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

Abstract

The application provides a hierarchical 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 and ball milling pitch-based soft carbon and potassium hydroxide, heating and activating under a nitrogen atmosphere, washing to neutral with hydrochloric acid after cooling, vacuum drying to obtain product A; dispersing the product A in anhydrous ethanol, adding polyether diamine and silane coupling agent (KH560), adding triethylamine solution dropwise, heating and stirring to perform reflux reaction, centrifuging to collect product B after the reaction is completed; vacuum heating and solidifying the product B to obtain product C; dispersing the product C in water, adding phenol, ultrasonic dispersing, adjusting the pH value to 8.5-9, then adding formaldehyde solution dropwise, stirring to react, centrifuging and drying to obtain product D; and carbonizing the product D under argon protection to obtain the hierarchical porous hard carbon silicon composite negative electrode material. The hierarchical porous hard carbon silicon composite negative electrode material utilizes soft carbon and hard carbon to construct a hierarchical porous structure.

Description

TECHNICAL FIELD

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

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

[0003] Porous carbon materials have the characteristics of chemical stability, high conductivity, good mechanical flexibility, large surface area, rich pore structure, adjustable pore size, etc., and are widely used in the fields of adsorption, catalysis, electrochemical energy storage, etc. However, carbon materials still have a big deficiency, that is, low specific capacity. Silicon material can well make up for the deficiency of carbon material. Therefore, how to develop suitable negative electrode materials by using porous carbon material and silicon material is the direction that researchers want to study. SUMMARY

[0004] In order to solve the problems mentioned in the background art, the present application provides a preparation method of a hierarchical porous hard carbon silicon composite negative electrode material, the inner core adopts soft carbon, the middle layer adopts the polymerization product of polyethylene diamine and KH560 to wrap the inner core, and the outer layer adopts phenolic resin hard carbon material. Soft carbon and hard carbon are both porous materials, and the pore sizes of the two are different to construct a hierarchical porous structure.

[0005] Specifically,

[0006] A preparation method of a hierarchical porous hard carbon silicon composite negative electrode material, the steps of which include:

[0007] Step one, mix pitch-based soft carbon and potassium hydroxide and ball mill, heat and activate under nitrogen atmosphere, wash to neutral with hydrochloric acid after cooling, and obtain product A after vacuum drying;

[0008] Step two, disperse product A obtained in step one in anhydrous ethanol, add polyether diamine and KH560, and then add triethylamine solution dropwise. After heating and stirring, reflux reaction, centrifuge to collect product B after reaction;

[0009] Step three, heat and solidify product B obtained in step two under vacuum to obtain product C;

[0010] Step four, disperse product C obtained in step three in water, add phenol, ultrasonic dispersion, adjust the pH value to 8.5-9, then add formaldehyde solution dropwise, stir and react, centrifuge and dry after reaction to obtain product D;

[0011] Step five, carbonize product D obtained in step four under argon protection to obtain a hierarchical porous hard carbon silicon composite negative electrode material.

[0012] Further, the mass ratio of the pitch-based soft carbon to potassium hydroxide in step one is 1: (3-3.5).

[0013] Further, the heating is to 700-710 DEG C in step one, and the activation is for 2-2.5 h.

[0014] Further, the solid content of product A in the anhydrous ethanol is controlled to be 10%-12% in step two; the mass fraction of triethylamine in the triethylamine solution is controlled to be 0.5%-0.7%; and the mass ratio of product A: polyether diamine: KH560: triethylamine solution is 1: (0.8-0.85): (0.65-0.7): (0.007-0.009).

[0015] Further, the heating is to 80-82 DEG C in step two, and the reflux is for 6-6.5 h.

[0016] Further, the heating is to 120-125 DEG C in step three, and the solidification is for 2-2.5 h.

[0017] Further, the mass fraction of formaldehyde in the formaldehyde solution is controlled to be 35%-37% in step four, and the mass ratio of product C: phenol: formaldehyde solution is 1: (0.4-0.45): (0.6-0.65).

[0018] Further, sodium hydroxide is used to adjust the pH value in step four; the stirring reaction is carried out at 55-58 DEG C for 8-8.5 h; and the drying temperature is 100-105 DEG C.

[0019] Further, the carbonization process in step five is that the temperature is first increased to 300 DEG C at a rate of 2 DEG C / min, and then the temperature is increased to 500 DEG C at a rate of 1 DEG C / min, and then the temperature is increased to 900 DEG C at a rate of 3 DEG C / min, and then the temperature is decreased to end the carbonization.

[0020] In addition, the application further provides a hierarchical porous hard carbon-silicon composite negative electrode material prepared by the above preparation method.

[0021] In the application, product A refers to a porous soft carbon inner core formed by activating pitch-based soft carbon;

[0022] Product B refers to a carbon-silicon composite particle in which a pre-polymer network is formed by ring-opening of epoxy of polyether diamine and KH560 to coat the porous soft carbon inner core;

[0023] Product C refers to a carbon-silicon core-shell particle in which a Si-O-Si / Si-O-C crosslinked network is formed by vacuum solidification of a silicon-nitrogen hybrid layer;

[0024] Product D refers to a precursor in which a phenolic resin coats the carbon-silicon core-shell particle.

[0025] Compared with the prior art, the application has the beneficial features that:

[0026] 1. The preparation method of the hierarchical porous hard carbon-silicon composite negative electrode material provided by the application adopts pitch-based soft carbon as the inner core, in-situ reaction of polyether diamine and silane coupling agent KH560 generates a high-capacity silicon-carbon intermediate layer and wraps the porous soft carbon inner core, the outermost layer is coated with phenol-formaldehyde resin formed by polymerization of phenol and formaldehyde, and after gradient carbonization, a nitrogen / silicon co-doped hard carbon coated soft carbon is formed, the soft carbon is mainly microporous and mesoporous, and the hard carbon is mainly microporous, thereby constructing a hierarchical porous structure; the high specific surface mesopore of the inner core serves as a rapid ion transport channel; the intermediate layer forms a molecularly dispersed active phase through in-situ hybridization of polyether diamine / KH560, contributes to the conversion reaction capacity; and the microporous hard carbon of the outer layer inhibits volume expansion and realizes fast ion transport through the gradient pores.

[0027] 2. The preparation method of the hierarchical porous hard carbon-silicon composite negative electrode material provided by the application utilizes the ring-opening reaction of the epoxy group of KH560 and the primary amine group of polyether diamine to form a β-hydroxyl tertiary amine structure , the generated hydroxyl group enhances hydrophilicity and promotes the interface compatibility of subsequent phenol-formaldehyde resin coating; the hydrolysis and condensation of KH560 trimethoxysilane generates a ≡Si-O-Si≡ network, locks the silicon atoms at the crosslinking points, and prevents silicon migration and agglomeration during high-temperature treatment; and after pyrolysis, a nano is generated, providing active lithium storage sites.

[0028] 3. The preparation method of the hierarchical porous hard carbon-silicon composite negative electrode material provided by the application utilizes polyether diamine to form multiple synergies with other materials in the system, which specifically embodies that: the primary amine group of polyether diamine attacks the epoxy group of KH560 to form a β-hydroxyl tertiary amine bond as the skeleton of the hybrid network, thereby anchoring the silicon source (KH560) on the surface of soft carbon with a covalent bond to avoid silicon agglomeration, and the amine group not participating in the epoxy ring-opening reaction condenses with the -COOH on the surface of soft carbon to form an amide bond, improving the interface bonding strength; during the carbonization process, the ether chain introduced by polyether diamine cracks to produce volatile small molecules (formaldehyde / acetaldehyde), forming 3-8 nm secondary mesopores in the intermediate layer to form channels connecting the inner layer (soft carbon) and the outer layer (hard carbon); in addition, polyether diamine also provides a nitrogen source and regulates the electronic structure, and during pyrolysis, the nitrogen-containing free radicals released by the decomposition of the amine group are embedded into the carbon lattice to form carbon-nitrogen dopants of graphite nitrogen and pyridine nitrogen, optimizing the performance of the porous carbon material, improving the electronic conductivity and additional storage sites, and the nitrogen atom forms a Si-N bond with silicon to lock the nano phase in the carbon matrix, reducing the expansion rate of silicon. DETAILED DESCRIPTION

[0029] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are some embodiments but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0030] In order to facilitate the implementation of the present application by those skilled in the art, some reagents used in the examples and comparative examples will be described as follows:

[0031] Pitch-based soft carbon: medium-temperature coal pitch, Hebei Zhengri Chemical Industry, finely pulverized into an output particle size: D50 = 8 ± 2 μm;

[0032] Polyether diamine: polyether amine D4000 aliphatic polyether diamine, Wuhan Lanna Bai Medicine Chemical Industry;

[0033] KH560: Shandong Boseng Chemical Industry;

[0034] Triethylamine: Shandong Hongyuan Chemical Industry;

[0035] Phenol: Shandong Feihong New Material.

[0036] In order to verify the beneficial effects of the present application, a number of examples and comparative examples are designed, and comparative analysis is carried out to verify.

[0037] Example 1

[0038] A hierarchical porous hard carbon-silicon composite negative electrode material, the preparation steps of which comprise:

[0039] Step one, mix pitch-based soft carbon and potassium hydroxide according to a mass ratio of 1:3 and ball mill, heat to 700 DEG C under nitrogen atmosphere, activate for 2h, wash to neutral with 1M hydrochloric acid after cooling, and obtain product A after vacuum drying;

[0040] Step two, disperse product A obtained in step one in anhydrous ethanol to control the solid content to be 10%, add polyether diamine and KH560, and then drop triethylamine solution; the triethylamine solution is prepared by using 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; after heating to 80 DEG C, stir and reflux for 6h, and then centrifuge to collect product B after the reaction is completed;

[0041] Step three, heat product B obtained in step two to 120 DEG C under vacuum, and solidify for 2h to obtain product C;

[0042] Step four, dispersing the product C obtained in step three in water, adding phenol, ultrasonic dispersion, adjusting the pH value to 8.5 with NaOH solution, then adding dropwise a formaldehyde solution, stirring and reacting at 55℃ for 8h; the formaldehyde solution is prepared by formaldehyde and deionized water, and the mass fraction of formaldehyde is controlled at 35%; the mass ratio of product C: phenol: formaldehyde solution is 1:0.4:0.6; after the reaction is completed, centrifugation is performed, and product D is obtained by drying at 100℃;

[0043] Step five, carbonizing the product D obtained in step four under argon protection, first increasing the temperature to 300℃ at 2℃ / min, keeping for 1h, then increasing the temperature to 500℃ at 1℃ / min, keeping for 1h, then increasing the temperature to 900℃ at 3℃ / min, keeping for 2h, and then decreasing the temperature to end the carbonization, to obtain the hierarchical porous hard carbon-silicon composite negative electrode material.

[0044] Example 2

[0045] A hierarchical porous hard carbon-silicon composite negative electrode material, the preparation steps of which comprise:

[0046] Step one, mixing pitch-based soft carbon and potassium hydroxide at a mass ratio of 1:3.5, ball milling, heating to 710℃ under a nitrogen atmosphere, activating for 2.5h, washing to neutral with 1M hydrochloric acid after cooling, and vacuum drying to obtain product A;

[0047] Step two, dispersing product A obtained in step one in anhydrous ethanol to control the solid content to 12%, adding polyether diamine, KH560, and then adding dropwise a triethylamine solution; the triethylamine solution is prepared by 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; after heating to 82℃, stirring and refluxing for 6.5h, product B is collected by centrifugation after the reaction is completed;

[0048] Step three, heating product B obtained in step two to 125℃ under vacuum, and solidifying for 2.5h to obtain product C;

[0049] Step four, dispersing product C obtained in step three in water, adding phenol, ultrasonic dispersion, adjusting the pH value to 9 with NaOH solution, then adding dropwise a formaldehyde solution, stirring and reacting at 58℃ for 8.5h; the formaldehyde solution is prepared by formaldehyde and deionized water, and the mass fraction of formaldehyde is controlled at 37%; the mass ratio of product C: phenol: formaldehyde solution is 1:0.45:0.65; after the reaction is completed, centrifugation is performed, and product D is obtained by drying at 105℃;

[0050] Step five, carbonize the product D obtained in step four under argon protection, first heat to 300℃ at 2℃ / min, keep for 1h, then heat to 500℃ at 1℃ / min, keep for 1h, then heat to 900℃ at 3℃ / min, keep for 2h, then cool down to end the carbonization, obtain the hierarchical porous hard carbon-silicon composite negative electrode material.

[0051] Example 3

[0052] A hierarchical porous hard carbon-silicon composite negative electrode material, the preparation steps thereof comprise:

[0053] Step one, mix pitch-based soft carbon and potassium hydroxide according to a mass ratio of 1:3, ball mill, heat to 710℃ under nitrogen atmosphere, activate for 2.5h, after cooling, wash to neutral with 1M hydrochloric acid, after vacuum drying, obtain product A;

[0054] Step two, disperse the product A obtained in step one in anhydrous ethanol to control the solid content to be 11%, add polyether diamine, KH560, and then drop triethylamine solution; the triethylamine solution is prepared by using triethylamine and deionized water, 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; after heating to 81℃, stir and reflux for 6h, after the reaction is completed, centrifugal collect product B;

[0055] Step three, heat the product B obtained in step two to 123℃ under vacuum, solidify for 2.5h, obtain product C;

[0056] Step four, disperse the product C obtained in step three in water, add phenol, ultrasonic dispersion, adjust the pH value to 8.6 by using NaOH solution, then drop formaldehyde solution, stir and react at 57℃ for 8h; the formaldehyde solution is prepared by using formaldehyde and deionized water, the mass fraction of formaldehyde is controlled to be 36%; the mass ratio of product C: phenol: formaldehyde solution is 1:0.4:0.65; after the reaction is completed, centrifugal, dry at 103℃ to obtain product D;

[0057] Step five, carbonize the product D obtained in step four under argon protection, first heat to 300℃ at 2℃ / min, keep for 1h, then heat to 500℃ at 1℃ / min, keep for 1h, then heat to 900℃ at 3℃ / min, keep for 2h, then cool down to end the carbonization, obtain the hierarchical porous hard carbon-silicon composite negative electrode material.

[0058] Comparative example 1

[0059] A negative electrode material, the preparation steps thereof comprise:

[0060] Step one, mix pitch-based soft carbon and potassium hydroxide with a mass ratio of 1:3 and ball mill, heat to 700℃ under nitrogen atmosphere, activate for 2h, wash with 1M hydrochloric acid to neutral after cooling, vacuum dry to obtain product A;

[0061] Step two, disperse product A obtained in step one in anhydrous ethanol to control the solid content to 10%, add KH560, and then drop 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℃ and stir reflux for 6h, then centrifuge to collect product B2 after the reaction is completed;

[0062] Step three, heat product B2 obtained in step two to 120℃ under vacuum, and solidify for 2h to obtain product C2;

[0063] Step four, disperse product C2 obtained in step three in water, add phenol, ultrasonic dispersion, adjust the pH value to 8.5 with NaOH solution, then drop formaldehyde solution, stir at 55℃ for 8h; the formaldehyde solution is prepared by formaldehyde and deionized water, and the mass fraction of formaldehyde is controlled at 35%; the mass ratio of product C2: phenol: formaldehyde solution is 1:0.4:0.6; centrifuge after the reaction is completed, and dry at 100℃ to obtain product D2;

[0064] Step five, carbonize product D2 obtained in step four under argon protection, first heat to 300℃ at 2℃ / min, keep for 1h, then heat to 500℃ at 1℃ / min, keep for 1h, then heat to 900℃ at 3℃ / min, keep for 2h, then cool down to end carbonization, to obtain a composite negative electrode material.

[0065] Comparative example 2

[0066] A negative electrode material, the preparation steps comprising:

[0067] Step one, mix pitch-based soft carbon and potassium hydroxide with a mass ratio of 1:3 and ball mill, heat to 700℃ under nitrogen atmosphere, activate for 2h, wash with 1M hydrochloric acid to neutral after cooling, vacuum dry to obtain product A;

[0068] Step two, disperse product A obtained in step one in anhydrous ethanol to control the solid content to 10%, add polyether diamine, and then drop 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℃ and stir reflux for 6h, then centrifuge to collect product B3 after the reaction is completed;

[0069] Step three, the product B3 obtained in step two is heated to 120 DEG C under vacuum, and solidified for 2h to obtain product C3;

[0070] Step four, the product C3 obtained in step three is dispersed in water, phenol is added, ultrasonic dispersion is performed, a NaOH solution is used to adjust the pH value to 8.5, then a formaldehyde solution is added dropwise, and the reaction is stirred at 55 DEG C for 8h; the formaldehyde solution is prepared by using formaldehyde and deionized water, and the mass fraction of formaldehyde is controlled to be 35%; the mass ratio of product C3:phenol:formaldehyde solution is 1:0.4:0.6; after the reaction is completed, centrifugation is performed, and product D3 is obtained by drying at 100 DEG C.

[0071] Step five, the product D3 obtained in step four is carbonized under argon protection, first heated to 300 DEG C at a rate of 2 DEG C / min, then heated to 500 DEG C at a rate of 1 DEG C / min, then heated to 900 DEG C at a rate of 3 DEG C / min, and then cooled to end the carbonization to obtain the negative electrode material.

[0072] The negative electrode material obtained in examples 1-3 and comparative examples 1-2 is applied to a battery for performance testing.

[0073] The negative electrode material, a conductive agent (SP), CMC and SBR are mixed according to a mass ratio of 95:1.5:1.5:2, coated on a copper foil to obtain a negative electrode sheet. The positive electrode active material lithium cobaltate, a conductive agent (SP) and PVDF are mixed uniformly according to a mass ratio of 96.5:2:1.5, and then coated on an aluminum foil to obtain a positive electrode sheet. An electrolyte is 1mol / L LiPF6+EC+EMC, and a separator is a polyethylene / propylene composite microporous membrane. They are assembled into a battery.

[0074] Cycle test: the electrochemical performance test of each group of batteries is performed on a Wuhan Lan electric CT2001A battery tester, the charge / discharge rate is 1C, the charge / discharge voltage range is 3V to 4.35V, the initial capacity and the capacity retention rate after 500 cycles are tested, and the test results are as follows:

[0075]

[0076] It can be known from the above results that the examples 1-3 of the present application have higher initial capacity and capacity retention rate.

[0077] Comparative example 1 and comparative example 2 are component missing controls, wherein comparative example 1 lacks polyether diamine, and comparative example 2 lacks KH560, and the initial capacity and capacity retention rate of the two control groups are obviously decreased.

[0078] It is found through comparison and test that the synergistic effect of polyether diamine and KH560 in the formula system designed in the present application and other components plays a key role in improving the battery performance.

[0079] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a hierarchically porous hard carbon-silicon composite anode material, characterized in that, The steps include: Step one, mix and ball mill the pitch-based soft carbon and potassium hydroxide, activate under nitrogen atmosphere, wash with hydrochloric acid to neutral after cooling, vacuum dry to obtain product A; Step two, disperse product A obtained in step one in anhydrous ethanol, add polyether diamine, KH560, and drop in triethylamine solution, heat and stir to reflux, centrifuge to collect product B after reaction; Step three, heat and solidify product B obtained in step two under vacuum to obtain product C; Step four, disperse product C obtained in step three in water, add phenol, ultrasonic dispersion, adjust pH value to 8.5-9, then drop in formaldehyde solution, stir to react, centrifuge and dry to obtain product D after reaction; Step five, carbonize product D obtained in step four under argon protection to obtain hierarchical porous hard carbon-silicon composite negative electrode material.

2. The production method according to claim 1, characterized by, The mass ratio of pitch-based soft carbon to potassium hydroxide in step one is 1:(3-3.5).

3. The preparation method according to claim 1, characterized in that Heat to 700-710℃ in step one, activate for 2-2.5h.

4. The method of claim 1, wherein, Control the solid content of product A in anhydrous ethanol to 10%-12% in step two; control the mass fraction of triethylamine in triethylamine solution to 0.5%-0.7%; the mass ratio of product A: polyether diamine: KH560: triethylamine solution is 1:(0.8-0.85):(0.65-0.7):(0.007-0.009).

5. The preparation method according to claim 1, characterized in that Heat to 80-82℃ in step two, reflux for 6-6.5h.

6. The method of claim 1, wherein, Heat to 120-125℃ in step three, solidify for 2-2.5h.

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

8. The method of claim 1, wherein, Use sodium hydroxide to adjust pH value in step four; stir to react at 55-58℃ for 8-8.5h; the drying temperature is 100-105℃.

9. The method of claim 1, wherein, In step five, first heat to 300℃ at 2℃ / min, keep for 1h, then heat to 500℃ at 1℃ / min, keep for 1h, then heat to 900℃ at 3℃ / min, keep for 2h, then cool down to end carbonization.

10. A hierarchically porous hard carbon-silicon composite anode material, characterized in that, The preparation method is as claimed in any one of claims 1-9. The preparation method is as claimed in any one of claims 1-9.

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