A method for preparing hard carbon anode materials using cotton stalks

Abstract

This invention discloses a method for preparing hard carbon anode materials using cotton stalks, comprising the following steps: (1) crushing the cotton stalks, mixing them with alkali, and then carbonizing them to obtain pyrolytic carbon; (2) crushing the pyrolytic carbon, compacting it, and wrapping it with a semi-permeable membrane to obtain a carbon rod, placing the carbon rod in an acidic solution containing phosphorus and sulfur, and electrolyzing it to obtain a doped carbon rod; (3) separating the semi-permeable membrane from the surface of the doped carbon rod, crushing and sieving the carbon material inside the doped carbon rod, washing and drying it, and then calcining it to obtain a hard carbon anode material. This invention uses a method of co-calcining biomass and alkaline substances, then uses the compacted pyrolytic carbon as an electrode immersed in an acidic sodium phosphorus and sulfur salt solution, and applies a directional electric field to dope it to improve the material performance. Finally, after calcination, a hard carbon anode material with high initial coulombic efficiency, high capacity, and good cycle performance is prepared.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, and particularly relates to a method for preparing a negative electrode material. Background Technology

[0002] Sodium-ion batteries have developed rapidly, quickly entering the energy storage and low-to-medium speed power battery markets due to their advantages of low cost and high energy storage capacity. Hard carbon, the main anode material for sodium-ion batteries, has become a limiting factor in improving battery performance. As an amorphous carbon with "short-range order and long-range disorder," hard carbon has a larger interlayer spacing than graphite, making it easier for sodium ions to intercalate. Currently, hard carbon materials are mainly made from biomass, due to its porous structure and high carbon content, which allows for the preparation of microporous hard carbon anode materials after high-temperature calcination.

[0003] Cotton stalks, as a widely available biomass raw material, can be used to prepare hard carbon anode materials. However, currently disclosed technologies using cotton stalks as raw materials for hard carbon material preparation generally suffer from low initial coulombic efficiency and poor cycle performance. Furthermore, existing technologies that directly treat biomass raw materials with acidic or alkaline solutions lead to the loss of lignin. Lignin is the primary carbon source, and most of the resulting carbon material is formed through the high-temperature conversion of lignin. Therefore, the reduction in lignin significantly decreases carbon production rate and increases production costs. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the shortcomings and defects mentioned in the background art above, and to provide a method for preparing hard carbon anode materials using cotton stalks that has high initial coulombic efficiency, excellent cycle performance, and low production cost. To solve the above technical problem, the technical solution proposed by this invention is as follows:

[0005] A method for preparing hard carbon anode materials using cotton stalks includes the following steps:

[0006] (1) The cotton stalks are crushed, mixed with alkali, and then carbonized to obtain pyrolytic carbon;

[0007] (2) The pyrolytic carbon is crushed and compacted, and then wrapped with a semi-permeable membrane to obtain a carbon rod. The carbon rod is placed in an acidic solution containing phosphorus and sulfur, and the acidic solution containing phosphorus and sulfur is divided into two sub-regions by the carbon rod (the solution must penetrate the carbon rod to flow between the two sub-regions). A pair of electrodes are placed in the two sub-regions respectively as the cathode and anode, and then energized. The carbon rod is then used as the anode, and at least one of the electrodes is used as the cathode, and energized again to obtain a doped carbon rod.

[0008] (3) Separate the semi-permeable membrane from the surface of the doped carbon rod, crush and screen the carbon material in the doped carbon rod, wash and dry it, and then calcine it to obtain hard carbon anode material.

[0009] Specifically, the above method may include the following steps:

[0010] (1) Crush the cotton stalks into small particles and sieve them through a sieve with a mesh size of 50, 100 or 150.

[0011] (2) The sieved cotton stalk particles are mixed with alkali in a certain proportion and then fed into a carbonization furnace. A certain flow rate of inert gas is introduced and heated at a certain heating rate to prepare pyrolytic carbon.

[0012] (3) The pyrolytic carbon is crushed and ball-milled again to control the particle size, then compacted and coated with a semi-permeable membrane to form a carbon rod. The carbon rod is placed in an acidic solution containing phosphorus and sulfur, and the solution is divided into two sub-regions by the carbon rod. A pair of platinum electrodes are placed in the two sub-regions respectively, serving as the cathode and anode. An electric field is applied to allow sodium ions in the solution to penetrate the carbon rod under the action of the electric field, constructing a microscopic channel suitable for sodium ion insertion and extraction, which facilitates sodium insertion at the negative electrode. Then, the carbon rod is used as the anode, and at least one of the electrodes is used as the cathode. The process involves applying an electric current again. Sulfate and phosphate ions, now negatively charged, move towards the carbon rod under the influence of the electric field. Since cotton stalks are biomass and porous, and further pore-forming is achieved using alkaline substances, sulfur and phosphorus ions can more easily enter the carbon rod under the electric field, thus achieving sulfur and phosphorus doping and obtaining doped carbon rods. The semi-permeable membrane ensures that micron-sized carbon materials cannot pass through it into the solution, while allowing sulfate, phosphate, and other metal ions to pass through.

[0013] (4) After step (3) is completed, the semi-permeable membrane is separated from the surface of the carbon rod, the carbon material inside the carbon rod is crushed and screened, the particle size is controlled, and then it is washed, filtered and dried until neutral. It is then sent into a high-temperature tube furnace and calcined at high temperature under the protection of an inert atmosphere to obtain the hard carbon anode material.

[0014] In the above method for preparing hard carbon anode materials using cotton stalks, preferably, the alkali includes one or more of sodium hydroxide, potassium hydroxide, and sodium carbonate; the mass ratio of cotton stalks to alkali is (60-95):(5-40).

[0015] In the above-mentioned method for preparing hard carbon anode materials using cotton stalks, preferably, flash carbonization is employed under an inert atmosphere. The carbonization temperature is controlled at 300-550℃, the carbonization time at 2-4 hours, the heating rate at 15-25℃ / min, and the inert gas flow rate at 200-500 mL / min. The inert gas can be argon, nitrogen, neon, xenon, etc. Carbonization removes the volatile components of the cotton stalks, producing pyrolytic carbon materials for subsequent processing. Within the 300-550℃ range, most of the volatile components of the cotton stalks are volatilized and removed. Simultaneously, within this temperature range, the cotton stalk material has not yet formed a hard carbon structure, thus not affecting the subsequent high-temperature calcination for crystal transformation. The carbonization time is controlled to ensure the complete volatilization of the volatile components in the cotton stalks.

[0016] In the above method for preparing hard carbon anode materials using cotton stalks, preferably, the D50 of the pyrolytic carbon is controlled to be 5-12 μm after crushing.

[0017] In the above method for preparing hard carbon anode materials using cotton stalks, preferably, the acidic solution containing phosphorus and sulfur is an aqueous solution composed of phosphoric acid, sodium sulfate, and sodium phosphate; the ratio of phosphoric acid, sodium sulfate, and sodium phosphate is configured according to a sulfur:phosphorus molar ratio of 1:(1-5), the phosphoric acid concentration is 1-5 mol / L, the phosphorus molar ratio of phosphoric acid to sodium phosphate is 1:(1-7), and the solid-liquid ratio of pyrolytic carbon to the phosphorus- and sulfur-containing acidic solution is controlled at 1:(5-20) (g / ml). The solid-liquid ratio of pyrolytic carbon to the phosphorus- and sulfur-containing acidic solution affects the doping effect of the carbon material. Appropriate doping of sulfur and phosphorus can effectively solve the specific capacity and cycle performance of the material. Too low a doping amount will not achieve the optimization effect, while too high a doping amount will affect the performance of the carbon material itself.

[0018] In the above-mentioned method for preparing hard carbon anode materials using cotton stalks, preferably, the sodium sulfate salt includes one or more of sodium sulfate, sodium sulfite, sodium thiosulfate, sodium pyrosulfate, sodium sulfide, sodium persulfate, and sodium perdisulfate; and the sodium phosphate salt includes one or more of sodium phosphate, sodium dihydrogen phosphate, sodium hypophosphite, sodium thiophosphate, and sodium phosphite.

[0019] In the above method for preparing hard carbon anode materials using cotton stalks, preferably, the pH of the acidic solution containing phosphorus and sulfur is 0-3. This invention controls the acidic conditions to inhibit the formation of iron phosphate precipitate, thus preventing the precipitate from affecting the purity of the material.

[0020] In the above method for preparing hard carbon anode materials using cotton stalks, preferably, the voltage is controlled at 2-4V during the electro-treatment, and the electro-treatment time is 15min-1h each time. If the voltage is lower than 2V, the conditions for sulfur and phosphorus ion doping and sodium ion etching penetration are not met. If the voltage is higher than 4V, a large amount of hydrogen and oxygen will be released from the solution, causing extensive etching of the carbon material surface and damaging the carbon material structure.

[0021] In the above-mentioned method for preparing hard carbon anode materials using cotton stalks, preferably, the calcination treatment is carried out under an inert atmosphere, with the calcination temperature controlled at 900-1600℃, the calcination time at 0.5-4h, the heating rate at 3-10℃ / min, and the inert gas flow rate at 200-500mL / min. The inert gas can be argon, nitrogen, neon, xenon, etc.

[0022] This invention discloses a method for preparing hard carbon anode materials using cotton stalks. The method employs a flash heating and co-calcination process using biomass and alkaline substances. Then, compacted pyrolytic carbon is immersed in an acidic sodium phosphate-sulfur salt solution as the electrode. Doping is performed by applying a directional electric field to improve material performance. Finally, after calcination, a hard carbon anode material with high initial coulombic efficiency, high capacity, and good cycle performance is prepared. The above steps are mutually synergistic and influence each other, contributing to the improvement of material performance. Specifically:

[0023] (1) Cotton stalks, as a byproduct of cotton harvesting, are mainly composed of lignin, cellulose, and hemicellulose, providing abundant carbon-producing raw materials. Therefore, using cotton stalks as raw materials results in a higher carbon production rate than general biomass materials. Furthermore, as a straw tissue, cotton stalks contain numerous fine channels for nutrient transport, making them more conducive to pore formation after being processed into hard carbon materials. In addition, this invention employs a solid alkaline substance for synergistic flash calcination with the cotton stalk material, rapidly forming lignin into pyrolytic carbon material. This reduces the amount of lignin that reacts chemically with the alkali, with only a small amount reacting with the alkaline substance. This reduces lignin loss in the material, which is beneficial for increasing the subsequent carbon production rate and facilitates the formation of C-C and CO bonds, providing a suitable bonding structure for subsequent sulfur and phosphorus doping. Since lignin reacts with alkaline solutions to form oxidized lignin, which has extremely high hydrophilicity, it is easily soluble in alkaline solutions. By using solid alkaline substances at higher temperatures, the hydroxyl groups of the lignin can undergo a saponification reaction with the ester groups in the cellulose of the material to create pores, and no water is produced to dissolve the oxidized lignin. Therefore, this effectively improves the situation of carbon loss caused by reacting alkaline substances with biomass materials.

[0024] (2) In this invention, pyrolytic carbon that has been crushed is compacted and coated with a semi-permeable membrane to form carbon rods. These rods are then immersed in an acidic sodium phosphate-sulfur salt solution. By applying an electric field, which acts as both an obstacle and an anode, sodium ions are facilitated to penetrate the carbon material under the influence of the electric field. This expands the interlayer spacing, providing favorable conditions for subsequent sodium intercalation as a negative electrode. Furthermore, concentration polarization is used to achieve efficient bonding and doping of sulfur and phosphorus ions. The presence of the semi-permeable membrane effectively prevents the carbon material from entering the solution while allowing sodium ions to pass through it. Cotton stalk material itself has high porosity. Alkaline pretreatment further increases the porosity of the material. Therefore, the carbon rods made from pyrolytic carbon of cotton stalks still contain a large number of pores. With the addition of an electric field, phosphate and sulfate ions can easily enter the pores, achieving doping and improving the electrochemical performance of the material.

[0025] (3) In this invention, an acidic sodium phosphate-sulfur salt solution is used as a doping solution. On the one hand, the material is doped, and on the other hand, the metallic impurities such as Ca and Fe in the carbon material are removed. At the same time, the pH of the solution is controlled below 3, which can effectively avoid the formation of precipitates such as iron phosphate (which exists in the form of precipitate at pH 4.5-7) and affect the purity of the material.

[0026] Compared with the prior art, the advantages of the present invention are as follows:

[0027] This invention utilizes a method for preparing hard carbon anode materials from cotton stalks. It employs a method of co-calcining biomass and alkaline substances, then uses pyrolytic carbon after compaction as an electrode immersed in an acidic sodium phosphate-sulfur salt solution. By applying a directional electric field, doping is performed to improve the material performance. Finally, after calcination, a hard carbon anode material with high initial coulombic efficiency, high capacity, and good cycle performance is prepared. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a TEM image of the hard carbon anode material prepared in Example 1.

[0030] Figure 2 The image shows the XRD spectrum of the hard carbon anode material prepared in Example 1. Detailed Implementation

[0031] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0032] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0034] Example 1:

[0035] A method for preparing hard carbon anode materials using cotton stalks includes the following steps:

[0036] Cotton stalks (mainly C, H, and O) were dried and crushed into small particles, which were then sieved through a 100-mesh sieve to control the particle size. The crushed cotton stalks were then uniformly mixed with sodium hydroxide at a mass ratio of 9:1 and spread evenly on a graphite crucible. The crucible was then covered and placed in a carbonization furnace. Nitrogen gas was introduced at a rate of 200 mL / min for 0.5 h. After the furnace was essentially free of oxygen, the temperature was increased to 500 °C at a rate of 20 °C / min and held for 2 h. The temperature was then decreased at a rate of 10 °C / min. Once cooled, the prepared pyrolytic carbon was removed.

[0037] The pyrolytic carbon was ball-milled again, and then sieved through a 200-mesh sieve to control the particle size D50 to approximately 12 μm. A 2 mol / L acidic mixed solution of sodium sulfate, sodium phosphate, and phosphoric acid (pH = 1) was prepared in a beaker with a sulfur-to-phosphorus molar ratio of 1:2 and a phosphorus element molar ratio of phosphate to sodium phosphate of 1:2. The pyrolytic carbon with controlled particle size was then compacted, coated with a semi-permeable membrane, and formed into carbon rods. These rods were then added to the prepared acidic mixed solution at a solid-liquid ratio of 1:10 g / ml, dividing the acidic solution into two sub-regions. A pair of platinum electrodes were placed in these two sub-regions as the cathode and anode, respectively. A power supply of 2.5V was turned on. First, the carbon rods were used as a barrier for 20 minutes. Then, the carbon rods were used as the anode, and one of the platinum electrodes as the cathode, for another 20 minutes, resulting in doped carbon rods.

[0038] After doping, the material was filtered, washed, dried, and weighed 10g into a graphite crucible. The crucible was then covered and placed in a high-temperature tube furnace. Nitrogen gas was introduced at a rate of 400mL / min for 0.5h. After the air in the furnace was basically purged, the temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3h. After the holding period, cooling was started. Once the furnace had cooled, the material was removed, yielding the hard carbon anode material.

[0039] During the battery loading stage, cotton stalk-based hard carbon anode material, PVDF, and acetylene black were mixed and ground in a 90:5:5 ratio. After grinding for 5 minutes, polyvinylidene fluoride binder was added dropwise, and grinding continued until a thin, viscous consistency was achieved. The ground slurry was evenly coated onto the surface of aluminum foil, sliced, and dried at 120°C to obtain the anode sheet. In a glove box under oxygen- and water-free conditions, the electrode material, battery casing, and electrolyte were assembled in a specific order. After assembly, the battery was compacted using a small hydraulic press, and electrochemical performance testing was performed after 8 hours.

[0040] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 5.32 m². 2 / g, electrochemical performance testing showed that its initial coulombic efficiency was 88.64%, its initial reversible specific capacity was 380.24 mAh / g, and its retention rate was 93% after 1000 cycles at 1C.

[0041] The TEM image and XRD spectrum of the hard carbon anode material prepared in this embodiment are shown below. Figure 1 , Figure 2 As shown. By Figure 1 It can be seen that this material possesses short-range order and long-range disorder, similar to the hard carbon structure of "House of Cards," indicating that the prepared material is a hard carbon material. Figure 2 It can be seen that the material has two characteristic peaks (002) and (100), which are the characteristic peaks of the standard type of hard carbon material, further indicating that the material is a hard carbon material.

[0042] Example 2:

[0043] A method for preparing hard carbon anode materials using cotton stalks includes the following steps:

[0044] Cotton stalks (mainly C, H, and O) were dried and crushed into small particles, which were then sieved through a 100-mesh sieve to control the particle size. The crushed cotton stalks were then uniformly mixed with sodium hydroxide at a mass ratio of 5:1 and spread evenly on a graphite crucible. The crucible was then covered and placed in a carbonization furnace. Nitrogen gas was introduced at a rate of 200 mL / min for 0.5 hours. After the furnace was nearly free of oxygen, the temperature was increased to 500°C at a rate of 20°C / min and held for 2 hours. The temperature was then decreased at a rate of 10°C / min. Once cooled, the prepared pyrolytic carbon was removed.

[0045] The pyrolytic carbon was ball-milled again, and then sieved through a 200-mesh sieve to control the particle size D50 to approximately 12 μm. A 2 mol / L acidic mixed solution of sodium sulfate, sodium phosphate, and phosphoric acid (pH = 1) was prepared in a beaker with a sulfur-to-phosphorus molar ratio of 1:2 and a phosphorus element molar ratio of phosphate to sodium phosphate of 1:2. The pyrolytic carbon with controlled particle size was then compacted, coated with a semi-permeable membrane, and formed into carbon rods. These rods were then added to the prepared acidic mixed solution at a solid-liquid ratio of 1:10 g / ml, dividing the acidic solution into two sub-regions. A pair of platinum electrodes were placed in these two sub-regions as the cathode and anode, respectively. A power supply of 2.5V was turned on. First, the carbon rods were used as a barrier for 20 minutes. Then, the carbon rods were used as the anode, and one of the platinum electrodes as the cathode, for another 20 minutes, resulting in doped carbon rods.

[0046] After doping, the material was filtered, washed, dried, and weighed 10g into a graphite crucible. The crucible was then covered and placed in a high-temperature tube furnace. Nitrogen gas was introduced at a rate of 400mL / min for 0.5h. After the air in the furnace was basically purged, the temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3h. After the holding period, cooling was started. Once the furnace had cooled, the material was removed, yielding the hard carbon anode material.

[0047] During the battery loading stage, cotton stalk-based hard carbon anode material, PVDF, and acetylene black were mixed and ground in a 90:5:5 ratio. After grinding for 5 minutes, polyvinylidene fluoride binder was added dropwise, and grinding continued until a thin, viscous consistency was achieved. The ground slurry was evenly coated onto the surface of aluminum foil, sliced, and dried at 120°C to obtain the anode sheet. In a glove box under oxygen- and water-free conditions, the electrode material, battery casing, and electrolyte were assembled in a specific order. After assembly, the battery was compacted using a small hydraulic press, and electrochemical performance testing was performed after 8 hours.

[0048] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 6.32 m². 2 / g, electrochemical performance testing showed that its initial coulombic efficiency was 83.73%, its initial reversible specific capacity was 320.24 mAh / g, and its retention rate was 87% after 1000 cycles at 1C.

[0049] Example 3:

[0050] Unlike Example 1:

[0051] The material after doping was calcined to a final temperature of 1300°C, and all other processes were consistent with those in Example 1.

[0052] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 5.45 m². 2 / g, electrochemical performance testing showed that its initial coulombic efficiency was 87.31%, its initial reversible specific capacity was 376.59mAh / g, and its retention rate was 90% after 1000 cycles at 1C.

[0053] Example 4:

[0054] Unlike Example 1:

[0055] The solid-liquid ratio of the pyrolytic carbon and the acidic mixed solution was 1:20, and all other aspects remained the same as in Example 1.

[0056] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 5.16 m². 2 / g, electrochemical performance testing showed that its initial coulombic efficiency was 82.32%, its initial reversible specific capacity was 382.63mAh / g, and its retention rate was 85% after 1000 cycles at 1C.

[0057] Example 5:

[0058] Unlike Example 1:

[0059] The power supply voltage was changed to 3.5V, and the power-on time was changed to 1 hour each time. Everything else remained the same as in Example 1.

[0060] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 5.97 m². 2 / g, electrochemical performance testing showed that its initial coulombic efficiency was 85.12%, its initial reversible specific capacity was 323.52mAh / g, and its retention rate was 93% after 1000 cycles at 1C.

[0061] Comparative Example 1:

[0062] The difference between this comparative example and Example 1 is that the crushed cotton stalks are not mixed with sodium hydroxide, but everything else is the same as in Example 1, and a hard carbon anode material is finally obtained.

[0063] During the battery loading stage, hard carbon anode material, PVDF, and acetylene black were mixed and ground in a 90:5:5 ratio. After grinding for 5 minutes, polyvinylidene fluoride binder was added dropwise, and grinding continued until a thin, viscous consistency was achieved. The ground slurry was then evenly coated onto the surface of aluminum foil, sliced, and dried at 120°C to obtain the anode sheet. In an oxygen- and water-free glove box, the electrode material, battery casing, and electrolyte were assembled in a specific order. After assembly, the battery was compacted using a small hydraulic press, and electrochemical performance testing was performed after 8 hours.

[0064] The specific surface area of ​​the material obtained in this comparative example is 5.14 m². 2 / g, electrochemical performance testing showed that its initial coulombic efficiency was 74.32%, its initial reversible specific capacity was 253.89mAh / g, and its retention rate was 70% after 1000 cycles at 1C.

[0065] Comparative Example 2:

[0066] The difference between this comparative example and Example 1 is that the power supply voltage is 0 during doping, that is, no power supply is applied. Everything else is the same as in Example 1, and a hard carbon anode material is finally obtained.

[0067] During the battery loading stage, hard carbon anode material, PVDF, and acetylene black were mixed and ground in a 90:5:5 ratio. After grinding for 5 minutes, polyvinylidene fluoride binder was added dropwise, and grinding continued until a thin, viscous consistency was achieved. The ground slurry was then evenly coated onto the surface of aluminum foil, sliced, and dried at 120°C to obtain the anode sheet. In an oxygen- and water-free glove box, the electrode material, battery casing, and electrolyte were assembled in a specific order. After assembly, the battery was compacted using a small hydraulic press, and electrochemical performance testing was performed after 8 hours.

[0068] The specific surface area of ​​the material obtained in this comparative example is 6.26 m². 2 / g, electrochemical performance testing showed that its initial coulombic efficiency was 80.26%, its initial reversible specific capacity was 264.24 mAh / g, and its retention rate was 85% after 1000 cycles at 1C.

[0069] Comparative Example 3:

[0070] The difference between this comparative example and Example 1 is that the power supply voltage during doping is 1V, while everything else is the same as in Example 1, ultimately yielding a hard carbon anode material.

[0071] The specific surface area of ​​the hard carbon anode material obtained in this comparative example is 6.32 m². 2 / g, electrochemical performance testing showed that its initial coulombic efficiency was 81.94%, its initial reversible specific capacity was 283.22mAh / g, and its retention rate was 85% after 1000 cycles at 1C.

[0072] Comparative Example 4:

[0073] The difference between this comparative example and Example 1 is that the pre-carbonization process is heated to 500°C at a rate of 5°C / min, while all other aspects are the same as in Example 1, ultimately yielding a hard carbon anode material.

[0074] The specific surface area of ​​the hard carbon anode material obtained in this comparative example is 8.12 m². 2 / g, electrochemical performance testing showed that its initial coulombic efficiency was 76.71%, its initial reversible specific capacity was 243.07mAh / g, and its retention rate was 67% after 1000 cycles at 1C.

Claims

1. A method for preparing hard carbon anode materials using cotton stalks, characterized in that, Includes the following steps: (1) The cotton stalks are crushed, mixed with alkali, and then carbonized to obtain pyrolytic carbon; (2) The pyrolytic carbon is crushed and compacted, and then wrapped with a semi-permeable membrane to obtain a carbon rod. The carbon rod is placed in an acidic solution containing phosphorus and sulfur, and the acidic solution containing phosphorus and sulfur is divided into two sub-regions by the carbon rod. A pair of electrodes are placed in the two sub-regions respectively as cathode and anode, and then energized. The carbon rod is then used as the anode, and at least one of the electrodes is used as the cathode, and energized again to obtain a doped carbon rod. (3) Separate the semi-permeable membrane from the surface of the doped carbon rod, crush and screen the carbon material in the doped carbon rod, wash and dry it, and then calcine it to obtain hard carbon anode material; The acidic solution containing phosphorus and sulfur is an aqueous solution composed of a mixture of phosphoric acid, sodium sulfate, and sodium phosphate. The carbonization process employs flash heating and is carried out under an inert atmosphere. The carbonization temperature is controlled at 300-550℃, the carbonization time is 2-4h, the heating rate is 15-25℃ / min, and the inert gas flow rate is 200-500mL / min. During power-on processing, the control voltage is 2-4V, and the power-on time is 15min-1h each time.

2. The method for preparing hard carbon anode materials using cotton stalks according to claim 1, characterized in that, The alkali includes one or more of sodium hydroxide, potassium hydroxide and sodium carbonate; the mass ratio of the cotton stalk to the alkali is (60-95):(5-40).

3. The method for preparing hard carbon anode materials using cotton stalks according to claim 1, characterized in that, The pyrolytic carbon is crushed and its D50 is controlled to be 5-12μm.

4. The method for preparing hard carbon anode materials using cotton stalks according to any one of claims 1-3, characterized in that, The phosphoric acid, sodium sulfate, and sodium phosphate are configured according to a sulfur to phosphorus molar ratio of 1:(1-5). The phosphoric acid concentration is 1-5 mol / L, the phosphorus molar ratio of phosphoric acid to sodium phosphate is 1:(1-7), and the solid-liquid ratio of pyrolytic carbon to the phosphorus- and sulfur-containing acidic solution is controlled at 1:(5-20).

5. The method for preparing hard carbon anode materials using cotton stalks according to claim 4, characterized in that, The sodium sulfate salt includes one or more of sodium sulfate, sodium sulfite, sodium thiosulfate, sodium pyrosulfate, sodium sulfide, sodium persulfate, and sodium perdisulfate; the sodium phosphate salt includes one or more of sodium phosphate, sodium dihydrogen phosphate, sodium hypophosphite, sodium thiophosphate, and sodium phosphite.

6. The method for preparing hard carbon anode materials using cotton stalks according to any one of claims 1-3, characterized in that, The pH of the acidic solution containing phosphorus and sulfur is 0-3.

7. The method for preparing hard carbon anode materials using cotton stalks according to any one of claims 1-3, characterized in that, The calcination process is carried out under an inert atmosphere, with the calcination temperature controlled at 900-1600℃, the calcination time at 0.5-4h, the heating rate at 3-10℃ / min, and the inert gas flow rate at 200-500mL / min.

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