Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode active material layer containing a positive electrode active material layer composition, and the negative electrode includes a negative electrode active material layer containing a negative electrode active material layer composition. The positive electrode active material layer composition contains a positive electrode active material including a nickel-containing layered active material and an olivine-based active material, and the negative electrode active material layer composition contains a negative electrode active material including a silicon-based active material. When the parts by weight of the olivine-based active material per 100 parts by weight of the positive electrode active material are denoted as A, and the parts by weight of the silicon-based active material per 100 parts by weight of the negative electrode active material are denoted as B, A and B satisfy Expressions 1 and 2 (Expression 1: 4.524+0.939×e0.0537×A < B < -4.312+5.183×e0.0537×A, and Expression 2: 10 ≤ A ≤ 90).

Description

lithium secondary battery

[0001] This application claims the benefit of Korean Patent Application No. 10-2023-0148983, filed with the Korean Intellectual Property Office on November 1, 2023, the entire contents of which are incorporated herein by reference.

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

[0003] Due to the rapid increase in fossil fuel use, the demand for alternative or clean energy is increasing, and as part of this, the most actively researched field is power generation and storage using electrochemical reactions.

[0004] A representative example of an electrochemical device that currently utilizes this electrochemical energy is the secondary battery, and its application area is gradually expanding.

[0005] With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used. Furthermore, active research is being conducted on methods for manufacturing high-density electrodes with even higher energy density per unit volume as electrodes for these high-capacity lithium secondary batteries.

[0006] Typically, secondary batteries consist of a cathode, anode, electrolyte, and a separator. Lithium secondary batteries are typically manufactured using lithium-intercalated compounds such as LiCoO2 and LiMn2O4 for the cathode, and non-lithium-intercalated materials such as carbon-based and Si-based for the anode. When charging, lithium ions inserted into the cathode move to the cathode through the electrolyte, and when discharging, lithium ions move from the cathode to the anode again.

[0007] Lithium secondary batteries are being applied in various industrial fields such as automobiles, small modules, and mobile phones, and the performance of lithium secondary batteries targeted for each field includes various factors, but in general, the development of technology aimed at increasing energy density, ensuring stability, ensuring rapid charging, and securing life performance is fundamentally required.

[0008] In particular, carbon-based materials such as graphite, while excellent in stability and reversibility as anode materials, have limitations in terms of capacity. Therefore, in fields where the goal is to maximize high capacity, or energy density, attempts are increasing to use Si-based materials with high theoretical capacity as anode materials. However, when the purpose of high capacity is simply to include a high content of the Si-based material, the life performance deteriorates rapidly due to issues related to volume expansion compared to carbon-based materials, making it difficult to apply in real life.

[0009] In order to solve the above problems when using Si-based materials in the anode, various methods are being discussed, such as a method of controlling the driving potential, a method of additionally coating a thin film on the active material layer, a method of suppressing the volume expansion itself such as a method of controlling the particle size of the silicon-based compound, or the development of a binder that can control the volume expansion of the silicon-based compound to prevent the conductive path from being cut off. In addition, research is also being conducted to supplement the life characteristics of silicon-based anodes by limiting the proportion of silicon-based active materials used during initial charge and discharge and providing a reservoir role through a method of prelithiating the silicon-based active material layer.

[0010] As a counter electrode to the Si-based cathode, a cathode such as NCM(A) with a high nickel content has been developed. When a cathode such as NCM(A) with a high nickel content is used, the high-capacity characteristic, which is an advantage of Si-based cathodes, can be maintained, while also ensuring high energy density and rapid charging performance.

[0011] However, due to the characteristics of the Si-based cathode and the NCM(A) cathode containing a high nickel content, there has been a problem that the stability has dropped sharply, and in particular, ignition related to electric vehicles has also emerged as a major problem, and accordingly, the need for lithium secondary batteries with increasingly strengthened thermal stability (Thermal Propagation) specifications is increasing, but the batteries of the Si-based cathode and the NCM(A) cathode containing a high nickel content mentioned above have a problem in that the higher the energy stored in the same volume as the life performance, the lower the thermal stability.

[0012] To address this, an olivine-based cathode such as LFP can be applied as the positive electrode, which is the opposite electrode of the Si-based cathode. That is, in order to address the thermal stability of a battery including a Si-based cathode and a NCM(A) cathode containing a high nickel content, research has been conducted to secure stability by using an olivine-based cathode of LFP, although its energy density and capacity characteristics are relatively low.

[0013] However, when an olivine-based cathode such as LFP is applied as the positive electrode, which is the opposite electrode of the Si-based cathode, the aforementioned stability can be secured, but the capacity drops sharply, so there is no advantage over existing batteries.

[0014] To solve the above problems, research is being conducted to combine and apply various types of active materials to the positive and negative electrodes, but problems of securing high energy density, thermal stability, and life performance, which are incompatible with each other, continue to arise.

[0015] Therefore, research is continuously being conducted on the development of technologies aimed at increasing the energy density of lithium secondary batteries, ensuring stability, ensuring rapid charging, and securing life performance.

[0016] The background information provided herein is generally intended to provide context for the disclosure. Unless otherwise stated herein, the material described in this section is not prior art to the claims of this application, and its inclusion in this section does not constitute prior art or a suggestion of prior art.

[0017] <Prior Art Literature>

[0018] (Patent Document 1) Japanese Patent Publication No. 2009-080971

[0019] As a result of research on the aforementioned problems, it was found that when a silicon-based active material is included in the negative electrode, a nickel-containing layered active material is included in the positive electrode, and an olivine-based active material is mixed and included, it is possible to simultaneously secure energy density and thermal stability characteristics that were previously incompatible, and also to solve the problem of life characteristics.

[0020] Accordingly, the present application seeks to provide a lithium secondary battery capable of solving the aforementioned problems.

[0021] One embodiment of the present specification provides a lithium secondary battery comprising a positive electrode; a negative electrode; and an electrolyte, wherein the positive electrode comprises a positive electrode active material layer comprising a positive electrode active material layer composition; and the negative electrode comprises a negative electrode active material layer comprising a negative electrode active material layer composition, wherein the positive electrode active material layer composition comprises a positive electrode active material comprising a layered active material comprising nickel; and an olivine-based active material; and wherein the negative electrode active material layer composition comprises a negative electrode active material comprising a silicon-based active material, and the weight part of the olivine-based active material based on 100 parts by weight of the positive electrode active material is A, the weight part of the silicon-based active material based on 100 parts by weight of the negative electrode active material is B, and the A and B satisfy the following equations 1 and 2.

[0022] [Formula 1]

[0023] 4.524+0.939×e 0.0537×A< B < -4.312+5.183×e 0.0537×A

[0024] [Formula 2]

[0025] 10 ≤ A ≤ 90

[0026] The present application has found that, in particular, when the composition ratio of the positive and negative electrodes is adjusted within the range of Equations 1 and 2 as described above, it is possible to simultaneously secure energy density and lifespan characteristics, which were previously incompatible, and also to solve the problem of thermal stability.

[0027] The lithium secondary battery according to the present application is characterized by including a layered active material including nickel in the positive electrode and an olivine-based active material, and a silicon-based active material in the negative electrode. That is, through the above combination, an energy density (ED of 700 Wh / L or more) can be secured.

[0028] Instead of simply applying carbon-based active materials and olivine-based active materials alone, in order to secure energy density, a layered active material containing nickel and a silicon-based active material are included in the positive electrode, respectively, to satisfy the energy density, and the problem of thermal stability (TP) due to the resulting increase in capacity is solved by deriving a weight ratio that satisfies Equations 1 and 2. In general, when the content of silicon-based active materials in the negative electrode increases, the energy density increases, but the thermal stability is inferior, and accordingly, when the content of olivine-based active materials in the positive electrode increases, the problem of thermal stability is improved, but the energy density decreases. However, the present applicant derived the ratios of Equations 1 and 2 through research, and when applying these, both energy density and thermal stability are secured.

[0029] That is, by controlling the composition and content as described above, energy density can be secured while thermal stability can be secured, and by applying a silicon-based active material to a certain portion of the negative electrode as described above, the thickness of the active material layer can be reduced due to a decrease in the loading amount, and the porosity can be secured, thereby improving the movement speed of Li, and thus, it has the characteristic of also securing rapid charging performance.

[0030] In conclusion, in the case of the lithium secondary battery according to the present application, the thermal stability that cannot be maintained at the same time as securing high energy density has been resolved, and the performance of rapid charging can be secured, and although it shows some inferior performance compared to other cells (LFP / Gr, LMFP / Gr, NCM / Gr) with enhanced life performance, it is characterized by showing superior life performance compared to existing cells aimed at high energy density (Si / NCM, Si / LFP).

[0031] The attached drawings illustrate exemplary embodiments of the present application and, together with the detailed description below, are intended to provide a deeper understanding of the technical aspects of the present application, and therefore, the present application should not be construed as being limited to the drawings.

[0032] Figure 1 is a diagram showing a lithium secondary battery according to the present application.

[0033] Figure 2 is a diagram showing a structure for evaluation of lithium secondary batteries manufactured in the present application examples and comparative examples.

[0034] Figure 3 shows a distribution diagram based on the olivine-based active material and silicon-based active material of the examples and comparative examples of the present application.

[0035] <Explanation of symbols>

[0036] 10: Negative current collector layer

[0037] 20: Negative active material layer

[0038] 30: Membrane

[0039] 40: Positive active material layer

[0040] 50: Positive current collector layer

[0041] 100: Negative

[0042] 200: Bipolar

[0043] Before explaining the present invention, some terms are first defined.

[0044] When a part of this specification is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0045] In this specification, ‘p to q’ means a range of ‘p or more and q or less.’

[0046] In this specification, "specific surface area" is measured by the BET method, and specifically, is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan. That is, in this application, the BET specific surface area may mean the specific surface area measured by the above measurement method.

[0047] In this specification, "Dn" means particle size distribution, and means the particle size at the n% point of the cumulative distribution of particle numbers according to particle size. That is, D50 is the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size, D90 is the particle size at the 90% point of the cumulative distribution of particle numbers according to particle size, and D10 is the particle size at the 10% point of the cumulative distribution of particle numbers according to particle size. Meanwhile, the particle size distribution can be measured using the laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction pattern according to particle size is measured when the particles pass through the laser beam, thereby calculating the particle size distribution.

[0048] As used herein, the term "a polymer comprises a monomer as a monomer unit" means that the monomer participates in a polymerization reaction and is included as a repeating unit within the polymer. As used herein, "a polymer comprises a monomer" is interpreted to mean that the polymer comprises the monomer as a monomer unit.

[0049] In this specification, the term 'polymer' is understood to be used in a broad sense including copolymers unless 'homopolymer' is specified.

[0050] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-converted 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 materials. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0051] Hereinafter, the present invention will be described in detail with reference to the drawings so that those skilled in the art can easily practice it. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0052] One embodiment of the present specification provides a lithium secondary battery comprising a positive electrode; a negative electrode; and an electrolyte, wherein the positive electrode comprises a positive electrode active material layer comprising a positive electrode active material layer composition; and the negative electrode comprises a negative electrode active material layer comprising a negative electrode active material layer composition, wherein the positive electrode active material layer composition comprises a positive electrode active material comprising a layered active material comprising nickel; and an olivine-based active material; and wherein the negative electrode active material layer composition comprises a negative electrode active material comprising a silicon-based active material, and the weight part of the olivine-based active material based on 100 parts by weight of the positive electrode active material is A, the weight part of the silicon-based active material based on 100 parts by weight of the negative electrode active material is B, and the A and B satisfy the following equations 1 and 2.

[0053] [Formula 1]

[0054] 4.524+0.939×e 0.0537×A < B < -4.312+5.183×e 0.0537×A

[0055] [Formula 2]

[0056] 10 ≤ A ≤ 90

[0057] In the case of the lithium secondary battery according to the present application, the thermal stability that cannot be achieved simultaneously with securing high energy density is solved by a combination of positive and negative active materials including the ranges of Equations 1 and 2, and in addition, the performance of rapid charging can be secured, and although it shows some inferior performance to other cells (LFP / Gr, LMFP / Gr, NCM / Gr) with enhanced life performance, it is characterized by showing superior life performance compared to existing cells (Si / NCM, Si / LFP) aimed at high energy density.

[0058] FIG. 1 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, an anode (100) including a negative electrode active material layer (20) on one surface of an anode current collector layer (10) can be confirmed, and a cathode (200) including a positive electrode active material layer (40) on one surface of an anode current collector layer (50) can be confirmed, and it is shown that the anode (100) and a cathode (200) for a lithium secondary battery are formed in a laminated structure with a separator (30) interposed therebetween.

[0059] In the present application, the lithium secondary battery may further include a separator between the positive electrode and the negative electrode.

[0060] Below, the positive electrode, negative electrode, electrolyte, and separator included in the lithium secondary battery are each described.

[0061] In the present application, the negative electrode includes a negative electrode active material layer including a negative electrode active material layer composition.

[0062] In the present application, the 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.

[0063] At this time, the negative electrode active material layer composition may include at least one selected from the group consisting of a negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0064] In the present application, the positive electrode includes a positive electrode active material layer including a positive electrode active material layer composition.

[0065] In the present application, 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.

[0066] At this time, the positive electrode active material layer composition may include at least one selected from the group consisting of a positive electrode active material; a positive electrode conductive material; and a positive electrode binder.

[0067] In one embodiment of the present application, the negative electrode active material may include a silicon-based active material, and the positive electrode active material may include a layered active material including nickel and an olivine-based active material.

[0068] Carbon-based materials such as graphite as negative active materials have excellent stability and reversibility, but have limitations in terms of capacity. Therefore, in fields that aim for high capacity, silicon-based active materials with high theoretical capacity are applied.

[0069] However, while the issue of volume expansion must be adequately addressed when applying silicon-based active materials alone, no alternative solution has been developed. Accordingly, the negative active material according to the present application utilizes a silicon-based active material, while simultaneously applying a layered active material containing nickel as the positive active material; and an olivine-based active material.

[0070] In one embodiment of the present application, a lithium secondary battery is provided, wherein the olivine-based active material comprises 10 parts by weight or more and 90 parts by weight or less based on 100 parts by weight of the positive electrode active material, and the layered active material including nickel comprises 10 parts by weight or more and 95 parts by weight or less.

[0071] In another embodiment, the olivine-based active material may be included in an amount of 10 parts by weight or more and 90 parts by weight or less, preferably 10 parts by weight or more and 85 parts by weight or less, and more preferably 20 parts by weight or more and 80 parts by weight or less, based on 100 parts by weight of the positive electrode active material.

[0072] In the present application, the weight part of the olivine-based active material based on 100 weight parts of the positive electrode active material may be represented by the above-mentioned A.

[0073] In another embodiment, the layered active material containing nickel may be included in an amount of 10 parts by weight or more and 90 parts by weight or less, preferably 15 parts by weight or more and 90 parts by weight or less, and more preferably 20 parts by weight or more and 80 parts by weight or less, based on 100 parts by weight of the positive electrode active material.

[0074] In the present application, a lithium secondary battery is provided, wherein the silicon-based active material comprises 5 parts by weight or more and 100 parts by weight or less based on 100 parts by weight of the negative active material.

[0075] In another embodiment, the silicon-based active material may be included in an amount of 5 parts by weight or more and 70 parts by weight or less, preferably 7 parts by weight or more and 60 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the negative active material.

[0076] In the present application, the weight part of the silicon-based active material based on 100 weight parts of the negative active material may be represented by the above-mentioned B.

[0077] At this time, silicon (Si) in the silicon-based active material may be included in an amount of 30 parts by weight or more and 100 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0078] That is, in the present application, the silicon-based active material is SiOx (x=0, SiOx (0 <x<2), Si / C, 및 Si 합금으로 이루어진 군에서 선택되는 1 이상을 포함할 수 있으며, 이 때 실리콘계 활물질 내 실리콘(Si)의 중량 비율이 상기 범위를 만족할 수 있다.

[0079] In the present application, the negative electrode active material further includes a carbon-based active material, and the silicon-based active material may include 5 parts by weight or more and 100 parts by weight or less based on 100 parts by weight of the negative electrode active material, and the carbon-based active material may include 0 parts by weight or more and 95 parts by weight or less.

[0080] In another embodiment, the carbon-based active material may include 30 parts by weight or more and 95 parts by weight or less, preferably 40 parts by weight or more and 93 parts by weight or less, and more preferably 50 parts by weight or more and 90 parts by weight or less, based on 100 parts by weight of the negative active material.

[0081] Typically, high-energy cells store more energy per volume, leading to poor thermal stability. Increasing the content of silicon-based active materials in the negative electrode increases energy density but degrades thermal stability. Increasing the content of olivine-based active materials in the positive electrode improves thermal stability but reduces energy density.

[0082] However, the present application has the characteristics of securing energy density and thermal stability by applying a specific composition and contents of formulas 1 and 2 to the positive and negative electrodes as described above, respectively. That is, the lithium secondary battery of the present application may have a lower energy density than when simply applying a silicon-based negative electrode and a positive electrode including a layered active material including nickel, but the main purpose of the present invention is to secure an energy density of 700 Wh / L or more and to secure thermal stability at the same time by satisfying the composition and contents as described above.

[0083] That is, when the content of the olivine-based active material (A) and the content of the silicon-based active material (B) satisfy the range of Equation 1, the energy density can be secured at 700 Wh / L or more, and the TR rate can be satisfied at 4 or less. When the range of Equation 1 is not satisfied, the energy density of the cell is not secured, and the Tr rate is not secured, so the problem of thermal stability cannot be solved.

[0084] In one embodiment of the present application, a lithium secondary battery is provided, wherein the layered active material including nickel included in the positive electrode active material is lithium nickel-cobalt-aluminum (NCA) oxide; lithium nickel-cobalt-manganese (NCM) oxide; or lithium nickel-cobalt-manganese-aluminum (NCMA) oxide, and the olivine-based active material is lithium manganese iron phosphate (LMFP); or lithium iron phosphate (LFP).

[0085] In this application, LMFP means lithium manganese iron phosphate, and LFP means lithium iron phosphate.

[0086] At this time, in the case of LMFP, LiMn x Fe 1-x PO4 can be represented as LFP, and LFP can be represented as LiFePO4, wherein x can have a value of 0 < x < 1.

[0087] In general, cathode active materials can be broadly classified into layered, spinel, or olivine types depending on the type of crystal lattice structure.

[0088] In the present application, the layered active material including nickel may generally include a ternary alloy material, such as lithium nickel-cobalt-aluminum (NCA) oxide; lithium nickel-cobalt-manganese (NCM) oxide; or lithium nickel-cobalt-manganese-aluminum (NCMA) oxide. In the case of the layered active material, the constituent elements of the positive electrode active material are positioned in a layered structure, so that lithium ions are stored between the crystal lattice layers when the lithium secondary battery is charged. At this time, a large amount of lithium ions can be stored between the wide and flat interlayers, so that when the material is used, there is an advantage of high energy capacity, but there is a problem of low stability when charging at high voltage.

[0089] In the present application, the olivine-based active material may be LMFP or LFP, and is generally hexahedral in shape, and has higher lattice structural stability compared to layered active materials. This allows for less crystal structure degradation when lithium ions escape during discharge, resulting in higher cycle life and thermal stability. However, this material has the disadvantage of having a slow lithium ion diffusion rate and a relatively low energy density.

[0090] In addition, in the case of the spinel structure, since it is a crystal structure of an oxide structure and does not use cobalt, the lattice structure has a three-dimensional form and thus has excellent safety, but it has a problem in that the capacity and lifespan decrease as charging and discharging proceeds.

[0091] In the case of the positive electrode active material according to the present application, the layered active material containing nickel, in particular lithium nickel-cobalt-manganese (NCM) oxide and olivine-based active material are characterized by using LMFP.

[0092] In one embodiment of the present application, the Mn may be included in an amount of 0 at% or more and 90 at% or less based on 100 at% of the total elements included in the LMPF.

[0093] The above olivine-based active material can use LFP or LMFP, and has the same structure, but in the case of LMFP, since Mn is substituted for Fe, it has the effect of increasing the voltage, and thus has the characteristic of increasing the energy density among olivine-based active materials with relatively low energy density.

[0094] In the present application, a lithium secondary battery is provided in which the positive electrode active material is a single particle positive electrode active material.

[0095] In addition, a lithium secondary battery is provided in which nickel included in the layered active material including the nickel is included in an amount of 75 mol% or less of the total metal excluding lithium.

[0096] In general, when implementing a high-voltage cell in a lithium secondary battery containing a silicon-based active material, it is necessary to use secondary particles as a cathode active material to solve the resistance problem. However, in a high-voltage cell, secondary particle breakage occurs and there is an issue of gas generation. Therefore, when a single-particle cathode active material is applied as described above, it has the characteristic of being able to drive a high-voltage cell.

[0097] In the present application, the carbon-based active material included in the negative electrode active material includes natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotube, fullerene, or activated carbon, and the silicon-based active material includes SiOx (0 <x<2), Si / C, 및 Si 합금으로 이루어진 군에서 선택되는 1 이상을 포함할 수 있다.

[0098] More specifically, the carbon-based active material included in the negative electrode active material may include natural graphite or artificial graphite, and the silicon-based active material may include Si / C.

[0099] In the present application, the Si / C may be expressed as a silicon carbon composite.

[0100] In this specification, the silicon-carbon composite is a composite of Si and C, and is distinct from silicon carbide, denoted as SiC. Since the silicon carbide does not electrochemically react with lithium, all performances, including lifespan, may be measured as 0.

[0101] The above silicon-carbon composite may be a composite of silicon and graphite, and may also form a structure in which a core composed of silicon and graphite is surrounded by graphene or amorphous carbon. The silicon in the silicon-carbon composite may be nano-silicon. For example, the nano-silicon may be silicon having a particle size ranging from 1 nm to 999 nm.

[0102] Lithium secondary batteries have specific sizes for their intended use, and therefore must be designed within a limited space. While consumer demand for increased energy density and high-power performance is growing, the use of high-capacity cathode materials necessitates increased anode content to meet these demands. This limits the ability to increase battery efficiency within a limited space. Furthermore, depending on the type of anode material, it's necessary to design a cathode material with an efficiency level that matches that of the anode material.

[0103] Accordingly, the present application has the characteristics of securing energy density while simultaneously securing life performance and thermal stability by applying a mixture of Si / C as a silicon-based active material and using a material of the aforementioned composition and content as a cathode active material.

[0104] The negative electrode according to the present application may include a negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer.

[0105] The negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and it can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0106] However, the thickness can be varied depending on the type and purpose of the cathode used and is not limited thereto.

[0107] Meanwhile, the average particle diameter (D50) of the silicon-based active material of the present invention may be 1 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle diameter is less than 5 μm, the specific surface area of ​​the particles increases excessively, so that the viscosity of the negative electrode slurry increases excessively. Accordingly, the dispersion of the particles constituting the negative electrode slurry is not smooth. In addition, when the size of the silicon-based active material is excessively small, the contact area between the silicon particles and the conductive material is reduced by the complex composed of the conductive material and the binder in the negative electrode slurry, so that the possibility of the conductive network being disconnected increases, resulting in a decrease in the capacity retention rate. On the other hand, when the average particle diameter exceeds 10 μm, excessively large silicon particles are present, so that the surface of the negative electrode becomes unsmooth, and thus, current density unevenness occurs during charge and discharge. Additionally, if the silicon particles are excessively large, the phase stability of the cathode slurry becomes unstable, reducing processability. Consequently, the battery's capacity retention rate decreases.

[0108] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET surface area. The BET 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, especially 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. BET surface area is measured according to DIN 66131 (using nitrogen).

[0109] In one embodiment of the present application, the silicon-based active material may exist in a crystalline or amorphous form, for example, and is preferably non-porous. The silicon particles are preferably spherical or fragment-shaped. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or be present in the form of a silicon-containing film or coating.

[0110] In one embodiment of the present application, the silicon-based active material may be included in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0111] In another embodiment, the silicon-based active material may be included in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may be included 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.

[0112] The negative electrode active material layer composition according to the present application uses a specific negative electrode conductive material and negative electrode binder that can control the volume expansion rate during the charge and discharge process even when a silicon-based active material with a significantly high capacity is used within the above range, so that the performance of the negative electrode is not deteriorated even within the above range, and the negative electrode has excellent output characteristics during charge and discharge.

[0113] Traditionally, graphite compounds were used exclusively as anode active materials. However, with the increasing demand for high-capacity batteries, attempts to blend silicon-based compounds to increase capacity are increasing. However, silicon-based compounds have limitations: their rapid volume expansion during charge / discharge processes damages the conductive paths formed within the anode active material layer, thereby degrading battery performance.

[0114] Accordingly, 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 hold the negative electrode conductive material during charging and discharging.

[0115] In one embodiment of the present application, the negative electrode conductive material may include at least one selected from the group consisting of a dot-shaped conductive material; a planar conductive material; and a linear conductive material.

[0116] In one embodiment of the present application, the dot-shaped conductive material can be used to improve conductivity of the negative electrode, and refers to a conductive material having a circular or dot-shaped shape that forms conductivity without causing chemical change. 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, paneth black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black in terms of implementing high conductivity and excellent dispersibility.

[0117] In one embodiment of the present application, the dot-shaped conductive material has a BET specific surface area of ​​40 m 2 / g or more than 70m 2 / g or less, preferably 45m 2 / g or more than 65m 2 / g or less, more preferably 50m 2 / g or more than 60m 2 / g can be less.

[0118] 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.

[0119] In one embodiment of the present application, the conductive material may include a planar conductive material.

[0120] The above-mentioned planar conductive material refers to a conductive material that improves conductivity by increasing planar contact between silicon particles within the cathode, while simultaneously suppressing the disconnection of conductive paths due to volume expansion. The above-mentioned planar conductive material may be expressed as a plate-shaped conductive material or a bulk-shaped conductive material.

[0121] In one embodiment of the present application, the planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-shaped graphite.

[0122] In one embodiment of the present application, the average particle diameter (D50) of the surface-shaped 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, the sufficient particle size facilitates dispersion without causing excessive viscosity increase in the negative electrode slurry. Therefore, the dispersion effect is excellent when dispersion is performed using the same equipment and time.

[0123] In one embodiment of the present application, the surface-shaped conductive material provides a negative electrode composition having a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 4.0 μm or more and 5.0 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0124] 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 surface area; or a low-specific surface area planar conductive material.

[0125] In one embodiment of the present application, a high surface area surface conductive material or a low surface area surface conductive material can be used without limitation as the surface conductive material, but in particular, since the surface conductive material according to the present application may be affected by dispersion to some extent in electrode performance, it may be particularly preferable to use a low surface area surface conductive material that does not cause dispersion problems.

[0126] In one embodiment of the present application, the surface-shaped conductive material has a BET specific surface area of ​​1 m 2 / g can be more than that.

[0127] In another embodiment, the surface-shaped conductive material has a BET surface area of ​​1 m 2 / g or more than 500m 2 / g or less, preferably 5m 2 / g or more than 300m 2 / g or less, more preferably 5m 2 / g or more than 250m 2 / g can be less.

[0128] In another embodiment, the surface-shaped conductive material is a high surface area surface-shaped conductive material, and has a BET surface area of ​​50 m 2 / g or more than 500m 2 / g or less, preferably 80m 2 / g or more than 300m 2 / g or less, more preferably 100m 2 / g or more than 250m 2 / g can satisfy the range below.

[0129] In another embodiment, the surface-shaped conductive material is a low surface area surface-shaped conductive material, and has a BET surface area of ​​1 m 2 / g or more than 40m 2 / g or less, preferably 5m 2 / g or more than 30m 2 / g or less, more preferably 5m 2 / g or more than 25m 2 / g can satisfy the range below.

[0130] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may include a plurality of carbon nanotube units. Specifically, the term "bundle type" herein refers to a secondary shape in the form of a bundle or rope, in which a plurality of carbon nanotube units are arranged in a substantially identical orientation in parallel or entangled with their longitudinal axes in the carbon nanotube unit direction, unless otherwise specified. The carbon nanotube units have a cylindrical shape of a graphite sheet with a nano-sized diameter and an sp2 bonding structure. At this time, the graphite sheets may exhibit conductor or semiconductor properties depending on the curling angle and structure. The above bundled carbon nanotubes can be uniformly dispersed during the manufacture of a cathode compared to entangled type carbon nanotubes, and can smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

[0131] In one embodiment of the present application, the negative conductive material includes a linear conductive material, and the linear conductive material may be a carbon nanotube.

[0132] In one embodiment of the present application, the carbon nanotube may be a SWCNT or / and a MWCNT. When the linear conductive agent is a SWCNT, the length of the SWCNT may be 0.5 μm to 100 μm, preferably 1 μm to 80 μm.

[0133] In one embodiment of the present application, the negative electrode conductive material may include 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.

[0134] In another embodiment, the negative electrode conductive material may include 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.

[0135] 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.

[0136] In one embodiment of the present application, since the negative electrode conductive material includes a planar conductive material and a linear conductive material and satisfies the above composition and ratio, respectively, the life characteristics of an existing lithium secondary battery are not significantly affected, and the number of points at which charging and discharging are possible increases, resulting in excellent output characteristics at a high C-rate.

[0137] The negative electrode conductive material according to the present application has a completely separate composition from the conductive material applied to the positive electrode. That is, the negative electrode conductive material according to the present application serves to secure the contact between silicon-based active materials, which undergo a significant volume expansion of the electrode due to charging and discharging, and the positive electrode conductive material serves to provide some conductivity while acting as a buffer during rolling, and is completely different in composition and role from the negative electrode conductive material of the present invention.

[0138] In addition, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different composition from the conductive material applied to a graphite-based active material. That is, the conductive material used in 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 some conductivity, and is completely different in composition and role from the negative electrode conductive material applied together with a silicon-based active material as in the present invention.

[0139] In one embodiment of the present application, the plate-shaped conductive material used as the aforementioned negative electrode conductive material has a structure and function different from those of carbon-based active materials generally used as negative electrode active materials. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material processed into a spherical or dot-shaped form to facilitate the storage and release of lithium ions.

[0140] On the other hand, the plate-shaped conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape, and can be expressed as plate-shaped graphite. In other words, it refers to a material included to maintain a conductive path within the negative electrode active material layer, and is not a material that plays a role in storing and releasing lithium, but rather a material that secures a conductive path in a planar shape within the negative electrode active material layer.

[0141] That is, in the present application, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate-shaped form and used as a material that secures a conductive path rather than a role for storing or releasing lithium. In this case, the included negative electrode active material has high capacity characteristics for lithium storage and release, and serves to store and release all lithium ions delivered from the positive electrode.

[0142] On the other hand, in the present application, the use of a carbon-based active material as an active material means that it is processed into a dot or spherical shape and used as a material that plays a role in storing or releasing lithium.

[0143] In one embodiment of the present application, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and a material in which hydrogens thereof are substituted with Li, Na, Ca, or the like, and may also include various copolymers thereof.

[0144] The negative electrode binder according to one embodiment of the present application serves to hold the silicon-based active material and the negative electrode conductive material in order to prevent distortion and structural deformation of the negative electrode structure when the volume of the silicon-based active material expands and relaxes. If the above-mentioned role is satisfied, all general negative electrode binders can be applied, and specifically, an aqueous binder can be used, and more specifically, a PAM binder can be used.

[0145] In one embodiment of the present application, the negative electrode binder may be included in an amount of 30 parts by weight or less, preferably 25 parts by weight or less, and more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition, and may be included in an amount of 5 parts by weight or more, or 8 parts by weight or more.

[0146] In one embodiment of the present application, the negative electrode can be formed by coating a negative electrode slurry containing the negative electrode active material layer composition on one or both sides of a negative electrode current collector layer.

[0147] In one embodiment of the present application, the negative electrode slurry may include a negative electrode active material layer composition; and a slurry solvent.

[0148] In one embodiment of the present application, the solid content of the cathode slurry can satisfy 5% or more and 40% or less.

[0149] In another embodiment, the solid content of the cathode slurry can satisfy a 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.

[0150] The solid content of the above cathode slurry may mean the content of the cathode composition included in the cathode slurry, and may mean the content of the cathode composition based on 100 parts by weight of the cathode slurry.

[0151] When the solid content of the above negative electrode slurry satisfies the above range, the viscosity is appropriate when forming the negative electrode active material layer, thereby minimizing particle agglomeration of the negative electrode composition, and thus has the characteristic of efficiently forming the negative electrode active material layer.

[0152] In one embodiment of the present application, the slurry solvent may be used without limitation as long as it can disperse the above-described negative electrode composition, but specifically, water or NMP may be used.

[0153] In one embodiment of the present application, the positive electrode includes a positive electrode current collector layer; and a positive electrode active material layer provided on one or both sides of the positive electrode current collector layer.

[0154] In the above positive electrode, the positive electrode current collector layer is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector layer may typically have a thickness of 1 to 500 ㎛, and fine unevenness may be formed on the surface of the positive electrode current collector layer to increase adhesion to the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0155] In the present application, the average particle diameter (D50) of the single-particle positive electrode active material may be 1 ㎛ or more and 12 ㎛ or less, 1 ㎛ or more and 8 ㎛ or less, 1 ㎛ or more and 6 ㎛ or less, more than 1 ㎛ and 12 ㎛ or less, more than 1 ㎛ and 8 ㎛ or less, or more than 1 ㎛ and 6 ㎛ or less.

[0156] Even if the above single particle cathode active material is formed into a small particle size with an average particle diameter (D50) of 1 ㎛ to 12 ㎛, the particle strength can be excellent. For example, the single particle can have a particle strength of 650 kgf / cm. 2 When rolled with a force of 100 to 300 MPa, the particle strength can be achieved. Accordingly, the single particle can be rolled with a force of 650 kgf / cm. 2 Even when rolled with a strong force, the phenomenon of fine particle increase in the electrode due to particle breakage is alleviated, thereby improving the life characteristics of the battery.

[0157] The above single-particle cathode active material can be manufactured by mixing and calcining a transition metal precursor and a lithium raw material. The secondary particles can be manufactured using a different method from the single particles, and their composition may be the same as or different from that of the single particles.

[0158] The method for forming the above single-particle positive electrode active material is not particularly limited, but it can generally be formed by increasing the firing temperature and overfiring, using an additive such as a grain growth accelerator that helps overfiring, or by changing the starting material.

[0159] For example, the sintering is performed at a temperature capable of forming single particles. To form these, the sintering should be performed at a higher temperature than that during secondary particle production. For example, when the precursor composition is the same, the sintering should be performed at a temperature that is about 30°C to 100°C higher than that during secondary particle production. The sintering temperature for forming the single particles may vary depending on the metal composition in the precursor. For example, when a high-content nickel (High-Ni) NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more is intended to be formed into single particles, the sintering temperature may be about 700°C to 1000°C, preferably about 800°C to 950°C. When the sintering temperature satisfies the above range, a cathode active material including single particles having excellent electrochemical properties can be produced. When the sintering temperature is lower than 790°C, a cathode active material including a lithium complex transition metal compound in the form of secondary particles can be manufactured, and when it exceeds 950°C, excessive sintering occurs and a layered crystal structure is not properly formed, which may result in a deterioration in electrochemical properties.

[0160] In this specification, the term "single-particle positive electrode active material" is used to distinguish it from secondary particles formed by the aggregation of tens to hundreds of primary particles in the past, and is a concept that includes a single particle formed of one primary particle and a pseudo-single-particle form that is an aggregation of 30 or fewer primary particles.

[0161] Specifically, in the present invention, the single particle cathode active material may be in the form of a single particle composed of one primary particle or a quasi-single particle that is an aggregate of 30 or fewer primary particles, and the secondary particle may be in the form of an aggregate of hundreds of primary particles.

[0162] In one embodiment of the present application, the positive electrode active material may be included 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, in 100 parts by weight of the positive electrode active material layer composition.

[0163] The above-described 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.

[0164] At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used.

[0165] In addition, the positive electrode binder plays a role of improving the adhesion between positive electrode active material particles and the adhesiveness between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene 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), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0166] In one embodiment of the present application, a lithium secondary battery is provided in which the porosity of the positive electrode active material layer is 15% or more and 30% or less, and the porosity of the negative electrode active material layer is 20% or more and 45% or less.

[0167] In another embodiment, the porosity of the negative electrode active material layer can satisfy a range of 20% or more and 35% or less, preferably 23% or more and 33% or less, and more preferably 25% or more and 30% or less.

[0168] In another embodiment, the porosity of the positive electrode active material layer can satisfy a range of 15% or more and 45% or less, preferably 17% or more and 28% or less, and more preferably 20% or more and 25% or less.

[0169] The above porosity varies depending on the composition and content of the active material, conductive material, and binder included in each active material layer, the degree of rolling, etc., and in particular, when the above range is satisfied, it has the characteristics of being able to solve the problem of resistance due to lithium ion diffusion and rapid charging performance without breaking the active material.

[0170] In one embodiment of the present application, the discharge capacity loading amount of the positive electrode active material layer composition is 2 mAh / cm 2 More than 5mAh / cm 2 Hereinafter, a lithium secondary battery is provided in which the discharge capacity loading amount of the negative electrode active material layer composition is 1 to 1.1 times greater than the discharge capacity loading amount of the positive electrode active material layer composition.

[0171] The discharge capacity loading amount of the negative active material layer composition as described above is 1 to 1.1 times the positive active material layer loading amount (NP100 to 110). If the discharge capacity loading amount of the positive active material layer composition is less than the above range, it is difficult to secure energy density, and if it exceeds the above range, problems such as rapid charging and heat generation occur.

[0172] In the present application, a lithium secondary battery is provided in which the thickness of the positive and negative electrode current collector layers is 1 μm or more and 100 μm or less, and the thickness of the positive and negative electrode active material layers is 20 μm or more and 500 μm or less.

[0173] In one embodiment of the present application, the negative electrode may be a lithium-ion negative electrode.

[0174] In one embodiment of the present application, the positive electrode may be a lithium-ion positive electrode.

[0175] At this time, the above-mentioned lithiumization method can be applied in a manner generally applied in the industry.

[0176] Specifically, the lithiumization of the negative electrode can be performed through a lithium electrolytic plating process; a lithium metal transfer process; a lithium metal deposition process; or a stabilized lithium metal powder (SLMP) coating process.

[0177] In the present application, the lithium ionization of the positive or negative electrode can increase energy density and further enhance lifespan. In other words, it has the characteristic of securing lifespan performance and energy density through the Li reservoir effect.

[0178] The separator is used to separate the negative electrode and the positive electrode and to provide a passage for lithium ions. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0179] 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.

[0180] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0181] As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used.

[0182] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte with high electrical conductivity can be produced, so that they can be used even more preferably.

[0183] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, the anion of the lithium salt is 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.

[0184] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine 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 battery capacity decrease, and improving the discharge capacity of the battery.

[0185] 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. The battery module and battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, and thus can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0186] In the present application, the lithium secondary battery may have an energy density of 700 Wh / L or more and a TR rate of 4 mbar / Ah sec or less.

[0187] At this time, the TR rate can be calculated using the following equation 3.

[0188] [Formula 3]

[0189] TR rate = (Max pressure - pre-ignition pressure) / (cell capacity) / (time before ignition - time to max pressure)

[0190] Specifically, the pressure and time of Equation 3 can be measured through a pressure gauge attached to the autoclave, and when the thermal runaway of the cell progresses, the pressure inside the autoclave increases due to the generated gas. The pressure at the point where the pressure starts to increase can be measured as the pre-ignition pressure and the time immediately before ignition, and the pressure at the point where the pressure reaches its maximum can be measured as the Max pressure and the time until the Max pressure, and this can be used to calculate.

[0191] That is, by applying the positive and negative electrodes as described above, it has the characteristics of being able to secure energy density and thermal stability as described above.

[0192] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0193] <Manufacturing Example>

[0194] (1) Manufacturing of anode

[0195] Li(Ni) as a cathode active material a Co b Mn c )O2 and LMFP were used.

[0196] At this time, NCM excluding lithium (Li) and oxygen (O2) of the positive electrode active material had a ratio of Ni:Co:Mn=70:20:10, satisfying the ratio of a:b:c=70:20:10 (a:b:c=0.70:0.20:0.10). In addition, D50 was 3.8 μm, Dmin and Dmax were 1.2 μm and 13 μm, and the BET specific surface area was 0.64 m 2 , and true density 4.78~4.80g / cm 3 am.

[0197] The content of Mn in the above LMFP was 60 at%.

[0198] And, the positive electrode slurry was prepared by adding the positive electrode active material, positive electrode conductive agent (LB.CNT), and binder (PVdF, KF9700) in a weight ratio of 97.96:0.8:1.24 to a solvent (N-methylpyrrolidone, NMP). The positive electrode slurry was applied to an aluminum (Al) thin film, which is a positive electrode current collector, with a thickness of 12 μm (4 mAh / cm). 2 ) and dried, and then rolled using a roll press to manufacture a positive electrode (porosity 23%).

[0199] (2) Manufacturing of cathode

[0200] A negative electrode active material layer composition was prepared using Si / C: artificial graphite (20:80) as a silicon-based active material, polyacrylamide as a first and second conductive agent and binder at a weight ratio of 80:9.6:0.4:10. A negative electrode slurry was prepared by adding it to distilled water as a solvent for forming a negative electrode slurry (solid content concentration 28 wt%).

[0201] The first challenge material is a plate-shaped graphite (specific surface area: 17 m 2 / g, average particle diameter (D50): 3.5 um), and the second conductive material is a carbon nanotube.

[0202] As a mixing method, the first conductive agent, the second conductive agent, the binder, and water were dispersed using a homo mixer at 2500 rpm for 30 minutes, and then the active material was added and dispersed at 2500 rpm for 30 minutes to produce a slurry.

[0203] The negative electrode slurry was applied to both sides of a copper current collector (thickness: 8㎛) as a negative electrode current collector at 3.78 mAh / cm 2 The coating was carried out with a capacity loading amount, rolled (roll pressed), and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 23 μm) (porosity 28%).

[0204] (3) Manufacturing of secondary batteries

[0205] An electrode assembly was manufactured by interposing a compressible thin film separator (PE 12um) ceramic coating 3um / 3um between the positive and negative electrodes. After positioning the electrode assembly inside a case, an electrolyte was injected into the case to manufacture a lithium secondary battery.

[0206] At this time, the positive and negative electrodes satisfied the composition and content of Table 1 below.

[0207] For reference, Fig. 3 shows a distribution diagram based on the olivine-based active material and silicon-based active material of the examples and comparative examples of the present application, and specifically, the shaded portion corresponds to the area satisfying the range of Equation 1.

[0208] Cathode active material composition Cathode active material content Cathode active material composition Cathode active material content Example 1 Li (Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1050:50Si / C: Artificial graphite20:80Example 2Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1055:45Si / C: Artificial graphite20:80Example 3Li(Ni a Co b Mnc )O2:LMFPa:b:c=70:20:1060:40Si / C: Artificial graphite20:80Example 4Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1065:35Si / C: Artificial graphite20:80Example 5Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1070:30Si / C: Artificial graphite20:80Example 6Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1080:20Si / C: Artificial graphite10:90Example 7Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1075:25Si / C: Artificial graphite10:90Example 8Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1070:30Si / C: Artificial graphite10:90Example 9Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1030:70Si / C: Artificial graphite50:50Example 10Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1040:60Si / C: Artificial graphite50:50Example 11Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1050:50Si / C: Artificial graphite50:50Example 12Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1020:80Si / C: Artificial graphite100:0Example 13Li(Ni a Co b Mn c)O2:LMFPa:b:c=70:20:1030:70Si / C: Artificial graphite100:0Example 14Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1040:60Si / C: Artificial graphite100:0Comparative example 1Li(Ni a Co b Mn c )O2a:b:c=70:20:10100Si / C: Artificial graphite20:80Comparative example 2Li(Ni a Co b Mn c )O2a:b:c=70:20:10100Si / C100Comparative example 3Li(Ni a Co b Mn c )O2a:b:c=70:20:10100 Artificial graphite100 Comparative example 4LMFP100Si / C: Artificial graphite20:80 Comparative example 5LMFP100Si / C100 Comparative example 6LMFP100 Artificial graphite100 Comparative example 7Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1050:50Si / C100Comparative example 8Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1050:50Artificial graphite100Comparative example 9Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1097:3Si / C: Artificial graphite20:80Comparative example 10Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:105:95Si / C: Artificial graphite20:80Comparative example 11Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1071.28:28.72Si / C: Artificial graphite39.02:60.98Comparative example 12Li(Ni a Co b Mn c)O2:LMFPa:b:c=70:20:1071.28:28.72Si / C: Artificial graphite58.82:41.18Comparative example 13Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1071.28:28.72Si / C: Artificial graphite70.73:29.27Comparative example 14Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1071.28:28.72Si / C: Artificial graphite82.35:17.65Comparative example 15Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1073.4:26.6Si / C: Artificial graphite70.73:29.27Comparative example 16Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1073.4:26.6Si / C: Artificial graphite 100:0 Comparative example 17Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1090:10Si / C: Artificial graphite20:80Comparative example 18Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1080:20Si / C: Artificial graphite30:70Comparative example 19Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1070:30Si / C: Artificial graphite40:60Comparative example 20Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1060:40Si / C: Artificial graphite60:40Comparative example 21Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1050:50Si / C: Artificial graphite90:10Comparative example 22Li(Ni aCo b Mn c )O2:LMFPa:b:c=70:20:1060:40Si / C: Artificial graphite10:90Comparative example 23Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1040:60Si / C: Artificial graphite20:80Comparative example 24Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1030:70Si / C: Artificial graphite30:70Comparative example 25Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1020:80Si / C: Artificial graphite50:50Comparative example 26Li(Ni a Co b Mn c )O2:LMFPa:b:c=70:20:1010:90Si / C: Artificial graphite 90:10

[0209] <Experimental Example>

[0210] 1) TP evaluation

[0211] For the lithium secondary batteries manufactured in the above examples and comparative examples, a structure as shown in Fig. 2 was formed for evaluation, and a heat pad in contact with the cell was heated to induce thermal runaway of the cell.

[0212] The experiment was conducted in an autoclave (isolated from the external environment / atmosphere) under an N2 atmosphere, and the pressure of the gas emitted when thermal runaway occurred was measured using a pressure gauge in the autoclave. To prevent confusion between cell capacity and footprint, the 40Ah A5-A cell was used for evaluation, and the TR rate according to this is shown in Table 2 below.

[0213] The pressure below was measured through a pressure gauge attached to the autoclave. As the thermal runaway of the cell progresses, the pressure inside the autoclave increases due to the generated gas. The pressure at the point where the pressure starts to increase can be measured as the pre-ignition pressure and the time immediately before ignition, and the pressure at the point where the pressure reaches its maximum can be measured as the Max pressure and the time until the Max pressure, which can be used to calculate.

[0214] TR Rate = (Max pressure - Pre-ignition pressure) / (Cell capacity) / (Time to ignition - Max pressure)

[0215] TR rate (mbar / Ah sec) Example 11.7 Example 22.0 Example 32.3 Example 42.6 Example 53.0 Example 62.9 Example 72.6 Example 82.3 Example 91.7 Example 102.1 Example 112.9 Example 121.6 Example 132.4 Example 143.3 Comparative Example 19 Comparative Example 220 Comparative Example 34 Comparative Example 40.4 Comparative Example 50.6 Comparative Example 60.1 Comparative Example 74.5 Comparative Example 80.9 Comparative Example 97 Comparative Example 100.4 Comparative Example 114.4 Comparative Example 125.7 Comparative Example 136.4 Comparative Example 147.0 Comparative Example 156.7 Comparative Example 168.3 Comparative Example 174.9 Comparative Example 184.7 Comparative Example 194.3 Comparative Example 204.3 Comparative Example 214.2 Comparative Example 221.7 Comparative Example 231.3 Comparative Example 241.2 Comparative Example 251.1 Comparative Example 261.0

[0216] 2) ED evaluation

[0217] For the lithium secondary batteries manufactured in the above examples and comparative examples, the energy density is calculated using the discharge energy obtained during 0.33C charge / discharge and the volume of the battery. However, since the batteries used in experiments are generally manufactured in a smaller size than the batteries installed in automobiles, resulting in low space utilization, when conducting the ED evaluation, the discharge energy and volume are converted and calculated based on the size of the battery installed in automobiles.

[0218] ED Example 1700 Example 2710 Example 3720 Example 4730 Example 5740 Example 6718 Example 7710 Example 8700 Example 9710 Example 10725 Example 11740 Example 12709 Example 13720 Example 14735 Comparative Example 1800 Comparative Example 2950 Comparative Example 3650 Comparative Example 4580 Comparative Example 5653 Comparative Example 6480 Comparative Example 7780 Comparative Example 8560 Comparative Example 9730 Comparative Example 10580 Comparative Example 11804 Comparative Example 12830 Comparative Example 13845 Comparative Example 14855 Comparative Example 15852 Comparison Example 16867 Comparison Example 17801 Comparison Example 18810 Comparison Example 19804 Comparison Example 20802 Comparison Example 21796 Comparison Example 22676 Comparison Example 23676 Comparison Example 24681 Comparison Example 25679 Comparison Example 26678

[0219] In the case of the lithium secondary battery according to the present application, instead of simply applying a carbon-based active material and an olivine-based active material alone, in order to secure energy density, a layered active material containing nickel and a silicon-based active material are included in the positive electrode, respectively, so that the energy density can be satisfied, and the problem of thermal stability (TP) due to the resulting increase in capacity is solved by deriving a weight ratio that satisfies Equations 1 and 2. In general, when the content of the silicon-based active material in the negative electrode increases, the energy density increases, but the thermal stability is inferior, and accordingly, when the content of the olivine-based active material in the positive electrode is increased, the problem of thermal stability is improved, but the energy density decreases. However, the present applicant derived the ratios of Equations 1 and 2 through research, and it was found through the above examples and comparative examples that when this is applied, both energy density and thermal stability can be secured at the same time.

[0220] From the perspective of cell energy density, as the olivine-based active material increases, the positive electrode becomes thicker, and the content of silicon-based active material in the negative electrode must increase to compensate for the thickness. In the present application, the lower limit of the silicon-based active material content (B) is determined according to the content (A) of the olivine-based active material in terms of achieving a specific energy density, and in particular, from the perspective of energy density, 4.524+0.939×e in Equation 1 0.0537×A

[0221] Meanwhile, as the content of olivine-based active materials increases, the thermal stability is excellent, so more silicon-based active materials can be applied. From the perspective of TR rate, the upper limit of the content (B) of silicon-based active materials is determined according to the content (A) of olivine-based active materials, and in particular, to satisfy the TR rate, B < -4.312 + 5.183 × e in Equation 1 0.0537×A We were able to verify that the values ​​must be satisfied.

[0222] That is, in the case of the lithium secondary battery according to the present application, it was found that it is possible to secure both energy density and thermal stability, which were previously difficult to achieve, and that this can be achieved when the olivine-based active material and the silicon-based active material satisfy the relationship of Equation 1 of the present application.

[0223] In the case of Comparative Examples 1 to 3, the positive electrode of NCM was simply applied as the counter electrode of the negative electrode, and this corresponds to the case where the content of the silicon-based active material was adjusted or a graphite-based negative electrode was used.

[0224] In the case of Comparative Examples 1 and 2, the energy density is satisfactory, but the content of silicon-based active material is high, so thermal stability is low and TR characteristics are deteriorated. In contrast, when a graphite-based negative electrode is used as the negative electrode, thermal stability is secured, but it is confirmed that the energy density is deteriorated.

[0225] ​In Comparative Examples 4 to 6, an olivine-based positive electrode was applied as the counter electrode of the negative electrode, and the content of the silicon-based active material was adjusted or a graphite-based negative electrode was used.

[0226] In the case of Comparative Examples 4 to 6, in which an olivine-based cathode was applied, the thermal stability was judged to be excellent, but it was confirmed that the energy density was reduced because NCM was not mixed.

[0227] In Comparative Examples 7 to 9, olivine-based and NCM are used together as positive electrodes, but Comparative Example 7 does not satisfy the range of Equation 1 of the present application, Comparative Example 8 is a case where a graphite-based negative electrode is used alone, and Comparative Example 9 is a case where the content of the olivine-based active material is low, so the ranges of Equations 1 and 2 are not satisfied.

[0228] In the case of Comparative Examples 7 and 9, the energy density can be satisfied at the desired level, but it can be confirmed that the TR characteristics are deteriorated. In particular, through Comparative Examples 7 and 9, it can be confirmed that the TR characteristics are deteriorated when the range of Equation 1 of the present application is exceeded, and in the case of Comparative Example 8, it can be confirmed that the TR characteristics are satisfied by using a graphite-based negative electrode, but the energy density is not secured.

[0229] In addition, Comparative Examples 10 to 26 do not satisfy the range of Formula 1 of the present invention, and as can be seen in Tables 2 and 3, it can be confirmed that the energy density and / or TR characteristics are not satisfied, and in particular, through Comparative Examples 17 to 26, it can be confirmed that the effect according to Formula 1 of the present invention is superior to that of the Comparative Examples.

[0230] For reference, Examples 2 to 5 correspond to cases where the amount of NCM active material among the positive electrode active materials was increased and the amount of LMFP was reduced while keeping the negative electrode fixed based on Example 1. As can be seen from the data in Tables 2 and 3, when the amount of NCM is increased to the range of the present application, the energy density increases, but it can be seen that it is inferior to Example 1 in terms of thermal stability. Examples 7 and 8 are similar when compared to Example 6, and Examples 10, 11, 13, and 14 also show the same tendency. That is, in the case of the lithium secondary battery according to the present application, when used within the range of Equation 1, it has the characteristic of being able to control the energy density and thermal stability according to the purpose.

Claims

1. A lithium secondary battery comprising a positive electrode; a negative electrode; and an electrolyte, The above positive electrode includes a positive electrode active material layer including a positive electrode active material layer composition; The above negative electrode includes a negative electrode active material layer including a negative electrode active material layer composition, The above positive electrode active material layer composition includes a positive electrode active material including a layered active material including nickel; and an olivine-based active material; The above negative electrode active material layer composition includes a negative electrode active material including a silicon-based active material, The weight portion of the olivine-based active material based on 100 parts by weight of the positive electrode active material is A, and the weight portion of the silicon-based active material based on 100 parts by weight of the negative electrode active material is B. A lithium secondary battery wherein the above A and B satisfy the following equations 1 and 2. [Formula 1] 4.524+0.939×e 0.0537×A < B < -4.312+5.183×e 0.0537×A [Formula 2] 10 ≤ A ≤ 90 2. In claim 1, A lithium secondary battery, wherein the layered active material containing the nickel is included in an amount of 10 parts by weight or more and 90 parts by weight or less based on 100 parts by weight of the positive electrode active material.

3. In claim 1, A lithium secondary battery comprising 5 parts by weight or more and 100 parts by weight or less of the silicon-based active material based on 100 parts by weight of the negative active material.

4. In claim 1, The above negative active material further includes a carbon-based active material, The silicon-based active material comprises 5 parts by weight or more and 100 parts by weight or less based on 100 parts by weight of the negative active material. A lithium secondary battery comprising the carbon-based active material in an amount of 0 parts by weight or more and 95 parts by weight or less.

5. In claim 1, The layered active material containing the nickel is lithium nickel-cobalt-aluminum (NCA) oxide; lithium nickel-cobalt-manganese (NCM) oxide; or lithium nickel-cobalt-manganese-aluminum (NCMA) oxide. A lithium secondary battery wherein the above olivine-based active material is lithium manganese iron phosphate (LMFP); or lithium iron phosphate (LFP).

6. In claim 1, The layered active material containing the nickel is lithium nickel-cobalt-manganese (NCM) oxide, The above olivine-based active material is LMFP, A lithium secondary battery comprising Mn in an amount of 0 at% or more and 90 at% or less based on 100 at% of all elements included in the LMPF.

7. In claim 1, The above silicon-based active material is SiOx (0 <x<2), Si / C, 및 Si 합금으로 이루어진 군에서 선택되는 1 이상을 포함하는 것인 리튬 이차 전지.

8. In claim 1, A lithium secondary battery wherein the above positive electrode active material is a single particle positive electrode active material.

9. In claim 1, A lithium secondary battery comprising nickel in a layered active material containing the nickel in an amount of 75 mol% or less of the total metal excluding lithium.

10. In claim 1, The porosity of the above positive electrode active material layer is 15% or more and 30% or less, A lithium secondary battery, wherein the porosity of the negative active material layer is 20% or more and 45% or less.

11. In claim 1, The discharge capacity loading amount of the above positive electrode active material layer composition is 2 mAh / cm 2 More than 5mAh / cm 2 Below is the following: A lithium secondary battery, wherein the discharge capacity loading amount of the negative electrode active material layer composition is 1 to 1.1 times greater than the discharge capacity loading amount of the positive electrode active material layer composition.

12. In claim 1, The above positive electrode includes a positive electrode current collector layer, The above negative electrode includes a negative electrode current collector layer, The thickness of the positive and negative current collector layers is 1 μm or more and 100 μm or less, A lithium secondary battery, wherein the thickness of the positive and negative electrode active material layers is 20 μm or more and 500 μm or less.

13. In claim 1, The above lithium secondary battery is a lithium secondary battery having an energy density of 700 Wh / L or more and a TR rate defined by Equation 3 below of 4 mbar / Ah sec or less. [Formula 3] TR rate = (Max pressure - pre-ignition pressure) / (cell capacity) / (time before ignition - time to max pressure) 14. In claim 1, A lithium secondary battery, wherein the average particle diameter (D50) of the above silicon-based active material is 1 μm or more and 10 μm or less.

15. In claim 1, The BET surface area of ​​the above silicon-based active material is 0.01 m 2 / g to 150.0 m 2 A lithium secondary battery having a mass of / g.

16. In claim 1, A lithium secondary battery wherein the above silicon-based active material is in a crystalline or amorphous form and is not porous.

17. In claim 1, A lithium secondary battery, wherein at least one of the positive and negative electrodes is a lithium-ion electrode.

18. In claim 1, A lithium secondary battery further comprising a separator between the positive electrode and the negative electrode.

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