Lithium secondary battery

Abstract

This application relates to a lithium secondary battery.

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0183766, filed with the Korean Intellectual Property Office on December 23, 2022, and all of its content is 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 the use of alternative energy and clean energy is increasing. As part of this, the most actively studied fields are power generation and energy storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage 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 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 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 high theoretical capacity as the negative electrode material are increasing.

[0007] That is, a lithium secondary battery is usually manufactured by using a compound with lithium inserted therein, such as LiCoO2, LiMn2O4, etc. for the positive electrode, and a substance without lithium inserted therein, such as a carbon-based or Si-based material, for the negative electrode. During charging, the lithium ions inserted in 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, the 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 passivation 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. In order 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, a battery design is carried out to reduce the internal resistance and achieve high power output by forming the negative electrode active material layer to a thin film level thickness to reduce the diffusion distance of lithium and forming a carbon coating layer on its surface to increase the conductivity.

[0009] However, it is difficult to achieve high capacity with a negative electrode having such a thin film negative electrode active material layer. Also, it is difficult to achieve rapid charging with a negative electrode having high capacity. Further, when using a silicon-based negative electrode, in order to increase the energy density, the Si content of the negative electrode is increased. Therefore, during the charging process, the volume rapidly expands, breaking the conductive path and degrading the battery characteristics, thereby reducing the capacity from the beginning. In addition, when the silicon-based negative electrode repeats the charge and discharge cycles, lithium ions are not uniformly charged in the depth direction of the negative electrode, and the reaction proceeds on the surface, accelerating surface degradation. Therefore, it is necessary to improve the performance on the side of the battery cycle.

[0010] Therefore, in order to solve the above problems when using a silicon-based compound with excellent rapid charging performance alone as a negative electrode active material, various solutions are discussed, such as a solution for adjusting the driving potential, additionally, a method of further coating a thin film on the active material layer, a method of suppressing the volume expansion itself such as adjusting the particle size of the silicon-based compound, or the development of a binder that controls the volume expansion of the silicon-based compound to prevent the conductive path from being broken.

[0011] However, in the case of the above solutions, there are limitations in application as they may instead reduce the performance of the battery. There are still limitations in the widespread use of manufacturing negative electrode batteries with a high content of silicon-based compounds that are excellent in rapid charging performance. The higher the ratio of the silicon-based active material contained in the silicon-based active material layer, the more pre-lithiation is concentrated on the surface of the negative electrode. Instead, damage to the silicon-based active material on the surface side occurs, and non-uniform pre-lithiation occurs, resulting in problems in improving the life characteristics.

[0012] Therefore, research on lithium secondary batteries with improved cycle performance is required while using a negative electrode containing a silicon-based active material for high capacity.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0014] As a result of research on the above-described problems, when a silicon-based negative electrode (particularly, a Pure Si negative electrode) is used as the negative electrode to ensure capacitance characteristics, it has been found that the use range of the silicon-based negative electrode can be restricted by adjusting the NP ratio (NP Ratio) and incorporating a prelithiation process, and it has been confirmed by research that the life characteristics can be ensured accordingly.

[0015]

Means for Solving the Problems

[0016] One embodiment of the present specification is a lithium secondary battery including a silicon-based negative electrode, a positive electrode, a separator, and an electrolyte, wherein the positive electrode or the silicon-based negative electrode is a prelithiated electrode, the silicon discharge capacity use range of the silicon-based negative electrode is 35% or less of the total negative electrode discharge capacity, the upper end of the silicon discharge capacity of the silicon-based negative electrode is 57% or less, and the lower end is 13% or more, and a lithium secondary battery is provided.

Effects of the Invention

[0017] The lithium secondary battery according to the present application applies a prelithiation process to the silicon-based negative electrode or the positive electrode, and when using the silicon-based negative electrode, restricts the total discharge capacity use range, specifically, controls the upper end and the lower end of the discharge capacity, which is the main feature.

[0018] Thereby, it is possible to produce a battery that can achieve high capacitance and high energy density, which are advantages when using a silicon-based negative electrode, and also has a feature of solving the problem of deterioration of life performance due to volume expansion when repeating the cycle, which is a conventional problem.

[0019] That is, the lithium secondary battery according to the present application is mainly characterized in that the use area of silicon contained in the negative electrode is restricted to ensure the life performance of the lithium secondary battery.

Brief Description of the Drawings

[0020]

Figure 1

Embodiments for Carrying Out the Invention

[0021] Before explaining the present invention, first, several terms are defined.

[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, "p to q" means "p or more and q or less".

[0024] In this specification, the "specific surface area" is measured by the BET method. Specifically, it is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan. That is, in the present application, the BET specific surface area can mean the specific surface area measured by the above measurement method.

[0025] In this specification, "Dn" means the particle size distribution and refers to 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.

[0026] 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 it is said that a polymer contains a monomer, this is interpreted to be the same as the polymer containing the monomer in monomer units.

[0027] In this specification, the term "polymer" is understood to be used in a broad sense including copolymers unless otherwise specified as "homopolymer".

[0028] 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 standard substances. In this specification, unless otherwise specified, the molecular weight means the weight average molecular weight.

[0029] Hereinafter, for those with ordinary knowledge in the technical field to which the present invention belongs 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.

[0030] One embodiment of the present specification is a lithium secondary battery including a silicon-based negative electrode, a positive electrode, a separator, and an electrolyte, wherein the positive electrode or the silicon-based negative electrode is a pre-lithiated electrode, and the silicon discharge capacity usage range of the silicon-based negative electrode is 35% or less of the total negative electrode discharge capacity, and the upper end of the silicon discharge capacity of the silicon-based negative electrode is 57% or less, and the lower end is 13% or more, and a lithium secondary battery is provided.

[0031] This application can produce a battery capable of achieving high capacity and high energy density, which are advantages when using a silicon-based negative electrode, and also has the feature of solving the problem of deterioration of life performance due to volume expansion during repeated cycling, which is a conventional problem. That is, the lithium secondary battery according to this application is mainly characterized in that the use area of silicon contained in the negative electrode is limited to ensure the life performance of the lithium secondary battery.

[0032] FIG. 1 is a diagram showing a 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 a negative electrode current collector layer 10, and a positive electrode 200 including a positive electrode active material layer 40 can be confirmed on one surface of a 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] In one embodiment of the present application, a lithium secondary battery is provided, wherein the silicon discharge capacity usage range of the silicon-based negative electrode is 35% or less of the total negative electrode discharge capacity, and the upper end of the silicon discharge capacity of the silicon-based negative electrode is 57% or less, and the lower end is 13% or more.

[0034] In one embodiment of the present application, a lithium secondary battery is provided, wherein the NP ratio of the lithium secondary battery is 170% or more and 280% or less.

[0035] In one embodiment of the present application, the NP ratio can satisfy the following formula A.

[0036] [Formula A] N / P ratio = Discharge capacity per unit area of the negative electrode / Discharge capacity per unit area of the positive electrode.

[0037] In the present invention, the "discharge capacity per unit area" means the discharge capacity per unit area in the first cycle of the negative electrode or the positive electrode.

[0038] The discharge capacity per unit area of the negative electrode is obtained by the following method. Specifically, a half-cell is manufactured using a negative electrode sample containing a negative electrode active material and a counter electrode (for example, a lithium metal electrode) facing the negative electrode sample. The discharge capacity measured by charging and discharging the half-cell is divided by the weight of the negative electrode active material to obtain the "discharge capacity of the negative electrode sample per unit weight of the negative electrode active material". A secondary battery is manufactured using a negative electrode containing the same negative electrode active material as that used in the half-cell and a positive electrode containing a positive electrode active material. The "discharge capacity of the negative electrode sample per unit weight of the negative electrode active material" is multiplied by the weight of the negative electrode active material contained in the secondary battery, and this is divided by the area of the negative electrode contained in the secondary battery to obtain the discharge capacity per unit area of the negative electrode.

[0039] The discharge capacity per unit area of the positive electrode is obtained by the following method. Specifically, a half-cell is manufactured using a positive electrode sample containing a positive electrode active material and a counter electrode (for example, a lithium metal electrode) facing the positive electrode sample. The discharge capacity measured by charging and discharging the half-cell is divided by the weight of the positive electrode active material to obtain the "discharge capacity of the positive electrode sample per unit weight of the positive electrode active material". A secondary battery is manufactured using a positive electrode containing the same positive electrode active material as that used in the half-cell and a negative electrode containing a negative electrode active material. The "discharge capacity of the positive electrode sample per unit weight of the positive electrode active material" is multiplied by the weight of the positive electrode active material contained in the secondary battery, and this is divided by the area of the positive electrode contained in the secondary battery to obtain the discharge capacity per unit area of the positive electrode.

[0040] The lithium secondary battery according to the present application is characterized in that a pre-lithiation process is introduced into the positive electrode or the negative electrode, and the NP ratio is adjusted to limit the USOC of the negative electrode for application.

[0041] In this application, the upper and lower ends of the discharge capacity mean the upper and lower end values of the discharge reference active Li in terms of the total amount carried by the negative electrode, calculated as percentage values based on USOC, and may also be values calculated from the amount carried by the positive electrode, the initial efficiency, and the initial efficiency of the negative electrode.

[0042] In one embodiment of this application, a lithium secondary battery is provided, wherein the upper end of the silicon discharge capacity of the silicon-based negative electrode is 45% or more and 57% or less, and the lower end of the silicon discharge capacity of the silicon-based negative electrode is 13% or more and 28% or less.

[0043] In another embodiment, the upper end of the silicon discharge capacity of the silicon-based negative electrode may be 45% or more and 57% or less, preferably 46% or more and 53% or less, and more preferably 48% or more and 52% or less.

[0044] In another embodiment, the lower end of the silicon discharge capacity of the silicon-based negative electrode may satisfy 13% or more and 28% or less, preferably 14% or more and 25% or less, and more preferably 16% or more and 24.5% or less.

[0045] In one embodiment of this application, a lithium secondary battery is provided, wherein the difference between the upper and lower ends of the silicon discharge capacity is less than 35%.

[0046] That is, the difference between the upper and lower ends of the silicon discharge capacity may be represented by △Si, which may mean the capacity range used in the silicon-based negative electrode.

[0047] In another embodiment, the difference between the upper and lower ends of the silicon discharge capacity may be less than 35%, preferably 34.8% or less, and more preferably 34.5% or less, and may also satisfy 20% or more, preferably 25% or more.

[0048] That is, as described above, the usable range of the negative electrode can be adjusted as described above by the N / P ratio and pre-lithiation, and thus, while maintaining the characteristics of the silicon-based negative electrode as they are, it is possible to secure the life characteristics.

[0049] In one embodiment of the present application, the silicon-based negative electrode or positive electrode may be a pre-lithiated electrode. Pre-lithiation means pre-supplying lithium to the electrode, and all methods used in the art such as a transfer process, an electrochemical process, and an SLMP process can be applied.

[0050] Hereinafter, the positive electrode, negative electrode, electrolyte, and separator included in the lithium secondary battery will be described respectively.

[0051] 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 composition provided on one or both surfaces of the negative electrode current collector layer, and may include a negative electrode active material layer.

[0052] 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 a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, a surface-treated product of copper or stainless steel with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. may be used. Further, 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 a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric body.

[0053] However, the thickness may be variously deformed according to the type and use of the negative electrode used, and is not limited thereto.

[0054] 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.

[0055] In one embodiment of the present application, the negative electrode active material layer contains a negative electrode active material layer composition, and the negative electrode active material layer composition may contain one or more selected from the group consisting of a silicon-based active material, a negative electrode conductive material, and a negative electrode binder.

[0056] In one embodiment of the present application, the negative electrode active material layer contains a negative electrode active material layer composition, and the negative electrode active material layer composition may contain a silicon-based active material, a negative electrode conductive material, and a negative electrode binder.

[0057] In one embodiment of the present application, the silicon-based active material may contain one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys.

[0058] In one embodiment of the present application, the silicon-based active material contains 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 contain 70 parts by weight or more.

[0059] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may contain 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0060] In one embodiment of the present application, particularly pure silicon (Si) may be used as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material means that, as described above, when the silicon-based active material is based on 100 parts by weight in total, it contains pure Si particles (SiOx (x = 0)) that are not combined with other particles or elements within the above range.

[0061] On the one 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 is reduced by the composite composed of the conductive material and the binder in the negative electrode slurry, so the possibility of the conductive network being disconnected is increased, and the capacity retention rate is reduced. 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 is reduced. As a result, the capacity retention rate of the battery is reduced.

[0062] In one embodiment of the present application, the silicon-based active material has a BET specific surface area that is typical and specific. 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 in accordance with DIN 66131 (using nitrogen).

[0063] In one embodiment of the present application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or multi-piece particles. Alternatively, the silicon particles may have a fibrous structure, or may exist in the form of a silicon-containing film or coating, but this is not very preferred.

[0064] In one embodiment of the present application, the negative electrode 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.

[0065] 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.

[0066] 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.

[0067] The negative electrode active material layer composition according to the present application uses a silicon-based active material with a significantly high capacity within the above range, and 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 within the above range, the performance of the negative electrode is not deteriorated, and it has the characteristic of excellent output characteristics during charging and discharging.

[0068] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape, 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.

[0069] In the present application, the sphericity is determined by the following formula (1), where A is the area and P is the boundary line.

[0070] [Formula 1] 4πA / P 2

[0071] 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 rather degrading the performance of the battery.

[0072] 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 plays a role of securing a conductive path, and the binder plays a role of being able to control such a negative electrode conductive material during charge and discharge.

[0073] 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.

[0074] In one embodiment of the present application, the dot-shaped conductive material can be used to improve the conductivity of the negative electrode, and forms conductivity without inducing a chemical change, and its form means a circular or dot-shaped conductive material. 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.

[0075] 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.

[0076] In one embodiment of the present application, the particle size of the dot-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 40 nm to 60 nm.

[0077] In one embodiment of the present application, the negative electrode conductive material may include a planar conductive material.

[0078] 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.

[0079] 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.

[0080] 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 equipment and time, the dispersion effect is excellent.

[0081] 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.

[0082] In one embodiment of the present application, the planar conductive material may be a high specific surface area planar conductive material having a high BET specific surface area; or a low specific surface area planar conductive material.

[0083] 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, in particular, the planar conductive material according to the present application may be affected to some extent by the dispersion on the electrode performance, and it is particularly preferable to use a low specific surface area planar conductive material that does not cause problems in dispersion.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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 225 m or more per g 2 It may satisfy the range of 25 m or less per g.

[0088] In addition, as the conductive material, there may be a linear conductive material such as a carbon nanotube. The carbon nanotube may be a bundled carbon nanotube. The bundled carbon nanotube may include a plurality of carbon nanotube unit bodies. Specifically, here, the "bundle type" refers to a bundle or rope-like secondary shape in which a plurality of carbon nanotube unit bodies are arranged in parallel with substantially the same orientation of the longitudinal axis of the carbon nanotube unit body, or are intertwined, unless otherwise mentioned. The carbon nanotube unit body 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 around which the graphite sheet is wound, it can exhibit the characteristics of a conductor or a semiconductor. The bundled carbon nanotube can be uniformly dispersed during the production of the negative electrode compared to the entangled type carbon nanotube, and a conductive network can be smoothly formed in the negative electrode, improving the conductivity of the negative electrode.

[0089] In one embodiment of the present application, the negative electrode conductive material includes a linear conductive material, and the linear conductive material may be a carbon nanotube.

[0090] In one embodiment of the present application, the carbon nanotube 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.

[0091] 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.

[0092] In another embodiment, the negative electrode conductive material may contain 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.

[0093] 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.

[0094] 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 composition and ratio, it does not significantly affect the life characteristics of conventional lithium secondary batteries, and there are many points where charging and discharging are possible, and it has the characteristic of excellent output characteristics at a high C-rate.

[0095] 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 contact points between silicon-based active materials with 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 its configuration and role are completely different from those of the negative electrode conductive material of the present invention.

[0096] Also, the negative electrode conductive material according to the present application is applied to silicon-based active materials and has a completely different configuration from the conductive material applied to graphite-based active materials. That is, the conductive material used for an electrode having a graphite-based active material simply has smaller particles than the active material, and thus has the characteristics of improving output characteristics and imparting partial conductivity, and is completely different in configuration and role from the negative electrode conductive material applied together with silicon-based active materials as in the present invention.

[0097] In one embodiment of the present application, the plate-shaped conductive material used as the aforementioned negative electrode conductive material has 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.

[0098] On the other hand, the plate-shaped conductive material used as the negative electrode conductive material is a material having a surface or plate-like form and can be represented by plate-shaped graphite. That is, it is a material included to maintain a conductive path within the negative electrode active material layer, and means a material for securing a conductive path in a surface form inside the negative electrode active material layer that does not play a role in the storage and release of lithium.

[0099] That is, in the present application, the fact that plate-shaped graphite is used as the conductive material means that it is used as a material processed into a planar or plate-like form to secure a conductive path that does not play 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.

[0100] 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 used as a material processed into a dot-like or spherical form to play a role in storing or releasing lithium.

[0101] In one embodiment of the present application, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, 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, poly acrylic acid, and substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0102] 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 twist 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, ordinary negative electrode binders can all be applied. Specifically, an aqueous binder may be used, and more specifically, a PAM-based binder may be used.

[0103] In one embodiment of the present application, based on 100 parts by weight of the negative electrode active material layer composition, it may include 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less of the negative electrode binder, and may also include 5 parts by weight or more, 8 parts by weight or more.

[0104] Compared with conventional carbon-based negative electrodes, 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.

[0105] 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.

[0106] In one embodiment of the present application, the negative electrode slurry may contain a negative electrode active material layer composition and a slurry solvent.

[0107] In one embodiment of the present application, the solid content of the negative electrode slurry may satisfy 5% or more and 40% or less.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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, it has the characteristic that 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.

[0112] In one embodiment of the present application, the slurry solvent may be used without limitation as long as it can disperse the negative electrode composition, and specifically, water or NMP may be used.

[0113] 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.

[0114] 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.

[0115] 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 appropriate ranges.

[0116] 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.

[0117] 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 positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

[0118] 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 surface-treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Further, the positive electrode current collector layer may usually have a thickness of 1 to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector layer to increase the adhesive force with 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.

[0119] Provided is a lithium secondary battery in which, in one embodiment of the present application, the thicknesses of the positive electrode and negative electrode current collector layers are 1 μm or more and 100 μm or less, and the thicknesses of the positive electrode and negative electrode active material layers are 20 μm or more and 500 μm or less.

[0120] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is 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 may contain one or more selected from the group consisting of these. Here, the positive electrode active material is not limited to only these.

[0121] Specifically, as the positive electrode active material, commonly used NCM or NCMA may be used.

[0122] Generally, the positive electrode active material includes layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), and compounds substituted with one or more transition metals; lithium iron oxides such as LiFe3O4; chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 Mc2O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.6) of Ni-site type lithium nickel oxide; chemical formula LiMn 2-c3 M c3O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≦ c3 ≦ 0.6) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn), and lithium manganese composite oxides represented thereby; examples include LiMn2O4 in which a part of Li in the chemical formula is substituted with an alkaline earth metal ion, but are not limited thereto. The positive electrode may be Li-metal.

[0123] In one embodiment of the present application, the positive electrode active material contains a lithium composite transition metal containing nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal contains single particles or secondary particles, and the average particle diameter (D50) of the single particles may be 1 μm or more.

[0124] For example, the average particle diameter (D50) of the single particles may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, more than 1 μm and 12 μm or less, more than 1 μm and 8 μm or less, or more than 1 μm and 6 μm.

[0125] The single particles may be formed into small particle sizes with an average particle diameter (D50) of 1 μm or more and 12 μm or less, and may have excellent particle strength. For example, when the single particles are rolled with a force of 650 kgf / cm 2 they can have a particle strength of 100 MPa to 300 MPa. Thereby, 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 are improved.

[0126] The single particles can be manufactured by mixing and firing a transition metal precursor and a lithium raw material substance. The secondary particles may be manufactured 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.

[0127] The method for forming the single particles is not particularly limited. Generally, it may be formed by raising the firing temperature and over-firing, or by using additives such as a particle growth promoter useful for over-firing, or by changing the starting material, etc.

[0128] For example, the firing is carried out at a temperature capable of forming single particles. To form this, firing needs to be carried out at a higher temperature than when producing secondary particles. For example, when the composition of the precursor is the same, firing needs to be carried out at a temperature about 30°C to 100°C higher than when producing secondary particles. The firing temperature for forming the single particles may vary depending on the metal composition 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 700°C to 1000°C, preferably 800°C to 950°C. When the firing temperature satisfies the above range, a positive electrode active material containing single particles with excellent electrochemical properties can be produced. When the firing temperature is less than 790°C, a positive electrode active material containing a lithium composite transition metal in the form of secondary particles can be produced. When it exceeds 950°C, firing is carried out excessively, and there is a risk that the layered crystal structure cannot be properly formed and the electrochemical properties are deteriorated.

[0129] 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 is a concept including a single particle composed of one primary particle and an aggregate of 30 or fewer primary particles in a similar-single particle form.

[0130] Specifically, in the present invention, the single particle may be a single particle composed of one primary particle or a similar-single particle form 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.

[0131] In one embodiment of the present application, the lithium composite transition metal as the positive electrode active material further includes secondary particles, and the average particle diameter (D50) of the single particles is smaller than the average particle diameter (D50) of the secondary particles.

[0132] In the present invention, the single particle may be a single particle composed of one primary particle or an aggregated form of 30 or fewer primary particles in a similar-single particle form, and the secondary particle may be a form in which several hundreds of primary particles are aggregated.

[0133] The aforementioned lithium composite transition metal may further include 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 a single primary particle, a single particle, or an aggregated form of 30 or fewer primary particles in a similar-single particle form.

[0134] The particle size (D50) of the secondary particles may be 1 μm to 20 μm, 2 μm to 17 μm, preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles may be 0.05 m 2 / g 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.

[0135] In an additional embodiment of the present application, the secondary particles are aggregates of primary particles, and the average particle size (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be a form in which several hundreds of primary particles are aggregated, and the average particle size (D50) of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0136] When the average particle size (D50) of the primary particles satisfies the above range, a single-particle cathode active material excellent in electrochemical characteristics can be formed. If the average particle size (D50) of the primary particles is too small, the number of aggregated primary particles forming the lithium nickel-based oxide particles increases, and the effect of suppressing particle cracking during rolling decreases. If the average particle size (D50) of the primary particles is too large, the lithium diffusion path inside the primary particles becomes long, the resistance increases, and the output characteristics may deteriorate.

[0137] According to an additional embodiment of the present application, the average particle size (D50) of the single particles is characterized by being smaller than the average particle size (D50) of the secondary particles. Thereby, even if the single particles are formed with a small particle size, their particle strength may be excellent, whereby the phenomenon of an increase in fine particles in the electrode due to particle cracking is alleviated, and the life characteristics of the battery can be improved.

[0138] In one embodiment of the present application, the average particle size (D50) of the single particles is 1 μm to 18 μm smaller than the average particle size (D50) of the secondary particles.

[0139] For example, the average particle size (D50) of the single particles may be 1 μm to 16 μm smaller than the average particle size (D50) of the secondary particles, may be 1.5 μm to 15 μm smaller, or may be 2 μm to 14 μm smaller.

[0140] When the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles, for example, when satisfying the above range, even if the single particles are formed with a small particle size, their particle strength is excellent, whereby the phenomenon of an increase in fine particles in the electrode due to particle cracking is alleviated, and there are effects of improving the life characteristics and energy density of the battery.

[0141] According to an additional embodiment of the present application, 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 cathode 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 cathode active material.

[0142] 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, based on 100 parts by weight of the positive electrode active material. The single particles may be contained in an amount of 100 parts by weight or less, based on 100 parts by weight of the positive electrode active material.

[0143] When the single particles within the above range are included, excellent battery characteristics can be exhibited in combination with the negative electrode material described above. 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 particle cracking during the rolling process after the production of the electrode can be alleviated, and the life characteristics of the battery can be improved.

[0144] In one embodiment of the present application, the lithium composite transition metal compound may further include secondary particles, and the secondary particles may be 85 parts by weight or less, 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, or 70 parts by weight or less, based on 100 parts by weight of the positive electrode active material. The secondary particles may be 0 parts by weight or more, based on 100 parts by weight of the positive electrode active material.

[0145] 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 positive electrode active material includes secondary particles, the components thereof may be the same as those exemplified by the above-described single-particle positive electrode active material, or may be different, and the single-particle form may mean an aggregated form.

[0146] In one embodiment of the present application, the positive electrode active material in 100 parts by weight of the positive electrode active material layer 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 98 parts by weight or more and 99.9 parts by weight or less.

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

[0148] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the configured battery, 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] In addition, the positive electrode binder plays a role in improving the adhesion between the 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.

[0150] As the separation membrane, it separates the negative electrode and the positive electrode and provides a migration path for lithium ions. It can be used without particular limitation as long as it is usually used as a separation membrane 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 homopolymer of ethylene, a homopolymer of propylene, 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, a coated separation membrane containing a ceramic component or a polymer substance may be used to ensure heat resistance or mechanical strength, and optionally, it may be used in a single-layer or multi-layer structure.

[0151] In the present application, 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.

[0152] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0153] 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.

[0154] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and can well dissociate lithium salts, so they can be preferably used. If such cyclic carbonates are mixed with linear carbonates such as dimethyl carbonate and diethyl carbonate having low viscosity and low dielectric constant in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, so they can be more preferably used.

[0155] The metal salt may be a lithium salt. 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 - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0156] 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 for the purpose of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, improving the discharge capacity of the battery, etc.

[0157] 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 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.

[0158] [Examples] Hereinafter, in order to facilitate understanding of the present invention, preferred embodiments are presented. However, these embodiments are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications can be made within the scope of the description and the scope of the technical idea. It is natural that such variations and modifications belong to the scope of the claims. [Production Example]

[0159] (1) Production of negative electrode Production of negative electrode active material layer As the silicon-based active material, a negative electrode active material layer composition was prepared with Si (average particle size (D50): 5 μm), a first conductive material, a second conductive material, and polyacrylamide as a binder at a weight ratio of 80:9.6:0.4:10. It was added to distilled water as a solvent for forming the negative electrode slurry to produce a negative electrode slurry (solid content concentration: 28% by weight).

[0160] 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 nanotube.

[0161] 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, and then the active material was added. Thereafter, it was dispersed at 2500 rpm for 30 minutes to produce a slurry.

[0162] The negative electrode slurry was coated on both sides of a copper current collector (thickness: 15 μm) as a negative electrode 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 a negative electrode active material layer (thickness: 23 μm).

[0163] (2) Production of positive electrode As the positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2O2 (average particle size (D50): 15 μm), carbon black as the conductive material (product name: Super C65, manufacturer: Timcal), polyvinylidene fluoride as the binder, and N-methyl-2-pyrrolidone (NMP) as the solvent for forming the positive electrode slurry were added in a weight ratio of 97:1.5:1.5 to produce a positive electrode slurry (solid content concentration: 78 wt%).

[0164] The positive electrode slurry was coated on both sides of an aluminum current collector (thickness: 12 μm) as the positive electrode current collector at a loading of 537 mg / 25 cm 2 and rolled (roll press), and then dried in a vacuum oven at 130 °C for 10 hours to form a positive electrode active material layer (thickness: 65 μm) to produce a positive electrode (thickness of the positive electrode: 77 μm, porosity: 26%).

[0165] An electrolyte was injected with a polyethylene separator interposed between the positive electrode and the negative electrode to produce a lithium secondary battery shown in Table 1 below.

[0166]

Table 1

[0167] The method for manufacturing the pre-lithiated applicable electrode in Table 1 above was as follows.

[0168] <Transfer method pre-lithiation> Lithium metal was deposited on the upper part of the PET substrate by PVD method at the thickness level (pre-lithiation dosage) shown in Table 1 on the upper part of the PET (PET with a release layer coating on one side, ionefilm, thickness 20 μm to 50 μm) layer where the release layer was coated to produce a transfer laminate, and the lithium metal layer was transferred onto the electrode shown in Table 1 to perform pre-lithiation.

[0169] Experimental Example 1: Life performance 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 charger / discharger, and the capacity retention rate was evaluated. The secondary batteries were subjected to a cycle test at 4.2 - 3.2 V and 1C / 0.5C, and the number of cycles at which the capacity retention rate reached 80% was measured and shown in Table 2 below.

[0170] Retention rate of life (%) = {(Discharge capacity at the Nth cycle) / (Discharge capacity at the first cycle)} × 100

[0171] Experimental Example 2: Measurement and evaluation of resistance increase rate When testing in Experimental Example 1, charge / discharge was carried out at 0.33C / 0.33C (4.2 - 3.0V) every 50 cycles, and after measuring the capacity retention rate, discharge was carried out at 2.5C pulse at SOC50 to measure the resistance, and the resistance increase rate was compared and analyzed.

[0172] Regarding the measurement and evaluation of the resistance increase rate, the data at 600 cycles were calculated respectively, and the results are shown in Table 2 below.

[0173]

Table 2

[0174] As can be seen from Table 1 and Table 2 above, the lithium secondary battery according to the Example, when using a silicon-based negative electrode with a specific amount of pre-lithiation on the positive electrode or the negative electrode, restricts the full discharge capacity usage range, specifically, it was confirmed that the main feature is that the upper and lower ends of the discharge capacity were controlled.

[0175] Thereby, it was confirmed that a battery capable of achieving high capacity and high energy density, which are advantages when using a silicon-based negative electrode, can be produced, and it has the feature of solving the problems of deterioration of life performance and increase in resistance due to volume expansion during repeated cycling, which are conventional problems.

[0176] That is, the lithium secondary battery according to the present application is mainly characterized in that the use area of silicon contained in the negative electrode is restricted to ensure the life performance of the lithium secondary battery.

[0177] In the case of Comparative Example 1, when pre-lithiation is not applied to the positive electrode or the negative electrode, the NP ratio range is also formed low, and all the upper end and the lower end are used deeply. It was confirmed that the degradation of the life performance of lithium due to charge and discharge becomes serious, and it was confirmed that the increase rate of resistance is high.

[0178] In the cases of Comparative Example 2 and Comparative Example 3, pre-lithiation was performed, but pre-lithiation was performed to such an extent that the capacities of the upper end and the lower end of the present invention were not satisfied. Specifically, in the case of Comparative Example 3, the upper end range of the negative electrode capacity exceeds the range according to the present application, and in the case of Comparative Example 3, the lower end range of the negative electrode capacity corresponds to less than the range according to the present application. Also in this case, it was confirmed that the performance does not deteriorate as much as in Comparative Example 1, but the life performance due to the volume expansion of the negative electrode is deteriorated as compared with Examples 1 to 3.

Explanation 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 silicon-based negative electrode; a positive electrode; a separator; and an electrolyte, wherein the positive electrode or the silicon-based negative electrode is a pre-lithiated electrode, the range of silicon discharge capacity of the silicon-based negative electrode is 35% or less of the total negative electrode discharge capacity, a lithium secondary battery, wherein the upper end of the silicon discharge capacity of the silicon-based negative electrode is 57% or less and the lower end is 13% or more.

2. The lithium secondary battery according to Claim 1, wherein the NP ratio of the lithium secondary battery is 170% or more and 280% or less.

3. The lithium secondary battery according to Claim 1, wherein the difference between the upper end and the lower end of the silicon discharge capacity is less than 35%.

4. The lithium secondary battery according to Claim 1, wherein the upper end of the silicon discharge capacity of the silicon-based negative electrode is 45% or more and 57% or less, and the lower end of the silicon discharge capacity of the silicon-based negative electrode is 13% or more and 28% or less.

5. The silicon-based negative electrode includes a negative electrode current collector layer and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer, the positive electrode includes a positive electrode current collector layer and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector layer, the negative electrode active material layer composition includes a silicon-based active material, a negative electrode conductive material, and a negative electrode binder, 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 any one of Claims 1 to 4.

6. The lithium secondary battery according to Claim 5, wherein 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.

7. The positive electrode active material layer composition includes a positive electrode active material, The positive electrode active material is 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 5, comprising one or more selected from the group consisting of.

8. the thicknesses of the positive electrode and the negative electrode current collector layers are 1 μm or more and 100 μm or less, and the thicknesses of the positive electrode and the negative electrode active material layers are 20 μm or more and 500 μm or less. The lithium secondary battery according to Claim 5.

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