Electrode for active material-encapsulated lithium secondary battery and method for manufacturing same

Abstract

The present disclosure relates to a method for manufacturing an electrode for a lithium secondary battery that encapsulates an active material by applying energy, which contributes to minimizing the volume change or negative side effects of the electrode, such as high internal stress, fracture, crushing, delamination, electronic insulation of conductive agents, formation of an unstable solid electrolyte interface, and loss of battery energy capacity as much as possible.

Description

[Technical Field]

[0001] This application discloses an electrode for a lithium secondary battery (e.g., lithium ion battery, lithium metal battery, lithium sulfur battery, lithium air battery, etc.), particularly for an active material-encapsulated lithium secondary battery, and a method for manufacturing the same, which can ensure improved performance and reliability of the lithium secondary battery. [Background technology]

[0002] Lithium batteries, such as lithium-ion batteries, are used in a wide range of products, from small portable electronic devices to large electric vehicles, and demand for them is increasing. Furthermore, the shift from fossil fuel-powered vehicles to electric vehicles is becoming more pronounced. Against this backdrop, high-performance lithium batteries are attracting attention. Therefore, technological research is underway to develop lithium-ion batteries that offer higher capacity, longer life, faster charging, and greater safety. One of these technologies involves the development of electrodes using active materials with high energy density.

[0003] Silicon (Si, theoretical capacity 3600 mAh / g) has become an emerging anode active material for lithium-based batteries due to its high energy density. Sulfur (S, theoretical capacity 1675 mAh / g) is also being considered as a cathode active material for lithium-based batteries due to its high energy density. However, silicon and sulfur are known to exhibit high volume expansion rates upon repeated lithiation. This rapid volume change can lead to crushing and delamination of the active material, resulting in poor electrode integrity and electrical insulation and reduced battery performance.

[0004] To solve the problem of active material volume expansion rates, researchers have proposed and tested various ideas. As shown in other intellectual property or academic references below, some ideas involve reducing the particle size of the active material to prevent shattering. Other ideas involve encapsulating the active material using a hard outer shell to inhibit volume change, or providing enough space for a single active material to expand and contract without applying stress to other active materials.

[0005] There are also some ideas for increasing the contact surface area and facilitating ion diffusion by forming a nanoporous structure on the active material or its coating. However, these techniques involve high economic or environmental costs in terms of procedures, which increases the cost of battery products.

[0006] Secondary battery, its manufacturing method, and secondary battery manufacturing apparatus, US 2004 / 0 107 564 A1

[0007] The present disclosure relates to a method for manufacturing a secondary battery including a supply mechanism for anode and cathode sheet materials. The first supply device includes a drive roller rotatable by a motor. The supply devices are connected to a common equipment frame or separate frames via bearings. A pressure device such as a cylinder, spring, or screw shaft presses the rolling roll against the roll of the device with a predetermined force. The first supply system supplies positive electrode plates to the first application system. The second supply device has a structure similar to the first supply device. This device supplies negative electrode plates to the second application system.

[0008] Carbon nanotube polymer lithium-ion battery and its manufacturing method, CN 2016 / 105 720 265A

[0009] This application relates to a cathode made of lithium cobalt oxide and lithium nickel cobalt manganese oxide and having a carbon nanotube polymer coating. This application also describes a battery manufacturing process. The battery has high gram capacity and energy density, high residual capacity after repeated charging and discharging, and a long cycle life.

[0010] Hybrid Nanowire Anode Compositions for Lithium-Ion Batteries, Global Graphene Group, US 2017 / 9 564 629 B2

[0011] This application relates to a hybrid nanowire electrode composition for electrochemical batteries. The composition comprises a collection of nanoscale conductive wires. The collection can be made of materials such as carbon nanotubes (CNTs) or carbon nanofibers (CNFs) that are interconnected to form an interconnected void network. The micro- / nanoscale surfaces are coated with the wires and made of anode active materials capable of absorbing and releasing lithium ions. The cathode active materials can be made of various materials, such as silicon, silicon alloys, and silicon oxides.

[0012] Compositions Comprising Nanoparticles and Nanostructured Support Matrices, and Methods for Fabricating Reversible High-Capacity Anodes in Energy Storage Systems, University of Pittsburgh, US 2020 / 10 878 977 B2

[0013] This application relates to compositions and methods for fabricating lithium-ion battery anodes. The methods form vertically aligned nanostructured support matrices composed of nanostructures, such as carbon nanotubes. Interfacial bonding between the nanostructured support matrix and nanoparticles forms high-performance electrodes for lithium-ion batteries. The support matrix may be grown on a matrix composed of a current collector material.

[0014] Electrodes and methods using porous silicon nanostructures, JP 2017 / 518 621 A

[0015] This application relates to a silicon-based microstructured material for battery electrodes. The material consists of porous silicon spheres mixed with CNTs. The porous silicon spheres are synthesized through a hydrolysis process in which magnesium is thermally reduced while the surface is protected. By mixing the porous silicon spheres with CNTs, battery electrodes are formed with better charge transfer and minimize the degradation of the electronic contact between the silicon and the additive or binder.

[0016] Nanotube Composite Anode Materials for Lithium-Ion Battery Applications, Argonne, University of Chicago, US 2011 / 0 104 551 A1

[0017] This application relates to anode materials for lithium-ion batteries that consist of carbon nanotube composites. The materials consist of aligned carbon nanotubes with lithium alloying materials on their internal or external surfaces. A commonly used lithium alloying material is silicon. The combination of silicon and aligned carbon nanotubes can achieve faster charge / discharge rates, higher capacity, and greater stability during cycling. This is because the CNTs can compensate for the large volume expansion through elastic deformation, preventing delamination.

[0018] Method for producing negative electrode material for lithium ion batteries, WO 2015 / 124 049 A1

[0019] This application relates to the formation of anode materials for lithium-ion batteries. Carbon nanotubes are dispersed in a solution and then subjected to multiple sintering and drying processing steps to form a composite material consisting of CNTs, silicon, and carbon. Silicon is sandwiched between the carbon nanotube network and the outer carbon shell, acting as a buffer layer to prevent expansion. Additionally, the CNT network and outer carbon shell improve the electrical conductivity of the silicon.

[0020] Silicon-carbon negative electrode active material and its manufacturing method, silicon-carbon negative electrode material, and lithium-ion battery, CN 2020 / 110 697 685 A

[0021] This application relates to a composite material for forming the negative electrode of a lithium-ion battery. The composite material consists of silicon particles mixed with metal particles and a carbon material present in some form. The silicon-carbon material is coated with a carbon nanotube conductive network. The silicon particles produced by this manufacturing method are uniformly coated with a dot-wire composite conductive network of one-dimensional linear carbon nanotube composites containing metal particles. This improves the silicon conductivity, resulting in improved cycle stability and rate performance.

[0022] Positive electrode active material for secondary batteries and its manufacturing method, LG New Energy, KR 2015 / 68 458 B1

[0023] Physical damage to silicon due to repeated charge-discharge cycles is a common issue in the field of LIBs. Double-walled CNTs (DWCNTs) can be used as a protective layer for silicon particles to minimize physical damage due to expansion. The present positive electrode active material comprises CNTs with multiple silicon particles embedded within nanotubes. The nanotubes are open at the top and bottom, allowing the silicon particles to freely enter the structure. The outer layer of DWCNTs has a hexagonal structure, which allows radial breathing vibrations. This allows the internal volume of the CNT to freely change depending on the silicon particles. The maximum weight percentage of silicon within a single DWCNT is 80 wt.%. Above this threshold, the lithium ion adhesion effect decreases, and the silicon expands during charge and discharge, making it difficult to maintain the internal space of the CNT. If the silicon content is less than 20 wt.%, electrical conductivity decreases. Finally, to ensure that the particles are retained within the nanotubes during charge and discharge and that sufficient free space remains within the nanotubes, the radius of the silicon particles must be within the range of 50–200 nm. CNT sheet 10 -6 The nanotubes are placed in an ultra-high vacuum (UHV) chamber at less than Torr, and high-purity silicon particles (99.98% or higher) are embedded in the vapor phase. The silicon vapor enters the nanotubes through van der Waals and capillary forces. Finally, the chamber temperature is set to 600°C and the nanotubes are cooled under UHV for 8 to 24 hours. During the cooling process, the silicon vapor forms nanoparticles with a radius of 50 to 200 nm.

[0024] Electrodes for lithium batteries with large volume changes, US 2015 / 0099187A1

[0025] This application relates to a pomegranate-like hierarchical structure with electrically interconnected primary silicon nanoparticles and individually designed nanoscale empty spaces. The spaces are encapsulated by carbon layers to form micron-scale secondary particles. The adaptability to internal volume expansion and spatial restriction of SEI formation provide excellent cycle life (e.g., at 1000 cycles, capacity retention is at least about 97%), while the secondary structure reduces the electrode / electrolyte contact area, thereby improving CE and increasing tap density. Furthermore, the structure exhibits unprecedented stable cycling (e.g., at 100 cycles, capacity retention is at least about 94%) and large-area capacity similar to that of commercially available lithium-ion batteries (e.g., at least about 3.7 mAh / cm). 2 ) has been demonstrated. The design principles developed in this study can be widely applied to other high-capacity lithium battery electrodes, such as germanium (Ge), tin (Sn), tin oxide (SnO), silicon oxide (SiO), phosphorus (P), and sulfur (S). Furthermore, the present study developed an electroless plating method to form a substantially uniform copper coating on the silicon pomegranate-like structure. The presence of the copper plating layer significantly improves the interparticle conductivity in the electrode. This allows the copper-plated structure to exhibit stable cycling performance under high mass loading (e.g., at least about 4.10 mg / cm after 100 cycles). 2 At a mass loading of 1000 mAh / cm, the areal capacity is at least about 3.13 mAh / cm 2 ), and excellent rate performance (e.g., at least about 86.1 mAhg at 1C rate) -1 , at least about 467mAhg at 4C rate -1 ) and has excellent electrochemical properties.

[0026] Carbon silicon composite and its manufacturing method, US 10193148B2

[0027] This application relates to a method for producing a silicon-carbon composite, including the steps of: (a) preparing a silicon-carbon polymer matrix slurry containing silicon slurry, carbon particles, a polymer monomer, and a crosslinking agent; (b) preparing a carbonized silicon-carbon polymer matrix by heat-treating the silicon-carbon polymer matrix slurry; (c) pulverizing the carbonized silicon-carbon polymer matrix structure; and (d) preparing a silicon-carbon composite by combining the carbonized silicon-carbon polymer matrix structure with a first carbon source and conducting a carbonization process. The present invention utilizes heat to carbonize the polymer to form a silicon-carbon polymer matrix, similar to the proposed embodiment. However, this carbonization method is limited to a heating process.

[0028] Si / C composite material, its manufacturing method, and electrode, US 2014 / 0234722A1

[0029] This application relates to a composite material having a novel silicon-carbon composite structure, a method for producing the same, and an anode material for lithium-ion batteries that can ensure high charge / discharge capacity and high cycle performance. The novelty of this application lies in the use of a carbon-containing source gas when heating silicon nanoparticles to induce the formation of a carbon layer on the silicon nanoparticles.

[0030] Encapsulated positive electrode active material particles, lithium battery containing the same, and method for manufacturing the same, WO 2018 / 186963A1

[0031] The present application relates to positive electrode active material particles for lithium batteries, which include one or more positive electrode active material granules coated or encapsulated with a thin layer of a highly elastic polymer. The highly elastic polymer described herein has a recovery tensile strain of 5% or more and a tensile strength of 10% at room temperature. -6 It has a lithium ion conductivity of 5 S / cm or more.

[0032] Encapsulated negative electrode active material granules, lithium battery containing the same, and method for manufacturing the same, WO 2018 / 191026A1

[0033] The present application relates to negative electrode active material particles for lithium batteries that include one or more negative electrode active material particles coated or encapsulated with a thin layer of a highly elastic polymer.

[0034] Prior art documents

[0035] Charter document

[0036] (Document 001) US 2004 / 0107564 A1 (June 10, 2004)

[0037] (Document 002) CN 105720265 A (June 29, 2016)

[0038] (Document 003) US 9,564,629 B2 (February 7, 2017)

[0039] (Document 004) US 10,878,977 B2 (December 29, 2020)

[0040] (Document 005) JP 2017 / 518621 A (July 16, 2017)

[0041] (Document 006) US 2011 / 0104551 A1 (May 5, 2011)

[0042] (Document 007) WO 2015 / 124049 A1 (August 27, 2015)

[0043] (Document 008) CN 110697685 A (January 17, 2020)

[0044] (Document 009) KR10-1568458 B1 (November 5, 2015)

[0045] (Document 010) US 2015 / 0099187 A1 (April 9, 2015)

[0046] (Document 011) US 10,193,148 B2 (January 29, 2019)

[0047] (Document 012) US 2014 / 0234722 A1 (August 21, 2014)

[0048] (Document 013) WO 2018 / 186963 A1 (October 11, 2018)

[0049] (Reference 014) WO 2018 / 191026 A1(2018.10.18)

[0050] (Reference 015)US 2010-0035152 A1(2010.02.11)

[0051] Non-patent literature

[0052] (Reference 001) Li, L., Yang, H., Zhou, D., & Zhou, Y. (2014). Progress in Application of CNTs in Lithium-Ion Batteries. Journal of Nanomaterials, 2014, 1-8. https: / / doi.org / 10.1155 / 2014 / 187891

[0053] (Reference 002) Tagawa*, K., & Brodd, RJ (2008). Production Processes for Fabrication of Lithium-Ion Batteries. Lithium-Ion Batteries, 1-14. https: / / doi.org / 10.1007 / 978-0-387-34445-4_8 (Production Processes for Fabrication of Lithium-Ion Batteries. Lithium-Ion Batteries)

[0054] (Reference 003) BJ Landi, MJ Ganter, CD Cress, RA DiLeo, and RP Raffaelle, “Carbon nanotubes for lithium-ion batteries,” Energy & Environmental Science, vol. 2, no. 6, p. 638, Apr. 2009. L. Xue, G. Xu, Y. Li, S. Li, K. Fu, Q. Shi, and X. Zhang, “Carbon-Coated Si Nanoparticles Dispersed in Carbon Nanotube Networks As Anode Material for Lithium-Ion Batteries,” ACS Applied Materials & Interfaces, vol. 5, no. 1, pp. 21-25, 2012.

[0055] (Reference 004) BJ Landi, MJ Ganter, CD Cress, RA DiLeo, and RP Raffaelle, “Carbon nanotubes for lithium-ion batteries,” Energy & Environmental Science, vol. 2, no. 6, p. 638, April 2009.

[0056] (Reference 005) Song, DP, Li, W., Park, J., Fei, HF, Naik, AR, Li, S., Zhou, Y., Gai, Y., & Watkins, JJ (2021). Millisecond photothermal carbonization for in-situ fabrication of mesoporous graphitic carbon nanocomposite electrode films. Carbon, 174, 439-444. https: / / doi.org / 10.1016 / j.carbon.2020.12.036

[0057] (Reference 006) Song, DP, Naik, A., Li, S., Ribbe, A., & Watkins, JJ (2016). Rapid, Large-Area Synthesis of Hierarchical Nano-porous Silica Hybrid Films on Flexible Substrates. Journal of the American Chemical Society, 138(41), 13473-13476. https: / / doi.org / 10.1021 / jacs.6b06947

[0058] (Reference 007) Bhandavat, R., & Singh, G. (2013). Stable and Efficient Li-Ion Battery Anodes Prepared from Polymer-Derived Silicon Oxycarbide-Carbon Nanotube Shell / Core Composites. The Journal of Physical Chemistry C, 117(23), 11899-11905. https: / / doi.org / 10.1021 / jp310733b

[0059] (Reference 008) Colombo, P., Mera, G., Riedel, R., &Soraru, GD (2010). Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced Ceramics. Journal of the American Ceramic Society, no. https: / / doi.org / 10.1111 / j.1551-2916.2010.03876.x

[0060] (Reference 009) S. Choi, DS Jung, JW Choi, Scalable fracture-free SiOC glass coating for robust silicon nanoparticle anodes in lithium secondary batteries, Nano Lett., 14 (2014), pp. 7120-7125.

[0061] (Reference 010) Muhammad Idrees, Saima Batool, Qiang Zhuang, Jie Kong, Ilwoo Seok, Jiaoxia Zhang, Hu Liu, Vignesh Murugadoss, Qiang Gao, Zhanhu Guo, Achieving carbon-rich silicon-containing ceramic anode for advanced lithium-ion battery, Ceramics International, Volume 45, Issue 8, 2019, Pages 10572-10580.

[0062] (Reference 011) V. Liebau-Kunzmann, C. Fasel, R. Kolb, R. Riedel, Lithium containing silazanes as precursors for SiCN: Li ceramics-a potential material for electrochemical applications, J. Eur. Ceram. Soc., 26 (2006), pp. 3897-3901.

[0063] (Reference 012) M. Graczyk-Zajac, G. Mera, J. Kaspar, R. Riedel, Electrochemical studies of carbon-rich polymer-derived SiCN ceramics as anode materials for lithium-ion batteries, J. Eur. Ceram. Soc., 30 (30) (2010), pp. 3235-3243.

[0064] (Reference 013) J. Kaspar, M. Graczyk-Zajac, R. Riedel, Lithium insertion into carbon-rich SiOC ceramics: influence of pyrolysis temperature on electrochemical properties, J. Power Sour., 244 (2013), pp. 450-455

[0065] (Reference 014) D. Su, YL Li, Y. Feng, J. Jin, Electrochemical properties of polymer-derived SiCN materials as the anode in lithium-ion batteries, J. Am. Ceram. Soc., 92 (2009), pp. 2962-2968.

[0066] (Reference 015) H. Fukui, K. Eguchi, H. Ohsuka, T. Hino, K. Kanamura, Structures and lithium storage performance of Si-OC composite materials depending on pyrolysis temperatures, J. Power Sour., 243 (2013), pp. 152-158

[0067] (Reference 016) Byoung-Sun Lee, Jihyun Yoon, Changhoon Jung, Dong Young Kim, Seung-Yeol Jeon, Ki-Hong Kim, Jun-Ho Park, Hosang Park, Kang Hee Lee, Yoon-Sok Kang, Jin-Hwan Park, Heechul Jung, Woong-Ryeol Yu, and Seok-Gwang Doo, Silicon / Carbon Nanotube / BaTiO3 Nanocomposite Anode: Evidence for Enhanced Lithium-Ion Mobility Induced by the Local Piezoelectric Potential, ACS Nano 2016 10 (2), 2617-2627

[0068] (Reference 017) S. Satapathy, PK Gupta, S. Pawar, and KBR Varma, “Crystallization of Beta-phase Poly(vinylidene fluoride) films using dimethyl sulfoxide (DMSO) solvent and at suitable annealing condition,” arXiv:0808.0419 [cond-mat], Aug. 2008.

[0069] (Reference 018) KR May, The collison nebulizer: description, performance and application, J. Aerosol Sci., 4 (1973), pp. 239-243 Summary of the Invention [Problem to be solved by the invention]

[0070] The present disclosure relates to lithium secondary batteries, such as lithium ion batteries, lithium metal batteries, lithium sulfur batteries, and lithium air batteries. A lithium secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode and negative electrode each include a current collector and an active material.

[0071] The present disclosure relates to a novel active material encapsulation method that provides a multilayer structure with a hard protective shell, space for volume expansion, and a nanoporous structure for ion diffusion, employing a manufacturing process that saves energy and time while minimizing initial installation costs.

[0072] An embodiment of the manufacturing process according to the present disclosure is a roll-to-tall (R2R) manufacturing process, which makes several additions to the conventional R2R manufacturing process while maintaining essentially the same efficiency as the conventional R2R manufacturing process. [Means for solving the problem]

[0073] The present disclosure aims to provide a method for encapsulating active materials (e.g., silicon or sulfur) that have a large volume expansion coefficient by mixing the active material with one or more polymer binders to encapsulate the active material within the polymer, and then carbonizing the outer shell of the active material by applying energy (e.g., electromagnetic radiation).

[0074] In the present disclosure, techniques for applying energy may include electromagnetic radiation such as laser, microwave, or intense pulsed light (IPL), or Joule heating processes that may partially carbonize the polymer binder material.

[0075] The polymer binder includes 1D or 2D carbon-based materials, such as carbon nanotubes and / or graphene oxide, which can enhance the absorption of electromagnetic energy over a wide wavelength range and improve the electrical conductivity of the resulting structure.

[0076] Polymer binder materials are used in combination with two binders with different boiling points, or formed from double-network (DN) hydrogels. In this way, an energy-intensive carbonization process can evaporate the low-boiling material along with the solvent, leaving behind a nanoporous structure that allows lithium ions to diffuse into the core active material.

[0077] Among the various energy application methods, the IPL process relies on the spontaneous irradiation of a high-power xenon lamp within a few milliseconds, so that the carbonization process is primarily concentrated on the surface of the outer shell, resulting in a multilayer structure with a hard carbonized outer layer and a soft polymer inner layer.

[0078] The carbonized outer shell provides electrical conductivity and structural support at the solid electrolyte interface (SEI), while the soft polymer inner layer is elastic and provides volumetric expansion space for the active material without creating high mechanical stress.

[0079] The binder material may be a silicone polymer (i.e., polysiloxanes and polycarbosiloxanes) and / or a sulfur-containing polymer (i.e., polysulfoxides and poly(sulfur nitride)) that incorporates an active element. The active element within the polymer binder provides additional energy capacity to the electrode.

[0080] The binder material may also be a piezoelectric polymer, such as polydifluoroethylene (PVDF), which converts the internal stress generated during volume expansion of the active material into a piezoelectric charge, further speeding up the charging process.

[0081] The encapsulation and energy application process may be performed during the preparation of the powdered active material or after the slurry is deposited on the current collector. The encapsulated active material can be powdered using an atomizer or electrospray process to form particles with a diameter of several hundred nanometers. The encapsulated active material can be formed by exposing the powder to energy irradiation. Another method is to deposit the slurry mixture on the current collector using a coater and then roll it to form a thin electrode film. The encapsulated active material can be formed by exposing the thin film to energy irradiation.

[0082] Another method is to form an electrode using electrospinning. A polymer binder can form fibers and encapsulate the active material within the fibers. Carbonizing the spun fibers can further enhance their mechanical strength, electrical conductivity, and nanoporous structure. The fiber felt produced by electrospinning does not require additional deposition processes; it can be directly placed on top of a current collector as an electrode layer.

[0083] Specifically, the method for lithium secondary batteries of the present disclosure contributes to minimizing volume changes or negative side effects (e.g., high internal stress, fracture, crushing, delamination, electronic insulation of conductive agents, formation of unstable solid electrolyte interfaces, and battery energy capacity loss) of the anode and cathode of lithium secondary batteries (e.g., lithium ion batteries, lithium metal batteries, lithium-air batteries, lithium-sulfur batteries, lithium solid-state batteries, etc.) as much as possible.

[0084] The composition according to the method for producing an electrode for a lithium secondary battery of the present disclosure includes an active material, a polymer binder, a carbon-based additive, and a solvent. The composition contains 80 to 95 parts by weight of the active material, 1 to 10 parts by weight of the conductive carbon-based additive, and 3 to 10 parts by weight of the polymer binder, per 100 parts by weight of the solid content excluding the solvent. The contents of the active material, conductive carbon-based additive, and polymer binder may vary depending on the types of materials used. Furthermore, depending on the type of polymer binder used, 50 to 90 parts by weight of the solvent may be used per 100 parts by weight of the solid content. The above material contents are preferred to ensure uniform dispersion of the materials, smooth deposition, and an appropriate thickness of the active material container, but are not limited thereto.

[0085] The disclosed method for encapsulating active materials includes preparing an encapsulated powder, preparing an encapsulated electrode based on the slurry, and applying energy to carbonize the encapsulated layer and generate nanopores.

[0086] According to the present disclosure, the electrode active materials have high energy capacity and large volume change upon lithiation. Positive electrode materials include silicon, silicon oxide, silicon carbide, magnesium silicide, silicon-iron-manganese alloy, manganese silicate, various silicon alloys, aluminum, tin, and Li. x Possible anode materials include, but are not limited to, Si-LiO core-shell nanoparticle pre-lithiated alloys and mixtures thereof, as well as conventional intercalated graphite in different formulations. Negative electrode materials may include, but are not limited to, sulfur.

[0087] According to the present disclosure, the polymeric binder material for encapsulating the active material comprises a mixture of two or more polymers and copolymers with different boiling points, which may include, but are not limited to, two or more of polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS), polydiacetylene (PDA), polypropylene (PP), polystyrene (PS), polyurethane (PU), polyethylene oxide (PEO), polyethylene terephthalate (PET), styrene-ethylene-butylene-styrene (SEBS), glycerol, asphaltenes, mesophase pitch, sucrose, cellulose, and lignin.

[0088] According to the present disclosure, the polymeric binder material for encapsulating active materials is formed from a double-network (DN) hydrogel, which is composed of a conventional covalently cross-linked polymer reproducibly bound with another network. DN hydrogels may include combinations of carboxymethylcellulose (CMC) and polyacrylic acid (PAA), polyacrylic acid (PAA) and polyethylene glycol (PEG), polyacrylic acid (PAA) and polyethyleneimine (PEI), polyacrylic acid (PAA) and chitosan, styrene / butadiene copolymer (SBR) and polymethyl methacrylate (PMMA), and many more.

[0089] According to the present disclosure, the polymer binder material may include a polymer having an active material element including a silicone material (e.g., polysiloxane, polysilsesquioxane, polycarbosiloxane, polyborosiloxane, and polysilylcarbodiimide) capable of providing an additional charge, and a sulfur-containing polymer (e.g., polysulfoxide and poly(sulfur nitride)). A portion of the polymer having the active material element may be carbonized by applying energy to form an outer shell. In this case, the outer shell may include SiOC (silicon oxycarbide), SiC (silicon carbide), SiBCN (silicon boron carbonitride), SiCN (silicon carbonitride), SC (sulfur-carbon composite), SCN (thiocyanate), etc. Furthermore, when the active material includes a substance such as magnesium, zinc, titanium, or iron, a polymer containing such a substance may be used as a binder, and a portion of the binder may be carbonized by applying energy.

[0090] According to the present disclosure, the polymer binder material is comprised of a polymer with piezoelectric properties that can provide additional charge during lithiation cycling due to internal stress generated by the increase in volume of the active material. Examples of polymers with piezoelectric properties include, but are not limited to, semi-crystalline polymers such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene (PVDF-TRFE), and parylene-C.

[0091] Carbon-based additive materials may include, but are not limited to, nanoparticles such as single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) such as double-walled and triple-walled CNTs, thin-walled carbon nanotubes (TWCNTs), graphene, graphene oxide, and carbon dots. Carbon-based additive materials are used as conductive agents in active materials with low electrical conductivity or polymer binders. Carbon-based additive materials can also provide structural support due to their high strength-to-weight ratio. Furthermore, because carbon-based additive materials have a wide wavelength range and can achieve high energy absorption rates, they can be used as energy absorbers in methods that apply light or laser energy.

[0092] The solvent may include, but is not limited to, water, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylsulfoxide (DMSO), or combinations thereof.

[0093] According to the present disclosure, the method for encapsulating the powdered active material comprises:

[0094] Step a) of preparing an electrode slurry mixture including the active material, a polymer binder material, a carbon-based additive material, and a solvent;

[0095] Step b. atomizing the electrode slurry mixture to generate small droplets using an atomization method such as impact atomization, ultrasonic atomization, or electrospray;

[0096] Step c) drying the droplets in the air suspension chamber using an infrared heater system to circulate the droplets in air and dry the particles of active material encapsulated in the polymer binder;

[0097] applying energy to transform dry particles of active material encapsulated in a polymeric binder;

[0098] i. A nanoporous structure layer formed after evaporating the low boiling point solvent and polymer to facilitate the diffusion of lithium ions;

[0099] ii. a carbonized outer surface layer that provides structural hardness and electrical conductivity; and

[0100] iii. Step d) of forming a partially carbonized or non-carbonized polymer inner surface layer that provides elastic deformation space for the volume change of the active material upon lithiation.

[0101] According to the present disclosure, techniques for applying the energy may include electromagnetic radiation such as laser, microwave, or intense pulsed light (IPL), or a Joule heating process that partially carbonizes the polymer binder material.

[0102] According to the present disclosure, the method for encapsulating the active material comprises obtaining a coated electrode configuration using the following steps:

[0103] a. An electrode slurry mixture is prepared containing the active material, polymeric binder material, carbonaceous additive material, and solvent, and after processing, the encapsulated active material is powdered by ball milling or freeze milling.

[0104] b. The electrode slurry mixture is deposited onto a current collector using a heated coater.

[0105] c. applying energy to the electrode slurry mixture;

[0106] i. A nanoporous structure layer formed after evaporating the low boiling point solvent and polymer to facilitate the diffusion of lithium ions;

[0107] ii. a carbonized outer surface layer that provides structural hardness; and

[0108] iii. Converting into an encapsulated active material that includes a partially carbonized or non-carbonized polymeric inner layer that provides elastic deformation space for the volume change of the active material upon lithiation.

[0109] According to the present disclosure, the energy application method includes:

[0110] The target sample is

[0111] a. In powder form, suspended in air, placed in a transparent cylindrical chamber with a reflector covering the surface to maximize energy efficiency; and

[0112] b. When it is applied to a current collector in the form of an electrode and rolled, Uses strong pulsed light. According to the present disclosure, the energy application method includes:

[0113] a. In powder form, suspended in air and flowing at high speed through a small hole that is continuously irradiated with laser or microwaves; and

[0114] b. When it is applied to a current collector in the form of an electrode and rolled, Laser or microwave is used.

[0115] According to the present disclosure, the energy application method includes applying the target sample in the form of an electrode to a current collector and rolling it while supplying electrical energy by Joule heating.

[0116] According to the present disclosure, the method for forming the carbon-silicon composite or silicon oxide uses carbon precursor materials, including but not limited to pitch, mesophase pitch, isotropic pitch, asphaltenes, and the like.

[0117] According to the present disclosure, the method for producing the mixture includes mixing a carbon precursor material with silicon or silicon oxide using a solvent, dispersing the silicon or silicon oxide in the mixture by stirring and ultrasonication, and then drying the solvent. Mixing can be performed in a high-viscosity state using a spherical mixer without using a solvent.

[0118] According to the present disclosure, the carbonization method involves applying energy to the mixture by one or a combination of intense pulsed light (IPL), microwave, IR, laser, or other techniques to embed the silicon or silicon oxide into carbon.

[0119] According to the present disclosure, the method for preparing the electrode mixture includes using electrospray technology to emulsify a mixture of active material, carbon-based material, polymer binder, and solvent under an electric field to form microspheres with a diameter of less than 5 μm before preparing an electrode slurry.

[0120] In another embodiment, instead of the slurry preparation method described above, an electrode fabrication method uses electrospinning technology to produce a polymer fiber felt, encapsulating the active material within the hollow structure of the electrospun fibers rather than a spherical coating. The electrospun fiber felt then undergoes the energy application process described above to become a nanoporous carbonized fiber felt, encapsulating the active material within its hollow core, thereby reducing the volumetric change of the active material during lithiation cycling.

[0121] According to the present disclosure, a method for manufacturing the pre-lithiated anode that can improve Coulombic efficiency includes:

[0122] a step a) of prelithiating the powdered active material prior to the encapsulation and carbonization processes;

[0123] Step b: prelithiating the powdered active material after the encapsulation and carbonization processes;

[0124] Step c) of prelithiating the electrode after the electrode manufacturing process and carbonization process;

[0125] step d) prelithiating the electrode by direct contact with lithium metal on the electrode;

[0126] and step e) prelithiating the powdered active material by energetically treating the lithium salt to reduce the lithium.

[0127] According to the present disclosure, the powdered active material is prelithiated prior to the encapsulation and carbonization. The prelithiation is performed by mixing the active material with high-temperature (above 200°C) solid lithium, molten lithium, or a lithium solution, thereby forming Li x S., Li. x Si or Li x SiO x The pre-lithiated active material particles are then dried with dry air to form lithium alloy active material nanoparticles coated with a lithium oxide shell for stabilization. The pre-lithiated active material is mixed with a polymer binder and a carbon additive and treated with energy such as IPL, microwave, laser, and Joule heating to produce an encapsulated multilayer nanoporous active material powder. The core of the multilayer structure is the pre-lithiated active material. The encapsulated pre-lithiated powder is then used to fabricate electrodes by a slurry deposition process.

[0128] According to the present disclosure, the method involves prelithiating active material encapsulated in a multilayer nanoporous carbonized shell by applying energy such as IPL, microwave, laser, or Joule heat. The encapsulated active material particles are mixed with high-temperature (above 200°C) solid lithium, molten lithium, or lithium solution to form lithium alloy active material particles within the core. The nanoporous structure can achieve prelithiation of the active material within the core. The encapsulated prelithiated powder is then used to fabricate an electrode via a slurry deposition process.

[0129] According to the present disclosure, the method involves encapsulating the active material and then prelithiating the anode by applying energy such as IPL, microwave, laser, Joule heat, etc. The fabricated electrode is prelithiated by immersion in molten lithium, contacting a current-carrying lithium foil, or immersing in a lithium solution.

[0130] According to the present disclosure, the method involves depositing lithium metal on an electrode to prelithiate the electrode. The effect of this method is to add a small amount of lithium to the anode by depositing lithium metal on the electrode before fabricating the battery. The battery, in which the cathode and anode are coated with lithium metal, is subjected to one charge-discharge cycle at 0.1 C, thereby electrochemically lithiating the active material in the anode. Lithium metal deposition methods include physical vapor deposition (PVD), chemical vapor deposition (CVD), molten lithium spraying, and hot pressing using lithium flakes. Applying energy such as IPL or Joule heat melts the lithium metal deposited by the above method, enhancing electrode adhesion and achieving uniform prelithiation of the anode.

[0131] According to the present disclosure, the method involves pre-lithiating a powdered active material by treating a lithium salt with energy to reduce lithium. The method employs a thermal reduction method in which lithium oxide is reduced to metallic lithium by heat treatment. When using a metal whose oxidation reaction free energy is significantly different from that of lithium, lithium is reduced to oxidize the metal. For example, when silicon metal, which is an anode material, is used as a reducing agent, lithium oxide is reduced to lithium metal by applying energy such as IPL, microwave, laser, or Joule heat. Furthermore, depending on the temperature at which energy is applied, the silicon surface is coated with lithium metal, and Li is oxidized. x SiO x Prelithiated silicon particles such as [Brief explanation of the drawings]

[0132] [Figure 1] This figure shows a comparison of the schematic structure of active materials encapsulated in a polymer binder material before and after the energy application process. Application of energy via intense pulsed light (IPL), laser, microwave, or Joule heating rapidly vaporizes the low-boiling polymer. The escaped gas forms nanopores in the binder material. Furthermore, after the energy application, the surface of the polymer binder is carbonized, while the inner layer of the polymer binder remains a soft polymer binder. [Figure 2] It shows how polymer encapsulation and application of energy to the active material prevents shattering. [Figure 3] It shows the piezoelectric charge generated by the volume change of the active material. [Figure 4] 1 shows the nanoporous structure that develops upon application of energy. [Figure 5] 1 shows the electrospray process and the application of the slurry during the encapsulation process. [Figure 6] The application of electrospinning process and its fiber felt in the encapsulation process is demonstrated. [Figure 7] The active material, encapsulated in suspended powder form, is dried using an infrared (IR) heater. [Figure 8] The application of IPL energy carbonizes the outer surface, forming a nanoporous structure on the polymer binder and encapsulating the active material in a suspended powder. [Figure 9] 1 shows a scanning electron microscopy (SEM) image of the active material encapsulated in the polymer binder, which clearly shows the nanoporous structure of the polymer binder after encapsulation. [Figure 10] Energy dispersive X-ray (EDX) and Raman spectra of a sample electrode formed from active material encapsulated in a polymer binder are shown in Figure 10. The diagram in Figure 10 demonstrates the formation of the expected encapsulation layer, showing peaks representing the active material (silicon), carbon at the carbonized surface and carbon-based additive material, as well as peaks representing the polymer. [Figure 11] A comparison of the electrical conductivity of different electrode materials encapsulated in a polymer binder and processed through an energy application process is shown in Figure 11. After the application of energy via IPL, laser, microwave, or Joule heating, the electrode conductivity significantly increases. [Figure 12]1 shows a comparison of the capacity of half-cells before and after employing the encapsulation method of the present disclosure, where the samples encapsulated and processed using the method of the present disclosure have better energy capacity, even after extensive charge and discharge cycles. [Figure 13] 1 shows a comparison of the electrochemical impedance of half-cells before and after employing the encapsulation method of the present disclosure, with the sample encapsulated and processed using energy having a lower impedance across the entire frequency range. [Figure 14] Prelithiation before encapsulation and carbonization (FIG. 14), prelithiation after encapsulation and carbonization methods (FIG. 15) and prelithiation for manufacturing processes are shown. [Figure 15] Prelithiation before encapsulation and carbonization (FIG. 14), prelithiation after encapsulation and carbonization methods (FIG. 15) and prelithiation for manufacturing processes are shown. DETAILED DESCRIPTION OF THE INVENTION

[0133] Referring now to the drawings, several aspects according to the present disclosure will be described in detail by way of example and not by way of limitation.

[0134] The following description and examples described herein are provided by way of example to illustrate specific implementations of the principles of each aspect of the subject matter of the present disclosure. These examples are for illustrative purposes only and are not intended to limit the principles and aspects of the subject matter described above. In the description, like reference numerals are used throughout the disclosure and in the drawings to refer to like parts, respectively. The drawings are not necessarily drawn to scale, and in some cases the scale may be increased to more clearly depict particular features.

[0135] 1. Expansion of active material

[0136] Silicon, along with aluminum, tin, and sulfur, is an active material for future lithium-ion battery electrodes due to its high energy capacity. Graphite, currently the most commonly used anode material, reacts with lithium ions through an intercalation process, storing up to one lithium ion per six-carbon ring at 372 mAh / g [Obrovac, 2018]. Silicon is also known to react with lithium ions through an alloying process, storing up to 15 lithium ions in a chain of four silicon atoms at 3579 mAh / g [Obrovac and Krause, 2007].

[0137] However, silicon and other active materials that undergo metal alloying reactions during repeated lithiation processes present their own challenges. Lithium-silicon alloys can form with expansion rates of as much as 280% [Lee et al., 2012], causing various problems. The high mechanical stresses experienced by active materials can lead to fracture and crushing, electronic insulation of conductive materials, the formation of unstable solid electrolyte interfaces (SEIs), and lithium ion trapping, all of which result in losses of energy capacity and electrical performance [Obrovac and Chevrier, 2014]. Table 1 compares the theoretical energy capacity and volumetric expansion rate during the lithiation process for various active materials.

[0138] [Table 1] Various solutions have been proposed to address volumetric expansion and the problems associated with it. One solution is to use only active materials smaller than 50 nm in size, thereby nanoparticleizing the active material to prevent shattering. By reducing the dimensional scale of particle size and film thickness, the rate of strain energy release can be reduced, thereby preventing fracture. However, the active material still undergoes significant volumetric changes, placing unnecessary stress on the internal battery structure and packaging.

[0139] Another potential solution is to suppress volume expansion by providing structural support. Several intellectual property rights and published academic papers have demonstrated that incorporating carbon nanotubes (CNTs) into electrode materials suppresses volume change. CNTs are extremely lightweight, have very high tensile strength, and have high electrical conductivity, making them suitable for use as a conductive network to minimize loss of electrical performance even as volume expands. In one study, silicon nanobeads were roped together using CNTs to ensure constant contact between the silicon and the CNT frame [Sun et al., 2013]. This ensures stable electrical connection with the CNTs, strengthening expansion / contraction control during lithiation / delithiation cycling and preventing cracking. Furthermore, a similar effect can be achieved by simply dispersing (rather than embedding) silicon nanoparticles within a CNT network, achieving a similar CNT framework in a different way. Silicon nanoparticles can be coated with amorphous carbon and then dispersed into a CNT network by simple mixing [Xue et al., 2012]. Constant current charge / discharge tests showed that the addition of CNTs prevented cracking and shattering of the electrode due to significant volume changes, improving stability.

[0140] However, these methods are known to be costly, energy intensive, or require long processing times. The embodiments of the present disclosure encapsulate active materials using a cost-effective method while achieving the desired characteristics of suppressing volume expansion, preventing shattering, and stabilizing the nanoporous structure and solid electrolyte interface (SEI).

[0141] 2. Encapsulating active materials

[0142] This disclosure describes how encapsulating an active material with a polymer can suppress the volume expansion of the active material and its resulting side effects, such as fracture, shattering, and loss of electrical performance. The goal of this disclosure is to form a multi-layer encapsulation structure. Figure 1 shows a schematic diagram of the structure and manufacturing process of the encapsulated active material.

[0143] Referring to FIG. 1, in the method of manufacturing the electrode of the present disclosure, after the active material 110 is encapsulated with a polymer binder 120, a carbon-based additive 130 is dispersed in the polymer binder 120.

[0144] The encapsulated active material 100 includes an outer shell 121 and an inner shell 122 formed by the application of energy, and an active material 200 having encapsulated and carbonized nanopores 125. After the application of energy, only a portion of the polymer binder 120 is carbonized. Thus, the polymer binder 120 may include the outer shell 121 and the inner shell 122. The outer shell 121 is carbonized to become rigid. The outer shell 121 provides electrical conductivity and structural support, forming a stable thin solid electrolyte interface. The inner shell 122 between the outer shell 121 and the core active material 110 includes an uncarbonized soft polymer, which can reduce mechanical stress caused by volume changes in the active material during the lithiation and delithiation processes. The polymer binder 120 has multiple nanopores 125 formed therein to facilitate the diffusion of lithium ions.

[0145] FIG. 2 shows how polymer encapsulation and application of energy to the active material prevents shattering.

[0146] On the left side of Figure 2, active material 10 is coated with a polymer binder 20 to secure the active material to the current collector. In this case, active material 10 can expand during lithiation, and the greater stress experienced by the active material can result in crushing 22 of the active material.

[0147] On the right, the active material 110 is encapsulated in polymeric materials 121, 122 and is energized. The outer shell 121 is made of a hard, carbonized binder, while the inner shell 122 is made of a soft, uncarbonized polymer. The polymeric binder 10 outside the outer shell 121 is used to seal and secure the carbonized active material to the current collector after the carbonization process. The active material is allowed to expand in volume, while the inner shell 122, which contains the soft polymer, is able to absorb stress.

[0148] The following sections describe the materials used for encapsulation and how the desired multilayer structure is produced. First, we describe how the active material is encapsulated and manufactured in powder form. Then we describe the electrode manufacturing process, whether using encapsulated powders, raw materials encapsulated after electrode deposition, or other methods to form the electrospun felt for the electrode.

[0149] 2.1 Production of active material encapsulated powder

[0150] In this process, active materials with high volume expansion coefficients are encapsulated with a polymer binder and processed to form multilayer encapsulated powders, which can be used to produce electrodes using conventional manufacturing processes.

[0151] 2.1.1 Materials

[0152] The encapsulation active material forms a desired structure by combining various materials, such as active material, polymer binder, carbon-based additive, and solvent. The polymer binder employs four potential polymer types: polymers for producing nanoporous structures, double-network (DN) hydrogels, polymers containing active elements, and piezoelectric polymers.

[0153] For example, Figure 3 shows the piezoelectric charge generated by the volume change of the active material when a piezoelectric polymer is used as the polymeric binder.

[0154] 3 includes an active material core 110 and piezoelectric binder shells 221, 222 that encapsulate the active material core 110. The piezoelectric binder shells include a carbonized outer shell 221 and a non-carbonized inner shell 222. Because the non-carbonized inner shell 222 contains a piezoelectric binder, upon lithiation (A), the active material generates internal stress due to volume expansion, generating an electric charge (B).

[0155] Hereinafter, polymer materials containing piezoelectric binders that can be used in the present disclosure and their roles in lithium secondary batteries will be specifically described.

[0156] active material

[0157] Active materials that require encapsulation have a large volume expansion rate, primarily due to the lithiation mechanism of these active materials. For example, silicon is a promising anode material with a theoretical capacity of 3600 mAh / g and a volume expansion rate of 320% due to the metal alloying lithiation mechanism. Sulfur has also been recognized as a promising cathode material, capable of forming lithium polysulfide with a theoretical capacity of 1675 mAh / g and a volume expansion rate of 80%. This disclosure primarily describes optimization processes for improving the electrochemical properties of silicon- or sulfur-based electrodes. However, these processes are not limited to silicon or sulfur, and are applicable to other active materials, such as aluminum and tin.

[0158] polymer binder

[0159] Polymer binder materials are the primary encapsulating material for active materials. Traditionally, binders bond active materials together within an electrode and adhere the electrode to the current collector. However, as silicon emerges as a promising active material, polymer binder materials are key to mitigating volume expansion, maintaining integrity, and stabilizing charge and recharge cycles. This disclosure describes an energetically engineered polymer binder encapsulation layer that achieves the desired structure consisting of a nanoporous layer, a hard shell layer, and a soft inner layer.

[0160] Polymeric binders for nanoporous structures.

[0161] In conventional lithium-ion batteries, the charge / discharge rate is a key factor in determining battery performance, along with stability and energy capacity. The lithiation process of the anode is usually slower than the delithiation process of the cathode, and the slow lithiation rate of graphite anodes causes many problems, especially lithium deposition [Liu et al., 2019].

[0162] The lithiation rate of graphite can be improved through techniques, many of which involve enhancing the lithium ion diffusion rate by creating voids within the graphite structure. Cheng et al. [Cheng et al., 2015] etched graphite using potassium hydroxide (KOH) to create holes on the pristine graphite surface. This increased the number of holes available for lithium entry, reducing the specific area and the lithium ion diffusion distance, thereby improving coulombic efficiency, rate capability, and cyclability [Cheng et al., 2015]. Similarly, Chen et al. used laser patterning techniques to create patterns of holes on the graphite surface. These holes provided linear or short-distance diffusion paths for rapid lithium ion transport [Chen et al., 2020].

[0163] A highly porous matrix provides more pathways for lithium ions to reach the active material, so metal-alloyed active materials benefit from accessible interconnected porosity even in silicon active materials [Antartis et al., 2015]. demonstrated that in anodes fabricated with tin (Sn) / PVDF / AB (acetylene black) composites, the energy capacity increases with increasing porosity, with the maximum capacity achieved at porosities above 44% [Antartis et al., 2015].

[0164] As mentioned above, providing accessible pathways for lithium ions is crucial, especially since the active material is encapsulated within the polymer. The question is how to create a porous encapsulation structure for the active material.

[0165] For example, Sohn et al. employed a chemical etching method to create voids in nonporous Si-C composite powders using sodium hydroxide (NaOH) solution [Sohn et al., 2016]. This method creates a porous structure within the Si-C structure, but involves simultaneous etching of silicon and carbon. The process also involves mixing alkaline and acidic solutions with the powder, etching the mixture, and neutralizing it, adding an additional step.

[0166] Shao et al. proposed a more straightforward nanocomposite structure using porous carbon to encapsulate silicon nanoparticles. The silicon nanoparticles were individually coated with a porous carbon shell layer 15–20 nm thick and 3–5 nm in pore size [Shao et al., 2013]. Shao et al. achieved this structure by carbonizing glucose, using Pluronic F127 ((C3H6O·C2H4O)x) as a pore-forming agent. The glucose was converted to carbon at high temperatures (700°C) for a prolonged period (12 hours), while the Pluronic F127 evaporated, forming a porous structure within the carbonized glucose. This method was unpopular due to its high energy consumption and time required, but its concept forms the basis of this disclosure.

[0167] In this disclosure, nanoporous structures are formed using a mixture of two or more polymers and copolymers with different boiling points. Theoretically, by applying thermal energy in various ways, the lower-boiling polymer can be evaporated along with the solvent, resulting in the formation of a nanoporous structure of the higher-boiling polymer. The claimed polymers include a mixture of two or more polymers and copolymers with different boiling points. The polymer mixture may include, but is not limited to, two or more different combinations of polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS), polydiacetylene (PDA), polypropylene (PP), polystyrene (PS), polyurethane (PU), polyethylene oxide (PEO), polyethylene terephthalate (PET), styrene-ethylene-butylene-styrene (SEBS), polyvinyl alcohol (PVA), glycerol, sucrose, asphaltenes, mesophase pitch, cellulose, and lignin.

[0168] Figure 4 shows the nanoporous structure produced by energy application using two polymer binders with different boiling points.

[0169] 4, the carbon additive 130 is dispersed in polymer binders 410, 420. For example, the low boiling point polymer 410 may be placed in powder form within the high boiling point polymer 420. Upon application of energy, the low boiling point polymer 410 rapidly evaporates, unlike the high boiling point polymer 420. This results in nanopores 125 at the locations of the low boiling point polymer 410.

[0170] Double network hydrogel as a binder

[0171] Another potential polymer binder material is double-network (DN) hydrogel. Hydrogels have a three-dimensional cross-linked network structure, are highly flexible, and have a high water content. Due to their biocompatibility and functionality, hydrogels have been applied in various fields, including tissue engineering, drug delivery, soft actuators, and even sensors. However, hydrogels have poor mechanical properties [Chen et al., 2020]. To overcome this weakness, various types of self-healing hydrogels, including double-network hydrogels, have been developed [Basu et al., 2017]. Self-healing double-network (DN) hydrogels consist of conventional covalently cross-linked polymers and other networks through renewable bonds. In addition to their ion transport capabilities, their self-healing properties and stronger mechanical properties have also attracted the interest of battery researchers, making them potential solid electrolyte candidates [Duan et al., 2018; Wu et al., 2018] and polymer binder materials [Gendensuren and Oh, 2018].

[0172] Gendensuren and Oh grafted alginate with polyacrylamide (PAAm) and crosslinked it physically and chemically to form double crosslinks. Alg-g-PAAm also formed double crosslinks when mixed with an active material (silicon and graphite) slurry. Gendensuren and Oh noted that Alg-g-PAAm significantly enhanced adhesion between the active material and the current collector, further enhancing adhesion when the binder was crosslinked. Most importantly, crosslinked Alg-g-PAAm exhibited excellent properties in suppressing the volumetric expansion of Si-C electrodes. When Alg alone was used as the binder, the volumetric expansion rate of the Si-C electrode reached 451%, whereas when crosslinked Alg-g-PAAm was used, the volumetric expansion rate was reduced to 97%. Furthermore, the crosslinked Alg-g-PAAm binder improved the reversible capacity and Coulombic efficiency of Si-C electrodes with large volumetric changes [Gendensuren and Oh, 2018]. Thus, DN hydrogels are polymeric binders that are potential candidates for encapsulable active materials.

[0173] This disclosure explores the potential application of DN hydrogels as polymeric binder materials for encapsulating silicon active materials. DN hydrogels may include combinations of carboxymethyl cellulose (CMC) and polyacrylic acid (PAA), polyacrylic acid (PAA) and polyethylene glycol (PEG), polyacrylic acid (PAA) and polyethyleneimine (PEI), polyacrylic acid (PAA) and chitosan, styrene / butadiene copolymer (SBR) and polymethyl methacrylate (PMMA), and many more.

[0174] Polymers containing active elements

[0175] To minimize capacity degradation due to volumetric changes of silicon during lithiation / delithiation cycling, silicon-based polymer-based ceramics containing highly crystalline amorphous carbon have been investigated [Liebau-Kunzmann et al., 2006]. Electrodes fabricated from silicon carbonitride (SiCN) [Graczyk-Zajac et al., 2010], silicon oxycarbide (SiOC)-coated silicon nanoparticles [Choi et al., 2014], SiOC [Halim et al., 2016], silicon composites, carbon and silicon oxycarbide [Vrankovic et al., 2017], and SiCN and graphite composites [Graczyk-Zajac et al., 2011] have demonstrated good stability and recyclability compared to silicon-based electrodes. Idrees et al. concluded that these materials performed well because their porous structures accommodate volumetric changes and the presence of carbon contributes to their high electrical conductivity [Idrees et al., 2019]. Therefore, the precursor materials and the conditions of their pyrolysis process can significantly affect the structure and carbon components of the electrode, which can directly determine the final electrochemical properties [Riedel et al., 2013; Su et al., 2009; Fukui et al., 2013].

[0176] This disclosure proposes the use of silicones, silicon-based polymer-derived ceramic precursor materials, and sulfur-containing polymers as polymer binder materials to encapsulate the corresponding active materials (silicon and sulfur). When encapsulating the active materials (silicon and sulfur), silicones (e.g., polysiloxanes, polysilsesquioxanes, polycarbosiloxanes, polyboronsilanes, polysilylcarbodiimides) and sulfur-containing polymers (e.g., polysulfoxides, poly(sulfur nitride)) can be converted into SiOC, SiC (silicon carbide), SiCN, SC (sulfur carbide), and SCN (sulfur-doped carbon nitride), which have excellent electrochemical properties. While these materials themselves are used as electrode materials, they are also expected to play a role as binder materials and as active sites for lithiation, thereby further improving energy capacity. However, the pyrolysis process employs a new technology other than the general pyrolysis techniques described below.

[0177] Piezoelectric polymer

[0178] Although volume expansion of active materials is known as a negative characteristic, some efforts have been made to utilize this volume change during lithiation cycling. Lee et al. proposed that the electrochemical properties of silicon CNT electrodes can be improved by incorporating barium titanate (BaTiO3) nanoparticles as a piezoelectric material [Lee et al., 2016]. Lee et al. believe that the internal stress caused by the volume expansion of the electrode activates the piezoelectric particles, accelerating the lithiation rate as the piezoelectric potential increases. The charge / discharge cycles are shorter than those of electrodes without piezoelectric material [Lee et al., 2016].

[0179] Similarly, it has been proposed to use polymer binders with piezoelectric properties to enhance the electrochemical performance of lithium-ion batteries. This example provides a series of potential polymers with piezoelectric properties, including, but not limited to, semi-crystalline polymers such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene (PVDF-TRFE), and parylene-C.

[0180] Piezoelectric polymers, especially PVDF, require a phase transition to the β phase to form a crystalline structure with piezoelectric properties. Electric polarization is known to induce the β phase transition in PVDF [Sanati et al., 2018]. However, thermal annealing is also known to induce the β phase transition in PVDF depending on the annealing conditions [Satapathy et al., 2008].

[0181] Carbon-based additives

[0182] Silicon and sulfur, the active materials recommended for encapsulation, both have low electrical conductivity. Carbon-based additives, such as carbon black, graphite, carbon nanofibers (CNFs), carbon nanotubes (CNTs), graphene, and graphene nanosheets (GNPs), are typically used to enhance the conductivity of electrodes. Carbon-based additives are more popular than other metal-based conductive additives due to their high electrical conductivity, light weight, and chemical stability. Some carbon-based additives, such as carbon nanotubes, carbon nanofibers, and graphene, have high aspect ratios and electrical permeability, allowing them to form conductive networks even in small amounts.

[0183] Furthermore, carbon-based additives are used for further purposes in the proposed encapsulation method. Carbon-based additives are known to improve electromagnetic absorption and reduce electromagnetic reflectance [Kong et al., 2014]. In this study, the structure and properties of the encapsulation layer are altered by irradiating it with electromagnetic energy, such as intense pulsed light (IPL), microwaves, and lasers. Therefore, the addition of carbon-based additives can form a nanoporous structure, increasing the absorption rate of IPL, microwaves, or lasers required to carbonize the encapsulation polymer, thereby reducing the energy required. Due to their inherent IPL absorption capabilities, several studies have shown that adding CNTs to metal inks improves the sintering performance of IPL [Kim et al., 2017]. In particular, UV-Vis measurements have confirmed that CNTs have good light absorption in the wavelength range of 400–1000 nm. Graphene nanosheets (GNPs) also have high electromagnetic radiation absorption [Verma et al., 2017]. Due to the difference in polarization, the mixture of GNPs and multi-walled carbon nanotubes (MWCNTs) is particularly advantageous for microwave absorption ( Chen et al., 2016 ).

[0184] The carbon-based additive is embedded in a polymer binder that encapsulates the active material, which can improve electrical conductivity and energy absorption, and its high tensile strength can provide additional structural support to limit the volume expansion of the active material.

[0185] 2.1.2 Encapsulation process

[0186] This section describes a method for fabricating encapsulated active materials with the expected multilayer hard conductive outer shell and soft polymer inner shell within a nanoporous structure. The process involves the general steps of mixing the materials, forming granules, drying the mixed powder, and finally applying energy to carbonize the outer surface and create the nanoporous structure.

[0187] mixture

[0188] A ball mill is used to mix a slurry of active material, encapsulating polymer binder, carbon additive, and solvent. Silicon nanoparticles with an average diameter of 100 nm are mixed with polyacrylic acid (PAA), COOH-functionalized multi-walled CNTs, and N-methyl-2-pyrrolidone (NMP). The mixing process involves 3 hours of ball milling and 2 minutes of sonication.

[0189] Granule formation

[0190] To powder the individually encapsulated active materials, a granular mixture must be formed prior to drying and energizing. The granular mixture may be formed by a variety of methods, including impact atomization, piezoelectric atomization, ultrasonic atomization, and electrospray.

[0191] The collision nebulizer, developed by KR May in 1972 [May, 1972], has long been recognized as a suitable atomization technique for a variety of liquids. In a collision nebulizer, air passes at high velocity through small holes in the nebulizer, drawing liquid from the nebulizer tank and breaking it into small droplets. The atomized liquid then impacts the tank wall, creating smaller droplets. An outlet bend removes larger particles from the aerosol [CH Technologies, 2017].

[0192] Both piezoelectric and ultrasonic nebulizers use a piezoelectric transducer to generate atomized particles. High-frequency voltage can be applied to the transducer, causing it to vibrate at high frequencies. In an ultrasonic nebulizer, the liquid is placed on the surface of the piezoelectric transducer and vibrates through the transducer. The vibrations create capillary waves (standing waves) in the liquid, and small droplets are released from the liquid mass as an aerosol. In an ultrasonic nebulizer, the sample principle is applied because the liquid is atomized when it reaches the vibrating nozzle surface. The particle size of the atomized particles depends on the applied vibration frequency. The vibration frequency required to generate nanoparticles is several megahertz (MHz). Due to geometric constraints, ultrasonic nebulizers often use frequencies of several megahertz, while nebulizers often use frequencies of tens of kilohertz.

[0193] FIG. 5 shows the electrospray process and the application of the slurry during the encapsulation process.

[0194] According to the present disclosure, as shown in Figure 5, electrospraying using a Collision nebulizer 501 can be used to encapsulate active material 110 in a polymer binder 120 to produce encapsulated active material granules, and to disperse carbon-based active material 130 in the polymer binder 120. Furthermore, as shown in Figure 5, the encapsulated active material granules are used as a substrate 510 such as a current collector.

[0195] Figure 6 shows the application of the electrospinning process and its fiber felt in the encapsulation process.

[0196] In the manufacturing process of an electrode for a lithium secondary battery according to the present disclosure, the electrospinning method shown in Fig. 6 can be used to encapsulate the active material. By electrospinning a precursor solution 601 containing the active material, a polymer binder, a carbon-based additive, and a solvent, the polymer binder forms high-strength fibers 610, encapsulating the active material 110 within the fibers 610. The fiber felt manufactured by the electrospinning process can be directly placed on the top surface of a current collector as an electrode layer without any additional coating process.

[0197] In the experiment, a mixture of silicon nanoparticles as the active material, PAA as the polymer binder, acid-modified multi-walled CNTs as the carbon-based additive, and water as the solvent was fed into a Collison Nebulizer 501 and atomized using flowing compressed air. The ejected granules were collected and dried in a specially designed dryer system.

[0198] 7 shows a schematic of an example dryer system. The dryer system shown includes a transparent cylindrical chamber 710, an atom nozzle 720 that delivers encapsulated active material, an infrared heater 730 that applies heat 735 to the encapsulated active material, and a blower 740 that continuously suspends the encapsulated active material within the transparent cylindrical chamber 710.

[0199] In the dryer system shown in Figure 7, air is circulated by a blower 740 within a sealed transparent cylindrical chamber 710, and granules ejected from an atomic nozzle 720 are continuously suspended in the air and dried by irradiation using an infrared (IR) heater 730 (see Figure 7). The dried nanoparticles are collected while undergoing an additional IPL process and are then observed using a scanning electron microscope (SEM).

[0200] Energy irradiation

[0201] Energy must be applied to carbonize the outer shell and form a nanoporous structure on the encapsulating polymer binder. In conventional methods, the most common method for applying thermal energy is pyrolysis, which often requires a lot of energy and time. The present disclosure uses intense pulsed light (IPL), microwave (MW), laser, and Joule heating techniques to form the desired multilayer encapsulation structure. However, IPL technology is more suitable for powdered materials.

[0202] Intense pulsed light (IPL) is one of many energy delivery technologies, specifically employing rapid-fire electromagnetic radiation generated by a xenon lamp. A high-intensity electrical pulse is applied by a xenon lamp, exciting xenon gas into a high-energy state and then back to a low-energy state, achieving photon irradiation. IPL energy in the form of intense pulsed light is also called flash light. IPL technology has advantages over other electromagnetic energy delivery processes, such as lasers and microwaves, because it can cover large surface areas in a short time. Furthermore, IPL pulse spectra are broad, typically between 200 and 1100 nm, whereas laser or microwave technologies have more targeted wavelength spectra. Modern IPL devices utilize computer-controlled capacitor groups to generate IPL with controlled pulse duration, pulse spacing, number of pulses, and intensity. The fluence (radiant energy received per unit surface area) is a function of the distance from the energy source to the target surface, the angle of the reflector, and the absorbance of the target surface. As mentioned in 2.1.1, a carbon additive with high absorbance over a broad spectrum is present in the mixture encapsulating the active material and converts the absorbed energy into the thermal energy required to produce the carbonized polymer and nanoporous structure.

[0203] The IPL process is a suitable energy application method for powdered encapsulated active materials because IPL can cover large surface areas at once. It is not possible to energize all surfaces of air-suspended colloids encapsulating active materials using lasers focused on smaller, specific areas, or Joule heating, which requires the use of a conductive network. Furthermore, the spectral range of light emitted from a typical IPL system is 200 nm to 1100 nm, with pulse durations of a few milliseconds, resulting in a final energy density of 12 J / cm. 2[Kramer, Wunderlich, and Muranyi, 2017]. Considering a typical IPL system, the diffusion depth of IPL irradiation only reaches approximately 1 μm from the surface. This limited diffusion depth can be a disadvantage for processing large materials. However, in this method, since the energy cannot be diffused into the core, high energy can be used to carbonize the outer shell while leaving the soft polymer inner layer intact, achieving the desired multilayer structure.

[0204] FIG. 8 shows an example of an IPL irradiation device for suspending encapsulated particles in air.

[0205] Referring to Figure 8, to uniformly irradiate the encapsulated active material powder 801 with IPL 835 energy, the dry encapsulated granules 801 are suspended in air by a blower 840 using a specially designed chamber 810. The chamber 810 is made of a light-transmitting material (such as glass or clear polycarbonate). The blower 840 suspends the active material granules 801 in air by continuously blowing air. An IPL lamp 830 faces the chamber 810 using a xenon lamp, and a reflector 820 covers the other side of the chamber 810 to irradiate all sides of the active material granules obtained by the IPL process.

[0206] Figure 9(a) shows an SEM image of dry nanoparticles before energy application. The mass median diameter (MMD) of the dry nanoparticles is approximately several tens to several hundreds of nanometers. The polymer material encapsulates a single silicon nanoparticle. The average thickness of the encapsulating polymer is expected to be several nanometers, considering the diameter of the silicon nanoparticles used.

[0207] Figure 10 shows the energy-dispersive X-ray (EDX) and Raman spectra of sample electrodes formed from active materials encapsulated in a polymer binder. Backscattered X-ray EDX analysis revealed a decrease in the number of oxygen atom peaks, while the number of carbon atom peaks increased. This indicates that the outer shell of the oxygen-containing polymer was carbonized by the IPL process (see Figures 10(a) and 10(b)). Unlike EDX, FT-IR analysis allows scanning through the nanoporous structure to reveal the internal structure. Upon application of IPL, FT-IR analysis clearly showed silicon-related peaks near 965 nm, 668 nm, and 615 nm. Furthermore, upon application of IPL, the intensity of the C-C bond (approximately 2344 nm) peak increased significantly, indicating carbonization of the material. In both cases, the presence of C=O bonds near 1660 nm indicates the presence of a residual PAA polymer layer within the material, and the EDX measurements reveal a highly carbonized surface.

[0208] laser

[0209] Laser energy application also utilizes electromagnetic waves, but lasers emit a narrow wavelength spectrum rather than a broad one. The specific wavelength range varies depending on the laser source. A common Nd:YAG (neodymium-doped yttrium aluminum garnet) laser operates at 1064 nm, while another common CO2 (carbon dioxide) laser operates at a wavelength close to 9.6 μm. Another difference between lasers and IPL is that the laser's irradiation spot area is generally small (typically about 1.0 mm). This is advantageous for focused energy application, but applying energy to a large surface area (e.g., battery electrodes) requires scanning the area. Lasers are commonly used to carbonize carbon precursor materials because their energy is highly concentrated over a short period of time (a few milliseconds). The time scale of the laser carbonization process is known to suppress oxidation reactions even in atmospheric environments, compared to the several hours required for conventional pyrolysis techniques. In this disclosure, selective laser carbonization is a method of applying potential energy after the electrode is fabricated using a slurry mixture.

[0210] 2.2 Electrode fabrication

[0211] The electrochemical properties of lithium-ion batteries fabricated using the methods of this disclosure must be verified by electrode morphology. This section describes three different electrode fabrication methods. One method uses the encapsulated and energy-processed active material powder described above, another method uses a mixture slurry that is applied and processed by applying energy, and yet another method uses a felt of electrospun and carbonized material.

[0212] 2.2.1 Electrode fabrication using encapsulated powder

[0213] Electrodes are manufactured using active material powder encapsulated in a polymer binder and processed by applying energy. The powder obtained in 2.1.2 is mixed with a polymer binder material, a carbon-based additive, and a solvent to form a slurry mixture, which is then applied to a current collector (copper film) using a coater and dried in a vacuum oven at 110°C. The slurry mixture contains 80-90% active material powder, 5-10% carbon-based additive, and 5-10% polymer binder material. The solvent may vary depending on the viscosity of the slurry mixture. The coated slurry is then vacuum dried and processed and compressed using a rolling process.

[0214] 2.2.2 Electrode fabrication using the slurry mixture

[0215] The active material may be encapsulated in a coated electrode layer and then energized. First, a slurry mixture is prepared by mixing the active material, polymer binder, carbon-based additive, and solvent. In this experiment, 100 nm diameter silicon nanoparticles, PAA, and COOH-functionalized MWCNTs (commercially available multi-walled carbon nanotubes with 10–15 walls) are mixed in an 85:5:10 weight ratio using NMP solvent. To promote uniform dispersion, the mixture is ball-milled for 3 hours and then treated with an ultrasonic generator for 2 minutes. The resulting slurry is applied to a current collector at 100 °C using a coater (TMAX-H200T). The deposited / settled slurry is dried in a vacuum oven for 30 minutes and then processed using an energy application method. In this experiment, the IPL method is used, but other techniques such as laser, microwave, and Joule heating can also be used for coated electrodes.

[0216] In an exemplary experiment, IPL was performed at a voltage of 2200 V for 6 ms at a distance of 2 cm. Some embodiments of the present disclosure can realize a silicon / CNT anode three-stage structure design similar to a neural network structure (Figure 9). A spherical or nearly spherical micron-scale porous carbon frame (or other encapsulating structure) contains silicon / CNTNPs. As shown in Figure 9(a), before IPL treatment, 100 nm-sized silicon nanoparticles surround 30 nm-diameter MWACNTs. After 6 ms of IPL treatment at 2.2 kV, silicon begins to aggregate around the ACNTs. After the first IPL treatment, the silicon nanoparticles aggregate into silicon clumps with diameters of several hundred nanometers. As the number of IPL treatments increases from two to three, the size of the silicon clumps increases from 2 μm to 4 μm, and their total mass also increases. Furthermore, IPL treatment connects the individual silicon clumps with a nanoscale-thick multiwalled carbon nanotube frame. Furthermore, nanoscale multi-walled carbon nanotube frames connect the silicon blocks created by the IPL process, a structure resembling a neural network that can facilitate electron transfer.

[0217] Figure 10(a) shows the FT-IR results of the silicon, ACNT, and PAA anodes before and after IPL treatment. Before IPL treatment, the binder PAA peak was at 1100–1700 cm -1 Within the range of 1245cm -1 , which appears in the CO bond of ACNT. As shown in Figures 10(b), (c), and (d), after IPL treatment, all PAA peaks are removed and silicon-related peaks appear. -1 and 2159 cm -1 At 965 cm, a large peak related to the Si-H bond is formed. -1 and 688 cm -1 At 1245 cm, peaks corresponding to Si-OH bonds and SiO2 are formed. -1 The peak at 1245 cm (i.e., the C-O bond) still existed, confirming that the ACNTs were not completely defunctionalized. However, as the number of IPL treatments increased to two and three times, the peak at 1245 cm -1 The peaks at these locations were removed, indicating that all of the ACNTs were defunctionalized. Similar to the FT-IR results, the oxygen content in the EDX results decreased with increasing IPL treatments. Before IPL treatment, the atomic percentages were 64.1% Si, 28.3% C, and 7.6% O. As the IPL treatments increased from one to three, the C atomic percentage decreased from 28.3% to 48%, and the O atomic percentage decreased from 7.6% to 2.12%. The increase in the C atomic percentage indicates that the PAA covering the silicon surface was carbonized, while the decrease in the O atomic percentage indicates that the PAA was carbonized, resulting in defunctionalization of the ACNTs.

[0218] The encapsulation of silicon, carbonization of the PAA surface, and defunctionalization of ACNTs by IPL treatment significantly improved the electrical properties of the anode surface. Figures 11(a) and (b) show the changes in sheet resistance and conductivity of the silicon anode before and after IPL treatment. Before IPL treatment, the sheet resistance of the silicon anode was approximately 13.7 kΩ / sq. As the number of IPL treatments increased from 1 to 3, the sheet resistance decreased from 586.9 Ω / sq to 0.821 Ω / sq, representing a maximum decrease in sheet resistance of 99.99%. The average conductivity was 1.83 S / m before IPL treatment, and gradually increased to 93.12 S / m, 9911.03 S / m, and 29974 S / m with increasing IPL treatments. The maximum increase was 1637608%. The significant improvement in electrical properties due to IPL treatment is due to the formation of neural network structures, carbonization of the PAA surface, and defunctionalization of ACNTs. Before IPL treatment, nanoscale silicon exists between CNTs, preventing them from connecting, resulting in high sheet resistance and extremely low electrical conductivity. However, IPL treatment forms silicon clusters, which contribute to CNT connection. Furthermore, PAA carbonization on the silicon surface and defunctionalization of ACNTs further improves the electrical properties.

[0219] The electrochemical properties of the fabricated electrodes were characterized by electrochemical impedance spectroscopy (EIS) and battery testing. EIS was performed using a Biologic SP-150 potentiometer at room temperature, in the frequency range of 100 mHz to 200 kHz, with a potential amplitude of 5 mV open circuit voltage (OCV). All samples underwent EIS testing before charge / discharge testing.

[0220] Figures 12(a) and 12(b) show a comparison of Nyquist plots determining the change in sample impedance after IPL treatment. The linear portion in Figure 12(a) indicates the diffusion of lithium ions at both electrodes. Impedance spectra are observed within the linear portion. Carbonization of the polymer and defunctionalization of the ACNTs reduce the diffusion resistance by 65% ​​after IPL treatment. The semicircular portion in Figure 12(b) shows a semicircular impedance spectrum at high frequencies. This semicircular portion represents the charge transfer resistance, indicating the redox of lithium ions at the electrode-electrolyte interface. After IPL treatment, the semicircular size decreases by approximately 31%. The improvement in surface conductivity due to IPL treatment is expected to reduce the rate of lithium ion oxidation and reduction, leading to improved charging speeds.

[0221] The neural network Si-CNT anodes with excellent capacity exhibit good cycling performance at different current densities. In both cases, the electrodes were tested at different current densities ranging from 0.1C to 1C. As shown in Figure 13, the IPL-treated Si-CNT composites exhibit excellent performance and battery capacity recovery. In the first cycle, the capacity of the Si-CNT composites subjected to multiple IPL treatments at a 0.1C rate is 25–50% higher than that of the non-IPL-treated Si-CNT composites. As the C rate increases from 0.1C to 0.5C, the Si-CNT composites are completely reduced. The stability of the IPL-treated Si-CNT composites is determined by 20 cycle tests at a 1C rate. After 20 cycles, the capacity of the non-IPL-treated Si-CNT composites decreases by 59%. However, over the course of 20 cycles, the capacity of the Si-CNT composites subjected to multiple IPL treatments decreases by 29–33% compared to the initial point. This is because the carbonization of the silicon surface after IPL treatment suppresses the expansion of silicon that occurs during charging and discharging.In terms of stability, the capacity of Si-CNT composites that have been IPL-treated multiple times is 200% to 256% higher than that of Si-CNT composites that have not been IPL-treated after 20 cycles.

[0222] 2.2.3 Electrospun felt

[0223] The electrospinning process employs a horizontal electrospinning configuration. The electrospinning apparatus uses a high-voltage power supply (Gamma High Voltage Research). This power supply is connected to a syringe needle attached to a syringe pump (New Era 4000). The pump base and drum are grounded. The drum rotates at approximately 200 rpm. The base is connected to a 100 MΩ resistor to maximize coating on the drum and reduce fiber coating elsewhere. The system inlet flow rate is set to 0.5 mL / hr, and a single droplet is maintained at the tip of the needle. The syringe pump is mounted on an XY table programmed to uniformly coat the fibers across the entire drum with a rocking motion. Electrospinning is a cost-effective, simple alternative that can be used to produce nanoscale fibers and nonwoven felts. Porosity and surface area can be controlled during electrospinning.

[0224] As shown in Figure 6, after electrospinning a mixture of polymer, solvent, carbonaceous additive, and active material, IPL or microwave irradiation can be used to partially carbonize the electrospun fibers, creating voids therein. The porosity within the spun fibers facilitates ion exchange. Lithium ions can freely enter the fibers and accumulate within the silicon particles. Silicon particles are also encapsulated within the fibers. The mechanical strength of the fiber structure can inhibit silicon expansion during lithiation cycling.

[0225] 2.2.4 Prelithiation

[0226] In lithium-ion batteries, the first charge process is crucial to their performance. During the first charge process, the organic electrolyte may be reduced, forming a solid electrolyte interface on the anode surface, or during the first lithiation process, some lithium ions may be trapped by the electrode. This can result in an irreversible loss of the battery's net energy capacity. The first cycle is particularly important when silicon is used as the anode. This is because the first-cycle coulombic efficiency of silicon anodes is between 50% and 80% [Wu et al., 2012; Wu et al., 2013; Yi et al., 2013], which is lower than that of graphite anodes (>80%) [Cui et al., 2009].

[0227] A method to compensate for the energy density loss during the first charge cycle is to employ prelithiation, which adds lithium ions to a battery before the first charge cycle to compensate for the irreversible lithium loss during the first charge cycle and provide an additional lithium ion reservoir for battery aging.

[0228] Various lithiation methods were investigated in four different categories. The first method involves the preparation of an electrode slurry using a lithiated active material. The second method is an electrochemical method in which a lithium half-cell is formed using an external short circuit to induce the lithiation process. The third method involves chemical reduction of the active material using a lithium-organic complex. The last method involves reduction of the active material by direct contact with lithium foil or lithium powder when a potential difference exists between the intended anode and a lithium source.

[0229] Each of the above-mentioned prelithiation processes has its own advantages and disadvantages. The lithium additives used in prelithiation face challenges due to their high chemical reactivity and incompatibility with common binders and solvents. Electrochemical prelithiation requires the adoption of a battery pack configuration, making it difficult to scale beyond laboratory experiments. Chemical prelithiation generates chemical waste and may require additional cleaning processes to remove by-products. Direct contact prelithiation presents difficulties in handling highly reactive lithium metal. Among these techniques, the direct contact prelithiation method is used as a scalable industrial process due to its simplicity. To mitigate the challenges associated with highly reactive lithium metal, the use of stable lithium metal powder (SLMP) is considered. In this example, a prelithiation process performed using one of the above methods is implemented in an anode manufacturing process.

[0230] 14 and 15 show the prelithiation method before encapsulation and carbonization (FIG. 14), the prelithiation method after encapsulation and carbonization (FIG. 15), and the prelithiation for manufacturing process.

[0231] This disclosure provides three methods and manufacturing processes for prelithiating anodes. The first method is to prelithiate the active material 110 before encapsulation and carbonization, as shown in Figure 14. Prelithiating an active material 110, such as silicon or sulfur, with a prelithiation solution 1401 or lithium powder creates Li on the surface of the active material 110. x S., Li. x Si, Li x A lithiated material 1415, such as SiO, can be produced to produce the pre-lithiated active material 115. The pre-lithiated active material 115 is encapsulated in a polymer binder 120. When the positive electrode is processed by applying energy using an apparatus such as an IPL system 1402, the surface encapsulating the pre-lithiated active material 400 becomes a polymer inner shell 122 and a carbonized outer shell 121. The active material expands during pre-lithiation, and this expansion occurs primarily due to reaction with lithium during charge and discharge, making the encapsulation of the pre-lithiated active material necessary.

[0232] As shown in Figure 15, a second method is to prelithiate the active material after encapsulation and carbonization. The encapsulated and carbonized active material 200 is prelithiated with a prelithiation solution 1401 or lithium powder, allowing lithium ions to pass through the porous surface of the active material, thereby lithiating the active material and the carbonized surface. In other words, lithiation of the active material 110 forms a prelithiated active material 1415 encapsulated with a polymer binder comprising a carbonized polymer 121 whose surface is also prelithiated 1425. The encapsulated and carbonized prelithiated active material 300 is then coated onto an electrode with a slurry of an addition polymer binder 1450 and dried using a drying system 1403.

[0233] A third method is to prelithiate the electrodes after the electrode fabrication and carbonization process for prelithiation before battery assembly.

[0234] In the above-described method for manufacturing an electrode for a lithium secondary battery according to the present disclosure, an active material is encapsulated and carbonized by applying energy, thereby making it possible to minimize volume changes in the electrode and negative side effects such as high internal stress, fracture, crushing, delamination, electronic insulation of the conductive agent, formation of an unstable solid electrolyte interface, and loss of battery energy capacity.

[0235] Therefore, the method for manufacturing an electrode for a lithium secondary battery according to the present disclosure can be applied to the manufacture of batteries (for example, lithium ion batteries, lithium metal batteries, lithium air batteries, lithium sulfur batteries, lithium solid state batteries, etc.).

[0236] The above embodiments have referred to many exemplary embodiments thereof. However, those skilled in the art can design many other modifications and embodiments. Therefore, it should be understood that such modifications and variations are within the scope of the present disclosure and therefore also within the scope of the technical spirit of the present disclosure. [Explanation of symbols]

[0237] 100: Encapsulated active material 110: Active material (active material core) 115: Pre-lithiated active material 120: Polymer binder 121, 221: Outer shell (carbonized polymer) 122, 222: Inner shell 125: Nanopore 130: Carbon-based additives 200: Carbonized active material 300: Lithium-ion active material (encapsulated and carbonized) 410: Low boiling point polymer 420: High boiling point polymer 501: Collison Nebulizer 510: Base material 601: Precursor solution 610: Fiber 710: Chamber 720: Atomic nozzle 730: Infrared heater 735: Heat 740: Blower 801: Active material granules 810: Chamber 820: Reflector 830:IPL lamp 835: Intense Pulsed Light (IPL) 840: Blower 1401: Pre-lithiated solution 1402:IPL system 1403: Dryer system 1415: Lithium compounds 1450: Additional polymer binder

Claims

1. A method for producing an electrode for a lithium secondary battery, comprising: mixing an active material, a polymer binder, a carbon-based additive, and a solvent; encapsulating the active material with a polymer binder; applying energy to the polymer binder to carbonize a portion of the polymer binder; generating nanopores in the polymer binder by applying energy to the polymer binder; said carbonizing a polymeric binder to form a hard outer shell and a soft inner shell.

2. The active material may be silicon, silicon oxide, silicon carbide, magnesium silicide, silicon-iron-manganese alloy, manganese silicate, silicon alloy, aluminum, tin, Li ｘ Si-Li ２ 10. The method of claim 1, wherein the nanoparticles are one or more of: O core-shell nanoparticles or sulfur.

3. the polymeric binder comprises a first polymer having a low boiling point and a second or third polymer having a boiling point higher than the boiling point of the first polymer; 10. The method of claim 1, wherein the polymer binder comprises two or more of polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS), polydiacetylene (PDA), polypropylene (PP), polystyrene (PS), polyurethane (PU), polyethylene oxide (PEO), polyethylene terephthalate (PET), styrene-ethylene-butylene-styrene (SEBS), glycerol, asphaltene, mesophase pitch, sucrose, cellulose, and lignin.

4. The method of claim 3 , wherein the first polymer is evaporated by applying energy, and the nanopores are formed by evaporation.

5. The method of claim 1 , wherein the polymeric binder comprises a double network hydrogel.

6. 6. The method of claim 5, wherein the double network hydrogel is selected from carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyacrylic acid (PAA), polyacrylic acid (PAA) and polyethylene glycol (PEG), polyacrylic acid (PAA) and polyethyleneimine (PEI), polyacrylic acid (PAA) and chitosan, styrene / butadiene copolymer (SBR), polymethyl methacrylate (PMMA), and combinations thereof.

7. The method of claim 1 , wherein the polymeric binder comprises a polymer having active material elements.

8. The polymer having an active material element includes a silicone selected from polysiloxane, polysilsesquioxane, polycarbosiloxane, polyborosiloxane, and polysilylcarbodiimide, and a sulfur-containing polymer selected from polysulfoxide and poly(sulfur nitride), and 8. The method of claim 7, wherein the application of energy converts a portion of the polymer having the active material element into one or more of SiOC (silicon oxycarbide), SiC (silicon carbide), SiBCN (silicon boron carbonitride), SiCN (silicon carbonitride), SC (sulfur-carbon composite), or SCN (thiocyanate).

9. The method of claim 1 , wherein the polymeric binder comprises a piezoelectric polymer.

10. 10. The method of claim 9, wherein the piezoelectric polymer comprises one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene (PVDF-TRFE), and parylene-C.

11. 10. The method of claim 1, wherein the carbon-based additive comprises one or more of single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), thin-walled carbon nanotubes (TWCNTs), carbon fibers, graphene, graphene oxide, and carbon dots.

12. 10. The method of claim 1, wherein the solvent comprises water, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylsulfoxide (DMSO), or a combination thereof.

13. The encapsulation of the active material is preparing a slurry mixture including an active material, a polymer binder, a carbon-based additive, and a solvent; atomizing the slurry mixture to generate droplets; 2. The method of claim 1, further comprising: drying the droplets in the air suspension chamber with a heater while circulating the droplets in air.

14. The method of claim 1 , wherein the energy application is performed in powder form, electrospun fiber form, or deposited on a current collector.

15. The method of claim 1 , wherein the energy application uses one or more of IPL, laser, microwave, and Joule heat.

16. 2. The method of claim 1, wherein the step of mixing the active material, the polymer binder, the carbon-based additive, and the solvent further comprises mixing a carbon precursor material selected from pitch, mesophase pitch, isotropic pitch, and asphaltenes to form the active material, which is a carbon-silicon composite, silicon oxide, or silicon carbide.

17. Step a) prelithiating the powdered active material prior to the encapsulation and carbonization processes; Step b: prelithiating the powdered active material after the encapsulation and carbonization processes; Step c) of prelithiating the electrode after the electrode manufacturing and carbonization processes; Step d. prelithiating the electrode by direct contact with lithium metal on the electrode; e. prelithiating the powdered active material by energetically treating a lithium salt to reduce lithium.

18. An electrode for a secondary battery comprising an active material, a polymer binder, and a carbon-based additive, where the active material is encapsulated in a polymer binder, A portion of the polymer binder is carbonized, The carbon-based additive is dispersed in a polymer binder; the polymer binder has nanopores; An electrode for a secondary battery comprising a hard outer shell and a soft inner shell formed by carbonizing the polymer binder.

19. A method for producing an electrode material for a secondary battery, comprising: encapsulating the active material with a polymer binder; applying IPL energy to the polymeric binder to carbonize an outer surface of the polymeric binder and to partially carbonize or not carbonize an inner surface layer of the polymeric binder; Including, A method of manufacturing wherein the polymeric binder is carbonized to form a hard outer shell and a soft inner shell.

20. A method for producing an electrode material for a secondary battery, comprising: preparing a slurry mixture including an active material, a polymer binder, a carbon-based additive, and a solvent; breaking the slurry mixture into droplets by an atomization process; drying the droplets using a heater to form a dry powder; suspending the dry powder with a blower in a chamber surrounded by a reflector while applying IPL to the dry powder; applying said IPL energy to said polymeric binder to carbonize an outer surface of said polymeric binder, thereby carbonizing said polymeric binder to form a carbonized hard outer shell and a non-carbonized soft inner shell.

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