Lithium-ion rechargeable battery

Abstract

This application relates to lithium secondary batteries.

Description

Technical Field

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

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

Background Art

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

[0004] <00 , the lithium ions inserted into the positive electrode move to the negative electrode through the electrolyte, and during discharge, the lithium ions move from the negative electrode to the positive electrode again.

[0007] ​​​​​​​​Lithium-ion batteries are used in a variety of industrial fields, including automobiles, small modules, and mobile phones. While the performance of lithium-ion batteries in each field involves various factors, the development of technologies that aim to increase energy density, ensure stability, enable rapid charging, and ensure long lifespan is generally required.

[0008] In particular, carbon-based materials such as graphite excel in stability and reversibility as anode materials, but have limitations in terms of capacity. Therefore, in fields aiming for high capacity, i.e., maximizing energy density, there is an increasing trend to use Si-based materials, which have high theoretical capacity, as anode materials. However, when Si-based materials are simply included in high content for the purpose of high capacity, the lifetime performance deteriorates rapidly due to volume expansion issues compared to carbon-based materials, making them difficult to apply in real life.

[0009] To overcome the aforementioned problems when using Si-based materials as a negative electrode, various methods are being discussed, such as adjusting the driving potential, further coating a thin film on the active material layer, suppressing volume expansion itself by adjusting the particle size of the silicon-based compound, or developing a binder that can control the volume expansion of the silicon-based compound to prevent the conduction path from being interrupted. Research is also being conducted to compensate for the life characteristics of the silicon-based negative electrode by pre-lithifying the silicon-based active material layer to limit the ratio of silicon-based active material used during initial charging and discharging, thereby imparting a reservoir role.

[0010] As a counter electrode to the aforementioned Si-based anode, a positive electrode such as NCM(A) containing a high nickel content has been developed. When using a positive electrode such as NCM(A) containing a high nickel content, the high capacity characteristics that are an advantage of the Si-based anode can be maintained, and the energy density is also high, ensuring fast charging performance.

[0011] However, due to the characteristics of the Si-based anode and the high nickel content of the NCM(A) cathode itself, a problem arose where stability rapidly deteriorated. In particular, ignition related to electric vehicles has emerged as a major problem, and as a result, the need for lithium secondary batteries with gradually strengthened thermal propagation (TP) standards is increasing. However, batteries with the aforementioned Si-based anode and high nickel content NCM(A) cathode suffer from the problem that, similar to lifespan performance, the higher the energy cell, the more energy is stored in the same volume, resulting in inferior thermal stability.

[0012] To solve this problem, an olivine-based cathode such as LFP can be used as the positive electrode, which is the counter electrode to the Si-based anode. In other words, in order to solve the aforementioned thermal stability of batteries containing a Si-based anode and an NCM(A) cathode with a high nickel content, research has been conducted to ensure stability by using an LFP olivine-based cathode, even though the energy density and capacity characteristics are relatively reduced.

[0013] However, when an olivine-based cathode such as LFP is used as the cathode opposite to the Si-based anode, the aforementioned stability can be ensured, but the capacity drops sharply, and it has no advantages compared to conventionally used batteries.

[0014] To solve the aforementioned problems, research is being conducted on combining and applying various types of active materials to the positive and negative electrodes. However, the problem of ensuring high energy density, thermal stability, and lifetime performance, which are incompatible with each other, persists.

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

[0016] The background information provided herein is intended to present a general context of public disclosure. Unless otherwise explicitly stated herein, the materials described in this section are not prior art to the claims of this application and, by being included in this section, shall not be deemed prior art or a proposal of prior art. [Prior art documents] [Patent Documents]

[0017] [Patent Document 1] Japanese Patent Publication No. 2009-080971 [Overview of the project] [Problems that the invention aims to solve]

[0018] As a result of research into the aforementioned problems, it was found that when the negative electrode contains a silicon-based active material, and the positive electrode (counter electrode) contains a layered active material containing nickel and a mixture of olivine-based active materials, it is possible to simultaneously achieve energy density and thermal stability, which were previously incompatible, and the problem of lifetime characteristics can also be solved.

[0019] Therefore, this application provides a lithium secondary battery that can solve the aforementioned problems. [Means for solving the problem]

[0020] One embodiment of this 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, the negative electrode comprises a negative electrode active material layer comprising a negative electrode active material layer composition, the positive electrode active material layer composition comprises a layered active material comprising nickel and a positive electrode active material comprising an olivine-based active material, the negative electrode active material layer composition comprises a negative electrode active material comprising a silicon-based active material, the part by weight of the olivine-based active material is A based on 100 parts by weight of the positive electrode active material, the part by weight of the silicon-based active material is B based on 100 parts by weight of the negative electrode active material, and A and B satisfy the following formulas 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

[0021] This application demonstrates that, in particular, when the composition ratio of the positive and negative electrodes is adjusted to the ranges of Equations 1 and 2 as described above, it is possible to simultaneously achieve energy density and lifetime characteristics that were previously incompatible with each other, and to solve the problem of thermal stability. [Effects of the Invention]

[0022] The lithium secondary battery according to this application is characterized in that the positive electrode basically contains a layered active material containing nickel and an olivine-based active material, and the negative electrode contains a silicon-based active material. In other words, an energy density (ED 700 Wh / L or more) can be secured by the above combination.

[0023] Instead of simply applying carbon-based and olivine-based active materials individually, the positive electrode contains a layered active material containing nickel and a silicon-based active material, respectively, to ensure energy density. The problem of thermal stability (TP) due to the resulting increase in capacity was solved by deriving weight ratios that satisfy equations 1 and 2. Generally, increasing the content of silicon-based active material in the negative electrode increases energy density but degrades thermal stability. Consequently, increasing the content of olivine-based active material in the positive electrode improves thermal stability but decreases energy density. However, through research, the applicant has derived the ratios of equations 1 and 2 described above, and by applying these ratios, both energy density and thermal stability are ensured simultaneously.

[0024] In other words, by adjusting the composition and content as described above, it is possible to ensure energy density and thermal stability simultaneously. Furthermore, by applying a certain portion of silicon-based active material to the negative electrode, the thickness of the active material layer is reduced due to a decrease in the loading amount, and the mobility of Li is improved by ensuring porosity. Consequently, the ability to perform rapid charging is also ensured.

[0025] In conclusion, the lithium secondary battery described in this application solves the problem of thermal stability, which is incompatible with securing high energy density, and also ensures rapid charging performance. Although it exhibits some performance inferiority to other cells with enhanced lifespan (LFP / Gr, LMFP / Gr, NCM / Gr), it exhibits superior lifespan performance compared to conventional cells aimed at high energy density (Si / NCM, Si / LFP).

[0026] The accompanying drawings illustrate exemplary embodiments of this application and, together with the following detailed description, are intended to provide a deeper understanding of the technical aspects of this application; therefore, this application should not be construed as being limited to the drawings. [Brief explanation of the drawing]

[0027] [Figure 1] This figure shows the lithium secondary battery according to this application. [Figure 2] This figure shows the structure for evaluating the lithium secondary batteries manufactured in the examples and comparative examples of this application. [Figure 3] This figure shows the distribution of olivine-based and silicon-based active materials in the examples and comparative examples of this application, based on the current application. [Modes for carrying out the invention]

[0028] Before describing the present invention, let us first define some terms.

[0029] In this specification, when a part "includes" a component, this means, unless otherwise stated, that it may include other components rather than excluding them.

[0030] In this specification, "p~q" means "p or greater and q or less".

[0031] In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan. In other words, in this application, BET specific surface area can mean the specific surface area measured by the above measurement method.

[0032] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the 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. Alternatively, the particle size distribution may be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). When the particles pass through the laser beam, the difference in diffraction patterns due to particle size is measured to calculate the particle size distribution.

[0033] In this specification, the statement that a polymer contains a monomer as a monomer unit means that the monomer participates in the polymerization reaction and is included as a repeating unit within the polymer. In this specification, when a polymer is said to contain a monomer, this is interpreted as being equivalent to the polymer containing a monomer as a monomer unit.

[0034] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise specified as "homopolymer."

[0035] In this specification, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers of various degrees of polymerization (standard samples) commercially available for molecular weight measurement. In this specification, molecular weight refers to weight-average molecular weight unless otherwise specified.

[0036] The present invention will be described in detail below with reference to the drawings, so that a person with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0037] One embodiment of this 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, the negative electrode comprises a negative electrode active material layer comprising a negative electrode active material layer composition, the positive electrode active material layer composition comprises a layered active material comprising nickel and a positive electrode active material comprising an olivine-based active material, the negative electrode active material layer composition comprises a negative electrode active material comprising a silicon-based active material, the part by weight of the olivine-based active material is A based on 100 parts by weight of the positive electrode active material, the part by weight of the silicon-based active material is B based on 100 parts by weight of the negative electrode active material, and A and B satisfy the following formulas 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

[0038] In the case of the lithium secondary battery according to this application, the thermal stability that cannot be achieved simultaneously with securing high energy density is resolved by a combination of positive and negative electrode active materials that includes the ranges of Equations 1 and 2, and rapid charging performance can be ensured. Although it shows some inferiority in performance compared to other cells with enhanced lifespan (LFP / Gr, LMFP / Gr, NCM / Gr), it exhibits superior lifespan performance compared to conventional cells aimed at high energy density (Si / NCM, Si / LFP).

[0039] Figure 1 shows a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 containing a negative electrode active material layer 20 can be seen on one side of a negative electrode current collector layer 10, and a positive electrode 200 containing a positive electrode active material layer 40 can be seen on one side of a positive electrode current collector layer 50, showing that the negative electrode 100 and the positive electrode 200 for the lithium secondary battery are formed in a laminated structure with a separation membrane 30 in between.

[0040] In this application, the lithium secondary battery may further include a separator membrane between the positive electrode and the negative electrode.

[0041] The following sections will explain the positive electrode, negative electrode, electrolyte, and separator membrane included in lithium secondary batteries.

[0042] In this application, the negative electrode includes a negative electrode active material layer containing a negative electrode active material layer composition.

[0043] In this application, the negative electrode comprises a negative electrode current collector layer; and a negative electrode active material layer comprising a negative electrode active material layer composition provided on one or both sides of the negative electrode current collector layer.

[0044] In this case, the negative electrode active material layer composition may include one or more selected from the group consisting of negative electrode active material; negative electrode conductive material; and negative electrode binder.

[0045] In this application, the positive electrode includes a positive electrode active material layer containing a positive electrode active material layer composition.

[0046] In this application, the positive electrode comprises a positive electrode current collector layer; and a positive electrode active material layer comprising a positive electrode active material layer composition provided on one or both sides of the positive electrode current collector layer.

[0047] In this case, the positive electrode active material layer composition may include one or more selected from the group consisting of positive electrode active material; positive electrode conductive material; and positive electrode binder.

[0048] In one embodiment of this application, the negative electrode active material includes a silicon-based active material, and the positive electrode active material may include a layered active material containing nickel and an olivine-based active material.

[0049] While carbon-based materials like graphite offer excellent stability and reversibility as negative electrode active materials, they have limitations in terms of capacity. Therefore, in fields where high capacity is required, silicon-based active materials with high theoretical capacity are used.

[0050] However, in order to apply silicon-based active materials alone, the issue of volume expansion must be appropriately resolved, but no alternative has been implemented. As a result, the negative electrode active material in this application uses a silicon-based active material, and a layered active material containing nickel and an olivine-based active material are used as a positive electrode active material in combination.

[0051] In one embodiment of this application, a lithium secondary battery is provided, wherein, based on 100 parts by weight of the positive electrode active material, the olivine-based active material is included in an amount of 10 to 90 parts by weight, and the nickel-containing layered active material is included in an amount of 10 to 95 parts by weight.

[0052] In another embodiment, the olivine-based active material may be present in an amount of 100 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, relative to 100 parts by weight of the positive electrode active material.

[0053] In this application, the amount of the olivine-based active material in parts by weight can be represented by A above, based on 100 parts by weight of the positive electrode active material.

[0054] In another embodiment, based on 100 parts by weight of the positive electrode active material, the layered active material containing nickel may be contained 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.

[0055] In the present application, there is provided a lithium secondary battery in which, based on 100 parts by weight of the negative electrode active material, the silicon-based active material is contained in an amount of 5 parts by weight or more and 100 parts by weight or less.

[0056] In another embodiment, based on 100 parts by weight of the negative electrode active material, the silicon-based active material may be contained 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.

[0057] In the present application, based on 100 parts by weight of the negative electrode active material, the parts by weight of the silicon-based active material may be represented by B described above.

[0058] At this time, silicon (Si) in the silicon-based active material may be contained 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.

[0059] That is, in the present application, the silicon-based active material may include one or more selected from the group consisting of SiO x (x = 0), SiO x (0 < x < 2), Si / C, and Si alloy, and at this time, the weight ratio of silicon (Si) in the silicon-based active material can satisfy the above range.

[0060] In the present application, the negative electrode active material further includes a carbon-based active material. Based on 100 parts by weight of the negative electrode active material, the silicon-based active material is contained in an amount of 5 parts by weight or more and 100 parts by weight or less, and the carbon-based active material may be contained in an amount of 0 parts by weight or more and 95 parts by weight or less.

[0061] In another embodiment, the carbon-based active material may be included in an amount of 30 to 95 parts by weight, preferably 40 to 93 parts by weight, and more preferably 50 to 90 parts by weight, relative to 100 parts by weight of the negative electrode active material.

[0062] Generally, the higher the energy of a cell, the more energy it stores in the same volume, which leads to a problem of fragile thermal stability. Specifically, increasing the content of silicon-based active material in the negative electrode ensures energy density but reduces thermal stability, while increasing the content of olivine-based active material in the positive electrode improves thermal stability but decreases energy density.

[0063] However, as described above, this application has the characteristic that energy density can be ensured and thermal stability can be ensured by applying specific compositions and the contents of formulas 1 and 2 to the positive electrode and negative electrode, respectively. In other words, although the energy density of the lithium secondary battery of this application may be lower than when a silicon-based negative electrode and a positive electrode containing a layered active material containing nickel are simply applied individually, the main objective of the present invention is to ensure an energy density of 700 Wh / L or more and thermal stability by satisfying the above-mentioned composition and contents.

[0064] In other words, if 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, an energy density of 700 Wh / L or more can be secured, and the TR rate can be 4 or less. If the range of Equation 1 cannot be satisfied, the energy density of the cell cannot be secured, and the TR rate cannot be secured, so the thermal stability problem cannot be solved.

[0065] In one embodiment of the present application, the layered active material containing 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), and a lithium secondary battery is provided.

[0066] In the present application, LMFP means lithium manganese iron phosphate, and LFP means lithium iron phosphate.

[0067] At this time, in the case of LMFP, LiMn x Fe 1-x PO4 may be expressed, and LFP may be expressed as LiFePO4. Here, the x may have a value of 0 < x < 1.

[0068] Generally, in the case of the positive electrode active material, depending on the type of crystal lattice structure, it is roughly divided into a layered type, a spinel type or an olivine type.

[0069] In the present application, the layered active material containing nickel is lithium nickel-cobalt-aluminum (NCA) oxide; lithium nickel-cobalt-manganese (NCM) oxide; or lithium nickel-cobalt-manganese-aluminum (NCMA) oxide, and generally may contain a ternary alloy material. In the case of the layered active material, the constituent elements of the positive electrode active material are located in a layered structure, and lithium ions are stored between the crystal lattice layers during charging of the lithium secondary battery. At this time, a large amount of lithium ions can be stored between the wide and flat layers, and when using this material, there is an advantage of high energy capacity, but on the other hand, it causes a problem that the stability decreases during high voltage charging.

[0070] In this application, the olivine-based active material may be LMFP or LFP, but generally exhibits a hexahedral form, has higher lattice structure stability compared to layered active materials, exhibits less degradation of the crystal structure even when lithium ions escape during discharge, and has high lifetime and thermal stability. However, it suffers from the problem of a slow lithium ion diffusion rate and relatively low energy density.

[0071] Furthermore, in the case of the spinel structure, since it is an oxide crystal structure and does not use cobalt, the lattice structure has a three-dimensional form and is highly stable, but it has the problem that the capacity and lifespan decrease as charging and discharging progress.

[0072] In the case of the positive electrode active material according to this application, the layered active material containing nickel is characterized in that lithium nickel-cobalt-manganese (NCM) oxide and olivine-based active materials use LMFP.

[0073] In one embodiment of this application, the amount of Mn may be 0 at% or more and 90 at% or less, based on a total of 100 at% of the elements contained in the LMFP.

[0074] The olivine-based active material may be LFP or LMFP, exhibiting the same structure. However, in the case of LMFP, Mn is substituted for Fe, which has the effect of increasing the voltage, and thus has the characteristic of being able to increase the energy density even among olivine-based active materials, which have a relatively low energy density.

[0075] In this application, the present invention provides a lithium secondary battery in which the positive electrode active material is a single-particle positive electrode active material.

[0076] Furthermore, the present invention provides a lithium secondary battery in which the nickel contained in the layered active material containing nickel is present in an amount of 75 mol% or less of the total metals excluding lithium.

[0077] Generally, when implementing a high-voltage cell in a lithium secondary battery containing a silicon-based active material, in order to solve the resistance problem, it is necessary to use secondary particles as the positive electrode active material. However, in a high-voltage cell, there is an issue of cracking of the secondary particles and gas generation. As described above, when applying a single-particle positive electrode active material, it becomes possible to drive a high-voltage cell.

[0078] In the present application, the carbon-based active material contained 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 is SiO x (0 < x < 2), Si / C, and one or more selected from the group consisting of Si alloys may be included.

[0079] More specifically, the carbon-based active material contained in the negative electrode active material includes natural graphite or artificial graphite, and the silicon-based active material may include Si / C.

[0080] In the present application, the Si / C may be expressed as a silicon carbon composite.

[0081] In this specification, the silicon carbon composite is a composite of Si and C and is distinguished from silicon carbide (Silicon carbide) denoted as SiC. Since the silicon carbide does not react electrochemically with lithium, all performances such as lifespan may be measured as 0.

[0082] The silicon carbon composite may be a composite of silicon and graphite or the like, and may form a structure surrounded by graphene or amorphous carbon or the like around a core in which silicon and graphite or the like are composite. The silicon in the silicon carbon composite may be nanosilicon. For example, the nanosilicon may be silicon in the range of 1 nm to 999 nm.

[0083] Lithium-ion batteries have size requirements depending on their application, which necessitates their design within limited space. While consumer demand for increased energy density and improved high-power performance is growing, using high-capacity cathode materials necessitates increasing the content of the anode material to match, thus limiting the ability to improve battery efficiency within a limited space. Furthermore, depending on the type of anode material, it is necessary to design a cathode material with an efficiency suitable for the anode material's efficiency.

[0084] As a result, this application has the characteristic of being able to ensure energy density while simultaneously ensuring lifetime performance and thermal stability by using a mixture of Si / C as the silicon-based active material and a material with the aforementioned composition and content as the positive electrode active material.

[0085] The negative electrode according to this 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.

[0086] The negative electrode current collector layer typically 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, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys may be used. Furthermore, fine irregularities can be formed on the surface to strengthen the bonding force of the negative electrode active material, and it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0087] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0088] On the other hand, the average particle size (D50) of the silicon-based active material of the present invention may be 1 μm to 10 μm, more specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. If the average particle size is less than 5 μm, the specific surface area of ​​the particles increases too much, causing the viscosity of the negative electrode slurry to increase too much. As a result, the dispersion of the particles constituting the negative electrode slurry is not smooth. Also, if the size of the silicon-based active material is too small, the contact area between the silicon particles and the conductive material decreases due to the composite consisting of the conductive material and the binder in the negative electrode slurry, increasing the likelihood of the conductive network being interrupted and reducing the capacity retention rate. On the other hand, if the average particle size exceeds 10 μm, there will be silicon particles that are too large, resulting in an uneven surface on the negative electrode, which causes non-uniformity in current density during charging and discharging. Also, if the silicon particles are too large, the phase stability of the negative electrode slurry becomes unstable, reducing processability. Therefore, the capacity retention rate of the battery decreases.

[0089] In one embodiment of this application, the silicon-based active material typically has a characteristic BET surface area. The BET surface area of ​​the silicon-based active material is preferably 0.01 m². 2 / g~150.0m 2 / g, comfortably, 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 The value is / g. The BET surface area (using nitrogen) is measured according to DIN 66131.

[0090] In one embodiment of this application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably non-porous. The silicon particles are preferably spherical or flaky particles. Alternatively, the silicon particles may have a fibrous structure, or exist in the form of a silicon-containing thin film or coating, but these are less preferred.

[0091] In one embodiment of this application, the silicon-based active material may be present in an amount of 60 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer composition.

[0092] In another embodiment, the silicon-based active material may be present in amounts of 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and 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.

[0093] The negative electrode active material layer composition according to this application uses a specific negative electrode conductive material and negative electrode binder that can control the volume expansion rate during the charge-discharge process even when using a silicon-based active material with significantly high capacity within the aforementioned range, thereby having the characteristic of not degrading the performance of the negative electrode even when including the aforementioned range, and having excellent output characteristics during charging and discharging.

[0094] Traditionally, graphite-based compounds were used exclusively as the negative electrode active material. However, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based active materials to increase capacity. However, silicon-based active materials have a limitation: their volume expands rapidly during the charge / discharge process, damaging the conductive pathways formed within the negative electrode active material layer and actually degrading the battery's performance.

[0095] Therefore, in one embodiment of this application, the negative electrode active material layer composition may include a negative electrode conductive material and a negative electrode binder. That is, the negative electrode conductive material plays a role in securing the conductive path, and the binder plays a role in controlling such negative electrode conductive material during charging and discharging.

[0096] In one embodiment of this application, the negative electrode conductive material may include one or more selected from the group consisting of point conductive materials, planar conductive materials, and linear conductive materials.

[0097] In one embodiment of this application, the point-shaped conductive material can be used to improve conductivity in the negative electrode and has conductivity without inducing chemical changes, and means a conductive material that is circular or point-shaped. Specifically, the point-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 derivatives, and preferably contains carbon black in terms of embodying high conductivity and having excellent dispersibility.

[0098] In one embodiment of this application, the point conductive material has a BET specific surface area of ​​40 m². 2 / g or more 70m 2 It may be less than or equal to / g, preferably 45m 2 / g or more 65m 2 / g or less, more comfortably, 50m 2 / g or more 60m 2 It may be less than / g.

[0099] In one embodiment of this application, the particle size of the dot-like conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 40 nm to 60 nm.

[0100] In one embodiment of this application, the conductive material may include a planar conductive material.

[0101] The aforementioned planar conductive material refers to a conductive material that improves conductivity by increasing surface contact between silicon particles within the negative electrode, while simultaneously suppressing the disruption of the conductive path due to volume expansion. The aforementioned planar conductive material may also be described as a plate-type conductive material or a bulk-type conductive material.

[0102] In one embodiment of this application, the planar conductive material may include at least one selected from the group consisting of plate-type graphite, graphene, graphene oxide, and graphite flakes, and preferably plate-type graphite.

[0103] In one embodiment of this application, the average particle size (D50) of the planar conductive material may be 2 μm to 7 μm, more specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the above range is satisfied, the particle size is sufficient, making dispersion easy while preventing the viscosity of the negative electrode slurry from increasing too much. Therefore, the dispersion effect is superior when dispersion is performed using the same equipment and time.

[0104] In one embodiment of this application, a negative electrode composition is provided 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.

[0105] In one embodiment of this application, the planar conductive material may be a planar conductive material with a high specific surface area and a high BET specific surface area; or a planar conductive material with a low specific surface area.

[0106] In one embodiment of this application, the planar conductive material may be any planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area without limitation. In particular, the planar conductive material according to this application may be affected to some extent by dispersion depending on the performance of the electrodes, and it is especially preferable to use a planar conductive material with a low specific surface area that does not cause dispersion problems.

[0107] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​1 m². 2 It may be more than / g.

[0108] In another embodiment, the planar conductive material has a BET specific surface area of ​​1 m². 2 / g or more 500m 2 It may be less than / g, preferably 5m 2 / g or more 300m2 / g or less, more preferably 5m 2 / g or more 250m 2 / g is also acceptable.

[0109] In another embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and the BET specific surface area is 50 m². 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 Less than / g, more comfortably, 100m 2 / g or more 250m 2 The range of / g or less may also be satisfied.

[0110] In another embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and the BET specific surface area is 1 m². 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 The range of / g or less may also be satisfied.

[0111] 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 contain multiple carbon nanotube units. Specifically, here, "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged in parallel with substantially the same orientation along their longitudinal axes, or are twisted into a bundle or rope. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, the properties of a conductor or semiconductor can be exhibited depending on the angle and structure in which the graphite sheet is wound. Compared to entangled-type carbon nanotubes, the bundle-type carbon nanotubes can be uniformly dispersed during the manufacture of the negative electrode, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0112] In one embodiment of this application, the negative electrode conductive material includes a linear conductive material, which may be a carbon nanotube.

[0113] In one embodiment of this application, the carbon nanotubes may be single-walled carbon nanotubes (SWCNTs) and / or multi-walled carbon nanotubes (MWCNTs). When the linear conductive material is SWCNTs, the length of the SWCNTs may be 0.5 μm to 100 μm, preferably 1 μm to 80 μm.

[0114] In one embodiment of this application, the negative electrode conductive material may be included in an amount of 5 to 40 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0115] In another embodiment, the negative electrode conductive material may be present in an amount of 5 to 40 parts by weight, preferably 5 to 30 parts by weight, and more preferably 5 to 25 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0116] In one embodiment of this 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.

[0117] In one embodiment of this application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, each satisfying the above composition and ratio, thereby increasing the number of points where charging and discharging are possible without significantly affecting the life characteristics of conventional lithium secondary batteries, and providing the characteristic of having excellent output characteristics at a high C-rate.

[0118] The negative electrode conductive material of this application has a completely different configuration from the conductive material applied to the positive electrode. Specifically, the negative electrode conductive material of this application plays a role in controlling the contact points between silicon-based active materials, which experience very large volume expansion of the electrodes due to charging and discharging. The positive electrode conductive material, when rolled, acts as a buffer while partially imparting conductivity, and its configuration and role are completely different from the negative electrode conductive material of the present invention.

[0119] Furthermore, the negative electrode conductive material described in this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. In other words, conductive materials used in electrodes with graphite-based active materials simply have smaller particles compared to the active material, thus improving output characteristics and imparting some conductivity. This is completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials, as in the present invention.

[0120] In one embodiment of this application, the plate-shaped conductive material used as the negative electrode conductive material has a different structure and role from the carbon-based active material typically 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 refers to a material that is processed into a spherical or point-like form to facilitate the storage and release of lithium ions.

[0121] On the other hand, planar conductive materials used as negative electrode conductive materials are substances having a planar or plate-like form, and can be represented as plate-type graphite. In other words, they are substances included to maintain conductive pathways within the negative electrode active material layer, and do not play a role in lithium storage and release, but rather substances that secure conductive pathways in a planar manner within the negative electrode active material layer.

[0122] In other words, in this 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 to secure a conductive path that does not serve the role of storing or releasing lithium. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0123] On the other hand, in this application, the use of a carbon-based active material as the active material means that it was processed into a point-like or spherical shape and used as a substance that plays a role in storing or releasing lithium.

[0124] In one embodiment of this application, the negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms of these are substituted with Li, Na, or Ca, or may contain a variety of copolymers thereof.

[0125] The negative electrode binder according to one embodiment of this application plays a role in controlling the silicon-based active material and the negative electrode conductive material in order to prevent twisting and deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. Any ordinary binder can be applied as long as it fulfills the above role, and specifically, an aqueous binder may be used, and more specifically, a polyacrylamide (PAM) binder may be used.

[0126] In one embodiment of this application, the negative electrode binder may be included in a quantity of 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition, and may also be included in a quantity of 5 parts by weight or more, or 8 parts by weight or more.

[0127] In one embodiment of this application, the negative electrode can be formed by coating one or both sides of a negative electrode current collector layer with a negative electrode slurry containing the negative electrode active material layer composition.

[0128] In one embodiment of this application, the negative electrode slurry may include a negative electrode active material layer composition and a slurry solvent.

[0129] In one embodiment of this application, the solid content of the negative electrode slurry can satisfy the requirement of 5% or more and 40% or less.

[0130] In another embodiment, the solid content of the negative electrode slurry can be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0131] The solid content of the negative electrode slurry can refer to the content of the negative electrode composition contained in the negative electrode slurry, and can refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0132] When the solid content of the negative electrode slurry satisfies the aforementioned range, the viscosity is appropriate during the formation of the negative electrode active material layer, minimizing the particle caking phenomenon of the negative electrode composition and enabling efficient formation of the negative electrode active material layer.

[0133] In one embodiment of this application, the slurry solvent may be any solvent that can disperse the aforementioned negative electrode composition, and specifically, water or N-methyl-2-pyrrolidone (NMP) may be used.

[0134] In one embodiment of this 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.

[0135] In the positive electrode, the positive electrode current collector layer is not particularly limited as long as it is conductive without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., may be used. The positive electrode current collector layer may also have a thickness of 1 μm to 500 μm, and fine irregularities can 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 film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0136] In this application, the average particle size (D50) of the single-particle positive electrode active material may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, greater than 1 μm and 12 μm or less, greater than 1 μm and 8 μm or less, or greater than 1 μm and 6 μm or less.

[0137] Even when the single-particle positive electrode active material is formed with a small particle size (average particle size (D50) of 1 μm or more and 12 μm or less), its particle strength may be excellent. For example, the single particle may have a strength of 650 kgf / cm². 2 When rolled with this force, the particle strength can be 100 MPa to 300 MPa. This allows the single particle to have a strength of 650 kgf / cm². 2 Even when rolled with strong force, the phenomenon of increased fine particles within the electrode due to particle cracking is mitigated, thereby improving the battery's lifespan characteristics.

[0138] The single-particle positive electrode active material can be manufactured by mixing a transition metal precursor and a lithium raw material and firing the mixture. The secondary particles may be manufactured by a different method than the single particles, and their composition may be the same as or different from that of the single particles.

[0139] The method for forming the single-particle positive electrode active material is not particularly limited, but it can generally be formed by increasing the firing temperature and over-firing. Additives such as grain growth promoters that are useful for over-firing may be used, or the material may be manufactured by changing the starting material.

[0140] For example, the firing is performed at a temperature at which a single particle can be formed. In order to form this, firing must be performed at a higher temperature than when the secondary particles were manufactured. For example, if the composition of the precursor is the same, firing must be performed at a temperature about 30°C to 100°C higher than when the secondary particles were manufactured. The firing temperature for forming the single particle may vary depending on the metal composition in the precursor. For example, when attempting to form a single particle of a high-nickel (High-Ni) NCM-based lithium composite transition metal oxide with a nickel (Ni) content of 80 mol% or more, the firing temperature may be 700°C to 1000°C, preferably about 800°C to 950°C. When the firing temperature satisfies the above range, a positive electrode active material containing a single particle with excellent electrochemical properties can be manufactured. If the firing temperature is below 790°C, a positive electrode active material containing a lithium composite transition metal compound in secondary particle form can be manufactured. If it exceeds 950°C, excessive firing may occur, preventing the normal formation of a layered crystal structure and potentially degrading the electrochemical properties.

[0141] In this specification, the term "single-particle cathode active material" is used to distinguish it from conventional secondary particles formed by the aggregation of tens to hundreds of primary particles, and is a concept that includes a single particle consisting of one primary particle and an agglomeration of 30 or fewer primary particles, known as a similar-single-particle form.

[0142] Specifically, in the present invention, the single-particle positive electrode active material may be a single particle consisting of one primary particle or an aggregate of 30 or fewer primary particles in a similar-single-particle form, and the secondary particles may be in a form in which several hundred primary particles are aggregated.

[0143] In one embodiment of this application, the positive electrode active material may be included in 100 parts by weight of the positive electrode active material layer composition in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0144] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0145] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitations as long as it does not cause chemical changes in the battery that is constructed and has electronic conductivity. 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, 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, and one of these alone or a mixture of two or more may be used.

[0146] Furthermore, the positive electrode binder plays a role in improving adhesion between positive electrode active material particles and the adhesion 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used.

[0147] In one embodiment of this 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.

[0148] In another embodiment, the porosity of the negative electrode active material layer can be in the range of 20% to 35%, preferably 23% to 33%, and more preferably 25% to 30%.

[0149] In another embodiment, the porosity of the positive electrode active material layer can be in the range of 15% to 45%, preferably 17% to 28%, and more preferably 20% to 25%.

[0150] The aforementioned porosity varies depending on the composition and content of the active material, conductive material, and binder contained in each active material layer, as well as the degree of rolling. In particular, when the aforementioned range is met, the active material does not crack, and the rapid charging performance and resistance problems due to lithium ion diffusion can be solved.

[0151] In one embodiment of this application, the discharge capacity loading amount of the positive electrode active material layer composition is 2 mAh / cm². 2 More than 5mAh / cm 2 The present invention provides a lithium secondary battery in which the discharge capacity loading amount of the negative electrode active material layer composition is 1 to 1.1 times the discharge capacity loading amount of the positive electrode active material layer composition.

[0152] The discharge capacity loading amount of the negative electrode active material layer composition described above is set to be between 1 and 1.1 times the positive electrode active material layer loading amount (NP100~110). If the discharge capacity loading amount of the positive electrode 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.

[0153] This application provides a lithium secondary battery in which the thickness of the positive electrode and negative electrode current collector layers is 1 μm or more and 100 μm or less, and the thickness of the positive electrode and negative electrode active material layers is 20 μm or more and 500 μm or less.

[0154] In one embodiment of this application, the negative electrode may be a pre-lithified negative electrode.

[0155] In one embodiment of this application, the positive electrode may be a pre-lithified positive electrode.

[0156] In this case, the pre-lithiation method can be one that is generally applied in this industry.

[0157] Specifically, the pre-lithiation of the negative electrode can be carried out by a lithium electroplating process; a lithium metal transfer process; a lithium metal deposition process; or a stabilized lithium metal powder (SLMP) coating process.

[0158] In this application, the pre-lithiation of the positive or negative electrode has the characteristic of being able to increase energy density and additionally extend lifespan. In other words, it has the characteristic of being able to ensure lifespan performance and energy density through the lithium reservoir (Li reservoir) effect.

[0159] The separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a membrane typically used in secondary batteries, but it is especially preferable to have low resistance to ion movement of the electrolyte and excellent moisture-retaining capacity for the electrolyte. Specifically, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, may be used. Alternatively, ordinary porous nonwoven fabrics, such as those made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances to ensure heat resistance or mechanical strength may be used, and they may be selectively used in single-layer or multi-layer structures.

[0160] Examples of the aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

[0162] As the non-aqueous organic solvent, for example, 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, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate may be used.

[0163] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are suitable for use because they are high-viscosity organic solvents with high dielectric constants and readily dissociate lithium salts. Furthermore, by mixing such cyclic carbonates with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, electrolytes with high electrical conductivity can be produced, making them even more suitable for use.

[0164] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, the anion of the lithium salt may be 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 - You may use one or more selected from the group consisting of the following:

[0165] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0166] 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 battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

[0167] In this 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.

[0168] In this case, the TR rate can be calculated using the following formula 3. [Formula 3] TR rate = (Max pressure - Pre-ignition pressure) / (Cell capacity) / (Time just before ignition - Time to reach max pressure)

[0169] Specifically, the pressure and time in Equation 3 can be measured through a pressure gauge attached to the autoclave. As thermal runaway of the cell progresses, the internal pressure of the autoclave increases due to the generated gas. The pressure at the point when the pressure starts to increase can be measured as the pre-ignition pressure and the time immediately before ignition. The pressure at the point where the pressure is maximum can be measured as the max pressure and the time to max pressure, and the calculation can be performed using these values.

[0170] In other words, by applying the positive and negative electrodes described above, the energy density and thermal stability can be ensured as described above.

[0171] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative of the description, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the description and the technical concept, and such variations and modifications naturally fall within the scope of the claims. [Examples]

[0172] <Manufacturing example> (1) Manufacturing of the positive electrode As the positive electrode active material, Li(Ni a Co b Mn c )O2 and LMFP were used.

[0173] In this case, the NCM, excluding lithium (Li) and oxygen (O2) from the positive electrode active material, had a ratio of Ni:Co:Mn = 70:20:10, satisfying the ratio a:b:c = 70:20:10 (a:b:c = 0.70:0.20:0.10). Furthermore, D50 had a surface area of ​​3.8 μm, Dmin and Dmax of 1.2 μm and 13 μm, and a BET specific surface area of ​​0.64 m². 2 Therefore, its true density is 4.78-4.80 g / cm³. 3 That is the case.

[0174] The Mn content in the aforementioned LMFP was 60 at%.

[0175] Then, the positive electrode active material, positive electrode conductive material (LB.CNT), and binder (PVdF, KF9700) were added to a solvent (N-methylpyrrolidone, NMP) in a weight ratio of 97.96:0.8:1.24 to produce a positive electrode slurry. The positive electrode slurry was then coated onto an aluminum (Al) thin film, which was a positive electrode current collector with a thickness of 12 μm (4 mAh / cm²). 2 After drying, the material was rolled in a roll press to produce a positive electrode (porosity 23%).

[0176] (2) Manufacturing of the negative electrode A negative electrode active material layer composition was prepared using Si / C:artificial graphite (20:80) as the silicon-based active material, a first conductive material and a second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10. A negative electrode slurry was produced by adding these materials to distilled water as a solvent for forming the negative electrode slurry (solid content concentration 28% by weight).

[0177] The first conductive material is a plate-shaped graphite (specific surface area: 17 m²). 2 The second conductive material is carbon nanotubes, with a particle size of 3.5 μm (average particle size D50) per g.

[0178] As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the active material was added and dispersed again at 2500 rpm for 30 minutes to produce the negative electrode slurry.

[0179] As the negative electrode current collector layer, the negative electrode slurry is applied to both sides of a copper current collector (thickness: 8 μm) at a rate of 3.78 mAh / cm². 2 The material was coated with the specified capacity loading amount, rolled (roll press), 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%).

[0180] (3) Manufacturing of secondary batteries An electrode assembly was manufactured by interposing a 3μm / 3μm compression-resistant thin film separation membrane (PE12μm) with a ceramic coating 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.

[0181] In this process, the positive and negative electrodes met the composition and content requirements shown in Table 1 below.

[0182] For reference, Figure 3 shows a distribution map based on the olivine-based and silicon-based active materials of the examples and comparative examples of this application. Specifically, the shaded areas correspond to regions that satisfy the range of Equation 1.

[0183] [Table 1-1] [Table 1-2]

[0184] <Example of experiment> 1) Thermal stability (Thermal Propagation, TP) evaluation To evaluate the lithium secondary batteries produced in the above examples and comparative examples, a structure as shown in Figure 2 was formed, and the heating pad in contact with the cell was heated to induce thermal runaway of the cell.

[0185] The experiment was conducted in an autoclave (isolated from the external environment / atmosphere) under an N2 atmosphere, and the pressure of the gas ejected during thermal runaway was measured using a pressure gauge in the autoclave. To prevent interference between cell capacity and footprint, the evaluation was performed using a 40Ah A5-A cell, and the resulting TR rate is shown in Table 2 below.

[0186] The following pressures are measured using a pressure gauge attached to the autoclave. As thermal runaway of the cell progresses, the internal pressure of the autoclave increases due to the gas generated. The pressure at the point when the pressure starts to increase can be measured as the pre-ignition pressure and the time immediately before ignition. The pressure at the point where the pressure is maximum can be measured as the max pressure and the time to max pressure, and the calculation can be performed using these measurements.

[0187] TR rate = (Max pressure - Pre-ignition pressure) / (Cell capacity) / (Time from just before ignition to Max pressure)

[0188] [Table 2]

[0189] 2) Energy Density (ED) Evaluation The energy density of the lithium secondary batteries manufactured in the above examples and comparative examples is calculated using the discharge energy obtained during 0.33C charging and discharging and the volume of the batteries. However, batteries used in experiments are generally manufactured to be smaller in size than batteries installed in automobiles, resulting in a low utilization rate of space. When performing ED evaluation, the discharge energy and volume are converted and calculated based on the size of batteries installed in automobiles.

[0190] [Table 3]

[0191] In the case of the lithium secondary battery according to this application, instead of simply applying carbon-based active material and olivine-based active material individually, in order to ensure energy density, the positive electrode contains a layered active material containing nickel and a silicon-based active material, respectively, and the problem of thermal stability (TP) due to the increase in capacity was solved by deriving a weight ratio that satisfies the above equations 1 and 2. Generally, when the content of silicon-based active material in the negative electrode increases, the energy density increases, but the thermal stability deteriorates. Consequently, when the content of olivine-based active material in the positive electrode is increased, the thermal stability problem improves, but the energy density decreases. However, through research, the applicant has derived the above ratios of equations 1 and 2. When this is applied, it has been found through the above examples and comparative examples that energy density and thermal stability can be ensured simultaneously.

[0192] From the perspective of cell energy density, as the olivine-based active material increases, the positive electrode becomes thicker. To compensate for the thickness, the content of the silicon-based active material in the negative electrode must increase. From the perspective of achieving a specific energy density, the lower limit of the silicon-based active material content (B) based on the olivine-based active material content (A) is determined. In particular, from the perspective of energy density, it can be confirmed through the above examples that the energy density can be ensured through 4.524 + 0.939 × e 0.0537 ×A < B.

[0193] On the other hand, as the content of the olivine-based active material increases, the thermal stability is excellent, and more silicon-based active materials can be applied. From the perspective of the TR rate, the upper limit of the silicon-based active material content (B) based on the olivine-based active material content (A) is determined. In particular, to meet the TR rate, it can be confirmed that B in Equation 1 needs to satisfy B < -4.312 + 5.183 × e 0.0537×A value needs to be satisfied.

[0194] That is, in the case of the lithium secondary battery according to the present application, it is possible to ensure both energy density, which has been difficult to achieve simultaneously in the past, and thermal stability, which 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.

[0195] Comparative Examples 1 to 3 are cases where an NCM positive electrode is simply applied as the counter electrode of the negative electrode, either by adjusting the content of the silicon-based active material or using a graphite-based negative electrode.

[0196] In the cases of Comparative Examples 1 and 2, although the energy density is satisfied, it can be confirmed that the content of the silicon-based active material is high, the thermal stability decreases, and the TR characteristics deteriorate. When a graphite-based negative electrode is used as the negative electrode, which is the counter electrode here, it can be confirmed that the thermal stability is ensured, but the energy density decreases.

[0197] Comparative Examples 4 to 6 correspond to cases where an olivine-based positive electrode is applied as the counter electrode of the negative electrode, either by adjusting the content of the silicon-based active material or using a graphite-based negative electrode.

[0198] Comparative Examples 4 to 6, when using an olivine-based cathode, were judged to have excellent thermal stability, but it was confirmed that the energy density decreased because NCM was not mixed.

[0199] In Comparative Examples 7 to 9, olivine-based material and NCM are used together as the positive electrode. However, in Comparative Example 7, the range of Formula 1 of this application cannot be satisfied. In Comparative Example 8, a graphite-based negative electrode is used alone. In Comparative Example 9, the content of the olivine-based active material is low, and the ranges of Formulas 1 and 2 cannot be satisfied.

[0200] In Comparative Examples 7 and 9, while the energy density can meet the desired level, it can be confirmed that the TR characteristics deteriorate. In particular, in Comparative Examples 7 and 9, it can be confirmed that the TR characteristics deteriorate when the range of Equation 1 of this application is deviated, and in the case of Comparative Example 8, although the TR characteristics are met using a graphite-based negative electrode, it can be confirmed that the energy density cannot be secured.

[0201] Furthermore, Comparative Examples 10 to 26 did not satisfy the range of Formula 1 of the present invention, and as can be seen in Tables 2 and 3, they did not satisfy the energy density and / or TR characteristics. In particular, Comparative Examples 17 to 26 confirmed that the effect of Formula 1 of the present invention was superior to that of the comparative examples.

[0202] For reference, Examples 2 to 5 are based on Example 1, with the negative electrode fixed, while increasing the amount of NCM active material in the positive electrode active material and decreasing the amount of LMFP. As can be seen from the data in Tables 2 and 3, when the amount of NCM is increased to the scope of this application, the energy density increases, but the thermal stability is inferior to that of Example 1. Examples 7 and 8 are similar when compared to Example 6, and Examples 10, 11, 13, and 14 show the same trend. In other words, in the case of the lithium secondary battery according to this application, when used within the range of Equation 1, it has the characteristic that the energy density and thermal stability can be adjusted according to the application. [Explanation of symbols]

[0203] 10 ···Negative electrode current collector layer 20...Negative electrode active material layer 30...Separation membrane 40...Cathode 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 negative electrode; and an electrolyte; The positive electrode includes a positive electrode active material layer containing a positive electrode active material layer composition, The aforementioned negative electrode includes a negative electrode active material layer containing a negative electrode active material layer composition, The positive electrode active material layer composition comprises a layered active material containing nickel and a positive electrode active material containing an olivine-based active material. The aforementioned negative electrode active material layer composition includes a negative electrode active material containing a silicon-based active material, Based on 100 parts by weight of the positive electrode active material, the amount of the olivine-based active material is A, and based on 100 parts by weight of the negative electrode active material, the amount of the silicon-based active material is B. A and B are lithium secondary batteries that 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. The lithium secondary battery according to claim 1, wherein the layered active material containing 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. The lithium secondary battery according to claim 1, wherein the silicon-based active material is included in an amount of 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.

4. The negative electrode active material further comprises a carbon-based active material, Based on 100 parts by weight of the negative electrode active material, the silicon-based active material is included in an amount of 5 parts by weight or more and 100 parts by weight or less. The lithium secondary battery according to claim 1, wherein the carbon-based active material is contained in an amount of 0 parts by weight or more and 95 parts by weight or less.

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

6. The aforementioned layered active material containing nickel is lithium nickel-cobalt-manganese (NCM) oxide. The olivine-based active material is an LMFP, The lithium secondary battery according to claim 1, wherein, based on a total of 100 at% of elements contained in the LMFP, Mn is contained in an amount of 0 at% to 90 at%.

7. The aforementioned silicon-based active material is SiO ｘ A lithium secondary battery according to claim 1, comprising one or more selected from the group consisting of (0 < x < 2), Si / C, and Si alloy.

8. The lithium secondary battery according to claim 1, wherein the positive electrode active material is a single-particle positive electrode active material.

9. The lithium secondary battery according to claim 1, wherein the nickel contained in the layered active material containing nickel is present in an amount of 75 mol% or less of the total metals excluding lithium.

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

11. The discharge capacity loading amount of the positive electrode active material layer composition is 2 mAh / cm². ２ More than 5mAh / cm ２ The following: The lithium secondary battery according to claim 1, wherein the discharge capacity loading amount of the negative electrode active material layer composition is 1 to 1.1 times the discharge capacity loading amount of the positive electrode active material layer composition.

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

13. The lithium secondary battery according to any one of claims 1 to 12, wherein the lithium secondary battery has an energy density of 700 Wh / L or more and a TR rate (TR rate) defined by the following formula 3 is 4 mbar / Ah sec or less. [Formula 3] TR rate = (Max pressure - Pre-ignition pressure) / (Cell capacity) / (Time immediately before ignition - Time to reach max pressure)

14. The lithium secondary battery according to claim 1, wherein the average particle size (D50) of the silicon-based active material is 1 μm or more and 10 μm or less.

15. The BET surface area of ​​the silicon-based active material is 0.01 m². ２ / g ~ 150.0m ２ A lithium secondary battery according to claim 1, wherein the value is / g.

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

17. The lithium secondary battery according to claim 1, wherein at least one of the positive electrode and the negative electrode is a pre-lithified electrode.

18. The lithium secondary battery according to claim 1, further comprising a separation membrane between the positive electrode and the negative electrode.

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