JPH11297309A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqeous electrolyte secondary battery of high capacity, without lowering productivity in the nonaquoeus electrolyte secondary battery using a negative active material with has high irreversible capacity. SOLUTION: In a nonaqueous electrolyte secondary battery having a positive electrode 1, a negative electrode 2 and a nonaqueous electrolyte and constituted by winding or layering the positive electrode 1 and the negative electrode 2 via a separator 3, a lithium compound metal oxide expressed by the formula Lix My Ni1-y Oz (where x>=0, 0<y<=0.5, 0.5<=z<=3.5, M represents at least one kind of alkali metal excepting Li or alkaline-earth metal, or a combination of at least one kind from among them and a metal excepting Ni) is used for a positive pole active material, when at least one kind out of negative active materials in an alloy, an oxide or a compound oxide selected from the IV group elements in the periodic table, except carbon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonaqueous electrolyte secondary battery, and more particularly, to a nonaqueous electrolyte secondary battery in which a positive electrode and a negative electrode are sheet-shaped, and the sheet-shaped positive electrode and the sheet-shaped negative electrode are wound or separated via a separator. The present invention relates to a non-aqueous electrolyte secondary battery having a stacked configuration.

[0002]

2. Description of the Related Art Carbon is generally used as a negative electrode material for non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries, but lithium alloys, metals or semimetals are used as higher capacity materials. Oxides, sulfides, nitrides, and the like have been studied. However, in many of these materials, part of lithium inserted into the negative electrode in the first charge is not released in subsequent discharge, and a capacity loss occurs as irreversible capacity. Therefore, it is necessary to provide an extra irreversible part.

As one of the means, a method has been proposed in which a metal lithium foil is attached to a negative electrode and lithium is inserted into the negative electrode by chemical conversion. However, this method is effective for a button-type battery or the like, but involves a difficulty in manufacturing a battery using an electrode body having a wound structure or an electrode body having a laminated structure. In particular, when the capacity of the negative electrode is more than twice the capacity of the positive electrode, the thickness of the negative electrode must be reduced in the battery design to balance the capacity with the positive electrode. The metal lithium foil must also be relatively thin, and there is a limit to the thickness of the metal lithium foil that can be handled, so that it is virtually impossible to manufacture a battery.

As another method for compensating for the irreversible capacity of the negative electrode,
A method of charging the battery in advance outside the battery or a method of chemically inserting lithium has been studied, but these methods have not been put to practical use due to poor production efficiency.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and uses a non-aqueous solution in which an active material having a large irreversible capacity is used for a negative electrode using a wound structure or a laminated structure. An object of the present invention is to provide a high-capacity non-aqueous electrolyte secondary battery without lowering productivity in an electrolyte secondary battery.

[0006]

The present invention comprises at least a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode and the negative electrode are sheet-shaped, and the sheet-shaped positive electrode and the sheet-shaped negative electrode are interposed via a separator. In a non-aqueous electrolyte secondary battery configured by winding or laminating, at least one of the negative electrode active materials
Species alloy of the periodic table group 14 elements excluding carbon, when an oxide or a composite oxide, as a cathode active material, the general formula _{(I) Li x M y Ni} 1-y O z (I) ( Where x ≧ 0, 0 <y ≦ 0.5, 1.5 ≦ z ≦ 3.
5, M is at least one alkali metal or alkaline earth metal other than Li, or a combination of at least one of them and a metal other than Ni), thereby achieving the above object. It is a solution.

To explain this in detail, first, the irreversible capacity of the negative electrode active material occurs because lithium ions are absorbed during charging but are not released during discharging. On the other hand, when Li _x NiO ₂ (x ≧ O) is used as the positive electrode active material, the initial irreversible capacity is about 10%, which is opposite to the irreversible capacity of the negative electrode. This is caused by the fact that some are not absorbed by the discharge.
Therefore, if both are combined to form a battery, lithium ions corresponding to the irreversible capacity of the positive electrode can compensate for the irreversible capacity of the negative electrode.

However, when an alloy, oxide or composite oxide of an element belonging to Group 14 of the periodic table is used as the negative electrode active material, 30% of lithium ions inserted into the negative electrode during the first charge can be obtained.
６０60% becomes irreversible capacity, and Li _x N
Even if iO ₂ is used, the irreversible capacity of the negative electrode cannot be compensated.

Therefore, the present inventor has conducted various studies to compensate for the irreversible capacity of the negative electrode when the above-mentioned negative electrode active material is used. As a result, the present inventors have made Li _x NiO ₂ (x ≧ O) as a main component, When a part of is replaced with an alkali metal or an alkaline earth metal as the positive electrode active material,
It has been found that the irreversible capacity of the positive electrode can be increased in accordance with the amount of addition. Except for changing the raw material of the positive electrode, by adjusting the addition amount of similar metals and complementing the irreversible capacity of the positive electrode and the negative electrode with each other,
They have found that a high-capacity non-aqueous electrolyte secondary battery can be manufactured in the same manufacturing process as before.

[0010]

In DETAILED DESCRIPTION OF THE INVENTION The present invention, as described above, as a positive electrode active material, in the general formula _{(I) Li x M y Ni} 1-y O z (I) ( wherein, x ≧ 0,0 <y ≦ 0.5, 1.5 ≦ z ≦ 3.
5, M uses a lithium composite metal oxide represented by at least one kind of alkali metal or alkaline earth metal other than Li, or a combination of at least one kind thereof and a metal other than Ni).

In the above general formula (I), M may be any alkali metal or alkaline earth metal except Li, but preferably low cost Na, K, Mg, Ca and the like. Two or more kinds may be used in combination. Examples of the metal to be combined with the alkali metal or the alkaline earth metal include, for example, Al, Ti, M
n, Fe, Cr and the like.

Further, y in the general formula (I) is 0 <y ≦
The reason for setting the value to 0.5 is that if the amount of the alkali metal or alkaline earth metal represented by M exceeds the above range, the high capacity and high voltage characteristics of Ni cannot be sufficiently exhibited. Is determined substantially uniquely within the range of 1.5 ≦ z ≦ 3.5 by setting the oxidation number of M and the y value.

In the present invention, the alloy, oxide or composite oxide of Group 14 element except for carbon used as the negative electrode active material is, for example, NiSi _a (0.5 ≦ a
≦ 6), MgSi _b (0.5 ≦ b ≦ 6), wood alloy,
Li _c SiO (0 ≦ c ≦ 6), Li _d SnSiO _e (d
≧ 0,2 ≦ e ≦ 4), Li f SnP g B h O k (f ≧
0, 0 ≦ g, h ≦ 1, 2 ≦ k ≦ 8) and the like, but are not limited to these.

Further, other transition metals may be added simultaneously for cycle stability and thermal stability.
It is preferable to add Al, Co, or the like because thermal stability is improved. The addition amount of these transition metals cannot be uniquely indicated because it varies slightly depending on the type of transition metal to be added, but is adjusted so that the ratio of the irreversible capacity to the discharge capacity of the negative electrode is almost equal to that of the positive electrode. Is preferred. However, to get some capacity,
Substitution at 50 atomic% or less is preferred, more preferably 5 atomic%.
0 at% or less and 20 at% or more. However, Co or M
When n is added, since the decrease in capacity is slight,
That is not the case.

When an alloy, oxide or composite oxide of the Group 14 elements except for carbon is used alone as the negative electrode active material, the negative electrode expands and contracts with charging and discharging, and the negative electrode It is preferable to use a graphite-based carbon material in combination, since it may cause fine deterioration of the substance and the like and cause cycle deterioration, particularly from the viewpoint of securing conductivity when an oxide is used as an active material of the negative electrode. preferable.

The graphite-based carbon material preferably has a (002) plane spacing (d _{00 2} ) of 3.5 ° or less, more preferably 3.45 ° or less, in X-ray diffraction analysis. More preferably, it is 3.4 ° or less. The graphite carbon material preferably has a crystallite size (Lc) in the c-axis direction of 30 ° or more, more preferably 80 ° or more, and further preferably 250 ° or more. Further, the graphite-based carbon material preferably has an average particle size of 8 to 15 μm, particularly preferably 10 to 13 μm, and preferably has a purity of 99.9% or more.

Specific examples of the graphite-based carbon material include, for example, flaky graphite, massive graphite, fibrous graphite, spherical graphite, and the like. The amounts of the alloys, oxides or composite oxides of the present invention are, by weight, alloys, oxides or composite oxides of Group 14 elements excluding carbon: graphite-based carbon material =
95: 5: to 40:60 is preferred.

In the present invention, the preparation of the positive electrode is performed, for example, by
If necessary, a conductive additive, a binder, and the like are added to the positive electrode active material composed of the lithium composite metal oxide represented by the general formula (I) and mixed to form a positive electrode mixture, which is formed into a paste with a solvent. (However, the binder may be dissolved in a solvent in advance and then mixed with the positive electrode active material or the like), and the positive electrode mixture paste is applied to a current collector, dried, and dried on at least one surface of the current collector. This is performed by forming a positive electrode mixture layer on the substrate. However, the production of the positive electrode is not limited to the method exemplified above.

For the preparation of the negative electrode, for example, a conductive additive, a binder and the like are added to the negative electrode active material, if necessary, and mixed to prepare a negative electrode mixture, which is made into a paste with a solvent. (However, the binder may be dissolved in a solvent in advance and then mixed with the negative electrode active material, etc.),
This is performed by applying the negative electrode mixture paste to a current collector, drying and forming a negative electrode mixture layer on at least one surface of the current collector. However, the production of the negative electrode is not limited to the method exemplified above.

As the conductive aid, for example, flaky graphite, carbon black, acetylene black and the like are used, and as the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid and the like are used. Can be

As the current collector for the positive electrode or the negative electrode, for example, a metal foil or a net made of aluminum, copper, nickel, stainless steel or the like is used. As the current collector for the positive electrode, an aluminum foil is used. It is preferable to use a copper foil as the current collector of the negative electrode.

In the present invention, a non-aqueous electrolyte prepared by dissolving an electrolyte in an organic solvent is used as the electrolyte. Examples of the solvent for the electrolytic solution include dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 5-dimethyltetrahydrofuran, 1,2-diethoxyethane, 1-methoxypropane, 1-methoxybutane, γ-butyrolactone, ethylene carbonate, and propylene carbonate. , Diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and other organic solvents may be used alone or in combination of two or more, and examples of the electrolyte include LiClO ₄ , LiPF
_{6, LiBF 4, LiAsF 6,} LiSbF 6, LiC
F ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiCF ₃ CO ₂ ,
Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ )
₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃
(N ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] or the like is used alone or in combination of two or more. Among them, LiPF ₆ and LiC _{4 are used.}
F ₉ SO ₃ is preferably used because of its good charge / discharge characteristics. The concentration of these electrolytes in the electrolytic solution is not particularly limited, but is usually 0.1 mol / L or more, particularly 0.4 mol / L or more, and particularly preferably 1.2 mol / L or more. Mol / l or less, particularly 1.7 mol / l or less, particularly preferably 1.5 mol / l or less.

As the separator, for example, a microporous polyethylene film, a microporous polypropylene film, a microporous polyethylene-polypropylene composite film and the like are preferably used, but other materials may be used.

The above-described positive electrode and negative electrode are manufactured in a sheet shape,
The sheet-shaped positive electrode and the sheet-shaped negative electrode are wound in a spiral shape with a separator interposed therebetween to form a wound electrode body, or the positive electrode and the negative electrode are stacked with a separator interposed therebetween and laminated. The structure of the electrode body increases the surface area of the electrode, making it suitable for use at high power.

[0025]

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only these examples.

Example 1 Methyl ethyl carbonate and ethylene carbonate were mixed at a volume ratio of 75:25, and LiPF ₆ was added to the mixed solvent.
Was dissolved in 1.4 mol / l to give a composition of 1.4 mol.
1 / l LiPF ₆ / EC: MEC (25:75 volume ratio)
Was prepared.

Separately, flaky graphite is added to LiK _0.3 Ni _0.7 O ₂ as a conductive aid at a weight ratio of 90: 6.3 and mixed, and this mixture and polyvinylidene fluoride are mixed with N-
A solution dissolved in methylpyrrolidone was mixed to form a paste. The amount of polyvinylidene fluoride used as the binder for the positive electrode active material with respect to LiK _0.3 Ni _0.7 O ₂ is a ratio of 10 parts by weight of polyvinylidene fluoride to 90 parts by weight of LiK _0.3 Ni _0.7 O ₂ . This positive electrode mixture paste is passed through a 70-mesh net to remove large pieces, and then uniformly applied to both sides of a positive electrode current collector made of aluminum foil having a thickness of 20 μm, and dried to form a positive electrode mixture layer. Then, after compression-molding with a roller press machine, it was cut and the lead body was welded to produce a belt-shaped positive electrode.

Next, flaky graphite was added to a nickel-silicon alloy powder having a composition of NiSi _2.4 at a weight ratio of 60:40, which also slightly acts as a conductive additive, and mixed. Mixed with a solution dissolved in methylpyrrolidone to form a paste. The amount of the polyvinylidene fluoride used was 10 parts by weight based on 90 parts by weight of the mixture of NiSi _2.4 and flaky graphite. Further, the spacing (d) of the (002) plane of the flake graphite
₀₀₂ ) was 3.354 ° and the crystallite size (Lc) in the c-axis direction was 768 °. The negative electrode mixture paste was passed through a 70-mesh net to remove large pieces, and then uniformly applied to both sides of a negative electrode current collector made of a 10 μm-thick strip-shaped copper foil, dried, and dried. Was formed by compression with a roller press, cut, and then the lead body was welded to produce a strip-shaped negative electrode.

The strip-shaped positive electrode is overlaid on the strip-shaped negative electrode via a microporous polyethylene film having a thickness of 25 μm, and is spirally wound into an electrode body having a spirally wound structure.
mm, and the lead bodies of the positive electrode and the negative electrode were welded.

Next, the electrolytic solution was poured into a battery can.
After the electrolyte has sufficiently penetrated into the separator, etc., seal it,
Preliminary charging and aging were performed to produce a cylindrical non-aqueous electrolyte secondary battery having a structure as shown in the schematic diagram of FIG.

Here, the battery shown in FIG. 1 will be described. 1 is the above positive electrode, and 2 is the negative electrode. However, FIG.
Here, in order to avoid complication, a metal foil or the like as a current collector used in manufacturing the positive electrode 1 and the negative electrode 2 is not illustrated. The positive electrode 1 and the negative electrode 2 are connected to a separator 3
, And is housed in a battery can 5 together with the electrolytic solution 4 as an electrode body having a spirally wound structure.

The battery can 5 is made of stainless steel and also serves as a negative electrode terminal. An insulator 6 made of polypropylene is arranged at the bottom of the battery can 5 before inserting the spirally wound electrode body. ing. The sealing plate 7 is made of aluminum,
It has a disk shape, is provided with a thin portion 7a at the center, and a hole is provided around the thin portion 7a as a pressure introduction port 7b for applying an internal pressure of the battery to the explosion-proof valve 9. The projection 9a of the explosion-proof valve 9 is welded to the upper surface of the thin portion 7a to form a welded portion 11. In addition, the thin portion 7a provided on the sealing plate 7 and the protruding portion 9a of the explosion-proof valve 9 are illustrated only in a cut plane so as to be easily understood in the drawings, and a contour line behind the cut plane is shown. Is not shown. Further, the thin portion 7a of the sealing plate 7 and the projection 9 of the explosion-proof valve 9 are provided.
The welded portion 11 with "a" is illustrated in an exaggerated state rather than the actual one so that the drawing can be easily understood.

The terminal plate 8 is made of rolled steel, has a nickel-plated surface, and has a hat-like shape with a peripheral edge formed in a flange shape. The terminal plate 8 is provided with a gas discharge hole 8a. . The explosion-proof valve 9 is made of aluminum and has a disk shape. A projection 9a having a tip portion is provided at a center portion of the explosion-proof valve on the power generation element side (the lower side in FIG. 1), and a thin portion 9b is provided. Provided, and the lower surface of the protruding portion 9a is, as described above,
The welding portion 11 is welded to the upper surface of the thin portion 7a of the sealing plate 7.
Is composed. The insulating packing 10 is made of polypropylene and has an annular shape. The insulating packing 10 is disposed above the peripheral edge of the sealing plate 7, and the explosion-proof valve 9 is disposed thereon.
And the explosion-proof valve 9 and the gap between the two is sealed so that the electrolyte does not leak from between the two. The annular gasket 12 is made of polypropylene, the lead body 13 is made of aluminum, connects the sealing plate 7 and the positive electrode 1, and an insulator 14 is disposed above the spirally wound electrode body,
The negative electrode 2 and the bottom of the battery can 5 are connected to a lead 15 made of nickel.
Connected by

Example 2 LiMg _0.4 Ni _0.6 instead of LiK _0.3 Ni _0.7 O ₂
O ₂ is used as the positive electrode active material, and S ₂ is used instead of NiSi _2.4.
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that iO was used as the negative electrode active material.

Comparative Example 1 A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that LiNiO ₂ was used as a positive electrode active material instead of LiK _0.3 Ni _0.7 O ₂ .

Comparative Example 2 A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 2, except that LiNiO ₂ was used as a positive electrode active material instead of LiMg _0.4 Ni _0.6 O ₂ .

The irreversible capacity ratios of the positive electrodes and negative electrodes of Examples 1 and 2 and Comparative Examples 1 and 2 prepared as described above were examined, and the discharge capacity of the batteries was examined by charging and discharging. The results are shown in Tables 1 and 2. The measuring method is as follows.

<Irreversible Capacity Ratio> With respect to the positive electrode and the negative electrode of Examples 1 and 2 and Comparative Examples 1 and 2, the counter electrode was made of metallic lithium, and a voltage of 1.8 to 3.2 V at 0.2 C was applied.
The battery was repeatedly charged and discharged, the difference between the charge capacity and the discharge capacity in the first cycle was obtained, and the irreversible capacity was divided by the discharge capacity to obtain an irreversible capacity ratio (irreversible capacity in the first cycle / charge capacity). Table 1 shows the results.

<Discharge Capacity> With respect to the batteries of Examples 1 and 2 and Comparative Examples 1 and 2, a voltage of 2.75 V and 0.2 C was obtained.
The battery was charged and discharged in the range of 4.1 V, and the initial discharge capacity was examined. Table 2 shows the results.

[0040]

[Table 1]

[0041]

[Table 2]

As shown in Table 2, Examples 1 and 2 had a large discharge capacity and a high capacity. This is presumably because, as shown in Table 1, in Examples 1 and 2, the irreversible capacity ratios of the positive electrode and the negative electrode were equal, and the irreversible capacity of the positive electrode compensated for the irreversible capacity of the negative electrode.

On the other hand, in Comparative Examples 1 and 2, as shown in Table 1, the irreversible capacity ratio of the negative electrode was larger than that of the positive electrode, and the irreversible capacity of the positive electrode did not compensate for the irreversible capacity of the negative electrode. As shown in Table 2, the discharge capacity was reduced.

In Examples 1 and 2, as shown in Table 1, the irreversible capacity ratio of the positive electrode was equal to the irreversible capacity ratio of the negative electrode. This is because the capacity was adjusted, and it is necessary to go through such a preliminary test even in actual battery fabrication.

According to the present invention, as is apparent from the above-described embodiment, the battery can be manufactured without the necessity of attaching a metallic lithium foil to the negative electrode, so that the productivity does not decrease. Therefore, according to the present invention, a high-capacity non-aqueous electrolyte secondary battery can be manufactured without reducing productivity.

[0046]

As described above, according to the present invention, a high-capacity non-aqueous electrolyte secondary battery can be provided without reducing productivity.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view schematically showing one example of a non-aqueous electrolyte secondary battery of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Electrolyte

Claims (3)

[Claims] 1. A battery comprising at least a positive electrode, a negative electrode, and a non-aqueous electrolytic solution, wherein the positive electrode and the negative electrode are sheet-shaped, and the sheet-shaped positive electrode and the sheet-shaped negative electrode are wound or laminated with a separator interposed therebetween. When at least one of the negative electrode active materials is an alloy, oxide or composite oxide of a Group 14 element of the periodic table excluding carbon, a non-aqueous electrolyte secondary battery having the general formula ( _{I) Li x M y Ni 1} -y O z (I) ( wherein, x ≧ 0,0 <y ≦ 0.5,1.5 ≦ z ≦ 3.
5. M is a lithium composite metal oxide represented by at least one of alkali metals or alkaline earth metals other than Li, or a combination of at least one of them and a metal other than Ni). Non-aqueous electrolyte secondary battery. 2. M in the general formula (I) is K, Na, Mg
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is any one of Ca and Ca, a combination thereof, or a combination thereof with a metal other than Ni. 3. The negative electrode, together with the negative electrode active material, comprises (0
02) (d) ₀₀₂) Is 3.5% or less graphite-based carbon
The non-aqueous electrolyte secondary battery according to claim 1, comprising a material.