Biomass-based hard carbon negative electrode material with high specific capacity and high magnification as well as preparation method and application of biomass-based hard carbon negative electrode material

Abstract

The invention discloses a biomass-based hard carbon negative electrode material with high specific capacity and high magnification as well as a preparation method and application of the biomass-based hard carbon negative electrode material. The method comprises the following steps: pretreating lignocellulose biomass by a hot pressing method, and carbonizing in a protective gas atmosphere to obtain the hard carbon material. A hot-pressing pretreatment process adopted by the invention can decompose part of hemicellulose to obtain a precursor rich in lignin and cellulose, so that the thermal stability of the material is improved. In the process, the lignin can effectively inhibit the rapid centralized pyrolysis of the cellulose and weaken the rearrangement of the pyrolysis product of the cellulose. The method not only helps to prevent overgrowth of hard carbon graphite microcrystals during high-temperature carbonization, but also promotes generation of a small-size closed-pore structure, so that the microstructure of the hard carbon material is optimized. The hard carbon material shows high specific capacity and excellent rate capability when being applied to a sodium-ion battery negative electrode. The method has the advantages of simplicity in operation, low requirements on equipment, no need of adding chemical reagents, greenness, environmental protection and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a biomass-based hard carbon anode material with high specific capacity and high rate, and a preparation method and application thereof. Background Art

[0002] With the continuous expansion of the grid-connected scale of renewable energy, the development of large-scale energy storage technologies with low cost and high safety has become the core requirement for the construction of smart grids. Lithium-ion batteries have become the most representative electrochemical energy storage technology due to their high energy density, excellent cycle performance, and long cycle life. However, the limited global lithium resource reserves and uneven geographical distribution have led to high costs of lithium-ion batteries, making it difficult to meet the economic requirements of large-scale electrochemical energy storage. In contrast, sodium resources have shown significant advantages due to their rich reserves, wide distribution, and low cost, making sodium-ion batteries the most promising alternative to lithium-ion batteries. However, the performance of sodium-ion battery anode materials remains the key bottleneck restricting their commercial application.

[0003] Hard carbon materials, due to their unique disordered graphite-like microcrystalline structure, large interlayer spacing (0.37 - 0.4 nm), and abundant nanoporous structure, provide sufficient storage sites for sodium ions. Based on these characteristics, hard carbon exhibits advantages such as high reversible capacity (200 - 400 mAh g -1 ) and long cycle life, and has become one of the most promising anode materials for sodium-ion batteries. Currently, the precursors of hard carbon materials mainly include three categories: pitch-based, resin-based, and biomass-based. Pitch-based precursors are difficult to obtain high-performance hard carbon anode materials due to their relatively high volatile content and high graphitization degree, and their preparation processes have not been optimized; resin-based precursors are difficult to achieve large-scale production due to their high costs; in contrast, biomass precursors have become the most ideal precursor choice for hard carbon materials due to their wide sources, low costs, and environmental friendliness.

[0004] Lignocellulosic biomass mainly comes from plant tissues. Currently, lignocellulosic biomass such as bamboo, straw, and coconut shells has been widely used to prepare various carbon materials due to their renewability and low cost. They are potential precursors for hard carbon electrode materials. However, due to the complex composition and structure of lignocellulosic biomass, complex interactions occur during the pyrolysis carbonization process, which leads to difficult control of the structure of the directly carbonized hard carbon materials, usually with a narrow interlayer spacing and a small closed pore volume. This severely restricts the improvement of their specific capacity and rate performance. Therefore, it is very necessary to pretreat lignocellulosic biomass and regulate its pyrolysis carbonization process to prepare hard carbon materials with high specific capacity and high rate performance.

[0005] The literature (Advanced Energy Materias 2019, 9, 1902852) reported a method to increase the closed pore volume of hard carbon materials by pre-carbonization and high-temperature carbonization. The hard carbon prepared by pre-carbonizing at 800 °C and high-temperature carbonizing at 1600 °C from cork stoppers has the largest closed pore volume, reaching 0.29 cm 3 g -1 . This increased its plateau capacity from 160 mAh g -1 significantly to 231 mAh g -1 , and the total capacity also increased significantly from 256 mAh g -1 to 358 mAh g -1 . However, the excessively high carbonization temperature results in too large closed pore diameters (4.5 nm), which leads to poor rate performance. When the current density is 2000 mA g -1 , the total capacity is only about 100 mAh g -1 , and the capacity retention rate is about 27.9%.

[0006] Chinese Patent Application CN117963885A discloses a method for preparing hard carbon materials by pre-oxidation crosslinking combined with low-temperature alkali etching and its application. This method first impregnates biomass in an alkali solution, and then directly performs low-temperature pre-oxidation in an air atmosphere at 150 - 300 °C without washing. This process promotes the shrinkage and crosslinking of the material at low temperature and etches and creates pores in the biomass. Finally, the precursor powder obtained by pre-oxidation is mixed with asphalt and high-temperature carbonized to obtain hard carbon materials. The hard carbon materials prepared by this method have a total capacity of 305 mAh g -1 at 0.1C, and still have a total capacity of 260 mAh g -1 at 5C, and the capacity retention rate is as high as 85%. However, the production process of this method is relatively complex and requires the use of alkali solutions such as sodium hydroxide solution or potassium hydroxide solution, which has problems of high production cost and environmental unfriendliness and is not conducive to large-scale industrial production.

[0007] Chinese Patent Application CN118894521A discloses a method for preparing hard carbon materials by thermomechanical coupling. This method first pre-carbonizes the biomass precursor at 200 - 400 °C, and then uses the coupling effect of the thermal field and force field in hot-press carbonization to prepare hard carbon materials with high tap density. The hard carbon materials prepared by this invention have good electrochemical performance, with a total capacity of 331.9 mAh g -1 at 0.1C, and still 143.5 mAh g -1 at 5C. However, this method requires applying pressure and heating for carbonization to the pre-carbonized biomass precursor in a vacuum environment. The production process is complex and requires high equipment requirements, which is also not conducive to large-scale industrial applications.

[0008] The above method for preparing hard carbon materials with high specific capacity and high rate is difficult to simultaneously meet the industrial production indicators such as low cost, simple production process, and environmental friendliness. Therefore, it is very meaningful to seek a simple, efficient, low-energy-consuming, and green pretreatment method to selectively regulate the composition and structure of biomass to prepare hard carbon materials with high specific capacity and high rate. Summary of the Invention

[0009] To solve the disadvantages and deficiencies of the prior art, the primary object of the present invention is to provide a method for preparing hard carbon materials with high specific capacity and high rate by pretreating lignocellulosic biomass precursors by a hot pressing method.

[0010] The present invention selects lignocellulosic biomass (such as bamboo powder, pine wood powder, corn cob, and coconut shell powder, etc.) as the hard carbon precursor, and removes hemicellulose with relatively low thermal stability through a simple hot pressing method, thereby making the combination between components closer. In addition, by regulating the composite structure of the three components (cellulose, lignin, and hemicellulose) in lignocellulosic biomass, the interaction between lignin and hemicellulose is significantly weakened, enabling lignin to more effectively inhibit the rapid and concentrated pyrolysis of cellulose and suppress the excessive rearrangement of pyrolysis products. The hard carbon prepared by this method has a large interlayer spacing, a small crystallite size, a large closed pore volume, and a small closed pore aperture. These structural features endow the prepared lignocellulosic biomass-based hard carbon materials with high specific capacity and excellent rate performance.

[0011] Another object of the present invention is to provide a biomass-based hard carbon negative electrode material with high specific capacity and high rate prepared by the above preparation method.

[0012] Another object of the present invention is to provide the application of the above biomass-based hard carbon negative electrode material with high specific capacity and high rate in sodium ion batteries.

[0013] The object of the present invention is achieved through the following technical solutions:

[0014] A method for preparing a biomass-based hard carbon negative electrode material with high specific capacity and high rate, comprising the following steps:

[0015] (1) Thermally pressing the biomass material at 100 - 250 °C and 10 - 40 MPa to obtain a hard carbon precursor;

[0016] (2) Carbonizing the hard carbon precursor in an inert gas atmosphere to obtain a biomass-based hard carbon negative electrode material.

[0017] Preferably, the biomass material in step (1) is at least one of bamboo powder, pine wood powder, corn cob, and coconut shell powder; more preferably, it is at least one of bamboo powder and coconut shell powder.

[0018] Preferably, the time of the hot pressing treatment in step (1) is 0.5 to 4 h; more preferably 1 to 4 h.

[0019] Preferably, the temperature of the hot pressing in step (1) is 100 to 200 °C, and the hot pressing pressure is 5 to 15 MPa; further preferably, the temperature of the hot pressing is 150 °C and the hot pressing pressure is 15 MPa.

[0020] Preferably, the inert gas in step (2) is at least one of noble gases and nitrogen; the noble gas is at least one of argon and helium.

[0021] Preferably, the flow rate of the inert gas in step (2) is 40 to 80 mL min -1 ; more preferably 60 mL min -1 .

[0022] Preferably, the temperature of the carbonization in step (2) is 1100 to 1500 °C, and the time is 0.5 to 8 h; more preferably, carbonization is carried out at 1100 to 1300 °C for 2 to 6 h; most preferably, carbonization is carried out at 1300 °C for 4 h.

[0023] Preferably, the heating rate of the carbonization in step (2) is 1 to 10 °C min -1 ; more preferably 5 °C min -1 .

[0024] A biomass-based hard carbon anode material with high specific capacity and high rate prepared by the above preparation method.

[0025] Application of the above biomass-based hard carbon anode material with high specific capacity and high rate in sodium-ion batteries.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] (1) The present invention uses natural lignocellulosic biomass as the hard carbon precursor and directly prepares the hard carbon precursor by the hot pressing method. This method has a simple preparation process, does not require the introduction of any chemical additives, and is easy to realize industrial application.

[0028] (2) In the lignocellulosic biomass precursor after hot pressing in the present invention, the content of hemicellulose is significantly reduced, while the proportion of lignin and cellulose is significantly increased, and the combination between components is closer. This structural change significantly improves the thermal stability of the precursor, enables lignin to effectively inhibit the rapid and concentrated pyrolysis of cellulose, and thus weakens the rearrangement of pyrolysis products. This characteristic helps to prevent the excessive growth of hard carbon graphite microcrystals during the high-temperature carbonization process, and thus is beneficial to the formation of a larger interlayer spacing and abundant small-sized closed pores in the hard carbon material.

[0029] (3) The hard carbon material prepared by the hot pressing method of the present invention has a large interlayer spacing, a large closed pore volume, and a small closed pore aperture. Among them, the large interlayer spacing provides a channel for the rapid diffusion of sodium ions, the large closed pore volume increases the sodium storage active sites, and the small closed pore aperture reduces the energy barrier that needs to be overcome during the sodium ion filling process. Therefore, the hard carbon negative electrode material prepared by the hot pressing method exhibits high specific capacity and excellent rate performance, and has high commercial value. Description of the Drawings

[0030] Figure 1 It is a diagram showing the proportion of three elements (cellulose, lignin, and hemicellulose) of the hard carbon precursor after hot pressing pretreatment for Example 1, Example 2, Example 3, Example 4, and Comparative Example 1.

[0031] Figure 2 It is an XRD diagram of the lignocellulosic biomass-based hard carbon materials prepared in Example 1 and Comparative Example 1.

[0032] Figure 3 It is a SAXS diagram of the lignocellulosic biomass-based hard carbon materials prepared in Example 1 and Comparative Example 1.

[0033] Figure 4 It is the second charge-discharge diagram of the carbon materials prepared in Example 1 and Comparative Example 1 as the negative electrode of a sodium-ion battery at a current density of 50 mA g -1 -1.

[0034] Figure 5 It is the rate performance diagram of the hard carbon prepared in Example 1 and Comparative Example 1 as the negative electrode of a sodium-ion battery at different current densities (50 - 1000 mA g -1 -1).

[0035] Figure 6 It is the cycle performance diagram of the hard carbon prepared in Example 1 as the negative electrode of a sodium-ion battery at a current density of 1000 mA g -1 -1. Detailed Embodiments

[0036] The present invention will be further described in detail below with reference to the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0037] For those conditions not specified in the embodiments of the present invention, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The raw materials, reagents, etc. used without indicating the manufacturer can be obtained as conventional products through commercial purchase.

[0038] Example 1

[0039] (1) Place 5 g of bamboo powder in a hot press, hot press at 150 °C for 2 h, and the hot press pressure is 15 MPa to obtain the hard carbon precursor B-150-2-15.

[0040] (2) The hard carbon precursor in step (1) is in a nitrogen atmosphere with a gas flow rate of 60 mL / min -1 and is heated to 1300 °C at a heating rate of 5 °C / min -1 for pyrolytic carbonization for 4 h to obtain a hard carbon material named BHC-150-2-15-1300.

[0041] Example 2

[0042] (1) Place 5 g of bamboo powder in a hot press and hot press it at 100 °C for 2 h with a hot pressing pressure of 15 MPa to obtain a hard carbon precursor B-100-2-15.

[0043] (2) The hard carbon precursor in step (1) is in a nitrogen atmosphere with a gas flow rate of 60 mL / min -1 and is heated to 1300 °C at a heating rate of 5 °C / min -1 for pyrolytic carbonization for 4 h to obtain a hard carbon material named BHC-100-2-15-1300.

[0044] Example 3

[0045] (1) Place 5 g of bamboo powder in a hot press and hot press it at 200 °C for 2 h with a hot pressing pressure of 15 MPa to obtain a hard carbon precursor B-200-2-15.

[0046] (2) The hard carbon precursor in step (1) is in a nitrogen atmosphere with a gas flow rate of 60 mL / min -1 and is heated to 1300 °C at a heating rate of 5 °C / min -1 for pyrolytic carbonization for 4 h to obtain a hard carbon material named BHC-200-2-15-1300.

[0047] Example 4

[0048] (1) Place 5 g of bamboo powder in a hot press and hot press it at 150 °C for 1 h with a hot pressing pressure of 15 MPa to obtain a hard carbon precursor B-150-1-15.

[0049] (2) The hard carbon precursor in step (1) is in a nitrogen atmosphere with a gas flow rate of 60 mL / min -1 and is heated to 1300 °C at a heating rate of 5 °C / min -1 for pyrolytic carbonization for 4 h to obtain a hard carbon material named BHC-150-1-15-1300.

[0050] Example 5

[0051] (1) Place 5 g of bamboo powder in a hot press and hot press it at 150 °C for 4 h under a hot press pressure of 15 MPa to obtain a hard carbon precursor B-150-4-15.

[0052] (2) The hard carbon precursor in step (1) is pyrolyzed and carbonized at a heating rate of 5 °C / min to 1300 °C for 4 h in a nitrogen atmosphere with a gas flow rate of 60 mL / min to obtain a hard carbon material named BHC-150-4-15-1300. -1 under a heating rate of 5 °C / min -1 to obtain a hard carbon material named BHC-150-4-15-1300.

[0053] Example 6

[0054] (1) Place 5 g of pine powder in a hot press and hot press it at 150 °C for 2 h under a hot press pressure of 15 MPa to obtain a hard carbon precursor C-150-2-15.

[0055] (2) The hard carbon precursor in step (1) is pyrolyzed and carbonized at a heating rate of 5 °C / min to 1300 °C for 4 h in a nitrogen atmosphere with a gas flow rate of 60 mL / min to obtain a hard carbon material named CHC-150-2-15-1300. -1 under a heating rate of 5 °C / min -1 to obtain a hard carbon material named CHC-150-2-15-1300.

[0056] Example 7

[0057] (1) Place 5 g of corncob in a hot press and hot press it at 150 °C for 2 h under a hot press pressure of 15 MPa to obtain a hard carbon precursor D-150-2-15.

[0058] (2) The hard carbon precursor in step (1) is pyrolyzed and carbonized at a heating rate of 5 °C / min to 1300 °C for 4 h in a nitrogen atmosphere with a gas flow rate of 60 mL / min to obtain a hard carbon material named DHC-150-2-15-1300. -1 under a heating rate of 5 °C / min -1 to obtain a hard carbon material named DHC-150-2-15-1300.

[0059] Example 8

[0060] (1) Place 5 g of coconut shell powder in a hot press and hot press it at 150 °C for 2 h under a hot press pressure of 15 MPa to obtain a hard carbon precursor E-150-2-15.

[0061] (2) The hard carbon precursor in step (1) is pyrolyzed and carbonized at a heating rate of 5 °C / min to 1300 °C for 4 h in a nitrogen atmosphere with a gas flow rate of 60 mL / min to obtain a hard carbon material named EHC-150-2-15-1300. -1 under a heating rate of 5 °C / min -1 to obtain a hard carbon material named EHC-150-2-15-1300.

[0062] Example 9

[0063] (1) Place 5 g of bamboo powder in a hot press and hot press it at 150 °C for 2 h under a hot pressing pressure of 15 MPa to obtain a hard carbon precursor B-150-2-15.

[0064] (2) The hard carbon precursor obtained in step (1) is pyrolyzed and carbonized at a heating rate of 5 °C min -1 under a nitrogen atmosphere with a gas flow rate of 60 mL min -1 to 1100 °C for 4 h to obtain a hard carbon material named BHC-150-2-15-1100.

[0065] Example 10

[0066] (1) Place 5 g of bamboo powder in a hot press and hot press it at 150 °C for 2 h under a hot pressing pressure of 15 MPa to obtain a hard carbon precursor B-150-2-15.

[0067] (2) The hard carbon precursor obtained in step (1) is pyrolyzed and carbonized at a heating rate of 5 °C min -1 under a nitrogen atmosphere with a gas flow rate of 60 mL min -1 to 1500 °C for 4 h to obtain a hard carbon material named BHC-150-2-15-1500.

[0068] Comparative Example 1

[0069] Take 5 g of bamboo powder (without any treatment) and pyrolyze and carbonize it at a heating rate of 5 °C min -1 under a nitrogen atmosphere with a gas flow rate of 60 mL min -1 to 1300 °C for 4 h to obtain a hard carbon material named BHC-1300.

[0070] Comparative Example 2

[0071] (1) Place 5 g of bamboo powder in a hot press and hot press it at 150 °C for 2 h under a hot pressing pressure of 0 MPa to obtain a hard carbon precursor B-150-2-0.

[0072] (2) The hard carbon precursor obtained in step (1) is pyrolyzed and carbonized at a heating rate of 5 °C min -1 under a nitrogen atmosphere with a gas flow rate of 60 mL min -1 to 1300 °C for 4 h to obtain a hard carbon material named BHC-150-2-0-1300.

[0073] Comparative Example 3

[0074] (1) Place 5 g of bamboo powder in a hot press and hot press it at 150 °C for 2 h under a hot pressing pressure of 50 MPa to obtain a hard carbon precursor B-150-2-50.

[0075] (2) The hard carbon precursor in step (1) is under a nitrogen atmosphere with a gas flow rate of 60 mL / min -1 and is heated to 1300 °C at a heating rate of 5 °C / min -1 for pyrolytic carbonization for 4 h to obtain a hard carbon material named BHC-150-2-50-1300.

[0076] Comparative Example 4

[0077] (1) 5 g of bamboo powder is placed in a hot press and hot pressed at 300 °C for 2 h under a hot pressing pressure of 15 MPa to obtain a hard carbon precursor B-300-2-15.

[0078] (2) The hard carbon precursor in step (1) is under a nitrogen atmosphere with a gas flow rate of 60 mL / min -1 and is heated to 1300 °C at a heating rate of 5 °C / min -1 for pyrolytic carbonization for 4 h to obtain a hard carbon material named BHC-300-2-15-1300.

[0079] Comparative Example 5

[0080] (1) 5 g of bamboo powder is under a nitrogen atmosphere with a gas flow rate of 60 mL / min -1 and is heated to 600 °C at a heating rate of 5 °C / min -1 for pyrolytic carbonization for 2 h to obtain a pre-carbonized precursor.

[0081] (2) The pre-carbonized precursor in step (1) is placed in a hot press and hot pressed at 150 °C for 2 h under a hot pressing pressure of 15 MPa to obtain a hard carbon precursor pre-B-150-2-15.

[0082] (3) The hard carbon precursor in step (2) is under a nitrogen atmosphere with a gas flow rate of 60 mL / min -1 and is heated to 1300 °C at a heating rate of 5 °C / min -1 for pyrolytic carbonization for 4 h to obtain a hard carbon material named pre-BHC-150-2-15-1300.

[0083] Comparative Example 6

[0084] (1) 5 g of bamboo powder is placed in a hot press and hot pressed at 150 °C for 2 h under a hot pressing pressure of 15 MPa to obtain a hard carbon precursor B-150-2-15.

[0085] (2) The hard carbon precursor in step (1) is under a nitrogen atmosphere with a gas flow rate of 60 mL / min -1 and is heated to 1000 °C at a heating rate of 5 °C / min -1 for pyrolytic carbonization for 4 h to obtain a hard carbon material named BHC-150-2-15-1000.

[0086] Comparative Example 7

[0087] (1) Place 5 g of bamboo powder in a hot press and hot press at 150 °C for 2 h under a hot press pressure of 15 MPa to obtain a hard carbon precursor B-150-2-15.

[0088] (2) The hard carbon precursor from step (1) is pyrolyzed and carbonized at a heating rate of 5 °C / min to 1600 °C for 4 h in a nitrogen atmosphere with a gas flow rate of 60 mL / min to obtain a hard carbon material named BHC-150-2-15-1600. -1 under a heating rate of 5 °C / min -1 to obtain a hard carbon material named BHC-150-2-15-1600.

[0089] Comparative Example 8

[0090] Take 5 g of pine wood powder (without any classification treatment) and pyrolyze and carbonize it at a heating rate of 5 °C / min to 1300 °C for 4 h in a nitrogen atmosphere with a gas flow rate of 60 mL / min to obtain a hard carbon material named CHC-1300. -1 under a heating rate of 5 °C / min -1 to obtain a hard carbon material named CHC-1300.

[0091] Comparative Example 9

[0092] Take 5 g of corncob (without any classification treatment) and pyrolyze and carbonize it at a heating rate of 5 °C / min to 1300 °C for 4 h in a nitrogen atmosphere with a gas flow rate of 60 mL / min to obtain a hard carbon material named DHC-1300. -1 under a heating rate of 5 °C / min -1 to obtain a hard carbon material named DHC-1300.

[0093] Comparative Example 10

[0094] Take 5 g of coconut shell powder (without any classification treatment) and pyrolyze and carbonize it at a heating rate of 5 °C / min to 1300 °C for 4 h in a nitrogen atmosphere with a gas flow rate of 60 mL / min to obtain a hard carbon material named EHC-1300. -1 under a heating rate of 5 °C / min -1 to obtain a hard carbon material named EHC-1300.

[0095] The specific preparation method of the negative electrode material and the sodium ion battery includes the following steps:

[0096] Place the hard carbon material in an 80 °C drying oven and dry for 12 h. Mix the hard carbon material, conductive carbon black, and sodium polyacrylate in a mass ratio of 8:1:1, grind evenly, coat it on a copper foil, and place it in an 80 °C vacuum drying oven and dry for 12 h to obtain a pole piece. Assemble the battery in a glove box under argon protection, and the electrolyte is a 1 mol / L -1 ethylene glycol dimethyl ether solution of NaPF6, and a sodium metal sheet is used as the counter electrode.

[0097] Figure 1 It is a diagram showing the proportion of three elements (cellulose, lignin, and hemicellulose) in the hard carbon precursor after hot pressing pretreatment in Example 1, Example 2, Example 3, Example 4, and Comparative Example 1 of the present invention. As can be seen from the figure, a part of hemicellulose is removed by hot pressing, and the proportions of cellulose and lignin increase, demonstrating that hot pressing has the effect of regulating the components and structure of biomass.

[0098] Figure 2 It is an XRD diagram of the carbon materials prepared in Example 1 and Comparative Example 1. Compared with the carbon materials in Comparative Examples 1 and 2, the hard carbon in Example 1 has a larger interlayer spacing, facilitating the rapid transport of sodium ions. This may be because hot pressing can remove hemicellulose with low thermal stability, making the connection between components denser; it changes the composite structure of the three elements in bamboo powder, weakens the interaction between lignin and hemicellulose, so that lignin can better inhibit the pyrolysis and carbonization process of cellulose and suppress its excessive graphitization during high-temperature carbonization.

[0099] Figure 3 It is a SAXS diagram of the hard carbons prepared in Example 1 and Comparative Example 1. As Figure 3 shown, the shoulder peak of the SAXS curve of the hard carbon in Example 1 is more obvious at , indicating that it has a larger closed pore volume. This is because its smaller graphite microcrystals are more conducive to the formation of closed pores. At the same time, through fitting with the Teubner-Strey model, it is found that the hard carbon prepared in Example 1 has a smaller closed pore diameter (1.72 nm), which is significantly smaller than that of the hard carbon prepared in Comparative Example 1 (2.12 nm).

[0100] Figure 4 Shows the second charge-discharge performance of the carbon materials prepared in Example 1 and Comparative Example 1 as the negative electrode of a sodium-ion battery at a current density of 50 mA g -1 From the figure, it can be seen that the hard carbon negative electrode prepared in Example 1 exhibits a higher specific capacity, reaching 346 mAh g -1 , among which the plateau capacity is 234 mAh g -1 . Compared with Comparative Example 1, the plateau capacity of Example 1 increases by 51 mAh g -1 , and the total capacity increases by 72 mAh g -1 . This significant performance improvement is attributed to the fact that the hard carbon material in Example 1 has a larger closed pore volume, thus providing more filling sites for sodium ions and significantly enhancing its plateau capacity and total capacity.

[0101] Figure 5 Shows the rate performance of the hard carbon materials prepared in Example 1 and Comparative Example 1 as the negative electrode of a sodium-ion battery at different current densities. The hard carbon negative electrode prepared in Example 1 exhibits excellent rate performance, at 5000 mA g -1can still maintain 215 mAh g at a high current density -1 The specific capacity, and the capacity retention rate reaches 62%. In contrast, the specific capacity of the hard carbon negative electrode of Comparative Example 1 is only 53 mAh g-1 at the same current density, and the capacity retention rate is 19%. The reason why the hard carbon negative electrode of Example 1 can achieve such excellent rate performance is mainly attributed to its larger interlayer spacing, which provides a faster diffusion channel for sodium ions, and at the same time, the smaller closed pore diameter reduces the energy barrier that needs to be overcome during the sodium ion filling process.

[0102] Figure 6 is the cycle performance graph of the hard carbon prepared in Example 1 as the negative electrode of a sodium ion battery at a current density of 1000 mA g -1 The hard carbon negative electrode shows good cycle stability and can still retain 96% of the initial capacity after 1500 cycles. This benefits from the larger interlayer spacing of the hard carbon negative electrode, which can buffer the volume change of the carbon layer caused by the insertion and extraction of sodium ions, thus showing stable sodium storage performance.

[0103] Table 1 shows the comparison of the hard carbon materials prepared in the above examples and the hard carbon materials prepared in the above comparative examples in terms of specific capacity, plateau capacity (50 mA g -1 ), and rate performance, etc. Among them, the capacity retention rate is the ratio of the specific capacity at 5000 mA g -1 to the specific capacity at 50 mA·g -1 .

[0104] Table 1

[0105]

[0106]

[0107] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing a biomass-based hard carbon negative electrode material, characterized in that: The following steps are involved: (1) hot pressing the biomass material at 100-250° C. and 10-40 MPa to obtain a hard carbon precursor; (2) Carbonizing the hard carbon precursor in an inert gas atmosphere to obtain a biomass-based hard carbon negative electrode material.

2. The method for preparing a biomass-based hard carbon negative electrode material according to claim 1, characterized in that: The time of the hot pressing treatment in step (1) is 0.5 to 4 hours; And / or, the biomass material in step (1) is at least one of bamboo powder, pine wood powder, corn cob and coconut shell powder.

3. The method for preparing a biomass-based hard carbon negative electrode material according to claim 2, characterized in that: The time of the hot pressing treatment in step (1) is 1 to 4 hours; And / or, the biomass material in step (1) is at least one of bamboo powder and coconut shell powder.

4. The method for preparing a biomass-based hard carbon negative electrode material according to claim 1 or 2, characterized in that: The carbonization temperature in step (2) is 1100-1500° C. and the time is 0.5-8 h; And / or, the heating rate of the carbonization in step (2) is 1-10°C min -1 .

5. The method for preparing a biomass-based hard carbon negative electrode material according to claim 4, characterized in that: The carbonization temperature in step (2) is 1100-1300° C. and the time is 2-6 hours.

6. The method for preparing a biomass-based hard carbon negative electrode material according to claim 1 or 2, characterized in that: The hot pressing temperature in step (1) is 100-200° C., and the hot pressing pressure is 5-15 MPa.

7. The method for preparing a biomass-based hard carbon negative electrode material according to claim 6, characterized in that: The hot pressing temperature in step (1) is 150° C. and the hot pressing pressure is 15 MPa.

8. The method for preparing a biomass-based hard carbon negative electrode material according to claim 1 or 2, characterized in that: The inert gas in step (2) is at least one of a rare gas and nitrogen; And / or, the rare gas is at least one of argon and helium; And / or, the inert gas flow rate in step (2) is 40-80 mL min -1 .

9. A biomass-based hard carbon negative electrode material obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the biomass-based hard carbon negative electrode material according to claim 9 in sodium ion batteries.

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