WO2012124015A1

WO2012124015A1 - Non-aqueous secondary battery

Info

Publication number: WO2012124015A1
Application number: PCT/JP2011/055762
Authority: WO
Inventors: 丈主加味根; 澤木　裕子; 基志上原
Original assignee: 株式会社日立製作所
Priority date: 2011-03-11
Filing date: 2011-03-11
Publication date: 2012-09-20

Abstract

[Problem] To provide a non-aqueous secondary battery having a large capacity during high output discharge, even if a positive electrode mixture layer is thickened. [Solution] The problem is solved by a non-aqueous secondary battery provided with a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte, and characterized in that: the positive electrode has a positive electrode mixture layer containing an active material on at least one surface of a current collector; the positive electrode mixture layer has a thickness of 70 to 400 μm, and has a plurality of layers; and of the plurality of layers, the layer in contact with the current collector has a thickness of 60 μm, and a porosity of 1% to less than 30%, and the layers other than the layer in contact with the current collector have porosities of at least 30%.

Description

Non-aqueous secondary battery

The present invention relates to a non-aqueous secondary battery having a large capacity at the time of high output discharge even when the positive electrode mixture layer is thickened.

In recent years, non-aqueous secondary batteries have been desired to have a high capacity at a low cost so that they can be used as secondary batteries for storage batteries such as industrial machinery or solar power generation systems.

One of the means to meet the demand for such non-aqueous secondary batteries is to increase the amount of active material per battery and increase the capacity by reducing the number of members not involved in battery capacity. Yes. For example, Patent Document 1 discloses that the negative electrode is configured without using a current collecting conductor, thereby increasing the proportion of the active material in the entire negative electrode, and the energy per unit volume and unit mass of the secondary battery. Technologies for improving the density have been proposed.

There is also a method for increasing the capacity of the non-aqueous secondary battery by increasing the thickness of the electrode mixture layer (positive electrode mixture layer and negative electrode mixture layer) of the electrodes (positive electrode and negative electrode). However, when the thickness of the electrode mixture layer is simply increased, there is a problem that the initial discharge capacity is greatly reduced during high output discharge.

For example, Patent Document 2 discloses a non-aqueous secondary battery in which the apparent density of the positive and negative active material layers (electrode mixture layer) and the mass balance between the positive and negative active materials and the current collector are adjusted. . In patent document 2, it is supposed that the high capacity | capacitance battery from a practical viewpoint can be provided by employ | adopting the said structure.

However, even in the non-aqueous secondary battery disclosed in Patent Document 2, for example, if the thickness of the positive electrode mixture layer is increased, it is difficult to extract a sufficient capacity during high output discharge.

In addition, as a technique for improving battery characteristics by changing the electrode structure, for example, there is a proposal of an electrode in which a positive electrode mixture layer and a negative electrode mixture layer are multilayered and the porosity is changed in each layer ( Patent Documents 3 and 4).

JP 2006-4903 A Japanese Patent Application Laid-Open No. 5-74494 JP 2010-86711 A JP 2009-289586 A

As described above, various techniques for increasing the capacity of the non-aqueous secondary battery by adjusting the structure of the electrode are known, but these techniques also provide high power discharge when the positive electrode mixture layer is thickened. It is difficult to suppress a decrease in capacity.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous secondary battery having a large capacity at the time of high output discharge even if the positive electrode mixture layer is thickened.

The non-aqueous secondary battery of the present invention that has achieved the above object includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the positive electrode contains an active material on at least one surface of a current collector. The positive electrode mixture layer has a thickness of 70 to 400 μm and has a plurality of layers, and the layer in contact with the current collector among the plurality of layers has a thickness of 60 μm. In the following, the porosity is 1% or more and less than 30%, and the layers other than the layer in contact with the current collector have a porosity of 30% or more.

According to the present invention, it is possible to provide a non-aqueous secondary battery having a large capacity at the time of high output discharge even if the positive electrode mixture layer is thickened.

It is a partial longitudinal cross-sectional view which represents typically an example of the positive electrode which concerns on the nonaqueous secondary battery of this invention.

FIG. 1 is a partial longitudinal sectional view schematically showing an example of a positive electrode according to the nonaqueous secondary battery of the present invention. A positive electrode 10 shown in FIG. 1 has positive

electrode mixture layers

20 and 21 containing an active material (positive electrode active material) on both surfaces of a current collector 30. The positive electrode mixture layer 20 has two

layers

20a and 20b with different porosity, and the positive electrode mixture layer 21 also has two

layers

21a and 21b with different porosity.

Thus, the positive electrode according to the nonaqueous secondary battery of the present invention has a positive electrode mixture layer containing an active material on at least one surface of the current collector, and the positive electrode mixture layer has a thickness of 70. The layer in contact with the current collector among the plurality of layers (20a and 21a in the positive electrode shown in FIG. 1) has a thickness of 60 μm or less and a porosity of about 400 μm. The porosity of the layers other than the layer that is 1% or more and less than 30% and is in contact with the current collector (in the positive electrode shown in FIG. 1, 20b and 21b) is 30% or more.

For non-aqueous secondary batteries that have a higher capacity by increasing the amount of active material inside the cathode mixture layer, when the power is discharged, the battery's original capacity can be fully exploited. The discharge capacity is reduced. This is considered to be due to the following reasons.

The positive electrode active material is usually secondary particles in which primary particles are aggregated. When the positive electrode active material in which the secondary particles are aggregated is dispersed in the positive electrode mixture layer of the positive electrode, the area that can be involved in the battery reaction in the positive electrode active material is reduced. In addition, increasing the density of the positive electrode mixture layer and increasing the amount of the positive electrode active material to increase the capacity reduces voids in the positive electrode mixture layer, lowers the permeability of the nonaqueous electrolyte, and makes contact with the nonaqueous electrolyte. The surface area (that is, the reaction area of the positive electrode active material) of the positive electrode active material that can be reduced.

Such a phenomenon does not cause much problems when the positive electrode mixture layer is thin, but becomes obvious when the positive electrode mixture layer becomes thicker, for example, 70 μm or more, and the resistance inside the layer increases. The problem due to the above phenomenon becomes more remarkable at the time of high output discharge in which the resistance in the positive electrode mixture layer is increased as compared with that at the time of low output discharge, and as a result, the capacity of the positive electrode mixture layer is sufficiently increased. It cannot be pulled out, and the discharge capacity decreases.

Therefore, in the non-aqueous secondary battery of the present invention, the positive electrode mixture layer has a multilayer structure, and among these layers, in the layer having a relatively low internal resistance by contacting the current collector, the porosity is reduced and the positive electrode active layer is reduced. In the layer where the filling amount of the substance can be increased while the internal resistance is relatively high without being in contact with the current collector, the porosity is increased, and the nonaqueous electrolyte interface in the positive electrode mixture layer is increased. By increasing the reaction area and improving the permeability of the non-aqueous electrolyte, it is possible to satisfactorily suppress a decrease in discharge capacity during high output discharge even when the positive electrode mixture layer is thickened.

It should be noted that the problem caused by increasing the thickness of the positive electrode mixture layer related to the nonaqueous secondary battery is, for example, that the positive electrode mixture layer is a single layer and the porosity thereof is increased so that It is also conceivable to increase the reaction area with the water electrolyte interface and to improve the permeability of the non-aqueous electrolyte into the positive electrode mixture layer to suppress a decrease in discharge capacity during high-power discharge. However, when the positive electrode mixture layer is subjected to press treatment for controlling the thickness and density (porosity) of the positive electrode mixture layer (details will be described later), the positive electrode mixture layer is a single layer and the thickness is If it is large, a strong press is applied locally, and the distribution of pores tends to be uneven. And in the area | region where the porosity became small locally, there exists a possibility that the reaction area with a nonaqueous electrolyte interface may become small, or a nonaqueous electrolyte may become difficult to osmose | permeate.

On the other hand, in the positive electrode according to the nonaqueous secondary battery of the present invention, the positive electrode mixture layer has a multilayer structure, so a layer in contact with the current collector is first formed, and then a layer in contact with this layer is formed. Thus, it is possible to adopt a manufacturing method in which the positive electrode mixture layer is formed step by step. Since the thickness of each layer constituting the positive electrode mixture layer is smaller than the total thickness of the positive electrode mixture layer, the pore distribution in each of these layers becomes relatively uniform. Therefore, in the nonaqueous secondary battery of the present invention, the effect of better suppressing the reduction in discharge capacity during high output discharge can be expected due to the uniformity of the pore distribution of each layer constituting the positive electrode mixture layer.

For example, the positive electrode according to the non-aqueous secondary battery of the present invention and the positive electrode mixture layer having a single positive electrode mixture layer with a large overall porosity, the same amount of positive electrode active material is charged. (That is, when the positive electrode capacity is the same), the positive electrode mixture layer has a multilayer structure, and the porosity is changed between the layer in contact with the current collector and the other layers. The positive electrode can make the positive electrode mixture layer thinner. Therefore, the nonaqueous secondary battery of the present invention has an advantage that the increase in the thickness of the positive electrode can be suppressed as much as possible while increasing the capacity.

Among the positive electrode mixture layers related to the positive electrode of the nonaqueous secondary battery of the present invention, the layer in contact with the current collector is used from the viewpoint of increasing the battery capacity per unit volume by increasing the filling amount of the positive electrode active material. The porosity is less than 30% and preferably 25% or less. However, if the porosity of the layer in contact with the current collector of the positive electrode mixture layer is too small, there is a possibility that the capacity cannot be sufficiently extracted. Therefore, the porosity is 1% or more, 15% The above is preferable.

Of the positive electrode mixture layer relating to the positive electrode of the nonaqueous secondary battery of the present invention, the layer other than the layer in contact with the current collector may be a single layer or a plurality (two layers, three layers, four layers, etc.) However, from the viewpoint of increasing the productivity of the positive electrode, the number of layers is preferably small, and more preferably one layer. That is, the positive electrode material mixture layer is more preferably composed of two layers including a layer in contact with the current collector.

The layers other than the layer in contact with the current collector have good nonaqueous electrolyte permeability, and the overall porosity is 30% or more from the viewpoint of suppressing a decrease in discharge capacity during high output discharge. Yes, it is preferably 35% or more.

However, if the porosity of the layers other than the layer in contact with the current collector is too large, the reaction area with the nonaqueous electrolyte interface in these layers increases, but on the other hand, the distance between the positive electrode active material particles is The conductive contact between the positive electrode active material particles and the conductive auxiliary agent forming the conductive path between the positive electrode active material particles is also cut off. The resistance contact between them also increases. Therefore, there is a possibility that the effect of suppressing the decrease in capacity at the time of high output discharge of the battery is reduced. Therefore, the porosity of layers other than the layer in contact with the current collector is preferably 45% or less.

In the positive electrode mixture layer, the porosity of the layer in contact with the current collector and the porosity of the layers other than the layer in contact with the current collector are obtained by scanning a cross-sectional image in the thickness direction of the positive electrode mixture layer with a scanning electron microscope ( This is a value measured by the following procedure using a SEM image taken at a magnification of 1000 times.
(1) The captured image is read using image analysis software ("A Image-kun" manufactured by Asahi Kasei Engineering).
(2) Cut out the layer whose porosity is to be measured in the image (a layer in contact with the current collector or a layer other than a layer in contact with the current collector).
(3) The void portion is extracted using the command “particle extraction”.
(4) The command “binarization processing” is performed at the threshold value.
(5) The hole area ratio is calculated using the command “area ratio measurement”, and the value is set as the porosity of the measurement target layer.

The positive electrode active material contained in the positive electrode mixture layer relating to the positive electrode of the nonaqueous secondary battery of the present invention is the same as various positive electrode active materials used in conventionally known nonaqueous secondary batteries. Although it can be used, it is preferable to use a lithium-containing composite oxide having a spinel structure containing Mn. Since the spinel-structured lithium-containing composite oxide containing Mn is excellent in thermal stability, for example, a highly safe non-aqueous secondary battery can be configured.

The lithium-containing composite oxide having a spinel structure containing Mn includes a general formula Li _{1 + x} M ₂ O ₄ (wherein −0.1 ≦ x ≦ 0.1, and M is at least one type including Mn. A composite oxide represented by the above-described elements and represented by the Mn atomic ratio of all elements constituting M is 70 mol% or more is preferably used.

Specific examples of the lithium-containing composite oxide having a spinel structure containing Mn include, for example, spinel manganese composite oxides represented by compositions such as LiMn ₂ O ₄ and LiNi _0.5 Mn _1.5 O ₄ ; Some of the elements related to the manganese composite oxide are replaced with other elements such as Ca, Mg, Sr, Sc, Zr, V, Nb, W, Cr, Mo, Fe, Co, Ni, Zn, Al, Si, and Ga. Lithium-containing composite oxides having a spinel structure substituted with elements such as Ge, Sn, etc. (such as lithium-containing composite oxides containing Mn and one or more of the above-exemplified elements as element M in the general formula); Etc.

Further, as the positive electrode active material, a positive electrode active material other than a spinel-structured lithium-containing composite oxide containing Mn can be used. As such a positive electrode active material, for example, a layered structure represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, Zr, Ti, etc.) And an olivine type compound represented by LiMPO ₄ (M: Co, Ni, Mn, Fe, etc.). Specific examples of the lithium-containing transition metal oxide having a layered structure include LiCoO ₂ and LiNi _1-x Co _xy Al _y O ₂ (0.1 ≦ x ≦ 0.3, 0.01 ≦ y ≦ 0. 2) and other oxides containing at least Co, Ni and Mn (LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _5/12 Ni _5/12 Co _1/6 O ₂ , LiNi _{3 / 5} Mn _1/5 Co _1/5 O ₂ etc.).

In the positive electrode active material according to the non-aqueous secondary battery of the present invention, only one of the above-described various positive electrode active materials may be used, or two or more of them may be used in combination. In addition, as described above, it is preferable to use a spinel-structured lithium-containing composite oxide containing Mn as the positive electrode active material, which is used alone, or contains this and the exemplified Mn. It is desirable to use together with a positive electrode active material other than the spinel-structured lithium-containing composite oxide (hereinafter referred to as “other positive electrode active material”).

In the case where the lithium-containing composite oxide having a spinel structure containing Mn and another positive electrode active material are used in combination, the content of the lithium-containing composite oxide having a spinel structure containing Mn in the total positive electrode active material is: It is preferable that it is 70 mass% or more, and it is more preferable that it is 80 mass% or more.

In addition to the positive electrode active material, the positive electrode mixture layer preferably contains a conductive additive or a binder. Examples of the conductive assistant include acetylene black; ketjen black; carbon blacks such as channel black, furnace black, lamp black, and thermal black; carbon materials such as carbon fibers; and conductive fibers such as metal fibers. Carbon fluoride, metal powders such as copper and nickel, organic conductive materials such as polyphenylene derivatives, and the like. These may be used alone or in combination of two or more.

Examples of the binder related to the positive electrode mixture layer include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyvinylpyrrolidone (PVP). It is done.

The composition of the positive electrode mixture layer is, for example, 80.0 to 99.3 mass% for the positive electrode active material, 0.1 to 10 mass% for the conductive assistant, and 0.1 to 10 mass% for the binder. It is preferable.

The thickness of the positive electrode mixture layer (when the positive electrode mixture layer is provided on both sides of the current collector, the thickness per side of the current collector. The same applies to the thickness of the positive electrode mixture layer). From the viewpoint of achieving the above, it is 70 μm or more, and preferably 100 μm or more. However, if the positive electrode mixture layer is too thick, lithium ion diffusion polarization increases and the internal resistance of the battery increases. Therefore, the thickness of the positive electrode mixture layer is 400 μm or less, and preferably 200 μm or less.

Of the positive electrode mixture layer, the thickness of the layer in contact with the current collector is 60 μm or less, and preferably 35 μm or less. If the layer in contact with the current collector is too thick, the resistance in the vicinity of the surface on the side opposite to the current collector of this layer increases, and the effect of suppressing the decrease in discharge capacity during high-power discharge is reduced. Further, if the layer in contact with the current collector of the positive electrode mixture layer is too thin, the capacity per unit volume of the battery may be reduced. Therefore, the thickness of the layer in contact with the current collector is 5 μm or more. The thickness is preferably 10 μm or more.

As the positive electrode current collector, aluminum foil, punching metal, net, expanded metal, or the like can be used, but aluminum foil is usually used. The thickness of the positive electrode current collector is preferably 10 to 30 μm.

The positive electrode can be manufactured, for example, by the following method. First, a positive electrode mixture containing a positive electrode active material, a conductive additive and a binder is dispersed in a solvent [an organic solvent such as N-methyl-2-pyrrolidone (NMP) or water] to form a positive electrode mixture-containing composition ( Paste, slurry, etc.) are prepared, applied to the surface of the current collector, dried, and subjected to a press treatment to form a layer in contact with the current collector. Then, the positive electrode mixture-containing composition is applied to the surface of the layer in contact with the current collector, dried and subjected to a press treatment, and then the layer in contact with the current collector is subjected to the pressing process. Other layers are formed. When a plurality of layers other than the layer in contact with the current collector are provided, the steps of applying, drying, and pressing the positive electrode mixture-containing composition may be sequentially repeated as many times as necessary.

The porosity of each layer in the positive electrode mixture layer can be determined by, for example, selecting the conditions of the press treatment to be applied after the positive electrode mixture-containing composition is applied to the current collector or the surface of the previously formed layer and dried. Can be adjusted. Usually, in order to increase the density of the positive electrode mixture layer, press treatment is performed at a relatively large linear pressure. In the positive electrode according to the present invention, first, when forming a layer in contact with the current collector, the normal positive electrode is applied. The press treatment may be performed at the same linear pressure as that of the press treatment, specifically, for example, a linear pressure of about 100 to 400 kgf / cm, and when a layer other than the layer in contact with the current collector is formed, for example, 10 The press treatment may be performed with a linear pressure of about 200 kgf / cm and smaller than the linear pressure during the press treatment applied to the layer in contact with the current collector.

The non-aqueous secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the positive electrode may be any of the positive electrodes described above. Other configurations and structures are not particularly limited, and are conventionally known. The configuration and structure employed in the non-aqueous secondary battery used can be applied.

As the negative electrode, for example, one having a negative electrode mixture layer containing a negative electrode active material or a binder on at least one surface of the current collector can be used.

Examples of the negative electrode active material include graphite materials such as natural graphite (flaky graphite), artificial graphite, and expanded graphite; graphitizable carbonaceous materials such as coke obtained by firing pitch; furfuryl alcohol resin (PFA) ), Polyparaphenylene (PPP), and a non-graphitizable carbonaceous material such as amorphous carbon obtained by baking a phenol resin at a low temperature. In addition to the carbon material, lithium or a lithium-containing compound can also be used as the negative electrode active material. Examples of the lithium-containing compound include a lithium alloy such as Li—Al, and an alloy containing an element that can be alloyed with lithium such as Si and Sn. Furthermore, oxide-based materials such as Sn oxide and Si oxide can also be used.

As the binder related to the negative electrode mixture layer, the same binders as those exemplified above as those that can be used for the positive electrode mixture layer can be used.

In addition, the negative electrode mixture layer may contain a conductive aid as necessary. As the conductive auxiliary agent related to the negative electrode mixture layer, the same conductive auxiliary agents as those exemplified above as those that can be used for the positive electrode mixture layer can be used.

As the composition of the negative electrode mixture layer, for example, the negative electrode active material is preferably 80.0 to 99.8% by mass and the binder is preferably 0.1 to 10% by mass. When the conductive additive is contained in the negative electrode mixture layer, the amount of the conductive additive in the negative electrode mixture layer is preferably 0.1 to 10% by mass. The thickness of the negative electrode mixture layer (when the negative electrode mixture layer is provided on both sides of the current collector, the thickness per side of the current collector) is preferably 70 to 350 μm.

The negative electrode is, for example, a negative electrode mixture-containing composition prepared by dispersing a negative electrode mixture containing a negative electrode active material and a binder and, if necessary, a conductive auxiliary agent in a solvent (an organic solvent such as NMP or water). An object (paste, slurry, etc.) can be produced by applying it to one or both sides of a current collector and drying it, and subjecting it to a press treatment as necessary.

The separator according to the non-aqueous secondary battery of the present invention has a property that the pores are blocked (that is, a shutdown function) at 80 ° C. or higher (more preferably 100 ° C. or higher) and 170 ° C. or lower (more preferably 150 ° C. or lower). It is preferable that a separator used in a normal non-aqueous secondary battery, for example, a microporous film made of polyolefin such as polyethylene (PE) or polypropylene (PP) can be used. The microporous film constituting the separator may be, for example, one using only PE or one using PP, or a laminate of a PE microporous film and a PP microporous film. There may be. The thickness of the separator is preferably 10 to 30 μm, for example.

The positive electrode, the negative electrode, and the separator are formed in the form of a laminated electrode body in which a separator is interposed between the positive electrode and the negative electrode, or a wound electrode body in which the separator is wound in a spiral shape. It can be used for the non-aqueous secondary battery of the invention.

For the nonaqueous electrolyte according to the nonaqueous secondary battery of the present invention, for example, a solution (nonaqueous electrolyte) prepared by dissolving a lithium salt in the following nonaqueous solvent can be used.

Examples of the solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone (γ-BL ), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), 1,3-dioxolane, formamide, dimethylformamide (DMF), dioxolane, acetonitrile, nitromethane, Methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran Aprotic organic solvents such as derivatives, diethyl ether and 1,3-propane sultone can be used singly or as a mixed solvent in which two or more are mixed.

The inorganic ion salt according to the non-aqueous electrolyte, for _{_{_{example, LiClO 4, LiPF 6, LiBF}}} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO 3 (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] At least one selected from the above. The concentration of these lithium salts in the electrolytic solution is preferably 0.6 to 1.8 mol / l, and more preferably 0.9 to 1.6 mol / l.

In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexyl benzene, biphenyl, fluorobenzene, for the purpose of improving the safety, charge / discharge cycleability, and high-temperature storage properties of these non-aqueous electrolytes. Additives such as t-butylbenzene can be added as appropriate.

The non-aqueous electrolyte used in the non-aqueous secondary battery of the present invention is a non-aqueous electrolyte, and the kinematic viscosity at 25 ° C. is preferably 10 cSt or less, and more preferably 5 cSt or less. If it is a non-aqueous electrolyte solution having such a kinematic viscosity, even if the positive electrode mixture layer is thickened, it becomes easy to penetrate in the thickness direction, so the capacity reduction at the time of high output discharge in the non-aqueous secondary battery, It can suppress more favorably.

The kinematic viscosity of the non-aqueous electrolyte can be adjusted by, for example, using two or more solvents for the non-aqueous electrolyte and adjusting the balance between the viscosity and the ratio. However, if the non-aqueous electrolyte has a too low kinematic viscosity, it may be difficult to obtain a non-aqueous electrolyte having a solvent composition that can ensure good battery characteristics. The viscosity is preferably 1 cSt or more, and more preferably 3 cSt or more.

The kinematic viscosity at 25 ° C. of the non-aqueous electrolyte referred to in the present specification is a value measured by the following method. Using a Canon-Fenske viscometer, the measurement is started when the temperature of the non-aqueous electrolyte placed in the thermostatic layer reaches 25 ° C. After sucking the tube and raising the liquid level up to 5-10 mm above the upper reference line of the timepiece ball, the time required for the liquid surface to naturally flow and pass between the upper and lower reference lines of the timepiece ball (falling seconds) Number). The same measurement is repeated three times or more. When the two outflow times agree within 0.2%, the kinematic viscosity is calculated using the following formula using the average value.
Kinematic viscosity (cSt) = falling seconds x viscometer constant

For the viscometer constant in the above equation, the number of seconds dropped in a thermostatic water bath is measured using a standard solution for viscometer calibration, and the value obtained by gradually reducing the kinematic viscosity of the standard solution over this time is used.

As a form of the non-aqueous secondary battery of the present invention, a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can, an aluminum can, or the like as an outer can is cited. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of positive electrode>
Lithium manganate (LiMn ₂ O ₄ ) as a positive electrode active material: 74% by mass and LiNi _0.8 Co _0.15 Al _0.05 O ₂ : 19% by mass, acetylene black as a conductive auxiliary agent: 3.5% by mass % And a binder of PVDF: 3.2 mass% and PVP: 0.3 mass%, an appropriate amount of NMP is added, and mixed and dispersed using a planetary mixer. The containing slurry was prepared. This slurry was applied to one side of an aluminum foil having a thickness of 13 μm at a constant thickness, dried at 85 ° C., and then vacuum dried at 100 ° C. Thereafter, a press process was performed using a roll press machine at a linear pressure of 130 kgf / cm to form a layer having a thickness of 30 μm and a porosity of 22% (a layer in contact with the current collector) on one side of the current collector.

The positive electrode mixture-containing slurry was applied to the surface of the layer formed on one side of the current collector at a constant thickness, dried at 85 ° C, and then vacuum dried at 100 ° C. Thereafter, a roll press machine is used to perform a press treatment at a linear pressure of 30 kgf / cm to form a layer having a thickness of 80 μm and a porosity of 41% (a layer other than the layer in contact with the current collector). A positive electrode having a positive electrode mixture layer having a structure on one side of the current collector was obtained. The positive electrode was adjusted so that the amount of the positive electrode mixture layer was 20 mg / cm ² . Furthermore, this positive electrode was cut so that the area of the positive electrode mixture layer was 30 mm × 30 mm.

<Production of negative electrode>
Add appropriate amount of water to negative electrode mixture consisting of natural graphite as negative electrode active material: 48 mass% and artificial graphite: 48 mass%, and binder as CMC: 2.0 mass% and SBR: 2.0 mass% And mixed well to prepare a negative electrode mixture-containing slurry. This slurry was applied to one side of a copper foil having a thickness of 7 μm at a constant thickness, dried at 85 ° C., and then vacuum dried at 100 ° C. Thereafter, press treatment was performed to obtain a negative electrode having a negative electrode mixture layer having a thickness of 70 μm on one side of the current collector. Furthermore, this negative electrode was cut so that the area of the mixture layer was 35 mm × 35 mm.

<Battery assembly>
The positive electrode and the negative electrode after cutting are overlapped via a PE microporous membrane separator (thickness 18 μm) to form a laminated electrode body, and this laminated electrode body is accommodated in an aluminum laminate sheet exterior body of 90 mm × 160 mm. . Subsequently, a non-aqueous electrolyte (a solution obtained by dissolving LiPF6 at a concentration of 1.2 mol / l in a mixed solvent having a volume ratio of EC: DEC = 3: 7, a kinematic viscosity at 25 ° C. of 4.2 cSt) in the outer package. After injecting 1 ml, the exterior + body was sealed to obtain a laminated nonaqueous secondary battery.

Comparative Example 1
The same positive electrode mixture-containing slurry as used in Example 1 is formed to have a constant thickness on one surface of an aluminum foil having a thickness of 13 μm, and the amount of the positive electrode mixture layer after drying is 20 mg / cm ^2. Thus, it was applied only once, dried at 85 ° C., and then vacuum dried at 100 ° C. Then, the press process was performed with the linear pressure of 10 kgf / cm using the roll press machine, and the positive electrode which has a porosity of 48% and has the single-layered positive mix layer on one side was obtained. A laminated nonaqueous secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 2
A positive electrode having a porosity of 22% and a single-layered positive electrode mixture layer on one side was obtained in the same manner as in Comparative Example 1 except that the linear pressure during the press treatment was 130 kgf / cm. A laminated nonaqueous secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 3
A positive electrode having a porosity of 41% and a single-layered positive electrode mixture layer on one side was obtained in the same manner as in Comparative Example 1 except that the linear pressure during the press treatment was 30 kgf / cm. A laminated nonaqueous secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

The following charge / discharge characteristics evaluation was performed on the laminated nonaqueous secondary batteries of Examples and Comparative Examples.

<Charge / discharge characteristics evaluation>
About each battery of an Example and a comparative example, after performing the constant current charge to 4.2V with the electric current value (20mA) of 1C, the charge which carries out constant voltage charge with 4.2V until an electric current value will be 2mA, and after that A series of operations for performing discharge under a predetermined condition is defined as one cycle, and charge / discharge of 4 cycles is performed. In addition, the current value of the first cycle is 20 mA, the current value of the second cycle is 40 mA, the current value of the third cycle is 60 mA, and the current value of the fourth cycle is 80 mA until each reaches 2.5V. went. Then, the discharge capacity at a current value of 20 mA of each battery was taken as 100%, and the relative value of the discharge capacity at other current values was calculated.

Table 1 shows the porosity and thickness of the positive electrode mixture layer (each layer constituting the positive electrode mixture layer) of the positive electrode used in the battery of the example and the comparative example, and the charge / discharge characteristic evaluation result of the battery of the example and the comparative example Is shown in Table 2.

As shown in Table 1 and Table 2, the nonaqueous secondary battery of Example 1 using a positive electrode having a positive electrode mixture layer that has a layer in contact with the current collector and other layers and that has an appropriate configuration of each layer As compared with the battery of the comparative example, the decrease in capacity is suppressed even at the time of high output discharge with a large discharge current. The battery of Example 1 has a capacity of 97% with respect to the discharge capacity at a current value equivalent to 1 C, for example, even when discharging at a current value of 40 mA (equivalent to 2 C) required for the current industrial machine battery. Therefore, it can be said that it is suitable for applications requiring high output discharge.

In addition, the battery of Comparative Example 3 having a positive electrode mixture layer having a single layer structure in which the porosity is increased and the permeability of the nonaqueous electrolyte is increased is also maintained, for example, at a current value of 40 mA (equivalent to 2C). The rate is the same as that of the battery of Example 1, but the current value of 60 mA (equivalent to 3C) and 80 mA (equivalent to 4C) is higher, and the battery of Example 1 maintains the capacity. The rate is large. Further, the positive electrode according to the non-aqueous secondary battery of Example 1 has the same amount of the positive electrode mixture layer, that is, the amount of the positive electrode active material, as compared with the positive electrodes according to the batteries of Comparative Example 1 and Comparative Example 3. The thickness of the entire positive electrode mixture layer can be reduced.

Since the non-aqueous secondary battery of the present invention can satisfactorily suppress a decrease in capacity at the time of high output discharge even if the positive electrode mixture layer is thickened, it can be used for power supplies for industrial machines, solar power generation systems, wind power generation systems. It can be used for the same applications as various applications where conventionally known non-aqueous secondary batteries are applied, including applications requiring high capacity and high output discharge, such as it can.

10

Positive electrode

20, 21 Positive

electrode mixture layer

20a, 21a Layer in contact with

current collector

20b, 21b Layer other than layer in contact with current collector 30 Current collector

Claims

A non-aqueous secondary battery comprising a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte,
The positive electrode has a positive electrode mixture layer containing an active material on at least one side of a current collector,
The positive electrode mixture layer has a thickness of 70 to 400 μm and a plurality of layers.
Among the plurality of layers, the layer in contact with the current collector has a thickness of 60 μm or less and the porosity is 1% or more and less than 30%. The layers other than the layer in contact with the current collector have a porosity of 30. % Non-aqueous secondary battery characterized by being at least%.
The nonaqueous secondary battery according to claim 1, wherein a porosity of a layer other than the layer in contact with the current collector among the plurality of layers of the positive electrode mixture layer is 45% or less.
3. The nonaqueous secondary battery according to claim 1, wherein the active material contained in the positive electrode mixture layer is a lithium-containing composite oxide having a spinel structure containing Mn.