JP2006331937A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery realizing high energy density and with adhesiveness and plasticity of a cathode mixture improved. <P>SOLUTION: In the nonaqueous electrolyte secondary battery 1 equipped with a cathode plate 4 with a cathode mixture containing carbon black and polyvinylidene fluoride and pressed under 100°C, a ratio of the carbon black to the cathode mixture is to be 1% by mass or more and 3% by mass or less, a ratio of the polyvinylidene fluoride to the cathode mixture 2% by mass or more and 4% by mass or less, and a mass ratio of the carbon black to the polyvinylidene fluoride is to be 0.33 or more and 0.75 or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery having a positive electrode mixture containing carbon black and polyvinylidene fluoride and having a positive electrode pressed at 100 ° C. or lower.

Secondary batteries such as lithium-ion batteries are used as power sources for portable electronic devices such as mobile phones, but with the enhancement of functionality of portable electronic devices, the demand for higher energy density of secondary batteries has become stronger. . In order to increase the energy density, for example, the content of the positive electrode active material in the positive electrode mixture is increased, or the packing density of the positive electrode mixture is increased. In order to increase the packing density of the positive electrode material mixture, it is necessary to press the positive electrode under pressing conditions suitable for increasing the density. For example, a method of pressing the positive electrode material by heating to 60 ° C. or more has been proposed (Patent Document 1). reference).
Japanese Patent Laid-Open No. 10-255563

  However, when the positive electrode is pressed by heating to 60 ° C. or higher, the packing density of the positive electrode mixture increases, but the positive electrode mixture becomes hard because the adhesiveness of the binder in the positive electrode mixture increases, The problem arises that flexibility is reduced. When the flexibility of the positive electrode plate is lowered, the positive electrode plate is likely to be cracked or cut, and defects are likely to occur during the production of the electrode element.

  This invention is made | formed in view of such a situation, The positive electrode is pressed at 100 degrees C or less, The ratio of the carbon black with respect to a positive mix is 1 to 3 mass%, and with respect to a positive mix When the ratio of polyvinylidene fluoride is 2% by mass or more and 4% by mass or less, and the mass ratio of carbon black to polyvinylidene fluoride is 0.33 or more and 0.75 or less, the adhesion and flexibility of the positive electrode mixture can be improved. An object of the present invention is to provide a non-aqueous electrolyte secondary battery with improved energy density.

  Another object of the present invention is to provide a nonaqueous electrolyte secondary battery in which the number of presses is reduced and the production efficiency of the positive electrode is improved by using a positive electrode pressed at a temperature of 70 ° C. or higher. To do.

  Another object of the present invention is to provide a non-aqueous electrolyte secondary battery capable of improving high rate discharge characteristics by using acetylene black as carbon black.

  The non-aqueous electrolyte secondary battery according to the first aspect of the present invention is a non-aqueous electrolyte secondary battery having a positive electrode mixture containing carbon black and polyvinylidene fluoride, and comprising a positive electrode pressed at 100 ° C. or lower. The ratio of the carbon black to the agent is 1% by mass to 3% by mass, the ratio of the polyvinylidene fluoride to the positive electrode mixture is 2% to 4% by mass, and the carbon black to the polyvinylidene fluoride The mass ratio is 0.33 or more and 0.75 or less.

  A non-aqueous electrolyte secondary battery according to a second invention has a positive electrode mixture containing carbon black and polyvinylidene fluoride, and includes a positive electrode pressed at 70 ° C. or higher and 100 ° C. or lower. The ratio of the carbon black to the positive electrode mixture is 1% by mass or more and 3% by mass or less, the ratio of the polyvinylidene fluoride to the positive electrode mixture is 2% by mass or more and 4% by mass or less, and relative to the polyvinylidene fluoride. The mass ratio of the carbon black is 0.33 or more and 0.75 or less.

  The non-aqueous electrolyte secondary battery according to a third aspect of the present invention is characterized in that, in the first or second aspect, the carbon black contains acetylene black.

  In the first invention, if the ratio of carbon black to the positive electrode mixture is less than 1% by mass, the electrical conductivity is insufficient, so that the high rate discharge characteristic is lowered, and if it exceeds 3% by mass, the content of the active material is lowered. In order to prevent the battery capacity from being increased, the energy density is increased to 1% by mass or more and 3% by mass or less. Further, when the proportion of polyvinylidene fluoride with respect to the positive electrode mixture is less than 2% by mass, the adhesion of the positive electrode mixture is insufficient, and the positive electrode mixture is peeled off. 2% by mass or more and 4% by mass or less because the high rate discharge characteristic of the battery is deteriorated because the resistance of the positive electrode mixture is increased in addition to hindering the high density of the battery capacity due to the decrease in the content rate. Thus, the energy density and the adhesion of the positive electrode mixture are increased. Further, when the mass ratio of carbon black to polyvinylidene fluoride is less than 0.33, the high-rate discharge characteristics of the battery are deteriorated due to insufficient conductivity of the positive electrode plate, and when it exceeds 0.75, the positive electrode mixture Therefore, the energy density and the adhesion of the positive electrode mixture are improved. When the temperature at the time of pressing the positive electrode plate exceeds 100 ° C., the flexibility of the positive electrode plate is greatly reduced, and the positive electrode plate is cut or cracked when the positive electrode plate and the negative electrode plate are wound to produce an electrode element. Therefore, the flexibility of the positive electrode mixture is increased to 100 ° C. or lower. Thereby, the adhesiveness and flexibility of the positive electrode mixture can be improved, and a high energy density non-aqueous electrolyte secondary battery can be manufactured.

  In the second invention, since the positive electrode is pressed at a temperature of 70 ° C. or higher, the binder contained in the positive electrode mixture is softened, so the stress during pressing is reduced, the number of presses can be reduced, and the positive electrode production efficiency. Will improve.

  In the third invention, acetylene black is excellent in conductivity, and by using acetylene black as carbon black, good conductivity can be obtained even in a small amount and high-rate discharge characteristics can be improved.

  According to the first invention, it is possible to improve the adhesion and flexibility of the positive electrode mixture and to manufacture a non-aqueous electrolyte secondary battery having a high energy density.

  According to the second invention, the number of positive electrode pressings can be reduced, and the production efficiency is improved.

  According to the third invention, it is possible to improve the high rate discharge characteristics.

  Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof. In addition, the positive electrode, negative electrode, electrolyte solution, separator, production method of a battery, etc. which were described in the present Example are examples, and do not limit this invention.

Example 1
FIG. 1 is a cross-sectional view showing a schematic configuration of a nonaqueous electrolyte secondary battery according to the present invention. A non-aqueous electrolyte secondary battery (hereinafter referred to as a battery) 1 includes a negative electrode plate 3 in which a negative electrode mixture is applied to a copper current collector and a positive electrode plate 4 in which a positive electrode mixture is applied to an aluminum current collector. 5, the electrode element 2 wound in a flat winding shape via 5, the rectangular battery case 6 that houses the electrode element 2 and the nonaqueous electrolyte (electrolyte), and the battery that is laser welded to the opening of the battery case 6 And a lid 7. The battery lid 7 has a safety valve 8 and a negative electrode terminal 9, and the negative electrode terminal 9 is connected to the negative electrode plate 3 through a negative electrode lead 10. The positive electrode plate 4 is electrically connected to the inner surface of the battery case 6. The battery has a width of 30 mm, a height of 48 mm, a thickness of 4.2 mm, and a discharge capacity of 600 mAh.

The positive electrode plate 4, as a positive electrode active material, a cobalt oxide (Co ₃ O ₄₎ and lithium carbonate (Li ₂ CO _3), the molar ratio of lithium and cobalt is 1: After mixing to be 1, Calcination was performed at 950 ° C. for 3 hours to obtain lithium cobalt oxide (LiCoO ₂ ). A positive electrode mixture obtained by mixing 97% by mass of the positive electrode active material, 1% by mass of acetylene black (AB) as carbon black as a conductive agent, and 2% by mass of polyvinylidene fluoride (PVDF) as a binder is added to N as a solvent. A positive electrode paste was prepared by adding an appropriate amount of methyl-2-pyrrolidone (NMP) and stirring. This positive electrode paste was applied to both sides of an aluminum foil current collector having a thickness of 15 μm using a doctor blade so that the mass of the mixture from which NMP was removed was 0.025 g / cm ² per side and dried. Then, pressing was performed once at 70 ° C. so as to have a thickness of 175 μm, and the positive electrode plate 4 was produced. Here, granular acetylene black made by Denki Kagaku Kogyo Co., Ltd. having a BET specific surface area of about 70 m ² / g is used as acetylene black (AB). Moreover, the mass ratio of AB to PVDF (AB / PVDF) is 0.5.

For the negative electrode plate 3, an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to the negative electrode mixture in which graphite (graphite) as the negative electrode active material and polyvinylidene fluoride (PVDF) as the binder were 90:10 in mass ratio. A negative electrode paste was prepared. This negative electrode paste was applied to both sides of a 10 μm thick copper foil current collector using a doctor blade so that the mass of the mixture with NMP removed was 0.012 g / cm ² per side and dried. The negative electrode plate 3 was manufactured by pressing to a thickness of 175 μm.

A polyethylene microporous film was used as the separator. As the electrolytic solution (electrolyte), a solution obtained by dissolving 1 mol / l of LiPF _{6 in} a mixed solvent of ethylene carbonate (EC): diethyl carbonate (DEC) = 3: 7 (volume ratio) was used.

(Example 2)
A battery was manufactured in the same manner as in Example 1 except that the press temperature during the production of the positive electrode was 100 ° C.

(Example 3)
Example 1 except that a positive electrode mixture (AB / PVDF = 0.33) in which 96% by mass of a positive electrode active material, 1% by mass of acetylene black (AB) and 3% by mass of polyvinylidene fluoride (PVDF) were mixed was used. A similar battery was produced.

Example 4
A battery was manufactured in the same manner as in Example 3 except that the press temperature during the production of the positive electrode was 100 ° C.

(Example 5)
A battery was manufactured in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 0.67) in which 95% by mass of the positive electrode active material, 2% by mass of AB, and 3% by mass of PVDF were mixed was used.

(Example 6)
A battery was manufactured in the same manner as in Example 5 except that the press temperature during the production of the positive electrode was 100 ° C.

(Example 7)
A battery was manufactured in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 0.50) in which 94% by mass of the positive electrode active material, 2% by mass of AB, and 4% by mass of PVDF were mixed was used.

(Example 8)
A battery was manufactured in the same manner as in Example 7 except that the press temperature during the production of the positive electrode was 100 ° C.

Example 9
A battery was manufactured in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 0.75) in which 93% by mass of the positive electrode active material, 3% by mass of AB, and 4% by mass of PVDF were mixed was used.

(Example 10)
A battery was manufactured in the same manner as in Example 9 except that the press temperature during the production of the positive electrode was 100 ° C.

(Example 11)
A battery was manufactured in the same manner as in Example 1 except that the press temperature during the production of the positive electrode was normal temperature and the number of presses was two.

(Example 12)
Using a positive electrode mixture (AB / PVDF = 0.33) in which 96% by mass of the positive electrode active material, 1% by mass of AB, and 3% by mass of PVDF were mixed, the press temperature at the time of producing the positive electrode was room temperature and the number of presses was 2 times. A battery was prepared in the same manner as in Example 1 except for the above.

(Example 13)
Using a positive electrode mixture (AB / PVDF = 0.67) in which 95% by mass of the positive electrode active material, 2% by mass of AB, and 3% by mass of PVDF were mixed, A battery was prepared in the same manner as in Example 1 except for the above.

(Example 14)
Using a positive electrode mixture (AB / PVDF = 0.50) in which 94% by mass of the positive electrode active material, 2% by mass of AB, and 4% by mass of PVDF are mixed, the press temperature at the time of producing the positive electrode is room temperature and the number of presses is 2 times. A battery was prepared in the same manner as in Example 1 except for the above.

(Example 15)
Using a positive electrode mixture (AB / PVDF = 0.75) in which 93% by mass of the positive electrode active material, 3% by mass of AB, and 4% by mass of PVDF were mixed, A battery was prepared in the same manner as in Example 1 except for the above.

(Comparative Example 1)
Using a positive electrode mixture (AB / PVDF = 1.00) in which 99% by mass of the positive electrode active material, 0.5% by mass of AB, and 0.5% by mass of PVDF are mixed, the press temperature at the time of producing the positive electrode is normal temperature and the number of presses is 2. Otherwise, a battery similar to that of Example 1 was produced.

(Comparative Example 2)
A battery was manufactured in the same manner as in Comparative Example 1 except that the press temperature during the production of the positive electrode was 70 ° C. and the number of presses was one.

(Comparative Example 3)
A battery was manufactured in the same manner as in Comparative Example 1 except that the press temperature during the production of the positive electrode was 100 ° C. and the number of presses was one.

(Comparative Example 4)
A battery was manufactured in the same manner as in Comparative Example 1 except that the press temperature during the production of the positive electrode was 110 ° C. and the number of presses was one.

(Comparative Example 5)
A battery was manufactured in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 0.50) in which 98.5% by mass of the positive electrode active material, 0.5% by mass of AB, and 1% by mass of PVDF were mixed was used. .

(Comparative Example 6)
A battery was manufactured in the same manner as in Comparative Example 5 except that the press temperature during the production of the positive electrode was 100 ° C.

(Comparative Example 7)
A battery was manufactured in the same manner as in Comparative Example 5 except that the press temperature during the production of the positive electrode was 110 ° C.

(Comparative Example 8)
A battery was manufactured in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 0.25) in which 97.5% by mass of the positive electrode active material, 0.5% by mass of AB, and 2% by mass of PVDF were mixed was used. .

(Comparative Example 9)
A battery was manufactured in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 1.00) in which 98% by mass of the positive electrode active material, 1% by mass of AB, and 1% by mass of PVDF were mixed was used.

(Comparative Example 10)
A battery was manufactured in the same manner as in Comparative Example 9 except that the press temperature during the production of the positive electrode was 100 ° C.

(Comparative Example 11)
A battery was manufactured in the same manner as in Comparative Example 9 except that the press temperature during the production of the positive electrode was 110 ° C.

(Comparative Example 12)
A battery was manufactured in the same manner as in Example 11 except that the press temperature during the production of the positive electrode was 110 ° C., the number of presses was one, and the other.

(Comparative Example 13)
A battery was manufactured in the same manner as in Example 12 except that the press temperature during the production of the positive electrode was 110 ° C. and the number of presses was one.

(Comparative Example 14)
A battery was manufactured in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 0.25) in which 95% by mass of the positive electrode active material, 1% by mass of AB, and 4% by mass of PVDF were mixed was used.

(Comparative Example 15)
A battery was manufactured in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 1.00) in which 96% by mass of the positive electrode active material, 2% by mass of AB, and 2% by mass of PVDF were mixed was used.

(Comparative Example 16)
A battery was manufactured in the same manner as in Comparative Example 15 except that the press temperature during the production of the positive electrode was 100 ° C.

(Comparative Example 17)
A battery was manufactured in the same manner as in Comparative Example 15 except that the press temperature during the production of the positive electrode was 110 ° C.

(Comparative Example 18)
A battery was manufactured in the same manner as in Example 13 except that the press temperature during the production of the positive electrode was 110 ° C. and the number of presses was one.

(Comparative Example 19)
A battery was manufactured in the same manner as in Example 14 except that the press temperature during the production of the positive electrode was 110 ° C. and the number of presses was one.

(Comparative Example 20)
A battery was manufactured in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 0.40) in which 93% by mass of the positive electrode active material, 2% by mass of AB, and 5% by mass of PVDF were mixed was used.

(Comparative Example 21)
A battery was manufactured in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 1.00) in which 94% by mass of the positive electrode active material, 3% by mass of AB, and 3% by mass of PVDF were mixed was used.

(Comparative Example 22)
A battery was manufactured in the same manner as in Comparative Example 21 except that the press temperature during the production of the positive electrode was 100 ° C.

(Comparative Example 23)
A battery was manufactured in the same manner as in Comparative Example 21 except that the press temperature during the production of the positive electrode was 110 ° C.

(Comparative Example 24)
A battery was manufactured in the same manner as in Example 15 except that the press temperature during the production of the positive electrode was 110 ° C. and the number of presses was one.

(Comparative Example 25)
A battery was manufactured in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 0.60) in which 92% by mass of the positive electrode active material, 3% by mass of AB, and 5% by mass of PVDF were mixed was used.

(Comparative Example 26)
A battery was prepared in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 1.00) in which 92% by mass of the positive electrode active material, 4% by mass of AB, and 4% by mass of PVDF were mixed was used.

(Comparative Example 27)
A battery was produced in the same manner as in Comparative Example 26 except that the press temperature during the production of the positive electrode was 100 ° C.

(Comparative Example 28)
A battery was manufactured in the same manner as in Comparative Example 26 except that the press temperature during the production of the positive electrode was 110 ° C.

(Comparative Example 29)
A battery was manufactured in the same manner as in Example 1 except that a positive electrode mixture (AB / PVDF = 0.80) in which 91% by mass of the positive electrode active material, 4% by mass of AB, and 5% by mass of PVDF were mixed was used.

(Comparative Example 30)
A battery was manufactured in the same manner as in Comparative Example 29 except that the press temperature during the production of the positive electrode was 100 ° C.

(Comparative Example 31)
A battery was produced in the same manner as in Comparative Example 29 except that the press temperature during the production of the positive electrode was 110 ° C.

  About the positive electrode plate of the Example mentioned above and the comparative example, the adhesiveness of the positive electrode mixture and the softness | flexibility of the positive electrode plate were evaluated. Moreover, the high-rate discharge characteristics of the batteries of the above-described examples and comparative examples were evaluated. Regarding the evaluation of the adhesion of the positive electrode mixture, a battery was prepared for the case where a part of the positive electrode mixture was peeled off or dropped when the positive electrode plate 4 was slit (cut) in accordance with the width of the electrode element 2. It was regarded as defective because it caused an internal short circuit. The number of tests was 10 with respect to the positive electrode plates of each Example and each Comparative Example, and when any one of them was peeled or dropped, it was regarded as defective. Moreover, about the comparative example in which peeling or dropping of the positive electrode mixture occurred at the time of slitting, the electrode element 2 was not manufactured, and the evaluation of the flexibility of the positive electrode plate and the evaluation of the high rate discharge characteristics were not performed.

  Regarding the evaluation of the flexibility of the positive electrode plate 4, when there is no problem in the evaluation of the adhesion of the positive electrode mixture, the positive electrode plate 4 and the negative electrode plate 3 are wound through the separator 5 to produce the electrode element 2 and bent. Whether the innermost peripheral positive electrode plate 4 having the largest angle was cut or cracked was confirmed. The number of tests was 10 with respect to the positive electrode plates of each Example and each Comparative Example, and when any one of them was found to have a cut or crack, it was considered defective. Moreover, about the comparative example by which the positive electrode plate 4 was cut | disconnected or cracked when producing the electrode element 2, the battery was not produced and the high rate discharge characteristic was not evaluated.

  As for the evaluation of the high rate discharge characteristics, when there is no problem in the evaluation of the flexibility of the positive electrode plate 4, it is 2.5 hours at a constant current and a constant voltage of a charging current of 600 mA and a charging voltage of 4.20 V in an atmosphere at a room temperature of 20 ° C. After charging, discharge was performed under the conditions of a discharge current of 1 CmA (= 600 mA) and a final voltage of 2.75 V, and the discharge capacity was measured. Further, using the same battery, the discharge capacity during high rate discharge with a discharge current of 2 CmA (= 1200 mA) was measured. The number of test batteries was 3 for each example and each comparative example, and the average value of 3 was obtained. Further, when the discharge capacity of 2 CmA was lower than 420 mAh, it was regarded as defective. The results of each evaluation are shown in Tables 1, 2, and 3.

  Comparative Examples 1 to 4 in which the content of acetylene black (AB) is 0.5% by mass, the content of polyvinylidene fluoride (PVDF) is 0.5% by mass, the content of AB is 0.5% by mass, PVDF In Comparative Examples 5 to 7 in which the content ratio is 1.0 mass%, and in Comparative Examples 9 to 11 in which the AB content ratio is 1.0 mass% and the PVDF content ratio is 1.0 mass%, The positive electrode mixture was peeled off even at the press temperature. On the other hand, in Comparative Example 8 where the AB content is 0.5% by mass and the PVDF content is 2.0% by mass (AB / PVDF is 0.25), peeling of the positive electrode mixture at a press temperature of 70 ° C. Did not occur. Therefore, in order to ensure the adhesion of the positive electrode mixture, it is considered that 2.0% by mass or more of PVDF is necessary.

  However, the AB content is 2.0% by mass, the PVDF content is 2.0% by mass (AB / PVDF is 1.0), and the AB content is 3.0% by mass. Comparative Examples 21 to 23 having a PVDF content of 3.0% by mass (AB / PVDF is 1.0), an AB content of 4.0% by mass, and a PVDF content of 4.0% by mass ( AB / PVDF is 1.0) Comparative Examples 26 to 28, and the AB content is 4.0% by mass and the PVDF content is 5.0% by mass (AB / PVD is 0.80) In Examples 29 to 31, peeling of the positive electrode mixture occurred at any pressing temperature.

  On the other hand, in Examples 1 to 15 and Comparative Examples 8, 12 to 14, 18 to 20, 24, and 25 where PVDF is 2.0% by mass or more and mass ratio AB / PVDF is 0.75 or less, a positive electrode mixture No peeling occurred. Even when the content of PVDF is large (2.0% by mass or more), when the content of AB is large, a large amount of PVDF is bulky (low packing density) AB. PVDF necessary for bonding the positive electrode active material or current collector to the aluminum foil is insufficient, and the adhesion between the positive electrode mixture and the aluminum foil is reduced. It is thought that. Therefore, in order to ensure the adhesion of the positive electrode mixture, it is necessary that the PVDF content is 2.0 mass% or more and AB / PVDF is 0.75 or less.

  However, even when the mass ratio AB / PVDF is 0.75 or less, the high rate discharge characteristics (discharge capacity of 2 cmA) of the batteries of Comparative Examples 20 and 25 in which the PVDF content is 5.0% by mass are greatly reduced. is doing. This is considered to be because the content ratio of the positive electrode active material was reduced because the absolute amount of PVDF as an insulator was large, and the discharge capacity of 2 CmA was reduced. Therefore, in order to improve the high rate discharge characteristics (discharge capacity), the content of PVDF needs to be 4.0% by mass or less.

  Similar to PVDF, when the AB content is high, the ratio of the positive electrode active material is reduced, and the battery capacity is prevented from being increased. Therefore, the AB content is set to 3.0% by mass or less for the high density of the battery. There is a need. Further, in Comparative Examples 8 and 14 where the mass ratio AB / PVDF is 0.25, the discharge capacity of 2 CmA is 107 mAh and the AB content in the battery of Comparative Example 8 where the AB content is 0.5 mass%. In the battery of Comparative Example 14 having a content of 1.0 mass%, the current is 323 mAh, none of which is good, and Comparative Example 8 is particularly inferior. Moreover, the discharge capacity of 2 CmA of the batteries of Examples 3 and 4 in which the AB content is 1.0 mass% and the PVDF content is 3.0 mass% (AB / PVDF is 0.33) is 445 to 446 mAh. And good. Therefore, in order to improve the high rate discharge characteristics of the battery, it is necessary that the AB content is 1.0 mass% or more and the mass ratio AB / PVDF is 0.33 or more.

  The positive electrode plates of Examples 11 to 15 where the press temperature of the positive electrode plate is normal temperature need to be pressed twice in order to obtain a predetermined thickness, which is not desirable from the viewpoint of suppressing the manufacturing cost. On the other hand, the positive plates of Examples 1, 3, 5, 7, and 9 in which the press temperature is 70 ° C. and the positive plates of Examples 2, 4, 6, 8, and 10 in which the press temperature is 100 ° C. Can be done once. This is considered to be because PVDF contained in the positive electrode mixture is softened and the workability is increased by pressing the positive electrode plate while heating. The pressing temperature is preferably 70 ° C or higher. When the press temperature was lower than 70 ° C., it was almost the same as that at room temperature.

  Further, in Comparative Examples 12, 13, 18, 19, and 24 where the positive electrode mixture was not peeled off and the press temperature was 110 ° C., the press workability was good, but the positive electrode plate was too hard, When forming the electrode element 2 by winding the positive electrode plate 4 and the negative electrode plate 3, the positive electrode plate 4 was cut or cracked. The cause of the curing of the positive electrode plate (positive electrode mixture) is considered to be that PVDF softened by heating at a high temperature spreads in the gaps of AB or the positive electrode active material and bonds them firmly. Therefore, in order to improve both the press workability and flexibility of the positive electrode plate 4, it is necessary to set the press temperature to 100 ° C. or less.

  In the present invention, carbon black used as the conductive agent for the positive electrode is a colloidal fine powder of carbon obtained by incomplete combustion or thermal decomposition of hydrocarbons. There are various types of carbon black depending on the type of hydrocarbon raw material used and the manufacturing method, for example, acetylene black obtained by pyrolyzing acetylene, but there are other raw materials, manufacturing methods and uses, etc. Depending on the difference, ketjen black, gas black, oil black, naphthalene black, thermal black, furnace black, lamp black, channel black, roll black, disc black, battery black, conductive black, rubber black, color black, etc. There is.

In the above-mentioned examples, granular acetylene black manufactured by Denki Kagaku Kogyo Co., Ltd. having a BET specific surface area of about 70 m ² / g was used as carbon black used for the conductive agent of the positive electrode. However, acetylene black of other grades was used. Alternatively, carbon black such as furnace black other than acetylene black can be used. These BET specific surface areas are sufficiently larger than the BET specific surface area of the positive electrode active material, and these powder characteristics are similar to each other, showing the same properties as in this example. In the present invention, the type of carbon black is not limited, but acetylene black is particularly preferable because of its high conductivity.

  The raw material of the positive electrode active material is not limited to the above-described examples, and lithium compounds represented by lithium carbonate, lithium hydroxide, lithium nitrate, and the like, and cobalt oxide, cobalt hydroxide, cobalt carbonate, cobalt nitrate salt Cobalt compounds represented by the above may be used. Further, as trace elements in the positive electrode active material, for example, magnesium (Mg), aluminum (Al), calcium (Ca), manganese (Mn), iron (Fe), nickel (Ni), zinc (Zn), zirconium ( Zr), strontium (Sr), sodium (Na), fluorine (F), sulfur (S), and other elements, and trace amounts of oxides, hydroxides, salts, and the like may be included. Further, the BET specific surface area and particle size distribution of the active material particles are controlled by controlling the particle shape of the lithium raw material and the cobalt raw material, adjusting the mixing ratio of the lithium raw material and the cobalt raw material, granulation of the mixed raw material, or lithium cobalt oxide You may control by baking conditions, addition of other elements, etc. In addition, lithium cobaltate may be used alone or in combination with other transition metal compounds such as nickel and manganese.

It is sectional drawing which shows schematic structure of the nonaqueous electrolyte secondary battery which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery 2 Electrode element 3 Negative electrode plate 4 Positive electrode plate 5 Separator 6 Battery case 7 Battery cover 8 Safety valve 9 Negative electrode terminal 10 Negative electrode lead

Claims (3)

In a non-aqueous electrolyte secondary battery having a positive electrode mixture containing carbon black and polyvinylidene fluoride and having a positive electrode pressed at 100 ° C. or lower,
The ratio of the carbon black to the positive electrode mixture is 1% by mass or more and 3% by mass or less,
The ratio of the polyvinylidene fluoride to the positive electrode mixture is 2% by mass or more and 4% by mass or less,
A nonaqueous electrolyte secondary battery, wherein a mass ratio of the carbon black to the polyvinylidene fluoride is 0.33 or more and 0.75 or less. In a non-aqueous electrolyte secondary battery having a positive electrode mixture containing carbon black and polyvinylidene fluoride and comprising a positive electrode pressed at 70 ° C. or higher and 100 ° C. or lower,
The ratio of the carbon black to the positive electrode mixture is 1% by mass or more and 3% by mass or less,
The ratio of the polyvinylidene fluoride to the positive electrode mixture is 2% by mass or more and 4% by mass or less,
A nonaqueous electrolyte secondary battery, wherein a mass ratio of the carbon black to the polyvinylidene fluoride is 0.33 or more and 0.75 or less.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the carbon black contains acetylene black.

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