A method for screening stability of biomass shell-derived hard carbon feedstock

Abstract

This invention provides a method for screening the stability of biomass shell-derived hard carbon raw materials. The method investigates the optimal ratio and relationship between the lignin content and sugar content measured after alkali treatment in biomass shell materials, thereby screening the stability of biomass shell materials from different sources and batches. When the lignin content of the biomass shell material itself and the sugar content measured after alkali treatment satisfy the relationship 15≤β×L≤60, an effective balance between the lignin and sugar content in the biomass shell material can be achieved, resulting in a good porous structure. This method provides a simple and rapid screening process to obtain biomass shell materials with better stability. When biomass shell materials with better stability are subsequently used to prepare hard carbon battery materials, the resulting hard carbon battery materials exhibit good overall performance in terms of cycle life, capacity, and coulombic efficiency.

Description

Technical Field

[0001] This invention belongs to the field of battery anode materials, specifically relating to a method for screening the stability of biomass shell-derived hard carbon raw materials. Background Technology

[0002] In today's world, with the increasing severity of the energy crisis and environmental pollution, the development and utilization of renewable energy and environmentally friendly materials have become a global focus. Hard carbon materials, as a preferred anode material for sodium-ion batteries, have attracted widespread attention due to their excellent electrochemical performance. The popularity of hard carbon materials is mainly attributed to their high reversible capacity, excellent cycle performance, and structural stability. These characteristics give hard carbon materials enormous application potential in the field of energy storage.

[0003] However, the production cost and sourcing of hard carbon materials have always been bottlenecks limiting their large-scale application. To address this issue, researchers have turned their attention to biomass materials, which are considered ideal precursors for preparing hard carbon materials due to their wide availability, low cost, and renewability.

[0004] However, researchers face a key challenge in preparing hard carbon materials using biomass as precursors: the structural and compositional differences between different batches of biomass precursors directly affect the electrochemical performance of hard carbon materials. This inconsistency mainly stems from factors such as the origin, batch, and season of the biomass precursors, leading to fluctuations in the performance of hard carbon materials.

[0005] To address this issue, researchers need to perform high-temperature carbonization on different batches of biomass precursors to obtain derived hard carbon materials. Subsequently, electrochemical testing is used to evaluate the performance of these hard carbon materials to determine the stability of the raw material batches. However, this evaluation process is time-consuming, involving multiple stages including raw material preparation, battery coating and assembly, battery operation, and data collection. Therefore, developing a rapid and effective screening method for biomass-derived hard carbon raw materials is crucial for determining the stability of biomass materials from different sources and batches, thereby contributing to the achievement of stable biomass hard carbon materials. Summary of the Invention

[0006] This invention addresses the problems in existing technologies by disclosing a method for screening the stability of biomass shell-derived hard carbon raw materials. By testing the relationship between sugar and lignin content in biomass shell materials from different sources and batches after alkali treatment, this invention screens out biomass shell materials that meet certain ranges, thereby reflecting their stability as raw materials for preparing biomass shell-derived hard carbon anode materials; and obtaining biomass shell-derived hard carbon materials with excellent battery cycle performance and electrochemical performance.

[0007] This invention is achieved through the following technical solution:

[0008] In a first aspect, the present invention provides a method for screening the stability of biomass shell-derived hard carbon raw materials. The screening method involves testing the lignin content of the biomass shell material and its sugar content after alkali treatment, and using the relationship β×L to evaluate the stability of the biomass shell material as a derived hard carbon raw material. When β and L satisfy the relationship 15≤β×L≤60, the biomass shell material is considered to have good stability; where 0.3≤β≤3; 20≤L≤50; β is the sugar content of the alkali-treated biomass shell material solution, in g / L; and L is the lignin content of the untreated biomass shell material, in % (%).

[0009] The alkali treatment refers to an alkali solution with a molar concentration of 0.1 mol / L to 10 mol / L; molar concentration refers to the ratio of the number of moles of alkali solute in the alkali solution to the total volume of the solution.

[0010] The alkaline treatment step includes stirring the biomass shell material evenly in an alkaline solution and then heating it in an oven.

[0011] As a further option, in the relationship, 0.5≤β≤1.5, 30≤L≤40, and 25≤β×L≤40.

[0012] The lignin content mentioned in this invention refers to the lignin content inherent in the biomass fruit shell material itself. This invention does not specifically limit the testing method for lignin content. Those skilled in the art can select appropriate methods to test the lignin content inherent in the biomass fruit shell material as needed. As a specific example, the lignin measurement method can be selected from the Panthen washing method.

[0013] When determining whether the lignin and sugar content of biomass fruit shell materials meet the range of the formula and have a better ratio, the alkali treatment conditions are also important, as they directly affect the accuracy of sugar content testing. Therefore, the inventors have studied and optimized the alkali treatment conditions.

[0014] As a further embodiment, the heating reaction temperature is selected from 70-100℃, and the heating reaction time is selected from 10-16h.

[0015] As a further option, the alkali treatment is preferably an alkali solution with a molar concentration of 0.1 mol / L to 3 mol / L.

[0016] As a further embodiment, the ratio of the mass of the biomass fruit shell material to the total mass of the alkaline solution is selected from 2.5 to 7 times the mass of the biomass fruit shell material.

[0017] As a further option, the alkaline solution is selected from one or more of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, or potassium carbonate solution.

[0018] As a further option, the biomass shell material is selected from one or more of the following: walnut shells, macadamia nut shells, pine nut shells, pistachio shells, coconut shells, hazelnut shells, durian shells, almond shells, jujube shells, camellia fruit shells, or peanut shells.

[0019] The features and beneficial effects of this invention are as follows:

[0020] This invention investigates the optimal ratio and relationship between lignin content and sugar content measured after alkali treatment in biomass fruit shell materials, thereby screening the stability of biomass fruit shell materials from different sources and batches. When the lignin content of the biomass fruit shell material itself and the sugar content measured after alkali treatment satisfy the relationship 15≤β×L≤60, an effective balance between lignin and sugar content in the biomass fruit shell material can be achieved. This maximizes the utilization of the structure and chemical properties of the wood fibers, forming a hard carbon material with a stable carbon skeleton and a uniform porous structure. Furthermore, the effective carbonization of the sugar content promotes the formation of a uniform and dense porous structure, which is beneficial for improving the coulombic efficiency, cycle life, and capacity performance of hard carbon battery materials. Simultaneously, this invention optimizes the alkali treatment conditions to further ensure the accuracy of the sugar content test, thereby more accurately screening biomass fruit shell-derived hard carbon battery materials with better overall electrochemical performance. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a SEM image of the hard carbon material from Example 1. Detailed Implementation

[0023] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0024] This invention has discovered that biomass shells, such as walnut shells, coconut shells, and peanut shells, are common agricultural wastes. They are not only widely available and inexpensive, but also exhibit good electrical conductivity and a well-developed pore structure. Therefore, biomass shell materials can be ideal raw materials for synthesizing high-performance hard carbon materials. The lignocellulose content in biomass shell materials directly affects the structure and electrochemical performance of hard carbon materials during carbonization. However, different batches of biomass shells vary in lignocellulose and impurity content, leading to fluctuations in the performance of hard carbon materials. Therefore, exploring the relationship between the lignocellulose content and its availability in biomass shells is the focus of this invention. To this end, this invention has conducted a series of studies to explore the interrelationships between various parameters to reflect the stability of biomass shell-derived hard carbon raw materials. This allows for rapid screening of different raw materials and batches of biomass shell materials to determine their excellent stability. When biomass shell materials exhibit good stability, it indicates that the prepared hard carbon battery materials have good overall performance in terms of cycle life, capacity, and coulombic efficiency.

[0025] In a first aspect, the present invention provides a method for screening the stability of biomass shell-derived hard carbon raw materials. The screening method involves testing the lignin content of the biomass shell material and its sugar content after alkali treatment, and using the relationship β×L to evaluate the stability of the biomass shell material as a derived hard carbon raw material. When β and L satisfy the relationship 15≤β×L≤60, the biomass shell material is considered to have good stability; where 0.3≤β≤3; 20≤L≤50; β is the sugar content of the alkali-treated biomass shell material solution, in g / L; and L is the lignin content of the untreated biomass shell material, in % (%).

[0026] The alkali treatment refers to an alkali solution with a molar concentration of 0.1 mol / L to 10 mol / L; molar concentration refers to the ratio of the number of moles of alkali solute in the alkali solution to the total volume of the solution.

[0027] The alkaline treatment step includes stirring the biomass shell material evenly in an alkaline solution and then heating it in an oven.

[0028] This invention tests the lignin content and sugar content of biomass fruit shell materials after alkali treatment. When β and L satisfy the relationship 15≤β×L≤60, 0.3≤β≤3; 20≤L≤50, the measured biomass-derived hard carbon battery exhibits better cycle performance and capacity, meeting electrochemical performance requirements. Under this relationship, the sugar content and lignin content of the biomass fruit shell material achieve a good balance, maximizing the utilization of the structure and chemical properties of its lignocellulose. This provides a suitable carbon source during hard carbon material preparation, forming a specific pore structure that is more conducive to sodium ion insertion, providing more sodium storage sites and promoting sodium ion conduction rate. Simultaneously, alkali treatment of the biomass fruit shell material removes some inorganic components. With a suitable sugar content range, a certain amount of ash can undergo a self-activation reaction at high temperatures, which is beneficial for obtaining a more uniform pore distribution, thus ensuring the excellent electrochemical performance of the hard carbon material during battery cycling.

[0029] In biomass materials, the main components include lignocellulose (containing cellulose, lignin, and hemicellulose) and inorganic components (such as potassium, zinc, carbonates, and phosphates). Among them, cellulose in lignocellulose is a linear polysaccharide, composed of repeating cellobiose units linked by glycosidic bonds, and exists in crystalline or amorphous form; hemicellulose is another polysaccharide in plant cell walls, which is a heteropolymer composed of various types of sugar units; while lignin is a complex aromatic macromolecule with a non-crystalline and irregular 3D structure, bound together by carbon-oxygen and carbon-carbon bonds, existing in the form of three phenylpropane monomer units or monolignin alcohols. When treated with alkaline solutions, the binding groups such as acetyl and uronic acid on hemicellulose and cellulose in biomass shells are more easily removed, thus increasing the treatment rate. Furthermore, the high lignin content and looser structure of biomass shells facilitate better penetration of the alkaline solution, resulting in a more responsive treatment. The interaction between hydroxide ions in the alkaline solution and the chemical bonds in lignin molecules promotes the transformation of some lignin, generating aromatic monomers richer in G-lignin. This facilitates the conversion of these monomers into monosaccharides, reducing the influence of other chemical factors on the lignin itself. Accurate sugar content testing, and by adjusting the ratio of convertible sugar content to the lignin content of the biomass shell material, biomass shell materials with an appropriate balance between the two can be screened. This facilitates the selection of biomass shell-derived hard carbon materials with excellent electrochemical cycling performance, good capacity, and coulombic efficiency.

[0030] When the sugar and lignin contents in biomass nutshells meet the following conditions: 15 ≤ β × L ≤ 60; 0.3 ≤ β ≤ 3; 20 ≤ L ≤ 50, the biomass nutshell material is more conducive to forming a more suitable specific pore structure during the subsequent decomposition and carbonization process to prepare derived hard carbon materials. This specific pore structure has both sufficient porosity to accommodate electrolytes and ion transport, and good stability to support the recycling of battery materials. This is mainly due to the fact that when the sugar and lignin contents in biomass nutshells reach a balance within a certain range, on the one hand, the large amount of volatile substances released by lignin during pyrolysis can be fully utilized to form a porous structure; on the other hand, the aromatic structure in lignin helps to form a stable carbon skeleton, supporting the stability of the pore structure, thereby providing more active sites, promoting the interaction between ions and electrode materials, and thus increasing the energy storage capacity of the battery. At the same time, the sugar content in the balance will decompose into small molecule sugars during pyrolysis, and then be converted into carbon; during carbonization, it can fill the pores and form a uniform and dense pore structure. At the same time, they can also serve as carbon sources, increasing the carbon content of carbonization products, thereby improving the coulombic efficiency of batteries made from hard carbon materials.

[0031] When the lignin and sugar content in biomass shell materials is not well balanced, excessive lignin can lead to overly rapid release of volatile substances, resulting in unstable pore structures that are prone to collapse during carbonization. Furthermore, excessive lignin can cause excessively large pores, which is detrimental to ion transport and charge storage in the battery material. Large pores reduce the electrolyte wetting area, affecting battery performance; conversely, excessive sugar content can cause small-molecule sugars to overfill pores during carbonization, leading to pore blockage and further hindering electrolyte wetting and ion transport. This unbalanced pore structure can cause the battery material to easily expand and contract during charge and discharge, reducing cycle performance. Therefore, screening biomass shell materials with a balanced lignin-to-sugar ratio is beneficial for obtaining higher-performance hard carbon materials and ensuring battery stability and efficiency during cycling.

[0032] When testing different biomass shell materials, this invention first processes them to a uniform particle size using physical means to ensure experimental consistency. This invention does not limit the processing method or particle size principle; those skilled in the art can select appropriate particle size and processing method as needed.

[0033] As a further refinement, in the aforementioned relationship, 0.5 ≤ β ≤ 1.5, 30 ≤ L ≤ 40, and 25 ≤ β × L ≤ 40. Relationships satisfying this range exhibit superior electrochemical performance, and the biomass shell material is more conducive to obtaining a uniform and dense porous structure in the preparation of hard carbon materials. Within this optimized range, the balance of lignin and sugar content in the biomass shell material ensures the full utilization of lignin's ability to form a porous structure during pyrolysis, while reducing unnecessary pore collapse or over-porosification, thereby maintaining good structural stability during battery cycling. Furthermore, the optimized lignin and sugar content ratio helps form a more uniform carbon layer during carbonization, reducing the internal resistance of the electrode material and improving electron and ion conduction efficiency. This results in higher capacity retention and longer cycle life, meeting the demands of high-performance battery applications.

[0034] The lignin content mentioned in this invention refers to the lignin content inherent in the biomass fruit shell material itself. This invention does not specifically limit the testing method for lignin content. Those skilled in the art can select appropriate methods to test the lignin content inherent in the biomass fruit shell material as needed. As a specific example, the lignin measurement method can be selected from the Panthen washing method.

[0035] When determining whether the lignin and sugar content of biomass fruit shell materials meet the range of the formula and have a better ratio, the alkali treatment conditions are also important, as they directly affect the accuracy of sugar content testing. Therefore, the inventors have studied and optimized the alkali treatment conditions.

[0036] As a further embodiment, the heating reaction temperature is selected from 70-100℃, and the heating reaction time is selected from 10-16h.

[0037] Choosing appropriate alkaline solutions and treatment conditions helps reduce the impact of impurities on the accuracy of sugar content measurements. However, excessively high temperatures or prolonged treatment times can lead to over-degradation or transformation of sugars in the biomass shells, generating non-sugar compounds. These compounds may interfere with accurate sugar content determination, resulting in lower test results or failing to accurately reflect the actual sugar content. Conversely, excessively low temperatures or short treatment times may weaken the effect of alkaline treatment, potentially leaving some bound groups in the biomass shells and affecting sugar release and measurement.

[0038] The concentration of the alkaline solution used during alkaline treatment is also crucial. High-concentration alkaline solutions may excessively disrupt the structure of the biomass husk, leading to rapid degradation of sugars and other components, thus interfering with sugar content determination. Conversely, excessively low-concentration alkaline solutions may fail to effectively remove binding groups and other components, resulting in insufficient sugar release and consequently, lower test results. Therefore, we need to conduct tests under appropriate alkaline treatment conditions to obtain the most accurate results.

[0039] As a further option, the alkali treatment is preferably an alkali solution with a molar concentration of 0.1 mol / L to 3 mol / L.

[0040] As a further embodiment, the ratio of the mass of the biomass fruit shell material to the total mass of the alkaline solution is selected from 2.5 to 7 times the mass of the biomass fruit shell material.

[0041] As a further option, the alkaline solution is selected from one or more of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, or potassium carbonate solution.

[0042] As a further option, the biomass shell material is selected from one or more of the following: walnut shells, macadamia nut shells, pine nut shells, pistachio shells, coconut shells, hazelnut shells, durian shells, almond shells, jujube shells, camellia fruit shells, or peanut shells.

[0043] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0044] The chemical raw materials used in the following examples and comparative examples are all prior art and commercially available. The experimental apparatus and testing equipment used in the following examples and comparative examples are all conventional equipment in the art, and there are no special requirements or limitations.

[0045] Example 1

[0046] 30% of 100g of pine nut shells was used for lignin testing. The remaining 30% was then mixed with 180g of a 0.1mol / L alkaline solution and stirred at room temperature for 7 minutes until homogeneous. The mixture was then placed in a 100℃ oven and reacted for 12 hours. The supernatant was then used for sugar content testing. The remaining 40% of the pine nut shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0047] The sugar content β was determined to be 0.68 g / L by colorimetric testing, and the lignin content L was determined to be 38.7% by the Panthen washing method. β×L=26.316.

[0048] Example 2

[0049] 30% of 100g of walnut shells was used for lignin testing. The remaining 30% was then mixed with 120g of a 0.35mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in an 80℃ oven and reacted for 12 hours. The supernatant was then used for sugar content testing. The remaining 40% of the walnut shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0050] The sugar content β was determined to be 0.94 g / L by colorimetric testing, and the lignin content L was determined to be 37.3% by the Panthen washing method. Therefore, β×L=35.062.

[0051] Example 3

[0052] 30% of 100g of coconut shell was used for lignin testing. The remaining 30% was then mixed with 100g of a 2mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in an 80℃ oven and reacted for 12 hours. The supernatant was then used for sugar content testing. The remaining 40% of the coconut shell was dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0053] The sugar content β was determined to be 1.06 g / L by colorimetric testing, and the lignin content L was determined to be 36.4% by the Panthen washing method. Therefore, β×L=38.584.

[0054] Example 4

[0055] 30% of 100g of almond shells was used for lignin testing. The remaining 30% was then mixed with 90g of a 5mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in an 80℃ oven and reacted for 10 hours. The supernatant was then used for sugar content testing. The remaining 40% of the almond shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0056] The sugar content β was determined to be 1.36 g / L by colorimetric testing, and the lignin content L was determined to be 23.9% by the Panthen washing method. Therefore, β×L=32.504.

[0057] Example 5

[0058] 30% of 100g of pistachio shells was used for lignin testing. The remaining 30% was then mixed with 90g of a 6mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in an 80℃ oven and reacted for 12 hours. The supernatant was then used for sugar content testing. The remaining 40% of the pistachio shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0059] The sugar content β was determined to be 2.35 g / L by colorimetric testing, and the lignin content L was determined to be 20.3% by the Panthen washing method. β×L=47.705.

[0060] Example 6

[0061] 30% of 100g of hazelnut shells was used for lignin testing. The remaining 30% was then mixed with 120g of a 4mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in an 80℃ oven and reacted for 10 hours. The supernatant was then used for sugar content testing. The remaining 40% of the hazelnut shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0062] The sugar content (β) was determined to be 1.44 g / L by colorimetric analysis, and the lignin content (L) was determined to be 32.6% by the Panthen washing method. Therefore, β × L = 46.944.

[0063] Example 7

[0064] The biomass materials were the same as in Example 2. 30% of 100g of walnut shells from different batches were used for lignin testing. The remaining 30% was then mixed with 150g of a 6mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in a 70℃ oven and reacted for 10 hours. The supernatant was then used for sugar content testing. The remaining 40% of the walnut shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0065] The sugar content β was determined to be 1.51 g / L by colorimetric testing, and the lignin content L was determined to be 39.4% by the Panthen washing method. Therefore, β×L=59.494.

[0066] Example 8

[0067] The biomass materials were the same as in Example 1. 30% of 100g of pine nut shells from different batches were used for lignin testing. The remaining 30% was then mixed with 120g of a 0.5mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in an 80℃ oven and reacted for 10 hours. The supernatant was then used for sugar content testing. The remaining 40% of the pine nut shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0068] The sugar content (β) was determined to be 0.88 g / L by colorimetric testing, and the lignin content (L) was determined to be 47.2% by the Panthen washing method. Therefore, β × L = 41.536.

[0069] Example 9

[0070] The biomass materials were the same as in Example 3. 30% of 100g of coconut shells from different batches were used for lignin testing. The remaining 30% was then mixed with 120g of a 5mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in an 80℃ oven and reacted for 12 hours. The supernatant was then used for sugar content testing. The remaining 40% of the coconut shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0071] The sugar content β was determined to be 1.89 g / L by colorimetric testing, and the lignin content L was determined to be 20.5% by the Panthen washing method. β×L=38.745.

[0072] Example 10

[0073] 30% of 100g of jujube shells was used for lignin testing. The remaining 30% was then mixed with 100g of a 4mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in a 90℃ oven and reacted for 12 hours. The supernatant was then used for sugar content testing. The remaining 40% of the jujube shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0074] The sugar content (β) was determined to be 1.89 g / L by colorimetric analysis, and the lignin content (L) was determined to be 28.7% by the Panthen washing method. Therefore, β × L = 54.243.

[0075] Comparative Example 1

[0076] 30% of 100g of walnut shells from the same batch as in Example 2 was used for lignin testing. The remaining 30% was then mixed with 180g of a 15mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in an oven at 80°C and reacted for 12 hours. The supernatant was then used for sugar content testing. The remaining 40% of the walnut shells were dried at 120°C until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0077] The sugar content β was determined to be 10.11 g / L by colorimetric testing, and the lignin content L was determined to be 37.3% by the Panthen washing method. Therefore, β×L=377.103.

[0078] Comparative Example 2

[0079] 30% of 100g of walnut shells from the same batch as in Example 2 was used for lignin testing. The remaining 30% was then mixed with 180g of a 0.05mol / L alkaline solution and stirred at room temperature for 7 minutes until homogeneous. The mixture was then placed in a 150℃ oven and reacted for 12 hours. The supernatant was then used for sugar content testing. The remaining 40% of the walnut shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0080] The sugar content β was determined to be 0.28 g / L by colorimetric testing, and the lignin content L was determined to be 37.3% by the Panthen washing method. β×L=10.444.

[0081] Comparative Example 3

[0082] 30% of 100g of walnut shells from the same batch as in Example 2 was used for lignin testing. The remaining 30% was then mixed with 180g of a 0.35mol / L alkaline solution and stirred at room temperature for 7 minutes until homogeneous. The mixture was then placed in an oven at 80°C and reacted for 20 hours. The supernatant was then used for sugar content testing. The remaining 40% of the walnut shells were dried at 120°C until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0083] The sugar content β was determined to be 5.68 g / L by colorimetric testing, and the lignin content L was determined to be 37.3% by the Panthen washing method. β×L=211.864.

[0084] Comparative Example 4

[0085] The biomass materials were the same as in Example 4. 30% of 100g of almond shells from different batches were used for lignin testing. The remaining 30% was mixed with 90g of a 1mol / L alkaline solution and stirred at room temperature for 7 minutes until homogeneous. The mixture was then placed in an 80℃ oven and reacted for 10 hours. The supernatant was then used for sugar content testing. The remaining 40% of the almond shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0086] The sugar content (β) was determined to be 1.6 g / L by colorimetric analysis, and the lignin content (L) was determined to be 44.9% by the Panthen washing method. Therefore, β × L = 71.84.

[0087] Comparative Example 5

[0088] The biomass materials were the same as in Example 5. 30% of 100g of pistachio shells from different batches were used for lignin testing. The remaining 30% was then mixed with 90g of a 0.8mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in an 80℃ oven and reacted for 12 hours. The supernatant was then used for sugar content testing. The remaining 40% of the pistachio shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0089] The sugar content β was determined to be 0.6 g / L by colorimetric testing, and the lignin content L was determined to be 20.7% by the Panthen washing method, with β×L=12.42.

[0090] Comparative Example 6

[0091] 30% of 100g of peanut shells was used for lignin testing. The remaining 30% was then mixed with 120g of a 4mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in an 80℃ oven and reacted for 10 hours. The supernatant was then used for sugar content testing. The remaining 40% of the peanut shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0092] The sugar content (β) was determined to be 4.7 g / L by colorimetric analysis, and the lignin content (L) was determined to be 18.8% by the Panthen washing method. Therefore, β × L = 88.36.

[0093] Comparative Example 7

[0094] 30% of 100g of Camellia oleifera fruit shells were used for lignin testing. The remaining 30% was then mixed with 150g of an 8mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in a 70℃ oven and reacted for 10 hours. The supernatant was then used for sugar content testing. The remaining 40% of the Camellia oleifera fruit shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0095] The sugar content β was determined to be 7.11 / L by colorimetric testing, and the lignin content L was determined to be 19.6% by the Panthen washing method. β×L=139.356.

[0096] Comparative Example 8

[0097] 30% of 100g of durian shells was used for lignin testing. The remaining 30% was then mixed with 120g of a 5mol / L alkaline solution at room temperature for 7 minutes until homogeneous. The mixture was then placed in an 80℃ oven and reacted for 10 hours. The supernatant was then used for sugar content testing. The remaining 40% of the durian shells were dried at 120℃ until the moisture content was below 3%. The dried powder was then carbonized to produce hard carbon.

[0098] The sugar content (β) was determined to be 3.8 g / L by colorimetric testing, and the lignin content (L) was determined to be 15.4% by the Panthen washing method. Therefore, β × L = 58.52.

[0099] Specific testing methods and conditions:

[0100] Button battery test: The negative electrode material, polyvinylidene fluoride (PVDF) and conductive agent (SP) are dispersed and dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 90:5:5. The mixture is stirred and dispersed to obtain a slurry with a solid content of 55%. After coating and drying, the slurry is cut into circular electrode sheets. A sodium metal sheet is used as the counter electrode, polypropylene (PP) is used as the separator material, and a small amount of sodium ion battery electrolyte is added to prepare a button battery with a negative electrode material.

[0101] Within the 0-2V voltage range, at room temperature, the following tests were performed: 1) stand for 2 hours; 2) discharge at a higher rate (0.1C, 0V); 3) stand for 10 minutes; 4) discharge at a higher rate (0.02C, 0V); 5) stand for 30 seconds; 6) charge at a higher rate (0.1C, 2.0V). The first reversible specific capacity, i.e., the derived hard carbon capacity (mAh / g), was recorded.

[0102] The test results of Examples 1-10 and Comparative Examples 1-8 are shown in Table 1.

[0103] Table 1

[0104]

[0105]

[0106] As can be seen from the data in Table 1, compared with the comparative example, the biomass shell material of the present invention exhibits better electrochemical performance. In this case, β and L in the examples satisfy the formula 15 ≤ β × L ≤ 60; this indicates that screening within a suitable range of the formula is beneficial for obtaining biomass shell materials with a relatively balanced lignin and sugar content. Furthermore, during the preparation of hard carbon materials, these materials possess a uniform and stable pore structure, which is beneficial for increasing sodium storage sites and the sodium ion transport rate; thus, a battery material with better hard carbon capacity, coulombic efficiency, and stable cycle efficiency is obtained.

[0107] pass Figure 1 It can be seen that the hard carbon derived from walnut shells exhibits a blocky structure with relatively uniform size. Data from Example 2, Comparative Examples 1-3, and Table 1 show that the lignin content, hard carbon capacity, coin cell cycle count, and coulombic efficiency of Comparative Examples 1-3 are not significantly different from those of Example 1. However, the formula range of Comparative Examples 1-3 is not within the optimized formula range of this invention. This data reveals that for the same batch of walnut shell raw materials, the concentration, temperature, and time of the alkali treatment during sugar content testing can affect our judgment when screening biomass walnut shell materials. Therefore, to further ensure the accuracy of the screening method, the concentration, temperature, and time of the alkali treatment need to be optimized to ensure the accuracy of the sugar content test. The alkaline solution concentration chosen in Comparative Example 1 was too high compared to that in Example 1, which may have caused the alkaline treatment conditions to be too harsh, damaging the structure of the biomass shells and leading to the rapid degradation of other components, thus interfering with the sugar content test. Similarly, in Comparative Examples 2 and 3, the alkaline treatment temperature was too high or the treatment time too long compared to Example 1, which could also cause excessive degradation or transformation of sugars in the biomass shells during alkaline treatment, generating other non-sugar compounds, thus failing to accurately reflect the sugar content. Furthermore, using the formula for screening could easily lead to misjudgments of the stability of the biomass shell materials. Therefore, this invention optimizes the alkaline treatment conditions to ensure accurate screening of biomass shell raw materials with good comprehensive electrochemical performance.

[0108] As can be seen from Table 1 and Examples 1-10 and Comparative Examples 4 and 5, although the lignin and sugar contents obtained by Comparative Examples 4 and 5 meet the optimization range compared to Examples 1-10, their overall electrochemical performance is still lower than that of the examples. This indicates that further regulation of sugar and lignin content is needed. By regulating the sugar and lignin content of the biomass shell material, a more uniform and dense pore structure can be formed during the pyrolysis and carbonization of hard carbon battery materials, thereby improving the sodium storage capacity and ion transport efficiency of the hard carbon material. Furthermore, a more balanced lignin and sugar content is more conducive to fully utilizing the utilization value of lignin, maintaining a more stable carbon skeleton, and improving the cycling performance of the hard carbon material during the cycling process.

[0109] As can be seen from Table 1 and Examples 1-10 and Comparative Examples 6, 7, and 8, the electrochemical performance of the comparative examples is generally worse than that of the examples. This is because when the ratio and relationship between lignin and sugar content in the biomass shell material are inappropriate, it is not conducive to fully utilizing the availability of lignin during subsequent pyrolysis and carbonization to prepare hard carbon materials, thus hindering the formation of hard carbon materials with a stable carbon skeleton and a uniform porous structure; and it is also not conducive to fully utilizing the sugar content during carbonization to promote the conductivity of hard carbon materials and obtain a special pore structure. Excessively high sugar content may also lead to overfilling of pores during the carbonization preparation of hard carbon materials, causing pore blockage, thereby resulting in the biomass shell material not possessing a comprehensive balance of electrochemical performance when prepared into hard carbon battery materials.

[0110] As can be seen from Examples 1-4 and Examples 5-10, when the lignin content and sugar content have the optimal ratio, the prepared hard carbon battery material has a better pore structure and obtains more sodium storage sites, thereby promoting the wetting and transport capacity of sodium ions and electrolytes. The biomass shell material obtained by screening has the best cycle performance and high sodium storage capacity and coulombic efficiency.

[0111] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for screening the stability of biomass shell-derived hard carbon raw materials; the screening method involves testing the lignin content and sugar content of the biomass shells after alkali treatment, and using the relationship β×L to evaluate the stability of the biomass shell materials as derived hard carbon raw materials; when β and L satisfy the relationship 15≤β×L≤60, the biomass shell materials are considered to have better stability; wherein, 0.3≤β≤3; 20≤L≤50; β is the sugar content of the alkali-treated biomass shell material solution, in g / L; L is the lignin content of the untreated biomass shell material, in %; The alkali treatment refers to an alkali solution with a molar concentration of 0.1 mol / L to 10 mol / L; molar concentration refers to the ratio of the number of moles of alkali solute in the alkali solution to the total volume of the solution. The alkaline treatment step includes stirring the biomass shell material evenly in an alkaline solution and then heating it in an oven.

2. The method for screening the stability of biomass shell-derived hard carbon raw materials according to claim 1, characterized in that, In the given formula, 0.5≤β≤1.5, 30≤L≤40, and 25≤β×L≤40.

3. The method for screening the stability of biomass shell-derived hard carbon raw materials according to claim 1, characterized in that, The heating reaction temperature is selected from 70-100℃, and the heating reaction time is selected from 10-16h.

4. The method for screening the stability of biomass shell-derived hard carbon raw materials according to claim 1, characterized in that, The alkali treatment is preferably performed with an alkali solution having a molar concentration of 0.1 mol / L to 3 mol / L.

5. The method for screening the stability of biomass shell-derived hard carbon raw materials according to claim 1, characterized in that, The ratio of the mass of the biomass fruit shell material to the total mass of the alkaline solution is selected from 2.5 to 7 times the mass of the biomass fruit shell material.

6. The method for screening the stability of biomass shell-derived hard carbon raw materials according to claim 1, characterized in that, The alkaline solution is selected from one or more of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, or potassium carbonate solution.

7. The method for screening the stability of biomass shell-derived hard carbon raw materials according to claim 1, characterized in that, The biomass shell material is selected from one or more of the following: walnut shells, macadamia nut shells, pine nut shells, pistachio shells, coconut shells, hazelnut shells, durian shells, almond shells, jujube shells, camellia fruit shells, or peanut shells.

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