JP4952193B2 - Lithium secondary battery - Google Patents

Description

  The present invention relates to a lithium secondary battery provided with a gel electrolyte containing a swelling solvent.

  Batteries are becoming increasingly important as power sources for portable electronic devices such as mobile phones, video cameras, and notebook personal computers. In order to reduce the size and weight of electronic devices, there is a need for a light and space-saving battery as well as a large capacity. From such a viewpoint, a lithium battery having a high energy density and a high output density is suitable as a power source for the portable electronic device. A lithium battery using a carbon material as a negative electrode has an average discharge voltage of 3.7 V or more, and has a relatively small cycle deterioration at the time of charge and discharge, and thus has an advantage of easily realizing a high energy density.

  Among lithium batteries, there are demands for batteries of various shapes, such as batteries having flexibility and a high degree of freedom of shape, thin and large area sheet type batteries, thin and small area card type batteries, etc. It is difficult to make batteries of various shapes as described above by the conventional method of enclosing a battery element composed of a positive electrode and a negative electrode and an electrolyte in the outer can. In addition, the use of the electrolytic solution complicates the process and requires countermeasures against liquid leakage.

  In order to solve the above-described problems, a solid electrolyte using a conductive organic polymer or inorganic ceramic, or a gel-like solid electrolyte in which a matrix polymer is impregnated with an electrolytic solution (hereinafter referred to as a gel electrolyte). ) Is being studied. In a solid electrolyte battery using these solid electrolytes and a gel electrolyte battery using a gel electrolyte, since the electrolyte is fixed, the contact between the electrode and the electrolyte can be maintained. Therefore, in these batteries, there is no need to enclose the electrolytic solution in a metal outer can or apply pressure to the battery element, and the battery can be made thinner by using a film-like outer packaging material, which has higher energy than conventional batteries. It is possible to provide density.

  In general, solid electrolyte batteries themselves have appropriate mechanical strength, as described in “Material Technology for High Performance Secondary Batteries and Their Evaluation and Application Development (Technical Information Society 1998)”. It is possible to select a battery structure different from that of a battery using a conventional electrolytic solution. As an example, it has been reported that a battery can be manufactured without providing a separator between the positive electrode and the negative electrode, which is recognized as an advantage of the solid electrolyte.

  However, the solid electrolytes reported so far have relatively lower mechanical strength including piercing strength and the like than conventional separators made of a polyolefin microporous membrane or the like. Therefore, in the conventional solid electrolyte battery, when the thickness of the solid electrolyte layer is reduced to, for example, 40 μm or less in order to improve the energy density, an internal short circuit is often generated after the battery is assembled. Yes. Thus, it has been difficult to increase the energy density of the solid electrolyte battery by reducing the thickness of the solid electrolyte layer.

  On the other hand, it is pointed out that the conventional solid electrolyte battery is relatively low also about the heat resistance item used as the parameter | index which evaluates the reliability of a battery. Some of the commercially available batteries have been devised to ensure heat resistance by using a so-called shutdown effect. On the other hand, no solid electrolyte material having the shutdown effect has been found in solid electrolyte batteries.

  Furthermore, regarding the reliability and safety of the battery, as a general tendency, as the energy density of the battery increases, it becomes difficult to ensure the reliability and safety, so that the solid electrolyte battery has a higher energy density. At the same time, it is necessary to incorporate the technology to ensure the safety into the battery design.

  In the construction of a thin battery, a polyolefin-based separator, particularly a polyethylene separator, is used as a separator.

  Under normal conditions, even if the battery temperature melts down and the positive and negative electrodes are short-circuited, thermal runaway does not occur. However, a dangerous situation can occur when the battery temperature rises when used in an abnormal environment, such as when the charging voltage is higher than the voltage that is routinely used. When polyethylene is used as a separator when falling into the above situation, the meltdown temperature of polyethylene is lower than that of polypropylene, and the meltdown of the separator, that is, the film breakage of the separator is likely to occur. Short circuit may occur and heat may be generated.

  The present invention has been proposed in view of the conventional situation as described above, and provides a lithium secondary battery including a gel electrolyte containing a swelling solvent that greatly improves energy density and safety. With the goal.

The lithium secondary battery according to the present invention includes a positive electrode, a negative electrode disposed opposite to the positive electrode, a separator disposed between the positive electrode and the negative electrode, and between the positive electrode and the separator and the above A gel electrolyte containing a swelling solvent interposed between the separator and the negative electrode, the separator is made of a composite of polyethylene and polypropylene, and has a thickness in the range of 5 μm to 15 μm, The down temperature is higher than the melt down temperature of the separator made of polyethylene by 10 ° C. or more and 30 ° C. or less, the breaking strength is less than 1650 kg / cm ² , and the breaking elongation is 135% or more, As swelling solvents, ethylene carbonate, propylene carbonate, γ-butyrolactone, acetonitrile, diethyl ether, diethyl carbo Nate, dimethyl carbonate, 1,2-dimethoxyethane, dimethyl sulfoxide, 1,3-dioxolane, methyl sulfomate, 2-methyltetrahydrofuran, tetrahydrofuran, sulfolane, 2,4-difluoroanisole, vinylene carbonate Of at least one of them.

  Here, the gel electrolyte includes a matrix polymer, and the mixing ratio of the matrix polymer and the swelling solvent is desirably in a range of weight ratio of matrix polymer: swelling solvent = 1: 5 or more and 1:10 or less.

Further, the lithium secondary battery according to the present invention includes a positive electrode, a negative electrode disposed opposite to the positive electrode, a separator disposed between the positive electrode and the negative electrode, and between the positive electrode and the separator. And a gel electrolyte containing a swelling solvent interposed between the separator and the negative electrode, wherein the separator is formed by laminating a first separator made of polyethylene and a second separator made of polypropylene. The thickness is in the range of 5 μm or more and 15 μm or less, the meltdown temperature is equivalent to that of a separator made of polypropylene, the breaking strength is less than 1650 kg / cm ² , and the breaking elongation is 135% or more. As the swelling solvent, ethylene carbonate, propylene carbonate, γ-butyrolactone, acetonitrile, diethyl ether , Diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, dimethyl sulfoxide, 1,3-dioxolane, methyl sulfomate, 2-methyltetrahydrofuran, tetrahydrofuran, sulfolane, 2,4-difluoroanisole, vinylene carbonate Containing at least one of the group consisting of

  Here, the gel electrolyte includes a matrix polymer, and the mixing ratio of the matrix polymer and the swelling solvent is desirably in a range of weight ratio of matrix polymer: swelling solvent = 1: 5 or more and 1:10 or less.

  The lithium secondary battery according to the present invention includes a separator made of a composite of polyethylene and polypropylene, which defines mechanical properties and thermal properties, or a first separator made of polyethylene and a second separator made of polypropylene. By using a separator that is bonded together, it has become possible to achieve both high energy density and safety of the battery, which has been considered difficult in the past, and high-performance lithium secondary that has excellent battery characteristics and safety. A battery can be realized.

Prior to the description of the present invention, a gel electrolyte battery as a reference example will be described.

A configuration example of a gel electrolyte battery 1 shown in FIGS. The gel electrolyte battery 1 includes a strip-shaped positive electrode 2, a strip-shaped negative electrode 3 disposed to face the positive electrode 2, a gel electrolyte layer 4 formed on the positive electrode 2 and the negative electrode 3, and a gel electrolyte layer 4. And a separator 5 disposed between the positive electrode 2 and the negative electrode 3 on which the gel electrolyte layer 4 is formed.

  In this gel electrolyte battery 1, the positive electrode 2 on which the gel electrolyte layer 4 was formed and the negative electrode 3 on which the gel electrolyte layer 4 was formed were laminated via the separator 5 and wound in the longitudinal direction. The electrode winding body 6 shown in FIG. 3 is covered and sealed with an exterior film 7 made of an insulating material. A positive electrode terminal 8 is connected to the positive electrode 2, and a negative electrode terminal 9 is connected to the negative electrode 3, and the positive electrode terminal 8 and the negative electrode terminal 9 are sandwiched between sealing portions that are peripheral portions of the exterior film 7. ing. Further, a resin film 10 is disposed in a portion where the positive electrode terminal 8 and the negative electrode terminal 9 are in contact with the exterior film 7.

  As shown in FIG. 4, in the positive electrode 2, positive electrode active material layers 2a containing a positive electrode active material are formed on both surfaces of the positive electrode current collector 2b. For example, a metal foil such as an aluminum foil is used as the positive electrode current collector 2b.

  As the positive electrode active material, lithium composite oxides such as lithium cobaltate, lithium nickelate, and spinel lithium manganate can be used. These lithium composite oxides may be used alone or in combination of two or more.

  Furthermore, it is preferable to use a lithium composite oxide having an average particle size of 15 μm or less as described above. By using a lithium composite oxide having an average particle size of 15 μm or less as a positive electrode active material, a gel electrolyte battery having low internal resistance and excellent high output characteristics can be obtained.

  4 shows a state where a gel electrolyte layer 4 described later is formed on the positive electrode active material layer 2a of the positive electrode 2. FIG.

  Further, in the negative electrode 3, as shown in FIG. 5, a negative electrode active material layer 3a containing a negative electrode active material is formed on both surfaces of the negative electrode current collector 3b. For example, a metal foil such as a copper foil is used as the negative electrode current collector 3b.

  As the negative electrode active material, a material that can be doped or dedoped with lithium can be used. As a material capable of doping and dedoping such lithium, lithium metal and an alloy thereof, a carbon material, or the like can be used. Specific examples of carbon materials include carbon blacks such as natural graphite, artificial graphite, pyrolytic carbons, cokes, acetylene black, glassy carbon, activated carbon, carbon fiber, organic polymer fired body, coffee bean fired body, A cellulose fired body, a bamboo fired body, etc. are mentioned.

  Among the materials described above, as a result of intensive studies by the inventors, it has been found that it is preferable to use mesocarbon microbead carbon graphitized at a firing temperature of about 2800 ° C. Since the mesocarbon microbead carbon exhibits high electrochemical stability with respect to the electrolytic solution, the mesocarbon microbead carbon is particularly effective in combination with a gel electrolyte that uses an electrolytic solution containing propylene carbonate.

  Further, the mesocarbon microbead carbon preferably has an average particle size in the range of 6 μm to 25 μm. As the average particle size of mesocarbon microbead carbon is smaller, it is possible to reduce the overvoltage in the electrode reaction, and as a result, the battery output characteristics can be improved. However, in order to improve the electrode packing density, it is advantageous to use a mesocarbon microbead carbon having an average particle diameter in the range of 6 μm to 25 μm because it is advantageous that the average particle diameter is large.

  FIG. 5 shows a state where a gel electrolyte layer 4 described later is formed on the negative electrode active material layer 3 a of the negative electrode 3.

  The gel electrolyte layer 4 contains an electrolyte salt, a matrix polymer, and a swelling solvent as a plasticizer.

As the electrolyte salt, LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiBF ₄ , LiN (CF ₃ SO ₃ ) ₂ , C ₄ F ₉ SO ₃ Li, or the like can be used alone or in combination. Among them, it is preferable to use LiPF ₆ from the viewpoint of ion conductivity and the like.

  The matrix polymer is not particularly limited in chemical structure as long as the polymer alone or a gel electrolyte using the polymer exhibits an ionic conductivity of 1 mS / cm or more at room temperature. Examples of the matrix polymer include polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polysiloxane compounds, polyphosphazene compounds, polypropylene oxide, polymethyl methacrylate, polymethacrylonitrile, polyether compounds, and the like. Alternatively, a material obtained by copolymerizing the above polymer with another polymer can be used. From the viewpoint of chemical stability and ionic conductivity, it is preferable to use a material in which the copolymerization ratio of polyvinylidene fluoride and polyhexafluoropropylene is less than 8% by weight.

  As swelling solvents, ethylene carbonate, propylene carbonate, γ-butyrolactone, acetonitrile, diethyl ether, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, dimethyl sulfoxide, 1,3-dioxolane, methyl sulfomate, 2 -Nonaqueous solvents such as methyltetrahydrofuran, tetrahydrofuran, sulfolane, 2,4-difluoroanisole, vinylene carbonate and the like can be used alone or in combination.

  Among the solvents described above, it is preferable to use a solvent having a relatively wide potential window, such as ethylene carbonate, propylene carbonate, and γ-butyrolactone. Here, the potential window refers to a potential region where the solvent can exist stably.

  In addition, battery characteristics may be improved by adding 2,4-difluoroanisole and vinylene carbonate in the range of 0.5% to 5% with respect to the total solvent weight.

  Here, in the gel electrolyte layer 4, the mixing ratio of the matrix polymer and the swelling solvent described above is preferably in the range of matrix polymer: swelling solvent = 1: 5 or more and 1:10 or less by weight ratio. When the amount of the swelling solvent is less than 5 times the amount of the matrix polymer, the electrolyte solution component in the gel electrolyte is deficient, and the ionic conductivity of the gel electrolyte layer 4 is lowered. On the other hand, if the amount of the swelling solvent is more than 10 times the amount of the matrix polymer, the gel electrolyte itself becomes brittle, and sufficient liquid holding performance of the matrix polymer is not exhibited.

  By setting the mixing ratio of the matrix polymer and the swelling solvent in the above range, the ionic conductivity of the gel electrolyte layer 4 can be ensured while maintaining the liquid retention performance of the matrix polymer.

  And it is preferable that the thickness of such a gel electrolyte layer 4 is 5 micrometers or more and 19 micrometers or less. If the thickness of the gel electrolyte layer 4 is smaller than 5 μm, it is difficult to ensure the amount of gel necessary for smoothly proceeding the electrode reaction. Moreover, when the thickness of the gel electrolyte layer 4 is larger than 19 μm, the distance between the positive electrode 2 and the negative electrode 3 is increased, and the battery energy density and output characteristics are unnecessarily lowered with an increase in the distance between the electrodes. Absent. Therefore, by setting the thickness of the gel electrolyte layer 4 to 5 μm or more and 19 μm or less, the electrode reaction can be performed smoothly without deteriorating the battery energy density and output characteristics.

  The separator 5 is disposed between the positive electrode 2 and the negative electrode 3 and prevents a short circuit due to physical contact between the positive electrode 2 and the negative electrode 3.

The thickness of the separators 5, 5 [mu] m or more, is defined in the range 15μm or less. If the thickness of the separator 5 is smaller than 5 μm, it becomes difficult to handle the separator 5 during battery manufacture, and the yield of the gel electrolyte battery 1 is reduced. On the other hand, when the thickness of the separator 5 is larger than 15 μm, the internal resistance of the gel electrolyte battery 1 increases and the loss of energy density increases. Therefore, by setting the thickness of the separator 5 in the range of 5 μm or more and 15 μm or less, it is possible to prevent the yield of the gel electrolyte battery 1 from decreasing, the internal resistance of the gel electrolyte battery 1 from increasing, or the loss of energy density.

The porosity of the separators 5, 25% or more, as defined in the range of 60% or less. When the porosity of the separator 5 is smaller than 25%, the internal resistance of the gel electrolyte battery 1 increases and a predetermined output characteristic cannot be obtained. Moreover, when the porosity of the separator 5 is larger than 60%, it becomes difficult to express the mechanical strength of the separator 5 itself. Therefore, by setting the porosity of the separator 5 in the range of 25% or more and 60% or less, the mechanical strength of the separator 5 itself can be ensured without increasing the internal resistance of the gel electrolyte battery 1.

Further, separators 5, the battery temperature is 100 ° C. or higher, indicating a shutdown effect in the range of 160 ° C. or less. In order to obtain the shutdown effect when the battery temperature is in the range of 100 ° C. or higher and 160 ° C. or lower, the melting point of the material constituting the separator 5 needs to be in the range of 100 ° C. or higher and 160 ° C. or lower. Further, since the separator 5 is disposed between the electrodes, it is required that the separator 5 is rich in electrochemical stability.

Here, separators 5 100 ° C. or higher, and shows the shutdown effect in the battery temperature range of 160 ° C. or less, 100 ° C. or higher, the battery temperature in the range of 160 ° C. or less, the battery internal impedance, 2 than at room temperature Indicates that it will be more than an order of magnitude larger.

  A typical example of a material that satisfies the above-described conditions is a polyolefin polymer, and polyethylene, polypropylene, or the like can be used. Among these, it is preferable to use polyethylene as a material for the separator 5. In addition to the above-described polyolefin polymer, any resin having chemical stability against gel electrolyte can be used by copolymerizing or blending with the polyethylene or polypropylene. .

  As described above, that is, the thickness is in the range of 5 μm to 15 μm, the porosity is in the range of 25% and 60%, and the shutdown effect is exhibited in the range of 100 ° C. to 160 ° C. By adopting the separator 5, it is possible to achieve both high energy density and safety of the gel electrolyte battery 1.

Furthermore, as a result of intensive studies on the relationship between the physical properties of the separator 5 and the battery characteristics, the inventor has a thickness in the range of 5 μm to 15 μm, and a porosity in the range of 25% and 60%. The separator 5 was found to have a breaking strength of less than 1650 kg / cm ² and a breaking elongation of 135% or more. If the breaking strength or breaking elongation of the separator 5 is out of the above range, it becomes difficult to handle the separator 5 in the battery preparation process, the yield of the gel electrolyte battery 1 is reduced, and sufficient battery characteristics are obtained. Disappear. Therefore, by using the separator 5 having a breaking strength of less than 1650 kg / cm ² and a breaking elongation of 135% or more, the yield reduction of the gel electrolyte battery 1 can be prevented and sufficient battery characteristics can be obtained. Can do.

  Here, a tensile test of the separator 5 for evaluating the breaking strength or breaking elongation of the separator 5 as described above will be described.

  First, after the test piece of the separator 5 is cut out into a substantially rectangular shape of 30 mm × 70 mm, cellophane tape having a width of 10 mm is pasted to both ends in the longitudinal direction.

  Next, the obtained test piece is sufficiently sandwiched between the sample clamp portions of the tensile test apparatus. As the tensile test apparatus, for example, IKO Engineering model 1310f is used. At that time, the portion of the test piece that is sandwiched between the sample clamp portions is adjusted to be a portion that is reinforced with cellophane tape in advance. That is, the part to be tested in the tensile test is a part having a length of 50 mm excluding 10 mm of the part reinforced with the cellophane tape at both ends.

  In this state, after confirming that the test piece is perpendicular to the test table, the tensile test is started. The tensile strength is set to 40 mm per minute, for example. The data of the load value and the elongation value are recorded in a personal computer through an A / D conversion board, and the breaking strength and breaking elongation are obtained from the obtained data. The load value when the test piece breaks is defined as the breaking strength. Further, the length (mm) of the test piece immediately before breakage is measured, and the elongation at break (%) is obtained from (Equation 1).

Elongation at break = 100 × (length of specimen immediately before break / 50) (Formula 1)
By the measuring method as described above, the separator 5 according to the present embodiment has a breaking strength of less than 1650 kg / cm ² and a breaking elongation of 135% or more. By using the separator 5 that satisfies the mechanical characteristics as described above, it is possible to prevent a decrease in the yield of the gel electrolyte battery 1 and to obtain sufficient battery characteristics.

From the above, that is, the thickness is in the range of 5 μm or more and 15 μm or less, the porosity is in the range of 25% or less, 60% or less, the breaking strength is less than 1650 kg / cm ² , and the breaking elongation is By adopting the separator 5 having 135% or more, it is possible to achieve both high energy density and safety of the gel electrolyte battery 1.

  The separator 5 as described above has one purpose of preventing a short circuit due to physical contact between the positive electrode 2 and the negative electrode 3, and the dimensions thereof are the dimensions of the positive electrode 2 and the negative electrode 3 and the form of the electrode element. Depends on. That is, it is important that the electrodes facing each other are completely separated from each other by the separator 5, and it is also necessary that the electrode terminal and the electrode are similarly insulated by the separator 5. In order to realize such a state, the size of the separator 5 needs to be always larger than the ends of the positive electrode 2 and the negative electrode 3.

The separators 5 are the found empirically that the microstructure has a so-called fibril structure as shown in FIG. Here, FIG. 6 is an electron micrograph of the microstructure of the separator 6 taken at a magnification of 50000 times.

  Several means can be considered as means for obtaining the separator 5 having such a fibril structure, and an example of the method will be described below.

  First, a polyolefin having a uniform concentration is obtained by supplying and kneading a liquid low-volatile solvent (good solvent for the polyolefin composition) in a molten state into an extruder containing the molten polyolefin composition. A highly concentrated solution of the composition is prepared.

  Examples of the polyolefin include polyethylene, polypropylene, and the like, but it is preferable to use polyethylene. Moreover, as said low-volatile solvent, low volatile aliphatic or cyclic hydrocarbons, such as nonane, decane, decalin, p-xylene, undecane, a liquid paraffin, etc. can be used, for example.

  The blending ratio of the polyolefin composition and the low-volatile solvent is 100 parts by weight of the total of both, and the polyolefin composition is in the range of 10 to 80 parts by weight, preferably 15 to 70 parts by weight. It is preferable that it is the range below a part. When the polyolefin composition is less than 10 parts by weight, swelling and neck-in become too large at the die outlet, and sheet formation becomes difficult. If the polyolefin composition exceeds 80 parts by weight, it is difficult to prepare a uniform solution. Therefore, when the ratio of the polyolefin composition is in the range of 10 parts by weight or more and 80 parts by weight or less, preparation of a uniform solution and sheet formation can be easily performed.

  Next, the sheet of the polyolefin composition solution obtained by extruding the heated solution of the polyolefin composition from the die is cooled to obtain a gel-like sheet. Cooling is performed to at least the gelation temperature or lower. As a cooling method, a method of directly contacting cold air, cooling water, or other cooling medium, a method of contacting a roll cooled by a refrigerant, or the like can be used.

  The polyolefin composition solution extruded from the die can be drawn at a take-up ratio in the range of 1 to 10 and preferably in the range of 1 to 5 before or during cooling. When the take-up ratio is 10 or more, the neck-in becomes large, and breakage tends to occur during stretching, which is not preferable. By setting the take-up ratio in the range of 1 or more and 10 or less, neck-in or breakage of the gel-like sheet can be prevented.

  Next, the obtained gel-like sheet is heated and stretched at a predetermined magnification to obtain a stretched film. For stretching the gel-like sheet, a normal tenter method, roll method, rolling method, or a method combining these methods can be employed, but biaxial stretching is preferred. Biaxial stretching may be either longitudinal or transverse simultaneous stretching or sequential stretching, but is particularly preferably simultaneous biaxial stretching.

  The stretching temperature of the gel-like sheet is preferably about the melting point of the polyolefin composition + about 10 ° C. or less, and a more preferable temperature range is the crystal dispersion temperature of the polyolefin composition or more and less than the melting point. When the stretching temperature exceeds the melting point of the polyolefin composition + 10 ° C., the resin melts, and effective molecular chain orientation cannot be achieved by stretching, which is not preferable. On the other hand, when the stretching temperature is lower than the crystal dispersion temperature, the resin is not sufficiently softened, and the film is likely to be broken in the stretching process, so that it becomes impossible to stretch at a high magnification. Therefore, by setting the stretching temperature of the gel sheet within the above range. In addition to uniform and high-stretching, molecular chain orientation can be effectively performed.

  Next, the obtained stretched film is washed with a volatile solvent, and the remaining low-volatile solvent is removed. Solvents used for washing include hydrocarbons such as pentane, hexane and heptane, basic hydrocarbons such as methylene chloride and carbon tetrachloride, hydrogen fluoride such as ethane trifluoride, ethers such as diethyl ether and dioxane, etc. These volatile compounds are used alone or in combination. The solvent used for washing the stretched film may be appropriately selected according to the low-volatile solvent used for dissolving the polyolefin composition.

  The stretched film cleaning method includes a method of immersing the stretched film in a solvent and extracting a low-volatile solvent remaining in the stretched film, a method of showering the solvent on the stretched film, or a combination of these methods, etc. Can be performed. The stretched film is washed until the low-volatile solvent remaining in the stretched film is less than 1 part by weight.

  Finally, the solvent used for washing the stretched film is dried and removed. The solvent can be dried by a method such as heat drying or air drying. The separator 5 can be obtained through the above steps. The separator 5 obtained as described above has a fibril structure as shown in FIG.

  And the gel electrolyte battery 1 using the separator 5 as mentioned above is manufactured as follows.

  First, as the positive electrode 2, a positive electrode active material containing a positive electrode active material and a binder is uniformly coated on a metal foil such as an aluminum foil, for example, an aluminum foil to be the positive electrode current collector 2b, and then dried. The layer 2a is formed to produce a positive electrode sheet. As the binder of the positive electrode mixture, a known binder can be used, and a known additive or the like can be added to the positive electrode mixture.

  Next, the gel electrolyte layer 4 is formed on the positive electrode active material layer 2a of the positive electrode sheet. In order to form the gel electrolyte layer 4, first, an electrolyte salt is dissolved in a non-aqueous solvent to prepare a non-aqueous electrolyte. Then, a matrix polymer is added to this non-aqueous electrolyte, and the mixture is well stirred to dissolve the matrix polymer to obtain a sol electrolyte solution.

  Next, a predetermined amount of this electrolyte solution is applied onto the positive electrode active material layer 2a. Subsequently, the matrix polymer is gelled by cooling at room temperature, and the gel electrolyte layer 4 is formed on the positive electrode active material 2a.

  Next, the positive electrode sheet on which the gel electrolyte layer 4 is formed is cut into a strip shape. Then, for example, an aluminum lead wire is welded to the non-formed portion of the positive electrode active material layer 2 a of the positive electrode current collector 2 b to form the positive electrode terminal 8. In this way, a belt-like positive electrode 2 on which the gel electrolyte layer 4 is formed is obtained.

  In addition, the negative electrode 3 is formed by uniformly applying a negative electrode mixture containing a negative electrode active material and a binder onto a metal foil such as a copper foil to be the negative electrode current collector 3b and drying the negative electrode active material layer. 3a is formed and a negative electrode sheet is produced. As the binder of the negative electrode mixture, a known binder can be used, and a known additive or the like can be added to the negative electrode mixture.

  Next, the gel electrolyte layer 4 is formed on the negative electrode active material layer 3b of the negative electrode sheet. In order to form the gel electrolyte layer 4, first, a predetermined amount of an electrolyte solution prepared in the same manner as described above is applied onto the negative electrode active material layer. Subsequently, the matrix polymer is gelled by cooling at room temperature, and the gel electrolyte layer 4 is formed on the negative electrode active material 3b.

  Next, the negative electrode sheet on which the gel electrolyte layer 4 is formed is cut into a strip shape. Then, a lead wire made of nickel, for example, is welded to a non-formation portion of the negative electrode active material layer 3a of the negative electrode current collector 3b to form the negative electrode terminal 9. Thus, the strip-shaped negative electrode 3 having the gel electrolyte layer 4 formed thereon is obtained.

  Then, the strip-shaped positive electrode 2 and the negative electrode 3 manufactured as described above are bonded to each other with the side on which the gel electrolyte layer 4 is formed facing each other and the separator 5 is disposed between the positive electrode 2 and the negative electrode 3. Press to obtain an electrode laminate. Further, this electrode laminate is wound in the longitudinal direction to form an electrode winding body 6.

  Finally, the electrode winding body 6 is sandwiched between exterior films 7 made of an insulating material, and the resin film 10 is disposed on a portion where the positive electrode terminal 8 and the negative electrode terminal 9 overlap the exterior film 7. Then, the outer peripheral edge of the exterior film 7 is sealed, the positive electrode terminal 8 and the negative electrode terminal 9 are sandwiched between the sealed portions of the exterior film 7, and the wound electrode body 6 is sealed in the exterior film 7. Further, the electrode winding body 6 is subjected to heat treatment in a state packed with the exterior film 7. As described above, the gel electrolyte battery 1 is completed.

  When packing the wound electrode body 6 into the exterior film 7, the resin film 10 is arranged at the contact portion between the exterior film 7, the positive electrode terminal 8, and the negative electrode terminal 9, thereby preventing a short circuit due to burrs or the like of the exterior film 7. Moreover, the adhesiveness between the exterior film 7, the positive electrode terminal 8, and the negative electrode terminal 9 is improved.

  The material of the resin film 10 is not particularly limited as long as it exhibits adhesion to the positive electrode terminal 8 and the negative electrode terminal 9, but polyethylene, polypropylene, modified polyethylene, modified polypropylene, copolymers thereof, and the like. It is preferable to use a polyolefin resin. Moreover, it is preferable that the thickness of the said resin film 10 is the range of 20 micrometers-300 micrometers by the thickness before heat sealing | fusion. When the thickness of the resin film 10 is less than 20 μm, the handleability is deteriorated, and when the thickness is more than 300 μm, moisture easily penetrates and it is difficult to maintain the airtightness inside the battery.

In the above mentioned, the belt-shaped positive electrode 2 and the strip-shaped anode 3 are laminated, but further the case of the electrode winding body 6 wound in a longitudinal direction is described as an example, it is limited to Re this However, the present invention can be applied to a case where the rectangular positive electrode 2 and the rectangular negative electrode 3 are laminated to form an electrode laminated body, or when the electrode laminated body is folded alternately.

Furthermore, above mentioned, as the electrolyte interposed between the positive electrode 2 and negative electrode 3 has a case of using a gel electrolyte containing swelling solvent described as an example, it is limited to Re this The present invention is also applicable to the case where a solid electrolyte containing no swelling solvent is used.

  The chemical structure of the solid electrolyte is not particularly limited as long as it exhibits an ionic conductivity of 1 mS / cm or more at room temperature. Examples of such solid electrolytes include polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polysiloxane compounds, polyphosphazene compounds, polypropylene oxide, polymethyl methacrylate, polymethacrylonitrile, polyether compounds, and other inorganic salts. An organic solid electrolyte, an ion conductive ceramic material, an ion conductive glass and the like in which is dissolved.

Gel electrolyte cell 1 as described above, cylindrical, square, coin or the like is not particularly limited as to its shape, also can be thin, the various sizes of the large and the like. The present invention can be applied to both a primary battery and a secondary battery.

<Implementation of the form>
One structural example of the gel electrolyte battery 20 of this Embodiment is shown in FIG.7 and FIG.8. The gel electrolyte battery 20 includes a strip-shaped positive electrode 21, a strip-shaped negative electrode 22 disposed to face the positive electrode 21, a gel electrolyte layer 23 formed on the positive electrode 21 and the negative electrode 22, and a gel electrolyte layer 23. And a separator 24 disposed between the positive electrode 21 and the negative electrode 23 on which the gel electrolyte layer 23 is formed.

  In the gel electrolyte battery 20, a positive electrode 21 on which a gel electrolyte layer 23 is formed and a negative electrode 22 on which a gel electrolyte layer 23 is formed are stacked via a separator 24 and wound in a longitudinal direction. The electrode winding body 25 shown in FIG. 2 is covered and sealed with an exterior film 26 made of an insulating material. A positive electrode terminal 27 is connected to the positive electrode 21, and a negative electrode terminal 28 is connected to the negative electrode 22, and the electrode terminal 27 and the negative electrode terminal 28 are sandwiched between sealing portions that are peripheral portions of the exterior film 26. It is rare. Further, a resin film 29 is disposed in a portion where the positive electrode terminal 27 and the negative electrode terminal 28 are in contact with the exterior film 26.

  As shown in FIG. 10, in the positive electrode 21, a positive electrode active material layer 21a containing a positive electrode active material is formed on a positive electrode current collector 21b. For example, a metal foil such as an aluminum foil is used as the positive electrode current collector 21b.

As the positive electrode active material, a material capable of inserting and releasing cations is used, and a typical example of the ions includes Li ions. Specific examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _{4 and the} like. The transition metal element can be used not only in one type but also in two or more types. More specific examples thereof include _LiNi0.5Co 0.5 _{O 2} or the like.

  For example, the positive electrode active material layer 21a is mixed with a positive electrode active material as described above, a carbon material as a conductive material, and polyvinylidene fluoride as a binder, and N-methylpyrrolidone as a solvent is added to form a slurry. Next, the obtained slurry is uniformly applied on an aluminum foil serving as a positive electrode current collector by a doctor blade method, dried at a high temperature, and N-methylpyrrolidone is blown off.

  Here, the mixing ratio of the positive electrode active material, the conductive material, the binder, and the N-methylpyrrolidone is not particularly limited as long as the mixture is a slurry in which the mixture is uniformly dispersed.

  FIG. 10 shows a state where a gel electrolyte layer 23 described later is formed on the positive electrode active material layer 21 a of the positive electrode 21.

  As shown in FIG. 11, the negative electrode 22 has a negative electrode active material layer 22a containing a negative electrode active material formed on a negative electrode current collector 22b. As the negative electrode current collector 22b, for example, a metal foil such as a copper foil is used.

  Examples of the negative electrode active material include materials capable of inserting and removing Li, such as graphite, non-graphitizable carbon, and graphitizable carbon.

  The negative electrode active material layer 22a is, for example, mixed with a negative electrode active material as described above and polyvinylidene fluoride as a binder, and added with N-methylpyrrolidone as a solvent to form a slurry. Next, the obtained slurry is uniformly applied on a copper foil serving as a negative electrode current collector by a doctor blade method, dried at a high temperature, and N-methylpyrrolidone is blown off.

  Here, the mixing ratio of the negative electrode active material, the binder, and the N-methylpyrrolidone is not particularly limited as long as the mixture is in a slurry form in which the mixture is uniformly dispersed. In addition, the above-described Li insertion / desorption is not limited to taking in and out Li in the crystal structure, and any Li / O battery that can be charged / discharged when used as a battery is regarded as being insertable / desorbable. A Li metal negative electrode, a Li-Al alloy negative electrode, etc. are mentioned.

  FIG. 11 shows a state where a gel electrolyte layer 23 described later is formed on the negative electrode active material layer 22 a of the negative electrode 22.

  The gel electrolyte layer 23 contains an electrolyte salt, a matrix polymer, and a solvent as a plasticizer.

  Examples of the matrix polymer include those that are compatible with a solvent. Examples thereof include polyacrylonitrile, polyethylene oxide polymer, polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, styrene-butadiene rubber, and polymethyl methacrylate. The matrix polymer can be used not only in one type but also in two or more types. In addition, polymers that are not included in the above-described examples and that are compatible with the solvent and become a gel can also be used.

  As the solvent, a solvent that can be dispersed in the matrix polymer is used. Examples of the aprotic solvent include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, dimethoxyethane and the like. In addition, a solvent may use only 1 type or may use 2 or more types.

The electrolyte salt corresponds to one that dissolves in the above solvent. The cations include alkali metals and alkaline earth metals, and the anions include Cl ₋ , Br ₋ , I ₋ , SCN ₋ , ClO ₄₋ , BF ₄₋ , BF ₄₋ , PF ₆₋ , CF ₃ SO ₃₋ , ( CF ₃ SO _{2) 2} N _-, and the like. The electrolyte salt concentration may be any concentration that can be dissolved in a solvent.

  The thickness of the gel electrolyte layer 23 is preferably in the range of 5 μm to 15 μm. If the thickness of the gel electrolyte layer 23 is less than 5 μm, it is impossible to sufficiently prevent a short circuit due to contact between the positive electrode and the negative electrode. Further, if the thickness of the gel electrolyte layer 23 is thicker than 15 μm, there are problems that the high load characteristics are deteriorated and the volume energy density is lowered.

  The separator 24 is disposed between the positive electrode 2 and the negative electrode 3 and prevents a short circuit due to physical contact between the positive electrode 2 and the negative electrode 3. Here, the separator 24 according to the present embodiment is made of a polyethylene-polypropylene composite in which polypropylene is added to polyethylene. By constituting the separator 24 from a polyethylene-polypropylene composite, only the meltdown temperature can be increased while maintaining the shutdown temperature of the separator 24 equivalent to that of the polyethylene separator.

  Specifically, the meltdown temperature of the separator 24 is preferably higher in the range of 10 ° C. or more and 30 ° C. or less than the meltdown temperature of the polyethylene separator. The meltdown temperature referred to here is a temperature at which the shutdown separator 24 melts and breaks.

  When the meltdown temperature of the separator 24 is higher than the meltdown temperature of the polyethylene separator in a range smaller than 10 ° C., the effect of the present invention of increasing the meltdown cannot be sufficiently obtained. The reason why the meltdown temperature of the separator 24 is higher than the meltdown temperature of the polyethylene separator in the range of 30 ° C. or less is that the difference in meltdown temperature between the polypropylene separator and the polyethylene separator is about 30 ° C. It is.

  The thickness of the separator 24 in this embodiment is preferably in the range of 5 μm or more and 15 μm or less. When the thickness of the separator 24 is smaller than 5 μm, it becomes difficult to handle the separator 24 at the time of manufacturing the battery, and the yield of the battery is lowered. On the other hand, when the thickness of the separator 24 is larger than 15 μm, the internal resistance of the battery is increased and the loss of energy density is increased. Therefore, by setting the thickness of the separator 24 in the range of 5 μm or more and 15 μm or less, it is possible to prevent a decrease in battery yield, an increase in internal resistance of the battery, or a loss in energy density.

  The porosity of the separator 24 is preferably 25% or more and 60% or less. When the porosity of the separator 24 is less than 25%, the internal resistance of the battery increases and a predetermined output characteristic cannot be obtained. Moreover, when the porosity of the separator 24 is larger than 60%, it becomes difficult to develop the mechanical strength of the separator 24 itself. Therefore, by setting the porosity of the separator 24 in the range of 25% or more and 60% or less, the mechanical strength of the separator 24 itself can be ensured without increasing the internal resistance of the battery.

  The separator 24 of the present embodiment as described above is manufactured as follows, for example. In the following example, specific numerical values will be described. However, the manufacturing method of the separator 24 is not limited to this. Further, the mixing ratio of polyethylene and polypropylene constituting the separator 24 is not particularly limited.

First, 20% by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight Mw of 2.5 × 10 ⁶ and 30% by weight of high density polyethylene (HDPE) having a weight average molecular weight Mw of 3.5 × 10 ⁵ Then, 0.375 parts by weight of an antioxidant is added to 100 parts by weight of a polyolefin mixture comprising 50% by weight of polypropylene having a weight average molecular weight Mw of 5.1 × 10 ⁵ to obtain a polyolefin composition.

  Next, 30 parts by weight of this polyolefin composition is put into a twin screw extruder (58 mmφ, L / D = 42, strong kneading type). Further, 70 parts by weight of liquid paraffin is supplied from the side feeder of this twin-screw extruder and melt kneaded at 200 rpm to prepare a polyolefin solution in the extruder.

Then, it extrudes at 190 degreeC from T-die installed in the front-end | tip of this extruder, and shape | molds a gel-like sheet | seat, winding up with a cooling roll. Subsequently, this gel-like sheet is subjected to simultaneous biaxial stretching at 115 ° C. in 5 × 5 to obtain a stretched film. The obtained stretched membrane is washed with methylene chloride to extract and remove the remaining liquid paraffin, followed by drying and heat treatment, whereby a microporous separator 24 composed of a composite of polyethylene and polypropylene is obtained.

  Further, the separator 24 of the present embodiment is not only composed of a composite of polyethylene and polypropylene, but also a structure in which a separator 24a made of polyethylene and a separator 24b made of polypropylene are bonded together one by one as shown in FIG. It can also be. By laminating the separator 24a made of polyethylene and the separator 24b made of polypropylene, the shutdown temperature of the separator 24 remains at the polyethylene temperature, and the meltdown temperature of the separator 24 can be increased to the meltdown temperature of polypropylene.

  The separator 24 has a configuration in which a separator 24a made of polyethylene and a separator 24b made of polypropylene are bonded to each other. When three or more separators are stacked, the separator thickness increases and the internal resistance of the battery increases. Another disadvantage is that the loss of energy density increases. Therefore, by making the separator 24a made of polyethylene and the separator 24b made of polypropylene one by one, the separator thickness can be made as thin as possible to obtain the maximum effect.

  In the case where the separator 24 is laminated as described above, a total film in which two separators 24a and polypropylene 24b are laminated in a thickness range of 2.5 μm to 7.5 μm. The thickness is preferably in the range of 5 μm to 15 μm. When the thickness of the separator 24 is smaller than 5 μm, it becomes difficult to handle the separator 24 at the time of manufacturing the battery, and the yield of the battery is lowered. On the other hand, when the thickness of the separator 24 is larger than 15 μm, the internal resistance of the battery is increased and the loss of energy density is increased. Therefore, by setting the thickness of the separator 24 in the range of 5 μm or more and 15 μm or less, it is possible to prevent a decrease in battery yield, an increase in internal resistance of the battery, or a loss in energy density.

As shown in FIG. 13, the separator 24 of the present embodiment having the above-described configuration needs to be wider than the positive electrode 22 and the negative electrode 23. When the positive electrode 22, the negative electrode 23, and the separator 24 are overlapped and wound, the positive electrode 22, the negative electrode 23, and the separator 24 may be displaced. As shown in FIG. 13, when L ₁ and L ₂ are the shift amounts in the width direction when the positive electrode 22 and the negative electrode 23 and the separator 24 are overlapped, L ₁ <0 or L ₂ <0, that is, the separator When the end portion of 24 is inside the end portion of the positive electrode 22 or the negative electrode 23, the positive electrode 22 and the negative electrode 23 come into contact with each other, an internal short circuit occurs, and the yield of manufacturing the battery decreases.

Therefore, when winding the positive electrode 22, the negative electrode 23, and the separator 24 in an overlapped manner, the width of the separator 24 is made larger than that of the positive electrode 22 and the negative electrode 23 so that the positive electrode 22 and the negative electrode 23 do not contact each other even if a deviation occurs. It needs to be somewhat wide. However, if the width of the separator 24 is too wide, the energy density of the battery is lowered. In view of the above, in FIG. 13, if the width of the separator 24 is determined so that L ₁ > 0.5 mm, L ₂ > 0.5 mm, and L ₁ + L ₂ <4 mm. Good. By making the width of the separator 24 as described above, even if a winding deviation occurs between the positive electrode 22, the negative electrode 23, and the separator 24, an internal short circuit due to contact between the positive electrode 22 and the negative electrode 23 is prevented, and the yield is increased. Can keep.

  The gel electrolyte battery 20 according to the present embodiment using the separator 24 as described above is manufactured through the following steps.

  First, as the positive electrode 21, a positive electrode active material containing a positive electrode active material and a binder is uniformly applied onto a metal foil such as an aluminum foil, which becomes the positive electrode current collector 21 b, and dried, thereby drying the positive electrode active material. The layer 21a is formed to produce a positive electrode 2 sheet. As the binder of the positive electrode mixture, a known binder can be used, and a known additive or the like can be added to the positive electrode mixture.

  Next, the gel electrolyte layer 23 is formed on the positive electrode active material layer 21a of the positive electrode sheet. In order to form the gel electrolyte layer 23, first, an electrolyte salt is dissolved in a non-aqueous solvent to prepare a non-aqueous electrolyte. Then, a matrix polymer is added to this non-aqueous electrolyte, and the mixture is well stirred to dissolve the matrix polymer to obtain a sol electrolyte solution.

  Next, a predetermined amount of this electrolyte solution is applied onto the positive electrode active material layer 21a. Subsequently, the matrix polymer is gelled by cooling at room temperature, and the gel electrolyte layer 23 is formed on the positive electrode active material 21a.

  Next, the positive electrode sheet on which the gel electrolyte layer 23 is formed is cut into a strip shape. Then, for example, an aluminum lead wire is welded to the non-formed portion of the positive electrode active material layer 21 a of the positive electrode current collector 21 b to form the positive electrode terminal 27. In this way, a belt-like positive electrode 21 in which the gel electrolyte layer 23 is formed is obtained.

  In addition, the negative electrode 22 is formed by uniformly applying and drying a negative electrode mixture containing a negative electrode active material and a binder on a metal foil such as a copper foil to be the negative electrode current collector 22b. 22a is formed and a negative electrode sheet is produced. As the binder of the negative electrode mixture, a known binder can be used, and a known additive or the like can be added to the negative electrode mixture.

  Next, the gel electrolyte layer 4 is formed on the negative electrode active material layer 22b of the negative electrode sheet. In order to form the gel electrolyte layer 23, first, an electrolyte solution prepared in the same manner as described above is applied on the negative electrode active material layer in a predetermined amount. Subsequently, the matrix polymer is gelled by cooling at room temperature, and the gel electrolyte layer 23 is formed on the negative electrode active material 22b.

  Next, the negative electrode sheet on which the gel electrolyte layer 4 is formed is cut into a strip shape. Then, a lead wire made of, for example, nickel is welded to the non-formation portion of the negative electrode active material layer 22a of the negative electrode current collector 22b to form the negative electrode terminal 28. Thus, the strip-shaped negative electrode 3 having the gel electrolyte layer 23 formed thereon is obtained.

  The strip-shaped positive electrode 21 and negative electrode 22 produced as described above are pressed with the separator 24 disposed between the positive electrode 21 and the negative electrode 22 with the side on which the gel electrolyte layer 23 is formed facing each other. The electrode laminate is used. Further, this electrode laminate is wound in the longitudinal direction to form an electrode winding body 25.

  Finally, the electrode winding body 25 is sandwiched between outer packaging films 26 made of an insulating material, and a resin film 29 is disposed on a portion where the positive electrode terminal 27 and the negative electrode terminal 28 overlap the outer packaging film 26. Then, the outer peripheral edge of the exterior film 26 is sealed, the positive electrode terminal 27 and the negative electrode terminal 28 are sandwiched between the sealed portions of the exterior film 26, and the wound electrode body 25 is sealed in the exterior film 26. As described above, the gel electrolyte battery 20 is completed.

  Here, for example, as shown in FIG. 14, the exterior film 26 includes a first polyethylene terephthalate layer 26a, an aluminum layer 26b, a second polyethylene terephthalate layer 26c, and a linear low-density polyethylene layer 26d. They are laminated in order. Here, the linear low-density polyethylene layer 26d serves as a heat-sealing layer, and when the electrode winding body 25 is sealed, the linear low-density polyethylene layer 26d serves as an inner side. In addition to the linear low density polyethylene, polyethylene terephthalate, nylon, cast polypropylene, high density polyethylene, and the like can be used as the material for the heat fusion layer.

  The configuration of the exterior film 26 is not limited to the above-described one, and at least one aluminum layer is included in the layer, and the heat-fusible polymer film is present on at least one surface. Just do it.

  Further, when the electrode winding body 25 is packed in the exterior film 26, the resin film 29 is disposed at the contact portion between the exterior film 26 and the positive electrode terminal 27 and the negative electrode terminal 28, thereby causing a short circuit due to burrs or the like of the exterior film 26. In addition, adhesion between the exterior film 26 and the positive and negative terminals 27 and 28 is improved.

  The material of the resin film 29 is not particularly limited as long as it exhibits adhesion to the positive electrode terminal 17 and the negative electrode terminal 18, but polyethylene, polypropylene, modified polyethylene, modified polypropylene, and copolymers thereof, etc. It is preferable to use a polyolefin resin. Moreover, it is preferable that the thickness of the said resin film 29 is the range of 20 micrometers-300 micrometers by the thickness before heat sealing | fusion. When the thickness of the resin film 29 is less than 20 μm, the handleability is deteriorated, and when the thickness is more than 300 μm, moisture easily penetrates and it is difficult to maintain the airtightness inside the battery.

  In the above-described embodiment, the case where the belt-like positive electrode 21 and the belt-like negative electrode 22 are stacked and wound in the longitudinal direction to form the electrode winding body 25 has been described as an example. The present invention is not limited to this, and the present invention can also be applied to a case where the rectangular positive electrode 21 and the rectangular negative electrode 22 are laminated to form an electrode laminated body, or when the electrode laminated body is folded alternately.

  Furthermore, in the above-described embodiment, the case where a gel electrolyte containing a matrix polymer, an electrolyte salt, and a solvent is used as the electrolyte interposed between the positive electrode 21 and the negative electrode 22 has been described as an example. The present invention is not limited to this, and can also be applied to the case where a solid electrolyte not containing a solvent is used or the case where an electrolyte containing no matrix polymer is used.

  The gel electrolyte battery 20 of the present embodiment as described above is not particularly limited with respect to its shape, such as a cylindrical shape, a square shape, a coin shape, and the like, and has various sizes such as a thin shape and a large size. be able to. The present invention can be applied to both a primary battery and a secondary battery.

In order to confirm the effect of the present invention, a battery having the above-described configuration was produced and its characteristics were evaluated.
· In the first experiment Reference Example 1 to Reference Example 8 below, to prepare a battery using a separator made in Reference Example, and evaluate its characteristics.

Preparation of sample battery < Reference Example 1>
First, a positive electrode was produced as follows.

  First, commercially available lithium carbonate and cobalt carbonate are mixed so that the composition ratio of lithium atoms and cobalt atoms is 1: 1, and are fired in air at 900 ° C. for 5 hours, thereby forming cobalt as a positive electrode active material. Lithium acid was obtained. Here, the average particle diameter of this lithium cobaltate was 10 μm.

  Next, 91 parts by weight of the obtained positive electrode active material, 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder were mixed to obtain a positive electrode mixture. Furthermore, this positive electrode mixture was dispersed in N-methyl-2-pyrrolidone serving as a solvent to form a paste.

Next, the obtained positive electrode mixture paste was uniformly applied to both surfaces of a 20 μm-thick strip-shaped aluminum foil serving as a positive electrode current collector, and then subjected to a drying treatment. After drying, a positive electrode active material layer having a thickness of 40 μm was formed by compression molding with a roller press. Furthermore, an aluminum lead was welded to a portion where the positive electrode active material layer of the positive electrode current collector was not formed to form a positive electrode terminal, thereby producing a positive electrode. The density of the positive electrode active material layer at this time was 3.6 g / cm ³ .

  Next, a negative electrode was produced as follows.

  First, mesocarbon microbeads having an average particle size of 25 μm were fired at 2800 ° C. to obtain graphite as a negative electrode active material.

  Next, 90 parts by weight of the obtained negative electrode active material and 10 parts by weight of polyvinylidene fluoride as a binder were mixed to obtain a negative electrode mixture. Furthermore, this negative electrode mixture was dispersed in N-methyl-2-pyrrolidone serving as a solvent to form a paste.

Next, the obtained negative electrode mixture paste was uniformly applied to both surfaces of a 15 μm-thick strip-shaped copper foil serving as a negative electrode current collector, and then subjected to a drying treatment. After drying, the negative electrode active material layer having a thickness of 55 μm was formed by compression molding with a roller press. Furthermore, a nickel lead was welded to a portion where the negative electrode active material layer of the negative electrode current collector was not formed to form a positive electrode terminal, thereby producing a negative electrode. At this time, the density of the negative electrode active material layer was 1.6 g / cm ³ .

Next, a gel electrolyte layer was formed on the positive electrode and the negative electrode as follows.
First, 80 g of dimethyl carbonate, 40 g of ethylene carbonate, 40 g of propylene carbonate, 9.2 g of LiPF ₆ , 0.8 g of vinylene carbonate, and 0.8 g of 2,4-difluoroanisole are mixed. 10 g of a copolymer of polyvinylidene fluoride (PVdF) and hexafluoropropylene (HFP) (copolymerization weight ratio PVdF: HFP = 97: 3) is added to the solution obtained and dispersed uniformly with a homogenizer. Then, the mixture was further heated and stirred at 75 ° C. until it became colorless and transparent to obtain an electrolyte solution.
Next, the obtained electrolyte solution was uniformly applied to both surfaces of the positive electrode and the negative electrode by a doctor blade method. Thereafter, the positive electrode and the negative electrode coated with the electrolyte solution are placed in a dryer maintained at a temperature of 40 ° C. for 1 minute to gel the electrolyte solution. An 8 μm gel electrolyte layer was formed.

  Next, the battery was assembled as follows.

First, a belt-like positive electrode having a gel electrolyte layer formed on both sides and a belt-like negative electrode having a gel electrolyte layer formed on both sides, prepared as described above, are laminated via a separator to form a laminate, Furthermore, this laminated body was wound in the longitudinal direction to obtain an electrode winding body. Here, as the separator, a polyethylene porous film having a porosity of 36% and a thickness of 8 μm was used.
Next, the wound electrode body is sandwiched between a moisture-proof exterior film in which 25 μm-thick nylon, 40 μm-thick aluminum, and 30 μm-thick polypropylene are laminated in order from the outermost layer, and the outer peripheral edge of the exterior film is decompressed. Sealing was performed by heat-sealing underneath, and the electrode winding body was sealed in an exterior film. At this time, the positive electrode terminal and the negative electrode terminal were sandwiched between the sealing portions of the exterior film, and a polyolefin film was disposed at a contact portion between the exterior film, the positive electrode terminal, and the negative electrode terminal.

Finally, the electrode element was subjected to a heat treatment while being sealed with the exterior film. In this way, a gel electrolyte battery was completed.
< Reference Example 2>
A gel electrolyte battery was produced in the same manner as in Reference Example 1 except that a polyethylene porous membrane having a porosity of 37% and a thickness of 9 μm was used as the separator.
< Reference Example 3>
A gel electrolyte battery was produced in the same manner as in Reference Example 1 except that a polyethylene porous membrane having a porosity of 35% and a thickness of 10 μm was used as the separator.
< Reference Example 4>
A gel electrolyte battery was produced in the same manner as in Reference Example 1 except that a polyethylene porous membrane having a porosity of 30% and a thickness of 12 μm was used as the separator.
< Reference Example 5>
A gel electrolyte battery was produced in the same manner as in Reference Example 1 except that a polyethylene porous membrane having a porosity of 39% and a thickness of 15 μm was used as the separator.
< Reference Example 6>
A gel electrolyte battery was produced in the same manner as in Reference Example 1 except that a polypropylene porous membrane having a porosity of 36% and a thickness of 8 μm was used as the separator.
< Reference Example 7>
A gel electrolyte battery was produced in the same manner as in Reference Example 1 except that a polypropylene multi-membrane having a porosity of 36% and a thickness of 16 μm was used as the separator.
< Reference Example 8 >
A gel electrolyte battery was produced in the same manner as in Reference Example 1 except that no separator was used.

Table 1 summarizes the materials, porosity, thickness, breaking strength, and breaking elongation of the separators used in Reference Examples 1 to 8 for evaluating characteristics of the sample batteries.

-Charging / discharging characteristic evaluation And about the battery produced as mentioned above, the charging / discharging test was done and the battery characteristic was evaluated. Here, in the charge / discharge test of the battery, a potentiogalvanostat was used, and charge / discharge was performed by a constant current constant voltage method.

  First, constant current charging was performed on each battery at 200 mA. When the closed circuit voltage reached 4.2 V, switching from constant current charging to constant voltage charging was performed, and constant voltage charging was continued. The end of charging was 9 hours after the start of charging. Subsequently, discharge was performed under a constant current condition of 200 mA, and the discharge was terminated when the closed circuit voltage reached 3.0V.

  And charge capacity and discharge capacity were calculated | required about each battery, and also charge / discharge efficiency and energy density were computed.

Table 2 shows the charge capacity, discharge capacity, charge / discharge efficiency, and energy density obtained for the batteries of Reference Examples 1 to 8 .

From Table 2, the battery of Reference Example 1 to Reference Example 7, the charge capacity, discharge capacity, charge and discharge efficiency and any and good values are obtained for the energy density, and provides excellent characteristics as designed I found out. In the battery of Reference Example 1 to Reference Example 5 using a separator made of polyethylene Among them, it was found that particularly good properties are obtained.

On the other hand, in the battery of Reference Example 8 , a tendency of being short-circuited during charging was observed, and good battery characteristics were not recognized.
Sample Battery safety evaluation Regarding the battery of Reference Example 1 to Reference Example 8, was examined and shutdown initiation point temperature of the separator, and a maximum value of battery surface temperature when the external short circuit the battery.

  As the measurement of the shutdown temperature, the battery was heated at a temperature rising rate of 5 ° C./min, and the battery temperature at the time when the AC resistance value when applying 1 kHz increased by two digits or more was measured.

  In addition, as a measurement of the battery surface temperature when the battery is externally short-circuited, first, the battery is charged under the same conditions as in the above-described charge / discharge test, and the battery is heated to 60 ° C. The maximum value of the battery surface temperature when short-circuited using the resistance of was measured using a thermocouple.

Table 3 shows the shutdown temperature and the battery surface temperature during external short-circuiting for the batteries of Reference Examples 1 to 8 .

As is apparent from Table 3, the battery of Reference Example 1 to Reference Example 5 using a separator made of polyethylene, the shutdown was observed at a temperature in the range of 100 ° C. to 160 ° C.. FIG. 15 shows the relationship between the battery temperature and the battery internal impedance for the battery of Reference Example 1. From FIG. 15, it can be seen that the battery internal impedance rapidly increases around the battery temperature of 126 ° C.

The batteries of Reference Example 6 and Reference Example 7 using a separator made of polypropylene were also 160 ° C. or higher, but shutdown was recognized. FIG. 16 shows the relationship between the battery temperature and the battery internal impedance for the battery of Reference Example 6. From FIG. 16, it can be seen that the battery internal impedance suddenly increases when the battery temperature is around 163 ° C.

Further, the battery of Reference Example 1 to Reference Example 5, not more than the battery surface temperature 120 ° C. in the case of by external short circuit a charged battery, to effectively suppress heat generation when a battery is misused It was confirmed that the safety of the battery was ensured. On the other hand, in the batteries of Reference Example 6 and Reference Example 7, when the charged battery was externally short-circuited, the battery surface temperature was 160 ° C. or higher, and a tendency to generate heat when the battery was misused was observed. . In addition, about the battery of the reference example 1-the reference example 7 by which shutdown was recognized, when the charged battery was externally short-circuited, the smoke from the battery inside was not recognized in any case.

On the other hand, in the battery of Reference Example 8 , shutdown was not observed even when the battery temperature reached 180 ° C. Moreover, when the charged battery was short-circuited externally, the battery surface temperature reached a maximum of 200 ° C., and smoke was observed from the inside of the battery.
Separator of the physical properties of the specified addition, the separator used in the battery of Reference Example 1 to Reference Example 7, shown in Figure 17 the relationship between the breaking strength and breaking elongation. 17 and the battery characteristics evaluation results described above, particularly good separator used in the battery of Reference Example 1 to Reference Example 5 in which battery characteristics are obtained, both, breaking strength is less than 1650kg / cm ^2, And it turned out that it has the mechanical strength of the range whose breaking elongation is 135% or more.

It has been confirmed that all the separators having the mechanical strength in the above range have a fibril structure as shown in FIG. FIG. 18 shows an electron micrograph of the separator microstructure used in Reference Example 6 taken at a magnification of 50000 times. By comparing FIG. 6 and FIG. 18, the mechanical strength of the separator is related to its microstructure, and in order to satisfy the mechanical strength in the above range, the separator microstructure needs to be a fibril structure. It can be seen that it is.

  From the above results, the battery temperature has a thickness in the range of 5 μm to 15 μm, a porosity in the range of 25% to 60%, and a range of 100 ° C. to 160 ° C. It was found that the use of a polyolefin porous membrane exhibiting a shutdown effect as a separator makes it possible to achieve both high energy density and safety of the battery.

Further, the thickness is in the range of 5 μm or more and 15 μm or less, the porosity is in the range of 25% or more and 60% or less, the breaking strength is less than 1650 kg / cm ² , and the elongation at break It has been found that by using a polyolefin porous membrane having a mechanical strength in the range of 135% or more as a separator, it is possible to achieve both high energy density and safety of the battery.
Second Experiment In Example 1 , Example 2, and Comparative Example 1 shown below, a battery is manufactured using the separator according to the second embodiment, and its characteristics are evaluated.
<Example 1 >
In order to produce a positive electrode, first, 95% by weight of LiCoO ₂ as a positive electrode active material, ₂ % by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder are mixed to form a positive electrode mixture. did. Furthermore, N-methylpyrrolidone was added in an amount 0.6 times that of the positive electrode mixture to form a slurry.

  Next, the obtained slurry was uniformly applied to one side of an aluminum foil serving as a positive electrode current collector by a doctor blade method, dried at a high temperature, and N-methylpyrrolidone was blown to form a positive electrode active material layer. Finally, it was pressed using a roll press machine with an appropriate pressure and cut into a size of 300 mm × 50 mm to produce a positive electrode. This positive electrode was spot-welded with rod-shaped aluminum to obtain a positive electrode terminal.

  In order to produce the negative electrode, first, 91% by weight of graphite as a negative electrode active material and 9% by weight of polyvinylidene fluoride as a binder were mixed to form a negative electrode mixture. Furthermore, N-methylpyrrolidone was added in an amount 1.1 times that of the negative electrode mixture to form a slurry.

  Next, the obtained slurry was uniformly applied to one side of a copper foil serving as a negative electrode current collector by a doctor blade method, dried at a high temperature, and N-methylpyrrolidone was blown to form a negative electrode active material layer. Finally, it was pressed by applying a suitable pressure using a roll press machine, and cut into 370 mm × 52 mm to produce a negative electrode. This negative electrode was spot welded with rod-shaped copper to obtain a negative electrode terminal.

Meanwhile, 6.7% by weight of polyvinylidene fluoride, 9.2% by weight of ethylene carbonate, 11.6% by weight of propylene carbonate, 2.3% by weight of γ-butyrolactone, and 6.67 of dimethyl carbonate. A polyelectrolyte solution was prepared by mixing 5% by weight and 3.5% by weight of LiPF ₆ . Dimethyl carbonate is used as a solvent for dissolving polyvinylidene fluoride.

  The obtained polymer electrolyte solution was applied in a liquid state on the positive electrode and the negative electrode using a doctor blade method, dried in a thermostatic bath at 35 ° C. for 3 minutes, and formed into a thin film. At that time, dimethyl carbonate does not remain in the polymer electrolyte. The polymer electrolyte on the positive electrode and the negative electrode was applied so that the thickness was 10 μm.

  As the separator, a 10 μm thick separator made of a composite of polyethylene and polypropylene was used. The ratio of polyethylene to polypropylene in the composite is 1: 1. In addition, this composite separator was produced as follows.

First, 20% by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight Mw of 2.5 × 10 ⁶ and 30% by weight of high density polyethylene (HDPE) having a weight average molecular weight Mw of 3.5 × 10 ⁵ A polyolefin composition was prepared by adding 0.375 parts by weight of an antioxidant to 100 parts by weight of a polyolefin mixture comprising 50% by weight of polypropylene having a weight average molecular weight Mw of 5.1 × 10 ⁵ .

  Next, 30 parts by weight of this polyolefin composition was put into a twin screw extruder (58 mmφ, L / D = 42, strong kneading type). Further, 70 parts by weight of liquid paraffin was supplied from the side feeder of this twin-screw extruder, and melt-kneaded at 200 rpm to prepare a polyolefin solution in the extruder.

  Subsequently, a gel-like sheet was formed while being extruded at 190 ° C. from a T die installed at the tip of the extruder and wound up with a cooling roll. Subsequently, this gel-like sheet was subjected to simultaneous biaxial stretching at 115 ° C. in 5 × 5 to obtain a stretched film. The obtained stretched membrane was washed with methylene chloride to extract and remove the remaining liquid paraffin, followed by drying and heat treatment to obtain a microporous separator composed of a composite of polyethylene and polypropylene.

  Then, the belt-shaped positive electrode formed with the gel electrolyte layer and the belt-shaped negative electrode formed with the gel electrolyte layer, which are produced as described above, are laminated via a separator to form a laminate, and this laminate Was wound in the longitudinal direction to obtain an electrode wound body of 36 mm × 52 mm × 5 mm.

Next, the electrode winding body is sandwiched between outer packaging films made of a moisture-proof multilayer film having a thickness of 100 μm, and the outer peripheral edge of the outer packaging film is sealed by heat-sealing under reduced pressure. Sealed inside. At this time, the positive electrode terminal and the negative electrode terminal were sandwiched between the sealing portions of the exterior film.
<Example 2 >
A battery was fabricated in the same manner as in Example 1 except that a separator obtained by laminating a 5 μm thick polyethylene separator and a 5 μm thick polypropylene separator was used as the separator.
<Comparative Example 1 >
A battery was fabricated in the same manner as in Example 1 except that a polyethylene separator having a thickness of 10 μm was used as the separator.

  The battery produced as described above was charged / discharged several times, put in a thermostatic chamber in a discharged state, and while measuring resistance at 1 kHz, 140 ° C., 145 ° C., 150 ° C., respectively, at a heating rate of 5 ° C./min. The temperature was raised to 155 ° C., 160 ° C., 165 ° C., and 170 ° C. and held at that temperature for 30 minutes. When the resistance did not drop while maintaining the predetermined temperature, it was determined that no short circuit occurred, and when the resistance decreased, it was determined that the short circuit occurred.

  The results are shown in Table 4.

In the battery of Example 1 and Example 2 using a separator made of a polyethylene-polypropylene composite as a separator or a laminated separator of a polyethylene separator and a polypropylene separator, compared to the battery of Comparative Example 1 using a polyethylene single separator, It can be seen that the meltdown temperature has increased by about 15 ° C. And since the battery using a separator with a high meltdown temperature has an internal short circuit start temperature due to the meltdown, even when the battery temperature rises, it is less likely to cause an internal short circuit than the polyethylene separator. It was confirmed that it can be suppressed.

  In addition, the prepared new battery was charged and discharged for several cycles. After that, it was placed in a high-temperature bath in an overcharged state of 4.4 V, and the temperature was raised to 135 ° C., 140 ° C., 145 ° C., 150 ° C., and 155 ° C., respectively, at a temperature rising rate of 5 ° C./min. Held at that temperature for 30 minutes. When the resistance did not drop while maintaining the predetermined temperature, it was determined that no short circuit occurred, and when the resistance decreased, it was determined that the short circuit occurred. In this case, since the voltage is above 4.4V, heat may be generated due to a short circuit. Therefore, the measurement was finished when it was confirmed that the resistance was lowered.

  The results are shown in Table 5.

In the batteries of Example 1 and Example 2 using a separator made of a polyethylene-polypropylene composite as a separator or a laminated separator of a polyethylene separator and a polypropylene separator, even under an abnormal situation of 4.4 V overcharge, It can be seen that the meltdown temperature is increased by about 15 ° C. compared to the battery of Comparative Example 1 using a single separator. And since the battery using a separator with a high meltdown temperature has an internal short circuit start temperature due to the meltdown, even when the battery temperature rises, it is less likely to cause an internal short circuit than the polyethylene separator. It was confirmed that it can be suppressed.

It is a perspective view which shows one structural example of the solid electrolyte battery of this invention. In FIG. 1, it is sectional drawing in the XY line. It is a perspective view which shows the state by which the positive electrode and the negative electrode were made into the electrode winding body. It is a perspective view which shows one structural example of a positive electrode. It is a perspective view which shows one structural example of a negative electrode. It is the photograph which showed the fibril structure of the separator based on this invention. It is a perspective view which shows one structural example of the solid electrolyte battery of this invention. In FIG. 7, it is sectional drawing in the XY line. It is a perspective view which shows the state by which the positive electrode and the negative electrode were made into the electrode winding body. It is a perspective view which shows one structural example of a positive electrode. It is a perspective view which shows one structural example of a negative electrode. It is sectional drawing which shows one structural example of the separator which concerns on this invention. It is the schematic diagram which showed the relationship between the width | variety of a separator, and the width | variety of an electrode. It is sectional drawing which shows one structural example of an exterior film. It is the figure which showed the relationship between battery temperature and battery internal impedance about the battery of the reference example 1. FIG. It is the figure which showed the relationship between battery temperature and battery internal impedance about the battery of the reference example 6. FIG. The separator used in the battery of Reference Example 1 to Reference Example 7, a diagram showing the relationship between the breaking strength and breaking elongation. 4 is a photograph showing a fibril structure of a separator used in the battery of Reference Example 6.

1,20 gel electrolyte battery, 2,21 positive electrode, 3,22 negative electrode, 4,23 gel electrolyte layer, 5,24 separator, 6,25 electrode winding body, 7,26 exterior film, 8,27 positive electrode terminal, 9 , 28 Negative terminal, 10,29 Resin film

Claims (4)

A positive electrode, a negative electrode disposed opposite to the positive electrode, a separator disposed between the positive electrode and the negative electrode, and interposed between the positive electrode and the separator and between the separator and the negative electrode. And a gel electrolyte containing a swelling solvent,
The separator consists of a complex of polyethylene and polypropylene, is 5μm or more in thickness, 15 [mu] m Ri following ranges der, meltdown temperature, 10 ° C. or higher than the meltdown temperature of the separator made of polyethylene, 30 ° C. or less The breaking strength is less than 1650 kg / cm ² and the elongation at break is 135% or more,
Examples of the swelling solvent include ethylene carbonate, propylene carbonate, γ-butyrolactone, acetonitrile, diethyl ether, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, dimethyl sulfoxide, 1,3-dioxolane, methyl sulfomate, 2 A lithium secondary battery containing at least one member selected from the group consisting of methyltetrahydrofuran, tetrahydrofuran, sulfolane, 2,4-difluoroanisole, and vinylene carbonate. The gel electrolyte includes a matrix polymer, the mixing ratio of the matrix polymer and the swelling solvent is in a weight ratio of matrix polymer: swelling solvent = 1: 5 or more, 1: the 請 Motomeko 1, wherein in the range of 10 or less Lithium secondary battery . A positive electrode, a negative electrode disposed opposite to the positive electrode, a separator disposed between the positive electrode and the negative electrode, and interposed between the positive electrode and the separator and between the separator and the negative electrode. And a gel electrolyte containing a swelling solvent,
Separator The separator includes a first separator made of polyethylene, will be bonded together and the second separator made of polypropylene, 5μm or more thickness, Ri following ranges der 15 [mu] m, meltdown temperature, of polypropylene and have the same or the like, the breaking strength is less than 1650kg / cm ^2, and is the elongation at break of 135% or more,
Examples of the swelling solvent include ethylene carbonate, propylene carbonate, γ-butyrolactone, acetonitrile, diethyl ether, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, dimethyl sulfoxide, 1,3-dioxolane, methyl sulfomate, 2 A lithium secondary battery containing at least one member selected from the group consisting of methyltetrahydrofuran, tetrahydrofuran, sulfolane, 2,4-difluoroanisole, and vinylene carbonate. The gel electrolyte includes a matrix polymer, the mixing ratio of the matrix polymer and the swelling solvent is in a weight ratio of matrix polymer: swelling solvent = 1: 5 or more, 1: the 請 Motomeko 3, wherein the range of 10 or less Lithium secondary battery .

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