JP3131976B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a spirally wound state in which strip-shaped first and second electrodes and strip-shaped first and second separators are alternately stacked. The present invention relates to a non-aqueous electrolyte secondary battery including a spirally wound wound electrode body, wherein a charge and discharge reaction is performed by doping and undoping of lithium in first and second electrodes.

[Summary of the Invention]

The present invention relates to a strip-shaped first and second electrode and a non-aqueous electrolyte secondary battery as described above, wherein at least the first or second
By making the amount of active material in the outer layer of one of the electrodes larger than the amount of active material in the inner layer of this electrode, deterioration of the active material and abnormal deposition of the active material on the electrode surface can be prevented. This is to prevent the capacity from being reduced due to repeated charge and discharge of the electrolyte secondary battery.

[Conventional technology]

In recent years, there has been a remarkable increase in the performance and miniaturization of electronic devices such as video cameras and headphone stereos, and there is also a demand for improving the heavy load characteristics and increasing the capacity of secondary batteries that power these electronic devices. It is getting stronger. As a secondary battery, a lead secondary battery or a nickel cadmium battery has been conventionally used.

Furthermore, recently, active development of a non-aqueous electrolyte secondary battery using a material capable of doping and undoping lithium ions, such as lithium metal, a lithium alloy, or a carbon material such as coke or a fired organic material, as a negative electrode material has been actively performed. Have been.

In such a nonaqueous electrolyte secondary battery, a spirally wound electrode body is used to improve the heavy load characteristics. This conventional wound electrode body will be described with reference to FIGS. 4A and 4B.

FIG. 4A shows a strip-shaped negative electrode 1 and a strip-shaped first separator 3a.
(Shown in FIG. 4B), a strip-shaped positive electrode 2 and a strip-shaped second separator 3b (shown in FIG. 4B) are stacked in this order, and a large number of the negative electrodes 1 are spirally arranged so as to be located at the innermost periphery. FIG. 4 is a perspective view of a wound electrode body 40 obtained by winding. No.
FIG. 4B is a partially enlarged cross-sectional view showing a cross-section near the center of the wound electrode body 40.

As shown in FIG. 4B, the negative electrode 1 in the wound electrode body 40
Includes a negative electrode current collector 11 and a negative electrode inner peripheral layer 12 and a negative electrode outer peripheral layer 13 each having a negative electrode active material on the inner peripheral surface and the outer peripheral surface of the current collector 11. The positive electrode 2 includes a positive electrode current collector 21 and the current collector
Positive electrode inner peripheral layer having positive electrode active material on inner and outer peripheral surfaces of 21
22 and a positive electrode outer peripheral layer 23 are provided.

A first separator is interposed between the negative electrode outer layer 13 and the positive electrode inner layer 22, and a second separator is interposed between the negative electrode inner layer 12 and the positive electrode outer layer 23.
Separator is interposed.

The first and second metal current collectors are formed of thin strip-shaped metal foils. Also, the negative electrode inner peripheral layer 12
And the negative electrode outer peripheral layer 13 have substantially the same thickness, and the positive electrode inner peripheral layer 22 and the positive electrode outer layer 23 have substantially the same thickness. Also, separator
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, the current per unit area is small even when a large current flows through the secondary battery. The secondary battery can be used 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.

[Problems to be solved by the invention]

However, the secondary battery including the above-mentioned wound electrode body using the metal foil as the electrode current collector has a problem that the battery capacity is likely to be reduced when the charge / discharge cycle is repeated. Was. This is mainly due to the fact that the active material, which should be deposited or doped uniformly on the electrode surface during the charging of the battery, does not deposit or dope uniformly during repeated charging and discharging, and the electrode surface is abnormally unevenly distributed. (For example, in the form of a 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 knowledge. This will be described with reference to FIG. 4B.

As shown in FIG. 4B, the negative electrode 1 is provided on the innermost circumference thereof, that is, the negative electrode outer peripheral layer 16 and the negative electrode 17
The positive electrode 2 is provided with a positive electrode inner peripheral layer 25 and a positive electrode outer peripheral layer 26 on the first positive electrode 24 in the first round.
It has.

The first outer circumferential layer 16 of the negative electrode and the inner circumferential layer 25 of the first positive electrode face each other with the first separator 3a interposed therebetween, and a charging / discharging reaction is performed between them. 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. 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 the approximate center, respectively, 12 (2
There is no movement of ions between 2) and the outer layer 13 (23).

Here, for example, when focusing on the negative electrode outer peripheral layer 16 in the first cycle and the negative electrode inner peripheral layer 18 in the second cycle, the negative electrode inner peripheral layer 18 is present on the outer circumference for one round as compared with the negative electrode outer layer 16. Therefore, the circumferential length of the charge / discharge reaction becomes longer, and the amount of the negative electrode active material increases. In comparison, the first inner circumferential layer 25 of the positive electrode and the outer circumferential layer of the positive electrode are compared.
There is not much difference between the 26 and the active material. Therefore,
The negative electrode active material in the negative electrode outer peripheral layer 16 and the negative electrode inner peripheral layer 18 opposed to the positive electrode inner peripheral layer 25 and the positive electrode outer peripheral layer 26 having substantially the same positive electrode active material,
Less than 18.

When a fixed amount of charge is performed in the secondary battery including 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 outer material has a smaller negative electrode active material. The load related to charging is heavy in the layer 16, and the load is relatively light in the negative electrode inner peripheral layer 18. This is the second
The same applies between the outer peripheral layer 19 of the negative electrode 17 in the circumference and the inner peripheral layer of the third negative electrode (not shown).
Load becomes relatively heavy.

Therefore, in the wound electrode body 40 shown in FIG. 4B, the load on the negative electrode outer layer 13 is always heavier than that on the negative electrode inner peripheral layer 12, so that the active material is degraded in the negative electrode 1, and the active material is abnormally deposited on the electrode surface. Etc. easily 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.

[Means for solving the problem]

The present invention has been made based on the above-described findings of the present inventors to achieve the above object, and the first and second electrode activities capable of doping and undoping with lithium. Band-shaped first and second electrodes in which a mixture layer containing a substance is formed on both surfaces of a current collector made of a band-shaped metal foil, and band-shaped first and second separators are alternately laminated. By being spirally wound in the state, the first electrode is formed between the outer peripheral layer, which is the mixture layer of the first electrode, and the inner peripheral layer, which is the mixture layer of the second electrode. A winding in which a separator is interposed, and the second separator is interposed between the inner peripheral layer, which is the mixture layer of the first electrode, and the outer peripheral layer, which is the mixture layer of the second electrode. In a nonaqueous electrolyte secondary battery including a rotating electrode body, the outer peripheral layer of the first or second electrode and the second or Each charge-discharge reaction between the said inner layer of one electrode is the first electrode active material and the second
The amount of active material in the outer peripheral layer of at least one of the first and second electrodes is such that the amount of active material in the inner peripheral layer of the electrode is at least one of the first and second electrodes so as to be performed substantially uniformly with the electrode active material. More than the amount.

Further, in order to increase the amount of active material in the outer peripheral layer of the electrode more than that of the inner peripheral layer of the electrode, the thickness of the outer peripheral layer is made larger than that of the inner peripheral layer, or the active material content in the outer peripheral layer is increased. The ratio is made higher than that of the inner peripheral layer.

Note that 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.

[Action]

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 Each charge / discharge reaction is performed so as to face the inner peripheral layer of the first or second electrode located on the outer periphery by one rotation of the first or second electrode having the outer peripheral layer. Then, at least the outer periphery of 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 layer is larger than that of the inner peripheral layer of the electrode, the amount of the active material in the outer peripheral layer of the electrode is smaller than that of the electrode having the outer peripheral layer by one rotation. The amount of the active material in the peripheral layer 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.

〔Example〕

Hereinafter, Examples 1 and 2 of the nonaqueous electrolyte secondary battery according to the present invention will be described with reference to FIGS. 1 to 3C. 4A and 4B are denoted by the same reference numerals, and description thereof will be omitted.

Example 1 In Example 1, the thickness of the negative electrode inner peripheral layer and the negative electrode outer peripheral layer was changed.

FIG. 1 shows a schematic longitudinal section of a non-aqueous electrolyte secondary battery of this example. 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. The negative electrode mixture was dispersed in a solvent N-methylpyrrolidone to form a slurry (paste).

Next, this negative electrode mixture slurry was applied to both sides of a 10 μm-thick strip-shaped copper foil serving as the negative electrode current collector 11 by changing the application amount on one surface and the other surface, followed by drying, and then the roller A belt-shaped negative electrode 1 was formed by compression molding using a press machine. At this time, one of the anode mixture the thickness of the side (corresponding to the thickness t ₁₃ of the negative electrode outer peripheral layer 13 shown in Figure 2A and Figure 3A below) is 84 .mu.m, the other surface of the anode current collector 11 anode mixture the thickness of the 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,
Baking in air at 900 ° C. for 5 hours to obtain LiCoO ₂ , used as a positive electrode active material, 91 parts by weight of LiCoO _2, 6 parts by weight of graphite as a conductive material, and polyvinylidene fluoride (PVDF) as a binder 3 parts by weight were added and mixed to obtain a positive electrode mixture. Then, this positive electrode mixture was dispersed in a solvent N-methylpyrrolidone to obtain a slurry (paste).

Next, this positive electrode mixture slurry is uniformly applied to both sides of a 20 μm-thick strip-shaped aluminum foil as a positive electrode current collector 21, dried, and then compression-molded by a roller press to form a strip-shaped positive electrode 2. Had made. At this time, one side of the positive electrode mixture thickness of the positive electrode current collector 21 (corresponding to the thickness t ₂₃ of the positive electrode outer peripheral layer 23 shown in Figure 2A and Figure 3A below) and the other side positive electrode mixture thickness (corresponding to the thickness t ₂₂ of the positive electrode peripheral layer 22)
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 a thickness of 25 μm
First and second made of microporous polypropylene film
The separators 3a and 3b were laminated in the order of the second separator 3b, the positive electrode 2, the first separator 3a, and the negative electrode 1 to obtain a laminate 31 as shown in FIG. 2A. The spirally wound electrode body 10 was formed by spirally winding the stacked body 31 multiple times on the winding core 33 in the longitudinal direction of the stacked body 31 so that the negative electrode 1 was positioned at the innermost circumference.

A cross section near the center of the wound electrode body 10 is shown in FIG. 3A. The wound electrode body 10 of Figure 3A, as shown in Figure 4B, 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, except for this same Structure.

The sum T of the thickness of the positive electrode 2, the thickness of the negative electrode 1, and the thickness of the first and second separators 3a and 3b in the laminate 31 is as follows.
It was 400 μm. Further, in the laminate 31, the negative electrode 1
The order of lamination of the positive electrode 2 and the positive electrode 2 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 housed in a nickel-plated iron battery can 5 as shown in FIG. Then, in order to collect the current of the positive electrode 2, an aluminum positive electrode lead 9 was attached to the positive electrode 2, led out from the positive electrode 2, and welded to the projection 34 a of the metal safety valve 34. In order to collect the current of the negative electrode 1, a negative electrode lead 8 made of nickel was attached to the negative electrode 1, led out from the negative electrode 1, and welded to the battery can 5. In this battery can 5, 1 mol / mol of lithium hexafluorophosphate / propylene carbonate and 1.2 mol
-Non-aqueous electrolyte obtained by mixing with dimethoxyethane was injected.

Next, a pair of insulating plates 4a and 4b were provided in the battery can 5 so as to face the upper and lower surfaces of the wound electrode body 10, respectively. Further, the battery can 5 is provided with a safety valve 34 which is in close contact with the outer periphery of the battery can 5.
Then, the battery lid 7 was swaged via the insulating sealing gasket 6 to seal the battery can 5. At this time, the lower end of the gasket 6 in FIG. 1 contacts the outer peripheral surface of the insulating plate 4a, and the insulating plate 4a comes into close contact with the upper surface of the spirally wound electrode body 10.

As described above, a cylindrical nonaqueous electrolyte secondary battery having a diameter of 14 mm and a height of 50 mm was produced. This battery is referred to as battery A for convenience, as shown in Table 1 below.

The cylindrical non-aqueous electrolyte secondary battery has a safety valve 34,
A stripper 36 is provided with an intermediate fitting 35 made of an insulating material for integrating the safety valve 34 and the stripper 36. Although not shown, the safety valve 34 is provided with a cleaving portion which is cleaved when the safety valve 34 is deformed, and the battery cover 7 is provided with a hole. If the voltage internal pressure rises for some reason, the safety valve 34 will
By deforming upward in the figure, the connection between the positive electrode lead 9 and the protruding portion 34a is disconnected, so that the battery current is interrupted, or the gas generated in the battery due to the cleavage of the safety valve 34 being opened is exhausted. Respectively.

Further, the first and second separators 3a and 3b are slightly larger in the length direction and the width direction than the negative electrode 1 and the positive electrode 2, and as shown in FIGS. 1 and 2A, the negative electrode 1 and the positive electrode 2 respectively. Slightly protruding from the end of the.

Further, in the nonaqueous electrolyte secondary battery, as the active material of the negative electrode 1, lithium, a lithium alloy, or a conductive polymer such as polyacetylene as an active material carrier;
A carbon material such as coke can be used, and any of these can be doped with lithium and undoped. On the other hand, manganese dioxide,
A transition metal compound such as vanadium pentoxide, a transition metal chalcogen compound such as iron sulfide, or 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 in an organic solvent (non-aqueous solvent) is used.

Here, the organic solvent is not particularly limited, but for example, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-
A single solvent or a mixture of two or more solvents such as dioxolan, 4-methyl-1,3-dioxysolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile and the like can be used.

Any known electrolyte can be used as the electrolyte. LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , L
There are iCl, LiBr, 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 the negative electrode outer peripheral layer 1
3 of the combination of the thickness t _13, as shown in Table 1 below 6
Cylindrical non-aqueous electrolyte secondary batteries B, C, D, E, F, and K were produced in the same manner as the battery A, except that the above conditions were changed. In addition, the electrodes and thickness of these secondary batteries A to F and K (the laminate
All 31) T were 400 μm.

Next, increase the thickness of the negative electrode 1 and the thickness of the negative electrode inner peripheral layer 12.
The combination of the thickness t ₁₃ of t ₁₂ and the negative electrode outer peripheral layer 13, the following 1
As shown in the table, it was changed to 5 ways,
Thickness t ₂₂ to 105 .mu.m, the thickness t ₂₃ of the positive electrode outer peripheral layer 23 99 .mu.m
Other than the above, cylindrical non-aqueous electrolyte secondary batteries G, H, I, M, and N were produced in the same manner as in Battery A. 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, as a comparative example for confirming the effect of the present invention, the thickness of the thickness t ₁₂ and the negative electrode outer peripheral layer of the battery A and battery negative electrode inner layer 12 in the G except that equal and t _13, the battery a and the battery G in exactly the same manner as the cylindrical nonaqueous electrolyte secondary battery J, and the L respectively were prepared. The battery J has the same configuration as the conventional one.

Note that Δt ₁ , Δt _2, and Δt in the above Table ₁ are values defined as follows.

Each of the 14 types of batteries A to N was charged at a current of 460 mA at an upper limit voltage of 4.1 V for 2 hours, and then charged at 18Ω.
Then, a charge / discharge cycle of discharging to a discharge end voltage of 2.75 V was performed, and the capacity retention was examined.

Table 2 shows the first discharge capacity, the 200th discharge capacity, and the capacity retention obtained from these values.

As shown in Table 2, the batteries A to I have a capacity retention of 85% or more, showing good results.

In addition, the battery L of the comparative example includes the inner peripheral layer 12 and the outer peripheral layer 13 of the negative electrode 1.
Thickness equal with, and because more of the thickness t ₂₂ of the inner circumferential layer 22 of the positive electrode 2 is a thick structure than the thickness t ₂₃ of the outer peripheral layer 23,
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 example having the same configuration as the conventional example.

From the above results, in the case of the wound electrode body 10 shown in FIG. 3A,
For example, paying attention to the first and second rounds of the negative electrode 1, the amounts of the active materials in the negative electrode outer peripheral layer 16 and the negative electrode inner peripheral layer 18 are substantially the same, and the load relating to charging of the active material in the outer peripheral layer 16 is the third.
It is considered that the diameter 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 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 of the present inventors, the ratio of the thickness of the inner layer to the outer layer in one electrode (the above equation (1))
Δt ₁ ), which is the sum of the ratio of the thickness of the inner layer and the outer layer in the other electrode (Δt ₂ shown in the above equation (2)), is preferably 2 ≦ Δt ≦ 0.055 T (4) Here, the unit of T is μm.

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

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

Note that Δt ₁ defined by the above equation (1) is a ratio of the thickness of the outer peripheral layer and the inner peripheral layer with respect to one of the electrodes located at the innermost circumference in the spirally wound electrode body.
Δt ₂ defined by is the ratio of the thickness of the outer peripheral layer to the thickness of the inner peripheral layer with respect to the other electrode not located at the innermost periphery. 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), if the Δt defined by the equation (3) satisfies at least the equation (4), the capacity retention rate of the battery becomes 85. %
It can be seen that Δt is given by the equation (5) and the equation (6).
It can be seen that the capacity retention rate further increases as the condition is satisfied. 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.

Modified Example FIGS. 2B, 2C, 3B and 3C show two examples of modified examples of the first embodiment.

Figure 2B, in the laminate 31 shown in Figure 2A, equal the thickness of the inner circumferential layer 13 and the outer peripheral layer 12 of the negative electrode 1, the inner circumferential layer thickness t ₂₃ of the outer peripheral layer 23 of the positive electrode 2 22 thicker than the thickness t ₂₂ illustrates a laminate 31a which is configured for. FIG. 3B shows such a laminate 3
A wound electrode body 10 obtained in the same manner as in Example 1 using 1a
The cross section near the center of a is shown.

According to the wound electrode body 10a, the outer layer 12 and the inner layer 13 of the negative electrode 1 have the same thickness, but the outer layer 23 of the positive electrode 2 has the same thickness t.
Since ₂₃ is greater than the thickness t ₂₂ of the inner peripheral layer 22, the negative electrode outer peripheral layer 13
The positive electrode active material of the positive electrode outer peripheral layer 23 facing the negative electrode inner peripheral layer 12 located further around the outer periphery of the negative electrode outer peripheral layer 13 is further reduced, and the positive electrode active material of the positive electrode outer peripheral layer 23 facing the negative electrode inner peripheral layer 12 is further increased. .

Therefore, the load related to charging of the negative electrode active material of the negative electrode outer layer 13 is not too heavy as compared with the negative electrode inner peripheral layer 12 which is located one outer circumference of the outer peripheral layer 13. Obtainable.

Next, in FIG. 2C, in the laminate 31 shown in FIG. 2A,
Both the negative electrode 1 and the positive electrode 2 show a laminate 31b in which the outer layer is thicker than the inner layer. FIG. 3C shows a cross section near the center of a wound electrode body 10b obtained in the same manner as in Example 1 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.

Example 2 In Example 2, the content of the negative electrode active material carrier in the negative electrode inner peripheral layer and the negative electrode outer peripheral layer was changed.

The non-aqueous electrolyte secondary battery according to the second embodiment has the same configuration as that shown in FIG.
It can be manufactured in the same manner as described above, 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 support and 13 parts of PVDF as a binder were used.
Parts by weight were mixed to obtain a slurry of the first negative electrode mixture.

Separately, 85 parts by weight of pitch coke and 15 parts by weight of PVDF were mixed to obtain a second slurry of the negative electrode mixture.

One surface of the negative electrode current collector 11 (the wound electrode body 40 shown in FIG. 4B)
The above-mentioned slurry of the first negative electrode mixture was applied to the negative electrode outer peripheral layer 13). Then, the slurry of the second negative electrode mixture was applied to the other surface (the side corresponding to the negative electrode inner peripheral layer 12 in the wound electrode body 40). Subsequently, a strip-shaped negative electrode 1 was obtained through the same steps as in Example 1.

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 is 41.5
The length L was 5 mm and the length L was 270 mm.

Next, the positive electrode 2 obtained in the same manner as in Example 1, in both the positive electrode current collector 21 were equally 80μm and the thickness t ₂₃ and t ₂₂ of both layers. The width of the positive electrode 2 is 40.55 mm,
The length L was 230 mm.

The content of the pitch coke as a negative electrode active material carrier on the outer layer 13 side and the inner layer 12 side of the negative electrode 1 is 1st.
And the mixing ratio (mixing ratio) of the pitch coke in the second negative electrode mixture is as described above, and therefore, each is 87% by weight.
And 85% by weight.

Next, the above-described negative electrode 1 and positive electrode 2 were laminated with the first and second separators 3a and 3b in the order shown in FIG. 2A to obtain a laminate. Thus, a wound electrode body 40 was obtained. In this case, since the thicknesses of the inner layer and the outer layer are equal in both electrodes, 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 Example 1 by using the wound electrode body 40 is referred to as a battery B 'for convenience.

Further, 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 was changed as 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 are referred to as batteries C', D ', and E', respectively.

Also, except that the content of the pitch coke was changed to four in the same manner as in the batteries B ′ to E ′, and the thicknesses of the negative electrode outer peripheral layer 13 and the negative electrode inner peripheral layer 12 were set to 100 μm and 80 μm, respectively.
Non-aqueous electrolyte secondary battery obtained in the same manner as battery B '
As shown in Table 3 below, batteries G ', H',
I 'and J'. The structure of the electrode winding body in this case is
It is substantially the same as that shown in FIG. 3A.

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

Each of the 10 batteries was charged at a current of 460 mA at an upper limit voltage of 4.1 V for 2 hours, and then subjected to 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 rates obtained from these values.

As shown in Table 4 above, batteries B ', C', D ',
H 'and I' have a capacity retention of 85% or more, showing good results.

Further, the battery A 'of Comparative Example 2 having the same configuration as the conventional one has the lowest capacity retention. Since the thickness of the negative electrode outer peripheral layer 13 of the battery F 'is larger than that of the negative electrode inner peripheral layer 12, the battery A'
It is thought to show a higher capacity retention rate.

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 is smaller than that in the inner layer 12. Since the number can be increased, the same effect as in the first embodiment can be obtained.

The same effect can be obtained by making the content ratio of the positive electrode active material in the outer peripheral layer 23 of the positive electrode 2 higher than that in the inner peripheral layer 22. The same effect can be obtained by making the content of the active material or the active material carrier in the outer layer higher than that in the inner layer in both electrodes.

Further, the above results suggest that there is a certain preferable range for the content ratio ( _Xa / _Xb ) of the active material or the active material carrier in the inner peripheral layer and the outer peripheral layer of the electrode.

According to further studies 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 and the content (X _a ) of the active material or the active material carrier in the inner peripheral layer in the electrode are described. a preferred range of _b) the ratio of (X _a / X _b), the It is. 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)
It is.

Further, _a more preferable range of X _a / X _b is: It is.

The electrode may be a negative electrode or a positive electrode.

Considering the results in Tables 3 and 4 from the above equations (7) and (8), the content ratio (X _a / X) of the active material or the active material carrier in the outer layer and the inner layer of the electrode is considered. _b )
If at least equation (7) is satisfied, the battery capacity retention rate is 85
%, And it can be seen that when X _a / X _b further satisfies the expression (8), the capacity retention rate further increases.
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 spirally 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 the non-aqueous electrolyte secondary battery includes a spirally wound electrode body.

〔The invention's effect〕

According to the present invention, in the wound electrode body of the non-aqueous 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, whereby the outer layer of the electrode is formed. In this case, the load on the charge / discharge reaction of the active material can be made approximately the same as that of the inner peripheral layer of the electrode. 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]

1 to 3C show Embodiments 1, 2 and modifications according to the present invention. FIG. 1 shows a cylindrical nonaqueous electrolyte having a wound electrode body shown in FIG. 3A. 2A to 2C show a laminate obtained by laminating a negative electrode, a positive electrode, and first and second separators, and FIG. 2A shows a negative electrode. The thickness of the outer layer of the negative electrode is larger than the thickness of the inner layer of the negative electrode, and the thickness of the outer layer and the inner layer of the positive electrode is equal to each other. FIG. 2C is a side view of a laminated body of a modified example in which the thickness of the outer peripheral layer side is made larger than the thickness of the inner peripheral layer side of the positive electrode and the thickness of the outer peripheral layer side and the inner peripheral layer side of the negative electrode are equal. The negative electrode and the positive electrode are both side views of the laminate of another modified example in which the thickness of the outer layer side is larger than the thickness of the inner layer side, and FIG. 3A is a spiral of the laminate shown in FIG. 2A. Winding 3B is a partial cross-sectional view near the center of the wound electrode body, and FIG. 3B is a partial cross-sectional view near the center of a wound electrode body of a modified example obtained by spirally winding the laminate shown in FIG. 2B. FIG. 3C is a partial cross-sectional view near the center of a spirally wound electrode body of another modified example obtained by spirally winding the laminate shown in FIG. 2C. FIG. 4A is a perspective view of the wound electrode body in the conventional example, the comparative example, and the present example, and FIG. 4B is the thickness of the outer peripheral layer and the inner peripheral layer of each of the conventional example, the comparative example, and the example. FIG. 4 is a partial cross-sectional view near the center of a wound electrode body configured equally. In addition, in the code | symbol used for drawing, 1 ... Negative electrode (1st or 2nd electrode) 2 ... Positive electrode (2nd or 1st electrode) 3a ... 1st separator 3b ... 2nd separator 10 , 10a, 10b, 40 ...... wound electrode body 11 ...... thickness t ₁₃ ...... anode peripheral layer of the negative electrode current collector 12 ...... Fukyokunai peripheral layer 13 ...... anode peripheral layer t ₁₂ ...... Fukyokunai circumferential layer of the thickness of the thickness 21 ...... cathode current collector 22 ...... positive electrode peripheral layer 23 ...... positive peripheral layer t ₂₂ ...... positive electrode peripheral layer thickness t ₂₃ ...... positive peripheral layer of.

Continued on the front page (72) Inventor Kuniyasu Oya 1-1, Shimosugishita, Takakura, Hiwada-cho, Koriyama-shi, Fukushima Prefecture Sony Energy Tech Koriyama Plant (56) References JP-A-2-56871 (JP, A JP-A-2-51875 (JP, A) JP-A-1-279578 (JP, A) JP-A-61-77255 (JP, A) JP-A-63-285878 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01M 10/40 H01M 10/04 H01M 4/02-4/04

Claims (4)

(57) [Claims] 1. A negative electrode mixture layer in which a carbon material is used as an active material carrier capable of doping and undoping lithium, and a transition metal as an electrode active material capable of doping and undoping lithium. A first electrode layer and a second electrode formed on both sides of a current collector formed of a strip-shaped metal foil; and a first strip-shaped electrode formed on both sides of a collector formed of a strip-shaped metal foil. And the second separator are spirally wound in a state of being alternately laminated, and are an outer peripheral layer that is the mixture layer of the first electrode and the mixture layer of the second electrode. The first separator is interposed between the inner layer and the inner layer, and the inner layer that is the mixture layer of the first electrode and the outer layer that is the mixture layer of the second electrode The second separator is interposed therebetween, and at least one of the first and second electrodes Since the thickness of the outer layer of one electrode is greater than the thickness of the inner layer of the electrode, the amount of active material in the outer layer of the one electrode is reduced by the amount of active material in the inner layer of the electrode. In a non-aqueous electrolyte secondary battery including a wound electrode body that is larger than the above, the thickness t ₁₂ of the inner peripheral layer and the thickness t _{13 of the} outer peripheral layer in the first electrode and the second electrode the thickness t ₂₃ of the thickness t ₂₂ and the peripheral layer of the inner peripheral layer, the sum T of the thickness of the first and second electrodes and the first and second separators in the electrode, Delta] t ₁ = ｛(T ₁₃ −t ₁₂ ) / t ₁₂ ｝ × 100 Δt ₂ = ｛(t ₂₃ −t ₂₂ ) / t ₂₂ ｝ × 100 Δt = Δt ₁ + Δt ₂ 2 ≦ Δt ≦ 0.055T Non-aqueous electrolyte secondary battery. 2. The strip-shaped first and second electrodes and the strip-shaped first and second separators are laminated in the order of the second separator, the positive electrode, the first separator, and the negative electrode. 2. The non-woven fabric according to claim 1, wherein the stacked body is spirally wound many times on a winding core in a length direction of the stacked body such that the negative electrode is located at an innermost circumference. 3. Water electrolyte secondary battery. 3. A negative electrode mixture layer in which a carbon material is used as an active material carrier capable of doping and undoping lithium, and a transition metal as an electrode active material capable of doping and undoping lithium. A first electrode layer and a second electrode formed on both sides of a current collector formed of a strip-shaped metal foil; and a first strip-shaped electrode formed on both sides of a collector formed of a strip-shaped metal foil. And the second separator are spirally wound in a state of being alternately laminated, and are an outer peripheral layer that is the mixture layer of the first electrode and the mixture layer of the second electrode. The first separator is interposed between the inner layer and the inner layer, and the inner layer that is the mixture layer of the first electrode and the outer layer that is the mixture layer of the second electrode The second separator is interposed therebetween, and at least one of the first and second electrodes The active material content in the peripheral layer of the square of the electrode is higher than the active material content in the inner peripheral layer of the electrode,
In a nonaqueous electrolyte secondary battery including a wound electrode body in which the amount of active material in the outer peripheral layer of the one electrode is larger than the amount of active material in the inner peripheral layer of the electrode, the ratio between the content of X _b of the electrode active material or the active material support of the electrode active material or the active material carrying member content X _a and the inner peripheral layer of the peripheral layer in the second electrode
X _a / X _b is, the thickness t _b of the lengths of the first and second electrodes L, the thickness of the peripheral layer t _a and the inner peripheral _{layer, (L + 40t a) /} (L-40t b A non-aqueous electrolyte secondary battery characterized by the following relationship: ≦ X _a / X _b ≦ (L + 120 t _a ) / (L−120 t _b ). 4. The strip-shaped first and second electrodes and the strip-shaped first and second separators are laminated in the order of the second separator, the positive electrode, the first separator, and the negative electrode. The non-woven fabric according to claim 3, wherein the stacked body is spirally wound a number of times on a winding core in a length direction of the stacked body such that the negative electrode is located at an innermost circumference. Water electrolyte secondary battery.