Silicon-containing biomass hard carbon negative electrode material and preparation method thereof

Abstract

The invention relates to the field of lithium ion battery material preparation, in particular to a silicon-containing biomass hard carbon composite negative electrode material as well as a preparation method and application thereof. Comprising the following steps: S1, uniformly mixing starch and carbohydrate raw materials according to a certain mass ratio to obtain a biomass precursor A1; s2, mixing a liquid silane coupling agent with a solid initiator according to a certain mass ratio to prepare a silicon precursor A2; s3, uniformly mixing the biomass precursor A1 and the silicon precursor A2 to prepare a composite precursor A3; and S4, performing high-temperature carbonization on the composite precursor A3, and crushing to obtain the silicon-containing biomass hard carbon negative electrode material. According to the invention, a simple pretreatment process is adopted to convert an industrially common silane coupling agent into a specific silicon precursor, the precursor is easy to be uniformly mixed with a biomass precursor, and alkoxy groups around each silicon site are easy to ablate and escape in the carbonization process, so that pores are formed near the silicon sites.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion battery material preparation, and in particular to a silicon-containing biomass hard carbon composite negative electrode material, a preparation method and application thereof. Background Art

[0002] With the continuous expansion of the portable electronic products and electric vehicle markets, the demand for energy storage technology is rising sharply. Compared with traditional energy storage systems, lithium-ion batteries are recognized by the industry as the core energy storage system in the field of efficient electrochemical energy storage due to their outstanding advantages such as high energy density, long cycle life, safety and pollution-free. The electrochemical performance of lithium-ion batteries depends largely on the selection of negative electrode materials. Graphite, as a widely used low-cost commercial negative electrode material, is widely used for its excellent conductivity and excellent reversibility. However, the relatively low theoretical capacity of graphite (372 mAh / g) restricts its further development. Compared with graphite negative electrode, hard carbon has a higher specific surface area and a more developed pore structure, which helps to provide more lithium storage sites, thereby increasing the lithium storage capacity of negative electrode materials. Moreover, hard carbon has a wide range of raw material sources and excellent safety performance. Therefore, hard carbon negative electrode materials have been widely studied in the field of lithium-ion batteries in recent years.

[0003] At present, the raw materials used to prepare hard carbon are mainly biomass, asphalt, resin and organic polymer. Among these raw materials, biomass (starch, sugar, etc.) has become an ideal precursor for preparing hard carbon negative electrode materials due to its wide source, environmental friendliness and low cost. However, the capacity of pure biomass hard carbon materials is still difficult to meet the application needs of high energy density lithium-ion batteries.

[0004] In order to further improve the lithium storage capacity of hard carbon negative electrode materials, researchers have tried to composite silicon with hard carbon. Silicon is a negative electrode material with a high theoretical specific capacity (4200 mAh / g), but its volume expansion during charging and discharging is serious (3~4 times the volume expansion), resulting in poor cycle stability and weak conductivity, which limits its practical application. In principle, the composite of hard carbon and silicon can take advantage of the structural stability and excellent conductivity of the former and the high capacity characteristics of the latter to achieve complementary advantages. However, the current related composite processes (such as carbon-coated silicon, deposition of silicon on porous carbon surfaces, construction of carbon / silicon eggshell-yolk structures, etc.) have problems such as cumbersome processes, high production costs, or uneven silicon distribution and low utilization, which restricts its practical application. Summary of the invention

[0005] In view of the above existing technical problems, the present invention provides a silicon-containing biomass hard carbon anode material, a preparation method thereof and an application thereof, which are used to overcome the technical problems existing in the current silicon-carbon composite process, such as cumbersome operation, high cost, uneven silicon distribution, low utilization rate, etc. The present invention selects a common mixture of starch and sugar as the biomass precursor, and at the same time converts a common silane coupling agent into a specific silicon precursor through a simple pretreatment process. After mixing the two precursors in a suitable ratio, further through processes such as pre-oxidation, pulverization, carbonization, and re-pulverization, a class of silicon-containing biomass hard carbon anode materials with high lithium storage capacity and excellent cycle stability is obtained.

[0006] In the present invention, a preparation method of a silicon-containing biomass hard carbon anode material includes the following steps: S1. Mix starch and sugar raw materials evenly according to a certain mass ratio to obtain a biomass precursor A1; S2. Mix a liquid silane coupling agent and a solid initiator according to a certain mass ratio, stir until the solid initiator is completely dissolved, react for a period of time, then dry and pulverize to obtain a silicon precursor A2; S3. After mixing the biomass precursor A1 and the silicon precursor A2 evenly according to a certain mass ratio, carry out pre-oxidation treatment, and after cooling, pulverize to obtain a composite precursor A3; S4. Further carry out high-temperature carbonization on the composite precursor A3, and after cooling, pulverize to obtain a silicon-containing biomass hard carbon anode material.

[0007] Further, in step S1, the starch is wheat starch or corn starch; The sugar raw material is one or a combination of several of glucose, sucrose, and fructose; And the mass ratio of the starch to the sugar raw material is 1:1 to 5.

[0008] Further, in step S2, the selected silane coupling agent is one or a combination of several of KH550, KH560, and KH570; The solid initiator is one or a combination of several of dibenzoyl peroxide, azobisisobutyronitrile, azobisisoheptonitrile, and dimethyl azobisisobutyrate; And the mass ratio of the solid initiator to the silane coupling agent is 1 to 5:100; Further, in step S2, the reaction time is 4 to 36 h; The temperature condition for drying is 50 to 80 °C, and the heat preservation time condition is 24 to 48 h.

[0009] Further, in step S3, the mass ratio of the biomass precursor A1 to the silicon precursor A2 is 1:1 to 5.

[0010] Further, in step S3, the conditions for the pre-oxidation treatment are as follows: the heating rate is 2 - 5 °C / min, after heating to 150 - 250 °C, keep the temperature for 5 - 10 h, and the pre-oxidation atmosphere is one of air or oxygen.

[0011] Further, in step S4, the conditions for the high-temperature carbonization treatment of the composite precursor A3 are as follows: the heating rate is 2 - 5 °C / min, after heating to 1100 - 1400 °C, keep the temperature for 2 - 5 h, the carbonization atmosphere is one of argon or nitrogen, and the gas flow rate is 50 - 150 mL / min.

[0012] The silicon-containing biomass hard carbon anode material prepared by the above preparation method.

[0013] The application of the above silicon-containing biomass hard carbon anode material in a lithium-ion battery.

[0014] The present invention has the following advantages and beneficial effects compared with the prior art: 1. The present invention uses a simple pretreatment process to convert a commonly used silane coupling agent in industry into a specific silicon precursor. This precursor is not only easy to uniformly mix with the biomass precursor, but also the alkoxy groups around each silicon site are easy to ablate and escape during the carbonization process, thereby forming pores near the silicon sites.

[0015] 2. In the silicon-containing biomass hard carbon anode material prepared by the present invention, the silicon is evenly distributed and has a high utilization rate. Moreover, based on the buffering effect of the abundant internal pores on volume expansion, the electrochemical effects of high lithium storage capacity and good stable cycle performance are synchronously achieved.

[0016] 3. The material preparation process of the present invention is simple and easy to scale up. Moreover, no solvent is used during the preparation process and no waste liquid is generated, which has the advantages of safety and environmental protection. Description of the Drawings

[0017] Figure 1 is the scanning electron microscope image of the silicon-containing biomass hard carbon anode material obtained in Example 1 of the present invention; Figure 2 is the first charge-discharge curve of the silicon-containing biomass hard carbon anode material obtained in Example 1 of the present invention at a current density of 0.03 Ag -1 in the lithium-ion battery test; Figure 3 is the cycle curve of the silicon-containing biomass hard carbon anode material obtained in Example 1 of the present invention at a current density of 0.5 Ag -1 in the lithium-ion battery test. Detailed Embodiments

[0018] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings. For those not specified in the embodiments, the techniques or conditions are described in the literature in the field or according to the product specifications. The reagents or instruments used without indicating the manufacturer can be obtained through commercial purchases as conventional products.

[0019] The first object of the present invention is to provide a preparation method of a silicon-containing biomass hard carbon anode material, comprising the following steps: S1. Mix starch and a saccharide raw material evenly according to a certain mass ratio to obtain a biomass precursor A1; specifically, the starch is wheat starch or corn starch; the saccharide raw material is one or a combination of glucose, sucrose, and fructose; and the mass ratio of the starch to the saccharide raw material is 1:1 to 5. Preferably, the mass ratio of starch to the saccharide raw material can be 1:1, 1:2, 1:3, 1:4, 1:5.

[0020] S2. Mix a liquid silane coupling agent and a solid initiator according to a certain mass ratio, stir until the solid initiator is completely dissolved, react for a period of time, then dry and pulverize to obtain a silicon precursor A2; specifically, the selected silane coupling agent is one or several of KH550, KH560, and KH570; the solid initiator is one or several of benzoyl peroxide, azobisisobutyronitrile, azobisisoheptonitrile, and dimethyl azobisisobutyrate; and the mass ratio of the solid initiator to the silane coupling agent is 1 to 5:100. Preferably, it can be 1:100, 2:100, 3:100, 4:100, 5:100; preferably, in this step, the reaction time is 4 to 36 h; the drying temperature condition is 50 to 80 °C, and the heat preservation time condition is 24 to 48 h.

[0021] S3. After mixing the biomass precursor A1 and the silicon precursor A2 evenly according to a certain mass ratio, perform pre-oxidation treatment, cool, and pulverize to obtain a composite precursor A3; among them, the mass ratio of the biomass precursor A1 to the silicon precursor A2 is 1:1 to 5. Preferably, it can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5. The pre-oxidation treatment conditions are: heat up to 150 to 250 °C and keep warm for 5 to 10 h, the heating rate is 2 to 5 °C / min, and the pre-oxidation atmosphere is one of air or oxygen.

[0022] S4. Further perform high-temperature carbonization on the composite precursor A3, and after cooling, crush it to obtain a silicon-containing biomass hard carbon anode material. Among them, the conditions for the high-temperature carbonization treatment of the composite precursor A3 are as follows: the heating rate is 2-5 °C / min, after heating to 1100-1400 °C, keep it warm for 2-5 h, the carbonization atmosphere is one of argon or nitrogen, and the gas flow rate is 50-150 mL / min.

[0023] The second object of the present invention is to provide the silicon-containing biomass hard carbon anode material prepared by the above preparation method.

[0024] The third object of the present invention is to provide the application of the above-mentioned silicon-containing biomass hard carbon anode material in a lithium-ion battery.

[0025] <Example 1> A preparation method of a silicon-containing biomass hard carbon anode material specifically includes the following steps: S1. Take 50 g of sucrose and 50 g of corn starch and mix them in a high-speed crusher to obtain a biomass precursor A1; S2. Dissolve 5 g of azobisisobutyronitrile in 500 mL of silane coupling agent KH570, stir with a stirrer at room temperature for 6 h until completely dissolved to obtain a colorless transparent solution, dry the solution in an oven at 60 °C for 48 h, and crush the obtained solid in a high-speed crusher to obtain a powdery silicon precursor A2; S3. Take 40 g of the biomass precursor A1 obtained in step S1, add 60 g of the silicon precursor A2 obtained in step S2, mix them evenly in a high-speed crusher, heat the obtained product to 230 °C at a rate of 5 °C / min under air conditions and keep it warm for 8 h, and crush the pre-oxidized product in a high-speed crusher after cooling to obtain a composite precursor A3; S4. Heat the composite precursor A3 obtained in step S3 to 1300 °C at a rate of 2 °C / min under argon protection, keep it warm for 4 h with an inlet gas flow rate of 100 mL / min, and crush the obtained product evenly in a high-speed crusher after cooling to obtain a silicon-containing biomass hard carbon anode material.

[0026] Figure 1 is the scanning electron microscope image of the silicon-containing biomass hard carbon anode material obtained in this Example 1; from Figure 1 it can be seen that after pre-oxidation and high-temperature sintering, the material shows a smooth and irregular block structure on the surface, without obvious fragmentation and swelling, and the structure is relatively dense and stable. There are no obvious pores and defects on the surface of the material, corresponding to the lower specific surface area of the material.

[0027] Figure 2 is the first-cycle charge-discharge curve of the silicon-containing biomass hard carbon anode material obtained in this Example 1 at a current density of 0.03 A g -1 ; fromFigure 2 It can be seen that the discharge voltage of the first discharge material rapidly drops to 1.0 V, and a steep discharge slope appears at 1.0 - 0.5 V, indicating the formation of the SEI film. Subsequently, a long discharge plateau appears at 0.5 - 0.01 V, indicating the lithium ion intercalation process. In the charge curve, a large charge slope appears in the voltage range of 0.01 - 0.5 V, corresponding to the de-lithiation process of the material. The initial discharge specific capacity of the material is 1091.83 mAh g -1 , and the initial charge specific capacity is 853.11 mAh g -1 , and the first efficiency is 78.13%. The low initial Coulomb efficiency is mainly due to the formation of the SEI film, irreversible Li2O, and lithium silicate, which consume a large amount of Li + .

[0028] Figure 3 This is the cycle curve diagram of the silicon-containing biomass hard carbon anode material obtained in Example 1 at a current density of 0.5 A g -1 in the lithium-ion battery test; from Figure 3 it can be seen that the material is cycled 100 times at a current density of 0.5 A g -1 , and the initial cycle specific capacity of the material is 557 mAh g -1 and the specific capacity after 100 cycles is 556.35 mAh g -1 . The capacity of the material does not show obvious attenuation, and the capacity retention rate is close to 100%. This shows that the material prepared by this method has a stable structure, and while improving the capacity of the material, it also alleviates the volume expansion of silicon.

[0029] <Example 2> A preparation method of a silicon-containing biomass hard carbon anode material specifically includes the following steps: S1. Take 50 g of glucose and 100 g of corn starch and mix them in a high-speed grinder to obtain a biomass precursor A1; S2. Dissolve 10 g of azobisisobutyronitrile in 500 mL of silane coupling agent KH550, stir with a stirrer at room temperature for 4 h until completely dissolved to obtain a colorless transparent solution. Dry this solution in an oven at 60 °C for 48 h, and pulverize the obtained solid in a high-speed grinder to obtain a powdery silicon precursor A2; S3. Take 50 g of the biomass precursor A1 obtained in step S1, add 70 g of the silicon precursor A2 obtained in step S2, mix them evenly in a high-speed grinder, and heat the obtained product to 200 °C at a rate of 2 °C / min under air conditions and hold for 10 h. After cooling, pulverize the pre-oxidized product in a high-speed grinder to obtain a composite precursor A3; S4. Heat the composite precursor A3 obtained in step S3 to 1400 °C at a rate of 5 °C / min under nitrogen protection, keep it at this temperature for 3 h with an inlet gas flow rate of 80 mL / min, and after cooling, pulverize the obtained product evenly in a high-speed pulverizer to obtain a silicon-containing biomass hard carbon anode material.

[0030] <Example 3> A preparation method of a silicon-containing biomass hard carbon anode material specifically includes the following steps: S1. Take 20 g of fructose and 30 g of wheat starch, mix them in a high-speed pulverizer to obtain a biomass precursor A1; S2. Dissolve 15 g of azodiisobutyronitrile in 500 mL of silane coupling agent KH560, stir it with a stirrer at room temperature until completely dissolved to obtain a colorless transparent solution, dry this solution in an oven at 80 °C for 48 h, and pulverize the obtained solid in a high-speed pulverizer to obtain a powdery silicon precursor A2; S3. Take 50 g of the biomass precursor A1 obtained in step S1, add 100 g of the silicon precursor A2 obtained in step S2, mix them evenly in a high-speed pulverizer, heat the obtained product to 250 °C at a rate of 5 °C / min under air conditions and keep it at this temperature for 6 h, and after cooling, pulverize the pre-oxidized product in a high-speed pulverizer to obtain a composite precursor A3.

[0031] S4. Heat the composite precursor A3 obtained in step S3 to 1200 °C at a rate of 5 °C / min under argon protection, keep it at this temperature for 4 h with an inlet gas flow rate of 120 mL / min, and after cooling, pulverize the obtained product evenly in a high-speed pulverizer to obtain a silicon-containing biomass hard carbon anode material.

[0032] <Comparative Example 1> A preparation method of a silicon-containing biomass hard carbon anode material specifically includes the following steps: S1. Take 20 g of glucose and 40 g of wheat starch, mix them in a high-speed pulverizer to obtain a biomass precursor A1; S2. Dissolve 10 g of azodiisobutyronitrile in 500 mL of silane coupling agent KH570, stir it with a stirrer at room temperature until completely dissolved to obtain a colorless transparent solution, dry this solution in an oven at 75 °C for 48 h, and pulverize the obtained solid in a high-speed pulverizer to obtain a powdery silicon precursor A2; S3. Take 50 g of the biomass precursor A1 obtained in step S1, add 100 g of the silicon precursor A2 obtained in step S2, mix them evenly in a high-speed pulverizer, heat the obtained product to 250 °C at a rate of 5 °C / min under nitrogen conditions and keep it at this temperature for 6 h, and after cooling, pulverize the pre-carbonized product in a high-speed pulverizer to obtain a composite precursor A3; S4. The composite precursor A3 obtained in step S3 was heated to 1200°C at 5°C / min under nitrogen protection, and the temperature was kept at an air flow rate of 120 mL / min for 4 h. After cooling, the obtained product was evenly crushed in a high-speed crusher to obtain a silicon-containing biomass hard carbon negative electrode material.

[0033] <Comparative Example 2> A method for preparing a silicon-containing biomass hard carbon negative electrode material specifically comprises the following steps: S1. Take 20 g of fructose and 30 g of corn starch and mix them in a high-speed grinder to obtain a biomass precursor A1; S2. Dissolve 15 g of azobisisobutyronitrile in 500 mL of silane coupling agent KH560, stir with a stirrer at room temperature until completely dissolved to obtain a colorless transparent solution, dry the solution in an oven at 80 °C for 48 h, and grind the obtained solid in a high-speed grinder to obtain a powdered silicon precursor A2; S3. Take 50 g of the biomass precursor A1 obtained in step S1, add 100 g of the silicon precursor A2 obtained in step S2 and mix them evenly in a high-speed pulverizer, and heat the resulting product to 250 ° C at 5 ° C / min under nitrogen conditions for 6 h, and then pulverize the pre-oxidation product in a high-speed pulverizer after cooling to obtain a composite precursor A3; S4. The composite precursor A3 obtained in step S3 was heated to 1300°C at 5°C / min under nitrogen protection, and the temperature was kept at an air flow rate of 140 mL / min for 3 h. After cooling, the obtained product was evenly crushed in a high-speed crusher to obtain a silicon-containing biomass hard carbon negative electrode material.

[0034] The silicon-containing biomass hard carbon negative electrode materials prepared in the above Examples 1 to 3 and Comparative Examples 1 and 2 were used as negative electrode materials for lithium-ion batteries and the electrochemical performance was tested as follows: The silicon-containing biomass hard carbon negative electrode material, the conductive agent Super P and sodium carboxymethyl cellulose (CMC) were weighed in a mass ratio of 91:3:6, and a small amount of deionized water was added to the ball mill to fully ball mill to obtain a black paste slurry. The above slurry was coated on the copper foil current collector as a test electrode, and the metal lithium sheet was used as a comparative electrode to assemble into a button battery. The electrolyte was 1M lithium hexafluorophosphate in a mixed solution of dimethyl carbonate (DMC): ethylene carbonate (EC): ethyl methyl carbonate (EMC) with a volume ratio of 1:1:1, and the button battery was assembled with CR2430 stainless steel as the battery shell. The capacity and the first coulomb efficiency were tested at 0.03 A / g in the voltage range of 0.01~3 V, and the cycle performance was tested at 0.5 A / g; the electrochemical properties of the lithium ion batteries prepared in each embodiment and each comparative example are shown in Table 1 below.

[0035] Table 1

[0036] As can be seen from Table 1, the silicon-containing biomass hard carbon anode material prepared by the present invention has a high reversible capacity and exhibits good performance during the cycle and rate performance tests. When the pre-oxidation in the comparative example is changed to calcination under nitrogen protection, the lithium storage sites of the prepared silicon-containing biomass hard carbon anode material are significantly reduced, the reversible capacity of the silicon-containing biomass hard carbon anode material decreases, there are more internal defects in the silicon-containing biomass hard carbon anode material, and part of the lithium undergoes side reactions and is lost during the first charge and discharge process, resulting in a lower initial Coulombic efficiency of the silicon-containing biomass hard carbon anode material. In addition, during long-term cycling, there may be uneven distribution of some silicon, leading to a slight decrease in the capacity of the silicon-containing biomass hard carbon anode material during cycling.

[0037] Where not otherwise involved, it shall apply to the prior art.

[0038] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustration and not for limiting the scope of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to substitute, but will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a silicon-containing biomass hard carbon anode material, characterized in that: It includes the following steps: S1. Mix starch and saccharide raw materials evenly according to a certain mass ratio to obtain biomass precursor A1; S2. Mix liquid silane coupling agent and solid initiator according to a certain mass ratio, stir until the solid initiator is completely dissolved, react for a period of time, then dry and crush to obtain silicon precursor A2; S3. After mixing the biomass precursor A1 and the silicon precursor A2 evenly according to a certain mass ratio, carry out pre-oxidation treatment. After cooling, crush to obtain composite precursor A3; S4. Further carry out high-temperature carbonization on the composite precursor A3, and after cooling, crush to obtain a silicon-containing biomass hard carbon anode material.

2. The preparation method of the silicon-containing biomass hard carbon anode material according to claim 1, characterized in that: In step S1, the starch is wheat starch or corn starch; The saccharide raw material is one or more of glucose, sucrose, and fructose; And, the mass ratio of the starch to the saccharide raw material is 1:1 to 5.

3. The preparation method of the silicon-containing biomass hard carbon anode material according to claim 1, characterized in that: In step S2, the selected silane coupling agent is one or more of KH550, KH560, and KH570; The solid initiator is one or more of dibenzoyl peroxide, azobisisobutyronitrile, azobisisoheptonitrile, and dimethyl azobisisobutyrate; And, the mass ratio of the solid initiator to the silane coupling agent is 1 to 5:

100.

4. The preparation method of the silicon-containing biomass hard carbon anode material according to claim 3, characterized in that: In step S2, the reaction time is 4 to 36 h; The temperature condition for drying is 50 to 80 °C, and the heat preservation time condition is 24 to 48 h.

5. The preparation method of the silicon-containing biomass hard carbon anode material according to claim 1, characterized in that: In step S3, the mass ratio of the biomass precursor A1 to the silicon precursor A2 is 1:1 to 5.

6. The preparation method of the silicon-containing biomass hard carbon anode material according to claim 5, characterized in that: In step S3, the pre-oxidation treatment conditions are: the heating rate is 2 to 5 °C / min, after heating to 150 to 250 °C, keep warm for 5 to 10 h, and the pre-oxidation atmosphere is one of air or oxygen.

7. The preparation method of the silicon-containing biomass hard carbon anode material according to claim 1, characterized in that: In step S4, the conditions for high-temperature carbonization treatment of the composite precursor A3 are: the heating rate is 2 to 5 °C / min, after heating to 1100 to 1400 °C, keep warm for 2 to 5 h, the carbonization atmosphere is one of argon or nitrogen, and the gas flow rate is 50 to 150 mL / min.

8. A silicon-containing biomass hard carbon anode material prepared by the preparation method according to any one of claims 1-7.

9. Application of the silicon-containing biomass hard carbon anode material according to claim 8 in a lithium-ion battery.

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