JP3844931B2 - Negative electrode and secondary battery - Google Patents

Description

上記の全ての原料について、混練機により２時間混練し正極用ペーストとした。
【００５７】

上記組成全部を混合攪拌溶解し、電解質塗料とした。
【００５８】
［正極の作成」
上記の正極塗料を20μm厚のアルミニウム集電体基材上に、エクストルージョン型のダイコーティングによって塗布、乾燥し、活物質がバインダーによって集電体上に結着された膜を作成した。
次いで、ロールプレス（カレンダー）を用いて、線圧100kgf/cmの条件で圧密することによって正極を作製した。
【００５９】
［電池の作成］
上記正極ならびに実施例１〜５および比較例１〜３で製造した各負極に電解質塗料を塗布し、別に電解質塗料に浸した電極よりやや面積の広い高分子多孔質フィルムを間に挟んで積層し、電解質塗料を添加して挟んだ状態で９０℃にて１０分加熱することにより電解質を非流動化して、正極、負極を有し、非流動化された電解質成分を有する平板状の単位電池素子を形成した。その後単位電池素子に電流を取り出すタブを接続し、アルミニウム膜と高分子フィルムからなるラミネートフィルムを対向成形した袋状ケースに真空シールして収納することによって平板状電池とした。
【００６０】
得られた平板状電池を０．５ｍＡ／ｃｍ²で４．２Ｖまで充電し、目視にてガス発生の有無を確認した。ガス発生がある場合は、ケースに膨らみが生じる。
【００６１】
【表１】

【００６２】
【発明の効果】
本発明によれば、高容量で、充電時のガス発生が抑制された二次電池用、特にリチウム二次電池用の炭素質負極、並びにこの負極を用いた二次電池を提供することが出来る。
【図面の簡単な説明】
【図１】図１は、実施例１で製造した非晶質炭素被覆黒鉛についてのＴＧ測定結果を示すサーモグラムである。
【図２】図２は、比較例１で製造した黒鉛についてのＴＧ測定結果を示すサーモグラムである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a negative electrode and a secondary battery using the same, and more specifically, a negative electrode having graphite having a specific amount of an amorphous carbon coating film as an active material, and a secondary battery including the negative electrode, in particular, The present invention relates to a lithium secondary battery.
[0002]
[Prior art]
In recent years, various devices such as a camera-integrated VTR device, an audio device, a portable computer, a mobile phone, and the like have been reduced in size and weight, and a demand for higher performance of a battery as a power source of these devices is increasing. In particular, lithium secondary batteries capable of realizing high voltage and high energy density are actively developed.
A lithium secondary battery includes a positive electrode and a negative electrode capable of occluding and releasing lithium ions, and an electrolyte layer containing a non-aqueous electrolyte. Conventionally, a liquid made of a non-aqueous organic material has been used as the non-aqueous electrolyte. However, a lithium secondary battery using such a non-aqueous electrolyte has a risk of leakage and ignition such as heat generation and ignition due to an internal short circuit due to deposition of lithium dendrite. Therefore, in recent years, in order to improve safety, a polymer electrolyte that has been contained in a non-aqueous electrolyte, for example, a gel polymer, and has been made non-fluid has been developed.
[0003]
In addition, it was first attempted to use lithium metal as the negative electrode material, but during repeated charging and discharging, dendritic lithium precipitated and penetrated the separator to reach the positive electrode, causing a short circuit and a fire accident. It was found that there is a possibility of causing. Therefore, at present, attention is focused on the use of a carbon material capable of preventing the deposition of lithium metal by allowing the nonaqueous solvent to enter and exit between the layers during the charge / discharge process.
[0004]
As this carbon material, Japanese Patent Application Laid-Open No. 57-208079 proposes to use a graphite material. In particular, when graphite having good crystallinity was used as a carbon anode material for a lithium secondary battery, it was known that a capacity close to 372 mAh / g, which is the theoretical capacity of lithium storage of graphite, was obtained, which is preferable as a material. . However, since the graphite material is active with respect to the electrolytic solution, it generally has an irreversible capacity of several tens of mAh / g or more due to film formation or side reaction during the first charge / discharge.
In JP-A-5-299074, a carbon material is subjected to a chemical pretreatment with an inorganic acid or warmed sodium hydroxide, and then subjected to a vacuum heat treatment at a temperature of 800 ° C. or higher to improve the charge / discharge cycle efficiency. It is disclosed that it is possible to improve. Japanese Patent Application Laid-Open No. 6-20690 discloses a method of measuring the increase in negative electrode capacity by making an amorphous carbonaceous material while oxidizing the surface by chemical oxidation, electrolytic oxidation, or vapor phase oxidation. Furthermore, JP-A-6-44959 discloses a method of adding an acid to a carbonaceous material and heating it to obtain a capacity (370 mAh / g) close to the theoretical capacity of graphite.
[0005]
However, since graphite uses intercalation of lithium ions into graphite crystals as the principle of charge and discharge, LiC, the largest lithium-introduced compound, is used at room temperature and normal pressure.₆ There is a problem that a capacity of 372 mAh / g or more calculated from the above cannot be obtained. Therefore, a capacity exceeding 372 mAh / g, which is the theoretical capacity of graphite, is not obtained by any method. Moreover, the low wettability of the graphite material with the electrolytic solution has a problem that the lithium dedoping capacity at the initial stage of charge / discharge is lower than the capacity of 350 mAh / g or more that the graphite material should be originally developed. .
[0006]
Japanese Patent Application Laid-Open No. 7-022037 discloses a carbonaceous material obtained by coating the surface of a graphitic carbonaceous material with an organic material that can be carbonized, and firing the carbonaceous material. Similarly, although it has an advantage that it is close to the redox potential of lithium metal and can obtain a higher capacity than the graphitic carbonaceous material, a capacity exceeding 372 mAh / g, which is the theoretical capacity of graphite, has not been obtained.
Further, as an electrode material having a high capacity and excellent rate resistance characteristics, Japanese Patent Application Laid-Open No. Hei 10-284080 discloses that the surface of a graphitic carbonaceous material is coated with a carbonizable organic material, baked, pulverized, and then acidic. Alternatively, a carbonaceous material treated with an alkaline solution is disclosed. However, the negative electrode containing the carbon material as an active material has a problem that gas generation occurs during charging.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a negative electrode having a high capacity made of a graphitic carbonaceous material and suppressing gas generation during charging, and a secondary battery using the same.
[0008]
[Means for Solving the Problems]
    As a result of intensive studies to solve the above problems, the present inventor,Prepared in a prescribed way,The inventors have found that such a problem can be solved by using graphite coated with a specific coating film in a specific amount as a negative electrode active material, and have completed the present invention. That is, the gist of the present invention is as follows.A negative electrode containing amorphous carbon-coated graphite having an amorphous carbon-coated film as an active material, the amorphous carbon-coated graphite having an average particle size of 4 to 40 μm and a specific surface area (BET method) of 0. 1-20m ² / G graphite and a coating film thermoplastic resin formed after dry-mixing the amorphous carbon-coated graphite obtained by coating the coating film with the coating film thermoplastic resin, and the amorphous Carbon-coated graphiteIn thermogravimetry (TG), when the temperature was raised at a rate of temperature rise of 20 ° C./min in an air stream of 200 ml / min, the starting temperature of weight reduction in the first stage was 350 to 600 ° C., The first stage weight loss is 3-20% of the weight before the temperature riseRukoThe other gist lies in a secondary battery comprising the negative electrode and a non-fluidic electrolyte layer.
[0009]
      As a preferred embodiment of the present invention,The thermoplastic resin for an amorphous carbon coating film is a thermoplastic resin that is in a molten state at 200 ° C., and the thermoplastic resin for an amorphous carbon coating film isExamples thereof include polyvinyl chloride, polyvinyl alcohol, and polyvinyl pyrrolidone.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
In the thermogravimetric analysis (TG), the amorphous carbon-coated graphite as the negative electrode active material in the present invention is the first stage when it is heated at a temperature rising rate of 20 ° C./min in an air stream of 200 ml / min. It is essential that the starting temperature of the weight reduction of the eye is 350 to 600 ° C., and the weight reduction amount of the first stage is 3 to 20% of the weight before the temperature increase. Graphite has a relatively high oxidation resistance, and TG does not lose weight at 600 ° C. or lower. Therefore, the weight reduction of the first stage of the amorphous carbon-coated graphite indicates a weight reduction of the amorphous carbon-coated film portion, and it is non-existent that the weight reduction starts to occur at 350 to 600 ° C. It shows the characteristics of the crystalline carbon coating film. The weight reduction amount of 3 to 20% in the present invention is the weight reduction amount with respect to the weight of the amorphous carbon-coated graphite before the temperature rise, and is obtained by the following formula.
[0011]
[Expression 1]
Weight loss (%) = [(ab) / a] × 100
a: Weight of amorphous carbon-coated graphite before temperature increase
b: Weight of amorphous carbon-coated graphite after first stage weight reduction
[0012]
As described above, the amount of weight loss of the first stage when the amorphous carbon-coated graphite is heated at a heating rate of 20 ° C./min in an air stream of 200 ml / min is usually 3 to 20%. Preferably, it is 3 to 15% of the weight before the temperature rise. If the decrease in weight is too small, the effect of suppressing gas generation during initial charging will not be exhibited, and if too large, the voltage drop during discharging will be large and the capacity will be small, which is not preferable.
[0013]
The starting temperature of the first stage weight reduction in the present invention refers to the temperature at which the TG curve begins to move away from a straight line approximation based on the TG curve at 200 to 350 ° C. (A in FIG. 1). The first stage weight reduction amount in the present invention refers to the weight reduction amount during the temperature rise from the first stage weight reduction start temperature to the first stage weight reduction end point temperature. . The end point temperature of the first stage weight reduction is the temperature at which the first derivative (DTG) of the TG curve is minimized (B in FIG. 1).
[0014]
The amorphous carbon-coated graphite in the present invention is graphite having an amorphous carbon-coated film having the above-mentioned characteristics. However, as the graphite in the amorphous carbon-coated graphite, the properties of those graphites are known. In this case, highly crystalline natural graphite, highly crystalline artificial graphite, a reheated product of natural graphite or artificial graphite, a reheated product of expanded graphite, or a high purity purified product of these graphites is preferable.
[0015]
Examples of the types of graphite include those exemplified in the following (1) to (4), which can be selected from among these, and among these, graphite is particularly preferable.
(1) highly crystalline natural graphite or artificial graphite,
(2) Natural graphite, artificial graphite, or expanded graphite reheated at 2000 ° C. or higher,
(3) Graphite having the same performance as the above (1) and (2) obtained by graphitization of a graphitizable organic material, such as coal tar pitch, coal-based heavy oil, atmospheric residue, petroleum Heavy oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin , One or more organic substances selected from phenol-formaldehyde resins and imide resins, graphitized at a firing temperature of 2500 ° C. to 3200 ° C.,
[0016]
(4) The graphitizable organic substance of (3) above is replaced with lithium, beryllium, boron, magnesium, aluminum, silicon, potassium, calcium, titanium, vanadium, chromium, manganese, copper, zinc, nickel, platinum, palladium, cobalt In the presence of a catalyst such as at least one powder or thin film selected from ruthenium, tin, lead, iron, germanium, zirconium, molybdenum, silver, barium, tantalum, tungsten and rhenium, 400 ° C to 2500 ° C, and more Preferably graphitized by firing at 1000 ° C. or more and 2000 ° C. or less.
[0017]
The average particle diameter of graphite is usually 4 μm or more, preferably 10 μm or more, and is usually 40 μm or less, preferably 30 μm or less. When the particle size is too small, it is difficult to increase the packing density of the coating film, and when it is too large, the surface property of the electrode is lowered and the adhesion to the separator is lowered.
The specific surface area of graphite is the specific surface area of the BET method, usually 0.1 m²/ G or more, preferably 1 m²/ G or more, usually 20m²/ G or less, preferably 10 m²/ G or less. When the specific surface area is too small, the rapid charge / discharge characteristics are lowered, and when it is too large, the strength of the coating film is lowered and the safety is also lowered.
[0018]
The “amorphous carbon coating film” of the amorphous carbon-coated graphite in the present invention specifically includes a coating film formed by firing a thermoplastic resin. As the thermoplastic resin for forming the coating film, a resin that is in a molten state at 200 ° C. is preferable. More specifically, polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyvinyl alcohol (PVA), Examples include polyethylene (PE), polyethylene terephthalate (PET), and polyvinyl pyrrolidone (PVP), with polyvinyl chloride (PVC), polyvinyl alcohol (PVA), and polyvinyl pyrrolidone (PVP) being particularly preferred.
[0019]
  The amorphous carbon-coated graphite in the present invention can be obtained, for example, by mixing the above graphite and the above thermoplastic resin and firing.
  The mixing ratio of graphite and thermoplastic resin is usually 10 parts by weight or more, preferably 20 parts by weight or more, more preferably 40 parts by weight or more, and usually 150 parts by weight or less, with respect to 100 parts by weight of graphite. Preferably it is 80 weight part or less, More preferably, it is 60 weight part or less. If the amount of the thermoplastic resin is too small, the gas generation suppressing effect is lowered, and if it is too much, there are a voltage drop and a capacity drop during discharge.
  The graphite and the thermoplastic resin may be mixed in a dry manner using a known mixing device such as a V-type mixer. From the viewpoint of performing more precise mixing, a ball mill, a hammer mill, or the like that can apply a shearing force is used. An apparatus is preferably used.
  GraphiteNomaInstead, when the graphite and the thermoplastic resin are mixed, the resin is preferably melted by heating to 180 to 220 ° C. so that the thermoplastic resin is evenly distributed.
[0020]
Firing after mixing is usually performed in an inert gas atmosphere such as nitrogen or argon. The temperature of baking should just be more than the temperature which carbonization is completed, Usually 700 degreeC or more, Preferably it is 750 degreeC or more, Preferably it is 1100 degrees C or less, More preferably, it is 1000 degrees C or less, Most preferably, it is 950 degrees C or less. is there. If the temperature is too low, carbonization is insufficient and sufficient performance as an electrode active material cannot be obtained. Moreover, if the temperature is too high, the crystallinity of graphite may become too high. If the crystallinity is too high, gas may be generated. The temperature rising rate is not particularly limited, but is usually 10 to 500 ° C./h, preferably 20 to 100 ° C./h.
[0021]
The amorphous carbon-coated graphite obtained by firing can be produced, for example, as a dispersion paint using a solvent capable of dissolving the binder together with the binder, and the negative electrode can be produced by applying and drying the paint on a current collector.
As the binder in the present invention, it is necessary to be stable with respect to an electrolytic solution and the like, and various materials are used from the viewpoint of weather resistance, chemical resistance, heat resistance, flame retardancy, and the like. Specifically, inorganic compounds such as silicate and glass, alkane polymers such as polyethylene, polypropylene and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; polystyrene, polymethylstyrene, Examples thereof include polymers having a ring structure in a polymer chain such as polyvinyl pyridine and poly-N-vinyl pyrrolidone.
[0022]
Other specific examples include acrylic derivative polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide; Fluorine resins such as vinyl chloride, polyvinylidene fluoride and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; Polyvinyl alcohol polymers such as polyvinyl acetate and polyvinyl alcohol; Halogen-containing polymers such as vinylidene; conductive polymers such as polyaniline can be used.
[0023]
Further, a mixture such as the above-mentioned polymer, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, and the like can be used. The weight average molecular weight of these resins is usually about 10,000 to 3,000,000, preferably about 100,000 to 1,000,000. If it is too low, the strength of the coating film tends to decrease. On the other hand, if it is too high, the viscosity increases and it may be difficult to form an electrode. Preferable binder resins include fluorine resins and CN group-containing polymers, and more preferably polyvinylidene fluoride.
[0024]
The amount of the binder used is usually 0.1 parts by weight or more, preferably 1 part by weight or more, and usually 30 parts by weight or less, preferably 20 parts by weight or less with respect to 100 parts by weight of the amorphous carbon-coated graphite. is there. If the amount of the binder is too small, the strength of the electrode tends to decrease, and if the amount of the binder is too large, the ionic conductivity tends to decrease.
As the solvent in the present invention, a solvent capable of dissolving the binder to be used may be appropriately selected. For example, N-methylpyrrolidone and dimethylformamide may be mentioned, and N-methylpyrrolidone is preferable. The solvent concentration in the paint is at least 10% by weight, usually 20% by weight or more, preferably 30% by weight or more, and more preferably 35% by weight or more. Moreover, as an upper limit, it is 90 weight% or less normally, Preferably it is 80 weight% or less. If the solvent concentration is too low, coating may be difficult. If the solvent concentration is too high, it may be difficult to increase the coating thickness and the stability of the coating may be deteriorated.
[0025]
For dispersion coating, a commonly used disperser can be used, and a ball mill, a sand mill, a twin-screw kneader, or the like can be used.
There are no particular restrictions on the coating device for applying the paint on the current collector, such as slide coating, extrusion type die coating, reverse roll, gravure coater, knife coater, kiss coater, micro gravure coater, rod coater, blade coater, etc. The extrusion method is most preferable in consideration of the viscosity of the paint and the coating film thickness.
After the coating material was applied on the current collector, the coating film was dried, for example, dried at 120 ° C. for 10 minutes. When the drying temperature is low, the crystallization of the binder hardly occurs and the coating film strength is lowered. If the drying time is short and the drying is insufficient, the residual solvent adversely affects the battery characteristics. Conversely, if the temperature is high or the drying time is too long, the current collector is oxidized and the battery characteristics are deteriorated.
[0026]
In order to improve the electroconductivity and mechanical strength of an electrode, you may contain the additive, powder, filler, etc. which express various functions, such as an electroconductive material and a reinforcing material. The conductive material is not particularly limited as long as it can be mixed with an appropriate amount of the above-mentioned amorphous carbon-coated graphite to impart conductivity, but usually carbon powder such as acetylene black, carbon black, graphite, and various kinds of materials. Examples include metal fibers and foils. The DBP oil absorption amount of the carbon powder conductive material is preferably 120 cc / 100 g or more, and particularly preferably 150 cc / 100 g or more because the electrolyte solution is retained. Additives include trifluoropropylene carbonate, 1,6-dioxaspiro [4,4] nonane-2,7-dione, 12-crown-4-ether, vinylene carbonate, catechol carbonate, etc. Can be used to enhance. As the reinforcing material, various inorganic, organic spherical and fibrous fillers can be used.
[0027]
The thickness of the negative electrode is generally about 0.05 to 200 μm. Within this range, it is usually 10 μm or more, preferably 20 μm or more, and is usually 200 μm or less, preferably 150 μm or less. If it is too thin, the battery capacity may be too small. On the other hand, if it is too thick, the rate characteristics may be deteriorated too much. In addition, the negative electrode in the above means a layer containing an active material (amorphous carbon-coated graphite) and does not contain a current collector.
[0028]
As the current collector in the present invention, various materials that can function as a current collector of a battery without causing problems such as electrochemical dissolution can be used, and usually a metal or an alloy is used. For example, a copper foil is often used as the negative electrode current collector.
Roughening the surfaces of these current collectors in advance is a preferable method because the binding effect with the electrode material layer can be improved. Current roughening methods include a method of rolling with a blasting process or a rough roll, a polishing cloth with a fixed abrasive particle, a grinding wheel, emery buff, a wire brush with a steel wire, etc. Examples thereof include a mechanical polishing method for polishing the surface, an electrolytic polishing method, and a chemical polishing method.
[0029]
In addition, in order to reduce the weight of the secondary battery, that is, to improve the weight energy density, a perforated type substrate such as an expanded metal or a punching metal can be used. In this case, the weight can be freely changed by changing the aperture ratio. In addition, when a contact layer is formed on both surfaces of such a perforated type substrate, the rivet effect of the coating film through this hole tends to make the coating film more difficult to peel off, but the aperture ratio becomes too high. In this case, since the contact area between the coating film and the substrate is small, the adhesive strength may be lowered.
The thickness of the current collector is usually 1 μm or more, preferably 5 μm or more, and is usually 100 μm or less, preferably 50 or less. If it is too thick, the capacity of the entire battery will be too low. Conversely, if it is too thin, handling may be difficult.
[0030]
An undercoat primer layer can also be formed on the current collector. The function of the primer layer is to improve the adhesion of the negative electrode to the current collector. Compared to the case where the primer layer is not provided, the battery internal resistance is reduced by improving the adhesion, and the base material in the charge / discharge cycle test process This prevents rapid capacity reduction due to coating film detachment. The undercoat primer layer can be formed, for example, by applying an undercoat primer material paint containing a conductive material, a binder, and a solvent on a current collector, and then drying it.
Examples of the conductive material used for the undercoat primer layer include carbon materials such as carbon black and graphite, metal powders, and conductive organic conjugated resins.
[0031]
As the binder and solvent used for the undercoat primer layer, the same binders and solvents used for the coating material of the electrode material can be used. In addition, conductive resins such as polyaniline, polypyrrole, polyacene, disulfide compounds, polysulfide compounds and the like can have both functions of the conductive material and the binder. It can also be used for the undercoat primer layer. Of course, the binder and solvent used for the undercoat primer layer may be the same as or different from those used for the coating material of the electrode material.
[0032]
When a conductive material and a binder are used, the ratio of the binder to the conductive material is usually 1% by weight or more, preferably 5% by weight or more, and usually 300% by weight or less, preferably 100% by weight or less. is there. If the ratio is too low, peeling during the process is likely to occur when the battery is used, and if it is too high, the conductivity may decrease and the battery characteristics may deteriorate.
The thickness of the undercoat primer layer is generally about 0.05 to 200 μm. Within this range, it is usually 0.05 μm or more, preferably 0.1 μm or more, and usually 10 μm or less, preferably 1 μm or less. If it is too thin, it will be difficult to ensure uniformity, and if it is too thick, the volume capacity of the battery may be too low.
Since the gas generation of the negative electrode of the present invention is suppressed, it is preferable as the negative electrode of a secondary battery comprising a non-fluidic electrolyte layer.
[0033]
The electrolyte layer of the secondary battery in the present invention is made of a non-flowable electrolyte in which an electrolyte is held in a polymer, and is preferably a gel polymer electrolyte.
The gel polymer electrolyte requires a method using an electrolyte coating in which a polymer is first dissolved in an electrolyte solution, or a method in which a monomer-containing electrolyte coating is prepared and then a monomer is crosslinked to form a non-fluidized electrolyte. The material and manufacturing method according to can be adopted.
The electrolyte solution to be contained is preferably a non-aqueous electrolyte solution, which is generally a solution obtained by dissolving a supporting electrolyte that is a lithium salt in a non-aqueous solvent. The electrolyte is a non-aqueous electrolyte that is stable with respect to the positive electrode active material and the negative electrode active material described later as an electrolyte, and that can move for lithium ions to electrochemically react with the positive electrode active material or the negative electrode active material. What is a substance can be used.
[0034]
As a lithium salt as a supporting electrolyte, LiPF₆, LiAsF₆, LiSbF₆, LiBF_FourLiClO_Four, LiI, LiBr, LiCl, LiAlCl, LiHF₂, LiSCN, LiSO_ThreeCF₂ Etc. Of these, LiPF in particular₆And LiClO_FourIs preferred. The content of these supporting electrolytes in the electrolytic solution is generally 0.5 to 2.5 mol / l.
[0035]
The type of solvent used in the electrolytic solution is not particularly limited, but a solvent having a relatively high dielectric constant is preferably used. Specifically, cyclic carbonates such as ethylene carbonate and propylene carbonate, acyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, glymes such as tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane, γ-butyllactone, etc. Lactones, sulfur compounds such as sulfolane, nitriles such as acetonitrile, or a mixture of two or more thereof. Among these, in particular, one or two or more mixed solutions selected from cyclic carbonates such as ethylene carbonate and propylene carbonate, acyclic carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable. Particularly preferred are cyclic carbonates such as ethylene carbonate and propylene carbonate.
[0036]
When a non-fluidized electrolyte is obtained by a method of preparing a non-fluidized electrolyte by cross-linking the monomer after adjusting the monomer-containing electrolyte paint, a polymer is formed by applying a polymerization treatment such as ultraviolet curing or heat curing. A monomer to be added is previously added to the electrolytic solution to form a paint, and then a non-fluidization treatment is performed.
Examples of the polymerizable monomer include those having an unsaturated double bond such as an acryloyl group, a methacryloyl group, a vinyl group, and an allyl group. For example, acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, ethoxyethyl methacrylate, methoxyethyl methacrylate, ethoxyethoxyethyl methacrylate, polyethylene glycol monomethacrylate, N, Examples thereof include N-diethylaminoethyl acrylate, N, N-dimethylaminoethyl acrylate, glycidyl acrylate, and allyl acrylate.
[0037]
Other usable examples include acrylonitrile, N-vinylpyrrolidone, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene. Examples include glycol dimethacrylate, polyethylene glycol dimethacrylate, polyalkylene glycol diacrylate, and polyalkylene glycol dimethacrylate. Trifunctional monomers such as trimethylolpropane alkoxylate triacrylate and pentaerythritol alkoxylate triacrylate, pentaerythritol alkoxylate Tetraacrylate Ditrimethylolpropane alkoxylate monomers having four or more functional such tetraacrylate or the like can be also used. Of these, those preferable from the viewpoint of reactivity, polarity, safety, etc. may be used alone or in combination. Of these, diacrylates and triacrylates containing a plurality of ethylenoxide groups are particularly preferred.
[0038]
These monomers can be polymerized by heat, ultraviolet rays, electron beams or the like to make the electrolyte paint non-flowable. In this case, in order to make the reaction proceed effectively, a polymerization initiator can be added to the electrolytic solution. As the polymerization initiator, benzoin, benzyl, acetophenone, benzophenone, Michler ketone, biacetyl, benzoyl peroxide, etc. can be used, and t-butylperoxyneodecanoate, α-cumylperoxyneodecanoate, t -Peroxyneodecanoates such as hexylperoxyneodecanoate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, t-amylperoxyneodecanoate, t-butylperoxyneohepta Peroxy such as noate, α-cumylperoxyneoheptanoate, t-hexylperoxyneoheptanoate, 1-cyclohexyl-1-methylethylperoxyneoheptanoate, t-amylperoxyheptanoate Neoheptanoates can also be used. A peroxide polymerization initiator is preferred.
[0039]
Moreover, the monomer which produces | generates the polymer | macromolecule produced | generated by polyaddition, such as a polymer, such as a polyester, polyamide, a polycarbonate, a polyimide, polycondensation, a polyurethane, a polyurea, etc. can also be used as a polymerizable monomer.
The content of the monomer is not particularly limited, but preferably 1% or more in the electrolyte coating. When the content is low, the formation efficiency of the polymer is lowered, and it is difficult to make the electrolyte non-fluid.
[0040]
In a method for producing a non-fluidic electrolyte from the beginning using an electrolyte coating containing a polymer, it is preferable to use a polymer that dissolves in an electrolyte at a high temperature and forms a gel electrolyte at a normal temperature. Any polymer having such characteristics can be used as long as it is stable as a battery material. For example, a polymer having a ring such as polyvinylpyridine and poly-N-vinylpyrrolidone; polymethacrylic acid Acrylic derivative polymers such as methyl, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid polyacrylamide, etc .; fluorinated resins such as polyvinyl fluoride and polyvinylidene fluoride CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; Polyvinyl alcohol polymers such as polyvinyl acetate and polyvinyl alcohol; Halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride; Among these, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, or modified products thereof are preferable.
[0041]
Moreover, it can be used even if it is a mixture, such as said polymer, a modified body, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer. As will be described later, since the electrolyte and electrolyte used in the lithium battery have polarity, it is preferable that the polymer has a certain degree of polarity. The weight average molecular weight of these polymers is preferably in the range of 10,000 to 5,000,000. When the molecular weight is low, it is difficult to form a gel. If the molecular weight is high, the viscosity becomes too high and handling becomes difficult. The concentration of the polymer in the electrolyte solution is desirably changed according to the molecular weight, and is preferably 0.1% to 30%. When the concentration is 0.1% or less, it is difficult to form a gel, and the retention of the electrolytic solution is lowered, causing problems of flow and liquid leakage. When the concentration is 30% or more, the viscosity becomes too high, resulting in difficulty in the process, and the ratio of the electrolytic solution is lowered, the ionic conductivity is lowered, and the battery characteristics such as the rate characteristics are lowered.
[0042]
The electrolyte layer is preferably used in combination with a support such as a porous film. As the porous film, a film made of a polymer or a thin film made of a powder and a binder can be preferably used, and more preferably a porous film made of polyethylene, polypropylene or the like. On the electrode, the above-mentioned electrolyte coating that is made non-fluidized by a predetermined treatment is applied on the porous film in which the active material is bound by the binder on the current collector, and the voids in the porous film are impregnated. Thereafter, by performing a non-fluidization treatment, the electrolyte can be non-fluidized and an electrolyte layer can be formed.
[0043]
In the method of non-fluidization of the electrolyte, in the method of preparing a non-fluidized electrolyte by preparing a monomer-containing electrolyte coating and then making a non-fluidized electrolyte, a polymer is formed by thermosetting polymerization treatment and the electrolyte is de-fluidized. Is preferred. The temperature at which thermosetting is performed can be changed depending on the polymerization initiator used, but is not particularly limited as long as the non-fluidization treatment can be completed quickly at a rate that does not cause a problem in the process. Preferably, it can be stably stored at room temperature, and it is preferable that the polymerization proceeds by heating to 50 to 150 ° C. On the other hand, as a method for forming a non-fluidized electrolyte using a polymer that dissolves in an electrolytic solution at a high temperature and forms a gel electrolyte at a normal temperature, the polymer is heated and dissolved in the electrolyte. As heating temperature, it is 50-200 degreeC, Preferably, it is 100-160 degreeC. If it seems to dissolve at too low a temperature, the stability of the non-fluidized electrolyte is reduced. If the melting temperature is too high, the electrolyte and polymer may be decomposed. As a non-fluidization condition, it is preferable to cool at room temperature. Further, forced cooling may be performed.
[0044]
As a positive electrode, the positive electrode which uses a lithium compound as an active material is mentioned, for example. Examples of lithium compounds include composite oxides of lithium and transition metals. Specifically, LiNiO₂LiNiCoO₂Lithium nickel composite oxide such as LiCoO₂And lithium cobalt composite oxide. More preferred is a lithium cobalt composite oxide, and particularly preferred is LiCoO.₂It is. When the active material is granular, the particle size is usually about 1 to 30 μm, preferably about 1 to 10 μm, from the viewpoint of excellent battery characteristics such as rate characteristics and cycle characteristics. The positive electrode can be manufactured using these positive electrode active materials in the same manner as the above-described negative electrode manufacturing method.
[0045]
These positive electrode, negative electrode, and electrolyte layer are formed in a flat plate shape. Cutting to a required size, formation into a flat plate shape, and lamination of a positive electrode, a negative electrode, and an electrolyte layer can be performed at any place in the process.
A thin battery can be realized by stacking a plurality of unit battery elements including a positive electrode, an electrolyte layer, and a negative electrode formed in a flat shape, if necessary, and closely adhering them to a case made of a film having shape changeability. Examples of the case made of a film having shape variability include a lightweight and thin laminate film made of a polymer film. As the laminate film, a film made of a laminate material of a metal foil and a polymer film can be suitably used. When stored, it is preferable to vacuum seal. Of course, for the convenience of mounting the battery on the device, etc., it is possible to enclose the battery in a case and then store a plurality of cases in a rigid outer case if necessary.
[0046]
【Example】
  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not restrict | limited at all by these Examples, unless the summary is exceeded.
  In the following examples, TGThe measurement conditions are as follows.
  [TG measurement conditions]
    Measurement environment: In an air stream of 200 ml / min
    Temperature increase rate: 20 ° C / min
    Sample container: quartz sample container with a diameter of 4 mm and a height of 5 mm
[0047]
Example 1
Graphite powder (average particle size 15 μm, specific surface area 5 m²/ G) 50 parts by weight of powdered polyvinyl chloride per 100 parts by weight of Al₂O_Three30 minutes at room temperature using a manufactured ball mill, transferred to an electric furnace, heated to 200 ° C. over 1 hour in a nitrogen atmosphere, then heated to 900 ° C. at 300 ° C./h, 900 The amorphous carbon-coated graphite was obtained by holding at 1 ° C. for 1 hour.
When 2.5 mg of the obtained amorphous carbon-coated graphite was measured under the above TG measurement conditions, when the temperature was raised at a heating rate of 20 ° C./min in an air stream of 200 ml / min, the first stage The starting temperature of the weight reduction of the eyes was 520 ° C., and the weight reduction amount of the first stage was 9%. The measurement result of TG is shown in FIG.
[0048]
100 parts by weight of the obtained amorphous carbon-coated graphite (the amorphous carbon-coated graphite was used without being pulverized after firing), 10 parts by weight of polyvinylidene fluoride (binder), N-methyl- 100 parts by weight of 2-pyrrolidone (solvent) was prepared and kneaded with a kneader for 2 hours to obtain a dispersion paint for negative electrode.
The negative electrode dispersion paint was applied on a 20 μm thick copper current collector substrate by extrusion-type die coating, and dried at 120 ° C. for 10 minutes to produce a negative electrode.
[0049]
Example 2
Amorphous carbon-coated graphite was prepared in the same manner as in Example 1 except that the amount of polyvinyl chloride was 100 parts by weight with respect to 100 parts by weight of graphite powder.
When 5.1 mg of the obtained amorphous carbon-coated graphite was measured under the above TG measurement conditions, when the temperature was raised at a temperature rise rate of 20 ° C./min in an air stream of 200 ml / min, the first stage The starting temperature of the eye weight reduction was 505 ° C., and the weight reduction amount in the first stage was 16%.
A negative electrode was produced in the same manner as in Example 1 using the obtained amorphous carbon-coated graphite.
[0050]
Example 3
Amorphous carbon-coated graphite was produced in the same manner as in Example 1 except that polyvinyl alcohol was used instead of polyvinyl chloride.
When 4.0 mg of the obtained amorphous carbon-coated graphite was measured under the above TG measurement conditions, when the temperature was raised at a rate of temperature rise of 20 ° C./min in an air stream of 200 ml / min, the first stage The starting temperature of the weight reduction of the eyes was 420 ° C., and the weight reduction amount of the first stage was 6%.
A negative electrode was produced in the same manner as in Example 1 using the obtained amorphous carbon-coated graphite.
[0051]
Example 4
Amorphous carbon-coated graphite was produced in the same manner as in Example 1 except that polyvinyl alcohol was used instead of polyvinyl chloride, and the blending amount of polyvinyl alcohol was 100 parts by weight with respect to 100 parts by weight of graphite powder.
When 3.6 mg of the obtained amorphous carbon-coated graphite was measured under the above TG measurement conditions, when the temperature was raised at a temperature elevation rate of 20 ° C./min in an air stream of 200 ml / min, the first stage The starting temperature of the eye weight reduction was 410 ° C., and the weight reduction amount of the first stage was 13%.
A negative electrode was produced in the same manner as in Example 1 using the obtained amorphous carbon-coated graphite.
[0052]
Example 5
Amorphous carbon-coated graphite was prepared in the same manner as in Example 1 except that polyvinylpyrrolidone was used instead of polyvinyl chloride.
When 2.6 mg of the obtained amorphous carbon-coated graphite was measured under the above TG measurement conditions, when the temperature was raised at a temperature elevation rate of 20 ° C./min in an air stream of 200 ml / min, the first stage The starting temperature of the eye weight reduction was 540 ° C., and the weight reduction amount in the first stage was 7%.
A negative electrode was produced in the same manner as in Example 1 using the obtained amorphous carbon-coated graphite.
[0053]
Comparative Example 1
A graphite was prepared in the same manner as in Example 1 except that polyvinyl chloride was not blended (no amorphous carbon coating film). When 2.9 mg of the obtained graphite was measured under the above TG measurement conditions, when the temperature was raised at a temperature elevation rate of 20 ° C./min in an air stream of 200 ml / min, the first stage was at 350 to 600 ° C. No eye weight loss appeared. The measurement result of TG is shown in FIG.
A negative electrode was produced in the same manner as in Example 1 using the obtained graphite.
[0054]
Comparative Example 2
Amorphous carbon-coated graphite was prepared in the same manner as in Example 1 except that the amount of polyvinyl chloride was 5 parts by weight with respect to 100 parts by weight of graphite powder. When 2.5 mg of the obtained amorphous carbon-coated graphite was measured under the above TG measurement conditions, when the temperature was raised at a heating rate of 20 ° C./min in an air stream of 200 ml / min, the first stage The starting temperature of the eye weight reduction was 520 ° C., and the amount of weight reduction in the first stage was 1%.
A negative electrode was produced in the same manner as in Example 1 using the obtained amorphous carbon-coated graphite.
[0055]
Comparative Example 3
Amorphous carbon-coated graphite was produced in the same manner as in Example 1 except that the amount of polyvinyl chloride was 160 parts by weight with respect to 100 parts by weight of graphite powder. When 3.2 mg of the obtained amorphous carbon-coated graphite was measured under the above TG measurement conditions, when the temperature was raised at a temperature elevation rate of 20 ° C./min in an air stream of 200 ml / min, the first stage The starting temperature of the eye weight reduction was 520 ° C., and the weight reduction amount in the first stage was 40%.
A negative electrode was produced in the same manner as in Example 1 using the obtained amorphous carbon-coated graphite.
[0056]
Example 6
First, the following paints were prepared.

All the above raw materials were kneaded for 2 hours with a kneader to obtain a positive electrode paste.
[0057]

All the above compositions were mixed, dissolved and stirred to obtain an electrolyte paint.
[0058]
[Creating a positive electrode]
The above positive electrode paint was applied to an aluminum current collector substrate having a thickness of 20 μm by an extrusion type die coating and dried to form a film in which the active material was bound on the current collector by a binder.
Next, a positive electrode was produced by consolidation using a roll press (calendar) under conditions of a linear pressure of 100 kgf / cm.
[0059]
[Create battery]
Applying an electrolyte paint to the positive electrode and each negative electrode produced in Examples 1 to 5 and Comparative Examples 1 to 3, and laminating a polymer porous film having a slightly larger area than the electrode immersed in the electrolyte paint. A flat unit battery element having a positive electrode, a negative electrode, and a non-fluidized electrolyte component, which is made non-fluidized by heating at 90 ° C. for 10 minutes with an electrolyte coating added and sandwiched Formed. Thereafter, a tab for taking out current was connected to the unit battery element, and a flat battery was obtained by vacuum-sealing and storing the laminated film made of an aluminum film and a polymer film in a facing bag-shaped case.
[0060]
The obtained flat battery was 0.5 mA / cm.²Then, the battery was charged to 4.2 V and visually checked for gas generation. When gas is generated, the case bulges.
[0061]
[Table 1]

[0062]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the carbonaceous negative electrode for secondary batteries with which high capacity | capacitance and the gas generation at the time of charge were suppressed, especially a lithium secondary battery, and a secondary battery using this negative electrode can be provided. .
[Brief description of the drawings]
FIG. 1 is a thermogram showing TG measurement results for amorphous carbon-coated graphite produced in Example 1. FIG.
FIG. 2 is a thermogram showing the TG measurement results for the graphite produced in Comparative Example 1. FIG.

Claims (4)

A negative electrode containing an amorphous carbon-coated graphite having an amorphous carbon-coated film as an active material, the amorphous carbon-coated graphite having an average particle size of 4 to 40 μm and a specific surface area (BET method) of 0. 1 to ²⁰ m ² / g of graphite and a coating film thermoplastic resin are amorphous carbon-coated graphite obtained through a coating film formed of the thermoplastic resin for a coating film formed after dry-mixing; In addition, in the thermogravimetric measurement (TG), when the amorphous carbon-coated graphite was heated at a rate of temperature increase of 20 ° C./min in an air stream of 200 ml / min, the first stage weight reduction starting temperature was 350 is to 600 ° C., the negative electrode weight loss of the first stage is characterized by a 3-20% der Turkey of weight before heating. The negative electrode according to claim 1 , wherein the thermoplastic resin for an amorphous carbon coating film is a thermoplastic resin that is in a molten state at 200 ° C. Amorphous carbon coating film for the thermoplastic resin, polyvinyl chloride, a negative electrode according to claim 1 or 2, wherein the polyvinyl alcohol or polyvinylpyrrolidone down.   A secondary battery comprising the negative electrode according to claim 1 and a non-fluidic electrolyte layer.

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