JP2007311180A - Negative electrode for lithium secondary battery, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode for a lithium secondary battery capable of drastically improving initial capacity and first efficiency, improved in a discharge rate characteristic and a cycle characteristic, and suitable for a pulse-like large-current application; and to provide a lithium secondary battery. <P>SOLUTION: A negative electrode material for a lithium secondary battery is coated at least a part of carbon particle surfaces of pitch-based low-temperature-baked carbon with a metal or a metal compound selected from Sn, Pb, Pd, Mn, Ni, Si, Al, Ti, V, and a composite material or mixture material thereof. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a negative electrode for a lithium secondary battery. More specifically, the present invention relates to a negative electrode for a lithium secondary battery suitable for high current use, a method for producing the same, and a lithium secondary battery.

In recent years, with the increase in functionality and digitalization of electronic devices, battery performance is required to have higher capacity and higher output.
In particular, a lithium secondary battery has many advantages such as high voltage, high energy density, wide non-aqueous electrolyte, wide operating temperature range, excellent long-term storage, and miniaturization. Therefore, it is suitably used for applications such as cellular phones, portable personal computers, video cameras, and electric vehicles.

  For example, as mobile phones are becoming smaller and more multifunctional, the secondary power source used is reducing the average power consumption due to power saving, but it requires a pulse current that requires a large current during communication. The use is increasing.

It is also expected to be put to practical use in applications such as hybrid electric vehicles that combine an engine and a motor. However, when used as an in-vehicle power source, the use conditions become severe. That is, in addition to the requirement for high energy density, high output characteristics for several seconds are also required.
On the other hand, for example, a low resistance lithium secondary battery is being provided by thinning an electrode to improve characteristics such as high output, but there are still problems that are not suitable for high current pulse applications. It had been.

  Conventionally, lithium secondary battery negative electrodes have been widely used for graphite secondary materials and have been typified by lithium secondary battery negative electrode materials, but they are not suitable for the needs of high-capacity carbon materials and high-current pulse applications. Some problems remained. In order to solve the above problems, approaches from various battery constituent materials such as positive and negative electrode materials and electrolytes are necessary, but most of them are studies on graphite materials that are negative electrode materials. The limits are approaching.

  On the other hand, a low-temperature fired carbon fiber having a large initial charge capacity has been proposed as a negative electrode for a lithium secondary battery (see, for example, Patent Document 1). According to the publication, this low-temperature fired carbon fiber has a larger initial charge capacity as a negative electrode material than graphite fiber. However, there are problems such as low initial efficiency, inferior cycle characteristics, low electrical conductivity, etc., and it has not yet been put into practical use.

  In addition, for the purpose of eliminating the above-mentioned problem of conductivity, a negative electrode material for a lithium secondary battery in which a carbon material is coated with a metal conductive material has been proposed (for example, see Patent Document 2). Even when the amount was large relative to the carbon material and applied to the low-temperature fired carbon fiber, the initial capacity was greatly reduced, and the effect of improving the cycle characteristics was not observed.

  Furthermore, although a negative electrode material for a lithium secondary battery in which tin is supported on a carbon material has been proposed (see, for example, Patent Document 3), when metal tin is simply formed on the surface of the carbon material, the average particle diameter of metal tin is If large, there is no deterioration in cycle characteristics due to embrittlement and dropout due to alloying, but no increase in capacity is observed, soak a carbon material using tin tetrachloride liquid, and dry dry at a temperature above the boiling point of tin after filtration. It is said that an increase in capacity is permitted. However, even if this method is used, the effect of improving the performance is not so much. To further improve the capacity, it is necessary to increase the coating amount of metal tin. In addition, there is a problem that sufficient repeated charge / discharge cycle performance cannot be exhibited by coating a large amount of tin on the carbon surface.

  In addition, a material for supporting a negative electrode of a lithium ion secondary battery that has been coated with a metal for the purpose of conductivity and surface modification of low-temperature-fired carbon fibers has been proposed (for example, Patent Document 4). By coating the pitch-based carbon fiber fired in the temperature range with a specific metal, particularly with a specific method at an appropriate thickness, the electrical conductivity becomes more than a certain range, while suppressing a decrease in the initial capacity, It has been observed that cycle characteristics can be improved. However, there are many limitations such as the metal species to be coated on the carbon surface, the coating method, the thickness of the coating, and the like, and there is a problem that the effects such as the intended initial capacity, initial efficiency, and cycle characteristics cannot be seen. In addition, the manufacturing process is complicated and expensive.

  In addition, a metal-carbon hybrid electrode and a lithium secondary battery including a cluster or thin film of metal or metal oxide formed on the surface of carbon particles have been proposed (see, for example, Patent Document 5). According to the publication, the metal or metal cluster / thin film formed on the carbon surface has a composition different from that of a film formed on a pure carbon surface having good conductivity in an organic solvent, and is stable. A film can be formed to prevent entry of the solvent, and cycle characteristics can be improved. Therefore, it has been recognized that the capacity reduction of the electrode due to charge / discharge can be significantly reduced. However, the coating method of coating the metal on the carbon surface has a problem that the process surface is very complicated, and the coating amount and coating thickness change depending on the atmospheric conditions, and the surface state changes. In addition, there is a high possibility that the internal resistance due to the coating thickness will increase, and even if it is coated in a cluster state, there are problems that the effects such as the intended initial capacity, initial efficiency, discharge rate characteristics and cycle characteristics are not seen. there were.

Japanese Patent Laid-Open No. 7-6754 JP 7-335263 A JP-A-10-326612 JP-A-11-329434 JP 2003-249219 A

  The object of the present invention is to solve the above-mentioned problems of the prior art, greatly improve the initial capacity and initial efficiency, improve the discharge rate characteristics and cycle characteristics, and increase the pulse-like large current. An object of the present invention is to provide a negative electrode for a lithium secondary battery and a lithium secondary battery that are suitable for use.

  In order to solve the above-mentioned problems, the present inventors have conducted a mirror investigation while paying attention to the problems of the prior art, and as a result, the low-temperature fired carbon surface is coated with a specific metal or metal compound, thereby achieving the above-mentioned problems. The inventors have found that this can be solved and have reached the present invention.

That is, the object of the present invention is to
At least a part of the surface of the carbon particles of the pitch-based low-temperature calcined carbon is a particle coated with a metal and / or a metal compound, and the metal or metal compound is Sn, Pb, Pd, Mn, Ni, Si, Al, Ti, V and a negative electrode material for a lithium secondary battery selected from these composite materials or mixed materials.

The present invention includes at least Sn or a compound thereof as the metal and / or metal compound, a coating thickness of the metal and / or metal compound of 1 to 300 nm, and a particle diameter of the coated particles. The average particle size in the particle size distribution is 1 to 10 μm, the low-temperature calcined carbon has an interplanar spacing between [d ₀₀₂ ] layers of 0.33 to 0.44 nm by X-ray diffraction, the low-temperature calcined Carbon has an atomic ratio of hydrogen / carbon in the range of 0.25 to 0.01, an atomic ratio of oxygen / carbon in the range of 0.15 to 0.01, and the low-temperature calcined carbon has nitrogen adsorption. The specific surface area determined by the BET method is 10 to 100 m ² / g, and in the pore distribution determined by the BJH method from the nitrogen adsorption isotherm, the pore volume of the micropores which is 10 mm or less is 5% of the total pore volume. ~ 30% It is included in.

  Another object of the present invention is to provide an electrode for a lithium secondary battery negative electrode using the negative electrode material for a lithium secondary battery according to any one of claims 1 to 7, and the lithium secondary battery according to claim 8. This is achieved by a lithium secondary battery using the negative electrode as a negative electrode.

Still another object of the present invention is to
At least a part of the surface of the carbon particles of pitch-based low-temperature-fired carbon includes a coated metal and a metal compound, and the metal includes Sn, Pb, Pd, Mn, Ni, Si, Al, Ti, V, and a composite thereof. A method for producing a negative electrode material for a lithium secondary battery selected from a material or a mixed material, wherein pitch-based low-temperature calcined carbon is dispersed in a solution containing the metal ions, and the wet-pulverized treatment is performed by a pulverizer. A step of finely pulverizing carbon, a step of forming a layer containing the metal ions on the surface of the finely pulverized product, and a step of reducing the metal ions by a reducing agent. This is achieved by a method for producing a negative electrode material for a lithium secondary battery, which is characterized in that a metal or a metal compound is partially coated.

  In the present invention, the solution containing the metal ions is SnBr (OH), the reducing agent is a copper compound containing CuBr (OH), and the pitch-based low-temperature fired carbon is infusible. It is also included that the pitch-based carbon is fired at 600 to 1300 ° C., that the pulverizer is a rotary pulverizer, and that the rotary pulverizer is a high-speed rotary pulverizer.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to improve initial coulomb efficiency significantly, the negative electrode for lithium secondary batteries and a lithium secondary battery which are suitable for a pulse-like large current use can be provided.

Hereinafter, the present invention will be described in detail.
In the present invention, at least a part of the carbon particle surface of pitch-based low-temperature-fired carbon is a metal selected from Sn, Pb, Pd, Mn, Ni, Si, Al, Ti, V, and a composite material or mixed material thereof. Or it is necessary to coat | cover with a metal compound.
By doing so, the initial coulomb efficiency, the discharge rate characteristic, and the cycle characteristic can be improved when incorporated in a lithium secondary battery.

  In the present invention, a part of the carbon particle surface of pitch-based low-temperature calcined carbon is coated with a metal and / or a metal compound. This coating is made of Sn, Pb, Pd, Mn, Ni, Si, Al, Ti, It is a metal or a metal compound selected from V and a composite material or a mixed material thereof. When these metals are used, clusters on the carbon surface or metal and metal oxides form a coating on the carbon surface that is different from the conventional SEI coating layer, and further, in the micropores or pore surfaces present in the low-temperature calcined coal. Present as metal.

In the case of low-temperature calcined carbon, when lithium is occluded in the carbon structure, lithium ions are clustered and occluded in the fine pores of about 10 angstroms generated in the low-temperature calcining stage, thereby reducing the initial capacity and increasing the efficiency. From the viewpoint of solving the problem in the prior art due to the difficulty of discharge, Sn is more preferable.
Here, the mixed material means a mixture of Sn, Pb, Pd, Mn, Ni, Si, Al, Ti, V and a composite material thereof and other components other than these.

In the present invention, the coating thickness of these metals and / or metal compounds is preferably 1 to 300 nm, more preferably 10 to 100 nm, still more preferably 20 to 70 nm.
When the coating thickness is less than 1 nm, the reactivity with respect to lithium is small and the initial efficiency is remarkably reduced. When the coating thickness exceeds 300 nm, the reactivity with lithium is high, and the initial efficiency is improved. Although seen, the weight ratio of the coated metal increases, so the initial capacity per unit weight is significantly reduced. In addition, when the coating of a metal or metal compound with low electrical conductivity is thickened, Li ion mobility is hindered. This is not preferable.

Here, the measurement of the coating thickness was performed by the SIMS (secondary ion mass spectrometry) method. In this measurement, A-DIDA3000 (ATOMIKA) is used as a SIMS apparatus, sputtering is performed in a range of 60 × 60 μm at an energy of 12 KeV using O ₂ ⁺ as a primary ion source, and time correction is performed using a standard sample. did.
The thickness of the coating with the metal and / or metal compound can be appropriately set within the above range in consideration of the type of carbon material used, the shape such as the particle diameter, the metal to be coated, the physical properties of the metal compound, and the like. preferable.

In the present invention, the coated particles preferably have an average particle size of 1 to 10 μm in the particle size distribution.
If the specific surface area of the negative electrode material for a lithium secondary battery becomes too high, the initial efficiency is deteriorated, which is not preferable for practical use. However, in order to facilitate the insertion / extraction of lithium ions, the surface area per weight is made as large as possible. This leads to improved battery performance.

However, as the material is finely pulverized, the carbon material tends to have a small particle diameter, and the fiber is easily pulverized, such as being pulverized perpendicular to the fiber length, resulting in a decrease in the initial efficiency of the battery and the charge / discharge capacity. Since problems occur, it is required to have an appropriate particle size distribution and average particle size.
Since the negative electrode particle diameters are different from each other, it is preferable that the particle size is adjusted to a predetermined particle diameter by pulverization with a pulverizer such as a ball mill or a jet mill and then classification as necessary.

  In view of the above description, the particle diameter of the particles is determined in consideration of the target battery shape, characteristics, electrode thickness, density, and the like. It is preferable to set it as 10-10 micrometers, More preferably, it is 1-5 micrometers or less, It is more preferable to set it as 1 micrometer or less.

  Here, the average particle diameter can be measured by a laser diffraction measurement method, and the average particle diameter measured by this method means the central particle diameter (D50) in the volume particle size distribution. Moreover, the average particle diameter in the present invention is the average particle diameter of primary particles. When the active material particles are taken out from the electrode and the average particle diameter is confirmed, there is a possibility that the average particle diameter of the primary particles cannot be accurately estimated by the above-described method due to problems such as secondary aggregation. In such a case, the average particle diameter of the primary particles can be estimated by image analysis of the observation result with an electron microscope or the like.

The average particle size was measured using a laser diffraction particle size distribution analyzer “SALD-2000J” manufactured by Shimadzu Corporation. Water was used as the dispersion medium for the active material, and a small amount of nonionic surfactant “Triton X-100” was used as the dispersant. The circulation flow rate of the dispersion was about 1200 cm ³ / min, the maximum absorbance was 0.20, the minimum absorbance was 0.10, the refractive index was 1.70-0.20i, and the number of integrations was 64. The center particle size (D50) in the volume particle size distribution obtained from this was taken as the average particle size.

In the present invention, the low-temperature calcined carbon preferably has a [d ₀₀₂ ] interlayer spacing of 0.33 or more by X-ray diffraction, more preferably 0.33 to 0.44 nm, It is preferably 34 to 0.40 nm.
Since the above-mentioned low-temperature calcined carbon is much wider than the interlayer spacing such as ordinary graphite, lithium ions can be occluded and released smoothly. Also, the amount of occluded / released lithium ions can be greatly increased compared to carbon materials such as graphite. Thereby, charging / discharging capacity improves.

In the present invention, the low-temperature calcined carbon preferably has a hydrogen / carbon atomic ratio in the range of 0.25 to 0.01 and an oxygen / carbon atomic ratio in the range of 0.15 to 0.01. .
More preferably, the hydrogen / carbon atom ratio is 0.20 to 0.01, more preferably 0.15 to 0.1.

When the hydrogen / carbon atom ratio is high, the polycyclic aromatic conjugated structure in the product is not sufficiently developed, so that the initial charge / discharge capacity and the initial efficiency are lowered.
On the other hand, when the hydrogen / carbon atom ratio is low, carbonization has progressed too much, so that the expected capacity cannot be obtained.

When the oxygen / carbon atom ratio is high, the electrical conductivity is high and the rate and cycle characteristics are improved, but the initial charge / discharge capacity and the initial efficiency are lowered. On the other hand, when the oxygen / carbon atom ratio is low, the initial charge / discharge capacity and the initial efficiency are improved, but there is a problem that the rate and cycle characteristics cannot be obtained.
As a measuring method of hydrogen / carbon atom ratio and oxygen / carbon atom ratio, Yanaco CHN coder MT-6 type method was used. In this measurement, 30 mg of an oxidation accelerator tungsten trioxide was added, and H / C and O / C were calculated.

In the present invention, the low-temperature calcined carbon has a specific surface area of 10 to 100 m ² / g determined by the nitrogen desorption BET method, and a micro distribution of 10 μm or less in the pore distribution determined by the BJH method from the nitrogen adsorption isotherm. The pore volume of the pores is preferably 5-30% of the total pore volume.
The specific surface area by a lithium secondary battery negative electrode of the BET method is more preferably from 30 to 100 m ² / g, it is preferable in particular 30 to 60 m ² / g.
When the specific surface area of the negative electrode material is increased, the initial efficiency is deteriorated, which is not preferable for practical use.

In addition, in the pore distribution, the pore volume of 10 μm or less, which is a micropore, is preferably 5 to 30% of the total pore volume, and more preferably 5 to 20% of the total pore volume. preferable.
When micropores are developed and the total pore volume is large, the initial charge capacity is high, but the initial irreversible capacity is large and there is a problem that the initial efficiency is lowered. On the other hand, when the total pore volume is small, the lithium charge capacity is small, but the initial irreversible capacity is small and the initial efficiency can be improved.

  In the present invention, as the method for coating the carbon material with the metal and / or metal compound, a sputtering method, a dipping method, a vapor deposition method, an electroless plating method, etc. are usually considered. The compound is formed on the surface of the carbon material.

In the present invention, the following production method of the present invention is particularly preferable.
At least a part of the surface of the carbon particles of pitch-based low-temperature-fired carbon includes a coated metal and a metal compound, and the metal includes Sn, Pb, Pd, Mn, Ni, Si, Al, Ti, V, and a composite thereof. A method for producing a negative electrode material for a lithium secondary battery selected from a material or a mixed material, wherein pitch-based low-temperature calcined carbon is dispersed in a solution containing the metal ions, and the wet-pulverized treatment is performed by a pulverizer. A step of finely pulverizing carbon, a step of forming a layer containing the metal ions on the surface of the finely pulverized product, and a step of reducing the metal ions by a reducing agent. A part is coated with a metal or a metal compound.

  Here, the process of producing the pitch-based low-temperature calcined carbon of the present invention will be briefly described below. The raw material pitch is not limited to any of synthetic pitches using petroleum, coal or resin.

  The method of spinning the raw material pitch is preferably a melt blow method from the viewpoint of productivity at the time of spinning and the quality of the obtained fiber, but is not particularly limited. The spinning temperature is a temperature range where the pitch does not change above the softening point of the raw material pitch to be used, generally 220 to 380 ° C., preferably 250 to 350 ° C. Therefore, from the viewpoint of production cost and stability, those having a low softening point and a high infusibilization reaction rate are advantageous.

  Next, the infusibilization method is not particularly limited, but a method of heat treatment in an oxidizing gas atmosphere such as nitrogen dioxide or oxygen by a conventional method, a method of treatment in an oxidizing aqueous solution such as nitric acid, light or γ A simpler infusibilization method is preferably performed in air, and a method of heat treatment in air for 150 to 350 ° C. for a certain time, with an average heating rate of 5 ° C. / Min.

Without passing through the infusibilization process, if the pitch fiber as spun is passed through a subsequent heat treatment (firing) process, the pitch fiber is remelted, so that the graphite layer and orientation formed in the spinning process may be disturbed. The fiber shape may be lost.
The heat treatment (firing) step is a step of obtaining carbon fibers by heat-treating the infusible fibers in an inert gas.

  The low-temperature calcined carbon of the present application means that the pitch-based carbon that has been infusibilized is calcined at about 1000 ° C. or less, and the heating rate and holding time during the calcining are not particularly limited. It may be performed in a temperature region where the structure does not develop. The initial efficiency of the battery tends to increase with increasing firing temperature due to the tendency that the graphite structure develops with increasing firing temperature and the conductivity also improves. For this reason, if a calcination temperature is less than 600 degreeC, initial efficiency and cycle efficiency are bad. On the other hand, when the firing temperature exceeds 1300 ° C., the graphite structure is approached, and as a result, the initial charge / discharge capacity of the battery is significantly reduced as the firing temperature is increased.

  In consideration of the above, the firing temperature can be appropriately set according to purposes such as the initial charge / discharge capacity, initial efficiency, cycle efficiency, and rate efficiency of the battery, but the firing temperature is 600 ° C to 1000 ° C. It is preferably 800 ° C.

In the production method of the present invention, for example, the pitch-based low-temperature calcined carbon obtained as described above is contained in a solution containing metal ions selected from Sn, Pb, Pd, Mn, Ni, Si, Al, Ti, and V. Then, the pitch-based low-temperature calcined carbon is finely pulverized by a wet pulverization process using a pulverizer.
Here, the type of pulverizer is not particularly limited, but in order to obtain a powder having the above particle diameter, depending on the purpose such as the physical properties and properties of the carbon material, a rod mill, a ball mill, a jet mill, etc. It is possible to use a pulverizer.

Next, a layer containing the metal ions is formed on the surface of the finely pulverized product. Specifically, pulverization is performed until a predetermined particle size is obtained, and after obtaining a fine product having a large specific surface area and a target particle size, it may be left as it is for 24 hours.
Furthermore, the metal ions can be coated with a metal or a metal compound by reducing the metal ions with a reducing agent.

Hereinafter, more specifically, taking Sn, which is preferable among metals and / or metal compounds, as an example, the above-described method of the present invention can be performed using SnCl (OH) solution or Sn ion solubility and reducing agent copper. From the viewpoint of suppressing the reactivity with the carbon, preferably, a SnBrOH solution is used. The carbon material is dispersed in the SnBrOH solution, and the carbon is pulverized by a wet pulverization process using a pulverizer, particularly a high-rotation pulverizer. A step of forming a metal ion layer on the particle surface of the finely pulverized product, and a step of reducing the metal ions on the surface of the particle by using a reducing agent of the CuBrOH solution and coating with tin and a tin compound. Is called.
The carbon can be pulverized to reduce the particle diameter, and the coating thickness can be made thin and uniform, easy coating, uniform coating of carbon and metal, low cost, etc. can be achieved simultaneously.

The negative electrode for lithium secondary batteries is manufactured by a well-known method using the negative electrode material for lithium secondary batteries in this invention.
For example, an appropriate binder is mixed with the negative electrode material of the present invention, and a negative electrode active material is mixed as necessary to improve conductivity. A solvent for dissolving the binder is added to this mixture, and if necessary, it is sufficiently stirred using a homogenizer and glass beads to form a slurry.
The slurry is applied to a current collector such as rolled copper foil or copper electrodeposited copper foil using a doctor blade or the like, dried, and then consolidated by roll rolling to produce a negative electrode for a lithium secondary battery. can do.

Here, as the binder, rubber-based materials such as poly (vinylidene fluoride) (PVdF), polytetrafluoroethylene, fluororesin, fluororubber, and SBR can be used. The amount of the binder can be appropriately determined according to the type, particle diameter, shape, target electrode thickness, strength, etc. of the negative electrode material, and is not particularly limited.
As the solvent, an organic solvent such as NMP (N-methylpyrrolidone) or DMF (dimethylformamide) or water can be used depending on the binder.

  The negative electrode active material is not particularly limited as long as it is a material that can occlude and release lithium. For example, artificial graphite, natural graphite, mesophase pitch hydrocarbon, which becomes an intercalation compound by occlusion of lithium ions, difficult It is possible to use a graphitic carbon material, petroleum coke, an easily graphitizable carbon material, or a composite material or a mixed material of the above materials. Although metal fine particles can be used, a carbon material (especially acetylene black, ketjen black, carbon black) is preferable. Since the carbon material can occlude Li ions between the layers, the carbon material can contribute to the capacity of the negative electrode in addition to the conductivity, and also has excellent liquid retention.

  In producing a negative electrode for a lithium secondary battery using the negative electrode material for a lithium secondary battery in the present invention, for example, a known conductive material such as acetylene black, ketjen black, carbon black, graphite, and metal fine particles is used. Although it is possible, acetylene black, ketjen black, and carbon black are particularly preferable because they have a great effect of reducing internal resistance. The addition amount of the conductive material may be appropriately determined according to the type of active material used for the electrode, particle diameter, shape, target electrode thickness, strength, electrical conductivity, etc., but 1% by weight of the electrode weight The content is preferably 35% by weight or less. More preferably, the content is 3% by weight or more and 10% by weight or less. The addition amount of the binder is preferably 1% by weight or more and 20% by weight or less based on the active material. More preferably, the content is 3% by weight or more and 10% by weight or less. When the amount added is large, there is a problem that the internal resistance is large and sufficient output characteristics cannot be obtained.

A lithium secondary battery is produced using the negative electrode produced as described above. The lithium secondary battery includes a negative electrode, a positive electrode, a separator, and an electrolyte as a basic structure.
Although what was manufactured from the negative electrode material of this invention as mentioned above is used for a negative electrode, it does not restrict | limit especially about another positive electrode, a separator, and electrolyte, All can use a well-known thing.

  The active material of the positive electrode is not particularly limited as long as it is a material capable of inserting and extracting lithium. For example, lithium composite cobalt oxide, lithium composite nickel oxide, lithium composite manganese oxide, or a mixture of the above Alternatively, a lithium composite oxide such as a system in which one or more kinds of different metal elements are added to the composite oxide can be used. Moreover, although a disulfide type compound, a polyacene type substance, activated carbon, etc. can be used, in order to obtain a battery having a high voltage and a high capacity, it is preferable to use a lithium composite oxide.

  The separator plays a major role in holding the electrolyte, as well as serving as an insulator disposed between the positive electrode and the negative electrode. Although there is no particular limitation, a single-layer or multi-layer separator can be used. In addition, the separator material is not particularly limited, and examples thereof include polyolefins such as polyethylene and polypropylene, paper, glass, cellulose, and the like, depending on the heat resistance and safety design of the lithium secondary battery. Can be determined as appropriate.

The electrolyte is also the same as a conventional non-aqueous electrolyte in which an electrolyte material such as a known lithium salt is dissolved in a known solvent. The electrolyte can be appropriately determined according to a conventional method, comprehensively considering the types of electrode material, negative electrode material, etc., usage conditions such as charging voltage, and the like. More specifically, lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ are used in one or two kinds such as propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, dimethoxyethane, γ-butyrolactone, and the like. A solution dissolved in the above organic solvent is used.

  Further, the shape, size, etc. of the lithium ion secondary battery in the present invention are not particularly limited, and any shape such as a cylindrical type, a square type, a film type battery, a coin type, and the like may be used according to each application. What is necessary is just to select the thing of a dimension. The material for the battery container is appropriately selected depending on the use and shape of the battery, and is not particularly limited, and is typically stainless steel, aluminum, aluminum-laminated film, and the like, which can also be applied in the present invention. is there.

  Hereinafter, examples of the negative electrode material for lithium secondary batteries according to the present invention and methods for producing the same and comparative examples will be shown, and the features of the present invention will be described more specifically. There is no limitation.

[Example 1]
A pitch fiber was produced by using a petroleum-based mesophase pitch as a raw material, and using a die in a 350 ° C. temperature range that is equal to or higher than the softening point, and ejecting a molten pitch from the slit. A mat formed by collecting the pitch fibers on a wire mesh was pulverized by a high-speed rotary pulverizer to obtain a pitch fiber milled product. When the particle size of the milled product was determined by laser diffraction particle size distribution measurement, the average particle size was 10 μm.
Subsequently, this pitch fiber milled product was infusibilized by raising the temperature in the air from room temperature to 300 ° C. at an average rate of temperature increase of 6 ° C./min. The infusibilized pitch fibers thus obtained were fired at 800 ° C. to obtain pitch-based low-temperature fired carbon fibers.

Next, the low-temperature calcined carbon fiber is dispersed in a SnBr (OH) solution, and wet pulverization is performed by a high-speed rotary pulverizer to obtain particulate low-temperature calcined carbon and uniformly on the surface of the low-temperature calcined carbon particles. And a tin ion layer like a thin thin film was formed.
In this state, a reducing agent containing CuBr (OH) is mixed and dispersed and allowed to stand for one day, whereby tin and a tin compound are formed on the surface of the low-temperature calcined carbon particles in a uniform and thin thickness like a thin film in a cluster state. A coated low-temperature calcined carbon was produced. This metal-coated low-temperature fired carbon was immersed in a CuBr (OH) solution for about 6 hours to reliably produce metal-coated milled low-temperature fired carbon.

As shown in FIG. 1, Sn showed an energy peak of Sn by energy dispersive X-ray characteristic analysis of EDX (Energy Dispersion X-ray).
Moreover, as shown in FIG. 2, the diffraction pattern of SnO ₂ and SnO was recognized in addition to the broad diffraction pattern of low-temperature calcined carbon.
The diffraction patterns of these SnO ₂ and SnO are broad, it was confirmed SnO ₂ and SnO is amorphous state.

  The coating thickness was measured by SIMS, and the average thickness was 100 nm. Further, the tin-coated low-temperature calcined carbon particle size was measured by laser diffraction particle size distribution, and the average particle size was 1.5 μm. 87 parts by weight of the tin-coated low-temperature calcined carbon powder as a negative electrode active material, 3 parts by weight of acetylene black as a conductive material, 10 parts by weight of polyvinylidene fluoride (PVdF) as a binder, and N-methylpyrrolidone as a solvent (NMP) was mixed to obtain a slurry for forming a negative electrode material. The slurry was applied to one side of a copper foil as a current collector having a thickness of 16 μm, dried, and then pressed to obtain an electrode for negative electrode (thickness 70 μm) having a thickness of 86 μm.

This negative electrode is punched into a circular shape with a diameter of 7.0 mm to form a working electrode, metallic lithium is used as a counter electrode, a separator made of a porous polypropylene film is inserted between the working electrode and the counter electrode, and an electrolytic solution (ethylene carbonate and A lithium secondary battery half-cell was prepared in an argon dry box using a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / l in a solvent in which ethylmethyl carbonate was mixed at a volume ratio of 70:30. The discharge characteristics were evaluated.

The first charge was performed at a constant current of a current density of 0.1 mA / cm ² from a potential difference of 3.0 V to 0 V of lithium, whereas the discharge was performed at the same current density to 2.0 V. Then, the current density was similarly measured from 2.0 V to 0 V for 3 cycles of charge and discharge. The battery characteristics obtained as a result are summarized in Table 1.

[Comparative Example 1]
As a comparative example, an ordinary pitch-based low-temperature calcined carbon that is not treated at all is used as a negative electrode material, and electrode production and battery characteristics are produced and measured by the same method as in the examples. The results are summarized in Table 1.
The technical scope of the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention.

It is a figure which shows the EDX (Energy Dispersion X-ray) characteristic of the tin for secondary battery negative electrode materials obtained by operation of Example 1, and a tin compound coating | coated low-temperature baking carbon. It is a figure which shows the X-ray diffraction of the tin for secondary battery negative electrode materials obtained by operation of Example 1, and the tin compound covering low-temperature baking carbon negative electrode material.

Claims (15)

  At least a part of the surface of the carbon particles of the pitch-based low-temperature calcined carbon is a particle coated with a metal and / or a metal compound, and the metal or metal compound is Sn, Pb, Pd, Mn, Ni, Si, Al, Ti, A negative electrode material for a lithium secondary battery selected from V and a composite material or a mixed material thereof.   2. The negative electrode material for a lithium secondary battery according to claim 1, comprising at least Sn or a compound thereof as the metal and / or metal compound.   3. The negative electrode material for a lithium secondary battery according to claim 1, wherein the coating with the metal and / or metal compound has a thickness of 1 to 300 nm.   4. The negative electrode material for a lithium secondary battery according to claim 1, wherein an average particle size in a particle size distribution is 1 to 10 μm. 5. The negative electrode material for a lithium secondary battery according to claim 1, wherein the low-temperature calcined carbon has an interplanar spacing of [d ₀₀₂ ] layers of 0.33 to 0.44 nm by X-ray diffraction.   The low-temperature calcined carbon has a hydrogen / carbon atomic ratio in the range of 0.25 to 0.01, and an oxygen / carbon atomic ratio in the range of 0.15 to 0.01. The negative electrode material for lithium secondary batteries in any one. The low-temperature calcined carbon has a specific surface area of 10 to 100 m ² / g determined by a nitrogen adsorption BET method, and has a pore distribution of 10 μm or less in a pore distribution determined by a BJH method from a nitrogen adsorption isotherm. The negative electrode material for a lithium secondary battery according to claim 1, wherein the volume is 5 to 30% of the total pore volume.   The electrode for lithium secondary battery negative electrodes using the negative electrode material for lithium secondary batteries in any one of Claims 1-7.   A lithium secondary battery using the electrode for a lithium secondary battery negative electrode according to claim 8 as a negative electrode.   At least a part of the surface of the carbon particles of pitch-based low-temperature-fired carbon includes a coated metal and a metal compound, and the metal includes Sn, Pb, Pd, Mn, Ni, Si, Al, Ti, V, and a composite thereof. A method for producing a negative electrode material for a lithium secondary battery selected from a material or a mixed material, wherein pitch-based low-temperature calcined carbon is dispersed in a solution containing the metal ions, and the wet-pulverized treatment is performed by a pulverizer. A step of finely pulverizing carbon, a step of forming a layer containing the metal ions on the surface of the finely pulverized product, and a step of reducing the metal ions by a reducing agent. A method for producing a negative electrode material for a lithium secondary battery, characterized in that a metal or a metal compound is partially coated.   The method for producing a negative electrode material for a lithium secondary battery according to claim 10, wherein the solution containing metal ions is SnBr (OH).   The method for producing a negative electrode material for a lithium secondary battery according to claim 10, wherein the reducing agent is a copper compound containing CuBr (OH).   11. The method for producing a negative electrode material for a lithium secondary battery according to claim 10, wherein the pitch-based low-temperature fired carbon is obtained by firing the infusibilized pitch-based carbon at 600 to 1300 ° C. 11.   The method for producing a negative electrode material for a lithium secondary battery according to claim 10, wherein the pulverizer is a rotary pulverizer.   The method for producing a negative electrode material for a lithium secondary battery according to claim 14, wherein the rotary pulverizer is a high-speed rotary pulverizer.

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