KR20120009735A - Electrode for Secondary Battery - Google Patents

Abstract

PURPOSE: An electrode for secondary battery is provided to prevent the firing or explosion due to rapid rising of resistance, without decreasing battery properties. CONSTITUTION: An electrode for secondary battery comprises an electrode active material, a conductive material, a binder, and a current collector. The electrode active material and the conductive material are combined to the current collector by the binder. When the temperature of battery is risen over the normal operation temperature of a battery, the resistance of the binder is rapidly increased at least two or more temperature ranges. The maximum range of the normal operation temperature of a battery is 60-100 °C. Temperature range, in which the resistance is rapidly increased comprises the first temperature range of 130-150 °C, and the second temperature range of 160-180°C.

Description

Secondary Battery Electrode {Electrode for Secondary Battery}

The present invention relates to a secondary battery electrode, and more particularly, a secondary battery electrode in which an electrode active material and a conductive material are bonded to a current collector by a binder, wherein the binder is at least two when the temperature rises above a normal operating temperature range of the battery. It relates to a secondary battery electrode, characterized in that it has a characteristic that a sudden increase in resistance in the above temperature range.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most actively researched field is the generation and storage method using electrochemistry.

A representative example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is gradually increasing.

As the development and demand for mobile devices increases, the demand for secondary batteries is rapidly increasing as an energy source. Among such secondary batteries, lithium secondary batteries exhibiting high energy density and operating potential, long cycle life, and low self discharge rate Many studies have been conducted and are also commercialized and widely used.

In addition, as interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles, which can replace vehicles using fossil fuel, such as gasoline and diesel vehicles, which are one of the main causes of air pollution, are being conducted. . As a power source of such electric vehicles and hybrid electric vehicles, nickel-metal hydride secondary batteries are mainly used, but researches using lithium secondary batteries with high energy density and discharge voltage have been actively conducted and some commercialization stages are in progress.

High energy density means that the energy can be exposed to a higher risk according to the accumulation of energy. The higher the energy density, the higher the risk and intensity of ignition and explosion.

As a result, many researchers have continuously researched and continuously tried to solve the energy accumulation and the risk of accumulated energy and secure safety, but it is not enough to say that the results have been sufficiently achieved.

There are various ways to prevent the risk of fire or explosion caused by the discharge of integrated energy, but there are various methods such as the use of safe materials or additives, but fundamentally, the battery cannot be operated before the fire or explosion occurs. It is the best way to prevent risks.

In this regard, the present invention proposes a technique using as a binder a material exhibiting a characteristic of rapid increase in resistance when the temperature rises above the normal operating temperature range of the battery.

Secondary batteries currently in use often include a PTC device having a property of increasing resistance as a temperature rises as a safety device. This PTC device is mainly mounted in a structure electrically connected to the circuit of the battery cell and the protection circuit member.

However, it is difficult to meet the demand for light and small batteries because mounting space is required to mount the PTC element in an electrical connection state, and the assembly process is complicated because the PTC element must be electrically connected to a secondary battery having a small structure as a whole. do.

Furthermore, since the PTC element located on the circuit acts as a factor of increasing the internal resistance, it is not only difficult to use in a high output battery but also reacts by heat transmitted from the battery cell, and thus the temperature of the battery cell which is a source of heat generation. The problem is that it is difficult to react sensitively to change.

Therefore, there is a high demand for the development of a new concept of safety means for preventing ignition / explosion and safety without compromising overall performance of the battery.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

After extensive research and various experiments, the inventors of the present application have developed a binder in which a rapid increase in resistance occurs in at least two temperature sections when the temperature rises above the normal operating temperature range of the battery as described later. When using such a binder, it was confirmed that safety can be improved without impairing the overall performance of the battery, and the present invention has been completed.

Accordingly, the secondary battery electrode according to the present invention is a secondary battery electrode in which the electrode active material and the conductive material are bonded to the current collector by a binder, and the binder rapidly resists at least two or more temperature sections when the temperature rises above the normal operating temperature range of the battery. It consists of having the property that the increase occurs.

In the case of a general secondary battery electrode, a binder for connecting an active material, a conductive material, and a current collector is used in order to prevent a decrease in battery performance. The binder used is a polymer, which has a very low conductivity, so that the battery performance decreases as the electrode is contained in the electrode. There is a problem, but on the contrary, even when the binding force of the electrode components is lowered, it causes a problem in battery performance. Therefore, in the case of the conventional binder, the development has been focused on maintaining the binding force.

On the other hand, the present invention provides a configuration that can improve the safety based on the physical properties of the binder itself in addition to the property of the existing binder.

Therefore, according to the present invention, by using a binder that brings a change in resistance in two or more temperature ranges, maintaining the binding force, which is the basic property of the binder in a general temperature range, does not affect the performance of the battery, and the safety problems of the battery In the generated temperature range, the resistance is rapidly increased to improve battery safety.

In addition, according to the present invention, since the binder included in the electrode to which the electrochemical reaction directly occurs has the above characteristics, it can generally exhibit an accurate and rapid reaction to abnormal exothermic or local reaction of the battery.

In some cases, a method of using an additive that increases resistance above a specific temperature may be considered. However, the additive is not preferable because it reduces the capacity of the battery according to the amount of the additive.

The normal operating temperature range of the battery may vary slightly depending on the configuration and type of the battery, for example, the upper limit thereof may be 60 to 100 ° C. In general, when a secondary battery is exposed to an abnormal environment caused by an external shock such as a nail or crush, a thermal shock such as a hot box, or an internal short such as a micro short, a short circuit occurs, and in such a process, a short circuit occurs. An exothermic phenomenon is caused, and a sudden temperature rise occurs.

Specifically, this calorific value may be represented by I ² R, and in a battery disconnected from an external power source, the I value is limited by the movement of electrical energy stored therein, which may vary depending on the resistance. In addition, when a large amount of instantaneous electric movement, a rapid temperature rise is caused, which causes a problem of ignition and explosion when the temperature exceeds the activation energy of the heating elements constituting the battery.

Therefore, even when a problem occurs that the battery is exposed to an abnormal environment, it is possible to make the battery fundamentally safe if the electric heat can be limited in a predetermined temperature range.

In this aspect, the present invention is to disconnect the current by a sudden increase in resistance when the temperature rises above the normal operating temperature range by the binder as described above, thereby preventing further heat generation phenomenon to improve the safety of the battery.

According to the present invention, the binder has a characteristic that a sudden increase in resistance occurs in at least two or more temperature sections when the temperature rises above the normal operating temperature range of the battery.

As a binder used in a conventional secondary battery, a fluorine-based polymer such as PVdF also has a property of increasing resistance due to temperature rise. However, it is difficult to exert an effective disconnection effect to secure safety only by increasing the resistance once in a temperature section over the normal operating temperature range of the battery. For example, when the temperature of the battery rises rapidly, the increase in resistance may be difficult to follow quickly. Therefore, the conventional secondary battery, even though using the binder as described above is equipped with a separate safety device according to the temperature rise.

On the other hand, since the binder of the present invention causes a sudden increase in resistance in at least two or more temperature sections when the temperature rises, this problem is fundamentally solved.

The number of temperature sections is not particularly limited as long as two or more temperature sections cause a sudden increase in resistance, and may be, for example, a type including two resistance increasing temperature sections. In this case, considering the overall characteristics of the secondary battery, it may be the first temperature section of 130 ~ 150 ℃ and the second temperature section of 160 ~ 180 ℃.

The sudden increase in resistance may be such that the gradient of the increase in resistance with increasing temperature increases by at least 1.5 times, preferably 2 times or more, in the temperature range where the safety problem occurs. If the increase in the slope gradient is less than 1.5 times, it is not preferable because it may be difficult to ensure the safety of the battery due to the increased resistance. The increase in the slope gradient is all applied in each temperature section, and its upper limit is not particularly limited.

The type of binder is not particularly limited as long as it has the above-described specificity.

In one preferred example, the binder is a mixture of two or more binders and each binder may be a material having a melting point at different temperature intervals. In general, since the solid material has a characteristic of rapidly increasing resistance during conversion into a molten state, a mixture of binders having melting points at different temperature sections as described above may cause a sharp increase in resistance at each temperature section.

In another preferred embodiment, the binder may be a material causing a phase change in each of two or more temperature sections. In general, since the resistance may change due to the change in the properties of the material during phase transfer, the material causing the phase change in each temperature section and increasing the resistance by such phase change may be used in the binder of the present invention. have.

The material causing such a phase change is not particularly limited, and may be, for example, a polymer resin causing each phase change by showing a glass transition temperature in a first temperature section and a melting point in a second temperature section.

Therefore, the polymer resin serves as a binder to bind the electrode components in the normal operating temperature range of the battery, and causes a phase change in two or more temperature sections, so that the resistance is rapidly increased, causing the battery to ignite or explode due to the temperature rise. This prevents the problem to occur, and has a physical property to simultaneously perform the role of ensuring the safety of the battery.

As described above, the electrode for a secondary battery according to the present invention includes a binder in which a sudden increase in resistance occurs at least two or more temperatures when the temperature rises above the normal operating temperature range of the battery, It is possible to prevent the increase in resistance before ignition and explosion due to the temperature rise without inhibiting the battery performance and to prevent ignition and explosion, and has the advantage of excellent cycle characteristics by fundamentally improving the safety of the battery.

The secondary battery electrode according to the present invention may be a positive electrode or a negative electrode.

The secondary battery electrode is generally composed of an electrode active material, a current collector, a conductive material, and the like, and may further include a viscosity regulator and a filler.

For example, the positive electrode is prepared by applying a mixture of a positive electrode active material, a conductive material, a binder and the like on a positive electrode current collector and then drying the negative electrode. It is prepared by drying.

In the electrode, the current collector is a portion where electrons move in the electrochemical reaction of the active material, and a positive electrode current collector and a negative electrode current collector exist according to the type of electrode.

The positive electrode current collector is generally made of a thickness of 3 ~ 500 ㎛. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used.

These current collectors may form fine concavities and convexities on the surface thereof to enhance the bonding strength of the electrode active material, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

In the electrode, the electrode active material is a material capable of causing an electrochemical reaction, and a positive electrode active material and a negative electrode active material exist according to the type of electrode.

The positive electrode active material is a lithium transition metal oxide, and includes two or more transition metals, and for example, layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ) substituted with one or more transition metals. ; Lithium manganese oxide substituted with one or more transition metals; Formula _{LiNi 1-y M y O 2} ( where, M = Co, Mn, Al , Cu, Fe, Mg, B, Cr, Zn or Ga and Lim, 0.01≤y≤0.7 include one or more elements of the element) A lithium nickel-based oxide represented by the following formula: Li _{1 + z} Ni _1/3 Co _1/3 Mn _1/3 O ₂ , Li _{1 + z} Ni _0.4 Mn _0.4 Co _0.2 O _2, etc. Li _{1 + z} Ni _b Mn _c Co _{1- (b + c + d )} M _d O _(2-e) A _e (where -0.5≤z≤0.5, 0.1≤b≤0.8, 0.1≤c≤0.8, 0≤d≤0.2, 0≤e≤0.2, b + c + d Lithium nickel cobalt manganese composite oxide represented by <1, M = Al, Mg, Cr, Ti, Si or Y, and A = F, P or Cl; Although these etc. are mentioned, it is not limited only to these.

Examples of the negative electrode active material include carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotube, fullerene, and activated carbon; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt and Ti which can be alloyed with lithium and compounds containing these elements; Complexes of metals and their compounds and carbon and graphite materials; Lithium-containing nitrides, and the like. Among them, a carbon-based active material, a silicon-based active material, a tin-based active material, or a silicon-carbon based active material is more preferable, and these may be used singly or in combination of two or more.

The conductive material is a component for further improving the conductivity of the electrode active material, and may be added in an amount of 1 to 30 wt% based on the total weight of the electrode mixture. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Carbon derivatives such as carbon nanotubes and fullerenes, conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The viscosity adjusting agent may be added up to 30% by weight based on the total weight of the electrode mixture, so as to control the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the collector may be easy. Examples of such viscosity modifiers include carboxymethylcellulose, polyvinylidene fluoride and the like, but are not limited thereto. In some cases, the above-described solvent may play a role as a viscosity adjusting agent.

The filler is an auxiliary component that suppresses the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The present invention also provides a secondary battery, preferably a lithium secondary battery, comprising the secondary battery electrode.

The lithium secondary battery generally includes a separator and a lithium salt-containing nonaqueous electrolyte in addition to the electrode.

The separator is an insulating thin film interposed between the anode and the cathode and having high ion permeability and mechanical strength. The pore diameter of the separator is generally from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separation membrane, for example, a sheet or a nonwoven fabric made of an olefin-based polymer such as polypropylene which is chemically resistant and hydrophobic, glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium-containing non-aqueous electrolyte solution consists of a non-aqueous electrolyte solution and a lithium salt.

Examples of the nonaqueous electrolytic solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, But are not limited to, lactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, Nitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives , Tetrahydrofuran derivatives, ether, methyl pyrophosphate, ethyl propionate and the like can be used.

The lithium salt is a material that is easy to dissolve in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In some cases, an organic solid electrolyte, an inorganic solid electrolyte, or the like may be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the non-aqueous electrolyte solution includes, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, and hexaphosphate triamide. , Nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. are added May be In some cases, in order to impart nonflammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-Ethylene) may be further included. carbonate), PRS (propene sultone), FEC (Fluoro-Ethlene carbonate) and the like may be further included.

The secondary battery according to the present invention may be preferably used as a power source of an electric vehicle, a hybrid electric vehicle, etc., in which particularly excellent safety and high rate characteristics are required.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (13)

An electrode for secondary batteries in which an electrode active material and a conductive material are bonded to a current collector by a binder, wherein the binder has a characteristic of rapid increase in resistance at least two or more temperature sections when the temperature rises above a normal operating temperature range of the battery. Secondary battery electrode. The method of claim 1, wherein the normal operating temperature range of the battery, the upper limit electrode is a secondary battery electrode, characterized in that 60 to 100 ℃. The electrode of claim 1, wherein the temperature section in which the rapid increase in resistance of the binder occurs comprises a first temperature section of 130 to 150 ° C. and a second temperature section of 160 to 180 ° C. 7. The method of claim 1, wherein the binder is a secondary battery electrode, characterized in that the gradient of the increase in resistance (gradient) increases with the temperature increase at least 1.5 times in the temperature section. The electrode for secondary batteries of claim 4, wherein the slope gradient increases at least twice in the temperature section. The electrode of claim 1, wherein the binder is a mixture of two or more binders, and the binders have a melting point at different temperature intervals. The method of claim 1, wherein the binder is a secondary battery electrode, characterized in that the material causing a phase change in the temperature section, respectively. 8. The secondary battery electrode of claim 7, wherein the binder is a polymer resin exhibiting a glass transition temperature in a first temperature section and a melting point in a second temperature section. The electrode for secondary batteries of claim 1, wherein the electrode further comprises a viscosity regulator and / or a filler. The electrode for secondary batteries according to claim 1, wherein the electrode current collector has a thickness of 3 to 200 µm and fine irregularities are formed on a surface thereof. The electrode of claim 1, wherein the electrode active material is lithium transition metal oxide powder or carbon powder. A secondary battery comprising the electrode according to any one of claims 1 to 11. The secondary battery of claim 12, wherein the secondary battery is a lithium secondary battery.