JP2013218926A - Separator and lithium-ion secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery excellent in high-temperature storage characteristics and a separator therefor.SOLUTION: The separator according to the present invention is provided with a solid electrolyte layer on a porous film. The solid electrolyte layer contains inorganic particles having an average particle diameter of 0.05-2 μm. The separator has a total film thickness of 15 μm or less and such a flatness that the ratio of the roughness Ra of the separator to the total film thickness T of the separator satisfies 0<Ra/T<0.05.

Description

  The present invention relates to a separator and a lithium ion secondary battery using the separator.

  At present, various types of batteries are widely used from the field of electronics to automobile applications or large batteries intended for power storage.

  In particular, a large-scale power storage system is indispensable as a distributed power system represented by the word “smart grid” is becoming popular for the future denuclearization and construction of a clean energy society. Therefore, large-capacity large-sized batteries constituting this system are increasingly important.

  Liquid is used for the electrolyte of such a large battery. However, if the electrolyte can be made solid, liquid leakage can be prevented and a sheet structure can be formed. For this reason, the battery using a solid electrolyte like patent document 1 attracts attention as a next-generation type battery. As for the solid electrolyte, an electrolyte which is opposed to an electrolyte material which is a liquid usually used in a battery or an electrochemical element, and which allows ion movement (ionic conductivity) while maintaining a solid state is shown.

  In the case of using such a solid electrolyte, a ceramic material, a polymer material, or a material obtained by combining them has been proposed. Among these, a plasticized gel electrolyte using a polymer electrolyte and an electrolytic solution has both high liquid conductivity and high polymer plasticity, and has been regarded as promising for electrolyte development. This solid electrolyte (hereinafter referred to as a solid electrolyte) maintains a solid state as a whole, but it is presumed that the matrix exists in a state close to a liquid in the molecular level region. It is considered that the mobility (conductivity) of ions is increased.

  However, general solid electrolytes often require further improvements in terms of storage characteristics at high temperatures.

On the other hand, even in the case of a battery using a liquid electrolyte, in recent years, there has been a demand for further thinning and high capacity, and further improvement is desired. Under such circumstances, it is becoming necessary to make the separator thinner and to increase the porosity for improving the characteristics for stationary batteries for smart grids and large-sized batteries for industrial applications.
However, with the use of a thin separator with a high porosity, naturally, the distance between the electrodes is shortened, and the influence of variations in the distance between the electrodes is also increased. As a result, a local battery reaction between the electrodes proceeds, or mobile ions in the positive electrode material or the negative electrode material affect the storage characteristics at high temperatures. In particular, a battery that needs to maintain long-term battery characteristics, such as a large battery typified by a stationary battery, may cause significant deterioration.

JP 2000-123633 A

  An object of the present invention is to provide a battery excellent in high-temperature storage characteristics and a separator therefor.

  The separator according to the present invention is a separator provided with a solid electrolyte layer on a porous film, and the solid electrolyte layer contains inorganic particles having an average particle diameter of 0.05 to 2 μm, and the total of the separators. The thickness of the separator is 15 μm or less, and the flatness of the separator is 0 <Ra / T <0.05 as a ratio of the roughness Ra of the separator to the total thickness T of the separator. To do.

  By setting it as such a structure, it becomes a separator which can provide the battery excellent in the high temperature storage characteristic.

The flatness is determined by randomly selecting an area of 100 mm × 100 mm on the surface of the separator, that is, the surface of the solid electrolyte layer, and scanning the micro area in the area using a surface roughness meter. The film thickness of was measured. Specifically, the four corners of this square, the intersections of diagonal lines, and the midpoint area of each side are measured at a total of nine points, and the maximum thickness T _{max of the} separator (of the total film thickness of the separator) maximum and thickness _{T max)} and the minimum thickness _{T min,} defined as the roughness _{Ra =} T max _{-T min,} to evaluate the flatness by Ra / T using the value. Note that T is an average value calculated from the thickness of the obtained separator.

  According to such a separator, by interposing a solid electrolyte layer, a more uniform state can be realized in the separator, a local battery reaction between electrodes can be suppressed, and the mobility of mobile ions can also be reduced. Estimated. As a result, it is considered that the storage characteristics at high temperatures can be improved.

  Furthermore, the separator according to the present invention is stronger than the prior art and can be thinned to 10 μm or less. In this case, the solid electrolyte preferably has a film thickness of 5 μm or less, particularly 2 μm or less.

  The inorganic particles are preferably at least one of calcium carbonate, talcite, and barium titanate.

  The solid electrolyte layer preferably contains any one selected from polyvinylidene fluoride, butadiene rubber, epoxy resin, polyamideimide, and polyimide.

  Furthermore, the porous film preferably has a porosity of 50% or more.

  The separator according to the present invention is preferably a lithium ion secondary battery including the separator described above. According to such a lithium ion secondary battery, a battery having excellent high-temperature storage characteristics can be provided.

  The separator and the lithium ion secondary battery according to the present invention can provide a battery having excellent high-temperature storage characteristics.

It is a cross-sectional schematic diagram of the lithium ion secondary battery of this embodiment. It is a cross-sectional schematic diagram of the separator of this embodiment.

  Exemplary embodiments of a lithium ion secondary battery according to the present invention will be explained below in detail with reference to the accompanying drawings. However, the lithium ion secondary battery of the present invention is not limited to the following embodiments. In addition, the dimensional ratio of drawing is not restricted to the ratio of illustration.

  FIG. 1 schematically shows a lithium ion secondary battery 100 of the present embodiment. A lithium ion secondary battery 100 in FIG. 1 includes a positive electrode 20 and a negative electrode 30 containing materials (positive electrode active material and negative electrode active material) that occlude and release lithium ions, and a separator 10 between the positive electrode and the negative electrode. ing. The positive electrode 20 is configured with a positive electrode active material layer 24 on one side of a positive electrode current collector 22, and the negative electrode 30 is configured with a negative electrode active material layer 34 on one side of a negative electrode current collector 32. . The separator 10 has a configuration in which a solid electrolyte layer 12 is formed on a porous film 14.

  Moreover, the separator 10 of this embodiment is a separator of the two-layer structure provided with the solid electrolyte layer 12 on the porous film 14, as shown in FIG. The solid electrolyte layer 12 contains inorganic particles and a binder.

  Further, the solid electrolyte layer contains inorganic particles having an average particle diameter of 0.05 to 2 μm, and the total film thickness of the separator, that is, the total film thickness of the porous film and the solid electrolyte layer is 15 μm. The flatness of the separator is characterized by 0 <Ra / T <0.05 as the ratio of the roughness Ra of the separator to the total film thickness T of the separator. By setting it as such a structure, it becomes a separator which can provide the battery excellent in the high temperature storage characteristic. In addition, the separator according to the present invention is a separator capable of improving the volume energy density, that is, maintaining a high capacity. Surprisingly, by integrating the porous film and the solid electrolyte layer as a separator, the cycle characteristics could be improved in addition to the above effects.

The flatness is determined by randomly selecting an area of 100 mm × 100 mm on the surface of the separator, that is, the surface of the solid electrolyte layer, and scanning the micro area in the area using a surface roughness meter. The film thickness of was measured. Specifically, the four corners of this square, the intersections of diagonal lines, and the midpoint area of each side are measured at a total of nine points, and the maximum thickness T _{max of the} separator (of the total film thickness of the separator) maximum and thickness _{T max)} and the minimum thickness _{T min,} defined as the roughness _{Ra =} T max _{-T min,} to evaluate the flatness by Ra / T using the value. Note that T is an average value calculated from the thickness of the obtained separator.

  Although not necessarily clear, according to such a separator, by interposing a solid electrolyte layer, a more uniform state can be realized in the separator, a local battery reaction between electrodes can be suppressed, and the mobility of mobile ions It is presumed that can also be reduced. As a result, it is considered that the storage characteristics at high temperatures can be improved. Surprisingly, the separator according to the present invention can also improve cycle characteristics. This is because the liquid retention of the separator was improved by the solid electrolyte layer and that the current distribution was made uniform by ensuring the surface flatness, which led to the improvement of the cycle characteristics. Presumed.

<Inorganic particles>
Next, components according to the present embodiment will be described in order. The inorganic particles used in the present embodiment form pores for impregnating the electrolyte in the solid electrolyte, and are not particularly limited as long as they are electrochemically inactive. The electrical conductivity in the bulk of the inorganic particles is preferably 10 ⁻⁹ S · cm ⁻¹ or less, particularly preferably 10 ⁻¹⁵ S · cm ⁻¹ or less.

  The inorganic particles used in the present embodiment have an average particle size of 0.05 to 5 μm, and particularly preferably 0.1 to 2 μm. If the particle size is too small, the particles become too dense. If the particle size is too large, it may be difficult to reduce the film thickness, but it can be handled under slurrying conditions including the binder material. As the particle size distribution, a relatively narrow one is preferable because uniform voids can be obtained, and it is preferable that 50% by mass or more of all particles exist in 1/2 to 2 times the average particle size.

  The shape of the inorganic particles is not particularly limited as long as appropriate pores are formed, and may be any shape such as an irregular shaped piece, an irregular shape, and a spherical shape.

The material of such inorganic particles is not particularly limited, and for example, silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), calcium carbonate (CaCO ₃ ), magnesium oxide (MgO), barium titanate ( BaTiO ₃ ), talcite and the like can be mentioned, and these may be used alone or in combination of two or more.
Among these, calcium carbonate, talcite, and barium titanate are more preferable. In particular, high-purity calcium carbonate, talcite, and barium titanate synthesized by hydrothermal synthesis are inorganic compounds that are particularly effective for the production of a thin solid electrolyte. Further, in the case of barium titanate, the dielectric properties change depending on the crystal structure and crystal lattice size. For example, barium titanate prepared by hydrothermal synthesis preferably has a ratio of a-axis to c-axis in the crystal such that a / c> 1.0006.

<Binder>
The binder used in the present embodiment is not particularly limited as long as it binds inorganic particles as the binder.

  In particular, polyvinylidene fluoride, butadiene rubber, epoxy resin, polyimide amide, and polyimide can also be preferably used.

  Among these, butadiene rubber is preferable, and styrene butadiene rubber (SBR) is more preferable. Such water-based binders can contribute to the production of environmentally friendly products because they do not use organic solvents.

  The weight ratio of the inorganic particles to the binder is preferably inorganic particles: binder = 55: 45 to 90:10, particularly 60:40 to 85:15. If the content of the binder is higher than this, the porosity may be reduced, so that sufficient conductivity may not be obtained. If the content of the binder is less than this, it becomes difficult to sufficiently bind the inorganic particles, and sufficient sheet strength may not be obtained, and it becomes difficult to reduce the thickness.

  Further, the porous film used in the present embodiment is not particularly limited, but in consideration of the electrolytic solution resistance, a polyethylene porous film, a polypropylene porous film, or a polypropylene / polyethylene porous film is preferably used. It is done. Moreover, the porous film of an epoxy resin or a polyamide-imide resin may be sufficient. Further, it may be a porous film mainly composed of cellulose. At this time, the total thickness of the porous film including the solid electrolyte layer is 15 μm or less.

  Moreover, it is preferable that the porosity of a porous film is 50% or more. According to this configuration, the battery characteristics can be further improved.

  The flatness of the separator of this embodiment is important. The surface roughness Ra is 0 <Ra / T <0.05 with respect to the film thickness T of the separator. By maintaining the flatness of the surface, local current flow can be prevented, and a battery having excellent high-temperature storage characteristics can be provided. In this embodiment, cycle characteristics can also be improved.

  Regarding these effects, for example, the flatness of the surface of the solid electrolyte layer cannot be maintained, and if there is a thinned portion with respect to the adjacent electrode, current concentrates on that portion. This current concentration is also reflected on the electrode side and is hardly recognized in the initial state, but it is considered that it affects the electrode and causes local material deterioration at a long time or at a high temperature, thereby reducing the cycle characteristics. The flatness can be measured by cross-sectional observation with a scanning electron microscope, but here, the roughness Ra was calculated by measuring with a surface roughness meter. Further, the above-described flatness Ra / T can be adjusted according to the particle size and form of the inorganic particles to be used, and also by suppressing the aggregation state with inorganic particles or resin particles whose slurry concentration is adjusted as described later. It can be secured. Further, it can be flattened by applying pressure in a composite state of inorganic particles and a binder material. Moreover, since it tends to be influenced by the surface state of the porous film that is the base when applying the slurry that becomes the solid electrolyte layer, it is also possible to control the surface state of the porous film.

<Electrolyte>
The electrolytic solution generally comprises an electrolyte salt and a solvent. Considering application to a lithium battery, the electrolyte salt needs to contain lithium. Specifically, LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiSO ₃ CF ₃ , LiN (CF ₃ SO ₂ ) An electrolyte salt such as ₂ is applicable. In addition, according to the electrochemical device to be applied, an electrolyte salt that is compatible with the solvent described later may be appropriately selected. Such an electrolyte salt may be used alone, or a plurality of salts may be mixed at a predetermined ratio (for example, LiPF ₆ : LiBF ₄ = 0.01: 0.99 to 0.99: 0.01). It may be used.

  The solvent is not particularly limited as long as it has good compatibility with the binder material and the electrolyte salt, but is high when considering application to electrochemical devices such as lithium ion secondary batteries and capacitors. Those that do not decompose even when a voltage is applied are preferred, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. Carbonates, cyclic ethers such as tetrahydrofuran (THF), 2-methyltetrahydrofuran, cyclic ethers such as 1,3-dioxolane, 4-methyldioxolane, lactones such as γ-butyrolactone, sulfolane, 3-methylsulfolane, dimethoxy Ethane, Jie Kishietan, ethoxy methoxy ethane, can be preferably used ethyl diglyme or the like. These may be used alone or in combination. In addition, a suitable solvent may be appropriately selected from known solvents according to the device to be applied.

  The concentration of the electrolyte salt in the electrolytic solution is preferably 0.3 to 5 mol / l, and usually exhibits the highest conductivity in the vicinity of 1 mol / l.

  The content of the electrolytic solution is preferably 30 to 70% by mass, particularly 40 to 60% by mass of the solid electrolyte. If the content is higher than this, excess electrolyte solution increases, which is disadvantageous in weight when a battery is produced. Further, if the content is less than this, sufficient ionic conductivity may be difficult to obtain.

<Separator>
In the separator 10 provided with the solid electrolyte layer of the present embodiment, the thickness of the solid electrolyte layer 12 is preferably 0.1 to 5 μm, particularly preferably 0.5 to 2 μm. It is practical that the total film thickness including the porous film 14 is 5 μm or more and 15 μm or less. The separator provided with the solid electrolyte layer of the present embodiment is thinner than the conventional gel electrolyte that could not be practically made to be 15 μm or less, and further, a thin separator that has been developed in recent years for lithium ion batteries. Even if (10 μm or less) is used in combination, it can be made thinner than a conventional 10 μm separator. Therefore, the separator is suitable for thinning and large area, that is, sheet-like form.

  Further, the porosity in drying before impregnation with the electrolytic solution, that is, in a state where the inorganic particles are bound with the binder, is preferably 30% or more, particularly 45% or more. If the porosity is less than this, the electrolyte cannot be sufficiently retained, and the ionic conductivity and rate characteristics may be deteriorated. The upper limit of the porosity is usually preferably 70% or less. If it is too large, the strength may be insufficient. The porosity can be measured by the Archimedes method.

  The average pore diameter is preferably 0.05 to 2 μm, particularly preferably 0.1 to 0.8 μm. Usually, the pore diameter is larger than that of the conventional gel electrolyte. When the average pore diameter is larger than this, it becomes difficult to maintain a uniform pore diameter, and lithium dentrite may be generated. If it is smaller than this, a problem may occur in the diffusion of Li ions. The pore diameter can be measured with a mercury porosimeter.

<Manufacturing method>
Next, a specific method for producing a separator provided with the solid electrolyte layer of this embodiment will be described.

  First, a binder and inorganic particles are dissolved and dispersed in a solvent. The solvent at this time may be appropriately selected from various solvents and aqueous systems in which the binder can be dissolved. Industrially, a solvent having a high boiling point and high safety is preferable. For example, N, N-dimethylformamide (DMF), dimethylacetamide, N-methylpyrrolidone, acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone and the like are preferably used. The concentration of the binder with respect to the solvent is preferably 5 to 25% by mass.

  As a dispersion / dissolution method, a mixture of a binder and inorganic particles is added to a solvent, or inorganic particles are added to a binder solution, heated at room temperature or if necessary, a stirrer such as a magnetic stirrer or a homogenizer, a pot mill, a ball mill, Disperse and dissolve using a dispersing machine such as a super sand mill or a pressure kneader.

  And the mixed slurry which mixed the binder, the inorganic particle, and the solvent is apply | coated to the porous film with a high porosity. As yet another form, the solid electrolyte layer may be formed on the porous film when the battery is finally produced, so that the slurry can be applied directly to the electrode surface once. The means for applying the mixed slurry to the porous film is not particularly limited, and may be appropriately determined according to the material and shape of the substrate. In general, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a screen printing method and the like are used. Then, if necessary, a rolling process is performed using a flat plate press, a calendar roll, or the like.

  If the solvent in the mixed slurry is evaporated after coating, a separator having a solid electrolyte layer in which inorganic particles are bound with a binder is completed. The drying method may be drying under reduced pressure or air drying. Moreover, you may heat.

  The power generation element 40 is produced by sandwiching and laminating the separator provided with the solid electrolyte layer between the positive electrode and the negative electrode.

<Lithium ion secondary battery>
The lithium ion secondary battery 100 mainly includes a power generation element 40, a case 50 that houses the power generation element 40 in a sealed state, and a pair of leads 60 and 62 connected to the power generation element 40.

As described above, the power generation element 40 is configured such that the pair of positive electrodes 20 and the negative electrode 30 are disposed to face each other with the multilayer separator 10 interposed therebetween. Leads 62 and 60 are connected to the ends of the positive electrode current collector 22 which is a constituent member of the positive electrode 20 and the negative electrode current collector 32 which is a constituent member of the negative electrode 30, respectively. It extends to the outside of the case 50.
The structure of the lithium ion secondary battery using the separator of the present embodiment is not particularly limited, but is usually composed of a positive electrode and a negative electrode and the separator of the present embodiment, and is applied to a stacked battery, a cylindrical battery, or the like. .

  Moreover, the electrode combined with the separator of the present embodiment may be used by appropriately selecting from known ones as electrodes of a lithium ion secondary battery, preferably an electrode active material, a gel electrolyte, and optionally a conductive auxiliary agent. Use the composition.

  The negative electrode uses a negative electrode active material such as a carbon material, lithium metal, lithium alloy or oxide material, and the positive electrode such as an oxide or carbon material capable of intercalating / deintercalating lithium ions. It is preferable to use a positive electrode active material. By using such an electrode, a lithium ion secondary battery with good characteristics can be obtained.

  The carbon material used as the electrode active material may be appropriately selected from, for example, mesocarbon microbeads (MCMB), natural or artificial graphite, resin-fired carbon material, carbon black, carbon fiber, and the like. Further, a silicide-based or silicon-based negative electrode material exhibiting a high capacity may be used.

As an oxide capable of intercalating and deintercalating lithium ions, a composite oxide containing lithium is preferable. For example, lithium transition metal oxidation such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiV ₂ O _4, etc. In addition to these, phosphate compounds such as LiFePO ₄ (LiMnPO ₄ , LiVOPO _4, etc.) can be mentioned. The average particle size of these powders is preferably about 1 to 40 μm.

  If necessary, a conductive additive is added to the electrode. Preferred examples of the conductive aid include metals such as graphite, carbon black, carbon fiber, nickel, aluminum, copper, and silver, and graphite and carbon black are particularly preferable.

  The electrode composition is preferably in the range of active material: conducting aid: gel electrolyte = 30 to 90: 3 to 10:10 to 70 by weight ratio in the positive electrode, and active material: conducting aid in weight ratio in the negative electrode. : Gel electrolyte = The range of 30-90: 0-10: 10-70 is preferable. The gel electrolyte is not particularly limited, and a commonly used gel electrolyte may be used. Moreover, the electrode which does not contain a gel electrolyte is also used suitably. In this case, a fluororesin, fluororubber, or the like can be used as the binder, and the amount of the binder is preferably about 3 to 30% by mass.

  In this embodiment, the negative electrode active material or the positive electrode active material, preferably both active materials are mixed in a gel electrolyte or a binder and adhered to the current collector surface.

  In manufacturing the electrode, first, an active material and, if necessary, a conductive additive are dispersed in a gel electrolyte solution or a binder solution to prepare a coating solution.

  Then, this coating solution is applied to the current collector. The means for applying is not particularly limited, and may be appropriately determined according to the material and shape of the current collector. In general, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a screen printing method and the like are used. Then, if necessary, a rolling process is performed using a flat plate press, a calendar roll, or the like.

  The current collector may be appropriately selected from ordinary current collectors according to the shape of the device used by the battery, the method of arranging the current collector in the case, and the like. Generally, aluminum or the like is used for the positive electrode, and copper, nickel, or the like is used for the negative electrode. In addition, a metal foil, a metal mesh, etc. are normally used for a collector. The metal mesh has a smaller contact resistance with the electrode than the metal foil, but a sufficiently small contact resistance can be obtained even with the metal foil.

  Then, the solvent is evaporated to produce an electrode. In addition, it is preferable that the thickness of the film | membrane to apply | coat shall be about 0.1-5 micrometers.

  A battery is produced by stacking or winding the positive electrode, negative electrode, and separator obtained in this manner into an aluminum outer case.

  The case 50 is for sealing the power generation element 40 and the electrolyte therein. The case 50 is not particularly limited as long as it can suppress leakage of the electrolytic solution to the outside and entry of moisture and the like into the lithium ion secondary battery 100 from the outside. For example, as the case 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. For example, an aluminum foil can be used as the metal foil 52 and a film such as polypropylene can be used as the polymer film 54. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point, such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is polyethylene (PE) or polypropylene (PP). Etc. are preferred.

The present embodiment will be described specifically with reference to examples.
Evaluation of the separator provided with the solid electrolyte layer was judged by the high temperature storage characteristics at 60 ° C.
In the evaluation method, first, the initial discharge capacity is measured after the battery is manufactured. The initial discharge capacity is charged to 4.2V with a constant current equivalent to 1C (current value that is fully charged in 1 hour) with respect to the battery design capacity, and after reaching full charge, it is discharged to 2.7V with a current equivalent to 1C. Discharge capacity.
Thereafter, the evaluation battery was placed in a fully charged state at 60 ° C., the value of the discharge capacity after 4 weeks was measured, and the capacity change rate (%) from the initial discharge capacity was judged. As a criterion, 60% or more was regarded as acceptable.
The cycle characteristics were determined by measuring the discharge capacity after 350 cycles under 1C charge / discharge conditions, and the capacity retention rate (%) from the initial discharge capacity. As for the judgment criteria, 80% or more was regarded as acceptable products.
In addition, the flatness of the separator is determined by randomly selecting a 100 mm × 100 mm region on the surface of the separator, that is, the surface of the solid electrolyte layer, and scanning a minute region using a surface roughness meter in the region. Was used to measure the film thickness of the separator. Specifically, the four corners of this square, the intersections of diagonal lines, and the midpoint area of each side are measured at a total of nine points, and the maximum thickness T _{max of the} separator (of the total film thickness of the separator) maximum and thickness _{T max)} and the minimum thickness _{T min,} defined as the roughness _{Ra =} T max _{-T min,} to evaluate the flatness by Ra / T using the value. Note that T is an average value calculated from the thickness of the obtained separator.

<Example 1>
The separator was produced using the following as a component of the solid electrolyte layer.

<Components of the solid electrolyte layer>
As the components of the solid electrolyte layer, the inorganic particles were SiO ₂ (average particle size 1 μm), and the binder was PVDF.

Each of the above components was weighed so that the weight ratio was SiO ₂ : PVDF = 80: 20, and acetone was further added so that acetone: PVDF = 9: 1 (weight ratio), and at room temperature using a pot mill. By mixing and dissolving, a slurry electrolyte solution was obtained. In this slurry, only the PVDF copolymer was dissolved, and SiO ₂ was dispersed in the solution.

  Then, this electrolyte solution is applied to a polyethylene separator film (thickness 9 μm, porosity 52%) as a porous film by a microgravure method, and acetone is evaporated in the range of room temperature to 50 ° C. to obtain a solid electrolyte layer. A separator provided with was obtained. The film thickness of the solid electrolyte layer at this time was 0.1 μm.

Then, using this solid electrolyte separator, an electrode using lithium cobalt oxide LiCoO _{2 as} a positive electrode and graphite as a negative electrode was laminated, and the power generation element was enclosed using an aluminum laminate outer package. Thereafter, a LiPF ₆ 1M (mol / l) salt and a mixed solvent of EC and DMC (EC: DMC = 1: 2 (volume ratio)) are used as an electrolytic solution and injected into the outer layer housing the power generation element. A lithium ion secondary battery was produced.

  The battery thus fabricated was subjected to initial characteristics evaluation, then fully charged at 60 ° C., and the capacity change after 4 weeks was measured. The results (capacity change rate) are shown in Table 1.

<Example 2>
A lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the thickness of the solid electrolyte layer was changed as shown in Table 1. The results are shown in Table 1.

<Example 3>
A solid electrolyte layer was prepared and evaluated at the same solid electrolyte layer thickness as in Example 2 using styrene butadiene rubber as the binder material for the solid electrolyte layer and calcium carbonate as the inorganic particles. A mixed solution containing 30 parts by mass of calcium carbonate particles (average particle size: 0.2 μm) and 70 parts by mass of a binder, 25% by mass of an aqueous emulsion of styrene-butadiene rubber as a solvent, and 75 parts by mass of water was brought to room temperature. Then, the mixture was dispersed and dispersed for 30 hours by a ball mill, and 0.1 parts by mass of a surfactant was further added and dispersed for 1 hour to prepare an electrolyte solution.

  This electrolyte solution was applied to a polyethylene separator (thickness 9 μm, porosity 55%) as a porous film by a microgravure method, and acetone was evaporated in the range of room temperature to 50 ° C. to obtain a separator. The film thickness (dry film thickness) of the solid electrolyte sheet was 0.1 μm.

  And using this separator, the lithium ion secondary battery was produced similarly to Example 1, and the 60 degreeC storage characteristic was evaluated.

<Example 4> to <Example 6>
Examples 4-6 produced and evaluated the lithium ion secondary battery like Example 1 except having changed the film thickness of the solid electrolyte layer as Table 1 showed.

<Example 7> to <Example 9>
In Examples 7 to 9, lithium ion secondary batteries were produced and evaluated in the same manner as in Example 3 except that the thickness of the solid electrolyte layer was changed as shown in Table 1.

<Example 10>
A lithium ion secondary battery was produced under the same conditions as in Example 2 except that the inorganic particles were barium titanate.

<Example 11>
It was produced under the same conditions as in Example 1 except that talcite was used as the inorganic particles.

<Example 12>
A lithium ion secondary battery was fabricated under the same conditions as in Example 2 except that the inorganic particles were calcium carbonate by hydrothermal synthesis. As the calcium carbonate used in this example, calcium carbonate synthesized in a pressure vessel at a temperature of 100 ° C. to 200 ° C. and a pressure of 2 atm to 10 atm was used. At this time, the average particle diameter of calcium carbonate was 0.2 μm.

<Example 13>
A lithium ion secondary battery was produced under the same conditions as in Example 2 except that the inorganic particles were barium titanate by hydrothermal synthesis. At this time, the average particle diameter of barium titanate was 0.15 μm.

<Example 14>
A separator having the same configuration as that of Example 7 except that only flatness was changed was produced, and a lithium ion secondary battery was produced.

<Example 15>
A separator having the same configuration as that of Example 7 except that only flatness was changed was produced, and a lithium ion secondary battery was produced.

<Example 16>
A separator having the same configuration as that of Example 7 except that only flatness was changed was produced, and a lithium ion secondary battery was produced.

<Example 17>
A separator having the same configuration as that of Example 7 except that only flatness was changed was produced, and a lithium ion secondary battery was produced.

<Comparative Example 1>
As shown in Table 1, a separator having a porous film similar to that of Example 1 and having no solid electrolyte layer was prepared, a lithium ion secondary battery was prototyped, and 60 ° C. storage characteristics were evaluated.

<Comparative example 2>
As shown in Table 1, a lithium ion secondary battery was fabricated and evaluated basically in the same manner as in Example 1 except that the thickness of the solid electrolyte layer was changed to 7 μm. In addition, the total film thickness of the separator at this time was 16 μm.

<Comparative Example 3>
As shown in Table 1, a separator having the same configuration as that of Example 7 except that only flatness was changed was produced, and a lithium ion secondary battery was produced.

<Comparative example 4>
As shown in Table 1, a separator having the same configuration as that of Example 7 except that only flatness was changed was produced, and a lithium ion secondary battery was produced.

  As described above, as shown in Table 1, it can be seen that Examples 1 to 17 have improved storage characteristics at 60 ° C. and further improved cycle characteristics. On the other hand, the comparative example is not improved.

DESCRIPTION OF SYMBOLS 10 Separator 20 Positive electrode 12 Solid electrolyte layer 14 Porous film 22 Positive electrode collector 24 Positive electrode active material layer 30 Negative electrode 32 Negative electrode collector 34 Negative electrode active material layer 50 ... Case 52 Metal foil 54 Polymer film 60, 62 Lead 100 Lithium Ion secondary battery.

Claims (5)

A separator having a solid electrolyte layer on a porous film,
The solid electrolyte layer contains inorganic particles having an average particle diameter of 0.05 to 5 μm, and the total film thickness of the separator is 15 μm or less,
The separator is characterized in that the flatness of the separator is 0 <Ra / T <0.05 as the ratio of the roughness Ra of the separator to the total film thickness T of the separator.   The separator according to claim 1, wherein the inorganic particles are at least one of calcium carbonate, talcite, and barium titanate.   The separator according to claim 1, wherein the solid electrolyte layer contains any one selected from polyvinylidene fluoride, butadiene rubber, epoxy resin, polyamideimide, and polyimide.   The separator according to any one of claims 1 to 3, wherein the solid electrolyte layer is disposed on a porous film having a porosity of 50% or more. A lithium ion secondary battery comprising the separator according to any one of claims 1 to 4.

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