CN118044002A

CN118044002A - Polytetrafluoroethylene powder, binder for electrode, electrode mixture, electrode, and secondary battery

Info

Publication number: CN118044002A
Application number: CN202280065363.6A
Authority: CN
Inventors: 加藤丈人; 山田贵哉; 安田幸平; 山中拓; 寺田纯平; 山田雅彦; 宇佐美亮太; 佐藤洋之; 山本绘美; 西村贤汰
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2021-09-30
Filing date: 2022-09-30
Publication date: 2024-05-14

Abstract

The purpose of the present invention is to provide polytetrafluoroethylene powder for an electrode binder, an electrode mixture, an electrode, and a secondary battery, which can suppress the generation of gas in a battery cell and the deterioration of battery characteristics, and can also improve the strength of the electrode. A polytetrafluoroethylene powder for an electrode binder, wherein the polytetrafluoroethylene powder has a standard specific gravity of 2.200 or less and contains substantially no moisture.

Description

Polytetrafluoroethylene powder, binder for electrode, electrode mixture, electrode, and secondary battery

Technical Field

The present invention relates to polytetrafluoroethylene powder, a binder for an electrode, an electrode mixture, an electrode, and a secondary battery.

Background

Secondary batteries such as lithium ion secondary batteries are used in small-sized and portable electric and electronic devices such as notebook personal computers, mobile phones, smartphones, tablet personal computers, and ultra-notebooks for reasons such as high voltage, high energy density, less self-discharge, less memory effect, and capability of achieving ultra-light weight, and are further put into practical use as power sources for driving vehicle power sources for wide use in automotive applications and the like, and large-sized stationary power sources. Secondary batteries are required to have higher energy density and further improved battery characteristics.

Patent document 1 describes an energy storage device in which at least one of a cathode and an anode includes a polytetrafluoroethylene-mixed binder material.

Patent documents 2 and 3 describe the use of an aqueous dispersion of polytetrafluoroethylene as a binder for a battery.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2017-517862

Patent document 2: japanese patent application laid-open No. 2004-31179

Patent document 3: japanese patent laid-open No. 11-343317

Disclosure of Invention

Problems to be solved by the invention

The purpose of the present invention is to provide polytetrafluoroethylene powder for an electrode binder, an electrode mixture, an electrode, and a secondary battery, which can suppress the generation of gas in a battery cell and the deterioration of battery characteristics, and can also improve the strength of the electrode.

Means for solving the problems

The invention (1) provides polytetrafluoroethylene powder which is used as a binder for an electrode, wherein the polytetrafluoroethylene powder has a standard specific gravity of 2.200 or less and contains substantially no moisture.

The present invention also provides (2) a binder for an electrode, which is substantially composed of polytetrafluoroethylene powder alone, wherein the polytetrafluoroethylene powder has a standard specific gravity of 2.200 or less and contains substantially no moisture.

The invention (3) is the binder for an electrode of the invention (2), wherein the content of the moisture is 0.050 mass% or less relative to the polytetrafluoroethylene powder.

The invention (4) is the binder for an electrode of the invention (2) or (3), wherein the extrusion pressure of the polytetrafluoroethylene powder at a compression ratio of 100 is 10MPa or more.

The invention (5) is an electrode binder according to any combination of the invention (2) to (4), wherein the polytetrafluoroethylene powder is stretchable.

The invention (6) is the binder for an electrode according to any one of the combinations (2) to (5) of the invention, wherein the polytetrafluoroethylene contains a tetrafluoroethylene unit and a modified monomer unit based on a modified monomer copolymerizable with tetrafluoroethylene.

The invention (7) is the binder for an electrode of the invention (6), wherein the modifying monomer is at least 1 selected from the group consisting of perfluoro (methyl vinyl ether) and hexafluoropropylene.

The binder for an electrode according to any one of the combinations (2) to (7) of the present invention, wherein the polytetrafluoroethylene powder has an average primary particle diameter of 100nm to 350nm.

The present invention also provides (9) an electrode mixture comprising the polytetrafluoroethylene powder of the present invention (1) or the binder for an electrode in any combination with any of the present invention (2) to (8), and an electrode active material.

The present invention (10) also provides an electrode comprising the polytetrafluoroethylene powder of the invention (1) or the binder for an electrode, the electrode active material and the current collector in any combination with any of the inventions (2) to (8).

The present invention (11) also provides a secondary battery comprising the electrode of the present invention (10).

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide polytetrafluoroethylene powder for an electrode binder, an electrode mixture, an electrode, and a secondary battery, which can suppress the generation of gas in a battery cell and the deterioration of battery characteristics, and can also improve the strength of an electrode.

Detailed Description

The present invention will be specifically described below.

The invention provides a PTFE powder, which is Polytetrafluoroethylene (PTFE) powder used for an electrode binder, wherein the standard specific gravity of the PTFE powder is below 2.200, and the PTFE powder does not substantially contain moisture.

The PTFE powder of the present invention has the above-described structure, and therefore, when used as a binder for an electrode, can suppress the generation of gas inside a battery cell and the deterioration of battery characteristics (for example, the decrease in capacity during high-temperature storage), and can also improve the electrode strength. Further, since the electrode active material does not substantially contain moisture, the electrode active material to be combined can be widely selected, and is advantageous in the production process. In addition, since the electrode active material can be mixed with the powder, an organic solvent is not required, and the process and cost for using the organic solvent can be reduced. Further, the PTFE powder of the present invention has excellent adhesion to the active material, and therefore can be used in a reduced amount.

The Standard Specific Gravity (SSG) of the PTFE powder of the present invention is 2.200 or less. When the SSG is within the above range, gas generation and deterioration of battery characteristics can be further suppressed, and the electrode strength can be improved.

The SSG is preferably 2.180 or less, more preferably 2.170 or less, further preferably 2.160 or less, further more preferably 2.150 or less, further more preferably 2.145 or less, and particularly preferably 2.140 or less.

The SSG is preferably 2.130 or more.

The SSG was measured by the substitution method in water according to ASTM D792 using a sample molded according to ASTM D4895.

The PTFE powder of the present invention preferably has an average primary particle diameter of 100nm to 350nm. When the average primary particle diameter is within the above range, the molecular weight of the PTFE is high, and the adhesion and flexibility of the electrode are improved.

The average primary particle diameter is more preferably 330nm or less, still more preferably 320nm or less, still more preferably 300nm or less, still more preferably 280nm or less, particularly preferably 250nm or less, yet still more preferably 150nm or more, still more preferably 170nm or more, still more preferably 200nm or more.

The average primary particle diameter was measured by the following method.

The PTFE aqueous dispersion was diluted with water until the solid content reached 0.15 mass%, and the transmittance of 550nm of the resulting diluted emulsion per unit length of the projected light and the number-basis length average particle diameter determined by measuring the alignment diameter using a transmission electron micrograph were measured to prepare a calibration curve. The number average particle diameter was determined from the measured transmittance of 550nm of the projected light of each sample using the calibration curve, and the determined number average particle diameter was used as the average primary particle diameter.

The average secondary particle diameter of the PTFE powder of the present invention may be 350 μm or more, preferably 400 μm or more, more preferably 450 μm or more, still more preferably 500 μm or more, still more preferably 550 μm or more, particularly preferably 600 μm or more, and further preferably 1000 μm or less, still more preferably 900 μm or less, still more preferably 800 μm or less, still more preferably 700 μm or less.

The average secondary particle diameter was measured in accordance with JIS K6891.

The extrusion pressure of the PTFE powder of the present invention at the compression ratio (RR) 100 is preferably 10MPa or more, more preferably 12MPa or more, still more preferably 15MPa or more, still more preferably 16MPa or more, and particularly preferably 17MPa or more, from the viewpoint that the gas generation and the deterioration of the battery characteristics can be further suppressed, and the adhesion, the electrode strength, and the flexibility of the electrode are improved.

In addition, from the viewpoint of improving processability, the extrusion pressure at RR100 is preferably 50MPa or less, more preferably 40MPa or less, further preferably 35MPa or less, further preferably 30MPa or less, further preferably 25MPa or less, further preferably 21MPa or less, and particularly preferably 20MPa or less.

The extrusion pressure of the PTFE powder of the present invention at RR300 is preferably 18MPa or more, more preferably 23MPa or more, still more preferably 25MPa or more, still more preferably 28MPa or more, particularly preferably 30MPa or more, and particularly preferably 32MPa or more, from the viewpoint of further suppressing deterioration of gas generation and battery characteristics, and improving the adhesion, electrode strength, and electrode flexibility.

In addition, from the viewpoint of improving processability, the extrusion pressure at RR300 is preferably 45MPa or less, more preferably 40MPa or less.

Extrusion pressure at RR100 was measured by the following method.

50G of PTFE powder and 10.25g of a hydrocarbon oil (trade name: isopar E, manufactured by Exxon Mobil Co.) as an extrusion aid were mixed in a polyethylene container for 3 minutes. The above mixture was charged into the cylinder of the extruder at room temperature (25.+ -. 2 ℃ C.), and the piston inserted into the cylinder was subjected to a load of 0.47MPa and held for 1 minute. Then, the mixture was extruded from the hole at a punching speed of 18 mm/min. The ratio of the cross-sectional area of the cartridge to the cross-sectional area of the bore (compression ratio) was 100. In the latter half of the extrusion operation, the extrusion pressure (MPa) is a value obtained by dividing the load (N) at which the pressure reaches an equilibrium state by the cross-sectional area of the barrel.

Extrusion pressure at RR300 was measured by the following method.

50G of PTFE powder and 11.00g of hydrocarbon oil (trade name: isopar E, manufactured by Exxon Mobil Co.) as an extrusion aid were mixed in a polyethylene container for 3 minutes. The above mixture was charged into the cylinder of the extruder at room temperature (25.+ -. 2 ℃ C.), and the piston inserted into the cylinder was subjected to a load of 0.47MPa and held for 1 minute. Then, the mixture was extruded from the hole at a punching speed of 18 mm/min. The ratio of the cross-sectional area of the cartridge to the cross-sectional area of the bore (compression ratio) was 300. In the latter half of the extrusion operation, the extrusion pressure (MPa) is a value obtained by dividing the load (N) at which the pressure reaches an equilibrium state by the cross-sectional area of the barrel.

The PTFE powder of the present invention is preferably stretchable from the viewpoint of further suppressing gas generation and deterioration of battery characteristics, and from the viewpoint of improving adhesion, electrode strength, and electrode flexibility.

The drawable means that a stretched body was obtained in the following tensile test.

The bars obtained by extrusion of the paste under RR100 described above were dried at 230 ℃ for 30 minutes, removing the lubricant. The dried strips were cut to an appropriate length, placed in a furnace heated to 300 ℃ and stretched in the furnace at a stretching speed of 100%/sec.

The PTFE powder of the present invention is preferably stretchable up to 25 times, from the viewpoint of further suppressing the generation of gas and the deterioration of battery characteristics, and from the viewpoint of further improving the adhesion, electrode strength and electrode flexibility.

Whether or not the stretching can be performed to 25 times can be confirmed by the following tensile test.

The bars obtained by extrusion of the paste under RR100 described above were dried at 230 ℃ for 30 minutes, removing the lubricant. The dried strips were cut to the appropriate length and placed in a furnace heated to 300 ℃. Stretching in an oven at a stretching speed of 100%/second to 25 times the length of the strip before the stretching test. If the sheet breaks during stretching, it is determined that the sheet can be stretched up to 25 times.

The average aspect ratio of the PTFE powder of the present invention may be 2.0 or less, preferably 1.8 or less, more preferably 1.7 or less, still more preferably 1.6 or less, still more preferably 1.5 or less, still more preferably 1.4 or less, particularly preferably 1.3 or less, particularly preferably 1.2 or less, and most preferably 1.1 or less, from the viewpoint of excellent handleability. The average aspect ratio may be 1.0 or more.

The average aspect ratio was obtained by observing a PTFE powder or an aqueous PTFE dispersion diluted to a solid content of about 1 mass% with a Scanning Electron Microscope (SEM), and image-processing 200 or more randomly extracted particles, and averaging the ratio of the long diameter to the short diameter.

The apparent density of the PTFE powder of the present invention is preferably 0.40g/ml or more, more preferably 0.43g/ml or more, still more preferably 0.45g/ml or more, still more preferably 0.48g/ml or more, and particularly preferably 0.50g/ml or more, from the viewpoint of excellent handleability. The upper limit is not particularly limited and may be 0.70g/ml.

The apparent density was measured in accordance with JIS K6892.

The PTFE powder of the present invention preferably has non-melt secondary processability. The above-mentioned non-melt secondary processability means a property that the melt flow rate cannot be measured at a temperature higher than the melting point according to ASTM D-1238 and D-2116, in other words, a property that the flow is not easy even in the melting temperature region.

The PTFE may be a homopolymer of Tetrafluoroethylene (TFE), or may be modified PTFE including a polymerized unit (TFE unit) based on TFE and a polymerized unit (hereinafter also referred to as "modified monomer unit") based on a modified monomer. The modified PTFE may contain 99.0 mass% or more of TFE units and 1.0 mass% or less of modified monomer units. The modified PTFE may be composed of only TFE units and modified monomer units.

The PTFE is preferably modified PTFE, from the viewpoint of further suppressing gas generation and deterioration of battery characteristics, and from the viewpoint of improving adhesion, electrode strength, and electrode flexibility.

The modified PTFE preferably has a content of the modified monomer unit in a range of 0.00001 to 1.0 mass% relative to the total polymerized units, from the viewpoint of further suppressing the gas generation and the deterioration of battery characteristics, and from the viewpoint of improving stretchability, adhesion, electrode strength, and electrode flexibility. The lower limit of the content of the modifying monomer unit is more preferably 0.0001 mass%, still more preferably 0.001 mass%, still more preferably 0.005 mass%, and particularly preferably 0.010 mass%. The upper limit of the content of the modified monomer unit is preferably 0.90 mass%, more preferably 0.80 mass%, more preferably 0.50 mass%, further preferably 0.40 mass%, further preferably 0.30 mass%, further preferably 0.20 mass%, further preferably 0.15 mass%, further preferably 0.10 mass%, further preferably 0.08 mass%, particularly preferably 0.05 mass%, and most preferably 0.03 mass%.

In the present specification, the modified monomer unit refers to a part of the molecular structure of PTFE, and is a part derived from a modified monomer.

The content of each of the above-mentioned polymerized units can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis according to the kind of the monomer.

The modifying monomer is not particularly limited as long as it can be copolymerized with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene [ HFP ]; hydrofluoroolefins such as trifluoroethylene and vinylidene fluoride [ VDF ]; perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ether; perfluoro allyl ether; (perfluoroalkyl) ethylene, and the like. The number of the modifying monomers used may be 1 or 2 or more.

The perfluorovinyl ether is not particularly limited, and examples thereof include the following general formula (a):

CF₂＝CF-ORf(A)

(wherein Rf represents a perfluorinated organic group) and the like. In the present specification, the term "perfluorinated organic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The perfluorinated organic group may have ether oxygen.

As the perfluorovinyl ether, for example, perfluoro (alkyl vinyl ether) wherein Rf is a perfluoroalkyl group having 1 to 10 carbon atoms in the general formula (A) [ PAVE ] can be mentioned. The number of carbon atoms of the perfluoroalkyl group is preferably 1 to 5.

Examples of the perfluoroalkyl group in PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

The perfluorovinyl ether may further be one wherein Rf in the general formula (A) is a perfluoro (alkoxyalkyl) group having 4 to 9 carbon atoms, and Rf is the following formula:

[ chemical 1]

(Wherein m represents 0 or an integer of 1 to 4), and Rf is represented by the following formula:

[ chemical 2]

(Wherein n represents an integer of 1 to 4), and the like.

The (perfluoroalkyl) ethylene (PFAE) is not particularly limited, and examples thereof include (perfluorobutyl) ethylene (PFBE) and (perfluorohexyl) ethylene.

Examples of the perfluoroallyl ether include the general formula (B):

CF₂＝CF-CF₂-ORf¹(B)

(wherein Rf ¹ represents a perfluorinated organic group).

The Rf ¹ is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. As the above-mentioned perfluoroallyl ether, at least 1 selected from the group consisting of CF₂＝CF-CF₂-O-CF₃、CF₂＝CF-CF₂-O-C₂F₅、CF₂＝CF-CF₂-O-C₃F₇ and CF ₂＝CF-CF₂-O-C₄F₉ is preferable, at least 1 selected from the group consisting of CF ₂＝CF-CF₂-O-C₂F₅、CF₂＝CF-CF₂-O-C₃F₇ and CF ₂＝CF-CF₂-O-C₄F₉ is more preferable, and CF ₂＝CF-CF₂-O-CF₂CF₂CF₃ is further preferable.

As the above-mentioned modifying monomer, at least 1 selected from the group consisting of PAVE and HFP is preferable, and at least 1 selected from the group consisting of perfluoro (methyl vinyl ether) (PMVE) and HFP is more preferable from the viewpoints of stretchability, adhesion and improvement in electrode flexibility.

In addition, as the other modifying monomer, at least 1 selected from the group consisting of VDF, HFP, CTFE and PAVE, more preferably at least 1 selected from the group consisting of VDF, HFP and CTFE is preferable in view of being capable of forming an electrode mixture sheet more excellent in strength.

In view of improvement in heat resistance, the PTFE contains TFE units, VDF units, and HFP units, and the total amount of VDF units and HFP units is 1.0 mass% or less relative to the total of all the polymerization units, which is one of preferred embodiments.

The PTFE may have a core-shell structure. Examples of PTFE having a core-shell structure include modified PTFE including a core of PTFE having a high molecular weight and a PTFE or modified PTFE shell having a lower molecular weight in the particles. Examples of such modified PTFE include PTFE described in Japanese patent application laid-open No. 2005-527652.

The endothermic peak temperature of the PTFE is preferably 320 ℃ or higher, more preferably 325 ℃ or higher, further preferably 330 ℃ or higher, further preferably 335 ℃ or higher, further preferably 340 ℃ or higher, further preferably 342 ℃ or higher, particularly preferably 344 ℃ or higher, from the viewpoint of forming an electrode mixture sheet having more excellent strength. The endothermic peak temperature is preferably 350 ℃ or lower.

The endothermic peak temperature is a temperature corresponding to a minimum point in the obtained melting heat curve by performing differential scanning calorimetric measurement [ DSC ] at a temperature rise rate of 10 ℃/min on a fluororesin having no history of being heated to 300 ℃ or higher. When there are 2 or more very small points in 1 melting peak, each is regarded as an endothermic peak temperature.

The PTFE exhibits 1 or more endothermic peaks in the melting temperature curve at 333 to 347 ℃ when the temperature is raised at a rate of 10 ℃/min by using a differential scanning calorimeter [ DSC ], and the melting heat at 290 to 350 ℃ calculated from the melting temperature curve is preferably 62mJ/mg or more.

The number average molecular weight (Mn) of the PTFE is preferably 3.0×10 ⁶ or more, more preferably 3.2×10 ⁶ or more, still more preferably 3.5×10 ⁶ or more, still more preferably 3.7×10 ⁶ or more, and particularly preferably 4.0×10 ⁶ or more, from the viewpoint of enabling formation of an electrode mixture sheet having more excellent strength. The number average molecular weight is preferably 7.0X10 ⁶ or less, more preferably 6.5X10 ⁶ or less, still more preferably 6.0X10 ⁶ or less, still more preferably 5.5X10 ⁶ or less, particularly preferably 5.0X10 ⁶ or less.

The number average molecular weight is a molecular weight obtained from a crystallization heat estimated by melting a fluororesin and then measuring the temperature drop by a Differential Scanning Calorimeter (DSC) according to the method described in the following document. The measurement was performed 5 times, and an average value of 3 values excluding the maximum value and the minimum value was used.

Literature: suwa, t.; takehisa, m.; machi, S., J.appl.Polym.Sci.vol.17, pp.3253 (1973).

The PTFE powder of the present invention contains substantially no moisture. This can further suppress the generation of gas and the deterioration of battery characteristics, and can also improve the electrode strength. In addition, the electrode active materials to be combined can be widely selected, and thus are advantageous in the production process. Substantially not containing moisture means that the moisture content is 0.050 mass% or less relative to the PTFE powder.

The moisture content is preferably 0.040% by mass or less, more preferably 0.020% by mass or less, still more preferably 0.010% by mass or less, still more preferably 0.005% by mass or less, and particularly preferably 0.002% by mass or less.

The above moisture content was measured by the following method.

The mass of PTFE powder before and after heating at 150℃for 2 hours was measured and calculated according to the following formula. The average value was obtained by taking 3 samples and calculating the samples.

Moisture content (% by mass) = [ (mass (g) of PTFE powder before heating)) - (mass (g) of PTFE powder after heating))/(mass (g) of PTFE powder before heating)) ×100

The PTFE powder of the present invention preferably contains substantially no fluorine-containing compound having a molecular weight of 1000 or less. The substantial absence of the fluorine-containing compound means that the amount of the fluorine-containing compound is 25 ppb by mass or less relative to the PTFE powder.

The amount of the fluorine-containing compound is more preferably less than 25 ppb by mass, still more preferably 10 ppb by mass or less, still more preferably 5 ppb by mass or less, particularly preferably 3 ppb by mass or less, and particularly preferably 1 ppb by mass or less. The lower limit is not particularly limited, and may be an amount smaller than the detection limit.

The amount of the fluorine-containing compound having a molecular weight of 1000 or less is measured by the following method.

1G of a sample was weighed, 10g (12.6 ml) of methanol was added thereto, and the mixture was subjected to ultrasonic treatment for 60 minutes to obtain an extract. The obtained extract was concentrated by purging with nitrogen gas, and the fluorine-containing compound in the concentrated extract was subjected to LC/MS measurement. Molecular weight information was selected from the obtained LC/MS spectra, and it was confirmed that the molecular weight information matches the structural formula of the fluorine-containing compound as a candidate. An aqueous solution of 5 levels or more of the standard substance was prepared, LC/MS analysis was performed on each aqueous solution, and a calibration curve was drawn by plotting the relationship between the content and the area of the region corresponding to the content. The area of the LC/MS chromatogram of the fluorine-containing compound in the extract was converted into the content of the fluorine-containing compound by using the calibration curve.

The lower limit of detection in this measurement method was 10 ppb by mass.

The amount of the fluorine-containing compound having a molecular weight of 1000 or less can also be measured by the following method.

1G of a sample was weighed, 10g (12.6 ml) of methanol was added thereto, and the mixture was sonicated at 60℃for 2 hours, and after standing at room temperature, the solid content was removed to obtain an extract. The obtained extract was concentrated by purging with nitrogen gas, and the fluorine-containing compound in the concentrated extract was subjected to LC/MS measurement. Molecular weight information was selected from the obtained LC/MS spectra, and it was confirmed that the molecular weight information matches the structural formula of the fluorine-containing compound as a candidate. 5 standard solutions of methanol containing fluorine compounds at known concentrations were prepared, and measured by a liquid chromatograph mass spectrometer, and a calibration curve was prepared from the standard solution concentration and the integrated value of the peak at each concentration range using a one-time approximation. The content of the fluorine-containing compound contained in the extract was measured from the calibration curve, and the content of the fluorine-containing compound contained in the sample was converted.

The lower limit of detection in this measurement method was 1 ppb by mass.

Examples of the fluorine-containing compound having a molecular weight of 1000 or less include fluorine-containing compounds having a hydrophilic group and having a molecular weight of 1000g/mol or less. The molecular weight of the fluorine-containing compound is preferably 800 or less, more preferably 500 or less.

The polymerized particles obtained by polymerization in the presence of a fluorosurfactant generally contain a fluorosurfactant in addition to PTFE. In the present specification, the fluorosurfactant is used in polymerization.

The fluorine-containing compound having a molecular weight of 1000 or less may be a compound which is not added during polymerization, for example, a compound which is a by-product during polymerization.

In the case where the fluorine-containing compound having a molecular weight of 1000 or less contains an anionic moiety and a cationic moiety, the fluorine-containing compound having a molecular weight of 1000 or less in the anionic moiety is meant. The fluorine-containing compound having a molecular weight of 1000 or less does not contain PTFE.

Examples of the hydrophilic group include-COOM, -SO ₂ M, and-SO ₃ M, and examples thereof include anionic groups such as-COOM, -SO ₃ M (wherein M is H, a metal atom, NR ¹ ₄, an imidazolium group with or without a substituent, a pyridinium group with or without a substituent, or a phosphonium group with or without a substituent, and R ¹ is H or an organic group).

As the fluorine-containing surfactant, a surfactant containing fluorine having a molecular weight of 1000 or less in the anionic portion (anionic fluorine-containing surfactant) may be used. The "anionic portion" refers to a portion of the fluorosurfactant other than a cation. For example, in the case of F (CF ₂)_n1 COOM), the portion is "F (CF ₂)_n1 COO".

The anionic fluorosurfactant includes the following general formula (N ⁰):

Xⁿ⁰-Rfⁿ⁰-Y⁰(N⁰)

(wherein X ⁿ⁰ is H, cl or F.Rf ⁿ⁰ is an alkylene group having 3 to 20 carbon atoms and being substituted with F in part or all of H, which may contain 1 or more ether linkages and in part of H may be substituted with Cl. Y ⁰ is an anionic group).

The anionic group of Y ⁰ may be-COOM, -SO ₂ M or-SO ₃ M, or-COOM or-SO ₃ M.

M is H, a metal atom, NR ¹ ₄, an imidazolium with or without substituents, a pyridinium with or without substituents, or a phosphonium with or without substituents, R ¹ is H or an organic group.

Examples of the metal atom include alkali metal (group 1) and alkaline earth metal (group 2), and are Na, K, and Li.

R ¹ may be an organic group of H or C _1-10, an organic group of H or C _1-4, or an alkyl group of H or C _1-4.

M may be H, a metal atom or NR ¹ ₄, may be H, an alkali metal (group 1), an alkaline earth metal (group 2) or NR ¹ ₄, and may be H, na, K, li or NH ₄.

In Rf ⁿ⁰, 50% or more of H may be substituted with fluorine.

The above-mentioned fluorosurfactant may be 1 kind of fluorosurfactant or a mixture containing 2 or more kinds of fluorosurfactants.

Examples of the fluorosurfactant include compounds represented by the following formula. The fluorosurfactant can also be a mixture of these compounds.

F(CF₂)₇COOM、

F(CF₂)₅COOM、

H(CF₂)₆COOM、

H(CF₂)₇COOM、

CF₃O(CF₂)₃OCHFCF₂COOM、

C₃F₇OCF(CF₃)CF₂OCF(CF₃)COOM、

CF₃CF₂CF₂OCF(CF₃)COOM、

CF₃CF₂OCF₂CF₂OCF₂COOM、

C₂F₅OCF(CF₃)CF₂OCF(CF₃)COOM、

CF₃OCF(CF₃)CF₂OCF(CF₃)COOM、

CF₂ClCF₂CF₂OCF(CF₃)CF₂OCF₂COOM、

CF₂ClCF₂CF₂OCF₂CF(CF₃)OCF₂COOM、

CF₂ClCF(CF₃)OCF(CF₃)CF₂OCF₂COOM、

CF ₂ClCF(CF₃)OCF₂CF(CF₃)OCF₂ COOM

[ Chemical 3]

(In the formula, M is H, a metal atom, NR ¹ ₄, an imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent; R ¹ is H or an organic group.).

The PTFE powder of the present invention preferably does not substantially contain any of the fluorine-containing compounds represented by the above formulas.

In the above formulae, M may be H, a metal atom or NR ¹ ₄, may be H, an alkali metal (group 1), an alkaline earth metal (group 2) or NR ¹ ₄, or may be H, na, K, li or NH ₄.

R ¹ may be H or an organic group of C _1-10, may be H or an organic group of C _1-4, or may be H or an alkyl group of C _1-4.

When the PTFE powder of the present invention does not substantially contain any of the fluorine-containing compounds represented by the above formulas, the gas generation and the deterioration of the battery characteristics can be further suppressed, and the electrode strength can be further improved.

The substantial absence of any fluorine-containing compound represented by the above formula means that the amount of the fluorine-containing compound is 25 ppb by mass or less relative to the PTFE powder.

The amount of the fluorine-containing compound is preferably less than 25 ppb by mass, more preferably 10 ppb by mass or less, further preferably 5 ppb by mass or less, particularly preferably 3 ppb by mass or less, and particularly preferably 1 ppb by mass or less. The lower limit is not particularly limited, and may be an amount smaller than the detection limit.

The PTFE powder of the present invention also preferably does not substantially comprise the following formula:

[C_n-1F_2n-1COO^-]M⁺

(wherein n represents an integer of 9 to 14, preferably an integer of 9 to 12, and M ⁺ represents a cation). This can further suppress the generation of gas and the deterioration of battery characteristics, and can further improve the electrode strength.

M constituting the cation M ⁺ in the above formula is the same as M described above.

Substantially not including the fluorine-containing compound represented by the above formula means that the amount of the fluorine-containing compound is 25 ppb by mass or less relative to the PTFE.

The PTFE powder of the present invention can be suitably produced by a production method including, for example, a step (a) of preparing an aqueous dispersion of PTFE, a step (B) of precipitating the aqueous dispersion to obtain a wet powder of PTFE, and a step (C) of drying the wet powder.

The aqueous dispersion in the step (a) can be produced by emulsion polymerization, for example.

The emulsion polymerization can be carried out by a known method. For example, an aqueous dispersion containing particles (primary particles) of the PTFE is obtained by emulsion polymerization of monomers necessary for constituting the PTFE in an aqueous medium in the presence of an anionic fluorosurfactant and a polymerization initiator. In the emulsion polymerization, a chain transfer agent, a buffer, a pH adjuster, a stabilizing aid, a dispersion stabilizer, a radical scavenger, and the like can be used as necessary.

The SSG can be adjusted to the above range by appropriately selecting the conditions of the emulsion polymerization.

The step (a) may be a step of emulsion-polymerizing TFE and, if necessary, a modified monomer.

The emulsion polymerization may be carried out in an aqueous medium in the presence of an anionic fluorosurfactant and a polymerization initiator, for example.

The emulsion polymerization may be performed as follows: the polymerization reaction can be carried out by charging an aqueous medium, the above anionic fluorosurfactant, a monomer and other additives as needed into a polymerization reactor, stirring the contents of the reactor, maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of a polymerization initiator to initiate the polymerization. After the polymerization reaction is started, a monomer, a polymerization initiator, a chain transfer agent, the surfactant, and the like may be additionally added according to the purpose.

The polymerization initiator is not particularly limited as long as it can generate radicals in the polymerization temperature range, and known oil-soluble and/or water-soluble polymerization initiators can be used. Further, the polymerization may be initiated in a redox form in combination with a reducing agent or the like. The concentration of the polymerization initiator is appropriately determined according to the kind of the monomer, the molecular weight of the target PTFE, and the reaction rate.

As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, and the following peroxides are exemplified as typical examples: dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and di-sec-butyl peroxydicarbonate; peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate; dialkyl peroxides such as di-t-butyl peroxide; di (ω -hydro-dodecafluoroheptanoyl) peroxide, di (ω -hydro-tetradecahaloyl) peroxide, di (ω -hydro-hexadecahaloyl) peroxide, di (perfluorobutanoyl) peroxide, di (perfluoropentanoyl) peroxide, di (perfluorohexanoyl) peroxide, di (perfluoroheptanoyl) peroxide, di (perfluorooctanoyl) peroxide, di (perfluorononanoyl) peroxide, di (ω -chloro-hexafluorobutanoyl) peroxide, di (ω -chloro-decafluorohexanoyl) peroxide, di (ω -chloro-tetradecanoyl) peroxide, ω -hydro-dodecafluoroheptanoyl- ω -hexadecanoyl-peroxide, ω -chloro-hexafluorobutanoyl- ω -chloro-decafluorodecanoyl-peroxide, ω -hydrododecafluoroheptanoyl-perfluoroheptanoyl-peroxide, di (dichloro-penta-fluoropentanoyl) peroxide, di (trichlorooctahexanoyl) peroxide, di (tetrafluoroundecanoyl) peroxide, di (ω -chloro-dodecanoyl) peroxide, di (chloro-dodecanoyl) or di (fluoro-dodecanoyl) peroxide; etc.

The water-soluble radical polymerization initiator may be a known water-soluble peroxide, and examples thereof include ammonium salts, potassium salts, sodium salts, t-butyl peroxymaleate, t-butyl hydroperoxide, disuccinic acid peroxide, and the like of persulfuric acid, perboric acid, perchloric acid, perphosphoric acid, and percarbonic acid. Among them, ammonium persulfate and disuccinic peroxide are preferable. The composition may contain a reducing agent such as a sulfite or a sulfite salt in an amount of 0.1 to 20 times the amount of the peroxide.

The amount of the water-soluble radical polymerization initiator to be added is not particularly limited, and may be at least an amount (for example, several ppm relative to the concentration of water) at which the polymerization rate does not significantly decrease at one time, sequentially or continuously at the initial stage of polymerization. The upper limit is a range in which heat removal from the apparatus surface can be performed by using the polymerization reaction heat and the reaction temperature can be increased, and the upper limit is more preferably a range in which the polymerization reaction heat can be removed from the apparatus surface.

The amount of the polymerization initiator to be added is preferably an amount equivalent to 0.1ppm or more, more preferably an amount equivalent to 1.0ppm or more, and further preferably an amount equivalent to 100ppm or less, more preferably an amount equivalent to 10ppm or less, with respect to the aqueous medium, from the viewpoint of easy acquisition of the above-mentioned physical properties.

For example, when polymerization is carried out at a low temperature of 30 ℃ or lower, a redox initiator in which an oxidizing agent and a reducing agent are combined is preferably used as the polymerization initiator. Examples of the oxidizing agent include persulfates, organic peroxides, potassium permanganate, manganese triacetate, ammonium cerium nitrate, bromates, and the like. Examples of the reducing agent include sulfite, bisulfite, bromate, diimine, and oxalic acid. Examples of the persulfate include ammonium persulfate and potassium persulfate. The sulfite may be sodium sulfite or ammonium sulfite. In order to increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the combination of redox initiators. Copper salts include copper (II) sulfate, and iron salts Include Iron (II) sulfate.

The redox initiator is preferably selected from the group consisting of permanganate or a salt thereof, persulfate, manganese triacetate, cerium (IV) salt, and bromate or a salt thereof, and the reducing agent is selected from the group consisting of dicarboxylic acid or a salt thereof, and diimine.

More preferably, the oxidizing agent is permanganate or a salt thereof, persulfate, or bromate or a salt thereof, and the reducing agent is dicarboxylic acid or a salt thereof.

Examples of the redox initiator include combinations of potassium permanganate/oxalic acid, potassium permanganate/ammonium oxalate, manganese triacetate/oxalic acid, manganese triacetate/ammonium oxalate, ceric ammonium nitrate/oxalic acid, ceric ammonium nitrate/ammonium oxalate, and the like.

In the case of using a redox initiator, either one of the oxidizing agent and the reducing agent may be charged into the polymerization vessel in advance, and then the other may be continuously or intermittently added to initiate polymerization. For example, in the case of using potassium permanganate/ammonium oxalate, it is preferable to charge ammonium oxalate into a polymerizer and continuously add potassium permanganate thereto.

In the redox initiator of the present specification, the term "potassium permanganate/ammonium oxalate" refers to a combination of potassium permanganate and ammonium oxalate. The same applies to other compounds.

The redox initiator is particularly preferably a combination of an oxidizing agent as a salt and a reducing agent as a salt.

For example, the oxidizing agent as the above-mentioned salt is more preferably at least 1 selected from the group consisting of persulfates, permanganates, cerium (IV) salts and bromates, still more preferably permanganates, particularly preferably potassium permanganate.

The reducing agent as the above-mentioned salt is more preferably at least 1 selected from the group consisting of oxalate, malonate, succinate, glutarate and bromate, further preferably oxalate, and particularly preferably ammonium oxalate.

The redox initiator is preferably at least 1 selected from the group consisting of potassium permanganate/oxalic acid, potassium permanganate/ammonium oxalate, potassium bromate/ammonium sulfite, manganese triacetate/ammonium oxalate and cerium ammonium nitrate/ammonium oxalate, more preferably at least 1 selected from the group consisting of potassium permanganate/oxalic acid, potassium permanganate/ammonium oxalate, potassium bromate/ammonium sulfite and cerium ammonium nitrate/ammonium oxalate, and still more preferably potassium permanganate/oxalic acid.

In the case of using a redox initiator, the oxidizing agent and the reducing agent may be added at once in the initial stage of polymerization, the reducing agent may be added at once in the initial stage of polymerization and the oxidizing agent may be added continuously, the oxidizing agent may be added at once in the initial stage of polymerization and the reducing agent may be added continuously, or both the oxidizing agent and the reducing agent may be added continuously.

In the case where one of the above redox polymerization initiators is added at the initial stage of polymerization and the other is continuously added, the rate of slow addition is preferably decreased, and further, it is preferable that the polymerization is stopped during the polymerization, and it is preferable that 20 to 40 mass% of the total TFE consumed in the polymerization reaction be consumed before the termination of the addition.

When a redox initiator is used as the polymerization initiator, the amount of the oxidizing agent to be added is preferably 0.1ppm or more, more preferably 0.3ppm or more, still more preferably 0.5ppm or more, still more preferably 1.0ppm or more, particularly preferably 5ppm or more, particularly preferably 10ppm or more, and further preferably 10000ppm or less, more preferably 1000ppm or less, still more preferably 100ppm or less, still more preferably 10ppm or less, relative to the aqueous medium. The amount of the reducing agent to be added is preferably 0.1ppm or more, more preferably 1.0ppm or more, still more preferably 3ppm or more, still more preferably 5ppm or more, particularly preferably 10ppm or more, and further preferably 10000ppm or less, more preferably 1000ppm or less, still more preferably 100ppm or less, still more preferably 10ppm or less.

In the case of using a redox initiator in the emulsion polymerization, the polymerization temperature is preferably 100℃or lower, more preferably 95℃or lower, and still more preferably 90℃or lower. The temperature is preferably 10℃or higher, more preferably 20℃or higher, and still more preferably 30℃or higher.

As the polymerization initiator, a water-soluble radical polymerization initiator and a redox initiator are preferable from the viewpoints of improving the adhesion, the electrode strength and the flexibility of the electrode.

The aqueous medium is a reaction medium for conducting polymerization, and is a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and a non-fluorinated organic solvent such as alcohol, ether, ketone, and/or a fluorinated organic solvent having a boiling point of 40 ℃ or less.

In the emulsion polymerization, a nucleating agent, a chain transfer agent, a buffer, a pH adjuster, a stabilization aid, a dispersion stabilizer, a radical scavenger, a decomposition agent of a polymerization initiator, a dicarboxylic acid, and the like can be used as necessary.

For the purpose of adjusting the particle diameter, the emulsion polymerization is preferably carried out by adding a nucleating agent. The above-mentioned nucleating agent is preferably added before the polymerization reaction starts.

As the above-mentioned nucleating agent, a known nucleating agent can be used, and for example, at least 1 selected from the group consisting of fluorinated polyether, nonionic surfactant and chain transfer agent is preferable, and nonionic surfactant is more preferable.

Examples of the fluoropolyether include perfluoropolyether (PFPE) acid and salts thereof.

The perfluoropolyether (PFPE) acid or a salt thereof may have any chain structure in which oxygen atoms in the main chain of the molecule are separated by a saturated fluorocarbon group having 1 to 3 carbon atoms. In addition, 2 or more fluorocarbon groups may be present in the molecule. Representative structures have repeating units represented by the following formula.

(-CFCF₃-CF₂-O-)_n

(-CF₂-CF₂-CF₂-O-)_n

(-CF₂-CF₂-O-)_n-(-CF₂-O-)_m

(-CF₂-CFCF₃-O-)_n-(-CF₂-O-)_m

These structures are described by Kasai in J.Appl.Polymer Sci.57,797 (1995). As disclosed in this document, the above PFPE acid or a salt thereof may have a carboxylic acid group or a salt thereof at one or both ends. In addition, the above PFPE acid or a salt thereof may have a sulfonic acid group, a phosphonic acid group or a salt thereof at one end or both ends. In addition, the above PFPE acid or a salt thereof may have different groups at each end. With monofunctional PFPEs, the other end of the molecule is typically perfluorinated and may also contain hydrogen or chlorine atoms. The above-mentioned PFPE acid or a salt thereof has at least 2 ether oxygens, preferably has at least 4 ether oxygens, and even more preferably has at least 6 ether oxygens. Preferably at least one, more preferably at least two of such fluorocarbon groups, spaced apart by ether oxygen, have 2 or 3 carbon atoms. Even more preferably at least 50% of the fluorocarbon groups separating the ether oxygen have 2 or 3 carbon atoms. In addition, the PFPE acid or salt thereof preferably has at least 15 carbon atoms in total, for example, a preferred minimum value of n or n+m in the repeating unit structure is at least 5. More than 2 kinds of the above PFPE acids having an acid group at one end or both ends or salts thereof can be used in the production method of the present invention. The above-mentioned PFPE acid or salt thereof preferably has a number average molecular weight of less than 6000 g/mol.

The emulsion polymerization is preferably performed by adding a radical scavenger or a decomposition agent of a polymerization initiator, in order to further increase the molecular weight of PTFE and to improve the strength of the electrode mixture sheet. The radical scavenger or the decomposition agent of the polymerization initiator is preferably added after the polymerization reaction is started, preferably before 10 mass% or more, preferably 20 mass% or more, of the total TFE consumed in the polymerization reaction is polymerized, and is preferably added before 50 mass% or less, preferably 40 mass% or less, is polymerized. In the case of performing the pressure relief and repressurization described later, it is preferable to add the pressure relief and repressurization later.

As the radical scavenger, a compound which is added to a radical in the polymerization system or which does not have a reinitiation ability after chain transfer is used. Specifically, a compound having the following functions is used: chain transfer reaction with the primary radical or the growth radical is easy to occur, and then stable radicals which do not react with the monomer are generated, or addition reaction with the primary radical or the growth radical is easy to occur, so that stable radicals are generated.

The activity of substances commonly referred to as chain transfer agents is characterized by a chain transfer constant and a reinitiation efficiency, of which substances the reinitiation efficiency is substantially 0% are known as radical scavengers.

The radical scavenger is, for example, a compound having a chain transfer constant with TFE at a polymerization temperature greater than a polymerization rate constant and substantially zero reinitiation efficiency. By "substantially zero% reinitiation efficiency" is meant that the free radicals generated render the radical scavenger a stable free radical.

The chain transfer constant (Cs) (=chain transfer rate constant (kc)/polymerization rate constant (kp)) with TFE at the polymerization temperature is preferably more than 0.1, more preferably more than 0.5, still more preferably more than 1.0, still more preferably more than 5.0, and particularly preferably more than 10.

The radical scavenger is preferably at least 1 selected from the group consisting of aromatic hydroxyl compounds, aromatic amines, N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and copper chloride (CuCl ₂), for example.

Examples of the aromatic hydroxy compound include unsubstituted phenol, polyhydric phenol, salicylic acid, meta-salicylic acid, p-salicylic acid, gallic acid, naphthol, and the like.

Examples of the unsubstituted phenol include o-nitrophenol, m-nitrophenol, p-nitrophenol, o-aminophenol, m-aminophenol, p-aminophenol, and p-nitrosophenol. Examples of the polyhydric phenol include catechol, resorcinol, hydroquinone, pyrogallol, and naphthol resorcinol.

Examples of the aromatic amine include o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, and benzidine.

Examples of the quinone compound include o-benzoquinone, m-benzoquinone, p-benzoquinone, 1, 4-naphthoquinone, alizarin, and the like.

Examples of the thiocyanate include ammonium thiocyanate (NH ₄ SCN), potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN).

Among these, aromatic hydroxyl compounds are preferable, unsubstituted phenols or polyhydric phenols are more preferable, and hydroquinone is further preferable.

The amount of the radical scavenger added is preferably an amount equivalent to 3 to 500% by mole of the polymerization initiator concentration, from the viewpoint of appropriately reducing the standard specific gravity. The lower limit is more preferably 10% (by mol), still more preferably 15% (by mol). The upper limit is more preferably 400% (by mol), still more preferably 300% (by mol).

The decomposing agent for the polymerization initiator may be any compound capable of decomposing the polymerization initiator used, and is preferably at least 1 selected from the group consisting of sulfite, bisulfite, bromate, diimine, oxalic acid, oxalate, copper salt, and iron salt. The sulfite may be sodium sulfite or ammonium sulfite. Copper salts include copper (II) sulfate, and iron salts Include Iron (II) sulfate.

The amount of the decomposition agent to be added is preferably an amount equivalent to 3 to 500% by mole of the initiator concentration, from the viewpoint of appropriately reducing the standard specific gravity. The lower limit is more preferably 10% (by mol), still more preferably 15% (by mol). The upper limit is more preferably 400% (by mol), still more preferably 300% (by mol).

In order to reduce the amount of coagulum generated during the polymerization, the emulsion polymerization may be carried out in the presence of 5ppm to 500ppm of a dicarboxylic acid, preferably 10ppm to 200ppm of a dicarboxylic acid, relative to the aqueous medium. When the amount of the dicarboxylic acid is too small relative to the aqueous medium, there is a possibility that sufficient effects may not be obtained, and when the amount is too large, there is a possibility that chain transfer reaction occurs, and the obtained polymer becomes a polymer having a low molecular weight. The dicarboxylic acid is more preferably 150ppm or less. The dicarboxylic acid may be added before the start of the polymerization reaction or may be added during the polymerization.

The dicarboxylic acid is preferably represented by the general formula: HOOCRCOOH (wherein R represents an alkylene group having 1 to 5 carbon atoms), more preferably succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, and still more preferably succinic acid.

In the emulsion polymerization, the polymerization temperature and the polymerization pressure are appropriately determined according to the type of the monomer used, the molecular weight of the target PTFE, and the reaction rate. In general, the polymerization temperature is 5℃to 150℃and preferably 10℃or higher, more preferably 30℃or higher, and still more preferably 50℃or higher. Further, the temperature is more preferably 120℃or lower, and still more preferably 100℃or lower.

The polymerization pressure is 0.05 MPaG-10 MPaG. The polymerization pressure is more preferably 0.3MPaG or more, and still more preferably 0.5MPaG or more. Further, it is more preferably 5.0MPaG or less, and still more preferably 3.0MPaG or less.

In the case of using VDF as the modifying monomer, in the emulsion polymerization, the VDF concentration in the gas in the reactor at the start of the polymerization (at the time of adding the initiator) is preferably 0.001 mol% or more, more preferably 0.01 mol% or more, from the viewpoint of easily obtaining the above-mentioned physical properties. The concentration may be 15 mol% or less, preferably 6.0 mol% or less, more preferably 5.0 mol% or less, still more preferably 3.0 mol% or less, and particularly preferably 1.0 mol% or less. The VDF concentration may be maintained thereafter until the polymerization reaction is completed, or may be depressurized in the middle. The VDF is preferably fed at once before the start of polymerization, but a part may be added continuously or intermittently after the start of polymerization.

In the case of using VDF as the modifying monomer, in the emulsion polymerization, it is preferable that the pressure is not released until the polymerization is completed after the VDF is charged into the polymerization vessel. Thus, VDF can be left in the system until the polymerization is completed, and the strength of the electrode mixture sheet using the obtained PTFE can be further improved.

In the case of using HFP as the modifying monomer, in the emulsion polymerization, the concentration of HFP in the gas in the reactor at the start of the polymerization (at the time of adding the initiator) is preferably set to 0.01 to 3.0 mol% in view of the easiness of obtaining the above-mentioned physical properties. Further, the HFP concentration in the gas in the reactor at the time when 40 mass% of the total TFE consumed in the polymerization reaction is polymerized is preferably more than 0 mol% and 0.2 mol% or less. The HFP concentration is preferably maintained thereafter until the polymerization reaction is completed. The HFP may be added at one time before the start of polymerization, or may be added partially before the start of polymerization, and continuously or intermittently after the start of polymerization. By leaving HFP to the end of the polymerization reaction, the extrusion pressure is reduced although the strength of the electrode mixture sheet using the obtained PTFE is high.

In the case of using HFP as the modifying monomer, in the emulsion polymerization, it is preferable to perform pressure relief before 5 to 40 mass% of the total TFE consumed in the polymerization reaction is polymerized and then to perform repressurization only by TFE, in order to further improve the strength of the electrode mixture sheet using the obtained PTFE.

The pressure relief is preferably performed so that the pressure in the reactor becomes 0.2MPaG or less, more preferably 0.1MPaG or less, and even more preferably 0.05MPaG or less. It is preferable to perform the process so as to be 0.0MPaG or more.

The pressure relief and repressurization may be performed a plurality of times. The pressure relief may be performed to a reduced pressure using a vacuum pump.

In the case of using CTFE as the modifying monomer, in the emulsion polymerization, the CTFE concentration in the gas in the reactor at the start of the polymerization (at the time of adding the initiator) is preferably 0.001 mol% or more, more preferably 0.01 mol% or more, from the viewpoint of easily obtaining the above-mentioned physical properties. The concentration is preferably 3.0 mol% or less, more preferably 1.0 mol% or less. The CTFE concentration may be maintained thereafter until the polymerization reaction is completed, or may be depressurized in the middle. The CTFE is preferably added at one time before the start of polymerization, but a part may be added continuously or intermittently after the start of polymerization.

In the case of using CTFE as the modifying monomer, in the emulsion polymerization, it is preferable that after CTFE is charged into the polymerization vessel, pressure relief is not performed until the polymerization is completed. This can leave CTFE in the system until polymerization, and further improve the strength of the electrode mixture sheet using the obtained PTFE.

The precipitation in the step (B) may be performed by a known method.

In the step (C), the drying is usually performed by means of vacuum, high frequency, hot air, or the like while keeping the wet powder in a state of less flow, preferably in a state of standing. Friction between powders, especially at high temperatures, often has an adverse effect on fine powder PTFE. This is because such particles made of PTFE are easily fibrillated even when subjected to a small shearing force, and lose the state of an originally stable particle structure.

The drying temperature is preferably 300℃or lower, more preferably 250℃or lower, still more preferably 230℃or lower, still more preferably 210℃or lower, still more preferably 190℃or lower, and particularly preferably 170℃or lower, from the viewpoint of lowering the extrusion pressure. From the viewpoint of improvement in fracture strength, it is preferably 10 ℃ or higher, more preferably 100 ℃ or higher, still more preferably 150 ℃ or higher, still more preferably 170 ℃ or higher, still more preferably 190 ℃ or higher, and particularly preferably 210 ℃ or higher. In order to further increase the strength ratio, it is preferable to appropriately adjust the temperature range.

In the step (C), the wet powder obtained in the step (B) is preferably placed in a container having air permeability at the bottom surface and/or the side surface, and heat treatment is preferably performed at a temperature of 130 to 300 ℃ for a period of 2 hours or more. By performing the heat treatment under extremely limited conditions in this way, the fluorine-containing compound having a molecular weight of 1000 or less can be efficiently removed together with water, and the contents of the fluorine-containing compound and the water can be made to fall within the above-described ranges.

The temperature of the heat treatment in the step (C) is preferably 140 ℃ or higher, more preferably 150 ℃ or higher, still more preferably 160 ℃ or higher, still more preferably 180 ℃ or higher, still more preferably 200 ℃ or higher, particularly preferably 220 ℃ or higher, and still more preferably 280 ℃ or lower, still more preferably 250 ℃ or lower, in order to remove water and fluorine-containing compounds more efficiently.

The time of the heat treatment in the step (C) is preferably 5 hours or more, more preferably 10 hours or more, and even more preferably 15 hours or more, from the viewpoint of more efficiently removing moisture and fluorine-containing compounds. The upper limit is not particularly limited, and is, for example, preferably 100 hours, more preferably 50 hours, and still more preferably 30 hours.

The wind speed in the step (C) is preferably 0.01m/s or more, more preferably 0.03m/s or more, still more preferably 0.05m/s or more, and still more preferably 0.1m/s or more, from the viewpoint of more efficient removal of moisture and fluorine-containing compounds. Further, from the viewpoint of suppressing scattering of the powder, it is preferably 50m/s or less, more preferably 30m/s or less, and still more preferably 10m/s or less.

The heat treatment in the step (C) may be performed using an electric furnace or a steam furnace. For example, it is possible to use a parallel flow box type electric furnace, a vented conveyor type electric furnace, a belt type electric furnace, a radiation conveyor type electric furnace, a fluidized bed electric furnace, a vacuum electric furnace, a stirring type electric furnace, an air flow type electric furnace, a hot air circulation type electric furnace, or the like, or a steam furnace corresponding to the above (a device in which an electric furnace in the device name of each electric furnace is replaced with a steam furnace). In view of the capability of removing water more efficiently, a parallel-flow box type electric furnace, a vented conveyor type electric furnace, a belt type electric furnace, a fluidized bed electric furnace, a hot air circulation type electric furnace, and a steam furnace corresponding to the above (a device in which an electric furnace in the device name of each electric furnace is replaced with a steam furnace) are preferable.

The heat treatment in the step (C) is performed by disposing the wet powder in a container having air permeability on the bottom surface and/or the side surface. The container having the gas permeability on the bottom surface and/or the side surface is preferably made of metal such as stainless steel, as long as the container can withstand the heat treatment temperature.

As the container having the air-permeable bottom surface and/or side surface, a tray (basin) having the air-permeable bottom surface and/or side surface is preferable, and a tray (mesh tray) having the bottom surface and/or side surface made of a mesh is more preferable.

The mesh is preferably any one of a woven mesh and a punched mesh.

The mesh of the mesh is preferably 2000 μm or less (10 mesh or more according to ASTM standard), more preferably 595 μm or less (30 mesh or more), further preferably 297 μm or less (50 mesh or more), further more preferably 177 μm or less (80 mesh or more), particularly preferably 149 μm or less (100 mesh or more), and particularly preferably 74 μm or less (200 mesh or more). In addition, it is preferably 25 μm or more (500 mesh or less).

Examples of the weave method when the mesh is a woven mesh include plain weave, twill weave, flat weave, and diagonal weave.

The aperture ratio when the mesh is a punched mesh is preferably 10% or more, more preferably 20% or more, and still more preferably 30% or more. In addition, it is preferably 95% or less.

In the step (C), the amount of the wet powder to be placed is preferably 10g/cm ² or less, more preferably 8g/cm ² or less, still more preferably 5g/cm ² or less, particularly preferably 3g/cm ² or less, and further preferably 0.01g/cm ² or more, more preferably 0.05g/cm ² or more, still more preferably 0.1g/cm ² or more, from the viewpoint of more efficient removal of moisture and fluorine-containing compounds.

The moisture content of the wet powder subjected to the heat treatment in the step (C) is preferably 10 mass% or more, more preferably 20 mass% or more, still more preferably 30 mass% or more, and further preferably 150 mass% or less, more preferably 100 mass% or less, with respect to the wet powder, in view of more efficient removal of moisture and fluorine-containing compounds.

The PTFE powder of the present invention is used as a binder for an electrode. The PTFE powder of the present invention may be used alone or in combination with other materials (e.g., a polymer other than PTFE) in the binder for an electrode, and preferably, the PTFE powder of the present invention is used substantially alone, and more preferably, alone. The PTFE powder of the present invention is used substantially alone in such a manner that the amount of PTFE powder in the electrode binder falls within the range described below.

The present invention also provides an electrode binder consisting essentially of only PTFE powder, wherein the PTFE powder has a standard specific gravity of 2.200 or less and contains substantially no moisture.

The binder of the present invention contains a specific PTFE powder, and therefore can suppress gas generation in the battery cell and degradation of battery characteristics (for example, reduction in capacity during high-temperature storage), and can also improve electrode strength. Further, since the electrode active material does not substantially contain moisture, the electrode active material to be combined can be widely selected, and is advantageous in the production process. In addition, since the electrode active material can be mixed with the powder, an organic solvent is not required, and the process and cost for using the organic solvent can be reduced. In addition, the binder of the present invention has excellent adhesion to an active material, and thus can be used in a reduced amount.

As the PTFE powder in the binder of the present invention, the same PTFE powder as the PTFE powder of the present invention described above can be used, and the same preferable embodiment is also adopted.

The binder of the present invention is substantially composed of only the PTFE powder. This can significantly exert the effects of the PTFE powder. Substantially consisting of only the PTFE powder means that the content of the PTFE powder is 95.0 mass% or more with respect to the binder.

The content of the PTFE powder is preferably 98.0% by mass or more, more preferably 99.0% by mass or more, still more preferably 99.5% by mass or more, particularly preferably 99.9% by mass or more, and most preferably 99.95% by mass or more, relative to the binder.

The binder of the present invention is also preferably composed of only the PTFE powder.

The binder of the present invention preferably contains substantially no organic solvent. This can reduce the process and cost of using the organic solvent. Substantially not containing an organic solvent means that the content of the organic solvent with respect to the binder is 5 mass% or less.

The content of the organic solvent is preferably 3% by mass or less, more preferably 1% by mass or less, still more preferably 0.1% by mass or less, still more preferably 0.01% by mass or less, and particularly preferably 0.001% by mass or less.

The binder of the present invention is preferably in the form of a powder.

The binder of the present invention can be suitably used as a binder for an electrode of a secondary battery such as a lithium ion battery.

The present invention also provides an electrode mixture comprising the PTFE powder of the present invention or the electrode binder of the present invention and an electrode active material. When the electrode mixture of the present invention is used, an electrode that can suppress the generation of gas inside the battery cell and the deterioration of battery characteristics (for example, the reduction of capacity during high-temperature storage) can be obtained. In addition, the electrode strength can be improved. In addition, even if the amount of the binder is small, the electrode active material can be held.

Examples of the electrode active material include a positive electrode active material and a negative electrode active material.

The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release alkali metal ions, and for example, a material containing an alkali metal and at least 1 transition metal is preferable. Specific examples thereof include alkali metal-containing transition metal composite oxides, alkali metal-containing transition metal phosphate compounds, and conductive polymers. Among them, an alkali metal-containing transition metal composite oxide capable of generating a high voltage is particularly preferable as the positive electrode active material. Examples of the alkali metal ion include lithium ion, sodium ion, and potassium ion. In a preferred manner, the alkali metal ion can be lithium ion. That is, in this embodiment, the alkali metal ion secondary battery is a lithium ion secondary battery.

Examples of the alkali metal-containing transition metal composite oxide include

The formula: m _aMn_2-bM¹ _bO₄

(Wherein M is at least 1 metal selected from the group consisting of Li, na and K; 0.9.ltoreq.a; 0.ltoreq.b.ltoreq.1.5; M ¹ is at least 1 metal selected from the group consisting of Fe, co, ni, cu, zn, al, sn, cr, V, ti, mg, ca, sr, B, ga, in, si and Ge), a lithium manganese spinel composite oxide represented by the formula: MNi _1-cM² _cO₂

(Wherein M is at least 1 metal selected from the group consisting of Li, na and K; 0.ltoreq.c.ltoreq.0.5; and M ² is at least 1 metal selected from the group consisting of Fe, co, mn, cu, zn, al, sn, cr, V, ti, mg, ca, sr, B, ga, in, si and Ge), or a lithium-nickel composite oxide represented by the following formula (I)

The formula: MCo A _1-dM³ _dO₂

(Wherein M is at least 1 metal selected from the group consisting of Li, na and K; 0.ltoreq.d.ltoreq.0.5; and M ³ is at least 1 metal selected from the group consisting of Fe, ni, mn, cu, zn, al, sn, cr, V, ti, mg, ca, sr, B, ga, in, si and Ge). Among the above, M is preferably 1 metal selected from the group consisting of Li, na, and K, more preferably Li or Na, and even more preferably Li.

Among them, MCoO₂、MMnO₂、MNiO₂、MMn₂O₄、MNi_0.8Co_0.15Al_0.05O₂、, MNi _1/3Co_1/3Mn_1/3O₂, and the like are preferable from the viewpoint of providing a secondary battery having a high energy density and a high output, and a compound represented by the following general formula (3) is preferable.

MNi_hCo_iMn_jM⁵ _kO₂(3)

(Wherein M is at least 1 metal selected from the group consisting of Li, na and K, M ⁵ is at least 1 selected from the group consisting of Fe, cu, zn, al, sn, cr, V, ti, mg, ca, sr, B, ga, in, si and Ge, (h+i+j+k) =1.0, 0.ltoreq.h.ltoreq.1.0, 0.ltoreq.i.ltoreq.1.0, 0.ltoreq.j.ltoreq.1.5, 0.ltoreq.k.ltoreq.0.2.)

Examples of the alkali metal-containing transition metal phosphate compound include the following formula (4):

M_eM⁴ _f(PO₄)_g(4)

(wherein M is at least 1 metal selected from the group consisting of Li, na and K, M ⁴ is at least 1 selected from the group consisting of V, ti, cr, mn, fe, co, ni and Cu, 0.5.ltoreq.e.ltoreq.3, 1.ltoreq.f.ltoreq.2, 1.ltoreq.g.ltoreq.3.). Among the above, M is preferably 1 metal selected from the group consisting of Li, na, and K, more preferably Li or Na, and even more preferably Li.

The transition metal of the lithium-containing transition metal phosphate compound is preferably V, ti, cr, mn, fe, co, ni, cu, and specific examples thereof include iron phosphates such as LiFePO ₄、Li₃Fe₂(PO₄)₃、LiFeP₂O₇; cobalt phosphates such as LiCoPO ₄; and those obtained by replacing a part of the transition metal atoms that are the main body of these lithium transition metal phosphate compounds with other elements such as Al, ti, V, cr, mn, fe, co, li, ni, cu, zn, mg, ga, zr, nb, si. The lithium-containing transition metal phosphate compound preferably has an olivine-type structure.

As other positive electrode active materials, MFePO₄、MNi_0.8Co_0.2O₂、M_1.2Fe_0.4Mn_0.4O₂、MNi_0.5Mn_1.5O₂、MV₃O₆、M₂MnO₃ and the like can be mentioned. In particular, a positive electrode active material such as M ₂MnO₃、MNi_0.5Mn_1.5O₂ is preferable in that the crystal structure does not collapse even when the secondary battery is operated at a voltage exceeding 4.4V or a voltage exceeding 4.6V. Therefore, an electrochemical device such as a secondary battery using the positive electrode material containing the above-described positive electrode active material is preferable because the residual capacity is not easily reduced, the resistivity is not easily changed even when the device is stored at a high temperature, and the battery performance is not deteriorated even when the device is operated at a high voltage.

Examples of the other positive electrode active material include a solid solution material of M ₂MnO₃ and MM ⁶O₂ (where M is at least 1 metal selected from the group consisting of Li, na, and K, and M ⁶ is a transition metal such as Co, ni, mn, fe).

The solid solution material is, for example, an alkali metal manganese oxide represented by the general formula Mx [ Mn _(1-y)M⁷ _y]O_z ]. Here, M in the formula is at least 1 metal selected from the group consisting of Li, na, and K, and M ⁷ is composed of at least one metal element other than M and Mn, for example, contains one or two or more elements selected from the group consisting of Co, ni, fe, ti, mo, W, cr, zr and Sn. In the formula, the values of x, y and z are in the range of 1< x <2, 0.ltoreq.y <1, and 1.5< z < 3. Among them, a manganese-containing solid solution material based on Li ₂MnO₃ and having LiNiO ₂、LiCoO₂ dissolved therein, such as Li _1.2Mn_0.5Co_0.14Ni_0.14O₂, is preferable in that it is capable of providing an alkali metal ion secondary battery having a high energy density.

Further, when lithium phosphate is contained in the positive electrode active material, continuous charging characteristics are improved, which is preferable. The lithium phosphate is not limited in use, and the positive electrode active material is preferably used in combination with lithium phosphate. The lower limit of the amount of the lithium phosphate to be used is preferably 0.1 mass% or more, more preferably 0.3 mass% or more, still more preferably 0.5 mass% or more, and the upper limit is preferably 10 mass% or less, more preferably 8 mass% or less, still more preferably 5 mass% or less, relative to the total amount of the positive electrode active material and the lithium phosphate.

Examples of the conductive polymer include p-doped conductive polymers and n-doped conductive polymers. Examples of the conductive polymer include polyacetylene-based polymers, polyphenyl-based polymers, heterocyclic polymers, ionic polymers, ladder-shaped polymers, and network-shaped polymers.

The positive electrode active material obtained by this method may be used by attaching a material having a composition different from that of the positive electrode active material to the surface of the positive electrode active material. Examples of the surface-adhering substance include oxides such as alumina, silica, titania, zirconia, magnesia, calcia, boria, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; carbon; etc.

These surface-attached substances can be attached to the surface of the positive electrode active material by, for example, the following method: a method of dissolving or suspending in a solvent, impregnating the positive electrode active material with the solution, and drying the solution; a method in which a surface-attached substance precursor is dissolved or suspended in a solvent, impregnated into the positive electrode active material, and then reacted by heating or the like; a method of adding the active material to a positive electrode active material precursor and firing the active material precursor at the same time; etc. In the case of attaching carbon, a method of mechanically attaching carbon after the carbon is formed, for example, as activated carbon may be used.

The amount of the surface-adhering substance is preferably 0.1ppm or more, more preferably 1ppm or more, and still more preferably 10ppm or more, based on the mass of the positive electrode active material; the upper limit is preferably 20% or less, more preferably 10% or less, and still more preferably 5% or less, and the amount is used. The surface-adhering substance can suppress the oxidation reaction of the electrolyte on the surface of the positive electrode active material, thereby improving the battery life, and the effect cannot be sufficiently exhibited when the adhering amount is too small; if the amount of the binder is excessive, the ingress and egress of lithium ions are hindered, and thus the resistance may be increased.

Examples of the shape of the particles of the positive electrode active material include a block, a polyhedron, a sphere, an oval sphere, a plate, a needle, a column, and the like, which have been conventionally used. In addition, the primary particles may also agglomerate to form secondary particles.

The tap density of the positive electrode active material is preferably 0.5g/cm ³ or more, more preferably 0.8g/cm ³ or more, and still more preferably 1.0g/cm ³ or more. If the tap density of the positive electrode active material is less than the lower limit, the amount of the dispersion medium required for forming the positive electrode active material layer increases, the amount of the conductive material and the binder required increases, and the filling rate of the positive electrode active material in the positive electrode active material layer may be limited, and the battery capacity may be limited. By using a composite oxide powder having a high tap density, a high-density positive electrode active material layer can be formed. The higher the tap density, the better, but there is no particular upper limit, but if too large, the diffusion of lithium ions mediated by the electrolyte in the positive electrode active material layer becomes the rate-limiting, since the load characteristics tend to be easily lowered, the upper limit is preferably 4.0g/cm ³ or less, more preferably 3.7g/cm ³ or less, and still more preferably 3.5g/cm ³ or less.

The tap density was obtained by charging 5 to 10g of positive electrode active material powder into a 10ml glass cylinder, and obtaining the powder filling density (tap density) g/cm ³ when the powder was oscillated 200 times with a stroke of about 20 mm.

The median diameter d50 of the particles of the positive electrode active material (secondary particle diameter in the case where the primary particles are aggregated to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, still more preferably 0.8 μm or more, most preferably 1.0 μm or more, and further preferably 30 μm or less, more preferably 27 μm or less, still more preferably 25 μm or less, and most preferably 22 μm or less. If it is less than the above lower limit, a high tap density product may not be obtained; if the upper limit is exceeded, the diffusion of lithium in the particles takes time, and therefore, there are problems such as degradation of battery performance, or streaking when the active material, the conductive material, the binder, and the like are prepared into a slurry by using a solvent and applied in a film form in the production of a positive electrode of a battery. Here, by mixing two or more kinds of the above-mentioned positive electrode active materials having different median diameters d50, the filling property at the time of positive electrode production can be further improved.

The median diameter d50 is measured by a known laser diffraction/scattering particle size distribution measuring apparatus. LA-920 manufactured by HORIBA was used as a particle size distribution meter, and a 0.1 mass% aqueous solution of sodium hexametaphosphate was used as a dispersion medium for measurement, and after ultrasonic dispersion for 5 minutes, the measurement refractive index was set to 1.24 for measurement.

When the primary particles are aggregated to form secondary particles, the average primary particle diameter of the positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, still more preferably 0.2 μm or more, and the upper limit is preferably 5 μm or less, more preferably 4 μm or less, still more preferably 3 μm or less, and most preferably 2 μm or less. If the upper limit is exceeded, it is difficult to form spherical secondary particles, which adversely affects the powder filling property or greatly reduces the specific surface area, and therefore the possibility of lowering the battery performance such as the output characteristics may be increased. Conversely, if the temperature is lower than the lower limit, the crystallization is usually not developed, and thus there is a possibility that the charge/discharge reversibility is poor.

The average primary particle diameter is measured by observation using a Scanning Electron Microscope (SEM). Specifically, in a photograph at 10000 times magnification, the longest value of a slice taken along a horizontal straight line from the left and right boundary lines of the primary particles is obtained for any 50 primary particles, and the average value is obtained, thereby obtaining the primary particle diameter.

The BET specific surface area of the positive electrode active material is preferably 0.1m ²/g or more, more preferably 0.2m ²/g or more, still more preferably 0.3m ²/g or more, and the upper limit is preferably 50m ²/g or less, more preferably 40m ²/g or less, still more preferably 30m ²/g or less. If the BET specific surface area is less than this range, the battery performance tends to be lowered; when the BET specific surface area is larger than this range, the tap density is difficult to increase, and the coatability in forming the positive electrode active material layer may be easily problematic.

The BET specific surface area is defined as follows: the BET specific surface area is defined by a value obtained by predrying a sample at 150℃for 30 minutes under a nitrogen flow using a surface area meter (for example, a fully automatic surface area measuring apparatus manufactured by Dagaku Kogyo Co., ltd.), and then measuring by a nitrogen adsorption BET single point method using a nitrogen helium mixed gas accurately adjusted to a relative pressure value of nitrogen with respect to atmospheric pressure of 0.3.

In the case of the secondary battery of the present invention used as a large lithium ion secondary battery for a hybrid vehicle or a dispersion power source, the particles of the positive electrode active material are preferably composed mainly of secondary particles because of the high output required. The particles of the positive electrode active material preferably have an average particle diameter of 40 μm or less in the secondary particles and contain 0.5 to 7.0% by volume of fine particles having an average primary particle diameter of 1 μm or less. By containing fine particles having an average primary particle diameter of 1 μm or less, the contact area with the electrolyte increases, and lithium ion diffusion between the electrode mixture and the electrolyte can be further accelerated, as a result, the output performance of the battery can be improved.

As a method for producing the positive electrode active material, a method common to a method for producing an inorganic compound is used. In particular, various methods are considered for producing spherical or ellipsoidal active materials, and examples thereof include the following methods: the active material is obtained by dissolving or pulverizing a raw material of a transition metal in a solvent such as water, adjusting the pH with stirring, preparing a spherical precursor, recovering the precursor, drying the precursor as necessary, adding a Li source such as LiOH or Li ₂CO₃、LiNO₃, and firing the mixture at a high temperature.

In order to produce the positive electrode, the positive electrode active material may be used alone, or 2 or more kinds of different compositions may be used in combination in any combination or ratio. Preferable combinations in this case include a ternary combination of LiCoO ₂ and LiNi _0.33Co_0.33Mn_0.33O₂, a combination of LiCoO ₂ and LiMn ₂O₄, or a combination of substitution of a part of Mn with another transition metal, or a combination of LiFePO ₄ and LiCoO ₂, or a combination of substitution of a part of Co with another transition metal, or the like.

The content of the positive electrode active material is preferably 50 to 99.5% by mass, more preferably 80 to 99% by mass, of the positive electrode mixture, from the viewpoint of high battery capacity. The content of the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. The upper limit is preferably 99 mass% or less, more preferably 98 mass% or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the capacitance may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

The negative electrode active material is not particularly limited, and examples thereof include materials containing carbonaceous materials such as lithium metal, artificial graphite, graphite carbon fiber, resin-fired carbon, thermally decomposed vapor grown carbon, coke, mesophase Carbon Microsphere (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon fiber, vapor grown carbon fiber, natural graphite, and hardly graphitizable carbon, silicon-containing compounds such as silicon and silicon alloy, and a mixture of at least 2 kinds of Li ₄Ti₅O₁₂. Among them, a substance or a silicon-containing compound containing at least a part of a carbonaceous material can be particularly preferably used.

The negative electrode active material used in the present invention preferably contains silicon in constituent elements. By including silicon in the constituent elements, a high-capacity battery can be manufactured.

As the material containing silicon, silicon particles, particles having a structure in which fine particles of silicon are dispersed in a silicon-based compound, silicon oxide particles represented by the general formula SiOx (0.5.ltoreq.x.ltoreq.1.6), or a mixture thereof are preferable. By using these materials, a negative electrode mixture for a lithium ion secondary battery, which has higher initial charge/discharge efficiency, high capacity, and excellent cycle characteristics, is obtained.

The silicon oxide in the present invention is a generic term for amorphous silicon oxide, and the silicon oxide before disproportionation is represented by the general formula SiOx (0.5.ltoreq.x.ltoreq.1.6). x is preferably 0.8.ltoreq.x <1.6, more preferably 0.8.ltoreq.x <1.3. The silicon oxide can be obtained, for example, by heating a mixture of silicon dioxide and metallic silicon and cooling and precipitating the produced silicon monoxide gas.

Particles having a structure in which fine particles of silicon are dispersed in a silicon-based compound can be obtained, for example, as follows: a method in which fine particles of silicon are mixed with a silicon-based compound and the mixture is fired; the silica particles before disproportionation represented by the general formula SiOx are subjected to a heat treatment at 400 ℃ or higher, preferably 800 to 1,100 ℃ in an inert non-oxidizing atmosphere such as argon, and subjected to a disproportionation reaction, whereby the silica particles can be obtained. In particular, a material obtained by the latter method is preferable because crystallites of silicon are uniformly dispersed. The size of the silicon nanoparticles can be made to be 1nm to 100nm by the above disproportionation reaction. The silicon oxide in the particles having a structure in which silicon nanoparticles are dispersed in silicon oxide is preferably silicon dioxide. It was confirmed by a transmission electron microscope that silicon nanoparticles (crystals) were dispersed in amorphous silicon oxide.

The physical properties of the particles containing silicon can be appropriately selected according to the target composite particles. For example, the average particle diameter is preferably 0.1 μm to 50. Mu.m, and the lower limit is more preferably 0.2 μm or more, and still more preferably 0.5 μm or more. The upper limit is more preferably 30 μm or less, and still more preferably 20 μm or less. The average particle diameter is expressed as a weight average particle diameter in particle size distribution measurement by a laser diffraction method.

The BET specific surface area is preferably 0.5m ²/g～100m²/g, more preferably 1m ²/g～20m²/g. When the BET specific surface area is 0.5m ²/g or more, there is no possibility that the adhesiveness at the time of application to an electrode is lowered and the battery characteristics are lowered. When the ratio is 100m ²/g or less, the proportion of silica on the particle surface becomes large, and the battery capacity does not decrease when the material is used as a negative electrode material for a lithium ion secondary battery.

The above-mentioned silicon-containing particles were carbon-coated to impart conductivity, and improvement in battery characteristics was observed. Examples of the method for imparting conductivity include a method of mixing with particles having conductivity such as graphite, a method of coating the surface of the particles containing silicon with a carbon coating, and a method of combining both, preferably a method of coating with a carbon coating, and more preferably a method of performing Chemical Vapor Deposition (CVD).

In order to increase the capacity of the electrode mixture obtained, the content of the negative electrode active material in the electrode mixture is preferably 40 mass% or more, more preferably 50 mass% or more, and particularly preferably 60 mass% or more. The upper limit is preferably 99 mass% or less, more preferably 98 mass% or less.

The electrode mixture of the present invention preferably further comprises a conductive auxiliary agent.

As the above-mentioned conductive auxiliary agent, a known conductive material can be arbitrarily used. Specific examples thereof include metallic materials such as copper and nickel, graphite (graphite) such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black, and carbon materials such as needle coke, carbon nanotubes, fullerenes and amorphous carbon such as VGCF. The number of these may be 1 alone, or 2 or more may be used in any combination and ratio.

The conductive additive is used so that it is contained in the electrode mixture in an amount of usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and in addition, it is usually 50% by mass or less, preferably 30% by mass or less, more preferably 15% by mass or less. If the content is less than this range, the conductivity may be insufficient. Conversely, if the content exceeds this range, the battery capacity may be reduced.

The electrode mix of the present invention may further comprise a thermoplastic resin. Examples of the thermoplastic resin include polyvinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, and polyethylene oxide. The number of the components may be 1 alone, or 2 or more components may be combined in any combination and ratio.

The proportion of the thermoplastic resin to the electrode active material is usually 0.01 mass% or more, preferably 0.05 mass% or more, more preferably 0.10 mass% or more, and is usually 3.0 mass% or less, preferably 2.5 mass% or less, more preferably 2.0 mass% or less. By adding the thermoplastic resin, the mechanical strength of the electrode can be improved. If the amount exceeds this range, the proportion of the electrode active material in the electrode mixture may decrease, which may cause a problem of a decrease in the capacity of the battery or an increase in the resistance between the active materials.

In the electrode mixture of the present invention, the content of the binder may be 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and may be 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, more preferably 10% by mass or less, particularly preferably 5% by mass or less, and most preferably 3% by mass, relative to the electrode mixture. If the binder ratio is too low, the electrode mixture active material may not be sufficiently held, and the mechanical strength of the electrode mixture sheet may be insufficient, resulting in deterioration of battery performance such as cycle characteristics. On the other hand, if the binder ratio is too high, the battery capacity and conductivity may be reduced. The binder of the present invention has excellent adhesion, and therefore can sufficiently hold an electrode active material even in a small amount.

In the electrode mixture of the present invention, the binder component preferably consists essentially of only the PTFE powder, and more preferably consists of only the PTFE powder. The binder component being substantially composed of only the PTFE powder means that the content of the PTFE powder in the binder component constituting the electrode mixture is 95.0 mass% or more with respect to the binder component. The content of the PTFE powder is preferably 98.0% by mass or more, more preferably 99.0% by mass or more, still more preferably 99.5% by mass or more, particularly preferably 99.9% by mass or more, and most preferably 99.95% by mass or more, relative to the binder component.

The electrode mixture of the present invention is preferably in the form of a sheet.

The electrode mixture of the present invention can be suitably used as an electrode mixture for a secondary battery. In particular, the electrode mixture of the present invention is suitable for lithium ion secondary batteries. When the electrode mixture of the present invention is used in a secondary battery, it is usually used in a sheet form.

Hereinafter, an example of a specific method for manufacturing an electrode mixture sheet including an electrode mixture is shown. The electrode mixture sheet can be obtained by a production method comprising the steps of: a step (1) of mixing a raw material composition containing an electrode active material and a binder, and optionally a conductive auxiliary agent; a step (2) of molding the raw material composition obtained in the step (1) into a block; and (3) rolling the bulk raw material composition obtained in the step (2) into a sheet.

In the step (1) of mixing the raw material composition, the raw material composition is simply mixed with the electrode active material, the binder, and the like, and is not in a fixed shape. Specific examples of the mixing method include a method of mixing using a W-type mixer, a V-type mixer, a drum-type mixer, a ribbon mixer, a conical screw mixer, a single screw mixer, a twin screw mixer, a mixer mill, a stirrer mixer, a planetary mixer, and the like.

In the step (1), the binder mixing condition is preferably 1000rpm or less. The speed is preferably in the range of 10rpm or more, more preferably 15rpm or more, still more preferably 20rpm or more, and further preferably 900rpm or less, more preferably 800rpm or less, still more preferably 700rpm or less. If the ratio is less than the above range, the mixing takes time, which affects productivity. If the amount exceeds the above range, fibrillation proceeds excessively, and there is a possibility that the electrode mixture sheet is inferior in strength and flexibility.

In the step (2), the step of molding into a block means that the raw material composition is 1 block. Specific methods for molding the block include extrusion molding, compression molding, and the like. The "block" is not particularly limited as long as it is in the form of 1 block, and includes a rod-like, sheet-like, spherical, cube-like, or the like.

Specific rolling methods in the step (3) include rolling by a roll press, a platen press, a calender roll, and the like.

Further, it is preferable to have the step (4) after the step (3): the resulting rolled sheet was rolled into a thinner sheet shape with a larger load applied thereto. It is also preferable to repeat the step (4). Thus, the rolled sheet is not thinned at a time, but rolled in stages, whereby the flexibility is further improved. The number of the steps (4) is preferably 2 to 10 times, more preferably 3 to 9 times. Specific examples of the rolling method include the following: 2 or more rolls are rotated, and the sheet is rolled therebetween, thereby being processed into a thinner sheet shape.

In addition, from the viewpoint of adjusting the fibril diameter, it is preferable to have the step (5) after the step (3) or the step (4): coarsely crushing the rolled sheet, then forming the crushed sheet into a block again, and rolling the block into a sheet. It is also preferable to repeat the step (5). The number of the steps (5) is preferably 1 to 12 times, more preferably 2 to 11 times.

In the step (5), specific methods for coarsely crushing the rolled sheet and molding the crushed sheet into a block include a method of folding the sheet, a method of molding the sheet into a rod or film sheet shape, a method of chip formation, and the like. In the present invention, "coarse crushing" means that the rolled sheet obtained in the step (3) or the step (4) is changed to another form for the purpose of being rolled into a sheet shape in the next step, and includes a case where the rolled sheet is simply folded.

The step (4) may be performed after the step (5), or may be repeated. In addition, the uniaxial stretching or biaxial stretching may be performed in the steps (2) or (3), (4) and (5). The fibril diameter may be adjusted according to the degree of coarse pulverization in step (5).

In the above steps (3), (4) and (5), the rolling reduction is preferably 10% or more, more preferably 20% or more, and the rolling reduction is preferably 80% or less, more preferably 65% or less, more preferably 50% or less. If the number of times of rolling is smaller than the above range, the time is taken as the number of times of rolling increases, which affects productivity. If the amount exceeds the above range, fibrillation proceeds excessively, and there is a possibility that the electrode mixture sheet is inferior in strength and flexibility. The rolling percentage referred to herein means a reduction in the thickness of the sample after the processing relative to the thickness before the rolling processing. The sample before rolling may be a bulk raw material composition or a sheet-like raw material composition. The thickness of the sample is the thickness in the direction in which the load is applied during rolling.

The electrode mixture sheet may be suitably produced by a production method comprising:

Step (a): a step of mixing the powder component with a binder to form an electrode mixture; and

Step (b): a step of producing a sheet by calendaring or extrusion molding the electrode mixture,

The step (a) of mixing includes:

(a1) Homogenizing the powder component and the binder to obtain a powder;

(a2) And (c) a step of preparing an electrode mixture by mixing the powdery raw material mixture obtained in the step (a 1).

For example, PTFE has two transition temperatures at about 19 ℃ and about 30 ℃. When the temperature is less than 19 ℃, PTFE can be easily mixed while maintaining the shape. However, if the temperature exceeds 19 ℃, the structure of the PTFE particles becomes loose and more sensitive to mechanical shearing. At temperatures exceeding 30 ℃, a higher degree of fibrillation occurs.

Therefore, the homogenization of (a 1) is preferably carried out at a temperature of 19℃or less, preferably 0℃to 19 ℃.

That is, in such (a 1), it is preferable to homogenize the mixture while suppressing fibrillation.

The mixing in the next step (a 2) is preferably carried out at a temperature of 30 ℃ or higher to promote fibrillation.

The step (a 2) is preferably performed at a temperature of 30℃to 150℃and more preferably 35℃to 120℃and still more preferably 40℃to 80 ℃.

In one embodiment, the calendering or extrusion of step (b) above is performed at a temperature between 30 ℃ and 150 ℃, preferably between 35 ℃ and 120 ℃, more preferably between 40 ℃ and 100 ℃.

The mixing in the step (a) is preferably performed while applying a shearing force.

Specific examples of the mixing method include a method of mixing using a W-type mixer, a V-type mixer, a drum-type mixer, a ribbon mixer, a conical screw mixer, a single screw mixer, a twin screw mixer, a mixer mill, a mixer, a planetary mixer, a Henschel mixer, a high-speed mixer, and the like.

The mixing conditions may be appropriately set in terms of the rotational speed and the mixing time. For example, the rotation speed is preferably 15000rpm or less. The speed is preferably 10rpm or more, more preferably 1000rpm or more, still more preferably 3000rpm or more, and the speed is preferably 12000rpm or less, more preferably 11000rpm or less, still more preferably 10000 rpm. If the ratio is less than the above range, the mixing takes time, which affects productivity. If the amount exceeds the above range, fibrillation proceeds excessively, and the electrode mixture sheet may have poor strength.

In the step (a 1), the shearing force is preferably weaker than that in the step (a 2).

In the step (a 2), the raw material composition preferably contains no liquid solvent, but a small amount of lubricant may be used. That is, a lubricant may be added to the powdery raw material mixture obtained in the step (a 1) to prepare a paste.

The lubricant is not particularly limited, and examples thereof include water, ether compounds, alcohols, ionic liquids, carbonates, aliphatic hydrocarbons (low polar solvents such as heptane and xylene), isoparaffinic compounds, petroleum fractions (gasoline (C4-C10), naphtha (C4-C11), lamp oil/paraffin (C10-C16), and mixtures thereof.

The moisture content of the lubricant is preferably 1000ppm or less.

By making the moisture content 1000ppm or less, it is preferable in terms of reducing deterioration of the electrochemical device. The moisture content is more preferably 500ppm or less.

In the case of using the above lubricant, a low-polarity solvent such as heptane or xylene, or an ionic liquid is particularly preferable.

In the case of using the above lubricant, the amount thereof may be 5.0 parts by weight to 35.0 parts by weight, preferably 10.0 parts by weight to 30.0 parts by weight, more preferably 15.0 parts by weight to 25.0 parts by weight, relative to the total weight of the composition to be supplied to the step (a 1).

The above-mentioned raw material composition preferably contains substantially no liquid medium. In the conventional electrode mixture forming method, a solvent for dissolving a binder is generally used to prepare a slurry in which a powder as an electrode mixture component is dispersed, and the slurry is applied and dried to prepare an electrode mixture sheet. In this case, a solvent that dissolves the binder is used. However, the conventionally used solvent capable of dissolving the binder resin is limited to a specific solvent such as butyl butyrate. These react with the solid electrolyte and degrade the solid electrolyte, which may cause degradation of the battery performance. In addition, in the case of a low-polarity solvent such as heptane, the binder resin to be dissolved is very limited, and the flash point may be low, and the operation may become complicated.

When the electrode mixture sheet is formed, a powdery binder having little water is used without using a solvent, and a battery having little degradation of the solid electrolyte can be manufactured. Further, in the above-described production method, an electrode mixture sheet containing a binder having a fine fibrous structure can be produced, and the burden of the production process can be reduced by not producing a slurry.

Step (b) is calendering or extrusion. Calendering and extrusion can be performed by a known method. This enables the electrode mixture sheet to be molded into a shape.

The step (b) preferably includes: (b1) A step of molding the electrode mixture obtained in the step (a) into a block; and (b 2) a step of calendaring or extrusion-molding the electrode mixture in a block form.

The formation of the electrode mixture into a block means that the electrode mixture was 1 block.

Specific methods for molding the block include extrusion molding, compression molding, and the like.

The "block" is not particularly limited as long as it is in the form of 1 block, and includes a rod-like, sheet-like, spherical, cube-like, or the like. The block preferably has a cross-sectional diameter or smallest dimension of 10000 μm or more. More preferably 20000 μm or more.

Specific examples of the method for rolling or extrusion molding in the step (b 2) include a method of rolling the electrode mixture using a roll press, a calender roll, or the like.

The step (b) is preferably performed at 30℃to 150 ℃. As described above, PTFE has a glass transition temperature around 30 ℃, and therefore is easily fibrillated at 30 ℃ or higher. Thus, the step (b) is preferably performed at such a temperature.

In addition, since a shearing force is applied to the rolling or extrusion, PTFE is fibrillated and molded.

After the step (b), a step (c) of applying a larger load to the obtained rolled sheet to roll the sheet into a thinner sheet shape is also preferable. It is also preferable to repeat the step (c). Thus, the rolled sheet is not thinned at a time, but rolled in stages, whereby the flexibility is further improved.

The number of the steps (c) is preferably 2 to 10 times, more preferably 3 to 9 times.

Specific examples of the rolling method include the following: 2 or more rolls are rotated, and the sheet is rolled therebetween, thereby being processed into a thinner sheet shape.

In addition, from the viewpoint of the tab strength, it is preferable to further include the step (d) after the step (b) or the step (c): coarsely crushing the rolled sheet, then forming the crushed sheet into a block again, and rolling the block into a sheet. It is also preferable to repeat the step (d). The number of the steps (d) is preferably 1 to 12 times, more preferably 2 to 11 times.

In the step (d), specific methods for coarsely crushing the rolled sheet and forming the crushed sheet into a block include a method of folding the rolled sheet, a method of forming the rolled sheet into a rod or film sheet, a method of forming the rolled sheet into a chip, and the like. In the present invention, "coarse crushing" means that the rolled sheet obtained in the step (b) or the step (c) is changed to another form for the purpose of rolling into a sheet shape in the next step, and includes a case where the rolled sheet is simply folded.

The step (c) may be performed after the step (d), or may be repeated.

In addition, the uniaxial stretching or biaxial stretching may be performed in the steps (a) or (b), (c) and (d).

The sheet strength may be adjusted according to the degree of coarse crushing in the step (d).

In the above steps (b), (c) and (d), the rolling reduction is preferably 10% or more, more preferably 20% or more, and the rolling reduction is preferably 80% or less, more preferably 65% or less, more preferably 50% or less. If the number of times of rolling is smaller than the above range, the time is taken as the number of times of rolling increases, which affects productivity. If the amount exceeds the above range, fibrillation proceeds excessively, and there is a possibility that the electrode mixture sheet is inferior in strength and flexibility.

The rolling percentage referred to herein means a reduction in the thickness of the sample after the processing relative to the thickness before the rolling processing. The sample before rolling may be a bulk raw material composition or a sheet-like raw material composition. The thickness of the sample is the thickness in the direction in which the load is applied during rolling.

The steps (c) to (d) are preferably performed at 30℃or higher, more preferably 60℃or higher. In addition, it is preferably carried out at 150℃or lower.

The electrode mixture sheet can be used as an electrode mixture sheet for a secondary battery. Either one of the negative electrode and the positive electrode can be produced. The electrode mixture sheet is particularly suitable for lithium ion secondary batteries.

The present invention also provides an electrode comprising the PTFE powder of the present invention or the binder for an electrode of the present invention, an electrode active material, and a current collector. The electrode of the present invention can suppress the generation of gas inside the battery cell and the deterioration of battery characteristics (for example, the reduction of capacity at the time of high-temperature storage). In addition, the strength was also excellent.

The electrode of the present invention may comprise the electrode mixture of the present invention (preferably, electrode mixture sheet) and a current collector.

The electrode of the present invention may be a positive electrode or a negative electrode.

The positive electrode is preferably composed of a current collector and an electrode mixture sheet containing the positive electrode active material. The materials of the current collector for the positive electrode may be: metals such as aluminum, titanium, tantalum, stainless steel, nickel, or alloys thereof; carbon materials such as carbon cloth and carbon paper. Among them, a metallic material, particularly aluminum or an alloy thereof is preferable.

Examples of the shape of the current collector include a metal foil, a metal cylinder, a metal coil, a metal plate, a metal mesh, a punched metal, and a foamed metal in the case of a metal material, and a carbon plate, a carbon thin film, and a carbon cylinder in the case of a carbon material. Among these, metal foil is preferable. The metal foil may be suitably formed into a net shape. The thickness of the metal foil is arbitrary, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and is usually 1mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the metal foil is thinner than this range, the strength required as a current collector may be insufficient. Conversely, if the metal foil is thicker than this range, the handleability may be impaired.

In addition, from the viewpoint of reducing the electrical contact resistance between the current collector and the positive electrode active material layer, it is also preferable to coat the surface of the current collector with a conductive auxiliary agent. Examples of the conductive auxiliary agent include carbon, noble metals such as gold, platinum, and silver.

The ratio of the thickness of the current collector to the thickness of the positive electrode mixture is not particularly limited, and the value of (the thickness of the positive electrode mixture on one side immediately before the injection of the electrolyte)/(the thickness of the current collector) is preferably 20 or less, more preferably 15 or less, most preferably 10 or less, and further preferably 0.5 or more, more preferably 0.8 or more, most preferably 1 or more. If the current exceeds this range, heat generation by joule heat may occur in the current collector during charge and discharge at a high current density. If the amount is less than this range, the volume ratio of the current collector to the positive electrode active material may increase, and the capacity of the battery may decrease.

The positive electrode may be produced by a conventional method. Examples of the method include a method of laminating the electrode mixture sheet and the current collector with an adhesive and vacuum drying the laminate.

The density of the positive electrode mixture sheet is preferably 3.00g/cm ³ or more, more preferably 3.10g/cm ³ or more, still more preferably 3.20g/cm ³ or more, and is preferably 3.80g/cm ³ or less, more preferably 3.75g/cm ³ or less, still more preferably 3.70g/cm ³ or less. If the amount exceeds this range, the permeability of the electrolyte to the vicinity of the current collector/active material interface may be reduced, and in particular, the charge-discharge characteristics at high current density may be reduced, and high output may not be obtained. If the amount is less than this range, the conductivity between active materials may decrease, and the battery resistance may increase, so that high output may not be obtained.

The area of the positive electrode mixture sheet is preferably larger than the outer surface area of the battery case, from the viewpoint of high output and improved stability at high temperature. Specifically, the total area of the electrode mixture of the positive electrode is preferably 15 times or more, more preferably 40 times or more, the area ratio of the total area of the electrode mixture to the surface area of the exterior of the secondary battery. The outer surface area of the battery case, in the case of a bottomed square shape, means the total area calculated from the length, width, and thickness dimensions of the case portion filled with the power generating element except for the protruding portion of the terminal. In the case of a bottomed cylindrical shape, it means that the housing portion filled with the power generating element except the protruding portion of the terminal is approximated to the geometric surface area of a cylinder. The sum of electrode mixture areas of the positive electrode refers to the geometric surface area of the positive electrode mixture layer facing the mixture layer containing the negative electrode active material, and in the structure in which the positive electrode mixture layer is formed on both surfaces via the current collector foil, the sum of areas calculated for the respective surfaces is referred to.

The thickness of the positive electrode is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the mixture layer obtained by subtracting the thickness of the metal foil of the current collector is preferably 10 μm or more, more preferably 20 μm or more, and further preferably 500 μm or less, more preferably 450 μm or less, with respect to one surface of the current collector as a lower limit.

In addition, a positive electrode having a substance having a composition different from that of the positive electrode attached to the surface of the positive electrode may be used. Examples of the surface-adhering substance include oxides such as alumina, silica, titania, zirconia, magnesia, calcia, boria, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; carbon; etc.

The negative electrode is preferably composed of a current collector and an electrode mixture sheet containing the negative electrode active material. Examples of the material of the negative electrode current collector include metals such as copper, nickel, titanium, tantalum, and stainless steel, and metal materials such as alloys thereof; carbon materials such as carbon cloth and carbon paper. Among them, a metallic material is preferable, and copper, nickel, or an alloy thereof is particularly preferable.

The negative electrode may be produced by a conventional method. Examples of the method include a method of laminating the electrode mixture sheet and the current collector with an adhesive and vacuum drying the laminate.

The density of the negative electrode mixture is preferably 1.3g/cm ³ or more, more preferably 1.4g/cm ³ or more, still more preferably 1.5g/cm ³ or more, and is preferably 2.0g/cm ³ or less, more preferably 1.9g/cm ³ or less, still more preferably 1.8g/cm ³ or less. If the amount exceeds this range, the permeability of the electrolyte to the vicinity of the current collector/active material interface may be reduced, and in particular, the charge-discharge characteristics at high current density may be reduced, and high output may not be obtained. If the amount is less than this range, the conductivity between active materials may decrease, and the battery resistance may increase, so that high output may not be obtained.

The thickness of the negative electrode is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the mixture layer obtained by subtracting the thickness of the metal foil of the current collector is preferably 10 μm or more, more preferably 20 μm or more, and further preferably 500 μm or less, more preferably 450 μm or less, with respect to one surface of the current collector as a lower limit.

The invention also provides a secondary battery with the electrode.

The secondary battery of the present invention may be a secondary battery using an electrolyte solution, or may be a solid-state secondary battery.

The secondary battery using the above-described electrolyte may use an electrolyte, a separator, or the like used in a known secondary battery. These will be described in detail below.

As the above-mentioned electrolytic solution, a nonaqueous electrolytic solution is preferably used. As the nonaqueous electrolytic solution, an electrolytic solution obtained by dissolving a known electrolyte salt in a known organic solvent for dissolving an electrolyte salt can be used.

The organic solvent for dissolving the electrolyte salt is not particularly limited, and known hydrocarbon solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ -butyrolactone, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and methylethyl carbonate can be used; 1 or 2 or more of fluorosolvents such as fluoroethylene carbonate, fluoroether and fluorinated carbonate.

Examples of the electrolyte salt include LiClO₄、LiAsF₆、LiBF₄、LiPF₆、LiN(SO₂CF₃)₂、LiN(SO₂C₂F₅)₂ and the like, and LiPF₆、LiBF₄、LiN(SO₂CF₃)₂、LiN(SO₂C₂F₅)₂ or a combination thereof is particularly preferable in view of good cycle characteristics.

The concentration of the electrolyte salt is preferably 0.8 mol/liter or more, and more preferably 1.0 mol/liter or more. The upper limit also depends on the organic solvent for dissolving the electrolyte salt, and is usually 1.5 mol/liter.

The secondary battery using the above electrolyte preferably further includes a separator. The material and shape of the separator are not particularly limited as long as the electrolyte is stable and the liquid retention property is excellent, and a known separator may be used. Among them, a porous sheet or a nonwoven fabric-like substance formed of a material stable to the above electrolyte, which is excellent in liquid retention using a resin, glass fiber, inorganic substance, or the like, is preferably used.

As the material of the resin and the glass fiber separator, for example, polyolefin such as polyethylene and polypropylene, aromatic polyamide, polytetrafluoroethylene, polyether sulfone, glass filter, and the like can be used. The polypropylene/polyethylene 2 film, polypropylene/polyethylene/polypropylene 3 film and the like may be used alone in 1 kind, or may be used in combination of 2 or more kinds in any combination and ratio. Among them, the separator is preferably a porous sheet or nonwoven fabric using polyolefin such as polyethylene or polypropylene as a raw material, in view of good permeability of electrolyte and good shutdown effect.

The thickness of the separator is arbitrary, and is usually 1 μm or more, preferably 5 μm or more, more preferably 8 μm or more, and is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less. If the separator is too thin compared with the above range, the insulation properties and mechanical strength may be lowered. In addition, if the thickness is too large in comparison with the above-mentioned range, battery performance such as rate characteristics may be lowered, and the energy density of the entire electrolyte battery may be lowered.

In the case of using a porous material such as a porous sheet or a nonwoven fabric as the separator, the porosity of the separator is arbitrary, and is usually 20% or more, preferably 35% or more, more preferably 45% or more, and is usually 90% or less, preferably 85% or less, more preferably 75% or less. If the porosity is too small compared with the above range, the film resistance tends to be large and the rate characteristics tend to be poor. If the amount of the polymer is too large, the mechanical strength of the separator tends to be low and the insulation tends to be low.

The average pore diameter of the separator is also arbitrary, and is usually 0.5 μm or less, preferably 0.2 μm or less, and is usually 0.05 μm or more. If the average pore diameter exceeds the above range, short-circuiting is likely to occur. If the amount is less than the above range, the film resistance may be increased and the rate characteristics may be reduced.

On the other hand, as the inorganic material, for example, an oxide such as alumina or silica, a nitride such as aluminum nitride or silicon nitride, a sulfate such as barium sulfate or calcium sulfate, or a material in a particle shape or a fiber shape is used.

As the form, a film-shaped substance such as a nonwoven fabric, a woven fabric, or a microporous film is used. In the case of the film shape, a film having a pore diameter of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm is preferably used. In addition to the above-described independent film shape, a separator in which a composite porous layer containing particles of the above-described inorganic substance is formed on the surface layer of the positive electrode and/or the negative electrode by a binder made of a resin may be used. For example, a porous layer is formed by using a fluororesin as a binder and alumina particles having a particle diameter of less than 1 μm at 90% on both sides of the positive electrode.

The electrode mixture group may be any of an electrode mixture group having a laminated structure in which the separator is interposed between the positive electrode and the negative electrode, and an electrode mixture group having a structure in which the positive electrode and the negative electrode are wound in a spiral shape with the separator interposed therebetween. The volume of the electrode mixture group is usually 40% or more, preferably 50% or more, and is usually 90% or less, preferably 80% or less, based on the internal volume of the battery (hereinafter referred to as the electrode mixture group occupancy).

If the electrode mixture group occupancy is smaller than the above range, the battery capacity may be reduced. If the amount exceeds the above range, the void space is small, and the battery temperature increases to expand the member, the vapor pressure of the liquid component of the electrolyte increases, the internal pressure increases, various characteristics such as charge-discharge repetition performance and high-temperature storage of the battery are lowered, and the gas release valve for releasing the internal pressure to the outside may be operated.

The current collecting structure is not particularly limited, and in order to more effectively improve the charge/discharge characteristics of high current density due to the electrolyte, it is preferable to use a structure that reduces the resistance of the wiring portion or the junction portion. When the internal resistance is reduced in this way, the effect of using the electrolyte can be particularly well exhibited.

When the electrode mixture group has the above-described laminated structure, it is preferable to use a structure in which metal core portions of the electrode mixture layers are bundled and welded to terminals. When the area of one electrode mixture is increased, the internal resistance is increased, and therefore, it is preferable to provide a plurality of terminals in the electrode mixture to reduce the resistance. In the case where the electrode mixture group has the above-described wound structure, a plurality of lead structures may be provided on the positive electrode and the negative electrode, respectively, and the lead structures may be bundled on the terminals, thereby reducing the internal resistance.

The material of the case is not particularly limited as long as it is stable to the electrolyte to be used. Specifically, nickel-plated steel plates, stainless steel, aluminum or aluminum alloy, magnesium alloy, and other metals are used; or a laminated film (laminated film) of a resin and an aluminum foil. From the viewpoint of weight reduction, a metal or a laminated film of aluminum or an aluminum alloy is preferably used.

Among the cases using metals, there are cases in which the seal structure is formed by welding metals to each other by laser welding, resistance welding, ultrasonic welding; or a shell with a riveted structure formed by using the metal through a resin gasket. Examples of the case using the laminate film include a case in which a sealing structure is formed by thermally bonding resin layers to each other. In order to improve the sealing property, a resin different from the resin used for the laminate film may be interposed between the resin layers. In particular, when the resin layer is thermally bonded to form a sealed structure by the current collecting terminal, it is preferable to use a resin having a polar group or a modified resin having a polar group introduced as the resin to be interposed therebetween, because the metal is bonded to the resin.

The shape of the secondary battery using the above electrolyte is arbitrary, and examples thereof include cylindrical, square, laminated, button-shaped, and large-sized. The shape and structure of the positive electrode, the negative electrode, and the separator may be changed and used according to the shape of each battery.

The solid-state secondary battery is preferably an all-solid-state secondary battery. The solid-state secondary battery is preferably a lithium ion battery, and is also preferably a sulfide-based all-solid-state secondary battery.

The solid-state secondary battery preferably includes a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode.

The solid electrolyte used in the mixture for a solid-state secondary battery may be a sulfide-based solid electrolyte or an oxide-based solid electrolyte. In particular, when a sulfide-based solid electrolyte is used, there is an advantage of having flexibility.

The sulfide-based solid electrolyte is not particularly limited, and any one or a mixture of two or more selected from Li₂S-P₂S₅、Li₂S-P₂S₃、Li₂S-P₂S₃-P₂S₅、Li₂S-SiS₂、LiI-Li₂S-SiS₂、LiI-Li₂S-P₂S₅、LiI-Li₂S-P₂O₅、LiI-Li₃PO₄-P₂S₅、LiI-Li₂S-SiS₂-P₂S₅、Li₂S-SiS₂-Li₄SiO₄、Li₂S-SiS₂-Li₃PO₄、Li₃PS₄-Li₄GeS₄、Li_3.4P_0.6Si_0.4S₄、Li_3.25P_0.25Ge_0.76S₄、Li_4-xGe_1-xP_xS₄(X＝0.6～0.8)、Li_4+yGe_1-yGa_yS₄(y＝0.2～0.3)、LiPSCl、LiCl、Li_7-x-2yPS_6-x-yCl_x(0.8≤x≤1.7、0<y≤-0.25x+0.5) and the like may be used.

The sulfide-based solid electrolyte preferably contains lithium. The sulfide-based solid electrolyte containing lithium is particularly preferable in view of electrochemical devices having a high energy density for solid-state batteries using lithium ions as a carrier.

The oxide-based solid electrolyte is preferably the following compound: contains oxygen atoms (O), has ion conductivity of metals belonging to group 1 or group 2 of the periodic table, and has electronic insulation.

Specific examples of the compound include at least one or more elements of Al, mg, ca, sr, V, nb, ta, ti, ge, in, sn, Li_xaLa_yaTiO₃[xa＝0.3～0.7、ya＝0.3～0.7](LLT)、Li_xbLa_ybZr_zbM^bb _mbO_nb(M^bb, xb 5.ltoreq.xb.ltoreq.10, yb 1.ltoreq.yb.ltoreq.4, zb 1.ltoreq.zb.ltoreq.4, mb 0.ltoreq.mb.ltoreq.2, nb 5.ltoreq.nb.ltoreq.20, C, S, al, si, ga, ge, in, sn, xc 0.ltoreq.xc.ltoreq.5, yc 0.ltoreq.yc.ltoreq.1, zc 0.ltoreq.zc.ltoreq.1, nc 0.ltoreq.nc.ltoreq.6), li _xd(Al,Ga)_yd(Ti,Ge)_zdSi_adP_mdO_nd (wherein 1.ltoreq.xd.ltoreq.3, 0.ltoreq.yd.ltoreq.2, 0.ltoreq.ad.ltoreq.2, 1.md.ltoreq.7, 3.ltoreq.nd.ltoreq.15), li _(3-2xe)M^ee _xeD^ee O (xe represents a number of 0 to 0.1 or less, M ^ee represents a valence metal atom. D ^ee represents a halogen atom or a combination )、Li_xfSi_yfO_zf(1≤xf≤5,0<yf≤3,1≤zf≤10)、Li_xgS_ygO_zg(1≤xg≤3,0<yg≤2,1≤zg≤10)、Li₃BO₃-Li₂SO₄、Li₂O-B₂O₃-P₂O₅、Li₂O-SiO₂、Li₆BaLa₂Ta₂O₁₂、Li₃PO_(4-3/2w)N_w(w of 2 or more halogen atoms satisfying w < 1), li _3.5Zn_0.25GeO₄ having a LISICON (lithium super ion conductor) type crystal structure, la _0.51Li_0.34TiO_2.94、La_0.55Li_0.35TiO₃ having a perovskite type crystal structure, LiTi₂P₃O₁₂、Li_1+xh+yh(Al,Ga)_xh(Ti,Ge)_2-xhSi_yhP_3-yhO₁₂( having a NASICON (sodium super ion conductor) type crystal structure, wherein 0.ltoreq.xh.ltoreq.1, 0.ltoreq.yh.ltoreq.1, li ₇La₃Zr₂O₁₂ (LLZ) having a garnet type crystal structure, and the like. In addition, ceramic materials in which LLZ is subjected to element substitution are also known. For example, LLZ-based ceramic materials in which LLZ is substituted with at least one element selected from the group consisting of Mg (magnesium) and a (a is at least one element selected from the group consisting of Ca (calcium), sr (strontium), and Ba (barium)) are also included. In addition, phosphorus compounds containing Li, P and O are also preferred. For example, lithium phosphate (Li ₃PO₄), liPON in which a part of oxygen in lithium phosphate is replaced with nitrogen, liPOD ¹(D¹ is at least one selected from Ti, V, cr, mn, fe, co, ni, cu, zr, nb, mo, ru, ag, ta, W, pt, au, and the like), and the like are given. In addition, preferably, liA ¹ON(A¹ is at least one kind selected from Si, B, ge, al, C, ga and the like) and the like can be used. Specific examples thereof include Li₂O-Al₂O₃-SiO₂-P₂O₅-TiO₂-GeO₂、Li₂O-Al₂O₃-SiO₂-P₂O₅-TiO₂.

The oxide-based solid electrolyte preferably contains lithium. The oxide-based solid electrolyte containing lithium is particularly preferable in view of electrochemical devices having a high energy density for solid-state batteries using lithium ions as a carrier.

The oxide-based solid electrolyte is preferably an oxide having a crystal structure. Oxides having a crystal structure are particularly preferred from the viewpoint of good Li ion conductivity. Examples of the oxide having a crystal structure include perovskite type (La _0.51Li_0.34TiO_2.94 and the like), NASICON type (Li _1.3Al_0.3Ti_1.7(PO₄)₃ and the like), garnet type (Li ₇La₃Zr₂O₁₂ (LLZ) and the like), and the like. Among them, NASICON type is preferable.

The volume average particle diameter of the oxide-based solid electrolyte is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.03 μm or more. The upper limit is preferably 100 μm or less, more preferably 50 μm or less. The average particle diameter of the oxide-based solid electrolyte particles was measured in the following order. The oxide-based solid electrolyte particles were diluted with water (heptane in the case of a water-labile substance) in a 20ml sample bottle to prepare a1 mass% dispersion. The diluted dispersion sample was irradiated with ultrasonic waves of 1kHz for 10 minutes, and immediately thereafter used in the test. Using this dispersion sample, 50 times of acquisition was performed at a temperature of 25℃using a measuring Dan Yingmin by a laser diffraction/scattering particle size distribution measuring apparatus LA-920 (manufactured by HORIBA corporation) to obtain a volume average particle diameter. Other detailed conditions and the like are described in "particle size analysis-dynamic light scattering method" in JISZ8828:2013, if necessary. For each 1 grade 5 samples were prepared and their average value was used.

The solid-state secondary battery may include a separator between the positive electrode and the negative electrode. Examples of the separator include porous films such as polyethylene and polypropylene; nonwoven fabrics made of resins such as polypropylene, and nonwoven fabrics such as glass fiber nonwoven fabrics.

The solid-state secondary battery may further include a battery case. The shape of the battery case is not particularly limited as long as the positive electrode, the negative electrode, the solid electrolyte layer, and the like can be accommodated, and specifically, cylindrical, square, button, laminated, and the like are included.

The solid-state secondary battery can be manufactured by, for example, stacking a positive electrode, a solid electrolyte sheet, and a negative electrode in this order and pressing them.

Examples

The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

The physical properties were measured by the following methods.

Average primary particle diameter

The PTFE aqueous dispersion was diluted with water until the solid content reached 0.15 mass%, and the transmittance of 550nm of the resulting diluted emulsion per unit length of the projected light and the number-basis length average particle diameter determined by measuring the alignment diameter using a transmission electron micrograph were measured to prepare a calibration curve. Using this calibration curve, the number average particle diameter was determined from the measured transmittance of 550nm of the projected light of each sample as the average primary particle diameter.

Apparent density of

The measurement was carried out in accordance with JIS K6892.

Average secondary particle diameter

The measurement was carried out in accordance with JIS K6891.

Standard Specific Gravity (SSG)

The determination was made by the in-water displacement method according to ASTM D792 using a sample formed according to ASTM D4895.

PMVE content

PTFE powder was dissolved at 370℃and ¹⁹ F-NMR was measured, and the signal from the obtained functional group was calculated based on the following formula.

PMVE content (mass%) = (664B/(300a+364b)) ×100

( A: total integrated value of CF ₂ signal occurring around-120 ppm and CF signal occurring around-136 ppm, B: integration value of CF ₃ signal from PMVE occurring around-54 ppm )

The chemical shift value was used when the peak top of the CF ₂ signal from the polymer main chain was set to-120 ppm.

CTFE content

A film disk was produced by compression molding of PTFE powder, and the film disk was obtained by multiplying the ratio of the absorbance of 957cm ^-1 to the absorbance of 2360cm ^-1 by 0.58 from the infrared absorbance obtained by FT-IR measurement of the film disk.

HFP content

A film disk was produced by compression molding PTFE powder, and the film disk was obtained by multiplying the ratio of the absorbance of 982cm ^-1 to the absorbance of 935cm ^-1 by 0.3 by the infrared absorbance obtained by FT-IR measurement.

RR100 extrusion pressure (extrusion pressure at compression ratio 100)

50G of PTFE powder and 10.25g of a hydrocarbon oil (trade name: isopar E, manufactured by Exxon Mobil Co.) as an extrusion aid were mixed in a polyethylene container for 3 minutes. The above mixture was filled into a cylinder of an extruder at room temperature (25.+ -. 2 ℃ C.), and a load of 0.47MPa was applied to a piston inserted into the cylinder and held for 1 minute. Then, the mixture was extruded from the hole at a punching speed of 18 mm/min. The ratio of the cross-sectional area of the cartridge to the cross-sectional area of the bore was 100. In the latter half of the extrusion operation, the extrusion pressure (MPa) is a value obtained by dividing the load (N) at which the pressure reaches an equilibrium state by the cross-sectional area of the barrel.

Moisture content

The mass of about 20g of PTFE powder before and after heating at 150℃for 2 hours was measured and calculated according to the following formula. The average value was obtained by taking 3 samples and calculating the samples.

Stretchability of

The strands obtained by extrusion of the above paste were dried at 230 ℃ for 30 minutes to remove the lubricant. The dried strips were cut to the appropriate length and placed in a furnace heated to 300 ℃. In the oven, the strip was stretched to 25 times the length of the strip before the tensile test at a stretch rate of 100%/second. The tensile strength was evaluated as being stretchable when the tensile strength was not broken, and as being not stretchable when the tensile strength was broken.

Battery evaluation (1)

The mixture sheet preparation and electrode sheet evaluation and battery evaluation of examples 1 to 9 and comparative examples 1 to 2 were performed in the following order.

< Preparation of Positive electrode mixture sheet >

Li (Ni _0.6Mn_0.2Co_0.2)O₂ (NMC 622) as a positive electrode active material and carbon black as a conductive aid were weighed and stirred at 30rpm for 300 seconds using a pressure kneader to obtain a mixture.

After that, the PTFE powders obtained in each of the examples and comparative examples were added as a binder, and stirred at 50rpm for 300 seconds to obtain a mixture. Positive electrode active material in mass ratio: and (2) a binder: conduction aid = 95:2:3.

The obtained mixture was molded into a block shape, and rolled into a sheet shape.

After that, the rolled sheet obtained immediately before was folded in half and roughly crushed, formed again into a block shape, and then rolled into a sheet shape on a flat plate by a metal roll to promote fibrillation, and the above-mentioned steps were repeated 4 times. Thereafter, the resultant sheet was further rolled to obtain a positive electrode mixture sheet having a thickness of about 500. Mu.m. Further, the positive electrode mixture sheet was cut into 5cm×5cm pieces, and the cut pieces were put into a roll press and rolled. To further promote fibrillation, a load of 2kN was repeatedly applied to adjust the thickness. The gap was adjusted so that the final positive electrode mixture layer had a thickness of 90 μm and a density of 3.30g/cc. Examples 6 to 9 were adjusted to a thickness of 90 μm and a density of 3.60g/cc.

< Measurement of Positive electrode mixture sheet Strength >

The positive electrode mixture sheet was cut out to prepare a long test piece having a width of 4 mm. The measurement was performed under a condition of 100 mm/min by using a tensile tester (AGS-100 NX, manufactured by Shimadzu corporation). The distance between the chucks was set to 30mm. The maximum stress of the measurement result was set as the strength of each sample until the displacement was given and the fracture was completed. Comparative example 2 was set to 100 for comparison.

< Preparation of Positive electrode >

The positive electrode mixture sheet was bonded to a 20 μm aluminum foil as follows.

As the binder, a slurry in which polyvinylidene fluoride (PVDF) and Carbon Nanotubes (CNT) are dispersed in N-methylpyrrolidone (NMP) is used. The adhesive was applied to an aluminum foil, and dried at 120℃for 15 minutes using a hot plate to form a current collector with an adhesive layer.

Then, the positive electrode mixture sheet was placed on a current collector with an adhesive layer, the positive electrode mixture sheet was bonded to the current collector by a roll press heated to 180 ℃, and the positive electrode was cut into a desired size and attached to a tab.

< Preparation of negative electrode >

To 98 parts by mass of carbonaceous material (graphite), 1 part by mass of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose 1% by mass) and 1 part by mass of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber 50% by mass) were added as a thickener and a binder, and the mixture was mixed by a disperser to prepare a slurry. The obtained slurry was applied to a copper foil having a thickness of 10 μm, dried, rolled by a press, cut into a desired size, and attached to a tab to prepare a negative electrode.

< Preparation of electrolyte >

As the organic solvent, a mixed solvent of Ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) (EC: emc=30:70 (volume ratio)) was measured in a sample bottle, and fluoroethylene carbonate (FEC) and Vinylene Carbonate (VC) were dissolved therein by 1 mass%, respectively, to prepare a mixed solution. The LiPF ₆ salt was mixed into the mixed solution at 23 ℃ so that the concentration in the electrolyte was 1.0 mol/L, thereby obtaining a nonaqueous electrolyte.

< Production of aluminum laminate cell >

The positive electrode was faced to the negative electrode through a microporous polyethylene film (separator) having a thickness of 20 μm, and the nonaqueous electrolyte solution obtained was injected, and the nonaqueous electrolyte solution was sufficiently impregnated into the separator and then sealed, and the separator was subjected to pre-charging and aging to produce a lithium ion secondary battery.

< Evaluation of storage Property (residual Capacity Rate, gas production amount)

For the lithium ion secondary battery manufactured as described above, after constant-current-constant-voltage charging (hereinafter referred to as CC/CV charging) at 25 ℃ with a current corresponding to 0.5C (0.1C cut-off) to 4.3V, the initial discharge capacity was obtained from the discharge capacity at the 3 rd cycle with a constant current of 0.5C discharged to 3V as 1 cycle.

The volume of the battery was determined by charging the battery, whose initial resistance evaluation had been completed, again with CC/CV at 25℃until 4.3V was reached (0.1C cut-off). After the volume of the battery was determined, the battery was stored at a high temperature at 60℃for 30 days. After the end of the high-temperature storage, the volume of the battery was obtained at 25 ℃ after cooling sufficiently, and the gas generation amount was obtained from the difference in volume between the battery before and after the storage test. The gas generation amount of comparative example 1 was set to 100, and the gas generation amount was compared.

After the amount of gas generated was determined, discharge was performed at 25℃to 3V at 0.5℃to determine the residual capacity.

The ratio of the residual capacity after high-temperature storage to the initial discharge capacity was obtained and used as the residual capacity ratio (%).

(Residual capacity)/(initial discharge capacity) ×100=residual capacity ratio (%)

Synthesis example

A white solid A was obtained by the method described in Synthesis example 1 of International publication No. 2021/045228.

Preparation example 1

To a stainless steel autoclave having a content of 6 liters and equipped with stainless steel stirring blades and a temperature adjusting jacket, 3480g of deionized water, 100g of paraffin wax, and 5.25g of white solid A were charged, and the inside of the autoclave was replaced with nitrogen gas while heating to 70℃to remove oxygen. TFE was introduced under pressure to set the pressure in the system to 0.78MPaG, and the temperature in the system was kept at 70℃with stirring. Subsequently, an aqueous solution of 15.0mg of ammonium persulfate dissolved in 20g of water was introduced thereinto by pressing TFE thereinto to start polymerization. As the polymerization reaction proceeded, the pressure in the system was lowered, but TFE was added to maintain the temperature in the system at 70℃and the pressure in the system at 0.78MPaG.

At the time when 400g of TFE was consumed from the start of polymerization, an aqueous solution prepared by dissolving 18.0mg of hydroquinone as a radical scavenger in 20g of water was pressed with TFE. Thereafter, the polymerization was continued, and the stirring and the supply of TFE were stopped at a point when the polymerization amount of TFE reached 1200g from the start of the polymerization, and the gas in the system was immediately released to atmospheric pressure, thereby ending the polymerization reaction. Taking out the aqueous dispersion, cooling, and separating paraffin to obtain PTFE aqueous dispersion. The solid content concentration of the obtained PTFE aqueous dispersion was 25.3% by mass, and the average primary particle diameter was 310nm.

Example 1

The aqueous PTFE dispersion obtained in production example 1 was diluted to a solid content of 13 mass%, and after solidifying PTFE with stirring in a container, the PTFE dispersion was filtered with water to obtain a wet powder.

The obtained PTFE wet powder was placed on a mesh tray made of stainless steel, and the mesh tray was heat-treated in a hot air circulating electric furnace at 210 ℃. After 5 hours, the mesh tray was taken out, and after air-cooling the mesh tray, PTFE powder was obtained.

The SSG of the PTFE powder obtained was 2.159.RR100 extrusion pressure was 15.1MPa and was able to be stretched.

Comparative example 1

A PTFE powder was obtained in the same manner as in example 1, except that the mesh tray was changed to a flat tray (a tray having no ventilation on the bottom surface and the side surface).

Production example 2

To a stainless steel autoclave having a content of 6 liters and equipped with stainless steel stirring blades and a temperature adjusting jacket, 3560g of deionized water, 100g of paraffin wax, and 5.4g of white solid a were charged, and the inside of the autoclave was replaced with nitrogen gas while heating to 70 ℃. TFE was introduced under pressure to set the pressure in the system to 0.60MPaG, and the temperature in the system was kept at 70℃with stirring. Next, 0.60g of perfluoro (methyl vinyl ether) (PMVE) was pressed in with TFE. Subsequently, an aqueous solution containing 15.0mg of ammonium persulfate dissolved in 20g of water was pressurized with TFE to bring the pressure in the system to 0.78MPaG, and the polymerization was started. As the polymerization reaction proceeded, the pressure in the system was lowered, but TFE was added to maintain the temperature in the system at 70℃and the pressure in the system at 0.78MPaG.

At the time point when 429g of TFE was consumed from the start of polymerization, an aqueous solution prepared by dissolving 14.0mg of hydroquinone as a radical scavenger in 20g of water was pressed with TFE. Thereafter, polymerization was continued, stirring and TFE supply were stopped at a point when the polymerization amount of TFE reached 1225g from the start of polymerization, and the atmosphere in the system was immediately released to atmospheric pressure, thereby ending the polymerization reaction. Taking out the aqueous dispersion, cooling, and separating paraffin to obtain PTFE aqueous dispersion. The solid content concentration of the obtained PTFE aqueous dispersion was 25.4% by mass, and the average primary particle diameter was 243nm.

Example 2

The aqueous PTFE dispersion obtained in production example 2 was diluted to a solid content of 13 mass%, and after solidifying PTFE with stirring in a container, the PTFE dispersion was filtered with water to obtain a wet powder.

The obtained PTFE wet powder was placed on a mesh tray made of stainless steel, and the mesh tray was heat-treated in a hot air circulating electric furnace at 160 ℃. After 18 hours, the mesh tray was taken out, and the PTFE powder was obtained after air-cooling the mesh tray.

The obtained PTFE powder had a PMVE content of 0.046 mass% and an SSG of 2.145. In addition, the RR100 extrusion pressure was 17.4MPa, and the stretching was possible.

Example 3

A PTFE powder was obtained in the same manner as in example 2 except that the time period was changed from 18 hours to 5 hours. The obtained PTFE powder had a PMVE content of 0.046 mass% and an SSG of 2.145. In addition, the RR100 extrusion pressure was 16.8MPa, and the stretching was possible.

The physical properties of each PTFE powder obtained above were measured by the above-described method. Further, positive electrode mixture sheets, electrodes, and lithium ion secondary batteries were produced and evaluated by the above-described methods using the PTFE powders obtained above. The results are shown in Table 1.

TABLE 1

As is clear from the results shown in table 1, in examples 1 and 2 in which PTFE powder containing substantially no moisture was used, the amount of gas generated by the battery was smaller than in comparative examples 1 and 2 in which PTFE powder containing moisture was used.

PREPARATION EXAMPLE 3

To a polymerization reactor having a content of 6 liters and equipped with stainless stirring blades and a temperature adjusting jacket, 3600g of deionized water, 180g of paraffin wax, 5.4g of white solid A, and 0.025g of oxalic acid were charged, and the inside of the polymerization reactor was replaced with nitrogen gas while heating to 70℃to remove oxygen. After the temperature in the reactor was kept at 70℃with stirring, TFE gas was introduced and the pressure was set at 2.7 MPaG.

While stirring the content, deionized water in which 3.5mg of potassium permanganate was dissolved was continuously added at a constant rate, and TFE was continuously fed so that the pressure in the polymerization vessel became constant at 2.7 MPaG. At the time of 184g of TFE consumption, 5.3g of white solid A was added, and at the time of 900g of TFE consumption, the entire amount of deionized water in which 3.5mg of potassium permanganate was dissolved was added. At the time when the TFE consumption was 1540g, stirring and TFE supply were stopped, and TFE in the polymerizer was purged to terminate the polymerization reaction. Taking out the aqueous dispersion, cooling, and separating paraffin to obtain PTFE aqueous dispersion. The solid content concentration of the obtained PTFE aqueous dispersion was 29.7% by mass, and the average primary particle diameter was 296nm.

PREPARATION EXAMPLE 4

To a stainless steel autoclave having a content of 6 liters and equipped with stainless steel stirring blades and a temperature adjusting jacket, 3500g of deionized water, 100g of paraffin wax, and 5.3g of white solid a were charged, and the inside of the autoclave was replaced with nitrogen gas while heating to 85 ℃. TFE was introduced under pressure to set the pressure in the system to 0.70MPaG, and the temperature in the system was kept at 85 ℃ with stirring. Subsequently, an aqueous solution of 260mg of disuccinic peroxide dissolved in 20g of water was introduced thereinto by pressing with TFE. Thereafter, an aqueous solution of 15mg of ammonium persulfate dissolved in 20g of water was introduced thereinto by pressing TFE so that the pressure in the system became 0.8MPaG, and the polymerization reaction was started. As the polymerization reaction proceeded, the pressure in the system was lowered, but TFE was added to maintain the temperature in the system at 85℃and the pressure in the system at 0.8MPaG.

When the polymerization amount of TFE reached 1140g from the start of the polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to atmospheric pressure, thereby ending the polymerization reaction. Taking out the aqueous dispersion, cooling, and separating paraffin to obtain PTFE aqueous dispersion. The solid content concentration of the obtained PTFE aqueous dispersion was 24.3% by mass, and the average primary particle diameter was 330nm.

Preparation example 5

Into a stainless steel autoclave having an inner capacity of 6L and equipped with stirring blades, 3500g of deionized water, 100g of paraffin wax and 5.3g of white solid A were charged, and the inside of the system was replaced with TFE. The autoclave was purged with nitrogen while heating the inner temperature to 70 ℃. TFE was introduced under pressure so that the internal pressure became 0.78MPaG, and 10g of an aqueous solution of 0.6% by mass of ammonium persulfate [ APS ] was charged to start the reaction. As polymerization proceeds, the pressure in the polymerization system decreases, and therefore TFE is continuously added, the internal pressure is kept at 0.78mpa g, and the reaction is continued.

When the polymerization amount of TFE reached 1200g from the start of polymerization, stirring and TFE supply were stopped, and the atmosphere in the system was immediately released to atmospheric pressure, thereby ending the polymerization reaction. Taking out the aqueous dispersion, cooling, and separating paraffin to obtain PTFE aqueous dispersion. The solid content concentration of the obtained PTFE aqueous dispersion was 25.3% by mass, and the average primary particle diameter was 256nm.

Example 4

The aqueous PTFE dispersion obtained in production example 3 was diluted to a solid content of 13% by mass, and after solidifying PTFE with stirring in a container, the PTFE dispersion was filtered with water to obtain a wet powder.

The obtained PTFE wet powder was placed on a mesh tray made of stainless steel, and the mesh tray was heat-treated in a hot air circulating electric furnace at 210 ℃. After 18 hours, the mesh tray was taken out, and the PTFE powder was obtained after air-cooling the mesh tray.

Example 5

The aqueous PTFE dispersion obtained in production example 4 was diluted to a solid content of 13 mass%, and after solidifying PTFE with stirring in a container, the PTFE dispersion was filtered with water to obtain a wet powder.

Comparative example 2

The aqueous PTFE dispersion obtained in production example 5 was diluted to a solid content of 13 mass%, and after solidifying PTFE with stirring in a container, the PTFE dispersion was filtered with water to obtain a wet powder.

The physical properties of each PTFE powder obtained above were measured by the above-described method. Further, positive electrode mixture sheets, electrodes, and lithium ion secondary batteries were produced and evaluated by the above-described methods using the PTFE powders obtained above. The results are shown in Table 2.

TABLE 2

As is clear from the results shown in table 2, the electrode strength was increased by using PTFE powder having an SSG of 2.200 or less. In particular, it was found that when a stretchable PTFE powder was used, the electrode strength became extremely high, and excellent battery characteristics were exhibited.

Preparation example 6

To a SUS-made reactor having an internal volume of 6L and equipped with a stirrer, 3600g of deionized water, 180g of paraffin wax, 5.4g of white solid A, and 26.5mg of oxalic acid were charged. Then, the contents of the reactor were stirred by purging with Tetrafluoroethylene (TFE) while heating to 70 ℃. 2.60g of Chlorotrifluoroethylene (CTFE) was pressed into the reactor with TFE, followed by TFE to 2.70MPaG. An aqueous potassium permanganate solution in which 3.4mg of potassium permanganate was dissolved in deionized water was continuously added to the reactor as an initiator. After the initiator injection, a pressure drop occurred and polymerization was observed to begin. TFE was added to the reactor to maintain the pressure constant at 2.70MPaG. At the time when the amount of TFE fed reached 430g, the feeding of the potassium permanganate aqueous solution was stopped. The supply of TFE was stopped at a point when the amount of TFE fed reached 1660g, and stirring was stopped to terminate the reaction. Thereafter, the pressure of the exhaust gas in the reactor was set to normal pressure, and nitrogen substitution was performed to take out the content from the reactor and cool it. Paraffin wax was removed to obtain an aqueous PTFE dispersion. The solid content concentration of the obtained PTFE aqueous dispersion was 31.4% by mass, and the average primary particle diameter was 248nm.

Example 6

The aqueous PTFE dispersion obtained in production example 6 was diluted to a solid content of 13 mass%, and the diluted aqueous PTFE dispersion was vigorously stirred in a container equipped with a stirrer to be solidified, and then filtered with water to obtain a wet powder. The wet powder thus obtained was placed on a mesh tray made of stainless steel, and the mesh tray was heat-treated in a hot air circulating electric furnace at 210 ℃. After 18 hours, the mesh tray was taken out, and the PTFE powder was obtained after air-cooling the mesh tray. The CTFE content of the obtained PTFE powder was 0.100 mass%. The physical properties of the obtained PTFE powder were measured. The positive electrode mixture sheet, electrode and lithium ion secondary battery were produced and evaluated by the above method using the PTFE powder obtained above. The results are shown in Table 3.

PREPARATION EXAMPLE 7

Polymerization was carried out under the same conditions as in production example 6 except that the amount of CTFE charged was changed to 1.28g, the amount of potassium permanganate charged was changed to 3.87mg, and the final TFE content was changed to 1790g, to obtain an aqueous PTFE dispersion. The solid content concentration of the obtained PTFE aqueous dispersion was 33.0 mass%, and the average primary particle diameter was 263nm.

Example 7

Using the PTFE aqueous dispersion obtained in production example 7, a PTFE powder was obtained in the same manner as in example 6. The physical properties of the obtained PTFE powder were measured. The CTFE content of the obtained PTFE powder was 0.050 mass%. The positive electrode mixture sheet, electrode and lithium ion secondary battery were produced and evaluated by the above method using the PTFE powder obtained above. The results are shown in Table 3.

Preparation example 8

Into a stainless steel autoclave having a content of 6 liters and equipped with stainless steel stirring blades and a temperature adjusting jacket, 3580g of deionized water, 100g of paraffin wax, and 5.4g of white solid a were charged, and the inside of the autoclave was replaced with nitrogen gas while heating to 70 ℃. After 0.50g of HFP was introduced thereinto, TFE was introduced thereinto to set the pressure in the system to 0.78MPaG, and the temperature in the system was kept at 70℃with stirring. Subsequently, an aqueous solution of 15.4mg of ammonium persulfate dissolved in 20g of water was introduced thereinto by pressing TFE thereinto to start polymerization. As the polymerization reaction proceeded, the internal pressure of the system was decreased, but TFE was added thereto, the internal temperature of the system was maintained at 70℃and the internal pressure of the system was maintained at 0.78MPaG.

At the time point when 430g of TFE was consumed from the start of polymerization, an aqueous solution prepared by dissolving 18.0mg of hydroquinone as a radical scavenger in 20g of water was pressed with TFE. Thereafter, polymerization was continued, stirring and TFE supply were stopped at a point when the polymerization amount of TFE reached 1540g from the start of polymerization, and the atmosphere in the system was immediately released to atmospheric pressure, thereby ending the polymerization reaction. Taking out the aqueous dispersion, cooling, and separating paraffin to obtain PTFE aqueous dispersion. The solid content concentration of the obtained PTFE aqueous dispersion was 29.6 mass%, and the average primary particle diameter was 246nm.

Example 8

The aqueous PTFE dispersion obtained in production example 8 was diluted to a solid concentration of 13 mass%, stirred in a container with a stirrer to be solidified, and then filtered with water to obtain a wet powder. The wet powder thus obtained was placed on a mesh tray made of stainless steel, and the mesh tray was heat-treated in a hot air circulating electric furnace at 180 ℃. After 18 hours, the mesh tray was taken out, and the PTFE powder was obtained after air-cooling the mesh tray.

The physical properties of the obtained PTFE powder were measured. The HFP content of the obtained PTFE powder was 0.019 mass%. The PTFE powder obtained above was used to prepare a positive electrode mixture sheet, an electrode, and a lithium ion secondary battery by the above method, and evaluation was performed. The results are shown in Table 3.

Preparation example 9

An aqueous PTFE dispersion was obtained in the same manner as in production example 8 except that the amount of HFP charged was changed to 0.06 g. The solid content concentration of the obtained PTFE aqueous dispersion was 29.2% by mass, and the average primary particle diameter was 274nm.

Example 9

A PTFE powder was obtained in the same manner as in example 8, except that the heat treatment temperature of the PTFE aqueous dispersion obtained in production example 9 was changed to 160 ℃.

The physical properties of the obtained PTFE powder were measured. The HFP content of the obtained PTFE powder was 0.002% by mass. The PTFE powder obtained above was used to prepare a positive electrode mixture sheet, an electrode, and a lithium ion secondary battery by the above method, and evaluation was performed. The results are shown in Table 3.

TABLE 3

Battery evaluation (2)

The mixture pieces of examples 10 and 11 and comparative example 3 were prepared in the following manner.

< Preparation of Positive electrode mixture sheet >

The positive electrode active material, the conductive auxiliary agent and the binder were weighed so that the weight ratio was 97:2:1, into a container of a high-speed mixer (Wonder Crusher (WC-3) manufactured by Osaka chemical Co.).

After that, the mixture was sufficiently cooled in a constant temperature bath (5 ℃ C., 8 hours) together with the container. Next, the cooled vessel was set in a high-speed mixer, and stirred at 10000rpm for 3 minutes to disperse the material, thereby obtaining an electrode mix.

The following materials were used as the materials.

Positive electrode active material: li (Ni _0.8Mn_0.1Co_0.1)O₂, (NMC 811)

Conductive auxiliary agent: superP carbon black

And (2) a binder: PTFE powders obtained in examples 10 and 11 and comparative example 3

Then, the electrode mixture thus obtained was put into a pressure kneader heated to 50℃and kneaded at 30rpm for 100 seconds to promote fibrillation, whereby an electrode mixture was obtained.

The electrode mixture thus obtained was fed to a metal roll (80 ℃ C.) disposed in parallel to obtain a sheet of about 1 to 2cm ². The sheet was again put into a calender roll heated to 80℃a plurality of times to obtain a sheet.

The electrode mixture sheet was rolled by multiple passes to produce a self-standing electrode mixture sheet. The temperature of the metal roll was set at 80 ℃. Then, the positive electrode mixture sheet was obtained by adjusting the gap while gradually reducing the gap. The positive electrode mixture sheet was prepared to have a density of 3.50g/cc at a thickness of 80. Mu.m.

< Measurement of Positive electrode mixture sheet Strength >

The positive electrode mixture sheets of examples 10 and 11 and comparative example 3 were evaluated in the following manner.

Comparative example 3 was set to 100, and examples 10 and 11 and comparative example 3 were compared.

< Preparation of Positive electrode >

Electrode sheet fabrication and battery fabrication of examples 10 and 11 and comparative example 3 were performed in the following order.

As the adhesive, polyvinylidene fluoride (PVDF) was dissolved in N-methylpyrrolidone (NMP) to give a solid content ratio of 80:20, a slurry having carbon black dispersed therein. The adhesive was applied to an aluminum foil, and dried at 120℃for 15 minutes using a hot plate to form a current collector with an adhesive layer having a thickness of 4. Mu.m.

Then, the positive electrode mixture sheet was placed on a current collector with an adhesive layer, the positive electrode mixture sheet was bonded to the current collector by a roll press heated to 150 ℃, and the positive electrode was cut into a desired size and attached to a tab.

< Production of aluminum laminate cell >

The negative electrode, separator and positive electrode were laminated in the same manner as in example 1, and a nonaqueous electrolyte was injected, followed by pre-charging and aging, to prepare a lithium ion secondary battery, and evaluation was performed.

The battery evaluations of examples 10, 11 and comparative example 3 were performed in the following order.

The storage characteristics (residual capacity and gas generation amount) were evaluated in the same manner as in example 1. The gas generation amount of comparative example 3 was set to 100, and the gas generation amount was compared.

Production example 10

To a stainless steel autoclave having a content of 6 liters and equipped with stainless steel stirring blades and a temperature adjusting jacket, 3600g of deionized water, 180g of paraffin wax, and 5.4g of white solid A were charged, and the inside of the autoclave was replaced with nitrogen gas while heating to 85℃to remove oxygen. After the temperature in the reactor was kept at 85℃with stirring, TFE gas was introduced and the pressure was set at 2.4 MPaG. While stirring the content, 468mg of deionized water in which disuccinic acid peroxide was dissolved was added to start polymerization. As the polymerization proceeded, the pressure in the polymerizer was decreased, but TFE was continuously fed at a constant 2.4 MPaG.

At the time when the TFE consumption was 1580g, stirring and TFE supply were stopped, and TFE in the polymerizer was purged to terminate the polymerization reaction. Taking out the aqueous dispersion, cooling, and separating paraffin to obtain PTFE aqueous dispersion. The obtained PTFE aqueous dispersion had an average primary particle diameter of 294nm and a solid content concentration of 30.4% by mass.

Example 10

The aqueous PTFE dispersion obtained in production example 10 was diluted to a solid content of 13 mass%, and the diluted aqueous PTFE dispersion was vigorously stirred in a container equipped with a stirrer to be solidified, and then filtered with water to obtain a wet powder. The moisture content of the wet powder was about 40 mass%.

The wet powder thus obtained was placed on a mesh tray made of stainless steel (placement amount: 2.0g/cm ²), and the mesh tray was heat-treated in a hot air circulating electric furnace at 170 ℃. After 18 hours, the mesh tray was taken out, and the PTFE powder was obtained after air-cooling the mesh tray. The physical properties of the obtained PTFE powder were measured. The results are shown in Table 4. The positive electrode mixture sheet, electrode, and lithium ion secondary battery were produced and evaluated by the method of battery evaluation (2) using the PTFE powder obtained above. The results are shown in Table 5.

TABLE 4

Example 11

A positive electrode mixture sheet, an electrode, and a lithium ion secondary battery were produced and evaluated by the method of battery evaluation (2) using the PTFE powder obtained in example 4. The results are shown in Table 5.

Comparative example 3

A positive electrode mixture sheet, an electrode, and a lithium ion secondary battery were produced by the method of battery evaluation (2) using the PTFE powder obtained in comparative example 2, and evaluated. The results are shown in Table 5.

TABLE 5

From the results shown in table 5, it is clear that the use of the polytetrafluoroethylene powder of the present invention can provide a positive electrode mixture sheet having excellent strength. This can reduce the amount of binder added and maintain the battery characteristics satisfactorily. In addition, it was found that excellent battery characteristics can be produced, which are excellent in strength, less in gas generation, and high in capacity retention.

Claims

1. A polytetrafluoroethylene powder which is a polytetrafluoroethylene powder for an electrode binder, wherein the polytetrafluoroethylene powder has a standard specific gravity of 2.200 or less and contains substantially no moisture.

2. An electrode binder consisting essentially of polytetrafluoroethylene powder having a standard specific gravity of 2.200 or less and containing substantially no moisture.

3. The binder for electrodes according to claim 2, wherein the moisture content is 0.050% by mass or less relative to the polytetrafluoroethylene powder.

4. The binder for electrodes according to claim 2 or 3, wherein the polytetrafluoroethylene powder has an extrusion pressure of 10MPa or more at a compression ratio of 100.

5. The binder for electrodes according to any one of claims 2 to 4, wherein the polytetrafluoroethylene powder is stretchable.

6. The binder for an electrode according to any one of claims 2 to 5, wherein the polytetrafluoroethylene comprises tetrafluoroethylene units and modified monomer units based on a modified monomer copolymerizable with tetrafluoroethylene.

7. The binder for electrodes according to claim 6, wherein the modifying monomer is at least 1 selected from the group consisting of perfluoro (methyl vinyl ether) and hexafluoropropylene.

8. The binder for electrodes according to any one of claims 2 to 7, wherein the polytetrafluoroethylene powder has an average primary particle diameter of 100nm to 350nm.

9. An electrode mixture comprising the polytetrafluoroethylene powder according to claim 1 or the binder for an electrode according to any one of claims 2 to 8, and an electrode active material.

10. An electrode comprising the polytetrafluoroethylene powder according to claim 1 or the binder for an electrode according to any one of claims 2 to 8, an electrode active material, and a current collector.

11. A secondary battery provided with the electrode according to claim 10.