CN114261962A - Nitrogen-doped graphite composite negative electrode material, preparation method thereof and lithium ion battery - Google Patents
Nitrogen-doped graphite composite negative electrode material, preparation method thereof and lithium ion battery Download PDFInfo
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Abstract
The invention discloses a nitrogen-doped graphite composite negative electrode material, a preparation method thereof and a lithium ion battery. The preparation method of the nitrogen-doped graphite composite negative electrode material comprises the steps of adding soluble zinc salt into graphite, and uniformly stirring to obtain a first mixed solution; adding the 2-methylimidazole solution into the first mixed solution, and stirring until the reaction is complete to obtain a second mixed solution; carrying out suction filtration, cleaning and drying on the second mixed solution to obtain a 2-methylimidazole zinc salt coated graphite core-shell structure material; placing the prepared 2-methylimidazole zinc salt coated graphite core-shell structure material in inert atmosphereAnd (4) processing to obtain the nitrogen-doped graphite composite negative electrode material. The preparation method is simple and reasonable, the distance between the prepared nitrogen-doped graphite composite negative electrode material layers is increased, and Li can be effectively improved+Transport process dynamics of avoiding Li+And the graphite is accumulated and precipitated on the surface of the graphite. The lithium ion battery containing the negative electrode material has good lithium intercalation capability, good rapid charge and discharge capability and good high-rate charge and discharge performance.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a nitrogen-doped graphite composite negative electrode material, a preparation method thereof and a lithium ion battery.
Background
Lithium ion batteries have become more and more widely used in daily production and life due to their significant advantages of high energy density, long cycle life, and the like. Graphite materials are basically adopted as negative electrode materials in the current lithium ion battery market, and the graphite has a layered structure with good conductivity, high crystallinity and good performance. The graphite is used as the cathode material of the existing common lithium ion battery, and has the advantages of low charge and discharge voltage platform, high cycle stability, low cost and the like.
However, in the conventional graphite cathode material in the prior art, the lattice interlayer spacing of graphite is only 0.337nm, and the interlayer spacing is small, so that Li in the lithium intercalation process+The transport process dynamics is slow, and the lithium ion battery using the graphite cathode material has longer charging time and influenceThe customer experience of use. Meanwhile, in the process of high-rate charge and discharge of the conventional graphite cathode material, a large amount of Li+Flows from the positive electrode into the negative electrode surface through the electrolyte, and due to Li+Transport processes in conventional graphite negative electrode materials are slow in kinetics and are prone to build up and form lithium dendrites on the particle surface, thereby posing a safety risk.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a nitrogen-doped graphite composite negative electrode material, a preparation method thereof and a lithium ion battery, so that the quick charge performance of a graphite negative electrode is effectively improved, the charge time is shortened, the safety risk is reduced, and the use experience of a user is effectively improved.
The invention is realized by the following technical scheme:
a preparation method of a nitrogen-doped graphite composite negative electrode material comprises the following steps:
s1: adding soluble zinc salt into graphite, and uniformly stirring to obtain a first mixed solution;
s2: adding the 2-methylimidazole solution into the first mixed solution, and continuously stirring until the reaction is complete to obtain a second mixed solution;
s3: carrying out suction filtration, cleaning and drying on the second mixed solution to obtain a 2-methylimidazole zinc salt coated graphite core-shell structure material;
s4: and (4) placing the core-shell structure material of 2-methylimidazole zinc salt coated graphite prepared in the step S3 in an inert atmosphere for heat treatment to prepare the nitrogen-doped graphite composite negative electrode material.
Preferably, in step S1, the graphite is pre-treated with an anionic surfactant solution before adding the soluble zinc salt to the graphite.
Preferably, the anionic surfactant is one or more of sodium polystyrene sulfonate, sodium dodecyl sulfonate and sodium dodecyl benzene sulfonate.
Preferably, a supporting electrolyte is added to the anionic surfactant solution.
Preferably, D50 of graphite is 4-9 um.
Preferably, the thickness of the 2-methylimidazole zinc salt coating layer of the 2-methylimidazole zinc salt coated graphite core-shell structure material is 50-500 nm.
Preferably, the molar ratio of the soluble metal salt to 2-methylimidazole is (1:4) to (1: 32).
Preferably, the heat treatment temperature in the step S4 is 920 to 1000 ℃.
The nitrogen-doped graphite composite negative electrode material is prepared by the preparation method, and the surface layer of the nitrogen-doped graphite composite negative electrode material is a porous amorphous carbon layer
A lithium ion battery comprises the nitrogen-doped graphite composite negative electrode material; the lithium ion battery has the lithium intercalation performance of 190-230 mAh/g at the multiplying power of 1C at 25 ℃.
Compared with the prior art, the invention has the following beneficial technical effects:
a preparation method of a nitrogen-doped graphite composite negative electrode material is characterized in that 2-methylimidazole zinc salt is constructed on the surface of conventional graphite, pyrolysis and carbonization are carried out on the 2-methylimidazole zinc salt on the surface of the graphite through high-temperature heat treatment in inert atmosphere, formed metal zinc is gasified after the formed metal zinc is generated, a nitrogen-doped porous amorphous carbon layer is formed on the surface of the graphite, and the nitrogen-doped porous amorphous carbon layer and the conventional graphite on the inner layer form a core-shell structure.
Furthermore, before the soluble zinc salt is added into the graphite, the graphite is pretreated by adopting an anionic surfactant solution, and the anionic surfactant can enable the surface of the graphite to have negative charges and is beneficial to Zn2+The precursor is uniformly adsorbed on the surface of graphite particles, and can be anchored on the surface of the graphite particles to uniformly form a ZIF-8 coating precursor after 2-methylimidazole is added.
Furthermore, a supporting electrolyte is added into the anionic surfactant solution, which is helpful for coating modification of the anionic surfactant on the graphite surface.
Furthermore, the D50 of the graphite is 4-9 um, compared with the conventional graphite, the graphite with smaller size is preferred in the invention, and the small-particle-size graphite can further shorten Li remarkably+The diffusion path of (2) effectively improves the high-rate charging performance.
Furthermore, the thickness of the 2-methylimidazole zinc salt coating layer is 50-500 nm, and if the thickness of the coating layer is too small, the porous characteristic cannot be achieved; too large a coating thickness and too large a specific surface area can result in a severe reduction in first effect.
Furthermore, the pyrolysis temperature is higher than 950 ℃, Zn in the 2-methylimidazole zinc salt coated graphite core-shell structure material is effectively ensured to be fully volatilized, the surface organic material is fully carbonized, and a porous structure is constructed on the surface of graphite.
The nitrogen-doped graphite composite negative electrode material has the advantages that the carbon layer interlayer spacing of the nitrogen-doped porous amorphous carbon layer on the surface of the nitrogen-doped graphite composite negative electrode material is increased to 0.34-0.35 nm, and compared with the lattice interlayer spacing of 0.337nm of the conventional common graphite, the nitrogen-doped porous amorphous carbon layer formed by carbonizing the 2-methylimidazole zinc salt can effectively improve the Li ion transmission channel by being used as the lithium ion transmission channel+Transport process dynamics of avoiding Li+The accumulation on the graphite surface is separated out, the efficiency of high-rate charge and discharge of the material is effectively improved, the use experience of a user is improved, and the occurrence of safety accidents is avoided.
A lithium ion battery comprises the nitrogen-doped graphite composite negative electrode material, has good lithium intercalation capacity, has the lithium intercalation performance of 190-230 mAh/g at the 1C multiplying power of 25 ℃, has good rapid charge and discharge capacity, and has the nitrogen-doped graphite composite negative electrode material, and Li+The transmission speed in the graphite cathode material is high, the generation of lithium dendrite can be effectively avoided, and the use safety of the battery is effectively ensured.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a microscopic morphology of the core-shell structure material of 2-methylimidazole zinc salt-coated graphite obtained in step S2 in example 1 of the present invention;
FIG. 2 is XRD spectra of graphite alone, ZIF-8 alone in example 1 of the present invention, and core-shell material of graphite coated with zinc 2-methylimidazole salt in example 1 of the present invention;
FIG. 3 shows the results of comparative tests of rate lithium insertion performance of example 1 and example 2 of the present invention with untreated graphite;
FIG. 4 shows the comparative results of Raman tests of the nitrogen-doped graphite composite anode material prepared in example 1 of the present invention and untreated graphite;
FIG. 5 is a comparison of the surface morphology of the nitrogen-doped graphite composite negative electrode material (right) prepared in example 1 of the present invention and the untreated graphite (left);
FIG. 6 is an HR-TEM image of the nitrogen-doped graphite composite anode material prepared in example 1 of the present invention.
Detailed Description
To make the features and effects of the present invention comprehensible to those skilled in the art, general description and definitions are made below with reference to terms and expressions mentioned in the specification and claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The theory or mechanism described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.
All features defined herein as numerical ranges or percentage ranges, such as values, amounts, levels and concentrations, are for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to cover and specifically disclose all possible subranges and individual numerical values (including integers and fractions) within the range.
Unless otherwise specified herein, "comprising," including, "" containing, "" having, "or the like, means" consisting of … … "and" consisting essentially of … …, "e.g.," a comprises a "means" a comprises a and the other, "and" a comprises a only.
In this context, for the sake of brevity, not all possible combinations of features in the various embodiments or examples are described. Therefore, the respective features in the respective embodiments or examples may be arbitrarily combined as long as there is no contradiction between the combinations of the features, and all the possible combinations should be considered as the scope of the present specification.
The invention provides a nitrogen-doped graphite composite negative electrode material, a preparation method thereof and a lithium ion battery. The preparation method of the nitrogen-doped graphite composite negative electrode material comprises the following steps:
s1: pretreatment of graphite: adding graphite with a median particle size (D50) of 4-9 um into an anionic surfactant aqueous solution with a mass concentration of 10-100 g/L, and stirring for 6-8 hours to obtain a graphite dispersion liquid; after suction filtration, dissolving the mixture in a methanol solution, and stirring and dispersing the mixture to obtain a first reaction solution;
wherein the anionic surfactant activates graphite particles to make graphite surfaces negatively charged, thereby contributing to Zn2+The precursor is uniformly adsorbed on the surface of graphite particles, and can be anchored on the surface of the graphite particles to uniformly form a ZIF-8 coating precursor after 2-methylimidazole is added.
The mass ratio of the anionic surfactant to the graphite is (1:0.5) - (1:2), the dosage of the anionic surfactant is too small, the surface of graphite particles is not completely activated, and Zn is added2+The ZIF-8 can be formed in the solution without being completely adsorbed on the surface of the graphite; the consumption of the anionic surfactant is too much, and the material waste is serious.
0.5-2.0 mol/L of supporting electrolyte is dissolved in the anionic surfactant solution, and the coating modification of the anionic surfactant on the graphite surface is facilitated.
Wherein, the anionic surfactant can be one or more of sodium polystyrene sulfonate, sodium dodecyl sulfonate and sodium dodecyl benzene sulfonate.
The supporting electrolyte may preferably be sodium chloride (NaCl) or potassium nitrate (KNO)3) Or sodium sulfate (Na)2SO4) Any one of them.
S2: construction of the coating layer: adding a methanol solution of soluble zinc salt into the first reaction solution, stirring for 1-24 h, then dropwise adding the methanol solution of 2-methylimidazole, continuously stirring for 4-24 h until the reaction is complete to obtain a second reaction solution, carrying out suction filtration on the second reaction solution, washing for 1-3 times by using methanol, precipitating and drying to obtain a core-shell structure material of 2-methylimidazole zinc salt coated graphite, namely graphite @ ZIF-8 core-shell structure material;
the methanol solution of the 2-methylimidazole added dropwise in the step is beneficial to the uniformity of the reaction, and Zn adsorbed on the surface of graphite can be enabled2+Controllably reacts with 2-methylimidazole to generate 2-methylimidazole zinc salt, namely ZIF-8.
Wherein, Zn2+The proportion of the Zn to the graphite is 1g of graphite mixed with 0.25 to 1mmol of Zn2+；Zn2+The molar ratio of the compound to 2-methylimidazole is (1:4) to (1: 32). The thickness of the coating layer can be regulated and controlled according to the using amount and proportion, and therefore the first effect of the composite cathode material is maintained between 86% and 92%. The thickness of the 2-methylimidazole zinc salt coating is controlled to be 50-500 nm, and if the thickness of the coating is too small, the coating cannot have the porous characteristic; too large a coating thickness and too large a specific surface area can result in a severe reduction in first effect.
The soluble zinc salt can be one or more of zinc nitrate, zinc acetate, zinc chloride and zinc sulfate.
S3: and (3) heat treatment: and (4) placing the graphite @ ZIF-8 prepared in the step (S2) in an inert atmosphere for heat treatment, and finally grinding to obtain the nitrogen-doped graphite composite negative electrode material.
Wherein the heat treatment temperature is 920-1000 ℃, the heating rate is 5-10 ℃/min, and the uniform pyrolysis of the surface ZIF-8 is effectively ensured while the material synthesis efficiency is controlled by the heating rate. The heat preservation time is 2-4 h, and the sufficient pyrolysis of ZIF-8 is ensured.
The inert atmosphere is preferably nitrogen or helium.
After heat treatment, 2-methylimidazole zinc salt on the surface of graphite is pyrolyzed and carbonized, metal zinc is gasified after being pyrolyzed, ZIF-8 is pyrolyzed to form a nitrogen-doped porous amorphous carbon material in situ,the interlayer spacing of the porous amorphous carbon material coating layer is 0.34-0.35 nm, which is obviously larger than that of the conventional graphite. Power-assisted Li+And the multiplying power performance is effectively improved in the transportation process. The graphite structure doped with N element in the coating layer also contributes to the charge transfer process. The nitrogen-doped, porous amorphous carbon material derived after ZIF-8 carbonization serves as a lithium storage buffer coating. During heavy current charging, Li+Fast transmission through wide inter-layer gaps; the interlayer spacing of amorphous carbon is much greater than that of conventional graphite and can contribute to Li+Rapid diffusion within the material lattice; meanwhile, N doping can improve Li+Adsorption and charge transfer capabilities. The fast charging capacity of the graphite cathode can be obviously improved under the combined action of the porous structure, the wide layer spacing and the nitrogen doping of the coating layer.
The negative electrode material prepared by the method has beneficial performance, and compared with a button cell prepared from conventional graphite, the button cell containing the negative electrode material has the advantages that the 1C rate lithium intercalation performance at 25 ℃ is improved from 140mAh/g to 190-230 mAh/g, the mAh/g is improved by 50-90 mAh/g, and the improvement amplitude is obvious. Compared with the prior art, the fast-charging graphite cathode material can obviously improve the dynamic characteristics of the cathode, improve the capacity exertion under the condition of large-current charging, improve the charging rate and reduce the risk of fast-charging lithium separation.
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
The following examples use instrumentation conventional in the art. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out under conventional conditions or conditions recommended by the manufacturers. The various starting materials used in the examples which follow, unless otherwise indicated, are conventional commercial products having specifications which are conventional in the art. In the description of the present invention and the following examples, "%" represents weight percent, "parts" represents parts by weight, and proportions represent weight ratios, unless otherwise specified.
Example 1
S1: adding graphite powder of which the mass concentration is 4-9 um and 5g D50 into 1L of sodium polystyrene sulfonate solution with the mass concentration of 10g/L, and stirring for 6 hours to obtain graphite dispersion liquid; after suction filtration, dissolving the mixture in 300mL of methanol solution, and stirring and dispersing the mixture to obtain a first reaction solution; 0.5mol/L NaCl is dissolved in the sodium polystyrene sulfonate solution.
S2: adding 1.25mmol of zinc nitrate methanol solution into the first reaction solution, stirring for 1h, then dropwise adding 5mmol of 2-methylimidazole methanol solution, continuously stirring for 4h until the reaction is complete to obtain a second reaction solution, carrying out suction filtration on the second reaction solution, washing for 1-3 times by using methanol, precipitating and drying to obtain the 2-methylimidazole zinc salt coated graphite core-shell structure material, namely graphite @ ZIF-8 core-shell structure material, wherein the average thickness of the 2-methylimidazole zinc salt coating layer is 50 nm.
S3: and (4) placing the 2-methylimidazole zinc salt coated graphite core-shell structure material prepared in the step (S2) in a nitrogen atmosphere for heat treatment, wherein the heat treatment temperature is 920 ℃, the heating rate is 5 ℃/min, the heat preservation time is 2h, and finally grinding is carried out to obtain the nitrogen-doped graphite composite negative electrode material.
In the microstructure of the core-shell structure material of 2-methylimidazole zinc salt-coated graphite obtained in step S2 of this embodiment, as shown in fig. 1, ZIF-8 is a polyhedral particle with a particle size of about 200nm, and is uniformly coated on the surface of graphite. The method is proved to successfully realize the controllable uniform coating of the ZIF-8 on the graphite surface, which is the most critical step. Only when the ZIF-8 precursor is uniformly coated, a uniformly N-doped porous carbon coating layer can be formed in the subsequent carbonization pyrolysis process.
Further, the characteristic diffraction peaks of graphite and ZIF-8 are obviously seen from the XRD diffraction peak of the core-shell structure material of the 2-methylimidazole zinc salt coated graphite in figure 2, which shows that the ZIF-8 is successfully coated on the surface of the graphite by the method.
The results of the rate lithium insertion performance test of this example are shown in FIG. 3.
The Raman test of FIG. 4 shows that the D peak of the nitrogen-doped graphite composite negative electrode material prepared by the method is remarkably enhanced, which indicates that the defects on the surface of the graphite material are increased and mainly caused by the pores formed after the ZIF-8 is carbonized; the G peak intensity is obviously reduced, which shows that the graphitization degree of the composite material is reduced, mainly amorphous carbon is formed after ZIF-8 carbonization, which shows that the material structure is irregular, and the carbon layer spacing is large.
As can be seen from the surface morphology of the material in fig. 5, the original graphite surface is an obvious graphite sheet structure, and the surface of the nitrogen-doped graphite composite anode material prepared in this embodiment forms a porous structure.
As can be seen from the high-resolution transmission electron micrograph (HR-TEM) of FIG. 6, the surface layer of the prepared nitrogen-doped graphite composite negative electrode material is an amorphous carbon layer, the interlayer spacing of the carbon layer is obviously larger than that of the graphite layer, and the interlayer spacing is 0.34-0.35 nm.
Example 2
S1: adding graphite powder of 4-9 um 5g D50 into a sodium dodecyl sulfate solution of 20g/L mass concentration of 0.25L, and stirring for 8 hours to obtain a graphite dispersion liquid; after suction filtration, dissolving the mixture in 300mL of methanol solution, and stirring and dispersing the mixture to obtain a first reaction solution; the sodium dodecyl sulfate solution is dissolved with KNO of 0.7mol/L3。
S2: adding a methanol solution of 2.5mmol of zinc acetate into the first reaction solution, stirring for 3 hours, then dropwise adding a methanol solution of 15mmol of 2-methylimidazole, continuously stirring for 8 hours till the reaction is complete to obtain a second reaction solution, carrying out suction filtration on the second reaction solution, washing for 1-3 times by using methanol, precipitating and drying to obtain a core-shell structure material of the 2-methylimidazole zinc salt coated graphite, namely graphite @ ZIF-8, wherein the average thickness of the 2-methylimidazole zinc salt coated layer is 70 nm.
S3: and (4) placing the graphite @ ZIF-8 prepared in the step (S2) in a helium atmosphere for heat treatment, wherein the heat treatment temperature is 950 ℃, the heating rate is 7 ℃/min, the heat preservation time is 3h, and finally grinding is carried out to obtain the nitrogen-doped graphite composite negative electrode material.
As shown in fig. 3, the results of the 1C rate lithium intercalation performance comparison test of inventive example 1 and example 2 with untreated graphite are shown. The room-temperature rate lithium intercalation capacity of the embodiment 1 and the embodiment 2 is obviously better than that of untreated original graphite, namely, the fast charging performance of the negative electrode material prepared by the method is effectively improved.
Example 3
S1: adding graphite powder of 4-9 um 5g D50 into 0.07L sodium dodecyl benzene sulfonate solution with mass concentration of 50g/L, and stirring for 7h to obtain graphite dispersion liquid; after suction filtration, dissolving the mixture in 300mL of methanol solution, and stirring and dispersing the mixture to obtain a first reaction solution; the sodium dodecylbenzenesulfonate solution has 1.0mol/L NaCl dissolved therein.
S2: adding 3.75mmol of zinc chloride methanol solution into the first reaction solution, stirring for 8 hours, then dropwise adding 37.5mmol of 2-methylimidazole methanol solution, continuously stirring for 10 hours until the reaction is complete to obtain a second reaction solution, carrying out suction filtration on the second reaction solution, washing for 1-3 times by using methanol, precipitating and drying to obtain a 2-methylimidazole zinc salt coated graphite core-shell structure material, namely graphite @ ZIF-8 core-shell structure material, wherein the average thickness of the 2-methylimidazole zinc salt coating is 100 nm.
S3: and (4) placing the 2-methylimidazole zinc salt coated graphite core-shell structure material prepared in the step S2 in an argon atmosphere for heat treatment, wherein the heat treatment temperature is 970 ℃, the heating rate is 8 ℃/min, the heat preservation time is 4h, and finally grinding is carried out to obtain the nitrogen-doped graphite composite negative electrode material.
Example 4
S1: adding graphite powder of which the mass concentration is 4-9 um and 5g D50 into 0.036L of sodium polystyrene sulfonate solution with the mass concentration of 70g/L, and stirring for 7.5 hours to obtain graphite dispersion liquid; after suction filtration, dissolving the mixture in 300mL of methanol solution, and stirring and dispersing the mixture to obtain a first reaction solution; the sodium polystyrene sulfonate solution is dissolved with 1.3mol/L NaCl.
S2: adding 1.25mmol of zinc chloride methanol solution into the first reaction solution, stirring for 10 hours, then dropwise adding 18.75mmol of 2-methylimidazole methanol solution, continuously stirring for 13 hours until the reaction is complete to obtain a second reaction solution, carrying out suction filtration on the second reaction solution, washing for 1-3 times by using methanol, precipitating and drying to obtain a 2-methylimidazole zinc salt coated graphite core-shell structure material, namely graphite @ ZIF-8 core-shell structure material, wherein the average thickness of the 2-methylimidazole zinc salt coating is 200 nm.
S3: and (4) placing the 2-methylimidazole zinc salt coated graphite core-shell structure material prepared in the step (S2) in an argon atmosphere for heat treatment, wherein the heat treatment temperature is 980 ℃, the heating rate is 9 ℃/min, the heat preservation time is 4h, and finally grinding is carried out to obtain the nitrogen-doped graphite composite negative electrode material.
Example 5
S1: adding graphite powder of 4-9 um 5g D50 into a sodium polystyrene sulfonate solution of 80g/L mass concentration of 0.125L, and stirring for 8 hours to obtain a graphite dispersion liquid; after suction filtration, dissolving the mixture in 300mL of methanol solution, and stirring and dispersing the mixture to obtain a first reaction solution; the sodium polystyrene sulfonate solution is dissolved with 1.5mol/L NaCl.
S2: adding a methanol solution of 2.5mmol of zinc nitrate into the first reaction solution, stirring for 15h, then dropwise adding a methanol solution of 42.5mmol of 2-methylimidazole, continuously stirring for 15h until the reaction is complete to obtain a second reaction solution, carrying out suction filtration on the second reaction solution, washing for 1-3 times by using methanol, precipitating and drying to obtain a core-shell structure material of 2-methylimidazole zinc salt coated graphite, namely the graphite @ ZIF-8 core-shell structure material, wherein the average thickness of the 2-methylimidazole zinc salt coating layer is 300 nm.
S3: and (4) placing the 2-methylimidazole zinc salt coated graphite core-shell structure material prepared in the step S2 in an argon atmosphere for heat treatment, wherein the heat treatment temperature is 990 ℃, the heating rate is 5 ℃/min, the heat preservation time is 4h, and finally grinding is carried out to obtain the nitrogen-doped graphite composite negative electrode material.
Example 6
S1: adding graphite powder of 4-9 um 5g D50 into 0.056L sodium polystyrene sulfonate solution with mass concentration of 90g/L, and stirring for 8h to obtain graphite dispersion liquid; after suction filtration, dissolving the mixture in 300mL of methanol solution, and stirring and dispersing the mixture to obtain a first reaction solution; the sodium polystyrene sulfonate solution is dissolved with 1.7mol/L NaCl.
S2: adding a 2.5mmol zinc nitrate methanol solution into the first reaction solution, stirring for 15h, then dropwise adding a 50mmol 2-methylimidazole methanol solution, continuously stirring for 20h until the reaction is complete to obtain a second reaction solution, carrying out suction filtration on the second reaction solution, washing for 1-3 times by using methanol, precipitating and drying to obtain a 2-methylimidazole zinc salt coated graphite core-shell structure material, namely graphite @ ZIF-8 core-shell structure material, wherein the average thickness of a 2-methylimidazole zinc salt coating layer is 400 nm.
S3: and (4) placing the 2-methylimidazole zinc salt coated graphite core-shell structure material prepared in the step S2 in a nitrogen atmosphere for heat treatment, wherein the heat treatment temperature is 1000 ℃, the heating rate is 5 ℃/min, the heat preservation time is 4h, and finally grinding is carried out to obtain the nitrogen-doped graphite composite negative electrode material.
Example 7
S1: adding graphite powder of which the mass concentration is 4-9 um and 5g D50 into 0.025L of sodium polystyrene sulfonate solution with the mass concentration of 100g/L, and stirring for 8 hours to obtain graphite dispersion liquid; after suction filtration, dissolving the mixture in 300mL of methanol solution, and stirring and dispersing the mixture to obtain a first reaction solution; 2.0mol/L NaCl is dissolved in the sodium polystyrene sulfonate solution.
S2: adding a methanol solution of 5mmol of zinc nitrate into the first reaction solution, stirring for 24 hours, then dropwise adding a methanol solution of 160mmol of 2-methylimidazole, continuously stirring for 24 hours until the reaction is complete to obtain a second reaction solution, carrying out suction filtration on the second reaction solution, washing for 1-3 times by using methanol, precipitating and drying to obtain a core-shell structure material of 2-methylimidazole zinc salt coated graphite, namely graphite @ ZIF-8 core-shell structure material, wherein the average thickness of the 2-methylimidazole zinc salt coating layer is 500 nm.
S3: and (4) placing the 2-methylimidazole zinc salt coated graphite core-shell structure material prepared in the step S2 in an argon atmosphere for heat treatment, wherein the heat treatment temperature is 1000 ℃, the heating rate is 5 ℃/min, the heat preservation time is 4h, and finally grinding is carried out to obtain the nitrogen-doped graphite composite negative electrode material.
Comparative example 1
S1: adding graphite powder of which the mass concentration is 4-9 um and 5g D50 into 0.1L of sodium polystyrene sulfonate solution with the mass concentration of 10g/L, and stirring for 6 hours to obtain graphite dispersion liquid; after suction filtration, dissolving the mixture in 300mL of methanol solution, and stirring and dispersing the mixture to obtain a first reaction solution; 0.5mol/L NaCl is dissolved in the sodium polystyrene sulfonate solution.
S2: adding 1.25mmol of zinc nitrate methanol solution into the first reaction solution, stirring for 1h, then dropwise adding 5mmol of 2-methylimidazole methanol solution, continuously stirring for 4h until the reaction is complete to obtain a second reaction solution, carrying out suction filtration on the second reaction solution, washing for 1-3 times by using methanol, precipitating and drying to obtain the 2-methylimidazole zinc salt coated graphite core-shell structure material, namely graphite @ ZIF-8 core-shell structure material, wherein the average thickness of the 2-methylimidazole zinc salt coating layer is 50 nm.
S3: and (4) placing the 2-methylimidazole zinc salt coated graphite core-shell structure material prepared in the step (S2) in a nitrogen atmosphere for heat treatment, wherein the heat treatment temperature is 920 ℃, the heating rate is 5 ℃/min, the heat preservation time is 2h, and finally grinding is carried out to obtain the nitrogen-doped graphite composite negative electrode material.
In the comparative example, the dosage of the sodium polystyrene sulfonate is obviously too small, the surface of the graphite particles can not be activated incompletely, and Zn2+The ZIF-8 is not completely adsorbed on the surface of graphite, so that the ZIF-8 is detected in a solution, and the improvement of the material performance is not facilitated.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be construed as the protection scope of the present invention.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Claims (10)
1. The preparation method of the nitrogen-doped graphite composite negative electrode material is characterized by comprising the following steps of:
s1: adding soluble zinc salt into graphite, and uniformly stirring to obtain a first mixed solution;
s2: adding the 2-methylimidazole solution into the first mixed solution, and continuously stirring until the reaction is complete to obtain a second mixed solution;
s3: carrying out suction filtration, cleaning and drying on the second mixed solution to obtain a 2-methylimidazole zinc salt coated graphite core-shell structure material;
s4: and (4) placing the core-shell structure material of 2-methylimidazole zinc salt coated graphite prepared in the step S3 in an inert atmosphere for heat treatment to prepare the nitrogen-doped graphite composite negative electrode material.
2. The method for preparing the nitrogen-doped graphite composite anode material according to claim 1, wherein in the step S1, before the soluble zinc salt is added into the graphite, the graphite is pretreated by using an anionic surfactant solution.
3. The method for preparing the nitrogen-doped graphite composite negative electrode material as claimed in claim 2, wherein the anionic surfactant is one or more of sodium polystyrene sulfonate, sodium dodecyl sulfonate and sodium dodecyl benzene sulfonate.
4. The method for preparing the nitrogen-doped graphite composite anode material according to claim 2, wherein a supporting electrolyte is added into the anionic surfactant solution.
5. The preparation method of the nitrogen-doped graphite composite negative electrode material according to claim 4, wherein D50 of the graphite is 4-9 um.
6. The preparation method of the nitrogen-doped graphite composite negative electrode material according to claim 1, wherein the thickness of the 2-methylimidazole zinc salt coating layer of the 2-methylimidazole zinc salt coating graphite core-shell structure material is 50-500 nm.
7. The method for preparing the nitrogen-doped graphite composite anode material according to claim 1, wherein the molar ratio of the soluble metal salt to the 2-methylimidazole is (1:4) - (1: 32).
8. The method for preparing the nitrogen-doped graphite composite anode material according to claim 1, wherein the heat treatment temperature in the step S4 is 920-1000 ℃.
9. The nitrogen-doped graphite composite negative electrode material is characterized in that the surface layer of the nitrogen-doped graphite composite negative electrode material is a porous amorphous carbon layer, and is prepared by the preparation method of claims 1-8.
10. A lithium ion battery comprising the nitrogen-doped graphite composite anode material according to claim 9; the lithium ion battery has the lithium intercalation performance of 190-230 mAh/g at the multiplying power of 1C at 25 ℃.
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