JP2000082497A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration of active material and the abnormal precipitation of the active material on a battery surface, to thereby prevent the lower capacity of a nonaqueous electrolyte secondary battery due to repetition of its charging/discharging. SOLUTION: Outer periphery layers 13, 23 of at least one electrode of a negative electrode 1 and a positive electrode 2 are made thicker than inner periphery layers 12, 22 of the electrode, so that charging/discharging reactions between each of the outer periphery layers 13, 23 of the negative electrode 1 or the positive electrode 2 and each of the inner periphery layers 12, 22 of the positive electrode 2 or the negative electrode 1 is almost uniform between these electrode active materials, whereby the amount of the active material on the outer periphery layer 13, 23 also becomes greater than the amount of active material on the inner periphery layers 12, 22. Load on the outer periphery layers 13, 23 of the active material during charging/discharging is reduced nearly to that of the inner periphery layers 12, 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spirally wound electrode formed by spirally winding first and second strip-shaped electrodes and first and second strip-shaped separators alternately. TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery having a body and in which charge and discharge reactions are performed by doping and undoping of lithium in first and second electrodes.

[0002]

2. Description of the Related Art In recent years, there has been a remarkable increase in performance and miniaturization of electronic devices such as video cameras and headphone stereos, and improvement of heavy load characteristics and high capacity of secondary batteries serving as power supplies for these electronic devices have been remarkable. The demand for conversion is also increasing. As a secondary battery, a lead secondary battery or a nickel cadmium battery has been conventionally used.

Further, recently, carbon materials such as lithium metal, lithium alloy, coke, and fired organic materials have been used.
The development of non-aqueous electrolyte secondary batteries using a material capable of doping and undoping lithium ions as a negative electrode material has also been actively conducted. In such a non-aqueous electrolyte secondary battery,
A spirally wound electrode body is used to improve the heavy load characteristics. FIG. 4 shows this conventional wound electrode body.
This will be described with reference to FIG.

FIG. 4A shows a strip-shaped negative electrode 1 and a strip-shaped first electrode.
4a (shown in FIG. 4B) and the strip-shaped positive electrode 2
And a second separator 3b (shown in FIG. 4 (b)) are stacked in this order, and the negative electrode 1 is spirally wound many times so that the negative electrode 1 is located at the innermost periphery. FIG. 3 is a perspective view of an electrode body 40. FIG. 4B is a partially enlarged cross-sectional view showing a cross section near the center of the wound electrode body 40.

[0005] As shown in FIG.
The negative electrode 1 in the above is a negative electrode current collector 11 and this current collector 11
Negative electrode inner peripheral layer 1 having a negative electrode active material on the inner and outer peripheral surfaces of
2 and a negative electrode outer peripheral layer 13. The positive electrode 2 includes a positive electrode current collector 21, and a positive electrode inner peripheral layer 22 and a positive electrode outer peripheral layer 23 each having a positive electrode active material on the inner and outer peripheral surfaces of the current collector 21.

[0006] A first separator 3a is interposed between the negative electrode outer layer 13 and the positive electrode inner layer 22 and a second separator 3b is interposed between the negative electrode inner layer 12 and the positive electrode outer layer 23. . The negative electrode current collector 11 and the positive electrode current collector 21 are formed of a thin band-shaped metal foil. The thickness of the negative electrode inner peripheral layer 12 and the thickness of the negative electrode outer peripheral layer 13 are substantially equal, and the thickness of the positive electrode inner peripheral layer 22 and the positive electrode outer layer 23 are also substantially equal. The separators 3a and 3b are impregnated with a predetermined electrolytic solution.

According to the wound electrode body 40 as described above, since the strip-shaped negative electrode 1 and the strip-shaped positive electrode 2 have relatively large areas, even if a large current flows through the secondary battery, the current per unit area is small. This makes it possible to use this secondary battery under heavy load. Further, as the thickness of the electrode in the wound electrode body is reduced, an electrode having a larger area can be wound, so that the heavy load characteristics of the secondary battery become better. It is desirable to use a thin metal foil for the electrode current collector, and the discharge capacity is not impaired.

[0008]

However, in a secondary battery having the above-mentioned wound electrode body using a metal foil as an electrode current collector, the battery capacity is reduced when the charge / discharge cycle is repeated. There was a problem that it was easy to end up. this is,
Mainly at the time of charging the battery, the active material that should be deposited or doped uniformly on the electrode surface is not uniformly deposited or doped during repeated charging and discharging, and is abnormally biased toward the electrode surface (eg, (In the form of dendrite), which results in deterioration of the electrode.

The present inventors have earnestly studied the abnormal deposition of the active material on the electrode surface as described above, and have obtained the following findings. This will be described with reference to FIG. As shown in FIG. 4B, the negative electrode 1 is provided on the innermost periphery thereof, that is, the negative electrode outer peripheral layer 16 is provided on the negative electrode 14 in the first cycle, the negative electrode inner peripheral layer 18 and the negative electrode outer layer is provided on the negative electrode 17 in the second cycle. 19
The positive electrode 2 includes a positive electrode inner peripheral layer 25 and a positive electrode outer peripheral layer 26 on the positive electrode 24 of the first cycle.

The first outer peripheral layer 16 of the negative electrode and the inner peripheral layer 25 of the first positive electrode are opposed to each other with the first separator 3a interposed therebetween, and a charging / discharging reaction takes place therebetween. Further, the positive electrode outer peripheral layer 26 of the first cycle and the negative electrode inner peripheral layer 18 of the second cycle face each other with the second separator 3b interposed therebetween, and the charge / discharge reaction is performed in the same manner. The charge / discharge reaction takes place between the negative electrode 1 and the positive electrode 2 in this manner. Since both the negative electrode 1 and the positive electrode 2 have the current collectors 11 and 21 at substantially the center thereof, respectively, There is no movement of ions between 12 (22) and outer layer 13 (23).

Here, for example, the negative electrode outer peripheral layer 16 in the first cycle
When attention is paid to the negative electrode inner peripheral layer 18 in the second round, the negative electrode inner peripheral layer 18 is located on the outer circumference for one round as compared with the negative electrode outer peripheral layer 16, and thus has a longer circumferential length for the charge / discharge reaction. Become
More negative electrode active material. On the other hand, there is not much difference regarding the active material between the positive electrode inner peripheral layer 25 and the positive electrode outer peripheral layer 26 in the first round. Accordingly, the negative electrode active materials in the negative electrode outer peripheral layer 16 and the negative electrode inner peripheral layer 18 that face the positive electrode inner peripheral layer 25 and the positive electrode outer peripheral layer 26 having substantially the same positive electrode active material, respectively,
The negative electrode outer peripheral layer 16 is smaller than the negative electrode inner peripheral layer 18.

When a fixed amount of charge is performed in a secondary battery provided with the wound electrode body 40, the same amount of charge is performed in the negative electrode outer peripheral layer 16 and the negative electrode inner peripheral layer 18, but the negative electrode active material is The load related to charging is heavy in the small negative electrode outer peripheral layer 16, and the load is relatively light in the negative electrode inner peripheral layer 18.
This is the same between the outer peripheral layer 19 of the negative electrode 17 in the second cycle and the inner peripheral layer of the negative electrode in the third cycle not shown, and the load on the negative electrode outer layer 19 is relatively heavy. Become.

Therefore, the spirally wound electrode body 40 shown in FIG.
In this case, the load on the negative electrode outer layer 13 is always heavier than that on the negative electrode inner layer 12.
Abnormal deposition or the like of the active material on the electrode surface is likely to occur. An object of the present invention is to prevent a decrease in battery capacity due to a charge / discharge cycle of a nonaqueous electrolyte secondary battery including a wound electrode body.

[0014]

SUMMARY OF THE INVENTION The present invention has been made on the basis of the above-mentioned knowledge of the present inventors to achieve the above-mentioned object, and it is possible to dope and undope lithium. First and second strip-shaped electrodes in which a mixture layer containing first and second electrode active materials is formed on both sides of a current collector made of strip-shaped metal foil; and first and second strip-shaped electrodes. Are spirally wound in a state where the separators are alternately stacked, so that an outer peripheral layer which is the mixture layer of the first electrode and an inner periphery which is the mixture layer of the second electrode. The first separator is interposed between the first electrode and the second electrode, and the first separator is interposed between the inner peripheral layer that is the mixture layer of the first electrode and the outer peripheral layer that is the mixture layer of the second electrode. A non-aqueous electrolyte secondary battery including a wound electrode body with a second separator interposed therebetween; Each charge / discharge reaction between the outer peripheral layer and the inner peripheral layer of the second or first electrode is substantially uniformly performed between the first electrode active material and the second electrode active material. As can be seen, the thickness of the outer layer of at least one of the first and second electrodes is greater than the thickness of the inner layer of the electrode, whereby the amount of active material in the outer layer is reduced. It is characterized by being larger than the amount of active material in the inner peripheral layer.

The first electrode can form a negative electrode or a positive electrode, and the second electrode can form a positive electrode or a negative electrode.

In the above wound electrode body, the outer peripheral layer of the first or second electrode faces the inner peripheral layer of the second or first electrode located on the outer periphery thereof, and the outer peripheral layer of the second or first electrode is The outer peripheral layer is opposed to the inner peripheral layer of the first or second electrode which is located on the outer periphery by one turn of the first or second electrode having the outer peripheral layer, and each charge / discharge reaction is performed.

[0017] At least one of the first and second electrodes so that the reaction between the first electrode active material and the second electrode active material is uniformly performed in each of the charge and discharge reactions. Since the amount of the active material in the outer layer of the electrode is larger than that in the inner layer of the electrode, the amount of the active material in the outer layer of the electrode is located on the outer circumference of the electrode provided with the outer layer by one turn. The amount of the active material in the inner peripheral layer of the electrode does not become too small, and the load on the charge or discharge of the active material in the outer peripheral layer is reduced to about the inner peripheral layer.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a non-aqueous electrolyte secondary battery according to the present invention will be described below with reference to FIGS. The same parts as those of the spirally wound electrode body shown in FIGS. 4A and 4B are denoted by the same reference numerals, and description thereof will be omitted.

Embodiment In this embodiment, the thicknesses of the inner peripheral layer and the outer peripheral layer of the negative electrode are changed. FIG. 1 shows a schematic longitudinal section of the non-aqueous electrolyte secondary battery of the present embodiment. This battery was manufactured as described below. First, the negative electrode 1 was prepared as follows. Using the crushed pitch coke as a negative electrode active material carrier, 90 parts by weight of this pitch coke and 10 parts by weight of polyvinylidene fluoride as a binder were added and mixed to obtain a negative electrode mixture. Then, this negative electrode mixture was dispersed in a solvent N-methylpyrrolidone to form a slurry (a paste form).

Next, the negative electrode mixture slurry is applied to both sides of a 10 μm-thick strip-shaped copper foil as the negative electrode current collector 11 by changing the application amount on one side and the other side, and dried. Thereafter, compression molding was performed by a roller press machine to form a belt-shaped negative electrode 1. At this time, (corresponding to the thickness t ₁₃ of the negative electrode outer peripheral layer 13 shown in below FIG. 2 (a) and FIG. 3 (a)) one surface side of the negative electrode mixture thickness of the negative electrode current collector 11 is 84μm , anode mixture the thickness of the other side (corresponding to the thickness t ₁₂ in the negative electrode peripheral layer 12) is 82 .mu.m, the width of the negative electrode 1 was 41.5 mm.

Next, the positive electrode 2 was prepared as follows.
1 mol of lithium carbonate and 1 mol of cobalt carbonate are mixed, and 9
Calcined in air at 00 ° C. for 5 hours to obtain LiCoO ₂ ,
Using this as a positive electrode active material, 6 parts by weight of graphite as a conductive material and 3 parts by weight of polyvinylidene fluoride (PVDF) as a binder were added to 91 parts by weight of LiCoO ₂ ,
The mixture was mixed to form a positive electrode mixture. Then, this positive electrode mixture is mixed with a solvent N
The resultant was dispersed in monomethylpyrrolidone to form a slurry (a first paste).

Next, this positive electrode material mixture slurry is
Of a 20 μm-thick strip-shaped aluminum foil as the body 21
Apply evenly on both sides, dry, then roller press
A belt-shaped positive electrode 2 was formed by compression molding using a machine. At this time,
The thickness of the positive electrode mixture on one surface of the positive electrode current collector 21 (see FIG.
2 (a) and the thickness t of the positive electrode outer peripheral layer 23 shown in FIG.
_{twenty three}) And the thickness of the positive electrode mixture on the other side (the inner circumference of the positive electrode).
Thickness t of layer 22_{twenty two}77μ)
m, and the width of the positive electrode 2 was 40.5 mm.

The strip-shaped negative electrode 1, the strip-shaped positive electrode 2, and the first and second separators 3a and 3b made of a microporous polypropylene film having a thickness of 25 μm are combined with a second separator 3b, a positive electrode 2, and a first separator. 3a and the negative electrode 1 were laminated in this order to obtain a laminate 31 as shown in FIG.
The wound electrode body 10 was formed by spirally winding the stacked body 31 a number of times on the winding core 33 in the length direction of the stacked body 31 so that the negative electrode 1 was positioned at the innermost periphery.

FIG. 3A shows a cross section near the center of the wound electrode body 10. Wound electrode body 10 in FIG. 3 (a), as shown in FIG. 4 (b), only different and the thickness t ₁₃ of the thickness t ₁₂ and the negative electrode outer peripheral layer 13 in the negative electrode peripheral layer 12, which Other than that, it has the same structure. It should be noted that the positive electrode 2
Thickness, the thickness of the negative electrode 1 and the first and second separators 3
The sum T of the thicknesses a and 3b was 400 μm. Further, the order of lamination of the negative electrode 1 and the positive electrode 2 in the laminate 31 may be changed, and the positive electrode 2 in the wound electrode body 10 may be located at the innermost circumference.

The wound electrode body 10 produced as described above
Was stored in a nickel-plated iron battery can 5 as shown in FIG. Then, an aluminum positive electrode lead 9 is attached to the positive electrode 2 in order to collect the current of the positive electrode 2, and this is led out from the positive electrode 2 to be protruded from the metal safety valve 34.
a. To collect the current of the negative electrode 1, a negative electrode lead 8 made of nickel was attached to the negative electrode 1, and this was connected to the negative electrode 1.
And welded to the battery can 5. A non-aqueous electrolyte obtained by mixing propylene carbonate in which lithium hexafluorophosphate was dissolved at 1 mol / L and 1,2-dimethoxyethane was injected into the battery can 5.

Next, a pair of insulating plates 4a and 4b were disposed in the battery can 5 so as to face the upper and lower surfaces of the wound electrode body 10, respectively. The battery can 5, the safety valve 34 and the battery lid 7, which are in close contact with each other at their outer circumferences, were caulked via an insulating sealing gasket 6 to seal the battery can 5. At this time,
The lower end of the gasket 6 in FIG. 1 is in contact with the outer peripheral surface of the insulating plate 4a, and the insulating plate 4a is in close contact with the upper surface of the spirally wound electrode body 10. As mentioned above, diameter 14mm, height 50mm
Was manufactured. This battery
As shown in Table 1 below, a battery A is used for convenience.

The above cylindrical non-aqueous electrolyte secondary battery is
A safety valve 34, a stripper 36, and an intermediate fitting body 35 made of an insulating material for integrating the safety valve 34 and the stripper 36 are provided. Although not shown, the safety valve 3
4 is provided with a cleaving portion which is cleaved when the safety valve 34 is deformed, and a hole is provided in the battery cover 7. If the internal pressure of the battery rises for some reason, the safety valve 34 is deformed upward in FIG. 1 around the projection 34a, and the connection between the positive electrode lead 9 and the projection 34a is cut off. The configuration is such that the current is interrupted, or the gas generated in the battery due to the cleavage of the safety valve 34 is cleaved.

The first and second separators 3a, 3a
b is slightly larger than the negative electrode 1 and the positive electrode 2 in the length direction and the width direction, and slightly protrudes from the respective ends of the negative electrode 1 and the positive electrode 2 as shown in FIGS.

In the above non-aqueous electrolyte secondary battery,
As an active material of the negative electrode 1, lithium, a lithium alloy, or a conductive polymer such as polyacetylene or a carbon material such as coke as an active material carrier can be used. What you get. On the other hand, as the active material of the positive electrode 2, a transition metal compound such as manganese dioxide and vanadium pentoxide, a transition metal chalcogen compound such as iron sulfide, and a composite compound of a transition metal and lithium can be used.

As the electrolyte, for example, a non-aqueous electrolyte obtained by dissolving a lithium salt as an electrolyte in an organic solvent (non-aqueous solvent) is used. Here, the organic solvent is not particularly limited. For example, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3 dioxolan, and 4-methyl −
A single solvent or a mixed solvent of two or more such as 1,3-dioxysorane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile and the like can be used.

As the electrolyte, any of conventionally known electrolytes can be used, such as LiClO ₄ , LiAsF ₆ , and LiPF.
₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, L
iBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li and the like. Further, as the non-aqueous electrolyte, a conventionally known solid electrolyte can also be used.

Next, the thickness t ₁₂ of the negative electrode inner peripheral layer 12 of the negative electrode 1
And non-aqueous electrolyte secondary batteries B, C, and D in the same manner as Battery A, except that the combinations of the thickness of the negative electrode outer peripheral layer 13 and the thickness t ₁₃ of the negative electrode outer layer 13 were changed to six as shown in Table 1 below. , E, F, K
Was prepared. Note that the thickness (thickness of the laminate 31) T of the electrodes of these secondary batteries A to F and K was all 400 μm.

Next, changing the combination of the thickness t ₁₃ of the thickness t ₁₂ and the negative electrode outer peripheral layer 13 to increase the thickness of the negative electrode 1 and Fukyokunai peripheral layer 12 in five kinds as shown in Table 1 below With
105μm thickness t ₂₂ of the positive electrode peripheral layer 22, the positive electrode peripheral layer 2
Except that the third thickness t ₂₃ in 99μm, said cell A and Similarly cylindrical non-aqueous electrolyte secondary batteries G, H, I, M, N
Was prepared. The thicknesses T of the electrodes of these batteries G, H, I, M, and N were all 500 μm.

Comparative Example 1 As shown in Table 1 below, the effect of the present invention was confirmed.
As a comparative example of the above, in the battery A and the battery G, the negative electrode was used.
The thickness t of the inner peripheral layer 12₁₂And the thickness t of the negative electrode outer peripheral layer 13 ₁₃And
Exactly the same cylinder as Battery A and Battery G except that they were equal
Type non-aqueous electrolyte secondary batteries J and L were produced, respectively. In addition,
Pond J has the same configuration as the conventional one.

[0035]

[Table 1]

Note that Δt ₁ , Δt ₂ and Δt in Table 1 above are values defined as follows. Δt ₁ = {(t ₁₃ −t ₁₂ ) / t ₁₂ } × 100 (1) Δt ₂ = {(t ₂₃ −t ₂₂ ) / t ₂₂ } × 100 (2) Δt = Δt ₁ + Δt ₂ (3)

Each of the 14 types of batteries A to N was charged with a current of 460 mA at an upper limit voltage of 4.1 V for 2 hours, followed by a charge / discharge cycle of discharging at 18 Ω to a discharge end voltage of 2.75 V, thereby retaining capacity. The rates were investigated. Table 2 shows the discharge capacity on the first day, the 200th discharge capacity, and the capacity retention obtained from these values.

[0038]

[Table 2]

As shown in Table 2, the batteries A to I have a capacity retention of 85% or more, showing good results. In the battery L of the comparative example, the thickness of the inner layer 12 of the negative electrode 1 is equal to the thickness of the outer layer 13, and the thickness t ₂₂ of the inner layer 22 of the positive electrode 2 is greater than the thickness t _{23 of the} outer layer 23. Is also thick,
It is considered that the load related to charging of the negative electrode active material of the negative electrode outer peripheral layer 13 is further increased, and the capacity retention is lower than that of the battery J of the comparative embodiment having the same configuration as the conventional one.

From the above results, in the case of the wound electrode body 10 shown in FIG. 3A, for example, focusing on the first and second turns of the negative electrode 1, the negative electrode outer layer 16 and the negative electrode inner layer 18 4A and 4B, the load on the outer layer 16 for charging the active material is reduced as compared with the conventional case shown in FIG. Therefore, the possibility that abnormal precipitation such as dendrite is generated on the surface of the negative electrode 1 is extremely small, and it is considered that the capacity decrease is small. The above results also suggest that there is a certain preferred range for the ratio of the thickness of the inner and outer layers of the electrode.

According to a further study by the present inventors, the ratio of the thickness of the inner layer to the outer layer in one electrode (Δt ₁ shown in the above formula (1)) and the ratio of the inner layer to the The ratio with respect to the thickness of the outer peripheral layer (Δ
The preferred range of Δt, which is the sum of ₂ ) and ₂ ), is 2 ≦ Δt ≦ 0.055T (4). Here, the unit of T is μm.

A more preferable range of Δt is 4 ≦ Δt ≦ 0.048T (5). Further, a more preferable range of Δt is 6 ≦ Δt ≦ 0.040T (6).

Note that Δ defined by the above equation (1)
t ₁ is a ratio related to the thickness of the outer layer and the inner layer with respect to one electrode located at the innermost periphery in the wound electrode body,
Δt ₂ defined by the above equation (2) is a ratio related to the thickness of the outer peripheral layer and the inner peripheral layer with respect to the other electrode not located at the innermost circumference. The one electrode may be either a positive electrode or a negative electrode.

Considering the results in Tables 1 and 2 from the above equations (4) to (6), Δ
It can be seen that when t satisfies at least the expression (4), the capacity retention of the battery becomes 85% or more, and that the capacity retention further increases as Δt satisfies the expressions (5) and (6). . From the above, the capacitance holding is achieved by determining the thicknesses of the inner and outer layers of each electrode in the wound electrode body so that Δt defined by the equation (3) satisfies at least the equation (4). A highly efficient secondary battery can be obtained.

Modifications FIGS. 2 (b), 2 (c), 3 (b) and 3 (c) show two modifications of the present embodiment. FIG. 2B shows the outer peripheral layer 1 of the negative electrode 1 in the laminate 31 shown in FIG.
The thickness of the outer layer 2 of the positive electrode 2 is made equal to the thickness of the inner layer 13.
3 of the thickness t ₂₃ thicker than the thickness t ₂₂ of the inner circumferential layer 22 shows a laminate 31a which is configured. FIG. 3B shows a cross section near the center of the wound electrode body 10a obtained in the same manner as in the embodiment using such a laminate 31a.

According to the spirally wound electrode body 10 a, the outer peripheral layer 12 and the inner peripheral layer 13 of the negative electrode 1 have the same thickness, but the thickness t ₂₃ of the outer peripheral layer 23 of the positive electrode 2 is equal to the thickness of the inner peripheral layer 22. since the thicker than t _22, to the positive electrode active material becomes less and facing the negative electrode in the peripheral layer 12 located further on the outer periphery only one round of the negative electrode outer peripheral layer 13 of the negative electrode outer peripheral layer 13 opposite to the positive electrode peripheral layer 22 The positive electrode active material of the positive electrode outer peripheral layer 23 increases. Therefore, the load related to charging of the negative electrode active material of the negative electrode outer peripheral layer 13 is:
Since it is not too heavy as compared with the negative electrode inner peripheral layer 12 which is located one outer periphery of the outer peripheral layer 13, the same effect as described above can be obtained.

Next, FIG. 2 (c) shows a laminate 31b of the laminate 31 shown in FIG. 2 (a) in which the outer layer is thicker than the inner layer for both the negative electrode 1 and the positive electrode 2. Show.
FIG. 3C shows a cross section near the center of a spirally wound electrode body 10b obtained in the same manner as in the embodiment using such a laminate 31b. In the spirally wound electrode body 10b, the outer layer is formed thicker than the inner layer in both electrodes, so that the same effect as described above can be obtained.

Reference Embodiment In the present embodiment, the content of the negative electrode active material carrier in the negative electrode inner peripheral layer and the negative electrode outer peripheral layer is changed. The nonaqueous electrolyte secondary battery according to the present embodiment has the same configuration as that shown in FIG. 1 and can be manufactured in the same manner as the battery A in the embodiment, and differs in the following points.

To prepare the negative electrode 1, 87 parts by weight of pitch coke as a negative electrode active material carrier and 13 parts by weight of PVDF as a binder were mixed to obtain a slurry of a first negative electrode mixture. Also, 85 parts by weight of pitch coke and PV
15 parts by weight of DF were mixed to obtain a slurry of the second negative electrode mixture.

The slurry of the first negative electrode mixture is applied to one surface of the negative electrode current collector 11 (the side corresponding to the negative electrode outer peripheral layer 13 in the case of the wound electrode body 40 shown in FIG. 4B). did. Then, the other surface (the negative electrode inner peripheral layer 1 in the wound electrode body 40)
2) was coated with the slurry of the second negative electrode mixture. Subsequently, a strip-shaped negative electrode 1 was obtained through the same steps as in the embodiment. In both sides of the negative electrode current collector 11 were equally 80μm and the thickness t ₁₃ and t ₁₂ of both layers. The width of the negative electrode 1 was 41.55 mm and the length L was 270 mm.

Next, a positive electrode 2 is obtained in the same manner as in the embodiment, and the thickness t of both layers is formed on both surfaces of the positive electrode current collector 21.
₂₃ and the t ₂₂ was equally 80 [mu] m. The width of the positive electrode 2 was 40.55 mm, and the length L was 230 mm. The content ratio of the pitch coke as the negative electrode active material carrier on the outer peripheral layer 13 side and the inner peripheral layer 12 side of the negative electrode 1 is determined by the mixing ratio (mixing ratio) of the pitch coke in the first and second negative electrode mixtures. Therefore, they are 87% by weight and 85% by weight, respectively.

Next, the above-mentioned negative electrode 1 and positive electrode 2 are shown in FIG.
The first and second separators 3 in the order shown in FIG.
a and 3b were laminated to obtain a laminate, and a wound electrode body 40 was obtained from this laminate in the same manner as in the embodiment. In this case, since the thicknesses of the inner layer and the outer layer are the same in both electrodes, the structure of the wound electrode body 40 is substantially the same as that shown in FIG. 4B. The cylindrical non-aqueous electrolyte secondary battery obtained in the same manner as in the embodiment using the wound electrode body 40 is referred to as a battery B ′ for convenience.

By changing the mixing ratio of pitch coke in the first and second negative electrode mixtures, the content of pitch coke in the negative electrode outer peripheral layer 13 and the negative electrode inner peripheral layer 12 is shown in Table 3 below. The non-aqueous electrolyte secondary batteries obtained in the same manner as the battery B 'except that the negative electrode 1 was changed in three ways as described above are referred to as batteries C', D ', and E', respectively.

Similarly to the above-mentioned batteries B 'to E', the content of the pitch coke was changed in four ways, and the thickness of the negative electrode outer peripheral layer 13 and the negative electrode inner peripheral layer 12 was set to 100 μm and 80 μm.
The non-aqueous electrolyte secondary batteries obtained in the same manner as the battery B 'except that the thickness was set to μm are referred to as batteries G', H ', I', and J ', respectively, as shown in Table 3 below. The structure of the wound electrode body in this case is substantially the same as that shown in FIG.

Comparative Example 2 As shown in Table 3 below, the content of pitch coke in the outer peripheral layer 13 of the negative electrode and the inner peripheral layer 12 of the negative electrode were made equal (85% by weight), and the respective thicknesses were changed to the batteries B ', The non-aqueous electrolyte secondary batteries obtained in the same manner as the battery B 'except for the battery G' are referred to as batteries A 'and F', respectively, as comparative examples. Battery A 'has the same configuration as the conventional one.

[0056]

[Table 3]

For each of the above 10 types of batteries, 460
The battery was charged at a current of mA at an upper limit voltage of 4.1 V for 2 hours, followed by a charge / discharge cycle of discharging at 18Ω to a discharge end voltage of 2.75 V, and the capacity retention was examined. Table 4 shows the first discharge capacity, the 200th discharge capacity, and the capacity retention obtained from these values.

[0058]

[Table 4]

As shown in Table 4 above, the batteries B ', C',
D ', H', and I 'have a capacity retention of 85% or more, indicating good results. The battery A 'of Comparative Example 2 having the same configuration as the conventional one has the lowest capacity retention. It is considered that the battery F ′ exhibits a higher capacity retention than the battery A ′ because the thickness of the negative electrode outer peripheral layer 13 is thicker than the negative electrode inner peripheral layer 12.

From the above results, by increasing the content of the negative electrode active material carrier in the negative electrode inner peripheral layer 12 and the negative electrode outer layer 13 in the outer layer 13, the amount of active material in the outer layer 13 was reduced. Since the number can be set to more than 12, the same effect as that of the embodiment can be obtained. The content ratio of the positive electrode active material in the outer peripheral layer 23 of the positive electrode 2 was
The same effect can be obtained by setting it higher than 2. Also, by increasing the content of the active material or active material carrier in the outer layer in both electrodes than in the inner layer,
Similar effects can be obtained.

The above results indicate that the content ratio (X _a ) of the active material or the active material carrier in the inner layer and the outer layer of the electrode.
/ X _b ) suggests that there is some preferred range. According to a further study by the present inventors, the content (X _a ) of the active material or the active material carrier in the outer peripheral layer in the electrode is determined.
A preferable range of the ratio of the content of active material or active material carrying member of the inner circumferential layer _{(X b) (X a /} X b) is in the _{electrode, (L + 40t a) /} (L-40t b) ≦ ( X is _{a / X b) ≦ (L} + 120t a) / (L-120t b) (7), where L is the electrode length (mm), t _a is the thickness of the peripheral layer of the electrode (mm) and t _b is the thickness of the inner circumferential layer of the same electrode (mm).

A more preferable range of X _a / X _b is (L + 40 t _a ) / (L−40 t _b ) ≦ (X _a / X _b ) ≦ (L + 80 t _a ) / (L−80 t _b ) (8) It is. The electrode may be a negative electrode or a positive electrode.

Considering the results in Tables 3 and 4 from the above formulas (7) and (8), the content ratio of the active material or the active material carrier (X _a /
X _b) is at least to satisfy the equation (7) capacity retention of the battery was found to be 85% or more, X _a / X _b is further increased capacity retention if further satisfies equation (8) You can see that From the above, the content ratio of the active material or the active material carrier in the outer layer and the inner layer of the electrode in the wound electrode body is determined so that X _a / X _b satisfies at least the expression (7). Thereby, a secondary battery having a good capacity retention can be obtained.

The non-aqueous electrolyte secondary battery according to the present invention may have a shape other than a cylindrical shape, or may be a prismatic shape, as long as it is a non-aqueous electrolyte secondary battery having a spirally wound electrode body. .

[0065]

According to the present invention, in the wound electrode body of the nonaqueous electrolyte secondary battery, the amount of active material in the outer layer of at least one of the electrodes is made larger than that of the inner layer of the electrode. Since the load relating to the charge and discharge reaction of the active material in the outer layer of the electrode can be made comparable to that of the inner layer of the electrode, deterioration of the active material due to repeated charge and discharge and abnormal deposition of the active material on the electrode surface can be prevented. . Therefore, it is possible to prevent a decrease in battery capacity due to a charge / discharge cycle in the nonaqueous electrolyte secondary battery. As a result, a highly reliable nonaqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics and heavy load characteristics can be provided, and its industrial and commercial value is great.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a cylindrical non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

FIGS. 2A and 2B are side views of a laminate obtained by laminating a negative electrode, a positive electrode, and first and second separators, wherein FIG. 2A is a laminate in the embodiment, and FIG. (C) shows a laminate in another variant of the embodiment.

3 is a partial cross-sectional view near the center of a spirally wound electrode body obtained by spirally winding the laminate shown in FIG. 2;
(C) corresponds to FIGS. 2 (a) to (c), respectively.

FIG. 4A is a perspective view of a spirally wound electrode body, and FIG. 4B is a partial cross-sectional view near the center of the spirally wound electrode body in a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Negative electrode (1st or 2nd electrode), 2 ... Positive electrode (2nd or 1st electrode), 3a ... 1st separator, 3b ... 2nd separator, 10, 10a, 10b, 40 ... winding electrode body 11 ... anode current collector, 12 ... Fukyokunai circumferential layer, 13 ... anode peripheral layer, t ₁₂ ... Fukyokunai thickness of circumferential layer, t ₁₃ ... anode peripheral layer thickness of, 21 ... cathode current collector , 22 ... positive electrode peripheral layer, 23 ... cathode peripheral layer, t ₂₂ ... positive electrode of the circumferential layer thickness, the thickness of t ₂₃ ... cathode peripheral layer

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kuniyasu Oya 1-1, Shimosugishita, Takakura, Hiwada-cho, Koriyama-shi, Fukushima Prefecture Inside Sony Energy Tech Koriyama Factory

Claims (3)

[Claims] 1. A strip-shaped first collector in which a mixture layer containing first and second electrode active materials capable of doping and undoping lithium is formed on both surfaces of a current collector made of a strip-shaped metal foil. And the second electrode and the strip-shaped first and second separators are spirally wound in a state of being alternately stacked, so that the outer layer, which is the mixture layer of the first electrode, The first separator is interposed between the second electrode and the inner layer that is the mixture layer, and the inner layer that is the mixture layer of the first electrode and the inner layer that is the second electrode. In a nonaqueous electrolyte secondary battery including a wound electrode body in which the second separator is interposed between the outer peripheral layer that is the mixture layer, the outer peripheral layer of the first or second electrode, Each charge / discharge reaction between the second or first electrode and the inner peripheral layer is caused by the first electrode active material and the second electrode. The thickness of the outer peripheral layer of at least one of the first and second electrodes is larger than the thickness of the inner peripheral layer of this electrode so that the thickness is substantially uniform between the electrode and the polar active material. Thereby, the amount of active material in the outer peripheral layer is larger than the amount of active material in the inner peripheral layer. 2. A negative electrode in which a carbon material is used as an active material carrier capable of doping and undoping lithium, and a positive electrode in which a composite compound of a transition metal and lithium is used as the electrode active material. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the first and second electrodes are the first and second electrodes. Wherein the first thickness of the thickness t ₁₂ and the peripheral layer of the inner peripheral layer of the electrode t ₁₃ and the inner circumferential layer thickness t ₂₂ and the peripheral layer of the above second electrode Thickness t
₂₃ , the first and second electrodes and the first and second electrodes
The sum T of the thickness of the _{separator, Δt 1 = {(t 13} -t 12) / t 12} × 100 Δt 2 = {(t 23 one _{t 22) / t 22} ×} 100 Δt = Δt 1 + Δt 2 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a relationship of 2 ≦ Δt ≦ 0.055T is satisfied.