Anode comprising silicon-based anode active material and lithium secondary battery comprising anode

Abstract

Disclosed are an anode comprising a silicon-based anode active material, and a lithium secondary battery comprising the anode. Specifically, disclosed is a lithium secondary battery capable of improving the electrochemical performance of a battery comprising a silicon-based anode active material by using an electrolyte solvent including fluorine.

Description

A negative electrode comprising a silicon-based negative electrode active material and a lithium secondary battery comprising the negative electrode

[0001] The present invention relates to a negative electrode including a silicon-based negative electrode active material and a lithium secondary battery including the negative electrode, and more particularly, to a lithium secondary battery capable of improving the electrochemical performance of a battery including a silicon-based negative electrode active material by using an electrolyte solvent including fluorine.

[0002] With the rapid development of the electronics, communications, and computer industries, the application of energy storage technology is expanding to include camcorders, mobile phones, laptops, PCs, and even electric vehicles. Consequently, the development of lightweight, long-lasting, and highly reliable high-performance secondary batteries is underway.

[0003] Among the secondary batteries currently in use, lithium secondary batteries developed in the early 1990s have a higher operating voltage and much higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and lead-sulfur batteries that use aqueous electrolytes, and have been adopted as power sources for many portable devices.

[0004] Materials containing graphite are widely used as anode active materials for lithium secondary batteries. The average potential when graphite absorbs / releases lithium is approximately 0.1 to 0.2 V (Li / Li + ) and the discharge potential is relatively flat, so the voltage of a battery using graphite is high and constant. However, graphite has the disadvantage of having a very small theoretical capacity of 372 mAh / g.

[0005] To further increase the capacity of lithium secondary batteries, various anode active materials are being studied. Materials that form intermetallic compounds with lithium, such as silicon and tin, are expected to be promising high-capacity anode active materials. In particular, silicon, an alloy-type anode active material with a theoretical capacity (4,200 mAh / g) approximately 10 times higher than that of graphite, is attracting attention as a next-generation anode active material.

[0006] However, silicon-based negative active materials undergo a large volume change (~300%) during charge and discharge, which breaks physical contact between the active materials and causes fragmentation, resulting in rapid deterioration of ionic conductivity, electrical conductivity, etc., and a tendency for rapid reduction in life characteristics.

[0007] Accordingly, various attempts are being made to improve the properties of silicon-based active materials with high theoretical capacity, such as manufacturing Si / Carbon composites. However, the complex manufacturing process and low yield make it difficult to commercialize them.

[0008] The present invention seeks to improve the electrochemical performance of a battery by combining a specific electrolyte solvent used together with a silicon-based negative electrode active material rather than a silicon-based negative electrode active material.

[0009] In order to solve the above problems, the present invention aims to provide a non-aqueous electrolyte having excellent stability for a lithium secondary battery including a silicon-based negative electrode active material, thereby improving the electrochemical performance of the lithium secondary battery.

[0010] The purposes of the present invention are not limited to those mentioned above, and other unmentioned purposes and advantages of the present invention can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the purposes and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0011] In order to solve the above-mentioned technical problem, the present invention provides a lithium ion battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator interposed between the negative electrode and the positive electrode; and a non-aqueous electrolyte, wherein the non-aqueous electrolyte includes a solvent and a lithium salt represented by the following chemical formula 1, and the negative electrode active material includes a silicon-based active material.

[0012] [Chemical Formula 1]

[0013]

[0014] In chemical formula 1,

[0015] R 1 , R 2 and R 3 are each independently hydrogen and an alkyl group having 1 to 5 carbon atoms,

[0016] R 1 , R 2 and R 3 When is an alkyl group having 1 to 5 carbon atoms, X is F, Cl, Br, or I,

[0017] n is an integer from 1 to 5,

[0018] m, o, p are integers from 0 to 3.

[0019] In one embodiment of the present invention, the concentration of the lithium salt may be 0.5 M to 4.0 M (mol / L).

[0020] In one embodiment of the present invention, the solvent of the chemical formula 1 may be included in an amount of 50% to 100% by volume based on 100% by volume of the total non-aqueous solvent.

[0021] In one embodiment of the present invention, the solvent represented by the chemical formula 1 may be a compound represented by the following chemical formula 1a.

[0022] [Chemical Formula 1a]

[0023]

[0024] In one embodiment of the present invention, the positive electrode active material may be at least one selected from the group consisting of a composite oxide of lithium and a metal such as cobalt, manganese, nickel, aluminum, iron, or a combination thereof.

[0025] The solutions to the above problems do not enumerate all features of the present invention. The various features of the present invention, along with their corresponding advantages and effects, can be understood in more detail by referring to the specific examples below.

[0026] The non-aqueous electrolyte used in the present invention has excellent stability even when a silicon-based negative electrode active material is used, and thus can suppress electrolyte decomposition reactions. Therefore, when applied to a lithium secondary battery including a silicon-based negative electrode active material, the life characteristics and high-rate charging performance of the battery can be improved.

[0027] In addition, the non-aqueous electrolyte of the present invention has excellent stability not only for a silicon-based negative electrode active material but also for a battery including lithium metal as a negative electrode active material, thereby improving the life characteristics and high-rate performance of the battery.

[0028] In addition to the effects described above, specific effects of the present invention are described below while explaining specific details for carrying out the invention.

[0029] Figure 1 shows the chemical structures and properties of the solvents included in Example 1 and Comparative Examples 1 and 2.

[0030] Figure 2 shows the LSV evaluation results of the electrolytes of Example 1 and Comparative Examples 1 and 2.

[0031] Figure 3 shows the results of evaluating the Coulombic efficiency of lithium metal batteries containing the electrolytes of Example 1 and Comparative Examples 1 and 2.

[0032] Figure 4 is an FE-SEM image of an aluminum surface confirmed when aluminum corrosion was evaluated using the electrolytes of Example 1 and Comparative Examples 1 and 2.

[0033] Figure 5 shows the results of a comparison of the full-charge performance of lithium metal batteries containing electrolytes of Example 1 and Comparative Examples 1 and 2.

[0034] Figure 6 shows the results of a high rate life evaluation of a lithium metal battery (NP Ratio = 2.5) containing the electrolyte of Example 1.

[0035] Figure 7 shows the results of a high rate life evaluation of a lithium metal battery (NP Ratio = 1) containing the electrolyte of Example 1.

[0036] Figure 8 shows the results of evaluating the initial coulombic efficiency of a lithium battery (containing silicon as a negative electrode active material) containing the electrolytes of Example 2 and Comparative Example 3.

[0037] Figure 9 shows the results of rate characteristic evaluation of a lithium battery (containing silicon as a negative electrode active material) containing the electrolyte of Example 2 and Comparative Example 3.

[0038] Figure 10 shows the results of long-term life performance evaluation of lithium batteries (including silicon as a negative electrode active material) containing the electrolytes of Example 2 and Comparative Example 3.

[0039] Figure 11 shows the results of a high rate life evaluation of a lithium battery (containing silicon as a negative electrode active material) containing the electrolytes of Example 2 and Comparative Example 3.

[0040] Figure 12 shows the results of observing with the naked eye and FE-SEM images of the surface of a silicon negative electrode obtained after disassembling a lithium battery (containing silicon as a negative electrode active material) containing the electrolytes of Example 2 and Comparative Example 3 and conducting a high-rate life evaluation.

[0041] Figure 13 shows a high-magnification FE-SEM image and EDS element mapping results of the surface of a silicon negative electrode obtained after performing a high-rate life evaluation on a lithium battery (containing silicon as a negative electrode active material) containing the electrolyte of Example 2 and Comparative Example 3 and disassembling the battery.

[0042] The principles of preferred embodiments of the present invention will be described in detail with reference to the attached drawings and descriptions below. However, the drawings and descriptions below are intended to illustrate preferred implementation methods among various methods for effectively explaining the features of the present invention, and the present invention is not limited to the drawings and descriptions below.

[0043] While terms such as "first" or "second" may be used to describe various components, these terms should be interpreted solely to distinguish one component from another. For example, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component.

[0044] Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises" or "has" should be understood to indicate the presence of a described feature, number, step, operation, component, part, or combination thereof, but not to exclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0045] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms defined in commonly used dictionaries should be interpreted to have a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0046] Hereinafter, the present invention will be described in more detail.

[0047] The present invention provides a lithium ion battery comprising a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator interposed between the negative electrode and the positive electrode; and a non-aqueous electrolyte, wherein the non-aqueous electrolyte includes a solvent and a lithium salt represented by the following chemical formula 1, and the negative electrode active material includes a silicon-based active material.

[0048] [Chemical Formula 1]

[0049]

[0050] In chemical formula 1,

[0051] R 1 , R 2 and R 3 are each independently hydrogen and an alkyl group having 1 to 5 carbon atoms,

[0052] R 1 , R 2 and R 3 When is an alkyl group having 1 to 5 carbon atoms, X is F, Cl, Br, or I,

[0053] n is an integer from 1 to 5,

[0054] m, o, p are integers from 0 to 3.

[0055] The inventors of the present invention have repeatedly conducted research on a solvent for a non-aqueous electrolyte suitable for use in a lithium secondary battery containing lithium metal or silicon as an anode active material, and as a result, when a solvent of the above chemical formula 1, which has a changed backbone structure of the conventionally widely used DME (1,2-dimethoxyethane) solvent, is applied to a lithium secondary battery, it exhibits significantly improved stability compared to the existing electrolyte, and as a result, electrochemical performance is greatly improved, thereby completing the present invention (see Fig. 1).

[0056] In one embodiment of the present invention, the solvent represented by the above [chemical formula 1] may be 1,1,1-trifluoro-2,3-dimethoxypropane (TFDMP) represented by the following chemical formula 1a.

[0057] [Chemical Formula 1a]

[0058]

[0059] Silicon-based negative electrode active materials exhibit a theoretical capacity approximately 10 times higher than that of conventional graphite negative electrode active materials, making them very effective negative electrode active materials for improving the energy density of batteries. When used together with high-voltage positive electrode active materials, they have the advantage of dramatically improving the energy density of lithium secondary batteries.

[0060] However, lithium secondary batteries using anodes containing silicon-based cathode active materials have a problem in that large volume changes (~300%) occur during charge and discharge, and as a result, physical contact between active materials is broken, causing fragmentation, resulting in deterioration of ionic conductivity, electrical conductivity, and other electrochemical performances.

[0061] In order to solve the above-described problems, the present invention has developed an electrolyte containing a solvent having excellent oxidation stability, and has thus achieved the present invention.

[0062] The compound of formula 1 used as a solvent for the non-aqueous electrolyte of the present invention contains a halogen-containing group (-CX3) and an ether-containing group within one molecule. In a specific embodiment, the compound represented by formula 1a contains a fluorine-containing group (-CF3) and an ether-containing group within one molecule.

[0063] In general, when a fluorine-containing group is included in a molecule, the HOMO (highest occupied molecular orbital) energy level of the molecule is lowered due to the high electronegativity of fluorine, and the lowered HOMO energy level can improve the oxidation stability of the molecule.

[0064] In particular, the compound represented by chemical formula 1a, which is one of the embodiments of the present invention, has only one fluorine-containing group, thereby minimizing side effects (reduced solvability, reduced salt solubility, etc.) that occur when multiple fluorine-containing groups are present.

[0065] As a result, it was thought that the oxidation stability of the electrolyte could be improved when used as a solvent for a non-aqueous electrolyte by including a fluorine-containing group (-CF3) in the molecule, and this was confirmed in the LSV evaluation experiment described below.

[0066] If the oxidation stability of the electrolyte used in a lithium secondary battery containing a lithium metal or silicon-based negative electrode active material is secured, the energy density can be dramatically improved when used with a high-voltage positive electrode material, such as a high-nickel-based positive electrode active material or a high-manganese-based (or over-lithiated oxide) positive electrode active material.

[0067] In addition, the solvent used in the electrolyte of the present invention can provide a binding site for lithium ions by not directly bonding the carbon (-CX3) on which the halogen-containing group is located with an oxygen atom from the perspective of molecular design, which has the effect of improving the solvation power of lithium ions. Conventionally used solvents containing a fluorine-containing group had a phenomenon in which the solvation power was reduced by directly bonding the carbon on which the fluorine-containing group was located with an oxygen atom. However, it is thought that the solvent used in the electrolyte of the present invention can improve the solvation power of lithium ions by having the above-described molecular structure, thereby achieving excellent electrochemical performance.

[0068] In one embodiment of the present invention, the electrolyte contains lithium bis(fluorosulfonyl)imide (LiFSI) as a lithium salt.

[0069] Lithium salts that may be included in addition to LiFSI include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB, which are commonly used in electrolytes. 10 Cl 10 , LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiC4BO8, LiCF3CO2, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC4F9SO3, LiC(CF3SO2)3, (CF3SO2)2NLi, lithium chloroborate, lower aliphatic lithium carboxylates, lithium tetraphenylborate, lithium imide, etc. are possible.

[0070] At this time, the total concentration of LiFSI and other lithium salts in the electrolyte is 0.5 M (mol / L) to 4.0 M, preferably 1.0 M to 3.0 M. At such a high salt concentration, side reactions between lithium metal and the electrolyte can be suppressed, and the effect of preventing corrosion of the positive electrode current collector and dissolution of the positive electrode active material transition metal can be secured. If the concentration of the lithium salt is excessively high, there may be problems of performance deterioration due to low ionic conductivity and reduced electrolyte impregnation due to high viscosity, so it can be appropriately controlled within the above range.

[0071] Meanwhile, the solvent of the above chemical formula 1 may be included in an amount of 50% to 100% by volume based on 100% by volume of the total non-aqueous solvent, and the remaining volume may include a carbonate solvent, an ester solvent, etc., which will be described later.

[0072] Meanwhile, the electrolyte of the present invention may include a cyclic fluorocarbonate solvent together with the solvent of the above chemical formula 1. The cyclic fluorocarbonate solvent is not particularly limited as long as it is a compound in which at least two or more hydrogens are substituted with fluorine in a cyclic carbonate solvent commonly used as a solvent for an electrolyte. Specifically, the cyclic fluorocarbonate solvent may be at least one selected from the group consisting of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate, and preferably fluoroethylene carbonate.

[0073] Meanwhile, in addition to the cyclic fluorocarbonate solvent, the electrolyte of the present invention may include one or more solvents (hereinafter referred to as “chain solvents”) selected from the group consisting of chain carbonate, chain ester, and chain ether solvents as non-aqueous solvents.

[0074] The above chain-type solvent can be used without limitation as a chain-type solvent commonly used in electrolytes for lithium secondary batteries.

[0075] Specifically, the chain carbonate may be at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

[0076] The chain ester may be at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The chain ether may be at least one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether.

[0077] Preferably, the at least one solvent selected from the group consisting of the chain carbonate, chain ester, and chain ether solvents may be at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, methyl propionate, ethyl propionate, dimethyl ether, and diethyl ether.

[0078] Meanwhile, the electrolyte of the present invention may additionally include an SEI film forming additive to improve the overall performance of the battery as needed. The SEI film forming additives usable in the present invention include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), lithium difluorophospate (LiPO2F2), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate; Lithium bis(fluorosulfonyl)imide (LiFOB), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluoro bisoxalato phosphate (WCA), lithium bis(pentafluoroethylsulfonyl)amide (LiBETI), lithium (malonato oxalato) borate (LiMOB), LiPF2C4O8, LiSO3CF3, LiPF4(C2O4), LiP(C2O4)3, LiC(SO2CF3)3, LiBF3(CF3CF2), LiPF3(CF3CF2)3, Li2B 12 F 12, 1,3-propane sultone, 1,3-propene sultone, biphenayl, cyclohexyl benzene, 4-fluorotoluene, succinic anhydride, ethylene sulfate anhydride, tris(methylsilyl)borate, cyclic sulfites, saturated sultones, unsaturated sultones, acyclic sulfones, etc. may be used alone or in combination of two or more, but are not limited thereto. The additive for forming the SEI film may be included in an amount of 0.5 wt% to 10 wt% based on the total weight of the electrolyte to form an excellent film.

[0079] (1) Bipolar

[0080] In the lithium secondary battery of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on one or both surfaces of the positive electrode current collector. The positive electrode active material layer may be formed on the entire surface of the positive electrode current collector or may be formed on only a portion of the surface.

[0081] The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. At this time, the positive electrode current collector may be in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc. having fine irregularities formed on the surface so as to increase adhesion to the positive electrode active material.

[0082] The above positive electrode active material is a compound capable of reversible lithiation and de-lithiation of lithium, and specifically may include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium composite metal oxide may be a lithium-manganese oxide (e.g., LiMnO2, LiMn2O 4　 etc.), lithium-cobalt oxides (e.g., LiCoO2, etc.), lithium-nickel oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese oxides (e.g., LiNi 1-Y Mn Y O2 (here, 0 <Y<1), LiMn 2-z Ni z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn 2-z1 Co z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2(wherein, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni p1 Co q1 Mn r2 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2) etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2)O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1)), and one or more compounds of these may be included.

[0083] Among these, the lithium composite metal oxides are LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni)) in that they can improve the capacity characteristics and stability of the battery. 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.) etc.

[0084] Meanwhile, as another example, the cathode active material may be at least one selected from the group consisting of sulfur-containing compounds such as elemental sulfur (S8); disulfide compounds such as Li2Sn(n<1), 2,5-dimercapto-1,3,4-thiadiazole, 1,3,5-trithiocyanuic acid, organic sulfur compounds, or carbon-sulfur polymers ((C2Sx)n: x=2.5 to 50, n≥2).

[0085] The positive electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the solid content in the positive electrode slurry. In this case, if the content of the positive electrode active material is less than 80 wt%, the energy density may decrease, resulting in a decrease in capacity.

[0086] A binder is used to bind the electrode active material and conductive material and to bind the current collector. Non-limiting examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethacrylic acid (PMA), polymethyl methacrylate (PMMA), polyacrylamide (PAM), polymethacrylamide, polyacrylonitrile (PAN), polymethacrylonitrile, polyimide (PI), alginic acid, alginate, chitosan, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluoroelastomer, and various copolymers thereof.

[0087] Conductive materials are used to further improve the conductivity of electrode active materials. There are no particular limitations on the conductive material as long as it does not cause a chemical change in the battery and is conductive. Examples of conductive materials that can be used include graphite-based materials such as natural graphite or artificial graphite; carbon blacks such as Super-P, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives.

[0088] (2) Cathode

[0089] In the lithium secondary battery of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector. The negative electrode active material layer may be formed on the entire surface of the negative electrode current collector or may be formed on only a portion of the surface.

[0090] In the present invention, the negative active material may be a silicon-based active material, and the silicon-based active material may be Si, SiOx (0 <x<2), SiC, 및 Si 합금으로 이루어진 군에서 선택되는 1종 이상을 포함할 수 있다.

[0091] The above negative active material layer may further include a conductive material and a binder in addition to a silicon-based active material.

[0092] Meanwhile, the negative electrode of the present invention may use a lithium metal negative electrode using lithium metal as the negative electrode active material. The lithium metal negative electrode used in assembling a lithium metal battery may be composed solely of a current collector, a current collector coated with lithium metal, or composed solely of lithium metal.

[0093] The negative electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, aluminum-cadmium alloy, etc. In addition, various forms may be used, such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc., with or without fine unevenness formed on the surface. For example, copper foil may be used as the negative electrode current collector, but is not limited thereto.

[0094] The thickness of the negative electrode current collector is not particularly limited, but is preferably 5 to 100 μm, and more preferably 5 to 50 μm. If the thickness of the current collector is less than 5 μm, handling may be difficult during the process, and if it exceeds 100 μm, the thickness and weight of the battery may increase unnecessarily, which may affect battery performance, such as reducing energy density, so the above range is preferred.

[0095] (3) Membrane

[0096] The separator separates the anode and cathode and provides a path for lithium ions to travel. Any separator commonly used in lithium batteries can be used. Specifically, any separator with low resistance to electrolyte ion transport and excellent electrolyte impregnation capacity can be used. For example, the separator may be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or combinations thereof, and may be in either nonwoven or woven form.

[0097] For example, a polyolefin-based polymer membrane such as polyethylene or polypropylene, or a membrane including a coating layer containing a ceramic component or polymer material to secure heat resistance or mechanical strength may be used, and such a membrane may be used in a single-layer or multi-layer structure. In one embodiment, the membrane may be a membrane manufactured by coating a ceramic coating material containing ceramic particles and an ionic binder polymer on both sides of a polyolefin-based polymer substrate.

[0098] According to one embodiment of the present invention, a lithium secondary battery is provided, including the positive electrode, negative electrode, separator, and electrolyte of the present invention as described above. The shape of the lithium secondary battery is not particularly limited and may be formed into various shapes such as a cylindrical shape, a pouch shape, or a coin shape.

[0099] Hereinafter, preferred examples are presented to aid in understanding the present invention. However, the following examples are only illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is natural that such changes and modifications fall within the scope of the appended claims. Examples and comparative examples of the present invention are described below. Such examples below are only examples of the present invention, and the present invention is not limited to the following examples.

[0100] [Example]

[0101] Manufacturing Example 1 (Manufacture of TFDMP)

[0102] A 1 L round-bottom flask was charged with 600 mL of dry THF and 1 mol (24 g) of NaH, and stirred for 20 minutes under an argon atmosphere at 0°C. Then, 0.4 mol (54 g) of 1,1,1-trifluoro-2,3-propanediol was slowly added using a syringe pump. After adding 1,1,1-trifluoro-2,3-propanediol, the mixture was further stirred at 0°C for 1 hour to prepare a mixture. Then, 1 mol (62.4 mL) of iodomethane was added dropwise to the mixture at 0°C. The mixture was stirred at room temperature for 2 hours, and then slowly heated to reflux overnight. Afterwards, the liquid portion of the mixture was fractionally distilled using a 60 cm fractionating column, and this distillation process was performed three times to obtain the final product (TFDMP).

[0103] (1) Preparation of non-aqueous electrolyte

[0104] The electrolytes of Examples and Comparative Examples were prepared with the compositions shown in Table 1 below. In the table below, DME stands for 1,2-dimethoxyethane, DMP stands for 1,2-dimethoxypropane, EC stands for ethylene carbonate, DEC stands for diethyl carbonate, and FEC stands for fluoroethylene carbonate. The concentration (M) of the lithium salt is the number of moles (mol) of lithium salt per 1 L of total solvent contained in the electrolyte. All electrolytes were prepared in a glove box filled with an inert gas.

[0105] Lithium salt solvent additiveLiFSILiPF6DMEDMPTFDMPEC / DECFECComparative example 12.0M○Comparative example 22.0M○Comparative example 31.0M○Example 12.0M○Example 23.0M○

[0106] (2) Manufacturing of the anode

[0107] NCM 811 (LiNi) as a cathode active material 0.8 Co 0.1 Mn 0.1 O2), Super-P as a conductive agent, polyvinylidene fluoride (PVdF) as a binder, and N-methylpyrrolidone as a solvent were used to prepare a positive electrode active material slurry having a weight ratio of active material:conductive agent:binder of 8:1:1. Then, the positive electrode active material slurry was coated on one side of an aluminum foil, rolled, and dried, and the loading was 10.0 mg / cm 2 A human anode was manufactured.

[0108] (3) Manufacturing of cathode

[0109] lithium metal electrode

[0110] A lithium metal foil with a thickness of 20 μm (manufactured by China Energy Lithium) was used as the cathode.

[0111] silicon electrodes

[0112] An anode was manufactured using Micro Si as an anode active material. Specifically, a slurry of anode active material having a weight ratio of active material:conductive material:binder of 80:0.5:19.5 was manufactured using Micro Si as an anode active material, carboxymethyl cellulose (CMC) as a binder, CNT as a conductive material, and distilled water. Then, the slurry of anode active material was coated on one side of a copper foil, rolled, and dried, and the loading was 23.0 mg / cm. 2 A human negative electrode was manufactured.

[0113] (4) Production of full-cell

[0114] A Swagelok type cell or a 2032-type coin cell was manufactured in a glove box by stacking a separator and a lithium metal electrode of (3) on the positive electrode of the above (2) in the order of negative electrode / separator / positive electrode. A Celgard 2400 product (manufactured by Celgard) made of polyethylene was used as the separator, and the N / P Ratio was set to 2.5. 40 μl of the electrolyte of Example 1 and Comparative Examples 1 and 2 was injected to manufacture a complete cell.

[0115] A Swagelok type cell or a 2032-type coin cell was manufactured in a glove box by stacking a separator and a Micro Si electrode of (3) on the cathode of the above (2) in the order of cathode / separator / anode. A Celgard 2400 product (manufactured by Celgard) made of polyethylene was used as the separator, and the N / P Ratio was set to 2.5. 60 μl of the electrolyte of Example 2 and Comparative Example 3 was injected to manufacture a complete cell.

[0116] Evaluation Example 1. Oxidation Stability Evaluation

[0117] Experiments were conducted to evaluate the oxidation stability of the electrolytes of Example 1 and Comparative Examples 1 and 2. The oxidation stability was evaluated by performing linear sweep voltammetry (LSV) analysis. Specifically, Li / Al half cells were manufactured, and the electrolytes of Example 1 and Comparative Examples 1 and 2 were injected, and then the open circuit voltage (OCV) was 5.0 V (vs. Li / Li + ) up to 0.5mVs -1 The LSV analysis method was performed at a scan rate of . The evaluation results are shown in Fig. 2.

[0118] Referring to Figure 2, the electrolyte of Example 1 (TFDMP) has a voltage of about 4.8 V (vs. Li / Li + ) does not initiate a large oxidation current until 4.0 V (vs. Li / Li), whereas the electrolyte of Comparative Example 1 (DME) does not initiate a large oxidation current until 4.0 V (vs. Li / Li + ), the electrolyte (DMP) of comparative example 2 was 4.4 V (vs. Li / Li + ) it was confirmed that the oxidation current was rapidly initiated in the vicinity (Fig. 2). From this result, it can be confirmed that the electrolyte containing the solvent of the present invention has excellent oxidation stability.

[0119] Evaluation Example 2. Coulombic Efficiency Evaluation

[0120] To confirm the reversibility when the electrolytes of Example 1 and Comparative Examples 1 and 2 were used in a lithium metal battery, the coulombic efficiency was evaluated.

[0121] Specifically, Li / Cu half-cells were manufactured, and the electrolytes of Example 1 and Comparative Examples 1 and 2 were injected, and then 1 mA cm -2The coulombic efficiency was evaluated by applying a current. In a Li / Cu half-cell, lithium ions can be plated on Cu and stripped again depending on the applied current, and the ratio of the amount of lithium ions plated and stripped again was calculated as the coulombic efficiency, and the results are shown in Fig. 3.

[0122] Referring to Fig. 3, it can be confirmed that the half-cells containing the electrolytes of Comparative Examples 1 and 2 exhibit extremely extreme fluctuations in coulombic efficiency throughout the entire cycle range, which is believed to be due to unstable SEI formation and irreversible lithium ion deposition. On the other hand, it can be confirmed that the half-cells containing the electrolyte of Example 1 exhibit relatively stable coulombic efficiency throughout the entire cycle range.

[0123] Evaluation Example 3. Aluminum corrosion evaluation

[0124] To evaluate the oxidation stability of the electrolytes of Example 1 and Comparative Examples 1 and 2, aluminum corrosion was evaluated. Aluminum foil is used as a current collector for the positive electrode. If aluminum surface corrosion occurs due to a reaction between aluminum and the electrolyte under oxidizing conditions, it may adversely affect the performance of the positive electrode due to increased surface resistance, etc.

[0125] Specifically, Li / Al half-cells were fabricated, and the electrolytes of Example 1 and Comparative Examples 1 and 2 were injected, and then the voltage was 5.0 V (vs. Li / Li + ) was applied for 24 hours (Constant voltage experiment). Afterwards, the half-cell was disassembled, and the surface of the aluminum was observed using FE-SEM (field emission scanning electron microscopy; Tescan Mira3 LM FE) to confirm the corrosion of the aluminum (Fig. 4).

[0126] Figure 4 shows the aluminum surface of half cells using the electrolytes of Example 1 and Comparative Examples 1 and 2. It was confirmed that the aluminum surface of the half cells using the electrolytes of Comparative Examples 1 and 2 exhibited very severe corrosion (e.g., cracks, flakes), whereas the aluminum of the half cell using the electrolyte of Example 1 exhibited a very smooth surface without cracks.

[0127] Evaluation Example 4. Full Cell Performance Evaluation

[0128] Cathode: lithium metal electrode

[0129] A full cell containing the electrolyte of Example 1 and Comparative Examples 1 and 2 was manufactured, and a 1.0 C-rate (1.6 mA cm -2 ) was applied to charge / discharge, and the life performance of the complete battery was evaluated, and the results are shown in Fig. 5. The battery containing the electrolyte of Example 1 showed 100% retention up to 450 cycles, demonstrating excellent stability, whereas the battery containing the electrolyte of Comparative Example 1 was confirmed to have deteriorated life performance within 60 cycles, and the battery containing the electrolyte of Comparative Example 2 was confirmed to have deteriorated life performance within 175 cycles.

[0130] Meanwhile, in order to observe the high-rate life performance of the battery containing the electrolyte of the present invention, a complete battery (NP ratio = 2.5) containing the electrolyte of Example 1 was charged at a C-rate of 3.0 (4.8 mA cm -2 ) was applied to evaluate the life performance of the full cell, and the results are shown in Fig. 6. The battery including the electrolyte of the present invention has a life performance of 3.0 C-rate (4.8 mA cm -2 ) showed excellent performance, with a retention of 93% at 550 cycles even under high current charge / discharge conditions.

[0131] In addition, a complete electrode (NP Ratio = 1) containing the electrolyte of Example 1 was charged at a C-rate of 0.5 (2 mA cm -2 ), 1.0 C-rate(4.0 mA cm -2 ) while applying a current of 0.5 C-rate (2 mA cm) and evaluating the life performance of the full cell, and the results are shown in Fig. 7. The battery including the electrolyte of the present invention -2 ) shows 81% retention for 200 cycles under current application conditions and 1.0 C-rate (4.0 mA cm -2 ) showed a retention of 88% for 145 cycles even under current application conditions.

[0132] Cathode: Silicon electrode

[0133] A full cell containing the electrolyte of Example 2 and Comparative Example 3 was manufactured, and the initial coulombic efficiency, high-rate life performance, and long-term life performance were observed, and the results are shown in FIGS. 8 to 10.

[0134] It was confirmed that the battery including the electrolyte of Example 2 exhibited an initial coulombic efficiency of about 85.2%, and the battery including Comparative Example 3, which is a general electrolyte composition, exhibited an initial coulombic efficiency of about 83.5% (Fig. 8).

[0135] Meanwhile, it was confirmed that the battery including the electrolyte of Example 2 showed retention of about 75% even at a high rate of 5.0 C-rate and also showed stable coulombic efficiency throughout the cycle, whereas the battery including the electrolyte of Comparative Example 3, which is a general electrolyte composition, showed retention of about 67%, while at the same time, low coulombic efficiency was observed at a high rate (Fig. 9).

[0136] In addition, when comparing the long-term life performance of the batteries containing the electrolytes of Example 2 and Comparative Example 3, it was confirmed that the capacity retention rate of the battery containing the electrolyte of Comparative Example 3 was lower than that of the battery containing the electrolyte of Example 2 after about 200 cycles (Fig. 10).

[0137] Additionally, the high-rate life performance of the battery containing the electrolyte of the present invention was evaluated. Specifically, when fully charged with the electrolyte of Example 2 and Comparative Example 3, the battery was evaluated at a C-rate of 3.0 (4.8 mA cm -2 ) was applied with a 20-minute time cut-off condition, and a 1.0 C-rate constant current was applied during discharge to perform charge / discharge, and the resulting discharge capacity retention rate is shown in Fig. 11. The battery including the electrolyte of Example 2 showed a capacity retention rate of 81.6% after 300 cycles, while the complete battery including Comparative Example 3, which is a general electrolyte composition, showed a capacity retention rate of about 40.0%.

[0138] The battery, which had undergone a high-rate life performance evaluation for 300 cycles, was disassembled in a glove box to obtain a silicon anode, and the electrode surface was observed with the naked eye and FE-SEM-EDS (Field Emission Scanning Electron Microscopy Energy Dispersive X-ray spectroscopy; JSM-7800F Prime), as shown in Figs. 12 and 13.

[0139] The silicon electrode disassembled from the battery using the electrolyte of Example 2 showed a well-maintained, uniform electrode overall due to a uniform reaction with lithium, whereas the silicon electrode disassembled from the battery using the electrolyte of Comparative Example 3 showed a very uneven surface (Fig. 12).

[0140] Upon closer observation using FE-SEM, it was confirmed that the silicon electrode disassembled from the battery using the electrolyte of Example 2 had clear boundaries between particles, whereas the silicon electrode disassembled from the battery using the electrolyte of Comparative Example 3 had very unclear boundaries between particles due to fragmentation of the silicon particles during repeated charge / discharge processes (Fig. 13).

[0141] It was confirmed that the particles were fragmented and the boundaries between particles were very unclear (Fig. 13).

[0142] From these results, it was confirmed that the electrolyte containing the solvent of the present invention can improve the electrochemical performance of not only a lithium metal battery but also a battery containing silicon as an anode active material.

[0143] It should be understood that the above-described embodiments are illustrative in all respects and not restrictive, and the scope of the present invention is indicated by the patent registration claims described below rather than the detailed description, and all changes or modified forms derived from the meaning and scope of the patent registration claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims

1. A cathode containing a cathode active material; A cathode comprising a cathode active material; A separator interposed between the cathode and the anode; and In a lithium ion battery containing a non-aqueous electrolyte, The above non-aqueous electrolyte Containing a solvent and a lithium salt represented by the following chemical formula 1, A lithium ion battery, wherein the negative active material includes a silicon-based active material. [Chemical Formula 1] In chemical formula 1, R 1 , R 2 and R 3 are each independently hydrogen and an alkyl group having 1 to 5 carbon atoms, R 1 , R 2 and R 3 When is an alkyl group having 1 to 5 carbon atoms, X is F, Cl, Br, or I, n is an integer from 1 to 5, m, o, p are integers from 0 to 3.

2. In paragraph 1, A lithium ion battery, wherein the concentration of the lithium salt is 0.5 M to 4.0 M (mol / L).

3. In paragraph 1, A lithium ion battery, wherein the solvent of the above chemical formula 1 is included in an amount of 50 to 100 volume% with respect to 100 volume% of the total non-aqueous solvent.

4. In paragraph 1, A lithium ion battery, wherein the solvent represented by the above chemical formula 1 is a compound represented by the following chemical formula 1a. [Chemical formula 1a] 5. In paragraph 1, A lithium battery, wherein the positive electrode active material is at least one selected from the group consisting of a composite oxide of lithium and a metal such as cobalt, manganese, nickel, aluminum, iron or a combination thereof.

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