A method for preparing a lignin-coated cellulose nanofiber sodium-ion battery separator

Abstract

This invention discloses a method for preparing a lignin-coated cellulose nanofiber sodium-ion battery separator, relating to the fields of electrochemistry and battery separator technology. The preparation method includes: pretreating bamboo particles using a hydrothermal method; subsequently, nano-sizing the bamboo particles using a mechanical dissociation method to obtain a lignin-coated cellulose nanofiber suspension; and then forming a thin film from the lignin-coated cellulose nanofibers using a vacuum filtration method. The lignin nanoparticle-coated cellulose preparation process used in this invention is direct, simple, efficient, and environmentally friendly, eliminating the need for chemical reagents such as acids and alkalis to remove hemicellulose and lignin. Furthermore, the lignin nanoparticle coating effectively improves the diffusion rate of sodium ions during charge and discharge, as well as the discharge specific capacity and cycle stability.

Description

Technical Field

[0001] This invention relates to the fields of electrochemistry and battery separator technology, and specifically to a highly efficient method for preparing a lignin-coated cellulose nanofiber sodium-ion battery separator. Background Technology

[0002] Energy is the core driving force behind human prosperity and progress. However, with societal development, problems such as fossil fuel shortages and environmental crises caused by energy extraction are becoming increasingly severe. A key trend in solving this energy problem lies in the efficient storage of renewable energy using battery technology. Lithium-ion batteries, as a key technology, are widely used in smartphones, electric vehicles, and other fields. This widespread application has also triggered a supply-demand imbalance in lithium resources, leading to soaring lithium prices. Global lithium resources are unevenly distributed, with China accounting for only about 6% of the global lithium content. my country's sodium content is approximately 422 times that of lithium. Therefore, exploring alternative battery technologies, such as sodium-ion batteries, has become a crucial path to alleviate lithium shortages and promote sustainable energy development.

[0003] Sodium-ion batteries, as a new type of rechargeable battery, have advantages such as high energy density, low cost, and widespread resource availability. Besides the positive electrode, negative electrode, and electrolyte, the separator is also an indispensable key material in sodium-ion batteries. Its main function is to separate the positive and negative electrodes while allowing sodium ions to freely transport between them. For battery safety, the separator must be an excellent insulator; simultaneously, for battery operation, the separator must have certain pores to facilitate ion transport. Therefore, the quality of the separator material directly affects the battery's safety performance and capacity. Because sodium... + (0.098nm, 22.99g mol) -1 The radius and mass of ) are both greater than those of Li + (0.076nm, 6.94g mol) -1 The pore size of the separator used in sodium-ion batteries should also be larger than that of lithium-ion battery separators. Furthermore, the electrolyte commonly used in sodium-ion batteries is an organic electrolyte formulated with NaClO4 or NaPF6 as the sodium salt, propylene carbonate (PC) as the solvent, and fluoroethylene carbonate (FEC) as an additive. Propylene carbonate only has carbon-oxygen double bonds in its ester structure, and it has a cyclic structure. This unique structure results in poor wetting of the electrolyte on commonly available polymer separators. Therefore, there is an urgent need for a separator material suitable for both sodium ion pore size and electrolyte wettability to overcome current limitations. Summary of the Invention

[0004] In order to prepare sustainable, green, and high-performance energy storage materials, the present invention aims to propose an efficient preparation method for a lignin-coated cellulose nanofiber sodium-ion battery separator by controlling the time and temperature of hydrothermal pretreatment to obtain lignin-cellulose with different lignin concentrations and then obtaining it by vacuum filtration.

[0005] To achieve the above objectives, the present invention provides the following technical solutions:

[0006] A method for preparing a lignin-coated cellulose nanofiber sodium-ion battery separator includes the following steps:

[0007] (1) Pretreatment of bamboo particles by hydrothermal method;

[0008] The bamboo particles are 20-80 mesh in size; the pretreatment process is as follows: soaking in water for a period of time, heating to 120-240℃, and hydrothermal reaction for 30-180 minutes; to obtain a bamboo particle suspension.

[0009] (2) Subsequently, the bamboo particles were nano-sized using a mechanical dissociation method to obtain a lignin-coated cellulose nanofiber suspension;

[0010] A bamboo particle suspension with a solid content of 5%-10% was prepared. After grinding several times with a grinding disc, a lignin-coated cellulose nanofiber suspension was obtained. The lignin-coated cellulose nanofiber suspension, water and isopropanol solution were added in sequence according to a volume ratio of 15-50:4:32 and mixed thoroughly to form a mixture. The mixture was then ultrasonically vibrated and magnetically stirred at room temperature to make the suspension uniformly dispersed.

[0011] (3) The lignin-coated cellulose nanofiber suspension was then made into a thin film by vacuum filtration.

[0012] A vacuum filtration device was used to filter the lignin-coated cellulose nanofibers to obtain an initial membrane. The initial membrane was then immersed in tert-butanol for a period of time and finally vacuum dried to obtain a lignin-coated cellulose nanofiber membrane, which is a sodium-ion battery separator.

[0013] Furthermore, in step (1), the size of the bamboo particles is 30-60 mesh; the pretreatment process is: soaking in water for a period of time, heating to 160-220℃, and hydrothermal reaction for 30-90 minutes.

[0014] Furthermore, in step (1), the size of the bamboo particles is 40 mesh; the pretreatment process is: soaking in water for a period of time, heating to 180°C, and hydrothermal reaction for 60 minutes.

[0015] Furthermore, in step (1), the method for preparing bamboo particles is to clean the dust and dirt off the surface of the bamboo strips with distilled water, put the bamboo strips into a wall-breaking machine to crush them, and then sieve them through a 20-80 mesh screen.

[0016] Furthermore, in step (2), the grinding method is as follows: use a grinding disc with a gap of 0.1-2μ ultra-fine particles to grind for 30-40 times.

[0017] Furthermore, in step (2), a bamboo particle suspension with a solid content of 5% is prepared, and lignin-coated cellulose nanofiber suspension, water and isopropanol solution are added in sequence according to a volume ratio of 15:2:8 and mixed thoroughly to form a mixture.

[0018] Furthermore, in step (3), a vacuum filtration device is used for filtration and the obtained initial membrane is immersed in tert-butanol for 12-24 hours, sonicated for 1-2 hours and magnetically stirred for 6-12 hours, and then vacuum dried to obtain a lignin-coated cellulose nanofiber sodium-ion battery separator.

[0019] The present invention also provides a sodium-ion battery separator material, which is a lignin-coated cellulose nanofiber sodium-ion battery separator prepared by any of the preparation methods described above.

[0020] Furthermore, in the sodium-ion battery separator material, the lignin-coated cellulose nanofibers have an average diameter of 10-20 nm, and the lignin particles have an average particle size of 25-40 nm.

[0021] Finally, the present invention also provides a sodium-ion battery, wherein the separator material of the sodium-ion battery is the sodium-ion battery separator material described above.

[0022] The raw materials used in this invention are widely available, readily accessible, and renewable. Typically, nanocellulose is prepared by chemically removing lignin from biomass fibers, a process that is time-consuming, labor-intensive, and environmentally polluting. In contrast, the raw materials used in this invention do not require lignin removal and are prepared via a hydrothermal method, offering significant advantages such as simple processing, low cost, and high yield. The lignin-coated cellulose nanofiber sodium-ion battery separator prepared by this invention possesses advantages such as a large specific surface area and high electrolyte wettability, effectively promoting sodium ion transport, increasing the battery's initial discharge specific capacity, and making a significant contribution to achieving efficient and sustainable energy storage solutions. Attached Figure Description

[0023] Figure 1 This is a TEM image of the lignin-coated cellulose nanofibers in this invention.

[0024] Figure 2 This is a SEM image of the lignin-coated cellulose nanofiber sodium-ion battery separator of the present invention. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments, but these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. All reagents used in the present invention are analytical grade, all materials are commercially available, and the vacuum filtration apparatus used is (model ET-2535H), with a G3 glass funnel (60ml) used for filtration. Example 1:

[0026] 1. Clean the dust and dirt off the surface of the giant bamboo strips with distilled water, put the bamboo strips into a high-speed blender to crush them, and then sieve them through a 40-mesh sieve to obtain giant bamboo granules.

[0027] 2. The giant bamboo granules were then soaked in deionized water at room temperature for 24 hours, followed by hydrothermal reaction at 180℃ for 60 minutes to obtain a giant bamboo granule suspension.

[0028] 3. A suspension of *Phyllostachys edulis* granules with a solid content of 5% was obtained by adjusting the solid-liquid ratio. This suspension was then mechanically ground 30 times on a grinding disc with a 1 μm gap to obtain a lignin-coated cellulose nanofiber suspension. Characterization and size analysis of the lignin-coated cellulose using TEM (transmission electron microscopy) revealed that the average diameter of the lignin-coated cellulose nanofibers was 10-20 nm, and the average particle size of the lignin nanoparticles was 25-40 nm. Figure 1 As shown;

[0029] 4. According to the volume ratio of 15:4:32, add 15ml of lignin-coated cellulose nanofiber suspension, 4ml of water and 32ml of isopropanol solution in sequence and mix thoroughly to form a mixture; ultrasonically vibrate for 30min at room temperature and magnetically stir for 6h to make the lignin-coated cellulose nanofiber suspension uniformly dispersed.

[0030] 5. Vacuum filtration was performed to obtain a lignin-coated cellulose nanofiber initial membrane; the obtained initial membrane was immersed in tert-butanol for 24 hours, and finally vacuum dried for 6 hours to obtain the lignin-coated cellulose nanofiber membrane SP-1. Figure 2 As shown.

[0031] 6. Cut SP-1 into 19mm diameter discs and assemble them into coin cells in a vacuum glove box for electrochemical testing.

[0032] 7. Sodium Button Battery Assembly Method: First, prepare the materials. Use the prepared lignin-coated cellulose nanofiber membrane (SP-1) as the separator material. Cut sodium metal sheets and bamboo fiber negative electrode sheets into 14mm diameter circles to serve as the positive and negative electrode materials, respectively. Use sodium hypochlorite as the electrolyte. Prepare the gasket, positive and negative electrode shells, and separator, and place all the above materials in a vacuum glove box for later use. Second, assemble the battery. Place the negative electrode shell at the bottom, and then add the negative electrode material (bamboo charcoal negative electrode sheet), electrolyte (mainly sodium hypochlorite), separator (lignin-coated cellulose nanofiber membrane SP-1), electrolyte (mainly sodium hypochlorite), positive electrode material (sodium sheet), gasket, and positive electrode shell in sequence. Finally, seal the assembled battery using a sealing machine to obtain a complete sodium button battery.

[0033] Preparation method of bamboo charcoal negative electrode sheet: 20g of bamboo powder was weighed and carbonized in a tube furnace to obtain bamboo charcoal powder. Then, bamboo charcoal powder, conductive acetylene black and polyvinylidene fluoride (PVDF) were poured into a mortar in a mass ratio of 8:1:1, i.e., 0.8g bamboo charcoal powder, 0.1g carbon black and 0.1g PVDF. A certain amount of N-methyl-2-pyrrolidone (NMP) and a small amount of anhydrous ethanol were added and ground into a uniform colloidal slurry. The slurry was then uniformly coated on copper foil and dried at 120℃ for 6h to obtain bamboo charcoal negative electrode sheet.

[0034] Electrochemical performance testing methods: The coin cell battery was mainly tested for cycle life and constant current charge-discharge performance using the Blue Electric testing system. Example 2:

[0035] This embodiment provides an efficient preparation method for lignin-coated cellulose nanofiber sodium-ion battery separators. The basic method is the same as in Example 1, except that the hydrothermal treatment temperature is 160°C and the hydrothermal reaction time is 60 min. Example 3:

[0036] This embodiment provides an efficient preparation method for lignin-coated cellulose nanofiber sodium-ion battery separators. The basic method is the same as in Example 1, except that the hydrothermal treatment temperature is 200℃ and the hydrothermal reaction time is 60 min. Example 4:

[0037] This embodiment provides an efficient preparation method for lignin-coated cellulose nanofiber sodium-ion battery separators. The basic method is the same as in Example 1, except that the hydrothermal treatment temperature is 220℃ and the hydrothermal reaction time is 60 min. Example 5:

[0038] This embodiment provides an efficient preparation method for lignin-coated cellulose nanofiber sodium-ion battery separators. The basic method is the same as in Example 1, except that the hydrothermal treatment time is 30 min at 180°C. Example 6:

[0039] This embodiment provides an efficient preparation method for lignin-coated cellulose nanofiber sodium-ion battery separators. The basic method is the same as in Example 1, except that the hydrothermal treatment time is 90 min at 180°C. Example 7:

[0040] This embodiment provides an efficient preparation method for lignin-coated cellulose nanofiber sodium-ion battery separators. The basic method is consistent with that in Example 1, except that the grinding disc gap is 0.1 μm. Example 8:

[0041] This embodiment provides an efficient preparation method for lignin-coated cellulose nanofiber sodium-ion battery separators. The basic method is consistent with that in Example 1, except that the gap between the grinding discs used is 2 μm. Example 9:

[0042] This embodiment provides an efficient preparation method for lignin-coated cellulose nanofiber sodium-ion battery separators. The basic method is the same as in Example 1, except that the grinding is performed 40 times. Example 10:

[0043] This embodiment provides an efficient preparation method for lignin-coated cellulose nanofiber sodium-ion battery separators. The basic method is consistent with that in Embodiment 1, except that the liquid solid content of the giant bamboo pulp is 10%.

[0044] This comparative example mainly uses commercial glass fiber (GF) diaphragms (purchased from Shanghai Titan Technology Co., Ltd., model GF / A-1820).

[0045] This comparative example mainly uses commercial polypropylene (PP) diaphragms (purchased from Shanghai Dingze Industrial Co., Ltd., model Celgard 2500).

[0046] This comparative example mainly uses a commercial ceramic diaphragm (purchased from Shanghai Dingze Industrial Co., Ltd., model 12+2μm ceramic membrane, PE single-sided coated with alumina particles).

[0047] The electrochemical performance indicators of the sodium-ion batteries obtained in the above examples and comparative examples are compared in Table 1 below:

[0048] Table 1: Product Performance Indicators for Each Embodiment

[0049]

[0050] As can be seen from the performance indicators of the products prepared in Table 1, the membrane material prepared by the present invention has a significantly higher affinity for electrolyte than the two commercially available membranes, PP and ceramic membranes. Furthermore, when the membrane material prepared by the present invention is assembled into a sodium-ion coin cell, its initial discharge specific capacity, cycle performance at different numbers of cycles (discharge specific capacity at the same current density), and rate capability (discharge specific capacity at different current densities) are all significantly higher than those of the three commercially available membranes, GF, PP, and ceramic membranes.

[0051] In summary, the raw materials used in this invention are abundant and green, and the vacuum filtration technology is simple, efficient, and streamlined. It also provides high porosity for biomass-based membrane materials, which is beneficial for electrochemical reactions and sodium ion transport. By retaining lignin on the basis of cellulose, the time, manpower, and material costs associated with lignin removal are eliminated, and the prepared membrane material has a good specific surface area, improving sodium ion transport channels. Simultaneously, it overcomes the problem of poor electrolyte wettability in traditional polyolefin membranes. When the prepared lignin-coated cellulose nanofiber membrane is used as a membrane material, the battery exhibits excellent performance in specific capacity, cycle stability, and rate capability.

[0052] The above description is merely a further detailed explanation of the present invention, but is not intended to limit the present invention. For those skilled in the art, various modifications or substitutions can be made without departing from the concept of the present invention. These equivalent modifications or substitutions are all included within the scope defined by the claims of this application and are protected by patent law.

Claims

1. A method for preparing a lignin-coated cellulose nanofiber sodium-ion battery separator, characterized in that, Includes the following steps: Pretreatment of bamboo particles using a hydrothermal method; (1) The size of the bamboo particles is 20-80 mesh; the pretreatment process is: soaking in water for a period of time, heating to 120-240℃, hydrothermal reaction for 30-180 min; to obtain a bamboo particle suspension; Subsequently, a mechanical dissociation method was used to nano-size bamboo particles to obtain lignin-coated cellulose nanofibers. (2) Prepare a bamboo particle suspension with a solid content of 5%-10%. After grinding several times with a grinding disc, a lignin-coated cellulose nanofiber suspension is obtained. The lignin-coated cellulose nanofiber suspension, water and isopropanol solution are added in sequence according to a volume ratio of 15-50:4:32 and mixed thoroughly to form a mixture. The mixture is then ultrasonically vibrated and magnetically stirred at room temperature to make the suspension evenly dispersed. (3) The lignin-coated cellulose nanofiber suspension was made into a thin film by vacuum filtration; A vacuum filtration device was used to perform filtration to obtain an initial membrane of lignin-coated cellulose nanofibers. The initial membrane was immersed in tert-butanol for a period of time and then vacuum dried to obtain a lignin-coated cellulose nanofiber membrane, i.e., a sodium-ion battery separator. In step (2), the grinding method is as follows: use a grinding disc with a gap of 0.1-2μ ultra-fine particles to grind for 30-40 times; In step (2), a bamboo particle suspension with a solid content of 5% is prepared. The lignin-coated cellulose nanofiber suspension, water and isopropanol solution are added in sequence according to a volume ratio of 15:2:8 and mixed thoroughly to form a mixture. In the sodium-ion battery separator, the lignin-coated cellulose nanofibers have an average diameter of 10-20 nm, and the lignin particles have an average particle size of 25-40 nm.

2. The preparation method according to claim 1, characterized in that, In step (1), the size of the bamboo particles is 30-60 mesh; the pretreatment process is: soaking in water for a period of time, heating to 160-220℃, and hydrothermal reaction for 30-90 minutes.

3. The preparation method according to claim 2, characterized in that, In step (1), the size of the bamboo particles is 40 mesh; the pretreatment process is: soaking in water for a period of time, heating to 180℃, and hydrothermal reaction for 60 minutes.

4. The preparation method according to claim 1, characterized in that, In step (1), the bamboo granules are prepared by cleaning the dust and dirt off the surface of the bamboo strips with distilled water, crushing the bamboo strips in a wall-breaking machine, and sieving them through a 20-80 mesh sieve.

5. The preparation method according to claim 1, characterized in that, In step (3), a vacuum filtration device is used for filtration and the obtained initial membrane is immersed in tert-butanol for 12-24 hours, sonicated for 1-2 hours and magnetically stirred for 6-12 hours. After vacuum drying, a lignin-coated cellulose nanofiber sodium-ion battery separator is obtained.

6. A sodium-ion battery separator material, characterized in that, The lignin-coated cellulose nanofiber sodium-ion battery separator prepared by any of the preparation methods described in claims 1-5.

7. A sodium-ion battery, characterized in that, The separator material of the sodium-ion battery is the sodium-ion battery separator material as described in claim 6.

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