KR101483205B1 - Electrode Assembly Having Improved Electrolyte Wetting Property and Safety Property and Lithium Secondary Battery Comprising the Same - Google Patents

Abstract

More particularly, the present invention relates to an electrode assembly comprising an anode, a cathode, and a separator disposed between the anode and the cathode, the electrode assembly comprising: Wherein the separator comprises a non-woven fabric separator, wherein the separator is a non-woven fabric separator, and the area (mm ² ) of the upper and lower surfaces of the electrode assembly with respect to the thickness (mm) And a lithium secondary battery including the electrode assembly.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode assembly having improved electrolyte impregnability and safety, and a lithium secondary battery including the electrode assembly.

More particularly, the present invention relates to an electrode assembly comprising an anode, a cathode, and a separator disposed between the anode and the cathode, the electrode assembly comprising: Wherein the separator comprises a non-woven fabric separator, wherein the separator is a non-woven fabric separator, and the area (mm ² ) of the upper and lower surfaces of the electrode assembly with respect to the thickness (mm) And a lithium secondary battery including the electrode assembly.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operational potential, long cycle life, Batteries have been commercialized and widely used.

In recent years, there has been a growing interest in environmental issues, and as a result, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, And the like. Although a nickel metal hydride (Ni-MH) secondary battery is mainly used as a power source for such an electric vehicle (EV) and a hybrid electric vehicle (HEV), a lithium secondary battery having a high energy density, a high discharge voltage, Research is being actively carried out, and some are commercialized.

In general, the lithium secondary battery is assembled by inserting the positive electrode, the negative electrode and the separator into each other, alternately inserting the positive electrode, the negative electrode and the separator in a battery case made of a can or pouch having a predetermined size and shape, It proceeds. At this time, the electrolyte injected later is impregnated between the anode, the cathode and the separator by a capillary force. However, due to the nature of the materials, the anodes, the cathodes, and the separator are both hydrophobic substances, while the electrolyte is a hydrophilic material, so that wetting of the electrodes and the separator of the electrolyte may take a considerable amount of time, .

In recent years, as a device or a device becomes larger in size, a battery having a larger capacity and a larger size becomes a continuous requirement. However, in such a case, there is a problem of electrolyte injection. In other words, in addition to the fundamental hydrophilicity difference, as the volume of the electrolyte to be infiltrated decreases and the area becomes wider, the possibility that the electrolyte does not reach the inside of the cell but exists only locally on the outside becomes high. The battery thus produced has a disadvantage in that the amount of the electrolytic solution partially becomes insufficient in the inside of the battery, so that the capacity and performance of the battery are greatly reduced

In order to improve the impregnability of such an electrode with an electrolyte, a method of injecting an electrolyte at a high temperature or injecting an electrolyte at a pressure or a reduced pressure has been used. However, the conventional separation membrane is shrunk by heat and causes an internal short circuit.

Therefore, there is a great need for a large-area secondary battery technology having stability at a high temperature and improved electrolyte impregnability.

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 a nonwoven fabric separator is used in an electrode assembly containing a lithium metal oxide represented by a specific formula as an anode active material as described later, And that the desired effects can be achieved because the high rate charge / discharge characteristics are improved, and the present invention has been accomplished.

Accordingly, the present invention provides an electrode assembly comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode comprises a lithium metal oxide represented by the following Formula 1 as a negative electrode active material, The electrode assembly is characterized in that the electrode assembly is made of metal.

Li _a M ' _b O _{4-ca c} (1)

In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;

a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4;

c is determined according to the oxidation number in the range of 0? c <0.2;

A is one or more of an anion of -1 or -2.

Specifically, the negative electrode active material may be lithium titanium oxide (LTO) represented by the following formula (2), which is easy to charge at a high rate, specifically Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , Li _1.33 Ti _1.67 O ₄ and Li _1.14 Ti _1.71 O _4. However, the present invention is not limited to these examples. More specifically, Li 1 _.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ .

Li _a Ti _b O ₄ (2)

In the above formula, 0.5? A? 3, 1? B? 2.5.

As described above, when LTO is used as the negative electrode active material, it is possible to manufacture a large-capacity and large-area battery. In one specific example, the electrode assembly has a surface (upper surface) (Mm &lt; ² &gt;) may be 2000 or more, specifically, 3000 or more and 10000 or less.

Irrespective of the thickness of the electrode assembly, the area of the upper and lower surfaces of the electrode assembly may be 20000 mm ² or more, specifically 25000 mm ^{2 or} more, and 100000 mm ² or less.

In this case, the length in the direction of the shortest length in the three axes of the electrode assembly is the thickness (mm) of the electrode assembly, which means the stacking direction including the anode, the cathode and the separator. On the other hand, the product of the lengths in the two axial directions having the longest length is the area (mm ² ) of the upper surface and the lower surface of the electrode assembly. One side may be an anode or a cathode, so the kind is not a problem.

As described above, in the case of manufacturing such a large-capacity, large-area battery as described above, as the volume of the electrolyte to be infiltrated decreases and the area becomes wider, the possibility that the electrolyte does not reach the inside of the battery and exists only locally on the outside , The amount of the electrolytic solution partially becomes insufficient in the inside of the battery, and the capacity and performance of the battery are greatly reduced.

Thus, the inventors of the present application have found that the problem of electrolyte impregnability can be solved when a nonwoven fabric separator is used.

The nonwoven fabric separator is disposed between the positive electrode and the negative electrode and is preferably made of microfine fibers having an average thickness of 0.5 to 10 mu m and more preferably 1 to 7 mu m so that the length of the pores (the maximum diameter of the pores) It is preferable to form pores having a pore size of 0.1 to 70 mu m. It is difficult to manufacture a nonwoven fabric having many pores having a long diameter of less than 0.1 탆, and when the long diameter of the pores exceeds 70 탆, a problem of lowering the insulating property due to the pore size may occur. The thickness of the nonwoven fabric separator is preferably 5 to 300 탆.

The material forming the nonwoven fabric separating membrane is not particularly limited, and examples thereof include polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides such as aramid, polyacetal, polycarbonate, Polyolefins such as polyimide, polyether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, polytetrafluoroethylene, polyfluorinated vinylidene, polyvinyl chloride, polyacrylonitrile, cellulose, nylon, Polytetrafluoroethylene, polytetrafluoroethylene, polyparaphenylene benzobisoxazole, polyarylate, and glass.

If the nonwoven fabric separator is used in a conventional active material, the oxidation / reduction potential of the negative electrode is at a level similar to the oxidation / reduction potential of the lithium metal. Therefore, performance deterioration due to the generation of lithium metal at high rate charging / discharging / low temperature charging / discharging, However, when the lithium-titanium oxide (LTO) is used as an anode active material as in the present invention, the reaction occurs at a high potential of about 1.55 V compared to the oxidation / reduction potential of the lithium metal. It is possible to utilize a nonwoven fabric separator because it has a merit that it does not cause a problem. Therefore, large capacity batteries using lithium titanium oxide as a negative electrode active material and a nonwoven fabric as a separator have higher porosity than nonwoven fabric separator membranes, thereby improving electrolyte impregnability and high rate charge / discharge characteristics.

However, in manufacturing a large-capacity, large-area battery, the size of the nonwoven fabric separating membrane also becomes large. In this case, safety of the battery may be a problem depending on the rigidity of the nonwoven fabric separating membrane itself. , It may be an SRS nonwoven fabric separator.

The SRS nonwoven fabric separating membrane is an organic / inorganic composite porous separating membrane, which is produced by using inorganic particles and a binder polymer on the nonwoven fabric separating membrane substrate as active layer components. In addition to the pore structure contained in the nonwoven fabric separating membrane substrate itself, And has a uniform pore structure formed by the interstitial volume of the membrane.

When such an SRS nonwoven fabric separator is used, it is advantageous in that an increase in the thickness of the battery due to swelling at the time of chemical conversion can be suppressed as compared with the case where a conventional separator is used, When a gelable polymer is used, it can also be used as an electrolyte.

In addition, the SRS nonwoven fabric separator has many uniform pore structures in both the active layer and the nonwoven fabric separator. Since the lithium ion is smoothly transferred through the pores and a large amount of electrolyte is filled, The performance of the battery can be improved at the same time.

Since the SRS nonwoven fabric separator composed of the inorganic particles and the binder polymer has high heat resistance of the inorganic particles, high temperature heat shrinkage does not occur even when the nonwoven fabric separator is used alone. Therefore, the SRS nonwoven fabric separator can be prevented from greatly enlarging the short-circuited area even if a short circuit occurs in the nonwoven fabric separator, thereby improving the safety of the battery.

Since the SRS nonwoven fabric separating membrane is formed by coating directly on the nonwoven fabric separating membrane, the pores of the surface of the nonwoven fabric separating membrane substrate and the active layer exist as anchoring mutually so that the active layer and the porous substrate are physically and firmly bonded. Therefore, not only can the problems of mechanical properties such as brittleness be improved, but also the interfacial adhesion between the nonwoven fabric separator base material and the active layer becomes excellent and the interface resistance is reduced. In practice, the SRS nonwoven fabric separator has a structure in which the formed organic / inorganic complex active layer and the porous substrate are organically bonded to each other, and the pore structure existing in the porous substrate remains unaffected by the active layer, It can be seen that a uniform pore structure due to the particles is formed. Such a pore structure is filled with a liquid electrolyte to be injected at a later stage, which results in a significant reduction in interfacial resistance between the inorganic particles and between the inorganic particles and the binder polymer.

The SRS nonwoven fabric separator also exhibits excellent adhesion characteristics by controlling the content of the inorganic particles and the binder polymer in the separator, so that the battery assembling process can be easily performed.

In the SRS nonwoven fabric separator, one of the active layer components formed on the surface of the nonwoven fabric separator substrate and / or the pores of the substrate is an inorganic particle conventionally used in the art. The inorganic particles enable the formation of voids between the inorganic particles to form micropores and serve as a kind of spacer capable of maintaining the physical shape. In addition, since the inorganic particles generally have a characteristic that their physical properties do not change even at a high temperature of 200 DEG C or more, the formed SRS nonwoven fabric separation membrane has excellent heat resistance.

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as the oxidation and / or reduction reaction does not occur in the operating voltage range of the applied battery (for example, 0 to 5 V based on Li / Li +). Particularly, when inorganic particles having an ion-transporting ability are used, the ion conductivity in the electrochemical device can be increased and the performance can be improved. Therefore, it is preferable that the ionic conductivity is as high as possible. In addition, when the inorganic particles have a high density, it is difficult to disperse the particles at the time of coating, and there is a problem of an increase in weight during the production of the battery. In the case of an inorganic substance having a high dielectric constant, dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte also contributes to increase ionic conductivity of the electrolyte.

For the reasons stated above, the inorganic particles are preferably high-permittivity inorganic particles having a dielectric constant of 5 or more, specifically 10 or more, inorganic particles having piezoelectricity, inorganic particles having lithium ion transferring ability, or a mixture thereof Do.

The piezoelectricity inorganic particle means a non-conductive material at normal pressure or a material having electrical conductivity due to a change in internal structure when a certain pressure is applied, and exhibits a high permittivity with a dielectric constant of 100 or more, The charge is generated in the case of applying tensile or compressive force, so that one side is charged positively and the other side is negatively charged, thereby generating a potential difference between both sides.

When inorganic particles having the above-described characteristics are used as the porous active layer component, if an internal short-circuit of both electrodes occurs due to an external impact such as local crush or nail, due to the inorganic particles coated on the separator, Not only do not directly contact but also cause a potential difference in the particle due to the piezoelectricity of the inorganic particles. As a result, the electron transfer between the two electrodes, that is, the flow of a minute current, The safety can be improved.

Examples of the inorganic particles having piezoelectricity include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1 -x} La _x Zr _{1 -y} Ti _y O ₃ (PLZT), PB (Mg ₃ Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT) hafnia (HfO ₂ ), or mixtures thereof.

The inorganic particles having the lithium ion transferring ability refer to inorganic particles that contain a lithium element but do not store lithium but have a function of transferring lithium ions. The inorganic particles having lithium ion transferring ability exist in the particle structure Since lithium ions can be transferred and transferred due to a kind of defect, the lithium ion conductivity in the battery can be improved and the battery performance can be improved.

Examples of the inorganic particles having lithium ion transferring ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y < (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), Li _3.25 Ge (Li _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5) such as _0.25 P _0.75 S ₄ , Li ₃ lithium nitride such as _{N (Li x N y, 0} <x <4, 0 <y <2), Li 3 PO 4 -Li 2 Li x (SiS 2 based glass, such as _{S-SiS 2 Si y S z} , 0 <x <3, 0 < y <2, 0 <z <4), LiI-Li 2 SP 2 S 5 P 2 , such as S ₅ based _{glass (Li x P y S z} , 0 <x <3, 0 <y <3, 0 <z <7), or a mixture thereof, but are not limited thereto.

Examples of inorganic particles having a dielectric constant of 5 or more include SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , SiC, But is not limited thereto. When the above-mentioned high-permittivity inorganic particles, piezoelectric particles, and inorganic particles having lithium ion-transporting ability are mixed, their synergistic effect can be doubled.

INDUSTRIAL APPLICABILITY The SRS nonwoven fabric separating membrane of the present invention can control the size of inorganic particles, the content of inorganic particles, and the composition of inorganic particles and binder polymer constituting the active layer of the separator substrate to form pores in the active layer together with pores contained in the non- And the pore size and porosity can be adjusted together.

The size of the inorganic particles is not limited, but is preferably in the range of 0.001 to 10 mu m for the formation of a film of uniform thickness and a suitable porosity. When the thickness is less than 0.001 탆, the dispersibility of the SRS nonwoven fabric is lowered and the physical properties of the SRS nonwoven fabric separator are difficult to control. When the thickness exceeds 10 탆, the thickness of the SRS nonwoven fabric is increased, The size increases the probability of an internal short circuit occurring during charging and discharging of the battery.

The content of the inorganic particles is not particularly limited, but is preferably in the range of 50 to 99% by weight, more preferably 60 to 95% by weight, based on 100% by weight of the mixture of the inorganic particles and the binder polymer constituting the SRS nonwoven fabric separator. If the amount is less than 50% by weight, the content of the polymer becomes excessively large, and the pore size and the porosity due to the reduction of the void space formed between the inorganic particles may be decreased, resulting in deterioration of the performance of the final battery. On the contrary, when the content exceeds 99% by weight, the mechanical properties of the final SRS nonwoven fabric separator are deteriorated due to the weak adhesive force between the inorganic materials because the polymer content is too small.

In the SRS nonwoven fabric separator according to the present invention, the other of the active layer components formed on the surface of the nonwoven fabric separator substrate and / or the pores of the substrate is a polymer commonly used in the art. Particularly, it is possible to use a glass transition temperature (Tg) as low as possible, preferably in the range of -200 to 200 ° C. This is because the mechanical properties such as flexibility and elasticity of the final film can be improved. The polymer faithfully fulfills the role of binder to connect and stably fix inorganic particles and particles, inorganic particles and the surface of the separator substrate and porosity of the separator, thereby preventing the mechanical properties of the final SRS nonwoven fabric separator from deteriorating do.

In addition, although the binder polymer does not necessarily have ion conductivity, the performance of the electrochemical device can be further improved by using a polymer having ion conductivity. Therefore, it is preferable that the binder polymer has a high permittivity constant.

In fact, since the degree of dissociation of the salt in the electrolyte depends on the permittivity constant of the electrolyte solvent, the higher the permittivity constant of the polymer is, the better the salt dissociation degree in the electrolyte of the present invention can be. The dielectric constant of the polymer may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), more preferably 10 or more.

In addition to the above-mentioned functions, the binder polymer may be gelled upon impregnation with a liquid electrolyte to exhibit a high degree of swelling of the electrolyte. In fact, when the binder polymer is a polymer having an excellent electrolyte impregnation rate, the electrolyte injected after assembling the battery is impregnated with the polymer, and the polymer having the absorbed electrolyte has electrolytic ion conduction capability. Therefore, the performance of the electrochemical device can be improved compared to the conventional organic / inorganic composite electrolyte. In addition, compared with the conventional hydrophobic polyolefin-based separator, wetting of the electrolyte for a battery is improved, and polarity electrolytic solution for a battery, which has not been used conventionally, can be applied. In addition, when the polymer is a polymer that can be gelled when the electrolyte is impregnated, the gelled organic / inorganic composite electrolyte can be formed by allowing the injected electrolyte and the polymer to react with each other and gel. The thus formed electrolyte is easier to manufacture than the conventional gel type electrolyte, and exhibits high ion conductivity and electrolyte impregnation rate, thereby improving the performance of the battery. Therefore, if possible, a polymer having a solubility index of 15 to 45 MPa &lt; 1/2 &gt; is preferable, and 15 to 25 MPa &lt; 1/2 &gt; and 30 to 45 MPa & When the solubility index is less than 15 MPa &lt; 1/2 &gt; and more than 45 MPa &lt; 1/2 &gt;, it becomes difficult to swell by a common liquid electrolyte for a battery.

Examples of usable binder polymers include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotylchlorethylene, polymethylmethacrylate, Polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate (cellulose acetate), cellulose acetate Cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, hydroxypropylcellulose, hydroxypropylcellulose, hydroxypropylcellulose, Cyanoethyl Acrylonitrile-styrene-butadiene copolymer, polyimide, or a mixture thereof, and the like may be used as the binder resin. The binder may be selected from the group consisting of acrylonitrile-styrene-butadiene copolymer, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile- However, it is not limited thereto, and any material including the above-mentioned characteristics may be used alone or in combination.

The composition ratio of the inorganic particles and the binder polymer as the active layer component is not particularly limited, but can be adjusted within a range of 10:90 to 99: 1 wt.%, And is preferably in a range of 80:20 to 99: 1 wt. When the ratio is less than 10: 90% by weight, the content of the polymer is excessively increased, resulting in a decrease in the pore size and the porosity due to the reduction of the void space formed between the inorganic particles, , The mechanical properties of the final SRS nonwoven fabric separator may be deteriorated due to the weak adhesion between the inorganic materials because the polymer content is too small.

The active layer of the SRS nonwoven fabric separator may further include other commonly known additives in addition to the inorganic particles and polymers described above.

The SRS nonwoven fabric separator of the present invention formed by coating a mixture of inorganic particles and a binder polymer on a nonwoven fabric separator substrate includes not only pores in the separator body itself but also an empty space between inorganic particles formed on the substrate Both the substrate and the active layer form a pore structure due to the space. The pore size and the porosity of the SRS nonwoven fabric membrane are mainly dependent on the size of the inorganic particles. For example, when inorganic particles having a particle size of 1 μm or less are used, pores formed are also 1 μm or less. Such a pore structure is filled with an electrolyte solution to be injected at a later stage, and the filled electrolyte serves as an ion transfer function. Therefore, the pore size and the porosity are important factors for controlling the ionic conductivity of the SRS nonwoven fabric separator.

The thickness of the active layer on which the pore structure is formed by coating with the above mixture on the nonwoven fabric separator substrate is not particularly limited, but is preferably in the range of 0.01 to 100 mu m. The pore size and the porosity of the active layer are preferably in the range of 0.001 to 10 탆 and 5 to 95%, respectively, but are not limited thereto.

The pore size and the porosity of the SRS nonwoven fabric membrane thus prepared may be in the range of 0.001 to 10 탆, 45 to 90%, and more specifically, in the range of 0.1 to 7 탆 and 50 to 70% . When the size of the pores and the porosity are less than the above range, the wettability and charge / discharge characteristics are deteriorated as described above.

In addition, the thickness of the SRS nonwoven fabric separator is not particularly limited, and can be adjusted in consideration of battery performance. In detail, it may be in the range of 1 to 300 mu m, and more specifically in the range of 5 to 200 mu m.

Hereinafter, other components of the electrode assembly will be described.

The anode is prepared by applying a mixture of a cathode active material, a conductive material and a binder on a cathode current collector, followed by drying and pressing. If necessary, a filler may be further added to the mixture.

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 changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode 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.

When the cathode active material is not a lithium nickel manganese composite oxide (LNMO), for example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metal ; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2-x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

In one specific example, the cathode active material may be a lithium manganese composite oxide having a spinel structure, which corresponds to the high potential of the lithium titanium oxide and is a high-potential oxide represented by the following formula (3).

Li _x M _y Mn _2-y O _{4 -z z} (3)

Wherein 0 < y < 2, 0 z < 0.2,

M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;

A is one or more of an anion of -1 or -2.

In detail, the lithium manganese composite oxide may be a lithium nickel manganese composite oxide represented by the following formula (4), more specifically LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O ₄ .

Li _x Ni _y Mn _2-y O ₄ (4)

In the above formula, 0.9? X? 1.2 and 0.4? Y? 0.5.

The conductive material is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial 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.

The binder is a component that assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change 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.

On the other hand, the negative electrode is manufactured by applying, drying and pressing an anode active material on an anode current collector, and may optionally further include a conductive material, a binder, a filler, and the like as described above.

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 electrical conductivity without causing chemical changes in the battery, and examples of the anode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a 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. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The present invention provides a secondary battery comprising the electrode assembly, wherein the secondary battery is a lithium secondary battery having a structure in which an electrode assembly is impregnated with an electrolyte solution containing a lithium salt.

The electrolyte solution containing the lithium salt is composed of an electrolyte solution and a lithium salt. The electrolyte solution may be a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte, but is not limited thereto.

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.

In one specific _{example, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing non-aqueous electrolyte.

The present invention also provides a battery module including the secondary battery as a unit cell, and a battery pack including the battery module.

The battery pack may be used as a power source for devices requiring high temperature stability, long cycle characteristics, and high rate characteristics.

Specific examples of the device include a power tool which is powered by an electric motor and moves; 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; And a power storage system, but the present invention is not limited thereto.

As described above, the electrode assembly and the secondary battery using the nonwoven fabric separator according to the present invention have a higher porosity than the conventional separator, and are excellent in the electrolyte impregnation property and the high rate charge / discharge property of the electrolyte, It has an effect of preventing self-discharge and low voltage of a large-area battery used as a negative electrode active material, improving electrolyte impregnability, and safety.

In particular, when the SRS nonwoven fabric separator is used, the safety of the battery is further improved.

Hereinafter, the present invention will be described with reference to Examples. However, the following Examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto.

&Lt; Example 1 >

Preparation of Membrane

A polymer solution was prepared by adding about 8.5 wt% of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) polymer to acetone and dissolving at a temperature of 50 ° C for about 12 hours or longer. The Al ₂ O ₃ powder was added to the polymer solution so that Al ₂ O ₃ / PVdF-HFP = 90/10 (weight% ratio), and the slurry was produced by a ball mill method for 12 hours or more. The slurry thus prepared was coated on a cellulose nonwoven fabric separator (porosity of 45%) having a thickness of about 7 to 9 탆 by a dip coating method and the coating thickness was adjusted to about 4 to 5 탆, When measured by a porosimeter, SRS nonwoven membranes having pore sizes and porosities of 0.5 탆 and 58%, respectively, in the active layer coated on the nonwoven membrane were prepared. When the permeation time of 100 mL of air was measured using a Gurley densometer 4110 model, the Gurley number of the SRS nonwoven fabric separator was 1210 s / 100 mL.

Preparation of Polymer Battery

Denika black and a binder (PVdF) were mixed in NMP at a weight ratio of 90: 6.5: 3.5 using LiNi _0.5 Mn _1.5 O ₄ as a cathode active material and mixed to prepare a cathode mixture. , Rolled and dried to prepare a positive electrode.

(Denka black) and a binder (PVdF) were put into NMP (N-methyl-2-pyrrolidone) at a weight ratio of 90: 5: 5, respectively, using Li _4/3 Ti _5/3 O ₄ as a negative electrode active material The mixture was coated on a copper foil having a thickness of 20 탆, rolled and dried to prepare a negative electrode.

An electrode assembly was fabricated between the positive electrode and the negative electrode via the separator prepared above, and the electrode assembly was embedded in the battery case.

A lithium nonaqueous electrolyte solution containing 1 M of LiPF ₆ as a lithium salt was mixed with ethyl carbonate and ethyl methyl carbonate at a ratio of 1: 2 on the basis of volume ratio, and then sealed to prepare a 40 Ah small polymer battery Respectively.

&Lt; Example 2 >

A small polymer battery was prepared in the same manner as in Example 1, except that a cellulose nonwoven fabric separator (porosity of 45%) without a coating of an active layer was used as the separator in Example 1 above. At this time, the Gurley number of the SRS nonwoven fabric separator is 790 s / 100 mL.

<Experimental Example 1>

In order to evaluate the degree of improvement of the cell safety in the coating of the active layer containing the inorganic particles and the binder polymer, the center of the cells of Examples 1 and 2 was dried at a rate of 8 cm / sec using a nail of 2.5 mm in diameter The maximum temperature of the battery surface and whether or not it was ignited were observed. The results are shown in Table 1.

Maximum temperature Whether ignited Example 1 70 ℃ No ignition Example 2 140 ° C No ignition

Referring to Table 1, in the case of the battery of Example 1 using the nonwoven fabric separator in Example 1 and Example 2, in which the ignition did not occur but the SRS nonwoven fabric separator coated with the active layer containing the inorganic particles and the binder polymer was used , The maximum temperature was reduced to about 50% as compared with the cell of Example 2 using the cellulose-based nonwoven fabric separator without the coating of the active layer, and the cell safety was remarkably improved.

That is, when the nonwoven fabric separator is used, since there is little shrinkage due to the heat generated when the conventional polyolefin separator is used, even if the non-woven fabric separator is used at high temperatures, it does not cause a fire. However, when the active layer is coated, the maximum temperature is also lowered, which is more advantageous for securing the safety of the battery.

&Lt; Comparative Example 1 &

A small polymer battery was prepared in the same manner as in Example 1, except that the conventional polyolefin separator (Celgard ^TM , thickness: 20 μm) was used as the separator in Example 1. At this time, the Gurley number of the separation membrane is 1130 s / 100 mL.

&Lt; Comparative Example 2 &

A small polymer battery was prepared in the same manner as in Example 1, except that a separation membrane coated with an active layer on a conventional polyolefin-based porous substrate (Celgard ^TM , thickness: 20 μm) was used as a separation membrane in Example 1 above. At this time, the Gurley number of the separation membrane is 1650 s / 100 mL.

<Experimental Example 2>

In order to determine the improvement degree of the electrolyte impregnability, 10 batteries prepared in Example 1 and Comparative Example 2 were prepared, and the time until the electrolyte wettability of the secondary batteries reached about 90% was measured, And the results are shown in Table 2 below.

Dropping test
(time / average) Example 1 95 min Comparative Example 2 200 min

As shown in Table 2, the electrolyte impregnating property of the battery of Example 1 using the SRS nonwoven fabric separator was superior to the electrolyte impregnating property of the battery of Comparative Example 2 using the separator coated with the active layer on the conventional polyolefin porous substrate Able to know. That is, the nonwoven fabric separator exhibits excellent electrolyte impregnability compared to the polyolefin separator. Therefore, this can also be applied to the comparison of Example 2 and Comparative Example 1.

<Experimental Example 3>

The batteries prepared in Example 1 and Comparative Example 2 were formulated at 3.35 V and the resistance values at SOC 50 were measured at a 10 C-rate 10 sec output. The results are shown in Table 3 below.

Discharge Resistance (mΩ) Example 1 1.4 Comparative Example 2 1.67

Referring to Table 3, the discharge resistance of the battery of Example 1 using the SRS nonwoven fabric separator may be lower than the discharge resistance of the battery of Comparative Example 2 using the separator coated with the active layer on the conventional polyolefin-based porous substrate. This is because the discharge resistance of the battery of Comparative Example 2 increases as the electrolyte impregnability of the battery decreases. This can also be applied to the comparison of Example 2 and Comparative Example 1.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (21)

An electrode assembly comprising an anode, a cathode, and a separator disposed between the anode and the cathode,
Wherein the negative electrode comprises a lithium metal oxide represented by the following formula (1) as a negative electrode active material, and the separation membrane is a nonwoven fabric separation membrane,
The nonwoven fabric separating membrane is an SRS nonwoven separating membrane,
The SRS nonwoven fabric separator has a plurality of uniform pore structures on both the active layer and the nonwoven fabric separator. The pores on the surface of the nonwoven fabric separator and the active layer are mutually entangled.
Li _a M ' _b O _{4-ca c} (1)
In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;
a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4;
c is determined according to the oxidation number in the range of 0? c <0.2;
A is one or more of an anion of -1 or -2. The electrode assembly according to claim 1, wherein the electrode assembly has a ratio of a thickness (mm) of the electrode assembly to an area (mm ² ) of a top surface and a bottom surface of the electrode assembly is 2000 or more. The electrode assembly according to claim 2, wherein the electrode assembly has a ratio of an area (mm ² ) of a top surface and a bottom surface of the electrode assembly to an electrode assembly thickness (mm ² ) of 3000 or more. The electrode assembly according to claim 1, wherein an area of one surface of the electrode assembly is 20000 mm &lt; ^{2 &gt;} or more. The electrode assembly according to claim 4, wherein an area of the upper and lower surfaces of the electrode assembly is 25000 mm ² or more. [3] The electrode assembly of claim 2, wherein an area of the upper and lower surfaces of the electrode assembly is a product of two longest lengths of three axes of the electrode assembly. The nonwoven fabric separator according to claim 1, wherein the nonwoven fabric separator is formed of a material selected from the group consisting of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides such as aramid, polyacetal, polycarbonate, polyimide, , Polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, polytetrafluoroethylene, polyfluorinated vinylidene, polyvinyl chloride, polyacrylonitrile, cellulose, nylon, polyparaphenylenebenzobis Wherein the electrode assembly is formed of any one or a mixture of two or more selected from the group consisting of polyaniline, oxazole, polyarylate, and glass. delete The electrode assembly according to claim 1, wherein the porosity of the SRS nonwoven fabric separator is 45 to 90%. The electrode assembly according to claim 9, wherein the porosity of the SRS nonwoven fabric separator is 50 to 70%. The electrode assembly according to claim 1, wherein the lithium metal oxide represented by Formula 1 is Lithium Titanium Oxide (LTO) represented by Formula 2:
Li _a Ti _b O ₄ (2)
In the above formula, 0.5? A? 3, 1? B? 2.5. 12. The electrode assembly of claim 11, wherein the lithium titanium oxide is Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ . The electrode assembly according to claim 1, wherein the anode is a high-voltage anode comprising a lithium manganese composite oxide having a spinel structure represented by the following Formula 3 as a cathode active material:
Li _x M _y Mn _2-y O _{4 -z z} (3)
Wherein 0 < y < 2, 0 z < 0.2,
M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;
A is one or more of an anion of -1 or -2. 14. The electrode assembly according to claim 13, wherein the lithium manganese composite oxide represented by Formula (3) is a lithium nickel manganese complex oxide (LNMO) represented by Formula (4)
Li _x Ni _y Mn _2-y O ₄ (4)
In the above formula, 0.9? X? 1.2 and 0.4? Y? 0.5. 15. The electrode assembly according to claim 14, wherein the lithium nickel manganese composite oxide of Formula 4 is LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O ₄ . A secondary battery comprising the electrode assembly according to claim 1. The secondary battery according to claim 16, wherein the secondary battery is a lithium secondary battery. A battery module comprising a secondary battery according to claim 16 as a unit cell. A battery pack comprising the battery module according to claim 18. A device comprising a battery pack according to claim 19. 21. The device of claim 20, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.