Cross Citation with Related Applications
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0051914 dated May 3, 2019, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification.
[3]
technical field
[4]
The present invention relates to a method for manufacturing a positive electrode for a secondary battery, a positive electrode manufactured as described above, and a lithium secondary battery including the same.
[5]
background
[6]
Recently, 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, a lithium secondary battery has been in the spotlight as a driving power source for a portable device because it is lightweight and has a high energy density. Accordingly, research and development efforts for improving the performance of lithium secondary batteries are being actively conducted.
[7]
In a lithium secondary battery, an organic electrolyte or polymer electrolyte is charged between a positive electrode and a negative electrode made of an active material capable of intercalation and deintercalation of lithium ions, and lithium ions are intercalated/deintercalated from the positive electrode and the negative electrode. Electric energy is produced by a reduction reaction with
[8]
As a positive active material constituting the positive electrode of a lithium secondary battery, lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), lithium manganese oxide (LiMnO 2 or LiMn 2 O 4 , etc.), lithium iron phosphate compound (LiFePO 4 ), etc. this was used In addition, as a method for improving low thermal stability while maintaining the excellent reversible capacity of LiNiO 2 , a lithium composite metal oxide in which a part of nickel (Ni) is substituted with cobalt (Co) or manganese (Mn) (hereinafter simply referred to as ‘NCM-based lithium composite transition metal oxide') was developed. As an anode active material constituting the anode of a lithium secondary battery, a carbon based material such as metal lithium, graphite, or activated carbon, or silicon oxide (SiO α)) are used. Among the negative active materials, metallic lithium was mainly used in the beginning, but as the charging and discharging cycle proceeds, lithium atoms grow on the surface of metallic lithium to damage the separator and damage the battery. Recently, a carbon-based material is mainly used. However, in the case of a carbon-based material, the theoretical capacity is only about 400 mAh/g, so it has a disadvantage that the capacity is small. As an anode active material, a silicon (Si)-based material having a high theoretical capacity (4,200 mAh/g) is used. Therefore, various studies have been conducted to replace the carbon-based material.
[9]
Theoretically, lithium intercalation and desorption reactions into the positive electrode active material layer are completely reversible, but in practice, more lithium than the theoretical capacity of the positive electrode active material is consumed, and only a part of it is recovered during discharge. Accordingly, after the second cycle, a smaller amount of lithium ions are desorbed during charging, but most of the desorbed lithium ions are inserted during discharging. As such, the difference in capacity that appears in the first charge and discharge reaction is called irreversible capacity loss. In a commercial lithium secondary battery, lithium ions are supplied from the positive electrode and lithium is not present in the negative electrode. It is important to minimize losses.
[10]
It is known that the initial irreversible capacity loss of the positive electrode is mostly due to an electrolyte decomposition reaction on the surface of the active material layer, and an SEI film (solid electrolyte membrane, Solid Electrolyte Interface) is formed. Since many lithium ions are consumed in the formation of the SEI film, there is a problem of causing irreversible capacity loss. ), it functions to pass only lithium ions, thereby suppressing further electrolyte decomposition reactions and contributing to the improvement of cycle characteristics of lithium secondary batteries.
[11]
Therefore, there is a need for a method for improving the initial irreversibility caused by the formation of the SEI film, etc., and as one of the methods, pre-lithiation is performed before manufacturing a lithium secondary battery to prevent side reactions occurring during the first charge in advance. Here's a way to make it happen. In this way, when all-lithiation is performed, when charging and discharging of the actually manufactured secondary battery is performed, the first cycle proceeds in a state in which irreversibility is reduced as much as possible, thereby reducing the initial irreversibility.
[12]
Conventional prelithiation has been mostly applied to the negative electrode, and the method includes, for example, a method of depositing lithium on the negative electrode and a method of directly loading lithium powder on the negative electrode. However, in order to deposit lithium on the anode, it is costly to set up a device for deposition, and in mass production, there are disadvantages in that the processability is not good due to the time required. In addition, the method of directly placing the lithium powder on the negative electrode not only poses a risk of ignition in the process of handling the lithium powder, but also causes a problem that lithium is not completely lithiated.
[13]
Accordingly, there is a need to develop a positive electrode for a lithium secondary battery capable of more effective total lithiation.
[14]
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[15]
The present invention provides a positive electrode for a lithium secondary battery capable of securing initial reversibility of the positive electrode, preventing loss of capacity, and improving electrochemical performance such as excellent initial efficiency and lifespan characteristics of a lithium secondary battery, such a positive electrode can be efficiently manufactured An object of the present invention is to provide a method and a lithium secondary battery including the positive electrode.
[16]
means of solving the problem
[17]
The present invention provides a positive electrode comprising a positive electrode active material layer comprising a lithium transition metal oxide on a positive electrode current collector; and pre-lithiation of the positive electrode by immersing the positive electrode in an electrolyte containing a film-forming additive, and charging and discharging the positive electrode using a counter electrode.
[18]
[19]
In addition, the present invention is a positive electrode current collector; a positive electrode active material layer formed on the positive electrode current collector and including a lithium transition metal oxide; and a film formed on the positive electrode active material layer and formed by pre-lithiation.
[20]
[21]
In addition, the present invention provides an electrode assembly including the positive electrode, the negative electrode, and a separator interposed between the positive electrode and the negative electrode; a battery case housing the electrode assembly; and an electrolyte injected into the battery case.
[22]
Effects of the Invention
[23]
According to the present invention, effective prelithiation of the positive electrode can be performed, thereby securing initial reversibility of the positive electrode, preventing loss of capacity, forming a stable film, and excellent initial efficiency and lifespan of a lithium secondary battery It is possible to improve electrochemical performance such as properties.
[24]
Modes for carrying out the invention
[25]
Hereinafter, the present invention will be described in more detail to help the understanding of the present invention. At this time, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor appropriately defines the concept of the term to describe his invention in the best way. It should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention based on the principle that it can be done.
[26]
[27]

[28]
A method of manufacturing a positive electrode for a secondary battery of the present invention includes: providing a positive electrode having a positive electrode active material layer including a lithium transition metal oxide formed thereon on a positive electrode current collector; and pre-lithiation of the positive electrode by immersing the positive electrode in an electrolyte containing a film-forming additive, and charging and discharging the positive electrode using the counter electrode.
[29]
[30]
The manufacturing method of the positive electrode of the present invention will be described in detail step by step below.
[31]
First, a positive electrode in which a positive electrode active material layer including a lithium transition metal oxide is formed on a positive electrode current collector is prepared.
[32]
The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , silver or the like surface-treated may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the positive electrode current collector. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.
[33]
The cathode active material layer includes a cathode active material of lithium transition metal oxide. Any one selected from the group consisting of cobalt (Co), nickel (Ni) and manganese (Mn) may be applied without limitation, and the lithium transition metal oxide is generally used as a cathode active material of a lithium secondary battery. A lithium transition metal oxide containing the above transition metal cations may be used. For example, a layered compound such as lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), or the like, formula Li 1+n Mn 2-n O 4 (where n is 0 to 0.33), LiMnO 3 , LiMn Lithium manganese oxide, such as 2 O 3 , LiMnO 2 , with the formula LiNi 1-m M a m O 2 (where M a= Co, Mn, Al, Cu, Fe, Mg, B or Ga, m = 0.01 ~ 0.3) Ni site-type lithium nickel oxide, the formula LiMn 2-z M b z O 2 (where M b = Co, Ni, Fe, Cr, Zn or Ta, and z= 0.01 to 0.1) or Li 2 Mn 3 M c O 8 (here, M c = Fe, Co, Ni, Cu or Zn) lithium manganese composite oxide, lithium manganese composite oxide having a spinel structure represented by LiNi r Mn 2-r O 4 (here, r = 0.01 to 1), lithium iron phosphate compound (LiFePO 4 ), and the like, but is not limited thereto . Alternatively, the cathode active material may include a lithium composite transition metal oxide represented by Formula 1 below.
[34]
[Formula 1]
[35]
Li a Ni 1-bcd Co b Mn c Q d O 2+δ
[36]
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.
[37]
[38]
In addition, the positive active material layer may include a conductive material and a binder together with the above-described positive active material.
[39]
In this case, the conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it has electrical conductivity without causing chemical change. 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, summer black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, and the like, and one or a mixture of two or more thereof 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 active material layer.
[40]
In addition, the binder serves to improve adhesion between the positive electrode active material particles and the adhesive force 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, carboxymethyl cellulose (CMC) ), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive active material layer.
[41]
[42]
The positive electrode may be manufactured according to a conventional positive electrode manufacturing method. Specifically, the cathode active material and, optionally, a composition for forming a cathode active material layer including a binder and a conductive material may be coated on a cathode current collector, and then dried and rolled. In this case, the types and contents of the positive electrode active material, the binder, and the conductive material are as described above.
[43]
The solvent may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or water, and the like, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is enough to dissolve or disperse the positive electrode active material, the conductive material and the binder in consideration of the application thickness of the slurry and the production yield, and to have a viscosity capable of exhibiting excellent thickness uniformity during application for subsequent positive electrode manufacturing. do.
[44]
Alternatively, the positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating a film obtained by peeling it from the support on the positive electrode current collector.
[45]
[46]
Next, the positive electrode is immersed in an electrolyte containing a film forming additive, and the positive electrode is charged and discharged using a counter electrode to pre-lithiate the positive electrode.
[47]
In the present invention, the positive electrode is pre-lithiated through electrochemical charging and discharging. By pre-lithiation of the anode through electrochemical charging and discharging, it is possible to pre-lithiate the cathode more efficiently in terms of time and cost in the process, as well as to ensure a uniform and precise degree of pre-lithiation. can be adjusted to At this time, since lithium escapes when charging the positive electrode to increase the voltage, it is necessary to include the discharging process to lower the voltage after charging and put lithium back in to prevent loss of capacity.
[48]
In the present invention, a film-forming additive that helps to form a film during pre-lithiation of the positive electrode through electrochemical charging and discharging is added to the electrolyte solution. Through this, a film can be stably and well formed on the surface of the positive electrode during pre-lithiation of the positive electrode, and the lithium secondary battery cell manufactured using the positive electrode having a stable film can have a lifespan even if additives are not added to the electrolyte properties can be improved.
[49]
The film-forming additive may help form an anode film, and specifically, succinonitrile, ethylene glycol bis(propionitrile) ether, adiponitrile (Adiponitrile), sebaconitrile (Sebaconitrile), fluoroethylene carbonate (Fuoroethylene carbonate, FEC) and vinylene carbonate (Vinylene carbonate, VC) may be at least one selected from the group consisting of, more preferably succinonite It may be a reel (Succinonitrile).
[50]
The electrolyte may be used without particular limitation as long as it can serve as a medium through which lithium ions can move. Specifically, as the electrolyte, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based 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 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolanes and the like may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant; A mixture of a low-viscosity linear carbonate-based compound (eg, ethylmethyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 5:95 to 70:30, the performance of the electrolyte may be excellent.
[51]
The film-forming additive may be included in an amount of 0.2 to 15% by weight based on the electrolyte. More preferably, the film-forming additive may be included in an amount of 0.5 to 10% by weight, more preferably, in an amount of 1 to 5% by weight based on the electrolyte. By including the film-forming additive in the above content ratio, a stable film is formed on the surface of the positive electrode active material layer, and a film that is not too thick can be formed to improve the initial efficiency and lifespan characteristics of the lithium secondary battery.
[52]
In the case of the pre-lithiation, the counter electrode may use lithium metal, lithium metal-metal alloy, lithium metal oxide, or the like, and more preferably, lithium metal.
[53]
The pre-lithiation is performed after charging to 3.5 to 5.0V (vs. Li/Li + (based on lithium standard reduction potential)) and then 2.0 to 3.4V (vs. Li/Li + (based on lithium standard reduction potential) )) can be discharged. More preferably, it can charge up to 4.0 to 4.5V (vs. Li/Li + (based on lithium standard reduction potential)), and discharge to 2.9 to 3.2V (vs. Li/Li + (based on lithium standard reduction potential)) can do it During the pre-lithiation of the positive electrode, when electrochemical charging is performed, the lithium in the positive electrode escapes, so a discharge process must be performed after charging. In the present invention, since both charging and discharging processes are performed during pre-lithiation, both an oxide film generated during charging and a reduced film generated during discharging may be formed on the surface of the positive electrode active material layer. The oxide film may be in the form of a chemical bond such as polycarbonate, Li x PF y (x is 0 to 1, y is 1 to 5), OCO 2 - , CH, C=O, CO, etc. The film is Li 2 CO 3 , Li 2 O, LiF, LiOH, CH 2 OCO 2 Li may be in the form of a chemical bond. Since both the oxidation film and the reduction film are formed, there is an effect that a side reaction does not occur significantly even when an oxidation reaction and a reduction reaction occur. In addition, since the present invention discharges lithium after it is discharged through charging, the amount of lithium in the positive electrode after pre-lithiation is not exceeded than the amount of lithium in the positive electrode before pre-lithiation. does not Through this, there is an effect that the structural collapse of the anode due to overlithium does not occur.
[54]
[55]
As described above, the positive electrode manufactured according to the present invention includes a positive electrode current collector; a positive electrode active material layer formed on the positive electrode current collector and including a lithium transition metal oxide; and a film formed on the positive electrode active material layer and formed by pre-lithiation.
[56]
The film may include at least one selected from the group consisting of a nitrile-based compound, a fluorine-based compound, and a carbonate-based compound by a film-forming additive included in the electrolyte during pre-lithiation, more preferably It may include a nitrile-based compound.
[57]
[58]

[59]
According to another embodiment of the present invention, an electrochemical device including the positive electrode is provided. The electrochemical device may specifically be a battery or a capacitor, and more specifically, may be a lithium secondary battery.
[60]
[61]
Specifically, the lithium secondary battery may include: an electrode assembly including a positive electrode, a negative electrode facing the positive electrode, and a separator interposed between the positive electrode and the negative electrode; a battery case housing the electrode assembly; and an electrolyte injected into the battery case, wherein the positive electrode is the same as the positive electrode pre-lithiated according to the present invention described above. In addition, the lithium secondary battery may optionally further include a battery case for accommodating the electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery case.
[62]
In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.
[63]
The anode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface. Carbon, nickel, titanium, one surface-treated with silver, an aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 to 500 μm, and similarly to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.
[64]
The anode active material layer optionally includes a binder and a conductive material together with the anode active material. The anode active material layer may be formed by applying a composition for forming an anode including an anode active material, and optionally a binder and a conductive material on an anode current collector and drying, or casting the composition for forming the anode on a separate support, and then , may be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.
[65]
As the anode 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; metal oxides capable of doping and dedoping lithium, such as SiOα (0 < α < 2), SnO 2 , vanadium oxide, and lithium vanadium oxide; Alternatively, a composite including the metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof 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. Soft carbon and hard carbon are representative of low-crystalline carbon, and high-crystalline carbon is natural or artificial graphite, Kish graphite (Kish) in amorphous, plate-like, flaky, spherical or fibrous shape graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.
[66]
In addition, the binder and the conductive material may be the same as those described above for the positive electrode.
[67]
On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a movement path for lithium ions, and can be used without any particular limitation as long as it is normally used as a separator in a lithium secondary battery. It is preferable to have a low resistance to and excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.
[68]
In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, and are limited to these. it's not going to be
[69]
Specifically, the electrolyte may include an organic solvent and a lithium salt.
[70]
The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based 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 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolanes and the like may be used. Among these, carbonate-based solvents are preferable, and cyclic carbonates (eg, A mixture of ethylene carbonate or propylene carbonate) and a low-viscosity linear carbonate-based compound (eg, ethylmethyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.
[71]
The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. 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 and 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 included in the above range, since the electrolyte has an appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.
[72]
In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.
[73]
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 the field of electric vehicles such as hybrid electric vehicle, HEV).
[74]
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.
[75]
The battery module or battery pack is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium and large-sized devices in a system for power storage.
[76]
[77]
Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.
[78]
[79]
Example 1
[80]
97 wt% of LiCoO 2 as a cathode active material, 1 wt% of Denka black (conductive material), and 2 wt% of PVdF (polyvinylidene difluoride, binder) were added to NMP (N-Methylpyrrolidone) to prepare a cathode mixture slurry.
[81]
The prepared positive electrode mixture slurry was coated on one surface of an aluminum current collector, dried and rolled to prepare a positive electrode.
[82]
After the positive electrode prepared above was cut to a size of 10 cm X 10 cm, succino nitrile (SN) was added to a solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a volume ratio of 3:7. After wetting for 3 hours in an electrolyte in which 1M LiPF 6 is added and 1M LiPF 6 by weight is added, electrochemical charging and discharging are performed using lithium metal as a counter electrode in the presence of electrolyte to pre-lithiation the positive electrode. was carried out. At this time, the prelithiation process was performed as follows.
[83]
[ Charging with 1.0 mA/cm 2 current (OCV→4.35V) → rest 30 minutes → Discharging with 1.0 mA/cm 2 current (4.35V→3.0V)]
[84]
The pre-lithiated positive electrode was washed through EMC through the above process, and then dried at room temperature to prepare a pre-lithiated positive electrode.
[85]
[86]
Example 2
[87]
A pre-lithiated positive electrode was prepared in the same manner as in Example 1, except that succino nitrile (SN) was added in an amount of 3 wt %.
[88]
[89]
Example 3
[90]
A prelithiated positive electrode was prepared in the same manner as in Example 1, except that succino nitrile (SN) was added in an amount of 5% by weight.
[91]
[92]
Example 4
[93]
A pre-lithiated positive electrode was prepared in the same manner as in Example 1 except that succino nitrile (SN) was added in an amount of 20 wt %.
[94]
[95]
Example 5
[96]
A prelithiated positive electrode was prepared in the same manner as in Example 2, except that 3 wt% of fluoroethylene carbonate (FEC) was added instead of 3 wt% of succinonitrile (SN).
[97]
[98]
Example 6
[99]
A prelithiated positive electrode was prepared in the same manner as in Example 2, except that 3 wt% of vinylene carbonate (VC) was added instead of 3 wt% of succinonitrile (SN).
[100]
[101]
Example 7
[102]
A prelithiated positive electrode was prepared in the same manner as in Example 2, except that 3% by weight of diethyloxalate was added instead of 3% by weight of succinonitrile (SN).
[103]
[104]
Comparative Example 1
[105]
A positive electrode was manufactured in the same manner as in Example 1 except that succino nitrile (SN) was not added.
[106]
[107]
Comparative Example 2
[108]
A positive electrode was manufactured in the same manner as in Example 1, except that only the charging process was performed during pre-lithiation as follows.
[109]
[ Charging with 1.0 mA/cm 2 current (OCV→4.35V)]
[110]
[111]
Comparative Example 3
[112]
A positive electrode was manufactured in the same manner as in Example 1, except that a pre-lithiation process was not performed.
[113]
[114]
[Experimental Example 1: Evaluation of initial efficiency and lifespan characteristics]
[115]
After placing a polyethylene separator between the positive electrode and Li-metal prepared in Examples 1 to 7 and Comparative Examples 1 to 3 as a counter electrode, ethylene carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a volume ratio of 3:7 A coin-type half cell was prepared by injecting an electrolyte in which 1M LiPF 6 was dissolved in a solvent mixed with .
[116]
The coin-type full cell prepared above was tested for charging/discharging reversibility using an electrochemical charging/discharging device. At the time of charging, a current was applied at a current density of 0.2 C-rate up to a voltage of 4.35 V (vs. Li/Li+), and during discharging, it was discharged to a voltage of 3.0 V with the same current density. Table 1 shows the first cycle charge capacity and discharge capacity, and the 200 cycle capacity retention rate compared to the first cycle discharge capacity.
[117]
[Table 1]
1st cycle charge capacity (mAh/g) 1st cycle discharge capacity (mAh/g) 1st cycle efficiency (%) 200 cycle capacity retention rate (%)
Example 1 165.1 164.6 99.7 92.3
Example 2 165.2 164.8 99.8 93.1
Example 3 164.9 164.6 99.8 93.0
Example 4 159.7 159.2 99.2 89.3
Example 5 164.9 163.1 98.9 87.8
Example 6 165.5 163.7 98.9 87.2
Example 7 166.3 164.1 98.7 86.9
Comparative Example 1 167.3 164.3 98.2 83.2
Comparative Example 2 14.3 164.9 1153.1 85.2
Comparative Example 3 170.3 165.1 97.0 81.3
[118]
[119]
Referring to Table 1, in the case of Examples 1 to 4, since succino nitrile (SN) was decomposed on the surface of the anode during pre-lithiation of the anode to form a stable film, the first cycle efficiency and the capacity retention rate of 200 cycles were high. appear. On the other hand, the first cycle efficiency and 200 cycle capacity retention rate compared to Example 4, in which the concentration of succino nitrile (SN) during pre-lithiation is 0.2 to 15 wt% in Examples 1 to 3 exceeds 15 wt% This turned out to be better. In the case of Example 4, the concentration of succino nitrile (SN) was high during pre-lithiation, and the film was too thick, which was slightly lower than in Examples 1-3. In addition, as in Examples 5 to 7, when fluoroethylene carbonate, vinylene carbonate, and diethyl oxalate additives were used, the 200 cycle capacity retention rate was excellent compared to Comparative Examples 1 to 3, but compared to Examples 1 to 4 appeared somewhat lower. The reason is that the additives of Examples 5 to 7 also help to form the film of the positive electrode, and the cycle maintenance rate is improved compared to the comparative example. This is thought to be because there is a remarkable effect of suppressing the degradation of the positive electrode.
[120]
On the other hand, in the case of Comparative Example 1, since there is no succino nitrile (SN) during pre-lithiation, an unstable film without a nitrile group is formed on the surface film, so that the first cycle efficiency and the 200-cycle capacity retention rate are examples appeared significantly lower than In the case of Comparative Example 2, only charging was performed during pre-lithiation, so that the charging capacity of the first cycle was hardly observed. The reason that the first cycle discharge capacity was expressed as in the example is because lithium entered the positive electrode from the lithium metal electrode, which is the counter electrode, because it is a half cell. However, when used as a full cell, the capacity itself will not be expressed because there is no lithium source on the negative side either. In the case of Comparative Example 3, since the prelithiation itself was not performed, the surface film was unstable, so that the first cycle efficiency and the capacity retention rate of 200 cycles were remarkably low.
[121]
[122]
Claims
[Claim 1]
providing a positive electrode in which a positive electrode active material layer including a lithium transition metal oxide is formed on a positive electrode current collector; and pre-lithiation of the positive electrode by immersing the positive electrode in an electrolyte containing a film-forming additive, and charging and discharging the positive electrode using a counter electrode; A method of manufacturing a positive electrode for a secondary battery comprising a.
[Claim 2]
According to claim 1, wherein the film forming additive is succinonitrile (Succinonitrile), ethylene glycol bis (propionitrile) ether (Ethyleneglycolbis (propionitrile) ether), adiponitrile (Adiponitrile), sebaconitrile (Sebaconitrile) ), a method of manufacturing a positive electrode for a secondary battery at least one selected from the group consisting of fluoroethylene carbonate (FEC) and vinylene carbonate (VC).
[Claim 3]
The method of claim 1 , wherein the film-forming additive is succinonitrile.
[Claim 4]
The method of claim 1 , wherein the film-forming additive is included in an amount of 0.2 to 15% by weight based on the electrolyte.
[Claim 5]
The method of claim 1 , wherein in the pre-lithiation step, charging is performed to a lithium standard reduction potential of 3.5 to 5.0V.
[Claim 6]
The method of claim 1 , wherein the pre-lithiation comprises discharging to 2.0 to 3.4V based on a lithium standard reduction potential after charging.
[Claim 7]
positive electrode current collector; a positive electrode active material layer formed on the positive electrode current collector and including a lithium transition metal oxide; and a film formed on the positive electrode active material layer and formed by pre-lithiation. A positive electrode for a secondary battery manufactured according to claim 1 comprising a.
[Claim 8]
The positive electrode for a secondary battery according to claim 7, wherein the film comprises at least one selected from the group consisting of a nitrile-based compound, a fluorine-based compound, and a carbonate-based compound.
[Claim 9]
The positive electrode for a secondary battery according to claim 7, wherein the film includes a nitrile-based compound.
[Claim 10]
An electrode assembly comprising the positive electrode according to claim 7, the negative electrode, and a separator interposed between the positive electrode and the negative electrode; a battery case housing the electrode assembly; and an electrolyte injected into the battery case; A lithium secondary battery comprising a.