Preparation method of Basa wood biomass porous carbon material and application of Basa wood biomass porous carbon material in aqueous zinc-benzoquinone battery

Abstract

The invention provides a preparation method of a Basa wood biomass porous carbon material and application of the Basa wood biomass porous carbon material in an aqueous zinc-benzoquinone battery, Basa wood is used as a raw material, under the action of a pore-forming agent and a nitrogen-containing organic matter, the Basa wood biomass porous carbon is obtained through a pre-carbonization and carbonization two-step process, acid pickling and water washing. The biomass porous carbon obtained by the invention has relatively high specific surface area and proper pore size distribution, has relatively good p-benzoquinone loading capacity, and is beneficial to transmission and storage of ions and electrochemical reaction. The aqueous zinc-benzoquinone battery prepared from the porous carbon material obtained by the invention has relatively high specific capacity and excellent cycle performance. The raw materials are cheap, easy to obtain and environmentally friendly, and the preparation process is simple, convenient to operate and extremely suitable for large-scale production and has huge potential application value.

Description

Technical Field

[0001] The present invention relates to the technical field of aqueous zinc-benzoquinone battery materials, and specifically relates to a preparation method of a porous carbon material and its application in an aqueous zinc-benzoquinone battery. Background Art

[0002] With the continuous consumption of fossil energy, the demand for clean energy is more urgent. Developing high-performance and green secondary battery technologies is crucial for alleviating energy demand. Among many energy storage battery systems under research and industrialization, zinc-based aqueous batteries have become a hot topic in recent years due to their high energy density, low cost, green safety, and other advantages.

[0003] Metallic zinc has a high energy density, is abundant in content, and has good aqueous phase compatibility. Benzoquinone has a high theoretical capacity (496.0 mAh g -1 ), a stable voltage platform, and the organic material is renewable. Balsa wood biomass, as a renewable resource, has the advantages of rich yield, non-toxicity, low cost, etc., and has attracted wide attention in the preparation of carbon materials. Due to its unique microstructure, balsa wood biomass becomes a high-performance cathode material after a series of treatments. Summary of the Invention

[0004] The present invention aims to solve the problem of preparing nitrogen-doped porous carbon from balsa wood biomass materials to make it have high-efficiency benzoquinone adsorption ability, and to construct a high-loading and high-performance cathode material and its application in an aqueous zinc-benzoquinone battery system.

[0005] The present invention provides a preparation method and application of a balsa wood biomass porous carbon material. The method uses balsa wood, a biomass material, as a carbon source, prepares porous carbon through two-step processes of pre-carbonization and high-temperature tube furnace carbonization, absorbs benzoquinone on the prepared porous carbon by sublimation method, and prepares a cathode material for an aqueous zinc-benzoquinone battery with the composite material loaded with benzoquinone, realizing the high-value conversion of biomass materials, and showing relatively excellent electrochemical performance when used as a cathode material in a zinc-benzoquinone battery system.

[0006] The present invention can be realized through the following technical solutions. The technical solutions of the present invention are:

[0007] The object of the first aspect of the present invention is to provide a method for preparing a porous carbon material from balsa wood, and the method includes the following steps:

[0008] 1) Add an alkaline solution with a mass fraction of 5% to balsa wood and stir, then repeatedly wash and alkali-wash the balsa wood with ultrapure water until the pH value is neutral, and dry it in an oven to obtain the alkali-washed balsa wood;

[0009] 2) Mix the alkali-washed basa wood obtained in step 1) with a pore former and melamine, add water and mix evenly. Place it in an oven for pre-carbonization. Put the pre-carbonized black powder into a tube furnace with an inert gas flowing through it, and carry out high-temperature carbonization. Let the tube furnace cool naturally to room temperature and take out the black powder. Obtain the basa wood biomass porous carbon through steps such as pickling and water washing. Using BET testing, the specific surface area of the obtained basa wood biomass porous carbon is greater than 2000 m 2 / g. Specifically, it can reach 2804 m 2 / g.

[0010] In the technical solution of the present invention, in step 1), the alkaline solution is a sodium hydroxide solution, stir for 8 - 12 h, and the rotation speed is 300 - 500 r / min.

[0011] In the technical solution of the present invention, in step 1), the oven temperature is 100 - 120 °C, and the time is 10 - 14 h.

[0012] In the technical solution of the present invention, in step 2), the mass ratio of the basa wood to the pore former and melamine is 3:(1 - 3):1.

[0013] In the technical solution of the present invention, in step 2), the pre-carbonization temperature of the basa wood is 200 - 240 °C, and the pre-carbonization time is 12 - 24 h.

[0014] In the technical solution of the present invention, in step 2), the inert gas is helium or argon.

[0015] In the technical solution of the present invention, in step 2), the carbonization temperature is 700 - 900 °C, and the time is 1 - 2 h.

[0016] The purpose of the second aspect of the present invention is to provide a porous carbon, which is prepared by the above method of the present invention.

[0017] The purpose of the third aspect of the present invention is to provide a preparation method of a positive electrode material for an aqueous zinc-benzoquinone battery. Carry out the steps of absorbing benzoquinone and removing benzoquinone on the porous carbon prepared by the method of the present invention by sublimation method to prepare the positive electrode material for the aqueous zinc-benzoquinone battery.

[0018] In the technical solution of the present invention, for the absorption of benzoquinone, mix carbon and benzoquinone and grind them, then put them into an oven, and the temperature for absorbing benzoquinone is 70 - 100 °C.

[0019] In the technical solution of the present invention, the mass ratio of carbon to benzoquinone for the absorption of benzoquinone is 1:(1 - 3).

[0020] In the technical solution of the present invention, in step 2), the time for absorbing benzoquinone is 20 - 24 h.

[0021] In the technical solution of the present invention, for removing benzoquinone, the oven temperature is set at 60 - 70°C.

[0022] The purpose of the fourth aspect of the present invention is to provide a method for preparing a balsa wood porous carbon positive electrode sheet. Acetylene black is used as a conductive agent, styrene - butadiene rubber is used as a precipitant, sodium carboxymethyl cellulose is used as a binder, and a titanium sheet is used as a current collector. Sodium carboxymethyl cellulose is placed in a beaker and stirred with water for 1 - 2 h to fully dissolve it in water. Then, the positive electrode material obtained by the method of the present invention and acetylene black are added and stirred at 700 - 900 r / min for 5 - 8 h, and then styrene - butadiene rubber is added and slowly stirred at 200 - 400 r / min for 0.5 - 1 h to form a positive electrode paste. The paste is coated on the treated titanium sheet and dried at room temperature for 12 h to obtain the positive electrode sheet. The ratio of the positive electrode material: acetylene black: binder: precipitant is 8:1:0.5:0.5.

[0023] The advantages of the present invention are as follows:

[0024] 1. The present invention utilizes balsa wood biomass to prepare porous carbon materials. The raw materials used are abundant, the cost is low, the environment is friendly, the process is simple, suitable for industrialization, and has great application value.

[0025] 2. Using organic potassium salts reduces the cost of pore - forming agents. High - value porous carbon is generated through high - temperature calcination. The prepared porous carbon has a high specific surface area and a suitable pore size distribution, and has a strong adsorption capacity for benzoquinone.

[0026] 3. The present invention improves the electrochemical performance by changing the carbonization temperature. The first reversible capacity is 409 mAh g at a rate of 1C -1 , and the first reversible capacity is 353 mAh g at a rate of 5C -1 . After 2000 cycles, the reversible capacity is 285 mAh / g -1 , showing high reversible specific capacity and good cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the SEM image of the balsa wood porous carbon prepared in Example 4 of the present invention;

[0028] Figure 2 It is the cycle performance diagram of the balsa wood porous carbon at 1C prepared in Example 1 of the present invention;

[0029] Figure 3 It is the cycle performance diagram of the balsa wood porous carbon at 1C prepared in Example 2 of the present invention;

[0030] Figure 4 It is the cycle performance diagram of the balsa wood porous carbon at 1C prepared in Example 3 of the present invention;

[0031] Figure 5It is the 1C cycle performance diagram of the balsa wood porous carbon prepared in Example 4 of the present invention;

[0032] Figure 6 It is the 5C cycle performance diagram of the balsa wood porous carbon prepared in Example 4 of the present invention;

[0033] Figure 7 It is the cyclic voltammetry curve of the balsa wood porous carbon prepared in Example 4 of the present invention;

[0034] Figure 8 It is the thermogravimetric analysis diagram of the balsa wood porous carbon prepared in Example 4 of the present invention for absorbing benzoquinone;

[0035] Figure 9 It is the pore size distribution diagram of the balsa wood porous carbon prepared in Example 4 of the present invention;

[0036] Figure 10 It is the isothermal adsorption curve of the balsa wood porous carbon prepared in Example 4 of the present invention;

[0037] Figure 11 It is the 1C cycle performance diagram of the balsa wood porous carbon prepared in Example 5 of the present invention; Detailed implementation manners

[0038] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer with the description. However, these embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. Those skilled in the art should understand that the details and forms of the technical solutions of the present invention can be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the protection scope of the present invention.

[0039] The method for preparing a porous carbon material from balsa wood provided by the present invention includes the following steps:

[0040] 1) Add an alkaline solution with a mass fraction of 5% to the balsa wood and stir, then repeatedly wash the balsa wood with ultrapure water and alkaline solution until the pH value is neutral, and dry it in an oven to obtain the balsa wood after alkali washing;

[0041] 2) Mix the balsa wood after alkali washing obtained in step 1), a pore-forming agent, and melamine with water evenly, put it in an oven for pre-carbonization, put the black powder after pre-carbonization into a tubular furnace with inert gas passed through, carry out high-temperature carbonization, take out the black powder when the tubular furnace naturally cools to room temperature, and obtain balsa wood biomass porous carbon through the steps of acid washing and water washing. The inert gas can be selected from argon or helium.

[0042] In some embodiments of the present invention, in step 1), the alkaline solution is a sodium hydroxide solution, stirred for 8 - 12 h at a rotation speed of 300 - 500 r / min. Specifically, the stirring time can be selected as 8 h, 9 h, 10 h, 11 h, or 12 h. The rotation speed can be selected as 300 r / min, 400 r / min, or 500 r / min.

[0043] In some embodiments of the present invention, in step 1), the oven temperature is 100 - 120 °C, and the time is 10 - 14 h. Specifically, the oven temperature can be selected as 100 °C, 110 °C, or 120 °C. The time can be selected as 10 h, 11 h, 12 h, 13 h, or 14 h.

[0044] In some embodiments of the present invention, in step 2), the mass ratio of balsa wood, pore-forming agent, and melamine is 3:(1 - 3):1. Specifically, the mass ratio of balsa wood, pore-forming agent, and melamine can be selected as 3:1:1, 3:2:1, or 3:3:1.

[0045] In some embodiments of the present invention, in step 2), the pre-carbonization temperature of the balsa wood is 200 - 240 °C, and the pre-carbonization time is 12 - 24 h. Specifically, the pre-carbonization temperature can be selected as 200 °C, 210 °C, 220 °C, 230 °C, or 240 °C. The pre-carbonization time can be selected as 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 20 h, 22 h, 23 h, or 24 h.

[0046] In some embodiments of the present invention, in step 2), the carbonization temperature is 700 - 900 °C, and the time is 1 - 2 h. Specifically, the carbonization temperature can be selected as 700 °C, 800 °C, or 900 °C.

[0047] In some embodiments of the present invention, the preparation method of the aqueous zinc - benzoquinone battery cathode material is to absorb and remove benzoquinone from the porous carbon prepared by the present invention by sublimation to obtain the aqueous zinc - benzoquinone battery cathode material.

[0048] In some embodiments of the present invention, for benzoquinone absorption, carbon and benzoquinone crystals are mixed and ground and then placed in an oven, and the benzoquinone absorption temperature is 70 - 100 °C. Specifically, the benzoquinone absorption temperature can be selected as 70 °C, 80 °C, 90 °C, or 100 °C.

[0049] In some embodiments of the present invention, the mass ratio of carbon to benzoquinone during benzoquinone absorption is 1:(1 - 3). Specifically, the mass ratio can be selected as 1:1, 1:2, or 1:3.

[0050] In some embodiments of the present invention, the time for absorbing benzoquinone is 20 - 24 h. Specifically, the time for absorbing benzoquinone can be selected as 20 h, 21 h, 22 h, 23 h, or 24 h.

[0051] In some embodiments of the present invention, during the process of removing benzoquinone, the oven temperature is set at 60 - 70 °C, and the time for removing benzoquinone is 24 h to 48 h. Specifically, the temperature for removing benzoquinone can be selected as 60 °C or 70 °C. The time can be selected as 24 h, 25 h, 26 h, 27 h, 28 h, 29 h, 30 h, 31 h, 32 h, 33 h, 34 h, 35 h, 36 h, 37 h, 38 h, 39 h, 40 h, 41 h, 42 h, 43 h, 44 h, 45 h, 46 h, 47 h, or 48 h.

[0052] In some embodiments of the present invention, the method for providing the balsa wood porous carbon positive electrode sheet includes the following steps:

[0053] Using acetylene black as the conductive agent, styrene - butadiene rubber as the precipitant, sodium carboxymethyl cellulose as the binder, and titanium sheet as the current collector, wherein the ratio of the positive electrode material : acetylene black : binder : precipitant is 8 : 1 : 0.5 : 0.5.

[0054] Put sodium carboxymethyl cellulose into a beaker, add water, and stir for 1 - 2 h to dissolve it in water. Specifically, the stirring time of sodium carboxymethyl cellulose with water can be selected as 1 h or 2 h.

[0055] Add the ground positive electrode material prepared by the present invention and acetylene black, and stir at 700 - 900 r / min for 5 - 8 h. Specifically, the stirring speed in this step can be selected as 700 r / min, 800 r / min, or 900 r / min. The stirring time can be selected as 5 h, 6 h, 7 h, or 8 h.

[0056] Add styrene - butadiene rubber and stir at 200 - 400 r / min for 0.5 - 1 h to obtain the positive electrode paste. Specifically, the stirring speed in this step can be selected as 200 r / min, 300 r / min, or 400 r / min. The stirring time can be selected as 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, or 1 h.

[0057] Apply the positive electrode paste on the current collector by the coating method and air - dry it at room temperature to obtain the positive electrode sheet.

[0058] The following is further illustrated through specific examples.

[0059] Example 1

[0060] 1. Mix balsa wood, pore - forming agent, and melamine evenly with water, put them into an oven, and keep them at 240 °C for 24 h to obtain pre - carbonized balsa wood.

[0061] II. Thoroughly grind the pre-carbonized balsa wood, load it into a porcelain boat and place it in a tube furnace. Under an argon atmosphere, heat it to 800 °C at a rate of 5 °C / min, keep it warm for 2 h, then cool it to room temperature and take out the material. Put it into a beaker, add excessive hydrochloric acid for pickling, stir for 10 h at a rotation speed of 500 r / min. After sedimentation, pour the upper-layer waste liquid into the waste acid bucket, then add ultrapure water and wash repeatedly until the pH is neutral. Place the sample after washing with water in an oven at 120 °C and dry it for 12 h to obtain the balsa wood biomass porous carbon material.

[0062] III. Absorb benzoquinone with the obtained balsa wood biomass porous carbon material. The specific method is as follows: Weigh a certain mass of porous carbon and benzoquinone respectively, and the mass ratio of porous carbon to benzoquinone is 1:2. Then put their mixture into a black-cap bottle, tighten the lid, and place it in an oven at a temperature of 75 °C; the heat preservation time is 20 - 24 h. The step of removing benzoquinone is to take out the benzoquinone-carbon complex after the above absorption of benzoquinone from the oven and cool it naturally to room temperature. Put the benzoquinone-carbon complex into a petri dish, and then put it into an oven at a temperature of 65 °C. The time for removing benzoquinone is 24 h - 48 h. After the removal of benzoquinone is completed, perform thermogravimetric testing to calculate its adsorption rate.

[0063] The mass ratio of balsa wood to potassium oxalate and melamine is 3:1:1.

[0064] Prepare a slurry from the balsa wood porous carbon-benzoquinone complex prepared in Example 1. The specific method is as follows: Weigh 320 mg of the benzoquinone-carbon complex, weigh 40 mg of acetylene black, mix the benzoquinone-carbon complex and acetylene black, put them into a mortar and grind thoroughly. Then weigh 20 mg of CMC (sodium carboxymethyl cellulose) and put it into a small beaker, add 1.2 ml of deionized water and stir at a rotation speed of 900 r / min for 1 h. Add the ground benzoquinone-carbon complex and acetylene black and continue to stir at a rotation speed of 800 r / min for 5 h. Then add SBR (styrene-butadiene rubber) and continue to stir at a rotation speed of 300 r / min for 30 min. The usage ratio of benzoquinone-carbon complex:acetylene black:binder:precipitant is 8:1:0.5:0.5. Coat the prepared slurry on a titanium foil and dry it at room temperature to obtain the positive electrode sheet of the aqueous zinc-benzoquinone battery, and the unit area loading of the active material is 2 mg·cm 2 , use a zinc sheet as the counter electrode, a glass fiber as the separator, and 3M H2SO4·7H2O as the electrolyte to assemble an aqueous zinc-benzoquinone battery in the air.

[0065] Conduct electrochemical performance testing on the aqueous zinc-benzoquinone battery; the test voltage range is 0.6 V - 1.6 V, and the test rate is 1C - 5C.

[0066] Figure 2Cycling performance graph of the cathode material prepared from the balsa wood porous carbon material prepared in Example 1 of the present invention.

[0067] Example 2

[0068] I. Balsa wood, pore-forming agent, and melamine are added to water and mixed evenly, then placed in an oven at 240 °C for 24 h to obtain pre-carbonized balsa wood.

[0069] II. The pre-carbonized balsa wood is ground thoroughly, loaded into a porcelain boat and placed in a tube furnace. Under an argon atmosphere, it is heated to 800 °C at a rate of 5 °C / min and then held for 2 h. After cooling to room temperature, the material is taken out, placed in a beaker, and excess hydrochloric acid is added for pickling. Stir for 10 h at a rotation speed of 500 r / min. After pickling, the upper waste liquid is poured into a waste acid bucket, and then deionized water is added for repeated washing until the pH is neutral. The sample after washing is placed in an oven at 120 °C for drying for 12 h to obtain the balsa wood biomass porous carbon material.

[0070] III. The obtained balsa wood biomass porous carbon material is subjected to benzoquinone absorption. The specific method is as follows: Weigh a certain mass of porous carbon and benzoquinone crystals respectively. The mass ratio of porous carbon to benzoquinone is 1:2. Then the mixture is loaded into a black-cap bottle, the lid is tightened, and it is placed in an oven at 75 °C; the holding time is 20 h to 24 h. The step of removing benzoquinone is to take out the benzoquinone-carbon complex after the above benzoquinone absorption and let it cool naturally to room temperature. The benzoquinone-carbon complex is placed in a petri dish and then placed in an oven at 65 °C. The time for removing benzoquinone is 24 h to 48 h. After the benzoquinone removal is completed, a thermogravimetric test is carried out to calculate its adsorption rate.

[0071] The mass ratio of balsa wood, potassium oxalate, and melamine is 3:3:1.

[0072] The balsa wood porous carbon benzoquinone complex prepared in Example 2 is made into a slurry. The specific method is as follows: Weigh 320 mg of the benzoquinone-carbon complex, weigh 40 mg of acetylene black, mix the benzoquinone-carbon complex and acetylene black, and place them in a mortar for thorough grinding. Then weigh 20 mg of CMC (sodium carboxymethyl cellulose) and put it into a small beaker, add 1.2 ml of deionized water and stir at a rotation speed of 900 r / min for 1 h. Add the ground benzoquinone-carbon complex and acetylene black and continue stirring at a rotation speed of 800 r / min for 5 h. Then add SBR (styrene-butadiene rubber) and continue stirring at a rotation speed of 300 r / min for 30 min. The usage ratio of benzoquinone-carbon complex:acetylene black:binder:precipitant is 8:1:0.5:0.5. The prepared slurry is coated on a titanium foil and dried at room temperature to obtain a positive electrode sheet for an aqueous zinc-benzoquinone battery. The unit area loading of the active material is 2 mg·cm 2, a zinc sheet was used as the counter electrode, a glass fiber was used as the separator, and 3M H2SO4·7H2O was used as the electrolyte to assemble an aqueous zinc-benzoquinone battery in air.

[0073] The electrochemical performance of the aqueous zinc-benzoquinone battery was tested; the test voltage range was 0.6V to 1.6V, and the test rate was 1C - 5C.

[0074] Figure 3 This is the cycle performance graph of the positive electrode material prepared from the balsa wood porous carbon material prepared in Example 2 of the present invention.

[0075] Example 3

[0076] The difference between this example and Example 2 is that the material was loaded into a porcelain boat and placed in a tube furnace. Under an argon atmosphere, it was heated to 900°C at a rate of 5°C / min and then held for 2h. After that, it was cooled to room temperature and the material was taken out. It was repeatedly filtered and washed with deionized water until the pH was neutral. The sample after the water washing was placed in an oven at 120°C and dried for 12h to obtain the balsa wood biomass porous carbon material. Other steps and parameters are the same as those in Example 2.

[0077] The balsa wood porous carbon-benzoquinone composite prepared in Example 3 was made into a slurry. The specific method was as follows: Weigh 320mg of the benzoquinone-carbon composite, weigh 40mg of acetylene black, mix the benzoquinone-carbon composite and acetylene black, put them into a mortar and grind thoroughly. Then weigh 20mg of CMC (sodium carboxymethyl cellulose) and put it into a small beaker, add 1.2ml of deionized water and stir at a speed of 900r / min for 30min. Add the ground benzoquinone-carbon composite and acetylene black and continue to stir at a speed of 800r / min for 5h. Then add SBR (styrene-butadiene rubber) and continue to stir at a speed of 300r / min for 30min. The ratio of benzoquinone-carbon composite: acetylene black: binder: precipitant is 8:1:0.5:0.5. It was dried at room temperature to obtain the positive electrode sheet of the aqueous zinc-benzoquinone battery, and the unit area loading of the active material was 2mg·cm 2 , a zinc sheet was used as the counter electrode, a glass fiber was used as the separator, and 3M H2SO4·7H2O was used as the electrolyte to assemble an aqueous zinc-benzoquinone battery in air.

[0078] The electrochemical performance of the aqueous zinc-benzoquinone battery was tested; the test voltage range was 0.6V to 1.6V, and the test rate was 1C - 5C.

[0079] Figure 4 This is the cycle performance graph of the positive electrode of the balsa wood biomass porous carbon material prepared in Example 3 of the present invention.

[0080] Example 4

[0081] The difference between this example and Example 3 is as follows: Balsa wood is first added to a sodium hydroxide solution with a mass fraction of 5%, stirred for 12 h at a rotation speed of 400 r / min. Then, the alkali-washed balsa wood is repeatedly washed with ultrapure water until the pH value is neutral, and the balsa wood after the alkali washing is completed is obtained. The balsa wood is placed in an oven for drying, the drying temperature is 100 °C, and the time is 12 h - 24 h.

[0082] Other steps and parameters are the same as those in Example 3.

[0083] The prepared balsa wood biomass porous carbon benzoquinone composite is prepared into a slurry. The specific method is as follows: Weigh 320 mg of the benzoquinone carbon composite, weigh 40 mg of acetylene black, mix the benzoquinone carbon composite and acetylene black, and put them into a mortar for sufficient grinding. Then, weigh 20 mg of CMC and put it into a small beaker, add 1.2 ml of deionized water and stir at a rotation speed of 900 r / min for 1 h. Add the ground benzoquinone carbon composite and acetylene black and continue stirring at a rotation speed of 800 r / min for 5 h. Then, add SBR and continue stirring at a rotation speed of 300 r / min for 30 min. The ratio of the benzoquinone carbon composite: acetylene black: binder: precipitant is 8:1:0.5:0.5. The prepared slurry is coated on a titanium foil and dried at room temperature to obtain a positive electrode sheet for an aqueous zinc-benzoquinone battery, and the unit area loading of the active material is 2 mg·cm 2 −2, using a zinc sheet as the counter electrode, a glass fiber as the separator, and 3M H2SO4·7H2O as the electrolyte to assemble an aqueous zinc-benzoquinone battery in air.

[0084] The electrochemical performance of the aqueous zinc-benzoquinone battery is tested; the test voltage range is 0.6 V to 1.6 V, and the test rate is 1C - 5C.

[0085] Figure 5 Figure 1C cycling performance of the balsa wood biomass porous carbon material prepared in Example 4 of the present invention;

[0086] From Figure 5 it can be seen that: after 1000 cycles at a rate of 1C, the reversible capacity is 329 mAh g -1 .

[0087] Figure 6 Figure 5C cycling performance of the balsa wood biomass porous carbon material prepared in Example 4 of the present invention;

[0088] From Figure 6 it can be seen that: after 1000 cycles at a rate of 5C, the reversible capacity is 310 mAh g-1

[0089] Figure 7 Cyclic voltammogram (CV) of the balsa wood biomass porous carbon material prepared in Example 4 of the present invention;

[0090] Figure 8 This is a thermogravimetric analysis diagram of the porous carbon material made from balsa wood biomass prepared in Example 4 of the present invention;

[0091] from Figure 8 It can be seen that the adsorption capacity of benzoquinone by balsa wood biomass porous carbon is 53%.

[0092] Figure 9 This is a pore size distribution diagram of the balsa wood biomass porous carbon material prepared in Example 4 of the present invention.

[0093] from Figure 9 It can be seen that the prepared balsa wood biomass porous carbon material is mainly composed of a micro-mesoporous structure, and the pore size is concentrated in the range of 1-4 nm.

[0094] Figure 10 This is the isothermal adsorption curve of the balsa wood biomass porous carbon material prepared in Example 4 of the present invention.

[0095] Example 5

[0096] 1. First, add 5% sodium hydroxide solution to the balsa wood and stir for 12 hours at a speed of 400r / min. Then wash the alkali-washed balsa wood repeatedly with ultrapure water until the pH is neutral to obtain alkali-washed balsa wood. Put the balsa wood into an oven for drying at a temperature of 100°C for 12-24 hours.

[0097] 2. Add water to the balsa wood, the pore-forming agent and melamine, mix them evenly, put them into an oven and keep them at 240° C. for 24 hours to obtain pre-carbonized balsa wood.

[0098] 3. Grind the pre-carbonized balsa wood thoroughly, put the sample into a porcelain boat and put it into a tube furnace, heat it to 800℃ at a rate of 5℃ / min in an argon atmosphere, and keep it warm for 2h. After cooling to room temperature, take out the material, put it into a beaker, add excess hydrochloric acid for pickling, stir for 12h, and rotate at 600r / min. After pickling, pour the upper waste acid liquid into the waste acid barrel, then add ultrapure water and wash repeatedly until the pH is neutral. After washing, place the sample in a 100℃ oven and dry it for 12h to obtain the balsa wood biomass porous carbon material.

[0099] Fourth, the obtained balsa wood biomass porous carbon material is subjected to benzoquinone absorption. The specific method is as follows: a certain mass of porous carbon and benzoquinone are weighed respectively, and the mass ratio of porous carbon to benzoquinone is 1:2, and then the mixture is put into a black cap bottle, the lid is tightly closed, and it is placed in an oven at a temperature of 75°C; the insulation time is 20h to 24h. The step of removing benzoquinone is to take the above benzoquinone-absorbing benzoquinone carbon composite out of the oven and cool it naturally to room temperature, put the benzoquinone carbon composite into a culture dish, and then put it into an oven at a temperature of 65°C, and the benzoquinone removal time is 24h to 48h. After the benzoquinone removal is completed, a thermogravimetric test is performed to calculate its adsorption rate.

[0100] The mass ratio of balsa wood to potassium oxalate and melamine is 3:1:1.

[0101] The benzoquinone carbon composite of the balsa wood porous carbon material prepared in this embodiment is used to prepare a slurry. The specific method is as follows: weigh 320 mg of the benzoquinone carbon composite, weigh 40 mg of acetylene black, weigh and mix the benzoquinone carbon composite and acetylene black, put them in a mortar and grind them thoroughly, then weigh 20 mg of CMC (sodium carboxymethyl cellulose) and put them in a small beaker, add 1.2 ml of deionized water and stir at a speed of 900 r / min for 1 hour, add the ground benzoquinone carbon composite and acetylene black and continue stirring at a speed of 800 r / min for 5 hours, then add SBR (styrene-butadiene rubber) and continue stirring at a speed of 300 r / min for 30 minutes. The ratio of benzoquinone carbon composite: acetylene black: binder: precipitant is 8:1:0.5:0.5. Dry at room temperature to obtain a positive electrode sheet for an aqueous zinc-benzoquinone battery, and the unit area loading of the active material is 2 mg cm 2 , an aqueous zinc-benzoquinone battery was assembled in air with zinc sheet as counter electrode, glass fiber as separator, and 3M H2SO4·7H2O as electrolyte.

[0102] The electrochemical performance of the aqueous zinc-benzoquinone battery was tested; the test voltage range was 0.6V to 1.6V, and the test rate was 1C to 5C.

[0103] Figure 11 This is a cycle performance diagram of the balsa porous carbon material positive electrode prepared in Comparative Example 1 of the present invention.

Claims

1. A method for preparing porous carbon materials from balsa wood, characterized in that, The method comprises the following steps: 1) Add an alkaline solution with a mass fraction of 5% to balsa wood and stir. Then, repeatedly wash the balsa wood with ultrapure water and alkaline solution until the pH value is neutral. Dry the balsa wood in an oven to obtain the alkali-washed balsa wood. 2) Mix the alkali-washed balsa wood obtained in step 1), a pore-forming agent, and melamine with water evenly. Put the mixture into an oven for pre-carbonization. After the pre-carbonization is completed, put the black powder into a tubular furnace filled with inert gas for high-temperature carbonization. Take out the black powder when the tubular furnace cools naturally to room temperature. Obtain balsa wood biomass porous carbon through the steps of pickling and water washing. In step 1), the alkaline solution is a sodium hydroxide solution, and the stirring time is 8 - 12 h with a rotation speed of 300 - 500 r / min. In step 1), the oven temperature is 100 - 120 °C, and the time is 10 - 14 h. In step 2), the mass ratio of balsa wood, pore-forming agent, and melamine is 3:(1 - 3):

1. In step 2), the pre-carbonization temperature of balsa wood is 200 - 240 °C, and the pre-carbonization time is 12 - 24 h. In step 2), the carbonization temperature is 700 - 900 °C, and the time is 1 - 2 h.

2. The method for preparing porous carbon from balsa wood according to claim 1, characterized in that, In step 2), the inert gas is helium or argon.

3. The method for preparing porous carbon from balsa wood according to claim 1, characterized in that, Using the BET test, the specific surface area of the balsa wood biomass porous carbon obtained is 2804 m 2 / g.

4. A porous carbon, characterized in that, The porous carbon material is prepared by the method described in any one of claims 1 - 3.

5. A preparation method of a cathode material for an aqueous zinc-benzoquinone battery, characterized in that, Perform the steps of absorbing benzoquinone and removing benzoquinone on the porous carbon prepared by the method described in any one of claims 1 - 3 by sublimation method to prepare a positive electrode material for an aqueous zinc-benzoquinone battery.

6. The preparation method of the aqueous zinc-benzoquinone battery cathode material according to claim 5, wherein, For the absorption of benzoquinone, mix carbon and benzoquinone crystals and grind them, then put them into an oven. The temperature for absorbing benzoquinone is 70 - 100 °C. During the absorption of benzoquinone, the mass ratio of carbon to benzoquinone is 1:(1 - 3). The time for absorbing benzoquinone is 20 - 24 h.

7. The preparation method of the cathode material of the aqueous zinc-benzoquinone battery according to claim 5, characterized in that, The oven temperature during the removal of benzoquinone is set to 60 - 70 °C, and the time for removing benzoquinone is 24 h to 48 h.

8. A method for a balsa wood porous carbon positive electrode sheet, characterized in that, Use acetylene black as the conductive agent, styrene-butadiene rubber as the precipitant, sodium carboxymethyl cellulose as the binder, and titanium sheet as the current collector. Put sodium carboxymethyl cellulose into a beaker, add water and stir for 1 - 2 h to dissolve it in water. Add the positive electrode material obtained by the method described in any one of claims 5 - 7 after grinding and acetylene black, and stir at 700 - 900 r / min for 5 - 8 h. Finally, add styrene-butadiene rubber and stir at 200 - 400 r / min for 0.5 - 1 h to obtain a positive electrode slurry. Coat the positive electrode slurry on the current collector by a coating method and dry it at room temperature to obtain a positive electrode sheet, where the ratio of positive electrode material:acetylene black:binder:precipitant is 8:1:0.5:0.5.

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