JP2001229980A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery, that can impregnate a positive plate with a sufficient volume of lithium, has light weight, low self-discharging and high energy density, is resistant to its use with heavy load, and is superior in charging and discharging cycle characteristics. SOLUTION: In a nonaqueous electrolyte secondary battery comprising a vortex-type, wound-around electrode body, the relation for the separator width > anode width > cathode width is set up, and a vacant space is arranged in the center of the wound-around electrode body. Then, the volume of a nonaqueous electrolyte is set to be 2.5-4.5 μl per 1 mAh of discharge capacity of the battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery including a negative electrode mainly composed of a carbonaceous material, a positive electrode, and a non-aqueous electrolyte in which a lithium salt is dissolved. is there.

[0002]

2. Description of the Related Art In recent years, remarkable progress in electronic technology has enabled electronic devices to become smaller and lighter one after another. Along with this, there is a demand for increasingly smaller, lighter, and higher energy density batteries as power supplies for transportation.

Conventionally, aqueous batteries such as lead batteries and nickel-cadmium batteries have been the mainstream as secondary batteries for general use. Although these batteries have excellent cycle characteristics, they cannot be said to be sufficiently satisfactory in terms of battery weight and energy density.

Recently, as a secondary battery, a non-aqueous electrolyte secondary battery using lithium or a lithium alloy for a negative electrode has been replaced by a lead battery or a nickel cadmium battery, which are insufficient in battery weight and energy density. Research and development are actively conducted.

[0005] This battery has excellent features of high energy density, low self-discharge, and light weight. However, this battery has a drawback that, with the progress of the charge / discharge cycle, lithium grows in a dendrite shape at the time of charging at the negative electrode, and this dendrite-like crystal is likely to reach the positive electrode and cause an internal short circuit. , A major obstacle to its practical application.

[0006] On the other hand, according to the nonaqueous electrolyte secondary battery using a carbon material for the negative electrode, the lithium and the positive electrode active material previously supported on the carbon material of the negative electrode by a chemical and physical method are used. And lithium dissolved in the electrolyte are doped between the carbon layers and de-doped from the carbon layers in the negative electrode during charge and discharge. For this reason, even when the charge / discharge cycle proceeds, precipitation of dendrite-like crystals is hardly observed in the negative electrode at the time of charge, so that an internal short circuit hardly occurs and good charge / discharge cycle characteristics are exhibited. In addition, since the energy density is high and the weight is low, development is proceeding toward practical use.

[0007] Applications of the non-aqueous electrolyte secondary battery as described above include a video camera and a laptop personal computer. Since many of such electronic devices consume relatively large current, the batteries need to be able to withstand heavy loads.

Therefore, as a battery structure, a spirally wound electrode structure formed by winding a strip-shaped positive electrode and a strip-shaped negative electrode through a strip-shaped separator in the longitudinal direction thereof is effective. According to the battery having the spirally wound electrode structure, the electrode area can be increased, so that the battery can withstand heavy load.

[0009]

However, in a non-aqueous electrolyte secondary battery using a carbonaceous material for the negative electrode as described above, the capacity may decrease as the charge / discharge cycle progresses. In some cases, excellent cycle characteristics could not be obtained for a long period of time.

One of the important factors related to the cycle characteristics is the volume of the non-aqueous electrolyte contained in the non-aqueous electrolyte secondary battery (the amount of the non-aqueous electrolyte).

For example, if the amount of the non-aqueous electrolyte in the battery is small, a part of the electrode is not wetted by the non-aqueous electrolyte.
Since this portion does not participate in the charge / discharge reaction, the current density of the portion wet with the non-aqueous electrolyte becomes higher than usual. As a result, at the time of charging, the case where the lithium doping ability of the carbonaceous material of the negative electrode is likely to be exceeded is likely to occur, so that metal lithium is deposited on the negative electrode, penetrates through the separator, reaches the positive electrode, and an internal short circuit occurs. It is considered to be lost.

An object of the present invention is to provide a non-aqueous electrolyte secondary battery,
Light weight, low self-discharge, high energy density, and even when the charge-discharge cycle proceeds, the dentrite-like crystals are not seen so much at the time of charging at the negative electrode. It can withstand use by load, can reduce the decrease in battery capacity due to the progress of charge / discharge cycles, can contain a sufficient amount of lithium in the positive electrode, and can cause internal short-circuit of the battery. Is more preferably suppressed.

[0013]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a negative electrode mainly composed of a carbonaceous material applied to both sides of a negative electrode current collector and a positive electrode current collector. A positive electrode mainly composed of a composite metal oxide represented by the general formula LiMo ₂ (where M represents at least one of Co and Ni) or an intercalation compound containing lithium, formed on both surfaces of In a non-aqueous electrolyte secondary battery comprising a spirally wound electrode body formed by winding through a separator and a non-aqueous electrolyte in which a lithium salt is dissolved, The width of each of the positive electrode, the negative electrode, and the separator of the spirally wound electrode body has a relationship of separator width> negative electrode width> positive electrode width, and the spirally wound electrode body has a void in the center thereof, Water electrolyte volume Battery discharge capacity 1mAh
It is characterized in that it is not less than 2.5 μl and not more than 4.5 μl, preferably more than 3.0 μl and not more than 4.5 μl.

The carbonaceous material as the negative electrode active material carrier in the nonaqueous electrolyte secondary battery includes pyrolytic carbons, cokes (such as petroleum coke, pitch coke, and coal coke), and carbon black (such as acetylene black). ), Glassy carbon, a fired organic polymer material (a fired organic polymer material at an appropriate temperature of 500 ° C. or higher in an inert gas stream or in a vacuum), carbon fibers, and the like.

A preferred carbonaceous material has a (002) plane spacing (lattice spacing) of 3.70 ° or more and a true density of 1.70 g.
/ Cm ³ and does not have an exothermic peak at 700 ° C. or more in differential thermal analysis in an air stream. According to the carbonaceous material having such properties, a high-capacity battery can be obtained.

As the preferable carbonaceous material as described above, a carbonaceous material obtained by carbonizing an organic material by a method such as firing is exemplified. As a starting material for the carbonization, a furan resin composed of a homopolymer or copolymer of furfuryl alcohol or furfural is preferable. Specifically, polymers composed of furfural + phenol, furfuryl alcohol + dimethylol urea, furfuryl alcohol, furfuryl alcohol + formaldehyde, furfuryl alcohol + furfural, furfural + ketones, etc. show very good properties. .

Further, a petroleum pitch having a hydrogen / carbon atom ratio of 0.6 to 0.8 is used as a starting material, a functional group containing oxygen is introduced into the pitch, and a so-called oxygen cross-link is performed to obtain an oxygen content of 10 to 20% by weight. % Of a precursor, and then calcining the precursor to obtain a carbonaceous material.

When carbonizing the furan resin or petroleum pitch, it is possible to use a carbonaceous material in which the doping amount with respect to lithium is increased by adding a phosphorus compound or a boron compound.

As the positive electrode active material, it is preferable to use a material containing a sufficient amount of lithium. Specifically, a general formula LiMO ₂ (where M represents at least one of Co and Ni) And an intercalation compound containing lithium. In particular, high voltage,
High energy density is obtained, since the excellent cycle characteristics, LiCoO _2, LiCo0.8Ni0.2O ₂ is desirable.

As the non-aqueous electrolyte, a non-aqueous electrolyte obtained by dissolving a lithium salt as an electrolyte in a non-aqueous solvent (organic solvent) may be used.

Here, the non-aqueous solvent is not particularly limited, and various organic solvents can be used.
For example, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran,
3-Dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile and the like can be used alone or in combination of two or more.

As the electrolyte, any of conventionally known lithium salts can be used. For example, LiCO ₄ , LiAsF ₆ , L
_{iPF 6, LiBF 4, LiB (} C 6 H 5) 4, LiC, L
iBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, or the like can be used.

According to the present invention, a void is provided at the center of the spirally wound electrode body, and the amount of the nonaqueous electrolyte in the nonaqueous electrolyte secondary battery is 2.5 μl or more per mAh of discharge capacity and 4.
By setting the volume to 5 μl or less, the electrolyte can be distributed to the electrodes without excess or shortage. In addition, since the width of each of the positive electrode, the negative electrode, and the separator of the spirally wound electrode body was set to have a relationship of separator width> negative electrode width> positive electrode width, lithium in the positive electrode wrapped around the negative electrode during charging and crystallized in a dendrite shape at the negative electrode. It is possible to effectively prevent the dendrite-like crystal from growing or reaching the positive electrode and causing an internal short circuit.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below with reference to FIGS.

Example 1 FIG. 1 shows a schematic longitudinal section of a non-aqueous electrolyte secondary battery of this example . This battery was manufactured as follows.

First, the negative electrode 1 was manufactured as follows. After subjecting the petroleum pitch as a starting material to oxygen crosslinking in which 10 to 20% by weight of a functional group containing oxygen is introduced, this oxygen-crosslinked precursor is mixed in an inert gas stream at 1000
By firing at ℃, a carbonaceous material having properties close to glassy carbon was obtained.

As a result of X-ray diffraction measurement of this carbonaceous material, the (002) plane spacing was 3.76 °, and the true specific gravity was measured by a pycnometer method to be 1.58 g / cm ^3. Met. Further, when a differential thermal analysis was performed in an air stream, it did not have an exothermic peak at 700 ° C. or higher.

This carbonaceous material is pulverized to an average particle size of 10
μm carbon material powder.

The carbonaceous material obtained as described above was used as a negative electrode active material carrier, and 90 parts by weight of the carbonaceous material powder and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed. , To prepare a negative electrode mixture. This negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a slurry (paste).

Next, this negative electrode mixture slurry was applied to a thickness of 1
The negative electrode current collector 9, which is a 0-μm band-shaped copper foil, was uniformly coated on both sides and dried. After the drying, compression molding was performed using a roller press to obtain a band-shaped negative electrode 1.

The thickness of the negative electrode mixture after molding was the same at 80 μm on both sides, and the width of the strip-shaped negative electrode 1 was 33.5.
mm and the length were 700 mm.

Next, the positive electrode 2 was produced as follows. LiCoO ₂ was obtained by mixing 0.5 mol of lithium carbonate and 1 mol of cobalt carbonate and calcining the mixture in air at 900 ° C. for 5 hours.

This LiCoO ₂ was used as a positive electrode active material, and 91 parts by weight of LiCoO ₂ was mixed with 6 parts by weight of graphite as a conductive agent and 3 parts by weight of polyvinylidene fluoride as a binder to prepare a positive electrode mixture. . This positive electrode mixture was dispersed in a solvent N-methylpyrrolidone to form a slurry (paste).

Next, this positive electrode mixture slurry was coated with a thickness of 2
The positive electrode current collector 10, which is a 0-μm band-shaped aluminum foil, was uniformly coated on both sides and dried. After the drying, compression molding was performed with a roller press to obtain a band-shaped positive electrode 2.

The mixture film thickness after molding is 80 on both sides.
μm, the width of the band-shaped positive electrode 2 is 31.5 mm,
The length was 650 mm.

The strip-shaped negative electrode 1 produced as described above
And a band-shaped positive electrode 2 and a pair of band-shaped separators 3a and 3b made of a microporous polypropylene film having a thickness of 25 μm and a width of 36 mm, and in the order of the negative electrode 1, the separator 3a, the positive electrode 2, and the separator 3b. It was laminated in four layers. Then, a spirally wound electrode body 15 was manufactured by spirally winding the four-layered laminated electrode body many times along the length direction with the negative electrode 1 inside.

The inner diameter of the hollow portion at the center of the wound electrode body 15 was 3.5 mm, and the outer diameter was 19.7 mm. In addition,
As is apparent from FIG. 1, since the hollow core 33 is located in this hollow portion, the spirally wound electrode body 15 is formed of a hollow hole of the core 33 at the center thereof, and a space penetrating vertically. It has a part 37.

The spirally wound spirally wound electrode body 15 produced as described above was accommodated in a nickel-plated iron battery can 5 as shown in FIG.

In order to collect the current of the negative electrode 1 and the positive electrode 2 respectively, a negative electrode lead 11 made of nickel is attached to the negative electrode current collector 9 in advance, and this is led out of the negative electrode 1 to remove the battery can 5.
Welded to the bottom. Further, the positive electrode lead 12 made of aluminum was attached to the positive electrode current collector 10 in advance, and this was led out of the positive electrode 2 and welded to the projection 34a of the safety valve 34 made of metal.

Thereafter, a non-aqueous electrolyte obtained by dissolving LiPF ₆ as a lithium salt in a mixed solvent of a volume such as propylene carbonate and 1,2-dimethoxyethane at a ratio of 1 mol / l in a battery can 5 is used. 10 ml was injected, and the wound electrode body 15 was impregnated. In this case, the non-aqueous electrolyte injected into the battery can 5 from above the battery can 5 is a wound electrode body 1
5 as well as the gap 3 of the wound electrode body 15
7, the lower surface of the wound electrode body 15 was reached, and the wound electrode body 15 was impregnated also from this lower end surface (in other words, from both end surfaces).

Before and after this, disk-shaped insulating plates 4a and 4b were disposed in the battery can 5 so as to face the upper end surface and the lower end surface of the wound electrode body 15, respectively.

Thereafter, the battery can 5 and each of the safety valve 34 and the metal battery cover 7 whose outer circumferences are in close contact with each other are caulked via the insulating sealing gasket 6 coated with asphalt on the surface. The battery can 5 was sealed. As a result, the battery lid 7 and the safety valve 34 were fixed, and the airtightness in the battery can 5 was maintained. At this time, the lower end of the gasket 6 in FIG. 1 comes into contact with the outer peripheral surface of the insulating plate 4a, so that the insulating plate 4a is in close contact with the upper end surface of the spirally wound electrode body 15.

As described above, the diameter 20 mm and the height 4
A 2 mm cylindrical non-aqueous electrolyte secondary battery was produced. The battery of Example 1 is referred to as Battery B for convenience as shown in Table 1 below.

The above cylindrical non-aqueous electrolyte secondary battery is
In order to form a double safety device, 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 in the drawings, the safety valve 34 has a cleavage portion that cleaves when the safety valve 34 is deformed.
The battery cover 7 is provided with holes.

If the internal pressure of the battery rises for some reason, the safety valve 34 is turned around the projection 34a as shown in FIG.
To disconnect the positive electrode lead 12 and the protruding portion 34a so as to cut off the battery current, or exhaust the gas generated in the battery due to the open portion of the safety valve 34 breaking open. Respectively.

In the cylindrical non-aqueous electrolyte secondary battery, as described above, the width of the strip-shaped negative electrode 1 is 33.5 m.
m, the width of the band-shaped positive electrode 2 is 31.5 mm, and the width of the pair of band-shaped separators 3a, 3b is 36 mm. Therefore, the widths of the band-shaped negative electrode 1, the band-shaped positive electrode 2, and the band-shaped separators 3a and 3b have a relation of separator width> negative electrode width> positive electrode width, as clearly shown in FIG. For this reason, during charging, the lithium in the positive electrode 2 goes around the negative electrode 1 and grows in the negative electrode 1 in a dendrite-like crystal, and further, the dendrite-like crystal reaches the positive electrode 2 and causes an internal short circuit. Since it can be effectively prevented, better charge / discharge cycle characteristics can be obtained.

Examples 2, 3, 4, 5 In Examples 2 to 5, the amount of the nonaqueous electrolyte injected into the battery can 5 was 2.55 ml, 3.00 ml, 3.40 ml, respectively.
Cylindrical nonaqueous electrolyte secondary batteries B, C, D and E having a diameter of 20 mm and a height of 42 mm were produced in the same manner as in Example 1 except that the amount was 3.80 ml.

Next, as a comparative example for confirming the effect of the present invention, the following battery was manufactured.

Comparative Examples 1 and 2 The non-aqueous electrolyte solution injected into the battery can 5 was 1.70 m each.
In the same manner as in Example 1 except that the amounts were 1 and 4.25 ml, cylindrical nonaqueous electrolyte secondary batteries A and G having a diameter of 20 mm and a height of 42 mm were produced, respectively.

In the step of caulking the battery can 5 at the time of assembling the batteries A to G, the battery cover 7 is used only for the battery G.
Non-aqueous electrolyte overflowed on the top.

With respect to the above seven types of batteries A to G, the upper limit charging voltage was set to 4.1 V, the battery was charged with a constant current of 1 A for 2 hours, and then discharged to a final voltage of 2.75 V with a constant load of 7.5 Ω. The charge / discharge cycle was repeated.

The discharge capacity (initial capacity) after 10 cycles of this charge / discharge cycle and the discharge capacity after 100 cycles were measured, and the ratio of the capacity after 100 cycles to the capacity after 10 cycles was measured. The capacity retention rate was used.

Table 1 below shows the amount of non-aqueous electrolyte of each of the batteries A to G per 1 mAh of discharge capacity when the initial capacity and the initial capacity of the battery are 850 mAh.

FIG. 2 shows the relationship between the amount of nonaqueous electrolyte per 1 mAh of discharge capacity and the battery capacity retention rate after 100 cycles.

[0055]

[Table 1]

As is apparent from FIG. 2, the discharge capacity is 1 mA.
Batteries A to F having a nonaqueous electrolyte amount of 4.5 μl or less per hour
The batteries A to E having a battery capacity retention ratio exceeding 80% and having good cycle characteristics, and having a nonaqueous electrolyte amount of 4.0 μl or less per 1 mAh of discharge capacity have a battery capacity retention ratio of 85% or less.
% Is more preferable.

Next, 100 batteries each of the above-described batteries A to G were manufactured, and the occurrence rate of an internal short circuit during charging was examined.

FIG. 3 shows a discharge capacity of 1 m for each of the batteries A to G.
4 shows the relationship between the amount of nonaqueous electrolyte per Ah and the rate of occurrence of internal short circuits.

As is apparent from FIG. 3, the discharge capacity is 1 mA.
B to G having a nonaqueous electrolyte amount of 2.5 μl or more per hour
Has a low internal short-circuit occurrence rate. In addition, in the batteries D to G in which the amount of the nonaqueous electrolyte per 1 mAh of discharge capacity exceeds 3.0 μl, no internal short circuit occurs.

As described above, the void is provided in the center of the wound electrode body 15 and the non-aqueous electrolyte in the battery is contained in a moderately large amount. Does not form a part that is not wetted by the non-aqueous electrolyte, and therefore, the charge / discharge density of the electrode does not partially increase, and as a result, metal lithium does not precipitate on the negative electrode during charging. It is considered that no internal short circuit occurs.

From the above FIGS. 2 and 3, the amount of the non-aqueous electrolyte injected into the non-aqueous electrolyte secondary battery was 1 m
The amount of non-aqueous electrolyte per Ah is 2.5 μl or more and 4.5
μl or less, preferably more than 3.0 μl and 4.0 μl
It can be seen that the following is more preferable.

Although the battery of this embodiment was a cylindrical nonaqueous electrolyte secondary battery using a spirally wound electrode body, the present invention is not limited to this. It can be applied to a non-aqueous electrolyte secondary battery such as a prismatic type.

[0063]

The non-aqueous electrolyte secondary battery according to the present invention has a negative electrode mainly composed of a carbonaceous material formed on both sides of a strip-shaped negative electrode current collector and both sides of a strip-shaped positive electrode current collector. A spiral-type wound electrode body constituted by winding a coated positive electrode containing lithium through a band-shaped separator, and a nonaqueous electrolyte in which a lithium salt is dissolved, respectively. I have. Therefore, it is light in weight, has a low self-discharge, has a high energy density, and has good dendrite-like crystals in the negative electrode during charging even when a charge-discharge cycle proceeds, so that an internal short circuit does not easily occur. It shows discharge cycle characteristics, and can withstand heavy load due to the large electrode area.

A gap is provided at the center of the wound electrode body, and the amount of the non-aqueous electrolyte in the non-aqueous electrolyte secondary battery is not less than 2.5 μl and not more than 4.5 μl per 1 mAh of discharge capacity. The amount of the non-aqueous electrolyte is 4.5 μl or less per 1 mAh of discharge capacity of the battery, which is appropriately small and not too large. Therefore, the decrease in the battery capacity due to the progress of the charge / discharge cycle can be reduced, and The amount of the electrolyte is 2.5 μl or more per 1 mAh of discharge capacity of the battery, which is moderately large and not too small. Therefore, the occurrence of an internal short circuit can be more favorably suppressed, and the charge / discharge cycle characteristics are extremely excellent. ing.

Further, since the width of each of the positive electrode, the negative electrode and the separator of the spirally wound electrode body was set to the relation of separator width> negative electrode width> positive electrode width, the lithium in the positive electrode wrapped around the negative electrode during charging and dendrite It is possible to more effectively prevent the dendrite-like crystals from reaching the positive electrode and causing an internal short circuit, thereby exhibiting better charge / discharge cycle characteristics.

The positive electrode is a composite metal oxide represented by the general formula LiMO ₂ (where M represents at least one of Co and Ni) or an intercalation compound containing lithium. Of lithium.

Further, according to the second aspect of the present invention, the carbonaceous material mainly constituting the negative electrode has a (002) plane spacing of 3.70 ° or more, a true density of less than 1.70 g / cm ³ , and air Since a material that does not have an exothermic peak at 700 ° C. or more in differential thermal analysis in an airflow is used,
A high capacity non-aqueous electrolyte secondary battery can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a graph showing the relationship between the amount of non-aqueous electrolyte per 1 mAh of battery discharge capacity and the battery capacity retention rate for seven types of batteries in Examples and Comparative Examples according to the present invention.

FIG. 3 shows a battery discharge capacity of 1 m for the above seven types of batteries.
It is a figure which shows the relationship between the amount of non-aqueous electrolytes per Ah, and the internal short circuit occurrence rate.

[Explanation of symbols]

 Reference Signs List 1 negative electrode 2 positive electrode 3a separator 3b separator 9 negative electrode current collector 10 positive electrode current collector 15 wound electrode body 37 void

Claims (2)

[Claims] 1. A negative electrode composed mainly of a carbonaceous material formed on both sides of a strip-shaped negative electrode current collector and a general formula LiMo ₂ formed on both sides of a strip-shaped positive electrode current collector (wherein M represents at least one of Co and Ni) and a positive electrode mainly composed of an intermetallic compound containing lithium or an intermetallic compound represented by lithium, which is wound through a belt-shaped separator. In a non-aqueous electrolyte secondary battery including a spiral wound electrode body and a non-aqueous electrolyte in which a lithium salt is dissolved, each of the positive electrode, the negative electrode, and the separator of the wound electrode body The width has a relationship of separator width> negative electrode width> positive electrode width, the wound electrode body has a void portion in the center thereof, and the amount of the non-aqueous electrolyte is 2.5 per 1 mAh of battery discharge capacity.
A non-aqueous electrolyte secondary battery having a volume of not less than μl and not more than 4.5 μl. 2. The carbonaceous material has a (002) plane spacing of 3.70 ° or more, a true density of less than 1.70 g / cm ³ , and an exothermic peak of 700 ° C. or more in differential thermal analysis in an air stream. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is not provided.