JP5412853B2 - Method for producing positive electrode of lithium secondary battery, positive electrode and lithium secondary battery - Google Patents

Description

  The present invention relates to a method for producing a positive electrode of a lithium secondary battery, and a positive electrode and a lithium secondary battery.

  A positive electrode of a lithium secondary battery is manufactured by applying a paste obtained by kneading and dispersing a positive electrode active material and a binder in an aqueous dispersion medium to a current collector and drying it. A lithium-containing transition metal composite oxide is useful as the positive electrode active material, polytetrafluoroethylene (PTFE) is used as the binder, and a metal foil typified by aluminum foil is used as the current collector. Yes. However, although PTFE has good adhesion to the positive electrode active material, it has difficulty in adhesion to the current collector. Further, since the lithium-containing transition metal composite oxide is a hard material, it tends to impair the flexibility of the positive electrode.

  According to Patent Document 1, these points are the binding agent A (acrylic rubbery copolymer or rubber polymer) whose adhesive strength decreases at 200 to 400 ° C. and the adhesive strength which does not decrease at 200 to 400 ° C. Adhesive B (PTFE, FEP, PFA, etc.) is used in combination, and adhesiveness with the current collector during coating is secured with binder A, and then heat-treated at 200 ° C. or higher to decompose binder A The flexibility of the positive electrode is improved by removing and reducing the adhesive force with the current collector.

JP 2007-128660 A

  However, the technique proposed in Patent Document 1 requires heat treatment at a temperature of 200 ° C. or higher, and there are problems in manufacturing equipment and energy costs.

  An object of the present invention is to provide a positive electrode that can ensure a sufficient adhesive force by performing a heat treatment at a relatively low temperature and that does not adversely affect the characteristics of the lithium secondary battery.

  The present invention collects a positive electrode-forming paste for a lithium secondary battery containing a lithium-containing transition metal composite oxide (a), polytetrafluoroethylene (b), an acrylic resin (c) and an aqueous dispersion medium (d). The present invention relates to a method for producing a positive electrode of a lithium secondary battery including a step of applying a heat treatment at a temperature of less than 200 ° C.

As the lithium-containing transition metal composite oxide (a), a lithium-containing transition metal composite oxide is represented by the formula (1): Li _a Mn _2-b M ¹ _b O ₄ (where 0.9 ≦ a; 0 ≦ b ≦ 1.5; M ¹ is 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. Lithium-manganese composite oxide represented by formula (2): LiNi _1-c M ² _c O ₂ (where 0 ≦ c ≦ 0.5; M ² is Fe, Co, Lithium nickel represented by Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge) the composite oxide or ^{_{LiCo 1-d M 3 d O}} 2, ( wherein, 0 ≦ d ≦ 0.5; M 3 is Fe, Ni, Mn Lithium-cobalt composite oxidation represented by Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge) Of these, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , or LiNi _1/3 Co _1/3 Mn _1/3 O ₂ are particularly preferable.

  The acrylic acid resin (c) is at least selected from the group consisting of polyacrylic acid, ammonium polyacrylate, sodium polyacrylate, an ammonium salt of an acrylic acid copolymer, and a sodium salt of an acrylic acid copolymer. One type is preferable from the viewpoints of excellent adhesion to the current collector and excellent paste stability and oxidation resistance.

  The present invention also includes a positive electrode of a lithium secondary battery obtained by the production method of the present invention, and further includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the positive electrode is a positive electrode of the present invention. Related.

  ADVANTAGE OF THE INVENTION According to this invention, sufficient adhesive force can be ensured by performing the heat processing at a comparatively low temperature, and the positive electrode which does not have a bad influence on a lithium secondary battery characteristic can be provided.

It is a chart which shows the relationship between the electric potential of the electrode using the polyacrylic acid-type resin (A-10H) and polyvinylidene fluoride (PVdF) which measured LSV in the reference example in order to measure an oxidation potential.

  The method for producing a positive electrode of a lithium secondary battery according to the present invention includes a lithium-containing transition metal composite oxide (a), polytetrafluoroethylene (b), an acrylic acid resin (c), and an aqueous dispersion medium (d). It includes a step of applying a positive electrode forming paste for a secondary battery to a current collector and heat-treating it at a temperature of less than 200 ° C.

  First, the positive electrode forming paste for a lithium secondary battery will be described.

(A) Lithium-containing transition metal composite oxide As the lithium-containing transition metal composite oxide, the formula (1): Li _a Mn _2-b M ¹ _b O ₄ (where 0.9 ≦ a; 0 ≦ b ≦ 1.5; M ¹ is at least one 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 Lithium-manganese composite oxide represented by the formula (2): LiNi _1-c M ² _c O ₂ (where 0 ≦ c ≦ 0.5; M ² is Fe, Co, Mn, Lithium / nickel composite oxidation represented by Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge) Or LiCo _1-d M ³ _d O ₂ (where 0 ≦ d ≦ 0.5; M ³ is Fe, Ni, Mn, C lithium / cobalt composite oxidation represented by at least one metal selected from the group consisting of u, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge) A thing can be illustrated preferably.

Specifically, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , or LiNi _1/3 Co _1/3 Mn _1/3 O ₂ has an energy density. It is preferable from the viewpoint of providing a high and high output lithium secondary battery.

  The blending amount of the lithium-containing transition metal composite oxide (a) is preferably 50 to 99% by mass, more preferably 80 to 99% by mass, based on the whole positive electrode forming paste for a lithium secondary battery, from the viewpoint of high battery capacity.

(B) PTFE
PTFE (b) is mainly used as a binder for adhesion between lithium-containing transition metal composite oxides (a) that are positive electrode active materials. PTFE may be a tetrafluoroethylene homopolymer or a modified PTFE obtained by copolymerizing a small amount of other monomers such as hexafluoropropylene or perfluoro (alkyl vinyl ether).

  The blending amount of PTFE (b) is preferably 0.5 to 15% by mass, more preferably 0.5 to 10% by mass, based on the total positive electrode forming paste for a lithium secondary battery, from the viewpoint of high battery capacity.

(C) Acrylic acid-based resin Acrylic acid-based resin (c) is also a binder, but mainly for enhancing adhesion between lithium-containing transition metal composite oxide (a) or PTFE (b) and the current collector. Function.

  As the acrylic resin (not rubbery), those having a high oxidation potential are preferable. For example, polyacrylic acid, ammonium polyacrylate, sodium polyacrylate, ammonium salts of acrylic acid copolymers, and acrylic acid copolymers. A preferred example is at least one selected from the group consisting of sodium salts of polymers. These oxidation potentials in terms of lithium are 4.3 V or more. Examples of commercially available products of polyacrylic acid, ammonium salt of acrylic acid copolymer and sodium salt of acrylic acid copolymer include, for example, A-10H, A-93, and A-7100 manufactured by Toagosei Co., Ltd. , A-30, A-7185, and the like. In the present invention, “acrylic acid type” is a concept including not only acrylic acid but also methacrylic acid.

  The blending amount of the acrylic resin (c) is preferably 0.2 to 20% by mass, more preferably 0.5 to 10% by mass, based on the whole positive electrode forming paste for a lithium secondary battery. When the amount is too small, the adhesion to the positive electrode current collector is weakened. When the amount is too large, the paste becomes too viscous and difficult to apply, and the active material surface is covered with resin, resulting in high resistance and battery capacity. Tends to be smaller.

(D) Aqueous dispersion medium As the aqueous dispersion medium (d), water is most preferable. Moreover, you may use together hydrophilic organic solvents, such as ethanol.

  The amount of the aqueous dispersion medium (d) is the remaining amount of the positive electrode forming paste for a lithium secondary battery, and may be an amount that facilitates coating.

(E) Other component In addition to component (a)-(d), the additive used for manufacture of the positive electrode of a lithium secondary battery can be mix | blended as needed. Examples of such additives include conductive materials, thickeners, other polymers, and surfactants.

  Examples of the conductive material include conductive carbon black such as acetylene black and ketjen black; and carbonaceous materials such as graphite and carbon fiber.

  Examples of the thickener include carboxymethyl cellulose (CMC). The acrylic resin (c) also has an action of thickening the paste, and a stable paste can be prepared without adding a thickener separately.

  Examples of other polymers include various resins and rubbers that have been conventionally blended in positive electrodes for lithium secondary batteries, and may be blended in amounts that do not impair the effects of the present invention. Specifically, for example, fluororesin (vinylidene fluoride (VdF) / hexafluoropropylene (HFP) copolymer, tetrafluoroethylene (TFE) / VdF copolymer, VdF / TFE / HFP copolymer, TFE / ethylene). Copolymer, TFE / propylene copolymer, etc.) or fluororubber.

  These components are mixed as appropriate, and a positive electrode forming paste for a lithium secondary battery is prepared as a uniform mixture by stirring or the like.

  In the production method of the present invention, the positive electrode forming paste for a lithium secondary battery is applied to a current collector and heat-treated at a temperature of less than 200 ° C.

  The current collector is not particularly limited as long as it is a chemically stable electron conductor. Examples of the material constituting the current collector include aluminum and its alloys, stainless steel, nickel and its alloys, titanium and its alloys, carbon, conductive resin, etc., as well as carbon or aluminum on the surface of aluminum or stainless steel. A material obtained by treating titanium is used. Of these, aluminum and aluminum alloys are particularly preferable. These materials can also be used after oxidizing the surface. In addition, the surface of the current collector is preferably provided with irregularities on the surface, so that the adhesiveness is improved.

  As a coating method, a normal method may be used, and for example, a slit die coater, a reverse roll coater, a lip coater, a blade coater, a knife coater, a gravure coater, and a dip coater can be used.

  The positive electrode with the paste applied to the current collector is subjected to heat treatment.

  In the present invention, the heat treatment is performed at less than 200 ° C. Heat treatment at 200 ° C. or higher, particularly 300 ° C. or higher is disadvantageous in terms of manufacturing equipment and energy costs. A preferable upper limit is 180 ° C., further 160 ° C. If the heat treatment temperature is too low, the treatment takes too much time, so the preferred lower limit is 130 ° C., further 140 ° C.

  The heat treatment may be performed immediately after coating because it is sufficient if the electrode has no moisture, may be performed after being rolled (pressed), or may be performed after being naturally dried. Moreover, you may perform heat processing 2 times or more.

  The heat treatment time varies depending on the temperature, but is usually about 15 minutes to 7 hours.

  The heat-treated positive electrode is usually further subjected to a rolling treatment if necessary, and then cut and processed into a predetermined thickness and size to obtain a positive electrode for a lithium secondary battery. The rolling process and the cutting process may be ordinary methods.

  The present invention also relates to a positive electrode for a lithium secondary battery manufactured by the manufacturing method of the present invention. In the positive electrode for a lithium secondary battery of the present invention, the current collector includes a lithium-containing transition metal composite oxide (a), and if necessary, the other component (e) includes a binder PTFE (b) and acrylic acid. Bonded with a system resin (c).

  Since the positive electrode of the present invention is excellent in adhesive strength with the current collector, the flexibility of the positive electrode is improved, and even if it is wound like a wound type lithium secondary battery, it does not break or fall off.

  The present invention also relates to a lithium secondary battery. The lithium secondary battery of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. In particular, the positive electrode for a lithium secondary battery of the present invention is used as the positive electrode.

Examples of the negative electrode active material used for the negative electrode in the present invention include carbon materials, such as metal oxides and metal nitrides into which lithium ions can be inserted. Examples of carbon materials include natural graphite, artificial graphite, pyrolytic carbons, cokes, mesocarbon microbeads, carbon fibers, activated carbon, and pitch-coated graphite. Metal oxides capable of inserting lithium ions include tin and Examples of the metal compound include silicon and titanium, such as tin oxide, silicon oxide, and lithium titanate. Examples of the metal nitride include Li _2.6 Co _0.4 N.

  The non-aqueous electrolyte is not particularly limited as long as it is an electrolyte containing an electrolyte salt and an organic solvent for dissolving the electrolyte salt and is used in a lithium secondary battery.

Examples of the electrolyte include known electrolyte salts such as LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO ₂ C ₂ F ₅ ) _2. Examples of the organic solvent include ethylene carbonate and dimethyl Hydrocarbon solvents such as carbonate, methyl ethyl carbonate, diethyl carbonate, propylene carbonate; fluorine solvents such as HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, CF ₃ COOCF ₃ , CF ₃ COOCH ₂ CF ₃ , and mixtures thereof Although a solvent etc. can be illustrated, it is not limited only to these.

  A separator may be disposed in the lithium secondary battery of the present invention. There is no restriction | limiting in particular as a separator, A microporous polyethylene film, a microporous polypropylene film, a microporous ethylene propylene copolymer film, a microporous polypropylene / polyethylene two-layer film, a microporous polypropylene / polyethylene / polypropylene three-layer film Etc. In addition, a film in which an aramid resin is coated on a separator made for the purpose of improving safety such as a short circuit caused by Li dentrite, or a film in which a resin containing polyamideimide and an alumina filler is coated on a separator can be given (for example, JP, 2007-299612, A, JP, 2007-324073, A).

  The lithium secondary battery of the present invention is useful as a large-sized lithium secondary battery for a hybrid vehicle or a distributed power source, a small-sized lithium secondary battery such as a mobile phone or a personal digital assistant.

  EXAMPLES Next, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

Reference Example The oxidation potential of polyacrylic acid resin and PVdF, which is widely used as a binder, was examined in the following manner.

80:20 (mass) of acetylene black and polyacrylic acid resin (A-10H made by Toagosei Co., Ltd.) as a working electrode using a BAS 3-pole sealed glass cell by linear sweep voltammetry (LSV) Ratio) was applied so that the coating amount was 2.5 mg and the area was 0.25 cm ² . In addition, a lithium metal is used for the counter electrode and the reference electrode, and an ethylene carbonate / diethyl carbonate (= 30/70 (volume ratio)) solution (concentration: 1.0 mol / liter) containing LiPF ₆ as an electrolyte salt is used as the electrolyte. Using. The measurement was performed using a potentio-galvanostat (1287 type manufactured by Solartron) at 25 ° C. and a scanning speed of 5 mV / sec. The oxidation potential was a voltage at which the current value reached 0.5 mA / cm ² .

  Further, as a control, the oxidation potential was also examined when PVdF (# 1120 manufactured by Kureha Co., Ltd.) was used instead of the polyacrylic acid resin (A-10H). The results are shown in FIG.

  FIG. 1 shows that the polyacrylic acid resin has a high oxidation potential (4.5 V) equal to or higher than the oxidation potential (4.3 V) of PVdF, which is widely used.

Example 1
90 parts by mass of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by Nippon Chemical Industry Co., Ltd.), 3 parts by mass of acetylene black (manufactured by Denki Black Industry Co., Ltd.), 16.1 parts by mass of Polyacrylic acid resin aqueous solution (trade name: A-10H manufactured by Toagosei Co., Ltd., solid content 24.9% by mass), 94.9 parts by mass of water was stirred with a double arm kneader, 5.0 parts by mass of an aqueous PTFE suspension (solid content: 60% by mass) was added to prepare a positive electrode forming paste having a solid content of 50% by mass. The proportion of each component of the paste (in the solid content) is as follows: LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is 90% by mass, acetylene black is 3% by mass, polyacrylic acid resin is 4% by mass, and PTFE is It was 3 mass%.

  The obtained paste was applied to an aluminum foil having a thickness of 15 μm and dried to obtain a coating film having a thickness of about 120 μm. This coating film was pressed (rolled) to a total thickness of 80 μm, then cut into predetermined dimensions (300 mm × 100 mm), and then heat treated at 150 ° C. for 4 hours in a hot air dryer, A positive electrode was produced.

Example 2
In place of the polyacrylic acid resin aqueous solution (A-10H), 12.9 parts by mass of an aqueous solution of ammonium polyacrylate (trade name: A-30 manufactured by Toagosei Co., Ltd., solid content 30.9% by mass) A positive electrode forming paste was prepared in the same manner as in Example 1 except that it was used. The proportion of each component of the paste (in the solid content) is 90% by mass for LiNi _1/3 Co _1/3 Mn _1/3 O _2, 3% by mass for acetylene black, 4% by mass for ammonium polyacrylate, PTFE Was 3% by mass.

  The obtained paste was applied to an aluminum foil having a thickness of 15 μm and dried to obtain a coating film having a thickness of about 120 μm. This coating film was pressed (rolled) to a total thickness of 80 μm, then cut into predetermined dimensions (300 mm × 100 mm), and then heat treated at 150 ° C. for 4 hours in a hot air dryer, A positive electrode was produced.

Example 3
Instead of the polyacrylic acid resin aqueous solution (A-10H), an acrylic acid copolymer ammonium salt aqueous solution (trade name: A-93 manufactured by Toagosei Co., Ltd., solid content 31.7% by mass) is used. A positive electrode forming paste was prepared in the same manner as in Example 1 except that 0 part by mass was used. The proportion of each component of the paste (in the solid content) is 90% by mass for LiNi _1/3 Co _1/3 Mn _1/3 O _2, 3% by mass for acetylene black, and 4% for ammonium salt of acrylic acid copolymer. %, PTFE was 3 mass%.

  The obtained paste was applied to an aluminum foil having a thickness of 15 μm and dried to obtain a coating film having a thickness of about 120 μm. This coating film was pressed (rolled) to a total thickness of 80 μm, then cut into predetermined dimensions (300 mm × 100 mm), and then heat treated at 150 ° C. for 4 hours in a hot air dryer, A positive electrode was produced.

Example 4
A sheet-like positive electrode was produced in the same manner as in Example 1 except that the heat treatment temperature was changed to 160 ° C.

Example 5
A sheet-like positive electrode was produced in the same manner as in Example 1, except that the heat treatment temperature was 140 ° C.

Example 6
A positive electrode forming paste was prepared in the same manner as in Example 1 except that LiCoO ₂ was used instead of LiNi _1/3 Co _1/3 Mn _1/3 O _2. A positive electrode was prepared.

Example 7
In Example 1, a positive electrode forming paste was prepared in the same manner as in Example 1 except that LiMn ₂ O ₄ was used instead of LiNi _1/3 Co _1/3 Mn _1/3 O _2. A sheet-like positive electrode was produced.

Example 8
84 parts by mass of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by Nippon Chemical Industry Co., Ltd.), 3 parts by mass of acetylene black (manufactured by Denka Black Industry Co., Ltd.), 40.2 parts by mass of An aqueous polyacrylic acid resin solution (trade name: A-10H manufactured by Toagosei Co., Ltd., solid content 24.9% by mass), 83.8 parts by mass of water were stirred with a double-arm kneader, and 5.0 parts by mass of an aqueous PTFE suspension (solid content: 60% by mass) was added to prepare a positive electrode forming paste having a solid content of 50% by mass. The proportion of each component (in the solid content) of this paste is 84% by mass for LiNi _1/3 Co _1/3 Mn _1/3 O _2, 3% by mass for acetylene black, 10% by mass for polyacrylic resin, and PTFE It was 3 mass%.

  The obtained paste was applied to an aluminum foil having a thickness of 15 μm and dried to obtain a coating film having a thickness of about 120 μm. This coating film was pressed (rolled) to a total thickness of 80 μm, then cut into predetermined dimensions (300 mm × 100 mm), and then heat treated at 150 ° C. for 4 hours in a hot air dryer, A positive electrode was produced.

Example 9
93.5 parts by mass of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by Nippon Chemical Industry Co., Ltd.), 3 parts by mass of acetylene black (manufactured by Denka Black Industry Co., Ltd.), 2.0 masses Part of a polyacrylic acid resin aqueous solution (trade name: A-10H manufactured by Toagosei Co., Ltd., solid content 24.9% by mass) and 103 parts by mass of water were stirred with a double-arm kneader, 5.0 parts by mass of an aqueous PTFE suspension (solid content: 60% by mass) was added to prepare a positive electrode forming paste having a solid content of 50% by mass. The ratio of each component of the paste (in the solid content) was 93.5% by mass for LiNi _1/3 Co _1/3 Mn _1/3 O _2, 3% by mass for acetylene black, and 0.5% for polyacrylic acid resin. %, PTFE was 3 mass%.

  The obtained paste was applied to an aluminum foil having a thickness of 15 μm and dried to obtain a coating film having a thickness of about 120 μm. This coating film was pressed (rolled) to a total thickness of 80 μm, then cut into predetermined dimensions (300 mm × 100 mm), and then heat treated at 150 ° C. for 4 hours in a hot air dryer, A positive electrode was produced.

Comparative Example 1
90 parts by mass of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by Nippon Chemical Industry Co., Ltd.), 3 parts by mass of acetylene black (manufactured by Denki Black Industry Co., Ltd.), 17 parts by mass of TFE / HFP copolymer (FEP) aqueous dispersion (ND-1 manufactured by Daikin Industries, Ltd., solid content 20% by mass), 60 parts by mass of CMC sodium salt aqueous solution (trade name: Daiichi Kogyo Seiyaku Co., Ltd.) Serogen 4H manufactured by Solid Arm Co., Ltd. (solid content 1% by mass) was stirred with a double-arm kneader, and further 5.0 parts by mass of an aqueous PTFE suspension (solid content 60% by mass) was added. A positive electrode forming paste having a content of 50% by mass was prepared. The ratio of each component of the paste (in the solid content) is 90% by mass for LiNi _1/3 Co _1/3 Mn _1/3 O _2, 3% by mass for acetylene black, 0.6% by mass for sodium salt of CMC, FEP was 3.4% by mass and PTFE was 3% by mass.

  The obtained paste was applied to an aluminum foil having a thickness of 15 μm and dried to obtain a coating film having a thickness of about 120 μm. This coating film was pressed (rolled) to a total thickness of 80 μm, then cut into predetermined dimensions (300 mm × 100 mm), and then heat treated at 150 ° C. for 4 hours in a hot air dryer, A comparative positive electrode was produced.

Test Example 1 (Evaluation of flexibility: winding test)
The sheet-like positive electrode prepared in each Example and Comparative Example was wound around a cylinder having a diameter of 2 mm and then spread, and the occurrence of cracks in the positive electrode coating film was visually examined. The results are shown in Table 1.

  From the results in Table 1, it can be seen that the positive electrode of the present invention is rich in flexibility.

Test Example 2 (Evaluation of adhesion: adhesive tape peeling test)
The sheet-like positive electrode produced in each Example and Comparative Example was cut into a size of (15 mm × 20 mm) and scratched with a cutter knife in the horizontal direction and the vertical direction at intervals of 5 mm. Next, the pressure-sensitive adhesive tape was pressed, and then the tape was peeled off. From the weight of the positive electrode before and after the peel test, the ratio (mass%) of the coating film peeled and remained on the positive electrode after the test was calculated. The results are shown in Table 1.

  From the results in Table 1, it can be seen that the positive electrode produced by the production method of the present invention is excellent in adhesiveness in the current collector.

Test Example 3 (Battery characteristics)
(Production of cylindrical battery)
A lead body was welded to the sheet-like positive electrode produced in each example and comparative example to produce a belt-like positive electrode.

  Separately, styrene-butadiene rubber dispersed with distilled water is added to artificial graphite powder (manufactured by Hitachi Chemical Co., Ltd., trade name MAG-D) so that the solid content is 6% by mass, and mixed with a disperser. After applying the slurry in a uniform manner on a negative electrode current collector (copper foil having a thickness of 10 μm), drying, forming a negative electrode mixture layer, and then compression molding with a roller press machine and cutting, It dried and welded the lead body and produced the strip | belt-shaped negative electrode.

  Next, the belt-like positive electrode was overlapped with the belt-like negative electrode through a microporous polyethylene film (separator) having a thickness of 20 μm and wound in a spiral shape to obtain a laminated electrode body having a spiral winding structure. In that case, it wound so that the rough surface side of the positive electrode current collector could be the outer peripheral side. Thereafter, the electrode body was filled in a bottomed cylindrical battery case having an outer diameter of 18 mm, and the positive and negative lead bodies were welded.

Next, an ethylene carbonate / diethyl carbonate (= 30/70 (volume ratio)) solution (concentration: 1.0 mol / liter) containing LiPF ₆ as an electrolyte salt is injected into the battery case as the electrolyte solution, and the electrolyte solution becomes a separator or the like. After sufficiently infiltrating, a sealed lithium secondary battery having a capacity of 1800 mAh was prepared by sealing, precharging and aging.

  The cycle characteristics (capacity maintenance ratio) of this lithium secondary battery were examined as follows. The results are shown in Table 1.

  From the results in Table 1, it can be seen that the battery characteristics of the lithium secondary battery using the positive electrode of the present invention are maintained at a high level.

(Cycle characteristics)
When the charge / discharge current is represented by C, measurement is performed under the following charge / discharge measurement conditions with 1800 mA as 1C.

Charge / Discharge Condition Charging: Holds the charge current at 1 / 10C at 0.5C / 4.2V (CC / CV charge)
Discharge: 1C 2.5Vcut (CC discharge).

  As for the cycle characteristics, a charge / discharge test is performed under the above charge / discharge conditions, and a discharge capacity of 100 cycles is measured. Regarding the cycle characteristics, the value obtained by the following calculation formula is described as the capacity retention rate.

Capacity retention rate (%) = 100 cycle discharge capacity (mAh) / 1 cycle discharge capacity (mAh) × 100

  From the results in Table 1, it can be seen that the cycle characteristics of Examples 1 to 9 are improved compared to Comparative Example 1. As a cause of this, since the adhesion between the coating film and the current collector has been improved, it is considered that the cycle deterioration due to the failure to collect current during the cycle test did not occur.

Claims (4)

Applying a positive electrode forming paste for a lithium secondary battery containing a lithium-containing transition metal composite oxide (a), polytetrafluoroethylene (b), an acrylic resin (c) and an aqueous dispersion medium (d) to a current collector And a heat treatment step at a temperature of less than 200 ° C.,
The acrylic resin (c) is a method for producing a positive electrode of a lithium secondary battery, which is polyacrylic acid. The lithium-containing transition metal composite oxide (a) is represented by the formula (1): Li _a Mn _2-b M ¹ _b O ₄ (where 0.9 ≦ a; 0 ≦ b ≦ 1.5; M ¹ is Fe , Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge. Lithium / manganese spinel composite oxide, formula (2): LiNi _1-c M ² _c O ₂ (where 0 ≦ c ≦ 0.5; M ² is Fe, Co, Mn, Cu, Zn, Al, Sn) , Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, at least one metal selected from the group consisting of lithium and nickel, or LiCo _1-d M ³ _d O ₂ ^{(where, 0 ≦ d ≦ 0.5; M} 3 is Fe, Ni, Mn, lithium / cobalt composite oxidation represented by at least one metal selected from the group consisting of u, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge) The method according to claim 1, wherein the method is a product. The positive electrode of the lithium secondary battery obtained by the manufacturing method of Claim 1 or 2. A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode is the positive electrode according to claim 3.

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