Lithium secondary battery

Abstract

This application relates to a lithium secondary battery.

Description

Technical Field

[0001] This application claims the benefit of the filing dates of Korean Patent Application Nos. 10-2022-0186055 and 10-2022-0186066, filed with the Korean Intellectual Property Office on December 27, 2022, and all of its contents are incorporated herein by reference.

[0002] This application relates to a lithium secondary battery.

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, the demand for alternative and clean energy has been increasing. As part of this, the fields of power generation and energy storage using electrochemical reactions are the most actively studied.

[0004] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is showing a trend of increasing more and more.

[0005] With the development of technologies related to mobile devices and the increasing demand, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density, voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. In addition, research on methods for manufacturing high-density electrodes with a higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries has been actively conducted.

[0006] Generally, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode. Carbon-based materials such as graphite as the negative electrode material are excellent in stability and reversibility, but have limitations in terms of capacity. In fields aiming for high capacity, attempts to use Si-based materials with a high theoretical capacity as the negative electrode material are increasing.

[0007] That is, a lithium secondary battery is usually manufactured by using a compound in which lithium is inserted, such as LiCoO2, LiMn2O4, etc. for the positive electrode, and a substance in which lithium is not inserted, such as a carbon-based or Si-based material for the negative electrode. During charging, lithium ions inserted into the positive electrode move to the negative electrode through the electrolyte, and during discharging, the lithium ions move from the negative electrode to the positive electrode again. During the charging reaction, lithium moving from the positive electrode to the negative electrode reacts with the electrolyte to form a SEI (solid electrolyte interface), which is a kind of protective film, on the surface of the negative electrode. This SEI can stabilize the structure of the negative electrode by suppressing the movement of electrons required for the reaction between the negative electrode and the electrolyte and preventing the decomposition reaction of the electrolyte. However, since it is an irreversible reaction, it causes consumption of lithium ions. That is, the lithium consumed in the formation of SEI cannot return to the positive electrode during the subsequent discharging process, reducing the capacity of the battery.

[0008] On the other hand, as an effort to improve the performance of lithium secondary batteries, the development of technologies to increase the charging speed is required. To rapidly charge a lithium secondary battery, it is necessary for the lithium ions to move quickly during the process of being inserted into the negative electrode. Therefore, in order to reduce the internal resistance and achieve high power output, a battery design is carried out in which the negative electrode active material layer is formed to a thin film level thickness to reduce the diffusion distance of lithium, and a carbon coating layer is formed on its surface to increase conductivity.

[0009] In order to ensure such rapid charging performance and further ensure the energy density, attempts are increasing to use a silicon-based negative electrode instead of the conventional carbon-based (Graphite) negative electrode. That is, in order to improve the above performance, the content of the silicon-based active material must also be increased in the silicon-based negative electrode. However, when simply increasing the content of the silicon-based negative electrode, various problems such as resistance problems and volume expansion problems occur.

[0010] In order to solve the above problems, while increasing the content of the silicon-based active material, when applying the secondary particle cathode active material to the cathode, the resistance problem could be solved. However, the reaction potential of the silicon-based anode is about 0.05 V higher than that of the carbon-based anode, resulting in an environment where it is exposed to a high potential, and a cracking phenomenon occurs at a high voltage, so the problem of gas generation has occurred again. Therefore, research has also been conducted on applying a single particle cathode active material as the cathode active material. However, when using the single particle cathode active material alone, the use of the lower end of the silicon-based anode increases, resulting in the malfunction of the anode and the problem of deteriorated cycle characteristics.

[0011] Ultimately, in order to achieve capacity characteristics, high energy density, and rapid charging performance, regarding a lithium battery using a silicon-based anode and using an NCMA-based or NCM-based cathode as the counter electrode for this anode, it is continuously necessary to conduct research on a lithium secondary battery that can reduce the resistance difference and solve the cracking phenomenon of the active material and the problem of gas generation in a high voltage cell.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0013] As a result of researching the above-mentioned problems, it was found that when using a silicon-based anode to ensure capacity characteristics and rapid charging performance, and using a single particle cathode active material as the cathode, the amount of gas generation can be adjusted. In particular, it was found that the above problems can be solved when not simply containing only the single particle cathode active material, but mixing and using it with the secondary particle cathode active material, and adjusting the weight ratio of the silicon-based active material and the single particle active material to be higher than the cathode capacity loading amount.

[0014] Accordingly, the present application relates to a lithium secondary battery including a silicon-based negative electrode; and a positive electrode including a single positive electrode active material with a specific content.

Means for Solving the Problems

[0015] One embodiment of the present specification is a lithium secondary battery including a positive electrode; a silicon-based negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode includes a positive electrode current collector layer; and a positive electrode active material layer including a positive electrode active material layer composition provided on one or both surfaces of the positive electrode current collector layer, the silicon-based negative electrode includes a negative electrode current collector layer; and a negative electrode active material layer including a negative electrode active material layer composition provided on one or both surfaces of the negative electrode current collector layer, the negative electrode active material layer composition includes a silicon-based active material, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys, the positive electrode active material layer composition includes a positive electrode active material including one or more selected from the group consisting of a secondary particle positive electrode active material; and a single particle positive electrode active material, the positive electrode active material includes one or more selected from the group consisting of nickel, cobalt, manganese, and aluminum, includes 50 mol% or more of nickel among the total metals excluding lithium, based on 100 parts by weight of the positive electrode active material, includes 1 part by weight or more and 50 parts by weight or less of the single particle positive electrode active material, and the capacity loading amount of the positive electrode active material layer composition is 2 mAh / cm 2 or more and 5 mAh / cm 2 and provides a lithium secondary battery including 0.01 part by weight or more and 4 parts by weight or less of the single particle positive electrode active material based on 100 parts by weight of the silicon-based active material.

Advantages of the Invention

[0016] The lithium secondary battery according to the present application can ensure a battery with high capacity and high energy density by using a silicon-based negative electrode, and by using a silicon-based active material with excellent capacity characteristics, the negative electrode thickness is formed at the thin film level, and rapid charging performance can be ensured.

[0017] At this time, the lithium secondary battery according to the present application is characterized in that a secondary particle cathode active material and a single particle cathode active material are mixed and used for the cathode which is the counter electrode used, and the ratio of the single particle cathode active material is adjusted. In particular, the secondary battery according to the present application is characterized in that the weight ratio of the silicon-based active material of the silicon-based negative electrode used as the counter electrode to the single particle cathode active material is adjusted in comparison with the capacity loading amount of the cathode active material layer composition.

[0018] Thereby, the resistance problem in the lithium secondary battery can be solved, the cracking phenomenon in a high-voltage cell can be reduced compared with the cathode using secondary particles alone, the problem of gas generation can be solved compared with the cathode using single particles alone, and the main feature of the present application is that the composition and content of the cathode used as the counter electrode of the silicon-based negative electrode are optimized.

Brief Description of the Drawings

[0019]

Figure 1

Modes for Carrying Out the Invention

[0020] Before explaining the present invention, first, several terms are defined.

[0021] In this specification, when a certain part "includes" a certain component, this means that, unless otherwise specified, it does not exclude other components, but may further include other components.

[0022] In this specification, "p~q" means "p or more and q or less".

[0023] In this specification, the "specific surface area" is measured by the BET method. Specifically, it is calculated from the nitrogen gas adsorption amount at the liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan, Inc. That is, in the present application, the BET specific surface area can mean the specific surface area measured by the above measurement method.

[0024] In this specification, "Dn" means the particle size distribution and means the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size, median particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. On the other hand, the particle size distribution may be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500). When the particles pass through the laser beam, the difference in the diffraction pattern due to the particle size is measured to calculate the particle size distribution.

[0025] In this specification, the meaning that a polymer contains a certain monomer in monomer units means that the monomer participates in the polymerization reaction and is included as a repeating unit in the polymer. In this specification, when a polymer is said to contain a monomer, this is interpreted to be the same as the polymer containing the monomer in monomer units.

[0026] In this specification, it is understood that the term "polymer" is used in a broad sense including copolymers unless otherwise specified as "homopolymer".

[0027] In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are the polystyrene equivalent molecular weights measured by Gel Permeation Chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as the standard substance. In this specification, the molecular weight means the weight average molecular weight unless otherwise specified.

[0028] Hereinafter, for those with ordinary knowledge in the technical field to which the present invention pertains to be able to easily implement the present invention, a detailed description will be given with reference to the drawings. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0029] One embodiment of the present specification is a lithium secondary battery including a positive electrode; a silicon-based negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte. The positive electrode includes a positive electrode current collector layer; and a positive electrode active material layer including a positive electrode active material layer composition provided on one or both surfaces of the positive electrode current collector layer. The silicon-based negative electrode includes a negative electrode current collector layer; and a negative electrode active material layer including a negative electrode active material layer composition provided on one or both surfaces of the negative electrode current collector layer. The negative electrode active material layer composition includes a silicon-based active material. The silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys. The positive electrode active material layer composition includes a positive electrode active material including one or more selected from the group consisting of a secondary particle positive electrode active material and a single particle positive electrode active material. The positive electrode active material includes one or more selected from the group consisting of nickel, cobalt, manganese, and aluminum, and contains 50 mol% or more of nickel among the total metals excluding lithium. Based on 100 parts by weight of the positive electrode active material, the single particle positive electrode active material is included in an amount of 1 part by weight or more and 50 parts by weight or less. The capacity loading amount of the positive electrode active material layer composition is 2 mAh / cm 2 Above 5 mAh / cm 2 and provides a lithium secondary battery that includes the single particle positive electrode active material in an amount of 0.01 part by weight or more and 4 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0030] The lithium secondary battery according to the present application is characterized in that a secondary particle positive electrode active material and a single particle positive electrode active material are mixed and used for the positive electrode which is the counter electrode used, and the ratio of the single particle positive electrode active material is adjusted. In particular, the secondary battery according to the present application is characterized in that the weight ratio of the silicon-based active material and the single particle positive electrode active material of the silicon-based negative electrode used as the counter electrode is adjusted in comparison with the capacity loading amount of the positive electrode active material layer composition.

[0031] This application is mainly characterized by optimizing the composition and content of the positive electrode used as the counter electrode of the silicon-based negative electrode, thereby solving the resistance problem in lithium secondary batteries, reducing the cracking phenomenon in high-voltage cells compared to the positive electrode applying secondary particles alone, and solving the problem of gas generation compared to the positive electrode applying single particles alone.

[0032] Figure 1 is a diagram showing the laminated structure of a lithium secondary battery according to an embodiment of the present application. Specifically, a negative electrode 100 including a negative electrode active material layer 20 can be confirmed on one surface of the negative electrode current collector layer 10, a positive electrode 200 including a positive electrode active material layer 40 can be confirmed on one surface of the positive electrode current collector layer 50, and it is shown that the negative electrode 100 and the positive electrode 200 for a lithium secondary battery are laminated with a separator 30 interposed therebetween.

[0033] Hereinafter, the positive electrode, negative electrode, electrolyte, and separator included in the lithium secondary battery will be described respectively.

[0034] The silicon-based negative electrode according to the present application may include a negative electrode current collector layer; and a negative electrode active material layer including a negative electrode active material layer composition provided on one or both surfaces of the negative electrode current collector layer.

[0035] The negative electrode current collector layer usually has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. may be used. Also, fine irregularities may be formed on the surface to strengthen the binding force of the negative electrode active material, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics.

[0036] However, the thickness may be variously deformed according to the type and use of the negative electrode used, and is not limited thereto.

[0037] In one embodiment of the present application, the negative electrode active material layer includes a negative electrode active material layer composition, and the negative electrode active material layer composition may include a silicon-based active material.

[0038] In one embodiment of the present application, the negative electrode active material layer includes a negative electrode active material layer composition, and the negative electrode active material layer composition may include one or more selected from the group consisting of a silicon-based active material, a negative electrode conductive material, and a negative electrode binder.

[0039] In one embodiment of the present application, the negative electrode active material layer includes a negative electrode active material layer composition, and the negative electrode active material layer composition may include a silicon-based active material, a negative electrode conductive material, and a negative electrode binder.

[0040] In one embodiment of the present application, the silicon-based active material may include one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys.

[0041] In one embodiment of the present application, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), and metal impurities, and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more.

[0042] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included 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 included 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.

[0043] In one embodiment of the present application, the silicon-based active material may particularly use pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material means, as described above, that when based on 100 parts by weight of the entire silicon-based active material, pure Si particles (SiOx (x = 0)) not bonded to other particles or elements are included within the above range.

[0044] On the other hand, the average particle size (D50) of the silicon-based active material of the present invention may be 5 μm to 10 μm, specifically, it may be 5.5 μm to 8 μm, and more specifically, it may be 6 μm to 7 μm. When the average particle size is less than 5 μm, the specific surface area of the particles increases too much, and the viscosity of the negative electrode slurry rises too much. Therefore, the dispersion of the particles constituting the negative electrode slurry becomes non-smooth. Also, when the size of the silicon-based active material is too small, the contact area between the silicon particles and the conductive material in the negative electrode slurry decreases due to the composite composed of the conductive material and the binder, so the possibility of the conductive network being disconnected increases, and the capacity retention rate decreases. On the other hand, when the average particle size exceeds 10 μm, there are silicon particles that are too large, the surface of the negative electrode is not smooth, and the current density becomes non-uniform during charge and discharge. Also, when the silicon particles are too large, the phase stability of the negative electrode slurry becomes unstable, so the processability decreases. As a result, the capacity retention rate of the battery decreases.

[0045] In one embodiment of the present application, the silicon-based active material usually has a specific BET specific surface area. The BET specific surface area of the silicon-based active material is preferably 0.01 m 2 / g to 150.0 m 2 / g, more preferably 0.1 m 2 / g to 100.0 m 2 / g, particularly preferably 0.2 m 2 / g to 80.0 m 2 / g, most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET surface area is measured according to DIN 66131 (using nitrogen).

[0046] In one embodiment of the present application, the silicon-based active material may be present, for example, in a crystalline or amorphous form, and preferably is not porous. The silicon particles are preferably spherical or multi-piece particles. Alternatively, the silicon particles may have a fibrous structure or may be present in the form of a silicon-containing film or coating, but this is less preferred.

[0047] In one embodiment of the present application, the silicon-based active material may be contained in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0048] In another embodiment, the silicon-based active material may be contained in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may be contained in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0049] By using a negative electrode conductive material and a negative electrode binder capable of controlling the volume expansion rate during the charge and discharge process even when using a silicon-based active material with a significantly high capacity within the above range, the negative electrode active material layer composition according to the present application has the characteristic of not degrading the performance of the negative electrode even when the silicon-based active material is included within the above range and having excellent output characteristics during charging and discharging.

[0050] In one embodiment of the present application, the silicon-based active material may have a non-spherical form, and its sphericity 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.

[0051] In the present application, the sphericity is determined by the following formula 1, where A is the area and P is the boundary line.

[0052] [Formula 1] 4πA / P 2

[0053] Conventionally, it has been common to use only graphite-based compounds as the negative electrode active material. However, recently, as the demand for high-capacity batteries has increased, attempts to mix and use silicon-based compounds to increase the capacity have been increasing. However, in the case of silicon-based compounds, there is a limit in that the volume rapidly expands during the charge / discharge process, damaging the conductive path formed in the negative electrode active material layer and actually degrading the performance of the battery.

[0054] Therefore, in one embodiment of the present application, the negative electrode active material layer composition may include a negative electrode conductive material and a negative electrode binder. That is, the negative electrode conductive material serves to secure a conductive path, and the binder serves to be able to control such a negative electrode conductive material during charge and discharge.

[0055] In one embodiment of the present application, the negative electrode conductive material may include one or more selected from the group consisting of a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

[0056] In one embodiment of the present application, the dot-shaped conductive material can be used to improve the conductivity of the negative electrode, forms conductivity without inducing a chemical change, and its form means a conductive material in a circular or dot shape. Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivative, and preferably may include carbon black in terms of realizing high conductivity and having excellent dispersibility.

[0057] In one embodiment of the present application, the dot-shaped conductive material may have a BET specific surface area of 40 m 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m2 60 m or more per g 2 It may be 60 m or less per g.

[0058] In one embodiment of the present application, the particle size of the dot-like conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 40 nm to 60 nm.

[0059] In one embodiment of the present application, the negative electrode conductive material may include a planar conductive material.

[0060] The planar conductive material means a conductive material that plays a role of increasing the surface contact between silicon particles in the negative electrode to improve conductivity and at the same time suppressing the interruption of the conductive path due to volume expansion. The planar conductive material may be represented by a plate-shaped conductive material or a bulk conductive material.

[0061] In one embodiment of the present application, the planar conductive material may include at least any one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and preferably may be plate-shaped graphite.

[0062] In one embodiment of the present application, the average particle size (D50) of the planar 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 above range is satisfied, since the particle size is sufficient, the viscosity of the negative electrode slurry does not increase excessively and dispersion becomes easy. Therefore, when dispersing using the same apparatus and time, the dispersion effect is excellent.

[0063] In one embodiment of the present application, the planar conductive material provides a negative electrode composition having D10 of 0.5 μm or more and 1.5 μm or less, D50 of 4.0 μm or more and 5.0 μm or less, and D90 of 7.0 μm or more and 15.0 μm or less.

[0064] In one embodiment of the present application, the planar conductive material may be a high specific surface area planar conductive material with a high BET specific surface area; or a low specific surface area planar conductive material.

[0065] In one embodiment of the present application, as the planar conductive material, a high specific surface area planar conductive material; or a low specific surface area planar conductive material may be used without limitation. However, particularly for the planar conductive material according to the present application, since the electrode performance may be affected by dispersion to some extent, it is particularly preferable to use a low specific surface area planar conductive material that does not cause problems in dispersion.

[0066] In one embodiment of the present application, the planar conductive material may have a BET specific surface area of 1 m 2 / g or more.

[0067] In another embodiment, the planar conductive material may have a BET specific surface area of 1 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, more preferably 5 m 2 / g or more and 250 m 2 / g or less.

[0068] In another embodiment, the planar conductive material is a high specific surface area planar conductive material, and may satisfy the range of having a BET specific surface area of 50 m 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, more preferably 100 m 2 / g or more and 250 m 2 / g or less.

[0069] In another embodiment, the planar conductive material is a low specific surface area planar conductive material, and may satisfy the range of having a BET specific surface area of 1 m 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, more preferably 5 m 2 / g or more and 25 m2 It may satisfy the range of less than / g.

[0070] In addition, as the conductive material, there may be a linear conductive material such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include a plurality of carbon nanotube units. Specifically, here, "bundle type" refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in parallel with substantially the same orientation of the longitudinal axis of the carbon nanotube unit, or are intertwined, unless otherwise stated. The carbon nanotube unit has a cylindrical form with a nanosize diameter of a graphite sheet and has an sp2 bonding structure. At this time, depending on the angle and structure of the winding of the graphite sheet, it can exhibit the characteristics of a conductor or a semiconductor. The bundled carbon nanotubes can be uniformly dispersed during the production of the negative electrode compared to the entangled type carbon nanotubes, and can smoothly form a conductive network in the negative electrode to improve the conductivity of the negative electrode.

[0071] In one embodiment of the present application, the negative electrode conductive material includes a linear conductive material, and the linear conductive material may be carbon nanotubes.

[0072] In one embodiment of the present application, the carbon nanotubes may be SWCNT or / and MWCNT. When the linear conductive material is SWCNT, the length of the SWCNT may be 0.5 μm to 100 μm, preferably 1 μm to 80 μm.

[0073] In one embodiment of the present application, 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 based on 100 parts by weight of the negative electrode active material layer composition.

[0074] 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 active material layer composition.

[0075] In one embodiment of the present application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, and the ratio of the planar conductive material: linear conductive material can satisfy 1:0.001 to 1:0.3.

[0076] In one embodiment of the present application, when the negative electrode conductive material includes a planar conductive material and a linear conductive material and satisfies the respective compositions and ratios, it does not significantly affect the life characteristics of conventional lithium secondary batteries, and there are many points where charging and discharging are possible, resulting in excellent output characteristics at a high C-rate.

[0077] In the case of the negative electrode conductive material according to the present application, it has a completely different configuration from the conductive material applied to the positive electrode. That is, in the case of the negative electrode conductive material according to the present application, it plays a role in controlling the contacts between silicon-based active materials with a very large volume expansion of the electrode during charging and discharging. The positive electrode conductive material plays a role in imparting partial conductivity while having a buffering effect as a buffer during rolling, and the configuration and role of the negative electrode conductive material of the present invention are completely different.

[0078] Further, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different configuration from the conductive material applied to a graphite-based active material. That is, the conductive material used for an electrode having a graphite-based active material simply has smaller particles compared to the active material, and thus has the characteristics of improving the output characteristics and imparting partial conductivity. It is completely different in configuration and role from the negative electrode conductive material applied together with a silicon-based active material as in the present invention.

[0079] In one embodiment of the present application, the plate-shaped conductive material used as the aforementioned negative electrode conductive material generally plays a structure and role different from those of the carbon-based active material generally used as the 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 means a material processed into a spherical or dot-like form in order to facilitate the storage and release of lithium ions.

[0080] On the other hand, the plate-shaped conductive material used as the negative electrode conductive material is a material having a planar or plate-like form, and can be represented by plate-shaped graphite. That is, it is a material included in order to maintain a conductive path within the negative electrode active material layer, and means a material for securing a conductive path in a planar form inside the negative electrode active material layer rather than playing a role in the storage and release of lithium.

[0081] That is, in the present application, the fact that plate-shaped graphite is used as the conductive material means that it is processed into a planar or plate-like shape and used as a material for securing a conductive path rather than playing a role in storing or releasing lithium. At this time, the negative electrode active material included together has a high capacity characteristic for the storage and release of lithium and plays a role of being able to store and release all lithium ions transmitted from the positive electrode.

[0082] On the other hand, in the present application, the fact that the carbon-based active material is used as the active material means that it is processed into a dot-like or spherical shape and used as a material that plays a role in storing or releasing lithium.

[0083] In one embodiment of the present application, the negative electrode binder may include at least any one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, 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 thereof is substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0084] The negative electrode binder according to one embodiment of the present application plays a role in controlling the silicon-based active material and the negative electrode conductive material in order to prevent the twisting and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. When the above role is satisfied, any ordinary negative electrode binder can be applied. Specifically, an aqueous binder may be used, and more specifically, a PAM-based binder may be used.

[0085] In one embodiment of the present application, based on 100 parts by weight of the negative electrode active material layer composition, the negative electrode binder may be included in an amount of 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, and may also be included in an amount of 5 parts by weight or more, 8 parts by weight or more.

[0086] Compared with the conventional carbon-based negative electrode, when a Si-based negative electrode is used, an aqueous binder may be applied in the above parts by weight, and a dot-shaped conductive material with a low content of functional groups may be used. Due to the above characteristics, the dot-shaped conductive material has hydrophobicity and excellent bonding strength with the conductive material / binder.

[0087] In one embodiment of the present application, the silicon-based negative electrode may be formed by coating a negative electrode slurry containing the negative electrode active material layer composition on one or both surfaces of the negative electrode current collector layer.

[0088] In one embodiment of the present application, the negative electrode slurry may include a negative electrode active material layer composition and a slurry solvent.

[0089] In one embodiment of the present application, the solid content of the negative electrode slurry may satisfy 5% or more and 40% or less.

[0090] In another embodiment, the solid content of the negative electrode slurry may satisfy the range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0091] In another embodiment, the content of the solid component of the negative electrode slurry may satisfy the range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0092] The content of the solid component of the negative electrode slurry means the content of the negative electrode composition contained in the negative electrode slurry, and may mean the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0093] When the content of the solid component of the negative electrode slurry satisfies the above range, at the time of forming the negative electrode active material layer, the viscosity is appropriate, the aggregation phenomenon of the particles of the negative electrode composition is minimized, and the negative electrode active material layer can be efficiently formed.

[0094] In one embodiment of the present application, the slurry solvent may be used without limitation as long as it can disperse the above negative electrode composition, and specifically, water or NMP may be used.

[0095] In one embodiment of the present application, the porosity of the negative electrode active material layer may satisfy the range of 10% or more and 60% or less.

[0096] In another embodiment, the porosity of the negative electrode active material layer may satisfy the range of 10% or more and 60% or less, preferably 20% or more and 50% or less, and more preferably 30% or more and 45% or less.

[0097] The porosity is varied by the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, by including the silicon-based active material and conductive material according to the present application in specific compositions and content portions, the above range is satisfied, and thereby the electric conductivity and resistance in the electrode have an appropriate range.

[0098] In one embodiment of the present application, the positive electrode includes a positive electrode active material layer including a positive electrode current collector layer and a positive electrode active material layer composition provided on one or both surfaces of the positive electrode current collector layer.

[0099] In one embodiment of the present application, the positive electrode active material layer includes a positive electrode active material layer composition, and the positive electrode active material layer composition may include one or more selected from the group consisting of a primary particle positive electrode active material and a single positive electrode active material; a positive electrode conductive material; and a positive electrode binder.

[0100] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector layer may usually have a thickness of 1 μm to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector layer to enhance the adhesion to the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc.

[0101] In one embodiment of the present application, there is provided a lithium secondary battery in which the thickness of the positive electrode and negative electrode current collector layers is 1 μm or more and 100 μm or less, and the thickness of the positive electrode and negative electrode active material layers is 20 μm or more and 500 μm or less.

[0102] In one embodiment of the present application, the positive electrode active material may include one or more selected from the group consisting of secondary particle positive electrode active materials and single particle positive electrode active materials.

[0103] In another embodiment, the positive electrode active material may include a secondary particle positive electrode active material and a single particle positive electrode active material.

[0104] That is, the positive electrode active material according to the present application is characterized by using a mixed positive electrode active material of a secondary particle positive electrode active material and a single particle positive electrode active material.

[0105] The reaction potential of the silicon-based negative electrode is about 0.05 V higher than that of the carbon-based negative electrode, and the silicon-based negative electrode is in an environment where it is exposed to a high potential. When using the secondary particle positive electrode active material alone, a cracking phenomenon occurs at a high voltage, so the problem of gas generation occurs again. Therefore, research has also been conducted on applying a single particle positive electrode active material as the positive electrode active material. However, when using the single particle positive electrode active material alone, the use of the lower end of the silicon-based negative electrode increases, the negative electrode fails to function, and the problem of deterioration of cycle characteristics occurs. Therefore, the present application contains secondary particles and single particle positive electrode active materials at the same time.

[0106] In the lithium secondary battery according to the present application, the positive electrode active material contains one or more selected from the group consisting of nickel, cobalt, manganese, and aluminum, and contains 50 mol% or more of nickel among the total metals excluding lithium, that is, a high Ni or Mid Ni positive electrode active material is used. As a result, a problem occurs in that high-temperature storage gas is generated.

[0107] The lithium secondary battery according to the present application uses a mixed cathode active material of secondary particle cathode active material and single particle cathode active material, and by limiting the ratio of the single particle cathode active material and using it, it is possible to reduce high-temperature gas and ensure cycle performance as well.

[0108] In this specification, the presence or absence of elements and the content of elements in the cathode active material can be confirmed by ICP analysis, and the ICP analysis may be performed using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0109] In this specification, the single particle cathode active material means the smallest particle unit that can be distinguished as a single mass when observing the cross section of the cathode active material with a scanning electron microscope (SEM), and it may be composed of one crystal grain or a plurality of crystal grains.

[0110] The method for forming the single particle cathode active material is not particularly limited. Generally, it may be formed by raising the firing temperature and overfiring, or it may be manufactured by using additives useful for overfiring, changing the starting material, etc. By forming it into single particles as described above, the thermal stability can be improved and side reactions and resistance increase can be suppressed. The cathode active material in the form of the single particle cathode active material may be formed, for example, by adding a lithium source such as LiOH and Li2CO3 to a composite transition metal hydroxide containing nickel, cobalt, and manganese, mixing them, and then overfiring at 800°C to 900°C for 10 hours to 25 hours in an oxygen atmosphere.

[0111] In one embodiment of the present application, the single particle is a term used to distinguish from the cathode active material particles in the form of secondary particles formed by aggregation of dozens to hundreds of primary particles that have been generally used in the past, and it is a concept including single particles composed of one primary particle and aggregate particles of 10 or fewer primary particles.

[0112] In one embodiment of the present application, the secondary particle positive electrode active material may be the same as that described above and may be the same as the type of the single particle positive electrode active material, but may mean a form in which the single particle positive electrode active material is aggregated.

[0113] In one embodiment of the present application, the single particle positive electrode active material may be in a single particle form in a commonly used positive electrode active material.

[0114] In one embodiment of the present application, the single particle positive electrode active material contains one or more selected from the group consisting of nickel, cobalt, manganese, and aluminum, contains 50 mol% or more of nickel among the total metals excluding lithium, and the single particle positive electrode active material is characterized in that there is no H2-H3 phase change at a voltage of 4.0 V or higher.

[0115] In one embodiment of the present application, the single particle positive electrode active material is one that has no H2-H3 phase change at a voltage of 4.0 V or higher. Although various adjustment factors are included, when the content of Ni included together satisfies a value less than a predetermined range, the phase change is not observed. That is, when a general single particle active material is used, the gas generation reduction effect is high, but since the negative electrode side reaction increases in the high voltage phase transition section of the positive electrode, there has been a problem that a rapid cycle performance deterioration appears and the performance of the lithium secondary battery is degraded. However, in particular, by using a single particle positive electrode active material that is a Mid Ni single particle positive electrode active material and does not involve a specific phase change at a high voltage (4.0 V or higher), it becomes possible to ensure cycle performance together with the gas reduction effect.

[0116] In one embodiment of the present application, the single particle positive electrode active material is one that has no H2-H3 phase change at a voltage of 4.0 V or higher. At this time, the physical properties of the single particle positive electrode active material may mean physical properties having a characteristic that no phase change occurs when a voltage of 4.0 V or higher is applied to a half cell containing the single particle positive electrode active material described above after manufacturing the half cell.

[0117] In one embodiment of the present application, for the positive electrode half cell containing the single particle positive electrode active material, when the electrochemical capacitance result obtained by charging the positive electrode half cell at a constant current up to 4.3 V is differentiated with respect to voltage, there is no peak having a magnitude of 1.5 times or more the average value in the voltage range of 4.0 V to 4.3 V, and a lithium secondary battery is provided.

[0118] Particularly, in the case of a conventional single particle positive electrode material, when the electrochemical capacitance result obtained by charging the positive electrode half cell at a constant current up to 4.3 V is differentiated with respect to voltage, a peak is observed in the voltage range of 4.0 V to 4.3 V. However, for the single particle positive electrode active material as described above, no peak is observed in the above range, and it has the characteristic that cycle performance can be more ensured together with the gas reduction effect.

[0119] In one embodiment of the present application, the average particle diameter (D50) of the single particle positive electrode active material may be 1 μm to 10 μm, preferably 2 μm to 7 μm. That is, the single particle positive electrode active material may include a small particle form.

[0120] In one embodiment of the present application, the secondary particle positive electrode active material may include a large particle form and a small particle form in a bi-modal form, and the average particle diameter (D50) of the secondary particle positive electrode active material may be 5 μm to 20 μm, preferably 7 μm to 15 μm.

[0121] In one embodiment of the present application, a lithium secondary battery is provided in which the average particle diameter (D50) of the positive electrode active material is 1 μm or more and 20 μm or less.

[0122] The average particle diameter of the positive electrode active material corresponds to the overall average particle diameter including the above-mentioned single particle positive electrode active material and secondary particle positive electrode active material.

[0123] In one embodiment of the present application, there is provided a lithium secondary battery including 1 to 50 parts by weight of the single-particle positive electrode active material and 50 to 99 parts by weight of the secondary-particle positive electrode active material based on 100 parts by weight of the positive electrode active material.

[0124] In one embodiment of the present application, based on 100 parts by weight of the positive electrode active material, the single-particle positive electrode active material may be included in an amount of 1 to 50 parts by weight.

[0125] In another embodiment, based on 100 parts by weight of the positive electrode active material, the single-particle positive electrode active material can satisfy 1 to 50 parts by weight, preferably 5 to 50 parts by weight; more preferably 15 to 50 parts by weight.

[0126] In one embodiment of the present application, based on 100 parts by weight of the positive electrode active material, the secondary-particle positive electrode active material may be included in an amount of 50 to 99 parts by weight, preferably 50 to 95 parts by weight, more preferably 50 to 85 parts by weight.

[0127] As described above, the positive electrode according to the present application uses a mixed positive electrode material of secondary particles and single particles, and has the characteristic of being able to reduce the high-temperature storage gas generated in the positive electrode material. When the single-particle positive electrode active material according to the present application is used beyond the above range, although the high-temperature storage gas can be reduced, the cycle performance is deteriorated due to this, resulting in a problem that the life characteristics are rapidly reduced.

[0128] As described above, the positive electrode active material according to the present application is characterized in that the ratio of single particles to secondary particles is adjusted, and the parts by weight with respect to the silicon-based active material as the counter electrode are also adjusted.

[0129] That is, in one embodiment of the present application, the capacity loading of the positive electrode active material layer composition is 2 mAh / cm 2 or more and 5 mAh / cm 2Provided is a lithium secondary battery, wherein, based on 100 parts by weight of the silicon-based active material, the single-particle positive electrode active material is contained in an amount of 0.01 part by weight or more and 4 parts by weight or less.

[0130] In another embodiment, the capacity loading of the positive electrode active material layer is 2 mAh / cm 2 or more and 5 mAh / cm 2 Based on 100 parts by weight of the silicon-based active material, the single-particle positive electrode active material may be 0.01 part by weight or more and 4 parts by weight or less, preferably 0.03 part by weight or more and 3.9 parts by weight or less.

[0131] As described above, based on the capacity loading of the positive electrode, 100 parts by weight of the silicon-based active material contains the single-particle positive electrode active material as described above. When simply adjusting the weight ratio of the single-particle positive electrode active material in the positive electrode active material as described above, the problem of the life characteristics due to the volume expansion of the silicon-based negative electrode (particularly, Pure Si) used as the counter electrode could not be solved. However, as described above, by adjusting the ratio of the single-particle positive electrode active material to the silicon-based active material, it is possible to provide a lithium secondary battery with excellent life characteristics while reducing gas generation, which is the main object of the present invention.

[0132] In one embodiment of the present application, the single-particle positive electrode active material and the secondary-particle positive electrode active material are LiNi x Co y Mn z O2 (x + y + z = 1); LiNi a Co b Mn c Al d O2 (a + b + c + d = 1); LiMn2O4; LiNi 0.5 Mn 1.5 O2; and LiM x Fe y PO4 (M: transition metal, x + y = 1), and provides a lithium secondary battery containing one or more selected from the group consisting of these.

[0133] In one embodiment of the present application, the single positive electrode active material and the secondary particle positive electrode active material are nickel-cobalt-manganese (NCM) oxide; or nickel-cobalt-manganese-aluminum (NCMA) oxide, and nickel contained in the nickel-cobalt-manganese (NCM) oxide and nickel-cobalt-manganese-aluminum (NCMA) oxide is 50 mol% or more of the total metal excluding lithium, providing a lithium secondary battery.

[0134] In another embodiment, the single particle positive electrode active material and the secondary particle positive electrode active material are nickel-cobalt-manganese (NCM) oxide; or nickel-cobalt-manganese-aluminum (NCMA) oxide, and nickel contained in the nickel-cobalt-manganese (NCM) oxide and nickel-cobalt-manganese-aluminum (NCMA) oxide is 50 mol% or more, preferably 55 mol% or more, more preferably 58 mol% or more, and most preferably 60 mol% or more of the total metal excluding lithium. Also, based on the total metal, nickel (Ni) may be 99 mol% or less, 95 mol% or less.

[0135] When the content of nickel is less than the above range, although the content of cobalt increases and the thermal stability increases, there is a problem that the capacity of the positive electrode active material decreases and it cannot be applied to an electrochemical device that requires high capacity.

[0136] On the other hand, the higher the content of nickel within the above range, the lithium secondary battery containing it can exhibit high capacity characteristics. However, the higher the content of nickel, the relatively lower the content of cobalt and / or manganese, and therefore, there is a risk of decreasing thermal stability. Therefore, when nickel is present in the content within the above range, the efficiency of the lithium secondary battery according to the present application can be maximized.

[0137] In one embodiment of the present application, the nickel-cobalt-manganese (NCM) oxide can be represented as lithium nickel-cobalt-manganese oxide, and the lithium nickel-cobalt-manganese (NCM) oxide is Li 1+x (Ni a Co b Mn c )O2 (0.97 ≦ x ≦ 1.06, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), a three-component cathode active material of Ni-Co-Mn represented by, Li 1+x (Ni a Co b Mn c )O4 (0.97 ≦ x ≦ 1.06, 0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), a three-component cathode active material of Ni-Co-Mn represented by, or a mixture thereof, which is a composite combining the advantages such as the high capacity of nickel-containing oxides, the thermal stability of manganese-containing oxides, and the excellent electrochemical properties of cobalt-containing oxides. The lithium nickel-cobalt-manganese (NCM) oxide can be doped with trace metal elements to an extent suitable for the purpose of the present invention. For example, Li 1+x (Ni a Co b Mn c )O2 (0.97 ≦ x ≦ 1.06, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1) or Li 1+x (Ni a Co b Mn c )O4 (0.97 ≦ x ≦ 1.06, 0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), each of the lithium nickel-cobalt-manganese (NCM) oxides represented by the three-component cathode active material of Ni-Co-Mn can be independently doped with one or more metals selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr.

[0138] The content of the metal doped into the lithium nickel-cobalt-manganese (NCM) may be in a content range that does not significantly increase the cathode resistance. For example, the doping metal in the lithium nickel-cobalt-manganese (NCM) oxide may be in the range of 10 to 1500 ppm or 50 to 1000 ppm or 100 to 500 ppm based on each element, but is not limited thereto. As a non-limiting example, generally 2 to 3 kinds of elements are used as the doping metal in the lithium nickel-cobalt-manganese (NCM) oxide, and the doping metal may be present at several hundred ppm based on each element.

[0139] In one embodiment of the present application, the nickel contained in the nickel-cobalt-manganese (NCM) oxide may be 50 mol% or more, specifically 55 mol% or more, of the total metal excluding lithium, specifically 58 mol% or more, and more specifically 60 mol% or more.

[0140] The Li 1+x (Ni a Co b Mn C )O2 (0.97 ≦ x ≦ 1.06, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), the content of the nickel can mean the ratio of a contained. That is, in the case of a ternary system, it can mean the ratio occupied by nickel among the metals of nickel, cobalt, and manganese.

[0141] In one embodiment of the present application, the nickel-cobalt-manganese-aluminum (NCMA) oxide can be represented as a lithium nickel-cobalt-manganese-aluminum oxide as follows, and the lithium nickel-cobalt-manganese-aluminum (NCMA) oxide is Li 1+x (Ni a Co b Mn C Al d) A four-component cathode active material of Ni-Co-Mn-Al represented by O2 (0.97 ≦ x ≦ 1.06, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 < d < 1, a + b + c + d = 1), Li 1+x (Ni a Co b Mn C Al d ) O4 (0.97 ≦ x ≦ 1.06, 0 < a < 2, 0 < b < 2, 0 < c < 2, 0 < d < 2, a + b + c + d = 2), or a mixture thereof, is a composite that combines the advantages such as the high capacity of nickel-containing oxides, the thermal stability of manganese-containing oxides, and the excellent electrochemical properties of cobalt-containing oxides. The lithium nickel-cobalt-manganese-aluminum (NCMA) oxide can be doped with trace amounts of metal elements to an extent suitable for the purposes of the present invention.

[0142] For example, Li 1+x (Ni a Co b Mn c Al d ) O2 (0.97 ≦ x ≦ 1.06, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 < d < 1, a + b + c + d = 1) or Li 1+x (Ni a Co b Mn c Al d ) O4 (0.97 ≦ x ≦ 1.06, 0 < a < 2, 0 < b < 2, 0 < c < 2, 0 < d < 2, a + b + c + d = 2), each of the lithium nickel-cobalt-manganese (NCM) oxides represented by the four-component cathode active material of Ni-Co-Mn-Al can be independently doped with one or more metals selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr as non-limiting examples,

[0143] In one embodiment of the present application, the nickel contained in the nickel-cobalt-manganese-aluminum (NCMA) oxide may be 80 mol% or more, specifically 85 mol% or more, more specifically 88 mol% or more, and even more specifically 93 mol% or more of the total metals excluding lithium.

[0144] The Li 1+x (Ni a Co b Mn c Al d )O2 (0.97 ≦ x ≦ 1.06, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 < d < 1, a + b + c + d = 1), the content of the nickel can mean the ratio of a contained. That is, in the case of a four-component system, it can mean the ratio occupied by nickel among the metals of nickel, cobalt, manganese, and aluminum.

[0145] In one embodiment of the present application, a lithium secondary battery is provided in which the positive electrode active material is contained in an amount of 90 parts by weight or more based on 100 parts by weight of the positive electrode active material layer composition.

[0146] In another embodiment, based on 100 parts by weight of the positive electrode active material layer composition, the positive electrode active material may be contained in an amount of 90 parts by weight or more, preferably 93 parts by weight or more, more preferably 95 parts by weight or more, and may be contained in an amount of 99 parts by weight or less, 98 parts by weight or less.

[0147] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

[0148] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery being configured, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances 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.

[0149] Specifically, in one embodiment of the present application, the positive electrode conductive material includes single-walled carbon nanotubes (SWCNT); or multi-walled carbon nanotubes (MWCNT), and provides a lithium secondary battery including 0.1 parts by weight or more and 2 parts by weight or less of the positive electrode conductive material based on 100 parts by weight of the positive electrode active material layer composition.

[0150] In another embodiment, based on 100 parts by weight of the positive electrode active material layer composition, it may include 0.1 parts by weight or more and 2 parts by weight or less of the positive electrode conductive material, preferably 0.3 parts by weight or more and 1.5 parts by weight or less, more preferably 0.5 parts by weight or more and 1.2 parts by weight or less.

[0151] In addition, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (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.

[0152] At this time, the positive electrode binder may be contained in an amount of 0.1 part by weight or more and 10 parts by weight or less, preferably 1 part by weight or more and 5 parts by weight or less, based on 100 parts by weight of the positive electrode composition.

[0153] The separator is used to separate the negative electrode and the positive electrode and provide a migration path for lithium ions. It can be used without particular limitation as long as it is usually used as a separator in a secondary battery. In particular, those with low resistance to ion migration of the electrolyte and excellent electrolyte moisture retention ability are preferred. 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. Also, 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, for ensuring heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and optionally, it may be used in a single-layer or multi-layer structure.

[0154] In the present application, examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0155] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0156] 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, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, and ethyl propionate.

[0157] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are highly viscous organic solvents with high dielectric constants and can well dissociate lithium salts, so they can be preferably used. By mixing linear carbonates with low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate with such cyclic carbonates in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, so it can be more preferably used.

[0158] The metal salt may be a lithium salt. The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte solution. 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 - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0159] 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, triamide hexaline, 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 purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc.

[0160] One embodiment of the present invention provides a battery module including the secondary 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 high capacity, high rate characteristics, and cycle characteristics, they may be used as a power source for a medium to large-sized device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

Example

[0161] Hereinafter, in order to assist in understanding the present invention, preferred examples are presented. However, the following examples 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, and it is natural that such variations and modifications belong to the scope of the claims. (Manufacturing Example)

[0162] (1) Manufacturing of the positive electrode A positive electrode active material, a positive electrode conductive material (LB.CNT), and a binder (PVdF, KF9700) shown in Table 1 below were added to a solvent (N-methylpyrrolidone, NMP) at a weight ratio of 97.0:1.56:1.44 to produce a positive electrode slurry. After the positive electrode slurry was applied and dried on an aluminum (Al) thin film, which is a positive electrode current collector with a thickness of 12 μm, it was rolled by a roll press to produce a positive electrode. At this time, the capacity loading of the positive electrode was as shown in Table 1 below.

[0163]

Table 1

[0164] Table 1 shows the parts by weight of the single-particle positive electrode active material and the secondary-particle positive electrode active material based on 100 parts by weight of the total positive electrode active material.

[0165] In Table 1 above, single-particle A is Li(Ni a Co b Mn c Al d) It is O2, and NCMA excluding lithium (Li) and oxygen (O2) has a ratio of Ni:Co:Mn:Al = 86:5:8:1 and satisfies the ratio (a:b:c:d = 0.86:0.05:0.08:0.01).

[0166] In Table 1 above, the secondary particle A is Li(Ni a Co b Mn c Al d )O2, and NCMA excluding lithium (Li) and oxygen (O2) has a ratio of Ni:Co:Mn:Al = 86:5:7:2 and satisfies the ratio (a:b:c:d = 0.86:0.05:0.07:0.02).

[0167] In Table 1 above, the single particle B is Li(Ni a Co b Mn c )O2, and NCMA excluding lithium (Li) and oxygen (O2) has a ratio of Ni:Co:Mn = 86:8:6 and satisfies the ratio (a:b:c = 0.86:0.08:0.06).

[0168] In Table 1 above, the single particle C is Li(Ni a Co b Mn c )O2, and NCM excluding lithium (Li) and oxygen (O2) of the single particle cathode active material satisfies the ratio of Ni:Co:Mn = 60:20:20 and satisfies a:b:c = 0.60:0.20:0.20. At this time, no H2-H3 phase change was observed in the single particle C. Also, when the electrochemical capacitance result obtained by charging the cathode half cell containing the single particle C at a constant current up to 4.3V was differentiated by voltage, it was confirmed that there was no peak with a magnitude of more than 1.5 times the average value in the voltage range of 4.0V to 4.3V.

[0169] (2) Fabrication of the anode An anode active material layer composition was prepared using Si (average particle size (D50): 5 μm) as a silicon-based active material, a first conductive material, a second conductive material, and polyacrylamide as a binder at a weight ratio of 80:9.6:0.4:10. The composition was added to distilled water as a solvent for forming the anode slurry to produce an anode slurry (solid content concentration: 28% by weight).

[0170] The first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material is carbon nanotubes.

[0171] As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed in a homo mixer at 2500 rpm for 30 minutes, then the active material was added, and then dispersed at 2500 rpm for 30 minutes to prepare a slurry.

[0172] The anode slurry was coated on both sides of a copper current collector (thickness: 8 μm) as an anode current collector at a loading amount of 3.00 mg / cm 2 and rolled, and dried in a vacuum oven at 130 °C for 10 hours to form an anode active material layer (thickness: 23 μm).

[0173] (3) Manufacture of a secondary battery An electrode assembly was manufactured with a pressure-resistant thin film separator (PE 15 μm) ceramic coating (4 μm / 4 μm) interposed between the positive electrode and the negative electrode. After positioning the electrode assembly inside the case, an electrolyte was injected into the case to manufacture a lithium secondary battery.

[0174] Experimental Example 1: Life evaluation For the lithium secondary batteries containing the negative electrodes manufactured in the above Examples and Comparative Examples, life evaluation was carried out using an electrochemical charge and discharge device, and the capacity retention rate was evaluated. The secondary batteries were subjected to an In-situ cycle test at 4.2 - 3.27 V and 1C / 1C. During the test, charging and discharging were performed at 0.33C / 0.33C (4.2 - 3.11V) every 120 cycles, and the capacity retention rate was measured. The results are shown in Table 2. Retention rate of life (%) = {(Discharge capacity at the Nth cycle) / (Discharge capacity at the first cycle)} × 100

[0175] Experimental Example 2: Measurement and evaluation of resistance increase rate In the above Experimental Example 1, during the test, after measuring the capacity retention rate by charging and discharging at 0.33C / 0.33C (4.2 - 3.11V) every 120 cycles, discharging was performed at 2.5C pulse at SOC50, the resistance was measured, and the resistance increase rate was compared and analyzed. The results are as shown in Table 2 below.

[0176] Experimental Example 3: Evaluation of gas generation amount of fully charged positive electrode After fully charging the 1Ah cells manufactured in the above Examples and Comparative Examples, they were stored in an oven at 60°C for 8 weeks, and then the gas generation amount was confirmed and compared by GC (gas chromatography) method. The results are shown in Table 2 below.

[0177]

Table 2

[0178] As can be confirmed from Tables 1 and 2 above, the lithium secondary battery according to the present application applies a single-particle cathode active material to the cathode in the above parts by weight, and it is possible to reduce the amount of gas generation. Also, it was confirmed that the higher the content of the single-particle cathode active material, the more the amount of gas generation is reduced. However, in terms of cycle performance, the higher the blending ratio of the single-particle cathode active material, the worse the performance. As in Comparative Example 1 and Comparative Example 2, when the content of the single-particle cathode active material exceeds a specific content, it was confirmed that the life performance rapidly deteriorates. Further, Comparative Example 3 has the same gist as Comparative Example 1, where the content part of the single-particle cathode active material corresponds to less than the scope of the present application, and it was confirmed that the amount of gas generation is large and the cycle performance deteriorates.

Description of Reference Numerals

[0179] 10 ··· Negative electrode current collector layer 20 ··· Negative electrode active material layer 30 ··· Separator 40 ··· Positive electrode active material layer 50 ··· Positive electrode current collector layer 100 ··· Negative electrode 200 ··· Positive electrode

Claims

1. A lithium secondary battery comprising a positive electrode, a silicon-based negative electrode, a separator provided between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode current collector layer; and a positive electrode active material layer including a positive electrode active material layer composition provided on one or both surfaces of the positive electrode current collector layer; the silicon-based negative electrode includes a negative electrode current collector layer; and a negative electrode active material layer including a negative electrode active material layer composition provided on one or both surfaces of the negative electrode current collector layer; the negative electrode active material layer composition includes a silicon-based active material, and the silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0), SiO x (0 < x < 2), SiC, and Si alloys; the positive electrode active material layer composition includes a positive electrode active material including one or more selected from the group consisting of a secondary particle positive electrode active material and a single particle positive electrode active material; the positive electrode active material includes one or more selected from the group consisting of nickel, cobalt, manganese, and aluminum, and includes 50 mol% or more of nickel among the total metals excluding lithium; based on 100 parts by weight of the positive electrode active material, the single particle positive electrode active material is included in an amount of 1 part by weight or more and 50 parts by weight or less; The capacity loading amount of the positive electrode active material layer composition is 2 mAh / cm ２ or more and 5 mAh / cm ２ and is based on 100 parts by weight of the silicon-based active material, the single particle positive electrode active material is included in an amount of 0.01 part by weight or more and 4 parts by weight or less, the lithium secondary battery.

2. The silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0), SiO x (0 < x < 2), and metal impurities, and based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) is included in an amount of 70 parts by weight or more, the lithium secondary battery according to claim 1.

3. Based on 100 parts by weight of the negative electrode active material layer composition, the silicon-based active material is included in an amount of 60 parts by weight or more, the lithium secondary battery according to claim 1.

4. The single-particle cathode active material and the secondary-particle cathode active material are LiNi ｘ Co ｙ Mn ｚ O ２ (x + y + z = 1); LiNi ａ Co ｂ Mn ｃ Al ｄ O ２ (a + b + c + d = 1); LiMn ２ O ４ ; LiNi ０．５ Mn １．５ O ２ ; and LiM ｘ Fe ｙ PO ４ (M: transition metal, x + y = 1), the lithium secondary battery according to claim 1, comprising one or more selected from the group consisting of.

5. The single particle positive electrode active material and the secondary particle positive electrode active material are nickel-cobalt-manganese (NCM) oxide; or nickel-cobalt-manganese-aluminum (NCMA) oxide, and nickel included in the nickel-cobalt-manganese (NCM) oxide and nickel-cobalt-manganese-aluminum (NCMA) oxide is 50 mol% or more among the total metals excluding lithium, the lithium secondary battery according to claim 1.

6. The average particle diameter (D50) of the positive electrode active material is 1 μm or more and 20 μm or less, the lithium secondary battery according to claim 1.

7. The lithium secondary battery according to claim 1, wherein the positive electrode active material is contained in an amount of 90 parts by weight or more based on 100 parts by weight of the positive electrode active material layer composition.

8. The lithium secondary battery according to claim 1, wherein based on 100 parts by weight of the positive electrode active material, the single-particle positive electrode active material is contained in an amount of 1 part by weight or more and 50 parts by weight or less, and the secondary-particle positive electrode active material is contained in an amount of 50 parts by weight or more and 99 parts by weight or less.

9. The thickness of the positive electrode and negative electrode current collector layers is 1 μm or more and 100 μm or less, The lithium secondary battery according to claim 1, wherein the thickness of the positive electrode and negative electrode active material layers is 20 μm or more and 500 μm or less.

10. The lithium secondary battery according to claim 1, wherein the single-particle positive electrode active material has no H2-H3 phase change at a voltage of 4.0 V or more.

11. The single-particle positive electrode active material, with respect to a positive electrode half cell containing the single-particle positive electrode active material, The lithium secondary battery according to claim 1, wherein when the electrochemical capacitance result obtained by charging the positive electrode half cell at a constant current up to 4.3 V is differentiated by voltage, there is no peak having a magnitude of 1.5 times or more the average value in the voltage range of 4.0 V to 4.3 V.

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