Title of Invention: Positive electrode for lithium secondary battery, manufacturing method thereof, and lithium secondary battery including same
technical field
[One]
The present invention relates to a positive electrode for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same.
[2]
This application is an application claiming priority to Korean Patent Application No. 10-2019-0112317 filed on September 10, 2019, and all contents disclosed in the specification and drawings of the application are incorporated herein by reference.
background
[3]
Recently, interest in energy storage technology is increasing. Efforts for research and development of electrochemical devices are becoming more concrete as the fields of application are expanding to cell phones, camcorders, notebook PCs, and even the energy of electric vehicles.
[4]
Electrochemical devices are the field receiving the most attention in this respect, and among them, the development of rechargeable batteries that can be charged and discharged is the focus of interest. Research and development on the design of electrodes and batteries is in progress.
[5]
Among the currently applied secondary batteries, lithium secondary batteries developed in the early 1990s have a higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and lead sulfate batteries that use aqueous electrolyte solutions. is in the spotlight as
[6]
Among them, as the demand for medium and large-sized batteries increases, the demand for lithium secondary batteries is increasing. Among them, the demand for a nickel-rich, high-Nickel three-component positive active material (Li x (Ni a Co b Mn c )O 2 ) having a high energy density is particularly high.
[7]
However, in the case of a nickel-rich three-component positive active material, there are problems in that lifespan characteristics and high temperature stability are deteriorated. In order to solve this problem, an attempt was made to improve the lifespan characteristics by coating an oxide such as Al 2 O 3 , AlPO 4 on the surface of the positive active material particles to suppress a side reaction between the positive active material and the electrolyte, but even in this case, the thermal stability is still poor.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[8]
One aspect of the present invention is to solve the above problems, and to provide a positive electrode for a lithium secondary battery having a high energy density.
[9]
Another aspect of the present invention is to provide a positive electrode for a lithium secondary battery having improved lifespan characteristics.
[10]
Another object of the present invention is to provide a positive electrode for a lithium secondary battery having improved lifespan characteristics and improved thermal stability at the same time.
means of solving the problem
[11]
One aspect of the present invention provides a positive electrode for a lithium secondary battery according to the following embodiments.
[12]
A first embodiment is
[13]
current collector;
[14]
Li x (Ni a Co b Mn c )O 2 (0.5 < x < 1.3, a ≥ 0.6, 0 < b < 1, 0 < c < 1, a + b + c = 1 ) comprising a first positive electrode active material layer; and LiCoO 2 , LiMn 2 O 4 , LiAl 2 O 3 , LiCoPO 4 , LiFePO 4 , Li x (Ni a Co b Mn c )O 2 as a second positive active material layer positioned on the first positive electrode active material layer A second positive electrode comprising any one of (0.5 < x < 1.3, a ≤ 0.5, 0 < b < 1, 0 < c < 1, a+b+c=1) or a mixture of two or more thereof and a solid electrolyte It relates to a positive electrode for a lithium secondary battery comprising; an active material layer.
[15]
In the second embodiment, according to the first embodiment,
[16]
The second positive active material relates to a positive electrode for a lithium secondary battery, characterized in that coated or doped by the solid electrolyte.
[17]
A third embodiment, according to any one of the preceding embodiments,
[18]
The thickness of the first positive electrode active material layer relates to a positive electrode for a lithium secondary battery, characterized in that the same as or thicker than the thickness of the second positive electrode active material layer.
[19]
The fourth embodiment, according to the third embodiment,
[20]
The thickness of the first positive electrode active material layer relates to a positive electrode for a lithium secondary battery, characterized in that 20㎛ to 60㎛.
[21]
A fifth embodiment, according to the third or fourth embodiment,
[22]
The thickness of the second positive electrode active material layer relates to a positive electrode for a lithium secondary battery, characterized in that 10㎛ to 30㎛.
[23]
A sixth embodiment, according to any one of the preceding embodiments,
[24]
The content of the solid electrolyte relates to a positive electrode for a lithium secondary battery, characterized in that 20 parts by weight or more based on 100 parts by weight of the second positive electrode active material layer.
[25]
A seventh embodiment, according to any one of the preceding embodiments,
[26]
The solid electrolyte relates to a positive electrode for a lithium secondary battery, characterized in that it is any one of a polymer-based solid electrolyte, a sulfide-based solid electrolyte, and an oxide-based solid electrolyte, or a mixture thereof.
[27]
The eighth embodiment, according to the seventh embodiment,
[28]
The solid electrolyte is an oxide-based solid electrolyte, and the oxide-based solid electrolyte is an LLTO-based compound, Li 6 La 2 CaTa 2 O 12 , Li 6 La 2 ANb 2 O 12 (A is Ca or Sr), Li 2 Nd 3 TeSbO 12 , Li 3 BO 2.5 N 0.5 , Li 9 SiAlO 8 , LAGP-based compound, LATP-based compound, Li 1+x Ti 2-x Al x Si y(PO 4 ) 3-y (here, 0≤x≤1, 0≤y≤1), LiAl x Zr 2-x (PO 4 ) 3 (here, 0≤x≤1, 0≤y≤1 ) ), LiTi x Zr 2-x (PO 4 ) 3 (here, 0≤x≤1, 0≤y≤1), LISICON-based compound, LIPON-based compound, perovskite-based compound, Nasicon-based compound, LLZO-based compound It relates to a positive electrode for a lithium secondary battery comprising any one or two or more of them.
[29]
Another aspect of the present invention provides a lithium secondary battery according to the following embodiments.
[30]
A ninth embodiment relates to a lithium secondary battery including the positive electrode, the negative electrode, and a separator interposed between the positive electrode and the negative electrode according to any one of the above embodiments.
[31]
The tenth embodiment, according to the ninth embodiment,
[32]
The lithium secondary battery relates to a lithium secondary battery, characterized in that any one of a lithium ion secondary battery, a lithium polymer secondary battery, a lithium metal secondary battery, or a lithium ion polymer secondary battery.
[33]
Another aspect of the present invention provides a method of manufacturing a positive electrode for a lithium secondary battery according to the following embodiments.
[34]
The eleventh embodiment is
[35]
Li x (Ni a Co b Mn c )O 2 (0.5 < x < 1.3, a ≥ 0.6, 0 < b < 1, 0 < c < 1, a+b+c=1) as the first positive active material preparing a current collector in which a first positive active material layer is applied and dried; and
[36]
LiCoO 2 , LiMn 2 O 4 , LiAl 2 O 3 , LiCoPO 4 , LiFePO 4 , Li x (Ni a Co b Mn c )O 2 (0.5 ) < x < 1.3, a ≤ 0.5, 0 < b < 1, 0 < c < 1, a+b+c=1) or a mixture of two or more of these It relates to a method of manufacturing a positive electrode for a lithium secondary battery, comprising the step of forming a positive electrode active material layer.
[37]
The twelfth embodiment, according to the eleventh embodiment,
[38]
The second positive active material relates to a method of manufacturing a positive electrode for a lithium secondary battery, characterized in that coated or doped by the solid electrolyte.
Effects of the Invention
[39]
According to an embodiment of the present invention, a lithium secondary battery having a high energy density is provided by using a nickel rich, High-Nickel three-component positive active material (Li x (Ni a Co b Mn c )O 2 ) can do.
[40]
A positive electrode according to an embodiment of the present invention includes a first positive electrode active material layer and a second positive electrode active material layer, wherein the second positive electrode active material layer is a layer in direct contact with an electrolyte, and thus the first positive electrode active material layer and Direct contact with the electrolyte can be suppressed. Accordingly, a side reaction between the first positive electrode active material and the electrolyte may be suppressed, and thermal stability may be improved.
[41]
According to an embodiment of the present invention, the second positive electrode active material layer includes a solid electrolyte, and the solid electrolyte may act as a buffer material, so that the first positive active material and the second positive electrode active material are subjected to a rolling process to improve the density of the positive electrode. 2 It is possible to improve the lifespan characteristics and thermal stability by reducing the breakage of the cathode active material particles.
Brief description of the drawing
[42]
The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of ​​the present invention together with the above-described contents of the present invention, so the present invention is limited to the matters described in those drawings It should not be construed as being limited.
[43]
1 is a schematic cross-sectional view of an anode according to an embodiment of the present invention.
Modes for carrying out the invention
[44]
Hereinafter, the present invention will be described in detail with reference to the drawings. The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention.
[45]
Accordingly, the embodiments described in the present specification and the configurations described in the drawings are only the most preferred embodiment of the present invention, and do not represent all of the technical spirit of the present invention. It should be understood that there may be equivalents and variations.
[46]
[47]
Throughout this specification, when a part is "connected" with another part, this includes not only "directly connected" but also "indirectly connected" with another member interposed therebetween. . Also, the connection includes an electrochemical connection as well as a physical connection.
[48]
[49]
Throughout this specification, when a part "includes" a certain element, it means that other elements may be further included, rather than excluding other elements, unless otherwise stated.
[50]
Also, as used herein, “comprise” and/or “comprising” refers to the specified presence of the mentioned shapes, numbers, steps, actions, members, elements, and/or groups thereof. and does not exclude the presence or addition of one or more other shapes, numbers, movements, members, elements and/or groups.
[51]
[52]
As used throughout this specification, the terms "about", "substantially", etc. are used as meanings at or close to the numerical values ​​when manufacturing and material tolerances inherent in the stated meaning are presented, and are used precisely in order to facilitate the understanding of the present application. or absolute figures are used to prevent unreasonable use of the mentioned disclosure by an unconscionable infringer.
[53]
[54]
Throughout this specification, the term "combination(s) of these" included in the surface of the Markush-type means one or more mixtures or combinations selected from the group consisting of the components described in the expression of the Markush-type, It means to include one or more selected from the group consisting of the above components.
[55]
[56]
Throughout this specification, the description of “A and/or B” means “A or B or both”.
[57]
[58]
One aspect of the present invention relates to a positive electrode for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same.
[59]
[60]
As the demand for medium and large-sized batteries increases, the demand for lithium secondary batteries is increasing. For this purpose, a nickel-rich three-component positive electrode active material with high energy density is in particular high demand.
[61]
However, the nickel-rich three-component positive active material has disadvantages in that lifespan characteristics and thermal stability are relatively poor.
[62]
The present inventors were researching to invent a positive electrode for a lithium secondary battery with improved lifespan characteristics and thermal stability while maintaining high energy density. A positive electrode capable of suppressing side reactions between rich positive electrode active materials and improving lifespan characteristics and thermal stability as a solid electrolyte acts as a buffer material was invented.
[63]
[64]
Accordingly, one aspect of the present invention is,
[65]
current collector;
[66]
Li x (Ni a Co b Mn c )O 2 (0.5 < x < 1.3, a ≥ 0.6, 0 < b < 1, 0 < c < 1, a + b + c = 1) comprising a first positive active material layer; and LiCoO 2 , LiMn 2 O 4 , LiAl 2 O 3 , LiCoPO 4 , LiFePO 4 , Li x (Ni a Co b Mn c )O 2 , located on the first positive electrode active material layer, as a solid electrolyte and a second positive electrode active material a second positive active material layer including any one of (0.5 < x < 1.3, a ≤ 0.5, 0 < b < 1, 0 < c < 1, a+b+c=1) or a mixture of two or more thereof; It is characterized in that it includes.
[67]
[68]
Hereinafter, it will be described in detail with reference to FIG. 1 .
[69]
1, the positive electrode 100 for a lithium secondary battery according to an aspect of the present invention includes a current collector 10; a first positive active material layer 20 positioned on at least one surface of the current collector; and a second positive active material layer 30 positioned on the first positive active material layer.
[70]
In this case, the first positive electrode active material layer 20 includes a nickel-rich positive electrode active material as a first positive electrode active material, and the second positive active material layer 30 includes a solid electrolyte and a positive electrode active material other than the nickel-rich positive electrode active material as a second positive active material included as
[71]
That is, in one aspect of the present invention, the first positive electrode active material, which is a nickel-rich positive electrode active material, does not directly contact the electrolyte in a lithium secondary battery manufactured later. Accordingly, it is possible to reduce side reactions with the electrolyte, thereby improving the thermal stability of the first positive electrode active material layer.
[72]
In a specific embodiment of the present invention, the first positive active material is Li x (Ni a Co b Mn c )O 2 (0.5 < x < 1.3, a ≥ 0.6, 0 < b < 1, 0 < c < 1 , a+b+c=1). In other words, the first positive electrode active material is a three-component positive electrode active material including nickel, cobalt, and manganese, and is a positive electrode active material having a high nickel content.
[73]
The present invention is to solve a problem when the first positive active material is used alone, and the first positive active material is essentially included, and the first positive active material layer including the first positive active material is formed with an electrolyte. It is a layer in which direct contact is suppressed.
[74]
[75]
According to one aspect of the present invention, the second positive electrode active material layer is located on the first positive electrode active material layer, and includes a solid electrolyte and a second positive electrode active material.
[76]
The second positive active material is not the first positive active material, and may be a positive active material having less side reaction with an electrolyte. According to an aspect of the present invention, when the nickel-rich positive electrode active material is applied as the first positive electrode active material layer, a side reaction with the electrolyte can be suppressed and a high capacity positive electrode can be secured at the same time. On the other hand, since a material other than the nickel-rich positive electrode active material is used as the second positive electrode active material, side reactions with the electrolyte can be prevented in advance, and the thermal stability of the lithium secondary battery is improved according to the thermal and chemical resistance of the second positive electrode active material. can be improved and lifespan characteristics can be improved.
[77]
In a specific embodiment of the present invention, the second positive active material is LiCoO 2 , LiMn 2 O 4 , LiAl 2 O 3 , LiCoPO 4 , LiFePO 4 , Li x (Ni a Co b Mn c )O 2 (0.5 < x < 1.3, a ≤ 0.5, 0 < b < 1, 0 < c < 1, a+b+c=1), or two or more of them.
[78]
In a specific embodiment of the present invention, the second positive active material may be coated or doped by a solid electrolyte to be described later. In this case, all or part of the surface of the second positive electrode active material particles may be coated or doped.
[79]
[80]
In a specific embodiment of the present invention, the thickness of the first positive electrode active material layer may be the same as or thicker than the thickness of the second positive electrode active material layer. For example, the thickness of the first positive electrode active material layer may be 20 μm to 60 μm or 40 μm to 60 μm. In addition, the thickness of the second positive electrode active material layer may be 10 to 30 μm or 20 to 30 μm. As such, when the thickness of the first positive active material layer is equal to or thicker than that of the second positive active material layer, the energy density is high and side reactions with the electrolyte are suppressed to provide a positive electrode for a lithium secondary battery with improved lifespan characteristics and thermal stability can do.
[81]
[82]
Meanwhile, the second positive electrode active material layer according to an aspect of the present invention includes a solid electrolyte.
[83]
The solid electrolyte does not react with the first positive electrode active material or the second positive electrode active material, and may suppress direct contact between the electrolyte and the first positive electrode active material.
[84]
In addition, as the solid electrolyte acts as a buffer material, it is possible to suppress a phenomenon in which particles of the positive electrode active material are broken during a rolling process during the manufacturing of the positive electrode, thereby improving lifespan characteristics and thermal stability.
[85]
In a specific embodiment of the present invention, the solid electrolyte may include a polymer-based solid electrolyte, a sulfide-based solid electrolyte, and an oxide-based solid electrolyte alone or two or more thereof.
[86]
In a specific embodiment of the present invention, the polymer-based solid electrolyte is a solid polymer electrolyte formed by adding a polymer resin to each independently solvated lithium salt, or an organic electrolyte solution containing an organic solvent and a lithium salt is added to the polymer resin. It may be a polymer gel electrolyte contained therein.
[87]
In one embodiment of the present invention, the polymer-based solid electrolyte is a polymer resin, for example, a polyether-based polymer, a polycarbonate-based polymer, an acrylate-based polymer, a polysiloxane-based polymer, a phosphazene-based polymer, a polyethylene derivative, an alkyl Lene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, a polymer containing an ionic dissociation group, or two or more of these may be included. , but is not limited thereto.
[88]
In a specific embodiment of the present invention, the polymer-based solid electrolyte copolymerizes an amorphous polymer such as PMMA, polycarbonate, polysiloxane (pdms) and/or phosphazene as a comonomer in a polyethylene oxide (PEO) main chain as a polymer resin. It may include a branched copolymer, a comb-like polymer, a cross-linked polymer resin, or two or more of these.
[89]
In addition, in a specific embodiment of the present invention, the polymer gel electrolyte includes an organic electrolyte containing a lithium salt and a polymer resin, and the organic electrolyte may include 60 to 400 parts by weight relative to 100 parts by weight of the polymer resin. . The polymer resin applied to the gel electrolyte is not limited to a specific component, but for example, PVC (Polyvinyl chloride)-based, PMMA (Poly (methyl methacrylate))-based, polyacrylonitrile (PAN), polyvinyl fluoride It may include leadene (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), or a mixture of two or more thereof, but is not limited thereto.
[90]
In the electrolyte of the present invention, the above-described lithium salt is an ionizable lithium salt and may be expressed as Li + X − . The anion (X) of the lithium salt is not particularly limited, but F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , PF 6 - , ( CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , CF 3 SO 3 - , CF 3 CF 2 SO 3 - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) ) 2 N - , CF 3 CF 2 (CF 3 ) 2 CO - , (CF 3 SO 2 ) 2 CH - , (SF 5 ) 3 C - , (CF 3 SO 2 ) 3 C - , CF 3 (CF 2 ) 7 SO 3 - , CF 3 CO 2 - , CH 3 CO 2 -, SCN - , (CF 3 CF 2 SO 2 ) 2 N - and the like can be exemplified.
[91]
In a specific embodiment of the present invention, the sulfide-based solid electrolyte includes a sulfur atom among electrolyte components and is not particularly limited to specific components, and includes a crystalline solid electrolyte, an amorphous solid electrolyte (a glassy solid electrolyte), and a glass ceramic. one or more of a solid electrolyte. Specific examples of the sulfide-based solid electrolyte include LPS-type sulfide containing sulfur and phosphorus, Li 4-x Ge 1-x P x S 4 (x is 0.1 to 2, specifically, x is 3/4, 2/3 ), Li 10±1 MP 2 X 12 (M=Ge, Si, Sn, Al, X=S, Se), Li 3.833 Sn 0.833 As 0.166 S 4 , Li 4 SnS 4 , Li 3.25 Ge 0.25P 0.75 S 4 , Li 2 S-P 2 S 5 , B 2 S 3 -Li 2 S, xLi 2 S-(100-x)P 2 S 5 (x is 70 to 80), Li 2 S-SiS 2 -Li 3 N, Li 2 S-P 2 S 5 - LiI, Li 2 S-SiS 2 -LiI, Li 2 S-B 2 S 3-LiI, etc., but are not limited thereto.
[92]
In a specific embodiment of the present invention, the oxide-based solid electrolyte is, for example, Li 3x La 2/3-x TiO 3 LLT-based perovskide structure such as, Li 14 Zn(GeO 4 ) 4 Such as Appropriately select a LATP type such as LISICON, Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , a LAGP type such as (Li 1+x Ge 2-x Al x (PO 4 ) 3 ), and a phosphate type such as LiPON and can be used, but is not particularly limited thereto.
[93]
In one specific embodiment of the present invention, in particular, when an oxide-based solid electrolyte is used, thermal stability may be further improved compared to a polymer-based solid electrolyte or a sulfide-based solid electrolyte.
[94]
[95]
In a specific embodiment of the present invention, the content of the solid electrolyte may be 20 parts by weight or more, or 25 parts by weight or more, specifically 28.5 parts by weight to 50 parts by weight based on 100 parts by weight of the second positive electrode active material layer. . Within the above numerical range, it is advantageous in terms of minimizing a decrease in energy density due to an increase in the solid electrolyte and improving thermal stability at the same time.
[96]
[97]
In a specific embodiment of the present invention, the first positive active material layer and the second positive active material layer may further include a conductive material and/or a binder polymer. Alternatively, if necessary, other types of compounds may be used. In addition, composition ratios of components constituting the first positive active material layer and the second positive active material layer excluding the conductive material may be the same or different.
[98]
The conductive material is not particularly limited as long as it is an electronically conductive material that does not cause chemical change in the electrochemical device. The conductive material used in each of the first positive active material layer and the second positive active material layer may be the same or different, and each independently carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide , organic conductive materials, etc. can be used, and products currently marketed as conductive materials include acetylene black-based products (such as Chevron Chemical Company or Gulf Oil Company products), Ketjen Black (Ketjen). Black) EC series (product of Armak Company), Vulcan XC-72 (product of Cabot Company), and Super P (product of MMM Company), and the like.
[99]
[100]
In a specific embodiment of the present invention, as the binder polymer, a binder polymer commonly used may be used without limitation. For example, polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate ), styrene-butadiene rubber (SBR, styrene butadiene rubber), and various types of binder polymers such as carboxyl methyl cellulose (CMC, carboxyl methyl cellulose) may be used.
[101]
[102]
The current collector used for the positive electrode is a metal with high conductivity, a metal to which the positive electrode active material and the binder polymer can easily adhere, and any metal that has no reactivity in the voltage range of the electrochemical device may be used. Specifically, non-limiting examples of the current collector for the positive electrode include a foil made of aluminum, nickel, or a combination thereof.
[103]
The negative electrode usable together with the positive electrode may be any one selected from the group consisting of lithium metal, a carbon material, and a metal compound, or a mixture of two or more thereof.
[104]
Specifically, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch-based carbon fiber (mesophase pitch based carbon fiber), carbon microspheres (meso-carbon microbeads), liquid crystal pitches (Mesophase pitches), and high-temperature calcined carbon such as petroleum and coal tar pitch derived cokes are representative.
[105]
Examples of the metal compound include metal elements such as Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, Sr, and Ba. and compounds containing one or more of them. These metal compounds can be used in any form, such as a simple substance, an alloy, an oxide (TiO 2 , SnO 2 , etc.), a nitride, a sulfide, a boride, or an alloy with lithium. It can be high-capacity. Among them, one or more elements selected from Si, Ge, and Sn can be contained, and those containing one or more elements selected from Si and Sn can further increase the capacity of the battery.
[106]
Non-limiting examples of the current collector for the negative electrode include a foil made of copper, gold, nickel, or a copper alloy, or a combination thereof. In addition, the current collector may be used by stacking substrates made of the above materials.
[107]
[108]
The positive electrode and the negative electrode are kneaded using an active material, a conductive material, a binder polymer, and a high boiling point solvent, and two types of electrode active material slurries are prepared by varying the content of the conductive material, and then, each electrode active material slurry is applied to the current collector in two layers. After coating as much as possible, drying and press-molding, each can be prepared by heating at a temperature of 50 to 250° C. under vacuum for about 2 hours.
[109]
In addition, according to an embodiment of the present invention, an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a non-aqueous electrolyte for impregnating the electrode assembly; and a battery case containing the electrode assembly and the non-aqueous electrolyte, wherein at least one of the positive electrode and the negative electrode is an electrode of the present invention.
[110]
[111]
As the separator according to the present invention, any porous substrate used in an electrochemical device may be used, for example, a polyolefin-based porous membrane or a nonwoven fabric may be used, but is not particularly limited thereto.
[112]
Examples of the polyolefin-based porous membrane include polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, and polyolefin-based polymers such as polypropylene, polybutylene, and polypentene, respectively, individually or in a mixture thereof. One membrane is mentioned.
[113]
As the nonwoven fabric, in addition to the polyolefin-based nonwoven fabric, for example, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate ), polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalene, etc. alone or and a nonwoven fabric formed of a polymer obtained by mixing them. The structure of the nonwoven fabric may be a spunbond nonwoven fabric composed of long fibers or a melt blown nonwoven fabric.
[114]
The thickness of the porous substrate is not particularly limited, but may be 5 to 50 μm, and the pore size and pores present in the porous substrate are also not particularly limited, but may be 0.01 to 50 μm and 10 to 95%, respectively.
[115]
On the other hand, in order to improve the mechanical strength of the separator composed of the porous substrate and suppress a short circuit between the positive electrode and the negative electrode, a porous coating layer including inorganic particles and a binder polymer on at least one surface of the porous substrate may be further included.
[116]
Meanwhile, the non-aqueous electrolyte may include an organic solvent and an electrolyte salt, and the electrolyte salt is a lithium salt. As the lithium salt, those commonly used in non-aqueous electrolytes for lithium secondary batteries may be used without limitation. For example, as an anion of the lithium salt, F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , PF 6 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , CF 3 SO 3 - , CF 3 CF 2 SO 3 - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2 N - , CF 3 CF 2 (CF 3 ) 2 CO - , (CF 3 SO 2 ) 2 CH-, (SF 5 ) 3 C-, CF 3 (CF 2 ) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN- and (CF 3 CF 2 SO 2 ) 2 It may include any one selected from the group consisting of N-, or two or more of them.
[117]
As the organic solvent included in the above-mentioned non-aqueous electrolyte, those commonly used in the non-aqueous electrolyte for lithium secondary batteries may be used without limitation, for example, ether, ester, amide, linear carbonate, cyclic carbonate, etc. individually or in two types. It can be used by mixing the above.
[118]
Among them, cyclic carbonates, linear carbonates, or a carbonate compound that is a mixture thereof may be included.
[119]
Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, There is any one selected from the group consisting of 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of these halides include, but are not limited to, fluoroethylene carbonate (FEC).
[120]
In addition, specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate, or these A mixture of two or more of them may be typically used, but is not limited thereto.
[121]
In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have a high dielectric constant, so that lithium salts in the electrolyte can be better dissociated. An electrolyte having higher electrical conductivity can be prepared by mixing and using a low-viscosity, low-dielectric constant linear carbonate in an appropriate ratio.
[122]
In addition, as the ether of the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether and ethylpropyl ether or a mixture of two or more thereof may be used. , but is not limited thereto.
[123]
And esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ - Any one selected from the group consisting of valerolactone and ε-caprolactone or a mixture of two or more thereof may be used, but the present invention is not limited thereto.
[124]
The injection of the non-aqueous electrolyte may be performed at an appropriate stage in the manufacturing process of the electrochemical device according to the manufacturing process of the final product and required physical properties. That is, it may be applied before assembling the electrochemical device or in the final stage of assembling the electrochemical device.
[125]
In this case, the electrochemical device includes all devices that undergo an electrochemical reaction, and specific examples thereof include capacitors such as all kinds of secondary batteries, fuel cells, solar cells, or supercapacitor devices. In particular, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery among the secondary batteries is preferable.
[126]
[127]
Hereinafter, examples will be given to describe the present invention in detail. However, embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided in order to more completely explain the present invention to those of ordinary skill in the art.
[128]
[129]
Example 1 - Preparation of positive electrode
[130]
Based on 100 parts by weight of the first positive active material layer, 95 parts by weight of LiNi 0.88 Co 0.09 Mn 0.03 O 2 as the first positive active material , 2.5 parts by weight of carbon black as a conductive material, and 2.5 parts by weight of polyvinylidene fluoride (PVDF) as a binder polymer Part was added to N-methyl-2-pyrrolidone as a solvent to prepare a first positive electrode active material slurry.
[131]
Based on 100 parts by weight of the second positive active material layer, 66.5 parts by weight of LiNi 0.5 Co 0.2 Mn 0.3 O 2 as a second positive active material, 28.5 parts by weight of Li 1.3 Ti 1.7 Al 0.3 (PO 4 ) 3 as a solid electrolyte , 28.5 parts by weight as a conductive material A second cathode active material slurry was prepared by adding 2.5 parts by weight of carbon black and 2.5 parts by weight of polyvinylidene fluoride as a binder polymer to N-methyl-2-pyrrolidone as a solvent. That is, in the second cathode active material slurry, the solid electrolyte and the second cathode active material are simply mixed.
[132]
The first cathode active material slurry was coated on an aluminum foil to a thickness of 60 µm and vacuum dried, and then, the second cathode active material slurry was applied to a thickness of 20 µm and dried.
[133]
Accordingly, a positive electrode for a lithium secondary battery having a first positive electrode active material layer having a thickness of 60 μm and a second positive electrode active material layer having a thickness of 20 μm was manufactured.
[134]
[135]
Example 2 - Preparation of positive electrode
[136]
A positive electrode for a lithium secondary battery was manufactured in the same manner as in Example 1, except that the thickness of the first positive electrode active material layer was controlled to be 60 μm and the thickness of the second positive electrode active material layer was controlled to be 10 μm.
[137]
[138]
Example 3 - Preparation of positive electrode
[139]
A positive electrode for a lithium secondary battery was manufactured in the same manner as in Example 1, except that the thickness of the first positive active material layer was controlled to be 60 µm and the thickness of the second positive active material layer was controlled to be 30 µm.
[140]
[141]
Comparative Example 1
[142]
A positive electrode for a lithium secondary battery was prepared in the same manner as in Example 1, except that a solid electrolyte was not included in the preparation of the second positive electrode active material slurry.
[143]
[144]
Comparative Example 2
[145]
LiNi 0.88 Co 0.09 Mn 0.03 O 2 95 parts by weight as a cathode active material, 2.5 parts by weight of carbon black as a conductive material, and 2.5 parts by weight of polyvinylidene fluoride as a binder polymer were added to N-methyl-2-pyrrolidone as a solvent. A positive electrode active material slurry was prepared.
[146]
The cathode active material slurry was coated on aluminum foil in a loading amount of 80 μm, and then vacuum dried. Accordingly, a positive electrode for a lithium secondary battery having a positive electrode active material layer having a thickness of 80 μm was manufactured.
[147]
That is, Comparative Example 2 is a case in which a single-layer positive electrode active material layer is provided.
[148]
[149]
Experimental Example 1: Confirmation of high-temperature lifespan characteristics of lithium secondary batteries
[150]
After stacking the positive electrodes prepared in Example 1 and Comparative Examples 1 and 2 together with a lithium metal negative electrode and a separator, an electrolyte solution in which EC:DMC:EMC (1:2:1) solvent and 1M LiPF 6 were dissolved Coin half cells according to Example 1 and Comparative Examples 1 and 2 were prepared by injection.
[151]
For each of the prepared coin half cells of Example 1 and Comparative Examples 1 and 2, charging was carried out at a cutoff rate of 1/200C from 45°C to 4.2V with a constant current of 0.33C. Then, discharge was performed until it became 2.5V with a constant current of 0.33C.
[152]
The charging and discharging behavior was set as 1 cycle, and after repeating this cycle 30 times, high temperature (45° C.) lifespan characteristics were measured according to Example 1 and Comparative Examples 1 and 2, which are shown in Table 1 below.
[153]
[Table 1]
division Capacity retention rate (%)
Example 1 94.8
Example 2 93.6
Example 3 95.3
Comparative Example 1 93.1
Comparative Example 2 89.6
[154]
As shown in Table 1, in the case of Examples 1 to 3, the capacity retention rate was higher than those of Comparative Examples 1 and 2. In particular, compared to Comparative Example 2 having a simple single-layer positive electrode active material layer, Example exhibited a significantly higher capacity retention rate of up to 5.7%. In addition, from Examples 2, 1, and 3, it was confirmed that the capacity retention increased as the thickness of the positive electrode active material layer gradually increased to 10, 20, or 30 μm.
[155]
[156]
Experimental Example 2: Thermal stability evaluation
[157]
After stacking the positive electrodes prepared in Example 1 and Comparative Examples 1 and 2 together with a lithium metal negative electrode and a separator, an electrolyte solution in which EC:DMC:EMC (1:2:1) solvent and 1M LiPF 6 were dissolved Coin half cells according to Example 1 and Comparative Examples 1 and 2 were prepared by injection.
[158]
The prepared coin half cell was charged and discharged at 4.2V-2.5V with a constant current of 0.2C, and then charged at 4.2V with a constant current of 0.2C.
[159]
After collecting the fully charged coin half-cell, it was perforated to a size of 4Φ to obtain a positive electrode of about 4.5 mg. Using a differential gravimetric thermal analysis (DSC) device, the temperature was raised to 350 °C at a temperature increase rate of 10 °C/min. The change was measured, and it is shown in Table 2 below.
[160]
[Table 2]
exothermic temperature (℃) Calorific value (J/g)
Example 1 228.4 1089
Example 2 226.6 1165
Example 3 230.3 1013
Comparative Example 1 223.9 1367
Comparative Example 2 214.8 2048
[161]
As can be seen from Table 2, Examples 1 to 3 had a higher exothermic temperature than Comparative Examples 1 and 2, a low calorific value, and it was confirmed that the safety was excellent.
[162]
[163]
The above description is merely illustrative of the technical spirit of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be interpreted as being included in the scope of the present invention.
Claims
[Claim 1]
current collector; Li x (Ni a Co b Mn c )O 2 (0.5 < x < 1.3, a ≥ 0.6, 0 < b < 1, 0 < c < 1, a + b + c = 1) comprising a first positive active material layer; and LiCoO 2 , LiMn 2 O 4 , LiAl 2 O 3 , LiCoPO 4 , LiFePO 4 , Li x (Ni a Co b Mn c )O 2 as a second positive active material layer positioned on the first positive electrode active material layer A second positive electrode comprising any one of (0.5 < x < 1.3, a ≤ 0.5, 0 < b < 1, 0 < c < 1, a+b+c=1) or a mixture of two or more thereof and a solid electrolyte A positive electrode for a lithium secondary battery, comprising: an active material layer.
[Claim 2]
The positive electrode for a lithium secondary battery according to claim 1, wherein the second positive active material is coated or doped by the solid electrolyte.
[Claim 3]
The positive electrode for a lithium secondary battery according to claim 1, wherein the thickness of the first positive active material layer is the same as or thicker than that of the second positive active material layer.
[Claim 4]
The positive electrode for a lithium secondary battery according to claim 3, wherein the first positive active material layer has a thickness of 20 μm to 60 μm.
[Claim 5]
The positive electrode for a lithium secondary battery according to claim 3, wherein the thickness of the second positive active material layer is 10 μm to 30 μm.
[Claim 6]
The positive electrode for a lithium secondary battery according to claim 1, wherein the amount of the solid electrolyte is 20 parts by weight or more based on 100 parts by weight of the second positive electrode active material layer.
[Claim 7]
The positive electrode for a lithium secondary battery according to claim 1, wherein the solid electrolyte is any one of a polymer-based solid electrolyte, a sulfide-based solid electrolyte, and an oxide-based solid electrolyte, or a mixture thereof.
[Claim 8]
The method of claim 7, wherein the solid electrolyte is an oxide-based solid electrolyte, and the oxide-based solid electrolyte is an LLTO-based compound, Li 6 La 2 CaTa 2 O 12 , Li 6 La 2 ANb 2 O 12 (A is Ca or Sr) , Li 2 Nd 3 TeSbO 12 , Li 3 BO 2.5 N 0.5 , Li 9 SiAlO 8 , LAGP-based compound, LATP-based compound, Li 1+x Ti 2-x Al x Si y(PO 4 ) 3-y (here, 0≤x≤1, 0≤y≤1), LiAl x Zr 2-x (PO 4 ) 3 (here, 0≤x≤1, 0≤y≤1 ) ), LiTi x Zr 2-x (PO 4 ) 3 (here, 0≤x≤1, 0≤y≤1), LISICON-based compound, LIPON-based compound, perovskite-based compound, Nasicon-based compound, LLZO-based compound Any one or a positive electrode for a lithium secondary battery comprising two or more of them.
[Claim 9]
A lithium secondary battery comprising the positive electrode, the negative electrode, and a separator interposed between the positive electrode and the negative electrode according to any one of claims 1 to 8.
[Claim 10]
The lithium secondary battery according to claim 9, wherein the lithium secondary battery is any one of a lithium ion secondary battery, a lithium polymer secondary battery, a lithium metal secondary battery, and a lithium ion polymer secondary battery.
[Claim 11]
Li x (Ni a Co b Mn c )O 2 (0.5 < x < 1.3, a ≥ 0.6, 0 < b < 1, 0 < c < 1, a+b+c=1) as the first positive active material preparing a current collector in which a first positive active material layer is applied and dried; and LiCoO 2 , LiMn 2 O 4 , LiAl 2 O 3 , LiCoPO 4 , LiFePO 4 , Li x (Ni a Co b Mn c )O 2 as a solid electrolyte and a second positive electrode active material on the surface of the first positive electrode active material layer (0.5 < x < 1.3, a ≤ 0.5, 0 < b < 1, 0 < c < 1, a+b+c=1) by coating and drying a slurry in which any one or a mixture of two or more of them is mixed A method of manufacturing a positive electrode for a lithium secondary battery, comprising: forming a second positive electrode active material layer.
[Claim 12]
The method of claim 11, wherein the second positive active material is coated or doped with the solid electrolyte.