Additive for rechargeable lithium battery, electrolyte for rechargeable lithium battery including additive, and rechargeable lithium battery

Abstract

Provided are an additive for a rechargeable lithium battery, an electrolyte for a rechargeable lithium battery including the additive, and a rechargeable lithium battery, the additive including: a core including a polyethylene wax and a shell surrounding the core, where the shell includes a polymer having a melting point of 90 DEG C to 120 DEG C.

Description

Technical Field

[0001] The present disclosure relates to an additive for a rechargeable lithium battery, an electrolyte for a rechargeable lithium battery including the additive, and a rechargeable lithium battery. Background Art

[0002] Rechargeable lithium batteries are rechargeable and have an energy density per unit weight that is three times or more higher than that of conventional lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, etc. Rechargeable lithium batteries can also be charged at a high rate, and therefore are commercially manufactured for use in laptop computers, cellular phones, power tools, electric bicycles, etc., and research on improving the additional energy density has been actively conducted.

[0003] Such a rechargeable lithium battery is manufactured by injecting an electrolyte into a battery cell including a positive electrode containing a positive electrode active material capable of intercalating / deintercalating lithium ions and a negative electrode containing a negative electrode active material capable of intercalating / deintercalating lithium ions.

[0004] In particular, the electrolyte includes an organic solvent in which a lithium salt is dissolved and critically determines the stability and performance of a rechargeable lithium battery.

[0005] LiPF6, the most commonly used lithium salt for electrolytes, reacts with the electrolyte solvent, accelerating solvent consumption and generating large amounts of gas. When LiPF6 decomposes, it produces LiF and PF5, which deplete the electrolyte in the battery, leading to deterioration in high-temperature performance and safety vulnerabilities.

[0006] Accordingly, there is a need for an electrolyte having improved safety without deteriorating performance even under high temperature conditions. Summary of the Invention

[0007]

Technical Issues

[0008] Embodiments provide an additive for a rechargeable lithium battery having improved thermal stability.

[0009] Another embodiment provides an electrolyte for a rechargeable lithium battery having improved cycle-life characteristics, high-temperature safety, and high-temperature reliability through the application of additives.

[0010] Another embodiment provides a rechargeable lithium battery including the electrolyte for a rechargeable lithium battery.

[0011]

Technical solution

[0012] An additive for a rechargeable lithium battery according to an embodiment includes a core including polyethylene wax and a shell surrounding the core, wherein the shell includes a polymer having a melting point of 90° C. to 120° C.

[0013] The ratio of the thickness of the core to the thickness of the shell may be 1:1 to 4:1.

[0014] The core may have a thickness of 0.1 μm to 2.0 μm, and the shell may have a thickness of 0.025 μm to 0.5 μm.

[0015] The polymer may include poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyacrylic acid, polyethylene, poly(methyl methacrylate), polyalkylene oxide, polyalkylene succinate, or combinations thereof.

[0016] The additive may be in the form of fibers formed using electrospinning.

[0017] According to another embodiment, an electrolyte for a rechargeable lithium battery includes a non-aqueous organic solvent, a lithium salt, and the aforementioned additive for a rechargeable lithium battery.

[0018] The additive for a rechargeable lithium battery may be included in an amount of 0.1 wt % to 20 wt %, 0.1 wt % to 15 wt %, or 0.1 wt % to 10 wt % based on the total weight of the electrolyte for a rechargeable lithium battery.

[0019] According to another embodiment, a rechargeable lithium battery includes: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0020] Beneficial effects

[0021] The additive for a rechargeable lithium battery according to an embodiment may have excellent electrolyte impregnation characteristics and may maintain battery characteristics without increasing battery resistance when applied to an electrolyte.

[0022] In addition, the rechargeable lithium battery including the additive for a rechargeable lithium battery according to the embodiment may suppress the occurrence of a short circuit due to an increase in resistance exceeding a battery operating temperature and improve the safety of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a cross-sectional view of an additive according to an embodiment.

[0024] Figure 2 is a schematic diagram illustrating a rechargeable lithium battery according to an embodiment.

[0025] <Description of Symbols>

[0026] 100: Rechargeable lithium battery

[0027] 112: Negative electrode

[0028] 113: Diaphragm

[0029] 114: Positive electrode

[0030] 120: Battery housing

[0031] 140: Sealing component DETAILED DESCRIPTION

[0032] Hereinafter, the embodiments will be described in detail so that those skilled in the art can easily implement them. However, the structure of actual application can be implemented in several different forms and is not limited to the embodiments described herein.

[0033] In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity.

[0034] It will be understood that when an element (such as a layer, film, region, or substrate) is referred to as being "on" another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present.

[0035] In this specification, “at least one of A, B, or C,” “one of A, B, C, or a combination thereof,” and “one and a combination of A, B, C” mean each individual component and all combinations thereof (e.g., A; B; A and B; A and C; B and C; or A, B, and C).

[0036] Hereinafter, the term "combination" includes a mixture of two or more, mutual replacement and a stacked structure of two or more.

[0037] In this specification, when no other definition is provided, the particle size can be measured by methods well known to those skilled in the art, for example, by a particle size analyzer, or by an optical microscope photograph (such as a transmission electron micrograph or a scanning electron micrograph). Alternatively, the average particle size value can be obtained by measuring using a dynamic light scattering method, performing data analysis, counting the number of particles in each particle size range, and calculating therefrom. As used herein, when no other definition is provided, the particle size can refer to the diameter (D50) of the particles having a cumulative volume of 50% by volume in a particle size distribution.

[0038] Below, the following references Figure 1 An additive for a rechargeable lithium battery according to an embodiment is described.

[0039] Figure 1 is a cross-sectional view of an additive according to an embodiment.

[0040] refer to Figure 1, the additive 1 according to the embodiment includes a core 3 and a shell 5 surrounding the core 3. The core 3 includes polyethylene wax, and the shell 5 includes a polymer having a melting point of 90°C to 120°C.

[0041] Because additive 1 has a structure including core 3 and shell 5, additive 1 can maintain the battery's characteristics without increasing the battery's resistance, compared to when the core material is introduced into the battery as is. Furthermore, because core 3 includes a safety-enhancing material, when shell 5 of the additive melts at high temperatures, the material is released from core 3 to the outside, thereby increasing the battery's resistance, causing a voltage drop, and suppressing the occurrence of a short circuit in the battery.

[0042] The ratio of the thickness of the core 3 to the thickness of the shell 5 may be 1:1 to 4:1 (eg, 3:2, eg, 2:1, eg, 5:2, eg, 3:1), but is not limited thereto.

[0043] When the thickness ratio of the core 3 to the shell 5 is within the above range, the time required for the shell 5 to melt and release the core material can be adjusted to an appropriate range, and the occurrence of electrode short circuits at high temperatures can be effectively controlled. In addition, when not in a high temperature state, the shell 5 is not easily damaged, which prevents unnecessary increases in battery resistance and degradation of battery characteristics.

[0044] When the additive including the core 3 and the shell 5 is in the form of a fiber, the "thickness of the core" refers to the straight-line length of a line segment from the center of a circular surface which is a cross section of the fiber to a point on the circumference of the core, and the "thickness of the shell" refers to the straight-line length between the point where a line segment from the center of a circular surface which is a cross section of the fiber to a point on the circumference of the shell intersects the circumference of the core and the point where the line segment intersects the circumference of the shell when the line segment is connected.

[0045] When the additive including the core 3 and the shell 5 is spherical, the "thickness of the core" refers to the length of a line segment from the center of the sphere to a point on the surface of the core, and the "thickness of the shell" refers to the length of a line segment between the point where the line segment from the center of the sphere to the point on the surface of the shell intersects the surface of the core and the point where the line segment intersects the surface of the shell.

[0046] The thickness of the core 3 may be 0.1 μm to 2.0 μm, for example, greater than or equal to 0.1 μm, greater than or equal to 0.15 μm, greater than or equal to 0.20 μm, greater than or equal to 0.25 μm, greater than or equal to 0.30 μm or greater than or equal to 0.35 μm, and less than or equal to 2.0 μm, for example, less than or equal to 1.5 μm, less than or equal to 1.4 μm, less than or equal to 1.3 μm, less than or equal to 1.2 μm, less than or equal to 1.1 μm or less than or equal to 1.0 μm, but is not limited thereto.

[0047] Because the core 3 has a thickness within the above range, the material of the core is released in a timely manner together with the melting of the shell 5, thereby effectively controlling the occurrence of electrode short circuits while maintaining battery characteristics without degrading electrolyte impregnation characteristics and unnecessarily increasing battery resistance.

[0048] The particle size of the polyethylene wax may be 0.05 μm to 1.5 μm, for example, greater than or equal to 0.05 μm, greater than or equal to 0.10 μm, greater than or equal to 0.15 μm, greater than or equal to 0.20 μm, greater than or equal to 0.25 μm, or greater than or equal to 0.30 μm, and less than or equal to 1.5 μm, for example, less than or equal to 1.2 μm, less than or equal to 1.0 μm, less than or equal to 0.8 μm, or less than or equal to 0.6 μm, but is not limited thereto. Particle size may also be referred to as particle size, and if the polyethylene wax is spherical, the particle size may refer to the diameter, or if the polyethylene wax is not spherical, the particle size refers to the length of the longest axis.

[0049] Because the polyethylene wax has a particle size within the above range, the polyethylene wax may be effectively included in the core, and the polyethylene wax may be effectively released from the core as the shell melts at high temperature, thereby increasing battery resistance.

[0050] In addition, the polyethylene wax may have a melting point of 100° C. to 140° C., but is not limited thereto.

[0051] The thickness of the shell 5 may be 0.025 μm to 0.5 μm, for example, greater than or equal to 0.025 μm, greater than or equal to 0.05 μm, greater than or equal to 0.075 μm, greater than or equal to 0.10 μm, greater than or equal to 0.125 μm or greater than or equal to 0.15 μm, and less than or equal to 0.5 μm, for example, less than or equal to 0.45 μm, less than or equal to 0.40 μm, less than or equal to 0.35 μm or less than or equal to 0.30 μm, but is not limited thereto.

[0052] Because the shell 5 has a thickness within the above range, the occurrence of electrode short circuits can be effectively controlled while maintaining battery characteristics by not unnecessarily increasing battery resistance through melting of the shell 5 and release of the core material in a timely manner.

[0053] In an embodiment, the shell 5 may include a polymer having a melting point of 90° C. to 120° C., and for example, the melting point of the polymer may be greater than or equal to 90° C., for example, greater than or equal to 95° C., for example, greater than or equal to 100° C., and for example, the melting point of the polymer may be less than or equal to 120° C., for example, less than or equal to 115° C., for example, less than or equal to 110° C. For example, the polymer may be a thermoplastic resin.

[0054] Because the melting point of the polymer included in the shell 5 is within the above range, the shell 5 is stably maintained within the operating temperature range during charging and discharging of the battery, thereby not increasing the resistance of the battery, and the shell 5 can be properly melted at a high temperature of 100° C. or higher, and the safety-enhancing material of the core 3 is released in a timely manner, so that the occurrence of a short circuit in the battery is effectively controlled.

[0055] For example, the thermoplastic resin may be poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyacrylic acid, polyethylene, poly(methyl methacrylate), polyalkylene oxide, polyalkylene succinate, or a combination thereof, and for example, poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyalkylene oxide, polyalkylene succinate, or a combination thereof, but is not limited thereto.

[0056] The polyalkylene oxide may be polyethylene oxide, polypropylene oxide, polybutylene oxide, polypentane oxide, polyhexane oxide, polyheptane oxide, etc., and may be, for example, polyethylene oxide, polypropylene oxide, or polybutylene oxide, and may be, for example, polyethylene oxide, polypropylene oxide, etc., but is not limited thereto.

[0057] The polyalkylene succinate may be polyethylene glycol succinate, polypropylene glycol succinate, polybutylene glycol succinate, polypentylene glycol succinate, polyethylene glycol succinate, polyheptylene glycol succinate, or polyethylene oxide succinate, and may be, for example, polyethylene glycol succinate, polypropylene glycol succinate, or polybutylene glycol succinate, and may be, for example, polybutylene glycol succinate, but is not limited thereto.

[0058] The additive 1 may be in the form of fibers (i.e., fibers formed using electrospinning). When the additive is in the form of fibers, the core material can be effectively released at high temperatures, effectively controlling battery fires. In addition to the fiber form, the additive 1 may have a structure including a core 3 and a shell 5 surrounding the core 3, and may be irregular, plate-like, spherical, etc., but is not limited thereto.

[0059] When preparing the additive 1 having a core-shell structure, the electrospinning process may be performed by a known process in consideration of the material of the core and the melting point of the thermoplastic resin.

[0060] The polyethylene wax used in the electrospinning process may be in any form as long as it can be included in the core 3 , and may be in the form of, for example, particles, plates, sheets, and combinations thereof, but is not limited thereto.

[0061] An electrolyte for a rechargeable lithium battery according to another embodiment includes a non-aqueous organic solvent, a lithium salt, and the aforementioned additive 1.

[0062] The amount of the additive 1 included in the electrolyte for a rechargeable lithium battery may be 0.1 wt% to 20 wt%, 0.1 wt% to 15 wt%, or 0.1 wt% to 10 wt%, based on the total weight of the electrolyte for a rechargeable lithium battery. For example, the amount of the additive included may be greater than or equal to 0.1 wt%, for example, greater than or equal to 0.2 wt%, greater than or equal to 0.3 wt%, greater than or equal to 0.4 wt%, greater than or equal to 0.5 wt%, greater than or equal to 0.6 wt%, greater than or equal to 0.7 wt%, greater than or equal to 0.8 wt%, greater than or equal to 0.9 wt%, or greater than or equal to 1.0 wt% and less than or equal to 15.0 wt%, for example, less than or equal to 14.0 wt%, less than or equal to 13.0 wt%, less than or equal to 12.0 wt%, less than or equal to 11.0 wt%, less than or equal to 10.0 wt%, or less than or equal to 9.0 wt%, based on the total weight of the electrolyte for a rechargeable lithium battery, but is not limited thereto.

[0063] When the content of the additive 1 is within the above range, battery characteristics are maintained without increasing battery resistance at a battery operating temperature, and battery resistance is increased beyond the battery operating temperature, thereby realizing a rechargeable lithium battery with improved safety.

[0064] The non-aqueous organic solvent is used as a medium for transporting ions involved in the electrochemical reaction of the battery. The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, alcohol or aprotic solvent.

[0065] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanoic acid lactone, mevalonolactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraglyme, diglyme, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, tetrahydrofuran, etc. In addition, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitriles (such as R-CN, where R is a hydrocarbon group having a C2 to C20 linear, branched or cyclic structure, and may include a double bond, an aromatic ring or an ether bond, etc.), dioxolanes (such as 1,3-dioxolane, etc.), cyclopentane, etc.

[0066] The nonaqueous organic solvent may be used alone or in combination of one or more, and when a combination of one or more is used, the mixing ratio may be appropriately adjusted according to desired battery performance, which is widely understood by those skilled in the relevant art.

[0067] Carbonate solvents are prepared by mixing cyclic carbonates and chain carbonates. When the cyclic carbonates and chain carbonates are mixed in a volume ratio of 1:1 to 9:1, the electrolyte performance can be improved.

[0068] In addition to the carbonate-based solvent, the non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent. Herein, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0069] The aromatic hydrocarbon organic solvent may be an aromatic hydrocarbon compound of Chemical Formula 1.

[0070] [Chemical Formula 1]

[0071]

[0072] In Chemical Formula 1, R 201 ~R 206 are the same or different and are selected from hydrogen, halogen, C1-C10 alkyl, haloalkyl or a combination thereof.

[0073] Specific examples of aromatic hydrocarbon organic solvents may be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluoroform, Benzene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0074] The electrolyte may further include vinylene carbonate, vinyl ethylene carbonate, or the ethylene carbonate compound of Chemical Formula 2 as a cycle life enhancing additive to improve the battery cycle life.

[0075] [Chemical Formula 2]

[0076]

[0077] In Chemical Formula 2, R 207 and R 208 The same as or different from each other and may be selected from hydrogen, halogen, cyano (CN), nitro (NO2) or a fluorinated alkyl group having 1 to 5 carbon atoms.

[0078] Examples of the ethylene carbonate compound may include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of the cycle life enhancing additive may be used within an appropriate range.

[0079] 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.

[0080] Examples of lithium salts include those selected from the group consisting of LiPF6, LiBF4, LiDFOP, LiDFOB, LiPO2F2, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2), (wherein x and y are natural numbers, for example, integers from 1 to 20), at least one of LiCl, LiI or LiB(C2O4)2 (lithium bis(oxalato)borate: LiBOB).

[0081] The lithium salt may be used in a concentration range of 0.1 M to 2.0 M. If the lithium salt is included in the above concentration range, the electrolyte may have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

[0082] The additives and electrolytes can be applied to rechargeable lithium batteries.

[0083] Below, reference Figure 2 A rechargeable lithium battery according to an embodiment is described.

[0084] The rechargeable lithium battery 100 according to the embodiment includes: a positive electrode 114 including a positive electrode active material; a negative electrode 112 including a negative electrode active material; and the aforementioned electrolyte.

[0085] Rechargeable lithium batteries can be categorized as lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries, depending on the type of separator and electrolyte. Depending on their shape, they can also be classified as cylindrical, prismatic, coin-shaped, pouch-shaped, and other types. Furthermore, depending on their size, they can be either block-shaped or thin-film-shaped. The structures and manufacturing methods of these batteries are well known in the art.

[0086] Here, a cylindrical rechargeable lithium battery is exemplarily described as an example of the rechargeable lithium battery. Figure 2 Schematic diagram showing a rechargeable lithium battery according to an embodiment. Figure 2 The rechargeable lithium battery 100 includes a battery cell, an electrolyte for a rechargeable lithium battery (not shown), a battery case 120 that accommodates the battery cell, and a sealing member 140 that seals the battery case 120. The battery cell includes a positive electrode 114, a negative electrode 112 opposite to the positive electrode 114, and a separator 113 between the positive electrode 114 and the negative electrode 112. The electrolyte impregnates the positive electrode 114, the negative electrode 112, and the separator 113. The positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0087] The positive electrode active material may include a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). Specifically, at least one composite oxide of lithium and a metal including cobalt, manganese, nickel, or a combination thereof may be used.

[0088] A portion of the metal in the composite oxide may be replaced by a metal other than another metal, and the composite oxide may be at least one selected from phosphate compounds, for example, LiFePO 4 , LiCoPO 4 or LiMnPO 4 , and a composite oxide having a coating on its surface may also be used, or a composite oxide and a composite oxide having a coating may be mixed and used. The coating may include at least one coating element compound selected from an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, and a hydroxycarbonate of the coating element. The compound used for the coating may be amorphous or crystalline. The coating element included in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. By using these elements in the compound, the coating can be provided in a manner that does not adversely affect the properties of the positive electrode active material. For example, the method may include any coating method (e.g., spray coating, dip coating, etc.), but since it is well known to those skilled in the art, it is not explained in more detail.

[0089] The positive electrode active material may be, for example, at least one of the lithium composite oxides represented by Chemical Formula 3.

[0090] [Chemical Formula 3]

[0091] Li x M 1 y M 2 z M 3 1-y-z O2

[0092] In Chemical Formula 3,

[0093] 0.5 ≤ x ≤ 1.8, 0 < y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ y + z ≤ 1, and M 1 , M 2 and M 3 can each independently be a metal selected from Ni, Co, Mn, Al, Sr, Mg, or La, etc., and combinations thereof.

[0094] In an embodiment, the positive electrode active material can be selected from LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi a Mn b Co c O2 (a + b + c = 1), LiNi a Mn b Co c Al d O2 (a + b + c + d = 1), and LiNi e Co f Al g O2 (e + f + g = 1), and at least one of them.

[0095] For example, the positive electrode active material selected from LiNi a Mn b Co c O2 (a + b + c = 1), LiNi a Mn b Co c Al d O2 (a + b + c + d = 1), and LiNi e Co f Al g O2 (e + f + g = 1) can be a high nickel (high Ni) type positive electrode active material.

[0096] For example, in the case of LiNi a Mn b Co c O2 (a + b + c = 1) and LiNi a Mn b Co c Al d O2 (a + b + c + d = 1), the nickel content can be 60% or more (a ≥ 0.6), and more specifically, 80% or more (a ≥ 0.8).

[0097] For example, in LiNi e Co f Al gIn the case of O2 (e+f+g=1), the nickel content may be 60% or more (e≥0.6), and more specifically, 80% or more (e≥0.8).

[0098] The positive electrode active material may be included in an amount of 90 wt % to 98 wt % based on the total weight of the positive electrode active material layer.

[0099] The positive electrode active material layer may optionally include a conductive material and a binder. In this case, the conductive material and the binder may each be present in an amount of 1.0 wt % to 5.0 wt % based on the total weight of the positive electrode active material layer.

[0100] The conductive material is used to provide conductivity to the positive electrode, and any conductive material can be used as the conductive material unless it causes a chemical change, and examples of the conductive material may include: carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.); metal-based materials including metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0101] The binder improves the bonding properties between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of the binder include, but are not limited to, 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, acrylated styrene-butadiene rubber, epoxy resin, and nylon.

[0102] Al may be used as a positive electrode current collector, but is not limited thereto.

[0103] The negative electrode includes a negative electrode current collector and a negative electrode active material layer including a negative electrode active material formed on the negative electrode current collector.

[0104] 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, or a transition metal oxide.

[0105] The material that reversibly intercalates and deintercalates lithium ions may include a carbon material. The carbon material may be any carbon-based negative electrode active material commonly used in rechargeable lithium batteries, and examples of the carbon material may include crystalline carbon, amorphous carbon, or mixtures thereof. The crystalline carbon may be amorphous or in the form of flakes, sheets, spheres, or fibers of natural graphite or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, a mesophase pitch carbonization product, burned coke, or the like.

[0106] The lithium metal alloy includes an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0107] The material capable of doping / dedoping lithium can be Si, Si-C composite, SiO x (0 < x < 2), Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, Sn-R alloy (where R is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), etc. At least one of these materials can be mixed with SiO2.

[0108] The element Q and the element R can be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0109] The transition metal oxide can be vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

[0110] In a specific embodiment, the negative electrode active material can be a Si-C composite including a Si-based active material and a carbon-based active material.

[0111] The average particle size of the Si-based active material in the Si-C composite can be 50 nm to 200 nm. When the average particle size of the Si-based active material is within the above range, the volume expansion occurring during charging and discharging can be suppressed, and the interruption of the conduction path due to particle breakage during charging and discharging can be prevented.

[0112] Based on the total weight of the Si-C composite, the amount of the Si-based active material included can be 1 wt% to 60 wt%, for example, 3 wt% to 60 wt%.

[0113] In another specific embodiment, the negative electrode active material can further include crystalline carbon and the aforementioned Si-C composite.

[0114] When the negative electrode active material includes both the Si-C composite and the crystalline carbon, the Si-C composite and the crystalline carbon may be included in a mixture, and the weight ratio of the Si-C composite to the crystalline carbon may be 1:99 to 50:50. More specifically, the weight ratio of the Si-C composite to the crystalline carbon may be 5:95 to 20:80.

[0115] The crystalline carbon may include, for example, graphite, and more specifically, may include natural graphite, artificial graphite, or a mixture thereof.

[0116] The average particle size of the crystalline carbon may be 5 μm to 30 μm.

[0117] In the present specification, the average particle size may be a particle size (D50) at 50 volume % in a cumulative size distribution curve.

[0118] The Si-C composite may further include a shell surrounding a surface of the Si-C composite, and the shell may include amorphous carbon. The amorphous carbon may include soft carbon, hard carbon, mesophase pitch carbonization product, calcined coke, or a mixture thereof.

[0119] The amorphous carbon may be included in an amount of 1 to 50 parts by weight, for example, 5 to 50 parts by weight or 10 to 50 parts by weight, based on 100 parts by weight of the carbon-based active material.

[0120] In the negative electrode active material layer, the negative electrode active material may be included in an amount of 95 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0121] In an embodiment, the negative electrode active material layer includes a binder and optionally a conductive material. In the negative electrode active material layer, the binder may be present in an amount of 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer. When the negative electrode active material layer further includes a conductive material, the negative electrode active material layer includes 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0122] The binder improves the binding properties between the negative electrode active material particles and between the negative electrode active material particles and the current collector. The binder includes a non-water-soluble binder, a water-soluble binder, or a combination thereof.

[0123] The non-water-soluble binder may be selected from polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0124] The water-soluble binder can be a rubber-based binder or a polymer resin binder. The rubber-based binder can be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber and a combination thereof. The polymer resin binder can be selected from polytetrafluoroethylene, ethylene propylene copolymer, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol and a combination thereof.

[0125] When a water-soluble binder is used as the negative electrode binder, a cellulose compound may further serve as a thickener to increase viscosity. Cellulose compounds include one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium. The thickener may be included in an amount of 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0126] A conductive material is included to provide electrode conductivity, and any electronically conductive material can be used as the conductive material unless it causes chemical changes in the battery. Examples of the conductive material include: carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.); metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0127] The negative electrode current collector may include one selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0128] Depending on the type of battery, the rechargeable lithium battery may further include a separator between the negative electrode and the positive electrode. The separator may be a porous substrate or a composite porous substrate.

[0129] The porous substrate is a substrate including pores through which lithium ions can move. The porous substrate may include, for example, polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof (such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, and a polypropylene / polyethylene / polypropylene three-layer separator).

[0130] The composite porous substrate may have a form including a porous substrate and a functional layer on the porous substrate. From the perspective of ensuring additional functions, the functional layer may be, for example, at least one of a heat-resistant layer and an adhesive layer. For example, the heat-resistant layer may include a heat-resistant resin and optionally a filler. In addition, the adhesive layer may include an adhesive resin and optionally a filler. The filler may be an organic filler or an inorganic filler.

[0131] The additive for a rechargeable lithium battery according to an embodiment may be included in the electrolyte as described above, and may also be applied to a current collector, an electrode tab, a separator, etc. of a rechargeable lithium battery.

[0132] When the additive is applied to a current collector or an electrode tab, the additive may be applied to the uncoated area of ​​the current collector or electrode tab using a coating solution dispersed in a suitable solvent. When the additive is applied to a separator, the additive may be included in the separator assembly, or a coating solution in which the additive is dispersed in a suitable solvent may be applied to at least one surface of the separator.

[0133] Invention Mode

[0134] Hereinafter, the present invention will be explained in more detail with reference to Examples. However, these Examples are illustrative, and the present invention is not limited thereto.

[0135] Preparation of additives

[0136] Synthesis example 1

[0137] The fibrous additive was manufactured by preparing polymer solutions each including 10 wt % of polyethylene wax (particle size: 0.5 μm) and 10 wt % of poly(vinylidene fluoride hexafluoropropylene) (PVDF-HFP), and then electrospinning them to have a core and a shell having a thickness ratio of 2:1.

[0138] Synthesis example 2

[0139] The fibrous additive was manufactured by preparing 20 wt % of polyethylene wax (particle size 0.5 μm) and 10 wt % of poly(vinylidene fluoride hexafluoropropylene) (PVDF-HFP), and then electrospinning them to have a core and a shell with a thickness ratio of 2:1.

[0140] Synthesis example 3

[0141] The fibrous additive was manufactured by preparing 40 wt % of polyethylene wax (particle size: 0.5 μm) and 10 wt % of poly(vinylidene fluoride hexafluoropropylene) (PVDF-HFP), and then electrospinning them to have a core and a shell having a thickness ratio of 4:1.

[0142] Synthesis example 4

[0143] A fibrous additive was manufactured in the same manner as in Synthesis Example 1, except that electrospinning was performed to have a core and a shell having a thickness ratio of 1:2.

[0144] Comparative Synthesis Example 1

[0145] A fibrous additive was produced in the same manner as in Synthesis Example 1, except that a polymer solution including polyethylene glycol (PEG) instead of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) was used.

[0146] Comparative Synthesis Example 2

[0147] A fibrous additive was produced in the same manner as in Synthesis Example 1, except that a polymer solution including polypropylene (PP) instead of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) was used.

[0148] Manufacturing of rechargeable lithium battery cells

[0149] Example 1

[0150] By using LiNi as the positive electrode active material at a weight ratio of 96:2:2 0.88 Co 0.07 Al 0.05 O2, polyvinylidene fluoride as a binder and Ketjen black as a conductive material, and the mixture is dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0151] The positive electrode active material slurry was coated on a 14 μm thick Al foil, dried at 110° C., and pressed to produce a positive electrode.

[0152] A negative electrode active material was prepared by mixing artificial graphite and Si-C composite in a weight ratio of 93:7, and then the negative electrode active material, styrene-butadiene rubber binder as a binder, and carboxymethyl cellulose as a thickener were mixed in a weight ratio of 97:1:2, and then dispersed in distilled water to prepare a negative electrode active material slurry.

[0153] The Si—C composite is in the form of a core including artificial graphite and silicon particles, and coal pitch coated on the surface of the core.

[0154] The negative electrode active material slurry was coated on a 10 μm-thick Cu foil, dried at 100° C., and pressed to produce a negative electrode.

[0155] An electrode assembly was manufactured by assembling the manufactured positive and negative electrodes and a separator made of polyethylene having a thickness of 25 μm, and an electrolyte was injected to manufacture a rechargeable lithium battery cell, and the composition of the electrolyte was as follows.

[0156] (Composition of electrolyte)

[0157] Salt: 1.3M LiPF6

[0158] Solvent: Ethylene carbonate (EC): Propylene carbonate (PC): Ethyl propionate (EP): Propyl propionate (PP) = 15:15:25:45 (volume ratio)

[0159] Additives: 3 parts by weight of fluoroethylene carbonate, 1 part by weight of SN and 15 parts by weight of the additive prepared in Synthesis Example 1

[0160] (In the composition of the electrolyte, "parts by weight" means the relative weight of the additive based on 100 weight of the total electrolyte (lithium salt + non-aqueous organic solvent).)

[0161] Example 2

[0162] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that 15 parts by weight of the additive according to Synthesis Example 2 was used instead of the additive according to Synthesis Example 1.

[0163] Example 3

[0164] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that 15 parts by weight of the additive according to Synthesis Example 3 was used instead of the additive according to Synthesis Example 1.

[0165] Example 4

[0166] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that 30 parts by weight of the additive according to Synthesis Example 4 was used instead of the additive according to Synthesis Example 1.

[0167] Comparative Example 1

[0168] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that the additive according to Synthesis Example 1 was not used.

[0169] Comparative Example 2

[0170] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that 2 parts by weight of polyethylene wax was used instead of the additive according to Synthesis Example 1.

[0171] Comparative Example 3

[0172] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that 10 parts by weight of polyethylene wax was used instead of the additive according to Synthesis Example 1.

[0173] Comparative Example 4

[0174] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that 15 parts by weight of the additive according to Comparative Synthesis Example 1 was used instead of the additive according to Synthesis Example 1.

[0175] Comparative Example 5

[0176] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that 15 parts by weight of the additive according to Comparative Synthesis Example 2 was used instead of the additive according to Synthesis Example 1.

[0177] Assessment 1: High temperature cycle life assessment

[0178] At 45°C, the rechargeable lithium battery cells according to Examples 1 to 3 and Comparative Examples 1 to 5 were charged to a voltage of 4.4V at a current rate of 0.5C, and then cut off at a current rate of 0.05C in a 4.4V constant voltage mode. Subsequently, the battery cells were discharged to a voltage of 3.0V at a constant current rate of 0.5C. This process was repeated 100 times. The charge and discharge test results were used to calculate the capacity retention rate at the 100th cycle according to calculation equation 1, which is shown in Table 1.

[0179] [Calculation Equation 1]

[0180] Capacity retention rate at the 100th cycle [%] = [discharge capacity at the 50th cycle / discharge capacity at the 1st cycle] × 100

[0181] [Table 1]

[0182]

[0183]

[0184] Referring to Table 1, the rechargeable lithium battery cells according to Examples 1 to 3 exhibited excellent high-temperature cycle life characteristics of 85% or more at the 100th cycle. Compared with the rechargeable lithium battery cells according to Comparative Examples 2 to 5, the rechargeable lithium battery cells according to Examples 1 to 3 exhibited excellent high-temperature cycle life.

[0185] Assessment 2: Heat Exposure Assessment

[0186] The rechargeable lithium battery cells according to Examples 1 to 4 and Comparative Examples 1 to 5 were charged at 0.5C / 4.4V and cut off at 0.05C, and then subjected to heat exposure evaluation.

[0187] After the rechargeable lithium battery cells according to Examples 1 to 4 and Comparative Examples 1 to 5 were placed in a chamber, the temperature of the chamber was increased from room temperature to 136°C at a rate of 5±2°C to examine battery changes while maintaining the temperature for about 1 hour, and the results obtained by repeating this process twice are shown in Table 2.

[0188] [Table 2]

[0189]

[0190] Referring to Table 2, "NG" above means that thermal runaway phenomenon was observed at the exposure temperature, but "OK" above means that voltage drop phenomenon was observed instead of thermal runaway phenomenon at the exposure temperature. (-) means that thermal exposure evaluation was not performed.

[0191] When exposed to high temperatures, the rechargeable lithium battery cell of Comparative Example 1 exhibited a thermal runaway phenomenon, which deteriorated the safety of the battery. The rechargeable lithium battery cell of Comparative Example 1 that did not include the polyethylene wax was understood to not exhibit the battery safety effect of the polyethylene wax.

[0192] The rechargeable lithium battery cell of Comparative Example 4 exhibited a thermal runaway phenomenon at 134° C. It should be understood that the thermal runaway phenomenon was observed at 134° C. because the shell of the additive included in the rechargeable lithium battery cell of Comparative Example 4 easily melted into polyethylene glycol (PEG), releasing the core material prematurely.

[0193] The rechargeable lithium battery cell of Comparative Example 5 exhibited thermal runaway during evaluation. It is understood that the shell of the additive included in the rechargeable lithium battery cell of Comparative Example 5 did not melt into polypropylene (PP) in time, did not release the core material, and thus could not fully improve safety.

[0194] In contrast, when the rechargeable lithium battery cells of Examples 1 to 4 were exposed to high temperatures, the shell of the additive according to the embodiment melted, releasing the polyethylene wax included in the core, thereby rapidly increasing the battery resistance and rapidly decreasing the battery voltage. Accordingly, compared with the rechargeable lithium battery cells of Comparative Examples 1 to 5, the rechargeable lithium battery cells of Examples 1 to 4 all demonstrated excellent battery stability.

[0195] While the present invention has been described in connection with what are presently considered to be practical example embodiments, it should be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the claims.

Claims

1. An additive for rechargeable lithium batteries, include: A core comprising a polyethylene wax core, and a shell, surrounding the core, Wherein the shell comprises a polymer having a melting point of 90°C to 120°C.

2. The additive for rechargeable lithium batteries according to claim 1, wherein The ratio of the thickness of the core to the thickness of the shell is 1:1 to 4:

1.

3. The additive for rechargeable lithium batteries according to claim 1, wherein The core has a thickness of 0.1 μm to 2.0 μm, and the shell has a thickness of 0.025 μm to 0.5 μm.

4. The additive for rechargeable lithium batteries according to claim 1, wherein The polymer includes poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyacrylic acid, polyethylene, poly(methyl methacrylate), polyalkylene oxide, polyalkylene succinate, or a combination thereof.

5. The additive for rechargeable lithium batteries according to claim 1, wherein The additive is in the form of fibers formed using electrospinning.

6. An electrolyte for a rechargeable lithium battery, comprising Non-aqueous organic solvents, Lithium salts, and The additive for the rechargeable lithium battery according to any one of claims 1 to 5.

7. The electrolyte for a rechargeable lithium battery according to claim 6, wherein The additive for the rechargeable lithium battery may be included in an amount of 0.1 wt % to 20 wt % based on the total weight of the electrolyte for the rechargeable lithium battery.

8. The electrolyte for a rechargeable lithium battery according to claim 6, wherein The additive for the rechargeable lithium battery may be included in an amount of 0.1 wt % to 15 wt % based on the total weight of the electrolyte for the rechargeable lithium battery.

9. The electrolyte for a rechargeable lithium battery according to claim 6, wherein The additive for the rechargeable lithium battery may be included in an amount of 0.1 wt % to 10 wt % based on the total weight of the electrolyte for the rechargeable lithium battery.

10. A rechargeable lithium battery comprising a positive electrode, including a positive electrode active material; a negative electrode including a negative electrode active material; and The electrolyte according to claim 6.

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