Patent Application
20240266542
The present disclosure relates to a conductive material master batch for use in a dry electrode, a method for preparing the same, and an electrode obtained by using the same.
Due to a rapid increase in use of fossil fuel, there has been an increasing need for use of substitute energy and clean energy. The most actively studied field as a part of attempts to meet such a need is the field of power generation and power storage using electrochemistry.
Currently, typical examples of electrochemical devices using electrochemical energy include secondary batteries, and application thereof has been extended gradually.
A lithium secondary battery as a representative of such secondary batteries has been used not only as an energy source of mobile instruments but also as a power source of electric vehicles and hybrid electric vehicles capable of substituting for vehicles, such as gasoline vehicles and diesel vehicles, using fossil fuel and regarded as one of the main causes of air pollution, recently. In addition, application of such a lithium secondary battery has been extended even to a supplementary power source of electric power through the formation into a grid.
A process of manufacturing such a lithium secondary battery is broadly divided into an electrode-forming step, an electrode assembly-forming step and an aging step. The electrode-forming step is further divided into an active material-mixing step, an electrode-coating step, a drying step, a pressing step, a slitting step, a winding step, or the like.
Among the steps, the active material-mixing step is a step of mixing the coating ingredients for forming an electrode active layer configured to carry out electrochemical reactions actually in the electrode. Particularly, an electrode active material as an essential element of the electrode is mixed with other additives, including a conductive material, a filler, a binder used for the binding of powder particles among themselves and the adhesion to a current collector, a solvent for imparting viscosity and dispersing powder, or the like, to prepare a slurry having flowability. Such a composition mixed for forming an electrode active layer is also called an electrode mixture in a broad sense.
Then, an electrode-coating step of applying the electrode mixture onto a current collector having electrical conductivity and a drying step of removing the solvent contained in the electrode mixture are carried out, and then the resultant electrode is pressed to a predetermined thickness.
Meanwhile, as the solvent contained in the electrode mixture evaporates during the drying step, defects, such as pinholes or cracks, may be generated in the preliminarily formed electrode active layer. In addition, the active layer is not dried uniformly at the internal part and external part thereof, and thus a powder floating phenomenon may occur due to a difference in solvent evaporation rate. In other words, a powder present in a portion dried earlier may float, while forming a gap from a portion dried relatively later, resulting in degradation of electrode quality. Therefore, recently, active studies have been conducted to manufacture a dry electrode without using any solvent.
In general, the dry electrode is obtained by laminating a free standing-type film, including an active material, a binder and a conductive material and prepared in the form of a film, onto a current collector. To improve the workability of a dry electrode, there has been developed a method for preparing a powder mixture through the steps of mixing, kneading and pulverizing starting materials for a dry electrode, including an activated carbon conductive material, an active material, a binder, or the like. Herein, as the BET specific surface area of the conductive material is increased, it is more difficult to disperse the conductive material homogeneously. Therefore, there are problems in that the content of the conductive material is increased as compared to a wet electrode, and carbon nanotubes (CNTs) having a large specific surface area cannot be used efficiently.
Under these circumstances, there has been continuous research and development to improve the dispersibility of a conductive material and to improve the performance of a dry electrode obtained by using the conductive material.
The present disclosure is designed to solve the problems of the related art, and therefore the present disclosure is directed to providing a conductive material master batch for use in manufacturing a dry electrode and a method for preparing the same.
The present disclosure is also directed to providing a dry electrode obtained by using, as a conductive material, a conductive material master batch showing improved dispersibility of a conductive material, and a method for manufacturing the same.
One aspect of the present disclosure is directed to providing a conductive material master batch in which the dispersibility of a conductive material having a large BET specific surface area is improved, and a method for preparing the same. The present disclosure is also directed to providing a conductive material master batch in which a high content of conductive material is contained stably, and a method for preparing the same.
Another aspect of the present disclosure is directed to providing an electrode which uses, as a conductive material, a conductive material master batch showing improved dispersibility of a conductive material having a large BET specific surface area, and thus has a reduced content of conductive material and provides improved electrode resistance characteristics, and a method for manufacturing the same. The present disclosure is also directed to providing an electrode having improved electrode resistance characteristics, while maintaining excellent mechanical properties, such as tensile strength, and a method for manufacturing the same.
Still another aspect of the present disclosure is directed to providing a method for manufacturing an electrode which can provide an electrode with improved flexibility and mechanical properties by minimizing fine division of an active material and maximizing fibrilization of a binder.
In one aspect of the present disclosure, there is provided a conductive material master batch according to any one of the following embodiments.
According to some embodiments of the present disclosure, there is provided a conductive material master batch including a conductive material, a polyvinylidene fluoride (PVDF)-based binder, and a polytetrafluoroethylene (PTFE) binder, wherein the conductive material has a BET specific surface area of 80 m2/g or more, and each of the PVDF-based binder and the PTFE binder independently has a crystallization degree of 30% or less.
According to some embodiments of the present disclosure, there is provided the conductive material master batch, wherein the conductive material includes carbon nanotubes alone, or carbon nanotubes and a dot-like conductive material.
According to some embodiments of the present disclosure, there is provided the conductive material master batch, wherein the electrode conductive material includes carbon nanotubes and a dot-like conductive material, and the dot-like conductive material is carbon black, activated carbon, graphite, or a mixture of two or more of them.
According to some embodiments of the present disclosure, there is provided the conductive material master batch, wherein the weight ratio of the carbon nanotubes to the dot-like conductive material is 100:0-10:90.
According to some embodiments of the present disclosure, there is provided the conductive material master batch, wherein the carbon nanotubes are dispersed in the form of nanofibers.
According to some embodiments of the present disclosure, there is provided the conductive material master batch, wherein the carbon nanotubes have a diameter of 0.1-50 nm.
According to some embodiments of the present disclosure, there is provided the conductive material master batch, wherein the PVDF-based binder includes PVDF, polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) or a mixture thereof.
According to some embodiments of the present disclosure, there is provided the conductive material master batch, which includes 20-70 parts by weight of the conductive material, 5-60 parts by weight of the PVDF-based binder and 0.1-50 parts by weight of the PTFE binder.
In another aspect of the present disclosure, there is provided an electrode according to any one of the following embodiments.
According to some embodiments of the present disclosure, there is provided an electrode including:
According to some embodiments of the present disclosure, there is provided the electrode, wherein the content of the electrode conductive material is 1 wt % or less based on the total weight of the electrode active material layer.
According to some embodiments of the present disclosure, there is provided the electrode, wherein the electrode binder has a crystallization degree of 15% or less.
According to some embodiments of the present disclosure, there is provided the electrode, wherein the content of the electrode active material is 95 wt % or more based on the total weight of the electrode active material layer.
According to some embodiments of the present disclosure, there is provided the electrode, wherein the electrode conductive material includes a carbonaceous material having a BET specific surface area of 80 m2/g or more.
According to some embodiments of the present disclosure, there is provided the electrode, wherein the electrode conductive material includes carbon nanotubes alone, or carbon nanotubes and a dot-like conductive material.
According to some embodiments of the present disclosure, there is provided the electrode, wherein the electrode conductive material includes carbon nanotubes and a dot-like conductive material, and the dot-like conductive material is carbon black, activated carbon, graphite, or a mixture of two or more of them.
According to some embodiments of the present disclosure, there is provided the electrode, wherein the weight ratio of the carbon nanotubes to the dot-like conductive material is 100:0-10:90.
According to some embodiments of the present disclosure, there is provided the electrode, wherein the electrode conductive material and the electrode binder include those derived from the conductive material master batch.
In still another aspect of the present disclosure, there is provided a method for preparing a conductive material master batch according to any one of the following embodiments.
According to some embodiments of the present disclosure, there is provided a method for preparing a conductive material master batch, including the steps of:
According to some embodiments of the present disclosure, there is provided the method for preparing a conductive material master batch, wherein the step of preparing a mixture is carried out by mixing the ingredients at 200-1,700 rpm for 1-30 minutes.
According to some embodiments of the present disclosure, there is provided the method for preparing a conductive material master batch, wherein the step of forming an extrudate is carried out by introducing the mixture to a twin screw extruder and melt kneading the mixture at an extrusion temperature of 100-300° ° C. at a screw speed of 50-600 rpm to perform extrusion of the mixture through a die.
According to some embodiments of the present disclosure, there is provided the method for preparing a conductive material master batch, wherein the pulverization is carried out at 500-20,000 rpm for 5 seconds to 10 minutes.
In still another aspect of the present disclosure, there is provided a method for manufacturing an electrode according to any one of the following embodiments.
According to some embodiments of the present disclosure, there is provided a method for manufacturing an electrode, including the steps of:
According to some embodiments of the present disclosure, there is provided the method for manufacturing an electrode, wherein the step of forming an electrode active material layer includes the steps of:
According to some embodiments of the present disclosure, there is provided the method for manufacturing an electrode, wherein the first binder has a crystallization degree of 30% or less.
According to some embodiments of the present disclosure, there is provided the method for manufacturing an electrode, wherein the mixture film has a tensile strength of 0.2 MPa or more.
According to some embodiments of the present disclosure, there is provided the method for manufacturing an electrode, wherein the resultant electrode has an electrode resistance of 55 ohm·cm or less.
In yet another aspect of the present disclosure, there is provided an electrochemical device according to the following embodiment.
According to some embodiments of the present disclosure, there is provided an electrochemical device including a positive electrode, a negative electrode and a separator layer interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is the electrode.
According to some embodiments of the present disclosure, it is possible to provide a conductive material master batch which uses a conductive material having a large BET specific surface area and shows excellent adhesion to an active material in manufacturing an electrode. In addition, the conductive material master batch according to some embodiments of the present disclosure can provide an effect of significantly improving the dispersibility of a conductive material having a large BET specific surface area.
According to another aspect of the present disclosure, it is possible to provide an electrode showing a reduced resistance, particularly, reduced electrode resistance. Particularly, the electrode according to an aspect of the present disclosure is one (i.e. a dry electrode) using no solvent during the manufacture thereof. Therefore, it is possible to provide a dry electrode using a reduced content of conductive material as compared to a conventional dry electrode, and thus having an increased content of electrode active material.
According to still another aspect of the present disclosure, it is possible to provide a dry electrode which shows an improved electrode resistance and improved electrode film strength, and thus has excellent electrical performance and improved stability, as well as to provide an electrochemical device using the dry electrode.
According to still another aspect of the present disclosure, it is possible to provide a dry electrode, which minimizes fine division of an electrode active material, maximizes fibrilization of a binder and minimizes cutting of a fibrilized binder, by introducing a process including a high-temperature low-shear kneading step, followed by pulverizing, instead of a high-shear mixing process.
Further, it is possible to provide a method for manufacturing an electrode which does not use a high-shear jet-milling step but uses a kneading step through a kneader and a pulverization step to avoid the problem of the blocking of a flow path caused by aggregation of the ingredients forming the electrode, and thus is favorable to mass production of electrodes.
The accompanying drawings illustrate a preferred embodiment of the present disclosure and together with the foregoing disclosure, serve to provide further understanding of the technical features of the present disclosure, and thus, the present disclosure is not construed as being limited to the drawing.
Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.
The present disclosure relates to a conductive material master batch for use in a dry electrode obtained by pressurizing a mixed powder for an electrode, an electrode obtained by using the same, a method for preparing the conductive material master batch and a method for manufacturing the electrode.
According to the present disclosure, the dry electrode may be used as an electrode for an electrochemical device, such as a lithium-ion secondary battery, but the use according to the present disclosure is not limited thereto.
According to the present disclosure, the term ‘BET specific surface area’ refers to a specific surface area determined by the BET method, wherein the BET specific surface area is a value calculated from the nitrogen gas adsorption at the temperature (77K) of liquid nitrogen measured by using TriStar II 3020 system available from Micromeritics Instruments Corporation.
As used herein, the term ‘melting point’ refers to a value measured by a conventional method for measuring the melting point (Tm) of a polymer. For example, the melting point may be measured by using a differential scanning calorimeter (DSC).
As used herein, the term ‘crystallization degree’ is a measure for predicting the kneadability and fibrilization degree of a polymer, and may be determined by using a differential scanning calorimeter (DSC), or the like.
As used herein, the term ‘diameter (D50)’ means the particle diameter at the point of 50% in the particle volume accumulated distribution as a function of particle diameter. The particle diameter may be determined by using the laser diffraction method. Particularly, a material to be analyzed is dispersed in a dispersion medium and introduced to a commercially available laser diffraction particle size analyzer (e.g. Microtrac S3500) to measure a difference in diffraction pattern depending on particle size, when the particles pass through laser beams, and then particle size distribution can be calculated. Then, D50 may be determined by calculating the particle diameter at the point of 50% in the particle volume accumulated distribution depending on particle diameter in the analyzer system.
As used herein, the term ‘CNT dispersibility’ refers to the property of CNT dispersing in the form of nanofibers without clumping into bundles. For example, the CNT dispersibility may be evaluated by the method of SEM shape analysis.
In one aspect of the present disclosure, there is provided a conductive material master batch which allows application of a conductive material having a large BET specific surface area to a dry electrode.
The conductive material master batch according to an aspect of the present disclosure includes a conductive material, a polyvinylidene fluoride (PVDF)-based binder, and a polytetrafluoroethylene (PTFE) binder, wherein the conductive material has a BET specific surface area of 80 m2/g or more, and each of the PVDF-based binder and the PTFE binder independently has a crystallization degree of 30% or less.
According to the present disclosure, the conductive material has a BET specific surface area of 80 m2/g or more. When using such a conductive material having a BET specific surface area of 80 m2/g or more, it is possible to reduce the content of the conductive material and to increase the content of an active material, thereby accomplishing a function of increasing the capacity of a dry electrode, but the function of the conductive material is not limited thereto.
According to an aspect of the present disclosure, the conductive material is not particularly limited, as long as it has a BET specific surface area of 80 m2/g or more and has conductivity, while not causing any chemical change in the corresponding battery. Particular examples of the conductive material include: graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, ketjen black, channel black, furnace black, lamp black or thermal black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbon; metal powder, such as aluminum or nickel powder; conductive whisker, such as zinc oxide or potassium titanate; conductive metal oxide, such as titanium dioxide; conductive material, such as a polyphenylene derivative; or the like. Particularly, with a view to homogeneous mixing of the conductive material and improvement of the conductivity, the conductive material may be carbon nanotubes, activated carbon, graphite, carbon black or a mixture thereof.
According to some embodiments of the present disclosure, the conductive material may include carbon nanotubes alone.
According to other embodiments of the present disclosure, the conductive material may include carbon nanotubes and a dot-like conductive material. According to some embodiments of the present disclosure, the dot-like conductive material may include carbon black, activated carbon, graphite, or a mixture of two or more of them.
According to still other embodiments of the present disclosure, the conductive material may include carbon nanotubes and a dot-like conductive material at a weight ratio of 100:0-10:90. Herein, when the weight ratio of the carbon nanotubes to the dot-like conductive material is 100:0, it means that the conductive material includes carbon nanotubes alone.
According to still other embodiments of the present disclosure, the conductive material may include carbon nanotubes and a dot-like conductive material, and the weight ratio of the carbon nanotubes to the dot-like conductive material may be 99:1-50:50.
According to still other embodiments of the present disclosure, when the conductive material includes carbon nanotubes, the carbon nanotubes may be dispersed in the form of nanofibers by the PVDF-based binder and the PTFE binder in the conductive material master batch.
Particularly, according to some embodiments of the present disclosure, the conductive material may have a BET specific surface area of 80-2,000 m2/g. More particularly, the conductive material may have a BET specific surface area of 100 m2/g or more, 150 m2/g or more, 160 m2/g or more, 500 m2/g or more, 1,000 m2/g or more, 2,000 m2/g or less, 1,500 m2/g or less, 1400 m2/g or less, 300 m2/g or less, 250 m2/g or less, or 210 m2/g or less. According to other embodiments of the present disclosure, the conductive material may include carbon nanotubes having a BET specific surface area of 80-300 m2/g and a dot-like conductive material having a BET specific surface area of 100-2,000 m2/g. When the conductive material has the above-defined range of specific surface area, there is an advantageous effect in terms of the dispersion stability of the conductive material in the conductive material master batch, but the scope of the present disclosure is not limited thereto.
According to still other embodiments of the present disclosure, when the conductive material includes carbon nanotubes, the carbon nanotubes may have a diameter of 0.1-50 nm, 1-30 nm, 5-25 nm, 10-20 nm, or 10-15 nm. As used herein, the diameter of carbon nanotubes refers to a value of diameter measured at the cross-section orthogonal to the longitudinal direction of carbon nanotubes. For example, the diameter may be determined by observing the carbon nanotubes with an electronic microscope, such as a scanning electron microscope (SEM). When the diameter of carbon nanotubes falls within the above-defined range, it is possible to realize an advantageous effect in terms of CNT dispersibility, but the scope of the present disclosure is not limited thereto.
The conductive material master batch according to some embodiments of the present disclosure includes a PVDF-based binder and a PTFE binder, in combination with the conductive material.
According to some embodiments of the present disclosure, the conductive material master batch includes a PVDF-based binder as a binder, and thus can realize an advantageous effect in terms of improvement of the binding force with the conductive material. In this manner, it is possible to reduce the content of the binder in the conductive material master bath and to increase the content of conductive material, but the function of the PVDF-based binder is not limited thereto.
According to some embodiments of the present disclosure, the conductive material master batch may be used for a dry electrode in which a dry film is formed through a binder fibrilization process. Herein, when the conductive material master batch includes the PTFE binder, it is possible to realize an advantageous effect in terms of the formation of an electrode film through a binder fibrilization process, but the function of the PTFE binder is not limited thereto.
According to some embodiments of the present disclosure, the conductive material master batch includes the PVDF-based binder and the PTFE binder, and thus can provide excellent binding force with the conductive material and can realize an effect of improving the dispersibility of the conductive material having a high specific surface area. Further, when forming an electrode film by using the conductive material master batch through a binder fibrilization process, it is possible to form an electrode film stably and to realize an electrode having a low electrode resistance, but the mechanism of the present disclosure is not limited thereto.
According to some embodiments of the present disclosure, the PVDF-based binder may include a PVDF-based binder having a melting point of 200° C. or lower. When the PVDF-based binder used herein is a PVDF-based binder having a melting point of 200° C. or lower, it is possible to improve the dispersibility and dispersion stability of the conductive material in a molten state and to allow preparation of a master batch, but the function of the PVDF-based binder is not limited thereto.
According to some embodiments of the present disclosure, the PVDF-based binder may be any polymer, as long as it has a melting point of 200° C. or lower and contains at least one polyvinylidene fluoride repeating unit in its repeating units. For example, the PVDF-based binder may include PVDF, polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) or a mixture thereof.
According to some embodiments of the present disclosure, particularly, the PVDF-based binder may have a melting point of 100-200° ° C. For example, the PVDF-based binder may have a melting point of 100° C. or higher, 120° C. or higher, 140 or higher, 150° C. or higher, 160° ° C. or higher, 200° ° C. or lower, 190° C. or lower, 185° C. or lower, or 180° C. or lower. In a variant, the PVDF-based binder may have a melting point of 100° C. or higher, 110° C. or higher, 120° C. or higher, 200° ° C. or lower, 190° C. or lower, 180° ° C. or lower, 170° C. or lower, 160° C. or lower, 150° C. or lower, or 140° C. or lower.
According to some embodiments of the present disclosure, the PTFE binder may include a PTFE binder having a melting point of 300-380° C. When the PTFE binder used herein is a PTFE binder having a melting point of 300-380° ° C., it is possible to improve the dispersibility and dispersion stability of the conductive material in a molten state and to allow preparation of a master batch, but the function of the PTFE binder is not limited thereto.
According to some embodiments of the present disclosure, the PTFE binder may be any polymer, as long as it has a melting point of 300-380° C. and contains at least one polytetrafluoroethylene (PTFE) repeating unit in its repeating units.
According to some embodiments of the present disclosure, the PTFE binder may include polytetrafluoroethylene (PTFE).
According to some embodiments of the present disclosure, particularly, the PTFE binder may have a melting point of 300° C. or higher, 310° C. or higher, 320° C. or higher, 330° C. or higher, 335° C. or higher, 380° ° C. or lower, 370° C. or lower, 360° C. or lower, or 355° C. or lower.
According to some embodiments of the present disclosure, each of the PVDF-based binder and the PTFE binder contained in the conductive material master batch may independently have a crystallization degree of 30% or less.
Herein, the crystallization degree of the binder may be a value determined by using differential scanning calorimetry (DSC). Particularly, 5-12 mg of a sample is introduced to a differential scanning calorimeter (DSC), the melting point and heat of melting (ΔHm) are determined, while the temperature is increased at a rate of 10° C./min within a temperature range of 25-360° C. under nitrogen atmosphere, and the crystallization degree may be determined according to the following formula based on the heat of crystal fusion)(ΔHm° depending on the type of a binder:
In the above formula, with reference to the heat of crystal fusion)(ΔHm° of the binder, the heat of 100% crystal fusion)(ΔHm° of the PVDF binder is 105 J/g, the heat of 100% crystal fusion)(ΔHm° of the PVDF-HFP binder is 80 J/g, and the heat of 100% crystal fusion)(ΔHm° of the PTFE binder is 85.4 J/g, or the crystallization degree of each binder may be calculated by referring to other values known in documents.
According to some embodiments of the present disclosure, when the PVDF-based binder includes PVDF, the crystallization degree of PVDF in the conductive material master batch may be 30% or less, 28% or less, 27% or less, 26.5% or less, 26% or less, 25% or less, or 0%, more particularly.
According to some embodiments of the present disclosure, when the PVDF-based binder includes PVDF-HFP, the crystallization degree of PVDF-HFP may be 30% or less, 20% or less, 15% or less, 10% or less, 8% or less, 6% or less, or 0%, more particularly.
According to still other embodiments of the present disclosure, the crystallization degree of the PTFE binder may be 30% or less, 25% or less, 20% or less, 15% or less, 10% or less, 5% or less, or 0%, more particularly.
According to still other embodiments of the present disclosure, the PVDF-based binder may have a crystallization degree of 30% or less, and the PTFE binder may have a crystallization degree of 30% or less.
According to still another embodiment of the present disclosure, the PVDF-based binder may have a crystallization degree of 30% or less, and the PTFE binder may have a crystallization degree of 20% or less.
According to some embodiments of the present disclosure, when the crystallization degree of the PVDF-based binder satisfies the above-defined range, there is an advantageous effect in terms of improvement of the dispersibility and dispersion stability of CNT, but the scope of the present disclosure is not limited thereto.
According to some embodiments of the present disclosure, when the crystallization degree of the PTFE binder satisfies the above-defined range, there is an advantageous effect in terms of improvement of the physical properties of an electrode obtained by using the conductive material master batch, but the scope of the present disclosure is not limited thereto.
According to some embodiments of the present disclosure, the conductive material master batch includes 20-70 parts by weight of the conductive material, 5-60 parts by weight of the PVDF-based binder, and larger than 0 to 50 parts by weight of the PTFE binder. Particularly, the conductive material master batch may include 20-70 parts by weight of the conductive material, 5-60 parts by weight of the PVDF-based binder and 0.1-50 parts by weight of the PTFE binder. For example, the conductive material master batch may include 40-70 parts by weight of the conductive material, 40-50 parts by weight of the PVDF-based binder and 5-30 parts by weight of the PTFE binder. More particularly, the conductive material master batch may include 50-60 parts by weight of the conductive material, 30-40 parts by weight of the PVDF-based binder and 10-20 parts by weight of the PTFE binder.
According to some embodiments of the present disclosure, when the content ratio of the conductive material, the PVDF-based binder and the PTFE binder in the conductive material master batch satisfies the above-defined range, it is possible to significantly improve the dispersibility of the conductive material when mixing the conductive material master batch with an active material, to improve the ratio of the active material to the conductive material, and to realize excellent adhesion of the conductive material with the active material, but the scope of the present disclosure is not limited thereto.
According to some embodiments of the present disclosure, the conductive material master batch may further include a polyolefin binder, besides the PVDF-based binder and the PTFE binder.
According to still other embodiments of the present disclosure, the conductive material master batch may further include an active material without adversely affecting the objects of the present disclosure, besides the above-described ingredients.
In another aspect of the present disclosure, there is provided an electrode including: a current collector; and an electrode active material layer formed on at least one surface of the current collector, wherein the electrode active material layer includes an electrode active material, an electrode conductive material and an electrode binder, the electrode binder is fibrilized to accomplish the binding of the electrode active material and the electrode conductive material, and the electrode has an electrode resistance of 55 ohm·cm or less.
The electrode according to some embodiments of the present disclosure may be obtained by using the above-described conductive material master batch.
According to some embodiments of the present disclosure, the electrode may include a fibrilized electrode binder as a means for binding an electrode active material with an electrode conductive material. Such a fibrilized electrode binder shows less cleavage as compared to a conventional non-fibrilized binder and has an excellent elongation property in the longitudinal direction, and thus can improve the flexibility of an electrode active material layer and an electrode including the same itself. The fibrilization process of the electrode binder will be explained in more detail in the following method for manufacturing electrode.
According to some embodiments of the present disclosure, the electrode active material layer may be derived from a free standing-type electrode film. For example, the electrode may include a current collector, and an electrode active material layer disposed on at least one surface of the current collector and derived from an electrode film. In addition, the electrode film may be bound with the current collector through a lamination process, or the like.
According to some embodiments of the present disclosure, the electrode active material layer is an electrode film, and may be prepared in the form of a free standing-type sheet by using electrode materials, including an electrode conductive material and an electrode binder, without introducing any solvent. As used herein, the term ‘free standing-type’ refers to an object which can maintain its own shape without relying on other members and can be transferred or handled by itself.
As described hereinafter, the electrode active material layer may be formed by compressing a mixed powder for an electrode. For example, the electrode active material layer may have a shape of layered structure formed by integration of the mixed powder for an electrode through compression. The mixed powder for an electrode is a powdery electrode material containing an electrode active material, an electrode conductive material and an electrode binder. For example, as described hereinafter, the mixed powder for an electrode may be obtained by pulverizing mixture lumps containing the electrode active material, the electrode conductive material and the electrode binder.
According to the present disclosure, the electrode shows a resistance of 55 ohm·cm or less.
Herein, the electrode resistance may refer to a value determined as follows. As an electrode to be tested in terms of resistance, an electrode having a size of 50×50 mm2 is prepared. The prepared electrode sample is introduced to Multi-probe Tester (HIOKI, RM2610), the potential difference is measured among the probes (45 probes) under the conditions of a current at the positive electrode of 100 μA, current at the negative electrode of 10 mA and a voltage of 0.5 V, and the measured value is provided as an electrode resistance value.
Since the conventional method for manufacturing a dry electrode uses no solvent, there is a problem in that the conductive material shows poor dispersibility. Particularly, since a conductive material having a large BET specific surface area is not dispersed stably, it is not suitable for manufacturing a dry electrode, undesirably. Therefore, there have been some attempts to use a conductive material having a small BET specific surface area, while increasing the content thereof, so that the resultant electrode may have improved electrical characteristics. However, when increasing the content of the conductive material, the content of an active material is reduced to cause degradation of the electrode capacity, and the content of a binder is also reduced to cause degradation of current collection with a current collector and a decrease in binding force of the active material particles among themselves, thereby causing the problem of an increase in the electrode resistance.
According to some embodiments of the present disclosure, the electrode active material layer shows improved dispersibility of a conductive material having a large BET specific surface area. Therefore, it is possible to significantly reduce the electrode resistance value, even though a small amount of conductive material is used, thereby providing a dry electrode having improved electrical characteristics. However, the mechanism of the present disclosure is not limited thereto.
According to some embodiments of the present disclosure, the content of the electrode conductive material may be 1 wt % or less based on the total weight of the electrode active material layer. Particularly, the content of the electrode conductive material may be 0.1-1 wt % or 0.1-0.8 wt % based on the total weight of the electrode active material layer.
Therefore, according to some embodiments of the present disclosure, it is possible to increase the content of the electrode active material in the electrode active material layer. According to some embodiments of the present disclosure, the content of the electrode active material may be 95 wt % or more, 96 wt % or more, 97-99 wt %, 97-98 wt %, or 97-97.5 wt %, based on the total weight of the electrode active material layer.
As such, according to some embodiments of the present disclosure, it is possible to realize an effect of improving the electrode resistance value, while reducing the content of the electrode conductive material in the electrode active material layer. For example, the electrode resistance value may be 55 ohm·cm or less, while the electrode includes the conductive material in an amount of 0.8 wt % or less based on the total weight of the electrode active material layer.
Particularly, the electrode may provide a resistance value of 45 ohm·cm or less, as expressed by 1 wt % of the content of the conductive material in the electrode active material layer according to the following Formula 1:
wherein Rt represents an electrode resistance value expressed by 1 wt % of the content of the conductive material in the electrode active material layer, Cw represents the content of the conductive material based on the total weight of the electrode active material layer in the target electrode, and Rw represents the electrode resistance value of the target electrode.
As described above, according to some embodiments of the present disclosure, the conductive material and the binder contained in the electrode may be derived from the above-mentioned conductive material master batch.
In other words, ‘electrode conductive material’ may be ‘conductive material’ described hereinabove with reference to the conductive material master batch. Therefore, reference will be made to the above description about the conductive material in the conductive material master batch with reference to ‘electrode conductive material’.
In addition, ‘electrode binder’ may include ‘binder’ described hereinabove with reference to the conductive material master batch. Therefore, reference will be made to the above description about the binder in the conductive material master batch with reference to ‘electrode binder’.
For example, the electrode conductive material may have a BET specific surface area of 80 m2/g or more.
In addition, the electrode conductive material may include carbon nanotubes alone, or carbon nanotubes and a dot-like conductive material. Herein, reference will be made to the above description about the type of the dot-like conductive material and the weight ratio of the carbon nanotubes to the dot-like conductive material.
The electrode according to some embodiments of the present disclosure includes an electrode active material layer provided by using the above-described conductive material master batch, and thus shows improved dispersibility of a conductive material having a large BET specific surface area and allows the conductive material having a large BET specific surface area to be incorporated stably to the formation of the electrode active material layer. In this manner, it is possible to reduce the content of the conductive material in the electrode active material layer and to increase the content of the active material, thereby providing the electrode with improved resistance characteristics.
In addition, the electrode binder may include the PVDF-based binder and the PTFE binder derived from the conductive material master batch.
Further, the electrode binder is not particularly limited, as long as it can be fibrilized in the following step, particularly, the step for preparing mixture lumps. Herein, ‘fibrilization’ refers to fine division of a polymer, and may be carried out by using mechanical shear force, or the like. The polymer fibers fibrilized in this manner generates a lot of microfibers (fibrils) through the disentanglement of the surface.
According to some embodiments of the present disclosure, non-limiting examples of the electrode binder may include polytetrafluoroethylene (PTFE), polyolefin or a mixture thereof. Particularly, the electrode binder may be polytetrafluoroethylene (PTFE). More particularly, the polytetrafluoroethylene (PTFE) may be present in an amount of 60 wt % or more, based on the total weight of the binder polymer. Meanwhile, herein, the binder ingredient may further include at least one of polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) and polyolefin-based polymers.
According to some embodiments of the present disclosure, the binder polymer contained in the electrode active material layer may be one (i.e. a second binder) introduced for preparing a mixed powder for an electrode, or may be one (i.e. a first binder) introduced for preparing the conductive material master batch, as described in the following method for manufacturing an electrode.
According to some embodiments of the present disclosure, the electrode binder may have a crystallization degree of 15% or less, particularly 10% or less.
According to some embodiments of the present disclosure, the electrode binder may include one derived from the conductive material master batch. For example, the conductive material master batch may include a PVDF-based binder polymer and a PTFE binder polymer, and each of them may independently have a crystallization degree of 30% or less. In other words, the binder contained in the conductive material master batch may include one having a crystallization degree of 30% or less and showing a decrease in crystallization degree to 15% or less, while the binder is further fibrilized through the kneading step in preparing a mixed powder for an electrode by using the binder.
According to some embodiments of the present disclosure, when the crystallization degree of the PTFE binder satisfies the above-defined range, there is an advantageous effect in terms of improvement of the physical properties of the electrode obtained by using the conductive material master batch, but the scope of the present disclosure is not limited thereto.
According to some embodiments of the present disclosure, the content of the electrode binder may be 0.1-5 wt %, 0.1-4 wt %, 0.1-3 wt %, or 0.1-2.5 wt %, based on the total weight of the electrode active material layer, but the scope of the present disclosure is not limited thereto.
According to some embodiments of the present disclosure, the electrode active material layer may include a positive electrode active material or a negative electrode active material, depending on the polarity of the electrode.
Non-limiting examples of the positive electrode active material include, but are not limited to: lithium transition metal oxides; lithium metal iron phosphates, lithium nickel-manganese-cobalt oxides; lithium nickel-manganese-cobalt oxides partially substituted with other transition metals; or two or more of them. Particular examples of the positive electrode active material may include, but are not limited to: layered compounds, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide(LiNiO2), or those compounds substituted with one or more transition metals; lithium manganese oxides, such as Li1+xMn2−xO4 (wherein x is 0-0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium coper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, LiV3O4, V2O5 or Cu2V2O7; Ni site-type lithium nickel oxides represented by the chemical formula of LiNi1−xMxO2 (wherein M is Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x is 0.01-0.3); lithium manganese composite oxides represented by the chemical formula of LiMn2−xMxO2 (wherein M is Co, Ni, Fe, Cr, Zn or Ta, and x is 0.01-0.1) or Li2Mn3MO8 (wherein M is Fe, Co, Ni, Cu or Zn); LiMn2O4 in which Li is partially substituted with an alkaline earth metal ion; lithium metal phosphates LiMPO4 (wherein M is Fe, CO, Ni or Mn); lithium nickel-manganese-cobalt oxides Li1+x(NiaCobMnc)1−xO2 (x is 0-0.03, a is 0.3-0.95, b is 0.01-0.35, c is 0.01-0.5, a+b+c=1); lithium nickel-manganese-cobalt oxides partially substituted with aluminum Lia[NibCocMndAle]1-fM1fO2 (wherein M1 is at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, 0.8≤a≤1.2, 0.5≤b≤0.99, 0<c<0.5, 0<d<0.5, 0.01≤e≤0.1, and 0≤f≤ 0.1); lithium nickel-manganese-cobalt oxides partially substituted with another transition metal Li1+x(NiaCobMncMd)1−xO2 (wherein x is 0-0.03, a is 0.3-0.95, b is 0.01-0.35, c is 0.01-0.5, d is 0.001-0.03, a+b+c+d=1, and M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg and Mo); disulfide compounds; Fe2(MoO4)3; or the like.
Non-limiting examples of the negative electrode active material include: carbon, such as non-graphitizable carbon or graphite-based carbon; metal composite oxides, such as LixFe2O3 (0≤x≤1), LixWO2 (0≤x≤1) and SnxMe1−xMe′yOz (Me: Mn, Fe, Pb, Ge; Me′: Al, B, P, Si, elements of Group 1, 2 or 3 in the Periodic Table, halogen; 0<x≤1; 1≤ y≤3; 1≤ z≤8); lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; silicon-based oxides, such as SiO, SiO/C and SiO2; metal oxides, such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 and Bi2O5; and conductive polymers, such as polyacetylene; Li—Co—Ni-based materials, or the like.
According to some embodiments of the present disclosure, the current collector is not particularly limited, as long as it has high conductivity, while not causing any chemical change in the corresponding battery. Particular examples of the current collector include stainless steel, aluminum, nickel, titanium, baked carbon, copper, aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, or the like. In addition, fine surface irregularities may be formed on the surface of the current collector to enhance the binding force of the electrode active material. Further, the current collector may have various shapes, such as a film, a sheet, a foil, a net, a porous body, a foam or non-woven web body, or the like.
According to some embodiments of the present disclosure, the current collector may be totally or partially coated with a conductive primer for reducing the surface resistance and improving the adhesion. Herein, the conductive primer may include a conductive material and a binder, wherein the conductive material is not particularly limited, as long as it has conductivity. For example, the conductive material may be a carbonaceous material. The binder may include a fluorine-based binder (including PVDF and PVDF copolymer), acryl-based binder and an aqueous binder that can be dissolved in a solvent, or the like.
In still another aspect of the present disclosure, there is provided a method for preparing the above-described conductive material master batch.
The method for preparing a conductive material master batch according to some embodiments of the present disclosure includes the steps of: preparing a mixture by mixing a conductive material, a PVDF-based binder and a PTFE binder; forming an extrudate by kneading and extruding the mixture; and pulverizing the extrudate, wherein the conductive material has a BET specific surface area of 80 m2/g or more, and each of the PVDF-based binder and the PTFE binder in the resultant conductive material master batch independently has a crystallization degree of 30% or less.
In the method for preparing a conductive material master batch according to the present disclosure, reference will be made to the above description of the conductive material master batch with reference to the conductive material, the PVDF-based binder and the PTFE binder.
According to some embodiments of the present disclosure, the step of preparing a mixture by mixing the conductive material, the PVDF-based binder and the PTFE binder is carried out in such a manner that the conductive material, the PVDF-based binder and the PTFE binder may be distributed homogeneously. Since the above ingredients are mixed in the form of powder, the mixing may be carried out by using various processes with no particular limitation, as long as the ingredients can be mixed simply. The conductive material master batch may be mixed through dry mixing, and the mixing may be carried out by introducing the above ingredients to an instrument, such as a blender or a super-mixer.
According to some embodiments of the present disclosure, the step of preparing a mixture may be carried out in a super-mixer at 200-1,700 rpm for 1-30 minutes. Particularly, the above ingredients may be mixed in the mixer at 1,000-1,500 rpm for 2-7 minutes.
The method for preparing a conductive material master batch includes a kneading and extrusion step for fibrilizing the binder in the mixture to prepare an extrudate from the mixture.
For example, according to some embodiments of the present disclosure, the step of forming an extrudate may be carried out by using a twin screw extruder. When forming the extrudate by using a twin screw extruder, it is possible for each of the PVDF-based binder and the PTFE binder in the resultant conductive material master batch to realize a crystallization degree of 30% or less.
According to some embodiments of the present disclosure, each screw in the twin screw extruder may have a diameter (Φ) of 10-40, 15-35, 20-30, particularly 25, and a ratio (L/D) of length (L)/diameter (D) of 40-60, 45-55, particularly 48.
Particularly, according to some embodiments of the present disclosure, the step of forming an extrudate may be carried out by introducing the mixture to the twin screw extruder, and carrying out melt kneading at an extrusion temperature of 100-300° C. under a screw speed of 50-600 rpm to extrude the mixture through the die.
For example, according to some embodiments of the present disclosure, the extrusion temperature may be 130-230° C., or 140-220° C. According to some embodiments of the present disclosure, when the extrusion temperature is significantly lower than the above-defined range, formation of the mixture into lumps through the binder fibrilization and kneading cannot be accomplished sufficiently, and thus the extrudate may be compressed in the form of powder. When the extrusion temperature is significantly higher than the above-defined range, the crystallization degree of the binder is reduced rapidly and thermal decomposition may occur undesirably. However, the scope of the present disclosure is not limited thereto.
According to some embodiments of the present disclosure, the screw speed in the twin screw extruder may be 150-450 rpm, 300-450 rpm, 350-450 rpm, or 400 rpm.
According to some embodiments of the present disclosure, the die used in the extrusion may have a rectangular or circular shape, but the scope of the present disclosure is not limited thereto.
According to some embodiments of the present disclosure, the pulverization step is carried out by cutting the conductive material master batch to facilitate its mixing with the powdery active material in the subsequent process for manufacturing an electrode, and includes pulverizing the extrudate by a conventional process so that the extrudate may have a suitable size and shape with no particular limitation.
According to some embodiments of the present disclosure, the pulverization may be carried out by introducing the extrudate to a blender, and pulverizing the extrudate, for example, at 5,000-20,000 rpm for 10 seconds to 10 minutes. Particularly, the pulverization may be carried out at 8,000-15,000 rpm, or at 10,000 rpm, for 20 seconds to 1 minute, or for 30 seconds.
The prepared conductive material master batch includes the conductive material dispersed homogeneously therein, and allows each of the PVDF-based binder and the PTFE binder introduced thereto to realize a crystallization degree of 30% or less.
The resultant conductive material master batch may be used for manufacturing an electrode, particularly, a dry electrode, but the use of the conductive material master batch is not limited thereto.
In still another aspect of the present disclosure, there is provided a method for manufacturing the above-described electrode.
The method for manufacturing an electrode according to some embodiments of the present disclosure includes the steps of: preparing a mixture by mixing a conductive material with a first binder; forming an extrudate by kneading and extruding the mixture; pulverizing the extrudate to obtain a conductive material master batch; and forming an electrode active material layer on at least one surface of a current collector from a mixture containing an electrode active material, the conductive material master batch and a second binder.
According to some embodiments of the present disclosure, reference will be made to the above description of the conductive material master batch with reference to the conductive material.
According to some embodiments of the present disclosure, reference will be made to the above description of the electrode with reference to each of the first binder and the second binder. For example, each of the first binder and the second binder may be independently any conventional type of binder used for manufacturing an electrode with no particular limitation.
According to some embodiments of the present disclosure, the first binder may be a binder used for the conductive material master batch, and particularly, may include a PVDF-based binder, a PTFE-based binder or a mixture thereof.
According to some embodiments of the present disclosure, the second binder may be a conventional binder used for manufacturing an electrode, and for example, may include a PVDF-based binder, a PTFE-based binder, a polyolefin binder, or a mixture of two or more of them.
The method for manufacturing an electrode according to some embodiments of the present disclosure may include a step of forming an electrode active material layer by using the above-described conductive material master batch. In other words, the method for manufacturing an electrode may be broadly divided into a process of preparing a conductive material master batch and a process of manufacturing an electrode by using the resultant conductive material master batch as a conductive material.
In this context, the first binder may be a binder used for the process of preparing a conductive material master batch, and the second binder may be an electrode binder used for the process of manufacturing an electrode by using the conductive material master batch.
In addition, the step of preparing a mixture, the kneading step and the pulverization step included in the process of preparing a conductive material master batch may be referred to as a first mixing step, a first kneading step and a first pulverization step, respectively. In addition, the step of preparing a mixture, the kneading step and the pulverization step in the process of manufacturing an electrode by using the conductive material master batch may be referred to as a second mixing step, a second kneading step and a second pulverization step, respectively.
According to some embodiments of the present disclosure, the method for manufacturing an electrode includes the above-mentioned process of preparing a conductive material master batch and process of forming an electrode active material layer.
According to some embodiments of the present disclosure, the process of manufacturing an electrode by using the conductive material master batch includes a step of forming an electrode active material layer containing an electrode active material, the conductive material master batch and the second binder polymer, on at least one surface of a current collector.
According to some embodiments of the present disclosure, the step of forming an electrode active material layer may include preparing a mixed powder for an electrode from an electrode active material, the conductive material master batch and a binder polymer (second binder), and then laminating a free standing-type electrode film obtained from the mixed powder for an electrode onto at least one surface of a current collector.
In still another aspect of the present disclosure, there is provided a method for manufacturing an electrode, including the steps of: preparing a mixture by mixing a conductive material with the first binder (first mixing step); kneading and extruding the mixture to obtain an extrudate (first kneading step); pulverizing the extrudate to obtain a conductive material master batch (first pulverization step); preparing a mixture by mixing an electrode active material, the conductive material master batch and the second binder (second mixing step); kneading the resultant mixture at a high temperature and under a low shear rate to obtain mixture lumps (second kneading step); pulverizing the mixture lumps at a high shear rate to obtain a mixed powder for an electrode (second pulverization step); calendering the mixed powder for an electrode to obtain a mixture film; and disposing the mixture film on at least one surface of a current collector, and carrying out lamination to obtain an electrode.
Reference will be made to the above description with reference to the step of preparing a mixture (first mixing step) to the step of preparing a conductive material master batch (first pulverization step).
The second mixing step, the second kneading step and the second pulverization step are included in the process of preparing a mixed powder for an electrode.
The mixed powder for an electrode is a powdery electrode material including an electrode active material, a conductive material and a binder. For example, as described hereinafter, the mixed powder for an electrode may be obtained by pulverizing mixture lumps containing an electrode active material, an electrode conductive material and an electrode binder. As used herein, the term ‘mixed powder’ refers to an aggregate formed by aggregation of two or more electrode material particles. Each individual electrode material particle forming the mixed powder includes the electrode active material, the conductive material and the binder.
The mixed powder for an electrode may be obtained as follows.
First, prepared is an electrode material mixture containing an electrode active material, the conductive material master batch prepared as described above and a binder polymer (second binder). The mixing step for preparing the mixture is carried out in such a manner that the electrode materials, including the electrode active material, the conductive material master batch and the electrode binder, may have a homogeneous disperse phase in the mixture. The electrode according to some embodiments of the present disclosure is provided as a dry electrode using no solvent, and thus the mixing step is carried out in a powder phase without introducing any solvent thereto. Therefore, the mixing may be carried out by using various processes with no particular limitation, as long as the electrode materials can be mixed simply. For example, the mixing step may be carried out by introducing the electrode materials to a known instrument, such as a mixer or a blender, and carrying out agitation.
Next, the resultant electrode mixture is subjected to a fibrilization step (second kneading step) in order to fibrilize the electrode binder. Herein, the binder refers to at least one of the first binder contained in the conductive material master batch and the second binder introduced additionally in preparing the mixed powder for an electrode. As the fibrilization process, mixing based on shear stress, such as a mechanical milling process or a kneading process, may be used.
According to some embodiments of the present disclosure, low-shear kneading may be used for the fibrilization step. For example, the kneading may be carried out through a kneader. The electrode binder is fibrilized by the kneading step, and the electrode materials, including the electrode active material, introduced in the form of powder are bound or interconnected by the fibrilized binder, thereby forming mixture lumps. Since the kneading is carried out without introducing any solvent, the mixture lumps may have a solid content of 100%.
According to some embodiments of the present disclosure, the kneading may be carried out at a rate controlled to 10-100 rpm. For example, the kneading may be carried out at a rate controlled to 40-70 rpm, within the above-defined range. The kneading may be carried out for 1-10 minutes. For example, the kneading may be carried out at speed of 40-70 rpm for 3-7 minutes, within the above-defined ranges.
More preferably, the kneading may be carried out within 5 minutes, or within 3 minutes. The lower the tap compression ratio of the resultant mixed powder for an electrode is, the higher the processability of the manufacture of an electrode film using the powder is. In addition, the tap compression is reduced in the early stage of kneading, and then undergoes little change after a certain time point. When the kneading time falls within the above-defined range, there is a preferred effect in terms of a suitable degree of fibrilization and tensile strength of the fibrilized binder polymer, but the scope of the present disclosure is not limited thereto.
Meanwhile, the kneading in the second kneading step may be carried out at a shear rate controlled to a range of 10/s to 500/s. According to some embodiments of the present disclosure, the kneading may be carried out for 1-30 minutes, and the shear rate may be controlled to a range of 30/s to 100/s.
In addition, the kneading step may be carried out under the condition of a high temperature and a pressure equal to or higher than the ambient pressure. Particularly, the kneading step may be carried out under a pressure equal to or higher than the ambient pressure. More particularly, the kneading step may be carried out at 50-230° ° C., specifically 90-200° C. When the kneading step is carried out under the above-defined condition, there is a preferred effect in terms of the degree of fibrilization of the binder polymer, lumping of the introduced materials, easy filming of an electrode film and the tensile strength of an electrode film, but the scope of the present disclosure is not limited thereto.
In addition, the kneading step may be carried out under a pressure equal to or higher than the ambient pressure, particularly under a pressure of 1-60 atm, 1-30 atm, 1-10 atm, 1.1-10 atm, 1.1-6 atom, or 1.1-3 atm. When carrying out the kneading under the above-defined condition, there is a preferred effect in terms of the fiber crystallization degree and mixture lump density. According to some embodiments of the present disclosure, when carrying out a low-shear mixing process under the condition of a high temperature and a pressure equal to or higher than the ambient pressure, instead of high-shear mixing, it is possible to accomplish the desired effects of the present disclosure, but the scope of the present disclosure is not limited thereto.
Then, the mixture lumps obtained from the kneading step (second kneading step) is pulverized to obtain a powdery electrode mixture (second pulverization step).
The mixture lumps obtained through the kneading may be directly subjected to pressurization (calendering) to be molded in the form of a sheet. However, in this case, it is required to apply a high pressure and high temperature to the mixture lumps in order to mold them to a target thickness. As a result, there are problems in that the dry film may have excessively high density, or a uniform film cannot be obtained. Therefore, according to the present disclosure, the mixture lumps are subjected to a pulverization step to obtain a mixed powder for an electrode.
Herein, the pulverization step may be carried out by using a pulverizing instrument, such as a blender or a grinder, but is not limited thereto. Particularly, the pulverization step may be carried out at a speed of 5,000-20,000 rpm, or 10,000-18,000 rpm, for 30 seconds to 10 minutes, particularly for 30 seconds to 1 minute. When the pulverization is carried out under the above-defined condition, there is a preferred effect in terms of the particle size of the mixed powder for an electrode and controlling the micropowder generation, but the scope of the present disclosure is not limited thereto.
According to some embodiments of the present disclosure, the method may further include, after pulverizing the mixture lumps, a step of classifying the pulverized mixed powder for an electrode. The classified mixed powder for an electrode may be subjected to calendering. In the classification step, the pulverized mixed powder for an electrode may be screened by using a mesh having voids with a predetermined size or lower to obtain a powder for an electrode with a predetermined size or higher.
After that, the mixed powder for an electrode is subjected to compression molding to obtain a mixture film. Herein, the process of compressing the mixed powder for an electrode to obtain a sheet-like dry electrode film is referred to as a calendering process. The dry electrode film may be prepared in the form of a sheet having a predetermined thickness through the calendering process. For example, the dry electrode film may have a strip-like shape having an aspect ratio of larger than 1. According to some embodiments of the present disclosure, the dry electrode film may have a thickness of 50-300 μm.
For example, the calendering process may be carried out by supplying the mixed powder for an electrode to a calendering device and carrying out thermal compressing by using the roll press(es) contained in the calendering device. In addition, the calendering process may be carried out by a roll-to-roll continuous process.
According to some embodiments of the present disclosure, the calendering device includes a roll press unit including two rollers facing each other, and the mixed powder for an electrode may be passed through the roll press unit and compressed into a sheet-like shape. A plurality of roll press units may be disposed continuously so that compression of the dry electrode film may be carried out many times. The number of roll press unit may be controlled suitably considering the thickness or pressing ratio of the dry electrode film.
Meanwhile, independently in each roll press unit, the two rollers may be controlled to a suitable rotation speed ratio within a range of 1:1-1:10. For example, the rollers in at least one roll press unit may be controlled to a rotation speed ratio of 1:1-1:3. In addition, independently in each roll press unit, the rollers may be controlled to a temperature ranging from room temperature (25° C.) to 250° C. The mixture film may be obtained through such a calendering process.
According to some embodiments of the present disclosure, the mixture film may have a porosity of 20-50 vol %. Within the above-defined range, the porosity may be controlled preferably to a value of 40 vol % or less, or 35 vol % or less. When the porosity satisfies the above-defined range, there are various preferred effects. According to some embodiments of the present disclosure, the porosity may be obtained by determining the apparent density of the mixture film and by using the true density calculated based on the true density of each ingredient and composition, according to the following Formula 2:
According to some embodiments of the present disclosure, the mixture film may have a tensile strength of 0.2 MPa or more. According to some embodiments of the present disclosure, the mixture film may have a tensile strength of 0.2 MPa or more, 0.3 MPa or more, or 0.50 MPa or more.
The tensile strength may refer to a value determined as follows.
The film is cut into a size of width×length of 1 cm×10 cm to prepare a specimen. Both ends of the specimen are drawn according to the standard of ASTM (American Society for Testing and Materials) D 638 by using an UTM instrument (available from ZwichRoell) under the conditions of a pre-load of 0.01 kg/cm and a test speed of 5 mm/min. Herein, the force applied to the specimen at break is divided by the initial sectional area to determine the tensile strength. The tensile strength is provided as average of three measurements.
After the calendering, lamination is carried out to form the resultant mixture film on at least one surface of a current collector.
According to some embodiments of the present disclosure, the lamination may be a step of pressing and attaching the mixture film onto a current collector. Also, the lamination may be carried out by using a lamination roll, wherein the lamination roll may be maintained at a temperature ranging from room temperature (25° C.) to 250° C., but is not limited thereto.
The electrode can be obtained according to the method as described above.
The resultant electrode may have an electrode resistance of 55 ohm·cm or less.
In yet another aspect of the present disclosure, there is provided an electrochemical device including the above-described electrode.
The electrochemical device includes a positive electrode, a negative electrode and a separator layer interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is the above-described electrode.
According to some embodiments of the present disclosure, the separator layer may include a separator, a solid electrolyte membrane or both, used conventionally for an electrochemical device, and is not particularly limited, as long as it can prevent the positive electrode and the negative electrode from being in direct contact with each other.
According to some embodiments of the present disclosure, the electrochemical device includes any device which carries out electrochemical reaction, and particular examples thereof include all types of primary batteries, secondary batteries, fuel cells, solar cells or capacitors, such as super capacitor devices. Particularly, among the secondary batteries, preferred are lithium secondary batteries, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries or lithium-ion polymer secondary batteries.
The particular structure of such a secondary battery is known to those skilled in the art, and detailed description thereof will be omitted herein.
The secondary battery according to the present disclosure may be used as a unit cell in an energy storage system, but the use of the present disclosure is not limited thereto.
The particular structure of such an energy storage system is known to those skilled in the art, and detailed description thereof will be omitted herein.
Hereinafter, the present disclosure will be explained in more detail with reference to Examples, but the following Examples are for illustrative purposes only and the scope of the present disclosure is not limited thereto.
A conductive material master batch was prepared as follows.
First, 40 wt % of PVDF-HFP (m.p. 118° ° C.), 10 wt % of PTFE (m.p. 348° C.) and 50 wt % of carbon nanotubes (CNTs) (diameter (D50) 12 nm, BET specific surface area 185 m2/g) were introduced to a super-mixer (20 L Super Mixer available from Heesung techwin) and mixed at 1,200 rpm for 3 minutes to prepare a mixture.
The resultant mixture was supplied to a twin screw extruder (diameter Φ25, L/D 48) at 2-3 kg/hr through a metering pump, and melt kneaded at a temperature of the zone of extruder heaters #1-9 of 130-200° C. and a screw speed of 400 rpm to perform extrusion through the die.
The resultant extrudate was introduced to a blender (available from SHIN-IL n MILL CO., LTD.) and pulverized therein at 10,000 rpm for 30 seconds to obtain a conductive material master batch.
First, 40 wt % of PVDF (m.p. 174° ° C.), 10 wt % of PTFE (m.p. 347° C.) and 50 wt % of CNT (diameter (D50) 12 nm, BET specific surface area 185 m2/g) were introduced to a super-mixer (20 L Super Mixer available from Heesung techwin) and mixed at 1,200 rpm for 3 minutes to prepare a mixture.
The resultant mixture was supplied to a twin screw extruder (diameter Φ25, L/D 48) at 2-3 kg/hr through a metering pump, and melt kneaded at a temperature of the zone of extruder heaters #1-9 of 140-200° C. and a screw speed of 400 rpm to perform extrusion through the die.
The resultant extrudate was introduced to a blender and pulverized therein at 10,000 rpm for 30 seconds to obtain a conductive material master batch.
A conductive material master batch was obtained in the same manner as Example 2, except that 30 wt % of PVDF (m.p. 174° ° C.), 10 wt % of PTFE (m.p. 348° C.) and 60 wt % of CNT (diameter (D50) 12 nm, BET specific surface area 185 m2/g) were used.
A conductive material master batch was obtained in the same manner as Example 1, except that 20 wt % of PVDF-HFP (m.p. 118° C.), 20 wt % of PTFE (m.p. 348° C.) and 60 wt % of CNT (diameter (D50) 12 nm, BET specific surface area 185 m2/g) were introduced.
First, 70 wt % of PVDF-HFP (m.p. 118° C.) and 30 wt % of CNT (diameter (D50) 12 nm, BET specific surface area 185 m2/g) were introduced to a blender (available from SHIN-IL n MILL CO., LTD.) and mixed at 10,000 rpm for 1 minute to prepare a mixture.
Then, a rotor mixer (PVB-0.1 available from LM Tech) was stabilized at a temperature of 160° C., and the mixture prepared as described above was introduced to the rotor mixer and melt kneaded at a speed of 50 rpm for 10 minutes to obtain a conductive material master batch.
First, 35 wt % of PVDF-HFP (m.p. 118° C.), 35 wt % of PTFE (m.p. 347° ° C.) and 30 wt % of CNT (diameter (D50) 12 nm, BET specific surface area 185 m2/g) were introduced to a blender (PVB-0.1 available from LM Tech) and mixed at 10,000 rpm for 1 minute to prepare a mixture.
Then, a rotor mixer was stabilized at a temperature of 160° C., and the mixture prepared as described above was introduced to the rotor mixer and melt kneaded at a speed of 50 rpm for 10 minutes to obtain mixture lumps.
The resultant mixture lumps were introduced to a blender (available from SHIN-IL n MILL CO., LTD.) and pulverized therein at 10,000 rpm for 30 seconds to obtain a conductive material master batch.
A conductive material master batch was obtained in the same manner as Comparative Example 2, except that 40 wt % of PVDF-HFP (m.p. 118° C.), 10 wt % of PTFE (m.p. 348° C.) and 50 wt % of CNT (diameter (D50) 12 nm, BET specific surface area 185 m2/g) were used.
In addition, the result of the crystallization degree of each binder in the conductive material master batch determined by DSC thermal analysis using a differential scanning calorimeter (DSC 25 available from TA Instrument) is shown in the following Table 1.
First, 5-12 mg of a sample was introduced to a differential scanning calorimeter (DSC), the melting point and heat of melting (ΔHm) were determined, while the temperature was increased at a rate of 10° C./min within a temperature range of 25-360° C. under nitrogen atmosphere, and the crystallization degree was determined according to the following formula based on the heat of crystal fusion)(ΔHm° depending on the type of a binder:
Crystallization degree of binder(Xc)=(ΔHm/ΔHm°×100(%)
The crystallization degree was determined by reference to the heat of 100% crystal fusion)(ΔHm° of the PVDF binder of 105 J/g, the heat of 100% crystal fusion)(ΔHm° of the PVDF-HFP binder of 80 J/g, and the heat of 100% crystal fusion)(ΔHm° of the PTFE binder of 85.4 J/g.
The dispersibility of CNT was evaluated by measuring the CNT bundle diameter and nanofiber diameter in the SEM image as shown in
Referring to the photographic images of Examples 1-3 and Comparative Examples 1-3 as shown in
Referring to the SEM images of Examples 1-3 and Comparative Examples 1-3 as shown in
It can be seen from the result of Table 1 that since melt kneading is carried out by a rotor mixer in Comparative Examples 1-3, while not using a twin screw extruder, the kneading and extrusion were performed unstably and the crystallization degree of PTFE was larger than 30%, and thus Comparative Examples 1-3 cannot be used as a desired conductive master batch.
The conductive material master batch prepared as described above was used to manufacture an electrode according to the following method.
First, lithium nickel cobalt manganese oxide (NCMA, Li[Ni0.73Co0.05Mn0.15Al0.02]O2) as a positive electrode material, the conductive master batch according to Example 1 and polytetrafluoroethylene (PTFE) were introduced to a blender at a weight ratio of 97:1.6:1.4 and mixed at 10,000 rpm for 1 minute to prepare a mixture. A kneader was stabilized at a temperature of 180° C., and then the mixture was introduced to the kneader and kneaded at a speed of 40 rpm under a pressure of 4 atm to obtain mixture lumps. The mixture lumps were introduced to a blender and pulverized at 10,000 rpm for 30 seconds, and the pulverized product was classified with a sieve having pores of 1 mm to obtain a mixed powder for an electrode. Herein, PVDF-HFP and PTFE in the resultant mixed powder for an electrode had a crystallization degree of 0% and 6.8%, respectively.
Then, the mixed powder for an electrode was introduced to a lab calender (roll diameter: 200 mm, roll temperature: 100° C., roll speed ratio 1.5) and compressed therein to obtain an electrode mixture film. After that, the resultant electrode mixture film was disposed on both surfaces of aluminum foil (13 μm), and lamination was carried out through a roll press having a roll temperature of 30° ° C. to obtain an electrode.
An electrode was obtained in the same manner as Example 5, except that lithium nickel cobalt manganese aluminum oxide (NCMA, Li[Ni0.73Co0.05Mn0.15Al0.02]O2) as a positive electrode material, the conductive master batch according to Example 4 and polytetrafluoroethylene (PTFE) were used at a weight ratio of 97:1.34:1.66.
Herein, PVDF-HFP and PTFE in the resultant mixed powder for an electrode had a crystallization degree of 0% and 10.6%, respectively.
An electrode was obtained in the same manner as Example 5, except that the conductive material master batch according to Comparative Example 3 was used.
Herein, PVDF-HFP and PTFE in the resultant mixed powder for an electrode had a crystallization degree of 0% and 15.6%, respectively.
First, 96.3 wt % of lithium nickel cobalt manganese aluminum oxide (NCMA, Li[Ni0.73Co0.05Mn0.15Al0.02]O2) as a positive electrode material, 2.2 wt % of PTFE (m.p. 348° C.) and 1.5 wt % of carbon black (BET specific surface area 65 m2/g) were introduced to a super-mixer (20 L Super Mixer available from Heesung techwin) and mixed at 1,200 rpm for 3 minutes to prepare a mixture.
A kneader was stabilized at a temperature of 180° C., and then the mixture was introduced to the kneader and kneaded at a speed of 40 rpm under a pressure of 4 atm for 7 minutes to obtain mixture lumps.
Then, an electrode was obtained in the same manner as Example 5.
The following Table 2 shows the composition of the mixed powder for an electrode used for manufacturing the electrode according to each of Examples 5 and 6 and Comparative Examples 3 and 4.
In addition, the crystallization degree of the electrode binder contained in the mixed powder for an electrode was determined. The result is also shown in Table 2.
The crystallization degree of the binder was determined in the same manner as Test Example 1.
It can be seen from Table 2 that it was possible to reduce the content of the conductive material and to increase the content of the active material in the mixed powder for an electrode, when using the CNT conductive material master batch.
It can be also seen that Examples 5 and 6 using a twin screw extruder provided the electrode binder in the mixed powder for an electrode with a crystallization degree of 15% or less, as compared to Comparative Example 3 using a rotor mixer in the melt kneading step, when using the CNT conductive material master batch.
The tensile strength and electrode resistance value of the electrode mixture film according to each of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in the following Table 3.
In addition, the electrode resistance value expressed by 1 wt % of the content of the conductive material is also shown in Table 3.
The film was cut into a size of width×length of 1 cm×10 cm to prepare a specimen. Both ends of the specimen were drawn according to the standard of ASTM (American Society for Testing and Materials) D 638 by using an UTM instrument (available from ZwichRoell) under the conditions of a pre-load of 0.01 kg/cm and a test speed of 5 mm/min.
Herein, the force applied to the specimen at break was divided by the initial sectional area to determine the tensile strength. The tensile strength was provided as average of three measurements.
The electrode sample was introduced to Multi-probe Tester (HIOKI, RM2610), the potential difference was measured among the probes (45 probes) under the conditions of a current at the positive electrode of 100 μA, current at the negative electrode of 10 mA and a voltage of 0.5 V, and the measured value was provided as an electrode resistance value.
The resistance value determined as described above was expressed by 1 wt % of the content of the conductive material according to the following Formula 1:
Rt=Cw×Rw [Formula 1]
wherein Rt represents an electrode resistance value expressed by 1 wt % of the content of the conductive material, Cw represents the content of the conductive material based on the total weight of the electrode active material layer in the target electrode, and Rw represents the electrode resistance value of the target electrode.
As can be seen from Table 3, each of Examples 5 and 6 using the CNT conductive material master batch in preparing the mixed film for an electrode showed a significantly improved electrode resistance value, while maintaining a tensile strength of 0.2 Mpa or more.
Particularly, each of Examples 5 and 6 showed an electrode resistance value of 55 ohm·cm or less, while including the conductive material in an amount of less than 1 wt %. When the electrode resistance of the electrode according to each of Examples 5 and 6 is expressed by 1 wt % of the content of the conductive material, it can be seen that a significantly improved electrode resistance value was provided as compared to Comparative Examples 3 and 4.
Therefore, it can be seen that Examples 5 and 6 provided a significantly improved electrode resistance value. It is shown that this was because the CNT conductive material master batch was used for preparing the mixed powder for an electrode and the electrode mixture film, and thus the conductive material having a large BET specific surface area showed improved dispersibility, the binder in the mixed powder for an electrode showed a reduced crystallization degree, and the content of the active material was increased.
The present disclosure has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the disclosure, are given by way of illustration only, since various changes and modifications within the scope of the disclosure will become apparent to those skilled in the art from this detailed description.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0049191 | Apr 2022 | KR | national |
| 10-2022-0049192 | Apr 2022 | KR | national |
The present application is a national phase entry under 35 U.S.C. § 371 of international Application No. PCT/KR2023/005409, filed on Apr. 20, 2023, which claims priority from Korean Patent Application No. 10-2022-0049191 and Korean Patent Application No. 10-2022-0049192, filed on Apr. 20, 2022, the disclosures of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2023/005409 | 4/20/2023 | WO |
