KR20170019054A - Electrode Assembly Comprising Electrode Plate Having Different Loading Amounts of Active Material on both Sides - Google Patents

Abstract

The present invention relates to an electrode assembly which comprises: a first electrode group having a laminated structure in which a separation membrane is interposed between electrode plates; a second electrode group having a certain area on a plane different from the first electrode group having a laminated structure in which the separation membrane is interposed between the electrode plates; an asymmetric electrode plate interposed between the first electrode group and the second electrode group and containing different loading amounts of active materials on both sides of a collector.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electrode assembly including an electrode plate having different loading amounts of an active material on both sides thereof,

The present invention relates to an electrode assembly including an electrode plate on which an active material loading amount is different on both sides.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most active field of research is electric power generation and storage.

At present, a typical example of an electrochemical device utilizing such electrochemical energy is a secondary battery, and the use area thereof is gradually increasing.

The secondary battery is classified into a cylindrical battery and a prismatic battery in which the electrode assembly is housed in a cylindrical or rectangular metal can according to the shape of the battery case, and a pouch-shaped battery in which the electrode assembly is housed in a pouch-shaped case of an aluminum laminate sheet .

The electrode assembly incorporated in the battery case is a charge / dischargeable power generating element formed of a laminate structure of a positive electrode / separator / negative electrode. The electrode assembly is composed of a jelly-roll type in which a separator is interposed between a positive electrode and a negative electrode coated with an active material, Sized positive and negative electrodes are stacked in a stacked state in a state in which a separator is interposed therebetween.

A full cell or anode / separator / cathode / separator / separator / separator / cathode assembly having a positive electrode / separator / negative electrode structure with a constant unit size, which is a progressive structure of a jelly- A stack / folding type electrode assembly having a structure in which a bicell having a positive (negative) electrode structure is folded by using a continuous long separating film has been developed.

On the other hand, there has been an effort to reduce the volume occupied by the secondary battery in the portable device in accordance with the tendency toward miniaturization and miniaturization of the portable device. In particular, an irregular secondary battery such as a stepped or curved type has been developed in order to reduce dead space in a corner part or a curved part of a portable device.

However, in the case of the step-type secondary battery manufactured using the stacked or stacked / folded electrode assembly, the energy density is not improved to a desired level, and the cycle characteristics and stability are reduced.

Therefore, there is a high need for a technique capable of improving energy density, cycle characteristics, and stability of a secondary battery while manufacturing a stepped electrode assembly.

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, as will be described later, the inventors of the present application have found that when the loading amounts of the active material layers formed on both surfaces of the current collector are different from each other When the electrode plate is used, it has been confirmed that energy density, cycle characteristics and stability are further improved in manufacturing a step-like secondary battery, and the present invention has been accomplished.

Accordingly, the electrode assembly according to the present invention includes: a first electrode group having a laminated structure in which a separator is interposed between electrode plates; A second electrode group having a laminated structure in which an area of a planar surface is different from that of the first electrode group and a separation membrane is interposed between the electrode plates; And an asymmetric electrode plate sandwiched between the first electrode group and the second electrode group and having different loading amounts of the active material layers formed on both surfaces of the current collector.

In this specification, the amount of loading means the total weight of the active material layer formed on one side of the current collector.

According to the prior art, electrode assemblies having different areas on a plane are stacked to form an electrode assembly. The electrode assemblies are simply stacked without an asymmetric electrode plate having different amounts of loading on both sides of the current collector. In this case, the outermost active material layers located on the stacking plane of the electrode groups have different loading amounts depending on the coating area and thickness difference. The capacity ratio (N / P ratio) of the cathode to the anode in the laminated surface has a larger difference than that in the general case, resulting in a problem that energy density, cycle characteristics, and stability are reduced.

On the other hand, according to the present invention, an asymmetric electrode plate having different loading amounts of active material layers formed on both surfaces of the current collector is interposed between the first electrode group and the second electrode group, The N / P ratio of the anode to the cathode can be adjusted to an appropriate level. Therefore, the electrode assembly of the present invention has an effect of remarkably improving energy density, cycle characteristics, and stability as compared with the prior art.

Particularly, in the case of energy density, the active material layer, which is excessively contained on one surface of the laminated surface, is partially removed to adjust the capacity ratio (N / P ratio) of the cathode to the anode to a proper level, It is possible to improve the energy density.

In one specific example, the asymmetric electrode plate includes a first active material layer and a second active material layer, wherein the first active material layer faces the first electrode group, and the second active material layer faces the second electrode group As shown in FIG.

In detail, the first active material layer faces the third active material layer positioned at the outermost of the first electrode group with the separation membrane interposed therebetween, and the second active material layer faces the fourth electrode material It may be a structure in which the active material layer and the separator face each other.

More specifically, the loading amount of the third active material layer may be different from the loading amount of the fourth active material layer.

At this time, the ratio of the loading amount of the first active material layer to the second active material layer may be proportional to the ratio of the loading amount of the third active material layer to the fourth active material layer.

That is, since the loading amounts of the first active material layer and the second active material layer are different on both sides of the asymmetric electrode plate, the loading amount of the outermost active material layers between the first electrode group and the second electrode group It is possible to prevent the capacity ratio (N / P ratio) of the anode to the anode from deviating from an appropriate level. The ratio of the loading amount of the first active material layer to the second active material layer is proportional to the ratio of the loading amount of the third active material layer to the fourth active material layer, , It is possible to maintain the capacity ratio (N / P ratio) of the anode to the cathode at the same level.

In one specific example, the loading amount of the active material layer can be adjusted by changing the thickness of the active material layer, and / or the coating area.

For example, the thickness of the third active material layer may be different from the thickness of the fourth active material layer.

Specifically, the ratio of the thickness of the first active material layer to the second active material layer may be proportional to the ratio of the thickness of the third active material layer to the fourth active material layer.

The coating area of the third active material layer may be different from the coating area of the fourth active material layer.

Specifically, the ratio of the coating area of the first active material layer to the second active material layer may be proportional to the ratio of the coating area of the third active material layer to the fourth active material layer.

In one specific example, the polarity of the first active material layer may be different from the polarity of the third active material layer.

In the first active material layer and the third active material layer, the capacity ratio (N / P ratio) of the anode to the cathode may be more than 1.0 and less than 1.1, more specifically more than 1.0 and less than 1.06.

In one specific example, the polarity of the second active material layer may be different from the polarity of the fourth active material layer.

In the second active material layer and the fourth active material layer, the capacity ratio (N / P ratio) of the anode to the cathode may be more than 1.0 and less than 1.1, and more specifically 1.0 or more and 1.06 or less.

When the capacity ratio (N / P ratio) of the negative electrode to the positive electrode is 1.0 or less, the cycle characteristics and stability are deteriorated due to precipitation of lithium from the negative electrode. When the ratio is 1.1 or more, the irreversible capacity of the negative electrode increases, The cyclic characteristics and the stability may be deteriorated.

The capacity ratio (N / P ratio) of the cathode to the anode can be calculated by the following equation (1). The negative electrode charging capacity mAh can be calculated by the following equation (2), the negative electrode efficiency by the following equation (3), and the positive electrode design capacity mAh by the following equation (4). In addition, the cathode loading density and the anode loading density can be calculated by the following equations (5) and (6), respectively.

Equation (1): Capacity ratio of cathode to anode (N / P ratio) = Cathode charging capacity × Cathode efficiency / Anode design capacity

Equation (2): Cathode charging capacity (mAh) = Cathode loading (g) × Cathode loading density × Cathode charging capacity per unit weight (mAh / g)

Equation (3): Cathode Efficiency = Discharge capacity of the cathode per unit weight (mAh / g) / Capacity of the cathode per unit weight (mAh / g)

Equation (4): (MAh / g) - irreversible capacity (mAh / g) of negative electrode per unit weight (g) × amount of negative electrode loading (g)

Equation (5): Cathodic loading density = weight of negative active material (g) / total weight of negative electrode mixture (g)

Equation (6): Anode loading density = weight of cathode active material (g) / total weight of cathode mix (g)

The charge capacity of the anode per unit weight, the charge capacity of the anode per unit weight, the discharge capacity and the irreversible capacity can be measured by the following methods.

One) How to Measure the Charging Capacity of the Anode per Unit Weight: Measure the capacity when one electrode is made as the anode to be evaluated by making a half cell and the counter electrode is made of lithium metal and charged at a low rate (after 0.2C) Normalized by the weight of the half cell.

2) How to Measure the Charging Capacity of the Cathode per Unit Weight: Measuring the capacity when one electrode is made into a cathode to be evaluated by making a half cell and the counter electrode is made of lithium metal and charged at a low rate (after 0.2C) Normalized by the weight of the half cell.

3) Measuring Method of Discharge Capacity of Cathode per Unit Weight: The capacity when one electrode is made into a cathode to be evaluated by making a half cell and the counter electrode is made of lithium metal and charged at a low rate (after 0.2 C) and then discharged And normalized to the weight of a half cell.

4) Measuring the irreversible capacity of the cathode per unit weight: Measuring the difference in capacitance between one half cell of the cathode (charge and discharge).

The N / P ratio of the cathode to the anode in the first active material layer and the third active material layer and the N / P ratio of the cathode to the anode in the second active material layer and the fourth active material layer are controlled , The loading density and the electrode active material may be changed.

In one specific example, the loading density of the first active material layer may be the same as or different from the loading density of the second active material layer. When the loading density is different, there is an advantage that the capacity ratio (N / P ratio) of the anode to the anode can be independently controlled independently of the amount of loading.

In one specific example, the electrode active material contained in the first active material layer may be different from the electrode active material contained in the second active material layer, and more specifically, the electrode active material contained in the first active material layer The charging capacity per unit weight may be different from the electrode active material contained in the second active material layer.

Thus, even when the electrode active material having a different charge capacity per unit weight is used, the capacity ratio (N / P ratio) of the anode to the anode can be independently controlled independently of the amount of loading.

Meanwhile, the active material layers included in the first electrode group may have substantially the same amount of loading as the third active material layer, or the N / P ratio of the anode to the anode may be greater than 1.0 and less than 1.1. That is, the active material layers having the same polarity as that of the third active material layer may have substantially the same loading amount as that of the third active material layer, and the polar material layers having polarities different from those of the third active material layer may be formed on the basis of the loading amount of the third active material layer And the capacity ratio (N / P ratio) of the anode to the cathode may be included in the range.

The active material layers included in the second electrode group may have substantially the same loading amount as the fourth active material layer, or the N / P ratio of the anode to the anode may be greater than 1.0 and less than 1.1. That is, the active material layers having the same polarity as that of the fourth active material layer may have substantially the same loading amount as that of the fourth active material layer, and the polar material layers having polarity different from that of the fourth active material layer may be set based on the loading amount of the fourth active material layer And the capacity ratio (N / P ratio) of the anode to the cathode may be included in the range.

In one specific example, the total thickness of the first electrode group can be different from the total thickness of the second electrode group, and through this configuration, various types of electrode assemblies can be manufactured.

In addition, the electrode assembly may have a stepped structure having at least one step on the outer surface.

The electrode assembly according to the present invention may be, for example, a stacked type or a stacked / folded type electrode assembly, as long as it includes the above-described laminated structure and the asymmetric electrode plate. In particular, the first electrode group and the second electrode group may have the structure of a conventional stacked or stacked / folded electrode assembly as such.

The present invention also provides a secondary battery in which such an electrode assembly is embedded in a battery case together with an electrolytic solution.

Hereinafter, other components of the secondary battery will be described.

The electrode plate is collectively referred to as a positive electrode plate and a negative electrode plate. Hereinafter, the electrode plate, the positive electrode plate, and the negative electrode plate may be referred to as an electrode, a positive electrode, and a negative electrode, respectively.

The positive electrode may be prepared, for example, by applying a positive electrode mixture mixed with a positive electrode active material, a conductive material and a binder to a positive electrode collector, and if necessary, a filler may further be added to the positive electrode mixture.

The cathode current collector is generally formed to a thickness of 3 to 201 탆 and is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium , And a surface treated with carbon, nickel, titanium or silver on the surface of aluminum or stainless steel can be used. Specifically, aluminum can 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.

The cathode active material may be, 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 metals; 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 , LiV 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.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the positive electrode material mixture containing the positive electrode 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 contained in the positive electrode is added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the positive electrode active material, as a component that assists in bonding between the active material and the conductive material and bonding to the current collector. 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-butadiene 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 may be manufactured by applying a negative electrode mixture containing a negative electrode active material, a conductive material, and a binder to a negative electrode collector, and a filler or the like may further be optionally included.

The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, 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.

In the present invention, the thickness of the anode current collector may be the same within the range of 3 to 201 [mu] m, but may have different values depending on the case.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or 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.

In one specific example, the separation membrane may be a polyolefin-based film commonly used in the art, and may be, for example, high density polyethylene, low density polyethylene, linear low density polyethylene, ultra high molecular weight polyethylene, polypropylene, polyethylene terephthalate polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyetheretherketone, A sheet made of at least one selected from the group consisting of polyethersulfone, polyphenylene oxide, polyphenylenesulfrode, polyethylene naphthalene, and mixtures thereof.

The separation membrane may be made of the same material but is not limited thereto and may be made of materials different from each other depending on safety, energy density, and overall performance of the battery cell.

The pore size and porosity of the separation membrane are not particularly limited, but the porosity may be in the range of 10 to 95% and the pore size (diameter) may be 0.1 to 50 탆. When the pore size and porosity are 0.1 μm or less and 10% or less, respectively, it acts as a resistive layer. If the pore size and porosity are more than 50 μm and 95%, it is difficult to maintain the mechanical properties.

The electrolyte solution may be a non-aqueous electrolyte containing a lithium salt, and the non-aqueous electrolyte containing a lithium salt is composed of a non-aqueous electrolyte and a lithium salt. Non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, The present invention 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 derivatives, Tetrahydrofuran derivatives, ether, 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 acid 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 substance that is soluble in the nonaqueous electrolyte and includes, 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 carboxylate lithium, lithium tetraphenylborate, and imide.

The nonaqueous electrolyte may contain, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., 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 may be added have. 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 nonaqueous electrolyte.

The present invention also provides a battery pack including such a secondary battery as a unit cell, and a device including such a battery pack as a power source.

The device may be, for example, a notebook computer, a netbook, a tablet PC, a mobile phone, MP3, a wearable electronic device, a power tool, an electric vehicle (EV), a hybrid electric vehicle (HEV) , A plug-in hybrid electric vehicle (PHEV), an electric bike (E-bike), an electric scooter (E-scooter), an electric golf cart, However, the present invention is not limited thereto.

The structure and manufacturing method of such a device are well known in the art, so a detailed description thereof will be omitted herein.

As described above, since the electrode assembly according to the present invention includes asymmetric electrode plates having different loading amounts of the active material layers formed on both surfaces of the current collector, the capacity ratio (N / P ratio) of the anode to the cathode of the step- Is maintained at an appropriate level, and the energy density, cycle characteristics and stability are remarkably improved.

1 is a schematic view showing a general stepped electrode assembly;
2 is a schematic diagram illustrating a stepped electrode assembly according to one embodiment of the present invention;
3 is a schematic view showing a stepped electrode assembly according to another embodiment of the present invention.

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

Fig. 1 is a schematic view showing a general stepped electrode assembly.

Referring to FIG. 1, the electrode assembly 100 includes two electrode groups 110 and 120 and a separator 130.

The electrode group 110 has a larger planar area with respect to the electrode plates 111, 112, 113, 121 and 122 than the electrode group 120 and the separator 130 includes the electrode groups 110 and 120, Respectively.

The electrode group 110 includes two negative plates 111 and 113, one positive plate 112, and two separators 114 and 115. The electrode group 110 has a structure in which an anode plate 111, a separator 114, a cathode plate 112, a separator 115, and a cathode plate 113 are stacked in this order from below.

The negative electrode plates 111 and 113 and the positive electrode plate 112 are each formed with active material layers on both surfaces of the current collector and the negative electrode active material layer formed on the negative electrode plates 111 and 113 is formed on the positive electrode active material layer The coating area is wider than that of the coating layer.

Specifically, the negative electrode active material layers included in the electrode group 110 have substantially the same loading amount as the negative electrode active material layer 119, and the positive electrode active material layers have a negative electrode active material layer 119 in the relationship with the negative electrode active material layer 119 And the capacity ratio (N / P ratio) is more than 1.0 and less than 1.1.

The electrode group 120 includes one positive electrode plate 121, one negative electrode plate 122, and one separator 123. The electrode group 120 has a structure in which a cathode plate 121, a separator 123, and a cathode plate 122 are laminated in order from below.

The positive electrode plate 121 and the negative electrode plate 122 are each formed with active material layers on both sides of the current collector and the negative electrode active material layer formed on the negative electrode plate 122 has a coating area Is wider.

The positive electrode active material layers included in the electrode assembly 120 have substantially the same loading amount as that of the positive electrode active material layer 129 and the negative electrode active material layers have the capacity ratio N / P ratio) is more than 1.0 and less than 1.1.

The negative electrode active material layer 119 formed on the outermost side of the electrode assembly 110 faces the positive electrode active material layer 129 formed on the outermost side of the electrode assembly 120 with the separator 130 interposed therebetween have.

At this time, the anode active material layer 119 has a wider thickness and a coating area than the cathode active material layer 129, so that the loading amount of the anode active material layer 119 is about 4 times larger than the loading amount of the cathode active material layer 129 more. Therefore, the capacity ratio (N / P ratio) of the negative electrode to the positive electrode of the negative electrode active material layer 119 and the positive electrode active material layer 129 exceeds an appropriate range, and thus the energy density is reduced and the cycle characteristics and stability are deteriorated Lt; / RTI &gt;

FIG. 2 is a schematic view showing a stepped electrode assembly according to one embodiment of the present invention.

Referring to FIG. 2, the electrode assembly 200 includes two electrode groups 210 and 220, an asymmetric electrode plate 230, and two separators 240 and 250.

The electrode group 210 has a larger planar area with respect to the electrode plates 211, 212, 221 and 222 as compared with the electrode group 220.

The asymmetric electrode plate 230 is sandwiched between the electrode groups 210 and 220. More specifically, the electrode group 210 and the asymmetric electrode plate 230 are stacked with the separator 240 interposed therebetween And the electrode group 220 and the asymmetric electrode plate 230 are interposed with the separator 250 interposed therebetween.

More specifically, an electrode group 210, a separator 240, an asymmetric electrode plate 230, a separator 250, and an electrode group 220 are stacked in this order from below.

The electrode group 210 includes one negative electrode plate 211, one positive electrode plate 212, and one separator 213. The electrode group 210 has a structure in which an anode plate 211, a separation membrane 213, and a cathode plate 212 are stacked in this order from below.

The negative electrode plate 211 and the positive electrode plate 212 are each formed with active material layers on both sides of the current collector and the negative electrode active material layer formed on the negative electrode plate 211 has a coating area Is wider.

Specifically, the positive electrode active material layers included in the electrode group 210 have substantially the same loading amount as the positive electrode active material layer 219, and the negative electrode active material layers have a capacity ratio of the negative electrode to the positive electrode in relation to the positive electrode active material layer 219 (N / P ratio) is more than 1.0 and less than 1.1.

The electrode group 220 includes one positive electrode plate 221, one negative electrode plate 222, and one separator 223. The electrode group 220 has a structure in which a positive electrode plate 221, a separation membrane 223, and a negative electrode plate 222 are laminated in order from below.

The positive electrode plate 221 and the negative electrode plate 222 are each formed with active material layers on both sides of the current collector and the negative electrode active material layer formed on the negative electrode plate 222 has a coating area Is wider.

The positive electrode active material layers included in the electrode group 220 have substantially the same loading amount as that of the positive electrode active material layer 229 and the negative electrode active material layers have the capacity ratio N / P ratio) is more than 1.0 and less than 1.1.

At this time, the cathode active material layer 219 has a wider thickness and a coating area than the cathode active material layer 229, so that the loading amount of the cathode active material layer 219 is about 4 times as much as the loading amount of the cathode active material layer 229 more.

The asymmetric electrode plate 230 is a kind of negative electrode plate in which the anode active material layers 231 and 232 are formed on both sides of the current collector 233. The anode active material layer 232 has the same coating area as the anode active material layer 231, but is thinner by about 1/4 of the thickness and the loading amount is also about 1/4 less.

The anode active material layer 231 faces the anode active material layer 219 with the separator 240 interposed therebetween and the anode active material layer 232 covers the cathode active material layer 229 and the separator 250 I have to face each other.

That is, the ratio of the loading amount of the negative electrode active material layer 231 to the negative electrode active material layer 232 is proportional to the ratio of the loading amount of the positive electrode active material layer 219 to the positive electrode active material layer 229.

2, the electrode assembly 200 has a capacity ratio (N / P ratio) of the cathode to the cathode of the cathode active material layer 219 and the anode active material layer 231 in a proper range, The capacity ratio N / P ratio of the anode to the cathode of the active material layer 229 and the anode active material layer 232 also falls within a proper range by reducing the loading amount of the anode active material layer 232.

Accordingly, the electrode assembly 100 has a problem that the capacity ratio (N / P ratio) of the cathode to the anode in the stacking plane of the electrode groups 110 and 120 exceeds an appropriate range, while the electrode assembly 200 has the asymmetric electrode By including the plate 230, the capacity ratio (N / P ratio) of the cathode to the anode in the entire electrode assembly 200 can be maintained within an appropriate range.

FIG. 3 is a schematic view showing a stepped electrode assembly according to another embodiment of the present invention.

Referring to FIG. 3, the electrode assembly 300 includes two electrode groups 310 and 320, an asymmetric electrode plate 330, and two separators 340 and 350.

The electrode group 310 has a larger planar area with respect to the electrode plates 311, 312, 321, and 322 than the electrode group 320.

The asymmetric electrode plate 330 is sandwiched between the electrode groups 310 and 320. More specifically, the electrode group 310 and the asymmetric electrode plate 330 are stacked with the separator 340 interposed therebetween The electrode group 320 and the asymmetric electrode plate 330 are interposed with the separator 350 interposed therebetween.

More specifically, the electrode group 310, the separation membrane 340, the asymmetric electrode plate 330, the separation membrane 350, and the electrode assembly 320 are stacked in this order from below.

The electrode group 310 includes one negative electrode plate 311, one positive electrode plate 312, and one separator 313. The electrode group 310 has a structure in which an anode plate 311, a separation membrane 313, and a cathode plate 312 are stacked in this order from below.

The negative electrode plate 311 and the positive electrode plate 312 are each formed with active material layers on both sides of the current collector and the negative electrode active material layer formed on the negative electrode plate 311 has a coating area Is wider.

Specifically, the positive electrode active material layers included in the electrode group 310 have substantially the same loading amount as that of the positive electrode active material layer 319, and the negative electrode active material layers have the capacity ratio of the negative electrode to the positive electrode in relation to the positive electrode active material layer 319 (N / P ratio) is more than 1.0 and less than 1.1.

The electrode assembly 320 includes one positive electrode plate 321, one negative electrode plate 322, and one separator 323. The electrode assembly 320 has a structure in which a positive electrode plate 321, a separation membrane 323, and a negative electrode plate 322 are laminated in order from below.

The positive electrode plate 321 and the negative electrode plate 322 each have an active material layer formed on both surfaces of the current collector and the negative electrode active material layer formed on the negative electrode plate 322 has a coating area Is wider.

The positive electrode active material layers included in the electrode assembly 320 have substantially the same loading amount as that of the positive electrode active material layer 329. The negative electrode active material layers have the capacity ratio N of the positive electrode to the positive electrode of the positive electrode active material layer 319 / P ratio) is more than 1.0 and less than 1.1.

At this time, the thickness of the positive electrode active material layer 319 is wider than that of the positive electrode active material layer 329, and therefore the loading amount of the positive electrode active material layer 319 is about four times the loading amount of the positive electrode active material layer 329 more.

The asymmetric electrode plate 330 is a kind of negative electrode plate in which negative active material layers 331 and 332 are formed on both sides of the current collector 333. The anode active material layer 332 has a coating area and a thickness of about 1/2 each, as compared with the anode active material layer 331, and therefore, the loading amount is about 1/4 less.

The anode active material layer 331 faces the anode active material layer 319 with the separation membrane 340 interposed therebetween and the anode active material layer 332 is disposed between the cathode active material layer 329 and the separation membrane 350 I have to face each other.

That is, the ratio of the loading amount, the thickness, and the coating area of the negative electrode active material layer 331 to the negative electrode active material layer 332 depends on the loading amount and thickness of the positive electrode active material layer 319 with respect to the positive electrode active material layer 329, It is proportional to the ratio of area.

3, the electrode assembly 300 has a capacity ratio (N / P ratio) of the cathode to the anode of the cathode active material layer 319 and the anode active material layer 331 within a proper range, The capacity ratio (N / P ratio) of the cathode to the anode of the active material layer 329 and the anode active material layer 332 also falls within a suitable range by reducing the loading amount of the anode active material layer 332.

Therefore, in the electrode assembly 100, the capacity ratio (N / P ratio) of the anode to the cathode in the lamination plane exceeds a suitable range, while the electrode assembly 300 includes the asymmetric electrode plate 330, The capacity ratio (N / P ratio) of the cathode to the anode can be maintained within a proper range over the entire electrode assembly 300.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.

Claims (26)

A first electrode group having a laminated structure in which a separator is interposed between the electrode plates;
A second electrode group having a laminated structure in which an area of a planar surface is different from that of the first electrode group and a separation membrane is interposed between the electrode plates; And
An asymmetric electrode plate interposed between the first electrode group and the second electrode group and having different loading amounts of active material layers formed on both surfaces of the current collector;
Wherein the electrode assembly comprises: The method as claimed in claim 1, wherein the asymmetric electrode plate includes a first active material layer and a second active material layer, wherein the first active material layer faces the first electrode group and the second active material layer faces the second electrode group The electrode assembly comprising: 3. The electrochemical device according to claim 2, wherein the first active material layer faces the third active material layer positioned at the outermost of the first electrode group with the separator interposed therebetween, and the second active material layer is located at the outermost And the fourth active material layer and the separator face each other. The electrode assembly according to claim 3, wherein the loading amount of the third active material layer is different from the loading amount of the fourth active material layer. The electrode assembly according to claim 3, wherein the ratio of the loading amount of the first active material layer to the second active material layer is proportional to the ratio of the loading amount of the third active material layer to the fourth active material layer. The electrode assembly according to claim 3, wherein the thickness of the third active material layer is different from the thickness of the fourth active material layer. The electrode assembly according to claim 3, wherein the ratio of the thickness of the first active material layer to the second active material layer is proportional to the ratio of the thickness of the third active material layer to the fourth active material layer. The electrode assembly according to claim 3, wherein the coating area of the third active material layer is different from the coating area of the fourth active material layer. The electrode assembly according to claim 3, wherein a ratio of a coating area of the first active material layer to the second active material layer is proportional to a ratio of a coating area of the third active material layer to the fourth active material layer. The electrode assembly according to claim 3, wherein the polarity of the first active material layer is different from the polarity of the third active material layer. 11. The electrode assembly according to claim 10, wherein the ratio of the anode to the cathode in the first active material layer and the third active material layer is greater than 1.0 and less than 1.1. 11. The electrode assembly according to claim 10, wherein the ratio of the anode to the cathode in the first active material layer and the third active material layer is greater than 1.0 and less than 1.06. The electrode assembly according to claim 3, wherein the polarity of the second active material layer is different from the polarity of the fourth active material layer. 14. The electrode assembly according to claim 13, wherein the ratio of the anode to the cathode in the second active material layer and the fourth active material layer is greater than 1.0 and less than 1.1. 14. The electrode assembly according to claim 13, wherein the ratio of the anode to the cathode in the second active material layer and the fourth active material layer is greater than 1.0 and less than 1.06. The electrode assembly of claim 3, wherein the loading density of the first active material layer is the same as or different from the loading density of the second active material layer. The electrode assembly according to claim 3, wherein the electrode active material contained in the first active material layer is different from the electrode active material contained in the second active material layer. 18. The electrode assembly according to claim 17, wherein the electrode active material contained in the first active material layer is different in charging capacity per unit weight from the electrode active material contained in the second active material layer. The method of claim 3, wherein the active material layers included in the first electrode group have substantially the same loading amount as the third active material layer, or the capacity ratio (N / P ratio) of the third active material layer and the anode to the cathode is 1.0 &Lt; / RTI &gt; to less than 1.1. The method according to claim 3, wherein the active material layers included in the second electrode group have substantially the same loading amount as the fourth active material layer, or the N / P ratio of the cathode active material layer and the anode to the cathode is 1.0 &Lt; / RTI &gt; to less than 1.1. The electrode assembly of claim 1, wherein the total thickness of the first electrode group is different from the total thickness of the second electrode group. The electrode assembly of claim 1, wherein the electrode assembly has a stepped structure having at least one step on an outer surface thereof. The electrode assembly of claim 1, wherein the electrode assembly is a stacked or stacked / folded electrode assembly. The secondary battery according to claim 1, wherein the electrode assembly is embedded in the battery case together with the electrolyte solution. A battery pack comprising the secondary battery according to claim 24 as a unit cell. 26. A device comprising a battery pack according to claim 25 as a power source.

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