JP2005268066A - Battery and manufacturing method thereof - Google Patents

Abstract

A battery having improved current collection and PTC functions is provided.
In a battery including an electrode containing an active material and an electronically conductive material in contact with the active material, a resin such as high-density polyethylene, low-density polyethylene, polyurethane elastomer, and polyvinyl chloride is replaced with xylene or the like. It is obtained by dissolving a conductive filler such as carbon black having a particle diameter of 35 nm or more, cooling the obtained solution, and precipitating a mixture of the resin and the conductive filler. With electronically conductive material.
[Selection figure] None

Description

  The present invention relates to a battery and a method for manufacturing the same, and more particularly to a battery including an electrode containing an active material and an electronic conductive material that contacts the active material, and a method for manufacturing the same.

In recent years, with the development of electronic devices, the capacity and the output density of batteries used as power sources have been increasing. As a battery that satisfies these requirements, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are promising. In the active material layer constituting the electrode of this lithium ion secondary battery, in order to secure current collection (electron conduction path) from the active material to the current collector, the electron conductive material is used as the active material and current collector. It is known to make contact. It is also known to introduce a conductive additive into the layer in order to further improve current collection.
On the other hand, non-aqueous electrolyte secondary batteries have high energy density, but they generate more heat than water electrolyte secondary batteries due to charging troubles such as overcharging and short circuits inside and outside the battery. There is.
As a countermeasure, when the temperature rises due to an internal short circuit or the like and a large short circuit current is generated, the inside of the active material layer blocks the charge conduction electron conduction path by increasing the resistivity inside the battery nonlinearly. A non-aqueous electrolyte battery in which a PTC (Positive Temperature Coefficient) function is provided in the electronic conductive material is disclosed (for example, Patent Document 1).

Such an electronic conductive material is obtained by mixing a conductive filler (carbon black, etc.) and a resin (polyethylene, etc.) by a kneading method, and kneading the two at a temperature equal to or higher than the melting point of the resin. It is made by crushing the body.
However, when an electronic conductive material is produced by this kneading method, in order to uniformly disperse the conductive filler in the resin, it must be kneaded for a certain period of time while applying a shearing force at a certain torque or more. As a result, the temperature of the kneaded product rises and the resin may be decomposed or deteriorated. Further, when the amount of the conductive filler mixed in the resin is increased, the shearing force is excessively applied during the kneading and heat is generated, and the resin may be decomposed or deteriorated. Therefore, since the amount of the conductive filler to be mixed is limited, the manufactured electronic conductive material has a high resistivity. Furthermore, when the electronically conductive material produced in this way is pulverized, it is difficult to break down to a few μm or less because it is difficult to break due to the flexibility caused by the resin in the electronically conductive material. For this reason, the particle size of the electronic conductive material mixed into the electrode becomes large, and as a result, the number of contact points between the active material particles and the electronic conductive material cannot be secured, resulting in a decrease in current collection and a severe situation. It was difficult to ensure the PTC function.
As a countermeasure against this, since the current collecting property is insufficient only with the electronic conductive material, a conductive additive is added in the active material layer to compensate for this (for example, cited reference 2).
However, when a conductive additive is added, the current collecting property is improved, but the PTC function is lowered. That is, when the battery reaches a high temperature and exceeds the melting point of the resin in the electronic conductive material, the resistivity of the electronic conductive material increases and restricts the current flowing in the electrode. As a result, the change in resistivity of the entire electrode becomes small.

WO99 / 40640 pamphlet International Publication No. 00/77867 Pamphlet

  The present invention has been made to solve the above-described problems, and has improved current collection and PTC function in an active material layer by using an electronic conductive material having a low resistivity and a large resistivity change with respect to temperature. It aims at obtaining the battery which has this.

The present invention provides a battery comprising an electrode containing an active material and an electronically conductive material in contact with the active material, wherein the electronically conductive material is a mixture of a conductive filler and a resin, and the conductive material The filler has a particle size in the range of 35 nm or more and not more than the particle size of the active material.
Further, the method for manufacturing the battery includes a dispersion step of dispersing the conductive filler having a particle size of 35 nm or more and not more than the particle size of the active material in a solution in which the resin is dissolved; And depositing a mixture with the conductive filler to obtain the electronic conductive material.

  According to the present invention, by setting the particle size of the conductive filler to a range of 35 nm or more and not more than the particle size of the active material, the dispersibility of the conductive filler in the electronic conductive material becomes good and uniform, and the electron Since the proportion of the conductive filler in the conductive material can be increased, an electronic conductive material having a low resistivity and a large resistivity change with respect to temperature can be obtained. By using such an electronic conductive material in the active material layer, a battery having improved current collection and PTC function in the active material layer can be obtained. Moreover, since the addition amount of the conductive additive in the active material layer can be reduced, the change in resistivity with respect to temperature can be increased, and the PTC function of the battery can be further improved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing the structure of a cylindrical lithium ion secondary battery to which the present invention can be applied, and FIG. 2 is an enlarged cross-sectional view schematically showing the main part of the secondary battery. FIG. 3 is an enlarged cross-sectional view schematically showing an electronic conductive material which is a constituent component of the secondary battery.
As shown in FIG. 1, the secondary battery includes, for example, a stainless steel outer can 200 that also serves as a negative electrode terminal, and a battery body 100 accommodated in the outer can 200. The battery body 100 is configured by winding a positive electrode 1, a separator 3, and a negative electrode 2 in a spiral shape, and the separator 3 is disposed between the positive electrode 1 and the negative electrode 2. The separator 3 is composed of a porous film, and holds a nonaqueous electrolytic solution containing lithium ions.

Next, with reference to FIG.2 and FIG.3, the positive electrode 1 and the negative electrode 2 with which the secondary battery was equipped are demonstrated in detail.
The positive electrode 1 includes a positive electrode current collector 4 and a positive electrode active material layer 6 formed on the surface thereof. The positive electrode active material layer 6 is configured by bonding a positive electrode active material 8, an electronic conductive material 9, and a conductive additive 10 with a binder 11. The positive electrode active material 8 is in contact with the electronic conductive material 9 and the conductive auxiliary agent 10. For this reason, the electron conductive material 9 having a large particle diameter forms a fundamental path for electron conduction, while the conductive auxiliary agent 10 having a small particle diameter is dispersed throughout the periphery of the positive electrode active material 8 to form the positive electrode active material. An electron conduction path is secured so that current can be collected from 8 to the positive electrode current collector 4.

As shown in FIG. 3, the electronic conductive material 9 is composed of a conductive filler 12 and a resin 13.
In the present embodiment, the conductive filler 12 has a particle size of 35 nm or more and a particle size of the positive electrode active material 8 or less. Since the conductive filler 12 having such a particle size has a high bulk density, the dispersibility of the conductive filler 12 in the electronic conductive material 9 becomes good and uniform, and the conductive filler in the electronic conductive material 9 The ratio of 12 can be increased. Therefore, since it can be set as the electronic conductive material 9 which has a low resistivity and a big resistivity change with respect to temperature, the current collection property and PTC function in the positive electrode active material layer 6 can be improved. Furthermore, since the addition amount of the conductive auxiliary agent 10 can be reduced, the electronic conductive material 9 having a higher resistance change rate with respect to temperature can be obtained. When the particle diameter of the conductive filler 12 is less than 35 nm, the dispersibility becomes insufficient due to the aggregation of the conductive filler 12 itself, and the low-resistivity electronic conductive material 9 cannot be obtained. On the other hand, when the particle size of the conductive filler 12 exceeds the particle size of the positive electrode active material 8, the electronic conductive material 9 itself is too large. It cannot be secured, and the current collecting property becomes insufficient.

For the conductive filler 12, for example, a carbon material and a non-oxidizing conductor can be used. Examples of the carbon material include carbon black, graphite, carbon fiber, and metal carbide. Examples of the carbon black include acetylene black, furnace black, and lamp black. Non-oxidizing conductors include, for example, metal carbides, metal nitrides, metal silicides, and metal borides. Examples of the metal carbide include TiC, ZrC, VC, NbC, TaC, Mo ₂ C, WC, B ₄ C, and Cr ₃ C ₂ , and examples of the metal nitride include TiN, ZrN, VN, NbN, There are TaN, Cr ₂ N and the like, and examples of the metal boride include TiB ₂ , ZrB ₂ , NbB ₂ , TaB ₂ , CrB, MoB and WB.

The resin 13 may be a resin having a large density change due to a phase transition such as melting, such as high-density polyethylene (melting point: 130 to 140 ° C.), low-density polyethylene (melting point: 110 to 112 ° C.), There are polymer compounds such as polyurethane elastomer (melting point: 140 to 160 ° C.) and polyvinyl chloride (melting point: about 145 ° C.).
By using such a resin 13, the electronic conductive material 9 is formed between the conductive fillers 12 by causing the resin 13 contained therein to undergo a phase transition in the vicinity of the melting point thereof to expand in volume. The PTC function is manifested by separating and increasing the resistivity of the electronic conductive material 9 itself. That is, when the temperature rises to the melting point of the resin, the PTC function of the electronic conductive material 9 expands in volume due to melting of the resin 13, disconnects the current collecting network of the conductive filler 12, and makes the resistivity nonlinear. Increase. In a battery having such a function, the electrode itself limits the current when the battery generates heat not only by an external short circuit but also by an internal short circuit.
In addition, the magnitude | size of the resistance of the electrode at the time of normal, ie, before a PTC function expresses, can be adjusted by changing the ratio of the electronic conductive material 9 and the conductive support agent 10 with respect to the positive electrode active material layer 6 whole. .
The proportion of the electronic conductive material 9 contained in the positive electrode active material layer 6 is preferably 3 to 15% by weight.

For the positive electrode active material 8, a cobalt-based oxide, a manganese-based oxide, an iron-based oxide, or the like can be used. Examples of the cobalt-based oxide include LiCoO ₂ crystals or those in which some Co atoms are replaced with transition metal atoms (eg, Ni atoms, Mn atoms, etc.) in the LiCoO ₂ crystals. Further, the manganese-based oxide, for example _{LiMnO 2, LiMn 2 O 4,} LiM y Mn 2-y O 4 (M: Cr, Co, Ni , etc.). Furthermore, examples of the iron-based oxide include LiFeO ₂ , Li ₅ FeO ₄ , Fe ₂ (SO ₄ ) _{3, and the} like. The proportion of the positive electrode active material 8 contained in the positive electrode active material layer 6 is preferably 80 to 95% by weight. The particle size of the positive electrode active material 8 is preferably 0.5 μm to 10 μm. Within this range, the packing density of the active material can be increased, and contact with other materials can be improved, so that the current collecting property can be improved.

  Carbon black, graphite, carbon fiber, or the like can be used for the conductive assistant 10. The proportion of the conductive auxiliary agent 10 contained in the positive electrode active material layer 6 varies depending on the type of the conductive auxiliary agent 10 to be used. If too much is added, even if the PTC function of the electronic conductive material 9 is manifested at a high temperature. Since a current flows through the conductive assistant 10 and the change in resistivity as the whole electrode is reduced, several weight% is preferable. Further, the particle diameter of the conductive auxiliary agent 10 is not particularly limited as long as the conductive auxiliary agent 10 can be brought into contact with the electronic conductive material 9 to ensure a path of electron conduction between the positive electrode active material 8 and the positive electrode current collector 4. In addition, the shape of the conductive support agent 10 is not limited to a particulate form, and may be a fiber-like piece or a scale-like piece.

  For the binder 11, homopolymers or copolymers such as vinylidene fluoride, tetrafluoroethylene, acrylonitrile, ethylene oxide, styrene-butadiene rubber, or the like can be used. The ratio of the binder 11 contained in the positive electrode active material layer 6 varies depending on the type of the binder 11 used and the types of the positive electrode active material 8, the electronic conductive material 9, and the conductive additive 10, but if the ratio increases, the current collecting property is increased. Is preferably several weight%.

  The thickness of the positive electrode active material layer 6 is not particularly limited because it varies depending on the intended use, but is preferably several μm to 300 μm. If it exceeds 300 μm, the ionic resistance in the electrode increases, so that the discharge voltage becomes low and a sufficient discharge capacity cannot be obtained, which is not preferable. On the other hand, if it is less than several μm, a sufficient energy density cannot be obtained, which is not preferable.

  The positive electrode current collector 4 may be any metal that is stable in the battery, and aluminum is preferably used. As the shape of the positive electrode current collector 4, any shape such as a foil, a net shape, and an expanded metal can be used. The thickness of the positive electrode current collector 4 is not particularly limited because it varies depending on the intended use.

  On the other hand, the negative electrode 2 includes a negative electrode current collector 5 made of a metal film such as copper, and a negative electrode active material layer 7 formed on the surface thereof. The negative electrode active material layer 7 is configured by bonding a negative electrode active material with a binder 11 (not shown).

Examples of the negative electrode active material include graphitizable carbon, non-graphitizable carbon, natural graphite, artificial graphite, carbonaceous materials such as polyacetone, V-Sn, Cu-Sn, Fe-Sn, Sn-S ₂ , SnO, and the like. A tin-based alloy compound, a boron-based oxide, a nitride such as Li _2.6 Co _0.4 N, or the like can be used.

Next, a method for manufacturing the battery will be described.
[Production method of positive electrode]
The positive electrode 1 is obtained by dispersing a positive electrode active material 9, a positive electrode active material 8, a binder 11, and a conductive additive 10 in a dispersion medium to obtain a positive electrode active material paste, which is used as a positive electrode current collector 4. After being coated on a body substrate and dried, it is manufactured by pressing at a predetermined temperature and surface pressure to form a positive electrode active material layer 6 having a desired thickness.
The electronic conductive material 9 can be obtained by mixing the resin 13 and the conductive filler 12.

  Here, the mixing method in the present embodiment is kneaded using a kneader or the like at a temperature not lower than the melting point of the resin 13 and not higher than the decomposition temperature of the resin 13 until the conductive filler 12 is uniformly dispersed in the resin 13. This is a so-called kneading method including a kneading step. In the case of this kneading method, the conductive filler 12 having a particle size of 35 nm or more and not more than the particle size of the active material is blended in an amount of 70% by weight or less with respect to the entire electronic conductive material. Within this range, too much shearing force is applied and no heat is generated, and the conductive filler 12 and the resin 13 are made uniform and good by setting the particle size of the conductive filler 12 to 35 nm or more. It can mix so that it may disperse | distribute and the current collection property in the positive electrode active material layer 6 can be improved by making the particle size of the electroconductive filler 12 into the particle size of the positive electrode active material 8 or less.

A preferred mixing method in the present embodiment includes a dispersion step of dispersing the conductive filler 12 having a particle size of 35 nm or more and not more than the particle size of the active material in a solution in which the resin 13 is dissolved, and the resin obtained from the obtained solution. And a deposition step in which a mixture of the conductive filler 12 and the conductive filler 12 is deposited to obtain the electronic conductive material 9.
Here, the precipitation process should just cool the solution obtained by the dispersion | distribution process. Cooling of the solution only needs to reach a temperature at which the mixture of the resin 13 and the conductive filler 12 precipitates, for example, around 80 ° C., and there is no particular limitation on the cooling method such as natural cooling.
Alternatively, in the precipitation step, the solution obtained by the dispersion step may be added to the poor solvent. As the poor solvent, alcohols such as methanol and ethanol, water, and acetone are preferably used. The compounding amount of such a poor solvent is not particularly limited, and may be an amount that allows the mixture to precipitate.

According to this wet method, since the resin 13 is coated on the conductive filler 12 having a predetermined particle size, an electronic conductive material 9 having a smaller particle size than that produced by the kneading method can be obtained. it can. Thereby, the number of contact points of the electronic conductive material 9 with respect to the active material is increased, and the current collecting property can be further improved. Thus, by using the wet method, it is possible to easily obtain the electronic conductive material 9 having a small particle size, a low resistivity, and a large resistance change rate with respect to temperature.
In addition, according to the wet method, the mixing ratio of the resin 13 and the conductive filler 12 can be freely changed. Therefore, the ratio of the conductive filler 12 is increased to further reduce the resistivity of the electronic conductive material. 9 can be easily obtained.
Here, the proportion of the conductive filler 12 contained in the obtained electronic conductive material 9 is preferably 20 to 95% by weight. If it is less than 20% by weight, the resistivity cannot be lowered sufficiently, while if it exceeds 95% by weight, a sufficient PTC function cannot be obtained, which is not preferable.

The solvent for dissolving the resin 13 is preferably a solvent in which the resin 13 in the electronic conductive material 9 does not dissolve at about room temperature but dissolves at a temperature lower than the temperature at which the resin 13 decomposes when heated. , Organic solvents such as benzene, hexane, decalin and tetralin.
The blending amount of such a solvent is not particularly limited, and an amount sufficient to dissolve the resin 13 may be used.
Further, in order to dissolve the resin 13 in such a solvent, it is preferably applied to a temperature not lower than room temperature and not higher than the decomposition temperature of the resin 13, and more preferably 120 to 130 ° C.
In order to disperse the conductive filler 12 in the solution in which the resin 13 is dissolved, a stirrer or the like that can be stirred may be used and stirred until the conductive filler 12 is uniformly dispersed in the solution.

Further, a dispersing agent can be further added in the precipitation step. Thereby, the aggregation of the electronic conductive material 9 is suppressed and the dispersibility of the conductive filler 12 is improved, so that the electronic conductive material 9 having a small particle size, a lower resistivity, and a large resistivity change with respect to temperature can be obtained. Can be obtained.
It is preferable to use a polymer dispersant as the dispersant. The blending amount of such a dispersant is preferably 0.01 to 10% by weight with respect to the amount of the conductive filler 12.

The obtained electronic conductive material 9 is finely pulverized to form fine particles of the electronic conductive material 9.
As a method of pulverizing the electronic conductive material 9, it is preferable to pulverize using a pulverizer such as a multi-blender mill or a ball mill. In this way, the electron conductive material 9 can be made into particles of 1 μm to 20 μm, and the electron conductive material 9 obtained by a wet method can be made into small particles of less than 1 μm. Note that the lower limit of the particle size in this case is substantially the same as the particle size of the original conductive filler, only increasing by the particle size of the conductive filler (35 nm) + the thickness of the resin.
In the pulverization, the electronic conductive materials 9 placed on the supersonic flow collide with each other or collide with the wall surface, or the electronic conductive material 9 is subjected to a combination of shearing force, grinding force and impact force. You may go.

N-methylpyrrolidone (NMP) etc. can be used for the dispersion medium used when obtaining a positive electrode active material paste. The blending amount of the dispersion medium is not particularly limited, and an amount capable of uniformly dispersing the positive electrode active material paste component may be used.
The method for applying the positive electrode active material paste onto the current collector base material is not particularly limited, but a method suitable for the desired thickness and application form is preferable. For example, doctor blade method, screen printing method, bar coater The method, the roll coater method, the gravure printing method and the die coater method can be used.

  Here, an example in which the positive electrode active material paste is pressed at a predetermined temperature and a predetermined surface pressure has been described. However, after the positive electrode active material paste is pressed at a predetermined surface pressure, the positive electrode active material paste is heated at a predetermined temperature. By doing so, the positive electrode 1 may be obtained.

[Production method of negative electrode]
A negative electrode active material paste obtained by dispersing a negative electrode active material and a binder 11 in a dispersion medium is applied on a current collector base material to be a negative electrode current collector 5, and the negative electrode 2 having the negative electrode active material layer 7 formed thereon Can be obtained.
Note that copper is preferably used as the negative electrode current collector. The method of obtaining the negative electrode 2 by applying the negative electrode active material paste on the current collector substrate is the same as the case of obtaining the positive electrode 1 by applying the positive electrode active material paste on the current collector substrate.

[Battery manufacturing method]
A battery having the positive electrode 1 and the negative electrode 2 can be obtained by sandwiching the separator 3 between the two electrodes obtained by the above-described method, that is, the positive electrode 1 and the negative electrode 2, or by bonding the both electrodes together. Since the battery obtained by such a method has a characteristic that the positive electrode 1 has a resistance that increases as the temperature rises, even if a short circuit occurs outside or inside the battery and the temperature of the battery rises, It has an excellent PTC function to suppress an increase in short circuit current.

The battery having such a configuration can be used for a primary battery such as a non-aqueous electrolyte type, a solid electrolyte type, a gel electrolyte type lithium ion secondary battery, or a lithium / manganese dioxide battery. It is also effective for aqueous primary batteries and secondary batteries.
In addition, since the capacity can be increased by winding, stacking, and folding, it can be used in primary and secondary batteries as a power source for large equipment. Furthermore, it is possible to reduce the size and weight by packaging the battery body having a large capacity with an exterior material such as aluminum coated with insulation.

In the present embodiment, the positive electrode active material layer 6 has been described as an example having the positive electrode active material 8, the electronic conductive material 9, the conductive auxiliary agent 10, and the binder 11, but is not limited thereto. Further, other components such as a dispersant may be added as long as the current collecting property is not impaired.
In the present embodiment, the electron conductive material 9 is a particle, but the shape may be a fiber-like piece or a scale-like piece. In short, as long as it has such a size that the electron conductive material 9 can be positioned between the adjacent positive electrode active materials 8, the shape thereof may be any. Such a shape can be obtained by changing conditions such as pressure during pulverization.

  In the present embodiment, the configuration of the electronic conductive material 9 including the conductive filler 12 and the resin 13 in the positive electrode active material layer 6 in the positive electrode 1 is shown, but this is not limited to the positive electrode 1. Even when the configuration of the present embodiment is applied to the negative electrode 2 and a battery is configured using the same, the same effect can be obtained.

Specific examples of the present invention will be described below. Note that the present invention is not limited to these examples.
<Example 1>
(Production method of positive electrode)
40 g of high-density polyethylene is put in a kneading vessel set at 200 ° C., kneaded for 3 minutes at a rotation speed of 70 rpm, and then 68.1 g of carbon black (particle size 95 nm) is added while kneading little by little. Kneaded for 30 minutes. After kneading, the product was passed through a roller, cooled and cut to produce pellets having a diameter of about 2 mm. This pellet was made into a powder having an average particle diameter of 100 μm by a multi-blender mill, and further an electronic conductive material powder having an average particle diameter of 6.8 μm was produced by a jet mill. Next, 5.5 wt% of the electronically conductive material powder, 90 wt% of LiCoO ₂ (particle diameter: 7.3 μm), 0.5 wt% of carbon (particle diameter of 34 nm), 4 wt% of PVdF were used as a dispersion medium. A positive electrode active material paste was prepared by dispersing in a certain NMP.
Next, the positive electrode active material paste was applied onto a 20 μm thick aluminum foil by a doctor blade method. Furthermore, after drying at 80 ° C., a positive electrode active material layer having a thickness of about 70 μm was formed by pressing at room temperature at a surface pressure of 2 ton / cm ² to obtain a positive electrode.

(Method for producing negative electrode)
A negative electrode active material paste prepared by dispersing 90 wt% MCMB and 10 wt% PVdF in NMP was applied onto a negative electrode current collector made of copper foil having a thickness of 16 μm by a doctor blade method, and the thickness was about 70 μm. A negative electrode was produced by forming a negative electrode active material layer.
(Battery manufacturing method)
The positive electrode of the produced electrode was cut into a size of 250 mm × 48 mm and the negative electrode was cut into a size of 340 mm × 50 mm, and current collecting terminals (positive electrode terminal: aluminum, negative electrode terminal: nickel) were attached to current collecting portions of both electrodes by spot welding. A porous polypropylene sheet (trade name: Celgard # 2400, manufactured by Hoechst Co., Ltd.) was sandwiched between the positive electrode and the negative electrode as a separator, and these were wound into an elliptic cylinder to produce a battery element. This battery element was vacuum-dried at about 60 ° C. for 9 hours. This was put in a bag prepared using an aluminum laminate sheet, and lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (molar ratio 3: 7) at a concentration of 1.2 l / dm ³ . After injecting the electrolytic solution, vacuum impregnation was performed, and the battery was sealed by heat fusion to obtain a battery.

<Example 2>
A pellet having a diameter of about 2 mm was prepared in the same manner as in Example 1 except that 60 g of carbon black (particle size: 95 nm) was used and the proportion of carbon black in the electronic conductive material was reduced. This pellet was made into a powder having an average particle size of 100 μm by a multi-blender mill, and further a powder having an average particle size of 9.8 μm was produced by a jet mill. Next, a positive electrode active material paste was prepared from 5.5 wt% of the electronic conductive material powder in the same manner as in Example 1 to obtain a positive electrode.
The method for producing the negative electrode and the method for producing the battery are the same as those shown in Example 1.

<Example 3>
(Production method of positive electrode)
4.5 g of high-density polyethylene was added to 800 g of xylene and heated to 120 ° C. with stirring. 40.5 g of carbon black (particle size 95 nm) was added in small portions and stirred at high speed for 30 minutes, then cooled slowly and filtered at 60 ° C. to recover the product. This was dried at 80 ° C. overnight to obtain an electronic conductive material composite. The obtained electronic conductive material composite was pulverized to an average particle size of 1 μm by a multi blender mill. Next, 5.5 wt% of the electronic conductive material powder, 90 wt% of LiCoO ₂ (particle size: 7.3 μm), 0.5 wt% of carbon (particle size of 34 nm), and 4 wt% of PVdF are dispersion media. Adjustment was made by dispersing in NMP to obtain a positive electrode active material paste.
By producing the positive electrode in this way, an electronic conductive material composite having a fine particle size was obtained, and by using it, a smooth positive electrode active material paste having an appropriate viscosity was obtained.
Next, the positive electrode active material paste was applied onto a 20 μm thick aluminum foil by a doctor blade method. Furthermore, after drying at 80 ° C., a positive electrode active material layer having a thickness of about 70 μm was formed by surface pressure pressing at 2 ton / cm ² at room temperature to obtain a positive electrode 1.
The negative electrode and the battery were manufactured in the same manner as in Example 1.

<Example 4>
A battery was fabricated in the same manner as in Example 3, except that the particle diameter of LiCoO ₂ was 9.2 μm and the particle diameter was increased.

<Example 5>
(Production method of positive electrode)
4.5 g of high-density polyethylene was added to 800 g of xylene and heated to 120 ° C. with stirring. After adding 40.5 g of carbon black (particle size 95 nm) little by little and stirring at high speed for 30 minutes, in addition to 800 g of methanol, an electronically conductive material composite was obtained. The obtained electronic conductive material composite was pulverized to an average particle size of 1 μm by a multi blender mill. Next, 5.5 wt% of the electronic conductive material powder, 90 wt% of LiCoO ₂ (particle size: 7.3 μm), 0.5 wt% of carbon (particle size of 35 nm), and 4 wt% of PVdF are used as a dispersion medium. Adjustment was made by dispersing in NMP to obtain a positive electrode active material paste.
By producing the positive electrode in this way, an electronic conductive material composite having a fine particle size was obtained, and by using it, a smooth positive electrode active material paste having an appropriate viscosity was obtained.
Next, the positive electrode active material paste was applied onto a 20 μm thick aluminum foil by a doctor blade method. Furthermore, after drying at 80 ° C., the cathode active material layer having a thickness of about 70 μm was formed by pressing at room temperature with a surface pressure of 2 ton / cm ² to obtain the cathode 1.
The negative electrode and the battery were manufactured in the same manner as in Example 1.

<Example 6>
(Production method of positive electrode)
41.5 g of carbon black (particle size 95 nm) was added to 800 g of xylene in which 0.315 g of a polymeric dispersant (hypermer) was dissolved, and the stirred solution was dispersed for 15 minutes by an ultrasonic disperser. It was. This solution was heated to 120 ° C. with stirring, and then 4.5 g of high-density polyethylene was added little by little to dissolve. After 30 minutes, the product was recovered by gradually cooling with stirring and filtering at 60 ° C. This was dried at 80 ° C. overnight to obtain an electronic conductive material composite. The obtained electronic conductive material composite was pulverized to an average particle size of 1 μm by a multi blender mill.
Next, 5.5 wt% of the electronic conductive material powder, 90 wt% of LiCoO ₂ (particle diameter: 7.3 μm), 0.5 wt% of carbon (particle diameter of 34 nm), and 4 wt% of PVdF are dispersion media. Adjustment was made by dispersing in NMP to obtain a positive electrode active material paste.
By producing the positive electrode in this way, an electronic conductive material composite having a fine particle size was obtained, and by using it, a smooth positive electrode active material paste having an appropriate viscosity was obtained.
Next, the positive electrode active material paste was applied onto a 20 μm thick aluminum foil by a doctor blade method. Furthermore, after drying at 80 ° C., the cathode active material layer having a thickness of about 70 μm was formed by pressing at room temperature with a surface pressure of 2 ton / cm ² to obtain the cathode 1.
The negative electrode and the battery were manufactured in the same manner as in Example 1.

<Comparative Example 1>
In this comparative example, in order to compare with Examples 1 and 2, the proportion of the conductive filler in the electronic conductive material is increased.
10 g of high-density polyethylene was put in a kneading vessel set at 200 ° C., and kneaded for 3 minutes at 70 rpm, followed by 90 g of kneading at 70 rpm. When carbon black (particle size 95 nm) was charged, the temperature exceeded 300 ° C. 4 minutes after the start of charging, and reached the modification temperature of polyethylene, so that kneading could not be performed.

<Comparative example 2>
A battery was fabricated in the same manner as in Example 1 except that only graphite having no PTC function was used as the electronic conductive material.

<Comparative Example 3>
In Example 1, 80 g of high-density polyethylene is put in a kneading vessel set at 200 ° C., kneaded for 3 minutes at a rotation speed of 70 rpm, and then carbon black (particle diameter 34 nm) is gradually added to knead. As a result of charging up to the maximum amount, 20 g could be input. Carbon black was added and kneaded for 30 minutes. After kneading, the product was passed through a roller, cooled and cut to produce pellets having a diameter of about 2 mm. The pellets were made into a powder having an average particle size of 100 μm by a multi-blender mill, and further a powder having an average particle size of 10 μm was produced by a jet mill.

<Comparative example 4>
An electron conductive material powder was prepared in the same manner as in Example 3 except that the carbon black particle size was 34 nm.
<Comparative Example 5>
A battery was fabricated in the same manner as in Example 3, except that the carbon black particle size was 10.8 μm and the carbon black particle size was larger than the active material particle size.
<Comparative Example 6>
A battery was fabricated in the same manner as in Example 3, except that the carbon black particle size was 10.8 μm, the LiCoO ₂ particle size was 9.2 μm, and the carbon black particle size was larger than the active material particle size. did.

(Evaluation)
In order to evaluate the electronic conductive material and battery of the present invention, evaluation was performed using the following method.
<Resistivity measurement>
The electronic conductive material powder produced in Examples 1, 2, 3, 5, 6 and Comparative Examples 3 and 4 and the graphite (electronic conductive material) used in Comparative Example 2 were compacted at 2 ton / cm ² . Thus, a disk-shaped green compact having a diameter of 13 mm and a thickness of 3 mm was produced. The resistance of the green compact at room temperature and 140 ° C. was measured, and the resistivity at each temperature was determined. The resistance change rate was obtained by dividing the resistivity at 140 ° C. by the resistivity at room temperature.
<Capacity test>
The batteries prepared in Examples 1, 2, 3, 5, 6 and Comparative Example 2 were CC / CV charged to 4.2 V at 560 mA, and then the discharge capacity when discharged at a current of 1120 mA was measured.
<Cycle test>
The batteries prepared in Examples 1, 2, 3, 5, 6 and Comparative Example 2 were subjected to CC / CV charge at room temperature to 4.2 V at a current of 600 mA, and then constant current discharge to 3.0 V at a current of 560 mA. This cycle was repeated with charging / discharging performed as one cycle, and the discharge capacity value at the 200th cycle was determined with the discharge capacity at the first cycle as 100%.
<Short-circuit test>
The batteries prepared in Examples 2, 3, 5, 6 and Comparative Example 2 were subjected to CC / CV charging up to 4.4 V at a current of 600 mA at room temperature. These batteries are placed in a constant temperature bath heated to room temperature and 140 ° C., and after reaching a predetermined temperature, the batteries are short-circuited. At this time, the current value flowing through the shunt resistance of 100 A-50 mV is measured, thereby short-circuit current. Asked.

  Table 1 shows the particle diameter of carbon black, the resistivity of the green compact at room temperature, and the resistance change rate from room temperature to 140 ° C. for the electronic conductive materials used in Examples 1 and 3 and Comparative Examples 3 and 4. Moreover, about Example 1 and the comparative example 2, when producing by the kneading | mixing method, the maximum weight% of the carbon black which could be mixed is shown.

  As shown in Table 1, when the electronic conductive material was prepared by the kneading method, in Example 1, a good electronic conductive material having a low resistivity and a large resistance change rate was obtained, whereas In Comparative Example 3, an electronic conductive material having a high resistivity and a small resistance change rate was obtained. In Example 1, since the carbon black has a large particle size and a high bulk density, the proportion of carbon black that can be mixed is large, whereas in Comparative Example 3, the carbon black has a small particle size and a bulk density. This is due to the fact that the ratio that can be mixed is small.

When manufactured by a wet method, in Example 3, a good electronic conductive material having a low resistivity and a larger resistance change rate was obtained, whereas in Comparative Example 4, a low resistivity and a small resistance change were obtained. An electronically conductive material having a rate was obtained. This is because, according to the wet method, in Example 3, the particle size of carbon black was large and easily dispersed, so that a uniform electronic conductive material could be produced, whereas in Comparative Example 3, the particle size of carbon black was This is because carbon black aggregates in the solution and is not uniformly dispersed.
Thus, it was found that the resistivity and the resistance change rate depend on the particle size of the conductive filler. For this reason, the resistance change rate about the electroconductive material which has the electroconductive filler of each particle size produced with the wet method was investigated in detail. The result is shown in FIG.
As shown in FIG. 4, when the particle size of the conductive filler is less than 35 nm, the rate of change in resistance is small and less than one digit, whereas when it exceeds 35 nm, the rate of change in resistance is more than two digits. It was.
Therefore, the particle size of the conductive filler in the electronic conductive material needs to be 35 nm or more.

  Table 2 shows the discharge capacities when the batteries of Examples 3 and 4 and Comparative Examples 5 and 6 were discharged at 1120 mA.

As shown in Table 2, the batteries of Examples 3 and 4 in which the particle size of the conductive filler was smaller than the particle size of the active material showed a high discharge capacity. On the other hand, the batteries of Comparative Examples 5 and 6 in which the particle size of the conductive filler was equal to or greater than the particle size of the active material exhibited a low discharge capacity. This is because when the particle size of the conductive filler is larger than that of the active material, the number of contact points between the active material and the electronic conductive material is extremely reduced, and the current collection in the electrode is very poor. This is because the resistivity of the electrode is increased.
Therefore, the particle size of the conductive filler in the electronic conductive material is preferably in the range of 35 nm to the particle size of the active material.

  Table 3 shows the resistivity of the green compact at room temperature and the rate of change in resistance from room temperature to 140 ° C. for the electronic conductive materials used in Examples 2, 3, 5, 6 and Comparative Example 2.

As shown in Table 3, Example 2 by the kneading method was an electronically conductive material having a low green compact resistivity and a large resistance change rate. Also, in Examples 3, 5, and 6 by the wet method, since the conductive filler is uniformly dispersed and the ratio of the resin is small, electronic conductivity having a lower green compact resistivity and a larger resistance change rate is obtained. Material. On the other hand, Comparative Example 2 did not contain a resin in the electronic conductive material, so the resistivity of the green compact was low, but there was almost no change in resistance.
Therefore, the electronic conductive material produced by the kneading method has a low resistivity and a large resistance change rate, and the electronic conductive material produced by the wet method has a lower resistivity and a large resistance change rate. Met.

  Table 4 shows the discharge capacity value at the 200th cycle when the cycle test was performed on the batteries of Examples 2, 3, 5, 6 and Comparative Example 2, and the discharge capacity when discharged at 1120 mA. The discharge capacity value at the 200th cycle is indicated by the ratio (%) of the discharge capacity at the 200th cycle to the discharge capacity at the 1st cycle.

  As shown in Table 4, the battery of Example 2 using the electronically conductive material powder produced by the kneading method had good discharge capacity value and discharge capacity at the 200th cycle. The batteries of Examples 3, 5, and 6 using the electronically conductive material produced by the wet method have a higher discharge capacity value at the 200th cycle and a higher discharge capacity at 1120 mA, and the electronically conductive material. A value equivalent to that of the battery of Comparative Example 2 containing no resin was shown. This is due to the fact that current can be efficiently collected in detail because the resistivity of the electronic conductive material is small.

  Table 5 shows the maximum short-circuit current when the short-circuit test was performed at room temperature and 140 ° C. for the batteries of Examples 2, 3, 5, 6 and Comparative Example 2.

As shown in Table 5, there is no difference in the short-circuit current at room temperature, but the battery of Comparative Example 2 shows a value nearly one digit higher than that of Examples 2, 3, 5, and 6 in the short-circuit current at 140 ° C. It was. This is because, in Comparative Example 2, the electrode active material layer does not contain an electronic conductive material, so that the PTC function does not appear at a high temperature and the current is not limited. On the other hand, in the batteries of Examples 2, 3, 5, and 6, since the PTC function worked at 140 ° C. and the resistivity of the electrode increased and the current at the time of the short circuit was greatly limited, the short circuit current was a small value. It was.
Therefore, by making the particle size of the conductive filler 35 nm or more and not more than the particle size of the active material, an electronic conductive material having a low resistivity and a large resistivity change with respect to temperature can be obtained. By using such an electronic conductive material, a battery having improved current collecting property and PTC function can be obtained.

1 is a schematic cross-sectional view of a cylindrical lithium ion secondary battery in an embodiment. It is a cross-sectional schematic diagram of the principal part of the battery in embodiment. It is a cross-sectional schematic diagram of the electronically conductive material in embodiment. It is a figure which shows the relationship between the particle size of the electroconductive filler in the electronic electroconductive material which concerns on this invention, and resistance change rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode, 2 Negative electrode, 3 Separator, 4 Positive electrode collector, 5 Negative electrode collector, 6 Positive electrode active material layer, 7 Negative electrode active material layer, 8 Positive electrode active material, 9 Electroconductive material, 10 Conductive auxiliary agent, 11 Binder, 12 conductive filler, 13 resin, 100 battery body, 200 outer can.

Claims (7)

  In a battery provided with an electrode containing an active material and an electronic conductive material in contact with the active material, the electronic conductive material is a mixture of a conductive filler and a resin, and the conductive filler particles A battery having a diameter of 35 nm or more and a particle diameter of the active material or less.   The electronic conductive material was obtained by dispersing the conductive filler in a solution in which the resin was dissolved, and cooling the solution to precipitate a mixture of the resin and the conductive filler. The battery according to claim 1, wherein the battery is a battery.   The electronic conductive material disperses the conductive filler in a solution in which the resin is dissolved, and a poor solvent is added to the solution to precipitate a mixture of the resin and the conductive filler. The battery according to claim 1, which is obtained. In a method for producing a battery comprising an electrode containing an active material and an electronically conductive material in contact with the active material,
A dispersion step of dispersing a conductive filler having a particle size of 35 nm or more and not more than the particle size of the active material in a solution in which the resin is dissolved;
Depositing a mixture of the resin and the conductive filler from the solution to obtain the electronically conductive material;
A method for producing a battery comprising:   The method for manufacturing a battery according to claim 4, wherein the deposition step cools the solution to deposit the mixture.   The method for producing a battery according to claim 4, wherein the deposition step deposits the mixture by adding the solution to a poor solvent.   The battery manufacturing method according to claim 5, wherein a dispersing agent is further added in the precipitation step.

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