JP4393075B2 - Negative electrode material, negative electrode using the same, and lithium ion battery and lithium polymer battery using the negative electrode - Google Patents

Description

【００３６】
【表２】

【００３７】
表１及び表２より明らかなように、従来より使用されている平均粒径が大きい球状黒鉛材料を負極材料として用いた比較例１及び２では、高率放電容量の低下が著しい結果となった。また、粒径の大きな比較例２の方が比較例１よりも電極密度が低い値を示していた。これに対して本発明の負極材料を用いた実施例１〜８ではそれぞれ高い電極密度を示し、かつ低率放電容量と高率放電容量に大きな差はなく、この材料を用いて電極を作製した場合、高率放電特性が向上できることが判った。
【００３８】
【発明の効果】
以上述べたように、本発明の負極材料は、平均粒径５μｍ〜４０μｍの粒子状の第１炭素材料と平均直径１０ｎｍ〜５００ｎｍの平面状のグラファイト網が複数積層され、グラファイト網がファイバの縦軸に対して実質的に垂直であるカーボンナノファイバを主成分とする第２炭素材料をそれぞれ含み、第２炭素材料に含まれるカーボンナノファイバが１０００ｎｍ以上の長さと、１０以上のアスペクト比を有し、第１炭素材料が９８重量％〜７０重量％、第２炭素材料が２重量％〜３０重量％の割合で構成される。
平均粒径の大きな第１炭素材料とナノサイズの第２炭素材料をそれぞれ含む本発明の負極材料を用いて電池の電極を作製した場合、第１炭素材料が形成する空隙に第２炭素材料が充填されるため、電極中の炭素材料の充填密度が効果的に向上する。また第２炭素材料の主成分である１０００ｎｍ以上の長さと、１０以上のアスペクト比を有するカーボンナノファイバはグラファイト網のエッジ面が多く露出するため、このカーボンナノファイバを主成分とした第２炭素材料と従来より用いられてきた炭素材料である第１炭素材料とをそれぞれ含む本発明の負極材料を用いることによって、従来の炭素材料のみを負極材料として用いた場合に比べて充放電に伴うリチウムイオンの挿入、脱離反応がスムーズに進行し、高率充放電特性が向上する。更に、第２炭素材料は従来より用いられてきた炭素材料に比べて、平均直径が小さい材料であるため、電池の電極を作製した場合、高密度での充電が可能となり、電池のエネルギー密度向上に繋がる。
【図面の簡単な説明】
【図１】本発明の負極材料の模式図。
【図２】本発明の第２炭素材料の主成分であるカーボンナノファイバの模式図。
【図３】グラファイト網層間にリチウムイオンが挿入、脱離する反応を示す模式図。
【図４】図２に対応する別の構造を有するカーボンナノファイバの模式図。
【図５】カーボンナノファイバと粒子状凝集体を示す模式図。
【図６】本発明の負極材料を作製する熱処理炉の断面構成図。
【図７】実施例及び比較例のリチウム二次電池用負極活物質の充放電サイクル試験に用いられる装置。
【符号の説明】
１１ 第１炭素材料
１２ グラファイト網
１３ カーボンナノファイバ
１４ 第２炭素材料
１６ 粒子状凝集体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a negative electrode material that can improve high rate charge / discharge characteristics and increase the energy density of a battery, a negative electrode using the negative electrode material, and a lithium ion battery and a lithium polymer battery using the negative electrode.
[0002]
[Prior art]
In recent years, along with the development of portable electronic devices such as mobile phones and laptop computers, and the practical application of electric vehicles, secondary batteries with small size and light weight and high capacity have been required. Currently, LiCoO as a positive electrode material as a high-capacity secondary battery that meets this requirement₂Lithium ion batteries using a lithium-containing composite oxide such as a carbon-based material as a negative electrode active material have been commercialized. In the secondary battery using carbon as the negative electrode active material, various types of carbon have been studied so far.
For these, carbon-based materials such as coal, coke, polyacrylonitrile (PAN) -based carbon fibers, pitch-based carbon fibers, carbonized organic materials (low-temperature heat treatment), etc. are being studied. Artificial graphite, synthetic graphite, mesocarbon microbeads, graphitized (high-temperature heat-treated) products of organic substances, graphite fibers, and the like have been studied.
[0003]
A negative electrode material using a carbon-based material is excellent in initial charge capacity, but initial charge / discharge efficiency is low and cycle characteristics are inferior. On the other hand, a negative electrode material using a graphite-based material is a carbon-based material. Compared with, the cycle characteristics are excellent, but the initial charge capacity is low and the charge / discharge rate is low.
In order to compensate for these problems, the use of a mixture of carbon-based materials and graphite-based materials has also been studied. However, a negative electrode material obtained by mixing a carbon-based material and a graphite-based material has many problems such as a small charge / discharge capacity, a low initial charge / discharge efficiency, a slow charge / discharge rate, and a short cycle life.
[0004]
As a technique for solving the above problems, pitch carbonaceous fiber milled having an average particle diameter of less than 10 μm obtained at a heat treatment temperature of 550 ° C. or more and 1300 ° C. or less is contained in an amount of 60 wt% or more and 98 wt% or less and 2400 ° C. or more. There is disclosed a negative electrode material for a lithium ion secondary battery comprising 2 wt% or more and 40 wt% or less of pitch-based graphite fiber milled having an average particle size of 10 μm or more and 30 μm or less obtained at a heat treatment temperature of (for example, (See Patent Document 1).
In this negative electrode material, the pitch-based carbon fiber mill is subjected to heat treatment to reduce the radical concentration of the defective portion existing in the surface layer portion, and by removing oxygen-containing functional groups, the irreversible capacity of Li is reduced. This significantly improves the charge / discharge rate and cycle characteristics. Furthermore, a negative electrode material was prepared by mixing the pitch-based carbon fiber milled and pitch-based graphite fiber milled thus surface-modified in a predetermined ratio, and a negative electrode was manufactured using this negative electrode material. In this case, the negative electrode has a large discharge capacity, suppresses decomposition of the electrolytic solution, and has excellent cycle characteristics.
[0005]
[Patent Document 1]
JP-A-9-310591
[0006]
[Problems to be solved by the invention]
However, it is difficult for the pitch-based carbonaceous fiber milled contained in the negative electrode material disclosed in Patent Document 1 to have an average particle size of 1 μm or less, and the pitch-based carbonaceous fiber milled has an average particle size of 1 μm. There is a problem that a sufficient charge / discharge capacity cannot be obtained if the size exceeds this range.
An object of the present invention is to provide a negative electrode material and a negative electrode using the same, in which insertion and desorption reactions of lithium ions accompanying charge / discharge proceed smoothly and high-rate charge / discharge characteristics are improved.
Another object of the present invention is to provide a lithium ion battery and a lithium polymer battery that can increase the energy density of the battery.
[0007]
[Means for Solving the Problems]
In the invention according to claim 1, as shown in FIGS. 1 and 2, a plurality of particulate first carbon materials 11 having an average particle diameter of 5 μm to 40 μm and a planar graphite net 12 having an average diameter of 10 nm to 500 nm are laminated. The second carbon material 14 is mainly composed of carbon nanofibers 13 whose graphite net is substantially perpendicular to the longitudinal axis of the fiber, and the carbon nanofibers 13 contained in the second carbon material 14 are 1000 nm or more. The first carbon material 11 is composed of 98 wt% to 70 wt%, and the second carbon material 14 is composed of 2 wt% to 30 wt%. It is a negative electrode material.
In the invention according to claim 1, when an electrode of a battery is produced using the negative electrode material of the present invention including the first carbon material 11 having a large average particle size and the second carbon material 14 having a nano size, Since the second carbon material 14 is filled in the void formed by the first carbon material 11 having a shape, the packing density of the carbon material in the electrode is effectively improved. Further, since the carbon nanofiber 13 having a length of 1000 nm or more and an aspect ratio of 10 or more, which is the main component of the second carbon material 14, exposes many edge surfaces of the graphite network 12, the carbon nanofiber 13 is used as the main component. By using the negative electrode material of the present invention that includes the second carbon material 14 and the first carbon material 11 that is a carbon material that has been conventionally used, compared to the case where only the conventional carbon material is used as the negative electrode material, As a result, lithium ion insertion and desorption reactions during charging and discharging proceed smoothly, and high rate charge and discharge characteristics are improved. Furthermore, since the second carbon material 14 is a material having an average diameter smaller than that of conventionally used carbon materials, when a battery electrode is manufactured, charging can be performed at a high density, and the energy density of the battery. It leads to improvement.
[0009]
  Claim2The invention according to claim1The invention relates to a carbon nano-fibre contained in the second carbon material.BaLamination spacing d of the graphite mesh plane measured in X-ray diffraction₀₀₂Is a negative electrode material having a thickness of 0.3354 nm to 0.339 nm.
  Claim3The invention according to claim 1Or 25, as shown in FIG. 5, 0.5% by weight to 10% by weight of either or both of a metal and a metal oxide 17 having an average particle diameter of 10 nm to 500 nm are added to the second carbon material 14. Further, the negative electrode material is included.
  Claim3In the invention according to the present invention, since the second carbon material 14 further includes a metal or metal oxide 17 having an average particle diameter of 10 nm to 500 nm, the metal or metal oxide serves as a base point for electron conduction. Is possible.
[0010]
  Claim4The invention according to claim 1 to claim 13The invention according to any one of claims, wherein the carbon nanofibers 13 are exposed.PartAt least 85% of the negative electrode material is the edge of the graphite mesh.
  Claim5The invention according to claim3In this invention, either one or both of a metal and a metal oxide is a negative electrode material on the long axis of the carbon nanofiber.
[0011]
  Claim6The invention according to claim3Or5The metal is a negative electrode material in which the metal is at least one element selected from the group consisting of Fe, Co, Ni, Mg, Al, Mn, and Cu.
[0012]
  Claim7The invention according to claim 1 is the invention according to claim 1, wherein the particulate first carbon material 11 is coal, coke, PAN-based carbon fiber, pitch-based carbon fiber, organic carbonized product, natural graphite, artificial graphite, It is a negative electrode material containing at least one selected from the group consisting of synthetic graphite, mesocarbon microbeads, graphitized organic products, and graphite fibers.
  Claim8The invention according to claim 1 to claim 17It is the negative electrode formed using the negative electrode material of any one, and a conductive support agent.
  This claim8In the negative electrode described in the above, the high rate charge / discharge characteristics are improved because the carbon nanofibers formed by laminating a plurality of graphite nets, which are the main component of the second carbon material, smoothly move in and out of lithium ions. To do.
[0013]
  Claim9The invention according to claim8It is a lithium ion battery formed using the described negative electrode.
  Claim10The invention according to claim8It is a lithium polymer battery formed using the described negative electrode.
  This claim9Or10In the lithium ion battery or lithium polymer battery described in 1), the insertion and extraction of lithium ions proceeds smoothly by the carbon nanofibers formed by laminating a plurality of graphite nets, which are the main components of the second carbon material. The rate charge / discharge characteristics are improved. In addition, since the second carbon material uses carbon nanofibers that are smaller in size than conventionally used carbon materials, charging at a high density is possible, leading to an improvement in the energy density of the battery.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, the negative electrode of the lithium ion battery or the lithium polymer battery includes a particulate first carbon material 11 having an average particle diameter of 5 μm to 40 μm and a planar graphite network 12 having an average diameter of 10 nm to 500 nm. A plurality of laminated negative electrodes are used, each including a second carbon material 14 mainly composed of carbon nanofibers 13 whose graphite net is substantially perpendicular to the longitudinal axis of the fiber. The carbon nanofibers 13 included in the second carbon material 14 are configured to have a length of 1000 nm or more and an aspect ratio of 10 or more. When a battery electrode is produced using the negative electrode material of the present invention including the first carbon material 11 having a large average particle size and the second carbon material 14 having a nano size, voids formed by the first carbon material 11 Since the second carbon material 14 is filled, the packing density of the carbon material in the electrode is effectively improved. Also, as shown in FIG. 4, one side of the end portion 12a having the graphite mesh 12 is joined to one side of the end portion of another graphite mesh, and one side of the other end portion is one side of the end portion of another graphite net. Carbon nanofibers 13 formed by bonding to each other and having a structure folded from each side may be used.
[0015]
In the negative electrode material of the present invention, the first carbon material 11 is composed of 98 wt% to 70 wt% and the second carbon material 14 is composed of 2 wt% to 30 wt%. The ratio of the first carbon material 11 to 95 wt% to 80 wt% and the second carbon material 14 to 5 wt% to 20 wt% is preferable. When a negative electrode is formed using a negative electrode material in which the proportion of the first carbon material 11 is less than 70% by weight, the packing density of the carbon material does not increase, and a negative electrode material in which the proportion of the first carbon material 11 exceeds 98% by weight is used. When the negative electrode is formed, the content ratio of the second carbon material is small, and the void formed by the first carbon material is not sufficiently filled.
[0016]
Since the second carbon material 14 mainly composed of the carbon nanofibers 13 of the present invention has a shape in which a plurality of graphite nets 12 are laminated and the graphite nets are substantially perpendicular to the longitudinal axis of the fiber. Many edge surfaces of the mesh 12 are exposed, and there are a number of layers formed by each graphite mesh in which lithium ions are inserted and desorbed. Therefore, a high rate discharge is possible because many lithium ions can be inserted and desorbed between the graphite network layers. Moreover, the insertion and detachment | desorption reaction of lithium ion accompanying charging / discharging advances smoothly by making the average diameter of the graphite network 12 into the range of 10 nm-500 nm. If the average diameter of the graphite net 12 is less than 10 nm, the space for inserting lithium ions is insufficient, and the effect of improving the energy density is difficult to obtain. If the thickness exceeds 500 nm, it is difficult to diffuse even if lithium ions are inserted between the layers formed by the graphite network, and the charge / discharge reaction does not proceed smoothly.
[0017]
As shown in FIG. 3A, a reaction occurs in which lithium ions are inserted between graphite network layers during charging. The inserted lithium ions diffuse between the graphite network layers (FIG. 3B). During discharge, lithium ions diffused between the graphite network layers cause a desorption reaction smoothly (FIG. 3 (c)). As described above, by using the carbon nanofiber of the present invention for the second carbon material, the lithium ion insertion and desorption reactions that accompany charge / discharge proceed smoothly, so that high rate charge / discharge characteristics are improved. In addition, carbon nanofibers are smaller in size than carbon materials that have been used in the past, so when battery electrodes are fabricated, charging at high density is possible, leading to improved battery energy density. .
[0018]
  The second carbon material of the present invention further includes a particulate aggregate 16 made of carbon fine powder having a graphite structure in addition to the carbon nanofiber 13.Is preferable.in this case,The content of the carbon nanofibers 13 in the second carbon material is 80 wt% to 99.5 wt%, and the content of the particulate aggregate 16 is a ratio of 0.5 wt% to 20 wt%.Is preferred.MorePreferably, the carbon nanofibers 13 are 90 wt% to 99 wt%, and the particulate aggregates 16 are 1 wt% to 10 wt%. The reason why the content of the carbon nanofibers 13 is limited to the range of 80% by weight to 99.5% by weight is that when the amount is less than 80% by weight, a sufficient electrode density cannot be obtained, and the energy density is hardly improved. This is because it is difficult to obtain sufficient high rate discharge characteristics when it exceeds 5% by weight.
[0019]
When a carbon nanofiber or a mixture each containing a carbon nanofiber and a particulate aggregate is measured by X-ray diffraction, the stacking distance d of the graphite network plane obtained is measured.₀₀₂Is in the range of 0.3354 nm to 0.339 nm. Preferred stacking distance d₀₀₂Is 0.3355 nm to 0.3380 nm.
[0020]
It is preferable that at least 85% of the exposed portion of the carbon nanofiber 12 or the exposed portion of the mixture including the carbon nanofiber 12 and the particulate aggregate 13 is an end portion of the graphite network. More preferably, it is 90% or more. Here, the end portion of the graphite net indicates a portion represented by reference numeral 12a in FIGS.
[0021]
By further including 0.5% by weight to 10% by weight of either or both of the metal and metal oxide 17 having an average particle diameter of 10 nm to 500 nm, the metal or metal oxide 17 having an average particle diameter of 10 nm to 500 nm can be obtained. Since it becomes a base point for electron conduction, a higher rate of discharge becomes possible. Either the metal or the metal oxide or both are configured to lie on the long axis of the carbon nanofiber. As the metal, at least one element selected from the group consisting of Fe, Co, Ni, Mg, Al, Mn, and Cu is selected and used in the form of a single metal, an alloy, or a metal oxide.
[0022]
The particulate first carbon material 11 is made of coal, coke, PAN-based carbon fiber, pitch-based carbon fiber, organic carbonized product, natural graphite, artificial graphite, synthetic graphite, mesocarbon microbead, organic graphite. And at least one selected from the group consisting of chemicals and graphite fibers.
[0023]
Next, the manufacturing method of the negative electrode material of this invention is demonstrated.
First, a catalyst necessary for producing the second carbon material of the present invention is synthesized. The average particle diameter of this catalyst is a size suitable for producing a second carbon material with fine powder in the range of 10 nm to 500 nm. As the catalyst, Fe-based fine powder, specifically, Fe-Ni alloy, Fe-Mn alloy, Fe-Cu alloy, Co metal, Al₂O_ThreeAnd MgO metal oxide. The catalyst is pretreated and activated before producing the second carbon material. Catalysts are He and H₂It is activated by heating in a mixed gas atmosphere containing.
[0024]
FIG. 6 shows a heat treatment furnace 20 for producing the second carbon material of the present invention. The heat treatment furnace 20 includes an apparatus main body 21 made of a heat insulating material, and the inside of the apparatus main body 21 is horizontally partitioned by two partition plates 26 at a predetermined interval. A heating element 22 is installed on the top and bottom of the apparatus main body 21 partitioned by the partition plates 26, 26, respectively. Examples of the heating source of the heating element 22 used for heat treatment in the heat treatment furnace include an incandescent lamp, a halogen lamp, an arc lamp, and a graphite heater. A gas supply port 24 is provided on one side of the apparatus main body 21 so as to supply the source gas to the space partitioned by the partition plates 26 and 26. Source gases include CO and H₂The mixed gas containing is mentioned. C instead of CO₂H₂, C₆H₆Etc. may be used. The space 27 partitioned by the partition plates 26 and 26 has a size that can accommodate a table 28 in which a fine powder catalyst is dispersed. The other side of the apparatus main body 21 is placed outside the system in the heat treatment furnace 20. A gas outlet 29 for discharging the supplied source gas is provided. The table 28 accommodated in the space 27 is placed on the take-out table 31, and is provided so as to be accommodated and unloaded in the heat treatment furnace.
[0025]
After the fine powder catalyst 32 is placed on the table 28, the table 28 is taken out, placed on the stand 31, transported to the heat treatment furnace 20, and stored in the space 27 of the apparatus main body 21. Thereafter, the source gas is supplied from the gas supply port 24 and heated by the heating elements 22 and 22. The supply amount of the source gas is set to 0.2 L / min to 10 L / min, and the heating temperature is set to 500 ° C. to 700 ° C. The mixture 33 is heated while supplying the raw material gas and kept for 1 hour to 10 hours, whereby the mixture 33 containing the carbon nanofibers and the particulate aggregates grows through the catalyst 32. Since the obtained mixture 33 containing the carbon nanofibers and the particulate aggregate contains a catalyst, the mixture 33 obtained by unloading the table 28 from the heat treatment furnace 20 is taken out, and the mixture 33 is mixed with nitric acid, The catalyst 32 contained in the mixture 33 is removed by dipping in an acidic solution such as hydrochloric acid, sulfuric acid, or hydrofluoric acid. The catalyst 32 may be included in the mixture as it is, and the catalyst may be a metal or a metal oxide.
[0026]
Next, as the particulate first carbon material 11, coal, coke, PAN-based carbon fiber, pitch-based carbon fiber, carbonized product of organic matter, natural graphite, artificial graphite, synthetic graphite, mesocarbon microbeads, graphitization of organic matter A material having an average particle diameter of 5 μm to 40 μm including at least one selected from the group consisting of a product and a graphite fiber is prepared.
Mixing the first carbon material 11 and the obtained second carbon material 14 at a ratio of 98 wt% to 70 wt% for the first carbon material 11 and 2 wt% to 30 wt% for the second carbon material 14. Thus, a negative electrode material is prepared.
[0027]
A negative electrode is prepared using the negative electrode material of the present invention thus obtained.
First, a predetermined negative electrode material (negative electrode active material), a conductive additive (carbon powder or metal powder that is difficult to be alloyed with lithium such as copper or titanium), and a binder such as polyvinylidene fluoride (PVdF) are predetermined. A negative electrode slurry is prepared by mixing at a ratio of Here, the binder is mixed in a state dissolved in a solvent such as acetone. Next, the negative electrode slurry is applied to the upper surface of the negative electrode current collector foil by a screen printing method, a doctor blade method, or the like, and dried to produce a negative electrode. In addition, after apply | coating a negative electrode slurry on a glass substrate and drying, it peels from a glass substrate and produces a negative electrode film, Furthermore, this negative electrode film is piled up on a negative electrode collector, and is press-molded by predetermined pressure, and negative electrode May be produced. In the negative electrode manufactured in this way, the insertion and extraction of lithium ions proceed smoothly by the carbon nanofibers formed by laminating a plurality of graphite nets, so that the high rate charge / discharge characteristics are improved.
[0028]
The obtained negative electrode of the present invention, a non-aqueous electrolyte [for example, a mixed solvent composed of ethylene carbonate (EC) and diethylene carbonate (DEC) (mixing weight ratio 1: 1) and lithium perchlorate dissolved in 1 mol / liter A positive electrode formed by applying and drying a positive electrode slurry composed of a binder, a positive electrode material, and a conductive auxiliary agent on a positive electrode current collector by a doctor blade method. Thus, a lithium ion battery is obtained. In addition, a negative electrode of the present invention, a polymer electrolyte layer made of polyethylene oxide, polyvinylidene fluoride, or the like, and a positive electrode slurry made of a binder, a positive electrode material, and a conductive auxiliary agent are applied onto the positive electrode current collector and dried. A lithium polymer battery is obtained by laminating the positive electrode formed in this way. In the lithium ion battery and the lithium polymer battery manufactured in this way, the insertion and release of lithium ions proceed smoothly due to the carbon nanofibers formed by laminating a plurality of graphite nets, thereby improving the high rate charge / discharge characteristics. . In addition, since carbon nanofibers that are smaller in size than conventional carbon materials are used, charging at a high density is possible, leading to an improvement in the energy density of the battery.
[0029]
【Example】
Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
(1) Production of second carbon materials
First, an Fe—Ni alloy having an average particle size of 0.1 μm was used as a catalyst, and this catalyst was converted into He and H.₂It was activated by heating in a mixed gas atmosphere containing. Next, the activated catalyst was placed on a table, and the table was accommodated in a heat treatment furnace. Next, the inside of the heat treatment furnace is heated to a temperature of 550 ° C. to 630 ° C., and CO and H₂A mixed gas containing carbon nanofibers and particulate agglomerates was synthesized by holding the raw material gas at a flow rate of 10 L / min for about 10 hours while supplying the raw material gas into the heat treatment furnace. The obtained mixture was immersed in a nitric acid solution to remove the catalyst contained in the mixture to obtain a second carbon material. When this second carbon material was measured by X-ray diffraction, the stacking distance d on the graphite network plane of the mixture containing carbon nanofibers and particulate aggregates was determined.₀₀₂Was 0.3362 nm.
[0030]
(2) Production of negative electrode (working electrode)
First, mesocarbon microbeads having an average particle diameter of 14 μm were prepared as a first carbon material, and the first carbon material and the second carbon material were mixed at a ratio of 95 wt%: 5 wt% to prepare a negative electrode material. . A negative electrode slurry was prepared by mixing 18 g of this negative electrode material, 2 g of polyvinylidene fluoride (PVdF), and 18 g of n-methylpyrrolidone. Next, the negative electrode slurry having a thickness of 0.09 cm was prepared by coating the negative electrode slurry on a glass substrate, drying it, and then peeling it off. This negative electrode film was cut into squares each having a length × width of 1.2 cm × 1.2 cm to obtain two square negative electrode films. Next, these negative electrode films were arranged on both sides of a square metal net-like negative electrode current collector of 1 cm × 1 cm × 0.1 cm in length × width × thickness, respectively, to prepare a laminate. A copper foil formed in a mesh shape was used for the negative electrode current collector. Further, the laminate was pressure-bonded by applying a pressure of 0.5 to 3 MPa with a press machine heated to 110 to 130 ° C. This obtained the negative electrode (working electrode).
[0031]
<Example 2>
A negative electrode (working electrode) was produced in the same manner as in Example 1 except that the negative electrode material was prepared by mixing the first carbon material and the second carbon material in a ratio of 90% by weight to 10% by weight.
<Example 3>
A negative electrode (working electrode) was produced in the same manner as in Example 1 except that the negative electrode material was prepared by mixing the first carbon material and the second carbon material in a ratio of 80% by weight to 20% by weight.
<Example 4>
A negative electrode (working electrode) was produced in the same manner as in Example 1 except that the negative electrode material was prepared by mixing the first carbon material and the second carbon material in a ratio of 70% by weight to 30% by weight.
[0032]
<Example 5>
A negative electrode (working electrode) was produced in the same manner as in Example 1 except that mesocarbon microbeads having an average particle diameter of 23 μm were used as the first carbon material.
<Example 6>
A negative electrode (working electrode) was produced in the same manner as in Example 2 except that mesocarbon microbeads having an average particle diameter of 23 μm were used as the first carbon material.
<Example 7>
A negative electrode (working electrode) was produced in the same manner as in Example 3 except that mesocarbon microbeads having an average particle size of 23 μm were used as the first carbon material.
<Example 8>
A negative electrode (working electrode) was produced in the same manner as in Example 4 except that mesocarbon microbeads having an average particle diameter of 23 μm were used as the first carbon material.
[0033]
<Comparative Example 1>
A negative electrode (working electrode) was produced in the same manner as in Example 1 except that a spherical graphite material having an average particle size of 10 μm was used as the negative electrode material.
<Comparative example 2>
A negative electrode (working electrode) was produced in the same manner as in Example 1 except that a spherical graphite material having an average particle size of 25 μm was used as the negative electrode material.
[0034]
<Comparison test and evaluation>
As shown in FIG. 7, the negative electrode 41 (working electrode) produced in each of Examples 1 to 8 and Comparative Examples 1 and 2 was attached to a charge / discharge cycle test apparatus 51. In this device 51, an electrolytic solution 53 (lithium salt dissolved in an organic solvent) is stored in a container 52, the negative electrode 41 is immersed in the electrolytic solution 53 together with the positive electrode 42 and the reference electrode 43, and further the negative electrode 41 (working electrode). ), The positive electrode 42 (counter electrode) and the reference electrode 43 are electrically connected to a potentiostat 54 (potentiometer), respectively. Lithium salt contains 1M LiPF₆A solution containing ethylene carbonate and diethyl carbonate was used as the organic solvent. Using this apparatus, a charge / discharge cycle test was performed to measure the low rate and high rate discharge capacity of each negative electrode (working electrode). The low-rate discharge capacity was measured at 70 mA / g, and the high-rate discharge capacity was measured at 500 mA / g. The measurement voltage range was 0 V to 2.0 V. The measurement results of the electrodes of Examples 1 to 8 are shown in Table 1, and the measurement results of the electrodes of Comparative Examples 1 and 2 are shown in Table 2, respectively.
[0035]
[Table 1]

[0036]
[Table 2]

[0037]
As is clear from Tables 1 and 2, in Comparative Examples 1 and 2 in which spherical graphite material having a large average particle diameter that has been used conventionally is used as the negative electrode material, the reduction in the high rate discharge capacity was remarkable. . Further, Comparative Example 2 having a larger particle diameter showed a lower electrode density than Comparative Example 1. On the other hand, Examples 1 to 8 using the negative electrode material of the present invention each showed a high electrode density, and there was no significant difference between the low rate discharge capacity and the high rate discharge capacity, and electrodes were produced using this material. In this case, it was found that the high rate discharge characteristics can be improved.
[0038]
【The invention's effect】
  As described above, the negative electrode material according to the present invention is formed by laminating a plurality of particulate first carbon materials having an average particle diameter of 5 μm to 40 μm and a planar graphite network having an average diameter of 10 nm to 500 nm. Each of the second carbon materials mainly includes carbon nanofibers that are substantially perpendicular to the axis, and the carbon nanofibers included in the second carbon material have a length of 1000 nm or more and an aspect ratio of 10 or more. The first carbon material is composed of 98% by weight to 70% by weight, and the second carbon material is composed of 2% by weight to 30% by weight.
  When an electrode of a battery is produced using the negative electrode material of the present invention including the first carbon material having a large average particle size and the nano-sized second carbon material, the second carbon material is in the void formed by the first carbon material. Since it is filled, the packing density of the carbon material in the electrode is effectively improved. In addition, carbon nanofibers having a length of 1000 nm or more, which is the main component of the second carbon material, and an aspect ratio of 10 or more expose many edges of the graphite network. By using the negative electrode material of the present invention each including the first carbon material, which is a carbon material that has been conventionally used, and lithium associated with charge and discharge compared to the case where only the conventional carbon material is used as the negative electrode material Ion insertion and desorption reactions proceed smoothly, improving high rate charge / discharge characteristics. Furthermore, since the second carbon material is a material having an average diameter smaller than that of the conventionally used carbon material, when the battery electrode is produced, it becomes possible to charge at a high density and to improve the energy density of the battery. Lead to.
[Brief description of the drawings]
FIG. 1 is a schematic view of a negative electrode material of the present invention.
FIG. 2 is a schematic view of a carbon nanofiber that is a main component of the second carbon material of the present invention.
FIG. 3 is a schematic diagram showing a reaction in which lithium ions are inserted and desorbed between graphite network layers.
4 is a schematic view of a carbon nanofiber having another structure corresponding to FIG. 2. FIG.
FIG. 5 is a schematic diagram showing carbon nanofibers and particulate aggregates.
FIG. 6 is a cross-sectional configuration diagram of a heat treatment furnace for producing the negative electrode material of the present invention.
FIG. 7 shows an apparatus used for a charge / discharge cycle test of negative electrode active materials for lithium secondary batteries of Examples and Comparative Examples.
[Explanation of symbols]
11 First carbon material
12 Graphite net
13 Carbon nanofiber
14 Second carbon material
16 particulate aggregates

Claims (10)

A plurality of particulate first carbon materials (11) having an average particle diameter of 5 μm to 40 μm and a planar graphite network (12) having an average diameter of 10 nm to 500 nm are laminated, and the graphite network substantially corresponds to the longitudinal axis of the fiber. A second carbon material (14) mainly composed of carbon nanofibers (13) perpendicular to
The carbon nanofiber (13) contained in the second carbon material (14) has a length of 1000 nm or more and an aspect ratio of 10 or more,
The first carbon material (11) is composed of 98 wt% to 70 wt%, and the second carbon material (14) is composed of 2 wt% to 30 wt%,
The negative electrode material second carbon material (14) is characterized that you have filled in the gap to form the first carbon material (11). Graphite-net measured in X-ray diffraction of the carbon nanofibers in the second carbon material (14) (13) (12) according to claim 1 Symbol mounting laminate spacing d ₀₀₂ of the planes is 0.3354nm~0.339nm Negative electrode material. The negative electrode according to claim 1 or 2, further comprising 0.5 wt% to 10 wt% of one or both of a metal and a metal oxide (17) having an average particle diameter of 10 nm to 500 nm in the second carbon material (14). material. The negative electrode material according to any one of claims 1 to 3 , wherein at least 85% of the exposed portion of the carbon nanofiber (13) is an end portion of the graphite network. 4. The negative electrode material according to claim 3 , wherein either one or both of metal and metal oxide are on the long axis of the carbon nanofiber. The negative electrode material according to claim 3 or 5 , wherein the metal is at least one element selected from the group consisting of Fe, Co, Ni, Mg, Al, Mn, and Cu.   Particulate primary carbon material (11) is coal, coke, polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, organic carbonized product, natural graphite, artificial graphite, synthetic graphite, mesocarbon microbeads, organic graphitization The negative electrode material according to claim 1, comprising at least one selected from the group consisting of a product and graphite fibers. Negative electrode formed using the negative electrode material according to claims 1 to 7 any one, and a conductive additive. A lithium ion battery formed using the negative electrode according to claim 8 . A lithium polymer battery formed using the negative electrode according to claim 8 .

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