Preparation method and application of silicon-carbon negative electrode material for lithium-ion batteries

Abstract

The present invention discloses a preparation method and application of a silicon-carbon negative electrode material for a lithium-ion battery. The core-shell structure Si@LiNbO3@C material is constructed by a hydrothermal-assisted ball milling method; an environmentally friendly chitosan is used to construct a three-dimensional porous biochar with a high specific surface area and a hierarchical pore structure; the core-shell structure Si@LiNbO3@C material is loaded into the conductive network of the three-dimensional porous biochar to obtain a silicon-carbon negative electrode material with an "in-situ microelectric field-assisted double-interface protection effect", endowing the silicon-carbon negative electrode material with stable interfacial properties and multifunctional coupling effects. The present invention utilizes the space confinement effect of the core-shell structure carbon spheres and the three-dimensional porous biochar, and based on the ferroelectric and piezoelectric effects of LiNbO3 during charge and discharge, a local microelectric field is formed in-situ, which not only converts the harmful expansion of silicon into a beneficial one, but also accelerates the Li + transport, realizing the fast charge and discharge ability; it has the advantages of simple preparation process and environmental friendliness, etc.

Description

Technical Field

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

[0002] Lithium-ion batteries have the advantages of high energy density, high voltage platform, low self-discharge, long service life, strong environmental adaptability, and no memory effect. They have developed rapidly in the past three decades and almost occupied the entire consumer electronics market. In recent years, they have also begun to develop rapidly in the fields of electric vehicles and large-scale energy storage. The ever-expanding scope of application has also put forward higher and higher requirements for lithium batteries. Electric vehicles and new energy storage require batteries with higher energy density. The energy density of traditional graphite negative electrodes is close to the theoretical value, and there is very limited room for improvement in the future. At present, countries around the world are developing lithium-ion battery electrode materials with higher specific capacity.

[0003] Silicon (Si) anode has a theoretical specific capacity comparable to that of lithium metal, a low delithiation potential (0.40V vs. Li / Li + ), low cost and abundant resources, it is considered to be one of the most promising negative electrode materials. However, Si-based materials have serious volume expansion (>400%) and poor conductivity (crystalline silicon is a semiconductor, so the electronic conductivity is relatively low, about 10 -3 S cm -1 ) and other problems still exist, making it not suitable for large-scale commercial development, which further limits its practical application.

[0004] At present, the most widely studied solution is to design a silicon / carbon composite structure, taking advantage of the conductivity of the carbon matrix and the buffer layer provided. The composite silicon-carbon material can complement the advantages of the two, make up for their respective shortcomings, and obtain a new composite negative electrode material with significantly improved reversible capacity and cycle performance (such as patent document application number 202010628246.9, name a core-shell structure silicon-carbon negative electrode material; application number 202010084393.4, name a porous core-shell structure silicon-carbon negative electrode material for lithium-ion batteries and its preparation method; application number 202010084393.4, name a porous core-shell structure silicon-carbon negative electrode material for lithium-ion batteries and its preparation method; application number 202211649745.1, name a core-shell structure silicon-carbon negative electrode material and preparation method and lithium-ion battery; application number 201711018067.8, name a core-shell structure silicon-carbon negative electrode material and its preparation method, etc.). In addition, the fast charging of batteries is a key factor and technical challenge in whether electric vehicles can be widely popularized.

[0005] Therefore, in order to suppress the expansion of silicon to a greater extent and improve its fast charging capability, it is necessary to regulate the microstructure of the silicon-carbon negative electrode material, thereby alleviating the volume expansion of silicon during the cycle and improving the fast charging capability of the silicon-carbon negative electrode material. Summary of the invention

[0006] The technical problem solved by the present invention is to provide a method for preparing silicon-carbon negative electrode materials for lithium-ion batteries that is simple in process, environmentally friendly and can be mass-produced. The method constructs a three-dimensional biocarbon conductive network channel silicon-carbon negative electrode material with "in-situ micro-electric field assisted double interface protection", which not only solves the volume expansion of silicon and realizes the transformation of harmful damage to silicon into a beneficial process, but also improves the rapid charge and discharge capacity of the silicon-carbon negative electrode material. The structure has a triple protection effect: the first: using LiNbO 3 The ferroelectric piezoelectric effect turns the harmful expansion of silicon into a favorable process, accelerating the Li + transmission, realizing the rapid charging and discharging capability of the battery; the second level: constructing core-shell carbon spheres for Si@LiNbO 3 The third layer: three-dimensional porous biocarbon can make up for the fact that the second layer of core-shell structure carbon spheres cannot completely cover Si@LiNbO 3 Therefore, the porous biocarbon-core-shell structure Si@LiNbO constructed by the above triple protection effect can effectively reduce the problem of failure in converting the harmful destruction of silicon into a beneficial process. 3 @C composite material will not only solve the volume expansion of silicon negative electrode, but also effectively improve the fast charging and discharging capability of silicon-carbon negative electrode material. Therefore, the carbon negative electrode material can be used to prepare lithium-ion battery negative electrode and further assembled into lithium-ion battery.

[0007] The present invention adopts the following technical solution to solve the above technical problems: a method for preparing a silicon-carbon negative electrode material for a lithium-ion battery, wherein the specific preparation steps are as follows:

[0008] Step S1: Si@LiNbO 3 Preparation of materials

[0009] Nano-Si and LiNbO 3 Mix well to get Si@LiNbO 3 Material;

[0010] Step S2: Core-shell structure Si@LiNbO 3 Preparation of @C materials

[0011] The Si@LiNbO obtained in step S1 3The material was dispersed in an organic carbon solution, hydrothermally reacted at 150-200°C for 4-12 hours, and then washed and dried, and calcined at 600-800°C for 1-3 hours in an oxygen-free atmosphere to obtain a core-shell structure Si@LiNbO 3 @C material;

[0012] Step S3: Preparation of porous biocarbon aerogel

[0013] Disperse chitosan in deionized water to obtain a chitosan solution with a concentration of 3wt% to 5wt%, stir the chitosan solution in a water bath at 20 to 40°C for 1 to 3h, then add acetic acid, a crosslinking agent, dropwise to carry out a crosslinking reaction, stop heating and stirring after observing that the chitosan solution is completely crosslinked and condensed, and place the reaction product at room temperature, dispense it into a mold, and freeze-dry it to obtain a porous biocarbon aerogel;

[0014] Step S4: Porous biocarbon aerogel-core-shell structure Si@LiNbO 3 Preparation of @C composite materials

[0015] The core-shell structure Si@LiNbO obtained in step S2 3 The @C material is mixed with anhydrous ethanol evenly, and then the porous biocarbon aerogel obtained in step S3 is immersed in the core-shell structure Si@LiNbO 3 @C solution, ultrasonically mixed and heated until anhydrous ethanol evaporated, and then freeze-dried to obtain porous biocarbon aerogel-core-shell structure Si@LiNbO 3 @C Composite materials;

[0016] Step S5: Porous biocarbon-core-shell structure Si@LiNbO 3 Preparation of @C composite materials

[0017] The porous biocarbon aerogel-core-shell structure Si@LiNbO obtained in step S4 3 The @C composite material was subjected to microwave heating to carbonize the aerogel inside to obtain a porous biocarbon-core-shell structure Si@LiNbO with a three-dimensional structure. 3 @C composite material is the silicon-carbon negative electrode material for lithium-ion batteries, in which the power of microwave heating treatment is 300~700W and the time is 5~10min.

[0018] It is further defined that the nano-Si and LiNbO in step S1 3 The mass ratio is 1:0.2%~4%.

[0019] It is further defined that the concentration of the organic carbon solution in step S2 is 0.2-1 mol / L, and the organic carbon solution is one or more of a sucrose solution and a starch solution.

[0020] It is further defined that the oxygen-free atmosphere in step S2 is a nitrogen atmosphere or an argon atmosphere.

[0021] It is further defined that in step S3, the feed ratio of chitosan to cross-linking agent acetic acid is 1 g: 0.5-3 mL, and the concentration of the cross-linking agent acetic acid is 0.5-1.2 mol / L.

[0022] It is further defined that the freeze-drying temperature in step S3 and step S4 is both -80 to -50°C and the time is both 8 to 48 hours.

[0023] It is further defined that the core-shell structure Si@LiNbO in step S4 3 The mass ratio of @C material to porous biocarbon aerogel is 0.5~2.5:1.

[0024] The application of the lithium-ion battery silicon-carbon negative electrode material prepared based on the above method in the preparation of lithium-ion battery negative electrode.

[0025] The lithium ion battery negative electrode prepared based on the above method is used to assemble a lithium ion battery.

[0026] Compared with the prior art, the present invention has the following technical advantages and beneficial effects:

[0027] 1. The hydroxyl groups in the crosslinking agent acetic acid of the present invention can react with the amino groups (NH 3+ ) and hydroxyl groups to form a three-dimensional network structure. The three-dimensional porous biocarbon formed by carbonization improves the conductivity of nano-silicon. In addition, the three-dimensional porous biocarbon has a good effect on the core-shell structure Si@LiNbO 3 The @C composite material plays a role of confined protection, and at the same time suppresses the extreme situation where some nano-Si is not completely wrapped when constructing the core-shell structure and comes into contact with the electrolyte, resulting in rapid capacity decay.

[0028] 2. LiNbO 3 It is a ferroelectric piezoelectric material. + When embedded in silicon-carbon negative electrode materials, LiNbO 3 Due to the ferroelectric effect, the polarization occurs spontaneously, aligning the dipole moments and LiNbO 3 The particles are charged and separated, thus forming a local micro-electric field, which promotes the Li + In addition, in the embedded Li + During the process, Si inevitably produces a huge volume expansion (400%) to squeeze LiNbO 3 At this time, LiNbO 3 The piezoelectric effect will further increase the polarization strength, thereby accelerating the Li +At the same time, the soft environment of the carbon structure will not only inhibit the volume expansion of Si, but also act as a confined structure to separate Si and LiNbO 3 The space confinement deepens the LiNbO 3 Piezoelectric effect. 3 As an inert material, the dosage needs to be strictly controlled. If too much is added, the utilization rate of Si will be reduced accordingly, and the electrochemical properties of the material will not be utilized. In addition, sucrose as a carbon carrier can form a dense and smooth amorphous carbon coating on the surface of the silicon-carbon composite material particles, thereby showing better reversible specific capacity.

[0029] 3. The porous biocarbon aerogel in the present invention has a unique three-dimensional interconnected structure. The ultra-thin three-dimensional biocarbon formed by microwave carbonization has a three-dimensional interconnected network structure and good mechanical strength, which is more conducive to the rapid transmission of ions and electrons and can buffer the volume expansion of Si and poor conductivity during charging and discharging.

[0030] 4. The present invention adopts "in-situ micro-electric field assisted dual interface protection" to construct a silicon-carbon negative electrode material with triple protection, which realizes the transformation of harmful damage to silicon into a beneficial process, effectively solves the volume expansion of the Si negative electrode, and improves the rapid charge and discharge capacity of the silicon-carbon negative electrode material. The first level: transforming the harmful damage to silicon into a beneficial process, using LiNbO 3 The piezoelectric effect and the volume expansion effect of silicon during lithium insertion are used to construct a local micro-electric field in situ, which inhibits the volume expansion of the silicon negative electrode and accelerates the Li + The second stage: In order to further transform the harmful damage of silicon into a beneficial process, a core-shell structure is constructed to Si@LiNbO 3 The three-dimensional porous biocarbon can further buffer the volume expansion of the silicon anode and improve the conductivity. In addition, the three-dimensional porous biocarbon can make up for the fact that the second-layer core-shell structure carbon spheres cannot completely cover the Si@LiNbO 3 , which leads to the failure of the purpose of converting the harmful damage of silicon into a beneficial process. Obviously, the use of the above triple protection can inhibit the expansion of silicon and realize the conversion of the harmful expansion of silicon into a beneficial process as soon as possible. At the same time, the core-shell carbon spheres and three-dimensional porous biocarbon not only improve the conductivity of silicon, but also achieve double confinement (core-shell carbon spheres can be Si@LiNbO 3 Playing a confining role, three-dimensional porous biocarbon can be used to confine the core-shell structure Si@LiNbO 3@C plays a further confinement role). Therefore, the porous biocarbon-core-shell structure Si@LiNbO 3 @C composite materials will not only solve the volume expansion of silicon-carbon negative electrode materials, but also effectively improve the rapid charging and discharging capabilities of silicon-carbon negative electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The core-shell structure Si@LiNbO in Example 1 3 @C SEM image of composite material;

[0032] Figure 2 is the XRD pattern of the silicon-carbon negative electrode material in Example 1;

[0033] Figure 3 It is a comparison chart of the rate charge and discharge performance of the silicon-carbon negative electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4. DETAILED DESCRIPTION

[0034] The present invention constructs a unique three-dimensional biocarbon conductive network channel with "in-situ micro-electric field assisted double interface protection effect", which effectively promotes the efficient transmission of lithium ions and electrons, accelerates reaction kinetics, and improves rapid charge and discharge capabilities.

[0035] The present invention specifically prepares the silicon-carbon negative electrode material by the following method, comprising the following steps:

[0036] Step S1: Si@LiNbO 3 Preparation of materials

[0037] Nano-Si and LiNbO 3 Weigh in proportion (Si and LiNbO 3 The mass ratio of the Si@LiNbO@Si ... 3 Material;

[0038] Step S2: Core-shell structure Si@LiNbO 3 Preparation of @C materials

[0039] Si@LiNbO 3The material is dispersed in an organic carbon solution (the organic carbon solution can be selected from one or more of a sucrose solution or a starch solution; the concentration of the organic carbon solution can be selected from 0.2 to 1 mol / L); a hydrothermal reaction (the hydrothermal reaction temperature can be selected from 150 to 200°C) is performed (the hydrothermal reaction time can be selected from 4 to 12 hours); after washing and drying, the material is calcined in an oxygen-free atmosphere (nitrogen or argon can be selected) (the calcination temperature can be selected from 600 to 800°C, and the calcination time can be selected from 1 to 3 hours) to obtain a core-shell structured Si@LiNbO 3 @C material;

[0040] Step S3: Preparation of porous biocarbon aerogel

[0041] Disperse chitosan in an appropriate amount of deionized water to prepare a chitosan solution of a certain concentration (the concentration of the chitosan solution can be selected as 3wt%~5wt%), and stir for 1~3h in a water bath (the water bath temperature can be selected as 20~40℃) after ultrasonic dispersion. Add a crosslinking agent dropwise (the crosslinking agent can be acetic acid, the concentration can be selected as 0.5~1.2mol / L, and the ratio of chitosan to acetic acid is 1g:0.5~3mL), and stop heating and stirring after observing that the chitosan solution is completely cross-linked and condensed. After standing at room temperature, slowly dispense it into a mold to avoid bubbles during the dispensing process. Then, freeze-dry it (the freeze-drying temperature can be selected as -80~-50℃, and the freeze-drying time can be selected as 8~48h) to obtain a porous biocarbon aerogel.

[0042] Step S4: Porous biocarbon aerogel-core-shell structure Si@LiNbO 3 Preparation of @C composite materials

[0043] The core-shell structure Si@LiNbO 3 @C composite materials and porous biocarbon aerogel were weighed according to a certain mass ratio (core-shell structure Si@LiNbO 3 @C composite material and porous biocarbon aerogel can be selected from 0.5 to 2.5:1); the core-shell structure Si@LiNbO 3 @C composite material was mixed evenly with anhydrous ethanol; then the porous biocarbon aerogel was immersed in the mixed core-shell structure Si@LiNbO 3 @C solution, ultrasonically treated for 1-3 hours, then heated until the anhydrous ethanol evaporated, and then freeze-dried (freeze-drying temperature can be -80--50℃, freeze-drying time can be 8-48 hours) to obtain porous biocarbon aerogel-core-shell structure Si@LiNbO 3 @CComposite materials.

[0044] (5) Porous biocarbon-core-shell structure Si@LiNbO 3 Preparation of @C composite materials

[0045] Porous biocarbon aerogel-core-shell structure Si@LiNbO 3 The composite material is subjected to microwave heating treatment (the microwave heating power can be selected to be 300-700 W, and the microwave heating time can be selected to be 5-10 min) to carbonize the aerogel inside it to obtain a porous biocarbon-core-shell structure Si@LiNbO with a three-dimensional structure. 3 @C composite material is the silicon-carbon negative electrode material for lithium-ion batteries.

[0046] In order to better illustrate the above technical solution, the above technical solution will be described in detail below in conjunction with specific embodiments. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies implemented based on the above content of the present invention belong to the scope of the present invention. Example 1

[0047] Step S1: Si@LiNbO 3 Preparation

[0048] According to nano-Si:LiNbO 3 The mass ratio of Si@LiNbO was 1:3%, and the mixture was accurately weighed and ball-milled in a ball mill at a speed of 400 r / min for 8 h to obtain Si@LiNbO 3 Material;

[0049] Step S2: Core-shell structure Si@LiNbO 3 Preparation of @C materials

[0050] The Si@LiNbO obtained in step S1 3 The material was evenly dispersed in a sucrose solution with a concentration of 0.7 mol / L; hydrothermally reacted at 180 °C for 8 h, then washed and dried, and calcined at 700 °C for 2 h in a nitrogen atmosphere to obtain a core-shell structured Si@LiNbO 3 @C material;

[0051] Step S3: Preparation of porous biocarbon aerogel

[0052] 24g chitosan powder was dispersed in 588mL deionized water to prepare a chitosan solution with a concentration of 4wt%. After ultrasonic dispersion, the solution was stirred for 2h in a 30℃ water bath using a magnetic stirrer. 36mL of 1.05mol / L acetic acid crosslinking agent was added, and heating and stirring were stopped after the chitosan solution was observed to be completely crosslinked and condensed. After standing at room temperature, the solution was slowly dispensed into a mold to avoid bubbles during the dispensing process. The solution was then freeze-dried at -70℃ for 24h to obtain a porous biocarbon aerogel.

[0053] Step S4: Porous biocarbon aerogel-core-shell structure Si@LiNbO 3 Preparation of @C composite materials

[0054] According to the core-shell structure Si@LiNbO 3 The mass ratio of @C material to porous biocarbon aerogel is 1.8:1. Weigh 500 mg of the core-shell structure Si@LiNbO in step S2. 3 @C material and mix it evenly with anhydrous ethanol. Weigh 278 mg of the porous biocarbon aerogel in step S3 and soak it in the core-shell structure Si@LiNbO 3 @C solution, ultrasonicated for 2 h, heated until anhydrous ethanol evaporated, and then freeze-dried at -70 °C for 24 h to obtain porous biocarbon aerogel-core-shell structure Si@LiNbO 3 @C Composite materials;

[0055] Step S5: Porous biocarbon-core-shell structure Si@LiNbO 3 Preparation of @C composite materials

[0056] The porous biocarbon aerogel-core-shell structure Si@LiNbO 3 The composite material was subjected to microwave heating at 600 W for 8 min to carbonize the aerogel inside to obtain a porous biocarbon-core-shell structure Si@LiNbO with a three-dimensional structure. 3 @C composite material is the silicon-carbon negative electrode material for lithium-ion batteries. Example 2

[0057] Step S1: Si@LiNbO 3 Preparation of materials

[0058] According to nano-Si:LiNbO 3 The mass ratio of Si@LiNbO was 1:0.2%, and the mixture was accurately weighed and ball-milled in a ball mill at a speed of 400 r / min for 8 h to obtain Si@LiNbO 3 Material;

[0059] Step S2: Core-shell structure Si@LiNbO 3 Preparation of @C materials

[0060] The Si@LiNbO obtained in step S1 3 The material was evenly dispersed in a sucrose solution with a concentration of 0.2 mol / L, hydrothermally reacted at 150 °C for 4 h, and then washed and dried, and calcined at 600 °C for 1 h in a nitrogen atmosphere to obtain a core-shell structure Si@LiNbO 3 @C material;

[0061] Step S3: Preparation of porous biocarbon aerogel

[0062] 24 g of chitosan powder was dispersed in 800 mL of deionized water to prepare a chitosan solution with a concentration of 3 wt%. After being evenly dispersed by ultrasonication, the solution was stirred with a magnetic stirrer in a water bath at 20 °C for 1 h. 12 mL of 0.5 mol / L acetic acid crosslinking agent was added, and heating and stirring were stopped after the chitosan solution was observed to be completely crosslinked and condensed. After standing at room temperature, the solution was slowly dispensed into a mold to avoid bubbles during the dispensing process. The solution was then freeze-dried at -80 °C for 8 h to obtain a porous biocarbon aerogel.

[0063] Step S4: Porous biocarbon aerogel-core-shell structure Si@LiNbO 3 Preparation of @C composite materials

[0064] According to the core-shell structure Si@LiNbO 3 The mass ratio of @C composite material to porous biocarbon aerogel is 0.5:1. Weigh 500 mg of the core-shell structure Si@LiNbO 3 @C composite material and mix it evenly with anhydrous ethanol. 1000 mg of the porous biocarbon aerogel in step S3 is soaked in the core-shell structure Si@LiNbO 3 @C solution, ultrasonicated for 1 h, heated until anhydrous ethanol evaporated, and then freeze-dried at -80 °C for 8 h to obtain porous biocarbon aerogel-core-shell structure Si@LiNbO 3 @C Composite materials;

[0065] Step S5: Porous biocarbon-core-shell structure Si@LiNbO 3 Preparation of @C composite materials

[0066] The porous biocarbon aerogel-core-shell structure Si@LiNbO 3 The composite material was heated by microwave at 300 W for 5 min to carbonize the aerogel inside to obtain a porous biocarbon-core-shell structure Si@LiNbO with a three-dimensional structure. 3 @C composite material is the silicon-carbon negative electrode material for lithium-ion batteries. Example 3

[0067] Step S1: Si@LiNbO 3 Preparation of materials

[0068] According to nano-Si:LiNbO 3 The mass ratio of Si@LiNbO was 1:4%, and the mixture was accurately weighed and ball-milled in a ball mill at a speed of 400 r / min for 8 h to obtain Si@LiNbO 3 Material;

[0069] Step S2: Core-shell structure Si@LiNbO 3 Preparation of @C materials

[0070] The Si@LiNbO obtained in step S1 3 The material was evenly dispersed in a sucrose solution with a concentration of 1 mol / L, hydrothermally reacted at 200 °C for 12 h, and then washed and dried, and calcined at 800 °C for 3 h in a nitrogen atmosphere to obtain a core-shell structure Si@LiNbO 3 @C material;

[0071] Step S3: Preparation of porous biocarbon aerogel

[0072] 24g chitosan powder was dispersed in 456mL deionized water to prepare a chitosan solution with a concentration of 5wt%. After ultrasonic dispersion, the solution was stirred for 3h in a water bath at 40℃ using a magnetic stirrer. 72mL of 1.2mol / L acetic acid crosslinking agent was added, and heating and stirring were stopped after the chitosan solution was observed to be completely crosslinked and condensed. After standing at room temperature, the solution was slowly dispensed into a mold to avoid bubbles during the dispensing process. The solution was then freeze-dried at -50℃ for 48h to obtain a porous biocarbon aerogel.

[0073] Step S4: Porous biocarbon aerogel-core-shell structure Si@LiNbO 3 Preparation of @C composite materials

[0074] According to the core-shell structure of nano-silicon@LiNbO 3 The mass ratio of @C composite material to porous biocarbon aerogel is 2.5:1. Weigh 500 mg of the core-shell structure nanosilicon @LiNbO prepared in step S2. 3 @C composite material and mix it evenly with anhydrous ethanol, and soak 200 mg of the porous biocarbon aerogel in step S3 in the core-shell structure nanosilicon @LiNbO 3 @C solution, ultrasonically treated for 3 h, heated until anhydrous ethanol evaporated, and then freeze-dried at -50 °C for 48 h to obtain porous biocarbon aerogel-core-shell structure Si@LiNbO 3 @C Composite materials;

[0075] Step S5: Porous biocarbon-core-shell structure Si@LiNbO 3 Preparation of @C composite materials

[0076] The porous biocarbon aerogel-core-shell structure Si@LiNbO 3 The composite material was subjected to microwave heating at 700 W for 10 min to carbonize the aerogel inside it to obtain a porous biocarbon-core-shell structure Si@LiNbO with a three-dimensional structure. 3 @C composite material is the silicon-carbon negative electrode material for lithium-ion batteries.

[0077] Comparative Example 1 (No Ferroelectric Material Added)

[0078] Step S1: Preparation of core-shell structured Si@C materials

[0079] Nano-Si was uniformly dispersed in a sucrose solution with a concentration of 0.7 mol / L, and subjected to hydrothermal reaction at 180°C for 8 h. After washing and drying, the nano-Si@C material was calcined at 700°C for 2 h in a nitrogen atmosphere to obtain a core-shell structured Si@C material.

[0080] Step S2: Preparation of porous biocarbon aerogel

[0081] 24g chitosan powder was dispersed in 588mL deionized water to prepare a chitosan solution with a concentration of 4wt%. After ultrasonic dispersion, the solution was stirred for 2h in a 30℃ water bath using a magnetic stirrer. 36mL of 1.05mol / L acetic acid crosslinking agent was added, and heating and stirring were stopped after the chitosan solution was observed to be completely crosslinked and condensed. After standing at room temperature, the solution was slowly dispensed into a mold to avoid bubbles during the dispensing process. The solution was then freeze-dried at -70℃ for 24h to obtain a porous biocarbon aerogel.

[0082] Step S3: Preparation of porous biocarbon aerogel-core-shell structure Si@C composite material

[0083] According to the mass ratio of core-shell structure nano-silicon@C material to porous bio-carbon aerogel of 1.8:1, 500 mg of the core-shell structure Si@C material in step S1 was weighed and mixed evenly with anhydrous ethanol, 278 mg of the porous bio-carbon aerogel in step S2 was weighed and immersed in the core-shell structure nano-silicon@C solution, and then heated to evaporate the anhydrous ethanol after ultrasonication for 2 hours, and then freeze-dried at -80°C for 8 hours to obtain a porous bio-carbon aerogel-core-shell structure Si@C composite material;

[0084] Step S4: Preparation of porous biocarbon-core-shell structure Si@C composite material

[0085] The porous biocarbon aerogel-core-shell structure Si@C composite material in step S3 was subjected to microwave heating treatment at a power of 600 W for 8 minutes to carbonize the aerogel inside to obtain a silicon-carbon negative electrode material.

[0086] Comparative Example 2 (core-shell structure not used)

[0087] Step S1: Si@LiNbO 3 Preparation of materials

[0088] According to nano-Si:LiNbO 3 The mass ratio of Si@LiNbO was 1:3%, and the mixture was accurately weighed and ball milled in a ball mill at 400 r / min for 8 h to obtain Si@LiNbO 3 Material;

[0089] Step S2: Preparation of porous biocarbon aerogel

[0090] 24g chitosan powder was dispersed in 588mL deionized water to prepare a chitosan solution with a concentration of 4wt%. After ultrasonic dispersion, the solution was stirred for 2h in a 30℃ water bath using a magnetic stirrer. 36mL of 1.05mol / L acetic acid crosslinking agent was added, and heating and stirring were stopped after the chitosan solution was observed to be completely crosslinked and condensed. After standing at room temperature, the solution was slowly dispensed into a mold to avoid bubbles during the dispensing process. The solution was then freeze-dried at -70℃ for 24h to obtain a porous biocarbon aerogel.

[0091] Step S3: Porous biocarbon aerogel-Si@LiNbO 3 Preparation of composite materials

[0092] Follow the steps in step S1 to prepare Si@LiNbO 3 The mass ratio of the material to the porous biocarbon aerogel is 1.8:1. Weigh 500 mg of Si@LiNbO 3 The materials were mixed with anhydrous ethanol and 278 mg of the porous biocarbon aerogel prepared in step S2 was soaked in Si@LiNbO 3 The solution was ultrasonicated for 2 h, heated until the anhydrous ethanol evaporated, and then freeze-dried at -70 °C for 24 h to obtain the porous biocarbon aerogel-Si@LiNbO 3 Composite materials.

[0093] Step S4: Porous Biocarbon-Si@LiNbO 3 Preparation of composite materials

[0094] The porous biocarbon aerogel-Si@LiNbO 3 The composite material was subjected to microwave heating treatment at a power of 600 W for 8 minutes to carbonize the aerogel inside it to obtain a silicon-carbon negative electrode material.

[0095] Comparative Example 3 (without adding porous biochar)

[0096] Step S1: Si@LiNbO 3 Preparation of materials

[0097] According to nano-Si:LiNbO 3 The mass ratio of Si@LiNbO was 1:3%, and the mixture was accurately weighed and ball-milled in a ball mill at a speed of 400 r / min for 8 h to obtain Si@LiNbO 3 Material;

[0098] Step S2: Core-shell structure Si@LiNbO 3 Preparation of @C materials

[0099] The Si@LiNbO obtained in step S1 3 The material was evenly dispersed in a sucrose solution with a concentration of 0.7 mol / L, hydrothermally reacted at 180°C for 8 hours, washed and dried, and then calcined at 700°C for 2 hours in a nitrogen atmosphere to obtain a silicon-carbon negative electrode material.

[0100] Comparative Example 4 (Changing microwave heating to ordinary tube furnace sintering)

[0101] Step S1: Si@LiNbO 3 Preparation of materials

[0102] According to nano-Si:LiNbO 3 The mass ratio of 3%:1 was accurately weighed, and the mixture was ball-milled at a speed of 400 r / min for 8 h to obtain Si@LiNbO 3 Material;

[0103] Step S2: Core-shell structure Si@LiNbO 3 Preparation of @C materials

[0104] The Si@LiNbO obtained in step S1 3 The material was evenly dispersed in a sucrose solution with a concentration of 0.7 mol / L, hydrothermally reacted at 180 °C for 8 h, and then washed and dried, and calcined at 700 °C for 2 h in a nitrogen atmosphere to obtain a core-shell structure Si@LiNbO 3 @C material;

[0105] Step S3: Preparation of porous biocarbon aerogel

[0106] 24g chitosan powder was dispersed in 588mL deionized water to prepare a chitosan solution with a concentration of 4wt%. After ultrasonic dispersion, the solution was stirred for 2h in a 30℃ water bath using a magnetic stirrer. 36mL of 1.05mol / L acetic acid crosslinking agent was added, and heating and stirring were stopped after the chitosan solution was observed to be completely crosslinked and condensed. After standing at room temperature, the solution was slowly dispensed into a mold to avoid bubbles during the dispensing process. The solution was then freeze-dried at -70℃ for 24h to obtain a porous biocarbon aerogel.

[0107] Step S4: Porous biocarbon aerogel-core-shell structure Si@LiNbO 3 Preparation of @C composite materials

[0108] According to the core-shell structure Si@LiNbO 3 The mass ratio of @C composite material to porous biocarbon aerogel is 1.8:1. Weigh 500 mg of the core-shell structure Si@LiNbO in step S2. 3@C material and mix it evenly with anhydrous ethanol. Weigh 278 mg of the porous biocarbon aerogel in step S3 and soak it in the core-shell structure Si@LiNbO 3 @C solution, ultrasonicated for 2 h, heated until anhydrous ethanol evaporated, and then freeze-dried at -70 °C for 24 h to obtain porous biocarbon aerogel-core-shell structure Si@LiNbO 3 @C Composite materials;

[0109] Step S5: Porous biocarbon-core-shell structure Si@LiNbO 3 Preparation of @C composite materials

[0110] The porous biocarbon aerogel-core-shell structure Si@LiNbO 3 The @C composite material was transferred to a tubular furnace and calcined at 600 °C for 2 h in a nitrogen atmosphere to obtain a silicon-carbon negative electrode material.

[0111] Product performance test:

[0112] Before the electrochemical test, the electrodes are prepared and button cells are assembled, and then the battery electrical performance is tested using a charge and discharge test cabinet.

[0113] The silicon-carbon negative electrode material prepared in Example 1 of the present invention enables the lithium-ion battery to have better rate and cycle stability.

[0114] from Figure 1 It can be seen from the SEM image that the core-shell structure Si@LiNbO 3 @C composite material. Figure 2 It can be seen from the XRD diagram that the composite material prepared according to the method of Example 1 has superposition of characteristic peaks of amorphous carbon and silicon, indicating that the silicon-carbon negative electrode material has been successfully synthesized.

[0115] from Figure 3 It can be seen from the electrical performance test results that the silicon-carbon negative electrode material prepared in Example 1 has better rate performance and capacity recovery performance.

[0116] Based on the above test results, it can be seen that the present invention controls the ferroelectric piezoelectric material LiNbO 3The addition of, the construction of core-shell structured carbon balls, the loading of three-dimensional porous biochar and other key factors can realize the regulation of the microstructural properties of silicon-carbon negative electrode materials. The unique "in-situ micro-electric field assisted double interface protection" three-dimensional conductive network channel effectively promotes the efficient transmission of lithium ions and electrons, accelerates the reaction kinetics, and improves the rapid charge and discharge capabilities. Example 1 of the present invention adopts a three-dimensional biocarbon conductive network, a core-shell structure and an in-situ micro-electric field strategy to achieve a coupling effect of different functions: this structure not only solves the volume expansion of silicon, but also converts the harmful expansion of silicon into a beneficial one, while achieving a comprehensive improvement in high-rate charge and discharge performance and stability. However, the use of a single material structure or the lack of a certain material structure (Comparative Examples 1-4) and the improper use of certain key parameters in the preparation process (Examples 2-3) cannot optimize the solution to the volume expansion of silicon and the improvement of electrochemical performance.

[0117] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-ion battery silicon-carbon negative electrode material, characterized in that The specific preparation steps are: Step S1: Preparation of Si@LiNbO3 material The nano-Si and LiNbO3 are uniformly mixed to obtain Si@LiNbO3 material; Step S2: Preparation of core-shell structure Si@LiNbO3@C material The Si@LiNbO3 material obtained in step S1 is dispersed in an organic carbon solution, wherein the concentration of the organic carbon solution is 0.2-1 mol / L, and the organic carbon solution is one or more of a sucrose solution or a starch solution, and subjected to a hydrothermal reaction at 150-200°C for 4-12 hours, and then washed and dried, and then calcined at 600-800°C for 1-3 hours in an oxygen-free atmosphere to obtain a core-shell structured Si@LiNbO3@C material; Step S3: Preparation of porous biocarbon aerogel Disperse chitosan in deionized water to obtain a chitosan solution with a concentration of 3wt% to 5wt%, stir the chitosan solution in a water bath at 20 to 40°C for 1 to 3h, then add acetic acid, a crosslinking agent, dropwise to carry out a crosslinking reaction, stop heating and stirring after observing that the chitosan solution is completely crosslinked and condensed, and place the reaction product at room temperature, dispense it into a mold, and freeze-dry it to obtain a porous biocarbon aerogel; Step S4: Preparation of porous biocarbon aerogel-core-shell structure Si@LiNbO3@C composite material The core-shell structure Si@LiNbO3@C material obtained in step S2 is mixed with anhydrous ethanol, and then the porous biocarbon aerogel obtained in step S3 is immersed in the core-shell structure Si@LiNbO3@C solution, and then ultrasonically mixed and heated until the anhydrous ethanol is volatilized, and then freeze-dried to obtain a porous biocarbon aerogel-core-shell structure Si@LiNbO3@C composite material, wherein the mass ratio of the core-shell structure Si@LiNbO3@C material to the porous biocarbon aerogel is 0.5-2.5:1; Step S5: Preparation of porous biocarbon-core-shell structure Si@LiNbO3@C composite material The porous biocarbon aerogel-core-shell structure Si@LiNbO3@C composite material obtained in step S4 is subjected to microwave heating treatment to carbonize the aerogel inside it to obtain a porous biocarbon-core-shell structure Si@LiNbO3@C composite material with a three-dimensional structure, namely, a lithium-ion battery silicon-carbon negative electrode material, wherein the power of the microwave heating treatment is 300~700W, and the time is 5~10min.

2. The method for preparing the silicon-carbon negative electrode material for lithium-ion batteries according to claim 1, characterized in that: The mass ratio of nano-Si to LiNbO3 in step S1 is 1:0.2%~4%.

3. The method for preparing the silicon-carbon negative electrode material for lithium-ion batteries according to claim 1, characterized in that: The oxygen-free atmosphere in step S2 is a nitrogen atmosphere or an argon atmosphere.

4. The method for preparing the silicon-carbon negative electrode material for lithium-ion batteries according to claim 1, characterized in that: In step S3, the feeding ratio of chitosan to cross-linking agent acetic acid is 1 g: 0.5-3 mL, and the concentration of the cross-linking agent acetic acid is 0.5-1.2 mol / L.

5. The method for preparing the silicon-carbon negative electrode material for lithium-ion batteries according to claim 1, characterized in that: The freeze-drying temperature in step S3 and step S4 is both -80 to -50°C, and the time is both 8 to 48 hours.

6. Use of the lithium ion battery silicon-carbon negative electrode material prepared by the method according to any one of claims 1 to 5 in the preparation of lithium ion battery negative electrode.

7. Use of the lithium ion battery silicon-carbon negative electrode material prepared by the method according to any one of claims 1 to 5 in the preparation of lithium ion batteries.

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