Porous silicon-carbon negative electrode material and preparation method and application thereof

Abstract

The application discloses a kind of porous silicon carbon negative electrode material and its preparation method and application, the preparation method includes: (1) nanometer silicon is mixed with binder emulsion stirring, then sequentially ultrasonic dispersion, freeze drying, obtain nanometer silicon colloidal material;(2) pine cone powder and nanometer silicon colloidal material are respectively crushed, then mixed, subsequently again the mixture is carried out high-temperature carbonization treatment, obtain silicon-carbon composite material;(3) silicon-carbon composite material is stirred and mixed with acid solution, carries out etching treatment, the etching liquid obtained is washed to pH value 6~7 after filtration, obtain washing material;(4) the washing material is dried, then carried out airflow mill crushing, screening removes magnet, i.e. porous silicon carbon negative electrode material is obtained.The application uses nanometer silicon and pine cone as raw material to prepare porous silicon carbon negative electrode material, raw material source is extensive, cost is low, and the porous silicon carbon negative electrode material prepared has higher porosity and good cycle stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion battery negative electrode materials, and in particular, relates to a porous silicon-carbon negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] In modern lithium ion batteries, although the traditional carbon negative electrode material has reliable performance, its energy storage capacity is relatively low. In contrast, silicon material has a higher theoretical specific capacity and a lower lithium ion diffusion coefficient, making it an ideal high-capacity negative electrode material. However, due to the volume expansion and shrinkage of silicon during lithium ion intercalation and deintercalation, the silicon electrode material is prone to cracking and causes capacity decay, greatly reducing the cycle stability and long-term durability of the electrode. The carbon material has good stability, and by introducing carbon into the silicon material, the stability and life of the silicon negative electrode material can be effectively improved. And the carbon material can improve the electrical conductivity of silicon and provide an elastic support structure to reduce the stress caused by volume expansion, further improving the cycle stability and electrode life of the silicon negative electrode material. However, the carbon material added in the current silicon-carbon negative electrode material is mostly petroleum pitch, and petroleum is a non-renewable resource, and resources are becoming increasingly scarce. Therefore, a new carbon material needs to be selected for preparing the silicon-carbon negative electrode material. SUMMARY

[0003] The present application aims to at least partially solve one of the technical problems in the related art. To this end, the present application embodiment proposes a porous silicon-carbon negative electrode material and a preparation method and application thereof.

[0004] In a first aspect, the present application embodiment proposes a preparation method of a porous silicon-carbon negative electrode material, comprising the following steps:

[0005] (1) mixing and stirring nano-silicon and a binder emulsion, and then sequentially performing ultrasonic dispersion and freeze-drying to obtain a nano-silicon colloidal material;

[0006] (2) crushing the nano-silicon colloidal material and pinecone powder respectively, then mixing them, and then performing high-temperature carbonization treatment on the mixture to obtain a silicon-carbon composite material;

[0007] (3) stirring and mixing the silicon-carbon composite material and an acid solution to perform etching treatment, and then filtering and washing the obtained etching solution to a pH value of 6-7 to obtain a washing material;

[0008] (4) drying the washing material, then performing airflow milling and crushing, and screening and removing magnetism to obtain the porous silicon-carbon negative electrode material.

[0009] This invention utilizes nano-silicon and pine cones as raw materials to prepare silicon-carbon anode materials. The vacancies between the nano-silicon and pine cone-derived carbon provide sufficient expansion space for silicon, maintaining the stability of the electrode material during lithium insertion and extraction, thereby extending battery life. Furthermore, this invention employs an acid solution to etch the silicon-carbon composite material, transforming its structure into a porous structure, further reserving space for silicon volume expansion. Simultaneously, the carbon framework surrounding the silicon restricts its expansion, solving the failure problem of silicon anode materials during lithium insertion and extraction. Moreover, the preparation method in this invention is simple, easy to operate, highly efficient, uses widely available raw materials, and is low in cost, making it suitable for industrial-scale production.

[0010] In some embodiments, in step (1), the mass ratio of the nano-silicon to the binder emulsion is (7-10):1;

[0011] Preferably, the particle size of the nano-silicon is 20–60 nm;

[0012] Preferably, the adhesive emulsion includes at least one of styrene-butadiene rubber emulsion, silane coupling agent A-171, silane coupling agent KH-560, and silane coupling agent KH-570.

[0013] In some embodiments, in step (1), the mixing and stirring time is 30-90 min, the ultrasonic dispersion time is 30-60 min, and the freeze-drying time is 24-72 h.

[0014] In some embodiments, in step (2), the mass ratio of the pine cone powder to the nanosilicone material is (10-12):1.

[0015] In some embodiments, in step (2), the high-temperature carbonization process is as follows: the mixture is first purified and impurities removed at 200°C for 30-60 minutes under an inert gas protective atmosphere, and then heated to 1200-1600°C at a heating rate of 5-10°C / min, kept at the temperature for 1-3 hours, and then cooled to room temperature.

[0016] Preferably, the inert gas includes at least one of nitrogen and argon, and the flow rate of the inert gas is 1 to 5 m / s.

[0017] In some embodiments, in step (3), the acid solution includes at least one of hydrochloric acid solution, citric acid solution, sulfuric acid solution, and nitric acid solution;

[0018] Preferably, the mass concentration of the acid solution is 5-20%.

[0019] In some embodiments, in step (3), the stirring speed is 80-120 r / min;

[0020] And / or, the etching process time is 1-1.5h.

[0021] In some embodiments, in the step (4), the drying temperature is 80-120℃, and the mass content of free water in the washed material after drying is <500ppm.

[0022] And / or, the particle size of the washed material after air jet milling is 3-20μm.

[0023] In a second aspect, the embodiments of the present application further provide a porous silicon-carbon negative electrode material, which is prepared by the preparation method of the first aspect.

[0024] The porous silicon-carbon negative electrode material in the embodiments of the present application has high porosity and good cycle stability.

[0025] In a third aspect, the embodiments of the present application further provide the application of the porous silicon-carbon negative electrode material of the second aspect in a lithium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 SEM image of the porous silicon-carbon negative electrode material prepared in Example 3 of the present application. DETAILED DESCRIPTION

[0027] The embodiments of the present application are described in detail below, which are exemplary and intended to explain the present application, and cannot be understood as a limitation of the present application.

[0028] In this document, where a range of values is described, it is understood that disclosure of all possible subranges between the stated range of values, and disclosure of all specific values within the stated range of values, are intended to be included.

[0029] In this document, the words "comprise" and "include" and their various variants are meant to encompass possible inclusion of elements or integers not specifically recited.

[0030] In this document, the term "and / or" is merely an association relationship to describe the associated objects, and can represent three relationships, for example, A and / or B, which can represent three cases of existence of A alone, existence of A and B simultaneously, and existence of B alone.

[0031] In a first aspect, the embodiments of the present application provide a preparation method of a porous silicon-carbon negative electrode material, which comprises the following steps:

[0032] (1) mixing and stirring nano-silicon and binder emulsion, and then sequentially performing ultrasonic dispersion and freeze-drying to obtain a nano-silicon colloid material;

[0033] (2) crushing pinecone powder and the nanosilica colloidal material respectively, then mixing, and then high-temperature carbonization treatment of the mixture to obtain a silicon-carbon composite material;

[0034] (3) stirring and mixing the silicon-carbon composite material with an acid solution to perform etching treatment, and then filtering and washing the obtained etching solution to a pH value of 6-7 to obtain a washing material;

[0035] (4) drying the washing material, then airflow milling, and screening and removing magnetism to obtain the porous silicon-carbon negative electrode material.

[0036] In some embodiments, in the step (1), the mass ratio of the nanosilica to the binder emulsion is (7-10):1, for example, 7:1, 8:1, 9:1, 10:1, etc.

[0037] Preferably, the particle size of the nanosilica is 20-60 nm, for example, 20 nm, 30 nm, 45 nm, 50 nm, 60 nm, etc.

[0038] Preferably, the binder emulsion includes at least one of a styrene-butadiene rubber emulsion, silane coupling agent A-171, silane coupling agent KH-560, and silane coupling agent KH-570.

[0039] By using the binder emulsion, better adhesion can be provided; and in the subsequent carbonization and drying process, the binder emulsion can be stably aggregated, thereby ensuring the stability of the overall material; in addition, the selected binder emulsion has a large elastic modulus, which can make the thickness of the pole piece rebound low, and can ensure the stability of the internal structure of the battery when used as a negative electrode of the battery.

[0040] In some embodiments, in the step (1), the mixing and stirring time is 30-90 min, for example, 30 min, 45 min, 60 min, 75 min, 80 min, 90 min, etc.

[0041] And / or, the ultrasonic dispersion time is 30-60 min, for example, 30 min, 45 min, 50 min, 60 min, etc. By ultrasonic dispersion treatment, the agglomeration of raw material particles can be avoided.

[0042] And / or, the freeze-drying time is 24-72 h, for example, 24 h, 30 h, 36 h, 40 h, 48 h, 50 h, 60 h, 72 h, etc.

[0043] In some embodiments, in the step (2), the mass ratio of the pinecone powder to the nanosilica colloidal material is (10-12):1, for example, 10:1, 10.5:1, 11:1, 11.2:1, 11.8:1, 12:1, etc. By using pinecone powder as the carbon source, the raw material source is extensive, easy to obtain, and green. In addition, the derived carbon pores generated after high-temperature carbonization of pinecone have larger pore sizes and more reserved volume spaces, thereby reserving more spaces for the expansion of silicon. The inventors have found that if the addition amount of pinecone powder is too high, the capacity of the obtained material is too low; if the addition amount of pinecone powder is too low, the cycle performance of the obtained material is poor. Therefore, it is advantageous to control the mass ratio of the pinecone powder to the nanosilica colloidal material to be (10-12):1.

[0044] Further, the particle size of the crushed pinecone powder and the nanosilica colloidal material is 8-12 μm, for example, 8 μm, 10 μm, 12 μm, etc.

[0045] In some embodiments, in the step (2), the high-temperature carbonization process is as follows: the mixture is first purified and impurity-removed at 200℃ for 30-60 min (for example, 30 min, 45 min, 50 min, 60 min, etc.) under an inert gas protective atmosphere, then heated to 1200-1600℃ (for example, 1200℃, 1300℃, 1400℃, 1500℃, 1600℃, etc.) at a heating rate of 5-10℃ / min (for example, 5℃ / min, 8℃ / min, 10℃ / min, etc.), kept warm for 1-3 h (for example, 1 h, 1.5 h, 2 h, 2.8 h, 3 h, etc.), and cooled to room temperature. It should be noted that the porous silicon-carbon negative electrode material prepared in the embodiments has a carbon material as the main body. If the carbonization temperature is too high, the growth rate of graphite grains is too fast, the specific surface area is too large, the side reaction is increased, and the initial efficiency is greatly reduced when used as a battery negative electrode. If the carbonization temperature is too low, the structure of the carbon material is not completely transformed, there are too many impurities and internal defects, and the battery negative electrode cannot work in a high SOC state. Therefore, it is advantageous to control the carbonization temperature to be 1200-1600℃.

[0046] Preferably, the inert gas includes at least one of nitrogen and argon, and the flow rate of the inert gas is 1-5 m / s, for example, 1 m / s, 3 m / s, 5 m / s, etc.

[0047] In some embodiments, in the step (3), the acid solution includes at least one of a hydrochloric acid solution, a citric acid solution, a sulfuric acid solution, and a nitric acid solution.

[0048] Preferably, the mass concentration of the acid solution is 5-20%, for example, 5%, 8%, 10%, 12%, 15%, 20%, etc.

[0049] By using acid etching, the reaction speed is fast, and since the carbon source used in the embodiment of the application is pinecone, which is a kind of biomass, the pinecone shell often contains lignin, which can react with the acid to achieve the purposes of purification and internal pore formation, thereby not only increasing the surface area of the silicon-carbon composite material to provide more lithium ion insertion positions, but also enhancing the interaction between silicon and carbon materials, which is conducive to improving the electrochemical performance of the silicon-carbon composite material.

[0050] In some embodiments, in step (3), the stirring speed is 80-120 r / min, for example, 80 r / min, 100 r / min, 110 r / min, 120 r / min, etc.

[0051] And / or, the etching time is 1-1.5 h, for example, 1 h, 1.2 h, 1.5 h, etc.

[0052] In some embodiments, in step (4), the drying temperature is 80-120℃, for example, 80℃, 100℃, 120℃, etc.; and the mass content of free water in the washed material after drying is <500 ppm.

[0053] And / or, the particle size of the washed material after air jet milling is 3-20 μm, for example, 3 μm, 5 μm, 10 μm, 15 μm, 18 μm, 20 μm, etc.

[0054] In a second aspect, the embodiment of the application further provides a porous silicon-carbon negative electrode material, which is prepared by the preparation method of the first aspect.

[0055] In a third aspect, the embodiment of the application further provides the application of the porous silicon-carbon negative electrode material of the second aspect in a lithium ion battery, which is used as a negative active material in the lithium ion battery.

[0056] The following are non-limiting examples and comparative examples of the application. It should be noted that the scheme of the comparative examples is not prior art, but is set only for comparison with the scheme of the examples, and does not limit the application. Unless otherwise specified, the various raw materials used in the examples and comparative examples are conventional commercially available products or can be prepared by known methods.

[0057] Example 1

[0058] A preparation method of a porous silicon-carbon negative electrode material, comprising the following steps:

[0059] (1) Nanometer silicon with a particle size of 20 nm and butadiene rubber emulsion were mixed at a mass ratio of 7:1 and stirred for 60 min, then ultrasonic dispersed for 30 min to avoid particle agglomeration, and then the mixed colloidal liquid was placed in a freeze dryer for freeze drying for 24 h to obtain a nanometer silicon colloidal material;

[0060] (2) The pinecone powder and the nanometer silicon colloidal material were weighed at a mass ratio of 12:1 and then were placed in an airflow mill for crushing treatment until the particle size of both was 10 μm (wherein the frequency of the screw feeder was set to 4 Hz, the frequency of the grading motor was set to 195 Hz, and the frequency of the crushing motor was set to 230 Hz); then the crushed pinecone powder and the nanometer silicon colloidal material were placed in a mixer for high-speed mixing, with the stirring speed controlled at 400 rpm and the mixing time controlled at 30 min; then the mixed material was placed in an atmosphere furnace, and the mixed material was first purified and impurity-removed at 200 ℃ for 30 min under a nitrogen atmosphere, and then was heated to 1200 ℃ at a heating rate of 8 ℃ / min and was kept for 2 h (the flow rate of nitrogen was 2 m / s, and the oxygen volume concentration in the atmosphere furnace was less than 50 ppm); after the high-temperature carbonization treatment was completed, the temperature was cooled to room temperature to obtain a silicon-carbon composite material;

[0061] (3) The silicon-carbon composite material and 5 wt% dilute hydrochloric acid solution were stirred and mixed at a stirring speed of 100 r / min for 1 h for etching treatment; the obtained etching liquid was filtered and then was washed with water until the pH value of the washing water was 6-7 to stop the washing to ensure that the residual dilute hydrochloric acid was completely removed, to obtain a washed material;

[0062] (4) The washed material was placed in a blast drying oven, and nitrogen was introduced to make the oxygen volume content in the blast drying oven less than 10 ppm, and then the washed material was dried at 80 ℃; then the dried washed material was crushed by airflow milling to a particle size of 12 μm, and finally the obtained material was subjected to two-stage screening demagnetization by using an electromagnetic demagnetizer to make the ash content of the obtained material less than or equal to 0.05% and the magnetic substance less than or equal to 0.5 ppm, to obtain a porous silicon-carbon negative electrode material.

[0063] Example 2

[0064] A preparation method of a porous silicon-carbon negative electrode material, comprising the following steps:

[0065] (1) Nanometer silicon with a particle size of 30 nm and butadiene rubber emulsion were mixed at a mass ratio of 7:1 and stirred for 60 min, then ultrasonic dispersed for 30 min to avoid particle agglomeration, and then the mixed colloidal liquid was placed in a freeze dryer for freeze drying for 36 h to obtain a nanometer silicon colloidal material;

[0066] (2) The pineal powder and nano-silica colloidal material are weighed according to the mass ratio of 11:1, and then are put into an airflow mill grinder for crushing treatment until the particle sizes of the two are 10 μm (wherein the frequency of the screw feeder is set to 4 Hz, the frequency of the grading motor is set to 195 Hz, and the frequency of the crushing motor is set to 230 Hz); then the crushed pineal powder and nano-silica colloidal material are put into a mixer for high-speed mixing, the stirring speed is controlled to be 400 rpm, and the mixing time is 30 min; then the mixed material is put into an atmosphere furnace, the mixed material is first purified and impure under a nitrogen atmosphere at 200 ℃ for 30 min, and then is heated to 1400 ℃ at a heating rate of 8 ℃ / min, and is kept for 2 h (the flow rate of nitrogen is 2 m / s, and the oxygen volume concentration in the atmosphere furnace is less than 50 ppm), after the high-temperature carbonization treatment is completed, the temperature is cooled to room temperature, and a silicon-carbon composite material is obtained;

[0067] (3) The silicon-carbon composite material and 10 wt% of a dilute hydrochloric acid solution are stirred and mixed at a stirring speed of 100 r / min for 1.2 h for etching treatment, the obtained etching liquid is filtered, and then is washed with water until the pH value of the washing water is 6-7, and then the washing is stopped to ensure that the residual dilute hydrochloric acid is completely removed, and a washed material is obtained;

[0068] (4) The washed material is placed in a blast drying oven, nitrogen is introduced, so that the oxygen volume content in the blast drying oven is less than 10 ppm, and then the dried washed material is crushed by an airflow mill to a particle size of 13 μm, and finally the obtained material is subjected to two-stage screening demagnetization by using an electromagnetic demagnetizer, so that the ash content in the obtained material is ≤0.05%, and the magnetic substance is ≤0.5 ppm, and a porous silicon-carbon negative electrode material is obtained.

[0069] Example 3

[0070] A preparation method of a porous silicon-carbon negative electrode material, comprising the following steps:

[0071] (1) The particle size of the nano-silicon is 40 nm, and the nano-silicon is mixed and stirred with a butadiene-styrene rubber emulsion according to a mass ratio of 7:1 for 60 min, and then is ultrasonically dispersed for 30 min to avoid particle agglomeration, and then the mixed colloidal liquid is put into a freeze dryer for freeze drying for 48 h to obtain a nano-silica colloidal material;

[0072] (2) The pineal powder and nano-silica colloidal material are weighed according to a mass ratio of 10:1, and then are respectively put into an airflow mill pulverizer for pulverization treatment until the particle sizes of the two are both 10 μm (wherein, the frequency of a screw feeder is set to 4 Hz, the frequency of a grading motor is set to 195 Hz, and the frequency of a pulverization motor is set to 230 Hz); then the pulverized pineal powder and nano-silica colloidal material are put into a mixer for high-speed mixing, the stirring speed is controlled to be 400 rpm, and the mixing time is 30 min; then the mixed material is put into an atmosphere furnace, the mixed material is first purified and impurity-removed at 200℃ under a nitrogen atmosphere for 30 min, and then is heated to 1600℃ at a heating rate of 8℃ / min, and is kept for 2 h (the flow rate of nitrogen is 2 m / s, and the oxygen volume concentration in the atmosphere furnace is less than 50 ppm), after the high-temperature carbonization treatment is completed, the temperature is cooled to room temperature, and a silicon-carbon composite material is obtained;

[0073] (3) The silicon-carbon composite material and 20 wt% of a dilute hydrochloric acid solution are stirred and mixed at a stirring speed of 100 r / min for 1.3 h for etching treatment, the obtained etching solution is filtered, and then is washed with water until the pH value of the washing water is 6-7, and the washing is stopped, so that the residual dilute hydrochloric acid is completely removed, and a washed material is obtained;

[0074] (4) The washed material is placed in a blast drying oven, nitrogen is introduced, so that the oxygen volume content in the blast drying oven is less than 10 ppm, and then the washed material is dried at 80℃, and then the dried washed material is pulverized by an airflow mill until the particle size of the washed material is 14 μm, and finally the obtained material is screened and demagnetized by a two-stage electromagnetic demagnetizer, so that the ash content in the obtained material is ≤0.05%, and the magnetic substance is ≤0.5 ppm, and a porous silicon-carbon negative electrode material is obtained.

[0075] Figure 1 The SEM image of the porous silicon-carbon negative electrode material prepared in the embodiment is shown in the figure, and it can be seen from the figure that the silicon-carbon negative electrode material has a porous structure and has a high porosity, and provides a reserved space for silicon expansion.

[0076] Embodiment 4

[0077] A preparation method of a porous silicon-carbon negative electrode material, comprising the following steps:

[0078] (1) Nano-silicon with a particle size of 50 nm and butadiene styrene rubber emulsion are mixed and stirred according to a mass ratio of 7:1 for 60 min, and then are ultrasonically dispersed for 30 min after stirring to avoid particle agglomeration, and then the mixed colloidal liquid is put into a freeze dryer for freeze drying for 48 h, and a nano-silica colloidal material is obtained;

[0079] (2) The pineal powder and nano-silica colloidal material are weighed according to a mass ratio of 10:1, and then are respectively put into an airflow mill pulverizer for pulverization treatment until the particle sizes of the two are both 10 μm (wherein, the frequency of a screw feeder is set to 4 Hz, the frequency of a grading motor is set to 195 Hz, and the frequency of a pulverization motor is set to 230 Hz); then the pulverized pineal powder and nano-silica colloidal material are put into a mixer for high-speed mixing, the stirring speed is controlled to be 400 rpm, and the mixing time is 30 min; then the mixed material is put into an atmosphere furnace, the mixed material is first purified and impurity-removed at 200℃ under a nitrogen atmosphere for 30 min, and then is heated to 1600℃ at a heating rate of 8℃ / min, and is kept for 2 h (the flow rate of nitrogen is 2 m / s, and the oxygen volume concentration in the atmosphere furnace is less than 50 ppm), after the high-temperature carbonization treatment is completed, the temperature is cooled to room temperature, and a silicon-carbon composite material is obtained;

[0080] (3) The silicon-carbon composite material and 20 wt% of a dilute hydrochloric acid solution are stirred and mixed at a stirring speed of 100 r / min for 1.4 h for etching treatment, the obtained etching liquid is filtered, and then is washed with water until the pH value of the washing water is 6-7, and then the washing is stopped, so that the residual dilute hydrochloric acid is completely removed, and a washed material is obtained;

[0081] (4) The washed material is placed in a blast drying oven, nitrogen is introduced, so that the oxygen volume content in the blast drying oven is less than 10 ppm, and then the washed material is dried at 80℃, and then the dried washed material is pulverized by an airflow mill until the particle size of the washed material is 14 μm, and finally the obtained material is screened and demagnetized by a two-stage electromagnetic demagnetizer, so that the ash content in the obtained material is ≤0.05%, and the magnetic substance is ≤0.5 ppm, and a porous silicon-carbon negative electrode material is obtained.

[0082] Example 5

[0083] A preparation method of a porous silicon-carbon negative electrode material, comprising the following steps:

[0084] (1) Nano-silicon with a particle size of 60 nm and butadiene-styrene rubber emulsion are mixed and stirred according to a mass ratio of 7:1 for 60 min, and then are ultrasonically dispersed for 30 min after stirring to avoid particle agglomeration, and then the mixed colloidal liquid is put into a freeze dryer for freeze drying for 48 h, and a nano-silica colloidal material is obtained;

[0085] (2) Pineal powder and nano-silica colloidal material are weighed according to a mass ratio of 10:1, and then are respectively put into an airflow mill pulverizer for pulverization treatment until the particle sizes of the two are both 10 μm (wherein, the frequency of a screw feeder is set to 4 Hz, the frequency of a grading motor is set to 195 Hz, and the frequency of a pulverization motor is set to 230 Hz); then the pulverized pineal powder and nano-silica colloidal material are put into a mixer for high-speed mixing, the stirring speed is controlled to be 400 rpm, and the mixing time is 30 min; then the mixed material is put into an atmosphere furnace, the mixed material is first purified and impurity-removed at 200 ℃ under a nitrogen atmosphere for 30 min, and then is heated to 1600 ℃ at a heating rate of 8 ℃ / min, and is kept for 2 h (the flow rate of nitrogen is 2 m / s, and the oxygen volume concentration in the atmosphere furnace is less than 50 ppm), after the high-temperature carbonization treatment is completed, the temperature is cooled to room temperature, and a silicon-carbon composite material is obtained;

[0086] (3) The silicon-carbon composite material and 20 wt% dilute hydrochloric acid solution are stirred and mixed at a stirring speed of 100 r / min for 1.5 h for etching treatment, the obtained etching liquid is filtered, and then is washed with water until the pH value of the washing water is 6-7, and then the washing is stopped, so as to ensure that the residual dilute hydrochloric acid is completely removed, and a washed material is obtained;

[0087] (4) The washed material is placed in a blast drying oven, nitrogen is introduced, so that the oxygen volume content in the blast drying oven is less than 10 ppm, and then the washed material is dried at 80 ℃, and then the dried washed material is pulverized by an airflow mill until the particle size of the washed material is 14 μm, and finally the obtained material is screened and demagnetized by a two-stage electromagnetic demagnetizer, so that the ash content in the obtained material is ≤0.05%, and the magnetic substance is ≤0.5 ppm, and a porous silicon-carbon negative electrode material is obtained.

[0088] Comparative Example 1

[0089] A preparation method of a silicon-carbon negative electrode material, comprising the following steps:

[0090] (1) Nano-silicon with a particle size of 60 nm and butadiene-styrene rubber emulsion are mixed and stirred according to a mass ratio of 7:1 for 60 min, and then are ultrasonically dispersed for 30 min after stirring, so as to avoid particle agglomeration, and then the mixed colloidal liquid is put into a freeze dryer for freeze drying for 48 h, and a nano-silica colloidal material is obtained;

[0091] (2) Pineal powder and nano-silica colloidal material were weighed according to a mass ratio of 10:1, and then were respectively put into a jet mill pulverizer for pulverization treatment until the particle sizes of both were 10 μm (wherein, the frequency of the screw feeder was set to 4 Hz, the frequency of the grading motor was set to 195 Hz, and the frequency of the pulverization motor was set to 230 Hz); then the pineal powder and the nano-silica colloidal material after pulverization were put into a mixer for high-speed mixing, the stirring speed was controlled to be 400 rpm, and the mixing time was 30 min; then the mixture was put into an atmosphere furnace, the mixture was first purified and impurity-removed at 200 ℃ under a nitrogen atmosphere for 30 min, then was heated to 1600 ℃ at a heating rate of 8 ℃ / min, and was kept for 2 h (the flow rate of nitrogen was 2 m / s, and the oxygen volume concentration in the atmosphere furnace was less than 50 ppm), after the high-temperature carbonization treatment was completed, the mixture was cooled to room temperature, and a silicon-carbon composite material was obtained;

[0092] (3) The silicon-carbon composite material was placed in a blast drying oven, and nitrogen was introduced to make the oxygen volume content in the blast drying oven less than 10 ppm, then the silicon-carbon composite material was dried at 80 ℃, then was pulverized by a jet mill until the particle size was 14 μm, and finally was subjected to two-stage screening and demagnetization by an electromagnetic demagnetizer, so that the ash content in the obtained material was ≤0.05%, and the magnetic substance was ≤0.5 ppm, thereby obtaining a silicon-carbon negative electrode material.

[0093] Comparative Example 2

[0094] A preparation method of a porous silicon-carbon negative electrode material, comprising the following steps:

[0095] (1) Nano-silicon with a particle size of 15 μm and butadiene-styrene rubber emulsion were mixed and stirred according to a mass ratio of 7:1 for 60 min, and then were ultrasonically dispersed for 30 min to avoid particle agglomeration, then the mixed colloidal liquid was put into a freeze dryer, and was freeze-dried for 48 h, thereby obtaining a nano-silica colloidal material;

[0096] (2) Pineal powder and nano-silica colloidal material were weighed according to a mass ratio of 10:1, and then were respectively put into a jet mill pulverizer for pulverization treatment until the particle sizes of both were 10 μm (wherein, the frequency of the screw feeder was set to 4 Hz, the frequency of the grading motor was set to 195 Hz, and the frequency of the pulverization motor was set to 230 Hz); then the pineal powder and the nano-silica colloidal material after pulverization were put into a mixer for high-speed mixing, the stirring speed was controlled to be 400 rpm, and the mixing time was 30 min; then the mixture was put into an atmosphere furnace, the mixture was first purified and impurity-removed at 200 ℃ under a nitrogen atmosphere for 30 min, then was heated to 1600 ℃ at a heating rate of 8 ℃ / min, and was kept for 2 h (the flow rate of nitrogen was 2 m / s, and the oxygen volume concentration in the atmosphere furnace was less than 50 ppm), after the high-temperature carbonization treatment was completed, the mixture was cooled to room temperature, and a silicon-carbon composite material was obtained;

[0097] (3) The above-mentioned silicon-carbon composite material is mixed with a 20wt% dilute hydrochloric acid solution at a stirring speed of 100r / min for 1.5h, etching treatment is performed, the obtained etching solution is filtered, then washed with clean water until the pH value of the washing water is 6-7, then the washing is stopped to ensure that the residual dilute hydrochloric acid is completely removed, to obtain a washing material;

[0098] (4) The washing material is placed in a blast drying oven, nitrogen is introduced to make the oxygen volume content in the blast drying oven less than 10ppm, then dried at 80℃, then the dried washing material is pulverized by a jet mill until the particle size of the washing material is 14μm, finally two-stage screening demagnetization is performed by an electromagnetic demagnetizer to make the ash content in the obtained material ≤0.05% and the magnetic substance ≤0.5ppm, so that a porous silicon-carbon negative electrode material is obtained.

[0099] Comparative Example 3

[0100] A preparation method of a porous silicon-carbon negative electrode material, comprising the following steps:

[0101] (1) Nanosilicon with a particle size of 15μm is mixed with a butadiene-styrene rubber emulsion at a mass ratio of 7:1 for 60min, then ultrasonic dispersion is performed for 30min after stirring to avoid particle agglomeration, then the mixed colloid solution is placed in a freeze dryer for 48h to obtain a nanosilicon colloid material;

[0102] (2) Pinecone powder and the nanosilicon colloid material are weighed at a mass ratio of 10:1, then respectively placed in a jet mill pulverizer for pulverization treatment until the particle size of both is 10μm (wherein the frequency of the screw feeder is set to 4Hz, the frequency of the grading motor is set to 195Hz, and the frequency of the pulverization motor is set to 230Hz); then the pulverized pinecone powder and the nanosilicon colloid material are placed in a mixer for high-speed mixing, the stirring speed is controlled to be 400rpm, and the mixing time is 30min; then the mixed material is placed in an atmosphere furnace, the mixed material is first purified and impurity-removed at 200℃ under a nitrogen atmosphere for 30min, then heated to 800℃ at a heating rate of 8℃ / min, and kept for 2h (the flow rate of nitrogen is 2m / s, and the oxygen volume concentration in the atmosphere furnace is less than 50ppm), after high-temperature carbonization treatment, cooled to room temperature, to obtain a silicon-carbon composite material;

[0103] (3) The above-mentioned silicon-carbon composite material is mixed with a 20wt% dilute hydrochloric acid solution at a stirring speed of 100r / min for 1.5h, etching treatment is performed, the obtained etching solution is filtered, then washed with clean water until the pH value of the washing water is 6-7, then the washing is stopped to ensure that the residual dilute hydrochloric acid is completely removed, to obtain a washing material;

[0104] (4) The washed material is placed in a blast drying oven, and nitrogen is introduced to make the oxygen volume content in the blast drying oven less than 10 ppm, and then dried at 80°C, and then the dried washed material is pulverized by a jet mill to a particle size of 14 μm, and finally two-stage screening and demagnetization are performed by using an electromagnetic demagnetizer, so that the ash content in the obtained material is ≤0.05%, and the magnetic substance is ≤0.5 ppm, and thus a porous silicon-carbon negative electrode material is obtained.

[0105] The silicon-carbon negative electrode materials prepared in the above examples and comparative examples are assembled into lithium ion batteries, and then subjected to charge-discharge cycle performance test and porosity test, and the results are shown in Table 1.

[0106] Table 1

[0107] Porosity Initial capacity Initial efficiency Capacity retention after 400 weeks Example 1 51％ 628 mAh / g 81％ 89％ Example 2 53％ 637 mAh / g 83％ 88％ Example 3 54％ 656 mAh / g 84％ 86％ Example 4 56％ 658 mAh / g 86％ 84％ Example 5 58％ 665 mAh / g 89％ 82％ Comparative Example 1 23％ 564 mAh / g 71％ 72％ Comparative Example 2 43％ 587 mAh / g 71％ 73％ Comparative Example 3 55％ 383 mAh / g 65％ 71％

[0108] As can be seen from Table 1, in Comparative Example 1, since acid etching is not used, the porosity of the obtained silicon-carbon negative electrode material is relatively low, and since lithium ions will directly react with silicon to produce expansion, the expansion process will cause the SEI film to increase, and thus more lithium ions are needed to participate in the reaction, resulting in that part of the lithium ions cannot return to the positive electrode, and thus the capacity initial efficiency and retention rate are poor; in Comparative Example 2, since large particle size silicon powder is used, it will cause the expansion to be intensified, resulting in the structure of the negative electrode material to be pulverized, and thus the initial efficiency and retention rate are seriously decreased; in Comparative Example 3, since large particle size silicon powder is used, and the carbonization temperature is low, only 800°C, it will cause too many impurities such as volatile matter and sulfur in the silicon-carbon negative electrode material, resulting in that lithium ions are difficult to enter the inside, and thus the capacity of the material is too low, and there are a large number of metal salt substances in the inside, and self-discharge is serious, and thus the initial efficiency and capacity retention rate performance are also poor. In comparison, the porous silicon-carbon negative electrode material prepared in the examples of the present application exhibits better electrochemical performance.

[0109] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0110] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and that variations, modifications, substitutions and changes can be made by those skilled in the art without departing from the scope of the present application.

Claims

1. A method for preparing a porous silicon-carbon negative electrode material, characterized by, The method comprises the following steps: (1) mixing and stirring nano-silicon and a binder emulsion at a mass ratio of (7-10):1, then performing ultrasonic dispersion and freeze-drying in sequence to obtain a nano-silica gel material; the binder emulsion comprises at least one of a styrene-butadiene rubber emulsion, silane coupling agent A-171, silane coupling agent KH-560, and silane coupling agent KH-570; (2) separately crushing the pinecone powder and the nano-silica gel material, then mixing them at a mass ratio of (10-12):1, then purifying and removing impurities at 200℃ for 30-60 min under an inert gas protective atmosphere, then heating to 1200-1600℃ at a heating rate of 5-10℃ / min, maintaining the temperature for 1-3 h, and cooling to room temperature to obtain a silicon-carbon composite material; (3) stirring and mixing the silicon-carbon composite material with an acid solution to perform etching treatment, filtering the obtained etching solution, and washing it to a pH value of 6-7 to obtain a washed material; (4) drying the washed material, then performing airflow milling and crushing, and removing magnetic substances by sieving to obtain the porous silicon-carbon negative electrode material.

2. The method for preparing porous silicon-carbon anode material according to claim 1, characterized in that, In the step (1), the particle size of the nano-silicon is 20-60 nm.

3. The method for preparing porous silicon-carbon anode material according to claim 1, characterized in that, In the step (1), the mixing and stirring time is 30-90 min, the ultrasonic dispersion time is 30-60 min, and the freeze-drying time is 24-72 h.

4. The method for preparing porous silicon-carbon anode material according to claim 1, characterized in that, In the step (2), the inert gas comprises at least one of nitrogen and argon, and the flow rate of the inert gas is 1-5 m / s.

5. The method for preparing porous silicon-carbon anode material according to claim 1, characterized in that, In the step (3), the acid solution comprises at least one of a hydrochloric acid solution, a citric acid solution, a sulfuric acid solution, and a nitric acid solution; and the mass concentration of the acid solution is 5-20%.

6. The method for preparing porous silicon-carbon anode material according to claim 1, characterized in that, In the step (3), the stirring and mixing speed is 80-120 r / min. In the step (3), the etching treatment time is 1-1.5 h.

7. The method for preparing porous silicon-carbon anode material according to claim 1, characterized in that, In the step (4), the drying temperature is 80-120℃, and the mass content of free water in the dried washed material is <500 ppm. In the step (4), the particle size of the washed material after airflow milling and crushing is 3-20 μm.

8. A porous silicon-carbon anode material, characterized in that, The porous silicon-carbon negative electrode material is prepared by the method of any one of claims 1-7.

9. Use of the porous silicon-carbon negative electrode material of claim 8 in a lithium ion battery.

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