JP3517117B2 - Lithium secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery having an improved negative electrode containing a carbonaceous material and a method for manufacturing the lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, a non-aqueous electrolyte battery using metallic lithium as a negative electrode active material has attracted attention as a high energy density battery, and manganese dioxide (MnO 2) is used as a positive electrode active material.
₂ ), fluorocarbon [(CF ₂ ) _n ], thionyl chloride (S
A primary battery using OCl ₂ ) or the like has already been widely used as a power source for calculators and watches and a backup battery for memories.
Furthermore, in recent years, with the miniaturization and weight reduction of various electronic devices such as VTRs and communication devices, the demand for high energy density secondary batteries as their power source has increased, and research on lithium secondary batteries using lithium as a negative electrode active material. Is actively carried out.

Lithium secondary batteries use lithium as a negative electrode and use propylene carbonate (PC), 1,2-dimethoxyethane (DME), γ-butyrolactone (γ-) as an electrolyte.
BL), tetrahydrofuran (THF) or the like, a non-aqueous electrolyte solution or a lithium ion conductive solid electrolyte in which a lithium salt such as LiClO ₄ , LiBF ₄ , or LiAsF ₆ is dissolved in a non-aqueous solvent, and a positive electrode active material is mainly used. TiS ₂ ,
The use of compounds such as MoS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , and MnO ₂ that undergo a topochemical reaction with lithium has been studied.

However, the lithium secondary battery described above has not yet been put into practical use. This is because when metallic lithium is used for the negative electrode, the charge / discharge efficiency is lowered due to the deterioration of the metal, and the cycle life is shortened. In addition, the biggest demerit is that metallic lithium becomes fine powder during repeated charging and discharging, and becomes a reactive dendrite, which impairs the safety of the battery and eventually causes damage to the battery, short circuit, and thermal runaway. That is.

From the above, it has been proposed to use a carbonaceous material that absorbs and releases lithium, such as coke, a resin fired body, carbon fiber, and pyrolytic vapor phase carbon, as the negative electrode incorporated in the lithium secondary battery. There is. The carbonaceous material can suppress the reaction between lithium and the non-aqueous electrolyte.

However, there is a strong demand to further improve the capacity of the battery due to recent miniaturization of equipment and continuous use for a long time. There is a limit to the improvement of charge / discharge capacity with conventional carbon materials. Further, in low-temperature fired carbon, which is considered to have a high capacity, it is difficult to increase the charge / discharge capacity per unit volume because the density of the substance is low. In order to develop high capacity batteries, it is necessary to develop new negative electrode materials.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery with high capacity and long life.

Another object of the present invention is to provide a method of manufacturing a lithium secondary battery having a high capacity and a long life.

[0009]

A lithium secondary battery according to the present invention is a lithium secondary battery provided with a negative electrode containing a carbonaceous material that absorbs and releases lithium ions, wherein the carbonaceous material has an average particle size. With element M having a particle size of 100 nm or less
Containing (excluding those containing S),
Element M is Mg, Al, Si, Ca, Sn and Pb
The X-ray intensity ratio (I) of carbon to the X-ray intensity of the element M, which is composed of at least one element selected, is 0. 1 when the cross section is measured by an electron beam microanalyzer (EPMA) in a visual field of 10 × 10 μm. 7X ≦ I ≦ 1.3X is satisfied, and the X is represented by the following formula (1).

X = (100−n) m / cn (1) where n is the content (% by weight) of the element M of the carbonaceous material, m is the atomic weight of the element M contained in the carbonaceous material, The c represents the atomic weight of carbon.

A method for manufacturing a lithium secondary battery according to the present invention is the method for manufacturing a lithium secondary battery according to claim 1 , wherein the carbonaceous material is Mg, Al, Si, Ca, Sn.
And an organometallic complex containing at least one element selected from Pb (excluding those containing S) are prepared by a method including a step of firing.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a lithium secondary battery (for example, a cylindrical lithium secondary battery) according to the present invention will be described in detail with reference to FIG.

A cylindrical container 1 having a bottom and made of stainless steel, for example, has an insulator 2 at the bottom. Electrode group 3
Are stored in the container 1. The electrode group 3 is
It has a structure in which a band-shaped material in which a positive electrode 4, a separator 5 and a negative electrode 6 are laminated in this order is spirally wound.

The container 1 contains a non-aqueous electrolytic solution. The PTC element 7 having a hole at the center, the P
A safety valve 8 arranged on the TC element 7 and a hat-shaped positive electrode terminal 9 arranged on the safety valve 8 are caulked and fixed to an upper opening of the container 1 via an insulating gasket 10. A gas vent hole (not shown) is opened in the positive electrode terminal 9. One end of the positive electrode lead 11 is connected to the positive electrode 4 and the other end is connected to the PTC element 7. The negative electrode 6 is connected to the container 1, which is a negative electrode terminal, via a negative electrode lead (not shown).

Next, the positive electrode 4, the separator 5, the negative electrode 6 and the electrolytic solution will be described in detail.

1) Positive electrode 4 The positive electrode 4 is obtained by adding a conductive agent and a binder to the positive electrode active material,
It is prepared by suspending these in an appropriate solvent, applying the suspension to a current collector, and drying to form a thin plate.

As the positive electrode active material, various oxides,
For example, manganese dioxide, lithium manganese composite oxide,
Examples thereof include lithium-containing nickel oxide, lithium-containing cobalt compound, lithium-containing nickel-cobalt oxide, lithium-containing iron oxide, lithium-containing vanadium oxide, and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among them, lithium-containing cobalt oxide (for example, LiCoO ₂ ), lithium-containing nickel oxide (for example, LiNiO ₂ ), lithium manganese composite oxide (for example, LiMn ₂ O ₄ , LiMnO ₂ ).
_The use of ₂ ) is preferable because a high voltage can be obtained.

Examples of the conductive agent include acetylene black, carbon black, graphite and the like.

As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), etc. may be used. it can.

The mixing ratio of the positive electrode active material, the conductive agent and the binder is 80 to 95% by weight of the positive electrode active material and the conductive agent 3 to 2.
It is preferable that the content is 0% by weight and the binder is 2 to 7% by weight.

As the current collector, for example, aluminum foil, stainless foil, nickel foil or the like can be used.

2) Separator 5 The separator 5 is, for example, a synthetic resin non-woven fabric,
A polyethylene porous film, a polypropylene porous film, or the like can be used.

3) Negative Electrode 6 The negative electrode 6 contains a carbonaceous material that occludes and releases lithium ions. The carbonaceous material is Mg, Al, Si, Ca,
Carbon containing the element M consisting of at least one element selected from Sn and Pb, and carbon with respect to the X-ray intensity of the element M when a cross section is measured in a visual field of 10 × 10 μm by an electron beam microanalyzer (EPMA). The X-ray intensity ratio (I) is within the range of 0.7X ≦ I ≦ 1.3X. Further, the X is represented by the following formula (1).

X = (100−n) m / cn (1) where n is the content (% by weight) of the element M of the carbonaceous material, m is the atomic weight of the element M contained in the carbonaceous material, The c represents the atomic weight of carbon.

The element M has a structure capable of forming an alloy with lithium or occluding and releasing lithium in some form. As the element M, Al,
Si and Sn are preferable. In the carbonaceous material, the element M is generally contained in the form of particles. This particle is
It is composed of the element M, an alloy containing the element M, or a compound containing the element M. It is presumed that the particles are present in the voids between crystallites in the amorphous region of the carbonaceous material, and in the carbon layers or in the crystal gaps in the region where the crystallinity is relatively advanced.

X calculated from the above equation (1) is 10 × 1 when the element M is theoretically uniformly dispersed in a carbonaceous material in which the content of the element M is a certain amount.
The ratio of the number of carbon atoms to the number of element M atoms in the cross section in the region of 0 μm is almost shown. The ratio of the X-ray intensity of carbon to the X-ray intensity of the element M obtained by measuring the cross section of the carbonaceous material with an electron microanalyzer (EPMA) is the ratio of the number of carbon atoms to the number of atoms of the element M in the cross section. Indicates. Therefore, 10x by EPMA
The X-ray intensity ratio (I) of carbon to the X-ray intensity of the element M when measuring the cross section of the carbonaceous material in a visual field of 10 μm is within the range of 0.7X ≦ I ≦ 1.3X, that is, the above X
Or the deviation from X is within ± 30%, the element M is substantially uniformly dispersed in the carbonaceous material. Uniform dispersion here means EPMA
As inferred from the size of the visual field defined in the image, it is a microscopic dispersion of the element M in the carbon matrix. For example, microcluster-like metal (element M) in the interstices of unorganized carbon constituting the carbonaceous material. It means the compounding of materials from the raw material level, such as dispersion of particles and insertion into lattice defects. When the deviation of the above-mentioned X-ray intensity ratio (I) from X is more than ± 30%, the element M is not uniformly dispersed in the carbonaceous material, and the expansion of the carbonaceous material due to lithium occlusion / release. The strain in the contraction can cause cycle degradation due to structural stress. The X-ray intensity ratio (I) is equal to the X, or the deviation from the X is within a range of ± 20%, that is, 0.8X ≦ I
It is preferably in the range of ≦ 1.2X.

The carbonaceous material is randomly selected from 50 to 50.
X-ray intensity ratio (I) of 100 fields of view is 0.7X ≦ I ≦ 1.3
It is preferably within the range of X. Particularly, the randomly selected X-ray intensity ratio (I) in 70 or more fields of view is 0.7X ≦ I
It is preferably in the range of ≦ 1.3X.

The content of the element M in the carbonaceous material is 3
It is preferably 0% by weight or more. The content is 30
If it is less than wt%, it may be difficult to improve the charge / discharge capacity per volume of the negative electrode. Although the content is more preferably 40% by weight or more, 90
When the content exceeds the weight%, particles containing the element M may be fused and grown, exhibiting properties as a bulk metal and possibly causing deterioration in charge / discharge cycle. The content of the element M is 9
It is preferably 0% by weight or less, more preferably 8%.
It is 0% by weight or less.

The average particle size of the particles containing the element M is
It is preferably 100 nm or less. Average particle size is 10
If it exceeds 0 nm, it exhibits properties as a bulk metal rather than as fine particles, and may cause pulverization due to charge / discharge, which may cause cycle deterioration of charge / discharge capacity. In addition, the lattice defects of the carbonaceous material may become large. The average particle diameter is preferably 1 nm or more and 100 nm or less. In addition, the average particle diameter is a transmission electron microscope (T
EM).

Considering that the element M (heterogeneous element) is evenly dispersed on the surface of the carbonaceous material, the carbonaceous material has an element M with respect to the peak intensity of carbon atoms analyzed by X-ray photoelectron spectroscopy (XPS). It is desirable that the peak intensity ratio (P) of 1 satisfies the following expression (2).

P ≦ 1.3 {cn / m (100−n)} (2) where c is the atomic weight of carbon, m is the atomic weight of the element M contained in the carbonaceous material, and n is the element based on the weight of carbon. It is the weight ratio (%) of M.

1.3 {cn / in the above equation (2)
The value calculated from m (100-n)} represents the theoretical atomic number ratio (element M / carbon) on the surface of the carbonaceous material, which is obtained from the content of the element M of the carbonaceous material. It is desirable that the atomic number ratio of the element M actually existing on the surface of the carbonaceous material be equal to this value or fall within 30% from this value. When many particles containing the element M appear on the surface of the carbonaceous material, the particles may be separated from the carbon matrix during repeated charging / discharging, or the particles may react with the electrolytic solution to cause deterioration of the carbonaceous material. Because there is. Further, the ratio of the peak intensity of the element M measured by XPS to the carbon peak intensity indicates the atomic ratio of the element M to the number of carbon atoms on the surface of the carbonaceous material. Therefore, the ratio of the peak intensity of the element M measured by XPS to the carbon peak intensity is not more than the value calculated from 1.3 {cn / m (100-n)} in consideration of the detection depth and variations. Is preferred.

The carbonaceous material is powder X-ray diffraction (powder XR
It is better that the X-ray reflection peak due to each element M measured in D) does not appear clearly or becomes broad.

The carbonaceous material is, for example, Mg, Al or S.
It is produced by firing an organometallic complex containing at least one element selected from i, Ca, Sn and Pb in an inert atmosphere.

As the organic metal complex, for example, the following polymer metal complexes (a) to (c) can be used.

(A) A homopolymer of a metal-containing monomer containing a chain carbon-carbon unsaturated bond in the molecule shown in the following chemical formula 1. Alternatively, a copolymer of the metal-containing monomer and a general-purpose monomer exemplified in Chemical Formula 2 below. Examples of the general-purpose monomer include styrene, acrylonitrile, vinyl pyridine and the like.

(B) As exemplified by the following chemical formula 3, for example, an organometallic compound having an organic homopolymer having a functional group such as COOH, NR ₂ , OH, and PR ₂ groups as a Lewis base as a ligand, Metal complexed with a metal salt. Alternatively, as exemplified in Chemical Formula 4 below, a metal complex of an organic copolymer having the functional group with an organometallic compound or a metal salt having a Lewis base as a ligand. As the organic homopolymer, for example, polyacrylic acid, polyacrylonitrile, polyvinyl alcohol, polyvinyl pyridine, polyvinyl pyrrolidone, addition polymers having the functional group represented by 1,2-polybutadiene and the like,
Various sugars, peptides, petroleum coal pitch, etc. can be mentioned. Examples of the organic copolymer include modified polystyrene having the functional group introduced therein, and a copolymer having the functional group.

(C) A mixture of an organic polymer and a metal-containing polymer as exemplified in the following chemical formulas 5 and 6. The organic polymer is preferably one that is soluble in a solvent and has a high residual carbon rate after firing. On the other hand, it is preferable that the metal-containing polymer is a soluble high-molecular weight metal compound that does not easily sublime during firing. Further, it is desirable that the polymer main chain is a polymer mainly composed of carbon.

The synthesis of the polymer metal complex as described in the above (a) and (b) can be carried out at a low temperature of, for example, 300 ° C. or lower. For some metals, in addition to the method of synthesizing the polymer metal complex and then calcining, the raw material for forming the polymer metal complex can be calcined to produce the carbonaceous material.

The firing temperature is preferably 550 ° C. or higher and lower than the temperature at which carbide of each metal is formed. This is due to the following reasons. When the firing temperature is lower than 550 ° C., carbonization does not proceed so much, which may make it difficult to secure conductivity of the carbonaceous material. In addition, it may be difficult for the carbonaceous material to occlude and release lithium, and it may be difficult to improve the effective charge / discharge capacity. The firing temperature is 800
It is more preferable that the temperature is not lower than ° C. The firing temperature is 80
By setting the temperature to 0 ° C. or higher, cycle deterioration due to the amorphous structure of the carbonaceous material itself can be suppressed. On the other hand, if the firing temperature exceeds the formation temperature of various metal carbides, the introduced element M may not be able to participate in charge / discharge, and it may not be possible to expect an increase in capacity.

[0041]

[Chemical 1]

[0042]

[Chemical 2]

[0043]

[Chemical 3]

[0044]

[Chemical 4]

[0045]

[Chemical 5]

[0046]

[Chemical 6] In Chemical Formulas 1 to 6, X is a functional group (for example, CO
OH, NR ₂ , OH, PR ₂ groups), MLn is Mg, Al,
A mononuclear complex, a binuclear complex, or a polynuclear complex of at least one metal selected from Si, Ca, Sn, and Pb, and R represents a hydrocarbon group.

Although the metal-containing carbonaceous material can be synthesized by other methods, the types of metal compounds that can be introduced are limited, and the moldability, composition ratio and stability of the product are limited. Further, in terms of the uniform dispersion of the element M in the carbonaceous material, it is simply adsorption of the metal fine particles on the surface of the carbonaceous material, or conversely, the carbon is supported on the surface of the metal particles having a bulk property. May be generated,
It is not preferable from the viewpoint of ensuring the cycle characteristics of the lithium secondary battery.

The negative electrode 6 is produced, for example, by kneading the carbonaceous material and the binder in the presence of a solvent, applying the obtained suspension to a current collector, drying and then pressing. It

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR),
Carboxymethyl cellulose (CMC) or the like can be used.

The blending ratio of the carbonaceous material and the binder is
The carbon material is preferably in the range of 90 to 95% by weight and the binder in the range of 2 to 10% by weight.

As the current collector, for example, foil, mesh, punched metal, lath metal or the like made of copper, stainless steel or nickel can be used.

4) Electrolyte Solution The non-aqueous electrolyte solution is prepared by dissolving an electrolyte in a non-aqueous solvent.

The non-aqueous solvent may be a non-aqueous solvent known as a solvent for lithium secondary batteries, and is not particularly limited, but it has a lower melting point than ethylene carbonate (EC) and the ethylene carbonate, and a donor. It is preferable to use a non-aqueous solvent mainly composed of a mixed solvent with one or more non-aqueous solvents having a number of 18 or less (hereinafter referred to as a second solvent).

As the second type solvent, for example, chain carbon is preferable, and among them, dimethyl carbonate (DM
C), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, or propylene carbonate (P
C), γ-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate (EA), toluene, xylene or methyl acetate (MA). These second solvents can be used alone or in the form of a mixture of two or more kinds. In particular, it is more preferable that the second type solvent has a donor number of 16.5 or less.

The viscosity of the second solvent is 2 at 25 ° C.
It is preferably 8 mp or less.

The blending amount of the ethylene carbonate in the mixed solvent is preferably 10 to 80% by volume. A more preferable blending amount of ethylene carbonate is 20 to 75% by volume.

A more preferable composition of the mixed solvent is EC
And MEC, EC and PC and MEC, EC and MEC and DE
C, EC and MEC and DMC, EC and MEC and PC and DE
The volume ratio of MEC in the mixed solvent of C is preferably 30 to 80%. More preferable volume ratio of MEC is
It is in the range of 40 to 70%.

As the electrolyte contained in the non-aqueous electrolyte, for example, lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride ( LiAs
F ₆ ), lithium trifluorometasulfonate (LiC
F ₃ SO _3), bis (trifluoromethylsulfonyl) imide lithium _{[LiN (CF 3 SO 2)} 2] Lithium salt such as (electrolyte) can be mentioned. Above all, LiPF ₆ , Li
It is preferred to use BF ₄ .

The amount of the electrolyte dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / 1.

The lithium secondary battery according to the present invention described above is a lithium secondary battery provided with a negative electrode containing a carbonaceous material that absorbs and releases lithium ions, and the carbonaceous material is Mg, Al, Si, It contains an element M consisting of at least one element selected from Ca, Sn and Pb, and is 10 by an electron beam microanalyzer (EPMA).
X of the element M when the cross section is measured in the visual field of × 10 μm
The X-ray intensity ratio (I) of carbon to the line intensity is 0.7X ≦ I
≦ 1.3X is satisfied, and the X is represented by the following formula (1).

X = (100-n) m / cn (1) Since the element M is uniformly dispersed in the carbonaceous material, the amount of occlusion / release of lithium ions per unit volume can be improved. . Further, since it is possible to prevent the carbonaceous material from being distorted when the carbonaceous material expands / contracts in association with the absorption / desorption of lithium, the amount of absorption / desorption of lithium ions decreases as the charge / discharge cycle progresses. Can be suppressed. Therefore, a lithium secondary battery having a high capacity and a long life can be realized. Furthermore, the secondary battery can detect the remaining capacity of the battery from the voltage drop at the end of discharge.

In the method for manufacturing a lithium secondary battery according to the present invention, Mg, Al, Si, Ca, Sn and Pb are used.
A carbonaceous material is produced by a method including a step of firing an organometallic complex containing at least one element selected from According to such a manufacturing method, Mg, Al,
Since a carbonaceous material in which the element M, which is at least one element selected from Si, Ca, Sn, and Pb, is uniformly dispersed can be produced, a lithium secondary battery with high capacity and long life is provided. be able to.

[0063]

Embodiments of the present invention will now be described in detail with reference to FIG.

Example 1 <Production of Positive Electrode> First, lithium cobalt oxide (LiC
91 parts by weight of oO ₂ ) powder, 6 parts by weight of graphite and 3 parts by weight of polyvinylidene fluoride were mixed and dispersed in N-methyl-2-pyrrolidone to prepare a slurry.
A positive electrode was produced by applying the slurry to an aluminum foil and then pressing. <Preparation of Negative Electrode> After the organic Sn complex shown in Chemical Formula 7 below (Me in Chemical Formula 7 represents a methyl group) and the anisotropic pitch that is the carbon precursor are mixed in a weight ratio of 3: 1, 350 ℃
A metal-containing carbon polymer was grown by heat treatment at. The metal-containing carbon polymer was subjected to 9
A carbon-metal composite material was produced by firing at 00 ° C.

[0065]

[Chemical 7] The obtained material has a Sn content of 75% by weight and
The average particle size obtained by TEM of n particles was 10 nm. In addition, a desirable X-ray intensity ratio X (X of carbon is calculated from the composition ratio of the obtained composite material, when the cross section of the material is measured by EPMA in a visual field of 10 × 10 μm.
The line intensity / Sn X-ray intensity) was calculated from the above equation (1), and was 3.3. Therefore, the acceptable X-ray intensity ratio of the obtained composite material is 2.31 to 4.29. Actually, the cross section of the composite material is 1 by EPMA.
When measured in a visual field of 0 × 10 μm (the number of visual fields is 70), the X-ray intensity ratio (I) of carbon to the X-ray intensity of Sn in each obtained visual field is in the range of 2.7 to 4.0. Was the value of.

The value of 1.3 {cn / m (100-n)} in the above-mentioned equation (2) in the composite material is
It is 0.4. The peak intensity ratio (P) of Sn to the peak intensity of carbon atoms analyzed by X-ray photoelectron spectroscopy (XPS) of the composite material was actually measured.
It was 3 and it was confirmed that the composite material satisfies the above-mentioned formula (2).

Then, the obtained carbon-metal composite material 97
By weight, 2 parts by weight of styrene-butadiene rubber and 1 part by weight of carboxymethyl cellulose were mixed and dispersed in water to prepare a paste. The paste was applied to a copper foil, dried, and pressed to produce a negative electrode.

The positive electrode, the separator made of a polyethylene porous film, and the negative electrode were laminated in this order and then spirally wound to form an electrode group. <Preparation of non-aqueous electrolyte> Lithium hexafluorophosphate (LiP
F ₆ ) is a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1:
A non-aqueous electrolytic solution was prepared by dissolving 1.0 mol / 1 in 2).

The electrode group and the electrolytic solution were respectively housed in a bottomed cylindrical container made of stainless steel to assemble the cylindrical lithium secondary battery having the structure shown in FIG.

Example 2 A lithium secondary battery similar to that of Example 1 was assembled except that the carbon-metal composite material (carbonaceous material) described below was used.

<Preparation of Carbon-Metal Composite Material> The organic Sn complex shown in Chemical formula 7 above was mixed with anisotropic pitch which is a carbon precursor in a weight ratio of 3: 1 and then heat-treated at 350 ° C. To grow a metal-containing carbon polymer. The metal-containing carbon polymer was heated to 1200 ° C. under an argon atmosphere.
A carbon-metal composite material was produced by firing at.

The obtained material had a Sn content of 75% by weight and an average particle size of Sn particles determined by TEM of 10 nm. Further, a desirable X-ray intensity ratio X (X-ray intensity of carbon / X-ray intensity of Sn) calculated from the composition ratio of the obtained composite material when the cross section of the material is measured by a field of view of 10 × 10 μm by EPMA. ) Was calculated from the above formula (1), it was 3.3. Therefore, the allowable X-ray intensity ratio of the obtained composite material is
2.31 to 4.29. Actually, when the cross section of the composite material was measured by EPMA in a visual field of 10 × 10 μm (the number of visual fields is 70), the obtained X-ray intensity ratio of carbon to Sn X-ray intensity ratio (I) was obtained. Is 2.
It was a value within the range of 6 to 3.7.

Further, the value of 1.3 {cn / m (100-n)} in the above-mentioned equation (2) in the composite material is
It is 0.4. The peak intensity ratio (P) of Sn to the peak intensity of carbon atoms analyzed by X-ray photoelectron spectroscopy (XPS) of the composite material was actually measured.
It was 3 and it was confirmed that the composite material satisfies the above-mentioned formula (2).

(Example 3) A lithium secondary battery similar to that of Example 1 was assembled except that the carbon-metal composite material (carbonaceous material) described below was used.

<Preparation of Carbon-Metal Composite Material> Organic Al complex shown in the following chemical formula 8 (in chemical formula 8, py represents a pyridinyl group and Me represents a methyl group) and an anisotropic pitch which is a carbon precursor. After mixing and with a 3: 1 weight ratio, 350
The metal-containing carbon polymer was grown by heat treatment at ℃. The metal-containing carbon polymer under an argon atmosphere,
A carbon-metal composite material was produced by firing at 1200 ° C.

[0076]

[Chemical 8] The obtained material has an Al content of 60% by weight and
The average particle size obtained by TEM of 1 particle is 100 nm
Met. Also, a desirable X-ray intensity ratio X (X-ray intensity of carbon / X-ray intensity of Al) calculated from the composition ratio of the obtained composite material when the cross section of the material is measured by EPMA in a visual field of 10 × 10 μm. ) Was calculated from the above-mentioned formula (1), it was 1.5. Therefore, the acceptable X-ray intensity ratio of the obtained composite material is 1.05 to 1.95.
Is. Actually, the cross section of the composite material was measured by EPMA in a visual field of 10 × 10 μm (the number of visual fields was 70).
The X-ray intensity ratio (I) of carbon to the X-ray intensity of Al in each obtained visual field was a value within the range of 1.2 to 1.9.

The value of 1.3 {cn / m (100-n)} of the above-mentioned equation (2) in the composite material is
It is 0.9. The peak intensity ratio (P) of Al to the peak intensity of carbon atoms analyzed by X-ray photoelectron spectroscopy (XPS) of the composite material was actually measured.
5 and it was confirmed that the composite material satisfies the above-mentioned formula (2).

Example 4 A lithium secondary battery was assembled in the same manner as in Example 1 except that the carbon-metal composite material (carbonaceous material) described below was used.

<Preparation of Carbon-Metal Composite Material> Organic Si complex shown in Chemical Formula 9 below (in Chemical Formula 9, R represents a hydrocarbon group,
Me represents a methyl group, respectively, and in this case, R is a methyl group) and the carbon precursor anisotropic pitch is 2:
After mixing in a weight ratio of 1, the metal-containing carbon polymer was grown by heat treatment at 350 ° C. A carbon-metal composite material was produced by firing the metal-containing carbon polymer at 1200 ° C. in an argon atmosphere.

[0080]

[Chemical 9] The obtained material has a Si content of 40% by weight and an S content of
The average particle size obtained by TEM of i particles is 100 nm
Met. Also, a desirable X-ray intensity ratio X (X-ray intensity of carbon / X-ray intensity of Si) calculated from the composition ratio of the obtained composite material when the cross section of the material is measured by EPMA in a visual field of 10 × 10 μm. ) Was calculated from the above formula (1), it was 3.5. Therefore, the acceptable X-ray intensity ratio of the obtained composite material is 2.45 to 4.55.
Is. Actually, the cross section of the composite material was measured by EPMA in a visual field of 10 × 10 μm (the number of visual fields was 70).
The X-ray intensity ratio (I) of carbon to the X-ray intensity of Si in each obtained visual field was a value within the range of 2.8 to 4.1.

The value of 1.3 {cn / m (100-n)} in the above-mentioned equation (2) in the composite material is
It is 0.4. When the peak intensity ratio (P) of Si to the peak intensity of carbon atoms analyzed by X-ray photoelectron spectroscopy (XPS) of the composite material was actually measured, it was 0.
It was 3 and it was confirmed that the composite material satisfies the above-mentioned formula (2).

Example 5 A lithium secondary battery similar to that of Example 1 was assembled except that the carbon-metal composite material (carbonaceous material) described below was used.

<Preparation of Carbon-Metal Composite Material> Acrylonitrile and the organic Si complex shown in Chemical formula 9 above are mixed in a ratio of 1: 2.
After being mixed at a weight ratio of 3, the metal-containing carbon polymer was grown by heat treatment at 300 ° C. in the presence of a catalyst. The metal-containing carbon polymer was heated to 1200 ° C. under an argon atmosphere.
A carbon-metal composite material was produced by firing at.

The obtained material had a Si content of 40% by weight, and the Si particles had an average particle diameter of 100 nm as determined by TEM. Also, a desirable X-ray intensity ratio X (X-ray intensity of carbon / X-ray intensity of Si) calculated from the composition ratio of the obtained composite material when the cross section of the material is measured by EPMA in a visual field of 10 × 10 μm. ) Was calculated from the above formula (1), it was 3.5. Therefore, the allowable X-ray intensity ratio of the obtained composite material is
It is 2.45 to 4.55. Actually, when a cross section of the composite material was measured by EPMA in a visual field of 10 × 10 μm (the visual field number is 70), the obtained X-ray intensity ratio of carbon to Si X-ray intensity ratio (I) was obtained. Is 2.
It was a value within the range of 7 to 4.5.

The value of 1.3 {cn / m (100-n)} in the above-mentioned equation (2) in the composite material is
It is 0.4. When the peak intensity ratio (P) of Si to the peak intensity of carbon atoms analyzed by X-ray photoelectron spectroscopy (XPS) of the composite material was actually measured, it was 0.
It was 3 and it was confirmed that the composite material satisfies the above-mentioned formula (2).

Example 6 A lithium secondary battery was assembled in the same manner as in Example 1 except that the carbon-metal composite material (carbonaceous material) described below was used.

<Preparation of Carbon-Metal Composite Material> A mixture of petroleum pitch and the organic Si polymer shown in the following chemical formula 10 was mixed at a ratio of 1: 2, and the mixture was fired at 1200 ° C. in an argon atmosphere to make the carbon-metal composite material. Was produced.

[0088]

[Chemical 10] The obtained material has a Si content of 40% by weight and an S content of
The average particle size obtained by TEM of i particles is 100 nm
Met. Also, a desirable X-ray intensity ratio X (X-ray intensity of carbon / X-ray intensity of Si) calculated from the composition ratio of the obtained composite material when the cross section of the material is measured by EPMA in a visual field of 10 × 10 μm. ) Was calculated from the above formula (1), it was 3.5. Therefore, the acceptable X-ray intensity ratio of the obtained composite material is 2.45 to 4.55.
Is. Actually, the cross section of the composite material was measured by EPMA in a visual field of 10 × 10 μm (the number of visual fields was 70).
The X-ray intensity ratio (I) of carbon to the X-ray intensity of Si in each obtained visual field was a value within the range of 2.8 to 4.0.

The value of 1.3 {cn / m (100-n)} of the above-mentioned equation (2) in the composite material is
It is 0.4. When the peak intensity ratio (P) of Si to the peak intensity of carbon atoms analyzed by X-ray photoelectron spectroscopy (XPS) of the composite material was actually measured, it was 0.
It was 3 and it was confirmed that the composite material satisfies the above-mentioned formula (2).

Comparative Example 1 A lithium secondary battery was assembled in the same manner as in Example 1 except that the carbonaceous material described below was used.

<Production of Carbonaceous Material> A carbonaceous material was produced by polymerizing an anisotropic pitch, which is a carbon precursor, at 350 ° C., and then firing at 1200 ° C. in an argon atmosphere.

Comparative Example 2 A lithium secondary battery was assembled in the same manner as in Example 1 except that the carbon-metal composite material (carbonaceous material) described below was used.

<Preparation of Carbon-Metal Composite Material> Sn metal powder having an average particle size of 10 μm was mixed with a carbon precursor anisotropic pitch at a weight ratio of 2: 1 and then heat treated at 350 ° C. To grow a metal-containing carbon polymer. The metal-containing carbon polymer was heated to 1200 ° C. under an argon atmosphere.
A carbon-metal composite material was produced by firing at.

The obtained material had a Sn content of 75% by weight, and had an average particle size of 10 μm as determined by TEM of Sn particles. Further, a desirable X-ray intensity ratio X (X-ray intensity of carbon / X-ray intensity of Sn) calculated from the composition ratio of the obtained composite material when the cross section of the material is measured by a field of view of 10 × 10 μm by EPMA. ) Was calculated from the above formula (1), it was 3.3. Therefore, the allowable X-ray intensity ratio of the obtained composite material is
2.31 to 4.29. Actually, when the cross section of the composite material was measured by EPMA in a visual field of 10 × 10 μm (the number of visual fields is 70), the obtained X-ray intensity ratio of carbon to Sn X-ray intensity ratio (I) was obtained. Is 0.
The value was within the range of 3 to ∞ (infinity).

Comparative Example 3 A lithium secondary battery was assembled in the same manner as in Example 1 except that the carbon-metal composite material (carbonaceous material) described below was used.

<Preparation of Carbon-Metal Composite Material> Anisotropic pitch, which is a carbon precursor, was heated at 1200 ° C. in an argon atmosphere.
A carbonaceous material was produced by firing at. A Sn-metal powder having an average particle size of 10 μm and the carbonaceous material were mixed at a weight ratio of 3: 1 to prepare a carbon-metal composite material.

The obtained material had a Sn content of 75% by weight, and had an average particle size of 10 μm as determined by TEM of Sn particles. Further, a desirable X-ray intensity ratio X (X-ray intensity of carbon / X-ray intensity of Sn) calculated from the composition ratio of the obtained composite material when the cross section of the material is measured by a field of view of 10 × 10 μm by EPMA. ) Was calculated from the above formula (1), it was 3.3. Therefore, the allowable X-ray intensity ratio of the obtained composite material is
2.31 to 4.29. Actually, when the cross section of the composite material was measured by EPMA in a visual field of 10 × 10 μm (the number of visual fields is 70), the obtained X-ray intensity ratio of carbon to Sn X-ray intensity ratio (I) was obtained. Is 0
It was a value within the range of ∞ (infinity).

Comparative Example 4 A lithium secondary battery was assembled in the same manner as in Example 1 except that the carbon-metal composite material (carbonaceous material) described below was used.

<Preparation of Carbon-Metal Composite Material> Anisotropic pitch, which is a carbon precursor, was polymerized at 350 ° C. in an argon atmosphere and then calcined at 1200 ° C. to prepare a carbonized material. SnCl ₂ was mixed with this carbonized material, and the mixture was further baked at 1200 ° C. for 1 hour in an argon atmosphere to prepare a carbon-metal composite material.

The obtained material had a Sn content of 10% by weight and an average particle size of Sn particles determined by TEM of 100 nm. Further, a desirable X-ray intensity ratio X (X-ray intensity of carbon / X-ray intensity of Sn) calculated from the composition ratio of the obtained composite material when the cross section of the material is measured by a field of view of 10 × 10 μm by EPMA. ) Was 88 from the equation (1). Therefore,
An acceptable X-ray intensity ratio of the resulting composite material is 61.
6 to 114.4. Actually, when the cross section of the composite material was measured by EPMA in a visual field of 10 × 10 μm (the visual field number is 70), Sn in each visual field obtained was obtained.
X-ray intensity ratio (I) to the X-ray intensity of 30 to ∞
It was a value within the range of (infinity).

The value of 1.3 {cn / m (100-n)} in the above-mentioned equation (2) in the composite material is
It is 0.02. The peak intensity ratio (P) of Sn to the peak intensity of carbon atoms analyzed by X-ray photoelectron spectroscopy (XPS) of the composite material was actually measured.
It was 0, and it was found that most of the Sn particles were supported on the surface of the composite material.

Comparative Example 5 A lithium secondary battery was assembled in the same manner as in Example 1 except that the carbon-metal composite material (carbonaceous material) described below was used.

<Preparation of Carbon-Metal Composite Material> SnCl ₂ was roughly mixed with an anisotropic pitch which is a carbon precursor, and calcined at 1200 ° C. for 1 hour in an argon atmosphere to prepare a carbon-metal composite material. .

The obtained material had a Sn content of 75% by weight and an average particle size of Sn particles determined by TEM of 100 nm. Further, a desirable X-ray intensity ratio X (X-ray intensity of carbon / X-ray intensity of Sn) calculated from the composition ratio of the obtained composite material when the cross section of the material is measured by a field of view of 10 × 10 μm by EPMA. ) Was calculated from the above formula (1), it was 3.3. Therefore, the allowable X-ray intensity ratio of the obtained composite material is
2.31 to 4.29. Actually, when the cross section of the composite material was measured by EPMA in a visual field of 10 × 10 μm (the number of visual fields is 70), the obtained X-ray intensity ratio of carbon to Sn X-ray intensity ratio (I) was obtained. Is 1.
It was a value within the range of 2 to 8.2.

Each of the 10 lithium ion secondary batteries obtained in Examples 1 to 6 and Comparative Examples 1 to 5 was charged with a charging current of 1.5 A to 4.2 V for 2 hours, and then to 2.7 V for 1. A charge / discharge cycle test of discharging at 5 A was performed, and the average discharge capacity and capacity retention rate were measured.
Shown in. The capacity retention rate was the discharge capacity ratio at the 300th cycle to the discharge capacity at the first cycle.

[0106]

[Table 1] As is clear from Table 1, 10 × 10μ by EPMA
Example 1 equipped with a negative electrode containing a carbonaceous material in which the X-ray intensity ratio (I) of carbon to the X-ray intensity of the element M when measuring the cross section in the field of view of m satisfies 0.7X ≦ I ≦ 1.3X The secondary battery of No. 6 is a secondary battery of Comparative Example 1 including a negative electrode containing a carbonaceous material that does not contain the element M, and a comparative example including a negative electrode including a carbonaceous material having the intensity ratio (I) outside the range. It can be seen that the average discharge capacity is higher and the charge / discharge cycle life is longer than the secondary batteries of Nos. 2 to 5. In addition, although the secondary battery of Comparative Example 4 had excellent initial charge / discharge efficiency, Sn was distributed only on the surface of the carbonaceous material, so that it was easily deteriorated when the cycle was repeated, and the probability of short circuit was high.

In the above embodiment, the example applied to the cylindrical lithium secondary battery has been described, but the present invention can also be applied to the prismatic lithium secondary battery. Further, the electrode group housed in the battery container is not limited to the spiral shape, and may have a configuration in which a plurality of positive electrodes, separators and negative electrodes are laminated in this order.

[0108]

As described in detail above, according to the present invention,
A lithium secondary battery with high capacity and long life can be provided. Further, according to the present invention, it is possible to provide a method for manufacturing a lithium secondary battery having a high capacity and a long life.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing an example of a lithium secondary battery according to the present invention.

[Explanation of symbols]

1 ... container, 3 ... electrode group, 4 ... Positive electrode, 6 ... Negative electrode, 8 ... Sealing plate.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-11-260367 (JP, A) JP-A-11-260369 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/00-4/04 H01M 4/36-4/62 H01M 10/40

Claims (2)

(57) [Claims] 1. A lithium secondary battery comprising a negative electrode containing a carbonaceous material that occludes and releases lithium ions, wherein the carbonaceous material contains an element M having an average particle size of 100 nm or less.
Those containing particles (excluding those containing S)
The element M is Mg, Al, Si, Ca, Sn and
Consists of at least one element selected from Pb, and 10x by electron beam microanalyzer (EPMA)
The X-ray intensity ratio (I) of carbon to the X-ray intensity of the element M when the cross section is measured in the visual field of 10 μm is 0.7X ≦ I ≦
A lithium secondary battery satisfying 1.3X, wherein X is represented by the following formula (1). X = (100−n) m / cn (1) where n is the content (% by weight) of the element M of the carbonaceous material, m is the atomic weight of the element M contained in the carbonaceous material, and c is Indicates the atomic weight of carbon. 2. The carbonaceous material is Mg, Al, Si, C
Organometallic complex containing at least one element selected from a, Sn and Pb (excluding those containing S)
The method for producing a lithium secondary battery according to claim 1, wherein the method is produced by a method including a step of firing.