WO2019124123A1 - Method for manufacturing electrode for lithium ion secondary battery including composite consisting of active material and electrically conductive carbon material - Google Patents

Abstract

Provided is a method for manufacturing an electrode for a lithium ion secondary battery for which good rate characteristics are obtained even with a small usage amount of carbon material, and a lithium ion secondary battery using said electrode. The present invention is a method for manufacturing an electrode for a lithium ion secondary battery, the method including: a step for producing a composite by doing mixing processing of an active material that is a positive electrode active material or a negative electrode active material, and an electrically conductive carbon material; a step for producing a slurry by kneading the composite, a binder, and a solvent; and a step for producing an electrode that includes an active material layer by applying the slurry on a current collector and removing the solvent, wherein in the composite, the weight ratio of the active material:the electrically conductive carbon material is 88:12 to 96:4, when the active material is the positive electrode active material, the mean particle diameter of the composite is 20 µm or less, when the active material is the negative electrode active material, the mean particle diameter of the composite is 15 µm or less, and with the step for producing the slurry, there is no additional use of the electrically conductive carbon material.

Description

Method of manufacturing electrode for lithium ion secondary battery including composite composed of active material and conductive carbon material

The present invention relates to a method of manufacturing an electrode for a lithium ion secondary battery and a lithium ion secondary battery.

Lithium ion secondary batteries are used in portable devices, hybrid vehicles, electric vehicles, home storage batteries and the like. Lithium ion secondary batteries are required to have a well-balanced performance in terms of rate characteristics, cycle characteristics, and safety. Electrodes are one of the components that determine their performance. The active carbon material contained in the electrode and the conductive carbon material as the conductive support agent have large electrode properties obtained by the combination of the kind, mixing amount and mixing method, and further, the battery characteristics when the electrode is used are large. It is different.

With respect to the active material of the lithium ion secondary battery, lithium titanate and lithium manganese composite oxide attract attention as a highly safe active material. However, since these active materials have low conductivity, improvement of rate characteristics corresponding to high-speed charge and discharge is required.

As a technique for improving the conductivity of lithium titanate, there is disclosed a technique in which a conductive carbon material and lithium titanate are mixed in advance while applying a compressive force and a shear force (Patent Document 1). By performing this mixing process, lithium titanate and the conductive carbon material are uniformly mixed, and the density of lithium titanate is increased, so that the conductivity of lithium titanate as an active material is improved.

JP, 2015-5444, A

However, in the technique disclosed in the above patent document, lithium titanate and the conductive carbon material are mixed and treated in advance, and the conductive carbon material is additionally used in the slurry production process. Therefore, the amount of conductive carbon material used has increased. Furthermore, since the number of battery manufacturing processes is increased as compared with the conventionally known electrode manufacturing method, there is a problem such as an increase in loss of material, which is disadvantageous from the viewpoint of cost and there is room for improvement. Moreover, the effect of rate characteristic improvement was unknown as compared with the electrode using the slurry manufactured by only increasing the usage-amount of a conductive carbon material.

As a result of intensive studies to solve the above problems, the inventors of the present invention mixed and processed an active material and a conductive carbon material at a weight ratio in a specific range in a method of manufacturing an electrode for a lithium ion secondary battery. And finding that a lithium secondary battery having excellent rate characteristics can be obtained by using an electrode obtained from a production method including a step of producing a slurry comprising a composite having an optimum average particle size, a binder and a solvent. , Completed the present invention.

The present invention therefore aims to solve the improvement of the rate characteristics without using many carbon materials. That is, it is an object of the present invention to provide a method for producing an electrode for a lithium ion secondary battery, and a lithium ion secondary battery using the electrode, in which good rate characteristics can be obtained even with a small amount of carbon material used.

The present invention includes the following aspects.

(1) a step of mixing and processing an active material which is a positive electrode active material or a negative electrode active material, and a conductive carbon material to produce a composite;
Kneading the composite, the binder and the solvent to produce a slurry;
Applying the slurry on a current collector, removing the solvent, and producing an electrode including an active material layer, and a method of producing an electrode for a lithium ion secondary battery,
In the composite, the weight ratio of the active material to the conductive carbon material is 88:12 to 96: 4,
When the active material is a positive electrode active material, the average particle diameter of the composite is 20 μm or less, and when the active material is a negative electrode active material, the average particle diameter of the composite is 15 μm or less,
In the step of preparing the slurry, a conductive carbon material is not additionally used.

(2) The method according to (1), wherein the active material is a negative electrode active material composed of lithium titanate, and the average particle diameter of the composite is 5 μm or less.

(3) The method according to (1), wherein the active material is a positive electrode active material composed of a lithium manganese composite oxide, and the average particle diameter of the composite is 20 μm or less.

(4) The lithium manganese complex oxide is preferably Li _{1 + x} Al _y Mn _2-xy O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1), Li _{1 + x} Mg _y Mn _{2-x- y} O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1), Li _{1 + x} Zn _y Mn _2-xy O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1) a _{Li 1 + x Cr y Mn 2} -x-y O 4 (0 ≦ x ≦ 0.1,0 <y ≦ 0.1) 1 or more of the spinel-type lithium manganate which is selected from the group consisting of the above Method (3).

(5) The method according to any one of the above (1) to (4), wherein the mixing process is performed by a mechanochemical method.

(6) A lithium ion secondary battery using an electrode obtained by the method of any of the above (1) to (5).

(7) A lithium ion secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, a non-aqueous electrolyte, and the packaging material,
A lithium ion secondary battery, wherein the positive electrode and / or the negative electrode is an electrode manufactured by any of the methods (1) to (5).

The electrode produced by the method of the present invention can easily maintain the conductive path of the composite contained in it, and the electrode resistance becomes low, so it is more active than in the case where it is produced using a conventional known slurry. The proportion of conductive carbon material not in contact with the substance is small. Therefore, the binder is easily dispersed uniformly, whereby the adhesion to the current collector is improved. Furthermore, the falling off of the material contained in the slurry is suppressed. As a result, by using the electrode, a lithium ion secondary battery excellent in rate characteristics can be obtained. Furthermore, since the amount of conductive carbon material used does not increase without increasing the number of electrode manufacturing steps, it is also advantageous from the viewpoint of reduction in production cost.

It is a SEM photograph which shows an example of the complex of this invention. It is a SEM photograph which shows another example of the complex of this invention.

Production of Electrode for Lithium Ion Secondary Battery The method for producing an electrode for a lithium ion secondary battery according to the present invention comprises subjecting an active material which is a positive electrode active material or a negative electrode active material and a conductive carbon material to a mixture treatment. A step of preparing a body, a step of kneading the composite, a binder and a solvent to prepare a slurry, and applying the slurry on a current collector, removing the solvent, and an electrode including an active material layer Manufacturing the In the composite, the weight ratio of the active material to the conductive carbon material is 88:12 to 96: 4. When the active material is a positive electrode active material, the average particle size of the composite is 20 μm or less, and when the active material is a negative electrode active material, the average particle size of the composite is 15 μm or less. Furthermore, in the step of producing the slurry, a conductive carbon material is not additionally used.

In the following, the case where the active material is a positive electrode active material and the case where it is a negative electrode active material, that is, the case where the electrode is a positive electrode and the case where it is a negative electrode will be separately described.

(1) Production Method of Positive Electrode (Electrode) When the electrode is a positive electrode, charging and discharging of the lithium ion secondary battery are performed by insertion and detachment of lithium ions, and lithium ion insertion and detachment are possible. Active material (positive electrode active material). The positive electrode active material has an average working potential of 3.0 V or more and 4.5 V (vs. Li ^/ Li ⁺ ) or less. Note that “(vs. Li ^/ Li ⁺ )” indicates a potential difference between an operating electrode made of an electrode containing a positive electrode active material and a counter electrode made of lithium metal. In addition, the positive electrode is manufactured by a method including the steps of preparing a composite, preparing a slurry, and preparing an electrode. The details of each process are as follows.

<Step of preparing complex>
In the step of producing a composite, the positive electrode active material (active material) and the conductive carbon material are mixed and processed to form a composite. The composite is made of an active material and a conductive carbon material, and the active material: conductive carbon material = 88: 12 to 96: 4 (wt%). If the active material is less than 88 wt%, the capacity of the battery is too small. In addition, conductive carbon materials that are not fused to the active material will be present. Therefore, when it is made a slurry, it becomes difficult to adhere to the binder, and the adhesion to the current collector is reduced. On the other hand, when the content is more than 96 wt%, the conductivity is not ensured, and the resistance is increased, so that the battery characteristics are deteriorated.

From the viewpoint of enhancing the battery characteristics to be obtained, preferably, active material: conductive carbon material = 90: 10 to 95: 5 (wt%), and more preferably, active material: conductive carbon material = 91: 9 to 94: 6 (wt%).

When the active material is a positive electrode active material, the average particle diameter of the composite is preferably 20 μm or less, more preferably 17 μm or less, and still more preferably 15 μm or less. By setting the average particle size of the composite of the positive electrode active material to 20 μm or less, the particle size of the composite is optimized, and the filling property of the electrode is improved. In addition, it is considered that the contact between the active materials is improved, an electrode having high conductivity can be manufactured, and the rate characteristics are improved when used in a secondary battery. Furthermore, by reducing the proportion of the conductive carbon material not in contact with the active material, the adhesion to the current collector is improved, and the falling of the material contained in the slurry is suppressed.

In the present specification, the particle size of the composite is defined as an average particle size (median size, D50), and the particles are uniformly dispersed in a solvent, and a particle size distribution analyzer of laser diffraction / scattering method (for example, Microtrac MT 3000) Mean the value measured by Nikkiso Co., Ltd.). As a solvent to be used, an aqueous system or an organic solvent system can be used, and examples thereof include water and alcohol.

The complex can be produced, for example, by a mechanochemical method. The mechanochemical method is preferable because the particles of the active material and the conductive carbon material can be mechanically mixed while applying energy such as shear force, compression force, collision force and centrifugal force. In general, in the case of producing a composite using particles of different materials, firing is performed at a high temperature of, for example, 500 ° C. or higher. However, the mechanochemical method is capable of forming a good interface on the particles and fusing different particles under relatively low temperature conditions. In addition, compared with the conventional method, the number of steps of the entire electrode manufacturing process is not increased, and the amount of the conductive carbon material is not increased, resulting in an increase in production efficiency.

Although it does not specifically limit as an apparatus to be used, For example, Nobilta (made by Hosokawa Micron company), a planetary ball mill (made by Fritsch company) can be used suitably. Moreover, as a mixing method, it may be dry mixing or wet mixing. In the case of wet mixing, the solvent to be used is not particularly limited, and water and an organic solvent can be used. As an organic solvent, alcohol, such as ethanol, can be used, for example. The mixing time is preferably 5 to 90 minutes, more preferably 10 to 60 minutes. The mixed atmosphere is not particularly limited, and can be performed under an inert gas atmosphere or an air atmosphere. The treatment temperature is preferably 5 to 100 ° C., more preferably 8 to 80 ° C., and still more preferably 10 to 50 ° C.

As the positive electrode active material, preferably, a lithium manganese composite oxide is used, equation _{(1): Li 1 + x} M y Mn 2-x-y O 4 ( provided that, 0 ≦ x ≦ 0.2,0 <y ≦ The spinel-type lithium manganate represented by the general formula (1) is more preferably 0.6, and M is at least one selected from the group consisting of elements belonging to Groups 2 to 13 and Period 3 to 4).

In the spinel-type lithium manganate, M is preferably Al, Mg, Zn, Ni, Co, Fe, Ti, Cu, Zr or Cr, since the effect of improving the stability of the positive electrode active material itself is large, and the positive electrode active material itself Al, Mg, Zn, Ti, and Ni are more preferable because the effect of improving the stability of is particularly large.

Since spinel lithium manganate has a high average voltage and good energy density,
Li _{1 + x} Al _y Mn _2-xy O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1),
Li _{1 + x} Mg _y Mn _2-xy O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1),
_{Li 1 + x Zn y Mn 2} -x-y O 4 (0 ≦ x ≦ 0.1,0 <y ≦ 0.1), and _{Li 1 + x Cr y Mn 2} -x-y O 4 (0 ≦ x ≦ 0. It is preferable that one or more selected from 1 and 0 <y ≦ 0.1),
Li _{1 + x} Al _y Mn _2-xy O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1), and Li _{1 + x} Mg _y Mn _2-xy O ₄ (0 ≦ x ≦ 0. It is more preferable that one or more selected from 1 and 0 <y ≦ 0.1),
Li _{1 + x} Al _y Mn _2-xy O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1),
Is more preferred.

Among these positive electrode active materials, the positive electrode active material may be appropriately selected in consideration of the battery performance in combination with the negative electrode active material. In addition, the plurality of positive electrode active materials may be used in combination.

The conductive carbon material is preferably a carbon material. In particular, carbon black is preferable, and examples thereof include natural graphite, artificial graphite, vapor grown carbon fiber, carbon nanotubes, acetylene black, ketjen black, and furnace black. These may be one type or two or more types.

<Slurry preparation process>
In the slurry preparation step, the positive electrode composite and the binder are kneaded in a solvent to prepare a positive electrode slurry. The preparation of the slurry may be carried out using a conventionally known technique. In the present specification, depending on the type of active material used for the composite, it may be referred to as a positive electrode slurry or a negative electrode slurry.

In the production method of the present invention, the conductive carbon material is not additionally used in the step of producing the slurry. When the conductive carbon material is additionally used, the capacity retention rate of discharge or charge is lowered. It is believed that this is because the dispersion of the added conductive carbon material becomes uneven.

The solvent is not particularly limited, and conventionally known materials may be used, and examples thereof include water and N-methylpyrrolidone. Moreover, a binder is a material which improves the binding property of the composite (it is also mentioned the composite for positive electrodes) which consists of a positive electrode active material and a conductive carbon material, and a collector. The binder is not particularly limited, but it is preferably at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber, polyimide, and derivatives thereof. Used.

The amount of the binder is the weight ratio of the composite for the positive electrode, preferably the composite for the positive electrode: binder = 98: 2 to 90: 10, more preferably the composite for the positive electrode: binder = 97: 3 to 92: 8, further Preferably, the positive electrode composite: binder = 96: 4 to 93: 7. Within the above range, sufficient adhesion between the positive electrode composite and the current collector can be obtained.

In order to further improve the dispersibility of the binder, a dispersant or a thickener may be added to the slurry. The type and amount of dispersant added, and the method of addition can use conventionally known techniques. For example, when using a binder of styrene-butadiene rubber, carboxymethyl cellulose can be used in combination as a thickener. Furthermore, in order to improve the dispersibility of the binder, the binder may contain a dispersant.

<Production process of positive electrode (electrode)>
Thereafter, the positive electrode slurry is applied onto the current collector, and the solvent is removed to produce a positive electrode (electrode) including the positive electrode active material layer. Here, the positive electrode active material layer refers to a layer in the positive electrode, and includes a positive electrode composite that contributes to the insertion and removal of lithium ions in the positive electrode. The application to the current collector and the removal of the solvent may be carried out using a known technique.

The thickness of the positive electrode active material layer is preferably 10 μm or more and 200 μm or less. The density of the positive electrode active material layer is preferably 1.0 g / cm ³ or more and 4.0 g / cm ³ or less, more preferably 1.5 g / cm ³ or more and 3.5 g / cm ³ or less, and 2 .0g / cm ³ or more 3.0 g / cm ³ or less is more preferred. If the density is 1.0 g / cm ³ or more, the contact with the current collector is good, and if the density is 4.0 g / cm ³ or less, the non-aqueous electrolyte is likely to penetrate into the positive electrode. The density of the positive electrode active material layer may be adjusted by compression of the positive electrode. As a compression method, a roll press, a hydraulic press or the like is suitably used.

The current collector is a member that collects current from the positive electrode active material. The thickness of the current collector is not particularly limited, but is preferably 10 μm or more and 100 μm or less. Moreover, as a collector, copper, nickel, aluminum, or its alloy etc. are mentioned. However, in view of corrosion resistance and weight, aluminum and its alloy are preferable, and high purity aluminum represented by JIS standard 1030, 1050, 1085, 1N90, 1N99 or the like is more preferable. Aluminum or alloys thereof are further preferred.

The positive electrode may have the same active material layer formed on one side or both sides of the current collector, and the positive electrode active material layer is formed on one side of the current collector and the negative electrode active material layer is formed on one side, that is, bipolar It may be a (bipolar) electrode.

(2) Method of Producing Negative Electrode (Electrode) When the electrode is a negative electrode, the negative electrode has an average operating potential of 0.5 V (vs. Li ^/ Li ⁺ ) or more and 2.0 V (vs. The active material (negative electrode active material) which is less than Li / Li ^<+ > is included. The negative electrode is produced by a method including the steps of producing a composite, producing a slurry, and producing an electrode. The details of each process are as follows.

<Step of preparing complex>
In the step of producing a composite, the negative electrode active material (active material) and the conductive carbon material are mixed and processed to form a composite. The composite is made of an active material and a conductive carbon material, and the active material: conductive carbon material = 88: 12 to 96: 4 (wt%). If the active material is less than 88 wt%, the capacity of the battery is too small. In addition, conductive carbon materials that are not fused to the active material will be present. Therefore, when it is made a slurry, it becomes difficult to adhere to the binder, and the adhesion to the current collector is reduced. On the other hand, when the content is more than 96 wt%, the conductivity is not ensured, and the resistance is increased, so that the battery characteristics are deteriorated.

From the viewpoint of enhancing the battery characteristics to be obtained, preferably, active material: conductive carbon material = 90: 10 to 95: 5 (wt%), and more preferably, active material: conductive carbon material = 91: 9 to 94: 6 (wt%).

When the active material is a negative electrode active material, the average particle diameter of the composite is preferably 15 μm or less, more preferably 10 μm or less, and still more preferably 5 μm or less. By setting the average particle size of the composite to 15 μm or less, preferably 5 μm or less, the particle size of the composite is optimized, and the filling property of the electrode is improved. In addition, it is considered that the contact between the active materials is improved, an electrode having high conductivity can be manufactured, and the rate characteristics are improved when used in a secondary battery. Furthermore, by reducing the proportion of the conductive carbon material not in contact with the active material, the adhesion to the current collector is improved, and the falling of the material contained in the slurry is suppressed.

The composite can be produced, for example, by the mechanochemical method, as in the case of the positive electrode. The apparatus used and conditions are the same as that of the case of a positive electrode.

As the negative electrode active material, preferably, lithium titanate is used. Lithium titanate may contain trace amounts of elements other than titanium, such as lithium or niobium (Nb). As the lithium titanate spinel structure is preferably a Rams Delight type, Li ₄ Ti ₅ O represented by is more preferable at ₁₂ as molecular formula. The spinel structure is preferable because the expansion and contraction of the active material is small in the reaction of insertion and desorption of lithium ions.

A carbon material is suitably used as the conductive carbon material. In particular, carbon black is preferably used, and examples thereof include natural graphite, artificial graphite, vapor grown carbon fibers, carbon nanotubes, acetylene black, ketjen black, and furnace black. These may be used alone or in combination of two or more.

<Slurry preparation process>
Next, the composite (composite for negative electrode) composed of the negative electrode active material and the conductive carbon material and the binder are kneaded in a solvent to prepare a negative electrode slurry. The preparation of the slurry may be carried out using a conventionally known technique. The solvent is not particularly limited, and conventionally known materials may be used, and examples thereof include water and N-methylpyrrolidone. The negative electrode contains a binder. The kind of binder is the same as that of the positive electrode.

In the production method of the present invention, the conductive carbon material is not additionally used in the step of producing the slurry. When the conductive carbon material is additionally used, the capacity retention rate of discharge or charge is lowered. It is considered that this is because the dispersion of the added conductive carbon material becomes uneven.

<Production process of electrode (negative electrode)>
Thereafter, the negative electrode slurry is applied onto the current collector, and the solvent is removed to prepare a negative electrode (electrode) including the negative electrode active material layer. Here, the negative electrode active material layer is a layer in the negative electrode, and indicates a layer including the composite for the negative electrode which contributes to insertion and detachment of lithium ions in the negative electrode. For application to the current collector and removal of the solvent, conventionally known techniques may be used.

The thickness of the negative electrode active material layer is preferably 10 μm to 200 μm. The density of the negative electrode active material layer is preferably 0.5 g / cm ³ or more and 3.0 g / cm ³ or less, more preferably 0.7 g / cm ³ or more and 2.7 g / cm ³ or less. More preferably, it is 0 g / cm ³ or more and 2.5 g / cm ³ or less. When the density is 1.0 g / cm ³ or more, the contact with the current collector is good, and when the density is 3.0 g / cm ³ or less, the non-aqueous electrolyte is likely to penetrate into the negative electrode. The density of the negative electrode active material layer may be adjusted by compression of the negative electrode. As a compression method, a roll press, a hydraulic press or the like is suitably used.

The current collector is a member that collects current from the negative electrode active material. The thickness and material of the current collector are the same as in the case of the positive electrode.

In the negative electrode, the same active material layer may be formed on one side or both sides of the current collector, and the positive electrode active material layer is formed on one side of the current collector and the negative electrode active material layer is formed on one side, that is, bipolar It may be a (bipolar) electrode.

Lithium Ion Secondary Battery The lithium ion secondary battery of the present invention is composed of a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, a non-aqueous electrolyte, and an exterior material. A terminal is electrically connected to each positive electrode and negative electrode, and each terminal further has a terminal extending portion extending to the outside of the package. Alternatively, a plurality of lithium ion secondary batteries may be connected to form an assembled battery.

The positive electrode and / or the negative electrode (electrode) are produced by the above method. The details are as described above. Therefore, in the following, the separator, the non-aqueous electrolyte and the packaging material will be described.

<Separator>
The separator is disposed between the positive electrode and the negative electrode and has a function as a medium that mediates the conduction of lithium ions between them while blocking the conduction of electrons and holes therebetween, at least the electrons and holes. It does not have the conductivity of

As the separator, nylon, cellulose, polysulfone, polyethylene, polypropylene, polybutene, polyacrylonitrile, polyimide, polyamide, polyethylene terephthalate, and composites of two or more of them are suitably used.

The shape of the separator may be any structure provided between the positive electrode and the negative electrode and capable of containing an insulating non-aqueous electrolyte, and a woven fabric, a non-woven fabric, a microporous film or the like is suitably used.

The separator may contain a plasticizer, an antioxidant or a flame retardant, or may be coated with a metal oxide or the like.

The thickness of the separator is preferably 10 μm or more and 100 μm or less, and more preferably 12 μm or more and 50 μm or less.

The porosity of the separator is preferably 30% or more and 90% or less, more preferably 35% or more and 85% or less from the viewpoint of good balance between lithium ion diffusibility and short circuit prevention property, and the balance is particularly excellent. Therefore, 40% or more and 80% or less is more preferable.

<Non-aqueous electrolyte>
Nonaqueous electrolytes mediate ion transfer between the negative and positive electrodes. The non-aqueous electrolyte contains at least a non-aqueous solvent and an electrolyte. The non-aqueous solvent is preferably an aprotic non-polar solvent and / or an aprotic polar solvent, more preferably an aprotic polar solvent. Examples include carbonates, esters, lactones, sulfones, nitriles and ethers. Specifically, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methyl propyl carbonate, acetonitrile, γ-butyrolactone, 1,2-dimethoxyethane, sulfolane, dioxolane, methyl propionate Etc.

These solvents may be used as a mixture of plural kinds in order to adjust the balance such as viscosity and solubility lithium ion conductivity.

The electrolyte is a lithium salt such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiBOB (Lithium Bis (Oxalato) Borate), Li [N (SO ₂ CF ₃ ) ₂ ], Li [N (N) SO ₂ C ₂ F ₅ ) ₂ ], Li [N (SO ₂ F) ₂ ], or Li [N (CN) ₂ ], etc., and the concentration of the lithium salt is 0.5 mol / L or more. If it is 5 mol / L or less, it is used suitably.

The non-aqueous electrolyte may be contained in advance in the positive electrode, the negative electrode and the separator, or may be added after laminating one in which the separator is disposed between the positive electrode and the negative electrode.

The non-aqueous electrolyte may be an electrolyte in which the electrolyte is dissolved in a non-aqueous solvent, or may be a gel electrolyte in which a polymer is impregnated with an electrolyte in which the electrolyte is dissolved in the non-aqueous solvent.

The amount of the non-aqueous electrolyte is appropriately adjusted in accordance with the area of the positive electrode, the negative electrode and the separator, the amount of the active material, and the volume of the battery.

The non-aqueous electrolyte may contain an additive such as a flame retardant. For example, tris (2,2,2-trifluoroethyl) phosphate and ethoxy (pentafluoro) cyclotriphosphazene as flame retardants, and vinylene carbonate, 1,3-propane sultone, succinonitrile etc. as additives .

<Exterior material>
The packaging material is a laminated body formed by alternately laminating or winding a positive electrode, a negative electrode and a separator, and a member for sealing a terminal for electrically connecting the laminated body. The number of stacked layers may be appropriately adjusted in order to obtain a desired voltage value and battery capacity.

As the exterior material, a composite film in which a thermoplastic resin layer for heat sealing is provided on a metal foil, and a metal layer formed by vapor deposition or sputtering are suitably used. As its shape, a metal can of square, oval, cylindrical, coin, button or sheet form is preferably used.

The present invention will be more specifically described below based on Examples and Comparative Examples. However, the present invention is not limited to this.

Example 1
Preparation of electrode (negative electrode) and battery 40 g of lithium titanate (LTO) and 2.8 g of acetylene black as a conductive carbon material were mixed. At this time, lithium titanate and acetylene black had a weight ratio of 93.5: 6.5. The resulting mixture was introduced into a precision dispersion / complexation processing device Nobilta-MINI (manufactured by Hosokawa Micron), and treated at a rotational speed of 2000 to 3500 rpm at 25 to 35 ° C. for 10 minutes to obtain a complex A. The average particle size of Complex A was 3.0 μm. The scanning electron micrograph of the obtained complex A is shown in FIG.

The negative electrode slurry was prepared by mixing the complex A and a solution obtained by dissolving PVdF as a binder in N-methylpyrrolidone (NMP) as a solvent. The composition of the slurry was LTO: acetylene black: PVdF = 91.6: 6.4: 2.0 by weight ratio. The negative electrode slurry was coated on a 15 μm-thick current collector of aluminum, dried overnight at 120 ° C., pressed to a thickness of 60 μm, and punched to 16 mm diameter to prepare a negative electrode.

The negative electrode was used as an operating electrode, metal lithium was used as a counter electrode, and a separator of 20 μm in thickness was interposed, and stacked in a test cell (HS cell, manufactured by Takasen Co., Ltd.). A lithium ion secondary battery was manufactured by charging 0.15 mL of the non-aqueous electrolyte. At this time, ethylene carbonate (EC) / propylene carbonate (PC) / ethyl-methyl-carbonate (EMC) = 15/15/70 vol% as a solvent for the non-aqueous electrolyte, and LiPF ₆ as a solute 1 mol / L.

Evaluation of electrodes and batteries As evaluation of rate characteristics, the battery is connected to a charge / discharge test device (HJ1005SD8, manufactured by Hokuto Denko), constant current charge / discharge at 0.2C and 10C rate in a voltage range of 1 to 3 V at 25 ° C. The charge capacity and the discharge capacity were measured, and the capacity retention rate was calculated.

The C rate described above defines the current value required to charge or discharge the entire capacity of the lithium ion secondary battery in one hour as 1 C, for example, 0.02 C is 0.02 times the current value Point to

Further, the capacity retention rate refers to the ratio of the discharge and charge capacities at 10 C to the discharge and charge capacities at 0.2 C as a capacity retention rate. For example, assuming that the discharge capacity of 0.2 C is 100, if the discharge capacity of 10 C is 80, the capacity retention ratio is 80%.

Furthermore, as evaluation of the adhesiveness of an electrode, 20 mm width aluminum tape was affixed and it measured using the autograph as peeling strength in a 90 degree state. The results are shown in Table 1.

Example 2
A composite B was prepared with lithium titanate and acetylene black at a weight ratio of 89: 11, and the electrode and battery were prepared and evaluated in the same manner as in Example 1 except that an electrode was prepared using this composite B. went.

[Example 3]
A composite C was prepared using lithium titanate and acetylene black at a weight ratio of 95: 5, and the electrode and battery were prepared and evaluated in the same manner as in Example 1 except that this composite C was used to prepare an electrode. went.

Comparative Example 1
The electrode and the battery were prepared and evaluated in the same manner as in Example 1 except that a slurry was prepared using the composite D in the preparation of the electrode. Complex D was produced as follows. 40 g of lithium titanate and 2.0 g of acetylene black were mixed. At this time, the weight ratio of lithium titanate to acetylene black was 95.2: 4.8. The resulting mixture was loaded into a precision dispersion / complexation processor Nobilta-MINI (manufactured by Hosokawa Micron), and treated at a rotation number of 2000 to 3500 rpm at 25 to 35 ° C. for 10 minutes to obtain Complex D.

A slurry was prepared by mixing 32.1 g of the complex D, a solution of PVdF dissolved in NMP, and 0.6 g of acetylene black. The weight ratio of lithium titanate, acetylene black, and PVdF contained in the slurry was 91.6: 6.4: 2.0.

Comparative Example 2
In the case of electrode preparation, preparation and evaluation of the electrode were performed in the same manner as Example 1 except that a slurry was prepared as follows. A slurry was prepared by mixing lithium titanate, acetylene black, and a solution of PVdF dissolved in NMP. The weight ratio of lithium titanate, acetylene black, and PVdF contained in the slurry was 91.6: 6.4: 2.0.

Comparative Example 3
The electrode and the battery were prepared and evaluated in the same manner as in Example 1 except that a slurry was prepared using the composite D in the preparation of the electrode. 12 g of lithium titanate and 6.0 g of acetylene black were mixed at a weight ratio of lithium titanate to acetylene black of 67:33. This mixture was introduced into a precision dispersion and compounding processor Nobilta-MINI (manufactured by Hosokawa Micron), and treated at a rotational speed of 2000 to 3500 rpm at 25 to 35 ° C. for 10 minutes to obtain complex E.

A slurry was prepared by mixing Complex E and a solution of PVdF in NMP. The weight ratio of lithium titanate, acetylene black, and PVdF contained in the slurry was 64: 32: 4.0.

Comparative Example 4
The electrode and the battery were prepared and evaluated in the same manner as in Example 1 except that a slurry was prepared using the composite F in the electrode preparation. 40 g of lithium titanate and 0.8 g of acetylene black were mixed at a weight ratio of lithium titanate to acetylene black of 98: 2. This mixture was introduced into a precision dispersion and compounding processor Nobilta-MINI (manufactured by Hosokawa Micron), and treated at a rotational speed of 2000 to 3500 rpm at 25 to 35 ° C. for 10 minutes to obtain a complex F.

A slurry was prepared by mixing Complex F and a solution of PVdF in NMP. The weight ratio of lithium titanate, acetylene black, and PVdF contained in the slurry was 96: 2: 2.

Comparative Example 5
The electrode and the battery were prepared and evaluated in the same manner as in Example 1 except that a slurry was prepared as follows in the preparation of the electrode. 40 g of lithium titanate and 2.8 g of acetylene black were mixed at a weight ratio of lithium titanate to acetylene black of 93.5: 6.5. This mixture was charged into a precision dispersion / combination processor Nobilta-MINI (manufactured by Hosokawa Micron), and treated at a rotation number of 2000 to 3500 rpm at 25 to 35 ° C. for 30 minutes to obtain a complex G.

Example 4
Preparation of Electrode (Positive Electrode) and Battery 40 g of Li _1.1 Al _0.1 Mn _1.8 O ₄ (LAMO) and 3 g of acetylene black as a conductive carbon material were mixed. At this time, LAMO and acetylene black had a weight ratio of 93: 7. The resulting mixture was charged into a precision dispersion / complexation processor Nobilta-MINI (manufactured by Hosokawa Micron), and treated at a rotational speed of 2000 to 3500 rpm at 25 to 35 ° C. for 10 minutes to obtain a complex H. The average particle size of Complex H was 15.9 μm. The scanning electron micrograph of the obtained complex H is shown in FIG.

The positive electrode slurry was prepared by mixing the complex H and a solution in which PVdF as a binder was dissolved in N-methylpyrrolidone (NMP) as a solvent. The composition of the slurry was LAMO: acetylene black: PVdF = 91: 7: 2 in weight ratio. The positive electrode slurry was coated on a 15 μm-thick current collector of aluminum, dried overnight at 120 ° C., pressed to a thickness of 62 μm, and punched into 16 mm diameter to prepare a positive electrode.

The positive electrode is used as an operating electrode, metal lithium is used as a counter electrode, and a 20 μm-thick separator is interposed in a test cell (HS cell, manufactured by Hosen Co., Ltd.). A battery was made. At this time, ethylene carbonate (EC) / propylene carbonate (PC) / ethyl-methyl-carbonate (EMC) = 15/15/70 vol% as a solvent for the non-aqueous electrolyte, and LiPF ₆ as a solute 1 mol / L.

Evaluation of electrodes and batteries As evaluation of rate characteristics, the battery is connected to a charge / discharge test device (HJ1005SD8, manufactured by Hokuto Denko), constant current at 0.2C and 10C rate in a voltage range of 3 to 4.5 V at 25 ° C. Charge and discharge were performed to measure the charge capacity and the discharge capacity, and the capacity retention rate was calculated.
Further, in the same manner as in Example 1, the adhesion of the electrode was evaluated. The results are shown in Table 2.

[Example 5]
The electrode and the battery were prepared and evaluated in the same manner as in Example 4 except that a slurry was prepared using the complex I in the preparation of the electrode. 30 g of LAMO and 3.7 g of acetylene black were mixed at a weight ratio of 89:11 for LAMO and acetylene black. This mixture was introduced into a precision dispersion and compounding processor Nobilta-MINI (manufactured by Hosokawa Micron), and treated at a rotational speed of 2000 to 3500 rpm at 25 to 35 ° C. for 10 minutes to obtain Complex I. Complex I and a solution of PVdF dissolved in NMP were mixed to prepare a slurry. The weight ratio of LAMO, acetylene black, and PVdF contained in the slurry was 86: 11: 3.

Comparative Example 6
The electrode and the battery were manufactured and evaluated in the same manner as in Example 4 except that a slurry was manufactured in the following manner. A slurry was prepared by mixing LAMO, acetylene black, and a solution of PVdF dissolved in NMP. The weight ratio of LAMO, acetylene black, and PVdF contained in the slurry was 91: 7: 2.

Comparative Example 7
The electrode and the battery were prepared and evaluated in the same manner as in Example 4 except that a slurry was prepared using the composite J during the preparation of the electrode. 40 g of LAMO and 0.6 g of acetylene black were mixed at a weight ratio of LAMO to acetylene black of 98.5: 1.5. This mixture was introduced into a precision dispersion and compounding processor Nobilta-MINI (manufactured by Hosokawa Micron), and treated at a rotational speed of 2000 to 3500 rpm at 25 to 35 ° C. for 10 minutes to obtain a complex J.

The slurry was prepared by mixing the complex J and a solution of PVdF dissolved in NMP. The weight ratio of LAMO, acetylene black, and PVdF contained in the slurry was 95.5: 1.5: 3.

Comparative Example 8
The electrode and the battery were prepared and evaluated in the same manner as in Example 4 except that a slurry was prepared using the composite K in the preparation of the electrode. 20 g of LAMO and 5 g of acetylene black were mixed at a weight ratio of LAMO to acetylene black of 80:20. This mixture was charged into a precision dispersion and compounding processor Nobilta-MINI (manufactured by Hosokawa Micron), and treated at a rotation speed of 2000 to 3500 rpm at 25 to 35 ° C. for 10 minutes to obtain a complex K.

A slurry was prepared by mixing the complex K and a solution of PVdF dissolved in NMP. The weight ratio of LAMO, acetylene black, and PVdF contained in the slurry was 77: 19: 4.

As shown in Tables 1 and 2, the weight ratio and the average particle size of the lithium titanate and the conductive carbon material contained in the composite, and the spinel lithium manganate and the conductive carbon material contained in the composite are as follows: In the optimum range, it is possible to obtain an electrode excellent in adhesion, and it is further understood that the secondary battery using the electrode exhibits excellent rate characteristics.

In Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 6, and Comparative Example 8, the peel strength indicating adhesiveness decreased. It is presumed that this is because PVdF is adsorbed to acetylene black having a large surface area, and a sufficient amount of binder does not exist for binding of the active material and the complex. Moreover, the capacity | capacitance maintenance factor of discharge in the comparative example 1 and the comparative example 2 became low. This is considered to be because, in Comparative Example 1, since the acetylene black was added at the time of slurry production, the dispersion of the added excess acetylene black was uneven. Further, Comparative Example 2 is considered to be because the conductive path was not sufficiently formed because the dispersion state of acetylene black in the electrode was insufficient due to the conventional mixing method.

It is considered that Comparative Examples 4 and 7 have low capacity retention rates of charge and discharge because the amount of the conductive carbon material is small.

It is considered that Comparative Example 5 had a low capacity retention rate because the conductive particles in the electrode were insufficient because the average particle size of the composite was large.

From the above, an electrode including a composite of a conductive carbon material and lithium titanate, or a conductive carbon material and spinel-type lithium manganate provides an electrode with high adhesion, and the use of the electrode makes it possible to It became clear that the lithium ion secondary battery excellent in the characteristic was obtained.

Claims (7)

Mixing the active material which is the positive electrode active material or the negative electrode active material and the conductive carbon material to produce a composite;
Kneading the composite, the binder and the solvent to produce a slurry;
Applying the slurry on a current collector, removing the solvent, and producing an electrode including an active material layer, and a method of producing an electrode for a lithium ion secondary battery,
In the composite, the weight ratio of the active material to the conductive carbon material is 88:12 to 96: 4,
When the active material is a positive electrode active material, the average particle diameter of the composite is 20 μm or less, and when the active material is a negative electrode active material, the average particle diameter of the composite is 15 μm or less,
In the step of preparing the slurry, a conductive carbon material is not additionally used. The method according to claim 1, wherein the active material is a negative electrode active material composed of lithium titanate, and the average particle diameter of the composite is 5 μm or less. The method according to claim 1, wherein the active material is a positive electrode active material composed of a lithium manganese composite oxide, and the average particle diameter of the composite is 20 μm or less. The lithium manganese complex oxide is Li _{1 + x} Al _y Mn _2-xy O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1), Li _{1 + x} Mg _y Mn _2-xy O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1), Li _{1 + x} Zn _y Mn _2-xy O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1), and Li _4. One or more spinel-type lithium manganates selected from the group consisting of _{1 + x} Cr _y Mn _2-xy O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1). The method described in. The method according to any one of claims 1 to 4, wherein the mixing treatment is performed by a mechanochemical method during the step of producing the complex. A lithium ion secondary battery using an electrode obtained by the method according to any one of claims 1 to 5. What is claimed is: 1. A lithium ion secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, a non-aqueous electrolyte, and the packaging material,
A lithium ion secondary battery, wherein the positive electrode and / or the negative electrode is an electrode produced by the method according to any one of claims 1 to 5.

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