CN1237651C - Lithium-ion secondary battery - Google Patents

Abstract

The present invention relates to a lithium ion secondary battery. The lithium ion secondary battery can sustain electric connection between active substance layers and a separator without using a firm shell body and realize any shape of high-energy density, thinness, etc., and the lithium ion secondary battery has the advantages of good characteristics of charge and discharge and large battery capacity. The particles of an anode active substance and the particles of a cathode active substance are respectively bounded with an anode electricity collecting body and a cathode electricity collecting body by adhesion resin to form an anode and a cathode; an anode active substance layer and a cathode active substance layer are bonded with the separator by the adhesion resin, and bond strength among the separator, the anode active substance layer and the cathode active substance layer is larger than that among the anode electricity collecting body, the anode active substance layer, the cathode electricity collecting body and the cathode active substance layer to manufacture a battery body with a flat plate-shaped lamination structure of the lamination body of a multilayer electrode. An electrolytic solution containing lithium ions is kept in a gap among the anode active substance layer, the cathode active substance layer and the separator to form the electric connection between the electrodes.

Description

Lithium-ion secondary battery

technical field

The present invention relates to a lithium-ion secondary battery in which a separator holding an electrolyte is sandwiched so that the positive electrode and the negative electrode face each other. Specifically, it relates to improving the electrical connection between the positive electrode, the negative electrode and the separator, and does not require a firm The metal case can be made into a battery structure of any shape such as a thin shape.

Background technique

There is a strong demand for miniaturization and weight reduction of portable electronic devices, and its realization largely depends on the improvement of battery performance. Development and improvement of various batteries to solve this problem are underway. Among the characteristics expected to be improved in batteries are higher voltage, higher energy density, higher load resistance, optional shape, and safety assurance. Among them, the lithium-ion battery is also the secondary battery that can achieve high voltage, high energy density, and high load resistance among existing batteries, and people are actively improving it now.

This lithium ion secondary battery has, as its main components, a positive electrode, a negative electrode, and an ion conductive layer sandwiched between the two electrodes. In the lithium-ion secondary battery that has been practically used now, the positive electrode is made by mixing active material powder such as lithium-cobalt composite oxide with electronic conductor powder and binder resin, and then coating it on the aluminum collector. For the plate-shaped positive electrode and negative electrode, a carbon-based active material powder is mixed with a binder resin and coated on a copper current collector to form a plate-shaped negative electrode. In addition, as the ion conductive layer, a porous film such as polyethylene or polypropylene is impregnated with a non-aqueous solvent containing lithium ions.

For example, FIG. 5 is a schematic cross-sectional view showing the structure of a conventional cylindrical lithium ion secondary battery disclosed in JP-A-8-83608. In FIG. 5 , 1 is a stainless steel outer can that doubles as a negative electrode terminal, and 2 is an electrode body accommodated in the outer can. The structure of the electrode body 2 is spirally wound and disposed between the positive electrode 3 and the negative electrode 5. The electrode laminate of the separator 4. In order to maintain the electrical connection between the faces of the positive electrode 3, the separator 4 and the negative electrode 5, pressure must be applied to the electrode body 2 from the outside. For this reason, the contact between the above-mentioned surfaces is maintained by placing the electrode body 2 in the firm outer can 1 and applying pressure. In addition, in the case of a prismatic battery, the rectangular electrode laminates are bundled and placed in a prismatic metal can, and pressed from the outside.

As described above, in lithium ion secondary batteries currently on the market, a method of using a strong case made of metal or the like is used as a method of bringing the positive electrode and the negative electrode into close contact. If there is no case, the surfaces of the electrodes will be peeled off, making it difficult to maintain electrical connection, deteriorating battery characteristics. On the other hand, due to the large weight and volume of the case in the battery as a whole, this not only reduces the energy density of the battery itself, but also because the case itself is rigid, the shape of the battery is limited, and it is difficult to make any shape.

Against such a background, weight reduction and thinning are aimed at, and lithium-ion secondary batteries that do not require a strong case are being developed. The difficulty in developing the above-mentioned battery without a case is how to maintain the electrical connection between the positive electrode and the negative electrode and the ion-conducting layer (separator) sandwiched between them without applying force from the outside.

As such a bonding means that does not require external force, a structure in which a positive electrode and a negative electrode (electrode) are bonded with a liquid bonding mixture (gel electrolyte) is disclosed in U.S. Patent No. Electron-conductive polymers bond active materials to form positive and negative electrodes, and then use polymer electrolytes to connect the positive and negative electrodes.

Existing lithium ion secondary batteries are structured as described above. In order to ensure the adhesion and electrical connection between the positive electrode and the negative electrode and the separator, there is a case other than the power generation part in the battery using a strong case. The ratio of occupied volume and weight is large, which is unfavorable for making batteries with high energy density.

On the other hand, in a structure in which electrodes are joined using a liquid mixture, there are problems in that the production process is complicated, and it is difficult to obtain sufficient adhesive force and improve the strength as a battery. In addition, in the structure of connecting electrodes with a polymer electrolyte, safety must be ensured, that is, short circuits between electrodes must be prevented, and the polymer electrolyte layer must be thickened, so there is a problem that it cannot be made sufficiently thin as a battery. When using a solid electrolyte, the bonding between the electrolyte layer and the electrode active material is difficult, and improvement of battery characteristics such as charge and discharge efficiency is difficult, and the process is complicated and expensive.

In addition, an important factor that determines the charge and discharge efficiency of a battery is the efficiency of doping and dedoping of lithium ions associated with the charge and discharge of the active material. The properties are equal in the electrolyte, so the doping and dedoping of lithium ions are concentrated near the surface of the electrode close to the separator, and there is a problem that the active material inside the electrode cannot be effectively used, and ideal charge and discharge characteristics cannot be obtained. question.

Therefore, in order to realize a thin lithium ion battery that can be used practically, it is necessary to develop a battery structure that can easily ensure safety and strength as a battery, and can obtain good battery characteristics such as charge and discharge characteristics. That is, in order to ensure safety, it is necessary to have a separator between the electrodes, and a structure in which the separator and the electrodes have sufficient strength and can be bonded so that good battery characteristics can be obtained.

Contents of the invention

The present invention is the result of earnest research by the present inventors on an ideal joining method between a separator, a positive electrode, and a negative electrode in order to solve such a problem, and its purpose is to provide a It is also possible to provide a lithium ion secondary battery in which the positive electrode, the negative electrode, and the separator are tightly adhered to each other. The lithium ion secondary battery of the present invention can achieve high energy density, thinning, and multi-layering in any form, has excellent charge and discharge characteristics, and has a large battery capacity, which is compact and stable.

The lithium ion secondary battery of the present invention includes a plurality of electrode stacks, wherein each electrode stack has: a positive electrode containing a particulate positive active material material bonded to a positive current collector with an adhesive resin; The negative electrode of the particulate negative active material material bonded to the negative electrode current collector with a binding resin; and the separator inserted between the positive active material layer and the negative active material layer with the binding resin, in which The electrolyte solution containing lithium ions is kept in the gap between the layer, the negative electrode active material layer and the separation layer, and the positive electrode active material and the negative electrode active material near the separation layer are composed of the positive electrode active material and the negative electrode active material near the positive electrode collector and the negative electrode collector. The bonding resin with a large amount of negative active material is covered, thereby making the bonding strength between the separator and the positive active material layer and the negative active material layer greater than or equal to that of the positive active material layer, the negative active material layer and each current collector The bonding strength between the positive electrode active material layer and the negative electrode active material layer is bonded to the separator layer with a bonding resin, and the bonding resin and the particle-shaped positive electrode active material and the granular negative electrode active material are respectively connected to the positive electrode. The adhesive resin used to bond the current collector and the negative electrode current collector is the same.

If such a structure is adopted, a strong case is no longer required, and it is possible to reduce the weight and thickness of the battery, and it is possible to obtain an arbitrary shape, and at the same time, the charge and discharge efficiency is improved, and excellent charge and discharge characteristics can be obtained. High safety lithium-ion secondary battery.

And it is possible to obtain a lithium-ion secondary battery having excellent charge-discharge characteristics that can realize high energy density and thinning, and can be formed in any form. In addition, a stable battery with light weight, small size and high battery capacity can be obtained by multilayering the electrode laminate.

Since the difference in the speed of doping and dedoping of lithium ions on the side of the separator of the positive and negative active material layers and the internal active material can be eased, the active material inside the electrode can be effectively used to improve the performance of charge and discharge. efficiency.

In the lithium ion secondary battery of the present invention, the positive electrodes and negative electrodes of the multiple layers of the electrode stack can be alternately arranged between the cut separators, and can also be alternately arranged on the wound separators. It can also be arranged alternately between the folded spacers.

In this way, a battery with a stable multilayer structure having excellent charge-discharge performance, light weight, small size, and large battery capacity can be easily obtained.

In the lithium ion secondary battery of the present invention, the density ratio of the active material particles of each positive electrode material layer and the negative electrode material layer on one side of the separator is located at one side of each positive electrode current collector and negative electrode current collector. side low.

In the lithium ion secondary battery of the present invention, the density ratio of the binder resin of each positive electrode material layer and the negative electrode material layer on the side of the separator is located at one of the positive electrode current collectors and the negative electrode current collectors. side high.

In the lithium ion secondary battery of the present invention, the active material particles have a particle size in the range of 0.3-20 μm, or the active material particles have a particle size in the range of 1-5 μm.

Description of drawings

1, 2 and 3 are cross-sectional views each showing a battery structure of an embodiment of the lithium ion secondary battery of the present invention. Fig. 4 is a schematic cross-sectional view showing a battery laminate constituting an embodiment of the present invention. Fig. 5 is a cross-sectional view showing an example of a conventional lithium ion secondary battery.

Best form for carrying out the invention

Embodiments of the present invention are described with reference to the drawings.

Fig. 1, Fig. 2 and Fig. 3 are cross-sectional schematic diagrams each showing the battery structure of an embodiment of the lithium ion secondary battery of the present invention. FIG. 1 shows a battery body with a flat laminated structure having a multilayered electrode laminate formed by repeatedly laminating a positive electrode 3 , a separator 4 , and a negative electrode 5 in this order. What Fig. 2 shows is to roll up the object that has joined the strip-shaped positive electrode 3 between the strip-shaped separators 4, and sandwich a plurality of negative electrodes in the middle and stick them together to form a flat plate-shaped multilayer electrode body. Roll-type laminated battery body. Figure 3 shows that a strip-shaped positive electrode 3 is arranged between strip-shaped separators 4, and a strip-shaped negative electrode 5 is arranged on one side, and then wound into a long circle to form a multilayer electrode laminate. The flat-shaped roll-type laminated structure of the battery body. FIG. 4 is a schematic cross-sectional view showing an example of an electrode laminate 2 constituting the above battery of the present invention. In the figure, 3 is a positive electrode formed by bonding positive electrode active material particles 7a to the positive electrode body 6 with adhesive resin 11, and 7 is a positive electrode active material formed by bonding positive electrode active material particles 7a to each other with adhesive resin 11. Material layer, 5 is the negative electrode that uses adhesive resin 11 to join the negative electrode active material particle 9a on the negative electrode body 10 constituted, and 9 is the negative electrode active material that the negative electrode active material particle 9a is bonded to each other with adhesive resin 11 Layer 4 is configured between the positive electrode 3 and the negative electrode 5, and the positive electrode and the negative electrode active material layers 7 and 9 are bonded with the separator with the adhesive resin 11, and 12 is the spacer between the positive electrode and the negative electrode active material layers 7 and 9 and the separator. The gap formed in 4 can hold the electrolyte solution containing lithium ions.

A lithium ion secondary battery configured as described above can be produced, for example, as follows.

First, an active material paste prepared by dispersing the positive electrode active material particles 7a and the binder resin 11 in a solvent is applied to the positive electrode body 6 by a roller coating method and dried to prepare the positive electrode 3 . Negative electrode 5 is produced in the same way. Next, the adhesive resin 11 is applied to the separator 4 as an adhesive, and the positive electrode 3 or the negative electrode 5 is respectively pasted on the separator 4 as described above, and laminated or wound, etc. A battery body having a multilayer structure of a plurality of electrode laminates shown in FIG. 3 . After immersing the entire battery body of the multilayer structure in the electrolyte solution by immersion method, it is packaged with an aluminum laminated film, and after heat-melt bonding and sealing treatment, a lithium ion secondary battery with a multilayer structure is obtained.

In addition, the bonding strength between the separator 4 and the positive electrode and negative electrode active material layers 7 and 9 is equal to or greater than the bonding strength between the positive electrode current collector 6 and the positive electrode active material layer 7, and the negative electrode current collector 10 and the negative electrode active material layer 9. The active material particles 7 a and 9 a on the side of the separator 4 are covered by the binder resin 11 more than the active material particles on the side of the positive and negative electrode current collectors 6 and 10 .

In this example, the electrodes (positive electrode 3 and negative electrode 5 ) were bonded with the active material and the current collector with the adhesive resin 11 as in the conventional case, and the structure was maintained. In addition, since the positive electrode 3 and the negative electrode 5 (that is, the positive and negative electrode active material layers 7, 9) and the separator 4 are also bonded with the same adhesive resin, the active material layer 7 can be maintained even without external force. , 9 and the electrical connection between the spacer 4. Therefore, a strong case for maintaining the structure of the battery is no longer necessary, and the battery can be reduced in weight and thinned, and an arbitrary form can be obtained. Moreover, the bonding strength between the positive electrode and negative electrode active material layers 7, 9 and the separator 4 is bonded to the strength of bonding the active material and the current collector inside the electrode and integrating them, that is, the positive electrode collector The bonding strength between the electrode 6 and the positive electrode active material layer 7, the negative electrode current collector 10 and the negative electrode active material layer 9 is equal to or higher than that between the positive electrode and the negative electrode active material layer 7,9 and the separator 4. Delamination of the electrode structure will preferentially occur. For example, when an external force or internal thermal stress acts to deform the formed battery, it is the electrode structure, not the separator, that is damaged, so that safety can be maintained.

In addition, in order to make the adhesion between the electrodes and the separator more reliable and to make the above-mentioned effect more remarkable, it is desirable to form a thin adhesive resin layer especially between the electrodes and the separator.

Furthermore, in the present embodiment, since most of the adhesive resin of the adhesive exists on the separator 4 side (surface portion) of the positive electrode and negative electrode active material layers 7, 9, that is, because the positive electrode on the separator 4 side The number of positive and negative active material particles 7a, 9a on the side of the positive and negative current collectors 6 and 10 is covered by the binder resin 11, so although the doping of lithium ions is usually Impurity and de-impurity concentrate on the separator 4 side of the positive and negative active material layers 7,9, but this example can ease the tension on the separator 4 side of the positive and negative active material layers 7,9 and in the internal active material. The difference in the doping and dedoping speed of lithium ions can effectively use the active material inside the electrode and improve the charge and discharge efficiency. Such an excellent effect of improving the charge and discharge characteristics of the battery is exhibited.

In addition, in this embodiment, the method of soaking the battery body with a flat laminated structure in the electrolyte, and then reducing the pressure of the electrolyte can replace the positive and negative active material layers 7, 9 and the separator. The gas in the void 12 formed in the object 4 and the above-mentioned electrolytic solution can be easily injected into the electrolytic solution. Also after injection. It is desirable to heat and dry the above-mentioned flat-plate laminated battery body.

In addition, after covering with a flexible outer body such as an aluminum laminated film, decompressing the inside of the outer body, and adhering the outer surface of the battery with a flat laminated structure to the above-mentioned outer body, the outer surface can be removed from the outer body Electrolyte is injected into the opening of the outer body, at least the electrolyte is injected into the gap, and finally the opening of the outer body is sealed. If such a method is adopted, since the back of the battery body and the exterior body are already in close contact when the electrolyte is supplied, the infiltration of the electrolyte into the back of the battery body can be eliminated, and unnecessary electrolyte that does not contribute to the electrolysis can be eliminated. Reduce the weight of the battery as a whole.

As the active material provided in the present invention, in the positive electrode, for example, composite oxides between lithium and transition metals such as cobalt, nickel, and manganese, lithium-containing chalcogenides, or composite compounds thereof, and Composite compounds having various additive elements in the above-mentioned composite oxides, lithium-containing chalcogen compounds, or composite compounds thereof can be used. In the negative electrode, it is desirable to use easily graphitizable carbon, difficult graphitizable carbon, carbon-based compounds such as polyacene and polyacetylene, and acene-containing (-acene) structures such as pyrene and perylene. Aromatic hydrocarbons can be used as long as they can store and release lithium ions which are the main components of battery operation. In addition, these active materials are used in the form of particles, and as the particle size, particles of 0.3 to 20 micrometers can be used, and particles of 1 to 5 micrometers are particularly preferable. When the particle size is too small, the coverage area of the surface of the active material produced by the adhesive during bonding will become too large, so that the doping and dedoping of lithium ions cannot be performed with good efficiency, which will reduce the battery characteristics. If the particle size is too large, it will not be easy to reduce the thickness, and not only will the packing density be reduced, but also the unevenness of the surface of the formed electrode plate will become larger, so that the adhesion with the separator cannot be performed well. . So it is unsatisfactory.

In addition, as the binder resin for forming the active material into an electrode plate, any resin can be used as long as it does not dissolve in the electrolytic solution and does not undergo electrochemical reaction inside the electrode laminate. For example, a fluorine-based resin or a mixture mainly composed of a fluorine-based resin, polyvinyl alcohol or a mixture mainly composed of polyvinyl alcohol can be used. Specifically, polymers or copolymers with fluorine atoms in the molecular structure of vinylidene fluoride, 4-vinyl fluoride, etc., polymers or copolymers with vinyl alcohol in the molecular skeleton, or polymethylmethacrylate can be used. A mixture of methyl acrylate, polystyrene, polyethylene, polypropylene, polyvinylidene chloride, polyvinyl chloride, polyacrylonitrile, polyethylene oxide, etc. In particular, polyvinylidene fluoride, which is a fluorine-based resin, is suitable.

In addition, any metal that is stable in the battery can be used as the current collector, but aluminum is preferably used for the positive electrode, and copper is preferably used for the negative electrode. As the shape of the current collector, a foil shape, a mesh shape, and a metal mesh can be used, but a shape such as a mesh shape or a metal mesh with large gaps is easy to hold the electrolyte solution after bonding. is ideal.

In addition, as the separator, any film may be used as long as it is a film having sufficient strength such as an electronically insulating porous film, a net, or a nonwoven fabric. In the case of using a film or the like of a fluorine-based resin, it may be necessary to perform surface treatment with plasma or the like in order to ensure adhesive strength. The material is not particularly limited, but polyethylene and polypropylene are preferable from the viewpoint of adhesiveness and safety.

In addition, as the solvent supplied to the electrolytic solution used as the ion conductor, as the electrolytic salt, non-aqueous solvents and lithium-containing electrolytic salts conventionally used in batteries can be used. Specifically, ether solvents such as dimethoxyethane, diethoxyethane, diethyl ether, and dimethyl ether, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and the like can be used. A single solution of the above-mentioned ester-based solvent, and a mixture of two kinds of the above-mentioned same solvent or sometimes composed of different solvents. In addition, LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ and the like can be used as the electrolyte salt supplied to the electrolytic solution.

In addition, the adhesive resin used in the bonding of the current collector and the electrode and the adhesive resin used in the bonding of the electrode and the separator can be used, which is insoluble in the electrolyte and does not generate heat in the battery. The resin for electrochemical reaction is more preferably a porous membrane, such as a fluorine-based resin or a mixture mainly composed of a fluorine-based resin, polyvinyl alcohol or a mixture mainly composed of polyvinyl alcohol. Specifically, polymers or copolymers with fluorine atoms in the molecular structure of vinylidene fluoride, 4-vinyl fluoride, etc., polymers or copolymers with vinyl alcohol in the molecular skeleton, or polymethylmethacrylate can be used. A mixture of methyl acrylate, polystyrene, polyethylene, polypropylene, polyvinylidene chloride, polyvinyl chloride, polyacrylonitrile, polyethylene oxide, etc. In particular, polyvinylidene fluoride, which is a fluorine-based resin, is suitable.

Hereinafter, the present invention will be described concretely by giving examples, but it goes without saying that the present invention is not limited thereto.

Example 1

A method of dispersing 87 parts by weight of LiCoO ₂ , 8 parts by weight of graphite powder (KS-6, produced by Ronza), and 5 parts by weight of polyvinylidene fluoride as the binder resin into N-methylpyrrolidone (abbreviated as NMP) The prepared positive electrode active material paste was applied to a thickness of about 100 μm while being adjusted on a 20 μm thick aluminum foil serving as a positive electrode current collector by the doctor blade method to form a positive electrode.

90 parts by weight of メソフェ-ズマイクロビ-ズカ-bon (trade name, produced by Osaka Gas), as a binder resin, disperse 5 parts by weight of polyvinylidene fluoride in N-methylpyrrolidone and prepare the negative electrode active material paste. In the doctor blade method, a copper foil with a thickness of 12 microns, which is the negative electrode current collector, is coated while adjusting to a thickness of about 100 microns to form a negative electrode.

On one side of each of two spacers (ヘキストセラニニ-ズ product Seruga-do #2400), evenly coat the polyvinylidene fluoride of the adhesive resin used to bond the active material particles to the current collector. 5% by weight NMP solution. Before drying the NMP solution of polyvinylidene fluoride, the negative electrode 5 is sandwiched between the polyvinylidene fluoride NMP solution coated surfaces of two separators 4 and tightly pasted, and then placed in a warm air dryer at 60°C The NMP was evaporated for 2 hours, and the negative electrode 5 was bonded between the two separators. Punch out the two spacers 4 joined together with the negative electrode 5 sandwiched in the middle to a specified size, and evenly coat the NMP solution of polyvinylidene fluoride on one side of the stamped spacer, and paste the stamped spacers. A positive electrode 3 having a predetermined size is formed into a laminate in which a separator 4 , a negative electrode 5 , and a positive electrode 3 are sequentially joined. In addition, the NMP solution of polyvinylidene fluoride is coated on one surface of another separator that has been punched into a predetermined size and joined with the negative electrode in the middle, and the coated surface of the other separator is pasted on the previous surface. The surface of the positive electrode of the above-mentioned laminate that has been pasted. This process is repeated to form a battery body having a multilayered positive electrode and a negative electrode laminated with a separator sandwiched between them, and the battery body is dried while pressing to form a flat plate-shaped stack as shown in FIG. 1 . The battery body is constructed in layers. Next, the collector tabs that have been connected to the respective ends of the flat-plate laminated battery body are spot-welded between the positive electrodes and the negative electrodes to make the above-mentioned flat laminated structure battery body electrically connected in parallel. Next, an electrolytic solution containing ethylene carbonate and 1,2-dimethoxyethane as a solvent and lithium hexafluorophosphate as an electrolyte is injected into this flat laminated battery body, and then laminated with aluminum The film is packaged, hot-melt bonded and sealed to complete the lithium-ion secondary battery.

The manufactured battery does not require external pressure, maintains its original state stably and intact, and can maintain the electrical connection between the electrodes. After the battery is formed, when the aluminum laminate film is removed and the separator and the electrode are peeled off, it is known that the active material layer is peeled off with the separator already attached, and the active material layer near the surface of the electrode is separated from the active material layer inside the electrode. The bonding strength between the separators is greater than the bonding strength between the active material layer and the current collector. This is considered to be because the binder resin is more on the separator side of the positive electrode and negative electrode active material layers than on the current collector side. Since the destruction of the electrodes occurs preferentially over the peeling between the positive and negative electrode active material layers and the separator, safety can be maintained.

In addition, the battery characteristics were evaluated, and the gravimetric energy density was about 100 Wh/kg due to effective use of the active material inside the electrode. In addition, even after 200 charge-discharge cycles at the current value C/2, the charge capacity can maintain a high value of 75% of the initial value. It is believed that this is because the binder resin is more present on the side of the separator, that is, the ratio of the active material particles on the separator side to be covered by the binder resin is higher than that of the active material particles on the collector side. The corresponding ratio is large, so the difference in the speed of doping and dedoping of lithium ions in the positive and negative active material layers on the side of the separator and the active material inside can be alleviated, and the active material inside the electrode can be effectively used.

As described above, since there is no need for a strong case, it is possible to reduce the weight and thickness of the battery, and any form can be adopted. At the same time, the charge-discharge efficiency is improved, so it is possible to obtain a battery with excellent charge-discharge characteristics and high safety. , A lithium-ion secondary battery with the possibility of increasing the capacity.

In this embodiment, it is also possible to repeatedly stick the positive electrode 3 between two separators 4 in the same manner as above, and apply an adhesive resin to one surface of the separator 4 sandwiching the positive electrode 3. Liquid, the negative electrode is pasted on the coating surface, and another separator that has pasted the positive electrode between the two spacers is pasted on the top of the negative electrode 5.

Example 2

Under the same conditions as in Example 1 above, the thickness of the active material of the positive electrode and the negative electrode was made to be about 200 micrometers to form a battery with a multilayer structure. As a result, as in Example 1 above, the obtained battery was stable and could maintain its original shape and electrical connection between electrodes without applying pressure from the outside. In addition, after the electrode was formed, when the aluminum laminate film was removed and the separator and the electrode were peeled off, it was found that the active material layer was peeled off in a state where the active material layer was already attached to the separator, and the active material near the surface of the electrode inside the electrode The bonding strength between the layer and the separator is greater than the bonding strength between the active material layer and the current collector. The battery characteristic is about 113 Wh/kg in gravimetric energy density. In addition, even after 200 charge-discharge cycles at the current value C/2, the charge capacity can maintain a high value of 60% of the initial value. In addition, similarly to the above-mentioned Example 1, a lithium-ion secondary battery with a reduced thickness, which can take any form, and which has excellent charge-discharge characteristics and a large capacity can be obtained.

Example 3

A positive electrode and a negative electrode were fabricated in the same manner as in Example 1 above. A 12% by weight NMP solution of polyvinylidene fluoride was used for bonding the separator and the electrodes. The battery thus produced was stable and could maintain its original shape and electrical connection between electrodes without applying pressure from the outside, as in the case of Example 1 above. After the electrode was formed, when the aluminum laminate film was removed and the separator and the electrode were peeled off, it was found that the active material layer was peeled off in the state that the separator was already attached, and the active material layer near the electrode surface was separated from the inside of the electrode. The bonding strength between the separators is greater than the bonding strength between the active material layer and the current collector. Since a thin polyvinylidene fluoride layer is formed between the separator and the electrode by using a high-concentration polyvinylidene fluoride solution, the bonding strength becomes stronger, and the electrical connection is maintained after being stabilized. The battery characteristic is about 100Wh/kg in terms of gravimetric energy density, and even after charging and discharging 200 times with a current value C/2, the charging capacity can still maintain a high value of 60% of the initial stage.

As in the above-mentioned Example 1, a thinner lithium ion secondary battery that can take any form and has excellent charge-discharge characteristics can be obtained.

Example 4

Make 87 parts by weight of LiCoO ₂ , 8 parts by weight of graphite powder (KS-6, produced by ロンザ), as the binder resin, 5 parts by weight of polystyrene are mixed, and an appropriate amount of toluene and 2-propanol are added to prepare the positive electrode active material paste, The aluminum foil with a thickness of 20 micrometers used as a positive electrode collector was coated with adjustments to a thickness of about 100 micrometers by the doctor blade method to form a positive electrode.

95 parts by weight of メソフェ-ズマイイクロビ-ズカ-bon (trade name, produced by Osaka Gas) and 5 parts by weight of polystyrene as the binding resin are mixed, and toluene and 2-propanol are added in an appropriate amount to prepare the negative electrode active material paste. In the doctor blade method, the copper foil with a thickness of 12 micrometers used as the negative electrode current collector is coated to a thickness of about 100 micrometers while adjusting to form a positive electrode.

Use nitrocellulose porous membrane (pore diameter 0.8 micron) as separator, as the bonding agent of bonding positive electrode and negative electrode (being positive electrode and negative electrode active material layer) and separator, use the 5wt of polystyrene as adhesive resin % toluene solution, through the same treatment as in the above-mentioned embodiment, the battery body with a flat laminated structure as shown in FIG. 1 was made. Next, the current collectors connected to the respective ends of the flat-plate laminated structure battery body are welded between positive electrodes and negative electrodes, so that the above-mentioned flat-plate laminated structure battery bodies are connected in parallel. Ground connection. Next, an electrolytic solution containing ethylene carbonate and 1,2-dimethoxyethane as a solvent and lithium hexafluorophosphate as an electrolyte is injected into this flat laminated battery body, and then laminated with aluminum The film is packaged, hot-melt bonded and sealed to complete the lithium-ion secondary battery.

The manufactured battery does not require external pressure, maintains its original state stably and intact, and can maintain the electrical connection between the electrodes. After the battery is formed, when the aluminum laminate film is removed and the separator and the electrode are peeled off, it is known that the active material layer is peeled off with the separator already attached, and the active material layer near the surface of the electrode is separated from the active material layer inside the electrode. The bonding strength between the separators is greater than the bonding strength between the active material layer and the current collector. The characteristics of the battery were evaluated, and it was found that the gravimetric energy density was about 90 Wh/kg. Even after charging and discharging 100 times with the current value C/10, the charging capacity can still maintain 60% of the initial stage.

As in the above-mentioned Example 1, a thinner lithium ion secondary battery that can take any form and has excellent charge-discharge characteristics can be obtained.

Example 5

A positive electrode and a negative electrode were fabricated in the same manner as in Example 1 above. In the bonding of the separator and the electrode, the weight ratio of polyvinylidene fluoride and polymethacrylic acid used to bond the active material particles to the current collector is 10% by weight of 1:2. Using the toluene solution, a battery with a flat laminated structure was produced in the same manner as in the above-mentioned examples. In this case, drying after pasting was carried out in a vacuum while heating to 80°C. The thus fabricated battery maintained its original state stably and without external pressure, as in the first embodiment described above. After the battery is formed, when the aluminum laminate film is removed and the separator and the electrode are peeled off, it is known that the active material layer is peeled off with the separator already attached, and the active material layer near the surface of the electrode is separated from the active material layer inside the electrode. The bonding strength between the separators is greater than the bonding strength between the active material layer and the current collector. Battery characteristics, in terms of gravimetric energy density is about 95Wh/kg. Even after charging and discharging 100 times with the current value C/2, the charging capacity can still maintain 80% of the initial stage.

As in the above-mentioned Example 1, a thinner lithium ion secondary battery that can take any form and has excellent charge-discharge characteristics can be obtained.

Example 6

The production of negative electrode 5 and positive electrode 3 was carried out in the same manner as in Example 1 above. On one side of each of two strip-shaped spacers (ヘキストセラニニ-ズ product Seruga-do #2400), evenly coat the polymeric resin that is used to bond the active material particles to the current collector. 5% by weight solution of vinyl fluoride in NMP. Sandwich the strip-shaped positive electrode between the coated surfaces and stick it tightly, put it in a warm air dryer at 60°C for 2 hours to evaporate the NMP in the resin solution, and bond the positive electrode to two separators between. On one surface of two strip-shaped separators joined together with the positive electrode sandwiched in the middle, a 5% by weight NMP solution of polyvinylidene fluoride is evenly coated, so that the one surface is in the middle, and the spacer of the above-mentioned separator One end is bent to a specified amount and cut to a specified size at the crease. The negative electrode 5 cut off in this way is sandwiched in the middle and superimposed and passed into the laminator. Then, on the other side of the strip-shaped separator, a 5% by weight NMP solution of polyvinylidene fluoride was evenly coated, and pasted at a position opposite to the negative electrode 5 sandwiched at the crease before, it was cut into a predetermined shape. For another negative electrode of the same size, the above-mentioned strip-shaped separator is wound in a half circle in an oblong shape so that it is sandwiched in the middle, and then the process of winding the above-mentioned separator while pasting other negative electrodes is repeated to form a multi-layered negative electrode. The battery body of the battery laminate described above was dried while pressing the battery body to produce a flat-plate laminated battery body as shown in FIG. 2 .

The battery bodies having a flat-plate-like laminate structure are electrically connected in parallel by spot-welding the collector tabs connected to the respective ends of the plate-like laminate-structure battery bodies. In the same manner as in the above-mentioned Example 1, the battery body with a flat laminated structure was immersed in the electrolyte solution and sealed to obtain a secondary battery.

Also in this flat-shaped rolled-type laminated battery body, as in the first embodiment described above, the original shape is stably maintained without applying pressure from the outside. After the battery is formed, when the aluminum laminate film is removed and the separator and the electrode are peeled off, it is known that the active material layer is peeled off in the state that the separator is already attached, and the active material layer near the electrode surface is separated from the inside of the electrode. The bonding strength between the separators is greater than the bonding strength between the active material layer and the current collector. The battery characteristic is about 90Wh/kg in terms of gravimetric energy density. Even after charging and discharging 100 times with the current value C/2, the charging capacity can still maintain 80% of the initial stage.

As in the above-mentioned Example 1, a thinner lithium ion secondary battery that can take any form and has excellent charge-discharge characteristics can be obtained.

In this embodiment, an example is shown in which a plurality of negative electrodes 5 of a predetermined size are sandwiched between them while winding a strip-shaped positive electrode 3 bonded between strip-shaped separators 4 and pasted. , but can also be reversed, while winding the strip-shaped negative electrode 5 joined to the object between the strip-shaped separators 4, while sandwiching a plurality of positive electrodes 3 of a predetermined size and pasting them.

In addition, in this embodiment, although the method of winding the separator 4 is shown, it is also possible to fold the strip-shaped negative electrode 5 or the positive electrode 3 between the strip-shaped separators 4 while folding the object, It is a method of sticking the positive electrode 3 or the negative electrode 5 of a predetermined size in between.

Example 7

The production of negative electrode 5 and positive electrode 3 was carried out in the same manner as in Example 1 above. A strip-shaped positive electrode 3 is arranged between two strip-shaped separators (ヘキストセラニニ-ズ product Seluga-do #2400) 4, and a strip-shaped negative electrode 5 is arranged on the outside of one separator so that it protrudes by a certain amount. . On the inner surface of each separator 4 and the outer surface of the separator 4 where the negative electrode 5 is arranged, evenly coat the polyvinylidene fluoride 5 of the adhesive resin used to bond the active material particles to the current collector in advance. wt% NMP solution. A certain amount of one end of the negative electrode 5 is first passed into the laminator, and then the negative electrode 5, the separator 4, the positive electrode 3, and the separator 4 are overlapped while being passed into the laminator to form a strip-shaped laminate. A 5% by weight NMP solution of polyvinylidene fluoride was evenly applied to the outer surface of the separator on the other side of the strip-shaped laminate, and the protruding negative electrode 5 was bent and pasted on the coated surface. , the laminated laminate is wound in an oval shape so that the bent negative electrode 5 is wrapped inside to form a battery body with a multilayer electrode laminate as shown in Figure 3, and it is dried while heating. In this battery body, the negative electrode, the separator, and the positive electrode were simultaneously bonded to form a flat sheet-shaped rolled-type battery body. In the same manner as in Example 1 above, an electrolytic solution was injected into the flat-shaped roll-type laminated battery body, followed by sealing treatment to obtain a battery.

Also in this flat-shaped rolled-type laminated battery body, as in the case of the above-mentioned first embodiment, the original shape is stably maintained without applying pressure from the outside. After the battery is formed, when the aluminum laminate film is removed and the separator and the electrode are peeled off, it is known that the active material layer is peeled off in the state that the separator is already attached, and the active material layer near the electrode surface is separated from the inside of the electrode. The bonding strength between the separators is greater than the bonding strength between the active material layer and the current collector. The battery characteristics are about 80Wh/kg in terms of gravimetric energy density. Even after charging and discharging 100 times at the current value C/2, the charging capacity can still maintain a high value of 80% of the initial value.

As in the above-mentioned Example 1, a thinner lithium ion secondary battery that can take any form and has excellent charge-discharge characteristics can be obtained.

In this embodiment, although the example in which the strip-shaped positive electrode 3 is arranged between the strip-shaped separators 4 is shown, and the negative electrode 5 is arranged outside one of the separators 4 for winding, it may also be reversed. Conventionally, the strip-shaped negative electrode 5 is arranged between the strip-shaped separators 4, and each positive electrode 3 is arranged on the outside of one of the separators 4 for winding.

In the above-described embodiments, the number of stacked layers was varied in various ways, and the battery capacity increased in proportion to the number of stacked layers.

comparative example

A method of dispersing 87 parts by weight of LiCoO ₂ , 8 parts by weight of graphite powder (KS-6, produced by Ronza), and 5 parts by weight of polyvinylidene fluoride as the binder resin into N-methylpyrrolidone (abbreviated as NMP) The prepared positive electrode active material paste was applied to the aluminum foil with a thickness of 20 microns as the positive electrode current collector while being adjusted by the doctor blade method, and the thickness was about 100 microns.

95 parts by weight of メソフェ-ズマイクロビ-ズカ-bon (trade name, produced by Osaka Gas), as a binder resin, disperse 5 parts by weight of polyvinylidene fluoride in N-methylpyrrolidone and prepare the negative electrode active material paste. The blade (doctor blade) method is adjusted while applying to the copper foil with a thickness of 12 microns to become the negative electrode current collector, and the thickness is about 100 microns.

Sandwich the spacer (ヘキストセラニニ-ズ product セルガ-ド#2400) in the middle, and in the time that the aluminum foil coated with the above-mentioned positive electrode active material layer and the copper foil coated with the negative electrode active material layer are not dried, alternately Laminate sequentially, extrude from both sides, make it dry, and make a flat laminated structure battery body with multi-layered electrode laminates as shown in Figure 1, and use spot welding between the positive electrodes and the negative electrodes. The method is connected electrically in parallel. Next, an electrolytic solution containing ethylene carbonate and 1,2-dimethoxyethane as a solvent and lithium hexafluorophosphate as an electrolyte is injected into this flat laminated battery body, and then laminated with aluminum The film is packaged, hot-melt bonded and sealed to complete the lithium-ion secondary battery.

The manufactured battery is stable and maintains its original shape. After the battery was formed, the aluminum laminate film was removed, and the separator and electrodes were peeled off. It was found that after peeling, only the active material was sparsely attached to the separator, and the adhesion between the active material layer and the separator near the electrode surface was The strength is extremely low compared with the strength of bonding the active material layer and the current collector inside the electrode, and there is almost no bonding. In addition, battery characteristics were evaluated, and it was about 70 Wh/kg in terms of gravimetric energy density. After charging and discharging 200 times at a current value C/2, the charging capacity was as low as 40% of the initial value.

Facts have proved that compared with the above-mentioned embodiment, the characteristics of the battery have deteriorated a lot, and the method of pasting the positive and negative electrodes and the separator with an adhesive can improve the characteristics of the battery. In other words, it was found that the distribution of the binder and the binder resin plays a large role in the improvement of battery characteristics.

In addition, as the adhesive, it is not necessary to use the same adhesive as the adhesive used for bonding the active material layer, and a different adhesive may be used.

Possibility of industrial use

A secondary battery that can be used as a portable electronic device such as a portable personal computer and a handy phone can realize miniaturization, weight reduction, and arbitrary shape while improving the performance of the battery.

Claims (8)

1. A lithium ion secondary battery comprising a plurality of electrode stacks, wherein, Each electrode stack has: A positive electrode comprising a particulate positive active material material bonded to a positive current collector with a binding resin; An anode electrode comprising a particulate anode active material material bonded to an anode current collector with a binding resin; and a separator interposed between the positive electrode active material layer and the negative electrode active material layer with a binder resin, The electrolyte solution containing lithium ions is kept in the gap between the positive electrode active material layer, the negative electrode active material layer and the separator layer, The positive electrode active material and the negative electrode active material near the separator are covered with an adhesive resin having a larger amount than the positive electrode active material and the negative electrode active material near the positive electrode collector and the negative electrode collector, thereby making the separator layer and the positive electrode active material layer The bonding strength between the negative electrode active material layer is greater than or equal to the bonding strength between the positive electrode active material layer and the negative electrode active material layer and each current collector, and The positive electrode active material layer and the negative electrode active material layer are bonded to the separator with an adhesive resin, and the adhesive resin binds the particulate positive active material and the granular negative active material to the positive collector and the negative collector respectively. The bonding resin is the same. 2 . The lithium ion secondary battery according to claim 1 , wherein the positive electrodes and the negative electrodes in the plurality of layers of the electrode laminate are arranged alternately between the cut separators. 3 . 3 . The lithium ion secondary battery according to claim 1 , wherein the positive electrodes and the negative electrodes in the plurality of layers of the electrode laminate are arranged alternately between the rolled separators. 4 . 4. The lithium ion secondary battery according to claim 1, characterized in that: the positive electrodes and the negative electrodes in the plurality of layers of the electrode laminate are arranged alternately between the folded separators. 5. The lithium ion secondary battery according to claim 1, characterized in that: the density ratio of the active material particles of each positive electrode material layer and negative electrode material layer positioned on one side of the separator is located at each positive electrode current collector. The body and the negative electrode collector side are low. 6. The lithium-ion secondary battery according to claim 1, characterized in that: the density ratio of the bonding resin of each positive electrode material layer and the negative electrode material layer on one side of the separator is located at each positive electrode current collector. The body and the negative electrode collector side are high. 7. The lithium ion secondary battery according to claim 1, wherein the active material particles have a particle size in the range of 0.3-20 μm. 8. The lithium ion secondary battery according to claim 1, wherein the active material particles have a particle size in the range of 1-5 μm.

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