A method for preparing a coated porous silicon-oxygen negative electrode based on polymethylsilsesquioxane

Abstract

The present application relates to the field of lithium ion battery electrode material, the present application uses polymethylsilsesquioxane as raw material, uses the reaction of magnesium salt and silicon oxygen to improve the initial efficiency, and improves the stability and conductivity of the material through carbon source coating, and the expansion of the material is weakened by the auxiliary acid etching means, and the stability of the material is improved. Finally, the porous silicon oxygen negative electrode material with coating structure is prepared by the scheme, the material has high initial capacity and initial efficiency, and still has high specific capacity after 50 cycles. The excellent performance of the silicon-carbon composite material has excellent application prospect in the field of lithium ion battery negative electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing a coated porous silicon-oxygen composite negative electrode based on polymethylsilsesquioxane. Polymethylsilsesquioxane is prepared through a series of processes such as ball milling mixing, high-temperature calcination, acid etching, etc. with magnesium source, silicon source, carbon source, etc. This preparation technology is beneficial to improve the energy density of the material, the first coulombic efficiency and reduce the volume expansion. It belongs to the field of lithium ion battery negative electrode of lithium battery new energy materials technology. BACKGROUND

[0002] Lithium ion batteries have a wide range of applications in the field of new energy. Graphite, as the most widely used negative electrode material in lithium ion batteries, has stable voltage platform and long cycle stability characteristics. However, the theoretical capacity of the material is only 372 mAh / g, which cannot meet the demand of mankind for high energy density energy storage devices. Silicon-based negative electrode material has become the most potential negative electrode material in the future due to its ultra-high specific capacity. However, the volume expansion of pure silicon material is large, and the silicon-oxygen material can alleviate the volume expansion problem of the material to a certain extent due to its special structural characteristics. The main structure of silicon-oxygen material is that silicon nanocrystalline particles are dispersed in silicon dioxide. In the first charge and discharge process, silicon dioxide will consume lithium salt, resulting in a decrease in the first efficiency of the material. Therefore, how to improve the first efficiency of silicon-oxygen material is crucial. In addition, the silicon-oxygen negative electrode itself has poor conductivity, and how to improve the conductivity of the material itself is also a problem we need to consider.

[0003] In order to solve the above problems, multiple means are used to solve them. In patent CN117855434A, a kind of lithium ion battery pre-magnesium silicon-oxygen negative electrode material and preparation method are disclosed. The invention simply mixes magnesium source and silicon monoxide in liquid phase, and then obtains the product through high-temperature pre-magnesium sintering and carbon coating. The preparation scheme is simple, the cost is low, and the experiment is safe and easy to enlarge. In patent CN110550635B, a new preparation method of carbon-coated silicon-oxygen negative electrode material is disclosed. The invention adopts a combination of segmented mechanical fusion and carbon coating technology, which achieves good coating effect on SiO material particles. The coated material has high first coulombic efficiency, good cycle performance, low cost, and environmental friendliness. In patent CN117038926A, a kind of porous silicon-oxygen negative electrode material obtained by etching and its preparation method and application are disclosed. The porous silicon particles have a porous structure, and the pore depth of the pores contained in the porous silicon particles is more than 200 nm. In the present application, pores are etched on the surface of silicon material through a porosification process, increasing the lithium ion transmission channel and shortening the lithium ion diffusion path. The combination of metal-assisted acid etching, alkaline etching and other etching methods has the characteristics of deep pore forming effect and good morphology control. The existence of the ion conductor layer makes the outer carbon shell more compact, and the ion migration rate and cycle are effectively improved. SUMMARY

[0004] The purpose of the present application is to pre-magnify the polysiloxane material formed by the poly-methyl-siloxane with magnesium source and silicon source, and coat the material with carbon source, and finally obtain the silicon-oxygen negative electrode material with porous structure through acid etching.

[0005] The theoretical capacity of the silicon-oxygen negative electrode material can be maintained at 1500-1800 mAh / g. During the charging and discharging process, lithium ions first react with oxygen atoms, replace the oxygen atoms in silicon monoxide, and form Li2O compounds and silicon elements. Therefore, the first cycle coulombic efficiency of the silicon-oxygen negative electrode material can reach about 75%. The volume expansion can be limited to within 30% due to the introduction of oxygen atoms, which can be further limited to within 20%, and further limited to within 10%, which has good cycle stability and is a silicon-based negative electrode material that is expected to be widely used. Ball milling modification process: the ball milling is used to crush and uniformly mix the multi-component material, which provides a basis for stable reaction in the subsequent high-temperature calcination process.

[0006] High-temperature calcination process: the poly-methyl-siloxane is converted into a silicon-oxygen negative electrode material by high-temperature calcination in an inert atmosphere. In addition, the carbon source material added will also be pyrolyzed on the outer layer to form an amorphous carbon coating layer.

[0007] Pre-magnification process: through the synergistic effect of magnesium salt and silicon source, the silicon-magnesium salt with hard structure is formed as a protective layer of the silicon-oxygen negative electrode while adjusting the silicon-oxygen ratio of the silicon-oxygen material, which inhibits the expansion of the material.

[0008] In some embodiments, the present application also includes an acid etching process: using dilute acid to etch the material, removing the magnesium salt and other components that have not completely reacted, treating the material to form pores, providing expansion space, and improving the wettability of the electrolyte to the material.

[0009] The dilute acid includes any one of 0.001-1 mol / L dilute hydrochloric acid, 0.001-1 mol / L dilute sulfuric acid, and 0.001-1 mol / L dilute nitric acid.

[0010] Based on the above related means, the material is prepared by adding magnesium salt, silicon source and carbon source to polymethylsilsesquioxane as the basic raw material: first, the raw materials such as polymethylsilsesquioxane and magnesium salt are further mixed during ball milling to ensure the uniformity of the subsequent reaction and to ensure the formation of a more uniform magnesium silicate layer and carbon layer to protect the material; second, the silicon-oxygen composite material after high-temperature calcination is etched by dilute acid to form a void structure inside the material, which can improve the ion mobility and reduce the volume expansion of the material; third, carbon source is added to coat the material, and after high-temperature calcination, the carbon source material is converted into an amorphous carbon layer to coat the outer layer of the material, which can improve the electrical conductivity of the material and support the structure of the material.

[0011] Based on the above related technical means, the present application provides a coated porous silicon-oxygen negative material prepared based on polymethylsilsesquioxane.

[0012] The technical scheme provided by the present application comprises the following steps:

[0013] Step (1): A certain mass ratio of polymethylsilsesquioxane, magnesium salt and anhydrous ethanol is weighed and mixed uniformly, and is denoted as mixed solution A.

[0014] Step (2): The mixed solution A is transferred to a ball mill tank, zirconium beads are added, and ball milling is carried out at a speed of 300-800 rpm for 1-5 h, then silicon powder and organic carbon source are added and ball milling is continued for 1-2 h, and the ball milling liquid is removed by filtration to remove the dispersion liquid. The solid component after removing the dispersion liquid is denoted as solid A.

[0015] Step (3): A certain amount of solid A is placed in a corundum boat, and the corundum is transferred to a tube furnace, and the material is calcined at high temperature under argon atmosphere, and two temperature gradients are set for calcination. The first section is heated to 300-500 DEG C at a heating rate of 1-3 DEG C / min, and the temperature is kept for 1-5 h; the second section is heated to 800-1200 DEG C at a heating rate of 3-5 DEG C / min, and the temperature is kept for 5-10 h, and then natural annealing is carried out. The material is cooled to room temperature and taken out for standby, denoted as solid B.

[0016] Step (4): Solid B is added to dilute hydrochloric acid in multiple batches, and the concentration of dilute hydrochloric acid is 0.001-1 mol / L. A centrifuge is used at a speed of 400-2000 rpm for 2-7 min, and after centrifugation, the dilute hydrochloric acid is removed, and the sample is washed with deionized water and anhydrous ethanol for three times, and then dried and standby, denoted as solid C.

[0017] Step (5): The silicon-oxygen negative electrode material prepared above is mixed with a binder (CMC) and acetylene black (AB) at a mass ratio of 8:1:1, uniformly mixed in a deionized water solvent, coated on a copper foil, vacuum dried at 80 DEG C, and then punched into a sheet as a working electrode. A lithium sheet is used as a counter electrode, and a 1 M LiTFSI in DOL:DME (V:V=1:1)+1 wt.% LiNO3 is used as an experimental electrolyte system to assemble a coin-type battery (half cell) and perform charge-discharge cycle tests.

[0018] Preferably, the mass ratio in step (1) is polymethylsilsesquioxane:magnesium salt:silicon powder:organic carbon source=90:(1~5):(1~5):(1~5); preferably, the magnesium salt in step (1) is one of magnesium oxide, magnesium chloride, and magnesium carbonate; preferably, the silicon powder in step (1) has a micron size, and the size is 5~20 μm; preferably, the organic carbon source is one of glucose, citric acid, and oxalic acid; preferably, the amount of anhydrous ethanol in step (1) is 10~50 ml, and further preferably, the amount of anhydrous ethanol is 150~250 ml.

[0019] Preferably, the rotation speed in step (2) is set to 350~550 rpm, and the ball milling time is controlled to be 2~3 h.

[0020] Preferably, the temperature in step (3) is controlled to be 350~400 DEG C in the first stage, and the holding time is 2~4 h; the temperature in the second stage is controlled to be 1000~1150 DEG C, and the holding time is 6~8 h.

[0021] The numerical range of the present application includes not only the point values listed above, but also any point values between the numerical ranges listed above. Due to the limited space and for the sake of simplicity, the present application does not list all the specific point values included in the range.

[0022] The technical solution of the present application has the following beneficial effects:

[0023] Improving the initial efficiency: using magnesium salt and silicon source as additives to control the interface layer of the silicon-oxygen material, improving the silicon-oxygen ratio of the material, and forming a hard structure of silicate to protect the material structure. To achieve the purpose of improving the initial efficiency of the material.

[0024] Improving the conductivity: using the method of adding carbon source to form a carbon layer structure with good conductivity outside the material, realizing the improvement of the conductivity of the material.

[0025] Reducing volume expansion: In addition to the polymethylsilsesquioxane converted silicon-oxygen material, a double protective layer structure of silicate and amorphous carbon layer is formed, which can realize the function of limiting the volume expansion of the silicon-oxygen material. In addition, the material is subjected to pore forming by acid etching, thereby providing more volume expansion space for the material.

[0026] Improving electrochemical stability: Under the double protective layer structure, the material has better electrochemical stability and higher reversible specific capacity after cycling. DETAILED DESCRIPTION

[0027] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0028] Example 1

[0029] (1) 30 g of polymethylsilsesquioxane was weighed and placed in a beaker, 300 ml of anhydrous ethanol was added for dispersion, and the mixture was fully mixed.

[0030] (2) The mixed solution was transferred to a 500 ml volume ball mill tank, an appropriate amount of 3 mm zirconium beads was added, the rotation speed of the ball mill was adjusted to 400 rpm, and the ball milling was carried out for 3 h. The ball milling liquid was removed by filtration to remove the dispersion liquid and collect the solid components, which were reserved for use.

[0031] (3) The material was calcined at high temperature using an atmosphere tube furnace. The first stage temperature was increased to 350℃ at a rate of 3 ℃ / min, and the temperature was maintained for 3 h. The second stage temperature was increased to 1000℃ at a rate of 5 ℃ / min, and the temperature was maintained for 6 h. After sintering, the sample was naturally annealed and cooled, and then taken out for standby.

[0032] (4) The calcined sample was subjected to batch acid washing. The dilute hydrochloric acid had a concentration of 0.015 mol / L, and the single hydrochloric acid dosage was 7 ml. The centrifuge rotation speed was 700 rpm, and the centrifugation time was 4 min. After centrifugation, the material was washed and dried for standby, and a silicon-oxygen negative electrode material was obtained.

[0033] (5) The material in step (4) was used to assemble a battery.

[0034] Example 2

[0035] (1) 30 g of material with a total mass ratio of polymethylsilsesquioxane: magnesium oxide = 95:5 was weighed and placed in a beaker, 300 ml of anhydrous ethanol was added for dispersion, and the mixture was fully mixed.

[0036] (2) The mixed solution is transferred to a 500 ml volume ball mill tank, an appropriate amount of 3 mm zirconium beads is added, the ball mill speed is adjusted to 400 rpm, and the ball milling is performed for 3 h. The ball milling solution is removed by filtration to remove the dispersion liquid and collect the solid components, which are reserved for later use.

[0037] (3) The material is subjected to high temperature calcination using an atmosphere tube furnace. The first stage temperature is increased to 350°C at a rate of 3°C / min, and the temperature is maintained for 3 h. The second stage temperature is increased to 1000°C at a rate of 5°C / min, and the temperature is maintained for 6 h. After sintering is completed, natural annealing is performed, and the sample is removed after cooling is completed for later use.

[0038] (4) The calcined sample is subjected to batch acid washing. The dilute hydrochloric acid concentration is 0.015 mol / L, the single hydrochloric acid dosage is 7 ml, and the centrifuge speed is 700 rpm. The centrifugation time is 4 min. After centrifugation is completed, the material is washed and dried for later use to obtain a silicon-oxygen negative electrode material.

[0039] (5) The material in step (4) is used for battery assembly.

[0040] Example 3

[0041] (1) A total mass of 30 g of material is weighed, with a mass ratio of polymethylsilsesquioxane:silicon powder = 95:5, and placed in a beaker. 300 ml of anhydrous ethanol is added for dispersion, and the mixture is thoroughly mixed.

[0042] (2) The mixed solution is transferred to a 500 ml volume ball mill tank, an appropriate amount of 3 mm zirconium beads is added, the ball mill speed is adjusted to 400 rpm, and the ball milling is performed for 3 h. The ball milling solution is removed by filtration to remove the dispersion liquid and collect the solid components, which are reserved for later use.

[0043] (3) The material is subjected to high temperature calcination using an atmosphere tube furnace. The first stage temperature is increased to 350°C at a rate of 3°C / min, and the temperature is maintained for 3 h. The second stage temperature is increased to 1000°C at a rate of 5°C / min, and the temperature is maintained for 6 h. After sintering is completed, natural annealing is performed, and the sample is removed after cooling is completed for later use.

[0044] (4) The calcined sample is subjected to batch acid washing. The dilute hydrochloric acid concentration is 0.015 mol / L, the single hydrochloric acid dosage is 7 ml, and the centrifuge speed is 700 rpm. The centrifugation time is 4 min. After centrifugation is completed, the material is washed and dried for later use to obtain a silicon-oxygen negative electrode material.

[0045] (5) The material in step (4) is used for battery assembly.

[0046] Example 4

[0047] (1) Take 30 g of material with a mass ratio of polymethylsilsesquioxane: magnesium oxide = 95:2.5, place it in a beaker, and add 300 ml of anhydrous ethanol for dispersion, and mix thoroughly.

[0048] (2) Transfer the mixed solution to a 500 ml volume ball mill tank, add an appropriate amount of 3 mm zirconium beads, adjust the ball mill speed to 400 rpm, and mill for 3 h. Add 7.5 g of silicon powder and mill for another 1 h. Remove the ball mill solution and filter to remove the dispersion liquid to collect the solid components, which are reserved for later use.

[0049] (3) Use an atmospheric tube furnace to perform high-temperature calcination on the material. The first stage temperature is raised to 350°C at a rate of 3°C / min, and the temperature is maintained for 3 h. The second stage temperature is raised to 1000°C at a rate of 5°C / min, and the temperature is maintained for 6 h. After sintering is completed, natural annealing is performed, and the sample is removed after cooling is completed for later use.

[0050] (4) Perform batch acid washing on the calcined sample. The dilute hydrochloric acid concentration is 0.015 mol / L, and the single hydrochloric acid dosage is 7 ml. The centrifuge speed is 700 rpm, and the centrifugation time is 4 min. After centrifugation is completed, the material is washed and dried for later use to obtain a silicon-oxygen negative electrode material.

[0051] (5) Use the material in step (4) to assemble a battery.

[0052] Example 5

[0053] (1) Take 30 g of material with a mass ratio of polymethylsilsesquioxane: glucose = 95:5, place it in a beaker, and add 300 ml of anhydrous ethanol for dispersion, and mix thoroughly.

[0054] (2) Transfer the mixed solution to a 500 ml volume ball mill tank, add an appropriate amount of 3 mm zirconium beads, adjust the ball mill speed to 400 rpm, and mill for 3 h. Remove the ball mill solution and filter to remove the dispersion liquid to collect the solid components, which are reserved for later use.

[0055] (3) Use an atmospheric tube furnace to perform high-temperature calcination on the material. The first stage temperature is raised to 350°C at a rate of 3°C / min, and the temperature is maintained for 3 h. The second stage temperature is raised to 1000°C at a rate of 5°C / min, and the temperature is maintained for 6 h. After sintering is completed, natural annealing is performed, and the sample is removed after cooling is completed for later use.

[0056] (4) Perform batch acid washing on the calcined sample. The dilute hydrochloric acid concentration is 0.015 mol / L, and the single hydrochloric acid dosage is 7 ml. The centrifuge speed is 700 rpm, and the centrifugation time is 4 min. After centrifugation is completed, the material is washed and dried for later use to obtain a silicon-oxygen negative electrode material.

[0057] (5) Use the material in step (4) to assemble the battery.

[0058] Example 6

[0059] (1) Take a total mass of 30 g of material with a mass ratio of polymethylsilsesquioxane: magnesium oxide = 95:1, place it in a beaker, and add 300 ml of anhydrous ethanol for dispersion, and mix thoroughly.

[0060] (2) Transfer the mixed solution to a 500 ml volume ball mill tank, add an appropriate amount of 3 mm zirconium beads, adjust the ball mill speed to 400 rpm, and mill for 3 h. Then add 3 g of silicon powder and 9 g of glucose, and mill for another 1 h. Remove the ball mill liquid and filter to remove the dispersion liquid to collect the solid components, and reserve for later use.

[0061] (3) Use an atmospheric tube furnace to perform high-temperature calcination on the material. The first stage temperature is raised to 350°C at a rate of 3°C / min, and the temperature is maintained for 3 h. The second stage temperature is raised to 1000°C at a rate of 5°C / min, and the temperature is maintained for 6 h. After sintering is completed, natural annealing is performed, and the sample is removed after cooling is completed for later use.

[0062] (4) Perform batch acid washing on the calcined sample. The dilute hydrochloric acid concentration is 0.015 mol / L, the single hydrochloric acid dosage is 7 ml, the centrifuge speed is 700 rpm, and the centrifugation time is 4 min. After centrifugation is completed, the material is washed and dried for later use, and a silicon-oxygen negative electrode material is obtained.

[0063] (5) Use the material in step (4) to assemble the battery.

[0064] Example 7

[0065] (1) Take a total mass of 30 g of material with a mass ratio of polymethylsilsesquioxane: magnesium oxide = 95:2.5, place it in a beaker, and add 300 ml of anhydrous ethanol for dispersion, and mix thoroughly.

[0066] (2) Transfer the mixed solution to a 500 ml volume ball mill tank, add an appropriate amount of 3 mm zirconium beads, adjust the ball mill speed to 400 rpm, and mill for 3 h. Then add 3 g of silicon powder and 9 g of glucose, and mill for another 1 h. Remove the ball mill liquid and filter to remove the dispersion liquid to collect the solid components, and reserve for later use.

[0067] (3) Use an atmospheric tube furnace to perform high-temperature calcination on the material. The first stage temperature is raised to 350°C at a rate of 3°C / min, and the temperature is maintained for 3 h. The second stage temperature is raised to 1000°C at a rate of 5°C / min, and the temperature is maintained for 6 h. After sintering is completed, natural annealing is performed, and the sample is removed after cooling is completed for later use.

[0068] (4) The calcined sample was subjected to batch acid washing, the dilute hydrochloric acid concentration was 0.015 mol / L, the single hydrochloric acid dosage was 7 ml, the centrifuge speed was 700 rpm, and the centrifugation time was 4 min. After centrifugation, the material was washed and dried for standby, and the silicon-oxygen negative electrode material was obtained.

[0069] (5) The material in step (4) was used for battery assembly.

[0070] The preparation process of the above-mentioned battery assembly of examples 1-7 is as follows: the silicon-oxygen negative electrode material is mixed with the binder (CMC) and acetylene black (AB) at a mass ratio of 8:1:1, uniformly mixed in a deionized water solvent, coated on a copper foil, and after vacuum drying at 80°C, the sheet is punched as a working electrode, with a lithium sheet as a counter electrode, with 1 M LiTFSI in DOL:DME (V:V=1:1)+1wt.% LiNO3 as the experimental electrolyte system to assemble the coin cell (half cell) and conduct charge-discharge cycle test, the performance indicators include: first circle discharge capacity, reversible capacity after 100 cycles, first coulombic efficiency, and expansion ratio (50 cycle after the thickness of the electrode sheet / thickness of the original electrode sheet) data are summarized in the table below.

[0071] Table 1 Cycle stability and first efficiency of the materials prepared in each example

[0072]

[0073] It should be understood that the above examples are only for illustrating the technical concepts and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A method for preparing a coated porous silicon-oxygen anode based on polymethylsilsesquioxane, characterized in that, The preparation steps include the following: Step (1): Weigh out polymethylsilsesquioxane and magnesium salt in a certain mass ratio, add anhydrous ethanol, mix thoroughly and evenly, and record as mixture A; Step (2): Ball mill the mixture A, add silicon powder and organic carbon source and continue ball milling, take out the ball milling liquid and filter to remove the dispersion; the solid component after removing the dispersion is recorded as solid A; Step (3): Use the corundum boat to assemble a certain amount of solid A, and transfer the corundum to the tube furnace. Calcinate the material at high temperature under an argon atmosphere. After sintering, anneal naturally. After the material cools to room temperature, take it out for use and record it as solid B, which is the porous silicon-oxygen anode.

2. The method for preparing a coated porous silicon-oxygen anode based on polymethylsilsesquioxane according to claim 1, characterized in that: The mass ratio of the materials is polymethylsilsesquioxane: magnesium salt: silicon powder: organic carbon source = 90:(1~5):(1~5):(1~5).

3. The method for preparing a coated porous silicon-oxygen anode based on polymethylsilsesquioxane according to claim 2, characterized in that: The magnesium salt in step (1) is one of magnesium oxide, magnesium chloride, and magnesium carbonate; the silicon powder in step (1) is micron-sized with a size of 5~20 μm; the selected organic carbon source is one of glucose, citric acid, and oxalic acid.

4. The method for preparing a coated porous silicon-oxygen anode based on polymethylsilsesquioxane according to claim 1, characterized in that: In step (2), the rotation speed is set between 350 and 550 rpm, and the ball milling time is controlled between 2 and 3 hours.

5. The method for preparing a coated porous silicon-oxygen anode based on polymethylsilsesquioxane according to claim 1, characterized in that: The high-temperature calcination process in step (3) is divided into two stages. In the first stage, the temperature is raised to 300-500 ℃ at a rate of 1-3 ℃ / min and held at this temperature for 1-5 h. In the second stage, the temperature is raised to 800-1200 ℃ at a rate of 3-5 ℃ / min and held at this temperature for 5-10 h. After sintering, the temperature is naturally annealed.

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