Title of invention: cathode for secondary battery, manufacturing method thereof, and lithium secondary battery including the same
Technical field
[One]
Mutual citation with related applications
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0107294 filed on September 7, 2018, and all contents disclosed in the literature of the Korean patent application are incorporated as part of this specification.
[3]
[4]
Technical field
[5]
The present invention relates to a positive electrode for a secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same.
[6]
Background
[7]
In recent years, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight, and relatively high capacity secondary batteries is rapidly increasing. In particular, lithium secondary batteries are in the spotlight as a driving power source for portable devices because they are lightweight and have high energy density. Accordingly, research and development efforts for improving the performance of lithium secondary batteries are being actively conducted.
[8]
A lithium secondary battery includes a positive electrode including a positive electrode active material capable of intercalating/detaching lithium ions, a negative electrode including a negative active material capable of intercalating/deintercalating lithium ions, and an electrode with a microporous separator interposed between the positive electrode and the negative electrode It refers to a battery in which the assembly contains an electrolyte containing lithium ions.
[9]
Lithium transition metal oxide is used as a positive electrode active material of a lithium secondary battery, and a lithium metal, a lithium alloy, a metalloid such as Si and Sn, a crystalline or amorphous carbon, or a carbon composite is used as the negative electrode active material. The active material is applied to the current collector with an appropriate thickness and length, or the active material itself is coated in a film shape and wound or stacked together with a separator as an insulator to form an electrode group, and then placed in a can or similar container, and then an electrolyte is injected. To manufacture a secondary battery.
[10]
Some of the lithium ions provided by the positive electrode of the lithium secondary battery react with the electrolyte on the surface of the negative electrode and are consumed to form a passivation layer called a solid electrolyte interphase (SEI) film. That is, there arises a problem of consuming lithium ions and reducing the reversible capacity in the SEI film formation process. Therefore, in order to make the most of the positive electrode active material, it is necessary to supplement the lithium ions consumed in forming the SEI (Solid electrolyte interface) film of the negative electrode. Accordingly, in order to develop a high-capacity lithium secondary battery, a lot of research has been conducted on the development of an irreversible additive that can supplement the capacity limit due to the formation of the SEI film. However, most of the conventional irreversible additives have a negative effect on the performance of the lithium secondary battery by generating reversible charging and discharging at the operating voltage range. Therefore, there is still a need to develop a lithium ion supply material as an irreversible additive that does not contribute to reversible charging/discharging in the operating voltage range.
[11]
Detailed description of the invention
Technical challenge
[12]
An object of the present invention is to provide a positive electrode for a secondary battery including a new irreversible additive that provides lithium ions in the initial charging process and does not contribute to charging/discharging thereafter, and a lithium secondary battery including the same.
[13]
Means of solving the task
[14]
The present invention provides a positive electrode for a secondary battery comprising a positive electrode active material and a lithium-based alloy (Alloy).
[15]
[16]
In addition, the present invention provides a lithium secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and including the positive electrode.
[17]
[18]
In addition, the present invention comprises the steps of forming a positive electrode mixture layer containing a positive electrode active material, and forming a coating layer containing a lithium-based alloy (Alloy) on the positive electrode mixture layer; Alternatively, a method of manufacturing a positive electrode for a secondary battery comprising a; forming a positive electrode mixture layer by coating a positive electrode forming slurry including a positive electrode active material and a lithium-based alloy on a positive electrode current collector and then rolling it.
[19]
Effects of the Invention
[20]
According to the present invention, by providing lithium ions during the initial charging process and then providing a positive electrode for secondary batteries containing a new irreversible additive that does not contribute to charging/discharging, effectively supplementing the capacity limitation due to SEI film formation and high capacity The lithium secondary battery can be implemented.
[21]
Brief description of the drawing
[22]
1 is a schematic diagram of a lithium secondary battery using a lithium ion additive according to an embodiment of the present invention.
[23]
2 is a view schematically showing a manufacturing method of forming a lithium-based alloy coating layer according to an embodiment of the present invention.
[24]
3 is a graph showing the capacity of a lithium secondary battery cell using a positive electrode according to Example 1 and Comparative Example 1.
[25]
4 is a graph showing the capacity of a lithium secondary battery cell using the positive electrode according to Example 2 and Comparative Example 1.
[26]
5 is a graph showing the capacity of a lithium secondary battery cell using a positive electrode according to Example 3 and Comparative Example 1.
[27]
Mode for carrying out the invention
[28]
Hereinafter, the present invention will be described in more detail to aid understanding of the present invention. At this time, terms or words used in the present specification and claims should not be construed as being limited to a conventional or dictionary meaning, and the inventor appropriately defines the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of ​​the present invention on the basis of the principle that it can be done.
[29]
[30]

[31]
The positive electrode for a secondary battery of the present invention includes a positive electrode active material and a lithium-based alloy.
[32]
The positive electrode active material may be applied without limitation, a lithium transition metal oxide commonly used as a positive electrode active material, more preferably any one or more transition selected from the group consisting of cobalt (Co), nickel (Ni) and manganese (Mn). Lithium transition metal oxides containing metal cations may be used. For example, layered compounds such as lithium cobalt oxide (LiCoO 2 ) and lithium nickel oxide (LiNiO 2 ), or the formula Li 1+n Mn 2-n O 4 (where n is 0 to 0.33), LiMnO 3 , LiMn 2 O 3 , lithium manganese oxides such as LiMnO 2 , formula LiNi 1 - m M a m O 2 (here, M a= Co, Mn, Al, Cu, Fe, Mg, B or Ga, and m = 0.01 ~ 0.3) Ni site type lithium nickel oxide represented by the formula LiMn 2 - z M b z O 2 (where M b = Co, Ni, Fe, Cr, Zn or Ta, z= 0.01 ~ 0.1) or Li 2 Mn 3 M c O 8 (here, M c = Fe, Co, Ni, Cu or Zn) lithium manganese composite Oxide, LiNi r Mn 2-r O 4 (here, r = 0.01 ~ 1) spinel structure lithium manganese composite oxide, lithium iron phosphate compound (LiFePO 4 ), etc., but are not limited thereto. . Alternatively, a lithium composite transition metal oxide represented by Formula 1 below may be included as the positive electrode active material.
[33]
[Formula 1]
[34]
Li a Ni 1-bcd Co b Mn c Q d O 2+δ
[35]
In the above formula, Q is any one or more elements selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo, and Cr, 0.9≤a≤1.5, 0≤b≤0.5, 0≤c≤0.5, 0≤d≤0.1, -0.1≤δ≤1.0.
[36]
[37]
The lithium-based alloy (Alloy) refers to an alloy composed of lithium metal and at least one or more other metals, and is included as a lithium ion additive, that is, an irreversible additive.
[38]
2 is a schematic diagram of a lithium secondary battery using a lithium ion additive according to an embodiment of the present invention. Referring to FIG. 2, lithium ions supplied from the lithium ion additive included in the positive electrode are consumed to form a solid electrolyte interface (SEI) film on the surface of the negative electrode, and lithium ions supplied from the positive electrode active material contribute to charging and discharging.
[39]
In the present invention, by adding the lithium-based alloy as a lithium ion additive, lithium ions consumed to form the SEI film of the negative electrode are additionally supplied to prevent consumption of lithium ions of the positive electrode active material in forming the SEI film, and the positive electrode active material The reversible capacity can be increased by making the most of
[40]
In addition, the lithium-based alloy of the present invention may be capable of increasing the capacity by only adding a small amount due to the high capacity characteristic of the material itself. In addition, the lithium-based alloy of the present invention provides lithium ions in the initial charging process, and afterwards does not contribute to reversible charging/discharging in the operating voltage range of the lithium secondary battery, negatively affecting the performance of the lithium secondary battery. May not be
[41]
The lithium-based alloy (Alloy) can be applied without limitation as long as it is a lithium-based alloy (Alloy) capable of supplementing the irreversible capacity, but more preferably, a Li-Al-based alloy, a Li-Si-based alloy, or a Li-Sn-based alloy , Li-Bi-based alloys and Li-Sb-based alloys may be at least one selected from the group consisting of. For example, Li 9 Al 4 , Li 3 Al 2 as a Li-Al alloy, Li 21 Si 5 as a Li-Si alloy, Li 17 Sn 14 as a Li-Sn alloy , and , Li 3 as a Li-Bi-based alloy It can be Bi. More preferably, a Li-Al alloy may be used as the lithium alloy (Alloy). In the case of using the Li-Al alloy, lithium (Li) can be mixed up to 80at% and has high capacity characteristics, so it is possible to achieve high capacity with only a small amount of addition, and aluminum (Al) is relatively light and inexpensive. Therefore, it is possible to increase the energy density and reduce the cost. The Li-Al-based alloy may contain lithium (Li) 30 to 80 at% and aluminum (Al) 20 to 70 at%, more preferably lithium (Li) 50 to 70 at% and aluminum (Al) 30 to 50 at %, and more preferably 50 to 60 at% of lithium (Li) and 40 to 50 at% of aluminum (Al).
[42]
[43]
The positive active material and the lithium-based alloy may be included in a weight ratio of 99:1 to 1:99. More preferably, the positive active material and the lithium-based alloy (Alloy) may be included in a weight ratio of 95:5 to 50:50, more preferably 90:10 to 80:20. By including a lithium-based alloy within the weight ratio range, an appropriate amount of lithium ions as consumed in forming the SEI film can be additionally supplied from the lithium ion additive, so that the reversible capacity can be increased and battery performance deterioration can be prevented. .
[44]
[45]
A positive electrode for a secondary battery according to an embodiment of the present invention includes a positive electrode mixture layer including the positive electrode active material; And a coating layer formed on the surface of the positive electrode mixture layer and including the lithium-based alloy. That is, the positive electrode active material of the lithium transition metal oxide and the lithium-based alloy (Alloy), which is an irreversible additive, may be included in different layers. In this way, when a positive electrode active material of lithium transition metal oxide is included in the positive electrode mixture layer, and a coating layer including a lithium alloy is separately formed on the positive electrode mixture layer, a lithium-based alloy is formed in the positive electrode formation process. It may be more effective in realizing a high capacity as it can prevent the capacity from being reduced by reacting with a solvent or a binder.
[46]
In addition, a positive electrode for a secondary battery according to another embodiment of the present invention may include a positive electrode mixture layer in which the positive electrode active material and a lithium alloy are mixed. That is, the positive electrode active material of the lithium transition metal oxide and the lithium-based alloy (Alloy), which is an irreversible additive, may be included in the same layer.
[47]
[48]
The positive electrode mixture layer may be formed on a positive electrode current collector, and the positive electrode mixture layer may further include a conductive material and a binder together with the positive electrode active material.
[49]
The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , Silver, or the like may be used. In addition, the positive electrode current collector may generally have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.
[50]
The positive active material may be included in an amount of 80 to 98% by weight, more preferably 85 to 98% by weight, and most preferably 90 to 95% by weight, based on the total weight of the positive electrode mixture layer.
[51]
The conductive material is used to impart conductivity to an electrode, and in the battery to be configured, it may be used without particular limitation as long as it does not cause chemical changes and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or a conductive polymer such as a polyphenylene derivative may be used, and one of them alone or a mixture of two or more may be used. The conductive material may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode mixture layer.
[52]
The binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC). ), starch, hydroxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene Butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like, and one of them alone or a mixture of two or more may be used. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode mixture layer.
[53]
[54]

[55]
A method of manufacturing the positive electrode for a lithium secondary battery according to the present invention will be described.
[56]
The method of manufacturing a positive electrode for a secondary battery of the present invention comprises the steps of: forming a positive electrode mixture layer including a positive electrode active material, and forming a coating layer containing a lithium alloy (Alloy) on the positive electrode mixture layer; Or forming a positive electrode mixture layer by applying a positive electrode-forming slurry containing a positive electrode active material and a lithium-based alloy on a positive electrode current collector and rolling it.
[57]
[58]
2 is a view schematically showing a manufacturing method of forming a lithium-based alloy coating layer according to an embodiment of the present invention.
[59]
As an embodiment of the present invention as shown in FIG. 2, a method of forming a positive electrode mixture layer including a positive electrode active material and forming a coating layer including a lithium alloy on the positive electrode mixture layer is specifically, A coating layer may be formed by applying a lithium-based alloy powder on the positive electrode mixture layer including, and rolling the positive electrode mixture layer coated with the lithium-based alloy powder. In this way, a lithium-based alloy coating layer can be formed on the positive electrode mixture layer by applying the existing positive electrode manufacturing process.
[60]
In this case, in the step of forming the positive electrode mixture layer, a slurry for forming a positive electrode further comprising a positive electrode active material, a conductive material, a binder and a solvent may be prepared. The types and contents of the positive electrode active material, the conductive material, and the binder are as described above for the positive electrode for a secondary battery. The solvent for forming the slurry for forming the positive electrode may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP). ), acetone, or water, and one of them alone or a mixture of two or more may be used. The amount of the solvent is determined by dissolving or dispersing the radical polymer-coated positive electrode active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and then exhibiting excellent thickness uniformity when applied for manufacturing the positive electrode. It is enough to have it. Next, after applying the slurry for forming the positive electrode on the positive electrode current collector, it is possible to prepare a positive electrode mixture layer by drying and rolling. At this time, when forming the positive electrode mixture layer, the positive electrode may be produced by rolling first, applying lithium alloy powder, and then rolling it secondarily. (Alloy) powder may be coated on the positive electrode mixture layer and then rolled together to produce a positive electrode.
[61]
Meanwhile, as another method, a positive electrode mixture layer may be prepared by casting the slurry for forming the positive electrode on a separate support, and then laminating a film obtained by peeling from the support on a positive electrode current collector.
[62]
[63]
As another embodiment of the present invention, a method of forming a positive electrode mixture layer by applying a positive electrode forming slurry including a positive electrode active material and a lithium alloy on a positive electrode current collector and rolling to form a positive electrode mixture layer is specifically, It is possible to prepare a slurry for forming a positive electrode that includes an alloy and further includes a conductive material and a binder. The types and contents of the positive electrode active material, the conductive material, and the binder are as described above. In this case, the slurry for forming a positive electrode including the lithium-based alloy may not contain an organic solvent. In general, when an organic solvent used to prepare a slurry for forming a positive electrode is used, a lithium-based alloy and an organic solvent react, resulting in a problem that the initial capacity is not expressed. Therefore, more preferably, the slurry for forming a positive electrode including the lithium-based alloy may not contain an organic solvent, and may be performed through a dry mixing process. Next, after applying the slurry for forming the positive electrode on the positive electrode current collector, it is possible to prepare a positive electrode mixture layer by drying and rolling. Meanwhile, as another method, a positive electrode mixture layer may be prepared by casting the slurry for forming the positive electrode on a separate support, and then laminating a film obtained by peeling from the support on a positive electrode current collector.
[64]
[65]
In addition, the kind and content ratio of the lithium-based alloy (Alloy) is as described above for the positive electrode for secondary batteries.
[66]
[67]

[68]
According to another embodiment of the present invention, an electrochemical device including the anode is provided. The electrochemical device may specifically be a battery or a capacitor, and more specifically, a lithium secondary battery.
[69]
[70]
Specifically, the lithium secondary battery includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.
[71]
[72]
In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector.
[73]
The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, and the like may be used. In addition, the negative electrode current collector may generally have a thickness of 3 to 500 μm, and, like the positive electrode current collector, microscopic irregularities may be formed on the surface of the current collector to enhance the bonding strength of the negative electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.
[74]
[75]
The negative electrode mixture layer optionally includes a binder and a conductive material together with a negative active material. The negative electrode mixture layer is, for example, coated on a negative electrode current collector with a negative electrode active material, and optionally a composition for forming a negative electrode including a binder and a conductive material and dried, or casting the negative electrode composition on a separate support , It may be produced by laminating a film obtained by peeling from this support on a negative electrode current collector.
[76]
[77]
As the negative active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; Metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO α (0 <α <2), SnO 2Metal oxides capable of doping and undoping lithium such as vanadium oxide and lithium vanadium oxide; Or a composite including the metal compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more of them may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, 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 typical, and high crystalline carbon is amorphous, plate-like, scale-like, spherical or fibrous natural or artificial graphite, Kish graphite (Kish). graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes) is typical.
[78]
In addition, the binder and the conductive material may be the same as described above for the positive electrode.
[79]
[80]
Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions, and can be used without particular limitation as long as it is generally used as a separator in a lithium secondary battery. On the other hand, it is preferable that it has low resistance and excellent electrolyte-moisturizing ability. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A stacked structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and optionally, a single layer or a multilayer structure may be used.
[81]
[82]
In addition, electrolytes used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that can be used in the manufacture of lithium secondary batteries, and are limited to these. It does not become.
[83]
[84]
Specifically, the electrolyte may include an organic solvent and a lithium salt.
[85]
The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of a battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate-based solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 straight chain, branched or cyclic hydrocarbon group, and may contain a double bonded aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolanes, etc. may be used. Among them, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant that can increase the charge/discharge performance of the battery Ethylene carbonate or propylene carbonate, etc.), and a low-viscosity linear carbonate-based compound (eg, ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9, the electrolyte may exhibit excellent performance.
[86]
[87]
The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAl0 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 . LiCl, LiI, or LiB(C 2 O 4 ) 2 or the like may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, since the electrolyte has an appropriate conductivity and viscosity, excellent electrolyte performance can be exhibited, and lithium ions can effectively move.
[88]
[89]
In addition to the electrolyte constituents, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and tri- Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, or aluminum trichloride may be further included. At this time, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.
[90]
[91]
As described above, since the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful in electric vehicle fields such as hybrid electric vehicle, HEV).
[92]
[93]
Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.
[94]
The battery module or battery pack may include a power tool; Electric vehicles including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); Alternatively, it may be used as a power source for any one or more medium and large-sized devices in a power storage system.
[95]
[96]
Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art may easily implement the present invention. However, the present invention may be implemented in various different forms, and is not limited to the embodiments described herein.
[97]
[98]
Example 1
[99]
LiCoO 2 , carbon black, and PVDF binder were mixed in a N-methylpyrrolidone solvent in a weight ratio of 95:2.5:2.5 to prepare a slurry for forming a positive electrode, and after coating it on one surface of an aluminum current collector, 130°C After drying in, rolling to form a positive electrode mixture layer.
[100]
Li-Al alloy (Li 50at%, Al 50at%) powder was applied on the positive electrode mixture layer in a ratio of 95:5 by weight of a positive electrode active material: Li-Al alloy, and then rolled to prepare a positive electrode having a coating layer.
[101]
[102]
Example 2
[103]
A positive electrode was manufactured in the same manner as in Example 1, except that the positive electrode active material: Li-Al alloy was in a weight ratio of 90:10.
[104]
[105]
Example 3
[106]
LiCoO 2 , carbon black, PTFE binder was added to the reactor, and Li-Al alloy (Li 50at%, Al 50at%) powder was added to the reactor so that the positive electrode active material: Li-Al alloy was 98:2 by weight, and dried without solvent. Dry mixing was performed to prepare a slurry for forming a positive electrode. This was applied to one side of an aluminum current collector and rolled to form a positive electrode mixture layer.
[107]
[108]
Comparative Example 1
[109]
LiCoO 2 , carbon black, and PVDF binder were mixed in a N-methylpyrrolidone solvent in a weight ratio of 95:2.5:2.5 to prepare a slurry for forming a positive electrode, and after coating it on one surface of an aluminum current collector, 130°C After drying in, rolling to form a positive electrode mixture layer.
[110]
[111]
[Experimental Example: Battery Capacity Evaluation]
[112]
The positive electrodes prepared in Examples 1 to 3 and Comparative Example 1 were used, respectively.
[113]
Moreover, lithium metal was used as a negative electrode.
[114]
An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive electrode and the negative electrode prepared as described above, and after placing the electrode assembly in the case, an electrolyte was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF 6 ) in an organic solvent consisting of ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate (EC/DMC/EMC mixing volume ratio = 3/4/3 ). I did.
[115]
Each half coin cell of lithium secondary battery prepared as described above is charged at 25°C in CCCV mode to 0.1C and 4.2V, and discharged to 2.5V at a constant current of 0.1C. Initial charging and discharging experiments were conducted. The results are shown in Table 1 and FIGS. 3 to 5 below.
[116]
[Table 1]
Initial charging capacity (mAh/g) Initial discharge capacity (mAh/g) Initial efficiency (%)
Example 1 190 140 73.7
Example 2 230 135 58.7
Example 3 155 140 90.3
Comparative Example 1 148 140 94.6
[117]
Referring to Table 1 and FIGS. 3 to 5, in Examples 1 to 3 using a Li-Al alloy, which is a lithium alloy, as an irreversible additive, in Comparative Example 1 in which a lithium alloy was not added. In comparison, it can be seen that the initial charging capacity significantly increased and the initial efficiency decreased. Through this, in the case of Examples 1 to 3, it can be seen that the lithium-based alloy (Alloy) is effectively implemented as an irreversible additive.
Claims
[Claim 1]
A positive electrode for a secondary battery containing a positive electrode active material and a lithium alloy.
[Claim 2]
The method of claim 1, further comprising: a positive electrode mixture layer including the positive electrode active material; And a coating layer formed on the surface of the positive electrode mixture layer and including the lithium-based alloy.
[Claim 3]
The cathode for a secondary battery according to claim 1, comprising a cathode mixture layer in which the cathode active material and lithium alloy are mixed.
[Claim 4]
According to claim 1, The lithium-based alloy (Alloy) is at least one selected from the group consisting of a Li-Al-based alloy, Li-Si-based alloy, Li-Sn-based alloy, Li-Bi-based alloy, and Li-Sb-based alloy. The above positive electrode for secondary battery.
[Claim 5]
The positive electrode according to claim 1, wherein the lithium-based alloy is a Li-Al-based alloy.
[Claim 6]
The cathode for a secondary battery according to claim 5, wherein the Li-Al-based alloy contains 30 to 80 at% of lithium and 20 to 70 at% of aluminum.
[Claim 7]
The cathode for a secondary battery according to claim 1, wherein the cathode active material and the lithium-based alloy are included in a weight ratio of 99:1 to 1:99.
[Claim 8]
The positive electrode of claim 1, wherein the positive electrode active material is a lithium transition metal oxide containing at least one transition metal cation selected from the group consisting of cobalt (Co), nickel (Ni), and manganese (Mn).
[Claim 9]
A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode for a secondary battery according to any one of claims 1 to 8.
[Claim 10]
Forming a positive electrode mixture layer including a positive electrode active material, and forming a coating layer including a lithium alloy (Alloy) on the positive electrode mixture layer; Or forming a positive electrode mixture layer by applying a positive electrode forming slurry including a positive electrode active material and a lithium-based alloy on a positive electrode current collector and rolling it; Method for producing a positive electrode for a secondary battery comprising a.
[Claim 11]
The method of claim 10, wherein forming a positive electrode mixture layer containing the positive electrode active material, and forming a coating layer containing a lithium alloy (Alloy) on the positive electrode mixture layer, the lithium-based alloy on the positive electrode mixture layer A method of manufacturing a positive electrode for a secondary battery in which a coating layer is formed by applying (Alloy) powder and rolling the positive electrode mixture layer coated with the lithium-based alloy powder.
[Claim 12]
The method of claim 10, wherein forming a positive electrode mixture layer by coating and rolling the positive electrode forming slurry containing the positive electrode active material and a lithium alloy (Alloy) on a positive electrode current collector, wherein the positive electrode forming slurry is organic A method of manufacturing a positive electrode for a secondary battery that does not contain a solvent.
[Claim 13]
The method of claim 10, wherein the lithium-based alloy (Alloy) is at least one selected from the group consisting of a Li-Al-based alloy, a Li-Si-based alloy, a Li-Sn-based alloy, a Li-Bi-based alloy, and a Li-Sb-based alloy. The above method of manufacturing a cathode for a secondary battery.
[Claim 14]
The method of claim 10, wherein the positive electrode active material and the lithium-based alloy are included in a weight ratio of 99:1 to 1:99.
[Claim 15]
The method of claim 10, wherein the positive electrode active material is a lithium transition metal oxide containing at least one transition metal cation selected from the group consisting of cobalt (Co), nickel (Ni), and manganese (Mn).