Negative electrode composition, negative electrode, lithium secondary battery, battery module, and battery pack

Abstract

The present invention relates to a negative electrode composition, a negative electrode, a lithium secondary battery, a battery module, and a battery pack. The negative electrode composition includes a negative electrode active material containing a silicon-carbon composite and graphite, and the tab density of the graphite is the same as or greater than the tab density of the silicon-carbon composite.

Description

Technical Field

[0001] The present invention claims the benefit of the filing dates of Korean Patent Application No. 10-2022-0177137 filed with the Korean Intellectual Property Office on December 16, 2022, and Korean Patent Application No. 10-2023-0178444 filed with the Korean Intellectual Property Office on December 11, 2023, and all of its contents are included herein.

[0002] The present invention relates to a negative electrode composition, a negative electrode, a lithium secondary battery, a battery module, and a battery pack.

Background Art

[0003] In recent years, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, electric vehicles, power tools, and vacuum cleaners, there has been a rapid increase in the demand for secondary batteries that are small, lightweight, and have relatively high capacity and / or high output. In particular, lithium secondary batteries are lightweight and have a high energy density, and are in the spotlight as a driving power source for electronic devices. As a result, research and development efforts to improve the performance of lithium secondary batteries are being actively carried out.

[0004] A lithium secondary battery produces electrical energy through oxidation and reduction reactions when lithium ions are inserted / desorbed from the positive and negative electrodes in a state where an organic electrolyte or a polymer electrolyte is filled between a positive electrode and a negative electrode made of an active material capable of inserting (intercalations) and desorbing (deintercalation) lithium ions.

[0005] As the positive electrode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (such as LiMnO2 or LiMn2O4), lithium iron phosphate compound (LiFePO4), etc. are used. Among them, lithium cobalt oxide (LiCoO2) has the advantages of a high operating voltage and excellent capacity characteristics, so it is widely used and applied as a positive electrode active material for high voltage. However, due to the rising price and supply instability of cobalt (Co), there is a limit to its large-scale use as a power source in fields such as electric vehicles, and the need to develop a replaceable positive electrode active material has emerged.

[0006] As a result, a nickel cobalt manganese-based lithium composite transition metal compound (hereinafter simply referred to as "NCM-based lithium composite transition metal compound") in which a part of cobalt (Co) is replaced with nickel (Ni) and manganese (Mn) has been developed. In recent years, research has been conducted to increase the content of Ni in the NCM-based lithium composite transition metal compound to increase the capacity. However, in the case of a high-concentration nickel (Ni-rich) positive electrode active material with a high nickel content, there are disadvantages such as a decrease in thermal stability, an increase in resistance due to an increase in side reactions during the electrochemical reaction, and an increase in gas generation.

[0007] On the other hand, graphite is mainly used as the negative electrode active material of a lithium secondary battery. However, since the capacity per unit mass of graphite is as small as 372 mAh / g, it is difficult to increase the capacity of the lithium secondary battery. For this reason, as a non-carbon-based negative electrode material having a higher energy density than graphite for increasing the capacity of the lithium secondary battery, negative electrode materials such as silicon, tin, and their oxides have been developed. However, in the case of such non-carbon-based negative electrode materials, although the capacity is large, there are problems such as low initial efficiency, a large lithium consumption during the initial charge and discharge, and a large irreversible capacity loss.

[0008] In addition, lithium secondary batteries have a size required according to their applications and must be designed within a limited space accordingly. Although the demands of consumers for an increase in energy density and an improvement in high output performance are increasing, when using a high-capacity cathode material, the content of the anode material must be increased to match it, so there is a limit to improving the efficiency of the battery within a limited space. Therefore, there is a need to develop a battery with improved performance such as efficiency and lifespan within a limited space.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The inventors of the present invention have found that in a lithium secondary battery designed within a limited space, by adjusting the tap density of the anode active material, optimal battery performance can be achieved in an anode having a specific combination, and thus the present invention has been completed.

[0011] The present invention relates to an anode composition, an anode, a lithium secondary battery, a battery module, and a battery pack.

Means for Solving the Problems

[0012] One embodiment of the present invention provides an anode composition including an anode active material containing a silicon-carbon composite and graphite, wherein the tap density of the graphite is the same as or higher than the tap density of the silicon-carbon composite.

[0013] One embodiment of the present invention provides an anode including an anode current collector; and an anode active material layer provided on one or both surfaces of the anode current collector and including the anode composition according to the above-described embodiment.

[0014] One embodiment of the present invention provides a lithium secondary battery including a positive electrode; a negative electrode according to the above-described embodiment; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0015] In the above-described embodiment, the positive electrode includes a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn) as a positive electrode active material, and the lithium composite transition metal compound may include single particles.

[0016] One embodiment of the present invention provides a battery module including the lithium secondary battery.

[0017] One embodiment of the present invention provides a battery pack including the battery module.

Advantages of the Invention

[0018] In the negative electrode composition according to one embodiment of the present invention, since the tap density of graphite in the negative electrode active material is the same as or higher than the tap density of the silicon-carbon composite, graphite can be densely dispersed throughout the electrode. As a result, the flow of current in the negative electrode is not interrupted, and it is easy to adjust the degree of orientation of graphite in the negative electrode. Therefore, by adjusting the degree of orientation of graphite to be constant, the ion transfer path in the electrode can be designed uniformly, and lithium diffusion occurs well, so that excellent performance can be exhibited during rapid charging of the battery.

[0019] Also, by adjusting the degree of orientation of graphite to be constant, the cracking phenomenon of particles during rolling can be prevented, which is advantageous for the dispersion of the electrode slurry, makes rolling easier, can reduce the thickness of the electrode, and increases the mass per unit volume, so that a denser characteristic can be exhibited.

[0020] Therefore, by using the negative electrode in which the tap density between the negative electrode active materials is adjusted as described above, the rapid charging performance, efficiency, life, and / or energy density of the lithium secondary battery designed in a limited space can be easily improved.

Best Mode for Carrying Out the Invention

[0021] Hereinafter, the present specification will be described in more detail.

[0022] In this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0023] In this specification, when a certain member is "above" another member, this includes not only the case where a certain member is in contact with another member, but also the case where there is another member between the two members.

[0024] The terms and words used in this specification should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the principle that they can appropriately define the concepts of the terms in order to explain their invention in the best way, and they should be interpreted in a meaning and concept that conforms to the technical idea of the present invention.

[0025] In this specification, the singular expressions of the terms used include plural expressions unless the context clearly indicates otherwise.

[0026] In this specification, the term "single particle" is used to distinguish from the secondary particle-shaped positive electrode active material particles formed by aggregation of dozens to hundreds of conventional primary particles, and means a single particle composed of one primary particle and an agglomerate of 30 or fewer primary particles, i.e., a similar-single particle.

[0027] In this specification, the average particle size (D 50) can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve (graph curve of the particle size distribution diagram). The average particle size can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes in the range from the submicron region to about several millimeters, and high reproducibility and high resolution results can be obtained.

[0028] The measurement of the average particle size can be confirmed using a Microtrac device (manufacturer: Microtrac, model name: S3500) with water and triton-X100 dispersant. Specifically, the average particle size of the positive electrode active material can be measured in the refractive index range of 1.5 - 1.7, and the negative electrode active material can be measured under the conditions of refractive index 1.97 or 2.42. For example, after dispersing the particles in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device, irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then after obtaining a volume cumulative particle size distribution graph, it can be measured by determining the particle size corresponding to 50% of the volume cumulative amount.

[0029] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be deformed into various forms, and the scope of the present invention is not limited to the embodiments described below.

[0030] One embodiment of the present invention provides a negative electrode composition including a negative electrode active material containing a silicon carbon composite and graphite, wherein the tap density of the graphite is the same as or greater than the tap density of the silicon carbon composite.

[0031] In one embodiment of the present invention, the negative electrode active material may include a silicon carbon composite and graphite, and the tap density of the graphite may be the same as or greater than the tap density of the silicon carbon composite.

[0032] Generally, lithium secondary batteries have a size required according to their applications and must be designed within a limited space accordingly. Although the demands of consumers for an increase in energy density and an improvement in high-power performance are increasing, when using a high-capacity cathode material, the content of the anode material must be increased accordingly. Therefore, there is a limit to enhancing the efficiency of the battery within a limited space. In addition, it is necessary to design a cathode material having an efficiency that matches the efficiency of the anode material according to the type of the anode material.

[0033] Since the tap density of graphite in the anode active material in the anode composition according to the present invention is the same as or higher than the tap density of the silicon-carbon composite, the graphite can be densely dispersed throughout the electrode. As a result, the flow of current in the anode is not interrupted, and it is easy to adjust the degree of orientation of graphite in the anode. Therefore, by adjusting the degree of orientation of graphite to be constant, the ion transfer path in the electrode can be designed uniformly, and lithium diffusion occurs well. Thus, excellent performance can be exhibited during rapid charging of the battery.

[0034] In addition, by adjusting the degree of orientation of graphite to be constant, the phenomenon of particle cracking during rolling can be prevented, which is advantageous for the dispersion of the electrode slurry, makes rolling easier, can reduce the thickness of the electrode, and increases the mass per unit volume. Therefore, a denser characteristic can be exhibited.

[0035] Therefore, by using the anode in which the tap density between the anode active materials is adjusted as described above, the rapid charging performance, efficiency, life, and / or energy density of the lithium secondary battery designed within a limited space can be easily improved.

[0036] On the contrary, when the tap density of graphite is smaller than the tap density of the silicon-carbon composite, the graphite aggregates without being dispersed in the electrode, the dispersibility of the slurry decreases, which is disadvantageous for rolling, the thickness of the electrode increases, a void region is formed in the electrode, and it is disadvantageous in terms of the uniformity of the electrode.

[0037] In this specification, the silicon-carbon composite is a composite of Si and C, where Si and C (e.g., graphite) exist respectively. For example, the respective peaks of Si and C can be observed by elemental analysis methods such as XRD or NMR. In this specification, the silicon-carbon composite can be represented as Si / C. The silicon-carbon composite may consist of Si and C that are not bonded to each other, but may also contain additional components as necessary. For example, the silicon-carbon composite may or may not contain silicon carbide (Silicon carbide) represented by SiC. When the silicon-carbon composite contains silicon carbide, its content is 3 wt% or less. The silicon-carbon composite may exist in a crystalline, amorphous, or mixed state thereof. According to one example, C in the silicon-carbon composite may exist in an amorphous state. The silicon-carbon composite may be one in which the carbon and silicon materials are physically or chemically compounded, and is not limited as long as the carbon and silicon materials form a composite structure.

[0038] Specifically, the silicon-carbon composite may have a structure in which the carbon material is coated on the surface of the particles by heat treatment (firing) in a state where the carbon is bonded to silicon or silicon oxide particles, or a structure in which carbon is dispersed in an atomic state inside the silicon particles, or a structure in which a core in which silicon and carbon are compounded is surrounded by graphite, graphene, or amorphous carbon, etc.

[0039] According to one embodiment, the silicon-carbon composite includes porous carbon-based particles and silicon located on the surface or internal pores of the porous carbon-based particles.

[0040] According to one embodiment, the silicon-carbon composite can be manufactured by a method including the step of forming silicon on the surface and internal pores of the porous carbon-based particles.

[0041] The porous carbon-based particles can be produced using methods known in the art. As an example, they can be obtained by carbonizing organic substances such as petroleum-based materials, polymers, etc., or by carbonizing substances existing in nature such as coconut husk after chemical treatment. As another example, the porous carbon-based particles can be obtained by a method including a step of etching carbon-based particles containing internal pores to expand the internal pores of the carbon-based particles.

[0042] The step of expanding the internal pores of the carbon-based particles may be performed in a nitrogen (N2) atmosphere, an oxygen (O2) atmosphere, or an air atmosphere. Specifically, the flow rate of the oxygen (O2) or the air containing the oxygen may be controlled to be 0.1 L / min to 10 L / min.

[0043] The step of expanding the internal pores of the carbon-based particles may be performed in a temperature range of 400°C to 1200°C for 30 minutes to 4 hours.

[0044] Depending on the conditions for expanding the internal pores of the carbon-based particles, the pore characteristics of the obtained porous carbon-based particles can be different.

[0045] The step of forming the silicon may be performed using a chemical vapor deposition method. At this time, silicon nanoparticles may be deposited on the surface and / or internal pores of the carbon-based particles with expanded internal pores, and silicon in the form of a film, an island, or a mixed form thereof may be formed.

[0046] The silicon nanoparticles may be crystalline, quasi-crystalline, amorphous, or a combination thereof.

[0047] In one embodiment of the present invention, the tap density of the graphite may be 0.9 g / cc or more and 1.2 g / cc or less. Specifically, it may be 1 g / cc or more and 1.2 g / cc or less, 1.03 g / cc or more and 1.15 g / cc or less, or 1.05 g / cc or more and 1.12 g / cc or less.

[0048] When the tap density of graphite satisfies the above range, the graphite can be uniformly dispersed without aggregating in the electrode. In contrast, when the tap density of graphite is less than the above range, the graphite either aggregates without being dispersed in the electrode or void regions are formed in the electrode, which is disadvantageous in terms of the uniformity of the electrode. When the tap density of graphite exceeds the above range, since the density of graphite in the electrode becomes excessively high, cracks in the particles may occur during rolling, which is disadvantageous in terms of lithium diffusion.

[0049] In one embodiment of the present invention, the tap density of the silicon-carbon composite may be 0.5 g / cc or more and 1.15 g / cc or less. Specifically, it may be 0.55 g / cc or more and 1.1 g / cc or less, or 0.58 g / cc or more and 1.08 g / cc or less.

[0050] When the tap density of the silicon-carbon composite satisfies the above range, the silicon-carbon composite can be uniformly dispersed without aggregating in the electrode. In contrast, when the tap density of the silicon-carbon composite is less than the above range, the silicon-carbon composite either aggregates without being dispersed in the electrode or void regions are formed in the electrode, which is disadvantageous in terms of the uniformity of the electrode. When the tap density of the silicon-carbon composite exceeds the above range, since the density of the silicon-carbon composite in the electrode becomes excessively high, cracks in the particles may occur during rolling, which is disadvantageous in terms of lithium diffusion.

[0051] In one embodiment of the present invention, the tap density of the graphite may have the same value as the tap density of the silicon-carbon composite.

[0052] In one embodiment of the present invention, the tap density of the graphite may have a value greater than the tap density of the silicon-carbon composite.

[0053] In this specification, the tap density can be measured using a normal tap density measuring device. Specifically, it can be measured using the TAP-2S manufactured by LOGAN. For example, the tap density may be the density calculated by putting 40 g of a sample into a container and tapping it 1000 times.

[0054] The graphite may be natural graphite or artificial graphite, or a mixture of natural graphite and artificial graphite.

[0055] When the graphite is a mixture of natural graphite and artificial graphite, the weight ratio of natural graphite to artificial graphite may be 50:50 to 90:10, specifically 60:40 to 80:20, or 65:35 to 75:25.

[0056] In one embodiment of the present invention, the average particle diameter (D 50 ) of the silicon-carbon composite may be 1 μm or more. Also, the average particle diameter of the silicon-carbon composite may be 15 μm or less. For example, the average particle diameter (D 50 ) of the silicon-carbon composite may be 1 μm or more and 15 μm or less, more than 1 μm and less than 15 μm, 2 μm or more and 14 μm or less, 3 μm or more and 13 μm or less, 3 μm to 10 μm, 4 μm to 8 μm, or 5 μm to 8 μm.

[0057] Even if the silicon-carbon composite is formed to have a small particle diameter with an average particle diameter of about 1 μm or more and 15 μm or less, the life characteristics of the battery can be improved. For example, when the average particle diameter of the silicon-carbon composite is in the range of 1 μm or more and 15 μm or less, the volume expansion and shrinkage rates due to charge and discharge are reduced, and the life performance can be improved. Also, since an excessive increase in the specific surface area is prevented and side reactions with the electrolytic solution do not occur during cycle progress, the life performance can be improved.

[0058] In one embodiment of the present invention, the average particle diameter (D 50) may be 10 μm to 20 μm. Specifically, it may be 15 μm to 20 μm. When the average particle size of the graphite satisfies the above range, the influence due to particle aggregation is reduced, and the dispersibility of the slurry can be improved.

[0059] According to one embodiment of the present invention, the average particle size of the silicon-carbon composite is smaller than the average particle size of the graphite.

[0060] According to one embodiment of the present invention, the aspect ratio of the graphite is 0.8 to 0.9, and the aspect ratio of the silicon-carbon composite is 0.3 to 0.7. When the aspect ratios of the graphite and the silicon-carbon composite are within the above ranges, there are advantages in terms of production yield and rolling density. When the aspect ratio is below the upper limit, the yield of the material is excellent and the production cost ratio is reduced. When the aspect ratio is above the lower limit, the rolling density of the electrode is high, and the possibility of phenomena such as dents in the particles is reduced.

[0061] According to one embodiment of the present invention, the aspect ratio of the graphite may be 0.8 to 0.9, or 0.83 to 0.90, and the aspect ratio of the silicon-carbon composite may be 0.3 to 0.7, or 0.42 to 0.70.

[0062] In this specification, the aspect ratio may be a value obtained by dividing the circumference of a circle having the same area as the projected image by the perimeter of the projected image when the particle is projected. Specifically, it can be represented by the following formula 1. The aspect ratio can be obtained from the SEM image. The cross-sectional analysis of the negative electrode active material can be performed using an ion milling apparatus. Specifically, an electrode sample prepared by coating the negative electrode active material on a copper foil (Cu Foil) is milled using a Hitachi IM4000 apparatus. Specifically, after irradiating with an ion beam at a voltage of 1.5 kV and treating for about 3 to 4 hours per sample, a cross-sectional image can be measured with a Hitachi S-4800 SEM. The aspect ratio of the negative electrode active material can be measured based on the measured SEM cross-sectional image.

[0063] [Formula 1] Sphericity = Circumference of a circle with the same area as the projected image of the particle / Circumference of the projected image

[0064] According to one embodiment of the present invention, the true density of the graphite is 2 g / cc to 3 g / cc, and the true density of the silicon-carbon composite is 1.8 g / cc to 2.2 g / cc. When the true density of the graphite and the silicon-carbon composite is 2.2 g / cc or less, dispersion in the slurry is relatively easy, and generation of deviation due to the position after coating of the negative electrode active material layer can be prevented. When it is 1.8 g / cc or more, phenomena such as particle scattering can be prevented, and adjustment of the solid content of the slurry is easy. According to one embodiment of the present invention, the true density of the graphite may be 2 g / cc to 3 g / cc, 2 g / cc to 2.24 g / cc, or 2.23 g / cc to 2.24 g / cc, and the true density of the silicon-carbon composite may be 1.8 g / cc to 2.2 g / cc, or 1.9 g / cc to 2.2 g / cc.

[0065] The true density can be calculated by dividing the weight of the sample by the volume calculated from the volume difference of the He gas filled before and after putting the sample into a container whose volume is known.

[0066] According to one embodiment of the present invention, the BET specific surface area of the graphite is 1 m 2 / g to 3 m 2 / g, and the BET specific surface area of the silicon-carbon composite is 1 m 2 / g to 10 m 2 / g. Also, the BET specific surface area of the graphite may be 1 m 2 / g to 3 m 2 / g, 1.0 m 2 / g to 2.2 m 2 / g, 1.0 m 2 / g to 2.1 m 2 / g, 1.7 m 2 / g to 3.0 m 2 / g, 1.7 m 2 / g to 2.2 m 2 / g, or 1.7 m 2 / g to 2.1 m2 It may also be / g, and the BET specific surface area of the silicon-carbon composite is 1 m 2 / g to 10 m 2 / g, 1.0 m 2 / g to 7.1 m 2 / g, 1.0 m 2 / g to 6.7 m 2 / g, 3.1 m 2 / g to 10 m 2 / g, 3.1 m 2 / g to 7.1 m 2 / g, or 3.1 m 2 / g to 6.7 m 2 / g may also be acceptable.

[0067] Generally, the smaller the BET of the material, the easier the dispersion of the substances in the slurry during mixing, which is advantageous for increasing the electrode density. When the BET specific surface areas of the graphite and the silicon-carbon composite are within the above ranges, it is possible to prevent the acceleration of side reactions of the electrolytic solution, and to prevent the deterioration of the cycle life and the acceleration of side reactions during high-temperature storage. According to an example, the specific surface area is measured by the BET method. Specifically, for the measurement object, using a BET measurement device (BEL-SORP-mini, Nippon Bell), the gas is removed (degassing) at 300 °C for 1 hour, and the N2 adsorption / desorption is performed at 77 K for measurement. That is, in this specification, the BET specific surface area means the specific surface area of the particles themselves measured by the above-described measurement method.

[0068] According to an embodiment of the present invention, the negative electrode composition contains 3 to 30 parts by weight of a silicon-carbon composite based on 100 parts by weight of the total negative electrode active material. According to an example, based on 100 parts by weight of the negative electrode active material, the silicon-carbon composite may be contained in an amount of 3 to 20 parts by weight, or 3 to 13 parts by weight, preferably 5 to 10 parts by weight. By using the silicon-carbon composite within such a range, excellent battery characteristics can be exhibited in combination with the above-described positive electrode material. In particular, when the silicon-carbon composite is contained in an amount of 3 parts by weight or more, the effects of using the silicon-carbon composite can be sufficiently exhibited. Further, since the silicon-carbon composite has a higher capacity than the SiOx-based active material, it is difficult to balance the capacity with the positive electrode active material when used in excess. In particular, when the silicon-carbon composite is contained in an amount of 30 parts by weight or less, expansion during charge and discharge can be prevented and the cycle characteristics can be improved.

[0069] The silicon-carbon composite is a material having a higher capacity and higher efficiency than silicon-based oxides, and can exhibit excellent effects in terms of resistance compared to a negative electrode containing a silicon-based oxide and a conductive material even when no conductive material is included. Further, since the silicon-carbon composite exhibits higher Si crystallinity than silicon-based oxides, excellent effects can be exhibited during high-power evaluation.

[0070] In one embodiment of the present invention, the graphite may be natural graphite, artificial graphite, or a mixture thereof. Based on 100 parts by weight of the total negative electrode active material contained in the negative electrode active material layer, the graphite may be contained in an amount of 70 parts by weight or more and 97 parts by weight or less.

[0071] Based on 100 parts by weight of the total negative electrode active material, the graphite may be contained in an amount of 75 parts by weight or more, 80 parts by weight or more, or 85 parts by weight or more. Based on 100 parts by weight of the total negative electrode active material, the graphite may be contained in an amount of 95 parts by weight or less, 93 parts by weight or less, or 90 parts by weight or less. When the graphite is a mixture of artificial graphite and natural graphite, based on 100 parts by weight of the graphite, the artificial graphite and the natural graphite may be contained in an amount of 90:10 to 50:50 parts by weight, 85:15 to 60:40 parts by weight, 80:20 to 60:40 parts by weight, 80:20 to 65:35 parts by weight, or 75:25 to 65:35 parts by weight.

[0072] In one embodiment of the present invention, the weight ratio of the graphite to the silicon-carbon composite may be 0.1:99.9 to 30:70, 1:99 to 20:80, 5:95 to 20:80, 5:95 to 15:85, 8:92 to 12:88, or 10:90 to 12:88.

[0073] In one embodiment of the present invention, based on 100 parts by weight of the solid content of the negative electrode composition, the negative 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 still more preferably 97 parts by weight or more and 99.9 parts by weight or less.

[0074] In one embodiment of the present invention, in addition to the silicon-carbon composite and the graphite, the negative electrode composition may further contain a negative electrode binder.

[0075] The negative electrode binder can play a role in improving the adhesion between negative electrode active material particles and the adhesive force between the negative electrode active material particles and the negative electrode current collector. As the negative electrode binder, any material well-known in the technical field can be used. Non-limiting examples include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and at least any one selected from the group consisting of substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and various copolymers thereof may also be included.

[0076] The negative electrode binder may be contained in an amount of 0.1 part by weight or more and 50 parts by weight or less based on 100 parts by weight of the solid content of the negative electrode composition. For example, preferably, it may be contained in an amount of 0.3 part by weight or more and 35 parts by weight or less, more preferably 0.5 part by weight or more and 10 parts by weight or less.

[0077] The negative electrode composition may not contain a conductive material, but may further contain a conductive material if necessary. The conductive material contained in the negative electrode composition is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbons, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used. The content of the conductive material in the negative electrode active material layer may be 0.01 part by weight to 30 parts by weight, preferably 0.03 part by weight to 25 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

[0078] One embodiment of the present invention provides a negative electrode including a negative electrode current collector; and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector and containing the negative electrode composition according to the above-described embodiment.

[0079] According to one embodiment of the present invention, the porosity of the negative electrode active material layer is 23% to 28%, for example, 24% to 27%, or 25% to 26%. When the porosity is below the upper limit of the range, a decrease in the energy density of the cell can be prevented by preventing a decrease in the electrode density. When the porosity is above the lower limit of the range, cracking of the particles of the active material in the electrode can be prevented. The porosity can be measured as follows. The porosity of the electrode active material layer can be determined from a value calculated from the true density of the material constituting the electrode active material layer, the weight, thickness, etc. of the active material. Specifically, the porosity is a value calculated by the following formula. Porosity (%) of electrode active material layer = {1 - (true density of electrode active material layer / density of electrode active material layer)} × 100

[0080] The true density of the electrode active material layer is 3 * 4 (cm 2) It is the density of the positive electrode active material layer measured with an electrode when an electrode of a certain size is pressed with a pressing device until the thickness of the negative electrode does not change, and the density of the positive electrode active material layer is the density of the positive electrode active material layer measured by collecting and measuring the electrode before pressing with the same size.

[0081] One embodiment of the present invention provides a lithium secondary battery including a positive electrode; a negative electrode according to the above-described embodiment; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0082] The positive electrode may include a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector.

[0083] The porosity of the positive electrode active material layer may be 18% to 21%, for example, 20% to 21%.

[0084] According to one embodiment, the positive electrode includes a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn) as the positive electrode active material.

[0085] In one embodiment of the present invention, the positive electrode active material contains the nickel, cobalt, and manganese, and may further contain aluminum.

[0086] In this specification, the positive electrode active material contains 80 mol% or more of nickel among the metals excluding lithium, or contains 80 mol% or more and less than 100 mol% of nickel among the metals excluding lithium. The lithium composite transition metal compound containing 80 mol% or more and less than 100 mol% of nickel among the metals excluding lithium may include one or more mixtures represented by the following Chemical Formula 1.

[0087] [Chemical Formula 1] Li a Ni 1-b-c-d Co b Mn c Q d O 2+δ In the above formula, Q is any one or more elements selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr, 1 ≦ a ≦ 1.5, 0 < b ≦ 0.5, 0 < c ≦ 0.5, 0 ≦ d ≦ 0.1, 0 < b + c + d ≦ 20, and -0.1 ≦ δ ≦ 1.0.

[0088] In the lithium composite transition metal compound of Chemical Formula 1 above, Li may be contained in an amount corresponding to a, that is, 1 ≦ a ≦ 1.5. If a is less than 1, the capacity may decrease, and if it exceeds 1.5, the particles may sinter in the firing process, making it difficult to manufacture the positive electrode active material. Considering the improvement effect of the capacity characteristics of the positive electrode active material by controlling the content of Li and the balance of the sinterability during the manufacture of the active material, the Li may more preferably be contained in an amount of 1.1 ≦ a ≦ 1.2.

[0089] In the lithium composite transition metal compound of Chemical Formula 1 above, Ni may be contained in an amount corresponding to 1-(b + c + d), for example, 0.8 ≦ 1-(b + c + d) < 1. If the content of Ni in the lithium composite transition metal compound of Chemical Formula 1 is a composition of 0.8 or more, a sufficient amount of Ni contributing to charge and discharge can be ensured, and high capacity can be achieved. Preferably, 1-(b + c + d), which is the content of Ni, may be 0.88, preferably 0.9 or more, and more preferably 0.93 or more. Preferably, 1-(b + c + d), which is the content of Ni, may be 0.99 or less, 0.95 or less.

[0090] In the lithium composite transition metal compound of Chemical Formula 1 above, Co may be contained in an amount corresponding to b, that is, 0 < b ≦ 0.5. If the content of Co in the lithium composite transition metal compound of Chemical Formula 1 exceeds 0.5, there is a risk of cost increase. Considering the significance of the improvement effect of the capacity characteristics by including Co, the Co may more specifically be contained in an amount of 0.03 ≦ b ≦ 0.2.

[0091] In the lithium composite transition metal compound of the above Chemical Formula 1, Mn may be contained in a content corresponding to c, that is, a content of 0 < c ≤ 0.5. When c in the lithium composite transition metal compound of the above Chemical Formula 1 exceeds 0.5, on the contrary, the output characteristics and capacity characteristics of the battery may deteriorate. More specifically, Mn may be contained in a content of 0.01 ≤ c ≤ 0.2.

[0092] In the lithium composite transition metal compound of the above Chemical Formula 1, Q may be a doping element contained in the crystal structure of the lithium composite transition metal compound, and Q may be contained in a content corresponding to d, that is, 0 ≤ d ≤ 0.1. Q may be one or more selected from Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr. For example, Q may be Al.

[0093] In one embodiment of the present invention, the lithium composite transition metal compound may contain single particles.

[0094] In one embodiment of the present invention, the lithium composite transition metal compound may further contain secondary particles.

[0095] The single particles can be produced by mixing and firing a transition metal precursor and a lithium raw material. The secondary particles may be produced by a method different from that of the single particles, and their composition may be the same as or different from that of the single particles.

[0096] For example, the firing is performed at a temperature capable of forming single particles. To form them, firing must be performed at a temperature higher than that during the production of secondary particles. For example, when the composition of the precursor is the same, firing must be performed at a temperature about 30°C to 100°C higher than that during the production of secondary particles. The firing temperature for forming the single particles may vary depending on the composition of the metal in the precursor. For example, when attempting to form a high-content nickel (High-Ni) NCM-based lithium composite transition metal oxide with a nickel (Ni) content of 80 mol% or more into single particles, the firing temperature may be about 700°C to 1000°C, preferably about 800°C to 950°C. When the firing temperature satisfies the above range, a cathode active material containing single particles with excellent electrochemical properties can be produced. When the firing temperature is less than 790°C, a cathode active material containing a secondary particle-like lithium composite transition metal compound is produced. When it exceeds 950°C, the firing is excessive, the layered crystal structure is not properly formed, and the electrochemical properties may deteriorate.

[0097] As used herein, the term "single particle" is used to distinguish from secondary particles formed by aggregation of dozens to hundreds of conventional primary particles, and includes a concept of a single particle composed of one primary particle and a quasi-single particle which is an aggregate of 30 or fewer primary particles.

[0098] Specifically, in the present invention, the single particle may be a single particle composed of one primary particle or a quasi-single particle which is an aggregate of 30 or fewer primary particles, and the secondary particle may be in a form in which hundreds of primary particles are aggregated.

[0099] In one embodiment of the present invention, the tap density of the secondary particles may be greater than the tap density of the single particles.

[0100] In one embodiment of the present invention, the tap density of the secondary particles may be 2 g / cc or more and 3.2 g / cc or less. Specifically, it may be 2.1 g / cc or more and 3 g / cc or less, 2.2 g / cc or more and 2.9 g / cc or less, or 2.3 g / cc or more and 2.8 g / cc or less.

[0101] When the tap density of the secondary particles of the positive electrode active material satisfies the above range, the secondary particles of the positive electrode active material can be uniformly dispersed without aggregating in the electrode.

[0102] In one embodiment of the present invention, the tap density of the single particles may be 1.3 g / cc or more and 2.3 g / cc or less. Specifically, it may be 1.4 g / cc or more and 2.3 g / cc or less, 1.5 g / cc or more and 2.3 g / cc or less, or 1.6 g / cc or more and 2.25 g / cc or less.

[0103] When the tap density of the single particles of the positive electrode active material satisfies the above range, the single particles of the positive electrode active material can be uniformly dispersed without aggregating in the electrode.

[0104] In one embodiment of the present invention, the tap density of the single particles may be greater than the tap density of the graphite.

[0105] In one embodiment of the present invention, the average particle size (D 50 ) of the single particles may be 1 μm or more. Also, the average particle size of the single particles may be 12 μm or less. For example, the average particle size 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 6 μm or less, 2 μm or more and 6 μm or less, or 3 μm or more and 5 μm or less.

[0106] Even if the single particles are formed into small particle sizes with an average particle size of about 1 μm or more and 12 μm or less, their particle strength can be excellent. As a result, the phenomenon of an increase in fine particles in the electrode due to particle cracking is alleviated, and thereby, the life characteristics of the battery can be improved. For example, the single particles may have a particle strength of 100 MPa to 300 MPa during rolling with a force of 650 kgf / cm 2 . As a result, even when the single particles are rolled with a strong force of 650 kgf / cm 2 , the phenomenon of an increase in fine particles in the electrode due to particle cracking is alleviated, and thereby, the life characteristics of the battery can be improved.

[0107] The method for forming the single particles is not particularly limited. Generally, it may be formed by increasing the firing temperature and overfiring, using additives such as grain growth promoters useful for overfiring, or by changing the starting materials, etc.

[0108] The single particles have high rigidity of the particle itself, and even when the electrode density is high, the decrease in battery performance is relatively good. Therefore, the energy density can be increased by adjusting the average particle size range of the single particles and the silicon-carbon composite.

[0109] In one embodiment of the present invention, the average particle size of the single particles may be smaller than the average particle size of the silicon-carbon composite.

[0110] When the average particle size of the single particles is smaller than the average particle size of the silicon-carbon composite, the diffusion resistance of the single particles is relatively reduced, and the life performance can be improved. That is, the larger the average particle size of the single particles, the greater the diffusion resistance. When the average particle size of the single particles is larger than the average particle size of the silicon-carbon composite, the diffusion resistance relatively increases, resulting in the occurrence of lithium precipitation, etc., the battery performance deteriorates, and the life performance may deteriorate.

[0111] Also, when the average particle size of the single particles is smaller than the average particle size of the silicon-carbon composite, the occurrence of side reactions with the electrolyte due to the increase in specific surface area can be prevented, and the life performance can be improved.

[0112] According to one embodiment of the present invention, the average particle size of the single particles may be 1 μm to 12 μm smaller than the average particle size of the silicon-carbon composite. Specifically, it may be 1.5 μm to 11.5 μm, or 2 μm to 11 μm smaller.

[0113] When the average particle size of the single particles is smaller than the average particle size of the silicon-carbon composite, for example, when the above range is satisfied, the diffusion resistance of the single particles relatively decreases, and the life performance can be improved. That is, the larger the average particle size of the single particles, the greater the diffusion resistance. When the average particle size of the single particles is larger than the average particle size of the silicon-carbon composite, the relative increase in diffusion resistance may cause lithium precipitation and the like, resulting in a decrease in battery performance and a possible decrease in life performance.

[0114] Also, when the average particle size of the single particles is smaller than the average particle size of the silicon-carbon composite, for example, when the above range is satisfied, the occurrence of side reactions with the electrolyte due to an increase in specific surface area can be prevented, and the life performance can be improved.

[0115] According to an embodiment of the present invention, the ratio of the average particle size of the single particles to the average particle size of the silicon-carbon composite may be 1.5:2 to 1.5:20.

[0116] When the above range is satisfied, the diffusion resistance of the single particles relatively decreases, and the life performance can be improved. That is, the larger the average particle size of the single particles, the greater the diffusion resistance. When the average particle size of the single particles is larger than the average particle size of the silicon-carbon composite, the relative increase in diffusion resistance may cause lithium precipitation and the like, resulting in a decrease in battery performance and a possible decrease in life performance.

[0117] Also, when the average particle size of the single particles is smaller than the average particle size of the silicon-carbon composite, for example, when the above range is satisfied, the occurrence of side reactions with the electrolyte due to an increase in specific surface area can be prevented, and the life performance can be improved.

[0118] In an embodiment of the present invention, the lithium composite transition metal compound further includes secondary particles, and the average particle size of the single particles is smaller than the average particle size of the secondary particles.

[0119] In the present invention, the single particle may be a single particle composed of one primary particle or a pseudo-single particle which is an aggregate of 30 or fewer primary particles, and the secondary particle may be in a form in which several hundreds of primary particles are aggregated.

[0120] The above-described lithium composite transition metal compound may further contain secondary particles. The secondary particle means a form formed by aggregation of primary particles, and can be distinguished from the concept of a single particle including one primary particle, one single particle, or a pseudo-single particle which is an aggregate of 30 or fewer primary particles.

[0121] The average particle size (D 50 ) of the secondary particles may be 1 μm to 20 μm. Specifically, it may be 2 μm to 17 μm, 3 μm to 15 μm, 5 μm to 15 μm, 7 μm to 15 μm, or 9 μm to 15 μm.

[0122] The specific surface area (BET) of the secondary particles may be 0.05 m 2 / g to 10 m 2 / g, preferably 0.1 m 2 / g to 1 m 2 / g, more preferably 0.3 m 2 / g to 0.8 m 2 / g.

[0123] In one embodiment of the present invention, the secondary particle is an aggregate of primary particles, and the average particle size of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particle may be in a form in which several hundreds of primary particles are aggregated, and the average particle size 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.

[0124] When the average particle size of the primary particles satisfies the above range, single-particle positive electrode active materials with excellent electrochemical properties can be formed. When the average particle size of the primary particles is excessively small, the number of aggregated primary particles forming the lithium nickel-based oxide particles increases, and the effect of suppressing the generation of cracks in the particles during rolling decreases. When the average particle size of the primary particles is excessively large, the lithium diffusion path inside the primary particles becomes long, the resistance increases, and the output characteristics may deteriorate.

[0125] In one embodiment of the present invention, the average particle size of the single particles may be smaller than the average particle size of the secondary particles. Thereby, even if the single particles are formed with a small particle size, their particle strength can be excellent, whereby the phenomenon of an increase in fine particles in the electrode due to cracking of the particles is alleviated, and thereby the life characteristics of the battery can be improved.

[0126] In one embodiment of the present invention, the average particle size of the single particles is 1 μm to 18 μm smaller than the average particle size of the secondary particles.

[0127] For example, the average particle size of the single particles may be 1 μm to 16 μm smaller than the average particle size of the secondary particles, may be 1.5 μm to 15 μm smaller, or may be 2 μm to 14 μm smaller.

[0128] When the average particle size of the single particles is smaller than the average particle size of the secondary particles, for example, when the above range is satisfied, even if the single particles are formed with a small particle size, their particle strength can be excellent, whereby the phenomenon of an increase in fine particles in the electrode due to cracking of the particles is alleviated, and there are effects of improving the life characteristics of the battery and the energy density.

[0129] In one embodiment of the present invention, the average particle size of the silicon-carbon composite may be smaller than the average particle size of the graphite. When the average particle size of the silicon-carbon composite is smaller than the average particle size of the graphite, there is an effect that the cracking of the particles is reduced due to the decrease in the volume expansion / contraction rate during charge and discharge, and the life performance of the battery is improved.

[0130] In the lithium secondary battery according to the above-described embodiment, the negative electrode active material may further contain a carbon-based active material. Specifically, the carbon-based active material may be graphite. The graphite may be natural graphite, artificial graphite, or a mixture thereof.

[0131] According to an embodiment of the present invention, the average particle diameter of the silicon-carbon composite may be 1 μm to 25 μm smaller than the average particle diameter of the graphite. For example, the average particle diameter of the silicon-carbon composite may be 2 μm to 24 μm smaller than the average particle diameter of the graphite, may be 3 μm to 23 μm smaller, or may be 4 μm to 22 μm smaller.

[0132] When the average particle diameter of the silicon-carbon composite is smaller than the average particle diameter of the graphite, for example, when the above range is satisfied, there is an effect that the life performance of the battery is further improved.

[0133] In an embodiment of the present invention, when the average particle diameters of the secondary particles, the single particles, the graphite, and the silicon-carbon composite included in the lithium secondary battery are A, B, C, and D, respectively, B < D ≦ A < C may be satisfied.

[0134] The embodiments of the secondary particles, the single particles, the graphite, and the silicon-carbon composite are as described above.

[0135] When the average particle diameters of the secondary particles, the single particles, the graphite, and the silicon-carbon composite are A, B, C, and D, respectively, when B < D ≦ A < C, there is an effect that the life performance of the battery is improved.

[0136] According to an embodiment of the present invention, the negative electrode active material further contains graphite, and when the average particle diameters of the single particles, the graphite, and the silicon-carbon composite are B, C, and D, respectively, B < D < C may be satisfied.

[0137] When the average particle diameters of the secondary particles, the single particles, and the silicon-carbon composite are A, B, and D, respectively, B < D ≦ A may be satisfied.

[0138] When the average particle diameters of the secondary particles, the single particles, and the graphite are A, B, and C, respectively, B < A < C may be satisfied.

[0139] When the average particle diameters of the secondary particles, the graphite, and the silicon-carbon composite are A, C, and D, respectively, D ≤ A < C may be satisfied.

[0140] When the above range is satisfied, there is an effect that the life performance of the battery is improved.

[0141] In one embodiment of the present invention, in the lithium secondary battery according to the above-described embodiment, the single particles are contained in an amount of 15 parts by weight to 100 parts by weight with respect to 100 parts by weight of the positive electrode active material, and the silicon-carbon composite is contained in an amount of 3 parts by weight to 30 parts by weight with respect to 100 parts by weight of the negative electrode active material.

[0142] In one embodiment of the present invention, the single particles are contained in an amount of 15 parts by weight to 100 parts by weight with respect to 100 parts by weight of the positive electrode active material. The single particles may be contained in an amount of 20 parts by weight to 100 parts by weight, or 30 parts by weight to 100 parts by weight with respect to 100 parts by weight of the positive electrode active material.

[0143] For example, the single particles may be contained 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 with respect to 100 parts by weight of the positive electrode active material. For example, the single particles may be contained in an amount of 100 parts by weight or less, 90 parts by weight or less, 80 parts by weight or less, 70 parts by weight or less, or 60 parts by weight or less with respect to 100 parts by weight of the positive electrode active material.

[0144] When the single particles within the above range are included, excellent battery characteristics can be exhibited in combination with the above-described negative electrode material. In particular, when the single particles are 15 parts by weight or more, the phenomenon of an increase in fine particles in the electrode due to cracking of the particles during the rolling process after electrode fabrication is alleviated, and thereby, the life characteristics of the battery can be improved.

[0145] In one embodiment of the present invention, the lithium composite transition metal compound may further include secondary particles, and the secondary particles may be 85 parts by weight or less based on 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, 70 parts by weight or less, or 60 parts by weight or less based on 100 parts by weight of the positive electrode active material. The secondary particles may be 10 parts by weight or more, 20 parts by weight or more, 30 parts by weight or more, or 40 parts by weight or more based on 100 parts by weight of the positive electrode active material.

[0146] In one embodiment of the present invention, the weight ratio of the single particles to the secondary particles may be 1:9 to 9:1, 2:8 to 8:2, 3:7 to 7:3, or 4:6 to 6:4.

[0147] 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 particles contain a positive electrode active material, the components thereof may be the same as those exemplified as the single-particle positive electrode active material described above, or may be other components, and may mean a form in which single particles are aggregated.

[0148] In one embodiment of the present invention, based on 100 parts by weight of the positive electrode active material layer, 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.

[0149] According to one embodiment of the present invention, the positive electrode active material layer further includes a positive electrode binder and a conductive material.

[0150] The positive electrode binder can play a role in improving the adhesion between positive electrode active material particles and the adhesive force between the positive electrode active material particles and the positive electrode current collector. As the positive electrode binder, any material well-known in the technical field can be used. Non-limiting examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds may be used.

[0151] The positive electrode binder may be contained in an amount of 0.1 part by weight or more and 50 parts by weight or less based on 100 parts by weight of the positive electrode active material layer. For example, preferably, it may be contained in an amount of 0.3 part by weight or more and 35 parts by weight or less, and more preferably 0.5 part by weight or more and 20 parts by weight or less.

[0152] The conductive material contained in the positive electrode active material layer is used to impart conductivity to the electrode, and any material having electron conductivity without causing chemical changes in the battery can be used without particular limitation. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used.

[0153] Specifically, in one embodiment, the conductive material may include one or more of single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT). The conductive material may be included in an amount of 0.1 part by weight or more and 2 parts by weight or less based on 100 parts by weight of the composition for the positive electrode active material layer. For example, preferably, it may be included in an amount of 0.3 part by weight or more and 1.5 parts by weight or less, and more preferably, 0.5 part by weight or more and 1.2 parts by weight or less.

[0154] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Further, the positive electrode current collector may usually have a thickness of 1 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc.

[0155] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Specifically, transition metals that adsorb carbon well, such as copper and nickel, may be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but the thickness of the current collector is not limited thereto.

[0156] In one embodiment of the present invention, the thicknesses of the positive electrode active material layer and the negative electrode active material layer are each 10 μm or more and 500 μm or less. The thickness of the positive electrode active material layer may be 90% to 110%, for example, 95% to 105% of the thickness of the negative electrode active material layer, or these thicknesses may be the same. Specifically, the thicknesses of the positive electrode and the negative electrode active material layer may each be 15 μm or more and 400 μm or less, 20 μm or more and 300 μm or less, 25 μm or more and 200 μm or less, or 30 μm or more and 100 μm or less.

[0157] In one embodiment of the present invention, the loading amount per unit volume of the positive electrode active material layer is 250 mg / 25 cm 2 ~900 mg / 25 cm 2 and the loading amount per unit volume of the negative electrode active material layer is 100 mg / 25 cm 2 ~600 mg / 25 cm 2 Specifically, the loading amount per unit volume of the positive electrode active material layer may be 270 mg / 25 cm 2 ~800 mg / 25 cm 2 、285 mg / 25 cm 2 ~700 mg / 25 cm 2 、or 300 mg / 25 cm 2 ~600 mg / 25 cm 2 and the loading amount per unit volume of the negative electrode active material layer may be 120 mg / 25 cm 2 ~500 mg / 25 cm 2 、135 mg / 25 cm 2 ~400 mg / 25 cm 2 、150 mg / 25 cm 2 ~300 mg / 25 cm 2 and may be.

[0158] The positive electrode and the negative electrode can be manufactured by the ordinary manufacturing methods of positive and negative electrodes, except that the above-described positive electrode active material and negative electrode active material are used. Specifically, after applying a composition for forming an active material layer, which contains the above-described active material and optionally a binder and a conductive material, onto a current collector, it can be manufactured by drying and rolling. At this time, the types and contents of the positive electrode active material, negative electrode active material, binder, and conductive material are as described above. As the solvent, any solvent generally used in the art may be used, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the active material, conductive material, and binder, and then to have a viscosity that can exhibit excellent thickness uniformity during coating for the manufacture of the positive electrode and the negative electrode, considering the coating thickness of the slurry and the manufacturing yield. Further, as another method, the positive electrode and the negative electrode can also be manufactured by casting the composition for forming the active material layer onto another support, and then laminating a film obtained by peeling it from the support onto a current collector.

[0159] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any separator that can be used as a separator in a secondary battery can be used without particular limitation. In particular, it is preferably low in resistance to the ion migration of the electrolyte and excellent in electrolyte moisture retention ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Further, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0160] 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 the manufacture of lithium secondary batteries.

[0161] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0162] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0163] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, can be preferably used as high-viscosity organic solvents because they have a high dielectric constant and can well dissociate lithium salts. When such cyclic carbonates are mixed and used in an appropriate ratio with linear carbonates having low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate, an electrolyte having high electrical conductivity can be produced, so they can be more preferably used.

[0164] As the metal salt, a lithium salt may be used. The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte. For example, as the anion of the lithium salt, 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 - 、および(CF3CF2SO2)2N - One or more selected from the group consisting of may also be used.

[0165] In addition to the constituent components of the electrolyte, 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, hexamethylphosphoric 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 in order to improve the life characteristics of the battery, suppress the decrease in battery capacity, improve the discharge capacity of the battery, etc.

[0166] The energy density of the lithium secondary battery according to one embodiment of the present invention may be 400 Wh / L to 900 Wh / L. Specifically, the energy density of the lithium secondary battery may be 425 Wh / L to 875 Wh / L, 450 Wh / L to 850 Wh / L, 475 Wh / L to 825 Wh / L, or 500 Wh / L to 800 Wh / L. When the above range is satisfied, the energy density of the lithium secondary battery designed within a limited space can be increased, the high-power performance can be improved, and the cycle performance of the battery can also be improved.

[0167] The lithium secondary battery according to an embodiment of the present invention may be a cylindrical battery. The cylindrical battery may mean that the shape of the battery itself including the assembly containing the positive electrode, negative electrode, separator, and electrolyte is cylindrical. Specifically, it may be composed of a cylindrical can, a battery assembly provided inside the cylindrical can, and a top cap. However, the lithium secondary battery is not limited thereto, and may be a prismatic battery or a pouch-type battery.

[0168] An embodiment of the present invention provides a battery module including the above-described cylindrical battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having a high capacity, high rate characteristics, and cycle characteristics, they can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0169] The lithium secondary battery according to an embodiment of the present invention can stably exhibit excellent discharge capacity, output characteristics, and cycle performance, and thus can be used not only as a power source for portable devices such as mobile phones, notebook computers, and digital cameras, but also as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. For example, the battery module or the battery pack can be used as a power source for any one or more of power tools; electric vehicles including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); or power storage systems.

Examples

[0170] Hereinafter, preferred embodiments are presented to assist in understanding the present invention. However, these embodiments are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the description and the scope of the technical idea. Needless to say, such variations and modifications belong to the scope of the appended claims.

[0171] <Examples and Comparative Examples> [Example 1] (1) Manufacture of negative electrode Based on 100 parts by weight of the negative electrode active material layer, 97.7 parts by weight of graphite (artificial graphite:natural graphite = 70:30 by weight ratio, 90 parts by weight based on 100 parts by weight of the negative electrode active material) and silicon-carbon composite (10 parts by weight based on 100 parts by weight of the negative electrode active material), 1.15 parts by weight of SBR (styrene-butadiene rubber) and 1 part by weight of CMC (carboxymethyl cellulose) as binders are included. In addition, a composition for forming a negative electrode active material layer containing 0.09 parts by weight of a dispersant and a CNT pre-dispersion liquid containing 0.06 parts by weight of single-walled CNTs is manufactured. The composition for forming the negative electrode active material layer is coated on a copper foil with a thickness of 15 μm so that the dry thickness becomes 86 μm, and then dried to manufacture a negative electrode.

[0172] At this time, as the graphite, one having a tap density of 1.1 g / cc and D 50 of 17 μm is used. As the silicon-carbon composite, one having a tap density of 0.65 g / cc and D 50 of 5.1 μm is used.

[0173] (2) Manufacture of positive electrode Based on 100 parts by weight of the positive electrode active material layer, the content of Ni is 93.3 mol%, Co is 4.9 mol%, and Mn is 1.8 mol% among the metals excluding lithium as the positive electrode active material. 98.04 parts by weight of a lithium composite transition metal compound containing single particles and secondary particles (weight ratio of single particles:secondary particles = 80:20), 1 part by weight of PVDF as a binder, and a CNT pre-dispersion liquid containing 0.8 parts by weight of CNT and 0.16 parts by weight of a dispersant were used to produce a composition for forming a positive electrode active material layer. The composition for forming the positive electrode active material layer was coated on an aluminum foil with a thickness of 30 μm so that the dry thickness became 103 μm and then dried to produce a positive electrode.

[0174] At this time, as the single particles of the lithium composite transition metal compound, those with a tap density of 1.8 g / cc and D 50 of 3.47 μm were used. As the secondary particles of the lithium composite transition metal compound, those with a tap density of 2.4 g / cc and D 50 of 9.5 μm were used.

[0175] (3) Manufacture of a lithium secondary battery The positive electrode and the negative electrode were laminated with a separator interposed therebetween, and an electrolytic solution (1.0 M LiPF6, EC (ethylene carbonate) / EMC (ethyl methyl carbonate) = 30 / 70 (Vol%), VC (vinylene carbonate) 1.5%) was injected to fabricate a lithium secondary battery.

[0176] [Examples 2 to 4] A lithium secondary battery was fabricated in the same manner as in Example 1, except that positive electrode active materials and negative electrode active materials having tap densities and particle sizes as shown in Table 1 below were used.

[0177] [Comparative Examples 1 to 6] A lithium secondary battery was fabricated in the same manner as in Example 1, except that positive electrode active materials and negative electrode active materials having tap densities and particle sizes as shown in Table 1 below were used.

[0178] The configurations of the negative electrode active materials manufactured in the above Examples and Comparative Examples are as shown in Table 1 below.

[0179]

Table 1

[0180] The tap density of the positive electrode active material and the negative electrode active material was calculated by putting 40 g of the sample into a container and tapping it 1000 times using a TAP-2S device manufactured by LOGAN.

[0181] The D of the positive electrode active material and the negative electrode active material 50 was analyzed by the PSD measurement method using a microtrac device.

[0182] The porosity of the active material layers of the positive electrode and the negative electrode was calculated using the following relational expression. Porosity of the electrode active material layer (%) = {1 - (true density of the active material layer / density of the active material layer)} × 100

[0183] The sphericity, true density, and BET specific surface area of the graphite and silicon-carbon composite of the negative electrode active material produced in the examples and comparative examples are shown in Table 2 below.

[0184] Hereinafter, the true density of the active material layer is the density of the electrode active material layer measured with an electrode when an electrode with a size of 3 * 4 (cm 2 ) is pressed with a pressing device until the thickness of the negative electrode does not change, and the density of the active material layer is the density of the active material layer measured by collecting the electrode before pressing with the same size.

[0185]

Table 2

[0186] <Experimental Example: Evaluation of Discharge Capacity, Initial Efficiency, and Life (Capacity Retention Rate) Characteristics> The lithium secondary batteries produced in the examples and comparative examples were charged and discharged to evaluate the discharge capacity, initial efficiency, and capacity retention rate, which are shown in Table 3 below.

[0187] For the first cycle and the second cycle, charging and discharging were performed at 0.1 C, and from the third cycle to the forty-ninth cycle, charging and discharging were performed at 0.5 C. The fiftieth cycle ended in a charged state (with lithium in the negative electrode).

[0188] Charging conditions: CC (constant current) / CV (constant voltage) (5 mV / 0.005 C current cut-off) Discharging conditions: CC (constant current) condition 1.5 V

[0189] From the results of one charge-discharge cycle, the discharge capacity (mAh / g) and the initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived by the following calculation. Initial efficiency (%) = (one-time discharge capacity / one-time charge capacity) × 100

[0190] The capacity retention rate was derived by the following calculation respectively. Capacity retention rate (%) = (forty-ninth discharge capacity / one-time discharge capacity) × 100

[0191] <Experimental example: Evaluation of electrode thickness> The thicknesses of the positive and negative electrodes manufactured in the examples and comparative examples were measured using a Micro-Hite 350 (Tesa) device respectively and then added together. The average value of about three measured values was taken and calculated as the thickness of the electrode. The calculated thickness of the electrode in Example 1 was set to 100%, and based on this, the thicknesses of the electrodes in Examples 2 to 4 and Comparative Examples 1 to 6 were calculated relatively and shown in Table 3 below.

[0192] <Experimental example: Evaluation of Li plating time point> For the first cycle and the second cycle, charging / discharging was performed at 0.1 C, and while charging and discharging at a rate of 3 C from the third cycle, the resistance of the cell was measured.

[0193] Charging conditions: CC (constant current) / CV (constant voltage) (5 mV / 0.005 C current cut-off) Discharging conditions: CC (constant current) condition 1.5 V

[0194] The time point at which the resistance of the cell rapidly decreases and a rapid change occurs in the current value was calculated as the time point when Li plating occurs.

[0195]

Table 3

[0196] According to Tables 1 to 3 above, the secondary batteries of Examples 1 to 4 using a negative electrode in which the tap density of graphite is the same as or higher than that of the silicon-carbon composite showed a thinner electrode thickness, an excellent capacity retention rate, and a significant improvement in the time point of Li plating generation at which lithium is deposited, such as being 95% or more of the SOC and the charge capacity. It was confirmed that this is because the tap density of graphite is the same as or higher than that of the silicon-carbon composite, so that graphite can be densely dispersed throughout the electrode, thereby preventing the flow of current in the negative electrode from being interrupted and making it easy to adjust the orientation degree of graphite in the negative electrode. On the other hand, in the case of Comparative Examples 1 to 6, the tap density of graphite is smaller than that of the silicon-carbon composite, and graphite aggregates without being dispersed in the electrode, resulting in a decrease in the dispersibility of the slurry, which is disadvantageous for rolling, a significant increase in the electrode thickness, a decrease in the capacity retention rate, and a poor charge capacity such as the time point of Li plating generation being 82% to 90% of the SOC.

Claims

1. A negative electrode composition comprising a negative electrode active material containing a silicon-carbon composite and graphite, wherein the tap density of the graphite is the same as or greater than the tap density of the silicon-carbon composite.

2. The negative electrode composition according to Claim 1, wherein the tap density of the graphite is 0.9 g / cc to 1.2 g / cc.

3. The negative electrode composition according to Claim 1, wherein the tap density of the silicon-carbon composite is 0.5 g / cc to 1.15 g / cc.

4. The negative electrode composition according to Claim 1, wherein the average particle diameter of the silicon-carbon composite is 1 μm or more and 15 μm or less.

5. The negative electrode composition according to Claim 1, wherein the average particle diameter of the silicon-carbon composite is smaller than the average particle diameter of the graphite.

6. The negative electrode composition according to Claim 1, wherein the sphericity of the graphite is 0.8 to 0.9, and the sphericity of the silicon-carbon composite is 0.3 to 0.

7.

7. The negative electrode composition according to Claim 1, wherein the true density of the graphite is 2 to 3 g / cc, and the true density of the silicon-carbon composite is 1.8 to 2.2 g / cc.

8. The BET specific surface area of the graphite is 1 m ２ / g to 3 m ２ / g, and the BET specific surface area of the silicon-carbon composite is 1 m ２ / g to 10 m ２ / g. The negative electrode composition according to claim 1.

9. A negative electrode comprising a negative electrode current collector; and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector and containing the negative electrode composition according to any one of Claims 1 to 8.

10. The negative electrode according to Claim 9, wherein the porosity of the negative electrode active material layer is 23% to 28%.

11. A lithium secondary battery comprising a positive electrode; the negative electrode according to Claim 9; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

12. The positive electrode comprises a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn) as a positive electrode active material, and the lithium composite transition metal compound contains single particles, the lithium secondary battery according to Claim 11.

13. The lithium secondary battery according to Claim 12, wherein the lithium composite transition metal compound further contains secondary particles.

14. The lithium secondary battery according to Claim 13, wherein the tap density of the secondary particles is greater than the tap density of the single particles.

15. The lithium secondary battery according to Claim 12, wherein the tap density of the single particles is greater than the tap density of the graphite.

16. The lithium secondary battery according to Claim 12, wherein the average particle diameter of the single particles is 1 μm or more and 12 μm or less.

17. The lithium secondary battery according to claim 12, wherein the average particle diameter of the single particles is smaller than the average particle diameter of the silicon-carbon composite.

18. The single particles are contained in an amount of 15 parts by weight to 100 parts by weight based on 100 parts by weight of the positive electrode active material. The lithium secondary battery according to claim 12, wherein the silicon-carbon composite is contained in an amount of 3 parts by weight to 30 parts by weight based on 100 parts by weight of the negative electrode active material.

19. The lithium secondary battery according to claim 12, wherein the lithium composite transition metal compound contains 80 mol% or more of nickel among the metals excluding lithium.

20. A battery module including the lithium secondary battery according to claim 11.

21. A battery pack including the battery module according to claim 20.

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