KR19980076259A - Cathode electrode coating liquid for lithium ion battery or lithium ion polymer battery containing isocyanate compound, anode electrode using same and method for manufacturing same - Google Patents

Abstract

The present invention is a cathode electrode coating liquid for a lithium ion battery composed of at least one cathode electrode active material, at least one electron conductive material, at least one binder, at least one isocyanate compound, and at least one solvent. The present invention relates to a manufactured lithium ion battery or a cathode electrode for a lithium ion polymer battery and a method of manufacturing the same. The anode coating liquid used in the present invention may further include at least one catalyst for improving the reaction of HOH / NCO and / or OH / NCO, and at least one amine compound for removing unreacted isocyanate groups.

Description

Cathode electrode coating liquid for lithium ion battery or lithium ion polymer battery containing isocyanate compound, anode electrode using same and method for manufacturing same

The present invention relates to a cathode electrode coating liquid for a lithium ion battery or a lithium ion polymer battery containing an isocyanate compound, a cathode electrode prepared using the same, and a method of manufacturing the same. More preferably, the present invention is for a lithium ion battery or a lithium ion polymer battery made by mixing at least one positive electrode active material, at least one electron conductive material, at least one binder, and at least one isocyanate compound with at least one solvent. The present invention relates to a cathode electrode coating liquid, a cathode electrode for a lithium ion battery or a lithium ion polymer battery, which is coated on a cathode electrode plate and dried to increase adhesion between the electrode material and the electrode plate, and a method of manufacturing the same.

The isocyanate-containing compound reacts with hydroxyl groups on the electrode plate and the electrode active material to form allophanate bonds which are urethane bonds and / or crosslinked structures. Such urethane bonds and / or cross-linked allopanate bonds improve adhesion between the electrode plate and the film formed thereon and increase the bonding force between the electrode plate and the electrode active material, thereby maintaining performance even after repeated charging and discharging. And the life is extended.

In recent years, with the trend toward miniaturization, light weight, and portability of electronic devices, demands for high performance such as high energy density and long life as well as miniaturization and light weight are increasing. Lithium ion batteries are the most popular among the many batteries developed to date due to high energy density, light weight, and excellent recharging characteristics.

A lithium ion battery electrode comprising an electrode electrode plate and a coating layer composed of an electrode active material and a binder coated thereon is prepared by dissolving the electrode active material and the binder in a solvent therefor to prepare a coating solution, and the resulting coating solution is formed on the electrode electrode plate which is a metal current collector. It may be prepared by a solvent casting method for coating on.

The electrode of the battery repeatedly contracts and expands due to heat generation during charging and discharging, thereby degrading a bonding material that couples the electrode plate and the electron active material, thereby gradually decreasing the adhesion between the electrode plate and the electron active material. If the adhesion between the electrode plate containing the metal foil and the electrode material is poor, as the charge and discharge continues, the electrode materials are separated or separated from the electrode plate, which is the metal current collecting plate, thereby reducing the electronic life, reducing the battery capacity and output stability. Not only problems such as deterioration occur, but also great problems arise in the safety of the battery.

In general, a cathode of a lithium ion battery includes a cathode electrode active material including LiCoO 2, LiNiO 2, and LiMn 2 O 4, an electron conductive material carbon and a binder mixed with a solvent, and the resulting mixture is coated on a metal electrode plate such as aluminum foil. And drying the coating solution to form a coating layer on the electrode plate. However, when aluminum is used as the electrode plate, since the aluminum has a dense oxide layer on the surface, it is difficult for the bonding material to have a high adhesion between the electrode active material and the electrode plate. Therefore, as described above, due to heat generation during charging and discharging, the lithium ion anode electrode contracts and expands, thereby deteriorating a binder that combines the aluminum electrode plate, the cathode active material, and the electron conductive carbon, and thus the adhesive force between them gradually increases. Degrades. Therefore, the lifespan and capacity of the lithium ion battery are reduced and the safety of the output is reduced.

For this reason, the coating process of the positive electrode has been recognized as one of the most difficult processes in the manufacturing process of lithium ion batteries or lithium ion polymer batteries.

Accordingly, many methods have been proposed to improve adhesion between the metal thin film, the cathode electrode active material, and the electron conductive material.

As an example, a method of increasing the mechanical adhesion by forming a micro crack in a dense oxide layer on an aluminum surface is known. However, surface treatment using a brush or the like in an aluminum foil having a thickness of 20 micrometers does not have a good effect, and the process complexity And it is a simple improvement of physical adhesive force, there is a disadvantage that there is a limit to increase the adhesive strength.

In order to solve the above problems, the present inventors have conducted extensive research, and as a result, when the isocyanate compound is added to the lithium ion battery cathode electrode coating liquid, the isocyanate compound is a hydroxide on the electrode plate and the electrode active material and the electron conductive material. By forming a urethane bond and / or allophanate bond in response to the actual group, the adhesion between the electrode plate and the electrode active material and the electroconductive material is improved, thereby maintaining performance and prolonging the life through repeated charging and discharging of the battery. Found to be effective.

Accordingly, an object of the present invention is a coating liquid for producing a positive electrode of a lithium ion battery or a lithium ion polymer battery containing an isocyanate compound, and lithium ions having increased adhesion between electrode materials such as electrode active materials and electron conductive materials and electrode plates. It is to provide a positive electrode for a battery or a lithium ion polymer battery.

Still another object of the present invention is to prepare a cathode electrode for a lithium ion battery or a lithium ion polymer battery, by using the coating liquid for preparing a cathode electrode of a lithium ion battery or a lithium ion polymer battery containing an isocyanate compound, thereby increasing the adhesion between the electrode material and the electrode plate. To provide a way.

The lithium ion positive electrode prepared according to the method of the present invention can be usefully used in lithium ion polymer batteries as well as conventional lithium ion primary and secondary batteries.

FIG. 1 is a graph showing Re, Rt and Rct values, which are impedance measurement results obtained from lithium ion positive electrode half cells prepared by varying the content of isocyanate compounds according to the present invention.

2 is a graph showing a change in discharge capacity according to the number of charge and discharge cycles of the lithium ion positive electrode half battery manufactured in the present invention to show the effect of the addition of MDI according to repeated charge and discharge.

The coating liquid for preparing a cathode electrode of a lithium ion battery or a lithium ion polymer battery according to the present invention is mainly composed of an electrode active component, an electron conductive material, a binder, a solvent, and an isocyanate compound. The isocyanate in the isocyanate compound forms a urethane bond and / or an allophanate bond between the hydroxyl group on the aluminum foil surface and the electrode active material and the carbon surface, which is an electron conductive material, with the hydroxyl group. The anode electrode manufactured by the method of the present invention having such a urethane bond provides a significantly improved bonding force between the electrode active material and the electrode plate than the conventional anode electrode having a bonding force mainly composed of only other physical bonds or physical bond forces.

The lithium ion battery used in the present invention should be understood to mean both a lithium ion battery in which the electrolyte is a liquid and a lithium ion polymer battery in which the electrolyte contains a polymer and the like.

Isocyanate compounds used in the present invention are compounds containing at least one isocyanate group (-NCO), for example, 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2 , 6-TDI), 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-dicyclohexyl methane diisocyanate (H12MDI), 1,5-naphthalene diisocyanate (NDI), 1,6- Hexamethylene diisocyanate (HDI), xylene diisocyanate (XDI), isophorone diisocyanate (IPDI), 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl diisocyanate (TMDI).

The cathode electrode coating liquid of the lithium ion battery or the lithium ion polymer battery according to the present invention is 0.1% by weight or more, preferably 0.1% by weight to 3% by weight, based on the weight of the electrode active material contained in the isocyanate compound in the cathode electrode coating liquid. It may contain in the range of.

In addition, the coating solution for producing a positive electrode of a lithium ion battery or a lithium ion polymer battery of the present invention facilitates a urethane formation reaction between an isocyanate group (-NCO) and a hydroxyl group (-OH) in an electrode plate and / or an electrode active material. It may further include a catalyst to make. Examples of catalysts to enhance the reaction of OH / NCO include organometallic salts such as dibutyltin dilaurate (DBTLD), octocaate tin, tetrabutyl titanate.

In addition, at the high temperature of the solvent drying process, the urethane functional groups already formed may further react with unreacted isocyanate groups to form allophanate bonds, which are crosslinked structures, thereby further improving the mechanical properties of the positive electrode. You can.

In addition, by reacting with a small amount of water that may be present in the coating solution to form a urethane bond and / or allophanate bond, it is possible to prevent the decomposition reaction by moisture in the battery. This is more useful in a lithium ion polymer battery that is difficult to control the moisture in the electrode.

Therefore, the coating solution for preparing a lithium ion positive electrode of the present invention may further include a catalyst for improving the HOH / NCO reaction between the isocyanate group (-NCO) and the moisture (HOH) in the battery. Examples of catalysts to enhance this HOH / NCO reaction include triethylene diamine (DABCO), dimethylethanolamine (DMEA), tetramethylbutanediamine (TMBDA), dimethylcyclohexyl amine (DMCHA), triethylamine (TEA) and Same tertiary amines.

R-NCO + R '-OH → RNHCOOR' (urethane bond)

R-NCO + R '-NHCOOR → R'N (CONHER) HCOOR' '(allophanate bond)

The presence of unreacted isocyanate groups in the cell causes decomposition reactions above 3 volts, thereby inducing an oxidation potential. Therefore, care should be taken to avoid the presence of unreacted isocyanate groups in lithium ion batteries with high electrode potentials. For this purpose, stoichiometric control of added isocyanate groups should be carried out so that unreacted isocyanate groups do not remain, but the amount of hydroxyl groups present in the electrode active material and the electrode plate greatly affects the pretreatment process such as manufacturing method, storage and drying. Since it changes, it is difficult to determine the addition amount of an isocyanate compound uniformly. In this case, an instrument such as an infrared spectrometer or a cyclic voltmeter (CV) may be used to quantify the amount of isocyanate to be added.

Furthermore, the coating liquid for producing a positive electrode of a lithium ion battery or a lithium ion polymer battery according to the present invention may further include any amine compound for removing unreacted isocyanate groups in the battery.

That is, when an isocyanate group exists in the positive electrode of a lithium ion battery or a lithium ion polymer battery, since it is preferable to remove these reliably, it adds the compound containing the amine group whose reactivity with an isocyanate group is lower than a hydroxyl group, and is lithium ion battery. Remove isocyanate groups that may be present in the These amine compounds react with isocyanate groups to form urea bonds. Furthermore, the urea bond formed by reacting the amine compound with isocyanate groups reacts with another isocyanate group to form a crosslinked structure such as a biuret bond. As such, the amine compounds that can optionally be added serve as crosslinking structure formers for improving adhesion as well as as unreacted isocyanate group removers. Examples of amine compounds that can be used in the present invention for this purpose include 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA), m-phenylenediamine (m-PDA), and cumenediamine; m-PDA mixture (Caytur 7).

R-NCO + R '-NH2 → RNHCONHR' (urea bond)

R-NCO + R '-NHCOOR → R'N (CONHR) HCONHR (biuret bond)

As the binder that can be used in the present invention, a binder for a cathode electrode known in the art may be used, for example, a polymeric binder such as polyvinylidene fluoride or a copolymer thereof.

As the electrode active material that can be used in the present invention, an electrode active material for anode electrodes known in the art may be used, and examples thereof include LiCoO 2, LiNiO 2, and LiMn 2 O 4.

The present invention is described in more detail with reference to the following Examples. These examples are intended to illustrate the invention, not to limit it.

Example 1

8 parts by weight of polyvinylidene fluoride, which is a binder, of a mixture obtained by milling 82 parts by weight of LiNiO2, which is a positive electrode active material, and 10 parts by weight of cathodic black (manufactured by Akzo Chemical Ltd.), an electron conductive material, is 60 parts by weight of N-. It was added to the solution dissolved in methyl-2-pyrrolidinone (NMP) to obtain a homogeneous mixture. 0.5% of 4,4'-diphenylmethane diisocyanate (MDI) was added to the homogeneous mixture as an isocyanate-containing compound to obtain an anode coating solution of the present invention.

The obtained positive electrode coating liquid was coated on an aluminum foil having an appropriate thickness using a hot air coater. At this time, hot air of approximately 120 ° C. was attached and NMP, which was a solvent, was evaporated to form a film having an appropriate thickness on the aluminum foil. At this temperature, unreacted MDI reacts with the urethane bonds already formed to form crosslinked allophanate bonds.

The cathode electrode thus obtained was used as a working electrode and lithium was used as a counter electrode to prepare a cathode half cell. As an electrolyte, a 1 mol solution of LiPF 6 in an ethylene carbonate (EC) / diethyl carbonate (DEC) mixed solvent was used, and a polypropylene film (Celgard 2400) was used as a diaphragm.

For the positive electrode half battery manufactured in this example, potential stability and impedance were measured using CV.

Example 2-4

As isocyanate compounds, MDI was the same as in Example 1 except that MDI was added in amounts of 1% (Example 2), 2% (Example 3) and 3% (Example 4), respectively, based on the electrode active material. A positive electrode was prepared using the positive electrode coating liquid prepared by the method, and the positive electrode half cells were prepared in the same manner as in Example 1, respectively.

The potential stability and impedance of the cathode half cells thus prepared were measured as in Example 1.

In Example 4, an oxidation current was observed at 3 volts or more in the positive electrode half cell prepared with the coating liquid containing 3% MDI. At this time, the oxidation potential was not observed even at 3 V or higher in the positive electrode half cell manufactured by using the positive electrode electrode which completed the reaction of isocyanate by adding a small amount of amine compound.

When the potential stability and impedance of the positive electrode half cells made of the coating liquid further containing a small amount of the amine compound were measured as in Example 1, the results were substantially similar to those of the positive electrode half cells made of the coating liquid containing no amine compound. Obtained.

Example 5-8

Anodes of Examples 5, 6, 7, and 8 by adding a small amount of DABCO and octocanic acid tin as reaction catalysts of the anode coating liquid prepared by varying the amount of MDI obtained in Examples 1, 2, 3 and 4, respectively. Each cell was prepared.

Comparative Example 1

Except not using an isocyanate compound, a positive electrode was made using a positive electrode coating solution prepared in the same manner as in Example 1, and a positive electrode half cell was prepared therefrom.

1 is a graph showing the results of impedance measurements obtained from the positive electrode half cells prepared in Examples 1-4 and Comparative Example 1. FIG. Along the horizontal axis of the graph, the content of MDI was 0% (Comparative Example 1), 0.5% (Example 1), 1% (Example 2), 2% (Example 3) and 3% (Example 4), respectively. Rt (total resistance), Rct (charge transfer resistance) and Re (electrolyte resistance) values are shown from above along the longitudinal axis.

When the MDI was added, the Re value did not change significantly compared to the embossed half cell (Comparative Example 1) prepared with the coating solution without the MDI, but the Rt and Rct values showed excellent results. In particular, a positive electrode half cell (Example 2) prepared with a coating solution containing 1% MDI shows the best results.

Figure 2 shows the effect of the addition of MDI with repeated charging and discharging. The positive electrode half cell obtained in Example 2 (MDI added amount 1%) and Comparative Example 1 (MDI added amount 0%) was charged with constant current at 4.1 volts with C / 5, and then charged with constant voltage for 2 hours. After charging, the procedure of discharging up to 2.7V was repeated 20 times, and each discharge capacity was calculated based on the first discharge capacity.

The results show that the discharge capacity of the positive electrode half cell manufactured in Example 2 (MDI addition amount 1%) is smaller and the reduction rate is smaller than that of the positive electrode half cell obtained in Comparative Example 1 (0% MDI addition amount), respectively. have.

Example 9

To a 1 mol LiPF6 electrolyte solution in EC / DEC, 12 parts by weight of polyvinylidene fluoride (PVdF, manufactured by Elf Atochem) as a binder was added to prepare a uniform solution. Acetone was used for the solvent at this time. 84 parts by weight of LiNiO2 (manufactured by Cypress Foote Mineral) and 4 parts by weight of cathodic black (manufactured by Akzo Chemical Ltd.), which are electron conductive materials, were milled using a ball mill to obtain a homogeneous mixture. It was mixed with the solution containing the binder. MDI was added to the resultant uniform mixture in an amount of 0%, 0.5%, 1%, 2%, and 3% based on the electrode active material, respectively. Prepared. The coating solution was coated on an aluminum foil, and blown with hot air at 50 to 60 ° C. to form a coating for the positive electrode of the lithium ion polymer battery, thereby preparing five positive electrode for the lithium ion polymer battery.

A homogeneous coating solution was prepared by mixing a 1 mol LiPF6 electrolyte solution in EC / DEC, polyvinylidene fluoride (PVdF, manufactured by Elf Atochem), and THF solvent, and coating and drying the coating solution on a release paper to prepare a polymer electrolyte. Prepared.

Each of the five cathode electrodes prepared above was used together with the prepared polymer electrolyte to prepare five cathode half cells of a lithium ion polymer battery.

CV measurements, impedance measurements, and charge and discharge tests were performed on the lithium ion positive electrode half cell using the polymer electrolyte, and the results were substantially the same as in Examples 1 to 8.

According to the present invention, a cathode electrode prepared from a cathode electrode coating solution of a lithium ion battery or a lithium ion polymer battery containing an isocyanate group-containing compound shows high potential stability and excellent impedance characteristics even after repeated charging and discharging. It is shown to be useful as a positive electrode of a polymer battery. In addition, the positive electrode of a lithium ion battery or a lithium ion polymer battery according to the present invention has improved adhesion between the electrode plate and the film formed thereon due to isocyanate groups, and thus the battery can maintain its performance for a long time even after repeated charging and discharging. It can have an effect.

Claims (8)

A cathode electrode coating liquid made by mixing at least one cathode electrode active material, at least one electron conductive material, at least one binder, and at least one isocyanate compound with at least one solvent is applied to the cathode electrode plate and dried. Anode electrode for lithium ion battery or lithium ion polymer battery. The method of claim 1, wherein the isocyanate-containing compound is 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI), 4,4'-diphenylmethanedi Isocyanate (MDI), 4,4'-dicyclohexylmethane diisocyanate (H12MDI), 1,5-naphthalene diisocyanate (NDI), 1,6-hexamethylene diisocyanate (HDI), xylene diisocyanate (XDI), An isophorone diisocyanate (IPDI), 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl diisocyanate (TMDI) at least one compound selected from the group consisting of a positive electrode. The cathode electrode according to claim 1, wherein the isocyanate-containing compound in the cathode electrode coating liquid is in the range of 0.1% by weight or more, preferably 0.1% by weight to 3% by weight. The cathode electrode according to claim 1, wherein the electrode plate of the anode electrode is made of aluminum foil or mesh. The method of claim 1, wherein the positive electrode coating liquid, triethylenediamine (DABCO), dimethylethanolamine (DMEA), tetramethylbutanediamine (TMBDA), dimethylcyclohexylamine (DMCHA) as a catalyst for improving the HOH / NCO reaction Dibutyltindilaurate (DBTDL), octocanic acid tin as a catalyst to enhance the reaction of at least one compound selected from the group consisting of tertiary amines such as triethylamine (TEA) and / or OH / NCO And at least one compound selected from the group consisting of organometallic salts such as tetrabutyl titanate. The method of claim 1, wherein the positive electrode coating liquid is 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA), m-phenylenediamine (m-PDA), cumene diamine and m-PDA A positive electrode, characterized in that it further comprises at least one amine compound selected from the group consisting of (Caytur 7). A cathode electrode coating liquid made by mixing at least one cathode electrode active material, at least one electron conductive material, at least one binder, and at least one isocyanate compound with at least one solvent is applied to the cathode electrode plate and dried. A method for producing a positive electrode for a lithium ion battery or a lithium ion polymer battery. A cathode electrode coating liquid for a lithium ion battery or a lithium ion polymer battery, comprising at least one cathode electrode active material, at least one electron conductive material, at least one binder, at least one isocyanate compound, and at least one solvent.