JP7254941B2 - Electrodes, laminates and secondary batteries - Google Patents

Description

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 pressing. On the other hand, secondary batteries are also required to reduce manufacturing costs. For example, when a roll used in roll press processing wears out, not only does the roll itself require maintenance, but the production line must be stopped during maintenance. Therefore, in addition to maintenance costs, losses due to production interruptions occur. If the frequency of roll maintenance can be reduced, manufacturing costs can be reduced, and high-performance electrodes can be provided at a lower cost.

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

Embodiments provide a high-performance electrode, a laminate including the electrode, and a secondary battery.

According to embodiments, an electrode is provided 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 part of the surface of the active material-containing layer. The first film contains 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 Ra1>Ra2.

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

According to other embodiments, secondary batteries are provided that include the electrodes of the embodiments.

FIG. 4 is a schematic diagram showing a method of calculating an arithmetic average value Ra of roughness; FIG. 5 is a diagram showing an equation for calculating an arithmetic average value Ra of roughness; The figure which shows the potential curve by cyclic voltammetry of a lithium titanate electrode. Sectional drawing which shows an example of the laminated body of embodiment. FIG. 5 is a perspective view showing a first electrode of the laminate shown in FIG. 4; FIG. 5 is a perspective view showing a second electrode of the laminate shown in FIG. 4; FIG. 4 is a perspective view showing another example of the first electrode; Sectional drawing which shows another example of the laminated body of embodiment. Sectional drawing which shows another example of the laminated body of embodiment. FIG. 10 is a perspective view showing a first electrode of the laminate shown in FIG. 9; FIG. 4 is a cross-sectional view showing a shape example of an end including a first end face of the first active material-containing layer; FIG. 4 is a cross-sectional view showing a shape example of an end including a first end face of the first active material-containing layer; FIG. 4 is a cross-sectional view showing a shape example of an end including a first end face of the first active material-containing layer; FIG. 4 is a cross-sectional view showing a shape example of an end including a first end face of the first active material-containing layer; FIG. 4 is a cross-sectional view showing a shape example of an end including a first end face of the first active material-containing layer; FIG. 4 is a cross-sectional view showing a shape example of an end including a first end face of the first active material-containing layer; FIG. 4 is a cross-sectional view showing a shape example of an end including a first end face of the first active material-containing layer; FIG. 4 is a cross-sectional view showing a shape example of an end including a first end face of the first active material-containing layer; FIG. 10 is a perspective view showing a second electrode of the laminate shown in FIG. 9; FIG. 4 is a perspective view showing another example of the first electrode; Sectional drawing which shows another example of the laminated body of embodiment. Schematic of 1 process in the manufacturing method of the laminated body of embodiment. Schematic of 1 process in the manufacturing method of the laminated body of embodiment. Schematic of 1 process in the manufacturing method of the laminated body of embodiment. 1 is a partially cutaway perspective view showing an example of a secondary battery according to an embodiment; FIG. 4 is an exploded view of another example of the secondary battery of the embodiment; FIG. FIG. 4 is a diagram showing the relationship between the MSE test time and the amount of wear in the electrodes of Examples and Comparative Examples.

First Embodiment According to a first embodiment, 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 of the active material-containing layer having a front surface and a back surface and the back surface being the back surface and a first film comprising 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 following formula (1).

Ra1>Ra2 (1)
The present inventors have found that the wear of the surface of the roll used for roll pressing is due to the active material particles adhering to the surface of the active material-containing layer of the electrode contacting 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 electrode 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 tend to bite into it. When the surface in such a state is subjected to a roll press treatment, the active material particles that have bitten into the surface of the active material-containing layer cut the hard surface of the roll, resulting in abrasion of the roll surface. Abrasion occurs more remarkably when the active material particles that have bitten into the surface of the active material-containing layer are positive electrode active material particles.

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

Surface roughnesses 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 secondary battery exterior member. . This electrode group is unwound and a measurement sample of about 10 mm×10 mm is cut out. The cut sample is placed in a stirred beaker filled with EMC (EthylMethylCarbonate) and washed for 30 minutes. The washed sample is dried and cross-sectioned. This sample is cross-sectionally milled using an ion milling device (IM4000PLUS manufactured by Hitachi High-Technologies Corporation). A cross-sectional image obtained by cross-sectional milling is taken, image-processed, and an arithmetic average value of roughness is obtained. We define this as Ra. As shown in FIG. 1, the arithmetic average value Ra of roughness is obtained by extracting a reference length l from the roughness curve in the direction of the average line, and setting the x axis in the direction of the average line of this extracted portion l, and the direction of the longitudinal magnification. , and the roughness curve is represented by y=f(x).

The electrodes will be described in detail below.

The electrode may further include current collectors and current collecting tabs as needed. Each component will be described below.
(1) Active material-containing layer (first active material-containing layer)
The active material-containing layer may be carried on a current collector. In that case, the back surface of the active material-containing layer may face or be in contact with 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, the active material-containing layer containing positive electrode active material particles as active material particles, that is, the 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 (e.g. Li _x Mn ₂ O ₄ or Li _x MnO ₂ ), lithium nickel composite oxide (e.g. Li _x NiO ₂ ), lithium-cobalt composite oxides, lithium-nickel-manganese-cobalt composite oxides, lithium-nickel-cobalt composite oxides (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). 0 ≤ y ≤ 0.5 and 0 ≤ z ≤ 0.1)), lithium manganese cobalt composite oxide (for example, 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 and 0 ≤ z ≤ 0.1)), lithium manganese nickel composite compound ( Li _x Mn _1/2 Ni _1/2 O ₂ ), spinel-type lithium manganese nickel composite oxides (e.g. Li _x Mn _2-y Ni _y O ₄ ), lithium phosphorous oxides having an olivine structure (e.g. Li _{x FePO4} , _{LixFe1 - yMnyPO4} , _{LixCoPO4 , etc. ) ,} iron sulfate (e.g. _Fe2 ( _SO4 ) ₃ ), vanadium oxide (e.g. _V2O5 ), _{LixNi1- ab CoaMnbMcO2} (0.9<x≤1.25, 0 _< a≤0.4 _, 0≤b≤0.45, 0≤c≤0.1, M is Mg, Al _, represents at least one element selected from the group consisting of Si, Ti, Zn, Zr, Ca and Sn). Also included are conductive polymer materials such as polyaniline and polypyrrole, disulfide polymer materials, sulfur (S), carbon fluoride and other organic and inorganic materials. It should be noted that x, y, and z, which have no preferred ranges described above, are preferably in the range of 0 or more and 1 or less.

The kind of positive electrode active material can be one kind or two or more kinds.

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

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 proportion 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. preferably. As a result, it is possible to realize a positive electrode that has a high capacity and is less likely to deteriorate due to overcharge. A more preferable range of the proportion of the positive electrode active material particles B is 4% by mass or more and 30% by mass or less. More preferably, the content of the positive electrode active material particles A is 60% by mass or more and 80% by mass or less, and the content of the positive electrode active material particles B is 4% by mass or more and 20% by mass or less.

The spinel structure lithium-manganese composite oxide is desirably 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 within the range of 0<w≤1.1. The molar ratio w can vary due to intercalation and deintercalation of lithium ions. The molar ratio x is preferably in the range of 0≤x<2, more preferably 0.22≤x≤0.7.

Lithium nickel manganese cobalt composite oxide is Li _1-x Ni _1-a-b Co _a Mn _b O ₂ (−0.2≦x≦0.5, 0<a≦0.4, 0<b≦0 .4). The molar ratio x may vary due to intercalation and deintercalation 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 ensured.

The lithium-cobalt composite oxide is desirably represented by the general formula Li _x CoO ₂ . Lithium cobalt oxide in which the molar ratio x in the general formula is within the range of 0<x≦1.1 is desirable. The molar ratio x may vary due to intercalation and deintercalation 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 primary particles are agglomerated. 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. Conductive agents include, for example, acetylene black, carbon black, graphite, or mixtures thereof. Examples of binders 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. Preferably.

The surface roughness Ra1 of the surface of the positive electrode active material containing layer can be set to 1 μm or less. A positive electrode active material-containing layer that satisfies this requirement 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.

Carbon materials such as graphite, tin-silicon alloy materials, and the like can be used as the negative electrode active material, but lithium titanate is preferably used. Titanium oxide or lithium titanate containing other metals such as Nb may also be used as the 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 rhamsteride structure. 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 to 1 μm. The average particle size can be obtained, for example, by observing the negative electrode active material with an SEM. The particle shape may be either granular or fibrous. When fibrous, 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. In addition, when lithium titanate is used, the negative electrode potential becomes nobler than that of a lithium ion secondary battery using a general carbon negative electrode, so deposition of lithium metal does not occur in principle. Since the negative electrode active material containing lithium titanate undergoes little expansion and contraction due to charge-discharge reactions, 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 conductive agents include carbon-containing materials (acetylene black, ketjen black, graphite, etc.) and metal powders. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, and styrene-butadiene rubber.

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. Preferably.

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 each 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.
(2) current collector (first current collector)
The current collector can be a conductive sheet. Examples of conductive sheets include foils made of conductive material. Examples of electrically conductive materials include aluminum and aluminum alloys.

Each of the current collectors can have a thickness of 5 μm or more and 40 μm or less.
(3) current collecting tab (first current collecting tab)
The current collecting tab may be made of the same material as the current collector, but a current collecting tab prepared separately from the current collector and connected to the current collector by welding or the like may be used. .
(4) First Film The first film contains titanium oxide particles. The first film has insulating properties. It is sufficient for the first film to cover at least a portion of the surface of the first active material-containing layer. However, if the entire surface of the first active material-containing layer is covered, the wear suppressing effect can be enhanced. , can act as a separator. Also, the first film can cover at least a portion of the current collector and/or the current collecting tab. This can prevent an internal short circuit in which the current collector or the current collecting tab contacts the counter electrode.

Examples of titanium oxide include lithium titanate having a spinel structure (eg, 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. Rutile-type titanium dioxide particles are preferable because they are difficult to agglomerate and easy to uniformly disperse in the first film.
Lithium titanate and titanium dioxide each having a spinel structure are excellent in resistance to hydrogen fluoride (HF), and are also excellent in oxidation resistance in 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 Al foil as a current collector. The conditions for performing cyclic voltammetry are described below. The applied potential was 1.0 V-4.5 V (vs. Li/Li ⁺ ). The environmental temperature was set at 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 the range corresponding to the positive electrode potential of 3 to 4 V (vs. Li/Li ⁺ ), and electron transfer does not proceed. Therefore, when the electrode including 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. This can improve the smoothness of the surface of the first film. 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 hold a non-aqueous electrolyte.

The content of the titanium oxide particles in the first film is desirably 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 enhanced.

The first film may contain a binder. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, and mixtures thereof. The content of the binder in the first film is desirably 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 a first embodiment, an electrode is provided that includes an active material-containing layer and a first film that includes 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 formula (1): Ra1>Ra2. Therefore, abrasion of the surface of the roll used in the roll press can be suppressed, and improvement in battery performance such as battery capacity and rate performance can be expected.

Second Embodiment According to a second embodiment, there is provided a laminate comprising the electrode of the first embodiment (hereinafter first electrode). The laminate can further include a second electrode that is a counter electrode to the first electrode. Moreover, the laminate may further include a separator. Any separator can be used as long as it can electrically insulate the first electrode and the second electrode while maintaining ion conduction.

The first film of the first electrode may also serve as a separator. A second film or an insulating film other than the first and second films may be used as the separator. A combination of a plurality of types of membranes may be used as the separator. Examples of insulating films include synthetic resin nonwoven fabrics, polyolefin porous films such as polyethylene porous films and polypropylene porous films, and cellulosic separators. Moreover, a separator made of a composite of these materials, for example, a separator made of a polyolefin porous film and cellulose can be used. The insulating film 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 on the surface of the second electrode, and the back surface faces the surface or back surface of the second current collector. Examples of the second current collector and second active material-containing layer include the same as those described for the first electrode (first current collector, first active material-containing layer). . The second electrode may further include a second current collecting tab. The second collector tab may be made of the same material as the second collector, but a second collector tab is prepared separately from the second collector and used as the second collector. A material connected to the current collector by welding or the like may also be used.

The laminate can further include a second membrane. The second film may be formed on the second active material containing layer, or may be formed on the first film. Alternatively, the second film may be formed on both the surfaces of 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 contact the surface of the first film.

The second membrane contains organic fibers. The second film may be a porous film in which organic fibers are deposited in the plane direction. The second membrane has a front side and a back side. 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). . Polyolefins include, for example, polypropylene (PP) and polyethylene (PE). One type or two or more types of organic fibers can be used. Preferred is at least one selected from the group consisting of polyimide, polyamide, polyamideimide, cellulose, PVdF, and PVA, and more preferred is polyimide, polyamide, polyamideimide, cellulose, and PVdF. at least one type

Since polyimide is insoluble and infusible at 250 to 400° C. and does not decompose, a second film having excellent heat resistance can be obtained.

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

Since it is necessary to ensure ion permeability and electrolyte retention, 30% or more of the total volume of the fibers forming the second membrane is preferably organic fibers with an average diameter of 1 μm or less, and 350 nm or less. , more preferably organic fibers of 50 nm or less.

It is more preferable that the volume of the organic fibers with an average diameter of 1 μm or less (more preferably 350 nm or less, still more preferably 50 nm or less) accounts for 80% or more of the total volume of the fibers forming the second film. Such a state can be confirmed by scanning ion microscope (SIM) observation of the second film. More preferably, the organic fibers with a thickness of 40 nm or less occupy 40% or more of the volume of the entire fibers forming the second film. If the diameter of the organic fiber is small, the effect of impeding the movement of ions is small.

It is preferred that cation exchange groups are present on at least part of the entire surface including the front and back surfaces of the organic fiber. The cation exchange groups facilitate the movement of ions, such as lithium ions, through the separator, thus enhancing battery performance. Specifically, rapid charging and rapid discharging can be performed over a long period of time. Although the cation exchange group is not particularly limited, examples thereof include a sulfonic acid group and a carboxylic acid group. Fibers having cation exchange groups on their surfaces can be formed, for example, by electrospinning using sulfonated organic materials.

The second film has pores, and the average pore diameter of the pores is preferably 5 nm or more and 10 μm or less. Moreover, the porosity is preferably 70% or more and 90% or less. With such pores, a separator having excellent ion permeability and excellent impregnating properties with electrolyte can be obtained. More preferably, the porosity is 80% or more. The average pore size and porosity of pores can be confirmed by a mercury intrusion method, calculation from volume and density, SEM observation, SIM observation, and gas adsorption method. It is desirable to calculate the porosity from the volume and density of the second membrane. Also, the average pore size is desirably measured by a mercury intrusion method or a gas adsorption method. A higher porosity in the second membrane will have less of an impact on impeding ion migration.

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 can be 1 μm.

In the second film, the porosity can be increased by sparse organic fibers contained therein. Therefore, it is not difficult to obtain a layer having a porosity of about 90%, for example. It is extremely difficult to form such a highly porous layer with particles.

The second membrane has advantages over deposits of inorganic fibers in terms of unevenness, brittleness, electrolyte content, adhesion, bending properties, porosity, and ion permeability.

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

The thicknesses of the first film and the second film are measured according to the JIS standard (JIS B 7503-1997). Specifically, these thicknesses are measured using a contact digital gauge. It uses a digital gauge fixed to a stone plate. Place the sample on the granite platen. A flat type measuring terminal with a tip of φ5.0 mm is used. The measurement terminal is brought close to the sample from a distance of 1.5 mm or more and less than 5.0 mm above the sample, and the distance of contact with the sample is the thickness of the sample. The thickness to be determined is the average of the measured values at any five locations on the sample.

A laminate including the electrodes of the embodiment will be described with reference to FIG. 4 as an example. FIG. 4 is a cross-sectional view showing an example of the laminate of the embodiment. The cross-sectional view of FIG. 4 is a cross-sectional view of the laminate 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 surface 40 and a first back surface 41, and a first current collecting tab 1c. The first current collector 1a is a conductive sheet. The first active material-containing layer 1b is held on a portion of each 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-retaining portion formed parallel to one side of the first collector 1a functions as the first collector tab 1c. The first current collecting tab 1c protrudes in the first direction d1 from the first active material containing layer 1b. Of the surfaces 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.

As shown in FIG. 6, the second electrode 2 includes a second current collector 2a, a second active material-containing layer 2b having a second surface 42 and a second back surface 43, Includes tab 2c. The second current collector 2a is a conductive sheet. Second active material-containing layer 2b is held on a portion of each of both main surfaces of 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 and its vicinity. The active material containing layer non-retaining portion formed parallel to one side of the second collector 2a functions as the second collector tab 2c. The second current collecting tab 2c protrudes in the first direction d2 from the second active material containing layer 2b. The second back surface 43 is the surface of the second active material-containing layer 2b that is in contact with the second current collector 2a.

Separator 3 includes a second membrane 5 comprising organic fibers. A first film 4 containing titanium oxide particles can also function as a separator 3 . The first membrane 4 has a front side A and a back side B, and the second membrane 5 has a front side C and a back side D. FIG. As shown in FIGS. 4 and 5, the back surface B of the first film 4 covers the first surface 40 of each first active material containing layer 1b. Although there is no particular limitation on how the first film 4 is fixed to the first active material-containing layer 1b, 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, the second film 5, as shown in FIG. Covering the three end surfaces 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 surfaces of the second current collecting tab 2c are doing. Therefore, the first active material containing layer 1b and the second active material containing layer 2b face each other with the first film 4 and the second film 5 interposed therebetween.

According to the laminate having the structure shown in FIG. 4, it is possible to suppress the abrasion of the roll surface and realize the laminate including electrodes with excellent performance. In addition, the second film 5 separates the end surface 45 of the second collector 2a and the portion 46 of the surface of the second collector tab 2c including the boundary with the second active material-containing layer 2b. The covering reduces internal short circuits due to contact between the first electrode and the second electrode 2 .

Note that the first and second collector tabs are not limited to one side of the first and second collectors on which the active material-containing layer is not supported. For example, a plurality of band-like portions projecting from one side of the first and second collectors can be used as the first and second collector tabs. An example of this is shown in FIG. FIG. 7 shows another example of the first electrode 1. FIG. As shown in FIG. 7, a plurality of band-like portions projecting from one side of the first collector 1a may be used as the first collector tab 1c.

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

Also, 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. Also, 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 laminate of the second embodiment, since the electrodes of the first embodiment are included, abrasion of the roll surface can be suppressed, and a laminate including electrodes with excellent performance can be realized. is.

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

According to a third embodiment there is provided a laminate comprising the electrode of the third embodiment as the first electrode. The laminate can further include a second electrode that is a counter electrode to the first electrode. Moreover, the laminate may further include a separator. Any separator can be used as long as it can electrically insulate the first electrode and the second electrode while maintaining ion conduction.

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

A laminate including 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 laminate of the embodiment. The cross-sectional view of FIG. 9 is a cross-sectional view of the laminate cut in the first direction, which is the extending direction of the current collecting tabs. The laminate shown in FIG. 9 includes a first electrode 1, a second electrode 2 and a separator 3 as electrodes of the third embodiment. The first electrode 1, as shown in FIGS. 9 and 10, includes a first collector 1a, a first active material-containing layer 1b, and a first collector tab 1c. First active material-containing layer 1 b has first surface 40 and first back surface 41 . The first collector tab 1c extends in the first direction 51 from the first collector 1a. The first current collector 1a is a conductive sheet having a front side and a back side. 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 intersects perpendicularly with the front surface and the back surface. The first active material-containing layer 1b is held on each of the front and back surfaces of the first collector 1a except for the portion that will be the first collector tab 1c. An active material-containing layer is not held on one side (for example, long side or short side) or its vicinity on each of the front and back surfaces of the first current collector 1a. The active material containing layer non-retaining portion formed parallel to one side of the first collector 1a functions as the first collector tab 1c. Of the surfaces 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. The first active material-containing layer 1b has two sets of end faces facing each other. A set of end faces thereof 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 . In addition, thickness T1 defined by first end surface 52 of first active material containing layer 1b is smaller than thickness T2 defined by second end surface 53 of first active material containing layer 1b. A method for measuring the thicknesses T1 and T2 is described below.

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. This electrode group is unwound and a measurement sample of about 10 mm×10 mm is cut out. The cut sample is placed in a stirred beaker filled with EMC (EthylMethylCarbonate) and washed for 30 minutes. Dry the washed sample. This sample is cross-sectionally milled using an ion milling device (IM4000PLUS manufactured by Hitachi High-Technologies Corporation). A cross section obtained by cross-sectional milling is observed, for example, with a scanning electron microscope (TM3030Plus, Hitachi High-Technologies Corporation) to measure thicknesses T1 and T2.

11 to 18 show examples of cross-sectional shapes obtained by cutting an end including the first end surface 52 along the first direction 51. FIG. 11 to 18, the thickness of the first active material-containing layer 1b is reduced in the first direction 51 and is minimized at the first end surface 52 at the end portions shown in FIGS. 11, 12, 14, 17, and 18, the thickness of the end portion of the first active material-containing layer 1b gradually decreases and becomes the minimum at the first end face 52. As shown in FIG. The end including the first end face 52 has a substantially semi-cylindrical shape extending in a direction orthogonal to the first direction 51 . 13 and 16, the thickness of the end portion of the first active material-containing layer 1b is reduced so that the vertical cross-sectional shape draws a needle-like or dome-like shape, and is minimized at the first end surface 52. It's becoming On the other hand, in the end portion shown in FIG. 15, the thickness of the end portion of the first active material-containing layer 1b is reduced so that the vertical cross-sectional shape draws a projection, and is minimized at the first end face 52. As shown in FIG. The end shapes shown in FIGS. 11, 12, 14, 17 and 18 are desirable in order to increase the contact area with the current collector.

The second electrode 2 includes a second collector 2a, a second active material-containing layer 2b, and a second collector tab 2c, as shown in FIG. The second active material-containing layer 2b has a second surface 42 and a second back surface 43. As shown in FIG. The second collector tab 2c extends in the second direction 54 from the second collector 2a. The second current collector 2a is a conductive sheet having a front side and a back side. 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 intersects perpendicularly with the front surface and the back surface. The second active material-containing layer 2b is held on each of the front and back surfaces of the second current collector 2a except for the portion that will become the second current collecting tab 2c. An active material-containing layer is not held on one side and its vicinity on each of the front and back surfaces of the second current collector 2a. The active material containing layer non-retaining portion formed parallel to one side of the second collector 2a functions as the second collector tab 2c. The second back surface 43 is the surface of the second active material-containing layer 2b that is in contact with the second current collector 2a. The second active material-containing layer 2b has two sets of end faces facing each other. A set of end faces thereof 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 face 55 faces the second end face 56 in the second direction 54 . Thickness T1 defined by first end face 55 of second active material containing layer 2b may be smaller than thickness T2 defined by second end face 56 of second active material containing layer 2b.

Separator 3 includes a second membrane 5 comprising organic fibers. First membrane 4 may function as separator 3 . The first membrane 4 has a front side A and a back side B, and the second membrane 5 has a front side C and a back side D. FIG. As shown in FIGS. 9 and 10, the back surface B of the first film 4 is in contact with and covers 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 side surfaces perpendicular to the main surface is covered with the first film 4. As shown in FIG. The first film 4 is a portion adjacent to the first end surface 52 of the first active material-containing layer 1b on each of the front and back surfaces of the first current collecting tab 1c, in other words, the surface of the first current collecting tab 1c. and the boundary portions with the first end face 52 of each of the rear surfaces are also covered. The portion of the first film 4 adjacent to the first end face 52 is located near the end face of the second electrode opposite to the side from which the second current collecting tab 2c extends. By providing the first film 4, it is possible to reduce an internal short circuit due to contact between the first collector 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 examples shown in FIGS. 11 to 18 are examples. can be mentioned. In FIG. 11, the first film 4 covers the edge (hereinafter referred to as the edge) including the first end face 52 of the first active material-containing layer 1b so as to follow the outer shape. Also, the first film 4 covers a portion adjacent to the first end face 52 (hereinafter referred to as an adjacent portion) with a sufficient width, and its thickness decreases along the first direction 51 . In FIG. 12, the first film 4 covers the end including the first end surface 52 of the first active material-containing layer 1b along its contour. Also, the first film 4 covers the adjacent portion with a sufficient width and thickness. In FIG. 13, the first film 4 covers the edge of the first active material containing layer 1b along its contour. Also, the first film 4 covers the adjacent portion with a sufficient width and its thickness decreases along the first direction 51 . In FIG. 14, the first film 4 covers the edge of the first active material containing layer 1b along its contour. In FIG. 15, the first film 4 covers the edge of the first active material-containing layer 1b and also covers the adjacent portion with a sufficient width, the thickness of which decreases along the first direction 51. are doing. In FIG. 16, the first film 4 covers the edges 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. are discontinuous and independent of each other. In FIG. 18, the first film 4 partially covers the edge of the first active material-containing layer 1b.

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

Although there is no particular limitation on how the first film 4 is fixed to the first active material-containing layer 1b, examples thereof include adhesion and heat fusion.

On the other hand, the second film 5, as shown in FIG. , three end surfaces 45 exposed on the surface of the second electrode 2 of the second current collector 2a, and end surfaces 55 of the second active material-containing layer 2b on the front and back surfaces of the second current collecting tab 2c. Adjacent portion 46 is covered. Therefore, the first active material containing layer 1b and the second active material containing layer 2b face each other with the first film 4 and the second film 5 interposed therebetween. The second film may be integrated with the second electrode, but is not limited to this. For example, the second membrane may be integrated with the surface of the first membrane. There is no particular limitation on how the second film is integrated with the first film or the second active material-containing layer. or the surface of the second active material-containing layer.

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 abrasion of the roll surface and includes electrodes with excellent performance. It is possible to realize laminates. Also, 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 surface and the back surface of the first current collecting tab. part is covered. According to such a structure, it is possible to suppress peeling of the first film from the first active material-containing layer. As a result, in order to obtain a high capacity, when an electrode group is produced by spirally winding the laminate, or when the packing rate of the laminate in the exterior member is increased, the first film becomes the first film. Therefore, it is possible to suppress the occurrence of an internal short circuit and provide a high-capacity battery. Therefore, it is excellent in practicality. Moreover, 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 be prevented from peeling off from the first active material containing layer. Therefore, life such as charge-discharge cycle life of the battery can be improved.

Note that the first and second collector tabs are not limited to one side of the first and second collectors on which the active material-containing layer is not supported. For example, a plurality of band-shaped portions protruding from one side surface of the first and second collectors can be used as the first and second collector tabs. An example of this is shown in FIG. FIG. 20 shows another example of the first electrode 1. FIG. As shown in FIG. 20, a plurality of band-shaped portions projecting 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 collecting tab 1c. The first film 4 covers the front surface and first end surface 52 of the first active material-containing layer 1b, and the portions adjacent to the first end surface 52 on the front surface and rear surface of the first current collecting tab 1c. . The other three end surfaces of the first active material-containing layer 1b, the four side surfaces 49 of the first current collector 1a, or the two opposing side surfaces 48 of the first current collecting tab 1c are covered with the first film 4. It may be covered.

Also, 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 consists of the surface of the first film 4 and the three electrode end faces not covered with the first film 4, that is, the three electrode end faces from which the first current collecting tabs 1c do not extend. is covered. According to the configuration of FIG. 21, it is possible to prevent the first film from peeling off from the first active material-containing layer while ensuring necessary insulation between the first electrode and the second electrode. Therefore, the battery capacity and charge/discharge cycle life can be improved.

Also, 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. Also, 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.

A method for manufacturing the first electrode, which is an example of the electrodes of the first and third embodiments, will be described below.

First manufacturing 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) are applied to at least one main surface of a first current collector. ) are applied at the same time. An example of the coating process is shown in FIGS. 22 and 23. FIG. The coating device 30 includes a tank 32 containing slurry I and a tank 33 containing slurry II, and is configured to simultaneously apply slurry I and slurry II to a substrate. The long first current collector 1 a before being cut into a predetermined size is transported to the slurry discharge port of the coating device 30 by the transport rollers 31 . In FIG. 23, the slurry I discharge port 32a is positioned upstream of the current collector from the slurry II discharge port 33a. Due to such a discharge port arrangement, 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 application area of the slurry I. Since the slurry II is overcoated on the slurry I, the slurry II can easily follow the surface shape of the slurry I. After drying the slurry, the dried slurry is roll-pressed and cut into a predetermined size to obtain a first electrode. If the step of applying slurry I and the step of applying slurry II are performed substantially at the same time, the difference in surface roughness can be reduced. Also, increasing the period between steps increases the difference in surface roughness. The difference in surface roughness can be reduced by shortening the slurry drying time. Furthermore, the difference in surface roughness can be reduced by increasing the pressing pressure. 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 higher than the surface roughness Ra1 of the surface of the first active material-containing layer. A first electrode having a small height Ra2 is obtained.
It is desirable that the viscosity of Slurry II is higher than that of Slurry I. As a result, the fluidity of Slurry II becomes lower than that of Slurry I, so that Slurry I diffuses on the surface of the first current collector, and when the thickness of the terminal portion of the coating becomes thin, The slurry II spreads over the slurry I while following the shape of the 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 Slurry II is higher than that of Slurry I over the range of viscosity shear rate from 1.0 (1/s) to 1000 (1/s). The viscosity of the slurry I is preferably 0.01 Pa s or more and 1000 Pa s or less in the viscosity shear rate range of 1.0 (1 / s) or more and 1000 (1 / s) or less, especially 0.1 Pa s or more. 100 Pa·s or less is more preferable. On the other hand, the viscosity of Slurry II is preferably 0.1 Pa s or more and 1000 Pa s or less in the viscosity shear rate range of 1.0 (1 / s) or more and 1000 (1 / s) or less, especially 1 Pa s or more. 1000 Pa·s or less is more preferable.

A method of manufacturing a 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 the second electrode. . A second film is formed on the second electrode by an electrospinning method. Pressing may then be applied. As a pressing method, a roll press or a flat plate press may be used.

The laminate of the embodiment is obtained by laminating the first electrode and the second electrode such that they face each other with the first film and the second film interposed therebetween.

Third Production Method A second film is formed by an electrospinning method on the first electrode produced by the first production method. Pressing may then 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 the second electrode. .

The laminate of the embodiment is obtained by laminating the first electrode and the second electrode such that they face each other with the first film and the second film interposed therebetween.

Next, the electrospinning method will be explained. The second film is formed, for example, by an electrospinning method. In the electrospinning method, the first electrode or the second electrode on which the second film is to be formed is grounded and used as the ground electrode. When forming on the first electrode, the first electrode on which the first film is already formed is prepared.

A liquid raw material (for example, raw material solution) is charged by the voltage applied to the spinning nozzle, and the amount of charge per unit volume of the raw material solution increases due to volatilization of the solvent from the raw material solution. Volatilization of the solvent and an accompanying increase in the amount of charge per unit volume occur continuously, so that the raw material solution ejected from the spinning nozzle extends in the longitudinal direction, and as nano-sized organic fibers, the first electrode, which is the ground electrode. Deposit 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 fibers, and the organic fibers can be deposited on the first electrode or the second electrode by the Coulomb force. It is possible to increase the peel strength of the film from the electrode. The peel strength can be controlled, for example, by adjusting the solution concentration, the sample-nozzle distance, and the like. When the second film is not formed on the first and second current collecting tabs, it is preferable to form the second film after masking the first and second current collecting tabs. 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 as organic fibers on the second active material-containing layer 2b and the second current collecting tab 2c. be done. One side of the second current collecting tab 2c and its vicinity are covered with a mask M. As shown in FIG. 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, the second film can be easily formed on the electrode surface. In principle, the electrospinning method forms a single continuous fiber, so that a thin film can ensure resistance to breakage due to bending and cracking of the film. If the organic fibers forming the second film are seamless and continuous, the possibility of the second film becoming frayed or partially damaged is low, which is advantageous in suppressing self-discharge.

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

A second film is formed by applying a voltage to the spinning nozzle using a high voltage generator and ejecting the raw material from the spinning nozzle over the surface of the predetermined electrode. The applied voltage is appropriately determined according to the type of solvent/solute, boiling point/vapor pressure curve of the solvent, solution concentration, temperature, nozzle shape, sample-nozzle distance, and the like. It can be 100 kV. The feed 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 a syringe type, for example, it can be about 0.1 to 500 μl/min per nozzle. Also, in the case of multiple nozzles or slits, 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, the penetration of the solvent contained in the raw material into the interior of the electrode is substantially avoided. The amount of solvent remaining inside the electrode is extremely low, below the ppm level. Residual solvent inside the electrode causes an oxidation-reduction reaction, causes battery loss, and leads to deterioration of battery performance. According to the present embodiment, the possibility of such inconveniences occurring is reduced as much as possible, so the performance of the battery can be enhanced.

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

A secondary battery, wherein a plurality of laminates are laminated such that the first film and/or the second film are positioned 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 laminates wound in a spiral or flat spiral may be used as the electrode group.

The secondary battery may further comprise a first electrode terminal electrically connected to the first current collecting tab and a second electrode terminal 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 an electrolyte in an organic solvent, a gel non-aqueous electrolyte obtained by combining a liquid electrolyte and a polymer material, and the like. The liquid nonaqueous 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 electrolytes include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), trifluoromethane Lithium salts such as lithium sulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [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 organic solvents 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), 2methyltetrahydrofuran (2MeTHF), and dioxolane (DOX); chain ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL); Acetonitrile (AN), sulfolane (SL), and the like. Such organic solvents may be used alone or as a mixture of two or more.

Polymer materials include, for example, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

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 shape of the secondary battery is not particularly limited, and various shapes such as cylindrical, flat, thin, rectangular, and coin-shaped can be used.

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 laminate film as an exterior member. A secondary battery 10 shown in FIG. 25 includes an exterior member 11 made of a laminate 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 laminates of the embodiment, and has a structure in which a first electrode and a 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 . A first collecting tab of the first electrode is electrically connected to the first electrode terminal 13 . A second collector tab of the second electrode is electrically connected to the second electrode terminal 14 . As shown in FIG. 25 , the first electrode terminal 13 and the second electrode terminal 14 are spaced apart from each other, and their tips protrude outside from one side of the exterior member 11 .

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 rectangular 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 laminate of the embodiment is wound in a flat spiral shape. In the wound-type electrode group 21, a flat spirally wound first current collecting tab 25 is positioned on one circumferential end face, and a flat spirally wound second current collecting tab 25 is located on one end face. An electrical tab 26 is located on the other circumferential end face. 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 collector tab 25 and also electrically connected to the first electrode terminal 23 . Also, the second electrode lead 28 is electrically connected to the second current collecting tab 26 and is also electrically connected to the second electrode terminal 24 . The electrode group 21 is arranged inside the exterior member 20 such 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 are included, wear of the press roll surface can be suppressed and the battery performance is improved. can.

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

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

_{LiNi0.33Co0.33Mn0.33O2} particles with an average particle size of ₆ μm and _LiCoO2 particles with an average particle _size of 5 μm as positive electrode active materials, carbon black as a conductive agent, and polyvinylidene fluoride (PVdF) as a _binder . prepared. These were mixed in a mass ratio of 80:20:5:5 to obtain a mixture. Next, the resulting mixture was dispersed in n-methylpyrrolidone (NMP) solvent to obtain a viscosity of 10 Pa·s at a viscosity shear rate of 1.0 (1/s) and 0.0 Pa·s at a viscosity shear rate of 1000 (1/s). A positive electrode slurry was prepared so as to have a viscosity of 5 Pa·s.

Lithium titanate (Li ₄ Ti ₅ O ₁₂ ) particles with 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 the titanium oxide-containing slurry was adjusted to 100 Pa s at a viscosity shear rate of 1.0 (1 / s) and 2 Pa s at a viscosity shear rate of 1000 (1 / s). was prepared.

Therefore, the viscosity of the titanium oxide-containing slurry (slurry II) is higher than that of the positive electrode slurry (slurry I) over a range of viscosity shear rates of 1.0 (1/s) to 1000 (1/s). .

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, the lower layer is the positive electrode slurry, the upper layer is the titanium oxide-containing slurry, and the upper layer is overcoated so that the titanium oxide-containing slurry protrudes, and dried. rice field. This was done on both sides of the aluminum foil. After that, it was roll-pressed and cut into a predetermined size to obtain a positive electrode. As shown in FIG. 9, the insulating inorganic material layer covered the surface and first end face of the positive electrode active material containing layer, and the portions adjacent to the first end face on the front and back surfaces of the positive electrode current collecting tab.

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 protrudes from the positive electrode active material-containing layer. 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 surface was 5 μm, and the thickness T2 of the second end surface was 20 μm. The shape of the end including the first end face was shown in FIG. That is, the thickness of the positive electrode active material-containing layer 1b containing a large number of particles decreases 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 where the positive electrode active material-containing layer was not supported was provided on one long side of the current collector, and this portion was used as a positive electrode current collecting tab.

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

The resulting slurry was applied to both sides of a 15 μm thick aluminum foil and dried. Then, the dried coating film was pressed to obtain a negative electrode. The thickness of each negative electrode active material-containing layer was 30 μm. A portion where the negative electrode active material-containing layer was not supported was provided on one long side of the current collector, and this portion was used as a negative electrode current collecting tab.

Organic fibers were deposited on the 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 mass % to prepare a raw material solution as a liquid raw material. The obtained raw material solution was supplied to the surface of the negative electrode from the spinning nozzle 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 2 μm organic fiber layer was formed on the surface of the negative electrode active material-containing layer while moving the single spinning nozzle over a range of 100×200 mm. In addition, electrospinning was performed with the surface of the negative electrode current collecting tab masked, except for a portion of 10 mm from the boundary with the negative electrode active material-containing layer on both surfaces (principal surfaces) of the negative electrode current collecting tab. Obtained. As shown in FIG. 19, the organic fiber layer includes the surfaces of the negative electrode active material-containing layer and the four side surfaces perpendicular to the surface, the three end surfaces of the negative electrode current collector exposed on the negative electrode surface, and the negative electrode current collector. It covered the end faces and adjacent portions of the negative electrode active material-containing layer on the front and back surfaces of the tab.

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, thereby obtaining an electrode group as a laminate.

(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 first film were measured by the above-described method for measuring the arithmetic mean value Ra of roughness. are shown in Table 1. As shown in Table 1, the positive electrodes of Examples 1 and 2 satisfied Ra1>Ra2.

Further, for the positive electrodes of Examples and Comparative Examples, a microslurry erosion (MSE) test (a test in which a slurry prepared with an abrasive agent and a solvent is sprayed onto a test piece to erode the surface) was performed. The test procedure is as follows. First, a slurry containing abrasive particles having a solid content ratio of 10% by mass and containing water as a solvent was prepared and placed in a tank in the tester. The slurry was sucked up while stirring with a mixer. The sucked slurry was sprayed at a high pressure onto the surface of each electrode, which was a test piece, at a flow rate 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 abrasion was measured with a stylus type roughness meter. In addition, the test was implemented at room temperature. FIG. 27 shows the relationship between the MSE test time (minutes) and the amount of wear (μm).

As is clear from FIG. 27, the electrodes of Examples 1 and 2 having the first film containing titanium oxide particles had a wear amount of less than 10 μm even after the test time of 300 minutes. On the other hand, the electrodes of Comparative Examples 1 and 2 provided with the first film containing alumina or magnesia and the electrode of Comparative Example 3 not provided with the first film showed no wear within 120 minutes of the test time. reached 40 μm. From the above results, it was confirmed that the wear of the roll surface was suppressed by the electrode according to the embodiment. Further, the electrode groups of Examples 1 and 2 were vacuum-dried overnight at room temperature and then left in a glove box with a dew point of −80° C. or less for one day. This was placed in a metal container together with an electrolytic solution to obtain a non-aqueous electrolyte battery. The electrolyte used was LiPF ₆ dissolved in ethylene carbonate (EC) and dimethyl carbonate (DMC). The obtained batteries of Examples 1 and 2 exhibited an initial capacity of 1 Ah, which is the same as the design capacity.

In the positive electrode of Example 1, the positive electrode active material was 80% by mass of spinel-structured lithium-manganese composite oxide particles represented by LiMn ₂ O ₄ with an average particle size of 7 μm, and LiCoO ₂ particles with an average particle size of 5 μm. was changed to 20% by mass, the same results as in Example 1 were obtained.

The electrode according to at least one of the embodiments and examples described above includes an active material-containing layer and a first film containing titanium oxide particles, and the surface roughness Ra1 of the surface of the active material-containing layer and the first The surface roughness Ra2 of the surface of the film No. 1 satisfies the formula (1): Ra1>Ra2. Therefore, abrasion of the surface of the roll used in the roll press can be suppressed, and improvement in battery performance such as battery capacity and rate performance can be expected.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 1... 1st electrode, 1a... 1st collector, 1b... 1st active material containing layer, 1c... 1st collector tab, 2... 2nd electrode, 2a... 2nd collector , 2b... second active material-containing layer, 2c... second current collecting tab, 3... separator, 4... first film, 5... second film, 10... secondary battery, 11... exterior member, 12 ... electrode group, 13, 23 ... first electrode terminal, 14, 24 ... second electrode terminal, 20 ... exterior member, 21 ... electrode group, 22 ... lid, 25 ... first current collecting tab, 26 ... second 2 current collecting tabs, 27... first electrode lead, 28... second electrode lead, 40... first surface, 41... first back surface, 42... second surface, 43... second back surface, 45... the end surface 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 surface of the first film Back surface, C... Front surface of the second film, D... Back surface of the second film, 51... First direction, 52, 55... First end face, 53, 56... Second end face, 54... Second direction.

Claims (11)

an active material-containing layer containing active material particles and having a front surface and a back surface;
a first film having a front surface and a back surface, the back surface being in contact with at least part of the surface of the active material-containing layer, and containing titanium oxide particles;
The electrode, wherein 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. 2. The electrode of claim 1, wherein the titanium oxide particles comprise at least one of spinel-structured lithium titanium oxide particles and titanium dioxide particles. 2. The active material particles include at least one selected from the group consisting of spinel-structured lithium-manganese composite oxide particles, lithium-cobalt composite oxide particles, and lithium-nickel-manganese-cobalt composite oxide particles. 2. The electrode according to 2. 3. The electrode according to claim 1, wherein the active material particles include at least one of spinel-structured lithium-manganese composite oxide particles and lithium-nickel-manganese-cobalt composite oxide particles, and lithium-cobalt composite oxide particles. . a current collector having a front surface and a back surface;
a current collecting tab extending in a first direction from the current collector;
a first end face where 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 is adjacent to the current collecting tab; a second end face facing the first end face in one direction;
the thickness defined by the first end surface of the active material-containing layer is smaller than the thickness defined by the second end surface of the active material-containing layer,
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 5. The electrode according to any one of Items 1 to 4. 6. The electrode according to claim 5, wherein the thickness of said active material containing layer decreases along said first direction and the thickness defined by said first end face is the smallest. a first electrode made of the electrode according to any one of claims 1 to 6;
a second electrode;
and a separator. 8. The laminate according to claim 7, wherein said first electrode is a positive electrode. 9. The laminate according to claim 7, wherein said first film also serves as said separator. 9. The laminate according to claim 7, wherein said separator includes an insulating film different from said first film. A secondary battery comprising the electrode according to any one of claims 1 to 6.

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