CN101728526B - Lithium ion battery cathode material and preparation method thereof - Google Patents

Abstract

The invention relates to a lithium ion battery cathode material and a preparation method thereof. The cathode material comprises a carbon-coated nano-metal oxide composite material, wherein a carbon-coated nano-metal oxide has a nuclear shell structure, grains are uniformly dispersed, the diameter range of the grains is 10-80nm, and the thickness of a carbon coating is 2.5-10nm. An electrode made of the cathode material has higher reversible capacity and excellent cyclical stability.

Description

A kind of negative electrode material of lithium ion battery and preparation method thereof

Technical field:

The invention relates to a lithium ion battery negative electrode material and a preparation method thereof, belonging to the field of lithium ion secondary battery electrode materials. the

Background technique:

Lithium-ion secondary batteries have the advantages of high voltage, high specific energy, long life, and no pollution. They have replaced nickel-cadmium batteries and nickel-metal hydride batteries in the field of small secondary batteries and become the mainstream of commercial secondary batteries. The rapid rise, the practical application of electric vehicles has received great attention from all over the world, and the application of lithium batteries in the automotive industry will become more and more popular, so higher requirements are put forward for chemical power materials. the

Compared with the current industrially used carbon anode materials (such as: natural graphite, artificial graphite), transition metal oxides have a high theoretical specific capacity when used as lithium battery anode materials [Poizot P et al.Nano-sized transition- metal oxides as negative electrode materials for lithium-ion batteries.Nature 2000; 28: 407], at the same time has the characteristics of low cost and environmental friendliness, which has attracted widespread attention from the scientific and business circles [Peter GB et al.Nanomaterials for RechargeableLithium Batteries. Lithium Batteries, 2008:47:2-19]. However, transition metal oxides have large volume changes during charge-discharge cycles, high irreversible capacity loss, and poor cycle stability[YG.Guo et al.Superior electrode performance of nanostructured mesoporous TiO ₂ (Anatase) through efficient hierarchical mixed conducting networks. Adv. Mater. 2007, 19, 2087]. Nanoizing transition metal oxides can partially solve this problem, making it easier for lithium ions to intercalate and release between the electrode and the electrolyte, and improve its electrochemical cycle performance. The specific surface area is high, and agglomeration between nanoparticles is easy to cause serious irreversibility and reduce cycle stability [F.Cheng et al.Template-directed materials for rechargeable Lithium-Ion batteries.Chem.Mater. 2008, 20, 667 ]. Therefore, adding a layer of carbon coating on the surface of transition metal oxide nanoparticles is one of the most effective methods to improve their electrochemical cycle stability [LJFu et al.Surface modifications of electrode materials for lithium ion batteries.Electrochem.Commun.2006 , 8, 1].

The carbon-coated transition metal oxide material not only improves the conductivity of the oxide material because the oxide particles are effectively protected by the coating layer, but also can well inhibit the inner shell oxide material due to the existence of the coating carbon layer. The volume expansion and mutual agglomeration are beneficial to improve the cycle stability of the electrode. The traditional preparation method of carbon-coated nano-metal oxide composites is mainly hydrothermal method. The hydrothermal method is a method for preparing materials through multi-step continuous oxidation-reduction reactions in the liquid phase. Generally [LQ.Xu et al.Formation, characterization, and magnetic properties of Fe ₃ O ₄ nanowire encapsulated in carbon microtubes.J.Phys.Chem.B 2004, 108.] The pressure and temperature used in the experiment are very high (≥16Mpa, ≥600°C), the purity of the product is poor (while the formation of nanoparticles is accompanied by the generation of fullerenes and carbon nanotubes), the preparation process is complicated, and the yield is also very low; : one-pot synthesis, rational conversion, and Li storage property.Chem.Mater.2006, 18.] Polysaccharide or polysaccharide as a carbon source, at high temperature (180 ~ 1000 ℃) with highly dispersed nano-scale metal oxide particles Catalyst reaction to prepare nano-metal oxide/carbon materials, this method is often mixed with vapor-phase grown carbon fibers or carbon nanotubes, the product components are complex, difficult to separate, the yield is very small, the reaction time is long, and it is difficult to achieve large-scale production; Liu Hao et al.[Hao Liu et al.Magnetite/carbon core-shell nanorods as anode materials forlithium-ion batteries.Electrochemistry Commun.2008, 10.] used α-Fe ₂ O ₃ nanorods as templates to prepare carbon core-shell nanorods by hydrothermal method Covered with Fe ₃ O ₄ . Apparently, this method requires pre-preparation of nanometer α-Fe ₂ O ₃ template, which requires many steps and complicated preparation process, and is not suitable for industrial scale preparation.

Invention content:

One of the objectives of the present invention is to provide a new type of battery negative electrode material for the shortcomings of transition metal oxides as lithium battery negative electrode materials, which can improve its cycle stability while maintaining a high specific capacity. the

A lithium ion battery negative electrode material provided by the invention is a carbon-coated nano metal oxide composite material with a core-shell structure, the particle diameter ranges from 10nm to 80nm, the thickness of the carbon coating layer is 2.5nm to 10nm, and the particles are uniformly dispersed , the mass percentage of each component is: nano metal oxide 20%-60%; carbon 40-80%. the

Another object of the present invention is to provide a method for preparing the above-mentioned lithium ion battery negative electrode material. the

A kind of method for preparing described lithium-ion battery negative electrode material provided by the present invention, comprises the following steps:

A: Mix oxygen-containing hydrocarbons with a transition metal compound and an organic solvent in a mass ratio of 1:0.1 to 1:5, stir until uniform, and then dry. The obtained solid is placed in a high-pressure reactor, and the temperature is raised to 400-550° C. under an inert atmosphere, and then the temperature rise is stopped, and the pyrolysis product is obtained when the temperature drops to room temperature. the

The reaction that occurs in step A is the thermal decomposition of oxygen-containing hydrocarbons, which provide carbon and oxygen sources for the final product, and transition metal oxides serve as high-temperature catalysts while providing metal sources; oxygen-containing hydrocarbons The preferred range of the mass ratio of the compound to the transition metal compound is 1:1-1:4. the

The organic solvent is preferably tetrahydrofuran, acetone, ethanol or benzene, and the amount used is based on the sufficient dissolution of the oxygen-containing hydrocarbon and the transition metal compound in the organic solvent. the

B: using pyridine or tetrahydrofuran as a solvent to wash, filter and dry the pyrolysis product obtained in step A to obtain the target product. the

The oxygen-containing hydrocarbon is selected from one or more alcohols, acids or anhydrides, aldehydes, and phenols with aromatic hydrocarbon groups, alkenyl groups, alkane groups, and heterocyclic groups, or is Carbohydrates composed only of C, H, and O. the

The alkene or alkane group in the organic oxygen-containing hydrocarbon refers to an alkene group or alkane group with more than 4 and less than 30 carbon atoms. the

Among them, alcohols with one or more groups of aromatic hydrocarbon groups, alkenyl groups, alkane groups, and heterocyclic groups are preferably stearyl alcohol and phenylpropanol. the

Aldehydes with one or more groups of aromatic hydrocarbon groups, alkenyl groups, alkane groups, and heterocyclic groups, preferably: o-tolualdehyde, 4-methyl-3-pentenal, 3-benzene Propionaldehyde. the

Acids or acid anhydrides with one or more groups of aromatic hydrocarbon groups, alkenyl groups, alkane groups, and heterocyclic groups are preferably o-toluic acid, crotonic acid, sorbic acid, and phthalic anhydride. the

The phenol with one or more groups of aromatic hydrocarbon group, alkenyl group, alkane group and heterocyclic group is preferably: resorcinol, phloroglucinol or o-cresol. the

Carbohydrates consisting only of C, H, and O are sorbitol, xylitol, or glucose. the

The transition metal compound is selected from one of a transition metallocene compound, a carbonyl transition organometal compound, an acetylacetonate transition organometal compound, a transition metal acetate or a transition metal nitrate. the

Among them, the transition metal compound based on cyanocene is preferably ferrocene, cobaltocene or nickelocene. the

The transition metal carbonyl compound is preferably iron carbonyl, cobalt carbonyl or nickel carbonyl. the

The acetylacetonate transition metal compound is preferably iron acetylacetonate, nickel acetylacetonate or cobalt acetylacetonate. the

The transition metal acetate is preferably cobalt acetate, nickel acetate or iron acetate. the

The transition metal nitrate is preferably iron nitrate, cobalt nitrate or nickel nitrate. the

Since the present invention adopts the carbon-coated nano-metal oxide composite material as the lithium-ion battery negative electrode material, the first reversible capacity is as high as 750-1000mAh/g through the electrochemical performance test. Maintaining 350-500mAh/g effectively overcomes the problems that occur when transition metal oxides are used as negative electrode materials, making the negative electrode materials have higher reversible capacity and good cycle stability. the

The method provided by the invention can obtain carbon-coated nano-metal oxide composite materials only through mixing, carbonization, and extraction processes. Under medium temperature conditions, the self-rising final pressure of the system is generally lower than 10.0Mpa, and has the advantages of simple process and low material preparation cost. , high purity, and a wide range of metal types can be selected, and it is easy to achieve large-scale preparation. the

Description of drawings:

Figures 1 to 5 are test diagrams of carbon-coated Fe ₃ O ₄ nanoparticles produced by resorcinol and ferrocene at a mass ratio of 1:2 in Example 1 of the present invention at a final temperature of 450°C.

Fig. 1 is X-ray diffraction (XRD) figure;

Fig. 2 is thermogravimetric analysis figure;

Figure 3 is a transmission electron microscope picture;

Figure 4 is a cycle charge and discharge diagram when used as a lithium battery negative electrode material;

Figure 5 is the first charge and discharge curve when used as a lithium battery negative electrode material. the

Detailed ways:

The present invention will be further described below in conjunction with the examples, but it does not constitute a limitation to the present invention. the

Example 1

Weigh 10g of analytically pure resorcinol and 20g of ferrocene according to a mass ratio of 1:2, mix with 200ml of acetone solvent and stir until uniform, then dry in a constant temperature water bath at 40°C until the acetone is completely volatilized to obtain a solid, and place the solid in In a high pressure reactor. Heating is carried out under the protection of nitrogen, and the heating rate is maintained at 3°C/min. When the temperature rises from normal temperature to 450°C, the heating is stopped. When the temperature drops to normal temperature, pyrolysis products are obtained. the

Using pyridine as a solvent, at a temperature of 120°C, the pyrolysis product was repeatedly washed and extracted until the filtrate became colorless and clear. The filter residue after drying is the carbon-coated nano Fe ₃ O ₄ composite material, and the yield is 68%. Through thermogravimetric analysis, it is obtained that the material contains 39.8% Fe ₃ O ₄ .

As shown in Figure 1 X-ray diffraction (XRD) analysis shows that the metal oxide particles are Fe ₃ O ₄ ; as shown in Figure 2 Thermogravimetric (TG) analysis results show that the mass percentage of Fe ₃ O ₄ is about 40.0%, and the content of carbon element is about 40.0%. It is 60.0%; as shown in Figure 3 Transmission Electron Microscope (TEM), the particle size of the carbon-coated nano-Fe ₃ O ₄ composite material is between 20-60 nm, has a core-shell structure and is uniformly dispersed in the carbon matrix.

The electrode is made by coating method. The specific process is as follows: mix the prepared product, binder PVDF, and acetylene black in a mass ratio of 80:10:10, prepare a paste with N-2 methyl-pyrrolidone and spread it evenly on the copper foil, and then Dry it in a vacuum oven at 120°C for 16 hours, and finally cut the copper foil coated with the active material into discs to make working electrodes. The simulated battery uses a button-type CR2032 system, in which the counter electrode is a metal lithium sheet. The assembly of the simulated battery was done in a Unilab type glove box of M. Braun Company in Germany. Battery test method: In order to investigate the reversible capacity, coulombic efficiency, and cycle performance of carbon materials and composite materials, constant current charge and discharge were tested and analyzed in the experiment. The charging and discharging conditions are as follows: the current density is 50mA/g, and the voltage range is 0.01-2.5V. The number of cycles is generally 30-50 times. the

As shown in Figure 5: As a lithium battery negative electrode material, the first discharge capacity reached 960mAh/g, and the reversible specific capacity of the wrapping reached 449.8mA h/g; as shown in Figure 4, it was cycled 30 times at a current density of 50mA/g Finally, the capacity can be maintained at 375mAh/g, while the traditional industrial ferroferric oxide (particle size range of 100nm to 1000nm) is used as the negative electrode material, the first discharge capacity can reach 1100mAh/g, and the current density is 50mA/g cycle After 30 times, the capacity can only be maintained at 145mAh/g. the

Example 2

The operation method is the same as in Example 1. Weigh 10 g of analytically pure benzaldehyde and 20 g of iron acetylacetonate according to a mass ratio of 1:2, add them to 200 ml of ethanol solvent, mix and stir until uniform, and then dry in a constant temperature water bath at 40 ° C until the ethanol is completely volatilized A solid was obtained, and the solid was placed in an autoclave. Heating is carried out under the protection of nitrogen, and the heating rate is maintained at 3°C/min. When the temperature rises from normal temperature to 450°C, the heating is stopped immediately. When the temperature drops to room temperature, pyrolysis products are obtained, and the system self-increasing pressure finally reaches 6.0Mpa. the

Using pyridine as a solvent, at a temperature of 120°C, the pyrolysis product was repeatedly washed and extracted until the filtrate became colorless and clear. Finally, the carbon-coated nano-Fe3O4 composite material with particle size distribution between 20-60nm is obtained. Through thermogravimetric analysis, the content of metal oxide in the material is 37.2%. Using the same method as in Example 1 to carry out charge and discharge tests, the results show that the negative electrode material exhibits good cycle stability, the first discharge capacity is as high as 950mAh/g, and after 30 cycles at a current density of 50mA/g, the capacity can be maintained. At 368mAh/g. the

Example 3

Weigh 10 g of analytically pure isophthalic acid and 20 g of ferrocene according to a mass ratio of 1:2, and the other steps are the same as in Example 1. Finally, a carbon-coated nano-Fe ₃ O ₄ composite material with a particle size distribution of 20-80 nm was obtained. Through thermogravimetric analysis, it was found that the content of metal oxide in the material was 38.3%. Using the same method as in Example 1 to carry out charge and discharge tests, the results show that the negative electrode material exhibits good cycle stability, the first discharge capacity is as high as 985mAh/g, and the capacity can be maintained after 30 cycles at a current density of 50mA/g. At 379mAh/g.

Example 4

Weigh 10g of analytically pure cinnamic acid and 5g of ferric nitrate at a mass ratio of 2:1, add 100ml of tetrahydrofuran solvent and stir until uniform, then dry in a constant temperature water bath at 40°C until tetrahydrofuran is completely volatilized to obtain a solid, and place the obtained solid in In the high-pressure reactor, heating is carried out under the protection of nitrogen, and the heating rate is maintained at 3°C/min. When the temperature rises from normal temperature to 550°C, the heating is stopped immediately, and the pyrolysis product is obtained when the temperature drops to room temperature. The final pressure of the system is 8.0Mpa. the

Using acetone as a solvent, the pyrolysis product was repeatedly washed and extracted at room temperature until the filtrate became colorless and clear. The filter residue after drying is the carbon-coated nano Fe ₃ O ₄ composite material, and the yield is about 50%. Through transmission electron microscope analysis, the particle size of the carbon-coated nano-Fe ₃ O ₄ composite material is between (30nm and 80nm), has a core-shell structure and is uniformly dispersed in the carbon matrix; through thermogravimetric analysis, the metal oxide content is 20.5%. The same method as in Example 1 was used to carry out charge and discharge tests, and the results showed that after 30 cycles at a current density of 50mA/g, the capacity could be maintained at 375mAh/g.

Example 5

The operation method is the same as that in Example 1, except that the transition metal compound is replaced by iron tetracarbonyl, and other conditions are kept unchanged to obtain a carbon-coated nano-Fe ₃ O ₄ composite material. Through thermogravimetric analysis, the metal oxide content was found to be 56%. The same method as in Example 1 was used to carry out charge and discharge tests, and the results showed that the initial discharge capacity was as high as 1340mAh/g, and after 30 cycles at a current density of 50mA/g, the capacity could be maintained at 369mAh/g.

Example 6

Weigh 10g of analytically pure 4-methyl-3-pentenal and 40g of ferrocene according to a mass ratio of 1:4, mix them uniformly, dissolve and stir them with 100ml tetrahydrofuran solvent until uniform, and then dry them in a constant temperature water bath at 40°C to Tetrahydrofuran was completely volatilized to obtain a solid, which was placed in a high-pressure reactor. Heating is carried out under the protection of nitrogen, and the heating rate is maintained at 3°C/min. When the temperature rises from normal temperature to 550°C, the heating is stopped immediately. When the temperature drops to room temperature, a pyrolysis product is obtained, and the system self-increases the pressure to 7.0Mpa. the

Using pyridine as a solvent, at a temperature of 120°C, the pyrolysis product was repeatedly washed and extracted until the filtrate became colorless and clear. The filter residue after drying is the carbon-coated nano Fe ₃ O ₄ composite material, and the yield is 65%.

The XRD analysis shows that the metal oxide particles are Fe ₃ O ₄ ; the carbon-coated nano-Fe ₃ O ₄ composite material particle size is between 25-70nm and has a core-shell structure as shown by transmission electron microscopy (TEM). and uniformly dispersed in the carbon matrix. Through thermogravimetric analysis, the metal oxide content was 30.7%. Adopt the method identical with embodiment 1 to carry out charge and discharge test, the result shows, its electrochemical performance test result shows that as lithium battery negative electrode material, discharge specific capacity for the first time is as high as 785mAh/g, after current density is 50mA/g cycle 50 times, The capacity can be maintained at 305mAh/g.

Example 7

Weigh 10g of analytically pure resorcinol and 10g of cobalt acetylacetonate according to a mass ratio of 1:1 and mix evenly with 100ml of acetone, then dry in a constant temperature water bath at 40°C until the acetone is completely volatilized to obtain a solid, and place the solid in the In the autoclave, heating is carried out under the protection of nitrogen, and the heating rate is maintained at 3°C/min. When the temperature rises from normal temperature to 500°C, the heating is stopped immediately, and the pyrolysis product is obtained when the temperature drops to room temperature. Then, the pyrolysis product was repeatedly washed and filtered with tetrahydrofuran at 70°C until the filtrate became colorless and clear. The filter residue after drying is the carbon-coated nano-cobalt oxide composite material, and the yield is about 48%. the

The metal oxide particles are CoO, with an average particle size of about 50nm, uniformly dispersed in carbon with an amorphous structure. Through thermogravimetric analysis, the metal oxide content was analyzed to be 44.2%. The charging and discharging test was carried out by the same method as in Example 1, and the results showed that the initial discharge specific capacity was 980mAh/g, and after 30 cycles at a current density of 50mA/g, the capacity could maintain 365mAh/g. When the traditional industrial cobalt oxide (with a particle size range of 100nm to 1000nm) is used as the negative electrode material, the first discharge capacity reaches 1350mAh/g, and the capacity can be maintained at 355mAh/g after 30 cycles at a current density of 50mA/g. the

Example 8

The operation method is the same as in Example 7, keeping other conditions unchanged, replacing resorcinol with glucose, and obtaining a carbon-coated nano-cobalt composite material after the reaction, wherein the metal oxide content is 28.5%. The charging and discharging test was carried out by the same method as in Example 1, and the results showed that the first discharge specific capacity was as high as 855mAh/g, and after 30 cycles at a current density of 50mA/g, the capacity could be maintained at 326mAh/g. the

Example 9

The operation method is the same as that in Example 7, and other conditions are kept unchanged, and the transition metal compound is replaced with nickel acetylacetonate, and the carbon-coated nano-nickel oxide composite material is also obtained through the reaction. Among them, the metal oxide content is 33.8%. The charging and discharging test was carried out by the same method as in Example 1, and the results showed that the first discharge specific capacity was 784mAh/g, and after 30 cycles at a current density of 50mA/g, the capacity could maintain 337mAh/g. When traditional industrial nickel oxide (particle size ranges from 100nm to 1000nm) is used as the negative electrode material, the first discharge capacity reaches 850mAh/g, and the capacity can be maintained at 145mAh/g after 30 cycles at a current density of 50mA/g. the

Claims (6)

1. A lithium-ion battery negative electrode material, characterized in that: the lithium-ion battery negative electrode material is a carbon-coated nano-metal oxide composite material with a core-shell structure, the particle diameter range is 10nm to 80nm, and the thickness of the carbon coating layer is 2.5nm-10nm, the mass percentage of each component is: nano metal oxide 20%-60%, carbon 40%-80%; It is characterized in that: the carbon-coated nano-metal oxide composite material is prepared by the following method: A: Mix oxygen-containing hydrocarbons with a mass ratio of 1:0.1 to 1:5 with transition metal compounds and organic solvents and stir until uniform, then dry until the organic solvents are completely volatilized, and place the resulting solids in an autoclave. In an inert atmosphere, heat up to 400-550°C, then stop the temperature rise, and wait until the temperature drops to room temperature to obtain pyrolysis products; The oxygen-containing hydrocarbon is selected from one or more alcohols, acids or anhydrides, aldehydes, and phenols with aromatic hydrocarbon groups, alkenyl groups, alkane groups, and heterocyclic groups; The transition metal compound is selected from one of the transition metallocene compounds, carbonyl transition organometallic compounds, acetylacetonate transition organometallic compounds, transition metal acetates or transition metal nitrates; B: using pyridine or tetrahydrofuran as a solvent to wash, filter and dry the pyrolysis product to obtain the target product. 2. A method for preparing a carbon-coated nano-metal oxide composite material, characterized in that: the carbon-coated nano-metal oxide composite material has a core-shell structure, the particle diameter ranges from 10nm to 80nm, and the thickness of the carbon coating layer 2.5nm to 10nm, the mass percentage of each component is: nanometer metal oxide 20% to 60%, carbon 40% to 80%; the specific steps and methods are: A: Mix oxygen-containing hydrocarbons with a mass ratio of 1:0.1 to 1:5 with transition metal compounds and organic solvents and stir until uniform, then dry until the organic solvents are completely volatilized, and place the resulting solids in an autoclave. In an inert atmosphere, heat up to 400-550°C, then stop the temperature rise, and wait until the temperature drops to room temperature to obtain pyrolysis products; The oxygen-containing hydrocarbon is selected from one or more alcohols, acids or anhydrides, aldehydes, and phenols with aromatic hydrocarbon groups, alkenyl groups, alkane groups, and heterocyclic groups; The transition metal compound is selected from one of the transition metallocene compounds, carbonyl transition organometallic compounds, acetylacetonate transition organometallic compounds, transition metal acetates or transition metal nitrates; B: using pyridine or tetrahydrofuran as a solvent to wash, filter and dry the pyrolysis product to obtain the target product. 3 . The method for preparing the carbon-coated nano-metal oxide composite material according to claim 2 , wherein the mass ratio of the oxygen-containing hydrocarbon to the transition metal compound is 1:1˜1:4. 4. The method for preparing carbon-coated nano-metal oxide composite material according to claim 2, characterized in that: the number of carbon atoms of the olefin group or alkane group in the oxygen-containing hydrocarbon is greater than 4 and less than 30. 5. The method for preparing carbon-coated nano-metal oxide composites according to claim 2, wherein the transition metal compound is ferrocene, cobaltocene or nickelocene, and the transition metal carbonyl compound is carbonyl Iron, cobalt carbonyl or nickel carbonyl, acetylacetonate transition metal compound is nickel acetylacetonate or cobalt acetylacetonate, transition metal acetate is cobalt acetate, nickel acetate or iron acetate, transition metal nitrate is iron nitrate, cobalt nitrate or nitric acid nickel. 6. The method for preparing carbon-coated nano-metal oxide composite materials according to claim 2 or 4, characterized in that: one or more groups with aromatic hydrocarbon groups, alkene groups, alkane groups, heterocyclic groups Alcohols with groups are octadecyl alcohol and phenylpropanol; aldehydes with one or more groups of aromatic hydrocarbon groups, alkenyl groups, alkane groups, and heterocyclic groups are o-tolualdehyde, 4-methyl- 3-pentenal or 3-phenylpropanal; acids or anhydrides with one or more groups of aromatic hydrocarbon groups, alkenyl groups, alkane groups, and heterocyclic groups are o-toluic acid, lauric acid, Cinnamic acid, sorbic acid, crotonic acid or phthalic anhydride; phenols with one or more groups of aromatic hydrocarbon groups, alkenyl groups, alkane groups, and heterocyclic groups are resorcinol and resorcinol phenol or o-cresol.

Images