JP2005203249A - Manufacturing method of positive electrode for nonaqueous electrolyte battery, and nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery of a high capacity and a long life by using a positive electrode fabricated by a manufacturing method by which an electrode plate resistivity, liquid absorbing property, and liquid-retaining property become optimum. <P>SOLUTION: This manufacturing method of the positive electrode for the nonaqueous electrolyte battery is provided with an active material fabricating process in which by coating carbonaceous conductive agent on the surface of positive electrode active material particles to obtain a conductive agent coated active material, a conductive agent paste fabricating process in which by making the carbonaceous conductive agent kneaded and dispersed in a solution with an adhesive to obtain a conductive agent paste, a positive electrode paste fabricating process in which the conductive agent coated active material and the conductive agent paste are kneaded and dispersed to obtain an positive electrode paste, and an active material applying process in which the positive electrode paste is applied to a positive electrode core body. By this, the positive electrode for the nonaqueous electrolyte battery of which electrode plate resistivity is low, and which is superior in load performance and cycle performance is obtained, and the nonaqueous electrolyte battery of the high capacity and the long life becomes to be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a positive electrode for a nonaqueous electrolyte battery comprising an active material, a conductive agent, and a binder, and a nonaqueous electrolyte secondary battery comprising a positive electrode produced by this production method.

In recent years, non-aqueous electrolyte batteries have been used as power sources for various portable devices. In this type of nonaqueous electrolyte battery, a carbon material capable of occluding and releasing lithium ions is used as a negative electrode active material, and lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing manganese oxide ( Lithium-containing transition metal oxides such as LiMn ₂ O ₄ ) and lithium-containing nickel oxide (LiNiO ₂ ) are generally used.

  By the way, since the lithium-containing transition metal oxide has a low specific conductivity, a conductive agent made of carbon powder or the like is added to the positive electrode mixture to provide electronic conductivity between the individual metal oxide particles. The redox reaction is promoted. However, when the lithium-containing transition metal oxide and the conductive agent are not uniformly and frequently in contact with each other, a portion where electrons are not sufficiently supplied to the positive electrode active material occurs. As a result, a positive electrode active material remaining unreacted is generated, resulting in a problem that the utilization rate of the positive electrode active material is lowered. For this reason, a positive electrode mixture in which a certain amount of a conductive agent is uniformly mixed with a lithium-containing transition metal oxide is used.

  However, even if the lithium-containing transition metal oxide and the conductive agent are mixed, it is difficult to uniformly disperse both, and there is a problem that sufficient contact between the positive electrode active material powder particles cannot be obtained. It was. This is because when a solvent is added to the positive electrode mixture to produce a slurry, the binder added to the positive electrode mixture is absorbed by the carbon powder serving as the conductive agent and unevenly distributed. Therefore, even if the lithium-containing transition metal oxide and the conductive agent are simply mixed, the lithium-containing transition metal oxides or the conductive agents are aggregated and apparently evenly mixed evenly. It was difficult to obtain a complete mixed state.

  Therefore, when mixing a conductive agent composed of a lithium-containing transition metal oxide and carbon powder, the mixed powder is mixed so as to apply a compressive shear stress, and a part of the surface of the lithium-containing transition metal oxide is electrically conductive. A method of coating with an agent has been proposed in Patent Document 1. In the method proposed in Patent Document 1, first, a mixed powder composed of a lithium-containing transition metal oxide and carbon powder is put into a carbon film forming apparatus. Next, the rotating drum disposed in the carbon film forming apparatus is rotated at a predetermined number of rotations to apply a compressive shear stress between the inner peripheral surface of the rotating drum and the pressing shear head, and then scraped with a nail. Drop and mix. This makes it possible to obtain a positive electrode active material in which a part of the surface of the lithium-containing transition metal oxide is coated with carbon powder, and such a positive electrode active material is unevenly distributed as the binder is absorbed by the carbon powder. Therefore, the adhesion between the positive electrode active materials is improved.

  However, it has become clear that even when the positive electrode active material powder produced by the method proposed in Patent Document 1 is used, the adhesion between the positive electrode active materials is not improved so much. This is because the positive electrode active material whose surface is partially coated with the conductive agent is simply that the conductive agent is mechanically pressure-bonded to the surface of the lithium-containing transition metal oxide. This is because the binding power is weak. For this reason, when the positive electrode mixture layer is formed on the positive electrode current collector, the positive electrode mixture comes off from the positive electrode current collector, the mechanical strength is reduced, and the cycle life is reduced. occured.

Therefore, Patent Document 2 proposes a positive electrode in which the adhesion between the positive electrode mixture and the positive electrode current collector is improved even if a positive electrode active material in which a part of the surface of the positive electrode active material is coated with a conductive agent is used. It became so. The positive electrode proposed in Patent Document 2 contains a mixed positive electrode active material composed of a positive electrode active material partially covered with a conductive agent and a positive electrode active material not covered with a conductive agent, and a binder. A positive electrode mixture is provided. In this way, when a positive electrode mixture is constituted by a mixed positive electrode active material composed of a positive electrode active material whose surface is coated with a conductive agent and a positive electrode active material not coated with a conductive agent, and a binder. Since the conductive agent is fixed to the surface of the positive electrode active material, the binder can be prevented from being absorbed by the conductive agent, and the binder is prevented from being unevenly distributed. Thereby, the adhesiveness of a positive mix and a positive electrode electrical power collector improves.
JP-A-9-92265 JP 2002-231222 A

  By the way, in order to satisfy the demand for higher capacity and longer life of this type of nonaqueous electrolyte battery, the positive electrode active material is filled with a high density and the conductive agent is used to increase the filling amount of the positive electrode active material. It is necessary to reduce the amount of addition to the minimum necessary. In addition, even if the amount of the conductive agent added is reduced to the minimum necessary in this way, it is necessary to obtain a sufficiently high output and cycle performance. However, even when the positive electrode manufactured by the method proposed in Patent Document 2 described above is used, it is difficult to achieve a sufficiently high capacity and long life due to the large amount of conductive agent added. It was.

  Thus, as a result of examining the existence state of the active material and the conductive agent in the positive electrode, the present inventors have found a positive electrode manufacturing method in which the electrode plate resistance, liquid absorption, and liquid retention properties are optimum, and are manufactured by this manufacturing method. It is an object of the present invention to provide a non-aqueous electrolyte battery having a high capacity and a long life by using the prepared positive electrode.

  In order to achieve the above object, a method for producing a positive electrode for a non-aqueous electrolyte battery according to the present invention includes an active material preparation step in which a surface of positive electrode active material particles is coated with a carbon-based conductive agent to form a conductive agent-coated active material, A conductive agent paste preparation step in which a conductive agent is kneaded and dispersed in a solution together with a binder to make a conductive agent paste, and a positive electrode paste in which a conductive agent-coated active material and a conductive agent paste are kneaded and dispersed It is characterized by comprising a production process and an active material application process for applying a positive electrode paste to a positive electrode core.

  Thus, a conductive agent-coated active material in which the surface of the positive electrode active material particles is coated with the carbon-based conductive agent, and a conductive agent paste in which the carbon-based conductive agent is kneaded and dispersed in the solution together with the binder are kneaded. When dispersed into a positive electrode paste, a positive electrode paste having good conductivity and good liquid absorption and liquid retention can be obtained. As a result, a positive electrode for a nonaqueous electrolyte battery having a low electrode plate resistance and excellent load performance and cycle performance can be obtained, and a high capacity and long life nonaqueous electrolyte battery can be obtained.

  In addition, if the surface of the positive electrode active material particles is coated with the carbon-based conductive agent while applying mechanical stress in the active material preparation process, the surface of the positive electrode active material particles is uniformly coated with the conductive agent and has excellent conductivity. It is desirable because a conductive agent-coated active material can be obtained. In this case, as the coating amount of the carbon-based conductive agent covering a part of the surface of the positive electrode active material increases, the liquid absorbency decreases. Therefore, the coating amount of the conductive agent is 1. It is desirable to regulate the content to be 0% by mass or less.

  Moreover, since the conductivity of the positive electrode is improved by using a conductive agent paste that is uniformly dispersed so that the average particle size of the carbon-based conductive agent is 5 μm or less, the average of the carbon-based conductive agent in the conductive agent paste The particle size is desirably 5 μm or less. Furthermore, in order to improve the load performance and cycle performance with a low surface resistance, excellent electrolyte absorption and liquid retention, the amount of carbon-based conductive agent added to the conductive agent paste is It is desirable to set it to 1.0 mass% or more and 3.0 mass% or less with respect to mass.

  Next, an embodiment of the present invention will be described below. However, the present invention is not limited to this embodiment, and can be implemented with appropriate modifications within a range that does not change the object of the present invention. is there.

1. Preparation of positive electrode First, lithium carbonate (Li ₂ CO ₃ ) was prepared as a starting material for a lithium source, and tricobalt tetroxide (Co ₃ O ₄ ) obtained by a pyrolysis reaction was prepared as a starting material for a cobalt source. These were weighed so that the molar ratio of lithium to cobalt was 1: 1, and then mixed. Subsequently, the obtained mixture was baked in an air atmosphere (for example, baked at a temperature of 850 ° C. for 20 hours) to synthesize a sintered body of lithium cobaltate (LiCoO ₂ ). Thereafter, the synthesized fired body was pulverized until the average particle size became 10 μm to obtain a positive electrode active material (LiCoO ₂ ) α.

Next, the positive electrode active material α (LiCoO ₂ ) prepared as described above is mixed with a predetermined amount of acetylene black as a carbon-based conductive agent, and this mixture is mixed with a carbon film forming apparatus (for example, manufactured by Hosokawa Micron: Mechano-Fusion). (See Patent Document 2 mentioned above). Next, the rotating drum of this apparatus is rotated at a predetermined rotational speed, and the mixed powder is pressed between the inner peripheral surface of the rotating drum and the pressing shearing head by the rotating pressure to generate a strong compressive force and a strong shearing force. The carbon-based conductive agent was rubbed into the surface of the positive electrode active material α (LiCoO ₂ ).

As a result, conductive agent-coated active materials β1, β2, and β3 in which a part of the surface was coated with the conductive agent were produced. The conductive agent-coated active material β1 was coated so that the coating amount of the conductive agent (acetylene black) was 0.1% by mass with respect to the mass of the positive electrode active material α (LiCoO ₂ ). A conductive agent-coated active material β2 is coated with the conductive agent (acetylene black) so that the coating amount is 1.0% by mass with respect to the mass of the positive electrode active material α (LiCoO ₂ ). The conductive agent-coated active material β3 was coated so that the coating amount of (acetylene black) was 2.0% by mass with respect to the mass of the positive electrode active material α (LiCoO ₂ ).

  Thereafter, the addition amount of acetylene black as shown in Table 1 below is adjusted so that the total addition amount of acetylene black as the carbon-based conductive agent is 3.0% by mass (relative to the mass of the positive electrode active material). While being selected, 3% by mass (based on the mass of the positive electrode active material) of polyvinylidene fluoride (PVdF) powder as a binder was added and mixed. Next, N-methylpyrrolidone (NMP) as a solvent is added to these and mixed to form a mixed solution, and then dispersed and kneaded until the average particle diameter of acetylene black as a carbon-based conductive agent in the mixed solution becomes 3 μm. Thus, conductive agent pastes γ1 to γ3 were prepared.

  Here, the addition amount of acetylene black in the conductive agent paste is 2.9% by mass with respect to the mass of the positive electrode active material as the conductive agent paste γ1, and 2.0% by mass is the conductive agent paste γ2. 1.0% by mass was designated as conductive agent paste γ3. The average particle diameter of the carbon-based conductive agent is a value obtained by irradiating the conductive agent pastes γ1 to γ3 with a laser beam, evaluating by a laser diffraction and scattering method, and using a volume median diameter. Next, the conductive agent-coated active materials β1 to β3 produced as described above were added to and mixed with the obtained conductive agent pastes γ1 to γ3, and then kneaded to prepare positive electrode pastes δ1 to δ3. In this case, the conductive agent-coated active material β1 and the conductive agent paste γ1 are used as the positive electrode paste δ1, and the conductive agent-coated active material β2 and the conductive agent paste γ2 are used as the positive electrode paste δ2, and the conductive agent-coated active material. A paste using β3 and conductive agent paste γ3 was designated as positive electrode paste δ3.

  Thereafter, the obtained positive electrode pastes δ1 to δ3 are applied to both surfaces of a positive electrode current collector (aluminum foil or aluminum alloy foil) having a thickness of 20 μm by the doctor blade method, and the positive electrode active material is applied to both surfaces of the positive electrode current collector. A material layer was formed. After drying this, it is rolled to a predetermined thickness (for example, 160 μm) using a compression roll, cut into predetermined dimensions (width is 55 mm, length is 500 mm), and positive electrodes a1, a2, and a3 are Produced. In addition, the thing using positive electrode paste (delta) 1 was made into positive electrode a1, the thing using positive electrode paste (delta) 2 was made into positive electrode a2, and the thing using positive electrode paste (delta) 3 was made into positive electrode a3.

  On the other hand, conductive agent-coated active material β2, acetylene black 2% by mass (based on the mass of the positive electrode active material) as a carbon-based conductive agent, and 3% by mass of polyvinylidene fluoride (PVdF) powder as a binder (positive electrode) The N-methylpyrrolidone (NMP) as a solvent was added to and mixed with them, and then kneaded to prepare a positive electrode paste δ4. Next, in the same manner as described above, the obtained positive electrode paste δ4 was applied to both surfaces of the positive electrode current collector, dried and rolled, and then cut into predetermined dimensions to produce a positive electrode x1.

In addition, a conductive agent paste γ4 was prepared such that the amount of acetylene black added in the conductive agent paste was 3.0% by mass with respect to the mass of the positive electrode active material, and the positive electrode active material ( LiCoO ₂ ) α was added and mixed, and then kneaded to prepare a positive electrode paste δ5. Subsequently, in the same manner as described above, the obtained positive electrode paste δ5 was applied to both surfaces of the positive electrode current collector, dried and rolled, and then cut into predetermined dimensions to produce a positive electrode x2.

Furthermore, positive electrode active material (LiCoO ₂ ) α, acetylene black 3% by mass (based on the mass of the positive electrode active material) as a carbon-based conductive agent, and polyvinylidene fluoride (PVdF) powder 3% by mass as a binder (Based on the mass of the positive electrode active material), N-methylpyrrolidone (NMP) as a solvent was added and mixed with these, and kneaded to prepare a positive electrode paste δ6. Next, in the same manner as described above, the obtained positive electrode paste δ6 was applied to both surfaces of the positive electrode current collector, dried and rolled, and then cut into predetermined dimensions to produce a positive electrode x3.

2. Measurement of Physical Properties of Positive Electrode Next, the surface resistance and liquid absorption time of each of the positive electrodes a1 to a3 and x1 to x3 produced as described above were measured as follows. Here, in terms of surface resistance, a pair of measurement electrodes are arranged on the surface of each of the positive electrodes a1 to a3, x1 to x3 with an interval of 1 cm, and then a current of 1 mA is applied between the pair of measurement electrodes. The resistance value at that time was measured, and the results shown in Table 1 below were obtained. Furthermore, about liquid absorption time, 3 microliters (3 microliters) of electrolyte solution is dripped at the surface of each positive electrode a1-a3, x1-x3 after rolling, and the dripped electrolyte solution is completely each positive electrode a1-a3. The time until the liquid was absorbed in x1 to x3 was measured, and the results shown in Table 1 below were obtained.

  As is clear from the results in Table 1 above, the surface resistances of the positive electrodes a1 to a3 using the conductive agent-coated active materials β1, β2, and β3 in which part of the surface is coated with a conductive agent are 40 to 50Ω, It can be seen that the surface resistance is low. On the other hand, it can be seen that the surface resistances of the positive electrodes x2 and x3 without using the conductive agent-coated active material are 100Ω and 180Ω, and the surface resistance is high. In addition, even when the conductive agent-coated active material β2 partially coated with the conductive agent is used, the surface resistance of the positive electrode x1 without using the conductive agent paste is 80Ω, and the surface resistance is high. .

  From these facts, it can be seen that sufficient conductivity and liquid absorption can be obtained by using a conductive agent-coated active material whose surface is partially coated with a conductive agent and using a conductive agent paste. However, like the positive electrode a3 using the conductive agent-coated active material β3, the liquid absorbency decreases when the coating amount of the conductive agent covering a part of the surface is 2.0% by mass with respect to the mass of the active material. Therefore, it can be said that it is desirable to regulate the coating amount of the conductive agent to be 1.0% by mass or less with respect to the mass of the active material.

3. Preparation of Nonaqueous Electrolyte Secondary Battery Next, the mixture was mixed so that the natural graphite powder was 95% by mass and the polyvinylidene fluoride (PVdF) powder as the binder was 5% by mass, and this was mixed with N-methylpyrrolidone ( NMP) solution was mixed to prepare a negative electrode paste. Thereafter, the obtained negative electrode paste was applied to both surfaces of a negative electrode current collector (copper foil) having a thickness of 18 μm by a doctor blade method to form a negative electrode active material layer on both surfaces of the negative electrode current collector. After drying this, it rolled until it became predetermined thickness (for example, 155 micrometers) using the compression roll, and it cut | disconnected to the predetermined dimension (for example, width 57mm, length 550mm), and produced the negative electrode.

Next, each of the positive electrodes a1 to a3 and x1 to x3 prepared as described above and the negative electrode prepared as described above were used, and a separator made of a polypropylene microporous film was interposed therebetween and laminated. Thereafter, these were wound in a spiral shape to form a spiral electrode group. After these are inserted into cylindrical metal outer cans, current collecting tabs extending from each current collector are welded to each terminal, and an equal volume mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) Then, a nonaqueous electrolytic solution in which 1 mol / liter of LiPF ₆ was dissolved was injected.

  Thereafter, a positive electrode lid was attached to the opening of the outer can and sealed to prepare non-aqueous electrolyte secondary batteries (height 65 mm, diameter 18 mm) A1 to A3, X1 to X3 having a design capacity of 1800 mAh. Note that a battery using the positive electrode a1 is referred to as a battery A1, a battery using the positive electrode a2 is referred to as a battery A2, and a battery using the positive electrode a3 is referred to as a battery A3. A battery using positive electrode x1 was designated as battery X1, a battery using positive electrode x2 was designated as battery X2, and a battery using positive electrode x3 was designated as battery X3.

  Next, using each of these batteries A1 to A3 and X1 to X3, a charging current of 1800 mA (1 It: It is a numerical value represented by rated capacity (mA) / 1 h (hour)) at room temperature (about 25 ° C.). Then, the battery was charged at a constant current until the battery voltage reached 4.2 V, and then charged at a constant voltage until the battery voltage was 4.2 V and the end current reached 36 mA. Thereafter, the battery was discharged at a discharge current of 1800 mA (1 It) until the battery voltage reached 2.75 V, and this was charged and discharged in the first cycle, and the discharge capacity in the first cycle was determined from the discharge time.

  Next, at room temperature (about 25 ° C.), with a charging current of 1800 mA (1 It), after constant current charging until the battery voltage becomes 4.2 V, the battery voltage becomes a constant voltage of 4.2 V and the termination current becomes 36 mA. Until constant voltage charging. Thereafter, the battery was discharged at a discharge current of 5400 mA (3 It) until the battery voltage reached 2.75 V. This was charged and discharged in the second cycle, and the discharge capacity in the second cycle was determined from the discharge time. Next, the ratio of the discharge capacity at the second cycle to the calculated discharge capacity at the first cycle is the discharge capacity maintenance rate (discharge capacity maintenance rate (%) = (discharge capacity at the second cycle / discharge capacity at the first cycle) × 100. ), The results shown in Table 2 below were obtained. In Table 2, the discharge capacity maintenance rate is shown as load performance (%).

  In addition, after constant current charging at room temperature (about 25 ° C.) with a charging current of 1800 mA (1 It) until the battery voltage reaches 4.2 V, the end current becomes 36 mA at a constant voltage of 4.2 V. Until constant voltage charging. Thereafter, the battery was discharged at a discharge current of 1800 mA (1 It) until the battery voltage became 3.2 V, and this was charged and discharged in the first cycle, and the discharge capacity in the first cycle was determined from the discharge time. Discharge after 2 cycles was discharged with a discharge current of 5400 mA (3 It) until the battery voltage reached 3.2V. Such a charge / discharge cycle was repeated 300 times, and the discharge capacity at the 300th cycle was determined. Next, the ratio of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle is the 300 cycle capacity retention rate (300 cycle capacity retention rate (%) = (discharge capacity after 300 cycles / discharge capacity after 1 cycle) × 100. ), The results shown in Table 2 below were obtained. In Table 1, the 300 cycle capacity retention rate is shown as cycle performance (%).

  From the results in Table 2 above, the following became clear. That is, in the batteries A1 to A3 provided with the positive electrodes a1 to a3 using the conductive agent-coated active materials β1, β2, and β3 partially coated with the conductive agent, the surface resistance of the positive electrodes a1 to a3 is 40 to 40. It can be seen that the cycle performance is improved to 95 to 96% as low as 50Ω. On the other hand, in the batteries X2 and X3 provided with the positive electrodes x2 and x3 that do not use the conductive agent-coated active material, the surface resistance of the positive electrodes x2 and x3 is as high as 100Ω and 180Ω, and the cycle performance is reduced to 89 to 92%. I understand that Further, even when the conductive agent-coated active material β2 whose surface is partially coated with the conductive agent is used, in the battery X1 including the positive electrode x1 without using the conductive agent paste, the surface resistance of the positive electrode x1 is as high as 80Ω. It can be seen that the cycle performance is reduced to 91%.

  Therefore, by using a conductive agent-coated active material whose surface is partially coated with a conductive agent and using a conductive agent paste, sufficient conductivity and liquid absorption can be obtained, and excellent load performance and cycle can be obtained. It can be seen that performance is obtained. However, when the coating amount of the conductive agent covering a part of the surface is 2.0% by mass with respect to the mass of the active material as in the battery A3 including the positive electrode a3 using the conductive agent-coated active material β3. Since the liquid absorption is reduced, the supply of the electrolyte to the active material is prevented from being promptly performed, and the load performance is reduced. Therefore, the coating amount of the conductive agent is 1.0% by mass or less based on the mass of the active material. It can be said that it is desirable to regulate so that

4). Examination of the average particle diameter of the conductive agent in the conductive agent paste Next, the average particle diameter of the conductive agent in the conductive agent paste was examined. Therefore, the addition amount of acetylene black as the carbon-based conductive agent in the conductive agent paste is 2.0 mass% (based on the mass of the positive electrode active material), and the addition of polyvinylidene fluoride (PVdF) powder as the binder It added and mixed so that the quantity might be 3 mass% (with respect to the mass of a positive electrode active material). Next, N-methylpyrrolidone (NMP) as a solvent is added to these and mixed to form a mixed solution, and then dispersed until the average particle size of the carbon-based conductive agent in the mixed solution becomes 5 μm or 7 μm, and kneaded. Thus, conductive agent pastes γ5 and γ6 were prepared. Note that the average particle diameter of the carbon-based conductive agent is a value obtained by irradiating the conductive agent pastes γ5 and γ6 with a laser beam and evaluating the volume using the volume median diameter, as described above.

  Here, a conductive agent paste γ5 having a carbon-based conductive agent average particle diameter of 5 μm was used, and a conductive agent paste γ6 having a carbon-based conductive agent average particle diameter of 7 μm. Next, the conductive agent-coated active material β2 prepared as described above was added to and mixed with the obtained conductive agent pastes γ5 and γ6, and kneaded to prepare positive electrode pastes δ7 and δ8. In this case, the paste using the conductive agent paste γ5 was designated as the positive electrode paste δ7, and the paste using the conductive agent paste γ6 was designated as the positive electrode paste δ8.

  Thereafter, the obtained positive electrode pastes δ7 and δ8 are applied to both surfaces of a positive electrode current collector (aluminum foil or aluminum alloy foil) having a thickness of 20 μm by the doctor blade method, and the positive electrode active material is applied to both surfaces of the positive electrode current collector. A material layer was formed. After drying this, it is rolled to a predetermined thickness (for example, 160 μm) using a compression roll, and cut into predetermined dimensions (width is 55 mm and length is 500 mm) to produce positive electrodes b1 and b2, respectively. did. The positive electrode paste δ7 was used as the positive electrode b1, and the positive electrode paste δ8 was used as the positive electrode b2.

  Next, when the surface resistance and the liquid absorption time of each of the positive electrodes b1 and b2 produced as described above were measured in the same manner as described above, the results shown in Table 3 below were obtained. Further, using these positive electrodes b1 and b2, non-aqueous electrolyte secondary batteries (height 65 mm, diameter 18 mm) B1 and B2 having a design capacity of 1800 mAh were respectively produced in the same manner as described above. A battery using positive electrode b1 was designated as battery B1, and a battery using positive electrode b2 was designated as battery B2.

  Then, using these batteries B1 and B2, the discharge capacity of the first cycle and the discharge capacity of the second cycle were obtained in the same manner as described above, and then the ratio of the discharge capacity of the second cycle to the discharge capacity of the first cycle was determined. When calculated as the discharge capacity retention rate (load performance), the results shown in Table 3 below were obtained. Further, after determining the discharge capacity at the 300th cycle, the ratio of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle is calculated as the 300 cycle capacity retention rate (cycle performance). The results shown in Table 3 below are obtained. It became. Table 3 below also shows the results of the battery A2 described above.

  As is clear from the results of Table 3 above, the surface resistance of the positive electrode a2 using the conductive agent paste γ2 having an average particle diameter of the carbon-based conductive agent of 3.0 μm is as small as 40Ω, and this positive electrode a2 was used. It can be seen that the cycle performance of the battery A2 is increased to 96% due to the improved conductivity. Further, the surface resistance of the positive electrode b1 using the conductive agent paste γ5 in which the average particle diameter of the carbon-based conductive agent is 5.0 μm is as small as 40Ω, and the conductivity of the battery A2 using the positive electrode a2 is also improved. It can be seen that the cycle performance has increased to 96% due to the above.

On the other hand, the surface resistance of the positive electrode b2 using the conductive agent paste γ6 in which the average particle diameter of the carbon-based conductive agent is 7 μm is as large as 120Ω, and the conductivity of the battery B using the positive electrode b2 decreases. It can be seen that the cycle performance is reduced to 90%.
This means that a positive electrode paste is formed using a conductive agent paste in which the average particle diameter of the carbon-based conductive agent is uniformly dispersed so as to be an appropriate size, preferably 5 μm or less, and this positive electrode paste is used to form a positive electrode. It is shown that the conductivity of the positive electrode is improved by forming.

5). Study on the amount of conductive agent added Next, the amount of conductive agent added was examined. Therefore, the addition amount of acetylene black as the carbon-based conductive agent in the conductive agent paste is 0.5% by mass, 1.0% by mass, 3.0% by mass, 4.0% by mass (both of the positive electrode active material). And added and mixed so that the amount of polyvinylidene fluoride (PVdF) powder added as a binder is 3% by mass (relative to the mass of the positive electrode active material). Next, N-methylpyrrolidone (NMP) as a solvent is added to these and mixed to form a mixed solution, and then dispersed until the average particle diameter of the carbon-based conductive agent in this mixed solution becomes 3 μm and kneaded. Conductive agent pastes γ7 to γ10 were prepared. Note that the average particle diameter of the carbon-based conductive agent is a value obtained by irradiating the conductive agent pastes γ7 to γ10 with a laser beam and evaluating the volume using a volume median diameter, as described above.

  A conductive agent paste γ7 having an addition amount of acetylene black as a carbon-based conductive agent of 0.5% by mass was used. Similarly, a conductive agent paste γ8 with an addition amount of acetylene black of 1.0% by mass and a conductive agent paste γ9 with an addition amount of acetylene black of 3.0% by mass, and an addition amount of acetylene black of 4%. The conductive material paste γ10 was 0.0% by mass. Subsequently, the obtained conductive agent pastes γ7 to γ10 were each coated with a conductive agent-coated active material β1 (with a coating amount of 0.1% by mass) or a conductive agent-coated active material β2 (with a coating amount of 1). 0.0 mass%) was added and mixed, and then kneaded to prepare positive electrode pastes ε1 to ε4 and ζ1 to ζ4, respectively.

  In this case, the conductive agent-coated active material β1 is used, the one using the conductive agent paste γ7 is the positive electrode paste ε1, the one using the conductive agent paste γ8 is the positive electrode paste ε2, and the one using the conductive agent paste γ9. A positive electrode paste ε3 and a conductive paste γ10 were used as a positive electrode paste ε4. In addition to using the conductive agent-coated active material β2, the one using the conductive agent paste γ7 is the positive electrode paste ζ1, the one using the conductive agent paste γ8 is the positive electrode paste ζ2, and the one using the conductive agent paste γ9 is the positive electrode. The paste ζ3 and the conductive paste γ10 were used as the positive electrode paste ζ4.

  After that, the obtained positive electrode pastes ε1 to ε4 and ζ1 to ζ4 were each applied to both surfaces of a positive electrode current collector (aluminum foil or aluminum alloy foil) having a thickness of 20 μm by the doctor blade method. A positive electrode active material layer was formed on both sides. After drying this, it is rolled to a predetermined thickness (for example, 160 μm) using a compression roll, cut into predetermined dimensions (width is 55 mm, length is 500 mm), and positive electrodes c1 to c4 and positive electrode d1 ˜d4 was prepared.

  The positive electrode paste ε1 was used as the positive electrode c1, the positive electrode paste ε2 was used as the positive electrode c2, the positive electrode paste ε3 was used as the positive electrode c3, and the positive electrode paste ε4 was used as the positive electrode c4. . Also, the positive electrode d1 is the one using the positive electrode paste ζ1, the positive electrode d2 is the one using the positive electrode paste ζ2, the positive electrode d3 is the one using the positive electrode paste ζ3, and the positive electrode d4 is the one using the positive electrode paste ζ4. .

  Subsequently, when the surface resistance and the liquid absorption time of each of the positive electrodes c1 to c4 and the positive electrodes d1 to d4 produced as described above were measured in the same manner as described above, the results shown in Table 4 below were obtained. Also, using these positive electrodes c1 to c4 and positive electrodes d1 to d4, non-aqueous electrolyte secondary batteries (height 65 mm, diameter 18 mm) C1 to C4 and D1 to D4 having a design capacity of 1800 mAh are respectively produced in the same manner as described above. did. Note that a battery using the positive electrode c1 was referred to as a battery C1, a battery using the positive electrode c2 was referred to as a battery C2, a battery using the positive electrode c3 was referred to as a battery C3, and a battery using the positive electrode c4 was referred to as a battery C4. A battery using the positive electrode d1 is referred to as a battery D1, a battery using the positive electrode d2 is referred to as a battery D2, a battery using the positive electrode d3 is referred to as a battery D3, and a battery using the positive electrode d4 is referred to as a battery D4.

  Then, using these batteries C1 to C4 and D1 to D4, respectively, the discharge capacity at the first cycle and the discharge capacity at the second cycle were obtained in the same manner as described above, and then the second cycle with respect to the discharge capacity at the first cycle. When the ratio of the discharge capacity was calculated as the discharge capacity maintenance ratio (load performance), the results shown in Table 4 below were obtained. Further, after determining the discharge capacity at the 300th cycle, the ratio of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle is calculated as the 300 cycle capacity retention rate (cycle performance), and the results shown in Table 4 below are obtained. It became. Table 4 below also shows the results of the battery A2 described above.

  As is clear from the results of Table 4 above, even when the conductive agent-coated active material β1 with a coating amount of 0.1% by mass is used, or the conductive agent-coated active material β2 with a coating amount of 1.0% by mass is used. However, in the batteries C1 and D1 including the positive electrodes c1 and d1 using the conductive agent paste γ7, it can be seen that the surface resistances of the positive electrodes c1 and d1 are as large as 100Ω and the cycle performance is decreased to 90%. This is because the conductive agent paste γ7 has a small addition amount of acetylene black of 0.5% by mass, and therefore the conductivity of the positive electrodes c1 and d1 decreases due to the increase in the surface resistance of the positive electrode, and the cycle performance is reduced. It is thought that it fell.

  In addition, in the batteries C4 and D4 including the positive electrodes c4 and d4 using the conductive agent paste γ10, the conductive agent-coated active material β1 or the conductive agent-coated active material β2 is used. It can be seen that the electrolyte absorption time increased to 16 minutes and the load performance decreased to 88%. This is because the conductive agent paste γ10 has an excessively large addition amount of acetylene black of 4.0% by mass, so that the loading amount of the active material is relatively reduced, the load performance is lowered, and the active material is rapidly applied. It is thought that the supply of a proper electrolyte was hindered.

On the other hand, in the batteries C2, C3 and D2, D3 provided with the positive electrodes c2, c3 and d2, d3 using the conductive agent pastes γ8, γ9, and the battery A2 provided with the positive electrode a2 using the conductive agent paste γ2. The surface resistance of each positive electrode is as small as 40 to 50Ω, the electrolyte absorption time is as short as 11 to 12 minutes, the load performance is as large as 92 to 93%, and the cycle performance is improved to 95 to 96%. I understand that. From the above, the addition amount of acetylene black as a carbon-based conductive agent in the conductive agent paste is 1.0% by mass or more and 3.0% by mass or less with respect to the mass of the active material (LiCoO ₂ ). It can be said that regulation is desirable.

  By summing up the results of Tables 1 to 4 described above, the following can be estimated. That is, the carbon-based conductive agent covering a part of the surface of the positive electrode active material particle is mainly responsible for ensuring conductivity (reducing electrode plate resistance), and the carbon-based conductive agent in the conductive agent paste (not fixed) Conductive agent) is in charge of improving liquid absorption, liquid retention and electrical conductivity. As a result, it is possible to obtain a nonaqueous electrolyte battery excellent in load performance and cycle performance due to the synergistic effect of these conductive agent-coated active material and conductive agent paste.

  In this case, as the coating amount of acetylene black as a carbon-based conductive agent that covers a part of the surface of the active material increases, the liquid absorbency decreases. Therefore, the coating amount of the conductive agent is based on the mass of the active material. It is desirable to regulate the amount to 1.0% by mass or less. Moreover, since the conductivity of the positive electrode is improved by using a conductive agent paste that is uniformly dispersed so that the average particle size of the carbon-based conductive agent is 5 μm or less, the average of the carbon-based conductive agent in the conductive agent paste The particle size is desirably 5 μm or less. Furthermore, in order to improve the load performance and cycle performance with a low surface resistance, excellent electrolyte absorption and liquid retention, the amount of carbon-based conductive agent added to the conductive agent paste is It is desirable to set it to 1.0 mass% or more and 3.0 mass% or less with respect to mass.

  In the above-described embodiment, an example in which acetylene black is used as the carbon-based conductive agent has been described. However, as the carbon-based conductive agent other than acetylene black, either ketjen black, furnace black, or a mixture thereof can be used. It is desirable to select and use.

In the above-described embodiment, an example in which lithium cobaltate (LiCoO ₂ ) is used as a positive electrode active material has been described. However, as a positive electrode active material other than lithium cobaltate (LiCoO ₂ ), spinel type lithium manganate (LiMn) Various lithium-containing transition metal oxides such as ₂ O ₄ ) and lithium nickelate (LiNiO ₂ ) can be used. Among them, LiCo _1-x M _x O ₂ (where M is at least one selected from Mg, V, Cr, Fe, Mn, Ni, Al, Ti, Zr, and 0 ≦ x <1). Li _{1 + x} Mn _{2 -y} M _x O ₄ (wherein M is at least one selected from B, Mg, Si, V, Cr, Fe, Al, and Zn; 54 ≦ ((1 + x) + z) / (2-y) ≦ 0.62, lithium represented by −0.15 ≦ x ≦ 0.15, y ≦ 0.5, 0 ≦ z ≦ 0.1) containing manganese composite _{oxide, LiNi x M 1-x O} 2 ( where, M is Li, B, Mg, Co, Mn, Ti, Zr, Cr, Fe, Al, at least one selected from Zn, 0. 3 ≦ x ≦ 0.9) selected from any of the lithium-containing nickel composite oxides or mixtures thereof It is desirable to make use.

Claims (6)

A method for producing a positive electrode for a non-aqueous electrolyte battery comprising a positive electrode active material, a conductive agent, and a binder,
An active material preparation step in which the surface of the positive electrode active material particles is coated with a carbon-based conductive agent to form a conductive agent-coated active material;
A conductive agent paste preparation step in which a carbon conductive agent is kneaded and dispersed in a solution together with a binder to form a conductive agent paste;
A positive electrode paste preparation step of kneading and dispersing the conductive agent-coated active material and the conductive agent paste to form a positive electrode paste;
A method for producing a positive electrode for a non-aqueous electrolyte battery, comprising: an active material application step of applying the positive electrode paste to a positive electrode core.   The positive electrode for a nonaqueous electrolyte battery according to claim 1, wherein the carbon-based conductive agent is coated on the surface of the positive electrode active material particles while applying mechanical stress in the active material preparation step. Method.   The amount of the carbon-based conductive agent coated on the surface of the positive electrode active material particles in the active material preparation step is 0.1% by mass or more and 1.0% by mass or less with respect to the mass of the positive electrode active material. The manufacturing method of the positive electrode for nonaqueous electrolyte batteries of Claim 1 or Claim 2 characterized by the above-mentioned.   The average particle diameter of the said carbon type electrically conductive agent disperse | distributed in the said electrically conductive agent paste in the said electrically conductive agent paste preparation process is 5.0 micrometers or less, The Claim 1 characterized by the above-mentioned. A method for producing a positive electrode for a non-aqueous electrolyte battery.   The addition amount of the carbon-based conductive agent in the conductive agent paste is 1.0 mass% or more and 3.0 mass% or less with respect to the mass of the positive electrode active material. 5. A method for producing a positive electrode for a non-aqueous electrolyte battery according to any one of 4 above. A nonaqueous electrolyte comprising: a positive electrode produced by the manufacturing method according to any one of claims 1 to 5; a negative electrode; a separator that separates both electrodes; and a nonaqueous electrolyte. battery.