Liquid electrolyte and rechargeable lithium battery including same

Abstract

The invention relates to a liquid electrolyte and a rechargeable lithium battery including the same. The liquid electrolyte includes: a lithium salt; a non-aqueous organic solvent; and an additive, in which the additive includes a polymer represented by Chemical Formula 1: Chemical Formula 1 # imgabs0 # in Chemical Formula 1, R1-R3 are each independently hydrogen, fluorine, or a substituted or unsubstituted C1-C10 alkyl group, and n and m are molar fractions, 50 mol% < = n < = 90 mol%, 10 mol% < = m < = 50 mol%, respectively.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0100657 filed in the Korean Intellectual Property Office on August 1, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] One or more aspects of embodiments of the present disclosure relate to a liquid electrolyte and a rechargeable lithium battery including the liquid electrolyte. Background Art

[0004] Rechargeable lithium batteries are rechargeable and have an energy density per unit weight that is up to three or more times higher than comparable lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, etc. Rechargeable lithium batteries can be highly charged (e.g., can carry relatively more charge), and therefore, are commercially used in the manufacture of laptop computers, cellular phones, power tools, electric bicycles, etc., and research on further improvement of energy density has been actively conducted or devoted to.

[0005] A rechargeable lithium battery may be utilized by injecting an electrolyte into a battery cell including a positive electrode including a positive electrode active material that can intercalate and deintercalate lithium and a negative electrode including a negative electrode active material that can intercalate and deintercalate lithium.

[0006] Current commercially available electrolytes utilize organic carbonate-based solvents to withstand the high operating voltages of rechargeable lithium batteries.

[0007] However, organic carbonate-based solvents are highly volatile and flammable, and have a relatively low flash point, and thus may be gasified at high temperatures, which may cause the battery to swell and the polyethylene (PE) separator to melt and shrink, thereby causing safety issues for rechargeable lithium batteries.

[0008] However, despite attempts to address these safety issues of rechargeable lithium batteries through extensive research on separators, current collectors, active materials, and / or battery management systems (BMS), these issues cannot be easily resolved as long as highly flammable organic carbonate-based solvents are utilized.

[0009] Recently, the safety issues of rechargeable lithium batteries, for example, those used in electric vehicles, have been actively discussed. In particular, it is necessary or desirable to fundamentally solve the problem of flammable solvents and to find a solution from the perspective of electrolytes. Summary of the invention

[0010] One or more aspects of the disclosed embodiments relate to a liquid electrolyte that can achieve excellent or adequate battery safety.

[0011] One or more aspects of the present embodiments relate to a rechargeable lithium battery including a liquid electrolyte.

[0012] According to one or more embodiments, a liquid electrolyte includes a lithium salt; a non-aqueous organic solvent; and an additive, wherein the additive includes a polymer represented by Chemical Formula 1.

[0013] Chemical formula 1

[0014]

[0015] In Chemical Formula 1,

[0016] R 1 ~R 3 may each independently be hydrogen, fluorine or a substituted or unsubstituted C1-C10 alkyl group, and

[0017] n and m can be mole fractions, respectively, 50 mol%≤n≤90 mol%, 10 mol%≤m≤50 mol%.

[0018] According to one or more embodiments of the present disclosure, a rechargeable lithium battery may include: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and a liquid electrolyte according to the present embodiment.

[0019] Rechargeable lithium batteries offer improved safety that can prevent or reduce battery short circuits, heating, and explosions by blocking or reducing the battery's ionic conduction if (e.g., when) a problem occurs, inhibiting or reducing swelling caused by evaporation of the liquid electrolyte, and inhibiting or reducing shrinkage of the separator. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 to Figure 4 A schematic diagram illustrating a rechargeable lithium battery according to one or more embodiments.

[0021] Figure 5 is a graph showing specific capacity and coulombic efficiency according to the number of cycles during high temperature charging and discharging of a rechargeable lithium battery cell.

[0022] Figure 6 Graphs showing the results of a hot box test of a pouch-type full-battery cell.

[0023] Figure 7 Graphs showing the results of TGA analysis of the liquid electrolytes of Example 1 and Comparative Examples 1 and 2 according to the present invention.

[0024] Figure 8Results of measuring the cell resistance of a rechargeable lithium battery cell after reaching room temperature (25° C.) or high temperature (120° C.) and keeping it for 1 hour are shown.

[0025] Reference numerals

[0026] 100: Rechargeable lithium battery 10: Positive electrode

[0027] 11: Positive electrode lead tab 12: Positive terminal

[0028] 20: Negative electrode 21: Negative electrode lead lug

[0029] 22: Negative terminal 30: Separator

[0030] 40: electrode assembly 50: shell

[0031] 60: Sealing member 70: Electrode terminal piece

[0032] 71: Positive electrode terminal tab 72: Negative electrode terminal tab DETAILED DESCRIPTION

[0033] Hereinafter, the embodiments will be described in more detail so that those skilled in the art can easily implement them. However, the present disclosure may be embodied in many different forms and is not to be construed as limited to the example embodiments set forth herein.

[0034] The terms utilized herein are for describing example embodiments only and are not intended to limit the present disclosure.A singular expression includes a plural expression unless the context clearly indicates otherwise.

[0035] As utilized herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like, of the components.

[0036] In this document, it should be understood that terms (such as "comprises", "includes", or "has") are intended to mark the presence of specified aspects, quantities, operations (e.g., steps, tasks, actions, etc.), elements and / or combinations thereof (e.g., any appropriate combination), but do not exclude the possibility of the presence or addition of one or more other features, quantities, operations (e.g., steps, tasks, actions, etc.), elements and / or combinations thereof (e.g., any appropriate combination).

[0037] As used herein, if no limitation is otherwise provided (e.g., when limitation is not otherwise provided), the particle size may be an average particle size. The particle size refers to an average particle size (D50), which is the diameter of particles with a cumulative volume of 50% by volume in a particle size distribution. The average particle size (D50) can be measured by any appropriate method, for example, by measurement with a particle size analyzer, a transmission electron microscope and / or a scanning electron microscope. In some embodiments, a dynamic light scattering measurement device can be used for data analysis, and particles of each particle size range are counted. Thus, the average particle size (D50) can be obtained relatively easily by calculation. The average particle size (D50) can also be measured using a laser diffraction method. When measuring by laser diffraction, the particles to be measured are dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measuring device (e.g., MT 3000 available from Microtrac) using ultrasonic waves of about 28 kHz, and after irradiation with an output of 60 W, the average particle diameter (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0038] In the accompanying drawings, for the sake of clarity, the thickness of layers, films, panels, regions, etc. is exaggerated and the same reference numerals are used to mark the same elements throughout the specification, and repeated descriptions thereof may not be provided. It will be understood that if an element (such as a layer, film, region, and / or substrate) is referred to as being "on" another element (such as a layer, film, region, and / or substrate) (for example, when an element (such as a layer, film, region, and / or substrate) is referred to as being "on" another element (such as a layer, film, region, and / or substrate)), it may be directly on another element (such as a layer, film, region, and / or substrate) (for example, without any intervening elements (such as layers, films, regions, and / or substrates) therebetween), or there may also be intervening elements (such as layers, films, regions, and / or substrates). In contrast, if an element (such as a layer, film, region and / or substrate) is referred to as being “directly on” another element (such as a layer, film, region and / or substrate) (for example, when an element (such as a layer, film, region and / or substrate) is referred to as being “directly on” another element (such as a layer, film, region and / or substrate)), there are no intervening elements (such as layers, films, regions and / or substrates).

[0039] In one or more embodiments, if viewed in a plan view (for example, when viewed in a plan view), the “layer” herein includes not only a shape formed on the entire surface but also a shape formed on a partial surface.

[0040] In this document, “or” is not interpreted as being exclusive. For example, “A or B” is interpreted as including A, B, A+B, etc.

[0041] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0042] Further, when describing embodiments of the present disclosure, the use of “may” refers to “one or more embodiments of the present disclosure.”

[0043] As used herein, the terms "use," "using," and "used" may be considered synonymous with the terms "utilize," "utilizing," and "utilized," respectively.

[0044] As used herein, expressions such as “at least one of,” “one of,” and “selected from,” when preceding / following a list of elements, modify the entire list of elements and do not modify the individual elements of the list. For example, “at least one selected from a, b, and c” may indicate only a, only b, only c, both a and b (e.g., both a and b), both a and c (e.g., both a and c), both b and c (e.g., both b and c), all of a, b, and c, or variations thereof.

[0045] For ease of description, spatially relative terms (such as "below," "below," "below," "above," "on," "bottom," "top," etc.) may be used herein to describe the relationship of one element or feature illustrated in the figures to another element or feature. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figure is turned over, an element described as being "below" or "below" other elements or features will then be oriented "above" or "on" the other elements or features. Thus, the term "below" may encompass both orientations above and below. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein should be interpreted accordingly.

[0046] As used herein, the terms "substantially," "about," and similar terms are used as terms of approximation and not as terms of degree, and are intended to take into account the inherent deviations in measured or calculated values ​​that one of ordinary skill in the art will recognize. "About" or "approximately," as used herein, include the recited value and mean within the range of acceptable deviations determined for the particular value as determined by one of ordinary skill in the art taking into account the measurement in question and the errors associated with the measurement of the particular quantity (i.e., the limitations of the measurement system). For example, "about" may mean within one or more standard deviations of the recited value, or within ±30%, ±20%, ±10%, or ±5% of the recited value.

[0047] Any numerical range set forth in this article is intended to include all sub-ranges of the same numerical precision falling within the range set forth. For example, the range of "1.0-10.0" is intended to be included between the minimum value of 1.0 set forth and the maximum value of 10.0 set forth (and including 1.0 and 10.0), that is, all sub-ranges with a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as, for example, 2.4-7.6. Any maximum numerical limit set forth in this article is intended to include all lower numerical limits falling therein and any minimum numerical limit set forth in this specification is intended to include all higher numerical limits falling therein. Accordingly, the applicant reserves the right to modify this specification (including claims) to explicitly set forth any sub-range falling within the range explicitly set forth in this article.

[0048] The term "metal" is interpreted as including common metals, transition metals, and semimetals.

[0049] As utilized herein, if no limitation is otherwise provided (e.g., when no limitation is otherwise provided), "substituted" refers to replacement of at least one hydrogen in a substituent or compound with deuterium, halo, hydroxyl, amino, amine, nitro, silyl, C1-C30 alkyl, C1-C10 alkylsilyl, C6-C30 arylsilyl, C3-C30 cycloalkyl, C3-C30 heterocycloalkyl, C6-C30 aryl, C2-C30 heteroaryl, C1-C20 alkoxy, C1-C10 fluoroalkyl, cyano and / or combinations thereof (e.g., any suitable combination).

[0050] In some embodiments, "substituted" refers to at least one hydrogen in a substituent or compound being replaced by: deuterium, halogen, C1-C30 alkyl, C1-C10 alkylsilyl, C6-C30 arylsilyl, C3-C30 cycloalkyl, C3-C30 heterocycloalkyl, C6-C30 aryl, C2-C30 heteroaryl, C1-C10 fluoroalkyl or cyano. In some embodiments of the present disclosure, "substituted" refers to at least one hydrogen in a substituent or compound being replaced by: deuterium, halogen, C1-C20 alkyl, C6-C30 aryl, C1-C10 fluoroalkyl or cyano. For example, "substituted" refers to at least one hydrogen in a substituent or compound being replaced by: deuterium, halogen, C1-C5 alkyl, C6-C18 aryl, C1-C5 fluoroalkyl or cyano. In some embodiments, "substituted" refers to at least one hydrogen in a substituent or compound being replaced by deuterium, cyano, halo, methyl, ethyl, propyl, butyl, phenyl, biphenyl, terphenyl, trifluoromethyl, or naphthyl.

[0051] The rechargeable lithium battery may be classified into a cylindrical battery, a prismatic battery, a pouch-type or pouch-like battery, a coin-type or coin-like battery, etc., depending on the shape of the rechargeable lithium battery. Figure 1 to Figure 4 A schematic diagram illustrating a rechargeable lithium battery according to one or more embodiments. Figure 1 A cylindrical battery is shown, Figure 2 A prismatic cell is shown, and Figure 3 and Figure 4 A pouch type or bag type battery is shown. Figure 1 to Figure 4 , the rechargeable lithium battery 100 may include: an electrode assembly 40 including a separator 30 between a positive electrode 10 and a negative electrode 20, and a case 50 including the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte. Figure 1 As shown in FIG. 1 , the rechargeable lithium battery 100 may include a sealing member 60 that seals the housing 50. Figure 2 In the embodiment, the rechargeable lithium battery 100 may include a positive electrode lead tab 11, a positive terminal 12, a negative electrode lead tab 21, and a negative terminal 22. Figure 3 and Figure 4 As shown in , the rechargeable lithium battery 100 may include electrode tabs 70, which may be, for example, positive electrode tabs 71 and negative electrode tabs 72 used as electrical paths for guiding (e.g., providing) current formed in the electrode assembly 40 to the outside.

[0052] Hereinafter, an electrolyte according to one or more embodiments will be described.

[0053] The electrolyte according to one or more embodiments may be a liquid electrolyte including a lithium salt, a non-aqueous organic solvent, and an additive, wherein the additive includes a polymer represented by Chemical Formula 1.

[0054] Chemical formula 1

[0055]

[0056] In Chemical Formula 1,

[0057] R 1 ~R 3 may each independently be hydrogen, fluorine or a substituted or unsubstituted C1-C10 alkyl group, and

[0058] n and m are mole fractions respectively, 50 mol% ≤ n ≤ 90 mol%, 10 mol% ≤ m ≤ 50 mol%.

[0059] If the polymer represented by Chemical Formula 1 is exposed to a high temperature of 100° C. or higher (for example, when the polymer represented by Chemical Formula 1 is exposed to a high temperature of 100° C. or higher), the polymer represented by Chemical Formula 1 can be crystallized and gelled in the liquid electrolyte, thereby not only inhibiting or reducing the gasification of the liquid electrolyte and the resulting expansion of the battery, but also inhibiting or reducing the ion conduction and electron conduction of the battery and by preventing or reducing the violent energy release caused by direct contact (short circuit) between the positive electrode and the negative electrode (for example, by a mechanism of physically fixing the PE separator that melts and shrinks at about 140° C.), thereby inhibiting or reducing the fire and explosion of the battery, thereby improving the safety of the battery.

[0060] In one or more embodiments, before any problem occurs, such as high temperature, shock, etc., the polymer represented by Chemical Formula 1 is dispersed in a liquid electrolyte. Here, the liquid electrolyte including the polymer represented by Chemical Formula 1 is different from a solid electrolyte formed by polymerizing the polymer with a polymerization initiator in terms of electrolyte phase.

[0061] Since the solid electrolyte exists in the battery in a solid state, the battery may exhibit relatively low output and short cycle life due to relatively low ion conductivity. By comparing with the comparative example, the battery to which the liquid electrolyte according to the present disclosure is applied may exhibit significantly different effects.

[0062] For example, the ratio of n to m (n:m) may be about 80 mol %: about 20 mol % to about 60 mol %: about 40 mol % or about 80 mol %: about 20 mol % to about 70 mol %: about 30 mol %.

[0063] The higher the content (eg, amount) of the vinylidene fluoride structural unit in the polymer relative to the content (eg, amount) of the trifluoroethylene structural unit, the more effective the improvement in battery stability is.

[0064] The molecular weight of the polymer may be from about 100,000 g / mol to about 400,000 g / mol.

[0065] For example, the molecular weight of the polymer may be from about 200,000 g / mol to about 400,000 g / mol.

[0066] The polymer may be in the form of (or provided in the form of) particles having an average particle size (ie, average particle size (D50)) of about 10 nm to about 1 μm.

[0067] For example, the average particle size of the polymer may be about 10 nm to about 900 nm, about 10 nm to about 800 nm, about 10 nm to about 700 nm, or about 10 nm to about 600 nm.

[0068] For example, the average particle size of the polymer is about 30 nm to about 1 μm, about 50 nm to about 1 μm, about 100 nm to about 1 μm, about 100 nm to about 900 nm, about 100 nm to about 800 nm, about 100 nm to about 700 nm, or about 100 nm to about 600 nm.

[0069] The polymer may be in the form of particles, and if the average particle size is within any one of the above ranges (for example, when the average particle size is within any one of the above ranges), the precipitation of the polymer in the liquid electrolyte can be alleviated or reduced, thereby reducing the capacity degradation caused by repetition of cycles.

[0070] In some embodiments, R in Chemical Formula 1 1 ~R 3 They may each independently be hydrogen or a substituted or unsubstituted C1-C5 alkyl group.

[0071] For example, the polymer may be poly(vinylidene fluoride-co-trifluoroethylene).

[0072] The polymer may gel at a temperature of about 100°C to about 120°C.

[0073] For example, the polymer may be included in an amount of about 0.1 parts by weight to about 15 parts by weight based on a total of 100 parts by weight of the liquid electrolyte.

[0074] For example, the polymer may be included in an amount of about 0.5 to about 15 parts by weight, for example, about 1 to about 15 parts by weight or about 5 to about 15 parts by weight, based on a total of 100 parts by weight of the liquid electrolyte.

[0075] When the polymer content (eg, amount) is within the range as described above, a rechargeable lithium battery with improved stability may be implemented by preventing or reducing an increase in resistance at high temperatures while securing (eg, substantially maintaining) cycle-life characteristics and output characteristics.

[0076] The nonaqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0077] The non-aqueous organic solvent may include a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent and / or an aprotic solvent.

[0078] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. In one or more embodiments, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitriles (such as R 1 -CN, where R 1 It is a C2-C20 straight-chain hydrocarbon group, a branched hydrocarbon group or a cyclic hydrocarbon group, and may include a double bond, an aromatic ring or an ether bond, etc.), an amide (such as dimethylformamide), a dioxolane (such as 1,3-dioxolane and / or 1,4-dioxolane), sulfolane, etc.

[0079] The nonaqueous organic solvent may be used alone (eg, only the nonaqueous organic solvent itself) or in a mixture. When the nonaqueous organic solvent is used in a mixture, the mixture ratio may be controlled or selected according to desired battery performance.

[0080] The nonaqueous organic solvent according to one or more embodiments may include the cyclic carbonate and the chain carbonate in a volume ratio of about 10 vol%:90 vol% to about 50 vol%:50 vol%.

[0081] For example, the nonaqueous organic solvent may include cyclic carbonates and chain carbonates in a volume ratio of about 10 vol%:90 vol% to about 40 vol%:60 vol%, for example, about 10 vol%:90 vol% to about 30 vol%:70 vol% or about 10 vol%:90 vol% to about 25 vol%:75 vol%.

[0082] When a non-aqueous organic solvent of the composition mentioned above is used, as the polymer in the liquid electrolyte gels above a specific temperature or a set temperature, the viscosity of the liquid electrolyte increases, and as the resistance increases, the gel polymer acts as an insulator and blocks or reduces the ion conduction and electron conduction of the battery, thereby ensuring (or improving) the stability of the battery.

[0083] The liquid electrolyte may further include at least one other additive selected from the following: vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetrinitrile (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2) and 2-fluorobiphenyl (2-FBP).

[0084] By further including any of the other additives mentioned above, the cycle life of the battery can be further improved, and / or if the battery is stored at high temperature (for example, when the battery is stored at high temperature), the gas generated from the positive electrode and the negative electrode can be effectively or appropriately controlled.

[0085] The other additives may be included in an amount of about 0.2 to about 20 parts by weight, for example, about 0.2 to about 15 parts by weight or about 0.2 to about 10 parts by weight, based on a total of 100 parts by weight of the liquid electrolyte for a rechargeable lithium battery.

[0086] If the content (eg, amount) of the other additives is within any one of the above ranges, the other additives may contribute to improving battery performance by minimizing or reducing an increase in membrane resistance.

[0087] The lithium salt dissolved in the non-aqueous organic solvent supplies lithium ions in the battery, ensures the basic operation of the rechargeable lithium battery, and improves the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts include at least one selected from the following: LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+ 1SO2) (wherein x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB) and lithium bis(oxalato)borate (LiBOB).

[0088] One or more embodiments of the present disclosure provide a rechargeable lithium battery including: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and a liquid electrolyte according to the present embodiment.

[0089] The positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material and may optionally further include a binder and / or a conductive material.

[0090] The positive electrode active material may include a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). For example, a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and a combination thereof may be used.

[0091] The composite oxide may be a lithium transition metal composite oxide. Examples of the composite oxide may include lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, nickel manganese oxides without cobalt, and / or combinations thereof (eg, any appropriate combination).

[0092] For example, the following compounds represented by any one of the following chemical formulas may be used: Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, and 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, and 0<α<2); Li a Ni b Co c L 1 d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, and 0≤e≤0.1); Li a NeG bO2(0.90≤a≤1.8 and 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn b O4 (0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn 1- g G g PO4(0.90≤a≤1.8 and 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2); and / or Li a FePO4(0.90≤a≤1.8).

[0093] In the above chemical formula, A is Ni, Co, Mn and / or a combination thereof (e.g., any suitable combination); X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element and / or a combination thereof (e.g., any suitable combination); D is O, F, S, P and / or a combination thereof (e.g., any suitable combination); G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and / or a combination thereof (e.g., any suitable combination); and L 1 is Mn, Al, and / or combinations thereof (eg, any suitable combination).

[0094] The positive electrode active material may be, for example, a high nickel-based positive electrode active material having a nickel content (e.g., amount) of about 80 mol%, about 85 mol%, about 90 mol%, about 91 mol%, or about 94 mol% and about 99 mol% or less based on 100 mol% of metals other than lithium in the lithium transition metal composite oxide. The high nickel-based positive electrode active material may be capable of achieving a relatively or appropriately high capacity and may be applied to high-capacity, high-density rechargeable lithium batteries.

[0095] The amount of the positive electrode active material may be about 90 wt % to about 99.9 wt % based on 100 wt % of the positive electrode active material layer, and the amount of the binder and the amount of the conductive material may be about 0.1 wt % to about 5 wt % based on 100 wt % of the positive electrode active material layer, respectively.

[0096] The binder is used to make the positive electrode active material particles well or properly attached to each other and also to make the positive electrode active material well or properly attached to the positive electrode current collector. Examples of binders may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth) acrylated styrene-butadiene rubber, epoxy resin, (meth) acrylic resin, polyester resin, nylon, etc. as non-limiting examples.

[0097] Conductive materials can be used to impart electrical conductivity (e.g., electrical conductivity) to the electrodes. Any suitable material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in a rechargeable lithium battery) and conducts electrons can be used in the battery. Examples of conductive materials may include carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and / or carbon nanotubes); metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powders and / or metal fibers; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0098] Al foil may be used as a positive electrode current collector, but the present disclosure is not limited thereto.

[0099] The negative electrode includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material and may optionally further include a binder and / or a conductive material.

[0100] The negative electrode active material may include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, and / or a transition metal oxide.

[0101] The material that reversibly intercalates / deintercalates lithium ions may include a carbon-based negative electrode active material (such as, for example, crystalline carbon, amorphous carbon and / or a combination thereof (e.g., any suitable combination)). The crystalline carbon may be graphite (such as amorphous (e.g., not in any specific shape), flaky, sheet-like, spherical and / or fibrous natural graphite and / or artificial graphite). The amorphous carbon may be soft carbon, hard carbon, a mesophase pitch carbonization product, calcined coke, etc.

[0102] Lithium metal alloys include alloys of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0103] Materials capable of doping / de-doping lithium can be Si-based negative electrode active materials and / or Sn-based negative electrode active materials. Si-based negative electrode active materials can include silicon, silicon-carbon composites, SiO x (0 < x < 2), Si-Q alloys (where Q is selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and / or combinations thereof (e.g., any suitable combination)). Sn-based negative electrode active materials can include Sn, SnO2, Sn-based alloys, and / or combinations thereof (e.g., any suitable combination).

[0104] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one or more embodiments, the silicon-carbon composite can be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite can include secondary particles (cores) in which primary silicon particles are assembled and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon can also be between the primary silicon particles, and, for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be present in an amorphous carbon matrix (e.g., can be dispersed in the amorphous carbon matrix).

[0105] The silicon-carbon composite can further include crystalline carbon. For example, the silicon-carbon composite can include: a core including crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core.

[0106] Si-based negative electrode active materials and / or Sn-based negative electrode active materials can be used in combination with carbon-based negative electrode active materials.

[0107] For example, the negative electrode active material layer can include about 90 wt% to about 99 wt% of the negative electrode active material, about 0.5 wt% to about 5 wt% of the binder, and about 0 wt% to about 5 wt% of the conductive material.

[0108] The binder can be used to make the negative electrode active material particles attach well or properly to each other and also to make the negative electrode active material attach well or properly to the negative electrode current collector. The binder can include non-aqueous binders, aqueous binders, dry binders, and / or combinations thereof (e.g., any suitable combination).

[0109] Non-aqueous binders can include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and / or combinations thereof (e.g., any suitable combination).

[0110] The aqueous binder can be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol and / or combinations thereof (e.g., any suitable combination).

[0111] When the aqueous binder is used as the negative electrode binder, the aqueous binder may further include a cellulose compound capable of imparting appropriate viscosity. The cellulose compound includes one or more selected from carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose and alkali metal salts thereof. The alkali metal may be Na, K and / or Li.

[0112] The dry binder may be a polymer material that can be appropriately fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, and / or combinations thereof (eg, any suitable combination).

[0113] A conductive material is included to provide electrode conductivity, and any suitable conductive material may be used as the conductive material unless it causes chemical changes in the battery (e.g., undesirable chemical changes). Examples of the conductive material may be carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.); metal-based materials in the form of metal powder and / or metal fiber (such as copper, nickel, aluminum, silver, etc.); conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0114] The negative electrode current collector may include one selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and / or combinations thereof (eg, any appropriate combination), but the present disclosure is not limited thereto.

[0115] Depending on the type or kind of rechargeable lithium battery, the separator may be present between the positive electrode and the negative electrode. The separator may include a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, and / or a multilayer film of two or more layers thereof such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.

[0116] The separator may include a porous substrate and a coating including an organic material, an inorganic material, and / or a combination thereof (eg, any suitable combination) on one or both surfaces (eg, opposing surfaces) of the porous substrate.

[0117] The porous substrate may be a polymer film formed by any one selected from the group consisting of polymer polyolefins (such as polyethylene and / or polypropylene), polyesters (such as polyethylene terephthalate and / or polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyarylether ketones, polyetherimides, polyamideimides, polybenzimidazoles, polyether sulfones, polyoxyxylenes, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, Teflon, and polytetrafluoroethylene, or may be a copolymer or mixture of two or more thereof.

[0118] The organic material may include a polyvinylidene fluoride-based polymer and / or a (meth)acrylic polymer.

[0119] The inorganic material may include inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof (e.g., any suitable combination), but the present disclosure is not limited thereto.

[0120] An organic material and an inorganic material may be mixed in one coating layer, or a coating layer including an organic material and a coating layer including an inorganic material may be stacked.

[0121] Hereinafter, examples and comparative examples of the present disclosure are described. However, these examples are not to be construed as limiting the scope of the present disclosure in any sense.

[0122] Example: Fabrication of a rechargeable lithium battery cell

[0123] Example 1

[0124] LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed in a weight ratio of 97.5:1:1.5, and then dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0125] The positive electrode active material slurry was coated on a 15 μm thick Al foil, then, dried at 100° C., and pressed to manufacture a positive electrode.

[0126] Negative electrode active material slurry was prepared by mixing artificial graphite as a negative electrode active material, a styrene-butadiene rubber binder, and carboxymethyl cellulose at a weight ratio of 98:1:1, and then dispersing the mixture in distilled water.

[0127] The negative electrode active material slurry was coated on a 10 μm thick Cu foil, and then, dried at 100° C. and pressed to manufacture a negative electrode.

[0128] The manufactured positive electrode and negative electrode were assembled with a 10 μm thick polyethylene separator to manufacture an electrode assembly, and the following liquid electrolyte was injected therein to manufacture a rechargeable lithium battery cell.

[0129] The composition of the liquid electrolyte is as follows.

[0130] Liquid electrolyte composition

[0131] Lithium salt: 1.15M LiPF6

[0132] Non-aqueous organic solvent: ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate (EC:EMC:DMC=20:40:40 volume ratio)

[0133] additive:

[0134] (1) Polymer: 15 parts by weight 200 / P200 (Mw=200,000, n:m=80 mol%:20 mol%; from Solvay SA),

[0135] (2) 1 part by weight of vinylene carbonate (VC)

[0136] In the above composition of the liquid electrolyte, "parts by weight" refers to the relative weight of the additive with respect to 100 parts by weight of the total weight (lithium salt and nonaqueous organic solvent) of the liquid electrolyte excluding the additive.

[0137] Example 2

[0138] A rechargeable lithium battery cell was manufactured in substantially the same manner as in Example 1, except that 200 / P400 (Mw = 400,000, n:m = 80 mol%: 20 mol%; Solvay SA) instead 200 / P200.

[0139] Example 3

[0140] A rechargeable lithium battery cell was manufactured in substantially the same manner as in Example 1, except that 250 / P400 (Mw = 400,000, n:m = 75 mol%: 25 mol%; Solvay SA) instead 200 / P200.

[0141] Example 4 and Example 5

[0142] Rechargeable lithium battery cells were each manufactured in substantially the same manner as in Example 1, except that the content (eg, amount) of the polymer was changed to 5 parts by weight and 10 parts by weight, respectively, instead of 15 parts by weight.

[0143] Comparative Example 1

[0144] A rechargeable lithium battery cell was manufactured in substantially the same manner as in Example 1, except that no polymer was used.

[0145] Comparative Example 2

[0146] A rechargeable lithium battery cell was manufactured in substantially the same manner as in Example 1, except that 1 g of the polymer ( 200 / P200) and 0.5 g of a polymerization initiator (AIBN) were added to 95.5 g of a non-aqueous organic solvent (ethylene carbonate: ethylmethyl carbonate: dimethyl carbonate = 20:40:40, volume ratio) in which 1.15 M LiPF6 and 1 part by weight of vinyl carbonate (VC) were dissolved to prepare a gel polymer electrolyte, and then the mixture was heated at 60°C for 24 hours.

[0147] Evaluation 1: Evaluation of high temperature (45°C) cycle life characteristics

[0148] The rechargeable lithium battery cells according to Example 1, Example 4 and Example 5 and Comparative Example 1 were charged and discharged at 1C for 3 cycles, and charged at 1.5C and discharged at 1C for 50 consecutive cycles, and then measured for specific capacity and coulombic efficiency, and the results are shown in Figure 5 Herein, the voltage range for charge and discharge was 3.0 V to 4.2 V (discharge as low as 3.0 V and charge as high as 4.2 V), and the evaluation was performed at 45°C.

[0149] Figure 5 is a graph showing specific capacity and coulombic efficiency according to the number of cycles during high temperature charging and discharging of a rechargeable lithium battery cell.

[0150] refer to Figure 5 , a liquid electrolyte including the polymer of the present disclosure is able to maintain (e.g., has maintained) a specific capacity and coulombic efficiency substantially equal to or at a higher level than that of a liquid electrolyte not including the polymer. Accordingly, it can be expected that the cycle life characteristics of a rechargeable lithium battery cell including the polymer of the present disclosure will not deteriorate, but will be substantially maintained at an excellent or appropriate level.

[0151] Assessment 2: Hot Box Assessment

[0152] After the formation cycle, the pouch-type full-battery cells of Examples 1 to 5 and Comparative Example 1 were charged to SOC50 (e.g., state of charge 50%) (3.94 V) and exposed to silicone oil at 130° C. for 5 minutes to compare the degree of volume expansion (thickness), and the results are shown in Figure 6 middle.

[0153] Figure 6 Graphs showing the results of a hot box test of a pouch-type full-battery cell.

[0154] refer to Figure 6 , the pouch-type full-battery cell (Comparative Example 1) not including the polymer was ruptured due to volume expansion by gasification of the liquid electrolyte (e.g., as a result of gasification of the electrolyte), but in the pouch-type full-battery cell (Examples 1 to 5) including the polymer of the present embodiment, gasification of the liquid electrolyte was suppressed or reduced, and the pouch-type full-battery cell showed reduced volume expansion. In one or more embodiments, if a liquid electrolyte containing a polymer is included (e.g., when a liquid electrolyte containing a polymer is included), thermal safety is improved even in an environment stored at high temperatures.

[0155] Evaluation 3: TG (thermogravimetric analysis) evaluation

[0156] In order to measure the weight change of the material according to the temperature change, TGA analysis was performed on Example 1 and Comparative Examples 1 and 2, and the results are shown in Figure 7 middle.

[0157] Figure 7 Graphs showing the results of TGA analysis of the liquid electrolytes of Example 1 and Comparative Examples 1 and 2 according to the present invention.

[0158] refer to Figure 7 As a result of TGA analysis, in the liquid electrolyte of Example 1, the mass at room temperature was halved due to gasification and thermal decomposition at 124°C, which was 42°C higher than the temperature of 82°C at which the mass of the liquid electrolyte of Comparative Example 1 (excluding the polymer) was halved. Without being bound by any particular theory, it is believed that the reason is that if a liquid electrolyte in which a polymer is dissolved is introduced (for example, when a liquid electrolyte in which a polymer is dissolved is introduced), a non-aqueous organic solvent participates in the dissolution of the polymer so that the boiling point is increased due to the van der Waals force between the polymer and the non-aqueous organic solvent, thereby delaying the gasification of the liquid electrolyte at high temperature, and thus delaying the explosion of the rechargeable lithium battery cell due to battery expansion and an increase in the internal pressure of the battery.

[0159] In contrast, if the polymer itself is evaluated (for example, when the polymer itself is evaluated), since mass halving does not occur in Comparative Example 2 where the gel polymer electrolyte is applied, the effect of delaying the gasification of the liquid electrolyte and the effect of delaying the battery explosion due to battery swelling and increased internal pressure similar to the effects expected in the present disclosure are not expected.

[0160] Evaluation 4: Evaluation of high temperature DC internal resistance DC-IR characteristics

[0161] The rechargeable lithium battery cells of Example 1 and Comparative Example 1 were measured for initial DC internal resistance (DC-IR) by ΔV / ΔI (voltage change / current change), and then, after the internal maximum energy state of the rechargeable lithium battery cell was made to be a fully charged state (SOC 100%), the battery cell resistance at room temperature (25°C) was remeasured, and if kept for 1 hour after reaching a high temperature (120°C) (for example, when kept for 1 hour after reaching a high temperature (120°C)), the battery cell resistance at high temperature (120°C) was remeasured, and the results are shown in FIG. Figure 8 middle.

[0162] Figure 8 Results of measuring the cell resistance of a rechargeable lithium battery cell after reaching room temperature (25° C.) and high temperature (120° C.) for 1 hour, respectively, are shown.

[0163] refer to Figure 8 If the temperature of the rechargeable lithium battery cell of Example 1 in which a liquid electrolyte is introduced rises to 120°C (for example, when the temperature of the rechargeable lithium battery cell of Example 1 in which a liquid electrolyte is introduced rises to 120°C), the resistance increases significantly at least in part due to the gel of the liquid electrolyte, and the gelled liquid electrolyte serves as an insulator between the positive electrode and the negative electrode, thereby reducing the risk of sudden energy release, explosion and / or fire due to a short circuit between the positive electrode and the negative electrode.

[0164] Evaluation 5: Evaluation of DC internal resistance (DC-IR) characteristics after exposure to high temperature

[0165] The initial DC internal resistance (DC-IR) was measured for the rechargeable lithium battery cells of Example 1 and Comparative Example 2 by ΔV / ΔI (voltage change / current change), and then, after the internal maximum energy state of the rechargeable lithium battery cells was brought to a fully charged state (SOC 100%), the high temperature (60°C) DC internal resistance was remeasured, and after being placed at high temperature (60°C) for 5 days, the DC internal resistance was remeasured, and the DC internal resistance increase rate was calculated, and the results are shown in Table 1.

[0166] Table 1

[0167]

[0168] Referring to Table 1, during the formation of the gel polymer (Comparative Example 2), even at 50°C to 60°C (for example, where the polymerization initiator works), the rechargeable lithium battery cell of Comparative Example 2 shows a significant increase in DC internal resistance compared to the rechargeable lithium battery cell of Example 1 and shows a higher DC internal resistance after being placed at high temperature. In addition, compared with the rechargeable lithium battery cell of Example 1, it shows a significantly higher DC internal resistance increase rate due to the additional increase in DC internal resistance (at least partially due to the substantially continuous cross-linking reaction).

[0169] In contrast, the polymer in the liquid electrolyte of Example 1 gels at 100°C to 120°C, has almost no increase in DC internal resistance at 60°C, and exhibits relatively low DC internal resistance after being left at 60°C.

[0170] Accordingly, it is believed that the liquid electrolyte including the polymer additive according to the present disclosure gels due to crystallization of the polymer at a relatively high temperature, and the gelled liquid electrolyte forms a solid film, which acts as an insulator and blocks or reduces the ionic conductivity and electrical conductivity between the positive electrode and the negative electrode, thereby inhibiting or reducing the fire and / or explosion of the rechargeable lithium battery cell.

[0171] In addition, it is considered that the gel liquid electrolyte of the present embodiment suppresses or reduces the shrinkage of the separator at high temperature by physically bonding the positive electrode-separator-negative electrode, thereby preventing or reducing the short circuit between the positive electrode and the negative electrode.

[0172] Although the embodiments of the present disclosure have been described herein above, the present disclosure is not limited thereto and may be implemented by one or more appropriate modifications within the scope of the detailed description, the accompanying drawings and the claims, and their equivalents.

Claims

1. A liquid electrolyte comprising: Lithium salts; Non-aqueous organic solvents; as well as additive, The additive comprises a polymer represented by Chemical Formula 1: Chemical formula 1 In Chemical Formula 1, R 1 ~R 3 are each independently hydrogen, fluorine or a substituted or unsubstituted C1-C10 alkyl group, and n and m are mole fractions respectively, 50 mol% ≤ n ≤ 90 mol%, 10 mol% ≤ m ≤ 50 mol%.

2. The liquid electrolyte according to claim 1, wherein The ratio of n to m is 80 mol%:20 mol% to 60 mol%:40 mol%.

3. The liquid electrolyte according to claim 1, wherein The molecular weight of the polymer is 100,000 g / mol to 400,000 g / mol.

4. The liquid electrolyte according to claim 1, wherein The polymer is in the form of particles having an average particle size of 10 nm to 1 μm.

5. The liquid electrolyte according to claim 1, wherein R in Formula 1 1 ~R 3 Each is independently hydrogen or substituted or unsubstituted C1-C5 alkyl.

6. The liquid electrolyte according to claim 1, wherein The polymer is poly(vinylidene fluoride-co-trifluoroethylene).

7. The liquid electrolyte according to claim 1, wherein The polymer gels at a temperature of 100°C to 120°C.

8. The liquid electrolyte according to claim 1, wherein The amount of the polymer is 0.1 parts by weight to 15 parts by weight based on 100 parts by weight in total of the liquid electrolyte.

9. The liquid electrolyte according to claim 1, wherein The non-aqueous organic solvent includes cyclic carbonate and chain carbonate in a volume ratio of 10 vol%:90 vol% to 50 vol%:50 vol%.

10. The liquid electrolyte according to claim 1, wherein The liquid electrolyte further includes at least one other additive selected from vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate, adiponitrile, succinonitrile, 1,3,6-hexanetrinitrile, propylene sultone, propane sultone, lithium tetrafluoroborate, lithium difluorophosphate and 2-fluorobiphenyl.

11. A rechargeable lithium battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; as well as The liquid electrolyte according to any one of claims 1 to 10.

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