JPH103920A - Lithium secondary battery, and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery, wherein both of the discharge capacity and the cycle life can be improved, and a manufacturing method for the lithium secondary battery. SOLUTION: This battery is equipped with a positive electrode 4, a negative electrode 6 containing active material for storing and releasing lithium ions, and a nonaqueous electrolyte, where the active material of the negative electrode 6 contains fine particles wherein a carbonaceous layer is formed on the surface. The fine particles are composed of at least one element M selected from among Mg, Al, Si, Ca, Sn, and Pb, their mean particle diameter is 1-500nm, and the atomic ratio of the fine particles in the active material is 15% or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte batteries using lithium as a negative electrode active material have attracted attention as high energy density batteries, and manganese dioxide (MnO ₂ ) has been used as a positive electrode active material.
Fluorocarbon [(CF ₂ ) _n ], thionyl chloride (SOCl
Primary batteries using ₂ ) and the like are already widely used as power supplies for calculators, watches, and as backup batteries for memories.

Further, in recent years, with the reduction in size and weight of various electronic devices such as VTRs and communication devices, the demand for secondary batteries having a high energy density as a power source for these devices has increased, and lithium secondary batteries using lithium as a negative electrode active material have been required. Battery research is being actively conducted.

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

[0005] However, the above-mentioned lithium secondary battery has not been put to practical use. The main reason for this is that the charge / discharge efficiency is low and the number of times that charge / discharge can be performed (cycle life) is short. It is considered that this is largely due to the deterioration of lithium due to the reaction between the lithium of the negative electrode and the non-aqueous electrolyte. That is, lithium dissolved in the non-aqueous electrolyte as lithium ions at the time of discharge reacts with the solvent at the time of deposition at the time of charging, and its surface is partially inactivated. Therefore, when charge and discharge are repeated, lithium precipitates in a dendritic (dendritic) or small spherical shape, and further, phenomena such as detachment of lithium from the current collector occur.

[0006] For these reasons, as a negative electrode incorporated in a lithium secondary battery, a carbonaceous material that absorbs and desorbs lithium, such as graphite, coke, a resin fired body, carbon fiber,
It has been proposed to improve the reaction between lithium and the non-aqueous electrolyte, and further to reduce the deterioration of the negative electrode characteristics due to dendritic deposition, by using pyrolytic gas phase carbon or the like, which is currently in practical use. However, this lithium secondary battery has a problem that the discharge capacity is low.

On the other hand, from the viewpoint of increasing the capacity of a lithium secondary battery, the use of a lithium alloy represented by a composition formula of Li _X A (A is made of a metal such as Al) as a negative electrode has been studied. . Although this negative electrode has a large amount of lithium ions stored and released per unit volume, and has a high capacity, it expands and contracts when lithium ions are stored and released, so that pulverization proceeds with the progress of a charge and discharge cycle. For this reason, the lithium secondary battery provided with the negative electrode has a higher discharge capacity than the secondary battery provided with the negative electrode containing the carbonaceous material, but has a problem that the charge / discharge cycle life is short.

Further, J. J. Electrochem. So
c. , 142, 326 (1995) discloses that a capacity of 372 mAh / g or more, which is a theoretical capacity with respect to graphite, can be obtained by using, as a negative electrode of a lithium secondary battery, a substance obtained by introducing Si into pyrolytic gas phase carbon by vapor phase deposition. Is disclosed.

However, since the pyrolytic carbon into which Si has been introduced is produced by vapor deposition, it is difficult to adjust the amount of Si contained and to synthesize it in large quantities. In addition, the amount of Si that can be introduced into the pyrolytic carbon is limited, and the weight ratio is at most 10%. Therefore, it is difficult to improve the discharge capacity. Further, there is a problem that the pyrolytic carbon in which Si is introduced is limited to the non-graphitic one.

It has also been proposed to use a mixture of a carbonaceous material powder that absorbs and releases lithium ions and aluminum particles for the negative electrode, but the negative electrode suppresses the pulverization of the aluminum particles as the charge-discharge cycle progresses. However, there is a problem that the charge / discharge cycle life is short.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery having improved discharge capacity and cycle life, and a method of manufacturing the same.

[0012]

SUMMARY OF THE INVENTION A lithium secondary battery according to the present invention comprises a positive electrode, a negative electrode containing an active material for absorbing and releasing lithium ions, and a non-aqueous electrolyte. The carbonaceous material layer includes fine particles formed on the surface,
The fine particles are composed of Mg, Al, Si, Ca, Sn and Pb.
And a mean particle size of 1 to 500 nm, and an atomic ratio of the fine particles in the active material is 15% or more.

A method of manufacturing a lithium secondary battery according to the present invention is a method of manufacturing a lithium secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. 50% of a precursor and fine particles having a weight ratio of 15% or more to the raw carbonaceous material or the carbon precursor
Produced by a method including a step of heating to 0 ° C. to 2800 ° C., wherein the fine particles are made of Mg, Al, Si, Ca, Sn
And at least one element M selected from Pb and Pb and having an average particle diameter of 1 nm to 500 nm.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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. For example, a cylindrical container 1 with a bottom made of stainless steel has an insulator 2 disposed at the bottom. The electrode group 3 is housed in the container 1. The electrode group 3 has a structure in which a strip formed by laminating a positive electrode 4, a separator 5 and a negative electrode 6 in this order is spirally wound so that the negative electrode 6 is located outside.

The container 1 contains an electrolytic solution. The insulating paper 7 having a central portion opened is placed above the electrode group 3 in the container 1. The insulating sealing plate 8
The sealing plate 8 is disposed at the upper opening of the container 1 and caulked in the vicinity of the upper opening inward.
Is fixed to the container 1 in a liquid-tight manner. The positive terminal 9 is
The insulating sealing plate 8 is fitted at the center. Positive lead
One end of the cathode 10 is connected to the positive electrode 4, and the other end is connected to the positive electrode terminal 9.
Connected to each other. The negative electrode 6 is connected to the container 1 as a negative terminal via a negative 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 produced by suspending a conductive agent and a binder in a suitable solvent in a positive electrode active material, 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 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 cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (L
iNiO ₂ ), lithium manganese oxide (LiMn ₂ O)
₄ or LiMnO ₂ ) is preferable because a high voltage can be obtained.

Examples of the conductive agent include acetylene black, carbon black, graphite and the like. Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVD).
E), ethylene-propylene-diene copolymer (EPD)
M), styrene-butadiene rubber (SBR) and the like can be used.

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, 3 to 2% of the conductive agent.
It is preferable that the content be in the range of 0% by weight and 2 to 7% by weight of the binder.

As the current collector, for example, aluminum foil, stainless steel foil, nickel foil or the like can be used. 2) Separator 5 As the separator 5, for example, a synthetic resin nonwoven fabric,
A polyethylene porous film, a polypropylene porous film, or the like can be used.

3) Negative Electrode 6 The negative electrode 6 contains an active material that stores and releases lithium ions. The active material includes fine particles having a surface on which a carbonaceous material layer that stores and releases lithium ions is formed. The fine particles are made of at least one element M selected from Mg, Al, Si, Ca, Sn and Pb, and have an average particle size of 1n.
m to 500 nm. The atomic ratio of the fine particles in the active material is 15% or more.

The active material may be formed only from the fine particles forming the carbonaceous material layer, or may include a carbonaceous material not forming such fine particles. As the carbonaceous material without the fine particles, a carbonaceous material that absorbs and releases lithium ions is used.

Such a negative electrode 6 is produced, for example, by suspending the active material and the binder in an appropriate solvent, applying the suspension to a current collector, drying and pressing the current collector. be able to.

The reason why the average particle diameter of the fine particles is limited to the above range is as follows. If the average particle size exceeds 500 nm, the fine particles may be finely divided as the charge / discharge cycle progresses. The smaller the average particle size is, the better. A more preferred average particle size is 250 nm or less, and a still more preferred average particle size is 200 nm or less. The lower limit of the average particle size is preferably set to 1 nm.

The reason for limiting the atomic ratio of the fine particles in the active material to the above range is as follows. If the atomic ratio is less than 15%, it is difficult to improve the capacity of the negative electrode. However, when the atomic ratio exceeds 60%, the fine particles of the element M aggregate and become large, and there is a possibility that the fine particles are formed into fine particles as the charge / discharge cycle proceeds. Therefore, the upper limit of the atomic ratio is preferably set to 60%. A more preferred upper limit is 50%.

The fine particles having the carbonaceous material layer formed on the surface thereof are, for example, as shown in FIG. 2, between a hexagonal mesh layer 11 of graphite crystallites constituting the carbonaceous material layer and a tangent 1 to the surface of the fine particles 12. It is preferable to have a structure in which the average of the angles α is 20 ° to 90 °. The average of the angle α is 20
If it is less than ゜, the orientation of graphite crystallites constituting the carbonaceous material layer may be parallel to the surface of the fine particles, which may hinder rapid diffusion of lithium ions to the negative electrode. The average of the angle α is more preferably set in the range of 40 ° to 90 °.

It is preferable that the thickness of the carbonaceous material layer formed on the surface of the fine particles is thin so that the amount of the fine particles occupying in the negative electrode does not become insufficient. It is necessary to set the carbonaceous material layer so that it can function as a reinforcing layer that suppresses pulverization due to expansion and contraction accompanying the above.

The carbonaceous material layer-forming fine particles preferably form secondary particles. As the secondary particles,
Examples include those having a structure in which the carbonaceous material layer-forming fine particles are bonded so as to ensure conduction between the fine particles, and those having a structure in which the carbonaceous material layer-forming fine particles are dispersed in a carbonaceous material in which no fine particles are formed. it can. It is preferable that the carbonaceous material layer-forming fine particles are uniformly dispersed in the carbonaceous material without the fine particles. It is more preferable that the negative electrode has a fine structure capable of inserting and extracting lithium ions in gaps between the secondary particles.

The true density of the active material is 1.7 g / cm ³
It is preferable to make the above. The true density is 1.7 g / c
If it is less than m ³ , the volume specific capacity of the negative electrode may decrease.

The active material has, for example, a weight ratio of the raw material carbonaceous material or carbon precursor to the raw material carbonaceous material or carbon precursor of 15% or more and an average particle size of 1 nm to 1 nm.
500 nm fine particles (where the fine particles are Mg, Al,
(At least one element M selected from Si, Ca, Sn, and Pb) is heated to 500 ° C. to 2800 ° C.

In the above method, the weight ratio of the fine particles to the raw carbonaceous material or the carbon precursor may be 15%.
If it is less than 10%, the atomic ratio of the fine particles in the active material may be lower than 15%. However, if the weight ratio exceeds 60%, the content of fine metal particles after the heat treatment may exceed 60% due to the decrease in the weight of the carbonaceous material that occurs when the raw material mixture is heated. Therefore, the upper limit of the weight ratio is preferably set to 60%. A more preferred weight ratio is in the range of 15% to 50%.

In the above method, the reason why the synthesis temperature is limited to the above range is as follows. If the synthesis temperature is lower than 500 ° C., there is a possibility that a film mainly composed of the element M may be formed without forming the carbonaceous material layer on the surface of the fine particles. In addition, carbonization of the carbonaceous material becomes insufficient, and lithium ions may be trapped in the material. On the other hand, when the synthesis temperature exceeds 2800 ° C., the degree of graphitization of the carbonaceous material layer formed on the surface of the fine particles increases, and the orientation of graphite crystallites constituting the carbonaceous material layer is parallel to the particle surface. There is a possibility that a complicated laminated structure may be obtained. The synthesis temperature is more preferably 800 °-
2500 °, more preferably in the range of 800 ° to 2300 °.

Examples of the raw carbonaceous material include carbon having a large specific surface area, such as acetylene black and activated carbon. Further, the raw material carbonaceous material is preferably in the form of fine particles sufficiently small to be uniformly mixed with the fine particles.

Examples of the carbon precursor include a graphitizable carbon precursor (eg, petroleum pitch, coal pitch as a raw material, mesophase pitch, coke, etc.), and a non-graphitizable carbon precursor (eg, isotropic). , Pitch, polyacrylonitrile, furfuryl alcohol, furan resin, phenolic resin, cellulose, sugar, polyvinylidene chloride, etc.), and precursors of carbonaceous materials synthesized by a sol-gel method. Among them, a graphitizable carbon precursor is preferably used. Since the graphitizable carbon precursor can increase the lithium diffusion rate of the negative electrode, the discharge capacity in a rapid charge / discharge cycle of 1 C or more can be improved.

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 mixing ratio of the active material and the binder is preferably in the range of 90 to 98% by weight of the active material and 2 to 10% by weight of the binder. In particular, it is preferable that the amount of the active material is in the range of 5 to ²⁰ mg / cm ^{2 when} the negative electrode is manufactured.

As the current collector, for example, a copper foil, a stainless steel foil, a nickel foil or the like can be used. 4) Electrolyte The non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent.

As the non-aqueous solvent, a known non-aqueous solvent as a solvent for a lithium secondary battery can be used, and is not particularly limited. Ethylene carbonate (EC) has a melting point lower than that of 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). Such a non-aqueous solvent is advantageous in that it is stable with respect to the carbonaceous material having a graphite structure that constitutes the negative electrode, hardly causes reductive decomposition or oxidative decomposition of the electrolytic solution, and has high conductivity.

The non-aqueous electrolyte containing ethylene carbonate alone has the advantage of being hardly reductively decomposed to the graphitized carbonaceous material, but has a high melting point (39 ° C. to 40 ° C.).
℃) Because of high viscosity, the conductivity is small and not suitable for a secondary battery operated at room temperature. The second solvent mixed with ethylene carbonate has a lower viscosity than the ethylene carbonate in the mixed solvent to improve conductivity. Further, by using the second solvent having a donor number of 18 or less (provided that the number of donors of ethylene carbonate is 16.4), the ethylene carbonate is not easily solvated selectively with lithium ions, and the graphite structure is developed. It is considered that the reduction reaction of the second solvent with respect to the carbonaceous material is suppressed. Further, by setting the number of donors of the second solvent to 18 or less, the oxidative decomposition potential becomes 4 with respect to the lithium electrode.
V or more, and has an advantage that a high-voltage lithium secondary battery can be realized.

As the second type of 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. In particular, the second type solvent more preferably 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 10 to 10 by volume.
Preferably it is 80%. If you deviate from this range,
There is a possibility that charge and discharge efficiency may decrease due to a decrease in conductivity or decomposition of the solvent. A more preferable blending amount of the ethylene carbonate is 20 to 75% by volume ratio. By increasing the amount of ethylene carbonate in the non-aqueous solvent to 20% by volume or more, solvation of ethylene carbonate with lithium ions is facilitated, so that the effect of suppressing the decomposition of the solvent can be improved.

A more preferred composition of the mixed solvent is EC
And MEC, EC and PC and MEC, EC and MEC and DE
C, EC, MEC, DMC, EC, MEC, PC, DE
In the mixed solvent of C, the volume ratio of MEC is preferably 30 to 80%. Thus, the volume ratio of MEC is set to 30.
By setting the content to 80%, more preferably 40% to 70%, the conductivity can be improved. On the other hand, from the viewpoint of suppressing the reductive decomposition reaction of the solvent, using an electrolytic solution in which carbon dioxide (CO ₂ ) is dissolved is effective in improving the capacity and cycle life.

The main impurities present in the mixed solvent (non-aqueous solvent) include water and organic peroxides (eg, glycols, alcohols, carboxylic acids). It is considered that each of the impurities forms an insulating film on the surface of the graphitized material and increases the interfacial resistance of the electrode. Therefore, there is a possibility that the cycle life and capacity may be reduced. In addition, self-discharge during high-temperature (60 ° C. or higher) storage may increase. For this reason, it is preferable that the impurities be reduced as much as possible in the electrolytic solution containing the non-aqueous solvent. Specifically, the water content is 50 pp
m or less, and the amount of the organic peroxide is preferably 1000 ppm or less.

Examples of the electrolyte contained in the nonaqueous electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), and lithium arsenide hexafluoride (LiBF ₄ ). LiAsF
₆ ), lithium trifluorometasulfonate (LiCF
₃ SO ₃ ) and lithium bis (trifluoromethylsulfonylimide) [LiN (CF ₃ SO ₂ ) ₂ ]. Among them, LiPF ₆ , LiB
It is preferable to use F ₄ and LiN (CF ₃ SO ₂ ) ₂ .

The amount of the electrolyte dissolved in the non-aqueous solvent is desirably 0.5 to 2.0 mol / 1. A lithium secondary battery according to the present invention includes a positive electrode, a negative electrode including an active material that stores and releases lithium ions, and a nonaqueous electrolyte. The active material of the negative electrode has a carbonaceous material layer formed on a surface. Microparticles, wherein the microparticles are Mg, Al, Si, C
It is made of at least one element M selected from a, Sn and Pb, has an average particle diameter of 1 nm to 500 nm, and has an atomic ratio of the fine particles in the active material of 15% or more. The fine particles having the above-mentioned specific average particle diameter can be suppressed from being pulverized due to expansion and contraction caused by insertion and extraction of lithium ions. The carbonaceous material layer formed on the surface of the fine particles can reinforce the fine particles. Therefore, the negative electrode including the carbonaceous material layer-forming fine particles can avoid the fine particles of the fine particles accompanying the progress of the charge / discharge cycle, thereby improving the charge / discharge cycle life of the secondary battery.

Further, since the fine particles are formed from the element M, the amount of lithium ion occlusion / release per unit volume is large. Since the negative electrode contains an active material containing 15% or more of such fine particles in an atomic ratio, the capacity can be improved, and the discharge capacity of a secondary battery can be improved.

In such a negative electrode of a secondary battery, when the carbonaceous material layer-forming fine particles form secondary particles, the true density of the active material can be improved, so that the capacity per unit volume can be improved. can do. As a result, the secondary battery including the negative electrode can dramatically improve the discharge capacity.

In the fine particles having the carbonaceous material layer formed on the surface thereof, the average angle between the hexagonal mesh layer of graphite crystallites constituting the carbonaceous material layer and the tangent to the surface of the fine particles is 20 °. With a structure of up to 90 °, the layers of the hexagonal mesh layer face the surface of the negative electrode, so that the negative electrode can quickly occlude and release a large amount of lithium ions. Therefore, the secondary battery including the negative electrode can improve the discharge capacity at the time of rapid charging and discharging.

According to the method of manufacturing a lithium secondary battery according to the present invention, the weight ratio of the raw material carbonaceous material or carbon precursor to the raw material carbonaceous material or carbon precursor is 15%.
As described above, fine particles having an average particle diameter of 1 nm to 500 nm (the fine particles are made of at least one element M selected from Mg, Al, Si, Ca, Sn and Pb) are heated to 500 ° C.
A negative electrode is manufactured by a method including a step of heating to about 2800 ° C. According to such a method, an active material including the fine particles having a carbonaceous material layer formed on a surface thereof is provided, and a negative electrode in which the atomic ratio of the fine particles in the active material is 15% or more can be manufactured. A lithium secondary battery having improved discharge capacity and charge / discharge cycle life can be manufactured.

[0050]

An embodiment of the present invention will be described below in detail with reference to FIG. Example 1 First, lithium cobalt oxide (Li _x CoO ₂ (0.
8 ≦ x ≦ 1)) 91% by weight of powder was added to 3.5% by weight of acetylene black, 3.5% by weight of graphite, and 2% by weight of ethylene propylene diene monomer powder and mixed together, and aluminum foil (30 μm) was collected. After coating on the electric body, pressing was performed to produce a positive electrode.

Further, the mesophase pitch obtained from petroleum pitch is added with an average particle diameter obtained by a gas phase synthesis method of 100 n.
After adding 15% by weight of Al fine particles with respect to the mesophase pitch in a weight ratio and stirring uniformly with a raikai machine for at least 24 hours, the mixture is heated at 800 ° C. for 5 hours in an inert gas atmosphere to obtain lithium. An active material capable of inserting and extracting ions was obtained.

The obtained active material was subjected to a transmission electron microscope (TE).
Observation in M) revealed that the active material consisted of secondary particles having a structure in which Al fine particles having a mesophase pitch-based carbon layer formed on the surface were dispersed in a mesophase pitch-based carbon matrix in which no fine particles were formed. . The angle between the hexagonal mesh layer of graphite crystallites constituting the carbon layer and the tangent to the surface of the fine particles was determined from the observation of the cross section of the fine particles by the TEM, and the average angle was 45 °. The active material contained Al in an atomic ratio of 30%, and the true density was 2.0 g / cm ³ .

Next, 96.7% by weight of the active material was mixed with 2.2% by weight of styrene-butadiene rubber and 1.1% by weight of carboxymethylcellulose, applied to a copper foil as a current collector, and dried. A negative electrode was produced by pressing. The packing density of the obtained negative electrode was 1.45 g /
cm ³ .

The positive electrode, the separator made of a porous film made of polyethylene, and the negative electrode were laminated in this order, and then spirally wound so that the negative electrode was located outside, thereby producing an electrode group.

Further, lithium hexafluorophosphate (LiP)
F ₆ ) in 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 mol / l in 1).

The electrode group and the electrolytic solution were respectively housed in a stainless steel bottomed cylindrical container to assemble the above-described cylindrical lithium secondary battery shown in FIG. Example 2 A cylindrical lithium secondary battery similar to that of Example 1 was assembled except that the active material described below was used.

The active material was added to a mesophase pitch obtained from a petroleum pitch by adding 10% by weight of Al fine particles having an average particle diameter of 100 μm obtained by a gas phase synthesis method to the mesophase pitch. , And uniformly dispersed by stirring for 24 hours or more under an inert gas atmosphere.
Produced by heating at 5 ° C. for 5 hours.

The obtained active material was subjected to a transmission electron microscope (TE).
Observation in M) revealed that the active material consisted of secondary particles having a structure in which Al fine particles having a mesophase pitch-based carbon layer formed on the surface were dispersed in a mesophase pitch-based carbon matrix in which no fine particles were formed. . The angle between the hexagonal mesh layer of graphite crystallites constituting the carbon layer and the tangent to the surface of the fine particles was determined from the observation of the cross section of the fine particles by the TEM, and the average angle was 45 °. The active material contained Al in an atomic ratio of 15%, and the true density was 1.95 g / cm ³ .

Example 3 A cylindrical lithium secondary battery similar to that of Example 1 was assembled except that the active material described below was used.

The active material is prepared by adding 15% by weight of Al fine particles having an average particle diameter of 100 nm obtained by a gas phase synthesis method to a mesophase pitch obtained from a petroleum pitch by weight with respect to the mesophase pitch. , And uniformly dispersed by stirring for 24 hours or more under an inert gas atmosphere for 150 hours.
Produced by heating at 0 ° C. for 1 hour.

The obtained active material was subjected to a transmission electron microscope (TE).
Observation in M) revealed that the active material consisted of secondary particles having a structure in which Al fine particles having a mesophase pitch-based carbon layer formed on the surface were dispersed in a mesophase pitch-based carbon matrix in which no fine particles were formed. . The angle between the hexagonal mesh layer of the graphite crystallites constituting the carbon layer and the tangent to the surface of the fine particle was determined from the observation of the cross section of the fine particle by the TEM, and the average of the formed angle was 30 °. The active material contained Al in an atomic ratio of 30%, and the true density was 2.20 g / cm ³ .

Example 4 A cylindrical lithium secondary battery similar to that of Example 1 was assembled except that the active material described below was used.

The active material is prepared by adding 25% by weight of Mg fine particles having an average particle diameter of 150 nm obtained by a gas phase synthesis method to carbon black with respect to the carbon black, and mixing with a raikai machine for 24 hours to obtain a uniform. And then heated at 900 ° C. for 1 hour in an inert gas atmosphere.

The obtained active material was subjected to a transmission electron microscope (TE).
Observation in M) revealed that the active material consisted of secondary particles having a structure in which Mg fine particles having a carbon black layer formed on the surface were dispersed in a carbon black matrix having no fine particles formed thereon. The angle between the hexagonal mesh layer of the graphite crystallites constituting the carbon black layer and the tangent to the surface of the fine particles was determined by observing the cross section of the fine particles by the TEM, and the average angle was 45 °. The active material contained 50% of Mg in atomic ratio, and the true density was 1.9 g / cm ³ .

Example 5 A cylindrical lithium secondary battery similar to that of Example 1 was assembled except that the active material described below was used.

The active material has a mesophase pitch obtained from petroleum pitch having an average particle size obtained by a gas phase synthesis method of 2%.
After adding 30% by weight of Sn fine particles of 00 nm to the mesophase pitch in a weight ratio, mixing and uniformly dispersing the mixture for at least 24 hours with a raikai machine, and then 2,000 under an inert gas atmosphere.
Produced by heating at 1 ° C. for 1 hour.

The obtained active material was subjected to a transmission electron microscope (TE).
Observed in M), the active material is composed of secondary particles having a structure in which Sn fine particles having a mesophase pitch-based carbon layer formed on the surface are dispersed in a non-fine-particle-formed mesophase pitch-based carbon matrix. I understand. The angle between the tangent line between the hexagonal mesh layer of the graphite crystallites constituting the carbon layer and the surface of the fine particle was determined from the observation of the cross section of the fine particle by the TEM, and the average of the formed angle was 40 °. The active material contained Sn in an atomic ratio of 50%, and the true density was 4.0 g / cm ³ .

Example 6 A cylindrical lithium secondary battery was assembled in the same manner as in Example 1 except that the active material described below was used.

The active material has a mesophase pitch obtained from petroleum pitch and an average particle diameter obtained by a gas phase synthesis method is 2%.
After adding 50% of Ca fine particles at a weight ratio of 30% with respect to the mesophase pitch, mixing them for at least 24 hours with a raikai machine and uniformly dispersing them, under an inert gas atmosphere, 1000
Produced by heating at 1 ° C. for 1 hour.

The obtained active material was subjected to a transmission electron microscope (TE).
Observation in M) revealed that the active material consisted of secondary particles having a structure in which Ca fine particles having a mesophase pitch-based carbon layer formed on the surface were dispersed in a mesophase pitch-based carbon matrix in which no fine particles were formed. . The angle between the tangent line between the hexagonal mesh layer of the graphite crystallites constituting the carbon layer and the surface of the fine particle was determined from the observation of the cross section of the fine particle by the TEM, and the average of the formed angle was 40 °. The active material contained 50% of Ca in atomic ratio, and the true density was 1.8 g / cm ³ .

Example 7 A cylindrical lithium secondary battery was assembled in the same manner as in Example 1 except that the active material described below was used.

The active material has a mesophase pitch obtained from a petroleum pitch having an average particle diameter of 2 obtained by a gas phase synthesis method.
After adding 30% by weight of Pb fine particles of 00 nm to the mesophase pitch in a weight ratio and mixing and dispersing them uniformly for at least 24 hours with a raikai machine, under an inert gas atmosphere, 1500
Produced by heating at 1 ° C. for 1 hour.

The obtained active material was subjected to transmission electron microscopy (TE
Observation in M) revealed that the active material consisted of secondary particles having a structure in which Pb fine particles having a mesophase pitch-based carbon layer formed on the surface were dispersed in a mesophase pitch-based carbon matrix in which no fine particles were formed. . The angle between the tangent line between the hexagonal mesh layer of the graphite crystallites constituting the carbon layer and the surface of the fine particle was determined from the observation of the cross section of the fine particle by the TEM, and the average of the formed angle was 40 °. The active material contained 40% of Pb in atomic ratio, and the true density was 5.7 g / cm ³ .

Example 8 A cylindrical lithium secondary battery similar to that of Example 1 was assembled except that the active material described below was used.

The active material has a mean particle size obtained by a gas phase synthesis method in a mesophase pitch obtained from a petroleum pitch.
After adding 35% by weight of Si fine particles of 00 nm with respect to the mesophase pitch in a weight ratio, mixing them for 24 hours or more with a raikai machine to uniformly disperse them, and then 2,000 under an inert gas atmosphere.
Produced by heating at 1 ° C. for 1 hour.

The obtained active material was examined with a transmission electron microscope (TE).
Observation in M) revealed that the active material consisted of secondary particles having a structure in which Si fine particles having a mesophase pitch-based carbon layer formed on the surface were dispersed in a mesophase pitch-based carbon matrix in which no fine particles were formed. . The angle between the tangent line between the hexagonal mesh layer of the graphite crystallites constituting the carbon layer and the surface of the fine particle was determined from the observation of the cross section of the fine particle by the TEM, and the average of the formed angle was 40 °. The active material contained 50% of Si in atomic ratio, and the true density was 2.2 g / cm ³ .

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

The active material was added to a mesophase pitch obtained from a petroleum pitch by adding 15% by weight of Al fine particles having an average particle diameter of 100 μm obtained by a gas phase synthesis method to the mesophase pitch. , And uniformly dispersed by stirring for 24 hours or more under an inert gas atmosphere.
Produced by heating at 5 ° C. for 5 hours.

The obtained active material was subjected to a transmission electron microscope (TE).
Observation in M) revealed that the active material consisted of secondary particles having a structure in which Al fine particles having a mesophase pitch-based carbon layer formed on the surface were dispersed in a mesophase pitch-based carbon matrix in which no fine particles were formed. . The angle between the hexagonal mesh layer of the graphite crystallites constituting the carbon layer and the tangent to the surface of the fine particles was determined from the observation of the cross section of the fine particles by the TEM, and the average of the formed angles was 45 °. The active material contained Al in an atomic ratio of 30%, and the true density was 2.0 g / cm ³ .

Comparative Example 2 A cylindrical lithium secondary battery was assembled in the same manner as in Example 1 except that the active material described below was used.

The active material was added to a mesophase pitch obtained from a petroleum pitch by adding 5% by weight of Al fine particles having an average particle diameter of 100 nm obtained by a gas phase synthesis method to the mesophase pitch. , And uniformly dispersed by stirring for more than 24 hours at 800 ° C. in an inert gas atmosphere.
For 5 hours.

The obtained active material was subjected to a transmission electron microscope (TE).
Observation in M) revealed that the active material consisted of secondary particles having a structure in which Al fine particles having a mesophase pitch-based carbon layer formed on the surface were dispersed in a mesophase pitch-based carbon matrix in which no fine particles were formed. . The angle between the hexagonal mesh layer of the graphite crystallites constituting the carbon layer and the tangent to the surface of the fine particles was determined from the observation of the cross section of the fine particles by the TEM, and the average of the formed angles was 45 °. The active material contained Al in an atomic ratio of 10%, and the true density was 1.9 g / cm ³ .

Comparative Example ³ A carbonaceous material having a true density of 1.7 g / cm ³ obtained by heating a mesophase pitch obtained from a petroleum pitch at 800 ° C. for 5 hours in an inert gas atmosphere is used as an active material. Except for this, a cylindrical lithium secondary battery similar to that of Example 1 was assembled.

Comparative Example 4 A cylindrical lithium secondary battery similar to that of Example 1 was assembled except that the active material described below was used.

The active material was added to a mesophase pitch obtained from petroleum pitch by adding 15% by weight of Al fine particles having an average particle diameter of 100 nm obtained by a gas phase synthesis method to the mesophase pitch. , And uniformly dispersed by stirring for 24 hours or more, and then 450 under an inert gas atmosphere.
Produced by heating at 5 ° C. for 5 hours.

The obtained active material was subjected to a transmission electron microscope (TE).
Observation in M) revealed that the active material consisted of secondary particles having a structure in which Al fine particles having a mesophase pitch-based carbon layer formed on the surface were dispersed in a mesophase pitch-based carbon matrix in which no fine particles were formed. . From the observation of the cross section of the fine particles by the TEM, the graphite crystallites constituting the carbon layer did not have an orientation with respect to the surface of the fine particles. The active material contained Al in an atomic ratio of 25%, and the true density was 1.6 g / cm ³ .

Comparative Example 5 Example 1 was repeated except that a negative electrode formed of a lithium alloy composed of lithium aluminum (Li _x Al) was used.
A cylindrical lithium secondary battery similar to the above was assembled.

Comparative Example 6 A carbonaceous material obtained by calcining a mesophase pitch obtained from petroleum pitch was mixed with Al fine particles having an average particle diameter of 100 nm obtained by a gas phase synthesis method in a weight ratio of 3 to the carbonaceous material.
A cylindrical lithium secondary battery was assembled in the same manner as in Example 1, except that the active material obtained by adding 0% and uniformly dispersing the mixture by stirring with a raikai machine for 24 hours or more was used as the negative electrode.

Comparative Example 7 Except for using a vapor-grown carbon body containing 10% by atomic ratio of Si fine particles having an average particle size of 2 nm as an active material,
A cylindrical lithium secondary battery similar to that of Example 1 was assembled.

With respect to the obtained secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 7, the charging current was 1.5 A and the voltage was increased to 4.2 V.
After charging for 1.5 hours, a charge-discharge cycle test was performed in which the battery was discharged at 1.5 A to 2.7 V.
The capacity retention ratio at the 00th cycle (relative to the discharge capacity at the first cycle) was determined, and the results are shown in Table 1 below.

[0091]

[Table 1]

As is evident from Table 1, the average particle size was 1n.
Examples 1 to 5 having an active material including an element M fine particle of m to 500 nm having an active material including a carbonaceous material layer formed on the surface thereof, wherein the atomic ratio of the fine particle in the active material is 15% or more. It can be seen that the secondary battery of No. 8 has a high discharge capacity and a high capacity retention rate at 300 cycles.

On the other hand, the average particle diameter of the fine particles is 50
It can be seen that the secondary battery of Comparative Example 1 exceeding 0 nm has a high discharge capacity but a low capacity retention rate. It can be seen that the secondary batteries of Comparative Example 2 in which the atomic ratio of the fine particles in the active material is less than 15% and Comparative Example 3 not including the fine particles have a significantly low discharge capacity. Further, it can be seen that the secondary battery of Comparative Example 4 did not have sufficient discharge capacity. this is,
This is because the carbon precursor was not completely carbonized because the synthesis temperature was lower than 500 ° C., thereby significantly lowering the conductivity of the active material. On the other hand, the secondary battery of Comparative Example 5 including the negative electrode made of a lithium alloy has a high discharge capacity,
It can be seen that the capacity retention rate is extremely low. It can be seen that the secondary battery of Comparative Example 6 including the negative electrode containing, as an active material, a mixture of the carbonaceous material powder and the metal fine particles has a high discharge capacity but a remarkably low capacity retention rate. This is because the metal fine particles are not structurally held by the carbonaceous material. Also, it can be seen that the discharge capacity of the secondary battery of Comparative Example 7 including the negative electrode including the vapor-grown carbon body containing 10% of Si particles having an average particle diameter of 2 nm in an atomic ratio of 10% was extremely low.

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

[0095]

As described above in detail, according to the present invention, it is possible to provide a lithium secondary battery having a high capacity and an excellent cycle life, and a method for manufacturing the same.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing a cylindrical lithium secondary battery according to the present invention.

FIG. 2 is a schematic diagram showing a cross section of fine particles having a carbonaceous material layer formed on a surface included in a negative electrode of the secondary battery of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... container, 3 ... electrode group, 4 ... positive electrode, 6 ... negative electrode, 8 ... sealing plate.

Claims (4)

[Claims] 1. A positive electrode, a negative electrode containing an active material that stores and releases lithium ions, and a non-aqueous electrolyte. The active material of the negative electrode contains fine particles having a carbonaceous material layer formed on the surface thereof, Fine particles are Mg, Al, Si, Ca, Sn
A lithium secondary battery comprising at least one element M selected from Pb and Pb, having an average particle diameter of 1 nm to 500 nm, and an atomic ratio of the fine particles in the active material of 15% or more. 2. The lithium secondary battery according to claim 1, wherein the carbonaceous material layer forming fine particles form secondary particles. 3. An average angle between a hexagonal reticular layer of graphite crystallites constituting the carbonaceous material layer and a tangent to the surface of the fine particles is 20 ° to 90 °. Lithium secondary battery. 4. A method for producing a lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode comprises: a raw material carbonaceous material or a carbon precursor; Weight ratio to precursor of 15
% Of fine particles at a temperature of 500 ° C. to 2800 ° C., wherein the fine particles are made of Mg, Al, Si, Ca, Sn and Pb.
A method for producing a lithium secondary battery, comprising at least one element M selected from the group consisting of: and an average particle diameter of 1 nm to 500 nm.