Anode composition, anode for lithium secondary battery including the same, and lithium secondary battery including the anode

Abstract

The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0180142, filed with the Korean Intellectual Property Office on December 15, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched fields is power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that utilizes such electrochemical energy is a secondary battery, and the range of its use is tending to expand more and more.

[0005] As technological development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. In addition, active research is being conducted on methods for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. The negative electrode active material may be silicon-based particles with a high discharge capacity.

[0007] In recent years, in response to the demand for high-density energy batteries, Si / C and SiO2, which have capacities 10 times larger than those of graphite-based materials, have been used as negative electrode active materials.x Active research is being conducted into methods of increasing capacity by using silicon-based compounds such as those mentioned above. However, silicon-based compounds, which are high-capacity materials, have a problem in that while they have a large capacity compared to conventionally used graphite, they suddenly expand in volume during charging, cutting off the conductive path and reducing battery performance.

[0008] In response to this, various methods have been discussed to resolve the issues associated with using silicon-based compounds as negative electrode active materials, such as methods for controlling volume expansion itself or preventing the conductive path from being broken, such as methods for adjusting the driving potential, methods for additionally coating a thin film on the active material layer, and methods for adjusting the particle size of the silicon-based compound. However, these methods have limitations in their applicability because they may actually degrade battery performance, and there are still limitations to the commercialization of negative electrode batteries with a high content of silicon-based compounds.

[0009] In particular, research into binder composition that responds to volume expansion is also underway, and research is underway to use binder polymers that have strong lateral stress in order to suppress the volume expansion of negative electrode active materials, which have large volume changes during charging and discharging. However, these binder polymers alone have limitations in suppressing the increase in electrode thickness due to the contraction and expansion of negative electrode active materials and the resulting performance degradation of lithium secondary batteries.

[0010] To solve these problems, research has been conducted into incorporating a crosslinking agent into the binder polymer, but this method can cause problems with the viscosity of the slurry and phase stability during long-term storage of the battery, making it difficult to apply to actual processes.

[0011] Therefore, even when a negative electrode active material with large volume expansion is used, research is needed into a negative electrode binder that can minimize the change in thickness of the negative electrode and thereby improve the capacity retention rate. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0013] Research into anode compositions that can suppress volume expansion and contraction during charge and discharge of active materials and minimize thickness changes due to electrode swelling, and have excellent lifespan performance, has revealed that when graphene oxide is used under specific conditions with a binder, it is possible to suppress volume changes in the electrode and increase capacity retention.

[0014] Accordingly, the present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0015] One embodiment of the present specification provides a negative electrode composition including: a negative electrode binder including graphene oxide and at least one water-soluble polymer; a negative electrode active material; and a negative electrode conductive material, wherein the graphene oxide has a lateral size of 0.3 μm or more and 20 μm or less, and a carbon (C) / oxygen (O) ratio of the graphene oxide is 0.5 or more and 3.5 or less.

[0016] In yet another embodiment, there is provided a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector layer, the negative electrode active material layer comprising the negative electrode composition according to the present application.

[0017] Finally, there is provided a lithium secondary battery including: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte. [Effects of the Invention]

[0018] A negative electrode composition according to one embodiment of the present invention is characterized in that it contains graphene oxide in a negative electrode binder, the graphene oxide having a lateral size of 0.3 μm to 20 μm and a carbon (C) / oxygen (O) ratio of 0.5 to 3.5.

[0019] As a result, even when using a negative electrode active material (especially a silicon-based active material) that exhibits large volume expansion during charge / discharge, the volume expansion and contraction can be suppressed, minimizing thickness changes due to electrode swelling, resulting in excellent life performance of the lithium secondary battery.

[0020] That is, in the case of an anode composition according to one embodiment of the present invention, a silicon-based active material with a high theoretical capacity is included as an anode active material to improve capacity characteristics, and the problem of volume expansion during charge and discharge, which is a problem of silicon-based active materials, is solved by using an anode binder containing the specific graphene oxide according to the present application, which is a feature of the present invention. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present application. [Figure 2] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0022] Prior to describing the present invention, some terms will first be defined.

[0023] In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless specifically stated to the contrary.

[0024] In this specification, "p to q" means a range of "not less than p and not more than q."

[0025] In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mini II manufactured by BEL Japan Co., Ltd. That is, in the present application, the BET specific surface area may mean the specific surface area measured by the above-mentioned measurement method.

[0026] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution by particle size. Alternatively, particle size distribution may be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in diffraction patterns due to particle size when the particles pass through a laser beam.

[0027] In this specification, when a polymer contains a certain monomer as a monomer unit, it means that the monomer is involved in a polymerization reaction and is contained as a repeating unit in the polymer. In this specification, when a polymer contains a monomer, this is interpreted as the same as when a polymer contains a monomer as a monomer unit.

[0028] It is understood that the term "polymer" is used in the broad sense herein to include copolymers unless "homopolymer" is specifically stated.

[0029] 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 commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization that are commercially available for molecular weight measurement as standard substances. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0030] The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in various different forms and is not limited to the following description.

[0031] One embodiment of the present specification provides a negative electrode composition including: a negative electrode binder including graphene oxide and at least one water-soluble polymer; a negative electrode active material; and a negative electrode conductive material, wherein the graphene oxide has a lateral size of 0.3 μm or more and 20 μm or less, and a carbon (C) / oxygen (O) ratio of the graphene oxide is 0.5 or more and 3.5 or less.

[0032] In the case of an anode composition according to one embodiment of the present invention, a silicon-based active material with a high theoretical capacity is used as an anode active material to improve capacity characteristics, and the problem of volume expansion during charge and discharge, which is a problem of silicon-based active materials, is solved by using an anode binder containing graphene oxide, which is a specific substance according to the present application.

[0033] In one embodiment of the present application, the negative electrode binder may include graphene oxide and at least one water-soluble polymer.

[0034] In one embodiment of the present application, the lateral size of the graphene oxide may be 0.3 μm or more and 20 μm or less.

[0035] In yet another embodiment, the particle size (lateral size) of the graphene oxide is 0.3 μm or more and 20 μm or less, preferably 0.5 μm or more and 15 μm or less, more preferably 0.5 μm or more and 10 μm or less, and may satisfy the range of 1 μm or more and 10 μm or less.

[0036] In the present application, graphene oxide having the above particle size can be used to provide sufficient mechanical strength to act as a binder. That is, if the particle size of the graphene oxide is below the lower limit of the above range, the electrode connectivity is insufficient, and if the particle size is above the upper limit of the above range, the electrode itself cannot have sufficient mechanical strength.

[0037] In one embodiment of the present application, the carbon (C) / oxygen (O) ratio of the graphene oxide may be 0.5 or more and 3.5 or less.

[0038] In another embodiment, the carbon (C) / oxygen (O) ratio of the graphene oxide may satisfy the range of 0.5 or more and 3.5 or less, preferably 1.0 or more and 3.0 or less, and more preferably 1.5 or more and 2.5 or less.

[0039] In one embodiment of the present application, the carbon (C) / oxygen (O) ratio of graphene oxide may mean the number of carbon atoms and oxygen atoms contained in the entire graphene oxide expressed as a ratio.

[0040] When the graphene oxide satisfies the carbon / oxygen ratio, the number of functional groups in the molecule is appropriate, resulting in excellent charge / discharge efficiency and excellent aqueous dispersion stability. That is, if the carbon / oxygen ratio is below the lower limit of the range, the number of functional groups in the graphene oxide molecule increases, resulting in reduced charge / discharge efficiency. If the carbon / oxygen ratio is above the upper limit of the range, the aqueous dispersion stability decreases, making it difficult for the graphene oxide to be uniformly distributed in the negative electrode composition.

[0041] As a result, the negative electrode binder according to the present application, by including graphene oxide under specific conditions as described above, can suppress volume expansion and contraction even when using a negative electrode active material (especially a silicon-based active material) that exhibits large volume expansion during charge / discharge, and can minimize thickness changes due to electrode swelling, thereby improving the lifespan performance of a lithium secondary battery.

[0042] That is, it can be confirmed that the effects of the present application are achieved when the negative electrode binder contains graphene oxide that satisfies the above two conditions.

[0043] In one embodiment of the present application, the negative electrode binder may include at least one water-soluble polymer.

[0044] In one embodiment of the present application, the water-soluble polymer may specifically include at least one selected from the group consisting of carboxymethyl cellulose and its derivatives; water-soluble polyacrylic acid (PAA, Polyacrylic acid); polyvinyl alcohol (PVA, Polyvinyl alcohol); polyacrylonitrile (PAN, Polyacrylonitrile); and polyacrylamide (PAM, Polyacrylamide).

[0045] In one embodiment of the present application, there is provided a negative electrode composition, wherein the water-soluble polymer is a polymer of at least one monomer selected from the group consisting of a (meth)acrylamide group-containing compound; an unsaturated organic acid or a salt of an unsaturated organic acid; and an α,β-unsaturated nitrile and a hydroxyalkyl (meth)acrylate.

[0046] In one embodiment of the present application, the negative electrode binder polymer may include a (meth)acrylamide group-containing compound.

[0047] In one embodiment of the present application, the (meth)acrylamide may include methacrylamide; or acrylamide.

[0048] In one embodiment of the present application, the unsaturated organic acid may be any organic acid that can be contained in a binder, and specifically, acrylic acid may be used. In this case, the salt of the unsaturated organic acid may refer to a salt form containing ions of the unsaturated organic acid, and this may also be used without limitation.

[0049] In one embodiment of the present application, the at least one monomer selected from the group consisting of α,β-unsaturated nitriles and hydroxyalkyl (meth)acrylates may be acrylonitrile.

[0050] In one embodiment of the present application, the water-soluble polymer may include a polymer resin having at least one carboxyl group.

[0051] In one embodiment of the present application, some or all of the carboxyl groups are Li + , Na + , or K + It may have a structure substituted with

[0052] In one embodiment of the present application, there is provided a negative electrode composition in which the water-soluble polymer has a weight-average molecular weight of 100,000 g / mol or more and 3,000,000 g / mol or less.

[0053] In another embodiment, the weight average molecular weight of the water-soluble polymer may be in the range of 100,000 g / mol or more and 3,000,000 g / mol or less, preferably 200,000 g / mol or more and 1,500,000 g / mol or less.

[0054] When the weight-average molecular weight of the water-soluble polymer satisfies the above range, the polymer exhibits excellent mechanical strength, high intermolecular interaction, and excellent electrode binding strength. Furthermore, when the weight-average molecular weight satisfies the above range, the viscosity of the negative electrode binder can be selected within an appropriate range, and when a negative electrode is manufactured using the binder, the electrode exhibits excellent coating properties.

[0055] In one embodiment of the present application, the water-soluble polymer may be included in an amount of 1 part by weight to 20 parts by weight, preferably 1.5 parts by weight to 15 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0056] When the content is within the above range, the negative electrode active material can be effectively dispersed, and the electrode adhesive force and the binding strength between the active material inside the electrode can be maintained against the contraction and expansion of the negative electrode active material due to the charge and discharge of the lithium secondary battery.

[0057] In one embodiment of the present application, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, K, or the like, or may further include various copolymers thereof.

[0058] The binder according to one embodiment of the present application serves to hold down the negative electrode active material and the negative electrode conductive material in order to prevent twisting and structural deformation of the negative electrode structure due to volume expansion and relaxation of the silicon-based active material. As long as it fulfills this role, any common negative electrode binder may be applied, and specifically, a water-based binder may be used.

[0059] In one embodiment of the present application, a negative electrode composition is provided in which the negative electrode binder contains 0.1 parts by weight or more and 30 parts by weight or less of the graphene oxide based on 100 parts by weight of the negative electrode binder.

[0060] In another embodiment, the negative electrode binder may satisfy the range in which the graphene oxide is 0.1 parts by weight or more and 30 parts by weight or less, preferably 0.5 parts by weight or more and 20 parts by weight or less, and more preferably 1 part by weight or more and 10 parts by weight or less based on 100 parts by weight of the negative electrode binder.

[0061] By including the graphene oxide in the above parts by weight in the negative electrode binder, the negative electrode active material can be effectively dispersed, and it will have the characteristics of having high electrode adhesion and high adhesion between the active materials inside the electrode against the shrinkage and expansion of the negative electrode active material due to charge and discharge of the lithium secondary battery.

[0062] In one embodiment of the present application, a negative electrode composition is provided in which the negative electrode binder is contained 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.

[0063] In yet another embodiment, the negative electrode binder may be contained in an amount of 1 part by weight or more and 20 parts by weight or less, preferably 2 parts by weight or more and 15 parts by weight or less, and more preferably 3 parts by weight or more and 15 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0064] In one embodiment of the present application, a negative electrode composition is provided in which the negative electrode active material contains at least one selected from the group consisting of a silicon-based active material and a carbon-based active material.

[0065] <00003​​​​​​​​​x , Si / C, Si. SiO x is SiO x The negative electrode active material may contain a compound represented by the formula (0≦x<2). In the case of SiO2, x is preferably within the above range because SiO2 does not react with lithium ions and cannot store lithium. The silicon-based active material may be Si / C or Si, which is a composite of Si and C. Two or more of the above silicon-based active materials may be mixed and used. The negative electrode active material may further contain a carbon-based active material in addition to the above silicon-based active material. The carbon-based active material can contribute to improving the excellent cycle characteristics or battery life performance of the negative electrode or secondary battery of the present invention.

[0067] Generally, silicon-based active materials are known to have a capacity 10 times higher than that of carbon-based active materials. Therefore, when silicon-based active materials are applied to anodes, it is expected that an electrode having a high level of energy density can be realized even with a thin thickness.

[0068] In one embodiment of the present application, the carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, and soft carbon, and preferably at least one selected from the group consisting of artificial graphite and natural graphite.

[0069] In one embodiment of the present application, the negative electrode active material is (1) at least one of artificial graphite, natural graphite, surface-modified graphite, coke, hard carbon, soft carbon, carbon fiber, conductive carbon, and combinations thereof; (2) a silicon-based alloy; (3) i) at least one of artificial graphite, natural graphite, surface-modified graphite, coke, hard carbon, soft carbon, carbon fiber, conductive carbon, and combinations thereof, and ii) a metal selected from the group consisting of Al, Ag, Bi, In, Ge, Mg, Pb, Si, Sn, Ti, and combinations thereof, or a complex compound containing or consisting of these; (4) a lithium complex metal oxide; (5) a lithium-containing nitride; (6) silicon-graphene; (7) silicon-carbon nanotube; (8) silicon oxide; (9) silicon; and (10) any substance containing combinations thereof may be used.

[0070] In one embodiment of the present application, the silicon-based active material is SiO x (x = 0) and SiO x (0 < x < 2), and provides a negative electrode composition containing at least one selected from the group consisting of these and containing 70 parts by weight or more of the SiO x (x = 0) based on 100 parts by weight of the silicon-based active material.

[0071] In another embodiment, the SiO x (x = 0) may be contained 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 be contained in an amount of 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.

[0072] In one embodiment of the present application, only pure silicon (Si) may be used as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material means that, as described above, when based on a total of 100 parts by weight of the silicon-based active material, pure Si particles (SiO x (x = 0)) not bonded to other particles or elements are contained within the above range.

[0073] Silicon-based active materials have significantly higher capacities than conventionally used graphite-based active materials, and attempts to use them are increasing. However, because of their high volume expansion rate during charging and discharging, they are only used in small amounts by mixing with graphite-based active materials.

[0074] Therefore, in the present invention, a silicon-based active material is used as the negative electrode active material to improve capacity performance, while a binder meeting specific conditions is used to solve the problems of maintaining the conductive path and maintaining the bond between the conductive material, binder, and active material due to the volume expansion.

[0075] Meanwhile, the average particle size (D50) of the silicon-based active material of the present invention may be 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size is within this range, the specific surface area of ​​the particles falls within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is equal to or greater than the lower limit, the composite of the conductive material and the binder in the negative electrode slurry has an excellent contact area between the silicon particles and the conductive material, increasing the likelihood of maintaining a conductive network, and thereby increasing the capacity retention rate. Meanwhile, when the average particle size is within this range, excessively large silicon particles are excluded, resulting in a smooth negative electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0076] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 m 2 / g~150.0m 2 / g, more preferably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0077] In one embodiment of the present application, the silicon-based active material may be, for example, in a crystalline or amorphous form and is preferably not porous. The silicon particles are preferably spherical or shard-like particles. Alternatively, but less preferably, the silicon may have a granular or fibrous structure or may be in the form of a silicon-containing film or coating.

[0078] In one embodiment of the present application, the negative electrode composition is provided in which the negative electrode active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0079] In one embodiment of the present application, the negative electrode composition contains 60 parts by weight or more of the silicon-based active material based on 100 parts by weight of the negative electrode composition.

[0080] In another embodiment, the silicon-based active material may be included in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, and more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be included in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 85 parts by weight or less.

[0081] The negative electrode composition according to the present application uses a silicon-based active material with extremely high capacity within the above range, and by using a specific conductive material and binder that suppress the volume expansion rate during charge and discharge, the negative electrode performance is not reduced even when the above range is included, and the negative electrode composition has the characteristic of excellent output characteristics during charge and discharge.

[0082] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape, and the circularity thereof is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0083] In this application, the circularity is determined by the following formula 1-1, where A is the area and P is the perimeter.

[0084] [Formula 1-1] 4πA / P 2 While graphite-based compounds have traditionally been used exclusively as anode active materials, attempts to incorporate silicon-based compounds into batteries to increase capacity have been increasing in recent years as demand for high-capacity batteries has grown. However, silicon-based compounds have limitations, such as their rapid volume expansion during charge / discharge processes, damaging the conductive pathways formed within the anode active material layer and reducing battery performance.

[0085] Therefore, in one embodiment of the present application, a binder having the above characteristics may be used and may also contain a specific negative electrode conductive material.

[0086] In one embodiment of the present application, there is provided a negative electrode composition in which the negative electrode conductive material includes at least one selected from the group consisting of a dot-like conductive material, a planar conductive material, and a linear conductive material.

[0087] In one embodiment of the present application, the dot-like conductive material may be used to improve the conductivity of a negative electrode, and refers to a conductive material that forms conductivity without inducing a chemical change and has a circular or dot-like shape. Specifically, the dot-like 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, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black because it achieves high conductivity and has excellent dispersibility.

[0088] In one embodiment of the present application, the point-like conductive material has a BET specific surface area of ​​40 m 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 / g or less.

[0089] In one embodiment of the present application, the particle size of the dotted conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 40 nm to 60 nm.

[0090] In one embodiment of the present application, the conductive material may include a planar conductive material.

[0091] The planar conductive material refers to a conductive material that increases surface contact between silicon particles in the negative electrode to improve conductivity and simultaneously prevents the conductive path from being broken due to volume expansion. The planar conductive material may be referred to as a plate-type conductive material or a bulk-type conductive material.

[0092] In one embodiment of the present application, the sheet conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may be preferably platelet graphite.

[0093] In one embodiment of the present application, the average particle size (D50) of the sheet conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the average particle size is within this range, the sufficient particle size facilitates dispersion without excessively increasing the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0094] In one embodiment of the present application, the sheet conductive material provides a negative electrode composition having a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 4.0 μm or more and 5.0 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0095] In one embodiment of the present application, the sheet conductive material may be a high-specific surface area sheet conductive material having a high BET specific surface area; or a low-specific surface area sheet conductive material.

[0096] In one embodiment of the present application, the planar conductive material may be a high-specific surface area planar conductive material or a low-specific surface area planar conductive material without any restrictions. However, the planar conductive material of the present application may be affected to some extent by dispersion in terms of electrode performance, and it may be particularly preferable to use a low-specific surface area planar conductive material that does not cause dispersion problems.

[0097] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of ​​1 m 2 / g or more.

[0098] In another embodiment, the sheet conductive material has a BET specific surface area of ​​1 m 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 / g or less.

[0099] In another embodiment, the sheet conductive material is a high specific surface area sheet conductive material having a BET specific surface area of ​​50 m 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 / g or less.

[0100] In another embodiment, the sheet conductive material is a sheet conductive material with a low specific surface area, and has a BET specific surface area of ​​1 m 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 / g or less.

[0101] Other conductive materials include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include multiple carbon nanotube monomers. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in the form of a bundle or rope in which multiple carbon nanotube units are arranged side by side or entangled with their longitudinal axes aligned in substantially the same direction. The carbon nanotube monomers have graphite sheets in the form of cylinders with nanosized diameters and an sp2 bonding structure. Depending on the angle and structure of the graphite sheet, the properties of conductors or semiconductors can be determined. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication and can smoothly form a conductive network within the negative electrode, improving the conductivity of the negative electrode.

[0102] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material includes a linear conductive material, and the linear conductive material is a carbon nanotube.

[0103] In one embodiment of the present application, the carbon nanotubes may be SWCNTs (single-walled carbon nanotubes) and / or MWCNTs (multi-walled carbon nanotubes). When the linear conductive agent is SWCNTs, the length of the SWCNTs may be 0.5 μm to 100 μm, preferably 1 μm to 80 μm.

[0104] In one embodiment of the present application, the negative electrode composition is provided in which the negative electrode conductive material is 5 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0105] In another embodiment, the negative electrode conductive material may be included in an amount of 5 parts by weight or more and 40 parts by weight or less, preferably 5 parts by weight or more and 30 parts by weight or less, and more preferably 5 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0106] In one embodiment of the present application, the negative electrode conductive material may include dot-like conductive materials and linear conductive materials, and the ratio of the dot-like conductive materials to the linear conductive materials may satisfy 1:0.1 to 1:0.5.

[0107] In one embodiment of the present application, the negative electrode conductive material includes dot-like conductive materials and linear conductive materials, each of which satisfies the above-mentioned composition and ratio, thereby increasing the number of points at which charging and discharging are possible without significantly affecting the life characteristics of existing lithium secondary batteries, and providing the characteristic of excellent output characteristics at a high C-rate.

[0108] The negative electrode conductive material according to the present application has a completely different structure from the conductive material used in the positive electrode. That is, the negative electrode conductive material according to the present application serves to form a contact point between silicon-based active materials, which undergo a large volume expansion during charging and discharging, while the positive electrode conductive material serves to provide some conductivity while acting as a buffer during rolling, and is completely different in structure and role from the negative electrode conductive material of the present invention.

[0109] Furthermore, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes having graphite-based active materials simply have smaller particles than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity, and their structure and role are completely different from those of negative electrode conductive materials applied together with silicon-based active materials as in the present invention.

[0110] In one embodiment of the present application, the plate-like conductive material used as the negative electrode conductive material has a structure and function different from that of a carbon-based active material generally used as a negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dot-like shape to facilitate the storage and release of lithium ions.

[0111] Meanwhile, the plate-like conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape and may be referred to as plate-like graphite. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path within the layer, and does not play a role in storing and releasing lithium, but rather serves to ensure a planar conductive path within the negative electrode active material layer.

[0112] That is, in this application, the use of plate-like graphite as a conductive material means that it is processed into a planar or plate-like shape and used as a material to ensure a conductive path rather than to store or release lithium. In this case, the negative electrode active material contained therein has high capacity characteristics for storing and releasing lithium, and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

[0113] Meanwhile, in the present application, the use of a carbon-based active material as an active material means that the carbon-based active material is processed into a dot-like or spherical shape and is used as a material that stores or releases lithium.

[0114] In one embodiment of the present application, the negative electrode composition may be used to form a negative electrode slurry containing a solvent for forming a negative electrode slurry, and the negative electrode slurry may be applied to a negative electrode current collector layer to form a negative electrode.

[0115] At this time, the solid content of the negative electrode slurry may be 10% to 60%.

[0116] In one embodiment of the present application, the solvent for forming the negative electrode slurry can be used without limitation as long as it can dissolve the negative electrode composition, and specifically, distilled water or NMP may be used.

[0117] In one embodiment of the present invention, the method for mixing the negative electrode slurry is not particularly limited, and examples thereof include a ball mill, a sand mill, a pigment disperser, an ultrasonic disperser, a homogenizer, a planetary mixer, a Hobart mixer, and the like. Preferably, the negative electrode slurry is mixed using a homogenizer and / or a planetary mixer.

[0118] In one embodiment of the present application, the means for applying the negative electrode slurry to the negative electrode current collector layer is not particularly limited, and a conventionally known coating device such as a comma coater, a gravure coater, a microgravure coater, a die coater, or a bar coater may be used.

[0119] After the negative electrode slurry is applied, a drying step can be carried out. The drying method is not particularly limited, and the temperature is suitably 60°C to 200°C, preferably 100°C to 180°C. The atmosphere can be dry air or an inert atmosphere. The thickness of the electrode (cured coating film) is not particularly limited, but is suitably 5 μm to 300 μm, preferably 10 μm to 250 μm.

[0120] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer formed on one or both sides of the negative electrode current collector layer, the negative electrode active material layer comprising the negative electrode composition according to the present application.

[0121] 1 is a diagram showing the laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode for a lithium secondary battery 100 can be seen, including a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. While FIG. 1 shows the negative electrode active material layer formed on one side, it may be formed on both sides of the negative electrode current collector layer.

[0122] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. Furthermore, the surface may be provided with fine irregularities to strengthen the binding force of the negative electrode active material, and the current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric. Among these, when the electrode active material is used in a negative electrode, copper foil is preferred as the current collector.

[0123] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

[0124] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0125] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the thickness change rate of the negative electrode active material layer satisfies the following formula 1:

[0126] [Formula 1] 0%≦[(X2-X1) / X1]×100(%)≦15% In the formula 1, X1 is the thickness of the negative electrode active material layer at 0 cycle of the negative electrode for lithium secondary battery, X2 is the thickness of the negative electrode active material layer after 30 cycles of the negative electrode for a lithium secondary battery.

[0127] The term "0 cycle" refers to a state in which the negative electrode for a lithium secondary battery is not yet charged / discharged after being manufactured, and specifically may refer to the negative electrode for a lithium secondary battery after being manufactured.

[0128] That is, in the case of the negative electrode for a lithium secondary battery according to the present application, a negative electrode binder containing a specific graphene oxide is used as a binder, which prevents volume expansion of the negative electrode active material even with repeated cycles and reduces change in thickness.

[0129] In one embodiment of the present application, there is provided a lithium secondary battery including: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0130] 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery anode 100 including an anode active material layer 20 on one side of an anode current collector layer 10 can be seen, and a lithium secondary battery cathode 200 including a cathode active material layer 40 on one side of a cathode current collector layer 50 can be seen, and the lithium secondary battery anode 100 and lithium secondary battery cathode 200 are stacked with a separator 30 sandwiched between them.

[0131] A secondary battery according to an embodiment of the present specification may include the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0132] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

[0133] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. 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. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0134] The 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) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.6 is satisfied); 2-c3 M c3 Examples of suitable lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.6) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li metal.

[0135] In one embodiment of the present application, the positive electrode active material includes a lithium transition metal composite compound including nickel (Ni), cobalt (Co), and manganese (Mn), and the lithium transition metal composite compound may include single particles or secondary particles, and the single particles may have an average particle size (D50) of 1 μm or more.

[0136] For example, the average particle size (D50) of the single particles may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, more than 1 μm and 12 μm or less, more than 1 μm and 8 μm or less, or more than 1 μm and 6 μm or less.

[0137] The single particles can have excellent particle strength even when they are formed with a small particle size (D50) of 1 μm or more and 12 μm or less. For example, the single particles can have a strength of 650 kgf / cm 2 When the particle is rolled with a force of 650 kgf / cm, the particle strength is 100 MPa to 300 MPa. 2 Even if the electrode is rolled with a strong force, the phenomenon of an increase in fine particles in the electrode due to cracking of particles is alleviated, thereby improving the life characteristics of the battery.

[0138] The single particles may be prepared by mixing a transition metal precursor and a lithium source material and calcining the mixture. The secondary particles may be prepared by a method different from that for the single particles, and the composition thereof may be the same as or different from that of the single particles.

[0139] The method for forming the single particles is not particularly limited, but may generally be formed by over-firing at an elevated firing temperature. The single particles may be prepared by using an additive such as a grain growth promoter that is useful for over-firing, or by changing the starting material.

[0140] For example, the calcination is performed at a temperature that allows the formation of single particles. To achieve this, the calcination must be performed at a temperature higher than that used for producing secondary particles. For example, when the precursor composition is the same, the calcination temperature should be about 30°C to 100°C higher than that used for producing secondary particles. The calcination temperature for forming the single particles may vary depending on the metal composition of the precursor. For example, when a high-nickel (Ni) NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more is to be formed as single particles, the calcination temperature may be about 700°C to 1000°C, preferably about 800°C to 950°C. When the calcination temperature satisfies the above range, a positive electrode active material containing single particles with excellent electrochemical properties can be produced. When the calcination temperature is lower than 790°C, a positive electrode active material containing a lithium composite transition metal compound in the form of secondary particles may be produced. However, when the calcination temperature exceeds 950°C, excessive calcination may occur, resulting in an improper formation of a layered crystal structure and reduced electrochemical properties.

[0141] In this specification, the term "single particle" is used to distinguish it from conventional secondary particles formed by agglomeration of tens to hundreds of primary particles, and is a concept that includes a single particle consisting of one primary particle and a pseudo-single particle form that is an agglomeration of 30 or less primary particles.

[0142] Specifically, in the present invention, a single particle may be in the form of a single particle consisting of one primary particle or a pseudo-single particle which is an aggregate of 30 or less primary particles, and a secondary particle may be in the form of an aggregate of several hundred primary particles.

[0143] In one embodiment of the present application, the lithium transition metal composite compound serving as the positive electrode active material further includes secondary particles, and the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles.

[0144] In the present invention, the single particle may be in the form of a single particle consisting of one primary particle or a pseudo-single particle which is an aggregate of 30 or less primary particles, and the secondary particle may be in the form of an aggregate of several hundred primary particles.

[0145] The lithium transition metal composite compound may further include secondary particles. The secondary particles refer to a form formed by aggregation of primary particles, and can be distinguished from the concept of single particles, which includes a form of one primary particle, one single particle, or a quasi-single particle that is an aggregation of 30 or less primary particles.

[0146] The particle diameter (D50) of the secondary particles may be 1 μm to 20 μm, 2 μm to 17 μm, preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles may be 0.05 m 2 / g~10m 2 / g, preferably 0.1m 2 / g~1m 2 / g, and more preferably 0.3m 2 / g~0.8m 2 / g may also be used.

[0147] In another embodiment of the present application, the secondary particles are aggregates of primary particles, and the average particle size (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of aggregates of several hundred primary particles, and the average particle size (D50) of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0148] When the average particle size (D50) of the primary particles satisfies the above range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size (D50) of the primary particles is too small, the number of agglomerates of the primary particles forming the lithium nickel-based oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size (D50) of the primary particles is too large, the lithium diffusion path within the primary particles becomes longer, increasing resistance and potentially reducing output characteristics.

[0149] According to a further embodiment of the present application, the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles, so that the single particles can have excellent particle strength even when formed with a small particle size, thereby mitigating the phenomenon of an increase in fine particles in the electrode due to particle cracking, thereby improving the life characteristics of the battery.

[0150] In one embodiment of the present application, the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles by 1 μm to 18 μm.

[0151] For example, the average particle size (D50) of the single particles may be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle size (D50) of the secondary particles.

[0152] When the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles, for example, when the above range is satisfied, the single particles can have excellent particle strength even when formed with a small particle size, thereby mitigating the phenomenon of an increase in fine particles in the electrode due to particle cracking, and improving the life characteristics and energy density of the battery.

[0153] According to a further embodiment of the present application, the single particles are contained in an amount of 15 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material, or may be contained in an amount of 20 to 100 parts by weight, or 30 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material.

[0154] For example, the single particles may be included in an amount of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, relative to 100 parts by weight of the positive electrode active material. The single particles may be included in an amount of 100 parts by weight or less, relative to 100 parts by weight of the positive electrode active material.

[0155] When the single particles are contained in the above range, excellent battery characteristics can be exhibited in combination with the above-mentioned negative electrode material. In particular, when the single particles are contained in an amount of 15 parts by weight or more, the increase in fine particles in the electrode due to particle cracking during the rolling process after electrode fabrication can be mitigated, thereby improving the battery life characteristics.

[0156] In one embodiment of the present application, the lithium composite transition metal compound may further include secondary particles, and the secondary particles may be 85 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The secondary particles may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The secondary particles may be 0 parts by weight or more relative to 100 parts by weight of the positive electrode active material.

[0157] When the above range is satisfied, the above-described effects due to the presence of the single particle positive electrode active material can be maximized. When the secondary particle positive electrode active material is included, the components thereof may be the same as or different from those exemplified in the single particle positive electrode active material described above, and may refer to a form in which the single particles are aggregated.

[0158] In one embodiment of the present application, the positive electrode active material may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less, in 100 parts by weight of the positive electrode active material layer.

[0159] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0160] The positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery. Specific examples include graphite such as natural graphite and artificial graphite; carbonaceous materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination.

[0161] The positive electrode binder improves adhesion between positive electrode active material particles and 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, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0162] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to electrolyte ion migration and excellent electrolyte humidification capacity is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be used in a single-layer or multi-layer structure.

[0163] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0164] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0165] Examples of the non-aqueous organic solvent that may be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0166] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferred because they are high-viscosity organic solvents with high dielectric constants and can dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, and these cyclic carbonates are more preferred.

[0167] The metal salt can be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt can be 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:

[0168] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0169] The lithium secondary battery according to the present invention is useful in mobile devices such as mobile phones, laptop computers, and digital cameras, and in electric vehicles such as hybrid electric vehicles (HEVs), and is particularly suitable as a component battery of medium- to large-sized battery modules. Accordingly, the present invention also provides a medium- to large-sized battery module including the above-described lithium secondary battery as a unit cell.

[0170] According to one embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, excellent rate-limiting characteristics, and excellent cycle characteristics, and therefore can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0171] While preferred examples are presented below to aid in understanding the present invention, these examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical spirit of the present invention. Such changes and modifications are naturally intended to fall within the scope of the appended claims.

[0172] <Production example> <Production of Water-Soluble Polymer> Synthesis Example 1 A reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube was charged with 45 g of PVA (polyvinyl alcohol, Mw=2400) and 500 g of water, and the temperature was raised to 90°C to dissolve the PVA. 0.3 g of glutaraldehyde (25% aqueous solution) and 30 g of water were mixed and added to this solution, which was then maintained for 2 hours. The reaction mixture was then cooled to 50°C, and a solution of 1 g of ammonium persulfate (APS) dissolved in 10 g of water and 0.3 g of NaHSO3 dissolved in 3 g of water were sequentially added and maintained for 10 minutes.

[0173] While introducing nitrogen, 35g of acrylic acid (AA), 15g of N-hydroxyethylacrylamide (HEAA), and 250g of water were mixed and added dropwise over 30 minutes and held for 2 hours. Next, an aqueous solution of 0.5g of NaOH dissolved in 3g of water was gradually added to produce a polymer aqueous solution.

[0174] Synthesis Example 2 A reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet pipe was charged with 1254 g of water, 200 g of acrylamide (50% aqueous solution), 40 g of acrylic acid (AA (acrylic acid 80% aqueous solution)), 20 g of 48% sodium hydroxide (48% aqueous solution), and 50 g of acrylonitrile, and the temperature was raised to 50°C. 2.0 g of 2,2'-azobis-2-amidinopropane dihydrochloride and 20 g of water were added, and the temperature was raised to 80°C. The mixture was reacted for 3 hours to produce a polyacrylamide polymer aqueous solution.

[0175] <Production of negative electrode slurry> Example 1 As the negative electrode active material, 1) artificial graphite with d50 = 15 μm was used, and 2) silicon was used as SiO x The negative electrode composition was prepared by mixing graphite and silicon in a weight ratio of 7:3 using graphite (d50 = 1 μm to 6 μm), and the conductive material was Super-P black and SWCNT (Super-P:SWCNT weight ratio = 1:0.001) in a weight ratio of 85:5:10 active material:conductive material:binder. The amount of water used as a solvent was adjusted taking into consideration coating properties, viscosity, and solid content. The viscosity of the resulting slurry composition was adjusted to 5,000 cps to 6,000 cps.

[0176] The binder used was the polymer of Synthesis Example 1 and graphene oxide in a weight ratio of 98:2, with the graphene oxide having a C / O ratio of 1.5 and a particle size (lateral size) of 2 μm.

[0177] <Example 2> The same procedure as in Example 1 was repeated, except that the weight ratio of active material:conductive material:binder was 85:5:10, the weight ratio of the polymer of Synthesis Example 2 and graphene oxide was 98:2 as the binder, the C / O ratio of graphene oxide was 2.0, and the lateral size of graphene oxide was 5 μm.

[0178] Example 3 The same procedure as in Example 1 was repeated, except that the weight ratio of active material:conductive material:binder was 85:5:10, the polymer of Synthesis Example 1 and graphene oxide were used as the binder in a weight ratio of 65:35, the C / O ratio of graphene oxide was 2.0, and the lateral size of graphene oxide was 5 μm.

[0179] Example 4 The negative electrode composition was prepared in the same manner as in Example 1, except that the silicon-based active material was Si (average particle size (D50): 3.5 μm), the conductive material was Super-P black and SWCNT (Super-P:SWCNT weight ratio = 1:0.001), and the active material:conductive material:binder were mixed in a weight ratio of 85:5:10 to prepare a negative electrode composition.

[0180] <Example 5> In Example 4, the binder was a mixture of the polymer of Synthesis Example 1 and graphene oxide in a weight ratio of 98:2, and the graphene oxide had a C / O ratio of 1.5 and a lateral particle size of 1 μm.

[0181] Example 6 In Example 4, the binder was a mixture of the polymer of Synthesis Example 1 and graphene oxide in a weight ratio of 98:2, and the graphene oxide had a C / O ratio of 1.5 and a lateral particle size of 10 μm.

[0182] Example 7 In Example 4, the polymer of Synthesis Example 1 and graphene oxide were used as the binder in a weight ratio of 98:2, and the graphene oxide had a C / O ratio of 2.5 and a lateral particle size of 10 μm.

[0183] Example 8 In Example 4, the polymer of Synthesis Example 1 and graphene oxide were used as the binder in a weight ratio of 98:2, and the graphene oxide had a C / O ratio of 2.5 and a lateral particle size of 1 μm.

[0184] <Comparative Example 1> The same preparation as in Example 1 was carried out, except that the weight ratio of active material:conductive material:binder was 85:5:10 and graphene oxide was not used as the binder.

[0185] <Comparative Example 2> The same procedure as in Example 1 was repeated, except that the weight ratio of active material:conductive material:binder was 85:5:10, the polymer of Synthesis Example 1 and graphene oxide were used as the binder in a weight ratio of 95:5, the C / O ratio of graphene oxide was 4.0, and the lateral size of graphene oxide was 2 μm.

[0186] <Comparative Example 3> The same procedure as in Example 1 was repeated, except that the weight ratio of active material:conductive material:binder was 85:5:10, the weight ratio of the polymer of Synthesis Example 1 and graphene was 98:2 as the binder, and pure graphene was used and had a lateral size of 40 μm.

[0187] <Comparative Example 4> The same procedure as in Example 1 was repeated, except that the weight ratio of active material:conductive material:binder was 85:5:10, the polymer of Synthesis Example 1 and graphene oxide were used as the binder in a weight ratio of 95:5, the C / O ratio of graphene oxide was 3.0, and the lateral size of graphene oxide was 60 μm.

[0188] <Comparative Example 5> In Example 4, the binder was a mixture of the polymer of Synthesis Example 1 and graphene oxide in a weight ratio of 98:2, and the graphene oxide had a C / O ratio of 1.5 and a lateral particle size of 25 μm.

[0189] <Comparative Example 6> In Example 4, the binder was a mixture of the polymer of Synthesis Example 1 and graphene oxide in a weight ratio of 98:2, and the graphene oxide had a C / O ratio of 1.5 and a lateral particle size of 0.1 μm.

[0190] <Comparative Example 7> In Example 4, the polymer of Synthesis Example 1 and graphene oxide were used as the binder in a weight ratio of 98:2, and the graphene oxide had a C / O ratio of 2.5 and a lateral particle size of 25 μm.

[0191] <Comparative Example 8> In Example 4, the polymer of Synthesis Example 1 and graphene oxide were used as the binder in a weight ratio of 98:2, and the graphene oxide had a C / O ratio of 2.5 and a lateral particle size of 0.1 μm.

[0192] <Battery manufacturing and battery characteristic evaluation> The negative electrode slurries of the examples and comparative examples were coated onto 18 μm-thick copper foil and dried. A 50 μm-thick active material layer was formed on one side of the copper foil, and the foil was punched into a circle with a diameter of 14 Φ to prepare a test electrode (negative electrode). A 0.3 mm-thick metallic lithium foil was used as the positive electrode, a 0.1 mm-thick porous polyethylene sheet was used as the separator, and a lithium salt, LiPF6, dissolved at a concentration of approximately 1 mol / L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1, was used as the electrolyte.

[0193] The negative electrode, positive electrode, separator, and electrolyte were sealed in a stainless steel container to prepare a coin cell for evaluation, 2 mm thick and 32 mm in diameter. The evaluation results are shown in Tables 1 and 2 below.

[0194] [Table 1]

[0195] [Table 2]

[0196] - Initial efficiency (%): The coin cell was charged at a constant current of 0.05 C until the voltage reached 0.01 V, and then discharged at a constant current of 0.05 C until the voltage reached 1.5 V. The discharge capacity and initial efficiency were calculated and expressed as (discharge capacity / charge capacity) x 100 (%).

[0197] -Capacity retention rate (%): The coin cell was charged at a constant current of 0.05C until the voltage reached 0.01V, and then discharged at a constant current of 0.05C until the voltage reached 1.5V. The cycle characteristics were then tested at a constant current of 0.2C within the same voltage range as above, and the capacity retention rate was calculated based on 30 cycles.

[0198] - Thickness increase rate (%): The thickness (X1) of the negative electrode active material layer of the manufactured coin cell was measured, and the coin cell was charged at a constant current of 0.05 C until the voltage reached 0.01 V, and then discharged at a constant current of 0.05 C until the voltage reached 1.5 V. Thereafter, the cycle characteristics were measured at a constant current of 0.2 C within the same voltage range as above, and the thickness (X2) of the negative electrode active material layer of the coin cell was measured after 30 cycles.

[0199] As can be seen from the results of Tables 1 and 2, the batteries according to Examples 1 to 8 were able to suppress volume expansion and contraction and minimize thickness changes due to electrode swelling, even when using negative electrode active materials (especially silicon-based active materials) that exhibit large volume expansion during charge / discharge. As a result, it was confirmed that the life performance of the lithium secondary batteries was excellent.

[0200] In particular, Examples 4 to 8 use 100% Si as the negative electrode active material. Pure Si generally experiences significant volume expansion during charge and discharge, making its application difficult. However, by incorporating the specific binder according to the present invention, it was confirmed that the initial efficiency was superior to Examples 1 to 3, as described above. Although the thickness increase was also greater than Examples 1 to 3 due to the use of pure Si particles, the thickness increase rate was within the range of 0% to 15% by applying the binder according to the present invention, which is at a level that does not pose a problem when operating the negative electrode. In other words, it was confirmed that the negative electrodes of Examples 4 to 8 maximized capacity characteristics while easily suppressing volume expansion.

[0201] Comparative Example 1 is a case where a specific graphene oxide is not included, Comparative Example 2 is a case where graphene oxide is used but the C / O ratio is outside the range of the present application, Comparative Example 3 is a case where graphene is used instead of graphene oxide (no C / O ratio), and Comparative Example 4 is a case where the particle size (lateral size) of graphene oxide is outside the range of the present application.

[0202] It should be noted that Comparative Examples 5 to 8 use graphene oxide, and describe combinations in which the C / O ratio satisfies the range of the present application, but the particle size (lateral size) does not satisfy the range of the present application.

[0203] As can be seen from each of Comparative Examples 1 to 8, the initial efficiency itself is calculated similarly to that of the Examples, but it was confirmed that the capacity retention rate is reduced and the thickness increase rate of the negative electrode active material layer due to the volume expansion of the silicon-based active material is increased because the specific graphene oxide according to the present application is not contained.

[0204] Furthermore, when comparing Examples 1 to 3, the graphene oxide contained in Examples 1 and 2 was present in an amount of 0.1 to 30 parts by weight, based on 100 parts by weight of the negative electrode binder. Comparing Examples 1 and 2 with Example 3, it was confirmed that the negative electrode of Example 3 had particularly excellent capacity retention and efficiently suppressed thickness increase. This is because the presence of graphene oxide in this amount by weight effectively dispersed the negative electrode active material, providing strong electrode adhesion and strong binding strength between the active materials within the electrode against contraction and expansion of the negative electrode active material during charge and discharge of the lithium secondary battery. [Explanation of symbols]

[0205] 10 Negative electrode current collector layer 20...Negative electrode active material layer 30...Separation membrane 40...Cathode active material layer 50 Positive electrode current collector layer 100 ···Negative electrode for lithium secondary battery 200 ···Positive electrode for lithium secondary battery

Claims

1. a negative electrode binder comprising graphene oxide and at least one water-soluble polymer; a negative electrode active material, and A negative electrode composition comprising a negative electrode conductive material, The lateral size of the graphene oxide is 0.3 μm or more and 20 μm or less, The graphene oxide has a carbon (C) / oxygen (O) ratio of 0.5 or more and 2.5 or less.

2. The negative electrode composition of claim 1 , wherein the negative electrode binder comprises 0.1 to 30 parts by weight of the graphene oxide based on 100 parts by weight of the negative electrode binder.

3. The negative electrode composition of claim 1 , wherein the negative electrode binder is present in an amount of 1 part by weight to 20 parts by weight based on 100 parts by weight of the negative electrode composition.

4. 2. The negative electrode composition according to claim 1, wherein the water-soluble polymer has a weight average molecular weight of 100,000 g / mol or more and 3,000,000 g / mol or less.

5. The negative electrode composition described in claim 1, wherein the water-soluble polymer comprises at least one selected from the group consisting of carboxymethyl cellulose and its derivatives, water-soluble polyacrylic acid, polyvinyl alcohol, polyacrylonitrile, and polyacrylamide.

6. 2. The negative electrode composition according to claim 1, wherein the water-soluble polymer is a polymer of at least one monomer selected from the group consisting of a (meth)acrylamide group-containing compound; an unsaturated organic acid or a salt of an unsaturated organic acid; and an α,β-unsaturated nitrile and a hydroxyalkyl (meth)acrylate.

7. The negative electrode composition according to claim 1 , wherein the negative electrode conductive material comprises at least one selected from the group consisting of a dot-like conductive material, a sheet-like conductive material, and a linear conductive material.

8. The negative electrode composition according to claim 1 , wherein the negative electrode active material comprises at least one selected from the group consisting of a silicon-based active material and a carbon-based active material.

9. The silicon-based active material is SiO ｘ (x=0) and SiO ｘ (0<x<2), and based on 100 parts by weight of the silicon-based active material, the SiO ｘ The negative electrode composition according to claim 8 , comprising 70 parts by weight or more of (x=0).

10. The negative electrode composition of claim 1 , wherein the negative electrode active material is present in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

11. a negative electrode current collector layer, and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector layer, the negative electrode active material layer comprising the negative electrode composition according to any one of claims 1 to 10; A negative electrode for a lithium secondary battery comprising:

12. the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, 12. The negative electrode for a lithium secondary battery according to claim 11, wherein the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

13. The negative electrode for a lithium secondary battery according to claim 11, wherein the thickness change rate of the negative electrode active material layer satisfies the following formula 1: [Formula 1] 8%≦[(X2-X1) / X1]×100(%)≦15% In the formula 1, X1 is the thickness of the negative electrode active material layer of the negative electrode for lithium secondary battery at 0 cycle, X2 is the thickness of the negative electrode active material layer of the negative electrode for a lithium secondary battery after 30 cycles.

14. positive electrode, The negative electrode for a lithium secondary battery according to claim 11 . a separator provided between the positive electrode and the negative electrode for the lithium secondary battery; and A lithium secondary battery comprising an electrolyte.

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