Method for manufacturing electrodes for lithium batteries with improved electrical and ionic conductivity

Abstract

The present invention provides a method for making an electrode for a lithium battery with improved electrical and ionic conductivity, comprising the step of applying energy to an electrode nanocomposite (including an active material, a binder, and a conductive carbon additive) by applying light electromagnetic energy using IPL, laser, plasma, or microwave.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an electrode for a lithium battery, and more particularly to a method for manufacturing an electrode for a lithium battery, which includes the steps of photo-electromagnetically treating a carbon additive and a polymer binder, removing crystallinity in the polymer binder, and inducing alignment of the carbon additive material with an electric or magnetic field. [Background technology]

[0002] Lithium batteries, such as lithium-ion batteries, are widely used in portable energy storage devices because they have high energy density, excellent charge / discharge characteristics, and a relatively long lifespan compared to other rechargeable batteries.

[0003] Demand for lithium batteries is growing rapidly due to the growing demand for portable electronic devices and electric vehicles. In lithium batteries, electrodes consist of an active material, a binder, and a conductive carbon additive. The active material provides sites for storing lithium ions and can be conductive or non-conductive. The binder adheres the active material to the current collector and mechanically secures them within the electrode. The conductive carbon additive is mixed with the polymer binder and active material to form a conductive network within the electrode, providing electrical conductivity.

[0004] Carbon black is the most commonly used conductive carbon additive due to its high surface area-to-volume ratio and relatively low cost. However, a recent trend is to use carbon nanoparticles such as carbon nanotubes (CNTs), graphene, and graphene nanosheets (GNPs). Carbon nanoparticles have superior aspect ratios and electrical conductivity compared to carbon black. This allows electrodes to achieve the desired conductivity with less carbon additive (approximately 20 wt.%), increasing the amount of active material used and further increasing the energy capacity of the battery. Carbon additives (e.g., high-aspect-ratio CNTs) can also be used as mechanical support for electrode composites.

[0005] Carbon nanotubes (CNTs) are known for their high tensile strength and are often used in polymer nanocomposites to improve their mechanical and electrical properties. As electrode additives, CNTs maintain a conductive network within the electrode, preventing loss of conductivity due to mechanical stress or strain. Furthermore, CNTs ensure the structural stability of the electrode by mechanically bonding the polymer binder and the active material [Gonzalez et al., 2017]. Different configurations of various types of CNTs, such as single-walled CNTs (SWCNTs), multi-walled CNTs (MWCNTs), and thin-walled carbon nanotubes (TWCNTs), can improve the electrical properties of lithium batteries.

[0006] The literature on the use of CNTs in lithium battery electrodes is as follows:

[0007] Carbon nanotube polymer lithium-ion battery and its manufacturing method, CN 2016 / 105 720 265A

[0008] This application relates to a cathode made of lithium cobalt oxide and lithium nickel cobalt manganese oxide coated with a carbon nanotube polymer. A manufacturing process for such a battery is also described. According to this application, batteries containing the cathode have increased power capacity per gram, increased energy density, improved residual capacity after repeated charge / discharge cycles, and extended cycle life.

[0009] Hybrid nanowire anode compositions for lithium-ion batteries, US 2017 / 9 564 629 B2

[0010] This application relates to a composition for use in an electrode of a hybrid nanowire electrochemical battery. The composition consists of an assembly of nanoscale conductive wires made of materials such as carbon nanotubes (CNTs) and carbon nanofibers (CNFs), which are interconnected to form an interconnected porosity network. The fiber wires are coated with a micro / nanoscale surface consisting of a lithium-ion-capable anode active material that can be made from several materials, including silicon, silicon alloys, and silicon oxides.

[0011] Compositions Comprising Nanoparticles and Nanostructured Support Matrices, and Methods for Fabrication as Reversible High-Capacity Anodes in Energy Storage Systems, US 2020 / 10 878 977 B2

[0012] This application relates to a composition for a lithium-ion battery anode electrode, and a method for making the same, in which the electrode is composed of nanostructures, such as carbon nanotubes, within which a vertically aligned nanostructured support matrix is ​​formed. The interfacial bonding between the nanostructured support matrix and the nanoparticles results in an electrode with improved performance and usefulness in lithium-ion batteries. The support matrix may be grown on a substrate made of a current collector material.

[0013] Nanotube composite anode materials suitable for lithium-ion battery applications, US 2011 / 0 104 551 A1

[0014] This application relates to anode materials for lithium-ion batteries that consist of carbon nanotube composites. These materials are composed of aligned carbon nanotubes, with a lithium alloying material coated on the inner or outer surfaces of the carbon nanotubes. Silicon is a typical lithium alloying material. Combining silicon with aligned carbon nanotubes can increase charge / discharge rates, improve capacity, and maintain high stability during cycling. This is due to the elastic deformation ability of CNTs, which compensates for the large volume expansion and prevents delamination.

[0015] Method for producing negative electrode material for lithium ion batteries, WO 2015 / 124 049 A1

[0016] This paper relates to the development of anode materials for lithium-ion batteries. Carbon nanotubes are dispersed in a solution and then processed through several steps, including sintering and drying, to form a composite material consisting of CNTs, silicon, and carbon. Silicon is sandwiched between the carbon nanotube network and the carbon outer shell, acting as a buffer layer to prevent expansion. Furthermore, the CNT network and carbon outer shell can improve the electrical conductivity of the silicon.

[0017] The above documents relate to the use of CNTs and other carbon additives to improve the electrical, electrochemical, and mechanical properties of electrodes. However, CNTs have limited use as carbon conductive additives due to their poor dispersibility in electrode nanocomposites. Due to the action of van der Waals forces, carbon additives have an inherent tendency to agglomerate, resulting in poor dispersibility. To improve the dispersibility of carbon additives in the mixture, various mixing processes, such as ball milling and planetary ball milling, are used in addition to chemical and physical modification of carbon nanotubes through functionalization.

[0018] Functionalized CNTs improve the dispersion of CNTs in composites and increase overall conductivity, but the conductivity of functionalized CNTs is slightly reduced compared to pristine CNTs. The use of surfactants typically leaves non-conductive surfactant material behind in the composite after dispersion. These methods for dispersing CNTs contribute to an overall conductivity improvement, but may not achieve the maximum potential conductivity. There have been few studies reported on defunctionalizing functionalized CNTs in solution to return them to pristine CNTs.

[0019] Heat treatment of functionalized carbon nanotubes in solution to affect their defunctionalization, WO 2005049488A2

[0020] This application relates to thermal defunctionalization of CNTs in solution to facilitate their resuspension. Unlike prior art techniques, which involve thermal defunctionalization in a dry state to recover the original CNTs, which cannot be resuspended in a liquid due to the presence of covalent crosslinks between the CNTs, this method involves thermal defunctionalization and allows for suspension in a solution, which may include a mixture of a polymeric material and a surfactant. The mixture or mixed material is then heat-treated to defunctionalize the suspended CNTs.

[0021] However, the poor dispersion of the pristine CNTs in suspended form in viscous slurry mixtures makes this method difficult to apply to the fabrication of electrodes. Therefore, a method for dispersing CNTs and defunctionalizing them after curing the composite is needed for electrode fabrication. One promising method is intense pulsed light (IPL) irradiation, which is the application of optical electromagnetic energy.

[0022] Method for producing an electrode, an electrode produced by the method, a supercapacitor including the electrode, and a rechargeable lithium battery including the electrode, US 2014 / 0255776 A1

[0023] This application relates to the application of xenon intense pulsed light (IPL) to treat electrodes made from metal oxides, conductive polymers, and carbon materials. Examples demonstrate that the IPL process applied to relatively low-conductivity materials (such as metal oxides and graphene oxide) reduces the materials to conductive metals and graphene, making them usable as electrode materials. This is a fast and simple method for electrode fabrication.

[0024] Another way to increase the conductivity of electrodes is to carbonize relatively inexpensive, poorly conductive materials. There is a lot of prior art related to this process, but some examples are provided here.

[0025] Negative electrode material made by combining soft carbon or hard carbon, its manufacturing method, and capacitor including the negative electrode material, CN107993853B

[0026] This application relates to the use of soft and hard carbon precursors in electrode fabrication and their conversion into carbon electrodes through a carbonization process. Soft carbon precursors include coal tar pitch and pitch, and hard carbon precursors include sucrose. The examples in this application demonstrate the pre-carbonization and carbonization processes at elevated temperatures for extended periods of time, detailing the temperature, duration, and atmospheric conditions for different materials.

[0027] Carbon electrode and its manufacturing method, KR101647960B1

[0028] This application relates to natural carbon materials and their heat treatment for producing carbon-based electrodes. The natural carbon materials include natural fibers such as cotton, hemp, flax, jute, sheep's wool, henequen hemp, wool, and silk. The carbonization process involves pre-carbonization at 600°C, carbonization at 900-1100°C, and secondary carbonization of the resulting cellulose at 1300-1500°C to produce alkali metals or alkaline earth metals on the surface of the carbon electrode.

[0029] Prior art documents

[0030] Charter document

[0031] (Document 001) CN 105720265 A (June 29, 2016)

[0032] (Document 002) US 9,564,629 B2 (February 7, 2017)

[0033] (Document 003) US 10,878,977 B2 (December 29, 2020)

[0034] (Document 004) US 2011 / 0104551 A1 (May 5, 2011)

[0035] (Document 005) WO 2015 / 124049 A1 (August 27, 2015)

[0036] (Document 006) WO 2005 / 049488 A2 (June 2, 2005)

[0037] (Document 007) US 2014 / 0255776 A1 (September 11, 2014)

[0038] (Document 008) CN 107993853 B (September 17, 2019)

[0039] (Document 009) KR 10-1647960 B1 (August 8, 2016)

[0040] (Document 010) US 2010-0035152 A1 (2010.02.11)

[0041] unlicensed literature

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[0076] (Reference 035) Yuen, S.-M. et al., 2006. Preparation, morphology and properties of acid and amine modified multiwalled carbon nanotube / polyimide composite. Summary of the Invention [Problem to be solved by the invention]

[0077] SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing an electrode for a lithium battery having higher electrical conductivity based on the above-mentioned prior art.

[0078] Specifically, the objective of this invention is to improve ionic conductivity by dispersing and drying the electrode nanocomposite, then defunctionalizing the carbon nanotubes and carbonizing the polymer binder to remove the crystalline structure. Furthermore, the electrical conductivity and anisotropy of the composite can be controlled by the alignment and steering direction of the embedded carbon nanotubes and other carbon additives.

[0079] It is a further object of the present invention to provide an electrode for a lithium battery having improved electrical conductivity. [Means for solving the problem]

[0080] The present invention relates to an electrode for a lithium battery, particularly to an electrode for a lithium battery such as a lithium ion battery, a lithium metal battery, a lithium sulfur battery, a lithium air battery, etc. The lithium battery includes a current collector, a positive electrode, a negative electrode, an electrolyte, and a separator.

[0081] The present invention relates to the use of carbon additives (e.g., carbon nanotubes, carbon nanofibers, graphene, graphene oxide, graphene nanosheets, etc.) to improve the conductivity of electrode composites and to improve their dispersibility in the composites using dispersion methods.

[0082] Furthermore, the present invention also relates to a photoelectromagnetic energy application process for further improving the conductivity of carbon materials by defunctionalizing them. The photoelectromagnetic energy application process may include intense pulsed light (IPL) irradiation using a xenon lamp, laser irradiation, microwave irradiation, or Joule heating. In the IPL process, a flash of light from a xenon lamp is used. The flash of light used is characterized by short period, high power, and broad spectrum. The IPL process is a spontaneous process, and the absorption effect of carbon additives is good, which is the main purpose of defunctionalization. In the microwave irradiation process, high-power microwave spectrum is used to excite molecular vibrations with high energy through heating.

[0083] Carbon additives, including single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) (e.g., double-walled carbon nanotubes (DWCNTs)), carbon nanotubes (DWCNTs), carbon nanofibers (CNFs), graphene, graphene oxide, and graphene nanosheets (GNPs), are typically chemically functionalized with functional groups (e.g., carboxyl or amino) to improve dispersion in mixtures; however, the presence of the functional groups reduces the electrical conductivity of individual carbon additive particles. Application of optical electromagnetic energy can remove the functional groups, further improving the electrical conductivity of the carbon additive.

[0084] The applied light electromagnetic energy can also have some beneficial effects on the electrode: if the carbon additive contains metal impurities (traces of catalysts used in the manufacturing process), the application of light electromagnetic energy can oxidize these impurities, making them inactive in the cell's electrochemical reactions.

[0085] The energy can also be used to change the material properties of polymer binder materials. These binder materials mechanically secure active materials together and adhere them to current collectors. The application of light-induced electromagnetic energy can affect binder materials and change their properties. Applying sufficiently high energy to the binder material carbonizes it, forming a carbon structure around the active materials, improving electrical and ionic conductivity. This facilitates lithium ion diffusion, improving electrical and ionic conductivity, thereby improving battery charge / discharge rates and reducing resistance. Furthermore, the application of light-induced electromagnetic energy can eliminate the crystallinity of some binder materials. Polyvinylidene fluoride (PVDF) is a commonly used polymer binder material for lithium-ion battery electrodes due to its chemical, heat, and mechanical resistance. However, PVDF is known to have a high crystallinity ratio regardless of its phase. The application of light-induced electromagnetic energy contributes to the elimination of crystallinity, increasing the proportion of PVDF in the amorphous phase relative to the crystalline phase.

[0086] Optical electromagnetic energy application is a simple and cost-effective method that can improve various aspects of electrode properties. Furthermore, other simple alignment methods for carbon additives can be combined with the optical electromagnetic energy application process to improve the material properties of electrodes. The alignment process for carbon additives can be achieved using various methods, such as mechanical shear stress, electric polarization, or magnetic polarization, all of which are suitable for achieving by modifying the equipment during the rolling process. Carbon additives with high aspect ratios (e.g., CNTs and graphene) can produce anisotropic material properties depending on their alignment direction. Most importantly, electrical conductivity increases in the direction parallel to the alignment direction and then decreases in the direction perpendicular to the alignment direction.

[0087] The rolling process performed during the roll-to-roll (R2R) manufacturing process can apply mechanical shear stress that aligns the carbon additive during material shear flow due to compression or shear flow due to vacuum suction. Furthermore, a sufficiently high electric or magnetic field (AC or DC) between two rollers can also promote alignment of the carbon additive. To facilitate alignment, the carbon additive may be functionalized by chemical or physical methods and then defunctionalized by the light electromagnetic energy application process described above.

[0088] The applied electric field to align the carbon additives may also have the additional effect of altering the crystallinity of certain binder materials. Electrical polarization can induce a phase transition of PVDF from another crystalline phase (α-phase or γ-phase) to the β-phase. While the crystallinity of PVDF increases the ionic resistance of the material, the crystallinity of the β-phase increases the hydrophilicity of PVDF, potentially enhancing the diffusion of electrolyte to the electrode.

[0089] The present invention proposes materials, methods, and equipment for improving the conductivity of electrodes and achieving desired material properties. By using this method to improve the conductivity of electrodes, it is possible to reduce the proportion of conductive carbon additives, add more active material, and improve overall energy density.

[0090] To support the explanation of the present invention, exemplary experiments and their results are also described. IPL application experiments were conducted on PVDF-ACNT (acid-modified CNT) nanocomposites, and the results of FT-IR analysis, EDX analysis, and electrical conductivity analysis were provided.

[0091] The subject matter of the present invention is outlined below.

[0092] The method for manufacturing an electrode for a lithium battery according to the present invention includes the steps of (a) mixing an active material, a carbon additive, and a polymer binder to form a slurry, (b) depositing the slurry on a substrate to form a coating, (c) drying the coating, and (d) applying energy to the dried coating.

[0093] The carbon additive in step (a) may be functionalized by chemical methods or mixed with a surfactant, such that after the application of energy in step (d), the carbon additive is defunctionalized or the surfactant is carbonized.

[0094] The polymer binder may be carbonized by the action of energy in (d).

[0095] The application of energy in (d) may cause at least a portion of the polymer binder to become amorphous or may change the crystalline phase of at least a portion of the polymer binder.

[0096] The application of energy in step (d) may oxidize metal impurities contained in the dried coating. The application of energy in step (d) may be carried out in a vacuum environment or an inert gas environment, and oxygen gas released from the surfactant or polymer binder upon application of energy is used to oxidize the metal impurities.

[0097] For example, in (d), intense pulsed light (IPL) may be used, and in (d), one or more of laser, microwave, or Joule heating may be used with or without IPL.

[0098] The carbon additive may include one or more of carbon nanotubes, graphene, graphene oxide, carbon nanofibers, and graphite.

[0099] The method may further include, after (c), a step of rolling using two rollers.

[0100] The two rollers may be applied with different potentials.

[0101] In the rolling step, mechanical, electrical or magnetic polarization is performed to align the carbon additives in a direction parallel to or perpendicular to the substrate.

[0102] The rolling step is

[0103] Step a) thermally annealing the semi-crystalline polymer binder to induce a β-phase transition;

[0104] Step b: electrically poling the semi-crystalline polymer binder to induce a β-phase transition;

[0105] Step c) aligning the carbon additive parallel to the electrode surface by heating and compressing;

[0106] Step d: applying vacuum pressure to align the carbon additive perpendicular to the electrode surface;

[0107] and step e) applying an electric or magnetic field between the two rollers to align the carbon additive perpendicular to the electrode surface. [Brief explanation of the drawings]

[0108] Referring now to the drawings, certain aspects of the present invention will now be described in detail, by way of example and not by way of limitation. [Figure 1] The functionalization and defunctionalization processes of CNTs are presented, where functionalized CNTs undergo a functionalization process based on acid and urea treatment to attach carboxyl, hydroxyl, or amine groups to their carbon walls, and are restored to their original state by a defunctionalization process upon application of energy (IPL, microwave, and Joule heating). [Figure 2] This shows the transformation of PVDF crystal structure from α-phase to β-phase upon electrical polarization and annealing. β-phase PVDF enhances the hydrophilicity of the surface, thereby improving the diffusion of electrolytes. [Figure 3] Demonstrates a modified R2R process using an electric field to align carbon additives and change the crystalline phase of PVDF. [Figure 4]To improve the material properties, a fabrication method for the electrodes is presented, including slurry mixing and mixing sonication, followed by functionalization of the CNTs, blade application to the current collector, drying, R2R rolling and defunctionalization, and a final IPL process for defunctionalization of the CNTs. [Figure 5] MWCNTs suspended in a solvent are shown, with (a) the original MWCNT sample, (b) the acid-modified MWCNT sample, and (c) the IPL-treated MWCNT sample. When the MWCNT samples were stirred and sonicated under the same conditions, (b) the acid-modified MWCNT sample remained dispersed the longest, while (a) the original MWCNT sample and (c) the IPL-treated MWCNT sample sank to the bottom and aggregated quickly. [Figure 6] This is an SEM image of an active material encapsulated with a polymer binder and carbon additive after IPL. The active material contains 89.1 wt.% NMC 811, 10 wt.% PVDF as a polymer binder, and 0.9 wt.% acid-modified MWCNT. IPL is applied in a nitrogen-filled chamber at 2900 V for 6 ms. [Figure 7a-7c] (a) 1500-500 cm-1 FT-IR, (b) 3500-1500 cm-1 FT-IR, and (c) EDX of the PVDF-ACNT thin film show the changes with IPL irradiation power. [Figure 8a-8b] (a) Sheet resistance and (b) conductivity variations with IPL irradiation power are shown. [Figure 9a-9b] The results show a comparison of half-cell capacity before and after IPL application. [Figure 10] Electrochemical impedance spectra of the electrodes before and after IPL application are shown. DETAILED DESCRIPTION OF THE INVENTION

[0109] The following description and the above examples of the present invention are intended to explain the principles of the present subject matter. These examples are illustrative, not limiting, of various aspects of the principles and subject matter of the present invention. In the present invention and the drawings, like numerals represent like elements. The drawings are not necessarily to scale, and in some cases, proportions may be exaggerated to more clearly depict certain features.

[0110] Figure 1 shows the functionalization and defunctionalization processes of CNTs. Functionalized CNTs have carboxyl, hydroxyl, or amine groups attached to the carbon walls through the functionalization process using acid and urea treatment. The functionalized CNTs can be returned to their original state through the application of energy such as IPL, microwaves, or Joule heating during the defunctionalization process.

[0111] Effect of carbon additives

[0112] To understand the material properties of nanocomposites, one must first understand the matrix and filler. In most cases, fillers are added to enhance specific properties that the matrix lacks. CNTs have high electrical conductivity, high thermal conductivity, and high tensile strength, properties that most polymer matrices lack, making polymer-CNT nanocomposites an ideal choice [Breuer & Sundararaj, 2004].

[0113] The properties of CNTs quickly attracted the attention of the lithium-ion battery industry. They were first applied to cathode composites, such as layered LiCoO2 compounds. Initially, carbon black (CB) and carbon fiber (CF) were used, but multi-walled CNTs (MWCNTs) were eventually found to improve the capacity, charge / discharge rate, and lifespan of lithium-ion batteries [Wang et al., 2008]. Experiments have shown that cathodes using MWCNTs are superior to those using conventional conductive materials (e.g., carbon black) [Kang and Shen, 2006; Sheem et al., 2006]. Research has also revealed that the electrical conductivity of MWCNTs is superior, and the high aspect ratio of MWCNTs contributes to maintaining a conductive network during repeated charge / discharge cycles and mechanically fixing the nanocomposite electrode. This effect is evident in most composite cathodes, especially compared to less effective carbon fiber and carbon black.

[0114] CNTs are also known as suitable conductive additives for anodes. Due to their unique lithium ion embedding ability, CNTs are promising alternatives to active materials such as graphite, but their production costs are inferior to commercially available graphite. With the development of metal alloy active materials with large volume changes, such as silicon, tin, bismuth, and titanium oxides, CNTs have become popular as conductive additives for anode materials. Compared to traditional graphite anodes, these materials are known for their high energy density, but they also suffer from large volume changes, which can subsequently lead to pulverization, delamination, and poor formation of the solid electrolyte interphase (SEI). CNTs and their high electrical conductivity can utilize their conductive network to suppress volume changes in the active material and fix the active material and binder material, thereby reducing the loss of electrochemical properties.

[0115] Carbon additive dispersion

[0116] Both CNTs and carbon additive nanoparticles tend to aggregate. Aggregation is a result of van der Waals forces between CNTs. This has been a long-standing problem in the fabrication of polymer-CNT nanocomposites and any other composites containing carbon-based nanofillers [Atif & Inam, 2016].

[0117] To achieve uniform material properties (macroscale), we investigated the uniform dispersion of nanofillers. Nanofiller dispersion is directly related to the solvent in which the nanofillers are dispersed. Research has shown that all CNT and solvent systems tend to aggregate because dispersion is energetically unfavorable [Pramanik et al., 2017], but some solvents require less energy to disperse CNTs and maintain their dispersion for a longer period of time.

[0118] In general, pristine CNTs are hydrophobic, so they disperse better in nonpolar solvents than in polar solvents such as water [Wusiman et al., 2013]. The molecular geometry of the solvent also influences dispersion, as pyramidal DMSO has a lower interaction with CNTs than DMF (dimethylformamide) or DMC (dimethyl carbonate), which are planar and oriented parallel to the CNT surface. The molecular geometry and polarity of the polymer matrix also affect CNT dispersion [Pramanik et al., 2017].

[0119] Before designing a CNT dispersion, it is common to select the solvent and polymer, because the type of polymer matrix often determines the material's properties. Therefore, additional techniques are needed to reduce or provide the required dispersion energy. Mechanical dispersion methods, such as ultrasound (high-frequency vibrations to agitate particles in solution), rolling (rolling a viscous mixture with shear) [Gojny et al., 2004], and ball milling (wrapping and bundling fillers) [Li et al., 1999], are commonly used to provide the energy required for CNT dispersion.

[0120] We compared the dispersion of CNTs as a function of ultrasonic time. Prior to measurement, CNTs were dispersed in a solution of distilled water and sodium lauryl sulfate (SDS) (ratio 1:300). Because the bands of surfactant and CNTs may overlap in UV-visible measurements, the spectrum of the surfactant solution was measured and the baseline corrected. Increasing the ultrasonic time increased the absorbance, suggesting good dispersion of CNTs in the solution [Sobolkina et al., 2012].

[0121] Mechanical dispersion methods are easy to apply and are not limited by the type of polymer or solvent used. However, mechanical dispersion methods by themselves are often insufficient to completely disperse CNTs and other nanofillers because these methods can transfer excessive energy, damaging the surface and shortening the length of the nanofillers [Lu et al., 1996]. In many cases, damage occurs before the CNTs are fully dispersed. Therefore, mechanical dispersion methods are commonly used in conjunction with other techniques, limiting the exposure time and strength of the nanofillers.

[0122] Another process, functionalization, involves attaching different molecules to the surface of CNTs to give them different properties. Depending on the type of functionalization, it can enhance the electrical properties of CNTs, provide magnetic properties, establish connections between CNTs and the surrounding polymer, or improve dispersion of CNTs. There are two types of functionalization: physical functionalization and chemical functionalization. Hirsch divides chemical functionalization into defect group functionalization and covalent sidewall functionalization, and physical functionalization into external and internal functionalization.

[0123] Physical functionalization (using surfactants)

[0124] Physical functionalization is a non-covalent bond between CNTs and molecules, typically maintained by π-deposition (π-π interactions) or physical adsorption of molecules onto the CNT surface. This occurs on the outer shell of the CNT, hence the term external functionalization. There is also a form of physical functionalization called internal functionalization, where atoms or molecules are inserted into the interior of the CNT, but internal functionalization methods have little effect on CNT dispersion [Georgakilas et al., 2007].

[0125] Surfactants are a common example of dispersing and physically functionalizing nanofillers. Defect group functionalization or covalent sidewall functionalization techniques damage the original carbon chains of nanofillers, thereby altering their mechanical and electrical properties. Surfactants form non-covalent bonds with nanofillers, altering their surface energy while preserving their original properties.

[0126] The effect of various surfactants on CNT dispersion was investigated based on the UV-Vis spectra of solutions containing different surfactants. Since the absorbance value at a specific wavelength is proportional to the number of debundled CNTs [Grossiord et al., 2005], the UV-Vis spectrum can be used to determine the degree of dispersion of CNTs. Inam et al.'s study showed that GA (gum arabic) has a better dispersing effect than SDS (sodium dodecyl sulfate), but the highest dispersion effect was achieved when two surfactants were used together [Inam et al., 2014]. Triton TM X-100 (polyoxyethylene phenyl octyl ether) or Twain-20 TM This study investigated how a nonionic surfactant called Triton and its dispersion could improve the material properties of MWCNT-polypropylene (MWCNT-PP) nanocomposites. TM X-100 enhances the dispersion of CNTs in MWCNT-PP nanocomposites. Improved CNT dispersion also improves the electrical conductivity and tensile modulus of MWCNT-PP nanocomposites. Similar results were observed in a study using a silane coupling agent (ZFDA, Dow Corning Z-6173) as a surfactant [Xin & Li, 2012].

[0127] Disadvantages of surfactants

[0128] However, the use of surfactants is not necessarily the optimal method for dispersing CNTs. It has been reported that adding excess surfactants can substantially decrease the conductivity of CNTs [Xin and Li, 2012]. This does not mean that the dispersion effect is reduced, but rather that the increased volume of non-conductive surfactants offsets the increase in conductivity due to improved CNT dispersion. This phenomenon has also been demonstrated with SDS and SDBS (sodium dodecylbenzenesulfonate), and nanocomposites containing surfactants have lower thermal conductivity than those without surfactants [Wusiman et al., 2013].

[0129] chemical functionalization

[0130] Other functionalizations, called covalent or defect group functionalization, involve the addition of different atoms or molecules to CNTs. This chemical functionalization is thought to disrupt the extended π-conjugation of nanotubes, reducing the electrical conductivity of isolated nanotubes, but has limited effect on their mechanical and thermal properties. However, it has often been reported that the dispersion improvements of chemical functionalization far outweigh the drawbacks compared to the electrical conductivity of CNTs [Moniruzzaman & Winey, 2006].

[0131] There are two main methods for covalent bonding by building molecular chains. The "grafting" method involves synthesizing a polymer with a specific molecular weight and terminated with an active group or radical precursor. In a subsequent reaction, the polymer chains are attached to the nanotube surface by an addition reaction. The "grafting" method grows polymers from the CNT surface by in situ polymerization of monomers with chemicals immobilized on the sidewalls or edges of the CNTs [Spitalsky et al., 2010].

[0132] The primary reason for adopting the "grafting" method in this invention is the availability of preformed commercially available polymers with controlled molecular weights and polydispersities, which can be used to achieve the goal of dispersing CNTs through functionalization. This functionalization method generally begins with carboxylic acid functionalization of CNTs, commonly referred to as CNT "acid treatment."

[0133] Acid treatment of CNTs can be performed using various types of acids and different process parameters. Some conventional methods involve mixing sulfuric acid and nitric acid in a 3:1 ratio [Gao et al., 2005; SYahoo et al., 2006; Meng et al., 2008], while others use a 3:2 ratio [Yuen et al., 2006]. The stirring time of CNTs in the acid solution also varies, with a general rule of thumb being that the lower the stirring temperature, the longer the stirring time for the CNTs. The reacted CNTs are then washed with copious amounts of deionized water, filtered, and dried to remove excess acid, leaving only the functionalized CNTs.

[0134] Samples untreated or treated with very mild acids showed precipitation of aggregated CNTs, while other acid-treated samples showed dispersed CNTs remaining suspended in solution even after 24 hours. Carboxylic acid-functionalized CNTs were better dispersed in acid-treated polymer nanocomposites, improving their mechanical properties. Although the polarity of amino groups is slightly lower than that of carboxylic acid groups, amine- and diamine-functionalized CNTs have been reported to be more uniformly dispersed in certain polymer matrices (polyamides) than carboxylic acid-functionalized CNTs. Both acid- and amino-modified MWCNTs were more effectively dispersed in polyamides than pristine MWCNTs, and the Young's modulus of PA-MWCNT nanocomposites was maximized at low concentrations of amino-modified MWCNTs.

[0135] CNT alignment

[0136] Enhanced nanofiller dispersion not only improves the mechanical, electrical, and thermal properties of nanocomposites, but also improves the uniformity of material properties throughout the nanocomposite's volume. Furthermore, research has shown that high-aspect-ratio nanofillers (e.g., CNTs) can be aligned in specific directions in nanocomposites to achieve anisotropic material properties. Anisotropic material properties can be used in a variety of applications. One example is oriented conductivity, where the material is electrically conductive in the vertical direction but not in the lateral direction. This may be ideal for conventional lithium-ion batteries, which have been fabricated using a layered structure.

[0137] There are three main methods for aligning CNTs in carbon additives: the first is mechanical alignment, which uses shear stress caused by flow to align the CNTs; the second is magnetic alignment, which uses a magnetic field to align the CNTs; and the third is electric field alignment, which uses an electric field to align the CNTs.

[0138] When melt blending is used to produce polymer-CNT nanocomposites, mechanical alignment methods are used. Unlike magnetic field alignment and electric field alignment, which align fibers in a low-viscosity solution, mechanical alignment methods utilize the flow of the viscous polymer itself to generate shear stress and align the fibers. Injection molding or compression molding of polymer-CNT nanocomposites are good examples.

[0139] Compression molding of polycarbonate-MWCNT (PC-MWCNT) disks and microinjection molding of dogbone-like samples were investigated at different shear rates. Results showed that compression molding of disk samples resulted in radially aligned CNTs, while microinjection molding of dogbone-like samples resulted in linearly aligned CNTs. Higher shear rates also resulted in greater CNT alignment [Abbasi et al., 2010]. Furthermore, injection molding of PC-MWCNT nanocomposites has been reported to result in CNT alignment, resulting in anisotropic electrical conductivity [Mahmoodi et al., 2012; Parmar et al., 2013; Arjmand et al., 2011] and thermal conductivity [Mahmoodi et al., 2015].

[0140] The drawbacks of this technique are that it generates higher shear stresses / strains near the surface (which are difficult to control) and a greater degree of alignment, i.e., higher shear stresses, which leads to inhomogeneous material properties throughout the nanocomposite volume.

[0141] The magnetic and electric field alignment methods can produce more uniform nanocomposite samples than mechanical alignment methods. While the magnetic and electric field alignment methods require magnetic or electrical properties in the nanofillers, the injection molding method for aligning nanofillers can be applied to any nanofiller.

[0142] While it is possible to align pristine CNTs in a magnetic field [Camponeschi et al., 2007], the low magnetic susceptibility of CNTs requires a relatively high magnetic field (over 15 T). Researchers have discovered that CNTs can be modified with magnetically susceptible nanoparticles (such as iron oxide). Maghemite (γ-Fe2O3) MWCNTs are synthesized, mixed with epoxy resin, and exposed to a 0.3 T magnetic field. These mixtures produce aligned magnetic CNTs that are strongly oriented in the direction of the magnetic field [Kim et al., 2010; Kim et al., 2011].

[0143] The electric field alignment method is characterized by its ease of processing and high efficiency in aligning CNTs compared to mechanical and magnetic field alignment methods [Yang et al., 2017]. This method utilizes the dielectrophoresis phenomenon, in which a force is applied to dielectric particles (i.e., CNTs) to move to the position where the electric field strength is maximum. Furthermore, a 3D printer has been developed that can align CNTs in any desired direction in each layer of printed material using a direct current electric field [Yang et al., 2017]. However, the direct current electric field alignment method has the same problems as the magnetic field alignment method. If the magnetic field is strong enough, CNTs will not only align along the electric (or magnetic) field, but will also likely migrate depending on the direction of the magnetic field [Lee et al., 2016].

[0144] To overcome the problems of the DC electric field alignment method, an AC electric field alignment method was developed. The alternating direction of the electric field prevents the CNTs from moving, and the CNTs are aligned by the dielectrophoretic induced moment. After mixing the pristine MWCNTs in a PSF (polysulfone) matrix, an electric field of 13.3 kVp / pm at a frequency of 1 kHz is applied. There is a large difference in the resistance measured parallel and perpendicular to the electric field, especially at low CNT concentrations [Oliva-Aviles et al., 2012].

[0145] This invention describes a novel electrode fabrication process in which CNTs or other conductive carbon additives are induced to align in a desired direction, and the electrode slurry mixture is deposited onto a current collector while controlling the electrical and mechanical properties to align the conductive carbon additives within the electrode. As the electrode passes between two rollers, the rollers can induce alignment of the CNTs or other additives in a variety of ways (see Figure 3), including mechanical shear stress, vacuum suction, and electric or magnetic fields.

[0146] Figure 2 shows the change in PVDF crystal structure from the α phase to the β phase upon electrical polarization and annealing. The β phase PVDF increases the surface hydrophilicity and improves electrolyte diffusion.

[0147] Figure 3 shows a modified R2R process in which an electric field is used to align the carbon additives and change the crystalline phase of PVDF.

[0148] Mechanical shear stress may be applied by compressing two rollers. When the slurry material is compressed flat, the compression force causes shear flow in the slurry material, applying the shear stress necessary to induce alignment. This method can induce the carbon additive to align parallel to the electrode surface. An electric or magnetic field may also be applied to the electrode to induce the carbon additive to align perpendicular to the electrode surface.

[0149] The electric field can be applied by applying a potential to the roller as a conductive electrode. The voltage difference can be direct current (DC) or alternating current (AC). The alignment of the carbon additive depends on the viscosity of the material, the electric field strength, and the exposure time, so the feed rate of the roll-to-roll process can be slowed down or multiple feeds can be repeated to achieve the desired degree of alignment.

[0150] The rollers in the roll-to-roll delivery system can be permanent magnets or electromagnets to generate a magnetic field. A high-intensity magnetic field is required to align the pristine CNTs and carbon additives, but as mentioned previously, physical functionalization with iron oxide nanoparticles can help induce alignment.

[0151] In an exemplary experiment, CNTs are aligned in a polymer nanocomposite using an alternating current. Nanocomposite samples are fabricated using a solution casting technique. PVDF and dimethylthiocarbamate (DMF) are mixed in a 1:10 ratio to create a PVDF matrix. The mixture is stirred on a hot plate at 80°C for 24 hours until the PVDF is completely dissolved in the DMF. Carboxyl-functionalized MWCNTs (10 wt.%) are added to the solution, mixed, and ultrasonically dispersed for 30 minutes.

[0152] The mixture was poured into a mold containing an electric field generator. A high-voltage piezoelectric amplifier (PI E-463) was used in conjunction with a function generator to generate 230 V at a frequency of 250 Hz across a 3 cm gap between two copper electrodes. p-p A sine wave of 7.68 kV is applied between the two electrodes. p-p After applying the electric field for 12 hours, the sample was irradiated with IPL to achieve rapid polymerization and defunctionalization of the CNTs.

[0153] Next, a four-point probe resistivity meter was used to analyze the samples obtained during AC electric field CNT alignment. The square samples were measured along their width and length, one parallel to the applied electric field and the other perpendicular to the applied field.

[0154] [Table 1] The resistance of randomly oriented nanocomposite materials without electric field alignment hardly changes regardless of the measurement direction. When an AC electric field is applied to a nanocomposite material (aligned CNTs), the resistance measured perpendicular to the CNT alignment direction is clearly higher than the resistance measured parallel to the CNT alignment direction. A significant anisotropic resistance value was observed, with the ratio of the resistance in the width direction to the resistance in the length direction being 7.48. The resistance value, which is strongly dependent on the measurement direction, indicates that the CNTs are aligned.

[0155] Fabrication and characterization of experimental electrodes

[0156] To verify the effect of IPL on the application of photoelectromagnetic energy, sample electrodes were prepared. First, experimental PVDF-ACNT (acid-modified MWCNT) nanocomposite thin films were fabricated. PVDF-ACNT containing 6 wt.% CNTs was mixed in a ball mill at 300 RPM for 3 hours and then stirred in an ultrasonic generator for 2 minutes. The resulting slurry mixture was then applied to an aluminum foil and dried in a vacuum oven for 1 hour. Next, IPL was applied to the sample at a distance of 20 mm using various powers ranging from 2.2 kV to 2.8 kV. The fabrication process for the sample electrodes is shown schematically in Figure 4. As shown in Figure 4, the electrode fabrication process may include mixing the slurry mixture, which includes CNT functionalization, ultrasonic treatment, blade coating onto a current collector, drying, roll-to-roll rolling, and defunctionalization. The resulting samples were analyzed using FT-IR, EDX, and resistivity measurements.

[0157] Defunctionalization

[0158] The advantage of chemical functionalization of CNTs with acids is that it provides a strong dispersing effect. One potential drawback of chemical functionalization of CNTs is that the process is complex and can damage the CNT surface, thereby reducing the electrical conductivity of individual CNTs.

[0159] In this study, we address the potential drawback of reduced electrical conductivity by introducing a technique called "in situ defunctionalization by intense pulsed light (IPL) irradiation." The defunctionalization process of functionalized CNTs can vary depending on the type of functional group attached to the CNTs. In the case of acid-modified CNTs, the functionalized CNTs can be restored to their original state simply by chemical reduction or by applying energy in the form of heating in a reducing environment. However, once functionalized CNTs are defunctionalized, they lose their ability to be uniformly dispersed in polymer nanocomposites.

[0160] To take advantage of the dispersion effect of functionalized CNTs while maintaining the electrical conductivity of the original CNTs, heat treatment of the cured polymer-CNT nanocomposite is recommended. PVDF-MWCNT nanocomposites were fabricated by functionalizing MWCNTs with polymers such as N-(4-hydroxyphenyl)maleimide (NHMI) via the Diels-Alder reaction, resulting in uniform dispersion of the MWCNTs in the PVDF matrix. After curing, the MWCNT-PVDF composite was heated at 160°C for 3 hours to induce the Diels-Alder reaction. This resulted in improved electrical conductivity after heat treatment [Chang & Liu, 2011].

[0161] In this invention, instead of heating the nanocomposite for a long time, we use intense pulsed light (IPL) to provide the desired energy, significantly improving production efficiency. Other studies have shown that graphene oxide can be successfully reduced to reduced graphene oxide by IPL irradiation [Yim et al., 2017; Park & ​​Kim, 2015].

[0162] In this study, acid-modified MWCNTs are defunctionalized by applying IPL, especially in polymer solutions. This application demonstrates the rapid defunctionalization of acid-modified MWCNTs by applying IPL, which can restore the high electrical conductivity of the original CNTs while maintaining the position of the dispersed CNTs.

[0163] In this experiment, acid-modified MWCNTs were produced using a formic acid treatment. One gram of pristine MWCNTs (industrial grade; diameter 10–30 nm, length 10–30 μm) was mixed with 250 mL of reagent-grade formic acid. The mixture was sonicated in a reaction vessel for 10 minutes and then stirred at 90 °C for 100 minutes to functionalize the CNTs. The mixture was cooled to room temperature while stirring, diluted with 750 mL of deionized water, and then filtered. The mixture of diluted formic acid and functionalized MWCNTs was filtered using a vacuum funnel, and the filtered MWCNTs were washed with deionized water until the pH reached 7. The filtered MWCNTs were washed again with acetone to remove any excess water or residual acid and then further dried under vacuum for 24 hours. The dried MWCNTs were then collected, with a yield of approximately 80%.

[0164] To investigate the effect of IPL on CNT defunctionalization and dispersion, a simple colloidal experiment was performed. Half of the acid-treated MWCNTs prepared above were exposed to a 3600 W xenon flash IPL for 6 ms. Pristine MWCNTs, acid-modified MWCNTs, acid-modified MWCNTs, and IPL-exposed MWCNT samples were suspended in deionized water and sonicated for 30 minutes. Photographs of the colloidal samples were taken 1 hour after sonication.

[0165] Figure 5 shows MWCNTs suspended in a solvent: (a) the original MWCNT sample, (b) the acid-modified MWCNT sample, and (c) the acid-modified and IPL-treated MWCNT sample.

[0166] From the colloidal tests in Figure 5, it was observed that (a) the original MWCNT sample settled to the bottom of the container, (b) the acid-modified MWCNT sample remained dispersed and suspended, and (c) the acid-modified and IPL-treated MWCNT sample subsequently settled more than the acid-modified MWCNT sample, but (c) the acid-modified and IPL-treated MWCNT sample settled less than the (a) original MWCNT sample.

[0167] This indicates that after acid functionalization, the functionalized CNTs are reduced to original CNTs to some extent after exposure to IPL.

[0168] To better understand this, we fabricated MWCNT-PDMS nanocomposite samples using carboxylic acid-functionalized MWCNTs to determine the effects of functionalization and defunctionalization. 2.5 g of PDMS, 0.25 g of curing agent, and 0.25 g of acid-modified MWCNTs were mixed in 6 g of chloroform. The samples were stirred at room temperature for 2 hours and then sonicated in an ultrasonic bath for 30 minutes.

[0169] The samples were evenly distributed among three petri dishes. Two of the samples were heated at 45°C for 8 hours to completely evaporate the solvent and induce polymerization. The other samples were irradiated with a 3600W xenon flash IPL for 6 ms. Another MWCNT-PDMS petri dish was fabricated using the original MWCNT as a reference sample. The resulting MWCNT samples were compared by measuring the resistance at two points 2 cm apart from the top and bottom surfaces. Five measurements were performed for each sample, and the average resistance for each sample was calculated and listed in Table 2.

[0170] [Table 2] As expected, the acid-modified MWCNT samples exhibited reduced resistance compared to the pristine MWCNT samples due to enhanced dispersion. Interestingly, the effect of IPL irradiation on the samples varied depending on the irradiation time. Irradiation before curing / polymerization produced minimal sample resistance, implying improved conductivity due to defunctionalization. Irradiation after polymerization significantly increased the resistance compared to samples with pristine MWCNTs. Based on the observations made during the IPL irradiation process, we hypothesized that when IPL irradiation was performed before curing / polymerization, excess energy from the IPL irradiation was absorbed during solvent evaporation and rapid polymerization, whereas when IPL irradiation was performed after curing, excess energy was used to burn and damage the MWCNT-PDMS nanocomposite samples.

[0171] Figure 6 shows an SEM image of the active material encapsulated with the polymer binder and carbon additive after IPL application.

[0172] The active material was 89.1 wt.% NMC 811, the polymer binder was 10 wt.% PVDF, and the acid-modified MWCNTs were 0.9 wt.%. IPL was applied at 2900 V for 6 ms in a nitrogen-filled chamber.

[0173] Referring to Figure 6, upon application of IPL, the polymer binder forms a thin, neural network-like network and adheres to the NMC active material, which contributes to an increase in contact surface area and electrical conductivity, improving lithium ion diffusion.

[0174] Figures 7a, 7b, and 7c show (a) 1500–500 cm -1 FT-IR, (b) 3500–1500 cm -1 (c) FT-IR and (d) EDX of the PVDF-ACNT thin film as a function of applied IPL power. The PVDF-ACNT thin film consists of PVDF and 1 wt.% acid-modified MWCNT. IPL is applied for 6 ms at various power levels from 2.2 kV to 2.8 kV with a distance of 2 cm between the IPL lamp and the film.

[0175] For the ACNT / PVDF thin film without IPL treatment, the peaks were 763, 854, 1148, and 1423 cm -1 The α phase of PVDF is shown at 1070 and 1170 cm -1 The β phase, 833, 1231 and 1401 cm -1 When IPL treatment was performed at 2.2 kV, the crystallinity of PVDF was improved, and the peaks at 794, 973, 1208, and 1380 cm -1 The α phase was observed at 1277cm -1 However, as the IPL voltage increased from 2.4 kV to 2.8 kV, the peak intensities corresponding to α, β, and γ gradually decreased, and in the 2.8 kV IPL treatment, the peak intensity at 854 cm -1 Only the α phase was observed. From these results, we concluded that IPL application reduced the crystallinity of PVDF (α, β, and γ) and carbonized the PVDF. By reducing the crystallinity of PVDF, the ionic conductivity can be improved.

[0176] As shown in Figure 7b, the crystallinity of PVDF decreases with increasing IPL voltage, while the carbonization of PVDF improves. Without IPL treatment, the peak peaks are 1900–2000 cm -1 C=C=C between 2140 and 2100 cm -1 There is no peak corresponding to C≡C between these two peaks. However, as the IPL voltage increases from 2.2 kV to 2.8 kV, the intensity of these peaks gradually increases. Similar to the FT-IR results, the fluorine content in the EDX results in Figure 7c decreases with increasing IPL voltage. Before IPL, the atomic percentages of C, F, and O were 65.75%, 28.6%, and 5.65%, respectively. As the IPL voltage increased from 2.2 kV to 2.8 kV, the atomic percentages of C increased from 65.75% to 84.08%, while the atomic percentages of F and O decreased from 28.6% to 13.98% and from 5.65% to 1.91%, respectively. This decrease in the crystallinity of PVDF (i.e., the decrease in the peak values ​​of the α and γ phases) improves the ionic conductivity of PVDF, while the carbonization process ensures the mechanical and chemical stability of PVDF.

[0177] As shown in Figure 7b, the acid-modified carbon nanotubes can be defunctionalized by applying IPL. Before the IPL treatment, the peak at 1710 cm -1 ~1680 cm -1 There is a peak corresponding to C=O between 3024 cm and 3024 cm, and -COOH groups are present in acid-modified carbon nanotubes. The peak was also present during IPL treatment at 2.2 kV and 2.4 kV. However, at IPL voltages above 2.6 kV, the peak was completely eliminated. Furthermore, when the IPL voltage was increased, the peak at 3024 cm was observed. -1 and 2984cm -1 The peaks corresponding to OH and CH between are removed, and during the IPL treatment, both peaks are removed at 2.8 kV.

[0178] Therefore, the FT-IR analysis in Figures 7a and 7b shows that with increasing IPL power, the peaks of the α- and γ-phase crystalline structure of PVDF decrease, and the peak corresponding to OH decreases, indicating the defunctionalization of the acid-modified carbon nanotubes. The EDX analysis in Figure 7c shows that with increasing IPL power, the carbon content increases, indicating the carbonization of PVDF. Figure 7c shows that with increasing IPL power, the carbon content increases, indicating the carbonization of PVDF. The C=C peak value increases with increasing IPL power, indicating that IPL carbonizes the PVDF binder.

[0179] 8a and 8b show (a) sheet resistance and (b) conductivity as the IPL power increases from 2.2 kV to 2.8 kV.

[0180] Carbonization of PVDF and defunctionalization of the acid-modified carbon nanotubes significantly improved the electrical properties of the PVDF-CNT sample electrode surface. Before IPL treatment, the average sheet resistance of the thin film was 2,458 kΩ / sq. As the IPL voltage increased from 2.2 kV to 2.8 kV, the sheet resistance decreased to 112.5 kΩ / sq, 61.58 kΩ / sq, 31.9 kΩ / sq, and 21.8 kΩ / sq, respectively, for a maximum decrease in sheet resistance of 99.11%. The sheet resistance based on IPL voltage showed a more significant improvement in conductivity than sheet resistance compared to the conductivity based on IPL voltage. The average conductivity before IPL treatment was 20.5 mS / m. With increasing IPL voltage, the conductivity gradually increased from 805.2 mS / m to 1246.1 mS / m, 1619.4 mS / m, and 2299.8 mS / m, with a maximum increase rate of 10997%.

[0181] Figure 9a shows a comparison of the half-cell capacity before and after IPL application. Silicon was used as the active material, MWCNTs as the carbon material, and a 1:1 ratio of CMC and SBR as the binder. The ratio of the active material, acid-modified carbon nanotubes, and binder was 72:8:20. Performance evaluation was performed for 20 cycles at a fixed rate of 0.1 C over a voltage range of 0.01 to 1.5 V. At the first cycle, the discharge capacity density of the battery without IPL was approximately 1610 mAh / g, while that of the battery with 2.5 kV IPL was approximately 1780 mAh / g. Therefore, IPL treatment improved the discharge capacity density by 10%. After 20 cycles, there was a significant difference in the discharge capacity density before and after IPL application. The discharge capacity density of the battery without IPL was approximately 150 mAh / g, while that of the battery with IPL was 1180 mAh / g. The capacity density of the battery with IPL applied is approximately 7.8 times higher than that of the battery without IPL applied. As shown in Figure 9a, as the number of cycles increases, the capacity density of the battery without IPL applied decreases rapidly, while the capacity density of the battery with IPL applied decreases gradually. Furthermore, as shown in the charge-discharge efficiency results in Figure 9b, the efficiency of the battery without IPL applied remains around 99% until the second cycle, but decreases to 80% as the number of cycles increases. In contrast, the efficiency of the battery with IPL applied does not decrease and remains above 95% even with increasing cycles. The carbonization of the binder during charge and discharge forms a uniform SEI layer around the active material, improving efficiency.

[0182] Figure 10 shows the results of electrochemical impedance spectroscopy before and after IPL application to the electrode. The charge transport resistance of the battery before IPL was approximately 250 Ω, and after 2.5 kV IPL, the charge transport resistance of the battery was approximately 100 Ω. The charge transport resistance was reduced by approximately 60%. Furthermore, the diffusion resistance decreased by 50%, from approximately 400 Ω to approximately 200 Ω after IPL application. This is due to the improved electrical conductivity between the active materials resulting from the defunctionalization of the acid-modified carbon, and the improved charge transfer between the active materials and the binder due to the carbonization of the binder.

[0183] The subject matter of the present invention can be summarized as follows.

[0184] The present invention provides a method for improving the electrochemical properties of electrodes for lithium batteries, such as lithium ion batteries, lithium metal batteries, lithium air batteries, lithium sulfur batteries or lithium solid state batteries.

[0185] a. the electrode is an anode and / or cathode comprising an active material, a carbon additive, and a polymer binder;

[0186] b. The carbon additive is chemically functionalized or mixed with a surfactant to ensure improved dispersing effect;

[0187] c. Chemically functionalized or surfactant-mixed carbon additives can be defunctionalized by applying energy, thereby improving conductivity or oxidizing and deactivating metal impurities in the carbon additive.

[0188] d. Applying energy to carbonize the polymer binder to further improve electrical conductivity or improve binder properties such as ionic conductivity depending on the increase in crystallinity of the binder's amorphous or beta phase.

[0189] In a method for improving conductivity by adding a highly conductive carbon additive to an anode or cathode composed of an active material and a binder, the carbon additive may include carbon nanotubes such as multi-walled, single-walled, or thin-walled carbon nanotubes, graphene, graphene nanosheets, graphene oxide, carbon nanofibers, or graphite.

[0190] In the method using chemically functionalized dispersed carbon additive materials, the carbon additive is uniformly dispersed in the electrode layer to achieve maximum conductivity. Chemical functionalization techniques using acid and / or urea are used to disperse the originally aggregated carbon additive. Chemical functionalization allows the functional groups (e.g., carboxyl, amine) attached to the carbon additive to repel each other, improving the dispersion effect.

[0191] In a method of using a surfactant to disperse a carbon additive material, the surfactant may be selected from alkylphenol polyoxyethylene ethers (APEOs), silane-modified polycarboxylic acid esters (silane PCEs), cationic polycarboxylic acid esters (C-PCEs), Triton®, and the like, to effect non-covalent physical functionalization of the carbon additive. TM X-100, Twain-20™, sodium dodecyl sulfate (SDS), and sodium dodecylbenzene sulfonate (SDBS).

[0192] In the physical dispersion method of the carbon additive material, the chemically functionalized or surfactant-mixed carbon additive material is dispersed in the electrode mixture slurry using ball milling or ultrasonic treatment at ultrasonic frequencies, followed by drying to solidify the dispersion.

[0193] In a method to restore high conductivity, after the dispersion state is fixed, IPL flash energy application is used to defunctionalize the chemically functionalized carbon additive material.

[0194] In a method for improving the properties of an electrode by carbonizing a polymeric binder material, the polymeric binder may include, but is not limited to, one or more of polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), poly(3,4-ethylenedioxythiophene) polysulfostyrene (PEDOT:PSS), polydiethylene (PDA), polypropylene, polystyrene (PS), polyurethane (PU), polyethylene oxide (PEO), polyethylene terephthalate (PET), styrene-ethylene-butene-styrene (SEBS), glycerin, sucrose, cellulose, lignin, mesophase pitch, polyvinylidene fluoride (PVDF), polyvinylidene trifluoroethylene fluoride (PVDF-TRFE), and parylene-C. Carbonization of the binder and surfactant improves electrical conductivity, thereby improving the hydrophilicity of the electrode and improving electrolyte absorption.

[0195] In this method, the electrode performance is improved by carbonizing the residual surfactant in the electrode composite using IPL instantaneous energy. The surfactants are alkylphenol polyoxyethylene ether (APEO), silane-modified polycarboxylic acid ester (silane PCE), cationic polycarboxylic acid ester (C-PCE), Triton TM The carbonization of the binder or surfactant improves the electrical conductivity, which in turn improves the hydrophilicity of the electrode and improves the absorption of the electrolyte.

[0196] In a method for oxidizing metal impurities such as iron, IPL instantaneous energy application is used. Even in a vacuum or in an inert gas-filled environment, the applied energy utilizes oxygen released from surfactants and polymer binders to carbonize and oxidize the metal impurities.

[0197] In a method for improving electrode properties by making a semi-crystalline polymer binder more amorphous using high-intensity IPL instantaneous energy application, the semi-crystalline polymer binder includes, but is not limited to, one or more of PET, PTFE, PVDF, and PVDF-TRFE. Semi-crystalline polymer binders have a relatively high proportion of crystalline phase, which suppresses the ionic conductivity of the binder material. The application of high-intensity energy reduces the crystalline phase and increases the amorphous PVDF, improving ionic conductivity.

[0198] Electrode properties are improved by repeated cycling at low intensity using IPL pulse energy application in a manner that anneals semi-crystalline polymer binders and induces a β-phase transition in the polymer chains, including, but not limited to, one or more of PET, PTFE, PVDF, and PVDF-TRFE. Polymer crystallinity reduces the ionic conductivity of the material, but can change the surface properties to enhance electrolyte diffusion into the electrode.

[0199] After the dispersion state is fixed, the chemically functionalized carbon additive is defunctionalized to restore high electrical conductivity in a method of defunctionalizing the carbon additive material using one or more of the following energy application methods to pass the energy through the thicker electrode and improve the electrode properties: laser, microwave, or Joule heating.

[0200] In a method for improving electrode properties by carbonizing a polymer binder using one or more energy application methods, including laser, microwave, or Joule heating, and passing the energy through a thicker electrode, the polymer binder may include, but is not limited to, one or more of polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), poly(3,4-ethylenedioxythiophene)polysulfostyrene (PEDOT:PSS), polydiethylene (PDA), polypropylene, polystyrene (PS), polyurethane (PU), polyethylene oxide (PEO), polyethylene terephthalate (PET), styrene-ethylene-butene-styrene (SEBS), glycerin, sucrose, cellulose, lignin, mesophase pitch, polyvinylidene fluoride (PVDF), polyfluorinated VDF-TRFE, and parylene-C. Carbonization of the binder and surfactant improves electrical conductivity, thereby improving the hydrophilicity of the electrode and improving electrolyte absorption.

[0201] The method for improving the properties of an electrode by carbonizing the surfactant remaining in the electrode composite using one or more energy application methods of laser, microwave, or Joule heating, and passing the energy through a thicker electrode, is described. The surfactant is selected from alkylphenol polyoxyethylene ether (APEO), silane-modified polycarboxylic acid ester (silane PCE), cationic polycarboxylic acid ester (C-PCE), Triton TM The carbonization of the binder or surfactant improves the electrical conductivity, which in turn improves the hydrophilicity of the electrode and improves the absorption of the electrolyte.

[0202] In a method for oxidizing metal impurities such as iron, one or more of the energy application methods of laser, microwave, and Joule heating are used to pass energy through a thicker electrode, improving the electrode properties. The applied energy can oxidize metal impurities using oxygen released from a polymer binder and a surfactant, even in a vacuum or in an environment filled with an inert gas.

[0203] In a method for improving electrode properties, a semi-crystalline polymer binder is rendered more amorphous using one or more energy application methods, including laser, microwave, or Joule heating, to pass energy through a thicker electrode, where the semi-crystalline polymer binder includes, but is not limited to, one or more of PET, PTFE, PVDF, and PVDF-TRFE. Semi-crystalline polymer binders have a relatively high proportion of crystalline phase, which inhibits the ionic conductivity of the binder material. High-intensity energy application reduces the crystalline phase and increases the amorphous PVDF, improving ionic conductivity.

[0204] The device for improving the properties of electrode materials includes a roll-to-roll machine with two rollers (to which different potentials are applied), a heater, and a vacuum generator. The device can control the mechanical stress by the roll-to-roll machine and the vacuum generator, the temperature by the heater, and the electric field by the potential applied between the two rollers. The device can improve the properties of materials in the following ways:

[0205] a. Heat treating a semi-crystalline polymer binder to induce a β phase transition.

[0206] b. Electrically poling the semi-crystalline polymer binder to induce a β-phase transition.

[0207] c. The carbon additive material is aligned parallel to the electrode surface by heating and compression.

[0208] d. Apply vacuum pressure to align the carbon additive perpendicular to the electrode surface.

[0209] e. Applying an electric or magnetic field between the two rollers aligns the carbon additive perpendicular to the electrode surface.

[0210] In the method of inducing the β-phase transition of a semi-crystalline polymer binder by heat treatment using the above-mentioned device, the viscosity of the electrode material is reduced by applying heat, and mechanical stress is applied by compressing, resulting in the formation of a more compact and ordered crystalline structure.

[0211] In the method of inducing the β-phase transition of a semi-crystalline polymer binder by electrical polarization using the above device, the phase transition ratio of the semi-crystalline polymer binder is determined by the potential difference applied between two rollers.

[0212] In a method of aligning carbon additives in an electrode by applying compression using the device, heat reduces the viscosity of the electrode material as it moves between two rollers, and the compression applied by the rollers induces a radial shear flow, thereby inducing the carbon additive material to align along the shear flow in a direction parallel to the electrode surface. The degree of alignment can be determined by the viscosity of the electrode material, the temperature, the amount of roll pressing, and the degree of vacuum generated.

[0213] In this method of aligning the carbon additive in the electrode by applying a vacuum using the device, heat reduces the viscosity of the electrode material as it moves between two rollers, and vacuum applied from above and below the electrode induces a shear flow in the material, aligning the carbon additive material in a direction parallel to the electrode surface along the shear flow. The degree of alignment can be determined by the viscosity of the electrode material, the temperature, the amount of roll pressing, and the degree of vacuum generated.

[0214] In the method for aligning carbon additives in an electrode by applying an electric or magnetic field using the device, the electric field generated by AC or DC current or the magnetic field generated by an electromagnet or permanent magnet induces alignment of the carbon additives as the electrode material moves between two rollers. The carbon additives can be original, chemically functionalized, or physically modified with magnetic materials such as iron oxide or cobalt to improve the degree of alignment. The degree of alignment can be determined by the viscosity of the electrode material, the geometry of the carbon additive, the strength of the applied electric or magnetic field, and the frequency of the applied electric or magnetic field.

Claims

1. A method for manufacturing an electrode for a lithium battery, comprising: (a) mixing an active material, a carbon additive, and a polymer binder to form a slurry mixture; (b) depositing the slurry mixture onto a substrate to form a coating; (c) drying the coating; and (d) applying energy to the dried coating, wherein the carbon additive in (a) is chemically functionalized or mixed with a surfactant; The method, wherein the application of energy in (d) defunctionalizes the carbon additive or carbonizes the surfactant.

2. A method for manufacturing an electrode for a lithium battery, comprising: (a) mixing an active material, a carbon additive, and a polymer binder to form a slurry mixture; (b) depositing the slurry mixture onto a substrate to form a coating; (c) drying the coating; and (d) applying energy to the dried coating, wherein the application of energy in (d) carbonizes the polymer binder; method.

3. The method of claim 1 , wherein the application of energy in (d) carbonizes the polymer binder.

4. The method of claim 1 , wherein the application of energy in (d) amorphizes at least a portion of the polymeric binder or changes the crystalline phase of at least a portion of the polymeric binder.

5. 3. The method of claim 2, wherein the application of energy in (d) is carried out in a vacuum or inert atmosphere, and oxygen released from the polymer binder upon application of energy is used to oxidize the metal impurities.

6. 3. The method of claim 1 or 2, wherein in (d) intense pulsed light (IPL) is used.

7. 3. The method of claim 1 or 2, wherein (d) uses one or more of laser, microwave, plasma, or Joule heating.

8. 3. The method of claim 1 or 2, wherein the carbon additive comprises one or more of carbon nanotubes, graphene, graphene oxide, graphene nanosheets, carbon nanofibers, and graphite.

9. 3. The method of claim 1 or 2, further comprising the step of rolling using two rollers after (c).

10. The method of claim 9, wherein the two rollers are applied with different potentials.

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