Wood-based elastic battery diaphragm, preparation method thereof and energy storage battery

Abstract

The invention provides a wood-based elastic battery diaphragm, a preparation method thereof and an energy storage battery. The wood-based elastic battery diaphragm comprises a biomass matrix, the biomass matrix has a xylem skeleton structure, the xylem skeleton structure comprises a multi-level structure with a pore structure, and the multi-level structure is derived from wood fibers; the hydrogel exists on the surface of the biomass matrix and / or in the biomass matrix through in-situ polymerization or cross-linking. The cycle life of the wood-based elastic battery diaphragm is greatly prolonged, the conductivity of the wood-based elastic battery diaphragm is greatly improved, and the wood-based elastic battery diaphragm is green, environment-friendly, low in cost, simple and easy to implement, has mechanical stability and uniform ion flux and has stress strain, so that an energy storage battery which is high in performance, green and long in cycle life can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to a wood-based elastic battery separator, a preparation method thereof and an energy storage battery, and belongs to the field of battery materials. BACKGROUND

[0002] Wood, as a sustainable, renewable and biodegradable natural material, is expected to become a substitute for petroleum-based materials. Although wood has been used by humans for thousands of years, it has long been used as an engineering material, ignoring the potential application of wood in other aspects. In the natural evolution of hundreds of millions of years, wood has formed a highly hierarchical gradient structure, which enables the transport of nutrients (such as water, ions, etc.) throughout the tree. It is this characteristic that makes it an ideal substrate in various fields, especially in the field of energy storage.

[0003] With the rapid development of new energy and energy storage market, the application scenarios of high-performance batteries are increasingly diversified, and the demand for batteries with high safety, high energy density and long cycle life is also rising. As the "safety valve" of the battery, the separator is the key to determining the safety of the battery. The performance of the battery separator determines the capacity, cycle performance, charge and discharge current density and other key characteristics of the battery. Therefore, how to improve the safety and cycle life of the battery and develop a high-heat-resistant and high-performance battery separator has always been the direction of electrochemical exploration.

[0004] Therefore, it is a technical problem to be solved to study a wood-based elastic battery separator that is green, environmentally friendly, low in cost, simple and easy to implement, and has mechanical stability, uniform ion flux, and stress and strain, so as to obtain a high-performance, green and long-cycle-life energy storage battery. SUMMARY

[0005] Problems to be solved by the application

[0006] In view of the technical problems existing in the prior art, the present application first provides a wood-based elastic battery separator that is green, environmentally friendly, low in cost, simple and easy to implement, and has mechanical stability, uniform ion flux, and stress and strain, so as to obtain a high-performance, green and long-cycle-life energy storage battery.

[0007] Further, the present application also provides a preparation method of the wood-based elastic battery separator, which removes lignin, retains wood skeleton structure and part of cell morphology, forms a multi-level structure with a large number of pores, and then introduces a hydrogel to polymerize or cross-link in situ in the wood skeleton to form a wood-based hydrogel. The preparation method is simple and easy to implement, raw materials are easy to obtain, and is suitable for mass production.

[0008] Solution for solving the problem

[0009] The present application first provides a wood-based elastic battery separator, which comprises:

[0010] a biomass matrix having a lignin skeleton structure, the lignin skeleton structure comprising a multi-level structure having a pore structure, the multi-level structure originating from wood fibers; and

[0011] a hydrogel formed by in-situ polymerization or cross-linking on the surface and / or inside of the biomass matrix.

[0012] The wood-based elastic battery separator according to the present application, wherein the multi-level structure comprises cellulose and hemicellulose; and wherein the content of the cellulose is 70% to 85% and the content of the hemicellulose is 15% to 30% based on the total mass of the biomass matrix.

[0013] The wood-based elastic battery separator according to the present application, wherein the content of the biomass matrix is 30% to 60% and the content of the hydrogel is 40% to 70% based on the total mass of the wood-based elastic battery separator.

[0014] The wood-based elastic battery separator according to the present application, wherein the hydrogel originates from a high molecular compound, preferably the high molecular compound comprises polyvinyl alcohol and / or polyacrylamide.

[0015] The present application also provides a preparation method of the wood-based elastic battery separator according to the present application, comprising the step of compounding a biomass matrix and a hydrogel.

[0016] Preferably, the preparation method comprises the following steps:

[0017] obtaining a hydrogel precursor solution;

[0018] immersing the biomass matrix in the hydrogel precursor solution, and allowing the hydrogel precursor to cross-link or in-situ polymerize on the surface and / or inside of the biomass matrix to form the hydrogel, thereby obtaining the wood-based elastic battery separator.

[0019] The preparation method according to the present application, wherein the cross-linking comprises cross-linking by 2 or more freeze-thaw cycles under vacuum; and / or,

[0020] The in-situ polymerization is performed at a temperature of 50°C to 80°C for 3h to 5h.

[0021] The preparation method according to the present application, wherein the preparation method of the biomass matrix comprises the following steps:

[0022] oxidizing a wood raw material using an oxidizing agent under acidic conditions to obtain a pretreated product;

[0023] Freeze-drying the pretreated product to obtain a biomass matrix.

[0024] According to the preparation method, the freeze-drying time is more than 12 hours.

[0025] Preferably, before freeze-drying, the pretreated product is further subjected to a freezing step, and more preferably, the freezing temperature is below -20°C, and the freezing time is 1-10 hours.

[0026] According to the preparation method, the preparation method of the hydrogel precursor solution comprises the following steps:

[0027] The high-molecular compound is dissolved in a solvent to obtain a hydrogel precursor solution, or monomers, a crosslinking agent and an initiator are mixed in a solvent to obtain a hydrogel precursor solution.

[0028] Preferably, in the hydrogel precursor solution, the mass concentration of the high-molecular compound is 5-20%, and / or the mass ratio of the monomers, the crosslinking agent, the initiator and the solvent is 1:0.0001-0.001:0.001-0.01:1-5.

[0029] The application further provides an energy storage battery comprising the wood-based elastic battery separator.

[0030] Effects of the application

[0031] The wood-based elastic battery separator has greatly improved cycle life and conductivity, and is a wood-based elastic battery separator that is green, low in cost, simple and easy to implement, and has mechanical stability, uniform ion flux and stress-strain, thereby obtaining an energy storage battery with high performance, greenness and long cycle life.

[0032] The preparation method of the wood-based elastic battery separator is simple and easy to implement, raw materials are easy to obtain, and is suitable for mass production. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Electron microscope images of balsa wood (NW), balsa wood biomass matrix (DW) and wood-based elastic battery separator (DW-PVA) of Example 1 are shown, as well as electron microscope images of the wood-based elastic battery separator (DW-PVA) in each direction, wherein a is a transverse section, b is a radial section and c is a tangential section.

[0034] Figure 2 Ion conductivity comparison charts of traditional glass fiber separator (GF), polyvinyl alcohol (PVA) and wood-based elastic battery separator (DW-PVA) of Example 1 are shown.

[0035] Figure 3 A comparison graph showing the cycle life of a conventional glass fiber (GF) separator, polyvinyl alcohol (PVA), and the wood-based elastic battery separator (DW-PVA) of Example 1 in a half-cell charge-discharge cycle test is presented.

[0036] Figure 4 A comparison graph showing the cycle life of a conventional glass fiber separator (GF) and the wood-based elastic battery separator (DW-PAM) of Example 2 in a half-cell charge-discharge cycle test is presented.

[0037] Figure 5 The diagram shows a full-cell charge-discharge cycle test of the wood-based elastic battery separator of Example 3.

[0038] Figure 6 The diagram shows a full-cell charge-discharge cycle test of the wood-based elastic battery separator of Example 4.

[0039] Figure 7 Infrared spectra of balsa wood (NW), balsa wood biomass matrix (DW), polyvinyl alcohol (PVA), and wood-based elastic battery separator (DW-PVA) of Example 1 are shown.

[0040] Figure 8 A photograph of the wood-based elastic battery separator of Embodiment 1 of the present invention is shown. Detailed Implementation

[0041] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments.

[0042] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In other instances, methods, means, apparatus, and steps well known to those skilled in the art have not been described in detail in order to highlight the spirit of the present invention.

[0043] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0044] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0045] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0046] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0047] <First Aspect>

[0048] A first aspect of the present invention provides a wood-based elastic battery separator, the wood-based elastic battery separator comprising:

[0049] A biomass matrix having a xylem framework structure, the xylem framework structure comprising a multi-level structure with a porous structure, the multi-level structure originating from wood fibers; and...

[0050] Hydrogel, which exists on the surface and / or inside the biomass matrix through in-situ polymerization or cross-linking.

[0051] The wood-based elastic battery separator of the present invention has significantly improved cycle life and conductivity. It is a green, environmentally friendly, low-cost, simple and easy-to-implement wood-based elastic battery separator that also has mechanical stability, uniform ion flux, and stress-strain properties, thereby enabling the production of a high-performance, green, and long-cycle-life energy storage battery.

[0052] In some specific embodiments, the multi-level structure comprises cellulose and hemicellulose; wherein, based on the total mass of the biomass matrix (100%), the cellulose content is 70%–85%, for example: 72%, 75%, 78%, 80%, 82%, etc.; the hemicellulose content is 15%–30%, for example: 18%, 20%, 22%, 25%, 28%, etc. In this invention, the lignin originally present in the biomass matrix has been substantially removed. After lignin removal, the porosity of the wood increases, which is beneficial for subsequent impregnation (such as impregnation using acrylamide or polyvinyl alcohol precursor solutions). The multi-level structure may have three or more layers.

[0053] In some specific embodiments, based on the total mass of the wood-based elastic battery separator, the content of the biomass matrix is ​​30% to 60%, preferably 30% to 50%, for example: 35%, 40%, 45%, 50%, 55%, etc.; the content of the hydrogel is 40% to 70%, preferably 50% to 70%, for example: 45%, 50%, 55%, 60%, 65%, etc. The wood matrix provides a natural ion transport framework, and the elastic hydrogel enhances the mechanical properties of the electrolyte.

[0054] In some specific embodiments, the hydrogel is derived from a polymer compound. This invention does not particularly limit the specific composition of the polymer compound, as long as it is a material capable of forming a gel network structure. Preferably, the polymer compound includes synthetic polymer compounds and / or natural polymer compounds. Specifically, the polymer compound includes one or more combinations of polyvinyl alcohol, polyacrylamide gelatin, sodium carboxymethyl cellulose, polyacrylic acid, or their sodium salts.

[0055] <Second aspect>

[0056] A second aspect of the present invention provides a method for preparing a wood-based elastic battery separator according to the first aspect of the present invention, comprising the step of composite molding of a biomass matrix and a hydrogel.

[0057] Preferably, the preparation method includes the following steps:

[0058] Obtain the hydrogel precursor solution;

[0059] The biomass matrix is ​​immersed in the hydrogel precursor solution, causing the hydrogel precursor to undergo cross-linking or in-situ polymerization on the surface and / or inside the biomass matrix to form a hydrogel, thereby obtaining a wood-based elastic battery separator.

[0060] This invention removes lignin while retaining the xylem skeleton structure and some cell morphology to form a multi-layered structure with numerous pores. Subsequently, hydrogels are introduced into the wood skeleton for in-situ polymerization or cross-linking to form wood-based hydrogels. This preparation method is simple and easy to implement, the raw materials are readily available, and it is suitable for mass production.

[0061] Preparation of biomass substrate

[0062] In this invention, the method for preparing the biomass matrix includes the following steps:

[0063] Under acidic conditions, wood raw materials are oxidized using oxides to obtain pretreated products;

[0064] The pretreated product was freeze-dried to obtain a biomass matrix.

[0065] In this invention, the wood raw material is not particularly limited and can be any commonly used wood raw material with ray tissue in the art. Examples include: coniferous wood, broadleaf wood, balsa wood, poplar, birch, linden, oak, etc. During preparation, the wood raw material can be cut into smaller sizes for ease of processing.

[0066] The present invention does not specifically limit the oxides used; any oxide commonly used in the art can be used. Specifically, the oxide may include one or more of the following: H₂O₂, NaClO₂, NaClO, KClO₂, KClO, etc.

[0067] Furthermore, when using oxides for oxidation treatment, the wood raw material can be soaked in an oxide solution to obtain wood-based materials. Specifically, the oxides can be dissolved in a solvent. This invention does not particularly limit the specific solvent; it can be a commonly used polar solvent in the art, such as water. Specifically, the mass fraction of the oxides in the oxide solution is 0.5% to 5%, for example: 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, etc. When the mass fraction of the oxides in the oxide solution is 0.5% to 5%, lignin oxidation and removal can be effectively achieved, while ensuring the controllability and safety of the treatment process.

[0068] In this invention, to better achieve the oxidation process, the oxidation is carried out under acidic conditions. When preparing the oxide solution, glacial acetic acid needs to be added to adjust the pH of the sodium chlorite solution to be acidic, specifically below pH 4.6.

[0069] Specifically, during oxidation treatment, the mass ratio of wood raw material to oxide solution is 1:30~80, for example: 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, etc. When the mass ratio of wood raw material to oxide solution is 1:30~80, it can ensure that the wood is in complete contact with the oxidation solution, promoting a full reaction.

[0070] In some specific implementation schemes, heating can be used during chemical treatment with oxides to accelerate lignin removal. Specifically, the heating temperature can be 60℃~100℃, for example, 70℃, 80℃, 90℃, etc.; the heating time can be 4 h~24 h, for example, 8 h, 12 h, 16 h, 20 h, etc. The relationship between lignin removal efficiency and wood structural integrity is investigated when the heating temperature is 60℃~100℃ and the heating time is 4 h~24 h.

[0071] Furthermore, after oxidation treatment, appropriate cleaning can be performed to facilitate the formation of the biomass matrix. Specifically, it can be soaked in water for 10 to 30 hours, such as 15 hours, 20 hours, or 25 hours. Cleaning can thoroughly wash away residual oxides and byproducts, preventing them from interfering with subsequent performance.

[0072] Furthermore, the pretreated product is freeze-dried to obtain a biomass matrix. Specifically, the freeze-drying time is 12 hours or more, generally 12 to 24 hours, to ensure thorough drying and maintain structural integrity.

[0073] Furthermore, the pretreated product can be pre-frozen before freeze-drying. Specifically, the freezing temperature is below -20°C, and the freezing time is 1 hour to 10 hours, for example, 3 hours, 5 hours, 7 hours, 9 hours, etc.

[0074] Preparation of hydrogel

[0075] In this invention, the preparation method of the hydrogel precursor solution includes the following steps:

[0076] A hydrogel precursor solution is obtained by dissolving a polymer compound in a solvent; or by mixing a monomer, a crosslinking agent, and an initiator in a solvent.

[0077] Preferably, when the hydrogel is obtained by crosslinking, the mass concentration of the polymer compound in the hydrogel precursor solution is 5% to 20%, for example: 8%, 10%, 12%, 15%, 18%, etc. When the mass concentration of the polymer compound is 5% to 20%, it can ensure that the solution has good fluidity and permeability, while forming a stable three-dimensional gel network structure.

[0078] When hydrogels are obtained using in-situ polymerization, the mass ratio of monomer, crosslinking agent, initiator, and solvent is 1:0.0001~0.001:0.001~0.01:1~5, preferably 1:0.0002~0.0006:0.002~0.006:2~3. A mass ratio of 1:0.0001~0.001:0.001~0.01:1~5 ensures uniform reaction and sufficient gel formation.

[0079] In some specific implementations, the crosslinking involves crosslinking through two or more freeze-thaw cycles under vacuum to obtain a hydrogel. Crosslinking through two or more freeze-thaw cycles allows for the construction of a stable hydrogen bond network under low-energy conditions, improving gelation efficiency and mechanical strength, while avoiding the introduction of organic solvents, thus offering green and environmentally friendly advantages.

[0080] Specifically, the biomass matrix is ​​placed in a petri dish, and the hydrogel precursor solution is poured in until the wood chips are completely submerged. Then, the petri dish is placed in a vacuum device, and degassing is performed under vacuum to remove air bubbles from the solution. Vacuuming is repeated 2-3 times, followed by freeze-thaw cycles 4-6 times until a wood-based hydrogel is formed.

[0081] In some specific implementations, the in-situ polymerization includes immersing the precursor solution in the treated wood chips for 0.5 h to 2 h using a vacuum pump, followed by in-situ polymerization until a wood-based hydrogel is formed.

[0082] Specifically, the in-situ polymerization temperature is 50 ℃~80 ℃, for example: 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, etc.; the in-situ polymerization time is 3 h~5 h, for example: 3.5 h, 4 h, 4.5 h, etc. When the in-situ polymerization temperature is 50 ℃~80 ℃ and the in-situ polymerization time is 3 h~5 h, the polymerization reaction can be promoted to proceed completely, ensuring the stability of the gel structure and avoiding side reactions or degradation.

[0083] <Third aspect>

[0084] A third aspect of the present invention provides an energy storage battery comprising the wood-based elastic battery separator described in the first aspect of the present invention. The wood-based elastic battery separator of the present invention can be directly assembled into a battery after soaking or adding electrolyte.

[0085] The energy storage battery of this invention includes lithium, sodium, potassium, and other metal-ion batteries, various aqueous batteries, and capacitors. The electrolyte of this invention includes electrolytes used in lithium, sodium, potassium, and other metal / ion batteries, various aqueous batteries, and capacitors. Specifically, the electrolyte is added using a conventional dropping method, with a volume of 0.1 mL or more.

[0086] In some specific implementations, the assembly process of the energy storage battery includes the following steps: cutting the prepared wood-based elastic battery separator to a size suitable for the battery casing and placing it between the two electrodes; the positive and negative electrode materials can be selected according to the battery type, such as zinc foil, graphite, sodium foil, etc.; then, an appropriate amount of electrolyte is dropped onto the separator, and the battery is sealed in a sealed environment. If it is a button cell battery, a CR2032 casing can be used, and it can be packaged by a pressing machine; if it is a pouch or stacked battery, it can be heat-pressed or heat-sealed in a glove box.

[0087] Example

[0088] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0089] In the example: a conventional glass fiber diaphragm (GF) was purchased from Whatman Ltd. (Shanghai, China).

[0090] Example 1

[0091] Balsa wood (NW) sheets with a tangential thickness of 1 mm were cut. The balsa wood sheets were mixed with a 2 wt% sodium hypochlorite solution at a mass ratio of 1:50. The pH of the solution was adjusted to below 4.6 using glacial acetic acid, and the mixture was heated at 85°C for 10 h. After the reaction, the balsa wood sheets were rinsed with ultrapure water and then soaked in ultrapure water for 24 h to thoroughly remove residual reactants. The treated wood sheets were then frozen at -70°C for 5 h and dried in a freeze dryer for 72 h to obtain lignin-free balsa wood matrix (DW).

[0092] Accurately weigh 5g of polyvinyl alcohol (PVA) powder, slowly add it to 45mL of deionized water and stir well. After standing for 10 minutes, heat in a 95℃ water bath for 4-5 hours with stirring until the PVA is completely dissolved, forming a PVA solution for later use. Mix the obtained balsa wood matrix with the PVA solution at a mass ratio of 1:15, place it in a petri dish, and pour in the PVA solution until the balsa wood matrix is ​​completely submerged. Then, perform vacuum degassing in a vacuum device to remove air bubbles from the solution. Continue vacuuming 2-3 times to ensure that the PVA fully penetrates into the balsa wood matrix. Then, perform 4-6 freeze-thaw cycles. After drying the formed wood-based hydrogel, it becomes the wood-based elastic battery separator. Figure 8 As shown; wherein, the mass of the balsa wood matrix is ​​approximately 0.079 g, and the total mass of the wood-based hydrogel membrane is approximately 0.21 g.

[0093] Battery assembly: The wood-based elastic battery separator was immersed in electrolyte (1M ZnSO4) for about 1 hour to complete the activation treatment. Then the battery was assembled. A zinc sheet with a diameter of 14 mm was used as the negative electrode, and a V2O5 sheet with a diameter of 14 mm was used as the positive electrode. The wood-based elastic battery separator was used as the electrolyte and separator material. The zinc sheet (negative electrode), the wood-based elastic battery separator (electrolyte / separator), and the zinc sheet (positive electrode) were stacked in sequence into the button cell casing. After adding an appropriate amount of electrolyte, i.e., 1 mol / L ZnSO4 solution, the battery was packaged in a tablet press to finally obtain the battery for performance testing.

[0094] Example 2

[0095] A 1 mm thick balsa wood veneer was cut. The balsa wood veneer was mixed with a 2 wt% sodium hypochlorite solution at a mass ratio of 1:50. The pH of the solution was adjusted to below 4.6 using glacial acetic acid, and the mixture was heated at 85°C for 10 hours. After the reaction was completed, the wood veneer was rinsed with ultrapure water and then soaked in ultrapure water for 24 hours to thoroughly remove residual reactants. The cleaned wood veneer was then frozen at -70°C for 5 hours and then dried in a freeze dryer for 72 hours to obtain lignin-free balsa wood matrix (DW).

[0096] 15g of acrylamide (AM) powder was accurately weighed and dissolved in 35g of deionized water. 0.006g of crosslinking agent methylenebisacrylamide (MBAA) and 0.06g of initiator ammonium persulfate (APS) were added to the solution, and the mixture was stirred until clear and transparent to obtain the precursor solution. This precursor solution was then impregnated into a lignin-free biomass matrix using a vacuum pump for approximately 1 hour. The impregnated wood chips were then heated at 65°C for approximately 4 hours until a wood-based hydrogel was formed, after which it was dried to obtain the wood-based elastic battery separator. The mass of the balsa wood matrix was approximately 0.079g, and the total mass of the wood-based hydrogel battery separator was approximately 0.21g.

[0097] Battery Assembly: The obtained wood-based elastic battery separator was immersed in a 1 mol / L ZnSO4 electrolyte solution for about 1 hour to complete the activation treatment. A 14 mm diameter zinc sheet was used as the negative electrode, and a 14 mm diameter V2O5 sheet was used as the positive electrode. A 19 mm diameter wood-based elastic battery separator was cut to isolate the positive and negative electrodes and provide ion channels during battery assembly. The zinc sheet (negative electrode), the wood-based elastic battery separator (electrolyte / separator), and the zinc sheet (positive electrode) were stacked sequentially in a coin cell casing, and an appropriate amount of electrolyte, i.e., a 1 mol / L ZnSO4 solution, was added dropwise to fully wet the entire system. Finally, the coin cell casing was pressed and sealed using a tablet press to obtain a battery suitable for performance testing.

[0098] Example 3

[0099] Poplar veneers with a tangential thickness of 1 mm were cut. The poplar veneers were mixed with a 2 wt% sodium hypochlorite solution at a mass ratio of 1:50. The pH of the solution was adjusted to below 4.6 using glacial acetic acid, and the mixture was heated at 85°C for 10 hours. After the reaction, the poplar veneers were rinsed with ultrapure water and soaked for 24 hours to thoroughly remove residual reactants. The cleaned veneers were then frozen at -70°C for 5 hours, followed by freeze drying for 72 hours to obtain a lignin-free poplar matrix (DW).

[0100] Accurately weigh 5g of polyvinyl alcohol (PVA) powder, slowly add it to 45mL of deionized water and stir well. After standing for 10 minutes, heat in a 95℃ water bath for 4-5 hours with stirring until the PVA is completely dissolved. Seal and set aside. Place the prepared DW in a petri dish, pour in the PVA solution until the wood chips are completely submerged, and then place the petri dish in a vacuum device for degassing to remove air bubbles from the solution. Vacuum the solution 3-4 times to ensure that the PVA fully impregnates the wood chips. Then, cycle through freeze-thaw 4-6 times to form a wood-based hydrogel, and then dry it. This hydrogel is the wood-based elastic battery separator. The mass of the poplar wood matrix is ​​approximately 0.096 g, and the total mass of the wood-based hydrogel separator is approximately 0.23 g.

[0101] Electrolyte preparation: Lithium hexafluorophosphate (solute) is dissolved in dimethyl phosphate and ethylene carbonate (solvent) in a volume ratio of 1:1 to form a 1 mol / L lithium hexafluorophosphate electrolyte.

[0102] Battery Assembly: The freeze-dried or oven-dried separator is immersed in the electrolyte for approximately 1 hour to complete the activation treatment. A 14mm diameter lithium sheet is used as the positive electrode, and a 14mm diameter graphite electrode as the negative electrode. A 19mm diameter wood-based elastic battery separator is cut for isolation and ion conduction during battery assembly. In a glove box, the lithium sheet (positive electrode), wood-based elastic battery separator (electrolyte / separator), and graphite negative electrode are stacked sequentially in a coin cell casing. An appropriate amount of the above-mentioned electrolyte is added to fully wet the system. Finally, the cells are pressed and sealed using a tablet press to obtain the battery for performance testing.

[0103] Example 4

[0104] Poplar veneers with a tangential thickness of 1 mm were cut. The poplar chips were mixed with a 2 wt% sodium hypochlorite solution at a mass ratio of 1:50. The pH of the solution was adjusted to below 4.6 using glacial acetic acid, and the mixture was heated at 85°C for 10 hours. After the reaction, the wood chips were rinsed with ultrapure water and soaked for 24 hours to thoroughly remove residual reactants. The cleaned wood chips were then frozen at -70°C for 5 hours, followed by freeze drying for 72 hours to obtain lignin-free biomass matrix (DW).

[0105] Accurately weigh 15g of acrylamide (AM) powder and dissolve it in 50g of deionized water. Add 0.006g of crosslinking agent methylenebisacrylamide (MBAA) and 0.06g of initiator ammonium persulfate (APS) to the above solution, and stir until the solution is clear and transparent to obtain the precursor solution. Then, use a vacuum pump to impregnate the pretreated wood chips with the precursor solution for about 1 hour. Heat the impregnated wood chips at 65°C for about 4 hours to polymerize until a wood-based hydrogel is formed, and then dry it. This wood-based hydrogel is the wood-based elastic battery separator; the mass of the poplar wood matrix is ​​about 0.096g, and the total mass of the wood-based elastic battery separator is about 0.23g.

[0106] Electrolyte preparation: Dissolve sodium hexafluorophosphate (solute) in diethyl carbonate and ethylene carbonate (solvent) in a volume ratio of 1:1 to form a 1 mol / L sodium hexafluorophosphate electrolyte.

[0107] Battery Assembly: The freeze-dried or oven-dried separator is immersed in a suitable electrolyte solution for approximately 1 hour for pre-wetting. Then, using a 14mm diameter sodium sheet as the positive electrode and a 14mm diameter sodium iron phosphate as the negative electrode, a 19mm diameter wood-based elastic battery separator is cut for use in battery assembly to isolate the positive and negative electrodes and provide ion channels. In a glove box, the sodium sheet (positive electrode), wood-based elastic battery separator (electrolyte / separator), and sodium iron phosphate (negative electrode) are stacked sequentially in a coin cell casing. An appropriate amount of the aforementioned electrolyte solution is added to fully wet the system. Finally, the cells are packaged using a pressing machine to obtain a battery suitable for performance testing.

[0108] Performance testing

[0109] 1. Electron microscopy observation

[0110] The balsa wood (NW), balsa wood biomass matrix (DW), and wood-based flexible battery separator (DW-PVA) of Example 1 were observed using a scanning electron microscope (FESEM, JSM-7800F, Japan). The results are as follows: Figure 1 As shown.

[0111] Figure 1 Electron micrographs of balsa wood (NW), balsa wood biomass matrix (DW), and wood-based elastic battery separator (DW-PVA) are shown. Figure 1 It can be seen that the balsa biomass matrix is ​​obtained by removing lignin from balsa. Because the lignin is removed, the cell walls of the wood matrix become thinner, which increases the porosity of the wood and facilitates the filling of polymer compounds. Furthermore, the electron micrograph shows that the cell walls of the balsa remain intact throughout the entire process.

[0112] In addition, electron micrographs of the wood-based elastic battery separator from various directions show that the wood-based elastic battery separator has a highly hierarchical structure.

[0113] 2. Ionic conductivity (σ) test

[0114] The ionic conductivity of conventional glass fiber (GF) membranes, polyvinyl alcohol (PVA) membranes, and the wood-based elastic battery membrane (DW-PVA) of Example 1 was measured using a stainless steel symmetrical electrode electrochemical workstation at different temperatures and frequencies ranging from 0.01 to 100,000 Hz. Charge-discharge cycling was performed on a Newway testing system under half-cell current conditions of 0.5 or 2 mA·cm⁻¹. -2 The charge / discharge time is 30 minutes. The full-cell current condition is 5 A·g. -1The ionic conductivity (σ) was calculated using the following formula (2), and the result is as follows: Figure 2 As shown:

[0115] (1)

[0116] Where L is the membrane thickness (mm) and A is the active area (mm²). 2 R is the charge transfer resistance (Ω).

[0117] Depend on Figure 2 As can be seen from the comparison of the ionic conductivity of the wood-based hydrogel membrane, the traditional glass fiber membrane, and polyvinyl alcohol in Example 1 at temperatures of 0°C, 15°C, 30°C, 45°C, and 60°C, the wood-based hydrogel membrane exhibits superior ionic conductivity at all temperatures, indicating that the wood-based elastic battery membrane significantly improves ion transport.

[0118] 3. Half-cell charge-discharge cycle test

[0119] Half-cell charge-discharge cycle tests were performed on conventional glass fiber (GF) membranes, polyvinyl alcohol (PVA) membranes, and the wood-based hydrogel membranes (DW-PVA) of Example 1 and (DW-PAM) of Example 2 using the Xinwei testing system. The results are as follows: Figure 3 and Figure 4 As shown. Among them, Figure 3 Under current conditions of 0.5 mA·cm -2 -0.25 mAh·cm -2 Below, Zn / / Zn battery cyclic charge and discharge test. Figure 4 Under current conditions of 2 mA·cm -2 - 1 mAh·cm -2 Cyclic charge-discharge test of Zn / / Zn battery.

[0120] Depend on Figure 3 As can be seen, the wood-based hydrogel separator (DW-PVA) of Example 1 exhibits a significantly higher cycle life (7000 h) than traditional glass fiber separators and polyvinyl alcohol. The hierarchical structure and abundant -OH groups of the wood-based hydrogel separator regulate ion transport capabilities, thereby significantly extending the battery cycle life. This indicates that the wood-based hydrogel separator has stable electrodes and commercialization potential.

[0121] Depend on Figure 4 It can be seen that at 2 mA·cm -2 - 1 mAh·cm -2 Under these conditions, the Zn / / Zn battery using the wood-based hydrogel separator of Example 2 exhibited a cycle life of 100 h, which is significantly better than that of the conventional glass fiber separator.

[0122] 4. Full battery charge-discharge cycle test

[0123] The assembled full cells containing the wood-based hydrogel separators of Examples 3 and 4 were tested using the Newway testing system at 0.5 A·g -1 Under the conditions of charge and discharge testing, the results are as follows: Figure 5 and Figure 6 As shown.

[0124] Depend on Figure 5 As can be seen, the cyclic testing shows that the average coulombic efficiency is close to 100%. Figure 6 As can be seen, the capacity of the wood-based hydrogel membrane used in Example 4 reached 250 mAh·g during charge-discharge cycle testing. -1 Therefore, the wood-based hydrogel separator of the present invention can be used as a battery separator. It is evident that the unique hierarchical structure of the wood-based elastic battery separator significantly improves ion transport and accelerates ion diffusion at the cathode, thereby enabling the battery to have high coulombic efficiency and specific capacity.

[0125] 5. Infrared testing

[0126] The chemical structure of the samples was characterized using a Nicolet 6700 Fourier transform infrared spectrometer. Specifically, infrared spectroscopy tests were performed on balsa wood (NW), balsa wood biomass matrix (DW), polyvinyl alcohol (PVA), and wood-based elastic battery separator (DW-PVA) from Example 1, and the results are as follows. Figure 7 As shown.

[0127] Depend on Figure 7 It can be seen that, compared with balsa wood, 1237 cm³ of balsa wood biomass matrix... - The disappearance of the characteristic lignin peak (CO stretching vibration) at ¹ indicates that lignin in balsa wood has been completely removed. In the wood-based elastic cell separator, 1413 cm⁻¹ - ¹ and 1085 cm - The absorption peaks at ¹ correspond to the stretching vibrations of CH2 and CO in the polyvinyl alcohol molecule, respectively. This indicates that the polyvinyl alcohol hydrogel was successfully introduced into the balsa wood biomass matrix.

[0128] 6. Detection of cellulose and hemicellulose

[0129] The cellulose and hemicellulose content of the biomass matrix in Examples 1-4 was tested according to the national standard GB / T 35818-2018, and the results are shown in Table 1 below.

[0130] Table 1

[0131]

[0132] As shown in Table 1, lignin was completely removed from the wood-based elastic battery separator of the present invention, while cellulose and hemicellulose were well preserved, indicating that the basic structure of the wood was not damaged. The removal of lignin not only exposed a rich porous channel structure, but also provided favorable conditions for the subsequent full infiltration and filling of the hydrogel.

[0133] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0134] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A wood-based elastic battery separator, characterized in that, include: A biomass matrix having a xylem framework structure, the xylem framework structure comprising a multi-level structure with a porous structure, the multi-level structure originating from wood fibers; and... Hydrogel, which exists on the surface and / or inside the biomass matrix through in-situ polymerization or cross-linking.

2. The wood-based elastic battery separator according to claim 1, characterized in that, The multi-level structure comprises cellulose and hemicellulose; wherein, based on the total mass of the biomass matrix as 100%, the cellulose content is 70%~85% and the hemicellulose content is 15%~30%.

3. The wood-based elastic battery separator according to claim 1 or 2, characterized in that, Based on the total mass of the wood-based elastic battery separator, the biomass matrix content is 30%~60%, and the hydrogel content is 40%~70%.

4. The wood-based elastic battery separator according to any one of claims 1-3, characterized in that, The hydrogel is derived from a polymer compound, preferably, the polymer compound includes polyvinyl alcohol and / or polyacrylamide.

5. A method for preparing a wood-based elastic battery separator according to any one of claims 1-4, characterized in that, This includes the step of combining a biomass matrix with a hydrogel. Preferably, the preparation method includes the following steps: Obtain the hydrogel precursor solution; The biomass matrix is ​​immersed in the hydrogel precursor solution, and the hydrogel precursor undergoes cross-linking or in-situ polymerization on the surface and / or inside the biomass matrix to form the hydrogel, thereby obtaining a wood-based elastic battery separator.

6. The preparation method according to claim 5, characterized in that, The crosslinking includes crosslinking under vacuum conditions through two or more freeze-thaw cycles; and / or, The in-situ polymerization temperature is 50℃~80℃, and the in-situ polymerization time is 3h~5h.

7. The preparation method according to claim 5 or 6, characterized in that, The method for preparing the biomass matrix includes the following steps: Under acidic conditions, wood raw materials are oxidized using oxides to obtain pretreated products; The pretreated product was freeze-dried to obtain a biomass matrix.

8. The preparation method according to claim 7, characterized in that, The freeze-drying time is 12 hours or more; Preferably, before freeze-drying, the pretreated product is further subjected to a freezing step. More preferably, the freezing temperature is below -20°C and the freezing time is 1-10 hours.

9. The preparation method according to any one of claims 5-8, characterized in that, The preparation method of the hydrogel precursor solution includes the following steps: A hydrogel precursor solution is obtained by dissolving a polymer compound in a solvent; or by mixing a monomer, a crosslinking agent, and an initiator in a solvent. Preferably, in the hydrogel precursor solution, the mass concentration of the polymer compound is 5-20%; and / or, the mass ratio of the monomer, the crosslinking agent, the initiator, and the solvent is 1:0.0001-0.001:0.001-0.01:1-5.

10. An energy storage battery, characterized in that, Including the wood-based elastic battery separator according to any one of claims 1-4.

Images