Electrode materials and methods of making the same and lithium ion battery structures

Abstract

The present application provides an electrode material, a manufacturing method thereof and a lithium ion battery structure. The electrode material comprises: an electrode active material; and an elastic layer coated on the surface of the electrode active material, wherein the elastic layer comprises carbon (C) element, hydrogen (H) element, oxygen (O) element, nitrogen (N) element and sulfur (S) element, and is prepared by using Bi 1+ The electrode material is analyzed by TOF-SIMS as primary ions, and it is found that the electrode material contains characteristic peaks with mass-to-charge ratios (m / z) of 261±0.5, 155±0.5, 80±0.5, 32±0.5 and 14±0.5.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrode material and a manufacturing method thereof, in particular to an electrode material and a manufacturing method thereof, and a lithium ion battery containing the electrode material. BACKGROUND

[0002] In order to solve the problem of energy shortage and environmental pollution, electric vehicles have become an important industrial trend in the next wave. At present, the energy of electric vehicles mainly uses lithium ion batteries (LIB). Although lithium ion batteries have been widely used in portable consumer electronics, the requirements for high energy density and fast charge-discharge capability of lithium ion batteries for electric vehicles are more severe. Therefore, the way to introduce silicon electrode material into the electrode material to improve the capacity per gram is the most important electrode material in recent years, which is a silicon-carbon composite material made of graphite or various forms of carbon material, which can improve the capacity and energy density of the battery without changing the existing commercial battery materials and assembly conditions.

[0003] Although the silicon-carbon electrode material can improve the capacity per gram, the volume of silicon will expand significantly during the charge-discharge cycle. The difference in volume expansion between silicon and carbon material leads to an increase in electrode thickness, even forming cracks and disintegration, resulting in poor cycle stability. For this reason, Cao et al. used a modified polymer of chitosan cross-linked with glutaraldehyde as an adhesive to prepare a silicon-carbon electrode material to limit the volume expansion of the silicon-carbon electrode material to improve cycle stability (Rational Design of a Multifunctional Binder for High-Capacity Silicon-Based Anodes. ACS Energy Letters 2019, 4(5), 1171-1180.).

[0004] However, the use of a large amount of chitosan adhesive will sacrifice part of the negative active material content in the electrode, and glutaraldehyde is a toxic reagent that will cause limitations in the mass production of electrode materials and environmental pollution. Therefore, finding a more suitable non-toxic formula to develop electrode materials to improve the cycle stability and capacity per gram of lithium ion batteries can lay a good foundation for the development of the next generation of lithium ion batteries. SUMMARY

[0005] The present application provides an electrode material, comprising: an electrode active material; and an elastic layer coated on the surface of the electrode active material, wherein the elastic layer comprises carbon (C) elements, hydrogen (H) elements, oxygen (O) elements, nitrogen (N) elements, and sulfur (S) elements, and is prepared by using Bi 1+The electrode material was analyzed by TOF-SIMS as a primary ion, and the mass-to-charge ratio (m / z) was measured to be 261±0.5, (m / z) 155±0.5, and (m / z) .

[0006] Characteristic peaks are present at 80±0.5, (m / z)32±0.5 and (m / z)14±0.5.

[0007] On the other hand, the present invention provides a method for manufacturing an electrode material, comprising the following steps: sulfonating chitosan with sulfuric acid and chlorosulfonic acid; replacing monovalent cations with sulfonate groups of chitosan using an acid-base neutralization reaction to form sulfonate-containing chitosan; functionalizing polyethylene glycol end-bilaterally using epichlorohydrin to form epoxy-modified polyethylene glycol; and mixing and crosslinking the electrode active material, sulfonate-containing chitosan, and epoxy-modified polyethylene glycol in an alkaline solution to obtain the electrode material.

[0008] In another aspect, the present invention provides a lithium-ion battery structure comprising: a separator, an electrolyte, and an electrode made of the aforementioned electrode material.

[0009] The electrode material provided by this invention has several advantages. The electrode active material is coated with an elastic layer that restricts the volume expansion of the electrode active material. Specifically, the elastic layer is formed by cross-linking chitosan containing sulfonate groups with polyethylene glycol. Compared to using glutaraldehyde as a cross-linking agent, polyethylene glycol is not only non-toxic but also provides the coated elastic layer with elasticity and ductility. The elastic layer, formed on the electrode active material by a cross-linking reaction in a coating form, can deform to accommodate the volume expansion of the electrode active material during battery cycling, thereby eliminating excess stress and ensuring the integrity of the elastic layer.

[0010] Furthermore, by employing chitosan containing sulfonate groups, the electrode material of this invention can maintain an active material content of up to 90% during electrode fabrication, and the lithium sulfonate groups further enhance lithium-ion conductivity. Simultaneously, the polyethylene glycol segments also aid in the dissociation and conduction of lithium sulfonate, further improving the ion conductivity of the elastic layer in the electrode material of this invention. Because the cross-linked elastic layer prevents direct contact between the electrolyte and the active electrode material, it protects the active electrode material, thereby slowing down the thickening of the solid-electrolyte-interphase (SEI) and the continuous consumption and decomposition of the electrolyte, maintaining a dense and stable SEI. Moreover, the electrode material of this invention exhibits good structural stability in acidic environments, preventing it from easily dissolving during subsequent electrode fabrication processes. Attached Figure Description

[0011] Figure 1A The graph shows the mechanical property analysis results of each group of materials in Table 1. Figure 1BThermogravimetric analysis results of each group of materials in Table 1.

[0012] Figures 2A-2D From top to bottom are the scanning electron microscope images of the raw silicon-carbon active particles Si@G and the electrode materials Si@G-XPEO-SCS1, Si@G-XPEO-SCS2, Si@G-XPEO-SCS3 of the embodiments of the present application, respectively.

[0013] Figure 3A From top to bottom are the partial mass spectrum images obtained after analyzing the electrode materials Si@G-XGA-SCS3-1, Si@G-XPEO-SCS1 and Si@G-XPEO-SCS3 by TOF-SIMS, and the characteristic peak intensities in the mass-to-charge ratio 10 to 40 section are shown in the images. Figure 3B From top to bottom are the partial mass spectrum images obtained after analyzing the electrode materials Si@G-XGA-SCS3-1, Si@G-XPEO-SCS1 and Si@G-XPEO-SCS3 by TOF-SIMS, and the characteristic peak intensities in the mass-to-charge ratio 250 to 270 section are shown in the images.

[0014] Figures 4A-4B From top to bottom are the specific capacitance-cycle number relationship diagrams and coulombic efficiency-cycle number relationship diagrams of the batteries made using the electrode materials NG and the electrode materials NG-XPEO-SCS1, NG-XPEO-SCS2, NG-XPEO-SCS3, respectively.

[0015] From top to bottom are the specific capacitance-cycle number relationship diagrams and coulombic efficiency-cycle number relationship diagrams of the batteries made using the electrode materials NG and the electrode materials NG-XPEO-SCS1, NG-XPEO-SCS2, NG-XPEO-SCS3, respectively.

[0016] Figures 5A-5C From top to bottom are the specific capacitance-cycle number relationship diagrams, retention rate-cycle number relationship diagrams and coulombic efficiency-cycle number relationship diagrams of the batteries made using the electrode materials Si@G and the electrode materials Si@G-XPEO-SCS1, Si@G-XPEO-SCS2, Si@G-XPEO-SCS3, respectively, and the enlarged view of the cycle number 1-50 cycles is shown in the images.

[0017] Figures 6A-6D From top to bottom are the scanning electron microscope images of the battery pole pieces made using the electrode materials Si@G and the electrode materials Si@G-XPEO-SCS1, Si@G-XPEO-SCS2, Si@G-XPEO-SCS3 before the battery is cycled, respectively. Figures 6E-6H From top to bottom are the scanning electron microscope images of the battery pole pieces made using the electrode materials Si@G and the electrode materials Si@G-XPEO-SCS1, Si@G-XPEO-SCS2, Si@G-XPEO-SCS3 after the battery is cycled, respectively.

[0018] Figures 7A-7C Figures 6A, 6B, and 6C are respectively the specific capacitance-cycle number, coulombic efficiency-cycle number, and retention rate-cycle number graphs of the batteries using electrode material Si@G, electrode material Si@G-XGA-SCS3-1, and electrode material Si@G-XPEO-SCS3 at different charge-discharge rates.

[0019] Figure 8A Figures 6A, 6B, and 6C are respectively the specific capacitance-cycle number, coulombic efficiency-cycle number, and retention rate-cycle number graphs of the batteries using electrode material Si@G, electrode material Si@G-XGA-SCS3-1, and electrode material Si@G-XPEO-SCS3 at different charge-discharge rates.

[0020] Figures 6A, 6B, and 6C are respectively the specific capacitance-cycle number, coulombic efficiency-cycle number, and retention rate-cycle number graphs of the batteries using electrode material Si@G, electrode material Si@G-XGA-SCS3-1, and electrode material Si@G-XPEO-SCS3 at different charge-discharge rates. Figure 8B Figures 6A, 6B, and 6C are respectively the specific capacitance-cycle number, coulombic efficiency-cycle number, and retention rate-cycle number graphs of the batteries using electrode material Si@G, electrode material Si@G-XGA-SCS3-1, and electrode material Si@G-XPEO-SCS3 at different charge-discharge rates. Figure 8A Figures 6A, 6B, and 6C are respectively the specific capacitance-cycle number, coulombic efficiency-cycle number, and retention rate-cycle number graphs of the batteries using electrode material Si@G, electrode material Si@G-XGA-SCS3-1, and electrode material Si@G-XPEO-SCS3 at different charge-discharge rates. DETAILED DESCRIPTION

[0021] The first aspect of the present application provides an electrode material, comprising: an electrode active material; and an elastic layer coated on the surface of the electrode active material, wherein the elastic layer comprises carbon (C) element, hydrogen (H) element, oxygen (O) element, nitrogen (N) element, and sulfur (S) element, and is formed by using Bi 1+ The electrode material is analyzed by TOF-SIMS as a primary ion, and it is found that the electrode material has characteristic peaks at mass-to-charge ratio (m / z) 261±0.5, (m / z)

[0022] 155±0.5, (m / z) 80±0.5, (m / z) 32±0.5, and (m / z) 14±0.5. The elastic layer can serve as a protective layer, and the electrode material can be a positive electrode material or a negative electrode material.

[0023] The other aspect of the present application provides a manufacturing method of an electrode material, comprising the following steps: sulfonating chitosan by using sulfuric acid and chlorosulfonic acid; replacing monovalent cations on the sulfonate of chitosan by using acid-base neutralization reaction to form chitosan containing sulfonate; functionalizing the end of polyethylene glycol by using epichlorohydrin (i.e. attaching the epoxy group of epichlorohydrin to polyethylene glycol) to form epoxy-functionalized polyethylene glycol; and mixing and cross-linking the electrode active material, the chitosan containing sulfonate, and the epoxy-functionalized polyethylene glycol in an alkaline solution to obtain the electrode material.

[0024] The present application also provides a lithium ion battery structure, comprising: a separator, an electrolyte, and an electrode, at least one electrode is made of the electrode material of the embodiment of the present application. The separator and the electrolyte include but are not limited to the separators and electrolytes listed in the embodiments of the present application.

[0025] In some specific embodiments, Bi 1+ TOF-SIMS analysis of the primary ions showed that the summation intensity of the characteristic peaks of the electrode material at a mass-to-charge ratio (m / z) of 261 ± 0.5 was 3 x 10⁻⁶. 2 above.

[0026] In some specific embodiments, Bi 1+ TOF-SIMS analysis of the primary ions showed that the summation intensity of the characteristic peaks of the electrode material at a mass-to-charge ratio (m / z) of 32 ± 0.5 was 4 x 10⁻⁶. 3 above.

[0027] In some specific embodiments, Bi 1+ TOF-SIMS analysis of the primary ions showed that the summation intensity of the characteristic peaks of the electrode material at a mass-to-charge ratio (m / z) of 80 ± 0.5 was 6 x 10⁻⁶. 3 above.

[0028] In some specific embodiments, Bi 1+ TOF-SIMS analysis of the primary ions showed that the summation intensity of the characteristic peaks of the electrode material at a mass-to-charge ratio (m / z) of 14 ± 0.5 was 2 x 10⁻⁶. 4 above.

[0029] In some specific embodiments, Bi 1+ TOF-SIMS analysis of the primary ions showed that the summation intensity of the characteristic peaks of the electrode material at a mass-to-charge ratio (m / z) of 155 ± 0.5 was 2 x 10⁻⁶. 3 above.

[0030] In some specific embodiments, Bi 1+ In TOF-SIMS analysis of primary ions, the sum of characteristic peaks of the electrode material at a mass-to-charge ratio of 261±0.5 is more than 0.2% higher than the sum of characteristic peaks at a mass-to-charge ratio of 80±0.5.

[0031] In some specific embodiments, Bi 1+ In TOF-SIMS analysis of primary ions, the sum of characteristic peaks of the electrode material at a mass-to-charge ratio of 261 ± 0.5 was 2% higher than that at a mass-to-charge ratio of 32 ± 0.5.

[0032] In some specific embodiments, Bi 1+ In TOF-SIMS analysis of primary ions, the sum of the characteristic peaks of the electrode material at a mass-to-charge ratio of 261 ± 0.5 was 0.5% higher than the sum of the characteristic peaks at a mass-to-charge ratio of 14 ± 0.5.

[0033] In certain embodiments, the electrode active material can be a positive electrode active material or a negative electrode active material, and the negative electrode active material includes, but is not limited to, a carbon material, a silicon-carbon composite material, or a combination thereof. The carbon material includes, but is not limited to, natural graphite, artificial graphite, hard carbon, soft carbon. The silicon-carbon composite material includes, but is not limited to, a composite of silicon and graphite, a composite of silicon and carbon, a composite of silicon and graphene. For example, the electrode active material can be silicon-carbon nanoparticles.

[0034] In certain embodiments, the sulfonated chitosan has a structural formula of Formula 1,

[0035]

[0036] In Formula 1, R1 is -H, -COCH3, or -C3H6SO3H, R2 is -SO3H, -SO3Na, -SO3K, -SO3Li, or

[0037] H. For example, the sulfonated chitosan is a sulfonated chitosan grafted with lithium sulfonate groups, and an example structural formula is Formula 1-1,

[0038]

[0039] In certain embodiments, the elastic layer is a polymer formed by crosslinking sulfonated chitosan and epoxy-alkylated polyethylene glycol, and the weight ratio of the sulfonated chitosan to the epoxy-alkylated polyethylene glycol is 1:0.2 to 1:1.1, for example, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1.

[0040] In certain embodiments, the volume ratio of sulfuric acid to chlorosulfonic acid is 3:1 or 2:1.

[0041] In certain embodiments, the equivalent ratio of chlorosulfonic acid to the hydroxyl groups on the chitosan is 5:1 to 1:1, for example, 5:1, 4:1, 3:1, 2:1, 1:1, and most preferably 5:1.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. In case of conflict, the definitions herein prevail.

[0043] As used herein, the "integrated intensity at mass-to-charge ratio X ± 0.5" or "integrated intensity of the feature peak at mass-to-charge ratio X ± 0.5" represents the sum of all intensity values in the interval of mass-to-charge ratio X plus or minus 0.5, but does not count noise values less than 10. For example, the integrated intensity at mass-to-charge ratio 261 ± 0.5 can be the sum of all intensity values at positions between 260.5 and 261.5 (e.g., 260.5, 260.6, 260.7, 260.8, etc.), but does not count the intensity values of positions with intensity values less than 10.

[0044] As used herein, the articles "a", "an", and "any" refer to one or more than one (i.e., to at least one) of the grammatical article. For example, "an element" means one element or more than one element.

[0045] The terms "about", "approximately", or "substantially" as used herein, means within 20%, preferably within 10%, and more preferably within 5% of a stated numerical value or range. Numerical quantities given herein are approximate, meant to be

[0046] As used herein, the term "chitosan" refers to a linear polysaccharide consisting of randomly distributed β-(1->4)-linked D-glucosamine (deacetylated units) and N-acetyl-D-glucosamine (acetylated units) with a weight average molecular weight between 100,000 and 500,000, and having the chemical structure of Formula 2,

[0047]

[0048] As used herein, the "degree of deacetylation" refers to the molar ratio of D-glucosamine to monosaccharide units of chitosan. In certain embodiments, the degree of deacetylation is 10% to 99%, preferably 50% to 99%, and most preferably 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, or 99%.

[0049] As used herein, "degree of sulfonation (DS)" refers to the relative atomic ratio of sulfur to nitrogen in sulfonate-containing chitosans (the relative atomic ratio is the ratio of the number of sulfur atoms to nitrogen atoms). In some specific embodiments, the degree of sulfonation of sulfonate-containing chitosans can be 150%–200%, for example, 150%, 155%, 160%, 165%, 170%, 175%, 180%, 185%, 190%, 195%, and 200%.

[0050] As used herein, "epoxy-oxidized polyethylene glycol (ePEO)" refers to polyethylene glycol with epoxy groups on both ends, with a molecular weight between 100 and 5000, preferably between 100 and 2000, and most preferably between 150 and 1000. Those skilled in the art will understand that polyethylene glycol and polyethylene oxide or polyethylene oxide are synonyms, differing only in preparation method, nomenclature system, or molecular weight. In this case, they are interchangeable and the substantive scope of this application is not limited by the nomenclature method. An exemplary structural formula can be Formula 3.

[0051]

[0052] Example 1: Synthesis method of chitosan containing sulfonate group

[0053] In the sulfonation step, 40 mL of concentrated sulfuric acid was poured into a 500 mL round-bottom flask in an ice bath at 4 °C to avoid excessive temperature and a violent reaction. After stirring for a period of time, a certain amount of chlorosulfonic acid (chlorosulfonic acid to chitosan equivalent ratio of 5:1) was added dropwise to the round-bottom flask. The ice bath was not removed until the exothermic reaction was complete. Finally, 5 g of chitosan (purchased from [unspecified source]) with an average molecular weight of 350,000 was added.

[0054] The product (approximately 80% deacetylated) was added to a round-bottom flask and stirred for 1 hour to carry out the sulfonation reaction.

[0055] In the purification step, diethyl ether was used as a non-solvent to precipitate the product. The reaction mixture from the round-bottom flask was poured into a beaker containing 300 mL of diethyl ether and placed in an ice bath to allow the product to precipitate. The solution was filtered through filter paper, and the precipitate was collected as the product. The product was then dissolved in water to obtain a product solution, which was collected in a 1000 mL beaker.

[0056] In the lithium ion substitution step, the above product solution exhibiting strong acidity is neutralized with a 1M lithium hydroxide alkaline solution until the pH value reaches neutral, while the sulfonate groups attached to the chitosan are substituted with lithium ions using the acid-base neutralization reaction. The neutralized aqueous solution is concentrated using a rotary evaporator, and the solution volume is concentrated to about 100 mL. The small molecules are dissolved in deionized water by dialysis to remove the salts and impurities that can be generated, and the sulfonated chitosan (SCS) aqueous solution is further purified.

[0057] In the freeze-drying step, the SCS aqueous solution is poured into a 250 mL round-bottom flask, the flask wall is frozen using liquid nitrogen, a vacuum system is connected to allow the pressure to drop, and the solvent is directly sublimated into a gas. The SCS aqueous solution is left to stand at room temperature for 6 hours until the water is completely removed to obtain SCS flakes, which are then ground into a powder and collected.

[0058] Nuclear Magnetic Resonance spectroscopy (NMR) can be used to detect whether the sulfonate groups of SCS are successfully grafted and whether the solvent is completely removed. Elemental analysis (instrument: Germany elementar Vario EL cube) is used to determine the degree of sulfonation, and the sulfonation mole percentage = (14 x sulfur element weight percentage) / (32 x nitrogen element weight percentage). For example, when the degree of sulfonation = 150%-200%, the structure of the sulfonated chitosan with lithium sulfonate groups is as shown in Formula 1-1:

[0059]

[0060] The lithium sulfonate groups are grafted on O, not N, to facilitate the subsequent crosslinking of the epoxy-PEG.

[0061] Example 2: Synthesis method of epoxy-PEG

[0062] In the process of functionalizing both ends of the polyethylene glycol, 10 g of polyethylene glycol (PEO) with a molecular weight of 400 (equivalent weight of 1) (purchased from Alfa Aesar Company) is placed in a 500 mL three-necked flask, and vacuum is applied for 24 hours to remove water. Then, 150 mL of anhydrous tetrahydrofuran (THF) is added, and the three-necked flask is placed in a water bath and heated to 40°C to completely dissolve the PEO in THF, and then the temperature is returned to room temperature. 2.2 equivalents of sodium hydride (NaH) are added to the three-necked flask, and the reaction is carried out for 6 hours, with the generated hydrogen gas replacing the nitrogen atmosphere. After 6 hours, 10 equivalents of epichlorohydrin are injected into the three-necked flask using a syringe, and the reaction is carried out for 20 hours. The synthesis reaction formula is shown in Formula 5 (in the formula, "RT" represents "room temperature"):

[0063]

[0064] In the purification step, the sodium chloride salts and excess sodium hydride produced in the reaction were filtered out, and the solution appeared transparent orange red. THF was removed using a rotary evaporator, and the flask was placed in a 45 °C water bath connected to a vacuum system for 6 hours to remove epichlorohydrin and residual THF. Finally, the synthesized epoxy poly(ethylene oxide) (ePEO) was stored in the refrigerator. Nuclear magnetic resonance spectroscopy can be used to detect whether there are epoxy groups and whether the solvent is completely removed.

[0065] Example Three: Method of Manufacturing Electrode Material

[0066] Silicon (Si) feed particles with a metallurgical purity of > 98% and an average particle size of 17.1 pm (PyroPowders GmbH, Germany) were ground into silicon nanoparticles with an average size of 118 nm in ethanol. In a MiniGlatt (Glatt GmbH, Germany) fluidized bed granulator, an ethanol suspension containing 10 wt% silicon nanoparticles, 0.2 wt% ethyl cellulose, and 0.2 wt% carbon black was sprayed onto graphite particles to form a coating, resulting in composite particles. The composite particles were then mixed with pitch particles (China Steel, Taiwan) in a rotating plastic cylinder at a weight ratio of composite particles: pitch particles = 90: 10 at 900 rpm for 50 minutes. Then, they were placed in a tube furnace and pyrolyzed at 1000 °C for 3 hours in N2containing 3% H2, resulting in the desired silicon-carbon active particles (Si@G).

[0067] The silicon-carbon active particles described above were used as electrode (negative electrode) active materials. A simple preparation method was used to coat the outer layer of the silicon-carbon active particles with an elastic layer. The elastic layer can be cross-linked using the sulfonated chitosan with a sulfonate content of 200% in Example One and the epoxy poly(ethylene oxide) in Example Two.

[0068] A 20 mL of the basic solution was loaded into a round bottom flask and placed in an oil bath preheated to 80°C, and the silicon-carbon active particle powder was uniformly and sufficiently dispersed in the preheated basic solution, the pH value of the basic solution was about 7-11, preferably 7-9, for example 7, 8 or 9. The SCS and ePEO were respectively dissolved in 3 mL of the basic solution, and an ultrasonic machine was used to shake for 20 minutes, and after complete dissolution, the above-mentioned basic solution containing SCS and ePEO was mixed, and then dropped into the above-mentioned round bottom flask, and after stirring for 4 hours, the flask was placed in a vacuum oven at 80°C for 12 hours to dry the remaining solvent, and the solidification crosslinking reaction was carried out in the vacuum oven at the same time, to obtain a sulfonate-containing chitosan crosslinked epoxy-oxidized polyethylene glycol (XPEO-SCS) coated silicon-carbon active particle powder (Si@G-XPEO-SCS), the powder was collected and washed with 20 mL of methanol and 5 mL of deionized water, and then placed in a vacuum oven at 80°C for 12 hours to dry, to obtain the electrode material of the present embodiment. The crosslinked network structure of the XPEO-SCS on the outer layer of the silicon-carbon active particle powder (Si@G-XPEO-SCS) can be represented by the following structural formula 4, and the PEO is crosslinked on N:

[0069]

[0070] R1 is -H, -COCH3 or -C3H6SO3H, R2 is -SO3H, -SO3Na, -SO3K, -SO3Li or H.

[0071] In order to further understand the properties of the elastic layer, a solvent casting method was used to form a film, and the substrate was Teflon paper. First, the chitosan (CS) solution or the SCS and crosslinking agent solution were added to the film holder and placed in an oven at 60°C for about 72 hours to form a film. The crosslinking agent solution was selected from glutaraldehyde (GA) or the epoxy-oxidized polyethylene glycol of Example 2. When the film was dry, a higher temperature was used for curing, and then the formed film was subjected to dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). There were five groups for comparison, as shown in Table 1. The chitosan with a sulfonation degree of 100 mol% was obtained by sulfonating 1,3-propanesulfonic acid lactone, and the sulfonated chitosan with a sulfonation degree of 200% was obtained by sulfonating chitosan with chlorosulfonic acid.

[0072] Table 1: Parameter table of each group of materials

[0073] Group No. Group CS or SCS (mg) Crosslinking agent (mg) Film forming thickness (micron) 1 CS 100 None 38 2 XGA-SCS1 100 (100 mol% sulfonated) 10 20 3 XPEO-SCS1 100 (200 mol% sulfonated) 30 300 4 XPEO-SCS2 100 (200 mol% sulfonated) 60 250 5 XPEO-SCS3 100 (200 mol% sulfonated) 100 288.7

[0074] The sample was cut into a rectangle of 10 mm x 5 mm, clamped on both sides, and the sample was stressed using a TA instrument (model: SDT-Q800) with the stress applied increasing every minute, with an initial stress of 0.1 Newton until 18 Newtons was applied, and the stress-strain relationship of the sample was observed. As Figure 1A As shown in Table 2, it can be clearly seen that the film properties of the two crosslinking agents, GA and PEO (in the embodiment of the present application, ePEO is abbreviated as PEO), are significantly different. The film formed by adding GA as a crosslinking agent has no ductility and breaks easily. The film formed by adding PEO as a crosslinking agent exhibits high ductility. The PEO added in XPEO-SCS1 is less, and it is relatively easy to break, but it is still better than the film formed by adding GA as a crosslinking agent. After adding more PEO in XPEO-SCS2, the PEO grafted on the SCS main chain is more, and thus the elongation is improved. In XPEO-SCS3, more PEO is added, not only the PEO grafted on the SCS main chain is more, but also the crosslinking degree is higher, and the elongation is further improved, and the toughness of the film is greatly increased. Therefore, the crosslinked elastic structure of XPEO-SCS3 can become an excellent elastic layer for coating the negative active material, can simultaneously limit the volume expansion of the negative active material, and also has sufficient toughness to eliminate stress.

[0075] Table 2 Shape strain parameters of materials in each group

[0076] Group No. Group Young's modulus (MPa) Elongation rate (%) Tensile strength (MPa) 1 CS 872.7 2.19 19 2 XGA-SCS1 1022.7 2.35 24 3 XPEO-SCS1 20.4 9.7 1 4 XPEO-SCS2 3.5 40 1.1 5 XPEO-SCS3 137.7 52 8.2

[0077] Thermogravimetric analysis is to measure the weight change of a sample in a nitrogen atmosphere at different temperatures, from 100°C at a rate of 10°C per minute to 800°C, to understand the changes in physical or chemical properties of each group of substances. As Figure 1B As shown in Table 3, it can be seen that the XPEO-SCS1, XPEO-SCS2 and XPEO-SCS3 groups have two stages of decomposition temperature. One is the decomposition temperature related to the sulfonic acid group (represented by T d1 ), about 205°C, and the other is the decomposition temperature related to the epoxy group of ePEO (represented by T d2 ), about 440°C. Since these two stages of decomposition temperature have exceeded the working temperature of battery charging and discharging, there will be no thermal cracking during charging and discharging, and the film properties of the two crosslinking agents, GA and PEO, are significantly different.

[0078] Table 3 Thermogravimetric analysis results of materials in each group

[0079]

[0080] As Figures 2A-2DTo understand the appearance of the electrode materials coated with the elastic layer of different formulations, the original silicon-carbon active particles (Si@G) were used as a comparison, and the electrode materials Si@G-XPEO-SCS1, Si@G-XPEO-SCS2, and Si@G-XPEO-SCS3 were prepared using the elastic layer of the formulation proportions in Table 4 below. The surface morphology was observed using a scanning electron microscope (SEM) (model: JEOL JSM6510, operating voltage: 15 kilovolts). Figure 2A The large block of material in the center is graphite, and the light white small particles indicated by the white arrow are silicon particles. It can be observed that Figures 2B-2D The silicon-carbon active particles coated with the elastic layer of different formulations are similar in appearance to the original silicon-carbon active particles, indicating that the alkaline solution did not etch the outer surface of the silicon-carbon active particles during the coating process, and there was no accumulation of residual salts, and the elastic layer appeared uniform and thin.

[0081] Table 4 Formulation proportions of each group of materials

[0082] Weight ratio (Si@G is 300 mg) Si@G SCS PEO Sulfonation degree mol% Si@G-XPEO-SCS1 100 3 0.9 200％ Si@G-XPEO-SCS2 100 3 1.8 200％ Si@G-XPEO-SCS3 100 3 3 200％

[0083] The electrode materials of the embodiments of the present application were analyzed using a Time-of-Flight Secondary Ion Mass Spectrometer (TOF-SIMS) (brand and model: ION-TOF, TOF-SIMS V, Germany), and were compared with electrode materials having GA as the crosslinking agent. The comparison groups are shown in Table 5 below. Bismuth Bi + The primary ion beam was used to hit the surface of each sample in Table 5, with a current of 1 pA, accelerated at a voltage of 30 keV, and a gas pressure of 1 x 10 -8 ~ 7 x 10 -8 torr, with a mass resolution range (m / Δm) of 3000 to 6000, and the data was collected in negative ion mode, and the results were calculated, as shown in Table 5 below.

[0084] Table 5 TOF-SIMS analysis results of each group of materials

[0085]

[0086] As Figure 3A , Figure 3B and Table 5 show the intensity of several important characteristic peaks, with a negative ion mass-to-charge ratio of 261 ± 0.5 being a characteristic peak related to the C 12 H 23 O5N group, and the total intensity was 3 x 10 2The above is the crosslinker segment of PEO, and the electrode material Si@G-XPEO-SCS1 and Si@G-XPEO-SCS2 using PEO as the crosslinker have obviously higher total intensity than the electrode material Si@G-XGA-SCS3-1 using GA as the crosslinker. The position with anion mass-to-charge ratio of 32±0.5 is a characteristic peak related to the sulfur element of sulfonate, and the total intensity of the signal is 4x10 3 The above is the crosslinker segment of PEO, and the electrode material Si@G-XPEO-SCS1 and Si@G-XPEO-SCS2 using PEO as the crosslinker have obviously higher total intensity than the electrode material Si@G-XGA-SCS3-1 using GA as the crosslinker. The position with anion mass-to-charge ratio of 32±0.5 is a characteristic peak related to the sulfur element of sulfonate, and the total intensity of the signal is 4x10 4 The above is the crosslinker segment of PEO, and the electrode material Si@G-XPEO-SCS1 and Si@G-XPEO-SCS2 using PEO as the crosslinker have obviously higher total intensity than the electrode material Si@G-XGA-SCS3-1 using GA as the crosslinker. The position with anion mass-to-charge ratio of 32±0.5 is a characteristic peak related to the sulfur element of sulfonate, and the total intensity of the signal is 4x10 3 The above is the crosslinker segment of PEO, and the electrode material Si@G-XPEO-SCS1 and Si@G-XPEO-SCS2 using PEO as the crosslinker have obviously higher total intensity than the electrode material Si@G-XGA-SCS3-1 using GA as the crosslinker. The position with anion mass-to-charge ratio of 32±0.5 is a characteristic peak related to the sulfur element of sulfonate, and the total intensity of the signal is 4x10 3 The above is the crosslinker segment of PEO, and the electrode material Si@G-XPEO-SCS1 and Si@G-XPEO-SCS2 using PEO as the crosslinker have obviously higher total intensity than the electrode material Si@G-XGA-SCS3-1 using GA as the crosslinker. The position with anion mass-to-charge ratio of 32±0.5 is a characteristic peak related to the sulfur element of sulfonate, and the total intensity of the signal is 4x10

[0087] Therefore, the electrode material of the embodiment of the present application provides C 12 H 23 O5N segment, thus having different functions of helping lithium ion transfer between segments, and has obvious difference in properties and functions from the crosslinker GA. The total intensity value of the characteristic peak (mass-to-charge ratio 261±0.5) having great relevance to the crosslinker PEO is divided by the total intensity value of the characteristic peak (for example, mass-to-charge ratio 14±0.5 or 32±0.5) taken as the reference value, so as to distinguish the crosslinker segment of the embodiment of the present application. For example, the value of the total intensity of the characteristic peak at mass-to-charge ratio 261±0.5 is higher than that of the characteristic peak at mass-to-charge ratio 32±0.5 by 2 percentage points, preferably 5 percentage points, and most preferably 10 percentage points. Or the value of the total intensity of the characteristic peak at mass-to-charge ratio 261±0.5 is higher than that of the characteristic peak at mass-to-charge ratio 14±0.5 by 0.5 percentage points, preferably 1 percentage point, and most preferably 2 percentage points. Or the value of the total intensity of the characteristic peak at mass-to-charge ratio 261±0.5 is higher than that of the characteristic peak at mass-to-charge ratio 80±0.5 by 0.2 percentage points or more.

[0088] Example Four: Manufacturing of the negative electrode and its properties

[0089] In the graphite system experiment, the proportions in Table 4 and the electrode material manufacturing method of Example 3 were used, and a negative electrode used natural graphite (NG) (specific capacity 372 mAh / g) instead of Si@G as the negative active material to perform active material coating stability tests. In the silicon-carbon system experiment, silicon-carbon active particles (Si@G) (specific capacity 800 mAh / g) were used as the negative active material. The conductive additive was carbon black (Super P, a product of Taiwan Power Tech Co., Ltd.), and the binder was sodium alginate. The weight percentage of graphite:carbon black:sodium alginate was 93:3:4, and the weight percentage of Si@G:carbon black:sodium alginate was 90:3:7.

[0090] After the materials were all stirred to form a mixture, water was added as the solvent in an amount of 40 to 50 μL / mg of binder, and the final slurry composition was adjusted to a specific viscosity. The slurry composition was coated on a copper foil about 15 μm thick using an adjustable doctor blade (KTQ-80F) in a heated flatbed coater (MSK-AFA-HC100), and the coated electrode sheet (i.e., copper foil) was dried in a vacuum oven at 80°C for 12 hours to completely remove the water and complete the PEO intercalation reaction. The completed electrode sheet was rolled to a thickness of 70-80% of the original thickness, about 50 μm, to increase the density of the electrode and obtain an appropriate porosity. Finally, the electrode sheet was cut into a disc with a diameter of 13 mm using a die press.

[0091] The disc electrode sheet was assembled into a button cell CR2032 to test its electrochemical performance. Celgard® 1600 battery polypropylene separator film was used, and lithium foil was used as the counter electrode. The cell was assembled in a glove box under an argon atmosphere. The electrolyte was composed of a mixture containing 1 mole per liter (1 M) of lithium hexafluorophosphate (LiPF6), 1:2 by volume of ethylene carbonate (EC) and ethyl methyl carbonate (EMC), and 2 volume percent of vinylene carbonate (VC) as an additive. In the graphite (NG) system experiment, 40 volume percent of propylene carbonate (PC) was additionally used for active material coating stability tests. Similarly, in the silicon-carbon (Si@G) system, 10 weight percent of fluroethylene carbonate (FEC) was additionally added, which is helpful for forming a stable solid electrolyte interface for the silicon negative electrode.

[0092] Battery cycling charge-discharge test uses Arbin BT-2043 battery test instrument. In any battery test, such as long term cycling test or rate performance test, all batteries must first undergo three low charge-discharge rate procedures to form stable SEI for subsequent tests. The cut-off voltage is from 1 millivolt to 1.2 volts. The test conditions are (i) discharge (lithiation) process uses constant current mode (CC mode) to slowly discharge at 0.1C to 1 millivolt and constant voltage mode (CV mode) to trickle discharge the battery to the limit current 0.01C. (ii) Charging (delithiation) process uses constant current mode at 0.1C rate corresponding to the cut-off voltage of 1.2 volts. In long cycle test, the charge-discharge rate is increased to 0.5C according to the negative electrode capacity in the formation cycle. In rate performance test, the charging current is variable and the discharging current is fixed at 0.1C rate. All batteries are operated at room temperature.

[0093] Experiment 1: Test the protection ability and coating effect of the elastic layer

[0094] The elastic layer of the electrode material in Example Three has a good SEM surface morphology, but it is not known how it affects the battery performance. In order to understand this, the electrode of the graphite system is used, because graphite has a layered structure, and when used in an electrolyte containing PC, solvent co-intercalation occurs, the unstable solid electrolyte interface leads to electrode peeling, and there is a large irreversible capacity. It is very suitable to confirm whether the elastic layer is coated stably and can form a good protection.

[0095] Figure 4A The battery without any elastic layer protection has the worst specific capacity, and the battery with the elastic layer protection in Example Three has a higher specific capacity, wherein the specific capacity refers to the amount of electricity given by the battery under certain discharge conditions. Figure 4B The battery without any elastic layer protection has poor coulombic efficiency at the beginning of the cycle, and

[0096] The battery with XPEO-SCS1 elastic layer protection may not form sufficient protection due to poor cross-linking, and the other groups increase the coulombic efficiency of the battery at the beginning of the cycle due to stable elastic layer coating, wherein the coulombic efficiency is the ratio of the charge capacity to the discharge capacity in the same cycle. From this experiment, it can be known that when the cross-linking degree of the elastic layer of the electrode material in Example Three is high, it can be coated stably and greatly improve the specific capacity and coulombic efficiency.

[0097] Experiment 2: Test the long-term cycle test of the electrode material battery in Example 3

[0098] like Figure 5A As shown, after confirming the coating capability of the elastic layer, the performance of batteries made with electrode materials of different proportions in Table 4 was actually tested. It can be observed that the battery protected by the XPEO-SCS elastic layer in Example 3 has a higher specific capacity than the battery without the elastic layer, and data shows that it can maintain long-term stability at a charge-discharge rate of 0.5C for 300 cycles, maintaining a capacity of 487 mAh / g. Capacity retention rate is defined as the specific capacity of this cycle divided by the specific capacity of the first cycle, and can be used to understand the battery's lifespan. Figure 5B As shown, from a long-term stability perspective, the retention rate of unprotected electrode material batteries (Si@G group) drops to less than 30% within the first 50 cycles. Groups with elastic layer protection can achieve retention rates as high as 80%, and even the Si@G-XPEO-SCS1 group with a lower degree of cross-linking still achieves a 70% retention rate. Figure 5C As shown, batteries protected by a highly cross-linked elastic layer, especially the Si@G-XPEO-SCS3 group, exhibited more stable coulombic efficiency than other groups, and even reached over 99% in the first few laps until the 300-lap test was completed. These electrical properties indicate that a highly cross-linked elastic layer can effectively release stress caused by volume expansion, which is more effective than a brittle protective layer and thus improves battery performance.

[0099] Experiment 3: Morphology observation of the electrode material battery in Example 3 before / after long-term cycle

[0100] After the battery was completely delithiated, it was disassembled. The electrodes were rinsed and dried with an EC / EMC (volume ratio 1:2) electrolyte, and then the surface morphology of the electrodes was analyzed by SEM. Figures 6A-6D To study the internal particle morphology of the electrode before battery cycling, Figures 6E-6H This shows the internal particle morphology of the electrode after 300 cycles at 0.5C. The electrode made of Si@G without the protection of the elastic layer has obvious cracks after battery cycling compared to before cycling. This is mainly due to the formation of a thick solid electrolyte interface layer and severe volume expansion, which causes silicon to disintegrate. However, the silicon particles protected by the XPEO-SCS elastic layer basically show a relatively flat surface, which shows that the elastic layer can effectively maintain the strength of Si@G particles.

[0101] Table 6 shows the volume expansion of the battery before and after cycling. It can be seen that the Si@G-XPEO-SCS3 group, which has the highest degree of cross-linking, also has relatively small electrode variability after 300 cycles compared with other groups. Therefore, it is believed that the elastic covalent cross-linked polymer structure formed by adding PEO cross-linking agent has the ability to slow down the occurrence of volume expansion and limit the shedding of silicon particles to a certain extent.

[0102] Table 6. Volume expansion data before and after battery cycling.

[0103] Thickness (micron) Si@G Si@G-XPEO-SCS1 Si@G-XPEO-SCS2 Si@G-XPEO-SCS3 Before cycle 35 27.5 28 38.4 After cycle 81.4 40.5 41.9 47.7 Variability (%) 132.5 47.2 49.6 24.2

[0104] Experiment 4: Test the charge-discharge rate performance of the electrode material battery in Example 3

[0105] Next, charge / discharge rate performance testing was conducted. Before the test, all batteries were subjected to 50 charge / discharge cycles at 0.3C to achieve stable capacity and coulombic efficiency. Then, the charge / discharge rate test was performed under the condition of slow insertion and fast extraction. That is, de-lithiation was carried out at different charge / discharge rates (C-rate), while lithiation was carried out at 0.1C.

[0106] like Figure 7A As shown, it can be clearly observed that even with different charging rates in each segment, the Si@G-XPEO-SCS3 group maintains a stable specific capacity exceeding 500 mAh / g. In contrast, the Si@G group without elastic layer protection does not even reach a specific capacity of 400 mAh / g. Figure 7B It also shows that the coulombic efficiency of the Si@G-XPEO-SCS3 group is relatively more stable. Figure 7C The results show that the Si@G-XPEO-SCS3 group maintains a high retention rate of 95% regardless of whether it is 2C or 5C, indicating that the PEO segments should help facilitate the transfer of lithium ions between structurally different segments. Even at 5C, it still retains a specific capacity of 521 mAh / g.

[0107] These results show that the battery's performance improvement is significant not only because the lithium sulfonate groups act as a lithium-ion storage tank, with the elastic layer acting as a transport channel for lithium-ion transfer, but also because the presence of the PEO crosslinking agent allows the PEO segments, even in their amorphous state, to facilitate lithium-ion transfer, enabling the elastic layer like XPEO-SCS to operate at high charge-discharge rates. PEO provides a range of flexibility to the elastic layer, allowing the battery to maintain excellent electrochemical properties even after 300 charge-discharge cycles.

[0108] Experiment 5: Comparison of the retention rate of the electrode material battery using different crosslinking agents

[0109] Table 1 of Example 3 uses two different crosslinking agents, GA and PEO. After extensive testing, the GA crosslinking agent system with 200% SCS sulfonation showed the best protective effect. Therefore, the battery retention rate was compared between the groups with the best GA and PEO crosslinking agents, and long-term cycle tests and charge-discharge rate performance tests were also conducted. Table 7 shows the detailed composition of each group.

[0110] Table 7. Composition of each group

[0111] Weight ratio (Si@G is 300 mg) Si@G SCS GA or PEO Sulfonation degree mol% Si@G 100 X X X Si@G-XGA-SCS3-1 100 3 1.2 200％ Si@G-XPEO-SCS3 100 3 3 200％

[0112] As shown in Figure 8A Si@G-XPEO-SCS3 effectively slowed down the degradation of the electrode in the first 50 cycles and showed very good cycle stability in the long-term cycling test. Si@G-XGA-SCS3-1 group gradually stabilized near 100 cycles. This is mainly due to the variability of volume expansion, as the electrolyte is absorbed during charging and discharging, the XPEO-SCS elastic layer has a range of elasticity and toughness, can accept a little volume expansion, accommodate more lithium ions, can expand and stretch when lithium is inserted, and return to a similar appearance to the original electrode when lithium is removed, slowing down the initial silicon particle drop and unstable SEI formation.

[0113] As shown in Figure 8B At different charge rates, the retention rate of the Si@G-XPEO-SCS3 group can reach 95%. Even though the Si@G-XGA-SCS3-1 group uses SCS with a sulfonated degree of 200%, its performance in high charge and discharge rates is not as good as that of the Si@G-XPEO-SCS3 group. The PEO crosslinking agent segment can help the transmission of lithium ions in different structural intervals. According to the results of TOF-SIMS in Comparative Example Three, the characteristic peak at mass-to-charge ratio 261 ± 0.5 does not have a higher total intensity when GA is used as the crosslinking agent for the electrode material.

Claims

1. An electrode material, characterized in that, Include: One electrode active material; and An elastic layer is coated on the surface of the electrode active material, wherein the elastic layer comprises carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S) elements, and utilizes Bi... 1+ The electrode material was analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS) as a primary ion, and characteristic peaks were found at mass-to-charge ratios (m / z) of 261±0.5, 155±0.5, 80±0.5, 32±0.5 and 14±0.

5. The elastic layer is a polymer obtained by crosslinking chitosan containing sulfonate groups with epoxy-modified polyethylene glycol; The weight ratio of the sulfonate-containing chitosan to the epoxide-modified polyethylene glycol is 1:0.2 to 1:1.1; The degree of sulfonation of the chitosan containing sulfonate groups is 150-200%.

2. The electrode material as described in claim 1, characterized in that, Bi 1+ TOF-SIMS analysis of the electrode material as a primary ion revealed a total intensity of characteristic peaks at a mass-to-charge ratio (m / z) of 261 ± 0.5 of 3 x 10⁻⁶. 2 above.

3. The electrode material as described in claim 1, characterized in that, Bi 1+ TOF-SIMS analysis of the electrode material as a primary ion revealed a total intensity of characteristic peaks at a mass-to-charge ratio (m / z) of 32 ± 0.5 of 4 x 10⁻⁶. 3 above.

4. The electrode material as described in claim 1, characterized in that, Bi 1+ TOF-SIMS analysis of the electrode material as a primary ion revealed a total intensity of characteristic peaks at a mass-to-charge ratio (m / z) of 14 ± 0.5, which was approximately 2 x 10⁻⁶. 4 above.

5. The electrode material as described in claim 1, characterized in that, In Bi 1+ In TOF-SIMS analysis of the primary ions, the sum of the characteristic peaks of the electrode material at a mass-to-charge ratio of 261 ± 0.5 was 2% higher than the sum of the characteristic peaks at a mass-to-charge ratio of 32 ± 0.

5.

6. The electrode material as described in claim 1, characterized in that, The active material of the electrode is one or both of graphite materials and silicon-carbon composite materials.

7. A method for manufacturing an electrode material, characterized in that, Includes the following steps: Sulfonation of chitosan was performed using sulfuric acid and chlorosulfonic acid. Acid-base neutralization reaction is used to replace monovalent cations onto the sulfonate group of chitosan to form sulfonate-containing chitosan; Bilateral functionalization of the ends of polyethylene glycol using epichlorohydrin to form epoxy-based polyethylene glycol; and The electrode material is obtained by mixing and cross-linking the electrode active material, sulfonate-containing chitosan, and epoxylated polyethylene glycol in an alkaline solution. The degree of sulfonation of the chitosan containing sulfonate groups is 150-200%; The weight ratio of the sulfonate-containing chitosan to the epoxylated polyethylene glycol is 1:0.2 to 1:1.

1.

8. The manufacturing method as described in claim 7, characterized in that, The electrode active material is one or both of graphite materials and silicon-carbon composite materials.

9. The manufacturing method as described in claim 7, characterized in that, The equivalent ratio of the chlorosulfonic acid to the hydroxyl groups on the chitosan is 5:1 to 1:

1.

10. A lithium-ion battery structure, comprising: a separator, an electrolyte, and electrodes, characterized in that, At least one of the electrodes is an electrode made of the electrode material described in any one of claims 1 to 8.

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