Chitosan and sodium carboxymethyl cellulose synergistically assembled and coated lithium iron phosphate composite thick electrode material and preparation method thereof

Abstract

The invention discloses a lithium iron phosphate composite thick electrode material synergistically assembled and coated with chitosan and sodium carboxymethyl cellulose and a preparation method of the lithium iron phosphate composite thick electrode material. The preparation method comprises the following steps: 1, dissolving CMC-Na and CS, magnetically stirring to form a mixed solution, and forming a composite hydrogel substrate through the synergistic effect of electrostatic crosslinking and hydrogen bonds in the magnetic stirring process; 2, uniformly dispersing an active substance and a conductive agent in the composite hydrogel matrix, carrying out ultrasonic oscillation and mechanical stirring synergistic treatment to improve the dispersion uniformity, then adding deionized water, transferring to a homogenizer, and carrying out high-speed shearing to form a stable homogeneous suspension; and step 3, densifying the stable homogeneous suspension through vacuum filtration, removing redundant solvent, and curing the network structure through vacuum drying to obtain the CMC-CS / LFP flexible paper electrode material, namely the composite thick electrode material. According to the invention, the problems of defects of a traditional adhesive composite LFP electrode, serious performance restriction caused by a high-pollution process and the like can be solved to a certain extent.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a chitosan and sodium carboxymethyl cellulose synergistically assembled coated lithium iron phosphate composite thick electrode material and a preparation method thereof. BACKGROUND

[0002] In recent years, battery technology has undergone diversification, with constant innovation driving transformative progress in energy storage and power systems. Lithium-ion batteries (LIBs) using lithium iron phosphate (LiFePO4, LFP) cathodes have achieved widespread commercialization in electric transportation and grid-level energy storage systems due to their inherent safety advantages and long-term cycle durability. They are playing an increasingly critical role in various fields such as automobiles, aerospace, and portable consumer electronics.

[0003] Cathode materials, as a key component of lithium-ion batteries, play a decisive role in the overall performance of the battery. However, current research focuses on the development of high-capacity electrode materials, ignoring the critical role of electrode microstructure in transport dynamics and interface stability. Zhang et al. (Chem. Eng. J. 2024, 489, 151189) pointed out in their research that traditional binder-composite LFP electrodes are severely limited in performance due to poor adhesion interface contact, disordered pore distribution, and high-pollution processes, and urgent structural innovation and green manufacturing technology breakthroughs are needed. SUMMARY

[0004] To overcome the problems existing in the prior art, the purpose of the present application is to provide a chitosan (CS) and sodium carboxymethyl cellulose (CMC-Na) synergistically assembled coated lithium iron phosphate composite thick electrode material and a preparation method thereof, which constructs a LFP electrode with a multi-level pore structure, namely a self-supporting CMC-CS / LFP flexible paper electrode. The electrostatic cross-linking and hydrogen bonding of the cellulose derivative molecular chain allows the homogeneous arrangement of conductive substances, forming a three-dimensional continuous conductive path throughout the thickness of the electrode; at the same time, the vacuum filtration-driven active material dense accumulation eliminates the traditional binder and metal current collector, achieving efficient loading of active substances. The layered porous structure of the composite electrode significantly improves the charge transport dynamics and mechanical flexibility, and to some extent solves the problems of defects in traditional binder-composite LFP electrodes and high-pollution processes severely limiting performance.

[0005] To achieve the above purpose, the technical solution adopted by the present application is:

[0006] The preparation method of the chitosan and sodium carboxymethyl cellulose synergistically assembled coated lithium iron phosphate composite thick electrode material comprises the following steps:

[0007] Step 1: CMC-Na and CS are dissolved by magnetic stirring to form a mixed solution, and a composite hydrogel base is formed by the synergistic effect of electrostatic crosslinking and hydrogen bonding during magnetic stirring;

[0008] Step 2: The active substance and the conductive agent are uniformly dispersed in the composite hydrogel base, and the dispersion uniformity is improved by ultrasonic oscillation and mechanical stirring. Then, deionized water is added to transfer to a homogenizer, and a stable homogeneous suspension is formed by high-speed shearing.

[0009] Step 3: The stable homogeneous suspension is densified by vacuum filtration to remove excess solvent, and the network structure is solidified by vacuum drying to obtain a CMC-CS / LFP flexible paper electrode material, i.e. a composite thick electrode material.

[0010] In step 1, CS is dissolved in 0.1-0.3 mol / L hydrochloric acid aqueous solution, and a homogeneous solution A is formed by magnetic stirring, and is placed for standby;

[0011] CMC-Na is dissolved in a deionized water solution under constant temperature conditions of 40-60°C to form a transparent homogeneous solution B, which is placed for standby;

[0012] Solution A is poured into solution B, and magnetic stirring is carried out at 500 rpm at room temperature for 4-8 hours. After the reaction is terminated, a CMC / CS composite hydrogel base is obtained.

[0013] In step 1, the mass ratio of CS to CMC-Na is (0.06-0.14):(0.06-0.14), which aims to optimize the synergistic bonding effect of CS and CMC-Na (electrostatic crosslinking and hydrogen bonding), thereby improving the mechanical properties of the composite electrode, maintaining the stability of the three-dimensional network structure, improving the ion / electron transport capacity, and obtaining optimized electrochemical performance.

[0014] In step 2, the specific preparation process of the composite hydrogel base and the homogeneous suspension is as follows:

[0015] a) The CMC / CS composite hydrogel base prepared in step 1 is added with LFP nanoparticles and KB nanoparticles in a mass ratio of 8:1:1 or 7:2:1 (LFP:KB:CMC-CS) in sequence, and a three-dimensional conductive hydrogel composite base uniformly loaded with LFP and KB is obtained by ultrasonic treatment and magnetic stirring.

[0016] b) The three-dimensional conductive hydrogel composite base is homogenized with 100-200 mL of deionized water, and then sheared in a high-speed shearing homogenizer to obtain a homogeneous suspension with excellent dispersion stability.

[0017] In step 2, the active substance is LFP nanoparticles, and the conductive agent is conductive carbon black (KB) nanoparticles.

[0018] In the step 2a), the ultrasonic oscillation time is 20-30 minutes, the ultrasonic oscillation power is 40-60 kHz, the ultrasonic oscillation power is 100-140 W, and the magnetic stirring speed is 500-800 rpm for 2-4 hours.

[0019] In the step 2b), the homogenizer speed is 8000-12000 rpm for 10-30 minutes.

[0020] In the step 3, a Buchner funnel is used as a filtering device for vacuum filtration, and a quantitative filter paper with a diameter of 90 mm is used.

[0021] In the step 3, during the densification process of the composite slurry by vacuum filtration, the solvent is added to the slurry three times while stirring and filtration are performed simultaneously. The total volume of the three times of solvent addition is about 100-300 ml, and the solvent is a mixed solvent composed of deionized water and ethanol in a mass ratio of 2:1.

[0022] In the step 3, the temperature of the vacuum drying oven is 60-80℃, and the holding time is 12-24 hours. The vacuum environment is used to improve the evaporation efficiency of the solvent, and a thin film with a dense structure and excellent performance is obtained.

[0023] In the step 3, the specific preparation process of the CMC-CS / LFP flexible paper electrode is as follows:

[0024] a) In the vacuum filtration device, the suspension obtained in step 2 is subjected to vacuum filtration to realize slurry densification. During this process, the solvent is added to the suspension three times, and stirring is maintained during the addition and filtration is performed simultaneously. This operation avoids local high concentration through a gradual dilution strategy, which is beneficial to improving the film uniformity and structural integrity of the self-supporting electrode. The total volume of the three times of solvent addition is about 100-300 ml, and the solvent is a mixed solvent composed of deionized water and ethanol in a mass ratio of 2:1. After filtration, the excess solvent is removed, and a dense wet film is obtained.

[0025] b) The obtained wet film is placed in a vacuum drying oven at 60-80℃ for drying treatment, and the holding time is 12-24 hours. This process effectively improves the evaporation efficiency of the solvent in a vacuum environment, while ensuring the integrity of the network structure of the solidified material. Finally, a CMC-CS / LFP flexible paper electrode thin film material with a dense structure and excellent performance is obtained.

[0026] The chitosan / carboxymethyl cellulose sodium synergistically assembled coated lithium iron phosphate composite thick electrode material, through the electrostatic crosslinking and hydrogen bond effect of the cellulose derivative molecular chain, makes the KB nanoparticles uniformly dispersed on the fiber skeleton to form a conductive path, forms a three-dimensional continuous conductive path penetrating through the thickness of the electrode, and significantly enhances the electron transmission; meanwhile, with the help of vacuum filtration driving active material dense accumulation, the efficient loading of active material is realized under the condition of eliminating the traditional binder and metal current collector; and the hierarchical porous structure promotes the penetration of electrolyte, and synergistically optimizes the lithium ion diffusion kinetics.

[0027] The application further provides a lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the positive electrode sheet is the CMC-CS / LFP flexible paper electrode.

[0028] The application has the following beneficial effects:

[0029] The application constructs a conductive three-dimensional fiber network with an optimized electron and ion transmission path, for manufacturing a CMC-CS-based high-loading LFP thick electrode, i.e., a self-supporting CMC-CS / LFP flexible paper electrode. Through the electrostatic crosslinking-hydrogen bond synergistic effect of CMC-Na and CS, a mechanically reinforced composite hydrogel base is formed, and the surface charge characteristics guide the LFP active particles and carbon black (KB) to be oriented self-assembled, so as to construct a continuous electron path and a uniformly dispersed active phase. Compared with the traditional slurry casting technology, this strategy does not need an insulating polymer binder and a metal current collector, and the anisotropic electron transmission of the traditional electrode is derived from the random dispersion of conductive carbon, forming isolated conductive islands. The electrostatic co-assembly of the cationic chitosan (-NH3 + ) and the anionic CMC-Na (-COO - ) adsorbs the KB nanoparticles through the negatively charged cellulose fibers, and the intermolecular hydrogen bond of CS / CMC-Na fixes the KB into a continuous path, and the fiber-interconnected microstructure drives the electron to be oriented transmitted along the three-dimensional network, thereby effectively improving the anisotropic electron transmission problem caused by the random dispersion of carbon particles in the traditional electrode.

[0030] In addition, the ion channel formed by the self-supporting porous structure significantly optimizes the ion diffusion kinetics, and the LFP mass loading of this flexible paper electrode is 20 mg cm -2 , the specific capacity at 0.1C is as high as 165 mAh g -1 , the LFP mass loading is 40 mg cm - 2, the volume energy density is 587 Wh / L under the condition of high loading, and the concentration polarization during high-speed charging and discharging is effectively inhibited. The whole water treatment process of the biomass material avoids toxic solvents, and the application provides an eco-friendly method for developing high-energy-density, low-environmental-impact energy storage technology. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a scanning electron microscope (SEM) image of the CMC-CS / LFP flexible paper electrode material obtained in Example 2 of the present application.

[0032] Figure 2 is a transmission electron microscope (TEM) image of the CMC-CS / LFP flexible paper electrode material obtained in Example 2 of the present application.

[0033] Figure 3 is an X-ray diffraction (XRD) pattern of the CMC-CS / LFP flexible paper electrode material obtained in Examples 1-3 of the present application.

[0034] Figure 4 is a first charge-discharge performance curve of the CMC-CS / LFP flexible paper electrode material obtained in Examples 1-3 of the present application at a 0.1C rate.

[0035] Figure 5 is a first charge-discharge performance curve of the CMC-CS / LFP flexible paper electrode material obtained in Example 2 of the present application at different rates.

[0036] Figure 6 is a cycle performance graph of the CMC-CS / LFP flexible paper electrode material obtained in Example 2 of the present application and the commercial lithium iron phosphate material obtained in Comparative Example 1 at a 1C rate. DETAILED DESCRIPTION

[0037] The present application will be further described in detail below with reference to the accompanying drawings.

[0038] Example 1:

[0039] The present embodiment provides a preparation method of a CMC-CS / LFP flexible paper electrode material, which is prepared by the following steps:

[0040] Step 1: 0.14 g of CS was dissolved in 30 ml of 0.1 mol / L hydrochloric acid aqueous solution, and a homogeneous solution A was formed by magnetic stirring, and then it was left to stand for defoaming. Meanwhile, 0.06 g of CMC-Na was dissolved in 20 mL of deionized water in a 60°C constant temperature water bath, and a transparent homogeneous solution B was formed by magnetic stirring, and then it was left to stand for defoaming. Solution A was poured into solution B, and magnetic stirring was carried out at 500 rpm at room temperature for 5 hours. After the reaction was terminated, a composite hydrogel base was obtained.

[0041] Step 2: The CMC-Na / CS composite hydrogel substrate prepared in step 1 is sequentially added with LFP nanoparticles and KB nanoparticles at a mass ratio of 8:1:1 (LFP:KB:CMC-CS), and then subjected to ultrasonic treatment for 30 minutes and magnetic stirring for 3 hours (rotation speed: 500 rpm) to obtain a three-dimensional conductive hydrogel composite substrate uniformly loaded with LFP and KB. The three-dimensional conductive hydrogel composite substrate is mixed with 100 mL of deionized water, and then subjected to shearing at a rotation speed of 10,000 rpm for 15 minutes in a high-speed shearing homogenizer to obtain a homogeneous suspension with excellent dispersion stability.

[0042] Step 3: The suspension obtained in step b) is subjected to vacuum filtration in a vacuum filtration device to realize densification of the slurry; in this process, solvent (deionized water and ethanol at a mass ratio of 2:1) is added to the slurry in three times, each time with an addition amount of 50 mL, and the addition is performed while continuously stirring and synchronously performing the filtration operation; the total volume of the three times of solvent addition is about 150 mL, and the solvent is a mixed solvent composed of deionized water and ethanol at a mass ratio of 2:1. After the filtration is completed, the excess solvent is removed to obtain a dense wet film. Subsequently, the obtained wet film is placed in a vacuum drying oven at 70°C for drying treatment, and the holding time is 12 hours; this process effectively improves the solvent evaporation efficiency in a vacuum environment, while ensuring the integrity of the network structure of the material after solidification, and finally obtains a CMC-CS / LFP flexible paper electrode film material with dense structure and excellent performance.

[0043] Example 2:

[0044] The present embodiment provides a preparation method of a CMC-CS / LFP flexible paper electrode material, which is prepared by the following steps:

[0045] Step 1: 0.1 g of CS is dissolved in 20 ml of 0.1 mol / L hydrochloric acid aqueous solution, and a homogeneous solution A is formed by magnetic stirring, and then the solution is left to stand for defoaming. Meanwhile, 0.1 g of CMC-Na is dissolved in 20 mL of deionized water in a 60°C constant temperature water bath, and a transparent homogeneous solution B is formed by magnetic stirring, and then the solution is left to stand for defoaming. Solution A is poured into solution B, and the mixture is stirred at a rotation speed of 500 rpm at room temperature for 5 hours. After the reaction is terminated, a composite hydrogel substrate is obtained.

[0046] Step 2: The basic operation for preparing the CMC-CS / LFP flexible paper electrode material in step 2 of the present embodiment is basically the same as that in step 2 of Example 1, which will not be repeated here.

[0047] Step 3: The basic operation for preparing the CMC-CS / LFP flexible paper electrode material in step 3 of the present embodiment is basically the same as that in step 3 of Example 1, which will not be repeated here.

[0048] Example 3:

[0049] The embodiment provides a preparation method of a CMC-CS / LFP flexible paper electrode material, and the CMC-CS / LFP flexible paper electrode material is prepared through the following steps:

[0050] Step 1: 0.06 g of CS is dissolved in 20 ml of 0.1 mol / L hydrochloric acid aqueous solution, and a homogeneous solution A is formed through magnetic stirring, and the solution is left to stand for defoaming. Meanwhile, 0.14 g of CMC-Na is dissolved in 30 mL of deionized water in a 60°C constant temperature water bath, and a transparent homogeneous solution B is formed through magnetic stirring, and the solution is left to stand for defoaming. Solution A is poured into solution B, and magnetic stirring is performed at 500 rpm at room temperature for 5 hours, and after the reaction is terminated, a composite hydrogel base is obtained.

[0051] Step 2: The basic operation of preparing the CMC-CS / LFP flexible paper electrode material in step 2 of the embodiment is basically the same as that in step 2 of embodiment 1, and details are not repeated here.

[0052] Step 3: The basic operation of preparing the CMC-CS / LFP flexible paper electrode material in step 3 of the embodiment is basically the same as that in step 3 of embodiment 1, and details are not repeated here.

[0053] Comparative example 1:

[0054] The comparative example provides a preparation method of a commercial lithium iron phosphate electrode material, and the commercial lithium iron phosphate electrode material is prepared through the following steps:

[0055] Step 1: 1.6 g of commercial LFP nanoparticles, 0.2 g of KB nanoparticles and 0.2 g of polyvinylidene fluoride (PVDF) binder are weighed according to the mass ratio of 8:1:1 (LFP:KB:PVDF). First, the LFP nanoparticles and the KB nanoparticles are placed in a planetary ball mill, and dry grinding is performed at a speed of 500 rpm for 1 hour to realize preliminary mixing; then the PVDF binder is added, and the mixture is transferred to a maroon mortar for manual grinding for 40 minutes until uniform mixing. Finally, the mixed powder is added to N-methyl pyrrolidone (NMP) solvent, and mechanical stirring is continuously performed for 12 hours to obtain a uniform black slurry.

[0056] Step 2: The black viscous slurry obtained in step 1 is uniformly coated on the surface of an aluminum foil current collector, and is placed in a vacuum oven to be vacuumized to-0.1 MPa, and is dried at 120°C for 12 hours. After the system is naturally cooled to room temperature, it is taken out and placed in a desiccator for standby.

[0057] Comparative example 2:

[0058] The comparative example provides a preparation method of a commercial lithium iron phosphate electrode material, and the commercial lithium iron phosphate electrode material is prepared through the following steps:

[0059] Step 1: Commercial LFP nanoparticles 1.4 g, KB nanoparticles 0.4 g and polyvinylidene fluoride (PVDF) binder 0.2 g were weighed according to the mass ratio of 7:2:1 (LFP:KB:PVDF). First, the LFP nanoparticles and KB nanoparticles were placed in a planetary ball mill and dry ground at a speed of 500 rpm for 1 hour to achieve preliminary mixing; then the PVDF binder was added and transferred to a manual agate mortar for 40 minutes of manual grinding to achieve uniform mixing. Finally, the mixed powder was added to N-methyl pyrrolidone (NMP) solvent and continuously mechanically stirred for 12 hours to obtain a uniform black slurry.

[0060] Step 2: The basic operation of preparing commercial lithium iron phosphate electrode material in this example step 2 is basically the same as that in comparative example 1 step 2, which will not be repeated here.

[0061] Performance test

[0062] (1) Preparation of positive electrode: The CMC-CS / LFP flexible paper electrode material provided by Examples 1-3 and the commercial lithium iron phosphate electrode material provided by Comparative Examples 1-2 were used as positive electrode materials, respectively, and were punched into circular electrode pieces with a diameter of 10 mm using a manual slicer for standby.

[0063] (2) Assembly of button cell

[0064] The positive electrode piece, negative electrode piece (metal lithium sheet), separator (Celgard 2500 polypropylene separator) and electrolyte (1M LiPF6 / EC+DEC+EMC (volume ratio 1:1:1)) prepared above were placed in an argon glove box to assemble a CR2032 type button cell. After the battery was placed for 12 hours, the electrochemical performance test was carried out.

[0065] (3) Battery performance test

[0066] The battery after standing was tested by a CT3002A type test system for constant current charge and discharge test. The test parameters included current density, cycle number and voltage range (2.5-4.2V).

[0067] Test Example 1:

[0068] The CMC-CS / LFP flexible paper electrode material prepared by Example 2 was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively, and the obtained micrographs are shown in Figure 1 and Figure 2 .

[0069] From Figure 1It can be observed that CS and CMC-Na interweave to form a three-dimensional porous network structure, and the three-dimensional porous network presents hierarchical size characteristics. The CS / CMC-Na composite fiber diameter is between 50-100 nm, and 100-300 nm macropores are formed between the fiber gaps, which further reduces the agglomeration of nanoscale carbon black particles and lithium iron phosphate particles.

[0070] Among them, 70-100 nm KB nanoparticles are attached to the fiber surface to construct a continuous electron channel, and 200-500 nm LFP active particles are embedded in the macropore. This multi-scale structure cooperatively realizes short-range lithium ion diffusion, efficient electron transmission and mechanical stress buffering.

[0071] And the structure is conducive to the penetration of electrolyte and the rapid diffusion of lithium ions, making the reaction between electrode material and electrolyte at the interface more smooth, thereby improving the structure and cycle stability of the material. This design not only provides a channel for the penetration of electrolyte, but also reduces the mechanical stress in the cycle process through the elastic buffering effect of the fiber network.

[0072] Figure 2 The high-resolution TEM image of the CS / CMC-Na composite fiber shows clear continuous lattice fringes, and the measured lattice spacing is 0.252 nm, which is attributed to the (311) crystal plane of LiFePO4 phase. It can be observed that 200-500 nm lithium iron phosphate particles are uniformly embedded in the macropores of the fiber skeleton. This structure helps to stabilize the crystal structure of the electrode material and promote the electrochemical reaction kinetics process.

[0073] The CS / CMC-Na composite fiber diameter is 50-100 nm, forming 100-300 nm macropores, and 200-500 nm LFP active particles are embedded in the macropores. This multi-scale structure cooperatively realizes short-range lithium ion diffusion, efficient electron transmission and mechanical stress buffering.

[0074] Figure 3 The X-ray diffraction (XRD) spectrum of the CMC-CS / LFP flexible paper electrode material prepared in Examples 1-3 is shown. The results show that the main diffraction peaks of the three examples are matched with the pure orthorhombic lithium phosphate iron standard spectrum (JCPDS 01-075-7725), which is characterized by the olivine structure of space group Pnma, indicating that the material has good crystallinity. In addition, in the CMC-CS / LFP system, the introduction of CS and CMC-Na does not cause impurity diffraction peaks, confirming the successful synthesis of pure composite electrode material.

[0075] Figure 4 The first charge-discharge curve of the CMC-CS / LFP flexible paper electrode material prepared in Examples 1-3 at 0.1C rate is shown. All materials show a flat voltage platform region near 3.4V, which is characteristic of Fe2 + / Fe3+ The characteristic platform of the redox couple at 3.4 V corresponds to the lithium ion insertion / extraction process in the electrochemical reaction.

[0076] Figure 5 The first cycle charge-discharge curves of the CMC-CS / LFP flexible paper electrode material prepared in Example 2 at different rates are shown. The results show that the discharge specific capacity of the material decreases with the increase of the rate. All curves show that Fe2 + / Fe3 + The characteristic voltage platform of the redox couple, and the flatness of the charge-discharge platform area is good. In the 0.1C to 1C rate range, the increase of the charge-discharge platform voltage difference of the electrode is small, indicating that it has excellent redox reaction kinetics characteristics; while the rate is increased to 2C to 5C, the voltage difference shows a significant widening trend.

[0077] Figure 6 The cycle performance comparison of the CMC-CS / LFP flexible paper electrode material prepared in Example 2 and the commercial lithium iron phosphate electrode of Comparative Example 1 at 1C rate is shown. As shown in the figure, the first discharge specific capacity of Example 2 and Comparative Example 1 is 135 and 117 mAh g -1 , respectively, and the corresponding coulombic efficiency is 98.72% and 92.73%, respectively; after 300 cycles, the capacity retention rate of the CMC-CS / LFP flexible paper electrode material is 88.91%, which is significantly higher than that of the commercial lithium iron phosphate electrode of Comparative Example 1.

Claims

1. A method for preparing a thick lithium iron phosphate composite electrode material synergistically assembled and coated with chitosan and sodium carboxymethyl cellulose, characterized in that: The following steps are included: Step 1: CMC-Na and CS are dissolved and magnetically stirred to form a mixed solution. During the magnetic stirring process, a composite hydrogel substrate is formed through the synergistic effect of electrostatic crosslinking and hydrogen bonding; Step 2: The active substance and the conductive agent are uniformly dispersed in the composite hydrogel matrix, and the dispersion uniformity is improved by synergistic treatment of ultrasonic oscillation and mechanical stirring. Deionized water is then added and transferred to a homogenizer, where a stable homogeneous suspension is formed by high-speed shearing. Step 3: Densify the stable homogeneous suspension by vacuum filtration to remove excess solvent, and solidify the network structure by vacuum drying to obtain CMC-CS / LFP flexible paper electrode material, i.e., composite thick electrode material.

2. The method for preparing a thick lithium iron phosphate composite electrode material prepared by synergistic assembly of chitosan and sodium carboxymethyl cellulose according to claim 1, characterized in that: In step 1, CS is dissolved in a 0.1-0.3 mol / L hydrochloric acid aqueous solution, magnetically stirred to form a homogeneous solution A, and allowed to stand for standby use; CMC-Na is dissolved in a deionized water solution at a constant temperature of 40-60°C to form a transparent homogeneous solution B, which is then allowed to stand for use; Solution A was poured into solution B, and the mixture was stirred at 500 rpm for 4-8 hours at room temperature. After the reaction was terminated, a CMC / CS composite hydrogel substrate was obtained.

3. The method for preparing a thick lithium iron phosphate composite electrode material prepared by synergistic assembly of chitosan and sodium carboxymethyl cellulose according to claim 2, characterized in that: In the step 1, the mass ratio of CS to CMC-Na is (0.06-0.14): (0.06-0.14).

4. The method for preparing a thick lithium iron phosphate composite electrode material prepared by synergistic assembly of chitosan and sodium carboxymethyl cellulose according to claim 2, characterized in that: In step 2, the specific preparation process of the composite hydrogel matrix and the homogeneous suspension is as follows: a) adding the CMC / CS composite hydrogel substrate prepared in step 1, LFP nanoparticles, and KB nanoparticles in a mass ratio of 8:1:1 or 7:2:1, and performing ultrasonic treatment and magnetic stirring to obtain a three-dimensional conductive hydrogel composite matrix uniformly loaded with LFP and KB; b) homogenizing the three-dimensional conductive hydrogel composite matrix with 100-200 mL of deionized water, and then shearing the mixture in a high-speed shear homogenizer to obtain a homogeneous suspension with excellent dispersion stability.

5. The method for preparing a thick lithium iron phosphate composite electrode material synergistically assembled and coated with chitosan and sodium carboxymethyl cellulose according to claim 4, characterized in that: In step 2, the active material is LFP nanoparticles, and the conductive agent is conductive carbon black nanoparticles.

6. The method for preparing a thick lithium iron phosphate composite electrode material synergistically assembled and coated with chitosan and sodium carboxymethyl cellulose according to claim 4, characterized in that: In step 2 a), the ultrasonic oscillation time is 20 to 30 minutes, 40 to 60 kHz, the ultrasonic oscillation power is 100 to 140 W, the magnetic stirring speed is 500 to 800 rpm, and the time is 2 to 4 hours; In step 2 b), the homogenizer speed is 8000-12000 rpm, and the time is 10-30 minutes.

7. The method for preparing a thick lithium iron phosphate composite electrode material synergistically assembled and coated with chitosan and sodium carboxymethyl cellulose according to claim 2, characterized in that: In step 3, the vacuum filtration operation uses a Buchner funnel as a filtration device, and a quantitative filter paper with a diameter of 90 mm is used in conjunction with it; In step 3, during the process of densification of the composite slurry by vacuum filtration, solvent is added to the slurry three times while stirring and filtering are performed; the total volume of the three solvent additions is about 100 to 300 ml, and the solvent is a mixed solvent composed of deionized water and ethanol in a mass ratio of 2:

1.

8. The method for preparing a thick lithium iron phosphate composite electrode material synergistically assembled and coated with chitosan and sodium carboxymethyl cellulose according to claim 7, characterized in that: In step 3, the temperature of the vacuum drying oven is 60 to 80° C., and the insulation time is 12 to 24 hours.

9. The chitosan / sodium carboxymethyl cellulose synergistically assembled and coated lithium iron phosphate composite thick electrode material prepared by the method according to any one of claims 1 to 8, characterized in that: Through the electrostatic cross-linking and hydrogen bonding of the cellulose derivative molecular chains, KB nanoparticles are evenly dispersed on the fiber skeleton to form a conductive path, forming a three-dimensional continuous conductive path that runs through the thickness of the electrode, significantly enhancing electron transport; at the same time, with the help of vacuum filtration, the active materials are densely stacked, and efficient loading of active materials is achieved while eliminating traditional binders and metal current collectors; the hierarchical porous structure promotes electrolyte penetration and synergistically optimizes lithium ion diffusion dynamics.

10. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the positive electrode sheet is the chitosan / sodium carboxymethyl cellulose collaboratively assembled and coated lithium iron phosphate composite thick electrode material prepared by the method according to any one of claims 1 to 8.

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