JP2013134865A - Electrode for nonaqueous electrolyte battery, and nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure excellent adhesion between an active material layer including a ceramic film, and a conductive core material.SOLUTION: A positive electrode for a nonaqueous electrolyte battery comprises: a sheet-type conductive core material; a carbon layer disposed on the surface of the conductive core material; an active material layer disposed on the surface of the carbon layer; and a coating layer covering the active material layer. The carbon layer has a thickness greater than 0.5 μm and smaller than or equal to 30 μm, and contains a conductive carbon material, the active material layer includes at least one ceramic film that has a thickness of 20 to 120 μm, the ceramic film is a sintered body of a transition metal oxide capable of absorbing and/or desorbing lithium, and the coating layer has a thickness greater than 0.1 μm and smaller than or equal to 20 μm, and contains an ion-conducting polymer.

Description

  The present invention relates to a non-aqueous electrolyte battery, and in particular, for a non-aqueous electrolyte battery having a sheet-like conductive core material and an active material layer composed of a ceramic film disposed on the surface thereof and having flexibility. It relates to an electrode.

  In recent years, electronic devices such as personal computers and mobile phones are rapidly becoming mobile. As power sources for these electronic devices, small, light, and high capacity primary batteries and secondary batteries are required. Further, as a power source for a hybrid vehicle (HEV) or an electric vehicle, a secondary battery excellent in high rate charge / discharge characteristics is required. For these reasons, non-aqueous electrolyte batteries having high capacity and excellent output characteristics have been widely developed.

  The nonaqueous electrolyte battery includes a positive electrode, a negative electrode, and a separator interposed therebetween. The electrode generally includes a conductive core material and an active material layer disposed on the surface of the conductive core material. The mainstream of the active material layer is a mixture layer, and the mixture layer includes an active material as an essential component, and includes a binder, a conductive material, and the like as optional components. On the other hand, in order to increase the active material density of the electrode, studies have been made to use a ceramic film containing no binder or conductive material as an active material layer.

The ceramic film is a sintered body of an inorganic active material (for example, metal oxide) that can be sintered, and can be obtained by, for example, the following method.
First, an active material, a binder, and a dispersion medium are mixed to prepare an active material slurry. Next, an active material slurry is apply | coated to a support body and it is made to dry, and an active material green sheet is produced. An active material green sheet is laminated so as to have a desired thickness, and the laminate is fired at, for example, 500 to 1000 ° C. to obtain a ceramic film that is a sintered body of the active material. An active material layer is obtained by fixing the obtained sintered body to the conductive core material.

  However, as described above, when the ceramic material is formed and then fixed to the conductive core material to form the active material layer, the contact resistance between the active material layer and the conductive core material tends to increase. When the contact resistance between the active material layer and the conductive core is increased, the current collection efficiency is lowered, and sufficient capacity cannot be obtained or the output characteristics are deteriorated.

  On the other hand, when the active material green sheet is fired together with the conductive core material, the contact resistance between the active material layer and the conductive core material can be reduced, but the conductive core material tends to deteriorate. In particular, since the conductive core material containing Al has low heat resistance, such deterioration is remarkable.

  Moreover, since the ceramic film has a high density and does not contain a resin binder or the like, it is poor in flexibility. When the flexibility is insufficient, handling becomes difficult, and in the secondary battery, it becomes difficult to relieve stress accompanying charge / discharge. Therefore, the ceramic film is easily pulverized, and the cycle characteristics are likely to deteriorate.

Here, Patent Document 1 states that the adhesiveness between the active material layer and the core material can be improved by forming slits or the like in the active material layer.
Patent Document 2 proposes to disperse a fibrous reinforcing material inside the sintered body in order to improve the mechanical strength of the sintered body.

JP 2010-86717 A JP 2000-243381 A

  The adhesion of the active material layer formed of the ceramic film to the conductive core material is considered to be improved to some extent by forming a groove in the active material layer as in Patent Document 1. However, when a large impact or stress is applied to the ceramic film, it is difficult to prevent the pulverization. Therefore, even if a groove is formed in the active material layer, the contact resistance between the active material layer and the conductive core material cannot be reduced.

  As in Patent Document 2, if the fibrous reinforcing material is dispersed inside the sintered body, it is considered that the mechanical strength of the sintered body is improved, but the effect of suppressing the pulverization of the sintered body is limited. . Moreover, sufficient active material density may not be obtained due to the mixing of the fibrous reinforcing material. Furthermore, even if the strength of the sintered body is increased, the contact resistance between the active material layer and the conductive core cannot be reduced.

  As described above, it is difficult to reduce the contact resistance between the active material layer formed of the ceramic film and the conductive core material, and it is possible to impart flexibility to the electrode while suppressing pulverization of the ceramic film. Have difficulty.

  In view of the above, one aspect of the present invention is a sheet-like conductive core, a carbon layer disposed on the surface of the conductive core, an active material layer disposed on the surface of the carbon layer, A coating layer covering the active material layer, wherein the carbon layer has a thickness of greater than 0.5 μm and less than or equal to 30 μm and includes a conductive carbon material, and the active material layer has a thickness of 20 to 120 μm of at least one ceramic film, the ceramic film is a transition metal oxide sintered body capable of inserting and extracting lithium, and the coating layer has a thickness greater than 0.1 μm and less than 20 μm. The present invention also relates to an electrode for a nonaqueous electrolyte battery, which includes an ion conductive polymer.

  Another aspect of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The positive electrode, the negative electrode, and the separator are stacked or wound to form an electrode group. The present invention relates to a nonaqueous electrolyte battery in which at least one of the positive electrode and the negative electrode is an electrode including the ceramic film.

  According to the present invention, in order to obtain a high-capacity non-aqueous electrolyte battery electrode, when a ceramic film which is a sintered body of an active material is used, the adhesion between the active material layer and the conductive core material is improved. be able to. As a result, the contact resistance between the active material layer and the conductive core material can be reduced. In addition, the ceramic film is less likely to be pulverized, and even when pulverized, it is possible to suppress a decrease in cycle characteristics of the secondary battery.

It is a flowchart which shows the procedure of the manufacturing method of the ceramic film which concerns on one Embodiment of this invention. It is a longitudinal cross-sectional view which shows notionally the structure of the electrode for nonaqueous electrolyte batteries which concerns on one Embodiment of this invention. It is a top view which shows notionally the structure of the electrode for nonaqueous electrolyte batteries which concerns on one Embodiment of this invention. It is a longitudinal section showing the structure of the nonaqueous electrolyte battery concerning one embodiment of the present invention.

  An electrode for a nonaqueous electrolyte battery of the present invention includes a sheet-like conductive core material, a carbon layer disposed on the surface of the conductive core material, an active material layer disposed on the surface of the carbon layer, and an active material layer And a covering layer covering. The active material layer includes at least one ceramic film. That is, the ceramic film is fixed to the surface of the conductive core material via the carbon layer. The coating layer reinforces the fixing of the ceramic film to the conductive core material. The ceramic film is a sintered body of an active material that is a transition metal oxide capable of occluding and / or releasing lithium.

  The carbon layer contains a conductive carbon material and has a function of improving current collection efficiency. Since the conductive carbon material has higher flexibility than the ceramic film, the carbon layer also has an action of relaxing stress applied to the active material layer. When the ceramic film is fixed to the surface of the conductive core material without using a carbon layer, the contact area between the conductive core material and the ceramic film is reduced, and the contact resistance between the active material layer and the conductive core material is increased. Become.

  The coating layer covering the active material layer contains an ion conductive polymer. The ion conductive polymer has a viscosity. Therefore, the adhesion between the active material layer and the conductive core material is dramatically improved by the presence of the coating layer. As a result, the contact resistance between the active material layer and the conductive core material is further reduced, and the current collection efficiency is further improved. When there is no coating layer, a very thick carbon layer is required to sufficiently reduce the contact resistance between the active material layer and the conductive core material. Moreover, even if it is a thick carbon layer, the function which fixes a ceramic layer to an electroconductive core material is very limited. On the other hand, when the coating layer is present, the carbon layer acts effectively, so that even if the carbon layer is thin, the contact resistance between the active material layer and the conductive core is likely to be reduced.

  The covering layer covering the active material layer also has an effect of reinforcing the strength of the ceramic film itself. Since the ceramic film is reinforced by the coating layer, the pulverization can be suppressed even when a stress or a large impact due to repeated charge / discharge is applied to the ceramic film.

  Furthermore, the coating layer prevents the active material from falling off the conductive core material when the ceramic film is pulverized. Even when the ceramic film is pulverized by the action of fixing the ceramic film by the coating layer to the conductive core material, it is difficult to lose contact with the carbon layer. Therefore, for example, even when the ceramic film is pulverized due to stress due to repeated charge and discharge of the secondary battery, it is possible to maintain relatively good cycle characteristics.

  The covering layer may contain a conductive material. As the conductive material, for example, a material that can be used as the conductive carbon material constituting the carbon layer can be used, but it is not particularly limited.

  In a preferred embodiment of the present invention, a plurality of ceramic films are arranged randomly or regularly on the surface of the carbon layer. For example, the plurality of ceramic films are preferably arranged in a lattice shape or a tile shape on the surface of the carbon layer.

  The ion conductive polymer contained in the coating layer is preferably at least one selected from the group consisting of a fluororesin, a resin containing an ethylene oxide unit, a resin containing an acrylonitrile unit, and a resin containing an acrylate unit. Moreover, it is preferable that a fluororesin contains the copolymer or polyvinylidene fluoride containing a vinylidene fluoride unit. These resins may be used alone or in combination of two or more.

Hereinafter, the configuration of the nonaqueous electrolyte battery electrode of the present invention will be described in more detail.
[Active material layer]
The active material layer is formed of at least one ceramic film, and the ceramic film is a sintered body of a transition metal oxide capable of occluding and / or releasing lithium. The transition metal oxide may be used as a positive electrode active material or may be used as a negative electrode active material.

  The thickness of the active material layer (that is, the ceramic film) is preferably set to at least 20 μm or more from the viewpoint of obtaining a high-capacity electrode taking advantage of the sintered body. When the thickness of the active material layer is less than 20 μm, the proportion of the active material layer in the battery becomes excessively small, and it is difficult to increase the capacity. Further, the strength of the ceramic film is reduced and the ceramic film is easily pulverized.

  On the other hand, from the viewpoint of securing current collection efficiency and output characteristics, it is desirable that the thickness of the active material layer be 120 μm or less. When the thickness exceeds 120 μm, the flexibility of the electrode becomes insufficient, or it becomes difficult to ensure the adhesion between the active material layer and the conductive core material. Further, it becomes difficult to diffuse lithium ions into the active material layer, and the output characteristics are deteriorated. Furthermore, the ceramic film is easily pulverized by the expansion and contraction stress accompanying the charge / discharge.

  From the viewpoint of obtaining an excellent balance of capacity, contact resistance, flexibility, etc., the lower limit of the thickness range of the active material layer may be 20 μm, 30 μm, or 50 μm. The upper limit of the thickness range of the active material layer may be 100 μm, 90 μm, or 80 μm. The preferable range of the thickness of the active material layer is, for example, 50 to 100 μm, 50 to 80 μm, and the like.

  What is necessary is just to obtain | require the thickness of an active material layer as an average value of the thickness of arbitrary 10 points | pieces or more. In addition, when the two main flat surfaces of the ceramic film have irregularities, the distance between the center lines of these surfaces becomes the thickness of the ceramic film.

  The active material layer can include a plurality of ceramic films. When an active material layer is formed by arranging a plurality of ceramic films in the plane direction of the conductive core material, there are gaps between the ceramic films. Therefore, an electrode having flexibility can be obtained. The plurality of ceramic films may be arranged randomly (irregularly) on the surface of the carbon layer, or may be regularly arranged. For example, the plurality of ceramic films can be arranged in a lattice shape or a tile shape on the surface of the carbon layer. From the viewpoint of the uniformity of the active material layer and the increase in capacity, the plurality of ceramic films are preferably arranged regularly, and more preferably arranged in a lattice pattern. Such an electrode has a particularly high capacity and excellent flexibility. In addition, the shape of the plurality of ceramic films is not particularly limited, and may be all the same, or each may have a unique shape.

  When one surface of the conductive core material is viewed from the normal direction, the ratio of the ceramic film covering the surface (core material coverage A) is preferably 80 to 98%. When the core material coverage A is 80% or more, it is easy to increase the capacity. Further, by setting the core material coverage A to 98% or less, a sufficient gap can be formed between adjacent ceramic films. Therefore, it is easy to design an electrode having a high capacity and excellent flexibility.

Moreover, it is preferable that the area (henceforth, upper surface area) of the ceramic film when it sees from the normal line direction of an electroconductive core material is 0.4-100 mm < ² > per ceramic film. What is necessary is just to obtain | require the upper surface area per one ceramic film as an average of the upper surface area of ten or more ceramic films, for example. By setting the upper surface area per ceramic film to 0.4 mm ² or more, handling of the ceramic film becomes easy. Further, when the upper surface area per ceramic film is 100 mm ² or less, the ceramic film is more difficult to be pulverized.

The lower limit of the preferable range of the upper surface area per ceramic film may be 0.5 mm ² , 1 mm ² , 3 mm ² or 5 mm ² . Further, the upper limit of the preferable range may be 80 mm ² , 70 mm ² , 60 mm ² or 25 mm ² . These lower limits and upper limits may be combined arbitrarily.

The transition metal oxide capable of occluding and / or releasing lithium may be a composite oxide containing lithium and the transition metal element Me. The composite oxide preferably has a layered or hexagonal crystal structure, a spinel structure, or an olivine structure. Examples of the transition metal element Me include, but are not limited to, Co, Ni, Mn, Fe, Ti, and the like. For example, a lithium-containing composite oxide having a layered or hexagonal crystal structure is generally Li _x MO ₂ (0.9 ≦ x ≦ 1.1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, M is at least And at least one transition metal selected from the group consisting of Co, Ni, and Mn. The metal element M may include a typical metal element such as Al, Mg, or Ca as a part thereof.

Specific examples of the transition metal oxide include LiCoO ₂ , LiNi _1/2 Mn _1/2 O ₂ , LiNi _1/2 Co _1/2 O ₂ , LiNiO ₂ , LiNi _1/3 Mn _1/3 Co _1/3. Examples thereof include O ₂ , LiNi _1/2 Fe _1/2 O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ , and Li _4/3 Ti _5/3 O ₄ . A transition metal oxide may be used individually by 1 type, and may be used in combination of 2 or more type.

  The ceramic film constituting the active material layer is an aggregate of transition metal oxide particles that are diffusion-bonded to each other by sintering. Therefore, it has a porous structure due to a gap between particles before diffusion bonding, a resin component burned out during sintering, and the like. Here, the porosity of the ceramic film is preferably 3 to 15%. The porosity of the ceramic film may be obtained, for example, by measuring the porosity of 10 or more ceramic films with a mercury porosimeter and averaging them. A ceramic film having a porosity of 3% or more is relatively high in flexibility, so that it is difficult to be pulverized and it is difficult to deteriorate the cycle characteristics of the secondary battery. Further, when the porosity is 3% or more, sufficient ion conductivity is ensured and the output characteristics are easily maintained. On the other hand, by setting the porosity of the ceramic film to 15% or less, it is possible to maintain a high ratio of the active material in the entire battery, and thus it is easy to achieve a sufficiently high capacity.

  The ceramic film may contain a component other than the transition metal oxide in a small amount. Examples of the components other than the transition metal oxide include metals that promote sintering, residues of resin components, and the like. Even when these components are contained in the ceramic film, the function as the active material layer is not greatly affected. That is, the ceramic film only needs to be substantially composed of a transition metal oxide.

[Method of manufacturing ceramic film]
Next, a method for manufacturing a ceramic film will be described with reference to the flowchart of FIG. However, the following method is only an example, and does not limit the method of manufacturing the ceramic film.
(1) Preparation of active material slurry (S11)
First, a transition metal oxide powder, a binder and a dispersion medium, which are active materials, are mixed to prepare an active material slurry. You may add additives, such as a plasticizer, to an active material slurry as needed. The average particle diameter (volume-based median diameter) of the transition metal oxide powder contained in the active material slurry is 0.1 to 10 μm from the viewpoint of improving the sinterability and obtaining a high-density ceramic. Preferably, it is 0.5-5 micrometers.

  The amount of the binder in the active material slurry is, for example, 5 to 20 parts by weight per 100 parts by weight of the transition metal oxide. The amount of the plasticizer in the active material slurry is, for example, 0.5 to 10 parts by weight per 100 parts by weight of the transition metal oxide. Both the binder and the plasticizer are resin components that decompose and burn out during firing for sintering the active material, and are not included in the ceramic film.

  As the dispersion medium, for example, an alcohol solvent such as 2-propanol or an ester solvent such as n-butyl acetate is used. The binder and plasticizer added to the active material slurry may be dispersed in a dispersion medium or may be dissolved. Examples of the binder include polyvinyl butyral. Examples of the plasticizer include dibutyl phthalate. By using a plasticizer, the green sheet can be provided with appropriate flexibility and elasticity.

(2) Green sheet formation (S12)
The active material slurry is applied to a support having a release agent layer on the surface. An active material green sheet is obtained by drying the applied active material slurry. As the support, for example, a film having a polyester resin as a main component and having a release agent layer on the surface can be used.

  The method for applying the active material slurry is not particularly limited as long as it is a slurry applying method capable of forming a thin-film active material green sheet. Examples thereof include a method using a die coater and a doctor blade method.

  What is necessary is just to adjust the thickness of an active material green sheet according to the thickness of the desired ceramic film | membrane, for example, is 3-50 micrometers. If necessary, a plurality of active material green sheets may be laminated to form a laminate. When the thickness of the active material layer is large, for example, 50 μm or more, a plurality of active material green sheets may be laminated so as to have a desired thickness.

(3) Green chip formation (S13)
Next, the active material green sheet or the laminate thereof is cut to form a green chip having a desired upper surface area (for example, 1 to 25 mm ² ). The shape of the green chip may be determined according to the desired shape of the ceramic film. For example, it may be cut into polygonal tiles such as rectangles, rhombuses, and triangles.

(4) Green chip firing (S14)
Next, the green chip is fired to sinter the active material. At this time, it is preferable to perform the firing in two or more stages. The first stage is a debinding process, where the binder reacts with oxygen and burns and is removed. Therefore, in the second stage, the active material can be sufficiently sintered and the density can be easily increased.

  In the first stage, the green chip cut to a desired size is temporarily fired at 200 to 400 ° C. for 2 to 10 hours in an oxygen atmosphere. By this firing, the binder and plasticizer contained in the green chip are decomposed and released from the green chip as gas. Subsequently, the second stage baking is performed. In the second stage, the temporarily fired green chip is fired at 500 to 1000 ° C. for 1 to 5 hours in an oxygen atmosphere. By such two-stage firing, a ceramic film that is a sintered body of a transition metal oxide is obtained. The porosity of the ceramic film can be controlled by changing firing conditions such as temperature and time.

[Carbon layer]
The carbon layer is disposed between the conductive core material and the active material layer. The carbon layer relieves stress applied to the active material layer and reduces the contact resistance between the ceramic film and the conductive core material. Moreover, it is integral with the coating layer and takes part of the function of fixing the ceramic film to the conductive core. The carbon layer preferably contains a conductive carbon material and a binder.

  From the viewpoint of productivity, when one surface of the conductive core material is viewed from the normal direction, the ratio of the carbon layer covering the surface (core material coverage B) is 75 to 100%. For example, it may be 75 to 95%. That is, the carbon layer does not have to completely cover the surface of the conductive core material. Moreover, as long as the core material coverage B as described above is satisfied, there may be a portion where no carbon layer is partially interposed between each ceramic film and the conductive core material.

  The conductive carbon material contained in the carbon layer is not particularly limited as long as it is an electron conductive material that hardly undergoes a chemical change during charge and discharge. For example, natural graphite (flaky graphite and the like), graphite such as artificial graphite, carbon blacks such as acetylene black and ketjen black, carbon fibers and the like can be mentioned. The average particle diameter (volume-based median diameter) of the conductive carbon material may be selected according to the desired carbon layer thickness.

  Although the binder contained in a carbon layer is not specifically limited, For example, a fluororesin, an acrylic rubber, a nitrile rubber etc. are mentioned. Of these, fluororesins are preferable, and polyvinylidene fluoride is particularly preferable in consideration of stability and handling in the battery.

  The content of the conductive carbon material in the carbon layer is preferably 25 to 70% by weight, and more preferably 35 to 55% by weight. By setting the content of the conductive carbon material to 25% by weight or more, it becomes easy to ensure sufficient conductivity. Further, by setting the content of the conductive carbon material to 70% by weight or less, the content of the binder is relatively increased, and it is easy to ensure sufficient contact between the ceramic film and the conductive core material. The remainder of the carbon layer other than the conductive carbon material is substantially occupied by the binder, but the carbon layer may contain a small amount (for example, 10% by weight or less) of various additives in addition to the conductive carbon material and the binder. Good.

  The thickness of the carbon layer is greater than 0.5 μm and not greater than 30 μm. What is necessary is just to obtain | require about the thickness of a carbon layer as an average value of the thickness of arbitrary 10 points | pieces or more. When the surface of the conductive core material or the carbon layer has irregularities, the distance between the center lines of those surfaces becomes the thickness of the carbon layer. When the thickness of the carbon layer is 0.5 μm or less, the contact resistance between the ceramic film and the conductive core cannot be sufficiently reduced. On the other hand, when the thickness of the carbon layer exceeds 30 μm, the proportion of the carbon layer in the battery becomes excessively large, and it is difficult to increase the capacity. The lower limit of the thickness range of the carbon layer may be 1 μm, 3 μm, or 5 μm. Further, the upper limit of the thickness range of the carbon layer may be 25 μm, 20 μm, 15 μm, or 10 μm. These lower limits and upper limits may be combined arbitrarily. A preferable range of the thickness of the carbon layer is, for example, 3 to 20 μm.

[Coating layer]
The coating layer formed so as to cover the active material layer includes an ion conductive polymer. Here, the ion conductive polymer means a polymer capable of expressing ion conductivity (particularly lithium ion conductivity) by holding a non-aqueous electrolyte. Since it has such ionic conductivity, even if the active material layer is covered with the coating layer, the movement of ions is hardly inhibited. In addition to the surface of the ceramic film, the ion conductive polymer may be present in a gap between a plurality of adjacent ceramic films. Such a gap may or may not be filled with an ion conductive polymer. Each ceramic film may be completely covered with the coating layer, or a part thereof may be exposed without being covered with the coating layer.

  When the ion conductive polymer and the carbon layer are used in combination, even a small amount of the ion conductive polymer exhibits a high ability to fix the ceramic film to the conductive core material. The ion conductive polymer imparts flexibility to the electrode. The coating layer containing the ion conductive polymer can be easily formed thin, and the volume of the coating layer in the battery can be reduced, so that the increase in capacity of the electrode is not hindered.

  The polymer capable of expressing ionic conductivity by holding a non-aqueous electrolyte is preferably one that forms a gel by holding the non-aqueous electrolyte. The gel may contain a conductive additive as necessary. Due to the action of the gel, the effect of suppressing breakage of the ceramic film due to external stress and peeling of the active material from the conductive core material is increased. For example, the stress generated by winding the electrode can be effectively relieved, and even when the ceramic film is pulverized by the expansion and contraction of the active material due to charge and discharge, the active material is hardly peeled off from the conductive core material. On the other hand, since ions can move relatively easily in the nonaqueous electrolyte in the gel, the charge / discharge characteristics at a high current density are also maintained well.

  Examples of the polymer capable of exhibiting ionic conductivity by retaining the nonaqueous electrolyte include a fluororesin, a resin containing an ethylene oxide unit, a resin containing an acrylonitrile unit, and a resin containing an acrylate unit. These may be used individually by 1 type and may be used in combination of 2 or more type. Among these, it is preferable to use a fluororesin because it has a high ability to retain a non-aqueous electrolyte and is chemically stable. The fluororesin preferably contains a copolymer containing polyvinylidene fluoride units or polyvinylidene fluoride.

  The copolymer containing a vinylidene fluoride (VDF) unit includes, for example, a vinylidene fluoride unit and a hexafluoropropylene (HFP) unit. In this case, the content ratio of hexafluoropropylene units in the copolymer is preferably 0.1 to 20 mol%. When the content ratio of the hexafluoropropylene unit is increased, the affinity for the nonaqueous electrolyte is increased, so that the ionic conductivity tends to be increased. On the other hand, when the content ratio of the hexafluoropropylene unit is small, the affinity for the non-aqueous electrolyte is lowered, and therefore the amount of the non-aqueous electrolyte held by the ion conductive polymer tends to be reduced. In this case, the amount of non-aqueous electrolyte held by the polymer is reduced, but it is easy to maintain adhesion with the ceramic film. By setting the content ratio of the hexafluoropropylene unit as described above, the coating layer can exert a good balance between adhesion to the ceramic film and ion conductivity.

  The copolymer containing vinylidene fluoride units may further contain tetrafluoroethylene units in addition to vinylidene fluoride units and hexafluoropropylene (HFP) units. There exists a tendency for the intensity | strength of an ion conductive polymer to improve because a copolymer contains a tetrafluoroethylene unit. In this case, the content of hexafluoropropylene units in the entire copolymer is preferably 3 to 20 mol%.

  The thickness of the coating layer is greater than 0.1 μm and not greater than 20 μm. Here, the thickness of the coating layer is the thickness from the main flat surface of the ceramic layer, and an average value of the thicknesses of arbitrary 10 points or more may be obtained. When the main flat surface of the ceramic layer or the surface of the coating layer has irregularities, the distance between the center lines of those surfaces becomes the thickness of the coating layer. When the thickness of the coating layer is 0.1 μm or less, sufficient adhesion between the active material layer and the conductive core material cannot be obtained. Moreover, when the thickness of the coating layer is too small, the active material layer may not be sufficiently prevented from falling off. On the other hand, if the thickness of the coating layer exceeds 20 μm, the proportion of the coating layer in the battery becomes excessively large, and it becomes difficult to increase the capacity, or the output characteristics deteriorate due to the inhibition of ion migration. Or

  The lower limit of the thickness range of the coating layer may be 0.2 μm, 0.5 μm, 1 μm, or 5 μm. Further, the upper limit of the thickness range of the coating layer may be 18 μm, 15 μm, or 10 μm. These lower limits and upper limits may be combined arbitrarily. The preferable range of the thickness of the coating layer is, for example, 0.5 to 20 μm, 1 to 20 μm, and the like.

  In addition, since the electrode includes both the carbon layer and the coating layer, the respective functions are effectively exhibited as compared with the case where each electrode is provided alone. That is, the adhesion between the ceramic film and the conductive core material is greatly improved, and the flexibility of the electrode is also increased. And crushing of a ceramic film is suppressed and deterioration of cycling characteristics is also suppressed. Therefore, when using a carbon layer and a coating layer together, each can be formed thin. For example, even if the carbon layer is thinned to 30 μm or less, sufficient adhesion between the ceramic film and the conductive core material is maintained, and the contact resistance between them can be kept small. Therefore, it is easy to achieve a high capacity of the electrode.

[Conductive core]
The sheet-like conductive core material is a so-called current collector, and a metal foil is preferably used. The metal foil may be obtained by rolling or may be obtained by electrolysis. The material of the metal foil is not particularly limited, but Al, Fe, Cu, Ti, Ni and the like are preferable. These may form metal foil independently, and multiple types may become an alloy and may form metal foil. Especially as a conductive core material of a positive electrode, Al foil or Al alloy foil containing Fe etc. is suitable, and especially copper foil or copper alloy foil is suitable as a conductive core material of a negative electrode. The thickness of the conductive core material is, for example, 8 to 20 μm.

  In addition, although the conductive core material containing Al has excellent conductivity, it has low heat resistance. Therefore, it is difficult to obtain a ceramic film by applying an active material slurry to a conductive core material containing Al and firing the conductive core material to which the active material slurry is adhered. Therefore, this invention exhibits a big effect, when using the electroconductive core material containing Al.

[Electrode manufacturing method]
Next, the manufacturing method of the electrode for nonaqueous electrolyte batteries of this invention is demonstrated, referring FIG.
(I) Formation of carbon layer First, a conductive carbon material, a binder, and a dispersion medium are mixed at a predetermined ratio to prepare a conductive paste. A conductive paste is applied to one or both surfaces of a sheet-like conductive core, and dried at 60 to 120 ° C. to form a carbon layer. A fluorine resin or the like may be used for the binder, and N-methyl-2-pyrrolidone or the like may be used for the dispersion medium.

(Ii) Production of active material layer A plurality of ceramic films are arranged on the surface of the carbon layer to form an active material layer. At this time, it is preferable to arrange the ceramic films regularly. The method for mounting the ceramic film on the surface of the carbon layer is not particularly limited, but for example, it can be easily mounted by using an element mounting apparatus used when mounting a semiconductor element or the like on a substrate. Such a mounting device comprises a mounting head having at least one suction nozzle. The mounting head picks up one or more ceramic films supplied to a predetermined supply position, then moves to a desired position of the conductive core material, and releases the ceramic film at that position. By such an operation, a plurality of ceramic films can be disposed on the surface of the carbon layer in a short time. In addition, when the carbon layer includes a binder and has adhesiveness, it is easy to release the ceramic film and fix it to the conductive core, and it is easy to prevent displacement of the ceramic film.

(Iii) Formation of coating layer An ion conductive polymer and a solvent are mixed to prepare a coating layer forming paste. At this time, N-methyl-2-pyrrolidone or the like may be used as the solvent, or a non-aqueous electrolyte may be used. The obtained paste for forming a coating layer is applied to the surface of the active material layer, and the obtained coating film is dried at 60 to 100 ° C.

  In forming the coating layer, the coating layer forming paste may be applied to the surface of the active material layer using, for example, a die coater, a doctor blade, or a dip coat. Moreover, the viscosity of the coating layer forming paste may be adjusted, and the conductive core material in which the active material layer is disposed via the carbon layer may be immersed in the coating layer forming paste.

  When a non-aqueous electrolyte is used as the solvent for the coating layer forming paste, a coating layer containing an ion conductive polymer is formed after the above process. On the other hand, when a non-electrolyte solvent such as N-methyl-2-pyrrolidone is used as the solvent for the coating layer forming paste, the dried coating film is then brought into contact with a liquid non-aqueous electrolyte to thereby obtain an ionic conductive polymer. A coating layer containing is formed.

  FIG. 2 is a longitudinal sectional view conceptually showing an example of the structure of an electrode including an active material layer made of a ceramic film, and FIG. 3 is a top view of the electrode. 2 corresponds to a cross-sectional view taken along line II-II in FIG.

  The electrode 10 includes a sheet-like conductive core material 11, a carbon layer 12 disposed on both surfaces of the conductive core material 11, an active material layer 13 disposed on the surface of the carbon layer, and a coating covering the active material layer Layer 14. In FIG. 2, the carbon layer 12, the active material layer 13, and the coating layer 14 are formed on both surfaces of the conductive core material 11, but the electrode of the present invention is not limited to such a structure, and the carbon layer 12, the active material It is also possible to form the layer 13 and the covering layer 14 only on one side of the conductive core material 11.

  The active material layer 13 is composed of a plurality of ceramic films 13a having substantially the same shape, and these ceramic films 13a are arranged in a lattice shape or a tile shape. However, the shape and arrangement of the ceramic film are not limited to this.

  The gap (G1 and G2 in FIG. 3) between adjacent ceramic films is preferably 0.05 mm to 1 mm. If the gap is set in such a range, the core material coverage A can be easily set in the above range.

[battery]
The nonaqueous electrolyte battery of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte, and the positive electrode, the negative electrode, and the separator are stacked or wound to constitute an electrode group. In addition, the present invention relates to a nonaqueous electrolyte battery in which at least one of a positive electrode and a negative electrode is an electrode including the ceramic film. Since the electrode including the ceramic film has a high capacity and high resistance to bending, the electrode is suitable not only for a laminated electrode group but also for a wound electrode group.
FIG. 4 is a longitudinal sectional view conceptually showing an example of the structure of a nonaqueous electrolyte battery including a stacked electrode group including the electrode 10. FIG. 4 is only an example of the battery of the present invention, and does not limit the present invention.

  In FIG. 4, the first electrode 10, a pair of second electrodes 20 sandwiching the first electrode 10, and a microporous separator 30 interposed between the first electrode 10 and the second electrode 20, A stacked electrode group is formed. The first electrode 10 includes a first conductive core material 11 and a first active material layer 13 made of a plurality of ceramic films 13a formed on both surfaces thereof. The second electrode 20 includes a second conductive core material 21 and a second active material layer 23 attached to one surface thereof. In FIG. 4, the second active material layer 23 is depicted as a single sheet. However, like the first electrode 10, the second active material layer may be formed of a plurality of ceramic films. The second active material layer is disposed so as to face the first active material layer with the separator 30 interposed therebetween. The electrode group is impregnated with a non-aqueous electrolyte (not shown).

  The non-aqueous electrolyte is preferably liquid. The liquid non-aqueous electrolyte is held by the polymer that forms the coating layer 14 that covers the surface of the first electrode 10, and is also impregnated in the separator 30, the ceramic film 13a, and the like. The liquid nonaqueous electrolyte can easily enter the voids of the ceramic film. The liquid non-aqueous electrolyte includes a liquid non-aqueous solvent and a solute (such as a lithium salt) dissolved therein.

  The electrode group is housed in an envelope-shaped exterior body 40 made of a flexible sheet together with the nonaqueous electrolyte. However, the first lead 15 connected to the first electrode 10 and the second lead 25 connected to the second electrode 20 are led out from the opening of the exterior body 40. By interposing the sealing resin 41 between the opening end portion of the exterior body 40 and each lead, it becomes easy to seal the opening. For the flexible sheet constituting the envelope-shaped exterior body, for example, a laminate film of a barrier layer against water vapor and a resin film attached to both surfaces thereof can be used. As the barrier layer, Al foil is preferable.

  As the non-aqueous solvent constituting the non-aqueous electrolyte, a mixed solvent of cyclic carbonates such as ethylene carbonate and propylene carbonate and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is preferable. Further, the carbonates can be used in combination with other various conventionally used solvents.

Examples of the lithium salt include inorganic lithium fluoride and a lithium imide compound. Examples of the inorganic lithium fluoride include LiPF ₆ and LiBF ₄ . Examples of the lithium imide compound include LiN (CF ₃ SO ₂ ) ₂ .

  The second active material layer may be formed of any of a mixture layer, a deposited film formed by a vapor phase method (evaporation or the like), a ceramic film, a metal foil, or the like. The mixture layer is a layer of a mixture containing a second active material capable of occluding and / or releasing lithium ions as an essential component, and a binder, a thickener, a conductive material and the like as optional components.

The second active material may be selected according to the type of ceramic film used as the first active material and the application. Examples thereof include carbon materials such as graphite particles, materials containing Si, and materials containing Sn. Examples of the graphite particles include natural graphite, artificial graphite, and graphitized mesophase carbon particles. Examples of the material containing Si include Si simple substance, Si alloy, and SiO _x (0 <x <2). Examples of the material containing Sn include Sn alone, Sn alloy, SnO _x (0 <x <2), and the like. A 2nd active material may be used individually by 1 type, and may be used in combination of 2 or more type.

  When using the second active material as described above, as the second conductive core material, for example, a copper foil, a copper alloy foil, a nickel foil, or the like is used.

  Various resin materials are used as the binder constituting the mixture layer. For example, a fluororesin, an acrylic resin, a rubber particle, etc. are mentioned. Examples of the thickener include carboxymethyl cellulose (CMC). Examples of the conductive material include carbon black and carbon nanotube.

  As the separator, a microporous film made of polyethylene, polypropylene or the like is generally used. The thickness of the separator is, for example, 5 to 30 μm.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not necessarily limited to a following example.

Example 1
(I) Fabrication of ceramic film [first step]
100 parts by weight of LiNi _0.80 Co _0.15 Al _0.05 O ₂ powder having an average particle diameter of 1 μm as an active material, 16 parts by weight of polyvinyl butyral as a binder, 7.5 parts by weight of dibutyl phthalate as a plasticizer, and n-acetate as a dispersion medium Butyl was added and mixed with a zirconia ball in a ball mill for 24 hours to prepare an active material slurry.

[Second step]
The active material slurry was applied to a polyester resin carrier film having a release agent layer on the surface by a doctor blade method. Thereafter, the applied slurry was dried to form an active material green sheet (thickness: 5 μm).

[Third step]
Green sheets were laminated. Specifically, a polyester film having an adhesive layer on both sides is attached on a support base, a green sheet is attached to the adhesive layer, and the carrier film is applied at 80 ° C. with a pressure of 100 kg / cm ² . A hot press was performed. After hot pressing, the carrier film was peeled off. Further, another green sheet was placed on the green sheet fixed to the support base, and hot pressing was performed in the same manner. This operation was repeated to obtain a laminate having a desired thickness, and then the laminate was peeled from the polyester film and cut into a size of 7 mm × 7 mm to produce a green chip. The green chip was sandwiched between two alumina ceramic plates.

[Fourth step]
The green chip sandwiched between the ceramic plates is introduced into a firing apparatus, heated to 350 ° C. at a heating rate of 400 ° C./h in an oxygen atmosphere, and held at 350 ° C. for 5 hours to remove organic components such as a binder. Burned out. Subsequently, the temperature was raised to 780 ° C. at a rate of temperature rise of 1000 ° C./h in an oxygen atmosphere, and held for 1 hour to sinter the active material powder. Thus, a ceramic film having a thickness of 80 μm and a size of 7 mm × 7 mm (L1 = 7 mm, L2 = 7 mm in FIG. 3) was produced.

(Ii) Fabrication of positive electrode [Formation of carbon layer]
Polyvinylidene fluoride (PVDF, # 7200 manufactured by Kureha Co., Ltd.) and acetylene black were mixed at a weight ratio of 80: 100, and mixed with N-methyl-2-pyrrolidone to prepare a conductive paste. This conductive paste was applied to one side of a conductive core material (thickness 15 μm) made of Al foil by the doctor blade method and dried at 100 ° C. Thus, a carbon layer having a thickness of 15 μm was formed. The ratio of the surface of the conductive core material covered with the carbon layer (core material coverage B) was 100%.

[Formation of active material layer]
A ceramic film was arranged on the surface of the carbon layer in a grid pattern (10 rows × 10 rows) to form a positive electrode active material layer, and then vacuum dried at 60 ° C. The width of the gap between adjacent ceramic films was 0.5 mm, and the ratio of the surface of the conductive core material covered with the ceramic film (core material coverage A) was 96%.

[Formation of coating layer]
A copolymer of vinylidene fluoride and hexafluoropropylene (content ratio of hexafluoropropylene unit: 0.2 mol%, number average molecular weight: 300,000, hereinafter “VDF-HFP copolymer”) is converted to N-methyl-2. -An N-methyl-2-pyrrolidone solution containing 3% by weight of VDF-HFP copolymer was prepared by dissolving in pyrrolidone. The degree of swelling (weight increase rate) when the VDF-HFP copolymer is impregnated with the following nonaqueous electrolyte is 20%. The active material layer obtained above was immersed in this solution (liquid temperature: 25 ° C.), applied to the surface, and dried at 110 ° C. for 30 minutes to form a coating layer having a thickness of 5 μm.

(Iii) Production of Negative Electrode Spherical artificial graphite having an average particle diameter of 20 μm as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and water were mixed to prepare a negative electrode mixture paste. The amount of SBR was 1 part by weight per 100 parts by weight of the artificial graphite particles. After apply | coating the negative mix paste on the direction of the electrolytic copper foil (thickness 8 micrometers) which is a negative electrode conductive core material, it was dried at 110 degreeC. Thereafter, rolling was performed to obtain a negative electrode.

(Iv) Preparation of non-aqueous electrolyte A non-aqueous electrolyte was prepared by dissolving LiPF ₆ as a solute at a concentration of 1.25 mol / L in a non-aqueous solvent. The non-aqueous solvent is a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1: 1: 8, and 4% by volume of vinylene as an additive thereto. Carbonate (VC) was added.

(V) Production of Battery After connecting the lead to the positive electrode and the negative electrode, respectively, these were laminated so that the positive electrode active material layer and the negative electrode active material layer were opposed to each other through a separator to obtain an electrode group. The electrode group was inserted into an envelope-shaped exterior body made of a laminate film having an Al foil as a barrier layer, and then a nonaqueous electrolyte was injected to impregnate the electrode group with the nonaqueous electrolyte. Thereafter, the opening of the outer package was sealed with each lead led out.

(Vi) Electrochemical evaluation [initial capacity]
Under a 25 ° C. environment, constant current charging is performed at a rate of 0.5 C until the battery voltage reaches 4.2 V, then charging is continued until 0.05 C at a constant voltage of 4.2 V, and then 0.2 C Discharge was performed at a constant current of 2.5 V until the initial discharge capacity was obtained.

[Cycle characteristics]
Charging / discharging was repeated 20 cycles under the same conditions as described above, and the ratio of the discharge capacity obtained at the 20th cycle to the initial capacity was determined as a percentage.

[Rate characteristics]
Under a 25 ° C. environment, the first battery is charged at a constant current rate of 0.5 C until the battery voltage reaches 4.2 V, and then charged at a constant voltage of 4.2 V until it reaches 0.05 C. Discharging was performed at a constant current of 1 C until it reached 2.5 V, and the initial discharge capacity was determined.
The ratio (1C / 0.2C) of the discharge capacity at 1C to the discharge capacity at 0.2C was determined as a percentage.
The evaluation results are shown in Table 1.

Example 2
A battery was prepared in the same manner as in Example 1 except that the thickness of the ceramic film was 20 μm, and evaluated in the same manner.
Example 3
A battery was prepared in the same manner as in Example 1 except that the thickness of the ceramic film was 120 μm, and evaluated in the same manner.

Example 4
A battery was prepared in the same manner as in Example 1 except that the thickness of the carbon layer was 1 μm, and evaluated in the same manner.
Example 5
A battery was prepared in the same manner as in Example 1 except that the thickness of the carbon layer was 30 μm, and evaluated in the same manner.

Example 6
A battery was produced in the same manner as in Example 1 except that the thickness of the coating layer was 0.5 μm, and was similarly evaluated.
Example 7
A battery was prepared in the same manner as in Example 1 except that the thickness of the coating layer was 20 μm, and evaluated in the same manner.

<< Comparative Example 1 >>
A battery was prepared and evaluated in the same manner as in Example 1 except that the thickness of the ceramic film was 130 μm.
<< Comparative Example 2 >>
A battery was prepared and evaluated in the same manner as in Example 1 except that the thickness of the carbon layer was 0.5 μm.

<< Comparative Example 3 >>
A battery was produced in the same manner as in Example 1 except that the thickness of the carbon layer was 40 μm, and evaluated in the same manner.
<< Comparative Example 4 >>
A battery was prepared in the same manner as in Example 1 except that the thickness of the coating layer was 0.1 μm, and evaluated in the same manner.

<< Comparative Example 5 >>
A battery was prepared in the same manner as in Example 1 except that the thickness of the coating layer was 25 μm, and evaluated in the same manner.
The evaluation results of Examples 2 to 7 and Comparative Examples 1 to 4 are shown in Table 1.

  In the batteries of Examples 1 to 7, good and well-balanced electrochemical characteristics were obtained. On the other hand, Comparative Examples 1 to 5 could not obtain a well-balanced electrochemical characteristic.

  In Comparative Example 1, since the thickness of the ceramic film was as thick as 130 μm, it is considered that sufficient adhesion between the conductive core material and the ceramic film could not be ensured. In addition, it is presumed that the diffusion of lithium ions inside the ceramic film slowed down, and the rate characteristics deteriorated.

  In Comparative Example 2, since the carbon layer was as thin as 0.5 μm, it was presumed that sufficient conductivity could not be secured, and the discharge capacity, cycle characteristics, and rate characteristics were lowered.

  In Comparative Example 3, the carbon layer was as thick as 40 μm, so it is estimated that the rate characteristics were deteriorated.

  In Comparative Example 4, since the coating layer was as thin as 0.1 μm, it was estimated that sufficient adhesion between the conductive core material and the ceramic film could not be ensured, and the cycle characteristics and rate characteristics were deteriorated.

  In Comparative Example 5, since the coating layer was as thick as 25 μm, it is estimated that the diffusion of lithium ions between the electrodes was slowed and the rate characteristics were lowered.

  Next, when the positive electrodes of Examples 1 to 7 were wound around a core having a diameter of 4 mm, the ceramic film was not peeled off. On the other hand, peeling of the ceramic film was observed in the positive electrodes of Comparative Examples 2, 3, and 5.

In addition, when the positive electrode active material was changed to LiCoO ₂ and batteries similar to those in Examples 1 to 7 and Comparative Examples 1 to 5 were prepared and evaluated in the same manner, similar results were obtained.

  According to the present invention, it is possible to secure adhesion between the active material layer and the conductive core material and resistance to bending while increasing the capacity of the electrode for the nonaqueous electrolyte battery. The non-aqueous electrolyte battery of the present invention is useful as a power source for electronic devices such as personal computers and mobile phones, hybrid vehicles, and electric vehicles.

  10: electrode (first electrode), 11: conductive core material (first conductive core material), 12: carbon layer, 13: active material layer (first active material layer), 13a: ceramic film, 14: coating Layer: 15: first lead, 20: second electrode, 30: separator, 21: second conductive core material, 23: second active material layer, 25: second lead, 40: exterior body, 41: sealing resin

Claims (9)

A sheet-like conductive core;
A carbon layer disposed on the surface of the conductive core;
An active material layer disposed on the surface of the carbon layer;
A coating layer covering the active material layer,
The carbon layer has a thickness greater than 0.5 μm and 30 μm or less, and includes a conductive carbon material,
The active material layer includes at least one ceramic film having a thickness of 20 to 120 μm, and the ceramic film is a transition metal oxide sintered body capable of inserting and extracting lithium,
The coating layer is an electrode for a non-aqueous electrolyte battery having a thickness greater than 0.1 μm and 20 μm or less and containing an ion conductive polymer.   The electrode for a nonaqueous electrolyte battery according to claim 1, wherein the ceramic film has a thickness of 50 to 100 μm.   The electrode for a nonaqueous electrolyte battery according to claim 1 or 2, wherein the coating layer has a thickness of 1 to 20 µm.   The electrode for a nonaqueous electrolyte battery according to any one of claims 1 to 3, wherein the plurality of ceramic films are arranged randomly or regularly on the surface of the carbon layer.   The electrode for a nonaqueous electrolyte battery according to any one of claims 1 to 3, wherein the plurality of ceramic films are arranged on the surface of the carbon layer in a lattice shape or a tile shape.   The ion-conductive polymer is at least one selected from the group consisting of a fluororesin, a resin containing an ethylene oxide unit, a resin containing an acrylonitrile unit, and a resin containing an acrylate unit. An electrode for a nonaqueous electrolyte battery according to Item.   The electrode for a nonaqueous electrolyte battery according to claim 6, wherein the fluororesin contains a copolymer containing polyvinylidene fluoride units or polyvinylidene fluoride.   A positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte; the positive electrode, the negative electrode, and the separator are stacked to form an electrode group; the positive electrode and the negative electrode A nonaqueous electrolyte battery, at least one of which is the electrode according to any one of claims 1 to 7.   A positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the positive electrode, the negative electrode, and the separator are wound to form an electrode group, and the positive electrode and the negative electrode A nonaqueous electrolyte battery, wherein at least one of the electrodes is the electrode according to claim 4 or 5.

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