Porous anode composite material and preparation method thereof

Abstract

The present application relates to a composite anode material comprising a core with a plurality of active materials and pores formed through the agglomeration of said active materials and the pyrolysis of polymer material. It also includes a conductive material, a carbon conductive network derived from the carbonization of polymer material and present on some surfaces of the active materials and conductive material, as well as a first shell layer coated on the core containing graphene. Additionally, the application discusses an anode electrode incorporating the composite anode material and the associated manufacturing methods.

Description

DescriptionTitle of Invention:

[0001] porous anode composite material and preparation method thereofTechnical Field

[0002] This invention generally relates to lithium-ion electrochemical cells and batteries and specifically focuses on a novel and enhanced anode composition, as well as the method for manufacturing it.Background Art

[0003] Lithium-ion batteries, extensively utilized in various applications like electric vehicles, electronic devices, and power plants, are renowned for their high energy density. These second-generation rechargeable batteries are composed of four primary components: a negative electrode, a positive electrode, an electrolyte, and a separator plate. In traditional lithium-ion batteries, the negative electrode is predominantly made of graphite or graphite with a small proportion of high-capacity active materials, such as silicon, which act as the electrochemically active material. Despite their widespread use, graphite-based electrodes exhibit a relatively low charge / discharge capacity. Consequently, researchers are actively seeking alternative active materials capable of absorbing higher quantities of lithium ions to enhance the specific capacity of these batteries. Proposed replacements include metals that can form alloys with lithium or oxides of these metals, such as tin, silicon, aluminum, gallium, lead, zinc, bismuth, germanium, cadmium, and antimony.

[0004] During the charging and discharging cycles of lithium-ion batteries, the active metals involved in the electrochemical process undergo volume changes as lithium ions are absorbed and desorbed. Over multiple cycles, this repeated volume change can result in the pulverization of these metals, leading to wear and a subsequent decrease in battery capacity.

[0005] Silicon, a primary active material in next-generation lithium-ion batteries, experiences a threefold volume expansion upon absorbing lithium ions, resulting in a noticeable decline in performance. The proximity of the electrolyte to the electrode surface contributes to this issue, as the electrolyte undergoesdecomposition at a specific voltage, dependent on the type of active material. This decomposition leads to the formation of a passive, non-conductive layer, known as the solid-electrolyte interphase (SEI), on the electrode's surface. The solidelectrolyte interphase (SEI) layer is characterized by its non-conductive and brittle nature, rendering it susceptible to fracture under conditions of stress and strain.

[0006] A primary cause of failure in the solid-electrolyte interphase (SEI) layer is the expansion and contraction of the active material within the negative electrode. While the 10% volume change of graphite materials does not significantly impact the integrity of the SEI layer, metals such as silicon, which exhibit high volume expansion, can cause the SEI layer to fracture. This results in a detrimental effect on battery performance, as the continuous formation of new SEI layers consumes lithium. Consequently, mitigating volume change, minimizing direct contact between silicon and the SEI layer, and reducing capacity loss constitute the foremost challenges in implementing next-generation active materials. Addressing these issues has been the focus of numerous research efforts.

[0007] Various structural approaches have been proposed to address these challenges, including the shell-yolk configuration. In this method, silicon particles are initially coated with a removable material (e.g., via heat or a suitable solvent) to mitigate or eliminate the effects of volume change. Subsequently, the coated silicon is encapsulated with a conductive material, such as carbon. The initial coating is then removed, effectively trapping the silicon within the carbon shell. While this method shows promise, its multi-step process makes it rather complex. Furthermore, the low electrical conductivity of silicon limits the structure's ability to achieve maximum lithium absorption capacity, resulting in relatively low overall capacities.

[0008] Another approach involves the deposition of silicon nanoparticles and nanowires, measuring less than 100 nm, within carbon structures such as carbon black and graphite, utilizing the chemical vapor deposition (CVD) method. Subsequently, a carbon coating is applied to the composite structure via a layercoating technique, followed by the application of a chemical vapor layer. Despite the promising results yielded by this composite structure, the cost-intensive and time-consuming nature of the CVD method hinders its industrial scalability and limits its potential applications. Single-layer carbon coatings have been applied tosilicon-based active materials using various methods and precursors to enhance conductivity properties. However, due to the inherent brittleness of carbon, this coating alone is insufficient to withstand the stress induced by silicon's volume changes during cycling. As a result, the carbon coating eventually fractures and loses its functionality.

[0009] In another method, silicon is encapsulated within graphene oxide sheets using a spray drying method, resulting in a powdered structure. To mitigate the adverse effects of silicon's volume changes, a removable polymer material is introduced to create void space within the composite. Additionally, the integration of polymer- based carbon materials enables the modulation of electrical conductivity within the graphene-encapsulated composite. However, the high cost of removable polymer nanoparticles and the challenge of achieving consistent dispersion among all composite materials pose obstacles in ensuring uniform void space distribution around the silicon in each composite.

[0010] To address the issue of silicon particles losing connection with conductive components, such as current collectors and carbon additives, during volume changes, researchers have employed conductive binders. These binders can maintain the connection between silicon particles and conductive components even after multiple charging / discharging cycles. However, their high cost limits their widespread adoption in the industry. Alternative approaches include utilizing polymers like polyacrylonitrile, polyamide, and polyamide-imide as binders, which can also be carbonized. In one example, polyacrylonitrile is employed as a binder for silicon microparticle-based anodes. A slurry consisting of a polyacrylonitrile solution, silicon microparticles, and conductive additives is coated onto a copper foil. The electrode is then subjected to a thermal process, converting the polyacrylonitrile into carbon. This process creates a conductive binder that helps mitigate the issue of silicon isolation. However, it should be noted that the copper foil tends to wrinkle post-thermal treatment, an issue that remains unaddressed by the said invention.

[0011] To address the challenges posed by silicon as an active material, a novel structure was developed with the primary objective of controlling volume changes. This structure is designed to minimize direct contact between silicon and the solidelectrolyte interphase (SEI) layer while also addressing the issue of silicon's lowconductivity. The ultimate aim of this invention is to create a silicon-based negative electrode that exhibits high cycle stability.Summary of InventionTechnical Problem

[0012] In composite structures integrating active particles, conductive materials, and porous elements within a graphite layer, uneven distribution of components can undermine the stability of the solid-electrolyte interphase (SEI) layer, thereby diminishing battery capacity. Furthermore, the current collector's susceptibility to wrinkling post-thermal treatment, notably observed in copper foil, poses a persistent challenge in anode electrode fabrication, warranting attention in the manufacturing process. Hence, employing methodologies facilitating porous composite fabrication is pivotal. These methods should ensure uniform distribution of internal components within the core, accommodating volume changes of active particles effectively. This strategy preserves structural integrity and boosts composite performance, underscoring the significance of innovative fabrication techniques in patent applications. Furthermore, employing fabrication techniques to reduce anode wrinkling proves advantageous.Solution to Problem

[0013] The following summary is not intended to include all features and aspects of the present application, nor does it imply that the application must include all features and aspects discussed in this summary.

[0014] Various embodiments presented herein disclose a novel composite anode material designed for utilization in energy storage systems, particularly lithium-ion batteries. The composite anode material comprises a first core and a first shell layer coated on the first core. The first shell layer encompasses crumpled sheets of graphene, graphene oxide, or partially reduced graphene oxide, while the first core comprises electrochemically active materials, conductive materials, and pores derived from the pyrolysis of a first polymer and agglomeration of active materials. A carbon conductive network, derived from the carbonization of a second polymer, envelops the active materials and conductive materials, enhancing overall conductivity and structural integrity.

[0015] Moreover, disclosed manufacturing methods offer various embodiments for producing the composite anode material. Initially, a mixture of electrochemically active materials, solvent, and a first polymer forms a first mixture, followed by dispersing a second polymer and conductive materials to form a second mixture. Electrospinning and subsequent heat treatment generate a fibrous morphology, facilitating subsequent ball milling to prepare ball-milled particles with high specific surface area and uniform distribution. Further processing involves mixing the ball-milled particles with graphene oxide to form a third mixture, which is spray-dried to yield composite particles comprising the first shell layer and a second core. Heat treatment then pyrolyzes the remaining polymers, yielding the final composite anode material.

[0016] Furthermore, disclosed methods include both double-stage and single-stage processes for fabricating anode electrodes. The double-stage method involves preparing a slurry of the composite anode material, conductive additives, and binders, applying and drying the slurry on a copper foil current collector, and heat treating the resulting electrode under pressure. Conversely, the single-stage method entails preparing a slurry of the composite particle, conductive additives, and water-soluble polyacrylonitrile, followed by applying and drying on a copper foil current collector and subsequent heat treatment under pressure. Both methods yield anode electrodes suitable for integration into lithium-ion batteries, offering enhanced performance and longevity.Advantageous Effects of Invention

[0017] The present invention unveils novel methods for fabricating anode electrodes. The process comprises two pivotal stages: firstly, ensuring uniform distribution of components and porosity within the composite material; secondly, employing an innovative approach to avert cracking in the copper foil. Additionally, a specialized binder for anode production is disclosed, markedly streamlining and augmenting the efficiency of anode manufacturing.Brief Description of Drawings

[0018] The novel features which are believed to be characteristic of the present disclosure, as to its structure, organization, use, and method of operation, together with further objectives and advantages thereof, will be better understood from thefollowing drawings in which a presently preferred embodiment of the present disclosure will now be illustrated by way of example. It is expressly understood, however, that the drawings are for illustration and description only and are not intended as a definition of the limits of the present disclosure. Embodiments of the present disclosure will now be described by way of example in association with the accompanying drawings in which:

[0019] The invention will now be described by reference to the preferred embodiments.Fig.1

[0020] [Fig.1 ] shows an embodiment of the composite anode material, consistent with one or more exemplary embodiments of the present disclosure;Fig.2

[0021] [Fig.2] shows an embodiment of the mixture having fibrous morphology of the composite anode material.Fig.3

[0022] [Fig.3] shows anSEM image of the mixture having fibrous morphology prepared by the electrospinning process.Fig.4

[0023] [Fig.4] illustrates an embodiment of the ball-milled particles of the composite anode material.Fig.5

[0024] [Fig.5] shows an SEM image of the ball-milled particles prepared by the ballmilling process.Fig.6

[0025] [Fig.6] illustrates an embodiment of a composite particle of the composite anode material.Fig.7

[0026] [Fig.7] shows a SEM image of the composite particles prepared by the spray drying process, consistent with one or more exemplary embodiments of the present disclosure;Fig.8

[0027] [Fig.8] shows a SEM image of the composite anode material prepared by the heat-treating process.Fig.9

[0028] [Fig.9] includes a block diagram illustrating the method of forming the composite anode material.Fig.lOA

[0029] [Fig.l OA] includes block diagrams illustrating the double-stage method of manufacturing anode electrodes.Fig.lOB

[0030] [Fig.l OB] includes block diagrams illustrating the single-stage method of manufacturing anode electrodes.Fig.11

[0031] [Fig.1 1 ] shows a TEM image of the composite anode material prepared by the heat-treating process.Description of Embodiments

[0032] The novel features that are believed to be characteristic of the present disclosure, as to its structure, organization, use, and method of operation, together with further objectives and advantages thereof, will be better understood from the following discussion.

[0033] Aspects of the invention are illustrated by way of example and not by way of limitation in the Figures of the accompanying drawings in which references indicate similar elements. It should be noted that references to “an” and “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. In the following description, numerous specific details are set forth to provide a thorough description of the invention. However, it will be apparent to one skilled in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail so as not to obscure the invention.

[0034] Composite Anode Material

[0035] The following description details various embodiments of a composite anode material and a method associated with creating the composite, with various embodiments of the resulting compositions of matter.

[0036] According to Fig.1 an embodiment of the present invention provides a composite anode material 100 including a first core 150 and a first shell layer 142 coated on the first core 150 comprising crumpled sheets of graphene, crumpled sheets of graphene oxide, crumpled sheets of at least partially reduced graphene oxide, or any combinations thereof. The first core 150 may include a plurality of electrochemically active materials 102, a plurality of conductive materials 104, a first plurality of pores 114 obtained from the pyrolysis of a first polymer 106, a second plurality of pores 116 formed by agglomerating of the plurality of active materials 102, a carbon conductive network 112 obtained from the carbonization of a second polymer 108, wherein the carbon conductive network 112 may at least partially surrounds the active materials 102 and the conductive materials 104. The pores can be configured to accommodate volumetric expansion of the active materials 102 during charging of the composite anode material 100.

[0037] In an exemplary embodiment, the electrochemically active materials 102 can be selected from the group consisting of silicon, silicon oxide with oxidation number from 0 to 2, porous silicon, tin, tin oxide, germanium, lead, zinc, aluminum, an alloy thereof, an intermetallic compound thereof, and the metal capable of reversibly absorbing and desorbing lithium ions.

[0038] In an exemplary embodiment, the first polymer 106 can be selected from the group consisting of polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose, lignin, polystyrene, polyether ketone, polyacrylic acid, sodium alginate, polyvinyl chloride, polyvinylidene fluoride or a mixture of two or more thereof.

[0039] In an exemplary embodiment, the second polymer 108 can be selected from the group consisting of polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, phenolic resins, epoxy resin, resorcinol formaldehyde resin, polyamide, polyamide, polyamide imide, glucose, citric acid or a mixture of two or more thereof.

[0040] A typical example of the conductive materials 104 may be at least one selected from the group consisting of carbon black, graphene layers, thermal modified graphene oxide, carbon nanotube, and carbon fibers.

[0041] Method of Manufacturing Composite Anode Material

[0042] A further embodiment of the present invention provides a method of manufacturing the composite anode material 100 of the present invention. Fig.9 includes a block diagram illustrating method 200 of forming the composite anode material 100 of Figs.1 and 8, according to various embodiments of the present disclosure. Fig.1 illustrates an embodiment of the composite anode material 100 and Fig.8 shows a SEM image of the composite anode material 100, consistent with one or more exemplary embodiments of the present disclosure. Referring to Fig.9, in step 202, method 200 may include mixing a plurality of active materials 102, solvent, and the first polymer 106 to form a first mixture. The first polymer 106 is used to produce pores by burning off the polymers.

[0043] In particular, step 204 may include dispersing the second polymer 108 and the conductive materials 104 in the first mixture to form a second mixture, wherein, the second polymer 108 is used to produce carbon by pyrolysis process to form a carbon network, as shown in Fig.8. The second mixture may include from about 0.1 wt % to about 40 wt % active materials 102, from about 0.1 wt % to 40 wt % first polymer 106, from about 0.1 wt % to about 30 wt % second polymer 108, and 0.01 wt % to 5 wt % conductive materials 104 based on the total solvent content.

[0044] In an embodiment, the solvent may be selected from the group consisting of dimethylformamide, acetone, acetonitrile, -nmethyl2-pyrrolidone, chloroform, deionized water, heptane, hexane, or a combination thereof.

[0045] In some embodiment, the morphology of the active materials 102 can be in the form of spherical, plate, wire, and porous particles with an average particle size from about 3 nm to about 5 pm. In an exemplary embodiment, one possible approach may include a precursor such as silicon monoxide or silica to produce silicon and obtain a porous structure. This porous silicon can be employed independently or in conjunction with silicon as an active component.

[0046] In an embodiment, the first polymer 106 may comprise any thermally removable polymer. Alternatively, materials that can be removed via dissolution or etchingprocesses, instead of thermal removal, may be employed within the structure. One such example may include the removal of silica through exposure to a fluoric acidcontaining solution.

[0047] Subsequently, it is necessary to remove the solvent from the second mixture structure using appropriate techniques to ensure that the dispersed and dissolved components are uniformly distributed without solvent. Examples of suitable methods for solvent removal include film casting, electrospinning, and vacuum filtration.

[0048] In step 206, method 200 may include electrospinning the second mixture to remove solvent and achieve a mixture having fibrous morphology 124 comprising fibers 122 having an average fiber diameter from 10 nm to 5 pm as shown in Figs.2 and 3. The utilization of the electrospinning method facilitates the attainment of appropriate distribution and homogeneity in the arrangement of solid materials adjacent to one another. The voltage of the electrospinning machine can vary from 1 to 30 KV depending on the type of morphology required. The distance between the tip of the nozzle and the collector can be adjusted between 4 and 20 cm. Fig.2 provides a schematic representation that illustrates the overall arrangement of the active material 102, conductive materials 104, and a polymer shell 110. In one embodiment the conductive material can be graphene sheets. In one embodiment, the polymer shell 1 10, can include the first polymer 106 and the second polymers 108 within a polymer fiber 120. Fig.3, clarifies in more detail what was disclosed generally in Fig.2 and shows a SEM image illustrating the fibrous structures obtained through the electrospinning process.

[0049] In one embodiment, the mixture obtained from the electrospinning and subsequent drying process forms soft fibers with a fibrous morphology. To prevent agglomeration and adhesion during the subsequent ball milling step, these fibers undergo a crucial heat treatment process. This intermediate step effectively maintains the fiber morphology, mitigating potential processing issues during ball milling and ensuring the production of a high-quality final product. As part of step 208, a specific heat treatment process can be applied to enhance the brittleness of the fibers, typically conducted at temperatures ranging from 80°C to 160°C for a duration of 1 to 24 hours. Upon completion of the designated time period, the fibers are cooled in ambient air to room temperature. In step 210, method 200 mayinclude the ball milling step of the heat-treated mixture having fibrous morphology 124. This step is implemented to obtain a plurality of ball-milled particles 130 with a homogeneous distribution of active materials 102 and conductivity materials 104 in the polymer shell 110 including the first polymer 106 and the second polymer 108 as shown in Figs.4 and 5.

[0050] Fig.4 depicts an embodiment of the ball-milled particles 130 representing a composite anode material particle, while Fig.5 presents a SEM image of these ball- milled particles 130 produced through the ball-milling process, aligning with various exemplary embodiments of this disclosure. The sequential processes of electrospinning, heat treatment, and ball milling offer significant advantages, notably in achieving an augmented specific surface area of the resulting ball-milled particles 130 while ensuring a consistent distribution.

[0051] In step 212, as illustrated in Fig.9, the ball-milled particles 130 may be gathered, and combined with graphene oxide 132 in a solvent, to form a third mixture. The third mixture may include between about 0.1 wt and 5 wt % of graphene oxide 132, based on the total weight of the active materials 102 for example silicone. The graphene oxide 132 can be incorporated either by directly adding its dry powdered form or by utilizing an aqueous suspension. In step 214 according to Fig.9, the method may include spray-drying the third mixture to prepare a spray-dried composite particle which briefly is written as the composite particle 140. The composite particle 140 including a second core 155 which is covered by the first shell layer 142 as shown in Fig.6. Fig.6 illustrates an embodiment of a composite particle 140 of the composite anode material. Moreover, Fig.7 shows a SEM image of composite particles 140 prepared by the spray drying process, consistent with one or more exemplary embodiments of the present disclosure. Referring back to Fig.6, the second core 155 may comprise the plurality of ball-milled particles 130. In step 214, by removing the solvent, the graphene oxide 132 sheets are crumpled to form a first shell layer 142 to cover the second core 155, the second core may include the plurality of active materials 102, conductive materials 104, the first 106 and the second polymer 108. In this exemplary embodiment of step 214 of method 200, an inlet temperature of spray drying can range between 150° C and 500° C. Furthermore, the outlet temperature of the spray drying step may be lower than the melting temperature of the materials in the composite. The flow rate of the spraymay range from 10% to 90% of the maximum power of the device, and the inert gas flow of the spray may range from 100 to 800 L / h.

[0052] In step 216, the method may involve heat treating the composite particles 140 to facilitate the pyrolysis and / or burn off of any polymers present, thereby inducing the formation of the plurality of the first 114 and the second pores 116 and the carbon conductive networks 112. This process substantially enhances the electrical conductivity and mechanical strength of the composite particles 140. For a detailed illustration of the process described in step 216 of Fig.9, refer to Fig.1 , which provides a more comprehensive depiction of the composite anode material 100. This material comprises the first core 150 covered by the first shell layer 142. In this embodiment, the first polymer 106 may be subjected to burning off, thereby creating augmented void spaces within the composite anode material 100 which accommodates for additional volume expansion of particles of the first core 150 material. Furthermore, the second polymer 108 may be subjected to pyrolysis wherein, the heat is employed to convert the polymer into carbon or a residue containing carbon. In this embodiment, the heating process comprises at least two sequential steps to fabricate the composite anode material 100. The initial step involves heating the composite particles 140 in a furnace under an inert atmosphere, such as air, argon, nitrogen, or a combination thereof, from ambient temperature to a predetermined temperature range spanning approximately 180 °C to 320 °C. This temperature ramp-up is conducted at a controlled rate falling within the range of 1 to 10 °C / min.-The composite particles 140 may then be held for 1 to 12 hr hold time to stabilize the carbon precursor. In the second step, the composite particles 140 may be then heated to carbonization final temperature ranging from 450 °C to 1200 °C with a rate ranging from about 3 °C / min to about 15 °C / min, and then may be isothermally heated at the carbonization final temperature for 1 to 6 hr. After the desired time, the furnace may be cooled down to room temperature and the composite anode material 100 can then be removed in an inert atmosphere. The SEM image of the composite anode material 100 manufactured is as illustrated in Fig.8. Furtheremore, Fig.11 provides a more comprehensive depiction of the composite anode material 100 and show a TEM image of composite anode material 100. Referring to Figs.1 and 11 , it may beconfirmed that the composite anode material 100 including a plurality of pores was coated with graphene and a conductive carbon network.

[0053] In certain embodiments, the mechanical strength of the composite anode material 100 structure may be enhanced by applying at least one coating layer either before or after the heat-treatment step. For example, the spray-dried particle 140 can be dispersed in a polymer solution. Methods such as film casting, electrospinning, and vacuum filtration can be employed to remove the solvent and polymer coating on the spray-dried composite. To apply a carbon shell coating to the spray-dried particles, the resulting composite may be subjected to ball milling followed by a heat treatment process. Furthermore, an additional coating can be generated by repeating the spray dry process. The spray-dried composite from the previous stage is reintroduced into the spray-dry process, wherein cellulose nanofibers or cellulose microfibers are employed as a covering agent. These cellulose fibers are used as carbon precursors and are subjected to heat treatment following the dry spray process. Additionally, in some embodiment, the formation of the initial and secondary coatings can involve the utilization of cellulose nano or microfibers as the primary encapsulating layer, with graphene oxide as a second shell.

[0054] In another embodiment, to apply a second coating shell, the spray-dried composite can be spun using the electrospinning method or sprayed with the electrospray method. The coating morphology in this method may comprise fibers, droplets, or a combination thereof. The polymer used for coating can be polyacrylonitrile, polyamide, polyimide, polyamide-imide, polyvinyl alcohol, and polyvinyl pyrrolidone. Upon completion of this stage, a heating process is performed to convert the polymer coating into a carbon layer.

[0055] In an embodiment, to deposit a carbon coating on the spray-dried composite, various techniques such as chemical vapor deposition (CVD), physical vapor deposition (PVD), or enhanced chemical vapor deposition with plasma can be employed. In this process, carbon precursors such as methane gas or ethane may be utilized.

[0056] Anode Electrode

[0057] The following description outlines various embodiments of the methods related to creating anode electrodes 300, along with various resulting compositions of matter. The description is divided into sections covering single-stage and doublestage methods for manufacturing anode electrodes, in accordance with the steps illustrated in Figs.lOA and 10B.

[0058] In the double-stage anode electrode fabrication method, the composite undergoes full carbonization via heat treatment before anode manufacturing. The last step in this process entails carbonizing the binder. In contrast, the uncarbonized composite can be directly used in the single-stage method for anode fabrication. The final step of this method triggers simultaneous carbonization of the binder and the composite containing active materials.

[0059] Double-Stage Method of Manufacturing Anode Electrode

[0060] Fig.lOA includes a block diagram illustrating method 400 for forming the anode electrode 300, according to various embodiments of the present disclosure. In step 402, as shown in Fig.lOA, an anode, such as anode electrode 300, can be prepared by mixing the composite anode material 100 with binder 302 and conductive additives 304, such as carbon black, in a solvent 306 that may include dimethylformamide, acetone, acetonitrile, N-methyl-2-pyrrolidone, chloroform, deionized water, heptane, hexane, or a combination thereof, to create a slurry. In this embodiment, the binder 302 used in preparing the slurry may consist of carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, gelatin, sodium alginate, polyacrylonitrile, polyvinylidene fluoride, or a combination of these materials. When employing a polyacrylonitrile binder to improve adhesion and reduce slurry shrinkage during drying, the addition of carboxylic acids like oxalic acid, citric acid, acetic acid, lactic acid, or tartaric acid is necessary to adjust the slurry pH to an acidic level. The pH of the slurry can be adjusted within the range of 1 to 4.5.

[0061] In particular, step 404 may involve applying the slurry onto a copper foil current collector 308 substrate using methods such as Doctor Blade coating, followed by a heat treatment process to remove any solvent and create an anode electrode 300.

[0062] In step 406, to achieve electronic conductivity, the anode electrode 300 can undergo a two-step heat treatment process in an inert environment. The first heat treatment step may involve heating the anode electrode 300 from ambient temperature to a stabilization temperature at a rate of 1 to 10 °C / min and holding it for 1 to 12 hours. The stabilization temperature can range from 180 to 320°C. In the second step, the anode electrode 300 may be further treated to reach a final temperature of 800°C at a rate of 3 to 15 °C / min, with a holding time of 1 to 10 hours at the peak temperature under the same inert atmosphere, after which the furnace is cooled back to ambient temperature. Upon completion of the aforementioned thermal treatment, the binder such as polyacrylonitrile binder may undergo a carbonization process.

[0063] To prevent wrinkling of the anode electrode 300 during heat treatment and maintain its flatness, in certain embodiments, the heat-treating process in step 406 can be conducted under pressure. In this embodiment, the anode electrode 300 can be pressed between graphite plates in a furnace, and the continuous heat- treating process can be applied. Pressures ranging from 0.1 to 100 MPa can be utilized.

[0064] In some embodiments, a plurality of anode electrodes 300 may be placed between the graphite plates, and this assembly of anode electrodes 300 and graphite plates can then be placed between two steel plates. The graphite plates possess heat resistance properties and function to prevent direct contact between electrodes, as well as contact between electrodes and the metal sheet.

[0065] Single-Stage Method of Manufacturing Anode Electrode

[0066] In another embodiment, Fig.10B includes a block diagram illustrating method 450 for forming the anode electrode 300, according to various embodiments of the present disclosure. In step 452, as shown in Fig.lOB, an anode, such as anode electrode 300, may be prepared by mixing composite particle 140 with a modified binder 310, such as modified and water-soluble polyacrylonitrile, and conductive additives 304, for example, carbon black, in a solvent 312. In this embodiment, the LA133 aqueous binder, which is a water dispersion of acrylonitrile multi-copolymer, can be used as the modified binder 310. Additionally, in method 450, the use of composite particle 140 in the slurry preparation process requires a differentapproach compared to the double-stage method. Using solvents from the doublestep method would compromise the structural integrity of the composite. Therefore, water can be used as the solvent to effectively maintain the composite structure throughout the process, ensuring optimal performance and stability.

[0067] Specifically, step 454 may involve applying the slurry on a copper foil current collector 308 substrate using methods such as Doctor Blade coating, followed by a heat treatment process.

[0068] Moreover, step 456 may simultaneously induce the carbonization of the binder 310 and the composite particles 140 containing the active materials. In this embodiment, the anode electrode 300 can undergo a two-step heat treatment process in an inert environment. The first heat treatment step may involve heating the anode electrode 300 from ambient temperature to a stabilization temperature at a rate of 1 to 10 °C / min and holding it for 1 to 12 hours. The stabilization temperature can range from 180 to 320°C. In the second step, the anode electrode 300 is subsequently treated to reach a final temperature of 800°C at a rate of 3 to 15 °C / min, with a holding time of 1 to 10 hours at the peak temperature under the same inert atmosphere, after which the furnace is cooled back to ambient temperature.

[0069] In a specific embodiment, step 456 of the current method can be similar to step 406 of the double-stage method, in terms of positioning the anode electrode 300 between the graphite plates.Industrial Applicability

[0070] The negative electrode of the present invention is expected to realize, at a low price, a high-performance lithium secondary battery using silicon as a negative active material.Patent Literature

[0071] PTL1 : U.S. Pat. No. 8,889,295

[0072] PTL2: U.S. Pat. No. 10,862,1 14

[0073] PTL3: U.S. Pat. No. 10,622,624

[0074] PTL4: International Publication No. WO 2020 / 154235Non Patent Literature

[0075] NPL1 : Zimin, She., et al., ACS Publications. (2021 ), 12293-12305.

Claims

Claims

1. A method of manufacturing composite anode material 100 comprising: a) mixing the plurality of electrochemically active material 102, a solvent, and a first polymer 106 to form a first mixture; b) dispersing a second polymer 108 and a conductive material 104 into the first mixture to form a second mixture; c) electrospinning the second mixture to remove the solvent and forming a mixture having a fibrous morphology 124; d) heat treating the mixture having fibrous morphology 124 to prevent agglomeration and adhesion took place during the subsequent ball milling step; e) ball milling the cooled, heat-treated mixture having fibrous morphology 124 to prepare ball-milled particles 130, wherein the ball-milled particles have a high specific surface area and comprise a homogeneous distribution of active materials, first polymer, second polymer, and conductive materials; f) mixing the ball-milled particles 130 with a solvent and graphene oxide 132 to form a third mixture; g) spray drying the third mixture to form a composite particle 140, wherein the composite particle 140 includes a first shell layer 142 and a second core 155, wherein the first shell layer coated on the second core 155 and comprises crumpled sheets of graphene, crumpled sheets of graphene oxide, crumpled sheets of at least partially reduced graphene oxide, or any combinations thereof; h) heat treating the composite particle 140 to pyrolyze and burn off any polymers to prepare composite anode material 100, wherein the composite anode material including a first core 150 and the first shell layer 142 coated on the first core 150, wherein, the first core 150 comprised of: a plurality of electrochemically active particles 102,- a plurality of conductive materials 104,- a first plurality of pores 114 obtained from pyrolysis of the first polymer material 106;- a second plurality of pores obtained from the agglomeration of the plurality of active particles 102, wherein the plurality of pores is configured to accommodate volumetric expansion of the active particles 102 during charging of the composite anode material 100, and- carbon conductive network 112 obtained from the carbonization of the second polymer material 108, wherein carbon conductive network 112 at least partially surrounds the active particles 102 and conductive material 104.

2. The method of claim 1 , wherein the solvent selected from the group consisting of water, ethanol, acetone, acetonitrile, toluene, xylene, dimethylformamide, -N-methyl-2-pyrrolidone, formamide, hexane, heptane, or a mixture of two or more thereof.

3. The method of claim 1 , wherein the electrochemically active material 102 comprises silicon, silicon oxide with oxidation number from 0 to 2, porous silicon, tin, tin oxide, germanium, lead, zinc, aluminum, an alloy thereof, an intermetallic compound thereof, the metal capable of reversibly absorbing and desorbing lithium ions.

4. The method of claim 1 , wherein the first polymer 106 selected from the group consisting of polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose, lignin, polystyrene, polyether ketone, polyacrylic acid, sodium alginate, polyvinyl chloride, polyvinylidene fluoride or a mixture of two or more thereof.

5. The method of claim 1 , wherein the second polymer 108 selected from the group consisting of polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, phenolic resins, epoxy resin, resorcinol formaldehyde resin, polyamide, polyamide, polyamide imide, glucose, citric acid or a mixture of two or more thereof.

6. The method of claim 1 , wherein the fibers 122 of the electrospinning step, have an average fiber diameter from 10 nm to 5 pm.

7. The method of claim 1 , wherein in the electrospinning step, the electrospinning machine’s voltage is adjusted between 1 to 30 KV.

8. The method of claim 1 , wherein in the electrospinning step, the distance between the tip of the nozzle and the collector of the electrospinning machine is adjusted between 4 and 20 cm.

9. The method of claim 1 , wherein in the heat treatment step, the mixture having fibrous morphology 124 is heat treated between 100 °C to 160 °C for 1 to 24 hr.

10. The method of claim 1 , wherein the composite particles 140 are heat treated in two steps including stabilization of the carbon precursor, and carbonization.

11. The method of claim 1 , wherein the composite anode material 100 is coated with at least one shell layer of graphene oxide.

12. A double-stage method of fabricating an anode electrode, the method comprising:- mixing the composite anode material 100 of claim 1 , with conductive additives 304 and binders 302 in a solvent to prepare a slurry;- applying the slurry on a copper foil current collector 308;- drying the applied slurry to remove any solvents to form an anode electrode 300;- heat treating the anode electrode 300 under pressure by placing it between graphite plates.

13. The method of claim 12, wherein the binder 302 comprises carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, gelatin, sodium alginate, polyacrylonitrile, modified and water-soluble polyacrylonitrile, polyvinylidene fluoride or a combination of these materials.

14. The method of claim 12, wherein the applied pressure is between 0.1 to 100 MPa.

15. The method of claim 12, wherein the anode electrode 300 is first heated with a rate of 1 to 10 ° C. / min to a stabilization temperature ranging from 180 to 320° C.

16. The method of claim 15, wherein the anode electrode 300 is second heated with a rate of 3 to 15 ° C. / min to a temperature of 800 ° C.

17. A single-stage method of fabricating an anode electrode, the method comprising:- mixing the composite particle 140 of claim 1 , with conductive additives 304 and water-soluble polyacrylonitrile in water to prepare a slurry;- applying the slurry on a copper foil current collector 308;- drying the applied slurry to remove any solvents to form an anode electrode 300;- heat treating the anode electrode 300 to carbonization of the water-soluble polyacrylonitrile binder and the spray-dried composite particles 140 containing the active materials under pressure by placing it between graphite plates;

18. The method of claim 17, wherein water-soluble polyacrylonitrile binder is LA133 aqueous binder.

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