KR100773671B1 - Method for manufacturing secondary battery - Google Patents

Abstract

A secondary battery comprising a positive electrode, a negative electrode, and a porous electronic insulating layer adhered to a surface of at least one electrode selected from the group consisting of a positive electrode and a negative electrode, and an electrolyte, wherein the porous electronic insulating layer comprises a particulate filler and a resin binder. The fine particle filler contains the amorphous particle which the some primary particle connected and fixed. It is preferable that the neck is formed between primary particles. Since the porous electronic insulating layer has a high porosity, it is possible to obtain a secondary battery which is excellent in low temperature characteristics which are particularly important in practical use and capable of high current discharge.

Secondary Battery, Porous, Separator, Particulate, Filler, Indeterminate

Description

Manufacturing method of secondary battery {METHOD FOR MANUFACTURING SECONDARY BATTERY}

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the amorphous particle which the some primary particle which concerns on this invention connected and fixed.

2 is a scanning electron microscope (SEM) photograph of a porous electronic insulating layer according to an embodiment of the present invention.

3 is a schematic view of a conventional particulate filler.

4 is a SEM photograph of the porous electronic insulating layer according to one comparative example of the present invention.

[Description of Symbols for Main Parts of Drawing]

10 ... amorphous particles 11 ... primary particles

12 ... neck

TECHNICAL FIELD The present invention relates to a secondary battery, and more particularly, to an improvement in discharge characteristics of a secondary battery by improvement of a porous electronic insulating layer adhered to an electrode surface.

A secondary battery generally includes a positive electrode and a negative electrode and a sheet-shaped separator interposed therebetween. The sheet separator serves to electrically insulate the positive electrode and the negative electrode and to hold the electrolyte solution. For example, in the conventional lithium ion secondary battery, the polyolefin microporous film is used a lot as a sheet-like separator. Moreover, the sheet-like separator which consists of polyolefin resin and an inorganic powder, etc. are also proposed (refer patent document 1). Such sheet-like separators are usually produced by stretching a resin sheet obtained by a molding method such as extrusion molding.

In recent years, in order to improve the quality of a secondary battery, bonding a porous electronic insulating layer to the electrode surface is proposed (refer patent document 1). The porous electronic insulating layer is formed on the electrode surface by applying a slurry containing a particulate filler and a resin binder to the electrode surface and drying the applied slurry with hot air. Although a porous electronic insulation layer may be used as a substitute for the conventional sheet-like separator, it may be used together with the conventional sheet-like separator.

The slurry containing the particulate filler and the resin binder is generally mixed with the particulate filler and the resin binder with the liquid component, and by dispersing the particulate filler uniformly in the liquid component with a dispersing device such as a bead mill. It is prepared. As shown in FIG. 3, a conventional particulate filler is mainly composed of spherical or nearly spherical primary particles 31, and a plurality of primary particles 31 are collected by weak van der Waals forces. Agglomerated particles 30 are formed.

Conventionally, from the viewpoint of stabilizing the thickness and porosity (porosity) of the porous electronic insulating layer, a dispersion device such as a bead mill releases the primary particles as much as possible and uniformly disperses the independent primary particles in the liquid component. Efforts have been made (see Patent Document 3).

Patent Document 1: Japanese Patent Application Laid-Open No. 10-50287

Patent Document 2: Patent No. 3371301

Patent Document 3: Japanese Patent Application Laid-Open No. 10-106530 (FIG. 2)

When a slurry in which spherical or nearly spherical primary particles independent of each other are uniformly dispersed is applied to an electrode surface, dried with hot air, and a porous electronic insulating layer is formed, short-circuit defects at the time of battery production And so on. However, primary particles which are independent of each other are easily filled with high density in the porous electronic insulating layer, and the porosity of the porous electronic insulating layer tends to be low. As a result, there arises a problem that the high rate charge / discharge characteristics of the secondary battery and the charge / discharge characteristics under low temperature environment tend to be insufficient.

On the other hand, for example, it is difficult to apply a conventional secondary battery as a power source for such a device because a certain high rate charge / discharge characteristic or a charge / discharge characteristic in a low temperature environment is required for a power supply of a mobile phone or a notebook PC. Occurs. In particular, under a low temperature environment of 0 ° C or lower, there is a possibility that the charge and discharge characteristics of a conventional secondary battery may be remarkably reduced.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to improve a high rate charge / discharge characteristic or a charge / discharge characteristic under a low temperature environment in a secondary battery in which a porous electronic insulating layer is adhered to an electrode surface to improve battery safety. .

The present invention is a secondary battery comprising a positive electrode, a negative electrode, a porous electronic insulating layer adhered to a surface of at least one electrode selected from the group consisting of a positive electrode and a negative electrode, and an electrolyte, wherein the porous electronic insulating layer is a particulate filler. And a resin binder, wherein the particulate filler relates to a secondary battery including amorphous particles in which a plurality of primary particles are connected and fixed. Herein, the term 'amorphous' is a shape having bumps, bumps or bulges derived from the primary particles, unlike a spherical or egg shape or a shape similar to these. For example, a shape such as a branch, grape cluster or coral is used. Say

It is preferable that a neck is formed between at least one pair of mutually fixed primary particles constituting the amorphous particles. That is, the amorphous particles are formed by partially melting and fixing a plurality of primary particles by heat treatment or the like. The neck is formed when the primary particles diffusely bond with each other. However, even if the particle | grains which diffused enough advance and the neck cannot be discriminated clearly can be used as an amorphous particle.

The average particle diameter of the amorphous particles is at least two times the average particle diameter of the primary particles, and is preferably 10 μm or less, more preferably three times or more the average particle diameter of the primary particles, and more preferably 5 μm or less. Moreover, it is preferable that the average particle diameter of a primary particle is 0.05-1 micrometer.

It is preferable that an amorphous particle consists of a metal oxide. In this case, the particulate filler may further include resin fine particles such as polyethylene fine particles.

It is preferable that the resin binder contained in a porous electronic insulating layer contains a polyacrylic acid derivative.

When applying this invention to a lithium ion secondary battery, it is preferable that a positive electrode contains composite lithium oxide and a negative electrode contains the material which can charge / discharge lithium. In addition, it is preferable to use the nonaqueous electrolyte which consists of a nonaqueous solvent and the lithium salt melt | dissolved as an electrolyte.

The secondary battery of the present invention may include a sheet-shaped separator independent from either of the positive electrode and the negative electrode. As the sheet separator, a conventional sheet separator including a microporous membrane made of polyolefin can be used without particular limitation.

To practice the invention  Best form for

The secondary battery of the present invention includes a positive electrode, a negative electrode, a porous electronic insulating layer adhered to a surface of at least one electrode selected from the group consisting of a positive electrode and a negative electrode, and an electrolyte. Although it is preferable to apply this invention to a lithium ion secondary battery, it is applicable also to various other secondary batteries, for example, alkaline storage battery.

This invention includes all the cases where a porous electronic insulation layer is arrange | positioned so that it may interpose between an anode and a cathode. That is, this invention includes the case where the porous electronic insulation layer is adhere | attached only on the anode surface, the case where it is adhere | attached only on the cathode surface, and the case where it is adhere | attached on both of the anode surface and the cathode surface. The present invention also relates to a case in which the porous electronic insulating layer is adhered to only one side of the anode, to the side of the anode, to the side of the cathode, and to the both sides of the cathode. It includes the case that it is.

The porous electronic insulating layer includes a particulate filler and a resin binder, and the particulate filler includes amorphous particles in which a plurality of primary particles (for example, about 2 to 10, preferably 3 to 5) are bonded and fixed to each other. Include. An example of such an amorphous particle is shown typically in FIG. The amorphous particles 10 are composed of a plurality of connected and fixed primary particles 11, and a neck 12 is formed between a pair of primary particles to be connected and fixed to each other. On the other hand, since the primary particles are usually composed of a single crystal, the amorphous particles 10 always become polycrystalline particles. That is, the amorphous particles are composed of polycrystalline particles, and the polycrystalline particles are composed of a plurality of primary particles which are diffusion bonded.

The amorphous particles to which the plurality of primary particles are connected and fixed are, for example, heat treated with a conventional particulate filler, that is, a particulate filler including primary particles independent of each other or aggregated particles in which primary particles are aggregated by van der Waals forces. And primary particles are partially melted to obtain a plurality of primary particles. The amorphous particles obtained by this method are difficult to separate into independent primary particles even when shearing force is applied.

On the other hand, even if mechanical shearing force is applied to the conventional particulate filler, it is difficult to connect and fix a plurality of primary particles. Moreover, even when aggregating primary particle using a binder previously, when preparing a slurry, it is confirmed that primary particles dissociate and return to independent primary particle.

The porous electronic insulating layer also has a similar action to that of a conventional sheet separator, but its structure is significantly different from that of a conventional sheet separator. The porous electronic insulating layer has a structure in which the particles of the particulate filler are bonded to the resin binder, unlike the microporous membrane obtained by stretching the resin sheet. Therefore, the tensile strength in the surface direction of the porous electronic insulating layer is lower than that of the sheet-shaped separator. However, the porous electronic insulating layer is excellent in that it does not thermally shrink like a sheet-like separator even when exposed to high temperature. The porous electronic insulating layer has the effect of preventing the expansion of the short circuit, preventing abnormal heating and increasing the safety of the secondary battery when an internal short circuit occurs or when the battery is exposed to high temperature.

The porous electronic insulating layer has voids for appropriately passing the nonaqueous electrolyte. The large current behavior in a low temperature environment of a secondary battery having an electrode having a porous electronic insulating layer adhered to its surface, for example, a discharge characteristic when discharged at a current value of 2 hours (2C) under an environment of 0 ° C, It depends on the porosity of the porous electronic insulation layer (the ratio of the pore volume to the porous electronic insulation layer).

The porosity of the porous electronic insulating layer can be measured by the following method, for example.

First, the particulate filler, the resin binder, and the liquid component are mixed to prepare a raw material slurry of the porous electronic insulating layer. A liquid component is suitably selected according to the kind of resin binder, etc. For example, organic solvents, such as N-methyl- 2-pyrrolidone and cyclohexanone, and water can be used. As a dispersing apparatus used when preparing a raw material slurry, the apparatus which can provide the shearing force of the grade which an amorphous particle does not disintegrate into a primary particle is preferable. For example, a median dispersing device, a bead mill to which mild conditions are applied, etc. are preferable, but it is not limited to this.

After passing through the filter of a suitable mesh size, the obtained slurry is apply | coated so that it may become predetermined thickness on the base material which consists of metal foil, for example using a doctor blade, and it will dry. The coating film formed on the base material can be considered to have the same structure as the porous electronic insulating layer adhered to the electrode surface. Therefore, the porosity of the coating film formed on the base material can be regarded as the porosity of the porous electronic insulating layer.

The porosity p of the coating film formed on the substrate is determined by the formula: p (%) = {100 × (Va-Vt)} / Va from the apparent volume Va and the true volume Vt of the coating film. Can be obtained by

The apparent volume Va of the coating film corresponds to the product (S × T) of the thickness T of the coating film and the surface area S of the coating film. On the other hand, the true volume (Vt) of the coating film is the weight ratio of the weight (W) of the coating film, the true density (Df) of the particulate filler, the true density (Db) of the resin binder, and the particulate filler and the resin binder in the coating film. Can be calculated from

For example, when the weight ratio of the particulate filler and the resin binder is x: (1-x), the true volume Vt of the coating film is the true volume (xW / Df) of the particulate filler and the true volume of the resin binder { It corresponds to the sum of (1-x) W / Db}.

In the case of using a conventional particulate filler as shown in FIG. 3, the aggregated particles 30 are easily separated into independent primary particles 31 by dispersion treatment during slurry preparation. Therefore, the porosity P of the porous electronic insulation layer is usually a low value of less than 45%, and it is difficult to form a porous electronic insulation layer having a higher porosity. The secondary battery provided with such a porous electronic insulating layer having a low porosity has insufficient high rate charge / discharge characteristics and low charge / discharge characteristics at low temperatures.

On the other hand, when using the amorphous particle 10 which the some primary particle 11 connected and fixed as shown in FIG. 1, the porous electronic insulation layer easily makes the porosity P 45% or more, and also 50% or more. Can be achieved. Achieving such a high porosity does not depend on the material of a particulate filler. Therefore, if the amorphous particles have the same shape, particle size distribution, or the like, even if any one of titanium oxide (titania), aluminum oxide (alumina), zirconium oxide (zirconia), tungsten oxide, or the like is used, high porosity is similarly achieved. can do.

When applying this invention to a lithium ion secondary battery, it is preferable that the largest particle diameter of a primary particle is 4 micrometers or less, and it is more preferable that it is 1 micrometer or less. On the other hand, in the amorphous particle, when the primary particle cannot be clearly identified, the thickest part of the knot of the amorphous particle can be regarded as the particle diameter of the primary particle.

When the primary particle diameter exceeds 4 micrometers, securing of the porosity of a porous electronic insulation layer may become difficult, or it may become difficult to bend a pole plate.

The maximum particle diameter of a primary particle can be calculated | required as these maximum values, for example by measuring the particle diameter of at least 1000 primary particle in the SEM photograph or the transmission electron microscope (TEM) photograph of an amorphous particle. In addition, when the amorphous particles are obtained by heating the primary particles, partially dissolving them, and fixing them, the maximum particle diameter of the primary particles of the raw material can be regarded as the maximum particle diameter of the primary particles constituting the amorphous particles. have. It is because the particle diameter of a primary particle hardly fluctuates in the heat processing of the grade which promotes the diffusion bonding of primary particles. The maximum particle diameter of the primary particles of the raw material can be measured, for example, by a wet laser particle size distribution measuring device manufactured by Micro Track Corporation.

When measuring the particle size distribution of primary particles, which are raw materials for amorphous particles, by a wet laser particle size distribution measuring device or the like, 99% of the primary particles (D ₉₉ ) in terms of volume are regarded as the maximum particle diameter of the primary particles. Can be.

In addition, the average particle diameter of a primary particle can also be measured as mentioned above. That is, for example, by measuring the particle diameter of at least 1000 primary particles by SEM or transmission electron microscopy (TEM) images of amorphous particles, the particle size of the primary particles that are obtained as their average value or a raw material of the amorphous particles is measured. The distribution is measured by a wet laser particle size distribution measuring device or the like, and the 50% value (median diameter: D ₅₀ ) of the primary particles on the volume basis can be regarded as the average particle diameter of the primary particles.

The average particle diameter of the amorphous particles is two times or more of the average particle diameter (preferably 0.05 µm to 1 µm) of the primary particles, and preferably 10 µm or less. In addition, from the viewpoint of obtaining a stable porous electronic insulating layer capable of maintaining high porosity over a long period, the average particle diameter of the amorphous particles is more than three times the average particle diameter of the primary particles, and more preferably 5 μm or less.

The average particle diameter of the amorphous particles can be measured, for example, by a wet laser particle size distribution measuring apparatus manufactured by Micro Track Corporation. In this case, the 50% value (median diameter: D ₅₀ ) of the amorphous particles on the volume basis can be regarded as the average particle diameter of the amorphous particles. If the average particle diameter of the amorphous particles is less than twice the average particle diameter of the primary particles, the porous electronic insulation layer may have a dense filling structure, and if it exceeds 10 µm, the porosity of the porous electronic insulation layer may be excessive (e.g., For example, more than 80%), the structure may fall.

In the case of a lithium ion secondary battery, although the thickness of a porous electronic insulation layer is not specifically limited, For example, it is preferable to set it as 20 micrometers or less. Application of the raw material slurry of the porous electronic insulating layer to the electrode surface is performed by a die nozzle method, a blade method, or the like. Therefore, when the average particle diameter of the amorphous particles increases, large particles are easily caught in the gap between the electrode surface and the front edge of the blade, for example, when the raw material slurry of the porous electronic insulating layer is applied to the electrode surface. Gold may generate | occur | produce and the ratio of a product produced may fall. Therefore, it is preferable that the average particle diameter of amorphous particle also is 10 micrometers or less from a viewpoint of a product ratio.

In the present invention, it is preferable to obtain amorphous particles from the primary particles of the metal oxide. As the metal oxide constituting the particulate filler, for example, titanium oxide, aluminum oxide, zirconium oxide, tungsten oxide, zinc oxide, magnesium oxide, silicon oxide, or the like can be used. These may be used independently and may be used in combination of 2 or more type. Among these, aluminum oxide (alumina) is particularly preferable from the viewpoint of chemical stability, and α-alumina is particularly preferable.

The particulate filler may comprise resin particulates. The specific gravity of the resin fine particles is about 1.1, and since it is considerably lighter than the metal oxide having a specific gravity of about 4 and around, it is effective for lightening the secondary battery. As the resin fine particles, polyethylene fine particles and the like can be used, for example.

However, since the production cost increases when the resin fine particles are used, the ratio of the resin fine particles to the whole of the fine particle filler is 50% by weight or less from the viewpoint of the production cost, even when the metal oxide is used alone or the resin fine particles are used. It is desirable to.

Although the component material of the resin binder contained in a porous electronic insulation layer is not specifically limited, For example, polyacrylic acid derivative, polyvinylidene fluoride (PVDF), polyethylene, a styrene-butadiene rubber, polytetrafluoroethylene (PTFE) And tetrafluoroethylene-hexafluoropropylene copolymer (FEP). These may be used independently and may be used in combination of 2 or more type.

In alkaline storage batteries and lithium ion secondary batteries, it is mainstream to use a group of electrode plates wound around a positive electrode and a negative electrode. However, in order to form a group of electrode plates having such a wound structure, flexibility is required for the porous electronic insulating layer bonded to the surface of the electrode plates. From the viewpoint of imparting such flexibility to the porous electronic insulating layer, it is preferable to use a polyacrylic acid derivative as the resin binder.

In the porous electronic insulating layer, the ratio of the resin binder to the total of the particulate filler and the resin binder is preferably 1 to 10% by weight, more preferably 2 to 4% by weight.

When the present invention is applied to a lithium ion secondary battery, a non-aqueous electrolyte consisting of a composite lithium oxide for the positive electrode, a material capable of charging and discharging lithium for the negative electrode, and a nonaqueous solvent and a lithium salt dissolved therein for the electrolyte. It is preferable to use.

As the composite lithium oxide, for example, lithium-containing transition metal oxides such as lithium cobalt acid, lithium nickelate and lithium manganate are preferably used. Moreover, the modified body which substituted a part of transition metal of lithium containing transition metal oxide with another element is also used preferably. For example, cobalt of lithium cobalt is preferably substituted with aluminum, magnesium, or the like, and nickel of lithium nickelate is preferably replaced with cobalt. Composite lithium oxide may be used individually by 1 type, and may be used in combination of multiple types.

Examples of the material capable of charging and discharging lithium used for the negative electrode include various natural graphites, various artificial graphites, silicon-based composite materials, various alloy materials, and the like. These materials may be used individually by 1 type, and may be used in combination of multiple types.

Although it does not specifically limit to a nonaqueous solvent, For example, Carbonate ester, such as ethylene carbonate (EC), a propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC); carboxylic acid esters such as γ-butyrolactone, γ-valerolactone, methyl formate, methyl acetate and methyl propionate; Ethers such as dimethyl ether, diethyl ether and tetrahydrofuran are used. A nonaqueous solvent may be used individually by 1 type, and may be used in combination of 2 or more type. In these, especially carbonic acid ester is used preferably.

Although it does not specifically limit to a lithium salt, For example, LiPF ₆ and LiBF ₄ Etc. are preferably used. These may be used alone or in combination.

In the nonaqueous electrolyte, in order to ensure stability during overcharging, an additive which forms a good film on the positive electrode and / or the negative electrode, for example, vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and cyclohexyl benzene (CHB) It is preferable to add a small amount and the like.

In addition to the porous electronic insulating layer, the secondary battery of the present invention may further include a separator independent of any of the positive electrode and the negative electrode. As such a separator, a conventional sheet-like separator can be used without particular limitation, including a polyolefin microporous membrane. On the other hand, when a conventional sheet-like separator is not used, the porous electronic insulating layer plays a role of the separator. In that case, a secondary battery can be provided at low cost.

In a lithium ion secondary battery, when the conventional sheet-like separator is not used, it is preferable that the thickness of a porous electronic insulation layer is 1-20 micrometers. In addition to the porous electronic insulating layer, when using a conventional sheet-like separator (preferable thickness of 5 to 20 µm), the thickness of the porous electronic insulating layer is preferably 1 to 15 µm.

As the sheet separator, it is necessary to use a material having resistance to the environment in the secondary battery. Generally, the microporous membrane which consists of polyolefin resins, such as polyethylene and a polypropylene, is used. By using a sheet-like separator, a short circuit becomes harder to occur and the safety and reliability of a secondary battery improve.

Hereinafter, when manufacturing a lithium ion secondary battery using the particulate filler which consists of aluminum oxide, this invention is demonstrated based on an Example, However, These Examples illustrate the secondary battery of this invention, and this invention It is not intended to limit.

Example  One

(i) Preparation of Particulate Filler Containing Amorphous Particles

(a) Primary particles of aluminum oxide (alumina) having an average particle diameter of 0.1 µm, which are raw materials for amorphous particles, are heated in air at a temperature of 1100 ° C. for 20 minutes to produce amorphous particles in which a plurality of primary particles are connected and fixed. I was. The size of the obtained amorphous particles was adjusted by using an alumina ball having a diameter of 15 mm and a wet ball mill to obtain a particulate filler A1 having an average particle diameter of 0.5 µm.

(b) Primary particles of titanium oxide (titania) having an average particle diameter of 0.2 μm, which are raw materials for amorphous particles, are heated at 800 ° C. in air for 20 minutes to produce amorphous particles in which a plurality of primary particles are connected and fixed. I was. The size of the obtained amorphous particle was adjusted by the method similar to particulate filler A1, and the fine particle filler A2 of 0.5 micrometer of average particle diameters was obtained.

(c) Primary particles of aluminum oxide (alumina) having an average particle diameter of 0.5 µm were used as the fine particle filler B1 in the state as it is.

(d) Fine particles containing agglomerated particles having an average particle diameter of 0.5 μm by applying a mechanical shearing force to a primary particle of aluminum oxide (alumina) having an average particle diameter of 0.1 μm by means of a vibration mill having an alumina bar having a diameter of 40 mm. Filler B2 was obtained.

(e) 4% by weight of polyvinylidene fluoride (PVDF) is added to the primary particles of aluminum oxide (alumina) having an average particle diameter of 0.1 µm, followed by mixing, and fine particle filler B3 containing aggregated particles having an average particle diameter of 0.5 µm. Got.

(Ii) Preparation of Raw Material Slurry of Porous Electronic Insulation Layer

(a) 100 parts by weight of fine particle filler A1, 4 parts by weight of a polyacrylic acid derivative (solid content of BM720H manufactured by Nihon Xeon Co., Ltd.) (resin binder), and an appropriate amount of N-methyl-2-pyrrolidone (liquid component ) Was mixed using a stirrer to prepare a mixture having a content of nonvolatile components of 60% by weight. This mixture was poured into a 0.6 L bead mill with a zirconia bead mill 3 mm in diameter in an amount equivalent to 80% by volume of the volume. The bead mill was operated to uniformly disperse the fine particle filler A1 in the liquid component to obtain slurry A1.

(b) Slurry A2, B1, B2, and B3 were respectively prepared by the method similar to slurry A1 except having used particulate filler A2, B1, B2, or B3 instead of particulate filler A1.

(Iii) the porosity of the porous electronic insulating layer

(a) Slurry A1 was apply | coated on metal foil using the doctor blade, and the coating film (porous electronic insulation layer A1) of about 20 micrometers in thickness after drying was formed. The apparent volume Va of this coating film is obtained from the thickness (T) of the coating film and the surface area (S) of the coating film, and the true volume (Vt) of the coating film is determined by the weight (w) of the coating film and the true density (Df) of the particulate filler. And the weight ratio of the fine particle filler and resin binder in the true density (Db) of the resin binder and the coating film.

It was 60% when the porosity p of the coating film was calculated | required by calculation formula: P (%) = {100x (Va-Vt)} / Va. Moreover, the top surface of the coating film, ie, the porous electronic insulation layer A1, was observed by SEM, and the SEM photograph shown in FIG. 2 was taken. It can be seen from FIG. 2 that large voids are formed in the porous electronic insulating layer A1 filled with the amorphous particles to which the plurality of primary particles are connected and fixed.

(b) Instead of slurry A1, porous electronic insulation layers A2, B1, B2 and B3 were formed using slurry A2, B1, B2 or B3, respectively, and these porosities were calculated | required. The porosities of the porous electronic insulating layers A2, B1, B2, and B3 were 58%, 44%, 45%, and 44%, respectively. Moreover, the upper surface of the porous electronic insulation layer B1 was observed by SEM, and the SEM photograph shown in FIG. 4 was taken. From FIG. 4, it turns out that independent primary particle is filled with high density in porous electronic insulation layer B1, and large void is not formed.

The above result is put together in Table 1 and shown.

 Porous electronic insulation layer Particulate filler Primary particle diameter (㎛) Secondary particle diameter * (㎛) Porosity (%) A1 Alumina Twig-Shaped Particles     0.1      0.5    60 A2 Titania twig particles     0.1      0.5    58 B1 Alumina Primary Particles     0.5       -    44 B2 Alumina Agglomerated Particle (Shear Force)     0.1      0.5    45 B3 Alumina Aggregated Particles (PVDF Added)     0.1      0.5    44

Secondary particles: Twig-shaped particles or aggregated particles

As is apparent from the above results, the porous electronic insulating layer using the particulate filler containing amorphous particles has a large porosity clearly compared with the use of the particulate filler containing independent primary particles or aggregated particles. Moreover, it turns out that the magnitude | size of a porosity is hardly influenced by the material (kind of oxide) which comprises a particulate filler.

In the case of using the particulate filler B2 in which the primary particles are agglomerated by applying a mechanical shearing force by vibrating mill, the porosity of the porous electronic insulation layer is low, and in the porous electronic insulation layer B2, the aggregated particles deviate and return to the primary particles. It was confirmed by the SEM photograph. Moreover, also about the fine particle filler B3 which added PVDF and aggregated the primary particle, in the porous electronic insulation layer B3, it was confirmed by SEM photograph that aggregated particle has separated and returned to the primary particle. This reason can be considered to be because agglomerated particles receive a shear force in the bead mill during slurry production.

On the other hand, it can be understood that the amorphous particles have a high porosity since the primary particles can almost maintain their shape even when subjected to a shearing force in the bead mill, without causing primary particles to deviate.

(iv) Fabrication of Lithium Ion Secondary Batteries

Using the slurry A1, A2, and B1, the lithium ion secondary battery to which the porous electronic insulation layer was affixed on both surfaces of the negative electrode was produced, and these charge / discharge characteristics were evaluated.

(Production of the cathode)

3 kg of artificial graphite (cathode active material), 75 g of rubber particles (cathode binder) made of a styrene-butadiene copolymer, and 30 g of carboxymethyl cellulose (CMC: thickener) were stirred together with an appropriate amount of water in a twin coupling machine, A negative electrode mixture paste was prepared. This paste was applied to both surfaces of a copper foil having a thickness of 10 µm, and dried to obtain a negative electrode disk. The negative electrode was rolled to a total thickness of 180 µm and an active material layer density of 1.4 g / cm 3.

(Production of the anode)

3 kg of lithium cobalt acid (LiCoO ₂ : positive electrode active material), 120 g of PVDF (anode binder) and 90 g of acetylene black (anode conductive agent) together with an appropriate amount of N-methyl-2-pyrrolidone (NMP) The mixture was stirred in an associator to prepare a positive electrode mixture paste. This paste was applied to both surfaces of an aluminum foil having a thickness of 15 µm and dried to obtain a positive electrode disk. This anode disk was rolled to a total thickness of 160 탆 and an active material layer density of 3.3 g / cm 3.

(Assembly of the battery)

Slurry A1 was apply | coated and dried on both surfaces of the negative electrode disk after rolling, and the porous electronic insulating layer of thickness 5micrometer was formed. Thereafter, the negative electrode disk having the porous electronic insulating layer bonded to both surfaces thereof was cut into a predetermined width that can be inserted into a cylindrical 18650 battery case, thereby obtaining a negative electrode having a predetermined size. The anode disc after rolling was also cut into a predetermined width that can be inserted into a cylindrical 18650 battery case to obtain an anode of a predetermined size.

The positive electrode and the negative electrode to which the porous electronic insulating layer were adhered to both surfaces were wound up through a sheet-shaped separator made of polyethylene resin having a thickness of 15 µm, thereby forming a pole plate group. This electrode plate group was inserted into a cylindrical 18650 battery case, and 5 g of nonaqueous electrolyte was injected.

As the nonaqueous electrolyte, LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 2: 3: 3, and 3% by weight of vinylene carbonate was used. .

Thereafter, the battery case was sealed to complete a lithium ion secondary battery A1 having a design capacity of 2000 mAh. In addition, lithium ion secondary batteries A2 and B1 were produced by the method similar to battery A1 except having used slurry A2 and B1 instead of slurry A1.

(v) battery evaluation

The completed lithium ion secondary batteries A1, A2, and B1 were subjected to two practice charging and discharging, and stored for 7 days in a 45 ° C environment. Thereafter, charging and discharging were performed under the following conditions in a 20 ° C environment.

(1) Constant current discharge: 400mA (3V end voltage)

(2) Constant current charge: 1400mA (end voltage 4.2V)

(3) Constant voltage charging: 4.2V (final current 100mA)

(4) constant current discharge: 400mA (end voltage 3V)

(5) Constant current charge: 1400mA (end voltage 4.2V)

(6) Constant voltage charge: 4.2V (final current 100mA)

After the above charging / discharging, each battery was left for 3 hours. Then, the following charging and discharging was performed in 0 degreeC environment.

(7) Constant current discharge: 4000mA (final voltage 3V)

The discharge capacity at this time was made into 0 degreeC-2C discharge characteristics. The 0 ° C-2C discharge characteristics of each battery are summarized in Table 2.

Slurry Particulate filler 0 ℃ -2C Discharge Characteristics (mAh) A1 Alumina Twig-Shaped Particles 1820 A2 Titania twig particles 1780 B1 Alumina Primary Particles 1590

From the above result, it turns out that the battery provided with the porous electronic insulating layer which has a large porosity shows the outstanding low temperature discharge characteristic. On the other hand, the battery provided with the porous electronic insulating layer with a small porosity formed without using amorphous particles can be seen that the low-temperature discharge characteristics are significantly reduced.

Example  2

The slurry after preparation is provided for formation of a porous electronic insulation layer after passing through processes, such as a refinement | purification by a filter. Therefore, in order to stabilize the physical property of a porous electronic insulation layer, it is preferable that sedimentation of a particulate filler hardly progresses for several days after slurry preparation. On the other hand, the inventors have found that the progress of sedimentation depends on the average particle diameter of the primary particles of the particulate filler. Therefore, in this Example, the relationship between the average particle diameter of the primary particle of a particulate filler, and settling degree is demonstrated.

The average particle diameter of the primary particle of aluminum oxide which is a raw material of amorphous particle was changed from 0.1 micrometer to 0.01 micrometer, 0.01 micrometer, 0.05 micrometer, 0.3 micrometer, 0.5 micrometer, 1 micrometer, 2 micrometer, 3 micrometer, or 4 micrometer. In the same manner as in the particulate filler A1 of 1, a plurality of primary particles were produced to form amorphous particles to which the primary particles were connected and fixed, and the size of the amorphous particles was adjusted so that the average particle diameters were 0.03 µm, 0.16 µm, 0.8 µm, 1.3 µm and 2.5, respectively. Particulate fillers C1, C2, C3, C4, C5, C6, C7 and C8 having a thickness of 6 m, 6 m, 8 m or 10 m were prepared.

Slurry C1, C2, C3, C4, C5, C6, and C7 in the same manner as slurry A1, except that particulate filler C1, C2, C3, C4, C5, C6, C7 or C8 was used instead of particulate filler A1. C8 was prepared. The obtained slurry was left to stand in 25 degreeC environment, and the progress of sedimentation was observed visually every day.

As a result, in the slurry C1-C5 whose average particle diameter of a primary particle is 0.01-1 micrometer, even if it passed over 4 days, sedimentation of the particulate filler was hardly seen. On the other hand, in the slurry C6-C8 whose average particle diameter of a primary particle is 1 micrometer or more, sedimentation of the particulate filler was observed in less than one day.

On the other hand, when the particle size distribution of the primary particle used for the raw material of particulate filler C1-C5 was measured, the maximum particle diameter ( _D99 ) was 3 micrometers or less in all. On the other hand, was a measure of the particle size distribution of the primary particles used for the raw material of the fine particle filler C6~C8, any image exceeds the maximum particle size (D ₉₉₎ is 3㎛.

Lithium ion secondary batteries C1 to C5 were produced in the same manner as in Example 1, except that slurries C1 to C5 were used, and their 0 ° C.-2C discharge characteristics were evaluated. It was significantly superior.

Example  3

Except for changing the average particle diameter of primary particles of aluminum oxide, which is a raw material of amorphous particles, from 0.1 µm to 0.2 µm, the amorphous particles in which a plurality of primary particles were bonded and fixed in the same manner as in the particulate filler A1 of Example 1 Generated. However, by adjusting the size of the amorphous particles in various ways, the particulate filler D1 having an average particle diameter of 0.3 µm, 0.4 µm, 0.5 µm, 0.7 µm, 1.2 µm, 3 µm, 8 µm, 10 µm, 12 µm or 15 µm, respectively, D2, D3, D4, D5, D6, D7, D8, D9 and D10 were prepared.

The size adjustment of the amorphous particle was performed using the wet ball mill filled with the alumina ball whose 30% of the inside volume was 3 mm in diameter. The average particle diameter of the amorphous particles was changed by changing the operating time of the ball mill.

Slurry D1, D2, D3, D4, D5, by the same method as slurry A1, except that particulate filler D1, D2, D3, D4, D5, D6, D7, D8, D9, or D10 was used instead of the particulate filler A1. D6, D7, D8, D9 and D10 were prepared.

Each slurry was applied onto a metal foil using a general blade coater. The target thickness of the coating film was 20 micrometers. As a result, in the slurry D1-D8 whose average particle diameter of amorphous particles was 10 micrometers or less, the coating film with a uniform surface was formed. On the other hand, when the slurry D9 and D10 containing the amorphous particle whose average particle diameter of amorphous particle | grains exceeded 10 micrometers were used, the frequency of generation | occurrence | production of the gold on the surface of a coating film was high, and the product product ratio fell large.

Subsequently, lithium ion secondary batteries D1 to D8 were produced in the same manner as in Example 1, except that slurries D1 to D8 were used, and their 0 ° C.-2C discharge characteristics were evaluated. It was superior in battery width B1.

In addition, the results of the batteries D2 to D5 were particularly good in the 0 ° C-2C discharge characteristics, and the results of the batteries D3 and D4 were particularly remarkably good. Therefore, the average particle diameter of the amorphous particles is preferably about 2 to 6 times the average particle diameter of the primary particles, and most preferably about 2.5 to 3.5 times.

Example  4

The most common structure of the pole plate group of a secondary battery is the structure which wound the positive electrode and the negative electrode through the sheet-shaped separator. Therefore, when the porous electronic insulating layer is hard, the porous electronic insulating layer cracks or peels off from the electrode surface. Therefore, in the present embodiment, the case where the flexibility of the porous electronic insulating layer is changed will be described.

Slurry E1 was prepared in the same manner as Slurry A1 of Example 1 except that polyvinylidene fluoride (PVDF) was used instead of the polyacrylic acid derivative, and using this, 500 cells similar to those of Battery A1 of Example 1 were used. Produced. In addition, 500 batteries A1 of Example 1 were similarly produced.

When the voltage between terminals of each battery was measured and the presence or absence of an internal short circuit was confirmed, the occurrence rate of short circuit failure was large at 10% for battery E1, but the occurrence rate of short circuit failure of battery A1 was 0.4%. On the other hand, the short-circuit defect occurrence rate of the conventional general lithium ion secondary battery is 0.5% or less. When the battery E1 in which short circuit failure was recognized was disassembled and the state of the porous electronic insulating layer containing PVDF as a resin binder was observed, many cracks were observed, and particularly, cracks were remarkable near the center of the electrode plate group.

On the other hand, when battery A1 was decomposed | disassembled and the state of the porous electronic insulation layer containing a polyacrylic acid derivative as a resin binder was observed, the crack was not seen at all. The above results show that PVDF provides a porous electronic insulating layer having a relatively high hardness, but the polyacrylic acid derivative provides a porous electronic insulating layer having excellent flexibility.

Example  5

The battery F1 was prepared in the same manner as the battery A1 of Example 1, except that the thickness of the porous electronic insulating layers formed on both sides of the negative electrode was changed from 5 µm to 20 µm, and a sheet-shaped separator made of polyethylene resin was not used. .

When the 0 degreeC-2C discharge characteristic of battery F1 was evaluated, 1750 mAh was achieved and it was confirmed that battery F1 has the outstanding low temperature discharge characteristic of the same level as battery A1. On the other hand, since battery F1 can omit the conventional expensive sheet-like separator, manufacturing cost becomes inexpensive and it is thought that it is very promising industrially.

In the amorphous particles according to the present invention, since a plurality of primary particles are connected and fixed, unlike the aggregated particles in which a plurality of primary particles are gathered by van der Waals, it is not easy to separate them into independent primary particles. none. By using such amorphous particles, it is avoided that the particulate filler is densely packed in the porous electronic insulating layer. Therefore, it is possible to easily form a porous electronic insulating layer having a significantly higher porosity than in the related art, and it is possible to greatly improve the high rate charge / discharge characteristics of the secondary battery or the charge / discharge characteristics under a low temperature environment.

Since the amorphous particles to which the plurality of primary particles are bonded and fixed have a complicated three-dimensional structure, it can be considered that the amorphous particles act together with each other when forming the porous electronic insulating layer, thereby preventing high-density filling of the particulate filler.

In the step of dispersing the amorphous particles in which a plurality of primary particles are connected and fixed in a liquid component to prepare a slurry, the shape can be maintained with high probability even when subjected to strong shearing force by the dispersing apparatus. Therefore, a porous electronic insulating layer having a stable and high porosity can be formed.

Moreover, according to this invention, the secondary battery which is excellent in the high-rate charge-discharge characteristic and the charge / discharge characteristic under low temperature environment, and excellent also in safety can be provided at low cost.

INDUSTRIAL APPLICABILITY The present invention is particularly effective for a lithium ion secondary battery that can be applied to various secondary batteries including a lithium ion secondary battery, and requires high security and compatibility with high temperature discharge characteristics and high rate discharge characteristics. Do. The market size of lithium ion secondary batteries is large, and the present invention plays a large role in improving performance and improving safety of products.

Claims (9)

Forming an amorphous particle comprising primary particles, having a shape of bumps or bulges, or a branch shape, grape cluster or coral shape, Adjusting the average particle diameter of the amorphous particles to obtain a particulate filler; Mixing the particulate filler, the resin binder, and a liquid component to prepare a slurry; Manufacturing a positive electrode and a negative electrode, Forming a porous electronic insulating layer by applying the slurry to at least one surface selected from the group consisting of the anode and the cathode; Winding the positive electrode and the negative electrode through the porous electronic insulating layer to produce an electrode plate group; And inserting the electrode plate group into the battery case to inject the electrolyte. The method for manufacturing a secondary battery according to claim 1, wherein the step of forming the amorphous particles includes a step of forming a neck between the primary particles. The method for manufacturing a secondary battery according to claim 1, wherein the step of forming the amorphous particles includes a step of partially melting the primary particles to fix the plurality of primary particles. The secondary battery manufacturing according to claim 1, wherein in the step of obtaining the particulate filler, the average particle diameter of the amorphous particles is adjusted to be at least 2 times the average particle diameter of the primary particles and to be 10 µm or less. Way. The method for manufacturing a secondary battery according to claim 1, wherein the amorphous particles are made of a metal oxide. The method of manufacturing a secondary battery according to claim 5, wherein the particulate filler further comprises resin fine particles. The method of manufacturing a secondary battery according to claim 1, wherein the resin binder contains a polyacrylic acid derivative. The method of manufacturing a secondary battery according to claim 1, wherein the positive electrode comprises a composite lithium oxide, the negative electrode comprises a material capable of charging and discharging lithium, and the electrolyte comprises a nonaqueous solvent and a lithium salt dissolved therein. The method for manufacturing a secondary battery according to claim 1, wherein the electrode plate group includes a sheet-shaped separator interposed between the positive electrode and the negative electrode and independent of any of the positive electrode and the negative electrode.

Images