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. 10-2022-0186045, filed with the Korean Intellectual Property Office on December 26, 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 fields of power generation and power 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 usage area is showing an increasing trend. [[ID=2I]]

[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 contains a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode. Although carbon-based materials such as graphite as a negative electrode material are excellent in stability and reversibility, they have limitations in terms of capacity, and 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 or LiMn2O4, 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 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 the SEI cannot return to the positive electrode during the subsequent discharging process and reduces 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, the movement speed of lithium ions needs to be fast during the process of lithium ions being inserted into the negative electrode. Therefore, a battery design is being 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 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, due to the efficiency reduction of the positive electrode with a high content (High) Ni, which is the material of the positive electrode, an excessive sacrificial positive electrode material is applied to balance with the negative electrode. In this case, an increase in the amount of gas in the battery cell itself and the resulting stability problems occur.

[0010] Ultimately, in order to achieve volumetric characteristics, high energy density, and rapid charging performance, for a lithium battery that uses a silicon-based negative electrode and, as the positive electrode, which is the counter electrode for this, uses a NCMA-based or NCM-based positive electrode with a high nickel content, in order to improve the performance, it is necessary to study the efficiency relationship and area relationship between the positive electrode and the negative electrode without using the section that involves volume changes during charge and discharge.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] As a result of research on the above-mentioned problems, while ensuring volumetric characteristics and rapid charging performance by using a silicon-based negative electrode, using an NCM(A)-based active material as the positive electrode, and in particular, adjusting the initial efficiency between the positive electrode and the negative electrode, it was confirmed that by adjusting the differences in area, total width, and total length between the positive electrode and the negative electrode, it becomes possible to avoid using the space that involves the rapid volume change of the silicon-based negative electrode during discharge.

[0013] Therefore, the present application relates to a lithium secondary battery in which the area ratio and initial efficiency of the positive electrode and the negative electrode are adjusted.

Means for Solving the Problems

[0014] One embodiment of this 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 sides 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 sides 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 is SiOx (x = 0), SiO x Comprising one or more selected from the group consisting of (0 < x < 2), SiC, and Si alloys, the initial efficiency of the silicon-based negative electrode is 0.2% or more and 4% or less higher than that of the positive electrode, and the area ratio of the positive electrode active material layer to the negative electrode active material layer satisfies 1:1.02 or more and 1:1.1 or less. The total width of the silicon-based negative electrode is 1 mm or more compared to the total width of the positive electrode, and the total length of the silicon-based negative electrode is 2.5 mm or more longer than the total length of the positive electrode, showing an asymmetric dimensional difference. A lithium secondary battery is provided.

Advantages of the Invention

[0015] 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.

[0016] In particular, by adjusting the initial efficiency between the positive electrode and the negative electrode and adjusting the differences in area, total width, and total length between the positive electrode and the negative electrode, it is possible to adjust so as not to use the section accompanied by a rapid volume change of the silicon-based negative electrode during the discharge process, and it has the feature of being able to improve the cycle performance of the lithium secondary battery.

[0017] That is, when using a silicon-based active material (especially, Pure Si active material), it has the advantage of being able to ensure high capacity characteristics and energy density. However, compared with conventional carbon-based active materials, when charging and discharging, there is a problem that the cycle performance deteriorates due to volume expansion of the negative electrode caused by lithium migration. However, the lithium secondary battery according to the present application, as described above, can solve the problem by adjusting the above-mentioned ratio even when applying a negative electrode using a silicon-based active material, and thus has the feature of ensuring the life performance.

[0018] Ultimately, by adjusting the conditions as described above to limit the rapid volume change interval of the silicon-based active material, the particle cracking of pure silicon can be minimized, the decomposition of the additional electrolyte can be controlled, the reversible Li loss and the conductive network between the Si active materials can be maintained, the amount of isolated lithium can be controlled, and the cycle performance improvement effect can be achieved.

Brief Description of the Drawings

[0019]

Figure 1

Embodiments 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 stated, 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 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.

[0024] In this specification, "Dn" means the particle size distribution and represents 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 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.

[0026] In this specification, the term "polymer" is understood to be 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 belongs 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 this 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, and the silicon-based active material includes SiO x (x = 0), SiO x (0 < x < 2), SiC, and one or more selected from the group consisting of Si alloys. The initial efficiency of the silicon-based negative electrode is 0.2% or more and 4% or less higher than that of the positive electrode. The area ratio of the positive electrode active material layer to the negative electrode active material layer satisfies 1:1.02 or more and 1:1.1 or less. The total width of the silicon-based negative electrode is 1 mm or more compared to the total width of the positive electrode, and the total length of the silicon-based negative electrode is 2.5 mm or more longer than the total length of the positive electrode, showing an asymmetric dimensional difference. A lithium secondary battery is provided.

[0030] When using a silicon-based active material (especially a pure silicon (Pure Si) active material), it has the advantage of being able to ensure high capacity characteristics and energy density. However, compared with conventional carbon-based active materials, when charging and discharging, there is a problem that the cycle performance deteriorates due to volume expansion of the negative electrode caused by lithium migration. However, as described above, the lithium secondary battery according to the present application has the feature that even when applying a negative electrode using a silicon-based active material, the problem is solved by adjusting the above-mentioned ratio, and thereby the life performance is also ensured.

[0031] FIG. 1 is a diagram showing a stacked 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, indicating that the negative electrode 100 and the positive electrode 200 for the lithium secondary battery are stacked with a separator 30 interposed therebetween.

[0032] In one embodiment of the present application, there is provided a lithium secondary battery in which the initial efficiency of the silicon-based negative electrode is 0.2% or more and 4% or less higher than that of the positive electrode.

[0033] In the present application, the method for measuring the initial efficiency of the positive electrode is as follows. After manufacturing a lithium coin half-cell with the positive electrode according to the present application as the working electrode and a counter electrode, this is charged at a constant current with a current density of 0.45 mAh / cm 2 (or 0.2C or less) or less until it reaches 4.3V, and the charging is terminated when the current density reaches 1 / 10 of the constant current at a constant voltage. This is defined as 1 st charging capacity. After a 1-hour rest, it is discharged again at a constant current of 0.45 mAh / cm 2 (or 0.2C or less) or less, and when it reaches 3.0V, the capacity is defined as 1 st discharge capacity. At this time, the initial efficiency of the positive electrode is 1 st discharge capacity / 1 st charging capacity × 100 (%).

[0034] In the present application, the method for measuring the initial efficiency of the negative electrode is as follows. After manufacturing a lithium coin half-cell with the negative electrode according to the present application as the working electrode and a counter electrode, this is discharged at a constant current with a current density of 0.45 mAh / cm 2 (or 0.2C or less) or less until it reaches 0.005V, and the discharging is terminated when the current density reaches 1 / 20 of the constant current at a constant voltage. This is defined as 1 st discharge capacity. After a 1-hour rest, it is charged again at a constant current of 0.45 mAh / cm 2 (or 0.2C or less) or less, and when it reaches 1.5V, the capacity is defined as 1 st charging capacity. At this time, the initial efficiency of the negative electrode is 1 stCharge capacity / 1 st It is calculated by Discharge capacity × 100 (%).

[0035] In one embodiment of the present application, the area ratio of the positive electrode active material layer to the negative electrode active material layer satisfies 1:1.02 or more and 1:1.1 or less, the total width of the silicon-based negative electrode is 1 mm or more compared to the total width of the positive electrode, and the total length of the silicon-based negative electrode is 2.5 mm or more compared to the total length of the positive electrode, showing an asymmetric dimensional difference that is long. A lithium secondary battery is provided.

[0036] In one embodiment of the present application, the area ratio of the positive electrode active material layer to the negative electrode active material layer satisfies 1:1.02 or more and 1:1.1 or less, the total width of the silicon-based negative electrode is 1 mm or more compared to the total width of the positive electrode, preferably 1.5 mm or more, and may be 10 mm or less, preferably 5 mm or less, showing an asymmetric dimensional difference.

[0037] In one embodiment of the present application, the area ratio of the positive electrode active material layer to the negative electrode active material layer satisfies 1:1.02 or more and 1:1.1 or less, the total length of the silicon-based negative electrode is 2.5 mm or more compared to the total length of the positive electrode, may be 2.7 mm or more, and may be 15 mm or less, preferably 8 mm or less, and specifically, may show an asymmetric dimensional difference of 5 mm or less.

[0038] In the present application, a lithium secondary battery is provided in which the total width of the silicon-based negative electrode is 1% or more based on the total width of the positive electrode, and the total length of the silicon-based negative electrode is 2% or more based on the total length of the positive electrode, showing an asymmetric dimensional difference that is long.

[0039] In another embodiment, a lithium secondary battery is provided in which the total width of the silicon-based negative electrode is 1% or more and 10% or less based on the total width of the positive electrode, and the total length of the silicon-based negative electrode is 2% or more and 15% or less based on the total length of the positive electrode, showing an asymmetric dimensional difference that is long.

[0040] In yet another embodiment, the total width of the silicon-based negative electrode may be 1% or more and 10% or less, or 1% or more and 8% or less based on the total width of the positive electrode, and the total length of the silicon-based negative electrode may be 2% or more and 15% or less, or 2% or more and 10% or less based on the total length of the positive electrode.

[0041] When the above range is satisfied, the irreversible capacity of the negative electrode relative to the positive electrode is compatible, and the negative electrode can be used in a restricted manner. Also, the cell expressed capacity is compatible, and it has the characteristic of being excellent in the improvement effect on the SOC limited cycle performance. That is, for a lithium secondary battery, when the area ratio of the positive electrode active material layer to the negative electrode active material layer corresponds to less than the above range, the irreversible capacity of the negative electrode relative to the positive electrode becomes large, and there is no effect of restricting the use of the negative electrode. When used exceeding the above range, the cell expressed capacity decreases, and no improvement effect appears on the SOC limited cycle performance.

[0042] In one embodiment of the present application, the total width may mean the length in the MD (Machine Direction) direction, and the total length may mean the length in the TD direction.

[0043] Hereinafter, the positive electrode, negative electrode, electrolyte, and separator included in the lithium secondary battery will be described respectively.

[0044] 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.

[0045] 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 bodies, etc.

[0046] However, the thickness may vary diversely according to the type and application of the negative electrode used, and is not limited thereto.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] In one embodiment of the present application, the silicon-based active material is SiO x (x = 0), SiO x (0 < x < 2), SiC, and one or more selected from the group consisting of Si alloys may be included.

[0051] In one embodiment of the present application, the silicon-based active material is SiO x (x = 0), SiO xIt contains one or more selected from the group consisting of (0 < x < 2) and metal impurities, and based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may be contained in an amount of 70 parts by weight or more.

[0052] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may be contained in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be contained in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0053] In one embodiment of the present application, as the silicon-based active material, particularly pure silicon (Si) may be used. 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, pure Si particles (SiO x (x = 0)) not combined with other particles or elements are contained within the above range.

[0054] On the other hand, the average particle size (D50) of the silicon-based active material of the present invention may be 3 μm to 15 μm, specifically, it may be 4 μm to 13 μm, and more specifically, it may be 4.5 μm to 11 μm. When the average particle size is less than 3 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 composite composed of the conductive material and the binder in the negative electrode slurry decreases, so the possibility of the conductive network being interrupted increases, and the capacity retention rate decreases. On the other hand, when the average particle size exceeds 10 μm, silicon particles that are too large exist, 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.

[0055] In one embodiment of the present application, the silicon-based active material has a BET specific surface area typical of it. 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).

[0056] In one embodiment of the present application, the silicon-based active material may be present, for example, in 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 be present in the form of a silicon-containing film or coating, but this is less preferred.

[0057] 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.

[0058] 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.

[0059] 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, a negative electrode conductive material and a negative electrode binder capable of controlling the volume expansion rate during the charge and discharge process, and even when including the above range, does not deteriorate the performance of the negative electrode and has the characteristic of excellent output characteristics during charging and discharging.

[0060] In one embodiment of the present application, the silicon-based active material may have a non-spherical form, and its sphericity may be, 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.

[0061] In the present application, the circularity is determined by the following formula (1), where A is the area and P is the boundary line.

[0062] [Formula (1)] 4πA / P 2

[0063] 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 have been made to mix and use silicon-based compounds to increase the capacity. 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.

[0064] 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 / discharge.

[0065] 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.

[0066] 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 chemical changes, 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 contain carbon black in terms of realizing high conductivity and excellent dispersibility.

[0067] In one embodiment of the present application, the BET specific surface area of the dot-shaped conductive material is 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 m 2 / g or more and 60 m 2 / g or less.

[0068] 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, more preferably 40 nm to 60 nm.

[0069] In one embodiment of the present application, the negative electrode conductive material may include a planar conductive material.

[0070] The planar conductive material means a conductive material that plays a role in increasing the surface contact between silicon particles in the negative electrode to improve conductivity and simultaneously suppressing the interruption of the conductive path due to volume expansion. The planar conductive material may be expressed as a plate-shaped conductive material or a bulk-type conductive material.

[0071] In one embodiment of the present application, the sheet conductive material may include at least one selected from the group consisting of plate-like graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-like graphite.

[0072] In one embodiment of the present application, the average particle size (D50) of the sheet conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the average particle size is within this range, the viscosity of the negative electrode slurry does not increase excessively, making dispersion easy. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0073] In one embodiment of the present application, there is provided a negative electrode composition in which the planar conductive material has a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 4.0 μm or more and 5.0 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0074] In one embodiment of the present application, the sheet conductive material may be a high-specific surface area sheet conductive material having a high BET specific surface area; or a low-specific surface area sheet conductive material.

[0075] In one embodiment of the present application, the sheet conductive material may be a high-specific surface area sheet conductive material or a low-specific surface area sheet conductive material without any restrictions, but the sheet conductive material in the present application may be particularly affected to some extent by dispersion effects on electrode performance, and it is particularly preferable to use a low-specific surface area sheet conductive material that does not cause dispersion problems.

[0076] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of 1 m 2 / g or more.

[0077] In another embodiment, the sheet conductive material has a BET specific surface area of 1 m 2 / g or more 500m 2 / g or less, and preferably 5m 2 / g or more 300m2 5 m / g or less, more preferably, 5 m / g 2 250 m / g or less and 5 m / g or more 2 It may be in the range of 250 m / g or less and 5 m / g or more.

[0078] In still another embodiment, the planar conductive material is a high specific surface area planar conductive material, and the BET specific surface area is 50 m / g or more and 500 m / g or less, preferably 80 m / g or more and 300 m / g or less, more preferably 100 m / g or more and 250 m / g or less. 2 500 m / g or less and 50 m / g or more 2 300 m / g or less and 80 m / g or more, preferably 2 300 m / g or less and 80 m / g or more 2 250 m / g or less and 100 m / g or more, more preferably 2 250 m / g or less and 100 m / g or more 2 It may satisfy the range of 250 m / g or less and 100 m / g or more.

[0079] In still another embodiment, the planar conductive material is a low specific surface area planar conductive material, and the BET specific surface area is 1 m / g or more and 40 m / g or less, preferably 5 m / g or more and 30 m / g or less, more preferably 5 m / g or more and 25 m / g or less. 2 40 m / g or less and 1 m / g or more 2 30 m / g or less and 5 m / g or more, preferably 2 30 m / g or less and 5 m / g or more 2 25 m / g or less and 5 m / g or more, more preferably 2 25 m / g or less and 5 m / g or more 2 It may satisfy the range of 25 m / g or less and 5 m / g or more.

[0080] 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, "bundle type" refers to a bundle or rope-shaped 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 graphite sheet in the form of a cylinder with a nanosize diameter 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 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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 to the linear conductive material can satisfy 1:0.001 to 1:0.3.

[0086] In one embodiment of the present application, by including a planar conductive material and a linear conductive material in the negative electrode conductive material and satisfying the respective compositions and ratios, it does not significantly affect the life characteristics of conventional lithium secondary batteries, and there are more points where charging and discharging are possible, and it has the characteristic of excellent output characteristics at a high C rate.

[0087] 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 very large volume expansion of the electrode during charging and discharging. The positive electrode conductive material plays a role of 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.

[0088] In addition, 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 compared to the active material, and thus has the characteristics of improving output characteristics and imparting partial conductivity. It 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.

[0089] In one embodiment of the present application, the plate-shaped conductive material used as the aforementioned negative electrode conductive material plays a different structure and role from 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.

[0090] On the one hand, the plate-shaped conductive material used as the negative electrode conductive material is a substance having a planar or plate-like form and can be represented by plate-shaped graphite. That is, it is a substance contained to maintain a conductive path within the negative electrode active material layer, meaning a substance for ensuring a planar conductive path inside the negative electrode active material layer that does not play a role in the storage and release of lithium.

[0091] 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-shaped form and used as a substance for ensuring a conductive path that does not play a role in storing or releasing lithium. At this time, the negative electrode active material contained together has high capacity characteristics 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.

[0092] On the other hand, in the present application, the fact that a 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 substance that plays a role in storing or releasing lithium.

[0093] 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, polyvinyl pyrrolidone, 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.

[0094] According to one embodiment of the present application, the negative electrode binder serves to control 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 fulfilling the above role, 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.

[0095] 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.

[0096] 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 between the conductive material and the binder.

[0097] In one embodiment of the present application, the silicon-based negative electrode may be formed by coating one or both sides of the negative electrode current collector layer with a negative electrode slurry containing the negative electrode active material layer composition.

[0098] In one embodiment of the present application, the negative electrode slurry may include a negative electrode active material layer composition and a slurry solvent.

[0099] In one embodiment of the present application, the solid content of the negative electrode slurry may satisfy 5% or more and 40% or less.

[0100] 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, more preferably 10% or more and 30% or less.

[0101] 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.

[0102] The solid content 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.

[0103] When the solid content 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.

[0104] 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. Specifically, water or NMP may be used.

[0105] 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.

[0106] 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.

[0107] The porosity varies depending on 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 parts, the above range is satisfied, and thereby the electrode has appropriate ranges of electrical conductivity and resistance.

[0108] 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.

[0109] In one embodiment of the present application, the positive electrode active material layer contains a positive electrode active material layer composition, and the positive electrode active material layer composition may contain one or more selected from the group consisting of a positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

[0110] 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 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, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0111] In one embodiment of the present application, there is provided a lithium secondary battery in which 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.

[0112] In one embodiment of the present application, the positive electrode active material layer composition contains a positive electrode active material, and the positive electrode active material contains one or more selected from the group consisting of a large particle size positive electrode active material having a median particle size (D50) of 9 μm or more; and a small particle size positive electrode active material having a median particle size (D50) of 10 μm or less, and based on 100 parts by weight of the positive electrode active material, the large particle size positive electrode active material is contained in an amount of 45 parts by weight or more and 100 parts by weight or less.

[0113] In yet another embodiment, the positive electrode active material includes at least one selected from the group consisting of a large particle size positive electrode active material having a median particle size (D50) of 10 μm or more; and a small particle size positive electrode active material having a median particle size (D50) of 10 μm or less. Based on 100 parts by weight of the positive electrode active material, the large particle size positive electrode active material may be included in an amount of 45 parts by weight or more and 100 parts by weight or less, preferably 46 parts by weight or more and 100 parts by weight or less, more preferably 48 parts by weight or more and 100 parts by weight or less.

[0114] At this time, including 100 parts by weight of the large particle size positive electrode active material may mean that the positive electrode active material consists only of the large particle size positive electrode active material.

[0115] In one embodiment of the present application, there is provided a lithium secondary battery, wherein the positive electrode active material includes a large particle size positive electrode active material and a small particle size positive electrode active material, the average particle size (D50) of the large particle size positive electrode active material is 9 μm or more and 15 μm or less, and the average particle size (D50) of the small particle size positive electrode active material is 3 μm or more and 6 μm or less.

[0116] In one embodiment of the present application, there is provided a lithium secondary battery, wherein the initial efficiency of the positive electrode is 90% or less. More specifically, it can satisfy 80% or more, and even more specifically, 85% or more.

[0117] As described above, when the large particle size positive electrode active material is included within the above range, it has the characteristic that the initial efficiency of the aforementioned positive electrode can be realized. That is, the initial efficiency of the positive electrode is maintained lower than the negative electrode efficiency, and the section accompanied by the rapid volume change of silicon during the discharge process is not used, so that the cycle performance can be improved.

[0118] In one embodiment of the present application, the large particle size positive electrode active material may have a median particle size (D50) of 9 μm or more, may be 9.3 μm or more, and can satisfy the range of 20 μm or less, preferably 13 μm or less.

[0119] In one embodiment of the present application, the small particle size active material may have a median particle size (D50) of 10 μm or less, 8 μm or less, more specifically, 7 μm or less, and even more specifically, 6 μm or less, and can satisfy the range of 1 μm or more, preferably 3 μm or more.

[0120] Ultimately, as described above, the weight portion of the large particle size positive electrode active material is adjusted to adjust the initial efficiency of the positive electrode, and thereby, as described above, the area ratio, total width, and total length of the positive electrode and the negative electrode are adjusted to form an asymmetric dimensional difference, so that the advantages in the case of using a silicon-based negative electrode can be obtained, and the main object of the present invention is to improve the problems due to the life characteristics.

[0121] 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 include one or more selected from the group consisting of these. Here, the positive electrode active material is not limited to only these.

[0122] In one embodiment of the present application, the positive electrode active material is nickel-cobalt-manganese (NCM) oxide; or nickel-cobalt-manganese-aluminum (NCMA) oxide, and the nickel contained in the nickel-cobalt-manganese (NCM) oxide and nickel-cobalt-manganese-aluminum (NCMA) oxide contains 50 mol% or more of the total metal excluding lithium, providing a lithium secondary battery.

[0123] In another embodiment, the positive electrode active material is nickel-cobalt-manganese (NCM) oxide; or nickel-cobalt-manganese-aluminum (NCMA) oxide, and the nickel contained in the nickel-cobalt-manganese (NCM) oxide and nickel-cobalt-manganese-aluminum (NCMA) oxide may be 50 mol% or more, preferably 55 mol% or more, more preferably 60 mol% or more, and most preferably 65 mol% or more of the total metal excluding lithium. Also, based on the total metal, nickel (Ni) may be 95 mol% or less, 90 mol% or less.

[0124] 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 a high capacity.

[0125] On the other hand, the higher the content of nickel within the above range, the higher the capacity characteristics of the lithium secondary battery containing it can be shown. However, the higher the content of nickel, the relatively lower the content of cobalt and / or manganese, and therefore, there is a risk of a decrease in thermal stability. Therefore, when the nickel content is within the above range, the efficiency of the lithium secondary battery according to the present application can be maximized.

[0126] In one embodiment of the present application, the nickel-cobalt-manganese (NCM) oxide can be represented as lithium nickel-cobalt-manganese oxide as follows, 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 positive electrode 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) as a ternary cathode active material of Ni-Co-Mn, or a mixture thereof, is a composite that combines the advantages such as the high capacity of nickel-containing oxide, the thermal stability of manganese-containing oxide, and the excellent electrochemical properties of cobalt-containing oxide. The lithium nickel-cobalt-manganese (NCM) oxide can be doped with trace amounts of metal elements within the limits suitable for the purposes 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) oxide represented by the ternary cathode active material of Ni-Co-Mn3 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.

[0127] The content of the metal doped in 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, the lithium nickel-cobalt-manganese (NCM) oxide generally uses 2 to 3 kinds of elements as the doping metal, and the doping metal may be present in several hundred ppm based on each element.

[0128] In one embodiment of the present application, the nickel contained in the nickel-cobalt-manganese (NCM) 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.

[0129] 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.

[0130] In one embodiment of the present application, the nickel-cobalt-manganese-aluminum (NCMA) oxide can be represented as lithium nickel-cobalt-manganese-aluminum oxide as follows. The lithium nickel-cobalt-manganese-aluminum (NCMA) oxide is a four-component cathode active material of Ni-Co-Mn-Al represented by 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), 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) represents a four-component cathode active material of Ni-Co-Mn-Al, or a mixture thereof, which is a composite combining the advantages such as the high capacity of nickel-containing oxide, the thermal stability of manganese-containing oxide, and the excellent electrochemical properties of cobalt-containing oxide. 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.

[0131] 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.

[0132] 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.

[0133] The Li 1+x (Ni a Co b Mn c Ald )In the formula 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), the nickel content can mean the proportion of a contained. That is, in the case of a four-component system, it can mean the proportion occupied by nickel among the metals of nickel, cobalt, manganese, and aluminum.

[0134] In one embodiment of the present application, the average particle size (D50) of the positive electrode active material may be 5 μm to 20 μm, preferably 6 μm to 15 μm. That is, the positive electrode active material can satisfy the above range of the overall average particle size by including a large particle size positive electrode active material.

[0135] Provided is a lithium secondary battery in which, based on 100 parts by weight of the positive electrode active material layer composition, the single-particle positive electrode active material is contained in an amount of 90 parts by weight or more.

[0136] In another embodiment, based on 100 parts by weight of the positive electrode active material layer composition, the single-particle 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.

[0137] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the single-particle positive electrode active material described above.

[0138] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery to be 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.

[0139] 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 part 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.

[0140] In another embodiment, based on 100 parts by weight of the positive electrode active material layer composition, it may include 0.1 part by weight or more and 2 parts by weight or less, preferably 0.3 part by weight or more and 1.5 parts by weight or less, more preferably 0.5 part by weight or more and 1.2 parts by weight or less of the positive electrode conductive material.

[0141] 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, polyvinyl pyrrolidone, 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.

[0142] 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.

[0143] 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 fiber, polyethylene terephthalate fiber, etc. may be used. Further, a coated separator 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.

[0144] 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.

[0145] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0146] 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.

[0147] 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.

[0148] A lithium salt may be used as the metal 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.

[0149] 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 oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, 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.

[0150] 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

[0151] Hereinafter, in order to facilitate the understanding of the present invention, preferred examples are presented. However, the following examples are merely illustrative of the present description, and it is obvious to those skilled in the art that various changes and modifications can be made within the scope of the present description and the scope of the technical idea. It is natural that such variations and modifications belong to the scope of the claims.

[0152] [Manufacturing Example] (1) Manufacture of the positive electrode A positive electrode active material having the characteristics shown in Table 1 below was used as the positive electrode active material.

[0153]

Table 1

[0154] In Table 1 above, each part by weight is based on 100 parts by weight of the entire positive electrode active material.

[0155] In Table 1 above, the large particle size positive electrode active material A is Li(Ni a Co b Mn c )O2. The NCM excluding lithium (Li) and oxygen (O2) of the single particle positive electrode active material satisfies a ratio of Ni:Co:Mn = 93:5:2, (a:b:c = 0.93:0.05:0.02), and the median particle size (D50) satisfies 11 μm.

[0156] In Table 1 above, the small particle size positive electrode active material A is Li(Ni a Co b Mn c)With O2, the NCM excluding lithium (Li) and oxygen (O2) of the single-particle cathode active material satisfied the ratio of Ni:Co:Mn = 93:5:2, (a:b:c = 0.93:0.05:0.02), and the median particle size (D50) satisfied 4 μm.

[0157] In Table 1 above, the large-particle-size cathode active material A is Li(Ni a Co b Mn c )With O2, the NCM excluding lithium (Li) and oxygen (O2) of the single-particle cathode active material satisfied the ratio of Ni:Co:Mn = 93:5:2, (a:b:c = 0.93:0.05:0.02), and the median particle size (D50) was 11 μm, corresponding to a single-particle active material in which the primary particles are a single particle aggregate.

[0158] Then, the cathode active material, cathode conductive material (LB.CNT), and binder (PVdF, KF9700) were added to a solvent (N-methylpyrrolidone, NMP) at a weight ratio of 97.96:0.8:1.24 to produce a cathode slurry. After the cathode slurry was coated and dried on an aluminum (Al) thin film, which is a cathode current collector with a thickness of 25 μm, it was rolled by a roll press to produce a cathode.

[0159] (2) Fabrication of the anode As a silicon-based active material, Si (average particle size (D50): 5 μm), a first conductive material, a second conductive material, and polyacrylamide as a binder were prepared as a negative electrode active material layer composition 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 nanotubes.

[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. After that, 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 the negative electrode current collector at a loading of 3.00 mg / cm 2 and rolled, and then dried in a vacuum oven at 130 °C for 10 hours to form a negative electrode active material layer (thickness: 23 μm).

[0163] (3) Manufacture of a secondary battery An electrode assembly was manufactured with a pressure-resistant thin film separator (PE 12 μm) having a ceramic coating of 3 μm / 3 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, which has the characteristics shown in Table 2 below.

[0164]

Table 2

[0165] Experimental Example 1: Energy density calculation Regarding the lithium secondary batteries manufactured in Example 3 and Comparative Examples 3 and 4, for a cell size of 102×548, assuming the sizes of the negative electrode and the positive electrode under these conditions, the energy density for 40 medium and large-sized cells in a stack was calculated, and the results are as shown in Table 3 below. Based on the high energy density Si cell design, it was indicated by ○ or × whether a design that satisfies 800 Wh / L is possible.

[0166]

Table 3

[0167] Experimental Example 2: Pouch cell life evaluation For the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1, 2, and 5, life evaluation was carried out using an electrochemical charge and discharge device, and the capacity retention rate was evaluated. The secondary battery was subjected to an In-situ cycle test at 4.2 - 3.2 V and 1C / 1C. During the test, charging and discharging were performed at 1C / 1C (4.2 - 3.2 V) every 50 cycles, and the capacity retention rate was measured. The results are shown in Table 4.

[0168] Lifetime retention rate (%) = {(Discharge capacity at the Nth cycle) / (Discharge capacity at the first cycle)} × 100

[0169] After the evaluation was completed, the cell was disassembled to check for the occurrence of lithium plating on the tab part or the electrode side. The results are as shown in Table 4 below.

[0170]

Table 4

[0171] As can be confirmed in Experimental Examples 1 and 2, the lithium secondary battery according to the present application can ensure a battery with a high capacity and a high energy density by using a silicon-based negative electrode. In particular, by adjusting the initial efficiency between the positive electrode and the negative electrode and adjusting the differences in area, total width, and total length between the positive electrode and the negative electrode, it is possible to adjust so as not to use the section accompanied by a rapid volume change of the silicon-based negative electrode during the discharge process, and it was confirmed that the lithium secondary battery has the feature of being able to improve the cycle performance.

[0172] That is, by adjusting the conditions as described above and restricting the rapid volume change section of the silicon-based active material, cracking of pure silicon (Pure Si) particles can be minimized, decomposition of the additional electrolyte can be controlled, the reversible Li loss and the conductive network between the Si active materials can be maintained, the amount of isolated lithium can be controlled, and it was confirmed that the cycle performance improvement effect can be achieved.

[0173] As can be confirmed from Table 3 above, in the case of the lithium secondary battery of Example 3 according to the present application, it was confirmed that the energy density was formed at a high level when compared with Comparative Examples 3 and 4.

[0174] As can be confirmed from Table 4 above, in the case of the lithium secondary batteries of Examples 1 to 3 according to the present application, it was confirmed that the life performance was higher than that of Comparative Examples 1 and 2. Additionally, in the case of Comparative Example 5, although the values of the total width and total length of the negative electrode and the positive electrode were different from those of the present application, the life performance showed the same level as that of the examples. However, it was confirmed that lithium plating occurred in the tab portion or the electrode side after decomposition, causing problems in the operation of the lithium secondary battery.

Description of Reference Numerals

[0175] 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 contains a silicon-based active material, and the silicon-based active material contains at least one selected from the group consisting of SiO ｘ (x = 0), SiO ｘ (0 < x < 2), SiC, and Si alloys. the initial efficiency of the silicon-based negative electrode is 0.2% or more and 4% or less higher than that of the positive electrode; the area ratio of the positive electrode active material layer to the negative electrode active material layer satisfies 1:1.02 or more and 1:1.1 or less; the lithium secondary battery exhibits an asymmetric dimensional difference in which the total width of the silicon-based negative electrode is 1 mm or more compared to the total width of the positive electrode, and the total length of the silicon-based negative electrode is 2.5 mm or more longer than the total length of the positive electrode.

2. The silicon-based active material contains at least one 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) contains 70 parts by weight or more. The lithium secondary battery according to claim 1.

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

4. The positive electrode active material layer composition includes a positive electrode active material, the positive electrode active material includes one or more selected from the group consisting of a large particle size positive electrode active material having a median particle size (D50) of 9 μm or more; and a small particle size positive electrode active material having a median particle size (D50) of 10 μm or less; The lithium secondary battery according to claim 1, wherein, based on 100 parts by weight of the positive electrode active material, the large particle size positive electrode active material is contained in an amount of 45 parts by weight or more and 100 parts by weight or less.

5. The lithium secondary battery according to claim 1, wherein the initial efficiency of the positive electrode is 90% or less.

6. 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 4, comprising one or more selected from the group consisting of.

7. the positive electrode active material is nickel-cobalt-manganese (NCM) oxide; or nickel-cobalt-manganese-aluminum (NCMA) oxide, The lithium secondary battery according to claim 4, wherein nickel contained in the nickel-cobalt-manganese (NCM) oxide and nickel-cobalt-manganese-aluminum (NCMA) oxide is contained in an amount of 50 mol% or more of the total metals excluding lithium.

8. the positive electrode active material includes a large particle size positive electrode active material and a small particle size positive electrode active material, the average particle size (D50) of the large particle size positive electrode active material is 9 μm or more and 15 μm or less, The lithium secondary battery according to claim 4, wherein the average particle size (D50) of the small particle size positive electrode active material is 3 μm or more and 6 μm or less.

9. The average particle diameter (D50) of the positive electrode active material is 5 μm or more and 20 μm or less, and the lithium secondary battery according to claim 4.

10. Based on 100 parts by weight of the positive electrode active material layer composition, the positive electrode active material is contained in an amount of 90 parts by weight or more, and the lithium secondary battery according to claim 4.

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

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