Manufacturing of Si-MWCNT nanocomposite materials (SMCs) as a negative electrode for lithium-ion batteries

Abstract

A hybrid composite negative electrode for lithium-ion batteries is disclosed, comprising silicon nanoparticles, multi-walled carbon nanotube (MWCNT) flakes, and a polymer binder. This hybrid composite negative electrode enables improved capacity retention performance. A manufacturing process for the negative electrode for lithium-ion batteries is also disclosed, which includes the following steps: manufacturing a carbon nanotube (CNT) mat on a negative electrode current collector; dispersing the manufactured CNT mat in a mixture of deionized water (DI water) and ethanol using a probe ultrasonic generator and a magnetic stirrer; and adding silicon nanoparticles, multi-walled carbon nanotube (MWCNT) flakes, and a polymer binder to the mixture to form a Si-MWCNT nanocomposite (SMC) negative electrode.

Description

[Technical Field]

[0001] This invention relates to the field of manufacturing anodes for lithium-ion batteries, and more particularly to the manufacturing of Si-MWCNT nanocomposite materials (SMCs) as anodes for lithium-ion batteries. [Background technology]

[0002] The background information includes information that may be useful in understanding the present invention. It is not acknowledged that any information provided herein constitutes prior art, or relates to the currently claimed invention, or that any publication specifically or implicitly cited constitutes prior art.

[0003] The increasing global energy demand, coupled with the shortage and environmental impact of conventional energy sources, are fundamental factors that will likely trigger an energy crisis within the next 20-30 years. At present, completely abandoning existing energy sources is impossible; instead, necessary improvements are needed to eliminate or reduce their environmental impact. Furthermore, new strategies are required to address the energy problem. In this context, the global automotive industry is aiming to replace all vehicles with zero-emission electric vehicles as an environmentally friendly and sustainable means of transportation. Lithium-ion batteries (LIBs), the most prevalent energy storage system in portable electronic devices, have the potential to address CO2 emissions and climate change issues through further development and their application in electric vehicles. Moreover, these rechargeable batteries are positioned as a crucial power source for electrical systems in military and civilian applications. Lithium-ion batteries can be recharged hundreds of times and are more stable. Compared to other rechargeable batteries, they have higher energy density, voltage capacity, and a lower self-discharge rate. This means that a single cell has a longer charge retention time than other battery types, resulting in higher power efficiency.

[0004] The energy density of a lithium-ion battery depends on the specific capacity of the negative and positive electrode materials. The specific capacity of currently used graphite negative electrodes is low for large-scale applications in electric vehicles, requiring a large number of graphite-based cells to supply the necessary energy, resulting in heavier battery packs. Silicon (Si) negative electrode batteries are an extension of lithium-ion batteries and are also called next-generation lithium-ion batteries. Using Si as the negative electrode in a battery provides more than 10 times the theoretical capacity compared to conventional lithium-ion batteries. This significantly increases energy storage capacity and extends battery life. Si negative electrode batteries are used in a variety of applications, including industrial, consumer electronics, automotive, power grids, and renewable energy. The theoretical specific capacity of Si is known to be 4,200 mAh / g, about 10 times that of commercially available graphite negative electrodes (372 mAh / g). However, Si as a negative electrode material for lithium-ion batteries has several limitations that require research and overcoming. Because Si negative electrodes incorporate a large amount of lithium ions during complete lithiation, they expand in volume by approximately 300-400% during charging, inducing mechanical stress. This destroys the Si anode, causing loss of electrical contact between particles, resulting in electrical isolation, reduced efficiency, and a limited cycle life of Si-based Li-ion batteries.

[0005] Several problems limit the practical application of Si as a negative electrode for lithium-ion batteries. These include volume expansion / contraction stresses of silicon that cause cracking and fracture, induced during lithiation (the process of bonding or impregnating with lithium or lithium compounds with lithium water) / desilitonization; reduced diffusion rate of lithium within silicon due to the low electrical conductivity of silicon resulting in loss of electrical contact; irreversible rapid capacity degradation over several cycles; insufficient cycle performance; and mechanical instability of the solid electrolyte interface (SEI) formed on the negative electrode. Various mechanisms of Si electrode failure include Si pulverization and cracking, continuous SEI growth, and changes in the morphology and volume of the entire Si electrode.

[0006] To address the performance issues of silicon over numerous charge-discharge cycles, various forms of Si-carbon (C) composite anode materials have been studied and implemented. By converting Si into a nanostructure, Li + The diffusion distance of ions and electrons is shortened, improving their dynamics for high electroactivity due to Si incorporation / desorption. Surface coatings of Si nanostructures block the physical pathway between the electrolyte and Si, improving electrical conductivity between Si particles and increasing the surface area. The structure of the carbon used in coating Si nanoparticles determines its physical and chemical properties, such as high electrical conductivity, stability with various electrolytes, and mechanical flexibility. The carbon structure may be amorphous and, when incorporated into a layer of Si nanoparticles, primarily acts as a conductive material. However, the bonding of amorphous carbon is not strong enough to maintain the structure during the expansion of the silicon anode; therefore, other protective carbon layers, such as carbon nanotube structures or graphite-carbon layer structures with high bonding strength, are used to buffer the volume expansion of silicon. Most conventional studies on basic mechanical mixing or coating of Si and carbon have not successfully demonstrated improvements in cycle stability. Methods such as encapsulating Si within carbon, bonding Si nanoparticles dispersed between shells with a carbon matrix, or layering are known to improve battery performance by addressing the problems of SEI stability, volume expansion, and electrical conductivity. One such approach involves the fabrication of Si-C hybrid nanocomposites using a double-matrix carbon. This method achieves an initial Coulomb efficiency (~80%) and charge capacity (1,800 mAh / g), and has been reported to retain a high capacity of approximately 80% after 500 cycles. However, for anode applications, the process of fabricating Si-C composites by coating the surface of Si nanoparticles with carbon material to avoid the problems of Si nanoparticles requires an established and reproducible process to deposit the carbon film with an optimal and uniform thickness, which affects the manufacturing cost of Si-C composites for anode applications.

[0007] Therefore, there is a need for a manufacturing method / process for Si negative electrodes for batteries that overcomes the shortcomings of conventionally used methods / processes. [Overview of the project]

[0008] Therefore, the object of the present invention is to propose a method / process for manufacturing a Si negative electrode for batteries that overcomes the drawbacks faced by conventionally used methods / processes.

[0009] A hybrid composite anode for lithium-ion batteries is disclosed, comprising silicon nanoparticles, multi-walled carbon nanotube (MWCNT) flakes, and a polymer binder that enhances the capacity retention capability of this hybrid composite anode.

[0010] In embodiments of the present invention, the silicon nanoparticles are in crystalline form, and the polymer binder is a polymer binder derived from polyacrylic acid (PAA).

[0011] In embodiments of the present invention, the silicon nanoparticles have a diameter of 50 to 60 nm, and the silicon nanoparticles are intrinsic nanoparticles without a carbon coating.

[0012] In embodiments of the present invention, the optimal composition of silicon nanoparticles is 60% by weight of silicon, the optimal composition of multi-walled carbon nanotube (MWCNT) flakes is 20% by weight of MWCNTs, and the optimal composition of the polymer binder is 20% by weight of polyacrylic acid (PAA).

[0013] In one embodiment of the present invention, the MWCNT comprises 92-93% MWCNT and 6-7% by weight of polyethylene glycol (PEG), the PEG acting as a wetting agent and dispersing agent.

[0014] In one embodiment of the present invention, the MWCNT flake has an outer diameter of 12.4 nm and an inner diameter of 6.4 nm, and a length of 8 to 10 microns.

[0015] Another aspect of the present invention is disclosed, which is a process for manufacturing a negative electrode for a lithium-ion battery, comprising the following steps: manufacturing a carbon nanotube (CNT) mat on a negative electrode current collector, and dispersing the manufactured CNT mat in a mixture of deionized water (DI water) and ethanol using a probe ultrasonic generator and a magnetic stirrer; and then adding silicon nanoparticles, multi-walled carbon nanotube (MWCNT) flakes, and a polymer binder to this mixture to form a Si-MWCNT nanocomposite (SMC) negative electrode.

[0016] In one embodiment of the present invention, the CNT mat is manufactured on the negative electrode current collector using a tape casting method or a doctor blade method.

[0017] In another embodiment of the present invention, the negative electrode current collector is copper foil.

[0018] In another embodiment of the present invention, the mixture of DI water and ethanol is a 1:1 mixture of 100 mL of DI water and ethanol.

[0019] In another embodiment, the polymer binder is a polymer binder derived from polyacrylic acid (PAA).

[0020] In another embodiment of the present invention, the proposed manufacturing process further includes placing the SMC anode in a vacuum oven to remove bubbles generated by a probe ultrasonic generator. The SMC anode is coated onto a glass plate covered with copper foil, and the glass plate is placed in an oven at 120°C.

[0021] In another embodiment of the present invention, the formed Si-MWCNT nanocomposite (SMC) anode comprises a crosslinked MWCNT matrix, providing a high-density packed configuration, which in turn results in efficient and rapid electron transport.

[0022] In another embodiment of the present invention, the high-density packed form is achieved by adding a polymer binder that enhances crosslinking with the help of hydrogen bonding.

[0023] The subject matter regarded as an invention is particularly pointed out and distinctly claimed in the claims. The above and other aspects, features, and advantages of the present invention will be apparent from the following detailed description in connection with the accompanying drawings.

Brief Description of the Drawings

[0024] [Figure 1] Images of original Si nanoparticles (left) and the XRD pattern of original Si nanoparticles (right) according to the present invention are shown (the scale bar of the SEM image is 100 nm). [Figure 2] It is a diagram showing a method for manufacturing an SMC negative electrode using the tape casting method according to the present invention. [Figure 3] SEM images of Si-MWCNT nanocomposite (SMC) negative electrodes are shown. The image (left) has a scale bar of 2 μm, and the image (right) has a scale bar of 500 nm. [Figure 4] A photograph of SMC fabricated on a Cu foil as a negative electrode current collector according to the present invention is shown. [Figure 5] The cycle performance (a) and charge-discharge curve (b) at a C rate of 0.1C in a half cell having a Si(60%):PAA(20%):CNT(20%) SMC electrode according to the present invention are shown.

Modes for Carrying Out the Invention

[0025] Aspects of a method / process for manufacturing a negative electrode for a lithium-ion battery according to the present invention, more specifically, aspects related to the manufacture of a Si-MWCNT nanocomposite material (SMC) as a negative electrode for a lithium-ion battery, will be described in connection with FIGS. 1 to 5. In the detailed description, reference is made to the accompanying drawings, which form a part of this specification and illustrate specific embodiments by which the present invention can be implemented. It should be understood that other embodiments may be utilized and logical changes may be made without departing from the scope of the present invention. Therefore, the following detailed description should not be construed in a limiting sense, and the scope of the present invention is defined by the claims.

[0026] Currently, with the increasing demand for applications in next-generation transportation, including electric vehicles (EVs), there is a growing need for higher energy densities in rechargeable batteries. Lithium-ion batteries (LIBs), first sold by Sony in 1991, are the most widespread rechargeable batteries for automobiles, as are those used in mobile phones and laptops. LIBs are efficient and have a long lifespan of approximately 15 to 20 years, which is about three times that of conventional lead-acid batteries. In particular, because LIBs store more energy and are much lighter, vehicles equipped with LIBs use less energy to move. The energy density of an LIB depends on the specific capacity of the negative and positive electrode materials. However, in current positive electrode chemistry-based LIBs, the specific capacity of these positive electrodes is already approaching its theoretical value, so there is relatively little room to further improve energy density. Silicon (Si) negative electrodes are attracting increasing attention due to their high capacity. The specific capacity of currently used graphite negative electrodes is low for large-scale EV applications, requiring many graphite-based cells to supply the necessary energy, making the battery pack heavy. Among the various negative electrode materials being studied, silicon (Si) is known to have the highest theoretical specific capacity (4,200 mAh / g), which is about 10 times that of commercially available graphite negative electrodes (372 mAh / g). However, silicon has limitations as a negative electrode material for lithium-ion batteries (LIBs), and these need to be investigated and overcome. In particular, the volume expansion problem of Si negative electrodes is a challenge for practical application.

[0027] According to the present invention, compared to Si-C hybrid composite anodes, multi-walled carbon nanotubes (MWCNTs) are used to fabricate Si-MWCNT nanocomposites (SMCs) due to their high capacity, which improves electronic conductivity and cycle stability. The use of Si nanoparticles in MWCNTs plays an essential role in achieving high specific capacity of anodes with high cycle stability. During charging, intercalation of Li occurs in the case of anodes, causing volume expansion of the Si structure and degrading the structure. Therefore, SMCs incorporate voids within the electrode structure and allow for volume expansion and contraction of Si nanoparticles. Such SMCs reduce mechanical stress induced by volume changes and maintain the anode structure. MWCNTs have been shown to have a wide three-dimensional conductive network, reducing residual stress due to volume changes during the charge-discharge process. Multipoint physical contact between MWCNTs and randomly dispersed Si nanoparticles improves the electrical conductivity of silicon, and Li + It shortens the diffusion distance of ions. Furthermore, the conductivity of MWCNTs has been reported to be at least an order of magnitude higher than that of graphite, and MWCNTs improve electrical conductivity, leading to Li in the active material. + It has the effect of accelerating the diffusion dynamics of ions.

[0028] Furthermore, the outermost layer of static multi-walled carbon nanotubes (MWCNTs) stabilizes the solid electrolyte interface (SEI) by protecting it from electrolyte penetration. The formation of a stable SEI protects the electrode by preventing direct electron transfer from the anode to the electrolyte and solvent decomposition. Therefore, SMCs absorb volume changes of Si nanoparticles, stabilizing the SEI over many charge-discharge cycles. Considering desirable combinations of binders with high elastic moduli is also a key factor in improving SMC-based battery performance, and polymer binders are often incorporated into the electrode matrix. This provides mechanical strength by offering strong cohesive forces between particles within the electrode matrix. These binders maintain the electrode structure by providing resistance to volume changes of Si particles, significantly improving the cycle performance of Si-based anodes. Moreover, the addition of binders is less costly than other methods in the functionalization of silicon. In this invention, it is shown that polymer binders derived from polyacrylic acid (PAA) are most effective in the production of Si-C hybrid composite anodes using MWCNTs, and that they can improve the anode's capacity retention capability. Previous studies have reported that carboxymethylcellulose (CMC) and N-methylpyrrolidone (NMP) have been used as binders in the production of carbon nanotube-based composite materials for anode applications. CMC is widely used as a thickener and electrode binder, particularly in graphite anodes. Compared to conventional polyvinylidene fluoride (PVDF), CMC is soluble in water, reducing the use of harmful NMP during processing. In the production of Si / MWCNT nanocomposite anodes according to the present invention, it was found that mixing Si / MWCNTs with NMP and CMC resulted in a problem of "heterogeneous dispersion." On the other hand, when PAA is used as a binder in the proposed Si-based CNT anode, the dispersion problem does not occur (this has also been confirmed by chemical analysis).

[0029] Based on the present invention, the properties of PAA as an optimal binder in the production of SMC as a negative electrode are detailed, and it has been shown that PAA-derived polymers improve capacity retention performance for more than 100 cycles due to superior mechanical strength compared to carboxymethylcellulose (CMC), alginic acid, and polyvinylidene fluoride (PVDF) binders. PAA binders contain many -COOH (carboxy) groups, and these carboxyl groups are SiO x It is believed that the formation of hydrogen bonds with the silicon surface terminated by the PAA has a positive effect on the silicon electrode. The high concentration of functional groups (carboxyl groups) in PAA may be a major factor in its superior performance, with some COOH groups in the PAA forming strong hydrogen bonds with the OH groups on the Si (or C) surface. The remaining carboxyl groups form ionic conductive COO-Li groups, which, along with the solid electrolyte interface (SEI) formed during the initial lithium insertion, protect the Si-C interface, thereby protecting the electrical connectivity of the negative electrode from degradation due to solvent penetration. From an electrochemical standpoint, the binder plays a role in influencing the formation rate of the SEI, its components, and its spatial distribution. Furthermore, the formation rate of LiF directly affects the formation of small inorganic SEI components (LiF and sulfides) that penetrate the electrode, based on the binder's bonding strength. The rapid decomposition of ionic species in the electrolyte to form LiF (lithium fluoride) leads to the formation of fluoride ions (F - ) becomes unavailable for subsequent SEI formation cycles. Fluoride ions (F - The rapid consumption of ) and the resulting LiF formation, along with the distribution of passive sulfides within the SEI, may improve the capacity retention performance in the PAA binder system compared to when CMC is used. Furthermore, neutralizing the acidic protons of PAA with LiOH to form LiPAA (lithium polyacrylic acid) and achieving an average of 80% lithium substitution has been shown to further improve performance. This operation may disperse the polymer chains and improve their interaction with the silicon surface due to the negatively charged carboxylate salt.

[0030] According to another embodiment of the present invention, the fabrication of an anode based on a Si-MWCNT nanocomposite (SMC) is disclosed. The SMC was fabricated using Si nanoparticles, MWCNT flakes, and polyacrylic acid (PAA) as a binder. Considering the Si nanoparticles, the intrinsic size of the Si particles is approximately 50-60 nm in diameter, and the crystalline quality of the Si particles is essential to exhibit high energy capacity with low degradation after multiple charge-discharge cycle tests. The polycrystalline material, as examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), is shown in Figure 1. Considering the MWCNTs, the MWCNT flakes contain approximately 92-93% MWCNTs and 6-7% by weight of polyethylene glycol (PEG). The PEG acts as a wetting and dispersing agent, and the MWCNTs have an outer diameter of 12.4 nm, an inner diameter of 6.4 nm, and a length of 8-10 microns. Figure 1 shows an image of the original Si nanoparticles according to the present invention (left) and the XRD pattern of the original Si nanoparticles (right) (the scale bar in the SEM image is 100 nm).

[0031] Figure 2 is a schematic diagram showing the manufacturing process of an SMC anode. The CNT mat on the anode current collector (Cu foil) is manufactured using the tape casting method. The CNTs are dispersed in a mixture of 100 mL of deionized water (DI water) and ethanol, prepared in a 1:1 ratio, and treated for 10 minutes using a probe-type ultrasonic device and a magnetic stirrer. Subsequently, 60 wt% Si nanopowder, 20 wt% MWCNTs, and 20 wt% PAA are added, and ultrasonic treatment is performed for 10 minutes without using a magnetic stirrer. According to the present invention, the manufacturing of the CNT mat on the anode current collector is not limited to the tape casting method. The CNT mat can also be manufactured using the doctor blade method, which is a simpler process of coating the anode current collector with slurry. In other words, a type of doctor blade method that controls the thickness is employed to manufacture the anode material on the anode current collector. However, in some cases, the doctor blade method can be said to be similar to the tape casting method. Conventionally, a drawback associated with tape casting methods is that the mold may have low toughness or high porosity, which reduces the strength of the final product. However, the tape casting method described in this invention does not require a mold. In contrast, the tape casting method according to this invention is a casting process used to manufacture thin ceramic tapes or sheets from ceramic slurry. This ceramic slurry is applied as a thin layer on a flat surface, and then dried and sintered. Therefore, issues such as low toughness and high porosity do not apply to composite materials for negative electrodes.

[0032] Next, the mixture was placed in a vacuum oven for 2 minutes to remove bubbles generated by an ultrasonic generator. Then, the mixture was applied to a copper foil-covered glass plate using a doctor blade and left in a 120°C oven for 1 hour. For good cell performance, a concentration of 0.5 to 0.6 mg / cm² was used. 2The coating amount is applied. Si nanoparticles are embedded in a crosslinked MWCNT matrix, providing a high-density packed porous structure for the composite electrode, resulting in efficient and rapid electron transport. This mechanically robust high-density packed form is achieved by the addition of a PAA binder, where the PAA further strengthens the crosslinking with the help of hydrogen bonding. Therefore, Li + This improves electron mobility during ion intercalation / deintercalation. Furthermore, in carbon-coated Si electrodes, a more uniform elemental distribution is observed due to enhanced crosslinking. Figure 3 shows SEM images of a Si-MWCNT nanocomposite (SMC) anode; the left image has a scale bar of 2 μm, and the right image has a scale bar of 500 nm.

[0033] The key features of this invention are as follows: a. Optimal composition of three components for nanocomposite negative electrode - Si 60 wt%, MWCNT 20 wt%, PAA (as binder) 20 wt% b. Requirements for Si particles - diameter 50-60 nm c. Requirements for MWCNTs - 92-93% MWCNTs functionalized with 6-7% by weight polyethylene glycol (PEG), with an outer diameter of 12.4 nm, an inner diameter of 6.4 nm, and a length of 8-10 μm.

[0034] PEG functions as a wetting and dispersing agent. The MWCNT has an outer diameter of 12.4 nm, an inner diameter of 6.4 nm, and a length of 8-10 μm. The above dimensions and the proportion and range of materials have been observed to be optimal for the manufacture of Si composite materials and to achieve high performance. Furthermore, the proposed Si-based composite material for the negative electrode uses Si particles without carbon coating. SMCs on Cu foil (negative electrode current collector) can be used in the manufacture of pouch-type and prismatic batteries. Figure 4 shows a photograph of an SMC manufactured using Cu foil as the negative electrode current collector.

[0035] In another embodiment of the present invention, electrochemical tests of the Si-MWCNT nanocomposite material (SMC) were carried out. Using the SMC electrode (60 wt% Si, 20 wt% MWCNT, 20 wt% PAA), a half-cell test was conducted with Li metal as the negative electrode, and the results are shown in Fig. 5a. The test was carried out at a C-rate of 0.05C for the first 3 cycles, 0.1C for the next 10 cycles, and 0.2C for the last 20 cycles. Fig. 5b shows the galvanostatic charge-discharge test voltage profile of a half-cell using a self-supporting electrode of the same Si-C composite material, measured in the range of 0.1 - 2V (vs. Li + / Li) at a C-rate of 0.1C (the electrolyte was 1M LiPF6 dissolved in a solvent of EC / DEC = 50 / 50). As shown in Fig. 5a, SMC shows a specific capacity of more than 1,200 mAh / g at a C-rate of 0.2C even after 40 cycles, and the degradation rate is less than 10%. In the present invention, a negative electrode using 40% Si material has also been successfully demonstrated. Furthermore, the manufacturing process of the SMC nanocomposite material negative electrode containing such a high ratio of Si is much simpler than conventional operations in terms of lower temperature and fewer steps, etc. (Increasing the specific capacity and enabling faster charging of LIBs by including more Si material in the negative electrode).

[0036] In the charging process of the full cell, the mechanisms of lithiumation of the negative electrode and de-lithiation of the positive electrode are involved, which is related to the large volume expansion of the Si negative electrode. In this process, in order for the Si negative electrode to reach the theoretical maximum capacity, about 4.4 Li atoms are accepted per one Si atom, and Li 22 Si5 can be formed. This large volume expansion and contraction usually cause mechanical fracture and pulverization of Si, form an unstable SEI, and cause loss of electrical contact between particles and with the current collector. As a result, it causes a decrease in Coulombic efficiency and irreversible rapid capacity degradation. Furthermore, the large deformation and elastic strain caused by the insertion of Li + ions cause pulverization and morphological changes of the electrode, and as a result, the kinetics of the lithiation process becomes slow. This ultimately leads to a decrease in the cycle performance of the battery.

[0037] A Si prototype based on the designed anode has been successfully demonstrated. The proposed SMC currently exhibits excellent performance, allowing for the incorporation of large amounts of Si material into the anode and facilitating scaling up to a low-cost, highly efficient process. The SMC manufacturing process is compatible with existing processes for manufacturing Si anodes for LIBs. However, by applying further strategies, it is possible to further improve the performance of lithium-ion batteries using SMC. Several challenges may need to be overcome to develop and industrialize this invention. For example, the availability of high-quality Si nanoparticles and the optimization of the "active" cathode and anode material balance for integration into full-cell lithium-ion batteries with high capacity and fast charging capabilities. The manufacturing process for the nanocomposite anode proposed in this invention is rapid, taking less than 1.5 hours per batch to complete, and operates at low temperatures (maximum temperature of 120°C). This process is compatible with currently used production lines for manufacturing lithium-ion battery anodes (simple slurry coating and firing processes). Currently, high-Ni cathode materials (e.g., NMC, NCA, etc.) are widely used with carbon-based additives and binders that do not contain MWCNTs (multiwall carbon nanotubes). However, there are limits to increasing the capacity of full-cell batteries using high-Ni cathode materials. In other words, the capacity of high-Ni cathode materials is already approaching its theoretical limit. In contrast, high-Si content anode materials have not yet been successfully commercialized for high-capacity battery applications (although the theoretical capacity of silicon anodes exceeds 3,600 mAh / g, reaching 10 times the capacity of graphite, potentially enabling long-distance driving and fast charging for EVs). In summary, this invention discloses a simple process for manufacturing high-energy-density Si-based composite anodes by mixing Si particles, MWCNTs, and a binder (PAA) of an optimal size or amount. This invention does not involve processes that require long hours or high temperatures.

[0038] With regard to this specification and the accompanying drawings disclosing preferred embodiments thereof, many changes, modifications, variations, and other uses and applications of the present invention will become apparent to those skilled in the art. All such changes, modifications, variations, and other uses and applications that do not depart from the spirit and scope of the present invention are deemed to be encompassed by the present invention, and the present invention is limited only by the claims.

Claims

1. A hybrid composite negative electrode for lithium-ion batteries, comprising silicon nanoparticles, multi-walled carbon nanotube (MWCNT) flakes, and a polymer binder to improve capacity retention.

2. The hybrid composite material anode according to claim 1, wherein the silicon nanoparticles are in a crystalline state.

3. The hybrid composite material anode according to claim 1, wherein the polymer binder is a polymer binder derived from polyacrylic acid (PAA).

4. The hybrid composite material anode according to claim 1, wherein the size of the silicon nanoparticles is 50 to 60 nm in diameter.

5. The hybrid composite material anode according to claim 1, wherein the silicon nanoparticles are intrinsic nanoparticles without a carbon coating.

6. The hybrid composite material anode according to claim 1, wherein the optimal composition of the silicon nanoparticles is 60% by weight of silicon.

7. The hybrid composite material anode according to claim 1, wherein the optimal composition of the multi-walled carbon nanotube (MWCNT) flakes is 20% by weight of MWCNTs.

8. The hybrid composite material anode according to claim 1, wherein the optimal composition of the polymer binder is 20% by weight of polyacrylic acid (PAA).

9. The hybrid composite material anode according to claim 7, wherein the MWCNT comprises 92-93% MWCNT and 6-7% by weight of polyethylene glycol (PEG).

10. The hybrid composite material anode according to claim 9, wherein the PEG acts as a wetting agent and a dispersing agent.

11. The hybrid composite material anode according to claim 1, wherein the MWCNT flake has an outer diameter of 12.4 nm and an inner diameter of 6.4 nm, and a length of 8 to 10 microns.

12. A method for manufacturing a negative electrode for a lithium-ion battery, A carbon nanotube (CNT) mat was fabricated on the negative electrode current collector. The prepared CNT mat was dispersed in a mixture of deionized (DI) water and ethanol using a probe ultrasonic generator and a magnetic stirrer. Silicon nanoparticles, multi-walled carbon nanotube (MWCNT) flakes, and a polymer binder are added to a mixture to form a Si-MWCNT nanocomposite (SMC) anode. A method for manufacturing a negative electrode for lithium-ion batteries.

13. The manufacturing method according to claim 12, wherein the CNT mat is manufactured on the negative electrode current collector using a tape casting method or a doctor blade method.

14. The manufacturing method according to claim 12, wherein the negative electrode current collector is a copper foil.

15. The manufacturing method according to claim 12, wherein the mixture of DI water and ethanol is a 1:1 mixture of 100 mL of DI water and ethanol.

16. The manufacturing method according to claim 12, wherein the polymer binder is a polymer binder derived from polyacrylic acid (PAA).

17. A manufacturing method according to claim 12, The SMC anode is placed in a vacuum oven, and bubbles generated by the probe ultrasonic generator are removed. A manufacturing method in which an SMC negative electrode is applied to a glass plate coated with copper foil, and this glass plate is placed in an oven at 120°C.

18. The manufacturing method according to claim 12, wherein the formed Si-MWCNT nanocomposite material (SMC) anode has a crosslinked MWCNT matrix, and the crosslinked MWCNT matrix provides a high-density packed form, resulting in efficient and rapid electron transport.

19. The manufacturing method according to claim 12, wherein the high-density packed form is achieved by adding a polymer binder that strengthens crosslinking with the help of hydrogen bonding.

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