JP2009259502A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery for aiming at improvement in energy density and input/output characteristics. <P>SOLUTION: The lithium-ion secondary battery includes a wound-around group winding around a cathode plate and an anode plate housed in a battery can. A top lid is fixed in caulking to a top part of the battery can. The cathode plate includes a cathode mixture layer containing lithium transition metal complex oxide of a cathode active material formed on either side of an aluminum foil. The anode plate includes an anode mixture layer containing graphite of an anode active material formed on either side of a copper foil. The cathode mixture layer as well as the anode mixture layer is so formed that each mixture density is changed nearly at a constant ratio in a winding direction from a winding start at a center side to a winding end at an outer periphery side of the wound-around group. With the cathode mixture layer as well as the anode mixture layer, a ratio of the active material gets larger at a part with a larger mixture density, and voids for nonaqueous electrolyte solution to infiltrate into are secured at a part with a smaller mixture density. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to a non-aqueous electrolyte secondary battery including positive and negative electrode plates each coated with an active material mixture on a current collector.

Non-aqueous electrolyte secondary batteries are widely used as power sources for portable devices such as VTR cameras, notebook computers, and mobile phones, and research and development of large batteries for electric vehicles and power storage are also underway. . In a lithium ion secondary battery representing a non-aqueous electrolyte, a positive electrode plate in which an active material mixture containing a lithium-containing metal oxide capable of reversibly occluding and releasing lithium ions is applied to a current collector, and a carbon material And a negative electrode plate coated with an active material mixture containing water infiltrated into a non-aqueous electrolyte solution in which a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ) is dissolved in several types of carbonate-based mixed organic solvents Has been. In order to apply the active material mixture to the current collector, a binder (binder) such as a resin is blended in the active material mixture. In recent years, higher energy density and higher input / output characteristics of lithium ion secondary batteries have been demanded.

  When the weight per unit volume of the active material mixture is increased in order to increase the energy density of the lithium ion secondary battery, voids (hole volume) in the active material mixture decrease and the nonaqueous electrolyte infiltrates. Cannot be obtained sufficiently. In particular, in charge / discharge at a large current value, only a capacity lower than the capacity calculated from the weight of the active material is often obtained. On the other hand, if the weight per unit volume of the active material mixture is reduced in order to obtain sufficient infiltration of the non-aqueous electrolyte, the amount of active material that can be filled in a certain volume decreases, and the battery capacity and energy density decrease. In order to solve these problems, for example, there is a technology that has a bulk density distribution in the thickness direction of a negative electrode plate formed of a carbon material, gains energy density in a high bulk density portion, and supplements input / output characteristics in a low bulk density portion. It is disclosed (see Patent Document 1).

JP-A-8-138650

  However, in the technique of Patent Document 1, a plurality of precursors prepared in advance in a sheet shape are prepared so that the contents of the resin (binder) and the carbon material are different. These precursors are multi-layered so as to have a symmetrical bulk density distribution in the thickness direction, and heat compression molded to produce a negative electrode plate. For this reason, a complicated manufacturing process is required and the cost is increased. In addition, since a plurality of precursors are required, there is a problem that manufacturing process management becomes difficult.

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery capable of improving energy density and input / output characteristics in view of the above-mentioned cases.

  In order to solve the above problems, the present invention provides a non-aqueous electrolyte secondary battery including a positive and negative electrode plate in which an active material mixture is applied to a current collector, and at least one of the positive and negative electrode plates includes: The active material mixture has a density changing portion in which the density of the active material mixture changes from one side in the plane direction to the other side at a substantially constant rate.

  In the present invention, since at least one of the positive and negative electrode plates has a density changing portion in which the density of the active material mixture changes from one side in the plane direction to the other side at a substantially constant rate, the active material ratio is high in the high density portion. The energy density can be increased and the energy density can be improved. In addition, a void infiltrated with the nonaqueous electrolyte can be secured in the low density portion, and the input / output characteristics can be improved.

  In this case, it is preferable that the density of the active material mixture of at least one of the positive and negative electrode plates is changed within a range of ± 15% with respect to the average value. Further, the positive and negative electrode plates may be wound, and at least one of the positive and negative electrode plates may have a density changing portion in a substantially winding direction or a winding axis direction. The density of at least one active material mixture of the positive and negative electrode plates may change at a substantially constant rate from one side in the surface direction of the positive and negative electrode plates to the other side. At this time, at least one of the positive and negative electrode plates may change the coating thickness of the active material mixture at a substantially constant rate from one side in the surface direction to the other side.

  According to the present invention, at least one of the positive and negative electrode plates has a density changing portion in which the density of the active material mixture changes from one side in the plane direction to the other side at a substantially constant rate. The ratio can be increased, the energy density can be improved, and the voids infiltrated with the non-aqueous electrolyte can be secured in the low density portion, and the input / output characteristics can be improved.

  Embodiments of a cylindrical lithium ion secondary battery to which the present invention is applied will be described below with reference to the drawings.

(Constitution)
As shown in FIG. 1, a cylindrical lithium ion secondary battery 20 of the present embodiment has a bottomed cylindrical battery can 17 made of iron plated with nickel and serving as a battery container. The battery can 17 accommodates a wound group 15 in which the belt-like positive electrode plate 1 and the negative electrode plate 3 are wound. That is, the inner diameter of the battery can 17 is set slightly larger than the diameter of the wound group 15.

  In the winding group 15, the positive electrode plate 1 and the negative electrode plate 3 are wound in a spiral shape with a polyethylene microporous membrane separator 5 interposed therebetween. In this example, the thickness of the separator 5 is set to 25 μm. On the upper side of the wound group 15, a ribbon-like positive electrode tab terminal 12 made of aluminum and having one end fixed to the positive electrode plate 1 is led out. The other end of the positive electrode tab terminal 12 is disposed on the upper side of the wound group 15 and is joined to the lower surface of a disk-shaped upper lid 16 serving as a positive electrode external terminal by ultrasonic welding. On the other hand, a ribbon-shaped negative electrode tab terminal 13 made of copper and having one end fixed to the negative electrode plate 3 is led below the winding group 15. The other end of the negative electrode tab terminal 13 is joined to the inner bottom surface of the battery can 17 by resistance welding. The positive electrode tab terminal 12 and the negative electrode tab terminal 13 are led out from the both end surfaces of the wound group 15 to the opposite sides. On both the upper and lower sides of the wound group 15, resin-made insulating plates having a diameter substantially the same as the diameter of the wound group 15 are omitted. An insulation coating (not shown) is applied to the entire outer peripheral surface of the wound group 15.

The battery can 17 has a grooving slightly on the bottom side from the upper end. The upper lid 16 is caulked and fixed to the upper portion of the battery can 17 via a gasket 18 designed to be fitted to the grooving portion with an insulating material such as polypropylene. For this reason, the inside of the lithium ion secondary battery 20 is sealed. Further, a non-aqueous electrolyte is injected into the battery can 17. In the non-aqueous electrolyte, for example, lithium hexafluorophosphate (LiPF ₆ ) is dissolved at a concentration of 1 mol / liter (mol / l) in a mixed solvent in which ethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc. are mixed. The ones used are used.

The positive electrode plate 1 constituting the wound group 15 has an aluminum foil as a positive electrode current collector. The thickness of the aluminum foil is set to 20 μm in this example. One end of the positive electrode tab terminal 12 is joined to the substantially central portion in the longitudinal direction of the aluminum foil by ultrasonic welding. A positive electrode mixture is applied to both surfaces of the aluminum foil, and a positive electrode mixture layer 2 is formed. In the positive electrode mixture, a metal represented by the chemical formula Li _{1 + x} M _1-x O ₂ (M is one or more transition metal elements, x is a real number satisfying a range of 0 <x <1) as a positive electrode active material. An oxide (lithium transition metal double oxide) powder, a carbon material as a conductive agent, and a polyvinylidene fluoride resin (hereinafter abbreviated as PVDF) as a binder (binder) are blended. In this example, the solid content ratio of metal oxide powder / carbon material / PVDF is adjusted to 85/10/5. The positive electrode mixture layer 2 is formed such that the mixture density changes at a substantially constant rate (in the winding direction) from the winding start end positioned on the center side of the winding group 15 to the winding end positioned on the outer peripheral side. ing. In other words, as shown in the pattern A in FIG. 2, the positive electrode mixture layer 2 has a mixture density with respect to a position in the longitudinal direction of the positive electrode plate 1 that changes with a substantially constant gradient from the winding start end to the winding end. Yes. For this reason, the density change part of the positive electrode plate 1 covers the whole winding direction.

The positive electrode plate 1 in which the mixture density of the positive electrode mixture layer 2 is changed is produced as follows. That is, a positive electrode mixture slurry in which the positive electrode mixture was kneaded substantially uniformly with a viscosity adjusting solvent N-methylpyrrolidone (hereinafter abbreviated as NMP) was prepared. The obtained positive electrode mixture slurry is intermittently applied to an aluminum foil of a length necessary for one battery so as to have a uniform thickness (the same amount of mixture is applied per unit area), dried, and pressed. A positive electrode plate was produced. The mixture density is changed by press molding with a roll press for each coating pattern. At this time, the clearance and linear pressure of the roll press are gradually reduced or gradually increased from the winding start end to the winding end (捲A positive electrode plate 1 (after pressing) was obtained in which the thickness was changed at a substantially constant rate (in the rotational direction) (having a thickness gradient). The density of the mixture decreases at a portion where the thickness is large, and increases at a portion where the thickness is small. In this example, mixture density of the thickest portion 2.6 g / cm ^3, mixture density of the thinnest portion was designed to be 3.0 g / cm ^3. In this case, since there is a thickness gradient in the winding direction, the average value (median value) of the mixture density is 2.8 g / cm ³ , which is the middle between the maximum value and the minimum value. Therefore, the mixture density of the positive electrode plate 1 changes in a range of about ± 7.1% with respect to the average value.

  On the other hand, the negative electrode plate 3 has a copper foil as a negative electrode current collector. The thickness of the copper foil is set to 10 μm in this example. A negative electrode mixture is applied to both surfaces of the copper foil, and a negative electrode mixture layer 4 is formed. In the negative electrode mixture, for example, graphite as a negative electrode active material, acetylene black as a conductive agent, and PVDF as a binder are blended. In this example, the solid content weight ratio of graphite / acetylene black / PVDF is adjusted to 90/5/5. A negative electrode tab terminal 13 is joined to the winding terminal side of the negative electrode plate 3 by ultrasonic welding. Similarly to the positive electrode mixture layer 2 in the positive electrode plate 1, the negative electrode mixture layer 4 is a mixture density at a substantially constant rate from the winding start end positioned on the center side of the winding group 15 to the winding end positioned on the outer peripheral side. Is formed to change. That is, in the negative electrode mixture layer 4, the mixture density with respect to the position in the longitudinal direction of the negative electrode plate 3 changes with a substantially constant gradient from the winding start end to the winding end (see pattern A in FIG. 2). For this reason, the density change part of the negative electrode plate 3 covers the whole winding direction.

The negative electrode plate 3 in which the mixture density of the negative electrode mixture layer 4 was changed was produced as follows. That is, a negative electrode mixture slurry in which the negative electrode mixture was kneaded substantially uniformly with NMP was prepared. The obtained negative electrode mixture slurry was intermittently applied to a copper foil having a length required for one battery so that the amount of the mixture applied per unit area was the same, and dried to prepare a negative electrode plate before pressing. . In the same manner as in the production of the positive electrode plate 1, a negative electrode plate 3 (after pressing) whose thickness changes at a substantially constant rate from the winding start end to the winding end (in the winding direction) is obtained. In this example, the mixture density was designed so that the thickest portion was 1.2 g / cm ³ and the thinnest portion was 1.5 g / cm ³ . In this case, the average value of the mixture density is 1.35 g / cm ³ , and the mixture density of the negative electrode plate 3 changes in a range of about ± 11.1% with respect to the average value.

(Battery assembly)
In assembling the lithium ion secondary battery 20, first, the produced positive electrode plate 1 and negative electrode plate 3 are wound around a hollow shaft core via a separator 5 to produce a wound group 15. At this time, the positive electrode mixture layer 2 and the negative electrode mixture layer 4 are arranged so that the portions having a high mixture density face each other, and the positive electrode tab terminal 12 and the negative electrode tab terminal 13 are led out in opposite directions. Turn. The produced wound group 15 is inserted into the battery can 17 with the negative electrode tab terminal 13 facing the bottom of the can. A welding rod is inserted into a hollow portion of the shaft core (a space for mounting on the winding machine shaft core), and the lead-out end portion of the negative electrode tab terminal 13 is resistance-welded to the inner bottom surface of the battery can 17. After the lead-out end portion of the positive electrode tab terminal 12 is welded to the lower surface of the upper lid 16, the moisture adhering to the inside of the battery such as the wound group 15 or the battery can 17 with the gasket 18 attached to the grooving portion of the upper portion of the battery can 17. In order to remove, vacuum drying was performed at 60 ° C. for 20 hours. After vacuum drying, a non-aqueous electrolyte is poured into the battery can 17. The nonaqueous electrolyte solution is injected in a glove box substituted with argon in order to prevent reattachment of moisture. After injecting the non-aqueous electrolyte, the upper lid 16 is caulked and fixed to the top of the battery can 17 to complete the assembly of the lithium ion secondary battery 20.

(Action etc.)
Next, the operation and the like of the lithium ion secondary battery 20 of the present embodiment will be described.

  In the lithium ion secondary battery 20 of the present embodiment, the positive electrode mixture layer 2 and the negative electrode mixture layer 4 both in the positive electrode plate 1 and the negative electrode plate 3 are substantially constant from the winding start end to the winding end (in the winding direction). The mixture density is changed. In the portion where the mixture density is large, the ratio of the positive electrode active material (active material ratio) in the positive electrode mixture layer 2 and the ratio of the negative electrode active material in the negative electrode mixture layer 4 are both large, so that the lithium ion secondary battery An energy density of 20 can be improved. On the other hand, in the portion where the mixture density is small, the positive electrode mixture layer 2 and the negative electrode mixture layer 4 both have voids infiltrated with the non-aqueous electrolyte, thereby improving the input / output characteristics of the lithium ion secondary battery 20. Can be made. Therefore, both high energy density and high input / output characteristics can be achieved.

  Further, if the mixture density is increased too much, voids (pore volume) of the positive electrode mixture layer 2 and the negative electrode mixture layer 4 are reduced, and infiltration of the non-aqueous electrolyte cannot be sufficiently obtained. Invite. On the other hand, if the mixture density is too small, the active material ratio is decreased, which causes a decrease in battery capacity and energy density. In the lithium ion secondary battery 20 of the present embodiment, the density of the active material mixture is adjusted so that both the positive electrode plate 1 and the negative electrode plate 3 change within a range of ± 15% with respect to the average value. For this reason, the infiltration of the non-aqueous electrolyte can be ensured even in a portion where the mixture density is large, and the active material ratio can be secured even in a portion where the mixture density is small. Thereby, energy density and input / output characteristics can be improved simultaneously.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, after the active material mixture is applied to the current collector, the mixture density is changed by continuously changing the clearance and linear pressure of the roll press. The positive electrode plate 1 and the negative electrode plate 3 were produced and used for battery assembly. For this reason, the process and material used for manufacture of a conventional general lithium ion secondary battery can be used. Thereby, it is possible to achieve both high energy density and high input / output characteristics without introducing new processes and materials.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, the mixture density has a density gradient that changes at a substantially constant rate along the winding direction, and the direction parallel to the winding axis (winding direction). In the direction intersecting with the same). For this reason, in the direction parallel to the winding axis, the thicknesses of the positive electrode plate 1 and the negative electrode plate 3 are substantially the same, and a winding gap or a non-uniform gap occurs between the separator 5 and the positive electrode plate 1 or the negative electrode plate 3. And the wound group 15 can be obtained. Thereby, current concentration or the like can be suppressed even during large current charging / discharging, and safety can be ensured by avoiding a short circuit due to heat generation.

  In the present embodiment, the positive electrode mixture layer 2 and the negative electrode mixture layer 4 both show an example in which the mixture density is changed at a substantially constant rate in the winding direction, but the present invention is limited to this. is not. For example, as shown in FIG. 2, the mixture density may be changed as in patterns B, C, and D instead of being changed at a constant rate as in pattern A. That is, in the pattern B, the mixture density is increased at a constant rate on the winding start end side and the winding end side, and is constant in the center portion. In the pattern C, the increase rate of the mixture density on the winding end side is set to be larger than the increase rate of the mixture density on the winding start end side and the central portion. In pattern D, the mixture density is increased at a constant rate on the winding start end side, is constant at the center, and is decreased at a constant rate on the winding end side. Of course, the change in the mixture density may be opposite between the winding start end side and the winding end side, that is, may be decreased at a constant rate from the winding start end side to the winding end side.

  Further, the mixture density may be changed in the winding axis direction instead of changing in the winding direction. The mixture density may be changed in a plurality of directions, for example, both the winding direction and the winding axis direction, and in this case, the gap between the positive and negative electrode plates is designed to be within a level where there is no practical problem. Needless to say, the above-described effects can be obtained.

  Furthermore, in this embodiment, although the example which changes the mixture density over the whole from the winding start end to the winding end end was shown, this invention is not limited to this. It is only necessary to have a portion that changes the mixture density at a substantially constant rate, and it is sufficient that a portion with a large mixture density and a portion with a small mixture density are formed. In the present embodiment, both the positive electrode mixture layer 2 and the negative electrode mixture layer 4 show examples in which the mixture density is changed, but the present invention is not limited to this, and at least the positive electrode plate, the negative electrode layer It is only necessary that one of the plates has a portion where the mixture density is changed.

  Furthermore, in this embodiment, each mixture slurry is intermittently applied to an aluminum foil and a copper foil so as to have a uniform thickness and dried, and then the roll press clearance and linear pressure are changed to change the positive electrode composite. Although the example which changes the mixture density by changing the thickness of the agent layer 2 and the negative electrode mixture layer 4 was shown, this invention is not restrict | limited to this. For example, by changing (gradually increasing or decreasing) the weight of the mixture per unit area, the coating amount changes at a substantially constant rate, and the mixture is pressed (rolled) so that the thickness becomes uniform. The density may be changed. In this way, a positive and negative electrode plate having a portion where the mixture density changes at a constant rate can be produced. In this method, since it is necessary to incorporate a mechanism for changing the coating clearance and the press line pressure both during coating of the mixture and during rolling, the manufacturing method becomes complicated, but the thickness of the positive and negative electrode plates is reduced. Since it can be made substantially constant, handling in the steps after winding can be facilitated.

  Furthermore, in this embodiment, lithium transition metal double oxide was exemplified as the positive electrode active material and graphite was exemplified as the negative electrode active material, but the present invention is not limited to these. Usually, you may use the positive electrode active material and negative electrode active material which are used for a lithium ion secondary battery. Moreover, there is no restriction | limiting also about the electrically conductive agent and binder mix | blended with a positive mix, and a negative mix, and, of course, there is no restriction | limiting in a mixture ratio. The non-aqueous electrolyte is not particularly limited.

  In the present embodiment, the cylindrical lithium ion secondary battery 20 is exemplified, but the present invention is not limited to the battery shape or the internal structure of the battery. For example, it may have a rectangular battery shape, or may have an internal structure in which the positive and negative external terminals penetrate through the battery lid and the positive and negative external terminals are pressed against each other via the shaft core in the battery container. In addition to the lithium ion secondary battery, the present invention does not deny its usefulness in a secondary battery using a non-aqueous electrolyte.

  Next, examples of the lithium ion secondary battery 20 manufactured according to the present embodiment will be described. A comparative example prepared for comparison is also shown.

(Example 1)
In Example 1, the lithium ion secondary battery 20 was produced using the positive electrode plate 1 and the negative electrode plate 3 in which the mixture density was changed at a substantially constant rate from the winding start end to the winding end. Mixture density of the positive electrode mixture layer 2 is the smallest part 2.6 g / cm ^3, was designed to be 3.0 g / cm ³ at the largest portion. Mixture density of the negative electrode mixture layer 4 is the smallest part 1.2 g / cm ^3, was designed to be 1.5 g / cm ³ at the largest portion.

(Comparative Example 1 and Comparative Example 2)
In Comparative Example 1 and Comparative Example 2, a lithium ion secondary battery was fabricated in the same manner as in Example 1 except that positive and negative electrode plates having a substantially uniform thickness were used for both the positive electrode mixture layer and the negative electrode mixture layer. In Comparative Example 1, the thicknesses of the positive electrode mixture layer and the negative electrode mixture layer were set to the thicknesses of the smallest portions of the positive electrode mixture layer 2 and the negative electrode mixture layer 4 in Example 1, respectively. That is, in Comparative Example 1, the mixture density of the positive electrode mixture layer is 3.0 g / cm ³ , and the mixture density of the negative electrode mixture layer is 1.5 g / cm ³ . In Comparative Example 2, the thicknesses of the positive electrode mixture layer and the negative electrode mixture layer were set to the thicknesses of the thickest portions of the positive electrode mixture layer 2 and the negative electrode mixture layer 4 in Example 1, respectively. That is, in Comparative Example 2, the mixture density of the positive electrode mixture layer is 2.6 g / cm ³ , and the mixture density of the negative electrode mixture layer is 1.2 g / cm ³ .

(Evaluation)
The discharge rate dependent characteristics were evaluated for the lithium ion secondary batteries of the examples and comparative examples. That is, after charging each lithium ion secondary battery to 4.2 V at room temperature (25 ° C.), 5 hour rate (0.2 C), 1 hour rate (1 C), 1/3 hour rate (3 C), 1 / The discharge capacity was measured when 3V was discharged as the final voltage at each time rate of 5 hours (5C).

  As shown in FIG. 3, the discharge capacity at a 5-hour rate was 6.7 Ah in Example 1, 7.1 Ah in Comparative Example 1, and 6.3 Ah in Comparative Example 2. In the same active material coating amount, both the positive and negative electrodes have the highest mixture density in Comparative Example 1, the lowest one in Comparative Example 2, and the middle in Example 1. Therefore, from the relationship between the positive and negative electrode thicknesses. If the batteries are designed to have the same wound group diameter, the energy density becomes Comparative Example 1, Example 1, and Comparative Example 2 in descending order, so this result is reasonable. On the other hand, at a discharge rate with a high 1/5 hour rate, the lower the mixture density of the positive and negative electrodes, the better the infiltration of the non-aqueous electrolyte, and the higher the discharge capacity. Therefore, the decrease rate of the discharge capacity by increasing the discharge rate was Comparative Example 2, Example 1, and Comparative Example 1 in ascending order. In such a continuous discharge, the influence of the mixture density appears almost linearly, so that an order appears in the order of the average value of the mixture density.

  The input / output characteristics of the lithium ion secondary batteries of the examples and comparative examples were evaluated. That is, after charging each lithium ion secondary battery with capacity regulation so that it becomes 10% to 90% of the rated capacity at room temperature (25 ° C.), 1 hour rate (1C), 1 / It was discharged for 10 seconds at a 3 hour rate (3C) and a 1/5 hour rate (5C) (after discharging for 10 seconds, the same amount of electricity was charged at an hour rate to correct the SOC so that it does not shift). The voltage at 10 seconds at this time was measured. The voltage at the 10th second was plotted against the discharge current value, and the product of the current and voltage at the intersection when this approximate line was extrapolated to the discharge end voltage was taken as the output value of the battery. Similarly, each SOC was charged at 1 hour rate (1C), 1/3 hour rate (3C), and 1/5 hour rate (5C) for 10 seconds, and the voltage at 10 seconds at this time was measured. The voltage at 10 seconds was plotted against the discharge current value, and the product of the current and voltage at the intersection when this approximate line was extrapolated to the end-of-charge voltage was taken as the input value of the battery. Values obtained by dividing the obtained output value and input value by the weight of the battery were taken as output density and input density, respectively, and plotted against the SOC.

  As shown in FIG. 4, as for the input / output density, the comparative example 2 having a small average value of the mixture density is the most excellent, as in the discharge rate dependence characteristics described above, and then the examples 1 and 1 are obtained. It was. However, the input / output characteristics of Example 1 were close to those of Comparative Example 2. This is because when the discharge is required for a short time with a large current value as in this measurement method, the low-density part of the positive and negative electrode plates where the nonaqueous electrolyte is sufficiently infiltrated is preferentially discharged or charged. It is thought that it contributes to. From the evaluation results of the discharge rate dependency characteristics and the input / output characteristics described above, while using the positive and negative electrode plates having the portion where the mixture density changes as in Example 1, the electric capacity at the time of low load is secured, while the short It has been found that a battery capable of handling a high load can be obtained with time.

  INDUSTRIAL APPLICABILITY Since the present invention provides a non-aqueous electrolyte secondary battery capable of improving energy density and input / output characteristics, it contributes to the manufacture and sale of non-aqueous electrolyte secondary batteries. Have

It is sectional drawing of the cylindrical lithium ion secondary battery of embodiment to which this invention is applied. It is a graph which shows typically the pattern of the change of the mixture density with respect to the position from the winding start end of the positive electrode plate used for the cylindrical lithium ion secondary battery of embodiment, and a negative electrode plate to the winding termination | terminus. It is a graph which shows the discharge rate dependence characteristic of the cylindrical lithium ion secondary battery of Example 1, Comparative Example 1, and Comparative Example 2, and shows the discharge capacity with respect to the discharge rate. It is a graph which shows the input-output characteristic of the cylindrical lithium ion secondary battery of Example 1, Comparative example 1, and Comparative example 2, and shows the input-output density with respect to a charge state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Positive electrode mixture layer 3 Negative electrode plate 4 Negative electrode mixture layer 15 Winding group 20 Cylindrical lithium ion secondary battery (nonaqueous electrolyte secondary battery)

Claims (5)

  In the non-aqueous electrolyte secondary battery including positive and negative electrode plates each coated with an active material mixture on a current collector, at least one of the positive and negative electrode plates has a density of the active material mixture on one side in the plane direction A non-aqueous electrolyte secondary battery having a density changing portion that changes at a substantially constant rate from one side to the other side.   2. The non-aqueous electrolyte secondary battery according to claim 1, wherein at least one of the positive and negative electrode plates has a density of the active material mixture changing in a range of ± 15% with respect to an average value. .   3. The positive and negative electrode plates are wound, and at least one of the positive and negative electrode plates has the density changing portion in a substantially winding direction or a winding axis direction. A nonaqueous electrolyte secondary battery according to 1.   2. The non-aqueous electrolyte according to claim 1, wherein at least one of the positive and negative electrode plates, the density of the active material mixture changes from the one side in the plane direction to the other side at a substantially constant rate. Secondary battery.   5. The non-positive electrode according to claim 4, wherein at least one of the positive and negative electrode plates has a coating thickness of the active material mixture changing at a substantially constant rate from one side in the plane direction to the other side. Water electrolyte secondary battery.

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