Hard and soft carbon negative electrode material derived from camellia oleifera shells as well as preparation method and application of hard and soft carbon negative electrode material

Abstract

The invention relates to the field of preparation of sodium ion battery negative electrode materials, and particularly discloses a preparation method of a hard and soft carbon negative electrode material derived from camellia oleifera shells, which comprises the following steps: obtaining camellia oleifera shell powder; uniformly mixing the camellia oleifera shell powder and the road petroleum asphalt according to the mass ratio of (10-20): 1 by adopting a ball mill; carbonizing the uniformly mixed mixture at the temperature of 1000 to 1400 DEG C; and performing acid pickling, water washing, suction filtration, drying and filtration on the powder formed after carbonization to obtain the hard and soft carbon negative electrode material. Compared with the prior art, the preparation method has the characteristics of low cost, high carbon yield, simple preparation process, high reaction efficiency and the like.

Description

Technical Field

[0001] The present invention relates to the field of preparation of negative electrode materials for sodium ion batteries, and in particular to a hard-soft carbon negative electrode material derived from oil-tea camellia shells, and a preparation method and application thereof. Background Art

[0002] Camellia oleifera shells, a byproduct of tea processing, are typically discarded or incinerated. Resource utilization of camellia oleifera shells not only increases their added value but also addresses the environmental pollution they cause. Camellia oleifera shells contain tannins, saponins, flavonoids, and polysaccharides, making them ideal for applications such as antibacterial, antioxidant, and antiviral treatments. In terms of materialization, activated carbon adsorbents derived from camellia oleifera shells have demonstrated excellent adsorption properties. However, capacitor materials prepared from camellia oleifera shells exhibit low electrical conductivity, and wood composites exhibit poor mechanical properties. In terms of fertilizer utilization, organic fertilizers and culture media prepared from camellia oleifera shells significantly improve soil quality, enhance fertilizer quality, and promote seedling growth. In terms of energy utilization, the high lignin, hemicellulose, and cellulose content of camellia oleifera shells offer advantages in direct-fired power generation, anaerobic fermentation for biogas production, and bioethanol and bio-oil production. However, these shells present challenges such as chloride corrosion in boilers, difficulty in lignin degradation, low bioethanol yields, and limited bio-oil production. In the preparation of carbon materials, camellia oleifera shells need to be carbonized specifically for use as electrode materials. In terms of the utilization of functional components, high-value-added deep-processing products need to be developed and the production scale expanded. In terms of energy, the integration problem of the biomass conversion process needs to be solved.

[0003] Road petroleum asphalt is a petrochemical raw material that is widely available and inexpensive. As a soft carbon precursor, it can effectively reduce the production cost of sodium-ion battery negative electrode materials.

[0004] The existing technology uses petroleum asphalt and tea oil shells to form carbon-based materials as negative electrode materials for sodium ion batteries.

[0005] For example, CN116344804A discloses a hard carbon material for a battery negative electrode and a preparation method thereof. The raw materials include camellia oleifera shells and asphalt, but a pore structure modifier needs to be added to improve the pore structure and sodium ion transport performance of the hard carbon material.

[0006] CN116654896A discloses a modified hard carbon negative electrode material, which uses biomass waste tea shells as raw materials, sulfuric acid and phosphoric acid as dopants, and obtains P and S diatomic doped pre-carbonized porous carbon material after carbonization; then, the modified hard carbon negative electrode material is obtained through the steps of co-carbonization of nano-SiO2 microspheres and pyrolysis of magnesium powder; its preparation process is complicated and not suitable for industrial production.

[0007] CN114477130A discloses that a hard carbon negative electrode material is prepared by using biomass materials such as camellia shells, cork and asphalt as raw materials through two steps of high-temperature carbonization.

[0008] In summary, existing technologies for preparing carbon-based materials using road petroleum asphalt and camellia oleifera shells suffer from complex processes or the need for the addition of pore structure modifiers to improve the pore structure and sodium ion transport properties of the hard carbon materials, thereby increasing the production cost of the carbon-based materials. Furthermore, the asphalt raw materials used in existing patents are mostly coal tar pitch or mesophase pitch, which has a high melting point and is difficult to co-carbonize with biomass at the molecular level during high-temperature pyrolysis to form a molecular structure with intertwined hard and soft carbons, making it impossible to control closed-pore sodium storage sites. Summary of the Invention

[0009] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a hard-soft carbon negative electrode material derived from camellia oleifera shells and its preparation method and application, so as to solve the problem of relatively high preparation cost in the existing technology of using low-priced and low-softening-point road petroleum asphalt and camellia oleifera shells to prepare carbon-based materials.

[0010] To achieve the above objectives, the first aspect of the present invention adopts the following technical solution: a method for preparing a hard-soft carbon negative electrode material derived from oil tea shells, comprising the following steps:

[0011] Obtaining camellia oleifera shell powder;

[0012] The camellia oleifera shell powder and road petroleum asphalt are mixed uniformly by ball milling at a mass ratio of 10 to 20:1;

[0013] Carbonizing the uniformly mixed mixture at a temperature of 1000-1400°C;

[0014] The powder formed after carbonization is acid-washed, water-washed, filtered, dried and filtered to obtain a hard-soft carbon negative electrode material.

[0015] Technical principle:

[0016] During the high-temperature carbonization process of 1000-1400°C, the composition and structural characteristics of camellia oleifera shells and road petroleum asphalt can naturally form a pore structure that is conducive to the storage and transmission of sodium ions.

[0017] Compared with coal tar and mesophase asphalt, the softening point (melting point) of road petroleum asphalt is lower. During high-temperature heat treatment, the light components in the asphalt are first vaporized, which is conducive to the formation of rich connected micro-nano open pores. The heavy components rich in condensed aromatic rings tend to form graphitized crystalline carbon components at high temperatures.

[0018] The lignin, hemicellulose, polysaccharides and other components in the oil-tea camellia shell will decompose and produce certain pores during the carbonization process. After mixing the oil-tea camellia shell with road asphalt and carbonizing it at high temperature, a composite structure of hard carbon and soft carbon is formed. The advantages of the disordered regions of the hard carbon and the ordered regions of the soft carbon are complementary, which not only increases the overall sodium storage capacity of the material, but also improves the rate performance and cyclic stability of the hard carbon. At the same time, the soft carbon will fill the micropores formed during the carbonization of the hard carbon with a closed-pore structure during the carbonization process, reducing the large specific surface area formed by the many defects in the hard carbon during the carbonization process and providing more active sites for sodium storage. The synergistic interaction between the hard and soft carbon composites and the mutual cooperation of the pore structure provide a good channel for the insertion and removal of sodium ions, simplify the carbonization process and preparation process, and reduce production costs.

[0019] Furthermore, the specific process of obtaining the camellia oleifera shell powder is:

[0020] The camellia oleifera shells are washed with water, dried at 80-120° C. for 4-12 hours, and then crushed and sieved in sequence to obtain camellia oleifera shell powder.

[0021] Furthermore, the mesh size of the sieve used in the screening is 100-500 meshes.

[0022] Furthermore, the road petroleum asphalt includes one or more of AH-50, AH-70, AH-90, AH-110 and AH-130.

[0023] Furthermore, the ball milling is dry ball milling, and the mass ratio of the mixture formed by the oil-tea camellia shell powder and the road petroleum asphalt to the grinding balls is 1:10-30;

[0024] The grinding speed during the dry ball milling process is 200-600 rpm, and the ball milling time is 3-6 hours.

[0025] Furthermore, the grinding balls are selected from one of zirconia balls, stainless steel balls and alumina ceramic balls, and the ball milling atmosphere during the dry ball milling process is one of air, nitrogen and argon.

[0026] Furthermore, the heating rate during the carbonization is 5 to 10° C. / min and the holding time is 1 to 3 hours.

[0027] Furthermore, the acid solution used in the pickling is one of hydrochloric acid, sulfuric acid and nitric acid, and its concentration is 0.1M to 2M, and the pickling time is 12 to 24 hours; the mesh number of the sieve used in the filtration is 100 to 500 meshes.

[0028] The second aspect of the present invention adopts the following technical solution: a hard-soft carbon negative electrode material derived from camellia oleifera shell is prepared by the preparation method of a hard-soft carbon negative electrode material derived from camellia oleifera shell described in the first aspect of the present invention.

[0029] The third aspect of the present invention adopts the following technical solution: an application, namely, the application of a hard-soft carbon negative electrode material derived from camellia oleifera shell as described in the second aspect of the present invention in a sodium ion battery.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The preparation method of the present invention has the characteristics of low cost, high carbon yield, simple preparation process, and high reaction efficiency. The prepared hard and soft carbon negative electrode material is applied in sodium ion batteries, making it a high value-added product, meeting the environmental requirements of green resources, and realizing the efficient utilization of waste resources.

[0032] 2. The hard-soft carbon negative electrode material of the present invention combines the respective advantages of soft carbon and hard carbon. The hard carbon neutralizes the problems of soft carbon such as high degree of graphitization, low interlayer spacing and being unfavorable for sodium storage; the soft carbon improves the problems of hard carbon such as poor rate performance, low initial charge and discharge efficiency, and poor cycle stability; the combination of hard and soft carbon reduces the large specific surface area formed by the hard carbon during the carbonization process due to the large number of defects, and at the same time provides more sodium storage active sites, thereby achieving the purpose of improving the capacity for sodium ions. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below through specific embodiments:

[0034] Example 1

[0035] A method for preparing a hard-soft carbon negative electrode material derived from oil-tea camellia shells comprises the following steps:

[0036] S1. Wash the camellia oleifera shells with water and dry them in a vacuum drying oven at 80°C for 12 h. After drying, grind them in a wall-breaking machine for 30 seconds and pass them through a 100-mesh sieve to obtain camellia oleifera shell powder.

[0037] S2. The camellia oleifera shell powder obtained in S1 and road petroleum asphalt (AH-50) were added to a planetary ball mill in a mass ratio of 15:1. The mass ratio of the zirconia balls in the planetary ball mill to the mixed material formed by the camellia oleifera shell powder and road asphalt was 10:1. The ball milling speed was 500 rpm and the ball milling time was 6 h.

[0038] S3. The ball-milled powder of S2 was placed in a tube furnace and heated to 1200°C at a rate of 5°C / min under a nitrogen atmosphere for carbonization, and kept at this temperature for 2 h.

[0039] S4. The carbonized tea oil shell mixed powder of S3 was soaked in a 2M hydrochloric acid solution and stirred for 12 hours for acid washing, and then washed with water, filtered, dried and passed through a 200-mesh sieve to obtain a hard-soft carbon negative electrode material.

[0040] Example 2

[0041] A method for preparing a hard-soft carbon negative electrode material derived from oil-tea camellia shells comprises the following steps:

[0042] S1. Wash the camellia oleifera shells with water and dry them in a vacuum drying oven at 100°C for 8 h. After drying, grind them in a wall-breaking machine for 60 seconds and pass them through a 300-mesh sieve to obtain camellia oleifera shell powder.

[0043] S2. The camellia oleifera shell powder obtained in S1 and road petroleum asphalt (AH-110) were added to a planetary ball mill in a mass ratio of 20:1. The mass ratio of the stainless steel balls in the planetary ball mill to the mixed material formed by the camellia oleifera shell powder and road asphalt was 20:1. The ball milling speed was 600 rpm and the ball milling time was 3 h.

[0044] S3. Place the ball-milled mixed powder of S2 in a tube furnace and heat it to 1000°C at a rate of 3°C / min under air atmosphere for carbonization, and keep it at this temperature for 3 h.

[0045] S4. The carbonized tea shell mixed powder of S3 was soaked in a 1M sulfuric acid solution and stirred for 18 hours for acid washing, and then washed with water, filtered, dried and passed through a 100-mesh sieve to obtain a hard-soft carbon negative electrode material.

[0046] Example 3

[0047] A method for preparing a hard-soft carbon negative electrode material derived from oil-tea camellia shells comprises the following steps:

[0048] S1. Wash the camellia oleifera shells with water and dry them in a vacuum drying oven at 120°C for 4 h. After drying, grind them in a wall-breaking machine for 50 seconds and pass them through a 500-mesh sieve to obtain camellia oleifera shell powder.

[0049] S2. The oil tea shell powder obtained in S1 and road petroleum asphalt (AH-70 and AH-130 with a mass ratio of 1:1) were added to a planetary ball mill in a mass ratio of 10:1. The mass ratio of the alumina ceramic balls in the planetary ball mill to the mixed material formed by the oil tea shell powder and road asphalt was 30:1. The ball milling speed was 200 rpm and the ball milling time was 6 h.

[0050] S3. The ball-milled powder of S2 was placed in a tube furnace and heated to 1400°C at a rate of 10°C / min under an argon atmosphere for carbonization, and kept at this temperature for 1 h.

[0051] S4. The carbonized tea oil shell mixed powder of S3 was soaked in a 0.1M nitric acid solution and stirred for 24 hours for acid washing, and then washed with water, filtered, dried and passed through a 500-mesh sieve to obtain a hard-soft carbon negative electrode material.

[0052] Comparative Example 1

[0053] The only difference from Example 1 is that the mass ratio of the camellia oleifera shell powder to the road petroleum asphalt is 2:1.

[0054] Comparative Example 2

[0055] The only difference from Example 1 is that the mass ratio of the camellia oleifera shell powder to the road petroleum asphalt is 50:1.

[0056] Comparative Example 3

[0057] The only difference from Example 1 is that the carbonization temperature is 800°C.

[0058] Comparative Example 4

[0059] The only difference from Example 1 is that the carbonization temperature is 1600°C.

[0060] Performance Testing

[0061] When the hard and soft carbon negative electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 4 are used as negative electrode materials for sodium ion batteries, the electrode test conditions are as follows:

[0062] The electrode consists of 80% hard and soft carbon active material, 10% Super P, and 10% polyvinylidene fluoride (PVDF) by weight, with N,N-dimethylformamide as the diluent. Constant current charge and discharge performance tests were conducted on a NEWARE charge-discharge instrument using glass fiber as the separator, copper foil as the current collector, and a 1 mol / L NaPF□-DME solution as the electrolyte. The current density was 30 mA / g and the voltage range was 0.01 to 3 V. Super P is a small particle conductive carbon black, and the NaPF□-DME solution is a solution of pure 1,2-dimethoxyethane with sodium hexafluorophosphate as the solute. The final electrochemical performance results are shown in the table below.

[0063]

[0064]

[0065] Table 1

[0066] As can be seen from Table 1, Examples 1-4 all exhibit good electrochemical properties. The reversible capacity can reach up to 366.75 mAh / g at a current density of 30 mA / g, and the coulombic efficiency can reach up to 89%. Under appropriate raw material ratios, the reversible capacity at 30 mA / g exceeds 342 mAh / g, and the coulombic efficiency is greater than 82%. This shows that the high-value-added hard-soft carbon negative electrode material obtained by mixing tea oil shells with road petroleum asphalt and then carbonizing them at high temperature has a good effect and can effectively improve the sodium storage performance of biomass-based hard carbon materials.

[0067] In Comparative Example 1, an excess of road petroleum asphalt was added during preparation. The reversible capacity at a current density of 30 mA / g was 244.92 mAh / g, and the initial coulombic efficiency was 66%. Compared with Example 1, the electrochemical performance was poor. The high degree of graphitization of the soft carbon and the small interlayer spacing hindered the insertion and extraction of sodium ions. When the soft carbon content was excessive, the interlayer spacing of the entire composite material remained small, making it difficult for sodium ions to be smoothly extracted and inserted into the carbon layers during charge and discharge, resulting in a decrease in sodium storage capacity.

[0068] In Comparative Example 2: a small amount of road asphalt was added during preparation, and its reversible capacity at a current density of 30 mA / g was 276.34 mAh / g, and the first coulombic efficiency was 63%. Compared with Example 1, the electrochemical performance was poor. This is because when the amount of soft carbon is too small, the conductivity of the composite material mainly depends on the hard carbon, and the electron transfer efficiency is not high, which will hinder the insertion and extraction of sodium ions. Soft carbon can block some of the open pores of hard carbon, reduce the specific surface area, thereby inhibiting the formation of SEI film and increasing the sodium storage capacity. When the amount of soft carbon is too small, this inhibitory effect is weakened, and the formation of SEI film may be more serious, resulting in the loss of active substances and low first charge and discharge efficiency, and reduced sodium storage capacity.

[0069] In Comparative Example 3, when the carbonization temperature was low during the carbonization process, the reversible capacity at a current density of 30 mA / g was 208.87 mAh / g, and the initial coulombic efficiency was 51%, indicating poor electrochemical performance compared to Example 1. This is because when the carbonization temperature is low, the hard carbon derived from camellia oleifera shells is severely undergraphitized, resulting in a small interlayer spacing, which is not conducive to the insertion and deintercalation of sodium ions. The soft carbon plays a dominant role, thus affecting the capacity of the sodium-ion battery.

[0070] In Comparative Example 4, when the carbonization temperature was high during the carbonization process, the reversible capacity at a current density of 30 mA / g was 280.15 mAh / g, and the first coulombic efficiency was 76%, indicating poor electrochemical performance compared to Example 1. This is because, while the first coulombic efficiency improves at a higher carbonization temperature, the hard carbon derived from camellia oleifera shells is highly graphitized, exhibiting an ordered structure and a reduced interlayer spacing. This also shrinks the pore structure of the hard carbon structure, hindering the insertion and deintercalation of sodium ions, thereby affecting the capacity of the sodium-ion battery.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the 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 purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a hard and soft carbon negative electrode material derived from camellia oleifera shell, characterized in that: The following steps are involved: Obtaining camellia oleifera shell powder; The camellia oleifera shell powder and road petroleum asphalt are mixed uniformly by ball milling at a mass ratio of 10 to 20:1; Carbonizing the uniformly mixed mixture at a temperature of 1000-1400°C; The powder formed after carbonization is acid-washed, water-washed, filtered, dried and filtered to obtain a hard-soft carbon negative electrode material.

2. The method for preparing a hard and soft carbon negative electrode material derived from camellia oleifera shell according to claim 1, characterized in that: The specific process of obtaining the camellia oleifera shell powder is: The camellia oleifera shells are washed with water, dried at 80-120° C. for 4-12 hours, and then crushed and sieved in sequence to obtain camellia oleifera shell powder.

3. The method for preparing a hard and soft carbon negative electrode material derived from camellia oleifera shell according to claim 2, characterized in that: The mesh size of the sieve used in the sieving is 100-500 meshes.

4. The method for preparing a hard and soft carbon negative electrode material derived from camellia oleifera shell according to claim 1, characterized in that: The road petroleum asphalt includes one or more of AH-50, AH-70, AH-90, AH-110 and AH-130.

5. The method for preparing a hard and soft carbon negative electrode material derived from camellia oleifera shell according to claim 1, characterized in that: The ball milling is dry ball milling, and the mass ratio of the mixture formed by the oil-tea camellia shell powder and the road petroleum asphalt to the grinding balls is 1:10-30; The grinding speed during the dry ball milling process is 200-600 rpm, and the ball milling time is 3-6 hours.

6. The method for preparing a hard and soft carbon negative electrode material derived from camellia oleifera shell according to claim 5, characterized in that: The grinding balls are selected from one of zirconia balls, stainless steel balls and alumina ceramic balls, and the ball milling atmosphere during the dry ball milling process is one of air, nitrogen and argon.

7. The method for preparing a hard and soft carbon negative electrode material derived from oil-tea camellia shell according to claim 1, characterized in that: The heating rate during the carbonization is 5-10°C / min and the holding time is 1-3h.

8. The method for preparing a hard and soft carbon negative electrode material derived from camellia oleifera shell according to claim 1, characterized in that: The acid solution used in the pickling is one of hydrochloric acid, sulfuric acid and nitric acid, and its concentration is 0.1M to 2M. The pickling time is 12 to 24 hours. The mesh number of the sieve used in the filtration is 100 to 500 meshes.

9. A hard-soft carbon negative electrode material derived from oil-tea camellia shell, characterized in that: The material is prepared by the method for preparing a hard and soft carbon negative electrode material derived from camellia oleifera shell according to any one of claims 1 to 8.

10. An application, characterized in that: Use of a hard-soft carbon negative electrode material derived from tea oil shells as claimed in claim 9 in a sodium ion battery.

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