CN114597384B - Method for preparing lithium ion battery cathode material by utilizing crystalline silicon wire saw waste mortar - Google Patents
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Abstract
The invention discloses a method for preparing a lithium ion battery cathode material by utilizing waste mortar of a crystal silicon wire saw. The method comprises the following steps: providing waste mortar of a crystal silicon wire saw; removing cutting fluid in the waste mortar of the crystal silicon wire saw to obtain a Si/SiC mixture; dispersing the Si/SiC mixture in water, adding zirconia grinding balls and ammonia water, and performing ball milling under the heating condition to obtain Si/SiC mixed suspension; carrying out oil-soaking flotation treatment on the Si/SiC mixed suspension, and collecting Si particle suspension; adding graphene oxide dispersion liquid into the Si particle suspension liquid, adjusting the pH value, adding an oil phase, and stirring to obtain water-in-oil emulsion; and carrying out spray drying treatment on the water-in-oil emulsion, and then carrying out high-temperature reduction treatment to obtain the graphene coated silicon lithium ion battery anode material. According to the preparation method, the graphene-coated silicon lithium ion battery anode material is prepared, so that the aim of changing waste into valuables is fulfilled.
Description
Technical Field
The invention relates to the technical field of materials, in particular to a method for preparing a lithium ion battery cathode material by utilizing waste mortar of a crystal silicon wire saw.
Background
The development of sustainable new energy is an important ring in the development of the emerging industry in China. Silicon wafers in the crystalline silicon industry are produced by wire-cutting techniques, i.e. thin wafers are cut from silicon ingots using very fine cutting wires and abrasive-laden cutting mortars. The cutting mortar is generally formed by mixing cutting fluid (polyethylene glycol) and SiC powder according to a certain proportion. Polyethylene glycol in the mortar is used as a disperse phase of silicon carbide to take away heat generated by cutting, and meanwhile, the silicon carbide powder has high hardness and can be used for rapidly cutting by grinding silicon blocks at edges and corners. In the mortar cutting process, as the cutting process proceeds, a large amount of silicon powder enters the mortar and adheres to the surface of the silicon carbide abrasive, thereby reducing the cutting performance thereof. When a certain amount of silicon powder is mixed, uneven saw teeth appear on the cutting line on the silicon wafer, and the cutting mortar becomes waste mortar at the moment. A large amount of mortar needs to be replaced after each cutting process is completed to ensure that the cutting performance meets the requirements. The loss amount of silicon powder is related to the thickness of the prepared silicon wafer, the silicon wafer prepared at present is developed towards the direction of thinning, and the thickness of the silicon wafer is generally between 150 and 200 microns, which means that the loss of silicon is also increased. At present, about 60% of the manufacturing cost of the solar cell comes from the raw material cost of silicon, and the loss of the silicon material in the silicon wafer preparation process is between 30% and 40%.
The total amount of demand for crystalline silicon worldwide has reached 14 ten thousand tons from the economic effect level, wherein 30% -40% is lost in the waste slurry generated in the preparation of silicon wafers. The successful recovery treatment of each ton of waste slurry will yield a direct economic value of 5.6 ten thousand yuan (where the recovery value of silicon powder is above 90%) calculated as about 35wt% polyethylene glycol (0.8 ten thousand yuan/ton), about 35wt% silicon carbide abrasive (1 ten thousand yuan/ton), about 9wt% high purity silicon powder (60 ten thousand yuan/ton), and about 5wt% scrap iron (fretting wear on the wire saw surface) per ton of waste slurry.
In terms of environmental protection, the production of the crystalline silicon raw material has the characteristics of high energy consumption and high carbon emission (the emission amount of carbon dioxide generated by producing one ton of crystalline silicon is about 46 tons), and the effective recovery and reutilization of the silicon powder in the wire saw waste slurry can reduce the carbon emission in the crystalline silicon industry and reduce the environmental pollution pressure.
At present, high-purity silicon powder is difficult to obtain by a simple physical method, and recovered silicon powder with higher purity can be generally obtained by a chemical method, but the method has the defects that high-cost chemical reactants are used in the process, meanwhile, the safety of production is greatly tested by acid-base treatment, and a large amount of chemical emissions are generated, so that the pressure of environmental pollution is caused. Many chemical separation methods aim to recover very high purity silicon materials. The silicon powder obtained by the common physical and chemical separation method is difficult to reach the purity requirement of the photovoltaic industry due to the fact that the silicon powder contains a small amount of silicon carbide impurities. But the need to use the recovered silicon powder in other fields is not lost as an economically viable approach.
Another application of silicon powder is in the field of negative electrode materials for lithium batteries. In all the cathode materials studied, the theoretical energy density of silicon reached 4200 mAh.g -1 Far higher than the energy density of the graphite which is the main current negative electrode material. However, silicon as a negative electrode material has the disadvantage that it undergoes a great volume expansion during lithiation, and thus produces a great stress on the internal structure of silicon, and in the course of multiple charge and discharge, the silicon material is susceptible to pulverization, resulting in a great decrease in the energy density of the negative electrode material with the number of charge and discharge cycles.
Accordingly, the prior art is still in need of improvement and development.
Disclosure of Invention
The inventors have found that in Si-C composite systems, silicon as the active material can provide a high storage capacity, while carbon as the cladding phase or backbone can effectively reduce the polymerization between the silicon and buffer the volume change of the silicon during charge and discharge. Graphene has good thermal stability, conductivity and mechanical strength as a carbon material with a 2D honeycomb structure, and lithium ions can be adsorbed on two sides of a graphene layer structure, so that the theoretical energy density of the graphene is more than twice that of common graphite. Graphene is well suited for cladding on silicon materials. The excellent mechanical strength (theoretical Young's modulus reaches 1.01 TPa) can reduce the volume expansion of the silicon material, absorb internal stress, and when the multi-layer graphene is adsorbed, the layers can mutually slide, and the volume expansion of the silicon is dealt with by enlarging the surface area.
Based on the method, a set of method for economically, simply and effectively recycling the silicon powder in the waste slurry of the wire saw is established, and the maximum value recycling of the recycled silicon powder is realized.
The technical scheme of the invention is as follows:
a method for preparing a lithium ion battery cathode material by utilizing waste mortar of a crystal silicon wire saw comprises the following steps:
providing waste mortar of the crystal silicon wire saw, wherein the waste mortar of the crystal silicon wire saw comprises Si particles, siC particles and cutting fluid;
washing and drying the waste mortar of the crystal silicon wire saw in sequence to remove cutting fluid in the waste mortar of the crystal silicon wire saw to obtain a Si/SiC mixture;
dispersing the Si/SiC mixture in water, adding zirconia grinding balls and ammonia water to obtain a dispersion liquid, and ball-milling the dispersion liquid under a heating condition to obtain Si/SiC mixed suspension;
carrying out oil foam flotation treatment on the Si/SiC mixed suspension to separate Si particles from SiC particles, and collecting to obtain Si particle suspension;
adding graphene oxide dispersion liquid into the Si particle suspension liquid, adjusting the pH, adding an oil phase, and stirring to obtain water-in-oil emulsion;
and carrying out spray drying treatment on the water-in-oil emulsion to obtain graphene oxide coated silicon particles, and carrying out high-temperature reduction treatment on the graphene oxide coated silicon particles to obtain the graphene coated silicon lithium ion battery anode material.
Optionally, the step of washing and drying the waste mortar of the crystal silicon wire saw sequentially specifically includes:
adding the waste mortar of the crystal silicon wire saw into a mixed solution of deionized water and acetone with the volume of 20-40 times, carrying out ultrasonic treatment, and then carrying out suction filtration to obtain a filter cake;
repeating the steps for a plurality of times, and drying a filter cake obtained by suction filtration.
Alternatively, the Si/SiC mixture has a concentration of 1 to 20g/L based on the dispersion.
Optionally, the diameter of the zirconia grinding balls is 0.1-50mm, the heating temperature is 40-80 ℃, and the ball milling time is 0.5-12h.
Optionally, the step of performing oil-bubble flotation treatment on the Si/SiC mixed suspension specifically includes:
providing an oil-bubble flotation column, and injecting the Si/SiC mixed suspension into the oil-bubble flotation column;
introducing kerosene containing a collector through an oil pipe at one side of the bottom of the oil bubble flotation column, introducing air through an air pipe at the other side of the bottom of the oil bubble flotation column, beating the air and the kerosene into air bubbles with an oil film under a magnetic stirrer, and carrying out oil bubble flotation treatment on the Si/SiC mixed suspension;
wherein the collector is fatty acid or long-chain anion organic salt.
Optionally, the air introducing amount is 100-1000mL/min, the stirring speed of the magnetic stirrer is 60-700rpm, the Si/SiC mixed suspension amount during each oil bubble flotation is 200-1000mL, the time for each oil bubble flotation treatment is 5-35min, and the adding amount of the collector is 50-300ppm.
Optionally, the collector is selected from one or more of tall oil, oxidized paraffin, naphthenic acid, sodium oleate, and dodecyl amine.
Optionally, the mass ratio of graphene oxide to silicon particles is 0.5:1-2:1.
optionally, the pH is adjusted to 4-12.
Optionally, the process parameters of spray drying the water-in-oil emulsion are as follows: the pressure of the spray drying is 0.1-0.5MPa, the spray speed is 50-500mL/h, and the temperature is 120 ℃.
Optionally, the technological parameters of the high-temperature reduction treatment are as follows: the temperature of the high-temperature reduction treatment is 400-800 ℃, and the time of the high-temperature reduction treatment is 2-4 hours.
The beneficial effects are that: the invention provides a method for preparing a lithium ion battery anode material with high added value by utilizing waste mortar of a crystal silicon wire saw. The selective separation of silicon and silicon carbide is then achieved using froth flotation. Because the surface property of silicon is more active than that of silicon carbide, more oxygen-containing functional groups are introduced on the surface of the silicon carbide by a hydrothermal ball milling method, the hydrophilicity of the silicon carbide is improved, the negative potential of the surface of the silicon carbide is lower, and then the silicon carbide is subjected to electrostatic repulsion between bubbles and silicon particles by a collector, so that the purpose of selectively floating the silicon carbide is achieved. After the purified aqueous silicon-rich waste slurry (namely Si particle suspension) is obtained, the interface property of Graphene Oxide (GO) is utilized to directly prepare water-in-oil emulsion in the Si particle suspension through the coating of a graphene oxide interface film, the water-in-oil emulsion is sprayed out through spray drying, and finally, the graphene-coated silicon lithium ion battery anode material is formed through high-temperature treatment, so that the aim of changing waste into valuables is fulfilled.
Drawings
Fig. 1 is a schematic flow chart of a method for preparing a lithium ion battery anode material by using a crystalline silicon wire saw waste mortar according to an embodiment of the invention.
Fig. 2 is a schematic diagram of oil bubble flotation in a method for preparing a lithium ion battery negative electrode material by using a crystalline silicon wire saw waste mortar according to an embodiment of the invention.
Fig. 3 is a charge-discharge cycle chart of the anode materials prepared in example 1, example 2 and comparative example.
Detailed Description
The invention provides a method for preparing a lithium ion battery cathode material by utilizing waste mortar of a crystal silicon wire saw, which is used for making the purposes, technical schemes and effects of the invention clearer and more definite, and is further described in detail below. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Referring to fig. 1, an embodiment of the present invention provides a method for preparing a negative electrode material of a lithium ion battery by using a waste mortar of a crystalline silicon wire saw, wherein the method includes the following steps:
s1, providing waste mortar of a crystal silicon wire saw, wherein the waste mortar of the crystal silicon wire saw comprises Si particles, siC particles and cutting fluid;
s2, washing and drying the waste mortar of the crystal silicon wire saw in sequence to remove cutting fluid in the waste mortar of the crystal silicon wire saw to obtain a Si/SiC mixture;
s3, dispersing the Si/SiC mixture in water, adding zirconia grinding balls and ammonia water to obtain a dispersion liquid, and ball-milling the dispersion liquid under a heating condition to obtain a Si/SiC mixed suspension;
s4, carrying out oil-bubble floatation treatment on the Si/SiC mixed suspension to separate Si particles from SiC particles, and collecting to obtain Si particle suspension;
s5, adding graphene oxide dispersion liquid into the Si particle suspension liquid, adjusting the pH value, adding an oil phase, and stirring to obtain water-in-oil emulsion;
and S6, carrying out spray drying treatment on the water-in-oil emulsion to obtain graphene oxide coated silicon particles, and carrying out high-temperature reduction treatment on the graphene oxide coated silicon particles to obtain the graphene coated silicon lithium ion battery anode material.
The embodiment provides a method for preparing a lithium ion battery anode material with high added value by utilizing waste mortar of a crystal silicon wire saw, which comprises the steps of firstly increasing the surface difference of two particles by surface pretreatment by utilizing the difference of the surface chemical activities of silicon and silicon carbide, and dissociating the material by adding an abrasive with hardness between that of the silicon and the silicon carbide. The selective separation of silicon and silicon carbide is then achieved using froth flotation. Because the surface property of silicon is more active than that of silicon carbide, more oxygen-containing functional groups are introduced into the surface of the silicon by a hydrothermal ball milling method, the hydrophilicity of the silicon is improved, the negative potential of the surface of the silicon is lower, and then electrostatic repulsion is formed between bubbles and silicon particles by a collector, so that the purpose of selectively floating the silicon carbide is achieved. After the purified aqueous silicon-rich waste slurry (namely Si particle suspension) is obtained, the interface property of Graphene Oxide (GO) is utilized to directly prepare water-in-oil emulsion in the Si particle suspension through the coating of a graphene oxide interface film, the water-in-oil emulsion is sprayed out through spray drying, and finally, the graphene-coated silicon lithium ion battery anode material is formed through high-temperature treatment, so that the aim of changing waste into valuables is fulfilled.
In step S1, the waste mortar of the crystalline silicon wire saw includes Si particles, siC particles and a cutting fluid (polyethylene glycol). Further, the waste mortar of the crystal silicon wire saw consists of cutting fluid (polyethylene glycol), siC particles and Si particles. The cutting fluid (polyethylene glycol) is used as a disperse phase of SiC particles, which can take away heat generated by cutting, and the SiC particles can be rapidly cut by utilizing the edge grinding silicon blocks due to the high hardness of the SiC particles. In the mortar cutting process, as the cutting process proceeds, a large amount of silicon powder enters the mortar and adheres to the surface of the silicon carbide abrasive.
In step S2, the cutting fluid in the waste mortar of the crystal silicon wire saw is removed by washing and drying.
In one embodiment, the steps of washing and drying the waste mortar of the crystal silicon wire saw sequentially comprise the following steps:
adding the waste mortar of the crystal silicon wire saw into a mixed solution of deionized water and acetone with the volume of 20-40 times, performing ultrasonic treatment (about 20 minutes), and performing suction filtration to obtain a filter cake;
the filter cake obtained by suction filtration was dried (drying temperature: about 60 ℃ C.) after repeating the above steps a plurality of times.
Further, the volume concentration of the acetone in the mixed solution of the deionized water and the acetone is 20% -100%, preferably 20% -30%.
In step S3, the surface of the silicon is pretreated and dissociated.
Specifically, the Si/SiC mixture is dispersed in water, zirconia grinding balls with hardness between that of silicon and silicon carbide are added as abrasive materials, then a certain amount of ammonia water is added to obtain dispersion liquid, and the dispersion liquid is ball-milled under the heating condition so as to carry out oxidation treatment on the surfaces of Si particles to different degrees by utilizing alkalinity and heat preservation time in the ball-milling process. Silicon undergoes oxidation reaction with water at its surface when milled in water, thereby forming a very thin surface oxide layer. The rich hydroxyl groups contained in the oxide layer can improve the hydrophilicity of particles and negatively charge the particles in an aqueous phase environment, so that the hydrophilic-hydrophobic difference between the particles and SiC is increased, and the subsequent flotation efficiency is improved.
In one embodiment, the Si/SiC mixture has a concentration of 1 to 20g/L, preferably 5 to 10g/L, based on the dispersion.
In one embodiment, the zirconia balls have a diameter of 0.1 to 50mm, preferably 0.2 to 0.8mm.
In one embodiment, the heating temperature is 40-80 ℃, preferably 50-60 ℃, and the ball milling time is 0.5-12 hours, preferably 3-6 hours.
In the step S4, large-particle zirconia and SiC particles in the ball-milled Si/SiC mixed suspension can be filtered and removed by a screen (such as a 200-mesh screen) and then subjected to oil foam flotation treatment.
Specifically, the oil bubble flotation column can be utilized, kerosene is adopted as an oil film, fatty acid or long-chain anion organic salt is selected as a collector, and the oil bubble flotation treatment is carried out on the Si/SiC mixed suspension after the oxidation treatment. The addition of the collector can change the surface chargeability of the oil bubbles, for example, negative ion organic salt can lead the surfaces of the oil bubbles to be negatively charged, and the oxide layer generated on the surfaces of the silicon particles is utilized to reduce the hydrophobic attraction between the silicon particles and the surfaces of the oil bubbles while the silicon particles subjected to oxidation treatment are repelled in an alkaline aqueous phase. Because the surface of the silicon carbide has a plurality of carbon element points, the carbon element points can have hydrophobic interaction with organic long chains in an oil film medium, so that the carbon element points are selectively adhered, and finally, the purpose of selectively floating the silicon carbide is achieved.
In one embodiment, the step of performing oil froth flotation treatment on the Si/SiC mixed suspension specifically includes:
providing an oil-bubble flotation column, and injecting the Si/SiC mixed suspension into the oil-bubble flotation column;
introducing kerosene containing a collector through an oil pipe at one side of the bottom of the oil bubble flotation column, introducing air through an air pipe at the other side of the bottom of the oil bubble flotation column, beating the air and the kerosene into air bubbles with an oil film under a magnetic stirrer, and carrying out oil bubble flotation treatment on the Si/SiC mixed suspension;
wherein the collector is fatty acid or long-chain anion organic salt.
In this embodiment, the oil-bubble flotation column is divided into an upper layer and a lower layer (see fig. 2), the upper layer and the lower layer are separated by porous glass, the left opening of the bottom is used for introducing kerosene through an oil pipe, the right opening is connected with an air pipe and connected with a compressed air pipe, when air passes through a coal oil layer and enters the upper layer through the porous glass, the upper layer magnetic stirrer is used for beating air and kerosene into air bubbles with an oil film, and then flotation is performed.
Further, the air is introduced into the tank in an amount of 100-1000mL/min, preferably 200-300mL/min, for each flotation; the stirring speed of the magnetic stirrer is 60-700rpm, preferably 100-200rpm; the size limit of the device is that the Si/SiC mixed suspension volume is 200-1000mL during each bubble flotation, and the time for each bubble flotation treatment is 5-35min.
Further, the fatty acid or long chain anion organic salt includes, but is not limited to, one or more of tall oil, oxidized paraffin, naphthenic acid, sodium oleate, and dodecyl amine. The addition of the oil is 50-300ppm for each froth flotation, depending on the collector composition.
In step S5, a water-in-oil emulsion is prepared.
Specifically, adding graphene oxide dispersion liquid into the collected Si particle suspension, adjusting the pH of the system to increase the interfacial activity of graphene oxide, stirring for 30-60 minutes (the stirring speed is 100 rpm), adding an oil phase, and vigorously stirring for 15-20 minutes (2600 rpm) to obtain a large amount of golden yellow water-in-oil emulsion.
Further, the mass ratio of graphene oxide to silicon particles is 0.5:1-2:1, preferably 1.5:1, with a pH of 4-12, preferably 11-12, after adjustment, in view of the integrity of the graphene oxide coating.
In step S6, preparing a graphene coated silicon lithium ion battery anode material.
Specifically, spraying the water-in-oil emulsion by using a spray dryer to obtain graphene oxide coated silicon particles, and then reducing the graphene oxide coated silicon particles in an atmosphere tube furnace at high temperature to obtain the high-performance graphene coated silicon lithium ion battery anode material.
Further, the technological parameters of the spray drying treatment of the water-in-oil emulsion are as follows: the spray drying pressure is 0.1-0.5MPa, the spray speed is 50-500mL/h, and the temperature is 120 ℃.
Further, the technological parameters of the high-temperature reduction treatment are as follows: the temperature of the high-temperature reduction treatment is 400-800 ℃, and the time of the high-temperature reduction treatment is 2-4 hours.
The invention will be further illustrated with reference to specific examples.
Example 1
S1: 500mL of the waste mortar of the crystal silicon wire saw is added into 10L of mixed solution of deionized water and acetone (the concentration of the acetone in the mixed solution is 20%), and after 20 minutes of ultrasonic vibration, a filter cake is obtained through suction filtration. The filter cake was further dispersed in 1L of a mixed solution of deionized water and acetone (the concentration of acetone in the mixed solution was 20%). And after repeating the steps for five times, drying a filter cake obtained by suction filtration at 60 ℃ to obtain the Si/SiC mixture.
S2: 10g of the obtained Si/SiC mixture is dispersed in 1L of deionized water, 50g of zirconia grinding balls with the diameter of 0.3mm are added as grinding materials, 20% of concentrated ammonia water is added into the dispersion liquid, the temperature of the dispersion liquid is heated to 60 ℃ for ball milling, and the ball milling and the heat preservation time are 3 hours, so that the Si/SiC mixed suspension is obtained.
S3: filtering and removing large-particle zirconia and SiC particles in the ball-milled Si/SiC mixed suspension by using a 200-mesh screen, using an oil foam flotation column, adopting kerosene as an oil film, selecting sodium oleate as a collector (the adding amount of the sodium oleate in the kerosene is 300 ppm), and performing oil foam flotation treatment on the oxidized Si/SiC mixed suspension. The flotation conditions are as follows: the air inflow is 300mL/min, the magnetic stirring speed is 150rpm, the Si/SiC mixed suspension volume for each flotation is 900mL, and the flotation time is 15min. Thereby removing excess SiC from the suspension.
S4: adding graphene oxide dispersion liquid into 200mL of collected Si particle suspension, controlling the mass ratio of graphene oxide to silicon particles to be 1.5:1, fully stirring for 15 minutes, and adding a certain amount of ammonia water into the system to adjust the pH of the system to 12 so as to increase the interface activity of the graphene oxide. 400mL of kerosene was added to the system after stirring for 30 minutes (100 rpm) and vigorously stirred for 15 minutes (2600 rpm), and after standing for 10 minutes, the golden water-in-oil emulsion appearing on the upper layer was collected.
S5: the water-in-oil emulsion obtained was discharged by a spray drying apparatus and granulated. The spray drying pressure was 0.3MPa, the spray speed was 300mL/h, and the temperature was 120 ℃. And then recycling the obtained particles, and heating and reducing the particles in an atmosphere tube furnace at 800 ℃ for 4 hours to obtain the high-performance graphene coated silicon lithium ion battery anode material.
Example 2
S1: 500mL of the waste mortar of the crystal silicon wire saw is added into 10L of mixed solution of deionized water and acetone (the concentration of the acetone in the mixed solution is 20%), and after 20 minutes of ultrasonic vibration, a filter cake is obtained through suction filtration. The filter cake was further dispersed in 1L of a mixed solution of deionized water and acetone (the concentration of acetone in the mixed solution was 20%). And after repeating the steps for five times, drying a filter cake obtained by suction filtration at 60 ℃ to obtain the Si/SiC mixture.
S2: 10g of the obtained Si/SiC mixture is dispersed in 1L of deionized water, 50g of zirconia grinding balls with the diameter of 0.3mm are added as grinding materials, 20% of concentrated ammonia water is added into the dispersion liquid, the temperature of the dispersion liquid is heated to 60 ℃ for ball milling, and the ball milling and the heat preservation time are 3 hours, so that the Si/SiC mixed suspension is obtained.
S3: filtering and removing large-particle zirconia and SiC particles in the ball-milled Si/SiC mixture suspension by using a 200-mesh screen, using an oil foam flotation column, adopting kerosene as an oil film, selecting xanthate as a collector (the addition amount of xanthate in the kerosene is 150 ppm), and performing oil foam flotation treatment on the oxidized Si/SiC mixture suspension. The flotation conditions are as follows: the air inflow is 300mL/min, the magnetic stirring speed is 150rpm, the Si/SiC mixed suspension volume for each flotation is 900mL, and the flotation time is 15min. Thereby removing excess SiC from the suspension.
S4: adding graphene oxide dispersion liquid into 200mL of collected Si particle suspension, controlling the mass ratio of graphene oxide to silicon particles to be 0.5:1, fully stirring for 15 minutes, and adding a certain amount of ammonia water into the system to adjust the pH of the system to 12 so as to increase the interface activity of the graphene oxide. 400mL of kerosene was added to the system after stirring for 30 minutes (100 rpm) and vigorously stirred for 15 minutes (2600 rpm), and after standing for 10 minutes, the golden water-in-oil emulsion appearing on the upper layer was collected.
S5: the water-in-oil emulsion obtained was discharged by a spray drying apparatus and granulated. The spray drying pressure was 0.3MPa, the spray speed was 300mL/h, and the temperature was 120 ℃. And then recycling the obtained particles, and heating and reducing the particles in an atmosphere tube furnace at 800 ℃ for 4 hours to obtain the high-performance graphene coated silicon lithium ion battery anode material.
Comparative example
S1: 500mL of the waste mortar of the crystal silicon wire saw is added into 10L of mixed solution of deionized water and acetone (the concentration of the acetone in the mixed solution is 20%), and after 20 minutes of ultrasonic vibration, a filter cake is obtained through suction filtration. The filter cake was further dispersed in 1L of a mixed solution of deionized water and acetone (the concentration of acetone in the mixed solution was 20%). And after repeating the steps for five times, drying a filter cake obtained by suction filtration at 60 ℃ to obtain the Si/SiC mixture.
S2: 10g of the obtained Si/SiC mixture is dispersed in 1L of deionized water, 50g of zirconia grinding balls with the diameter of 0.3mm are added as grinding materials, 20% of concentrated ammonia water is added into the dispersion liquid, the temperature of the dispersion liquid is heated to 60 ℃ for ball milling, and the ball milling and the heat preservation time are 3 hours, so that the Si/SiC mixed suspension is obtained.
S3: filtering and removing large-particle zirconia and SiC particles in the ball-milled Si/SiC mixture suspension by using a 200-mesh screen, using an oil foam flotation column, adopting kerosene as an oil film, selecting xanthate as a collector (the addition amount of xanthate in the kerosene is 150 ppm), and performing oil foam flotation treatment on the oxidized Si/SiC mixture suspension. The flotation conditions are as follows: the air inflow is 300mL/min, the magnetic stirring speed is 150rpm, the Si/SiC mixed suspension volume for each flotation is 900mL, and the flotation time is 15min. Thereby removing excess SiC from the suspension.
S4: to 200mL of the collected Si particle suspension, a certain amount of ammonia was added to adjust the pH of the system to 12. 400mL of kerosene was added to the system after stirring for 30 minutes (100 rpm) and vigorously stirred for 15 minutes (2600 rpm), and after standing for 10 minutes, the oil phase and part of the emulsion present in the upper layer were collected.
S5: and spraying the oil phase and part of the emulsion through spray drying equipment, and granulating. The spray drying pressure was 0.3MPa, the spray speed was 300mL/h, and the temperature was 120 ℃. And then recovering the obtained particles, and heating and reducing the particles in an atmosphere tube furnace at 800 ℃ for 4 hours to obtain the silicon lithium ion battery anode material.
The preparation method of the pole piece comprises the following steps:
the anode materials prepared in examples 1 and 2 and comparative example were milled in NMP (N-methylpyrrolidone) in a weight ratio (8:1:1) with PVDF and carbon nanotubes, respectively, to prepare a slurry, and the slurry was coated on a copper foil using a coater, and dried to obtain an anode sheet having a load of about 1.3mg/cm 2 。
The method for assembling and testing the battery comprises the following steps:
the half cell takes the prepared pole piece as an anode, the diaphragm is celgard2400, and the electrolyte adopts LiPF of 1mol/L 6 DMC (dimethyl carbonate) as a conductive salt: DEC (diethyl carbonate): EC (ethylene carbonate) (wt%) =1: 1:1 is conductive liquid. The test conditions were: the first cycle of activation at 0.01V-1.5V and 0.02C current is followed by 200-1000 cycles of charge and discharge at 0.2C current density.
As shown in fig. 3, the prepared silicon-carbon anode has higher coulombic efficiency (> 80%), the conductivity of the silicon material is improved after the graphene is coated, and the cycle stability of the silicon-carbon anode is also greatly improved. Wherein, the residual capacity 1169mAh/g after 300 circles is circulated in the example 1, the residual capacity 483mAh/g after 300 circles is circulated in the example 2, and the capacity of the comparative example is too fast to decay because the graphene coating is not used, and the capacity tends to 0mAh/g after 50 circles is circulated.
It is to be understood that the invention is not limited in its application to the examples described above, but is capable of modification and variation in light of the above teachings by those skilled in the art, and that all such modifications and variations are intended to be included within the scope of the appended claims.
Claims (10)
1. The method for preparing the lithium ion battery cathode material by utilizing the crystalline silicon wire saw waste mortar is characterized by comprising the following steps:
providing waste mortar of the crystal silicon wire saw, wherein the waste mortar of the crystal silicon wire saw comprises Si particles, siC particles and cutting fluid;
washing and drying the waste mortar of the crystal silicon wire saw in sequence to remove cutting fluid in the waste mortar of the crystal silicon wire saw to obtain a Si/SiC mixture;
dispersing the Si/SiC mixture in water, adding zirconia grinding balls and ammonia water to obtain a dispersion liquid, and ball-milling the dispersion liquid under a heating condition to obtain Si/SiC mixed suspension;
carrying out oil foam flotation treatment on the Si/SiC mixed suspension to separate Si particles from SiC particles, and collecting to obtain Si particle suspension;
adding graphene oxide dispersion liquid into the Si particle suspension liquid, adjusting the pH, adding an oil phase, and stirring to obtain water-in-oil emulsion;
and carrying out spray drying treatment on the water-in-oil emulsion to obtain graphene oxide coated silicon particles, and carrying out high-temperature reduction treatment on the graphene oxide coated silicon particles to obtain the graphene coated silicon lithium ion battery anode material.
2. The method for preparing the lithium ion battery cathode material by utilizing the waste mortar of the crystalline silicon wire saw according to claim 1, wherein the steps of washing and drying the waste mortar of the crystalline silicon wire saw sequentially comprise the following steps:
adding the waste mortar of the crystal silicon wire saw into a mixed solution of deionized water and acetone with the volume of 20-40 times, carrying out ultrasonic treatment, and then carrying out suction filtration to obtain a filter cake;
repeating the steps for a plurality of times, and drying a filter cake obtained by suction filtration.
3. The method for preparing a lithium ion battery anode material by utilizing the waste mortar of the crystalline silicon wire saw according to claim 1, wherein the concentration of the Si/SiC mixture is 1-20g/L based on the dispersion liquid;
the diameter of the zirconia grinding ball is 0.1-50mm, the heating temperature is 40-80 ℃, and the ball milling time is 0.5-12h.
4. The method for preparing the lithium ion battery cathode material by utilizing the crystalline silicon wire saw waste mortar according to claim 1, wherein the step of performing oil-bubble flotation treatment on the Si/SiC mixed suspension is specifically comprising the following steps:
providing an oil-bubble flotation column, and injecting the Si/SiC mixed suspension into the oil-bubble flotation column;
introducing kerosene containing a collector through an oil pipe at one side of the bottom of the oil bubble flotation column, introducing air through an air pipe at the other side of the bottom of the oil bubble flotation column, beating the air and the kerosene into air bubbles with an oil film under a magnetic stirrer, and carrying out oil bubble flotation treatment on the Si/SiC mixed suspension;
wherein the collector is fatty acid or long-chain anion organic salt.
5. The method for preparing the lithium ion battery cathode material by utilizing the crystalline silicon wire saw waste mortar according to claim 4, wherein the air introduction amount is 100-1000mL/min, the stirring speed of the magnetic stirrer is 60-700rpm, the Si/SiC mixed suspension amount during each oil bubble flotation is 200-1000mL, the time for each oil bubble flotation treatment is 5-35min, and the addition amount of the collector is 50-300ppm.
6. The method for preparing a negative electrode material of a lithium ion battery by utilizing the waste mortar of the crystalline silicon wire saw according to claim 4, wherein the collector is one or more selected from tall oil, oxidized paraffin, naphthenic acid, sodium oleate and dodecyl amine.
7. The method for preparing the lithium ion battery anode material by utilizing the crystalline silicon wire saw waste mortar according to claim 1, wherein the mass ratio of graphene oxide to silicon particles is 0.5:1-2:1.
8. the method for preparing the lithium ion battery cathode material by utilizing the crystalline silicon wire saw waste mortar according to claim 1, wherein the pH value is adjusted to be 4-12.
9. The method for preparing the lithium ion battery anode material by utilizing the crystalline silicon wire saw waste mortar according to claim 1, wherein the process parameters of the spray drying treatment of the water-in-oil emulsion are as follows: the pressure of the spray drying is 0.1-0.5MPa, the speed of the spray is 50-500mL/h, and the temperature is 120 ℃.
10. The method for preparing the lithium ion battery anode material by utilizing the crystalline silicon wire saw waste mortar according to claim 1, wherein the technological parameters of the high-temperature reduction treatment are as follows: the temperature of the high-temperature reduction treatment is 400-800 ℃, and the time of the high-temperature reduction treatment is 2-4 hours.
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