Electrode mixtures for secondary batteries, electrode mixture sheets for secondary batteries and their manufacturing methods, and secondary batteries.

Abstract

This invention provides an electrode compound for secondary batteries with good properties, an electrode compound sheet for secondary batteries containing the electrode compound, and a secondary battery using the electrode compound sheet. Furthermore, this invention provides a method for manufacturing an electrode compound sheet containing polytetrafluoroethylene resin with a microfiber structure. The electrode compound for secondary batteries of the present invention contains an electrode active material and a binder, and is characterized in that: the binder is polytetrafluoroethylene resin, and the polytetrafluoroethylene resin has a fibrous structure with a fiber diameter (central value) of less than 70 nm. Furthermore, the electrode compound sheet for secondary batteries of the present invention contains this electrode compound.

Description

Technical Field

[0001] This invention relates to an electrode mixture for secondary batteries, electrode mixture sheets for secondary batteries, a method for manufacturing the same, and a secondary battery. Prior Technology

[0002] In lithium-ion secondary batteries, the general process involves mixing electrode active materials and conductive additives with binders and solvents to obtain a slurry, and then coating and drying the slurry to produce an electrode binder.

[0003] On the other hand, polytetrafluoroethylene resin is a polymer that is easily fibrillated, so it is also used as an adhesive by fibrillating it.

[0004] Patent document 1 discloses a method for manufacturing an electrode, which involves using a jet mill to perform high-shear treatment on a mixture containing active materials and polytetrafluoroethylene (PTFE) mixed adhesive, thereby fibrillating the PTFE. Previous technical documents Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 2017-517862 Summary of the Invention

[0006] [The problem that the invention aims to solve]

[0007] The purpose of this invention is to provide an electrode compound for secondary batteries with good properties, an electrode compound sheet for secondary batteries containing the electrode compound, and a secondary battery using the electrode compound sheet. Furthermore, the present invention aims to provide a method for manufacturing an electrode compound sheet, the electrode compound sheet containing polytetrafluoroethylene resin having a microfiber structure. [Technical means to solve the problem]

[0008] This invention relates to an electrode compound for secondary batteries, comprising electrode active materials and a binder, and is characterized in that: The adhesive is polytetrafluoroethylene resin. Polytetrafluoroethylene resin has a fibrous structure with a fiber diameter (central value) of less than 70 nm.

[0009] The aforementioned electrode mixture for secondary batteries is preferably used in lithium-ion batteries. The electrode binder for secondary batteries is preferably obtained by using a raw material composition containing electrode active material and binder, and the binder of the raw material composition is powdered polytetrafluoroethylene resin. The above-mentioned raw material composition is preferably substantially free of liquid media.

[0010] The aforementioned powdered polytetrafluoroethylene resin preferably has a water content of less than 500 ppm. The preferred standard specific gravity of the above-mentioned powdered polytetrafluoroethylene resin is 2.11 to 2.20.

[0011] The aforementioned powdered polytetrafluoroethylene resin preferably contains 50% by mass or more of a polytetrafluoroethylene resin with a secondary particle size of 500 μm or more. The aforementioned powdered polytetrafluoroethylene resin preferably contains 80% by mass or more of a polytetrafluoroethylene resin with a secondary particle size of 500 μm or more.

[0012] This invention is also an electrode compound tablet for secondary batteries, which contains the above-mentioned electrode compound for secondary batteries. The aforementioned electrode compound sheet for secondary batteries is preferably used for the negative electrode, and the electrode active material contains silicon as a constituent element. The aforementioned electrode mixture sheet for secondary batteries is preferably used for the positive electrode and has a density of 3.00 g / cc or higher. The aforementioned electrode mixture sheet for secondary batteries is preferably used for the negative electrode, and has a density of 1.3 g / cc or higher.

[0013] This invention also relates to a method for manufacturing an electrode compound sheet for a secondary battery, comprising the following steps: Step (1), which involves mixing a raw material composition containing electrode active material and binder, while simultaneously applying shear force; Step (2) involves shaping the electrode mixture obtained through step (1) into a block shape; and Step (3) involves calendering the block-shaped electrode mixture obtained in step (2) into a sheet; and the method for manufacturing the electrode mixture sheet for secondary batteries is characterized by: The binder is a powdered polytetrafluoroethylene resin.

[0014] This invention is also a secondary battery having the aforementioned electrode compound sheet for secondary batteries. [Effects of the Invention]

[0015] In this invention, an electrode compound for obtaining electrodes with excellent flexibility and performance can be obtained. Therefore, a battery with high initial capacity, low resistance, and minimal gas generation can be produced. Furthermore, in the manufacturing method of this invention, an electrode compound sheet for producing electrodes with excellent flexibility and high-performance batteries can be manufactured. Simple Explanation of the Diagram

[0016] [Figure 1] is a scanning electron microscope photograph showing the cross-sectional state of the negative electrode compound tablet used in Example 5. Implementation

[0017] The present invention will now be described in detail. This invention provides an electrode compound for secondary batteries. More particularly, it provides an electrode compound that is well-suited for use in secondary batteries that utilize electrolytes. The electrode adhesive of this invention uses polytetrafluoroethylene resin (PTFE) as a binder. Regarding conventional electrode adhesives for secondary batteries, a common method involves using a solvent-soluble resin such as polyvinylidene fluoride as a binder, and preparing the electrode adhesive by coating a slurry containing the slurry and then drying it.

[0018] It is known that PTFE in powder form readily fibrillates when shear stress is applied. Utilizing this fibrillating property, PTFE can be used as a binder. That is, by winding fibrillated PTFE around other powder components, the powder components are bonded together, thus PTFE can function as a binder during the shaping of powder components.

[0019] However, even when using fibrillated PTFE as a binder, insufficient fibrillation results in suboptimal performance when used as an electrode binder. In this invention, research was conducted to address this issue by microfibrillating PTFE to achieve a fibrous structure with a fibrillary diameter (central value) of 70 nm or less. This fibrillated PTFE then exhibits excellent performance as a binder for electrode binders.

[0020] That is, the present invention discovers that when using PTFE as a binder, by giving it a microfiber structure, an electrode binder with good properties can be obtained, thereby completing the present invention.

[0021] The electrode mixture of the present invention is obtained using a raw material composition containing electrode active material and a binder, wherein the binder is preferably powdered PTFE. By using PTFE powder instead of PTFE aqueous dispersion as a raw material, the amount of water derived from the raw material in the electrode mixture is reduced, thereby avoiding problems caused by the presence of water mixture, and thus also having the advantage of improving battery performance.

[0022] Furthermore, the aforementioned raw material composition is preferably substantially free of liquid media. Thus, the electrode binder of the present invention has the advantage of not using solvents in its manufacturing process. That is, previous electrode binder forming methods generally use a solvent containing a binder to prepare a slurry dispersing powders that are components of the electrode binder, and then prepare the electrode binder by coating the slurry and drying it. In this case, a solvent that dissolves the binder is used. However, solvents capable of dissolving the previously commonly used binder resin, polyvinylidene fluoride, are limited to specific solvents such as N-methylpyrrolidone. Therefore, expensive solvents must be used, leading to increased costs.

[0023] The electrode compound of the present invention comprises PTFE as a constituent element, wherein the PTFE has a fibrous structure with a protofibrillary diameter (central value) of 70 nm or less. In the present invention, it is important that the protofibrillary diameter (central value) is 70 nm or less. Thus, the presence of PTFE with a finer protofibrillary diameter in the electrode compound enables it to bind the powder components constituting the electrode compound together and provides flexibility, thereby achieving the objective of the present invention.

[0024] The above-mentioned fibril diameter (central value) was measured by the following method. (1) The image was obtained by taking a magnified photograph (7000x) of the electrode mixture tablet using a scanning electron microscope (S-4800 type manufactured by Hitachi). (2) Draw two lines at equal intervals along the horizontal direction on the image to divide the image into three equal parts. (3) For all PTFE fibers located on the upper straight line, the diameter of each PTFE fiber is measured at three points, and the average value is taken as the diameter of the PTFE fiber. The three points to be measured are the intersection of the PTFE fiber and the straight line, the position offset upward from the intersection point by 0.5 μm, and the position offset downward from the intersection point by 0.5 μm. (Except for unfibrillated primary PTFE particles). (4) Perform the above (3) operation on all PTFE fibers located on the straight line below. (5) Using the first image as the starting point, move 1 mm to the right of the frame and take another picture. Measure the diameter of the PTFE fibers using steps (3) and (4) above. Repeat the above operation until the number of fibers measured exceeds 80. (6) Take the median value of the diameter of all the PTFE fibers measured above as the size of the original fiber diameter.

[0025] The diameter (central value) of the aforementioned fibrils is preferably below 65 nm. Furthermore, excessive fibrillation tends to result in a loss of flexibility. There is no particular lower limit, but from the point of view of strength, it is preferably above 15 nm, and even more preferably above 20 nm.

[0026] There are no particular limitations on the method for obtaining PTFE with the aforementioned fibril diameter (central value). For example, a method that can be carried out by the following steps can be cited: Step (1) involves mixing a raw material composition containing electrode active material and binder, while simultaneously applying shear force; Step (2) involves shaping the electrode mixture obtained through step (1) into a block shape; and Step (3) involves calendering the blocky electrode mixture obtained by step (2) into a sheet.

[0027] In this method, for example in step (1), by setting the mixing conditions of the raw material components to 1000 rpm or less, the softness can be maintained and the fibrillation of PTFE can be carried out. By controlling the applied shear stress, the diameter (central value) of the PTFE fibrils can be made to be 70 nm or less.

[0028] Furthermore, it is also preferable to perform step (4) after step (3), which involves applying a greater load to the obtained calendered sheet to calender it into a thinner sheet. It is also preferable to repeat step (4). Furthermore, after step (3) or step (4), there is step (5), in which the obtained calendered sheet is coarsely crushed, then formed into a block again, and calendered into a sheet, thereby adjusting the diameter of the original fiber. Step (5) is preferably repeated, for example, more than once and less than 12 times.

[0029] That is, by applying shear force, PTFE powder is fibrillated, and it becomes entangled with powder components such as electrode active materials, thereby producing an electrode mixture. Furthermore, the manufacturing method will be described below.

[0030] In this invention, the PTFE is not particularly limited and can be a homopolymer or a fibrillable copolymer, but is more preferably a homopolymer. In the case of copolymers, examples of monomers containing fluorine atoms that serve as comonomers include trifluorochloroethylene, hexafluoropropylene, fluoroalkylethylene, perfluoroalkylethylene, and fluoroalkyl-fluorovinyl ether.

[0031] Furthermore, the term "PTFE powder" as used above refers to a solid state as a powder, rather than a dispersed state in which it is mixed with a liquid medium. By using PTFE powder in this state, and PTFE in a state without a liquid medium, the electrode mixture can be manufactured, thereby effectively achieving the purpose of this invention.

[0032] The powdered form of PTFE used as a raw material in preparing the electrode mixture of the present invention preferably has a water content of less than 500 ppm. By reducing the water content to below 500 ppm, a secondary battery with less gas production as an initial characteristic can be manufactured, which is better in this respect. The aforementioned moisture content is preferably below 300 ppm.

[0033] The powdered PTFE used as a raw material in preparing the electrode mixture of the present invention preferably has a standard specific gravity of 2.11 to 2.20. By keeping the standard specific gravity within this range, it is advantageous to manufacture electrode mixture sheets with higher strength. The lower limit of the above-mentioned standard specific gravity is more preferably 2.12 or higher. The upper limit of the above-mentioned standard specific gravity is more preferably 2.19 or lower, and more preferably 2.18 or lower.

[0034] Standard specific gravity [SSG] is determined by preparing a sample according to ASTM D-4895-89 and measuring the specific gravity of the sample by the water displacement method.

[0035] The aforementioned powdered PTFE preferably contains 50% by mass or more of PTFE with a secondary particle size of 500 μm or more, and more preferably 80% by mass or more. By ensuring that the PTFE with a secondary particle size of 500 μm or more is within this range, it has the advantage of being able to manufacture electrode composite sheets with higher strength. By using PTFE with a secondary particle size of 500 μm or more, electrode composite sheets with lower resistance and greater toughness can be obtained.

[0036] The lower limit of the secondary particle size of the above-mentioned powdered PTFE is preferably 300 μm, and more preferably 350 μm. The upper limit of the secondary particle size is preferably 700 μm or less, and more preferably 600 μm or less. The secondary particle size can be determined, for example, by sieving.

[0037] In terms of obtaining electrode composite sheets with higher strength and better homogeneity, the aforementioned powdered PTFE preferably has an average primary particle size of 150 nm or more. More preferably, it has an average primary particle size of 180 nm or more, and even more preferably, it has an average primary particle size of 210 nm or more, and most preferably, it has an average primary particle size of 220 nm or more. The larger the average primary particle size of PTFE, the better it can suppress the rise in extrusion pressure and the better its formability when using this powder for extrusion molding. There is no particular upper limit, and it can be 500 nm. From the point of view of productivity in the polymerization step, 350 nm is preferred.

[0038] The aforementioned average primary particle size can be determined in the following manner: using an aqueous dispersion of PTFE obtained by polymerization, a calibration curve is prepared between the transmittance of 550 nm light per unit length of the aqueous dispersion with a polymer concentration adjusted to 0.22% by mass and the average primary particle size determined by measuring the unidirectional particle size in a transmission electron microscope image. For the aqueous dispersion to be measured, the aforementioned transmittance is measured, and the average primary particle size is determined based on the aforementioned calibration curve.

[0039] The PTFE used in this invention may have a core-shell structure. Examples of PTFE with a core-shell structure include polytetrafluoroethylene (PTFE), which comprises a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE. Examples of such PTFE include the PTFE described in Japanese Patent Application Publication No. 2005-527652.

[0040] Powdered PTFE that satisfies the parameters described above can be obtained by conventional manufacturing methods. For example, it can be manufactured according to the manufacturing methods described in International Publication No. 2015-080291 or International Publication No. 2012-086710.

[0041] The electrode compound for secondary batteries of the present invention contains electrode active materials and binders. The binder content in the electrode compound for secondary batteries is preferably 0.2 to 10% by mass, more preferably 0.3 to 6.0% by mass. If the binder is within the above range, it is possible to suppress the increase in electrode resistance while forming a self-supporting sheet with excellent processability.

[0042] Furthermore, the electrode mixture for secondary batteries of the present invention may also contain conductive additives as needed. The following section explains the electrode active materials and conductive additives.

[0043] (Electrode active material) First, as a positive electrode active material, there are no particular restrictions as long as it can absorb and release alkali metal ions in an electrochemical manner. For example, it is preferable to be a material containing an alkali metal and at least one transition metal. Specific examples include: transition metal complex oxides containing alkali metals, transition metal phosphate compounds containing alkali metals, and conductive polymers. Among these, the positive electrode active material is preferably a transition metal composite oxide containing an alkali metal that produces high voltage. Examples of alkali metal ions include lithium ions, sodium ions, and potassium ions. In a preferred embodiment, the alkali metal ion is lithium ion. That is, in this embodiment, the alkali metal ion secondary battery is a lithium-ion secondary battery.

[0044] Examples of transition metal composite oxides containing alkali metals include: Alkali metal-manganese spinel composite oxide represented by the formula: MaMn2-bM1bO4 (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K; 0.9 ≤ a; 0 ≤ b ≤ 1.5; M1 is at least one 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); Alkali metal-nickel composite oxides represented by the formula: MNi 1-cM 2cO 2 (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K; 0 ≤ c ≤ 0.5; M2 is at least one 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 Alkali metal-cobalt composite oxides represented by the formula: MCo 1-dM 3 dO 2 (In the formula, M is at least one metal selected from the group consisting of Li, Na and K; 0≦d≦0.5; M3 is at least one 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). In the above, M is preferably selected from a metal in the group consisting of Li, Na and K, more preferably Li or Na, and even more preferably Li.

[0045] From the viewpoint of providing a secondary battery with high energy density and high output, the preferred compounds are MCoO 2, MMnO 2, MNiO 2, MMn 2O 4, MNi 0.8Co 0.15Al 0.05O 2, or MNi 1 / 3Co 1 / 3Mn 1 / 3O 2, etc., and the compounds represented by the following general formula (3) are preferred. MNi hCo iMn jM 5 kO 2(3) (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K; M5 represents at least one metal 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≦h≦1.0, 0≦i≦1.0, 0≦j≦1.5, 0≦k≦0.2)

[0046] Examples of transition metal phosphate compounds containing alkali metals include those represented by the following formula (4): M eM 4 f(PO 4) g(4) (In the formula, M is at least one metal selected from the group consisting of Li, Na and K, M4 represents at least one metal selected from the group consisting of V, Ti, Cr, Mn, Fe, Co, Ni and Cu, 0.5≦e≦3, 1≦f≦2, 1≦g≦3). In the above, M is preferably selected from one of the metals in the group consisting of Li, Na and K, more preferably Li or Na, and even more preferably Li.

[0047] The transition metals used in lithium-containing transition metal phosphate compounds are preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, cobalt phosphates such as LiCoPO4, and compounds in which a portion of the transition metal atom that will form the main body of such lithium transition metal phosphate compounds is replaced by other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc. The lithium-containing transition metal phosphate compound mentioned above is preferably one with an olivine-type structure.

[0048] As other positive electrode active materials, examples include: MFePO4, MNi0.8Co0.2O2, M1.2Fe0.4Mn0.4O2, MNi0.5Mn1.5O2, MV3O6, M2MnO3 (where M is at least one metal selected from the group consisting of Li, Na, and K), and the like. In particular, positive electrode active materials such as M2MnO3 and MNi0.5Mn1.5O2 are preferable in that the crystal structure does not disintegrate when the secondary battery is operated at a voltage exceeding 4.4 V or a voltage of 4.6 V or higher. Therefore, regarding electrochemical devices such as secondary batteries using a positive electrode material containing the above-exemplified positive electrode active materials, even when stored at a high temperature, the remaining capacity is not easily reduced, the increase rate of the resistance does not easily change, and even when operated at a high voltage, the battery performance does not deteriorate. In this regard, it is preferable.

[0049] As other positive electrode active materials, examples also include solid solution materials of M2MnO3 and MM6O2 (where M is at least one metal selected from the group consisting of Li, Na, and K, and M6 is a transition metal such as Co, Ni, Mn, Fe), and the like.

[0050] As the above solid solution material, for example, it is an alkali metal manganese oxide represented by the general formula Mx[Mn(1 - y)M7y]Oz. Here, M in the formula is at least one metal selected from the group consisting of Li, Na, and K, M7 is composed of at least one metal element other than M and Mn, and for example, it includes one or more elements selected from the group consisting of Co, Ni, Fe, Ti, Mo, W, Cr, Zr, and Sn. Also, the values of x, y, and z in the formula are in the ranges of 1 < x < 2, 0 ≤ y < 1, and 1.5 < z < 3. Among them, from the viewpoint of providing an alkali metal ion secondary battery having a high energy density, a manganese-containing solid solution material such as Li1.2Mn0.5Co0.14Ni0.14O2 in which LiNiO2 or LiCoO2 is solid-solved based on Li2MnO3 is preferable.

[0051] Also, if the positive electrode active material contains lithium phosphate, the continuous charging characteristics are improved, so it is preferable. The use of lithium phosphate is not limited, and it is preferable to use it by mixing the above positive electrode active material and lithium phosphate. Regarding the total of the above positive electrode active material and lithium phosphate, the lower limit of the amount of lithium phosphate used is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.5% by mass or more, and the upper limit is preferably 10% by mass or less, more preferably 8% by mass or less, still more preferably 5% by mass or less.

[0052] Examples of conductive polymers include p-doped and n-doped conductive polymers. Examples of conductive polymers include polyacetylene-based polymers, polypropylene-based polymers, heterocyclic polymers, ionic polymers, ladder-like polymers, and network polymers.

[0053] Furthermore, the surface of the aforementioned positive electrode active material may be coated with a substance of a different composition. Examples of such surface coating substances include: oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, 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; and carbon.

[0054] Such surface-adhesive substances can be attached to the surface of the positive electrode active material by, for example, by dissolving or suspending them in a solvent, impregnating or adding them to the positive electrode active material, and then drying them; by dissolving or suspending the surface-adhesive substance precursor in a solvent, impregnating or adding it to the positive electrode active material, and then reacting it by heating or the like; by adding it to the positive electrode active material precursor and simultaneously calcining it; etc. Furthermore, in the case of carbon attachment, the following method can also be used, namely, to mechanically attach carbonaceous material, such as activated carbon, in a subsequent step.

[0055] The amount of surface-attached material, relative to the aforementioned positive electrode active material, is as follows by mass: preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more; preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The surface-attached material suppresses the oxidation reaction of the electrolyte on the surface of the positive electrode active material, thereby improving battery life. If the amount of material is too small, this effect cannot be fully realized; if it is too large, it will hinder the entry and exit of lithium ions, which may lead to an increase in resistance.

[0056] Regarding the shape of the particles of the positive electrode active material, examples include previously used blocky, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar shapes. Furthermore, primary particles can condense to form secondary particles.

[0057] The knock-tightness of the positive electrode active material is preferably 0.5 g / cm³ or higher, more preferably 0.8 g / cm³ or higher, and even more preferably 1.0 g / cm³ or higher. If the knock-tightness of the positive electrode active material is lower than the above-mentioned lower limit, it may lead to an increase in the amount of dispersion medium required when forming the positive electrode active material layer, as well as an increase in the amount of conductive material or binder required, limiting the filling rate of the positive electrode active material in the positive electrode active material layer, and thus limiting the battery capacity. By using composite oxide powder with higher knock-tightness, a high-density positive electrode active material layer can be formed. Generally speaking, the higher the knock-tightness, the better, and there is no particular upper limit. However, if it is too high, it may lead to a limited diffusion rate of lithium ions in the positive electrode active material layer using the electrolyte as a medium, and the loading characteristics may be easily reduced. Therefore, the upper limit is preferably 4.0 g / cm³ or lower, more preferably 3.7 g / cm³ or lower, and even more preferably 3.5 g / cm³ or lower. Furthermore, in this invention, the compactness is determined as follows: 5-10 g of positive electrode active material powder is placed into a 10 ml glass graduated cylinder and tapped 200 times with a stroke of approximately 20 mm. The powder filling density (compactness) g / cm³ at this time is then determined.

[0058] The median particle size d50 of the positive electrode active material (referring to the secondary particle size when primary particles agglomerate to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, further preferably 0.8 μm or more, and most preferably 1.0 μm or more. It is also preferably 30 μm or less, more preferably 27 μm or less, further preferably 25 μm or less, and most preferably 22 μm or less. If the particle size is below the lower limit, a high-density product may not be obtained. If the particle size exceeds the upper limit, the following problems may occur: lithium diffusion within the particles takes longer, which may lead to a decrease in battery performance; or streaks may occur during the fabrication of the positive electrode, i.e., when the active material is slurried with a solvent and coated into a thin film using a solvent. Here, by mixing two or more of the above-mentioned positive electrode active materials with different median particle sizes d50, the filling properties during the fabrication of the positive electrode can be further improved.

[0059] Furthermore, in this invention, the median particle size d50 is measured using a known laser diffraction / scattering particle size distribution measuring device. When using the HORIBA LA-920 as the particle size distributor, a 0.1% by mass sodium hexametaphosphate aqueous solution is used as the dispersion medium. After ultrasonic dispersion for 5 minutes, the refractive index is set to 1.24 for measurement.

[0060] When secondary particles are formed by the aggregation of primary particles, the average primary particle size of the aforementioned positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. The upper limit is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, and most preferably 2 μm or less. If the upper limit is exceeded, it becomes difficult to form spherical secondary particles, which adversely affects powder filling properties or leads to a significant reduction in specific surface area, thus increasing the likelihood of reduced battery performance, such as output characteristics. Conversely, if the lower limit is below the upper limit, problems such as poor charge-discharge reversibility may occur due to underdeveloped crystallization.

[0061] Furthermore, in this invention, the average primary particle size of the aforementioned positive electrode active material is determined by observation using a scanning electron microscope (SEM). Specifically, it is determined by: in a photograph at 10,000x magnification, finding the longest value of the intercept of the left and right boundary lines of any 50 primary particles relative to the horizontal straight line, and taking the average value.

[0062] The BET specific surface area of ​​the positive electrode active material is preferably 0.1 m² / g or more, more preferably 0.2 m² / g or more, and even more preferably 0.3 m² / g or more, with an upper limit preferably 50 m² / g or less, more preferably 40 m² / g or less, and even more preferably 30 m² / g or less. If the BET specific surface area is less than this range, the battery performance is prone to deterioration; if it is greater than this range, it is difficult to improve the compactness, and sometimes coating problems may occur when forming the positive electrode active material layer.

[0063] Furthermore, in this invention, the BET specific surface area is defined as follows: using a surface area meter (e.g., a fully automatic surface area measuring device manufactured by Riken Corporation of Okura), after pre-drying the sample at 150°C for 30 minutes under nitrogen flow, a nitrogen-helium mixed gas with the relative pressure of nitrogen relative to atmospheric pressure precisely adjusted to 0.3 is used to measure the BET specific surface area by the nitrogen adsorption BET single-point method based on gas flow method, and the measured value is defined as the above-mentioned BET specific surface area.

[0064] When using the secondary battery of the present invention as a large lithium-ion secondary battery for hybrid electric vehicles or distributed power sources, high output is required. Therefore, the particles of the positive electrode active material are preferably mainly secondary particles. The aforementioned positive electrode active material preferably comprises 0.5 to 7.0% by volume of secondary particles with an average particle size of less than 40 μm and an average primary particle size of less than 1 μm. By containing microparticles with an average primary particle size of less than 1 μm, the contact area with the electrolyte is increased, which can further accelerate the diffusion of lithium ions between the electrode additive and the electrolyte, thereby improving the output performance of the battery.

[0065] As a method for manufacturing positive electrode active materials, general methods for manufacturing inorganic compounds can be used. Especially when producing spherical or ellipsoidal active materials, various methods can be considered. For example, the following methods can be used: dissolving or pulverizing the transition metal raw material in a solvent such as water, adjusting the pH value while stirring to produce spherical precursors and recovering them, drying them as needed, adding Li sources such as LiOH, Li₂CO₃, or LiNO₃, and calcining at high temperature to obtain the active material.

[0066] To manufacture the positive electrode, the above-mentioned positive electrode active materials can be used alone, or they can be combined in any combination or ratio to form two or more different materials. Examples of preferred combinations include: ternary combinations such as LiCoO₂ and LiNi₀.₃Co₀.₃Mn₀.₃O₂; combinations such as LiCoO₂ and LiMn₂O₄, or combinations where a portion of the Mn is replaced by another transition metal; and combinations such as LiFePO₄ and LiCoO₂, or combinations where a portion of the Co is replaced by another transition metal.

[0067] From the viewpoint of higher battery capacity, the content of the above-mentioned positive electrode active material in the positive electrode compound is preferably 50 to 99.5% by mass, and more preferably 80 to 99% by mass. Furthermore, the content of the positive electrode active material is preferably 80% by mass or more, more preferably 82% by mass or more, and even more preferably 84% by mass or more. The upper limit is preferably 99% by mass or less, and more preferably 98% by mass or less. If the content of the positive electrode active material in the positive electrode mixture is too low, it may lead to insufficient capacity. Conversely, if the content is too high, it may lead to insufficient strength of the positive electrode.

[0068] There are no particular limitations on the negative electrode active material. Examples include any one or a mixture of two or more of the following: lithium metal, artificial graphite, graphite carbon fiber, resin-calcined carbon, thermally decomposed vapor-grown carbon, coke, mesophase microcarbon spheres (MCMB), furan-methanol resin-calcined carbon, polyphenylene oxide, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite and non-graphitizable carbon, silicon-containing compounds such as silicon and silicon alloys, and Li₄Ti₅O₁₂. Among these, it is particularly suitable to use materials containing at least a portion of carbonaceous materials or silicon-containing compounds.

[0069] The negative electrode active material used in this invention preferably contains silicon as a constituent element. By including silicon as a constituent element, high-capacity batteries can be manufactured.

[0070] The preferred silicon-containing particles are silicon particles, particles having a structure of silicon microparticles dispersed in a silicon-based compound, silicon oxide particles represented by the general formula SiOx (0.5≦x≦1.6), or mixtures thereof. By using these, a negative electrode mixture for lithium-ion secondary batteries with higher initial charge-discharge efficiency, higher capacity, and excellent cycle characteristics can be obtained.

[0071] In this invention, silicon oxide refers to a general term for amorphous silicon oxides. Silicon oxide before disproportionation is represented by the general formula SiOx (0.5 ≤ x ≤ 1.6). Preferably, x is 0.8 ≤ x < 1.6, and more preferably 0.8 ≤ x < 1.3. This silicon oxide can be obtained, for example, by heating a mixture of silicon dioxide and metallic silicon to generate silicon monoxide gas, and then cooling and precipitating the silicon monoxide gas to obtain the aforementioned silicon oxide.

[0072] Regarding particles having a structure in which silicon microparticles are dispersed in a silicon-based compound, they can be obtained, for example, by sintering a mixture of silicon microparticles and a silicon-based compound; or by heat-treating silicon oxide particles represented by the general formula SiOx before disproportionation at a temperature of 400°C or higher, preferably 800 to 1,100°C, in an inactive, non-oxidizing environment such as argon, to carry out a disproportionation reaction. The latter method, in particular, yields materials in which silicon crystallites are uniformly dispersed, and is therefore preferred. Through the disproportionation reaction described above, the size of silicon nanoparticles can be made to be 1 to 100 nm. Furthermore, regarding the silicon oxide in particles having a structure in which silicon nanoparticles are dispersed in silicon oxide, silicon dioxide is preferred. Moreover, by transmission electron microscopy, it can be confirmed that silicon nanoparticles (crystals) are dispersed in amorphous silicon oxide.

[0073] The physical properties of the silicon-containing particles can be appropriately selected based on the target composite particles. For example, the average particle size is preferably 0.1 to 50 μm, with a lower limit of 0.2 μm or more, and further preferably 0.5 μm or more. The upper limit is preferably 30 μm or less, and further preferably 20 μm or less. Furthermore, the average particle size in this invention refers to the weight-average particle size measured in particle size distribution determination based on laser diffraction.

[0074] The BET specific surface area of ​​the silicon-containing particles is preferably 0.5~100 m² / g, more preferably 1~20 m² / g. If the BET specific surface area is 0.5 m² / g or higher, the adhesion when coated onto the electrode decreases, but there is no risk of reduced battery performance. Furthermore, if it is 100 m² / g or lower, the proportion of silicon dioxide on the particle surface increases, and when used as a negative electrode material for lithium-ion secondary batteries, there is no risk of reduced battery capacity.

[0075] By carbon coating the aforementioned silicon-containing particles, conductivity is imparted, thus improving battery performance. Examples of methods for imparting conductivity include: mixing with conductive particles such as graphite; coating the surface of the silicon-containing particles in the form of a carbon film; and combining both methods. The method of coating in the form of a carbon film is preferred, and the method of chemical vapor deposition (CVD) is even more preferred.

[0076] To increase the capacity of the obtained electrode mixture, the content of the aforementioned negative electrode active material in the electrode mixture is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. Furthermore, the upper limit is preferably 99% by mass or less, and more preferably 98% by mass or less.

[0077] (Conductive additive) As the aforementioned conductive additives, any known conductive material can be used. Specific examples include: metallic materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, chimney black, furnace black, lamp black, and thermal black; carbon materials such as needle coke, carbon nanotubes, fullerenes, and amorphous carbon such as VGCF (vapor-grown carbon fiber). Furthermore, one of these materials can be used alone, or two or more can be used in any combination and ratio.

[0078] The conductive additive is used in the electrode mixture in the following amounts: typically 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and typically 50% by mass or less, preferably 30% by mass or less, more preferably 15% by mass or less. If the content is below this range, insufficient conductivity may result. Conversely, if the content is above this range, the battery capacity may be reduced.

[0079] (Other ingredients) The electrode mixture may further contain thermoplastic resins. Examples of thermoplastic resins include vinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, and polyethylene oxide. A single resin may be used, or two or more may be used in any combination and ratio.

[0080] The ratio of thermoplastic resin relative to the electrode active material is typically 0.01% by mass or more, preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more; and typically 3.0% by mass or less, preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less. Adding thermoplastic resin can improve the mechanical strength of the electrode. However, if the ratio exceeds this range, the proportion of electrode active material in the electrode mixture decreases, which may lead to problems such as reduced battery capacity or increased resistance between active materials.

[0081] In the electrode compound of the present invention, the binder content is calculated as the ratio of binder in the electrode compound, and is typically 0.1% by mass or more, preferably 0.5% by mass or more, and even more preferably 1.0% by mass or more. It is also typically 50% by mass or less, preferably 40% by mass or less, even more preferably 30% by mass or less, and most preferably 10% by mass or less. If the binder ratio is too low, the active material in the electrode compound may not be sufficiently retained, resulting in insufficient mechanical strength of the electrode compound sheet and deterioration of battery performance such as cycle characteristics. On the other hand, if the binder ratio is too high, it may lead to a decrease in battery capacity or conductivity.

[0082] The electrode compound of this invention can be used as an electrode compound for secondary batteries. In particular, the electrode compound of this invention is suitable for lithium-ion secondary batteries. When the electrode mixture of the present invention is used in secondary batteries, it is usually used in the form of sheets.

[0083] The following is an example of a specific manufacturing method for an electrode mixture tablet containing an electrode mixture. The electrode compound sheet of the present invention can be obtained by a manufacturing method for a secondary battery electrode compound sheet having the following steps: Step (1) involves mixing a raw material composition containing electrode active materials, binders, and conductive additives as needed, while simultaneously applying shear force; Step (2) involves shaping the electrode mixture obtained through step (1) into a block shape; and Step (3) involves calendering the blocky electrode mixture obtained by step (2) into a sheet.

[0084] In step (1) above, during the stage where the mixed raw material components are simultaneously subjected to shear force, the obtained electrode mixture exists in a state where the electrode active material, binder, etc., are simply mixed together without a fixed shape. Specific mixing methods include using the following machines: W-type mixer, V-type mixer, rotary drum mixer, belt mixer, conical spiral mixer, single-shaft mixer, twin-shaft mixer, mixing mill, stirring mixer, planetary mixer, etc.

[0085] In step (1) above, regarding the mixing conditions, it is sufficient to set the rotation speed and mixing time appropriately. For example, the rotation speed is suitable to be set below 1000 rpm. Preferably, it is above 10 rpm, more preferably above 15 rpm, and even more preferably above 20 rpm. Also, it is preferably below 900 rpm, more preferably below 800 rpm, and even more preferably in the range of 700 rpm. If it is below the above range, the mixing time will be long, which will affect productivity. Furthermore, if it is above the above range, the fibrillation will be excessive, which may result in electrode composite sheets with poor strength and flexibility.

[0086] In step (2) above, forming into a block means making the electrode mixture into a block. Specific methods for forming blocks include extrusion molding and pressure molding. Furthermore, the shape of the "block" is not particularly limited, as long as it is a single block shape, including rod-shaped, sheet-shaped, spherical, cubic, etc. The size of the block is preferably such that its cross-sectional diameter or the smallest side is 10,000 μm or more. More preferably, it is 20,000 μm or more.

[0087] As a specific calendering method in step (3) above, examples include calendering using a roller press, a flatbed press, a calendering roller, etc.

[0088] Furthermore, it is also preferable to perform step (4) after step (3), in which a greater load is applied to the obtained calendered sheet to calender it into a thinner sheet. It is also preferable to repeat step (4). In this way, calendering is carried out gradually in stages, rather than thinning the calendered sheet all at once, thereby improving its flexibility. The number of times step (4) is preferably more than 2 and less than 10, and more preferably more than 3 and less than 9. Specific calendering methods include, for example, methods that process calendered sheets into thinner sheets by rotating two or more rollers and passing them through the rollers.

[0089] Furthermore, from the viewpoint of adjusting the diameter of the fibrils, it is also preferable to have the following step (5) after step (3) or step (4), in which the calendered sheet is coarsely crushed, re-formed into a block, and calendered into a sheet. It is also preferable to repeat step (5). The number of times step (5) is performed is preferably more than once and less than 12 times, more preferably more than twice and less than 11 times.

[0090] In step (5), specific methods for forming the calendered sheet into a block after coarse crushing can be exemplified by: folding the calendered sheet, forming it into a rod or film sheet, or fragmenting it. In this invention, "coarse crushing" means changing the shape of the calendered sheet obtained in step (3) or step (4) into other shapes in order to calender it into a sheet in the next step, including the case of simply folding the calendered sheet.

[0091] Alternatively, step (4) can be performed after step (5), or it can be repeated. Furthermore, uniaxial or biaxial extension can be performed in steps (2), (3), (4), or (5). Furthermore, the diameter (central value) of the original fiber can also be adjusted by the degree of coarse grinding in step (5).

[0092] In steps (3), (4), or (5) above, the calendering rate is preferably 10% or more, more preferably 20% or more, and preferably 80% or less, more preferably 65% ​​or less, and even more preferably 50% or less. If it is below the above range, the number of calendering cycles increases while also consuming more time, thus affecting productivity. Furthermore, if it is above the above range, excessive fibrillation occurs, which may result in electrode composite sheets with poor strength and flexibility. Furthermore, the rolling rate mentioned here refers to the rate of reduction in the thickness of the sample after rolling relative to its thickness before rolling. The sample before rolling can be a block-shaped raw material or a sheet-shaped raw material. The thickness of the sample refers to the thickness in the direction in which the load is applied during rolling.

[0093] As described above, PTFE powder is fibrillated by applying shear force. However, when producing PTFE powder with a fibrous structure having a fibril diameter (central value) of 70 nm or less, excessive shear stress may over-promote fibrillation, impairing flexibility. Conversely, insufficient shear stress may result in insufficient strength. Therefore, by applying appropriate shear stress to PTFE during mixing or calendering to promote fibrillation, and by calendering and stretching the resin into sheets within the aforementioned range, a fibrous structure with a fibril diameter (central value) of 70 nm or less can be produced.

[0094] The electrode compound sheet of this invention can be used as an electrode compound sheet for secondary batteries. It can also be used as either a negative electrode or a positive electrode. In particular, the electrode compound sheet of this invention is suitable for lithium-ion secondary batteries.

[0095] (positive electrode) In this invention, the positive electrode is preferably composed of a current collector and an electrode compound sheet containing the above-mentioned positive electrode active material. Examples of materials that can be used as current collectors for the positive electrode include: metals such as aluminum, titanium, tantalum, stainless steel, and nickel, or their alloys; and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, especially aluminum or its alloys, are preferred.

[0096] Regarding the shape of the current collector, if it is a metallic material, examples include metal foil, metal cylinder, metal coil, metal plate, porous metal, perforated metal, foamed metal, etc.; if it is a carbon material, examples include carbon plate, carbon film, carbon cylinder, etc. Among these, metal foil is preferred. Furthermore, metal foil can be appropriately shaped into a mesh. The thickness of the metal foil is not limited, but is typically 1 μm or more, preferably 3 μm or more, and even more preferably 5 μm or more. It is also typically 1 mm or less, preferably 100 μm or less, and even more preferably 50 μm or less. If the metal foil is thinner than this range, it may result in insufficient strength required as a current collector. Conversely, if the metal foil is thicker than this range, it may result in impaired processability.

[0097] Furthermore, from the viewpoint of reducing the contact resistance between the current collector and the positive electrode, it is preferable to coat the surface of the current collector with a conductive additive. Examples of conductive additives include carbon, or precious metals such as gold, platinum, and silver.

[0098] There is no particular limitation on the thickness ratio of the current collector to the positive electrode composite sheet, but preferably, the ratio of (thickness of the positive electrode composite sheet on one side before electrolyte injection) to (thickness of the current collector) is 20 or less, more preferably 15 or less, and most preferably 10 or less. Furthermore, it is preferably 0.5 or more, more preferably 0.8 or more, and most preferably 1 or more. If it exceeds this range, the current collector may generate heat due to Joule heating during charging and discharging at high current densities. If it is below this range, the volume ratio of the current collector to the positive electrode active material may increase, resulting in a decrease in battery capacity.

[0099] The positive electrode can be manufactured using conventional methods. For example, a method can be used to laminate the electrode composite sheet and the current collector using an adhesive and then perform vacuum drying.

[0100] The density of the positive electrode compound sheet is preferably 3.00 g / cm³ or higher, more preferably 3.10 g / cm³ or higher, and even more preferably 3.20 g / cm³ or higher; further preferably 3.80 g / cm³ or lower, more preferably 3.75 g / cm³ or lower, and even more preferably 3.70 g / cm³ or lower. If the density is higher than this range, the permeability of the electrolyte to the interface between the current collector and the active material may decrease, especially reducing the charge-discharge characteristics at high current densities and preventing the achievement of high output. Conversely, if the density is lower than this range, the conductivity between the active materials may decrease, increasing the battery resistance and preventing the achievement of high output.

[0101] From the perspective of high output and improved stability at high temperatures, the area of ​​the positive electrode compound sheet is preferably larger than the outer surface area of ​​the battery packaging casing. Specifically, the total area of ​​the positive electrode compound sheet relative to the surface area of ​​the secondary battery packaging is preferably set to at least 15 times, and more preferably at least 40 times. Regarding the outer surface area of ​​the battery packaging casing, if it is a square shape with a base, it refers to the total area calculated based on the longitudinal, transverse, and thickness dimensions of the casing portion filled with the power generation elements excluding the terminal protrusions. If it is a cylindrical shape with a base, it refers to the geometric surface area approximated by the casing portion filled with the power generation elements excluding the terminal protrusions as a cylinder. The total area of ​​the positive electrode compound refers to the geometric surface area of ​​the positive electrode compound layer opposite to the compound layer containing the negative electrode active material. In a structure in which the dielectric current collector forms positive electrode compound layers on both sides, the total area of ​​the positive electrode compound refers to the sum of the areas obtained by calculating each side separately.

[0102] There is no particular limitation on the thickness of the positive electrode, but from the point of view of high capacity and high output, the lower limit of the thickness of the compound sheet obtained by subtracting the thickness of the current collector from the thickness of the current collector is preferably 10 μm or more, more preferably 20 μm or more, and more preferably 500 μm or less, and more preferably 450 μm or less.

[0103] Alternatively, a positive electrode with a different composition can be used. Examples of such surface adhering substances include: oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, 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; and carbon.

[0104] (negative electrode) In this invention, the negative electrode is preferably composed of a current collector and an electrode compound sheet containing the aforementioned negative electrode active material. Examples of materials that can be used as current collectors for the negative electrode include: metals such as copper, nickel, titanium, tantalum, and stainless steel, or their alloys; and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, especially copper, nickel, or their alloys, are preferred.

[0105] Regarding the shape of the current collector, if it is a metallic material, examples include metal foil, metal cylinder, metal coil, metal plate, porous metal, perforated metal, foamed metal, etc.; if it is a carbon material, examples include carbon plate, carbon film, carbon cylinder, etc. Among these, metal foil is preferred. Furthermore, metal foil can be appropriately shaped into a mesh. The thickness of the metal foil is not limited, but is typically 1 μm or more, preferably 3 μm or more, and even more preferably 5 μm or more. It is also typically 1 mm or less, preferably 100 μm or less, and even more preferably 50 μm or less. If the metal foil is thinner than this range, it may result in insufficient strength required as a current collector. Conversely, if the metal foil is thicker than this range, it may result in impaired processability.

[0106] The negative electrode can be manufactured using conventional methods. For example, a method can be used to laminate the electrode composite sheet and the current collector using an adhesive and then perform vacuum drying.

[0107] The density of the negative electrode compound sheet is preferably 1.3 g / cm³ or higher, more preferably 1.4 g / cm³ or higher, and even more preferably 1.5 g / cm³ or higher; further preferably 2.0 g / cm³ or lower, more preferably 1.9 g / cm³ or lower, and even more preferably 1.8 g / cm³ or lower. If the density is higher than this range, the permeability of the electrolyte to the interface between the current collector and the active material may decrease, especially reducing the charge-discharge characteristics at high current densities and preventing the achievement of high output. Conversely, if the density is lower than this range, the conductivity between the active materials may decrease, increasing the battery resistance and preventing the achievement of high output.

[0108] There is no particular limitation on the thickness of the negative electrode, but from the point of view of high capacity and high output, the lower limit of the thickness of the compound sheet obtained by subtracting the thickness of the current collector from the thickness of the current collector is preferably 10 μm or more, more preferably 20 μm or more, and more preferably 500 μm or less, and more preferably 450 μm or less.

[0109] (Secondary battery) This invention is also a secondary battery that uses the aforementioned electrode compound sheet. The secondary battery of this invention can use electrolytes, spacers, etc., as known in secondary batteries. These will be described in detail below.

[0110] (electrolyte) As a non-aqueous electrolyte, a solution prepared by dissolving a known electrolyte salt in a known organic solvent for dissolving electrolyte salts can be used.

[0111] There are no particular limitations on the organic solvent used for dissolving electrolyte salts. Known hydrocarbon solvents such as propylene carbonate, ethyl carbonate, butyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate can be used; one or more fluorinated solvents such as ethyl fluorocarbonate, fluoroether, and fluorinated carbonate can also be used.

[0112] Examples of electrolyte salts include LiClO4, LiAsF6, LiBF4, LiPF6, LiN(SO2CF3)2, and LiN(SO2C2F5)2. From the viewpoint of good cycling characteristics, LiPF6, LiBF4, LiN(SO2CF3)2, LiN(SO2C2F5)2, or combinations thereof are particularly preferred.

[0113] The concentration of the electrolyte salt must be at least 0.8 mol / L, and further at least 1.0 mol / L. The upper limit also depends on the organic solvent used to dissolve the electrolyte salt, and is usually 1.5 mol / L.

[0114] (spacer) The secondary battery of the present invention preferably further includes a spacer. Regarding the material or shape of the aforementioned spacer, there are no particular limitations as long as it is stable in the electrolyte and has excellent liquid retention properties; known materials can be used. Among them, resins, glass fibers, inorganic materials, etc., formed from materials that are stable with respect to the electrolyte of the present invention or the electrolyte used in the alkali metal secondary battery of the present invention can be used. It is preferable to use porous sheets or non-woven fabric-like objects with excellent liquid retention properties.

[0115] Materials used as spacers for resins and glass fibers include, for example, polyethylene, polypropylene and other polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, glass filters, etc. Polypropylene / polyethylene two-layer membranes, polypropylene / polyethylene / polypropylene three-layer membranes, etc., can be used alone, or two or more materials can be used in any combination and ratio. From the perspective of good electrolyte permeability and shutdown effect, the aforementioned spacer is preferably a porous sheet or non-woven fabric made of polyolefins such as polyethylene and polypropylene.

[0116] The thickness of the spacer is not limited, but is typically 1 μm or more, preferably 5 μm or more, and even more preferably 8 μm or more. It is also typically 50 μm or less, preferably 40 μm or less, and even more preferably 30 μm or less. If the spacer becomes too thin compared to the above ranges, it may lead to a decrease in insulation or mechanical strength. Conversely, if it becomes too thick compared to the above ranges, it may not only lead to a decrease in battery performance such as rate characteristics, but also to a decrease in the overall energy density of the electrolyte battery.

[0117] Furthermore, when using porous materials such as porous sheets or non-woven fabrics as spacers, the porosity of the spacer is not limited, but is typically 20% or more, preferably 35% or more, and even more preferably 45% or more. It is also typically 90% or less, preferably 85% or less, and even more preferably 75% or less. If the porosity becomes too small compared to the above ranges, the film resistance increases, and the rate characteristics tend to deteriorate. Conversely, if the porosity becomes too large compared to the above ranges, the mechanical strength of the spacer decreases, and the insulation performance tends to decrease.

[0118] Furthermore, the average aperture of the spacer is not limited, but is typically below 0.5 μm, preferably below 0.2 μm, and typically above 0.05 μm. If the average aperture is higher than the above range, short circuits are more likely to occur. Conversely, if it is lower than the above range, it may lead to increased film resistance and reduced rate characteristics.

[0119] On the other hand, as inorganic materials, for example, oxides such as aluminum oxide or silicon dioxide, nitrides such as aluminum nitride or silicon nitride, and sulfates such as barium sulfate or calcium sulfate can be used, and they can be in particle or fiber shape.

[0120] As a form, it can be a thin film such as non-woven fabric, woven fabric, or microporous membrane. If it is a thin film, it is suitable to use one with a pore size of 0.01~1 μm and a thickness of 5~50 μm. In addition to the above-mentioned independent thin film shapes, the following spacer can be used, which is formed by using a resin-based binder to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode. For example, a porous layer can be formed on both sides of the positive electrode by using fluororesin as a binder to form a layer with 90% of alumina particles having a diameter of less than 1 μm.

[0121] (Battery Design) The electrode assembly can be either a laminated structure formed by separating the positive and negative electrodes with the spacer, or a structure formed by winding the positive and negative electrodes with the spacer into a spiral shape. The ratio of the volume of the electrode assembly to the internal volume of the battery (hereinafter referred to as the electrode assembly occupancy) is typically 40% or more, preferably 50% or more, and typically 90% or less, preferably 80% or less.

[0122] If the electrode mixture occupancy rate is lower than the above range, it may result in a smaller battery capacity. Conversely, if it is higher than the above range, there will be less space, causing the components to expand due to the battery reaching high temperatures, or the vapor pressure of the electrolyte liquid components to increase, leading to an increase in internal pressure. This reduces the battery's charge-discharge repetition performance and high-temperature storage characteristics, which may cause the venting valve that releases internal pressure to the outside to activate.

[0123] There are no particular limitations on the current collector structure. However, to more effectively improve the high current density charge-discharge characteristics using the electrolyte, it is preferable to adopt a structure that reduces the resistance of the wiring or connection parts. In such cases of reduced internal resistance, the effect of using the electrolyte will be particularly well utilized.

[0124] If the electrode mixture assembly has the above-described laminated structure, it is suitable to use a structure in which the metal core portions of each electrode mixture layer are bundled together and fused to terminals. When the area of ​​an electrode mixture is large, the internal resistance increases, so it is also suitable to use multiple terminals within the electrode mixture to reduce resistance. If the electrode mixture assembly has the above-described wound structure, multiple lead structures are provided at the positive and negative electrodes respectively, and bundled together at terminals, thereby reducing internal resistance.

[0125] There are no particular restrictions on the material of the packaging shell, as long as it is a stable substance for the electrolyte used. Specifically, nickel-plated steel, stainless steel, aluminum or aluminum alloy, magnesium alloy, or laminated films of resin and aluminum foil can be used. From a lightweighting point of view, aluminum or aluminum alloy metals and laminated films are suitable.

[0126] For packaging shells made of metal, examples include welding the metal together using laser welding, resistance welding, or ultrasonic welding to create a sealed structure, or using the aforementioned metals with a resin liner to create a press-fit structure. For packaging shells made of laminated film, examples include creating a sealed structure by heat-melting the resin layers together. To improve sealing, a resin different from the resin used in the laminated film can be placed between the resin layers. Especially when heat-melting the resin layers to create a sealed structure by separating the current collector terminals, the metal and resin will bond together; therefore, it is suitable to use a resin with polar groups or a modified resin with polar groups as the intervening resin.

[0127] The shape of the secondary battery of this invention is not limited; for example, cylindrical, square, laminated, coin-shaped, and large shapes are possible. Furthermore, the shape and structure of the positive electrode, negative electrode, and spacer can be modified according to the shape of each battery. Example

[0128] The present invention will now be described in detail based on embodiments. In the following embodiments, unless otherwise specified, “parts” and “%” represent “parts by mass” and “% by mass”, respectively.

[0129] [Production example 1] Powdered PTFE-A was prepared with reference to Example 2 of International Publication No. 2015-080291.

[0130] [Production example 2] Powdered PTFE-B was prepared with reference to Example 3 of International Publication No. 2015-080291.

[0131] [Production example 3] Powdered PTFE-C was prepared with reference to Example 1 of International Publication No. 2012 / 086710.

[0132] [Production example 4] Powdered PTFE-D was prepared with reference to Adjustment 1 of International Regulation 2012-063622. The physical properties of the PTFE produced are shown in Table 1.

[0133] [Table 1] Making PTFE form Standard Specific Gravity Moisture content (ppm) after vacuum drying PTFE-A powder 2.16 <250 PTFE-B powder 2.15 <250 PTFE-C powder 2.16 <250 PTFE-D powder 2.19 <250

[0134] (Example 1) <Production of Positive Polarity Compound Tablets> Li(Ni 0.6Mn 0.2Co 0.2)O 2 (NMC622), which serves as the positive electrode active material, and carbon black, which serves as the conductive additive, were weighed and stirred in a mortar at 200 rpm for 1 hour to obtain a mixture. Powdered PTFE-C is dried at 50°C for 1 hour in a vacuum dryer before use. Furthermore, the powdered PTFE is pre-sieved using a stainless steel sieve with a mesh size of 500 μm, and the powdered PTFE remaining on the sieve is used. Then, powdered PTFE as a binder was added to the container containing the mixture, and the mixture was stirred at 40 rpm for 2 hours to obtain the final mixture. The mass ratio of positive electrode active material: binder: conductive additive was set to 95:2:3. The resulting mixture is shaped into blocks and then rolled into sheets. Then, the following steps are repeated four times: the calendered sheet obtained above is coarsely crushed by folding, reshaped into a block, and then calendered into a sheet using metal rollers on a flat plate, thereby promoting fibrillation. Then, further calendering is performed to obtain a positive electrode compound sheet with a thickness of approximately 500 μm. Next, the positive electrode compound sheet is cut into 5 cm × 5 cm pieces and fed into a roller press for calendering. Furthermore, to promote fibrillation, a load of 2 kN is repeatedly applied to adjust the thickness. The gap is adjusted so that the final thickness of the positive electrode compound layer is 101 μm. The initial calendering rate is the highest, at 27%.

[0135] <The Making of Positive Elements> It is bonded to a 20 μm aluminum foil. The adhesive used is a slurry in which polyvinylidene fluoride (PVDF) is dissolved in N-methylpyrrolidone (NMP) and carbon nanotubes (CNTs) are dispersed. The adhesive is applied to the aluminum foil, and the prepared sheet-like positive electrode is placed in a manner that prevents air bubbles from entering. It is then vacuum dried at 100°C for 30 minutes to produce a positive electrode sheet that is integrated with the current collector.

[0136] <The Making of the Negative Electrode> Artificial graphite powder as the negative electrode active material, an aqueous dispersion of sodium carboxymethyl cellulose (sodium carboxymethyl cellulose concentration 1.5% by mass) as a thickener, an aqueous dispersion of styrene-butadiene rubber (SBR) (styrene-butadiene rubber concentration 50% by mass) as a binder, and water as a solvent were added to the aqueous solvent at a ratio of 97.6:1.2:1.2 (mass %) based on solids content to prepare a negative electrode slurry. This slurry was uniformly coated onto a 20 μm thick copper foil and dried (110°C, 30 minutes). Then, it was compressed using a press under a 10 kN load to form a negative electrode sheet integrated with the current collector. The thickness of the negative electrode slurry layer was 99 μm.

[0137] <Electrolyte Production> An organic solvent was prepared by measuring a mixture of ethyl fluorocarbonate (EC) and ethyl methyl methyl carbonate (EMC) (EC:EMC = 30:70 (volume ratio)) into a sample vial, and dissolving fluoroethylene ethyl carbonate (FEC) and vinyl fluorocarbonate (VC) separately in the solvent at 1% by mass. The concentration of LiPF6 salt in the electrolyte was adjusted to 1.0 moles / L, and the mixture was stirred at 23°C to obtain the electrolyte solution.

[0138] Battery Manufacturing The aforementioned negative electrode sheet, positive electrode sheet, and polyethylene spacer are stacked in the order of negative electrode, spacer, and positive electrode to form a battery element. The battery element, with its positive and negative terminals protruding, is inserted into a bag made of laminated film. The laminated film is made of aluminum (40 μm thick) with resin layers on both sides. Then, electrolyte is injected into the bag and vacuum-sealed to produce a sheet-like lithium-ion secondary battery.

[0139] (Examples 2-4) Except for the use of PTFE as shown in Table 2, lithium-ion secondary batteries were manufactured in the same manner as in Example 1.

[0140] (Comparative Example 1) <Production of Positive Polarity Compound Tablets> Weigh NMC622, the positive electrode active material, and carbon black, the conductive additive, and stir them in a mortar at 200 rpm for 1 hour to obtain a mixture. Then, the powdered PTFE shown in Table 2, as a binder, was added to the container containing the mixture. After stirring at 40 rpm for 2 hours, the mixture was kneaded at 1400 rpm for 5 minutes using a mixer to obtain the final mixture. The solid composition was set at a mass ratio of positive electrode active material: binder: conductive additive = 95:2:3. The resulting mixture is shaped into blocks and then rolled into sheets. Then, the following steps are repeated four times: the calendered sheet obtained above is coarsely crushed by folding, reshaped into a block, and then rolled into a sheet using metal rollers on a flat plate to promote fibrillation. Then, calendering is performed to obtain a positive electrode compound sheet with a thickness of 500 μm. Next, the positive electrode compound sheet is cut into 5 cm × 5 cm pieces and fed into a roller press for calendering. Then, to promote fibrillation, a load of 10 kN is repeatedly applied to adjust the thickness. The gap is adjusted so that the final thickness of the positive electrode compound layer is 101 μm. The initial calendering yield is the highest, at 52%.

[0141] Battery Manufacturing Using the positive electrode compound sheet prepared above, the same procedure as in Example 1 was followed to produce a lithium-ion secondary battery.

[0142] (Comparative Example 2) The lithium-ion secondary battery was manufactured using the PTFE shown in Table 2, except that the process was the same as in Comparative Example 1.

[0143] (Example 5) <Production of Negative Electrode Compound Tablets> 25.65 g of artificial graphite powder and 2.85 g of SiO2, used as the negative electrode active materials, were weighed and stirred in a mortar at 200 rpm for 1 hour to obtain a mixture. The powdered PTFE was dried in a vacuum dryer at 50°C for 1 hour before use. Furthermore, the powdered PTFE-C was sieved beforehand using a stainless steel sieve with a mesh size of 500 μm, and the powdered PTFE-C remaining on the sieve was used. Then, 2.0 g of powdered PTFE as a binder was added to the container containing the mixture, and the mixture was stirred at 40 rpm for 2 hours to obtain the final mixture. The resulting mixture was then shaped into blocks and calendered into sheets. Then, the following steps are repeated four times: the calendered sheet obtained above is coarsely crushed by folding, reshaped into a block, and then rolled into a sheet using metal rollers on a flat plate to promote fibrillation. Then, calendering is performed to obtain a negative electrode compound sheet with a thickness of 500 μm. Next, the negative electrode compound sheet is cut into 5 cm × 5 cm pieces and fed into a roller press for calendering. Then, to promote fibrillation, a load of 2 kN is repeatedly applied to adjust the thickness. The gap is adjusted so that the final thickness of the negative electrode compound layer is 101 μm. The initial calendering yield is the highest, at 38%.

[0144] <The Making of the Negative Electrode> It is bonded to a 20 μm copper foil. The adhesive used is a slurry in which PVDF is dissolved in NMP and CNTs are dispersed. The adhesive is applied to the copper foil, and the prepared negative electrode composite sheet is placed in a manner that prevents air bubbles from entering. It is then vacuum dried at 100°C for 30 minutes to obtain a negative electrode sheet that is integrated with the current collector.

[0145] <The Making of Positive Elements> A mixture of 95% by mass of Li(Ni 1 / 3Mn 1 / 3Co 1 / 3)O 2 (NMC111) as the positive electrode active material, 3% by mass of acetylene black as a conductive additive, and 2% by mass of PVdF as a binder was prepared by mixing in NMP solvent to form a slurry. The resulting slurry was uniformly coated onto an aluminum foil with a thickness of 20 μm and dried (110°C, 30 minutes). Then, a positive electrode sheet was formed by applying a 10 kN load using a press, thus integrating the positive electrode with the current collector. The thickness of the electrode composite layer was approximately 100 μm.

[0146] Battery Manufacturing Using the negative and positive electrodes prepared above, the same procedure as in Example 1 was followed to produce a lithium-ion secondary battery.

[0147] (Examples 6-8) Lithium-ion secondary batteries were fabricated using the PTFE shown in Table 3, except that the process was the same as in Example 5.

[0148] (Comparative Example 3) <Production of Negative Electrode Compound Tablets> Weigh 25.65 g of artificial graphite powder and 2.85 g of SiO, which are used as the negative electrode active material, and stir them in a mortar at 200 rpm for 1 hour to obtain a mixture. Then, add 2.0 g of powdery PTFE shown in Table 3 as a binder to the container containing the mixture, and knead it at 1400 rpm for 5 minutes to obtain a mixture. Shape the obtained mixture into a块状, and roll it into a片状. Then, repeat the following steps 4 times: coarsely crush the rolled sheet obtained above by folding it in half, shape it into a块状 again, and then roll it into a片状 on a flat plate using a metal roller to promote fibrillation. Then, further roll it to obtain a negative electrode binder sheet with a thickness of 500 μm. Furthermore, cut the negative electrode binder sheet into 5 cm × 5 cm, and put it into a roller press for rolling. Repeatedly apply a load of 10 kN to adjust the thickness. Adjust the gap so that the thickness of the final negative electrode binder layer becomes 101 μm. The rolling rate of the first time is the largest, which is 78%.

[0149] <Fabrication of Battery> Using the negative electrode binder sheet fabricated above, except for this, fabricate a lithium-ion secondary battery in the same manner as in Example 5.

[0150] (Comparative Example 4) Using the PTFE shown in Table 2, except for this, obtain a lithium-ion secondary battery in the same manner as in Comparative Example 3.

[0151] (Reference Example 1) <Fabrication Method of SiO Negative Electrode Slurry> Prepare an SiO negative electrode binder slurry by mixing 25.65 g of artificial graphite powder as the negative electrode active material, 2.85 g of SiO, 2.0 g of polyacrylic acid as the binder, and 20 g of N-methylpyrrolidone (NMP) as the solvent in a mixer. Uniformly coat it on a copper foil with a thickness of 20 μm, and after drying (110 °C, 30 minutes), use a press to compress and form it to fabricate a negative electrode sheet integrated with the current collector. The thickness of the electrode binder layer is 95 μm.

[0152] <Fabrication of Battery> Using the negative electrode sheet fabricated above, except for this, fabricate a lithium-ion secondary battery in the same manner as in Example 5.

[0153] Each test is carried out by the following method. [Moisture Content Measurement] Powdered PTFE was dried in a vacuum dryer at 50°C for 1 hour. The moisture content of the vacuum-dried PTFE was determined as follows: using a Karl Fischer moisture meter (ADP-511 / MKC-510N, manufactured by Kyoto Electronics Industry Co., Ltd.) with a boat-shaped moisture vaporization device, the temperature was heated to 210°C in the moisture vaporization device, and the vaporized moisture was measured. Nitrogen gas was used as the carrier gas at a flow rate of 200 mL / min, and the measurement time was set to 30 minutes. KEMAQUA was used as the Karl Fischer reagent. The sample amount was set to 1.5 g.

[0154] [PTFE fibril diameter (center value) (nm)] (1) The image was obtained by taking a magnified photograph (7000x) of the electrode mixture tablet using a scanning electron microscope (S-4800 type manufactured by Hitachi). (2) Draw two lines at equal intervals along the horizontal direction on the image to divide the image into three equal parts. (3) For all PTFE fibers located on the upper straight line, the diameter of each PTFE fiber is measured at three points, and the average value is taken as the diameter of the PTFE fiber. The three points for measurement are the intersection of the PTFE fiber and the straight line, the position offset upward from the intersection point by 0.5 μm, and the position offset downward from the intersection point by 0.5 μm. (Except for unfiberized primary PTFE particles). (4) Perform the above (3) operation on all PTFE fibers located on the straight line below. (5) Using the first image as the starting point, move 1 mm to the right of the frame and take another picture. Measure the diameter of the PTFE fibers using steps (3) and (4) above. Repeat the above operation until the number of fibers measured exceeds 80. (6) Take the median value of the diameter of all the PTFE fibers measured above as the size of the original fiber diameter.

[0155] For reference, a scanning electron microscope photograph showing the cross-sectional state of the electrode mixture tablet used in Example 5 is shown in Figure 1.

[0156] [Strength Measurement] The tensile testing machine (Autograph AGS-X series AGS-100NX, Shimadzu Corporation) was used to measure the strength of a 4 mm wide short strip electrode sample at a speed of 100 mm / min. The distance between the clamps was set to 30 mm. The sample was displaced until it broke, and the maximum stress obtained was taken as the strength of each sample. Comparative Example 1 in Table 2 and Comparative Example 3 in Table 3 are set as 100% and used as standards.

[0157] [Softness] Cut out the prepared electrode mixture sheet to make a 2 cm × 10 cm test piece. Wind it into a round rod with a diameter of 4 mm, visually confirm the electrode mixture sheet, and evaluate it according to the following criteria. ○: No cracks were observed. △: Cracks were observed, but fracture was not observed. ×: Broken.

[0158] <Battery Test> [Initial Discharge Capacity Test] The lithium-ion secondary battery manufactured above was clamped in a plate and pressurized. Under this condition, it was charged at 25°C with a constant current-constant voltage (hereinafter referred to as CC / CV charging) at a current equivalent to 1 C (0.1 C cutoff) until 4.2 V was reached. Then, it was discharged at a constant current of 1 C until 3 V was reached. The above series of operations is defined as one cycle, and the initial discharge capacity is calculated from the discharge capacity of the third cycle. Comparative Example 1 in Table 2 is set to 100%, and Comparative Example 3 in Table 3 is set to 100% as the standard.

[0159] [60℃ 2 W Storage Test and Determination of Gas Production] The lithium-ion secondary batteries manufactured above were clamped in plates and pressurized. Under this condition, they were CC / CV charged with a current equivalent to 1 C (0.1 C cutoff) until 4.2 V was reached. The volume of the battery was then measured using the Archimedes method and taken as the volume before storage. Next, the batteries after charging were placed in a constant temperature bath set to 60°C and kept there for 2 weeks. Then, the batteries were removed from the constant temperature bath and left at room temperature for 2 hours. The volume was measured again using the Archimedes method and taken as the volume after storage. The difference between the volume after storage and the volume before storage was calculated, and this difference was taken as the gas production amount (ml). Comparative Example 1 in Table 2 was set as 100%, and Comparative Example 3 in Table 3 was set as 100% as the standard. (Volume after storage) - (Volume before storage) = Gas production (ml)

[0160] [Evaluation of Resistors] After evaluating the discharge capacity following 10 cycles at 25°C, the battery was charged at 25°C with a constant current of 1 C to achieve half of its initial discharge capacity. An AC voltage amplitude of 10 mV was applied at 25°C, and the battery impedance was measured to determine the real-axis resistance at 0.1 Hz. Comparative Example 1 in Table 2 and Comparative Example 3 in Table 3 are set to 100% as standards.

[0161] The experimental results are shown in Tables 2 and 3.

[0162] [Table 2] positive electrode Negative electrode (slurry) evaluate adhesive fibril diameter [nm] solvent Active substances adhesive solvent Active substances initial capacity gas resistance strength Softness density g / cc Comparative example 1 PTFE-D 76 No (dry type) NMC622 SBR water Artificial graphite 100 100 100 100 × 3.8 Comparative example 2 PTFE-A 71 No (dry type) NMC622 SBR water Artificial graphite 125 100 100 120 × 3.8 Example 1 PTFE-C 41 No (dry type) NMC622 SBR water Artificial graphite 144 97 90 181 ○ 3.4 Example 2 PTFE-B 33 No (dry type) NMC622 SBR water Artificial graphite 143 97 88 170 ○ 3.4 Example 3 PTFE-A 47 No (dry type) NMC622 SBR water Artificial graphite 149 96 88 208 ○ 3.4 Example 4 PTFE-B 28 No (dry type) NMC622 SBR water Artificial graphite 146 96 95 125 ○ 3.4

[0163] [Table 3] negative electrode Positive electrode (slurry) evaluate adhesive fibril diameter [nm] solvent Active substances adhesive solvent Active substances initial capacity gas resistance strength Softness density g / cc Comparative example 3 PTFE-D 85 none Artificial graphite PVDF NMP NMC 100 100 100 100 × 1.5 (Dry method) SiO 111 Comparative example 4 PTFE-A 76 none Artificial graphite PVDF NMP NMC 111 100 100 107 × 1.5 (Dry method) SiO 111 Example 5 PTFE-C 41 none Artificial graphite PVDF NMP NMC 125 97 90 172 ○ 1.5 (Dry method) SiO 111 Example 6 PTFE-B 65 none Artificial graphite PVDF NMP NMC 124 97 88 197 ○ 1.5 (Dry method) SiO 111 Example 7 PTFE-A 51 none Artificial graphite PVDF NMP NMC 126 96 88 154 ○ 1.5 (Dry method) SiO 111 Example 8 PTFE-B twenty three none Artificial graphite PVDF NMP NMC 125 98 98 124 ○ 1.5 (Dry method) SiO 111 refer to 1 Polyacrylic acid - NMP Artificial graphite PVDF NMP NMC 94 110 80 - ○ 1.5 SiO 111

[0164] As shown in Tables 2 and 3, the electrode compound sheets of the embodiments exhibit excellent flexibility, and the secondary batteries also have good physical properties. [Industrial Applicability]

[0165] The electrode mixture for secondary batteries of the present invention can be used to manufacture lithium-ion secondary batteries.

[0166] none

Claims

1. An electrode compound for secondary batteries, comprising an electrode active material and a binder, characterized in that: the electrode compound for secondary batteries is obtained by using a raw material composition comprising an electrode active material and a binder, wherein the binder of the raw material composition is a powdered polytetrafluoroethylene resin, the raw material composition substantially does not contain a liquid medium, and the polytetrafluoroethylene resin in the compound has a fibrous structure with a fiber diameter (central value) of less than 70 nm.

2. The electrode mixture for secondary batteries as described in claim 1, which is used in lithium-ion secondary batteries.

3. As in claim 1, the electrode mixture for secondary batteries, wherein, The water content of powdered polytetrafluoroethylene resin is below 500 ppm.

4. The electrode mixture for secondary batteries as described in claim 1, wherein, The standard specific gravity of powdered polytetrafluoroethylene resin is 2.11 to 2.

20.

5. The electrode mixture for secondary batteries as described in claim 1, wherein, The powdered polytetrafluoroethylene resin contains more than 50% by mass of polytetrafluoroethylene resin with a secondary particle size of more than 500 μm.

6. The electrode mixture for secondary batteries as described in claim 1, wherein, The powdered polytetrafluoroethylene resin contains more than 80% by mass of polytetrafluoroethylene resin with a secondary particle size of more than 500 μm.

7. An electrode compound tablet for a secondary battery, comprising the electrode compound for a secondary battery according to any one of claims 1 to 6.

8. The electrode compound sheet for secondary batteries as claimed in claim 7, which is used as the negative electrode, and the electrode active material contains silicon as a constituent element.

9. The electrode compound sheet for secondary batteries as described in claim 7, which is used as the positive electrode and has a density of 3.0 g / cc or higher.

10. The electrode compound sheet for secondary batteries as requested in item 7 or 8, which is used as the negative electrode and has a density of 1.3 g / cc or higher.

11. A secondary battery having an electrode compound sheet for a secondary battery according to any one of claims 7 to 10.

12. A secondary battery comprising: an electrode mixture sheet containing an electrode mixture for secondary batteries, and a non-aqueous electrolyte, characterized in that: the electrode mixture for secondary batteries contains an electrode active substance and a binder, the binder being polytetrafluoroethylene resin, the polytetrafluoroethylene resin having a fibrous structure with a fiber diameter (central value) of 41 nm or more and 70 nm or less.

13. A method for manufacturing an electrode compound sheet for a secondary battery, comprising the following steps: Step (1), mixing a raw material composition containing an electrode active material and a binder, while applying shear force; Step (2), forming the electrode compound obtained by step (1) into a block; Step (3), calendering the block electrode compound obtained by step (2) into a sheet; and Step (5), coarsely crushing the calendered sheet, forming it into a block again, and calendering it into a sheet; and the method for manufacturing the electrode compound sheet for a secondary battery is characterized in that: the binder is a powdered polytetrafluoroethylene resin, and the raw material composition substantially does not contain a liquid medium.

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