WO2016067402A1

WO2016067402A1 - Lithium ion battery

Info

Publication number: WO2016067402A1
Application number: PCT/JP2014/078834
Authority: WO
Inventors: 利光野口; 和明直江; 祐介加賀; 新平尼崎
Original assignee: 株式会社日立製作所
Priority date: 2014-10-29
Filing date: 2014-10-29
Publication date: 2016-05-06

Abstract

Provided is a lithium ion battery which is capable of achieving high output power without reducing the battery capacity and without deteriorating the reliability. In order to solve the above-described problem, a lithium ion battery according to the present invention comprises, on a first surface of a collector, an electrode to which an electrode mixture layer containing an active material, a conductive assistant and a binder is attached. The active material contains first active material particles having a first average particle diameter (D1) and second active material particles having a second average particle diameter (D2) that is larger than the first average particle diameter (D1). The thickness (T1) of the electrode mixture layer is within the range D1 ≤ T1 ≤ (3 × D1). Each second active material particle has a portion that is pushed into the collector and a portion that is exposed from the surface of the electrode mixture layer.

Description

Lithium ion battery

The present invention relates to a lithium ion battery.

As a background art in this technical field, there is JP-A-2008-146894 (Patent Document 1). In this publication, “T / 4 is the thickness of the electrode mixture layer on one side of the electrode plate obtained by coating, drying and pressing the electrode mixture layer containing the electrode active material on the current collector. A lithium ion secondary battery in which particles having a particle diameter are contained in an electrode plate is described.

JP 2008-146894 A

As a characteristic of lithium ion batteries, higher output is required. In order to achieve high output, for example, it is effective to reduce the thickness of the electrode. However, when the amount of the active material is reduced by reducing the thickness of the electrode, the battery capacity per unit electrode is reduced. In addition, when the electrode mixture layer becomes thinner due to the thinning of the electrode, primary particles having an average particle diameter larger than the thickness of the electrode mixture layer become apparent, the irregularities on the surface of the electrode increase, and the surface roughness of the electrode increases. Increases.

Patent Document 1 describes a battery electrode plate that contains particles that act on a current collector so as to be locally thin when pressed. However, it aims to provide a battery with excellent safety as an overcurrent interruption function at the time of a short circuit, and does not mention thinning of an electrode for realizing high output of a lithium ion battery.

Therefore, the present invention provides a lithium ion battery capable of realizing high output without reducing battery capacity and without deteriorating reliability.

In order to solve the above problems, a lithium ion battery according to the present invention has an electrode on which an electrode mixture layer containing an active material, a conductive additive, and a binder is attached to the first surface of a current collector, The active material includes first active material particles having a first average particle diameter (D1) and second active material particles having a second average particle diameter (D2) larger than the first average particle diameter (D1). It is out. The thickness (T1) of the electrode mixture layer is in the range of D1 ≦ T1 ≦ (3 × D1), and the second active material particles include a portion pressed into the current collector, and the electrode mixture layer. And a portion exposed on the surface of the substrate.

According to the present invention, it is possible to provide a lithium ion battery that can achieve high output without reducing battery capacity and without deteriorating reliability.

Issues, configurations, and effects other than those described above will be clarified by the following description of embodiments.

2 is a cross-sectional view schematically showing an electrode of a lithium ion battery according to Example 1. FIG. FIG. 3 is a process diagram illustrating a manufacturing process of an electrode of a lithium ion battery according to Example 1. 3 is a cross-sectional view schematically showing a method for manufacturing an electrode of a lithium ion battery according to Example 1. FIG. (A) is sectional drawing which shows typically the electrode in a drying process, (b) is sectional drawing which shows typically the electrode in a heating compression process. It is sectional drawing which shows typically the electrode of the lithium ion battery by a comparative example. FIG. 6 is a process diagram showing a manufacturing process of an electrode of a lithium ion battery according to Example 2. 6 is a cross-sectional view schematically showing a method for manufacturing an electrode of a lithium ion battery according to Example 2. FIG. (A) is sectional drawing which shows typically the electrode in an application | coating process, (b) is sectional drawing which shows typically the electrode in a drying process, (c) is sectional drawing which shows typically the electrode in a heating compression process. It is. 6 is a cross-sectional view schematically showing an electrode of a lithium ion battery according to Example 3. FIG. 6 is a cross-sectional view schematically showing an electrode of a lithium ion battery according to Example 4. FIG.

In the following embodiments, when necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant to each other, and one is the other. There are some or all of the modifications, details, supplementary explanations, and the like.

Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number.

Further, in the following embodiments, the constituent elements (including element steps) are not necessarily indispensable unless otherwise specified and clearly considered essential in principle. Needless to say.

In addition, when referring to “consisting of A”, “consisting of A”, “having A”, and “including A”, other elements are excluded unless specifically indicated that only that element is included. It goes without saying that it is not what you do. Similarly, in the following embodiments, when referring to the shapes, positional relationships, etc. of the components, etc., the shapes are substantially the same unless otherwise specified, or otherwise apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

In all the drawings for explaining the following embodiments, those having the same function are denoted by the same reference numerals in principle, and the repeated explanation thereof is omitted. Hereinafter, the present embodiment will be described in detail with reference to the drawings.

≪Lithium ion battery≫
First, the basics of the lithium ion battery, the schematic configuration of the lithium ion battery, and the charging / discharging mechanism of the lithium ion battery will be described.

<Basics of lithium-ion batteries>
Lithium has an oxidation-reduction potential of -3.03 V (vs. Normal Hydrogen Electrode, NHE), and is the most basic metal on the earth.The battery voltage is the potential difference between the positive electrode and the negative electrode. Therefore, when lithium is used as the negative electrode active material, the highest electromotive force can be obtained, and since the atomic weight of lithium is 6.94 and the density is 0.534 g / cm ³ , the unit is small. Therefore, when lithium is used for the negative electrode active material, a small and light battery can be manufactured.

As described above, lithium is an attractive material as a negative electrode active material of a battery, but problems arise when applied to a chargeable / dischargeable secondary battery. That is, when charging and discharging are repeated in a secondary battery using lithium as a negative electrode active material, a discharge reaction due to dissolution of lithium and a charge reaction due to lithium deposition occur. In this case, a lithium deposition reaction occurs due to repeated charging, which causes a problem in performance deterioration or safety of the secondary battery.

For example, lithium produced in the charging process reacts with the electrolyte solvent on the active surface, and part of it is consumed for the formation of a film called SEI (Solid Electrolyte Interface). For this reason, the internal resistance of the battery increases and the discharge efficiency also decreases. In other words, the battery capacity decreases each time the charge / discharge cycle is repeated. Furthermore, when rapidly charged, lithium precipitates in a needle-like / dendritic crystal form (lithium dendrite), which causes various troubles in the secondary battery. For example, lithium dendrite has a large specific surface area, accelerates the decrease in current efficiency due to side reactions, and also has a needle-like / dendritic shape, and may break through the separator to cause an internal short circuit between the positive electrode and the negative electrode. In such a state, the self-discharge is so large that it cannot be used as a battery, or gas may be ejected or ignited due to heat generated by an internal short circuit. From the above, it can be seen that a secondary battery using lithium as the negative electrode active material has a problem in performance deterioration or safety.

Therefore, a new type secondary battery having a principle different from the conventional principle of dissolution and precipitation has been studied. Specifically, a secondary battery using an active material that inserts and desorbs lithium ions into both the positive electrode and the negative electrode has been studied. In the charging / discharging process of the secondary battery, the phenomenon of dissolution and precipitation of lithium does not occur, and only lithium ions are inserted / extracted between the active materials. This type of secondary battery is called “rocking chair” type or “shuttle cock” type, and is stable because only lithium ions are inserted and desorbed with repeated charging and discharging. There is a feature. Hereinafter, this type of battery is referred to as a lithium ion battery.

As described above, the structure of the lithium ion battery is not changed during charging / discharging of both the positive electrode and the negative electrode, and only lithium ions are inserted and desorbed (however, the active material crystal lattice is lithium ion). In addition, it has a characteristic that it has a long life cycle characteristic and does not use metallic lithium for the positive electrode and the negative electrode, so that safety is drastically improved.

Here, a material capable of inserting / extracting lithium ions is used for the active material of the positive electrode and the negative electrode. The conditions required for this active material are as follows. That is, since ions of a finite size called lithium ions are inserted and desorbed, a site (position) where lithium ions should be stored and a channel (path) through which lithium ions can be diffused are required for the active material. Furthermore, electrons need to be introduced into the active material as lithium ions are inserted (occluded).

As the positive electrode active material that satisfies the above-described conditions, a lithium-containing transition metal oxide can be given. Examples of typical positive electrode active materials include, but are not limited to, lithium cobaltate, lithium nickelate, and lithium manganate. Specifically, the positive electrode active material is a material into which lithium can be inserted / extracted, and may be any lithium-containing transition metal oxide in which a sufficient amount of lithium has been inserted in advance. Examples of the transition metal include manganese, nickel, It may be a simple substance such as cobalt or iron, or a material mainly composed of two or more kinds of transition metals. Further, the crystal structure such as the spinel crystal structure or the layered crystal structure is not particularly limited as long as the above-described site and channel are ensured. In addition, transition metal in the crystal or a part of lithium is replaced with an element such as iron, cobalt, nickel, chromium, aluminum, or manganese, or iron, cobalt, nickel, chromium, aluminum, or manganese is included in the crystal. A material doped with these elements may be used as the positive electrode active material.

Furthermore, examples of the negative electrode active material that satisfies the above-described conditions include a crystalline carbon material or an amorphous carbon material. However, the negative electrode active material is not limited to these materials. For example, natural graphite, various artificial graphite agents, or carbon materials such as coke may be used. And also in the particle shape, various particle shapes such as a scale shape, a spherical shape, a fiber shape, or a lump shape are applicable.

<Schematic configuration of lithium-ion battery>
Next, a schematic configuration of the lithium ion battery will be described.

The lithium ion battery has a battery outer container, and the battery outer container is filled with an electrolytic solution. A positive electrode plate and a negative electrode plate are provided opposite to each other inside the battery outer container filled with the electrolytic solution, and a separator is disposed between the positive electrode plate and the negative electrode plate provided to face each other. Yes.

As a general battery exterior container, an aluminum or nickel-plated iron metal container or an aluminum laminate sheet is used.

In the positive electrode plate, the positive electrode active material is coated on the positive electrode current collector, and in the negative electrode plate, the negative electrode active material is coated on the negative electrode current collector. The positive electrode active material is formed of, for example, a lithium-containing transition metal oxide capable of inserting / extracting lithium ions. The positive electrode current collector and the positive electrode active material constitute a positive electrode. The negative electrode active material is formed of, for example, a carbon material capable of inserting / extracting lithium ions. The negative electrode is composed of the negative electrode current collector and the negative electrode active material.

The positive electrode is formed by applying a coating liquid containing a positive electrode active material and a binder to the current collector of the positive electrode and drying it, followed by pressurization. A positive electrode current collecting tab functioning as a lead wire is formed at the end or back surface of the positive electrode, and current is input and output through the positive electrode current collecting tab.

As the positive electrode active material constituting the positive electrode, for example, the above-described materials typified by lithium cobaltate, lithium nickelate, or lithium manganate can be used. As the binder, for example, polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, or the like can be used. Furthermore, in order to improve conductivity, particles such as natural graphite, artificial graphite, or acetylene black may be added as a conductive aid. The positive electrode current collector is made of, for example, a metal foil or a net-like metal made of a conductive metal such as aluminum, and the positive electrode current collecting tab is made of, for example, aluminum.

The negative electrode is formed by applying a coating liquid containing a negative electrode active material and a binder to the current collector of the negative electrode and drying it, followed by pressurization. A negative electrode current collecting tab functioning as a lead wire is formed on the end or back surface of the negative electrode, and current is taken in and out through the negative electrode current collecting tab.

As the negative electrode active material constituting the negative electrode, for example, the above-described materials typified by a carbon material or a silicon alloy can be used. As the binder, for example, polyvinylidene fluoride or polytetrafluoroethylene can be used. Furthermore, in order to improve conductivity, particles such as natural graphite, artificial graphite, or acetylene black may be added as a conductive aid. Further, for the current collector of the negative electrode, for example, a metal foil or a net-like metal made of a conductive metal such as copper is used, and the negative current collector tab is made of, for example, copper or nickel.

The separator has a function as a spacer that allows lithium ions to pass while preventing electrical contact between the positive electrode and the negative electrode. In recent years, a high-strength and thin microporous membrane has been used as the separator. This microporous membrane also has the functions of preventing abnormal current due to battery short circuit, rapid internal pressure, temperature rise, and ignition. In other words, the separator has a function of preventing electrical contact between the positive electrode and the negative electrode and allowing lithium ions to pass therethrough, and further has a function as a thermal fuse for preventing short circuit and overcharge. It will be.

The shutdown function of this microporous membrane can keep the lithium ion battery safe. For example, when a lithium ion battery causes an external short circuit for some reason, there is a risk that a large current flows instantaneously but the temperature rises abnormally due to Joule heat. At this time, if a microporous membrane is used as a separator, the microporous membrane blocks pores (microporous) in the vicinity of the melting point of the membrane material, thus preventing lithium ion permeation between the positive electrode and the negative electrode. can do. In other words, by using a microporous membrane as a separator, current can be interrupted when an external short circuit occurs, and the temperature rise inside the lithium ion battery can be stopped. For the separator composed of the microporous membrane, for example, polyethylene (Polythylene, PE), polypropylene (Polypropylene, PP), or a combination of these materials can be used.

Electrolytic solution is a non-aqueous electrolytic solution. A lithium ion battery is a battery that charges and discharges using insertion / extraction of lithium ions in an active material, and lithium ions move in an electrolyte solution. Lithium is a strong reducing agent and reacts violently with water to generate hydrogen gas. Therefore, in a lithium ion battery in which lithium ions move in the electrolytic solution, an aqueous solution cannot be used as the electrolytic solution. For this reason, in the lithium ion battery, a nonaqueous electrolytic solution is used as the electrolytic solution.

Specifically, as the electrolyte of the non-aqueous electrolyte, for example _{_{_{LiPF 6, LiClO 4, LiAsF 6}}} , LiBF 4, LiB (C 6 H 5) 4, CH 3 SO 3 Li, or the like _CF 3 _SO 3 Li, or Mixtures of these can be used. As the organic solvent, for example, ethylene carbonate, dimethyl carbonate, propylene carbonate, diethyl carbonate, or the like can be used. Further, examples of the organic solvent include 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl Sulfolane, acetonitrile, propionitrile or the like can be used. Further, a mixed solution of the organic solvent described above can be used.

<Mechanism of charge / discharge of lithium ion battery>
Next, the charging / discharging mechanism of the lithium ion battery will be described.

First, the charging mechanism will be described.

When charging the lithium ion battery, connect a charger between the positive electrode and the negative electrode. In this case, in the lithium ion battery, lithium ions inserted in the positive electrode active material are desorbed and released into the electrolytic solution. At this time, the lithium ions are desorbed from the positive electrode active material, whereby electrons flow from the positive electrode to the charger. Then, the lithium ions released into the electrolytic solution move in the electrolytic solution, pass through a separator made of a microporous film, and reach the negative electrode. The lithium ions that have reached the negative electrode are inserted into the negative electrode active material constituting the negative electrode. At this time, when lithium ions are inserted into the negative electrode active material, electrons flow into the negative electrode. In this way, charging is completed as electrons move from the positive electrode to the negative electrode via the charger.

Next, the discharge mechanism will be described.

Connect an external load between the positive and negative electrodes. Then, lithium ions inserted into the negative electrode active material are desorbed and released into the electrolytic solution. At this time, electrons flow from the negative electrode to the external terminal. Then, the lithium ions released into the electrolytic solution move in the electrolytic solution, pass through a separator made of a microporous film, and reach the positive electrode. The lithium ions reaching the positive electrode are inserted into the positive electrode active material constituting the positive electrode. At this time, lithium ions are inserted into the positive electrode active material, whereby electrons flow into the positive electrode. In this way, discharge is performed by the movement of electrons from the negative electrode to the positive electrode. In other words, a current can flow from the positive electrode to the negative electrode to drive the load.

As described above, in a lithium ion battery, lithium ions can be charged and discharged by being inserted and desorbed between the positive electrode active material and the negative electrode active material.

≪Detailed description of assignment≫
Next, since it seems that the lithium ion battery by this Embodiment becomes clearer, the problem which it tries to solve in the lithium ion battery discovered by the present inventors is demonstrated in detail.

With the development of portable electronic devices, small secondary batteries that can be repeatedly charged are used as a power supply source for the portable electronic devices. Among them, lithium ion batteries having high energy density, long cycle life, low self-discharge property, and high operating voltage are attracting attention. Lithium ion batteries have the advantages described above, and are therefore widely used in portable electronic devices such as digital cameras, notebook personal computers, and mobile phones.

Furthermore, in recent years, research and development of large-sized lithium ion batteries capable of realizing high capacity, high output, and high energy density as batteries for electric vehicles or power storage batteries have been promoted. In particular, in the automobile industry, in order to cope with environmental problems, development of an electric vehicle using a motor as a power source and a hybrid vehicle using both an engine (internal combustion engine) and a motor as a power source are in progress. . Lithium ion batteries have attracted attention as power sources for such electric vehicles and hybrid vehicles.

A lithium ion battery includes, for example, an electrode laminate in which a positive electrode plate coated with a positive electrode active material, a negative electrode plate coated with a negative electrode active material, and a separator that prevents contact between the positive electrode plate and the negative electrode plate are laminated. Yes. Alternatively, an electrode winding body in which a positive electrode plate coated with a positive electrode active material, a negative electrode plate coated with a negative electrode active material, and a separator that prevents contact between the positive electrode plate and the negative electrode plate is provided. And in a lithium ion battery, while an electrode laminated body or an electrode winding body is accommodated in the inside of a battery exterior container, electrolyte solution is inject | poured inside the battery exterior container. As the battery outer container, a metal cylindrical container or a rectangular container is used, but a laminate sheet made of a laminate of a metal sheet and a polymer resin sheet is also used for weight reduction and thickness reduction. Yes.

By the way, as a power source for electric vehicles such as electric vehicles and hybrid vehicles, high output for acceleration is required. As a method for realizing high output, it is effective to make the electrode thin to facilitate the diffusion of lithium ions. However, in this method, since the amount of the active material is reduced by reducing the thickness of the electrode, the battery capacity per unit electrode area is reduced. In order to increase the battery capacity, it is necessary to increase the number of stacked electrodes or the number of turns. However, the amount of the current collector increases, and the battery capacity per unit volume and unit weight of the electrode decreases. In addition, when the electrode mixture layer becomes thinner due to the thinning of the electrode, primary particles having an average particle diameter larger than the thickness of the electrode mixture layer become apparent, the irregularities on the surface of the electrode increase, and the surface roughness of the electrode increases. Increases.

≪Lithium-ion battery structure≫
The electrode of the lithium ion battery according to Example 1 will be described with reference to FIG. FIG. 1 is a cross-sectional view schematically showing an electrode of a lithium ion battery according to the first embodiment.

The electrode ER1 includes a current collector (also referred to as an electrode plate, a current collector foil, an electrode foil, a metal foil, etc.) CU, and both surfaces of the current collector CU (second surface opposite to the first surface S1 and the first surface S1). It consists of the electrode mixture layer EX formed in S2), and the electrode mixture layer EX contains an active material, a conductive additive (also referred to as a conductive agent), and a binder (also referred to as a binder). Furthermore, the active material is, for example, a first active material particle CP1 having a first average particle diameter of about 3 μm and a second active material particle having a second average particle diameter larger than the first average particle diameter, for example, about 10 μm. CP2 is included. The second active material particles are primary particles in which single crystals or crystallites close to them are collected, and are not aggregates or aggregates.

The thickness T1 of the electrode mixture layer EX is, for example, about 5 to 20 μm, and the thickness T2 of the current collector CU is, for example, about 5 to 20 μm.

Here, the thickness T1 of the electrode mixture layer EX is the average value of the thickness of the particle layer composed only of the first active material particles CP1 from the first surface S1 (or the second surface S2) of the current collector CU. When the first average particle diameter of the first active material particles CP1 is D1, the range is set to D1 ≦ T1 ≦ (3 × D1). That is, the electrode mixture layer EX corresponds to a state in which the first active material particles CP1 are in one layer to a state in which the first active material particles CP1 are in three layers.

The second active material particles CP2 are present in the particle layer composed only of the first active material particles CP1. Further, a part of the second active material particle CP2 is a part that is pushed into the current collector CU (A region shown in FIG. 1) and a part that is exposed on the surface of the electrode mixture layer EX (in FIG. 1). B region).

≪Lithium-ion battery manufacturing method≫
A method for manufacturing an electrode of a lithium ion battery according to Example 1 will be described with reference to FIGS. FIG. 2 is a process diagram showing the manufacturing process of the electrode of the lithium ion battery according to the first embodiment. 3A and 3B are cross-sectional views schematically showing a method for manufacturing an electrode of a lithium ion battery according to Example 1, wherein FIG. 3A is a cross-sectional view of the electrode in the drying process, and FIG. 3B is a cross-sectional view of the electrode in the heating and compression process. FIG.

(Kneading process)
First, the active material is formed by mixing the first active material particles CP1 having a first average particle diameter of, for example, about 3 μm with the second active material particles CP2 having a second average particle diameter of, for example, about 10 μm. At this time, the second active material particles CP2 are mixed so that the second active material particles CP2 are about 20% by weight with respect to the weight of the active material contained in the electrode mixture layer EX. The first average particle diameter of the first active material particle CP1 and the second average particle diameter of the second active material particle CP2 can be determined by, for example, a laser diffraction / scattering particle size distribution measuring apparatus.

In addition, graphite and carbon black are mixed as the conductive material into the active material, polyvinylidene fluoride is mixed as the binder, and further, a solvent capable of dissolving the binder, such as N-methyl-2-pyrrolidone, is used. The solution is added and mixed with a planetary mixer to form a slurry electrode mixture.

(Coating process)
Next, a slurry-like electrode mixture is applied to the first surface S1 of the current collector CU using a die coater. As the current collector CU, in the case of the positive electrode, for example, an aluminum foil having a thickness of about 20 μm is used, and in the case of the negative electrode, for example, a copper foil having a thickness of about 10 μm is used. As the application means, for example, an extrusion coater, a reverse roller, a doctor blade, an applicator, or a spray can be used.

(Drying process)
Next, a solvent such as an N-methyl-2-pyrrolidone solution is dried in a warm air drying oven at 120 ° C., for example.

Next, the above-described (coating step) and (drying step) are similarly performed on the second surface S2 of the current collector CU, and as shown in FIG. The electrode mixture layer EX is formed on the first surface S1 and the second surface S2).

(Heat compression process)
Next, as shown in FIG. 3B, the electrode mixture layer EX formed on both surfaces (the first surface S1 and the second surface S2) of the current collector CU is heated and compressed using a hot roll press RO. Thus, the electrode ER1 is formed. The temperature of the hot roll press RO is, for example, about 120 ° C., and the press pressure is about 5 to 10 times that when the second active material particles CP2 are not pushed into the current collector CU.

As a method of compressing the electrode mixture layer EX on both surfaces (first surface S1 and second surface S2) of the current collector CU, a uniaxial press method, a biaxial press method, a roll press method, an isostatic press method, or the like is used. Can be used. Although compression may be performed at room temperature, it is preferable to use a hot pressing method in which compression is performed at a temperature near the softening point of the binder from the viewpoint of adhesion to the current collector CU. Moreover, although the hot roll press RO was used for the continuous processing of roll to roll here, you may use a flat plate press by a batch type.

When the second active material particle CP2 is pushed into the current collector CU, there is a portion in which the electrolytic solution penetrates also between the second active material particle CP2 and the current collector CU. Can be used. That is, in the current collector CU, the portion where the second active material particles CP2 are pushed in is used for charging / discharging, which corresponds to replacing a part of the current collector CU with the active material. Therefore, when the second active material particle CP2 is pushed into the current collector CU, the battery capacity and the volume energy density per unit electrode volume are smaller than when the second active material particle CP2 is not pushed into the current collector CU. Can be increased. When the electrode mixture layer EX is thick, the contribution of the portion where the second active material particles CP2 are pushed into the increase in battery capacity is small, but when the electrode mixture layer EX is thin, the second active material particles CP2 are The contribution of the pushed-in portion to the increase in battery capacity increases.

The second active material particles CP2 pushed into the current collector CU by the hot roll press RO may or may not collapse. When the second active material particle CP2 is cracked or the second active material particle CP2 is collapsed, the surface area of the active material in contact with the electrolytic solution is increased, and the battery capacity is further increased. As a result, in the lithium ion battery, both high output and high capacity can be achieved.

The second active material particles CP2 do not necessarily have a substantially spherical shape. In order to be easily pushed into the current collector CU, it is desirable that there is an acute angle portion where pressure is concentrated on the second active material particle CP2.

The second active material particles CP2 are likely to appear in the electrode ER1 having the electrode mixture layer EX having a thickness of, for example, about 5 to 20 μm. The heads of the second active material particles CP2 are likely to jump out on the surface of the electrode ER1, and the irregularities on the surface of the electrode ER1 increase, thereby increasing the surface roughness of the electrode ER1. However, the surface of the electrode ER1 is flattened by pressing the second active material particles CP2 into the current collector CU. The surface roughness of the electrode ER1 including the second active material particle CP2 can be equal to or less than the surface roughness of the electrode not including the second active material particle CP2.

Furthermore, when the second active material particles CP2 are pushed into the current collector CU, the adhesion between the electrode mixture layer EX and the current collector CU is improved by the anchor effect. In the case of assembling as a battery, the electrode mixture layer EX may float from the current collector CU when the electrode ER1 is wound or laminated, or in the case of assembling as a battery, during repeated charging and discharging. No peeling off.

In addition, the adhesion between the electrode mixture layer EX and the current collector CU improves as the second active material particles CP2 are pushed deeper into the current collector CU. However, if the current collector CU is crushed and thinned, or the number of second active material particles CP2 penetrating the current collector CU increases, the tensile strength of the current collector CU required for winding or the like The mechanical strength such as Therefore, by adjusting the particle size and pressing pressure of the second active material particles CP2, the number of second active material particles CP2 penetrating the current collector CU is reduced, or the second is reduced to about half the thickness of the current collector CU. It is desirable to push in the active material particles CP2.

Further, the second active material particles CP2 are contained in a proportion of not more than 1% by weight (not including 1% by weight) and not more than 50% by weight with respect to the weight of the active material contained in the electrode mixture layer EX. Is desirable. When the ratio of the second active material particles CP2 is small, an increase in battery capacity per unit electrode volume is small. On the other hand, when the ratio of the second active material particles CP2 is large, the portion of the second active material particles CP2 that is pushed into the current collector CU increases, and the battery capacity per unit electrode volume increases. However, since the current collector CU is crushed and thinned and the current collector CU has more holes, the mechanical strength such as the tensile strength of the current collector CU required for winding is weak. There is a fear. Therefore, it is desirable that the second active material particle CP2 is contained in the electrode mixture layer EX within the above range.

(Cutting process)
Next, the current collector CU on which the electrode mixture layer EX is formed is cut to produce a film-like electrode sheet.

Note that Example 1 can be applied to both the positive electrode and the negative electrode.

Thus, according to Example 1, a high output can be realized by reducing the thickness T1 of the electrode mixture layer EX to about 5 to 20 μm. Furthermore, the electrode mixture layer EX is composed of, for example, a first active material particle CP1 having a first average particle diameter of about 3 μm and a second active material particle CP2 having a second average particle diameter of about 10 μm, for example. By pushing the second active material particles CP2 into the current collector CU, the battery capacity and volume energy density per unit electrode volume can be increased. As a result, both high output and high capacity can be achieved.

Furthermore, when the second active material particles CP2 are pushed into the current collector CU, the adhesion between the electrode mixture layer EX and the current collector CU is improved by the anchor effect. Thereby, the electrode mixture layer EX does not float or peel off from the current collector CU, and the reliability is improved.

≪Comparative example≫
In this comparative example, an electrode having a thickness of about 30 to 100 μm, for example, of the electrode mixture layer investigated by the present inventors will be described. FIG. 4 is a cross-sectional view schematically showing an electrode of a lithium ion battery according to a comparative example.

The electrode ER0 includes a current collector CU and an electrode mixture layer EX0 formed on both surfaces (first surface S1 and second surface S2) of the current collector CU. The electrode mixture layer EX0 includes an active material, Contains a conductive aid and a binder. Furthermore, the active material is, for example, a first active material particle CP1 having a first average particle diameter of about 3 μm and a second active material particle having a second average particle diameter larger than the first average particle diameter, for example, about 10 μm. CP2 is included.

However, the thickness T0 of the electrode mixture layer EX0 is, for example, about 30 to 100 μm, and the thickness T2 of the current collector CU is, for example, about 5 to 20 μm. Compared with Example 1 described above, when the electrode mixture layer EX0 is thick and the first average particle diameter of the first active material particles CP1 is D1, the thickness T0 of the electrode mixture layer EX0 is (4 × D1). ≦ T0 is set. That is, the electrode mixture layer EX0 corresponds to a state in which the first active material particles CP1 are four or more layers.

In general, the second active material particle CP2 having the second average particle size larger than the thickness T0 of the electrode mixture layer EX0 is actively applied by filtering or air classification before applying the slurry-like electrode mixture. Since it is removed, it does not enter the electrode mixture layer EX0. Therefore, none of the second active material particles CP2 has both the portion pushed into the current collector CU and the portion exposed on the surface of the electrode mixture layer EX0 at the same time. The material particles CP2 are either exposed on the surface of the electrode mixture layer EX0 or are not exposed on the surface of the electrode mixture layer EX0 and are buried in the electrode mixture layer EX0.

Since the second active material particles CP2 having the second average particle size smaller than the thickness T0 of the electrode mixture layer EX0 are not sandwiched between the hot roll press and the current collector CU, the second active material particles It is difficult to transmit the press pressure directly to CP2. Therefore, few are pushed into the current collector CU, and the depth to be pushed is shallow.

As described above, in this comparative example, it is difficult to increase the battery capacity and volume energy density per unit electrode volume by pushing the second active material particles CP2 into the current collector CU using a hot roll press.

Further, when the electrode mixture layer EX0 is thick and the current collector CU is thin, the battery capacity of the active material originally on the surface of the current collector CU is large, so the battery in the portion where the second active material particles CP2 are pushed in The contribution to capacity increase is small. Furthermore, since the anchor effect due to the second active material particles CP2 being pushed into the current collector CU is small, improvement in the adhesion between the electrode mixture layer EX0 and the current collector CU cannot be expected.

On the other hand, when the electrode mixture layer EX0 is thick, if the second active material particles CP2 having the second average particle diameter equal to or greater than the thickness T0 of the electrode mixture layer EX0 are mixed into the electrode mixture layer EX0, a fine active material is obtained. The surface area of the active material is smaller than when only the material is applied to the first surface S1 and the second surface S2 of the current collector CU. For this reason, the battery capacity per unit electrode volume is reduced or the output performance is lowered. Therefore, mixing the second active material particles CP2 having such a size is disadvantageous in terms of performance.

The difference between the lithium ion battery according to Example 2 and the lithium ion battery according to Example 1 described above is a method in which part of the second active material particles is pushed into the current collector.

≪Lithium-ion battery manufacturing method≫
A method for manufacturing an electrode of a lithium ion battery according to Example 2 will be described with reference to FIGS. FIG. 5 is a process diagram showing a manufacturing process of an electrode of a lithium ion battery according to the second embodiment. 6A and 6B are cross-sectional views schematically showing a method for manufacturing an electrode of a lithium ion battery according to Example 2, wherein FIG. 6A is a cross-sectional view of the electrode in the drying process, and FIG. 6B is a cross-sectional view of the electrode in the spraying process. (C) is sectional drawing of the electrode in a heat compression process.

(Kneading process)
First, for example, graphite and carbon black are mixed as a conductive additive, and polyvinylidene fluoride is mixed as a binder into an active material composed of only the first active material particles CP1 having a first average particle diameter of, for example, about 5 μm. Then, a solvent capable of dissolving the binder, for example, an N-methyl-2-pyrrolidone solution is added and mixed with a planetary mixer to form a slurry electrode mixture.

Next, similarly, the above-described (coating step) and (drying step) are performed on the second surface S2 of the current collector CU as shown in FIG. The electrode mixture layer EX is formed on the first surface S1 and the second surface S2).

(Spraying process)
Next, as shown in FIG. 6B, the second active material particles CP2 having a second average particle diameter of, for example, about 12 μm are placed on the surface of the electrode mixture layer EX. The second active material particles CP2 are dispersed on the surface of the electrode mixture layer EX using, for example, a nozzle. At this time, the second active material particles CP2 are dispersed so that the second active material particles CP2 are about 30% by weight with respect to the weight of the active material contained in the electrode mixture layer EX.

(Heat compression process)
Next, as shown in FIG.6 (c), electrode ER2 is formed by heat-compressing electrode mixture layer EX using hot roll press RO. At this time, the second active material particles CP2 are pushed into the current collector CU. The temperature of the hot roll press RO is about 120 ° C., for example, and the press pressure is about 10 to 20 times that when the second active material particles CP2 are not pushed into the current collector CU. In order to push the second active material particles CP2 into the solidified electrode mixture layer EX after the drying step, the press pressure was set higher than that in the heat compression step of Example 1 described above.

In the drying step, most of the solvent, for example, N-methyl-2-pyrrolidone solution is volatilized. In the spraying step, the second active material particles PC2 are placed on the surface of the electrode mixture layer EX in a semi-dry state. Subsequently, in the heat compression step, the electrode mixture layer EX may be heat compressed using a hot roll press RO. Moreover, after the coating process is completed, the spraying process may be performed before the drying process, followed by the drying process and then the heat compression process.

When the second active material particles CP2 are pushed into the electrode mixture layer EX formed on both surfaces (the first surface S1 and the second surface S2) of the current collector CU, first, one surface of the current collector CU (for example, After the second active material particle CP2 is pushed into the first surface S1), the electrode ER2 is reversed and the second active material particle CP2 is pushed into the other surface (for example, the second surface S2) of the current collector CU. Good.

Further, the second active material particles CP2 are placed on or attached to the surface of the hot roll press RO, and the electrode mixture layer EX is compressed in this state, whereby the second active material particles CP2 are applied to the current collector CU. You may push in.

In addition, a solvent or adhesive containing a binder is thinly attached in advance to the surface of the second active material particle CP2 or the surface of the electrode mixture layer EX, and the second active material is deposited on the surface of the electrode mixture layer EX. By simultaneously compressing the electrode mixture layer EX formed on both surfaces (the first surface S1 and the second surface S2) of the current collector CU without attaching the particles CP2 and inverting the electrode ER2, the second active layer The substance particles CP2 may be pushed into the current collector CU.

Note that Example 2 can be applied to both the positive electrode and the negative electrode.

Thus, according to the second embodiment, it is possible to achieve both high output and high capacity in substantially the same manner as in the first embodiment.

In Example 3, a lithium ion battery having an electrode in which an electrode mixture layer is formed only on one side of a current collector will be described with reference to FIG. FIG. 7 is a cross-sectional view schematically showing an electrode of the lithium ion battery according to the third embodiment.

The manufacturing method of the electrode ER3 of the lithium ion battery according to Example 3 is substantially the same as Example 1 and Example 2 described above, except that the electrode mixture layer EX is formed only on one side of the current collector CU. .

Similarly to Example 1 described above, first, in the (kneading step), the active material obtained by mixing the first active material particles CP1 and the second active material particles CP2, the conductive auxiliary agent, and the binder are mixed. To form a slurry-like electrode mixture. Subsequently, in the (coating step), this electrode mixture is applied to the first surface S1 of the current collector CU. Then, an electrode sheet is manufactured through (drying process), (heat compression process), and (cutting process).

Alternatively, as in Example 2 described above, in the (kneading step), an active material composed only of the first active material particles CP1, a conductive auxiliary agent, and a binder are mixed to form a slurry electrode mixture. Form. Subsequently, in the (coating step), this electrode mixture is applied to the first surface S1 of the current collector CU. Subsequently, after the (drying step), in the (spreading step), after the second active material particles CP2 are mounted on the surface of the electrode mixture layer EX, in the (heat compression step), the electrode mixture layer EX is heated and compressed. At the same time, the second active material particles CP2 are pushed into the current collector CU. Then, an electrode sheet is manufactured through (cutting process).

As shown in FIG. 7, it is necessary to prevent the second active material particles CP2 from jumping out from the second surface S2 of the current collector CU not coated with the electrode mixture. Therefore, in Example 3, when the second average particle diameter of the second active material particles CP2 is D2, the thickness of the electrode mixture layer EX is T1, and the thickness of the current collector CU is T2, T1 ≦ D2 ≦ These values are set so as to be (T1 + T2).

Thus, according to the third embodiment, even when the electrode mixture layer EX is formed only on one side of the current collector CU, the high output and the high capacity are substantially the same as in the first embodiment. Can be achieved.

In Example 4, a lithium ion battery having an electrode on which an electrode mixture layer including second active material particles having an average particle diameter larger than the thickness of the electrode mixture layer is formed will be described with reference to FIG. FIG. 8 is a cross-sectional view schematically showing an electrode of a lithium ion battery according to Example 4.

The manufacturing method of the electrode ER4 of the lithium ion battery according to Example 4 is almost the same as Example 1 and Example 2 described above.

As shown in FIG. 8, the electrode mixture layer in which the second active material particles CP2 contained in the electrode mixture applied to the first surface S1 of the current collector CU are formed on the second surface S2 of the current collector CU. It is necessary to prevent the surface roughness of the electrode mixture layer EX from jumping out from the surface of the EX and being formed on the second surface S2 of the current collector CU. Similarly, from the surface of the electrode mixture layer EX formed on the first surface S1 of the current collector CU, the second active material particles CP2 contained in the electrode mixture applied to the second surface S2 of the current collector CU. It is necessary to prevent the surface roughness of the electrode mixture layer EX formed on the first surface S1 of the current collector CU from popping out. Therefore, the second average particle diameter of the second active material particles CP2 is D2, the thickness of the electrode mixture layer EX formed on the first surface S1 of the current collector CU is T1, and the second surface S2 of the current collector CU. These values are set so that T1 ≦ D2 ≦ (T1 + T2 + T3), where T3 is the thickness of the electrode mixture layer EX formed on the substrate and T2 is the thickness of the current collector CU.

Usually, the thickness T1 of the electrode mixture layer EX formed on the first surface S1 of the current collector CU and the thickness T3 of the electrode mixture layer EX formed on the second surface S2 of the current collector CU are the same. However, they may be different from each other.

By the way, the second active material particles CP2 included in the electrode mixture layer EX formed on the first surface S1 of the current collector CU and the electrode mixture layer EX formed on the second surface S2 of the current collector CU are included. In some cases, the second active material particles CP2 collide with each other in the current collector CU. Further, the second active material particles CP2 included in the electrode mixture layer EX formed on the first surface S1 of the current collector CU penetrate the current collector CU and are formed on the second surface S2 of the current collector CU. The second active material particles CP2 contained in the electrode mixture layer EX entering the electrode mixture layer EX or formed on the second surface S2 of the current collector CU penetrates the current collector CU, and the current collector CU May enter the electrode mixture layer EX formed on the first surface S1.

As the second active material particle CP2 is pushed deeper into the current collector CU, the adhesion between the electrode mixture layer EX and the current collector CU is improved. However, if the current collector CU is crushed and thinned, or the number of second active material particles CP2 penetrating the current collector CU increases, the tensile strength of the current collector CU required for winding or the like The mechanical strength such as Therefore, by adjusting the particle size and press pressure of the second active material particles CP2, the number of second active material particles CP2 penetrating the current collector CU is reduced, and the second active material particles colliding with each other in the current collector CU It is desirable to reduce the number of CP2s or push the second active material particles CP2 down to about half the thickness of the current collector CU.

Thus, according to the present Example 4, even in the electrode mixture layer EX including the second active material particles CP2 having the second average particle diameter larger than the thicknesses T1 and T3 of the electrode mixture layer EX, By matching the second average particle diameter of the second active material particles CP2 within a predetermined range, both high output and high capacity can be achieved in substantially the same manner as in the first embodiment.

Although the invention made by the present inventors has been specifically described based on the embodiment, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

In the present embodiment, the technical idea of the present invention has been described by taking a lithium ion battery as an example. However, the technical idea of the present invention is not limited to a lithium ion battery but can be applied to various batteries. can do.

CU current collector (electrode plate, current collector foil, electrode foil, metal foil)
ER0, ER1, ER2, ER3, ER4 Electrode EX, EX0 Electrode mixture layer CP1 First active material particle CP2 Second active material particle S1 First surface S2 Second surface RO Hot roll press

Claims

A lithium ion battery having an electrode on which a first electrode mixture layer containing an active material, a conductive additive, and a binder is attached to a first surface of a current collector,
The active material includes first active material particles having a first average particle diameter (D1), second active material particles having a second average particle diameter (D2) larger than the first average particle diameter (D1), and Including
The thickness (T1) of the first electrode mixture layer is in the range of D1 ≦ T1 ≦ (3 × D1),
The second active material particle is a lithium ion battery having a portion pushed into the current collector and a portion exposed on the surface of the first electrode mixture layer.
The lithium ion battery according to claim 1,
The second average particle diameter (D2) of the second active material particles is a lithium ion battery in a range of T1 ≦ D2 ≦ (T1 + T2) where the thickness of the current collector is T2.
The lithium ion battery according to claim 1,
A second electrode mixture layer containing the active material, the conductive auxiliary agent, and the binder is attached to the second surface opposite to the first surface of the current collector,
When the thickness (T3) of the second electrode mixture layer is equal to or greater than the thickness (T1) of the first electrode mixture layer,
The second average particle diameter (D2) of the second active material particles is a lithium ion battery in a range of T1 ≦ D2 ≦ (T1 + T2 + T3) where the thickness of the current collector is T2.
The lithium ion battery according to claim 1,
The lithium ion battery, wherein the second active material particles are contained in the active material in a ratio of greater than 1% by weight and less than or equal to 50% by weight with respect to the weight of the active material contained in the electrode mixture layer. .
The lithium ion battery according to claim 1,
The lithium ion battery, wherein the second active material particles are contained in the active material at a ratio of 20 wt% or more and 30 wt% or less with respect to the weight of the active material contained in the electrode mixture layer.
The lithium ion battery according to claim 1,
The lithium ion battery, wherein the first electrode mixture layer has a thickness (T1) of 5 to 20 μm.