CN102190323B - Inorganic oxide powder, slurry containing inorganic oxide, lithium ion secondary battery having the slurry and preparation method thereof - Google Patents

Abstract

The present invention provides an inorganic oxide powder suitable for forming an inorganic oxide porous film with insulating properties on the surface of at least one of positive electrodes, negative electrodes and separators constituting a lithium ion secondary battery. Disclosed is an inorganic oxide powder for forming an inorganic oxide porous film having insulating properties on the surface of at least one of a positive electrode, a negative electrode, and a separator used in a lithium ion secondary battery, wherein (1) The oxide purity is 90% by weight or more, (2) the content of coarse particles having a particle diameter of 10 μm or more is 10 ppm or less in terms of mass ratio, and (3) at 29 MPa or more and 147 MPa or less The porosity of the green compact of the inorganic oxide powder obtained under a pressure within the range of 40% by volume or more and 80% by volume or less, the average pore diameter of the green compact is 0.06 μm or higher, and in The amount of change in porosity per 1 MPa of pressure when the compact is molded is 0.020% or more and 0.060% or less.

Description

Inorganic oxide powder and inorganic oxide-containing slurry, lithium ion secondary battery using the slurry, and method for producing the same

technical field

The present invention relates to an inorganic oxide powder for forming an inorganic oxide porous film having insulating properties on the surface of at least one of a positive electrode, a negative electrode, and a separator used in a lithium ion secondary battery. The present invention also relates to a slurry containing the inorganic oxide powder, and further relates to a lithium ion secondary battery using the slurry, and a method of producing the same.

Background technique

Because of its high energy density, lithium ion secondary batteries are used in portable digital instruments such as cellular phones and personal computers, and in addition to these digital instruments, development of lithium ion secondary batteries for automobiles has recently been accelerated.

Generally, a lithium ion secondary battery includes a positive electrode and a negative electrode, and includes a separator placed to electrically insulate spaces between these electrode sheets. As a separator for lithium ion secondary batteries, for example, a microporous sheet made of polyolefin resin is used.

When a short circuit occurs in the battery, the closing function of the separator causes clogging of the pores of the separator and makes it impossible to move lithium ions at the part where the short circuit occurs, so that the battery function at the short circuit site is lost. In this way, the separator composed of the microporous sheet plays a role of maintaining the safety of the lithium ion secondary battery. However, when the temperature of the battery is, for example, higher than 150° C. due to temporarily generated heat, the separator shrinks rapidly, and thus the short-circuited portion of the positive electrode and the negative electrode is sometimes enlarged. In this case, the temperature of the battery sometimes reaches a state where it is abnormally overheated to several hundred degrees or more, causing a problem in terms of safety.

Therefore, JP H09-147916A proposes a technique as a means to solve the above problems, in which a material having insulating properties is formed on an electrode (for example, on the surface of a positive electrode, a negative electrode, or a separator constituting a lithium ion secondary battery). Inorganic oxide porous membranes based on inorganic oxide fillers.

In addition, JP 2005-327680A discloses a lithium ion secondary battery comprising a porous membrane having a thickness of 2-10 μm and a porosity of 35-75% by volume using α-alumina particles as An inorganic oxide filler used in an oxide porous film, the particles have heat resistance in a state in which primary particles having an average particle diameter of 0.2 to 1.5 μm are connected. The same document describes the use of such alpha alumina particles suitable for controlling the pore structure of porous membranes.

In addition, International Publication WO 2005/124899 pamphlet discloses that by adjusting the porosity of the porous membrane in the range of 40-80%, preferably 45-80% and most preferably 50-70%, it is possible to prevent large Charging and discharging characteristics under current and charging and discharging characteristics in a low-temperature environment are drastically deteriorated; also described: α having a bulk density of 0.1-0.8 g/cm ³ and a BET specific surface area of 5-20 m ² /g Alumina particles are preferably used as the inorganic oxide filler used here, and polycrystalline particles obtained by firing and mechanically crushing an alpha alumina precursor are preferably used as the alpha alumina particles.

Furthermore, International Publication No. WO 2008/004430 pamphlet suggests that while the inorganic oxide porous membrane containing the inorganic oxide filler is prepared by dispersing the inorganic oxide powder in a solvent together with additives such as a binder and using a coating method Formed as in the gravure printing method, but coarse aggregates of inorganic oxides are removed because coarse particles (in which inorganic oxide filler particles have a size larger than the film thickness of the target porous film) are often mixed therein.

In addition, JP 2008-91192A discloses a method in which a porous membrane containing such an inorganic oxide filler is obtained by coating a slurry containing an inorganic oxide filler, a binder and a solvent, then drying the slurry and rolling into a Obtained by predetermined thickness.

However, when an inorganic oxide porous film is formed using an inorganic oxide powder satisfying the shape, bulk density, average particle diameter, and BET specific surface area described in the above patent documents, the target porosity cannot be achieved and the obtained porous film contains Many coarse aggregate particles, the latter causing problems in the production of porous membranes, so the powder is not necessarily satisfactory as a powder for forming inorganic porous membranes for lithium ion secondary batteries.

Contents of the invention

Under these circumstances, an object of the present invention is to provide an inorganic oxide having excellent heat resistance and insulating properties for forming on the surface of at least one of a positive electrode, a negative electrode, and a separator constituting a lithium ion secondary battery. An inorganic oxide powder for a porous film, and an inorganic oxide slurry containing the inorganic oxide powder. Another object of the present invention is to provide a lithium ion secondary battery including an inorganic oxide porous film composed of inorganic oxide powder, and a method of producing the same.

The present inventors have conducted intensive studies in order to achieve the above object, and have found that the following invention satisfies the above object, and thus the present invention has been accomplished.

The present invention provides the following inventions.

<1> An inorganic oxide powder for forming an inorganic oxide porous film having insulating properties on the surface of at least one of a positive electrode, a negative electrode, and a separator placed in a lithium ion secondary battery, wherein

(1) The oxide purity is 90% by weight or higher,

(2) The content of coarse particles having a particle diameter of 10 μm or more is 10 ppm or less in mass ratio, and

(3) The porosity of the green formed body (or compression-molded body) of the inorganic oxide powder obtained under a pressure in the range of 29 MPa or more and 147 MPa or less is 40% ( volume) or more and 80% (volume) or less, the average pore diameter of the compact is 0.06 μm or more, and the amount of change in porosity per 1 MPa of pressure when molding the compact is 0.020% or more High and 0.060% or lower.

<2> The inorganic oxide powder according to <1>, wherein the inorganic oxide is α alumina.

<3> The inorganic oxide powder according to <2>, wherein the thermal expansion coefficient at 40°C to 600°C of the green compact of the inorganic oxide powder obtained at a pressure of 147 MPa is 7×10 ^-6 /°C or Higher and 9×10 ^-6 /°C or lower.

<4> An inorganic oxide slurry comprising the inorganic oxide powder according to any one of <1> to <3>, a binder and a solvent.

<5> A method for producing a lithium ion secondary battery comprising an electrode group and an electrolytic solution obtained by laminating and winding a positive electrode, a negative electrode, and a separator, the method comprising the following steps:

The inorganic oxide slurry according to <4> is coated on the surface of a positive electrode and/or a negative electrode composed of an electrode mixture layer containing an electrode active material and a binder, and the slurry is dried to form an inorganic oxide porous film.

<6> A method for producing a lithium ion secondary battery comprising an electrode group and an electrolytic solution obtained by laminating and winding a positive electrode, a negative electrode and a separator, the method comprising the following steps:

The inorganic oxide slurry according to <4> is coated on the surface of the separator, and the slurry is dried to form an inorganic oxide porous film.

<7> A lithium ion secondary battery obtained by the method of <5> or <6>.

With the inorganic oxide powder of the present invention, it is possible to provide a thermally stable inorganic oxide porous film having a porosity related to lithium ion conductivity which is very suitable for lithium ion secondary battery applications and having high uniformity.

Detailed ways

The present invention provides inorganic oxide powders (hereinafter sometimes referred to as "inorganic oxide powders of the present invention", or sometimes simply referred to as "non-polar oxide powders"), which are used in positive electrodes, negative electrodes and separators (they are used to construct Lithium-ion secondary battery) Inorganic oxide powder with an inorganic oxide porous film having insulating properties formed on the surface of at least one of the three, wherein,

(1) The oxide purity is 90% by weight or higher,

(2) The content of coarse particles having a particle diameter of 10 μm or more is 10 ppm or less in mass ratio, and

(3) The porosity of the green compact of inorganic oxide powder obtained under a pressure in the range of 29 MPa or more and 147 MPa or less is 40% by volume or more and 80% by volume or less, the average pore diameter of the compact is 0.06 μm or more, and the amount of change in porosity per 1 MPa of pressure when the compact is molded is 0.020% or more and 0.060% or less.

In the present invention, the change in porosity per 1 MPa of pressure when molding the compact means the change in porosity value (in % value) when the pressure applied to the compact is changed by 1 MPa.

For example, for the compact prepared under a pressure of 73 MPa and the porosity of the compact obtained is 55.8% by volume, and another compact prepared under a pressure of 147 MPa and another compact obtained In the case where the porosity of the powder is 52.2% by volume, the change in porosity per 1 MPa of pressure when molding the pressed powder calculated by using these results is the absolute value of the change in porosity value (ie 55.8%- 52.2% = 3.6%) divided by the change in this pressure when molding the pressed powder (ie 73-147 = -74), thus it is 0.049% (ie 3.6%/74).

The inorganic oxide powder of the present invention is not particularly limited as long as it is a material having electrical insulating properties, which can use alumina, titania, magnesia, silica, etc., preferably alumina (alumina). In particular, α-alumina that is excellent in heat resistance and is chemically stable is most preferable.

The purity of the inorganic oxide powder of the present invention is preferably 90 wt% or higher, more preferably 99 wt% or higher, further preferably 99.9 wt% or higher, most preferably 99.99 wt% or higher.

Particularly, for the case where the inorganic oxide powder of the present invention is α-alumina powder and the purity is less than 90% by weight, the content of impurities such as Si, Na and Fe in the α-alumina powder increases. Therefore, not only satisfactory electrical insulation properties cannot be obtained, but also the mixing amount of foreign substances made of metals that can cause short circuits disadvantageously increases.

In addition, the porosity of the green compact made of the inorganic oxide powder of the present invention is 40% by volume or higher and 80% by volume under a pressure in the range of 29 MPa or higher and 147 MPa or lower. ) or less, and the average pore diameter is 0.06 μm or more. Further, the amount of change in porosity per 1 MPa of pressure when molding (or forming) the green compact of inorganic oxide powder is 0.020% or more, preferably 0.025% or more, and the amount of change in porosity is 0.080 % or lower, preferably 0.065% or lower, more preferably 0.060% or lower.

In the inorganic oxide powder of the present invention, when the pressure at the time of molding the compact is 29 MPa or lower, sometimes a uniform compact cannot be produced because of the low molding pressure. In addition, when the pressure at the time of molding the green compact is 147 MPa or higher, sometimes a uniform green compact cannot be produced because cracks occur at the time of molding.

In the case where the porosity of the compacted powder body of the inorganic oxide powder of the present invention is less than 40% by volume, by coating the slurry prepared from the inorganic oxide powder on an electrode active material (positive electrode active material or negative electrode active material) and the surface of the electrode mixture layer of the binder and drying the slurry will also reduce the porosity of the inorganic oxide porous membrane of the inorganic oxide powder of the present invention, and as a result, the porous inorganic oxide membrane The amount of electrolytic solution contained in it will disadvantageously decrease.

In the case where the porosity of the green compact of the inorganic oxide powder of the present invention is higher than 80% by volume, by coating the slurry prepared from the inorganic oxide powder of the present invention on The porosity of the inorganic oxide porous film of the inorganic oxide powder of the present invention obtained on the surface of the electrode (positive electrode or negative electrode) composed of the electrode mixture layer of the agent and drying the slurry will also increase, and the above-mentioned inorganic oxide porous film The strength of the film disadvantageously decreases. In the case where the average pore diameter is less than 0.06 μm, the same phenomenon as when the above-mentioned green compact has a small porosity disadvantageously occurs.

When the variation in porosity per 1 MPa of pressure when molding the compact of the inorganic oxide powder of the present invention is less than 0.020%, it is impossible to control-by coating the slurry prepared from the inorganic oxide powder of the present invention On the surface of an electrode (positive electrode or negative electrode) consisting of an electrode mixture layer containing an electrode active material and a binder and drying the slurry - the porosity of the inorganic oxide porous film of the inorganic oxide powder of the present invention. On the other hand, when the variation in porosity per 1 MPa of pressure when molding the green compact of the inorganic oxide powder of the present invention is more than 0.060%, by coating the slurry prepared from the inorganic oxide powder of the present invention on The porosity of the inorganic oxide porous film of the inorganic oxide powder of the present invention obtained on the surface of an electrode (positive electrode or negative electrode) composed of an electrode mixture layer containing an electrode active material and a binder and drying the slurry will be disadvantageously changed. obtained unevenly, thus making it impossible to maintain the electrolytic solution uniformly.

In addition, in the inorganic oxide powder of the present invention, the content of coarse particles having a particle diameter of 10 μm or more is 10 ppm or less in terms of mass ratio. In the case where the content of coarse particles having a particle diameter of 10 μm or more is greater than 10 ppm, defects due to aggregate particles, such as lines or coarse pores, are sometimes partially formed on the coating film.

As mentioned above, alpha alumina is preferred as the inorganic oxide powder in the present invention. In the case where the inorganic oxide powder of the present invention is α-alumina, when α-alumina powder, a binder and a solvent are mixed to prepare α-alumina slurry and the obtained α-alumina slurry is coated on an electrode containing When the surface of the electrode mixture layer of the active material is formed to form a coating film, and then the coating film is more preferably subjected to roll pressing, it is possible to sufficiently ensure the porosity and pore diameter of the α-alumina porous film related to lithium ion conductivity , and, at the same time, it is advantageously possible to arbitrarily control the porosity within a preferred range.

In addition, in the case where the inorganic oxide powder of the present invention is α-alumina, the thermal expansion coefficient of the compact of α-alumina powder at a temperature of 40°C to 600°C prepared under a pressure of 147 MPa is preferably 7× 10 ^-6 /°C or higher and 9×10 ^-6 /°C or lower.

Although an inorganic oxide porous film for a lithium ion secondary battery is required to have excellent heat resistance, it is known that the thermal expansion coefficient of α-alumina itself is about 8×10 ^-6 /°C (see, for example, "Introduction To Ceramics", p595 , Wiley Interscience). It is necessary that the α-alumina in the lithium ion secondary battery exerts a function of maintaining a stable state even when a short circuit occurs to cause an excessively overheated state.

For the case where the thermal expansion coefficient of the green compact prepared under the pressure of 147 MPa of α-alumina powder is lower than 7×10 ^-6 /°C at the temperature of 40°C-600°C, because the particles forming the green compact will cause Rearrangement and sintering are easily performed, and therefore, if the green compact is used for an inorganic oxide porous membrane, the physical properties (porosity, etc.) of the membrane itself sometimes change unfavorably.

In the case where the coefficient of thermal expansion is greater than 9×10 ⁻⁶ /° C., the mismatch between the coefficient of thermal expansion of the positive electrode and the coefficient of thermal expansion of the negative electrode may increase. When the green compact is used for an inorganic oxide porous membrane, cracks may disadvantageously occur in the inorganic oxide porous membrane.

The α-alumina powder preferred as the inorganic oxide powder of the present invention has an average particle diameter (average aggregate particle diameter) of 1 μm or less, and has a BET of 1-20 m ² /g, preferably 2-15 m ² /g specific surface area.

The method of producing the α-alumina powder of the present invention is not particularly limited, for example, the α-alumina powder can be produced by an aluminum alkoxide method.

The aluminum alkoxide method refers to a method in which aluminum alkoxide is hydrolyzed to obtain slurry-, sol- or gel-like aluminum hydroxide, followed by drying to obtain dry powder aluminum hydroxide.

Specifically, the aluminum alkoxide includes compounds represented by the following general formula (1):

Al(OR ¹ )(OR ² )(OR ³ ) (1)

wherein R ¹ , R ² and R ³ each independently represent an alkyl group.

Examples of the alkyl group in the general formula (1) include alkyl groups having 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert butyl. Specific examples of the aluminum alkoxide include aluminum isopropoxide, aluminum ethoxide, aluminum sec-butoxide and aluminum tert-butoxide.

Slurry aluminum hydroxide obtained by hydrolyzing the aluminum alkoxide with water generally has an average primary particle diameter in the range of 0.01-1 μm, preferably in the range of 0.02-0.05 μm.

The powdered aluminum hydroxide obtained by drying the slurry aluminum hydroxide is in the form of a bulky powder generally having an untamped density of about 0.1-0.8 g/cm ³ . The untamped density is preferably 0.4-0.8 g/cm ³ .

The target α-alumina can be obtained by calcining the above-mentioned dry powdery aluminum hydroxide. Baking is usually carried out in a state filled in a baking container. The firing vessel includes, for example, a square crucible. In consideration of pollution control, the roasting vessel is preferably made of a material such as alumina.

Examples of the roasting furnace used in the roasting include a material fixed type furnace, typically a tunnel kiln, an intermittent ventilation type flow box type roaster, an intermittent co-current flow box type roaster, and the like. Rotary kilns can also be exemplified.

The calcination temperature, the rate of temperature increase until the temperature reaches the calcination temperature, and the calcination time are appropriately selected so as to obtain α-alumina having predetermined physical properties as described above. The calcination temperature is 1100-1450°C, preferably 1200-1350°C, the heating rate until the temperature reaches the calcination temperature is usually 30-500°C/hour, and the calcination time is usually 0.5-24 hours, preferably 1-10 hours.

The firing atmosphere may be an inert gas such as nitrogen or argon in addition to atmospheric air. Calcination can be performed in an atmosphere having a high partial pressure of water vapor such as a gas furnace, in which calcining is performed by combustion using propane gas or the like.

The obtained α-alumina powder is preferably crushed because it aggregates in a state where the average particle diameter is larger than 1 μm in some cases. The crushing method is not particularly limited, and can be performed, for example, by using known equipment such as a vibration ball mill, a ball mill, and a jet mill. It is also possible to use either of the dry crushing method and the wet crushing method. As a method of crushing while maintaining purity without including coarse aggregate particles, a crushing method using a jet mill can be cited as a preferable method.

The inorganic oxide slurry of the present invention is composed of the above-mentioned inorganic oxide powder, binder and solvent of the present invention.

Known binders can be used as the binder, specifically, fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer can be used (FEP); polyacrylic acid derivatives such as polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate and polyhexyl acrylate; polymethacrylic acid derivatives such as polymethacrylic acid, polymethacrylic acid Methyl ester, polyethyl methacrylate and polyhexyl methacrylate; polyamide, polyimide, polyamideimide, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolyethylene Propylene, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylonitrile and their derivatives, polyethylene, polypropylene, aramid resin, etc.

selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid and hexadiene Copolymers of two or more starting materials in alkenes can be used.

Known solvents can be used as the solvent, specifically, water, acetone, tetrahydrofuran, dichloromethane, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, Xylene, cyclohexanone or their mixed solvents.

Known thickeners can be added in order to obtain an inorganic oxide slurry with a viscosity most suitable for coating.

The method of dispersing the above-mentioned inorganic oxide slurry is not particularly limited, and both a stirring method by a known planetary mixer and a method of dispersing by irradiation of ultrasonic waves can be used. At this point, the workability of the dispersing, mixing and transferring steps becomes satisfactory as the viscosity of the slurry at a shear rate of 100 S ⁻¹ decreases.

In addition, the method of coating the above-mentioned inorganic oxide slurry on the surface of the positive electrode or the electrode mixture layer containing the negative electrode active material and the binder or on the surface of the separator is not particularly limited, such as the known doctor blade coating A coating method, a gravure printing method, and the like can be used. In addition, the drying method is not particularly limited, and known hot air drying, vacuum drying and the like can be used. The thickness of the inorganic oxide porous membrane obtained in this case is preferably set in the range of 1 to 50 μm, more preferably in the range of about 2 to 10 μm.

The obtained inorganic oxide porous membrane produced from the inorganic oxide slurry has high heat resistance and insulating properties. The inorganic oxide porous film is formed on the surface of at least one of the positive electrode, negative electrode and separator, and then laminated and wound together with the positive electrode, negative electrode and separator to form an electrode group. As a result, the obtained lithium ion secondary battery including the electrode group and the electrolytic solution is preferably used.

Preferred examples of the method for producing the lithium ion secondary battery include a method having the steps of coating the above-mentioned inorganic oxide slurry on an electrode mixture containing an electrode active material (positive electrode active material or negative electrode active material) and a binder. layer on the surface of the positive electrode and/or negative electrode, followed by drying to form an inorganic oxide porous film. Alternatively, the method may be a method of coating the above-mentioned inorganic oxide slurry on the surface of the separator, not on the surface of the positive electrode and/or negative electrode, followed by drying to form an inorganic oxide porous film.

The specific method is exemplified below. That is, one end of the negative electrode lead is connected to the negative electrode lead joint part in which an inorganic oxide porous film is formed on the surface, and one end of the negative electrode is connected to the positive electrode lead joint part, and the positive electrode and the negative electrode are laminated and wound via a separator to form Electrode group (electrode sheet group). The electrode group (electrode sheet group) is installed in the battery can in a state of being inserted between the upper and lower insulating rings, and after the electrolytic solution is injected, the battery can is sealed by the battery cover, thereby producing a battery with excellent safety. Lithium-ion secondary battery.

In the case of producing the above-mentioned lithium ion secondary battery (including the inorganic oxide porous film), the above-mentioned inorganic oxide porous film can be obtained by coating the inorganic oxide slurry of the present invention on the surface of the separator and drying the slurry steps to produce.

The lithium ion secondary battery produced by the above method includes an inorganic oxide porous film formed from the inorganic oxide powder of the present invention, and thus has excellent heat resistance and insulating properties.

Example

The present invention will be described in detail using examples, but the present invention is not limited to the following examples. The evaluation methods of the respective physical properties are as follows.

(alumina purity)

The contents of Si, Na, Mg, Cu and Fe were measured by solid-state emission spectroscopy.

Alumina purity was determined by subtracting from 100 the total content (%) by weight of Si, Na, Mg, Cu, and Fe contained in α-alumina. Calculated as follows.

Purity (%) = 100 – total content of impurities by weight (%)

(BET specific surface area)

The BET specific surface area was measured by a nitrogen absorption method according to the method defined in JIS-Z-8830. As a measuring device for the specific surface area, "FlowSorb II 2300" manufactured by Shimadzu Corporation was used.

(average secondary particle size)

Using a particle size distribution analyzer ("Microtrack HRA X-100", manufactured by Honeywell Inc) using the laser light scattering method as a basic principle, the particle size distribution curve was measured, and the average secondary particle diameter was measured as a 50 wt% equivalent particle diameter . In the case of measurement, ultrasonic dispersion was performed by using a 0.2 wt % sodium hexametaphosphate aqueous solution.

(porosity of compressed powder)

A mold with a diameter of 30 mm was filled with 10 g of α-alumina powder, followed by uniaxial molding (uniaxial pressing) at a pressure of 29 MPa, followed by CIP molding at a pressure of 29, 73 or 147 MPa. The compacted powder was then measured for pore volume and pore diameter using a mercury porosimeter (AutoPore III 9430, manufactured by Micromeritics Instrument Corporation). The porosity of each compact was obtained from the following equation.

Porosity (volume%) = [pore volume (ml/g)/((1/3.98*) + pore volume (ml/g))]×100

*3.98 = theoretical density of alpha alumina (g/cm ³ )

Furthermore, the porosity dependence of the molding pressure was calculated from the relationship between the pressure and the porosity by using the least square method.

(Thermal expansion coefficient)

A mold with a diameter of 10 mm was filled with 1.5 g of α-alumina powder, then uniaxially molded at room temperature under a pressure of 49 MPa, followed by CIP molding under a pressure of 147 MPa to obtain a green compact, and then obtained by Thermo Mechanical Analyzer (TMA/SS6300, manufactured by SII NanoTechnology Inc) measures thermal expansion coefficient. Regarding the coefficient of thermal expansion, the expansion coefficient up to 600° C. is linearly approximated, and then defined as a gradient of an approximate straight line.

(Content of coarse aggregate particles of 10 μm or higher)

α-alumina powder (1.5-30 g) was dispersed in 800 g of pure water containing 0.2% sodium hexametaphosphate (as a dispersant) by irradiation with ultrasonic waves to prepare α-alumina slurry, and then the slurry flow Passed through a sieve having a pore diameter of 10 μm, and then the α-alumina powder remaining on the sieve was recovered and the content was measured.

(Example 1)

First, aluminum isopropoxide prepared from aluminum with a purity of 99.99% as a raw material is hydrolyzed with water to obtain aluminum hydroxide as a slurry, which is then dried to obtain a dry powder with an untamped density of 0.1 g/ ^cm Aluminum hydroxide.

Next, the dry powdery aluminum hydroxide was calcined by maintaining at 1200° C. for 3 hours in a gas furnace capable of calcining by combustion of propane gas, and then pulverized by a jet mill to obtain α alumina powder.

The obtained α alumina powder had a BET specific surface area of 5.2 m ² /g, an average particle diameter of 0.45 μm, and a content of coarse particles having a particle diameter of 10 μm or higher of 3 ppm or less. Regarding the content of impurities, the Si content was 4 ppm, the Fe content was 7 ppm, the Cu content was 1 ppm, the Na content was 2 ppm, the Mg content was 1 ppm, and the alumina purity was 99.99 wt% or more.

Next, the obtained α-alumina powders were molded under pressures of 29, 73 and 147 MPa to obtain green compacts. The porosity of each compressed powder is 59.2, 55.8 and 52.2% (volume), the average pore diameter is in the range of 0.08-0.11μm, and the porosity change per 1MPa is 0.059%. The coefficient of thermal expansion is 8.5×10 ^-6 /°C.

The α-alumina powder obtained by the method described above, polyvinylidene fluoride (PVDF) as a film binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a solvent are mixed and stirred, To prepare a porous coating (slurry), wherein the content of the filler accounts for 94wt% of the total amount of the filler and the membrane binder. The viscosity of the slurry was measured by a viscoelasticity analyzer (Physica MCR301, manufactured by Anton Paar). As a result, the viscosity was 0.32 Pa·s when the shear rate was 100 S ^-1 .

On the top surface of a sheet electrode manufactured by coating natural spherical graphite on a copper sheet, the porous coating was applied by a bar coater and then dried to obtain a uniform porous film having a thickness of 3-5 μm.

(Example 2)

Aluminum isopropoxide prepared from aluminum having a purity of 99.99% as a raw material was hydrolyzed with water to obtain aluminum hydroxide in a slurry state, which was dried to obtain a first dry powder aluminum hydroxide. Next, the first dry powdery aluminum hydroxide was wetted with pure water and then dried to obtain dry powdery aluminum hydroxide having an untamped density of 0.6 g/cm ³ .

Next, the dry powdery aluminum hydroxide was calcined by maintaining at 1220°C for 4 hours, and then pulverized by a jet mill to obtain α-alumina powder.

The obtained α-alumina powder had a BET specific surface area of 4.13 m ² /g, an average particle diameter of 0.69 μm, and a content of coarse particles having a particle diameter of 10 μm or higher of 3 ppm or higher. However, the level of coarse particles was less than 10 ppm. Regarding the content of impurities, Si content is 11 ppm, Fe content is 10 ppm, Cu content is 1 ppm or less, Na content is 5 ppm or less, Mg content is 1 ppm or less, alumina purity is 99.99wt % or higher.

Next, the obtained α-alumina powder was molded under pressures of 29, 73 and 147 MPa to obtain green compacts. The porosity of each compressed powder is 53.7, 52.0 and 50.5% (volume), the average pore diameter is in the range of 0.12-0.13μm, and the porosity change per 1MPa is 0.027%. The coefficient of thermal expansion is 8.7×10 ^-6 /°C.

In the same manner as in Example 1, except that aluminum alkoxide prepared from aluminum having a purity of 99.9% was used as a raw material, α alumina powder was obtained.

The α-alumina powder obtained by the method described above, polyvinylidene fluoride (PVDF) as a film binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a solvent are mixed and stirred, To prepare a porous coating (slurry), wherein the content of the filler accounts for 94wt% of the total amount of the filler and the membrane binder. The viscosity of the slurry was measured by a viscoelasticity analyzer (Physica MCR301, manufactured by Anton Paar). As a result, the viscosity was 0.19 Pa·s when the shear rate was 100 S ^-1 .

On the top surface of a sheet electrode manufactured by coating natural spherical graphite on a copper sheet, the porous coating was applied by a bar coater and then dried to obtain a uniform microporous film having a thickness of 3-5 μm.

The sheet-like electrode obtained by the above method was cut into a ring having a diameter of 1.45 cm to manufacture an electrode, and the obtained electrode was vacuum-dried at 120° C. for 8 hours. After vacuum drying, the obtained electrode was used as a negative electrode, a lithium foil as a positive electrode, and TF40-50 manufactured by NIPPON KODOSHI CORPORATION as a separator with a concentration of 1 mol/liter of LiPF ₆ /ethylene carbonate:dicarbonate Methyl ester: Ethyl methyl carbonate (= 20:30:30 v/v%) + 3 wt% vinylene carbonate as electrolytic solution, CR2032 type (IEC/JIS standard) coin cell to assemble bipolar battery, and then calculate the capacity retention ratio 1C/0.2C. Turns out, it's 99%.

Here, the capacity retention ratio 1C/0.2 in the present invention is calculated as follows. Using a charge and discharge evaluation device ("TOSCAT (registered trademark)-3100", manufactured by Toyo System Co., Ltd), constant current charge was performed at a current density of 60 mA/g until the bipolar battery reached 5 mV. After reaching 5 mV, charge at a constant voltage was performed until the current value became 6 mA/g, and then discharge was performed at a constant current with a current density of 60 mA/g until reaching 1.5 V. In the second cycle, the same charge and discharge were performed, and the integrated quantity of electricity when discharged in the second cycle was taken as the capacity at 0.2C. Subsequently, a third cycle was performed with constant current charging at a current density of 60 mA/g until reaching 5 mV. After reaching 5 mV, charge at a constant voltage until the current value reaches 6 mA/g. Then, discharge was performed at a constant current with a current density of 360 mA/g until reaching 1.5 V. In the fourth cycle, the same charge and discharge were performed, and the integrated amount of electric power when discharged in the fourth cycle was taken as the capacity at 1C. A value obtained by dividing the obtained capacity at 1C by the capacity at 0.2C and multiplying the value obtained by 100 was taken as the capacity retention ratio 1C/0.2C.

(comparative example 1)

First, according to the same method as in Example 1, dry powdered aluminum hydroxide was obtained. Next, the aluminum hydroxide was calcined by maintaining at 1250° C. for 2 hours, and then crushed by a vibration ball mill to obtain α alumina powder.

The obtained α-alumina powder had a BET specific surface area of 11.0 m ² /g, an average particle diameter of 0.22 μm, and a content of coarse particles having a particle diameter of 10 μm or higher of 7300 ppm or higher. Regarding the content of impurities, the Si content was 12 ppm, the Fe content was 3 ppm, the Cu content was 1 ppm, the Na content was 2 ppm, the Mg content was 1 ppm, and the alumina purity was 99.99 wt% or more.

Next, the obtained α-alumina powders were molded under pressures of 29, 73 and 147 MPa to obtain green compacts. The porosity of each pressed powder is 46.3, 44.5 and 43.7% (volume), the average pore diameter is about 0.04μm, the porosity change per 1MPa is 0.020%, and the thermal expansion coefficient of the pressed powder at 40°C-600°C is 6.1×10 ^-6 /°C.

The α-alumina powder obtained by the method described above, polyvinylidene fluoride (PVDF) as a film binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a solvent are mixed and stirred, To prepare a porous coating (slurry), wherein the content of the filler accounts for 94wt% of the total amount of the filler and the membrane binder. The viscosity of the slurry was measured by a viscoelasticity analyzer (Physica MCR301, manufactured by Anton Paar). As a result, the viscosity was 0.15 Pa·s when the shear rate was 100 S ^-1 .

On the top surface of a sheet electrode manufactured by coating natural spherical graphite on a copper sheet, the porous paint was applied by a bar coater, followed by drying. As a result, unevenness of the coating film thought to be caused by the aggregate particles occurs, and a uniform coating film cannot be obtained.

(comparative example 2)

First, according to the same method as in Example 1, dry powdered aluminum hydroxide was obtained. Next, the aluminum hydroxide was calcined by maintaining at 1270° C. for 4 hours, and then crushed by a vibration ball mill to obtain α alumina powder.

The obtained α-alumina powder had a BET specific surface area of 5.1 m ² /g, an average particle diameter of 0.52 μm, and a content of coarse particles having a particle diameter of 10 μm or higher of 800 ppm or higher. Regarding the content of impurities, the Si content was 15 ppm, the Fe content was 7 ppm, the Cu content was 1 ppm, the Na content was 4 ppm, the Mg content was 3 ppm, and the alumina purity was 99.99 wt% or more.

Next, the obtained α-alumina powder was molded under pressures of 29, 73 and 147 MPa to obtain green compacts. The porosity of each pressed powder is 42.9, 42.6 and 41.5% (volume), the average pore diameter is about 0.09μm, the porosity change per 1MPa is 0.012%, and the thermal expansion coefficient of the pressed powder at 40°C-600°C is 8.1×10 ^-6 /°C.

The α-alumina powder obtained by the method described above, polyvinylidene fluoride (PVDF) as a film binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a solvent are mixed and stirred, To prepare a porous coating (slurry), wherein the content of the filler accounts for 94wt% of the total amount of the filler and the membrane binder. The viscosity of the slurry was measured by a viscoelasticity analyzer (Physica MCR301, manufactured by Anton Paar). As a result, the viscosity was 0.11 Pa·s when the shear rate was 100 S ^-1 .

On the top surface of a sheet electrode manufactured by coating natural spherical graphite on a copper sheet, the porous paint was applied by a bar coater, followed by drying. As a result, unevenness of the coating film thought to be caused by the aggregate particles occurs, and a uniform coating film cannot be obtained.

The inorganic oxide powder of the present invention can provide an inorganic oxide porous film having an optimal porosity in relation to lithium ion conductivity which is highly suitable for lithium ion secondary battery applications and is highly uniform and thermally stable, Therefore, it is useful industrially.

Claims (6)

1. an inorganic oxide powder, it is for forming the inorganic oxide porous-film with insulating property at least one the surface in the middle of the positive pole, negative pole and the dividing plate three that use at lithium-ion secondary cell, wherein,

(1) oxide compound purity is 90wt% or higher,

(2), according to mass ratio, the coarse grained content with the particle diameter that is not less than 10 μ m is to be not more than 10 ppm,

(3) in the porosity that is not less than 29 MPa and is not more than the powder compact of the inorganic oxide powder obtaining under the pressure in the scope of 147 MPa, be to be not less than 40 volume % and to be not more than 80 volume %, the mean pore size of powder compact is 0.06 μ m or higher, and when molded powder compact under every 1MPa pressure the variable quantity of porosity be 0.020% or higher and 0.060% or lower, and

(4) this inorganic oxide is α-aluminum oxide.

2. according to the inorganic oxide powder of claim 1, the thermal expansivity of the powder compact of the inorganic oxide powder of wherein manufacturing under the pressure of 147 MPa at 40 ℃-600 ℃ is to be not less than 7 * 10 ^-6/ ℃ and be not more than 9 * 10 ^-6/ ℃.

3. an inorganic oxide slurry, it comprises according to the inorganic oxide powder of claim 1 or 2, binding agent and solvent.

4. produce the method for lithium-ion secondary cell, described battery comprises electrode group and the electrolytic solution by positive pole, negative pole and dividing plate lamination are also reeled and obtained, and the method comprises the following steps:

To according to the inorganic oxide slurry of claim 3, be coated on the surface of the positive pole that formed by the electrode mixture layer that contains electrode active material and binding agent and/or negative pole;

Then dry this slurry forms inorganic oxide porous-film.

5. produce the method for lithium-ion secondary cell, described battery comprises electrode group and the electrolytic solution by positive pole, negative pole and dividing plate lamination are also reeled and obtained, and the method comprises the following steps:

To be coated on the surface of dividing plate according to the inorganic oxide slurry of claim 3;

Then dry this slurry forms inorganic oxide porous-film.

6. a lithium-ion secondary cell, its method by claim 4 or 5 obtains.