Binding agent for secondary battery electrodes using non-aqueous electrolyte, electrode fabrication composition, electrode mixture, electrode, and lithium-ion secondary battery

Abstract

The present invention provides a binder for secondary battery electrodes that can lower the electrical resistance of electrodes using PTFE while simultaneously providing excellent strength. [Solution] A binder for secondary battery electrodes using a non-aqueous electrolyte containing a mixed powder of polytetrafluoroethylene resin and Ketjenblack and / or carbon nanotubes.

Description

Technical Field

[0001] The present disclosure relates to a binder for secondary battery electrodes using a non-aqueous electrolyte, a composition for electrode production, an electrode mixture, an electrode, and a lithium-ion secondary battery.

Background Art

[0002] The use of fibrillated polytetrafluoroethylene (PTFE) as a binder in the electrodes of lithium-ion batteries containing a non-aqueous electrolyte has been investigated (Patent Document 1).

[0003] Furthermore, obtaining a uniform mixed powder in which a conductive material is mixed with PTFE by spray drying has also been disclosed (Patent Documents 2 to 4).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the present disclosure, it is possible to provide a binder for secondary battery electrodes that can reduce the electrical resistance value of the electrodes and at the same time have excellent strength when using PTFE.

Means for Solving the Problems

[0006] The present disclosure is The present invention relates to a method for manufacturing electrodes for secondary batteries using a non-aqueous electrolyte, characterized by having a step (1) of preparing an electrode manufacturing composition that substantially does not contain a liquid medium, using a binder which is a powder that does not contain an active material and consists of a composition that is essential for polytetrafluoroethylene resin and a conductive additive.

[0007] The above-mentioned binder preferably has a moisture content of 1000 ppm or less. The above-mentioned binder is preferably manufactured by a manufacturing method that includes step (A) of mixing a polytetrafluoroethylene resin and a conductive additive in the presence of a liquid medium. The above liquid medium is preferably water.

[0008] Preferably, the binder described above is obtained by a manufacturing method comprising step (B) of drying the composition obtained in step (A) by spray drying. The above-mentioned polytetrafluoroethylene resin preferably has a standard specific gravity of 2.11 to 2.20. The above electrode manufacturing composition preferably contains a positive electrode active material.

[0009] The above-mentioned binder for secondary batteries is preferably a binder for lithium-ion secondary batteries. The above-mentioned PTFE preferably has a fibrous structure with a fibril diameter (median) of 150 nm or less. The above-mentioned binder preferably has an elemental ratio of fluorine to carbon (F / C ratio) of 0.4 or more and 3.0 or less, as measured by elemental analysis.

[0010] This disclosure also relates to a binder for secondary battery electrodes using a non-aqueous electrolyte, characterized by being a powder comprising a composition essential to polytetrafluoroethylene resin and a conductive additive, and not containing an electrode active material.

[0011] The above-mentioned binder for secondary battery electrodes preferably has an elemental ratio of fluorine to carbon (F / C ratio) of 0.4 or more and 3.0 or less, as measured by elemental analysis. This disclosure also relates to a binder for secondary battery electrodes that uses a non-aqueous electrolyte containing a mixed powder of polytetrafluoroethylene resin and Ketjenblack or carbon nanotubes. This disclosure is also characterized by containing the above-mentioned binder for secondary battery electrodes. This disclosure also relates to an electrode mixture characterized by containing the above-mentioned binder for secondary battery electrodes. This disclosure also relates to an electrode characterized by having the above-mentioned electrode mixture. This disclosure also relates to a binder for secondary battery electrodes using a non-aqueous electrolyte, comprising a mixed powder of polytetrafluoroethylene resin and Ketjenblack and / or carbon nanotubes. Preferably, the binder for secondary battery electrodes according to claim 1 has a moisture content of 1000 ppm or less. The polytetrafluoroethylene resin preferably has a standard specific gravity of 2.11 to 2.20. It is preferable that the elemental ratio of fluorine to carbon (F / C ratio), as measured by elemental analysis, is between 0.4 and 3.0. Preferably, the polytetrafluoroethylene resin and the Ketjenblack and / or carbon nanotubes are contained in a weight ratio of 99:1 to 60:40. The secondary battery is preferably a lithium-ion secondary battery. The moisture content is 500 ppm or less. The aforementioned polytetrafluoroethylene resin has a standard specific gravity of 2.11 to 2.20. The elemental ratio of fluorine to carbon (F / C ratio) measured by elemental analysis is between 0.4 and 3.0. The polytetrafluoroethylene resin and the Ketjenblack and / or carbon nanotubes are contained in a weight ratio of 99:1 to 60:40. The aforementioned secondary battery is a lithium-ion secondary battery, The carbon nanotube is preferably a multi-walled carbon nanotube. This disclosure also relates to an electrode manufacturing composition characterized by containing the above-mentioned binder for secondary battery electrodes. Preferably, the positive electrode active material is further included. This disclosure also relates to an electrode mixture characterized by containing the above-mentioned binder for secondary battery electrodes. This disclosure also relates to an electrode characterized by having the above-described electrode mixture. It is preferable that the polytetrafluoroethylene resin has a fibrous structure with a median fibril diameter of 20 nm or more. The polytetrafluoroethylene resin and the Ketjenblack and / or carbon nanotubes are contained in a weight ratio of 99:1 to 60:40. The carbon nanotube is a multi-walled carbon nanotube, It is preferable that the polytetrafluoroethylene resin has a fibrous structure with a median fibril diameter of 20 nm or more and 75 nm or less. This disclosure also relates to a lithium-ion secondary battery equipped with the electrodes described above. [Effects of the Invention]

[0012] In this disclosure, we can provide a binder for secondary battery electrodes that can lower the electrical resistance of electrodes using PTFE while simultaneously providing excellent strength. [Modes for carrying out the invention]

[0013] The details of this disclosure are described below. Electrode mixtures using PTFE as a binder sometimes resulted in high electrode resistance. This disclosure provides a method for manufacturing electrodes that can resolve this problem and produce electrodes with low resistance.

[0014] Electrode mixtures that use PTFE as a binder achieve their binding effect by fibrillating the PTFE. However, when electrodes are manufactured by mixing PTFE and conductive additives as separate powders, the electrodes may become highly resistive. This is presumed to be because the PTFE is unevenly distributed within the electrode, preventing sufficient conductive pathways from forming. Furthermore, uneven distribution of components within the electrode can also lead to a decrease in electrode strength. On the other hand, if the mixture is kneaded vigorously to eliminate uneven distribution, excessive fibrillation of the PTFE occurs, resulting in a decrease in flexibility and strength. Therefore, these problems can be solved by using a binder that prevents uneven distribution of PTFE and conductive additives.

[0015] The method for manufacturing electrodes for secondary batteries using a non-aqueous electrolyte according to this disclosure is characterized by the use of a binder, which is a powder containing a polytetrafluoroethylene resin and a conductive additive, and does not contain an active material. Hereinafter, this will be referred to as the first binder of this disclosure. The following describes in detail such a binder and the components incorporated into the binder.

[0016] On the other hand, it is known that when attempting to mix PTFE and a conductive additive with the active material beforehand, lithium leaches out of the active material due to moisture in the liquid medium, causing the active material to deteriorate and resulting in problems such as a decrease in battery capacity and an increase in battery resistance (Patent Document 5). For this reason, by using a binder that does not contain an active material and consists of a composition that requires PTFE and a conductive additive, the objectives of this disclosure can be achieved without being limited by the active material.

[0017] Furthermore, using a mixed powder of polytetrafluoroethylene resin and Ketjenblack or carbon nanotubes as a binder is preferable because it can reduce electrode resistance, and a binder using this can also achieve the objectives of this disclosure. Such an effect cannot be obtained when using other carbon-based conductive additives such as acetylene black. Such a binder will be referred to as the second binder of this disclosure.

[0018] The method for manufacturing a first secondary battery electrode using the non-aqueous electrolyte of this disclosure is characterized by using a binder that is a powder containing PTFE and a conductive additive as essential components, and does not contain an active material. That is, the particles constituting the powder do not consist only of PTFE and a conductive additive, but rather consist of a composition containing both PTFE and a conductive additive.

[0019] The following provides a detailed description of such binders and the components they contain.

[0020] (Polytetrafluoroethylene resin) In this disclosure, the PTFE is not particularly limited and may be a homopolymer or a copolymer that can be fibrillated, but a homopolymer is more preferred. In the case of copolymers, examples of fluorine atom-containing monomers that act as comonomers include chlorotrifluoroethylene, hexafluoropropylene, fluoroalkylethylene, perfluoroalkylethylene, and fluoroalkyl fluorovinyl ether.

[0021] The PTFE used as a raw material when preparing the electrode mixture according to this disclosure preferably has a standard specific gravity of 2.11 to 2.20. Having a standard specific gravity within this range has the advantage of enabling the production of an electrode mixture sheet with high strength. The lower limit of the standard specific gravity is more preferably 2.12 or higher. The upper limit of the standard specific gravity is more preferably 2.19 or lower, and even more preferably 2.18 or lower.

[0022] Standard specific gravity (SSG) is determined by preparing a sample in accordance with ASTM D-4895-89 and measuring the specific gravity of the obtained sample by the water displacement method.

[0023] The PTFE used in this disclosure may have a core-shell structure. Examples of PTFE having a core-shell structure include PTFE containing a high molecular weight PTFE core and a lower molecular weight PTFE or modified PTFE shell in the particle. Examples of such PTFE include the PTFE described in Japanese Patent Publication No. 2005-527652.

[0024] PTFE in powder form that satisfies the parameters described above can be obtained by conventional manufacturing methods. For example, it can be manufactured by following the manufacturing methods described in International Publication No. 2015-080291 and International Publication No. 2012-086710, etc.

[0025] (Conductive additive) Any known conductive material can be used as the conductive additive mentioned above. 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, channel black, furnace black, lamp black, and thermal black, and carbon materials such as needle coke, carbon nanotubes, carbon nanohorns, carbon nanofibers, fullerenes, graphene, and amorphous carbon such as VGCF. Ketjen black, acetylene black, and carbon nanotubes are particularly preferred. Among carbon nanotubes, multi-walled carbon nanotubes are preferred. These may be used individually or in any combination and ratio of two or more. Examples of commercially available carbon black include Tokai Carbon's #4300, #4400, #4500, #5500, etc. (Furnace Black), Printex L, etc. (Degussa, Furnace Black), Raven 7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, etc., Conductex SC ULTRA, Conductex 975ULTRA, etc., PUER BLACK100, 115, 205 etc. (Columbian Furnace Black), #2350, #2400B, #2600B, #30050B, #3030B, #3230B, #3350B, #3400B, #5400B etc. (Mitsubishi Chemical Furnace Black), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, LITX-50, LITX-200 etc. (Cabot Furnace Black), Ensaco250G, Ensaco260G, Ensaco350G, Super-P Examples include Li (manufactured by IMERYS, Furnace Black), Ketjenblack ECP, ECP-600JD, Lionite CB, etc. (manufactured by Lion Specialty Chemicals, Ketjenblack), Denka Black HS-100, Li-100, FX-35 (manufactured by Denka Co., Ltd., Acetylene Black), etc. Commercially available VGCF includes VGCF-H (manufactured by Showa Denko), etc. Commercially available multi-walled carbon nanotubes include FT7000 (manufactured by CNano), etc.As multi-walled carbon nanotubes, the average outer diameter is preferably 4 nm to 20 nm, and more preferably 6 nm to 12 nm. The average fiber length is preferably 1 to 30 μm, and more preferably 3 μm to 20 μm. This allows for good conductivity to be obtained. When manufacturing electrode sheets, it is also acceptable to add and mix in a conductive additive.

[0026] The binder of this disclosure preferably contains the above-mentioned conductive additive in a ratio of 1.0 to 60.0 by mass relative to the total amount of the binder. This makes it possible to obtain good conductivity and electrode strength. The lower limit is more preferably 1.5 or higher, and even more preferably 2.0 or higher. The upper limit is more preferably 55.0 or higher, and even more preferably 50.0 or lower.

[0027] While this disclosure requires the inclusion of a conductive additive in the binder, it is also permissible to further mix PTFE and conductive additives when manufacturing the electrode sheet using the electrode mixture.

[0028] The above-mentioned conductive additive is preferably used in the electrode mixture in an amount of 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.8% by mass or more, and preferably 50% by mass or less, preferably 30% by mass or less, and more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

[0029] When mixing conductive additives with PTFE, materials that may be added as needed include conductive materials, dispersants, and thickeners. For example, celluloses such as carboxymethylcellulose (CMC) and methylcellulose (MC) can be suitably used as thickeners.

[0030] When using components other than conductive additives and PTFE, it is preferable that the amount of such components is 5.0% by mass or less relative to the total amount of binder. If the amount of the above-mentioned other components exceeds 5.0% by mass, the objectives of the present invention may not be fully achieved.

[0031] (Binding agent) The binder used in this disclosure is a composition in powder form, in which PTFE and a conductive additive are essential components. That is, the composition is in a powder form in which PTFE and the conductive additive are mixed, and does not include mixtures of the PTFE powder and the conductive additive powder separately. While there are no particular limitations on such a state, it is especially preferable that the particles are in a state of granulation by spray drying.

[0032] The above-mentioned binder preferably contains PTFE and a conductive additive in a weight ratio of 99:1 to 50:50. In the above mixing ratio, it is preferably 95:5 to 60:40, and more preferably 90:10 to 65:35.

[0033] The method for producing the above-mentioned binder is not particularly limited and can be produced by any method, but it is preferable that the binder be produced by a method having a step (A) of mixing PTFE and a conductive additive in the presence of a liquid medium. In this case, examples include a method of adding and mixing a powdered conductive additive into a liquid dispersion of PTFE, or a method of mixing a liquid dispersion of PTFE and a liquid dispersion of a conductive additive. Mixing can be carried out using general methods. Examples include, but are not limited to, mixers such as dispersers, homomixers, and planetary mixers, homogenizers, and wet jet mills.

[0034] In step (A) above, a dispersion comprising PTFE, a conductive additive, and a liquid medium is used. Preferably, the total amount of PTFE and the conductive additive in such a dispersion is 1 to 60% by weight relative to the total amount of PTFE, the conductive additive, and the liquid medium. The lower limit is more preferably 2% by weight or more, and even more preferably 3% by weight or more. The upper limit is more preferably 50% by weight or less, and even more preferably 30% by weight or less.

[0035] Mixing these in a liquid medium is preferable because it allows for highly uniform mixing of PTFE and the conductive additive. The liquid medium in such mixing is preferably water.

[0036] In this case, it is preferable to use an aqueous dispersion of PTFE obtained by emulsion polymerization as the raw material.

[0037] The PTFE used as a raw material for the binder described above preferably has an average primary particle diameter of 150 nm or more, in order to obtain an electrode mixture sheet with higher strength and superior homogeneity. More preferably, it is 180 nm or more, even more preferably 210 nm or more, and particularly preferably 220 nm or more. The larger the average primary particle size of PTFE, the lower the increase in extrusion pressure when using the powder for extrusion molding, and the better the moldability. There is no particular upper limit, but it may be 500 nm. From the viewpoint of productivity in the polymerization process, an upper limit of 350 nm is preferable.

[0038] The above average primary particle diameter can be determined by creating a calibration curve using an aqueous dispersion of PTFE obtained by polymerization, adjusting the polymer concentration to 0.22% by mass, and comparing the transmittance of 550 nm projected light per unit length of the aqueous dispersion with the average primary particle diameter determined by measuring the directional diameter in transmission electron microscope images. The transmittance of the aqueous dispersion to be measured is then measured, and the average primary particle diameter can be determined based on the above calibration curve.

[0039] Preferably, the mixture of PTFE and conductive additive mixed in a liquid medium by step (A) above is then dried by spray drying (step (B)) to remove the liquid medium. Examples of drying methods include shelf dryers, vacuum dryers, freeze dryers, hot air dryers, drum dryers, and spray dryers. Spray drying is particularly preferred. Spray drying is a method of producing a dried powder by spraying a mixture of liquid and solid into a gas to dry it rapidly. This allows for obtaining a binder in powder form in which PTFE and a conductive additive are uniformly mixed. Spray drying is a generally known method and can be carried out in a general manner using any known apparatus. Step (B) above can be carried out in a general manner using a known general apparatus. The drying temperature is preferably in the range of 100°C to 250°C. Above 100°C, the solvent can be sufficiently removed, and below 250°C, energy consumption can be further reduced, which is preferable. The drying temperature is more preferably 110°C or higher, and more preferably 220°C or lower. The supply liquid volume may also be in the range of 0.1 L / h to 2 L / h, depending on the scale of production. The nozzle size for spraying the prepared solution may also be in the range of 0.5 mm to 5 mm in diameter, depending on the scale of production.

[0040] The binder obtained in this manner preferably has a moisture content of 1000 ppm or less. Having a moisture content of 1000 ppm or less is preferable because it allows for the creation of secondary batteries with low gas generation as an initial characteristic. The above moisture content is more preferably 500 ppm or less.

[0041] [Measurement of moisture content] The moisture content of the binder was measured using a Karl Fischer moisture meter (ADP-511 / MKC-510N, manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a boat-type moisture vaporizer. The moisture was heated to 210°C in the vaporizer 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 30 min. ChemAqua was used as the Karl Fischer reagent. The sample volume was 1.5 g.

[0042] The second binder of this disclosure is a mixed powder of polytetrafluoroethylene resin and Ketjenblack and / or carbon nanotubes. When used as a binder, such a mixed powder is preferable to the use of well-known carbon conductive additives such as acetylene black in that it can reduce electrode resistance and improve battery characteristics, and can be used in the same manner as the first binder described above.

[0043] In the second binder described above, the Ketjenblack and / or carbon nanotubes used are not particularly limited, and those described above can be used. Furthermore, it is preferable that the carbon nanotubes be multilayered, and more specifically, those with an average fiber length of 1 to 20 μm are used.

[0044] The polytetrafluoroethylene used in the second binder described above can be the same as that used in the first binder described above.

[0045] The second binder described above may be obtained through steps (A) and (B) described above, similar to the first binder described above, or it may be obtained by simply mixing these components. In the electrode fabrication compositions described in detail below, both the first binder and the second binder can be used in the same manner.

[0046] (Composition for electrode fabrication) The composition for electrode fabrication means a composition containing all the components essential for the electrode. That is, it means a composition in a state where other electrode components such as an electrode active material are mixed with the above-described binder. The composition for electrode fabrication is a composition containing, in addition to the above binder, an electrode active material, a conductive auxiliary agent to be additionally added, and the like.

[0047] (Electrode active material) The above positive electrode active material is not particularly limited as long as it can electrochemically occlude and release alkali metal ions. For example, a substance containing an alkali metal and at least one transition metal is preferable. Specific examples include alkali metal-containing transition metal composite oxides, alkali metal-containing transition metal phosphate compounds, conductive polymers, and the like. Among them, as the positive electrode active material, an alkali metal-containing transition metal composite oxide that produces a particularly high voltage is preferable. Examples of the above alkali metal ions include lithium ions, sodium ions, potassium ions, and the like. In a preferred embodiment, the alkali metal ion can be a lithium ion. That is, in this embodiment, the alkali metal ion secondary battery is a lithium ion secondary battery.

[0048] Examples of the above alkali metal-containing transition metal composite oxide include Formula: M a Mn 2-b M 1 b O4 (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; M 1 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) an alkali metal-manganese spinel composite oxide represented by Formula: MNi 1-c M 2 c O2 (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K; 0 ≦ c ≦ 0.5; M 2(This refers to an alkali metal-nickel composite oxide represented by 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 Formula:MCo 1-d M 3 d O2 (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0 ≤ d ≤ 0.5; M 3 (This refers to 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.) Examples include alkali metal-cobalt composite oxides represented by . In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.

[0049] In particular, MCoO2, MMnO2, MNiO2, MMn2O4, and MNi are used because they offer high energy density and can provide high-output secondary batteries. 0.8 Co 0.15 Al 0.05 O2, or MNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 is preferred, and it is preferable that the compound is represented by the following general formula (3). MNi h Co i Mn j M 5 k O2(3) (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, M 5 (This represents at least one element selected from the group consisting of Fe, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, where (h+i+j+k)=1.0, 0≦h≦1.0, 0≦i≦1.0, 0≦j≦1.5, and 0≦k≦0.2.)

[0050] Examples of the alkali metal-containing transition metal phosphate compounds mentioned above include the following formula (4): M e M 4 f (PO4)g (4) (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, M 4 Herein, M represents at least one selected from the group consisting of V, Ti, Cr, Mn, Fe, Co, Ni, and Cu, and is a compound represented by (0.5 ≤ e ≤ 3, 1 ≤ f ≤ 2, 1 ≤ g ≤ 3). In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.

[0051] Preferred transition metals for lithium-containing transition metal phosphate compounds include 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 those in which some of the transition metal atoms that make up the main component of these lithium transition metal phosphate compounds are substituted with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si. The lithium-containing transition metal phosphate compound described above is preferably one having an olivine-type structure.

[0052] Other cathode active materials include MFePO4 and MNi 0.8 Co 0.2 O2, M 1.2 Fe 0.4 Mn 0.4 O2, MNi 0.5 Mn 1.5 Examples include O2, MV3O6, M2MnO3 (wherein M is at least one metal selected from the group consisting of Li, Na, and K). In particular, M2MnO3, MNi 0.5 Mn 1.5Positive electrode active materials such as O2 are 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 of 4.6V or higher. Therefore, an electrochemical device such as a secondary battery using a positive electrode material containing the positive electrode active material exemplified above is preferable because the residual capacity hardly decreases even when stored at a high temperature, the resistance increase rate hardly changes, and the battery performance does not deteriorate even when operated at a high voltage.

[0053] As other positive electrode active materials, solid solution materials such as M2MnO3 and M 6 O2 (where M is at least one metal selected from the group consisting of Li, Na, and K, and M 6 is a transition metal such as Co, Ni, Mn, Fe, etc.) can also be mentioned.

[0054] Examples of the solid solution material include, for example, an alkali metal manganate represented by the general formula M x [Mn (1-y) M 7 y ]O z Here, M in the formula is at least one metal selected from the group consisting of Li, Na, and K, and M 7 consists of at least one metal element other than M and Mn, and includes, for example, 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 range of 1 < x < 2, 0 ≤ y < 1, and 1.5 < z < 3. Among them, a manganese-containing solid solution material in which LiNiO2 or LiCoO2 is solid-dissolved based on Li2MnO3 such as Li 1.2 Mn 0.5 Co 0.14 Ni 0.14 O2 is preferable in that it can provide an alkali metal ion secondary battery having a high energy density.

[0055] ​​​​​Furthermore, including lithium phosphate in the positive electrode active material is preferable because it improves continuous charging characteristics. There are no restrictions on the use of lithium phosphate, but it is preferable to use a mixture of the positive electrode active material and lithium phosphate. The amount of lithium phosphate used is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, relative to the total amount of the positive electrode active material and lithium phosphate, with an upper limit of preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0056] Examples of the conductive polymers mentioned above include p-doped and n-doped conductive polymers. Examples of conductive polymers include polyacetylene-based polymers, polyphenylene-based polymers, heterocyclic polymers, ionic polymers, ladder and network polymers, etc.

[0057] Furthermore, a positive electrode active material may be used in which a substance of a different composition is attached to its surface. Examples of surface-attached 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.

[0058] These surface-adhering substances can be attached to the surface of the positive electrode active material by, for example, dissolving or suspending them in a solvent and impregnating or adding them to the positive electrode active material, followed by drying; dissolving or suspending a surface-adhering substance precursor in a solvent and impregnating or adding it to the positive electrode active material, followed by a reaction by heating, etc.; or adding it to the positive electrode active material precursor and simultaneously firing it. In the case of attaching carbon, a method of mechanically attaching carbonaceous material afterwards, for example in the form of activated carbon, can also be used.

[0059] The amount of surface-adhered material is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more, relative to the positive electrode active material by mass, with a lower limit of preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The surface-adhered material can suppress the oxidation reaction of the electrolyte on the surface of the positive electrode active material, thereby improving battery life. If the amount of adhesion is too small, the effect will not be fully realized, and if it is too large, it may hinder the movement of lithium ions in and out, which may increase resistance.

[0060] The particle shapes of the positive electrode active material can include conventionally used shapes such as lumpy, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar. Furthermore, primary particles may aggregate to form secondary particles.

[0061] The tap density of the positive electrode active material is preferably 0.5 g / cm³ or higher, more preferably 0.8 g / cm³. 3 More preferably 1.0 g / cm³ 3 The above is the case. If the tap density of the positive electrode active material falls below the above lower limit, the amount of conductive material and binder required during the formation of the positive electrode active material layer increases, which may restrict the filling rate of the positive electrode active material into the positive electrode active material layer and limit the battery capacity. By using a composite oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. Generally, a higher tap density is preferable, and there is no particular upper limit, but if it is too high, the diffusion of lithium ions using the electrolyte as a medium within the positive electrode active material layer becomes the rate-limiting factor, and the load characteristics tend to deteriorate. Therefore, the upper limit is preferably 4.0 g / cm³. 3 More preferably, 3.7 g / cm³ 3 More preferably, 3.5 g / cm³ 3 The following applies: In this disclosure, the tap density is defined as the powder packing density (tap density) g / cm³ obtained when 5-10 g of positive electrode active material powder is placed in a 10 ml glass graduated cylinder and tapped 200 times with a stroke of approximately 20 mm. 3 We will seek it as follows.

[0062] The median diameter d50 of the positive electrode active material particles (or secondary particle diameter if primary particles aggregate to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, even more 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, even more preferably 25 μm or less, and most preferably 22 μm or less. If it falls below the lower limit, it may not be possible to obtain a high-tap density product, and if it exceeds the upper limit, the diffusion of lithium within the particles will take time, which may lead to problems such as a decrease in battery performance. Here, by mixing two or more of the above positive electrode active materials having different median diameters d50, the packing performance during positive electrode fabrication can be further improved.

[0063] In this disclosure, the median diameter d50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using the HORIBA LA-920 as the particle size distribution analyzer, a 0.1% by mass aqueous solution of sodium hexametaphosphate is used as the dispersion medium during measurement, and the measurement is performed after ultrasonic dispersion for 5 minutes with the measurement refractive index set to 1.24.

[0064] When primary particles aggregate 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, 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. Exceeding the upper limit makes it difficult to form spherical secondary particles, which can adversely affect powder packing properties and significantly reduce the specific surface area, potentially leading to a decrease in battery performance such as output characteristics. Conversely, below the lower limit usually results in problems such as poor reversibility of charge and discharge due to underdeveloped crystals.

[0065] In this disclosure, the average primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, it is determined by taking a photograph at 10,000x magnification, finding the longest value of the intercept between the left and right boundaries of the primary particle relative to a horizontal line for any 50 primary particles, and then taking the average value.

[0066] The BET specific surface area of ​​the positive electrode active material is preferably 0.1 m². 2 / g or more, more preferably 0.2m 2 / g or more, more preferably 0.3m 2 The value is 1 / g or more, and the upper limit is preferably 50m 2 / g or less, more preferably 40m 2 / g or less, more preferably 30m 2 It is less than / g. If the BET specific surface area is smaller than this range, battery performance tends to decrease, and if it is larger, problems may arise where it is difficult to increase the tap density.

[0067] In this disclosure, the BET specific surface area is defined as the value measured by a nitrogen adsorption BET single-point method using a gas flow method, after pre-drying the sample at 150°C for 30 minutes under nitrogen flow using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.), and then using a nitrogen-helium mixed gas that has been precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0068] When the secondary battery of this disclosure is used as a large lithium-ion secondary battery for hybrid vehicles or distributed power sources, high output is required, so it is preferable that the particles of the positive electrode active material consist mainly of secondary particles. The positive electrode active material particles preferably contain 0.5 to 7.0 volume percent of fine particles with an average secondary particle diameter of 40 μm or less and an average primary particle diameter of 1 μm or less. By including fine particles with an average primary particle diameter of 1 μm or less, the contact area with the electrolyte is increased, which allows for faster diffusion of lithium ions between the electrode mixture and the electrolyte, and as a result, the output performance of the battery can be improved.

[0069] For the production of positive electrode active materials, general methods for producing inorganic compounds are used. In particular, various methods can be considered for producing spherical or ellipsoidal active materials. For example, a method can be used in which transition metal raw materials are dissolved or pulverized and dispersed in a solvent such as water, the pH is adjusted while stirring to create and recover spherical precursors, these are dried as needed, and then a Li source such as LiOH, Li2CO3, or LiNO3 is added and calcined at a high temperature to obtain the active material.

[0070] For the manufacture of the positive electrode, the positive electrode active material may be used alone, or two or more materials with different compositions may be used in any combination or ratio. In this case, a preferred combination is LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33 Examples include combinations with ternary systems such as O2, combinations of LiCoO2 and LiMn2O4 or a combination in which part of the Mn is substituted with other transition metals, or combinations of LiFePO4 and LiCoO2 or a combination in which part of the Co is substituted with other transition metals.

[0071] The content of the above-mentioned positive electrode active material is preferably 50 to 99.5% by mass, and more preferably 80 to 99% by mass, in the positive electrode mixture, in terms of high battery capacity. Furthermore, the content of the positive electrode active material 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% 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 layer is too low, the electrical capacitance may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

[0072] The negative electrode active material is not particularly limited and includes, for example, lithium metal, artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolysis vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and carbonaceous materials such as non-graphitizable carbon, silicon and silicon alloys, silicon-containing compounds, Li4Ti5O 12Examples include any of the above, or a mixture of two or more types. Among these, materials containing at least a portion of carbonaceous material, or silicon-containing compounds, can be used particularly suitably.

[0073] The negative electrode active material used in this disclosure preferably contains silicon as a constituent element. By including silicon as a constituent element, a high-capacity battery can be manufactured.

[0074] Preferred silicon-containing materials include silicon particles, particles having a structure in which silicon fine particles are dispersed in a silicon-based compound, silicon oxide particles represented by the general formula SiOx (0.5 ≤ x ≤ 1.6), or mixtures thereof. Using these materials makes it possible to obtain a negative electrode mixture for lithium-ion secondary batteries that has higher initial charge-discharge efficiency, higher capacity, and excellent cycle characteristics.

[0075] In this disclosure, silicon oxide refers to a general term for amorphous silicon oxides, and silicon oxide before disproportionation is represented by the general formula SiOx (0.5 ≤ x ≤ 1.6). x is preferably 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 produce silicon monoxide gas, which is then cooled and precipitated.

[0076] Particles having a structure in which silicon nanoparticles are dispersed in a silicon-based compound can be obtained, for example, by calcining a mixture of silicon nanoparticles and a silicon-based compound, or by heat-treating silicon oxide particles before disproportionation, represented by the general formula SiOx, in an inert, non-oxidizing atmosphere such as argon at a temperature of 400°C or higher, preferably 800-1,100°C, to carry out a disproportionation reaction. The material obtained by the latter method is particularly preferable because the silicon microcrystals are uniformly dispersed. Through the disproportionation reaction described above, the size of the silicon nanoparticles can be made to 1-100 nm. It is desirable that the silicon oxide in the particles having a structure in which silicon nanoparticles are dispersed in silicon oxide is silicon dioxide. Furthermore, it can be confirmed by transmission electron microscopy that silicon nanoparticles (crystals) are dispersed in amorphous silicon oxide.

[0077] The physical properties of silicon-containing particles can be appropriately selected depending on the target composite particle. For example, the average particle size is preferably 0.1 to 50 μm, the lower limit is more preferably 0.2 μm or more, and even more preferably 0.5 μm or more. The upper limit is more preferably 30 μm or less, and even more preferably 20 μm or less. In this disclosure, the average particle size is expressed as the weight-average particle size measured by the particle size distribution method using laser diffraction.

[0078] The BET specific surface area of ​​silicon-containing particles is 0.5 to 100 m². 2 / g is preferred, 1 to 20m 2 / g is more preferable. BET specific surface area is 0.5m² 2 If the value is 1 / g or higher, there is no risk of reduced adhesion to the electrodes and a decrease in battery performance. Also, 100m 2 If the value is less than / g, the proportion of silicon dioxide on the particle surface will be high, and there will be no risk of a decrease in battery capacity when used as a negative electrode material for lithium-ion secondary batteries.

[0079] By carbon coating the silicon-containing particles mentioned above, conductivity is imparted, resulting in improved battery characteristics. Methods for imparting conductivity include mixing with conductive particles such as graphite, coating the surface of the silicon-containing particles with a carbon film, and combining both methods. Coating with a carbon film is preferred, and chemical vapor deposition (CVD) is more preferred as the coating method.

[0080] The content of the above-mentioned negative electrode active material is preferably 40% by mass or more, more preferably 50% by mass or more, and particularly preferably 60% by mass or more, in order to increase the volume of the resulting electrode mixture. The upper limit is preferably 99% by mass or less, and more preferably 98% by mass or less.

[0081] (Other ingredients) The above electrode fabrication composition may further contain a thermoplastic resin. Examples of thermoplastic resins include vinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, and polyethylene oxide. One type may be used alone, or two or more types may be used in any combination and ratio.

[0082] The ratio of thermoplastic resin to electrode active material is typically 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and typically within the range of 3.0% by mass or less, preferably 2.5% by mass or less, and more preferably 2.0% by mass or less. Adding thermoplastic resin can improve the mechanical strength of the electrode. If the ratio exceeds this range, the proportion of electrode active material in the electrode mixture decreases, which may lead to problems such as a decrease in battery capacity or an increase in resistance between active materials.

[0083] (Method of manufacturing electrodes) The electrode manufacturing method of this disclosure preferably involves using an electrode manufacturing composition obtained by mixing the above-mentioned components and forming it into a sheet. In sheet formation, since the drying process can be omitted, it is preferable to reduce or completely eliminate the use of liquid medium and apply shear stress to the powder electrode manufacturing composition without preparing a slurry. In addition, a small amount of solvent may be added as a lubricant to reduce the load on the equipment. The solvent is preferably an organic solvent, and the amount of solvent contained is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less relative to the electrode manufacturing composition. It is known that PTFE in powder form readily fibrillates when shear force is applied. This fibrillating property can be utilized to use PTFE as a binder. That is, the fibrillated PTFE entangles with other powder components, binding them together, and in this way, PTFE can act as a binder when molding the powder components.

[0084] Furthermore, even when fibrillated PTFE is used as a binder, if the fibrillation is insufficient, it will not perform well when used as an electrode mixture. Preferably, by performing fine fibrillation processing to have a fibrous structure with a median fibril diameter (hereinafter simply referred to as "fibril diameter") of 20 nm or more, the fibrillated PTFE can perform well as a binder for electrode mixtures.

[0085] The electrode manufacturing composition described above preferably contains substantially no liquid medium. In the electrode obtained by the manufacturing method of this disclosure, it is preferable that PTFE having a fibrous structure with a median fibril diameter of 20 nm or more is included as a component. In this disclosure, it is preferable that the median fibril diameter is 20 nm or more. That is, the presence of PTFE with such a fine fibril diameter in the electrode is preferable because it has the effect of binding the powder components constituting the electrode together and provides flexibility.

[0086] The above fibril diameter (median) was measured using the following method. (1) Using a scanning electron microscope (S-4800 model, manufactured by Hitachi, Ltd.), a magnified photograph (7000x) of the electrode mixture sheet is taken to obtain an image. (2) Draw two lines horizontally at equal intervals on this image to divide the image into three equal parts. (3) For all PTFE fibers on the straight line above, measure the diameter at three points for each PTFE fiber and take the average value as the diameter of that PTFE fiber. The three measurement points are selected as the intersection of the PTFE fiber and the straight line, and points shifted 0.5 μm above and below the intersection. (Excludes unfiberized PTFE primary particles). (4) Perform the procedure in (3) above for all PTFE fibers that lie in the straight line below. (5) Starting from the first image, move 1 mm to the right of the screen and take another picture, then measure the diameter of the PTFE fibers according to (3) and (4) above. Repeat this process until the number of measured fibers exceeds 80, at which point the process is complete. (6) The median of the diameters of all the PTFE fibers measured above was used as the fibril diameter.

[0087] The fibril diameter is preferably 15 nm or larger, more preferably 20 nm or larger, and more preferably 31 nm or larger. If fibrilization is advanced too much, flexibility tends to be lost. Furthermore, there is no particular upper limit, but from the viewpoint of flexibility, for example, it is preferably 150 nm or smaller, more preferably 100 nm or smaller, and particularly preferably 75 nm or smaller.

[0088] The method for obtaining PTFE having the above fibril diameter is not particularly limited, but for example, (2) A step in which shear force is applied while mixing the above electrode manufacturing composition. Step (3) is to form the electrode mixture obtained in step (2) into a bulk form, and Step (4) involves rolling the bulk electrode mixture obtained in step (3) into a sheet. Therefore, we can list the methods for doing so.

[0089] Step (2) above is a step of applying shear force while mixing the electrode manufacturing composition obtained in step (1) above. Alternatively, powder components for preparing the electrode manufacturing composition may be mixed, and at the same time as mixing, shear force may be applied to fibrillate the PTFE to form the electrode mixture.

[0090] In this method, for example, in step (2), by setting the mixing conditions of the electrode fabrication composition to 2000 rpm or less, the fibrillation of PTFE can be promoted while maintaining flexibility, and by controlling the applied shear stress, the fibril diameter of the PTFE can be made 20 nm or more.

[0091] Furthermore, it is preferable to have a step (5) after step (4) in which a larger load is applied to the obtained rolled sheet and it is further rolled into a thinner sheet. It is also preferable to repeat step (5). Furthermore, the fibril diameter can also be adjusted by having a step (6) after step (4) or step (5) in which the obtained rolled sheet is roughly crushed, then formed into a bulk form again and rolled into a sheet form. It is preferable that step (6) be repeated, for example, one to twelve times.

[0092] In other words, by applying shear force, PTFE is fibrillated, and this fibrillation then intertwines with powder components such as electrode active materials, thereby producing an electrode mixture. The manufacturing method will be described later.

[0093] In the electrode manufacturing method of this disclosure, the PTFE content is typically 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 1.0% by mass or more, as a percentage of PTFE in the electrode mixture, and is also typically 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, and most preferably 10% by mass or less. If the proportion of the binder is too low, the active material cannot be sufficiently held, resulting in insufficient mechanical strength of the electrode and deterioration of battery performance such as cycle characteristics. On the other hand, if it is too high, it may lead to a decrease in battery capacity and conductivity.

[0094] The electrode mixture of this disclosure can be used as an electrode mixture for secondary batteries. In particular, the electrode mixture of this disclosure is suitable for lithium-ion secondary batteries. The electrode mixture of this disclosure is typically used in sheet form when used in secondary batteries.

[0095] The following is an example of a specific manufacturing method for an electrode mixture sheet containing an electrode mixture. In the electrode manufacturing method disclosed herein, the electrode mixture sheet is (0) A step of preparing a mixture containing an electrode active material and, if necessary, a conductive additive. A step of preparing an electrode manufacturing composition containing a binder in the mixture obtained by step (0) above. (1) (2) A step in which shear force is applied while mixing the electrode fabrication composition. Step (3) is to form the electrode mixture obtained in step (2) into a bulk form, and Step (4) is to roll the bulk electrode mixture obtained in step (3) into a sheet. It can be obtained by a method for manufacturing electrode mixture sheets for secondary batteries having [the specified characteristic].

[0096] In step (2) above, when shear force is applied while mixing the electrode fabrication composition, the resulting electrode fabrication composition exists in a state without a defined shape, with the electrode active material, binder, etc., simply mixed together. Specific mixing methods include using a W-type mixer, V-type mixer, drum-type mixer, ribbon mixer, conical screw-type mixer, single-shaft kneader, twin-shaft kneader, mix muller, agitator mixer, planetary mixer, etc.

[0097] In step (2) above, the mixing conditions can be appropriately set by adjusting the rotation speed and mixing time. For example, the rotation speed is preferably 2200 rpm or less. Preferably it is 10 rpm or more, more preferably 15 rpm or more, and even more preferably 20 rpm or more. Also preferably it is in the range of 2000 rpm or less, more preferably 1800 rpm or less, and even more preferably 1500 rpm. If it is below the above range, mixing will take a long time and will affect productivity. If it is above the above range, fibrillation will proceed excessively, which may result in an electrode mixture sheet with poor strength and flexibility.

[0098] In step (3) above, forming into a bulk means forming the electrode manufacturing composition into a single mass. Specific methods for forming materials into bulk include extrusion molding and press molding. Furthermore, "bulk form" does not specify a particular shape, but rather refers to a state in which there is a single mass, and includes forms such as rod-shaped, sheet-shaped, spherical, and cube-shaped. The size of the mass is preferably such that the diameter of its cross-section or the shortest side is 10,000 μm or more. More preferably, it is 20,000 μm or more.

[0099] Specific rolling methods in step (4) above include methods using a roll press, a flat plate press, a calender roll machine, etc.

[0100] Furthermore, it is preferable to have a step (5) after step (4) in which a larger load is applied to the obtained rolled sheet and it is further rolled into a thinner sheet. It is also preferable to repeat step (5). In this way, rather than thinning the rolled sheet all at once, rolling it little by little in stages results in better flexibility. The number of times step (5) is performed is preferably 2 to 10 times, and more preferably 3 to 9 times. Specific rolling methods include, for example, a method in which two or more rolls are rotated and the rolled sheet is passed between them to process it into a thinner sheet. Heating is desirable during rolling. The lower limit of the temperature range is preferably 40 degrees Celsius or higher, more preferably 50 degrees Celsius or higher, and even more preferably 60 degrees Celsius or higher. The upper limit is preferably 300 degrees Celsius or lower, more preferably 250 degrees Celsius or lower, and even more preferably 200 degrees Celsius or lower. Heating softens the sheet, making it easier to roll.

[0101] Furthermore, from the viewpoint of adjusting the fibril diameter, it is also preferable to have a step (6) after step (4) or step (5) in which the rolled sheet is roughly crushed, then reshaped into a bulk form, and rolled into a sheet form again. It is also preferable to repeat step (6). The number of times step (6) is performed is preferably 1 to 12 times, and more preferably 2 to 11 times.

[0102] In step (6), specific methods for roughly crushing the rolled sheet and forming it into a bulk form include folding the rolled sheet, forming it into a rod or thin film sheet, or chipping it. In this disclosure, "rough crushing" means changing the form of the rolled sheet obtained in step (4) or step (5) to another form in order to roll it into a sheet in the next step, and includes cases such as simply folding the rolled sheet.

[0103] Alternatively, step (5) may be performed after step (6), and this process may be repeated. Furthermore, uniaxial stretching or biaxial stretching may be performed in steps (3) or (4), (5), or (6). Furthermore, the fibril diameter can be adjusted by the degree of coarse crushing in step (6).

[0104] In the above steps (4), (5), or (6), the rolling rate is preferably 10% or more, more preferably 20% or more, and also preferably in the range of 80% or less, more preferably 65% ​​or less, and even more preferably 50% or less. If it is below the above range, the time required will increase with the number of rolling cycles, affecting productivity. If it is above the above range, fibrillation may proceed excessively, potentially resulting in an electrode mixture sheet with poor strength and flexibility. The rolling ratio, as used here, refers to the percentage reduction in thickness after rolling relative to the thickness of the sample before rolling. The sample before rolling may be a bulk electrode manufacturing composition or a sheet-like electrode manufacturing composition. The thickness of the sample refers to the thickness in the direction in which the load is applied during rolling.

[0105] As mentioned above, PTFE powder undergoes fibrillation when shear force is applied. However, to obtain a fibrous structure with fibril diameters of 20 nm or more, excessive shear stress can accelerate fibrillation too much, impairing flexibility. Conversely, weak shear stress may not provide sufficient strength. Therefore, by applying appropriate shear stress to the PTFE during mixing and rolling to promote fibrillation, and then rolling the resin into a sheet, within the above-mentioned range, it is possible to obtain a fibrous structure with fibril diameters of 20 nm or more.

[0106] The electrode mixture sheet disclosed herein can be used as an electrode mixture sheet for secondary batteries. It can be used as either a negative electrode or a positive electrode. In particular, the electrode mixture sheet disclosed herein is suitable for lithium-ion secondary batteries.

[0107] (positive electrode) In this disclosure, the positive electrode is preferably composed of a current collector and an electrode mixture sheet containing the positive electrode active material. Suitable materials for the positive electrode current collector 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, particularly aluminum or its alloys, are preferred.

[0108] Examples of current collector shapes include metal foil, metal cylinders, metal coils, metal plates, expanded metal, punched metal, and foamed metal in the case of metal materials, and carbon plates, carbon thin films, and carbon cylinders in the case of carbon materials. Of these, metal foil is preferred. The metal foil may be formed into a mesh shape as appropriate. The thickness of the metal foil is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the metal foil is thinner than this range, it may lack the strength required for a current collector. Conversely, if the metal foil is thicker than this range, its handling may be impaired.

[0109] Furthermore, it is preferable that a conductive additive is applied to the surface of the current collector, as this reduces the electrical contact resistance between the current collector and the positive electrode compound sheet. Examples of conductive additives include carbon and precious metals such as gold, platinum, and silver.

[0110] The ratio of the thickness of the current collector to the thickness of the positive electrode mixture sheet is not particularly limited, but the value of (thickness of one side of the positive electrode mixture sheet immediately before pouring the electrolyte) / (thickness of the current collector) is preferably 20 or less, more preferably 15 or less, most preferably 10 or less, and also preferably 0.5 or more, more preferably 0.8 or more, 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 falls below this range, the volume ratio of the current collector to the positive electrode active material increases, which may reduce the battery capacity.

[0111] The positive electrode can be manufactured by conventional methods. For example, one method involves laminating the electrode mixture sheet and the current collector with an adhesive in between, and then vacuum drying.

[0112] The density of the positive electrode mixture sheet is preferably 3.00 g / cm³. 3 More preferably, 3.10 g / cm³ 3 More preferably 3.20 g / cm³ 3 The above is true, and preferably 3.80 g / cm³. 3 The following, more preferably, is 3.75 g / cm³. 3 More preferably, 3.70 g / cm³ 3 The range is as follows. If the range is exceeded, the penetration of the electrolyte near the interface between the current collector and the active material decreases, which can lead to a decrease in charge / discharge characteristics, especially at high current densities, and may prevent high output from being obtained. Conversely, if the range is below this, the conductivity between the active materials decreases, increasing the battery resistance and potentially preventing high output from being obtained.

[0113] From the viewpoint of increasing high output and stability at high temperatures, it is preferable that the area of ​​the positive electrode mixture sheet be large relative to the outer surface area of ​​the battery casing. Specifically, it is preferable that the total area of ​​the positive electrode mixture be 15 times or more the surface area of ​​the secondary battery casing, and more preferably 40 times or more. The outer surface area of ​​the battery casing refers to the total area calculated from the length, width, and thickness of the case portion filled with the power generation elements, excluding the terminal protrusions, in the case of a bottomed rectangular shape. In the case of a bottomed cylindrical shape, it is the geometric surface area approximating the case portion filled with the power generation elements, excluding the terminal protrusions, as a cylinder. The total area of ​​the positive electrode mixture refers to the geometric surface area of ​​the positive electrode mixture layer facing the mixture layer containing the negative electrode active material, and in a structure in which positive electrode mixture layers are formed on both sides via a current collector foil, it refers to the sum of the areas calculated separately for each surface.

[0114] The thickness of the positive electrode is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite sheet, after subtracting the thickness of the current collector, is preferably 10 μm or more, more preferably 20 μm or more, as a lower limit for one side of the current collector, and preferably 500 μm or less, more preferably 450 μm or less, as an upper limit.

[0115] Furthermore, a positive electrode with a different composition attached to its surface may also be used. Examples of surface-attached 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.

[0116] (Negative electrode) In this disclosure, the negative electrode is preferably composed of a current collector and an electrode mixture sheet containing the negative electrode active material. Suitable materials for the negative electrode current collector 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, particularly copper, nickel, or their alloys, are preferred.

[0117] Examples of current collector shapes include metal foil, metal cylinders, metal coils, metal plates, expanded metal, punched metal, and foamed metal in the case of metal materials, and carbon plates, carbon thin films, and carbon cylinders in the case of carbon materials. Of these, metal foil is preferred. The metal foil may be formed into a mesh shape as appropriate. The thickness of the metal foil is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the metal foil is thinner than this range, it may lack the strength required for a current collector. Conversely, if the metal foil is thicker than this range, its handling may be impaired.

[0118] The negative electrode can be manufactured by conventional methods. For example, one method involves laminating the electrode mixture sheet and the current collector with an adhesive in between, and then vacuum drying.

[0119] The density of the negative electrode mixture sheet is preferably 1.3 g / cm³.3 More preferably 1.4 g / cm³ 3 More preferably 1.5 g / cm³ 3 The above applies, and preferably 2.0 g / cm³. 3 More preferably, 1.9 g / cm³ 3 More preferably, 1.8 g / cm³ 3 The range is as follows. If the range is exceeded, the penetration of the electrolyte near the interface between the current collector and the active material decreases, which can reduce the charge / discharge characteristics, especially at high current densities, and may prevent high output from being obtained. Conversely, if the range is below this, the conductivity between the active materials decreases, increasing the battery resistance and potentially preventing high output from being obtained.

[0120] The thickness of the negative electrode is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite sheet, after subtracting the thickness of the current collector, is preferably 10 μm or more, more preferably 20 μm or more, as a lower limit for one side of the current collector, and preferably 500 μm or less, more preferably 450 μm or less, as an upper limit.

[0121] (The elemental ratio of fluorine to carbon (F / C ratio)) The binder of this disclosure preferably has an elemental ratio of fluorine to carbon (F / C ratio) of 0.40 to 3.00 in the electrode mixture sheet, and more preferably 0.50 to 2.50. Being within this range makes it possible to manufacture electrodes with high strength and low electrode resistance. This is preferable in that respect. Note that the elemental analysis values ​​were measured using standard, general methods. Specifically, the F / C ratio can be determined, for example, by using a MICRO CORDER JM10 (manufactured by J Science Lab), performing simultaneous CHN measurement under the conditions of a sample volume of 2 mg, combustion furnace temperature of 950°C, reduction furnace temperature of 550°C, helium flow rate of 200 mL / min, and oxygen flow rate of 15-25 mL / min, and averaging the value of four measurements. F / C ratio = average F(wt%) / average C(wt%)

[0122] (Secondary battery) Electrodes manufactured by the method for manufacturing electrodes for secondary batteries of this disclosure can be used as positive or negative electrodes in various types of secondary batteries. The secondary batteries mentioned above are batteries that use a non-aqueous electrolyte, and lithium-ion batteries are an example of such batteries.

[0123] (electrolyte) As the above-mentioned non-aqueous electrolyte, a known electrolyte salt dissolved in a known organic solvent for dissolving electrolyte salts can be used.

[0124] The organic solvent for dissolving the electrolyte salt is not particularly limited, but one or more of the following can be used: known hydrocarbon solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and fluorinated solvents such as fluoroethylene carbonate, fluoroether, and fluorinated carbonate.

[0125] Examples of electrolyte salts include LiClO4, LiAsF6, LiBF4, LiPF6, LiN(SO2CF3)2, and LiN(SO2C2F5)2. LiPF6, LiBF4, LiN(SO2CF3)2, LiN(SO2C2F5)2, or combinations thereof are particularly preferred due to their good cycling properties.

[0126] The electrolyte salt concentration must be 0.8 mol / liter or higher, and even higher, 1.0 mol / liter or higher. The upper limit depends on the organic solvent used to dissolve the electrolyte salt, but is usually 1.5 mol / liter or lower.

[0127] (Battery design) The electrode mixture group may be either a laminated structure in which the positive electrode and negative electrode are separated by a separator, or a structure in which the positive electrode and negative electrode are spirally wound around the separator.

[0128] (Separator) The secondary battery of this disclosure preferably further comprises a separator. The material and shape of the separator described above are not particularly limited as long as they are stable in the electrolyte and have excellent liquid retention properties, and known materials can be used. In particular, it is preferable to use a porous sheet or nonwoven fabric in the form of a material that is stable in the electrolyte of the present disclosure or the electrolyte used in the alkali metal secondary battery of the present disclosure, such as a resin, glass fiber, or inorganic material, and has excellent liquid retention properties.

[0129] For example, the resin and glass fiber separator materials can include polyolefins such as polyethylene and polypropylene, aromatic polyamides, PTFE, polyethersulfone, and glass filters. These materials, such as polypropylene / polyethylene two-layer films and polypropylene / polyethylene / polypropylene three-layer films, may be used individually or in any combination and ratio of two or more materials. In particular, the separator is preferably a porous sheet or nonwoven fabric made from polyolefins such as polyethylene or polypropylene, as it has good electrolyte permeability and shut-off effect.

[0130] The thickness of the separator is arbitrary, but is usually 1 μm or more, preferably 5 μm or more, more preferably 8 μm or more, and usually 50 μm or less, preferably 40 μm or less, and more preferably 30 μm or less. If the separator is too thin compared to the above range, the insulating properties and mechanical strength may decrease. If it is too thick compared to the above range, not only may the battery performance such as rate characteristics decrease, but the energy density of the electrolyte battery as a whole may decrease.

[0131] Furthermore, when using porous materials such as porous sheets or nonwoven fabrics as separators, the porosity of the separator is arbitrary, but is usually 20% or more, preferably 35% or more, more preferably 45% or more, and usually 90% or less, preferably 85% or less, and more preferably 75% or less. If the porosity is too small compared to the above range, the film resistance tends to increase and the rate characteristics tend to deteriorate. Also, if it is too large compared to the above range, the mechanical strength of the separator tends to decrease and the insulating properties tend to deteriorate.

[0132] Furthermore, while the average pore size of the separator is arbitrary, it is usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.05 μm or more. If the average pore size exceeds the above range, short circuits are more likely to occur. Conversely, if it falls below the above range, the film resistance increases and the rate characteristics may deteriorate.

[0133] On the other hand, inorganic materials such as oxides of alumina and silicon dioxide, nitrides of aluminum nitride and silicon nitride, and sulfates of barium sulfate and calcium sulfate are used, and these are available in particulate or fibrous form.

[0134] In terms of form, thin films such as nonwoven fabrics, woven fabrics, and microporous films are used. In the thin film form, those with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm are preferably used. In addition to the above independent thin film forms, a separator can be used in which a composite porous layer containing the above inorganic particles is formed on the surface of the positive electrode and / or negative electrode using a resin binder. For example, a porous layer can be formed on both sides of the positive electrode using alumina particles with a 90% particle size of less than 1 μm and a fluororesin as a binder.

[0135] (Percentage of electrode combination group) In a battery using electrodes manufactured by the method for manufacturing secondary battery electrodes of this disclosure, the ratio of the volume of the electrode mixture group to the internal volume of the battery (hereinafter referred to as the electrode mixture group occupancy rate) is usually 40% or more, preferably 50% or more, and usually 90% or less, preferably 80% or less.

[0136] If the electrode mixture occupancy rate falls below the above range, the battery capacity may decrease. Conversely, if it exceeds the above range, the void space is small, and as the battery heats up, the components expand, the vapor pressure of the electrolyte liquid component increases, and the internal pressure rises. This can reduce the battery's charge / discharge cycle performance and high-temperature storage capabilities, and may even cause the gas release valve, which releases internal pressure, to activate.

[0137] The current collection structure is not particularly limited, but in order to more effectively improve the high-current-density charge-discharge characteristics using the electrolyte, it is preferable to have a structure that reduces the resistance of the wiring and connection parts. When the internal resistance is reduced in this way, the effect of using the electrolyte is particularly well exhibited.

[0138] In the case of electrode mixtures having the above-described laminated structure, a structure formed by bundling the metal core portions of each electrode mixture layer and welding them to a terminal is preferably used. When the area of ​​a single electrode mixture is large, the internal resistance increases, so it is also preferable to provide multiple terminals within the electrode mixture to reduce the resistance. In the case of electrode mixtures having the above-described wound structure, the internal resistance can be lowered by providing multiple lead structures for both the positive and negative electrodes and bundling them to a terminal.

[0139] The material of the outer casing is not particularly limited as long as it is a stable material for the electrolyte used. Specifically, metals such as nickel-plated steel, stainless steel, aluminum or aluminum alloy, magnesium alloy, or laminated films of resin and aluminum foil can be used. From the viewpoint of weight reduction, aluminum or aluminum alloy metals or laminated films are preferably used.

[0140] Outer cases using metals may be sealed by welding the metals together using laser welding, resistance welding, or ultrasonic welding, or by using a crimped structure with the metals connected via a resin gasket. Outer cases using laminate film may be sealed by heat-fusing the resin layers together. To improve sealing performance, a resin different from the resin used in the laminate film may be interposed between the resin layers. In particular, when a sealed structure is formed by heat-fusing the resin layers via a current collector terminal, since it is a joint between metal and resin, a resin having polar groups or a modified resin with introduced polar groups is preferably used as the interposing resin.

[0141] The shape of the secondary battery in this disclosure is arbitrary and can be any shape, such as cylindrical, prismatic, laminated, coin-type, or large. The shape and configuration of the positive electrode, negative electrode, and separator can be changed and used according to the shape of each battery. [Examples]

[0142] The present disclosure will be described in detail below based on examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass," respectively.

[0143] [Example 1] A PTFE aqueous dispersion (solids content 31.2% by mass) PTFE-A was obtained by referring to Preparation Example 2 of International Publication No. 2015-080291. The measured standard specific gravity was 2.16.

[0144] [Example 2] A PTFE aqueous dispersion (solids content 30.9% by mass) PTFE-B was obtained by referring to Preparation Example 3 of International Publication No. 2015-080291. The amount of fluorine-containing surfactant used was 3290 ppm relative to the final PTFE yield. The measured standard specific gravity was 2.15.

[0145] [Example 3] A modified PTFE aqueous dispersion, PTFE-C, was obtained by referring to Preparation Example 1 in International Publication No. 2012 / 086710. The polymer concentration of the obtained aqueous dispersion was 30.1% by mass, and the average primary particle size was 0.18 μm. The standard specific gravity was measured to be 2.16.

[0146] [Example 4] Following the example of preparation 1 in International No. 2012-063622, an aqueous dispersion of PTFE particles, PTFE-D, was obtained. The measured standard specific gravity was 2.19.

[0147] 0.25 g of Li-100 (acetylene black) was weighed out as a conductive additive, ultrapure water was added as a solvent, and the mixture was stirred at 2000 rpm for 3 minutes using a mixer to prepare a conductive additive dispersion. Then, 4.75 g of aqueous dispersion PTFE-A was added as solid content, and ultrapure water was added to adjust the concentration of the solid content. The final amount of solvent was 45 g. The mixture was then stirred with a mixer rotor for 1 hour to prepare the mixture. A dried powder was then obtained using a spray dryer (manufactured by Tokyo Rikakikai Co., Ltd.) (inlet temperature 140°C, airflow 0.60 m³ / min, flow rate 5.5 g / min). Further vacuum drying (100°C, 8 hours) was performed to obtain binder 1. As shown in Table 1, binders 2 to 11 were obtained by changing the type and amount of PTFE aqueous dispersion, the type and amount of conductive additive, and the amount of solvent. The moisture content of binders 1 to 11 was measured, and all were found to be 250 PPM or less.

[0148] [Table 1]

[0149] [Example 5] The aqueous dispersion PTFE-D obtained in Preparation Example 4 was diluted to a solid content concentration of 15%, and the PTFE was gently stirred in a container with a stirrer in the presence of nitric acid to solidify it. The solidified PTFE was separated and dried at 160°C for 18 hours to obtain powdered PTFE-E without conductive additives.

[0150] (Example 1) <Preparation of positive electrode mixture sheet> Li(Ni) is used as the positive electrode active material. 0.6 Mn 0.2 Co 0.2 Taking into account the amount of conductive additive contained in the binder to be added later, O2(NMC622) and Li-100 was weighed out as a conductive additive, and the mixture was stirred in a mixer at 1500 rpm for 10 minutes to obtain a mixture. The prepared binder 1 was added to the container containing the mixture, and the mixture was stirred in a kneader at 40 rpm for 2 hours to obtain a mixed powder composition. The composition was set to a mass ratio of positive electrode active material:PTFE:total conductive additive = 95.5:2:2.5. The resulting mixed powder composition was formed into a bulk form and then rolled into a sheet. Subsequently, the rolled sheet obtained earlier was roughly crushed by folding it in half, and then reshaped into a bulk form. This was followed by rolling it into a sheet using metal rolls on a hot plate heated to 80 degrees Celsius, a process to promote fibrillation that was repeated four times. Further rolling was then performed to obtain a cathode mixture sheet with a thickness of approximately 500 μm. The cathode mixture sheet was then cut into 5 cm x 5 cm pieces and rolled in a roll press machine heated to 80 degrees Celsius. A load of 2 kN was repeatedly applied to further promote fibrillation and adjust the thickness. The gap was adjusted to obtain a cathode mixture sheet with a final cathode mixture layer thickness of 90 μm and a density of 3.20 g / cc.

[0151] Each test was conducted using the following method. [Intensity Measurement] The strength of each sample was measured using a tensile testing machine (Shimadzu Corporation Autograph AGS-X series AGS-100NX) at a rate of 100 mm / min on a 4 mm wide strip-shaped positive electrode mixture sheet test piece. The distance between the chucks was set to 30 mm. Displacement was applied until fracture, and the maximum stress measured was defined as the strength of each sample. Comparative Example 1 was set to 100 for comparison.

[0152] [Electrode resistance measurement] The positive electrode active material sheet was cut into a square with a width of 5.0 cm × a length of 10 cm to serve as a test piece. Using a resistivity meter Loresta GP (manufactured by Mitsubishi Chemical Corporation), the four-terminal resistance of the positive electrode active material layer was measured according to JIS K7194; 1994. The smaller the resistance value, the better the battery characteristics are indicated. A: Less than 20 Ωcm B: 20 to less than 50 Ωcm C: 50 to less than 100 Ωcm D: 100 to less than 200 Ωcm E: 200 or more

[0153] (Examples 2, 3) A positive electrode active material sheet was obtained in the same manner as in Example 1, except that a binder having the composition shown in Table 1 was used.

[0154] (Examples 4 to 7) The conductive assistant mixed with NMC by a mixer was changed to Super-P Li (furnace black), and a positive electrode active material sheet was obtained in the same manner as in Example 1, except that a binder having the composition shown in Table 1 was used. (Example 11) The conductive assistant mixed with NMC by a mixer was changed to carbon ECP (Ketjen black), and a positive electrode active material sheet was obtained in the same manner as in Example 1, except that a binder having the composition shown in Table 1 was used.

[0155] (Examples 8, 9) As the positive electrode active material, Li(Ni <00​​​​​​​​​​​​​​​​O2 (NMC811), Li-100 as a conductive additive, and binder 10 were used. The mixed powder composition was composed of positive electrode active material:PTFE:FT7000:Li-100 in mass ratio = 95.5:2:0.11:2.34. Otherwise, a positive electrode mixture sheet was obtained in the same manner as in Example 1.

[0157] <Fabrication of the positive electrode> A positive electrode mixture sheet was bonded to a 20 μm aluminum foil. The adhesive used was a slurry prepared by dissolving polyvinidene fluoride (PVDF) in N-methylpyrrolidone (NMP) and dispersing carbon nanotubes (CNTs). The aforementioned adhesive was applied to the aluminum foil, and the prepared sheet-like positive electrode mixture was placed on top, ensuring no air bubbles were present. The sheet was then vacuum-dried at 120°C for 30 minutes to produce a positive electrode sheet integrated with the current collector.

[0158] <Preparation of electrolyte solution> As an organic solvent, a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC = 30:70 (volume ratio)) was weighed into a sample bottle. Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) were dissolved in this mixture at 1% by mass each to prepare an electrolyte solution. The concentration of LiPF6 salt in the prepared electrolyte solution was adjusted to 1.0 mol / L, and the mixture was mixed at 23°C to obtain the electrolyte solution.

[0159] <Battery manufacturing> A coin cell was fabricated using the positive electrode sheet and polyethylene separator prepared above, and Li metal as the negative electrode. Specifically, the separator was sandwiched between the positive and negative electrodes in a dry room to form an electrode body battery. This electrode body battery was housed in a battery case made of stainless steel (a component for a CR2032 type coin cell battery). Electrolyte was injected into the battery case. The battery case was sealed with a crimping machine to obtain the non-aqueous electrolyte lithium-ion secondary battery of the example.

[0160] [Initial discharge capacity test] The lithium-ion secondary battery manufactured as described above was charged to 4.3V at 25°C using a constant current-constant voltage charge (hereinafter referred to as CC / CV charge) with a current equivalent to 0.5C (0.1C cutoff). Then, it was discharged to 3V with a constant current of 0.5C. This was considered one cycle, and the initial discharge capacity was determined from the discharge capacity of the third cycle. The initial capacity of the reference example was set to 100 for comparison.

[0161] (Comparative Example 1) A non-aqueous electrolyte lithium-ion secondary battery was obtained in the same manner as in Example 1, except that powdered PTFE-E without conductive additives was used.

[0162] (Comparative Example 2) A non-aqueous electrolyte lithium-ion secondary battery was obtained in the same manner as in Example 1, except that powdered PTFE-E without a conductive additive was used and the conductive additive was changed to Super-P Li.

[0163] (Reference example) NMC811 was weighed as the positive electrode active material, and Li-100 and FT7000 were weighed as conductive additives. The mixture was stirred in a mixer at 1500 rpm for 10 minutes to obtain a mixture. Powdered PTFE-E prepared was added to the container containing the mixture, and the mixture was stirred in a kneader at 40 rpm for 2 hours to obtain a mixed powder composition. The composition was a mass ratio of positive electrode active material:PTFE:FT7000:Li-100 = 95.5:2:0.04:2.46. An electrode mixture sheet was prepared using the same procedure as in Example 8 to obtain a non-aqueous electrolyte lithium-ion secondary battery.

[0164] (Comparative Example 3) Li(Ni) is used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1O2 (NMC811) and Li-100 as a conductive additive were weighed and stirred in a mixer at 2000 rpm for 10 minutes to obtain a mixture. The prepared aqueous dispersion PTFE-D was added to the container containing the mixture and stirred in a kneader at 40 rpm for 2 hours to obtain a mixed powder composition. The composition was set to a mass ratio of positive electrode active material:PTFE:conductive additive = 95.5:2:2.5. Since aggregates were observed in the dispersion before drying, spray drying was not performed, and the mixture was dried on a hot plate at 110°C for 1 hour. Further vacuum drying (100°C, 8 hours) was performed to obtain the mixed powder composition. An electrode mixture sheet was prepared in the same procedure as in Example 8 to obtain a non-aqueous electrolyte lithium-ion secondary battery.

[0165] [Table 2]

[0166] [Table 3]

[0167] The fibril diameters of Examples 1 and 3 were measured, and the median fibril diameters were 40 and 31 nm, respectively. The fibril diameters of Examples 4 and 5 were measured, and the median fibril diameters were 33 and 43 nm, respectively. The fibril diameters of Examples 9, 10, and 11 were measured, and the median fibril diameters were 51, 67, and 40 nm, respectively.

[0168] Comparative Example 1 and Examples 1-3 demonstrate that electrodes with high tensile strength and low resistance can be fabricated. Furthermore, a suitable range for conductive material and PTFE was identified from Comparative Example 2 and Examples 4-7. Additionally, Comparative Example 3 and Example 8 showed that using a binder that does not contain electrode active material improves battery characteristics. [Industrial applicability]

[0169] The method for manufacturing electrodes for secondary batteries using a non-aqueous electrolyte as disclosed herein can be used to manufacture electrodes for batteries such as lithium-ion secondary batteries.

Claims

1. A binder for secondary battery electrodes using a non-aqueous electrolyte, comprising a mixed powder of polytetrafluoroethylene resin and Ketjenblack and / or carbon nanotubes.

2. A binder for secondary battery electrodes according to claim 1, wherein the moisture content is 1000 ppm or less.

3. The binder for secondary battery electrodes according to claim 1 or 2, wherein the polytetrafluoroethylene resin has a standard specific gravity of 2.11 to 2.

20.

4. A binder for secondary battery electrodes according to claim 1 or 2, wherein the elemental ratio of fluorine to carbon (F / C ratio) measured by elemental analysis is 0.4 or more and 3.0 or less.

5. A binder for secondary battery electrodes according to claim 1 or 2, comprising the polytetrafluoroethylene resin and the Ketjenblack and / or the carbon nanotubes in a weight ratio of 99:1 to 60:

40.

6. The binder for secondary battery electrodes according to claim 1 or 2, wherein the secondary battery is a lithium-ion secondary battery.

7. The moisture content is 500 ppm or less. The aforementioned polytetrafluoroethylene resin has a standard specific gravity of 2.11 to 2.

20. The elemental ratio of fluorine to carbon (F / C ratio) measured by elemental analysis is between 0.4 and 3.

0. The polytetrafluoroethylene resin and the Ketjenblack and / or carbon nanotubes are contained in a weight ratio of 99:1 to 60:

40. The aforementioned secondary battery is a lithium-ion secondary battery, The binder for secondary battery electrodes according to claim 1 or 2, wherein the carbon nanotube is a multi-walled carbon nanotube.

8. A composition for manufacturing electrodes, characterized by containing the binder for secondary battery electrodes described in claim 1 or 2.

9. The electrode manufacturing composition according to claim 8, further comprising a positive electrode active material.

10. An electrode mixture characterized by containing the binder for secondary battery electrodes described in claim 1 or 2.

11. An electrode characterized by having the electrode mixture described in claim 10.

12. The electrode according to claim 11, wherein the polytetrafluoroethylene resin has a fibrous structure in which the median fibril diameter is 20 nm or more.

13. The polytetrafluoroethylene resin and the Ketjenblack and / or carbon nanotubes are contained in a weight ratio of 99:1 to 60:

40. The carbon nanotube is a multi-walled carbon nanotube, The electrode according to claim 11, wherein the polytetrafluoroethylene resin has a fibrous structure in which the median fibril diameter is 20 nm or more and 75 nm or less.

14. A lithium-ion secondary battery comprising the electrode described in claim 11.

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