WO2021038860A1

WO2021038860A1 - Electrode, laminate, and secondary battery

Info

Publication number: WO2021038860A1
Application number: PCT/JP2019/034243
Authority: WO
Inventors: 佑磨菊地; 森島　秀明; 隆史小林; 一樹伊勢; 好太郎渡邉
Original assignee: 株式会社東芝
Priority date: 2019-08-30
Filing date: 2019-08-30
Publication date: 2021-03-04
Also published as: JP7254941B2; JPWO2021038860A1

Abstract

The embodiments provide an electrode that includes: an active-material-containing layer that includes active material particles and has a front surface and a back surface; and a first film that has a front surface and a back surface. The back surface of the first film contacts at least a portion of the front surface of the active-material-containing layer. The first film includes titanium oxide particles. The surface roughness Ra1 of the front surface of the active-material-containing layer and the surface roughness Ra2 of the front surface of the first film satisfy Ra1>Ra2.

Description

Electrodes, laminates and rechargeable batteries

Embodiments of the present invention relate to electrodes, laminates and secondary batteries.

In order to increase the capacity of secondary batteries such as lithium secondary batteries, the density of electrodes is increased by roll press processing. On the other hand, secondary batteries are also required to reduce manufacturing costs. For example, when the roll used in the roll press process wears, not only the maintenance of the roll itself is required, but also the production line needs to be suspended during the maintenance. Therefore, in addition to the maintenance cost, a loss due to the interruption of manufacturing occurs. If the frequency of roll maintenance can be reduced, the manufacturing cost can be reduced, so that high-performance electrodes can be provided at a lower cost.

International Publication No. 2009/063747 Japanese Patent Application Laid-Open No. 2010-97720

According to the embodiment, a high-performance electrode, a laminate including the electrode, and a secondary battery are provided.

According to the embodiment, an electrode containing active material particles and containing an active material-containing layer having a front surface and a back surface and a first film having a front surface and a back surface is provided. The back surface of the first film is in contact with at least a part of the surface of the active material-containing layer. The first film contains titanium oxide particles. The surface roughness Ra1 on the surface of the active material-containing layer and the surface roughness Ra2 on the surface of the first film satisfy Ra1> Ra2.

Further, according to another embodiment, a laminate including the electrodes of the embodiment is provided.

According to another embodiment, a secondary battery including the electrodes of the embodiment is provided.

The schematic diagram which shows the calculation method of the arithmetic mean value Ra of roughness. The figure which shows the formula for calculating the arithmetic mean value Ra of roughness. The figure which shows the potential curve by cyclic voltammetry of a lithium titanate electrode. The cross-sectional view which shows an example of the laminated body of an embodiment. The perspective view which shows the 1st electrode of the laminated body shown in FIG. The perspective view which shows the 2nd electrode of the laminated body shown in FIG. The perspective view which shows another example of the 1st electrode. FIG. 5 is a cross-sectional view showing another example of the laminate of the embodiment. FIG. 5 is a cross-sectional view showing another example of the laminate of the embodiment. The perspective view which shows the 1st electrode of the laminated body shown in FIG. FIG. 5 is a cross-sectional view showing a shape example of an end portion including the first end surface of the first active material-containing layer. FIG. 5 is a cross-sectional view showing a shape example of an end portion including the first end surface of the first active material-containing layer. FIG. 5 is a cross-sectional view showing a shape example of an end portion including the first end surface of the first active material-containing layer. FIG. 5 is a cross-sectional view showing a shape example of an end portion including the first end surface of the first active material-containing layer. FIG. 5 is a cross-sectional view showing a shape example of an end portion including the first end surface of the first active material-containing layer. FIG. 5 is a cross-sectional view showing a shape example of an end portion including the first end surface of the first active material-containing layer. FIG. 5 is a cross-sectional view showing a shape example of an end portion including the first end surface of the first active material-containing layer. FIG. 5 is a cross-sectional view showing a shape example of an end portion including the first end surface of the first active material-containing layer. The perspective view which shows the 2nd electrode of the laminated body shown in FIG. The perspective view which shows another example of the 1st electrode. FIG. 5 is a cross-sectional view showing another example of the laminate of the embodiment. The schematic diagram of one step in the manufacturing method of the laminated body of an embodiment. The schematic diagram of one step in the manufacturing method of the laminated body of an embodiment. The schematic diagram of one step in the manufacturing method of the laminated body of an embodiment. A partially cutaway perspective view showing an example of the secondary battery of the embodiment. Exploded view of another example of the secondary battery of the embodiment. The figure which shows the relationship between the MSE test time and the wear amount in the electrode of an Example and a comparative example.

First Embodiment According to the first embodiment, there is an active material-containing layer containing active material particles and having a front surface and a back surface, and at least a part of the surface surface of the active material-containing layer having a front surface and a back surface. An electrode is provided that is in contact with and contains a first film containing titanium oxide particles. The surface roughness Ra1 of the surface of the active material-containing layer and the surface roughness Ra2 of the surface of the first film satisfy the following equation (1).

Ra1> Ra2 (1)
The present inventors have stated that the wear on the surface of the roll used in the roll press is due to the active material particles adhering to the surface of the active material-containing layer of the electrode coming into contact with the roll surface and cutting the roll surface. Was investigated. The active material particles adhering to the active material-containing layer are particles that have fallen off from the electrodes or the like for some reason during the manufacturing process. Since the surface of the active material-containing layer can be said to be a soft surface, the active material particles easily bite into it. When the surface in such a state is subjected to the roll press treatment, the active material particles that bite into the surface of the active material-containing layer cut the roll surface, which is a hard surface, and the roll surface is worn. Wear is more pronounced when the active material particles that bite into the surface of the active material-containing layer are positive electrode active material particles.

At least a part of the surface of the active material-containing layer is covered with a first film containing titanium oxide particles, and the surface roughness of the surface of the first film is larger than the surface roughness Ra1 of the surface of the active material-containing layer. For the first time, it was found that the wear of the roll surface can be suppressed by reducing Ra2. As a result, the frequency of roll maintenance can be reduced, and the electrode manufacturing cost can be reduced. Further, by making the surface of the first film the outermost surface of the electrode, it is possible to smooth the surface that greatly contributes to the electrode reaction (electrochemical reaction). As a result, the distance between the electrodes of this electrode and the counter electrode can be made more uniform, so that improvement in battery performance such as battery capacity and rate performance can be expected.

The surface roughness Ra1 and Ra2 are measured by the following method. When measuring the surface roughness of the active material-containing layer and the first film used in the secondary battery, the secondary battery is disassembled in an argon gas atmosphere, and the electrode group is taken out from the exterior member of the secondary battery. .. The electrode group is unwound and the measurement sample is cut out to a size of about 10 mm × 10 mm. The cut sample is placed in a beaker filled with EMC (Ethyl Methyl Carbonate) and stirred, and washed for 30 minutes. The washed sample is dried and cross-sectioned. This sample is cross-section milled using an ion milling device (IM4000PLUS of Hitachi High-Technologies Corporation). An image of the cross section obtained by cross-section milling is imaged, image processing is performed, and the arithmetic mean value of roughness is obtained. This is defined as Ra. As shown in FIG. 1, the arithmetic average value Ra of the roughness is obtained by extracting the reference length l from the roughness curve in the direction of the average line, the x-axis in the direction of the average line of the extracted portion l, and the direction of the vertical magnification. When the y-axis is taken and the roughness curve is represented by y = f (x), the value obtained by the formula shown in FIG. 2 is represented by micrometer (μm).

The electrodes will be described in detail below.

The electrode may further include a current collector and a current collector tab, if necessary. Hereinafter, each component will be described.
(1) Active material-containing layer (first active material-containing layer)
The active material-containing layer may be supported on the current collector. In that case, the back surface of the active material-containing layer may face or contact the main surface of the current collector.

Examples of active material particles include positive electrode active material particles and negative electrode active material particles. First, an active material-containing layer containing positive electrode active material particles as active material particles, that is, a positive electrode active material-containing layer will be described.

Examples of positive electrode active material particles include various oxides and sulfides. For example, manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (eg Li _x Mn ₂ O ₄ or Li _x MnO ₂ ), lithium nickel composite oxide (eg Li _x NiO _2). ), lithium-cobalt composite oxide, lithium nickel manganese cobalt composite oxide, lithium-nickel-cobalt composite oxide (e.g., _{_{_{Li x Ni 1-yz Co y}}} M z O 2 (M is selected from the group consisting of Al, Cr and Fe that is at least one element, which is 0 ≦ y ≦ 0.5,0 ≦ z ≦ 0.1)), lithium manganese cobalt composite oxides (e.g., _{_{Li x Mn 1-y-z}} Co y M z O ₂ (M is at least one element selected from the group consisting of Al, Cr and Fe, and 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.1)), Lithium manganese nickel composite compound ( For example, Li _x Mn _1/2 Ni _1/2 O ₂ ), spinel type lithium manganese nickel composite oxide (for example, Li _x Mn _2-y N _y O ₄ ), lithium phosphorus oxide having an olivine structure (for example, Li _x). FePO _4, such as _{_{_{Li x Fe 1-y Mn y}}} PO 4, Li x CoPO 4), iron sulfate (e.g. _{_{_{Fe 2 (SO 4) 3)}}} , vanadium oxide (e.g. _{_{_{V 2 O 5), Li x}}} Ni 1- _ab Co _a Mn _b M _c O ₂ (0.9 <x ≦ 1.25, 0 <a ≦ 0.4, 0 ≦ b ≦ 0.45, 0 ≦ c ≦ 0.1, M is Mg, Al, It represents at least one element selected from the group consisting of Si, Ti, Zn, Zr, Ca and Sn) and the like. Further, conductive polymer materials such as polyaniline and polypyrrole, disulfide-based polymer materials, organic materials such as sulfur (S) and carbon fluoride, and inorganic materials can also be mentioned. For x, y and z, which are not described in the above-mentioned preferable range, the range is preferably 0 or more and 1 or less.

The type of positive electrode active material can be one type or two or more types.

Examples of preferable positive electrode active materials include those containing at least one selected from the group consisting of lithium manganese composite oxide particles having a spinel structure, lithium cobalt composite oxide particles, and lithium nickel manganese cobalt composite oxide particles. Be done. The positive electrode containing the positive electrode active material can further enhance the effect of suppressing wear on the roll surface by the first film containing titanium oxide particles. At least one of the lithium manganese composite oxide particles and the lithium nickel manganese cobalt composite oxide particles having a spinel structure (hereinafter referred to as positive electrode active material particles A) and the lithium cobalt composite oxide particles (hereinafter referred to as positive electrode active material particles B). According to the positive electrode active material containing (referred to as), the effect of suppressing wear by the first film can be further enhanced.

In the positive electrode active material particles, the mixing ratio of the positive electrode active material particles A and the positive electrode active material particles B is such that the ratio of the positive electrode active material particles B is 40% by mass or less when the positive electrode active material particles are 100% by mass. It is preferable to do so. As a result, it is possible to realize a positive electrode having a high capacity and less deterioration due to overcharging. A more preferable range of the ratio of the positive electrode active material particles B is 4% by mass or more and 30% by mass or less. A more preferable range is that the positive electrode active material particles A are 60% by mass or more and 80% by mass or less, and the positive electrode active material particles B are 4% by mass or more and 20% by mass or less.

The lithium manganese composite oxide having a spinel structure is preferably represented by _{the general formula Li w} M _x Mn _2-x O _4. In this general formula, M is at least one element selected from the group consisting of Mg, Ti, Cr, Fe, Co, Zn, Al, Li and Ga. The molar ratio w in the general formula is preferably in the range of 0 <w ≦ 1.1. The molar ratio w can fluctuate due to the insertion and desorption of lithium ions. The molar ratio x is preferably in the range of 0 ≦ x <2, with a more preferred range of 0.22 ≦ x ≦ 0.7.

Lithium nickel-manganese-cobalt composite oxide is Li _1-x Ni _1-ab Co _a Mn _b O ₂ (-0.2 ≤ x ≤ 0.5, 0 <a ≤ 0.4, 0 <b ≤ 0). It is desirable that it is represented by (satisfying 4). The molar ratio x can vary due to the insertion and desorption of lithium ions. When the molar ratio a of Co is 0.4 or less, thermal stability as an active material can be ensured. When the molar ratio b of Mn is 0.4 or less, the discharge capacity can be secured.

The lithium cobalt composite oxide is preferably represented by the _{general formula Li x} CoO _2. Lithium cobalt oxide in which the molar ratio x in the general formula is in the range of 0 <x ≦ 1.1 is desirable. The molar ratio x can vary due to the insertion and desorption of lithium ions.

The form of the particles of the positive electrode active material is not particularly limited, and may be either primary particles or secondary particles in which the primary particles are aggregated. The positive electrode active material particles may contain both primary particles and secondary particles.

The average particle size of the positive electrode active material particles is, for example, 1 μm or more and 15 μm or less, preferably 3 μm or more and 10 μm or less.

The active material-containing layer may contain a binder and a conductive agent in addition to the active material. Examples of the conductive agent include acetylene black, carbon black, graphite, or a mixture thereof. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, and mixtures thereof. The binder has a function of binding the active material and the conductive agent.

In the positive electrode active material-containing layer, the contents of the active material, the conductive agent and the binder are 80% by mass or more and 97% by mass or less, 2% by mass or more and 18% by mass or less, and 1% by mass or more and 17% by mass or less, respectively. It is preferable to have.

The surface roughness Ra1 of the surface of the positive electrode active material-containing layer can be 1 μm or less. The positive electrode active material-containing layer satisfying this can have a sufficient specific surface area. A more preferable range is 0.2 μm or more and 0.8 μm or less.

Next, the negative electrode active material-containing layer will be described.

As the negative electrode active material, a carbon material such as graphite, a tin-silicon alloy material, or the like can be used, but lithium titanate is preferably used. Further, titanium oxide containing other metals such as Nb or lithium titanate is also mentioned as a negative electrode active material. Examples of lithium titanate include Li _{4 + x} Ti ₅ O ₁₂ (0 ≦ x ≦ 3) _{having a spinel structure and Li 2 + y} Ti ₃ O ₇ (0 ≦ y ≦ 3) having a ramsteride structure. Can be mentioned.

The negative electrode active material particles can be single primary particles, secondary particles in which primary particles are aggregated, or a mixture of primary particles and secondary particles.

The average particle size of the primary particles of the negative electrode active material is preferably in the range of 0.001 or more and 1 μm or less. The average particle size can be obtained, for example, by observing the negative electrode active material with SEM. The particle shape may be either granular or fibrous. In the case of fibrous form, the fiber diameter is preferably 0.1 μm or less. Specifically, the average particle size of the primary particles of the negative electrode active material can be measured from an image observed with an electron microscope (SEM). When lithium titanate having an average particle size of 1 μm or less is used as the negative electrode active material, a negative electrode active material-containing layer having a highly flat surface can be obtained. Further, when lithium titanate is used, the negative electrode potential becomes more noble as compared with a lithium ion secondary battery using a general carbon negative electrode, so that precipitation of lithium metal does not occur in principle. Since the negative electrode active material containing lithium titanate has a small expansion and contraction due to the charge / discharge reaction, it is possible to prevent the crystal structure of the active material from collapsing.

The negative electrode active material-containing layer can contain a conductive agent and a binder in addition to the active material. Examples of the conductive agent include carbon-containing materials (acetylene black, ketjen black, graphite, etc.) and metal powder. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber and the like.

In the negative electrode active material-containing layer, the contents of the negative electrode active material, the conductive agent and the binder are 70% by mass or more and 98% by mass or less, 1% by mass or more and 28% by mass or less, and 1% by mass or more and 28% by mass or less, respectively. It is preferable to have.

The surface roughness Ra1 of the surface of the negative electrode active material-containing layer can be 0.5 μm or less. A more preferable range is 0.1 μm or more and 0.5 μm or less.

The thickness of the positive electrode active material-containing layer and the negative electrode active material-containing layer can be 5 μm or more and 100 μm or less, respectively.
(2) Current collector (first current collector)
The current collector can be a conductive sheet. Examples of conductive sheets include foils made of conductive materials. Examples of conductive materials include aluminum and aluminum alloys.

The thickness of the current collector can be 5 μm or more and 40 μm or less, respectively.
(3) Current collection tab (first current collection tab)
The current collector tab may be formed of the same material as the current collector, but a current collector tab may be prepared separately from the current collector and connected to the current collector by welding or the like. ..
(4) First film The first film contains titanium oxide particles. The first film has an insulating property. It suffices for the first film to cover at least a part of the surface of the first active material-containing layer, but if the entire surface of the first active material-containing layer is covered, the wear suppressing effect can be enhanced. , Can function as a separator. In addition, the first membrane can cover at least a part of the current collector and / or the current collector tab. This makes it possible to prevent an internal short circuit in which the current collector or the current collector tab comes into contact with the counter electrode.

Examples of titanium oxides include lithium titanate having a spinel structure (for example, Li _{4 + x} Ti ₅ O ₁₂ (0 ≦ x ≦ 3)), titanium dioxide (Tio ₂ ) and the like. The crystal structure of titanium dioxide can be, for example, anatase, rutile, bronze or the like. The rutile-type titanium dioxide particles are suitable because they do not easily aggregate and are easily uniformly dispersed in the first film.
Lithium titanate and titanium dioxide having a spinel structure are each excellent in resistance to hydrogen fluoride (HF) and also excellent in oxidation resistance at the positive electrode. FIG. 3 shows a potential curve by cyclic voltammetry of an electrode (LTO / Al electrode) containing _{Li 4} Ti ₅ O _{12 as an active material and using an Al foil as a current collector.} The conditions for carrying out cyclic voltammetry are described below. The applied potential was 1.0V-4.5V (vs. Li ^/ Li +). The environmental temperature was set to 25 ° C. The sweep speed was 0.167 mV / s. As shown in FIG. 3, lithium titanate having a spinel structure has a current value of almost 0 in a range corresponding to a positive electrode potential of ^{3-4 V (vs. Li / Li +), and electron transfer does not proceed.} Therefore, when an electrode containing the first film is applied to the positive electrode, the first film exhibits oxidation resistance that can withstand practical use.

The surface roughness Ra2 of the surface of the first film can be 0.3 μm or less. Thereby, the smoothness of the surface of the first film can be improved. As a result, the wear suppressing effect can be enhanced. A more preferable range is 0.1 μm or more and 0.3 μm or less.

The average particle size D50 of the titanium oxide particles can be 1 μm or less. A more preferable range is 0.3 μm or more and 0.9 μm or less.

The first membrane can be porous. The porous first membrane can retain the non-aqueous electrolyte.

It is desirable that the content of titanium oxide particles in the first film is in the range of 80% by mass or more and 99.9% by mass or less. Thereby, the insulating property of the first film can be improved.

The first film may contain a binder. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, and mixtures thereof. The content of the binder in the first film is preferably in the range of 0.01% by mass or more and 20% by mass or less.

The thickness of the first film can be 1 μm or more and 30 μm or less.

According to the first embodiment, an electrode including an active material-containing layer and a first film containing titanium oxide particles is provided. The surface roughness Ra1 of the surface of the active material-containing layer and the surface roughness Ra2 of the surface of the first film satisfy the equation (1): Ra1> Ra2. Therefore, wear of the roll surface used in the roll press can be suppressed, and improvement of battery performance such as battery capacity and rate performance can be expected.

Second Embodiment According to the second embodiment, a laminate including the electrodes of the first embodiment (hereinafter, the first electrode) is provided. The laminate can further include a second electrode, which is the counter electrode of the first electrode. Further, the laminate may further contain a separator. The separator may be any as long as it can electrically insulate the first electrode and the second electrode while maintaining ionic conduction.

The first film of the first electrode may also serve as a separator. An insulating film other than the second film or the first and second films may be used as the separator. A combination of a plurality of types of films may be used as a separator. Examples of the insulating film include a non-woven fabric made of synthetic resin, a porous film made of polyethylene, a porous film made of polyolefin such as a porous film made of polypropylene, and a cellulosic separator. Further, a separator in which these materials are combined, for example, a separator made of a porous polyolefin film and cellulose can be used. The insulating membrane preferably has a porous structure.

The second electrode includes a second current collector having a front surface and a back surface, and a second active material-containing layer supported or formed on at least one of the front surface and the back surface of the second current collector. .. The surface of the second active material-containing layer can be exposed to the surface of the second electrode, and the back surface faces the front surface or the back surface of the second current collector. Examples of the second current collector and the second active material-containing layer include those similar to those described in the first electrode (first current collector, first active material-containing layer). .. The second electrode may further include a second current collecting tab. The second current collector tab may be formed of the same material as the second current collector, but a second current collector tab is prepared separately from the second current collector, and this is used as the second current collector tab. A current collector connected to the current collector by welding or the like may be used.

The laminate can further include a second film. The second film may be formed on the second active material-containing layer, but may also be formed on the first film. Alternatively, a second film may be formed on the surfaces of both the second active material-containing layer and the first film. In either case, one of the front and back surfaces of the second film may be in contact with the surface of the first film.

The second film contains organic fibers. The second membrane can be a porous membrane in which organic fibers are deposited in the plane direction. The second film has a front surface and a back surface. One main surface of the second film corresponds to the front surface, and the other main surface corresponds to the back surface.

Organic fibers include, for example, at least one organic material selected from the group consisting of polyamideimide, polyamide, polyolefin, polyether, polyimide, polyketone, polysulfone, cellulose, polyvinyl alcohol (PVA) and polyvinylidene fluoride (PVdF). .. Examples of the polyolefin include polypropylene (PP) and polyethylene (PE). The type of organic fiber may be one type or two or more types. Preferred is at least one selected from the group consisting of polyimide, polyamide, polyamideimide, cellulose, PVdF, and PVA, and more preferred is selected from the group consisting of polyimide, polyamide, polyamideimide, cellulose, and PVdF. At least one type.

Polyimide is insoluble and insoluble even at 250 to 400 ° C. and does not decompose, so that a second film having excellent heat resistance can be obtained.

The organic fiber preferably has a length of 1 mm or more and an average diameter of 2 μm or less, and more preferably an average diameter of 1 μm or less. Since such a second film has sufficient strength, porosity, air permeability, pore size, electrolyte resistance, oxidation-reduction resistance, and the like, it functions well as a separator. The average diameter of the organic fibers can be measured by observation with a focused ion beam (FIB) device. In addition, the length of the organic fiber is obtained based on the length measured by observation with a FIB device.

Since it is necessary to ensure ion permeability and electrolyte retention, it is preferable that 30% or more of the total volume of the fibers forming the second membrane is organic fibers having an average diameter of 1 μm or less, and 350 nm or less. The organic fiber of the above is more preferable, and the organic fiber of 50 nm or less is further preferable.

Further, it is more preferable that the volume of the organic fiber having an average diameter of 1 μm or less (more preferably 350 nm or less, further preferably 50 nm or less) occupies 80% or more of the volume of the entire fiber forming the second film. Such a state can be confirmed by scanning ion microscope (SIM) observation of the second film. It is more preferable that the organic fibers having a thickness of 40 nm or less occupy 40% or more of the total volume of the fibers forming the second film. The small diameter of the organic fiber means that the influence of obstructing the movement of ions is small.

It is preferable that a cation exchange group is present on at least a part of the entire surface including the front surface and the back surface of the organic fiber. The cation exchange group promotes the movement of ions such as lithium ions through the separator, thus enhancing the performance of the battery. Specifically, it is possible to perform rapid charging and rapid discharging for a long period of time. The cation exchange group is not particularly limited, and examples thereof include a sulfonic acid group and a carboxylic acid group. Fibers having a cation exchange group on the surface can be formed by, for example, an electrospinning method using a sulfonated organic material.

The second film has pores, and the average pore diameter of the pores is preferably 5 nm or more and 10 μm or less. The porosity is preferably 70% or more and 90% or less. If such pores are provided, a separator having excellent ion permeability and good electrolyte impregnation can be obtained. The porosity is more preferably 80% or more. The average pore diameter and porosity of the pores can be confirmed by the mercury intrusion method, calculation from volume and density, SEM observation, SIM observation, and gas adsorption method. The porosity is preferably calculated from the volume and density of the second membrane. Further, it is desirable to measure the average pore size by a mercury intrusion method or a gas adsorption method. A large porosity in the second membrane means that the effect of interfering with the movement of ions is small.

It is desirable that the thickness of the second film is in the range of 12 μm or less. The lower limit of the thickness is not particularly limited, but may be 1 μm.

In the second film, the porosity is increased by leaving the contained organic fibers in a sparse state, so it is not difficult to obtain a layer having a porosity of, for example, about 90%. It is extremely difficult to form such a layer with a large porosity with particles.

The second membrane is more advantageous than the deposit of inorganic fibers in terms of unevenness, fragility, electrolyte-containing property, adhesion, bending property, porosity, and ion permeability.

The second film may contain particles of an organic compound. The particles are made of, for example, the same material as organic fibers. The particles may be formed integrally with the organic fiber.

The thickness of the first film and the second film is measured by a method conforming to the JIS standard (JIS B 7503-1997). Specifically, these thicknesses are measured using a contact digital gauge. Use a digital gauge fixed to the stone surface plate. Place the sample on the stone surface plate. Use a flat type with a tip of φ5.0 mm for the measurement terminal. The measurement terminal is brought closer from a distance of 1.5 mm or more and less than 5.0 mm above the sample, and the distance in contact with the sample is the thickness of the sample. The average of the measured values at any five points in the sample is taken as the desired thickness.

The laminate including the electrodes of the embodiment will be described by taking FIG. 4 as an example. FIG. 4 is a cross-sectional view showing an example of the laminated body of the embodiment. The cross-sectional view of FIG. 4 is a cross-sectional view of the laminated body cut in the extending direction of the current collecting tab.

The laminate shown in FIG. 4 includes a first electrode 1, a second electrode 2, and a separator 3. As shown in FIGS. 4 and 5, the first electrode 1 includes a first current collector 1a, a first active material-containing layer 1b having a first front surface 40 and a first back surface 41, and a first. Includes the current collector tab 1c. The first current collector 1a is a conductive sheet. The first active material-containing layer 1b is held on each part of both main surfaces of the first current collector 1a. On each main surface of the first current collector 1a, the active material-containing layer is not held on one side (for example, long side, short side) and its vicinity. The active material-containing layer non-holding portion formed parallel to one side of the first current collector 1a functions as the first current collector tab 1c. The first current collecting tab 1c projects from the first active material-containing layer 1b in the first direction d1. Of the surface of the first active material-containing layer 1b, the surface in contact with the first current collector 1a is the first back surface 41.

As shown in FIG. 6, the second electrode 2 has a second current collector 2a, a second active material-containing layer 2b having a second front surface 42 and a second back surface 43, and a second current collector. Includes tab 2c. The second current collector 2a is a conductive sheet. The second active material-containing layer 2b is held on each part of both main surfaces of the second current collector 2a. On each main surface of the second current collector 2a, the active material-containing layer is not held on one side or in the vicinity thereof. The active material-containing layer non-holding portion formed parallel to one side of the second current collector 2a functions as the second current collector tab 2c. The second current collecting tab 2c projects from the second active material-containing layer 2b in the first direction d2. Of the surface of the second active material-containing layer 2b, the surface in contact with the second current collector 2a is the second back surface 43.

Separator 3 includes a second film 5 containing organic fibers. The first film 4 containing the titanium oxide particles can also function as the separator 3. The first film 4 has a front surface A and a back surface B, and the second film 5 has a front surface C and a back surface D. As shown in FIGS. 4 and 5, the back surface B of the first film 4 covers the first surface 40 of each of the first active material-containing layers 1b. How the first film 4 is fixed to the first active material-containing layer 1b is not particularly limited, and examples thereof include adhesion and heat fusion. The surface roughness Ra2 of the surface A of the first film 4 is smaller than the surface roughness Ra1 of the first surface 40 of the first active material-containing layer 1b. On the other hand, as shown in FIG. 6, the second film 5 has four side surfaces 44 intersecting the second surface 42 and the second surface 42 of the second active material-containing layer 2b, respectively, and a second current collector. Covers the three end faces 45 exposed on the surface of the second electrode 2 of 2a and the portion 46 including the boundary with the second active material-containing layer 2b on both main faces of the second current collecting tab 2c. doing. Therefore, the first active material-containing layer 1b and the second active material-containing layer 2b face each other via the first film 4 and the second film 5.

According to the laminated body having the structure shown in FIG. 4, it is possible to suppress the wear of the roll surface and realize the laminated body including the electrode having excellent performance. Further, the second film 5 includes an end face 45 of the second current collector 2a and a portion 46 of the surface of the second current collector tab 2c including a boundary between the second active material-containing layer 2b. Since it is coated, internal short circuits due to contact between the first electrode and the second electrode 2 are reduced.

The first and second current collector tabs are not limited to one side of the first and second current collectors that does not support the active material-containing layer. For example, a plurality of strips protruding from one side of the first and second current collectors can be used as the first and second current collector tabs. An example of this is shown in FIG. FIG. 7 shows another example of the first electrode 1. As shown in FIG. 7, a plurality of strips protruding from one side of the first current collector 1a may be used as the first current collector tab 1c.

The second film may be formed on the second electrode, but may be formed on the first electrode instead of being formed on the second electrode. An example of this is shown in FIG. The second film 7 covers the surface of the first film 4 and all the end faces of the first electrode. The second film 7 also covers the portions of both main surfaces of the first current collecting tab 1c, including the boundary with the first active material-containing layer 1b.

Further, the first film may be formed on both the first electrode and the second electrode. Thereby, the adhesion between the first film and the electrode can be further improved. Further, in this case, it is possible to interpose a second film between the first electrode and the second electrode. With this configuration, the insulation between the first electrode and the second electrode can be made more reliable. The second film can be formed on either or both of the first electrode and the second electrode.

According to the laminated body of the second embodiment, since the electrode of the first embodiment is included, it is possible to suppress wear of the roll surface and realize a laminated body including the electrode having excellent performance. Is.

Third Embodiment The electrode of the third embodiment includes a first active material-containing layer, a first current collector and a first film of the electrode of the first embodiment. The back surface of the first active material-containing layer is supported on at least a part of the front surface and the back surface of the first current collector. The first active material-containing layer includes a first end face adjacent to the first current collecting tab and a second end face facing the first end face in the first direction. The thickness defined by the first end surface of the first active material-containing layer is smaller than the thickness defined by the second end surface of the first active material-containing layer. The first film includes at least a part of the surface of the first active material-containing layer, the first end surface of the first active material-containing layer, and the first of the front and back surfaces of the first current collecting tab. It covers the end face and the adjacent portion.

According to the third embodiment, a laminate including the electrodes of the third embodiment as the first electrodes is provided. The laminate can further include a second electrode, which is the counter electrode of the first electrode. Further, the laminate may further contain a separator. The separator may be one that can electrically insulate the first electrode and the second electrode while maintaining ionic conduction.

The first film of the first electrode may also serve as a separator. An insulating film other than the second film or the first and second films may be used as the separator. A combination of a plurality of types of films may be used as a separator. As the type of the insulating film, the same ones as described in the second embodiment can be mentioned.

The laminate including the electrodes of the third embodiment will be described with reference to the drawings.

FIG. 9 is a cross-sectional view showing an example of the laminated body of the embodiment. The cross-sectional view of FIG. 9 is a cross-sectional view of the laminated body cut in the first direction, which is the extending direction of the current collecting tab. The laminate shown in FIG. 9 includes a first electrode 1, a second electrode 2, and a separator 3 as the electrodes of the third embodiment. As shown in FIGS. 9 and 10, the first electrode 1 includes a first current collector 1a, a first active material-containing layer 1b, and a first current collector tab 1c. The first active material-containing layer 1b has a first front surface 40 and a first back surface 41. The first current collector tab 1c extends from the first current collector 1a in the first direction 51. The first current collector 1a is a conductive sheet having a front surface and a back surface. One main surface of the first current collector 1a is the front surface, and the other main surface is the back surface. Each of the four side surfaces of the first current collector 1a is orthogonal to the front surface and the back surface. The first active material-containing layer 1b is held on each of the front surface and the back surface of the first current collector 1a except for the portion serving as the first current collection tab 1c. On each of the front surface and the back surface of the first current collector 1a, the active material-containing layer is not held on one side (for example, the long side and the short side) and its vicinity. The active material-containing layer non-holding portion formed parallel to one side of the first current collector 1a functions as the first current collector tab 1c. Of the surface of the first active material-containing layer 1b, the surface in contact with the first current collector 1a is the first back surface 41. The first active material-containing layer 1b has two sets of end faces facing each other. One set of end faces is perpendicular to the first direction 51. One of the end faces is the first end face 52 adjacent to the first current collecting tab 1c. The first end surface 52 faces the second end surface 53 in the first direction 51. Further, the thickness T1 defined by the first end surface 52 of the first active material-containing layer 1b is smaller than the thickness T2 defined by the second end surface 53 of the first active material-containing layer 1b. The method of measuring the thicknesses T1 and T2 will be described below.

Disassemble the secondary battery in an argon gas atmosphere, and take out the electrode group from the exterior member of the secondary battery. The electrode group is unwound and the measurement sample is cut out to a size of about 10 mm × 10 mm. The cut sample is placed in a beaker filled with EMC (Ethyl Methyl Carbonate) and stirred, and washed for 30 minutes. Dry the washed sample. This sample is cross-section milled using an ion milling device (IM4000PLUS of Hitachi High-Technologies Corporation). The cross section obtained by cross-section milling is observed with, for example, a scanning electron microscope (TM3030Plus, Hitachi High-Technologies Corporation), and the thicknesses T1 and T2 are measured.

11 to 18 show examples of cross-sectional shapes in which the end portion including the first end surface 52 is cut along the first direction 51. At each of the ends shown in FIGS. 11 to 18, the thickness of the first active material-containing layer 1b decreases toward the first direction 51 and becomes the minimum at the first end surface 52. At the ends shown in FIGS. 11, 12, 14, 17, and 18, the thickness of the end of the first active material-containing layer 1b gradually decreases to the minimum at the first end surface 52. The end portion including the first end surface 52 has a substantially semi-cylindrical shape extending in a direction orthogonal to the first direction 51. At the ends shown in FIGS. 13 and 16, the thickness of the end of the first active material-containing layer 1b is reduced so that the vertical cross-sectional shape is needle-shaped or dome-shaped, and is minimized at the first end surface 52. It has become. On the other hand, at the end shown in FIG. 15, the thickness of the end of the first active material-containing layer 1b is reduced so that the vertical cross-sectional shape draws a protrusion, and is minimized at the first end surface 52. In order to increase the contact area with the current collector, the end shapes shown in FIGS. 11, 12, 14, 17, and 18 are desirable.

As shown in FIG. 19, the second electrode 2 includes a second current collector 2a, a second active material-containing layer 2b, and a second current collector tab 2c. The second active material-containing layer 2b has a second front surface 42 and a second back surface 43. The second current collector tab 2c extends from the second current collector 2a in the second direction 54. The second current collector 2a is a conductive sheet having a front surface and a back surface. One main surface of the second current collector 2a is the front surface, and the other main surface is the back surface. Each of the four side surfaces of the second current collector 2a is orthogonal to the front surface and the back surface. The second active material-containing layer 2b is held on each of the front surface and the back surface of the second current collector 2a except for the portion serving as the second current collection tab 2c. On each of the front surface and the back surface of the second current collector 2a, the active material-containing layer is not held on one side or in the vicinity thereof. The active material-containing layer non-holding portion formed parallel to one side of the second current collector 2a functions as the second current collector tab 2c. Of the surface of the second active material-containing layer 2b, the surface in contact with the second current collector 2a is the second back surface 43. The second active material-containing layer 2b has two sets of end faces facing each other. One set of end faces is perpendicular to the second direction 54. One of the end faces is the first end face 55 adjacent to the second current collecting tab 2c. The first end surface 55 faces the second end surface 56 in the second direction 54. The thickness T1 defined by the first end surface 55 of the second active material-containing layer 2b may be smaller than the thickness T2 defined by the second end surface 56 of the second active material-containing layer 2b.

Separator 3 includes a second film 5 containing organic fibers. The first film 4 can function as a separator 3. The first film 4 has a front surface A and a back surface B, and the second film 5 has a front surface C and a back surface D. As shown in FIGS. 9 and 10, the back surface B of the first film 4 is in contact with and covered with the first surface 40 of each of the first active material-containing layers 1b. For each of the two first active material-containing layers 1b, the first end surface 52 of the four sides orthogonal to the main surface is covered with the first film 4. The first film 4 is a portion adjacent to the first end surface 52 of the first active material-containing layer 1b on the front surface and the back surface of the first current collecting tab 1c, in other words, the surface of the first current collecting tab 1c. And the boundary portion with the first end surface 52 of each of the back surface is also covered. The portion of the first film 4 adjacent to the first end surface 52 is located near the end surface located on the side opposite to the extending side of the second current collecting tab 2c of the second electrode. By providing the first film 4, it is possible to reduce an internal short circuit due to contact between the first current collecting tab 1c of the first electrode and the end face of the second electrode. The form in which the first film 4 covers the first end surface 52 of the first active material-containing layer 1b and the portion adjacent thereto is not particularly limited, but for example, the examples shown in FIGS. 11 to 18. Can be mentioned. In FIG. 11, the first film 4 covers an end portion (hereinafter, referred to as an end portion) including the first end surface 52 of the first active material-containing layer 1b so as to follow the outer shape thereof. Further, the first film 4 covers a portion adjacent to the first end surface 52 (hereinafter referred to as an adjacent portion) with a sufficient width, and the thickness thereof decreases along the first direction 51. In FIG. 12, the first film 4 covers the end portion of the first active material-containing layer 1b including the first end surface 52 so as to follow the outer shape thereof. Further, the first film 4 covers the adjacent portion with a sufficient width and thickness. In FIG. 13, the first film 4 covers the end portion of the first active material-containing layer 1b so as to follow its outer shape. Further, the first film 4 covers the adjacent portion with a sufficient width, and the thickness thereof decreases along the first direction 51. In FIG. 14, the first film 4 covers the end portion of the first active material-containing layer 1b so as to follow its outer shape. In FIG. 15, the first film 4 covers the end of the first active material-containing layer 1b and the adjacent portion with a sufficient width, the thickness of which decreases along the first direction 51. doing. In FIG. 16, the first film 4 covers the periphery of the end portion of the first active material-containing layer 1b. In FIG. 17, the first film 4 covers the end portion and the adjacent portion of the first active material-containing layer 1b, but the portion covering the end portion is covered with the adjacent portion. Are not continuous and are independent of each other. In FIG. 18, the first film 4 covers a part of the end portion of the first active material-containing layer 1b.

In order to enhance the effect of suppressing the first film 4 from peeling from the first active material-containing layer 1b, the structures shown in FIGS. 11 to 14 are desirable.

How the first film 4 is fixed to the first active material-containing layer 1b is not particularly limited, and examples thereof include adhesion and heat fusion.

On the other hand, as shown in FIG. 19, the second film 5 has four side surfaces (including end faces 55 and 56) orthogonal to the second surface 42 and the second surface 42 of the second active material-containing layer 2b, respectively. , Three end faces 45 exposed on the surface of the second electrode 2 of the second current collector 2a, and end faces 55 of the second active material-containing layer 2b on the front and back surfaces of the second current collector tab 2c. It covers the adjacent portion 46. Therefore, the first active material-containing layer 1b and the second active material-containing layer 2b face each other via the first film 4 and the second film 5. The second film may be integrated with the second electrode, but is not limited thereto. For example, the second film may be integrated with the surface of the first film. How the second film is integrated with the first film or the second active material-containing layer is not particularly limited, but for example, the organic fibers in the second film are the first. The state of being sunk or fitted into the surface of the film or the second active material-containing layer can be mentioned.

As shown in the examples described above, since the laminate of the third embodiment includes the electrodes of the first embodiment, it is possible to suppress wear on the roll surface and include electrodes having excellent performance. It is possible to realize a laminated body. Further, the thickness defined by the first end surface of the first active material-containing layer is smaller than the thickness defined by the second end surface of the first active material-containing layer. Further, the first film is adjacent to the surface and the first end surface of the first active material-containing layer and the first end surface of the first active material-containing layer of the front and back surfaces of the first current collecting tab. It covers the part. According to such a structure, it is possible to prevent the first film from peeling from the first active material-containing layer. As a result, in order to obtain a high capacity, the first film becomes the first film when the electrode group is produced by winding the laminate in a spiral shape or when the filling rate of the laminate in the exterior member is increased. Since peeling from the active material-containing layer can be suppressed, the occurrence of an internal short circuit can be suppressed, and a high-capacity battery can be provided. Therefore, it is excellent in practicality. In addition, the volume change due to expansion and contraction due to charge / discharge on the first end surface side of the first active material-containing layer can be alleviated. As a result, the first film can easily follow the deformation of the first active material-containing layer, and can suppress peeling from the first active material-containing layer. Therefore, the life such as the charge / discharge cycle life of the battery can be improved.

The first and second current collector tabs are not limited to one side of the first and second current collectors without supporting the active material-containing layer. For example, a plurality of strips protruding from one side surface of the first and second current collectors can be used as the first and second current collector tabs. An example of this is shown in FIG. FIG. 20 shows another example of the first electrode 1. As shown in FIG. 20, a plurality of strips protruding from one side surface (for example, one side surface along the long side) of the first current collector 1a may be used as the first current collector tab 1c. The first film 4 covers the front surface and the first end surface 52 of the first active material-containing layer 1b, and the portions of the front surface and the back surface of the first current collecting tab 1c adjacent to the first end surface 52. .. The other three end faces of the first active material-containing layer 1b, the four side surfaces 49 of the first current collector 1a, or the two opposite side surfaces 48 of the first current collector tab 1c are formed on the first film 4. It may be covered.

Further, the second film 5 may be integrated with the first electrode 1. An example of this is shown in FIG. In FIG. 21, the second film 5 includes the surface of the first film 4 and the electrode end faces not covered by the first film 4, that is, the three electrode end faces on which the first current collecting tab 1c does not extend. Is covered. According to the configuration of FIG. 21, it is possible to prevent the first film from peeling from the first active material-containing layer while ensuring the necessary insulating property between the first electrode and the second electrode. Therefore, the capacity of the battery and the life of the charge / discharge cycle can be improved.

The manufacturing method of the first electrode, which is an example of the electrodes of the first embodiment and the third embodiment, will be described below.

First Production Method A slurry containing a first active material (hereinafter referred to as slurry I) and a slurry containing titanium oxide particles (hereinafter referred to as slurry II) on at least one main surface of the first current collector ) At the same time. An example of the coating process is shown in FIGS. 22 and 23. The coating device 30 includes a tank 32 for accommodating the slurry I and a tank 33 for accommodating the slurry II, and is configured to simultaneously apply the slurry I and the slurry II to the base material. The long first current collector 1a before being cut to a predetermined size is conveyed to the slurry discharge port of the coating device 30 by the transfer roller 31. In FIG. 23, the slurry I discharge port 32a is located on the upstream side of the current collector with respect to the slurry II discharge port 33a. Due to such an arrangement of the discharge port, the slurry I is applied from the coating device 30 onto the first current collector 1a except for both ends in the short side direction. Next, before the slurry I dries, the slurry II is overcoated so as to protrude from the coating area of the slurry I. Since the slurry II is overcoated with the slurry I, the slurry II can easily follow the surface shape of the slurry I. Then, after the slurry is dried, the dried slurry is rolled and pressed to a predetermined size to obtain a first electrode. If the step of applying the slurry I and the step of applying the slurry II are performed at substantially the same time, the difference in surface roughness can be reduced. Further, if the period between the steps is lengthened, the difference in surface roughness increases. The difference in surface roughness can be reduced by shortening the drying time of the slurry. Further, increasing the press pressure can reduce the difference in surface roughness. By adjusting the timing of applying the slurry I and the slurry II, the drying conditions of the slurry, the pressing conditions, etc., the surface roughness of the surface of the first film is rougher than that of the surface roughness Ra1 of the first active material-containing layer. A first electrode having a small Ra2 is obtained.
It is desirable that the viscosity of the slurry II be made larger than the viscosity of the slurry I. As a result, the fluidity of the slurry II is lower than that of the slurry I, so that the slurry I diffuses on the surface of the first current collector to reduce the thickness of the end portion of the coating. Slurry II diffuses on slurry I while following the shape of slurry I. As a result, the thickness defined by the first end surface of the first active material-containing layer can be made smaller than the thickness defined by the second end surface of the first active material-containing layer. It is desirable that the viscosity of the slurry II is higher than the viscosity of the slurry I over a region of viscosity shear rate of 1.0 (1 / s) or more and 1000 (1 / s) or less. The viscosity of the slurry I is preferably 0.01 Pa · s or more and 1000 Pa · s or less in the region where the viscosity shear rate is 1.0 (1 / s) or more and 1000 (1 / s) or less, and among them, 0.1 Pa · s or more. More preferably 100 Pa · s or less. On the other hand, the viscosity of the slurry II is preferably 0.1 Pa · s or more and 1000 Pa · s or less in the region where the viscosity shear rate is 1.0 (1 / s) or more and 1000 (1 / s) or less, and particularly 1 Pa · s or more. More preferably 1000 Pa · s or less.

The method for manufacturing the laminate including the electrodes of the first embodiment or the third embodiment will be described below.

Second Manufacturing Method A first electrode (the electrode of the first or third embodiment) is obtained by the first manufacturing method.

On the other hand, after applying the slurry containing the second active material to the second current collector, the slurry is dried, the dried one is roll-pressed, and cut into a predetermined size to obtain a second electrode. .. A second film is formed on the second electrode by an electrospinning method. Then, a press may be applied. As the pressing method, a roll press or a flat plate press may be used.

The first electrode and the second electrode are laminated so that they face each other via the first film and the second film to obtain the laminate of the embodiment.

Third Production Method A second film is formed on the first electrode produced by the first production method by an electrospinning method. Then, a press may be applied. The pressing conditions are as described in the second manufacturing method.

On the other hand, after applying the slurry containing the second active material to the second current collector, the slurry is dried, the dried one is roll-pressed, and cut into a predetermined size to obtain a second electrode. ..

Next, the electrospinning method will be described. The second film is formed, for example, by an electrospinning method. In the electrospinning method, the first electrode or the second electrode, which is the object of forming the second film, is grounded to be a ground electrode. When forming on the first electrode, the first electrode on which the first film has been formed is prepared.

The voltage applied to the spinning nozzle charges the liquid raw material (for example, the raw material solution), and the volatilization of the solvent from the raw material solution increases the charge amount per unit volume of the raw material solution. Due to the continuous volatilization of the solvent and the accompanying increase in the amount of charge per unit volume, the raw material solution discharged from the spinning nozzle extends in the longitudinal direction, and as a nano-sized organic fiber, the first ground electrode. Accumulate on the electrode or the second electrode. A Coulomb force is generated between the organic fiber and the ground electrode due to the potential difference between the nozzle and the ground electrode. Therefore, the contact area with the first film can be increased by the nano-sized organic fiber, and the organic fiber can be deposited on the first electrode or the second electrode by the Coulomb force, so that the second electrode can be deposited. It is possible to increase the peeling strength of the film from the electrode. The peel strength can be controlled by adjusting, for example, the solution concentration, the distance between the sample and the nozzle, and the like. When the second film is not formed on the first and second current collecting tabs, it is preferable to mask the first and second current collecting tabs before forming the second film. An example of this is shown in FIG. FIG. 24 is a perspective view showing a step of forming a second film on the second electrode. As shown in FIG. 24, the second film 5 is directly formed by depositing the raw material solution discharged from the nozzle N on the second active material-containing layer 2b and the second current collecting tab 2c as organic fibers. Will be done. One side of the second current collecting tab 2c and its vicinity are covered with the mask M. Therefore, the second film 5 is deposited so as to straddle the surface of the second active material-containing layer 2b and the portion of the surface of the second current collecting tab 2c adjacent to the second active material-containing layer 2b. It becomes a porous film containing organic fibers.

By using the electrospinning method, a second film can be easily formed on the electrode surface. In principle, the electrospinning method forms a single continuous fiber, so that the thin film can ensure resistance to breakage due to bending and cracking of the film. The fact that the organic fibers constituting the second film are seamless and continuous has a low probability of fraying or partial loss of the second film, and is advantageous in terms of suppressing self-discharge.

As the liquid raw material used for electrospinning, for example, a raw material solution prepared by dissolving an organic material in a solvent is used. Examples of organic materials include those similar to those mentioned for organic materials constituting organic fibers. The organic material is used, for example, dissolved in a solvent at a concentration of about 5 to 60% by mass. The solvent for dissolving the organic material is not particularly limited, and any solvent such as dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N, N'dimethylformamide (DMF), N-methylpyrrolidone (NMP), water, alcohols and the like can be used. A solvent can be used. For organic materials with low solubility, electrospinning is performed while melting the sheet-shaped organic material with a laser or the like. In addition, it is permissible to mix a high boiling organic solvent with a low melting point solvent.

A second film is formed by discharging the raw material from the spinning nozzle over the surface of a predetermined electrode while applying a voltage to the spinning nozzle using a high-voltage generator. The applied voltage is appropriately determined according to the solvent / solute species, the boiling point / vapor pressure curve of the solvent, the solution concentration, the temperature, the nozzle shape, the distance between the sample and the nozzle, etc. For example, the potential difference between the nozzle and the work is 0.1 to 1. It can be 100 kV. The supply rate of the raw material is also appropriately determined according to the solution concentration, solution viscosity, temperature, pressure, applied voltage, nozzle shape and the like. In the case of the syringe type, for example, it can be about 0.1 to 500 μl / min per nozzle. Further, in the case of a multi-nozzle or a slit, the supply speed may be determined according to the opening area.

Since the organic fibers are formed directly on the surface of the electrode in a dry state, it is practically avoided that the solvent contained in the raw material penetrates into the electrode. The residual amount of solvent inside the electrode is as low as ppm level or less. The residual solvent inside the electrode causes a redox reaction, causing battery loss and leading to deterioration of battery performance. According to the present embodiment, the possibility of such inconvenience occurring is reduced as much as possible, so that the performance of the battery can be improved.

Fourth Embodiment The secondary battery of the fourth embodiment includes the laminate of the above embodiment. The secondary battery may further include an electrolyte and an exterior member capable of accommodating the electrolyte and the laminate.

A secondary battery in which a plurality of laminates are laminated so that the first film and / or the second film is located between the first active material-containing layer and the second active material-containing layer as an electrode group. May be used for. The shape of the electrode group is not limited to this shape, and one or more laminated bodies wound in a spiral or flat spiral shape may be used as the electrode group.

The secondary battery may further include a first electrode terminal that is electrically connected to the first current collecting tab and a second electrode terminal that is electrically connected to the second current collecting tab. Is.

As the electrolyte, for example, a non-aqueous electrolyte is used. Examples of the non-aqueous electrolyte include a liquid non-aqueous electrolyte prepared by dissolving the electrolyte in an organic solvent, a gel-like non-aqueous electrolyte in which a liquid electrolyte and a polymer material are combined, and the like. The liquid non-aqueous electrolyte can be prepared, for example, by dissolving the electrolyte in an organic solvent at a concentration of 0.5 mol / L or more and 2.5 mol / L or less.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium arsenic hexafluorophosphate (LiAsF ₆ ), and trifluorometh. Lithium salts such as lithium sulfonate (LiCF ₃ SO ₃ ), bistrifluoromethylsulfonylimide lithium [LiN (CF ₃ SO ₂ ) ₂ ], or mixtures thereof can be mentioned. It is preferable that it is difficult to oxidize even at a high potential, and LiPF ₆ is most preferable.

Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC) and vinylene carbonate, and chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC) and methyl ethyl carbonate (MEC). Cyclic ethers such as tetrahydrofuran (THF), dimethyltetrahydrofuran (2MeTHF) and dioxolane (DOX), chain ethers such as dimethoxyethane (DME) and diethoxyethane (DEE), γ-butyrolactone (GBL), Examples thereof include acetonitrile (AN) and sulfolane (SL). Such an organic solvent may be used alone or as a mixture of two or more kinds.

Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO) and the like.

As the non-aqueous electrolyte, a room temperature molten salt (ionic melt) containing lithium ions, a polymer solid electrolyte, an inorganic solid electrolyte, or the like may be used.

As the exterior member, for example, a metal container, a laminated film container, or the like can be used.

The form of the secondary battery is not particularly limited, and can be in various forms such as a cylindrical type, a flat type, a thin type, a square type, and a coin type.

FIG. 25 is a partially cutaway perspective view showing an example of the secondary battery according to the embodiment. FIG. 25 is a diagram showing an example of a secondary battery using a laminated film as an exterior member. The secondary battery 10 shown in FIG. 25 includes an exterior member 11 made of a laminated film, an electrode group 12, a first electrode terminal 13, a second electrode terminal 14, and a non-aqueous electrolyte (not shown). .. The electrode group 12 includes a plurality of laminated bodies of the embodiment, and has a structure in which the first electrode and the second electrode are laminated via a separator composed of a first film and a second film. A non-aqueous electrolyte (not shown) is retained or impregnated in the electrode group 12. The first current collecting tab of the first electrode is electrically connected to the first electrode terminal 13. The second current collecting tab of the second electrode is electrically connected to the second electrode terminal 14. As shown in FIG. 25, the tips of the first electrode terminal 13 and the second electrode terminal 14 project outward from one side of the exterior member 11 in a state where they are separated from each other.

FIG. 26 is an exploded perspective view showing another example of the secondary battery according to the embodiment. FIG. 26 is a diagram showing an example of a secondary battery using a square metal container as an exterior member. The secondary battery shown in FIG. 26 includes an exterior member 20, a wound electrode group 21, a lid 22, a first electrode terminal 23, a second electrode terminal 24, and a non-aqueous electrolyte (not shown). including. The wound electrode group 21 has a structure in which the laminated body of the embodiment is wound in a flat spiral shape. In the wound electrode group 21, the first current collecting tab 25 wound in a flat spiral shape is located on one end face in the circumferential direction, and the second current collecting tab 25 wound in a flat spiral shape is located on one end face. The electric tab 26 is located on the other end face in the circumferential direction. A non-aqueous electrolyte (not shown) is retained or impregnated in the electrode group 21. The first electrode lead 27 is electrically connected to the first current collecting tab 25 and is also electrically connected to the first electrode terminal 23. Further, the second electrode lead 28 is electrically connected to the second current collecting tab 26 and also electrically connected to the second electrode terminal 24. The electrode group 21 is arranged in the exterior member 20 so that the first electrode lead 27 and the second electrode lead 28 face the main surface side of the exterior member 20. The lid 22 is fixed to the opening 20a of the exterior member 20 by welding or the like. The first electrode terminal 23 and the second electrode terminal 24 are respectively attached to the lid 22 via an insulating hermetic seal member (not shown).

According to the secondary battery of the fourth embodiment described above, since the electrode and / or the laminate of any of the above embodiments is included, wear of the press roll surface can be suppressed and battery performance is improved. Can be done.

A secondary battery with the first electrode as the positive electrode and the second electrode as the negative electrode was produced by the following method.

(Example 1)
An insulating layer as a first film on the positive electrode and the positive electrode, and a nanofiber layer as a second film on the negative electrode and the negative electrode were produced by the following methods.

Average particle size

_{_{_{6μm LiNi 0.33 Co 0.33 Mn 0.33 O}}} 2 particles and an average particle size 5μm of LiCoO ₂ particles as a positive electrode active material, carbon black as a conductive agent, polyvinylidene fluoride (PVdF) Prepared. These were mixed at a mass ratio of 80:20: 5: 5 to obtain a mixture. Next, the obtained mixture was dispersed in an n-methylpyrrolidone (NMP) solvent, and the viscosity shear rate was 1.0 (1 / s) at 10 Pa · s, and the viscosity shear rate was 1000 (1 / s). A positive electrode slurry was prepared so as to have a concentration of 5 Pa · s.

_{Lithium titanate (Li 4} Ti ₅ O ₁₂ ) particles having an average particle diameter D50 of 1 μm and PVdF were prepared as insulating inorganic materials. These were mixed at a mass ratio of 100: 4 to obtain a mixture. Next, the obtained mixture was dispersed in NMP, and a titanium oxide-containing slurry was obtained so as to have a viscosity shear rate of 1.0 (1 / s) of 100 Pa · s and a viscosity shear rate of 1000 (1 / s) of 2 Pa · s. Was prepared.

Therefore, the viscosity of the titanium oxide-containing slurry (slurry II) is larger than the viscosity of the positive electrode slurry (slurry I) over a region of viscosity shear rate of 1.0 (1 / s) or more and 1000 (1 / s) or less. ..

The viscosities of the positive electrode slurry and the titanium oxide-containing slurry were measured using a Thermo Scientific HAAKE MARS III viscosity / viscoelasticity measuring device.

Next, on an aluminum foil having a thickness of 15 μm, a positive electrode slurry was applied to the lower layer, a titanium oxide-containing slurry was applied to the upper layer, and the titanium oxide-containing slurry of the upper layer was overcoated and dried. It was. This was done on both sides of the aluminum foil. Then, it was rolled-pressed and cut into a predetermined size to obtain a positive electrode. As shown in FIG. 9, the insulating inorganic material layer was coated with the front surface and the first end surface of the positive electrode active material-containing layer, and the front surface and the back surface of the positive electrode current collector tab adjacent to the first end surface.

The thickness of each of the positive electrode active material-containing layers is 20 μm, the thickness of the insulating inorganic material layer on the positive electrode active material-containing layer is 3 μm, and the insulating inorganic material layer formed on the aluminum foil protruding from the positive electrode active material-containing layer. The thickness of was 20 μm. The content of titanium oxide in the insulating inorganic material layer was 96% by mass. The thickness T1 of the first end face was 5 μm, and the thickness T2 of the second end face was 20 μm. The shape of the end portion including the first end face is as shown in FIG. That is, the thickness of the positive electrode active material-containing layer 1b containing a large number of particles becomes thinner toward the current collecting tab side. The first film 4 covers the surfaces of the positive electrode active material-containing layer 1b and the positive electrode current collector 1a. The thickness of the first film 4 is such that the portion in contact with the surface of the positive electrode current collector 1a is thicker than the portion in contact with the surface of the positive electrode active material-containing layer 1b.

A portion without a positive electrode active material-containing layer was provided on one long side of the current collector, and this portion was used as a positive electrode current collector tab.

Lithium titanate particles having an average primary particle size of 0.5 μm were prepared as the negative electrode active material, carbon black was prepared as the conductive agent, and polyvinylidene fluoride was prepared as the binder. These were mixed at a mass ratio of 90: 5: 5 to obtain a mixture. The resulting mixture was dispersed in an n-methylpyrrolidone (NMP) solvent to prepare a slurry.

The obtained slurry was applied to both sides of an aluminum foil having a thickness of 15 μm and dried. Then, the dried coating film was pressed to obtain a negative electrode. The thickness of each of the negative electrode active material-containing layers was 30 μm. A portion without a negative electrode active material-containing layer was provided on one long side of the current collector, and this portion was used as a negative electrode current collector tab.

Organic fibers were deposited on this negative electrode by an electrospinning method to form a nanofiber layer. Polyimide was used as the organic material. This polyimide was dissolved in DMAc as a solvent at a concentration of 20% by mass to prepare a raw material solution as a liquid raw material. The obtained raw material solution was supplied from the spinning nozzle to the surface of the negative electrode at a supply rate of 5 μl / min using a metering pump. A voltage of 20 kV was applied to the spinning nozzle using a high voltage generator, and a layer of 2 μm organic fibers was formed on the surface of the negative electrode active material-containing layer while moving the range of 100 × 200 mm with this spinning nozzle. The negative electrode was subjected to the electrospinning method with the surface of the negative electrode current collecting tab masked, except for the portion 10 mm from the boundary with the negative electrode active material-containing layer on both surfaces (main surfaces) of the negative electrode current collecting tab. Obtained. As shown in FIG. 19, the organic fiber layer has four side surfaces orthogonal to the respective surfaces and surfaces of the negative electrode active material-containing layer, three end faces exposed on the negative electrode surface of the negative electrode current collector, and a negative electrode current collector. The front surface and the back surface of the tab were covered with the end surface of the negative electrode active material-containing layer and the portion adjacent to the end surface.

The obtained positive electrode and negative electrode were wound and pressed so that the first film of the positive electrode and the second film of the negative electrode faced each other as shown in FIG. 9, and an electrode group was obtained as a laminated body.

(Example 2)
A laminate was obtained in the same manner as in Example 1 except that _{rutile-type titanium dioxide (TiO 2} ) particles having an average particle diameter D50 of 1 μm were used as the insulating inorganic material.
(Comparative Example 1)
A laminate was obtained in the same manner as in Example 1 except that _{alumina (Al 2} O ₃ ) particles having an average particle diameter D50 of 1 μm were used as the insulating inorganic material.

(Comparative Example 2)
A laminate was obtained in the same manner as in Example 1 except that magnesia (MgO) particles having an average particle diameter D50 of 3 μm were used as the insulating inorganic material.

(Comparative Example 3)
A laminate was obtained in the same manner as in Example 1 except that the first film was not provided.

For the positive electrodes of Examples and Comparative Examples, the surface roughness Ra1 of the positive electrode active material-containing layer and the surface roughness Ra2 of the surface of the first film were measured by the above-mentioned method for measuring the arithmetic mean value Ra of the roughness, and the results were obtained. Is shown in Table 1. As shown in Table 1, the positive electrodes of Examples 1 and 2 satisfied Ra1> Ra2.

In addition, the positive electrodes of Examples and Comparative Examples were subjected to a microslurry erosion (MSE) test (a test in which a slurry prepared with an abrasion agent and a solvent was sprayed onto a test piece to erode the surface). The test procedure is as follows. First, a slurry having a solid content ratio of the abrasion agent particles of 10% by mass and containing water as a solvent was prepared and placed in a tank in the testing machine. The slurry was sucked up while stirring with a mixer. The sucked slurry was sprayed at a high pressure on the surface of each electrode, which is a test piece, at a flow velocity of 300 m / s using a nozzle. The diameter of the nozzle was 3 mm × 3 mm. After spraying for a certain period of time, the depth of wear was measured with a stylus type roughness meter. The test was carried out at room temperature. The relationship between the MSE test time (minutes) and the amount of wear (μm) is shown in FIG.

As is clear from FIG. 27, the electrodes of Examples 1 and 2 provided with the first film containing the titanium oxide particles had a wear amount of less than 10 μm even after the test time of 300 minutes had elapsed. On the other hand, the electrodes of Comparative Examples 1 and 2 provided with the first film containing alumina or magnesia and the electrodes of Comparative Example 3 not provided with the first film all had a wear amount within 120 minutes of the test time. It reached 40 μm. From the above results, it was confirmed that the wear of the roll surface was suppressed according to the electrodes according to the embodiment. The electrode groups of Examples 1 and 2 were vacuum dried overnight at room temperature and then left in a glove box having a dew point of −80 ° C. or lower for one day. This was housed in a metal container together with the electrolytic solution to obtain a non-aqueous electrolyte battery. The electrolytic solution used was one in which _{LiPF 6} was dissolved in ethylene carbonate (EC) and dimethyl carbonate (DMC). The obtained batteries of Examples 1 and 2 showed the same initial capacity of 1 Ah as the design capacity.

In the positive electrode of Example 1, the positive electrode active material is 80% by mass of lithium manganese composite oxide particles having a spinel structure represented by _{LiMn 2} O ₄ _{having an average particle size of 7 μm, and LiCoO 2} particles having an average particle size of 5 μm. Was changed to 20% by mass, and the same results as in Example 1 were obtained.

The electrode according to at least one embodiment and the embodiment described above includes an active material-containing layer and a first film containing titanium oxide particles, and has surface roughness Ra1 and a first surface roughness of the surface of the active material-containing layer. The surface roughness Ra2 of the surface of the film 1 satisfies Eq. (1): Ra1> Ra2. Therefore, wear of the roll surface used in the roll press can be suppressed, and improvement of battery performance such as battery capacity and rate performance can be expected.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... 1st electrode, 1a ... 1st current collector, 1b ... 1st active material-containing layer, 1c ... 1st current collection tab, 2 ... 2nd electrode, 2a ... 2nd current collector , 2b ... 2nd active material-containing layer, 2c ... 2nd current collecting tab, 3 ... Separator, 4 ... 1st film, 5 ... 2nd film, 10 ... Secondary battery, 11 ... Exterior member, 12 ... Electrode group, 13, 23 ... 1st electrode terminal, 14, 24 ... 2nd electrode terminal, 20 ... Exterior member, 21 ... Electrode group, 22 ... Lid, 25 ... 1st current collecting tab, 26 ... 2 current collecting tabs, 27 ... 1st electrode lead, 28 ... 2nd electrode lead, 40 ... 1st surface, 41 ... 1st back surface, 42 ... 2nd surface, 43 ... 2nd back surface, 45 ... the end face of the second current collector, 46 ... the portion of the second current collector tab including the boundary with the second active material-containing layer, A ... the surface of the first film, B ... the first film. Back surface, C ... Second surface of film, D ... Back surface of second film, 51 ... First direction, 52, 55 ... First end face, 53, 56 ... Second end face, 54 ... Second direction.

Claims

An active material-containing layer containing active material particles and having front and back surfaces,
It has a front surface and a back surface, the back surface of which is in contact with at least a part of the surface of the active material-containing layer, and includes a first film containing titanium oxide particles.
An electrode in which the surface roughness Ra1 of the surface of the active material-containing layer and the surface roughness Ra2 of the surface of the first film satisfy Ra1> Ra2.
The electrode according to claim 1, wherein the titanium oxide particles include at least one of a spinel-structured lithium titanium oxide particles and titanium dioxide particles.
The active material particles include at least one selected from the group consisting of lithium manganese composite oxide particles having a spinel structure, lithium cobalt composite oxide particles, and lithium nickel manganese cobalt composite oxide particles, according to claim 1 or 2. The electrode according to 2.
The electrode according to claim 1 or 2, wherein the active material particles include at least one of a spinel-structured lithium manganese composite oxide particle and a lithium nickel manganese cobalt cobalt composite oxide particle, and the lithium cobalt composite oxide particle. ..
A current collector with front and back surfaces and
Further including a current collector tab extending in the first direction from the current collector.
The back surface of the active material-containing layer is supported on at least a part of the front surface and the back surface of the current collector, and the active material-containing layer has a first end surface adjacent to the current collector tab and the first end surface. It has a second end face facing the first end face in one direction.
The thickness of the active material-containing layer defined by the first end surface is smaller than the thickness of the active material-containing layer defined by the second end surface.
A claim that the first film covers at least the first end surface of the active material-containing layer and a portion of the front surface and the back surface of the current collecting tab adjacent to the first end surface. Item 2. The electrode according to any one of Items 1 to 4.
The electrode according to claim 5, wherein the thickness of the active material-containing layer decreases along the first direction, and the thickness defined by the first end face is minimized.
A first electrode comprising the electrode according to any one of claims 1 to 6 and a first electrode.
With the second electrode
Laminated body including a separator.
The laminate according to claim 7, wherein the first electrode is a positive electrode.
The laminate according to claim 7 or 8, wherein the first film also serves as the separator.
The laminate according to claim 7 or 8, wherein the separator contains an insulating film different from the first film.
A secondary battery including the electrode according to any one of claims 1 to 6.