阅读说明：本技术 磷酸钒锂在锂硫电池隔膜涂覆中的应用 (Application of lithium vanadium phosphate in coating of lithium-sulfur battery diaphragm ) 是由 王利霞 闫继 常鑫波 赵太宝 张林森 于 2021-06-02 设计创作，主要内容包括：本发明提供了一种磷酸钒锂在锂硫电池隔膜涂覆中的应用,将磷酸钒锂材料用于锂硫电池隔膜的涂覆材料中,隔膜中磷酸钒锂含量为5-15%,涂覆厚度为5-20μm。包括如下步骤：采用溶胶凝胶法制备磷酸钒锂材料,然后将所得材料与导电碳,粘结剂进行充分地混合；通过控制粘稠度,将该混合浆料,粘附于PP隔膜表面,真空烘干后,得到所需的磷酸钒锂涂覆PP隔膜,最后,将所得隔膜应用于锂硫电池中。本发明的工艺简单、成本低、性能优良,适用于规模化生产。(The invention provides an application of lithium vanadium phosphate in coating of a lithium-sulfur battery diaphragm, wherein the lithium vanadium phosphate material is used in the coating material of the lithium-sulfur battery diaphragm, the content of the lithium vanadium phosphate in the diaphragm is 5-15%, and the coating thickness is 5-20 mu m. The method comprises the following steps: preparing a lithium vanadium phosphate material by adopting a sol-gel method, and then fully mixing the obtained material with conductive carbon and a binder; the mixed slurry is adhered to the surface of a PP diaphragm by controlling the viscosity, the needed PP diaphragm coated with lithium vanadium phosphate is obtained after vacuum drying, and finally, the obtained diaphragm is applied to a lithium-sulfur battery. The invention has simple process, low cost and excellent performance, and is suitable for large-scale production.)

1. The application of lithium vanadium phosphate in coating of the lithium-sulfur battery separator is characterized in that: the vanadium lithium phosphate material is used in the coating material of the lithium-sulfur battery diaphragm, the content of the vanadium lithium phosphate in the diaphragm is 5-15wt%, and the coating thickness is 5-20 mu m.

2. Use according to claim 1, characterized in that: the micro-morphology of the lithium vanadium phosphate is a nano material/micron sphere-like material, and the crystal structure is a monoclinic structure.

3. Use according to claim 1, characterized in that: the lithium sulfur battery is used at-20 ℃ to 0 ℃.

4. Use according to any of claims 1-3, characterized by the following steps:

(1) fully mixing a lithium vanadium phosphate material, conductive carbon, a binder and a dispersing solvent; vacuumizing the obtained slurry;

(2) coating the slurry obtained in the step (1) on the surface of a PP diaphragm by adopting a single surface;

(3) and (3) drying after the coating in the step (2).

5. Use according to claim 4, characterized in that: in the step (1), the conductive carbon is acetylene black, the binder is polyvinylidene fluoride, and the dispersion solvent is nitrogen methyl pyrrolidone.

6. Use according to claim 4, characterized in that: the mass ratio of the vanadium lithium phosphate material, the conductive carbon and the binder in the step (1) is (70-85): (10-20): (5-10).

7. Use according to claim 4, characterized in that: and (2) stirring and mixing for 1-2h by adopting a planetary stirrer in the step (1).

8. Use according to claim 4, characterized in that: in the step (2), a flat plate casting coating mode is adopted, the coating thickness is 5-20 mu m, and the feeding speed of a scraper is 5-25 mm/s.

9. Use according to claim 4, characterized in that: in the step (3), the drying temperature is 40-60 ℃, and the drying time is 6-24 h.

Technical Field

The invention relates to the field of lithium batteries, in particular to application of lithium vanadium phosphate in coating of a lithium-sulfur battery diaphragm.

Background

Currently, lithium sulfur batteries, one of the ideal candidates for the late lithium ion battery age, have received much attention from researchers due to their theoretical specific capacity of up to 1675mAh/g and their enormous energy density (2500 Wh/kg).

Although the lithium-sulfur battery has a series of advantages of high energy density, low cost, green and pollution-free, the commercial lithium-sulfur battery is still in the development stage so far, mainly because of the limitations of low conductivity of sulfur itself, more sulfur anode discharge intermediate products, shuttle effect of sulfides, and the like. Therefore, the key to improving the electrical performance of lithium-sulfur batteries is to suppress the shuttling effect of polysulfides. One of the measures currently taken by academia is to coat the surface of the separator with a metal oxide or sulfide, and to block the diffusion of polysulfide to the negative electrode by using the adsorption effect of the compound on polysulfide. However, the materials used for coating have low electrical conductivity and poor electron transport capability, and have limited improvement in performance of lithium-sulfur batteries.

In order to solve the problems, a novel diaphragm modification material is developed, an electrode material with rapid charge and discharge characteristics is utilized, a composite material surface coating mode is adopted, and a compound of a metal oxide or a sulfide and the like and a carbon material is effectively compounded with a PP diaphragm, so that the shuttle effect of a lithium-sulfur battery can be obviously limited, and the utilization rate of sulfur is improved. For example: the invention patent (CN 109244340A) adopts anatase TiO₂And reduced graphene oxide are used as coating materials to obtain a diaphragm material containing the coating layer, and the diaphragm material is applied to a lithium-sulfur battery; the invention patent (CN 110492045A) uses the sulfide with a laminated structure and the nano-cellulose for coating the surface of a diaphragm and is applied to a lithium-sulfur battery; the invention patent (CN 110649213A) introduces one or more metal hydride materials to be compounded with a high molecular binder and a carbon black material, thereby effectively inhibiting the diffusion of polysulfide; the above methods all obtain ideal electrochemical performance, but the adopted coating materials are mostly metal oxides, sulfides, hydrides and the like, the conductivity of the materials is not high,the chemical adsorption capacity to polysulfide is limited, especially the electrochemical activity under low temperature is poor, meanwhile, chemical vapor deposition is still needed, or covalent organic framework materials and the like are introduced, the synthesis process is complex, and the industrial popularization and application are not facilitated. Therefore, a new preparation technology of a modified diaphragm which is simple in process and suitable for a lithium-sulfur battery is urgently needed.

Disclosure of Invention

The invention provides an application of lithium vanadium phosphate in coating of a lithium-sulfur battery diaphragm, and provides a preparation method of a modified diaphragm suitable for a lithium-sulfur battery, which solves the technical problems of low material conductivity, poor ion diffusion capability, poor low-temperature performance and the like in coating of a conventional lithium-sulfur battery diaphragm by using a fast ion conductor lithium vanadium phosphate.

The technical scheme for realizing the invention is as follows:

the application of lithium vanadium phosphate in coating of the lithium-sulfur battery diaphragm is characterized in that a lithium vanadium phosphate material is used in the coating material of the lithium-sulfur battery diaphragm, the content of the lithium vanadium phosphate in the diaphragm is 5-15% (the whole diaphragm accounts for the content of mixed solid powder), and the coating thickness is 5-20 mu m.

The micro-morphology of the lithium vanadium phosphate is a nano material/micron sphere-like material, and the crystal structure is a monoclinic structure.

The lithium sulfur battery can be measured at a low temperature ranging from-20 ℃ to 0 ℃.

The method comprises the following specific steps:

(1) fully mixing a lithium vanadium phosphate material, conductive carbon, a binder and a dispersing solvent; stirring and mixing for 1-2h by using a planetary stirrer, and vacuumizing the obtained slurry to remove bubbles in the slurry;

wherein the mass ratio of the lithium vanadium phosphate material to the conductive carbon to the binder is (70-85): (10-20): (5-10);

(2) coating the obtained material by adopting a flat plate tape casting coating mode, wherein the coating thickness is 5-20 mu m, the material feeding speed of a scraper is 5-25mm/s, and the obtained material is uniformly coated on the surface of the PP diaphragm on one side;

(3) and (3) completely removing the contained dispersing solvent by adopting a vacuum drying method at the drying temperature of 40-60 ℃ for 6-24 h.

In the step (1), the conductive carbon is acetylene black, the binder is polyvinylidene fluoride, and the dispersion solvent is nitrogen methyl pyrrolidone.

The invention has the beneficial effects that:

(1) the vanadium lithium phosphate with excellent low-temperature electrochemical performance is adopted, so that the heat generated by the discharge of the battery under the low-temperature condition can be effectively utilized to heat the battery, and an additional heat-insulating layer is not required.

(2) By controlling different preparation processes, lithium vanadium phosphate coating materials with different sizes can be obtained, and the coating thickness of the diaphragm can be effectively regulated and controlled.

(3) The adoption of the vanadium-lithium phosphate material with a fast ion conductor is beneficial to constructing a film electrode on the surface of the diaphragm and further improves the effective utilization rate of the active substance sulfur.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is an SEM image of the microstructure of the lithium vanadium phosphate material obtained in example 1.

FIG. 2 is the XRD pattern of the lithium vanadium phosphate material obtained in example 1.

Fig. 3 is a graph showing the first charge and discharge curves of the lithium vanadium phosphate coated separator obtained in example 1 and a blank separator used in a battery.

Fig. 4 is a graph of rate performance of the LVP coated separator and a blank separator obtained in example 1 used in a battery.

Fig. 5 is a graph of the cycle performance of the LVP coated separator and the blank separator obtained in example 1 in a battery.

Fig. 6 is a graph of the rate capability of the LVP coated membranes obtained from example 1 and example 2.

Fig. 7 is a graph of charge and discharge curves and rate performance of the LVP coated separator obtained in comparative example 1.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.

Example 1

The preparation method of the lithium vanadium phosphate coating diaphragm material comprises the following steps:

step (1): weighing 300 mg of lithium vanadium phosphate prepared by a sol-gel method, mixing the lithium vanadium phosphate with conductive carbon (super p) and polyvinylidene fluoride (PVDF) according to a mass ratio of 80:10:10, dropwise adding a certain amount of N-methyl pyrrolidone serving as a dispersing agent, and fully grinding for 30 minutes;

step (2): uniformly coating the slurry obtained in the step (1) on the surface of a PP diaphragm with the thickness of 20 microns in a casting coating mode, wherein the coating thickness is controlled to be 5 microns, and the running speed of a scraper is 25 mm/s;

and (3): and (3) drying the coated membrane obtained in the step (2) in a constant-temperature drying oven at 60 ℃ for 12 hours to obtain the membrane coating material.

FIG. 1 is an SEM image of lithium vanadium phosphate prepared by a sol-gel method; FIG. 2 is an XRD pattern of lithium vanadium phosphate prepared by a sol-gel method, and from FIG. 2, the prepared lithium vanadium phosphate is monoclinic structure.

The obtained LVP coated diaphragm is used in a lithium-sulfur battery, and the positive electrode is a carbon-sulfur compound (mass ratio of 3: 7), wherein the carbon-sulfur compound: conductive carbon black: adhesive =80:10:10, N-methylpyrrolidone as a dispersant, coated on 15 μm aluminum foil, vacuum dried at 60 ℃ for 12 hours; and (3) coating a diaphragm on the obtained positive plate, assembling the lithium plate into a lithium-sulfur battery in an argon glove box, wherein 1 mol of LiTFSI dissolved DOL/DME =1:1 electrolyte, and adding 2wt% of LiNO₃The amount of electrolyte added was 35. mu.L/g (sulfur powder), and the assembled CR2016 coin cell was allowed to stand for 12 hours,charging and discharging are carried out in the voltage range of 1.7-2.8V.

Fig. 3 is a graph showing the first charge and discharge curves of the resulting LVP coated separator and a blank separator in a battery. As can be seen in fig. 3, both the blank separator and the LVP coated separator exhibited two discharge plateaus and two charge plateaus typical of lithium sulfur batteries, indicating that there was no significant effect on the voltage plateaus during the electrochemical conversion of polysulfides before and after coating; it is noted that under the condition of 0.1C rate, the specific discharge capacity of the blank diaphragm assembled battery is only 557 mA.h/g, while the specific discharge capacity of the LVP coated diaphragm assembled battery reaches 1562 mA.h/g, and a huge capacity difference is shown. The LVP coated diaphragm is beneficial to improving the specific discharge capacity of the lithium-sulfur battery.

Fig. 4 is a graph of rate performance of the resulting LVP coated separator and a blank separator used in a battery. As can be seen from fig. 4, as the charging and discharging rate is increased from 0.1C to 0.2C, 0.4C, 1C, or even 2C, the specific discharge capacity of the LVP coated diaphragm assembled battery is much higher than that of the blank diaphragm assembled battery; when the charging and discharging multiplying power is recovered to 0.1C, the discharging specific capacity of the LVP coated diaphragm assembled battery can still be recovered to 1156 mA.h/g, which is far higher than 600 mA.h/g of a blank diaphragm assembled battery.

Fig. 5 is a graph of the cycling performance of the resulting separator of example 1 and a blank separator used in a battery. As can be seen from fig. 5, the specific capacity of the blank diaphragm assembled battery is gradually increased to 350 mA · h/g after 200 cycles under the condition of 1C rate; in contrast, after 200 cycles, the specific capacity of the LVP coated diaphragm assembled battery is also stabilized at 500 mA.h/g; the LVP coated diaphragm is beneficial to improving and maintaining the cycle stability and specific capacity characteristics of the lithium-sulfur battery.

Example 2

The preparation method of the lithium vanadium phosphate coating diaphragm material comprises the following steps:

step (1): weighing 300 mg of lithium vanadium phosphate prepared by a solid phase ball milling method, mixing the lithium vanadium phosphate with conductive carbon (super p) and polyvinylidene fluoride (PVDF) according to a mass ratio of 70:20:10, dropwise adding a certain amount of N-methyl pyrrolidone serving as a dispersing agent, and fully grinding for 30 minutes;

step (2): uniformly coating the slurry obtained in the step (1) on the surface of a PP diaphragm with the thickness of 20 microns in a casting coating mode, wherein the coating thickness is controlled to be 10 microns, and the running speed of a scraper is 25 mm/s;

and (3): and (3) drying the coated membrane obtained in the step (2) in a constant-temperature drying oven at 60 ℃ for 12 hours to obtain the membrane coating material.

Fig. 6 is a graph of rate performance of the LVP coated separators prepared in examples 1 and 2 in a cell. As can be seen from the figures, the LVP coated membranes all exhibited electrochemical behavior with increased specific volume as the thickness of the coated membrane was differentially controlled; however, due to the difference of coating thickness, there is a certain specific capacity difference.

Example 3

The preparation method of the lithium vanadium phosphate coating diaphragm material comprises the following steps:

step (1): weighing 300 mg of lithium vanadium phosphate prepared by a sol microwave method, mixing the lithium vanadium phosphate with conductive carbon (super p) and polyvinylidene fluoride (PVDF) according to a mass ratio of 75:15:8, dropwise adding a certain amount of N-methyl pyrrolidone serving as a dispersing agent, and fully grinding for 30 minutes;

step (2): uniformly coating the slurry obtained in the step (1) on the surface of a PP diaphragm with the thickness of 20 microns in a casting coating mode, wherein the coating thickness is controlled to be 12 microns, and the running speed of a scraper is 20 mm/s;

and (3): and (3) drying the coated membrane obtained in the step (2) in a constant-temperature drying oven at 60 ℃ for 12 hours to obtain the membrane coating material.

Example 4

The preparation method of the lithium vanadium phosphate coating diaphragm material comprises the following steps:

step (1): weighing 300 mg of lithium vanadium phosphate prepared by a hydrothermal method, mixing the lithium vanadium phosphate with conductive carbon (super p) and polyvinylidene fluoride (PVDF) according to a mass ratio of 80:10:10, dropwise adding a certain amount of N-methylpyrrolidone serving as a dispersing agent, and fully grinding for 30 minutes;

step (2): uniformly coating the slurry obtained in the step (1) on the surface of a PP diaphragm with the thickness of 20 microns in a casting coating mode, wherein the coating thickness is controlled to be 8 microns, and the running speed of a scraper is 20 mm/s;

and (3): and (3) drying the coated membrane obtained in the step (2) in a constant-temperature drying oven at 60 ℃ for 12 hours to obtain the membrane coating material.

Comparative example 1

The preparation method of the lithium vanadium phosphate coating diaphragm material comprises the following steps:

step (1): weighing 300 mg of lithium vanadium phosphate prepared by a hydrothermal method, mixing the lithium vanadium phosphate with conductive carbon (super p) and polyvinylidene fluoride (PVDF) according to a mass ratio of 80:10:10, dropwise adding a certain amount of N-methylpyrrolidone serving as a dispersing agent, and fully grinding for 30 minutes;

step (2): uniformly coating the slurry obtained in the step (1) on the surface of a PP diaphragm with the thickness of 20 microns in a casting coating mode, wherein the coating thickness is controlled to be 25 microns, and the running speed of a scraper is 20 mm/s;

and (3): and (3) drying the coated membrane obtained in the step (2) in a constant-temperature drying oven at 60 ℃ for 12 hours to obtain the membrane coating material.

Fig. 7 is a graph of the charge-discharge curve and rate performance of the LVP coated separator prepared in comparative example 1 in a cell. As can be seen from the figure, when the thickness of the LVP coated separator reached 25 μm, the assembled battery exhibited an electrochemical charge-discharge characteristic plateau and cycle characteristics of LVP as a negative electrode material of a lithium ion battery; the charge-discharge voltage plateau of lithium-sulfur batteries has not been significant. The rate cycling performance also shows the cycling stability and the capacity recovery performance of a typical lithium ion battery. The control of the coating thickness is explained, and the method has important significance for obtaining the high-specific-capacity lithium-sulfur battery coating diaphragm.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.