Chitosan hydrogel, preparation method and application thereof, and black phosphorus-based electrode sheet and application thereof

Abstract

The application provides a chitosan hydrogel and a preparation method and application thereof, and a black phosphorus-based electrode sheet and application thereof, and relates to the technical field of electrode materials.The chitosan hydrogel provided by the application comprises chitosan and catechol functional groups grafted on the chitosan through C-N bonds.The chitosan after grafting the catechol functional groups has a greatly improved solubility in water and is in a gel state.The catechol groups enable the chitosan hydrogel to have good wet adhesion resistance, so that the phosphorus negative electrode can well maintain the structure in the electrolyte, and further enable the black phosphorus-based electrode sheet to realize stable long cycle life and high capacity retention rate under a large current density.In addition, the chitosan hydrogel has excellent adhesion to the phosphorus-carbon composite material, and is rich in polar functional groups and can adsorb soluble polyphosphorus compounds generated in a side reaction, anchor a large amount of active substances, inhibit the loss of active substances caused by the side reaction, and significantly improve the capacity.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology, and in particular to a chitosan hydrogel, its preparation method and application, and a black phosphorus-based electrode sheet and its application. Background Technology

[0002] New energy sources are an indispensable part of supporting the development of modern society. As the demand for energy increases daily, people are pursuing the development of battery materials with higher energy density, environmental friendliness, low cost, and ease of preparation. Since Sony developed the first commercial carbon anode battery in 1991, the types of commercial anode materials have not changed significantly. However, their theoretical specific capacity is 372 mAh / g, while the actual specific capacity is only 300–330 mAh / g. Furthermore, graphite electrodes suffer from large initial irreversible losses and poor rate discharge performance, thus falling far short of practical needs, especially the high-capacity requirements of electric vehicles.

[0003] Black phosphorus, as an emerging two-dimensional material, possesses excellent electrical / ionic conductivity and a high theoretical capacity (2596 mAh / g for lithium / sodium / potassium storage). Its graphite-like layered structure facilitates ion shuttle, making it a promising anode material for lithium-ion batteries. However, black phosphorus-based anode materials exhibit poor structural stability during charge and discharge. The extremely high volume expansion (300%) caused by phase transitions during charge and discharge can lead to the fragmentation and shedding of active materials, severely affecting cycle stability. Simultaneously, the formation of soluble phosphides, with their "shuttle effect," can result in the loss of active materials, electrode corrosion, and a series of other problems, significantly impacting battery capacity and cycle life. Summary of the Invention

[0004] The purpose of this invention is to provide a chitosan hydrogel, its preparation method and application, and a black phosphorus-based electrode sheet and its application. Using the chitosan hydrogel provided by this invention as a binder to replace traditional PVDF in the preparation of black phosphorus-based electrode sheets results in high reversible specific capacity, excellent cycle performance, and structural stability.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] The present invention provides a chitosan hydrogel comprising chitosan and catechol functional groups grafted onto the chitosan via CN bonds.

[0007] This invention provides a method for preparing the chitosan hydrogel described above, comprising the following steps:

[0008] Chitosan solution was mixed with 3,4-dihydroxybenzaldehyde solution and subjected to Schiff base reaction. Catechol functional groups were grafted onto chitosan via imine bonds to obtain modified chitosan.

[0009] The modified chitosan was subjected to imine bond reduction to obtain the chitosan hydrogel.

[0010] Preferably, the mass ratio of chitosan in the chitosan solution to 3,4-dihydroxybenzaldehyde in the 3,4-dihydroxybenzaldehyde solution is (0.5-2):1.

[0011] Preferably, the Schiff base reaction time is 0.5 to 3 hours.

[0012] Preferably, the reducing agent used for the reduction of the imine bond is sodium borohydride.

[0013] This invention provides the application of the chitosan hydrogel described in the above-described scheme or the chitosan hydrogel prepared by the above-described preparation method as a binder in the preparation of electrode sheets.

[0014] This invention provides a black phosphorus-based electrode sheet, comprising a current collector and an electrode active material coated on the surface of the current collector; the electrode active material comprises a phosphorus-carbon composite material, a conductive agent, and a chitosan hydrogel; the phosphorus-carbon composite material comprises black phosphorus and carbon materials, which are covalently bonded together; the chitosan hydrogel is the chitosan hydrogel described in the above scheme or the chitosan hydrogel prepared by the preparation method described in the above scheme.

[0015] Preferably, the mass ratio of the phosphorus-carbon composite material, the conductive agent, and the chitosan hydrogel is (7-9):(0.5-2):(0.5-1).

[0016] Preferably, the mass percentage of black phosphorus in the phosphorus-carbon composite material is 30-80%, and the mass percentage of carbon material is 20-70%.

[0017] This invention provides the application of the black phosphorus-based electrode sheet described above as a negative electrode sheet in lithium-ion batteries or lithium-ion capacitors.

[0018] This invention provides a chitosan hydrogel, comprising chitosan and catechol functional groups grafted onto the chitosan via CN bonds. The grafted catechol functional groups significantly enhance the water solubility of the chitosan, resulting in a gel-like state. The catechol groups give the chitosan hydrogel excellent resistance to wet adhesion, allowing the phosphorus anode to maintain its structure well in the electrolyte. This, in turn, enables the black phosphorus-based electrode to achieve stable long cycle life and high capacity retention at high current densities.

[0019] In addition, chitosan hydrogel has excellent adhesion to phosphorus-carbon composite materials and contains abundant polar functional groups that can adsorb soluble polyphosphides produced by side reactions, anchor a large amount of active material, inhibit the loss of active material caused by side reactions, effectively maintain the integrity of the electrode, and significantly improve capacity.

[0020] This invention provides a method for preparing chitosan hydrogel according to the above-mentioned scheme, comprising the following steps: mixing a chitosan solution with a 3,4-dihydroxybenzaldehyde solution, performing a Schiff base reaction, grafting catechol functional groups onto chitosan via imine bonds to obtain modified chitosan; and reducing the imine bonds of the modified chitosan to obtain the chitosan hydrogel. Chitosan molecules contain a large number of highly reactive amino groups, giving this polysaccharide excellent biological functions and enabling chemical modification reactions. This invention utilizes 3,4-dihydroxybenzaldehyde to graft catechol functional groups onto chitosan via a Schiff base reaction (specifically, the aldehyde group of 3,4-dihydroxybenzaldehyde reacts with the primary amine on chitosan to form a Schiff base containing imine bonds), followed by the reduction of the imine bonds. The preparation method of the chitosan hydrogel is simple.

[0021] This invention provides a black phosphorus-based electrode sheet. In this electrode sheet, the phosphorus-carbon composite material is obtained by combining black phosphorus and carbon materials under high-energy ball milling conditions. High-energy ball milling tightly bonds the black phosphorus and carbon materials through covalent bonds, significantly improving the stability of the electrode structure. Furthermore, chitosan hydrogel is used instead of traditional, toxic, and expensive binders (PVDF, PAA, CMC) to prepare the black phosphorus-based electrode sheet, resulting in a black phosphorus-based electrode sheet with high reversible specific capacity, excellent cycle performance, and structural stability. Attached Figure Description

[0022] Figure 1 Transmission electron microscopy (TEM) image of the phosphorus-carbon composite material prepared in Example 1;

[0023] Figure 2 The X-ray diffraction (XRD) pattern of the phosphorus-carbon composite material prepared in Example 1;

[0024] Figure 3 The 1H NMR spectrum of the chitosan hydrogel prepared in Example 1;

[0025] Figure 4 The infrared spectrum of the chitosan hydrogel prepared in Example 1;

[0026] Figure 5 The image shows a scanning electron microscope (SEM) image and a distribution map of the three elements P, C, and N on the black phosphorus-based electrode sheet prepared in Example 1.

[0027] Figure 6 Cross-sectional morphology of different black phosphorus-based electrode sheets after charge-discharge cycles;

[0028] Figure 7 Charge-discharge curves of a coin cell prepared using the black phosphorus-based electrode sheet prepared in Example 1.

[0029] Figure 8The rate performance of a coin cell prepared using the black phosphorus-based electrode sheet prepared in Example 1 is shown in the figure.

[0030] Figure 9 For comparison, the rate performance diagram of the coin cell prepared using the black phosphorus-based electrode sheet prepared with PVDF as a binder in Application Example 1 is shown.

[0031] Figure 10 For comparison, the rate performance of the coin cell prepared using the black phosphorus-based electrode sheet prepared with PAA as a binder in Application Example 2 is shown in the figure.

[0032] Figure 11 For comparison, the rate performance diagram of the coin cell prepared using the black phosphorus-based electrode sheet prepared with CMC as a binder in Application Example 3 is shown.

[0033] Figure 12 Cycle performance of a coin cell prepared using the black phosphorus-based electrode sheet prepared in Example 1.

[0034] Figure 13 To compare the cycle performance of the coin cell prepared using the black phosphorus-based electrode sheet prepared with PVDF as a binder in Application Example 1;

[0035] Figure 14 To compare the cycle performance of the coin cell prepared using the black phosphorus-based electrode sheet prepared with PAA as a binder in Application Example 2;

[0036] Figure 15 The cycling performance of the coin cell prepared using the black phosphorus-based electrode sheet prepared with CMC as a binder in Application Example 3 is shown in the comparison diagram. Detailed Implementation

[0037] The present invention provides a chitosan hydrogel comprising chitosan and catechol functional groups grafted onto the chitosan via CN bonds.

[0038] The solubility of chitosan grafted with catechol functional groups is significantly improved in water, resulting in a gel-like state. The catechol groups give the chitosan hydrogel excellent resistance to wet adhesion, allowing the phosphorus anode to maintain its structure well in the electrolyte. This, in turn, enables the black phosphorus-based electrode to achieve stable long cycle life and high capacity retention at high current densities.

[0039] In addition, chitosan hydrogel has excellent adhesion to phosphorus-carbon composite materials and contains abundant polar functional groups that can adsorb soluble polyphosphides produced by side reactions, anchor a large amount of active material, inhibit the loss of active material caused by side reactions, effectively maintain the integrity of the electrode, and significantly improve capacity.

[0040] This invention provides a method for preparing chitosan hydrogel according to the above scheme, comprising the following steps:

[0041] Chitosan solution was mixed with 3,4-dihydroxybenzaldehyde solution and subjected to Schiff base reaction. Catechol functional groups were grafted onto chitosan via imine bonds to obtain modified chitosan.

[0042] The modified chitosan was subjected to imine bond reduction to obtain the chitosan hydrogel.

[0043] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0044] In this invention, a chitosan solution is mixed with a 3,4-dihydroxybenzaldehyde solution to carry out a Schiff base reaction, and the catechol functional group is grafted onto the chitosan through an imine bond to obtain modified chitosan.

[0045] In this invention, the chitosan solution is preferably obtained by dissolving chitosan in an acetic acid solution. In this invention, the chitosan is preferably low-viscosity chitosan (<200 mPa·s); the mass concentration of the acetic acid solution is preferably 0.5–3 wt%, more preferably 1–2.5 wt%, and even more preferably 1.5–2 wt%. This invention does not have special requirements on the amount of acetic acid solution used, as long as it is sufficient to completely dissolve the chitosan.

[0046] In this invention, the 3,4-dihydroxybenzaldehyde solution is preferably obtained by dissolving 3,4-dihydroxybenzaldehyde in water and methanol; the volume ratio of water to methanol is preferably 2:1; the concentration of the 3,4-dihydroxybenzaldehyde solution is preferably 2-6 mol / L, more preferably 4-5 mol / L.

[0047] In this invention, the preferred mass ratio of chitosan in the chitosan solution to 3,4-dihydroxybenzaldehyde in the 3,4-dihydroxybenzaldehyde solution is (0.5–2):1, more preferably (1–1.5):1. This invention does not impose special requirements on the mixing process of the chitosan solution and the 3,4-dihydroxybenzaldehyde solution; it is sufficient to ensure that the two are mixed evenly.

[0048] In this invention, the Schiff base reaction is preferably carried out at room temperature, and the reaction time is preferably 0.5 to 3 hours, more preferably 1 to 2.5 hours, and even more preferably 1.5 to 2 hours. In this invention, the Schiff base reaction is preferably carried out under stirring conditions. During the Schiff base reaction, the aldehyde group of 3,4-dihydroxybenzaldehyde reacts with the primary amine on chitosan to form an imine bond, grafting the catechol functional group onto chitosan to obtain modified chitosan.

[0049] After completing the Schiff base reaction, the present invention does not require any post-processing. A reducing agent is directly added to the reaction solution containing modified chitosan to reduce the imine bonds and obtain the chitosan hydrogel.

[0050] In this invention, the reducing agent is preferably sodium borohydride, which is preferably used in the form of a sodium borohydride solution; the concentration of the sodium borohydride solution is preferably 0.5–2 mol / L, more preferably 1–1.5 mol / L. In this invention, the reducing agent is preferably added dropwise. In this invention, the reduction of the imine bond is preferably carried out under ice bath conditions. This invention does not have special requirements on the amount of the reducing agent used; it is sufficient until a white polymer precipitates.

[0051] After the imine bond reduction is completed, the present invention preferably washes the obtained precipitate with deionized water, places the precipitate into a dialysis bag (the molecular weight cutoff of the dialysis bag is 3500 Da), places a 0.5-2 mol / L HCl solution in the dialysis bag, and performs a first dialysis for 6-12 hours. Then, a 0.5 wt% acetic acid solution is placed in the dialysis bag (the molecular weight cutoff of the dialysis bag is 3500 Da), and a second dialysis is performed for 1-4 hours. The gel-state polymer is then removed and freeze-dried in liquid nitrogen for 2-5 days to obtain chitosan hydrogel. In the present invention, the purpose of the first and second dialysis is to wash away residual sodium ions on the precipitate.

[0052] This invention provides the application of the chitosan hydrogel described in the above-described scheme or the chitosan hydrogel prepared by the above-described preparation method as a binder in the preparation of electrode sheets.

[0053] The present invention provides a black phosphorus-based electrode sheet, comprising a current collector and an electrode active material coated on the surface of the current collector; the electrode active material comprises a phosphorus-carbon composite material, a conductive agent, and the above-mentioned chitosan hydrogel; the phosphorus-carbon composite material comprises black phosphorus and carbon material, which are covalently bonded together.

[0054] The present invention does not have any special requirements for the current collector; any current collector well known in the art can be used. In an embodiment of the present invention, the current collector is a copper foil; the thickness of the copper foil is 10 μm.

[0055] In this invention, the conductive agent preferably includes conductive carbon black.

[0056] In this invention, the phosphorus-carbon composite material includes black phosphorus and carbon materials; the carbon materials preferably include graphene; the mass percentage of black phosphorus in the phosphorus-carbon composite material is preferably 30-80%, more preferably 40-70%, and even more preferably 50-60%; the mass percentage of carbon materials is 20-70%, more preferably 30-60%, and even more preferably 40-50%.

[0057] In this invention, the phosphorus-carbon composite material is preferably obtained by high-energy ball milling of black phosphorus powder and carbon material. The black phosphorus powder is preferably obtained by shearing and grinding black phosphorus lumps. The high-energy ball milling speed is preferably 300–500 rpm, more preferably 350–450 rpm; the high-energy ball milling time is preferably 12–48 hours, more preferably 20–40 hours (excluding interval time); the ball-to-material ratio is preferably (20–50):1; the high-energy ball milling is preferably carried out under inert gas protection. The high-energy ball milling is preferably carried out in a planetary ball mill; the high-energy ball milling is preferably performed by alternating forward and reverse rotation, preferably with a 10-minute interval between each hour of operation. This invention utilizes high-energy ball milling to tightly connect black phosphorus and carbon material through covalent bonds, greatly improving the stability of the electrode structure.

[0058] In this invention, the preferred mass ratio of the phosphorus-carbon composite material, the conductive agent, and the chitosan hydrogel is (7-9):(0.5-2):(0.5-1), and more preferably 7:2:1.

[0059] In this invention, the preferred loading of the electrode active material on the surface of the black phosphorus-based electrode sheet is 0.8–1.5 mg / cm³. -2 More preferably, it is 0.9–1.3 mg cm. -2 .

[0060] This invention uses chitosan hydrogel instead of traditional, toxic, and expensive binders (PVDF, PAA, CMC) to prepare black phosphorus-based electrode sheets. The catechol groups give the chitosan hydrogel excellent resistance to wet adhesion, allowing the phosphorus anode to maintain its structure well in the electrolyte. This enables the black phosphorus-based electrode sheets to achieve stable long cycle life and high capacity retention under high current density.

[0061] In addition, chitosan hydrogel has excellent adhesion to phosphorus-carbon composite materials and contains abundant polar functional groups that can adsorb soluble polyphosphides produced by side reactions, anchor a large amount of active material, inhibit the loss of active material caused by side reactions, effectively maintain the integrity of the electrode, and significantly improve capacity.

[0062] The present invention provides a method for preparing the black phosphorus-based electrode sheet described above, preferably comprising the following steps: mixing a phosphorus-carbon composite material, a conductive agent, a chitosan hydrogel, and water to obtain an electrode slurry; coating the electrode slurry onto the surface of a current collector and vacuum drying to obtain the black phosphorus-based electrode sheet.

[0063] The present invention does not have any special requirements for the solid content of the electrode paste; any solid content known in the art is acceptable. In the embodiments of the present invention, the solid content of the electrode paste is 20%.

[0064] In this invention, the vacuum drying temperature is preferably 80–100°C. There are no special requirements for the vacuum drying time; drying to constant weight is sufficient. In this invention, the vacuum degree of the vacuum drying is preferably <1 Pa.

[0065] This invention provides the application of the black phosphorus-based electrode sheet described above as a negative electrode sheet in lithium-ion batteries or lithium-ion capacitors.

[0066] The following examples illustrate the chitosan hydrogel, its preparation method, and its application, as well as the black phosphorus-based electrode sheet and its application provided by the present invention. However, these examples should not be construed as limiting the scope of protection of the present invention.

[0067] Example 1

[0068] Preparation of chitosan hydrogel:

[0069] 1 g of low-viscosity polysaccharide was dissolved in 50 mL of 1 wt% acetic acid solution and stirred for 8 hours. A 3,4-dihydroxybenzaldehyde solution (0.9 g / 6.0 mmol 3,4-dihydroxybenzaldehyde powder dissolved in 20 mL of water and 10 mL of methanol) was added, and the mixture was stirred for 2 hours. The solution was immersed in an ice bath, and NaBH4 solution was gradually added until a white polymer precipitated. The precipitate was washed three times with deionized water. The precipitate was placed in a dialysis bag and placed in 0.5 mol / L HCl solution for 6 hours (the molecular weight cutoff of the dialysis bag was 3500 Da). Further purification was then performed by dialysis in 0.5 wt% acetic acid solution for 2 hours. The gel-state polymer was then freeze-dried in liquid nitrogen for 2 days to obtain chitosan hydrogel.

[0070] Application Example 1

[0071] Preparation of black phosphorus-based electrode sheets:

[0072] A certain amount of black phosphorus powder and graphene were weighed and mixed in an inert gas atmosphere. The mixture was then sealed together with milling beads in a container. The ball-to-material ratio of stainless steel beads to the phosphorus-carbon material was 50:1. The mixture was transferred to a planetary ball mill for high-energy ball milling to obtain the milled product. The milling time was 24 hours, and the rotation speed was 500 rpm. The planetary ball mill operated in alternating forward and reverse directions for 1 hour, with a 10-minute interval between each rotation, to obtain the phosphorus-carbon composite material.

[0073] A phosphorus-carbon composite material, conductive carbon black, and chitosan hydrogel were mixed with deionized water in a mass ratio of 7:2:1. The resulting electrode slurry (solid content 20%) was coated onto the surface of a current collector with a thickness of 10 μm and then dried in a vacuum oven at 100℃ for 8 hours at a vacuum degree <1 Pa to obtain a black phosphorus-based electrode sheet. The areal loading of the electrode active material was 1 g·cm³. -2 .

[0074] Comparative Application Example 1

[0075] The difference from Application Example 1 is that PVDF is used as the adhesive:

[0076] A phosphorus-carbon composite material, conductive carbon black, and PVDF binder were mixed with an organic solvent (NMP) in a mass ratio of 7:2:1. The resulting electrode slurry (solid content 20%) was coated onto the surface of a 10 μm thick copper foil current collector and then vacuum-dried at 100 °C for 8 hours at a vacuum degree <1 Pa to obtain a black phosphorus-based electrode sheet, denoted as BP-G(PVDF). The areal loading of the electrode active material was 1 g·cm³. -2 .

[0077] Comparative Application Example 2

[0078] The difference from Application Example 1 is that polyacrylic acid (PAA) is used as the adhesive:

[0079] A phosphorus-carbon composite material, conductive carbon black, and polyacrylic acid (PAA) were mixed with an organic solvent (NMP) in a mass ratio of 7:2:1. The resulting electrode slurry (solid content 20%) was coated onto the surface of a 10 μm thick copper foil current collector and then dried in a vacuum oven at 100°C for 8 hours at a vacuum degree <1 Pa to obtain a black phosphorus-based electrode sheet, denoted as BP-G(PAA). The areal loading of the electrode active material was 1 g·cm³. -2 .

[0080] Comparative Application Example 3

[0081] The difference from Application Example 1 is that carboxymethyl cellulose (CMC) is used as the binder:

[0082] A phosphorus-carbon composite material, conductive carbon black, and carboxymethyl cellulose (CMC) were mixed with a solvent (deionized water) in a mass ratio of 7:2:1. The resulting electrode slurry (solid content 20%) was coated onto the surface of a 10 μm thick copper foil current collector and then dried in a vacuum oven at 80 °C for 8 hours at a vacuum degree <1 Pa to obtain a black phosphorus-based electrode sheet, denoted as BP-G(CMC). The areal loading of the electrode active material was 1 g·cm³. -2 .

[0083] Structural characterization and performance testing

[0084] The phosphorus-carbon composite material in Example 1 was characterized by TEM and XRD, and the results are shown in the figures below. Figure 1 and Figure 2 .Depend on Figure 1It can be seen that the morphology of the nanosheets obtained by high-energy ball milling shows that the addition of graphene not only stabilizes the structure but also significantly enhances the overall conductivity. The interlattice spacings of black phosphorus (BP) and graphite are 0.51 nm and 0.34 nm, respectively. Due to their different lattice spacings, the dislocations at the interface are more prominent. Figure 2 The uniform distribution of P, C, and N indicates that BP is uniformly dispersed in the carbon matrix, demonstrating excellent chitosan dispersibility and uniform encapsulation within the active material.

[0085] Figure 3 and Figure 4 The nuclear magnetic resonance (NMR) spectrum and infrared spectrum of the chitosan hydrogel prepared in Example 1 of this invention are shown respectively; Figure 3 It can be seen that the proton peak on chitosan appears at 3–4.0 ppm, and the proton peak of the methyl group appears at 1.9 ppm. The peak at 6.6–7.0 ppm represents the proton peak of the benzene ring on the catechol molecule, and the proton peak of the methylene group attached to the benzene ring at 4.3 ppm confirms the presence of the aromatic protons corresponding to the catechol molecule, proving that the catechol functional group is grafted onto the chitosan molecule. Figure 4 As can be seen, compared with the infrared spectrum of chitosan (CS), chitosan hydrogel (FCS) shows better infrared performance at 1620 cm⁻¹. -1 and 1514cm -1 The appearance of two distinct new absorption peaks, which are attributed to the stretching vibrations of the aromatic C=C group, proves that the catechol group has been successfully grafted onto the chitosan macromolecular chain.

[0086] The black phosphorus-based electrode sheet prepared for example 1 was subjected to SEM testing, and the elemental distribution was observed. The results are shown in [Figure 1]. Figure 5 .Depend on Figure 5 It can be seen that the modified chitosan has very good dispersibility and can be evenly distributed on the active material.

[0087] The electrochemical performance of the electrode sheets prepared for the corresponding use cases and comparative application examples was tested sequentially:

[0088] Using the electrode sheets prepared in the application examples and comparative application examples as negative electrodes, lithium metal sheets as counter and reference electrodes, polypropylene microporous membranes (Celgard 2400) as separators, and 1.0 mol / L LiPF6 solution (a mixture of ethylene carbonate EC, dimethyl carbonate DMC, and diethyl carbonate DEC in a volume ratio of 2:2:1, with 10% fluoroethylene carbonate FEC additive added) as the electrolyte, CR2025 coin cells were assembled in a glove box. Specifically, the electrode sheets, separator, and lithium metal sheets were stacked sequentially into a layered structure, then placed in a battery case, and the electrolyte was added to assemble the CR2025 coin cell. The assembled CR2025 coin cells were then transferred to a Xinwei charge-discharge tester for constant current charge-discharge cycle testing at a current density of 0.5 A·g. -1 The cutoff voltage was set to 0.01–3.0V. Simultaneously, the sweep rate for the cyclic voltammetry test was set to 0.2 mV·s. -1 The voltage range is 0.01 to 3.0V.

[0089] Figure 6 Cross-sectional morphology images of different black phosphorus-based electrode sheets after 200 charge-discharge cycles; from Figure 6 It is evident that the BP-G (PVDF) electrode exhibits significant volume expansion after prolonged cycling, while the structural integrity of the BP-G (PAA) and BP-G (CMC) electrodes is more severely affected, with irregular accumulation and aggregation of active materials and a tendency to detach. This indicates that the binder has a significant impact on volume expansion. Due to the strong adhesive properties of the modified chitosan binder, it demonstrates excellent ability to maintain electrode structural stability and mitigate volume expansion during long-term cycling.

[0090] Figure 7 The charge-discharge curves of a coin cell fabricated using the black phosphorus-based electrode sheet prepared in Example 1 are shown. Figure 7 The initial irreversibility of the cycle can be observed to be due to the formation of SEI. The black phosphorus-based anode exhibits a distinct three-step reaction during lithium-ion intercalation, with corresponding three plateaus in both the discharge and charge curves. The discharge curves measured during different cycles show a plateau between 0.75V and 0.5V, which is due to the formation of Li during lithium-ion intercalation into the active material. x Important characteristics of P.

[0091] Figure 8 The rate performance diagram of the coin cell prepared using the black phosphorus-based electrode sheet prepared in Example 1 is shown. Figure 8 It is evident that the black phosphorus-based electrode sheet of the present invention possesses excellent rate performance at 5Ag. -1 It has a current density as high as 1240 mAh g -1 The reversible capacity, while returning to a current density of 0.1Ag. -1It still has 1714mAh g -1 Reversible capacity. Figure 9 To compare the rate performance of the coin cell fabricated using the black phosphorus-based electrode sheet prepared with PVDF as a binder in Application Example 1. (From...) Figure 9 It can be seen that the rate performance of electrodes prepared with the commonly used binder PVDF is quite optimistic. Figure 10 To compare the rate performance of the coin cell fabricated using the black phosphorus-based electrode sheet prepared with PAA as a binder in Application Example 2; by Figure 10 It can be seen that the reversible capacity drops sharply during high-rate charge and discharge because the binder does not have good adhesion. Figure 11 To compare the rate performance of the coin cell fabricated using the black phosphorus-based electrode sheet prepared with CMC as a binder in Application Example 3; by Figure 11 It can be seen that, due to the poor adhesion of the binder, the reversible capacity drops sharply during high-rate charge and discharge, resulting in a capacity reduction at 5Ag. -1 At current density, black phosphorus does not contribute to capacity.

[0092] Figure 12 The cycling performance diagram of a coin cell fabricated using the black phosphorus-based electrode sheet prepared in Example 1 is shown. Figure 12 It is evident that the black phosphorus-based electrode sheet of the present invention possesses excellent cycling performance at 1 Ag. -1 The capacity retention rate is as high as 81% after 100 cycles at the current density. Figure 13 To compare the cycle performance of the coin cell fabricated using the black phosphorus-based electrode sheet prepared with PVDF as a binder in Application Example 1; by Figure 13 It can be seen that the electrode prepared with the conventionally used binder PVDF achieves relatively optimistic cycle performance at 1Ag. -1 The capacity retention rate can still reach 53% after 100 cycles at the current density. Figure 14 To compare the cycle performance of the coin cell fabricated using the black phosphorus-based electrode sheet prepared with PAA as a binder in Application Example 2; by Figure 14 It can be seen that the capacity of active substances to detach during long-term cycling cannot be maintained at a rapid rate of decay. Figure 15 To compare the cycle performance of the coin cell fabricated using the black phosphorus-based electrode sheet prepared with CMC as a binder in Application Example 3, the following diagrams are provided: Figure 15 It is known that the rapid capacity decay is caused by the shedding of a large amount of active material during long-term charging and discharging.

[0093] As can be seen from the above application examples and comparative application examples, the present invention uses chitosan hydrogel to replace traditional, toxic and expensive binders (PVDF, PAA, CMC) to prepare black phosphorus-based electrode sheets. The resulting black phosphorus-based electrode sheets have excellent cycle performance and stable structure. The preparation method has the characteristics of simple process, high yield and excellent electrochemical performance, which solves the problem of poor cycle performance of black phosphorus-based composite materials.

[0094] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. The application of chitosan hydrogel as a binder in the preparation of electrode sheets, characterized in that, The electrode sheet is a black phosphorus-based electrode sheet; the chitosan hydrogel includes chitosan and catechol functional groups grafted onto the chitosan via CN bonds; The preparation method of the chitosan hydrogel includes the following steps: Chitosan solution was mixed with 3,4-dihydroxybenzaldehyde solution and subjected to Schiff base reaction. Catechol functional groups were grafted onto chitosan via imine bonds to obtain modified chitosan. The modified chitosan was subjected to imine bond reduction to obtain the chitosan hydrogel; The mass ratio of chitosan in the chitosan solution to 3,4-dihydroxybenzaldehyde in the 3,4-dihydroxybenzaldehyde solution is (0.5~2):

1. The Schiff base reaction time is 0.5 to 3 hours; The reducing agent used for the reduction of the imine bond is sodium borohydride.

2. A black phosphorus-based electrode sheet, characterized in that, The device includes a current collector and an electrode active material coated on the surface of the current collector; the electrode active material includes a phosphorus-carbon composite material, a conductive agent, and a chitosan hydrogel; the phosphorus-carbon composite material includes black phosphorus and carbon materials, which are covalently bonded together; the chitosan hydrogel includes chitosan and catechol functional groups grafted onto the chitosan via CN bonds; The preparation method of the chitosan hydrogel includes the following steps: Chitosan solution was mixed with 3,4-dihydroxybenzaldehyde solution and subjected to Schiff base reaction. Catechol functional groups were grafted onto chitosan via imine bonds to obtain modified chitosan. The modified chitosan was subjected to imine bond reduction to obtain the chitosan hydrogel; The mass ratio of chitosan in the chitosan solution to 3,4-dihydroxybenzaldehyde in the 3,4-dihydroxybenzaldehyde solution is (0.5~2):

1. The Schiff base reaction time is 0.5 to 3 hours; The reducing agent used for the reduction of the imine bond is sodium borohydride.

3. The black phosphorus-based electrode sheet according to claim 2, characterized in that, The mass ratio of the phosphorus-carbon composite material, the conductive agent, and the chitosan hydrogel is (7~9):(0.5~2):(0.5~1).

4. The black phosphorus-based electrode sheet according to claim 2 or 3, characterized in that, The phosphorus-carbon composite material contains 30-80% black phosphorus by mass and 20-70% carbon material by mass.

5. The application of the black phosphorus-based electrode sheet according to any one of claims 2 to 4 as a negative electrode sheet in lithium-ion batteries or lithium-ion capacitors.

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