KR20180023688A - Secondary Battery Comprising Electrode Having Thin Electrode Active Material Layer - Google Patents

Abstract

Provided is a secondary battery. The present invention relates to a secondary battery including an electrode assembly having a structure of which a separator is interposed between at least two electrodes. The electrodes have structures on which an electrode active material layer containing electrode active material particles is applied to the top of a collector. The particle diameter of the electrode active material particles 1-5 micrometers, and the thickness of the electrode active material layer applied to the top of the collector is 5-15 micrometers.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a secondary battery having an electrode active material layer having a small thickness,

The present invention relates to a secondary battery having an electrode including a thin electrode active material layer.

In recent years, the demand for environmentally friendly alternative energy sources has become an indispensable factor for the future, as the increase in the price of energy sources due to depletion of fossil fuels and the interest in environmental pollution are amplified. 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.

Particularly, as technology development and demand for mobile devices increase, the demand for batteries as energy sources is rapidly increasing. Recently, the use of secondary batteries as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV) In addition, the use area has been expanded for use as a power auxiliary power source through a grid, and accordingly, a lot of researches on a battery that can meet various demands have been conducted.

Typically, in terms of the shape of a battery, there is a high demand for a prismatic secondary battery and a pouch-type secondary battery which can be applied to products such as mobile phones with a small thickness, and has advantages such as high energy density, discharge voltage, There is a high demand for lithium secondary batteries such as lithium ion batteries and lithium ion polymer batteries.

The lithium secondary battery including such an electrode can be varied depending on factors such as application and size of the applied device, and generally has an energy density of 550 Wh / L to 700 Wh / L and a level of about 0.5C to 1.5C Discharge rate.

However, in recent years, as the demand for mobile devices, electric vehicles, and the like using the lithium secondary batteries as a power source has increased, the necessity for rapid charging of such lithium secondary batteries has been gradually increasing. On the other hand, It is not satisfactory to satisfy the requirements of the present invention.

Particularly, such a problem is caused by the material characteristic of the electrode material constituting the lithium secondary battery.

Generally, a lithium secondary battery has a structure in which an electrode assembly having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is embedded in a battery case together with an electrolyte solution.

At this time, the electrode such as the anode or the cathode may be formed by mixing an electrode active material having a predetermined particle shape with a conductive material and a binder in a solvent, and then preparing the electrode mixture using a slurry coating method such as a slot die coating method, To form an electrode active material layer.

Particularly, the electrode active material is composed of powder having a particle size distribution of a Gaussian distribution of at least 0.5 micrometer to a maximum of 100 micrometers. Accordingly, when the electrode active material layer including the electrode active material is coated on the current collector, It will have a thicker thickness than micrometer.

However, when the electrode active material layer has a thickness of 100 micrometers or more, impregnation of the electrolytic solution to a portion adjacent to the current collector is lowered, and as the ion migration path becomes longer, the input / output characteristics of the secondary battery are lowered , And as a result, can serve as a major cause for lowering the charging speed.

Therefore, there is a high need for a technique capable of fundamentally solving such problems.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned 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 the particle size of the electrode active material particles is 1 micrometer to 5 micrometers and the thickness of the electrode active material layer including the electrode active material particles is The input / output characteristics of the secondary battery can be improved owing to the thinness of the electrode active material layer, thereby making it possible to further improve the charging / discharging speed of the secondary battery, It is possible to prevent lithium-plating on the surface of the electrode and to prevent deterioration in lifetime characteristics, and to uniformly control the particle size distribution of the electrode active material particles, Therefore, the design of the secondary battery for achieving the desired performance can also be made easier And have completed the present invention.

According to an aspect of the present invention, there is provided a secondary battery comprising:

A secondary battery comprising an electrode assembly having a structure in which a separation membrane is interposed between two or more electrodes,

Wherein the electrodes have a structure in which an electrode active material layer including electrode active material particles is coated on a current collector,

The electrode active material particles have a particle diameter of 1 micrometer to 5 micrometers,

The thickness of the electrode active material layer applied on the current collector may be a thickness of 5 micrometers to 15 micrometers.

Therefore, due to the thinness of the electrode active material layer, the input / output characteristics of the secondary battery can be improved and the charge / discharge speed of the secondary battery can be further improved.

If the particle size of the electrode active material particles is less than 1 micro-meter, the particle size of the electrode active material particles becomes excessively small, and as a side reaction with the electrolyte occurs, the operation efficiency decreases or the capacity of the battery decreases. .

On the contrary, when the particle size of the electrode active material particles exceeds 5 micrometers, the particle size of the electrode active material particles becomes too large, the electrode active material layer can not be easily formed in a desired thickness range, There is a problem that the input / output characteristics of the current as well as the charge / discharge characteristics may be degraded.

In addition, since the electrode active material particles have a small particle diameter of 1 micrometer to 5 micrometers, the electrode active material layer can be formed to have a thin thickness despite the use of a liquid coating method which can save a relatively small amount of money .

In addition, when the thickness of the electrode active material layer is less than 5 micrometers, the capacity of the secondary battery may be decreased. On the contrary, when the thickness of the electrode active material layer is more than 15 micrometers, The effect of the present invention depending on the thickness may not be exhibited and the lifetime characteristics may be deteriorated due to the lithium-plating phenomenon in which lithium precipitates on the electrode surface at the time of rapid charging.

In one specific example, the electrode active material particles may have a structure showing a particle diameter distribution within ± 10% based on the average particle diameter.

If the particle size distribution of the electrode active material particles exceeds ± 10% based on the average particle diameter, the energy density of the secondary battery may be lowered due to the gap between the particles, The physicochemical properties of the electrode active material particles can not be easily controlled, so that it is difficult to easily design the secondary battery.

Therefore, the electrode active material particles have a particle size distribution within ± 10% based on the average particle size, so that the parameters according to the particle size distribution can be more easily controlled, and accordingly, The design can also be performed more easily.

The electrode active material layer may have a thickness distribution within ± 10% based on the average thickness.

If the thickness distribution of the electrode active material layer is more than ± 10%, there may be a difference in the local capacitance characteristics and the input / output characteristics, which may make it difficult to control the electrochemical performance of the secondary battery. have.

On the other hand, if the electrode active material layer is applied on the current collector with a thin thickness of 5 micrometers to 15 micrometers, the coating method is not limited to a great extent, Can be applied on the current collector by a liquid coating method such as a die coating method or a gravure coating method, and more specifically, it can be applied on a current collector by a gravure coating method.

In one specific example, the electrode assembly may have a structure in which a plurality of electrodes cut in a predetermined size unit are sequentially stacked with a separator interposed therebetween.

More specifically, the secondary battery of the present invention can have a structure capable of rapid charging by improving the charge / discharge characteristics.

In this case, when the electrode assembly is formed of a jelly-roll structure in which the positive electrode, negative electrode, and separator are stacked in a sheet form, only one positive electrode tab and one negative electrode tab are included. , The desired rapid charging effect can not be exhibited as the charging speed of the secondary battery decreases and the area of the electrode tab that is the current path of the current is too small to increase the resistance of the electrode tab portion during the rapid charging process, There is a problem that safety may be deteriorated due to deterioration of the secondary battery.

Accordingly, the electrode assembly according to the present invention may include a plurality of electrode taps, and may have a structure in which a plurality of electrodes cut in a predetermined size unit are sequentially stacked with a separator interposed therebetween.

However, the structure of the electrode assembly according to the present invention can sufficiently improve the charging speed of the secondary battery and can exhibit the desired rapid charging effect, and at the same time, The structure of the electrode assembly is not limited thereto. Specifically, the electrode assembly may include a plurality of electrodes cut out in units of a predetermined size, which are sequentially stacked with a separator interposed therebetween, And the electrode assembly has a structure in which a plurality of electrodes cut in units of a predetermined size are sequentially stacked with a separator interposed therebetween, May be sequentially laminated and laminated in a state interposed therebetween.

The electrode is not limited in its polarity, but may be a positive electrode or a negative electrode, in particular, if the electrode active material layer can be formed to have a desired thickness in a desired range. More specifically, Both the positive electrode and the negative electrode may have a structure including the electrode active material layer having a small thickness.

In one specific example, the N / P ratio of the electrode assembly may be adjusted within a range of 1.0 to 1.5.

If the N / P ratio of the electrode assembly is less than 1.0, the capacity of the negative electrode becomes smaller than the capacity of the positive electrode. Therefore, depending on the type of the negative electrode active material, A lithium compound is generated on the surface of the negative electrode, thereby causing a problem that the reversible capacity is reduced.

On the contrary, when the N / P ratio of the electrode assembly exceeds 1.5, the capacity of the anode is excessively small as compared with the capacity of the cathode, and the capacity of the cathode becomes unnecessarily large, which may lead to waste of the inefficient electrode have.

In addition, when the N / P ratio of the electrode assembly is too narrow, it may not be easy to adjust the N / P ratio within a narrow range due to the thinness of the electrode active material layer.

Meanwhile, the energy density of the electrode assembly may range from 350 Wh / L to 400 Wh / L.

If the energy density of the electrode assembly is too small or too small, the electrochemical performance such as sufficient capacity and lifetime characteristics of the secondary battery may not be exhibited to a desired extent. On the contrary, the energy density of the electrode assembly Exceeds the above range and is excessively large, the thickness of the electrode active material layer necessarily becomes thick, and the desired rapid charging performance may not be exhibited.

In one specific example, the secondary battery may exhibit a charging rate of 5 C or higher.

As described above, in the conventional secondary battery, the electrode active material layer containing the electrode active material particles is formed thick by coating the electrode active material particles having a Gaussian distribution of the particle size distribution with a liquid coating method such as a slot die coating method. Accordingly, it exhibits a low charge / discharge rate of 0.5C to 1.5C.

On the other hand, the secondary battery according to the present invention has the electrode active material layer including the electrode active material particles having a uniform particle size distribution in a predetermined particle size, thereby being formed into a thin thickness, thereby improving the input / output characteristics, The secondary battery may exhibit a charging rate of 5C or more, more specifically, a charging rate of 5C to 100C.

However, the charging speed of the secondary battery according to the present invention is not limited thereto, and when the particle size of the electrode active material particle or the thickness of the electrode active material layer is adjusted, a charging speed of 100 C or more, more specifically 200 C or more Of course it is possible.

The secondary battery may be a lithium secondary battery such as a lithium ion battery or a lithium ion polymer battery having advantages such as high energy density, discharge voltage, and output stability, although the secondary battery is not particularly limited in its kind .

Generally, a lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

The positive electrode is prepared, for example, by coating a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, and then drying the mixture. Optionally, a filler may be further added to the mixture.

The conductive material is usually added in an amount of 1 to 30% 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 which 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 30% by weight 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.

The negative electrode is manufactured by applying and drying a negative electrode active material on a negative electrode collector, and if necessary, the above-described components may be selectively included.

Examples of the negative electrode active material include carbon such as non-graphitized carbon and graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separation membrane and the separation film are 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. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

Further, in one specific example, in order to improve the safety of a high energy density cell, the separation membrane and / or the separation film may be an organic / inorganic composite porous SRS (Safety-Reinforcing Separators) separator.

The SRS separator is manufactured by using inorganic particles and a binder polymer on the polyolefin-based separator substrate as an active layer component. In addition to the pore structure contained in the separator substrate itself, the SRS separator is formed by interstitial volume between inorganic particles And has a uniform pore structure.

The use of such an organic / inorganic composite porous separator has the advantage of suppressing an increase in thickness of the cell due to swelling at the time of chemical conversion compared with the case of using a conventional separator, When a gelable polymer is used when liquid electrolyte is impregnated, it can also be used as an electrolyte.

In addition, the organic / inorganic composite porous separator can exhibit excellent adhesion characteristics by controlling the contents of the inorganic particles and the binder polymer in the separator, so that the cell assembly process can be easily performed.

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.

The nonaqueous electrolyte solution containing a lithium salt is composed of a polar organic electrolyte and a lithium salt. As the electrolytic solution, a non-aqueous liquid electrolytic solution, an organic solid electrolyte, an inorganic solid electrolyte and the like are used.

Examples of the nonaqueous liquid electrolytic solution 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, 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 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 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving the charge-discharge characteristics and the flame retardancy, the non-aqueous liquid electrolyte may contain, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like are added It is possible. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The present invention also provides a battery pack including the secondary battery and a device including the battery pack. Since the battery pack and the device are known in the art, a detailed description thereof will be omitted herein. do.

As described above, the secondary battery according to the present invention is characterized in that the particle size of the electrode active material particles is 1 micrometer to 5 micrometers, the thickness of the electrode active material layer including the electrode active material particles is 5 micrometers to 15 micrometers Output characteristics of the secondary battery can be improved owing to the thinness of the electrode active material layer and thus the charging / discharging speed of the secondary battery can be further improved, and at the time of rapid charging, the lithium- It is possible to prevent plating from deteriorating the life characteristic and to control the parameters according to the particle size distribution more easily by making the particle size distribution of the electrode active material particles uniform, The design of the secondary battery for the secondary battery can be made easier.

1 is a graph showing the measurement of the capacity retention rate according to Experimental Example 1;
2 is a graph showing a Li-plating SOC according to a loading amount of a conventional carbonaceous anode active material;
FIG. 3 is a graph showing the capacity retention rate measured according to Experimental Example 2. FIG.

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

&Lt; Example 1 >

A negative electrode active material layer containing carbon based negative electrode active material particles having an average particle diameter of 5 micrometers and having a particle size distribution of 10% or less based on the average particle diameter was coated on a copper foil with a thickness of 15 micrometers Thereby preparing a negative electrode. A monocell was prepared using an electrolyte containing 1 M of LiPF ₆ in a solvent of EC: DMC: DEC = 1: 2: 1, using a positive electrode containing lithium cobalt oxide as the positive electrode active material.

&Lt; Comparative Example 1 &

The same monocell as Example 1 was prepared, except that carbon negative active material particles having an average particle size of 15 micrometers were used as the negative active material.

&Lt; Comparative Example 2 &

The same monocells as in Example 1 were prepared, except that the negative active material layer was formed to a thickness of 30 micrometers.

<Experimental Example 1>

The mono cells prepared in Example 1 and Comparative Examples 1 and 2 were charged and discharged at 20 C / 1 C, and the capacity retention rate was measured according to the number of cycles. The results are shown in FIG.

Referring to FIG. 1, it can be seen that, in the case of Example 1, unlike Comparative Examples 1 and 2, in which the capacity retention rate is sharply lowered as the cycle number is repeated, the change in the capacity retention rate changes very little.

Specifically, in Comparative Example 1, although the thickness of the negative electrode active material layer is small, the use of the negative electrode active material particles having an average particle diameter relatively larger than that in Example 1 causes the input / output characteristics to decrease as the cycle progresses, Intercalation of lithium ions can not be smoothly carried out in the lithium secondary battery, and the capacity retention rate is drastically lowered due to the lithium-plating. On the other hand, in Example 1, by using the negative electrode active material particles having relatively small average particle diameters, It is possible to effectively prevent a decrease in the capacity retention rate due to lithium-plating caused in the negative electrode.

2 showing a lithium-plating SOC with respect to a loading amount of a general carbon type negative electrode active material, in the case of a negative electrode using a general carbon type negative electrode active material, under loading conditions of 5C, the loading of the negative electrode active material The lithium ion transferred from the anode can not be rapidly intercalated in the cathode, and thus lithium-plating phenomenon in which lithium precipitates on the surface of the cathode at a lower SOC is easily generated.

Referring back to FIG. 1, in Example 1, the negative electrode active material layer is formed to have a relatively thin thickness as compared with Comparative Example 2, so that intercalation of lithium ions can be performed rapidly in the negative electrode, , It is possible to exhibit excellent lifetime characteristics despite rapid charging.

&Lt; Example 2 >

Except that lithium-titanium oxide (LTO) particles having an average particle diameter of 3 micrometers were used as the negative electrode active material and the negative active material layer was formed so as to have a thickness of 9 micrometers, .

&Lt; Comparative Example 3 &

Except that lithium-titanium oxide (LTO) particles having an average particle size of 10 micrometers were used as the negative electrode active material and the negative active material layer was formed so as to have a thickness of 10 micrometers, .

&Lt; Comparative Example 4 &

Except that lithium-titanium oxide (LTO) particles having an average particle size of 3 micrometers were used as the negative electrode active material and the negative active material layer was formed so as to have a thickness of 30 micrometers, .

<Experimental Example 2>

The monocells prepared in Example 2, Comparative Examples 3 and 4 were repeatedly charged and discharged at 20 C / 1 C, and the change in the capacity retention rate according to the number of cycles was measured. The results are shown in FIG.

3, in the case of Example 2, the negative electrode active material layer having a small average particle size was used to form the negative electrode active material layer, thereby obtaining a comparative example 3 including the negative electrode active material having a relatively large average particle diameter, As compared with Comparative Example 4 in which the thickness is relatively thick, it can be confirmed that a relatively high voltage is exhibited as the capacity retention ratio is exerted.

Therefore, when the average particle size of the electrode active material particles and the thickness of the electrode active material layer including the electrode active material particles are set to a specific range, more optimal effects can be exhibited. Specifically, the particle size of the electrode active material particles is 5 Micrometer, and the thickness of the electrode active material layer is most preferably 15 micrometers or less.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims (14)

A secondary battery comprising an electrode assembly having a structure in which a separation membrane is interposed between two or more electrodes,
Wherein the electrodes have a structure in which an electrode active material layer including electrode active material particles is coated on a current collector,
The electrode active material particles have a particle diameter of 1 micrometer to 5 micrometers,
Wherein the thickness of the electrode active material layer coated on the current collector is 5 micrometers to 15 micrometers. The secondary battery according to claim 1, wherein the electrode active material particles have a particle size distribution within ± 10% based on an average particle diameter. The secondary battery according to claim 1, wherein the electrode active material layer has a thickness distribution within ± 10% based on an average thickness. The secondary battery according to claim 1, wherein the electrode active material layer is coated on the current collector by a gravure coating method. The secondary battery according to claim 1, wherein the electrode assembly has a structure in which a plurality of electrodes cut in a predetermined size unit are sequentially stacked with a separator interposed therebetween. The electrode assembly according to claim 1, wherein the electrode assembly has a structure in which a plurality of electrodes cut out in units of a predetermined size are sequentially laminated with a separator interposed therebetween, Wherein the secondary battery comprises a secondary battery. The electrode assembly according to claim 1, wherein the electrode assembly has a structure in which a plurality of electrodes cut in a predetermined size are sequentially stacked with a separator interposed therebetween, and sequentially laminated and laminated ). &Lt; / RTI &gt; The secondary battery according to claim 1, wherein the electrode is a positive electrode or a negative electrode. The secondary battery according to claim 1, wherein the N / P ratio of the electrode assembly is adjusted within a range of 1.0 to 1.5. The secondary battery according to claim 1, wherein the energy density of the electrode assembly is from 350 Wh / L to 400 Wh / L. The secondary battery according to claim 1, wherein the secondary battery exhibits a charging speed of 5 C or more. The secondary battery according to claim 1, wherein the secondary battery is a lithium secondary battery. A battery pack comprising the secondary battery according to claim 1. A device comprising a battery pack according to claim 13.

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