Electrode slurry, electrode comprising same, lithium secondary battery, and battery pack

Abstract

The present specification relates to: an electrode slurry, an electrode comprising same, a lithium secondary battery, and a battery pack, the electrode slurry comprising an electrode active material, a conductive material, a binder, a solvent for slurry formation, and a flame retardant material, wherein the flame retardant material has solubility of less than 10 mg / cc at 20℃ in a carbonate-based solvent and comprises a specific type of compound. The electrode according to the embodiment can ensure battery characteristics while preventing thermal runaway.

Description

Electrode slurry, electrode containing the same, lithium secondary battery and battery pack

[0001] The present application relates to an electrode slurry, an electrode including the same, a lithium secondary battery, and a battery pack.

[0002] This application claims the benefit of the filing dates of Korean Patent Application Nos. 10-2023-0194499 and 10-2024-0197948, filed with the Korean Intellectual Property Office on December 28, 2023 and December 27, 2024, the entire contents of which are incorporated herein by reference.

[0003] Secondary batteries are batteries that can be reused by charging even after discharge, and can be used as an energy source for small devices such as mobile phones, tablet PCs, and vacuum cleaners, and as an energy source for medium-sized or large devices such as personal mobility, automobiles, and ESS (Energy Storage Systems) for smart grids.

[0004] In order to be utilized in such a wide range of applications, high performance is also required for secondary batteries. As a result of numerous research and development efforts, lithium secondary batteries with high energy density and ease of processing, which can be applied to various electronic devices, are attracting attention.

[0005] However, the aforementioned lithium secondary batteries are not only vulnerable to external shocks, but also prone to internal deterioration, leading to frequent ignition. This problem can lead to significant damage by causing heat transfer between multiple batteries / cells, resulting in thermal runaway in assembly units such as battery modules or battery packs connected in series and / or parallel.

[0006] Specifically, if the internal temperature of a lithium secondary battery exceeds a certain temperature, the internal pressure of the cell may increase due to the vaporization of the electrolyte, which may cause the electrolyte to be ejected from the cell or damage the separator. If the flammable gaseous substance is ignited due to the vaporization of the electrolyte or the separator is damaged, an internal short circuit may occur, which may cause an inappropriate exothermic reaction to continuously or serially occur due to the heating of adjacent cells, which may lead to ignition, and the fire may spread throughout the entire battery pack. However, since lithium ions are highly reactive to water, there is a problem that the fire may spread further even if it is attempted to be extinguished with water.

[0007] To solve the above problem, research is being conducted on materials that can early block or suppress the phenomenon of continuous or serial occurrence of inappropriate exothermic reactions on the electrode slurry side.

[0008] The present inventors have completed an electrode slurry that has the characteristics of maintaining the desired battery characteristics, blocking heat transfer and thermal runaway between cells in advance, and preventing leakage of the flame retardant material when forming a battery in the future, without having a separate layer, by including a specific type of flame retardant material and having low solubility in a specific solvent in the electrode slurry, thereby not limiting the lithium movement speed during charging and discharging.

[0009] Specifically, the present specification provides an electrode slurry including a flame retardant material having a solubility of less than 10 mg / cc at 20°C in a carbonate solvent, wherein the flame retardant material is a linear or branched polyphosphate compound, an electrode including the same, a lithium secondary battery, and a battery pack.

[0010] One embodiment of the present specification provides an electrode slurry comprising an electrode active material, a conductive material, a binder, a solvent for forming a slurry, and a flame retardant material, wherein the flame retardant material has a solubility of less than 10 mg / cc at 20°C in a carbonate solvent, and the flame retardant material is a linear or branched polyphosphate compound.

[0011] Another embodiment of the present specification provides an electrode including an electrode current collector layer; and an electrode active material layer having the electrode slurry applied to one or both surfaces of the electrode current collector layer.

[0012] Another embodiment of the present specification provides a lithium secondary battery comprising a first electrode; a second electrode; a separator interposed between the first electrode and the second electrode; and an electrolyte, wherein at least one of the first electrode and the second electrode is the electrode.

[0013] Another embodiment of the present specification provides a battery pack including the lithium secondary battery described above as a unit cell.

[0014] An electrode according to one embodiment of the present invention can maintain characteristics such as long life and low cell resistance, prevent further thermal runaway, or delay the time required for thermal runaway, and at the same time, prevent leakage of flame-retardant materials from the battery in the future, so that the viscosity of the electrolyte can be maintained below a certain level even during repeated charging and discharging, thereby maintaining the lithium movement speed. In addition, compared to flame-retardant electrolytes, the electrode according to the present invention is cost-effective, easier to apply to processes, and effective in suppressing side reactions.

[0015] Figure 1 is a schematic diagram of an electrode according to the present invention.

[0016] Figures 2 and 3 are schematic diagrams of a lithium secondary battery according to the present invention.

[0017] Figure 4 is a schematic diagram of a battery pack according to the present invention.

[0018] Figure 5 is a schematic diagram of a moving vehicle including a battery pack according to the present invention.

[0019] 1: Electrode current collector layer

[0020] 2: Electrode active material layer

[0021] 3: Flame retardant material

[0022] 4: Electrode slurry

[0023] 10: Electrode

[0024] 10-1: First electrode

[0025] 10-2: Second electrode

[0026] 11: Membrane

[0027] 20: Lithium secondary battery (cross-section)

[0028] 100: Lithium secondary battery

[0029] 201: Housing

[0030] 300: Battery Pack

[0031] 400: Means of transportation

[0032] Before explaining the present invention, some terms are first defined.

[0033] In this specification, 'p to q' may mean a range of 'p or more and q or less'.

[0034] In this specification, when a part is expressed as 'including' or 'having' a certain component, unless otherwise defined, it may mean that other components may be included rather than excluding other components.

[0035] In this specification, singular expressions include plural expressions unless otherwise defined.

[0036] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0037] Hereinafter, the present invention will be described in detail with reference to the drawings so that those skilled in the art can easily practice it. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0038] Electrode slurry

[0039] Hereinafter, the electrode slurry (4) included in the electrode active material layer (2) of Fig. 1 will be described.

[0040] An electrode slurry according to one embodiment of the present specification includes a flame retardant material, wherein the flame retardant material has a solubility of less than 10 mg / cc at 20°C in a carbonate solvent, and the flame retardant material is characterized in that it is a linear or branched polyphosphate compound.

[0041] The above electrode slurry has low solubility in carbonate solvents, thereby ensuring low combustibility, making it difficult for the electrode to self-combust by oxygen or to combust with other elements of the battery in the future, thereby preventing further thermal runaway or delaying the time required for thermal runaway, and preventing leakage of flame-retardant materials from the battery side in the future, thereby preventing an increase in the viscosity of the electrolyte, and thus preventing a decrease in the lithium movement speed during repeated charging and discharging.

[0042] The above 'linear or straight-chain type' refers to a structure in which atoms are connected in a row and the connection between atoms is continuously connected by single or double or more bonds.

[0043] The above 'branched-chain type' refers to a structure in which some atoms in the straight-chain structure are connected in a different direction away from the main chain.

[0044] According to one embodiment of the present specification, the linear or branched polyphosphate compound may include at least one of ammonium and halogen.

[0045] According to one embodiment of the present specification, the electrode slurry may further include a flame retardant additive in addition to the flame retardant material.

[0046] According to one embodiment of the present specification, the content of the flame retardant material may be 1 part by weight or more and 20 parts by weight or less based on 100 parts by weight of the entire electrode slurry.

[0047] If the flame retardant material satisfies the above range, the thermal runaway prevention aspect can be improved.

[0048] According to one embodiment of the present specification, the conductive material may be at least one of a planar conductive material, a linear conductive material, and a dot-shaped conductive material.

[0049] According to one embodiment of the present specification, the binder may be an aqueous binder or a non-aqueous binder.

[0050] According to one embodiment of the present specification, the bonding force of the electrode slurry may exceed 15 gf / 20 mm.

[0051] When an electrode slurry satisfying the above range of bonding force is used, detachment from the electrode edge can be prevented during a future punching process, and the structure can be maintained due to electrode swelling during cell operation.

[0052] In this specification, the bonding force can be evaluated by attaching an electrode plate to one side of an adhesive tape (double-sided), attaching the electrode plate to a 1 cm thick glass on the back side of the adhesive tape, and then using UTM (Instron 3345) to make the adhesive tape and the electrode plate form a 180° angle at the peeling surface.

[0053] Electrode

[0054] Below, the electrode (10) of Fig. 1 will be described.

[0055] According to one embodiment of the present specification, an electrode is provided, which includes an electrode current collector layer (1); and an electrode active material layer (2) on which the electrode slurry (4) is applied on one or both sides of the electrode current collector layer. That is, the electrode active material layer (2) including the electrode slurry is characterized in that a flame retardant material (3) is included.

[0056] The electrode of the above embodiment contains the electrode slurry described above, and thus can block in advance factors that may cause thermal runaway with components of a lithium secondary battery.

[0057] Lithium secondary battery

[0058] Hereinafter, the lithium secondary batteries of FIGS. 2 and 3 will be described.

[0059] According to one embodiment of the present specification, a lithium secondary battery comprising a first electrode (10-1); a second electrode (10-2); a separator (11) interposed therebetween; and an electrolyte, wherein one of the first electrode (10-1) and the second electrode (10-2) is the electrode (10) described above.

[0060] The lithium secondary battery of the above embodiment can block in advance factors that may cause thermal runaway with components of the lithium secondary battery, including the electrode described above.

[0061] Referring to Fig. 2, a separator (11) is interposed between a first electrode (10-1) and a second electrode (10-2), and at least one of the first electrode (10-1) and the second electrode (10-2) may be the above-described electrode. Specifically, one side of the separator (11) is in contact with one side of the electrode active material layer (2), and an electrode current collector layer (1) may be provided on the opposite side of the side of the electrode active material layer (2) that is in contact with the separator (11).

[0062] In this specification, the first electrode may be a cathode and the second electrode may be an anode, or the first electrode may be an anode and the second electrode may be a cathode.

[0063] Accordingly, when the above-described electrode is a negative electrode, the above-described electrode current collector layer may be referred to as a negative electrode current collector layer, and the above-described electrode active material layer may be referred to as a negative electrode active material layer. The specific details are as follows.

[0064] In this specification, the negative electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0065] In this specification, the negative electrode current collector may generally have a thickness of 1 μm to 100 μm, and may have fine unevenness formed on the surface of the current collector to increase the adhesive strength of the negative electrode active material. In addition, the negative electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0066] In one embodiment of the present specification, the negative electrode active material layer may include at least one of a silicon-based active material and a carbon-based active material.

[0067] In one embodiment of the present specification, the negative electrode active material layer may include a carbon-based active material.

[0068] The above carbon-based active material can prevent expansion due to repeated charging and discharging in the negative electrode or lithium secondary battery of the present invention, thereby contributing to excellent cycle characteristics or improved battery life performance.

[0069] In one embodiment of the present specification, the negative electrode active material layer may include a silicon-based active material.

[0070] In general, silicon-based active materials are known to have a capacity more than 10 times higher than carbon-based active materials. Therefore, applying silicon-based active materials to the cathode can create an electrode with a high energy density even with a thin thickness.

[0071] In one embodiment of the present specification, the silicon-based active material is SiOx (x=0), SiOx (0 <x<2), Si / C 복합재 및 Si 합금으로 이루어진 군에서 선택되는 1 이상을 포함할 수 있다.

[0072] Meanwhile, since SiO2 does not react with lithium ions and thus cannot store lithium, it is preferable that x be within the above range. The silicon-based active material may be a Si / C composite composed of a composite of Si and C or Si.

[0073] Depending on the need, the above silicon-based active material may refer to one type of single material or a mixed material of two or more types.

[0074] In one embodiment of the present specification, the silicon-based active material is SiOx (x=0) and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 실리콘계 활물질 100 중량부 기준 상기 SiOx (x=0)를 70 중량부 이상 포함하는 것인 음극 조성물을 제공한다.

[0075] In one embodiment of the present specification, the silicon-based active material may contain SiOx (x=0) in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less, based on 100 parts by weight of the silicon-based active material.

[0076] The silicon-based active material according to this specification contains 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the silicon-based active material, and SiOx(0 <x<2) 계열을 주된 물질로 사용하는 실리콘계 활물질과 대비할 때, 이론적 용량이 본 명세서의 실리콘계 활물질에 비하여 훨씬 높게 구현될 수 있다.

[0077] In one embodiment of the present specification, the silicon-based active material may be pure silicon (Si). Using pure silicon (Si) as the silicon-based active material may mean that, based on 100 parts by weight of the total silicon-based active material, pure Si particles (SiOx (x=0)) that are not combined with other particles or elements are included within the above range.

[0078] In one embodiment of the present specification, the negative electrode active material layer may further include a negative electrode conductive material and a negative electrode binder.

[0079] The above negative electrode conductive material is used to provide conductivity to the electrode, and can be used without any special restrictions as long as it does not cause chemical changes in the battery and has electronic conductivity. However, the negative electrode conductive material is applied to the negative electrode and has a completely separate composition from the positive electrode conductive material applied to the positive electrode. That is, the negative electrode conductive material plays a role in securing the contact between silicon-based active materials, which undergo a large volume expansion of the electrode due to charging and discharging, whereas the positive electrode conductive material acts as a buffer when rolled and provides some conductivity, so the negative electrode conductive material and the positive electrode conductive material have different compositions and roles.

[0080] Specific examples of the above negative conductive material may include at least one selected from the group consisting of point-shaped conductive materials, planar conductive materials, and linear conductive materials.

[0081] Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black and / or artificial graphite in terms of implementing high conductivity and excellent dispersibility.

[0082] The above-mentioned planar conductive material can improve conductivity by increasing planar contact between silicon particles within the cathode, and at the same time, suppress the disconnection of the conductive path due to volume expansion. The above-mentioned planar conductive material can be expressed as a plate-shaped conductive material or a bulk conductive material. An example of the above-mentioned planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and preferably plate-shaped graphite.

[0083] The linear conductive material may be a carbon nanotube. The carbon nanotube may be a bundle-type carbon nanotube. The bundle-type carbon nanotube may include a plurality of carbon nanotube units. Specifically, the term "bundle type" herein refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in a substantially identical orientation in a longitudinal direction of the carbon nanotube units or are entangled. The carbon nanotube unit has a graphite sheet having a cylindrical shape with a nano-sized diameter, and sp 2It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or semiconductor. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be uniformly dispersed during the manufacture of the cathode, and can smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

[0084] In one embodiment of the present specification, a negative electrode composition is provided in which the negative electrode conductive material is present in an amount of 0.1 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0085] In another embodiment, the negative electrode conductive material may be included in an amount of 0.1 to 40 parts by weight, preferably 0.2 to 30 parts by weight, more preferably 0.4 to 25 parts by weight, and most preferably 0.4 to 10 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0086] The above-mentioned negative electrode binder serves to improve the adhesion between negative electrode active material particles and the adhesive strength between the negative electrode active material and the negative electrode current collector, and can be divided into aqueous binders and non-aqueous binders (organic binders) depending on whether it dissolves well in an aqueous solvent such as water. Specific examples of the above-mentioned negative electrode binder include carboxymethyl cellulose (CMC)-based binders, styrene butadiene rubber (SBR)-based binders, polyacrylic acid (PAA)-based binders, polyacrylamide (PAM)-based binders, polyacrylonitrile (PAN)-based binders, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), etc., various copolymers derived therefrom, or a mixture of two or more selected therefrom.

[0087] In one embodiment of the present specification, a negative electrode composition is provided in which the weight average molecular weight of the negative electrode binder is 100,000 g / mol or more and 1,000,000 g / mol or less.

[0088] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as standard materials. In this specification, unless otherwise specified, molecular weight means weight average molecular weight.

[0089] By satisfying the above weight-average molecular weight range, the electrode exhibits excellent mechanical strength and high intermolecular interaction, resulting in superior electrode adhesion. Furthermore, satisfying the above range allows for the binder's viscosity to be appropriately selected, resulting in superior electrode coating properties when used to manufacture a cathode.

[0090] In one embodiment of the present specification, the negative electrode binder is provided in an amount of 1 part by weight or more and 20 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0091] In one embodiment of the present specification, the negative electrode binder may be included in an amount of 20 parts by weight or less, preferably 15 parts by weight or less, based on 100 parts by weight of the negative electrode composition, and may be 1 part by weight or more, 5 parts by weight or more, or 10 parts by weight or more.

[0092] As described above, when including a negative electrode active material, a negative electrode conductive material, and a negative electrode binder, it may be referred to as a negative electrode composition.

[0093] In some cases, a solvent may be added to the cathode composition, which may be referred to as a cathode slurry. The solvent used herein may be referred to as a solvent for forming a cathode slurry.

[0094] The solvent for forming the above cathode slurry may include, but is not limited to, N-methyl-2-pyrrolidone (NMP), water, etc.

[0095] In this specification, the negative electrode means an electrode that has undergone a series of electrode processes, including a coating step of applying negative electrode slurry to at least one surface of a negative electrode collector, a pressing step of compressing to a certain thickness by roll pressing, and a slitting step of cutting to fit the electrode specifications.

[0096] In one embodiment of the present specification, the negative electrode can form a negative electrode for a lithium secondary battery by coating a negative electrode slurry containing the negative electrode composition on one side or both sides of a current collector.

[0097] In one embodiment of the present specification, the solid content of the cathode slurry can satisfy 5% or more and 40% or less.

[0098] In another embodiment, the solid content of the cathode slurry can satisfy a range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0099] The solid content of the above cathode slurry may mean the content of the cathode composition included in the cathode slurry, and may mean the content of the cathode composition based on 100 parts by weight of the cathode slurry.

[0100] When the solid content of the above negative electrode slurry satisfies the above range, the viscosity is appropriate when forming the negative electrode active material layer, thereby minimizing particle agglomeration of the negative electrode composition, and thus has the characteristic of efficiently forming the negative electrode active material layer.

[0101] Other details regarding the above cathode are applied according to information known in the art.

[0102] Accordingly, when the above-described electrode is a positive electrode, the above-described electrode current collector layer may be referred to as a positive electrode current collector layer, and the above-described electrode active material layer may be referred to as a positive electrode active material layer. The specific details are as follows.

[0103] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 µm to 500 µm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0104] In one embodiment of the present specification, the thickness of the positive electrode current collector layer may be 1 μm or more and 100 μm or less, and the thickness of the positive electrode active material layer may be 20 μm or more and 500 μm or less. However, the thickness may be modified in various ways depending on the type and purpose of the positive electrode used and is not limited thereto.

[0105] The above positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4(0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2Ni-site type lithium nickel oxide represented by O2 (wherein, M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4, etc., in which a part of Li in the chemical formula is replaced with an alkaline earth metal ion, but is not limited thereto. The positive electrode may be Li-metal.

[0106] The above-described positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above. When the positive electrode active material, positive electrode conductive material and positive electrode binder are included, it is referred to as a positive electrode composition, and when the positive electrode composition further includes a solvent for forming a positive electrode slurry, it may be referred to as a positive electrode slurry.

[0107] The above-mentioned positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be formed, any material that does not cause a chemical change and has electronic conductivity can be used without special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used.

[0108] The above-described positive electrode binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, etc., various copolymers derived therefrom, or a mixture of two or more selected therefrom may be used.

[0109] When the above solvent refers to a solvent for forming a positive electrode slurry, N-methyl-2-pyrrolidone (NMP), water, etc. may be used, but are not limited thereto.

[0110] In this specification, the positive electrode means an electrode that has undergone a series of electrode processes, including a coating step of applying a positive electrode composition to at least one surface of a positive electrode current collector, a pressing step of compressing to a certain thickness by roll pressing, and a slitting step of cutting to fit the electrode specifications.

[0111] Other details regarding the above polarity are applied according to information known in the art.

[0112] According to one embodiment of the present specification, the electrolyte may include a solvent; a salt; and an additive.

[0113] According to one embodiment of the present specification, the electrolyte may include a carbonate solvent.

[0114] In the present specification, specific examples of the carbonate solvent include, but are not limited to, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, difluoroethylene carbonate, etc.

[0115] In particular, the carbonate-based solvent may be a carbonate-based organic solvent. Among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants, which easily dissociate lithium salts, and thus can be preferably used. In addition, when a low-viscosity, low-dielectric constant linear carbonate, such as dimethyl carbonate and diethyl carbonate, is mixed and used in an appropriate ratio with such cyclic carbonates, an electrolyte with high electrical conductivity can be produced, and thus can be used more preferably.

[0116] In the present specification, in addition to carbonate solvents, aprotic organic solvents such as gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate may be used.

[0117] In the present specification, the carbonate solvent may further include a metal salt, and a lithium salt may be used, and the lithium salt is a material that is easy to dissolve in the non-aqueous electrolyte, for example, an anion of the lithium salt is F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6- , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of can be used.

[0118] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0119] In this specification, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular limitations. In particular, the separator preferably has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0120] In this specification, a lithium secondary battery may be a concept including an electrode assembly including a positive electrode, a negative electrode, and a separator, and a battery can containing an electrolyte.

[0121] Battery Pack

[0122] The battery pack of this specification refers to Fig. 4.

[0123] One embodiment of the present specification provides a battery module and / or battery pack (300) including the lithium secondary battery (200) as a unit cell.

[0124] Since the above battery module and / or battery pack includes the lithium secondary battery (200), the contents of the above-described lithium secondary battery can be applied as is.

[0125] In this specification, the battery pack (300) may have a structure in which a lithium secondary battery (200) is included in a pack housing (201). However, the lithium secondary battery (200) may be replaced with a coin-shaped, pouch-shaped, square-shaped, etc., as well as the illustrated cylindrical shape, as needed.

[0126] In some cases, the battery pack of the present specification may include one or more battery module units.

[0127] According to FIG. 5, the battery pack (300) can be used as a power source for a medium- to large-sized device selected from the group consisting of a means of transportation (400) such as an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and an electric power storage system (EES), as needed.

[0128] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0129] Example. Fabrication of electrodes

[0130] Example 1

[0131] (1) Manufacturing of cathode

[0132] Graphite and Si / C (average particle size (D)) as negative active materials 50 ) 8 ㎛), the first and second conductive materials as conductive materials and polyacrylamide as binder and ammonium polyphosphate as flame retardant material were prepared in a weight ratio of 73:13:1.6:0.4:5:7 and added to a solvent (distilled water) to prepare a negative electrode slurry (solid concentration 35 wt%). Here, the first conductive material is plate-shaped graphite (specific surface area 17 m 2 / g, average particle size (D 50): 3.5 ㎛), and the second conductive material is a single-walled carbon nanotube (SWCNT). As a mixing method, the first and second conductive materials, binder, and water were dispersed at 2,500 rpm for 30 minutes using a HOMO MIXER (PRIMIX), and then the negative electrode active material was added and dispersed at 2,500 rpm for 30 minutes to prepare a negative electrode slurry.

[0133] Then, the negative electrode slurry was applied on both sides of the negative electrode current collector (copper (Cu) thin film, thickness: 8 ㎛) at 3.75 mAh / cm 2 After coating with a loading amount and drying in a vacuum oven at 130°C for 10 hours, a negative electrode was manufactured by rolling (performed using a roll press).

[0134] (2) Manufacturing of the anode

[0135] Cathode active material (LiNi6Co) 0.9 Mn 3.1 O2), anode conductive material (multi-walled carbon nanotubes, MWCNT) and binder (PVdF, KF9700) were added to a solvent (N-methylpyrrolidone, NMP) at a weight ratio of 97.3:1.3:1.4 to prepare a cathode slurry (solid concentration 67 wt%). The cathode slurry was prepared at a solid concentration of 3.6 mAh / cm 2 After coating and drying the positive electrode current collector (aluminum (Al) thin film, thickness: 12 ㎛) with a loading amount (same drying conditions applied to the negative electrode), a positive electrode was manufactured by rolling using a roll press to form a positive electrode active material layer on the positive electrode current collector.

[0136] (3) Manufacturing of lithium secondary batteries

[0137] An electrode assembly was manufactured by interposing a compressible thin film separator (PE 15 ㎛) Ceramic coating 4 ㎛ / 4 ㎛ between the negative electrode and the positive electrode. After positioning the electrode assembly inside a battery case, an electrolyte (an electrolyte solution in which 1.2 M LiPF6 is dissolved in a mixed solution of ethylene carbonate (EC) : methyl ethyl carbonate (EMC) = 80 : 20 (volume ratio)) was injected into the case to manufacture a lithium secondary battery.

[0138] Example 2

[0139] A lithium secondary battery was manufactured in the same manner as Example 1, except that ammonium polyphosphate was excluded from the manufacture of the negative electrode and 5 parts by weight of ammonium polyphosphate was added to the manufacture of the positive electrode.

[0140] Comparative Example 1

[0141] A lithium secondary battery was manufactured in the same manner as in Example 1, except that ammonium polyphosphate was excluded from the manufacture of the negative electrode.

[0142] Comparative Example 2

[0143] In the manufacture of the negative electrode, a lithium secondary battery was manufactured in the same manner as in Example 1, except that resorcinol bis(diphenyl phosphate) was used as a flame retardant material.

[0144] Comparative Example 3

[0145] In the manufacture of the negative electrode, a lithium secondary battery was manufactured in the same manner as in Example 1, except that melamine polyphosphate was used as a flame retardant material.

[0146] Experimental example.

[0147] Experimental Example 1: Stability Test

[0148] A heat pad was placed on one side of the cell (pouch type) of the lithium secondary battery of Examples 1 and 2 and Comparative Examples 1 to 3, and the temperature of the heat pad was increased until the cell exploded. At this time, the explosion pressure was measured using an autoclave device.

[0149] The reaction time is a value obtained from the test results of the autoclave equipment, and the definition of the reaction time is the pressure rise point (TR) during thermal runway as shown in Equation 1 below. initial ) from the point of maximum pressure reached (TR max ) means the time (in seconds) until the end.

[0150] [Formula 1]

[0151] Reaction time = TR max - TR initial

[0152] In addition, the TR rate is a value obtained by normalizing the cell explosion rate during thermal runaway to the cell capacity using the reaction time value derived from the above equation 2. This value is also calculated as a test result of the autoclave equipment, and the unit is mbar / (sec*mAh). The evaluation results are as follows in Table 1.

[0153] Experimental Example 2: Solubility Evaluation

[0154] 1 g of each of the flame retardant materials included in Examples 1 and 2 and Comparative Examples 1 to 3 was added to 100 cc of electrolyte (propylene carbonate solvent), mixed for 30 minutes using a touch mixer, and then the sedimentation of the flame retardant material was observed at 20°C to evaluate the solubility. The evaluation results are shown in Table 1 below. For reference, when the solubility was less than 10 mg / cc, it was evaluated as X (sedimentation), and when it was 10 mg / cc or more, it was evaluated as O (dissolution).

[0155] Experimental Example 3: Bonding Strength Evaluation

[0156] The bonding strength of the electrodes of Examples 1 and 2 and Comparative Examples 1 to 3 was evaluated based on the bonding strength. An electrode plate was attached to one side of an adhesive tape (double-sided), and the reverse side of the adhesive tape was attached to a 1 cm thick glass, and then the bonding strength of the electrode slurry was evaluated by peeling the adhesive tape and the electrode plate at a 180° angle using a UTM (Instron 3345). For reference, if the bonding strength was 15 gf / 20 mm or less, it was evaluated as X, and if it was more than 15 gf / 20 mm, it was evaluated as O.

[0157] No. Experimental Example 1: TR rate mbar / (sec*mAh) Experimental Example 2: Solubility (@20℃, mg / cc) Experimental Example 3: Adhesion Laboratory Test Example 14.3XO Example 24.5XO Comparative Example 16.7-O Comparative Example 25.2OO Comparative Example 34.6XX

[0158] According to Table 1 above, Examples 1 and 2 and Comparative Example 3 had a TR rate of up to 4.6 mbar / (sec*mAh), which was lower than the TR rate values ​​of Comparative Examples 1 and 2. This result suggests that even in lithium secondary batteries of the same capacity, the cell explosion rate of the lithium secondary batteries of Examples 1 to 3 is lower than that of Comparative Example 1, which does not include a flame retardant material, and Comparative Example 2, which does not satisfy the solubility even though it includes a flame retardant material (resorcinol bis(diphenyl phosphate)), and thus the stability of the lithium secondary battery of the present invention is improved.

[0159] In addition, in the case of Comparative Example 3, melamine polyphosphate was included as a flame retardant material and the solubility was low, but the electrode adhesive strength was less than 15 gf / 20 mm, confirming that it was not suitable for use as an electrode slurry. The result of this Comparative Example 3 is judged to be because the binder was not uniformly distributed during electrode coating, so sufficient adhesive strength (bonding strength) was not secured for manufacturing electrodes and cells. Accordingly, detachment may occur at the electrode edge during the stamping process in the future, and it may be difficult to maintain the structure due to electrode swelling during cell operation.

[0160] Experimental Example 4: Lifespan Characteristics

[0161] The lifespan of the lithium secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 3 was evaluated using an electrochemical charger / discharger, and the capacity retention rate was evaluated.

[0162] A lithium secondary battery was subjected to an in-situ cycle test at 4.2-3.0 V 1C / 0.5C, and during the test, 0.33C / 0.33C charge / discharge (4.2-3.0V) was performed every 50 cycles to calculate the capacity retention rate according to Equation 2 below. The evaluation results are shown in Table 2 below.

[0163] [Formula 2]

[0164] Life maintenance rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100

[0165] No. 200 Cycle Life Retention Rate (%) Example 182 Example 280 Comparative Example 184 Comparative Example 267 Comparative Example 377

[0166] According to Table 2 above, Examples 1 to 3 and Comparative Example 1 showed a life maintenance rate of 77% or more, suggesting that the lithium secondary battery (Examples 1 to 3) using the electrode slurry containing the flame retardant material has no difference in life maintenance rate from the lithium secondary battery using the electrode slurry not containing the flame retardant material.

[0167] However, even when using an electrode slurry containing a flame retardant material, Comparative Example 2, which did not satisfy the solubility criteria for carbonate-based solvents, showed a life maintenance rate of 67% lower than that of the example group. The life maintenance rate of Comparative Example 2 was lower than that of Comparative Example 1, which did not contain a flame retardant material, suggesting that the solubility of the flame retardant material in carbonate-based solvents also affects the life maintenance rate in terms of the battery.

[0168] In addition, Comparative Example 3, which included a linear or non-branched aromatic polyphosphate compound (i.e., melamine polyphosphate) with a solubility of less than 10 mg / cc, had a capacity retention rate of less than 80%, which was inferior to that of the Example group. This is believed to be because detachment may occur at the electrode edge during the future punching process, and structural maintenance due to electrode swelling during cell operation is disadvantageous, which has a detrimental effect on cell life performance.

Claims

1. Contains electrode active material, conductive material, binder, solvent for forming slurry and flame retardant material. The above flame retardant material has a solubility of less than 10 mg / cc at 20°C in a carbonate solvent, An electrode slurry wherein the flame retardant material comprises a linear or branched polyphosphate compound.

2. In claim 1, An electrode slurry wherein the linear or branched polyphosphate compound comprises at least one of ammonium and halogen.

3. In claim 1, An electrode slurry wherein the content of the flame retardant material is 1 part by weight or more and 20 parts by weight or less based on 100 parts by weight of the total electrode slurry.

4. In claim 1, An electrode slurry wherein the conductive material is at least one of a planar conductive material, a linear conductive material, and a dot-shaped conductive material.

5. In claim 1, An electrode slurry wherein the above binder is an aqueous binder or a non-aqueous binder.

6. Electrode current collector layer; and An electrode comprising an electrode active material layer having an electrode slurry of any one of claims 1 to 5 applied to one or both surfaces of the electrode current collector layer.

7. A first electrode; a second electrode; a separator interposed between the first electrode and the second electrode; and an electrolyte, A lithium secondary battery, wherein at least one of the first electrode and the second electrode is an electrode according to claim 6.

8. In claim 7, A lithium secondary battery, wherein the electrolyte comprises a solvent; a salt; and an additive.

9. In claim 7, A lithium secondary battery wherein the electrolyte comprises a carbonate solvent.

10. A battery pack comprising a lithium secondary battery according to claim 7 as a unit cell.

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