KR101470332B1 - Functional Separator and Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention provides a separation membrane for a secondary battery, wherein the separation membrane includes a pouch carrying a functional material for controlling an engineering parameter in a battery. The separation membrane can improve the safety of the secondary battery by controlling the engineering parameters inside the battery.

Description

{Functional Separator and Secondary Battery Comprising the Same}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a functional separator and a secondary battery using the functional separator. More particularly, the present invention relates to a separator for a secondary battery, which comprises a pouch carrying a functional material for controlling an engineering parameter .

As the price of energy sources increases due to exhaustion of fossil fuels and the interest of environmental pollution is amplified, demand for environmentally friendly alternative energy sources is an indispensable factor for future life. Various researches on power generation technologies such as nuclear power, solar power, wind power, and tidal power have been continuing, and electric power storage devices for more efficient use of such generated energy have also been attracting much attention. As such power storage devices, secondary batteries are mainly used. Especially, in the case of lithium secondary batteries, lithium secondary batteries have been mainly used for portable devices, and the demand for light weight, high voltage and capacity has increased, and electric vehicles or hybrid electric The use area for automobiles, power assisted power supply through gridization, etc. has been greatly expanded.

However, there are still many problems to be solved for using a lithium secondary battery with a large capacity power source, and the most important task is improvement of energy density and safety. In addition, homogenization of wetting due to large surface area and shortening of process time are also the most important problems to be solved. Therefore, many researchers are spurring research on materials that can meet low cost while improving energy density, and are also making efforts to study materials to improve safety.

As a material for improving the energy density, a Ni-based material or a Mn-based material having a capacity higher than that of LiCoO ₂ that has been used previously is being studied. As a cathode, The material by Li alloy reaction is being studied.

In order to improve safety, a stable olivine-based cathode active material such as LiFePO ₄ or an anode active material such as Li ₄ Ti ₅ O ₁₂ and the like are being studied. However, such a material for improving safety has a fundamentally low energy density and can not fundamentally solve the problem of safety in the structure of a lithium secondary battery.

The safety of the secondary battery can be divided into internal safety and external safety, and subdivided into electrical safety, impact safety and thermal safety. These various safety problems commonly involve an increase in temperature at the time of event occurrence, and in this case, contraction of the drawn membrane generally inevitably occurs.

In order to solve the safety problem, many researchers have devised a method of coating an inorganic material or the like on the membrane, but they have not been able to smoothly prevent the membrane shrinkage due to the rise of the internal temperature of the cell and thereby the formation of a short circuit.

Therefore, there is a high need for a structure of a battery which prevents a short circuit due to separation membrane shrinkage and has excellent electrical performance.

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.

The inventors of the present application have conducted intensive research and various experiments and have found that when the separator includes a pouch containing a functional material, it is possible to control the engineering parameters in the battery, And the present invention has been completed.

Accordingly, the present invention provides a separation membrane for a secondary battery, which comprises a pouch carrying a functional material for controlling an engineering parameter of the inside of the battery as a separation membrane for a secondary battery.

Generally, since the functional material reacts with the electrolyte inside the battery, it is difficult to apply the functional material to the separator. However, if a suitable functional material can be applied to the separator in a situation where a safety problem occurs due to shrinkage of the separator itself, the safety can be further improved.

The engineering parameter is not particularly limited, but a preferable example may be temperature.

The temperature of the battery is necessarily increased when the battery is abnormally operated such as overcharging, and short-circuiting occurs between the positive electrode and the negative electrode due to heat shrinkage of the drawn separator at such a high temperature. Therefore, if the separator has a functional material for controlling the temperature, the temperature can be controlled at a position close to the separator, so that heat shrinkage of the separator can be minimized.

The functional material may be any material that can control the engineering parameters inside the battery. However, in order to control the temperature, it is preferable that the functional material is at least one selected from the group consisting of an endothermic agent, an absorbent, and an electrolytic solution. The absorbent generally absorbs heat through a chemical reaction, and can generate moisture. On the other hand, when moisture is present in a secondary battery, a serious problem arises in terms of safety. Therefore, it is more preferable that the endothermic agent is used together with an absorbent. In addition, since the ion conductivity may be lowered through the pouch in which the functional material is carried, the performance of the battery may deteriorate, and thus an electrolyte may be further included. For the reasons described above, it is particularly preferable to include both of the endothermic agent, the absorbent, and the electrolytic solution. The electrolytic solution is preferably the same electrolytic solution as the electrolytic solution used in the secondary battery.

The heat absorbing agent may be any material having a property of absorbing heat, and there is no particular limitation on the kind thereof, but one preferred example is a group consisting of aluminum peroxide, magnesium peroxide, silacogel and zirconium oxide It can be one or more selected.

The absorbent may be any material having a property of absorbing water, but preferred examples thereof include porous polymer particles such as polyethylene glycol, polypropylene glycol, silica, pulp, cellulose, cork and wood powder, and other commercially available absorbent And at least one selected from the group consisting of

The pouch carrying the functional material may be located at the distal end of the separation membrane, for example. However, the pouch may be a structure that is located at a non-terminal portion of the separation membrane, that is, a non-terminal portion. In this case, although not the deepest part of the electrode assembly, it is located between the electrode and the electrode, and appropriate safety improvement can be achieved.

Preferably, the pouch may be a structure in which the pouch is located at the center of the electrode assembly. When heat is generated in the internal structure of the battery, the outside may be partially discharged through the case, but the core may accumulate heat, and the temperature rise may be further increased. Therefore, it is more preferable that the pouch in which the functional material such as the endothermic material is carried on the separation membrane located at the core of the electrode assembly is improved in safety.

Further, two or more pouches may be included in one electrode assembly. Accordingly, it is possible to position the pouch carrying a plurality of functional materials at appropriate positions of the electrode assembly, thereby improving the safety of the battery more efficiently.

The material of the pouch may be any material capable of exhibiting appropriate effects of the functional material while providing a sealing property, but may be made of the same material as that of the separation membrane. However, such a pouch is made of a non-porous material because it is necessary that the pouch is sealed in a state in which a functional material is carried therein. If it is not sealed, the functional substance can be separated from the pouch and the desired effect can not be exhibited.

The present invention provides an electrode assembly including a cathode, a cathode, and the separator between the anode and the cathode.

The electrode assembly may be a stack, a jelly-roll, a stack-folding, or the like. Particularly, the jelly-roll type and stack-folding type electrode assemblies may be preferable because they are rolled or folded into one separator or separator to manufacture an electrode assembly.

In the electrode assembly of the present invention, the positive electrode is prepared, for example, by applying and drying a slurry prepared by adding a positive electrode mixture containing a positive electrode active material to a solvent such as NMP on a positive electrode collector, May further include a binder, a conductive material, a filler, a viscosity adjusting agent, and an adhesion promoter.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used. The positive electrode current collector may have fine unevenness formed on the surface thereof to increase the adhesive force of the positive electrode active material as in the case of the negative electrode current collector. Alternatively, the positive electrode current collector may have various properties such as a film, sheet, foil, net, porous body, Form is possible.

The cathode active material is a material capable of causing an electrochemical reaction. Examples of the lithium transition metal oxide include lithium cobalt oxide (LiCoO ₂ ) containing two or more transition metals and substituted with one or more transition metals, lithium Layered compounds such as nickel oxide (LiNiO ₂ ); 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 , such as _{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 <1, M = Al, Mg, Cr, Ti, Si or Y, and A = F, P or Cl; lithium nickel cobalt manganese composite oxide; And the formula _{Li 1 + x M 1-y} M 'y PO 4-z X z ( wherein, M = a transition metal, preferably Fe, Mn, Co or Ni, M' = Al, Mg or Ti, X = F, S or N, and -0.5? X? +0.5, 0? Y? 0.5, and 0? Z? 0.1), but the present invention is not limited thereto.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, various copolymers, high molecular weight polyolefins such as polyolefin, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, Vinyl alcohol, and the like.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey 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. Concrete examples of commercially available conductive materials include acetylene black series such as Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

The filler is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The viscosity modifier may be added up to 30% by weight based on the total weight of the negative electrode mixture as a component for adjusting the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the current 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 adhesion promoter may be added in an amount of 10% by weight or less based on the binder, for example, oxalic acid, adipic acid, Formic acid, acrylic acid derivatives, itaconic acid derivatives, and the like.

The negative electrode may be formed by applying a slurry prepared by adding a negative electrode active material containing a negative active material on a negative electrode current collector to a solvent such as NMP and drying the negative electrode active material. Fillers, viscosity modifiers, and adhesion promoters, and the like.

The negative electrode 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. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the negative electrode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

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, Pt, and Ti that 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 tin-based active material, a silicon-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 separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used.

The present invention provides a lithium secondary battery including the electrode assembly. Preferably, the secondary battery is a lithium secondary battery. The lithium secondary battery is composed of the electrode assembly and a lithium-containing non-aqueous electrolyte.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can 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, A polymer containing an ionic dissociation group and the like may 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 and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble 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 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

Such a secondary battery can be used for a battery cell used as a power source of a small device, and a battery including a plurality of battery cells used as a power source of a device requiring high temperature stability, long cycle characteristics, Module and a battery pack including the battery module.

Preferred examples of the device include a mobile electronic device, a power tool powered by an electric motor, An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; Power storage devices, and the like, but the present invention is not limited thereto.

INDUSTRIAL APPLICABILITY As described above, the secondary battery separator according to the present invention has an advantage that the safety of the battery can be improved since the functional parameter can be controlled by supporting the functional material.

1 is a schematic view showing an arrangement of unit cells for manufacturing a stack-folding type electrode assembly using a conventional separator;
2 is a schematic view showing an arrangement of unit cells for manufacturing a stack-folding type electrode assembly using a separator according to an embodiment of the present invention.

Hereinafter, the present invention will be described with reference to the drawings, but the present invention is not limited by the scope of the present invention.

FIG. 1 schematically illustrates an arrangement of unit cells for fabricating a stack-folding type electrode assembly using a conventional separator, and FIG. 2 is a cross-sectional view of a stack-folding type electrode assembly using a separator according to an embodiment of the present invention. An arrangement of unit cells for manufacturing the electrode assembly is schematically shown.

Referring to these drawings, bi-cells 110 and 210 composed of a cathode / separator / anode / separator / cathode and sequentially bi-cells 120 and 220 composed of a cathode / separator / cathode / separator / Is arranged on the separating films 130 and 230, and the stack-folding type electrode assembly can be manufactured by sequentially winding up starting from the rightmost bi-cell.

The first bi-cell and the second bi-cell are located at a distance separated by a width interval corresponding to at least one bi-cell, so that in the winding process, the first bi- After the outer surface is completely coated with the separation films 130 and 230, the lower surface electrode (cathode) of the first biocell is brought into contact with the upper surface electrode (anode) of the second biocell.

The bi-cells after the second bi-cell are arranged so that the intervals between them in the winding direction are sequentially increased since the coating length of the separation films 130 and 230 increases in the sequential lamination process by winding.

These bi-cells must be configured so that the positive electrode and the negative electrode face each other at the stacked interface at the time of winding. In this case, except for the first bi-cell, there are two bi- And a plurality of sequential arrangements alternating with each other.

2, a pouch 240 is formed at a distal end portion of the separation film where the first bi-cell is located, and the functional material 250 is supported in the pouch 240.

When the stack-folding type electrode assembly is manufactured in the above-described manner, the pouch 240 is positioned at the center of the electrode assembly, and the safety of the secondary battery is improved by adjusting engineering parameters of the core, for example, .

Hereinafter, the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited thereto.

&Lt; Example 1 >

A pouch was formed of the same material as that of the separation membrane at one end of the separation membrane, and aluminum peroxide was used as an endothermic agent, polyethylene glycol and an electrolyte were injected as an absorbent into the pouch and sealed.

A stack-folding type electrode assembly was fabricated such that the pouch was located at the center of the electrode assembly with the end having the pouch as a winding starting point.

The electrode assembly and the electrolyte solution were injected into the laminate sheet case and then sealed to manufacture a battery cell.

&Lt; Example 2 >

An electrode assembly and a battery cell were prepared in the same manner as in Example 1, except that magnesium peroxide was used as an endothermic agent in the pouch and cellulose fibers were used as an absorbent.

&Lt; Example 3 >

An electrode assembly and a battery cell were prepared in the same manner as in Example 1, except that the pouch for supporting the endothermic agent, the absorbent and the electrolyte was formed so as to be located at an intermediate portion of the separator.

&Lt; Comparative Example 1 &

An electrode assembly and a battery cell were prepared in the same manner as in Example 1, except that the endothermic agent, the absorbent and the pouch carrying the electrolyte were not formed.

<Experimental Example 1>

The ten battery cells prepared in each of Examples 1 to 3 and Comparative Example 1 were stored in a high-temperature environment of 150 ° C or higher to confirm short-circuiting. The results are shown in Table 1 below.

battery Number of shorted cells Example 1 0/10 Example 2 0/10 Example 3 1/10 Comparative Example 1 3/10

As shown in Table 1, the battery in which the short circuit occurred in the batteries of Examples 1 and 2 according to the present invention was not identified, and the short circuit occurred in one of the batteries of Example 3, 1 cells confirmed that shorting occurred in three cells.

It can be confirmed that this is more effective than the case where a pouch for supporting an endothermic agent, an absorbent, and an electrolyte is formed at one end of the separation membrane in the non-end portion.

In addition, in the batteries of Examples 1 to 3 using the separator for a secondary battery including the pouch, the pouch suppressed the short circuit caused by the shrinkage of the separator itself due to the temperature rise inside the battery, It can be confirmed that there is an effect of remarkably improving.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (19)

A separation membrane for a secondary battery, wherein the separation membrane includes a pouch carrying a functional material for controlling an engineering parameter in a battery,
Wherein the functional material includes an endothermic agent and an absorbent,
The pouch is made of the same nonporous material as the separation membrane, and is sealed in a state that the functional material is supported therein.
A lithium secondary battery comprising: a positive electrode; a negative electrode; and a stack-folding type electrode assembly including the separator between the positive electrode and the negative electrode. The lithium secondary battery of claim 1, wherein the engineering parameter is a temperature. delete delete The lithium secondary battery according to claim 1, wherein the endothermic agent is at least one selected from the group consisting of aluminum peroxide, magnesium peroxide, silica gel and zirconium oxide. The lithium secondary battery according to claim 1, wherein the absorbent is selected from the group consisting of polyethylene glycol, polypropylene glycol, silica, pulp, cellulose, cork, and wood powder. The lithium secondary battery according to claim 1, wherein the pouch is located at a distal end of the separator. The lithium secondary battery according to claim 1, wherein the pouch is located at a non-end portion of the separator. The lithium secondary battery according to claim 1, further comprising two or more pouches. delete delete delete A battery module comprising the lithium secondary battery according to claim 1 as a unit cell. A battery pack comprising the battery module according to claim 13. The device according to claim 14, comprising the battery pack as a power source. 16. The apparatus of claim 15, wherein the device comprises: a power tool powered by an electric motor; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart, or a system for power storage. delete delete delete

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