CN111009659A - Preparation method and application of biomass carbon/poly-sodium manganese fluorophosphate composite material - Google Patents

Abstract

The invention discloses a preparation method and application of a biomass carbon/poly-sodium manganese fluorophosphate composite material. Firstly, soaking bagasse in a sodium hydroxide solution with the mass percentage concentration of 5% to prepare a carbon source, then ball-milling hydrated manganese acetate, sodium fluoride, ammonium dihydrogen phosphate, sodium acetate and the carbon source in absolute ethyl alcohol by a ball milling method to prepare rheological phase slurry, and then calcining the rheological phase slurry by an in-situ pyrolysis method to prepare the biomass carbon/poly-sodium manganese fluorophosphate composite material. The biomass carbon/poly-sodium manganese fluorophosphate composite material is used as a lithium ion battery anode material. The invention has the advantages that: the carbon layer is coated on the surface of the poly-sodium manganese fluorophosphate particles, so that the defects that the rate capability and the cycle performance of the poly-sodium manganese fluorophosphate cannot be greatly improved by preparing a pure phase of the poly-sodium manganese fluorophosphate and then adding biochar generated by high-temperature carbonization to prepare a composite material can be well solved.

Description

Preparation method and application of biomass carbon/poly-sodium manganese fluorophosphate composite material

Technical Field

The invention belongs to the field of anode materials of lithium ion batteries, and particularly relates to a preparation method and application of a biomass carbon/poly-sodium manganese fluorophosphate composite material.

Background

Lithium ion batteries have ultrahigh energy density, and lithium metal has the capability of repeated charging, so that the lithium ion batteries become a research hotspot of power batteries. The traditional lithium ion battery uses lithium alloy metal oxide as a positive electrode material, but the performance difference of the positive electrode material is large due to different configuration elements, so that the rapid development of the lithium ion battery is hindered. With the development of scientific technology and the increasing demand of energy storage equipment, the requirements on the aspects of specific capacity, service life and the like of the lithium ion battery are higher and higher. Under the current research level, the problems of rare resources, poor conductivity and the like of the traditional lithium ion battery anode material can not better adapt to the development requirement, so that the significance of developing and researching the novel lithium ion battery anode material is great. In view of the shortage of lithium resource, it is found that some sodium-based fluorinated phosphate system compounds in polyanion type can be considered as the anode material of lithium ion battery due to good electrochemical performance. The fluorine element with strong electronegativity of the compound can improve the charge and discharge voltage in a proper amount, and the sodium-based fluoridated phosphate system compound can possibly have two or more electron transfers, so that the specific capacity of the battery can be greatly improved.

In order to improve the comprehensive performance of lithium ion batteries, systematic research on battery materials is required, but the positive electrode material is heavy and heavy. As the positive electrode material can affect the energy density, power size, service life and cost of the battery. The main manifestation is two aspects: firstly, the power density of the battery can be improved by 28% when the capacity of the anode material is improved by 50%; another aspect is that in current commercial lithium ion battery production, the cost of the positive electrode material accounts for approximately 40% of the overall battery cost. The reduction in the price of the positive electrode material directly determines the reduction in the price of the lithium ion battery. Therefore, the research on the anode material of the lithium ion battery has great significance for improving the performance of the lithium ion battery and reducing the cost of the lithium ion battery.

By polyanionic compounds is meant a series of anionic structural units (XO) containing octahedral or tetrahedral groups_m)^n-(Y)^k-The general term of the compounds (X = P, S, Mo, W, etc., Y = F, OH, etc.) is that tetrahedrons and octahedrons are connected three-dimensionally in the framework of the structure, and finally, a network structure is formed, and the structure is very stable. Sodium-based fluorinated phosphates are an important polyanionic compound that exhibits excellent electrochemical performance in lithium ion batteries, and the electrode reaction can be described as a mixed Li/Na insertion mechanism. The discovery of sodium-based fluorinated phosphate materials breaks the conventional belief that the positive electrode material in lithium ion batteries must be a lithium-based compound and expands the scope of finding excellent electrode materials. However, sodium-based fluorinated phosphates have low electronic conductivity and low ion diffusion rate, and have weak electrochemical activity compared with other materials, so that increasing the conductivity and the diffusion rate by reducing the size of particles and combining with the research of a suitable modification means becomes a research focus of a novel positive electrode material.

Na, Mn are abundant in content on earth, and this patent has prepared polyfluorophosphoric acid manganese sodium, utilizes the biomass carbon material to wrap polyfluorophosphoric acid manganese sodium material as the carbon source simultaneously, can make the cost cheaper, uses normal position pyrolysis method to make organic carbon source decompose in sintering process, and the biological carbon material specific surface who finally obtains is great, and this biomass carbon material's cladding also can reduce electrode material's particle diameter, and biological carbon material is high conductive material simultaneously, helps the transmission of electron.

The south of China is a main sugar producing area, bagasse is a main byproduct of sugar industry, and is rich in resources, but at present, only a small amount of bagasse is used for making boards, paper making, cultivating crops and the like, and most of bagasse is directly used as fuel, so that the environment is polluted, and resources are wasted. The method utilizes the bagasse as a carbon source, can improve the comprehensive utilization degree of the bagasse, and is in line with green environmental protection.

Disclosure of Invention

The invention aims to provide a preparation method and application of a biomass carbon/poly-manganese sodium fluorophosphate composite material aiming at the defects of low electronic conductivity and slow ion diffusion speed of sodium-based fluorinated phosphate.

The preparation method of the biomass carbon/poly-sodium manganese fluorophosphate composite material comprises the following specific steps:

(1) soaking bagasse in a sodium hydroxide solution with the mass percentage concentration of 5%, heating at the constant temperature of 80 ℃ for 2 hours, soaking at room temperature for 4 hours, taking out the bagasse from the solution, washing the bagasse with distilled water until the pH of an eluate is neutral, drying the washed bagasse in a forced air drying oven, and grinding the dried bagasse in a sealed grinder into powder of 300-400 meshes as a carbon source for later use.

(2) 2.4509 g of manganese acetate hydrate (Mn (CH)₃COO)₂·4H₂O), 0.4199 g of sodium fluoride (NaF), 1.1502 g of ammonium dihydrogen phosphate (NH)₄H₂PO₄) 1.3608 g of sodium acetate (NaCH)₃COO·3H₂O) and 0.5382 g of the carbon source obtained in the step (1), adding 20 mL of absolute ethyl alcohol as a dispersing agent, performing ball milling for 6 h to obtain rheological phase slurry, and placing the rheological phase slurry in a forced air drying oven at 65 ℃ for heat preservation for 5 h to obtain precursor powder.

(3) And (3) transferring the precursor powder prepared in the step (2) into a crucible, placing the crucible into a tubular furnace protected by argon, heating to 300 ℃ at the heating rate of 5 ℃/min, preheating for 2 h, grinding the preheated precursor powder again, placing the ground precursor powder into the tubular furnace protected by argon, heating to 600 ℃ at the heating rate of 10 ℃/min, calcining for 6 h, and cooling to room temperature along with the tubular furnace to obtain the biomass carbon/poly-sodium manganese fluorophosphate composite material.

The biomass carbon/poly-sodium manganese fluorophosphate composite material is used as a lithium ion battery anode material.

Compared with the prior art, the invention has the following advantages:

the biomass carbon/sodium manganese polyfluorophosphate composite electrode material rheological phase slurry is prepared by a ball milling method, and then the biomass carbon/sodium manganese polyfluorophosphate composite material which can be used as a lithium ion battery anode material is obtained by in-situ pyrolysis treatment. Experiments prove that the carbon-coated manganese sodium fluorophosphate material has better electrochemical properties (such as rate capability, cycle performance and the like) than the non-carbon-coated poly-manganese fluorophosphate material, and the specific capacity of the material is larger, and the charge migration resistance of the material is smaller. The preparation method is simple and feasible, and is environment-friendly.

The electrochemical performance of the poly-sodium manganese fluorophosphate is improved, and carbon coating is one of the most effective methods. If the biological carbon material generated by high-temperature carbonization is added after the pure phase of the poly-sodium manganese fluorophosphate is formed, the effect is not ideal, because the biological carbon material generated by high-temperature carbonization is generally in an amorphous state with lower conductivity, and the rate capability and the cycle performance of the poly-sodium manganese fluorophosphate are difficult to be greatly improved. The invention coats the surface of the poly-sodium manganese fluorophosphate particle with a carbon layer, thereby well solving the problem.

Drawings

Fig. 1 is a scanning electron microscope image of the biomass carbon/sodium manganese polyfluorophosphate composite material prepared in the embodiment of the invention.

FIG. 2 is an X-ray energy spectrum of the biomass carbon/poly-sodium manganese fluorophosphate composite material prepared in the example of the invention.

FIG. 3 is an X-ray diffraction spectrum of the biomass carbon/poly-sodium manganese fluorophosphate composite material prepared in the example of the invention.

FIG. 4 is a graph showing the cycle performance of the biomass carbon/poly (manganese sodium fluorophosphate) composite material prepared in the example of the invention.

Fig. 5 is a rate performance curve diagram of the biomass carbon/sodium manganese polyfluorophosphate composite material prepared in the embodiment of the invention.

Fig. 6 is a coulombic efficiency curve diagram of the biomass carbon/sodium manganese polyfluorophosphate composite material prepared in the embodiment of the invention.

Detailed Description

The present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

Example (b):

(1) soaking bagasse in a sodium hydroxide solution with the mass fraction of 5%, heating at the constant temperature of 80 ℃ for 2 hours, soaking at room temperature for 4 hours again, taking out the bagasse from the solution, washing the bagasse with distilled water until the pH value of the solution is neutral, drying the bagasse in a forced air drying oven, and grinding the dried bagasse in a sealed grinder into powder with the particle size of 300-400 meshes, wherein the powder serves as a carbon source for later use.

(2) 2.4509 g of manganese acetate hydrate (Mn (CH)₃COO)₂·4H₂O), 0.4199 g of sodium fluoride (NaF), 1.1502 g of ammonium dihydrogen phosphate (NH)₄H₂PO₄) And 1.3608 g sodium acetate (NaCH)₃COO·3H₂And O), adding 0.5382 g of the carbon source obtained in the step (1), adding 20 mL of absolute ethyl alcohol as a dispersing agent, performing ball milling for 6 h to obtain rheological phase slurry, and placing the rheological phase slurry obtained after milling in a forced air drying oven at 65 ℃ for heat preservation for 5 h to obtain precursor powder.

(3) And (3) transferring the precursor powder obtained in the step (2) into a crucible, placing the crucible into a tubular furnace, controlling the heating rate to be 5 ℃/min, preheating for 2 h at 300 ℃ in the tubular furnace under the protection of argon, grinding the preheated powder again, calcining the powder for 6 h at 600 ℃ in the tubular furnace filled with argon, controlling the heating rate to be 10 ℃/min, and cooling the tubular furnace to room temperature to obtain the biomass carbon/poly-sodium manganese fluorophosphate composite material.

The biomass carbon/sodium manganese polyfluorophosphate composite material prepared in the embodiment is characterized and analyzed by using SEM, EDS and XRD, and the results are shown in fig. 1, fig. 2 and fig. 3.

FIG. 1 is a scanning electron micrograph. The biomass carbon/poly-manganese-sodium fluorophosphate (C/Na) can be seen from the figure₂MnPO₄F) The crystallinity of the composite material is good, and the particle size is compared with a ruler in an observation picture and is probably within the range of 400-500 nm.

FIG. 2 is an X-ray energy spectrum. All elements in the cathode material are found in an EDS spectrogram, the sum of the contents of all the elements is close to one hundred percent, and the result proves that the impurities in the cathode material are less, and carbon is uniformly distributed in the prepared C/Na₂MnPO₄And F, the surface of the anode material proves that the carbon material is successfully coated.

FIG. 3 is an X-ray powderDiffraction line spectrum. As can be seen from the figure, uncoated carbon and Na coated with carbon₂MnPO₄XRD diffraction spectrum of F material sample can be matched with Na₂MnPO₄F standard card (PDF #87-0467) is matched in map, and basically no redundant miscellaneous peak appears, which indicates that the prepared sample is Na₂MnPO₄F, and the crystal structure of the compound is not changed due to carbon coating.

Carrying out electrochemical performance test on the biomass carbon/poly-sodium manganese fluorophosphate composite material, and firstly assembling a lithium ion battery according to the following steps:

(1) and preparing an electrode plate of the lithium ion battery. According to the proportion of active substances, namely acetylene black and polyvinylidene fluoride (PVDF) =7:2:1, firstly respectively weighing a certain mass of the active substances, namely the acetylene black, mixing and grinding the substances, wherein the grinding time is about 60 min, then weighing a binder PVDF, adding the binder PVDF into a mortar, grinding for more than ten minutes to fully mix the substances, dropwise adding a proper amount of N-methyl pyrrolidone (NMP), adjusting the mixture to be proper thin consistency, coating the ground substances on an aluminum sheet, drying in vacuum for 12 h, and finally pressing into a pole piece with proper size for later use.

(2) And (5) assembling the battery. Taking the prepared pole piece as a research electrode, firstly weighing the mass of the pole piece, then putting the weighed pole piece into a positive electrode shell which is washed and dried in advance, matching a gasket, an elastic sheet and a negative electrode shell, taking a metal lithium piece as a counter electrode, taking a polypropylene porous membrane as a diaphragm and taking 1.0 mol/L LiPF₆The half cell assembly and the sheet formation were performed in an argon (Ar) -protected MIKPROUNA super-clean glove box (oxygen and water vapor contents less than 1 ppm) of MIKPROUNA, ltd.

In this embodiment, a new battery performance testing system is adopted to test a cycle performance curve (fig. 4), a rate performance curve (fig. 5) and a coulomb efficiency curve (fig. 6), and the charge and discharge performance of the new battery is analyzed. And (3) testing conditions are as follows: the temperature is 25 ℃, the voltage range is 1.5-4.5V, the current density of the cycle performance is 0.1C, and the multiplying power of the multiplying power performance is 0.1C, 0.2C, 0.5C, 1C and 2C.

Fig. 4 is a graph of cycle performance. As can be seen from the figure, C/Na₂MnPO₄F is subjected to charge-discharge circulation under the multiplying power of 0.1C, the first circle of discharge specific capacity is 8.71 m Ah/g, and the capacity is attenuated to 5.75m Ah/g after 30 circles of circulation; the first circle of the discharge specific capacity of the uncoated carbon material is 1.94m Ah/g, and the attenuation of the uncoated carbon material after 30 circles of circulation is 1.56m Ah/g, so that the carbon coating can enhance the discharge specific capacity of the anode material.

Fig. 5 is a graph of rate performance. As can be seen from the figure, C/Na₂MnPO₄The discharge capacity of the F material sample and its comparative material at five rates of 0.1C, 0.2C, 0.5C, 1C and 2C was not high, probably because of C/Na₂MnPO₄Mn in F positive electrode material²⁺Dissolved in the electrolyte, resulting in a low capacity. However, carbon coating can improve the electrical conductivity and capacity as compared with carbon coating.

Fig. 6 is a coulombic efficiency graph. As can be seen from the figure, the first coulombic efficiency was lower for both samples, probably because of the first Na depletion⁺Then, Li⁺And cannot be smoothly embedded. In the latter cycles, the coulombic efficiency gradually increases, and finally the C/Na₂MnPO₄The coulombic efficiency of F increased to 98.98% higher than that of the uncoated carbon material.

Claims (2)

1. A preparation method of a biomass carbon/poly-sodium manganese fluorophosphate composite material is characterized by comprising the following specific steps:

(1) soaking bagasse in a sodium hydroxide solution with the mass percentage concentration of 5%, heating at the constant temperature of 80 ℃ for 2 hours, soaking at room temperature for 4 hours, taking out the bagasse from the solution, washing the bagasse with distilled water until the pH of an eluate is neutral, drying the washed bagasse in a forced air drying oven, and grinding the dried bagasse into powder of 300-400 meshes in a sealed grinder to serve as a carbon source for later use;

(2) weighing 2.4509 g of manganese acetate hydrate, 0.4199 g of sodium fluoride, 1.1502 g of ammonium dihydrogen phosphate, 1.3608 g of sodium acetate and 0.5382 g of the carbon source obtained in the step (1), adding 20 mL of absolute ethyl alcohol serving as a dispersing agent, performing ball milling for 6 hours to obtain rheological phase slurry, and placing the rheological phase slurry in a forced air drying oven at 65 ℃ for heat preservation for 5 hours to obtain precursor powder;

(3) and (3) transferring the precursor powder prepared in the step (2) into a crucible, placing the crucible into a tubular furnace protected by argon, heating to 300 ℃ at the heating rate of 5 ℃/min, preheating for 2 h, grinding the preheated precursor powder again, placing the ground precursor powder into the tubular furnace protected by argon, heating to 600 ℃ at the heating rate of 10 ℃/min, calcining for 6 h, and cooling to room temperature along with the tubular furnace to obtain the biomass carbon/poly-sodium manganese fluorophosphate composite material.

2. The application of the biomass carbon/poly-sodium manganese fluorophosphate composite material prepared by the preparation method according to claim 1 is characterized in that: the biomass carbon/poly-sodium manganese fluorophosphate composite material is used as a lithium ion battery anode material.