Lithium-ion batteries, battery packs, and electronic devices including the same.

Abstract

This invention relates to lithium secondary batteries, battery packs, and electronic devices including the same. [Solution] The present invention relates to a lithium secondary battery, battery pack, and electronic device including the same, comprising a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode active material comprises a lithium composite transition metal compound containing nickel, cobalt, and manganese, the lithium composite transition metal compound comprises single particles, the silicon carbon composite comprises Si crystal grains, and the size of the Si crystal grains of the silicon carbon composite is less than or equal to the size of the crystal grains of the lithium composite transition metal compound. The size of the lithium is less than or equal to the crystal grains of the silicon carbon composite, and the single particle is one primary particle or an aggregate of two to thirty primary particles.

Description

[Technical Field]

[0001] This invention claims the benefit as of the filing date of Korean Patent Application No. 10-2022-0177120, filed with the Korean Intellectual Property Office on December 16, 2022, and Korean Patent Application No. 10-2023-0180420, filed with the Korean Intellectual Property Office on December 13, 2023, and all of its contents are contained herein.

[0002] This invention relates to lithium secondary batteries, battery packs, and electronic devices containing the same. [Background technology]

[0003] Recently, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptop computers, electric vehicles, power tools, and vacuum cleaners, the demand for small, lightweight, yet relatively high-capacity and / or high-power rechargeable batteries has been rapidly increasing. In particular, lithium-ion batteries are attracting attention as a power source for electronic devices due to their light weight and high energy density. As a result, research and development efforts to improve the performance of lithium-ion batteries are being actively pursued.

[0004] In a lithium-ion secondary battery, an organic or polymer electrolyte is charged between a positive electrode and a negative electrode, which are made of an active material that allows for the insertion and deintercalation of lithium ions. Electrical energy is generated by oxidation and reduction reactions that occur when lithium ions are inserted into and deintercalated at the positive and negative electrodes.

[0005] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compounds (LiFePO4) have been used as positive electrode active materials in lithium secondary batteries. Among these, lithium cobalt oxide (LiCoO2) has been widely used due to its advantages of high operating voltage and excellent capacity characteristics, and is applied as a positive electrode active material for high voltage applications. However, due to the rising price and unstable supply of cobalt (Co), there are limitations to its large-scale use as a power source in fields such as electric vehicles, and the need for the development of alternative positive electrode active materials is increasing.

[0006] Therefore, nickel-cobalt-manganese lithium composite transition metal compounds (hereinafter simply referred to as "NCM-based lithium composite transition metal compounds") were developed in which some of the cobalt (Co) is replaced with nickel (Ni) and manganese (Mn). Recently, techniques to increase capacity by increasing the nickel content in NCM-based lithium composite transition metal compounds have been studied. However, in the case of high-concentration nickel (Ni-rich) cathode active materials with a high nickel content, there are disadvantages such as decreased thermal stability, increased resistance due to increased side reactions during electrochemical reactions, and increased gas generation.

[0007] On the other hand, graphite is mainly used as the negative electrode active material for lithium secondary batteries, but graphite has a small capacity of 372 mAh / g per unit mass, making it difficult to increase the capacity of lithium secondary batteries. Therefore, in order to increase the capacity of lithium secondary batteries, non-carbon negative electrode materials such as silicon, tin, and their oxides have been developed as negative electrode materials that have a higher energy density than graphite. However, in the case of such non-carbon negative electrode materials, although the capacity is large, there are problems such as low initial efficiency, large lithium consumption during the initial charge and discharge process, and large irreversible capacity loss.

[0008] Furthermore, lithium-ion secondary batteries have size requirements depending on their application, and therefore need to be designed within a 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. Therefore, there is a need to develop batteries with improved efficiency, lifespan, and other performance characteristics within a limited space. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Korean Published Patent No. 10-2011-0112215 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The present inventors have demonstrated that in lithium secondary batteries designed within a limited space, optimal battery performance can be achieved with specific combinations by adjusting the crystal grain size of the lithium composite transition metal compound used as the positive electrode active material and the Si crystal grain size of the negative electrode active material, leading to the present invention.

[0011] This invention relates to lithium secondary batteries, battery packs, and electronic devices including the same. [Means for solving the problem]

[0012] One embodiment of the present invention provides a lithium secondary battery comprising a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode active material comprises a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound comprises a single particle, the negative electrode active material comprises a silicon carbon composite, the single particle comprises a crystal grain of the lithium composite transition metal compound, the silicon carbon composite comprises a Si crystal grain, the Si crystal grain size of the silicon carbon composite is 10% or less of the crystal grain size of the lithium composite transition metal compound, and the single particle is a single primary particle or an aggregate of 2 to 30 primary particles.

[0013] One embodiment of the present invention provides a battery pack including the lithium secondary battery.

[0014] One embodiment of the present invention provides an electronic device including the battery pack. [Effects of the Invention]

[0015] In one embodiment of the present invention, the lithium secondary battery has a silicon-carbon composite Si crystal grain size in the negative electrode active material that is 10% or less of the crystal grain size of the lithium-composite transition metal compound in the positive electrode active material. Therefore, when the crystal grain size is met, the cycle characteristics and swelling performance can be improved. Accordingly, as described above, by adjusting the crystal grains of the lithium-composite transition metal compound and the Si crystal grains of the negative electrode active material, the rapid charging performance, efficiency, lifespan, and / or energy density of a lithium secondary battery designed within a limited space can be easily improved. [Modes for carrying out the invention]

[0016] The following provides further details about this specification.

[0017] In this specification, when a part "includes" a component, this means, unless otherwise stated, that it may include other components rather than excluding them.

[0018] In this specification, when one member is said to be "on top of" another member, this includes not only cases where one member is in contact with another member, but also cases where another member exists between the two members.

[0019] Terms and words used herein should not be interpreted in their ordinary or dictionary sense, but rather in a sense and concept appropriate to the technical idea of ​​the present invention, in accordance with the principle that inventors themselves can appropriately define the concepts of terms in order to best describe the invention.

[0020] In this specification, singular expressions of terms include plural expressions unless the context clearly indicates otherwise.

[0021] In this specification, "single particle" is a term used to distinguish it from positive electrode active material particles in secondary particle form that are formed by the aggregation of 30 or more, 35 or more, 40 or more, 50 or more, 60 or more, 70 or more, 100 or more, 150 or more, or 200 or more primary particles, and includes single particles consisting of one primary particle and similar-single particle forms that are aggregates of 30 or fewer primary particles.

[0022] In this specification, the average particle size (D 50 The average particle size can be defined as the particle size that corresponds to 50% of the cumulative volume in the particle size distribution curve (graph curve of the particle size distribution diagram). The average particle size can be measured, for example, using the laser diffraction method. The laser diffraction method can usually measure particle sizes from the submicron region to about a few millimeters, and yields highly reproducible and high-resolution results.

[0023] The average particle size can be measured using a Microtrac system (manufacturer: Microtrac model: S3500) with water and triton-X100 dispersant. Specifically, the average particle size of the positive electrode active material can be measured in the range of refractive index 1.5 to 1.7, and the negative electrode active material can be measured under conditions of refractive index 1.97 or 2.42. For example, after dispersing the particles in a dispersion medium, they can be placed in a commercially available laser diffraction particle size analyzer, irradiated with ultrasound at approximately 28 kHz at an output of 60 W, and after obtaining a volume-cumulative particle size distribution graph, the particle size corresponding to 50% of the volume-cumulative amount can be determined.

[0024] Preferred embodiments of the present invention will be described in detail below. However, embodiments of the present invention may be modified in various forms, and the scope of the present invention is not limited to the embodiments described below.

[0025] One embodiment of the present invention provides a lithium secondary battery comprising a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode active material comprises a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound comprises a single particle, the negative electrode active material comprises a silicon carbon composite, the single particle comprises a crystal grain of the lithium composite transition metal compound, the silicon carbon composite comprises a Si crystal grain, the Si crystal grain size of the silicon carbon composite is 10% or less of the crystal grain size of the lithium composite transition metal compound, and the single particle is a single primary particle or an aggregate of 2 to 30 primary particles.

[0026] Generally, lithium-ion batteries have size requirements depending on the application, and therefore need to be designed within a 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.

[0027] The lithium secondary battery according to the present invention is characterized in that the Si crystal grain size of the silicon carbon composite contained in the negative electrode active material is 10% or less of the crystal grain size of the lithium composite transition metal compound contained in the positive electrode active material.

[0028] Due to the material properties of silicon-carbon composites, the larger the crystal grain size, the less likely crystalline Si is to become amorphous during the lithiation process, resulting in increased resistance. As the cycle continues, more lithium (Li) remains in the material, potentially leading to a deterioration in cycle performance and a serious degree of expansion. On the other hand, lithium-composite transition metal compounds, due to the material properties, can maintain a relatively stable crystal structure even after repeated lithiation / delithiation processes as the crystal grain size increases, thus stably maintaining the lithium diffusion path.

[0029] The inventors have found that by adjusting the crystal grain size of the lithium composite transition metal compound used as the positive electrode active material to a specific range relative to the Si crystal grain size of the silicon carbon composite, the aforementioned degradation of cycle performance and degree of expansion can be reduced.

[0030] Specifically, when the crystal grain size of the lithium-composite transition metal compound of the positive electrode active material is larger than the Si crystal grain size of the silicon-carbon composite within the aforementioned range, the positive electrode active material maintains a relatively stable crystal structure during the lithiation / delithiation process. This allows for stable maintenance of the lithium diffusion pathway, resulting in easier electrochemical reactions even with a small amount of lithium (Li), preventing relative capacity reduction and expansion. Furthermore, when the Si crystal grain size of the silicon-carbon composite meets the aforementioned range, the stress caused by volume expansion of the negative electrode active material particles during charging and discharging can be reduced, preventing particle cracking and improving cycle characteristics and swelling performance.

[0031] As mentioned above, by controlling the relationship between the crystal grain size of the lithium-composite transition metal compound contained in the positive electrode active material and the Si crystal grain size of the negative electrode active material, the crystal structure of the positive electrode active material can be relatively stably maintained, reducing the degradation of cycle performance and expansion due to residual lithium. Therefore, as described above, by adjusting the crystal grain size of the lithium-composite transition metal compound and the Si crystal grain size of the negative electrode active material, the rapid charging performance, efficiency, lifespan, and / or energy density of lithium secondary batteries designed within a limited space can be easily improved.

[0032] In one embodiment of the present invention, the silicon-carbon composite may be a Si / C-based active material.

[0033] In this specification, the silicon-carbon composite is a composite of Si and C, where Si and C (e.g., graphite) are present respectively. For example, the peaks for Si and C can be observed by elemental analysis methods such as XRD or NMR.

[0034] In this specification, the silicon-carbon composite may be denoted as Si / C. The silicon-carbon composite may consist of unbonded Si and C, but may contain additional components as needed. For example, the silicon-carbon composite may or may not contain silicon carbide, denoted as SiC. If the silicon-carbon composite contains silicon carbide, its content is 3% by weight or less. The silicon-carbon composite may exist in a crystalline, amorphous, or mixed state. For example, the C in the silicon-carbon composite may exist in an amorphous state.

[0035] The silicon-carbon composite may be a composite of silicon and carbon, and may form a structure in which a core of silicon and carbon is surrounded by graphite, graphene, or amorphous carbon. In the silicon-carbon composite, the silicon may be nanosilicon.

[0036] The silicon-carbon composite may be formed by physically or chemically compounding carbon and silicon material, and is not limited as long as carbon and silicon material form a composite structure.

[0037] Specifically, the silicon-carbon composite may be heat-treated (firing) in a state where carbon is bonded to silicon or silicon oxide particles, resulting in a configuration where the carbon material is coated on the surface of the particles, or a configuration where carbon is dispersed in an atomic state inside the silicon particles, or a structure in which a core made of silicon and carbon is surrounded by graphite, graphene, or amorphous carbon.

[0038] One embodiment of the present invention, the average particle size (D) of the silicon carbon composite. 50 The average particle size of the silicon carbon composite may be 1 μm or more. Also, the average particle size of the silicon carbon composite may be 15 μm or less. For example, the average particle size of the silicon carbon composite (D 50) may be 1 μm or more and 15 μm or less, greater than 1 μm and less than 15 μm, 2 μm or more and 14 μm or less, 3 μm or more and 13 μm or less, 3 μm to 10 μm, 4 μm to 8 μm, or 5 μm to 8 μm.

[0039] The silicon carbon composite has an average particle size (D 50 Even if the silicon-carbon composite is formed with a small particle size of approximately 1 μm to 15 μm, the battery's lifespan characteristics can be improved. For example, when the average particle size of the silicon-carbon composite is in the range of 1 μm to 15 μm, the volume expansion and contraction rates due to charging and discharging are reduced, improving lifespan performance. Furthermore, by preventing an excessive increase in specific surface area, side reactions with the electrolyte due to the progression of the cycle are not generated, improving lifespan performance.

[0040] In one embodiment of the present invention, the negative electrode active material may further contain graphite.

[0041] The aforementioned graphite may be natural graphite, artificial graphite, or a mixture of natural and artificial graphite.

[0042] If the graphite is a mixture of natural graphite and artificial graphite, the weight ratio of natural graphite to artificial graphite may be 50:50 to 90:10. Specifically, it may be 60:40 to 80:20 or 65:35 to 75:25.

[0043] In one embodiment of the present invention, the average particle size (D) of the graphite 50 The average particle size of the graphite may be 10 μm to 20 μm. Specifically, it may be 15 μm to 20 μm. When the average particle size of the graphite satisfies the above range, the effect of particle clumping is reduced, and the dispersibility of the slurry can be improved.

[0044] In one embodiment of the present invention, the positive electrode active material may include a lithium-compound transition metal compound comprising nickel (Ni), cobalt (Co), and manganese (Mn).

[0045] In one embodiment of the present invention, the positive electrode active material contains the nickel, cobalt, and manganese, and may further contain aluminum.

[0046] In the present specification, the positive electrode active material contains nickel at 80 mol% or more and less than 100 mol% among the metals excluding lithium, and the lithium composite transition metal compound containing nickel at 80 mol% or more and less than 100 mol% among the metals excluding lithium may contain one or more mixtures represented by the following Chemical Formula 1.

[0047] [Chemical Formula 1] Li a Ni 1-b-c-d Co b Mn c Q d O 2+δ

[0048] In the above formula, Q is any one or more elements selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr, and 1 ≦ a ≦ 1.5, 0 < b ≦ 0.5, 0 < c ≦ 0.5, 0 ≦ d ≦ 0.1, 0 < b + c + d ≦ 20, -0.1 ≦ δ ≦ 1.0.

[0049] In the lithium composite transition metal compound of Chemical Formula 1, Li may be contained at a content corresponding to a, that is, 1 ≦ a ≦ 1.5. When a is less than 1, the capacity may be reduced, and when it exceeds 1.5, the particles may be sintered in the firing process, which may make it difficult to manufacture the positive electrode active material. Considering the effect of improving the capacity characteristics of the positive electrode active material by controlling the Li content and the balance of sinterability when manufacturing the active material, the Li may more preferably be contained at a content of 1.1 ≦ a ≦ 1.2.

[0050] In the lithium composite transition metal compound of Chemical Formula 1, Ni may be contained in an amount corresponding to 1-(b + c + d), for example, 0.8 ≦ 1-(b + c + d) < 1. When the content of Ni in the lithium composite transition metal compound of Chemical Formula 1 is 0.8 or more, a sufficient amount of Ni for contributing to charge and discharge is ensured, and high capacity can be achieved. Preferably, 1-(b + c + d), which is the content of Ni, may be 0.88, preferably 0.9 or more, more preferably 0.93 or more. Preferably, 1-(b + c + d), which is the content of Ni, may be 0.99 or less, 0.95 or less.

[0051] In the lithium composite transition metal compound of Chemical Formula 1, Co may be contained in an amount corresponding to b, that is, 0 < b ≦ 0.5. When the content of Co in the lithium composite transition metal compound of Chemical Formula 1 exceeds 0.5, there is a risk of increased cost. Considering the significant effect of improving capacity characteristics by containing Co, more specifically, Co may be contained in an amount of 0.03 ≦ b ≦ 0.2.

[0052] In the lithium composite transition metal compound of Chemical Formula 1, Mn may be contained in an amount corresponding to c, that is, 0 < c ≦ 0.5. When c in the lithium composite transition metal compound of Chemical Formula 1 exceeds 0.5, there is a risk of conversely degrading the output characteristics and capacity characteristics of the battery. More specifically, Mn may be contained in an amount of 0.01 ≦ c ≦ 0.2.

[0053] In the lithium composite transition metal compound of Chemical Formula 1, Q may be a doping element contained in the crystal structure of the lithium composite transition metal compound, and Q may be contained in an amount corresponding to d, that is, 0 ≦ d ≦ 0.1. Q may be one or more selected from Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr. For example, Q may be Al.

[0054] In one embodiment of the present invention, the lithium composite transition metal compound may include single particles.

[0055] In one embodiment of the present invention, the lithium composite transition metal compound may further contain secondary particles.

[0056] The single particle can be produced by mixing a transition metal precursor and a lithium raw material and firing the mixture. The secondary particle may be produced by a different method than the single particle, and its composition may be the same as or different from that of the single particle.

[0057] For example, the firing is carried out at a temperature at which single particles can be formed. To form these, the firing should be carried out at a higher temperature than that used for the production of secondary particles. For example, if the composition of the precursor is the same, the firing needs to be carried out at a temperature approximately 30°C to 100°C higher than that used for the production of secondary particles. The firing temperature for forming the single particles may vary depending on the metal composition in the precursor. For example, when attempting to form a 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 800°C to 950°C. When the firing temperature meets the above range, a positive electrode active material containing single particles with excellent electrochemical properties can be produced. When 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 produced. When it exceeds 950°C, the firing may be excessive, preventing the proper formation of a layered crystal structure and potentially degrading the electrochemical properties.

[0058] In this specification, the term "single particle" is used to distinguish it from secondary particles formed by the aggregation of 30 or more, 35 or more, 40 or more, 50 or more, 60 or more, 70 or more, 100 or more, 150 or more, or 200 or more primary particles, and is a concept that includes single particles consisting of one primary particle and analogous single particle morphologies which are aggregates of 30 or fewer primary particles.

[0059] Specifically, in the present invention, a single particle may be a single particle consisting of one primary particle and / or an aggregate of 30 or fewer primary particles, and a secondary particle may be an aggregate of 30 or more primary particles. For example, a secondary particle may be an aggregate of 30 or more, 35 or more, 40 or more, 50 or more, 60 or more, 70 or more, 100 or more, 150 or more, or 200 or more primary particles.

[0060] In this specification, the size of the Si crystal grains contained in the silicon-carbon composite can be confirmed by X-ray diffraction analysis, which may be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: bruker). Specifically, XRD measurement can be performed by sampling a powder sample in a holder and measuring it with Cu K alpha X-ray. The size of the Si crystal grains can be calculated by fitting the XRD results to the Scherrer equation, and the reference for the crystal grains in this case can be measured using Si(220) as the reference. (2θ = 47.5° ~ 48.5°)

[0061] In one embodiment of the present invention, the Si crystal grain size of the silicon-carbon composite may be 0.1 nm or more and 20 nm or less. Specifically, it may be 0.5 nm or more and 15 nm or less, 1 nm or more and 15 nm or less, 1.5 nm or more and 12 nm or less, 1.5 nm or more and 10 nm or less, 2 nm or more and 10 nm or less, 3 nm or more and 10 nm or less, or 4 nm or more and 9 nm or less.

[0062] When the Si crystal grain size meets the aforementioned range, Li ions are uniformly diffused within the Si particles, which has the effect of stably maintaining the structure of the Si particles during charging and discharging. On the other hand, when the Si crystal grain size exceeds the aforementioned range, the stress caused by the contraction / expansion of the Si material during charging and discharging forms cracks in the particles, preventing Li ions from diffusing into the interior of the crystal grains. This leads to a problem where the non-uniformity of the reaction accelerates the degeneration of the material, reducing the lifespan of the cell.

[0063] In this specification, the crystal grain size of the lithium-complex transition metal compound can refer, for example, to the crystal size of the structure of chemical formula 1 described above. In this specification, the crystal grain size of the lithium-complex transition metal compound can be confirmed by X-ray diffraction analysis, which may be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: bruker). Specifically, XRD measurement can be performed by sampling a powder-form sample in a holder and measuring it with Cu K alpha X-ray. The crystal grain size of the lithium-complex transition metal compound can be calculated by fitting the XRD results to the Scherrer equation, and the crystal grain size in this case can be measured based on the largest peak that appears around 2θ = 10°~12°.

[0064] In one embodiment of the present invention, the crystal grain size of the lithium composite transition metal compound may be 100 nm or more and 200 nm or less. Specifically, it may be 100 nm or more and 170 nm or less, 100 nm or more and 160 nm or less, or 105 nm or more and 150 nm or less.

[0065] When the crystal grain size of the lithium-composite transition metal compound satisfies the aforementioned range, the phase stability of the lithium-composite transition metal compound is excellent, and it can react stably with Li. On the other hand, if the crystal grain size of the lithium-composite transition metal compound is smaller than the aforementioned range, there is a problem that the reaction with Li will occur for a long time, reducing the efficiency of the positive electrode. If it exceeds the aforementioned range, there is a problem that particle cracking of the positive electrode active material occurs during the rolling stage in the manufacturing process of the electrode.

[0066] In one embodiment of the present invention, the Si crystal grain size of the silicon carbon composite is 10% or less of the crystal grain size of the lithium composite transition metal compound. Specifically, the Si crystal grain size of the silicon carbon composite may be 0.5% to 10%, 1% to 10%, or 1% to 9.5% of the crystal grain size of the lithium composite transition metal compound. When the Si crystal grain size of the silicon carbon composite and the crystal grain size of the lithium composite transition metal compound satisfy the above relationship, it is possible to reduce the stress due to volume expansion of the negative electrode active material particles during charging and discharging, thereby preventing particle cracking. Furthermore, the stable crystal structure due to the relatively large crystal grain size of the positive electrode active material, the lithium composite transition metal compound, makes it easier for electrochemical reactions to occur even with a small amount of lithium (Li), thereby improving cycle characteristics and swelling performance.

[0067] On the other hand, even if the Si crystal grain size of the silicon-carbon composite and the crystal grain size of the lithium-composite transition metal compound each satisfy the aforementioned crystal grain sizes, if the Si crystal grain size of the silicon-carbon composite exceeds 10% of the crystal grain size of the lithium-composite transition metal compound, the residual lithium (Li) in the silicon-carbon composite may cause a serious deterioration in cycle performance and expansion. Furthermore, the increase in internal stress of Si due to charging and discharging can cause cracks to form in the particles, leading to a decrease in cycle performance.

[0068] In one embodiment of the present invention, the average particle size (D) of the single particle 50The particle size may be 1 μm or larger. The average particle size of the single particle may be 12 μm or less. For example, the average particle size of the single particle may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, more than 1 μm and 6 μm or less, 2 μm or more and 6 μm or less, or 3 μm or more and 5 μm or less.

[0069] Even if the single particle is formed with an average particle size of approximately 1 μm to 12 μm, its particle strength may be excellent. This mitigates the phenomenon of increased fine particles in the electrode due to particle fracture, thereby improving the battery's lifespan characteristics. For example, the single particle may have a strength of 650 kgf / cm². 2 When rolled with this force, the particle strength can be 100-300 MPa. Therefore, the single particle is rolled at 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, improving the battery's lifespan characteristics.

[0070] The method for forming the single particles is not particularly limited, but they may usually be formed by increasing the firing temperature and over-firing, or they may be produced by using additives such as grain growth promoters that are useful for over-firing, or by changing the starting material.

[0071] The aforementioned single particle exhibits relatively good performance degradation even when the particle itself has high rigidity and high electrode density. Therefore, the energy density can be increased by adjusting the average particle size range of the single particle and the silicon carbon composite.

[0072] In one embodiment of the present invention, the average particle size (D) of the single particle 50 ) is the average particle size (D) of the silicon carbon composite. 50 It can be smaller than ).

[0073] If the average particle size of the single particle is smaller than the average particle size of the silicon carbon composite, the diffusion resistance of the single particle decreases relatively, which can improve the lifespan performance. In other words, the larger the average particle size of the single particle, the greater the diffusion resistance may be, and if the average particle size of the single particle is larger than the average particle size of the silicon carbon composite, the relative increase in diffusion resistance may cause lithium deposition and other issues, which can reduce battery performance and thus the lifespan performance.

[0074] Furthermore, if the average particle size of the single particle is smaller than the average particle size of the silicon carbon composite, the occurrence of side reactions with the electrolyte due to an increase in specific surface area can be prevented, thereby improving the lifespan performance.

[0075] According to one embodiment of the present invention, the average particle size (D) of the single particle 50 ) is the average particle size (D) of the silicon carbon composite. 50 It may be 1 μm to 12 μm smaller than ). Specifically, it may be 1.5 μm to 11.5 μm, or 2 μm to 11 μm smaller.

[0076] The average particle size (D) of the single particle 50 ) is the average particle size (D) of the silicon carbon composite. 50 When the value is smaller than the above range, for example, when the above range is met, the diffusion resistance of the single particle decreases relatively, and the lifespan performance can be improved. That is, the larger the average particle size of the single particle, the greater the diffusion resistance may be, and when the average particle size of the single particle is larger than the average particle size of the silicon carbon composite, the diffusion resistance increases relatively, which may cause lithium deposition and other issues, leading to a decrease in battery performance and a decrease in lifespan performance.

[0077] Furthermore, the average particle size (D) of the single particle 50 ) is the average particle size (D) of the silicon carbon composite. 50When the value is smaller than the specified range, for example, when the specified range is satisfied, the occurrence of side reactions with the electrolyte due to an increase in specific surface area can be prevented, thereby improving the lifespan performance.

[0078] According to one embodiment of the present invention, the average particle size (D) of the single particle 50 ) and the average particle size (D) of the silicon carbon composite. 50 The ratio of ) may be 1.5:2 to 1.5:20.

[0079] When the above range is met, the diffusion resistance of the single particle decreases relatively, and the lifespan performance can be improved. That is, the larger the average particle size of the single particle, the greater the diffusion resistance may be, and if the average particle size of the single particle is larger than the average particle size of the silicon carbon composite, the diffusion resistance increases relatively, which may cause lithium deposition and other issues, potentially reducing battery performance and thus the lifespan performance.

[0080] Furthermore, the average particle size (D) of the single particle 50 ) is the average particle size (D) of the silicon carbon composite. 50 When the value is smaller than the specified range, for example, when the specified range is satisfied, the occurrence of side reactions with the electrolyte due to an increase in specific surface area can be prevented, thereby improving the lifespan performance.

[0081] In one embodiment of the present invention, the lithium composite transition metal compound further comprises secondary particles, wherein the average particle size (D) of the single particles 50 ) is the average particle size (D) of the secondary particles. 50 It is smaller than ).

[0082] In the present invention, a single particle 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. A secondary particle may be in the form of aggregates of 30 or more, 35 or more, 40 or more, 50 or more, 60 or more, 70 or more, 100 or more, 150 or more, or 200 or more primary particles.

[0083] The lithium-complex transition metal compounds described above may further contain secondary particles. Secondary particles refer to forms formed by the aggregation of primary particles and can be distinguished from the concept of single particles, which includes a single primary particle, a single particle, or an analogous-single-particle form that is an aggregate of 30 or fewer primary particles.

[0084] The average particle size (D) of the secondary particles 50 The particle size may be 1 μm to 20 μm. Specifically, it may be 2 μm to 17 μm, 3 μm to 15 μm, 5 μm to 15 μm, 7 μm to 15 μm, or 9 μm to 15 μm.

[0085] In one embodiment of the present invention, the secondary particles are aggregates of primary particles, and the average particle size (D 50 The particle size may be 0.5 μm to 3 μm. Specifically, the secondary particle may be in the form of aggregated 30 or more primary particles, and the average particle size of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0086] When the average particle size of the primary particles meets the above range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size of the primary particles is too small, the number of aggregated primary particles forming lithium nickel oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size of the primary particles is too large, the lithium diffusion path within the primary particles becomes longer, increasing resistance and potentially degrading the output characteristics.

[0087] In one embodiment of the present invention, the average particle size (D) of the single particle 50 ) is the average particle size (D) of the secondary particles. 50 ) may be smaller than ). As a result, even if the single particle is formed with a small particle size, its particle strength is excellent, and as a result the phenomenon of increasing fine particles in the electrode due to particle cracking is mitigated, thereby improving the battery's lifespan characteristics.

[0088] In one embodiment of the present invention, the average particle size (D) of the single particle 50) is the average particle size (D) of the secondary particles. 50 It is 1 μm to 18 μm smaller than ).

[0089] For example, the average particle size of the single particle may be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle size of the secondary particle.

[0090] When the average particle size of a single particle is smaller than the average particle size of secondary particles, for example, when the above range is met, even if the single particle is formed with a small particle size, it will have excellent particle strength, thereby mitigating the phenomenon of increased fine particles in the electrode due to particle cracking, and resulting in improved battery life characteristics and improved energy density.

[0091] One embodiment of the present invention, the average particle size (D) of the silicon carbon composite. 50 ) is the average particle size of the graphite (D 50 It may be smaller than the average particle size of the silicon-carbon composite. When the average particle size of the silicon-carbon composite is smaller than the average particle size of the graphite, particle cracking is reduced due to a decrease in the volume expansion / contraction rate during charging and discharging, which has the effect of improving the battery's lifespan.

[0092] In the lithium secondary battery according to the embodiment described above, the negative electrode active material may further include a carbon-based active material. Specifically, the carbon-based active material may be graphite. The graphite may be natural graphite, artificial graphite, or a mixture thereof.

[0093] According to one embodiment of the present invention, the average particle size (D) of the silicon carbon composite 50 ) is the average particle size of the graphite (D 50 The average particle size of the silicon-carbon composite may be 1 μm to 25 μm smaller than the average particle size of the graphite. For example, the average particle size of the silicon-carbon composite may be 2 μm to 24 μm smaller, 3 μm to 23 μm smaller, or 4 μm to 22 μm smaller than the average particle size of the graphite.

[0094] When the average particle size of the silicon-carbon composite is smaller than the average particle size of the graphite, for example, when the above range is satisfied, there is an effect that the life performance of the battery is further improved.

[0095] In one embodiment of the present invention, when the average particle sizes (D 50 ) of the secondary particles, the single particles, the graphite, and the silicon-carbon composite contained in the lithium secondary battery are A, B, C, and D, respectively, B < D ≤ A < C may be satisfied.

[0096] The embodiments of the secondary particles, the single particles, the graphite, and the silicon-carbon composite are as described above.

[0097] When the average particle sizes (D 50 ) of the secondary particles, the single particles, the graphite, and the silicon-carbon composite are A, B, C, and D, respectively, when B < D ≤ A < C, there is an effect that the life performance of the battery is improved.

[0098] According to one embodiment of the present invention, the negative electrode active material further contains graphite, and when the average particle sizes of the single particles, the graphite, and the silicon-carbon composite are B, C, and D, respectively, B < D < C may be satisfied.

[0099] When the average particle sizes (D 50 ) of the secondary particles, the single particles, and the silicon-carbon composite are A, B, and D, respectively, B < D ≤ A may be satisfied.

[0100] When the average particle sizes (D 50 ) of the secondary particles, the single particles, and the graphite are A, B, and C, respectively, B < A < C may be satisfied.

[0101] When the average particle sizes (D 50 ) of the secondary particles, the graphite, and the silicon-carbon composite are A, C, and D, respectively, D ≤ A < C may be satisfied. <0000,462>

[0102] When the above range is met, the battery life performance is improved.

[0103] In one embodiment of the present invention, in the lithium secondary battery according to the above-described embodiment, the single particle may be included in an amount of 15 to 100 parts by weight per 100 parts by weight of the positive electrode active material, and the silicon carbon composite may be included in an amount of 3 to 30 parts by weight per 100 parts by weight of the negative electrode active material.

[0104] In one embodiment of the present invention, the single particle may be present in an amount of 15 to 100 parts by weight per 100 parts by weight of the positive electrode active material. The single particle may also be present in an amount of 20 to 100 parts by weight, or 30 to 100 parts by weight per 100 parts by weight of the positive electrode active material.

[0105] For example, the single particle may be present in an amount of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, per 100 parts by weight of the positive electrode active material. For example, the single particle may be present in an amount of 100 parts by weight or less, 90 parts by weight or less, 80 parts by weight or less, 70 parts by weight or less, or 60 parts by weight or less, per 100 parts by weight of the positive electrode active material.

[0106] When a single particle within the aforementioned range is included, it can be combined with the aforementioned negative electrode material to exhibit excellent battery characteristics. In particular, when the single particle is 15 parts by weight or more, the phenomenon of increasing fine particles in the electrode due to particle cracking during the rolling process after electrode fabrication can be mitigated, thereby improving the battery's lifespan characteristics.

[0107] In one embodiment of the present invention, the lithium composite transition metal compound may further contain secondary particles, the amount of which the secondary particles may be 85 parts by weight or less per 100 parts by weight of the positive electrode active material. The amount of which the secondary particles may be 80 parts by weight or less, 75 parts by weight or less, 70 parts by weight or less, or 60 parts by weight or less per 100 parts by weight of the positive electrode active material. The amount of which the secondary particles may be 10 parts by weight or more, 20 parts by weight or more, 30 parts by weight or more, or 40 parts by weight or more per 100 parts by weight of the positive electrode active material.

[0108] In one embodiment of the present invention, the weight ratio of the single particle to the secondary particle may be 1:9 to 9:1, 2:8 to 8:2, 3:7 to 7:3, or 4:6 to 6:4.

[0109] When the above range is met, the aforementioned effect due to the presence of single-particle positive electrode active material can be maximized. If secondary-particle positive electrode active material is included, its components may be the same as or different from those exemplified in the single-particle positive electrode active material described above, and can represent a form in which the single-particle form is aggregated.

[0110] In one embodiment of the present invention, of the 100 parts by weight of the positive electrode active material layer, the positive electrode active material may be present 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.

[0111] According to one embodiment of the present invention, the positive electrode according to the above-described embodiment further comprises a positive electrode binder and a conductive material.

[0112] The positive electrode binder can play a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material particles and the positive electrode current collector. As the positive electrode binder, any known material in the art may be used, and non-limiting examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used.

[0113] The positive electrode binder may be included in an amount of 0.1 parts by weight or more and 50 parts by weight or less based on 100 parts by weight of the positive electrode active material layer, for example, preferably in an amount of 0.3 parts by weight or more and 35 parts by weight or less, and more preferably in an amount of 0.5 parts by weight or more and 20 parts by weight or less.

[0114] The conductive material contained in the positive electrode active material layer is used to impart conductivity to the electrode and can be used without particular limitations as long as it does not cause chemical changes within the battery 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. One of these alone or a mixture of two or more may be used.

[0115] Specifically, in one embodiment, the conductive material may include one or more single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The conductive material may be included in an amount of 0.1 parts by weight or more and 2 parts by weight or less based on 100 parts by weight of the positive electrode active material layer composition, for example, preferably 0.3 parts by weight or more and 1.5 parts by weight or less, and more preferably 0.5 parts by weight or more and 1.2 parts by weight or less.

[0116] In this specification, the silicon-carbon composite appears to be a Si-C composite, with Si and C (e.g., graphite) peaks observed in the XRD diffraction pattern, and a second phase, Si / C, does not appear to be formed.

[0117] According to the above-described embodiment of the present invention, the negative electrode active material layer contains 3 to 30 parts by weight of silicon carbon composite out of 100 parts by weight of total negative electrode active material. For example, the negative electrode active material layer may contain 3 to 20 parts by weight, or 3 to 13 parts by weight, preferably 5 to 10 parts by weight, of silicon carbon composite out of 100 parts by weight of total negative electrode active material. By using silicon carbon composite in this range, it can be combined with the above-described positive electrode material to exhibit excellent battery characteristics. In particular, when the silicon carbon composite is contained in amounts of 3 parts by weight or more, the effects of using the silicon carbon composite can be fully realized. Furthermore, since silicon carbon composite has a higher capacity than SiOx-based active material, using an excessive amount can make it difficult to balance the capacity with the positive electrode active material. In particular, when the silicon carbon composite is contained in amounts of 30 parts by weight or less, swelling can be prevented during charging and discharging, improving cycle characteristics.

[0118] The aforementioned silicon-carbon composite is a material that has higher capacity and efficiency compared to silicon-based oxides. Even without a conductive material, it can exhibit superior resistance compared to a negative electrode containing both silicon-based oxide and a conductive material. Furthermore, because the silicon-carbon composite exhibits higher Si crystallinity than silicon-based oxides, it can demonstrate superior performance when evaluating high power outputs.

[0119] In one embodiment of the present invention, in the lithium secondary battery according to the embodiment described above, the negative electrode active material may further contain a carbon-based active material. Specifically, the carbon-based active material may be graphite. The graphite may be natural graphite, artificial graphite, or a mixture thereof. Based on a total of 100 parts by weight of the negative electrode active material contained in the negative electrode active material layer, the graphite may be included in an amount of 70 parts by weight or more and 97 parts by weight or less.

[0120] Based on 100 parts by weight of the total negative electrode active material, the graphite may be included in an amount of 75 parts by weight or more, 80 parts by weight or more, or 85 parts by weight or more. Based on 100 parts by weight of the total negative electrode active material, the graphite may be included in an amount of 95 parts by weight or less, 93 parts by weight or less, or 90 parts by weight or less. If the graphite is a mixture of artificial graphite and natural graphite, based on 100 parts by weight of the graphite, the artificial graphite and natural graphite may be included in an amount of 90:10 parts by weight to 50:50 parts by weight, 85:15 parts by weight to 60:40 parts by weight, or 80:20 parts by weight to 65:35 parts by weight.

[0121] In one embodiment of the present invention, the weight ratio of the carbon-based active material to the silicon-carbon composite may be 0.1:99.9 to 30:70, 1:99 to 20:80, 5:95 to 20:80, 5:95 to 15:85, 8:92 to 12:88, or 10:90 to 12:88.

[0122] In one embodiment of the present invention, of the 100 parts by weight of the negative electrode active material layer, the negative electrode active material may be present 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.

[0123] In one embodiment of the present invention, in the lithium secondary battery according to the above-described embodiment, the negative electrode active material layer may further include a negative electrode binder in addition to the silicon carbon composite and graphite.

[0124] The negative electrode binder can play a role in improving the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material particles and the negative electrode current collector. The negative electrode binder may be one of those known in the art, and non-limiting examples include at least one selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogens of these are substituted with Li, Na, or Ca, and may also include a variety of copolymers thereof.

[0125] The negative electrode binder may be included in an amount of 0.1 parts by weight or more and 50 parts by weight or less based on 100 parts by weight of the negative electrode active material layer, for example, preferably in an amount of 0.3 parts by weight or more and 35 parts by weight or less, and more preferably in an amount of 0.5 parts by weight or more and 10 parts by weight or less.

[0126] The negative electrode active material layer does not necessarily contain a conductive material, but may further contain a conductive material as needed. The conductive material contained in the negative electrode active material layer is not particularly limited as long as it is conductive without inducing a chemical change in the battery, and may be, for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives. The content of the conductive material in the negative electrode active material layer may be 0.01 to 30 parts by weight, preferably 0.03 to 25 parts by weight, per 100 parts by weight of the negative electrode active material layer.

[0127] In one embodiment of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0128] The positive electrode current collector 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 with a surface treatment of carbon, nickel, titanium, silver, etc., may be used. The positive electrode current collector may typically have a thickness of 1 to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it may be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0129] In one embodiment of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector and containing the negative electrode active material.

[0130] The negative electrode current collector is not particularly limited, as long as it is conductive without inducing a chemical change in the battery. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Specifically, transition metals that readily adsorb carbon, such as copper and nickel, may be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but is not limited to this.

[0131] In one embodiment of the present invention, the positive electrode further comprises a positive electrode active material layer containing the positive electrode active material, and the negative electrode further comprises a negative electrode active material layer containing the negative electrode active material, with the thicknesses of the positive electrode and negative electrode active material layers being 10 μm or more and 500 μm or less, respectively. The thickness of the positive electrode active material layer may be 90% to 110% of the thickness of the negative electrode active material layer, for example, 95% to 105%, and these thicknesses may be the same. Specifically, the thicknesses of the positive electrode and negative electrode active material layers may be 15 μm or more and 400 μm or less, 20 μm or more and 30 μm or more and 30 μm or more and 100 μm or less, respectively.

[0132] In one embodiment of the present invention, the positive electrode further comprises a positive electrode active material layer containing the positive electrode active material, wherein the amount of the positive electrode active material layer per unit volume is 250 mg / 25 cm³. 2 ~900mg / 25cm 2 The negative electrode further comprises a negative electrode active material layer containing the negative electrode active material, and the amount of the negative electrode active material layer per unit volume is 100 mg / 25 cm³. 2 ~600mg / 25cm 2 Specifically, the amount of positive electrode active material carried per unit volume is 270 mg / 25 cm³. 2 ~800mg / 25cm 2 , 285mg / 25cm 2 ~700mg / 25cm 2 , or 300mg / 25cm 2 ~600mg / 25cm 2It may be the case that the amount of the negative electrode active material supported per unit volume of the negative electrode active material layer is 120 mg / 25 cm³. 2 ~500mg / 25cm 2 , 135mg / 25cm 2 ~400mg / 25cm 2 , 150mg / 25cm 2 ~300mg / 25cm 2 That's fine.

[0133] The positive electrode and the negative electrode may be manufactured by conventional methods for manufacturing positive and negative electrodes, except for the use of the positive and negative electrode active materials described above. Specifically, they may be manufactured by coating a composition for forming an active material layer, which includes the active material and, selectively, a binder and a conductive material, onto a current collector, followed by drying and rolling. In this case, the types and contents of the positive and negative electrode active materials, binder, and conductive material are as described above. The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used. The amount of solvent used should be such that it dissolves or disperses the active material, conductive material, and binder, and has a viscosity that allows for excellent thickness uniformity when later coated to manufacture the positive and negative electrodes, taking into consideration the coating thickness of the slurry and the manufacturing yield. Alternatively, the positive and negative electrodes may be manufactured by casting the active material layer-forming composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the current collector.

[0134] The separation membrane, which separates the negative and positive electrodes and provides a pathway for lithium ions to move, can be used without particular limitations as long as it is one that is normally used as a separation membrane in secondary batteries. In particular, it is preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte impregnation ability. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as 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 nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and they may be selectively used in single-layer or multi-layer structures.

[0135] The electrolytes mentioned above 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.

[0136] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0137] 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.

[0138] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used because they are high-viscosity organic solvents with high dielectric constants that dissociate lithium salts well. If such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate ratios, an electrolyte with high electrical conductivity can be produced, and this may be used even more preferably.

[0139] The metal salt may be a lithium salt, and the lithium salt is a substance that dissolves easily 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:

[0140] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery 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.

[0141] The energy density of a lithium secondary battery according to one embodiment of the present invention may be 400 Wh / L to 900 Wh / L. Specifically, the energy density of the lithium secondary battery may be 425 Wh / L to 875 Wh / L, 450 Wh / L to 850 Wh / L, 475 Wh / L to 825 Wh / L, or 500 Wh / L to 800 Wh / L. When the above range is satisfied, the energy density of a lithium secondary battery designed within a limited space can be increased, improving high-power performance and battery cycle performance.

[0142] A lithium secondary battery according to one embodiment of the present invention may be a cylindrical battery. The cylindrical battery means that the form of the battery itself, which includes an assembly comprising a positive electrode, a negative electrode, a separator membrane, and an electrolyte, is cylindrical, and specifically may consist of a cylindrical can, a battery assembly provided inside the cylindrical can, and a top cap. However, the lithium secondary battery is not limited to this, and may also be a prismatic battery or a pouch-type battery.

[0143] One embodiment of the present invention provides a battery pack and electronic device that include the cylindrical battery as a unit cell. Since the battery pack and electronic device include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they may 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.

[0144] The lithium secondary battery according to the embodiment of the present invention exhibits excellent discharge capacity, output characteristics, and cycle performance stably, and may be used not only as a power source for portable devices such as mobile phones, notebook computers, and digital cameras, but also as a power source for medium- and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. For example, the battery module or battery pack may be used as a power source for one or more medium- and large-sized devices from among power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0145] [Examples] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative of the present description, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present description and the technical concept, and such variations and modifications naturally fall within the scope of the claims.

[0146] <Examples and Comparative Examples> Example 1 A composition for forming a positive electrode active material layer was prepared, based on 100 parts by weight of positive electrode active material layer, comprising: a lithium composite transition metal compound as the positive electrode active material, containing 93.3 mol% Ni, 4.9 mol% Co, and 1.8 mol% Mn among metals excluding lithium, and containing 98.04 parts by weight of single particles and secondary particles (single particles:secondary particles = 50:50 by weight ratio); 1 part by weight of PVDF as a binder; and 0.8 parts by weight of CNTs as a conductive material, and a CNT predispersion containing 0.16 parts by weight of a dispersant.

[0147] The lithium composite transition metal compound used was heat-treated at 750°C for 8 hours under an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 110 nm. Furthermore, the size of the single particles was D 50 =3.57μm and the size of the secondary particle is D 50 The composition was manufactured to have a thickness of 9.5 μm. The positive electrode active material layer forming composition was coated onto a 30 μm thick aluminum foil to a dry thickness of 103 μm, and then dried to produce the positive electrode.

[0148] A composition for forming a negative electrode active material layer was prepared, based on 100 parts by weight of a negative electrode active material layer, containing 97.7 parts by weight of graphite (artificial graphite:natural graphite = 70:30 weight ratio, 90 parts by weight based on 100 parts by weight of negative electrode active material) and silicon carbon composite (10 parts by weight based on 100 parts by weight of negative electrode active material) as the negative electrode active material, and 1.15 parts by weight of SBR (styrene-butadiene rubber) and 1 part by weight of CMC (carboxymethyl cellulose) as binders, in addition to 0.09 parts by weight of a dispersant and a CNT predispersion containing 0.06 parts by weight of single-walled CNTs.

[0149] The silicon-carbon composite used was heat-treated at 300 °C for 2 hours under an Ar atmosphere, and the Si crystal grain size of the silicon-carbon composite used was 6 nm. Also, the size of the silicon-carbon composite was made D 50 = 5.2 μm and the size of the graphite was made D 50 = 17 μm by production. After coating the composition for forming the negative electrode active material layer on a copper foil with a thickness of 15 μm to a dry thickness of 86 μm, it was dried to produce a negative electrode.

[0150] The positive electrode and the negative electrode were laminated with a separator interposed therebetween, and an electrolytic solution (1.0 M LiPF6, EC (ethylene carbonate) / EMC (ethylmethyl carbonate) = 30 / 70 (Vol%), VC (vinylene carbonate) 1.5%) was injected to fabricate a battery.

[0151] Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium composite transition metal compound and the silicon-carbon composite were produced as follows.

[0152] For the composition for forming the positive electrode active material layer, a lithium composite transition metal compound heat-treated at 750 °C for 8 hours under an Ar atmosphere was used, and the crystal grain size of the lithium composite transition metal compound used was 120 nm. Also, the size of a single particle was made D 50 = 3.58 μm and the size of the secondary particle was made D 50 = 14.7 μm by production.

[0153] For the composition for forming the negative electrode active material layer, a silicon-carbon composite heat-treated at 200 °C for 2 hours under an Ar atmosphere was used, and the Si crystal grain size of the silicon-carbon composite used was 1.5 nm. Also, the size of the silicon-carbon composite was made D 50 = 6.2 μm and the size of the graphite was made D 50 = 17 μm by production.

[0154] Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium composite transition metal compound and the silicon carbon composite were produced as follows.

[0155] For the composition for forming the positive electrode active material layer, a lithium composite transition metal compound heat-treated at 750 °C for 8 hours in an Ar atmosphere was used, and the crystal grain size of the used lithium composite transition metal compound was 105 nm. Also, the size of single particles was D 50 = 3.63 μm and the size of secondary particles was D 50 = 10.5 μm were produced.

[0156] For the composition for forming the negative electrode active material layer, a silicon carbon composite heat-treated at 400 °C for 2 hours in an Ar atmosphere was used, and the Si crystal grain size of the used silicon carbon composite was 9 nm. Also, the size of the silicon carbon composite was D 50 = 7.1 μm and the size of graphite was D 50 = 17 μm were produced.

[0157] Example 4 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium composite transition metal compound and the silicon carbon composite were produced as follows.

[0158] For the composition for forming the positive electrode active material layer, a lithium composite transition metal compound heat-treated at 800 °C for 10 hours in an Ar atmosphere was used, and the crystal grain size of the used lithium composite transition metal compound was 150 nm. Also, the size of single particles was D 50 = 3.72 μm and the size of secondary particles was D 50 = 9.5 μm were produced.

[0159] In the composition for forming the negative electrode active material layer, a silicon carbon composite was used that had been heat-treated at 300°C for 2 hours in an Ar atmosphere, and the Si crystal grain size of the silicon carbon composite used was 4 nm. Furthermore, the size of the silicon carbon composite was D 50 = 6.3 μm and the size of the graphite is D 50 It was manufactured to a thickness of 17 μm.

[0160] Example 5 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium-composite transition metal compound and silicon-carbon composite were manufactured as described below.

[0161] The composition for forming the positive electrode active material layer used was a lithium composite transition metal compound that had been heat-treated at 750°C for 8 hours in an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 110 nm. Furthermore, the size of a single particle was D 50 =3.57μm and the size of the secondary particle is D 50 It was manufactured to a thickness of 9.5 μm.

[0162] In the composition for forming the negative electrode active material layer, a silicon carbon composite was used that had been heat-treated at 400°C for 2 hours in an Ar atmosphere, and the Si crystal grain size of the silicon carbon composite used was 10 nm. Furthermore, the size of the silicon carbon composite was D 50 =6.9μm and the size of the graphite is D 50 It was manufactured to a thickness of 17 μm.

[0163] Example 6 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium-composite transition metal compound and silicon-carbon composite were manufactured as described below.

[0164] The composition for forming the positive electrode active material layer used was a lithium composite transition metal compound that had been heat-treated at 800°C for 10 hours in an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 140 nm. Furthermore, the size of a single particle was D 50 =3.74μm and the size of the secondary particle is D 50 It was manufactured to a thickness of 16.5 μm.

[0165] In the composition for forming the negative electrode active material layer, a silicon carbon composite was used that had been heat-treated at 500°C for 2 hours in an Ar atmosphere, and the Si crystal grain size of the silicon carbon composite used was 12 nm. Furthermore, the size of the silicon carbon composite was D 50 = 7.0 μm and the size of the graphite is D 50 It was manufactured to a thickness of 17 μm.

[0166] Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium-composite transition metal compound and silicon-carbon composite were manufactured as described below.

[0167] The composition for forming the positive electrode active material layer used was a lithium composite transition metal compound that had been heat-treated at 750°C for 8 hours in an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 110 nm. Furthermore, the size of a single particle was D 50 = 3.63 μm and the size of the secondary particle is D 50 It was manufactured to a thickness of 9.6 μm.

[0168] In the composition for forming the negative electrode active material layer, a silicon carbon composite was used that had been heat-treated at 500°C for 2 hours in an Ar atmosphere, and the Si crystal grain size of the silicon carbon composite used was 12 nm. Furthermore, the size of the silicon carbon composite was D 50 =7.0μm and the size of the graphite is D 50 It was manufactured to a thickness of 17 μm.

[0169] Comparative Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium-composite transition metal compound and silicon-carbon composite were manufactured as described below.

[0170] The composition for forming the positive electrode active material layer used was a lithium composite transition metal compound that had been heat-treated at 650°C for 6 hours in an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 100 nm. Furthermore, the size of a single particle was D 50 =3.57μm and the size of the secondary particle is D 50 It was manufactured to a thickness of 9.5 μm.

[0171] In the composition for forming the negative electrode active material layer, a silicon carbon composite was used that was heat-treated at 700°C for 2 hours in an Ar atmosphere, and the Si crystal grain size of the silicon carbon composite used was 17 nm. Furthermore, the size of the silicon carbon composite was D 50 = 5.3 μm and the size of the graphite is D 50 It was manufactured to a thickness of 17 μm.

[0172] Comparative Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium-composite transition metal compound and silicon-carbon composite were manufactured as described below.

[0173] The composition for forming the positive electrode active material layer used was a lithium composite transition metal compound that had been heat-treated at 750°C for 8 hours under an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 120 nm. Furthermore, the size of a single particle was D 50 =3.60μm and the size of the secondary particles is D 50 It was manufactured to a thickness of 10.5 μm.

[0174] In the composition for forming the negative electrode active material layer, a silicon carbon composite was used that had been heat-treated at 700°C for 2 hours in an Ar atmosphere, and the Si crystal grain size of the silicon carbon composite used was 20 nm. Furthermore, the size of the silicon carbon composite was D 50 = 5.1 μm and the size of the graphite is D 50 It was manufactured to a thickness of 17 μm.

[0175] Comparative Example 4 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium-composite transition metal compound and silicon-carbon composite were manufactured as described below.

[0176] The composition for forming the positive electrode active material layer used was a lithium composite transition metal compound that had been heat-treated at 800°C for 10 hours in an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 140 nm. Furthermore, the size of a single particle was D 50 =3.74μm and the size of the secondary particle is D 50 It was manufactured to a thickness of 16.5 μm.

[0177] The composition for forming the negative electrode active material layer used was a silicon carbon composite heat-treated at 900°C for 2 hours in an Ar atmosphere, and the Si crystal grain size of the silicon carbon composite used was 41 nm. Furthermore, the size of the silicon carbon composite was D 50 =6.8μm and the size of the graphite is D 50 It was manufactured to a thickness of 17 μm.

[0178] Comparative Example 5 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium-composite transition metal compound and silicon-carbon composite were manufactured as described below.

[0179] The composition for forming the positive electrode active material layer used was obtained by heat-treating a lithium composite transition metal compound in an Ar atmosphere at 650°C for 6 hours, and the crystal grain size of the lithium composite transition metal compound used was 80 nm. Furthermore, the size of a single particle was D 50 = 3.52 μm and the size of the secondary particle is D 50 It was manufactured to a thickness of 12.5 μm.

[0180] In the composition for forming the negative electrode active material layer, a silicon carbon composite was used that had been heat-treated at 400°C for 2 hours in an Ar atmosphere, and the Si crystal grain size of the silicon carbon composite used was 10 nm. Furthermore, the size of the silicon carbon composite was D 50 =6.9μm and the size of the graphite is D 50 It was manufactured to a thickness of 17 μm.

[0181] Comparative Example 6 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium-composite transition metal compound and silicon-carbon composite were manufactured as described below.

[0182] The composition for forming the positive electrode active material layer used was a lithium composite transition metal compound that had been heat-treated at 650°C for 6 hours in an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 88 nm. Furthermore, the size of a single particle was D 50 = 3.52 μm and the size of the secondary particle is D 50 It was manufactured to a thickness of 12.7 μm.

[0183] In the composition for forming the negative electrode active material layer, a silicon carbon composite was used that had been heat-treated at 400°C for 2 hours in an Ar atmosphere, and the Si crystal grain size of the silicon carbon composite used was 10 nm. Furthermore, the size of the silicon carbon composite was D 50 =6.8μm and the size of the graphite is D 50 It was manufactured to a thickness of 17 μm.

[0184] Comparative Example 7 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium-composite transition metal compound and silicon-carbon composite were manufactured as described below.

[0185] The composition for forming the positive electrode active material layer used was obtained by heat-treating a lithium composite transition metal compound in an Ar atmosphere at 650°C for 6 hours, and the crystal grain size of the lithium composite transition metal compound used was 80 nm. Furthermore, the size of a single particle was D 50 = 3.52 μm and the size of the secondary particle is D 50 It was manufactured to a thickness of 12.5 μm.

[0186] In the composition for forming the negative electrode active material layer, a silicon carbon composite was used that had been heat-treated at 400°C for 2 hours in an Ar atmosphere, and the Si crystal grain size of the silicon carbon composite used was 9 nm. Furthermore, the size of the silicon carbon composite was D 50 = 7.1 μm and the size of the graphite is D 50 It was manufactured to a thickness of 17 μm.

[0187] The compositions of the negative electrode active material and positive electrode active material produced in the above examples and comparative examples are shown in Table 1 below.

[0188] [Table 1A]

[0189] [Table 1B]

[0190] The size of the crystal grains of the lithium-composite transition metal compound and the Si crystal grains contained in the silicon-carbon composite could be confirmed by X-ray diffraction analysis. X-ray diffraction analysis was performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: bruker). Specifically, XRD measurements were performed by sampling a powder-type sample in a holder and measuring it with Cu K alpha X-ray. The size of the crystal grains of the lithium-composite transition metal compound was calculated by fitting the XRD results to the Scherrer equation, using the peak appearing at the relevant position as the reference for the crystal grain size (2θ = 10°~12°). The size of the Si crystal grains was calculated by fitting the XRD results to the Scherrer equation, with Si(220) serving as the reference for the grain size. (2θ = 47.4°~48.5°) The D of the positive electrode active material and the negative electrode active material 50 The data was analyzed using the PSD measurement method with the use of microtrac equipment.

[0191] <Experimental Example: Evaluation of discharge capacity, initial efficiency, and lifespan (capacity retention rate) characteristics> The lithium secondary batteries manufactured in the examples and comparative examples were subjected to charging and discharging, and their discharge capacity, initial efficiency, and capacity retention rate were evaluated and are shown in Table 2 below.

[0192] The first and second cycles were charged and discharged at 0.1C, and from the third to the 199th cycle, the charge and discharge were performed at 0.5C. The 200th cycle ended in a charged state (lithium was in the negative electrode).

[0193] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V The discharge capacity (mAh / g) and initial efficiency (%) were derived from the results of a single charge-discharge cycle. Specifically, the initial efficiency (%) was derived by the following calculation.

[0194] Initial efficiency (%) = (Discharge capacity per cycle / Charge capacity per cycle) × 100

[0195] The capacity retention rates were derived using the following calculations.

[0196] Capacity retention rate (%) = (199 discharge capacity / 1 discharge capacity) × 100

[0197] <Experimental Example: Cell Thickness Evaluation> The thickness of the rechargeable battery fabricated as described above was compared before and after the following cycling procedure.

[0198] For the first and second cycles, charging and discharging were performed at 0.1C, and for the third to 200th cycles, charging and discharging were performed at 0.5C. The cell thickness after the second cycle was defined as the initial thickness, and the cell thickness after the 200th cycle was defined as the post-cycle thickness. The thickness was calculated using the following formula. The calculated cell thickness for Example 1 was set to 100%, and the cell thicknesses for Examples 2-6 and Comparative Examples 1-7 were calculated relatively using this as a baseline and are shown in Table 2 below.

[0199] Cell thickness = (Post-processing thickness - Initial thickness) / (Initial thickness) × 100

[0200] [Table 2]

[0201] According to Tables 1 and 2, the secondary batteries of Examples 1 to 6, in which the Si crystal grain size of the silicon carbon composite satisfies the condition that it is 10% or less of the crystal grain size of the lithium composite transition metal compound, were found to have thinner cell thicknesses and superior capacity retention compared to Comparative Examples 1 to 7. This is because, since the Si crystal grain size of the silicon carbon composite is 10% or less of the crystal grain size of the lithium composite transition metal compound, the stress due to volume expansion of the negative electrode active material particles during charging and discharging can be reduced, which appears to reduce particle cracking and improve cycle characteristics and swelling performance. On the other hand, in the case of Comparative Examples 1 to 7, since the Si crystal grain size of the silicon carbon composite exceeds 10% of the crystal grain size of the lithium composite transition metal compound, it was found that cracks occurred in the particles due to the increase in internal stress of Si during charging and discharging, resulting in a decrease in cycle performance.

[0202] In particular, in the cases of Example 5 and Comparative Example 5, Example 6 and Comparative Example 1, and Example 3 and Comparative Example 7, even though the Si crystal grain size of the silicon-carbon composite was the same, different effects were derived depending on the crystal grain size of the positive electrode active material. Therefore, it can be confirmed that the cycle characteristics and degree of expansion can be improved by the relative size of the Si crystal grain size of the silicon-carbon composite and the crystal grain size of the lithium-composite transition metal compound of the positive electrode active material.

Claims

1. A lithium secondary battery comprising: a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte, The positive electrode active material comprises a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn). The lithium composite transition metal compound comprises a single particle, The negative electrode active material includes a silicon carbon composite. The single particle comprises a crystal grain of the lithium composite transition metal compound, The silicon-carbon composite comprises Si crystal grains, The Si crystal grain size of the silicon-carbon composite is 10% or less of the crystal grain size of the lithium-composite transition metal compound. A lithium secondary battery in which the single particle is one primary particle or an aggregate of two to thirty primary particles.

2. The average particle size (D) of the primary particles ５０ The lithium secondary battery according to claim 1, wherein the particle size is 0.5 μm or more and 3 μm or less.

3. The aforementioned single particle has a load of 650 kgf / cm². ２ A lithium secondary battery according to claim 1, wherein when rolled with the force, the particle strength is 100 MPa or more and 300 MPa or less.

4. The lithium secondary battery according to claim 1, wherein the Si crystal grain size of the silicon-carbon composite is 0.1 nm or more and 20 nm or less.

5. The lithium secondary battery according to claim 1, wherein the crystal grain size of the lithium composite transition metal compound is 100 nm or more and 200 nm or less.

6. The lithium composite transition metal compound further comprises secondary particles, The lithium secondary battery according to claim 1, wherein the secondary particles are aggregates of 30 or more primary particles.

7. The average particle size (D) of the secondary particles ５０ The lithium secondary battery according to claim 6, wherein the diameter of the element is 1 μm or more and 20 μm or less.

8. The lithium secondary battery according to claim 1, wherein the negative electrode active material further comprises graphite.

9. The lithium secondary battery according to claim 8, wherein the graphite is natural graphite or artificial graphite, or a mixture of natural graphite and artificial graphite.

10. The aforementioned graphite is a mixture of natural graphite and artificial graphite. The lithium secondary battery according to claim 8, wherein the weight ratio of the natural graphite to the artificial graphite is 50:50 to 90:

10.

11. The average particle size of the graphite (D ５０ The lithium secondary battery according to claim 8, wherein the diameter is 10 μm or more and 20 μm or less.

12. The average particle size (D) of the single particle ５０ The lithium secondary battery according to claim 1, wherein the diameter of the element is 1 μm or more and 12 μm or less.

13. The average particle size (D) of the silicon carbon composite ５０ The lithium secondary battery according to claim 1, wherein the particle is 1 μm or more and 15 μm or less.

14. The average particle size (D) of the single particle ５０ ) is the average particle size (D) of the silicon carbon composite. ５０ A lithium secondary battery according to claim 1, which is smaller than ).

15. The average particle size (D ５０ ) of the silicon-carbon composite is smaller than the average particle size (D ５０ ) of the graphite, and the lithium secondary battery according to claim 8.

16. The single particle is included in an amount of 15 parts by weight or more and 100 parts by weight or less with respect to 100 parts by weight of the positive electrode active material. The lithium secondary battery according to claim 1, wherein the silicon carbon composite is included in an amount of 3 parts by weight or more and 30 parts by weight or less with respect to 100 parts by weight of the negative electrode active material.

17. The lithium secondary battery according to claim 1, wherein the lithium composite transition metal compound contains 80 mol% or more and less than 100 mol% nickel among the metals excluding lithium.

18. The positive electrode includes a positive electrode active material layer containing the positive electrode active material, The negative electrode includes a negative electrode active material layer containing the negative electrode active material, 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 are each 10 μm or more and 500 μm or less.

19. A battery pack comprising a lithium secondary battery according to any one of claims 1 to 18.

20. An electronic device comprising a lithium secondary battery according to any one of claims 1 to 18.

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