CN114373906A

CN114373906A - Honeycomb Li3VO4Preparation method of/C lithium ion battery cathode material

Info

Publication number: CN114373906A
Application number: CN202111562397.XA
Authority: CN
Inventors: 倪世兵; 李道波; 杨松; 石嘉悦; 张苗苗
Original assignee: China Three Gorges University CTGU
Current assignee: China Three Gorges University CTGU
Priority date: 2021-12-20
Filing date: 2021-12-20
Publication date: 2022-04-19
Anticipated expiration: 2041-12-20
Also published as: CN114373906B

Abstract

The invention provides a honeycomb Li₃VO₄A preparation method of a negative electrode material of a/C lithium ion battery. Adding polyvinyl alcohol, lithium nitrate, ammonium metavanadate and oxalic acid into a proper amount of deionized water, and stirring to obtain a uniform green solution. And (3) putting the mixed solution into a syringe for electrostatic spraying, wherein the syringe is connected with a steel needle with the inner diameter of 0.2-0.3 mm through a plastic pipe, a receiver is a rotatable steel roller coated with aluminum foil, when the electrostatic spraying is started, a voltage of 18-20 kV is applied, the precursor solution is atomized under high pressure, electrostatic fog drops are sprayed out, and finally the precursor composite material is uniformly distributed around the aluminum foil. When the spraying process is finished, the drying is carried out, and the temperature is raised to 200-300-Presintering for 2-5 hours at the temperature of 500 ℃ and 800 ℃ in a nitrogen environment to obtain the honeycomb Li₃VO₄a/C composite material. The invention synthesizes the honeycomb Li by simple electrostatic spraying for the first time₃VO₄the/C composite material is used as the cathode material of the lithium ion battery, and the prepared honeycomb Li₃VO₄the/C composite material is used as a lithium ion battery cathode material.

Description

Honeycomb Li3VO4Of negative electrode material of/C lithium ion batteryPreparation method

Technical Field

The invention relates to a novel lithium ion battery cathode material, in particular to a method for preparing honeycomb Li by electrostatic spraying₃VO₄A method for using a/C composite material as a lithium ion battery cathode material belongs to the field of electrochemical power sources.

Background

Lithium ion batteries have been rapidly developed in recent decades as one of the representatives of green energy storage materials. The appearance and development of the daily digital products such as mobile phones and notebook computers and the large product equipment such as electric vehicles and distributed energy storage power stations are closely related to the innovation and progress of the battery technology. In recent years, with the vigorous development of the pure electric vehicle market, the demand of the market for the lithium ion battery is continuously increased, which also puts higher and higher requirements on the performance of the lithium ion battery, and the lithium ion battery material with high energy density, high stability and low cost naturally becomes the focus of the current research.

Li₃VO₄Is a novel lithium ion battery cathode material, has higher volume specific capacity than commercial graphite, and has higher volume specific capacity than Li₄Ti₅O₁₂Has lower voltage platform and higher specific capacity, and is an ideal cathode candidate material of the lithium ion battery. However, Li₃VO₄The relatively low electronic and ionic conductivities of the negative electrode materials may lead to large polarization during charging/discharging, resulting in poor electrochemical reaction kinetics and poor battery cycling performance at high rates, and therefore, research mainly focuses on enhancing Li₃VO₄The conductivity of the material and how to improve the cycling performance of the material.

In addition, at present, no simple electrostatic spraying Li preparation method by using an electrostatic spinning machine exists₃VO₄And reporting of electrodes. Based on the above background, the present patent developed a method for preparing cellular Li based on electrostatic spraying₃VO₄A method for preparing the/C composite material. The prepared electrode material takes honeycomb carbon as a matrix, and a large number of ultra-small nano particles are embedded in the surface and the interior of the matrixThe particle-cellular morphology structure has strong bearing capacity, can effectively inhibit structural collapse caused by volume expansion in the charge-discharge process, and the ultra-small nano particles are beneficial to the permeation of electrolyte, show excellent electrochemical performance and have potential application value in lithium ion batteries.

Disclosure of Invention

Based on electrostatic spraying technology, the honeycomb Li is obtained by taking lithium nitrate, oxalic acid, ammonium metavanadate, polyvinyl alcohol and deionized water as raw materials₃VO₄the/C composite material comprises the following steps:

(1) adding a certain amount of polyvinyl alcohol, lithium nitrate, ammonium metavanadate and oxalic acid into a proper amount of deionized water, and stirring to obtain a uniform green solution;

(2) transferring the uniform solution obtained in the step (1) into an injector, and spinning for 6-8 hours under the conditions that the voltage is 18-20 kV and the temperature is 40-60 ℃ to obtain a precursor composite material;

(3) quickly transferring the precursor composite material obtained in the step (2) to a forced air drying oven at 60-80 ℃ for drying for 10-12 hours, placing the dried precursor composite material in an air environment after drying, heating to 200-300 ℃ for presintering for 2-5 hours, and then calcining at 500-800 ℃ for 5 hours in a nitrogen environment to obtain the honeycomb Li₃VO₄a/C composite material.

The molar ratio of lithium nitrate, oxalic acid and ammonium metavanadate in the mixed solution in the step (1) is 3-4:5-6:0.5-1, the mass of deionized water accounts for 76-80% of the total mass, and the mass of polyvinyl alcohol accounts for 6-10% of the total mass.

In the step (2), the electrostatic spraying voltage is 18-20 kV, the time is 6-8 hours, the ambient temperature is 40-60 ℃, the humidity is 20-30% and the spinning distance is 20-30cm during spinning.

After the electrostatic spraying is finished, the aluminum foil is quickly transferred to an oven at 60-80 ℃ to be dried for 10-12 hours.

In the step (3), the pre-sintering is carried out in the air at the temperature of 200 ℃ to 300 ℃, the temperature rising speed is 5-10 ℃/min, the pre-sintering time is 2-5 hours, and then the calcination is carried out at the temperature of 500 ℃ to 800 ℃ for 5-8 hours in the nitrogen atmosphere at the temperature rising speed of 4-5 ℃/min.

This patent uses polymer solution atomization in strong electric fieldForming charged fog drops, and obtaining the honeycomb Li by simple electrostatic spraying for the first time₃VO₄the/C electrode material is characterized in that a large number of ultra-small nano particles are embedded in a honeycomb carbon matrix, so that the lithium ion diffusion in the composite material is obviously enhanced.

The principle is as follows: (1) the actual structure of ammonium metavanadate is ammonium tetravanadate (NH)₄)₄V₄O₁₂In acidic solution V₄O₁₂ ⁴⁻Will obtain VO formed by chemical reaction of proton²⁺（V₄O₁₂ ⁴⁻+16H⁺+4e = 4VO²⁺+12H₂O). In the electrostatic spraying process, Li due to electrostatic interaction⁺、VO²⁺Mutually repel each other, thereby inhibiting the agglomeration of the two and respectively combine with^-OOC-COO^-Combining, and uniformly dispersing on a microscopic scale; (2) through electrostatic spraying, water in the liquid drops is atomized and then mutually repelled at the edges of the liquid drops and Li at the core under the electrostatic action⁺、VO²⁺The components are retained in the center of the droplets, and the droplets are arranged into an ordered structure under the action of capillary force and convection. In the subsequent drying, the water is completely evaporated, the polymer is completely solidified, and oxalic acid and ammonium metavanadate react chemically to form a stable complex and gas (2 NH)₄VO₃+4C₂H₂O₄ = (NH₄)₂[(VO)₂(C₂O₄)₃]+2CO₂+H₂O), the gas causes the formation of honeycomb cells, the pores of which are arranged in a hexagonal order, as is the case with honeycombs; (3) using polyvinyl alcohol as template through^-OOC-COO^-With Li⁺、VO²⁺And (4) combining. Presintering (pre-oxidizing) at 200-300 ℃ in air, carrying out dehydrogenation reaction on polyvinyl alcohol, and simultaneously generating conjugated C = C bonds to form a stable carbon skeleton, which is beneficial to maintaining a honeycomb structure, and simultaneously generating a large amount of free oxygen which is Li⁺、VO²⁺Formation of Li in subsequent sintering₃VO₄Providing an oxidizing environment; (4) during sintering, Li⁺、VO²⁺Bonding between the surface and interior of polyvinyl alcohol and formation of Li in an oxidizing environment₃VO₄Nanoparticles, while the polyvinyl alcohol is further carbonized, to obtain Li₃VO₄The nano particles are embedded in the honeycomb carbon matrix and have special appearance on the surface. The honeycomb carbon is beneficial to enhancing the structural stability of the material, and the activity of the composite material can be obviously improved by the ultra-small nano particles. Prepared honeycomb Li₃VO₄the/C composite material as the negative electrode of the lithium ion battery shows excellent comprehensive electrochemical performance.

The invention relates to a honeycomb Li₃VO₄The preparation method of the/C composite material as the lithium ion battery cathode material has the following remarkable characteristics:

(1) the manufacturing cost is low, and the environment-friendly effect is achieved;

(2) the synthesis process is simple, the electrostatic spraying can be carried out without extra high-temperature environment, and the repeatability is strong;

(3) prepared honeycomb Li₃VO₄The honeycomb structure of the/C composite material has strong bearing capacity and structure

The electrolyte has the characteristics of stability, capacity of bearing volume expansion caused by charging and discharging, and the ultra-small nanoparticles are beneficial to contact and permeation of the electrolyte;

(4) prepared honeycomb Li₃VO₄the/C composite material is used as the negative electrode material of the lithium ion battery for the first time

Has high capacity and excellent cycle stability.

Drawings

FIG. 1 optical photograph of sample prepared in example 1: (a) after spraying, (b) after drying, and (c) a partial enlarged view.

Figure 2 XRD pattern of the sample prepared in example 1.

FIG. 3 SEM image of sample prepared in example 1.

FIG. 4 graph of (a) the first three charge and discharge curves and (b) the cycle performance of the sample prepared in example 1.

Fig. 5 photo optics of the precursor solution prepared in example 2.

FIG. 6 optical photograph of sample prepared in example 3.

FIG. 7 is a graph of (a) the first three charge and discharge curves and (b) the cycle performance of the sample prepared in example 3.

FIG. 8 SEM image of sample prepared in example 4.

FIG. 9 is a graph of (a) the first three charge and discharge curves and (b) the cycle performance of the sample prepared in example 4.

Detailed Description

Example 1

Accurately weighing 7.5 mmol of lithium nitrate, 12.5 mmol of oxalic acid, 2.5 mmol of ammonium metavanadate and 1.2 g of polyvinyl alcohol according to the stoichiometric ratio, adding the lithium nitrate, 12.5 mmol of oxalic acid, 1.2 mmol of ammonium metavanadate into 15 mL of deionized water, stirring for 48 hours to obtain a uniform green solution, then transferring the obtained uniform solution into an injector, spraying for 8 hours under the conditions of 19 kV voltage and 40 ℃, quickly transferring a precursor material into an air-blowing drying box at 80 ℃ after spraying is finished, drying for 12 hours, placing the dried precursor material into an air environment, presintering for 3 hours at 250 ℃, and then calcining for 6 hours at 600 ℃ in a nitrogen environment to obtain the honeycomb Li₃VO₄a/C composite material. After electrostatic spraying, firstly obtaining an atomized precursor material on a received aluminum foil (figure 1a), drying to remove water and generating yellow particles (figure 1b) along with the reaction of oxalic acid and ammonium metavanadate, analyzing the carbonized composite material by an XRD (X-ray diffraction) pattern, and obtaining a diffraction peak and Li₃VO₄(PDF # 38-1247) corresponds well (FIG. 2). As can be seen from the SEM image, the composite material has a hexagonal honeycomb structure as a whole (FIG. 3a), and a large number of ultra-small nanoparticles are uniformly distributed on the surface of the honeycomb (FIG. 3 b).

The material was made into a battery as follows: mixing the prepared sample with acetylene black and polyvinylidene fluoride according to the weight ratio of 8:1:1, preparing slurry by using N-methyl pyrrolidone as a solvent, coating the slurry on a copper foil with the thickness of 10 mu m, drying the copper foil at 60 ℃ for 10 hours, cutting the copper foil into a wafer with the diameter of 14mm, and drying the wafer at 120 ℃ in vacuum for 12 hours. Using a metal lithium sheet as a counter electrode and a Celgard membrane as a diaphragm, and dissolving LiPF₆And (1 mmol/L) EC + DMC + DEC (volume ratio of 1: 1: 1) solution is used as electrolyte, and the electrolyte is assembled into a CR2025 type battery in an argon protective glove box. Standing for 8 hours after the battery is assembled, and then performing constant-current charging and discharging by using a CT2001 battery testing systemElectrical test with a test voltage of 3-0.01V and a current density of 200 mA-g^-1. FIG. 4 is the prepared honeycomb Li₃VO₄And the first three circles of charge and discharge curves and the cycle performance diagram of the negative electrode of the/C lithium ion battery. The first charge and discharge specific capacities are 614 mAh g and 913 mAh g respectively^-1The charging and discharging capacities after the circulation for 130 times are 555.7 mAh g and 560.7 mAh g respectively^-1And excellent electrochemical performance is shown.

Example 2

This example was identical to example 1 except that 7.5 mmol of lithium nitrate, 2.5 mmol of ammonium metavanadate and 1.2 g of polyvinyl alcohol were weighed out and added to 15 mL of deionized water without adding oxalic acid, and stirred for 48 hours, resulting in a non-uniform solution (FIG. 5a) and too viscous (FIG. 5b), so that electrostatic spraying was not possible and a battery product could not be realized.

Example 3

In this example, the procedure is exactly the same as that of example 1, and the material is obtained by directly calcining at 600 ℃ for 6 hours at a temperature rise rate of 5 ℃/min without pre-sintering, and the overall morphology of the prepared sample is not significantly changed (fig. 6). The material obtained in example 3 was used to prepare a battery in accordance with example 1. The first charge and discharge specific capacities are 268.1 mAh.g respectively^-1590.3 mAh g^-1(FIG. 7a), has obvious charge and discharge platform, and the charge and discharge capacity after 130 times of circulation are 269.1 mAh g^-1269.8 mAh g^-1(FIG. 7b), the electrochemical performance was poor.

Example 4

This example was carried out in the same manner as in example 1 except that the high polymer polyvinyl alcohol used in example 1 was changed to polyvinylpyrrolidone (PVP), and 7.5 mmol of lithium nitrate, 12.5 mmol of oxalic acid, 2.5 mmol of ammonium metavanadate and 1.2 g of polyvinylpyrrolidone were stoichiometrically weighed and added to 15 mL of deionized water and stirred for 48 hours. Then transferring the obtained uniform solution into an injector, simply spraying under the conditions of voltage of 19 kV and temperature of 40 ℃, finding that polyvinylpyrrolidone is stretched and refined under the action of static electricity, finally spinning to form a fiber membrane, quickly transferring the fiber membrane into an air-blast drying oven at 80 ℃ after spinning is finished, drying for 12 hours, and placing the fiber membrane into an air ring after dryingAnd in the atmosphere, pre-burning at 250 ℃ for 3 hours, and then calcining at 600 ℃ for 6 hours in a nitrogen environment to obtain the fiber composite material. The prepared sample has changed appearance, is fibrous as a whole (figure 8), and has a large amount of nano-particles dispersed on the surface. The material obtained in example 4 was used to prepare a battery in accordance with example 1. The specific capacities of charging and discharging for the first time are 489.4 mAh g respectively^-1622.2 mAh g^-1(FIG. 9a), has obvious charge and discharge platform, and the charge and discharge capacity after 130 times of circulation are 411.7 mAh g^-1And 413.5 mAh · g^-1(FIG. 9b), the electrochemical performance is good.

Claims

1. Honeycomb Li₃VO₄The preparation method of the/C lithium ion battery cathode material is characterized in that the specific preparation process of the material is as follows:

2. The honeycomb Li of claim 1₃VO₄The preparation method of the/C lithium ion battery cathode material is characterized in that the molar ratio of lithium nitrate, oxalic acid and ammonium metavanadate in the mixed solution in the step (1) is 3-4:5-6:0.5-1, the mass of deionized water accounts for 76-80% of the total mass, and the mass of polyvinyl alcohol accounts for 6-10% of the total mass.

3. The honeycomb Li of claim 1₃VO₄A preparation method of a negative electrode material of a/C lithium ion battery,the method is characterized in that in the step (2), the electrostatic spraying voltage is 18-20 kV, the time is 6-8 hours, the ambient temperature is 40-60 ℃, the humidity is 20-30% and the spinning distance is 20-30cm during spinning.

4. The honeycomb Li of claim 1₃VO₄The preparation method of the negative electrode material of the/C lithium ion battery is characterized in that after electrostatic spraying is finished, the aluminum foil is quickly transferred to a drying oven at the temperature of 60-80 ℃ to be dried for 10-12 hours.

5. The honeycomb Li of claim 1₃VO₄The preparation method of the/C lithium ion battery cathode material is characterized in that in the step (3), the anode material is pre-sintered in the air, the pre-sintering temperature is 200-.