CN108565426B

CN108565426B - Li3VO4/LiVO2Composite lithium ion battery cathode material and preparation method thereof

Info

Publication number: CN108565426B
Application number: CN201810339008.9A
Authority: CN
Inventors: 倪世兵; 康桃; 万智伟; 杨学林
Original assignee: China Three Gorges University CTGU
Current assignee: China Three Gorges University CTGU
Priority date: 2018-04-16
Filing date: 2018-04-16
Publication date: 2020-09-15
Anticipated expiration: 2038-04-16
Also published as: CN108565426A

Abstract

The present invention provides a Li₃VO₄/LiVO₂The preparation method of the composite lithium ion battery cathode material comprises the steps of mixing and dissolving lithium carbonate, vanadium pentoxide and hexamethylenetetramine in a beaker filled with 35ml of absolute ethyl alcohol, and rapidly stirring for 1 hour to fully mix all the components; transferring the obtained mixed solution into a lining of a hydrothermal kettle, reacting for 10-30 h in a blast oven at 100-180 ℃, and naturally cooling to room temperature to obtain an intermediate phase product which consists of upper-layer liquid and lower-layer precipitate; and separating supernatant in the intermediate phase product, drying the supernatant in a drying oven at 60-85 ℃, grinding the supernatant until the powder is light yellow, and calcining the powder for 5-10 hours at 450-650 ℃ in a nitrogen or argon protective atmosphere to obtain the composite material. The material is applied to the lithium ion battery cathode material, and shows good electrochemical performance.

Description

Li3VO4/LiVO2Composite lithium ion battery cathode material and preparation method thereof

Technical Field

The invention relates to a novel lithium ion battery cathode material, in particular to Li₃VO₄/LiVO₂Composite negative electrode

A material belongs to the field of electrochemical power sources.

Technical Field

In recent years, with the rapid development of lithium ion battery systems, the application fields of the lithium ion battery systems are continuously widened, and the fields of portable electronic equipment are gradually expanded to the fields of electric automobiles, large-scale energy storage engineering and the like, which undoubtedly puts higher requirements on the lithium ion batteries. Lithium ion battery negative electrode materials play an important role in batteries. Currently, the negative electrode of the commercialized lithium ion battery is made of graphite carbon material and Li₄Ti₅O₁₂However, the two methods have difficulty meeting the current market demands in terms of energy density, safety performance, cycle life and the like. The development of a novel high-performance lithium ion battery system with the characteristics of high energy density, high safety performance, long cycle life and environmental friendliness is a necessary way in the future. The types of the anode materials are relatively rich, the development is mature, the system of the cathode material is single, and the research and development of the cathode material are very important for developing a novel high-performance lithium ion battery system.

Li₃VO₄The lithium intercalation/deintercalation type cathode material has a lithium intercalation potential concentrated at 0.5-1.0V, and has a charge and discharge mechanism as follows: xLi⁺+ Li₃VO₄+ xe^-↔ Li_3+xVO₄(x is less than or equal to 3). Has higher theoretical capacity (592 mAh/g) and safe discharge platform compared with commercial graphite (372 mAh/g), compared with Li₄Ti₅O₁₂(175 mAh/g) has higher theoretical capacity and lower discharge platform, realizes the unification of safety performance and energy density, and has great research and practical values. Lifting of Li₃VO₄The main ways of performance of the anode material are to enhance its conductivity and lithium ion diffusion efficiency. Traditionally improved Li₃VO₄The method of conductivity is mainly to compound with carbon materials such as graphene, natural graphite, amorphous carbon and the like, but the particle size of the material is hardly influenced by the compounding, so that the lithium ion diffusion efficiency of the material is improved. LiVO₂Can be used as a cathode material and has much higher conductivity than Li₃VO₄. Li is hopeful to be obtained by adjusting the proportion of Li and V in the reaction raw materials and regulating and controlling the reaction environment₃VO₄/LiVO₂A composite material. High-conductivity LiVO₂Can enhance the overall conductivity of the composite material and effectively inhibit Li₃VO₄The crystal grain growth in the sintering process improves the lithium ion diffusion efficiency of the crystal grain, and the obtained Li₃VO₄/LiVO₂The composite material is expected to obtain excellent electrochemical performance. To this end, this patent developed a solvothermal based Li₃VO₄/LiVO₂The preparation method of the composite material comprises the steps of regulating the components and distribution of the intermediate phase precursor by using a solvent, and obtaining Li by combining solid phase sintering₃VO₄And LiVO₂Uniformly distributed Li₃VO₄/LiVO₂A composite material.

Disclosure of Invention

The invention relates to a composite lithium ion battery cathode material, which is Li₃VO₄/LiVO₂A composite material, the material being in particulate form. The preparation method comprises the following steps: mixing carbonRespectively dissolving lithium oxide, vanadium pentoxide and hexamethylenetetramine in a beaker of absolute ethyl alcohol, and quickly stirring to fully mix the components to obtain a mixed solution; transferring the obtained mixed solution into a lining of a hydrothermal kettle, reacting for 5-30 h in a blast oven at 100-180 ℃, and naturally cooling to room temperature to obtain a reactant; and separating out supernatant liquor in the obtained reactant, drying the supernatant liquor in an oven at the temperature of 60-85 ℃, grinding the supernatant liquor until the powder is light yellow, and calcining the powder for 5-10 hours at the temperature of 450-650 ℃ in the protective atmosphere of nitrogen or argon to obtain the composite material.

The molar ratio of the lithium to the vanadium to the hexamethylenetetramine is 1-5: 1: 2-10, wherein the solvent thermal solvent is absolute ethyl alcohol.

Li₃VO₄The self-prepared water-soluble organic silicon material has extremely strong water solubility and is difficult to directly obtain by a hydrothermal method. The Li with low yield can be obtained by solvothermal reaction₃VO₄Most of the Li, V will still be dissolved in the solvent. The principle of the method is to prepare the intermediate phase solution with uniformly dispersed Li and V by utilizing the ethanol solvothermal reaction. Reduction by ethanol on V⁵⁺And carrying out appropriate in-situ reduction and combining into a soluble precursor. Meanwhile, the special dispersing performance of the ethanol promotes the uniform dispersion of all components in the intermediate phase. In the subsequent sintering process, V is obtained by solid-phase reaction⁵⁺And V³⁺Li of (2)₃VO₄/LiVO₂A composite material.

Li according to the invention₃VO₄/LiVO₂The preparation method, the material and the performance of the composite material have the following remarkable characteristics:

1) the synthesis process is simple, easy to operate and good in controllability;

2) prepared Li₃VO₄/LiVO₂The composite particle size is small, about 100 nm. Wherein Li₃VO₄And LiVO₂And (4) uniformly compounding.

3) Li prepared by the invention₃VO₄/LiVO₂The composite material used as the lithium ion battery cathode material has higher capacity, lower charge and discharge platforms and good cycle performance.

Drawings

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

FIG. 2 SEM image of sample prepared in example 1.

FIG. 3 is a graph (a) of the charge and discharge curves and a graph (b) of the cycle performance of the first three samples prepared in example 1.

FIG. 4 is a graph of the cycle performance of the samples prepared in example 2.

FIG. 5 cycle performance plot of the samples prepared in example 3.

The specific implementation mode is as follows:

example 1

The material synthesis steps are as follows:

(1) lithium carbonate, vanadium pentoxide and hexamethylenetetramine are added according to a molar ratio of 4: 1: 5 respectively weighing 4mmol, 1mmol and 5mmol, dissolving in a beaker filled with 35ml of absolute ethyl alcohol, and rapidly stirring for 1 hour to fully mix the components to obtain a solution with uniform color;

(2) transferring the mixed solution obtained in the step (1) into a lining of a hydrothermal kettle, reacting in a blast oven at 120 ℃ for 24 hours, and naturally cooling to room temperature to obtain a reactant;

(3) and (3) separating supernatant liquor from the reactant obtained in the step (2), drying the supernatant liquor in a 70 ℃ drying oven, grinding the supernatant liquor until the powder is light yellow, and calcining the powder for 5 hours at 500 ℃ in a nitrogen protective atmosphere to obtain the composite material.

The prepared Li₃VO₄/LiVO₂The composite samples were subjected to XRD measurements as shown in figure 1. At 44.5 in the figure^oWith Li₃VO₄The (051) crystal face of (C) corresponds to 64.2^oAnd LiVO₂The (440) crystal face of (A) corresponds to the (B), and the test result shows that the prepared sample is Li₃VO₄And LiVO₂Mixtures of (1) corresponding to Li₃VO₄XRD card JCPDS, No.24-0666, corresponding to LiVO₂XRD card JCPDS, No. 36-0041. The morphology of the prepared sample was analyzed by SEM, and the prepared sample was granular as shown in fig. 2. The material obtained in example 1 was prepared as followsA battery: li to be prepared₃VO₄/LiVO₂Mixing the composite material sample with acetylene black and polyvinylidene fluoride according to a 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 at 60 ℃, cutting into 14mm round pieces, and drying in vacuum at 120 ℃ for 12 hours. Using lithium metal foil as counter electrode, Celgard 2400 as diaphragm, 1M LiPF₆the/DMC EC =1: 1 solution was used as electrolyte and assembled into a CR2025 type cell in an argon-protected glove box. And standing for 8 hours after the battery is assembled, and then performing constant-current charge and discharge test by using a CT2001A battery test system, wherein the test voltage is 3-0.02V. FIG. 3 is the Li prepared₃VO₄/LiVO₂The composite material as the lithium ion battery cathode material shows specific charge and discharge capacities of 573.9 and 931mAh/g for the first time, and the specific charge and discharge capacities of 486.9 and 494.7mAh/g after 40 cycles, and shows good cycling stability.

Example 2

The material synthesis steps are as follows:

(1) lithium carbonate, vanadium pentoxide and hexamethylenetetramine are mixed according to a molar ratio of 2: 1: 5 respectively weighing 2mmol, 1mmol and 5mmol, dissolving in a beaker filled with 35ml of absolute ethyl alcohol, and rapidly stirring for 1 hour to fully mix the components to obtain a solution with uniform color;

(2) transferring the mixed solution obtained in the step (1) into a lining of a hydrothermal kettle, reacting in a forced air oven at 140 ℃ for 24 hours, and naturally cooling to room temperature to obtain a reactant;

(3) and (3) separating supernatant liquid from the reactant obtained in the step (2), putting the supernatant liquid into a 70 ℃ oven until the supernatant liquid is dried, grinding the supernatant liquid until the powder is light yellow, and calcining the powder for 5 hours at 550 ℃ in a nitrogen protective atmosphere to obtain the composite material.

The material from example 2 was used to make a battery as described in example 1. FIG. 4 is the Li prepared₃VO₄/LiVO₂The specific charge and discharge capacities of the composite material as the negative electrode material of the lithium ion battery are 509.5 mAh/g and 887mAh/g respectively, the specific charge and discharge capacities after 40 cycles are 482.9 mAh/g and 488.4mAh/g respectively, and the composite material has obvious charge and discharge capacityShowing good cycling stability.

Example 3

The material synthesis steps are as follows:

(1) lithium carbonate, vanadium pentoxide and hexamethylenetetramine are added according to a molar ratio of 1: 1: 5 respectively weighing 1mmol, 1mmol and 5mmol, dissolving in a beaker filled with 35ml of absolute ethyl alcohol, and rapidly stirring for 1 hour to fully mix the components to obtain a solution with uniform color;

(2) transferring the mixed solution obtained in the step (1) into a lining of a hydrothermal kettle, reacting in a 160 ℃ forced air oven for 24 hours, and naturally cooling to room temperature to obtain a reactant;

(3) and (3) separating supernatant liquid from the reactant obtained in the step (2), putting the supernatant liquid into a 70 ℃ oven until the supernatant liquid is dried, grinding the supernatant liquid until the powder is light yellow, and calcining the powder for 5 hours at 600 ℃ in an argon protective atmosphere to obtain the composite material.

The material from example 3 was used to make a battery as described in example 1. FIG. 5 shows Li being produced₃VO₄/LiVO₂The composite material as the lithium ion battery cathode material shows specific charge and discharge capacities of 433.8 mAh/g and 721.1mAh/g for the first time, and the specific charge and discharge capacities of 397.5 and 397.6mAh/g after 40 cycles, and shows good cycle stability.

Claims

1. A preparation method of a lithium ion battery composite negative electrode material comprises the following steps:

(1) mixing and dissolving lithium carbonate, vanadium pentoxide and hexamethylenetetramine in absolute ethyl alcohol, and stirring to fully mix all the components to obtain a mixed solution, wherein the molar ratio of the lithium carbonate to the vanadium pentoxide to the hexamethylenetetramine is 4: 1: 5;

(2) transferring the mixed solution obtained in the step (1) into a lining of a hydrothermal kettle, reacting for 5-30 h in a blast oven at 120 ℃, and naturally cooling to room temperature to obtain a reactant;

(3) separating supernatant liquid from the reactant obtained in the step (2), drying the supernatant liquid, grinding the supernatant liquid until the powder is light yellow, and performing nitrogen or argon protectionCalcining at 500 ℃ for 5-10h in atmosphere to obtain Li₃VO₄/LiVO₂A composite material.