JP6589267B2 - Method for producing positive electrode of lithium ion battery - Google Patents

Description

  The present invention relates to a battery having a high energy density, in particular, a positive electrode of a lithium ion secondary battery, a method for producing the same, and a lithium ion battery using the same.

  Lithium-ion secondary batteries (hereinafter referred to as lithium-ion batteries or simply batteries) are superior in terms of their high energy density in terms of light weight and small footprint, compared to nickel-cadmium batteries and nickel-hydrogen batteries. Because it has the advantage of less memory effect, it is widely used in portable devices such as mobile phones and notebook computers. Moreover, in recent years, it has been increasingly used as a power source to replace fossil fuels such as oil that have been used in automobiles because of its environmental impact. In addition, recently, there are high expectations for stationary storage batteries that are responsible for a part of power supply to homes.

  Commonly used components of lithium ion batteries include electrodes, electrolytes, separators, current collectors, exterior bodies, etc., and the electrodes are generally positive electrode active materials or negative electrode active materials, conductive agents, It is composed of a binder and the like. The active material is a material capable of inserting and removing lithium ions at the positive electrode and the negative electrode of a lithium ion battery, and plays a role of flowing current by accompanying the exchange of electrons at the time of insertion and desorption. The conductive agent is disposed inside the electrode in order to smoothly move electrons between the active material and the active material and between the active material and the current collector. The binder is mixed inside the electrode in order to enhance the adhesion of the active material, the conductive additive and the current collector.

  As described above, when a lithium ion battery is used for the purpose of supplying power to an automobile or a home, a larger battery capacity is required as compared with a conventional consumer application such as a mobile phone. Thus, storing a large amount of energy in the battery means that the degree of danger when an abnormality occurs in the battery dramatically increases. In particular, when the battery is charged beyond the original charging potential, when the battery is overcharged, the inside of the battery is heated due to heat generation due to the change in the crystal structure of the positive electrode, decomposition of the electrolyte, and release of oxygen due to the collapse of the positive electrode structure. The temperature rises abnormally (becomes a so-called thermal runaway state), leading to heat generation and ignition. In general, as a countermeasure against such overcharge, a current interruption mechanism by an external circuit that detects the increase in internal pressure due to gas generation in the battery due to overcharge is provided as a detection means, so that charging current can be reduced before thermal runaway occurs. Stop and stop or stop ignition and heat generation. However, since it is not possible to ensure safety only by the above measures, various efforts have been made.

In Patent Documents 1 and 2, the increase in the internal pressure of the battery during overcharge is promoted by adding a material that decomposes at a potential that causes overcharge, such as Li ₂ CO ₃ or biphenyl, and generates gas in the electrolyte, Thermal runaway is prevented by operating a current interrupt mechanism that starts at a predetermined pressure at an early stage.

  In Patent Document 3, the thermal expansion microcapsule expands due to heat generated by overcharging by including the thermal expansion microcapsule in the electrode or in the layer provided between the electrode and the current collector, thereby increasing the resistance of the electrode. This interrupts the current and suppresses thermal runaway.

  In Patent Document 4, a positive electrode current collector, a conductive agent, a binder, and a substance that decomposes at a high potential in an overcharged state, a first layer, and a positive electrode active material, a conductive agent, and a binder formed on the first layer. By adopting a positive electrode having a two-layer structure composed of a second layer made of an adhesive, when a high potential is caused by overcharging, a substance that decomposes at a high potential is decomposed to generate gas. As a result, the first layer is structurally destroyed and acts to cause interface destruction between the first layer and the second layer, and the internal resistance of the battery is increased to cut off the charging current and suppress overcharge. A technique is disclosed.

Japanese Patent No. 3061759 Japanese Patent No. 3575735 Japanese Patent No. 4727021 Japanese Patent No. 4236308

  However, in the method of including a potential decomposable material in the electrolyte solution as shown in Patent Document 1 and Patent Document 2, the potential decomposable material dispersed in the electrolyte solution hinders lithium ion movement associated with charge / discharge of the battery. Battery capacity maintenance characteristics (hereinafter referred to as current load characteristics) when a large current is passed and battery capacity maintenance characteristics (hereinafter referred to as charge / discharge cycle characteristics) when charging / discharging is repeated are deteriorated.

  On the other hand, even when a thermally expandable microcapsule that functions by heat is contained in an electrode as shown in Patent Document 3 or in a layer provided between an electrode and a current collector, there is a problem from the following viewpoints. Remains. First, the basic structure of the electrode is composed of an active material, a conductive agent and a binder as described above, and the capacity of the battery is determined by the amount of the active material. Therefore, if a material other than the basic structure is mixed in the electrode layer, the electrode The active material ratio in the layer decreases, and the battery capacity per electrode volume decreases. In addition, when a layer is provided between the electrode and the current collector and the thermally expandable microcapsule is contained in the layer, the volume of the entire battery is increased by the amount of the newly provided layer. Leading to a decrease in battery capacity. Further, by providing a new layer between the electrode and the current collector, the electrical resistance between the electrode layer and the current collector increases, leading to a decrease in current load characteristics.

Further, Patent Document 4 discloses a technique for cutting off charging current and suppressing overcharge due to an increase in battery internal resistance, but the compound in the first layer decomposes at a high potential to generate gas. Although it is similar to the present invention in terms of gas generation, it is different from the present invention because the change of the compound generates gas at high potential. Because of the decomposition reaction at high potential, if the temperature inside the battery actually rises before the high potential, the decomposition reaction of the electrolyte will occur, and the runaway reaction of the battery cannot be suppressed immediately. .
On the other hand, even when the battery temperature does not increase excessively even at high potential, the decomposition reaction of the compound in the first layer occurs, so even if the temperature rises at a little high potential and the battery performance increases. A compound decomposition reaction occurs, and the battery does not function as a normal battery. Furthermore, because of the decomposition reaction under potential value control, there are cases where, when viewed in the electrode part micro, there are portions where electrons are easily passed and difficult to pass, resulting in a non-uniform reaction. In that case, the problem that the battery runaway cannot be stably suppressed remains.

  The present invention has been made in view of such problems, and its purpose is to use a temperature-sensitive volatile material, particularly a sublimation material, in the positive electrode first layer, and without any influence during normal battery use. The positive electrode of a lithium ion secondary battery that can prevent battery runaway, ignition, and explosion and ensure safety when the battery is in an exothermic state such as overcharge, a method of manufacturing the same, and lithium using the same An ion battery is provided.

Another aspect of the present invention is a method for producing a positive electrode of a lithium ion battery, which is sublimated at 80 ° C. or higher and 140 ° C. or lower on a positive electrode current collector of the lithium ion battery using a slot die method. 85 and the gas generating material parts, and the conductive agent 10 parts by weight, inline forming a positive electrode first layer and a binder 5 parts by weight, relative to the step of forming the Seikyokudai one layer in, the Seikyokudai one layer on, including a positive electrode active material, conductive agent, and, and forming a positive electrode second layer having a binder, a production process.

  According to the present invention, there is no effect when using a normal battery, and in the unlikely event that the battery is in a heat generation state such as overcharge, a lithium ion battery that can ensure safety by suppressing runaway, ignition, and explosion of the battery reaction The positive electrode, the manufacturing method thereof, and the lithium ion battery using the same can be provided.

Schematic sectional view of positive electrodes according to Examples 1 and 2 and Comparative Examples 2 to 4 Schematic cross-sectional view of the positive electrode according to Comparative Example 1 Schematic cross-sectional view of electrode state during positive electrode evaluation 2 of Examples 1 to 3 and Comparative Example 1 Schematic sectional view of the electrode state in the positive electrode evaluation 2 of Comparative Example 1 Schematic cross-sectional view of coin-type battery in positive electrode evaluation 3 to 5 of Examples 1 to 3 and Comparative Example 2 Schematic cross-sectional view of coin-type battery at positive electrode evaluation 3 to 5 of Comparative Example 1

  The positive electrode for a lithium ion battery according to the present invention comprises a positive electrode first layer having a gas generating material that volatilizes and generates a gas in a high temperature state due to an overcharged state, a conductive agent, and a binder on a positive electrode current collector. A positive electrode active material, a conductive agent, and a binder, and a positive electrode second layer formed on the positive electrode first layer. As the gas generating material in the layer volatilizes, the electrical resistance between the positive electrode current collector and the positive electrode second layer increases.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor does not introduce a compound that generates gas by being decomposed by a voltage increase accompanying overcharge in the positive electrode first layer, but increases a voltage accompanying overcharge. A uniform volatilization reaction is promoted by generating a gas in the positive electrode first layer due to a temperature rise due to the above, and the positive electrode first layer becomes porous and the layer cannot be formed. It has been found that by reducing the adhesion to the positive electrode second layer, it becomes a resistance and does not function as a battery so that electrical contact can be cut off. Of course, in the case of steady use, the positive electrode first layer did not become a resistance, and the performance as a battery was not deteriorated, and only the safety and the safety could be improved.

  As a result, according to the positive electrode of the lithium ion battery according to the present invention, when the lithium ion battery or its electrode becomes high temperature due to overcharge or the like, gas is generated in the positive electrode first layer, Lithium-ion battery that can increase the resistance of one layer or increase the interface resistance between the positive electrode first layer and the current collector or the positive electrode second layer and suppress thermal runaway reaction such as ignition and explosion caused by overcharge Can be operated with normal performance under normal conditions, and safety can be improved in abnormal situations. Hereinafter, a positive electrode of a lithium ion battery according to an embodiment of the present invention, a manufacturing method thereof, and a lithium ion battery using the same will be described.

(Positive electrode)
A positive electrode for a lithium ion battery has a positive electrode first layer composed of at least a gas generating material, a conductive material, a binder and the like formed on a positive electrode current collector, and the positive electrode second layer includes a positive electrode active material and a binder. This is a positive electrode that can be formed from two or more layers by mixing an agent, a conductive material, etc. in a solvent such as N-methylpyrrolidone, then laminating and drying on the first positive electrode layer and drying.
The gas generating material (volatile material) contained in the positive electrode first layer needs to be heat-sensitive, and it is necessary to immediately generate gas when the battery enters a temperature range that seems to be abnormal.
For example, in this embodiment, a sublimable material is mentioned as a gas generating material. As the sublimation material, both inorganic materials and organic materials exist, but either one may be selected as long as it meets the purpose.
For example, a typical inorganic material includes iodine.
Organic materials include paradichlorobenzene, salicylic acid (2-hydroxybenzoic acid), naphthalene, terephthalic acid, caffeine (anhydrous, monohydrate), menthol, and BHT (butylhydroxy) that is also used in food additives. Toluene), BHA (butylhydroxyanisole) and the like are also included.

Depending on the case, a light-stabilizing agent or a rust preventive agent that forms a coating film on the gas generating material while being dispersed in powder at the time of coating, has heat sensitivity at a predetermined temperature, and has a melting point at the temperature. May be used. This is because the effect is that the positive electrode first layer cannot form a coating film at that temperature. However, ambient temperature (25 ° C.), is preferably atmospheric pressure (1 atm) solid state below. This is to suppress the positive electrode first layer from becoming liquid especially when used as a battery.
In addition, examples of the material that sublimes in a temperature range of battery abnormality, for example, 60 ° C. or more and 140 ° C. or less, particularly 80 ° C. or more and 140 ° C. or less include iodine, naphthalene, BHT, and the like.
However, for example, oxalic acid, which is particularly toxic or causes an explosive reaction after volatilization by heat, may be difficult to use, and it is necessary to determine whether it can be used.
In particular, iodine is effective because the generated gas is also inactive, and thermal runaway is suppressed, and even if it ignites, the generated gas can be immediately suppressed.

  Next, as the conductive agent contained in the positive electrode first layer, for example, a known amorphous carbon material such as acetylene black, ketjen black, carbon black, graphite, or carbon nanotube can be used.

As the binder contained in the positive electrode first layer, a resin having an electrolyte solution resistance is used.
Specifically, (poly) acrylic resins, epoxy resins, polyurethane resins, polyester resins, (cyclo) olefin resins, polyether resins, engineering plastics, super engineering plastics, urea resins, melamine Resin, copolymer resin, acetate resin, silicon resin, silica resin, vinyl acetate resin, polystyrene resin, cellulose resin, fluorine resin, etc. Conventionally, in the solvent system, polyvinylidene fluoride is used. SBR (styrene, butadiene copolymer resin (rubber) is often used in resin and water systems.

Regarding the coating composition of the positive electrode first layer, when it is composed only of a gas generating material, a conductive agent, and a binder, the solid content ratio of the gas generating material is 10% by weight to 98% by weight, particularly is preferably 15 wt% or more 98 wt%.
It is good to fill the quantity that generates gas and ensures safety.
Of the remaining 2% by weight or more and 90% by weight or less, the amount of the binder may be the minimum amount. The minimum amount at this time refers to an amount that allows the paint to be kneaded, maintains adhesion with each layer, and does not degrade battery performance.
Other than that, there is no problem if the positive electrode first layer does not become a resistance layer in the normal state of the lithium ion battery, and the conductive agent can move electrons to the current collector without loss.

The above materials are kneaded with a planetary mixer or dispersed with a dissolver to form a paint.
In most cases, the binder is reduced as much as possible, and a large amount of gas generating material and conductive agent are incorporated so that the powder is in many cases, and kneading is often performed with a planetary mixer.
After kneading, considering the wettability to the solvent in which the binder is dissolved and the current collector (base material), it may be further diluted with a solvent or mixed with another solvent. There is no solid content and viscosity suitable for coating.

The coating thickness may be any thickness that can prevent thermal runaway of the battery. However, if it is extremely thin, the deterrent effect is thin, and if it is extremely thick, it takes up the volume in the battery, which is inconvenient.
The thickness of the positive electrode first layer is 0.1 μm or more and 10 μm or less, preferably 0.5 μm or more and 5 μm or less.

  As a typical method for applying the paint, there is a slot die method. In addition, the direct gravure method, the comma coat method, the gravure offset method, etc. may be selected in view of the solid content, viscosity, and rheological properties of the paint.

In particular, the slot die method is suitable because a highly viscous paint can be applied.
However, in the case where the first positive electrode layer is thinly coated, a wet tension die method can be selected, although not limited thereto.

  In the case of the slot die method, the shape of the blade edge of the head, the blade edge angle, the manifold shape, the manifold capacity, the specularity of the inner surface of the head, the supply port diameter, and the supply position are not particularly limited, and can be appropriately set according to each condition. Good.

As for the shim in the coating head, the thickness may be appropriately selected depending on the conditions such as the viscosity of the coating material, the solid content, the viscoelasticity, the discharge amount, etc.
It is natural that there is no unevenness in thickness, but in the case of multiple strips in particular, there are coated and uncoated portions in the width direction, so the distance from the end of the shim that forms each strip and the die head lip edge is small. Each strip needs to be formed with high precision so as to be the same. If possible, the dimensions can be defined with an accuracy of 1 μm or less, and it is more preferable that the dimensions are right angles.

  Further, since the coating position is basically applied to the center of the base material, it is preferable that the center coating can be performed even in the shim shape and setting. This is because if the application position is significantly deviated from the center, in some cases, problems such as meandering at the time of conveyance and tension may not be uniformly applied may occur.

The liquid feed pump may be appropriately selected according to characteristics such as paint viscosity, discharge amount, pulsation, sliding foreign matter, such as a Mono pump, a diaphragm pump, a sine pump, a bellows pump, a tube pump, a plunger pump, and a syringe pump. The discharge amount per rotation is determined by the amount to be applied within a certain period of time, that is, the application width, the application thickness, and the application speed, and is limited if the rotation speed is within the specification of the rotation speed per time of the liquid feed pump. Never happen. However, it is preferable to operate within the standard as much as possible and select an appropriate discharge amount.
Furthermore, you may attach the apparatus which reduces a pulsation.

  The positive electrode current collector is not particularly limited, and a current collector made of a known material such as aluminum, stainless steel, nickel-plated steel, a resin base material having conductivity, or a base material coated on the surface is used. can do.

The positive electrode active material contained in the positive electrode second layer is not particularly limited, and a conventionally known active material can be used. Examples of the positive electrode active material include a lithium transition metal composite oxide capable of releasing lithium ions, and examples thereof include LiNiO ₂ , LiMnO ₂ , LiCoO ₂ , and LiFePO ₄ .
In particular, when a layered compound such as LiCoO ₂ , LiNiO ₂ , LiNi (X) Co (Y) Mn (1-XY) O ₂ is used as a battery active material, thermal runaway is likely to occur during overcharge. Are known.
As the positive electrode active material, a mixture of a plurality of the above lithium transition metal oxides can be used, and binary or ternary materials may be used.

  The binder is the same as that of the positive electrode first layer. In particular, chemically and physically stable materials such as polyvinylidene fluoride, polytetrafluoroethylene, EPDM, SBR, NBR, and fluororubber are preferable. Examples of the conductive agent include ketjen black, acetylene black, carbon black, graphite, carbon nanotube, and amorphous carbon.

  The positive electrode second layer can be formed by mixing a positive electrode active material, a binder, a conductive agent, and the like in a solvent such as N-methylpyrrolidone, then laminating and drying on the positive electrode first layer.

In a method for manufacturing a positive electrode of a lithium ion battery, a positive electrode first layer having a gas generating material that volatilizes at a high temperature to generate gas, a conductive agent, and a binder is formed on a positive electrode current collector And a step of forming a positive electrode second layer having a positive electrode active material, a conductive agent, and a binder on the positive electrode first layer in-line or offline with respect to the step of forming the positive electrode first layer. Can be included.
Furthermore, when the positive electrode first layer and the positive electrode second layer are produced in a continuous manufacturing process (in-line), it is preferable to dry the positive electrode first layer and the positive electrode second layer in a low temperature in a short time. It is necessary to match the set temperature with the properties of the gas generating material.

(Negative electrode)
The negative electrode of a lithium ion battery is a negative electrode composed of at least one layer in which a layer composed of at least a negative electrode active material, a conductive agent and a binder is formed.
The negative electrode active material contained in the negative electrode is not particularly limited, and lithium ions such as metal materials such as lithium, alloy materials containing silicon, tin, titanium, etc., carbon materials such as graphite, coke, etc. Compounds that can be occluded / released can be used alone or in combination. When a lithium metal foil is used as the negative electrode active material, the lithium foil can be formed by pressure bonding on a metal current collector such as copper. When an alloy material or a carbon material is used as the negative electrode active material, the negative electrode active material, a binder, a conductive additive, etc. are mixed in a solvent such as water or NMP, and then on a metal current collector such as copper. It can be formed by coating and drying.

  The binder is preferably a chemically and physically stable material such as polyvinylidene fluoride, polytetrafluoroethylene, EPDM, SBR, NBR, or fluororubber. Examples of the conductive agent include ketjen black, acetylene black, carbon black, graphite, carbon nanotube, and amorphous carbon.

  The negative electrode current collector is not particularly limited, and may be a metal foil made of copper foil or the like, or a plastic film having conductivity.

(Nonaqueous electrolyte)
The non-aqueous electrolyte is not particularly limited, and a non-aqueous electrolyte solution in which a supporting salt is dissolved in a solvent such as an organic solvent, an ionic liquid that is an electrolyte and solvent, a solution in which a supporting salt is further dissolved in the ionic liquid, and the like. Can be mentioned.

  As the organic solvent, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds and the like can be used. A mixed solvent such as propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate can also be used.

The supporting salt used for the non-aqueous electrolyte is not particularly limited. For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF _{3 SO 2) 3, LiN (FSO} 2) 2, LiN (CF 3 SO 2) (C 4 F 9 SO 2), mention may be made of _LiN (CF 3 _{SO 2) 2} and the like.

  The ionic liquid used for the non-aqueous electrolyte is not particularly limited as long as it is a salt that is liquid at room temperature. For example, alkyl ammonium salt, pyrrolidinium salt, pyrazolium salt, piperidinium salt, imidazolium salt, pyridinium salt, sulfonium Examples thereof include salts and phosphonium salts. Further, it is more preferable that it is electrochemically stable in a wide potential region.

(battery)
Examples of the separator for preventing contact between the positive electrode and the negative electrode include a microporous membrane or nonwoven fabric made of polyolefin such as polyethylene and polypropylene, or an aromatic polyamide resin, and a porous resin coat containing inorganic ceramic powder. it can.

  The above-described positive electrode, negative electrode, non-aqueous electrolyte, and separator can be housed in a case for the purpose of preventing leakage of the electrolyte, preventing intrusion of outside air, and the like, so that a lithium ion battery can be manufactured.

  Hereinafter, the present invention will be described using examples. FIG. 1 is a schematic cross-sectional view of positive electrodes according to Examples 1 and 2 and Comparative Examples 2 to 4, FIG. 2 is a schematic cross-sectional view of positive electrodes according to Comparative Example 1, and FIG. 4 is a schematic cross-sectional view of the electrode state at the time of positive electrode evaluation 2, FIG. 4 is a schematic cross-sectional view of the electrode state at the time of positive electrode evaluation 2 of Comparative Example 1, and FIG. 5 is a schematic cross-sectional view of the coin-type battery in the case of 5, and FIG.

Example 1
As preparation of the positive electrode first layer 2, 10 parts by weight of acetylene black (HS-100, manufactured by Denki Kagaku Kogyo) as a conductive agent, 85 parts by mass of iodine (powder) as a material generating gas at high temperature, as a binder, 5 parts by weight of a styrene-butadiene copolymer (rubber) (BM-400, manufactured by JSR) was added and dispersed with a dissolver.
Furthermore, water addition was added and the dispersion process was performed and the solid content paste required for coating was prepared. This paste was applied onto an aluminum foil current collector 1 (20 μm thickness: manufactured by Toyo Aluminum Co., Ltd.) and subjected to a drying treatment, whereby a positive electrode first layer 2 was obtained. The coating amount of the positive electrode first layer 2 after the drying treatment was 10 g / m ² .

Next, the preparation of the positive electrode second layer 3 includes active material: LiCoO ₂ (manufactured by Nippon Chemical Industry) conductive agent: 90 parts by weight, acetylene black (HS-100, manufactured by Denki Kagaku Kogyo), binder: A homogeneous paste was prepared by adding 5 parts by weight of polyvinylidene fluoride (# 7200, manufactured by Kureha Battery Materials Japan) to the solvent: N-methylpyrrolidone (NMP) and performing a dispersion treatment. This paste was coated on the positive electrode first layer 2, by performing a drying treatment to obtain Seikyokudai two layers 3. The film thickness of the positive electrode second layer 3 after the drying treatment was applied to be 130 g / m ² .

For the negative electrode, the active material: scaly graphite (manufactured by Hitachi Chemical Co., Ltd.) 95 parts by weight, conductive agent: acetylene black (manufactured by HS-100 Denki Kagaku Kogyo Co., Ltd.) 4 considerations, binder: styrene butadiene rubber (BM-400, (Made by JSR) was mixed so as to be 2 parts by weight, and stirred for 1 hour using a dissolver to prepare a coating solution. At this time, in order to adjust the viscosity of the coating solution, 1 part by weight of carboxymethylcellulose was added to the total weight part 100 of the composition. The prepared coating liquid was applied onto a copper foil (12 μm thickness: manufactured by Furukawa Electric Co., Ltd.) so as to have a basis weight of 70 g / m ² . Further, in order to completely remove the solvent of the applied coating solution, a drying process was performed at 100 ° C. for 1 hour, and then a drying process was performed again at 100 ° C. for 12 hours in a vacuum environment.

  Using each of the produced positive and negative electrodes, a solvent in which 1 mol / L of lithium hexafluorophosphate is contained in the electrolytic solution and ethylene carbonate and diethyl carbonate are mixed in a ratio such that the weight ratio is 1: 1. A laminate type battery using was manufactured. The capacity of the battery was designed to be 500 mAh by stacking the positive electrode and the negative electrode.

(Example 2)
85 parts by weight of naphthalene was used as a material for generating gas at a high temperature of the positive electrode first layer 2. Otherwise, a laminated battery was produced in the same manner as in Example 1.

(Comparative Example 1)
The same as in Example 1 except that the positive electrode in which the positive electrode second layer 3 of Example 1 was directly formed on the aluminum foil current collector 1 (20 μm thickness) was used without forming the positive electrode first layer 2. Thus, a laminate type battery was produced.

(Comparative Example 2)
Preparation was carried out in the same manner as in Example 1, but at this time, no gas generating material was used for the positive electrode first layer 2 (0 parts by weight), and the amount of the conductive agent was increased accordingly, and 95 parts by weight of the conductive agent and the binder were added. A laminate type battery was produced in the same manner as in Example 1 except that the amount was 5 parts by weight.

(Comparative Example 3)
Preparation was performed in the same manner as in Example 1, except that 99 parts by weight of iodine, 1 part by weight of conductive agent, and 1 part by weight of binder were used as the gas generating material in the positive electrode first layer 2. A laminated battery was produced in the same manner as in Example 1.

(Comparative Example 4)
Preparations were made in the same manner as in Example 1, except that the positive electrode first layer 2 had 5 parts by weight of iodine as a gas generating material, 90 parts by weight of a conductive agent, and 5 parts by weight of a binder. Produced a laminated battery in the same manner as in Example 1.

(Evaluation 1)
To compare the battery change in appearance at the time of overcharging.
Using each of the positive electrodes prepared in Examples 1 and 2 and Comparative Examples 1 to 4 and the negative electrode of Example 1, the electrolyte contains 1 mol / L lithium hexafluorophosphate and the weight ratio is 1 A laminate type battery using a solvent in which ethylene carbonate and diethyl carbonate were mixed at a ratio of 1 to 1 was produced. The capacity of the battery was designed such that the positive electrode and the negative electrode were laminated to 500 mAh, and an overcharge test was performed on the battery.
When the measurement temperature was 25 ° C., the battery was charged up to 12 V at a charging current of 1500 mA, and the state of the battery at that time was observed. In the batteries of Examples 1 and 2 and Comparative Example 3, no particular change occurred. White smoke was produced from the batteries of No. 4 and No. 4, and in Comparative Examples 1 and 2, eventually fired. The results are shown in Table 1.

(Evaluation 2)
TG / DTA (differential heat / thermogravimetric change measurement) was performed.
About each electrode produced in Examples 1, 2 and Comparative Examples 1-4, the thermal analysis (TG / DTA) was performed.
The conditions were a nitrogen flow and a temperature increase rate of 2 ° C./min from room temperature to 200 ° C.
As a result, in Examples 1 and 2 and Comparative Example 3, weight loss due to volatilization was observed between 80 ° C and 140 ° C.
In Comparative Examples 1, 2, and 4, no significant weight change was observed.

To summarize the TG / DTA results for until 80 ° C. to 140 ° C., it was as shown in Table 2.

(Evaluation 3)
The charge / discharge capacity retention ratio after 100 cycles of the battery during normal operation was compared.
Using the electrodes prepared in Examples 1 and 2 and Comparative Examples 1 to 4, the counter electrode contains metallic lithium, the electrolyte contains 1 mol / L lithium hexafluorophosphate, and the weight ratio is 1: 1. A laminate type battery using a solvent in which ethylene carbonate and diethyl carbonate were mixed at such a ratio was produced, and the capacity retention rate after 100 cycles of charge / discharge was evaluated.

Examples 1 and 2 and Comparative Examples 1 and 2 show almost the same value, and in the case of normal operation in which no abnormality such as overcharge occurs, even if the first positive electrode layer is present, the battery performance is affected. Not confirmed.
However, when the gas generating material is remarkably large in the positive electrode first layer as in Comparative Example 3, it was confirmed that the battery performance was deteriorated.

(Evaluation 4)
The internal resistance during overheating was measured.
Using each electrode of Examples 1 and 2 and Comparative Examples 1 to 4, a laminate type battery was prepared in the same manner as in Evaluation 3, and the battery was overcharged to put it in an overheated state.
The measurement temperature was 25 ° C., and the battery was charged to 5 V with a charging current of 1 mA. Even if it exceeded 4.1 V which is a general charge end voltage when LiCoO ₂ was used as an active material, the potential increase was forcibly continued to increase the temperature inside the battery. The electrode provided with Seikyokudai one layer charge potential in overcharging was also confirmed that will easily rise.

Further, when the internal resistance of the battery was continuously measured when overcharging and overheating were continued, in Comparative Examples 1 and 2, there was no significant difference in resistance after the temperature increase due to overcharging. In Comparative Example 3, the internal resistance of the battery increased reliably after the overcharge test, and the effect of increasing the resistance in the battery due to polymerization in the first positive electrode layer and curing shrinkage of the positive first layer during overcharge was confirmed. It was done.
Table 4 shows a comparison of resistance values in each example when the resistance value of Comparative Example 1 having a normal laminate cell configuration is 1.

  Comparative Example 1 is a general battery electrode configuration in which the resistance is low. Compared to that, it can be seen that the resistance value increases in each. In particular, Examples 1 and 2 and Comparative Example 3 have a large resistance. From the above experiment, it is known from the above experiment that Comparative Example 3 becomes a resistance even during normal operation and the battery performance is difficult to be obtained.

(Evaluation 5)
The internal state of the overcharged and overheated battery was observed by visual inspection.
In Evaluation 4, the overcharged laminated batteries of Examples 1 and 2 and Comparative Examples 1 to 4 were disassembled, and the state on the positive electrode side was visually confirmed.

  As a result, in Examples 1 and 2 and Comparative Example 3, the positive electrode first layer 2 was very porous, cracked, or not formed as a film. It was in a state of peeling from the second layer 3. Further, in Comparative Example 4, although not as described above, the positive electrode first layer 2 was slightly peeled from the positive electrode current collector 1. In any case, it was confirmed that there was a large resistance between the positive electrode second layer 3 and the positive electrode current collector 1. In comparison, in Comparative Examples 1 and 2, the positive electrode second layer 3 and the positive electrode current collector 1 were in close contact, functioning as a battery, and no significant resistance was generated due to overcharging. It is. The results are shown in Table 5.

  From this result, when the positive electrode first layer 2 contains a material that generates gas, the positive electrode first layer 2 becomes porous and cracks, becomes brittle, and cannot be formed as a film. The adhesion failure of the body 1 and the positive electrode second layer 3 was caused, resulting in resistance, and suppression of the runaway reaction of the battery could be confirmed.

From the above results, as compared with the case of the positive electrode composed only of the positive electrode second layer 3 without introducing the positive electrode first layer 2, the positive electrode first layer 2 is appropriately mixed with materials that generate sublimation and gas from heat. As a result, the gas generating material in the positive electrode first layer 2 volatilizes when the battery is overheated due to overvoltage or the like, or when the battery itself is overheated and a thermal runaway reaction occurs. It was confirmed that the positive electrode first layer 2 became a resistance and the thermal runaway of the battery could be suppressed.
In addition, in the case of normal use, it was also confirmed that the presence of the positive electrode first layer 2 was not inferior to the battery performance as compared with the case where the positive electrode first layer 2 was not provided.

  Furthermore, the positive electrode first layer and the positive electrode second layer can be produced in a continuous production process depending on the solvent used, coating, drying equipment, and the like.

  The present invention is useful for various types of lithium ion batteries such as a laminate type, a cylindrical type, and a coin (button) type.

DESCRIPTION OF SYMBOLS 1 Positive electrode collector 2 Positive electrode 1st layer 3 Positive electrode 2nd layer 4 Separator 5 Negative electrode collector 6 Negative electrode layer 7 Electrolytic solution 8 Positive electrode case 9 Negative electrode case 10 Gasket 21 Positive electrode (the positive electrode 1st layer exists): Both sides at the time of lamination | stacking Application 22 Positive electrode (no positive first layer): Double-sided application during lamination 31 Negative electrode: Double-sided application during lamination

Claims (1)

A method of manufacturing a positive electrode of a lithium ion battery,
Using a slot die method, 85 parts by weight of a gas generating material that sublimates at 80 ° C. or higher and 140 ° C. or lower , 10 parts by weight of a conductive agent, and 5 parts by weight of a binder on the positive electrode current collector of the lithium ion battery. Forming a positive electrode first layer having an adhesive;
In inline against the step of forming the positive electrode first layer, the positive electrode first layer, including a positive electrode active material, conductive agent, and, and forming a positive electrode second layer having a binder ,Production method.

Images