JP7743304B2 - Electrode film raw material, electrodes, electrode laminates, electrochemical devices and equipment - Google Patents

Description

The present invention relates to electrode film substrates, electrodes, electrode laminates, electrochemical devices, and equipment.

In recent years, secondary batteries used as power sources have become increasingly important. Research and development of secondary batteries is being actively conducted, from small ones used as power sources for portable electronic devices to medium- and large-sized ones used in electric vehicles and home storage batteries.

A secondary battery has a pair of electrodes containing active materials and an electrolyte disposed between the electrodes. The pair of electrodes includes a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material. These electrodes are known to have a configuration in which an active material layer containing a positive electrode active material or a negative electrode active material is stacked with a highly conductive current collector.

The active material layer is formed by dispersing powdered active material and a binder in a solvent to prepare a slurry mixture, then applying the mixture to a current collector and pressing it. The laminate of the active material layer and current collector is cut into the desired battery shape and used as an electrode (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2019-169444

As mentioned above, producing electrodes requires multiple steps, including compound preparation, compound coating, drying, and pressing. There is room for improvement in materials to simplify the secondary battery manufacturing process and reduce manufacturing costs.

Similar issues can arise not only in secondary batteries, but also in other electrochemical elements such as capacitors.

In recent years, as secondary batteries have become larger and more versatile, there has been a demand for inexpensive electrode materials. Among known positive electrode active materials, lithium iron phosphate (LFP) is known as a relatively inexpensive material. Unlike other known positive electrode active materials such as lithium cobalt oxide, LFP does not contain rare earth elements and is based on iron. Therefore, it has the advantage of being inexpensive and unlikely to become depleted.

On the other hand, LFP is known to have poor electrical conductivity. As a result, using LFP as a positive electrode active material often requires ingenuity, such as coating the surface of the LFP particles with carbon or using a conductive filler in combination, which undermines its advantage of being inexpensive. This makes it a difficult material to use.

The present invention was made in light of these circumstances, and aims to provide a novel electrode film substrate to be used as an electrode material. It also aims to provide electrodes, electrode laminates, electrochemical devices, and equipment that use such electrode film substrate as materials.

The inventors believed that if they could create a material with properties that allowed it to be used as an electrode without a current collector, it would be possible to eliminate the steps described above, such as preparing the mixture and applying the mixture to the current collector. Furthermore, by forming the material into a film, electrochemical devices could be easily manufactured by cutting the film (raw electrode film) and attaching it to a battery element. Furthermore, by using inexpensive LFP as the active material, they believed they could provide a material that would enable the inexpensive manufacture of electrochemical devices.

The inventors conducted extensive research from the above perspectives and completed the invention. To solve the above problems, one aspect of the present invention includes the following:

[1] An electrode film raw sheet made of a mixture containing an active material and a binder, which satisfies the following (1) to (3):
(1) The breaking strength measured by the following measurement method is 0.2 MPa or more.
(Measurement method) The electrode film raw material was cut into a size of 15 mm in width and 50 mm in length to obtain a test piece, and the strength at 75% of the maximum stress when measured under conditions of a chuck distance of 30 mm and a tensile speed of 100 mm/min was taken as the breaking strength.
(2) The active material includes lithium iron phosphate, and the binder includes styrene butadiene rubber and polyvinylidene fluoride.
(3) The binder contains 0.75% by mass or more and 2.95% by mass or less of the styrene-butadiene rubber and 0.25% by mass or more and 5.25% by mass or less of the polyvinylidene fluoride relative to the entire mixture.

[2] An electrode film raw sheet having an active material layer made of a mixture containing an active material and a binder, no current collector, and satisfying the following (1) to (3):
(1) The breaking strength measured by the following measurement method is 0.2 MPa or more.
(Measurement method) The electrode film raw material was cut into a size of 15 mm in width and 50 mm in length to obtain a test piece, and the strength at 75% of the maximum stress when measured under conditions of a chuck distance of 30 mm and a tensile speed of 100 mm/min was taken as the breaking strength.
(2) The active material includes lithium iron phosphate, and the binder includes styrene butadiene rubber and polyvinylidene fluoride.
(3) The binder contains 0.75% by mass or more and 2.95% by mass or less of the styrene-butadiene rubber and 0.25% by mass or more and 5.25% by mass or less of the polyvinylidene fluoride relative to the entire mixture.

[3] The electrode film substrate described in [1] or [2], wherein the active material is lithium iron phosphate and the binder is made of styrene-butadiene rubber and polyvinylidene fluoride.

[4] An electrode film substrate described in any one of [1] to [3], on which a release film is laminated.

[5] An electrode made from the electrode film substrate described in any one of [1] to [4].

[6] An electrode laminate comprising the electrode described in [5] and a separator or a solid electrolyte membrane.

[7] An electrochemical device having the electrode stack described in [6].

[8] An apparatus having the electrochemical device described in [7].

The present invention provides a novel electrode film substrate for use as an electrode material. It also provides electrodes, electrode laminates, electrochemical devices, and equipment that use such electrode film substrate as materials.

FIG. 1 is a schematic diagram showing an electrode film raw sheet 1 of this embodiment. FIG. 2 is a schematic diagram showing the electrode film raw material 2 of this embodiment.

[Electrode film raw material, electrodes]
FIG. 1 is a schematic diagram showing an electrode film raw sheet 1 of this embodiment.

The term "raw electrode film" refers to a film-like molded product before it is processed into an electrode. Typically, the raw electrode film is a long, strip-shaped molded product, or a sheet-shaped molded product obtained by processing such a strip-shaped molded product into sheets.

The electrode film roll 1 shown in Figure 1 is sandwiched on both sides by release films 10. The release film 10 can be made of a known material, such as a PET film that has been treated for release properties.

The electrode film raw sheet 1 consists of a mixture containing an active material and a binder. The electrode film raw sheet 1 does not have a current collector.

The electrode film roll 1 has the characteristic functions of (a) being self-standing and (b) being usable as an electrode.

(a) Self-supporting The electrode film raw roll 1 can be processed into an electrode by cutting it into a desired shape. The electrode film raw roll 1 may be used as an electrode as is. The resulting electrode can maintain the cut shape without any attachments such as a substrate. In this specification, having such a property is sometimes referred to as "self-supporting" or "self-supporting type." In other words, the electrode film raw roll 1 has enough rigidity to exist without support.

(b) Usable as an electrode The electrode film raw sheet 1 can be cut into a desired shape and used as an electrode for electrochemical devices such as secondary batteries and capacitors. That is, the electrode film raw sheet 1 has low electronic resistance and high ionic conductivity that enable it to be used as an electrode.

The electrode obtained by cutting the electrode film roll 1 having the functions (a) and (b) is self-supporting (a free-standing electrode) and can be used as an electrode for electrochemical devices such as secondary batteries and capacitors simply by attaching it to a component of the device.

The following describes each component of the electrode film roll 1 in order.

(active material)
The electrode film raw sheet 1 contains lithium iron phosphate (LiFePO ₄ , hereinafter sometimes abbreviated as "LFP") with an olivine crystal structure as the active material. Because LFP contains iron as the main raw material, it has the advantage of being able to be produced more cheaply than other positive electrode active materials that contain rare metals. Furthermore, LFP is known to be highly safe because the bond between phosphorus atoms and oxygen atoms in the crystal is strong, making it less likely to collapse in crystal structure during use or in high-temperature environments.

The active material contained in the electrode film substrate 1 may include lithium manganese iron phosphate (LMFP), in which some of the iron contained in LFP is replaced with Mn. LMFP, like LFP, has an olivine crystal structure.

The active material contained in the electrode film substrate 1 contains LFP in an amount exceeding 50% by mass of the total active material, preferably 80% by mass or more, and even more preferably 100% by mass.

The active material contained in the electrode film roll 1 may include known positive electrode active materials other than LFP. Examples of such positive electrode active materials include at least one selected from composite oxides of lithium and transition metals such as cobalt, manganese, and nickel, and polymers with Li storage capacity. The positive electrode active material for lithium-ion secondary batteries may be any compound that can reversibly dope and undope lithium ions.

For example, examples of positive electrode active materials that can be used in combination with LFP include lithium cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LiMnO ₄ ), Ni-Mn-Co ternary (NMC-based) active materials (LiNi _x Mn _y Co _z O ₂ ), and Ni-Co-Al ternary (NCA-based) active materials (LiNi _x Co _y Al _z O ₂ ).

The active material used has a volume average particle size of 0.1 to 100 μm.

(binder)
The binder is a material used to bind particles of the active material, etc., and is, for example, a resin. As the binder, known thermoplastic resins used for the above-mentioned purposes as electrode materials can be used.

In addition to the aforementioned "binding of particles of active material, etc.", the functions of binders include (i) imparting high strength to the electrode film roll, (ii) adjusting electrical resistance (reducing resistance), and (iii) adjusting other physical properties. Binders that particularly strongly possess function (i) will be described as "high-strength binders," binders that particularly strongly possess function (ii) as "resistance-adjusting binders," and binders that particularly strongly possess function (iii) as "other binders."

(i) High-Strength Binder
An elastomer can be used as the high-strength binder. A binder with elastomeric properties can impart flexibility and strength to the electrode, and can suppress breakage due to volumetric changes of the active material during use of the electrode.

A high-strength binder desirably has a tensile strength of 5 MPa or more. Furthermore, high-strength binders are required to be stable against the electrolyte inside electrochemical elements (batteries, capacitors) and to be electrochemically stable.

For example, if a lithium-ion battery is used as the electrochemical element and an electrode obtained by cutting the electrode film roll 1 is used, the high-strength binder must not leach from the electrode into the electrolyte filled in the battery. Furthermore, the high-strength binder must not undergo oxidative decomposition at 3 to 5 V (vs. Li/Li+).

The tensile strength of the high-strength binder is measured using the breaking strength measurement method described below.

In this embodiment, styrene-butadiene copolymer (SBR) is used as the high-strength binder.

Furthermore, the binder may contain, as a high-strength binder, the following copolymer containing styrene and a conjugated diene in addition to SBR.
・Styrene-isoprene copolymer ・Styrene-butadiene-methyl methacrylate copolymer (MBS)
・Acrylonitrile-styrene-butadiene copolymer (ABS)
・Acrylonitrile-styrene-butadiene-methyl methacrylate copolymer (MABS)
・Carboxy-modified styrene butadiene rubber ・Styrene-butadiene-styrene block copolymer (SBS)
- Styrene-isoprene-styrene block copolymer (SIS)
Styrene-isoprene-butadiene-styrene block copolymer (SIBS)

The above copolymers, excluding SBR, may be copolymerized with other copolymerizable vinyl monomers.

Vinyl monomers include:
- Acrylate monomers such as alkyl acrylate - Methacrylate monomers such as alkyl methacrylate - Acrylamide monomers such as alkoxyacrylamide - Methacrylamide monomers such as alkoxymethacrylamide - Carboxylic acid monomers such as acrylic acid - Nitrile monomers such as acrylonitrile - Vinyl ester monomers such as vinyl acetate - Vinyl halide monomers such as vinyl chloride - Polyfunctional monomers such as allyl acrylate.

One or more of these vinyl monomers may be copolymerized in the copolymer.

(ii) Resistance Adjusting Binder
In this embodiment, polyvinylidene fluoride (PVdF) is used as the resistance adjusting binder.

In addition to PVdF, the binder may also contain an acrylate-based binder or a polyimide-based binder as a resistance-adjusting binder. The resistance-adjusting binder is required to not undergo oxidative decomposition at 3 to 5 V (vs. Li/Li+).

(i) High-strength binders are thought to be electrochemically inactive, and if the active material were completely covered with (i) high-strength binders, electrochemical reactions of the active material would not occur and the resistance of the electrode would increase. In contrast, by using the above-mentioned (ii) resistance-adjusting binders in combination, it is possible to suppress the increase in resistance caused by covering the active material with (i) high-strength binders.

((iii) Other binders (adhesive binders))
The adhesive binder can be a resin material having a reactive functional group or an anchoring effect. Examples of reactive functional groups include a hydroxyl group (-OH) and a carboxyl group (-COOH). If the electrode film raw roll contains such a binder, when an electrode obtained from the electrode film raw roll is laminated to another component, the reactive functional group is expected to react at the lamination surface, thereby increasing the adhesive strength.

In addition, since the electrode film raw roll contains an adhesive binder, the free-standing electrodes manufactured from the electrode film raw roll can be more easily adhered to other components.

It is desirable that the adhesive binder be electrochemically stable and maintain its adhesive properties even when exposed to other components, especially the electrolyte.

For example, if a lithium-ion battery is used as the electrochemical element and an electrode obtained by cutting the electrode film roll 1 is used, the adhesive binder is required to not dissolve from the electrode into the electrolyte filled in the battery, and to have reactive functional groups that are not easily deactivated even when exposed to the electrolyte.

In addition, the adhesive binder is required not to undergo oxidative decomposition at 3 to 5 V (vs. Li/Li+).

Such binders include at least one selected from the group consisting of carboxymethyl cellulose (CMC)-based binders, polyacrylic acid (PAA)-based binders, vinyl alcohol-based binders, and epoxy-based binders.

Polyisobutylene (PIB) can also be used as an adhesive binder.

In addition to the active material and binder described above, the mixture that makes up the electrode film roll may contain additives such as conductive materials as needed to adjust physical properties. Examples of conductive materials include at least one selected from carbon black such as acetylene black, carbon fiber, activated carbon, metal powder, conductive polymers, etc. The conductive material does not need to be as active as the active material; it need only be a material that improves conductivity within the electrode.

The mixture that makes up the electrode film base may also contain carbon nanotubes (CNTs). Electrode film base with added CNTs is expected to have improved breaking strength and conductivity.

Furthermore, it is preferable that the thickness of the electrode film raw material be 1 μm or more and 1000 μm or less.

The electrode film raw material made from the mixture of the above materials must satisfy the following requirements (1) to (3) in order to achieve the functions (a) and (b) above.

(Requirement (1))
As described above, the electrode film raw sheet 1 has the characteristic of “(a) being self-supporting.” The electrode film raw sheet 1 having such rigidity has a breaking strength of 0.2 MPa or more as determined by the following measurement method.

(Method for measuring breaking strength)
A test piece obtained by cutting an original electrode film into a size of 15 mm in width and 50 mm in length is measured under conditions of a chuck distance of 30 mm and a tensile speed of 100 mm/min. The strength at 75% of the maximum stress is defined as the breaking strength.

The tensile force (N) at which the test piece breaks is defined as the maximum stress, and the stress at 75% of the maximum stress is calculated. The breaking strength is calculated by dividing the 75% stress (N) by the cross-sectional area (mm ² ) of the test piece in a virtual plane perpendicular to the tensile direction (N/mm ² = MPa).

Measurements are performed five times and the arithmetic mean of the five measurements is used as the breaking strength.

Because the electrode film roll has this level of breaking strength, the electrodes cut from the electrode film roll can stand on their own. Making the electrodes stand on their own makes them easier to handle in the subsequent assembly process.

The breaking strength is preferably 0.1 MPa or more, and more preferably 0.2 MPa or more. It is preferable that the breaking strength is higher, as it is less likely to break, but it is sufficient that the breaking strength is 10 MPa or less, and it can also be 5 MPa or less.

(Requirements (2) and (3))
As described above, the electrode film raw sheet 1 has the characteristic of being “(b) usable as an electrode.” The electrode film raw sheet 1 having such properties satisfies the following requirements (2) and (3).
Requirement (2): The active material contains lithium iron phosphate, and the binder contains styrene-butadiene rubber and polyvinylidene fluoride.
Requirement (3): The binder contains 0.75% by mass or more and 2.95% by mass or less of styrene-butadiene rubber and 0.25% by mass or more and 5.25% by mass or less of polyvinylidene fluoride relative to the entire mixture.

The binder may include any of the various binders listed above, provided that requirement (3) is met.

In the electrode film raw sheet described above, the mixture that constitutes the electrode film raw sheet preferably contains 85% by mass or more and 97% by mass or less of active material and 3% by mass or more and 15% by mass or less of binder, based on the entire mixture.

If the mixture contains an additive such as a conductive material, the mixture should contain the additive in a proportion determined by preliminary experiments based on the additive's function. For example, if the mixture contains a conductive material as an additive, the mixture should contain 85% to 97% by mass of active material, 1% to 10% by mass of binder, and 2% to 5% by mass of conductive material, based on the total mixture.

[Method of manufacturing electrode film raw material]
The electrode film raw sheet can be produced by applying a slurry (paint) prepared by dissolving or dispersing the above-mentioned mixture in a solvent onto a support, and then removing the solvent.

The solvent used should be one that can dissolve at least the binder. Examples of solvents include hydrocarbon solvents, alcohol solvents, ether solvents, ketone solvents, ester solvents, amide solvents, halogen-based solvents, sulfur-based solvents, and inorganic solvents.

Hydrocarbon solvents include heptane, cyclohexane, toluene, xylene, etc.

Examples of alcohol-based solvents include methanol and ethanol.

Examples of ether solvents include tetrahydrofuran and dioxane.

Ketone solvents include acetone and methyl ethyl ketone.

Examples of ester solvents include ethyl acetate and ethyl lactate.

Examples of amide solvents include dimethylformamide and N-methyl-2-pyrrolidone.

Halogen-based solvents include chloroform and dichloromethane.

Sulfur-based solvents include dimethyl sulfoxide and sulfolane.

An example of an inorganic solvent is water.

The above solvents may be used alone or as a mixed solvent containing two or more solvents.

There are no particular limitations on the method for preparing the paint, but it is sufficient to mix the active material, binder, optional additives, etc., one by one or two or more at the same time with a solvent and dissolve or disperse them in the solvent.

There are no restrictions on the order in which the solid components (active material, binder, and optional additives) are added to the solvent. The insoluble components may be added to a solution in which the soluble components are dissolved in a solvent, and the insoluble components may be dispersed in the solution. Alternatively, the soluble components may be added to a dispersion in which the insoluble components are dispersed in a solvent, and the soluble components may be dissolved in the dispersion.

After preparing the slurry or solution, additional solvent may be added to adjust the viscosity of the paint.

The condition of the paint may be adjusted by processes such as degassing and filtration. Additives such as defoamers, viscosity modifiers, thickeners, diluents, surfactants, and stabilizers may also be added to the paint.

The method for applying the paint is not particularly limited, but examples include blade coating, dip coating, spray coating, bar coating, and die coating.

The object (substrate) to be coated with the paint is preferably a release-treated resin film. The substrate may be a long strip, or a small sheet obtained by processing a long substrate into sheets.

The object to be coated with the paint may also be a battery component such as a current collector, separator, or solid electrolyte. By applying the paint directly to these battery components, the coating film and the battery component may be integrated.

The electrode sheet raw material can be formed by applying a paint and removing the solvent from the coating film formed. The solvent can be removed by heating, reducing pressure, blowing air, or a combination of these.

The dried coating film may be pressed. For example, by compressing the dried coating film with a press, the contact state of the particles of the active material, conductive material, etc. contained in the electrode can be improved.

When a long, strip-shaped support is used, the electrode film raw material may be wound into a roll for storage and transportation, or may be further processed into multiple sheet-shaped electrode film raw material.

In this way, the electrode film roll is obtained.

FIG. 3 is a schematic diagram showing the electrode film raw material 2 of this embodiment.
3 has an active material layer 21 and a functional layer 22. The electrode film raw sheet 2 is also sandwiched on both sides by release films 10. The active material layer 21 is made of a mixture containing an active material and a binder.

The electrode film roll 2 does not have a current collector.

The mixture that constitutes the active material layer 21 can be the same as the mixture that constitutes the electrode film substrate 1 described above.

The functional layer 22 is not particularly limited as long as it is a layer added for the purpose of improving the function of the electrode. Examples of functional layers 22 include a heat dissipation layer, a planarization layer, a stress relief layer, and an adhesion layer.

The electrode film roll 2 also satisfies the above requirements (1) to (3).

The electrode film raw sheet 2 can be manufactured by producing an active material layer 21 corresponding to the electrode film raw sheet 1 in the same manner as the electrode film raw sheet 1 described above, and then forming a functional layer 22 on the surface of the active material layer 21. The functional layer 22 can be manufactured appropriately using known materials and known methods.

By using an electrode film base roll configured as described above, it is possible to provide a new electrode film base roll that can be used as an electrode material.

In addition, electrodes configured as described above are self-standing and easy to handle.

[Electrode laminate]
The electrode stack is a stack in which the above-mentioned electrode and a separator or a solid electrolyte membrane are stacked. In the electrode stack, the electrode may be in direct contact with the separator or the solid electrolyte membrane, or another member may be sandwiched between them.

Electrode laminates made of electrodes and separators are primarily used in electrochemical devices that use electrolyte solutions. Electrode laminates made of electrodes and solid electrolytes are used in all-solid-state secondary batteries, a type of electrochemical device.

The separator is a material that provides insulation between the positive and negative electrodes and has the ion permeability necessary for the electrodes to function. There are no particular limitations on the separator, and known resin films, porous membranes, etc. can be used.

Examples of resin films include polypropylene, polyethylene, polyolefin, aramid, polyvinylidene fluoride, polyacrylonitrile, polyimide, polyamide, and polyethersulfone. The resin film may be made porous to impart ion permeability.

Porous membranes include woven fabric, nonwoven fabric, cellulose, ceramic, etc.

A solid electrolyte membrane is a component made by processing a commonly known solid electrolyte into a plate or film. Both commonly known inorganic solid electrolytes and polymer solid electrolytes can be used as materials for the solid electrolyte membrane.

As the inorganic solid electrolyte, any of sulfide-based inorganic solid electrolytes, oxide-based inorganic solid electrolytes, and other lithium-based inorganic solid electrolytes can be used.

Examples of sulfide-based inorganic solid electrolytes include Li ₂ S—P ₂ S ₅ , Li ₂ S—SiS ₂ , Li ₂ S—GeS ₂ , Li ₂ S—Al ₂ S ₃ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li ₂ S—P ₂ S ₅ —GeS ₂ , Li ₂ S—Li ₂ O—P ₂ S ₅ —SiS ₂ , Li ₂ S—GeS ₂ —P ₂ S ₅ —SiS ₂ , Li ₂ S—SnS ₂ —P ₂ S ₅ —SiS _{2 ,} and the like.

Examples of oxide-based inorganic solid electrolytes include NASICON-type electrolytes such as LiTi ₂ (PO ₄ ) ₃ , LiZr ₂ (PO ₄ ) ₃ and LiGe ₂ (PO ₄ ) ₃ , and perovskite-type electrolytes such as (La _0.5+x Li _0.5-3x )TiO ₃ .

Other examples of lithium-based inorganic solid electrolyte materials include LiPON, LiNbO ₃ , LiTaO ₃ , Li ₃ PO ₄ , LiPO _4-x N _x (x is 0<x≦1), LiN, LiI, and LISICON.

Examples of polymer solid electrolytes include polymer materials that exhibit ionic conductivity, such as polyethylene oxide, polypropylene oxide, and copolymers of these.

An example of such a material is a protective film that protects the electrode surface. There are no particular restrictions on the protective film, as long as it is made of a material that can protect the electrode from particles such as active material falling off the electrode surface and excessive reactions between the electrolyte and the electrode.

[Electrochemical Devices]
An electrochemical device includes the electrode laminate, and examples of the electrochemical device include a secondary battery and a capacitor.

Secondary batteries include battery cells, modules made by connecting multiple cells, and packs made by connecting multiple modules. Electrochemical device products may also be equipped with sensors and control circuits to prevent abnormalities such as overcharging and over-discharging. Leads (terminals) may be attached to the electrodes to electrically connect the battery to the outside.

The electrode laminate having a separator is used in a secondary battery having an electrolytic solution. The electrolyte of the lithium ion secondary battery can be a solution _in which a lithium salt is dissolved in a non-aqueous _solvent . Examples of the lithium salt include _LiPF6 , _LiBF4 , LiAlCl4, _LiClO4 , _CF3SO3Li , _C4F9SO3Li , _CF3COOLi , ( _CF3CO ) _2NLi , ( _CF3SO2 ) _{2NLi ,} ( _C2F5SO2 ) _2NLi , etc. Examples of the non _- aqueous solvent can include _carbonates ( _carbonate esters) such as ethylene carbonate ( _EC ), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

An electrochemical device can be produced by combining the above-described electrode laminate with other necessary components, such as a separator and another electrode (counter electrode). The counter electrode may be different from the electrode in this embodiment.

The container that houses the electrode stack can be made of laminate film, metal, etc. The electrode stack may be placed flat inside the container, or may be housed in a curved, bent, wound, etc. state.

[device]
A module can be produced by connecting multiple cells. A pack can be produced by connecting multiple modules. Devices produced using batteries such as cells, modules, and packs include, but are not limited to, electronic devices such as smartphones, mobile phones, computers, and displays, and transportation devices such as electric vehicles and hybrid vehicles.

The above describes preferred embodiments of the present invention with reference to the accompanying drawings, but the present invention is not limited to these examples. The shapes and combinations of the components shown in the above examples are merely examples, and various modifications can be made based on design requirements, etc., without departing from the spirit of the present invention.

The present invention will be described below using examples, but the present invention is not limited to these examples.

(Examples 1 to 11, Comparative Examples 1 to 5)
The materials used in the examples and comparative examples are as follows.

(binder)
SBR: Styrene-butadiene rubber, manufactured by Sigma-Aldrich, model number 182877
PVdF: Polyvinylidene fluoride, Solvay, model number 5130

(Cathode active material)
LFP: Formosa Lithium Iron Corp., model number SFCM30050

(Conductive material)
AB: Acetylene black, manufactured by Alfa Aesar, model number 45527

Each binder was dissolved in a solvent to prepare a solution having the following concentration, and then the binders were mixed in the ratios shown in Table 1 to obtain a binder solution.
SBR: 24% by mass toluene solution PVdF: 6% by mass NMP (N-methyl-2-pyrrolidone) solution

The active material and conductive material (acetylene black) were mixed in the ratios shown in Table 1 using a vibration mixer to obtain a mixed powder.

The mixed powder and binder solution were mixed in the ratio shown in Table 1 to form a slurry. Toluene was then added to adjust the viscosity.

The slurry was degassed and passed through a sieve with 100 μm openings to obtain the paints of the examples and comparative examples.

The resulting coating material was applied to a release-treated PET film to a capacity of 5 mAh/ ^cm2 . Specifically, the mass per unit area of the active material (applied mass, unit: g/ ^cm2 ) was calculated and applied based on the target electrode capacity and the specific capacity (unit: mAh/g) of the active material used. The coating film was dried by heating at 120°C for 12 minutes. After drying, it was compressed using a roll press to a density of 2.4 g/ ^cm3 (positive electrode), and raw electrode film rolls for the Examples and Comparative Examples were obtained.

The specific capacity of the active material was determined using the manufacturer's nominal value for the active material used.

[Measurement of Breaking Strength]
The breaking strength of the raw electrode film was measured by the method described above in (Method for measuring breaking strength).

[Fabrication of Battery: Electrode Film Raw Sheet Having Positive Electrode Active Material]
A positive electrode for a coin-type battery R2032 was cut out from the electrode film roll.
After each component was dried in a vacuum at 105° C., assembly was carried out in a glove box under an argon atmosphere.

The prepared test electrode was placed on the bottom cover of a coin-type battery R2032. A separator (Celgard 2300, manufactured by Celgard) was placed on the test electrode, and then an electrolyte (1 mol/L solution of _LiPF6 ) was poured into the electrode. The electrolyte solvent was a mixed solvent of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a 1:1:1 (volume ratio).

A counter electrode (metallic lithium) was placed on top of the separator, the lid was placed on top, and the battery was left to stand for 12 hours to allow the entire battery to be soaked in the electrolyte, thereby producing a lithium secondary battery.

[Capacity maintenance rate]
The fabricated lithium secondary battery was charged to 3.80 V at 0.05 C (SOC 100%) and then rested for 5 minutes. Subsequently, a constant current discharge was performed at 0.05 C, and the discharge capacity during constant current discharge was measured. Three consecutive measurements were performed, and the arithmetic mean value of the first, second, and third discharge capacities was taken as the "0.05 C discharge capacity" (reference capacity) (1 C = 5 mA/cm ² ).

The "0.6C discharge capacity" was also determined using the same lithium secondary battery as that used to measure the "0.05C discharge capacity" under the same conditions as above, except that constant current discharge was performed at 0.6C.

(Calculation method)
The capacity retention rate was calculated using the following formula.
Capacity retention rate = 0.6C discharge capacity / 0.05C discharge capacity × 100%

The evaluation results are shown in Table 1. In the table, "Not measurable" for breaking strength means that the test piece was too brittle to measure.

These results demonstrate the usefulness of this invention.

1, 2... Electrode film roll, 10... Release film, 21... Active material layer, 22... Functional layer

Claims (8)

An electrode film raw sheet made of a mixture containing an active material and a binder, and satisfying the following (1) to (3):
(1) The breaking strength measured by the following measurement method is 0.2 MPa or more.
(Measurement method) The electrode film raw material was cut into a size of 15 mm in width and 50 mm in length to obtain a test piece, and the strength at 75% of the maximum stress when measured under conditions of a chuck distance of 30 mm and a tensile speed of 100 mm/min was taken as the breaking strength.
(2) The active material includes lithium iron phosphate, and the binder includes styrene butadiene rubber and polyvinylidene fluoride.
(3) The binder contains 0.75% by mass or more and 2.95% by mass or less of the styrene-butadiene rubber and 0.25% by mass or more and 5.25% by mass or less of the polyvinylidene fluoride relative to the entire mixture. an active material layer made of a mixture containing an active material and a binder;
No current collector is provided.
An electrode film substrate that satisfies the following (1) to (3):
(1) The breaking strength measured by the following measurement method is 0.2 MPa or more.
(Measurement method)
The electrode film raw sheet was cut into a size of 15 mm in width and 50 mm in length to obtain a test piece, and the strength at 75% of the maximum stress when measured under conditions of a chuck distance of 30 mm and a tensile speed of 100 mm/min was defined as the breaking strength.
(2) The active material includes lithium iron phosphate, and the binder includes styrene butadiene rubber and polyvinylidene fluoride.
(3) The binder contains 0.75% by mass or more and 2.95% by mass or less of the styrene-butadiene rubber and 0.25% by mass or more and 5.25% by mass or less of the polyvinylidene fluoride relative to the entire mixture. the active material is lithium iron phosphate;
3. The electrode film substrate according to claim 1, wherein the binder comprises styrene-butadiene rubber and polyvinylidene fluoride. The electrode film raw material described in any one of claims 1 to 3, having a release film laminated thereon. An electrode made from the electrode film substrate described in any one of claims 1 to 4. The electrode according to claim 5;
An electrode laminate in which a separator or a solid electrolyte membrane is laminated. An electrochemical device having the electrode stack described in claim 6. An apparatus having the electrochemical device described in claim 7.