CN114180568B - Pretreated microcrystalline graphite, negative electrode active material, and preparation and application thereof - Google Patents
Pretreated microcrystalline graphite, negative electrode active material, and preparation and application thereof Download PDFInfo
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- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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Abstract
The invention belongs to a battery cathode material, and particularly relates to a pretreatment method of microcrystalline graphite, which comprises the steps of carrying out first-stage roasting on the microcrystalline graphite in an ammonia-containing atmosphere in advance, and then carrying out second-stage roasting in a magnesium-containing steam atmosphere to obtain the pretreated microcrystalline graphite; the temperature of the first stage roasting is more than or equal to 300 ℃, and the temperature of the second stage roasting is more than or equal to 600 ℃. The invention also comprises the application of the prepared pretreated microcrystalline graphite in preparing a negative electrode material. The research of the invention finds that the cooperation can be realized by innovatively carrying out the first stage gas-solid reaction in the ammonia gas atmosphere in advance and further matching with the subsequent second stage gas-solid reaction of magnesium steam, the layer expansion and the physical structure and chemical phase adjustment can be carried out on the microcrystalline graphite, and the electrochemical performance of the pretreated microcrystalline graphite can be improved.
Description
Technical Field
The invention belongs to the technical field of battery cathode materials, and particularly relates to the technical field of alkali metal secondary battery cathode materials.
Background
The microcrystalline graphite is rich in mineral products in China, and is a graphite cathode material with great application potential. The microcrystalline graphite is used as the cathode material of the lithium ion battery, and has the advantages of low raw material price, good compatibility with electrolyte, stable cycle performance and good rate capability. However, the impurity content of the natural microcrystalline graphite is high, the crystal form of the natural microcrystalline graphite is not a complete graphite structure, the graphitization degree is low, and the initial coulomb efficiency of the natural microcrystalline graphite is low due to an amorphous structure. Therefore, if the microcrystalline graphite is modified by a simple and effective means to comprehensively improve the first coulombic efficiency, reversible specific capacity and cycle life of the microcrystalline graphite, the method has great significance for expanding the market of the natural graphite of the lithium ion battery.
Aiming at the purification research of natural microcrystalline graphite, a mixed acid process is mainly adopted at present, but because the microcrystalline graphite is a naturally formed ore, metal and non-metal impurities in the structure of the microcrystalline graphite are difficult to remove, so that the problems of common purification effect and large acid consumption exist in the conventional mixed acid purification process. Although the conventional high-temperature graphitization operation higher than 2800 ℃ can realize great improvement of purity and graphitization degree, the conventional high-temperature graphitization operation has the problem of high energy consumption.
Disclosure of Invention
Aiming at the defects of the prior art, the method for pretreating the microcrystalline graphite aims at realizing high-value utilization of the microcrystalline graphite.
The second purpose of the invention is to provide the pretreated microcrystalline graphite prepared by the method and the application of the pretreated microcrystalline graphite in preparing a negative electrode active material.
The third purpose of the invention is to provide a preparation method of the microcrystalline graphite negative active material, aiming at preparing the negative active material with high specific capacity, long cycle life and good rate capability.
The fourth purpose of the invention is to provide the microcrystalline graphite negative electrode active material prepared by the preparation method and the application of the microcrystalline graphite negative electrode active material in an alkali metal battery.
The fifth object of the present invention is to provide an alkali metal battery equipped with the microcrystalline graphite negative electrode active material, and a negative electrode sheet and other parts thereof.
A method for pretreating microcrystalline graphite comprises the steps of carrying out first-stage roasting on microcrystalline graphite in an ammonia-containing atmosphere in advance, and then carrying out second-stage roasting in a magnesium-containing steam atmosphere to obtain pretreated microcrystalline graphite;
the temperature of the first stage roasting is more than or equal to 300 ℃, and the temperature of the second stage roasting is more than or equal to 600 ℃.
The research of the invention finds that the cooperation can be realized by innovatively carrying out the first stage gas-solid reaction in the ammonia gas atmosphere in advance and further matching with the subsequent second stage gas-solid reaction of magnesium steam, the layer expansion and the physical structure and chemical phase adjustment can be carried out on the microcrystalline graphite, and the electrochemical performance of the pretreated microcrystalline graphite can be improved.
In the present invention, the raw material of the microcrystalline graphite may be natural and/or recycled waste, and the median particle size thereof is not particularly limited, and may be, for example, 12 to 15 μm.
In the invention, the combined control of the two-stage gas-solid treatment and the treatment sequence is the key for synergistically improving the performance of the pretreated microcrystalline graphite.
According to the invention, the structure and performance can be expanded, activated, hybridized and adjusted in physical and chemical structures through the first stage gas-solid reaction of ammonia gas in advance, so that the combined cooperation with the subsequent second stage gas-solid reaction of magnesium vapor is facilitated, and the electrochemical performance of the pretreated microcrystalline graphite is improved.
The ammonia-containing atmosphere in the invention is pure ammonia gas or the mixed gas of ammonia gas and protective gas;
preferably, in the ammonia-containing atmosphere, the volume content of ammonia is not particularly required, and for example, can be greater than or equal to 50%; preferably 50 to 90vol%;
preferably, the temperature of the first stage roasting is 300-600 ℃; further preferably 400 to 500 ℃;
preferably, the time of the first stage roasting is 1 to 3 hours.
Preferably, after the first-stage roasting treatment, the reaction system is subjected to gas washing treatment by using protective gas, the temperature is raised to the second-stage roasting temperature, and the second-stage roasting treatment is performed after magnesium-containing steam atmosphere is introduced. The protective gas is, for example, nitrogen or inert gas. The washing gas is used for replacing ammonia in the first stage roasting treatment system.
In the invention, after the first-stage gas-solid reaction of ammonia gas, the ammonia gas is further cooperated with the second-stage gas-solid reaction of magnesium steam, which is beneficial to adjusting the phase of impurity silicon and making the impurity silicon nanocrystallized, is beneficial to local graphitization and improves the crystallization performance; the performance of the pretreated microcrystalline graphite can be synergistically improved through the combination of the two-stage gas-solid reaction and the treatment sequence.
The magnesium vapor in the invention can be prepared outside the device and then is introduced into the second-stage roasting system.
In the invention, the magnesium-containing vapor atmosphere is a mixed gas of magnesium vapor and protective gas;
preferably, in the magnesium-containing vapor atmosphere, the volume content of magnesium vapor is not particularly required, and may be, for example, 50% or more; preferably 50 to 90 percent;
preferably, the temperature of the second stage roasting treatment is 600-750 ℃; preferably 650 to 700 ℃;
preferably, the time of the second stage roasting is 4-8 h.
The invention also provides the pretreated microcrystalline graphite prepared by the pretreatment method.
In the present invention, the treated microcrystalline graphite can be given a special microstructure and chemical structure by the sequential two-stage gas-solid reaction, and can be given good electrochemical performance.
The invention also provides application of the pretreated microcrystalline graphite, and the pretreated microcrystalline graphite is used for preparing a negative electrode active material.
The invention also provides a preparation method of the microcrystalline graphite cathode active material, which comprises the steps of carrying out liquid phase negative pressure treatment on the pretreated microcrystalline graphite, a carbon source and a transition metal source, drying to obtain a precursor, carrying out secondary calcination treatment on the precursor, washing and drying to obtain the microcrystalline graphite cathode active material;
the two-stage calcining treatment comprises a first-stage calcining treatment and a second-stage vacuum calcining treatment.
The research of the invention finds that on the basis of the sequential two-stage gas-solid pretreatment, the negative pressure liquid phase treatment and the subsequent two-stage calcination treatment are further matched, so that the electrochemical performance of the prepared cathode active material can be further improved in a synergistic manner.
The carbon source is not particularly required, for example, the carbon source is one or more of asphalt, phenolic resin, polypropylene, polyacrylonitrile, polypyrrole, glucose, sucrose, polylactic acid and nylon;
preferably, the mass ratio of the pretreated microcrystalline graphite to the carbon source is 100:5 to 20;
preferably, the transition metal source is a water-soluble salt of a transition metal element, preferably one or more of chloride, nitrate and oxalate of iron, cobalt and nickel;
preferably, the mass ratio of the pretreated microcrystalline graphite to the transition metal source is 100:5 to 15;
preferably, the solvent in the liquid phase negative pressure system is water or a mixed solvent of water and an organic solvent, and the organic solvent is preferably at least one of C1-C4 alcohol and toluene;
preferably, in the liquid phase negative pressure system, the solid-liquid ratio is not particularly required, and may be, for example, 1: 3-10 g/ml;
preferably, the negative pressure of the liquid phase negative pressure treatment stage is less than or equal to 500Pa, preferably 10-300 Pa;
the negative pressure liquid phase treatment process can be carried out in a conventional vacuum stirring kettle, and drying treatment is carried out after uniform stirring, wherein the drying treatment can be static drying by placing the material in an oven, or rapid desolventizing by operations such as spray drying, freeze drying and the like to obtain the precursor;
preferably, the atmosphere of the first stage calcination is a protective atmosphere, preferably one or more of hydrogen, argon, nitrogen and helium;
preferably, the temperature of the first stage calcination is 350-500 ℃;
preferably, the time of the first stage calcination is 2 to 4 hours;
preferably, the negative pressure of the second stage calcination is 10-200 Pa;
preferably, the temperature of the second stage calcination is 850-1000 ℃;
preferably, the time of the second stage calcination is 2 to 6 hours;
preferably, the product of the second stage calcination is subjected to acid washing, water washing, drying, crushing and screening to obtain the microcrystalline graphite negative electrode active material.
The invention discloses a preparation method of a preferable microcrystalline graphite negative electrode active material, which comprises the following steps:
step (1): heating the natural microcrystalline graphite to a first stage roasting temperature, and introducing ammonia gas for a certain time; the ammonia gas in the step (1) can also contain at least one of inert gases such as nitrogen, argon, helium and the like; preferably, the content of ammonia gas in the atmosphere is 50-90 vol%. The ammonia gas treatment temperature is 300-600 ℃; the temperature is preferably 400-500 ℃; the roasting time in the ammonia atmosphere is 1-3 h.
Step (2): heating the natural microcrystalline graphite to a second-stage roasting temperature, and introducing magnesium vapor for certain time; in the atmosphere, the content of magnesium vapor gas is 50-90 vol%. The magnesium vapor treatment temperature is 600-750 ℃; the temperature is preferably 650-700 ℃; the magnesium vapor treatment time is 4-8 h.
And (3): uniformly stirring the microcrystalline graphite material, the carbon source precursor, the transition metal salt and the solvent obtained in the previous step under a negative pressure condition, and drying to obtain mixed powder; the carbon source precursor in the step (3) can be one or more of asphalt, phenolic resin, polypropylene, polyacrylonitrile, polypyrrole, glucose, sucrose, polylactic acid, nylon and the like, and the mass ratio of the dry microcrystalline graphite material to the carbon source precursor is 100:5 to 20; the transition metal salt is one or more of chloride, nitrate, oxalate and the like of iron, cobalt and nickel, and the mass ratio of the dry microcrystalline graphite material to the transition metal salt is 100:5 to 15 percent; the solvent is a liquid substance capable of dissolving the transition metal salt, and can be water or a mixed solution of water and organic matters such as alcohol, toluene and the like; in the system (microcrystalline graphite, carbon source, transition metal salt and solvent), the solid-to-liquid ratio (g/ml) is 1:3 to 10.
And (4): carrying out secondary heat treatment on the dried powder; wherein, the temperature is increased to 350-450 ℃ at the heating rate of 5-10 ℃/min in advance, and then the temperature is preserved for 2-4 h, and the heat treatment atmosphere is one or more of hydrogen, argon, nitrogen and helium; then the system is vacuumized to maintain the vacuum degree of the system at 10-200 Pa, and then the system is heated to 850-1000 ℃ by program, treated for 2-6 h under the condition of negative pressure and then naturally cooled.
And (5): and performing conventional acid cleaning and purification, solid-liquid separation, slurry washing and drying on the powder after heat treatment, and then performing conventional material scattering and screening to finally obtain the high-performance natural microcrystalline graphite negative electrode material. The vacuum heat treatment operation in the step (4) is to place the mixed powder in an atmosphere furnace, and the purification treatment in the step (5) is to place the powder obtained after the heat treatment in conventional inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid, wherein the solid-to-liquid ratio (g/ml) is 1-3: 10, the stirring temperature is 30-80 ℃, and the stirring reaction time is 2-6 h. And after the reaction is finished, carrying out conventional solid-liquid separation, slurry washing, drying, crushing and screening to obtain the high-performance microcrystalline graphite cathode material.
In the prior art, natural microcrystalline graphite is usually purified by a mixed acid method or a high-temperature heat treatment method, but the method has high energy consumption and large consumption of acid and water; and because the natural microcrystalline graphite is a naturally formed ore, impurity elements in the structure of the natural microcrystalline graphite are difficult to completely remove, so that the purification efficiency is not high and the purification cost is high. Therefore, the invention provides the preparation method, which adopts ammonia gas for gas-solid pretreatment in an innovative way, so that the layer expansion and the pore forming can be realized; the interlayer of the microcrystalline graphite subjected to layer expansion and porosification is fully opened, the porous structure is more favorable for the diffusion of magnesium vapor, then magnesium vapor treatment is carried out at a certain temperature, and silicon oxide contained in the interlayer is reduced and nanocrystallized to obtain superfine nano silicon particles; and magnesium can catalyze and graphitize the microcrystalline graphite to a certain degree, so that the crystallization performance of the microcrystalline graphite is improved. And then, matching with subsequent negative pressure liquid phase treatment and two sections of calcining treatment, promoting the formation of local graphitized carbon and high-conductivity carbon nano tubes so as to synergistically promote the specific capacity and the large-current charge-discharge performance of the microcrystalline graphite. Thus, the natural microcrystalline graphite negative electrode active material which has high specific capacity, good cycling stability and can be charged and discharged greatly can be obtained unexpectedly.
The technical scheme of the invention also provides the microcrystalline graphite cathode active material prepared by the preparation method, which has a microcrystalline graphite, local graphitized carbon, carbon nano-tube and silicon composite structure, wherein the microcrystalline graphite is an inner core and is composed of high-crystallinity few-layer graphene, and a superfine nano-silicon crystal grain structure is arranged between graphene layers; the microcrystalline graphite is represented as hierarchical holes, and abundant carbon nano tube structures and local graphitized carbon structures are distributed in the holes; the surface of the microcrystalline graphite is adhered with a local graphitized carbon layer structure. The research of the invention discovers that the natural microcrystalline graphite material has the advantages of good specific capacity and rate capability, long cycle life and the like.
The natural microcrystalline graphite cathode material contains 92-99.5% of carbon and also contains silicon.
The invention also provides application of the microcrystalline graphite negative active material prepared by the preparation method, and the microcrystalline graphite negative active material is used as a negative active material of an alkali metal secondary battery.
The composite material is preferably applied as a negative electrode active material and is compounded with a conductive agent and a binder to prepare a negative electrode material. The conductive agent and the binder are all materials known in the industry.
In a further preferable application, the negative electrode material is arranged on the surface of a negative electrode current collector and used for preparing a negative electrode. The negative electrode may be formed by applying the negative electrode material of the present invention to a current collector by a conventional method, for example, by a coating method. The current collector is any material known in the industry.
In a further preferred application, the negative electrode, the positive electrode, the separator and the electrolyte are assembled into an alkali metal secondary battery.
In the present invention, the alkali metal secondary battery is a lithium secondary battery and/or a sodium secondary battery.
The negative electrode of the alkali metal secondary battery comprises a current collector and a negative electrode material compounded on the surface of the current collector, wherein the negative electrode material contains the microcrystalline graphite negative electrode active material prepared by the preparation method.
The invention also provides an alkali metal secondary battery comprising the cathode.
In the present invention, the alkali metal secondary battery may have conventional components and components except for the negative electrode of the present invention.
Has the advantages that:
(1) The research of the invention finds that the cooperation can be realized by innovatively carrying out the first stage gas-solid reaction in the ammonia gas atmosphere in advance and further matching with the subsequent second stage gas-solid reaction of magnesium steam, the layer expansion, the physical structure adjustment and the chemical property adjustment can be carried out on the microcrystalline graphite, and the electrochemical performance of the pretreated microcrystalline graphite can be unexpectedly improved.
(2): under the two-stage gas-solid pretreatment, the subsequent vacuum liquid phase treatment and the two-stage calcination treatment are further matched, so that the synergy can be further realized, and the material with a special structure and excellent electrochemical performance can be further improved.
(3): the invention has the advantages of low cost of raw materials, wide sources, mild and convenient operation conditions, easy realization of large-scale production and good practical prospect.
(4) The method has the greatest advantage of realizing high-quality utilization of the natural microcrystalline graphite.
Drawings
FIG. 1 is an SEM image of a sample after ammonia gas treatment in example 1.
FIG. 2 is an SEM image of a sample after magnesium vapor treatment in example 1.
FIG. 3 is an XRD pattern of the final sample obtained in example 1.
FIG. 4 is an SEM photograph of the final sample obtained in example 1.
FIG. 5 is a TEM image of the final sample obtained in example 1.
Detailed Description
The specific procedures of the present invention are illustrated below by way of examples, it being understood that these examples are only illustrative of the present invention and do not limit the scope of the invention in any way. Various procedures and methods not described in detail herein are conventional methods well known in the art.
Example 1
Step (1): placing natural microcrystalline graphite (D50 =13 μm) in an atmosphere furnace, heating to 400 deg.C (first stage calcination temperature) at 5 deg.C/min, introducing 200ml/min ammonia-containing atmosphere (80 vol, the balance being argon), keeping the temperature for 2h under the condition, changing the atmosphere to 400ml/min argon, heating to 650 deg.C (second stage calcination temperature) at 5 deg.C/min, introducing 50ml/min magnesium-containing vapor atmosphere (80 vol, the balance being argon), keeping the temperature for 5h at the temperature, and naturally cooling.
Step (2): and (3) mixing the cooled material, polyacrylonitrile and ferric nitrate according to the mass ratio of 100:10:10 (liquid-solid ratio: 10: 2ml/g), stirring uniformly under the condition of negative pressure (100 Pa), and removing the solvent by spray drying to obtain dry powder (precursor);
and (3): and (3) placing the obtained dry powder (precursor) in an atmosphere furnace, heating to 400 ℃ (the first stage calcination temperature) at a heating rate of 5 ℃/min under the protection of argon atmosphere, preserving heat for 3h, vacuumizing to maintain the vacuum degree of the system at 100Pa, heating to 900 ℃ (the second stage vacuum calcination temperature) at a heating rate of 10 ℃/min, preserving heat for 4h under the condition, and naturally cooling to room temperature.
And (4): placing the powder obtained by heat treatment in 0.2M hydrochloric acid aqueous solution, and mixing the solution at a solid-to-liquid ratio of 1:10 stirring for 2h at 40 ℃, filtering, washing the solid to be neutral, drying and scattering.
According to GB/T243358-2009, the graphite electrode is taken as a working electrode, metal lithium is taken as a negative electrode, and 1mol/L LiPF 6 The EC/EMC (volume ratio is 1; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio is 5C/0.2C =90.2%.
Example 2
Compared with the example 1, the difference is only that the content of the ammonia gas containing atmosphere is 90vol%, the temperature of the first stage roasting is 600 ℃, and the holding time is 1.5h. The other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection on the obtained material in a voltage range of 0.001-2.0V at room temperature, wherein when the charge-discharge test current density is 0.2C, the first reversible capacity is 542mAh/g, and the capacity retention rate is 87% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio is 5C/0.2C =91.1%.
Example 3
Compared with the example 1, the difference is only that the content of the ammonia gas-containing atmosphere is 50vol%, the temperature of the first stage roasting is 350 ℃, and the holding time is 3h. The other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection on the obtained material in a voltage range of 0.001-2.0V at room temperature, wherein when the current density of charge-discharge test is 0.2C, the first reversible capacity is 508mAh/g, and the capacity retention rate is 89% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio is 5C/0.2C =90%.
Example 4
The only difference from example 1 is that the content of magnesium-containing vapor atmosphere was 90vol%, the temperature of the second stage firing was 650 ℃ and the holding time was 5 hours. The other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection on the obtained material in a voltage range of 0.001-2.0V at room temperature, wherein when the current density of charge-discharge test is 0.2C, the first reversible capacity is 559mAh/g, and the capacity retention rate is 89% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio is 5C/0.2C=92%.
Example 5
The only difference from example 1 is that the content of the magnesium-containing vapor atmosphere was 50vol%, the temperature of the second-stage calcination was 700 ℃ and the holding time was 7 hours. The other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection on the obtained material in a voltage range of 0.001-2.0V at room temperature, wherein when the current density of charge-discharge test is 0.2C, the first reversible capacity is 501mAh/g, and the capacity retention rate is 91% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the rate capacity ratio is 5C/0.2C=92.5%.
Example 6
Compared with the embodiment 1, the difference is that in the vacuum mixing, the mass ratio of the cooled material, polyacrylonitrile and ferric nitrate is 100:20:10. the other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection in a voltage range of 0.001-2.0V at room temperature, wherein when the current density of the charge-discharge test is 0.2C, the first reversible capacity is 518mAh/g, and the capacity retention rate is 89% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio is 5C/0.2C =90.5%.
Example 7
Compared with the embodiment 1, the difference is that in the vacuum mixing, the mass ratio of the cooled material, polyacrylonitrile and ferric nitrate is 100:5:10. the other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection in a voltage range of 0.001-2.0V at room temperature, wherein when the charge-discharge test current density is 0.2C, the first reversible capacity is 548mAh/g, and the capacity retention rate is 87% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio is 5C/0.2C =90%.
Example 8
Compared with the example 1, the difference is only that in the step (3), the temperature of the first stage calcination is 500 ℃, and the holding time is 2 hours; the vacuum degree of the second stage vacuum calcination stage is 200Pa, the temperature is 1000 ℃, and the heat preservation time is 3h. The other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection in a voltage range of 0.001-2.0V at room temperature, wherein when the current density of the charge-discharge test is 0.2C, the first reversible capacity is 518mAh/g, and the capacity retention rate is 89% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the rate capacity ratio is 5C/0.2C=92.1%.
Example 9
Compared with the example 1, the difference is only that in the step (3), the temperature of the first stage of calcination is 350 ℃, and the holding time is 4h; the vacuum degree of the second stage vacuum calcination stage is 20Pa, the temperature is 850 ℃, and the heat preservation time is 5h. The other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection in a voltage range of 0.001-2.0V at room temperature, wherein when the current density of the charge and discharge test is 0.2C, the first reversible capacity is 529mAh/g, and the capacity retention rate is 87% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio is 5C/0.2C =90.1%.
Comparative example 1: treatment without introducing ammonia gas
The only difference compared with example 1 is that the first stage of calcination in step (1) is not fed with ammonia gas, but with a conventional inert gas (Ar). The distinguishing step (1) is as follows: placing natural microcrystalline graphite in an atmosphere furnace, heating to 400 ℃ (the first stage roasting temperature) at 5 ℃/min, introducing 200ml/min argon, keeping the temperature for 2h, changing the atmosphere to 400ml/min argon, heating to 650 ℃ (the second stage roasting temperature) at 5 ℃/min, introducing 50ml/min magnesium-containing steam atmosphere (80 vol, the balance being argon), keeping the temperature for 5h, and naturally cooling. The other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection in a voltage range of 0.001-2.0V at room temperature, wherein when the charge-discharge test current density is 0.2C, the first reversible capacity is 238mAh/g, and the capacity retention rate is 67% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio is 5C/0.2C =42.5%.
Comparative example 2: treatment with magnesium vapor
The only difference compared to example 1 is that the second stage of calcination does not involve the introduction of magnesium vapour, but instead uses a conventional inert gas (Ar). The distinguishing step (1) is as follows: placing natural microcrystalline graphite in an atmosphere furnace, heating to 400 ℃ (the first stage roasting temperature) at 5 ℃/min, introducing 200ml/min ammonia-containing atmosphere (80 vol%, the balance being argon), keeping the temperature for 2h under the condition, changing the atmosphere into 400ml/min argon, heating to 650 ℃ (the second stage roasting temperature) at 5 ℃/min, introducing 50ml/min argon, keeping the temperature for 5h at the temperature, and naturally cooling. The other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection in a voltage range of 0.001-2.0V at room temperature, wherein when the current density of the charge and discharge test is 0.2C, the first reversible capacity is 221mAh/g, and the capacity retention rate is 65% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying factor capacity ratio is 5C/0.2C =41.4%.
Comparative example 3: firstly carrying out magnesium steam first-stage heat treatment and then carrying out ammonia second-stage heat treatment
The only difference compared with example 1 is that the first stage calcination with magnesium vapour is carried out first, followed by the second stage calcination with ammonia. The distinguishing step (1) is as follows: step (1): placing natural microcrystalline graphite in an atmosphere furnace, heating to 650 deg.C at 5 deg.C/min, introducing 50ml/min magnesium-containing vapor atmosphere (80 vol, the balance being argon), maintaining the temperature for 5h, changing to 400ml/min argon, cooling to 400 deg.C, changing to 200ml/min ammonia-containing atmosphere (80 vol, the balance being argon), maintaining the temperature for 2h, and naturally cooling. The other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection in a voltage range of 0.001-2.0V at room temperature, wherein when the charge-discharge test current density is 0.2C, the first reversible capacity is 341mAh/g, and the capacity retention rate is 59% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the rate capacity ratio is 5C/0.2C =47.2%.
Comparative example 4: without vacuum mixing
The only difference compared to example 1 is that in step (2), the liquid phase treatment was not carried out at a negative pressure. The distinguishing step (2) is as follows: and (3) mixing the cooled material, polyacrylonitrile and ferric nitrate according to the mass ratio of 100:10:10 (liquid-solid ratio: 10: 2ml/g), stirring uniformly under normal pressure, and removing the solvent by spray drying to obtain dry powder (precursor); the other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection in a voltage range of 0.001-2.0V at room temperature, wherein when the current density of the charge-discharge test is 0.2C, the first reversible capacity is 321mAh/g, and the capacity retention rate is 57% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the rate capacity ratio is 5C/0.2C =48.9%.
Comparative example 5: instead of vacuum heat treatment, atmospheric heat treatment is used
The only difference compared with example 1 is that the second stage of calcination treatment in step (3) is not carried out under vacuum, but instead is an atmospheric heat treatment. The distinguishing step (3) is as follows: and (3) placing the obtained dry powder in an atmosphere furnace, heating to 400 ℃ (the first-stage calcination temperature) at a heating rate of 5 ℃/min under the protection of argon atmosphere, preserving heat for 3h, heating to 900 ℃ (the second-stage vacuum calcination temperature) at a heating rate of 10 ℃/min, preserving heat for 4h under the condition, and naturally cooling to room temperature. The other procedures, conditions and electrochemical measurement methods were the same as those in example 1.
Performing electrochemical performance detection in a voltage range of 0.001-2.0V at room temperature, wherein when the current density of the charge-discharge test is 0.2C, the first reversible capacity is 330mAh/g, and the capacity retention rate is 56.8% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio is 5C/0.2C=50.1%.
Claims (41)
1. The pretreatment method of the microcrystalline graphite is characterized in that the microcrystalline graphite is subjected to first-stage roasting in an ammonia-containing atmosphere in advance, and then subjected to second-stage roasting in a magnesium-containing steam atmosphere to obtain the pretreated microcrystalline graphite;
the temperature of the first stage roasting is more than or equal to 300 ℃, and the temperature of the second stage roasting is more than or equal to 600 ℃.
2. The method for pretreating microcrystalline graphite according to claim 1, wherein the ammonia gas-containing atmosphere is pure ammonia gas or a mixed gas of ammonia gas and a shielding gas.
3. The method for pretreating microcrystalline graphite according to claim 2, wherein the ammonia gas is contained in an atmosphere containing ammonia gas in an amount of 50% by volume or more.
4. The pretreatment method of microcrystalline graphite according to claim 3, wherein the volume content of ammonia in the ammonia-containing atmosphere is 50 to 90vol%.
5. The pretreatment method of microcrystalline graphite according to claim 1, wherein the temperature of the first stage baking is 300 to 600 ℃.
6. The pretreatment method of microcrystalline graphite according to claim 5, wherein the temperature of the first stage baking is 400 to 500 ℃.
7. The pretreatment method of microcrystalline graphite as claimed in claim 1, wherein the first baking time is 1 to 3 hours.
8. The method for pretreating microcrystalline graphite according to claim 1, wherein the atmosphere containing magnesium vapor is a mixed gas of magnesium vapor and a shielding gas.
9. The method for pretreating microcrystalline graphite according to claim 8, wherein the magnesium vapor is contained in an atmosphere containing magnesium in an amount of 50% by volume or more.
10. The pretreatment method of microcrystalline graphite according to claim 9, wherein the volume content of magnesium vapor in the magnesium-containing vapor atmosphere is 50 to 90%.
11. The method for pretreating microcrystalline graphite according to claim 1, wherein the temperature of the second baking treatment is 600 to 750 ℃.
12. The method for pretreating microcrystalline graphite according to claim 1, wherein the temperature of the second-stage baking treatment is 650 to 700 ℃.
13. The method for pretreating microcrystalline graphite as claimed in claim 1, wherein the second-stage roasting time is 4 to 8h.
14. The method for pretreating microcrystalline graphite according to claim 1, wherein after the first-stage calcination, the reaction system is subjected to a gas washing treatment with a shielding gas, and the temperature is raised to the second-stage calcination temperature, and then a magnesium-containing vapor atmosphere is introduced to carry out the second-stage calcination treatment.
15. A pretreated microcrystalline graphite prepared by the pretreatment method of any one of claims 1 to 14.
16. A preparation method of a microcrystalline graphite cathode active material is characterized in that the pretreated microcrystalline graphite, a carbon source and a transition metal source in the claim 15 are subjected to liquid phase negative pressure treatment, then dried to obtain a precursor, the precursor is subjected to secondary calcination treatment, and then washed and dried to obtain the microcrystalline graphite cathode active material;
the second-stage calcining treatment comprises a first-stage calcining treatment and a second-stage vacuum calcining treatment.
17. The preparation method of the microcrystalline graphite negative electrode active material of claim 16, wherein the carbon source is one or more of asphalt, phenolic resin, polypropylene, polyacrylonitrile, polypyrrole, glucose, sucrose, polylactic acid and nylon.
18. The method for preparing the microcrystalline graphite negative electrode active material as claimed in claim 16, wherein the mass ratio of the pretreated microcrystalline graphite to the carbon source is 100:5 to 20.
19. The method of preparing a microcrystalline graphite anode active material according to claim 16, wherein the transition metal source is a water-soluble salt of a transition metal element.
20. The method for preparing the microcrystalline graphite negative electrode active material according to claim 19, wherein the transition metal source is one or more of chloride, nitrate and oxalate of iron, cobalt and nickel.
21. The method for preparing the microcrystalline graphite negative electrode active material according to claim 16, wherein the mass ratio of the pretreated microcrystalline graphite to the transition metal source is 100:5 to 15.
22. The method for preparing a microcrystalline graphite negative electrode active material according to claim 16, wherein the solvent in the liquid-phase negative pressure system is water or a mixed solvent of water and an organic solvent.
23. The preparation method of the microcrystalline graphite anode active material, according to claim 22, wherein the organic solvent is at least one of C1-C4 alcohol and toluene.
24. The method for preparing a microcrystalline graphite negative electrode active material according to claim 16, wherein the negative pressure in the liquid phase negative pressure treatment stage is 500Pa or less.
25. The preparation method of the microcrystalline graphite negative electrode active material as claimed in claim 24, wherein the negative pressure in the liquid phase negative pressure treatment stage is 10 to 300Pa.
26. The method for preparing the microcrystalline graphite negative electrode active material according to claim 16, wherein the precursor is obtained by freeze drying or spray drying after liquid phase negative pressure treatment.
27. The method for preparing a microcrystalline graphite anode active material according to claim 16, wherein the atmosphere of the first stage calcination is a protective atmosphere.
28. The method for preparing the microcrystalline graphite negative electrode active material according to claim 27, wherein the atmosphere of the first stage calcination is one or more of hydrogen, argon, nitrogen and helium.
29. The preparation method of the microcrystalline graphite negative electrode active material as claimed in claim 16, wherein the temperature of the first-stage calcination is 350 to 500 ℃.
30. The preparation method of the microcrystalline graphite negative electrode active material as claimed in claim 16, wherein the time for the first stage of calcination is 2 to 4 hours.
31. The preparation method of the microcrystalline graphite anode active material as claimed in claim 16, wherein the negative pressure of the second stage of calcination is 10 to 200Pa.
32. The method for preparing the microcrystalline graphite negative electrode active material as claimed in claim 16, wherein the temperature of the second calcination is 850 to 1000 ℃.
33. The method for preparing a microcrystalline graphite anode active material according to claim 16, wherein the time of the second calcination is 2 to 6h.
34. The method for preparing a microcrystalline graphite negative electrode active material according to claim 16, wherein the microcrystalline graphite negative electrode active material is prepared by subjecting the product of the second stage calcination to acid washing, water washing, and subsequent drying, crushing, and sieving.
35. A microcrystalline graphite negative electrode active material prepared by the preparation method of any one of claims 16 to 34.
36. Use of the microcrystalline graphite negative electrode active material according to claim 35 as a negative electrode active material for an alkali metal secondary battery.
37. Use of the microcrystalline graphite negative electrode active material according to claim 36 as a negative electrode active material for the preparation of a negative electrode for an alkali metal secondary battery.
38. The use of microcrystalline graphite negative electrode active material according to claim 36, wherein said negative electrode is used to prepare an alkali metal secondary battery.
39. Use of a microcrystalline graphite negative electrode active material according to claim 35, wherein the alkali secondary battery is a lithium secondary battery and/or a sodium secondary battery.
40. An alkali metal secondary battery negative electrode comprises a current collector and a negative electrode material compounded on the surface of the current collector, and is characterized in that the negative electrode material contains the microcrystalline graphite negative electrode active material prepared by the preparation method of any one of claims 16 to 34.
41. An alkali metal secondary battery comprising the negative electrode according to claim 40.
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