Preparation method of lignin-coated cellulose nanofiber sodium-ion battery diaphragm

Abstract

The invention discloses a preparation method of a lignin-coated cellulose nanofiber sodium-ion battery diaphragm, and relates to the technical field of electrochemistry and battery diaphragms.The preparation method comprises the steps that bamboo particles are pretreated through a hydrothermal method; then carrying out bamboo particle nanocrystallization by adopting a mechanical dissociation method to obtain a lignin-coated cellulose nanofiber suspension, and preparing the lignin-coated cellulose nanofiber into a thin film by adopting a vacuum filtration method. The preparation process of the cellulose coated with the lignin nanoparticles is direct, simple, efficient and environment-friendly, chemical reagents such as acid and alkali do not need to be adopted for removing hemicellulose and lignin, meanwhile, the diffusion rate of sodium ions in the charging and discharging process is effectively increased due to coating of the lignin nanoparticles, and the sodium ion conductivity is improved. The specific discharge capacity and the cycling stability are realized.

Description

Technical Field

[0001] The present invention relates to the technical fields of electrochemistry and battery separator technology, and relates to an efficient preparation method for a lignin-coated cellulose nanofiber sodium-ion battery separator. Background Art

[0002] Energy is the core driving force for the prosperity and progress of human society. However, with the development of society, problems such as shortages of fossil energy and environmental crises caused by energy extraction have become increasingly serious. The core trend in solving this energy problem lies in the efficient storage of renewable energy using battery technology. Among them, lithium-ion batteries, as a key technology, are widely used in various fields such as smartphones and electric vehicles. This extensive application has also led to a tight supply and demand situation for lithium resources, resulting in rising lithium prices. The global distribution of lithium resources is uneven, and China's lithium content accounts for only about 6% of the global content. China's sodium content is approximately 422 times that of lithium. Therefore, exploring alternative battery technologies, such as sodium-ion batteries, has become a key path to alleviate lithium shortages and promote the development of sustainable energy.

[0003] As a new type of rechargeable battery, sodium-ion batteries have advantages such as high energy density, low cost, and wide availability of resources. Among the materials of sodium-ion batteries, in addition to the positive electrode, negative electrode, and electrolyte, the separator is also one of the indispensable key materials in sodium batteries. Its main function is to separate the positive and negative electrodes of the battery and enable sodium ions to freely transport through between the positive and negative electrodes. For the safety performance of the battery, the separator must be a very good insulator. At the same time, for the use of the battery, the separator must have certain pores for ion transport. Therefore, the quality of the separator material directly affects the safety performance and capacity of the battery. Since the radius and mass of Na + (0.098 nm, 22.99 g / mol -1 ) are both larger than those of Li + (0.076 nm, 6.94 g / mol -1 ), the pore size of the separator used should also be larger than that of the lithium-ion battery separator. In addition, the commonly used electrolyte for sodium-ion batteries is an organic electrolyte prepared with NaClO 4 or NaPF 6 as the sodium salt, propylene carbonate (PC) as the solvent, and fluoroethylene carbonate (FEC) as the additive. Propylene carbonate has only the carbon-oxygen double bond of the ester, and it has a cyclic structure. This special structure results in very poor wetting effects of the electrolyte on common polymer separators in the market. Therefore, there is an urgent need for a separator material suitable for the sodium-ion pore size and electrolyte wettability to overcome the current limitations. Summary of the Invention

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

[0005] To achieve the above object, the present invention provides the following technical solutions: A preparation method of a lignin-coated cellulose nanofiber sodium-ion battery separator, comprising the following steps: (1) Pretreat bamboo particles by hydrothermal method; The size of the bamboo particles is 20 mesh - 80 mesh; the pretreatment process is: soak in water for a period of time, heat to 120 - 240 °C, and carry out hydrothermal reaction for 30 - 180 min; obtain a bamboo particle suspension; (2) Subsequently, use the mechanical dissociation method to nanometerize the bamboo particles to obtain a lignin-coated cellulose nanofiber suspension; Prepare a bamboo particle suspension with a solid content of 5% - 10%, grind it several times with a grinding disc, and obtain a lignin-coated cellulose nanofiber suspension. Then, add the lignin-coated cellulose nanofiber suspension, water, and isopropanol solution in a volume ratio of 15 - 50:4:32 in sequence and mix well to form a mixed solution; ultrasonically vibrate and magnetically stir at room temperature to uniformly disperse the suspension; (3) Then, use the vacuum filtration method to make the lignin-coated cellulose nanofiber suspension into a film; Perform vacuum filtration using a vacuum filtration device to obtain an initial lignin-coated cellulose nanofiber film; immerse the obtained initial film in tert-butanol for a period of time, and finally vacuum dry to obtain a lignin-coated cellulose nanofiber film, which is the sodium-ion battery separator.

[0006] Further, in step (1), the size of the bamboo particles is 30 mesh - 60 mesh; the pretreatment process is: soak in water for a period of time, heat to 160 - 220 °C, and carry out hydrothermal reaction for 30 - 90 min.

[0007] Further, in step (1), the size of the bamboo particles is 40 mesh; the pretreatment process is: soak in water for a period of time, heat to 180 °C, and carry out hydrothermal reaction for 60 min.

[0008] Further, in step (1), the preparation method of the bamboo particles is to clean the dust and dirt on the surface of the bamboo strips with distilled water, put the bamboo strips into a wall breaker for crushing, and sieve with a 20 mesh - 80 mesh sieve.

[0009] Further, in step (2), the grinding method of the grinding disc is as follows: use a grinding disc with an ultra-fine particle grinding gap of 0.1 - 2 μm, and grind 30 - 40 times.

[0010] Further, in step (2), a bamboo particle suspension with a solid content of 5% is prepared, and a lignin-coated cellulose nanofiber suspension, water, and isopropanol solution are sequentially added in a volume ratio of 15:2:8 and mixed well to form a mixed solution.

[0011] Further, in step (3), a vacuum filtration device is used for filtration, and the obtained initial membrane is immersed in tert-butanol for 12 - 24 h, ultrasonically treated for 1 - 2 h, and magnetically stirred for 6 - 12 h, and then vacuum dried to obtain a lignin-coated cellulose nanofiber sodium-ion battery separator.

[0012] 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 above preparation methods.

[0013] Further, for the sodium-ion battery separator material, in the sodium-ion battery separator, the average diameter of the lignin-coated cellulose nanofibers is 10 - 20 nm, and the average particle size of the lignin particles is 25 - 40 nm.

[0014] Finally, the present invention also provides a sodium-ion battery, and the separator material of the sodium-ion battery is the above-mentioned sodium-ion battery separator material.

[0015] The raw materials used in the present invention are widely sourced, easily obtainable, and renewable. Generally, nanofibrillated cellulose is prepared by chemically removing lignin from biomass fibers, which is time-consuming, laborious, and environmentally polluting. However, the raw materials used in the present invention do not require lignin removal and are prepared by a hydrothermal method, which has the obvious advantages of simple process, low cost, and high yield. The lignin-coated cellulose nanofiber sodium-ion battery separator prepared by the present invention has advantages such as a large specific surface area and high electrolyte wettability, effectively promoting sodium-ion transport, improving the initial discharge specific capacity of the battery, and making an important contribution to the realization of efficient and sustainable energy storage solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a TEM image of the lignin-coated cellulose nanofibers in the present invention; Figure 2 It is an SEM image of the lignin-coated cellulose nanofiber sodium-ion battery separator in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The present invention is further described below in conjunction with specific examples, but these examples are only exemplary and do not constitute any limitation to the scope of the present invention. All reagents used in the present invention are analytically pure, all materials can be purchased from the market, and the vacuum filtration device (specification model ET-2535H) used is a G3 glass funnel (60ml). Embodiment 1:

[0018] 1. Use distilled water to clean the dust and dirt on the surface of the giant dragon bamboo strips, put the bamboo strips into a wall-breaking machine and crush them, and sieve them with a 40-mesh screen to obtain giant dragon bamboo particles; 2. Soak the giant dragon bamboo particles in deionized water at room temperature for 24 hours, and then perform a hydrothermal reaction at 180° C. for 60 minutes to obtain a giant dragon bamboo particle suspension; 3. A suspension of giant bamboo particles with a solid content of 5% was obtained by adjusting the solid-liquid ratio, and then the suspension of giant bamboo particles was mechanically dissociated and ground 30 times on a grinding disc with a gap of 1 μm to obtain a suspension of cellulose nanofibers coated with lignin. Among them, TEM (transmission electron microscopy) was used to characterize and measure the size of wood cellulose. It was found that the average diameter of cellulose nanofibers coated with lignin was 10-20nm, and the average particle size of lignin nanoparticles was 25-40nm. Figure 1 As shown; 4. Add 15 ml of lignin-coated cellulose nanofiber suspension, 4 ml of water and 32 ml of isopropanol solution in a volume ratio of 15:4:32 and mix thoroughly to form a mixed solution; ultrasonically vibrate for 30 min at room temperature and magnetically stir for 6 h to evenly disperse the lignin-coated cellulose nanofiber suspension; 5. Use a vacuum filtration device to filter and obtain a lignin-coated cellulose nanofiber initial membrane; immerse the obtained initial membrane in tert-butyl alcohol for 24 hours, and finally vacuum dry for 6 hours to obtain a lignin-coated cellulose nanofiber membrane SP-1, such as Figure 2 shown.

[0019] 6. Cut SP-1 into discs with a diameter of 19 mm and assemble them into button cells in a vacuum glove box for electrochemical testing.

[0020] 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 metal sodium sheets and bamboo fiber negative electrode sheets into circular pieces with a diameter of 14 mm as the positive and negative electrode materials respectively. Sodium hypochlorite is used as the electrolyte. Prepare basic equipment such as gaskets, positive and negative electrode cases, and separators. Place the above materials in a vacuum glove box for standby. Secondly, assemble the battery. Place the negative electrode case at the bottom layer, and sequentially add the negative electrode material (bamboo carbon 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 case. Finally, use a sealing machine to seal the assembled battery to obtain a complete sodium button battery.

[0021] Preparation method of bamboo carbon negative electrode sheet: Weigh 20 g of bamboo powder and carbonize it in a tube furnace to obtain bamboo carbon powder. Subsequently, pour the bamboo carbon powder, conductive acetylene black, and polyvinylidene fluoride (PVDF) into a mortar according to the mass ratio of 8:1:1, that is, 0.8 g of bamboo carbon powder, 0.1 g of carbon black, and 0.1 g of PVDF. Add a certain amount of N-methyl-2-pyrrolidone (NMP) and a small amount of absolute ethanol and grind them into a uniform colloidal slurry. Coat it evenly on the copper foil and dry it at 120 °C for 6 h to obtain the bamboo carbon negative electrode sheet.

[0022] Electrochemical performance testing method: The button battery mainly conducts cyclic life and constant current charge-discharge performance tests through a blue electrochemical workstation. Example 2:

[0023] This example provides an efficient preparation method of a lignin-coated cellulose nanofiber sodium-ion battery separator. The basic method is the same as that of Example 1, except that the hydrothermal treatment temperature is 160 °C and the hydrothermal reaction is 60 min. Example 3:

[0024] This example provides an efficient preparation method of a lignin-coated cellulose nanofiber sodium-ion battery separator. The basic method is the same as that of Example 1, except that the hydrothermal treatment temperature is 200 °C and the hydrothermal reaction is 60 min. Example 4:

[0025] This example provides an efficient preparation method of a lignin-coated cellulose nanofiber sodium-ion battery separator. The basic method is the same as that of Example 1, except that the hydrothermal treatment temperature is 220 °C and the hydrothermal reaction is 60 min. Example 5:

[0026] This embodiment provides a method for efficiently preparing a lignin-coated cellulose nanofiber sodium ion battery separator. The basic method is consistent with that in Example 1, except that the temperature is 180° C. and the hydrothermal treatment time is 30 min. Embodiment 6:

[0027] This embodiment provides a method for efficiently preparing a lignin-coated cellulose nanofiber sodium ion battery separator. The basic method is consistent with that of Example 1, except that the temperature is 180° C. and the hydrothermal treatment time is 90 min. Embodiment 7:

[0028] This embodiment provides a method for efficiently preparing a lignin-coated cellulose nanofiber sodium ion battery separator. The basic method is consistent with that of Example 1, except that the gap between the grinding discs used is 0.1 μm. Embodiment 8:

[0029] This embodiment provides a method for efficiently preparing a lignin-coated cellulose nanofiber sodium ion battery separator. The basic method is consistent with that of Example 1, except that the gap between the grinding discs used is 2 μm. Embodiment 9:

[0030] This embodiment provides a method for efficiently preparing a lignin-coated cellulose nanofiber sodium ion battery separator. The basic method is consistent with that of Example 1, except that the method is ground 40 times. Embodiment 10:

[0031] This embodiment provides an efficient preparation method of lignin-coated cellulose nanofiber sodium ion battery separator. The basic method is consistent with that of Example 1, except that the solid content of the giant dragon bamboo slurry is 10%.

[0032] This comparative example mainly refers to a commercial glass fiber (GF) separator (purchased from Shanghai Titan Technology Co., Ltd., model GF / A-1820).

[0033] This comparative example mainly uses a commercial polypropylene (PP) diaphragm (purchased from Shanghai Dingze Industrial Co., Ltd., model number is Celgard 2500).

[0034] This comparative example mainly refers to a commercial ceramic diaphragm (purchased from Shanghai Dingze Industrial Co., Ltd., model 12+2μm ceramic membrane, PE single-sided coated with alumina particles).

[0035] The electrochemical performance indicators of the sodium ion batteries obtained in the above examples and comparative examples are shown in Table 1 below: Table 1: Product performance indicators of various embodiments

[0036] As can be seen from the product performance indicators of each example prepared in Table 1, the affinity of the separator material prepared by the present invention for the electrolyte is significantly higher than that of the two commercial separators, namely PP and ceramic separator. At the same time, when the separator material prepared by the present invention is assembled into a sodium-ion button battery, the initial discharge specific capacity, the cycling performance at different numbers of cycles (the discharge specific capacity at the same current density), and the rate performance (the discharge specific capacity at different current densities) are all extremely significantly higher than those of the three commercial separators, namely GF, PP, and ceramic separator.

[0037] In summary, the raw materials of the present invention are rich in sources and have green renewable properties. By adopting the vacuum filtration technology, the operation is simple, streamlined and highly efficient, and it can also provide a high porosity for the biomass-based separator material, which is beneficial to the progress of the electrochemical reaction and the movement of sodium ions. Retaining lignin on the basis of cellulose saves the time, manpower and material resources consumed by removing lignin, and gives the prepared separator material a good specific surface area, improves the sodium ion transport channels, and at the same time overcomes the problems such as poor electrolyte wettability of traditional polyolefin separators. When the prepared lignin-coated cellulose nanofiber membrane is used as a separator material, the battery exhibits excellent performance in terms of specific capacity, cycling stability and rate performance.

[0038] The above description is only a further detailed explanation of the present invention, but not a limitation of the present invention. For those skilled in the art of the present invention, without departing from the concept of the present invention, several derivations, transformations or substitutions can still be made, and these equivalent variants or substitutions are all included in the scope defined by the claims of this application and are protected by the patent law.

Claims

1. A method for preparing a lignin-coated cellulose nanofiber sodium ion battery separator, characterized in that: The following steps are involved: The bamboo particles were pretreated by hydrothermal method; (1) The bamboo particles have a size of 20-80 mesh; the pretreatment process comprises: soaking in water for a period of time, heating to 120-240° C., and hydrothermal reaction for 30-180 minutes; and obtaining a bamboo particle suspension; The bamboo particles were then nanosized using a mechanical dissociation method to obtain lignin-coated cellulose nanofibers; (2) preparing a bamboo particle suspension with a solid content of 5% to 10%, grinding it several times with a grinding disc to obtain a lignin-coated cellulose nanofiber suspension, adding the lignin-coated cellulose nanofiber suspension, water and isopropanol solution in a volume ratio of 15 to 50:4:32 in sequence and mixing them thoroughly to form a mixed solution; ultrasonically vibrating and magnetically stirring at room temperature to uniformly disperse the suspension; The lignin-coated cellulose nanofiber suspension was made into a film by vacuum filtration; (3) using a vacuum filtration device to filter and obtain an initial cellulose nanofiber membrane coated with lignin; The obtained initial membrane was immersed in tert-butanol for a period of time and finally vacuum dried to obtain a lignin-coated cellulose nanofiber membrane, i.e., a sodium ion battery separator.

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

3. The preparation method according to claim 2, characterized in that: In step (1), the bamboo material particle size 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.

4. The preparation method according to claim 1, characterized in that: In step (1), the preparation method of bamboo particles is to clean the dust and dirt on the surface of bamboo strips with distilled water, put the bamboo strips into a wall breaking machine for crushing, and sieve them with a 20-80 mesh screen.

5. The method according to claim 1, characterized in that In step (2), the grinding method is: use a grinding disc with a gap of 0.1-2μ ultrafine particles to grind 30-40 times.

6. The preparation method according to claim 1, characterized in that: In step (2), a bamboo particle suspension with a solid content of 5% is prepared, and a lignin-coated cellulose nanofiber suspension, water and isopropanol solution are sequentially added in a volume ratio of 15:2:8 and mixed thoroughly to form a mixed solution.

7. 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 to 24 hours, ultrasonicated for 1 hour to 2 hours and magnetically stirred for 6 hours to 12 hours, and vacuum dried to obtain a lignin-coated cellulose nanofiber sodium ion battery separator.

8. A sodium ion battery separator material, characterized in that: A lignin-coated cellulose nanofiber sodium ion battery separator prepared by the preparation method described in any one of claims 1 to 7.

9. The sodium ion battery separator material according to claim 8, characterized in that: In the sodium ion battery separator, the average diameter of the cellulose nanofibers coated with lignin is 10-20 nm, and the average particle size of the lignin particles is 25-40 nm.

10. A sodium ion battery, characterized in that: The sodium ion battery diaphragm material is the sodium ion battery diaphragm material according to claim 8 or 9.

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