JP2009266708A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery capable of improving output by securing a chargeable/dischargeable capacity. <P>SOLUTION: The lithium secondary battery 20 has a battery container 7, and in the battery container 7, a wound group 6 in which a positive electrode plate W1 and a negative electrode plate W3 are wound around via a separator W5 is housed. The positive electrode plate W1 is formed by coating a positive electrode mixture that contains lithium manganate, on an aluminum foil of a positive electrode current collector as a positive electrode active material. In the positive electrode plate W1, the amount coated on a positive electrode is adjusted so as to be within a range of 70 to 90 g/m<SP>2</SP>. In the negative electrode plate W3, as the negative electrode active material, an amorphous carbon material is used of which the negative electrode utilization rate is within a range of 230 to 350 mAh/g. The negative electrode plate W3 is formed by coating a negative electrode mixture that contains the amorphous carbon material, on a rolled copper foil of a negative electrode current collector. The amount coated on the positive electrode is limited to the negative electrode utilization rate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery, and in particular, a positive electrode plate and a negative electrode in which an active material mixture including a lithium transition metal oxide as a positive electrode active material and an amorphous carbon material as a negative electrode active material is applied to a current collector. The present invention relates to a lithium secondary battery having a plate.

  Conventionally, in the field of rechargeable secondary batteries, aqueous batteries such as lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries have been mainstream. However, due to global warming and fuel depletion problems, electric vehicles that are driven only by electric motors and hybrid electric vehicles that are partially assisted by electric motors are attracting attention. High capacity and high input / output characteristics have been demanded. As a secondary battery meeting such requirements, a non-aqueous lithium secondary battery having high voltage characteristics has been attracting attention.

  In general, a lithium transition metal oxide is used as a positive electrode active material of a lithium secondary battery, and lithium cobalt oxide is used among them in terms of balance of capacity and cycle characteristics. However, in lithium cobaltate, the resource amount of cobalt as a raw material is small and the cost of the lithium secondary battery is increased. For this reason, lithium manganate using manganese, which has abundant resources, is promising as a positive electrode active material for lithium secondary batteries for electric vehicles and hybrid electric vehicles.

  On the other hand, as the negative electrode active material, since lithium input batteries for electric vehicles and hybrid electric vehicles require high input / output characteristics, amorphous carbon obtained by baking synthetic resin such as furan resin such as furfuryl alcohol is used. The material is generally used. Amorphous carbon material is a material that is attracting attention because it has a characteristic that it has a capacity higher than the theoretical capacity value of graphite-based carbon material, has excellent cycle life, and has high input / output characteristics. .

  Normally, in the case of amorphous carbon material, at the time of initial charge, a constant current region in which the voltage from the start of charge to the voltage becomes constant as the capacity increases and a constant voltage from when the voltage becomes constant to the end of charge And have a region. When the capacity of this constant voltage region is used for charging and discharging, lithium occlusion and release extend to the deep part of the amorphous structure, so that the deterioration of the amorphous carbon material proceeds and the cycle life is reduced. In order to avoid this, the battery is designed so that the charge / discharge utilization range of the amorphous carbon material is a constant current region while avoiding the constant voltage region. In addition, the amorphous carbon material has a disadvantage that it is difficult to increase the capacity of the battery because the irreversible capacity is larger than that of the graphite-based carbon material. In order to suppress the irreversible capacity | capacitance of an amorphous carbon material and to improve charging / discharging capacity | capacitance, the technique which adds a carbonate additive to nonaqueous electrolyte solution is disclosed (for example, refer patent document 1).

JP 2000-133306 A

  However, in the technique of Patent Document 1, since the reductive decomposition reaction of the nonaqueous electrolytic solution is suppressed on the surface of the amorphous carbon material, although a temporary effect is recognized in suppressing the irreversible capacity, the insertion and release of lithium ions However, since the amorphous carbon material is deteriorated by extending to the deep part of the amorphous structure, the cycle life is shortened. Moreover, there is a drawback that the cost of the lithium secondary battery is increased due to the high cost of the additive. On the other hand, when the charge / discharge utilization range of the amorphous carbon material is set to a constant current region, a decrease in cycle life is suppressed, but as the capacity of the constant voltage region increases, the amount of capacity not used for charge / discharge increases. The chargeable / dischargeable capacity decreases.

  In view of the above-described case, an object of the present invention is to provide a lithium secondary battery that can secure a chargeable / dischargeable capacity and improve output.

In order to solve the above problems, the present invention provides a positive electrode plate and a negative electrode in which an active material mixture containing a lithium transition metal oxide as a positive electrode active material and an amorphous carbon material as a negative electrode active material is applied to a current collector. In the lithium secondary battery having a plate, the negative electrode plate has a utilization rate of the negative electrode active material in the range of 230 mAh / g to 350 mAh / g, and the positive electrode plate has a coating amount of the positive electrode active material of 70 g / m ^2. It is the range of -90g / m < ² >.

In the present invention, by the utilization of the negative electrode active material in the range of 230mAh / g~350mAh / g, the range of coating amount of the positive electrode active material of ^{70g / m 2 ~90g / m 2} , the positive and negative electrodes The coating defects of the plate are reduced, and the output can be improved while ensuring the capacity available for charging and discharging as a battery. In this case, the negative electrode active material may be an easily graphitizable carbon material. Moreover, the ratio of the discharge capacity of the negative electrode plate to the discharge capacity of the positive electrode plate can be in the range of 1.0 to 1.1.

According to the present invention, by the utilization of the negative electrode active material in the range of 230mAh / g~350mAh / g, the range of coating amount of the positive electrode active material of ^{70g / m 2 ~90g / m 2} , the positive electrode plate And the coating defect of a negative electrode plate reduces, and the effect that an output can be improved, ensuring the capacity | capacitance which can be utilized for charging / discharging as a battery can be acquired.

  Hereinafter, an embodiment of a cylindrical lithium secondary battery for a hybrid electric vehicle to which the present invention is applied will be described with reference to the drawings.

(Constitution)
As shown in FIG. 1, the cylindrical lithium secondary battery 20 of the present embodiment has a bottomed cylindrical battery case 7 made of steel plated with nickel. The battery container 7 accommodates a winding group 6 in which a belt-like positive electrode plate W1 and a negative electrode plate W3 are wound in a spiral shape with a separator W5 on a hollow cylindrical shaft core 1 made of propylene.

  On the upper side of the winding group 6, a positive electrode current collection ring 4 for collecting a potential from the positive electrode plate W <b> 1 is disposed on a substantially extension line of the shaft core 1. The positive electrode current collecting ring 4 is fixed to the upper end portion of the shaft core 1. The edge part of the positive electrode lead piece 2 led out from the positive electrode plate W1 is joined to the periphery of the flange part integrally protruding from the periphery of the positive electrode current collecting ring 4 by ultrasonic welding. A disc-shaped battery lid serving as a positive electrode external terminal is disposed above the positive electrode current collecting ring 4. The battery lid is composed of a lid case 12, a lid cap 13, a valve retainer 14 that keeps airtightness, and a cleavage valve (internal gas discharge valve) 11 that is cleaved by an increase in internal pressure. It is assembled by caulking and fixing the periphery of 12. One end of two positive electrode leads 9 formed by superposing a plurality of aluminum ribbons is fixed to the upper portion of the positive electrode current collecting ring 4, and another one is fixed to the lower surface of the lid case 12. One end is welded. The other ends of the two positive electrode leads 9 are joined by welding.

  On the other hand, a negative electrode current collecting ring 5 for collecting the electric potential from the negative electrode plate W3 is disposed below the winding group 6. The outer peripheral surface of the lower end portion of the shaft core 1 is fixed to the inner peripheral surface of the negative electrode current collecting ring 5. The end of the negative electrode lead piece 3 led out from the negative electrode plate W3 is joined to the outer peripheral edge of the negative electrode current collecting ring 5 by welding. A negative electrode lead plate 8 for electrical conduction is welded to the lower part of the negative electrode current collecting ring 5, and the negative electrode lead plate 8 is joined to the inner bottom portion of the battery container 7 by welding. In this example, the battery container 7 has an outer diameter of 40 mm and an inner diameter of 39 mm.

The battery lid is caulked and fixed to the upper part of the battery container 7 via an insulating and heat resistant EPDM resin gasket 10. For this reason, the positive electrode lead 9 is accommodated in the battery container 7 so as to be folded, and the lithium secondary battery 20 is sealed. Further, a non-aqueous electrolyte solution (not shown) is injected into the battery container 7. The non-aqueous electrolyte includes lithium hexafluorophosphate (LiPF ₆₎ as a lithium salt in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a volume ratio of 1: 1: 1. ) Is dissolved in 1 mol / liter (mol / L).

  The winding group 6 is wound around the shaft core 1 through a polyethylene separator W5 having a width of 90 mm and a thickness of 30 μm so that the positive electrode plate W1 and the negative electrode plate W3 are not in direct contact with each other. Yes. The positive electrode lead piece 2 and the negative electrode lead piece 3 are respectively disposed on opposite end surfaces of the wound group 6. Insulation coating is applied to the entire circumference of the collar surface of the winding group 6 and the positive electrode current collecting ring 4. For the insulation coating, an adhesive tape in which a hexamethacrylate adhesive material is applied to one side of a polyimide base material is used. The pressure-sensitive adhesive tape is wound one or more times from the collar surface to the outer periphery of the wound group 6. By adjusting the lengths of the positive electrode plate W1, the negative electrode plate W3, and the separator W5, the diameter of the wound group 6 is set to 38 ± 0.1 mm.

  The positive electrode plate W1 constituting the wound group 6 has an aluminum foil as a positive electrode current collector, and the negative electrode plate W3 has a rolled copper foil as a negative electrode current collector. In this example, the thicknesses of the aluminum foil and the rolled copper foil are set to 20 μm and 10 μm, respectively. On the side edge on one side in the longitudinal direction of the aluminum foil and the rolled copper foil, uncoated portions of the positive electrode mixture and the negative electrode mixture are formed with a width of 30 mm, respectively. The uncoated part is cut out in a comb shape, and the positive electrode lead piece 2 and the negative electrode lead piece 3 are formed in the remaining part of the cutout. The interval between the adjacent positive electrode lead pieces 2 and the interval between the negative electrode lead pieces 3 is set to 50 mm, and the width of each of the positive electrode lead piece 2 and the negative electrode lead piece 3 is set to 5 mm.

In the positive electrode plate W1, lithium manganate as a lithium transition metal oxide is used as a positive electrode active material. A positive electrode mixture containing lithium manganate is applied almost evenly on both sides of the aluminum foil. In the positive electrode mixture, for example, 10 parts by weight of flaky graphite as a conductive material and 100% by weight of lithium manganate and polyvinylidene fluoride (hereinafter abbreviated as PVDF) as a binder (binder). 5 parts by weight is blended. When the positive electrode mixture is applied to the aluminum foil, the viscosity is adjusted with N-methylpyrrolidone (hereinafter abbreviated as NMP) as a dispersion solvent. In the positive electrode plate W1, the coating amount of the positive electrode active material (hereinafter referred to as the positive electrode coating amount) is adjusted to be in the range of 70 to 90 g / m ² . After drying, the positive electrode plate W1 is pressed so as to have a desired density and a constant density, and is cut into a width of 82 mm.

  On the other hand, the negative electrode plate W3 uses an amorphous carbon material as a negative electrode active material. As this negative electrode active material, an amorphous carbon material having a charge / discharge utilization rate (hereinafter referred to as negative electrode utilization rate) in the range of 230 to 350 mAh / g is used. The charge / discharge utilization rate here indicates the capacity excluding the irreversible capacity. In the negative electrode plate W3, the negative electrode mixture containing an amorphous carbon material is applied substantially evenly on both surfaces of the rolled copper foil. For example, 10 parts by weight of PVDF as a binder is blended with 90 parts by weight of the amorphous carbon material in the negative electrode mixture. When the negative electrode mixture is applied to the rolled copper foil, the viscosity is adjusted with the dispersion solvent NMP. The thickness of the negative electrode plate W3 is adjusted so that the ratio (− / + capacity ratio) of the discharge capacity of the negative electrode plate W3 to the discharge capacity of the positive electrode plate W1 is constant at 1.0. The negative electrode plate W3 is dried and then pressed in the same manner as the positive electrode plate W1, and is cut into a width of 86 mm.

  Next, examples of the lithium secondary battery 20 manufactured by changing the positive electrode coating amount and the negative electrode utilization rate according to the present embodiment will be described. In addition, it describes together about the lithium secondary battery of the comparative example produced for the comparison.

(Example 1-1, Example 1-2)
As shown in Table 1 below, in Example 1-1 and Example 1-2, a lithium secondary battery 20 was manufactured using a non-graphitizable carbon powder that is an amorphous carbon material as the negative electrode active material. The coating amount of the positive electrode was 90 g / m ^{2 in} both Example 1-1 and Example 1-2. The negative electrode utilization rate was 230 mAh / g in Example 1-1 and 350 mAh / g in Example 1-2. The non-graphitizable carbon powder is a carbon material obtained by firing a thermosetting resin in an inert atmosphere, whether natural or synthetic (the same applies to the examples and comparative examples below this example).

(Comparative Example 1-1, Comparative Example 1-2)
As shown in Table 1, in Comparative Example 1-1 and Comparative Example 1-2, lithium secondary batteries were produced using non-graphitizable carbon powder as the negative electrode active material. The amount of positive electrode applied was the same as that of Example 1-1 in both Comparative Example 1-1 and Comparative Example 1-2. The negative electrode utilization rate was 150 mAh / g in Comparative Example 1-1 and 400 mAh / g in Comparative Example 1-2.

(Example 2-1 and Example 2-2)
As shown in Table 1, in Example 2-1 and Example 2-2, a lithium secondary battery 20 was fabricated using a non-graphitizable carbon powder material for the negative electrode active material. The coating amount of the positive electrode was 70 g / m ^{2 in} both Example 2-1 and Example 2-2. The negative electrode utilization rate was 230 mAh / g in Example 2-1, and 350 mAh / g in Example 2-2.

(Comparative Example 2-1 and Comparative Example 2-2)
As shown in Table 1, in Comparative Examples 2-1 and 2-2, lithium secondary batteries were produced using non-graphitizable carbon powder as the negative electrode active material. The amount of positive electrode applied was the same as that of Example 2-1 in both Comparative Example 1-1 and Comparative Example 1-2. The negative electrode utilization rate was 150 mAh / g in Comparative Example 2-1, and 400 mAh / g in Comparative Example 2-2.

(Comparative Example 3-1 and Comparative Example 3-2)
As shown in Table 1, in Comparative Examples 3-1 and 3-2, lithium secondary batteries were produced using non-graphitizable carbon powder as the negative electrode active material. The positive electrode coating amount was 100 g / m ² for both Comparative Example 3-1 and Comparative Example 3-2. The negative electrode utilization rate was 230 mAh / g in Comparative Example 3-1, and 400 mAh / g in Comparative Example 3-2.

(Comparative Example 4)
As shown in Table 1, in Comparative Example 4, a lithium secondary battery was produced using non-graphitizable carbon powder as the negative electrode active material. The positive electrode coating amount was 60 g / m ² and the negative electrode utilization rate was 230 mAh / g.

(Example 3)
As shown in Table 1, in Example 3, a lithium secondary battery 20 was produced using graphitizable carbon powder as the negative electrode active material. The positive electrode coating amount was 90 g / m ² and the negative electrode utilization rate was 230 mAh / g. The graphitizable carbon powder is a carbon material obtained by firing a mesophase pitch at a low temperature of 900 to 700 ° C.

<Test and evaluation>
About each lithium secondary battery of an Example and a comparative example, after charging each battery, it discharged, and measured the initial stage discharge capacity in the atmosphere of environmental temperature 25 +/- 2 degreeC. The charging conditions were a 4.1 V constant voltage, a limiting current of 5.5 A, and 2.5 hours, and the discharging conditions were a 5.5 A constant current and a final voltage of 2.7 V. Moreover, after each battery was charged under the above-described charging conditions (fully charged state), the initial output was measured in an atmosphere having an environmental temperature of 25 ± 2 ° C. In the output measurement, discharge was performed at current values of 27.5 A, 55 A, and 100 A for 10 seconds each, and the battery voltage value at each 5 seconds was measured. With respect to the horizontal axis current value, the vertical axis plots the battery voltage value at the 5th second, reads the current value at the point where a straight line approximating 3 points intersects the end voltage 2.7V, and this current The product of the value and 2.7 V was taken as the output of the battery.

<Criteria for electrode plate>
In the production of the positive electrode plate W1 and the negative electrode plate W3, when defects (streaks, lumps, bubble marks) were observed by visual observation, the number of defects was measured and judged to be defective. Moreover, when the output per cell of each produced lithium secondary battery was 720 W or less, it was made impossible. Table 1 shows the number of defects of the positive electrode plate W1 and the negative electrode plate W3 and the measurement results of the output.

As shown in Table 1, from the results of Example 1-1, Example 1-2, Comparative Example 1-1, and Comparative Example 1-2, the negative electrode utilization rate was 230 to 200 at a positive electrode coating amount of 90 g / m ² . In the range of 350 mAh / g, both the positive and negative electrode plates had no coating defects, and the output was 720 W or more. In contrast, when the negative electrode utilization rate was 150 mAh / g, there were no coating defects on the positive and negative electrode plates, but the output did not reach 720 W, and when the negative electrode utilization rate was 400 mAh / g, the output was satisfactory, but the negative electrode plate There was a coating defect and it was determined to be defective (output was not measured and is indicated by “−” in Table 1). Moreover, from the results of Example 2-1, Example 2-2, Comparative Example 2-1, and Comparative Example 2-2, the negative electrode utilization rate is in a range of 230 to 350 mAh / g at a positive electrode coating amount of 70 g / m ² . The positive and negative electrode plates showed no coating defects and the output was 720 W or more. In contrast, when the negative electrode utilization rate was 150 mAh / g, there were no coating defects on the positive and negative electrode plates, but the output did not reach 720 W, and when the negative electrode utilization rate was 400 mAh / g, the output was satisfactory, but the negative electrode plate There was a coating defect, and it was considered defective.

Further, from the results of Comparative Examples 3-1 and 3-2, when the negative electrode utilization rate was 230 mAh / g at a positive electrode coating amount of 100 g / m ² , the output was 720 W or less, and the negative electrode utilization rate was 400 mAh / In g, since the negative electrode plate had a defect, it was determined to be defective. From the result of Comparative Example 4, since the positive electrode plate had a defect at a positive electrode coating amount of 60 g / m ^2, it was regarded as defective regardless of the negative electrode utilization rate. On the other hand, in Example 3 in which graphitizable carbon powder was used as the negative electrode active material, the output was 820 W. Since the output of Example 1-1 using the non-graphitizable carbon powder with the same positive electrode coating amount and the same negative electrode utilization rate was 730 W, the graphitizable carbon was replaced with the non-graphitizable carbon powder as the negative electrode active material. It was found that the output can be improved by using the powder.

As described above, when the negative electrode plate W3 having a negative electrode utilization ratio of 230 to 350 mAh / g and the positive electrode plate W1 having a positive electrode coating amount of 70 to 90 g / m ² are used, an output of 720 W or more is used. Can be obtained. Moreover, when an easily graphitized carbon powder is used as the negative electrode active material, a higher output can be obtained than other amorphous carbon materials such as a non-graphitizable carbon powder.

In the present embodiment, the negative electrode plate W3 is manufactured in the range of the negative electrode utilization rate of 230 to 350 mAh / g, and the positive electrode plate W1 is manufactured in the range of the positive electrode coating amount of 70 to 90 g / m ² . For this reason, the coating amount is sufficiently secured when the positive electrode plate W1 and the negative electrode plate W3 are produced, and the positive and negative electrode plates can be stably produced while reducing coating defects such as streaks, lumps and bubble marks. Moreover, since the amount of positive electrode coating is limited with respect to the negative electrode utilization rate, the output can be improved while securing the capacity available for charging and discharging as a battery. If the coating amount of the positive electrode is less than 70 g / m ² , the coating defects increase. On the other hand, if it exceeds 90 g / m ² , the conductivity decreases due to the increase in thickness, and the output is decreased. When the negative electrode utilization rate is less than 230 mAh / g, deterioration due to expansion and contraction tends to occur, and conversely, when the negative electrode utilization rate exceeds 350 mAh / g, the irreversible capacity increases and the capacity decreases. Therefore, the lithium secondary battery 20 can obtain an output of 720 W or more per battery (per cell), and can be suitably used as a power source for a hybrid electric vehicle or the like (Example 1-1, Example 1-2, Example 2-1, Example 2-2).

  In the present embodiment, graphitizable carbon powder is also used as the negative electrode active material instead of the non-graphitizable carbon powder. When the negative electrode utilization ratio is in the range of 230 to 350 mAh / g, it is used for charging and discharging up to the constant voltage region of the graphitizable carbon powder, and the battery voltage rises due to the potential difference between the positive electrode and the negative electrode. For this reason, compared with the case where amorphous carbon materials other than graphitizable carbon powder are used, an output can be improved further (refer Example 3).

  Furthermore, in this embodiment, the ratio (− / + capacity ratio) of the discharge capacity of the negative electrode plate W3 to the discharge capacity of the positive electrode plate W1 is set to 1.0. The charge / discharge characteristics of the amorphous carbon material include a constant voltage region in which the potential is substantially constant with respect to capacity change and a constant current region in which the potential increases with increase in capacity. When used for charging / discharging up to this constant voltage region capacity, the deterioration of the amorphous carbon material usually tends to progress, but among the amorphous carbon materials, the graphitizable carbon powder has little expansion and contraction and is difficult to deteriorate. . For this reason, by using easily graphitized carbon powder as the negative electrode active material and setting the-/ + capacity ratio to 1.0, it can be used up to a constant voltage region of the easily graphitized carbon powder during charging and discharging. Thereby, the battery voltage increases due to the potential difference between the positive and negative electrodes, so that the battery output can be improved. About this-/ + capacity | capacitance ratio, this inventor has confirmed that the effect mentioned above will be acquired if it is the range of 1.0-1.1.

  In addition, in this embodiment, although the cylindrical lithium secondary battery 20 which wound the positive electrode plate W1 and the negative electrode plate W3 was illustrated, this invention is not limited to this. For example, the battery shape can be applied to a rectangular or other polygonal battery in addition to the cylindrical shape. Also, the battery structure may be other than the structure in which the battery lid is sealed by caulking and fixing to the battery container. As an example of such a structure, a battery in which the positive and negative external terminals pass through the battery lid and the positive and negative external terminals are pressed against each other through the shaft core in the battery container can be mentioned. Furthermore, the positive electrode plate W1 and the negative electrode plate W3 are applicable not only to a wound structure but also to a lithium secondary battery having a stacked structure.

  In this embodiment, lithium manganate is exemplified as the positive electrode active material, but the present invention is not limited to this. The positive electrode active material that can be used in other than the present embodiment is a material capable of inserting and removing lithium ions, and may be any lithium transition metal oxide in which a sufficient amount of lithium ions has been previously inserted. Alternatively, a material obtained by substituting or doping a part of lithium or a transition metal with an element other than these may be used. Of course, the crystal structure may be either a spinel type or a layered type.

  Furthermore, in this embodiment, scaly graphite was exemplified as the conductive material, and PVDF was exemplified as the binder. However, the present invention is not limited to these, and any material normally used in lithium secondary batteries can be used. . For example, as binders that can be used other than the present embodiment, polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various types Mention may be made of polymers such as latex, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride and mixtures thereof.

Furthermore, in the present embodiment, a nonaqueous electrolytic solution in which LiPF ₆ is dissolved in a mixed solvent in which ethylene carbonate, dimethyl carbonate, and diethyl carbonate are mixed at a volume ratio of 1: 1: 1 is exemplified. A nonaqueous electrolytic solution obtained by dissolving the above in an organic solvent may be used, and the present invention is not particularly limited to the lithium salt or organic solvent used. For example, as the electrolyte, LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, or a mixture thereof can be used. Examples of the organic solvent include propylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, Sulfolane, methyl sulfolane, acetonitrile, propionitrile, or a mixed solvent in which two or more of these are mixed can be used. Furthermore, the mixing ratio is not limited. By using such a non-aqueous electrolyte, it is possible to improve battery capacity and adapt to use in cold regions.

  Since the present invention provides a lithium secondary battery capable of securing a chargeable / dischargeable capacity and improving output, it contributes to the manufacture and sale of lithium secondary batteries, and thus has industrial applicability.

It is sectional drawing of the cylindrical lithium secondary battery of embodiment to which this invention is applied.

Explanation of symbols

6 Electrode group 20 Cylindrical lithium secondary battery (lithium secondary battery)
W1 positive electrode plate W2 positive electrode active material mixture (active material mixture)
W3 Negative electrode plate W4 Negative electrode active material mixture (active material mixture)

Claims (3)

In the lithium secondary battery having a positive electrode plate and a negative electrode plate each coated with an active material mixture containing a lithium transition metal oxide as a positive electrode active material and an amorphous carbon material as a negative electrode active material, the negative electrode plate characterized in that the utilization rate of the negative active material ranges from 230mAh / g~350mAh / g, the positive electrode plate coated amount of the positive active material is in the range of ^70g / ^{m 2 ~90g} / m 2 Lithium secondary battery.   The lithium secondary battery according to claim 1, wherein the negative electrode active material is a graphitizable carbon material.   The lithium secondary battery according to claim 2, wherein the negative electrode plate has a ratio of discharge capacity to discharge capacity of the positive electrode plate in a range of 1.0 to 1.1.

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