CN114068885A - Graphite material with porous carbon layer and preparation method and application thereof - Google Patents
Graphite material with porous carbon layer and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a graphite material with a porous carbon layer, a preparation method and application thereof. The method comprises the following steps: 1) introducing inert gas and CO2Under the mixed atmosphere of (A), carrying out primary carbonization treatment on the graphite raw material, wherein the primary carbonization treatment temperature is T1600-1100 deg.C; optionally carrying out step 2) stopping the introduction of CO2Introducing an inert gas and NH3Under the mixed atmosphere of (A), performing secondary carbonization treatment on the graphite, wherein the temperature of the secondary carbonization treatment is T2，T2>T1. The invention can form the nitrogen-doped porous carbon layer on the surface of the graphite matrix, and has the advantages of uniform distribution of pores, good uniformity and uniform and sufficient nitrogen doping. The method can realize the respective regulation and control of the thickness of the porous carbon and the nitrogen doping amount in the porous carbon. The method is simple and suitable for industrial production.
Description
Technical Field
The invention relates to the technical field of new energy, and relates to a graphite material with a porous carbon layer, and a preparation method and application thereof.
Background
Graphite is a layered crystal formed by stacking graphite sheets under van der waals forces. The graphite has rich resources and low price, and has the advantages of high reversible capacity, low charge-discharge voltage platform, no voltage hysteresis, good conductivity and the like when being used as a negative electrode material for a lithium battery, and is widely researched in the lithium battery industry.
Although lithium ions can be completely and reversibly intercalated and deintercalated in graphite in theory, capacity fading occurs during the first cycle in the practical application process, and the main reason is that the graphite negative electrode reacts with the electrolyte solution to generate a passivation film (SEI film) having lithium ion conductivity and electronic insulation when lithium is first intercalated. Moreover, since the anisotropic structure of graphite restricts the free diffusion of lithium ions in the graphite structure, the rate capability is poor, and it is difficult to meet the requirements of practical application.
CN107749472A discloses a high-performance graphite composite negative electrode material and a preparation method thereof, the graphite composite negative electrode material has a core-shell structure, and includes an inner core part and an outer shell part coated on the inner core part, wherein the inner core part is a germanium oxide-graphite composite material, the outer shell part is an inorganic lithium compound, and the outer shell part of the graphite composite negative electrode material has a pore structure. However, the core and the shell are physically combined, so that the problem of shell layer falling is easy to occur, the preparation process is complex, and the cost is high.
CN107305949A discloses a porous graphite negative electrode material, a preparation method and an application thereof, wherein more pores are obtained by etching metal or metal compounds on the layered surface and the end face of graphite, the specific surface area of graphite is effectively increased on the basis of not obviously reducing the conductivity of graphite, meanwhile, the rate of lithium ions entering the graphite is increased, the rapid consumption of electrolyte on the surface of the graphite and the negative influence of lithium deposition under high-rate charge and discharge are reduced, and the rapid charge and discharge capacity of the graphite negative electrode is obviously improved. However, this method has the disadvantages that metal ions are difficult to remove, short circuits may be caused by the metal ions, and the preparation process is complicated and costly.
Disclosure of Invention
In view of the above problems in the prior art, the present invention aims to provide a graphite material having a porous carbon layer, and a preparation method and use thereof.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a graphite material with a porous carbon layer, where the graphite material includes a graphite substrate and a porous carbon layer coated on a surface of the graphite substrate, and the graphite substrate and the porous carbon layer are in an integral structure.
For a graphite negative electrode material, lithium ions can only enter from the end face of graphite due to the layered structure of the graphite, so that the multiplying power performance is poor.
The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.
Preferably, the graphite matrix comprises artificial graphite and/or natural graphite.
Preferably, the artificial graphite comprises petroleum coke artificial graphite and/or needle coke artificial graphite.
Preferably, the nitrogen-doped porous carbon layer is: carbon dioxide reacts with carbon on the surface of the graphite to generate carbon monoxide, and the carbon monoxide overflows from the porous carbon formed by pore-forming on the surface of the graphite carbon layer.
Preferably, the thickness of the porous carbon layer is 1nm to 20nm, such as 1nm, 2nm, 3nm, 5nm, 7nm, 9nm, 10nm, 12nm, 13nm, 14nm, 15nm, 17nm or 20nm, etc., if the thickness of the porous carbon layer is too small, the effect of increasing the Li ion transport rate is not ideal; if the thickness of the porous carbon layer is too large, the material activity is too high, the specific surface area is large, the 5T compacted density is small, the processability is deteriorated, and the irreversible capacity is increased, and more preferably 5nm to 15 nm.
Preferably, the graphite material has an average particle size of 5 μm to 25 μm, such as 5 μm, 7 μm, 8 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 17 μm, 18 μm, 20 μm, 23 μm, 25 μm, or the like.
In a second aspect, the present invention provides a method of preparing a graphitic material with a porous carbon layer, said method comprising the steps of:
(1) introducing inert gas and CO2Under the mixed atmosphere of (A), carrying out primary carbonization treatment on the graphite raw material, wherein the primary carbonization treatment temperature is T1600-1100 c to yield a graphite material with a porous carbon layer.
In the process of the invention, T1600 ℃ to 1100 ℃, e.g., 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, 825 ℃, 850 ℃, 900 ℃, 950 ℃, 1000 ℃, or 1100 ℃, etc. If the temperature is too low, the carbon dioxide is not completely decomposed into CO, and the pore-forming is not sufficient; if the temperature is too high, the reaction is too vigorous and the pore-forming is not uniform.
The method of the invention is carried out by first reacting under the conditions of 600-1100 deg.C in inert gas and CO2Primary carbonization in a mixed atmosphere of (C) and (C)2Reacting with graphite carbon at high temperature to convert into CO, allowing CO to escape to etch the surface of graphite material to form porous carbon with integral structure on the surface, and stopping introducing CO2Under an inert gas and NH3Is subjected to higher temperature secondary carbonization, NH3The porous carbon is decomposed at high temperature to realize doping to form the nitrogen-doped porous carbon layer, the distribution of the pores is uniform, the uniformity is good, and the nitrogen doping is uniform and sufficient. The invention firstly etches at lower temperature to form porous carbon,the porous carbon and graphite surface defects can be reduced, side reactions are reduced, and a more complete pore structure and a more sufficient nitrogen doping effect are obtained.
The method of the invention can be realized by changing CO2The flow and the primary carbonization time realize the regulation and control of the thickness, the pore structure and the pore distribution of the porous carbon. Moreover, the method has simple production process and is suitable for industrial production.
As a preferred technical scheme of the method, the method also comprises the step (2) after the step (1): stopping the introduction of CO2Introducing an inert gas and NH3Under the mixed atmosphere of (A), performing secondary carbonization treatment on the graphite, wherein the temperature of the secondary carbonization treatment is T2，T2>T1。
The method of the invention can be realized by changing CO2Flow rate, NH3The flow, the primary carbonization time, the secondary carbonization time and other parameters realize the regulation and control of the thickness, the pore structure, the pore distribution and the nitrogen doping amount in the porous carbon. Moreover, the method has simple production process and is suitable for industrial production.
Preferably, the graphite raw material in step (1) has an average particle diameter of 5 μm to 25 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 17 μm, 20 μm, 23 μm, 25 μm, or the like.
Preferably, the specific surface area of the graphite raw material in the step (1) is less than or equal to 5m2In g, e.g. 5m2/g、4m2/g、3m2In g or 2m2And/g, etc.
Preferably, the graphite raw material of the step (1) has a 5T compaction density of more than 2.0g/cm3For example 2.05g/cm3、2.1g/cm3、2.15g/cm3、2.2g/cm3、2.3g/cm3Or 2.4g/cm3And the like.
Preferably, the degree of graphitization of the graphite starting material in step (1) is > 90%, such as 91%, 92%, 93%, 94%, 95%, 96%, 98%, or the like.
Preferably, the inert gas in step (1) is selected from any one of nitrogen, helium, neon, argon, krypton, xenon or radon or a combination of at least two of the same.
Preferably, in the mixed atmosphere of step (1), inert gas and CO2The flow rate ratio of (A) is 1:1 to 5:1, for example 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 or 5:1, preferably 2:1 to 4: 1.
Preferably, in step (1), the CO is2At 0.5m3/h-3m3At a flow rate of, for example, 0.5m3/h、1m3/h、1.2m3/h、1.5m3/h、2m3/h、2.5m3H or 3m3H, etc., preferably at a flow rate of 1m3/h-2m3/h。
In the present invention, the inert gas and CO in the step (1)2Flow rate ratio of (A) and CO2The flow rate has important influence on the structure and performance of the product, if the CO is in mixed atmosphere2Too large of a proportion or CO2The reaction is violent due to overlarge flow, the etching is excessive, the specific surface area is overlarge due to the fact that the porous carbon structure formed on the surface of the graphite is easy to damage, and the first effect is reduced; if CO is present in the mixed atmosphere2Too small a proportion or CO2Too small a flow rate can result in insufficient etching and uneven pore distribution, which affects material properties.
Preferably, the temperature is raised to T1The temperature rise rate is 3 ℃/min to 10 ℃/min, for example, 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 8 ℃/min, or 10 ℃/min.
Preferably, the constant temperature time of the primary carbonization in the step (1) is 1h to 10h, such as 1h, 2h, 2.5h, 3.5h, 4h, 5h, 6h, 8h or 10h, etc., preferably 2h to 6 h.
Preferably, the primary carbonization in the step (1) is performed in a carbonization apparatus including a roller kiln, a pusher kiln, a rotary kiln and a box furnace.
Preferably, in the mixed atmosphere of step (2), inert gas and NH3The flow rate ratio of (A) is 1:1 to 5:1, for example 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 4:1 or 5:1, preferably 2:1 to 4: 1.
Preferably, in step (2), the NH is3At 0.5m3/h-5m3At a flow rate of, for example, 0.5m3/h、1m3/h、1.2m3/h、1.5m3/h、2m3/h、2.5m3/h、3m3/h、3.5m3/h、4m3/h、4.5m3H or 5m3H, etc., preferably at a flow rate of 1m3/h-3m3/h。
In the present invention, the inert gas and NH in the step (1)3Flow rate ratio of (3) and NH3The flow rate has important influence on the structure and performance of the product, if NH is in the mixed atmosphere3Too large of a proportion or NH3Too large flow can cause too many defects, and the pore structure is easy to collapse, so that the specific surface area is too large, and the first effect is reduced; if NH is present in the mixed atmosphere3Too small a proportion or NH3Too small a flow rate can result in uneven doping and affect product performance.
Preferably, in step (2), T2At 700 ℃ to 1300 ℃, for example 700 ℃, 750 ℃, 800 ℃, 900 ℃, 950 ℃, 1000 ℃, 1100 ℃, 1150 ℃, 1200 ℃ or 1300 ℃, etc.
Preferably, from T1Heating to T2The temperature rise rate is 3 ℃/min to 10 ℃/min, for example, 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 8 ℃/min, or 10 ℃/min, etc., preferably 3 ℃/min to 5 ℃/min.
Preferably, the time for the secondary carbonization in the step (2) is 1h to 6h, such as 1h, 2h, 3h, 4h, 5h or 6h, etc., preferably 2h to 4 h.
Preferably, the inert gas in step (2) is selected from any one of nitrogen, helium, neon, argon, krypton, xenon or radon or a combination of at least two of the same.
The inert gas is not particularly limited to the inert gas of the eighth group in the periodic table of the elements, and can also comprise other chemically inert gases such as nitrogen and the like, and the inert gas is used as a protective gas to prevent graphite from being oxidized and simultaneously enable CO to be oxidized2The reaction is violent without overhigh concentration, so that the graphite is fully subjected to pore-forming under relatively mild reaction conditions.
Preferably, the secondary carbonization in the step (2) is performed in a carbonization apparatus including a roller kiln, a pusher kiln, a rotary kiln and a box furnace.
Preferably, the method further comprises the step of cooling and sieving after the secondary carbonization treatment.
As a further preferred technical solution of the method of the present invention, the method comprises the steps of:
(1) in N2Placing graphite raw material in carbonization equipment under the atmosphere, introducing CO2Heating to 600-1100 deg.C at a rate of 3-10 deg.C/min, and CO2The flow rate is 0.5m3/h-3m3/h，N2And CO2The flow rate ratio of (1: 1) - (5: 1), keeping the temperature for 1-10 h, and then stopping introducing CO2；
(2) Continuously introducing N2After introduction of NH3Heating to 700-1300 ℃ at the speed of 3-10 ℃/min under the condition of (1), and NH3The flow rate is 0.5m3/h-5m3/h，N2And NH3The flow rate ratio of the graphite material is 1:1-5:1, the temperature is kept for 1-6 h, and the graphite material is obtained after cooling and screening;
the graphite raw material is artificial graphite and/or natural graphite, the average particle size of the graphite raw material is 5-25 mu m, and the specific surface area is less than or equal to 5m2(ii) a 5T compacted density of > 2.0g/cm3The graphitization degree is more than 90 percent.
In a second aspect, the present invention provides a graphite material prepared by the method of the first aspect, where the graphite material includes a graphite matrix and a nitrogen-doped porous carbon layer coated on the surface of the graphite matrix, and the graphite matrix and the nitrogen-doped porous carbon layer are in an integral structure.
Through pore forming on the surface of graphite, lithium ions can enter the graphite layer from pores on the base surface, so that the ion transmission performance is improved, and the multiplying power performance of the graphite is greatly improved; the nitrogen doping of the porous carbon on the surface of the graphite substrate improves the electronic conductivity of the graphite material. Moreover, the graphite material of the present invention has the advantage of high compacted density.
In a third aspect, the present invention provides an anode comprising the graphite material having a porous carbon layer as described in the first aspect.
In a fourth aspect, the present invention provides a lithium ion battery comprising the negative electrode of the third aspect.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a graphite material with a porous carbon layer and a preparation method thereof, which is characterized in that the graphite material is prepared by firstly under the conditions of 600-1100 ℃ and inert gas and CO2Primary carbonization in a mixed atmosphere of (C) and (C)2The carbon reacts with graphite carbon at high temperature to be converted into CO, and CO escapes to generate an etching effect on the surface of the graphite raw material, so that porous carbon with an integral structure is formed on the surface. The porous carbon layer and the graphite substrate are of an integral structure, lithium ions can enter the graphite layer from the pores of the base surface by forming pores on the graphite surface, the rate capability of the graphite is greatly improved, the electronic conductivity of the graphite material is improved by the pore structure, and the porous carbon layer is used as a negative electrode material to be applied to a lithium ion battery, so that the porous carbon layer has the advantages of high rate capability and excellent dynamic performance.
The preferred technical proposal of the invention is to adopt CO2Obtaining a graphite material with a porous carbon layer through primary carbonization, and then continuously adopting NH3Carrying out secondary carbonization, NH3The porous carbon is decomposed at high temperature to realize doping to form the nitrogen-doped porous carbon layer, the distribution of the pores is uniform, the uniformity is good, and the nitrogen doping is uniform and sufficient. Through pore forming on the surface of graphite, lithium ions can enter the graphite layer from pores on the base surface, so that the ion transmission performance is improved, and the multiplying power performance of the graphite is greatly improved; the nitrogen doping of the porous carbon on the surface of the graphite matrix improves the electronic conductivity of the graphite material, and the graphite material is used as a negative electrode material to be applied to a lithium ion battery, so that the graphite material has the advantages of high rate performance and excellent dynamic performance. In addition, according to the preferred technical scheme, porous carbon is formed by etching at a lower temperature, the pore structure on the surface of the graphite is complete and uniformly distributed, and nitrogen doping is performed at a higher temperature, so that the defects on the surfaces of the porous carbon and the graphite can be reduced, side reactions are reduced, and a more complete pore structure and a more sufficient nitrogen doping effect are obtained.
The method has simple production process and is suitable for industrial production.
Drawings
FIG. 1 is a schematic view of nitrogen-doped porous carbon-coated graphite.
Fig. 2 nitrogen doped porous carbon coated graphite SEM.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
Example 1
The embodiment provides modified graphite and a preparation method thereof, wherein the modified graphite is graphite coated with a nitrogen-doped porous carbon layer, and the method comprises the following steps:
(1) the artificial graphite secondary particles having a particle size d50 of 12 μm (specific surface area of 1.2 m)2A 5T compacted density of 2.05g/cm3Graphitization degree of 94%) in a pusher kiln at N2And CO2Raising the temperature to 1000 ℃ at the temperature rise speed of 2 ℃/min under the atmosphere, and raising the temperature to CO2Has a flow rate of 1m3/h，N2The flow rate is 3m3H, keeping the temperature for 5h, stopping introducing CO2；
(2) Continuously introducing N according to the original flow2Heating to 1150 deg.C at 2 deg.C/min, and heating at 2m3NH is introduced at a flow rate of3Preserving the heat for 2 hours, naturally cooling, and then sieving with a 400-mesh sieve to obtain a finished product.
Example 2:
the embodiment provides modified graphite and a preparation method thereof, wherein the modified graphite is graphite coated with a nitrogen-doped porous carbon layer, and the method comprises the following steps:
(1) the artificial graphite secondary particles having a particle size d50 of 12 μm (specific surface area of 1.2 m)2(ii)/g, compacted density of 2.05g/cm394% graphitization) was placed in a rotary furnace under Ar and CO2Raising the temperature to 800 ℃ at the temperature raising speed of 5 ℃/min in the atmosphere, and raising the temperature to CO2Has a flow rate of 2m3H, Ar flow rate of 2.5m3H, keeping the temperature for 3h, stopping introducing CO2；
(2) Continuously introducing Ar according to the original flow rate, heating to 1000 ℃ at the speed of 6 ℃/min, and heating at the speed of 2.5m in the process3NH is introduced at a flow rate of3Keeping the temperature for 4 hours, naturally cooling,and then sieving with a 400-mesh sieve to obtain a finished product.
Example 3:
the embodiment provides modified graphite and a preparation method thereof, wherein the modified graphite is graphite coated with a nitrogen-doped porous carbon layer, and the method comprises the following steps:
(1) artificial graphite secondary particles having a particle size d50 of 18 μm (specific surface area 1.2, compacted density 2.06, degree of graphitization 94%) were placed in a rotary kiln under He and CO2Raising the temperature to 750 ℃ at a temperature rise rate of 8 ℃/min in the atmosphere, and raising the temperature to CO2Has a flow rate of 3m3H, He flow 10m3H, keeping the temperature for 3h, stopping introducing CO2；
(2) Continuously introducing He according to the original flow rate, heating to 1100 ℃ at a speed of 4 ℃/min, and heating at a speed of 2.5m in the process3NH is introduced at a flow rate of3Preserving the heat for 2 hours, naturally cooling, and then sieving with a 400-mesh sieve to obtain a finished product.
Example 4:
the embodiment provides modified graphite and a preparation method thereof, wherein the modified graphite is graphite coated with a nitrogen-doped porous carbon layer, and the method comprises the following steps:
(1) natural graphite secondary particles having a particle size d50 of 17 μm (specific surface area 1.80, compacted density 2.15, graphitization degree 96.2%) were placed in a box furnace under N2And CO2Raising the temperature to 900 ℃ at the temperature rise speed of 4 ℃/min in the atmosphere, and raising the temperature to CO2At a flow rate of 0.5m3/h，N2The flow rate is 2.5m3H, keeping the temperature for 2.5h, stopping introducing CO2；
(2) Continuously introducing N according to the original flow2Heating to 1050 deg.C at 2 deg.C/min, and heating at 1.5m3NH is introduced at a flow rate of3Preserving the heat for 3.5h, naturally cooling, and then sieving with a 400-mesh sieve to obtain a finished product.
Example 5:
the difference from example 1 is that step (1) CO2The flow rate is adjusted to 3m3H, when N2And CO2The flow rate ratio of (a) to (b) is 1: 1.
Example 6:
the difference from example 1 is that the procedure is(1)CO2The flow rate is adjusted to 0.5m3H, when N2And CO2The flow rate ratio of (a) to (b) is 6: 1.
Example 7:
the difference from example 1 is that step (2) NH3The flow rate is adjusted to 5m3H, when N2And NH3The flow rate ratio of (A) is 0.6: 1.
Example 8:
the difference from example 1 is that step (2) NH3The flow rate is adjusted to 0.5m3H, when N2And NH3The flow rate ratio of (a) to (b) is 6: 1.
Comparative example 1:
the present comparative example provides a method of preparing a modified graphite material, the method comprising:
(1) the artificial graphite secondary particles having a particle size d50 of 12 μm (specific surface area of 1.2 m)2A 5T compacted density of 2.05g/cm3Graphitization degree of 94%) in a pusher kiln at N2And CO2Raising the temperature to 1000 ℃ at the temperature rise speed of 2 ℃/min under the atmosphere, and raising the temperature to CO2Has a flow rate of 1m3/h，N2The flow rate is 3m3H, keeping the temperature for 5 h;
(2) continuously introducing N according to the original flow2And CO2Raising the temperature to 1150 ℃ at the speed of 2 ℃/min, preserving the temperature for 2h, naturally cooling, and then sieving with a 400-mesh sieve to obtain a finished product.
Comparative example 2:
the present comparative example provides a method of preparing a modified graphite material, the method comprising:
(1) the artificial graphite secondary particles having a particle size d50 of 12 μm (specific surface area of 1.2 m)2A 5T compacted density of 2.05g/cm3Graphitization degree of 94%) in a pusher kiln at N2And NH3Raising the temperature to 1000 ℃ at the temperature raising speed of 2 ℃/min under the atmosphere, and NH3Has a flow rate of 2m3/h，N2The flow rate is 3m3H, keeping the temperature for 5 h;
(2) continuously introducing N according to the original flow2And NH3Heating to 1150 deg.C at a rate of 2 deg.C/min, keeping the temperature for 2h, naturally cooling, sieving with 400 mesh sieve,and obtaining a finished product.
Comparative example 3:
the difference from example 1 is that the primary carbonization temperature was 1150 ℃ and the secondary carbonization temperature was 1000 ℃.
Comparative example 4:
the difference from example 1 is that the temperature of the primary carbonization in step (1) is 500 ℃.
Comparative example 5:
the difference from example 1 is that the temperature of the primary carbonization in step (1) is 1200 ℃.
And (3) testing:
firstly, specific surface area test:
and testing by using a full-automatic nitrogen adsorption specific surface area tester.
Secondly, testing the compaction density:
and testing by using a compression and bending integrated testing machine.
Thirdly, testing electrochemical performance:
and (3) carrying out button cell test on the prepared negative pole piece, assembling the cell in an argon glove box, and carrying out test by taking a metal lithium piece as a negative pole and 1mol/L LiPF as electrolyte6+ EC + EMC, the diaphragm is a polyethylene/propylene composite microporous membrane, the electrochemical performance is carried out on a Xinwei battery test cabinet (5V,1A), the charging and discharging voltage is 0.01-1.5V, the charging and discharging speed is 0.1C, and the buckling capacitance and the first coulombic efficiency are tested.
TABLE 1
As can be seen by comparing examples 5 to 6 with example 1, CO2Flow rate and its inert gas N2The ratio of (A) has a significant influence on the product structure and properties, example 5 relative to example 1, CO2The flow rate and the ratio are large, the reaction is violent, the specific surface area is enlarged, and the first effect is reduced(ii) a Example 6 relative to example 1, CO2The flow rate and the ratio are small, so that the etching is insufficient, the pore distribution is not uniform, and the capacity and the 5C reversible capacity are reduced.
As can be seen by comparing examples 7 to 8 with example 1, NH3Flow rate and its inert gas N2The ratio of (A) has a significant influence on the product structure and properties, example 7 vs. example 1, NH3The flow and the ratio are large, so that on one hand, the defects are excessive, on the other hand, the specific surface area is large, the first effect is reduced, and the 5C reversible capacity is reduced; example 8 relative to example 1, NH3The flow and the ratio are small, so that nitrogen doping is uneven, the capacity and the first coulombic efficiency are slightly reduced, and the 5C reversible capacity is remarkably degraded.
Comparative example 1 compared with example 1, the inert gas N is used throughout2And CO2The carbonization treatment in the mixed atmosphere of (2) results in an increase in specific surface area, an increase in compaction density, a decrease in capacity, and a significant deterioration in 5C reversible capacity because of excessive formation of porous carbon and no nitrogen doping.
Comparative example 2 compared with example 1, the inert gas N is used throughout2And NH3The carbonization treatment in the mixed atmosphere of (2) is carried out, and since no porous carbon is coated and only N is doped, the compaction density is reduced, and the 5C reversible capacity is remarkably deteriorated.
Comparative example 3 compared to example 1, the secondary carbonization temperature was lower than the primary carbonization temperature, resulting in a decrease in the compacted density and a significant deterioration in the 5C reversible capacity due to insufficient reaction.
Comparison of comparative example 4 with example 1 shows that the temperature of primary carbonization is too low, which results in incomplete decomposition of carbon dioxide into CO, insufficient pore formation, slight decrease in capacity and primary coulombic efficiency, and significant deterioration of 5C reversible capacity.
Comparison of comparative example 5 with example 1 shows that the primary carbonization temperature is too high, the reaction is severe, and pore formation is not uniform, resulting in significant deterioration of the reversible capacity of 5C.
The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (10)
1. The graphite material with the porous carbon layer is characterized by comprising a graphite substrate and the porous carbon layer coated on the surface of the graphite substrate, wherein the graphite substrate and the porous carbon layer are in an integral structure.
2. The graphitic material according to claim 1, wherein said graphite matrix comprises artificial graphite and/or natural graphite;
preferably, the artificial graphite comprises petroleum coke artificial graphite and/or needle coke artificial graphite;
preferably, the porous carbon layer is: carbon dioxide reacts with carbon on the surface layer of the graphite to generate carbon monoxide, and the carbon monoxide overflows from porous carbon formed by pore forming on the surface of the carbon layer of the graphite;
preferably, the thickness of the porous carbon layer is 1nm-20nm, preferably 5nm-15 nm;
preferably, the graphite material has an average particle size of 5 μm to 25 μm;
preferably, the porous carbon layer is a nitrogen-doped porous carbon layer.
3. Method for preparing a graphitic material with a porous carbon layer according to claim 1 or 2, characterized in that it comprises the following steps:
(1) introducing inert gas and CO2Under the mixed atmosphere of (A), carrying out primary carbonization treatment on the graphite raw material, wherein the primary carbonization treatment temperature is T1600-1100 c to yield a graphite material with a porous carbon layer.
4. The method of claim 3, further comprising performing step (2) after step (1): stopping the introduction of CO2In general haveInert gas and NH3Under the mixed atmosphere of (A), performing secondary carbonization treatment on the graphite, wherein the temperature of the secondary carbonization treatment is T2，T2>T1。
5. The process according to claim 3 or 4, wherein the graphite raw material of step (1) comprises artificial graphite and/or natural graphite, preferably the artificial graphite comprises petroleum coke artificial graphite and/or needle coke artificial graphite;
preferably, the average particle size of the graphite raw material in the step (1) is 5-25 μm;
preferably, the specific surface area of the graphite raw material in the step (1) is less than or equal to 5m2/g；
Preferably, the graphite raw material of the step (1) has a 5T compaction density of more than 2.0g/cm3；
Preferably, the graphitization degree of the graphite raw material in the step (1) is more than 90%;
preferably, the inert gas in step (1) is selected from any one of nitrogen, helium, neon, argon, krypton, xenon or radon or a combination of at least two of the same;
preferably, in the mixed atmosphere of step (1), inert gas and CO2The flow rate ratio of (A) is 1:1 to 5:1, preferably 2:1 to 4: 1;
preferably, in step (1), the CO is2At 0.5m3/h-3m3A flow rate of 1m is preferably introduced3/h-2m3/h；
Preferably, the temperature is raised to T1The heating rate is 3-10 ℃/min;
preferably, the constant temperature time of the primary carbonization in the step (1) is 1h-10h, preferably 2-6 h;
preferably, the primary carbonization in the step (1) is performed in a carbonization apparatus including a roller kiln, a pusher kiln, a rotary kiln and a box furnace.
6. The method according to claim 4 or 5, wherein the inert gas and NH are mixed in the mixed atmosphere in the step (2)3The flow rate ratio of (1: 1) to (5: 1),preferably 2:1 to 4: 1;
preferably, in step (2), the NH is3At 0.5m3/h-5m3A flow rate of 1m is preferably introduced3/h-3m3/h；
Preferably, in step (2), T2700-1300 ℃;
preferably, from T1Heating to T2The heating rate is 3-10 ℃/min, preferably 3-5 ℃/min;
preferably, the time for the secondary carbonization in the step (2) is 1h-6h, preferably 2h-4 h.
Preferably, the inert gas in step (2) is selected from any one of nitrogen, helium, neon, argon, krypton, xenon or radon or a combination of at least two of the same;
preferably, the secondary carbonization in the step (2) is performed in a carbonization apparatus including a roller kiln, a pusher kiln, a rotary kiln and a box furnace.
7. The method according to any one of claims 4 to 6, further comprising the step of cooling and sieving after the secondary carbonization treatment.
8. A method according to claim 3, characterized in that the method comprises the steps of:
(1) in N2Placing graphite raw material in carbonization equipment under the atmosphere, introducing CO2Heating to 600-1100 deg.C at a rate of 3-10 deg.C/min, and CO2The flow rate is 0.5m3/h-3m3/h，N2And CO2The flow rate ratio of (1: 1) - (5: 1), keeping the temperature for 1-10 h, and then stopping introducing CO2；
(2) Continuously introducing N2After introduction of NH3Heating to 700-1300 ℃ at the speed of 3-10 ℃/min under the condition of (1), and NH3The flow rate is 0.5m3/h-5m3/h，N2And NH3The flow rate ratio of the graphite material is 1:1-5:1, the temperature is kept for 1-6 h, and the graphite material is obtained after cooling and screening;
the graphite raw material is artificial graphite and/or natural graphite, the average particle size of the graphite raw material is 5-25 mu m, and the specific surface area is less than or equal to 5m2(ii)/g, compacted density > 0.8g/cm3The graphitization degree is more than 90 percent.
9. An anode, characterized in that it comprises a graphite material having a porous carbon layer as claimed in claim 1 or 2.
10. A lithium ion battery, characterized in that it comprises the negative electrode of claim 9.
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