JP2005085716A - Manufacturing method of composite electrode of oxide and carbon material, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an electrode comprising an oxide and a carbon material without using a binder, in relation to a manufacturing method of an electrode; and to provide a lithium secondary battery equipped with a positive electrode without using a binder. <P>SOLUTION: The composite electrode of an oxide and a carbon material without containing a binder is manufactured by electrodepositing the oxide and the carbon material on a surface of a negative electrode (cathode) by controlling the moisture content of an electrodeposition bath by using an electrophoresis deposition method. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a composite electrode of an oxide and a carbon material and a lithium secondary battery. More specifically, the present invention relates to a method for producing a composite electrode of an oxide and a carbon material that does not contain a binder component (binder-free) by electrophoretic electrodeposition, and a high energy density lithium secondary battery using the composite electrode as a positive electrode. .

  In recent years, a secondary battery having a high capacity has been required along with miniaturization of electronic equipment. Among them, non-aqueous electrolyte secondary batteries, in particular lithium secondary batteries, are light and have high energy density, and thus research and development are actively promoted as power sources for driving portable devices. Usually, a particulate oxide and a carbon material are used for a positive electrode of a lithium secondary battery, and a binder (binder) is used to form them into an electrode. The binder has an effect of binding the particles to each other and the particles and the current collector.

  However, in recent years, in order to obtain a battery with high output and excellent large current characteristics, electrode thinning has progressed, and it has become difficult to produce a uniform and accurate active material layer by the conventional production method. In order to solve this problem, a method for producing a positive electrode by forming an active material layer having a thickness of 50 μm or less on a current collector using an electrophoretic electrodeposition method is disclosed in JP-A-2002-42790. ing. However, the cycle characteristics of this positive electrode are not as good as the discharge capacity at 20 cycles of about 84% of the initial discharge capacity (J. Power Sources, 97-98, 294-297 (2001)). .).

  In addition, since the binder does not directly participate in the electrode reaction, it is desirable not to use the binder or to reduce the amount of use in order to realize further higher energy density of the battery. Therefore, a method for producing a carbon material film not containing a binder (binder-free) and a lithium secondary battery using the carbon material film as a negative electrode have been proposed. For example, JP-A-2002-63894 discloses an electrophoretic electrodeposition method for producing a binder-free carbon material film. In this method, a conductive substrate as a positive electrode (anode) and a counter electrode as a negative electrode (cathode) are immersed in a solution in which carbon particles are dispersed in acetonitrile, which is an aprotic solvent, and a potential gradient is generated between both electrodes. The carbon powder is electrodeposited on the surface of the anode. A non-aqueous electrolyte secondary battery (lithium secondary battery) using the binder-free carbon material film obtained above as a negative electrode has also been proposed. However, there have been no successful examples of a method for producing a binder-free composite electrode using an oxide and a carbon material and a lithium secondary battery using it as a positive electrode.

JP 2002-42790 A

JP 2002-63894 A K. Kanamura, et al. , J .; Power Sources, 97-98, 294-297 (2001). (FIG. 3)

  Conventionally, when an electrode is produced, a binder (binder) has been required to bind between particles of an oxide and a carbon material, and to bond them to a current collector. If the binder is not used, not only the electrode cannot be molded, but also the binding property between the particles and the binding property with the current collector are lowered, so that the electrode characteristics, particularly the cycle characteristics, are remarkably lowered. However, since the binder is irrelevant to the electrode reaction, the energy density is reduced by an amount corresponding to its weight. In increasing the capacity of lithium secondary batteries, it is an important point to increase the filling amount per unit volume of the active material used for the electrode. Further, as the electrode thickness increases, the internal resistance increases. Therefore, considering the increase in energy density of the battery, it is preferable to reduce the binder having low electron conductivity.

  In Japanese Patent Application Laid-Open No. 2002-42790, only an active material, a conductive agent, and a binder are electrodeposited by an electrophoretic electrodeposition method, and no heat treatment is performed around the melting point of the binder. This creates a new problem of eliminating the step of reducing the contact resistance between the particles, that is, the step of reducing the internal resistance of the electrode. In addition, the electrode produced by the conventional coating method is subjected to a heat treatment before and after the melting point of the binder and then subjected to a press treatment in order to increase the binding strength. However, the porosity of the electrode produced by the electrophoretic electrodeposition method is approximately the same as the porosity of the electrode produced by the coating method and subjected to the press treatment. Therefore, considering the electrolyte solution capacity in the electrode and the expansion / contraction associated with charging / discharging of the electrode, compressing the electrode produced by the electrophoretic electrodeposition method by pressing is more void than the electrode produced by the conventional coating method. This is a problem to be solved in this respect as the rate decreases.

  In addition, when producing an electrode having a thickness of 50 μm or more, it is difficult to form a uniform film by generating bubbles in the vicinity of the cathode, and the cycle characteristic of the positive electrode is about 84% of the first time at the 20th cycle. The problem is that it is not good.

  This invention is made | formed in view of the said subject, and it aims at providing the manufacturing method of the electrode which does not use a binder in the manufacturing method of the electrode which consists of an oxide and a carbon material. Another object of the present invention is to provide a lithium secondary battery having a positive electrode that does not use a binder.

In view of the above problems, in order to improve the characteristics of the composite electrode manufacturing method of the oxide and carbon material and the characteristics of the lithium secondary battery, as a result of intensive studies, the electrophoretic electrodeposition method was used to include the aprotic solvent. Controlling the amount of water, electrodepositing an oxide and carbon material on the negative electrode (cathode) surface, and heat treatment to increase the binding strength produces a composite electrode of oxide and carbon material that does not require a binder As a result, the inventors have found out that the present invention can be achieved.

  That is, according to the present invention, 1 mg to 5 g of iodine is dissolved in 1 L of an aprotic solvent having a water content of 20 to 5,000 ppm, and a positive electrode (anode) is added to a solution in which an oxide and a carbon material are dispersed. A composite of oxide and carbon material in which the cathode and electrode are electrodeposited to generate an electric potential gradient between the electrodes, thereby depositing oxide and carbon material on the surface of the cathode, and subjecting the resulting electrodeposition film to heat treatment An electrode manufacturing method is provided.

  Further, according to the present invention, there is provided a non-aqueous electrolyte secondary battery including at least a positive electrode, a non-aqueous electrolyte, and a negative electrode, wherein the positive electrode does not include a binder, and the lithium secondary battery includes an oxide and a carbon material. Provided.

  Using electrophoretic electrodeposition, it has become clear that oxide and carbon materials can be deposited directly on the surface of a conductive substrate with a simple manufacturing process and control. Furthermore, the method for producing a composite electrode of an oxide and a carbon material according to the present invention can reduce the weight corresponding to the binder not involved in the electrode reaction, and increase the active material density of the electrode, that is, the active material. Since the filling amount per unit volume of oxide can be increased, it is effective in increasing the energy density of a non-aqueous electrolyte secondary battery, particularly a lithium ion battery. Therefore, the industrial significance of the present invention is very great.

  In the present invention, the positive electrode (anode) and the negative electrode (cathode) are immersed in a liquid (electrodeposition bath) in which an oxide and a carbon material are dispersed in an aprotic solvent in which iodine is dissolved. For example, it is effective to use an electrophoretic electrodeposition apparatus as shown in FIG. In this apparatus, an oxide 2 and a carbon material 3 are dispersed in a solution (aprotic solvent + iodine bath) in which 1 mg / L to 5 g / L of iodine is dissolved in an aprotic solvent 1 to form a conductive substrate as a cathode 4. The counter electrode is arranged as the anode 5 opposite to this. Both electrodes 4 and 5 are connected to a DC power source 6, whereby a potential gradient can be generated between both electrodes 4 and 5.

  As the aprotic solvent of the present invention, ketones such as acetone and acetylacetone, ethers such as diethyl ether, hydrocarbons such as toluene and n-hexane, nitrogen compounds such as acetonitrile, and the like are preferable. You may mix and use a seed | species or more. In particular, acetone and acetylacetone are preferably used.

  Further, for carrying out the present invention, a small amount of a proton source may be added to the aprotic solvent. Examples of the proton source include water or lower alcohols having 4 or less carbon atoms such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol and the like. Of these, water is particularly preferably used. In continuous production, it is desirable to supplement water or lower alcohol to compensate for the decrease in proton concentration.

  Although the water content of the aprotic solvent depends on the dispersion amount of the oxide and the carbon material, the present invention can be carried out when it is 20 to 5,000 ppm. By adsorbing on the surfaces of oxide particles and carbon material particles in which protons are dispersed, the particle surface can be positively charged. When direct current is applied in this state, it is considered that positively charged particles move toward the discharging electrode, that is, the cathode, and are deposited on the cathode surface. When the water content is less than 20 ppm, the charged amount of the particles becomes insufficient, and the particles are aggregated and settled without being dispersed. If the water content exceeds 5,000 ppm, depending on various conditions such as electrolysis voltage, gas generation due to proton reduction reaction is likely to occur near the cathode during electrodeposition, resulting in a non-uniform film. Furthermore, lithium and proton of the lithium-containing oxide cause an exchange reaction, and the lithium content is lowered. This leads to a decrease in electrode characteristics.

  As addition amount of the iodine of this invention, it is preferable to melt | dissolve 1 mg-5g with respect to 1L of aprotic solvents. If the amount of iodine added is less than 1 mg, it is considered that the generation of protons adsorbed on the oxide or the carbon material is reduced, the dispersibility is lowered, and further the electrodeposition amount is affected. Further, when the amount of iodine added is more than 5 g, the conductivity of the aprotic solvent increases. This leads to an increase in electrolysis current during electrophoretic deposition, and bubbles are generated by the proton reduction reaction, which not only facilitates formation of a non-uniform film, but also causes inhibition of electrodeposition. Decrease. Furthermore, the risk of ignition of electrodeposition baths increases.

No particular limitation is imposed on the oxide of the present invention, for example, considering the use as a positive electrode of a lithium secondary _{battery, LiCoO 2, LiNiO 2, LiMnO} 2, LiFeO 2 and, LiMe _1-X T X of this series O ₂ (where Me is any of Fe, Co, Ni, Mn, T represents a transition metal, a group 4B or 5B metal, and 0 ≦ X ≦ 1), LiMn ₂ O ₄ , Known positive electrode active materials for lithium secondary batteries such as V ₂ O ₅ can be used.

  The particle size distribution of the oxide of the present invention is preferably about 0.2 to 40 μm. When the particle diameter is smaller than 0.2 μm, it becomes difficult to disperse and aggregate and settle. There is a high risk of causing an internal short circuit through the pores of the separator even when the battery is configured. Even when the particle diameter is larger than 40 μm, the particles are settled without being dispersed.

  The addition amount of the oxide of the present invention is preferably about 10 to 5,000 mg / L. When the addition amount is less than 10 mg / L, the time spent for electrodeposition becomes long, and the particles also settle. Further, when the addition amount is more than 5,000 mg / L, the concentration of the electrodeposition bath is increased, and not only the migration speed of the particles is decreased, but also when the electrodeposit is lifted from the electrodeposition bath at the end of the electrodeposition, The attached particles are adhered.

  Although it does not specifically limit as a carbon material of this invention, For example, when considering functioning as a electrically conductive agent for positive electrodes of a lithium secondary battery, acetylene black (AB), carbon black, a carbon nanotube, carbon nanohorn, Ketchen black, Fullerene, artificial graphite, natural graphite and the like can be used. These carbon materials may be used alone or in combination of two or more.

  The particle size distribution of the carbon material of the present invention is preferably about 0.2 to 40 μm. When the particle diameter is smaller than 0.2 μm, it becomes difficult to disperse and aggregate and settle. There is a high risk of causing an internal short circuit through the pores of the separator even when the battery is configured. When dispersing acetylene black or the like having a particle size of about 0.04 μm, it is better to perform ultrasonic irradiation. Even when the particle diameter is larger than 40 μm, the particles are settled without being dispersed. The addition amount of the carbon material of the present invention is preferably about 10 to 5,000 mg / L. When the addition amount is less than 10 mg / L, the time spent for electrodeposition becomes long, and the particles also settle. Further, when the addition amount is more than 5,000 mg / L, the concentration of the electrodeposition bath is increased, and not only the migration speed of the particles is decreased, but also when the electrodeposit is lifted from the electrodeposition bath at the end of the electrodeposition, The attached particles are adhered.

  The material and shape of the negative electrode (cathode) of the present invention are not particularly limited. For example, in consideration of using as a positive electrode current collector of a lithium secondary battery, Conductors that are chemically and electrochemically stable can be used. Examples of the material for the current collector include aluminum, stainless steel, copper, nickel, and the like. Aluminum is preferable in view of electrochemical stability, stretchability, and economy. Moreover, the form of a collector is not specifically limited, For example, metal foil, a mesh, an expanded metal etc. are mentioned. The surface state, thickness, size, shape, etc. of the cathode are not particularly limited. For example, foil shape, plate shape, spiral wire shape, foam shape, non-woven shape, mesh shape, felt shape, expanded A porous metal substrate such as a foil is preferable, and among these, a foil or plate is preferable.

  As the positive electrode (anode) of the present invention, any known conductive substrate can be used. For example, chemically and electrochemically safe platinum, graphite and the like are preferably used. The shape of the negative electrode may be a plate shape as shown in FIG. 2, but may be various shapes such as a spiral shape.

  The method for dispersing the oxide and the carbon material in the aprotic solvent + iodine bath is not particularly limited, but the aprotic solvent + iodine bath containing the oxide and the carbon material is subjected to ultrasonic irradiation or stirring. And so on.

  As a method of generating a potential gradient between both electrodes, a direct current power source connected to both electrodes in a state where the cathode and the anode are immersed in a solution in which an oxide and a carbon material are dispersed in an aprotic solvent + iodine bath. The method of applying a constant voltage, a constant current, a pulse, etc. to both electrodes is mentioned. You may change the magnitude | size for these application and predetermined intervals. For example, in the case of a constant voltage, the potential gradient generated between both electrodes can be about 0.1 to 10,000 V / cm, more preferably about 1 to 1,000 V / cm. Moreover, the electrodeposition time can be applied continuously for 0.1 to 600 seconds. If necessary, application and stop may be repeated periodically at intervals of 0.1 to 1 second.

  As described above, the oxide and the carbon material can be electrodeposited on the surface of the cathode. The electrodeposition amount of the oxide and the carbon material can be controlled by the dispersion amount of the oxide and the carbon material in the aprotic solvent + iodine bath, the electrodeposition voltage, the electrodeposition time, and the like. For example, in order to increase the electrodeposition amount of the electrodeposition film, the dispersion amount of the oxide and the carbon material in the aprotic solvent + iodine bath is increased, or the electrodeposition voltage is increased, or the electrodeposition time is increased. Control may be performed such as lengthening. In continuous production, it is desirable to replenish oxides and carbon particles sequentially to compensate for a decrease in the amount of oxide and carbon material dispersed in the aprotic solvent.

Moreover, you may heat-process the composite electrode of this invention as needed. The method is preferably performed at a temperature of 100 ° C. or higher and below the melting point of the oxide and the current collector. The atmosphere is preferably an inert gas such as nitrogen. This is because when the heat treatment is performed in air or in an oxygen atmosphere, the current collector is oxidized. Also, the heat treatment time is shorter under reduced pressure than under normal pressure.
The lithium secondary battery of the present invention includes at least a positive electrode, a nonaqueous electrolyte, and a negative electrode.

  The component of the positive electrode is composed of an oxide and a constituent element of a carbon material. That is, it means that it does not contain a constituent element of a binder component such as polyvinylidene fluoride (PVdF), particularly a fluorine atom. The constituent elements of the positive electrode can be analyzed by, for example, elemental analysis or energy dispersive X-ray analysis (EDX).

  When the composite electrode obtained by the above production method is used as a positive electrode of this battery, a conductive film is used as a current collector, and a composite film made of an oxide and a carbon material electrodeposited thereon is used. The positive electrode. Alternatively, a composite film electrodeposited on a conductive substrate may be peeled off and separately attached as a positive electrode on a battery current collector. First, it is desirable to produce a composite film on a conductive substrate, and then peel the composite film as it is or from the conductive substrate, wash it with a solvent or the like as necessary, and dry it before use. Although it does not specifically limit as a solvent for washing | cleaning, Acetone and acetonitrile are used suitably from the point of economical efficiency or handleability. In order to increase the packing density of the composite film, which is the positive electrode of the battery, or to improve the moldability, compression molding may be performed as necessary. A roller press is usually used for compression molding, and the material, rotation method, temperature, atmosphere, and the like of the press surface when these presses are applied are not particularly limited. Thereafter, the lead is welded onto the positive electrode, that is, the portion where the composite film of the conductive substrate is not electrodeposited, or the portion where the composite film is not adhered, and is dried. A general method can be used for drying, for example, hot air, vacuum, far-infrared rays, electron beam, and low-humidity air can be used alone or in combination. The temperature in this case is suitably about 150 ° C., and the pressure may be optionally reduced.

A known carbon material can be used for the negative electrode. As the particle diameter of the negative electrode, carbon particles having a center diameter d ₅₀ of 7.5 to 10.5 μm are preferable. That is, in the carbon particles constituting the negative electrode, when the contact area with the non-aqueous electrolyte increases, side reactions such as SEI (Solid Electrolyte Interface) formation and gas generation increase, and the charge / discharge efficiency decreases. . Further, when the contact area with the non-aqueous electrolyte is reduced, the electrode reaction rate is reduced, and the load characteristics of the battery are reduced. The center diameter d ₅₀ is expressed as a center diameter d ₅₀ from a particle size distribution measurement result. For the particle size distribution measurement, for example, laser diffraction particle size distribution measurement can be used.

As the negative electrode of the present invention, one formed by mixing an active material, a binder and the like can be used. Specifically, first, the binder is dissolved in a solvent in a mortar or the like to disperse the active material and the conductive agent. For the dispersion treatment, a kneader, a ball mill or the like is usually used, and the paste is prepared so that the active material, the conductive agent, and the binder are uniformly dispersed. This paste is applied to a metal foil of a current collector, and this is temporarily dried at 40 to 100 ° C. Then, in order to heat-process at about 150 degreeC and to make a predetermined | prescribed active material density, it compression-molds using a press. Compression molding can be performed in the same manner as described above. Thereafter, the lead is welded to the uncoated portion of the metal foil of the current collector and dried in the same manner as described above. The mixing ratio of the active material and the binder is preferably 1 to 30 parts by weight of the binder with respect to 100 parts by weight of the active material. In order to produce a battery having a high energy density, the active material density of the negative electrode is preferably 1.0 g / cm ³ or more, more preferably 1.5 g / cm ³ or more. In order to improve the binding property in the production of the positive electrode, it is preferable to perform heat treatment at a temperature around the melting point of the binder. Further, as another negative electrode of the present invention, a binder-free carbon material film disclosed in JP-A-2002-63894 may be used for the negative electrode.

  Examples of non-aqueous electrolytes (ionic conductors) include known organic solvent electrolytes, room-temperature molten salts (ionic liquids), polymer solid electrolytes or gel solid electrolytes, and inorganic solid electrolytes.

  The organic solvent-based electrolytic solution can be prepared by dissolving a nonaqueous solvent or a lithium salt. Although it does not specifically limit as a nonaqueous solvent, For example, cyclic carbonates, such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), dimethyl carbonate (DMC), dimethyl carbonate (DEC), carbonic acid A known nonaqueous solvent such as chain carbonates such as methyl ethyl (MEC) and cyclic carboxylic acid esters such as γ-butyrolactone (γ-BL) can be used alone or in combination of two or more. . In the present invention, since a carbon material is used for the negative electrode, it is preferable to include EC, and the EC content in the non-aqueous solvent is preferably 10 to 80% by volume. Moreover, in order to improve a low temperature characteristic, it is preferable to contain (gamma) -BL. Furthermore, it is preferable to add DMC, DEC, MEC, etc. in a volume ratio of 0 to 50% with respect to the entire non-aqueous solvent in order to improve the permeability into the electrode active material or the separator substrate. Moreover, you may add vinylene carbonate (VC), ethylene sulfite (ES), etc. by weight ratio about 1 to 10% with respect to the total weight of a non-aqueous solvent as needed.

The lithium salt is not particularly limited. For example, lithium perchlorate (LiClO ₄ ), lithium tetrafluoride (LiBF ₄ ), lithium hexafluoride (LiPF ₆ ), lithium hexafluoroarsenate (LiAsF ₆ ), 6 Lithium fluorinated antimonate (LiSbF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium trifluoroacetate (LiCF ₃ COO), lithium chloroaluminate (LiAlCl ₄ ), lithium imide trifluoromethanesulfonate (LiN ( Examples thereof include lithium salts such as CF ₃ SO ₂ ) ₂ ), and these can be used alone or in combination. Lithium salt concentration is to obtain ionic conductivity necessary to obtain discharge characteristics at high load, lithium salt cost, difficulty of soaking into electrode due to increase in viscosity, dissolution time of lithium salt, etc. In consideration of industrial production efficiency and the like due to a prolonged period, it is preferably 0.8 to 2.5 mol / L with respect to the entire non-aqueous solvent.

Room temperature molten salts (ionic liquids) are AlCl ₃ -EMIC (1-ethyl-3-methyl-imidazolium chloride) -LiCl, AlCl ₃ -EMIC-LiCl-SOCl ₂ , EMIBF ₄ (1-ethyl-3- Methyl-imidazolium tetrafluoroborate) -LiBF _{4 and the} like.

  Examples of the polymer solid electrolyte include a substance composed of a polymer that dissociates the electrolyte and the electrolyte, and a substance that has an ion dissociation group on the polymer. Examples of the polymer that dissociates the electrolyte include a polyethylene oxide derivative or a polymer containing the derivative, a polypropylene oxide derivative, a polymer containing the derivative, and a phosphate polymer.

  As the gel electrolyte, a polymer solid electrolyte as described above and an organic solvent are used. The gel electrolyte is extremely advantageous because it combines the characteristics of a solid electrolyte that does not cause liquid leakage and ionic conductivity close to that of a liquid. The organic compound serving as the skeleton of the gel-like solid electrolyte is not particularly limited as long as it is a compound having an affinity for the electrolyte solution and having a polymerizable functional group. Examples of such compounds include those having a polyether structure and an unsaturated double bond group, oligoester acrylates, polyesters, polyimines, polythioethers, polysulfanes and the like alone or in combination of two or more. In addition, those having a polyether structure and an unsaturated double bond group are preferred from the viewpoint of affinity with a solvent. Examples of the polyether structural unit include ethylene oxide, propylene oxide, butylene oxide, glycidyl ethers and the like, and these are used alone or in combination of two or more. Further, in the case of a combination of two or more kinds, the form can be appropriately selected regardless of block or random. Furthermore, examples of the unsaturated double bond group include allyl, methallyl, vinyl, acryloyl, methacryloyl and the like. A method for producing a gel electrolyte is obtained by preparing an electrolytic solution by dissolving an electrolyte salt in an organic solvent, mixing the polymer with an organic compound serving as a skeleton of the gel solid electrolyte, and polymerizing the solution. Examples of the organic solvent used in the gel electrolyte include cyclic carbonates such as EC, PC and BC, chain carbonates such as DMC, DEC, EMC and dipropyl carbonate, lactones such as γ-BL and γ-valerolactone, Furans such as tetrahydrofuran and 2-methyltetrahydrofuran, ethers such as diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, dioxane, dimethyl sulfoxide, sulfolane, methylsulfolane, acetonitrile, formic acid Examples include methyl and methyl acetate. Examples of the electrolyte salt include the lithium salts described above.

Examples of the inorganic solid electrolyte include Li nitride, halide, oxyacid salt, and the like. Specifically, Li ₃ N, LiI, Li ₃ N—LiI—LiOH, LiSiO ₄ , LiSiO ₄ —LiI—LiOH, Examples include Li ₃ PO ₄ —Li ₄ SiO ₄ . Moreover, you may use together said inorganic solid electrolyte and organic solid electrolyte.

In the nonaqueous electrolyte secondary battery of the present invention, a separator is usually used to hold the electrolyte. Examples of the separator include nonwoven fabrics or woven fabrics such as electrically insulating synthetic resin fibers, glass fibers, and natural fibers. Among these, non-woven fabrics such as polyvinylidene chloride, polyethylene, and polypropylene are preferable from the viewpoint of quality stability. Some of these synthetic resin non-woven fabrics have a function in which when the battery abnormally generates heat, the separator is melted by heat to block between the positive and negative electrodes, and these can be suitably used from the viewpoint of safety. The thickness of the separator is not particularly limited, but it is sufficient that the separator can hold a necessary amount of liquid and has a thickness that prevents a short circuit between the positive electrode and the negative electrode. Usually, a thickness of about 0.01 to 1 mm is used. Preferably, it is about 0.02-0.05 mm. Moreover, it is preferable that the material constituting the separator has an air permeability of 1 to 500 seconds / cm ³ because it has a strength sufficient to prevent a battery internal short circuit while maintaining a low battery internal resistance.

  The non-aqueous electrolyte secondary battery of the present invention can have a known shape such as a laminate shape, a cylindrical shape, a square shape, a coin shape, or a button shape. For example, in a cylindrical or square battery, a sheet-like electrode is mainly inserted into a can, and the can and the sheet electrode are electrically connected. An electrolyte is injected and the sealing plate is sealed through an insulating packing, or the sealing plate and the can are insulated and sealed with a hermetic seal to produce a battery. At this time, a safety valve equipped with a safety element can be used as a sealing plate. Examples of the safety element include a fuse, a bimetal, and a PTC element as an overcurrent prevention element. In addition to the safety valve, as a countermeasure against the increase in the internal pressure of the battery can, a method of making a crack in the gasket, a method of making a crack in the sealing plate, a method of making a cut in the battery can, and the like are used. Further, an external circuit incorporating an overcharge or overdischarge countermeasure may be used. In the case of a coin-type or button-type battery, the positive electrode and the negative electrode are formed into pellets, placed in a can, injected with an electrolyte, and a lid is crimped through an insulating packing to produce a battery.

  Hereinafter, the method for producing a composite electrode of an oxide and a carbon material and a lithium secondary battery according to the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples.

(Example 1)
10.0 mg of iodine (hereinafter referred to as 0.10 g / L) was dissolved in 100 mL of acetone having a water content of 100 ppm. To this, 3.0 g / L of LiCoO ₂ (average particle diameter 10 μm) and 50 mg / L of acetylene black were added, and suspended for 10 minutes using an ultrasonic irradiator. By this operation, LiCoO ₂ particles and AB particles were sufficiently dispersed in an acetone bath. An aluminum foil (thickness: 20 μm) used for the current collector of the lithium secondary battery was used as the cathode 4, a platinum plate was arranged as the anode 5 on the other side with a distance of 10 mm, and settings were made as shown in FIG. After stopping the ultrasonic wave of the electrodeposition bath, 300 V / cm was applied for 30 seconds using the DC power source 6 and the power source was turned off.

When the cathode 4 was pulled out from the electrodeposition bath, a uniform film was formed. When elemental analysis was performed by SEM (scanning electron microscope) / EDX, oxygen and cobalt as constituent elements of LiCoO ₂ , carbon as a constituent element of AB, and aluminum as a constituent element of a current collector were detected. In addition, the sample obtained from the results of X-ray diffraction measurement using CuKα rays of 2 kW output from the target Cu enclosure as the X-ray source, cobalt valence analysis by iodometry method, and elemental analysis by ICP is LiCoO _2. It was confirmed that.

Thereafter, the LiCoO ₂ and AB composite electrode was washed with acetone, and temporarily dried under reduced pressure at 50 to 70 ° C. for 3 hours. From the measurement result of the electrodeposition amount on the composite electrode and the weight measurement result of LiCoO ₂ obtained from the elemental analysis by ICP, it was found that the weight ratio of LiCoO ₂ and AB was 92: 8. This electrode had a thickness of 70 μm and a porosity of 31%. A nickel foil (50 μm) lead was welded to the electrodeposited portion of the aluminum foil, and then dried under reduced pressure at about 300 ° C. for 12 hours as a heat treatment.

(Comparative Example 1)
In 100 mL of acetone, LiCoO _{2 as a} positive electrode active material, carbon black (CB) as a conductive agent, and polytetrafluoroethylene (PTFE) as a binder are respectively 10, 0.2,. 5 parts by weight were mixed. Further, 5 parts by weight of 0.5 mol / L acetone + iodine bath as a charging agent was added to 1000 parts by weight of acetone. This electrodeposition bath was subjected to ultrasonic irradiation for 5 minutes and sufficiently dispersed, and then an aluminum foil (thickness 15 μm) used as a cathode 4 for a current collector of a lithium secondary battery was used as the cathode 4 at a distance of 10 mm. A platinum plate was disposed as the anode 5 and set as shown in FIG. After stopping the ultrasonic wave of the electrodeposition bath, 400 V / cm was applied for 60 seconds using the DC power source 6 to turn off the power source.

When the cathode 4 was pulled out from the electrodeposition bath, a uniform film was formed. When elemental analysis was performed by SEM / EDX, oxygen and cobalt as constituent elements of LiCoO ₂ , carbon as constituent elements of AB, carbon and fluorine as constituent elements of a binder, and constituent elements of a current collector Aluminum was detected. In addition, the sample obtained from the results of X-ray diffraction measurement using CuKα rays of 2 kW output from the target Cu enclosure as the X-ray source, cobalt valence analysis by iodometry method, and elemental analysis by ICP is LiCoO _2. It was confirmed that.
This electrode was washed and temporarily dried under reduced pressure at 50 to 70 ° C. for 3 hours. From the measurement result of the electrodeposition amount on the composite electrode and the weight measurement result of LiCoO ₂ obtained from the elemental analysis by ICP, it was found that the weight ratio of LiCoO ₂ and (CB + PTFE) was 80:20. This electrode had a thickness of 45 μm and a porosity of 47%. Thereafter, a lead of nickel foil (50 μm) was welded to the non-electrodeposition portion of the aluminum foil.

(Comparative Example 2)
This comparative example was manufactured by a coating method which is a conventional manufacturing method. LiCoO ₂ (average particle diameter 10 μm) was used as the positive electrode active material. The binder PVdF was dissolved in N-methyl-2pyrrolidone (NMP) in a mortar to disperse the positive electrode active material and the conductive agent AB. For the dispersion treatment, a biaxial planetary kneader was used to prepare a paste in a state where the positive electrode active material, the conductive agent, and the binder were uniformly dispersed. The composition of the positive electrode was 100 parts by weight of LiCoO ₂ , 8.7 parts by weight of AB, and 5 parts by weight of PVdF. This paste was applied onto an aluminum foil having a thickness of about 20 μm and temporarily dried at 50 to 70 ° C. This electrode had a thickness of 70 μm and a porosity of 29%. Thereafter, heat treatment is performed at about 150 ° C. for 12 hours, and compression molding is performed using a roller press in the air until the active material density reaches about 3.0 g / cm ^{3. A} nickel foil (50 μm) is applied to the uncoated part. The lead was welded. In order to remove moisture, it was dried under reduced pressure at about 150 ° C. for 12 hours.

(Evaluation)
In order to investigate the performance of the obtained composite electrode as a positive electrode for a lithium secondary battery, electrochemical characteristics were evaluated using a three-electrode cell. The composite electrode was used as a test electrode, and metallic lithium was used as a counter electrode and a reference electrode. The cell configuration was set so that the surface area of the counter electrode was sufficiently larger than that of the test electrode and was regulated by the potential of the test electrode. As the electrolytic solution, 1.0 M LiClO ₄ / EC + DEC (50:50 vol%) was used. The charge / discharge operation test was performed at a constant current charge / discharge of 0.1 C (27.4 mA / g), a charge end potential of 4.2 V vs. Li / Li ⁺ , discharge end potential 3.5 Vvs. It was performed at 25 ° C. in a glove box under an argon atmosphere under the control conditions of Li / Li ⁺ . The capacity is capacity (mAh / g) = {current value (mA) × time (h) / weight of carbon material (g)}
It was calculated by the following formula.

The cycle characteristics of the electrodes obtained in the examples and comparative examples are shown in FIG. The cycle characteristics of the composite electrode of Example 1 of the present invention were better than those of Comparative Examples 1 and 2. From this cycle characteristic result, it was revealed that the composite electrode of the present invention can be used as a positive electrode of a lithium secondary battery. The discharge capacity of the electrode of Comparative Example 1 decreased as the cycle was repeated. When the electrode was observed after the end of 20 cycles, the edge portion of the electrode was peeled off from the current collector. Without the heat treatment step, the binder is not fused, so it is considered that the LiCoO ₂ particles could not withstand the expansion / contraction due to charge / discharge. The discharge capacity of the electrode of Comparative Example 2 suddenly decreased around 15 cycles. When the electrodes were observed after the end of the cycle test, most of the electrodes were peeled off from the current collector and barely adhered.

From the above, there is a limit to reducing the weight corresponding to the binder in the conventional positive electrode. Moreover, it became clear that a favorable electrode can be produced without using a binder by adding a heat treatment step. In order to reduce the weight and size of the battery, it is effective to manufacture a composite electrode of a binder-free oxide and a carbon material by the electrophoretic electrodeposition method of the present invention and use it for the positive electrode.

It is a graph which shows the cycling characteristics of the electrode obtained by the Example and the comparative example. It is a schematic explanatory drawing of the manufacturing method of the composite electrode of the oxide and carbon material of this invention.

Explanation of symbols

1 Aprotic solvent 2 Oxide 3 Carbon material 4 Negative electrode (cathode)
5 Positive electrode (anode)
6 DC power supply

Claims (6)

The surface of the negative electrode is obtained by immersing 1 mg to 5 g of iodine in 1 L of an aprotic solvent and immersing the positive electrode and the negative electrode in a solution in which an oxide and a carbon material are dispersed to generate a potential gradient between the two electrodes. A method of manufacturing a composite electrode of an oxide and a carbon material, characterized by electrodepositing an oxide and a carbon material. The method for producing a composite electrode of an oxide and a carbon material according to claim 1, wherein the water content in the aprotic solvent is 20 to 5,000 ppm. 2. The oxide-carbon material composite electrode according to claim 1, wherein the oxide is one or more oxides selected from LiCoO ₂ , LiNiO ₂ , LiMnO ₄ , and V ₂ O ₅ . Production method. 2. The oxide and carbon according to claim 1, wherein the carbon material is one or more carbon materials selected from acetylene black, carbon black, carbon nanotube, ketchen black, artificial graphite, and natural graphite. A method for producing a composite electrode of a material. The method for producing an oxide-carbon material composite electrode according to claim 1, wherein the negative electrode is selected from aluminum, nickel, and stainless steel. A non-aqueous electrolyte secondary battery comprising at least a positive electrode, a non-aqueous electrolyte, and a negative electrode, wherein the positive electrode is composed of an oxide obtained by the method according to any one of claims 1 to 5 and a carbon material. A lithium secondary battery characterized by comprising:

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