Electrode assembly and rechargeable battery including the same

Abstract

The invention discloses an electrode assembly and a rechargeable battery including the same, and the electrode assembly includes a plurality of unit cells overlapping in a thickness direction; a first functional unit cell provided on an outermost first surface of the plurality of unit cells; and a second functional unit cell on an outermost second surface opposite to the first surface, in which each of the first functional unit cell and the second functional unit cell includes an external unit cell including a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode, the positive electrode comprises a positive electrode current collector; a positive electrode active material layer provided on at least one surface of the positive electrode current collector and including a positive electrode active material having a first reference potential; and a first functional layer disposed on the positive electrode active material layer and including a first active material having a second reference potential lower than the first reference potential.

Description

[0001] Description of the case

[0002] This application is a divisional application of an invention patent application with an application date of April 10, 2019, a national application number of 201910283930.5, and an invention name of “Electrode assembly and a rechargeable battery including the electrode assembly”. Technical Field

[0003] The present disclosure relates to an electrode assembly and a rechargeable battery including the electrode assembly. Background Art

[0004] Portable information devices such as mobile phones, notebook computers, smart phones, etc. or electric vehicles have used rechargeable lithium batteries having high energy density and easy portability as a driving power source.

[0005] In particular, active research has recently been conducted on using rechargeable lithium batteries as power sources or energy storage devices for hybrid vehicles or electric vehicles using high energy density characteristics.

[0006] One of the main research tasks of a rechargeable lithium battery applied to automobiles, etc. is high capacity. For example, in order to achieve high capacity of a rechargeable lithium battery, a method of increasing its thickness and / or size has been proposed.

[0007] However, when the rechargeable lithium battery is thus thickened and has a larger size, the safety of the rechargeable lithium battery may be greatly deteriorated due to a difference in heat dissipation inside / outside the battery.

[0008] Therefore, various studies have been conducted on the development of technology for improving the safety of rechargeable lithium batteries while ensuring high power and high energy density thereof. Summary of the invention

[0009] The present disclosure provides an electrode assembly having improved safety while having excellent cycle-life characteristics and capacity characteristics, and a rechargeable battery including the electrode assembly.

[0010] In one aspect, the present disclosure provides an electrode assembly comprising a plurality of unit cells overlapping in a thickness direction; a first functional unit cell disposed on an outermost first surface of the plurality of unit cells; and a second functional unit cell on an outermost second surface opposite to the first surface, wherein the first functional unit cell and the second functional unit cell each comprise an external unit cell, the external unit cell comprising a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode, wherein the positive electrode comprises a positive current collector; a positive active material layer disposed on at least one surface of the positive current collector and comprising a positive active material having a first reference potential; and a first functional layer disposed on the positive active material layer and comprising a first active material having a second reference potential lower than the first reference potential.

[0011] In another aspect, the present invention provides an electrode assembly, comprising a plurality of unit cells overlapping in a thickness direction; and a third functional unit cell arranged at the center of the plurality of unit cells in the thickness direction, wherein the third functional unit cell comprises a central unit cell, the central unit cell comprising a negative electrode, a positive electrode and a separator arranged between the negative electrode and the positive electrode, the positive electrode comprising a positive current collector; a positive active material layer, which is arranged on at least one surface of the positive current collector and comprises a positive active material having a first reference potential; and a second functional layer, which is arranged on the positive active material layer and comprises a second active material having a third reference potential lower than the first reference potential.

[0012] In another aspect, the present invention provides a rechargeable battery including an electrode assembly.

[0013] When the electrode assembly according to the embodiment is applied, a rechargeable battery having improved safety and excellent cycle-life characteristics and capacity characteristics may be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1A The structure of an electrode assembly according to a first embodiment of the present disclosure is schematically shown.

[0015] Figure 1B A positive electrode according to another embodiment is schematically shown.

[0016] Figure 2 Shows Figure 1B Example variations of .

[0017] Figure 3 The structure of an electrode assembly according to a second embodiment of the present disclosure is schematically illustrated.

[0018] Figure 4 The structure of an electrode assembly according to a third embodiment of the present disclosure is schematically illustrated.

[0019] Figure 5 The structure of a cylindrical rechargeable battery according to an embodiment is schematically shown.

[0020] <Description of symbols>

[0021] 200, 201, 202, 210: Electrode assembly

[0022] 10: Single cell battery

[0023] 110: First functional unit battery

[0024] 120: Second functional unit battery

[0025] 130: The third functional unit battery DETAILED DESCRIPTION

[0026] Various embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. However, the present disclosure can be embodied in many different forms and should not be construed as being limited to the embodiments described herein.

[0027] In order to clearly explain the present invention, parts irrelevant to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

[0028] For the convenience of description, the sizes and thicknesses of components in the drawings are arbitrarily represented, and thus the present invention is not limited by the drawings.

[0029] In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

[0030] In one aspect of the present disclosure, an electrode assembly having improved safety and excellent cycle-life characteristics and capacity characteristics is provided.

[0031] Hereinafter, the reference potential of the positive electrode active material refers to the reference potential of the positive electrode active material based on lithium metal (Li / Li + ) of the discharge average potential. In addition, a unit cell is an electrode assembly in which a positive electrode, a separator, and a negative electrode are stacked in sequence.

[0032] Figure 1A The structure of an electrode assembly according to a first embodiment of the present disclosure is schematically shown.

[0033] refer to Figure 1A, the electrode assembly 200 according to the first embodiment includes a plurality of unit cells 10 , a first functional unit cell 110 , and a second functional unit cell 120 .

[0034] The term "functional unit cell" may refer to a unit cell specifically used to perform a function of preventing heat generation. The term "functional layer" may also refer to a layer specifically used to perform the above function.

[0035] A plurality of unit cells 10 overlap in the thickness direction. For convenience, Figure 1A A specific number of stacked unit cells 10 is shown, but the number of stacked unit cells 10 may be appropriately adjusted as needed.

[0036] like Figure 1A As shown, the first function unit cell 110 and the second function unit cell 120 may be disposed at an outermost portion, and will be referred to as outer unit cells in the following description.

[0037] The external unit cell includes a negative electrode 4, a positive electrode 2, and a separator 3 interposed between the negative electrode 4 and the positive electrode 2, as shown in an enlarged manner.

[0038] The positive electrode 2 includes a positive current collector 2a and a positive active material layer 2b provided on at least one surface of the positive current collector 2a and including a positive active material, and a first functional layer 2c provided on the positive active material layer 2b and including a first active material. Figure 1A Only the structure of the positive electrode 2 having the positive electrode active material layer provided on one surface of the current collector is shown, but the positive electrode active material may be provided on both surfaces of the current collector, and further, Figure 1A The structure of FIG. 1 shows that the first functional layer 2c is provided on one surface of the positive electrode active material layer 2b and contacts the separator 3, but as shown in FIG. Figure 1B As shown, when the positive electrode active material layers 2b and 2d may be provided on both surfaces of the positive electrode collector 2a, the first functional layers 2c and 2e may be provided on the positive electrode active material layers 2b and 2d, respectively.

[0039] In one embodiment, the positive active material included in the positive active material layer has a first reference potential, and the first active material included in the first functional layer has a second reference potential lower than the first reference potential of the positive active material.

[0040] For example, the first reference potential may be in the range of about 3.3V to about 4.3V, about 3.5V to about 4.0V, or about 3.6V to about 3.8V.

[0041] As used herein, the first reference potential (which is the reference potential of the positive electrode active material) is based on lithium metal (Li / Li + )'s average reduction potential.

[0042] On the other hand, the positive electrode active material may include a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). a A 1-b X b D2(0.90≤a≤1.8, 0≤b≤0.5); Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a E 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a E 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α≤2); Li a Ni 1-b-c Co b X c O 2-α T α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Co b X c O 2-α T2(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Mn b X c D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Mn b X c O 2-α T α(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α T2(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni b E c G d O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1); Li a Ni b Co c Mn d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1); Li a NeG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn b O4 (0.90≤a≤1.8, 0.001≤b≤0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiZO2; LiNiVO4 or a combination thereof. Preferably, the positive electrode active material may be at least one composite oxide of a metal selected from cobalt, manganese, nickel and a combination thereof and lithium.

[0043] In the above chemical formula, A is selected from Ni, Co, Mn and combinations thereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and combinations thereof; D is selected from O, F, S, P and combinations thereof; E is selected from Co, Mn and combinations thereof; T is selected from F, S, P and combinations thereof; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and combinations thereof; Q is selected from Ti, Mo, Mn and combinations thereof; and Z is selected from Cr, V, Fe, Sc, Y and combinations thereof.

[0044] In the positive electrode, the amount of the positive active material may be about 90 wt % to about 99.8 wt % based on the total weight of the positive active material layer.

[0045] The positive active material layer may further include a binder and a conductive material as needed. Here, the binder and the conductive material may be included in an amount of about 0.1 wt % to about 5 wt %, respectively, based on the total weight of the positive active material layer.

[0046] The binder improves the bonding performance of the positive electrode active material particles to each other and to the current collector. Examples of the binder may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0047] A conductive material is included to provide electrode conductivity. Any conductive material can be used as the conductive material unless it causes a chemical change. Examples of the conductive material may include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0048] The first functional layer is disposed on the positive electrode active material layer, and the first functional layer includes a first active material, and the first active material has a second reference potential lower than the first reference potential. For example, the second reference potential may be in the range of about 1.5V to about 3.8V, about 2.0V to about 3.6V, about 2.5V to about 3.5V, about 3.0V to about 3.5V, or about 3.1V to about 3.3V. When the second reference potential of the first active material satisfies the above numerical range and is lower than the first reference potential, the side reaction of the positive electrode active material can be suppressed, and safety can be ensured.

[0049] As used herein, the second reference potential (which is the reference potential of the first active material) is based on lithium metal (Li / Li + )'s average reduction potential.

[0050] The first active material may be, for example, Li a Fe 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li a Co 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li 4-x Mx Ti y O 12-z (0≤x≤3, 1≤y≤5, -0.3≤z≤0.3) or a combination thereof. In the above chemical formula, G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and a combination thereof; and M is selected from Mg, La, Tb, Gd, Ce, Pr, Nd, Sm, Ba, Sr, Ca or a combination thereof.

[0051] The first active material may be an active material having a reference potential lower than the first reference potential among the active materials. In other words, once the positive electrode active material included in the positive electrode active material layer is selected, an active material having a second reference potential lower than the first reference potential of the positive electrode active material may be selected as the first active material.

[0052] In this way, when the first active material is selected to have a lower reference potential than the positive electrode active material included in the positive electrode active material layer, a side reaction of the positive electrode can be suppressed and the safety of the positive electrode can be improved.

[0053] The first functional layer may further include a binder. When the first functional layer includes a binder, the amount of the first active material included may be about 90wt% to about 99.8wt% based on the total weight of the first functional layer, and the amount of the binder included may be about 0.2wt% to about 10wt% based on the total weight of the first functional layer. According to one embodiment, the amount of the binder included may be about 1wt% to about 6wt%.

[0054] In addition, if Figure 1B As shown, when the positive electrode active material layer is arranged on both surfaces of the collector and the first functional layers are respectively arranged on the positive electrode active material layers, the positive electrode active material layers on the two surfaces of the collector are respectively referred to as the first positive electrode active material layer and the second positive electrode active material layer, and the first functional layers are respectively referred to as 1a functional layer and 1b functional layer, and here, in the positive electrode active material having a first reference potential, the positive electrode active materials contained in the first and second positive electrode active material layers may be the same as or different from each other, and in the active material having a second reference potential, the active materials contained in the 1a and 1b functional layers may also be the same as or different from each other.

[0055] In the external unit cell, the difference between the first reference potential and the second reference potential may be in the range of about 0.01 V to about 2.0 V, about 0.05 V to about 1.5 V, about 0.1 V to about 1.0 V, about 0.1 V to about 0.6 V. When the difference between the reference potential of the positive active material included in the positive active material layer and the reference potential of the first active material included in the first functional layer satisfies the range, excellent cycle life characteristics and capacity characteristics may be exhibited.

[0056] The first functional layer may have a thickness of about 0.5 μm to about 8 μm, and according to one embodiment, the thickness is about 2 μm to about 5 μm. When the first functional layer has a thickness within this range, the first functional layer substantially covers the positive electrode active material layer and maintains conductivity, and the formation effect of the first functional layer can be further appropriately obtained.

[0057] In this way, when the external unit cell includes a positive electrode comprising a first functional layer arranged on a positive electrode active material layer (including a first active material in the first functional layer having a second reference potential lower than the first reference potential of the positive electrode active material), side reactions can be reduced by preventing overvoltage of the positive electrode active material layer, and combustion can be prevented by reducing the calorific value when a short circuit occurs internally by arranging a first active material with a low reference potential on the surface, thereby ensuring safety.

[0058] The positive electrode current collector may be, for example, selected from aluminum foil, nickel foil, or a combination thereof.

[0059] On the other hand, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material.

[0060] The negative electrode active material may include a substance that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a substance capable of doping / dedoping lithium, or a transition metal oxide.

[0061] The material that reversibly intercalates / deintercalates lithium ions can be a carbon material, that is, a carbon-based negative electrode active material commonly used in rechargeable lithium batteries. Examples of carbon-based negative electrode active materials can be crystalline carbon, amorphous carbon, or a combination thereof. Crystalline carbon can be shapeless (unspecified shape), or plate-like, flaky, spherical or fibrous natural graphite or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization product, coke, etc.

[0062] Lithium metal alloys include alloys of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0063] The material capable of doping / desodoping lithium may be a silicon-based material, such as Si, SiO x(0 < x < 2), Si-Q alloys (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Si-carbon composites, Sn, SnO2, Sn-R alloys (where R is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), Sn-carbon composites, etc. At least one of these materials can be mixed with SiO2. Elements Q and R can be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0064] Transition metal oxides include lithium titanium oxides.

[0065] In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the amount of the negative electrode active material included can be about 95 wt% to about 99 wt%.

[0066] The negative electrode active material layer includes a negative electrode active material and a binder, and may further include a conductive material as needed.

[0067] In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the amount of the negative electrode active material included can be about 95 wt% to about 99 wt%. In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the amount of the binder can be about 1 wt% to about 5 wt%. When the negative electrode active material layer includes a conductive material, the negative electrode active material layer includes about 90 wt% to about 99.4 wt% of the negative electrode active material, about 0.5 wt% to about 5 wt% of the binder, and about 0.1 wt% to about 5 wt% of the conductive material.

[0068] The binder improves the binding performance between negative electrode active material particles and the binding performance between negative electrode active material particles and the current collector. The binder can be a non-water-soluble binder, a water-soluble binder, or a combination thereof.

[0069] The non-water-soluble binder can be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide, polyimide, or a combination thereof.

[0070] The water-soluble binder may be styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, a copolymer of propylene and C2 to C8 olefin, a copolymer of (meth)acrylic acid and alkyl (meth)acrylate, or a combination thereof.

[0071] When a water-soluble binder is used as a negative electrode binder, a cellulose-based compound may be further used as a thickener to provide viscosity. The cellulose-based compound includes one or more of the following: carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose or an alkali metal salt thereof. The alkali metal may be Na, K or Li. Based on 100 parts by weight of the negative electrode active material, the amount of the thickener included may be from about 0.1 parts by weight to about 3 parts by weight.

[0072] A conductive material is included to provide electrode conductivity. Any conductive material can be used as the conductive material unless it causes a chemical change. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, Denka black, carbon fiber, etc.; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0073] The negative electrode current collector may be, for example, selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0074] At the same time, the separator can include any material commonly used in rechargeable lithium batteries, as long as the negative electrode is separated from the positive electrode and a transmission channel is provided for lithium ions. In other words, the separator can have low resistance to ion transport and excellent impregnation of electrolytes. The separator can be selected from glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene or a combination thereof, for example. It can have the form of a nonwoven fabric or a woven fabric. Alternatively, in order to ensure heat resistance or mechanical strength, a separator including a coating can be used on a substrate, and the coating uses a composition including a ceramic component or a polymer material. Optionally, the separator can have a single layer or a multilayer structure.

[0075] Next, a plurality of unit cells 10 stacked in the thickness direction are described.

[0076] Each unit cell 10 includes a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode.

[0077] Here, the negative electrode and the separator are the same as those described above for the negative electrode and the separator of the external unit cell, and thus a detailed description thereof will be omitted.

[0078] The positive electrode includes a positive electrode collector and a positive electrode active material layer, which is disposed on at least one surface of the positive electrode collector and includes a positive electrode active material. Here, the detailed description of the positive electrode collector and the positive electrode active material layer is the same as that described in the positive electrode of the external unit cell described above, so its detailed description will be omitted. That is, the positive electrode of each unit cell 10 has the same structure and features as the positive electrode of the external unit cell described above, except that the unit cell 10 does not include the first functional layer.

[0079] Figure 2 Shows Figure 1B Example variations of .

[0080] refer to Figure 2 , the electrode assembly 210 according to the exemplary modification may include a plurality of first functional unit cells 110 and second functional unit cells 120 disposed at the outermost portions, respectively.

[0081] For convenience, Figure 2 It is shown that the electrode assembly 210 includes two first functional unit cells 110 and two second functional unit cells 120. However, if necessary, the number of the first functional unit cells 110 and the second functional unit cells 120 may be appropriately adjusted.

[0082] In this exemplary variation, except for including a plurality of first functional unit cells 110 and a second functional unit cell 120, other features are the same as those of the above reference. Figure 1A The electrode assembly according to the first embodiment is described to be the same, and thus a detailed description thereof will be omitted.

[0083] Figure 3 The structure of an electrode assembly according to a second embodiment of the present disclosure is schematically illustrated.

[0084] refer to Figure 3 , the electrode assembly 201 according to the second embodiment includes a plurality of unit cells 10 , a first functional unit cell 110 , a second functional unit cell 120 , and a third functional unit cell 130 .

[0085] The third functional unit cell 130 is disposed at the center of the thickness direction of the plurality of unit cells 10 and is referred to as a center unit cell Here, the electrode assembly 201 may include at least one third functional unit cell 130 .

[0086] The center unit cell includes a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode.

[0087] In the present embodiment, the positive electrode of the center unit cell includes a positive current collector, a positive active material layer disposed on at least one surface of the positive current collector and including a positive active material, and a second functional layer disposed on the positive active material layer.

[0088] The positive electrode active material has a first reference potential, and the second active material included in the second functional layer has a third reference potential lower than the first reference potential of the positive electrode active material.

[0089] For example, the first reference potential may be in the range of about 3.3V to about 4.3V or about 3.5V to about 4.0V.

[0090] In this embodiment, the positive electrode current collector, the positive electrode active material layer including the positive electrode active material, and the negative electrode and the separator are the same as those in the above reference. Figure 1A The description is the same as that described in the electrode assembly according to the first embodiment, and thus will not be described again.

[0091] The second functional layer is provided on the positive electrode active material layer, and the second functional layer includes a second active material having a third reference potential lower than the first reference potential.

[0092] For example, the third reference potential may be in the range of about 1.5 V to about 3.8 V or about 3.0 V to about 3.5 V. When the third reference potential of the second active material satisfies the above numerical range and is lower than the first reference potential, the side reaction of the positive active material can be suppressed and safety can be ensured.

[0093] As used herein, the third reference potential (which is the reference potential of the second active material) is based on lithium metal (Li / Li + )'s average reduction potential.

[0094] The second active material may be at least one of the active materials described above as the first active material. The second active material, like the first active material, has a reference potential lower than that of the active material included in the positive electrode active material layer, that is, once the positive electrode active material included in the positive electrode active material layer is selected, an active material having a third reference potential lower than the first reference potential may be selected as the second active material.

[0095] In the central unit battery, the difference between the first reference potential and the third reference potential may be in the range of about 0.01 V to about 2.0 V, about 0.05 V to about 1.5 V, about 0.1 V to about 1.0 V, about 0.1 V to about 0.6 V. When the difference between the reference potential of the positive active material included in the positive active material layer and the reference potential of the first active material included in the first functional layer satisfies the range, excellent cycle life characteristics and capacity characteristics may be exhibited.

[0096] As shown in the embodiment, when a plurality of unit cells 10 include a first functional unit cell 110 and a second functional unit cell 120 on the first and second outermost surfaces facing each other and further include a third functional unit cell 130 at the center in the thickness direction, not only the capacity can be ensured but also heat generation when physical impact (such as penetration, etc.) is applied can be more effectively prevented.

[0097] For convenience, Figure 3 A case is shown in which one third functional unit battery cell 130 is included. However, if necessary, two or more third functional unit battery cells 130 may be included, which may be appropriately adjusted.

[0098] In the second embodiment, except for further including the third functional unit battery 130, the other components are the same as those of the reference Figure 1A The electrode assembly of the first embodiment shown is the same.

[0099] Figure 4 The structure of an electrode assembly according to a third embodiment of the present disclosure is schematically illustrated.

[0100] refer to Figure 4 , the electrode assembly 202 according to the third embodiment includes a plurality of unit cells 10 and a third functional unit cell 130 .

[0101] The third functional unit cell 130 is disposed at the center of the thickness direction of the plurality of unit cells 10 and is referred to as a center unit cell. Here, the electrode assembly 202 may include at least one third functional unit cell 130.

[0102] The center unit cell includes a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode.

[0103] In the present embodiment, the positive electrode of the center unit cell includes a positive current collector, a positive active material layer provided on at least one surface of the positive current collector and including a positive active material, and a second functional layer provided on the positive active material layer.

[0104] The positive electrode active material has a first reference potential, and the second active material included in the second functional layer has a third reference potential lower than the first reference potential of the positive electrode active material.

[0105] For example, the first reference potential may be in the range of about 3.3V to about 4.3V or about 3.5V to about 4.0V.

[0106] In this embodiment, the positive electrode current collector, the positive electrode active material layer including the positive electrode active material, the negative electrode and the separator are the same as those in the above reference. Figure 1AThe description is the same as that described in the electrode assembly according to the first embodiment, and thus will not be described again.

[0107] The second functional layer is provided on the positive electrode active material layer, and the second functional layer includes a second active material having a third reference potential lower than the first reference potential.

[0108] Specific description and reference of the second functional layer Figure 3 The electrode assembly shown in the second embodiment is the same as described above and thus will be omitted here.

[0109] As shown in the embodiment, when the central unit cell is arranged at the center of multiple unit cells 10 in the thickness direction, and includes a positive electrode including a second functional layer on a positive electrode active material layer, wherein the second active material included in the second functional layer has a third reference potential lower than the first reference potential of the positive electrode active material, and when a physical impact is applied thereto (for example, penetrating into the center of the electrode assembly, etc.), the heat generated from the center can be reduced and the safety can be further improved.

[0110] For convenience, Figure 4 It is shown that the third functional unit cell 130 includes one central unit cell. However, the third functional unit cell 130 may include two or more central unit cells, which may be adjusted appropriately.

[0111] In the third embodiment, except that the first and second functional unit cells are not included, but the third functional unit cell 130 is included, the reference Figure 1A The same electrode assembly shown in the first embodiment.

[0112] On the other hand, the present disclosure provides in another aspect a rechargeable battery including the electrode assembly according to one of the above embodiments.

[0113] A rechargeable battery according to an embodiment includes the electrode assembly according to the above-described embodiment and its modified embodiments, and a case accommodating the electrode assembly.

[0114] The detailed description of the electrode assembly is the same as above and will be omitted here.

[0115] In the above-mentioned electrode assembly, the positive electrode, the negative electrode, and the separator included in each of the unit cells, the outer unit cells, and the center unit cell may be immersed in an electrolyte.

[0116] The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0117] The non-aqueous organic solvent serves as a medium for transporting ions that participate in the electrochemical reaction of the battery.

[0118] The non-aqueous organic solvent may include a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent or an aprotic solvent. Carbonate-based solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc., and ester-based solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, etc. Ether-based solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, tetrahydrofuran, etc., and ketone-based solvents may be cyclohexanone, etc. Alcohol-based solvents may include ethanol, isopropanol, and the like, and aprotic solvents may include nitriles, such as R-CN (wherein R is a C2 to C20 straight chain, branched, or cyclic hydrocarbon group, or may include a double bond, an aromatic ring, or an ether bond), and the like; amides, such as dimethylformamide, and the like; dioxolanes, such as 1,3-dioxolane, and the like; cyclopentane sulfones, and the like.

[0119] The non-aqueous organic solvent may be used alone or in a mixture. When the organic solvent is used in a mixture, the mixing ratio may be controlled according to the desired battery performance.

[0120] In addition, the carbonate-based solvent may include a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed together in a volume ratio of 1:1 to 1:9, the performance of the electrolyte may be enhanced.

[0121] In addition to the carbonate-based solvent, the non-aqueous organic solvent of the present disclosure may further include an aromatic hydrocarbon-based organic solvent. Herein, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

[0122] The aromatic hydrocarbon-based organic solvent may be an aromatic hydrocarbon-based compound of Chemical Formula 1.

[0123] [Chemical formula 1]

[0124]

[0125] In Chemical Formula 1, R1 to R6 are the same or different and are selected from hydrogen, halogen, C1 to C10 alkyl, halogenated alkyl, and combinations thereof.

[0126] Specific examples of aromatic hydrocarbon-based organic solvents may be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorobenzene, Toluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0127] The nonaqueous electrolyte may further include an additive of vinylene carbonate or the ethylene carbonate-based compound of Chemical Formula 2 to improve the cycle life of the battery.

[0128] [Chemical formula 2]

[0129]

[0130] In Chemical Formula 2, R7 and R8 are the same or different and are selected from hydrogen, halogen, cyano (CN), nitro (NO2) and fluorinated C1 to C5 alkyl, provided that at least one of R7 and R8 is selected from halogen, cyano (CN), nitro (NO2) and fluorinated C1 to C5 alkyl, and R7 and R8 are not hydrogen at the same time.

[0131] Examples of the ethylene carbonate-based compound may be difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of the additive for improving the cycle life may be used within an appropriate range.

[0132] Lithium salts dissolved in organic solvents provide lithium ions to the battery, substantially operate rechargeable lithium batteries, and improve the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts include at least one supporting salt selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F2y+1 SO2) (wherein x and y are natural numbers, for example, integers ranging from 1 to 20), LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalato)borate: LiBOB). The concentration of the lithium salt may be in the range of about 0.1 M to about 2.0 M. When the lithium salt is included in the above concentration range, the electrolyte may have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

[0133] According to the shape of the electrode assembly, the case may be a pouch type, a prism type, or a cylinder type. Each case may be used as commonly used in the related art without any limitation, and a detailed description thereof will be omitted herein.

[0134] The rechargeable battery according to an embodiment of the present invention maintains the shape of the electrode assembly and may be a stacked type corresponding to a pouch type, or may be a wound type or a jelly roll type in which the electrode assembly is wound, such as a cylindrical or prismatic shape. Figure 5 A cross section of a cylindrical rechargeable battery according to an embodiment is shown. The battery 1 includes a wound electrode assembly including a positive electrode 2 and a negative electrode 4 and a separator 3 interposed therebetween; a case 5 accommodating the electrode assembly; and a sealing member 6 sealing the case 5. The positive electrode 2, the negative electrode 4, and the separator 3 may be immersed in an electrolyte (not shown). Figure 5 An embodiment is shown in which the first functional layer 2c is provided on the positive active material layer 2b, which is provided on one surface of the positive electrode current collector 2a and includes a positive electrode active material. However, as described above, the present invention is not limited thereto.

[0135] Meanwhile, at least one of the rechargeable batteries according to the embodiment may be included in the device. For example, such a device may be one of a mobile phone, a tablet computer, a laptop computer, a power tool, a wearable electronic device, an electric car, a hybrid car, a plug-in hybrid car, and an energy storage device. In this way, the device applying the rechargeable battery is well known in the relevant field, so it will not be described in detail in this description.

[0136] Hereinafter, the present disclosure will be specifically examined through examples.

[0137] Example 1

[0138] (1) Manufacturing of unit cells

[0139] 94wt% LiNi 0.6 Co 0.2 Mn 0.2O2 positive active material, 3wt% polyvinylidene fluoride binder and 3wt% Ketjen black conductive material were mixed in N-methylpyrrolidone solvent to prepare positive active material slurry. The positive active material slurry was coated on both surfaces of the aluminum current collector, and then dried and compressed to manufacture a positive electrode with a positive active material layer.

[0140] 98 wt% of graphite, 0.8 wt% of carboxymethyl cellulose and 1.2 wt% of styrene-butadiene rubber were mixed in pure water to prepare a negative electrode active material slurry. The negative electrode active material slurry was coated on both surfaces of a copper current collector, and then dried and compressed to manufacture a negative electrode having a negative electrode active material layer.

[0141] A negative electrode, a separator composed of a polyethylene and polypropylene multilayer substrate, and a positive electrode were sequentially stacked to manufacture a unit cell.

[0142] (2) Manufacturing of external unit cells

[0143] By adding 94 wt% of the positive electrode active material (whose composition is LiNi 0.6 Co 0.2 Mn 0.2 O2 and the reference potential (Li metal (Li / Li + ) as the reference reduction average potential) is 3.67 V), 3 wt % of polyvinylidene fluoride binder and 3 wt % of Ketjen black conductive material are mixed in N-methylpyrrolidone solvent to prepare positive electrode active material slurry.

[0144] A composition for a first functional layer was prepared by mixing 95 wt % of a first active material (whose composition was LiFePO 4 and whose reference potential was 3.15 V) and 5 wt % of a polyvinylidene fluoride binder in an N-methylpyrrolidone solvent.

[0145] The positive electrode active material slurry is coated on both surfaces of the aluminum current collector, and then dried and compressed to form a positive electrode active material layer, and the composition for the first functional layer is coated, and then dried and compressed to form the first functional layer on the positive electrode active material layer. Thus, a positive electrode having a first functional layer on the positive electrode active material layer is manufactured.

[0146] A negative electrode was produced according to the same method as in (1) above.

[0147] The negative electrode, the separator formed of a polyethylene and polypropylene multilayer substrate, and the positive electrode produced in the above (2) were sequentially stacked in this order to produce an outer unit cell.

[0148] (3) Manufacturing of rechargeable battery cells

[0149] The thirteen (13) unit cells manufactured in the above (1) are stacked in the thickness direction to manufacture a stacked body. The outer unit cells manufactured in the above (2) are stacked on the outermost first and second surfaces of the stacked body, respectively, to manufacture a stacked body having Figure 1B The electrode assembly of the structure shown is then packaged in a case, and an electrolyte is injected therein to manufacture a rechargeable battery cell.

[0150] The electrolyte was prepared by dissolving 1.0 M LiPF6 in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio of 50:50).

[0151] Example 2

[0152] (1) Manufacturing of unit cells

[0153] According to the same method as in Example 1, a unit cell was manufactured.

[0154] (2) Manufacturing of external unit cells

[0155] The outer unit battery cell was manufactured according to the same method as in Example 1.

[0156] (3) Manufacturing of the central unit battery

[0157] By adding 94 wt% of the positive electrode active material (whose composition is LiNi 0.6 Co 0.2 Mn 0.2 O2 and the reference discharge average potential is 3.67V), 3wt% of polyvinylidene fluoride binder and 3wt% of Ketjen black conductive material are mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry.

[0158] 95 wt % of a first active material (whose composition was LiFePO 4 and whose reference potential was 3.15 V) and 5 wt % of a polyvinylidene fluoride binder were mixed in an N-methylpyrrolidone solvent to prepare a composition for a first functional layer.

[0159] The positive electrode active material slurry is coated on both surfaces of the aluminum current collector, and then dried and compressed to form a positive electrode active material layer, and the composition for the first functional layer is coated on the positive electrode active material layer, and then dried and compressed to form the first functional layer. Thus, a positive electrode having a first functional layer on the positive electrode active material layer is manufactured.

[0160] A negative electrode was produced according to the same method as in (1) above.

[0161] The negative electrode, the separator formed of a multilayer substrate of polyethylene and polypropylene, and the positive electrode produced in the above (2) were stacked in order to produce a central unit cell.

[0162] (4) Manufacturing of rechargeable battery cells

[0163] Thirteen (13) unit cells manufactured in (1) of Example 2 are overlapped in the thickness direction to manufacture a stacked body. The outer unit cells manufactured in (2) of Example 2 are stacked on the outermost first and second surfaces of the stacked body manufactured in (2), respectively, and the center unit cell manufactured in (3) of Example 2 is disposed at the center in the thickness direction of the stacked body to manufacture a stacked body having Figure 3 The electrode assembly of the structure shown is packaged in a case, and an electrolyte is injected therein to manufacture a rechargeable battery cell.

[0164] The electrolyte included 1.0 M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (50:50 by volume).

[0165] Example 3

[0166] (1) Manufacturing of unit cells

[0167] According to the same method as in Example 1, a unit cell was manufactured.

[0168] (2) Manufacturing of the central unit battery

[0169] The center unit cell was manufactured according to the same method as in Example 2.

[0170] (3) Manufacturing of rechargeable battery cells

[0171] Thirteen (13) unit cells manufactured in (1) of Example 3 are stacked in the thickness direction to manufacture a stacked body. The center unit cell manufactured in (2) of Example 3 is disposed at the center in the thickness direction of the stacked body manufactured in (2) to manufacture a stacked body having Figure 4 The electrode assembly of the structure shown is packaged in a case, and an electrolyte is injected therein to manufacture a rechargeable battery cell.

[0172] The electrolyte included 1.0 M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (50:50 by volume).

[0173] Comparative Example 1

[0174] (1) Manufacturing of unit cells

[0175] According to the same method as in Example 1, a unit cell was manufactured.

[0176] (2) Manufacturing of rechargeable battery cells

[0177] The thirteen (13) unit cells manufactured in (1) are overlapped in the thickness direction to manufacture an electrode assembly. The electrode assembly is packaged in a case, and an electrolyte is injected therein to manufacture a rechargeable battery cell.

[0178] The electrolyte included 1.0 M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (50:50 by volume).

[0179] Comparative Example 2

[0180] (1) Manufacturing of unit cells

[0181] According to the same method as in Example 1, a unit cell was manufactured.

[0182] (2) Manufacturing of external unit cells

[0183] By adding 94 wt% of the positive electrode active material (whose composition is LiNi 0.6 Co 0.2 Mn 0.2 O2 and a reference potential of 3.67 V), 3 wt % of a polyvinylidene fluoride binder and 3 wt % of a Ketjen black conductive material were mixed in an N-methylpyrrolidone solvent to prepare a positive electrode active material slurry.

[0184] 94 wt % of a first active material (whose composition is that of LiCoO 2 and whose reference potential is 3.85 V), 3 wt % of a polyvinylidene fluoride binder, and 3 wt % of a Ketjen black conductive material are mixed in an N-methylpyrrolidone solvent to prepare a composition for a first functional layer.

[0185] The positive electrode active material slurry is coated on both surfaces of the aluminum current collector, and then dried and compressed to form a positive electrode active material layer, and the composition for the first functional layer is coated on the positive electrode active material layer, and then dried and compressed to form the first functional layer. Thus, a positive electrode having a first functional layer on the positive electrode active material layer is manufactured.

[0186] A negative electrode was produced according to the same method as in (1) above.

[0187] The negative electrode, the separator formed of a polyethylene and polypropylene multilayer substrate, and the positive electrode produced in the above (2) were stacked in order to produce an external unit cell.

[0188] (3) Manufacturing of rechargeable battery cells

[0189] The thirteen (13) unit cells manufactured in (1) are overlapped in the thickness direction to manufacture a stacked body. The outer unit cells manufactured in (2) are laminated on the outermost first and second surfaces of the stacked body, respectively, to manufacture a stacked body having Figure 1B The electrode assembly of the structure shown is enclosed in a case, and an electrolyte is injected therein to manufacture a rechargeable battery cell.

[0190] The electrolyte included 1.0 M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (50:50 by volume).

[0191] Experimental Example 1: Measurement of charge and discharge characteristics and cycle life characteristics

[0192] The rechargeable battery cells according to Examples 1 to 3 and Comparative Examples 1 to 2 were charged at a constant current and constant voltage of 0.1C and 4.3V, respectively, and cut off at 0.05C, paused for 10 minutes, discharged at a constant current of 0.1C, cut off at 2.7V, and paused for 10 minutes, which was considered as one cycle, and after performing one charge and discharge cycle, the charge and discharge capacity of the rechargeable battery cells was measured and shown in Table 1.

[0193] Subsequently, 500 cycles of charging and discharging were performed under the same conditions as above, and the discharge capacity of the rechargeable battery cell was measured. The capacity retention rate of the discharge capacity at the 500th cycle relative to the discharge capacity at the 1st cycle was calculated, and the results are shown in Table 1.

[0194] Table 1

[0195] Charging capacity Discharge capacity Capacity retention rate (%) Example 1 5058mAh 4403mAh 87 Example 2 5073mAh 4412mAh 86 Example 3 5053mAh 4398mAh 86 Comparative Example 1 5062mAh 4405mAh 83 Comparative Example 2 5012mAh 4380mAh 76

[0196] As shown in Table 1, the rechargeable battery cells according to Examples 1 to 3 (having a functional layer containing an active material having a reference potential lower than the reference potential of the active material contained in the active material layer) exhibited excellent capacity retention compared to the rechargeable battery cells according to Comparative Examples 1 and 2 (having no functional layer or having a functional layer containing an active material having a reference potential higher than the reference potential of the active material contained in the active material layer).

[0197] Experimental Example 2: Safety Measurement

[0198] Ten (10) rechargeable battery cells according to Examples 1 to 3 and Comparative Examples 1 to 2 were each manufactured and tested for penetration.

[0199] The penetration test was conducted by charging a rechargeable lithium battery cell at 0.5C and 4.3V, cutting off at 0.05C, and after about 1 hour, using a needle with a diameter of 3mm, completely penetrating the center of the battery at a speed of 80mm / second. The results are shown in Table 2. In Table 2, the numbers represent the number of batteries with no combustion, smoking, and combustion.

[0200] Table 2

[0201] Unburned Smoking combustion Example 1 7 3 0 Example 2 8 2 0 Example 3 5 2 3 Comparative Example 1 0 0 10 Comparative Example 2 0 0 10

[0202] As shown in Table 2, the batteries according to Examples 1 to 3 (having a functional layer containing an active material having a reference potential lower than the reference potential of the active material contained in the active material layer) exhibited excellent safety compared to the batteries according to Comparative Examples 1 and 2 (having no functional layer or having a functional layer containing an active material having a reference potential higher than the reference potential of the active material contained in the active material layer).

[0203] While the invention has been described in connection with what are presently considered to be practicable embodiments, it should 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

1. An electrode assembly, comprising: A plurality of unit cells overlapped in the thickness direction; a first functional unit cell disposed on an outermost first surface of the plurality of unit cells; and a second functional unit cell at an outermost second surface opposite to the first surface, Each of the plurality of unit cells includes a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode. Each of the first functional unit cell and the second functional unit cell comprises: an external unit cell including the negative electrode, an external positive electrode, and a separator disposed between the negative electrode and the external positive electrode, The outer positive electrode comprises: Positive electrode current collector, a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material having a first reference potential, and a first functional layer disposed on the positive electrode active material layer and comprising a first active material, wherein the first active material has a second reference potential lower than the first reference potential, wherein the positive electrodes of the plurality of unit cells overlapped in the thickness direction have the same structure and features as the outer positive electrodes of the outer unit cells, except that the positive electrodes of the plurality of unit cells overlapped in the thickness direction do not include the first functional layer, and The first functional layer has a thickness of 0.5 μm to 8 μm, The positive electrode active material is composed of Li a Ni b E c G d represented by O2, 0.90 ≤ a ≤ 1.8, 0 < b ≤ 0.9, 0 < c ≤ 0.5, 0.001 ≤ d ≤ 0.1, E is selected from Co, Mn and combinations thereof, G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and combinations thereof, The first active material is Li a Mn 1-g G g PO4 represents that 0.90≤a≤1.8, 0≤g≤0.5, and G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and combinations thereof.

2. The electrode assembly according to claim 1, wherein the first reference potential is in the range of 3.3V to 4.3V, wherein the second reference potential is in the range of 1.5 V to 3.8 V, and The difference between the first reference potential and the second reference potential is in the range of 0.01V to 0.6V.

3. The electrode assembly according to claim 1, wherein the plurality of unit cells further include a third functional unit cell disposed at a center in a thickness direction of the plurality of unit cells, in, The third functional unit battery comprises: a central unit battery cell including a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode, The positive electrode comprises: Positive electrode current collector, a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material having a first reference potential, and The second functional layer is provided on the positive electrode active material layer and includes a second active material, wherein the second active material has a third reference potential lower than the first reference potential.

4. The electrode assembly according to claim 3, wherein the third reference potential is in the range of 1.5V to 3.8V, and The difference between the first reference potential and the third reference potential is in the range of 0.01V to 0.6V.

5. An electrode assembly comprising: A plurality of unit cells overlapped in the thickness direction, and a third functional unit cell disposed at a center in a thickness direction of the plurality of unit cells; Each of the plurality of unit cells includes a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode. The third functional unit battery comprises: a central unit battery cell comprising a negative electrode, a central positive electrode and a separator disposed between the negative electrode and the central positive electrode, The central positive electrode comprises: Positive electrode current collector, a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material having a first reference potential, and a second functional layer disposed on the positive electrode active material layer and comprising a second active material, wherein the second active material has a third reference potential lower than the first reference potential, and wherein the positive electrodes of the plurality of unit cells overlapping in the thickness direction have the same structure and features as the central positive electrode of the central unit cell, except that the positive electrodes of the plurality of unit cells overlapping in the thickness direction do not include the second functional layer, The positive electrode active material is represented by Li a Ni b E c G d O2, where 0.90 ≤ a ≤ 1.8, 0 < b ≤ 0.9, 0 < c ≤ 0.5, 0.001 ≤ d ≤ 0.1, E is selected from Co, Mn, and combinations thereof, and G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof. The second active material is Li a Mn 1-g G g PO4 represents that 0.90≤a≤1.8, 0≤g≤0.5, and G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and combinations thereof.

6. The electrode assembly according to claim 1, wherein the first reference potential is in the range of 3.3V to 4.3V, wherein the third reference potential is in the range of 1.5V to 3.8V, and The difference between the first reference potential and the third reference potential is in the range of 0.01V to 0.6V.

7. A rechargeable battery comprising the electrode assembly according to any one of claims 1 to 6. 8 . The rechargeable battery according to claim 7 , wherein the rechargeable battery is a stacked type rechargeable battery, a wound type rechargeable battery, or a jelly roll type rechargeable battery.

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