Negative electrode active material, method for producing a negative electrode active material, negative electrode composition, negative electrode for lithium secondary battery containing the same, and lithium secondary battery containing the negative electrode

Abstract

The present application relates to a negative electrode active material, a method for manufacturing the negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Description

[Technical Field]

[0001] This application claims the benefit as of the filing date of Korean Patent Application No. 10-2022-0110078, filed with the Korean Intellectual Property Office on 31 August 2022, and all its contents are incorporated herein by reference.

[0002] This application relates to a negative electrode active material, a method for producing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery containing the same, and a lithium secondary battery containing the negative electrode. [Background technology]

[0003] The rapid increase in fossil fuel use has led to a growing demand for alternative and clean energy sources, and one of the most actively researched areas in this field is power generation and energy storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that utilizes this type of electrochemical energy is the secondary battery, and its range of applications is steadily expanding.

[0005] As technological development and demand for mobile devices increase, the demand for rechargeable batteries as an energy source is rapidly growing. Among these rechargeable batteries, lithium-ion batteries, which have high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used. Furthermore, research is actively underway on methods for manufacturing high-density electrodes with even higher energy density per unit volume for use in such high-capacity lithium-ion batteries.

[0006] Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator membrane. The negative electrode contains a negative electrode active material that inserts and de-inserts lithium ions released from the positive electrode, and silicon-based particles with a large discharge capacity may be used as the negative electrode active material.

[0007] In recent years, in response to the demand for high-density energy batteries, research has been actively conducted on methods to increase capacity by using silicon-based compounds such as Si / C and SiOx, which have more than 10 times the capacity of graphite-based materials, as negative electrode active materials. However, while silicon-based compounds are high-capacity materials, they have the problem of rapidly expanding in volume during the charging process, disrupting the conductive path and degrading battery performance.

[0008] Therefore, in order to resolve the problems when using silicon-based compounds as negative electrode active materials, various methods have been discussed to suppress volume expansion itself, such as adjusting the driving potential, further coating a thin film on the active material layer, and adjusting the particle size of the silicon-based compound, or to prevent the conduction path from being interrupted. However, in the case of the aforementioned methods, there are limitations to their application because they can actually degrade the performance of the battery, and there are still limitations to the commercialization of negative electrode battery manufacturing with a high content of silicon-based compounds.

[0009] Therefore, even when using silicon-based active materials as negative electrode active materials to improve capacity performance, research is needed on the silicon-based active materials themselves that can mitigate the silicon cracking phenomenon caused by lithium insertion and removal during charging and discharging. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2009-080971 [Overview of the project] [Problems that the invention aims to solve]

[0011] When producing a silicon-based active material by a chemical processing method instead of a conventional grinding processing method, it was confirmed that the physical properties of the silicon-based active material itself can be adjusted, and during the insertion / desorption reaction of lithium, the reaction occurs uniformly, reducing the stress on the silicon-based active material. Furthermore, through research, it was confirmed that when producing a silicon-based active material by a chemical processing method, the crystal grain orientation distribution of the silicon-based active material itself can be controlled, and it was confirmed that the insertion and desorption of lithium ions become uniform through crystal grain orientation control.

[0012] Thus, the present application relates to a negative electrode active material, a method for manufacturing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode, which can solve the above problems.

Means for Solving the Problems

[0013] One embodiment of the present specification provides a negative electrode active material including a silicon-based active material including (220) crystal plane and (111) crystal plane, the silicon-based active material satisfying the following formula 1, the silicon-based active material including one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and including 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material. [Formula 1] 45≦(X / Y)×100 In the above formula 1, Y means the ratio of the (111) crystal plane in the silicon-based active material, X means the ratio of the (220) crystal plane in the silicon-based active material.

[0014] In another embodiment, a method for manufacturing a negative electrode active material includes a step of chemically reacting silane gas to deposit a silicon-based active material on the crystal nucleus surface; and a step of obtaining the silicon-based active material deposited on the substrate, wherein the silicon-based active material satisfies the formula 1. The method for manufacturing a negative electrode active material according to the present application is provided.

[0015] In another embodiment, a negative electrode composition including a negative electrode active material, a negative electrode conductive material, and a negative electrode binder according to the present application is provided.

[0016] In another embodiment, a negative electrode for a lithium secondary battery is provided, which includes a negative electrode current collector layer and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer, and the negative electrode active material layer includes the negative electrode composition according to the present application or a cured product thereof.

[0017] Finally, a lithium secondary battery is provided, which includes a positive electrode, a negative electrode for a lithium secondary battery according to the present application, a separator provided between the positive electrode and the negative electrode, and an electrolyte.

Advantages of the Invention

[0018] The negative electrode active material of the present invention, as a silicon-based active material, includes at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2). Based on 100 parts by weight of the silicon-based active material, it contains 70 parts by weight or more of the SiOx (x = 0), that is, while having a pure silicon (Pure Si) active material, different from the conventional pulverization processing method, it is produced (silane gas) by controlling the reaction conditions of the chemical method. Thereby, it includes a silicon-based active material satisfying certain physical properties. When the silicon-based active material manufactured in this way is used, it can react uniformly during the insertion and desorption reactions of lithium during charge and discharge, reduce the stress received by the silicon-based active material, and relieve the cracking of particles, thereby improving the life of the electrode.

[0019] In particular, this application is characterized by controlling the grain direction distribution that satisfies the range of formula 1 when manufacturing a silicon-based active material as described above. That is, when a relatively large proportion of (111) crystal planes are formed, as in the conventional method, the (111) crystal planes have a lower lithium mobility than the (220) crystal planes, and lithium cannot enter and exit uniformly during lithium insertion and deinsertion reactions. However, the silicon-based active material according to this application contains a large proportion of (220) crystal planes, unlike the conventional method, and lithium enters and exits uniformly during lithium insertion and deinsertion reactions, which can mitigate silicon cracking phenomena on the electrode surface and thereby enhances the lifespan characteristics of the electrode. [Brief explanation of the drawing]

[0020] [Figure 1] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 2] This figure shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. [Figure 3] This figure shows a method for calculating crystal grain size. [Figure 4] This figure shows the unit structure of the silicon-based active material relating to this application. [Figure 5] This figure shows the (220) plane and the (111) plane of the silicon-based active material relating to this application. [Figure 6] This figure compares the densities of the (220) and (111) planes of silicon-based active materials. [Modes for carrying out the invention]

[0021] Before describing the present invention, let us first define some terms. In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0022] In this specification, "p~q" means the range "p or greater and q or less". In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mini II from BEL Japan. In other words, in this application, BET specific surface area may mean the specific surface area measured by the above measurement method.

[0023] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. On the other hand, the average particle size can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the difference in diffraction patterns due to particle size as the particles pass through the laser beam is measured to calculate the particle size distribution.

[0024] In one embodiment of this application, particle size can refer to the average diameter or representative diameter of each individual particle making up the metal powder.

[0025] In this specification, when a polymer contains a monomer as a monomer unit, it means that the monomer participates in the polymerization reaction and is included as a repeating unit within the polymer. In this specification, when a polymer contains a monomer, this is interpreted as meaning that the polymer contains monomers as monomer units.

[0026] In this specification, unless otherwise specified, the term "polymer" is understood to be used in a broad sense, including copolymers.

[0027] In this specification, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) are the molecular weights in terms of polystyrene measured by Gel Permeation Chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as the standard substances. In this specification, the molecular weight means the weight-average molecular weight unless otherwise specified.

[0028] Hereinafter, for those with ordinary knowledge in the technical field to which the present invention pertains to easily implement the present invention, a detailed description will be given with reference to the drawings. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0029] One embodiment of this specification includes a silicon-based active material including (220) crystal plane and (111) crystal plane, the silicon-based active material satisfies the following formula 1, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, it provides a negative electrode active material containing 70 parts by weight or more of the SiOx (x = 0).

[0030] [Formula 1] 45 ≦ (X / Y) × 100 In the above formula 1, Y means the ratio of the (111) crystal plane in the silicon-based active material, X means the ratio of the (220) crystal plane in the silicon-based active material.

[0031] This application is characterized by controlling the grain direction distribution that satisfies the range of formula 1 when manufacturing a silicon-based active material. That is, when a relatively large proportion of (111) crystal planes are formed, as in the conventional method, the (111) crystal planes have a lower lithium mobility than the (220) crystal planes, and lithium cannot enter and exit uniformly during lithium insertion and deinsertion reactions. However, the silicon-based active material according to this application contains a large proportion of (220) crystal planes, unlike the conventional method, and lithium enters and exits uniformly during lithium insertion and deinsertion reactions, which can mitigate silicon cracking phenomena on the electrode surface and thereby enhances the lifespan characteristics of the electrode.

[0032] Figure 4 shows the unit structure of the silicon-based active material according to this application. By including the crystal planes, the (220) plane and (111) plane of the silicon-based active material can be specifically confirmed in Figure 5. Figure 6 is a diagram comparing the densities of the (220) plane and the (111) plane of the silicon-based active material. When the density and direction of the (220) plane and the (110) plane were examined to confirm specifically, it was found that the (220) plane has a lower particle density within the same area, and therefore, when Li moves, the (220) plane with a lower particle density is more advantageous.

[0033] In one embodiment of this application, the silicon-based active material comprises at least one selected from the group consisting of spherical silicon-based active material and plate-shaped silicon-based active material, and the invention provides a negative electrode active material comprising 100 parts by weight of the silicon-based active material and 80 parts by weight or more of the spherical silicon-based active material.

[0034] In another embodiment, the silicon-based active material comprises at least one selected from the group consisting of spherical silicon-based active material and plate-shaped silicon-based active material, and may contain 100 parts by weight of the silicon-based active material, 80 parts by weight or more, 85 parts by weight or more, 90 parts by weight or more, 100 parts by weight or less, 99 parts by weight or less, and 95 parts by weight or less of the spherical silicon-based active material.

[0035] In this application, "plate-like silicon-based active material" can mean an active material in which the (111) crystal planes of the silicon-based active material are well-developed and have a broad planar shape rather than a spherical shape, and "spherical silicon-based active material" can mean that the (220) crystal planes of the silicon-based active material are more well-developed than those of the plate-like silicon-based active material and have spherical particles rather than a broadly spread planar shape.

[0036] In other words, the silicon-based active material may have a spherical shape, and its sphericity is, for example, 0.8 or more, for example, 0.8 to 0.95, for example, 0.9 to 0.95, for example, 0.93 to 0.95.

[0037] In this application, the spherical silicon-based active material refers to an active material whose particle circularity is 0.9 or higher when measured, and active materials whose circularity is less than 0.9 can be classified as plate-shaped active materials.

[0038] In this application, the degree of sphericity is determined by the following formula 2, where A is the area and P is the boundary line. [Formula 2] 4πA / P 2

[0039] Specifically, sphericity can be expressed by equation 2-1, which will be described later, and sphericity is given by equation [4π * actual area of ​​silicon-based active material / (boundary)] 2 It can also be represented as ].

[0040] In one embodiment of this application, X represents the proportion of (220) crystal planes within the silicon-based active material, and represents the proportion relative to the entire silicon-based active material, wherein X may satisfy 30 to 60, preferably 35 to 60, and more preferably 35 to 55.

[0041] In one embodiment of this application, Y represents the proportion of (111) crystal planes within the silicon-based active material, and represents the proportion relative to the entire silicon-based active material. Y may satisfy 50 to 80, preferably 55 to 80, and more preferably 55 to 75.

[0042] In one embodiment of the present application, the silicon-based active material may further include various crystal planes.

[0043] In one embodiment of the present application, the silicon-based active material includes at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more.

[0044] In one embodiment of the present application, the silicon-based active material includes SiOx (x = 0), and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more.

[0045] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be included in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0046] In one embodiment of the present application, as the silicon-based active material, those containing particularly pure silicon (Si) particles may be used. Using pure silicon (Si) particles as the silicon-based active material means that, as described above, when based on 100 parts by weight of the entire silicon-based active material, pure Si particles (SiOx (x = 0)) not bonded to other particles or elements are included within the above range.

[0047] In one embodiment of the present application, the silicon-based active material may be composed of silicon-based particles having 100 parts by weight of SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0048] In one embodiment of this application, the silicon-based active material may contain metallic impurities, in which case the impurities are metals that can generally be contained in silicon-based active materials, and specifically, may contain 0.1 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0049] In the case of silicon-based active materials, the capacity is significantly higher than that of conventionally used graphite-based active materials, and attempts to apply them are increasing. However, the volume expansion rate during the charge-discharge process is high, so their use is limited to cases where they are mixed in small amounts with graphite-based active materials.

[0050] Therefore, in the present invention, in order to improve capacity performance, while using only silicon-based active material as the negative electrode active material, the problems described above were resolved not by adjusting the composition of the conductive material and binder, but by adjusting the crystal grain size or surface area of ​​the silicon-based active material itself.

[0051] In one embodiment of this application, the crystal grain size of the silicon-based active material may be 200 nm or less.

[0052] In another embodiment, the crystal grain size of the silicon-based active material may be 200 nm or less, preferably 130 nm or less, more preferably 120 nm or less, even more preferably 100 nm or less, specifically 95 nm or less, and more specifically 91 nm or less. The crystal grain size of the silicon-based active material may also be in the range of 10 nm or more, preferably 15 nm or more.

[0053] The silicon-based active material has the aforementioned crystal grain size, and the crystal grain size of the silicon-based active material can be adjusted by changing the process conditions during the manufacturing process. In this case, by satisfying the aforementioned range and ensuring a wide distribution of grain boundaries, lithium ions will be inserted uniformly, reducing the stress applied when lithium ions are inserted into silicon particles, thereby mitigating particle cracking. As a result, the lifetime stability of the negative electrode can be improved. If the crystal grain size exceeds the aforementioned range, the crystal grain system within the particle becomes narrowly distributed, in which case lithium ions are inserted non-uniformly, the stress due to ion insertion is large, and particle cracking occurs.

[0054] In one embodiment of this application, the silicon-based active material includes a crystalline structure having a grain distribution of 1 nm to 200 nm, and the negative electrode active material is provided such that the area ratio of the crystalline structure is 5% or less based on the total area of ​​the silicon-based active material.

[0055] In another embodiment, the area ratio of the crystal structure to the total area of ​​the silicon-based active material may be 5% or less, 3% or less, or 0.1% or more.

[0056] In other words, the silicon-based active material according to this application has a crystal grain size of 200 nm or less, and the size of each crystal structure is formed to be small, thus satisfying the aforementioned area ratio. As a result, the distribution of crystal grain boundaries can be broadened, thereby achieving the aforementioned effects.

[0057] One embodiment of this application provides a negative electrode active material having 20 or more crystal structures contained in the silicon-based active material.

[0058] In another embodiment, the number of crystal structures contained in the silicon-based active material may be 20 or more, 30 or more, 35 or more, and may satisfy the range of 60 or less, or 50 or less.

[0059] In other words, as mentioned above, when the silicon-based active material satisfies the aforementioned range in terms of crystal grain size and the number of crystal structures satisfies the aforementioned range, the strength of the silicon-based active material itself will be within an appropriate range, providing flexibility when included in an electrode and having the characteristic of efficiently suppressing volume expansion.

[0060] In this application, a crystal grain refers to a crystalline particle in a metal or material that is a collection of irregularly shaped particles of microscopic size, and the crystal grain size may refer to the diameter of the observed crystal grain. In other words, in this application, the crystal grain size refers to the size of domains within a particle that share the same crystal orientation, and is a different concept from particle size or particle size, which represents the size of a substance.

[0061] In one embodiment of this application, the crystal grain size can be calculated as the FWHM (Full Width at Half Maximum) value through XRD analysis. Specifically, the method for calculating the crystal grain size can be seen in Figure 3. In Figure 3, the remaining values ​​excluding L are measured by XRD analysis of the silicon-based active material, and the crystal grain size can be measured by the fact that FWHM and crystal grain size are inversely proportional according to the Debey-Scherrer equation. In this case, the Debey-Scherrer equation is as shown in Equation 1-1 below.

[0062] [Formula 1-1] FWHM = Kλ / LCosθ In the above formula 1-1, L represents the crystal grain size, K is a constant, θ is the Bragg angle, and λ represents the wavelength of the X-ray.

[0063] The shape of the crystal grains is diverse and can be measured three-dimensionally. Generally, the size of the crystal grains can be measured using the commonly used circle method or diameter measurement method, but is not limited to these methods.

[0064] The diameter measurement method can be carried out by drawing 5 to 10 equilibrium lines each with a length of L mm on a micrograph of the target particles, counting the number of crystal grains z on the lines and averaging them. At this time, only those that are completely included are counted, excluding those that are merely touching. If the number of lines is P and the magnification is V, the average particle diameter can be calculated by the following formula (1-2).

[0065] [Formula 1-2] Dm=(L*P*10 3 ) / (zV)(μm)

[0066] In addition, the circle method can be calculated by the following formula (1-3) by a method of obtaining the average area of crystal grains based on the number of crystal grains within a circle and the number of crystal grains on the boundary line after drawing a circle with a determined diameter on a micrograph of the target particles.

[0067] [Formula 1-3] Fm=(Fk*10 6 ) / ((0.67n+z)V 2 )(μm 2 ) In the above formula (1-3), Fm represents the average particle area, Fk represents the measurement area on the photograph, z represents the number of particles inside the circle, n represents the number of particles on the arc, and V represents the magnification of the microscope, respectively.

[0068] In one embodiment of the present application, the negative electrode active material may contain a silicon-based active material having a specific surface area of 0.25 m 2 / g or more.

[0069] In another embodiment, the silicon-based active material may have a specific surface area of 0.25 m<00​​​​​​​​​​​ / g or less, more preferably 2.2m 2 It can satisfy a range of less than or equal to / g. The specific surface area can be measured (using nitrogen) according to DIN 66131.

[0070] The silicon-based active material has the aforementioned specific surface area, and the size of the specific surface area of ​​the silicon-based active material can be adjusted by changing the process conditions in the manufacturing process and the growth conditions of the silicon-based active material, as described later. In other words, when the negative electrode active material is manufactured using the manufacturing method according to this application, the rough surface results in a larger specific surface area compared to particles with the same particle size. In this case, the above range is satisfied, and the bonding strength with the binder is increased, which has the characteristic of mitigating electrode cracks caused by repeated charge-discharge cycles.

[0071] Furthermore, when lithium ions are inserted, they are inserted uniformly, reducing the stress applied when inserting lithium ions into silicon particles, thereby mitigating particle cracking. As a result, it has the characteristic of improving the life stability of the negative electrode. If the specific surface area is less than the aforementioned range, even if the particle size is the same, the surface is formed smoothly, the bonding force with the binder decreases, and electrode cracks occur. In this case, lithium ions are inserted non-uniformly within the particles, the stress due to ion insertion is large, and particle cracking occurs.

[0072] In one embodiment of this application, the silicon-based active material provides a negative electrode active material that satisfies the range of the following formula 2-1. [Formula 2-1] X1 / Y1 ≤ 0.960 In the above equation 2-1, X1 is the actual projected area of ​​the silicon-based active material. Y1 represents the projected area of ​​the surrounding spherical particles, which is the same as that of the silicon-based active material.

[0073] The measurement of Equation 2-1 can be performed using a granular analyzer. Specifically, the silicon-based active material according to this application is dispersed on a glass plate by air jetting, and then a shadow image of the scattered silicon-based active material particles is taken to measure the shape of 10,000 silicon-based active material particles in the photograph. In this case, Equation 2-1 represents the average value for 10,000 particles. From the above image, Equation 2-1 according to this application can be measured, and Equation 2-1 can be expressed as the degree of spherulity of the silicon-based active material. The degree of spherulity is given by the formula [4π * actual area of ​​silicon-based active material / (boundary)] 2 It may also be represented as ].

[0074] In one embodiment of this application, the degree of spheroidization of the silicon-based active material may be, for example, 0.960 or less, for example, 0.957 or less. The degree of spheroidization of the silicon-based active material may be 0.8 or more, for example, 0.9 or more, specifically 0.93 or more, and more specifically 0.94 or more, for example, 0.941 or more.

[0075] In one embodiment of this application, a negative electrode active material is provided in which the silicon-based active material satisfies the range of the following formula 2-2. [Formula 2-2] X2 / Y2 ≤ 0.995 In the above equation 2-2, Y2 is the actual surrounding area of ​​the silicon-based active material. X2 is the perimeter of the circumscribed figure of the silicon-based active material.

[0076] The measurement of Equation 2-2 can be performed using a granular analyzer. Specifically, the silicon-based active material according to this application is dispersed on a glass plate by air jetting, and then a shadow image of the scattered silicon-based active material particles is taken to measure the shape of 10,000 silicon-based active material particles in the photograph. In this case, Equation 2-2 represents the average value for 10,000 particles. From the above image, Equation 2-2 according to this application can be measured, and Equation 2-2 can be expressed as the convexity of the silicon-based active material.

[0077] In one embodiment of this application, the range X2 / Y2 ≤ 0.996, preferably X2 / Y2 ≤ 0.995, can be satisfied, and the range 0.8 ≤ X2 / Y2, preferably 0.9 ≤ X2 / Y2, more preferably 0.95 ≤ X2 / Y2, specifically 0.98 ≤ X2 / Y2 can be satisfied.

[0078] The smaller the value of equation 2-1 or equation 2-2, the greater the roughness of the silicon-based active material. By using a silicon-based active material having the aforementioned range, the bonding strength with the binder is increased, which has the advantage of mitigating electrode cracks caused by repeated charge-discharge cycles.

[0079] In one embodiment of this application, the silicon-based active material may include silicon-based particles having a particle size distribution of 0.01 μm to 30 μm.

[0080] The statement that the silicon-based active material contains silicon-based particles having a particle size distribution of 0.01 μm to 30 μm means that it contains a large number of individual silicon-based particles having particle sizes within the range, and the number of silicon-based particles included is not limited.

[0081] The particle size of the silicon-based particles can be expressed by their diameter if they are spherical, but even if they are not spherical, the particle size can be measured in comparison to the spherical case, and the particle size of individual silicon-based particles can be measured using methods generally used in this industry.

[0082] On the other hand, the average particle size (D50 particle size) of the silicon-based active material in the present invention is 3 μm to 10 μm, specifically 4 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size is within the above range, the specific surface area of ​​the particles is within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is greater than or equal to the lower limit range, the composite consisting of the conductive material and binder in the negative electrode slurry provides excellent contact area between the silicon particles and the conductive material, increasing the likelihood of a sustained conductive network and increasing the capacity retention rate. On the other hand, when the average particle size is within the above range, excessively large silicon particles are excluded, and the surface of the negative electrode is formed smoothly, thereby preventing the phenomenon of non-uniform current density during charging and discharging.

[0083] In one embodiment of this application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based electrode active material is preferably 0.01 m². 2 / g~150.0m 2 / g, more preferably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 The value is / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0084] One embodiment of this application provides a negative electrode composition comprising a negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0085] In one embodiment of this application, the present invention provides a negative electrode composition in which the silicon-based active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0086] In another embodiment, the silicon-based active material may contain 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may also contain 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less.

[0087] The negative electrode composition according to this application uses a negative electrode active material that satisfies a specific crystal grain size that can suppress the rate of volume expansion during the charge and discharge process even when using a silicon-based active material with remarkably high capacity within the aforementioned range, and does not degrade the performance of the negative electrode even when included in the aforementioned range, and has the characteristic of having excellent output characteristics during charging and discharging.

[0088] Traditionally, graphite-based compounds were commonly used as the negative electrode active material. However, in recent years, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based active materials to increase capacity. However, in the case of silicon-based active materials, even if the properties of the silicon-based active material itself are adjusted as described above, there is a possibility that the volume may expand rapidly during the charge / discharge process, damaging the conductive paths formed within the negative electrode active material layer.

[0089] Therefore, in one embodiment of this application, the negative electrode conductive material may include at least one selected from the group consisting of point conductive materials, planar conductive materials, and linear conductive materials.

[0090] In one embodiment of this application, the point-shaped conductive material can be used to improve conductivity to the negative electrode and means a point-shaped or spherical conductive material that has conductivity without inducing a chemical change. Specifically, the point-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and may preferably include carbon black in that it embodies high conductivity and has excellent dispersibility.

[0091] In one embodiment of this application, the point conductive material has a BET specific surface area of ​​40 m². 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 It may be less than / g.

[0092] In one embodiment of this application, the point-shaped conductive material may satisfy a volatile matter content of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0093] In particular, when the functional group content of the dot conductive material satisfies the aforementioned range, functional groups are present on the surface of the dot conductive material, and when water is used as the solvent, the dot conductive material can be smoothly dispersed in the solvent. In particular, in the present invention, by using a specific silicon-based active material, the functional group content of the dot conductive material can be reduced, thereby having an excellent effect on improving dispersibility.

[0094] In one embodiment of this application, a point-type conductive material having a functional group content within the aforementioned range is included together with a silicon-based active material, wherein the functional group content can be adjusted according to the degree of heat treatment of the point-type conductive material.

[0095] In one embodiment of this application, the particle size of the dot-like conductive material is 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm. In one embodiment of this application, the conductive material may include a planar conductive material.

[0096] The planar conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and at the same time suppress the disruption of the conductive path due to volume expansion. The planar conductive material can also be described as a plate-type conductive material or a bulk-type conductive material.

[0097] In one embodiment of this application, the planar conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and preferably plate graphite.

[0098] In one embodiment of this application, the average particle size (D50) of the planar conductive material is 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 3.5 μm to 5 μm. When this range is met, the sufficient particle size facilitates dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0099] In one embodiment of this application, a negative electrode composition is provided in which the planar conductive material has a D10 of 0.5 μm or more and 2.0 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.5 μm or more and 15.0 μm or less.

[0100] In one embodiment of this application, the planar conductive material may be a high specific surface area planar conductive material with a high BET specific surface area, or a low specific surface area planar conductive material.

[0101] In one embodiment of this application, a high specific surface area planar conductive material or a low specific surface area planar conductive material can be used without limitation as the planar conductive material. In particular, the planar conductive material according to this application may be affected to some extent by dispersion in terms of electrode performance, and it may be particularly preferable to use a low specific surface area planar conductive material in which dispersion does not cause problems.

[0102] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​1 m². 2 It may be more than / g.

[0103] In another embodiment, the planar conductive material has a BET specific surface area of ​​1 m². 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 It may be less than / g. The planar conductive material according to this application may be a high specific surface area planar conductive material or a low specific surface area planar conductive material.

[0104] In another embodiment, the planar conductive material is a high specific surface area planar conductive material with a BET specific surface area of ​​50 m². 2 / g or more 500m 2 / g or less, preferably 80mg 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0105] In another embodiment, the planar conductive material is a low specific surface area planar conductive material, with a BET specific surface area of ​​1 m². 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m2 / g or less, more preferably 5m 2 / g or more 25m 2 The range of / g or less may also be satisfied.

[0106] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Specifically, unless otherwise specified, "bundle type" here refers to a secondary shape in the form of a bundle or rope, in which multiple carbon nanotube units are arranged in substantially the same orientation along their longitudinal axes, or are intertwined. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, the properties of a conductor or semiconductor can be determined by the angle and structure in which the graphite sheet is wound. Compared to entangled type carbon nanotubes, the bundle-type carbon nanotubes can be uniformly dispersed during anode manufacturing, smoothly form a conductive network within the anode, and improve the conductivity of the anode.

[0107] In one embodiment of this application, the negative electrode conductive material is provided to be 10 to 40 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0108] In another embodiment, the negative electrode conductive material may contain 0.1 parts by weight or more and 40 parts by weight or less, preferably 0.2 parts by weight or more and 30 parts by weight or less, more preferably 0.4 parts by weight or more and 25 parts by weight or less, and most preferably 0.4 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0109] In one embodiment of this application, the negative electrode conductive material provides a negative electrode composition comprising a planar conductive material and a linear conductive material.

[0110] In one embodiment of this application, the negative electrode conductive material is provided as a negative electrode composition comprising 100 parts by weight of the negative electrode conductive material, 80 to 99.9 parts by weight of the planar conductive material, and 0.1 to 20 parts by weight of the linear conductive material.

[0111] In another embodiment, the negative electrode conductive material may include 100 parts by weight of the negative electrode conductive material, 80 to 99.9 parts by weight of the planar conductive material, preferably 85 to 99.9 parts by weight, and more preferably 95 to 98 parts by weight.

[0112] In another embodiment, the negative electrode conductive material may include 0.1 to 20 parts by weight, preferably 0.1 to 15 parts by weight, and more preferably 0.2 to 5 parts by weight, of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0113] In one embodiment of this application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, each satisfying the aforementioned composition and proportion, thereby not significantly affecting the life characteristics of existing lithium secondary batteries. In particular, when planar conductive materials and linear conductive materials are included, the number of charge and discharge points increases, resulting in excellent output characteristics at a high C-rate and reduced high-temperature gas generation.

[0114] In one embodiment of this application, the negative electrode conductive material may be a linear conductive material. In particular, when using linear conductive material alone, it is possible to simplify the electrode tortuosity, which is a problem with silicon-based negative electrodes, and improve the electrode structure, thereby reducing the resistance to lithium ion movement within the electrode.

[0115] In one embodiment of the present application, when the negative electrode conductive material includes a linear conductive material alone, the negative electrode conductive material may contain 0.1 parts by weight or more and 5 parts by weight or less, preferably 0.2 parts by weight or more and 3 parts by weight or less, and more preferably 0.4 parts by weight or more and 1 part by weight or less, based on 100 parts by weight of the negative electrode composition.

[0116] The negative electrode conductive material described in this application has a completely different structure from the positive electrode conductive material used for the positive electrode. Specifically, the negative electrode conductive material described in this application plays the role of capturing the contact points between silicon-based active materials, where the volume expansion of the electrodes is very large due to charging and discharging, while the positive electrode conductive material plays the role of a buffer during rolling while partially imparting conductivity, and its structure and role are completely different from the negative electrode conductive material of the present invention.

[0117] Furthermore, the negative electrode conductive material described in this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. In other words, conductive materials used in electrodes with graphite-based active materials simply have particles that are smaller than the active material, thus improving output characteristics and imparting some conductivity. Their structure and role are completely different from negative electrode conductive materials applied together with silicon-based active materials, as in the present invention.

[0118] In one embodiment of this application, the planar conductive material used as the negative electrode conductive material described above has a different structure and role from carbon-based active materials generally used as negative electrode active materials. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or point-like form for use in order to facilitate the storage and release of lithium ions.

[0119] On the other hand, planar conductive materials used as negative electrode conductive materials are substances having a planar or plate-like form, and can be described as plate-like graphite. In other words, they are substances included to maintain conductive pathways within the negative electrode active material layer, and do not play a role in lithium storage and release, but rather are substances that secure conductive pathways in a planar manner within the negative electrode active material layer.

[0120] In other words, the use of plate-shaped graphite as a conductive material in this application means that it was used not as a material to store or release lithium in a planar or plate-like form, but as a material to secure a conductive path. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release, and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0121] On the other hand, in this application, the use of a carbon-based active material as an active material means that it was processed into a point-like or spherical shape and used as a material that plays a role in storing or releasing lithium.

[0122] In other words, in one embodiment of this application, the carbon-based active material, artificial graphite or natural graphite, is point-like and has a BET specific surface area of ​​0.1 m². 2 / g or more 4.5m 2 The range of less than or equal to / g may also be satisfied. In addition, plate-shaped graphite, which is a planar conductive material, has a planar BET specific surface area of ​​5m². 2 It may be more than / g.

[0123] In one embodiment of this application, the negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms thereof are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0124] The negative electrode binder according to one embodiment of this application plays a role in suppressing the active material and conductive material in order to prevent twisting and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. Any general binder can be applied as long as it satisfies the above role, and specifically, an aqueous binder can be used, and more specifically, a PAM-based binder can be used.

[0125] In one embodiment of this application, the negative electrode binder is 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, and may be 5 parts by weight or more, or 10 parts by weight or more.

[0126] One embodiment of this application provides a method for producing a negative electrode active material, comprising the steps of: chemically reacting silane gas to deposit a silicon-based active material onto the surface of a crystal nucleus; and obtaining the silicon-based active material deposited on the substrate, wherein the silicon-based active material satisfies the following formula 1.

[0127] [Formula 1] 45 ≤ (X / Y) × 100 In the above formula 1, Y represents the proportion of (111) crystal planes within the silicon-based active material. X represents the proportion of (220) crystal planes within the silicon-based active material.

[0128] For example, the silane gas may include at least one gas selected from monosilane, dichlorosilane, and trichlorosilane, and more specifically, it may be trichlorosilane gas.

[0129] In this application, a method for producing a negative electrode active material is provided, wherein the step of chemically reacting the silane gas to deposit a silicon-based active material onto the crystal nucleus surface is performed under high temperature conditions of 100°C or higher.

[0130] In one embodiment of this application, the step of chemically reacting the silane gas to deposit a silicon-based active material onto the crystal nucleus surface may be carried out under pressure conditions of 10 Pa to 150 Pa. Such low pressure reduces the silicon growth rate, thereby enabling the formation of small crystal grains. The above step may be carried out under temperature conditions of 100°C or higher, specifically 500°C or higher, preferably 800°C or higher, and more preferably 800°C to 1300°C or 800°C to 2200°C. This is a lower temperature than the conventional gas atomizing method, which heats to 1600°C or higher to melt Si.

[0131] In one embodiment of this application, the steps include: chemically reacting silane gas to deposit a silicon-based active material onto the surface of a crystal nucleus; and subsequently growing the silicon-based active material through the generation of crystal nuclei.

[0132] In this process, the step of growing the silicon-based active material through crystal nucleation may be carried out at a temperature of 800°C or higher, preferably 800°C to 1300°C. This is a lower temperature than the conventional gas atomizing method, which heats to 1600°C or higher to melt the Si. Furthermore, the step of growing the silicon-based active material through crystal nucleation can be carried out under a pressure of 100 Pa to 150 Pa. This low pressure reduces the silicon growth rate, thereby enabling the formation of small crystal grains and a specific surface area.

[0133] One embodiment of this application provides a method for producing a negative electrode active material, comprising the steps of: chemically reacting silane gas to deposit a silicon-based active material onto the surface of a crystal nucleus; and further comprising the step of growing the silicon-based active material through the generation of crystal nuclei, wherein the step of growing the silicon-based active material through crystal nucleation includes generating crystal nuclei at a temperature of 800°C or higher for 1 to 24 hours.

[0134] By the manufacturing method described above, a silicon-based active material can be produced in which the distribution of Equation 1 within the particles is controlled.

[0135] Conventionally, silicon ingots are manufactured by crushing them with physical force. In this manufacturing method, the size of the crystal grains generally exceeds 200 nm, and the surface is smooth with a surface area of ​​0.25 m². 2 This results in a value of less than / g. When silicon-based active materials are simply manufactured using conventional methods, there is a drawback in that the surface area cannot be controlled, making it difficult to ensure the lifespan stability of the negative electrode.

[0136] However, the method for producing the negative electrode active material according to this application includes the step of forming silicon particles by chemically reacting a silicon lump under specific process conditions to produce silane gas, and then growing the silicon-based active material through crystal nucleation. This method satisfies the surface area size and crystal grain size requirements of this application and also allows for control of the crystal grain direction.

[0137] One embodiment of this application provides a negative electrode for a lithium secondary battery, comprising a negative electrode current collector layer; and a negative electrode active material layer formed on one or both sides of the negative electrode current collector layer, the negative electrode composition according to this application or a cured product thereof.

[0138] Figure 1 shows a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery can be seen, which includes a negative electrode active material layer 20 on one surface of a negative electrode current collector layer 10. Figure 1 shows that the negative electrode active material layer is formed on one surface, but it may also be included on both sides of the negative electrode current collector layer.

[0139] In one embodiment of this application, the negative electrode for the lithium secondary battery may be formed by applying and drying a negative electrode slurry containing the negative electrode composition to one or both sides of a negative electrode current collector layer.

[0140] In this case, the negative electrode slurry may contain the aforementioned negative electrode composition and slurry solvent.

[0141] In one embodiment of this application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0142] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0143] The solid content of the negative electrode slurry can refer to the content of the negative electrode composition contained in the negative electrode slurry, and can refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0144] When the solid content of the negative electrode slurry satisfies the aforementioned range, the viscosity during the formation of the negative electrode active material layer is appropriate, and the particle aggregation phenomenon of the negative electrode composition is minimized, resulting in the efficient formation of the negative electrode active material layer.

[0145] In one embodiment of this application, the slurry solvent can be used without limitation as long as it can dissolve the negative electrode composition, and specifically water or NMP can be used.

[0146] In one embodiment of this application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. Furthermore, fine irregularities can be formed on the surface to strengthen the bonding force of the negative electrode active material, and it can be used in various forms such as film, sheet, foil, net, porous body, foam, and nonwoven fabric.

[0147] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

[0148] However, the thickness can vary considerably depending on the type and application of the negative electrode used, and is not limited thereto.

[0149] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of 10% to 60%.

[0150] In another embodiment, the porosity of the negative electrode active material layer may be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0151] The aforementioned porosity varies depending on the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, the aforementioned range is satisfied by including the silicon-based active material and conductive material according to this application in specific compositions and content portions, thereby ensuring that the electrical conductivity and resistance of the electrode are within an appropriate range.

[0152] One embodiment of this application provides a lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte.

[0153] Figure 2 shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery, including a negative electrode active material layer 20, can be seen on one side of a negative electrode current collector layer 10, and a positive electrode 200 for a lithium secondary battery, including a positive electrode active material layer 40, can be seen on one side of a positive electrode current collector layer 50. The negative electrode 100 and the positive electrode 200 for a lithium secondary battery are formed in a stacked structure with a separation membrane 30 in between.

[0154] A secondary battery according to one embodiment of this specification may include, in particular, the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator membrane interposed between the positive and negative electrodes, and an electrolyte, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

[0155] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, which contains the positive electrode active material.

[0156] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can also have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0157] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented as O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.6); chemical formula LiMn2-c3 M c3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.6) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited to these. The positive electrode may be metallic lithium (Li-metal).

[0158] In one embodiment of this application, the positive electrode active material comprises a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn), wherein the lithium composite transition metal compound comprises single particles or secondary particles, and the average particle size (D50) of the single particles may be 1 μm or more.

[0159] For example, the average particle size (D50) 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, greater than 1 μm and 12 μm or less, greater than 1 μm and 8 μm or less, or 1 μm and 6 μm or less.

[0160] Even when the single particle is formed with a small particle size (average particle size (D50) of 1 μm or more and 12 μm or less), it can exhibit excellent particle strength. For example, the single particle can have a strength of 650 kgf / cm². 2 With this force, the particle strength can be increased to 100 MPa to 300 MPa during rolling. This allows the single particle to be rolled to 650 kgf / cm². 2 Even when rolled with strong force, the phenomenon of increased fine particles within the electrode due to particle cracking is mitigated, thereby improving the battery's lifespan characteristics.

[0161] The single particle can be produced by mixing a transition metal precursor and a lithium raw material and firing the mixture. The secondary particle can be produced by a method different from that of the single particle, and its composition may be the same as or different from that of the single particle.

[0162] The method for forming the single particles is not particularly limited, but generally they can be formed by increasing the firing temperature and over-firing. They can be manufactured by using additives such as grain growth promoters that help with over-firing, or by changing the initiating substance.

[0163] For example, the firing is performed at a temperature at which single particles can be formed. In order to form these, firing must be performed at a higher temperature than that used for secondary particle production. For example, if the precursor composition is the same, firing must be performed at a temperature approximately 30°C to 100°C higher than that used for secondary particle production. The firing temperature for single particle formation can vary depending on the metal composition in the precursor. For example, when forming single particles 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 satisfies the above range, a positive electrode active material containing single particles with excellent electrochemical properties can be produced. If the firing temperature is below 790°C, a positive electrode active material containing a lithium composite transition metal compound in secondary particulate form can be produced. If it exceeds 950°C, excessive firing may occur, the layered crystal structure may not be formed properly, and the electrochemical properties may deteriorate.

[0164] In this specification, the term "single particle" is used to distinguish it from a secondary particle formed by the aggregation of tens to hundreds of primary particles, and is a concept that includes a single particle consisting of one primary particle and a pseudo-single particle form which is an aggregate of 30 or fewer primary particles.

[0165] Specifically, the single particle in the present invention may be a single particle consisting of one primary particle or a pseudo-single particle which is an aggregate of 30 or fewer primary particles, and the secondary particle may be in the form of an aggregate of several hundred primary particles.

[0166] In one embodiment of this application, the lithium composite transition metal compound, which is the positive electrode active material, further contains secondary particles, and the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles.

[0167] In the present invention, a single particle may be a single particle consisting of one primary particle or a pseudo-single particle which is an aggregate of 30 or fewer primary particles, and a secondary particle may be an aggregate of several hundred primary particles.

[0168] The aforementioned lithium-complex transition metal compounds 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 a pseudo-single particle form that is an aggregate of 30 or fewer primary particles.

[0169] The particle size D50 of the secondary particles may be 1 μm to 20 μm, 2 μm to 17 μm, preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles is 0.05 m². 2 / g~10m 2 It is / g, preferably 0.1m 2 / g~1m 2 / g, and more preferably 0.3m 2 / g~0.8m 2 / g is also acceptable.

[0170] In a further embodiment of this application, the secondary particles are aggregates of primary particles, and the average particle size (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of aggregates of several hundred primary particles, and the average particle size (D50) 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.

[0171] When the average particle size (D50) of the primary particles satisfies the aforementioned range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size (D50) 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 (D50) 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.

[0172] According to a further embodiment of this application, the average particle size (D50) of the single particle is smaller than the average particle size (D50) of the secondary particle. As a result, even if the single particle is formed with a small particle size, it can have excellent particle strength, thereby mitigating the phenomenon of increasing fine particles in the electrode due to particle cracking, and thereby improving the battery life characteristics.

[0173] In one embodiment of this application, the average particle size (D50) of the single particle is 1 μm to 18 μm smaller than the average particle size (D50) of the secondary particle.

[0174] For example, the average particle size (D50) of the single particles can be 1 μm to 16 μm smaller than the average particle size (D50) of the secondary particles, and may be 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller.

[0175] When the average particle size (D50) of a single particle is smaller than the average particle size (D50) of a secondary particle, for example, when the above range is satisfied, the single particle can have excellent particle strength even if it is formed with a small particle size. This mitigates the phenomenon of increasing fine particles within the electrode due to particle cracking, resulting in improved battery life characteristics and energy density.

[0176] According to further embodiments of this application, the single particles are included in an amount of 15 to 100 parts by weight per 100 parts by weight of the positive electrode active material. The single particles may also be included 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.

[0177] For example, the single particles may be present in amounts 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. The single particles may be present in amounts of 100 parts by weight or less per 100 parts by weight of the positive electrode active material.

[0178] When single particles within the aforementioned range are included, the material can be combined with the aforementioned negative electrode material to exhibit excellent battery characteristics. In particular, when the single particles amount to 15 parts by weight or more, the phenomenon of increasing fine particles within the electrode due to particle cracking during the rolling process after electrode fabrication can be mitigated, thereby improving the battery's lifespan.

[0179] In one embodiment of this application, the lithium composite transition metal compound may further contain secondary particles, the amount of which may be 85 parts by weight or less per 100 parts by weight of the positive electrode active material. The amount of which may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less per 100 parts by weight of the positive electrode active material. The amount of which may be 0 parts by weight or more per 100 parts by weight of the positive electrode active material.

[0180] When the above range is satisfied, the aforementioned effects due to the presence of single-particle positive electrode active material can be maximized. When secondary-particle positive electrode active material is included, its components may be the same as those exemplified in the single-particle positive electrode active material described above, or they may be different, and can represent a form in which the single-particle form is aggregated.

[0181] In one embodiment of this application, the positive electrode active material in 100 parts by weight of the positive electrode active material layer 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.

[0182] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0183] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitations as long as it has electronic conductivity without undergoing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more can be used.

[0184] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0185] The separation membrane separates the negative and positive electrodes and provides a pathway for lithium ions to move. It can be used without particular limitations as long as it is the type typically used as a separation membrane in secondary batteries. Particularly preferred is a membrane that exhibits low resistance to electrolyte ion movement while maintaining excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, 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, coated separation membranes containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used in single-layer or multi-layer structures.

[0186] Examples of the aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0187] 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, ether, methyl propionate, and ethyl propionate may be used.

[0188] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferred because they are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts. When such cyclic carbonates are mixed with low-viscosity, low-dielectric-constant chain carbonates such as dimethyl carbonate and diethyl carbonate in appropriate proportions, an electrolyte with high electrical conductivity can be produced, and this mixture is even more preferable.

[0189] The metal salt can 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 is F - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of can be used.

[0190] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, improving the discharge capacity of the battery, etc.

[0191] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having a high capacity, high rate characteristics and cycle characteristics, they can be used 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.

Examples

[0192] The following are preferred embodiments to aid in understanding the present invention. These embodiments are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and that such variations and modifications fall within the scope of the appended claims.

[0193] <Manufacturing example> <Manufacturing of negative electrode active materials for Examples 1-5> Active materials were formed by depositing silicon onto crystal nuclei in the reactor through a chemical reaction with silane gas. By adjusting the growth time shown in Table 1 below, silicon-based active materials were produced, and the range of related formula 1 is shown in Table 1 below.

[0194] <Manufacturing of the negative electrode active material in Comparative Example 1> A silicon core was heated by electric current in a metal reaction furnace (reduction furnace), and a mixture of purified high-purity monosilane (SiH4) gas vapor and purified hydrogen was passed through it to deposit polycrystalline silicon on the surface of the silicon core, thereby producing a thick, rod-shaped polycrystalline silicon mass. Subsequently, silicon-based active materials were produced by crushing and classification.

[0195] <Manufacturing of the negative electrode active material in Comparative Example 2> In the above-described Example 1, instead of using crystal nuclei, a material obtained by crushing a material in which silicon had been grown on a substrate was used, and deposition was performed in the substrate with a gas flowing state instead of a reactor containing crystal nuclei.

[0196] [Table 1]

[0197] In Table 1 above, a spherical silicon-based active material refers to an active material whose circularity is 0.9 or higher after measuring the circularity of each particle, and the parts by weight of the spherical silicon-based active material refers to the parts by weight shown in Table 1 above, based on 100 parts by weight of the total silicon-based active material.

[0198] <Manufacture of Negative Electrode> The negative electrode active material containing the silicon-based active material, the first conductive material, the second conductive material, and polyacrylamide as a binder were added to distilled water as a solvent for forming a negative electrode slurry at a weight ratio of 80:9.6:0.4:10 to manufacture a negative electrode slurry (solid content concentration: 25% by weight).

[0199] Specifically, the first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material is SWCNT.

[0200] As a specific mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed at 2500 rpm for 30 min using a homomixer, then the silicon-based active material was added, and then dispersed at 2500 rpm for 30 min to prepare a negative electrode slurry.

[0201] The negative electrode slurry was coated on both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector layer at a loading amount of 85 mg / 25 cm 2 and rolled (roll press), and dried in a vacuum oven at 130 °C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), which was used as the negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0202] <Manufacture of Secondary Battery> As a positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry at a weight ratio of 97:1.5:1.5 to manufacture a positive electrode slurry (solid content concentration: 78% by weight).

[0203] The positive electrode slurry was coated on both sides of an aluminum current collector (thickness: 12 μm) as a positive electrode current collector at 537 mg / 25 cm 2The cathode was fabricated by coating with the specified loading amount, rolling (roll press), and drying in a vacuum oven at 130°C for 10 hours to form a cathode active material layer (thickness: 65 μm) (cathode thickness: 77 μm, porosity: 26%).

[0204] A lithium secondary battery was fabricated by injecting an electrolyte between the positive electrode and the negative electrode of the above example and comparative example via a polyethylene separation membrane.

[0205] The aforementioned electrolyte was prepared by adding vinylene carbonate at a concentration of 3% by weight relative to the total weight of the electrolyte to an organic solvent mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 10:90, and then adding LiPF6 as a lithium salt at a concentration of 1M.

[0206] Experimental Example 1: Evaluation of Monocell Lifespan The secondary batteries containing the negative electrodes manufactured in the above examples and comparative examples were evaluated for their lifespan using an electrochemical charger / discharger, and their capacity retention rate was assessed. The secondary batteries underwent in-situ cycle testing at 4.2-3.0V 1C / 0.5C, and during the test, the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles. The results are shown in Table 2. Capacity retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the 1st cycle)} × 100

[0207] [Table 2]

[0208] Experiment Example 2: Evaluation of discharge resistance increase rate (after 200 cycles) at @SOC50 2.5C In Experimental Example 1, during testing, the capacitance retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles. Then, the resistance was measured by discharging with a 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed. For the aforementioned resistance increase rate evaluation, data was calculated for 200 cycles, and the results are shown in Table 3 below.

[0209] [Table 3]

[0210] As can be seen from Tables 2 and 3 above, in Examples 1 to 5, in which the crystal planes of this application were adjusted, it was confirmed that they were superior to Comparative Examples 1 and 2 in terms of lifetime evaluation and resistance increase rate.

[0211] This is achieved by controlling the grain orientation distribution that satisfies the range of Equation 1. In other words, when a relatively large proportion of (111) crystal planes are formed, as in the conventional method, the (111) crystal planes have a lower lithium mobility than the (220) crystal planes, preventing lithium from entering and leaving uniformly during lithium insertion and removal reactions. However, the silicon-based active material according to this application contains a large proportion of (220) crystal planes, unlike the conventional method, allowing lithium to enter and leave uniformly during lithium insertion and removal reactions, mitigating silicon cracking phenomena on the electrode surface, and thereby enhancing the lifespan characteristics of the electrode.

[0212] For reference, in Comparative Example 1, a silicon core installed in a metal reaction furnace (reduction furnace) was electrically heated, and a gas mixture of purified high-purity monosilane (SiH4) gas vapor and purified hydrogen was flowed through it to deposit polycrystalline silicon on the surface of the silicon core. Subsequently, after going through a pulverization process, the value of Equation 1 (I(220) / I(111)×100) became relatively low, and it was confirmed that the lifetime evaluation and resistance increase rate evaluation were not as good as in the example.

[0213] In Comparative Example 2, the material was obtained by crushing a material in which silicon had been grown on a substrate, and was deposited into the substrate using a gas flow instead of a reactor with crystal nuclei. In this case as well, the value of Equation 1 was formed to be low, similar to Comparative Example 1, and it was confirmed that the lifetime evaluation and resistance increase rate evaluation were not as good as in the example. [Explanation of symbols]

[0214] 10 ···Negative electrode current collector layer 20...Negative electrode active material layer 30...Separation membrane 40...Cathode active material layer 50 ···Positive electrode current collector layer 100 ···Negative electrode for lithium secondary batteries 200 ···Positive electrode for lithium secondary batteries

Claims

1. The silicon-based active material includes (220) crystal planes and (111) crystal planes, The aforementioned silicon-based active material satisfies the following equation 1, The silicon-based active material comprises at least one selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and contains 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the silicon-based active material. The negative electrode active material having a crystal grain size of 10 nm or more and 130 nm or less: [Formula 1] 45≦(X / Y)×100 In the above formula 1, Y represents the proportion of (111) crystal planes within the silicon-based active material. X represents the proportion of (220) crystal planes within the silicon-based active material.

2. The silicon-based active material comprises at least one selected from the group consisting of spherical silicon-based active materials and plate-shaped silicon-based active materials. The negative electrode active material according to claim 1, comprising 100 parts by weight of the aforementioned silicon-based active material and 80 parts by weight or more of spherical silicon-based active material.

3. The negative electrode active material according to claim 1, wherein the D50 particle size of the silicon-based active material is 3 μm or more and 10 μm or less.

4. The steps include: chemically reacting silane gas to deposit a silicon-based active material onto the crystal nucleus surface, and The step of obtaining the deposited silicon-based active material, A method for producing a negative electrode active material, comprising: The silicon-based active material satisfies the following formula 1, the method for producing a negative electrode active material according to any one of claims 1 to 3: [Formula 1] 45≦(X / Y)×100 In the above formula 1, Y represents the proportion of (111) crystal planes within the silicon-based active material. X represents the proportion of (220) crystal planes within the silicon-based active material.

5. The method for producing a negative electrode active material according to claim 4, wherein the silane gas comprises at least one gas selected from monosilane, dichlorosilane, and trichlorosilane.

6. The method for producing a negative electrode active material according to claim 4, wherein the step of chemically reacting the silane gas to deposit a silicon-based active material onto the crystal nucleus surface is performed under high temperature conditions of 100°C or higher.

7. After the step of chemically reacting silane gas to deposit silicon-based active material onto the crystal nucleus surface, The process further includes the step of growing the silicon-based active material through crystal nucleation, The method for producing a negative electrode active material according to claim 4, wherein the step of growing the silicon-based active material through crystal nucleation includes a step of generating crystal nucleation at a temperature of 800°C or higher for 1 to 24 hours.

8. A negative electrode composition comprising a negative electrode active material, a negative electrode conductive material, and a negative electrode binder according to any one of claims 1 to 3.

9. The negative electrode composition according to claim 8, wherein the negative electrode active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

10. The negative electrode composition according to claim 8, wherein the negative electrode conductive material comprises at least one selected from the group consisting of a point conductive material, a planar conductive material, and a linear conductive material.

11. The material includes a negative electrode current collector layer and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer. The negative electrode for a lithium secondary battery comprises the negative electrode composition or a cured product thereof according to claim 8, wherein the negative electrode active material layer includes the negative electrode composition or a cured product thereof according to claim 8.

12. The thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less. The negative electrode for a lithium secondary battery according to claim 11, wherein the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

13. positive electrode, The negative electrode for a lithium secondary battery according to claim 11, A separation membrane provided between the positive electrode and the negative electrode, and electrolyte, Lithium-ion batteries, including lithium-ion batteries.

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