Biomass-based hard carbon active materials, preparation thereof and use in sodium-ion batteries

Abstract

The application belongs to the field of sodium ion battery materials, and particularly relates to a preparation method of biomass-based hard carbon active material. Biomass is pretreated by acid or alkali to obtain pretreated biomass, and then first-stage carbonization treatment is carried out to obtain first-stage carbon material. The first-stage carbon material is dispersed in a modification liquid containing reinforcing agent A and reinforcing agent B, and is modified under mechanical reinforcement, and then solid-liquid separation is carried out to obtain modified material. The reinforcing agent A is a compound containing at least one element of N, P and S. The reinforcing agent B is a carbonate source capable of providing carbonate ions. The modified material is subjected to second-stage carbonization to obtain the hard carbon active material. The application also includes the material prepared by the preparation method and the application of the material in sodium ion batteries. The technical scheme of the application has excellent universality, and can improve the fast charging and low-temperature performance of the prepared material.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery anode materials, and particularly relates to the field of biomass-based sodium-ion battery hard carbon anode materials. Background Technology

[0002] Currently, the global energy crisis and environmental pollution are intensifying, and the development and utilization of clean and renewable energy sources such as solar, wind, and tidal energy have gradually become a global consensus. The utilization of renewable energy has driven the development of the energy storage field, among which electrochemical energy storage has attracted much attention due to its advantages such as fast response speed, high conversion efficiency, and lack of geographical limitations. As the most widely used rechargeable battery, lithium-ion batteries dominate in electronic devices and electric vehicles. However, the limited and uneven distribution of lithium resources restricts the application of lithium-ion batteries in large-scale energy storage. Due to the abundance and wide distribution of sodium resources, sodium-ion batteries have received widespread attention in recent years. Furthermore, because their working principle and manufacturing methods are very similar to those of lithium-ion batteries, sodium-ion batteries have become a potential candidate for large-scale energy storage devices.

[0003] As a crucial component of batteries, the properties of anode materials significantly impact battery performance, including energy density and cycle life. Currently, existing sodium-ion battery anode materials include intercalated, alloyed, and conversion types. As an intercalated material, carbon-based materials are widely available, possess high conductivity, and exhibit structural stability, making them the most promising anode material. However, due to thermodynamic factors and the small interlayer spacing, graphite anode materials commonly used in lithium-ion batteries are difficult to apply in sodium-ion batteries. Therefore, there is an urgent need to develop suitable anode materials to drive the development of sodium-ion batteries. Hard carbon refers to carbon materials that are difficult to graphitize. In its microstructure, partially bent graphene sheets are locally stacked to form a disordered layer structure, while partially twisted graphene sheets form pores. This structural feature allows hard carbon materials to provide more sodium storage sites and exhibit higher specific capacity; therefore, hard carbon is considered the most promising anode material for sodium-ion batteries.

[0004] Currently, the steps required to prepare hard carbon materials from biomass precursors include purification, hydrothermal carbonization, air or liquid-phase oxidation, activation, and high-temperature carbonization. The resulting hard carbon materials generally have a reversible sodium storage capacity of 300–330 mAh / g, with an initial coulombic efficiency of around 80%. Besides the potential for improvement in sodium storage capacity, biomass-based hard carbon also faces challenges such as poor rate capability and low-temperature performance, and high production costs. Furthermore, existing research on the low-temperature performance of hard carbon is relatively scarce. For example, Chinese patent document CN111847418A discloses a method for preparing hard carbon materials, including the following steps: providing longan shells as raw material, soaking them in hot water and acidic solutions, and drying them to obtain a precursor; introducing a protective gas to preheat the precursor, cooling it, and then grinding it to obtain an intermediate product; carbonizing the intermediate product, and cooling it to obtain biomass hard carbon. This technology uses longan peels as raw material to prepare hard carbon materials with low-temperature performance. In addition, Chinese patent document CN113562718A discloses a method for preparing hard carbon anode materials for ultra-low temperature lithium-ion batteries. The steps are as follows: first, biomass is washed, dried, and pulverized; then, it is placed in a basket made of high-temperature resistant material, and the basket is fixed to a high-temperature resistant rod. The mixture is then immersed in molten salt under an inert atmosphere. The resulting immersion product is washed with water to remove salt, dried, and pressed into sheets. These sheets are then used as electrolytic cathodes and subjected to electrochemical polarization treatment in high-temperature molten salt. The resulting electrolytic product is then washed with water to remove salt and dried again, ultimately yielding a hard carbon anode material for lithium-ion batteries with a unique morphology. The hard carbon anode material prepared by this method exhibits rapid ion transport capabilities and maintains good cycle performance and rate performance even under ultra-low temperature conditions.

[0005] In summary, research on the low-temperature performance of biomass-based hard carbon materials is still relatively scarce, and the universality of the process and low-temperature performance need to be further improved. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the first objective of the present invention is to provide a method for preparing biomass-based hard carbon active materials, which aims to prepare hard carbon active materials with excellent low-temperature performance.

[0007] A second objective of this invention is to provide a biomass-based hard carbon active material obtained by the aforementioned preparation method and its application in sodium-ion batteries.

[0008] A third objective of the present invention is to provide a sodium-ion battery comprising the aforementioned biomass-based hard carbon active material, and its negative electrode and negative electrode material.

[0009] To address the problem that biomass-based hard carbon materials are difficult to adapt to low-temperature application requirements and have unsatisfactory low-temperature performance, this invention provides the following improvement solutions through research:

[0010] A method for preparing a biomass-based hard carbon active material involves pretreating biomass with an acid or alkali solution to obtain pretreated biomass, followed by a first-stage carbonization process to obtain a first-stage carbon material.

[0011] A section of carbon material is dispersed in a modification liquid containing reinforcing agent A and reinforcing agent B, and modified under mechanical strengthening. Subsequently, solid-liquid separation is performed to obtain the modified material. The reinforcing agent A is a compound containing at least one element that can provide N, P, and S. The reinforcing agent B is a carbonic acid source that can provide carbonate ions.

[0012] The modified material is then subjected to a second stage of carbonization to obtain the hard carbon active material.

[0013] This invention innovatively pre-treats and carbonizes biomass in the first stage, then mechanically strengthens it with the assistance of fortifiers A and B, and then performs a second stage of carbonization. This process can unexpectedly adjust the physicochemical structure of hard carbon, improve its sodium storage capacity and conductivity, and improve its low-temperature performance.

[0014] The technical solution described in this invention has good universality and can be adapted to any biomass raw materials known in any industry. For example, the biomass includes at least one of straw and fruit shells.

[0015] The straw mentioned includes, for example, at least one of rice straw, wheat straw, corn straw, bean straw, peanut straw, rapeseed straw, sugarcane straw, and cotton straw;

[0016] The aforementioned fruit shells include, for example, at least one of coconut shells, walnut shells, hazelnut shells, almond shells, and macadamia nut shells;

[0017] The research of this invention also shows that the combination of straw and fruit shell can unexpectedly achieve further synergy, can be further adapted to the process of this invention, and can further enhance the fast charging and low temperature performance of the prepared material.

[0018] In this invention, biomass can be pretreated by soaking in an acidic or alkaline solution, followed by solid-liquid separation to obtain pretreated material.

[0019] In this invention, the acid solution can be an aqueous solution of at least one of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid, wherein the concentration of the solute is, for example, 0.5 to 3 M.

[0020] The alkaline solution can be an aqueous solution of at least one of sodium hydroxide and potassium hydroxide, wherein the concentration of the solute is, for example, 0.5 to 3 M.

[0021] In this invention, the atmosphere for the first stage of carbonization can be an oxygen-free atmosphere, such as nitrogen, inert gas, or the like.

[0022] In this invention, the temperature of the first stage of carbonization is 1050–1450°C, preferably 1150–1250°C. At the preferred temperature, it can be further combined with the process to help further improve the low-temperature and fast-charging performance of the prepared material.

[0023] The carbonization time for the first stage is 1 to 5 hours, preferably 2 to 4 hours.

[0024] In this invention, a section of carbon material is first subjected to liquid-solid mechanical-chemical strengthening treatment in a system of reinforcing agents A and B. This helps to combine with the pre-carbonization process and the subsequent carbonization process, which can further synergistically endow the material with physicochemical structural characteristics suitable for low-temperature cycling and further improve the performance of the prepared material at low temperatures.

[0025] In this invention, the reinforcing agent A can be an organic and / or inorganic compound capable of providing N, P, and S, such as at least one of phosphoric acid and its water-soluble salts, phytic acid and its water-soluble salts, melamine, persulfate, and urea. It can further include at least one of phosphoric acid, phytic acid, thiourea, melamine, ammonium persulfate, diamine hydrogen phosphate, disodium hydrogen phosphate, ammonium phytate, sodium phytate, and urea. Further, the reinforcing agent A contains at least thiourea and also comprises a composite reinforcing agent containing at least one of phosphoric acid and phytic acid. Preferably, the thiourea content in the composite reinforcing agent can be 30–70 wt%. Studies have shown that the preferred composite reinforcing agent can unexpectedly further synergistically improve the fast-charging and low-temperature performance of the material.

[0026] In this invention, the reinforcing agent B is a water-soluble salt containing carbonate ions and / or carbon dioxide gas. Further, the reinforcing agent B includes at least one of ammonium carbonate, sodium carbonate, ammonium bicarbonate, and carbon dioxide; more preferably, ammonium carbonate. Studies have shown that the preferred reinforcing agent B can unexpectedly further synergistically improve the fast-charging and low-temperature performance of the material.

[0027] In this invention, the reinforcing agent A is 0.5 to 3 times the weight of the first stage of charcoal, and more specifically, 1.5 to 2.5 times; the reinforcing agent B is 0.25 to 1.5 times the weight of the first stage of charcoal, and more specifically, 0.5 to 1 times.

[0028] The solvent in the modified liquid includes water;

[0029] In this invention, the concentration of reinforcing agent A in the modified solution is not particularly required, for example it can be 10 to 100 g / L, and more specifically it can be 20 to 40 g / L;

[0030] Preferably, the pH of the modified solution is 5 to 8.

[0031] The present invention also provides an optimized solution, wherein a section of carbon material is pre-quenched and then subjected to a second carbonization process. The pre-quenching process is as follows: a section of carbon material is pre-quenched in a modified liquid while hot; or, a section of carbon material is pre-quenched in water, and then reinforcing agent A and reinforcing agent B are added.

[0032] The present invention shows that the cold quenching treatment can further enhance the synergistic effect of mechanical strengthening with strengthening agents A and B, further facilitate the construction of low-temperature adapted physicochemical structural characteristics, and further improve the low-temperature performance of the prepared hard carbon material.

[0033] Preferably, the initial temperature difference for cold quenching is above 300°C, and more preferably 350–450°C.

[0034] In this invention, the mechanical strengthening method can be ball milling;

[0035] Preferably, the rotational speed during the ball milling stage is 350–650 r / min;

[0036] In another optimized embodiment of the present invention, the mechanical enhancement stage is carried out in an auxiliary gas, wherein the auxiliary gas includes at least one of oxygen, air, and carbon dioxide.

[0037] The present invention demonstrates that, based on the mechanical strengthening of the solution system containing reinforcing agents A and B, further pressurization via the aforementioned auxiliary gas can construct a suitable gas-solid-liquid three-phase mechanical physicochemical treatment, which unexpectedly further facilitates the construction of low-temperature adapted physicochemical structural characteristics and can further improve the low-temperature performance of the prepared hard carbon material.

[0038] In this invention, the auxiliary gas may also include a dilution gas, such as at least one of air, nitrogen, and an inert gas.

[0039] The mechanical strengthening pressure is above 0.2 MPa.

[0040] An optimized scheme of the present invention includes a mechanical strengthening process comprising two mechanical strengthening processes. In the first mechanical strengthening process, the rotation speed is 350-400 r / min, the pressure is 0.2-0.3 MPa, and the time is 5-10 h. In the second mechanical strengthening process, the rotation speed is 450-600 r / min, the pressure is 0.3-1 MPa (e.g., 0.4-0.6 MPa), and the time is 2-5 h.

[0041] The present invention demonstrates that further two-stage gradient mechanical strengthening treatment can facilitate the construction of a low-temperature-adaptive physicochemical structure, thereby further improving the low-temperature performance of the prepared hard carbon.

[0042] In this invention, the modified material can undergo a second stage of carbonization treatment in a protective atmosphere.

[0043] In this invention, the temperature of the second stage of carbonization is 550–950°C, preferably 650–750°C. Studies have shown that at the preferred temperature, the physicochemical properties of the material can be further improved synergistically, which helps to further improve its low-temperature and fast-charging performance.

[0044] In this invention, the second stage of carbonization takes 1 to 3 hours.

[0045] This invention also provides a biomass-based hard carbon active material prepared by the aforementioned method.

[0046] This invention also provides an application of the biomass-based hard carbon active material prepared by the above-described method, using it as a negative electrode active material to prepare sodium-ion batteries.

[0047] Furthermore, the biomass-based hard carbon active material described in this invention can be used as a negative electrode active material, and can be compounded with conductive agents and binders to obtain a negative electrode material.

[0048] In a further preferred application, the negative electrode material is coated onto the surface of the negative electrode current collector to obtain the negative electrode. Existing conventional methods can be used, such as a coating method, to coat the negative electrode material of this invention onto the current collector to form the negative electrode. The current collector can be any material known in the industry.

[0049] In a further preferred application, the negative electrode, positive electrode, separator, and electrolyte are assembled into a sodium-ion secondary battery.

[0050] The present invention also provides a sodium-ion battery comprising a biomass-based hard carbon active material prepared by the preparation method described in the present invention;

[0051] In this invention, the negative electrode comprises the biomass-based hard carbon active material.

[0052] In the sodium-ion battery described in this invention, apart from the active material prepared using the method of this invention, all other processes and components can be conventional.

[0053] Beneficial effects

[0054] (1) In view of the problem of unsatisfactory low-temperature performance of biochar-based hard carbon, the present invention innovatively pre-treats and carbonizes biomass in the first stage, then mechanically strengthens it with the assistance of strengthening agent A and strengthening agent B, and then carbonizes it in the second stage. In this way, the physicochemical structure of hard carbon can be unexpectedly adjusted, its sodium storage capacity and conductivity can be improved, and its low-temperature performance can be improved.

[0055] (2) Based on the process innovations of pretreatment, first-stage carbonization, mechanical strengthening assisted by reinforcing agent A+B, and second-stage carbonization, further optimization of processes such as first-stage carbon material cold quenching, reinforcing agent A and reinforcing agent B composition, pressure of mechanical strengthening stage, and gradient mechanical strengthening process can further achieve synergy and further improve the low-temperature performance of the prepared hard carbon. Attached Figure Description

[0056] Appendix Figure 1 The image shows a TEM image of the final hard carbon material obtained in Example 1.

[0057] Appendix Figure 2 The image shows the XRD pattern of the final hard carbon material obtained in Example 1.

[0058] Appendix Figure 3 This is the first charge-discharge curve of the final hard carbon anode material obtained in Example 1 at a current density of 30 mA / g;

[0059] Appendix Figure 4 This is a long-cycle diagram of the final hard carbon anode material obtained in Example 1 at a current density of 30 mA / g. Detailed Implementation

[0060] The following examples illustrate the specific steps of the present invention. It should be understood that these examples are merely illustrative and not intended to limit the scope of the invention in any way. Various processes and methods not described in detail in this invention are conventional methods known in the art.

[0061] The present invention provides a preferred method for preparing a biomass-based hard carbon anode active material for sodium-ion batteries, comprising the following steps:

[0062] Step (1): Wash the biomass with water and dry it at a temperature of 60-80℃ for 12-24 hours. After drying, pulverize and sieve the dried material to obtain powder.

[0063] Step (2): The biomass powder obtained in step (1) is acid-washed or alkali-washed, then washed with water and dried to obtain purified biomass powder. The acid-washing or alkali-washing is performed by placing the powder in an acid such as hydrochloric acid, hydrofluoric acid, nitric acid, or sulfuric acid, or in an alkali such as potassium hydroxide or sodium hydroxide and stirring. The concentration of the acid or alkali solution is 0.5-3M, the liquid-to-solid ratio (ml / g) is (2-6):1, the reaction temperature is 30-60℃, and the reaction time is 4-12h. After the reaction is completed, the obtained powder is washed with water and dried in a conventional manner.

[0064] Step (3): Place the powder obtained in step (2) in an atmosphere furnace for the first stage of carbonization. Inert atmospheres such as nitrogen, argon, ammonia, and hydrogen-argon mixture are introduced. The first stage carbonization temperature T1 is 1050-1450℃, preferably 1150-1250℃, the time is 1-5h, preferably 2-4h, and the heating rate is 1-5℃ / min.

[0065] Step (4): Place the powder obtained in step (3) into a modified liquid containing reinforcing agents A and B, and strengthen it under ball milling. The additive A is, for example, at least one of phosphoric acid, phytic acid, thiourea, melamine, ammonium persulfate, diammonium hydrogen phosphate, disodium hydrogen phosphate, ammonium phytate, sodium phytate, and urea; the reinforcing agent B includes at least one of ammonium carbonate, sodium carbonate, ammonium bicarbonate, and carbon dioxide; the ball-to-material ratio of the ball mill is (10-20):1; the ball milling speed is 350-600 r / min.

[0066] Step (5): Place the powder obtained in step (4) into an atmosphere furnace for secondary carbonization. Inert atmospheres such as nitrogen, argon, ammonia, and hydrogen-argon mixture are introduced. The carbonization temperature is 600-900℃, the time is 2-3h, the heating rate is 2-5℃ / min, and the atmosphere furnace is cooled to room temperature to obtain biomass-based hard carbon anode active material.

[0067] Preferably, in this invention, a section of carbon material from step 3 is placed in the modified liquid from step 4 while still hot for cold quenching.

[0068] In a preferred embodiment of the present invention, step 4 involves pressurizing the gas using an auxiliary gas, such as carbon dioxide, CO, oxygen, or air.

[0069] In this invention, the mechanical activation process in step 4 includes two activation treatment processes.

[0070] Example 1

[0071] Step (1): Wash, dry, crush and sieve the biomass (rice straw and coconut shell in a weight ratio of 1:1) to obtain powder with a median particle size of about 50 μm; prepare a mixed solution of hydrochloric acid and hydrofluoric acid with a concentration of 2M, put the straw powder into it, control the liquid-solid ratio (ml / g) at 4:1, stir and react at 30℃ for 5h, filter after stirring, and wash and dry the filter residue to obtain purified biomass powder;

[0072] Step (2): The biomass powder obtained in step (1) is loaded into an atmosphere furnace and heated to 1200℃ (marked as T1) at a rate of 3℃ / min in an Ar atmosphere for high-temperature carbonization treatment for 2h. After cooling to room temperature, it is ground and pulverized to obtain a section of charcoal.

[0073] Step (3): Place a section of carbon material obtained in step (2) into a modified liquid containing reinforcing agent A and reinforcing agent B, and then perform ball milling.

[0074] Among them, reinforcing agent A contains phosphoric acid and thiourea in a weight ratio of 2:1, and reinforcing agent B is sodium carbonate; the weight ratio of reinforcing agent A to reinforcing agent B in the first-stage carbon material is 1:2:1; in the modified solution, the concentration of reinforcing agent A is 25g / L;

[0075] The ball milling media and tank material in the ball milling stage are stainless steel balls, the ball-to-material ratio is 15:1, the ball milling speed is 600 rpm, and the ball milling time is 10 hours to obtain modified material;

[0076] Step (4): The modified hard carbon material obtained in step (3) is loaded into an atmosphere furnace and subjected to secondary carbonization in Ar. The temperature is increased to 700℃ (marked as T2) at a rate of 5℃ / min and held for 2 hours. After cooling to room temperature, it is ground and pulverized to obtain biomass-based hard carbon negative electrode active material.

[0077] A carbon anode was formed by coating an active material, conductive carbon black, and sodium alginate (SA) in a mass ratio of 90:5:5 onto a current collector (Cu foil). Using this carbon electrode as the working electrode, a sodium sheet as the counter electrode, and either 1 mol / L NaPF6 EC / DEC (volume ratio 1:1) or 1 mol NaPF6 DME as the electrolyte, and glass fiber as the separator, CR2032 coin cells were assembled in an argon-filled dry glove box. Electrochemical performance was tested at room temperature (25°C) and low temperature (-20°C) within a voltage range of 0.01–2.0 V, with a charge / discharge test current density of 0.1C (1C = 300 mA / g). At room temperature, the initial reversible capacity at 0.1C was 358 mAh / g, the initial coulombic efficiency was 86.8%, and the capacity retention after 200 cycles was 96.4%. Under 2C rapid charge / discharge conditions, the reversible specific capacity was 227 mAh / g.

[0078] At -20℃, the initial reversible capacity at 0.1C is 224 mAh / g, the initial coulombic efficiency is 82.1%, and the capacity retention after 200 cycles is 88.4%.

[0079] Example 2:

[0080] Compared with Example 1, the only difference is that the type of biomass and the amount of biomass used are changed, while all other parameters are the same as in Example 1. The experimental groups are as follows:

[0081] Group A: Biomass is rice straw;

[0082] Group B: Biomass is coconut shells;

[0083] The test was conducted according to the method in Example 1, and the results are as follows:

[0084] Group A: At room temperature and 0.1C, the initial reversible capacity is 342 mAh / g, the initial coulombic efficiency is 79.3%, and the capacity retention after 200 cycles is 92.5%. Under 2C rapid charge and discharge conditions, its reversible specific capacity is 218 mAh / g.

[0085] At -20℃, the initial reversible capacity at 0.1C is 208 mAh / g, the initial coulombic efficiency is 77.2%, and the capacity retention after 200 cycles is 86.3%.

[0086] Group B: At room temperature and 0.1C, the initial reversible capacity is 331 mAh / g, the initial coulombic efficiency is 80.9%, and the capacity retention after 200 cycles is 93.7%. Under 2C rapid charge and discharge conditions, its reversible specific capacity is 209 mAh / g.

[0087] At -20℃, the initial reversible capacity at 0.1C is 197 mAh / g, the initial coulombic efficiency is 78.4%, and the capacity retention after 200 cycles is 87.1%.

[0088] As can be seen from Examples 1 and 2, straw, typically rice straw, and fruit shells, typically coconut shells, are both suitable for the process of this invention and can achieve good fast charging and low-temperature performance. In particular, the combination of rice straw and coconut shells can unexpectedly achieve synergy, which can further improve the fast charging and low-temperature performance of the material.

[0089] Example 3

[0090] Compared with Example 1, the only difference is that the value of T1 and the holding time in the high-temperature carbonization step are changed, respectively:

[0091] Group A: T1 is 1100℃, and the heat preservation time at this temperature is 4 hours;

[0092] Group B: T1 is 1400℃, and the holding time at this temperature is 2 hours.

[0093] Battery assembly and electrochemical testing were performed using the method described in Example 1, and the results are as follows:

[0094] Group A: At room temperature, the initial reversible capacity at 0.1C is 331 mAh / g, the initial coulombic efficiency is 85.4%, and the capacity retention after 200 cycles is 92.1%. Under 2C rapid charge and discharge conditions, its reversible specific capacity is 215 mAh / g.

[0095] At -20℃, the initial reversible capacity at 0.1C is 211 mAh / g, the initial coulombic efficiency is 79.6%, and the capacity retention after 200 cycles is 85.2%.

[0096] Group B: At room temperature, the initial reversible capacity at 0.1C is 337 mAh / g, the initial coulombic efficiency is 87.2%, and the capacity retention after 200 cycles is 94.1%. Under 2C rapid charge and discharge conditions, its reversible specific capacity is 196 mAh / g.

[0097] At -20℃, the initial reversible capacity at 0.1C is 206 mAh / g, the initial coulombic efficiency is 82.4%, and the capacity retention after 200 cycles is 87.5%.

[0098] Example 4

[0099] Compared with Example 1, the only difference is that the reinforcing agent A and reinforcing agent B added during the ball milling process are changed, respectively:

[0100] Group A: Fortifier A is thiourea;

[0101] Group B: Reinforcing agent A is phosphoric acid and melamine in a weight ratio of 1:1;

[0102] Group C: Reinforcing agent A is phytic acid and thiourea in a weight ratio of 1:2.

[0103] Group D: Fortifying agent B is ammonium carbonate;

[0104] Group E: The weight ratio of charcoal material and reinforcing agent A / reinforcing agent B is 1:0.5:0.5;

[0105] Battery assembly and electrochemical testing were performed using the method described in Example 1, and the results are as follows:

[0106] Group A: At room temperature, the initial reversible capacity at 0.1C is 340 mAh / g, the initial coulombic efficiency is 86.1%, and the capacity retention after 200 cycles is 90.8%. Under 2C rapid charge-discharge conditions, its reversible specific capacity is 213 mAh / g.

[0107] At -20℃, the initial reversible capacity at 0.1C is 208 mAh / g, the initial coulombic efficiency is 81.4%, and the capacity retention after 200 cycles is 85.5%.

[0108] Group B: The initial reversible capacity at 0.1C is 348 mAh / g, the initial coulombic efficiency is 85.4%, and the capacity retention after 200 cycles is 92.4%. Under 2C rapid charge and discharge conditions, its reversible specific capacity is 217 mAh / g.

[0109] At -20℃, the initial reversible capacity at 0.1C is 215 mAh / g, the initial coulombic efficiency is 80.1%, and the capacity retention after 200 cycles is 85.9%.

[0110] Group C: The initial reversible capacity at 0.1C is 352 mAh / g, the initial coulombic efficiency is 86.3%, and the capacity retention after 200 cycles is 94.7%. Under 2C rapid charge and discharge conditions, its reversible specific capacity is 220 mAh / g.

[0111] At -20℃, the initial reversible capacity at 0.1C is 218 mAh / g, the initial coulombic efficiency is 81.9%, and the capacity retention after 200 cycles is 86.3%.

[0112] Group D: The initial reversible capacity at 0.1C is 360 mAh / g, the initial coulombic efficiency is 85.9%, and the capacity retention after 200 cycles is 94.8%. Under 2C rapid charge and discharge conditions, its reversible specific capacity is 229 mAh / g.

[0113] At -20℃, the initial reversible capacity at 0.1C is 224 mAh / g, the initial coulombic efficiency is 81.3%, and the capacity retention after 200 cycles is 86.5%.

[0114] Group E: The initial reversible capacity at 0.1C is 332 mAh / g, the initial coulombic efficiency is 86.9%, and the capacity retention after 200 cycles is 94.2%. Under 2C rapid charge and discharge conditions, its reversible specific capacity is 215 mAh / g.

[0115] At -20℃, the initial reversible capacity at 0.1C is 209 mAh / g, the initial coulombic efficiency is 80.5%, and the capacity retention after 200 cycles is 86.1%.

[0116] Example 5

[0117] Compared to Example 1, the only difference is that the process in step 3 is changed, and the experimental groups are as follows:

[0118] Group A: Cold quenching process:

[0119] After the heat preservation in step 2 is completed, cool it to 350-450°C and then place it directly in the modified liquid for cold quenching while it is still hot, and then perform the ball milling treatment; other operations and parameters are the same as in Example 1;

[0120] Group B: Gas-assisted ball milling

[0121] In step 3, air is introduced into the ball mill system, and the system pressure is maintained at 0.5 MPa;

[0122] Group C: Gradient ball milling treatment

[0123] Compared to Group B, the difference is that the ball milling process includes two stages. The first stage of ball milling is performed at a speed of 350 r / min, a pressure of 0.2 MPa, and a time of 6 hours. The second stage of ball milling is then performed at a speed of 550 r / min, a pressure of 0.5 MPa, and a time of 4 hours.

[0124] Battery assembly and electrochemical testing were performed using the method described in Example 1. The results are as follows: Group A: At room temperature, the initial reversible capacity at 0.1C was 377 mAh / g, the initial coulombic efficiency was 86.4%, and the capacity retention after 200 cycles was 96.6%. Under 2C rapid charge-discharge conditions, its reversible specific capacity was 241 mAh / g. At -20℃, the initial reversible capacity at 0.1C was 235 mAh / g, the initial coulombic efficiency was 81.4%, and the capacity retention after 200 cycles was 87.2%.

[0125] Group B: At room temperature, the initial reversible capacity at 0.1C is 362 mAh / g, with an initial coulombic efficiency of 84.1%, and a capacity retention of 95.7% after 200 cycles. Under 2C rapid charge-discharge conditions, its reversible specific capacity is 235 mAh / g. At -20℃, the initial reversible capacity at 0.1C is 229 mAh / g, with an initial coulombic efficiency of 80.8%, and a capacity retention of 86.9% after 200 cycles.

[0126] Group C: At room temperature, the initial reversible capacity at 0.1C is 389 mAh / g, with an initial coulombic efficiency of 86.9%, and a capacity retention of 97.9% after 200 cycles. Under 2C rapid charge-discharge conditions, its reversible specific capacity is 252 mAh / g. At -20℃, the initial reversible capacity at 0.1C is 249 mAh / g, with an initial coulombic efficiency of 83.1%, and a capacity retention of 88.6% after 200 cycles.

[0127] As can be seen from Examples 1 and 5, the preferred process helps to improve the performance of the material.

[0128] Example 6

[0129] Compared with Example 1, the only difference is that the value of T2 and the holding time in the secondary carbonization step are changed, respectively:

[0130] Group A: T2 is 600℃, and the holding time at this temperature is 3 hours;

[0131] Group B: T2 is 900℃, and the holding time at this temperature is 1 hour.

[0132] Battery assembly and electrochemical testing were performed using the method described in Example 1, and the results are as follows:

[0133] Group A: At room temperature, the initial reversible capacity at 0.1C is 347 mAh / g, the initial coulombic efficiency is 82.2%, and the capacity retention after 200 cycles is 93.5%. Under 2C rapid charge-discharge conditions, its reversible specific capacity is 216 mAh / g.

[0134] At -20℃, the initial reversible capacity at 0.1C is 218 mAh / g, the initial coulombic efficiency is 81.3%, and the capacity retention after 200 cycles is 86.2%.

[0135] Group B: At room temperature, the initial reversible capacity at 0.1C is 340 mAh / g, the initial coulombic efficiency is 87.0%, and the capacity retention after 200 cycles is 92.8%. Under 2C rapid charge and discharge conditions, its reversible specific capacity is 203 mAh / g.

[0136] At -20℃, the initial reversible capacity at 0.1C is 207 mAh / g, the initial coulombic efficiency is 80.6%, and the capacity retention after 200 cycles is 85.3%.

[0137] Comparative Example 1

[0138] Compared with Example 1, the only difference is that the acid treatment in step 1 is not performed. Instead, the biomass is directly processed in step 2 and subsequent steps. Other operations and parameters are the same as in Example 1.

[0139] The test was conducted according to the method in Example 1, and the results are as follows:

[0140] At room temperature, the initial reversible capacity at 0.1C is 312 mAh / g, with an initial coulombic efficiency of 79.8%, and a capacity retention of 86.4% after 200 cycles. Under 2C rapid charge-discharge conditions, its reversible specific capacity is 195 mAh / g. At -20℃, the initial reversible capacity at 0.1C is 184 mAh / g, with an initial coulombic efficiency of 73.6%, and a capacity retention of 79.1% after 200 cycles.

[0141] Comparative Example 2

[0142] Compared with Example 1, the only difference is that the order of steps 2 and 3 is reversed. For example, the biomass powder obtained in step 1 is directly processed in step 3, followed by steps 2 and 4. All other operations and parameters are the same as in Example 1.

[0143] The test was conducted according to the method in Example 1, and the results are as follows:

[0144] At room temperature, the initial reversible capacity at 0.1C is 305 mAh / g, with an initial coulombic efficiency of 77.6%, and a capacity retention of 87.6% after 200 cycles. Under 2C rapid charge-discharge conditions, its reversible specific capacity is 184 mAh / g. At -20℃, the initial reversible capacity at 0.1C is 172 mAh / g, with an initial coulombic efficiency of 72.3%, and a capacity retention of 80.2% after 200 cycles.

[0145] Comparative Example 3

[0146] Compared with Example 1, the only difference is that in step 3, reinforcing agent A is missing; all other operations and parameters are the same as in Example 1.

[0147] The test was conducted according to the method in Example 1, and the results are as follows:

[0148] At room temperature, the initial reversible capacity at 0.1C is 316 mAh / g, with an initial coulombic efficiency of 85.1%, and a capacity retention of 90.5% after 200 cycles. Under 2C rapid charge-discharge conditions, its reversible specific capacity is 207 mAh / g. At -20℃, the initial reversible capacity at 0.1C is 198 mAh / g, with an initial coulombic efficiency of 79.2%, and a capacity retention of 84.8% after 200 cycles.

[0149] Comparative Example 4

[0150] Compared with Example 1, the only difference is that in step 3, reinforcing agent B is missing; all other operations and parameters are the same as in Example 1.

[0151] The test was conducted according to the method in Example 1, and the results are as follows:

[0152] At room temperature, the initial reversible capacity at 0.1C is 321 mAh / g, with an initial coulombic efficiency of 84.8%, and a capacity retention of 90.8% after 200 cycles. Under 2C rapid charge-discharge conditions, its reversible specific capacity is 210 mAh / g. At -20℃, the initial reversible capacity at 0.1C is 201 mAh / g, with an initial coulombic efficiency of 78.1%, and a capacity retention of 84.9% after 200 cycles.

[0153] Comparative Example 5

[0154] Compared with Example 1, the only difference is that mechanical ball milling is missing in step 3, while other operations and parameters are the same as in Example 1.

[0155] The test was conducted according to the method in Example 1, and the results are as follows:

[0156] At room temperature, the initial reversible capacity at 0.1C is 328 mAh / g, with an initial coulombic efficiency of 85.2%, and a capacity retention of 91.3% after 200 cycles. Under 2C rapid charge-discharge conditions, its reversible specific capacity is 196 mAh / g. At -20℃, the initial reversible capacity at 0.1C is 188 mAh / g, with an initial coulombic efficiency of 78.5%, and a capacity retention of 85.1% after 200 cycles.

[0157] Comparative Example 6

[0158] Compared to Example 1, the only difference is that step 4 is omitted.

[0159] The test was conducted according to the method in Example 1, and the results are as follows:

[0160] At room temperature, the initial reversible capacity at 0.1C is 315 mAh / g, with an initial coulombic efficiency of 76.3%, and a capacity retention of 87.2% after 200 cycles. Under 2C rapid charge-discharge conditions, its reversible specific capacity is 210 mAh / g. At -20℃, the initial reversible capacity at 0.1C is 192 mAh / g, with an initial coulombic efficiency of 72.1%, and a capacity retention of 80.3% after 200 cycles.

[0161] Comparative Example 7

[0162] Compared with Example 1, the only difference is that steps 3 and 4 are swapped. Specifically, the carbon material from step 2 is directly processed in step 4, and then modified in step 3.

[0163] The test was conducted according to the method in Example 1, and the results are as follows:

[0164] At room temperature, the initial reversible capacity at 0.1C is 298 mAh / g, with an initial coulombic efficiency of 74.5%, and a capacity retention of 84.6% after 200 cycles. Under 2C rapid charge-discharge conditions, its reversible specific capacity is 174 mAh / g. At -20℃, the initial reversible capacity at 0.1C is 162 mAh / g, with an initial coulombic efficiency of 70.6%, and a capacity retention of 78.1% after 200 cycles.

[0165] Comparative Example 8

[0166] Compared with Example 1, the only difference is that in step 3, a section of carbon material is dry-mixed with reinforcing agent A and reinforcing agent B and then directly subjected to ball milling.

[0167] The test was conducted according to the method in Example 1, and the results are as follows:

[0168] At room temperature, the initial reversible capacity at 0.1C is 325 mAh / g, with an initial coulombic efficiency of 84.91%, and a capacity retention of 91.1% after 200 cycles. Under 2C rapid charge-discharge conditions, its reversible specific capacity is 194 mAh / g. At -20℃, the initial reversible capacity at 0.1C is 185 mAh / g, with an initial coulombic efficiency of 77.2%, and a capacity retention of 84.8% after 200 cycles.

Claims

1. A method for preparing a biomass-based hard carbon active material, characterized in that, Biomass is pretreated with acid or alkali to obtain pretreated biomass, which is then subjected to the first stage of carbonization to obtain first-stage charcoal. A section of carbon material is dispersed in a modified liquid containing reinforcing agent A and reinforcing agent B, and modified under mechanical strengthening. Then, solid-liquid separation is performed to obtain the modified material. The modified material is then subjected to a second stage of carbonization to obtain the hard carbon active material. The reinforcing agent A includes at least one of phosphoric acid and its water-soluble salts, phytic acid and its water-soluble salts, melamine, persulfate, and urea. The reinforcing agent B is a carbonic acid source capable of providing carbonate ions; The mechanical strengthening method is ball milling; The temperature for the first stage of carbonization is 1050~1450℃; The temperature for the second stage of carbonization is 550~950℃; The biomass includes at least one of straw and fruit shells.

2. The preparation method according to claim 1, characterized in that, The straw mentioned includes at least one of rice straw, wheat straw, corn straw, bean straw, peanut straw, rapeseed straw, sugarcane straw, and cotton straw; The fruit shells mentioned include at least one of coconut shells, walnut shells, hazelnut shells, almond shells, and macadamia nut shells.

3. The preparation method according to claim 2, characterized in that, The biomass is rice straw and coconut shell in a weight ratio of 1:

1.

4. The preparation method according to claim 1, characterized in that, In the pretreatment stage, the acid solution is an aqueous solution of at least one of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid, wherein the concentration of the solute is 0.5~3M; The alkaline solution is an aqueous solution of at least one of sodium hydroxide and potassium hydroxide, wherein the concentration of the solute is 0.5~3M.

5. The preparation method according to claim 1, characterized in that, The temperature of the first stage of carbonization is 1150~1250℃.

6. The preparation method according to claim 5, characterized in that, The first stage of carbonization takes 1 to 5 hours.

7. The preparation method according to claim 6, characterized in that, The first stage of carbonization takes 2-4 hours.

8. The preparation method according to claim 1, characterized in that, The reinforcing agent A includes at least one of phosphoric acid, phytic acid, thiourea, melamine, ammonium persulfate, diammonium hydrogen phosphate, disodium hydrogen phosphate, ammonium phytate, sodium phytate, and urea.

9. The preparation method according to claim 8, characterized in that, The reinforcing agent A is a composite reinforcing agent that contains at least thiourea and at least one of phosphoric acid and phytic acid.

10. The preparation method according to claim 9, characterized in that, In the composite reinforcing agent, the content of thiourea is 30~70 wt.%.

11. The preparation method according to claim 1, characterized in that, The reinforcing agent B includes at least one of ammonium carbonate, sodium carbonate, ammonium bicarbonate, and carbon dioxide.

12. The preparation method according to claim 1, characterized in that, The reinforcing agent A is 0.5 to 3 times the weight of a section of charcoal, and the reinforcing agent B is 0.25 to 1.5 times the weight of a section of charcoal.

13. The preparation method according to claim 12, characterized in that, The reinforcing agent A is 1.5 to 2.5 times the weight of a section of charcoal, and the reinforcing agent B is 0.5 to 1 times the weight of a section of charcoal.

14. The preparation method according to claim 1, characterized in that, The solvent in the modified liquid includes water; In the modified solution, the concentration of reinforcing agent A is 10~100g / L; The pH of the modified solution is 5-8.

15. The preparation method according to claim 1, characterized in that, A section of carbon material is pre-quenched and then subjected to a second carbonization process. The pre-quenching process involves placing a section of carbon material in a modified liquid while it is still hot for pre-quenching; or, a section of carbon material is pre-quenched in water, followed by the addition of reinforcing agent A and reinforcing agent B. The initial temperature difference for cold quenching is above 300℃.

16. The preparation method according to claim 15, characterized in that, The initial temperature difference for cold quenching is 300~400℃.

17. The preparation method according to claim 1, characterized in that, The rotational speed during the ball milling stage is 350~650 r / min.

18. The preparation method according to claim 1, characterized in that, The mechanical enhancement stage is carried out in an auxiliary gas, which includes at least one of oxygen, air, and carbon dioxide.

19. The preparation method according to claim 1, characterized in that, The mechanical strengthening pressure is above 0.2 MPa.

20. The preparation method according to claim 1, characterized in that, The mechanical strengthening process consists of two stages. The first stage has a rotation speed of 350-400 r / min, a pressure of 0.2-0.3 MPa, and a time of 5-10 h. The second stage has a rotation speed of 450-600 r / min, a pressure of 0.3-1 MPa, and a time of 2-5 h.

21. The preparation method according to claim 1, characterized in that, The temperature for the second stage of carbonization is 650~750℃.

22. The preparation method according to claim 1, characterized in that, The second stage of carbonization takes 1 to 3 hours.

23. A biomass-based hard carbon active material prepared by the preparation method according to any one of claims 1 to 22.

24. The application of a biomass-based hard carbon active material prepared by the preparation method according to any one of claims 1 to 22, characterized in that, It was used as the negative electrode active material to prepare sodium-ion batteries.

25. A sodium-ion battery, characterized in that, It includes biomass-based hard carbon active materials prepared by the preparation method according to any one of claims 1 to 22.

26. The sodium-ion battery as described in claim 25, characterized in that, The negative electrode contains the aforementioned biomass-based hard carbon active material.

Images