JP2506572Y2 - Lithium ion secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a lithium ion secondary battery, and more particularly to the structure of a wound electrode body of the lithium ion secondary battery.

[Outline of device]

The present invention relates to a strip-shaped negative electrode using a carbonaceous material capable of doping and dedoping lithium ions as an active material, and
A band-shaped positive electrode using _x MO ₂ (M represents one kind or more than one kind of transition metals, and 0.05 ≦ x ≦ 1.10) as an active material, and a band-shaped separator are spirally wound. ,
A lithium ion secondary battery comprising a wound electrode body configured such that the separator is interposed between the negative electrode and the positive electrode, wherein the outermost wound portion of the positive electrode further has an outermost wound portion of the negative electrode on the outer circumference. The outer peripheral winding portion is arranged so as to have a protruding portion at its free end portion, and the innermost peripheral winding portion of the negative electrode is further free to the inner periphery of the innermost winding portion of the positive electrode. The positive and negative electrodes are arranged so as to have protruding portions at their ends, and the third and fourth protruding portions protruding from both end portions in the width direction of the positive electrode are provided at both end portions in the width direction of the negative electrode. Li _x MO ₂ constituting the active material
In order for lithium ions to dissociate very well from
Since the carbonaceous material forming the negative electrode active material is extremely well doped with lithium ions, the lithium ions doped in the carbonaceous material are very well dedoped from the carbonaceous material during discharge. , Li _x MO ₂ binds lithium ions very well, so compared to a lithium secondary battery using metallic lithium or a lithium alloy for the negative electrode, the charging and discharging cycle can be made extremely excellent, and moreover, Since the doping amount of lithium ions is less likely to be saturated near the surface of the negative electrode (particularly, the upper and lower end faces and both free end faces) of the wound electrode body of the lithium ion secondary battery, the lithium ions are projected as metallic lithium on these end faces. The lithium metal protruding from these end faces penetrates the separator and contacts the positive electrode. It is possible to extremely effectively prevent the internal short circuit caused by the discharge, and to maximize the discharge capacity. As a result, the charge and discharge cycle characteristics are always excellent, and the high-performance lithium ion with extremely stable usage performance is always available. The secondary battery can be provided.

[Conventional technology]

In recent years, there have been remarkable improvements in the performance and miniaturization of electronic devices such as video cameras and headphone stereos.
At the same time, there is an increasing demand for improving the heavy load characteristics and increasing the capacity of secondary batteries that are the power source of these electronic devices.
As a secondary battery, a lead secondary battery or a nickel-cadmium secondary battery has been conventionally used. Further, recently, a non-aqueous electrolyte secondary battery (lithium ion secondary battery) using a material capable of doping and dedoping lithium ions, such as carbonaceous materials such as coke and organic fired bodies, as a negative electrode.
However, it is attracting attention because it has excellent charge-discharge cycle characteristics as compared with a lithium secondary battery using metallic lithium or a lithium alloy for the negative electrode.

The lithium-ion secondary battery comprises a pair of strip-shaped separators each including a strip-shaped positive electrode made of, for example, a lithium-cobalt composite oxide (LiCoO ₂ ) and a strip-shaped negative electrode made of a carbonaceous material such as coke or a calcined organic material. It has a wound electrode body which is interposed and wound in a spiral shape along its length, and uses a non-aqueous electrolyte as an electrolyte. Then, the secondary battery is first charged and then used when the battery is first manufactured and then used.

[Problems to be solved by the device]

However, the lithium-ion secondary battery as described above has a problem in that the battery is internally short-circuited during repeated charging and discharging, resulting in unstable use performance of the battery. This is mainly because, during charging of the battery, the lithium ions originally to be doped in the negative electrode are projected as metallic lithium on the surface of the negative electrode, and in particular, the end faces in the width direction and the length direction of the negative electrode (upper end surface, This is because at the lower end surface, the inner peripheral side free end surface and the outer peripheral side free end surface, this metallic lithium grows in a dendrite shape, breaks through the separator and contacts the positive electrode, resulting in an internal short circuit. In this way, metallic lithium grows like a dendrite.
During charging of the battery, lithium ions are easily collected on the end faces in the width direction and the length direction of the negative electrode, and the doping amount of lithium ions is saturated at these end faces,
It is considered that this is because lithium ions are projected as metallic lithium.

Further, the above-mentioned lithium ion secondary battery has a drawback that the discharge capacity is smaller than that of a lithium secondary battery using metallic lithium or a lithium alloy for the negative electrode. this is,
This is because, as described above, metallic lithium protruding on the surface of the negative electrode has poor reactivity and acts to hinder the charging / discharging reaction of the battery, so that the charging / discharging capacity of the battery becomes small.

An object of the present invention is to provide a lithium-ion secondary battery in which metallic lithium is prevented from protruding on the surface of a negative electrode to prevent an internal short circuit of the battery and to increase the discharge capacity. .

[Means for solving the problem]

The present invention to achieve the above object is to provide a strip-shaped negative electrode using a carbonaceous material capable of doping and dedoping lithium ions as an active material, and Li _x MO ₂ (M is one kind or more than one kind). A band-shaped positive electrode using a transition metal, which is 0.05 ≦ x ≦ 1.10) as an active material, and a band-shaped separator are spirally wound along the length direction to form the negative electrode and the positive electrode. In a lithium ion secondary battery comprising a wound electrode body configured such that the separator is interposed between, the outermost wound portion of the negative electrode is further wound around the outermost wound portion of the positive electrode. A first protruding portion protruding from the free end of the outermost winding portion of the positive electrode is provided at the free end of the outermost winding portion of the negative electrode, and the innermost winding of the positive electrode is wound. The innermost wound portion of the negative electrode is further wound on the inner circumference. And a second protruding portion protruding from the free end of the innermost winding portion of the positive electrode is provided at the free end of the innermost winding portion of the negative electrode, and both ends of the negative electrode in the width direction are provided. The third and fourth protruding portions protruding from both ends in the width direction of the positive electrode are provided in the portion.

The negative electrode is preferably porous, and as the active material thereof, a carbonaceous material such as coke which can be doped with lithium ions and dedoped, a fired body of an organic substance, or the like is used. The positive electrode is preferably porous, and the active material thereof can be represented by Li _x MO ₂ (M represents one kind or more than one kind of transition metal, and 0.05 ≦ x ≦ 1.10). The material is not particularly limited as long as it is a lithium-cobalt composite oxide (LiCoO ₂ ).

As the non-aqueous electrolyte used in the lithium ion secondary battery of the present invention, for example, a non-aqueous electrolyte prepared by dissolving a lithium salt as an electrolyte in an organic solvent (non-aqueous solvent) can be used. Here, as the organic solvent, for example, propylene carbonate, ethylene carbonate,
1,2-dimethoxyethane, 1,2-diethoxyethane, γ-
Butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile and the like may be used alone or in combination of two or more. As the electrolyte, any of the conventionally known ones can be used, and specifically, LiCIO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB.
_{(C 6 H 5) 4,} LiCI, LiBr, CH 3 SO 3 Li, or the like can be used CF ₃ SC ₃ Li.

[Action]

Since the lithium ion secondary battery of the present invention has the outermost and innermost windings of the positive electrode, the outermost and innermost windings of the negative electrode are respectively disposed on the outermost and innermost windings of the positive electrode. Is one more than the number of windings of the positive electrode, and the outermost and innermost windings of the negative electrode and both ends in the width direction are provided with protruding portions protruding from the positive electrode. Therefore, the amount of the lithium ion doped in the negative electrode (the negative electrode lithium ion capacity) increases, and in particular,
It is possible to increase the lithium ion capacity of the negative electrode on the end faces in the width direction and the length direction of the negative electrode where lithium ions are easily broken out.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 4 shows a schematic vertical cross section of the lithium ion secondary battery of this example, which was prepared as described below.

First, the positive electrode 1 was prepared as follows. 0.5 mol of lithium carbonate and 1 mol of cobalt carbonate were mixed and fired in air at 900 ° C. for 5 hours to obtain LiCoO ₂ . Using this as a positive electrode active material, 91 parts by weight of LiCoO ₂ was mixed with 6 parts by weight of graphite as a conductive material and 3 parts by weight of polyvinylidene fluoride as a binder to obtain a positive electrode mixture. This positive electrode mixture was dispersed in a solvent N-methylpyrrolidone to form a slurry (paste form). Next, this positive electrode mixture slurry was uniformly applied to both surfaces of a strip-shaped aluminum foil having a thickness of, for example, 20 μm as a positive electrode current collector and dried. After drying, it is compression molded by a roller press machine and the width W ₁
A strip positive electrode 1 having a length of 34 mm and a length L ₁ of 239 mm was prepared. In this strip-shaped positive electrode 1, the positive electrode active material was formed on both surfaces of the positive electrode current collector to have substantially the same film thickness, and the sum of these film thicknesses was about 175 μm.

Next, the negative electrode 2 was prepared as follows. Using crushed pitch coke as the negative electrode active material, 90 parts by weight of this pitch coke and polyvinylidene fluoride 10 as a binder were used.
By mixing with parts by weight, a negative electrode mixture was obtained. This negative electrode mixture was dispersed in a solvent N-methylpyrrolidone to form a slurry (paste form). Next, this negative electrode mixture slurry was uniformly applied to both surfaces of a strip-shaped copper foil having a thickness of, for example, 10 μm as a negative electrode current collector, and dried. After drying, compression molding with a roller press machine, width W ₂ is 35 mm, length L ₂ is 290 mm
The strip | belt-shaped negative electrode 2 of was produced. In this strip-shaped negative electrode 2, the negative electrode active material was formed on both surfaces of the negative electrode current collector to have substantially the same film thickness, and the sum of these film thicknesses was about 175 μm.

FIG. 1 is an enlarged cross-sectional view of the spirally wound electrode body 12 used in the lithium-ion secondary battery shown in FIG. 4. In this case, the separators 3a and 3b described later are not cross-sectioned. 2 and 3 show a laminated electrode body 15 for producing the spirally wound electrode body 12 shown in FIG. By using the strip-shaped positive electrode 1 and the strip-shaped negative electrode 2, and further using a pair of strip-shaped separators 3a and 3b made of a microporous polypropylene film having a thickness of 25 μm, these were laminated together to obtain the laminated electrode body 15. next,
A spirally wound electrode body 12 shown in FIG. 1 was produced by spirally winding the laminated electrode body 15 along its length.

That is, as shown in FIG. 2, the laminated electrode body 15 includes the strip positive electrode 1, the strip negative electrode 2, and the strip separator 3a described above.
3b was obtained by laminating the separator 3a, the negative electrode 2, the separator 3b, and the positive electrode 1 in this order. In this case, as shown in FIG.
A material having a size larger by ΔW and longer than the positive electrode 1 by (l + a + b) in the length direction was used.

Here, ΔW means the width of each of the protruding portions 31 and 32 in the spirally wound electrode body 12 in which both ends in the width direction of the negative electrode 2 protrude from both ends in the width direction of the positive electrode.
It is 0.5 mm. Therefore, ΔW is the width W ₂ of the negative electrode ₂ and the positive electrode 1
Can be expressed as a value (= (W ₂ −W ₁ ) / 2) which is half the difference from the width W _{1 of}

In addition, 1 is the innermost wound portion 17 of the negative electrode 2 in the innermost wound portion 17 of the positive electrode 1 in the wound electrode body 12.
And the outermost winding portion 20 of the negative electrode 2 is arranged further outside the outermost winding portion 19 of the positive electrode 1, and the length is additionally required for the negative electrode 2. If only the above l is provided, the protruding portions 23 and 24 are not generated, the inner peripheral side free end surfaces 29 and 21 of the positive electrode 1 and the negative electrode 2 are radially aligned with each other, and the outer peripheral side free end surfaces 28 and 22 are formed. Radially coincide with each other. Therefore, the length a required for the protruding portion 23 and the length b required for the protruding portion 24.
Only, the negative electrode 2 is longer than the positive electrode 1.

Therefore, in the laminated electrode body 15, as shown in FIG. 3, the negative electrode 2 protrudes from the positive electrode 1 by ΔW at both end portions in the width direction, and at the inner peripheral free end portion by aW. Only protrudes from the outer peripheral side free end portion. In this case, the free end of the laminated electrode body 15 on the inner peripheral surface side is wound from the positive electrode 1 side toward the negative electrode 2 side with the negative electrode 2 inside, and spirally wound. When starting winding from the negative electrode 2 side toward the positive electrode 1 side with 1 as the inside, only (a + l ₁ ) protrudes at the inner peripheral side free end portion and (b + l ₂ ) at the outer peripheral side free end portion. ) Only needs to stick out. However, in this case, l≈l ₁ + l ₂
And l ₁ is substantially equal to the length of the innermost wound portion 18 of the negative electrode 2 (however, one roll over 360 ° excluding the protruding portion 23).

The laminated electrode body 15 as described above is wound around the hollow core 11 from the side of the positive electrode 1 toward the side of the negative electrode 2 with the negative electrode 2 inside, and is spirally wound many times, so that FIG. A wound electrode body 12 shown in was prepared. The widths and lengths of the strip separators 3a and 3b were made larger than those of the strip negative electrode 2. Further, if the above ΔW is less than 0.1 mm, when the above laminated electrode body 15 is wound, there is a risk that ΔW will be close to zero and it will be wound, so ΔW in the laminated electrode body 15 is 0.1 mm. The above is preferable.

The wound electrode body 12 produced as described above has a negative electrode 2 at any of its wound portions, as shown in FIG. 1, on the inner and outer circumferences of the positive electrode 1 via the separator 3a or 3b.
Is a structure that exists. Further, the negative electrode 2 has a protruding portion 23 at the inner peripheral side free end portion, and has a protruding portion 24 at the outer peripheral side free end portion.

Both a and b were 5 mm. Further, the upper and lower ends of the negative electrode 2 of the spirally wound electrode body 12 were respectively formed with protruding portions 31 and 32 protruding from the upper and lower ends of the positive electrode by a width ΔW (0.5 mm in this case).

The spirally wound electrode body 12 produced as described above was housed in a nickel-plated battery outer can 5 having an inner diameter of, for example, 13.3 mm, as shown in FIG. In addition, the positive electrode 1 and the negative electrode 2
In order to collect the current, the positive electrode lead 9 is attached to the positive electrode 1 in advance, this is led out from the positive electrode 1 and welded to the safety valve 8, and the negative electrode lead 10 is similarly attached to the negative electrode 2 in advance, which is then attached to the negative electrode. It was led out from No. 2 and welded to the bottom surface of the battery outer can 5.
Lithium hexafluorophosphate (LiP
A non-aqueous electrolyte obtained by mixing propylene carbonate in which 1 mol / l of F ₆ ) was dissolved with 1,2-dimethoxyethane was injected,
The wound electrode body 12 was impregnated. Before and after this, the wound electrode body 12
Disc-shaped insulating plates 13 and 14 were respectively disposed in the battery outer can 5 so as to face the upper end surface and the lower end surface thereof. Further, the safety valve 8 and the closing lid 7 are overlapped with each other and closely adhered to each other on the outer periphery thereof, and the battery outer can 5 is inserted through the sealing gasket 6.
After caulking, the battery outer can 5 was sealed. The safety valve 8 has a thin groove (not shown) that is cleaved when gas or the like is generated in the battery and the internal pressure of the battery rises above a predetermined value.
Further, the lid 7 is provided with a gas vent hole (not shown) for letting out the gas.

As described above, a cylindrical lithium ion secondary battery having a diameter of, for example, 13.8 mm and a height of, for example, 42 mm was prepared. The battery of this example is referred to as Battery A for convenience, as shown in Table 1 below.

In order to confirm the effect of the present invention, by changing the length L ₁ of the strip-shaped positive electrode 1 in two ways, the protrusion of the negative electrode 2 at the innermost circumference and the outermost circumference of the spirally wound electrode body 12 shown in FIG. As shown in Table 1 below, four combinations of the lengths a and b of the portions 23 and 24 were changed to prepare a wound electrode body 12, and these were used to produce a lithium ion according to an embodiment of the present invention. Secondary batteries B, C, D and E were prepared in the same manner as the above case. Further, a lithium ion secondary battery F in which both a and b are zero was prepared as a comparative example in the same manner as the above case. The wound electrode bodies 12 of these batteries BF are a, b.
The structure was substantially the same as that of the spirally wound electrode body 12 shown in FIGS. 1 and 4, except that the respective values of 1 were different. Further, Table 1 also shows the length (L ₁ , L ₂ ), width (W ₁ , W ₂ ) and ΔW of the strip positive electrode 1 and the strip negative electrode 2.

20 of each of the lithium ion secondary batteries A to F were prepared, and these secondary batteries were charged at a current of 190 mA with an upper limit voltage of 4.1 V for 3 hours, and subsequently, a discharge end voltage of 2.9 was applied at a load of 16 Ω. The charging / discharging cycle of discharging to V was performed for 30 cycles, the battery was charged again under the above conditions, and then left at room temperature for 10 days. As a result, the secondary battery whose circuit voltage has dropped to 3.9 V or less was used as an internal short-circuit product, and the occurrence rate was investigated. The results are shown in Table 1 below.

As can be seen from Table 1 above, in the battery F in which both a and b are zero (the protruding portions 23 and 24 of the negative electrode 2 are not present), a high rate of internal short-circuit products occurred. When disassembling and investigating the battery with the internal short circuit of the battery F,
On the inner peripheral side and outer peripheral side free end surfaces 21 and 22 of the negative electrode 2, metallic lithium was projected in a dendrite shape. And
It was observed that some of the dendrite-like metallic lithium penetrated through the separators 3a and 3b and reached the positive electrode 1. In addition, when disassembling and investigating the battery of the battery F which is not internally short-circuited, metal lithium was dendrite-shaped in the inner and outer free end faces 21 and 22 in the same manner as the above case. Was there. However, the dendrite-shaped metallic lithium did not penetrate the separators 3a and 3b to reach the positive electrode 1.

On the other hand, in the batteries D and E in which one of the a and b was 5 mm and the other was 0.5 mm, some internal short-circuit products occurred, but the internal short-circuit products were at a much lower rate than the battery F. It only happened. When these internal short-circuited products were disassembled and examined in the same manner as in the case described above, dendrite-shaped metallic lithium was projected at the inner and outer free end faces 21 and 22, and a part of the positive electrode 2 Was observed to have reached.

In addition, batteries A, B, and C in which both a and b are 1 mm or more
Then, the internal short-circuited product did not occur at all. When these batteries were disassembled and investigated, no dendrite-like metallic lithium was found on the surface of the negative electrode 2.

Next, by changing the widths W ₁ and W ₂ of the strip positive electrode 1 and the strip negative electrode 2 as shown in Table 2 below, the above ΔW
The wound electrode body 12 shown in FIG. 1 and FIG.
It was created. Using these wound electrode bodies 12, lithium ion secondary batteries G, H, I, J, K and L were prepared in the same manner as in the above case. All of the above a were 5 mm, and all the above b were 3 mm. In this case, the batteries G, H, I and J in which ΔW is a positive value are the embodiments of the present invention, and
The batteries K and L in which ΔW is zero or a negative value are comparative examples of the present invention.

20 lithium ion secondary batteries G to L were prepared, and the secondary battery was subjected to a charge / discharge cycle under the same conditions as in Table 1 to determine the occurrence rate of internal short-circuited batteries. investigated. The results are shown in Table 2 below. The discharge capacity is stable in the charge / discharge cycle.
The discharge capacity of each battery at the 10th cycle was measured, and the relationship between the discharge capacity and ΔW, which is the width of the protruding portions 31 and 32, is shown in FIG.

As can be seen from Table 2 above, in the battery K in which ΔW is zero (the widths of the negative electrode 2 and the positive electrode 1 are the same), some internally short-circuited products were generated, but in the batteries G to J in which ΔW was 0.1 mm or more. Then, the internal short-circuited product did not occur at all. Also, ΔW is −
In the battery L having a width of 1 mm (the width of the negative electrode 2 is shorter than the width of the positive electrode 1 by 1 mm at the upper and lower ends of the negative electrode 2), the internal short-circuit product occurred at a higher rate than that of the battery K.

Further, as can be seen from FIG. 5, the batteries G to J according to the embodiment of the present invention having ΔW of 0.1 mm or more (the protruding portions 31 and 32 of the negative electrode 2 are 0.1 mm or more) of the present invention are not. The discharge capacity was considerably larger than the batteries K and L according to the comparative example. However, when ΔW becomes large,
The discharge capacity gradually decreased.

As a result of disassembling and investigating these batteries G to L, metallic lithium was observed on the upper end surface 26 and the lower end surface 27 of the negative electrode 2 in the batteries K and L, and in particular, in the battery L, metallic lithium was extruded in a dendrite shape. Was recognized. In addition, the batteries K and L internally short-circuited have the upper end surface 26 of the negative electrode 2
At the lower end surface 27, dendrite-shaped metallic lithium may break through the separators 3a and 3b, or the separator 3
It reached the positive electrode 1 by overcoming the ends of a and 3b. In the batteries G to J, the upper end surface 26 and the lower end surface of the negative electrode 2 are
At 27, no metallic lithium was observed.

As described above, the outermost and innermost winding portions of the positive electrode 1
Since the outermost and innermost winding portions 20 and 18 of the negative electrode 2 are respectively arranged on the outer and inner circumferences of 19 and 17, the number of windings of the negative electrode 2 is one more than that of the positive electrode, and , Negative electrode 2
The outermost and innermost winding portions 20 and 18 and the widthwise end portions of the positive electrode 1 have protruding portions 24 and 23 and
31 and 32 are provided respectively. Therefore, the amount of lithium ions doped into the negative electrode (lithium ion capacity of the negative electrode) can be increased, so that the lithium ions are easily doped from the positive electrode 1 to the negative electrode 2 when the battery is charged. For this reason, the surface of the negative electrode 2,
Especially near the upper and lower end faces 26, 27 and the free end faces 21, 22,
Since the doping amount of lithium ions is less likely to be saturated, it is possible to prevent lithium ions from protruding as metallic lithium on these end faces.

In addition, since metallic lithium having poor reactivity does not stick out to the surface of the negative electrode, the charge / discharge reaction of the battery is not hindered, and the discharge capacity of the battery can be increased as shown in FIG.

The lengths a and b of the protruding portions 23 and 24 at the inner and outer free ends of the negative electrode 2 are preferably 0.5 mm or more in order to effectively prevent an internal short circuit of the battery. Further, it is more preferable that it is 1 mm or more.

In addition, the protruding portions 31, 32 at the upper and lower ends of the negative electrode 2
The width ΔW of each is 0.1 m in order to effectively prevent the internal short circuit of the battery and to obtain a relatively large discharge capacity.
It is preferably m or more and 2 mm or less. In addition, ΔW is 2 mm
If it is made larger than the above, a useless portion of the negative electrode 2 that does not face the positive electrode 1 and does not participate in the charge / discharge reaction (the protruding portion 31,
32) becomes too much and the discharge capacity also decreases,
Not very good.

As described above, the wound electrode body of the lithium ion secondary battery
12 has the structure shown in FIGS. 1 and 4, and a and b
Is 0.5 mm or more, preferably 1 mm or more, and ΔW is 0.
When the thickness is in the range of 1 to 2 mm, metallic lithium does not protrude at the upper and lower end surfaces 26, 27 and the free end surfaces 21, 22 of the negative electrode 2,
It is possible to prevent an internal short circuit of the battery caused by the dendrite-shaped metallic lithium reaching the positive electrode 1 and the negative electrode 2 coming into contact with the positive electrode 1, and it is possible to increase the discharge capacity.

In addition, in the present invention, the shape of the battery does not necessarily have to be a cylindrical shape, and may be a rectangular tube shape or the like. Also,
The non-aqueous electrolyte may be a solid, and in this case, a conventionally known solid electrolyte can be used.

[Effect of device]

As described above, the present invention provides a strip-shaped negative electrode using, as an active material, a carbonaceous material that can be doped with lithium ions and dedoped, and Li _x MO ₂ (M is one or more transition metals). And a strip-shaped positive electrode using as an active material (0.05 ≦ x ≦ 1.10) and a strip-shaped separator are spirally wound along the length direction thereof, and the space between the negative electrode and the positive electrode is Further, the present invention relates to a lithium ion secondary battery including a wound electrode body configured such that the separator is interposed therebetween. Therefore, at the time of charging, lithium ions are very favorably desorbed from Li _x MO ₂ that constitutes the positive electrode active material, so that the carbonaceous material that constitutes the negative electrode active material is extremely well doped with lithium ions. At the same time, during discharge, the lithium ions doped in the carbonaceous material are dedoped very well from this carbonaceous material, so that the lithium ions are bound to Li _x MO ₂ very well. The charging / discharging cycle is extremely superior to the lithium secondary battery using as a negative electrode.

Further, the outermost winding portion of the negative electrode is arranged further outside the outermost winding portion of the positive electrode, and the outermost winding portion of the positive electrode is attached to the free end of the outermost winding portion of the negative electrode. The first protruding portion protruding from the free end portion is provided, the innermost winding portion of the negative electrode is arranged further inside the innermost winding portion of the positive electrode, and the innermost winding portion of the negative electrode is formed. A second protruding portion protruding from the free end of the innermost winding portion of the positive electrode is provided at the free end of the wound portion, and both end portions in the width direction of the positive electrode are provided at both end portions in the width direction of the negative electrode. The third and fourth protruding portions protruding from each were provided. Therefore, since the doping amount of lithium ions is very unlikely to be saturated near the surface of the negative electrode (particularly, the upper and lower end faces and both free end faces) of the wound electrode body of the lithium ion secondary battery, the lithium ions are prevented from forming a metal on these end faces. Ejection as lithium can be controlled very effectively, which makes it extremely effective to prevent internal short circuit caused by the metal lithium protruding at these end faces breaking through the separator and coming into contact with the positive electrode. In addition to being able to prevent it, the discharge capacity can be maximized, and as a result, it is possible to provide a high-capacity lithium-ion secondary battery with excellent charge / discharge cycle characteristics and stable usage performance.

[Brief description of drawings]

1 to 5 show a lithium secondary battery according to an embodiment of the present invention. In FIG. 1, both ends of a separator of a spirally wound electrode body incorporated in a lithium secondary battery are cut away. FIG. 2 is a schematic cross-sectional bottom view, FIG. 2 is a schematic perspective view in which a middle portion of a laminated electrode body used for forming the wound electrode body shown in FIG. FIG. 3 is a front view in which the separator of the laminated electrode body shown in FIG. 2 is omitted, and FIG. 4 is a schematic vertical sectional view of a lithium secondary battery incorporating the wound electrode body shown in FIG. The figure shows the relationship between the width ΔW of the protruding portion of the spirally wound electrode body and the discharge capacity. In the reference numerals used in the drawings, 1 ... band positive electrode 2 ... band negative electrode 3 ... band separator 12 ... wound electrode body 17 ... positive electrode innermost wound portion 18 ... negative electrode maximum Inner circumference winding part 19 …… Positive electrode outermost circumference winding part 20 …… Negative electrode outermost circumference winding part 23 …… First protruding part 24 …… Second protruding part 31 …… Third part Overhanging part 32 …… The fourth overhanging part.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-1-128370 (JP, A) JP-A-2-262277 (JP, A) JP-A-60-112264 (JP, A) JP-A-63- 69154 (JP, A)

Claims (1)

(57) [Scope of utility model registration request] 1. A strip-shaped negative electrode using, as an active material, a carbonaceous material that can be doped with lithium ions and dedoped.
A strip-shaped positive electrode using _x MO ₂ (M represents one or more transition metals, and 0.05 ≦ x ≦ 1.10) as an active material, and a strip-shaped separator along the length direction thereof. A lithium-ion secondary battery comprising a spirally wound electrode body configured such that the separator is interposed between the negative electrode and the positive electrode, wherein the outermost spiral portion of the positive electrode is wound. The outermost wound portion of the negative electrode is arranged further on the outer periphery of the first negative electrode, and the first end of the outermost wound portion of the positive electrode protrudes from the free end of the outermost wound portion of the negative electrode. The protruding portion is provided, the innermost wound portion of the negative electrode is arranged further on the inner circumference of the innermost wound portion of the positive electrode, and the free end portion of the innermost wound portion of the negative electrode is provided. Second protruding portion protruding from the free end of the innermost winding portion of the positive electrode Provided, the lithium ion secondary battery, characterized in that respectively the third and fourth protruding portions protruding from both end portions in the width direction of the positive electrode at both ends in the width direction of the negative electrode.