Lithium secondary battery electrolyte and lithium secondary battery including the same

Abstract

The present invention relates to a lithium secondary battery electrolyte comprising a fluorinated phosphite compound 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 lowering power even at high voltage, 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 including the lithium secondary battery electrolyte. Background Art

[0002] In recent years, with the widespread popularity and miniaturization, thin-film formation, and light-weighting of portable electronic devices, active research has been conducted on secondary batteries used as their power sources to make them miniaturized and light-weighted and capable of long-term charge and discharge.

[0003] A lithium secondary battery generates electric energy through oxidation and reduction reactions when lithium ions are intercalated and deintercalated in the positive electrode and the negative electrode. The lithium secondary battery is manufactured by using substances capable of intercalating and deintercalating lithium ions as the negative electrode and the positive electrode, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

[0004] Examples of the currently widely used organic electrolytes include ethylene carbonate, propylene carbonate, dimethoxyethane, γ-butyrolactone, N,N-dimethylformamide, tetrahydrofuran, or acetonitrile. However, such organic electrolytes are generally volatile and highly flammable, and when applied to a lithium ion secondary battery, safety problems may occur at high temperatures. For example, when internal heat generation occurs due to overcharging or over-discharging, an internal short circuit may cause a fire.

[0005] In addition, when a lithium secondary battery is initially charged, lithium ions released from a lithium metal oxide serving as a positive electrode migrate to a carbon electrode serving as a negative electrode and are intercalated into the carbon. At this time, since lithium has strong reactivity, while the surface of carbon particles serving as a negative electrode active material reacts with the electrolyte, a thin film called a solid electrolyte interface (SEI) film is formed on the negative electrode surface.

[0006] The performance of a lithium secondary battery is greatly affected by the composition of the organic electrolyte and the SEI film formed by the reaction of the organic electrolyte with the electrode. That is, the formed SEI film suppresses side reactions between the carbon material and the electrolyte solvent, for example, suppresses the decomposition of the electrolyte on the surface of carbon particles serving as a negative electrode, and prevents the collapse of the negative electrode material due to the intercalation (co-intercalation) of the electrolyte solvent into the negative electrode material. Moreover, it sufficiently performs its role as a conventional lithium ion channel, thereby minimizing the degradation of battery performance.

[0007] However, as the lithium secondary battery is charged and discharged, the structure of the positive electrode active material collapses, resulting in the dissolution of metal ions on the surface of the positive electrode. The dissolved metal ions are electrodeposited on the negative electrode, leading to the deterioration of the negative electrode. This deterioration phenomenon tends to accelerate further when the potential of the positive electrode increases or the battery is exposed to high temperatures. Therefore, various studies have been conducted to develop a new type of organic electrolyte containing various additives for stabilizing the SEI film. Summary of the Invention

[0008] (I) Technical Problems to be Solved

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

[0010] Another object of a specific embodiment is to provide a lithium secondary battery with excellent battery characteristics such as high-temperature stability, charge-discharge characteristics, and power characteristics.

[0011] (II) Technical Solutions

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

[0013] [Chemical Formula 1]

[0014]

[0015] In Chemical Formula 1, X and Y are each independently -OR 1 or -O - M + ; the R 1 are each independently hydrogen; or a C 1-10 alkyl, C 2-10 alkenyl, C 3-10 cycloalkyl or C 6-20 aryl, which is substituted or unsubstituted with a halogen; and the M is a metal of Group 1 of the periodic table.

[0016] Another specific embodiment provides a lithium secondary battery, which includes the lithium secondary battery electrolyte, a negative electrode, and a positive electrode according to the above specific embodiment.

[0017] (III) Beneficial Effects

[0018] The present invention relates to a lithium secondary battery electrolyte containing a phosphorous hypofluorite compound and a lithium secondary battery including the lithium secondary battery electrolyte. The lithium secondary battery including the electrolyte according to a specific embodiment does not have a reduced power even at high voltages, has excellent life characteristics, has a high capacity recovery rate at high temperatures, and has excellent storage stability. In addition, the lithium secondary battery including the electrolyte according to a specific embodiment has a reduced internal resistance of the battery and thus has excellent power characteristics, and also has excellent cycle characteristics and stability during high-temperature and high-voltage charging. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0020] Figure 2 is a cross-sectional view taken along the Figure 1 line I-I' of BEST MODE FOR CARRYING OUT THE INVENTION

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

[0022] The numerical ranges used in this specification include the lower limit value and the upper limit value 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 the upper and lower limits of numerical ranges defined in different forms. As an example, when the composition content is defined as 10% to 80% or 20% to 50%, the numerical ranges of 10% to 50% or 50% to 80% should be interpreted as also being described in this specification. In the present invention, unless otherwise specifically defined, values outside the numerical range that may occur due to experimental errors or rounding of values are also included in the defined numerical range.

[0023] Hereinafter, unless otherwise specifically defined, "about" in this specification can be considered as 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-chain or branched-chain.

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

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

[0027] A specific embodiment provides an electrolyte for a lithium secondary battery, the electrolyte for a lithium secondary battery including: a lithium salt; a non-aqueous organic solvent; and a fluorophosphite compound represented by the following Chemical Formula 1.

[0028] [Chemical Formula 1]

[0029]

[0030] In Chemical Formula 1, X and Y are each independently -OR 1 or -O - M + ; the R 1 may be the same or different in X and Y, and are each independently hydrogen; or a C 1-10 alkyl group, a C 2-10 alkenyl group, a C 3-10 cycloalkyl group or a C 6-20 aryl group, which is substituted or unsubstituted with a halogen; and the M is a metal of Group 1 of the periodic table.

[0031] The electrolyte according to an embodiment includes a fluorophosphite compound in which a phosphorus (P) atom is substituted with one fluorine atom (monofluorination). Compared with an existing electrolyte including a difluorophosphite compound (for example, LiPO 2 F 2 , NaPO 2 F 2 etc.), battery characteristics such as high-temperature storage performance and power characteristics are excellently improved.

[0032] Specifically, as the charge and discharge of the lithium secondary battery proceed, the structure of the positive electrode active material collapses, resulting in the dissolution of metal ions on the surface of the positive electrode. The dissolved metal ions are electrodeposited on the negative electrode, leading to the deterioration of the negative electrode. This deterioration phenomenon may show a tendency to accelerate further when the potential of the positive electrode increases or the battery is exposed to high temperatures. In addition, when the driving voltage of the lithium secondary battery increases, the film on the surface of the positive electrode decomposes, and the surface of the positive electrode is exposed to the electrolyte, thereby possibly causing problems of side reactions with the electrolyte.

[0033] As a means of solving such problems, one embodiment provides a fluorophosphite compound represented by the following Chemical Formula 1. The fluorophosphite compound contained in the electrolyte according to one embodiment can further stabilize the cathode structure by coordinatively bonding with the transition metal of the cathode, thereby preventing the battery swelling phenomenon caused by the generation of gas during high-temperature storage. Therefore, the thickness increase rate at high temperatures can be significantly reduced, or the reduction of the normal-temperature life characteristics can be prevented even during high-voltage driving.

[0034] In one embodiment, each of the Rs 1 may independently be hydrogen; or a C 1-5 alkyl group, a C 2-5 alkenyl group, a C 3-6 cycloalkyl group, or a C 6-10 aryl group which is substituted or unsubstituted with a halogen, or may be a C 1-4 alkyl group, a C 1-3 alkyl group, a C 1-2 alkyl group, -CH 3 group, a C 2-4 alkenyl group, a C 2-3 alkenyl group, a C 3-5 cycloalkyl group, a C 5-6 cycloalkyl group, a C 6-8 aryl group, or a phenyl group.

[0035] In one embodiment, the M may be, for example, Li, Na, K, Rb, Cs, or Fr.

[0036] In one embodiment, the fluorophosphite compound may be, for example, a monofluorophosphate compound represented by the following Chemical Formula 2.

[0037] [Chemical Formula 2]

[0038]

[0039] In Chemical Formula 2, the M is a metal of Group 1 of the periodic table.

[0040] In one embodiment, the M may be, for example, Li, Na, K, Rb, Cs, or Fr.

[0041] Specific examples of the monofluorophosphate compound represented by Chemical Formula 2 may include a compound represented by the following Chemical Formula 2-1 or a compound represented by the following Chemical Formula 2-2. Therefore, the compound represented by Chemical Formula 2 may include any one or more of the compound represented by Chemical Formula 2-1 and the compound represented by Chemical Formula 2-2.

[0042] [Chemical Formula 2-1]

[0043]

[0044] [Chemical formula 2-2]

[0045]

[0046] The electrolyte of a lithium secondary battery according to an embodiment may contain any one or more of the above compounds. However, the above specific compounds are merely an example of the fluorophosphite compounds according to an embodiment. Therefore, the fluorophosphite compounds contained in the electrolyte of an embodiment do not have to be limited to monofluorophosphate compounds or to the above compounds, and as long as they are fluorophosphite compounds having a structure in which one fluorine atom is substituted by a phosphorus (P) atom (monofluorination), they are not particularly limited.

[0047] In one embodiment, the content of the fluorophosphite compound may be from 0.01% by weight to 5.0% by weight of the total weight of the electrolyte. Alternatively, the content of the fluorophosphite compound may be, for example, from 0.01% by weight to 3.0% by weight, from 0.1% by weight to 5.0% by weight, from 0.1% by weight to 4.0% by weight, from 0.1% by weight to 3.0% by weight, from 0.1% by weight to 2.0% by weight, from 0.1% by weight to 1.5% by weight, from 0.1% by weight to 1.0% by weight, from 0.2% by weight to 0.8% by weight, from 0.3% by weight to 0.7% by weight, or about 0.5% by weight. However, the above ranges are merely examples and do not have to be limited to the above ranges.

[0048] The non-aqueous organic solvent contained in the electrolyte according to an embodiment may contain a solvent selected from cyclic carbonate solvents, linear carbonate solvents, and a mixed solvent thereof. The cyclic carbonate solvent may be selected from ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, ethylene glycol ethyl carbonate, fluorinated ethylene carbonate, and mixtures thereof, and the linear carbonate may be selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, and mixtures thereof.

[0049] The cyclic carbonate solvent has a relatively high polarity and can dissociate lithium ions sufficiently, but has a high viscosity, so there may be a disadvantage of low ionic conductivity. Therefore, the cyclic carbonate solvent may also be mixed with and used with a linear carbonate solvent having a low polarity but a low viscosity. In one embodiment, when the non-aqueous organic solvent contains both a cyclic carbonate solvent and a linear carbonate solvent (i.e., when it contains a mixed solvent thereof), the volume ratio of the cyclic carbonate solvent to the linear carbonate solvent may be from 1:1 to 1:9, or may be, for example, from 1:1 to 1:8, from 1:1 to 1:6, from 1:1 to 1:5, from 1:2 to 1:4, or about 1:3.

[0050] In one embodiment, in addition to the fluorophosphite compound represented by the formula 1, the electrolyte may further contain an additive. The additive may include any one or more selected from, for example, fluorine-substituted carbonate-based compounds, sulfonyl group-containing compounds, oxalate borate-based compounds, oxalate phosphate-based compounds, and vinylene carbonate-based compounds.

[0051] In one embodiment, the sulfonyl group-containing compound may be any one or more selected from sulfone-based compounds, sulfite-based compounds, sulfonate-based compounds, sultone-based compounds, and sulfate-based compounds. In one embodiment, the fluorine-substituted carbonate-based compound may use fluoroethylene carbonate (FEC), and the sulfonyl group-containing compound may use 1,3-propene sultone (PRS), 1,3-propane sultone (PS), or ethylene sulfate (ESA). Therefore, the electrolyte according to one embodiment may further contain an additive containing any one or more selected from fluoroethylene carbonate (FEC), 1,3-propene sultone (PRS), 1,3-propane sultone (PS), and ethylene sulfate (ESA).

[0052] The electrolyte according to one embodiment contains the fluorophosphite compound represented by the formula 1 and ethylene carbonate (FEC) as an additive, and may further contain any one or more of 1,3-propene sultone (PRS), 1,3-propane sultone (PS), and ethylene sulfate (ESA).

[0053] Alternatively, the electrolyte according to one embodiment may further contain the fluorophosphite compound represented by the formula 1 and a composition composed of a combination of fluoroethylene carbonate (FEC), 1,3-propene sultone (PRS), 1,3-propane sultone (PS), and ethylene sulfate (ESA) as an additive.

[0054] Alternatively, the electrolyte according to one embodiment may further contain lithium difluoro bis(oxalate) phosphate (LiPF 2 (C 2 O 4 ) 2 , LiDFBOP) or lithium bis(oxalate) borate (LiB(C 2 O 4 ) 2 , LiBOB).

[0055] When the electrolyte according to an embodiment contains the above additives, the content of the additives may be 0.1% by weight to 10.0% by weight or 0.1% by weight to 8.0% by weight, 0.1% by weight to 6.0% by weight, 0.1% by weight to 5.0% by weight, 1.0% by weight to 5.0% by weight, 1.0% by weight to 4.0% by weight, 2.0% by weight to 4.0% by weight, 2.0% by weight to 3.0% by weight, or about 2.5% by weight of the total weight of the electrolyte.

[0056] In one embodiment, the lithium salt contained in the electrolyte is not particularly limited, but may be selected from, for example, LiPF 6 , LiBF 4 , LiClO 4 , LiSbF 6 , LiAsF 6 , LiN(SO 2 C 2 F 5 ), 2 , LiN(CF 3 SO 2 ), 2 , LiN(SO 3 C 2 F 5 ), 2 , LiN(SO 2 F), 2 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiC 6 H 5 SO 3 , LiSCN, LiAlO 2 , LiAlCl 4 , LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 )(wherein x and y are independently natural numbers), LiCl, LiI, and LiB(C 2 O 4 ), 2 or one or more of the above.

[0057] The concentration of the lithium salt can be 0.1 M to 2.0 M, 0.7 M to 1.5 M, or about 1.0 M. When the concentration of the lithium salt is less than 0.1 M, the conductivity of the electrolyte decreases, thus potentially reducing the performance of the electrolyte. When the concentration of the lithium salt exceeds 2.0 M, the viscosity of the electrolyte increases, which may reduce the mobility of lithium ions. The lithium salt serves as a source of lithium ions in the battery to enable the basic operation of the lithium secondary battery.

[0058] The electrolyte of a lithium secondary battery according to one embodiment is generally stable at -20°C to 60°C or 40°C to 60°C, and also maintains stable electrochemical characteristics at high voltages above 4.20 V, specifically above 4.30 V or above 4.35 V, 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.

[0059] Another specific embodiment provides a lithium secondary battery including the electrolyte of a lithium secondary battery according to the above one embodiment, a positive electrode, and a negative electrode.

[0060] A lithium secondary battery according to one embodiment includes an electrolyte containing a fluorophosphite compound in which one fluorine atom is substituted by a phosphorus (P) atom (monofluorination). Compared with the case of using an existing electrolyte containing a difluorophosphite compound (e.g., LiPO 2 F 2 ), it can improve battery characteristics such as high-temperature storage performance and power characteristics more excellently.

[0061] The fluorophosphite compound contained in the electrolyte of a lithium secondary battery according to one embodiment coordinates and binds with the transition metal of the positive electrode to further stabilize the positive electrode structure. Therefore, during high-temperature storage, the side reaction between the surface of the positive electrode and the electrolyte is suppressed, thereby preventing the decomposition of the electrolyte, preventing the generation of gas, and effectively suppressing the swelling phenomenon of battery swelling. Thus, the high-temperature storage stability of the lithium secondary battery can be improved. In addition, the cycle life characteristics and stability can also be improved at high temperatures and high voltages.

[0062] Specifically, when a lithium secondary battery prepared from the electrolyte of a lithium secondary battery according to one embodiment is placed at high temperature for a long time, the thickness increase rate of the battery is 110% or less and is very low. Therefore, it has excellent high-temperature storage stability.

[0063] Non-limiting examples of secondary batteries according to one embodiment include lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries, etc.

[0064] Figure 1 and Figure 2Are respectively a schematic plan view and a cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. Figure 2 is a cross-sectional view taken along the Figure 1 line I-I' of.

[0065] Referring to 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.

[0066] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 formed on the positive electrode current collector 105. For example, the positive electrode active material layer 110 may be formed on one or both surfaces of the positive electrode current collector 105.

[0067] For example, the positive electrode active material layer 110 may contain a positive electrode active material, and may contain a positive electrode binder and a conductive material as needed.

[0068] For example, the positive electrode 100 may be prepared by mixing and stirring a positive electrode active material, a positive electrode 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 current collector 105 and drying and calendering it.

[0069] For example, the positive electrode current collector 105 may contain stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably may contain aluminum or an aluminum alloy.

[0070] 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.

[0071] In one embodiment, the positive electrode active material may contain nickel-containing lithium metal oxide particles.

[0072] In one embodiment, based on the total molar number of all elements except lithium and oxygen, the lithium metal oxide particles may contain 80 mol% or more of nickel. In this case, a lithium secondary battery with high capacity can be achieved.

[0073] In one embodiment, based on the total molar number of all elements except lithium and oxygen, the lithium metal oxide particles may contain 83 mol% or more, 85 mol% or more, 90 mol% or more, or 95 mol% or more of nickel.

[0074] 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, etc. can be achieved.

[0075] In one embodiment, the lithium metal oxide particles may have the chemical formula Li a Ni x M 1-x O 2+y wherein, 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.

[0076] 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 life characteristics can be achieved.

[0077] 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 life characteristics can be achieved.

[0078] In one embodiment, the positive electrode may include a composite metal oxide of any one or more transition metals selected from 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.

[0079] In one embodiment, when a secondary battery electrolyte containing a fluorophosphite compound and a positive electrode active material containing a nickel-cobalt-manganese-based active material are simultaneously applied to a secondary battery, there are the following advantages, namely, the bulging phenomenon and the problem of reduced high-temperature stability of the nickel-cobalt-manganese-based active material having a high nickel content can be solved.

[0080] The positive electrode active material according to one embodiment may be, for example, Li x (Ni a Co b Mn c )O 2 (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 )O 4(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 )O 2 , 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 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNi 0.8 Co 0.1 Mn 0.1 O 2 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 or a mixture thereof.

[0081] In one embodiment, the positive electrode binder may include organic binders such as polyvinylidene fluoride (PVDF; polyvinylidenefluoride), vinylidene fluoride - co - hexafluoropropylene copolymer (PVDF - co - HFP), polyacrylonitrile, polymethylmethacrylate, etc.; 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).

[0082] 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 tin, tin oxide, titanium oxide, LaSrCoO 3 , LaSrMnO 3 and other perovskite substances such as LaSrMnO.

[0083] 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 sides of the negative electrode current collector 125.

[0084] 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.

[0085] For example, the negative electrode 130 can 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 rolling it.

[0086] For example, the negative electrode current collector 125 can include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably can include copper or a copper alloy.

[0087] For example, the negative electrode active material can be a material that allows lithium ions to be intercalated and deintercalated. For example, the negative electrode active material can include a lithium alloy, a carbon-based material, a silicon-based material, etc.

[0088] For example, the lithium alloy can include metal elements such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, and indium.

[0089] For example, the carbon-based active material can include crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.

[0090] For example, the amorphous carbon can include hard carbon, coke, mesocarbon microbeads (MCMB) calcined at a temperature below 1500 °C, mesophase pitch-based carbon fibers (MPCF), etc.

[0091] For example, the crystalline carbon can include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0092] For example, the negative electrode active material can include a silicon-based active material. For example, the silicon-based active material can include Si, SiO x (0 < x < 2), silicon-carbon composite materials (Si / C), SiO / C, Si-metal (Metal), etc. In this case, a lithium secondary battery with a high capacity can be realized.

[0093] For example, when the negative electrode active material includes 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 can slow down the increase rate of the battery thickness by including the above electrolyte.

[0094] In one embodiment, the content of silicon atoms in the negative electrode active material can be 1 wt% to 20 wt%, 1 wt% to 15 wt%, or 1 wt% to 10 wt%.

[0095] The negative electrode binder and the conductive material may be substantially the same or similar substances as the above-mentioned positive electrode binder and conductive material. For example, the negative electrode binder may be an aqueous binder such as styrene-butadiene rubber (SBR). In addition, for example, the negative electrode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0096] The electrolyte according to one embodiment can form a cathode electrolyte interphase with excellent stability on the surface of the electrode. Therefore, side reactions between the electrode active material (e.g., lithium metal oxide, carbon-based material, silicon-based material) and the electrolyte can be effectively suppressed.

[0097] In one embodiment, the area of the negative electrode 130 may be larger than the area of the positive electrode 100. In this case, lithium ions generated from the positive electrode 100 can migrate smoothly to the negative electrode 130 without precipitating midway.

[0098] For example, the positive electrode 100 and the negative electrode 130 may be alternately and repeatedly arranged to form the electrode assembly 150.

[0099] In one embodiment, the separator 140 may be inserted between the positive electrode 100 and the negative electrode 130. For example, the separator 140 may form the electrode assembly 150 by winding, stacking, z-folding, etc.

[0100] 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 further include a non-woven fabric formed of high melting point glass fibers, polyethylene terephthalate fibers, etc.

[0101] The lithium secondary battery according to an exemplary embodiment may include: a positive electrode lead 107, the positive electrode lead 107 being connected to the positive electrode 100 and protruding to the outside of the housing 160; and a negative electrode lead 127, the negative electrode lead 127 being connected to the negative electrode 130 and protruding to the outside of the housing 160.

[0102] For example, the positive electrode 100 and the positive electrode lead 107 may be electrically connected. Similarly, the negative electrode 130 and the negative electrode lead 127 may be electrically connected.

[0103] For example, the positive electrode lead 107 may be electrically connected to the positive electrode current collector 105. In addition, the negative electrode lead 130 may be electrically connected to the negative electrode current collector 125.

[0104] For example, the positive electrode current collector 105 may include a protruding portion (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 through the positive electrode tab.

[0105] Similarly, the negative electrode current collector 125 may include a protruding portion (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 through the negative electrode tab.

[0106] 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. Accordingly, a lithium secondary battery according to an embodiment of the present invention may include a plurality of positive electrode tabs and a plurality of negative electrode tabs respectively protruding from the plurality of positive electrodes and the plurality of negative electrodes.

[0107] For example, the positive electrode tab (or, the negative electrode tab) forms a positive electrode tab laminate (or, a negative electrode tab laminate) by stacking, rolling, and welding. The positive electrode tab laminate may be electrically connected to the positive electrode lead 107. In addition, the negative electrode tab laminate may be electrically connected to the negative electrode lead 127.

[0108] The electrode assembly 150 and the electrolyte according to the exemplary embodiments of the present invention described above may be accommodated in a case 160 to form a lithium secondary battery.

[0109] The lithium secondary battery may be made, for example, in a cylindrical, prismatic, pouch type, coin type, or the like.

[0110] Hereinafter, specific exemplary embodiments and experimental examples will be described. However, the following exemplary embodiments and experimental examples only illustrate a part of an embodiment, and thus should not be construed as limiting the technology described in this specification thereto. Detailed Description

[0111] <Examples 1 to 8> Fabrication of Lithium Secondary Battery

[0112] LiPF is dissolved in a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) mixed at a volume ratio of 25:75 6 to make 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 LiPF 6, EC / EMC = 25 / 75). Then, the components described in Table 1 below were further added and prepared.

[0113] The battery using the non-aqueous electrolyte is manufactured as follows.

[0114] Li[Ni 0.8 Co 0.1 Mn 0.1 O 2 , carbon black, and polyvinylidene fluoride (PVDF) were dispersed in N-methyl-2-pyrrolidone (NMP) at a weight ratio of 98:1:1 to prepare a positive electrode paste. The positive electrode paste was uniformly coated on the area of the aluminum foil having a protrusion (positive electrode tab) on one side except for the protrusion, and dried and calendered to manufacture a positive electrode.

[0115] The negative electrode active material obtained by mixing Si / C and graphite at a weight ratio of 15:85, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were dispersed in water at a weight ratio of 97:1:2 to prepare a negative electrode paste. The negative electrode paste was uniformly coated on the area of the copper foil having a protrusion (negative electrode tab) on one side except for the protrusion, and dried and calendered to manufacture a negative electrode.

[0116] A polyethylene separator (thickness: 13 μm) can be inserted between the positive electrode and the negative electrode to form an electrode assembly. The positive electrode lead and the negative electrode lead were respectively connected to the positive electrode tab and the negative electrode tab by welding. The electrode assembly was housed inside a soft package such that partial regions of the positive electrode lead and the negative electrode lead were exposed to the outside, and three sides except for the electrolyte injection part surface were sealed.

[0117] The electrolyte prepared above was injected into the soft package, and the electrolyte injection part surface was sealed to manufacture a lithium secondary battery.

[0118] <Comparative Example 1 and Comparative Example 2> Manufacture of Lithium Secondary Battery

[0119] A lithium secondary battery was manufactured by the same method as in the example, but the components added to the electrolyte were as shown in Table 1 below.

[0120] <Reference Example 1 to Reference Example 4> Manufacture of Lithium Secondary Battery

[0121] A lithium secondary battery was manufactured by the same method as in the example, but the components added to the electrolyte were as shown in Table 1 below.

[0122] [Table 1]

[0123]

[0124] (The weight % is based on the total weight of the electrolyte, and all electrolytes contain the following basic electrolyte)

[0125] Basic electrolyte: 1.0M LiPF 6 , EC / EMC = 25 / 75

[0126] FEC: Fluoroethylene carbonate

[0127] PRS: 1,3 - Propylene sultone

[0128] PS: 1,3 - Propane sultone

[0129] ESA: Ethylene sulfate

[0130] Phosphorous hypofluorite compound (Chemical formula 2 - 1): (Source: SK Innovation Co., Ltd.)

[0131] Phosphorous hypofluorite compound (Chemical formula 2 - 2): (Source: SK Innovation Co., Ltd.)

[0132] Diphosphorous hypofluorite compound (Chemical formula 3): (Source: EnChem Co., Ltd.)

[0133] <Experimental Example> Evaluation of the performance of lithium secondary batteries

[0134] In order to evaluate the performance of the lithium secondary batteries manufactured by the above Examples 1 to 8, Comparative Example 1, Comparative Example 2, and Reference Examples 1 to 4, the following experiments were conducted, and the results are shown in Table 2 below.

[0135] <Evaluation method>

[0136] 1. Evaluation of initial performance

[0137] 1) Discharge capacity

[0138] 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) 3 times at room temperature (25°C), and the discharge capacity of the third time was measured.

[0139] 2) Thickness

[0140] Measure the thickness of the lithium secondary battery that has ended discharge by the above method.

[0141] 3) D_DCIR (Discharge DCIR)

[0142] Charge the lithium secondary battery to a state of charge (SOC) of 60%. At SOC 60%, change the C-rate to 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and perform discharge for 10 seconds respectively. Plot the voltage during the discharge and use its slope as D_DCIR.

[0143] 2. Evaluation of storage stability at 60°C (5 weeks)

[0144] Place the lithium secondary battery in a chamber at 60°C for 5 weeks, and then perform the following evaluations.

[0145] 1) Thickness increase rate

[0146] Measure the initial thickness of the lithium secondary battery before placing it in the 60°C chamber using a flat plate thickness measuring device (Mitutoyo Corporation, 543 - 490B). Measure the thickness of the lithium secondary battery after placing it in the 60°C chamber for 5 weeks using the same device. Divide the thickness measured after placement by the initial thickness and calculate the thickness increase rate as a percentage.

[0147] Thickness increase rate (%) = (Battery thickness after high-temperature storage / Initial battery thickness) 100

[0148] 2) Resistance increase rate (Ret.)

[0149] Place the lithium secondary battery in a chamber at 60°C for 5 weeks, and then measure D_DCIR by the same method as in “3) D_DCIR in 1. Evaluation of initial performance” above.

[0150] Calculate the resistance increase rate as a percentage by dividing the measured D_DCIR by the initial D_DCIR measured in “3) D_DCIR in 1. Evaluation of initial performance” above.

[0151] Resistance increase rate (%) = (D_DCIR after high-temperature storage / Initial D_DCIR) 100

[0152] 3) Capacity recovery rate (Rec.)

[0153] The lithium secondary battery was placed in a chamber at 60 °C for 5 weeks and then discharged once (CC 1.0C cutoff at 3.0V). Then, the lithium secondary battery was charged (CC-CV 1.0C 4.2V cutoff at 0.05C) and discharged (CC 1.0C cutoff at 3.0V) once to measure the discharge capacity.

[0154] Divide the measured discharge capacity by the initial discharge capacity measured in "1. Evaluation of Initial Performance 1) Discharge Capacity" above and calculate the capacity recovery rate as a percentage.

[0155] Capacity recovery rate (%) = (Discharge capacity after high-temperature storage / Initial discharge capacity) 100

[0156] 3. Evaluation of Power Characteristics at -10 °C

[0157] 1) Discharge capacity

[0158] The lithium secondary battery was charged (CC-CV 1.0C 4.2V cutoff at 0.05C) and discharged (CC 1.0C cutoff at 3.0V) once at -10 °C to measure the charge capacity and discharge capacity at low temperature.

[0159] 2) Charge DCIR (C_DCIR) and Discharge DCIR (D_DCIR)

[0160] The lithium secondary battery was charged to SOC 60% at -10 °C. At SOC 60%, the C-rate was changed to 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and discharged and replenished for 10 seconds each. The voltages during the above discharge and replenishment were plotted respectively, and their slopes were taken as D_DCIR and C_DCIR.

[0161] [Table 2]

[0162]

[0163] It can be confirmed from Table 2 that compared with the lithium secondary batteries of the comparative examples containing phosphorous difluoride compounds, the lithium secondary batteries of the examples and reference examples prepared from the electrolytes containing phosphorous fluoride compounds have a high initial capacity, and it can be seen that due to the optimized binding force of the compounds with the transition metals of the positive electrode, the D_DCIR is reduced.

[0164] In addition, the thickness increase rate of the lithium secondary battery of the embodiment after being placed at 60 °C for 5 weeks is all 110% or less. Compared with the lithium secondary battery according to the comparative example, the thickness increase rate is effectively reduced, so it can be known that the long-term high-temperature stability is excellent. In addition, the lithium secondary battery of the embodiment shows a higher capacity and a lower resistance (C_DCIR) than the lithium secondary battery of the comparative example even at a low temperature of -10 °C.

[0165] As described above, through the embodiments and experimental examples, a specific implementation is described in detail. However, the scope of a specific implementation is not limited to a specific implementation, and should be interpreted according to the claims.

Claims

1. A lithium secondary battery electrolyte, comprising: a lithium salt; a non-aqueous organic solvent; and a fluorophosphite compound represented by the following Chemical Formula 1, [Chemical Formula 1] In the Chemical Formula 1, X and Y are each independently -OR 1 or -O - M + ; Said R 1 each independently is hydrogen; or a C 1-10 alkyl, C 2-10 alkenyl, C 3-10 cycloalkyl or C 6-20 aryl; the M is a metal of Group 1 of the periodic table.

2. The lithium secondary battery electrolyte according to claim 1, wherein, The R 1 are each independently hydrogen; or a C 1-5 alkyl group, C 2-5 alkenyl group, C 3-6 cycloalkyl group or C 6-10 aryl group.

3. The lithium secondary battery electrolyte according to claim 1, wherein, the M is Li, Na, K, Rb, Cs or Fr.

4. The lithium secondary battery electrolyte according to claim 1, wherein, the fluorophosphite compound is a compound represented by the following Chemical Formula 2, [Chemical Formula 2] In the Chemical Formula 2, the M is a metal of Group 1 of the periodic table.

5. The lithium secondary battery electrolyte according to claim 4, wherein, the fluorophosphite compound contains any one or more of a compound represented by the following Chemical Formula 2-1 and a compound represented by Chemical Formula 2-2, [Chemical Formula 2-1] [Chemical Formula 2-2] 。 6. The lithium secondary battery electrolyte according to claim 1, wherein, the content of the fluorophosphite compound is 0.01 wt% to 5.0 wt% of the total weight of the electrolyte.

7. The lithium secondary battery electrolyte according to claim 1, wherein, the non-aqueous organic solvent contains 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 contains any one or more additives selected from a fluorine-substituted carbonate group compound, a sulfinyl group-containing compound, an oxalate borate group compound, an oxalate phosphate group compound, and a vinylene carbonate group compound.

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

11. The lithium secondary battery electrolyte according to claim 9, wherein, the additive contains any one or more selected from fluoroethylene carbonate (FEC), 1,3-propylene sultone (PRS), 1,3-propane sultone (PS), and ethylene 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% of 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 any one of claims 1 to 12.

14. The lithium secondary battery according to claim 13, wherein, the positive electrode contains a composite metal oxide of any 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 contains a positive electrode active material containing a lithium-nickel-cobalt-manganese-based composite oxide.

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