Lithium secondary battery electrolyte and lithium secondary battery including the same

Abstract

The present invention relates to a lithium secondary battery electrolyte comprising a fluorophosphate compound represented by chemical formula 1 and a lithium secondary battery comprising the lithium secondary battery electrolyte, the lithium secondary battery comprising the electrolyte according to one embodiment of the present invention having excellent lifespan characteristics without being reduced in power even at high voltage, and a lithium secondary battery comprising the lithium secondary battery electrolyte. The present invention has a high capacity recovery rate at high temperatures and excellent storage stability. In addition, the lithium secondary battery including the electrolyte according to one specific embodiment has excellent power characteristics by reducing battery internal resistance, and also has excellent cycle characteristics and stability during high temperature and high voltage charging.

Description

Technical Field

[0001] The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery comprising the lithium secondary battery electrolyte. Background Art

[0002] In recent years, as portable electronic devices have become widespread and smaller, thinner, and lighter, research has been actively conducted on secondary batteries used as their power sources to reduce their size and weight and enable long-term charge and discharge.

[0003] Lithium secondary batteries generate electrical energy through oxidation and reduction reactions when lithium ions are intercalated and deintercalated in the positive and negative electrodes. The lithium secondary batteries are manufactured by using materials that can intercalate and deintercalate lithium ions as the negative and positive electrodes, and filling an organic electrolyte or a polymer electrolyte between the positive and negative electrodes.

[0004] Currently, widely used organic electrolytes include ethylene carbonate, propylene carbonate, dimethoxyethane, γ-butyrolactone, N,N-dimethylformamide, tetrahydrofuran, and acetonitrile. However, these organic electrolytes are generally volatile and highly flammable. When used in lithium-ion secondary batteries at high temperatures, they can cause safety issues, such as internal short circuits and fires caused by internal heat generated by overcharging or overdischarging.

[0005] In addition, during the initial charging of a lithium secondary battery, lithium ions released from the lithium metal oxide serving as the positive electrode migrate to the carbon electrode serving as the negative electrode and are embedded in the carbon. At this time, the reactivity of lithium is strong, and the surface of the carbon particles serving as the negative electrode active material reacts with the electrolyte while forming a thin film called a solid electrolyte interface (SEI) film on the surface of the negative electrode.

[0006] The performance of lithium secondary batteries is significantly influenced by the composition of the organic electrolyte and the SEI film formed by the reaction between the organic electrolyte and the electrodes. Specifically, the SEI film inhibits side reactions between the carbon material and the electrolyte solvent, such as inhibiting the decomposition of the electrolyte on the surface of the carbon particles used as the negative electrode, and preventing the collapse of the negative electrode material due to the electrolyte solvent intercalating (co-intercalating) into the negative electrode material. Furthermore, it fully fulfills its role as a conventional lithium ion channel, thereby minimizing the degradation of battery performance.

[0007] However, as lithium secondary batteries charge and discharge, the structure of the positive electrode active material collapses, causing metal ions to dissolve from the positive electrode surface. The dissolved metal ions are then electrodeposited on the negative electrode, causing negative electrode degradation. This degradation phenomenon tends to accelerate further when the positive electrode potential increases or the battery is exposed to high temperatures. Therefore, various studies have been conducted to develop new organic electrolytes containing various additives for stabilizing the SEI film. Summary of the Invention

[0008] (1) Technical issues to be resolved

[0009] An object of one embodiment is to provide a lithium secondary battery electrolyte that can achieve excellent battery characteristics such as high-temperature stability, charge and discharge characteristics, and power characteristics.

[0010] Another embodiment aims to provide a lithium secondary battery having excellent battery characteristics such as high-temperature stability, charge and discharge characteristics, and power characteristics.

[0011] (2) Technical solution

[0012] One embodiment provides a lithium secondary battery electrolyte, comprising: a lithium salt; a non-aqueous organic solvent; and a compound represented by the following Chemical Formula 1.

[0013] [Chemical Formula 1]

[0014]

[0015] In the chemical formula 1, R 11 、R 12 and R 13 are independently hydrogen, C 1-10 Alkyl, C 2-10 Alkenyl, C 3-10 Cycloalkyl or C 6-20 Aryl, R 21 、R 22 and R 23 are independently hydrogen, C 1-10 Alkyl, C 2-10 Alkenyl, C 3-10 Cycloalkyl or C 6-20 Aryl, the R 11 、R 12 、R 13 、R 21 、R 22 and R 23 The alkyl, alkenyl, cycloalkyl and aryl groups may be substituted with halogen groups.

[0016] Another embodiment provides a lithium secondary battery including the lithium secondary battery electrolyte according to the one embodiment, a negative electrode, and a positive electrode.

[0017] (3) Beneficial effects

[0018] The present invention relates to a lithium secondary battery electrolyte comprising a phosphorofluoridate compound represented by Chemical Formula 1 and a lithium secondary battery comprising the lithium secondary battery electrolyte. The lithium secondary battery comprising the electrolyte according to a specific embodiment does not reduce power even at high voltage, has excellent life characteristics, has a high capacity recovery rate at high temperatures, and has excellent storage stability. In addition, the lithium secondary battery comprising the electrolyte according to a specific embodiment has a reduced battery internal resistance and excellent power characteristics, and also has excellent cycle characteristics and stability when charged at high temperature and high voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic plan view of a lithium secondary battery according to one embodiment.

[0020] Figure 2 It is along Figure 1 A cross-sectional view taken along line II'. Best Practice

[0021] The embodiments described in this specification can be modified into various other forms, and therefore, the technology according to a specific embodiment is not limited to the embodiment described below. Furthermore, throughout the specification, when a description is made of "including or comprising," "having," "containing," or "having" a certain component, unless otherwise specifically stated to the contrary, it means that other components may be further included, rather than excluding other components, and does not exclude unlisted elements, materials, or processes.

[0022] The numerical ranges used in this specification include lower and upper limits and all values ​​within the range, increments logically derived from the form and width of the defined range, all values ​​defined therein, and all possible combinations of upper and lower limits of numerical ranges defined in different forms. As an example, when the content of a composition is defined as 10% to 80% or 20% to 50%, it should be interpreted that the numerical range of 10% to 50% or 50% to 80% is also recorded in this specification. In the present invention, unless otherwise specifically defined, values ​​outside the numerical range that may appear due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0023] Hereinafter, unless specifically defined otherwise, "about" in this specification may be considered to mean a value within 30%, 25%, 20%, 15%, 10%, or 5% of the explicitly stated value.

[0024] The terms "alkyl" and "alkenyl" used in this specification include all forms of straight or branched chains.

[0025] The term "discharge" used in this specification refers to the process of lithium ions being deintercalated from the negative electrode, and "charge" refers to the process of lithium ions being intercalated into the negative electrode.

[0026] Hereinafter, a lithium secondary battery electrolyte according to a specific embodiment will be described.

[0027] One embodiment provides a lithium secondary battery electrolyte, comprising: a lithium salt; a non-aqueous organic solvent; and a compound represented by the following Chemical Formula 1.

[0028] [Chemical Formula 1]

[0029]

[0030] In the chemical formula 1, R 11 、R 12 and R 13 are independently hydrogen, C 1-10 Alkyl, C 2-10 Alkenyl, C 3-10 Cycloalkyl or C 6-20 Aryl, R 21 、R 22 and R 23 are independently hydrogen, C 1-10 Alkyl, C 2-10 Alkenyl, C 3-10 Cycloalkyl or C 6-20 Aryl, the R 11 、R 12 、R 13 、R 21 、R 22 and R 23 The alkyl, alkenyl, cycloalkyl and aryl groups may be substituted by halogen groups. For example, they may be substituted by one or more halogen atoms selected from the group consisting of I, Br, Cl and F.

[0031] An electrolyte solution according to one embodiment includes a fluorinated phosphate compound in which a phosphorus (P) atom is substituted with one fluorine atom (monofluorinated), thereby achieving excellent battery characteristics such as high-temperature storage property and power characteristics.

[0032] Specifically, as lithium secondary batteries charge and discharge, the structure of the positive electrode active material collapses, leading to the dissolution of metal ions from the positive electrode surface. These ions are then electrodeposited on the negative electrode, causing negative electrode degradation. This degradation phenomenon can be accelerated when the positive electrode potential increases or the battery is exposed to high temperatures. Furthermore, as the driving voltage of lithium secondary batteries increases, the thin film on the positive electrode surface decomposes, exposing the positive electrode surface to the electrolyte, which can trigger side reactions with the electrolyte.

[0033] As a means of solving this problem, one embodiment provides a fluorophosphate compound represented by the chemical formula 1. The fluorophosphate compound contained in the electrolyte according to one embodiment can further stabilize the positive electrode structure by coordinating with the transition metal of the positive electrode, thereby preventing the battery swelling caused by gas generation during high-temperature storage. Therefore, the thickness increase rate at high temperature can be significantly reduced, or even when driven at high voltage, the reduction in normal temperature life characteristics can be prevented.

[0034] In one embodiment, the R 11 、R 12 and R 13 can be independently hydrogen, C 1-5 Alkyl, C 2-5 Alkenyl, C 3-6 Cycloalkyl or C 6-10 Aryl, the R 21 、R 22 and R 23 can be independently hydrogen, C 1-5 Alkyl, C 2-5 Alkenyl, C 3-6 Cycloalkyl or C 6-10 Aryl. The alkyl, alkenyl, cycloalkyl and aryl groups may be substituted with, but not limited to, halogen groups.

[0035] In one embodiment, the R 11 、R 12 and R 13 can be independently hydrogen, C 1-3 Alkyl, C 2-3 Alkenyl, C 5-6 Cycloalkyl or C 6-8 Aryl, the R 21 、R 22 and R 23 can be independently hydrogen, C 1-3 Alkyl, C 2-3 Alkenyl, C 5-6 Cycloalkyl or C 6-8 Aryl. The alkyl, alkenyl, cycloalkyl and aryl groups may be substituted with, but not limited to, halogen groups.

[0036] In one embodiment, the R 11 、R 12 and R 13 Can be independently C 1-3 Alkyl, the R 21 、R 22 and R 23 Can be independently C 1-3 alkyl.

[0037] In one embodiment, the R 11 、R 12 and R 13 Can be the same and C 1-3 Alkyl, the R 21 、R 22 and R 23 Can be the same and C 1-3 alkyl.

[0038] In one embodiment, the R 11 、R 12 and R 13 At least one of them may be an alkyl group, and the rest may be hydrogen. 21 、R 22 and R 23 At least one of them may be an alkyl group, and the rest may be hydrogen.

[0039] Specifically, the compound represented by Chemical Formula 1 may be a compound represented by the following Chemical Formula 1-1 or a compound represented by the following Chemical Formula 1-2.

[0040] [Chemical Formula 1-1]

[0041] ;

[0042] [Chemical formula 1-2]

[0043] .

[0044] However, this is merely an example of the compound represented by Chemical Formula 1 and is not necessarily limited thereto.

[0045] In one embodiment, the content of the compound represented by Chemical Formula 1 may be 0.01 wt % to 5.0 wt % of the total weight of the electrolyte. Alternatively, the content of the fluorophosphate compound may be, for example, 0.01 wt % to 3.0 wt %, 0.1 wt % to 5.0 wt %, 0.1 wt % to 4.0 wt %, 0.1 wt % to 3.0 wt %, 0.1 wt % to 2.0 wt %, 0.1 wt % to 1.5 wt %, 0.1 wt % to 1.0 wt %, 0.2 wt % to 0.8 wt %, 0.3 wt % to 0.7 wt %, or about 0.5 wt %. However, the above range is merely an example and is not necessarily limited to the above range.

[0046] The non-aqueous organic solvent included in the electrolyte according to an embodiment may include a solvent selected from cyclic carbonate solvents, linear carbonate solvents and their mixed solvents. The cyclic carbonate solvent may be selected from ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate and their mixtures, and the linear carbonate may be selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, isopropyl methyl carbonate, ethyl propyl carbonate and their mixtures.

[0047] The polarity of the cyclic carbonate solvent is higher, can fully dissociate lithium ion, but has high viscosity, therefore may have the shortcoming that ionic conductivity is low.Therefore, the cyclic carbonate solvent also can be mixed with the straight-chain carbonate solvent with low polarity but low viscosity and use.In one embodiment, when the nonaqueous organic solvent comprises cyclic carbonate solvent and straight-chain carbonate solvent simultaneously (that is, when comprising their mixed solvent), the volume ratio of cyclic carbonate solvent and straight-chain carbonate solvent can be 1:1 to 1:9, or for example can be 1:1 to 1:8,1:1 to 1:6,1:1 to 1:5,1:2 to 1:4 or about 1:3.

[0048] In one embodiment, the electrolyte may further include an additive in addition to the compound represented by Chemical Formula 1. The additive may include, for example, one or more selected from fluorine-substituted carbonate-based compounds, sulfinyl-containing compounds, oxaloborate-based compounds, oxalophosphate-based compounds, and vinylene carbonate-based compounds.

[0049] In one embodiment, the sulfinyl group-containing compound may be any one or more selected from a sulfone group, a sulfite group, a sulfonate group, a sultone group, and a sulfate group. In one embodiment, the fluorine-substituted carbonate group compound may use fluoroethylene carbonate (FEC), and the sulfinyl group-containing compound may use propene sultone (1,3-propene sultone (PRS; Prop-1-ene-1,3-sultone)), 1,3-propane sultone (PS), or vinyl sulfate (ESA). Therefore, the electrolyte according to one embodiment may further include an additive containing any one or more selected from fluoroethylene carbonate (FEC), propene sultone (PRS), 1,3-propane sultone (PS), and vinyl sulfate (ESA).

[0050] The electrolyte according to one embodiment includes the compound represented by Chemical Formula 1 and ethylene carbonate (FEC) as an additive, and may further include one or more of propylene sultone (PRS), 1,3-propane sultone (PS), and vinyl sulfate (ESA).

[0051] Alternatively, the electrolyte according to one embodiment may further include the compound represented by Chemical Formula 1 and a combination of fluoroethylene carbonate (FEC), propylene sultone (PRS), 1,3-propane sultone (PS), and vinyl sulfate (ESA) as additives.

[0052] Alternatively, the electrolyte according to one embodiment may further include lithium difluorobis(oxalato)phosphate (LiPF2(C2O4)2, LiDFBOP) or lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB) as an additive.

[0053] When the electrolyte according to one embodiment includes the above-mentioned additive, the content of the additive may be 0.1 wt % to 10.0 wt % or 0.1 wt % to 8.0 wt %, 0.1 wt % to 6.0 wt %, 0.1 wt % to 5.0 wt %, 1.0 wt % to 5.0 wt %, 1.0 wt % to 4.0 wt %, 2.0 wt % to 4.0 wt %, 2.0 wt % to 3.0 wt % or about 2.5 wt % of the total weight of the electrolyte.

[0054] In one embodiment, the lithium salt contained in the electrolyte is not particularly limited, but can be selected from, for example, LiPF6, LiBF4, LiClO4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, LiN(CF3SO2)2, LiN(SO3C2F5)2, LiN(SO2F)2, LiCF3SO3, LiC4F9SO3, LiC6H5SO3, LiSCN, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein x and y are independently natural numbers), one or more of LiCl, LiI and LiB(C2O4)2.

[0055] The concentration of the lithium salt may be 0.1M to 2.0M, 0.7M to 1.5M, or approximately 1.0M. When the concentration of the lithium salt is less than 0.1M, the conductivity of the electrolyte decreases, thereby potentially reducing the performance of the electrolyte. When the concentration of the lithium salt exceeds 2.0M, the viscosity of the electrolyte increases, potentially reducing the mobility of lithium ions. The lithium salt acts as a source of lithium ions in the battery, allowing the lithium secondary battery to perform basic operation.

[0056] The lithium secondary battery electrolyte according to one embodiment is generally stable at -20°C to 60°C or 40°C to 60°C, and maintains electrochemically stable characteristics above 4.20V, specifically above 4.30V or above 4.35V, based on the positive electrode potential. Therefore, it can be applied to all lithium secondary batteries such as lithium ion batteries and lithium polymer batteries.

[0057] Another specific embodiment provides a lithium secondary battery including the lithium secondary battery electrolyte according to one embodiment above, a positive electrode, and a negative electrode.

[0058] A lithium secondary battery according to one embodiment includes an electrolyte including a fluorophosphate compound in which one fluorine atom is substituted with a phosphorus (P) atom (monofluorinated), thereby achieving excellent battery characteristics such as high-temperature storage and power characteristics.

[0059] The fluorophosphate compound contained in the lithium secondary battery electrolyte according to one embodiment coordinates with the transition metal of the positive electrode to further stabilize the positive electrode structure, thereby suppressing side reactions between the positive electrode surface and the electrolyte during high-temperature storage, thereby preventing decomposition of the electrolyte, thereby preventing the generation of gas and effectively suppressing the swelling phenomenon of the battery, thereby improving the high-temperature storage stability of the lithium secondary battery. In addition, the cycle life characteristics and stability can also be improved at high temperatures and high voltages.

[0060] Specifically, when a lithium secondary battery prepared from the lithium secondary battery electrolyte according to one embodiment is placed at high temperature for a long time, the thickness increase rate of the battery is very low, being 110% or less, and thus having excellent high-temperature storage stability.

[0061] Non-limiting examples of the secondary battery according to one embodiment include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, a lithium ion polymer secondary battery, or the like.

[0062] Figure 1 and Figure 2 1 and 2 are schematic plan views and cross-sectional views respectively illustrating a lithium secondary battery according to an exemplary embodiment. Figure 2 It is along Figure 1 A cross-sectional view taken along line II'.

[0063] Reference Figure 1 and Figure 2 , a lithium secondary battery according to an exemplary embodiment may include a positive electrode 100 and a negative electrode 130 .

[0064] The positive electrode 100 may include a positive electrode collector 105 and a positive electrode active material layer 110 formed on the positive electrode collector 105. For example, the positive electrode active material layer 110 may be formed on one side or both sides of the positive electrode collector 105.

[0065] For example, the positive electrode active material layer 110 may include a positive electrode active material, and may include a positive electrode binder and a conductive material as needed.

[0066] For example, the positive electrode 100 can be manufactured by mixing and stirring a positive active material, a positive binder, a conductive material, a dispersion medium, etc. to prepare a positive electrode slurry, and then coating the positive electrode slurry on the positive electrode collector 105 and performing drying and rolling.

[0067] For example, the positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and preferably may include aluminum or an aluminum alloy.

[0068] The positive electrode active material may be a material that can reversibly intercalate and deintercalate lithium ions. For example, the positive electrode active material may be a lithium metal oxide containing metal elements such as nickel, cobalt, manganese, and aluminum.

[0069] In one embodiment, the positive active material may include lithium metal oxide particles containing nickel.

[0070] In one embodiment, the lithium metal oxide particles may contain 80 mol % or more of nickel based on the total molar number of all elements excluding lithium and oxygen. In this case, a lithium secondary battery with a high capacity can be realized.

[0071] In one embodiment, the lithium metal oxide particles may contain 83 mol % or greater, 85 mol % or greater, 90 mol % or greater, or 95 mol % or greater nickel, based on the total moles of all elements excluding lithium and oxygen.

[0072] In one embodiment, the lithium metal oxide particles may further contain at least one of cobalt and manganese. In this case, a lithium secondary battery with further improved power characteristics and penetration stability can be realized.

[0073] In one embodiment, the lithium metal oxide particles may be of the formula Li a Ni x M 1-x O 2+y In this case, in the chemical formula, M may be at least one of Co, Mn, Al, Zr, Ti, Cr, B, Mg, Ba, Si, Y, W, Sr, Na, Ca, Hf, V, Nb, Ta, Mo, Fe, Cu, Ag, Zn, Ga, C, Sn, and Zr. In the chemical formula, 0.9≤a≤1.2, 0.5≤x≤0.99, and 0.1≤y≤0.1 may be achieved.

[0074] In one embodiment, the lithium metal oxide particles may further include a doping element. For example, the doping element may include at least one of Al, Ti, Ba, Zr, Si, B, Mg, P, Sr, W, and La. In this case, a lithium secondary battery with further improved lifespan characteristics can be achieved.

[0075] In one embodiment, the lithium metal oxide particles may further include a coating element. For example, the coating element may include at least one of Al, Ti, Ba, Zr, Si, B, Mg, P, Sr, W, and La. In this case, a lithium secondary battery with further improved lifespan characteristics can be achieved.

[0076] In one embodiment, the positive electrode may include a composite metal oxide of a transition metal selected from any one or more of cobalt, manganese and nickel and lithium as a positive electrode active material. For example, the positive electrode may include a positive electrode active material containing a lithium-nickel-cobalt-manganese-based composite oxide.

[0077] In one embodiment, when a secondary battery electrolyte comprising a fluorophosphate compound and a positive electrode active material comprising a nickel-cobalt-manganese-based active material are simultaneously applied to a secondary battery, there is the advantage that the problems of swelling and reduced high-temperature stability of nickel-cobalt-manganese-based active materials having a high nickel content can be solved.

[0078] The positive electrode active material according to one embodiment may be, for example, Li x (Ni a Co b Mn c )O2 (0.5 < x < 1.3, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), Li x (Ni a Co b Mn c )O4 (0.5 < x < 1.3, 0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2) or a mixture thereof, or may be Li x (Ni a Co b Mn c )O2, where 0.90 ≤ x ≤ 1.10, 0.3 ≤ a ≤ 0.9, 0.05 ≤ b < 0.5, 0.05 ≤ c < 0.5, a + b + c = 1. Alternatively, the positive electrode active material may be, for example, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 or a mixture thereof.

[0079] In one embodiment, the positive electrode binder may include organic binders such as polyvinylidene fluoride (PVDF; polyvinylidenefluoride), vinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyacrylonitrile, polymethyl methacrylate; and water - based binders such as styrene - butadiene rubber (SBR). In addition, for example, the positive electrode binder may also be used together with thickeners such as carboxymethyl cellulose (CMC).

[0080] In one embodiment, the conductive material may include carbon - based conductive materials such as graphite, carbon black, graphene, carbon nanotubes; and metal - based conductive materials such as perovskite substances such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3.

[0081] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 formed on the negative electrode current collector 125. For example, the negative electrode active material layer 120 may be formed on one or both surfaces of the negative electrode current collector 125.

[0082] For example, the negative electrode active material layer 120 may contain a negative electrode active material and, if necessary, may contain a negative electrode binder and a conductive material.

[0083] For example, the negative electrode 130 may be manufactured by preparing a negative electrode paste by mixing and stirring a negative electrode active material, a negative electrode binder, a conductive material, a solvent, etc., and then coating the negative electrode paste on the negative electrode current collector 125 and drying and calendaring it.

[0084] For example, the negative electrode current collector 125 may contain gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably may contain copper or a copper alloy.

[0085] For example, the negative electrode active material may be a material that allows lithium ions to be inserted and extracted. For example, the negative electrode active material may contain a lithium alloy, a carbon-based material, a silicon-based material, etc.

[0086] For example, the lithium alloy may contain metal elements such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, and indium.

[0087] For example, the carbon-based active material may contain crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.

[0088] For example, the amorphous carbon may contain hard carbon, coke, mesocarbon microbeads (MCMB) calcined at a temperature below 1500 °C, mesophase pitch-based carbon fibers (MPCF), etc.

[0089] For example, the crystalline carbon may contain natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0090] For example, the negative electrode active material may contain a silicon-based active material. For example, the silicon-based active material may contain Si, SiO x (0 < x < 2), silicon-carbon composite (Si / C), SiO / C, Si-metal (Metal), etc. In this case, a lithium secondary battery with a high capacity can be achieved.

[0091] For example, when the negative electrode active material contains a silicon-based active material, there may be a problem of an increase in the battery thickness during repeated charge and discharge. The lithium secondary battery according to an exemplary embodiment may slow down the increase rate of the battery thickness by including the above electrolyte.

[0092] In one embodiment, the content of silicon atoms in the negative active material may be 1 wt % to 20 wt %, 1 wt % to 15 wt %, or 1 wt % to 10 wt %.

[0093] The negative electrode binder and conductive material may be substantially the same or similar to the positive electrode binder and conductive material described above. For example, the negative electrode binder may be a water-based binder such as styrene-butadiene rubber (SBR). Furthermore, the negative electrode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0094] The electrolyte according to one embodiment can form an electrode electrolyte interphase with excellent stability on the surface of the electrode, thereby effectively suppressing side reactions between the electrode active material (e.g., lithium metal oxide, carbon-based material, silicon-based material) and the electrolyte.

[0095] In one embodiment, the area of ​​the negative electrode 130 may be larger than that of the positive electrode 100. In this case, lithium ions generated from the positive electrode 100 may be smoothly transferred to the negative electrode 130 without being precipitated in the middle.

[0096] For example, the positive electrodes 100 and the negative electrodes 130 may be alternately and repeatedly disposed to form the electrode assembly 150 .

[0097] In one embodiment, the separator 140 may be interposed between the positive electrode 100 and the negative electrode 130. For example, the separator 140 may be formed into the electrode assembly 150 by winding, stacking, z-folding, or the like.

[0098] For example, the separator 140 may include a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. In addition, for example, the separator 140 may also include a non-woven fabric formed of high-melting-point glass fiber, polyethylene terephthalate fiber, etc.

[0099] The lithium secondary battery according to the exemplary embodiment may include a positive electrode lead 107 connected to the positive electrode 100 and protruding outside the case 160 , and a negative electrode lead 127 connected to the negative electrode 130 and protruding outside the case 160 .

[0100] For example, the positive electrode 100 and the positive electrode lead 107 can be electrically connected. Similarly, the negative electrode 130 and the negative electrode lead 127 can be electrically connected.

[0101] For example, the positive electrode lead 107 may be electrically connected to the positive electrode collector 105 . In addition, the negative electrode lead 130 may be electrically connected to the negative electrode collector 125 .

[0102] For example, the positive electrode current collector 105 may include a protrusion (positive electrode tab, not shown) on one side. The positive electrode active material layer 110 may not be formed on the positive electrode tab. The positive electrode tab may be integrally formed with the positive electrode current collector 105, or may be connected by welding or the like. The positive electrode current collector 105 and the positive electrode lead 107 may be electrically connected via the positive electrode tab.

[0103] Similarly, the negative electrode current collector 125 may include a protrusion (negative electrode tab, not shown) on one side. The negative electrode active material layer 120 may not be formed on the negative electrode tab. The negative electrode tab may be integrally formed with the negative electrode current collector 125, or may be connected by welding or the like. The negative electrode current collector 125 and the negative electrode lead 127 may be electrically connected via the negative electrode tab.

[0104] For example, the electrode assembly 150 may include a plurality of positive electrodes and a plurality of negative electrodes. For example, the plurality of positive electrodes and the plurality of negative electrodes may be alternately arranged, and a separator may be inserted between each positive electrode and negative electrode. Therefore, the lithium secondary battery according to one embodiment of the present invention may include a plurality of positive electrode tabs and a plurality of negative electrode tabs protruding from the plurality of positive electrodes and the plurality of negative electrodes, respectively.

[0105] For example, the positive electrode tabs (or negative electrode tabs) are stacked, rolled, and welded to form a positive electrode tab stack (or negative electrode tab stack). The positive electrode tab stack can be electrically connected to the positive electrode lead 107. In addition, the negative electrode tab stack can be electrically connected to the negative electrode lead 127.

[0106] The electrode assembly 150 and the electrolyte according to the exemplary embodiment of the present invention described above may be housed in the case 160 , thereby forming a lithium secondary battery.

[0107] The lithium secondary battery may be manufactured in a cylindrical, prismatic, pouch, or coin shape, for example. DETAILED DESCRIPTION

[0108] The following description will be given by way of specific examples and experimental examples. However, the following examples and experimental examples are merely examples of a part of one embodiment, and therefore should not be construed as limiting the technology described in this specification.

[0109] <Preparation Example 1> Preparation of Fluorinated Phosphate Compound (Chemical Formula 1-1)

[0110] [Chemical Formula 1-1]

[0111]

[0112] Sodium monofluorophosphate (14.5g, 100mmol) and tetrahydrofuran (50mL) solvent are added in a round-bottom flask in sequence, and then stirred while being cooled to 0 ℃. While maintaining 0 ℃, slowly drip trimethylchlorosilane (27.9mL, 220mmol) 1 hour in the mixture, and then stir 4 hours at room temperature. After the reaction is completed, the mixture is decompressed to remove remaining tetrahydrofuran and trimethylchlorosilane, and the mixture remaining after decompression is filtered to remove sodium chloride as a by-product. Finally, decompression and removal of the solvent of the remaining organic layer and drying obtain 20.5g of the target compound of a colorless liquid sample.

[0113] 1 H-NMR(CDCl3, 500MHz): 0.33(s, 18H)

[0114] <Preparation Example 2> Preparation of Fluorinated Phosphate Compound (Chemical Formula 1-2)

[0115] [Chemical formula 1-2]

[0116]

[0117] The target compound was prepared by the same method as in Preparation Example 1, except that ethyldimethylsilyl chloride was added instead of trimethylsilyl chloride.

[0118] <Examples 1 to 8> Manufacturing of Lithium Secondary Batteries

[0119] LiPF6 was dissolved in a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) at a volume ratio of 25:75 to form a 1.0 M solution, thereby preparing a non-aqueous electrolyte for a lithium secondary battery, and using it as a basic electrolyte (1.0 M LiPF6, EC / EMC=25 / 75). Then, the components described in Table 1 below were further added and prepared.

[0120] A battery using the non-aqueous electrolyte solution was manufactured as follows.

[0121] As the positive electrode active material, Li[Ni 0.8 Co 0.1 Mn 0.1 O2, carbon black, and polyvinylidene fluoride (PVDF) were dispersed in NMP at a weight ratio of 98:1:1 to prepare a positive electrode slurry. The positive electrode slurry was evenly coated on an aluminum foil having a protrusion (positive electrode tab) on one side, excluding the protrusion, and dried and rolled to produce a positive electrode.

[0122] A negative electrode slurry was prepared by dispersing a negative electrode active material composed of a mixture of Si / C and graphite at a weight ratio of 15:85, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) at a weight ratio of 97:1:2 in water. The negative electrode slurry was evenly coated on a copper foil having a protrusion (negative electrode tab) on one side, excluding the protrusion, and then dried and rolled to produce a negative electrode.

[0123] A polyethylene separator (13 μm thick) can be inserted between the positive electrode and the negative electrode to form an electrode assembly. The positive and negative electrode leads are connected to the positive and negative electrode tabs, respectively, by welding. The electrode assembly is housed in a soft pack so that portions of the positive and negative leads are exposed to the outside, and the three surfaces, excluding the electrolyte injection surface, are sealed.

[0124] The prepared electrolyte solution is injected into the soft package, and the electrolyte injection portion is sealed to manufacture a lithium secondary battery.

[0125] <Comparative Examples 1 and 2> Production of Lithium Secondary Batteries

[0126] A lithium secondary battery was manufactured by the same method as in the above-described embodiment, except that the components added to the electrolyte were as shown in Table 1 below.

[0127] [Table 1]

[0128]

[0129] (The weight % is based on the total weight of the electrolyte. All electrolytes contain the following basic electrolytes.)

[0130] Basic electrolyte: 1.0M LiPF6, EC / EMC=25 / 75

[0131] FEC: Fluoroethylene carbonate

[0132] PRS: Propylene sultone

[0133] PS: 1,3-propane sultone

[0134] ESA: Ethylene Sulfate

[0135] Chemical formula 1-1:

[0136]

[0137] Chemical formula 1-2:

[0138]

[0139] Chemical formula 2:

[0140]

[0141] <Experimental Example> Evaluation of Lithium Secondary Battery Performance

[0142] In order to evaluate the performance of the lithium secondary batteries manufactured in Examples 1 to 8, the following experiments were conducted, and the results are shown in Table 2 below.

[0143] <Evaluation Method>

[0144] 1. Initial performance evaluation

[0145] 1) Discharge capacity

[0146] The lithium secondary battery was repeatedly charged (CC-CV 0.5C 4.2V 0.05C cut-off) and discharged (CC 0.5C 3.0V cut-off) three times at room temperature (25°C), and the discharge capacity at the third time was measured.

[0147] 2) Thickness

[0148] The thickness of the lithium secondary battery after discharge was completed by the above method was measured.

[0149] 3) D_DCIR (discharge DCIR)

[0150] Charge a lithium secondary battery to a state of charge (SOC) of 60%. At SOC 60%, discharge for 10 seconds at various C-rates (0.2C, 0.5C, 1.0C, 1.5C, 2.0C, and 2.5C). Plot the voltage during these discharges, and use the slope as D_DCIR.

[0151] 2. Evaluation of storage stability at 60°C (5 weeks)

[0152] The lithium secondary battery was left in a chamber at 60° C. for 5 weeks, and then the following evaluation was performed.

[0153] 1) Thickness increase rate

[0154] The initial thickness of the lithium secondary battery before being placed in a 60°C chamber was measured using a flat plate thickness measuring device (Mitutoyo, 543-490B). The thickness of the lithium secondary battery after being placed in a 60°C chamber for 5 weeks was measured using the same device. The thickness measured after placement was divided by the initial thickness, and the thickness increase was calculated as a percentage.

[0155] Thickness increase rate (%) = (battery thickness after high temperature storage / initial battery thickness) 100

[0156] 2) Resistance increase rate (Ret.)

[0157] The lithium secondary battery was left in a chamber at 60° C. for 5 weeks, and then D_DCIR was measured by the same method as in the above “1. Evaluation of Initial Performance 3) D_DCIR”.

[0158] The resistance increase rate was calculated as a percentage by dividing the measured D_DCIR by the initial D_DCIR measured in the above “1. Evaluation of initial performance 3) D_DCIR”.

[0159] Resistance increase rate (%) = (D_DCIR after high temperature storage / initial D_DCIR) 100

[0160] 3) Capacity recovery rate (Rec.)

[0161] The lithium secondary battery was placed in a chamber at 60°C for 5 weeks and then discharged once (CC 1.0C 3.0V cutoff). The lithium secondary battery was then charged (CC-CV 1.0C 4.2V 0.05C cutoff) and discharged (CC 1.0C 3.0V cutoff) once to measure the discharge capacity.

[0162] The measured discharge capacity was divided by the initial discharge capacity measured in the above “1. Evaluation of initial performance 1) Discharge capacity” and the capacity recovery rate was calculated as a percentage.

[0163] Capacity recovery rate (%) = (discharge capacity after high temperature storage / initial discharge capacity) 100

[0164] 3. Evaluation of power characteristics at -10°C

[0165] 1) Discharge capacity

[0166] The lithium secondary battery was charged (CC-CV 1.0C 4.2V 0.05C cutoff) and discharged (CC 1.0C 3.0V cutoff) once at -10°C to measure the charge capacity and discharge capacity at low temperature.

[0167] 2) Charging DCIR (C_DCIR) and discharging DCIR (D_DCIR)

[0168] A lithium secondary battery was charged at -10°C to a SOC of 60%. At SOC 60%, discharge and boost charging were performed for 10 seconds at varying C-rates of 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, and 2.5C. The voltages during these discharge and boost charging cycles were plotted, and their slopes were designated as D_DCIR and C_DCIR.

[0169] [Table 2]

[0170]

[0171] It can be confirmed from Table 2 that the lithium secondary battery of the embodiment manufactured by the electrolyte containing the fluorophosphate compound has a high initial capacity compared to the lithium secondary battery of the comparative example. It can be seen that due to the optimized binding force between the compound and the transition metal of the positive electrode, it has a reduced D_DCIR. In addition, the thickness increase rate of the lithium secondary battery of the embodiment after being placed at 60°C for 5 weeks is less than 110%, which effectively reduces the thickness increase rate compared to the lithium secondary battery according to the comparative example, so it can be seen that the long-term high temperature stability is excellent. In addition, the lithium secondary battery of the embodiment shows a high capacity and low resistance (C_DCIR) compared to the lithium secondary battery of the comparative example even at a low temperature of -10°C.

[0172] A specific embodiment is described in detail above through examples and experimental examples, but the scope of a specific embodiment is not limited to the specific embodiment and should be interpreted according to the claims.

Claims

1. A lithium secondary battery electrolyte comprising: lithium salts; non-aqueous organic solvents; and A compound represented by the following Chemical Formula 1, [Chemical Formula 1] In the chemical formula 1, R 11 、R 12 and R 13 are independently hydrogen, C 1-10 Alkyl, C 2-10 Alkenyl, C 3-10 Cycloalkyl or C 6-20 Aryl, R 21 、R 22 and R 23 are independently hydrogen, C 1-10 Alkyl, C 2-10 Alkenyl, C 3-10 Cycloalkyl or C 6-20 Aryl, The R 11 、R 12 、R 13 、R 21 、R 22 and R 23 The alkyl, alkenyl, cycloalkyl and aryl groups may be substituted with halogen groups.

2. The lithium secondary battery electrolyte according to claim 1, wherein The R 11 、R 12 and R 13 are independently hydrogen, C 1-5 Alkyl, C 2-5 Alkenyl, C 3-6 Cycloalkyl or C 6-10 Aryl, The R 21 、R 22 and R 23 are independently hydrogen, C 1-5 Alkyl, C 2-5 Alkenyl, C 3-6 Cycloalkyl or C 6-10 Aryl, The R 11 、R 12 、R 13 、R 21 、R 22 and R 23 The alkyl, alkenyl, cycloalkyl and aryl groups may be substituted with halogen groups.

3. The lithium secondary battery electrolyte according to claim 1, wherein The R 11 、R 12 and R 13 Each independently is C 1-3 alkyl, The R 21 、R 22 and R 23 Each independently is C 1-3 alkyl.

4. The lithium secondary battery electrolyte according to claim 1, wherein The R 11 、R 12 and R 13 are the same and are C 1-3 alkyl, The R 21 、R 22 and R 23 are the same and are C 1-3 alkyl.

5. The lithium secondary battery electrolyte according to claim 1, wherein The compound represented by the Chemical Formula 1 is a compound represented by the following Chemical Formula 1-1 or a compound represented by the following Chemical Formula 1-2, [Chemical Formula 1-1] [Chemical formula 1-2] 。 6. The lithium secondary battery electrolyte according to claim 1, wherein The content of the compound represented by Chemical Formula 1 is 0.01 wt % to 5.0 wt % based on the total weight of the electrolyte.

7. The lithium secondary battery electrolyte according to claim 1, wherein The non-aqueous organic solvent includes a solvent selected from a cyclic carbonate solvent, a linear carbonate solvent, and a mixed solvent thereof.

8. The lithium secondary battery electrolyte according to claim 7, wherein The volume ratio of the cyclic carbonate solvent to the linear carbonate solvent is 1:1 to 1:

9.

9. The lithium secondary battery electrolyte according to claim 1, wherein The electrolyte further comprises at least one additive selected from the group consisting of a fluorine-substituted carbonate-based compound, a sulfinyl group-containing compound, an oxaloborate-based compound, an oxalophosphate-based compound, and a vinylene carbonate-based compound.

10. The lithium secondary battery electrolyte according to claim 9, wherein The sulfinyl group-containing compound is at least one selected from the group consisting of a sulfone compound, a sulfite compound, a sulfonate compound, a sultone compound, and a sulfate compound.

11. The lithium secondary battery electrolyte according to claim 9, wherein The additive includes at least one selected from fluoroethylene carbonate (FEC), propylene sultone (1,3-propylene sultone, PRS), 1,3-propane sultone (PS), and vinyl sulfate (ESA).

12. The lithium secondary battery electrolyte according to claim 9, wherein The content of the additive is 0.1 wt % to 10.0 wt % based on the total weight of the electrolyte. 13 . A lithium secondary battery comprising a positive electrode, a negative electrode, and the lithium secondary battery electrolyte according to claim 1 .

14. The lithium secondary battery according to claim 13, wherein The positive electrode includes a composite metal oxide of one or more transition metals selected from cobalt, manganese, and nickel and lithium as a positive electrode active material.

15. The lithium secondary battery according to claim 13, wherein The positive electrode includes a positive electrode active material containing a lithium-nickel-cobalt-manganese-based composite oxide.

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