A wood-based electrolyte and its preparation method and application

Abstract

The present invention discloses a wood-based electrolyte, a preparation method and an application thereof. The preparation method of the wood-based electrolyte of the present invention comprises the following steps: 1) immersing wood in a sodium chlorite solution for delignification treatment to obtain delignified wood; 2) immersing the delignified wood in a dopamine solution for modification treatment to obtain modified wood; 3) immersing the modified wood in an electrolyte solution made of a reversible phase transition polymer and an inorganic salt and water to perform vacuum-assisted impregnation treatment to obtain a wood-based electrolyte. The wood-based electrolyte of the present invention has good ionic conductivity, sensitive temperature responsiveness and excellent flame retardancy, and its thermal response in the direction parallel to and perpendicular to the wood pores is anisotropic, and has broad application prospects in the fields of overheating self-protection supercapacitors, temperature sensing and fire warning.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolyte materials, and in particular to a wood-based electrolyte and a preparation method and application thereof. Background Art

[0002] Electrochemical energy storage devices (such as supercapacitors and lithium batteries) have the advantages of good cycle performance, long service life, and no pollution. They have been widely used in portable electronic devices, electric vehicles, the Internet of Things and other fields.

[0003] Research has found that by adding reversible phase-change polymers to electrolytes, the electrolyte undergoes a sol-gel transition when the temperature reaches the critical temperature for thermal runaway (approximately 70°C), which can hinder the transmission of ions, thereby blocking the circuit and achieving a self-protection effect, ultimately preventing the electrochemical energy storage device from experiencing thermal runaway. However, the electrochemical performance of current electrolytes based on reversible phase-change polymers is poor at room temperature, and their electrochemical performance gradually decreases with increasing temperature within a relatively mild temperature range (20°C to 50°C), making it difficult to ensure the working requirements of electrochemical energy storage devices under normal conditions.

[0004] Therefore, it is of great significance to develop an electrolyte that has excellent electrochemical properties at normal temperature and can quickly self-protect when the critical temperature of thermal runaway is reached. Summary of the Invention

[0005] The purpose of the present invention is to provide a wood-based electrolyte and a preparation method and application thereof.

[0006] The technical solution adopted by the present invention is:

[0007] A method for preparing a wood-based electrolyte comprises the following steps:

[0008] 1) immersing the wood in a sodium chlorite solution for delignification treatment to obtain delignified wood;

[0009] 2) immersing the delignified wood in a dopamine solution for modification to obtain modified wood;

[0010] 3) Immersing the modified wood in an electrolyte solution prepared by adding water to a reversible phase transition polymer and an inorganic salt and performing vacuum-assisted impregnation treatment to obtain a wood-based electrolyte.

[0011] Preferably, the wood in step 1) is at least one of balsa, beech, poplar and pine.

[0012] Preferably, the mass fraction of the sodium chlorite solution in step 1) is 1% to 3%, and the pH value is 3.0 to 5.0.

[0013] Preferably, the delignification treatment in step 1) is carried out at a temperature of 80° C. to 120° C., and the treatment time is 4 h to 12 h.

[0014] Preferably, the mass fraction of the dopamine solution in step 2) is 0.2% to 0.5%, and the pH value is 8.0 to 10.0.

[0015] Preferably, the modification treatment in step 2) is carried out at a temperature of 20° C. to 30° C., and the treatment time is 12 h to 36 h.

[0016] Preferably, after the modification treatment in step 2) is completed, the reaction product is washed and dried.

[0017] Preferably, the specific operation of washing is: washing with deionized water at a temperature of 20° C. to 30° C. for 3 to 6 times.

[0018] Preferably, the specific operation of the drying is: drying at a temperature of 40° C. to 80° C. for 12 h to 36 h.

[0019] Preferably, the reversible phase transition polymer in step 3) is at least one of a polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer with a number average molecular weight of 2000-6000, methyl cellulose with a number average molecular weight of 50,000-150,000, and hydroxypropyl methyl cellulose with a number average molecular weight of 50,000-250,000.

[0020] Preferably, the inorganic salt in step 3) is at least one of lithium chloride, lithium nitrate and sodium chloride.

[0021] Preferably, in step 3), the mass fraction of the reversible phase-change polymer in the electrolyte solution is 20% to 40%, and the mass fraction of the inorganic salt is 2% to 10%.

[0022] Preferably, the electrolyte solution in step 3) is prepared by adding a reversible phase transition polymer and an inorganic salt to water, and then stirring for 1 h to 4 h at a stirring rate of 200 rpm to 800 rpm and a temperature of 20° C. to 30° C. to obtain an electrolyte solution.

[0023] Preferably, the vacuum-assisted impregnation treatment in step 3) is carried out at a temperature of 20° C. to 30° C. and a vacuum degree of 1 kPa to 10 kPa, and the treatment time is 0.2 h to 1 h.

[0024] A wood-based electrolyte is prepared by the above preparation method.

[0025] An electrochemical energy storage device comprises the wood-based electrolyte.

[0026] Preferably, the electrochemical energy storage device is a lithium battery or a supercapacitor.

[0027] A method for preparing the electrochemical energy storage device as described above includes the following steps: dispersing activated carbon, acetylene black and polyvinylidene fluoride in N-methylpyrrolidone to prepare an electrode slurry, coating the electrode slurry on the surface of a carbon cloth (current collector) and drying it to prepare an electrode sheet, attaching the electrode sheet in directions parallel and perpendicular to the pores of the wood-based electrolyte, respectively, and connecting it to an electrochemical workstation to obtain the electrochemical energy storage device.

[0028] A fire warning device comprises the above-mentioned wood-based electrolyte.

[0029] A preparation method of the fire warning device as described above includes the following steps: dispersing activated carbon, acetylene black and polyvinylidene fluoride in N-methylpyrrolidone to form an electrode slurry, then coating the electrode slurry on the surface of carbon cloth (current collector) and drying it to form an electrode sheet, then affixing the electrode sheet in the direction perpendicular to the holes of the wood-based electrolyte, and then connecting an alarm in series to obtain the fire warning device.

[0030] The present invention utilizes a wood-based electrolyte, first delignified and surface-modified to enhance its surface hydrophilicity. A vacuum-assisted impregnation process then fills the wood with an electrolyte solution containing a reversible phase-change polymer (RPC). Hydrogen bonds form between the hydroxyl groups on the cellulose surface and the water and RPC in the electrolyte. The RPC can be well aligned along the cellulose channels at room temperature, resulting in excellent electrochemical performance at room temperature and application in supercapacitors. Furthermore, the addition of an inorganic salt allows the electrolyte's phase transition temperature to be controlled within a reasonable range. Once the temperature reaches the phase transition temperature, the hydrogen bonds between the RPC, water, and cellulose weaken, forming intramolecular hydrogen bonds that cause molecular stacking and entanglement. The electrolyte transitions from a sol to a gel, and the RPC shifts from aligning along the cellulose channels to aligning perpendicularly to the wood channels. Consequently, the wood-based electrolyte exhibits anisotropic electrochemical performance in response to temperature. Leveraging this anisotropy, the wood-based electrolyte has promising applications in overheat-protected supercapacitors, temperature sensing, and fire warning systems. In addition, the wood-based electrolyte has excellent flame retardancy due to the heat absorption of water in the electrolyte and the charring effect promoted by inorganic salts.

[0031] The beneficial effects of the present invention are: the wood-based electrolyte of the present invention has good ionic conductivity, sensitive temperature responsiveness and excellent flame retardancy, and the thermal response in the direction parallel to and perpendicular to the wood pores is anisotropic, and has broad application prospects in the fields of overheating self-protection supercapacitors, temperature sensing and fire warning.

[0032] Specifically:

[0033] 1) The wood-based electrolyte of the present invention has good ionic conductivity at room temperature and can be used in supercapacitors;

[0034] 2) The wood-based electrolyte of the present invention has sensitive temperature responsiveness and anisotropic electrochemical response (in the direction parallel to the wood pores, the ionic conductivity of the electrolyte decreases rapidly when the temperature reaches the phase transition temperature; in the direction perpendicular to the pores, the ionic conductivity increases with increasing temperature). It has broad application prospects in the fields of overheat self-protection supercapacitors, temperature sensing, and fire warning.

[0035] 3) The wood-based electrolyte of the present invention has excellent flame retardancy, which improves its safety in harsh environments;

[0036] 4) The preparation process of the wood-based electrolyte of the present invention is simple, the raw materials are readily available, the cost is low, the equipment requirements are low, and it conforms to the concept of green and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 These are SEM images of cross sections of natural wood, modified wood, and wood-based electrolyte in Example 1 in the directions perpendicular and parallel to the pores.

[0038] Figure 2 The DSC curve and phase transition process diagram of the electrolyte solution in Example 1.

[0039] Figure 3 The ionic conductivity of the wood-based electrolyte in the direction parallel to the pores of Example 1 and Comparative Example 1 varies with temperature.

[0040] Figure 4 The ionic conductivity of the wood-based electrolyte in the direction perpendicular to the pores of Example 1 and Comparative Example 1 varies with temperature.

[0041] Figure 5 CV curves and GCD curves of the wood-based electrolyte of Example 1 in the direction parallel to the pores at different temperatures.

[0042] Figure 6 This is the thermal resistance temperature perception curve of the wood-based electrolyte in Example 1 in the direction perpendicular to the pores.

[0043] Figure 7 This is a screenshot of the fire warning test video of the wood-based electrolyte in Example 1. DETAILED DESCRIPTION

[0044] The present invention will be further explained and illustrated below with reference to specific embodiments.

[0045] Example 1:

[0046] A wood-based electrolyte, the preparation method of which comprises the following steps:

[0047] 1) immersing balsa wood in a 2% sodium chlorite solution (adjusting the pH with acetic acid) with a pH of 3.8, and then delignifying the wood at 105° C. for 6 hours to obtain delignified wood;

[0048] 2) immersing the delignified wood in a 0.4% by mass dopamine solution (pH adjusted with sodium hydroxide) at a pH of 8.5, and then performing a modification treatment at 25°C for 24 hours. The wood is then removed and washed five times with deionized water at 25°C, and then dried at 60°C for 24 hours to obtain modified wood;

[0049] 3) adding a polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer having a number average molecular weight of 2800 and lithium chloride to deionized water, and stirring the mixture at a stirring rate of 500 rpm and a temperature of 25° C. for 2 h to obtain an electrolyte solution having a mass fraction of 30% polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer and a mass fraction of 6% lithium chloride;

[0050] 4) Immersing the modified wood in an electrolyte solution, and then performing a vacuum-assisted impregnation treatment at a temperature of 25° C. and a vacuum degree of 5 kPa for 0.5 h to obtain a wood-based electrolyte.

[0051] Example 2:

[0052] A wood-based electrolyte, the preparation method of which comprises the following steps:

[0053] 1) immersing balsa wood in a 1% sodium chlorite solution (adjusting the pH with acetic acid) with a mass fraction and a pH of 3.0, and then delignifying the wood at 80° C. for 12 hours to obtain delignified wood;

[0054] 2) immersing the delignified wood in a 0.2% by mass dopamine solution (pH adjusted with sodium hydroxide) at a pH of 10.0, and then performing a modification treatment at 20°C for 36 hours. The wood is then removed and washed six times with deionized water at 20°C, and then dried at 40°C for 36 hours to obtain modified wood;

[0055] 3) adding a polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer having a number average molecular weight of 6000 and lithium chloride to deionized water, and stirring the mixture at a stirring rate of 800 rpm and a temperature of 30° C. for 1 hour to obtain an electrolyte solution having a mass fraction of 20% polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer and a mass fraction of 2% lithium chloride;

[0056] 4) Immersing the modified wood in an electrolyte solution, and then performing a vacuum-assisted impregnation treatment at a temperature of 20° C. and a vacuum degree of 1 kPa for 1 hour to obtain a wood-based electrolyte.

[0057] Example 3:

[0058] A wood-based electrolyte, the preparation method of which comprises the following steps:

[0059] 1) immersing the balsa wood in a 3% sodium chlorite solution (adjusting the pH with acetic acid) with a pH of 5.0, and then delignifying the wood at 120° C. for 4 hours to obtain delignified wood;

[0060] 2) immersing the delignified wood in a 0.5% by mass dopamine solution (pH adjusted with sodium hydroxide) at a pH of 8.0, and then performing a modification treatment at 30°C for 12 hours. The wood is then removed and washed three times with deionized water at 30°C, and then dried at 80°C for 12 hours to obtain modified wood;

[0061] 3) adding a polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer having a number average molecular weight of 2000 and lithium chloride to deionized water, and stirring the mixture at a stirring rate of 200 rpm and a temperature of 20° C. for 4 hours to obtain an electrolyte solution having a mass fraction of 40% polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer and a mass fraction of 10% lithium chloride;

[0062] 4) Immersing the modified wood in an electrolyte solution, and then performing a vacuum-assisted impregnation treatment at a temperature of 30° C. and a vacuum degree of 10 kPa for 0.2 h to obtain a wood-based electrolyte.

[0063] Example 4:

[0064] A wood-based electrolyte, the preparation method of which comprises the following steps:

[0065] 1) immersing beech wood in a 2% sodium chlorite solution (pH adjusted with acetic acid) with a pH of 3.8, and then delignifying the wood at 105° C. for 6 hours to obtain delignified wood;

[0066] 2) immersing the delignified wood in a 0.4% by mass dopamine solution (pH adjusted with sodium hydroxide) at a pH of 8.5, and then performing a modification treatment at 25°C for 24 hours. The wood is then removed and washed five times with deionized water at 25°C, and then dried at 60°C for 24 hours to obtain modified wood;

[0067] 3) adding methyl cellulose having a number average molecular weight of 100,000 and lithium nitrate to deionized water, and stirring the mixture at a stirring rate of 500 rpm and a temperature of 25° C. for 2 h to obtain an electrolyte solution having a mass fraction of 30% methyl cellulose and a mass fraction of 6% lithium nitrate;

[0068] 4) Immersing the modified wood in an electrolyte solution, and then performing a vacuum-assisted impregnation treatment at a temperature of 25° C. and a vacuum degree of 5 kPa for 0.5 h to obtain a wood-based electrolyte.

[0069] Example 5:

[0070] A wood-based electrolyte, the preparation method of which comprises the following steps:

[0071] 1) immersing beech wood in a 2% sodium chlorite solution (pH adjusted with acetic acid) with a pH of 3.8, and then delignifying the wood at 105° C. for 6 hours to obtain delignified wood;

[0072] 2) immersing the delignified wood in a 0.4% by mass dopamine solution (pH adjusted with sodium hydroxide) at a pH of 8.5, and then performing a modification treatment at 25°C for 24 hours. The wood is then removed and washed five times with deionized water at 25°C, and then dried at 60°C for 24 hours to obtain modified wood;

[0073] 3) adding methyl cellulose having a number average molecular weight of 150,000 and lithium nitrate to deionized water, and stirring the mixture at a stirring rate of 500 rpm and a temperature of 25° C. for 2 h to obtain an electrolyte solution having a mass fraction of 20% methyl cellulose and a mass fraction of 4% lithium nitrate;

[0074] 4) Immersing the modified wood in an electrolyte solution, and then performing a vacuum-assisted impregnation treatment at a temperature of 25° C. and a vacuum degree of 5 kPa for 0.5 h to obtain a wood-based electrolyte.

[0075] Example 6:

[0076] A wood-based electrolyte, the preparation method of which comprises the following steps:

[0077] 1) immersing beech wood in a 2% sodium chlorite solution (pH adjusted with acetic acid) with a pH of 3.8, and then delignifying the wood at 105° C. for 6 hours to obtain delignified wood;

[0078] 2) immersing the delignified wood in a 0.4% by mass dopamine solution (pH adjusted with sodium hydroxide) at a pH of 8.5, and then performing a modification treatment at 25°C for 24 hours. The wood is then removed and washed five times with deionized water at 25°C, and then dried at 60°C for 24 hours to obtain modified wood;

[0079] 3) adding methyl cellulose having a number average molecular weight of 50,000 and sodium chloride to deionized water, and stirring the mixture at a stirring rate of 500 rpm and a temperature of 25° C. for 2 h to obtain an electrolyte solution having a mass fraction of 40% methyl cellulose and a mass fraction of 6% sodium chloride;

[0080] 4) Immersing the modified wood in an electrolyte solution, and then performing a vacuum-assisted impregnation treatment at a temperature of 25° C. and a vacuum degree of 5 kPa for 0.5 h to obtain a wood-based electrolyte.

[0081] Example 7:

[0082] A wood-based electrolyte, the preparation method of which comprises the following steps:

[0083] 1) immersing the poplar wood in a 2% sodium chlorite solution (pH adjusted with acetic acid) with a pH of 3.8, and then delignifying the wood at 105° C. for 6 hours to obtain delignified wood;

[0084] 2) immersing the delignified wood in a 0.4% by mass dopamine solution (pH adjusted with sodium hydroxide) at a pH of 8.5, and then performing a modification treatment at 25°C for 24 hours. The wood is then removed and washed five times with deionized water at 25°C, and then dried at 60°C for 24 hours to obtain modified wood;

[0085] 3) adding hydroxypropyl methylcellulose (number average molecular weight: 150,000) and lithium chloride to deionized water, and stirring for 2 h at 500 rpm and 25° C. to obtain an electrolyte solution having a mass fraction of 40% hydroxypropyl methylcellulose and a mass fraction of 6% lithium chloride;

[0086] 4) Immersing the modified wood in an electrolyte solution, and then performing a vacuum-assisted impregnation treatment at a temperature of 25° C. and a vacuum degree of 5 kPa for 0.5 h to obtain a wood-based electrolyte.

[0087] Example 8:

[0088] A wood-based electrolyte, the preparation method of which comprises the following steps:

[0089] 1) immersing pine wood in a 2% sodium chlorite solution with a pH of 3.8 (the pH is adjusted with acetic acid), and then delignifying the wood at 105°C for 6 hours to obtain delignified wood;

[0090] 2) immersing the delignified wood in a 0.4% by mass dopamine solution (pH adjusted with sodium hydroxide) at a pH of 8.5, and then performing a modification treatment at 25°C for 24 hours. The wood is then removed and washed five times with deionized water at 25°C, and then dried at 60°C for 24 hours to obtain modified wood;

[0091] 3) adding hydroxypropyl methylcellulose (number average molecular weight: 250,000) and lithium chloride to deionized water, and stirring for 2 h at 800 rpm and 25° C. to obtain an electrolyte solution having a mass fraction of 20% hydroxypropyl methylcellulose and a mass fraction of 4% lithium chloride;

[0092] 4) Immersing the modified wood in an electrolyte solution, and then performing a vacuum-assisted impregnation treatment at a temperature of 25° C. and a vacuum degree of 5 kPa for 0.5 h to obtain a wood-based electrolyte.

[0093] Example 9:

[0094] A wood-based electrolyte, the preparation method of which comprises the following steps:

[0095] 1) immersing balsa wood in a 2% sodium chlorite solution (adjusting the pH with acetic acid) with a pH of 3.8, and then delignifying the wood at 105° C. for 6 hours to obtain delignified wood;

[0096] 2) immersing the delignified wood in a 0.4% by mass dopamine solution (pH adjusted with sodium hydroxide) at a pH of 8.5, and then performing a modification treatment at 25°C for 24 hours. The wood is then removed and washed five times with deionized water at 25°C, and then dried at 60°C for 24 hours to obtain modified wood;

[0097] 3) adding hydroxypropyl methylcellulose (number average molecular weight: 50,000) and lithium chloride to deionized water, and stirring for 2 h at a stirring rate of 500 rpm and a temperature of 25° C. to obtain an electrolyte solution having a mass fraction of 40% hydroxypropyl methylcellulose and a mass fraction of 10% lithium chloride;

[0098] 4) Immersing the modified wood in an electrolyte solution, and then performing a vacuum-assisted impregnation treatment at a temperature of 25° C. and a vacuum degree of 5 kPa for 0.5 h to obtain a wood-based electrolyte.

[0099] Comparative Example 1:

[0100] A wood-based electrolyte, the preparation method of which comprises the following steps:

[0101] 1) immersing balsa wood in a 2% sodium chlorite solution (adjusting the pH with acetic acid) with a pH of 3.8, and then delignifying the wood at 105° C. for 6 hours to obtain delignified wood;

[0102] 2) immersing the delignified wood in a 0.4% by mass dopamine solution (pH adjusted with sodium hydroxide) at a pH of 8.5, and then performing a modification treatment at 25°C for 24 hours. The wood is then removed and washed five times with deionized water at 25°C, and then dried at 60°C for 24 hours to obtain modified wood;

[0103] 3) adding lithium chloride to deionized water, and stirring for 2 h at a stirring rate of 500 rpm and a temperature of 25° C. to obtain an electrolyte solution with a mass fraction of lithium chloride of 6%;

[0104] 4) Immersing the modified wood in an electrolyte solution, and then performing a vacuum-assisted impregnation treatment at a temperature of 25° C. and a vacuum degree of 5 kPa for 0.5 h to obtain a wood-based electrolyte.

[0105] Comparative Example 2:

[0106] A wood-based electrolyte, the preparation method of which comprises the following steps:

[0107] 1) immersing balsa wood in a 2% sodium chlorite solution (adjusting the pH with acetic acid) with a pH of 3.8, and then delignifying the wood at 105° C. for 6 hours to obtain delignified wood;

[0108] 2) adding a polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer having a number average molecular weight of 2800 and lithium chloride to deionized water, and stirring the mixture at a stirring rate of 500 rpm and a temperature of 25° C. for 2 h to obtain an electrolyte solution having a mass fraction of 30% polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer and a mass fraction of 6% lithium chloride;

[0109] 3) Immersing the delignified wood in an electrolyte solution, and then performing a vacuum-assisted impregnation treatment at a temperature of 25° C. and a vacuum degree of 5 kPa for 0.5 h to obtain a wood-based electrolyte.

[0110] Performance testing:

[0111] Test method:

[0112] Phase transition temperature test: A differential scanning calorimeter (DSC, Netzsch, Germany, model: DSC-204F1) was used to test the phase transition temperature of the sample. 3 mg to 5 mg of sample was placed in a crucible and the temperature was raised from 20 °C to 100 °C for 2 min at a heating rate of 5 °C / min.

[0113] Electrochemical performance test: Activated carbon, acetylene black and polyvinylidene fluoride were dispersed in N-methylpyrrolidone at a mass ratio of 8:1:1 to prepare an electrode slurry. The electrode slurry was then drop-coated on a carbon cloth (activated carbon concentration was 2 mg / cm 3 ) and then dried to obtain electrode sheets, and then attached electrode sheets in the directions parallel and perpendicular to the pores of the wood-based electrolyte (the sample size is 10 mm × 10 mm × 10 mm, and the contact area between the electrode sheet and the sample is 10 mm × 10 mm). The sample was then heated using a Peltier, and the sample was subjected to ionic conductivity, cyclic voltammetry (CV), and constant current charge and discharge (GCD) tests using an electrochemical workstation (Shanghai Chenhua Co., Ltd., Model: CHI660E).

[0114] Temperature perception test: A sample (10 mm × 10 mm × 10 mm) was connected to a digital multimeter (Keithley, USA, model: DMM6500 6 1 / 2) and heated using a constant temperature heating table to obtain the resistance change rate curve at different temperatures.

[0115] Fire warning test: Connect the sample (size 10mm×10mm×10mm) to the alarm, use an alcohol lamp to burn the sample, the flame length is 40mm, the distance from the bottom of the sample to the wick is 20mm, and the resistance change rate is 80% when the warning is triggered.

[0116] Vertical combustion test: Place the sample (size 120mm×10mm×10mm) 20mm above the methane burner with a flame height of 40mm. Remove the flame after 20s and record the combustion phenomenon and data.

[0117] Limiting oxygen index test: An oxygen index tester (Nanjing Jiangning Analytical Instrument Co., Ltd., model: JF-3) was used for testing, and the sample size was 80 mm × 10 mm × 10 mm.

[0118] Specific tests:

[0119] 1) The scanning electron microscope (SEM) images of the cross sections of natural wood (balsa wood), modified wood and wood-based electrolyte in Example 1 in the directions perpendicular to and parallel to the pores are as follows: Figure 1 shown.

[0120] Depend on Figure 1It can be seen that natural wood is composed of many pores and has good channels inside. After chemical modification, the structure does not change significantly, and the channel surface becomes smoother, which is conducive to the transmission of ions. After being impregnated with electrolyte solution, the electrolyte completely fills the pores of the wood.

[0121] 2) The differential scanning calorimetry (DSC) curve and phase transition process of the electrolyte solution in Example 1 are shown in FIG. Figure 2 shown.

[0122] Depend on Figure 2 It can be seen that the phase transition temperature of the electrolyte solution is around 60°C. After the temperature reaches the phase transition temperature, a sol-gel transition occurs. When the temperature drops, the electrolyte returns to a sol state, indicating that it has good reversible phase transition characteristics.

[0123] 3) The ionic conductivity of the wood-based electrolyte in the direction parallel to the pores of Example 1 and Comparative Example 1 varies with temperature. Figure 3 As shown in the figure, the ionic conductivity in the vertical pore direction changes with temperature. Figure 4 shown.

[0124] Depend on Figure 3 and Figure 4 It can be seen that: before the phase transition temperature, the ionic conductivity of the wood-based electrolyte in Example 1 gradually increases with increasing temperature in the direction parallel to the pores, and when the temperature reaches the phase transition temperature, the ionic conductivity decreases. At a temperature of 70°C, the ionic conductivity decreases by more than 90%, while the ionic conductivity in the direction perpendicular to the pores increases with increasing temperature, indicating that it has thermal response anisotropy, while the wood-based electrolyte in Comparative Document 1 does not have this characteristic.

[0125] 4) Cyclic voltammetry (CV) curves and constant current charge-discharge (GCD) curves of the wood-based electrolyte of Example 1 in the parallel pore direction at different temperatures are shown in FIG. Figure 5 shown.

[0126] Depend on Figure 5 It can be seen that: in the parallel pore direction, wood-based electrolytes can be used for overheat self-protection supercapacitors. The supercapacitors have good electrochemical performance in a mild temperature range (20℃~50℃). When the temperature reaches 70℃, the CV curve area decreases significantly, and the charge and discharge time in the GCD curve is greatly shortened, showing good overheat self-protection performance. After the temperature drops to 20℃, the performance of the capacitor is basically restored.

[0127] 5) The thermal resistance temperature perception curve of the wood-based electrolyte in the vertical pore direction of Example 1 is as follows Figure 6 As shown, the fire warning test video screenshot is as follows Figure 7 shown.

[0128] Depend on Figure 6 and Figure 7 It can be seen that: in the vertical pore direction, the wood-based electrolyte has accurate temperature perception and sensitive fire warning performance, indicating that it has good protective safety.

[0129] 6) The phase transition temperature test results of the wood-based electrolytes of Examples 1 to 9 and Comparative Examples 1 to 2 are shown in Table 1, the ionic conductivity and specific capacitance test results at 20°C are shown in Table 2, the specific capacitance test results in the direction parallel to the pores are shown in Table 3, the fire warning test response time test results in the direction perpendicular to the pores are shown in Table 4, and the flame retardancy test results are shown in Table 5:

[0130] Table 1 Phase transition temperature

[0131]

[0132] Table 2 Ionic conductivity and specific capacitance at 20℃

[0133]

[0134]

[0135] Table 3 Specific capacitance parallel to the pore direction

[0136]

[0137] Table 4 Response time of fire warning test in vertical hole direction

[0138]

[0139]

[0140] Table 5 Flame retardancy

[0141]

[0142] As shown in Table 1, the wood-based electrolytes of Examples 1 to 9 have good phase transition properties. When no reversible phase transition polymer is added (Comparative Example 1), the electrolyte does not have sol-gel transition properties. However, after the reversible phase transition polymer is added to the electrolyte, the electrolyte has reversible sol-gel transition properties. This is because when the temperature reaches the phase transition temperature, the hydrophobicity of the reversible phase transition polymer increases, the molecular chains entangle and accumulate, and the electrolyte transforms from sol to gel.

[0143] As shown in Table 2, the ionic conductivity and specific capacitance of the wood-based electrolytes of Examples 1 to 9 in the direction parallel to the pores are higher than those in the direction perpendicular to the pores. This is because ions in the wood-based electrolytes are well transported along the pores of the wood, while ion movement in the direction perpendicular to the pores is blocked by the wood cell walls. More importantly, the ionic conductivity of the wood-based electrolyte of Comparative Example 1 increases with increasing temperature, while the temperature responsiveness of the wood-based electrolyte of Example 1 is anisotropic ( Figure 3 and Figure 4 ): In the direction parallel to the pores, the ionic conductivity decreases rapidly when the temperature reaches the phase transition temperature, while in the direction perpendicular to the pores, the ionic conductivity of the electrolyte increases with increasing temperature. The reason for its temperature response anisotropy can be attributed to the following: at room temperature, due to the hydrogen bonding between the reversible phase transition polymer and wood cellulose, the reversible phase transition polymer is arranged along the wood cellulose, and when the temperature rises to the phase transition temperature, the molecular hydrophobicity of the reversible phase transition polymer increases. At this time, the intramolecular hydrogen bonding is enhanced, causing it to accumulate and entangle, hindering the transmission of ions in the direction parallel to the pores, but increasing the movement area of ions in the direction perpendicular to the pores. The temperature response anisotropy of wood-based electrolytes can be used in different fields: in the direction parallel to the pores, it can be used in supercapacitors with overheating self-protection function (Table 3), and in the direction perpendicular to the pores, it has temperature sensing and fire warning performance (Table 4).

[0144] In addition, it can be seen from Comparative Example 2 that the ionic conductivity and specific capacitance of the wood-based electrolyte that has not undergone surface modification at room temperature (20°C) are significantly lower than those of the wood-based electrolyte that has undergone surface modification (Example 1). This is because after modification with dopamine, polydopamine is formed on the surface of the wood, which increases the hydrophilicity of the wood and enhances the affinity between the wood and the electrolyte solution; at the same time, polydopamine enhances the surface charge density, giving the electrolyte better electrochemical properties.

[0145] As shown in Table 5, the wood-based electrolyte of the present invention has excellent flame retardancy: the flame can be extinguished quickly when burned, and the limiting oxygen index is above 57.0%. The good flame retardancy of the wood-based electrolyte is attributed to the heat absorption effect of the water in the electrolyte and the good carbonization effect of the inorganic salt. The flame retardancy of the wood-based electrolyte further improves its safety in harsh environments.

[0146] In summary, the wood-based electrolyte of the present invention has good ionic conductivity, overheating self-protection, temperature sensing, fire warning and flame retardancy, and has broad application prospects in the design of high-safety electronic devices.

[0147] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a wood-based electrolyte, characterized in that: The following steps are involved: 1) immersing the wood in a sodium chlorite solution for delignification treatment to obtain delignified wood; 2) immersing the delignified wood in a dopamine solution for modification to obtain modified wood; 3) immersing the modified wood in an electrolyte solution prepared by adding water to a reversible phase transition polymer and an inorganic salt and performing vacuum-assisted impregnation treatment to obtain a wood-based electrolyte; Step 3) the reversible phase transition polymer is at least one of a polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer with a number average molecular weight of 2,000 to 6,000, a methylcellulose with a number average molecular weight of 50,000 to 150,000, and a hydroxypropyl methylcellulose with a number average molecular weight of 50,000 to 250,000; In step 3), the inorganic salt is at least one of lithium chloride, lithium nitrate and sodium chloride.

2. The preparation method according to claim 1, wherein: The wood in step 1) is at least one of balsa, beech, poplar, and pine; the mass fraction of the sodium chlorite solution in step 1) is 1% to 3%, and the pH value is 3.0 to 5.

0.

3. The preparation method according to claim 1 or 2, characterized in that: Step 1) The delignification treatment is carried out at a temperature of 80° C. to 120° C., and the treatment time is 4 h to 12 h.

4. The preparation method according to claim 1, wherein: In step 2), the mass fraction of the dopamine solution is 0.2% to 0.5%, and the pH value is 8.0 to 10.

0.

5. The preparation method according to claim 1 or 4, characterized in that: Step 2) The modification treatment is carried out at a temperature of 20° C. to 30° C., and the treatment time is 12 h to 36 h.

6. The preparation method according to claim 1, wherein: Step 3) The mass fraction of the reversible phase transition polymer in the electrolyte solution is 20% to 40%, and the mass fraction of the inorganic salt is 2% to 10%.

7. The preparation method according to claim 1 or 6, characterized in that: Step 3) The vacuum-assisted impregnation treatment is carried out at a temperature of 20° C. to 30° C. and a vacuum degree of 1 kPa to 10 kPa, and the treatment time is 0.2 h to 1 h.

8. A wood-based electrolyte, characterized in that Prepared by the preparation method according to any one of claims 1 to 7.

9. An electrochemical energy storage device, characterized in that: Contains the wood-based electrolyte according to claim 8.

10. A fire warning device, characterized in that: Contains the wood-based electrolyte according to claim 8.

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