Graded porous hard carbon-silicon composite negative electrode material and preparation method thereof

Abstract

The invention provides a graded porous hard carbon-silicon composite negative electrode material and a preparation method thereof, and belongs to the technical field of new energy battery electrode materials. The preparation method comprises the following steps: mixing pitch-based soft carbon and potassium hydroxide, performing ball milling, performing heating activation in a nitrogen atmosphere, performing cooling, performing washing with hydrochloric acid until the mixture is neutral, and performing vacuum drying to obtain a product A; dispersing the product A in absolute ethyl alcohol, adding polyether diamine and a silane coupling agent (KH560), dropwise adding a triethylamine solution, heating, stirring, performing reflux reaction, and centrifuging and collecting a product B after the reaction is completed; heating and curing the product B in vacuum to obtain a product C; dispersing the product C in water, adding phenol, carrying out ultrasonic dispersion, adjusting the pH value to 8.5-9, then dropwise adding a formaldehyde solution, carrying out a stirring reaction, and after the reaction is finished, carrying out centrifugation and drying to obtain a product D; and carbonizing the product D under the protection of argon to obtain the graded porous hard carbon-silicon composite negative electrode material. According to the graded porous hard carbon-silicon composite negative electrode material, soft carbon and hard carbon are utilized to construct a graded porous structure.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy battery electrode materials, and in particular to a hierarchical porous hard carbon-silicon composite negative electrode material and a preparation method thereof. Background Art

[0002] Traditional lithium-ion batteries use graphite as the negative electrode material, but with the continuous increase in market demand, industry researchers are also constantly exploring new negative electrode materials.

[0003] Porous carbon materials, characterized by chemical stability, high electrical conductivity, good mechanical flexibility, large surface area, rich pore structures, and adjustable pore size, are widely used in fields such as adsorption, catalysis, and electrochemical energy storage. However, a major drawback of carbon materials is their low specific capacity. Silicon materials can effectively compensate for these shortcomings. Therefore, researchers are interested in developing suitable anode materials using porous carbon and silicon materials. Summary of the Invention

[0004] In order to solve the problems mentioned in the background technology, the present invention provides a method for preparing a graded porous hard carbon-silicon composite negative electrode material, wherein the inner core is made of soft carbon, the middle layer is wrapped with a polymerization product of polyethylenediamine and KH560, and the outer layer is made of phenolic resin hard carbon material. Both the soft carbon and the hard carbon are porous materials, and the pore sizes of the two are different to construct a graded porous structure.

[0005] Specifically: A method for preparing a hierarchical porous hard carbon-silicon composite negative electrode material, comprising the following steps: Step 1: Mix the asphalt-based soft carbon and potassium hydroxide and ball-mill them, heat and activate them under a nitrogen atmosphere, cool them, wash them with hydrochloric acid until they are neutral, and vacuum dry them to obtain product A; Step 2: Disperse the product A obtained in step 1 in anhydrous ethanol, add polyether diamine and KH560, and then dropwise add triethylamine solution. Heat and stir under reflux for reaction. After the reaction is completed, centrifuge and collect the product B. Step 3: Heat and solidify the product B obtained in step 2 under vacuum to obtain product C; Step 4: Disperse the product C obtained in step 3 in water, add phenol, disperse by ultrasonication, adjust the pH value to 8.5-9, then dropwise add formaldehyde solution, stir to react, centrifuge after the reaction is complete, and dry to obtain product D; Step 5: Carbonize the product D obtained in step 4 under argon protection to obtain a hierarchical porous hard carbon-silicon composite negative electrode material.

[0006] Furthermore, in step one, the mass ratio of asphalt-based soft carbon to potassium hydroxide is 1:(3-3.5).

[0007] Furthermore, in step 1, the temperature is heated to 700-710° C. and activated for 2-2.5 hours.

[0008] Furthermore, in step 2, the solid content of product A in anhydrous ethanol is controlled to be 10% to 12%; the mass fraction of triethylamine in the triethylamine solution is controlled to be 0.5% to 0.7%; and the mass ratio of product A: polyether diamine: KH560: triethylamine solution is 1: (0.8 to 0.85): (0.65 to 0.7): (0.007 to 0.009).

[0009] Furthermore, in step 2, the mixture is heated to 80-82° C. and refluxed for 6-6.5 hours.

[0010] Furthermore, in step three, the mixture is heated to 120-125° C. and cured for 2-2.5 hours.

[0011] Furthermore, in step 4, the mass fraction of formaldehyde in the formaldehyde solution is controlled at 35% to 37%, and the mass ratio of product C: phenol: formaldehyde solution is 1: (0.4 to 0.45): (0.6 to 0.65).

[0012] Furthermore, in step 4, sodium hydroxide is used to adjust the pH value; the reaction is stirred at 55-58° C. for 8-8.5 hours; and the drying temperature is 100-105° C.

[0013] Furthermore, during the carbonization process in step five, the temperature was first increased to 300°C at 2°C / min and kept at this temperature for 1 hour, then increased to 500°C at 1°C / min and kept at this temperature for 1 hour, then increased to 900°C at 3°C / min and kept at this temperature for 2 hours, and then cooled to terminate the carbonization.

[0014] In addition, the present invention also provides a hierarchical porous hard carbon-silicon composite negative electrode material, which is prepared by the above-mentioned preparation method.

[0015] In the present invention, product A refers to a porous soft carbon core formed after activation of pitch-based soft carbon; Product B refers to carbon-silicon composite particles in which a porous soft carbon core is coated with a prepolymer network formed by polyether diamine and KH560 through epoxy ring opening; Product C refers to carbon silicon core-shell particles cured by vacuum curing to form a Si-O-Si / Si-OC cross-linked network of silicon nitrogen hybrid layers; Product D refers to the precursor of phenolic resin-coated carbon silicon core-shell particles.

[0016] Compared with the prior art, the present invention has the following advantages: 1. The preparation method of the hierarchical porous hard carbon silicon composite negative electrode material provided by the present invention adopts asphalt-based soft carbon as the core, polyether diamine and silane coupling agent KH560 in situ react to form a high-capacity silicon carbon middle layer and wrap the porous soft carbon core, the outermost layer is coated with phenolic resin formed by polymerization of phenol and formaldehyde, and after gradient carbonization, nitrogen / silicon co-doped hard carbon coated soft carbon is formed, the soft carbon is mainly composed of micropores and mesopores, and the hard carbon is mainly composed of micropores, thereby constructing a hierarchical porous structure; the high specific surface area mesopores of the core serve as rapid ion transport channels; the middle layer is formed by in-situ hybridization of polyether diamine / KH560 to form molecular-level dispersed The active phase contributes to the conversion reaction capacity; the outer layer of microporous hard carbon inhibits volume expansion and realizes fast ion transport through gradient pore penetration.

[0017] 2. The preparation method of the hierarchical porous hard carbon-silicon composite negative electrode material provided by the present invention utilizes the ring-opening reaction between the epoxy group of KH560 and the primary amine group of polyether diamine to form a β-hydroxy tertiary amine structure. The generated hydroxyl groups enhance hydrophilicity and promote the interface compatibility of subsequent phenolic resin coating; KH560 trimethoxysilane hydrolyzes and condenses to form a ≡Si-O-Si≡ network, which locks the silicon atoms at the cross-linking points to prevent silicon migration and agglomeration during high-temperature treatment; after pyrolysis, nanostructured , providing active lithium storage sites.

[0018] 3. The preparation method of the hierarchical porous hard carbon-silicon composite negative electrode material provided by the present invention uses polyether diamine to form multiple synergistic effects with other materials in the system, which is specifically embodied as follows: through the primary amino group of polyether diamine Attack the epoxy group of KH560 to form a β-hydroxy tertiary amine bond, which serves as the skeleton of the hybrid network, thereby anchoring the silicon source (KH560) to the soft carbon surface with a covalent bond to avoid silicon agglomeration. The amino group that does not participate in the epoxy ring opening condenses with the -COOH on the soft carbon surface to form an amide bond, thereby improving the interface bonding strength. During the carbonization process, the ether chain introduced by the polyether diamine breaks down to produce volatile small molecules (formaldehyde / acetaldehyde), forming 3-8nm secondary mesopores in the middle layer, forming pores that penetrate the inner layer (soft carbon) and the outer layer (hard carbon). In addition, the polyether diamine also plays the role of providing a nitrogen source and regulating the electronic structure. During pyrolysis, the nitrogen-containing free radicals released by the decomposition of the amino group are embedded in the carbon lattice to form carbon-nitrogen dopants of graphitic nitrogen and pyridinic nitrogen, which optimize the performance of the porous carbon material, improve the electronic conductivity and additional cashier sites, and the nitrogen atoms form Si-N bonds with silicon, which The phase is locked in the carbon matrix, reducing the expansion rate of silicon. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0020] In order to facilitate those skilled in the art to implement the present invention, some of the reagents used in the examples and comparative examples are now described: Asphalt-based soft carbon: medium-temperature coal tar, Hebei Zhengri Chemical, finely ground to a particle size of D50 = 8 ± 2 μm; Polyether diamine: polyetheramine D4000 aliphatic polyether diamine, Wuhan Lanabai Pharmaceutical Chemical; KH560: Shandong Bosheng Chemical; Triethylamine: Shandong Hongyuan Chemical; Phenol: Shandong Feihong New Materials.

[0021] In order to verify the beneficial effects of the present invention, several groups of embodiments and comparative examples are designed and verified by comparative analysis.

[0022] Example 1 A hierarchical porous hard carbon-silicon composite negative electrode material, the preparation steps of which include: Step 1: Mix pitch-based soft carbon and potassium hydroxide in a mass ratio of 1:3 and ball-mill, heat to 700°C under a nitrogen atmosphere, activate for 2 hours, cool, wash with 1M hydrochloric acid until neutral, and vacuum dry to obtain product A; Step 2: Disperse the product A obtained in step 1 in anhydrous ethanol to control the solid content to 10%, add polyether diamine and KH560, and then dropwise add triethylamine solution; the triethylamine solution is prepared with triethylamine and deionized water, and the mass fraction of triethylamine is 0.5%; the mass ratio of product A: polyether diamine: KH560: triethylamine solution is 1:0.8:0.65:0.007; heat to 80°C, stir and reflux for 6 hours, and after the reaction is completed, centrifuge and collect product B; Step 3: Heat the product B obtained in step 2 to 120° C. under vacuum and cure for 2 h to obtain product C; Step 4: Disperse the product C obtained in step 3 in water, add phenol, ultrasonically disperse, adjust the pH value to 8.5 with NaOH solution, then add formaldehyde solution dropwise, and stir and react at 55°C for 8 hours; the formaldehyde solution is prepared with formaldehyde and deionized water, and the formaldehyde mass fraction is controlled at 35%; the mass ratio of product C: phenol: formaldehyde solution is 1:0.4:0.6; after the reaction is completed, centrifuge and dry at 100°C to obtain product D; Step 5. Carbonize the product D obtained in step 4 under argon protection, first heating to 300°C at 2°C / min and keeping warm for 1 hour, then heating to 500°C at 1°C / min and keeping warm for 1 hour, then heating to 900°C at 3°C / min and keeping warm for 2 hours, and then cool down to end carbonization to obtain a graded porous hard carbon-silicon composite negative electrode material.

[0023] Example 2 A hierarchical porous hard carbon-silicon composite negative electrode material, the preparation steps of which include: Step 1: Mix pitch-based soft carbon and potassium hydroxide in a mass ratio of 1:3.5 and ball-mill, heat to 710°C under a nitrogen atmosphere, activate for 2.5 hours, cool, wash with 1M hydrochloric acid until neutral, and vacuum dry to obtain product A; Step 2: Disperse the product A obtained in step 1 in anhydrous ethanol to control the solid content to 12%, add polyether diamine and KH560, and then dropwise add triethylamine solution; the triethylamine solution is prepared with triethylamine and deionized water, and the mass fraction of triethylamine is 0.7%; the mass ratio of product A: polyether diamine: KH560: triethylamine solution is 1:0.85:0.7:0.009; heat to 82°C, stir and reflux for 6.5 hours, and after the reaction is completed, centrifuge and collect product B; Step 3: Heat the product B obtained in step 2 to 125° C. under vacuum and cure for 2.5 hours to obtain product C; Step 4: Disperse the product C obtained in step 3 in water, add phenol, ultrasonically disperse, adjust the pH value to 9 with NaOH solution, then add formaldehyde solution dropwise, and react with stirring at 58°C for 8.5 hours; the formaldehyde solution is prepared with formaldehyde and deionized water, and the formaldehyde mass fraction is controlled at 37%; the mass ratio of product C: phenol: formaldehyde solution is 1:0.45:0.65; after the reaction is completed, centrifuge and dry at 105°C to obtain product D; Step 5. Carbonize the product D obtained in step 4 under argon protection, first heating to 300°C at 2°C / min and keeping warm for 1 hour, then heating to 500°C at 1°C / min and keeping warm for 1 hour, then heating to 900°C at 3°C / min and keeping warm for 2 hours, and then cool down to end carbonization to obtain a graded porous hard carbon-silicon composite negative electrode material.

[0024] Example 3 A hierarchical porous hard carbon-silicon composite negative electrode material, the preparation steps of which include: Step 1: Mix pitch-based soft carbon and potassium hydroxide in a mass ratio of 1:3 and ball-mill, heat to 710°C under a nitrogen atmosphere, activate for 2.5 hours, cool, wash with 1M hydrochloric acid until neutral, and vacuum dry to obtain product A; Step 2: Disperse the product A obtained in step 1 in anhydrous ethanol to control the solid content to 11%, add polyether diamine and KH560, and then dropwise add triethylamine solution; the triethylamine solution is prepared with triethylamine and deionized water, and the mass fraction of triethylamine is 0.6%; the mass ratio of product A: polyether diamine: KH560: triethylamine solution is 1:0.82:0.7:0.008; heat to 81°C, stir and reflux for 6 hours, and after the reaction is completed, centrifuge and collect product B; Step 3: Heat the product B obtained in step 2 to 123° C. under vacuum and cure for 2.5 hours to obtain product C; Step 4: Disperse the product C obtained in step 3 in water, add phenol, ultrasonically disperse, adjust the pH value to 8.6 with NaOH solution, then add formaldehyde solution dropwise, and stir and react at 57°C for 8 hours; the formaldehyde solution is prepared with formaldehyde and deionized water, and the formaldehyde mass fraction is controlled at 36%; the mass ratio of product C: phenol: formaldehyde solution is 1:0.4:0.65; after the reaction is completed, centrifuge and dry at 103°C to obtain product D; Step 5. Carbonize the product D obtained in step 4 under argon protection, first heating to 300°C at 2°C / min and keeping warm for 1 hour, then heating to 500°C at 1°C / min and keeping warm for 1 hour, then heating to 900°C at 3°C / min and keeping warm for 2 hours, and then cool down to end carbonization to obtain a graded porous hard carbon-silicon composite negative electrode material.

[0025] Comparative Example 1 A negative electrode material, the preparation steps of which include: Step 1: Mix pitch-based soft carbon and potassium hydroxide in a mass ratio of 1:3 and ball-mill, heat to 700°C under a nitrogen atmosphere, activate for 2 hours, cool, wash with 1M hydrochloric acid until neutral, and vacuum dry to obtain product A; Step 2: Disperse the product A obtained in step 1 in anhydrous ethanol to control the solid content to 10%, add KH560, and then dropwise add triethylamine solution; the triethylamine solution is prepared by triethylamine and deionized water, and the mass fraction of triethylamine is 0.5%; the mass ratio of product A:KH560:triethylamine solution is 1:0.65:0.007; heat to 80°C and stir under reflux for 6 hours. After the reaction is completed, centrifuge and collect product B2; Step 3: Heat the product B2 obtained in step 2 to 120° C. under vacuum and cure for 2 h to obtain product C2; Step 4: Disperse the product C2 obtained in step 3 in water, add phenol, perform ultrasonic dispersion, adjust the pH value to 8.5 with NaOH solution, then add formaldehyde solution dropwise, and react with stirring at 55°C for 8 hours; the formaldehyde solution is prepared with formaldehyde and deionized water, and the formaldehyde mass fraction is controlled at 35%; the mass ratio of product C2: phenol: formaldehyde solution is 1:0.4:0.6; after the reaction is completed, centrifuge and dry at 100°C to obtain product D2; Step 5: Carbonize the product D2 obtained in step 4 under argon protection, first heating to 300°C at 2°C / min and keeping warm for 1 hour, then heating to 500°C at 1°C / min and keeping warm for 1 hour, then heating to 900°C at 3°C / min and keeping warm for 2 hours, and then cooling to end carbonization to obtain a composite negative electrode material.

[0026] Comparative Example 2 A negative electrode material, the preparation steps of which include: Step 1: Mix pitch-based soft carbon and potassium hydroxide in a mass ratio of 1:3 and ball-mill, heat to 700°C under a nitrogen atmosphere, activate for 2 hours, cool, wash with 1M hydrochloric acid until neutral, and vacuum dry to obtain product A; Step 2: Disperse the product A obtained in step 1 in anhydrous ethanol to control the solid content to 10%, add polyether diamine, and then dropwise add triethylamine solution; the triethylamine solution is prepared by triethylamine and deionized water, and the mass fraction of triethylamine is 0.5%; the mass ratio of product A: polyether diamine: triethylamine solution is 1:0.8:0.007; heat to 80°C, stir and reflux for 6 hours, and after the reaction is completed, centrifuge and collect product B3; Step 3: Heat the product B3 obtained in step 2 to 120° C. under vacuum and cure for 2 h to obtain product C3; Step 4: Disperse the product C3 obtained in step 3 in water, add phenol, perform ultrasonic dispersion, adjust the pH value to 8.5 with NaOH solution, then add formaldehyde solution dropwise, and stir and react at 55°C for 8 hours; the formaldehyde solution is prepared with formaldehyde and deionized water, and the formaldehyde mass fraction is controlled at 35%; the mass ratio of product C3:phenol:formaldehyde solution is 1:0.4:0.6; after the reaction is completed, centrifuge and dry at 100°C to obtain product D3; Step 5: Carbonize the product D3 obtained in step 4 under argon protection, first heating to 300°C at 2°C / min and keeping warm for 1 hour, then heating to 500°C at 1°C / min and keeping warm for 1 hour, then heating to 900°C at 3°C / min and keeping warm for 2 hours, then cooling to end carbonization and obtain the negative electrode material.

[0027] The negative electrode materials obtained from Examples 1-3 and Comparative Examples 1-2 were applied to batteries for performance testing.

[0028] The negative electrode material, conductive agent (SP), CMC, and SBR were mixed in a mass ratio of 95:1.5:1.5:2 and coated on copper foil to produce the negative electrode sheet. The positive electrode sheet was obtained by mixing the positive electrode active material, lithium cobalt oxide, conductive agent (SP), and PVDF in a mass ratio of 96.5:2:1.5 and coating on aluminum foil. The electrolyte was 1 mol / L LiPF6 + EC + EMC, and the separator was a polyethylene / propylene composite microporous membrane. These components were assembled into a battery.

[0029] Cycle test: The electrochemical performance of each battery group was tested on a Wuhan Blue Power CT2001A battery tester at a charge and discharge rate of 1C and a charge and discharge voltage range of 3V to 4.35V. The initial capacity and capacity retention after 500 cycles were tested. The test results are as follows:

[0030] From the above results, it can be seen that Examples 1-3 of the present invention have higher initial capacity and capacity retention rate.

[0031] Comparative Example 1 and Comparative Example 2 were subjected to component deficiency control, wherein Comparative Example 1 lacked polyether diamine and Comparative Example 2 lacked KH560. The initial capacity and capacity retention rate of the two control groups were significantly reduced.

[0032] Through comparative tests, it was found that the synergistic effect of polyether diamine, KH560 and other components in the formula system designed by the present invention played a key role in improving battery performance.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a hierarchical porous hard carbon-silicon composite negative electrode material, characterized in that: The steps include: Step 1: Mix the asphalt-based soft carbon and potassium hydroxide and ball-mill them, heat and activate them under a nitrogen atmosphere, cool them, wash them with hydrochloric acid until they are neutral, and vacuum dry them to obtain product A; Step 2: Disperse the product A obtained in step 1 in anhydrous ethanol, add polyether diamine and KH560, and then dropwise add triethylamine solution. Heat and stir under reflux for reaction. After the reaction is completed, centrifuge and collect the product B. Step 3: Heat and solidify the product B obtained in step 2 under vacuum to obtain product C; Step 4: Disperse the product C obtained in step 3 in water, add phenol, disperse by ultrasonication, adjust the pH value to 8.5-9, then dropwise add formaldehyde solution, stir to react, centrifuge after the reaction is complete, and dry to obtain product D; Step 5: Carbonize the product D obtained in step 4 under argon protection to obtain a hierarchical porous hard carbon-silicon composite negative electrode material.

2. The preparation method according to claim 1, characterized in that In step 1, the mass ratio of asphalt-based soft carbon to potassium hydroxide is 1: (3 to 3.5).

3. The preparation method according to claim 1, characterized in that In step 1, the mixture is heated to 700-710° C. and activated for 2-2.5 hours.

4. The preparation method according to claim 1, characterized in that In step 2, the solid content of product A in anhydrous ethanol is controlled to be 10% to 12%; the mass fraction of triethylamine in the triethylamine solution is controlled to be 0.5% to 0.7%; the mass ratio of product A: polyether diamine: KH560: triethylamine solution is 1: (0.8 to 0.85): (0.65 to 0.7): (0.007 to 0.009).

5. The preparation method according to claim 1, characterized in that In step 2, heat to 80-82° C. and reflux for 6-6.5 hours.

6. The preparation method according to claim 1, characterized in that In step 3, heat to 120-125° C. and cure for 2-2.5 hours.

7. The preparation method according to claim 1, characterized in that In step 4, the formaldehyde mass fraction in the formaldehyde solution is controlled at 35% to 37%, and the mass ratio of product C: phenol: formaldehyde solution is 1: (0.4 to 0.45): (0.6 to 0.65).

8. The preparation method according to claim 1, characterized in that In step 4, sodium hydroxide is used to adjust the pH value; the reaction is stirred at 55-58° C. for 8-8.5 hours; and the drying temperature is 100-105° C.

9. The preparation method according to claim 1, characterized in that During the carbonization process in step 5, the temperature was first increased to 300°C at 2°C / min and kept at this temperature for 1 hour, then increased to 500°C at 1°C / min and kept at this temperature for 1 hour, then increased to 900°C at 3°C / min and kept at this temperature for 2 hours, and then cooled to end the carbonization.

10. A hierarchical porous hard carbon-silicon composite negative electrode material, characterized in that: The method is as described in any one of claims 1 to 9.

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