Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, in which the positive electrode comprises a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material layer composition, the negative electrode comprises a negative electrode active material layer, and the negative electrode active material layer comprises a negative electrode active material layer composition. The positive electrode active material layer composition includes 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 includes a negative electrode active material including a silicon-based active material. When the part by weight of the olivine-based active material per 100 parts by weight of the positive electrode active material is indicated as A and the part by weight of the silicon-based active material per 100 parts by weight of the negative electrode active material is indicated as B, A and B satisfy Formula 1 and Formula 2 (Formula 1: 4.524 + 0.939 * e 0.0537 * Alt; blt; -4.312 + 5.183 * e < 0.0537 * A, formula 2: 10 < = A < = 90).

Description

Technical Field

[0001] This application claims the benefit and priority of Korean Patent Application No. 10-2023-0148983, filed with the Korean Intellectual Property Office on November 1, 2023, the disclosure of which is incorporated herein by reference in its entirety for all purposes, as fully set forth herein.

[0002] This disclosure relates to a lithium secondary battery. Background Technology

[0003] With the rapid increase in the use of fossil fuels, the demand for alternative or clean energy sources is growing. As part of this, the most active research area is the generation and storage of electricity using electrochemical reactions.

[0004] Currently, secondary batteries are a representative example of electrochemical devices that utilize this electrochemical energy, and their application is gradually expanding.

[0005] With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source has increased dramatically. Among these secondary batteries, lithium-ion batteries, characterized by high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used. Furthermore, methods for manufacturing high-density electrodes with even higher energy density per unit volume for use in such high-capacity lithium-ion batteries are being actively researched.

[0006] Typically, a secondary battery comprises a positive electrode, a negative electrode, an electrolyte, and a separator. Lithium-ion secondary batteries are usually manufactured by using lithium-intercalated compounds (such as LiCoO2 or LiMn2O4) for the positive electrode and non-lithium-intercalated materials (such as carbon-based or Si-based materials) for the negative electrode. During charging, lithium ions intercalated at the positive electrode move to the negative electrode through the electrolyte. During discharging, lithium ions move back from the negative electrode to the positive electrode.

[0007] Lithium-ion batteries are used in various industrial sectors such as automobiles, small modules, and mobile phones. The performance requirements for lithium-ion batteries in each sector encompass a variety of factors, but generally, technological development aimed at improving energy density while ensuring stability, fast charging, and long battery life are fundamental requirements.

[0008] In particular, carbon-based materials such as graphite, as anode materials, possess excellent stability and reversibility, but have limitations in terms of capacity. Therefore, in fields aiming for high capacity (i.e., maximizing energy density), there is an increasing trend towards using Si-based materials with high theoretical capacity as anode materials. However, when simply incorporating high amounts of Si-based materials for the purpose of high capacity, compared to carbon-based materials, the volume expansion leads to a rapid degradation in lifetime performance, making it difficult to apply Si-based materials in real-world scenarios.

[0009] To address the challenges encountered when using Si-based materials as anodes, various approaches have been discussed, such as controlling the driving potential, applying an additional thin film to the active material layer, suppressing volume expansion (e.g., controlling the particle size of the silicon-based compound), or developing adhesives capable of suppressing volume expansion of the silicon-based compound to prevent the breakage of conductive paths. Furthermore, research is underway to supplement the lifetime characteristics of silicon-based anodes by pre-lithiating the silicon-based active material layer, limiting the proportion of silicon-based active material used during the initial charge-discharge cycle, and imparting a reservoir-like effect.

[0010] As the counter electrode for Si-based anodes, cathodes such as lithium nickel-cobalt-manganese (aluminum) oxide (“lithium NCM(A) oxide”) containing a high nickel content have been developed. When using cathodes such as lithium NCM(A) oxide containing a high nickel content, the high capacity characteristics that are advantages of Si-based anodes can be maintained, while also ensuring high energy density and fast charging performance.

[0011] However, due to the characteristics of Si-based anodes and lithium NCM(A) oxide cathodes containing high nickel content, stability decreases rapidly. In particular, fire issues related to electric vehicles have emerged as a major concern, leading to a growing demand for lithium-ion rechargeable batteries with enhanced thermal stability (thermal propagation; TP) specifications. However, batteries containing Si-based anodes and lithium NCM(A) oxide cathodes containing high nickel content, like lifespan performance, exhibit poor thermal stability as higher-energy-density batteries store more energy in the same volume.

[0012] To address the aforementioned issues, olivine-based cathodes such as lithium iron phosphate (LFP) can be used as the cathode, serving as the counter electrode to the Si-based anode. Specifically, to resolve the aforementioned thermal stability problems of batteries containing a Si-based anode and a lithium NCM(A) oxide cathode with a high nickel content, research is underway to ensure stability through the use of LFP olivine-based cathodes, even with relatively low energy density and capacity characteristics.

[0013] However, when olivine-based cathodes (such as LFP) are used as the counter electrode, i.e., the cathode, of Si-based anodes, the above-mentioned stability can be ensured, but the capacity drops rapidly and there is no advantage compared with existing batteries.

[0014] To address these issues, research is underway on combining various types of active materials and applying them to both positive and negative electrodes. However, ensuring that high energy density, thermal stability, and lifetime performance cannot be simultaneously achieved remains a persistent challenge.

[0015] Therefore, ongoing development is underway of technologies aimed at improving energy density and ensuring the stability, fast charging, and lifespan performance of lithium-ion batteries.

[0016] The background description provided herein is for the purpose of generally presenting the context of this disclosure. Unless otherwise stated herein, the information described in this section is not prior art to the claims of this application, nor is it acknowledged as prior art or an implication of prior art by virtue of its inclusion in this section.

[0017] Existing technical documents

[0018] [Patent Document 1] Japanese Patent Application Publication No. 2009-080971 Summary of the Invention

[0019] Technical problems to be solved

[0020] The research results on the above problems revealed that when the negative electrode contains silicon-based active materials and the positive electrode contains a mixture of nickel-containing layered active materials and olivine-based active materials, it is possible to simultaneously ensure energy density and thermal stability characteristics that were previously unattainable, and also to solve the problem of lifetime characteristics.

[0021] Therefore, the invention according to this disclosure is aimed at providing a lithium secondary battery that can solve the above-mentioned problems.

[0022] Technical solution

[0023] An exemplary embodiment of this disclosure 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, the positive electrode active material layer comprises a positive electrode active material layer composition, the negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material layer composition, the positive electrode active material layer composition comprises a positive electrode active material, the positive electrode active material comprises a nickel-containing layered active material and an olivine-based active material, the negative electrode active material layer composition comprises a negative electrode active material, the negative electrode active material comprises a silicon-based active material, and the weight parts (A) of the olivine-based active material based on 100 parts by weight of the positive electrode active material and the weight parts (B) of the silicon-based active material based on 100 parts by weight of the negative electrode active material satisfy Equations 1 and 2: [Formula 1] 4.524 + 0.939 × e 0.0537×A < B < -4.312+5.183×e 0.0537×A [Equation 2] 10 ≤ A ≤ 90.

[0024] The inventors of this disclosure have discovered that when the composition ratio of the positive electrode and the negative electrode is adjusted to the range of Formulas 1 and 2 as described above, it is possible to simultaneously ensure energy density and lifetime characteristics that were previously unattainable, and also to solve the problem of thermal stability.

[0025] Technical effect

[0026] The lithium-ion secondary battery according to this disclosure essentially has the following characteristics: the positive electrode comprises a nickel-containing layered active material and an olivine-based active material, and the negative electrode comprises a silicon-based active material. That is, the above combination ensures an energy density (ED 700 Wh / L or higher).

[0027] By including a nickel-containing layered active material in the positive electrode and a silicon-based active material in the negative electrode, energy density is ensured, rather than simply using carbon-based and olivine-based active materials alone. Furthermore, by deriving the weight ratios satisfying Equations 1 and 2 above, the problem of thermal stability (TP) caused by the resulting increase in capacity is solved. Generally, as the content of silicon-based active material in the negative electrode increases, energy density increases, but thermal stability deteriorates. Correspondingly, when the content of olivine-based active material in the positive electrode increases, the thermal stability problem is improved, but the energy density decreases. However, through research, the inventors of this disclosure have derived the ratios of Equations 1 and 2 as described above, and by applying these ratios, both energy density and thermal stability are ensured simultaneously.

[0028] That is, by adjusting the composition and content as described above, thermal stability can be ensured while ensuring energy density. Furthermore, by applying a predetermined amount of silicon-based active material to the negative electrode as described above, the thickness of the active material layer can be reduced due to the reduced loading, and the migration rate of Li can be increased by ensuring porosity, which enables fast charging performance to be ensured.

[0029] As a result, the lithium secondary battery described in this disclosure can solve the problem of thermal stability, which cannot be balanced, while ensuring high energy density and fast charging performance. Although it exhibits some slightly inferior performance compared to other batteries with enhanced lifespan (LFP / graphite, lithium manganese iron phosphate (LMFP) / graphite, lithium NCM oxide / graphite), it exhibits excellent lifespan performance compared to existing batteries (lithium NCM oxide / Si, LFP / Si) which are designed for high energy density. Attached Figure Description

[0030] The accompanying drawings illustrate exemplary embodiments of this disclosure and, together with the following detailed description, are intended to provide a further understanding of the technical aspects of this disclosure; therefore, this disclosure should not be construed as limited to the drawings.

[0031] Figure 1 A lithium secondary battery according to an exemplary embodiment of the present disclosure is shown.

[0032] Figure 2 This is a diagram illustrating the structure of the lithium secondary batteries prepared in the embodiments and comparative examples of this disclosure for evaluation.

[0033] Figure 3 This is a diagram illustrating the distribution of olivine-based and silicon-based active materials based on embodiments and comparative examples of this disclosure.

[0034] Explanation of reference numerals in the attached figures: 10: Negative electrode current collector layer 20: Negative electrode active material layer 30: Diaphragm 40: Positive electrode active material layer 50: Positive current collector layer 100: Negative electrode 200: Positive electrode Detailed Implementation

[0035] Before describing the contents of this disclosure, let’s first define some terms.

[0036] In this disclosure, when a part "comprises", "includes" or "has" a constituent element, unless otherwise specifically stated, it does not mean that other constituent elements are excluded, but rather that other constituent elements may be included.

[0037] In this disclosure, "p to q" means the range of "p and below q".

[0038] In this disclosure, "specific surface area" is measured by the BET method, and specifically, it is calculated by the amount of nitrogen adsorbed at liquid nitrogen temperature (77 K) using the BELSORP-mini II, which is available from BEL Japan. That is, in this disclosure, BET specific surface area can refer to the specific surface area measured by the above-described method.

[0039] In this disclosure, "Dn" refers to particle size distribution, specifically the particle size at the n% point in the cumulative number distribution of particles according to particle size. That is, D50 is the particle size at the 50% point in the cumulative number distribution of particles according to particle size, D90 is the particle size at the 90% point, and D10 is the particle size at the 10% point. Alternatively, particle size distribution can be measured using laser diffraction. Specifically, after dispersing the powder to be measured in a dispersion medium, the resulting dispersion is introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac S3500), where the difference in diffraction patterns according to particle size is measured as the laser beam passes through the particles, and then the particle size distribution is calculated.

[0040] In this disclosure, the description "the polymer contains a specific monomer as a monomer unit" means that the monomer participates in the polymerization reaction and is included in the polymer as a repeating unit. In this disclosure, when the polymer contains a monomer, this is interpreted the same as when the polymer contains a monomer as a monomer unit.

[0041] In this disclosure, it should be understood that the term “polymer” is used in a broad sense to include copolymers, unless otherwise specified as “homogeneous polymer”.

[0042] In this disclosure, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are the converted molecular weights of polystyrene measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) of various degrees of polymerization as standard materials. In this disclosure, unless otherwise specified, molecular weight refers to weight-average molecular weight.

[0043] In the following, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, enabling those skilled in the art to readily implement the present disclosure. However, the present disclosure may be implemented in various different forms and is not limited to the following description.

[0044] An exemplary embodiment of this disclosure 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, the positive electrode active material layer comprises a positive electrode active material layer composition, the negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material layer composition, the positive electrode active material layer composition comprises a positive electrode active material, the positive electrode active material comprises a nickel-containing layered active material and an olivine-based active material, the negative electrode active material layer composition comprises a negative electrode active material, the negative electrode active material comprises a silicon-based active material, and when the weight part of the olivine-based active material is A based on 100 parts by weight of the positive electrode active material, and the weight part of the silicon-based active material is B based on 100 parts by weight of the negative electrode active material, A and B satisfy Equations 1 and 2: [Formula 1] 4.524 + 0.939 × e 0.0537×A < B < -4.312+5.183×e 0.0537×A [Equation 2] 10 ≤ A ≤ 90.

[0045] The lithium secondary battery according to this disclosure can solve the incompatible thermal stability by combining positive and negative electrode active materials that meet the range of Formulas 1 and 2 while ensuring high energy density. It can ensure fast charging performance and, although it exhibits some slightly inferior performance compared with other batteries with enhanced life performance (LFP / graphite, LMFP / graphite, lithium NCM oxide / graphite), it exhibits excellent life performance compared with existing batteries (lithium NCM oxide / Si, LFP / Si) which are aimed at high energy density.

[0046] Figure 1 This is a diagram illustrating a stacked structure of a lithium secondary battery according to an exemplary embodiment of the present disclosure. Specifically, a negative electrode 100 can be seen comprising a negative electrode active material layer 20 on one surface of a negative electrode current collector layer 10, and a positive electrode 200 can be seen comprising a positive electrode active material layer 40 on one surface of a positive electrode current collector layer 50. The negative electrode 100 and the positive electrode 200 for the lithium secondary battery are stacked together with a separator 30 inserted therebetween.

[0047] In this disclosure, the lithium secondary battery may also include a separator between the positive and negative electrodes.

[0048] The positive electrode, negative electrode, electrolyte, and separator contained in the lithium secondary battery will be described below.

[0049] In this disclosure, the negative electrode comprises a negative electrode active material layer, and the negative electrode active material layer comprises a negative electrode active material layer composition.

[0050] In this disclosure, the negative electrode comprises a negative electrode current collector layer and a negative electrode active material layer, wherein the negative electrode active material layer comprises a negative electrode active material layer composition and is disposed on one or both surfaces of the negative electrode current collector layer.

[0051] In this case, the negative electrode active material layer composition may comprise one or more of the group consisting of a negative electrode active material, a negative electrode conductive material, and a negative electrode binder.

[0052] In this disclosure, the positive electrode includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material layer composition.

[0053] In this disclosure, the positive electrode comprises a positive electrode current collector layer and a positive electrode active material layer, wherein the positive electrode active material layer comprises a positive electrode active material layer composition and is disposed on one or both surfaces of the positive electrode current collector layer.

[0054] In this case, the positive electrode active material layer composition may comprise one or more of the group consisting of positive electrode active material, positive electrode conductive material and positive electrode binder.

[0055] In one exemplary embodiment of this disclosure, the negative electrode active material comprises a silicon-based active material, and the positive electrode active material comprises a nickel-containing layered active material and an olivine-based active material.

[0056] Carbon-based materials such as graphite are excellent in terms of stability and reversibility as anode active materials, but they have limitations in terms of capacity. Therefore, silicon-based active materials with high theoretical capacity are used in fields where high capacity is required.

[0057] However, in order to apply silicon-based active materials alone, the problem of volume expansion needs to be properly addressed, but no alternative has yet been found. Therefore, the negative electrode active material according to this disclosure uses a silicon-based active material, while the positive electrode active material is a mixture of nickel-containing layered active material and olivine-based active material.

[0058] In one exemplary embodiment of this disclosure, a lithium secondary battery is provided, wherein, based on 100 parts by weight of the positive electrode active material, the content of the olivine-based active material can be more than 10 parts by weight and less than 90 parts by weight, and the content of the nickel-containing layered active material can be more than 10 parts by weight and less than 95 parts by weight.

[0059] In another exemplary embodiment, based on 100 parts by weight of the positive electrode active material, the content of the olivine-based active material may be 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.

[0060] In the present disclosure, when based on 100 parts by weight of the positive electrode active material, the parts by weight of the olivine-based active material can be represented as A as described above.

[0061] In another exemplary embodiment, based on 100 parts by weight of the positive electrode active material, the content of the nickel-containing layered active material may be 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.

[0062] In an exemplary embodiment of the present disclosure, a lithium secondary battery is provided, in which based on 100 parts by weight of the negative electrode active material, the content of the silicon-based active material may be 5 parts by weight or more and 100 parts by weight or less.

[0063] In another exemplary embodiment, based on 100 parts by weight of the negative electrode active material, the content of the silicon-based active material may be 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.

[0064] In the present disclosure, when based on 100 parts by weight of the negative electrode active material, the parts by weight of the silicon-based active material can be represented as B as described above.

[0065] In the present disclosure, based on 100 parts by weight of the silicon-based active material, the content of silicon (Si) in the silicon-based active material may be 30 to 100 parts by weight. That is, in the present disclosure, the silicon-based active material may include one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), Si / C, and Si alloys, and the weight ratio of silicon (Si) in the silicon-based active material may satisfy the above range.

[0066] In the present disclosure, the negative electrode active material may further include a carbon-based active material, and based on 100 parts by weight of the negative electrode active material, the content of the silicon-based active material may be 5 parts by weight or more and less than 100 parts by weight, and the content of the carbon-based active material may be more than 0 part by weight and 95 parts by weight or less.

[0067] In another exemplary embodiment, based on 100 parts by weight of the negative electrode active material, the content of the carbon-based active material may be 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.

[0068] Generally, the higher the energy density of a battery, the more energy it can store in the same volume. Therefore, there is a problem of poor thermal stability. That is, when the content of the silicon-based active material in the negative electrode increases, the energy density is ensured, but the thermal stability decreases. When the content of the olivine-based active material in the positive electrode increases, the thermal stability is improved, but the energy density decreases.

[0069] However, according to the present disclosure, as described above, specific compositions and contents satisfying Formula 1 and Formula 2 are applied to the positive electrode and the negative electrode, respectively. Therefore, it is possible to achieve the characteristics of ensuring both the energy density and the thermal stability. That is, in the lithium secondary battery of the present disclosure, compared with the case of separately applying a silicon-based negative electrode and a positive electrode containing a nickel-containing layered active material, the energy density may decrease. However, when the above compositions and contents are satisfied, an energy density of 700 Wh / L or more can be ensured, and at the same time, the thermal stability can be ensured, which is the main object of the present disclosure.

[0070] That is, when the content (A) of the olivine-based active material and the content (B) of the silicon-based active material satisfy the range of Formula 1, an energy density of 700 Wh / L or more can be ensured, and the TR rate can be satisfied to be 4 or less. If the range of Formula 1 is not satisfied, the energy density of the battery cannot be ensured, and the TR rate cannot be ensured either. Therefore, the problem of thermal stability cannot be solved.

[0071] In one exemplary embodiment of the present disclosure, the nickel-containing layered active material contained in the positive electrode active material may be 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 may be lithium iron manganese phosphate (LMFP) or lithium iron phosphate (LFP).

[0072] In this case, LMFP can be represented as LiMn x Fe 1-x PO4, and LFP can be represented as LiFePO4, where x may have a value of 0 < x < 1.

[0073] Generally, depending on the type of crystal lattice structure, the positive electrode active material can be roughly classified into a layered type, a spinel type, or an olivine type.

[0074] In this disclosure, the nickel-containing layered active material typically comprises 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 this layered active material, the constituent elements of the positive electrode active material are located in a layered structure, so that lithium ions are stored between the lattice layers when the lithium secondary battery is charged. At this time, a large number of lithium ions can be stored between wide and flat layers, thus achieving the advantage of high energy capacity when using this material, but causing poor stability during high-voltage charging.

[0075] In this disclosure, the olivine-based active material can be LMFP or LFP, and is typically hexahedral in form, thus exhibiting higher lattice structure stability compared to layered active materials. Furthermore, it suffers from less crystal structure degradation even during lithium-ion escape during discharge, resulting in long lifetime and high thermal stability. However, the olivine-based active material suffers from slow lithium-ion diffusion rate and relatively low energy density.

[0076] Furthermore, the spinel structure is an oxide crystal structure and does not use cobalt, thus its lattice structure has a three-dimensional shape and is excellent in terms of safety. However, the spinel structure has the problem that its capacity and lifetime decrease with charge and discharge.

[0077] The positive electrode active material described in this disclosure is characterized by comprising a nickel-containing layered active material (in particular, lithium nickel-cobalt-manganese (NCM) oxide) and an olivine-based active material (in particular, LMFP).

[0078] In one exemplary embodiment of this disclosure, based on 100 atomic percent of all elements contained in the LMFP, the LMFP may contain Mn greater than 0 atomic percent and equal to or less than 90 atomic percent.

[0079] For the olivine-based active material, LFP or LMFP with the same structure can be used, but in the case of LMFP, Mn is used instead of Fe, which has the effect of increasing voltage, and this can also increase the energy density even in olivine-based active materials with relatively low energy density.

[0080] This disclosure provides a lithium secondary battery, wherein the positive electrode active material is a single-particle positive electrode active material.

[0081] In addition, a lithium secondary battery is provided, wherein the nickel content in the nickel-containing layered active material is less than 75 mol% of all metals excluding lithium.

[0082] Generally, when implementing a high-voltage battery in a lithium secondary battery containing a silicon-based active material, secondary particles need to be used as the positive electrode active material to solve the resistance problem. However, in a high-voltage battery, the secondary particles break, resulting in a problem of gas generation. On the contrary, when applying a single-particle positive electrode active material as described above, a high-voltage battery can be driven.

[0083] In the present disclosure, the carbon-based active material contained in the negative electrode active material may include natural graphite, artificial graphite, expanded graphite, carbon fiber, graphitizable carbon, carbon black, carbon nanotube, fullerene, or activated carbon, and the silicon-based active material may include one or more selected from the group consisting of SiOx (0 < x < 2), Si / C, and Si alloy.

[0084] More specifically, the carbon-based active material contained in the negative electrode active material may include natural graphite or artificial graphite, and the silicon-based active material may include Si / C.

[0085] In the present disclosure, the Si / C may be expressed as a silicon-carbon composite.

[0086] In the present disclosure, the silicon-carbon composite is a composite of Si and C, and is distinguished from silicon carbide represented as SiC. Silicon carbide does not undergo an electrochemical reaction with lithium, so all properties (including lifespan) may be measured as 0.

[0087] The silicon-carbon composite may be a composite of silicon, graphite, etc., and may form a structure in which the core composite of silicon, graphite, etc. is surrounded by graphene, amorphous carbon, etc. In the silicon-carbon composite, the silicon may be nano-silicon. For example, the nano-silicon may be silicon within the range of 1 nm to 999 nm.

[0088] A lithium secondary battery has a size required depending on its application, so it should be designed within a limited space. Consumers' demand for increased energy density and improved high-output performance is increasing day by day, but when using a positive electrode material with a high capacity, the content of the negative electrode material should be increased accordingly to match the positive electrode material. Therefore, there are limitations in improving the battery efficiency within a limited space. In addition, a positive electrode material with an efficiency adapted to the efficiency of the negative electrode material needs to be designed according to the type of the negative electrode material.

[0089] Therefore, the present disclosure can apply a mixture of Si / C as the silicon-based active material, and at the same time use the materials with the above composition and content as the positive electrode active material, thereby ensuring the energy density while ensuring the lifespan performance and thermal stability.

[0090] According to the present disclosure, the negative electrode may include a negative electrode current collector layer and a negative electrode active material layer provided on one surface or both surfaces of the negative electrode current collector layer.

[0091] The negative electrode current collector layer typically has a thickness of 1 μm to 100 μm. This 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, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys, etc., can be used. Furthermore, the negative electrode current collector layer can have fine irregularities formed on its surface to enhance the adhesion of the negative electrode active material, and can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, or nonwoven fabrics.

[0092] However, the thickness can be modified in various ways depending on the type and purpose of the negative electrode used, and is not limited thereto.

[0093] Note that the average particle size (D50) of the silicon-based active material described in this disclosure can be from 1 μm to 10 μm, specifically from 5.5 μm to 8 μm, and more specifically from 6 μm to 7 μm. If the average particle size is less than 5 μm, the specific surface area of ​​the particles will increase excessively, resulting in an excessive increase in the viscosity of the negative electrode slurry. Therefore, the particles constituting the negative electrode slurry cannot be dispersed smoothly. Furthermore, if the size of the silicon-based active material is too small, the contact area between the silicon particles and the conductive material is reduced due to the composite of conductive material and binder in the negative electrode slurry, increasing the possibility of breakage of the conductive network and thus reducing the capacity retention rate. On the other hand, if the average particle size is greater than 10 μm, there are excessively large silicon particles, making the surface of the negative electrode uneven, resulting in uneven current density during charging and discharging. In addition, if the silicon particles are too large, the phase stability of the negative electrode slurry becomes unstable, thereby reducing processability. As a result, the capacity retention rate of the battery decreases.

[0094] In one exemplary embodiment of this disclosure, the silicon-based active material typically has a characteristic BET specific surface area. Preferably, the BET specific surface area of ​​the silicon-based active material is 0.01 m². 2 / g to 150.0 m 2 / g, more preferably 0.1 m 2 / g to 100.0 m 2 / g, particularly preferably 0.2 m 2 / g to 80.0 m 2 / g, most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0095] In one exemplary embodiment of this disclosure, the silicon-based active material may exist, for example, in crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or fragmented particles. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0096] In one exemplary embodiment of this disclosure, based on 100 parts by weight of the negative electrode active material layer composition, the content of the silicon-based active material can be 60 parts by weight or more.

[0097] In another exemplary embodiment, based on 100 parts by weight of the negative electrode active material layer composition, the content of the silicon-based active material may be 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may be 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less.

[0098] The negative electrode active material layer composition according to this disclosure uses specific negative electrode conductive materials and negative electrode binders, which can control the volume expansion rate during charge and discharge even when using the silicon-based active material with significantly high capacity within the aforementioned range. Therefore, even when the silicon-based active material is within the aforementioned range, the negative electrode active material layer composition does not degrade the performance of the negative electrode and has excellent output characteristics during charge and discharge.

[0099] In related technologies, graphite-based compounds are typically used as the negative electrode active material. However, in recent years, with the increasing demand for high-capacity batteries, there has been a growing attempt to use silicon-based compounds in combination to improve capacity. However, silicon-based compounds have a limitation: they expand rapidly in volume during charge and discharge, which damages the conductive paths formed in the negative electrode active material layer, thereby degrading battery performance.

[0100] Therefore, in one exemplary embodiment of this disclosure, the negative electrode active material layer composition may comprise a negative electrode conductive material and a negative electrode binder. That is, the negative electrode conductive material serves to ensure a conductive path, and the binder serves to retain the negative electrode conductive material during charging and discharging.

[0101] In one exemplary embodiment of this disclosure, the negative electrode conductive material may comprise one or more selected from the group consisting of point-like conductive materials, planar conductive materials, and linear conductive materials.

[0102] In one exemplary embodiment of this disclosure, the dot-shaped conductive material refers to a conductive material that can be used to improve the conductivity of the negative electrode, form conductivity without causing chemical changes, and has a circular or dot-like shape. Specifically, the dot-shaped conductive material may be one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, conductive fibers, fluorocarbons, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may contain carbon black in terms of high conductivity and excellent dispersibility.

[0103] In one exemplary embodiment of this disclosure, the dot-shaped conductive material may have a diameter of 40 μm. 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m 2 / g or less and 60 m 2 BET specific surface area below / g.

[0104] In one exemplary embodiment of this disclosure, the particle size of the dot-shaped conductive material can be from 10 nm to 100 nm, preferably from 20 nm to 90 nm, and more preferably from 40 nm to 60 nm.

[0105] In one exemplary embodiment of this disclosure, the conductive material may comprise a planar conductive material.

[0106] The planar conductive material refers to a conductive material that improves conductivity by increasing the surface contact between silicon particles in the negative electrode, while simultaneously suppressing the interruption of the conductive path due to volume expansion. The planar conductive material can be represented as a plate-shaped conductive material or a bulk-shaped conductive material.

[0107] In one exemplary embodiment of this disclosure, the planar conductive material may comprise one or more selected from the group consisting of plate graphite, graphene, graphene oxide and graphite flakes, and preferably plate graphite.

[0108] In one exemplary embodiment of this disclosure, the average particle size (D50) of the planar conductive material can be from 2 μm to 7 μm, specifically from 3 μm to 6 μm, and more specifically from 4 μm to 5 μm. When the above range is met, sufficient particle size results in easy dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, the dispersion effect is excellent when the same equipment and time are used for dispersion.

[0109] In one exemplary embodiment of this disclosure, a negative electrode composition is provided, wherein 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.

[0110] In one exemplary embodiment of this disclosure, the planar conductive material can be a high specific surface area planar conductive material with a high BET specific surface area or a low specific surface area planar conductive material.

[0111] In one exemplary embodiment of this disclosure, the planar conductive material can be either a high specific surface area planar conductive material or a low specific surface area planar conductive material without limitation. However, in particular, the planar conductive material according to this disclosure may be affected to some extent by dispersion in terms of electrode performance, thus a low specific surface area planar conductive material that does not cause dispersion problems is particularly preferred.

[0112] In one exemplary embodiment of this disclosure, the planar conductive material may have a 1 m 2 BET specific surface area above / g.

[0113] In another exemplary embodiment, the planar conductive material may have a 1 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, more preferably 5 m 2 / g or more and 250 m 2 BET specific surface area below / g.

[0114] In another exemplary embodiment, the planar conductive material is a high specific surface area planar conductive material, and the BET specific surface area can meet 50 m². 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, more preferably 100 m 2 / g or more and 250 m 2 The range below / g.

[0115] In another exemplary embodiment, the planar conductive material is a low specific surface area planar conductive material, and the BET specific surface area can meet the requirement of 1 m². 2 / g or more and 40 m 2 / g or less, preferably 5 m2 / g or more and 30 m 2 / g or less, more preferably 5 m 2 / g or more and 25 m 2 The range below / g.

[0116] Other conductive materials may include linear conductive materials, such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. A bundled carbon nanotube may comprise multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundled" herein refers to a bundled or rope-like secondary shape in which multiple carbon nanotube units are aligned side-by-side or entangled with substantially the same orientation along their longitudinal axes. The carbon nanotube units have cylindrical graphite sheets with nanometer-sized diameters and sp2 bonding structures. In this case, conductor or semiconductor properties may be exhibited depending on the winding angle and structure of the graphite sheets. Compared to entangled carbon nanotubes, bundled carbon nanotubes can be more uniformly dispersed during the fabrication of the negative electrode and can form a more stable conductive network within the negative electrode, thereby improving the conductivity of the negative electrode.

[0117] In one exemplary embodiment of this disclosure, the negative electrode conductive material may comprise a linear conductive material, and the linear conductive material may be a carbon nanotube.

[0118] In one exemplary embodiment of this disclosure, the carbon nanotubes may be single-walled carbon nanotubes (SWCNTs) and / or multi-walled carbon nanotubes (MWCNTs). When the linear conductive material is SWCNT, the length of the SWCNT may be from 0.5 μm to 100 μm, preferably from 1 μm to 80 μm.

[0119] In one exemplary embodiment of this disclosure, based on 100 parts by weight of the negative electrode active material layer composition, the content of the negative electrode conductive material can be more than 5 parts by weight and less than 40 parts by weight.

[0120] In another exemplary embodiment, based on 100 parts by weight of the negative electrode active material layer composition, the content of the negative electrode conductive material can be 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, more preferably 5 parts by weight or more and 25 parts by weight or less.

[0121] In one exemplary embodiment of this disclosure, the negative electrode conductive material may comprise planar conductive material and linear conductive material, and the ratio of the planar conductive material to the linear conductive material may satisfy 1:0.001 to 1:0.3.

[0122] In one exemplary embodiment of this disclosure, since the negative electrode conductive material comprises the planar conductive material and the linear conductive material, and satisfies the above composition and ratio respectively, the life characteristics of existing lithium secondary batteries are not significantly affected, and the number of charging and discharging sites of the battery increases, resulting in excellent output characteristics at high C-rates.

[0123] The negative electrode conductive material described in this disclosure has a completely different structure from the conductive material used in the positive electrode. That is, the negative electrode conductive material described in this disclosure is used to maintain contact between silicon-based active materials that expand significantly in electrode volume due to charging and discharging, and the positive electrode conductive material is used to provide some conductivity while acting as a buffer during rolling, and is completely different from the negative electrode conductive material described in this disclosure in terms of structure and function.

[0124] Furthermore, the negative electrode conductive material described in this disclosure is applied to silicon-based active materials and has a completely different structure from the conductive material applied to graphite-based active materials. That is, since the conductive material used in electrodes with graphite-based active materials simply has smaller particles than the active material, it possesses properties that improve output characteristics and impart some conductivity, and its structure and function are completely different from the negative electrode conductive material used in conjunction with the silicon-based active material as described in this disclosure.

[0125] In one exemplary embodiment of this disclosure, the plate-shaped conductive material used as the negative electrode conductive material has a structure and function different from those of 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 can be artificial graphite or natural graphite, and refers to a material processed into spherical or dot-like shapes to facilitate the storage and release of lithium ions.

[0126] On the other hand, the plate-shaped conductive material used as the negative electrode conductive material is a material having a planar or plate-shaped shape, and can be represented as plate-shaped graphite. That is, the plate-shaped conductive material is a material included to maintain a conductive path in the negative electrode active material layer, and refers to a material used to ensure a conductive path in a planar manner within the negative electrode active material layer, rather than playing a role in storing or releasing lithium.

[0127] That is, in this disclosure, using plate-shaped graphite as a conductive material means processing graphite into planar or plate-like shapes and using it as a material to ensure a conductive path, rather than playing a role in storing or releasing lithium. In this case, the negative electrode active material included together has high capacity characteristics in storing and releasing lithium, and is used to store and release all lithium ions transferred from the positive electrode.

[0128] On the other hand, in this disclosure, using carbon-based active materials as active materials means processing the carbon-based active materials into dot-like or spherical shapes and using them as materials for storing or releasing lithium.

[0129] In one exemplary embodiment of this disclosure, the negative electrode adhesive may comprise at least one material selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogen is replaced by Li, Na, Ca, etc., and may also comprise various copolymers thereof.

[0130] The negative electrode adhesive according to an exemplary embodiment of this disclosure is used to hold the silicon-based active material and the negative electrode conductive material together, thereby preventing distortion and structural deformation of the negative electrode structure during the volume expansion and mitigation of the silicon-based active material. All common negative electrode adhesives can be applied when such an effect is achieved. Specifically, aqueous adhesives can be used, and more specifically, polyacrylamide (PAM) based adhesives can be used.

[0131] In one exemplary embodiment of this disclosure, based on 100 parts by weight of the negative electrode active material layer composition, the content of the negative electrode adhesive may be less than 30 parts by weight, preferably less than 25 parts by weight, more preferably less than 20 parts by weight, and may be more than 5 parts by weight or more than 8 parts by weight.

[0132] In one exemplary embodiment of this disclosure, the negative electrode can be formed by coating one or both surfaces of the negative electrode current collector layer with a negative electrode slurry comprising the negative electrode active material layer composition.

[0133] In one exemplary embodiment of this disclosure, the negative electrode slurry may comprise a negative electrode active material layer composition and a slurry solvent.

[0134] In one exemplary embodiment of this disclosure, the solid content of the negative electrode slurry can be in the range of 5% or more and 40% or less.

[0135] In another exemplary embodiment, the solid content of the negative electrode slurry can be in the range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0136] The solid content of the negative electrode slurry may refer to the content of the negative electrode composition contained in the negative electrode slurry, and may refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0137] When the solid content of the negative electrode slurry meets the above range, the viscosity is appropriate during the formation of the negative electrode active material layer, thereby minimizing particle agglomeration of the negative electrode composition to effectively form the negative electrode active material layer.

[0138] In one exemplary embodiment of this disclosure, a slurry solvent may be used without limitation, as long as it is capable of dispersing the above-described negative electrode composition. Specifically, water or N-methyl-2-pyrrolidone (NMP) may be used.

[0139] In one exemplary embodiment of this disclosure, the positive electrode includes a positive electrode current collector layer and a positive electrode active material layer disposed on one or both surfaces of the positive electrode current collector layer.

[0140] In the positive electrode, the positive electrode current collector layer is not particularly limited, as long as it is conductive and will not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, and aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., can be used. Furthermore, the positive electrode current collector layer can typically have a thickness of 1 to 500 μm, and its surface can be formed with fine irregularities to enhance adhesion to the positive electrode active material. For example, the positive electrode current collector layer can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0141] In this disclosure, the average particle size (D50) of the single-particle positive electrode active material can be greater than 1 μm and less than 12 μm, greater than 1 μm and less than 8 μm, greater than 1 μm and less than 6 μm, greater than 1 μm and less than 12 μm, greater than 1 μm and less than 8 μm, or greater than 1 μm and less than 6 μm.

[0142] Even when the single-particle positive electrode active material is formed into small particles with an average particle size (D50) of 1 μm or more and 12 μm or less, the particle strength can still be excellent. For example, when the particle strength is 650 kgf / cm², the particle strength is excellent. 2 When rolled with a force of 650 kgf / cm², the single particle can have a particle strength of 100 to 300 MPa. Therefore, even when rolled with a force of 650 kgf / cm², the single particle can still achieve a particle strength of 100 to 300 MPa. 2 When a single particle is subjected to strong rolling, the phenomenon of increased microparticles in the electrode due to particle breakage is also alleviated, which improves the battery's lifespan characteristics.

[0143] The single-particle positive electrode active material can be manufactured by mixing and calcining a transition metal precursor and a lithium source material. Secondary particles can be manufactured using different methods than single-particle materials, and their composition can be the same as or different from that of single particles.

[0144] The method for forming single-particle positive electrode active materials is not particularly limited, but generally, the single-particle positive electrode active materials can be formed by increasing the firing temperature to achieve overfiring, or by using additives that facilitate overfiring (such as grain growth promoters), changing the starting materials, etc.

[0145] For example, firing is performed at a temperature capable of forming single particles. Therefore, firing should be carried out at a temperature higher than that during the secondary particle manufacturing process. For example, when the composition of the precursor is the same, firing should be performed at a temperature approximately 30°C to 100°C higher than that during the secondary particle manufacturing process. The firing temperature used to form single particles can vary depending on the metal composition in the precursor. For example, when forming single particles using a high-Ni NCM-based lithium composite transition metal oxide (with a nickel (Ni) content of 80 mol% or more), the firing temperature can be approximately 700°C to 1000°C, preferably approximately 800°C to 950°C. When the firing temperature meets the above range, a positive electrode active material containing single particles with excellent electrochemical performance can be manufactured. If the firing temperature is below 790°C, a positive electrode active material containing a lithium composite transition metal compound in the form of secondary particles can be manufactured; if the firing temperature exceeds 950°C, overfiring occurs, and a proper layered crystal structure cannot be formed, potentially degrading the electrochemical performance.

[0146] In this specification, the term "single-particle positive electrode active material" is used to distinguish it from typical secondary particles generated by the aggregation of tens to hundreds of primary particles, and is a concept that includes single particles consisting of one primary particle and quasi-single-particle forms as aggregates of less than 30 primary particles.

[0147] Specifically, in this disclosure, the single-particle positive electrode active material can be a single particle composed of a primary particle, or a quasi-single particle as an aggregate of less than 30 primary particles, and the secondary particle can be an aggregate of hundreds of primary particles.

[0148] In an exemplary embodiment of this disclosure, in 100 parts by weight of the positive electrode active material layer composition, the content of the positive electrode active material can be 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 most preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0149] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0150] In this context, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitation, as long as the positive electrode conductive material is electronically conductive without causing chemical changes in the battery to be constructed. Specific examples may include: graphite, such as natural graphite and artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking 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, etc., and any one of them or a mixture of two or more of them may be used.

[0151] Furthermore, the positive electrode adhesive is used to improve the bonding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more of them may be used.

[0152] In one exemplary embodiment of this disclosure, a lithium secondary battery is provided, wherein 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.

[0153] In another exemplary embodiment, the porosity of the negative electrode active material layer can be in the 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.

[0154] In another exemplary embodiment, the porosity of the positive electrode active material layer can be in the 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.

[0155] The porosity varies depending on the composition, content, and degree of calendering of the active materials, conductive materials, and binders contained in each active material layer. In particular, when the porosity meets the above-mentioned range, the problems of fast charging performance and resistance caused by lithium-ion diffusion can be solved without damaging the active materials.

[0156] In one exemplary embodiment of this disclosure, a lithium secondary battery is provided, wherein the discharge capacity loading of the positive electrode active material layer composition is 2 mAh / cm². 2 Above and 5 mAh / cm 2 Hereinafter, the discharge capacity load of the negative electrode active material layer composition is 1 to 1.1 times that of the positive electrode active material layer composition.

[0157] The discharge capacity load of the negative electrode active material layer composition described above is 1 to 1.1 times (NP100 to 110) the discharge capacity load of the positive electrode active material layer. If the discharge capacity load of the positive electrode active material layer composition is less than the above range, it is difficult to ensure energy density, while if it exceeds the above range, problems such as fast charging and heat generation will occur.

[0158] This disclosure provides a lithium secondary battery, wherein the thickness of the positive electrode current collector layer and the negative electrode current collector layer is more than 1 μm and less than 100 μm, and the thickness of the positive electrode active material layer and the negative electrode active material layer is more than 20 μm and less than 500 μm.

[0159] In one exemplary embodiment of this disclosure, the negative electrode may be a pre-lithiated negative electrode.

[0160] In one exemplary embodiment of this disclosure, the positive electrode may be a pre-lithiated positive electrode.

[0161] In this case, the pre-lithiation method can be a method commonly used in the art.

[0162] Specifically, the negative electrode can be pre-lithiated through a lithium plating process, a lithium metal transfer process, a lithium metal deposition process, or a stabilized lithium metal powder (SLMP) coating process.

[0163] In this disclosure, the pre-lithiation of the positive or negative electrode can improve energy density and further increase lifetime. That is, pre-lithiation enables lifetime performance and energy density to be ensured through the Li reservoir effect.

[0164] The separator is used to separate the negative electrode and the positive electrode and provide a migration path for lithium ions. Any separator can be used without particular limitation, as long as it is commonly used in secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion migration are preferred. Specifically, porous polymer membranes can be used, for example, porous polymer membranes made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof. Furthermore, conventional porous nonwoven fabrics can be used, for example, nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Additionally, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can be selectively used.

[0165] Examples of the electrolyte may include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used to manufacture the lithium secondary battery.

[0166] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0167] As the non-aqueous organic solvent, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, or ethyl propionate can be used.

[0168] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, as cyclic carbonates, are high-viscosity organic solvents and have high dielectric constants to effectively dissociate lithium salts, thus they are preferably used. When the cyclic carbonates are mixed in a suitable proportion with linear carbonates (such as dimethyl carbonate and diethyl carbonate) having low viscosity and low dielectric constants, electrolytes with high conductivity can be prepared, thus they are more preferably used.

[0169] Lithium salts can be used as the metal salts, and the lithium salts are materials that are readily soluble in non-aqueous electrolytes, wherein, for example, F is selected. - 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 of the group can be used as an anion of the lithium salt.

[0170] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, the electrolyte, in addition to containing the above-mentioned electrolyte components, may further contain one or more additives, such as alkylene carbonate halide compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0171] An exemplary embodiment of this disclosure provides a battery module comprising the secondary battery as a unit cell and a battery pack comprising the same. Because the battery module and the battery pack contain the secondary battery having high capacity, high rate capability, and high cycle characteristics, they 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 energy storage systems.

[0172] In this disclosure, the lithium secondary battery can have an energy density of 700 Wh / L or higher and a TR rate of 4 mbar / Ah second or lower.

[0173] At this point, the TR rate can be calculated using Equation 3 below.

[0174] [Formula 3]

[0175] TR rate = (maximum pressure - pre-ignition pressure) / (battery capacity) / (time from imminent ignition to maximum pressure)

[0176] Specifically, the pressure and time in Equation 3 can be measured using a pressure gauge attached to the autoclave. When thermal runaway of the battery occurs, the pressure inside the autoclave increases due to the generated gas. The pressure at the point where the pressure begins to increase can be measured by the pressure gauge at the time before and just before ignition, and the pressure at the point where the pressure reaches its maximum value can be measured as the maximum pressure and the time to reach the maximum pressure.

[0177] That is, by applying the above-mentioned positive and negative electrodes, the energy density and thermal stability described above can be ensured.

[0178] Preferred embodiments will be provided below to better understand this disclosure. It will be apparent to those skilled in the art that the embodiments described are merely illustrative of this disclosure, and various modifications and changes can be made within the scope and spirit of this disclosure. Such modifications and changes naturally fall within the scope of the claims contained herein.

[0179] Methods of implementing the invention

[0180] <Preparation Example>

[0181] (1) Preparation of the positive electrode

[0182] Li(Ni a Co b Mn c O2 and LMFP are used as positive electrode active materials.

[0183] In this case, the NCM of the positive electrode active material, excluding lithium (Li) and oxygen (O2), has a Ni:Co:Mn ratio of 70:20:10, thus satisfying an a:b:c ratio of 70:20:10 (a:b:c = 0.70:0.20:0.10). Furthermore, D50 is 3.8 μm, D... 最小 and D 最大 The thicknesses are 1.2 μm and 13 μm, and the BET specific surface area is 0.64 m². 2 / g, and the true density is 4.78 to 4.80 g / cm³. 3 .

[0184] The Mn content in LMFP is 60 atoms.

[0185] 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 prepare a positive electrode slurry. This positive electrode slurry (4 mAh / cm³) was then used to prepare the slurry. 2 The coating is applied to a 12 μm thick aluminum (Al) film, which serves as the positive electrode current collector. The film is then dried and rolled to prepare the positive electrode (porosity: 23%).

[0186] (2) Preparation of negative electrode

[0187] A negative electrode active material layer composition was prepared using Si / C:artificial graphite (20:80) (as a silicon-based active material), a first conductive material, a second conductive material, and polyacrylamide (as a binder) in a weight ratio of 80:9.6:0.4:10. A negative electrode slurry (solids concentration: 28% by weight) was prepared by adding the composition to distilled water as a solvent for forming the negative electrode slurry.

[0188] The first conductive material is plate-shaped graphite (specific surface area: 17 m²). 2 / g, average particle size (D50): 3.5 μm), the second conductive material is carbon nanotubes.

[0189] As a mixing method, a first conductive material, a second conductive material, a binder, and water are dispersed at 2500 rpm for 30 minutes using a homogenizer, an active material is added thereto, and the resulting mixture is dispersed at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0190] The negative electrode slurry was loaded with a capacity of 3.78 mAh / cm³. 2 The coating is applied to both surfaces of a copper current collector (thickness: 8 μm) used as the negative electrode current collector, then rolled 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%).

[0191] (3) Preparation of secondary batteries

[0192] An electrode assembly is fabricated by inserting a compression-resistant thin-film separator (PE 12 μm) with a ceramic coating of 3 μm / 3 μm between the positive and negative electrodes. After placing the electrode assembly inside a housing, an electrolyte is injected into the housing to fabricate a lithium secondary battery.

[0193] At this time, the positive electrode and the negative electrode satisfy the composition and content shown in Table 1 below.

[0194] Table 1

[0195] <Experimental Example>

[0196] 1) Evaluation of heat transfer (TP)

[0197] For the lithium secondary batteries prepared in the above embodiments and comparative examples, the following are formed: Figure 2 The structure shown was evaluated, and the thermal pad in contact with the battery was heated to induce thermal runaway of the battery.

[0198] Experiments were conducted in an autoclave (isolated from the external environment / atmosphere) and an N2 atmosphere. The pressure of the gas released during thermal runaway was measured using a pressure gauge in the autoclave. To avoid confusion between battery capacity and footprint, a 40Ah A5-A battery was used in this evaluation, and the TR rate based on this battery is shown in Table 2 below.

[0199] The following pressures are measured using a pressure gauge attached to the autoclave. As the battery thermal runaway progresses, the pressure inside the autoclave increases due to the generated gases. The pressure at which the pressure begins to rise can be measured as the pressure before ignition and the pressure momentarily before ignition. The pressure at which the pressure reaches its maximum value can be measured as the maximum pressure and the time taken to reach the maximum pressure. These data can be used for calculations.

[0200] TR rate = (maximum pressure - pre-ignition pressure) / (battery capacity) / (time from imminent ignition to maximum pressure)

[0201] Table 2

[0202] 2) Energy density (ED) evaluation

[0203] For the lithium secondary batteries prepared in the above examples and comparative examples, the energy density was calculated using the discharge energy obtained during charge-discharge at 0.33 C and the battery volume. However, the batteries used in the experiments are typically manufactured in smaller dimensions than batteries installed in automobiles and have low space utilization. Therefore, when performing ED evaluation, the discharge energy and volume were converted and calculated based on the size of batteries installed in automobiles.

[0204] Table 3

[0205] In the case of the lithium secondary battery according to this disclosure, energy density is ensured by including the nickel-containing layered active material in the positive electrode and the silicon-based active material in the negative electrode, rather than simply using the carbon-based active material and the olivine-based active material alone. Furthermore, by deriving the weight ratio satisfying Formulas 1 and 2 above, the problem of thermal stability (TP) caused by the resulting increase in capacity can be solved. Generally, as the content of the silicon-based active material in the negative electrode increases, the energy density increases, but the thermal stability deteriorates. Correspondingly, when the content of the olivine-based active material in the positive electrode increases, the thermal stability problem is improved, but the energy density decreases. However, through research, the inventors of this disclosure have derived the ratio of Formulas 1 and 2 as described above, and confirmed through examples and comparative examples that when the ratio is applied, both energy density and thermal stability can be ensured simultaneously.

[0206] From the perspective of battery energy density, as the amount of olivine-based active material increases, the positive electrode becomes thicker. To compensate for this thickness, the content of silicon-based active material in the negative electrode should increase. In this disclosure, from the perspective of achieving a specific energy density, the lower limit of the silicon-based active material content (B) is determined based on the content of the olivine-based active material (A). In particular, it can be confirmed through examples that, from the perspective of energy density, in Equation 1, it is possible to achieve the desired energy density through 4.524 + 0.939 × e 0.0537×A < B to ensure energy density.

[0207] On the other hand, with the increase of the olivine-based active material content, the thermal stability is excellent, thus enabling the application of more silicon-based active materials. From the perspective of TR ratio, the upper limit of the silicon-based active material content (B) is determined based on the olivine-based active material content (A). In particular, it can be confirmed that in order to satisfy the TR ratio, B < -4.312 + 5.183 × e in Equation 1 should be satisfied. 0.0537×A .

[0208] That is, it can be seen that the lithium secondary battery according to this disclosure can simultaneously ensure thermal stability and energy density, which were previously not possible to achieve simultaneously. This can be achieved when the olivine-based active material and the silicon-based active material satisfy the relationship in Equation 1 of this disclosure.

[0209] Comparative Examples 1 to 3, in which the lithium NCM oxide positive electrode is simply used as the negative electrode, correspond to cases where the content of the silicon-based active material is adjusted or a graphite-based negative electrode is used.

[0210] In Comparative Examples 1 and 2, it can be confirmed that the energy density is satisfactory, but the thermal stability is low due to the high content of silicon-based active material, which degrades the TR characteristics. It can also be confirmed that when a graphite-based negative electrode is used as the negative electrode of the counter electrode, the thermal stability is ensured, but the energy density is reduced.

[0211] Comparative Examples 4 to 6, in which an olivine-based positive electrode is used as the counter electrode of the negative electrode, correspond to cases where the content of the silicon-based active material is adjusted or a graphite-based negative electrode is used.

[0212] In Comparative Examples 4 to 6, which used olivine-based cathodes, the thermal stability was judged to be excellent, but it was confirmed that the energy density was reduced due to the lack of mixing with lithium NCM oxide.

[0213] In Comparative Examples 7 to 9, in which olivine-based materials and lithium NCM oxide are used together as the positive electrode, Comparative Example 7 does not satisfy the scope of Formula 1 of this disclosure, Comparative Example 8 uses a graphite-based negative electrode alone, and the content of the olivine-based active material in Comparative Example 9 is low, thus not satisfying the scope of Formulas 1 and 2.

[0214] In Comparative Examples 7 and 9, it can be confirmed that the energy density meets the required level, but the TR characteristics deteriorate. In particular, Comparative Examples 7 and 9 confirm that the TR characteristics deteriorate when the range of Equation 1 of this disclosure is not met, and it can be confirmed that in Comparative Example 8, the TR characteristics are met by using the graphite-based negative electrode, but the energy density cannot be guaranteed.

[0215] Furthermore, in the cases of Comparative Examples 10 to 26, the range of Equation 1 is not satisfied, and as shown in Tables 2 and 3, the energy density and / or TR characteristics are not satisfied. In particular, it can be confirmed by Comparative Examples 17 to 26 that the embodiments that satisfy Equation 1 are superior to the comparative examples.

[0216] For reference, Examples 2 to 5 correspond to cases where, based on Example 1, the amount of lithium NCM oxide active material in the positive electrode active material is increased while the amount of LMFP is decreased, while the negative electrode is kept constant. As can be seen from the data in Tables 2 and 3, when the amount of lithium NCM oxide is increased to the range of this disclosure, the energy density increases, but the thermal stability is worse compared to that in Example 1. Examples 7 and 8 are similar to Example 6, and Examples 10, 11, 13, and 14 also show the same trend. That is, when used within the range of Formula 1, the lithium secondary battery according to this disclosure has the characteristic of being able to adjust the energy density and thermal stability to suit the intended use.

Claims

1. 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, and the positive electrode active material layer includes a positive electrode active material layer composition, wherein the negative electrode includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material layer composition, wherein the positive electrode active material layer composition includes a positive electrode active material, and the positive electrode active material includes a nickel-containing layered active material and an olivine-based active material, wherein the negative electrode active material layer composition includes a negative electrode active material, and the negative electrode active material includes a silicon-based active material, and in, the weight part (A) of the olivine-based active material based on 100 weight parts of the positive electrode active material and the weight part (B) of the silicon-based active material based on 100 weight parts of the negative electrode active material satisfy Formula 1 and Formula 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, Based on 100 weight parts of the positive electrode active material, the content of the nickel-containing layered active material is 10 weight parts or more and 90 weight parts or less.

3. The lithium secondary battery according to claim 1, wherein, Based on 100 weight parts of the negative electrode active material, the content of the silicon-based active material is 5 weight parts or more and 100 weight parts or less.

4. The lithium secondary battery according to claim 1, wherein the negative electrode active material further includes a carbon-based active material, and wherein based on 100 weight parts of the negative electrode active material, the content of the silicon-based active material is 5 weight parts or more and less than 100 weight parts, and the content of the carbon-based active material is more than 0 weight parts and 95 weight parts or less.

5. The lithium secondary battery according to claim 1, wherein 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, and wherein the olivine-based active material is lithium manganese iron phosphate (LMFP) or lithium iron phosphate (LFP).

6. The lithium secondary battery according to claim 1, wherein the nickel-containing layered active material is lithium nickel-cobalt-manganese (NCM) oxide, wherein the olivine-based active material is lithium manganese iron phosphate (LMFP), and wherein based on 100 atomic% of all elements contained in the LMPF, the content of Mn is more than 0 atomic% and equal to or less than 90 atomic%.

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

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

9. The lithium secondary battery according to claim 1, wherein, The content of nickel contained in the nickel-containing layered active material is 75 mol% or less based on all metals other than lithium.

10. The lithium secondary battery according to claim 1, wherein the positive electrode active material layer has a porosity in the range of 15% to 30%, and wherein the negative electrode active material layer has a porosity in the range of 20% to 45%.

11. The lithium secondary battery according to claim 1, wherein the discharge capacity loading of the positive electrode active material layer composition is 2 mAh / cm³. 2 Above and 5 mAh / cm 2 Below, and The discharge capacity load of the negative electrode active material layer composition is 1 to 1.1 times that of the positive electrode active material layer composition.

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

13. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has an energy density of 700 Wh / L or higher, and a TR rate of 4 mbar / Ah second or lower as expressed by Equation 3: [Formula 3] TR rate = (maximum pressure - pre-ignition pressure) / (battery capacity) / (time from pre-ignition pressure to maximum pressure).

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

15. The lithium secondary battery according to claim 1, wherein the specific surface area of ​​the Brunauer-Emmett-Teller (BET) silicon-based active material is 0.01 m². 2 / g to 150.0 m 2 / g.

16. The lithium secondary battery according to claim 1, wherein the silicon-based active material is in 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-lithiated electrode.

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

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