Patent Application
20240258521
The present disclosure belongs to the field of preparation of carbon composites, and in particular relates to a dense and uniform carbon coated composite and a preparation method therefor and use thereof.
Carbon coating is a common material modification method. Carbon coating of a material may improve the electrical conductivity of the material on one hand, and on the other hand provide a stable chemical and electrochemical reaction interface.
Currently, carbon coating typically employs a solid-phase method, a liquid-phase method, and a gas-phase method. In the prior art, carbon coating can be carried out by the solid-phase method, i.e., solid-solid mixing in which a solid carbon source is dispersed in a material to be coated, and then heated to a certain temperature, and the solid carbon source is softened and coats the surfaces of particles of the material to be coated, and can be dehydrogenated to carbon by further increasing the temperature. However, a solid-phase carbon coating process is unlikely to achieve coating uniformity and avoid the problem of particle agglomeration. The liquid-phase method and the gas-phase method may better avoid the problem of particle agglomeration. The liquid-phase method usually uses a solvent such as water, ethanol, and the like to disperse a solute in a liquid phase, followed by high temperature carbonization to obtain a carbon coated material. However, liquid-phase carbon coating involves solvent recovery and the process is relatively cumbersome and difficult to apply on a large scale. The gas-phase method is in particular a process in which carbon-containing gas coats the surface of the material to be coated by vapor deposition. With the development of equipment and processes, gas-phase coating has been successfully applied to new energy-related materials, and especially has good effects for materials with large volume deformation, which can improve the electrical conductivity, improve the interface and reduce volume expansion during lithium intercalation. Furthermore, gas-phase coating has the characteristics of less pollution and controllable coating amount. However, a coating layer obtained by gas-phase coating is unstable in completeness, which is easy to cause incomplete coating, and the coating layer is also unlikely to achieve the effect of proper compactness, which is easy to cause leakage or dissolution of the inner coating material, affecting the properties of the carbon coated composite. The gas-phase coating process involves the selection of carbon source process gas and the screening of key parameters of raw materials in which crucial indicators are: the number of surface defects of the raw materials, the optimization of the particle size, and different numbers of active sites caused by different powder bulk pore structures, and the collocation of the number of active sites and the process gas results in a complex competitive reaction of diffusion and growth nucleation during chemical vapor deposition. Therefore, a uniform and dense carbon layer remains a difficulty for the gas-phase coating process. The uniform and dense carbon layer can significantly enhance product recycling and storage properties, and especially can inhibit side reactions under high temperature conditions.
In a silicon negative electrode material, volume expansion is one of the biggest problems, although volume expansion can be reduced to some extent through the silicon oxide technology in the prior art, there are also problems of low electrical conductivity and low initial coulombic efficiency, and although carbon coating can effectively solve the problem of low electrical conductivity, it is necessary to ensure the compactness and completeness of a carbon-coated coating layer in order to effectively improve the electrical conductivity of a carbon-coated silicon negative electrode material.
Therefore, there is an urgent need to develop a carbon coated composite with higher compactness and high coating completeness in order to more completely coat a coated material with a carbon layer and maximize the performance of the carbon coated composite.
For the deficiencies in the prior art, one of the objects of the present application is to provide a carbon coated composite including a core and a carbon coating layer coated outside the core material, wherein the density of the carbon coating layer is 1.0-2.0 g·cm−3, and the D50 of the material to be coated with carbon, is 1-40 μm, preferably 3-10 μm, more preferably 4-7 μm; a particle size distribution span is 0.5≤(D90−D10)/D50≤2, preferably 1≤(D90−D10)/D50≤1.5; a specific surface area is 1-5 m2·g−1, preferably 1-2 m2·g−1; a ratio of the surface area to the stacked pore volume is 0.50-2.00 cm−1, preferably 0.70-1.50 cm−1; and the increase of D50 of the composite after coating is 3 μm or less, preferably 1 μm or less.
The density of the carbon coating layer can be calculated by the following formula: ρ2=m2ρ1ρ3/(m1ρ3−m3ρ1), wherein ρ2 is the density of the carbon coating layer, and the carbon coated composite has a mass of m1 and a density of ρ1; the carbon coating layer has a mass of m2; the core has a mass m3 and a density of ρ3; the carbon coated composite is placed in an excess solution capable of dissolving a core characteristic element for dissolution determination of the core characteristic element, the dissolution amount of the core characteristic element being 100 ppm or less.
Preferably, the density of the carbon coating layer in the carbon coated material is 1.2 g·cm−3≤ρ2≤1.5 g·cm−3.
The carbon coated composite provided by the present application has a dense carbon coating layer with high density and a core element dissolution amount of 100 ppm or below, in other words, the carbon coated composite provided by the present application has a complete carbon coating layer with appropriate compactness. Coating a complete carbon coated composite effectively avoids the defects of coating and can characterize the uniformity of coating the outer layer of the core with the carbon coating layer, and uniform coating of the carbon layer is critical to the stability of the properties of the carbon coated material and on one hand can mitigate the volume change (e.g., volume expansion) of the core material; in addition to this, a complete and uniform carbon layer can effectively disperse surface charges to form a more stable electric double layer structure, forming a more uniform and stable interface during lithium intercalation; whereas a suitable density of the carbon coating layer may characterize the compactness of the carbon coating layer, and 1.0 g·cm−3≤ρ2≤2.0 g·cm−3 (1.1 g·cm−3, 1.2 g·cm−3, 1.3 g·cm−3, 1.4 g·cm−3, 1.5 g·cm−3, 1.6 g·cm−3, 1.7 g·cm−3, 1.8 g·cm−3, 1.9 g·cm−3, etc.) enables the carbon coating layer to have proper compactness, forming a more stable electric double layer structure.
The core material of the carbon coated composite is not particularly limited in the present application, and preferably includes inorganic particles, such as any one or a combination of at least two of graphite particles, metallic tin particles, tin oxide particles, silicon particles, silicon oxide particles, silicon nitride particles, element-doped silicon-oxygen composite particles, metallic germanium particles, and germanium oxide particles.
The resulting carbon coated composite of the present disclosure is placed in an excess solution capable of dissolving the core characteristic element for dissolution determination of the core characteristic element, the dissolution amount of the core characteristic element being 100 ppm or less. The core characteristic element refers to an element of the core material of which quantitative data of inductively coupled plasma (ICP) is obtained by a chemical reaction, etc., and if the core itself cannot be dissolved, other soluble elements need to be selected as a reference. When the core is the graphite particles, the dissolution solution is aqua regia and the core characteristic element is an impurity trace element such as an iron element. When the core is the metallic tin particles or the tin oxide particles, the dissolution solution is aqua regia and the core characteristic elements is a tin element; when the core is the metallic germanium particles or the germanium oxide particles, the dissolution solution is an aqua regia solution and the core characteristic element is a germanium element; and when the core is the silicon particles, the silicon oxide particles, the silicon nitride particles or the element-doped silicon-oxygen composite particles, the core characteristic element is silicon, the dissolution solution is a sodium hydroxide or a hydrofluoric acid solution, and the dissolution time is 24 h or more.
In the determination of the dissolution amount of the core characteristic element, the excess solution means that the amount of a solution added is more than the amount of a solution capable of completely dissolving the core characteristic element. Less dissolution of the core characteristic element indicates more dense and uniform carbon coating, complete coating of the core material is achieved without defects or weaknesses, and the complete coating structure is advantageous for reducing side reactions at the interface and is more helpful for improving the high temperature, low temperature, storage and cycling characteristics of a battery.
The carbon coated composite with a mass of m1 and a density ρ1 is taken, and if the carbon content of the carbon coated composite is A (the carbon coating content can be determined by a carbon sulfur meter for a composite without carbon in the core and the carbon coating content can be determined by TG-DSC for a composite with carbon in the core), then the carbon coating layer has a mass of m2=m1×A.
The density ρ1 of the carbon coated composite described in the present application and the density ρ3 of the core are both true densities of the corresponding substances, while the density ρ2 of the carbon coating layer defined in the present application should also be understood as a true density of the carbon coating layer. True density refers to an actual mass of a solid matter per unit volume of a material in an absolutely dense state, i.e. a density after removal of internal pores or voids between particles. True density is different from apparent density and stacked density, the apparent density refers to a ratio of a mass to an apparent volume of a material, and the apparent volume is a solid volume plus a closed pore volume, which does not take into account factors such as voids within the material; the bulk density is a mass per unit volume measured just after dust or powder is freely filled in a container, which also does not take into account the pores and voids formed by material accumulation. The density pi of the carbon coated composite of the present disclosure and the density ρ3 of the core can be measured by using a true density tester. The average particle size, particle size distribution, specific surface area, and stacked pore volume can all be determined by the prior art, and an exemplary test method is a specific surface area test instrument.
A second object of the present disclosure is to provide a preparation method for the carbon coated composite described in one of the objects, the preparation method including the following steps of.
Rotary revolution is performed in the rotary converter, and twice vapor deposition is performed on the dynamic feedstock surface to form a complete carbon coating layer with the dissolution amount of the core characteristic element being less than 100 ppm. In the preparation method provided in the present application, the size range, the particle size span, the specific surface area and the stacked pore of the feedstock enable the feedstock to have suitable voids and suitable particle surface roughness, thereby making it easier to deposit a carbon layer on the particle surfaces and pore walls during chemical vapor deposition, a suitable degree of deagglomeration after the primary chemical vapor deposition is performed such that the particles reach a specific size (the average diameter of the second intermediate product is 1-1.1 times the average diameter of the feedstock to be coated), and coating defects due to agglomeration during the primary chemical vapor deposition are exposed, thereby completing repair of the coating defects during the secondary chemical vapor deposition.
A treatment process in the step (1) is well known in the art, such as jet milling, ball milling, a high-speed pulverizer, 4-grading, and the like. It should be noted that if the feedstock to be coated does not meet the requirements that “the average diameter is 1-40 μm, the particle size distribution span is 0.5≤(D90−D10)/D50≤2, the specific surface area is 1-5 m2·g−1, the ratio of the specific surface area to the stacked pore volume is 0.5-2.0 cm−1”, those skilled in the art can treat the feedstock to be coated by the prior art such as crushing, grading, and the like to be within the requirements of this application for the feedstock to be coated, and then carbon coating is performed.
Preferably, the feedstock to be coated includes any one of graphite powder, metal tin, tin oxide, silicon, silicon oxide, silicon nitride, an element-doped silicon-oxygen composite, metallic germanium particles, and germanium oxide particles.
The silicon oxide exemplarily includes silicon oxide, silicon monoxide, or any silicon oxide with a silicon to oxygen ratio of 1:1 to 1:2; and the element-doped silicon-oxygen composite may exemplarily be lithium-doped silicon monoxide, magnesium-doped silicon monoxide, or the like.
The carbon coated composite of the present disclosure can be used as a negative electrode material for a lithium ion battery, and the effects of improving the electrical conductivity of the composite, alleviating the volume changes, and stabilizing the interface can be achieved; when a coated material is graphite, the composite has reduced lithium intercalation volume expansion, improved rate performance, and a stabilized interface; when the coated material is silicon monoxide, the composite can improve the electrical conductivity and solid electrolyte interface (SEI) film stability of the material, especially the dense carbon layer has a better effect in buffering volume changes, and the continuous dense carbon layer protection can improve high temperature performance and cycling performance.
The carbon-containing process gas in the step (2) includes C1-4 alkanes (such as methane, ethane and propane), C2-4 alkenes (such as ethylene, propylene, 1-butene, and 1,3-butadiene), and C2-4 alkynes (such as acetylene and propyne).
Preferably, during the first carbon element vapor deposition, the carbon-containing process gas is a compound of propylene and methane in a volume ratio of (1-2):(1-2), a flow rate at which the process gas is introduced meets the following condition: h=V/s, wherein V is the total volume of a chamber of the rotary converter in L; s is a process gas introducing velocity in L/min, and the process gas flow rate meets h at 20-60 min. Exemplarily, if the total volume of the converter is 100 L, the flow rate is 1.667-5.000 L/min; and if the total volume of the converter is 1200 L, the flow rate is 20-60 L/min.
More preferably, during the first carbon element vapor deposition, when the carbon-containing process gas is the compound of methane and propylene, propylene is introduced at a position between a converter opening position of the rotary converter and ⅕ of the entire converter length (i.e. a position close to the converter opening) and methane is introduced at a position between ⅓ and ⅔ of the entire converter length of the rotary converter (i.e. the middle of the rotary converter). It is well known to those skilled in the art how to introduce the carbon-containing process gas at different positions of the rotary converter, for instance, gas introducing pipes of different lengths can be used, or gas introducing pipes can be provided at different positions of the rotary converter. The inventors have found that propylene carbon-containing process gas is introduced at the position close to the converter opening and methane carbon-containing process gas is introduced at the middle of the rotary converter, which is more conducive to the compactness and uniformity of the carbon coating layer. The carbon-forming process of chemical vapor deposition is closely related to the carbon-hydrogen ratio of carbon source gas, when the carbon-hydrogen ratio is large, layered deposition is easy to occur, while when the carbon-hydrogen ratio is small, an isotropic carbon structure is easy to deposit. In addition to this, the content of polycyclic aromatic hydrocarbons, a by-product of carbon source gas deposition, also changes with adjustment of the carbon-hydrogen ratio, and the higher the content of the by-product, the easier it is to form carbon blocks and cause particle agglomeration. Therefore, the carbon source gas ratio as well as the concentration in the process is important. In the present disclosure, after secondary carbon coating, defects and weak locations that are not coated or not tightly coated can be fully supplemented, but the flow rate of the process gas during the second coating needs to be controlled to be lower than the flow rate during the first coating. The gas of the protective atmosphere is nitrogen or argon, and the protective atmosphere can be introduced into the rotary converter alone or pre-mixed with the carbon-containing gas to be introduced into the rotary converter. A volume ratio of protective gas and the carbon-containing gas is (1-3):(1-3).
Preferably, in the step (2), the number of revolutions of the rotary converter is 0.1-2 rpm (e.g. 0.2 rpm, 0.5 rpm, 0.8 rpm, 1.2 rpm, 1.5 rpm, 1.8 rpm, etc.). The number of revolutions of the rotary converter is in the range of 0.1-2 rpm and both the completeness and the compactness of the carbon coating layer perform better.
The first carbon element vapor deposition is performed at a temperature of 600-1200° C. for 0.5-10 h; or the first carbon element vapor deposition is plasma vapor deposition at 100-500° C. for 0.5-10 h.
Preferably, a flow rate at which the carbon-containing process gas of the second carbon element vapor deposition is introduced is ¼ to ⅘, preferably ½ to ⅘ of the flow rate of the carbon-containing process gas of the first carbon element vapor deposition.
The purpose of the second carbon element vapor deposition is to repair defects of the carbon coating layer of the first carbon element vapor deposition, achieving complete carbon layer coating, and after the first carbon element vapor deposition of core particles, the cross section of the carbon coating layer is derived from deagglomeration, and is not uniform, in the second carbon element vapor deposition, reducing the flow rate at which the carbon-containing process gas is introduced to ¼ to ⅘ of the flow rate at which the carbon-containing process gas of the first carbon element vapor deposition can better generate a carbon layer on the cross section of the carbon coating layer in the first carbon element vapor deposition for coating.
Preferably, in the step (3), the material with the large particle size is a material having a particle size greater than 50 μm, and the crushing deagglomeration can collide and disperse agglomerated particles by means of mechanical milling or jet milling.
Preferably, in the step (4), the number of revolutions of the rotary converter is 0.1-2 rpm (e.g. 0.2 rpm, 0.5 rpm, 0.8 rpm, 1.2 rpm, 1.5 rpm, 1.8 rpm, etc.). It should be noted that the number of revolutions of the rotary converter in the step (2) and the step (4) is each independently selected from the range of 0.1-2 rpm, preferably the number of revolutions of the rotary converter in the step (2) is 2 to 3 times the number of revolutions of the rotary converter in the step (4).
Preferably, the second carbon element vapor deposition is performed at a temperature of 600-1200° C. for 0.5-10 h; or the second carbon element vapor deposition is plasma vapor deposition at 100-500° C. for 0.5-10 h. As a preferred technical solution, according to the preparation method for the carbon coated composite according to the present disclosure, the process gas for the first carbon element vapor deposition and the process gas for the second carbon element vapor deposition are each independently selected from propylene and methane.
A third purpose of the present disclosure is to provide use of a carbon coated composite, wherein the carbon coated composite is used as any one of electrode materials for lithium batteries, sodium batteries, potassium batteries and the like.
Compared with the prior art, the present application has the following beneficial effects:
Hereinafter, the technical solution of the present disclosure will be described in further detail with reference to specific examples. The following examples merely illustrate and explain the present disclosure and are not to be construed as limiting the protection scope of the present disclosure. All technologies realized based on the above contents of the present disclosure are covered in the scope of protection of the present disclosure.
The test methods described in the following examples are conventional methods unless otherwise specified; and the reagents and materials can be commercially obtained unless otherwise specified.
A preparation method for carbon coated silicon monoxide, comprising the following steps:
The D50 of the carbon coated composite prepared in Example 1 is 5.2 μm, (D90−D10)/D50 is 1.1, the specific surface area is 1.3 m3·g−1, and the A/V (ratio of the specific surface area to stacked pore volume) is 1.09 cm−1.
A preparation method for carbon coated tin oxide differs from Example 1 only in that 500 kg of silicon monoxide was replaced by 500 kg of tin oxide in equal mass. And in the step (1), 500 kg of tin oxide was treated by jet milling to a D50 of 4.9 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.2 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.0 cm−1 to obtain a feedstock to be coated.
The carbon coated composite prepared in Example 2 has a D50 of 5.0 μm, (D90−D10)/D50 of 1.2, a specific surface area of 1.4 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.17 cm−1.
A preparation method for carbon coated silicon differs from Example 1 only in that 500 kg of silicon monoxide was replaced by 500 kg of silicon in equal mass. And in the step (1), 500 kg of silicon was treated by jet milling to a D50 of 5.3 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.3 m3·g−1 and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.15 cm−1 to obtain a feedstock to be coated.
The carbon coated composite prepared in Example 3 has a D50 of 5.5 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.5 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.39 cm−1.
A preparation method for carbon coated graphite differs from Example 1 only in that 500 kg of silicon monoxide was replaced by 500 kg of natural graphite in equal mass. And in the step (1), 500 kg of natural graphite was treated by jet milling to a D50 of 4.9 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.3 m3·g−1 and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.25 cm−1 to obtain a feedstock to be coated.
The carbon coated composite prepared in Example 4 has a D50 of 5 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.6 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.49 cm−1.
A preparation method for carbon coated silicon oxide differs from Example 1 only in that 500 kg of silicon monoxide was replaced by 500 kg of silicon oxide in equal mass. And in the step (1), 500 kg of silicon oxide was treated by jet milling to a D50 of 4.9 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.3 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.25 cm−1 to obtain a feedstock to be coated.
The carbon coated composite prepared in Example 5 has a D50 of 5 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.3 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.1 cm−1.
A preparation method for carbon coated magnesium-doped silicon monoxide differs from Example 1 only in that 500 kg of silicon monoxide was replaced by 500 kg of magnesium-doped silicon monoxide in equal mass. And in the step (1), 500 kg of magnesium-doped silicon monoxide was treated by jet milling to a D50 of 5.2 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.5 m3·g−1 and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.28 cm−1 to obtain a feedstock to be coated.
The carbon coated composite prepared in Example 6 has a D50 of 5.5 μm, (D90−D10)/D50 of 1.1, a specific surface area of 1.8 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.51 cm−1.
A preparation method for carbon coated lithium-doped silicon monoxide differs from Example 1 only in that 500 kg of silicon monoxide was replaced by 500 kg of lithium-doped silicon monoxide in equal mass. And in the step (1), 500 kg of lithium-doped silicon monoxide was treated by jet milling to a D50 of 5.2 μm, (D90-D10)/D50 of 1.0, a specific surface area of 1.4 m3·g−1 and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.24 cm−1 to obtain a feedstock to be coated.
The carbon coated composite prepared in Example 7 has a D50 of 5.4 μm, (D90-D10)/D50 of 1.1, a specific surface area of 1.6 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.49 cm−1.
The carbon coated composites provided in Examples 1-7 were subjected to the following tests:
The test results are shown in Table 1.
As can be seen from Table 1, when propylene was selected as the carbon-containing process gas, introducing propylene at 50 L/min during the first carbon element vapor deposition and introducing propylene at 25 L/min during the second carbon element vapor deposition at 850° C. enabled the density of the carbon layer to be controlled to be 1.30 g·cm−3 or above regardless of the inorganic particles of the core; especially for silicon monoxide, the density of the carbon layer can be controlled to be 1.40 g·cm−3 or above.
The difference from Example 1 was only that the temperature of the first carbon element vapor deposition and the temperature of the second vapor deposition were 830° C. (Example 8), 920° C. (Example 9), 800° C. (Example 10), and 1000° C. (Example 11).
A carbon coated composite prepared in Example 8 has a D50 of 5.1 μm, (D90−D10)/D50 of 1.1, a specific surface area of 1.3 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.03 cm−1; a carbon coated composite prepared in Example 9 has a D50 of 5.2 μm, (D90−D10)/D50 of 1.1, a specific surface area of 1.4 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.19 cm−1; a carbon coated composite prepared in Example 10 has a D50 of 5 μm, (D90-D10)/D50 of 1.1, a specific surface area of 1.3 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.27 cm−1; and a carbon coated composite prepared in Example 11 has a D50 of 5.3 μm, (D90−D10)/D50 of 1.1, a specific surface area of 1.5 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.49 cm−1.
The difference from Example 1 was only that the flow rate of propylene process gas of the second vapor deposition was 13 L/min (Example 12), 40 L/min (Example 13), 50 L/min (Example 14), and 7 L/min (Example 15).
A carbon coated composite prepared in Example 12 has a D50 of 5.1 μm, (D90−D10)/D50 of 1.1, a specific surface area of 1.3 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.27 cm−1; a carbon coated composite prepared in Example 13 has a D50 of 5.6 μm, (D90−D10)/D50 of 1.1, a specific surface area of 1.4 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.29 cm−1; a carbon coated composite prepared in Example 14 has a D50 of 6.4 μm, (D90−D10)/D50 of 1.1, a specific surface area of 1.7 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.68 cm−1; and a carbon coated composite prepared in Example 15 has a D50 of 5.3 μm, (D90−D10)/D50 of 1.1, a specific surface area of 1.6 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.55 cm−1.
The difference from Example 1 was only that the speed of revolution of the high temperature rotary converter in both the step (2) and the step (4) was 0.5 rpm.
The difference from Example 1 was only that the speed of revolution of the high temperature rotary converter in both the step (2) and the step (4) was 1.5 rpm.
A preparation method for carbon coated silicon monoxide included the following steps that:
A carbon coated composite prepared in Example 16 has a D50 of 5.6 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.3 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.19 cm−1; a carbon coated composite prepared in Example 17 has a D50 of 5.3 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.4 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.28 cm−1; and the resulting carbon coated silicon monoxide in Examples 8-17 was tested for the carbon layer density and the dissolution amount of silicon element according to the same test methods as those in Example 1, and Table 2 shows the results of the carbon layer density and the dissolution amount of the core characteristic element in the examples.
As can be seen from a comparison of Comparative example 1 and Examples, when only once carbon element vapor deposition was performed, the completeness of the carbon coating and the density of the carbon layer cannot be guaranteed even when the deposition time was extended. As can be seen from Examples 8-11, when the vapor deposition was performed at 830-920° C., the density of the carbon coating layer was 1.3 g·cm−3≤ρ2≤1.45 g·cm−3, and the dissolution rate was 60 ppm or below, and an increase in dissolution rate was caused when the temperature was too high or too low. As can be seen from Examples 12-15, when the gas flow rate of secondary coating was ¼ to ⅘ of the gas flow rate of the primary coating, the density of the carbon coating layer was 1.4 g·cm−3≤ρ2≤1.45 g·cm−3 and the characteristic element dissolution rate was 60 ppm or below; when the gas flow rate of the secondary coating was too low and the completeness of the carbon coating layer was reduced, the dissolution rate was increased but can also be guaranteed to be 100 ppm or below; and when the gas flow rate of the secondary coating was too high, the dissolution rate was reduced, but the reduction was not significant.
When propylene was selected as the carbon-containing process gas, introducing propylene at 50 L/min during the first carbon element vapor deposition and introducing propylene at 25 L/min during the second carbon element vapor deposition at 830-920° C. by using a 1200 L rotary converter as an example, the speed of revolution being 0.5-1.5 rpm, enable the density of the carbon layer to be controlled to be 1.38-1.43 g·cm−3 or above with core element dissolution less than 100 ppm.
The difference from Example 1 was only that the carbon-containing process gas of the first carbon element vapor deposition was methane, and the temperature was adaptively adjusted, specifically:
A carbon coated composite prepared in Example 18 has a D50 of 5.3 μm, (D90−D10)/D50 of 1.1, a specific surface area of 4.5 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 3.78 cm−1. Because methane was used as the process gas, disordered carbon coating was formed, the specific surface area was greatly increased.
The difference from Example 1 was only that the carbon-containing process gas of the second carbon element vapor deposition was methane, and the temperature was adaptively adjusted, specifically:
The material in the step (3) was fed into a high temperature rotary converter with the number of revolutions of 1.5 rpm at 5 kg/h, the temperature in the converter being 1000° C., nitrogen at 50 L/min and methane at 25 L/min were continuously introduced, and second carbon element vapor deposition was performed, the residence time of the material in the converter being controlled to be 2 h, to obtain a crude carbon coated composite with silicon monoxide as a core and an outer layer coated with carbon.
A carbon coated composite prepared in Example 19 has a D50 of 5.3 μm, (D90−D10)/D50 of 1.1, a specific surface area of 3.5 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 2.94 cm−1.
The difference from Example 1 was only that the carbon-containing process gas for both the first carbon element vapor deposition and the second carbon element vapor deposition was methane, and the temperature was adaptively adjusted, specifically:
The difference from Example 1 was only that the carbon-containing process gas of the first carbon element vapor deposition was acetylene, the temperature was adaptively adjusted, specifically:
A carbon coated composite prepared in Example 21 has a D50 of 5.1 μm, (D90−D10)/D50 of 1.1, a specific surface area of 1.5 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.38 cm−1.
The difference from Example 1 was only that the carbon-containing process gas of the second carbon element vapor deposition was acetylene, and the temperature was adaptively adjusted, specifically:
The carbon coated composite prepared in Example 22 has a D50 of 5.2 μm, (D90−D10)/D50 of 1.1, a specific surface area of 1.6 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.51 cm−1.
The difference from Example 1 was only that the carbon-containing process gas for both the first carbon element vapor deposition and the second carbon element vapor deposition was acetylene, and the temperature was adaptively adjusted, specifically:
The step (4) was adjusted as follows: the material in the step (3) was fed into a high temperature rotary converter with the number of revolutions of 1.5 rpm at a rate of 5 kg/h, the temperature in the converter being 900° C., nitrogen gas at 50 L/min and acetylene gas at 25 L/min were continuously introduced, and second carbon element vapor deposition was performed, the residence time of the material in the converter being controlled to be 2 h, to obtain a crude carbon coated composite with silicon monoxide as a core and an outer layer coated with carbon.
The carbon coated composite prepared in Example 23 has a D50 of 5.5 μm, (D90−D10)/D50 of 1.1, a specific surface area of 1.7 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.67 cm−1.
Tests of the carbon layer density and the dissolution of the core characteristic element were performed for the above examples, the test methods were as described in Example 1, and Table 3 shows the test results for the above examples.
As can be seen from Table 3, for methane and acetylene, after the first carbon element vapor deposition, deagglomeration was performed, and then the second carbon element vapor deposition was performed to improve the density of the carbon layer and the uniformity of carbon coating; of course, for other carbon-containing process gases, after the first carbon element vapor deposition, deagglomeration was performed, and then the second carbon element vapor deposition was performed to improve the density of the carbon layer and the uniformity of carbon coating.
The difference from Example 1 was only that the feedstock to be coated was replaced to be have a D50 of 5 μm, (D90−D10)/D50 of 1.2, a specific surface area of 1.5 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.1 cm−1, specifically:
The carbon coated composite prepared in Example 24 has a D50 of 5.3 μm, (D90−D10)/D50 of 1.2, a specific surface area of 1.6 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.58 cm−1.
The difference from Example 1 was only that the step (1) was as follows: 500 kg of silicon monoxide was treated by jet milling to a D50 of 5 μm, (D90−D10)/D50 of 1.2, a specific surface area of 2.5 m3·g−1 and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.5 cm−1 to obtain a feedstock to be coated.
The carbon coated composite prepared in Example 25 has a D50 of 5.5 μm, (D90−D10)/D50 of 1.2, a specific surface area of 1.9 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 2.44 cm−1.
The difference from Example 1 was only that the step (1) was as follows: 500 kg of silicon monoxide was treated by jet milling to a D50 of 10 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.1 m3·g−1 and A/V (a ratio of the specific surface area to the stacked pore volume) of 0.8 cm−1 to obtain a feedstock to be coated.
The carbon coated composite prepared in Example 26 has a D50 of 10.3 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.4 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.48 cm−1.
(1) Example 13 differed from Example 1 only in that the step (1) was as follows: 500 kg of silicon monoxide was treated by jet milling to a D50 of 30 μm, (D90−D10)/D50 of 1.0, a specific surface area of 1.1 m3·g−1 and A/V (a ratio of the specific surface area to the stacked pore volume) of 0.8 cm−1 to obtain a feedstock to be coated.
The carbon coated composite prepared in Example 27 has a D50 of 30.5 μm, (D90−D10)/D50 of 1.1, a specific surface area of 1.3 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 1.41 cm−1.
The difference from Example 1 was only that the feedstock to be coated was replaced to be have a D50 of 5 μm, (D90−D10)/D50 of 1.8, a specific surface area of 2.0 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 0.8 cm−1.
The carbon coated composite prepared in Example 28 has a D50 of 5.5 μm, (D90−D10)/D50 of 1.9, a specific surface area of 1.4 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 0.92 cm−1.
The difference from Example 1 was only that the feedstock to be coated was replaced to be have a D50 of 5 μm, (D90−D10)/D50 of 1.2, a specific surface area of 1.1 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 0.4 cm−1, specifically:
The difference from Example 1 was only that the feedstock to be coated was replaced to be have a D50 of 2.5 μm, (D90−D10)/D50 of 0.6, a specific surface area of 5.0 m3·g−1, and A/V (a ratio of the specific surface area to the stacked pore volume) of 7.0 cm−1, specifically:
Tests of the carbon layer density and the dissolution of the core characteristic element were performed for the above examples and comparative examples, and Table 4 shows the test results.
As can be seen from Table 4, a particular feedstock the average diameter of the feedstock to be coated is 1-40 μm, the particle size distribution span is 0.5≤(D90−D10)/D50≤2, the specific surface area is 1-50 m2·g−1, and the ratio of the specific surface area to the stacked pore volume is 0.5-5 cm−1) was used, rotary revolution was performed in the rotary converter, and twice vapor deposition was performed on the dynamic feedstock surface to form the complete and compact (the density ρ2 of the carbon coating layer is 1.0-2.0 g·cm−3; and the core element dissolution rate is within 100 ppm) carbon coating layer.
Other conditions were the same as those in Example 1, except that the step (2) was changed as follows: the feedstock to be coated was fed into a high temperature rotary converter with the number of revolutions of 0.5 rpm at a feeding rate of 5 kg/h, the total volume in the converter being 1200 L, and the temperature in the converter being 850° C., nitrogen gas at 50 L/min and propylene gas at 25 L/min and methane gas at 25 L/min were continuously introduced,
A carbon coated composite with uniform and dense carbon coating was finally obtained, and
The other conditions were the same as those in Example 29, except that both propylene gas and methane gas entered from the gas inlet 1. The carbon coated composite obtained in Example 30 was tested, the density of the carbon layer was 1.44 g·cm−3 and the dissolution amount of the core characteristic element silicon was 36 ppm. While the reason is not clear, a comparison of Example 29 and Example 30 illustrates that introducing propylene gas at the position close to the burner and introducing methane at the position close to the middle of the converter are more favorable for forming a complete, uniform and dense carbon coating layer.
Electrochemical performance characterization of the carbon coated composite negative electrode materials: the carbon coated composite negative electrode materials prepared in the above examples, Super P, and polyacrylic acid (a binder) were mixed in a mass ratio of 80:10:10 into a slurry and the slurry was uniformly applied to a copper foil current collector to obtain an electrode diaphragm. A button battery was assembled in an argon protected glove box with a metallic lithium sheet as a counter electrode, a polypropylene microporous membrane (Celgard 2400) as a separator, and 1 mol/L LiPF6 (a solvent was a mixed solution of ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1, in which 5% of vinylidene fluoride carbonate and 2% of vinylene carbonate were added) as an electrolyte, and subjected to charge and discharge testing with a test procedure of 100 mA g−1 and a charge and discharge voltage interval of 0.01-1.5 V, and Table 5 is the battery test results. Wherein application examples 1-30 and Comparative application examples 1-3 respectively used the carbon coated negative electrode materials in Examples 1-30 and Comparative examples 1-3. The battery performance test results for some of the application examples are shown in Table 5 below:
| Number | Date | Country | Kind |
|---|---|---|---|
| 202210154223.8 | Feb 2022 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2022/102629 | 6/30/2022 | WO |
