Electrode mixture film, and dry electrode, lithium secondary battery, and electric device comprising same

Abstract

The invention provides an electrode mixture film, and a dry electrode, a lithium secondary battery, and an electrical device including the same. The electrode mixture film according to the present invention comprises: an electrode active material comprising an active material core and a carbon coating layer provided on the surface of the active material core; and has a conductive path connection index (CPCI) defined by the degree of aggregation of the binder, the volume cumulative average particle diameter of the electrode active material, the average thickness of the carbon coating layer, and the like. According to the present invention, the CPCI is 0.09-0.45, and the dry electrode does not contain a conductive material, but still has excellent resistance characteristics due to good conductive path connectivity, so that the lithium secondary battery of the obtained dry electrode has good output characteristics and high energy density. The invention also provides a dry electrode, a lithium secondary battery and an electric device which are made of the electrode mixture film.

Description

Technical Field

[0001] The present invention relates to an electrode mixture film, a dry electrode including the same, a lithium secondary battery, and an electrical device, and belongs to the technical field of lithium batteries.

[0002] The present invention claims the priority of Korean Patent Application No. 10-2023-0172773, filed in Korea on December 1, 2023, the disclosure of which is incorporated herein by reference. Background Art

[0003] The process of manufacturing a lithium secondary battery mainly includes three steps: an electrode process, an assembly process, and a forming process. The electrode process includes an active material mixing process, an electrode coating process, a drying process, a rolling process, a cutting process, and a winding process.

[0004] The active material mixing process is a process of mixing coating materials for forming an electrode active layer in which an electrochemical reaction occurs in an electrode. Specifically, an electrode active material, which is a basic element of the electrode, is mixed with additives (such as a conductive material, a filler, a binder for binding powders and adhering to a current collector, and a solvent for generating viscosity and dispersibility to prepare a flowable slurry).

[0005] A mixture composition for forming an electrode active layer is generally referred to as an electrode mixture.

[0006] Subsequently, an electrode coating process of coating the electrode mixture on a conductive current collector and a drying process for removing the solvent from the electrode mixture are performed, and then rolling is carried out to manufacture an electrode having a predetermined thickness.

[0007] Currently, the manufacturing processes for electrodes of lithium-ion batteries include two types: a wet process and a dry process. Among them, the conventional wet process manufactures electrodes for lithium-ion batteries by coating a slurry liquid on a current collector and then volatilizing the solvent in a drying furnace; the existing dry electrode process is to put an electrode mixed powder based on an adhesive such as PTFE between two or more calender rolls to form a free-standing electrode film, and then combine it with a current collector coated with a conductive adhesive layer (primer) to manufacture electrodes for lithium-ion batteries.

[0008] Generally speaking, different from wet electrodes, the dry electrode process mixes materials without solvents and dispersants, so the method of dispersing to make each material evenly distributed is a key technology.

[0009] In current wet electrodes, linear conductive materials such as carbon nanotubes (CNT) are usually used, which can significantly reduce the content of conductive materials in the electrode composition. However, for the above-mentioned linear conductive materials commonly used in wet electrodes, it is difficult to achieve uniform dispersion using the mixing method in the existing dry electrode process. Therefore, a relatively high content of conductive materials is still required in dry electrodes, resulting in a loss in energy density. Thus, it is necessary to develop new materials or new process technologies for dry electrodes that can reduce the conductive materials. Summary of the Invention

[0010] To solve the above technical problems, an object of the present invention is to provide an electrode mixture film that can smoothly form a conductive path in the case of insufficient conductive materials and increase the loading amount of active materials by reducing the amount of conductive materials used.

[0011] Another object of the present invention is to provide a dry electrode and a lithium secondary battery including the above electrode mixture film. The lithium secondary battery can have improved resistance and life characteristics, as well as improved capacity characteristics, through the above electrode mixture film.

[0012] To achieve the above object, the present invention first provides an electrode mixture film (Electrode mixture film), which includes:

[0013] an electrode active material and a fibrillated binder,

[0014] the electrode active material includes an active material core and a carbon coating provided on the surface of the active material core;

[0015] the CPCI (Conductive Path Connectivity Index) defined by the following Equation 1 is 0.09 to 0.45,

[0016] [Equation 1]

[0017] CPCI = A B ×R×(T C / D AM )

[0018] In the above Equation 1,

[0019] A B is the aggregation degree of the binder in the electrode mixture film,

[0020] D AM is the volume cumulative average particle size D of the electrode active material 50 , with the unit of μm,

[0021] T C is the average thickness of the carbon coating, with the unit of μm,

[0022] R is calculated by [(W AM / W B )×(1 + 2W C )], where:

[0023] W B represents the weight fraction of the binder in the total weight of the electrode binder film, in %,

[0024] W AM represents the weight fraction of the electroactive material in the total weight of the electrode binder film, in %,

[0025] W C is a dimensionless value representing the weight fraction (in %) of the conductive material in the total weight of the electrode binder film.

[0026] In the above electrode binder film, preferably, the degree of aggregation (A B ) of the binder is defined by the following Equation 2:

[0027] [Equation 2]

[0028] A B = (number of aggregated binder pixels) / (total number of binder pixels)

[0029] In the above Equation 2, the number of aggregated binder pixels and the total number of binder pixels are derived by the following method:

[0030] 1) For the cross-section of the above electrode binder film formed by the ion milling method, a target image with a resolution of 1280×960 or higher is obtained by BSE (Back Scattered electron) measurement using a field emission scanning electron microscope (FESEM),

[0031] 2) For the above target image, the set contrast level of the electroactive material region is adjusted to the highest contrast level, the set contrast level of the binder region is adjusted to the lowest contrast level, and each region is divided into electroactive material pixels or binder pixels, and

[0032] 3) For the binder pixels, calculate the number of binder pixels aggregated in the aggregated binder region with an area of 3μm 2 or larger, which is composed of multiple adjacent binder pixels, and calculate the total number of binder pixels in the entire binder region.

[0033] In the above electrode binder film, preferably, the volume average particle size D of the electroactive material 50is from 0.1 μm to 5.0 μm.

[0034] In the above electrode mixture film, preferably, the average thickness (Tc) of the carbon coating of the electrode active material and the volume cumulative average particle size D of the electrode active material 50 (D AM ) have a ratio of 0.0002 to 0.1.

[0035] In the above electrode mixture film, preferably, the degree of aggregation (A B ) of the binder is 0.3 to 0.9.

[0036] In the above electrode mixture film, preferably, in the above formula 1, R is 16 to 70.

[0037] In the above electrode mixture film, preferably, the active material core contains at least one component selected from the following group: lithium manganese-based oxides, lithium nickel-based oxides, lithium nickel manganese-based oxides, lithium nickel cobalt-based oxides, lithium manganese cobalt-based oxides, lithium nickel manganese cobalt-based oxides, lithium nickel cobalt transition metal oxides, and lithium metal phosphate-based compounds.

[0038] In the above electrode mixture film, preferably, the active material core contains the lithium metal phosphate-based compound represented by the following Chemical Formula 1:

[0039] Chemical Formula 1: Li 1+a Fe 1-x M x PO 4

[0040] In the above Chemical Formula 1, M is at least one selected from Mn, Co, Ni, Al, Mg, and Ti, and a and x satisfy -0.5 ≤ a ≤ 0.5, 0 ≤ x < 1.

[0041] In the above electrode mixture film, preferably, the binder includes polytetrafluoroethylene (PTFE).

[0042] In the above electrode mixture film, preferably, the electrode mixture film contains 92 parts by weight to 99.5 parts by weight of the electrode active material and 0.5 parts by weight to 8 parts by weight of the fibrillated binder, and does not contain a conductive material.

[0043] In the above electrode mixture film, preferably, the porosity of the electrode mixture film is 29% or less.

[0044] In the above electrode mixture film, preferably, the powder resistance of the electrode active material is 1 Ω·cm to 100 Ω·cm.

[0045] The present invention also provides a method for preparing an electrode binder film, comprising mixing an electrode active material and a fibrillatable binder to form a material mixture (S1), kneading the material mixture under the application of a shear force to form a mixed aggregate (S2), pulverizing the mixed aggregate to prepare electrode powder (S3), and shaping the electrode powder to prepare a binder film (S4).

[0046] In the above method for preparing an electrode binder film, preferably, step S1 can be carried out at a mixing rate of 3000 rpm to 20000 rpm for 0.5 to 60 minutes.

[0047] In the above method for preparing an electrode binder film, preferably, step S2 can be carried out at a kneading rate of 10 rpm to 100 rpm for 3 to 60 minutes.

[0048] In the above method for preparing an electrode binder film, preferably, step S3 can be carried out in a pulverizer at a rate of 1000 rpm to 15000 rpm for 5 seconds to 30 minutes.

[0049] The present invention also provides a dry electrode, which comprises a current collector; and the above electrode binder film provided by the present invention disposed on the current collector.

[0050] In the above dry electrode, preferably, the electrode is a positive electrode.

[0051] The present invention also provides a lithium secondary battery, which includes a plurality of electrodes, and at least one of the electrodes comprises the above dry electrode provided by the present invention.

[0052] The present invention also provides an electrical device, which comprises the above lithium secondary battery provided by the present invention.

[0053] The electrode binder film provided by the present invention can have good conductive path connectivity by controlling the conductivity of the electrode active material itself, the contact between the electrode active materials, and the distribution of the binder in the case of insufficient conductive material, without relying on the conductive material to form a conductive path. At the same time, by using an active material with a low powder resistance (especially an active material containing a carbon coating) to improve the resistance characteristics of the battery, rather than using a conductive material or only using the least amount of conductive material, it is possible to avoid problems caused by uneven distribution of the conductive material and increase the loading amount of the electrode active material.

[0054] The electrode binder film provided by the present invention can manufacture a high-performance electrode with less influence from the conductive material, and there is no need to perform a dispersion treatment on the conductive material during the manufacturing process, which can reduce the manufacturing cost and process cost and greatly improve the competitiveness in terms of price.

[0055] The lithium secondary battery manufactured with the electrode mixture film provided by the present invention will not have problems caused by uneven distribution of the conductive material, can improve the resistance of the battery (for example, obtain a lower powder resistance) and the life characteristics, and due to an increase in the loading amount of the electrode active material, can improve the battery capacity and energy density, can achieve performance equivalent to that of a lithium secondary battery prepared with a dry electrode containing a conductive material, and moreover, has an appropriate electrode tensile strength. Detailed Description of the Invention

[0056] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention will be described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0057] It should be understood that the words or terms used in the specification and claims should not be construed as being limited to the general and dictionary meanings, but should be interpreted based on the meanings and concepts corresponding to the technical solutions of this specification, based on the principle that allows the inventor to appropriately define the words or terms for the best interpretation.

[0058] In the present invention:

[0059] The term "material mixture" refers to a mixture containing an electrode active material and a binder (optionally containing a conductive material), which is physically mixed to form a homogeneous dispersion phase and is the product of the mixing process as described herein, and it can be a mixture that basically does not involve a solvent. In this case, basically not involving a solvent means that no solvent is added or only a very small amount of solvent is added when mixing the material mixture.

[0060] The term "mixed aggregate" refers to a powder mixture that combines or connects and transforms into a dough-like aggregate as the material mixture is affected by shear force and the binder fibrillates, and it can be the product of the kneading process for the present invention, with a solid content of 100%.

[0061] The term "electrode powder" can refer to a material in a powder state, in which the mixed aggregate is crushed into smaller particle sizes.

[0062] The term "electrode mixture film" can refer to a self-supporting single sheet prepared using electrode powder in a solvent-free manner. Here, "self-supporting" means being able to maintain a form independent of other components and having the characteristics of being able to move or be handled independently. The electrode mixture film can be formed by pressing the electrode powder, which will be described in detail later. For example, the electrode powder can be integrated by pressing to form a layered structure.

[0063] The term "three-dimensional fiber network structure" may refer to a structure formed by the fibrillation of a binder during the process of forming an electrode paste film from a mixture including an electrode active material and a binder. Specifically, the three-dimensional fiber network structure may refer to various structures in which fine fibers formed by the fibrillation of the binder serve as a framework and can thus act as a support to make the electrode paste film a self-standing film. Here, the electrode active material and an optional conductive material may be accommodated in the pores formed in the three-dimensional fiber network structure.

[0064] The "conductive material" refers to a conductive material other than the electrode active material containing an active material core and having a carbon coating thereon.

[0065] That is to say, the "conductive material" here may exist separately from the electrode active material in the electrode paste film.

[0066] Here, the electrode paste film, its preparation method, the dry electrode, and the lithium secondary battery including the same may each include at least one technical feature and / or technical configuration described below, and these technical features and / or technical configurations may be combined in various ways.

[0067] The first aspect of the present invention provides an electrode paste film made of an electrode active material containing a carbon coating and a fibrillatable binder, which can improve the energy density of the battery and obtain good battery performance in the case of insufficient conductive material.

[0068] The electrode paste film according to the first aspect includes:

[0069] an electrode active material and a fibrillated binder,

[0070] the electrode active material includes an active material core and a carbon coating provided on the surface of the active material core;

[0071] The CPCI (Conductive Path Connectivity Index) defined by the following Equation 1 is 0.09 - 0.45;

[0072] [Equation 1]

[0073] CPCI = A B ×R×(T C / D AM )

[0074] In the above Equation 1,

[0075] A B is the aggregation degree of the binder in the electrode paste film,

[0076] D AM is the volume cumulative average particle size D of the electrode active material 50, in μm,

[0077] T C is the average thickness of the carbon coating, in μm,

[0078] R is calculated by [(W AM / W B ) × (1 + 2W C )], where:

[0079] W B represents the weight fraction of the binder in the total weight of the electrode mixture film, in %,

[0080] W AM represents the weight fraction of the electrode active material in the total weight of the electrode mixture film, in %,

[0081] W C is a dimensionless value representing the weight fraction (in %) of the conductive material in the total weight of the electrode mixture film.

[0082] Generally speaking, different from wet electrodes, dry electrodes are manufactured without using solvents. Therefore, uniformly dispersing the electrode materials is an important and difficult process and has a significant impact on the electrode performance. In addition, in order to increase the loading amount of the electrode active material, it may be necessary to use high-performance conductive materials to prevent performance degradation when the amount of the conductive material added is reduced. However, high-performance conductive materials (such as carbon nanotubes) have poor dispersibility. That is to say, during the manufacturing process of dry electrodes, there are difficulties in dispersion due to the non-use of solvents and due to the use of materials with poor dispersibility.

[0083] In order to solve the problem of dispersion difficulties caused by the above characteristics of the conductive material, the object of the present invention is to provide an electrode mixture film which has excellent conductive path connectivity, while having an increased loading amount of the active material, and which improves the resistance characteristics of the battery by using an active material with low powder resistance, especially an active material containing a carbon coating, rather than using a conductive material or using a conductive material in the minimum amount.

[0084] CPCI can be used as an index to evaluate the effect of forming a conductive path in the electrode mixture film that can improve the mobility of electrons and ions. When the preparation of the electrode mixture film meets the above range, even if it contains only a trace amount of conductive material or no conductive material, the resistance characteristics of the battery can be improved. CPCI can be defined as the product of the content ratio R of the electrode active material and the binder, the ratio of the average thickness T C of the carbon coating to the volume average particle diameter D AM of the electrode active material and the degree of aggregation A B of the binder.

[0085] In the present invention, the "degree of aggregation of the binder" is a measure that can evaluate the degree of dispersion and aggregation of the binder in the electrode mixture film, and the degree of aggregation of the binder can be measured by the method described below. By the degree of aggregation of the binder, the proportion of the fibrillated and aggregated binder in the binder in the electrode mixture film can be determined. In other words, by the level of aggregation of the binder, the contact area between the electrode active materials can be determined when the binder forms a three-dimensional fiber network structure through fibrillation.

[0086] When the binder aggregates excessively, rather than ensuring the contact area between the active materials and the trace conductive materials or between the active materials accommodated in the voids of the three-dimensional network structure, the diversity of the conduction paths may have a more significant impact, and the excessive aggregation of the binder may hinder the formation of the composite conduction paths. In addition, the mechanical properties of the electrode mixture film are poor, which may lead to a decline in appearance and durability, so it needs to be controlled at an appropriate level.

[0087] The average particle diameter of the electrode active materials may be related to the spacing between the pores in the three-dimensional fiber network structure of the fibrillated binder in the electrode mixture film. Therefore, a smaller particle diameter may result in an increased contact area between the electrode active material particles or between the electrode active material particles and the trace conductive material particles. That is to say, this may indicate that as the electrode active materials include carbon coatings, more conduction paths can be formed through contact.

[0088] In order to form an electrode mixture film as a self-supporting film with electrode powder, as the diameter of the active material particles decreases, the amount of the binder input needs to be increased. In a dry electrode, the binder is a key component for forming the film support structure, and when added in a larger amount within a certain range, it may improve the durability or the film-forming process. However, the increase in the amount of the binder may lead to a decrease in the loading amount of the active materials and a decrease in the contact area between the electrode active materials, thereby increasing the resistance. Intuitively, the binder, as a kind of resistance, may damage the conductivity, so the increase in the amount of the binder needs to be restricted. Therefore, it is difficult to simply rely on applying active materials with small particle diameters to improve the performance.

[0089] A high degree of aggregation of the binder may intuitively be understood as uneven distribution of the binder. On the contrary, the area where the binder aggregates may mean the area where the active material or both the active material and the conductive material aggregate. Therefore, the greater the degree of aggregation of the binder, the more the contact area between the electrode active materials can be increased, thus forming a conductive path, while the smaller the particle size of the electrode active material may improve the contact of the active material in the three-dimensional fiber network structure. The uniform distribution of the binder without aggregation areas can be interpreted as that although the active material is accommodated in the internal pores, since there is no contact between the active materials, the formation of a conductive path is almost impossible to achieve, which also means that the contact between the active materials or between the active material and the conductive material can be indirectly determined by the degree of aggregation of the binder.

[0090] However, the influence of the degree of aggregation of the binder may vary depending on the amount of the added binder. When the particle size of the electrode active material becomes smaller, the amount of the binder needs to be increased, which may increase the resistance. In addition, a carbon coating may be necessary, but its thickness may affect the migration of lithium ions. Therefore, in the electrode binder film with insufficient conductive material, it is necessary to identify the factors that play a role in ensuring the conductive path to define the CPCI.

[0091] For the electrode binder film according to the first aspect, the CPCI value of the electrode binder film is between 0.09 and 0.45. If the CPCI value is lower than 0.09, it indicates that the fibrosis of the binder is excessive, resulting in a lower degree of polymerization of the binder, which may lead to poor mechanical properties. In addition, this situation also shows that although the electrode active materials are evenly distributed, there are still many non-contact parts, so multiple disconnection parts may be formed in the conductive path, which means that a normal conductive path cannot be formed. When the conductive material exists only in a trace amount or does not contain the conductive material, there will be a problem of too high electrode resistance, resulting in very poor performance of the manufactured battery. If the CPCI value is larger, it may mean that the formed conductive path is better. However, different from the theoretical expectation, if the CPCI value exceeds 0.45, the degree of aggregation of the binder may be too high, which may lead to a decrease in conductivity due to the failure to form a composite conductive path, and at the same time, problems such as a decrease in the mechanical properties of the electrode binder film or appearance problems, such as stripes or cracks on the surface, may occur, resulting in poor durability. In addition, the thickness of the carbon coating may be relatively thick compared with the average particle size of the electrode active material, resulting in problems such as poor lithium ion mobility, relatively decreased capacity, and short battery life. That is to say, the larger the CPCI value, the more likely the conductive path is to be formed better, but this technical significance may be satisfied when the CPCI value is below 0.45. When it exceeds 0.45, various problems mentioned above may occur, so it may be necessary to adjust the CPCI value.

[0092] When the CPCI value satisfies the range of 0.09 to 0.45, even when the content of the conductive material is small or no conductive material is added, a synergistic effect will occur among the distribution of the binder, the average particle size of the electrode active material, and the thickness of the carbon coating, thereby improving the resistance characteristics of the battery. When a conductive material is contained, the resistance measured in the electrode state may be low, but the resistance measured during battery operation may better reflect the actual usage situation, because the resistance of the electrode only evaluates the electron migration ability, while the resistance of the battery may reflect both the electron migration ability and the ion migration ability. The CPCI value is preferably 0.10 or greater, 0.11 or greater, 0.12 or greater, 0.13 or greater, 0.15 or greater, 0.17 or greater, or 0.18 or greater and 0.43 or less, 0.40 or less, 0.38 or less, 0.36 or less, 0.35 or less, or 0.33 or less.

[0093] That is to say, the ion migration ability may be affected by various factors, such as the path for lithium ions to escape from the interior of the active material and the path for lithium ions to reach the outermost surface of the electrode binder film from the surface of the active material. Therefore, the resistance characteristics of the battery are not improved merely because the conductive material ensures the electron movement path. Thus, as described in this specification, an electrode binder film that can improve the resistance characteristics without containing a conductive material is provided.

[0094] In the present invention, the volume cumulative average particle size D 50 refers to the particle size at 50% of the volume cumulative particle size distribution of the particles. This volume cumulative average particle size D 50 can be measured by the laser diffraction method. The laser diffraction method generally allows the measurement of particle sizes from the sub-micron level to several millimeters and may produce highly reproducible and high-resolution results. For example, it can be carried out by the following method:

[0095] Disperse the particles (for example, LFP particles: generally take 0.02 g - 0.03 g for the primary particle type and 0.05 - 0.06 g for the secondary particle type) in a mixed solution of 9.9 mL of water and 0.1 mL of Triton X-100 (concentration 1%), shake well and perform ultrasonic treatment for 120 s to obtain a sample to be measured;

[0096] Test device settings: Non-spherical, the refractive index of the substance is 1.692, the refractive index of the filler is 1.33; the stirrer speed is 1500 revolutions, the ultrasonic intensity (Sonication intensity) is 100%, the time is 1000 seconds; the obscuration range is 8 - 15%;

[0097] Test background: The sample to be tested was introduced into a particle size distribution measuring device (Mastersizer 2000, manufactured by Malvern) with a light shielding degree of 9-10%, and then waited for 60 seconds. After adjusting the ultrasonic intensity to 30%, the detection was immediately carried out to obtain the test result.

[0098] In the present invention, the term "average particle size D" 50 can be defined as the arithmetic mean calculated by measuring the particle sizes of at least 30 particles observed in a scanning electron microscope (SEM) image at a magnification of 5000 to 20000 times. The particle size refers to the longest axis of the particle.

[0099] For the electrode mixture film according to the first aspect, preferably, the volume-average particle size D of the electrode active material 50 is 0.1 μm to 5.0 μm, more preferably 0.5 μm to 4.0 μm, and further preferably 0.7 μm to 3.5 μm. If the average particle size of the electrode active material is too large, problems such as a decrease in the battery capacity characteristics may occur, problems such as a decrease in the high-rate charge-discharge characteristics due to a high internal resistance and a decrease in the ion migration speed may occur, and problems such as the inability to achieve physical contact between the electrode active materials and the inability to form a conductive path inside the fibrous binder may occur. If the average particle size of the above-mentioned electrode active material is too small, problems such as a decrease in the mechanical properties such as the tensile strength and elongation at break of the electrode mixture film may occur when preparing the electrode mixture film containing the electrode active material.

[0100] Therefore, when the average particle size D of the electrode active material 50 meets the above range, the particle size of the obtained mixed powder may be more uniform, and an appropriate specific surface area of the electrode active material particles can be obtained, thereby improving the capacity characteristics, conductivity, and high-rate charge-discharge characteristics of the battery. In addition, when preparing the electrode mixture film, it will be easier to form a film, and the mechanical properties of the film (such as tensile strength and elongation at break) can also be improved.

[0101] For the electrode mixture film according to the first aspect, preferably, the average thickness of the carbon coating of the electrode active material can be 1 nm to 30 nm. Preferably, the average thickness can be greater than 2 nm or greater than 3 nm, and can also be less than or equal to 25 nm, 20 nm, 15 nm, or 10 nm. When the thickness of the carbon coating meets the above range, it helps to meet the CPCI value, thereby improving the connectivity of the conductive path without loss of capacity.

[0102] In the present invention, the average thickness (Tc) of the carbon coating refers to the thickness of the carbon coating measured at at least 100 points on the surface of the electrode active material particles by transmission electron microscopy, and the value obtained by averaging these measurement values, with the unit of μm. In this case, when more than 100 points are selected, these points can be selected at appropriate intervals to cover the entire particle.

[0103] For the electrode binder film according to the first aspect, preferably, the ratio of the average thickness (μm) of the carbon coating of the electrode active material to the volume cumulative average particle size (μm) of the electrode active material is 0.0002 to 0.1. For example, the ratio can be greater than or equal to 0.0004, 0.0006 or 0.0008, and can also be less than or equal to 0.08, 0.06, 0.05, 0.03 or 0.01. More preferably, it is 0.008 - 0.02, and further preferably 0.009 - 0.012. When the ratio of the average thickness (Tc) of the carbon coating to the volume cumulative average particle size D 50 (D AM ) of the electrode active material is within the above range, favorable effects can be exhibited in terms of stabilizing the activity of the electrode active material through the carbon coating, but the present invention is not limited thereto. If the ratio of the average thickness (Tc) of the carbon coating to the volume cumulative average particle size D 50 (D AM ) of the electrode active material is not within the above range, it indicates that the thickness of the carbon coating is relatively thick compared to the particle size of the electrode active material, and problems such as poor lithium ion mobility, relatively decreased capacity, and short battery life may occur. Before meeting the respective ranges of the volume cumulative average particle size and the average thickness of the carbon coating, the ratio of the thickness of the carbon coating in the entire electrode active material needs to be determined, which may play a major role in affecting CPCI, thereby contributing to improving battery performance.

[0104] In an exemplary specific embodiment of the present invention, introducing a carbon coating can endow the electrode active material with conductivity, thereby achieving a lower volume resistance, but the present invention is not limited thereto.

[0105] In an exemplary specific embodiment of the present invention, the carbon coating can cover the entire surface of the electrode active material, and thus favorable effects can be exhibited in terms of stabilizing the activity of the electrode active material through the carbon coating, but the present invention is not limited thereto.

[0106] In an exemplary specific embodiment of the present invention, the carbon coating may contain crystalline carbon. For example, in another exemplary embodiment of the present invention, the carbon coating may be composed of crystalline carbon. For example, the carbon coating may be composed only of crystalline carbon formed by carbonization of a carbon precursor.

[0107] For the electrode binder film according to the first aspect, preferably, the degree of aggregation (AB ) is from 0.3 to 0.9, for example, 0.35 or greater, 0.40 or greater, or 0.50 or greater and 0.88 or less, 0.87 or less, 0.85 or less, 0.83 or less, or 0.80 or less, preferably 0.3 - 0.8, more preferably 0.4 - 0.8. The degree of aggregation of the binder can be determined during the process of manufacturing the electrode binder film. For example, the electrode active material and the binder are mixed, shear force is applied for kneading, and the electrode powder is made into a sheet by roll pressing. In these steps, the degree of fibrillation of the binder affects the degree of aggregation of the binder. By appropriately controlling the mixing conditions, kneading conditions, and film-forming conditions, the desired degree of aggregation of the binder can be achieved.

[0108] When the degree of aggregation of the binder (A B ) is within the above range, it means that when forming the electrode binder film, the degree of fibrillation of the binder is appropriately controlled, and the spacing of the fibrillated binder matrix is also reasonably configured, which can enable the electrode active material to obtain a uniform dispersion effect within the electrode binder film, and physical contact can be achieved between the electrode active materials in the conductive coating, but the present invention is not limited thereto. If the degree of aggregation of the binder is lower than the above range, for example, lower than 0.3, it may mean that the degree of dispersion of the binder is relatively high, and as a result, the contact between the electrode active materials may be insufficient. If the degree of aggregation of the binder is higher than the above range, for example, higher than 0.9, it may mean that the degree of dispersion of the binder is relatively low, and as a result, the mechanical properties of the electrode binder film will decrease.

[0109] In the present invention, the degree of aggregation of the binder (A B ) is defined by the following Equation 2:

[0110] [Equation 2]

[0111] A B = (Number of aggregated binder pixels) / (Total number of binder pixels)

[0112] In the above Equation 2, the number of aggregated binder pixels and the total number of binder pixels are derived by the following method:

[0113] 1) Prepare the target image: For the cross-section of the above-mentioned electrode binder film formed by the ion milling method, a target image with a resolution of 1280×960 or higher is obtained by using BSE (Back Scattered electron) measurement of a field emission scanning electron microscope (FESEM).

[0114] 2) Adjust the contrast level: For the above-mentioned target image, the set contrast level of the electrode active material region is adjusted to the highest contrast level, and the set contrast level of the binder region is adjusted to the lowest contrast level. Each pixel is divided into an active material pixel or a binder pixel, and

[0115] 3) Calculate the percentage of the aggregated region: For the binder pixels, calculate the number of binder pixels aggregated in the aggregated binder region with an area of 3 μm 2 or larger, which is composed of multiple adjacent binder pixels, and calculate the total number of binder pixels in the entire binder region. Then, find the percentage of the number of aggregated binder pixels to the total number of binder pixels.

[0116] As described above, the aggregation degree of the binder can be calculated through a series of processes, including preparing the target image, adjusting the contrast level of the prepared image through an image program, and calculating the proportion of the aggregated region. When calculating the proportion of the aggregated region, the standard for determining the aggregated region can be set to 3 μm 2 or larger. When a region smaller than 3 μm 2 is included in the aggregated region, the contact effect with the active material may not be accurately reflected. Therefore, it is best to define the standard as described above. In addition, when fibrosis proceeds normally and the electrode sheet is normally formed, the aggregated region should generally not be too large. When the longest width of the aggregated region, that is, the maximum width within the region, is greater than 10 μm, this may be regarded as a production defect of the electrode.

[0117] In the present invention, when forming the cross-section of the above-mentioned binder film by an ion milling method, an ion beam of an ion milling machine can be used to irradiate the cross-section of the electrode including the above-mentioned electrode binder film to prepare a sample for field emission scanning electron microscope measurement. The specific ion milling process can refer to the existing method and be carried out according to the usual process conditions.

[0118] In the present invention, after obtaining the cross-section of the electrode binder film, the process of obtaining a target image with a resolution of 1280×960 or higher by using backscattered electron (BSE) measurement of a field emission scanning electron microscope (FESEM) can refer to the existing method and be carried out according to the usual test conditions. For example, the BSE measurement can be carried out using FESEM devices of Jeol company (Jeol7200, Jeol7900, Jeol IT800) or Hitachi company (Su8020, Su8220); regardless of the manufacturer, as long as the FESEM device is equipped with a BSE detector, the measurement can be carried out.

[0119] In the present invention, when adjusting the contrast level of the obtained target image, common image processing methods can be adopted, such as using a commercial image processing program (e.g., Mountains). The set contrast level of the electrode active material region is adjusted to the highest contrast level, and the set contrast level of the binder region is adjusted to the lowest contrast level. By adjusting the contrast, the active material region and the binder region can be clearly distinguished for subsequent processing. Specifically, the set contrast level of the electrode active material region can be adjusted to a value between 25 and 255, and the set contrast level of the binder region can be adjusted to a value greater than or equal to 0 and less than 25. For example, the set contrast level of the electrode active material region is adjusted to 255, and the set contrast level of the binder region is adjusted to 0.

[0120] According to the electrode binder film of the first aspect, the content ratio of the electrode active material to the fibrillated binder can be considered as a factor of CPCI. For example, in CPCI, the ratio of the content of the electrode active material to the content of the binder can be represented by R. Specifically, based on the total weight of the electrode binder film, R can be defined as the ratio of the weight percentage (wt%) of the electrode active material to the weight percentage (wt%) of the binder. Preferably, in the above Equation 1, R is between 16 and 70, between 17 and 66. Specifically, R can be greater than or equal to 19, greater than or equal to 21 or greater than or equal to 24 and can be less than or equal to 60, less than or equal to 50 or less than or equal to 47. When R satisfies the above range, the energy density can be improved by maximizing the active material loading, and CPCI can be satisfied by maximizing the contact area between the aggregation degree of the binder and the active material while diversifying and compounding the conductive paths.

[0121] In the present invention, R is calculated by [(W AM / W B ) x (1 + 2W C )], where W B represents the weight fraction of the binder in the total weight of the electrode binder film, W AM represents the weight fraction of the electrode active material in the total weight of the electrode binder film, and W C is a dimensionless value representing the weight fraction of the conductive material in the total weight of the electrode binder film. Generally, the conductive material makes a great contribution to forming the conductive path, but may be unevenly dispersed, which may indicate that the CPCI value will change according to the addition amount of the conductive material relative to the addition amount of the electrode active material or the binder.

[0122] Specifically, as an adjuvant, the conductive material can improve the resistance by promoting the migration of electrons. However, if the conductive material is not evenly distributed when filling the pores in the electrode, it may inhibit the movement of lithium ions. Therefore, when using a general addition amount, this addition amount may not improve the overall resistance characteristics.

[0123] For the electrode binder film according to the first aspect, preferably, the content of the electrode active material can be between 90 parts by weight and 99 parts by weight relative to the total weight of 100 parts by weight of the electrode binder film. Preferably, it can be 91 parts by weight or more, 92 parts by weight or more, 93 parts by weight or more, 94 parts by weight or more, or 95 parts by weight or more and can be 98.5 parts by weight or less, 98 parts by weight or less, or 97.5 parts by weight or less. When the content of the electrode active material is within the above range, it is ideal from the perspectives of improving the capacity and energy density of the electrode and optimizing the functions of the conductive material and the binder as auxiliary materials, and this can be directly reflected in the weight percentage value in R.

[0124] The content of the fibrillated binder can be between 0.5 parts by weight and 8.0 parts by weight relative to the total weight of 100 parts by weight of the electrode binder film. Preferably, it can be 1.0 parts by weight or more, 1.3 parts by weight or more, 1.5 parts by weight or more, 1.7 parts by weight or more, or 2.0 parts by weight or more and can be 7.0 parts by weight or less, 6.5 parts by weight or less, 6.0 parts by weight or less, 5.5 parts by weight or less, or 5.0 parts by weight or less. When the content of the fibrillated binder is within the above range, it will not cause an increase in resistance or an undesired degree of fibrillation for sheet manufacturing, and this can also be directly reflected in the weight percentage value in R.

[0125] For the electrode binder film according to the first aspect, the electrode binder film includes a trace amount of conductive material or no conductive material. Specifically, it can contain 0.8 parts by weight, 0.7 parts by weight, 0.5 parts by weight, 0.3 parts by weight, 0.1 parts by weight, 0.05 parts by weight, or 0.01 parts by weight of conductive material, and more preferably does not contain conductive material. Even when the conductive material is added at 1 / 10 or even 1 / 100 of the general addition amount or not added, as long as the relationship between the aggregation degree of the above binder, the thickness and average particle size of the carbon coating of the electrode active material, and their appropriate values are controlled, an electrode binder film with excellent conductive path connectivity can be obtained. Ultimately, the resistance characteristics of the battery can be improved, and the capacity can also be increased as the load amount increases.

[0126] For the electrode mixture film according to the first aspect, the electrode active material is not particularly limited as long as it is a commonly used electrode active material. For example, the electrode active material can be a positive electrode active material or a negative electrode active material, and includes a carbon coating on the surface of the active material core.

[0127] For the electrode mixture film according to the first aspect, the electrode mixture film includes an electrode active material containing a carbon coating and a fibrillated binder.

[0128] For the electrode mixture film according to the first aspect, the positive electrode active material is a compound capable of reversibly intercalating and deintercalating lithium, and preferably may include a lithium transition metal compound containing one or more selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe).

[0129] More specifically, the positive electrode active material may include a lithium metal oxide containing lithium and one or more metals (such as cobalt, manganese, nickel, and aluminum). More specifically, the lithium metal oxide may be a lithium manganese-based oxide (e.g., LiMnO 2 、LiMn 2 O 4 etc.), a lithium cobalt-based oxide (e.g., LiCoO 2 etc.), a lithium nickel-based oxide (e.g., LiNiO 2 etc.), a lithium nickel manganese-based oxide (e.g., LiNi 1-Y Mn Y O 2 (where 0 < Y < 1), LiMn 2-Z Ni Z O 4 (where 0 < Z < 2), etc.), a lithium nickel cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O 2 (where 0 < Y1 < 1), etc.), a lithium manganese cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O 2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O 4 (where 0 < Z1 < 2), etc.), a lithium nickel manganese cobalt-based oxide (e.g., Li(Ni p Co q Mn r )O 2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, and p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O 4(where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, and p1 + q1 + r1 = 2), etc., or lithium nickel cobalt transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O 2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of the respective independent elements, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc., and any one or two or more than two of the above compounds.

[0130] In particular, in terms of improving battery capacity and stability, the lithium metal oxide can be LiCoO 2 , LiMnO 2 , LiNiO 2 , lithium nickel manganese cobalt oxide (e.g., Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O 2 , Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2 , Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 , Li(Ni 0.7 Mn 0.15 Co 0.15 )O 2 , Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2 etc.), lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O 2 etc.), or lithium nickel manganese cobalt aluminum oxide (e.g., Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O 2 etc.), lithium iron phosphate (e.g., LiFePO 4 etc.), etc., and any one or two or more than two of the above compounds.

[0131] According to the electrode mixture film of the first aspect, the positive electrode active material (active material core) may include an iron-containing lithium metal phosphate-based compound, particularly may be lithium iron phosphate, and may be represented by the following Chemical Formula 1:

[0132] [Chemical Formula 1]

[0133] Li 1+a Fe 1-x M x PO 4

[0134] In the above Chemical Formula 1, M is at least one element selected from manganese (Mn), cobalt (Co), nickel (Ni), aluminum (Al), magnesium (Mg), and titanium (Ti), and a and x satisfy -0.5 ≤ a ≤ 0.5, 0 ≤ x < 1.

[0135] When the positive electrode active material is a lithium metal phosphate-based compound, particularly lithium iron phosphate, its safety can be guaranteed, but it has a smaller capacity compared to lithium nickel-based oxides. However, according to one aspect of the present invention, a dry electrode with a high active material loading amount can be achieved, so that a lithium secondary battery using lithium iron phosphate can be realized, which has improved safety and increased capacity, and provides superior unit price competitiveness.

[0136] According to the electrode mixture film of the first aspect, the negative electrode active material may include one or a combination of two or more selected from the group consisting of lithium metal, a carbon material capable of reversibly inserting / extracting lithium ions, a metal, or an alloy of these metals and lithium, a metal composite oxide, a material that can be doped or undoped with lithium, and a transition metal oxide.

[0137] As the carbon material capable of reversibly inserting / extracting lithium ions, the carbon-based negative electrode active materials commonly used in lithium secondary batteries can be used without particular limitation. As typical examples, they include crystalline carbon, amorphous carbon, or both. Examples of crystalline carbon can be graphite, such as irregular, planar, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of amorphous carbon can be soft carbon (low-temperature sintered carbon) or hard carbon, mesophase pitch carbide, and calcined coke.

[0138] As the metal or the alloy of these metals and lithium, a metal selected from the group consisting of the following can be used: Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or an alloy of lithium and the selected metal.

[0139] As the metal composite oxide, one selected from the group consisting of the following can be used: PbO, PbO 2 、Pb 2 O3 、 Pb 3 O 4 、 Sb 2 O 3 、 Sb 2 O 4 、 Sb 2 O 5 、 GeO, GeO 2 、 Bi 2 O 3 、 Bi 2 O 4 、 Bi 2 O 5 、 LixFe 2 O 3 (0 ≤ x ≤ 1), LixWO 2 (0 ≤ x ≤ 1), and Sn x Me 1-x Me' y O z (Me is selected from Mn, Fe, Pb, Ge; Me' is selected from Al, B, P, Si, elements of Groups I, II, and III of the periodic table, or halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8).

[0140] The material that may be doped or undoped with lithium may include Si, SiO x (0 < x ≤ 2), Si-Y alloy (where Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof and is not Si), Sn, SnO 2 , and Sn-Y (where Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof and is not Sn), and SiO 2 and a mixture of at least one material. The Y element may be selected from the group consisting of: Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0141] Transition metal oxides may include lithium-containing titanium composite oxides (LTO), vanadium oxides, and lithium vanadium oxides.

[0142] The electrode binder film according to the first aspect, the electrode active material comprising a carbon coating is preferably a positive electrode active material, and the positive electrode active material may include a lithium-based phosphate material. The volume cumulative average particle size of the lithium phosphate material is relatively small, and its powder resistance can be relatively easily reduced by the carbon coating, so it can be optimized to meet the CPCI value.

[0143] In addition, the powder resistance of the electrode active material can be between 1 Ωcm and 100 Ωcm, preferably it can be 2 Ωcm or more, or 3 Ωcm or more and 90 Ωcm or less, 80 Ωcm or less, or 70 Ωcm or less. The powder resistance can indicate that the active material has high conductivity. In the present invention, the electrode active material in the electrode binder film without a conductive material preferably has a powder resistance within the above range. In this case, the powder resistance can be measured by the following method: place 2 grams of active material powder in a ceramic container with a diameter of 22 mm, with four-point probes built into the bottom of the container, and apply a pressure of 2000 kgf (about 50 MPa) to compact the powder, use a commercial powder resistivity meter (for example, HPRM-AM2-L of Hantech), and multiply by the thickness of the compacted active material powder.

[0144] For the electrode binder film according to the first aspect, the fibrillated binder can be obtained by fibrillating any fibrillatable binder. Fibrillation refers to the process of refining and dividing high molecular weight polymers, and these polymers can be commercially available. For example, fibrillation can be carried out by using mechanical shear force or similar methods. The fibrillatable polymer fibers generate a large number of microfibers (fibrils) through surface disintegration, thereby forming a three-dimensional fiber network structure. Non-limiting examples of the fibrillatable binder may include polytetrafluoroethylene (PTFE) and polyolefins. Preferably, the fibrillatable binder includes polytetrafluoroethylene, and particularly preferably, the fibrillatable binder is polytetrafluoroethylene (PTFE). Specifically, the amount of polytetrafluoroethylene can be 60% by weight or more of the total weight of the fibrillatable binder. At the same time, in addition to the above components, the fibrillatable binder may further include polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and / or polyolefin-based binders.

[0145] For the electrode mixture film according to the first aspect, the conductive material used in the electrode mixture film is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, the following conductive materials can be used: carbon black (such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black); carbon fluoride powder; graphite materials (such as natural graphite or artificial graphite with a good crystal structure); fibrous carbon materials (such as carbon fiber, carbon nanotube, or carbon nanofiber), metal fiber; conductive powder (such as aluminum powder and nickel powder); conductive whiskers (such as potassium titanate whiskers); conductive metal oxides (such as titanium oxide); conductive polymers (such as polystyrene derivatives), etc.

[0146] Graphite materials, carbon black, and carbon nanotubes (CNTs) are preferably used to achieve uniform mixing of the conductive materials and improve conductivity.

[0147] For the electrode mixture film according to the first aspect, preferably, the porosity of the electrode mixture film is 29% or less, specifically, it can be between 17 vol% and 29 vol%, preferably 19 vol% or more, or 20 vol% or more, and 29 vol% or less, 27 vol% or less, or 26 vol% or less. When the porosity of the electrode mixture film is within the above range, the electrolyte can achieve good infiltration of the electrode mixture film, thereby improving the service life and output characteristics of the battery, and good energy density can also be obtained.

[0148] In the present invention, the porosity of the electrode mixture film refers to the ratio of the volume of pores in the electrode mixture film to the total volume. The porosity can be expressed in volume %, and can be used interchangeably with terms such as pore ratio, porosity, etc. The porosity can be calculated by the following formula A:

[0149] [Formula A]

[0150] Porosity (%) = {1 - (electrode density / true density)} × 100

[0151] In the above formula A, the true density refers to the density of the electrode mixture film measured by taking a certain size of the electrode mixture film and using a pressing device to press the film until the thickness of the film no longer changes, while the electrode density refers to the density of the electrode mixture film measured by taking a certain size of the electrode mixture film.

[0152] The second aspect of the present invention provides a method for preparing the electrode mixture film of the first aspect above, which is a dry process and includes the following steps:

[0153] Obtaining a material mixture containing an electrode active material, a fibrillatable binder, and an optional conductive material (step S1),

[0154] Knead the material mixture under the application of shear force to form a mixed aggregate (step S2).

[0155] Crush the mixed aggregate to produce an electrode powder mixture (step S3).

[0156] Mold the electrode powder mixture to produce the electrode binder film (step S4).

[0157] The description of the electrode active material and the fibrillatable binder (same as the fibrillatable binder) is the same as above, and thus will not be described in detail. The preparation process of each step will be described below.

[0158] Step S1:

[0159] According to the preparation method of the second aspect of the present invention, in step S1, the constituent components of the electrode binder film (such as the electrode active material, the fibrillatable binder, and optionally, the conductive material) are mixed at a predetermined mixing ratio to obtain a material mixture. In the step of manufacturing the mixture, the mixing for obtaining the mixture should ensure the uniform distribution of the electrode active material, the conductive material, and the fibrillatable binder, and optionally the conductive material. These components are mixed in powder form, so the mixing method is not limited to a specific method and can include various methods capable of simple mixing. However, since this method is used to manufacture a dry electrode without a solvent, the mixing can use a dry mixing process and can be performed by putting these materials into a device such as a blender, a super mixer, or a stirrer.

[0160] In an exemplary specific embodiment of the present invention, the mixing can be performed at 3000 rpm to 20000 rpm in a mixer (such as a stirrer), preferably at 5000 rpm to 15000 rpm. Mixing within the above range can ensure the mixing uniformity of the materials, thereby improving the battery performance. For example, the mixing rate can be 5500 rpm or higher, 6000 rpm or higher, or 6500 rpm or higher, and can be 14000 rpm or lower, 13000 rpm or lower, or 12000 rpm or lower. The mixing can be performed in a stirrer at the same above mixing speed, but can last for 0.5 to 60 minutes, preferably 1 to 30 minutes, 1 to 20 minutes, or 1 to 10 minutes.

[0161] When the mixing process is controlled within the above range, the degree of aggregation of the binder can be affected, so that an appropriate level of aggregation can be obtained. If the degree of aggregation is too low, it may lead to insufficient contact between the electrode active materials and increase the resistance; if the degree of aggregation is too high, it may lead to insufficient mechanical strength of the binder film, resulting in durability problems. Therefore, the mixing process is preferably controlled within the above range, so that an electrode binder film satisfying CPCI can be obtained.

[0162] Step S2:

[0163] According to the preparation method of the second aspect of the present invention, step 2 includes applying a shearing force to the material mixture obtained in step 1 to form mixed aggregates. That is to say, step 2 may be a step of fibrillating the fibrillable binder.

[0164] The fibrillation process can be carried out by commonly used methods such as mechanical grinding or kneading, without particular limitation, and is preferably carried out by high-temperature and low-shear kneading, for example, by stirring equipment such as a twin-screw extruder. Through the process such as kneading, the fibrillable binder will fibrillate, so that the powders of the electrode active material and the conductive material are combined or connected to form mixed aggregates with a solid content of 100%.

[0165] Specifically, the kneading for manufacturing the mixed aggregates can be carried out at a rate of 10 rpm to 100 rpm, preferably at a rate within the range of 20 rpm or higher, 30 rpm or higher, 40 rpm or higher, or 45 rpm or higher and 80 rpm or lower, 70 rpm or lower, or 60 rpm or lower. In addition, the kneading time can be 3 to 60 minutes, preferably 4 minutes or longer, 5 minutes or longer and can be 40 minutes or less, 30 minutes or less, 25 minutes or less, or 20 minutes or less. When the above range is satisfied, it is beneficial to the moderate fibrillation of the binder, so that the battery characteristics can be improved.

[0166] In addition, the amount of the material mixture added during kneading can also be controlled. For example, the added amount of the material mixture discharged from the mixing process can be 50 to 150 volume parts, preferably 60 to 140 volume parts, also 70 to 130 volume parts or 80 to 120 volume parts, relative to the internal volume of the stirring equipment (such as a stirrer). By controlling the amount of the material mixture added during kneading, the degree of fibrillation of the binder can be controlled, so as to control together with the adjustment of the conditions of the kneading process the influence of the binder network structure formed according to the degree of fibrillation of the binder on the contact area of the active material, as well as the degree of aggregation of the binder.

[0167] In addition, kneading can be carried out under high temperature and normal pressure or higher pressure conditions, specifically, under a pressure higher than normal pressure.

[0168] In the step of manufacturing the mixed aggregate, kneading can be carried out in the range between 50°C and 230°C, preferably in the range of 90°C to 200°C, more preferably in the range of 100°C or higher, 110°C or higher, or 120°C or higher and 180°C or lower, 170°C or lower, or 160°C or lower. When kneading is carried out at a low temperature outside the above temperature range, the binder cannot be well fibrillated during kneading, and the caking performance caused by kneading is poor, which makes it difficult to form a film during calendering in subsequent steps. When kneading is carried out at too high a temperature, the fibrillation of the binder occurs rapidly. Subsequently, the formed fibers may break due to excessive shear force. When kneading is carried out within the above high temperature range, the fibrillation of the binder and the formation of agglomerates by kneading can be carried out well, and the rupture of the binder under the action of fibrillation can be appropriately prevented.

[0169] In the step of manufacturing the mixed aggregate, kneading can be carried out under pressure conditions of normal pressure or higher, specifically at a pressure of 1 atm to 3 atm, more preferably at a pressure of 1.1 atm to 3 atm. When kneading is carried out within the above range, the rupture of the binder under the action of fibrillation can be appropriately prevented, and the polymer can be prevented from having too high a density. In the case of kneading under too high a pressure outside the above pressure range, excessive shear force and pressure will be applied, and the formed fibers may break or the density of the mixed aggregate may be too high. When kneading is carried out within the above pressure range, the above problems can be prevented, the rupture of the fibrillated binder can be avoided, and the density of the mixed aggregate can be prevented from being too high.

[0170] In an exemplary specific embodiment of the present invention, kneading can preferably be carried out by high-temperature low-shear kneading under high temperature and pressure conditions equal to or higher than normal pressure, rather than high-shear kneading, whereby the effects to be achieved by the present invention can be achieved.

[0171] By controlling the kneading conditions in step S2, a three-dimensional fiber network structure can be formed in the mixed polymer by the shear force applied to the binder. Since the degree of formation of this structure can affect the aggregation degree of the binder, these conditions can be adjusted as described above.

[0172] Step S3:

[0173] According to the preparation method of the second aspect of the present invention, step S3 is a step of grinding the mixed aggregate to obtain electrode powder.

[0174] The mixed aggregates prepared by kneading can be directly pressed into sheets (e.g., by a calendering process), but in this case, the mixed aggregates need to be pressed under strong pressure and high temperature to form a thin binder film, which may result in an overly high density of the binder film or may not yield a uniform binder film. Therefore, the above-prepared mixed aggregates may need to be pulverized to produce electrode powder.

[0175] The equipment used for pulverization is not particularly limited, but it is preferably pulverized using equipment such as a blender or a mill.

[0176] Specifically, grinding can be carried out at a rate of 1000 rpm to 15000 rpm for a time of 5 seconds to 30 minutes, preferably at a rate of 3000 rpm to 8000 rpm for a time of 30 seconds to 15 minutes. When pulverization is carried out within the above ranges, it can be sufficiently pulverized to prepare powder suitable for forming a binder film, and a large amount of fine powder will not be generated in the polymer. When grinding is performed at too low an rpm or for a short time outside the above ranges, the grinding is not sufficiently carried out, and powder with a size suitable for forming a film cannot be formed. When grinding is performed at too high a rotational speed or for a long time, many fine particles may be formed from the mixed aggregates. When grinding is carried out within the above ranges, it can be sufficiently pulverized to obtain a sufficient grinding effect to obtain powder of an appropriate size, and a large amount of fine particles may not be produced.

[0177] The pulverization process as described above helps to appropriately form a self-standing film in the subsequent film-forming process and can affect all factors influencing CPCI according to the degree of pulverization. Therefore, it is advisable to control this process to meet the above conditions.

[0178] In an exemplary specific embodiment of the present invention, the average particle size of the electrode powder can be between 10 μm and 3000 μm, preferably 50 μm to 1500 μm, and more preferably 100 μm to 700 μm. When the above ranges are met, an electrode binder film with a uniform thickness and density can be formed, and excellent physical properties of the electrode binder film can be obtained.

[0179] In an exemplary specific embodiment of the present invention, although not essential, the electrode powder can further include a filler to inhibit electrode swelling. The filler is not particularly limited as long as it is a fiber material that does not cause chemical changes in the battery. At least one of, for example, olefin-based polymers such as polyethylene and polypropylene; and fiber materials such as glass fiber and carbon fiber can be selected.

[0180] In an exemplary specific embodiment of the present invention, the method may further include sieving the ground electrode powder after manufacturing the electrode powder mixture and before calendering. In the sieving step, the ground electrode powder may be filtered through a sieve (mesh) having an opening of a predetermined size or smaller to obtain an electrode powder having a predetermined size or larger, for example, sieving is performed using a sieve having holes with a size of 1 mm.

[0181] Step S4:

[0182] According to the preparation method of the second aspect of the present invention, step S4 includes hot pressing the electrode powder.

[0183] In an exemplary specific embodiment of the present invention, step S4 may be a process of preparing an electrode binder film in the form of a self-supporting sheet by hot pressing the electrode powder obtained as described above, for example, using a roll pressing unit including two or more pairs of roller wheels in a roll-to-roll process (calendering process, film forming process).

[0184] The roll-to-roll process (calendering process) may include a roll pressing unit, which may be a pair of oppositely arranged rollers, and a plurality of such roller pairs may be continuously arranged in the roll pressing unit. When a plurality of roller wheels are continuously arranged, the temperature and rotation speed ratio (rotation speed ratio of the roller pairs) of each roller wheel may be the same or different.

[0185] In addition, the temperature of the roller wheels may be between 60°C and 120°C, preferably between 70°C and 100°C, and the rotation speed ratio of the roller wheels may be appropriately adjusted independently within the range of 1:1 to 1:10. In addition, the prepared electrode binder film may be put back into the roll pressing unit for hot pressing 1 to 10 times to adjust to an appropriate thickness.

[0186] The film forming process in step S4 may involve forming the electrode powder into an electrode binder film by the heat and pressure applied by the roller wheels in a roll-to-roll process. During this process, the binder may undergo additional shear forces, which further promote fibrillation. The formation and connection of these structures may affect the degree of aggregation of the binder, thereby enabling the control of the above conditions.

[0187] Since it does not include a solvent, the electrode film manufactured as described above has no or almost no fluidity, so it is easy to handle and can be formed into the desired shape for manufacturing various types of electrodes. In addition, when the electrode binder film is used to manufacture an electrode, the drying process for removing the solvent can be omitted, thereby significantly improving the efficiency of the electrode manufacturing process and solving problems generated in the manufacture of dry electrodes, such as granulation of active materials or breakage of fibrillated binders.

[0188] The third aspect of the present invention provides a dry electrode, which includes the above-mentioned electrode mixture film. For example, the dry electrode may include a current collector; and the electrode mixture film provided by the first aspect of the present invention disposed on the current collector.

[0189] For the dry electrode according to the third aspect of the present invention, preferably, the electrode is a positive electrode.

[0190] The dry electrode provided by the present invention can be prepared by laminating the above-mentioned electrode mixture film on at least one surface of the current collector.

[0191] In an exemplary specific embodiment of the present invention, the lamination can attach the electrode mixture film to the current collector by means of roll pressing. The lamination can be carried out by a roll pressing method using a lamination roll, and in this case, the lamination roll can be maintained at a temperature between room temperature (20°C) and 200°C, but is not limited thereto.

[0192] In an exemplary specific embodiment of the present invention, when the dry electrode is a positive electrode, the current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon (sintered carbon), or surface-treated aluminum or stainless steel (treatment materials include carbon, nickel, titanium, silver, etc.) can be used as the current collector.

[0193] In an exemplary specific embodiment of the present invention, when the dry electrode is a negative electrode, the current collector is not particularly limited as long as it has high conductivity and does not cause changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon (sintered carbon), or surface-treated copper or stainless steel (treatment materials include carbon, nickel, titanium, silver, etc.) can be used, and aluminum-cadmium alloys can also be used.

[0194] In an exemplary specific embodiment of the present invention, the thickness of the current collector can be between 3 μm and 100 μm, preferably between 8 μm and 80 μm, but is not limited thereto. In addition, fine irregularities can be formed on the surface of the current collector to improve the adhesion of the mixture film.

[0195] Specifically, the current collector can be wholly or partially coated with a conductive primer to reduce the surface resistance and improve the adhesion. In this case, the conductive primer may contain a conductive material and an adhesive. The conductive material is not limited as long as it has conductivity. For example, it can be a carbon-based material. The adhesive can include fluorine-based adhesives (including PVDF and PVDF copolymers), acrylic-based adhesives, and aqueous adhesives, all of which can be dissolved in solvents.

[0196] A fourth aspect of the present invention provides a lithium secondary battery, which includes the above-mentioned dry electrode, wherein the dry electrode includes an electrode mixture film located on a current collector. For example, the lithium secondary battery may be a secondary battery including a liquid electrolyte or an all-solid-state battery including a solid electrolyte.

[0197] In the lithium secondary battery according to the fourth aspect of the present invention, when the lithium secondary battery is a secondary battery including a liquid electrolyte, a separator may be provided between multiple electrodes in the lithium secondary battery. The separator is used to separate the negative electrode and the positive electrode and provide a movement channel for lithium ions. Any separator commonly used in lithium secondary batteries can be used, and a separator having a high ability to retain the moisture of the electrolyte and a low resistance to the movement of electrolyte ions is particularly preferred. Specifically, a porous polymer film may be used, and the porous polymer film is, for example, a porous polymer film prepared from a polyolefin-based polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or a laminated structure having two or more layers. In addition, a conventional porous non-woven fabric may be used. For example, a non-woven fabric formed from high-melting-point glass fibers or polyethylene terephthalate fibers, etc., but the present invention is not limited thereto. In addition, a coated separator containing a ceramic component or a polymer material may be used to ensure thermal stability or mechanical strength, and a separator having a single-layer structure or a multi-layer structure may be selectively used.

[0198] In addition, when the lithium secondary battery is an all-solid-state battery, the solid electrolyte layer may be designed to perform the function of the separator.

[0199] The electrolyte used in the present invention may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, an inorganic solid electrolyte, an inorganic molten electrolyte, etc. All of these can be used to manufacture lithium secondary batteries, but are not limited thereto.

[0200] Specifically, the electrolyte may include an organic solvent and a lithium salt. Any organic solvent can be used as long as it can serve as a medium for the movement of ions participating in the electrochemical reaction in the battery, without specific restrictions. Specifically, as the organic solvent, ester solvents (such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone) can be used; ether solvents (such as dibutyl ether or tetrahydrofuran); ketone solvents (such as cyclohexanone); aromatic hydrocarbon solvents (such as benzene and fluorobenzene); carbonate solvents (such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC)); alcohol solvents (such as ethanol and isopropanol); nitriles (such as R-CN, where R is a linear, branched, or cyclic C2 to C20 hydrocarbon group, which may contain a double bond aromatic ring or an ether bond); amides (such as dimethylformamide); dioxane solvents (such as 1,3-dioxane); or sulfoxide solvents, etc. Among these solvents, carbonate solvents are preferred, especially a mixture of a cyclic carbonate (such as ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and a linear carbonate compound with low viscosity (such as ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate), which can improve the charge and discharge performance of the battery.

[0201] Any compound can be used as the lithium salt as long as it can provide lithium ions and is used in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from at least one of the following groups: F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , CF 3 CF 2 , SO 3 - , (CF 3 , SO 2 ), 2 , N - , (FSO 2 ), 2 , N - , CF 3 CF 2 (CF 3 ), 2 , CO - , (CF 3 , SO 2 ), 2 , CH - , (SF 5 ), 3 , C- , (CF 3 SO 2 ) 3 C - , CF 3 (CF 2 ) 7 SO 3 - , CF 3 CO 2 - , CH 3 CO 2 - , SCN - and (CF 3 CF 2 SO 2 ) 2 N - . Examples of the lithium salt include LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAlO 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiCl, LiI or LiB(C 2 O 4 ) 2 . The concentration range of the lithium salt can be from 0.1 M to 4.0 M, preferably from 0.5 M to 3.0 M, more preferably from 1.0 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, thus exhibiting excellent performance, and lithium ions can also move effectively.

[0202] In addition to the above electrolyte components, the electrolyte may further contain one or more types of additives, such as fluoroolefin carbonate-based compounds (e.g., vinylene difluoride carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-ethylene glycol dimethyl ether (glyme), hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum chloride, to enhance the battery life, inhibit the decline of battery capacity, improve the battery discharge capacity, etc. In this case, the additive may be added in an amount of 0.1 wt% to 10.0 wt% based on the total weight of the electrolyte.

[0203] The detailed structure of the secondary battery is well-known and will not be described herein.

[0204] In addition, the above lithium secondary battery can stably exhibit excellent discharge capacity, output characteristics, and capacity retention ability, and thus is applicable to mobile devices such as mobile phones, laptop computers, and digital cameras, as well as the field of electric vehicles such as hybrid electric vehicles (HEV).

[0205] Therefore, according to another aspect of the present invention, there are provided a battery module including a lithium secondary battery as a unit cell, and a battery pack including the battery.

[0206] The battery module or battery pack can be used as a power source for one or more medium and large-sized devices, for example, power tools, electric vehicles (such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV)), or power storage systems.

[0207] Hereinafter, the present disclosure will be described in more detail by way of examples. However, the following examples are provided to describe the present invention by way of illustration, and the scope of the present invention is not limited thereto.

[0208] Examples 1-8 and Comparative Examples 1-8:

[0209] Prepare an electrode mixture film:

[0210] (1) Put LFP as the positive electrode active material, polytetrafluoroethylene (PTFE) as the binder, and the conductive material (the mass ratios of the three are shown in Table 1) into a blender, and stir and mix at a stirring speed of 10,000 rpm (the stirring and mixing time is shown in Table 1) to obtain a mixture;

[0211] (2) Stabilize the temperature of the kneader at 150 °C and control the pressure at 1.1 atm. Put the above mixture into the kneader, and then knead at a speed of 50 rpm (the blending time is shown in Table 1) to obtain a mixed aggregate;

[0212] (3) Put the mixed aggregates into a blender and grind them at a stirring speed of 10,000 rpm for 40 seconds, and then classify them with a sieve having a pore size of 1 mm to obtain the powder for the electrode.

[0213] (4) Put the manufactured powder for the electrode into a laboratory calender (roll diameter: 88 mm, roll temperature: 100 °C, roll speed: 20 rpm) to manufacture a self-standing electrode mixture film.

[0214] Preparation of dry electrode:

[0215] Set two pieces of the above self-standing electrode mixture films on both sides of an aluminum foil (thickness 15 μm) having a conductive primer layer, and laminate them by a roll press maintained at 150 °C to manufacture a dry electrode.

[0216] Preparation of secondary battery:

[0217] Use the above dry electrode to make the positive electrode, and manufacture the negative electrode with artificial graphite as the active material (the mass ratio of artificial graphite, CMC and SBR as the binder, and carbon black as the conductive material in the negative electrode is 96.7:2.8:0.5). The loading amount of the negative electrode active material layer is 277 mg / 25 cm 2 , the thickness is 67 μm, and the negative electrode current collector uses a copper foil with a thickness of 10 μm.

[0218] Assemble the positive electrode, negative electrode and porous polyethylene separator by the winding method, and inject an electrolyte into the assembled battery to manufacture a lithium secondary battery;

[0219] Among them, the electrolyte is a mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC = 3:7, volume ratio), and LiPF 6 (1.0 M) is added as the lithium salt.

[0220] Charge the lithium secondary battery at a charging rate of 0.1C to 3.6V, and then discharge it to 2.5V to carry out the formation process.

[0221] Some process parameters for preparing the electrode mixture film in Examples 1-8 and Comparative Examples 1-8 are shown in Table 1.

[0222] Table 1

[0223]

[0224] In Table 1, S20, SF-17, and M121 are LFP produced by Changzhou Lithium Source, Huayou, and ALEEES respectively. The conductive materials in Comparative Examples 7 and 8 are carbon black, Denka, and Li-400.

[0225] Measurement of the aggregation degree of the binder:

[0226] The degree of polymerization of the adhesives in the examples and comparative examples was obtained by the following method:

[0227] 1) For the cross-section of the electrode binder film, a target image with a resolution of 1280×960 or higher was obtained by measuring backscattered electrons (BSE) using a field emission scanning electron microscope (FESEM, Hitachi, Su8020);

[0228] 2) The contrast of the target image was adjusted using a commercial image processing program Mountains, where the contrast of the active material region was adjusted to the highest contrast, while the contrast of the binder region was adjusted to the lowest contrast, and then it was divided into binder pixels or active material pixels;

[0229] 3) For the binder pixels, calculate the number of aggregated binder pixels, that is, in an aggregated binder region with an area of 3 μm 2 or larger, the number of aggregated binder pixels in the binder region formed by multiple adjacent binder pixels, and calculate the total number of binder pixels in the entire binder region, so as to obtain the aggregation degree A of the binder using the following equation (Equation 2) B :

[0230] A B =(Number of aggregated binder pixels) / (Total number of binder pixels)

[0231] The porosity is measured according to the following formula A:

[0232] Formula A:

[0233] Porosity (%) = {1 - (electrode density / true density)} × 100

[0234] In the above Formula A, the true density refers to the density of the electrode binder film measured by taking a certain size of the electrode binder film and pressing the film using a pressing device until the thickness of the film no longer changes, while the electrode density refers to the density of the electrode binder film measured by taking a certain size of the electrode binder film.

[0235] Testing of relevant parameters of the dry electrode:

[0236] The CPCI calculated value was obtained according to Equation 1: CPCI = A B ×R×(T C / D AM );

[0237] In Equation 1, A B is the aggregation degree of the binder in the electrode binder film,

[0238] DAM is the volume cumulative average particle size D of the electrode active material 50 , with the unit of μm,

[0239] T C is the average thickness of the carbon coating, with the unit of μm,

[0240] R is calculated by [(W AM / W B ) × (1 + 2W C ), where:

[0241] W B represents the weight fraction of the binder in the total weight of the electrode binder film, with the unit of %,

[0242] W AM represents the weight fraction of the electrode active material in the total weight of the electrode binder film, with the unit of %,

[0243] W C is a dimensionless value representing the weight fraction of the conductive material in the total weight of the electrode binder film.

[0244] The relevant parameters of the dry electrodes of Examples 1 - 8 and Comparative Examples 1 - 8 are shown in Table 2.

[0245] Table 2

[0246]

[0247]

[0248] Testing of the physical properties of the dry electrode:

[0249] 1. Tensile strength (MPa):

[0250] In the examples and comparative examples, before laminating with the current collector, a 50 mm (MD) × 10 mm (TD) binder film was sampled, and according to the standard of ASTM 638, under the conditions of a preload of 0.01 kgf / cm and a speed of 50 mm / min, it was measured using a UTM device (ZwickRoell) to obtain the maximum force value applied before the sample broke.

[0251] 2. Powder resistivity (Ωcm):

[0252] The powders of the electrodes prepared in the examples and comparative examples were put into a cylindrical container, with an input amount of 2.0 g. Then, while gradually increasing the pressure with a press for measuring pressure, the surface resistance of the electrode powder was measured using a powder resistance meter (HPRM - AM2 - L, Hantech), and the volume of the electrode powder decreasing with the increase in pressure was measured. When the packing density reached 2.3 g / cc, the powder resistance of the electrode powder was measured.

[0253] 3. Interface Resistance (Ωcm 2 ):

[0254] After cutting the dry electrodes prepared in the examples and comparative examples into a size of 100 mm × 100 mm, a current of 100 μA was applied to the dry electrodes using the MP resistance measurement method, and the resistance value between the electrode binder film and the current collector layer was measured by the potential difference measured between 46 probes, which is the interface resistance.

[0255] The test results of the physical property parameters of the dry electrodes of Examples 1-8 and Comparative Examples 1-8 are shown in Table 3.

[0256] Table 3

[0257]

[0258] It can be seen from Table 3 that in Examples 1 to 8, the aggregation degree of the binder was well controlled according to the amount of the binder, and there was no significant decrease in the tensile strength during the film formation process. At the same time, although no conductive material was added, the interface resistance of the electrode remained at a satisfactory level. However, in Comparative Example 1, since the CPCI value was not controlled, for example, the amount of the binder was low but the aggregation degree of the binder increased significantly, so there was no significant improvement in terms of resistance. At the same time, the tensile strength of the binder film was too low, resulting in process defects and appearance defects during the film formation process compared with the examples; while in Comparative Example 2, the aggregation degree of the binder was too low, and poor mechanical properties were also shown, which may lead to the same problems. By analyzing other comparative examples, it can be seen that: to meet the mechanical properties and resistance properties, the factors related to CPCI need to be comprehensively controlled, rather than simply controlling the amount or aggregation degree of the binder alone.

[0259] Performance testing of the lithium secondary battery:

[0260] 1. Battery Resistance (mΩ):

[0261] After charging and discharging the lithium secondary battery, it was recharged and discharged again. At the same time, according to the change of SOC, a pulse current of 2.5C was applied within a specific time, and the pulse resistance (battery internal resistance at 0.1 second) was measured.

[0262] 2. Discharge Capacity (mAh):

[0263] The capacity measured by charging the lithium secondary battery in the CCCV mode at a constant current of 0.2C to 3.6V (the termination current is 1 / 20C) and then discharging it at a constant current of 0.2C to 2.5V is called the low-rate discharge capacity, while the capacity measured by discharging it at a constant current of 2.0C to 2.5V is called the high-rate discharge capacity.

[0264] 3. High / Low Discharge Capacity Ratio:

[0265] It is calculated as (High-rate Discharge Capacity ÷ Low-rate Discharge Capacity) × 100%.

[0266] The performance test data of the lithium secondary batteries prepared in Examples 1-8 and Comparative Examples 1-8 are shown in Table 4.

[0267] Table 4

[0268]

[0269] It can be seen from Table 4 that Examples 1 to 8 do not contain conductive materials. Therefore, the processability is significantly improved by omitting the conductive material dispersion process, and at the same time, it remains at a satisfactory level compared with the comparative examples in terms of battery resistance and discharge capacity.

[0270] In addition, it is determined that even without the inclusion of conductive materials, the ratio of the high-rate discharge capacity to the low-rate discharge capacity of Examples 1 to 8 is not low, indicating that their output performance is satisfactory. Although Comparative Examples 7 and 8 contain conductive materials, their high / low discharge capacity ratios are lower than those of the examples. Although they exhibit superior battery resistance characteristics, their output performance based on the overall battery resistance performance is poor.

[0271] Especially in Examples 1-3, 7 and Comparative Examples 3, 5 and 6, the amount of the active material is 97 parts by weight. Similar capacity characteristics and output are observed, but the battery resistance is poor, indicating poor lithium ion mobility, which means that there will be differences in the fast charging performance ultimately.

[0272] In addition, in Example 5 and Comparative Example 7, the amount of the active material is 96 parts by weight. Although there are differences in battery resistance, the capacity characteristics are superior. In terms of electrode performance, the tensile strength of the binder film in Comparative Example 7 is about half of that in Example 5, which may affect the binder film forming process, and the defect rate of the formed binder film will be significantly higher. When comparing Example 6 and Comparative Example 8, the amount of the active material in both is 95 parts by weight, and the same trend is also observed.

[0273] That is to say, when the CPCI value of the present invention cannot be satisfied, the tensile strength of the binder film is poor, so the binder film forming cannot proceed normally, or even if normal electrode manufacturing is achieved, the battery resistance is high, or at least one of the capacity characteristics or output characteristics is poor; while when the CPCI value is satisfied, the processability, capacity and output characteristics during the manufacturing process can be guaranteed without using conductive materials.

Claims

1. An electrode mixture film, comprising: Electrode active materials and fiberized binders, The electrode active material comprises an active material core and a carbon coating disposed on the surface of the active material core; The CPCI defined by the following equation 1 is 0.09 to 0.45, [Equation 1] CPCI=A B ×R×(T C / D AM ) In the above equation 1, A B is the degree of aggregation of the binder in the electrode mixture film, D AM is the volume cumulative average particle size D of the electrode active material 50 , in μm, T C is the average thickness of the carbon coating in μm, R by [(W AM / W B )×(1+2W C )], where: W B It indicates the weight fraction of the binder in the total weight of the electrode mixture film, in %, W AM It indicates the weight fraction of electrode active material in the total weight of electrode mixture film, in %, W C It is a dimensionless value representing the weight fraction of the conductive material in the total weight of the electrode mixture film.

2. The electrode mixture film according to claim 1, wherein: The degree of aggregation of the binder is defined by the following equation 2: [Equation 2] A B = (number of aggregated adhesive pixels) / (total number of adhesive pixels) In Equation 2 above, the number of aggregated adhesive pixels and the total number of adhesive pixels are derived as follows: 1) For a cross section of the electrode mixture film formed by the ion milling method, a target image with a resolution of 1280×960 or higher is obtained by BSE measurement using a field emission scanning electron microscope, 2) For the above target image, the set contrast of the electrode active material area is adjusted to the highest contrast, the set contrast of the binder area is adjusted to the lowest contrast, and each area is divided into active material pixels or binder pixels, and 3) For adhesive pixels, calculate the area at 3μm 2 or a larger range, the number of aggregated adhesive pixels in an aggregated adhesive region consisting of a plurality of adjacent adhesive pixels, and calculating the total number of adhesive pixels in the entire adhesive region.

3. The electrode mixture film according to claim 1, wherein: The volume cumulative average particle size D of the electrode active material 50 0.1μm to 5.0μm.

4. The electrode mixture film according to claim 1, wherein: The average thickness of the carbon coating of the electrode active material is related to the volume cumulative average particle size D of the electrode active material. 50 The ratio is 0.0002 to 0.

1.

5. The electrode mixture film according to claim 1, wherein: The degree of aggregation of the binder is 0.3 to 0.

9.

6. The electrode mixture film according to claim 1, wherein: In the above equation 1, R is 16 to 70.

7. The electrode mixture film according to claim 1, wherein: The active material core comprises at least one component selected from the following group: lithium manganese-based oxide, lithium nickel-based oxide, lithium nickel manganese-based oxide, lithium nickel cobalt-based oxide, lithium manganese cobalt-based oxide, lithium nickel manganese cobalt-based oxide, lithium nickel cobalt transition metal oxide, and lithium metal phosphate-based compound.

8. The electrode mixture film according to claim 1, wherein: The active material core includes a lithium metal phosphate-based compound represented by the following Chemical Formula 1: Chemical formula 1: Li 1+a Fe 1-x M x PO4 In the above Chemical Formula 1, M is at least one selected from the group consisting of Mn, Co, Ni, Al, Mg and Ti, and a and x satisfy -0.5≤a≤0.5, 0≤x<1.

9. The electrode mixture film according to claim 1, wherein: The binder includes polytetrafluoroethylene.

10. The electrode mixture film according to claim 1, wherein: The electrode mixture film comprises 92 to 99.5 parts by weight of an electrode active material and 0.5 to 8 parts by weight of a fiberized binder, and does not comprise a conductive material.

11. The electrode mixture film according to claim 1, wherein: The porosity of the electrode mixture film is less than 29%.

12. The electrode mixture film according to claim 1, wherein: The powder resistance of the electrode active material is 1 Ωcm to 100 Ωcm.

13. A dry electrode, comprising a current collector; and the electrode mixture film according to claim 1 disposed on the current collector.

14. The dry electrode according to claim 13, wherein: The electrode is a positive electrode. 15 . A lithium secondary battery comprising a plurality of electrodes, at least one of the electrodes comprising the dry electrode according to claim 13 or 14 . 16 . An electric device comprising the lithium secondary battery according to claim 15 .

Images