Method of preparing and application of carbon-selenium composites

Abstract

The present invention discloses a preparation method to make lithium selenium secondary battery cathode materials with a high energy density and stable electrochemical performances. Two dimensional carbon materials prepared from the presently-disclosed method is not only made from readily-available low-cost raw materials, but is also of simple preparation method. It can effectively shorten the migration distance of lithium ions in the charging and discharging process and improve conductivity and utilization of selenium after compounded with carbon and selenium; the selenium carbon cathode material can be assembled into lithium selenium secondary batteries with high energy density and stable electrochemical performances. By further scaling up, the assembled lithium selenium pouch-cell batteries still hold excellent electrochemical performances and high energy density, showing broad application prospects.

Claims

1. A lithium selenium secondary battery, comprising: a two-dimensional selenium carbon composite material as a cathode material, the two-dimensional selenium carbon composite material prepared by a method comprising: (a) carbonizing an alkali metal organic salt or an alkaline earth metal organic salt, washing the carbonized salt with an acid, and drying to obtain a two-dimensional carbon nanomaterial; and (b) mixing the two-dimensional carbon material obtained in step (a) with an organic solvent and selenium, evaporating the organic solvent from the mixture, and then conducting a multistage heat ramping and soaking process to form the two-dimensional selenium carbon composite material; a lithium-containing anode; a separator; and an electrolyte, wherein the lithium selenium secondary battery has a discharge specific capacity of at least 580 mAh/g and up to 756 mAh/g after 50 cycles of a constant current charge — discharge test with a test voltage range between 1.0 and 3.0 V and a test temperature of 25° C., and the two-dimensional selenium carbon composite material is free of sulfur.

2. The lithium selenium secondary battery of claim 1, wherein the lithium-containing anode comprises one or more of lithium metal, a lithiated graphite material, and a lithiated silicon carbon material.

3. The lithium selenium secondary battery of claim 1, wherein the separator is selected from a Celgard® membrane; a Whatman® membrane; a cellulose membrane; or a polymer membrane.

4. The lithium selenium secondary battery of claim 1, wherein the electrolyte is one or more of a carbonate electrolyte, an ether electrolyte, and ionic liquids.

5. The lithium selenium secondary battery of claim 4, wherein the carbonate electrolyte comprises a solvent of one or more of diethyl carbonate ester (DEC), dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), and a solute selected from one or more of lithium hexafluoro phosphate (LiPF.sub.6), lithium Bis(trifluoromethane)sulfonimide (LiTFSI), lithium perchlorate (LiClO.sub.4) and lithium bis(fluorosulfonyl)imide (LiFSI).

6. The lithium selenium secondary battery of claim 4, wherein the ether electrolyte comprises a solvent of one or more of 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (DME) and triethylene glycol dimethyl ether (TEGDME), and a solute selected from one or more of lithium hexafluorophosphate (LiPF.sub.6), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium perchlorate (LiClO.sub.4) and lithium bis(fluorosulfonyl)imide (LiFSI).

7. The lithium selenium secondary battery of claim 4, wherein the ionic liquids comprise one or more of room temperature ionic liquids selected from [EMIm] NTf.sub.2 (1-ethyl-3-methylimidazolium bis trifluoromethane sulfonimide salt), [Py13] NTf.sub.2 (N-Propyl-N-methylpyrrolidine bis trifluoromethane sulfonimide salt), [PP13] NTf.sub.2 (N-propyl-methylpiperidine alkoxy-N-Bis trifluoromethane sulfonimide salts), and a solute selected from one or more of lithium hexafluorophosphate (LiPF.sub.6), lithium Bis(trifluoromethane)sulfonimide (LiTFSI), lithium perchlorate (LiClO.sub.4) and lithium bis fluorosulfonylimide (LiFSI).

8. The lithium selenium secondary battery of claim 1, wherein the battery is a pouch-cell battery.

9. The lithium selenium secondary battery of claim 1, wherein the reduction of the discharge specific capacity between the first cycle and the fiftieth cycle of the constant current charge—discharge test is no more than about 34%.

10. The lithium selenium secondary battery of claim 1, wherein the battery has a first cycle Coulomb efficiency ranging from 70 to 78.1%.

11. A lithium selenium secondary battery, comprising: a two-dimensional selenium carbon composite material as a cathode, the two-dimensional selenium carbon composite material prepared by a method comprising: (a) carbonizing an alkali metal organic salt or an alkaline earth metal organic salt at a temperature≥600° C.; (b) washing the carbonized salt of step (a) with an acid; (c) drying the washed carbonized salt of step (b) to obtain a two-dimensional carbon nanomaterial; (d) mixing the two-dimensional carbon nanomaterial of step (c) with selenium and an organic solvent; (e) heating the mixture of step (d) to evaporate the organic solvent to form an organic solvent evaporated mixture; and (f) subjecting the organic solvent evaporated mixture of step (e) to a multistage heat ramping and soaking process to form the two-dimensional selenium carbon composite material; a lithium-containing anode; a separator; and an electrolyte, wherein the lithium selenium secondary battery has a discharge specific capacity of at least 580 mAh/g and up to 756 mAh/g after 50 cycles of a constant current charge— discharge test with a test voltage range between 1.0 and 3.0 V and a test temperature of 25° C., and the two-dimensional selenium carbon composite material is free of sulfur.

12. The lithium selenium secondary battery of claim 11, wherein the lithium-containing anode comprises one or more of lithium metal, a lithiated graphite, and a lithiated silicon carbon.

13. The lithium selenium secondary battery of claim 11, wherein the separator is a commercial Celgard® membrane, a commercial Whatman® membrane, a cellulose membrane, or a polymer membrane.

14. The lithium selenium secondary battery of claim 11, wherein the electrolyte is one or more of a carbonate electrolyte, an ether electrolyte, and an ionic liquid.

15. The lithium selenium secondary battery of claim 14, wherein the carbonate electrolyte comprises a solvent and a solute; the solvent being one or more of diethyl carbonate ester (DEC), dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC); and the solute being one or more of lithium hexafluoro phosphate (LiPF.sub.6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO.sub.4) and lithium bis(fluorosulfonyl)imide (LiFSI).

16. The lithium selenium secondary battery of claim 14, wherein the ether electrolyte comprises a solvent and a solute; the solvent being one or more of 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (DME) and triethylene glycol dimethyl ether (TEGDME); and the solute being one or more of lithium hexafluorophosphate (LiPF.sub.6), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium perchlorate (LiClO.sub.4) and lithium bis(fluorosulfonyl)imide (LiFSI).

17. The lithium selenium secondary battery of claim 14, wherein the ionic liquid comprises a room temperature ionic liquid and a solute; the room temperature ionic liquid being one or more [EMIm] NTf.sub.2 (1-ethyl-3-methylimidazolium bis trifluoromethane sulfonimide salt), [Py13] NTf.sub.2 (N-Propyl-N-methylpyrrolidine bis trifluoromethane sulfonimide salt), [PP13] NTf.sub.2 (N-propyl-methylpiperidine alkoxy-N-Bis trifluoromethane sulfonimide salts); and the solute being one or more of lithium hexafluorophosphate (LiPF.sub.6), lithium bis(trifluoromethanesufonyl)imide (LiTFSI), lithium perchlorate (LiClO.sub.4) and lithium bis (fluorosulfonyl)imide (LiFSI).

18. The lithium selenium secondary battery of claim 11, wherein the battery is a pouch-cell battery.

19. The lithium selenium secondary battery of claim 11, wherein the reduction of the discharge specific capacity between the first cycle and the fiftieth cycle of the constant current charge—discharge test is no more than about 34%.

20. The lithium selenium secondary battery of claim 11, wherein the battery has a first cycle Coulomb efficiency ranging from 70 to 78.1%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a 50,000× scanning electron microscope photograph for carbon material in the example 1.

(2) FIG. 2 is a 0.1 C charge and discharge curve of the lithium selenium battery in the example 1.

(3) FIG. 3 is a 0.1 C charge and discharge curve of the lithium selenium battery in the comparative example 2.

(4) FIG. 4 is an optical image of the pouch-cell battery case in the example 1.

(5) FIG. 5 is a 0.05 C charge and discharge curve of the pouch-cell battery case in the example 1.

DESCRIPTION OF THE INVENTION

(6) In conjunction with the specific examples, the present invention will be further described below. Unless otherwise specified, the experimental methods in the following examples are all conventional; the reagents and materials are all available from commercial sources.

Example 1

(7) (A) Preparation of Selenium Carbon Composite Material

(8) After grinding and milling, an appropriate amount of potassium citrate is calcined at 800° C. for 5 hours under an inert atmosphere, and cooled to room temperature. Washed with dilute hydrochloric acid to a neutral pH; filtered and dried to give a two-dimensional carbon nanomaterial (FIG. 1); according to the mass ratio of 50:50, weigh the two dimensional carbon material and selenium, and then stir and mix with the ethanol solution of selenium uniformly; after solvent evaporation, dry the mixture in dry oven; the dried mixture was heated at 5° C./min to 240° C. and soaked for 3 hours; then continues to heat up at 5° C./min to 450° C.; soaked for 20 hours; cooled to room temperatures, which resulted in the selenium carbon composite material.

(9) (B) Preparation of the Cathode Tab

(10) The above-prepared selenium carbon composites are mixed with carbon black Super-P and binder CMC/SBR (1:1) along with water by a fixed proportions by pulping, coating, drying and other procedures to obtain selenium carbon composite cathode.

(11) (C) Assembling Lithium-Selenium Battery

(12) The above-prepared selenium carbon composite cathode, lithium foil as anode, celgard diaphragm as separator and 1M LiPF.sub.6 in EC/DMC as the electrolyte were assembled into a lithium selenium button cell battery and lithium selenium pouch-cell battery (FIG. 4).

(13) (D) Lithium-Selenium Battery Test

(14) Use a charge-discharge apparatus to do constant current charge-discharge test on the said lithium-selenium button cell battery and lithium selenium pouch-cell battery. Test voltage range is between 1.0 and 3.0 V and test temperature is 25° C. Discharge specific capacity and the level of charge-discharge current are standardly calculated based on the mass of selenium. The charge-discharge current is 0.1 C or 0.05 C. Lithium selenium button coin battery charge and discharge curve is shown in FIG. 2, the specific test results are shown in Table 1. Lithium selenium pouch-cell battery test results are shown in FIG. 5.

Example 2

(15) Other experimental conditions are same as in Example 1; only exception is that the raw material carbonized for two-dimensional carbon is sodium citrate. Battery Test results are summarized in Table 1 below.

Example 3

(16) Other experimental conditions are same as in Example 1; only exception is that the raw material carbonized for two-dimensional carbon is potassium gluconate. Battery Test results are summarized in Table 1 below.

Example 4

(17) Other experimental conditions are same as in Example 1; only exception is that the high-temperature carbonization temperature for the carbon material is 650° C. Battery Test results are summarized in Table 1 below.

Example 5

(18) Other experimental conditions are same as in Example 1; only exception is that the dried mixture was heated at 5° C./min to 300° C. and soaked at this temperature for 3 hours. Battery Test results are summarized in Table 1 below.

Example 6

(19) Other experimental conditions are same as in Example 1; only exception is that the dried mixture was heated at 5° C. min to 240° C. and soaked at this temperature for 3 hours, then continued to heat up to 600° C., and soaked at this constant temperature for 20 hours. Battery Test results are summarized in Table 1 below.

Example 7

(20) Other experimental conditions are same as in Example 1; only exception is that the lithium-Se battery is packed with lithiated graphite anode, instead of the lithium anode sheet. Battery Test results are summarized in Table 1 below.

Example 8

(21) Other experimental conditions are same as in Example 1; only exception is that the lithium-Se battery is packed with lithiated silicon carbon anode, instead of the lithium anode sheet. Battery Test results are summarized in Table 1 below.

Comparative Example 1

(22) Other experimental conditions are the same as in Example 1; only exception is that the use of polyacrylonitrile as the raw material. Battery Test results are summarized in Table 1 below.

Comparative Example 2

(23) Other experimental conditions are the same as in Example 1; only exception is that using one-step compound method to prepare selenium and carbon composite. The dried selenium carbon mixture was heated at 5° C./min to 500° C. and soaked at this temperature for 23 hours to obtain selenium carbon composite material. The charge-discharge curve of a battery made from the thus obtained selenium carbon composite material is shown in FIG. 3; the battery test results are summarized in Table 1 below.

(24) TABLE-US-00001 TABLE 1 summarized Battery Test Results The first the first After cycling cycle discharge cycle Coulomb 50 laps capacity efficiency capacity Numbering (MAh/g) (%) (MAh/g) Example 1 1,050 78.1 756 Example 2 940 74.6 672 Example 3 962 75.3 683 Example 4 987 72.1 680 Example 5 936 73.2 653 Example 6 972 70 661 Example 7 836 72.5 580 Example 8 910 73 600 Comparative 635 55 350 Example 1 Comparative 980 40.8 386 Example 2

(25) Above, examples are only for the illustration of the embodiments of the present invention, which by no means is to be used in any form as a limit to the scope of the present invention. Although the present invention has been revealed above as the preferred embodiments, it is not intended to limit the present invention. Anybody with skills in the art can use the revealed technical content by making little changes or substitutions, without departing from the scope of the technical aspect of the present invention, as described above, to derive equivalent of examples of the present invention. But those that do not depart from the nature of the present invention by simple modification of any of the above embodiments or by making equivalent variations and modifications based on the technical nature of the present invention, would fall within the scope of the present invention of the technical solutions.