JP2013140714A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery that offers a high capacity in a high output discharge even with a thick positive electrode mixture layer.SOLUTION: The nonaqueous secondary battery includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. The positive electrode includes a positive electrode mixture layer containing an active material on at least one side of a collector, and the positive electrode mixture layer has a thickness (A) greater than or equal to 70 μm and smaller than 120 μm, and includes a plurality of layers of different porosities in the thickness direction. Of the plurality of layers, the layer that is in contact with the collector, has a thickness (B) smaller than or equal to 60 μm and a porosity of 15 to 34%, and satisfies the relation: (B)>(A)/2. All the plurality of layers except the layer that is in contact with the collector, has a porosity of 39 to 45%.

Description

  The present invention relates to 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.

  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 of increasing the capacity of the nonaqueous 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, when 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 JP-A-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 comprises 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 (A) on one side of 70 μm or more and less than 120 μm, and has a plurality of layers with different porosity in the thickness direction. Of these layers, the layer in contact with the current collector has a single-sided thickness (B) of 60 μm or less, a porosity of 15 to 34%, and satisfies the relationship of (B)> (A) / 2. Among the plurality of layers, layers other than the layer in contact with the current collector have a porosity of 39 to 45%.

  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 side of a current collector, and the positive electrode mixture layer has a single-sided thickness. (A) is 70 μm or more and less than 120 μm and has a plurality of layers with different porosity in the thickness direction, and among the plurality of layers, a layer in contact with the current collector (in the positive electrode shown in FIG. 1, 20a, 21a) has a thickness of 60 μm or less, a porosity of 15% or more and 34% or less, and satisfies the relationship of (B)> (A) / 2, and is a layer other than the layer in contact with the current collector ( In the positive electrode shown in FIG. 1, 20b and 21b) have a porosity of 39% or more and 45% or less.

  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 problem 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 is reduced (that is, the load characteristics are reduced).

  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 of the non-aqueous electrolyte and improving the permeability of the non-aqueous electrolyte, even if the positive electrode mixture layer is thick, the decrease in discharge capacity during high output discharge is suppressed well, and excellent load characteristics Can be secured.

  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 34% or less, 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 15% or more and 20% 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 porosity of the nonaqueous electrolyte, and the overall porosity is 35% or more from the viewpoint of suppressing a reduction in discharge capacity during high output discharge. Yes, preferably 40% 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 45% or less, and preferably 43% 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 + y} M ₂ O ₄ (where −0.1 ≦ y ≦ 0.1, and M is at least one type including Mn. A composite oxide represented by the above-described elements and represented by the atomic ratio of Mn among 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 + a} MO ₂ (−0.1 <a <0.1, M: Co, Ni, Mn, Al, Mg, Zr, Ti, etc.) And olivine type compounds 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-a Co _ab Al _b O ₂ (0.1 ≦ a ≦ 0.3, 0.01 ≦ b ≦ 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.).

  As the positive electrode active material according to the nonaqueous 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% of the positive electrode active material, 0.1 to 10 mass% of the conductive auxiliary agent, and 0.1 to 10 mass% of the binder. It is preferable.

  Thickness of one side of positive electrode mixture layer (A) [If the positive electrode mixture layer is formed only on one side of the positive electrode, it is the thickness. If the positive electrode mixture layer is formed on both sides of the positive electrode, The thickness of the positive electrode mixture layer per one side. The same applies to the thickness (A) of one surface of the positive electrode mixture layer. ] Is 70 μm or more and preferably 80 μm or more from the viewpoint of increasing the capacity of the battery. 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 (A) of one surface of the positive electrode mixture layer is less than 120 μm, and preferably 100 μm or less.

  Of the positive electrode mixture layer, the thickness (B) of the layer in contact with the current collector [If the positive electrode mixture layer is formed only on one side of the positive electrode, the thickness of the layer in contact with the current collector of the positive electrode mixture layer] When the positive electrode mixture layer is formed on both surfaces of the positive electrode, the thickness of the layer in contact with the current collector related to the positive electrode mixture layer per one surface. The same applies to the thickness (B) of the layer in contact with the current collector. ] Is 60 μm or less, preferably 55 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. Also, 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 (B) of the layer in contact with the current collector is 30 μm. It is preferable that it is above, and it is more preferable that it is 35 micrometers or more.

  In the positive electrode mixture layer, the thickness (A) on one side thereof and the thickness (B) of the layer in contact with the current collector satisfy the relationship (B)> (A) / 2. This makes it possible to increase the capacity per battery volume by increasing the thickness of the positive electrode mixture layer while satisfactorily suppressing the decrease in discharge capacity at the time of high output discharge. Can be made a non-aqueous secondary battery that is balanced at a high level.

  As the positive electrode current collector, an aluminum foil, a punching metal, a net, an expanded metal, or the like can be used, but an 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, a binder, and the like 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 structure having a negative electrode mixture layer containing a negative electrode active material or a binder on at least one surface of a current collector can be used.

  Examples of the negative electrode active material include graphite materials (graphite) such as natural graphite (flaky graphite), artificial graphite, and expanded graphite; graphitizable carbonaceous materials such as coke obtained by firing pitch; furfuryl alcohol Examples thereof include carbon materials such as non-graphitizable carbonaceous materials such as amorphous carbon obtained by low-temperature firing of resin (PFA), polyparaphenylene (PPP), and phenol resin. 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 lithium alloys such as Li—Al, and alloys containing elements 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 negative electrode active material, only one type may be used or two or more types may be used in combination.

Among the negative electrode active materials, in order to increase the capacity of the battery (particularly, increase the capacity at the time of high output discharge), a material containing Si and O as constituent elements (however, the atomic ratio x of O to Si is: 0.5 ≦ x ≦ 1.5 (hereinafter referred to as “SiO _x ”).

The SiO _x may contain Si microcrystal or amorphous phase. In this case, the atomic ratio of Si and O is a ratio including Si microcrystal or amorphous phase Si. That is, the SiO _p includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and is dispersed in the amorphous SiO ₂ . In combination with Si, the atomic ratio x may satisfy 0.5 ≦ x ≦ 1.5. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and the material has a molar ratio of SiO ₂ to Si of 1: 1, since x = 1, the structural formula is represented by SiO. . In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed, but when observed with a transmission electron microscope, the presence of fine Si Can be confirmed.

Since SiO _x has low conductivity, for example, it is more preferable to use it as a composite in which SiO _x is combined with a carbon material. The complex of the SiO _x and the carbon material, Zotsubutai and the SiO _x and the carbon material, the surface of the SiO _x is like composite coated with carbon material, coating the surface of the SiO _x carbon material More preferably, the composite is used. By using a composite of SiO _x and a carbon material, a conductive network in the negative electrode can be formed better.

As the carbon material for covering the surface of SiO _x , for example, low crystalline carbon, carbon nanotube, vapor grown carbon fiber, or the like can be used.

In addition, a method [vapor phase growth (CVD) method] in which a hydrocarbon-based gas is heated in a gas phase, and a carbon material generated by thermal decomposition of the hydrocarbon-based gas is deposited on the surface of the SiO _x particles is SiO 2. _When the surface of _x is coated with carbon, the hydrocarbon-based gas spreads to every corner of the SiO _x particle, and a thin and uniform film (carbon) containing a conductive carbon material is formed in the surface of the particle and in the pores of the surface. Since the coating layer can be formed, the SiO _x particles can be imparted with good conductivity with a small amount of carbon.

  As the liquid source of the hydrocarbon gas used in the CVD method, toluene, benzene, xylene, mesitylene and the like can be used, but toluene that is easy to handle is particularly preferable. A hydrocarbon-based gas can be obtained by vaporizing them (for example, bubbling with nitrogen gas). Moreover, methane gas, ethylene gas, acetylene gas, etc. can also be used.

As processing temperature of CVD method, it is preferable that it is 600-1200 degreeC, for example. Further, SiO _x subjected to CVD method is preferably granulated material was granulated by a known method (composite particles).

When the surface of SiO _x is coated with a carbon material, the amount of the carbon material is preferably 5 parts by mass or more, more preferably 10 parts by mass or more with respect to SiO _x : 100 parts by mass, 95 parts by mass or less, and more preferably 90 parts by mass or less.

Incidentally, SiO _x, because the volume change due to charging and discharging of the battery is large, the negative electrode active material, it is preferable to use a SiO _x and graphite. This makes it possible to maintain higher charge / discharge cycle characteristics while suppressing the expansion and contraction of the negative electrode accompanying charge / discharge of the battery while increasing the capacity by using SiO _x .

When SiO _x and graphite are used in combination for the negative electrode active material, the proportion of SiO _{x in} the total amount of the negative electrode active material should be 0.5% by mass or more from the viewpoint of ensuring the above-mentioned effects by using SiO _x. preferably, also, it is preferable that the negative electrode of the expansion and shrinkage due to SiO _x from the viewpoint of suppressing 10% by mass or less.

  As the binder for 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.

  Moreover, you may make a negative mix layer contain a conductive support agent as needed. 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 a composition of a negative mix layer, it is preferable that a negative electrode active material shall be 80.0-99.8 mass%, for example, and a binder shall be 0.1-10 mass%. Moreover, when making a negative mix layer contain a conductive support agent, it is preferable that the quantity of the conductive support agent in a negative mix layer shall be 0.1-10 mass%. Further, 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 active material, a binder, and, if necessary, a negative electrode mixture containing a conductive additive 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 non-aqueous electrolyte according to the non-aqueous secondary battery of the present invention, for example, a solution (non-aqueous electrolyte) prepared by dissolving a lithium salt in the following non-aqueous 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 derivative Aprotic organic solvents such as conductors, diethyl ether, and 1,3-propane sultone can be used alone 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, for the purpose of improving the safety, charge / discharge cycleability, and high-temperature storage properties of these nonaqueous electrolytes, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, 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 nonaqueous electrolytic solution can be adjusted, for example, by using two or more solvents for the nonaqueous electrolytic solution in combination 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 to 5-10 mm above the upper gauge line of the time measuring sphere, the time required for the liquid level to naturally flow and pass between the upper and lower marked lines of the time measuring sphere (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

  As the viscometer constant in the above equation, a numerical value obtained by measuring the falling seconds in a constant temperature water bath using a viscometer calibration standard solution and dividing the kinematic viscosity of the standard solution by this time is used.

  Further, as the non-aqueous electrolyte, a gel (gel electrolyte) obtained by adding a gelling agent such as a known polymer to the non-aqueous electrolyte may be used.

  Examples of the form of the non-aqueous secondary battery of the present invention include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can or an aluminum can as an outer can. 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.

  The non-aqueous secondary battery of the present invention can satisfactorily suppress the capacity reduction during high output discharge even when the positive electrode mixture layer is thick, and the load characteristics and the capacity per battery volume are ensured in a well-balanced manner. Therefore, it has been known for a long time, including applications that require high output and high capacity, such as power supply applications for industrial machinery, solar power generation systems, and storage battery applications for wind power generation systems. It can be used for the same purposes as various uses to which the water secondary battery is applied.

Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention. In addition, the bulk density (the bulk density of the layer in contact with the current collector and the bulk density of the layers other than the layer in contact with the current collector) related to the positive electrode mixture layer in each of Examples and Comparative Examples described later is as follows. Asked. First, the bulk density of the layer in contact with the current collector is the mass of the layer in contact with the current collector (g) / [area of the positive electrode mixture layer (cm ² ) × the thickness of the layer in contact with the current collector (cm) ] Was calculated using the formula. The bulk density of the layers other than the layer in contact with the current collector is [mass of positive electrode mixture layer (g) −mass of layer in contact with current collector (g)] / [area of positive electrode mixture layer (cm ² ) × thickness of layers other than the layer in contact with the current collector (cm)]. The mass of the layer in contact with the current collector is measured by measuring the mass of the current collector before forming the layer in contact with the current collector, and measuring the total mass after forming the layer in contact with the current collector. It was determined by subtracting the mass of the electric body.

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. A 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 is performed using a roll press machine at a linear pressure of 90 kgf / cm, and a layer having a thickness of 45 μm, a porosity of 27%, and a bulk density of 2.95 g / cm ³ (a layer in contact with the current collector) Was formed 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. After that, a roll press machine was used to perform press processing at a linear pressure of 30 kgf / cm, and a layer having a thickness of 38 μm, a porosity of 41%, and a bulk density of 2.38 g / cm ³ (other than the layer in contact with the current collector) The positive electrode having a two-layered positive electrode mixture layer on one side of the current collector was obtained. 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 thoroughly mixed 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 negative electrode 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 outer package was sealed to obtain a laminated nonaqueous secondary battery. The design capacity of this laminated non-aqueous secondary battery is 21 mAh (the same applies to the laminated non-aqueous secondary batteries of all examples and comparative examples described later).

Examples 2 and 3 and Comparative Examples 1 and 2
The amount of the positive electrode mixture-containing slurry applied during the formation of the layer in contact with the current collector layer, the linear pressure during the press treatment, and the positive electrode mixture contained in the formation of layers other than the layer in contact with the current collector A positive electrode was produced in the same manner as in Example 1 except that the amount of slurry applied and the linear pressure during the press treatment were changed to form a positive electrode mixture layer having the structure shown in Table 1, and these positive electrodes were used. Produced a laminated nonaqueous secondary battery in the same manner as in Example 1.

Example 4
Composite having negative electrode active material coated with carbon material on SiO surface (average particle diameter of SiO is 5 μm, amount of carbon material in composite is 15% by mass): 4% by mass, natural graphite: 46% by mass, and artificial graphite A negative electrode mixture-containing slurry prepared in the same manner as in Example 1 was used except that the content was changed to 46% by mass, and a negative electrode having a negative electrode mixture layer thickness of 59 μm was prepared in the same manner as in Example 1. A laminated nonaqueous secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used.

Comparative Example 3
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. Thereafter, a press treatment was performed using a roll press machine at a linear pressure of 30 kgf / cm, a thickness of 95 μm, a porosity of 41%, a bulk density of 2.38 g / cm ³ , and a positive electrode mixture layer having a single layer structure Was obtained on one side. A laminated nonaqueous secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Examples 4-6
A positive electrode having a single-layered positive electrode mixture layer having the structure shown in Table 1 on one side was prepared in the same manner as in Comparative Example 1 except that the coating amount of the positive electrode mixture-containing slurry and the linear pressure during the press treatment were changed. A laminated nonaqueous secondary battery was produced in the same manner as in Example 1 except that these positive electrodes were used.

Comparative Example 7
The amount of the positive electrode mixture-containing slurry applied during the formation of the layer in contact with the current collector layer, the linear pressure during the press treatment, and the positive electrode mixture contained in the formation of layers other than the layer in contact with the current collector A positive electrode was produced in the same manner as in Example 4 except that the amount of slurry applied and the linear pressure during the press treatment were changed to form a positive electrode mixture layer having the structure shown in Table 1, and these positive electrodes were used. Produced a laminated nonaqueous secondary battery in the same manner as in Example 4.

  Each of the following evaluations was performed on the laminated nonaqueous secondary batteries of Examples and Comparative Examples.

<Calculation of capacity per volume of positive electrode>
After charging with constant current up to 4.2V at a current value of 0.2C (4mA) and then charging with constant voltage charging at 4.2V until the current value reaches 0.4mA, The discharge capacity when the constant current discharge was performed up to 2.5 V at a value (4 mA) was defined as the battery capacity. The volume of the positive electrode was calculated using the formula of the area of the positive electrode mixture layer (cm ² ) × the thickness of the positive electrode mixture layer (cm) (that is, “the volume of the positive electrode” here is the positive electrode mixture layer) Means the volume). Then, the capacity per unit volume of the positive electrode was determined by dividing the battery capacity by the volume of the positive electrode. Moreover, the capacity per battery volume was also calculated from the capacity per volume of the positive electrode obtained.

<Evaluation of load characteristics (capacity measurement during high power discharge)>
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 discharging under a predetermined condition is defined as one cycle, and charging / discharging for 4 cycles was performed. In addition, the current value of the first cycle is 1 C (20 mA), the current value of the second cycle is 2 C (40 mA), the current value of the third cycle is 3 C (60 mA), and the current value of the fourth cycle is 5 C. The discharge capacity (capacity per mass of the positive electrode active material) at each current value was determined.

  Table 1 shows the structure of the positive electrode mixture layer (each layer constituting the positive electrode mixture layer) relating to the positive electrode used in the batteries of Examples and Comparative Examples, and Table 2 shows the evaluation results of the batteries of Examples and Comparative Examples.

  As shown in Table 1 and Table 2, the non-aqueous two of Examples 1 to 4 using a positive electrode having a positive electrode mixture layer having a layer in contact with the current collector and other layers and having an appropriate structure of each layer The secondary battery has a discharge current as compared with the batteries of Comparative Examples 1 and 2 using a positive electrode having a positive electrode mixture layer that is in contact with the current collector of the positive electrode mixture layer and the other layers having an inappropriate thickness. The decrease in capacity can be suppressed even at the time of the increased high output discharge.

  In the present invention, the battery of Comparative Example 4 is provided with a positive electrode having a positive electrode mixture layer having a large single layer structure, while having load characteristics (large capacity during high output discharge) and capacity per battery volume. Is intended to ensure both of the above characteristics at a higher level than this battery, but the batteries of Examples 1 to 4 have load characteristics, positive electrode volume. Each of the per capacities is superior to the battery of Comparative Example 4, and it can be said that the load characteristics and the capacity per battery volume are secured in a very high level with a good balance.

  The batteries of Examples 1 to 4 are 97% of the discharge capacity at a current value equivalent to 1 C, for example, even when discharging at a current value 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.

  On the other hand, 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 can suppress the decrease in capacity even during high-power discharge. The capacity per battery volume of the positive electrode is low. Moreover, the capacity | capacitance at the time of high output discharge has fallen in the battery of the comparative examples 5 and 6 which made the porosity low and increased the filling amount of the positive electrode active material.

  In addition, the battery of Example 4 using SiO (a composite of SiO and a carbon material) as the negative electrode active material had a higher output discharge than the batteries of Examples 1 to 3 using only graphite as the negative electrode active material. The capacity at the time is particularly high and has better load characteristics.

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 (4)

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 (A) on one side of 70 μm or more and less than 120 μm, and has a plurality of layers with different porosity in the thickness direction,
Of the plurality of layers, the layer in contact with the current collector has a single-sided thickness (B) of 60 μm or less, a porosity of 15 to 34%, and a relationship of (B)> (A) / 2. Meets
The non-aqueous secondary battery, wherein a layer other than the layer in contact with the current collector among the plurality of layers has a porosity of 39 to 45%.   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.   A negative electrode mixture layer containing, as an active material, a material containing Si and O as constituent elements (provided that the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5) The nonaqueous secondary battery according to claim 1, wherein the nonaqueous secondary battery has a negative electrode on one side or both sides.   The nonaqueous secondary battery according to claim 3, wherein the negative electrode mixture layer further contains graphite as an active material.

Images