A coffee grounds-based hard carbon material, a preparation method thereof and application thereof in a sodium electric negative electrode material

Abstract

The application discloses coffee residue-based hard carbon material and a preparation method and application thereof in sodium battery negative electrode materials, and relates to the field of sodium ion batteries. The preparation method of the coffee residue-based hard carbon material provided by the application firstly performs acid immersion and hydrothermal two-step pretreatment on coffee residue, and then performs calcination and alkali immersion, so that the coffee residue-based hard carbon material with excellent electrochemical performance is obtained, and the coffee residue-based hard carbon material can be applied to the preparation of sodium battery negative electrode materials. Specifically, the acid immersion-hydrothermal combined pretreatment mode in the application can retain the nitrogen element in the coffee residue raw material, so that the nitrogen element can be doped into the formed porous hard carbon material structure in the subsequent coffee residue calcination and carbonization process, and then the obtained hard carbon material has more abundant reaction active sites, and the electrochemical performance of the hard carbon material is improved.

Description

Technical Field

[0001] The present invention relates to the field of sodium ion batteries, and in particular to a coffee grounds-based hard carbon material, a preparation method thereof, and an application thereof in sodium battery negative electrode materials. Background Art

[0002] In recent years, new energy electric vehicles and related electronic products have developed rapidly. Among them, sodium-ion batteries are considered to be the next generation of energy storage devices that are expected to replace lithium-ion batteries due to their abundant reserves, low prices, and high safety. Some companies have already achieved mass production. At present, the negative electrode materials of sodium-ion batteries are mainly hard carbon materials, which can be roughly divided into fossil fuel-based, resin-based, and biomass-derived types. Fossil fuel-based materials are relatively low in cost, but soft carbon is easy to obtain and has a relatively low specific capacity. Resin-based hard carbon has high consistency and controllability, but is relatively expensive. Biomass-derived materials have unique microstructures and self-doping effects, are relatively low in cost, and have prospects for large-scale production and application.

[0003] Among the many biomass-derived hard carbon materials, hard carbon materials derived from coffee grounds are receiving increasing attention. The coffee consumption market has gradually expanded in recent years, but the vast majority of coffee grounds are discarded as domestic waste or directly incinerated, resulting in resource waste and environmental pollution. However, coffee grounds are a typical three-dimensional structural material that can provide shorter channels and more pore structures, which can accelerate the migration of ions and provide more reaction sites. How to use waste materials such as coffee grounds to prepare hard carbon materials suitable for sodium ion battery anodes, and then obtain sodium ion batteries with higher capacity and rate performance, is an urgent problem that needs to be solved. Summary of the Invention

[0004] In order to address the shortcomings of the existing technology, the present invention provides a method for preparing coffee grounds-based hard carbon materials. First, the coffee grounds are subjected to a two-step pre-treatment of acid leaching and hydrothermal treatment to fully remove impurities and deeply activate the coffee grounds. At the same time, the nitrogen element in the coffee grounds is retained, so that it can be doped into the porous hard carbon material structure formed by the coffee grounds during the subsequent carbonization process. As a result, the obtained hard carbon material has richer reaction active sites, thereby improving the electrochemical properties of the hard carbon material.

[0005] Another object of the present invention is to provide a coffee grounds-based hard carbon material.

[0006] Another object of the present invention is to provide a negative electrode material for a sodium ion battery.

[0007] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a coffee grounds-based hard carbon material comprises the following steps:

[0009] S1. Acid leaching: The coffee grounds are subjected to acid leaching, wherein the acid leaching is performed using an inorganic acid having a concentration of 5 to 30 wt %, and an acid leaching product is obtained after acid leaching;

[0010] S2 hydrothermal treatment: The acid leaching product obtained in step S1 is mixed with an inorganic acid having a concentration of 5 to 30 wt% and subjected to a hydrothermal reaction to obtain a hard carbon precursor;

[0011] S3 carbonization: The hard carbon precursor obtained in step S2 is calcined to obtain a carbonized product;

[0012] S4. Alkali leaching: The carbonized product obtained in step S3 is subjected to alkali leaching to obtain a coffee grounds-based hard carbon material.

[0013] The preparation method of coffee grounds-based hard carbon materials provided by the present invention adopts the combined method of acid leaching and hydrothermal treatment for the first time to pre-treat the coffee grounds, thereby achieving deep activation of the coffee grounds. Acid leaching can effectively remove inorganic components in the coffee grounds, and subsequent hydrothermal treatment can further release inorganic impurities inside the coffee grounds, which helps to form a porous structure during the high-temperature carbonization process, so that the obtained hard carbon has more reactive sites, thereby improving the electrochemical properties of the material. At the same time, the combined pre-treatment method of acid leaching and hydrothermal treatment in the present invention retains the nitrogen element in the coffee grounds, so that it can be doped into the porous hard carbon material structure formed by the coffee grounds during the subsequent carbonization process, thereby making the obtained hard carbon material have richer reactive sites, thereby improving the electrochemical properties of the hard carbon material.

[0014] After the carbonized product is obtained by calcination in step S3, the present invention further performs alkali leaching on the carbonized product to remove silicon dioxide in the material.

[0015] It should be noted that if the concentration of the inorganic acid in steps S1-2 of the present invention is too low, it will affect the removal effect of inorganic impurities, and thus affect the pore structure of the subsequent carbonization product; if the concentration of the inorganic acid is too high, the structure of the coffee grounds may be destroyed, resulting in the inability to obtain the expected product structure, and there will be a waste of resources, which will also increase the burden of post-reaction wastewater treatment.

[0016] It should be noted that in steps S1-2, it is only necessary to allow the coffee grounds or the acid-leached product to be immersed in the inorganic acid.

[0017] In a specific embodiment of the present invention, step S1 further includes washing the coffee grounds before acid leaching: washing the coffee grounds until the washing liquid is colorless and transparent, and then drying at 60°C to 100°C. The purpose of washing the coffee grounds before acid leaching is to remove surface scum, useless ash, and water-soluble impurities from the coffee grounds.

[0018] Preferably, the inorganic acid in step S1 includes at least one of hydrofluoric acid, hydrochloric acid, nitric acid, boric acid, and sulfuric acid.

[0019] In a specific embodiment of the present invention, the acid leaching in step S1 can be performed at 20°C to 60°C.

[0020] In a specific embodiment of the present invention, step S1 further comprises the steps of washing the acid leaching product with water until the washing liquid is colorless and transparent after acid leaching, and drying at 60° C. to 100° C.

[0021] Preferably, the acid leaching time in step S1 is 1 to 28 days.

[0022] More preferably, the acid leaching time in step S1 is 5 to 10 days.

[0023] When the acid leaching time is 1 to 28 days, especially 5 to 10 days, the electrochemical performance of the coffee grounds-based hard carbon material is superior. Longer or shorter acid leaching times can lead to a decrease in the electrochemical performance of the coffee grounds-based hard carbon material. Longer acid leaching times can damage the structure of the coffee grounds, leading to a decrease in electrochemical performance.

[0024] Preferably, the nitrogen content of the coffee grounds used in step S1 is 1-2%.

[0025] Coffee grounds contain approximately 1-2% nitrogen, primarily from inorganic components such as protein and caffeine. These inorganic components remain in the coffee grounds after the acid leaching and hydrothermal pretreatments described herein and are subsequently converted into nitrogen and doped into the hard carbon material after calcination.

[0026] Preferably, the hydrothermal temperature in step S2 is 100° C. to 200° C., and the hydrothermal time is 2 h to 12 h.

[0027] More preferably, the hydrothermal time in step S2 is 4 to 6 hours.

[0028] In a specific embodiment of the present invention, after the hydrothermal reaction in step S2 is completed, the steps of washing the product until the washing liquid is colorless and transparent and then drying are further included.

[0029] Preferably, the calcination in step S3 is performed in an inert atmosphere. Specifically, the inert atmosphere can be nitrogen or argon.

[0030] In a specific embodiment of the present invention, the calcination temperature in step S3 may be 600-2000° C., and the heating rate may be 2-10° C. / min.

[0031] Preferably, the calcination temperature in step S3 is 800-1700°C.

[0032] More preferably, the calcination temperature in step S3 is 1000-1400°C.

[0033] Preferably, the calcination time in step S3 is 2 to 15 hours.

[0034] More preferably, the calcination time in step S3 is 6 to 12 hours.

[0035] The calcination temperature and time affect the degree of graphitization of coffee ground-based hard carbon materials. Controlling the calcination time and temperature ensures that hard carbon is formed from coffee grounds while avoiding the formation of graphitized carbon. When the calcination temperature is increased to 800-1700°C and the calcination time is 2-15 hours, and especially when the calcination temperature reaches 1000-1400°C and the calcination time is 6-12 hours, the resulting hard carbon material has better electrochemical properties. However, when the calcination temperature is higher and the calcination time is too long, graphitized carbon may appear, affecting the performance of the hard carbon material.

[0036] Preferably, the alkali solution used in the alkali leaching in step S4 is an inorganic alkali solution with a concentration of 0.1 to 1 mol / L, and the inorganic alkali includes at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0037] In a specific embodiment of the present invention, the temperature of the alkali leaching in step S4 can be 20-60°C.

[0038] Preferably, the temperature of the alkali leaching in step S4 is 35-60°C.

[0039] Preferably, the alkali leaching time in step S4 is 9 to 24 hours.

[0040] In a specific embodiment of the present invention, after the alkali leaching in step S4, the process further includes washing and drying the product.

[0041] In a specific embodiment of the present invention, the N content of the coffee grounds-based hard carbon material obtained in step S4 is 1-3%.

[0042] The present invention also protects a coffee grounds-based hard carbon material prepared by the above-mentioned method for preparing a coffee grounds-based hard carbon material.

[0043] The present invention also provides a sodium ion battery negative electrode material, comprising the coffee grounds-based hard carbon material.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The method provided by the present invention is used to prepare coffee grounds-based hard carbon materials, which can fully remove impurities and deeply activate coffee grounds, and dope the nitrogen element contained in the raw coffee grounds into the structure of the subsequently formed hard carbon material. Therefore, the obtained material has excellent electrochemical properties and can reach a capacity of 179.8 mAh g when used in sodium batteries. -1The capacity retention rate after 200 cycles can reach more than 80.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a flow chart of the method for preparing the coffee grounds-based hard carbon material provided by the present invention.

[0047] Figure 2 This is the XRD pattern of the coffee grounds-based hard carbon material prepared in Example 2 of the present invention.

[0048] Figure 3 This is an SEM image of the coffee grounds-based hard carbon material prepared in Example 2 of the present invention.

[0049] Figure 4 This is the XPS graph of the coffee grounds-based hard carbon material prepared in Example 2 of the present invention.

[0050] Figure 5 The coffee grounds-based hard carbon material prepared in Example 2 of the present invention was heated to a current density of 0.1 A·g -1 The charge and discharge curves of the next cycle are 20 times.

[0051] Figure 6 This is a rate performance test diagram of the coffee grounds-based hard carbon material prepared in Examples 1 to 8 of the present invention.

[0052] Figure 7 This is a rate performance test diagram of the coffee grounds-based hard carbon materials prepared in Comparative Examples 1 to 7 of the present invention. DETAILED DESCRIPTION

[0053] The present invention will be further described below in conjunction with specific embodiments, but the examples do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the examples of the present invention are conventionally purchased raw materials and reagents. Among them, the raw material information used in each example and comparative example is as follows:

[0054] Coffee grounds: provided by Changzhou Kangruize Supply Chain Management Co., Ltd.

[0055] Example 1

[0056] A method for preparing a coffee grounds-based hard carbon material comprises the following steps:

[0057] S1. Acid leaching: Coffee grounds with a nitrogen content of 1-2% were washed with water until the washing liquid was colorless and transparent, dried at 80°C, and then acid-leached with a 10 wt% hydrochloric acid solution at 25°C for 7 days. The acid-leached product was washed with water until the washing liquid was colorless and transparent, and then dried at 80°C.

[0058] S2. Hydrothermal treatment: The acid leaching product obtained in step S1 was mixed with a 10 wt% hydrochloric acid solution so that the hydrochloric acid solution could submerge the acid leaching product. The reaction was carried out at 150 ° C for 6 h. After the reaction, the product was washed until the washing solution was colorless and transparent, and dried to obtain a hard carbon precursor.

[0059] S3 carbonization: the hard carbon precursor obtained in step S2 was calcined in an argon atmosphere at a heating rate of 5 ° C / min to 900 ° C for 2h to obtain a carbonized product after calcination;

[0060] S4. Alkali leaching: The carbonized product obtained in step S3 was immersed in a 0.5 mol / L sodium hydroxide solution at 40°C for 12 hours, and then washed and dried to obtain a coffee grounds-based hard carbon material with a nitrogen content of 2%.

[0061] Example 2

[0062] A method for preparing a coffee grounds-based hard carbon material, which differs from Example 1 only in that:

[0063] The calcination temperature in step S3 is 1300°C.

[0064] Example 3

[0065] A method for preparing a coffee grounds-based hard carbon material, which differs from Example 1 only in that:

[0066] The calcination temperature in step S3 is 1700°C.

[0067] Example 4

[0068] A method for preparing a coffee grounds-based hard carbon material, which differs from Example 1 only in that:

[0069] In step S3, the calcination temperature is 1100° C. and the calcination time is 6 h.

[0070] Example 5

[0071] A method for preparing a coffee grounds-based hard carbon material, which differs from Example 1 only in that:

[0072] In step S3, the calcination temperature is 1100° C. and the calcination time is 12 h.

[0073] Example 6

[0074] A method for preparing a coffee grounds-based hard carbon material, which differs from Example 2 only in that:

[0075] The acid leaching time in step S1 is 14 days.

[0076] Example 7

[0077] A method for preparing a coffee ground-based hard carbon material, wherein the only difference from Example 2 is that:

[0078] The acid immersion time in step S1 is 1 d.

[0079] Example 8

[0080] A method for preparing a coffee ground-based hard carbon material, wherein the only difference from Example 2 is that:

[0081] The hydrothermal time in step S2 is 12 h.

[0082] Comparative Example 1

[0083] A method for preparing a coffee ground-based hard carbon material, comprising the following steps:

[0084] S1. Carbonization: The coffee grounds are washed with water until the washing liquid is colorless and transparent, and then dried. The dried coffee grounds are calcined in an argon atmosphere at a temperature increasing rate of 5°C / min to 1300°C, and the calcination time is 2 h. A carbonized product is obtained after calcination.

[0085] S2. Alkali immersion: The carbonized product obtained in step S1 is soaked in a 40°C, 0.5 mol / L sodium hydroxide solution for alkali immersion treatment, and the alkali immersion time is 12 h. After alkali immersion, the product is washed and dried to obtain a coffee ground-based hard carbon material.

[0086] Comparative Example 2

[0087] A method for preparing a coffee ground-based hard carbon material, comprising the following steps:

[0088] S1. Acid immersion: The coffee grounds are washed with water until the washing liquid is colorless and transparent, and then dried. The dried coffee grounds are subjected to acid immersion treatment using a 10 wt% hydrochloric acid solution as the acid solution, and the acid immersion temperature is 25°C. The acid immersion time is 7 d. After acid immersion, the product is washed with water until the washing liquid is colorless and transparent, and then dried.

[0089] S2. Carbonization: The acid immersion product obtained in step S1 is calcined in an argon atmosphere at a temperature increasing rate of 5°C / min to 1300°C, and the calcination time is 2 h. A carbonized product is obtained after calcination.

[0090] S3. Alkali immersion: The carbonized product obtained in step S2 is soaked in a 40°C, 0.5 mol / L sodium hydroxide solution for alkali immersion treatment, and the alkali immersion time is 12 h. After alkali immersion, the product is washed and dried to obtain a coffee ground-based hard carbon material.

[0091] Comparative Example 3

[0092] A method for preparing a coffee ground-based hard carbon material, comprising the following steps:

[0093] S1. Hydrothermal treatment: Wash the coffee grounds with water until the washing liquid is colorless and transparent. After drying, mix the coffee grounds with a 10 wt% hydrochloric acid solution and hydrothermally react at 150°C for 6 h. After the reaction, wash the product until the washing liquid is colorless and transparent, and dry it to obtain a hard carbon precursor.

[0094] S2 carbonization: The acid leaching product obtained in step S1 was calcined in an argon atmosphere at a heating rate of 5 ° C / min to 1300 ° C for 2 hours to obtain a carbonized product after calcination;

[0095] S3. Alkali leaching: The carbonized product obtained in step S2 was immersed in a 0.5 mol / L sodium hydroxide solution at 40°C for 12 h, and then washed and dried to obtain a coffee grounds-based hard carbon material.

[0096] Comparative Example 4

[0097] A method for preparing a coffee grounds-based hard carbon material comprises the following steps:

[0098] S1. Acid leaching: The coffee grounds were washed with water until the washing liquid was colorless and transparent, and then dried and acid-leached with a 10 wt% hydrochloric acid solution at a temperature of 25°C for 14 days. The acid-leached product was washed with water until the washing liquid was colorless and transparent, and then dried.

[0099] S2. Alkali leaching: The acid leaching product obtained in step S1 was immersed in a 0.5 mol / L sodium hydroxide solution at 40 ° C for alkali leaching for 12 h. After alkali leaching, the product was washed and dried to obtain an alkali leaching product;

[0100] S3 hydrothermal treatment: The alkali leaching product obtained in step S2 was mixed with a 10wt% hydrochloric acid solution and subjected to a hydrothermal reaction at 150°C for 6h. After the reaction, the product was washed until the washing solution was colorless and transparent, and dried to obtain a hard carbon precursor;

[0101] S4. Carbonization: The hard carbon precursor obtained in step S3 was calcined in an argon atmosphere at a heating rate of 5°C / min to 1300°C for 2 h to obtain a coffee grounds-based hard carbon material.

[0102] Comparative Example 5

[0103] A method for preparing a coffee grounds-based hard carbon material comprises the following steps:

[0104] S1. Alkali leaching: Wash the coffee grounds with water until the washing liquid is colorless and transparent. After drying, soak the coffee grounds in a 0.5 mol / L sodium hydroxide solution at 40°C for 12 hours. The alkali-leached product is washed with water until the washing liquid is colorless and transparent, and then dried.

[0105] S2 hydrothermal treatment: The alkali leaching product obtained in step S1 was mixed with a 10wt% hydrochloric acid solution and subjected to a hydrothermal reaction at 150°C for 6h. After the reaction, the product was washed until the washing solution was colorless and transparent, and dried to obtain a hard carbon precursor;

[0106] S3 carbonization: the hard carbon precursor obtained in step S2 was calcined in an argon atmosphere at a heating rate of 5 ° C / min to 1300 ° C for 2h to obtain a carbonized product after calcination;

[0107] Comparative Example 6

[0108] A method for preparing a corncob powder-based hard carbon material, which differs from Example 2 only in that:

[0109] The raw coffee grounds in step S1 were replaced with corn cob powder.

[0110] Comparative Example 7

[0111] A method for preparing a coffee grounds-based hard carbon material, which differs from Example 2 only in that:

[0112] In step S2, the acid leaching product and deionized water are subjected to a hydrothermal reaction.

[0113] Performance Testing

[0114] Electrochemical Performance Testing: The hard carbon materials prepared in the Examples and Comparative Examples were dispersed with conductive carbon black and polyvinylidene fluoride in a solvent of N-methylpyrrolidone at a mass ratio of 8:1:1 to form a slurry. The slurry was then coated on copper foil and dried, cut into 12 mm discs for further assembly into button cells. CR2025 button cells were assembled in a high-purity argon atmosphere (water and oxygen contents were both below 10 ppm). The negative electrode was the hard carbon material disc prepared above, the counter electrode was a metallic sodium sheet, the separator was a Whatman glass fiber, and the electrolyte was a solution of 1 M sodium perchlorate dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1:1). The battery was sealed and allowed to stand at room temperature for 8 hours before electrochemical testing.

[0115] The performance test data is shown in Table 1. Figures 2 to 7 As shown:

[0116] Table 1. Capacity-related data of hard carbon materials obtained in Examples and Comparative Examples

[0117]

[0118]

[0119] As can be seen from Table 1 above, the coffee grounds-based hard carbon material prepared by the method provided by the present application has excellent electrochemical performance, and when applied to sodium electricity, the capacity can reach 161.7 mAh g -1 Above, the capacity retention rate after 200 cycles can also reach more than 76.3%. Among them, according to the data of Examples 1-5, it can be seen that when the calcination time is increased from 900°C (Example 1) to 1300°C (Example 2), and then to 1700°C (Example 3), the capacity first increases and then decreases, indicating that too high calcination temperature will also cause the performance of the hard carbon material to decrease, so the present application further preferably the calcination temperature is 1000-1400°C. When the calcination time is increased from 2h (Example 1) to 6h (Example 4) and then to 12h (Example 5), the capacity of the obtained hard carbon material has a certain increase, but the capacity retention rate does not show obvious differences, and considering the energy consumption and the increase range, the further preferred calcination time is 6-12h.

[0120] According to the data of Examples 1 and 6-7, it can be seen that when the acid immersion time is 7d (Example 1), the capacity and cycle capacity retention rate of the coffee grounds-based hard carbon material are significantly better than that of the hard carbon material obtained by acid immersion for 1d (Example 7); when the acid immersion time is further increased to 14d (Example 6), the electrochemical performance of the obtained hard carbon material decreases again, and it is speculated that too long acid immersion time may cause the coffee grounds-based structure to be destroyed. Based on this, the present application further preferably the acid immersion time is 5-10d.

[0121] According to the data of Examples 1 and 8, it can be seen that when the hydrothermal reaction time in step S2 is increased from 6h (Example 1) to 12h (Example 8), the electrochemical performance of the hard carbon material does not have obvious improvement, but the energy consumption is significantly increased, so the present application further preferably the hydrothermal time is 4-6h.

[0122] The data from Comparative Examples 1-5 demonstrate that the selection and order of the process steps in the method provided by the present invention are extremely critical. Comparative Examples 1-3, in which one of the acid leaching and hydrothermal pretreatment steps is omitted or no pretreatment is performed, respectively, yield hard carbon materials with significantly lower electrochemical capacities than those in the Examples. This demonstrates the superior performance of hard carbon obtained with a two-step pretreatment approach, highlighting the advantages of deep activation. The data from Comparative Examples 4-5 demonstrate that adjusting the order of acid leaching, hydrothermal treatment, calcination, and alkali washing can also affect material performance. For example, in Comparative Example 4, the performance of the material obtained with the acid leaching, alkali washing, hydrothermal treatment, and calcination treatment sequence is significantly lower than that of Example 2. The performance of the material obtained with the alkali washing, hydrothermal treatment, and calcination treatment in Comparative Example 5 is lower than that of both Examples 2 and Comparative Example 4, demonstrating the importance of acid leaching and the fact that the acid leaching step in the two-step pretreatment cannot be replaced by alkali washing. Furthermore, in Comparative Example 6, the treatment method is the same as in Example 2, but the raw material is changed to corncobs. Its rate performance is not only far lower than that of Example 2, but also lacks advantages compared to Comparative Examples 1-3, demonstrating the criticality of raw material selection. In addition, the hydrothermal reaction medium in Example 2 was changed to pure water (Comparative Example 7), and its performance was inferior to that of Example 2, which shows the importance of the selection of hydrothermal reaction medium.

[0123] Figure 2 This is the XRD pattern of the coffee grounds-based hard carbon material prepared in Example 2 of the present invention. Figure 2 As shown, the broad peaks at 22° and 43° correspond to the (002) and (100) crystal planes of hard carbon, indicating that hard carbon materials can be obtained by the preparation method of the present invention.

[0124] Figure 3 This is a SEM image of the coffee grounds-based hard carbon material prepared in Example 2 of the present invention. Figure 3 This SEM image confirms that the hard carbon material prepared in the present invention has a porous structure.

[0125] Figure 4 This is the XPS graph of the coffee grounds-based hard carbon material prepared in Example 2 of the present invention. Figure 4 It can be seen that the main elements in the hard carbon material prepared by the present invention are C, N, and O, among which the content of N is relatively small and is contained in the coffee grounds raw material, and is still retained after a series of treatments.

[0126] Figure 5 The coffee grounds-based hard carbon material prepared in Example 2 of the present invention was heated to a current density of 0.1 A·g -1 The charge-discharge curve at the time of 20 cycles shows that the hard carbon material of the present invention has a long voltage platform at around 0.1V. This phenomenon is the characteristic data of hard carbon, and it can also be confirmed that the material prepared by the present invention is a hard carbon material.

[0127] Figure 6This is a rate performance test diagram of coffee grounds-based hard carbon materials prepared in Examples 1 to 7 and Comparative Example 8 of the present invention. Figure 7 This is a rate performance test diagram of coffee grounds-based hard carbon materials prepared in Comparative Examples 1 to 7 of the present invention. Figure 6 and Figure 7 It can be seen that by using the method provided in the embodiment of the present invention to prepare coffee grounds-based hard carbon material, the rate performance of the obtained material is significantly improved.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a coffee grounds-based hard carbon material, characterized in that: The steps include: S1. Acid leaching: The coffee grounds are subjected to acid leaching, wherein the acid solution used in the acid leaching is an inorganic acid having a concentration of 5 to 30 wt %, and an acid leaching product is obtained after acid leaching; S2 hydrothermal treatment: The acid leaching product obtained in step S1 is mixed with an inorganic acid having a concentration of 5 to 30 wt% and subjected to a hydrothermal reaction to obtain a hard carbon precursor; S3 carbonization: The hard carbon precursor obtained in step S2 is calcined to obtain a carbonized product; S4 alkali leaching: The carbonized product obtained in step S3 was subjected to alkali leaching to obtain a coffee grounds-based hard carbon material after alkali leaching; The inorganic acid in step S1 is hydrochloric acid; the acid leaching time is 5-10 days; The inorganic acid in step S2 is hydrochloric acid, the temperature of the hydrothermal reaction is 100° C. to 200° C., and the time is 4 h to 6 h.

2. The method for preparing coffee grounds-based hard carbon material according to claim 1, wherein: The nitrogen content of the coffee grounds used in step S1 is 1-2%.

3. The method for preparing coffee grounds-based hard carbon material according to claim 1, wherein: The calcination in step S3 is carried out in an inert atmosphere at a temperature of 800 to 1700° C. for 2 to 15 hours.

4. The method for preparing coffee grounds-based hard carbon material according to claim 1, wherein: The alkali solution used in the alkali leaching in step S4 is an inorganic alkali solution with a concentration of 0.1 to 1 mol / L, and the inorganic alkali includes at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate.

5. The method for preparing coffee grounds-based hard carbon material according to claim 1, wherein: The temperature of the alkali leaching in step S4 is 35-60°C.

6. A coffee grounds-based hard carbon material prepared by the method for preparing a coffee grounds-based hard carbon material according to any one of claims 1 to 5.

7. A sodium ion battery negative electrode material, characterized in that The method comprises the coffee grounds-based hard carbon material according to claim 6.

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