negative electrode active material layer.

  According to the technology of the present invention, in a lithium ion secondary battery using lithium carbonate which is an overcharge inhibitor, the decomposition gas can be favorably discharged to the outside of the electrode body.

FIG. 2 is an explanatory view schematically showing a positive electrode, a negative electrode and a separator in the lithium ion secondary battery of Example 1. FIG. 3 is a partially cutaway view schematically showing a positive electrode in the lithium ion secondary battery of Example 1. FIG. 6 is an explanatory view schematically showing the inside of the container in the lithium ion secondary battery of Example 1; FIG. 6 is a partially cutaway view schematically showing a positive electrode and a separator in the lithium ion secondary battery of Example 2. FIG. 18 is a partially cutaway view schematically showing a positive electrode and a separator in the lithium ion secondary battery of Example 3.

  Hereinafter, the best mode for carrying out the present invention will be described. In addition, unless otherwise indicated, numerical value range "x-y" described in this specification includes the lower limit x and the upper limit y in the range. And, new numerical ranges can be configured by arbitrarily combining these upper and lower limit values and the numerical values listed in the examples. Further, numerical values arbitrarily selected from within the numerical value range can be used as upper limit and lower limit numerical values.

The lithium ion secondary battery of the present invention is
A container, a positive electrode contained in the container, a separator, a negative electrode, an electrolyte, and a pressure-sensitive safety mechanism that operates in response to an increase in the internal pressure of the container;
The positive electrode includes a positive electrode current collector, and a positive electrode active material layer including a positive electrode active material and lithium carbonate and provided on the positive electrode current collector.
The negative electrode includes a negative electrode current collector, and a negative electrode active material layer including a negative electrode active material and provided on the negative electrode current collector.
It is a lithium ion secondary battery in which each porous layer is provided on the said separator and the said negative electrode active material layer.

  In the lithium ion secondary battery of the present invention, by providing the porous layer on the separator and the negative electrode active material layer, it is possible to suppress the retention of decomposition gas in the vicinity of the electrode body including the positive electrode, the negative electrode and the separator. As a result, the decomposition gas can be well discharged to the outside of the electrode body. The reason is explained below.

As described above, since lithium carbonate is blended in the positive electrode active material layer, the decomposition gas is generated in the positive electrode active material layer. When the decomposition gas generated in the positive electrode active material layer stays in the vicinity of the electrode body, the movement of the subsequent decomposition gas is inhibited, and as a result, it is difficult to rapidly increase the internal pressure of the lithium ion secondary battery container during overcharge. become.
The responsiveness of the pressure sensitive safety mechanism at the time of overcharge is closely related to the rate of increase of the internal pressure of the container of the lithium ion secondary battery at the time of overcharge. Therefore, in order to enhance the responsiveness of the pressure-sensitive safety mechanism during overcharge, it is important to discharge the decomposition gas generated in the positive electrode active material layer to the outside of the electrode assembly quickly.

By the way, in order to increase the capacity of the lithium ion secondary battery, it is necessary to densely form the positive electrode active material layer of the positive electrode and the negative electrode active material layer of the negative electrode in the electrode body. It is considered that the number of pores that can be a flow path of the decomposition gas is not large in the densely formed positive electrode active material layer and the negative electrode active material layer. On the other hand, the separator provided between the positive electrode active material layer and the negative electrode active material layer has a relatively low density, and can allow passage of decomposition gas as compared to the positive electrode active material layer and the negative electrode active material layer. It is considered to have many pores.
For this reason, it is considered that the separator, the interface between the separator and the positive electrode active material layer, or the interface between the separator and the negative electrode active material can function as a main flow path of the decomposition gas generated in the positive electrode active material layer.

  However, in recent years, the positive and negative electrodes and the separator are often accommodated in a container in a compressed state in order to satisfy the demand for higher capacity of the lithium ion secondary battery. In such a case, the positive electrode, the negative electrode, and the separator are in a state of being in close contact or in pressure contact with each other in the container. In this case, it is difficult to say that the flow path of the decomposition gas constituted by the separator, the interface between the separator and the positive electrode active material layer, or the interface between the separator and the negative electrode active material is not sufficiently functional. It is difficult to say that the discharge of decomposition gas to the outside is also performed well.

  On the other hand, in the lithium ion secondary battery of the present invention, the porous layer is provided on the separator and the negative electrode active material layer, respectively. The porous layer provided on the negative electrode active material layer is disposed at the interface between the negative electrode active material layer and the separator. The porous layer provided on the separator is disposed at the interface between the positive electrode active material layer and the separator or at the interface between the negative electrode active material layer and the separator. Therefore, it can be said that the porous layer is disposed anywhere between the positive electrode active material layer, the separator and the negative electrode active material layer to constitute at least one of these interfaces.

  The porous layer literally has a large number of pores, which can serve as a flow path for decomposition gas. Therefore, in the lithium ion secondary battery of the present invention, the decomposition gas can be favorably discharged from the inside of the electrode body to the outside through the pores of the porous layer. The porous layer is disposed at the interface between the positive electrode active material layer and the separator or at the interface between the separator and the negative electrode active material layer, and the adhesion between the positive electrode active material layer and the separator, or between the separator and the negative electrode active material layer. It can also function as a spacer that regulates adhesion. For example, in the case where the porous layer is partially provided on the separator or the negative electrode active material layer, if the porous layer functions as a spacer, the interface between the positive electrode active material layer and the separator, the separator and the negative electrode The interface itself with the active material layer can function as a flow path for the decomposition gas.

As described above, in the lithium ion secondary battery of the present invention, it is possible to sufficiently secure the flow path of the decomposition gas derived from lithium carbonate and generated in the positive electrode active material layer. As a result, the responsiveness of the pressure sensitive safety mechanism during overcharge can be improved.
Hereinafter, the lithium ion secondary battery of the present invention will be described for each component. The matters common to both the positive electrode and the negative electrode will be described without particularly distinguishing the positive electrode and the negative electrode.

  The positive electrode in the lithium ion secondary battery of the present invention has a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

  The current collector refers to a chemically inert electron conductor for keeping current flowing to the electrode during discharge or charge of the lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, stainless steel, etc. A metal material can be illustrated. The current collector may be coated with a known protective layer. What processed the surface of a collector by a well-known method may be used as a collector. Among them, aluminum is preferably used as a current collector when the potential of the positive electrode is 4 V or more on the basis of a lithium counter electrode.

  The current collector can take the form of a foil, a sheet, a film, a line, a rod, a mesh or the like. Therefore, as the current collector, for example, metal foils such as copper foil, nickel foil, aluminum foil, and stainless steel foil can be suitably used. When the current collector is in the form of a foil, a sheet or a film, the thickness is preferably in the range of 1 μm to 100 μm.

  The shape of the current collector is not particularly limited. For example, the current collector may be configured of a general current collector and a tab. Among these, the general current collection portion is a portion where a positive electrode active material layer is formed in the positive electrode current collector and a negative electrode active material layer is formed in the negative electrode current collector. The tab portion is a portion which extends from the general current collection portion and is connected to a terminal, a lead wire or the like. The shape of the tab portion is not particularly limited. For example, when the general current collector portion is accommodated in the bag-like separator using a bag-like separator, the tab portion is narrower than the general current collector portion. Good to have. The term "width" as used herein refers to the length in the direction orthogonal to the extending direction of the tab portion. That is, assuming that the extension direction of the tab portion is a first direction, and the direction orthogonal to the first direction is a second direction, "the width of the general current collection portion" means the length of the general current collection portion in the second direction. means. Further, “the width of the tab portion” means the length of the tab portion in the second direction. Therefore, in the present specification, “the tab portion is narrower than the general current collector portion” means that the length of the tab portion in the second direction is shorter than the length of the general current collector portion in the second direction. Means

  The width and length of the general current collection portion and the width and length of the tab portion are not particularly limited, and may be appropriately designed according to the performance and shape required for the lithium ion secondary battery.

  The positive electrode active material layer essentially contains a positive electrode active material and lithium carbonate, and may contain additives such as a conductive additive and a binder as needed.

The positive electrode active material is not particularly limited as long as it can occlude and release lithium ions.
For example, as the positive electrode active material, a layered compound _{Li a Ni b Co c Mn d} D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D is Li, Fe, Cr, At least one element selected from Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 3), Li _a Ni _b Co _c Al _{d DeO f} (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg At least one element selected from S, Si, Na, K, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 3), Li ₂ MnO ₃ It can be mentioned. In addition, as a positive electrode active material, spinel such as LiMn ₂ O ₄ and a solid solution composed of a mixture of spinel and layered compound, LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (M in the formula is Co, Ni, Mn, Polyanionic compounds represented by (at least one of Fe) and the like can be mentioned. Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as a positive electrode active material may have the above composition formula as a basic composition, and one obtained by substituting a metal element contained in the basic composition with another metal element can also be used as a positive electrode active material . In addition, as a positive electrode active material, a positive electrode active material containing no lithium ion contributing to charge and discharge, for example, a simple substance of sulfur, a compound of sulfur and carbon, a metal sulfide such as TiS ₂ , V ₂ O ₅ , MnO Oxides such as ₂ , polyaniline and anthraquinone, and compounds containing these aromatics in the chemical structure, conjugated materials such as conjugated diacetic acid organic substances, and other known materials can also be used. Furthermore, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl or the like may be adopted as the positive electrode active material.

Among the above-mentioned positive electrode active materials, it is known that a compound having an olivine structure represented by LiFePO ₄ is a positive electrode active material excellent in thermal stability. These positive electrode active materials, in order to achieve both high capacity and thermal stability, when used in combination, for example, in _{Li a Ni b Co c Mn d} D e O f other positive electrode active material such layered compound is there.
Such an olivine-structured positive electrode active material is relatively hard. For this reason, the positive electrode active material layer mainly containing the positive electrode active material of the olivine structure as a positive electrode active material is higher in rigidity than a positive electrode active material layer mainly containing another positive electrode active material, and a lithium ion secondary battery It is difficult to compress even inside. Then, it can be said that the positive electrode active material layer mainly containing a positive electrode active material having an olivine structure can function as a flow path for decomposition gas as the porous layer.
Hereinafter, as needed, the positive electrode active material of an olivine structure is called an olivine active material. Moreover, the positive electrode active material layer mainly containing an olivine active material is called an olivine positive electrode active material layer as needed. In addition, "mainly included" as used herein means that an olivine active material occupies 50 mass% or more of the positive electrode active material contained in a positive electrode active material layer.

Considering that the olivine cathode active material layer is made to function as a suitable flow path for the decomposition gas while maintaining the capacity of the cathode high, separately providing the olivine cathode active material layer and the cathode active material layer not containing olivine Is preferred. Hereinafter, as needed, the positive electrode active material layer which does not contain olivine is called a general positive electrode active material layer.
Lithium carbonate may be contained in any of the olivine positive electrode active material layer and the general positive electrode active material layer, but considering that the olivine positive electrode active material layer becomes a flow path of decomposition gas, at least the olivine positive electrode active material layer Preferably contains lithium carbonate.

For example, the general positive electrode active material layer and the olivine positive electrode active material layer may be alternately formed in a band shape on the general current collection portion of the current collector. In this case, in order to suitably discharge the decomposition gas to the outside of the separator and the electrode assembly, it is preferable that the general positive electrode active material layer and the olivine positive electrode active material layer have their longitudinal direction coincide with the first direction described above. . In other words, in this case, it is preferable that the strip-like general positive electrode active material layer and the olivine positive electrode active material layer have the same strip-like tab portion and the same longitudinal direction.
Furthermore, in this case, the general positive electrode active material layer and the olivine positive electrode active material layer are alternately arranged along the width direction of the general current collecting portion, while the olivine positive electrode active material layer is a tab portion in the width direction of the general current collecting portion It is preferable to arrange in the same position. By so doing, the decomposed gas that has flowed out of the olivine positive electrode active material layer is easily discharged to the outside through the boundary between the tab portion and the separator.

Alternatively, one of the general positive electrode active material layer and the olivine positive electrode active material layer may be formed on the general current collection portion, and the other may be formed thereon.
In this case, in order to effectively utilize the thermal stability of the olivine active material, the olivine positive electrode active material layer is preferably formed on the lower layer of the general positive electrode active material layer, that is, on the current collector side. In other words, the olivine positive electrode active material layer is preferably interposed between the general positive electrode active material layer and the general current collection portion. In this case, it is more preferable that the entire surface of the general positive electrode active material layer be in contact with the olivine positive electrode active material layer. By doing this, the area of the portion of the positive electrode active material layer in contact with the flow path of the decomposition gas can be made extremely large, and the decomposition gas generated in the general positive electrode active material layer can be efficiently discharged to the outside of the electrode body.

As the olivine active material, LiM _h PO _{4 of} olivine structure (M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, Te, Mo At least one element selected, 0 <h <2) can be mentioned.

M of LiM _h PO ₄ is preferably at least one element selected from Mn, Fe, Co, Ni, Mg, V and Te, and h is 0.6 <h <1.1. Is preferred. The M is more preferably Mn and / or Fe, and more preferably h = 1. As LiM _h PO ₄ , one represented by LiMn _x Fe _y PO ₄ (x + y = 1, 0 <x <1, 0 <y <1) in which Mn and Fe coexist is more preferable. As a range of x and y, 0.1 ≦ x ≦ 0.9, 0.1 ≦ y ≦ 0.9, 0.2 ≦ x ≦ 0.8, 0.2 ≦ y ≦ 0.8 can also be exemplified.

Examples of LiM _h PO _4, for _{example, LiFePO 4, LiCoPO 4, LiNiPO} 4, LiMnPO 4, LiVPO 4, LiTePO 4, LiV 2/3 PO 4, LiFe 2/3 PO 4, LiMn 7/8 Fe 1 _{/ 8} PO ₄ , LiMn _0.67 Fe _0.33 PO ₄ can be mentioned.

  The olivine active material is known to have relatively low conductivity. Therefore, in order to fully utilize the function of the olivine active material as the positive electrode active material, it is preferable to use the olivine active material in combination with the conductive aid. Specifically, the olivine active material is preferably coated with carbon.

In consideration of the function as a flow path of the decomposition gas, the larger the pore diameter of the pores in the olivine positive electrode active material layer is, the better. In order to form an olivine positive electrode active material layer having large pores, it is effective to use one having a large particle size as the olivine active material. Specifically, the average particle size of the olivine active material is preferably larger than the average particle size of the positive electrode active material contained in the positive electrode active material layer.
The average particle diameter of the positive electrode active material contained in the positive electrode active material layer is preferably 100 μm or less, more preferably in the range of 0.1 to 50 μm, still more preferably in the range of 1 to 20 μm, and in the range of 3 to 12 μm Particularly preferred.
On the other hand, the average particle diameter of the olivine active material is preferably 100 μm or less, more preferably in the range of 1 to 50 μm, further preferably in the range of 5 to 30 μm, and particularly preferably in the range of 12 to 21 μm.

Lithium carbonate may be contained in the positive electrode active material layer in an amount according to the amount of decomposition gas required for the pressure-sensitive safety mechanism.
For example, the mixing ratio of lithium carbonate to the positive electrode active material is preferably in the range of lithium carbonate: positive electrode active material = 1: 10 to 1: 100 by mass ratio, and the range of 1:20 to 1:80 It is more preferable that the inner diameter is within the range of 1:30 to 1:60.

  Moreover, as lithium carbonate, it is preferable to use the thing of a powder state in consideration of the reactivity at the time of overcharge. As a suitable average particle diameter of lithium carbonate, 0.1-50 micrometers, 0.5-30 micrometers, 1-20 micrometers can be illustrated. In addition, the average particle diameter in this specification means D50 at the time of measuring with a common laser diffraction type particle size distribution measuring apparatus.

  A conductive aid is added to enhance the conductivity of the electrode. Therefore, the conductive additive may be optionally added when the conductivity of the electrode is insufficient, and may not be added when the conductivity of the electrode is sufficiently excellent. The conductive auxiliary agent may be any chemically active high electron conductor, and carbon black particles such as carbon black, graphite, acetylene black, ketjen black (registered trademark), vapor grown carbon fiber (vapor grown carbon) Fiber), and various metal particles are exemplified. These conductive assistants can be added to the active material layer singly or in combination of two or more.

  The compounding ratio of the conductive aid in the active material layer is, in mass ratio, preferably active material: conductive aid = 1: 0.005 to 1: 0.5, 1: 1 to 1: 0 It is more preferable that it is .2 and still more preferably 1: 0.03 to 1: 0.1. If the amount of the conductive additive is too small, efficient conductive paths can not be formed. If the amount of the conductive additive is too large, the formability of the active material layer deteriorates and the energy density of the electrode decreases.

  In order to impart excellent conductivity to lithium carbonate, a conductive aid excellent in conductivity may be coexistent with the lithium carbonate. In this case, a voltage can be efficiently applied to lithium carbonate, and decomposition of lithium carbonate during overcharge, that is, generation of a decomposition gas can be performed efficiently and rapidly. As an embodiment in which lithium carbonate and a conductive auxiliary are coexistent, lithium carbonate is coated with a conductive auxiliary, lithium carbonate is used as a conductive auxiliary, in addition to an embodiment in which both lithium carbonate and conductive auxiliary are mixed in the positive electrode active material layer. An aspect such as compounding can also be mentioned. A general method such as milling may be selected as a method of complexing lithium carbonate with the conductive aid.

  The binder plays the role of anchoring the active material and the conductive aid to the surface of the current collector and maintaining the conductive network in the electrode. The binder may, for example, be a fluorine-containing resin such as polyvinylidene fluoride, polytetrafluoroethylene or fluororubber, a thermoplastic resin such as polypropylene or polyethylene, an imide resin such as polyimide or polyamideimide, an alkoxysilyl group-containing resin, Acrylic resins such as acrylic acid, styrene-butadiene rubber (SBR), alginates such as carboxymethylcellulose, sodium alginate, ammonium alginate, water-soluble cellulose ester cross-linked product, starch-acrylic acid graft polymer it can. These binders may be used alone or in combination.

  The blending ratio of the binder in the active material layer is, in mass ratio, preferably active material: binder 1: 0.001 to 1: 0.3, 1: 0.005 to 1: 0 The ratio is more preferably 0.2, and more preferably 1: 0.01 to 1: 0.15. When the amount of the binder is too small, the formability of the electrode decreases, and when the amount of the binder is too large, the energy density of the electrode decreases.

  In order to form an active material layer on the surface of a current collector, current collection can be performed using conventionally known methods such as roll coating, die coating, dip coating, doctor blade method, spray coating, and curtain coating. The active material may be applied to the surface of the body. Specifically, the active material, the solvent, and, if necessary, the binder and / or the conductive auxiliary agent are mixed to prepare a slurry. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone and water. The slurry is applied to the surface of a current collector and then dried. The dried one may be compressed to increase the electrode density.

The lithium ion secondary battery of the present invention has a porous layer. Since the porous layer can function as a flow path for decomposition gas, the positive electrode active material layer in the lithium ion secondary battery of the present invention does not require much function as a flow path for decomposition gas. Therefore, in the lithium ion secondary battery of the present invention, the basis weight and density of the positive electrode active material layer can be increased. Specifically, the upper limit of the basis weight of the positive electrode active material layer can be increased to 30 mg / cm ² or less, 40 mg / cm ² or less, or 50 mg / cm ² or less per one surface of the general current collector in the current collector . There is no lower limit to the basis weight of the positive electrode active material layer, but if it is mentioned dare, each range of 10 mg / cm ² or more, 15 mg / cm ² or more, 20 mg / cm ² or more can be mentioned.
In addition, the upper limit of the density of the positive electrode active material layer can be increased to 3.6 g / cm ² or less, 4.0 g / cm ² or less, or 4.5 g / cm ² or less. There is no lower limit to the density of the positive electrode active material layer, but it is possible to cite 2.6 g / cm ³ or more, 2.7 g / cm ³ or more, 2.8 g / cm ³ or more, 2.9 g / cm ³ or more. Each range of 2.9 g / cm ^{3 or} more is mentioned.

  Similarly, in the lithium ion secondary battery of the present invention, the porosity of the positive electrode active material layer can be reduced. As an upper limit of the porosity of a positive electrode active material layer, each range of 40% or less, 30% or less, less than 30%, 25% or less, and 20% or less can be mentioned. The lower limit of the porosity of the positive electrode active material layer is, for example, 5% or more, 10% or more, or 15% or more. The porosity can be calculated from the mass ratio and true density of the components contained in the positive electrode active material layer, and the mass and volume of the positive electrode active material layer. In addition, the same may be said of the other porosity demonstrated in this specification.

  Similarly, in the lithium ion secondary battery of the present invention, the thickness of the positive electrode active material layer can be increased. The lower limit of the thickness of the positive electrode active material layer is, for example, 40 μm or more, 60 μm or more, 80 μm or more, or 100 μm or more. As an upper limit of the thickness of a positive electrode active material layer, each range of 500 micrometers or less, 400 micrometers or less, and 200 micrometers or less is mentioned.

  The separator isolates the positive electrode and the negative electrode, and allows the passage of lithium ions and an electrolytic solution while preventing a short circuit due to the contact of the both electrodes. The shape of the separator is not particularly limited, and various shapes such as a plate shape and a bag shape can be adopted. When the separator has a bag shape, the positive electrode or the negative electrode can be accommodated in the separator, so that there is an advantage that the positive electrode or the negative electrode and the separator can be positioned easily and stably. Moreover, in this case, the handleability between the positive electrode or the negative electrode and the separator is improved, which is advantageous in the production of a lithium ion secondary battery. As a bag-like separator, what makes the bag shape which the separator plate of 2 sheets adhered by the peripheral part can be illustrated. Hereinafter, the plate-like separator and the two separator plates constituting the bag-like separator may be collectively referred to simply as a separator plate. Further, in the separator, a portion where two separator plates are fixed at the peripheral portion may be referred to as a fixed peripheral portion.

  As the separator plate, a known one may be employed, and polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester, synthetic resin such as polyacrylonitrile, polysaccharide such as cellulose, amylose, Examples thereof include porous materials, non-woven fabrics, and woven fabrics using one or more kinds of natural polymers such as fibroin, keratin, lignin and suberin, and electrically insulating materials such as ceramics. Further, the separator plate may have a multilayer structure. The thickness of the separator plate is not particularly limited as long as it can separate the positive electrode and the negative electrode.

  When the separator has a bag-like shape, known methods such as adhesion and welding can be adopted as a method of fixing the two separator plates. When bonding two separator plates by bonding, the adhesive has electrical insulation and is physically and chemically stable under the conditions of use of the lithium ion secondary battery of the present invention. Is preferred. Specifically, as the adhesive, the material of the above separator plate or the resin material mentioned as the binder can be used. If the separator plate is made of a thermoplastic resin, it is reasonable to adopt welding as a method of fixing the two separator plates.

The fixing peripheral edge portion of the bag-like separator may be provided continuously or intermittently at the peripheral edge portion of the separator. That is, the separator may have only one or a plurality of gaps of the above-mentioned fixing peripheral edge. The tab portion of the positive electrode current collector may be disposed between the gaps of the fixing peripheral portion.
In some cases, the fixing peripheral edge may be provided continuously over the entire peripheral edge of the separator. In this case, since there is no gap in the fixing peripheral edge portion, the tab portion may penetrate the fixing peripheral edge portion and be continuous from the inside of the bag of the separator to the outside. In this case, for example, two rectangular separator plates are stacked, and the three sides of the peripheral portion are welded in advance, and the tab portion is exposed from the open side of the peripheral portion to the outside, and between the two separator plates The positive electrode may be accommodated and finally the free one of the peripheral portions may be welded together with the tab portion.

The separator plate is located between the positive electrode and the negative electrode to prevent contact between the positive electrode and the negative electrode. The separator plate preferably has a larger surface than the facing surfaces of the positive electrode active material layer and the negative electrode active material layer. From the viewpoint of short circuit prevention and metal lithium deposition prevention, as the size of the surface, the order of separator plate> negative electrode active material layer> positive electrode active material layer is preferable. In the facing state of the separator plate, the positive electrode active material layer, and the negative electrode active material layer, the negative electrode active material layer faces the positive electrode active material layer in a mode covering the entire surface of the positive electrode active material layer, and the positive electrode active material layer and the negative electrode It is preferable that the separator plate face the positive electrode active material layer and the negative electrode active material layer in such a manner as to cover the entire surface of the active material layer.
It is preferable that the size of the surface is in the order of separator plate> negative electrode active material layer> positive electrode active material layer. Therefore, when the separator has a bag shape, the positive electrode having the smallest positive electrode active material layer It is reasonable to store in a bag-like separator.

  In the lithium ion secondary battery of the present invention, porous layers are respectively formed on the separator and the negative electrode active material layer. The porous layer is literally porous, and the pores of the porous layer serve as a flow path for decomposition gas. The pore diameter of the pores in the porous layer is not particularly limited, but it is preferably large enough to allow the bubbles of the relatively large grown decomposition gas to pass through. As a preferable pore diameter of the pore in a porous layer, each range of 0.1 micrometer-300 micrometers, 0.2 micrometer-200 micrometers, 0.3 micrometer-100 micrometers, 0.5 micrometer-50 micrometers can be mentioned, for example.

It is considered that a larger proportion of pores in the porous layer is better in order to suitably circulate the decomposition gas. Specifically, the porous layer should be at least as rough as the positive electrode active material layer and the negative electrode active material layer.
When the porosity is employed as an index indicating the degree of roughness and density of the object, the porosity of the positive electrode active material layer is generally 10 to 40%. In consideration of this, the porosity of the porous layer is preferably 15% or more, more preferably 20% or more, still more preferably 30% or more, and still more preferably 40% or more. Preferably, it is 50% or more.
On the other hand, in order to function properly as a spacer between the negative electrode active material layer and the separator plate and between the positive electrode active material layer and the separator plate, the porous layer is required to have a certain degree of rigidity, In terms of points, it is considered that the smaller the porosity of the porous layer, the better. In consideration of this in addition to the above conditions, the porosity of the porous layer is preferably 15 to 75%, more preferably 20 to 73%, and particularly preferably 30 to 70%. It can be said.

  The porous layer preferably has the above-described pores and is physically and chemically stable under the conditions of use of the lithium ion secondary battery of the present invention, and the material is not particularly limited. As a specific example, a foam material mainly composed of various ceramics and polymers such as synthetic resins can be exemplified.

As the ceramics, Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , MgO, SiC, SiC, AlN, BN, CaCO ₃ , MgCO ₃ , BaCO ₃ , talc, mica, kaolinite, CaSO ₄ , MgSO ₄ , BaSO ₄ , CaO, ZnO, and zeolite can be exemplified. In the case of employing a ceramic, a composite in which ceramic particles are fixed with a binder may be employed, or a low density ceramic plate in which the composite is sintered may be employed, or other embodiments. You may use the one of

  As polymers constituting the above-mentioned foam materials, polyolefins represented by polyethylene and polypropylene, polyesters represented by polyethylene terephthalate and polybutylene terephthalate, amide resins represented by polyimide, polyamide and polyamideimide, polyvinylidene fluoride And fluorine-based resins represented by polytetrafluoroethylene, and silicone resins.

The silicone resin is represented by R _y SiO _{(4-y) × 0.5} (wherein each R independently represents a monovalent or divalent hydrocarbon group having 1 to 20 carbon atoms which may be substituted, and y is It is a polymer which has two or more unit structures represented by 0), and has a skeleton by a siloxane bond. The carbon number of the monovalent or divalent hydrocarbon group represented by R can be in the range of 1 to 14 or 1 to 12. As said hydrocarbon group, at least 1 sort (s) chosen from an alkyl group, an alkenyl group, an aryl group, an aralkyl group, or an alkylene group is mentioned. Two or more of R may be an alkenyl group. A methyl group is mentioned as a specific example of the said alkyl group. Specific examples of the alkenyl group include at least one selected from a vinyl group, an allyl group, a butenyl group, a pentenyl group, a hexenyl group or a heptenyl group. A phenyl group is mentioned as a specific example of the said aryl group. y is preferably 2.

  In addition, when a foaming material has a polymer as a main component, the foaming mechanism in the manufacturing process is not specifically limited. In general, a foaming material mainly composed of a polymer is manufactured using as a raw material a composition containing a polymer as a matrix and a foaming agent that generates a gas. As a foaming agent, one that chemically reacts with a foaming initiator to generate a gas is generally used, but the material is not limited to this, and one that generates a gas by thermal decomposition or one that increases in volume due to heat is used It is good.

Examples of known blowing agents include carbonates such as sodium hydrogen carbonate, ammonium hydrogen carbonate and ammonium carbonate, azodicarbonamide, 2,2'-azobisisobutyronitrile, azohexahydrobenzonitrile, and diazo Azo compounds such as aminobenzene, benzenesulfonyl hydrazide, benzene-1,3-sulfonyl hydrazide, diphenyl sulfone-3,3'-disulfonyl hydrazide, diphenyl oxide-4,4'-disulfonyl hydrazide, 4,4'-oxybis (Benzenesulfonyl hydrazide), and sulfonyl hydrazide compounds such as para-toluenesulfonyl hydrazide, N, N'-dinitrosopentamethylenetetramine, N, N'-dinitroso-N, and Nitose such as N'-dimethylphthalamide It is an azide compound such as a roso compound, terephthalazide, and p-t-butyl benzazide.
In addition, as a foaming agent which increases in volume by heat, a capsule foaming agent in which a volatile organic solvent is enclosed in an outer shell made of a thermoplastic resin can be mentioned. By appropriately setting conditions such as a combination of an outer shell and a volatile organic solvent in a capsule foaming agent and a foaming temperature, an outer shell is chipped to obtain a continuous foam type foam material in which pores communicate with each other. It is possible.

  The porous layer may be formed on the separator and the negative electrode active material layer by using the above-described materials singly or in combination. A method of forming a porous layer on a separator and a negative electrode active material layer is a method of pressure bonding the above-described material to the surface of the separator and the negative electrode active material layer, the material described above on the surface of the separator and the negative electrode active material layer A method of applying, drying or polymerizing a paste containing a precursor monomer and a solvent can be exemplified. Alternatively, a method of thermally fusing the above-described material to the surface of the separator and the negative electrode active material layer, or a method of bonding the above-described material to the surface of the separator and the negative electrode active material layer using an adhesive can be selected. In this case, for example, an end of the porous layer, or a part of the porous layer may be fixed to the separator or the negative electrode active material layer.

The porous layer may be formed on the separator and the negative electrode active material layer, and the size and the shape thereof are not particularly limited. The porous layer may be provided on the surface of the separator on the negative electrode active material layer side, or may be provided on the surface of the separator on the positive electrode active material layer side. In addition, a porous layer may be provided on the entire surface of the separator or the negative electrode active material layer, or a porous layer may be provided only on part of the separator or the negative electrode active material layer, or on the separator or the negative electrode active material A porous layer may be provided intermittently on the layer. In any case, in order to secure the flow path of the decomposition gas in a sufficient size, a porous layer is provided on the surface of the separator on the negative electrode active material layer side, and the porous layer on the separator and the negative electrode active are provided. It may be adjacent to the porous layer on the material layer. In this case, the two porous layers function as if they are integrated, and the porous layers can form a large flow path for the decomposition gas.
In addition to the above-mentioned porous layer, a porous layer may be further provided in other regions in the electrode body. For example, porous layers may be provided on the two opposing surfaces of the separator plate, or porous layers may be provided on the positive electrode active material layer.

  The thickness of the porous layer is not particularly limited, but it is better to be thicker in consideration of the function as a flow path of the decomposition gas. In comparison with the positive electrode active material layer, the porous layer is preferably 1/3 or more of the thickness of the positive electrode active material layer, more preferably 1/2 or more, and 2/3 or more. It is more preferable that there be. There is no particular upper limit to the thickness of the porous layer, but in order not to increase the size of the lithium ion secondary battery, it is preferably not more than twice the thickness of the positive electrode active material layer, 3/2 It is more preferably twice or less, more preferably 1 or less.

  The negative electrode includes a negative electrode current collector and a negative electrode active material layer bonded to the surface of the negative electrode current collector. As the negative electrode current collector, one similar to that described for the positive electrode may be appropriately adopted. The negative electrode active material layer contains a negative electrode active material and, if necessary, a conductive aid and / or a binder.

As the negative electrode active material, materials capable of inserting and extracting lithium ions can be used. Therefore, there is no particular limitation as long as it is a single body, an alloy or a compound capable of storing and releasing lithium ions. For example, Li as a negative electrode active material, a Group 14 element such as carbon, silicon, germanium, tin, a Group 13 element such as aluminum or indium, a Group 12 element such as zinc or cadmium, a Group 15 element such as antimony or bismuth, magnesium And alkaline earth metals such as calcium, and Group 11 elements such as silver and gold may be used alone. When silicon or the like is used as the negative electrode active material, one silicon atom reacts with a plurality of lithium, and thus a high-capacity active material is obtained. However, there is a problem that the volume expansion and contraction accompanying the lithium absorption and release become remarkable It is also preferable to use, as the negative electrode active material, an alloy or a compound in which another element such as a transition metal is combined with a single element such as silicon, since there is a possibility that such a risk may occur. Specific examples of the alloy or compound include tin-based materials such as Ag-Sn alloys, Cu-Sn alloys, Co-Sn alloys, carbon-based materials such as various types of graphite, and SiO _x (disproportionate into silicon alone and silicon dioxide) Examples thereof include silicon-based materials such as 0.3 ≦ x ≦ 1.6), a simple substance of silicon, or a composite obtained by combining a silicon-based material and a carbon-based material. In addition, as a negative electrode active material, an oxide such as Nb ₂ O ₅ , TiO ₂ , Li ₄ Ti ₅ O ₁₂ , WO ₂ , MoO ₂ , Fe ₂ O ₃ or Li _3-x M _x N (M = Co , Ni, Cu) may be employed. One or more of these can be used as the negative electrode active material.

  As a more specific negative electrode active material, graphite and silicon-based materials can be exemplified. The silicon-based material is a material containing silicon, contains Si, and may be a material that functions as a negative electrode active material.

Silicon-based materials undergo a large volume change as they absorb and release lithium ions. Specifically, the silicon-based material occludes lithium ions and expands when the lithium ion secondary battery is charged.
When lithium carbonate is decomposed during overcharge, lithium ions are also generated together with the decomposition gas. Therefore, during overcharge, not only lithium ions released from the positive electrode active material but also lithium ions released from lithium carbonate are supplied to the negative electrode. Therefore, when a silicon-based material is used as the negative electrode active material, it is considered that the negative electrode active material layer largely expands during overcharge, and the separator plate and the positive electrode active material layer are compressed due to the expansion of the negative electrode active material layer. At this time, the decomposition gas present in the separator plate or the positive electrode active material layer is pushed out and discharged to the outside of the separator plate or the positive electrode active material layer.
At this time, the flow path of the decomposition gas in the separator plate or the positive electrode active material layer is compressed or reduced by the negative electrode active material layer, and the flow path of the decomposition gas becomes smaller or smaller. Therefore, when lithium carbonate and a silicon-based material as a negative electrode active material are used in combination in a conventional lithium ion secondary battery, there is a possibility that retention of the decomposition gas in the electrode body is likely to occur.

However, the lithium ion secondary battery of the present invention has a porous layer which becomes a flow path of decomposition gas. Therefore, although the lithium ion secondary battery of the present invention has lithium carbonate, even if a silicon-based material is selected as the negative electrode active material, the decomposition gas is well discharged and the decomposition gas in the electrode body It is believed that the retention of
When a silicon-based material is selected as the negative electrode active material, it is preferable to select a relatively high rigidity porous layer, and specifically, it is effective to select a porous layer containing ceramics. . Furthermore, in this case, it is also effective to use the above olivine positive electrode active material layer in combination.

Specific examples of silicon-based materials include simple silicon, SiO _x (0.3 ≦ x ≦ 1.6), alloys of Si and other metals, and silicon materials described in WO 2014/080608. . The silicon-based material may be coated with carbon. Silicon-based materials coated with carbon are excellent in conductivity.

The silicon material described in WO 2014/080608 (hereinafter sometimes simply referred to as "silicon material") will be described in detail. For example, a silicon material may be reacted with CaSi ₂ and an acid to synthesize a layered silicon compound containing polysilane as a main component, and further, the layered silicon compound may be heated at 300 ° C. or higher to release hydrogen. It is manufactured.

The method for producing a silicon material described in WO 2014/080608 can be represented by the following ideal reaction formula when hydrogen chloride is used as an acid.
3CaSi ₂ +6 HCl → Si ₆ H ₆ +3 CaCl ₂
Si ₆ H ₆ → 6Si + 3H ₂ ↑

However, in the upper reaction for synthesizing Si ₆ H ₆ which is polysilane, water is generally used as a reaction solvent from the viewpoint of removal of by-products and impurities. And, since Si ₆ H ₆ can react with water, in the process of synthesizing the layered silicon compound including the reaction in the upper stage, the layered silicon compound is hardly produced as one containing only Si ₆ H ₆ , and the layered silicon compound is layered The silicon compound is represented by Si ₆ H _s (OH) _t X _u (X is an element or group derived from the anion of an acid, s + t + u = 6, 0 <s <6, 0 <t <6, 0 <u <6) Manufactured as In the above chemical formula, unavoidable impurities such as remaining Ca are not taken into consideration. And the silicon material obtained by heating the said layered silicon compound also contains the element derived from the anion of oxygen or an acid.

The silicon material has a structure in which a plurality of plate-like silicon bodies are stacked in the thickness direction. The plate-like silicon body preferably has a thickness in the range of 10 nm to 100 nm, and more preferably in the range of 20 nm to 50 nm, in order to efficiently insert and extract charge carriers such as lithium ions. The length in the longitudinal direction of the plate-like silicon body is preferably in the range of 0.1 μm to 50 μm. The plate-like silicon body preferably has a (longitudinal length) / (thickness) in the range of 2 to 1000. The layered structure of the plate-like silicon body can be confirmed by observation with a scanning electron microscope or the like. Moreover, this laminated structure is considered to be a remnant of the Si layer in the raw material CaSi ₂ .

  The silicon material preferably includes amorphous silicon and / or silicon crystallites. In particular, in the plate-like silicon body, it is preferable that amorphous silicon be a matrix and silicon crystallites be scattered in the matrix. The size of the silicon crystallite is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, still more preferably in the range of 1 nm to 50 nm, and particularly preferably in the range of 1 nm to 10 nm. The size of the silicon crystallite is calculated from the Scheller equation using the half width of the diffraction peak of the Si (111) plane of the obtained X-ray diffraction chart by performing X-ray diffraction measurement on the silicon material. .

  The amount and size of the plate-like silicon body, amorphous silicon and silicon crystallite contained in the silicon material mainly depend on the heating temperature and heating time. The heating temperature is preferably in the range of 350 ° C. to 950 ° C., and more preferably in the range of 400 ° C. to 900 ° C.

  60-100 mass% is preferable, as for mass% of the negative electrode active material in a negative electrode active material layer, 80-99 mass% is more preferable, and 85-98 mass% is more preferable.

  Although the above-mentioned thing may be used as a binder for negative electrodes, you may employ | adopt the polymer which has a hydrophilic group. By using a polymer having a hydrophilic group as a binder, the capacity of the lithium ion secondary battery is suitably maintained. As a hydrophilic group of the polymer which has a hydrophilic group, carboxyl group, a sulfo group, a silanol group, amino group, a hydroxyl group, phosphate group, such as a phosphate group, etc. are illustrated. Among them, polymers containing a carboxyl group in the molecule such as polyacrylic acid, carboxymethylcellulose and polymethacrylic acid, or polymers containing a sulfo group such as poly (p-styrenesulfonic acid) are preferable.

  A polymer containing a large amount of carboxyl groups and / or sulfo groups, such as polyacrylic acid or a copolymer of acrylic acid and vinyl sulfonic acid, becomes water soluble. The polymer having a hydrophilic group is preferably a water-soluble polymer, and in the chemical structure, a polymer containing a plurality of carboxyl groups and / or sulfo groups in one molecule is preferable.

  The polymer containing a carboxyl group in the molecule can be produced, for example, by a method of polymerizing an acid monomer, a method of giving a carboxyl group to a polymer, or the like. Examples of acid monomers include acrylic acid, methacrylic acid, vinylbenzoic acid, crotonic acid, pentenoic acid, angelic acid, tiglic acid, etc. Acid monomers having one carboxyl group in the molecule, itaconic acid, mesaconic acid, citraconic acid, fumaric acid And maleic acid, 2-pentenedioic acid, methylene succinic acid, allyl malonic acid, isopropylidene succinic acid, 2,4-hexadiene diacid, acetylene dicarboxylic acid, and other acid monomers having two or more carboxyl groups in the molecule. Be done.

  A copolymer formed by polymerizing two or more kinds of acid monomers selected from the above-mentioned acid monomers may be used as a binder.

  Also, a polymer containing an acid anhydride group formed by condensation of carboxyl groups of a copolymer of acrylic acid and itaconic acid as described in, for example, JP-A 2013-065493 is contained in the molecule. It is also preferable to use a binder as a binder. If the binder has a structure derived from a highly acidic monomer having two or more carboxyl groups in one molecule in the binder, it is easy for the binder to trap lithium ions etc. before the electrolytic decomposition reaction occurs during charging. It is considered. Furthermore, although the polymer has more carboxyl groups per monomer than polyacrylic acid and polymethacrylic acid, the acidity is increased, but the acidity is increased because a predetermined amount of carboxyl groups is changed to an acid anhydride group. Is not too high. Therefore, in the secondary battery having the negative electrode using the polymer as a binder, the initial efficiency is improved, and the input / output characteristics are improved.

  In addition, a crosslinked polymer obtained by crosslinking a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid disclosed in WO 2016/063882 with a diamine may be used as a binder for the negative electrode.

  Examples of the diamine used for the cross-linked polymer include alkylene diamines such as ethylene diamine, propylene diamine and hexamethylene diamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, isophorone diamine, bis (4-aminocyclohexyl) methane and the like. Saturated carbocyclic ring diamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylether, bis (4-aminophenyl) sulfone, benzidine, o-tolidine, 2,4- Aromatic diamines such as tolylene diamine, 2,6-tolylene diamine, xylylene diamine and naphthalene diamine can be mentioned.

  Further, a mixture or a reaction product of a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid and polyamideimide may be used as a binder for the negative electrode.

  Polyamideimide means a compound having two or more amide bonds and two or more imide bonds in the molecule. Polyamideimide is produced by reacting an acid component which is to be a carbonyl moiety in an amide bond and an imide bond, and a diamine component or a diisocyanate component which is to be a nitrogen moiety in an amide bond and an imide bond. In order to obtain a polyamideimide, it may manufacture by the said method, and may purchase a commercially available polyamideimide.

  Examples of acid components used for producing polyamideimides include trimellitic acid, pyromellitic acid, biphenyl tetracarboxylic acid, diphenyl sulfone tetracarboxylic acid, benzophenone tetracarboxylic acid, diphenyl ether tetracarboxylic acid, oxalic acid, adipic acid, malonic acid, Sebacic acid, azelaic acid, dodecanedicarboxylic acid, dicarboxypolybutadiene, dicarboxypoly (acrylonitrile-butadiene), dicarboxypoly (styrene-butadiene), cyclohexane-1,4-dicarboxylic acid, cyclohexane-1,3-dicarboxylic acid, Dicyclohexylmethane-4,4'-dicarboxylic acid, terephthalic acid, isophthalic acid, bis (carboxyphenyl) sulfone, bis (carboxyphenyl) ether, naphthalene dicarboxylic acid, and These anhydrides, acid halides, mention may be made of derivatives. As the acid component, the above compounds may be employed singly or in a plurality, but from the viewpoint of forming an imide bond, an acid component or a carboxyl group is present at the adjacent carbon of the carbon to which the carboxyl group is bonded The equivalent is essential. As the acid component, trimellitic anhydride is preferable in terms of reactivity, heat resistance, and the like. In addition to trimellitic anhydride, in addition to trimellitic anhydride, pyromellitic anhydride, benzophenonetetracarboxylic acid anhydride, biphenyltetramer as a part of the acid component from the viewpoint of tensile strength, tensile modulus of elasticity and electrolytic solution resistance of polyamideimide. It is preferred to employ a carboxylic acid anhydride.

  As a diamine component used for manufacture of polyamidoimide, what is necessary is just to employ | adopt the diamine used for the crosslinked polymer mentioned above. From the viewpoint of heat resistance and solubility, 4,4'-diaminodiphenylmethane, 2,4-tolylenediamine, o-tolidine, naphthalenediamine and isophoronediamine are preferable. From the viewpoint of tensile strength and tensile modulus of polyamideimide, o-tolidine and naphthalenediamine are preferred.

  As a diisocyanate component used for manufacture of polyamidoimide, what substituted the amine of the said diamine component by the isocyanate can be mentioned.

  0.1-20 mass% is preferable, as for mass% of the binder in a negative electrode active material layer, 0.5-15 mass% is more preferable, and 1-10 mass% is further more preferable. When the amount of the binder is too small, the formability is reduced. On the other hand, when the amount of the binder is too large, the energy density is reduced.

Like the positive electrode active material layer, the negative electrode active material layer in the lithium ion secondary battery of the present invention is not required to have a function as a flow path for decomposition gas. Therefore, in the lithium ion secondary battery of the present invention, the basis weight and density of the negative electrode active material layer can be increased. Specifically, the upper limit of the basis weight of the negative electrode active material layer can be increased to 20 mg / cm ² or less, 30 mg / cm ² or less, or 35 mg / cm ² or less per one surface of the general current collector in the current collector . There is no lower limit to the weight per unit area of the negative electrode active material layer, but if it is mentioned dare, each range of 8 mg / cm ² or more and 10 mg / cm ² or more can be mentioned.
The upper limit of the density of the negative electrode active material layer can be increased to 1.6 mg / cm ² or less, 2.0 mg / cm ² or less, or 2.5 mg / cm ² or less. There is no lower limit to the density of the negative electrode active material layer, but if it is mentioned dare, each range of 1.2 g / cm ³ or more, 1.3 g / cm ³ or more, 1.5 g / cm ³ or more can be mentioned.

  Similarly, in the lithium ion secondary battery of the present invention, the porosity of the negative electrode active material layer can be reduced. As an upper limit of the porosity of a negative electrode active material layer, each range of 60% or less, 50% or less, 40% or less, 30% or less, and 20% or less can be mentioned. The lower limit of the porosity of the negative electrode active material layer is, for example, 10% or more, 15% or more, or 20% or more.

  Similarly, in the lithium ion secondary battery of the present invention, the thickness of the negative electrode active material layer can be increased. The lower limit of the thickness of the negative electrode active material layer may be, for example, 50 μm or more, 60 μm or more, or 70 μm or more. As an upper limit of the thickness of a negative electrode active material layer, each range of 300 micrometers or less, 200 micrometers or less, and 150 micrometers or less is mentioned.

  There is no limitation in particular as electrolyte solution of the lithium ion secondary battery of this invention. As a density | concentration of the electrolyte containing lithium salt in electrolyte solution, 1.5-3 mol / L, 1.6-2.8 mol / L, 1.8-2.6 mol / L, 2-2.5 mol / L It can be illustrated. Furthermore, the electrolyte solution containing the electrolyte containing the lithium salt represented by following General formula (1) is preferable.

(R ¹ X ¹ ) (R ² SO ₂ ) NLi General formula (1)
(R ¹ is hydrogen, halogen, an alkyl group which may be substituted by a substituent, a cycloalkyl group which may be substituted by a substituent, an unsaturated alkyl group which may be substituted by a substituent, a substituent Or unsaturated cycloalkyl group which may be substituted, aromatic group which may be substituted by a substituent, heterocyclic group which may be substituted by a substituent, alkoxy group which may be substituted by a substituent An unsaturated alkoxy group which may be substituted by a substituent, a thioalkoxy group which may be substituted by a substituent, an unsaturated thioalkoxy group which may be substituted by a substituent, CN, SCN or OCN Be done.
R ² represents a hydrogen, a halogen, an alkyl group which may be substituted by a substituent, a cycloalkyl group which may be substituted by a substituent, an unsaturated alkyl group which may be substituted by a substituent, a substituent An unsaturated cycloalkyl group which may be substituted, an aromatic group which may be substituted by a substituent, a heterocyclic group which may be substituted by a substituent, an alkoxy group which may be substituted by a substituent, An unsaturated alkoxy group which may be substituted, a thioalkoxy group which may be substituted, an unsaturated thioalkoxy group which may be substituted, and a substituent selected from CN, SCN and OCN Ru.
Further, R ¹ and R ² may be bonded to each other to form a ring.
X ¹ is selected from SO ₂ , C = O, C = S, R ^a P = O, R ^b P = S, S = O, and SiOO.
R ^a and R ^b each independently represent hydrogen, a halogen, an alkyl group which may be substituted by a substituent, a cycloalkyl group which may be substituted by a substituent, or a substituent which may be substituted by a substituent A saturated alkyl group, an unsaturated cycloalkyl group which may be substituted by a substituent, an aromatic group which may be substituted by a substituent, a heterocyclic group which may be substituted by a substituent, a substituent Alkoxy group which may be substituted, unsaturated alkoxy group which may be substituted by a substituent, thioalkoxy group which may be substituted by a substituent, unsaturated thioalkoxy group which may be substituted by a substituent, OH , SH, CN, SCN, OCN.
In addition, R ^a and R ^b may combine with R ¹ or R ² to form a ring. )

  The wording "may be substituted with a substituent" in the chemical structure represented by the above general formula (1) will be described. For example, "an alkyl group which may be substituted by a substituent" means an alkyl group in which one or more of the hydrogens of the alkyl group is substituted by a substituent, or an alkyl group having no substituent. Do.

  Examples of the substituent in the phrase "may be substituted with a substituent" include alkyl group, alkenyl group, alkynyl group, cycloalkyl group, unsaturated cycloalkyl group, aromatic group, heterocyclic group, halogen, OH , SH, CN, SCN, OCN, nitro group, alkoxy group, unsaturated alkoxy group, amino group, alkylamino group, dialkylamino group, dialkylamino group, aryloxy group, acyl group, alkoxycarbonyl group, acyloxy group, aryloxycarbonyl group, Acylamino group, alkoxycarbonylamino group, aryloxycarbonylamino group, sulfonylamino group, sulfamoyl group, carbamoyl group, alkylthio group, arylthio group, sulfonyl group, sulfinyl group, ureido group, phosphoric acid amide group, sulfo group, carboxyl group, Hydroxamic acid group, Rufino group, a hydrazino group, an imino group, and a silyl group. These substituents may be further substituted by a substituent. When two or more substituents are present, the substituents may be the same or different.

  The lithium salt is preferably one represented by the following general formula (1-1).

(R ¹³ X ² ) (R ¹⁴ SO ₂ ) NLi general formula (1-1)
(R ¹³ and R ¹⁴ are each independently C _n H _a F _b Cl _{c B r d} I _e (CN) _f (SCN) _g (OCN) _h .
n, a, b, c, d, e, f, g and h are each independently an integer of 0 or more and satisfy 2n + 1 = a + b + c + d + e + f + g + h.
Further, R ²³ and R ²⁴ may be bonded to each other to form a ring, in which case 2n = a + b + c + d + e + f + g + h is satisfied.
X ² is selected from SO ₂ , C = O, C = S, R ^c P = O, R ^d P = S, S = O, Si = O.
R ^c and R ^d each independently represent hydrogen, a halogen, an alkyl group which may be substituted by a substituent, a cycloalkyl group which may be substituted by a substituent, or a group which may be substituted by a substituent A saturated alkyl group, an unsaturated cycloalkyl group which may be substituted by a substituent, an aromatic group which may be substituted by a substituent, a heterocyclic group which may be substituted by a substituent, a substituent Alkoxy group which may be substituted, unsaturated alkoxy group which may be substituted by a substituent, thioalkoxy group which may be substituted by a substituent, unsaturated thioalkoxy group which may be substituted by a substituent, OH , SH, CN, SCN, OCN.
R ^c and R ^d may combine with R ²³ or R ²⁴ to form a ring. )

  The meaning of the wording “in the substituent may be substituted” in the chemical structure represented by General Formula (1-1) is the same as that described in General Formula (1).

In the chemical structure represented by the above general formula (1-1), n is preferably an integer of 0 to 6, more preferably an integer of 0 to 4, and particularly preferably an integer of 0 to 2. When R ¹³ and R ^{14 in the} chemical structure represented by the above general formula (1-1) are combined to form a ring, n is preferably an integer of 1 to 8, and 1 to 7 The integer of is more preferable, and the integer of 1 to 3 is particularly preferable.

  The lithium salt is more preferably one represented by the following general formula (1-2).

(R ¹⁵ SO ₂ ) (R ¹⁶ SO ₂ ) NLi general formula (1-2)
(R ¹⁵ and R ¹⁶ are each independently C _n H _a F _b Cl _{c B r d} I _e .
n, a, b, c, d and e are each independently an integer of 0 or more and satisfy 2n + 1 = a + b + c + d + e.
R ¹⁵ and R ¹⁶ may be bonded to each other to form a ring, in which case 2n = a + b + c + d + e is satisfied. )

In the chemical structure represented by the above general formula (1-2), n is preferably an integer of 0 to 6, more preferably an integer of 0 to 4, and particularly preferably an integer of 0 to 2. When R ¹⁵ and R ^{16 in the} chemical structure represented by the above general formula (1-2) are combined to form a ring, n is preferably an integer of 1 to 8, and 1 to 7 The integer of is more preferable, and the integer of 1 to 3 is particularly preferable.

  Moreover, in the chemical structure represented by the said General formula (1-2), that whose a, c, d, e is 0 is preferable.

The lithium salt is (CF ₃ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, FSO ₂ (CF ₃ SO ₂ ) NLi, (SO ₂ CF ₂ CF ₂ SO ₂ ) NLi, (SO ₂ CF ₂ CF ₂ CF ₂ SO ₂ ) NLi, FSO ₂ (CH ₃ SO ₂ ) NLi, FSO ₂ (C ₂ F ₅ SO ₂ ) NLi, or FSO ₂ (C ₂ H ₅ SO ₂ ) NLi Particularly preferred is one selected from

  In the electrolytic solution, one type of lithium salt represented by General Formula (1) may be adopted, or a plurality of types may be used in combination. In addition, the electrolytic solution may contain an electrolyte other than the lithium salt represented by the general formula (1).

As an electrolyte other than lithium salt represented by the general formula _{(1), LiPF 6, LiPF} 2 (OCOCOO) 2, LiBF 4, the LiAsF ₆ and _Li 2 SiF ₆ Specific exemplified.

  The electrolytic solution contains an organic solvent for dissolving the electrolyte. As the organic solvent, an organic solvent usable for the non-aqueous secondary battery may be adopted, and in particular, it is preferable to adopt a low polarity organic solvent which hardly dissolves aluminum.

  Examples of the low polar organic solvent include linear carbonates represented by the following general formula (2).

R ²⁰ OCOOR ²¹ general formula (2)
^{(R 20, R 21} are each independently a linear alkyl _{C n H a F b Cl c} Br d I e, _{or, C m H f F g Cl} h Br i I contains a cyclic alkyl in the chemical structure .n selected from any of _j is an integer of 1 or more, m is an integer of 3 or more, a, b, c, d , e, f, g, h, i, j are each independently 0 or an integer And 2n + 1 = a + b + c + d + e, 2m-1 = f + g + h + i + j)

  In the linear carbonate represented by the above general formula (2), n is preferably an integer of 1 to 6, more preferably an integer of 1 to 4, and particularly preferably an integer of 1 to 2. m is preferably an integer of 3 to 8, more preferably an integer of 4 to 7, and particularly preferably an integer of 5 to 6.

  Among the linear carbonates represented by the above general formula (2), those represented by the following general formula (2-1) are particularly preferable.

R ²² OCOOR ²³ general formula (2-1)
(R ²² and R ²³ are each independently selected from any of C _n H _a F _b which is a linear alkyl, or C _m H _f F _g which includes cyclic alkyl in its chemical structure. N is 1 The above integer, m is an integer of 3 or more, a, b, f and g are each independently an integer of 0 or more, and 2n + 1 = a + b and 2m-1 = f + g are satisfied.

  In the linear carbonate represented by the above general formula (2-1), n is preferably an integer of 1 to 6, more preferably an integer of 1 to 4, and particularly preferably an integer of 1 to 2. m is preferably an integer of 3 to 8, more preferably an integer of 4 to 7, and particularly preferably an integer of 5 to 6.

  Among the linear carbonates represented by the above general formula (2-1), dimethyl carbonate (hereinafter sometimes referred to as "DMC"), diethyl carbonate (hereinafter sometimes referred to as "DEC"), ethyl methyl Carbonate (hereinafter sometimes referred to as "EMC"), fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate, bis (fluoromethyl) carbonate, bis (difluoromethyl) carbonate, bis (trifluoromethyl) Carbonate, fluoromethyl difluoromethyl carbonate, 2,2,2-trifluoroethyl methyl carbonate, pentafluoroethyl methyl carbonate, ethyl trifluoromethyl carbonate, bis (2,2,2-trifluoroethyl ether ) Carbonate is particularly preferred.

  As the linear carbonate, one type may be used for the electrolytic solution, or a plurality of types may be used in combination. By using a plurality of linear carbonates in combination, the low temperature fluidity of the electrolytic solution, the lithium ion transportability at low temperature, and the like can be suitably secured. As a combination example of a linear carbonate, two or three combinations selected from DMC, DEC and EMC can be mentioned. In the combined use of DMC and DEC or EMC, the molar ratio thereof is preferably in the range of DMC: DEC or EMC = 60: 40 to 95: 5, more preferably in the range of 70:30 to 95: 5, The range of 80:20 to 95: 5 is more preferable.

  In the electrolytic solution, in addition to the above-mentioned chain carbonate, other organic solvents (hereinafter, sometimes simply referred to as "other organic solvents") which can be used for electrolytic solution such as lithium ion secondary battery are contained. May be

  It is preferable that the above-mentioned linear carbonate is contained in 70% by volume, 70% by mass or more or 70% by mol or more, 80% by volume, 80% by mass or more based on the total organic solvent contained in the electrolytic solution. Or more preferably contained at 80% by mol or more, further preferably contained at 90% by volume, 90% by mass or more, or 90% by mol or more, and contained by 95% by volume, 95% by mass or more or 95% by mol or more Is particularly preferred. All organic solvents contained in the electrolytic solution may be the above-mentioned chain carbonate.

  Specific examples of other organic solvents include nitriles such as acetonitrile, propionitrile, acrylonitrile and malononitrile, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 1, 3-dioxane, 1,4-dioxane, 2,2-dimethyl-1,3-dioxolane, 2-methyltetrahydropyran, 2-methyltetrahydrofuran, ethers such as crown ether, fluoroethylene carbonate, 4- (trifluoromethyl) Fluorine-containing cyclic carbonates such as 1,3-dioxolan-2-one, fluorine-free cyclic carbonates such as ethylene carbonate and propylene carbonate, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, N) -Methyl Amides such as lolidone, isocyanates such as isopropyl isocyanate, n-propyl isocyanate, chloromethyl isocyanate, methyl acetate, ethyl acetate, butyl acetate, propyl acetate, methyl propionate, methyl formate, ethyl formate, vinyl acetate, methyl acrylate, Esters such as methyl methacrylate, epoxys such as glycidyl methyl ether, epoxy butane, 2-ethyl oxirane, oxazoles, oxazoles such as 2-ethyl oxazole, oxazoline, 2-methyl-2-oxazoline, acetone, methyl ethyl ketone, methyl isobutyl Ketones such as ketones, acid anhydrides such as acetic anhydride and propionic acid anhydride, sulfones such as dimethyl sulfone and sulfolane, sulfoxides such as dimethyl sulfoxide, 1-nit Nitros such as propane and 2-nitropropane, furans such as furan and furfural, cyclic esters such as γ-butyrolactone, γ-valerolactone and δ-valerolactone, aromatic heterocycles such as thiophene and pyridine, tetrahydro Heterocycles such as -4-pyrone, 1-methyl pyrrolidine, and N-methyl morpholine; and phosphoric esters such as trimethyl phosphate and triethyl phosphate can be given.

As a ratio of lithium salt represented by General formula (1) with respect to the whole electrolyte in electrolyte solution, 30-100 mol% is preferable, 50-95 mol% is more preferable, and 70-90 mol% is more preferable. The concentration of the electrolyte containing a lithium salt represented by the general formula (1) in the electrolytic solution is 1.5 to 3 mol / L, 1.6 to 2.8 mol / L, 1.8 to 2.6 mol / L And 2-2.5 mol / L can be exemplified.
Furthermore, it is preferable that the linear carbonate represented by General formula (2) is contained in the electrolyte solution by molar ratio 2-8 with respect to the lithium salt represented by General formula (1). And the molar ratio of 2.5 to 7.5 is more preferable, and the molar ratio of 3 to 6 is particularly preferable.

  By the way, since the concentration of the electrolyte in a general electrolytic solution is about 1 mol / L, the ratio of the lithium salt, the concentration of the electrolyte, or the chain carbonate represented by the general formula (2) and the general formula (1) An electrolyte having a molar ratio to the represented lithium salt within the above range may be said to have a relatively high concentration.

A high concentration electrolyte has a higher viscosity than a low concentration electrolyte and tends to interfere with the flow of decomposition gas. Therefore, in the lithium ion secondary battery using the high concentration electrolyte, the decomposition gas tends to be retained inside the separator bag and in the electrode body as compared to the lithium ion secondary battery using the low concentration electrolyte it is conceivable that.
However, the lithium ion secondary battery of the present invention has a porous layer to be a flow path for the decomposition gas, and the decomposition gas can be efficiently discharged to the outside of the electrode body through the porous layer, so a high concentration electrolyte Can be suitably selected.

  A known additive may be added to the electrolytic solution without departing from the scope of the present invention. Examples of known additives include cyclic carbonates having unsaturated bonds represented by vinylene carbonate (VC), vinyl ethylene carbonate (VEC), methyl vinylene carbonate (MVC), ethyl vinylene carbonate (EVC); phenyl ethylene carbonate and the like A carbonate compound represented by erythritan carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic acid anhydride, cyclopentane tetracarboxylic acid Dianhydrides, carboxylic acid anhydrides represented by phenylsuccinic anhydride; γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, ε-caprolactone Lactones; cyclic ethers represented by 1,4-dioxane; ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, tetramethylthiuram Sulfur-containing compounds represented by monosulfide; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methyl succinimide Nitrogen-containing compounds represented by: monofluorophosphate, phosphate represented by difluorophosphate; saturated hydrocarbon compounds represented by heptane, octane and cycloheptane; biphenyl, alkylbiphenyl, terphenyl, ter Partially hydrogenated form of phenyl Shirubenzen, t- butyl benzene, t-amyl benzene, diphenyl ether, unsaturated hydrocarbon compounds and the like typified by dibenzofuran.

  In the lithium ion secondary battery of the present invention, the electrode body in which the positive electrode, the separator and the negative electrode are stacked may be a wound type in which the electrode body is wound, or the positive electrode, the separator and the negative electrode are stacked in a planar state It may be a laminated type as it is. However, in the lithium ion secondary battery of the present invention, a porous layer is formed on the separator and the negative electrode active material layer. In order to control the flow path of the decomposition gas formed by the two porous layers to a suitable size and position, the lithium ion secondary battery of the present invention is preferably of the laminated type.

  As a material of the container of the lithium ion secondary battery of this invention, the laminated body which laminated | stacked metal, such as aluminum, stainless steel, resin, and aluminum, and resin can be illustrated. The shape of the container of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as cylindrical, square, coin, and laminate types can be adopted.

The pressure-sensitive safety mechanism changes the structure of the lithium ion secondary battery when the internal pressure of the container of the lithium ion secondary battery is increased to a predetermined value or more when the decomposition gas is generated at the time of overcharge and the decomposition gas It is a mechanism which stops the function as a battery of a lithium ion secondary battery.
Specifically, a current interrupt device (CID) can be mentioned which is activated by an increase in the internal pressure of the container to interrupt the electrical path of the lithium ion secondary battery. As the CID, for example, when the internal pressure of the battery container as disclosed in Japanese Patent Application Laid-Open No. 2013-131402, Japanese Patent Application Laid-Open No. 2014-10967, the Patent Document 1 described above, etc., a terminal of a lithium ion secondary battery There may be mentioned an apparatus for breaking an electrical path connecting the electrode and the electrode. Alternatively, an apparatus disclosed in, for example, JP-A-2017-157341, which shorts the positive electrode terminal and the negative electrode terminal when the internal pressure of the container of the battery increases can be mentioned.

  The lithium ion secondary battery of the present invention can be mounted on a vehicle. The lithium ion secondary battery maintains a large charge and discharge capacity and has excellent cycle performance, so a vehicle equipped with the lithium ion secondary battery is a high performance vehicle. In particular, since the lithium ion secondary battery of the present invention has a porous layer serving as a flow path for the decomposition gas, even when the basis weight of the active material layer is increased or the density of the active material layer is increased, The decomposition gas derived from lithium carbonate can be efficiently discharged to the outside of the electrode body. Therefore, the lithium ion secondary battery of the present invention is suitable to be a high capacity, high output lithium ion secondary battery. That is, the lithium ion secondary battery of the present invention is useful as a lithium ion secondary battery used for a large electric device represented by a vehicle.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. In the range which does not deviate from the summary of the present invention, it can carry out with various forms which gave change, improvement, etc. which a person skilled in the art can make.

  Below, various specific examples are shown and this invention is more concretely demonstrated to it. The present invention is not limited by these specific examples.

Example 1
An explanatory view schematically showing the positive electrode, the negative electrode and the separator in the lithium ion secondary battery of Example 1 is shown in FIG. 1, and a partially cutaway explanatory view schematically showing the positive electrode in the lithium ion secondary battery of Example 1. Is shown in FIG. An explanatory view schematically showing the inside of the container in the lithium ion secondary battery of Example 1 is shown in FIG. Hereinafter, the extension direction of the tab portion means the first direction shown in FIG. Further, the width direction means the second direction shown in FIG. The first direction and the second direction are orthogonal to each other. Furthermore, hereinafter, the front side in the first direction may be simply referred to as the front side, and the rear side in the first direction may be simply referred to as the rear side, as necessary.

The lithium ion secondary battery of Example 1 which is one aspect of the lithium ion secondary battery of the present invention is
A container 8, a positive electrode 1, a separator 2, a negative electrode 3 and an electrolyte 4 contained in the container 8; and a pressure sensitive safety mechanism 55 that operates in response to an increase in the internal pressure of the container;
The positive electrode 1 includes a positive electrode current collector 10, and a positive electrode active material layer 15 which contains a positive electrode active material and lithium carbonate and is provided on the positive electrode current collector 10.
The negative electrode 3 includes a negative electrode current collector 30 and a negative electrode active material layer 35 provided on the negative electrode current collector 30 and containing a negative electrode active material,
It is a lithium ion secondary battery in which the porous layer 18 is provided on the said separator 2 and the said negative electrode active material layer 35, respectively.

  As shown in FIG. 1, the lithium ion secondary battery of Example 1 has a plurality of positive electrodes 1, a separator 2 and a negative electrode 3.

  The porous layer 18 is formed on the separator 2 and the negative electrode active material layer 35 described later. Hereinafter, the porous layer formed on the separator plate 20 is referred to as the separator side porous layer 18s, and the porous layer formed on the negative electrode active material layer is referred to as the negative electrode side porous layer 18n. The separator side porous layer 18s is included in the separator 2, and the negative electrode side porous layer 18n is included in the negative electrode.

As shown in FIG. 2, the positive electrode 1 is composed of a positive electrode current collector 10 and a positive electrode active material layer 15.
As shown in FIG. 2, the positive electrode current collector 10 has a generally rectangular plate-like general current collector 11, and a strip extending from the one end in the first direction of the general current collector 11 in the first direction. And a tab portion 12. Hereinafter, as necessary, the general current collection portion 11 of the positive electrode current collector 10 may be referred to as a general positive electrode current collection portion 11. Also, the tab portion 12 of the positive electrode current collector 10 may be referred to as a positive electrode tab portion 12.
The base end 12 r of the positive electrode tab portion 12, that is, the end of the positive electrode tab portion 12 on the side of the general positive electrode current collector 11 is located rearward of the front end 12 t of the positive electrode tab portion 12 in the first direction. Therefore, the tip end 12 t of the positive electrode tab portion 12 is located on the front side in the first direction with respect to the base end 12 r of the positive electrode tab portion 12.

The positive electrode active material layer 15 contains a positive electrode active material, lithium carbonate, a conductive aid and a binder. The positive electrode active material layer 15 is formed on both sides of the general positive electrode current collector 11 in the positive electrode current collector 10.
More specifically, the positive electrode active material layer 15 is formed in the region on the rear side of the general positive electrode current collector portion 11. The area on the rear side is referred to as a coated part 11 r.
On the other hand, the positive electrode active material layer 15 is not formed in the region on the opposite side of the coated portion 11 r in the general positive electrode current collector 11, that is, the region on the front side of the general positive electrode current collector 11. In other words, the positive electrode current collector 10 is the general positive electrode current collector portion 11 and the positive electrode active material layer 15 is formed between the coated portion 11 r on which the positive electrode active material layer 15 is formed and the positive electrode tab portion 12. It has the uncoated part 11f which is not carried out. The uncoated parts 11 f are respectively present on both sides of the general positive electrode current collecting part 11.

  The separator 2 in the lithium ion secondary battery of Example 1 is composed of a separator main body 2m and a separator side porous layer 18s. The separator body 2m is in the form of a bag in which two rectangular separator plates 20 made of resin are welded at the peripheral portion 20r. A fixed peripheral edge portion 28 to which two separator plates 20 are fixed is formed on the peripheral edge portion 20r of the separator main body 2m. In the peripheral edge portion 20r of the rectangular separator main body 2m, the fixed peripheral edge portion 28 has a gap 29 on one side located on the front side, and is continuously formed on the entire periphery of the peripheral edge portion 20r except for that.

The separator side porous layer 18s is formed on each of the two separator plates 20. Each separator side porous layer 18s is located on the outer surface side of the bag-like separator body 2m.
The separator side porous layer 18s has a rectangular shape, and covers substantially the entire area of the inner periphery of the fixing peripheral edge 28 in the separator plate 20.

Of the positive electrode 1, the general positive electrode current collecting portion 11, the positive electrode active material layer 15, and the base end 12r of the positive electrode tab portion 12 are respectively accommodated in the bag interior 2c of the separator body 2m. The positive electrode tab portion 12 is inserted into the gap 29 of the fixed peripheral edge portion 28, and the tip 12t of the positive electrode tab portion 12 is exposed to the outside of the bag interior 2c of the separator body 2m.
As shown in FIGS. 1 and 2, in the area without the gap 29 and the positive electrode tab portion 12, the front and rear sides of the positive electrode active material layer 15 are shielded by the fixing peripheral portion 28. Further, the non-coated portion 11 f of the positive electrode current collector 10 is interposed between the positive electrode active material layer 15 and the fixing peripheral portion 28.
On the other hand, in the region where the gap 29 and the positive electrode tab portion 12 are present, there is no fixed peripheral edge portion 28 on the tip side of the positive electrode active material layer 15, and the uncoated portion 11 f Intervene in

As shown in FIG. 1, the negative electrode 3 includes a negative electrode current collector 30, a negative electrode active material layer 35 formed on both sides of the negative electrode current collector 30, and a negative electrode formed on each negative electrode active material layer 35. And the side porous layer 18n. The negative electrode current collector 30 has a substantially rectangular plate shape, and a general negative electrode current collector 31 which is slightly larger than the general positive electrode current collector 11, and further to the front end of the general negative electrode current collector 31. And an elongated strip-like negative electrode tab portion 32.
The negative electrode active material layer 35 is formed on both sides of the general negative electrode current collector 31.

As shown in FIG. 3, in the lithium ion secondary battery of Example 1, the positive electrode-separator complex 7 in which the positive electrode 1 is accommodated in the separator 2, the negative electrode 3, the container 8, the electrolyte solution 4, A pressure safety mechanism 55 is provided. The electrode assembly 6 in which the positive electrode-separator composite 7 and the negative electrode 3 are alternately stacked is accommodated in the container 8, and the electrolytic solution 4 is poured into the gap.
The positive electrode tab portions 12 of the respective positive electrodes 1 are put together and welded to the positive electrode conductive member 51. The positive electrode conductive member 51 is connected to the positive electrode terminal 52 via the pressure sensitive safety mechanism 55.
Hereinafter, a method of manufacturing the lithium ion secondary battery of Example 1 will be described.

(Positive electrode)
90 parts by mass of LiNi _82/100 Co _14/100 Al _4/100 O ₂ which is a positive electrode active material, 5 parts by mass of lithium carbonate, 2 parts by mass of acetylene black which is a conductive agent, polyfluoride which is a binder 3 parts by mass of vinylidene and an appropriate amount of N-methyl-2-pyrrolidone are mixed to form a slurry.
An aluminum foil corresponding to a JIS A 8000 series alloy having a thickness of 15 μm is prepared, and a predetermined portion of one surface of this aluminum foil is coated with the above-mentioned slurry in a film form using a doctor blade. Then, the aluminum foil coated with the slurry is dried to remove N-methyl-2-pyrrolidone. Do the same for the other side of the aluminum foil. Then, the positive electrode is obtained by pressing, heating and drying, and cutting into a predetermined shape. The application amount of the slurry and the pressing pressure are set so that the density of the positive electrode active material layer is 3.55 g / cm ³ , the thickness is 188 μm, and the porosity is 20%. The positive electrode current collector in this positive electrode has a general positive electrode current collector portion and a tab portion, and the general positive electrode current collector portion has a coated portion and an uncoated portion. The positive electrode active material layer is formed in the coated portion, and not formed in the uncoated portion.

(Separator)
As a separator plate, a rectangular polyethylene porous film having a thickness of 16 μm is prepared.
Apart from this, 96 parts by mass of powdery Al ₂ O ₃ which is a ceramic, 4 parts by mass of polyvinylidene fluoride which is a binder, and an appropriate amount of N-methyl-2-pyrrolidone are mixed to obtain a porous slurry Prepare. The porous slurry is applied in a rectangular shape on the central portion of one side of the separator plate. The coated separator plate is dried to remove N-methyl-2-pyrrolidone to form a separator-side porous layer. Thereafter, the separator plate having the porous layer formed thereon is obtained by pressing and drying by heating. The application amount of the porous slurry and the pressing pressure are set so that the density of the porous layer is 1.36 g / cm ³ , the thickness is 5 μm, and the porosity is 65.6%.
The integral product of the separator-side porous layer and the separator plate is stacked two sheets with the separator-side porous layer facing outward, and the three sides of the peripheral portion are welded while avoiding the separator-side porous layer, Do. Inside the said bag, the base end part of the general positive electrode current collection part of a positive electrode, a positive electrode active material layer, and a positive electrode tab part is accommodated. At this time, the positive electrode tab portion is taken out of the remaining side to the outside of the bag. Then, by welding the remaining one side of the separator plate while leaving a gap, a positive electrode-separator complex having a bag-like separator and a positive electrode accommodated inside the bag of the separator can be obtained. The porosity of the separator plate is 41%, and the density is 0.53 g / cm ³ .

(Negative electrode)
Prepare concentrated hydrochloric acid containing 1% by mass of hydrogen fluoride, add 5 g of CaSi ₂ to 20 ml of the concentrated hydrochloric acid in an ice bath at 0 ° C. and stir for 1 hour, then add water and stir for another 5 minutes The reaction solution is obtained. The reaction solution is filtered, and the yellow solid obtained is washed with water and ethanol, and dried under reduced pressure to obtain a layered polysilane. The layered polysilane is heated at 500 ° C. under an argon atmosphere to obtain a silicon material in which hydrogen is released from the polysilane.
The negative electrode is manufactured as follows using the said silicon material as a negative electrode active material.

  78 parts by mass of the above-mentioned silicon material as a negative electrode active material, 13 parts by mass of acetylene black as a conductive additive, and 9 parts by mass of a crosslinked polymer obtained by crosslinking polyacrylic acid with diamine as a binder . The mixture is dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry.

A copper foil having a thickness of 20 μm is prepared, and a predetermined portion of one side of the copper foil is coated with the above-mentioned slurry in the form of a film using a doctor blade. Then, the copper foil coated with the slurry is dried to remove N-methyl-2-pyrrolidone. The same operation is performed on the other surface of the copper foil, and then cut into a predetermined shape, whereby an integral product of the negative electrode current collector and the negative electrode active material layer can be obtained.
The same porous slurry as that used for the above-mentioned separator side porous layer is prepared, and it applies to the whole surface of each negative electrode active material layer. Thereafter, by pressing and drying, a negative electrode in which a negative electrode active material layer and a negative electrode side porous layer are formed on both surfaces of the negative electrode current collector can be obtained. The applied amount of slurry and the pressing pressure at this time are: density of the negative electrode active material layer is 1.45 g / cm ³ , thickness is 67 μm, porosity is 34%, and density of the porous layer is 1.36 g / cm ³ Make the thickness 5 μm and the porosity 65.6%.

(Electrolyte solution)
(FSO ₂ ) ₂ NLi is dissolved in a solvent in which dimethyl carbonate and ethyl methyl carbonate are mixed at a molar ratio of 9: 1 to produce an electrolyte solution having a concentration of (FSO ₂ ) ₂ NLi of 2 mol / L. In the said electrolyte solution, the organic solvent is contained by molar ratio 4 with respect to lithium salt.

(Assembly of lithium ion secondary battery)
The positive electrode-separator complex and the negative electrode are alternately stacked to form an electrode body, which is placed in a container. Each negative electrode tab part of an electrode body is put together and welded to the conductive member for negative electrodes. The negative electrode conductive member is electrically connected to the negative electrode external terminal. Similarly, the positive electrode tabs of the electrode assembly are welded together and welded to the positive electrode conductive member. The positive electrode conductive member is electrically connected to the positive electrode external terminal, but a pressure sensitive safety mechanism is interposed between the positive electrode conductive member and the positive electrode external terminal. The electrolytic solution is put in a container containing the electrode body, and the container is sealed to obtain the lithium ion secondary battery of Example 1.

Since the lithium ion secondary battery of Example 1 has a porous layer, the decomposition gas generated in the positive electrode active material layer by the decomposition of lithium carbonate at the time of overcharge is outside the bag of the separator through the porous layer, that is, of the electrode body It can be discharged outside. When the internal pressure of the container rises due to the decomposition gas discharged to the outside of the electrode body, a part of the pressure-sensitive safety mechanism is broken and the electrical connection between the positive electrode tab portion and the positive electrode external terminal is impaired. Charging of the lithium ion secondary battery of 1 stops.
Further, in the lithium ion secondary battery of Example 1, the porous layer is constituted of the separator side porous layer on the separator and the negative electrode side porous layer on the negative electrode active material layer, and the separator side porous layer It can function as one porous layer adjacent to the negative electrode side porous layer. Then, a relatively large porous layer intervenes between the separator and the negative electrode active material, and the decomposition gas can be more suitably discharged to the outside of the electrode body through the porous layer.

(Example 2)
The lithium ion secondary battery of Example 2 is substantially the same as the lithium ion secondary battery of Example 1, except that the positive electrode active material layer includes an olivine positive electrode active material layer. An explanatory view schematically showing a positive electrode and a separator in the lithium ion secondary battery of Example 2 is shown in FIG.

As shown in FIG. 4, the positive electrode 1 in the lithium ion secondary battery of Example 2 includes a positive electrode current collector 10 and a positive electrode active material layer 15. The positive electrode active material layer 15 is composed of a general positive electrode active material layer 16 and an olivine positive electrode active material layer 17.
The positive electrode current collector 10 has the same shape as that of the positive electrode current collector 10 in the lithium ion secondary battery of Example 1, and the coated portion 11 r of the general positive electrode current collector portion 11 on both sides of the positive electrode current collector 10 A general positive electrode active material layer 16 and an olivine positive electrode active material layer 17 are provided.
More specifically, the general positive electrode active material layer 16 and the olivine positive electrode active material layer 17 each have a band shape, and are alternately arranged along the second direction with the longitudinal direction directed to the first direction. One of the olivine positive electrode active material layers 17 is continued to the rear side of the positive electrode tab portion 12.
The thickness of each general positive electrode active material layer 16 is 188 μm, the porosity is 20%, and the density is 3.55 g / cm ³ . The thickness of each olivine positive electrode active material layer 17 is 176 μm, the porosity is 20.7%, and the density is 3.04 g / cm ³ .

The general positive electrode active material layer in the lithium ion secondary battery of Example 2 is 90 parts by mass of LiNi _82/100 Co _14/100 Al _4/100 O ₂ which is a positive electrode active material, 5 parts by mass of lithium carbonate, and a conductive support The positive electrode active material layer of Example 1 is prepared using a slurry in which 2 parts by mass of acetylene black as a binder, 3 parts by mass of polyvinylidene fluoride as a binder, and an appropriate amount of N-methyl-2-pyrrolidone are mixed. Form in the same way.
In the olivine positive electrode active material layer, 87.5 parts by mass of LiFePO ₄ as a positive electrode active material, 5 parts by mass of acetylene black as a conductive additive, 7.5 parts by mass of polyvinylidene fluoride as a binder, and an appropriate amount The slurry is used in the same manner as in the positive electrode active material layer of Example 1 using a slurry mixed with N-methyl-2-pyrrolidone.
The general positive electrode active material layer 16 and the olivine positive electrode active material layer 17 may be simultaneously formed by coating, or one of them may be formed first and the other may be formed later.

  The lithium ion secondary battery of Example 2 has a porous layer which can function as a flow path for the decomposition gas as in the lithium ion secondary battery of Example 1. Therefore, the lithium ion secondary battery is generated by decomposition of lithium carbonate during overcharge. The decomposition gas can be well discharged to the outside of the electrode body.

  In addition, since the olivine positive electrode active material layer 17 is excellent in rigidity as compared with the general positive electrode active material layer 16, the olivine positive electrode is obtained even when the positive electrode 1 is compressed to such an extent that the pores of the general positive electrode active material layer 16 are crushed. The pores of the active material layer 17 are not easily crushed. Therefore, the olivine positive electrode active material layer 17 can also preferably function as a flow path for the above-mentioned decomposition gas in the lithium ion secondary battery. That is, the lithium ion secondary battery of Example 2 has two discharge channels for the decomposition gas, that is, the porous layer 18 and the olivine positive electrode active material layer 17. For this reason, the lithium ion secondary battery of Example 2 can perform better discharge of the decomposition gas from the inside of the electrode body to the outside.

(Example 3)
The lithium ion secondary battery of Example 3 is the same as Example 1 except that the olivine positive electrode active material layer is provided on the positive electrode current collector, and the general positive electrode active material layer is further provided on the olivine positive electrode active material layer. It is roughly the same as a lithium ion secondary battery. An explanatory view schematically showing the positive electrode and the separator in the lithium ion secondary battery of Example 3 is shown in FIG.

As shown in FIG. 5, the positive electrode 1 in the lithium ion secondary battery of Example 3 includes a positive electrode current collector 10 and a positive electrode active material layer 15. The positive electrode active material layer 15 is composed of a general positive electrode active material layer 16 and an olivine positive electrode active material layer 17. The positive electrode current collector 10 has the same shape as the positive electrode current collector 10 in the lithium ion secondary battery of Example 1, and on both sides of the positive electrode current collector 10, the olivine is applied to the coated portion 11r of the general positive electrode current collector portion 11. The positive electrode active material layer 17 is provided, and the general positive electrode active material layer 16 is further provided on the olivine positive electrode active material layer 17.
The thickness of the general positive electrode active material layer 16 is 188 μm, the porosity is 20%, and the density is 3.55 g / cm ³ . The thickness of the olivine positive electrode active material layer 17 is 176 μm, the porosity is 20.7%, and the density is 3.04 g / cm ³ .

  The general positive electrode active material layer 16 and the olivine positive electrode active material layer 17 in the lithium ion secondary battery of Example 3 are respectively the general positive electrode active material layer 16 and the olivine positive electrode active material layer 17 in the lithium ion secondary battery of Example 2. The same composition as

  Like the lithium ion secondary battery of Example 1, the lithium ion secondary battery of Example 3 can well discharge the decomposition gas from the inside of the electrode body to the outside by having the porous layer 18.

  Further, in the lithium ion secondary battery of Example 3, as in the lithium ion secondary battery of Example 2, the olivine positive electrode active material layer 17 can be used as a discharge channel for the decomposition gas, so from the electrode assembly to the outside The discharge of decomposition gas can be performed better.

1: positive electrode 2: separator 2 c: inside of bag 3: negative electrode 4: electrolyte 55: pressure sensitive safety mechanism 6: electrode body 7: positive electrode-separator complex 8: container 10: positive electrode current collector 11: general positive electrode current collector (General current collector)
11r: coated portion 11f: uncoated portion 12: positive electrode tab portion (tab portion) 15: positive electrode active material layer 18: porous layer 18s: separator side porous layer 18n: negative electrode side porous layer 20: separator plate 20r : Peripheral part 28: Fixed peripheral part 29: Gap 30: Negative electrode current collector 31: General negative electrode current collector 32: Negative electrode tab part 35: Negative electrode active material layer

Claims (7)

A container, a positive electrode contained in the container, a separator, a negative electrode, an electrolyte, and a pressure-sensitive safety mechanism that operates in response to an increase in the internal pressure of the container;
The positive electrode includes a positive electrode current collector, and a positive electrode active material layer including a positive electrode active material and lithium carbonate and provided on the positive electrode current collector.
The negative electrode includes a negative electrode current collector, and a negative electrode active material layer including a negative electrode active material and provided on the negative electrode current collector.
The lithium ion secondary battery by which the porous layer is each provided on the said separator and the said negative electrode active material layer.   The lithium ion secondary battery according to claim 1, wherein the porosity of the porous layer is larger than the porosity of the positive electrode active material layer.   The lithium ion secondary battery according to claim 2, wherein the porosity of the positive electrode active material layer is 20% or less.   The lithium ion secondary battery according to claim 3, wherein the porosity of the porous layer is 20% or more.   The porous layer provided on the separator and the porous layer provided on the negative electrode active material layer are adjacent to each other in any one of claims 1 to 4. Lithium ion secondary battery as described.   The electrolyte solution according to any one of claims 1 to 5, wherein the electrolyte solution comprises an electrolyte containing a lithium salt and an organic solvent containing a chain carbonate, and the concentration of the electrolyte in the electrolyte is 1.5 to 3 mol / L. The lithium ion secondary battery according to any one of the preceding claims.   The lithium ion secondary battery according to any one of claims 1 to 6, wherein the negative electrode contains a silicon material having a structure in which a plurality of plate-like silicon bodies are stacked in a thickness direction.

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