JP5433484B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery.

  Lithium ion secondary batteries are used as power sources for portable devices such as VTR cameras, notebook computers, mobile phones, and the like for consumer use, taking advantage of the high energy density. In general, a wound-type internal structure is employed in a consumer lithium-ion secondary battery.

A wound lithium ion secondary battery consists of a strip of positive and negative electrodes, each of which has a positive electrode active material and a negative electrode active material applied to a metal foil, wound in a spiral shape with a separator interposed therebetween, thereby forming a wound electrode group To do.
The wound electrode group is housed in a cylindrical battery can and sealed after injecting an electrolytic solution.

  As a consumer lithium ion secondary battery, an 18650 type battery having a diameter of 18 mm and a height of 65 mm is widely used. The 18650 type battery is required to have a high capacity and a long life, and lithium cobaltate is mainly used for the positive electrode active material, and graphite graphite is mainly used for the negative electrode active material. The battery capacity is about 1.6 Ah to 2 Ah. .4Ah, battery output is about 30W.

  On the other hand, in the automobile industry, in order to cope with environmental problems, development of an electric vehicle (EV) using only a battery as a power source and a hybrid electric vehicle (HEV) using both an internal combustion engine and a battery as a power source are being developed. It is being advanced. Lithium ion batteries are attracting attention because batteries for mobile bodies mounted on electric vehicles and the like are required to have high output and high capacity characteristics.

  For lithium-ion secondary batteries for mobile objects, for example, lithium-manganese composite oxides that are resource-rich and low-cost are used for the positive electrode active material for the popularization of electric vehicles. Is planned.

  In the case of a lithium ion secondary battery for a mobile body, when the output and capacity performance deteriorates and the necessary capacity as a power source cannot be obtained, it is necessary to take measures such as replacing the battery with a new one. However, frequent battery replacement is time consuming and costly and is not practical, and there is a demand for longer battery life so that the frequency of replacement can be reduced or the battery can be used without replacement.

  In addition, in order to improve acceleration performance in mobile lithium-ion secondary batteries, charging and discharging at high loads are repeated without interruption, so there is a rapid and large amount of elemental materials required for charging and discharging such as electrons and ions inside the battery. The load on the positive electrode active material and the negative electrode active material increases, and the capacity balance between the positive and negative electrodes due to a decrease in crystallinity of the active material and side reactions becomes unbalanced. For this reason, there is a possibility that the output and the capacity of the battery are reduced.

  In order to cope with this, the life is extended by suppressing the deterioration of the performance by improving the electrode reaction area, the load distribution due to the increase in the specific surface area of the active material, the strengthening of the active material structure, etc. .

  For example, in Patent Document 1, the ratio of the surface area S (the specific surface area of the positive electrode active material × the weight of the positive electrode active material) of the positive electrode active material to the single-sided unit area of the positive electrode current collecting base material is set to 40 or more. The electrode reaction is made to follow charging / discharging while ensuring an area.

Patent Document 2 uses a carbon material having an average particle size of the negative electrode active material of 5 to 25 μm and a specific surface area of 1.0 to 12 m ² / g by the BET method of nitrogen gas adsorption.

JP 2003-308830 A JP 2006-236753 A

  However, by securing the electrode reaction area as in Patent Document 1 and increasing the specific surface area of the active material as in Patent Document 2, the receiving site (area) of lithium ions during charging and discharging is increased, Although a temporary effect such as suppression of capacity reduction and output reduction with respect to charging / discharging is recognized, sudden charge reduction and output reduction occur when charging / discharging is repeated at a high load.

  The reason for this is that although the speed of lithium ions released from the positive and negative electrodes into the electrolyte during charging and discharging is high, the speed of the lithium ions that move through the electrolyte is low. This results in non-uniformity in which the concentration of lithium ions increases, and this is because the movement of lithium ions is remarkably hindered by an increase in electrolyte viscosity or precipitation of lithium salts in the vicinity of the electrodes.

The present invention includes a positive electrode using the lithium manganate as a positive electrode active material, an electrode group disposed through a separator and a negative electrode using lithium ions removably carbon material in the negative electrode active material by charging and discharging, Ethylene The present invention is applied to a lithium ion secondary battery infiltrated with a nonaqueous electrolytic solution made by dissolving lithium hexafluorophosphate in a mixed solution containing carbonate, dimethyl carbonate, and diethyl carbonate and accommodated in a battery container. Conditions 1 and 2 are satisfied.
Condition 1: The relationship between the capacity C (Ah) of the lithium ion secondary battery and the battery volume V (cm3) is C / V = 0.08 or less. Condition 2: The amount of active material M (g) of the positive electrode and the non-aqueous The relationship of the electrolyte amount E (cm3) is E / M = 0.6 or more and 1.0 or less

  According to the present invention, a high capacity retention rate can be obtained while maintaining a high energy density.

1 is an exploded perspective view showing an embodiment in which a lithium ion secondary battery according to the present invention is applied to a cylindrical lithium ion secondary battery. The figure which shows the space | gap part in the battery can in the cylindrical lithium ion secondary battery of FIG. The enlarged view of the electrode part in the cylindrical lithium ion secondary battery of FIG. Table 1 which compares the specifications of Examples 1-8 of the cylindrical lithium ion secondary battery of FIG. 1 and a comparative example. Table 2 which compares the capacity | capacitance maintenance factor of Examples 1-8 of FIG. 4, and a comparative example. It is a figure which shows the relationship between E / M (electrolyte amount / positive electrode active material amount) and the capacity | capacitance maintenance factor after a cycle test. FIG. 2 is a model diagram of lithium ion heterogeneity in the cylindrical lithium ion secondary battery of FIG. 1. The graph which shows the relationship between E / M (amount of electrolyte solution / amount of positive electrode active material) and capacity retention ratio × energy density in Examples 1 to 8 and Comparative Example.

  Hereinafter, an embodiment in which a lithium ion secondary battery according to the present invention is applied to a cylindrical lithium ion secondary battery will be described with reference to the drawings.

  As shown in FIG. 1 and FIG. 2, a cylindrical lithium ion secondary battery 20 has a wound electrode group 8 housed inside a bottomed cylindrical container 1 having an opening at one end and electrolyzed inside the container. After the liquid is injected, the opening is closed by the battery lid 4. The wound electrode group 8 is configured by winding the positive electrode 16 and the negative electrode 17 around the shaft core 7 while being insulated by a separator 18.

[Positive electrode]
The positive electrode 16 is configured by applying a positive electrode mixture having a positive electrode active material 16a and a positive electrode conductive material 16b to both surfaces of a positive electrode sheet 14 formed of an aluminum foil and having a long shape. On the upper side edge along the longitudinal direction of the positive electrode sheet 14, a region where the positive electrode mixture is not applied and the aluminum foil is exposed is formed, and in this region, a number of protrusions projecting upward in parallel with the shaft core 7. The positive electrode tabs 12 are integrally formed at equal intervals.

  The positive electrode mixture includes a positive electrode active material 16a, a positive electrode conductive material 16b, and a positive electrode binder. The positive electrode active material 16a is preferably a lithium oxide. Examples include lithium cobaltate, lithium manganate, lithium nickelate, lithium composite oxide (lithium oxide containing two or more selected from cobalt, nickel, and manganese). In this embodiment, lithium manganate is used.

  The positive electrode conductive material 16b assists transmission of electrons generated by the occlusion / release reaction of lithium in the positive electrode mixture to the positive electrode. Examples of the positive electrode conductive material 16b include graphite (carbon black) and acetylene black. In this embodiment, carbon black is used.

  The positive electrode binder binds the positive electrode active material 16a and the positive electrode conductive material 16b, and binds the positive electrode mixture and the positive electrode current collector. Examples of the positive electrode binder include polyvinylidene fluoride (PVDF) and fluororubber. In this embodiment, polyvinylidene fluoride (PVDF) is used.

  Examples of the method for applying the positive electrode mixture to the positive electrode sheet 14 include a roll coating method and a slit die coating method. The positive electrode mixture uses lithium manganate as the lithium transition metal composite oxide, and is bound to 10 parts by weight of carbon black (DBP oil absorption 100 cc / 100 g) as a conductive material with respect to 100 parts by weight of lithium manganate. 10 parts by weight of polyvinylidene fluoride (PVDF) was added as an agent, and N-methylpyrrolidone (NMP) was added and kneaded as a dispersion solvent to prepare a positive electrode mixture (slurry). The prepared slurry is applied to both sides of an aluminum foil 14 having a thickness of 20 μm, dried, and then pressed and cut to form the positive electrode 16. The total application thickness of both surfaces of the positive electrode mixture not including the positive electrode sheet is, for example, 75 μm, and the width of the application part is, for example, 82 mm. When the positive electrode sheet 14 is cut, the positive electrode tab 12 is integrally formed.

[Negative electrode]
The negative electrode 17 is configured by applying a negative electrode mixture having a negative electrode active material 17a to both surfaces of a negative electrode sheet 15 formed of copper foil and having a long shape. A region where the negative electrode mixture is not applied and the copper foil is exposed is formed on the lower side edge along the longitudinal direction of the negative electrode sheet 15, and this region extends in the opposite direction to the positive electrode tab 12. In addition, a large number of negative electrode tabs 13 are integrally formed at equal intervals.

  The negative electrode mixture includes a negative electrode active material 17a, a negative electrode binder, and a thickener. The negative electrode mixture may have a negative electrode conductive material such as acetylene black. As the negative electrode active material 17a, amorphous carbon, for example, graphite carbon is preferably used. By using amorphous carbon, a lithium ion secondary battery for a plug-in hybrid vehicle or an electric vehicle requiring a large capacity can be manufactured. In this embodiment, polyvinylidene fluoride (PVDF) is used as the negative electrode binder.

  As an example of a method of applying the negative electrode mixture to the negative electrode sheet 15, a method of applying a dispersion solution of constituent materials of the negative electrode mixture onto the negative electrode sheet 15 can be given. Examples of the coating method include a roll coating method and a slit die coating method.

  In this embodiment, 10 parts by weight of polyvinylidene fluoride (PVDF) is added as a binder to 100 parts by weight of amorphous carbon powder, and N-methyl-2-pyrrolidone (NMP) is added as a dispersion solvent. An added and kneaded slurry is prepared, uniformly applied to both surfaces of a rolled copper foil having a thickness of 10 μm, dried, and then pressed and cut to form the negative electrode 17. The total application thickness of both surfaces of the negative electrode mixture not including the negative electrode sheet is, for example, 78 μm, and the width of the application part is, for example, 86 mm.

  The wound electrode group 8 insulates the produced positive electrode 16 and the negative electrode 17 with a polyethylene separator 18 having a width of 90 mm, a thickness of 30 μm, and a porosity of 47%, for example, so that these bipolar plates are not in direct contact with each other. It is composed by winding while doing.

  While the positive electrode tab 12 of the positive electrode 16 is deformed, all of the positive electrode tabs 12 are connected to the positive electrode current collecting ring 5 that is substantially on the extension line of the axis 7 of the wound electrode group 8. A flange is integrally projected around the positive electrode current collecting ring 5, and the positive electrode tab 12 is gathered in the vicinity of the periphery of the flange, and is joined to the periphery of the flange by ultrasonic welding. The negative electrode tab 13 is gathered near the collar peripheral surface of the negative electrode current collecting ring 6 disposed at the bottom of the battery container 1 and joined to the collar peripheral surface by ultrasonic welding.

  Thereafter, an insulation coating is applied to the entire circumference of the collar peripheral surface of the positive electrode current collecting ring 5. For this insulation coating, a base material is polyimide and an adhesive tape coated with an adhesive made of hexamethacrylate is used on one side, and the adhesive tape is single-layered from the peripheral surface of the buttocks to the outer peripheral surface of the wound electrode group 8. The insulating coating was formed by winding the above.

  The wound electrode group 8 adjusts the lengths of the positive electrode 16, the negative electrode 17, and the separator 18, and the diameter thereof is, for example, 38 ± 0.1 mm. On the other hand, the battery container 1 that houses the wound electrode group 8 is a nickel-plated steel can whose outer diameter and inner diameter are, for example, 40 mm and 39 mm, respectively.

  A negative electrode lead plate (not shown) for electrical conduction is welded to the negative electrode current collecting ring 6 in advance, and after inserting the wound electrode group 8 into the battery case 1, the bottom of the battery case 1 and the negative electrode Weld the lead plate.

A battery for sealing one end of a positive electrode lead 9 formed by superimposing a plurality of aluminum ribbons in advance on the positive electrode current collecting ring 5 and sealing the battery container 1 at the other end of the positive electrode lead 9 is provided. Welded to the lower surface of the lid 4. The battery lid 4 is provided with a cleavage valve 3 of an internal pressure release mechanism that cleaves in response to an increase in internal pressure of the cylindrical lithium ion secondary battery 20. The cleavage pressure of the cleavage valve 3 is set to about 9 × 10 ⁵ Pa, for example.

  A predetermined amount of non-aqueous electrolyte is injected into the battery container 1, and then the battery container 1 is sealed with the battery cover 4 so that the positive electrode lead 9 is folded, and the battery cover 4 is caulked through the EPDM resin gasket 2. The cylindrical lithium ion secondary battery 20 having a height of 108 mm and a design capacity of 5.0 Ah is completed.

As the non-aqueous electrolyte, for example, a solution obtained by dissolving 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1: 1: 1 is used. .

  FIG. 3 is an enlarged cross-sectional view of the wound electrode group 8 described above. As shown in FIG. 3, in the wound electrode group 8, a positive electrode mixture is applied to both surfaces of the aluminum foil 14 on the positive electrode 16, and a negative electrode mixture is applied to both surfaces of the rolled copper foil 15 on the negative electrode 17. Has been. The positive electrode 16 and the negative electrode 17 have a structure in which the separators 18 are alternately arranged via the separators 18.

  In the positive electrode mixture of the positive electrode 16 and the negative electrode mixture of the negative electrode 17, there are voids 30 in addition to the portions occupied by the active material and the conductive material. On the other hand, since the separator 18 is a polymer microporous film, voids 30 are also present inside the separator 18. The injected electrolyte solution penetrates into these gaps 30. In general, the ratio of the void volume to the total volume is hereinafter referred to as “porosity”.

  Further, as shown in FIG. 2, the gap between the outer peripheral surface of the wound electrode group 8 and the inner peripheral surface of the battery container 1, the periphery of the positive electrode current collector ring 5, the periphery of the negative electrode current collector ring 6, and the interior of the shaft core 7. Etc. also have voids 30, and the electrolyte penetrates into these voids.

As lithium ion secondary batteries capable of high-load charge / discharge (cycle), those having C / V = 0.08 or less are known, where the capacity is C (Ah) and the battery volume is V (cm ³ ). ing. The capacity C is a capacity of 1 CA constant current discharge (voltage 4.1 V to 2.7 V) in an atmosphere of 25 ° C., and the battery volume V is a volume outside the battery container 1. Here, the volume outside the battery case 1 is the volume inside the shell defined by the outer peripheral surface that defines the outer shape of the battery case 1 without including a current takeout terminal or the like.

-Example-
Next, Examples 1 to 8 of the cylindrical lithium ion secondary battery 20 manufactured according to the present embodiment will be described. In addition, it describes together about the lithium ion secondary battery of the comparative example produced in order to demonstrate the effect of this embodiment.

Example 1
As shown in Table 1 of FIG. 4, in Example 1, the positive electrode active material amount M = 47.9 g and the electrolyte solution amount E = 28.7 cm ³ were adjusted to be E / M (electrolyte solution amount / positive electrode active material). The substance ratio was 0.60.

(Example 2 to Example 4)
As shown in Table 1 of FIG. 4, in Examples 2 to 4, the porosity of the positive electrode conductive material 16b and the separator 18 was the same as that of Example 1. However, with respect to the positive electrode active material amount M, the electrolytic solution amount E was sequentially increased, and E / M (electrolytic solution amount / positive electrode active material amount ratio) was changed to 0.65, 0.81, and 0.97. .

(Example 5, Example 6)
As shown in Table 1 of FIG. 4, in Example 5 and Example 6, the E / M and the separator 18 were the same as those in Example 4. However, in Example 5, carbon black having a DBP oil absorption of 100 cc / 100 g was used for the positive electrode conductive material 16 b, and in Example 6, carbon black having a DBP oil absorption of 80 cc / 100 g was used.

(Example 7, Example 8)
As shown in Table 1 of FIG. 4, in Example 7 and Example 8, the materials of E / M, the positive electrode conductive material 16b, and the separator 18 were the same as in Example 4. However, in Example 7, the porosity of the separator 18 was 40%, and in Example 8, the porosity of the separator 18 was 35%.

(Comparative example)
As shown in Table 1 of FIG. 4, in the comparative example, the positive electrode conductive material 16 b, the material of the separator 18, the porosity of the separator 18, and the positive electrode active material amount M were the same as in Example 1. However, the amount of the electrolytic solution was adjusted to 25.9 cm ³ , and E / M (electrolytic solution amount / positive electrode active material amount ratio) was set to 0.54.

-Evaluation test-
A plurality of cylindrical lithium ion secondary batteries of Examples 1 to 8 and Comparative Examples as described above were produced, and a charge / discharge test as described below was performed, and the discharge capacities before and after the high duty cycle test were measured. .

  In the charge / discharge test, first, the “initial discharge capacity” was measured, the “high load cycle test” was performed, and then the “discharge capacity after the high load sile test” was measured.

[Measurement of initial discharge capacity]
In the measurement of the initial discharge capacity, the charging condition is an atmosphere 25 ± 2 ° C., the applied voltage is 4.1 V constant voltage, the limiting current is 5 A, the charging time is 2.5 hours, and the discharging condition is 5 A (1 CA) constant current, The initial discharge capacity (Ah) was measured with a final voltage of 2.7 V.

[High duty cycle test]
In the high duty cycle test, each battery was charged and discharged with a constant current of 50 A (10 CA) in an atmosphere of 50 ± 3 ° C. The end voltage of the high duty cycle test was set to an upper limit of 4.0 V and a lower limit of 3.0 V, and the battery was operated with a state of charge (SOC) of 80% to 20%. Further, charging and discharging in a high duty cycle test, and no pause between discharging and charging were assumed. This high duty cycle test was repeated 2000 times in succession.

[Measurement of discharge capacity after high duty cycle test]
After the high duty cycle test, the discharge capacity after the test is measured in the same manner as the initial discharge capacity, and the capacity retention rate (%) obtained by dividing the discharge capacity after the high duty cycle test by the initial discharge capacity as shown in Equation 1 The battery performance was calculated and evaluated.
Capacity retention rate (%) = discharge capacity after high duty cycle test / initial discharge capacity (1)

[Evaluation of Examples 1 to 4]
As shown in Table 2 of FIG. 5, in the batteries of Examples 1 to 4 in which E / M (amount of electrolytic solution / amount of positive electrode active material) was 0.60 to 0.97, It can be seen that the battery has a capacity retention rate of 90% or more and has an excellent long life.

  On the other hand, in the battery of the comparative example in which the electrolyte solution amount / positive electrode active material amount ratio E / M is 0.54, the capacity retention rate after the high duty cycle test is 80%, and sufficient performance is ensured. I could not.

  In FIG. 6, the horizontal axis is E / M (electrolyte amount / positive electrode active material amount), the vertical axis is the capacity retention rate after the cycle test, and the results of Examples 1 to 4 are plotted as E1 to E4, and Comparative Example. The results are shown as a C plot. As is apparent from FIG. 6, when E / M (ratio of electrolyte amount / positive electrode active material ratio) is 0.6 or more, the capacity retention rate after a high duty cycle test becomes a long life of 90% or more, and E / M The amount of change in the capacity retention rate with respect to the change in the battery was small, and an excellent battery was obtained. On the other hand, when EM (electrolyte solution amount / positive electrode active material amount ratio) is smaller than 0.6, the capacity retention rate after the high duty cycle test is rapidly reduced.

Therefore, if E / M (amount of electrolytic solution / amount of positive electrode active material) is 0.6 or more, a decrease in capacity is suppressed with respect to a high duty cycle, and further, capacity maintenance after a cycle test associated with a change in liquid volume is maintained. Excellent battery with little change in rate.
In FIG. 6, E / M = 0.6 is indicated by a vertical broken line, and an area where E / M> 0.6 is indicated by a white arrow.

[Evaluation of Example 5 and Example 6]
In the battery of Example 5 using carbon black having a DBP oil absorption of 100 cc / 100 g as the positive electrode conductive material 16b, as shown in Table 2 of FIG. 5, the capacity retention rate after the high duty cycle is 90%. In the battery of Example 6 using carbon black having a DBP oil absorption of 80 cc / 100 g, the capacity retention rate after high duty cycle is 88%. Although both of these capacity retention rates can be evaluated as being excellent, it is generally known that the capacity retention rate decreases when the positive electrode conductive material 16b having a small DBP oil absorption amount is used, so a capacity retention rate of about 90% is realized. In order to achieve this, the DBP oil absorption is preferably 100 cc / 100 g or more.

[Evaluation of Example 7 and Example 8]
In Example 7, the porosity of the separator 18 was 40%, and in Example 8, the porosity of the separator 18 was 35%. In Example 7, the capacity maintenance rate after the high duty cycle test is 90%, and in Example 8, the capacity maintenance rate after the high duty cycle test is 88%. Although both of these capacity retention rates can be evaluated as being excellent, it is generally known that the capacity retention rate decreases when the porosity is small. Therefore, the porosity of the separator is preferably 40% or more.

Here, the mechanism of non-uniform lithium ion in the lithium ion secondary battery will be described.
FIG. 7A shows that the lithium ion concentration between the positive and negative electrodes before the high duty cycle is uniform. When charging and discharging are repeated, lithium ions are released from the positive and negative electrodes at a higher rate than the rate of lithium ions migrating in the electrolytic solution. As a result, as shown in FIG. 7B, the lithium ion concentration around the positive and negative electrodes gradually increases, and the migration of lithium ions is significantly hindered by the concentration potential.

(Capacity maintenance rate after high duty cycle)
Cycle characteristics can be improved by adding an excessive amount of electrolyte, that is, by increasing the ratio E / M of the non-aqueous electrolyte amount E and the positive electrode active material amount M. However, the battery weight increases as the amount of electrolyte increases, and the energy per unit weight (energy density) decreases. Therefore, when evaluating the "capacity maintenance ratio after a high duty cycle", a lithium ion secondary battery It is necessary to evaluate the energy density.

(Capacity maintenance rate / energy density index)
Therefore, the inventor evaluates the battery based on a new index (capacity maintenance ratio / energy density index) obtained by multiplying capacity maintenance ratio after high duty cycle test × energy density [% · Wh / kg]. It was.

  The horizontal axis in FIG. 8 is E / M (amount of electrolytic solution / amount of positive electrode active material), and the vertical axis is the capacity retention ratio / energy density index. E1 to E4 in FIG. 8 show the results of Examples 1 to 4, and C shows the results of the comparative example. As is apparent from FIG. 8, when E / M is smaller than 0.6, the capacity retention ratio / energy density index is lowered, but conversely, E / M (electrolyte amount / positive electrode active material amount) is from 0.6. As it increases, the capacity retention ratio / energy density index once rises, but then decreases again.

Empirically, as a high performance lithium ion secondary battery, it is desirable that the capacity maintenance rate after a high duty cycle test is 90% or more and the energy density is 60 Wh / kg or more. In order to put it to practical use, the capacity retention ratio / energy density index should be 5400% · Wh / kg or more. For a range satisfying this condition, refer to FIG.
0.6 ≦ E / M ≦ 1.0 (2)
It turns out that it is.

As described above, in the lithium ion secondary battery of the embodiment, the positive electrode 16 using the lithium transition metal composite oxide as the positive electrode active material and the carbon material capable of inserting and removing lithium ions by charging and discharging are used as the negative electrode active material. The electrode group 8 in which the negative electrode 17 used is disposed via the separator 18 is infiltrated into the nonaqueous electrolyte solution and accommodated in the battery container 1, and the capacity C (Ah) and the battery volume V ( cm ³ ) is C / V = 0.08 or less, and the relationship between the positive electrode active material amount M (g) and the non-aqueous electrolyte amount E (cm ³ ) is E / M = 0.6 or more and 1.0. It was made to become. As a result, a lithium ion secondary battery having a high energy density and a good capacity retention rate can be provided.

[Modification]
The present invention can be carried out by modifying the above-described embodiment as follows.
(1) In the present embodiment, the cylindrical battery is exemplified, but the present invention is not limited to the shape of the battery, and can be applied to a rectangular battery and other polygonal batteries.
For example, even in a flat wound electrode group in which a positive electrode and a negative electrode having active material mixture formed on both surfaces of a metal foil and a separator that insulates the positive electrode and the negative electrode are overlapped and wound into a flat shape Good.

(2) The structure to which the present invention can be applied may be other than a battery having a structure in which a battery lid is sealed with a caulking to the battery container described above. As an example of such a structure, a battery in a state where positive and negative external terminals penetrate the battery lid and the positive and negative external terminals are pressed against each other via an axis in the battery container can be mentioned.

(3) The present invention can also be applied to a lithium secondary battery in which the positive electrode and the negative electrode are not stacked but have a stacked structure. The stacked electrode group is formed by insulating and laminating a positive electrode and a negative electrode, each formed in a sheet shape, via a sheet-like separator. Such a laminated electrode group is obtained by stacking a rectangular sheet-like positive electrode and a negative electrode in which an active material mixture is formed on both surfaces of a metal foil, and a rectangular sheet-like separator that insulates the positive electrode and the negative electrode. .

(4) Although lithium manganate is used as the lithium transition metal composite oxide in this embodiment, the present invention is not limited to this. The positive electrode active material for a lithium ion secondary battery that can be used in other embodiments is a material capable of inserting and removing lithium ions, and a lithium transition metal composite oxide in which a sufficient amount of lithium ions has been inserted in advance. If it is. A material in which a part of lithium or manganese in the crystal is substituted or doped with an element other than these may be used.

(5) In the present embodiment, an example in which amorphous carbon having excellent adhesion to the negative electrode current collector is used as the negative electrode active material as compared with the case where a crystalline carbon material is used. However, natural graphite, artificial graphite materials, carbon materials such as coke, and the like may be used, and the particle shape is not particularly limited, such as scaly, spherical, fibrous, or massive. When such a carbon material is used for the negative electrode active material, it is excellent in flexibility when it is wound in a cross-sectional spiral shape to form an electrode group, and separation and separation of the negative electrode active material layer from the negative electrode can be prevented.

(6) The present invention is not limited to the conductive material and binder (binder) exemplified in the present embodiment, and any commonly used material can be used. Examples of the electrode plate active material binder for lithium secondary batteries that can be used in other embodiments include Teflon (registered trademark), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber, There are polymers such as nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, and mixtures thereof.

(7) In the present embodiment, ethylene carbonate, dimethyl carbonate, the volume of diethyl carbonate ratio of 1: 1: illustrates a non-aqueous electrolyte prepared by dissolving LiPF ₆ in a mixed solvent obtained by mixing 1. However, a non-aqueous electrolyte obtained by using a general lithium salt as an electrolyte and dissolving it 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, etc., or a mixed solvent in which two or more of these are mixed can be used, and the blending 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.

  The embodiments, examples, and modifications described above are examples, and the present invention is not limited to them.

DESCRIPTION OF SYMBOLS 1: Battery container 2: Gasket 3: Cleavage valve 4: Battery cover 5: Positive electrode current collection ring 6: Negative electrode current collection ring 7: Shaft core 8: Winding electrode group 9: Positive electrode lead 12: Positive electrode tab 13: Negative electrode tab 14 : Aluminum foil 15: Rolled copper foil 16: Positive electrode 16a: Positive electrode active material 16b: Positive electrode conductive material 17: Negative electrode 17a: Negative electrode active material 18: Separator 20: Cylindrical lithium ion secondary battery 30: Void

Claims (7)

An electrode group in which a positive electrode using lithium manganate as a positive electrode active material and a negative electrode using a carbon material capable of inserting and removing lithium ions by charge and discharge as a negative electrode active material are disposed via a separator , ethylene carbonate, dimethyl Infiltrating a non-aqueous electrolyte composed of a solution of lithium hexafluorophosphate in a mixed solution containing carbonate and diethyl carbonate, and storing the solution in a battery container;
The relationship between the capacity C (Ah) of the lithium ion secondary battery and the battery volume V (cm3) is C / V = 0.08 or less,
A lithium ion secondary battery, wherein the relationship between the amount of active material M (g) of the positive electrode and the amount of non-aqueous electrolyte E (cm3) is E / M = 0.6 or more and 1.0 or less. The lithium ion secondary battery according to claim 1,
The lithium ion secondary battery, wherein the relationship between the amount of active material M (g) of the positive electrode and the amount of non-aqueous electrolyte E (cm3) is E / M = 0.81 or more and 1.0 or less. The lithium ion secondary battery according to claim 1 or 2 ,
A lithium ion secondary battery, wherein the positive electrode contains a conductive material having a butyl phthalate (DBP) oil absorption of 100 cc / 100 g or more. The lithium ion secondary battery according to any one of claims 1 to 3 ,
A lithium ion secondary battery, wherein the separator has a porosity of 40% or more. The lithium ion secondary battery according to any one of claims 1 to 4 ,
The electrode group includes:
A cylindrical wound electrode group in which a positive electrode and a negative electrode in which an active material mixture is formed on both surfaces of a metal foil and a separator that insulates the positive electrode and the negative electrode are overlapped and wound into a circular shape. Lithium ion secondary battery. The lithium ion secondary battery according to any one of claims 1 to 4 ,
The electrode group includes:
A flat wound electrode group in which a positive electrode and a negative electrode in which an active material mixture is formed on both surfaces of a metal foil and a separator that insulates the positive electrode and the negative electrode are overlapped and wound into a flat shape. Lithium ion secondary battery. The lithium ion secondary battery according to claim 1,
The electrode group includes:
It is a laminated electrode group in which a rectangular sheet-like positive electrode and negative electrode in which an active material mixture is formed on both surfaces of a metal foil, and a rectangular sheet-like separator that insulates the positive electrode and the negative electrode are laminated. Lithium ion secondary battery.

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