Cathode material for a Li—S battery and the method for preparing the same, a cathode made of the cathode material and a Li—S battery comprising the cathode

Abstract

The present invention provides a cathode material for a Li—S battery. The cathod material comprises dehydrogenized acrylonitrile based polymer, sulfur and GNS (Graphene NanoSheet), wherein the cathode material particles are spherical, the content of dehydrogenized acrylonitrile based polymer is 20-79 wt %, the content of sulfur is 20-79 wt % and the content of GNS is 1-30 wt %. Also provided a method for preparing a cathode material, a cathode made of the cathod material and a Li—S battery comprising the cathode.

Claims

1. A method for preparing a cathode material for a Li—S battery, the method comprising: dispersing a first amount of graphene nanosheet in water to form a dispersion; homogenizing the dispersion; adding a second amount of acrylonitrile based polymer with a particle size range of 10 nm-500 nm to the dispersion to form a suspension; homogenizing the suspension and drying the homogenized suspension by a spray drying process to obtain spherical secondary particles with a particle size range of 1-20 μm; mixing a third amount of sulfur with the obtained spherical secondary particles by pestle-milling to form a mixture; heating the mixture; and cooling the heated mixture to obtain the cathode material, the cathode material having spherically-shaped cathode material particles, wherein the first amount, the second amount, and the third amount are selected such that the cathode material is formed from 0.05 to 0.2 parts by weight graphene nanosheet, 1-2 parts by weight acrylonitrile based polymer, and 5-20 parts by weight sulfur.

2. The method according to claim 1, wherein heating the mixture includes heating the mixture at a temperature of 200-400° C.

3. The method according to claim 2, wherein heating the mixture includes heating the mixture for one to twenty hours.

4. The method according to claim 1, wherein the spherically shaped cathode material particles comprise a particle size distribution having a peak in the range of 1-30 μm.

5. The method according to claim 1, wherein: the acrylonitrile based polymer is an acrylonitrile copolymer selected from acrylonitrile-butadiene copolymer, acrylonitrile-vinyl chloride copolymer, acrylonitrile-methyl acrylate copolymer, acrylonitrile-methyl methacrylate copolymer, and acrylonitrile-styrene copolymer, and a molar percentage of acrylonitrile unit in the acrylonitrile copolymer is 90%-99%.

6. The method of claim 1, wherein the obtained spherical secondary particles contain graphene nanosheet and acrylonitrile-styrene copolymer.

7. The method of claim 1, wherein the obtained spherical secondary particles contain graphene nanosheet and polyacrylonitrile.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings, in which:

(2) FIG. 1 shows the SEM picture of the cathode material obtained from Example 1;

(3) FIG. 2 shows the particle size distribution of the cathode material obtained from Example 1;

(4) FIGS. 3 shows the SEM picture of the cathode material obtained from Example 2;

(5) FIGS. 4 shows the SEM picture of the cathode material obtained from the comparative example respectively;

(6) FIG. 5 shows the cycling stability of the Li—S batteries comprising the cathode made of the cathode material obtained from Example 1 and comparative example respectively;

(7) FIG. 6 shows the rate performance of the Li—S batteries comprising the cathode made of the cathode material obtained from Example 1 and comparative example respectively, wherein C indicates discharge power rate. For example, 1C represents a 1-hour discharge and 10C represents a 0.1-hour discharge; and

(8) FIG. 7 shows the cycling stability of the Li—S batteries comprising the cathode made of the cathode material obtained from Example 2

DETAILED DESCRIPTION OF THE INVENTION

(9) While the invention covers various modifications and alternative constructions, embodiments of the invention are shown in the drawings and will hereinafter be described in detail. However it should be understood that the specific description and drawings are not intended to limit the invention to the specific forms disclosed. On the contrary, it is intended that the scope of the claimed invention includes all modifications and alternative constructions thereof falling within the scope of the invention as expressed in the appended claims.

(10) All publications, patent applications, patents and other references mentioned herein, if not otherwise indicated, are explicitly incorporated by reference herein in their entirety for all purposes as if fully set forth.

(11) A Li—S battery according to the present invention may comprises a lithium anode, a cathode made of the cathode material of Example 1/2, and electrolyte.

(12) The comparative battery may comprises a lithium anode, a cathode made of the cathode material of the comparative example, and electrolyte.

(13) Graphene nanosheets may be prepared by the steps of adding graphite oxide into water and heating the solution or by the steps of adding graphite oxide into water and adding a reducing agent into the solution. The reducing agent may be for example selected from hydrazine hydrate, sodium borohydride, potassium borohydride, glucose and aqueous ammonia, sodium polysulfide.

EXAMPLE 1

The Preparation of the Cathode Material According to the Present Invention

(14) 0.1 g GNS is added into adequate water used as dispersant. The dispersion is sonicated. 1 g polyacrylonitrile with a particle size range of 10 nm-500 nm was added to the aqueous suspension of GNS. The mixed suspension is further sonicated and then dried by a spray drying process to remove water. Consequently, spherical secondary particles containing GNS and polyacrylonitrile and having a particle size range of 1-20 μm are obtained.

(15) 8 g sulfur is mixed with the obtained secondary particles by pestle-milling. The collected mixture is heated at 300° C. in an argon atmosphere for 5 h to get the target spherical cathode material particles with a particle size of 1-20 μm, as shown in FIG. 1. As shown in FIG. 2, the particle size distribution shows a single peak character in the range of 1-30 μm. Main particles sizes distribute in the range of 5-15 μm.

(16) The spherical ternary composite has 48 wt % dehydrogenized polyacrylonitrile, 47 wt % sulfur and 5 wt % GNS.

COMPARATIVE EXAMPLE

(17) 0.1 g GNS is added into adequate water used as dispersant. The dispersion is sonicated. 1 g polyacrylonitrile with a particle size range of 10 nm-500 nm was added to the aqueous suspension of GNS. The mixed suspension is further sonicated and then dried by a heating process during which the suspension is dried at 80° C. to remove water.

(18) 8 g sulfur is mixed with the obtained binary composite by pestle-milling. The collected mixture is heated at 300° C. in an argon atmosphere for 5 h to get comparative cathode material particles. As shown in FIG. 4, the composite particles are irregular.

(19) FIG. 5 shows the cycling stability of the Li—S batteries comprising the cathode made of the cathode material obtained from Example 1 and comparative example respectively. FIG. 6 shows the rate performance of the Li—S battery comprising the cathode made of the cathode material obtained from Example 1 and comparative example respectively.

(20) As shown in FIG. 5, the Li—S battery comprising the cathode made of the cathode material obtained from Example 1 demonstrates a first discharge capacity of 863 mAh/g and a reversible capacity of 680 mAh/g, utilization of active material higher than 86%, cycle life estimated up to 500 (80% retention). The Li—S battery comprising the cathode made of cathode material of the comparative example has similar first discharge and charge capacities and similar utilization of active material, but only has the cycle life estimated up to 300 (80% retention).

(21) When the cathode material obtained from Example 1 discharges at 10C, a capacity up to 331.5 mAh/g for Example 1 can be delivered, as shown in FIG. 6, The Li—S battery comprising the cathode made of cathode material of the comparative example can only deliver a similar capacity at a smaller rate of 8C.

(22) As shown in FIG. 5 and FIG. 6, results of these measurements show that the cycle stability of the Li—S battery according to the present invention is longer than the Li—S battery comprising the cathode made of the cathode material prepared according to comparative example and the power rate performance of the Li—S battery according to the present invention is superior to the Li—S battery comprising the cathode made of the cathode material prepared according to comparative example.

EXAMPLE 2

The Preparation of the Cathode Material According to the Present Invention

(23) 0.1 g GNS is added into adequate water used as dispersant. The dispersion is sonicated. 1 g acrylonitrile-styrene copolymer with a particle size range of 10 nm-500 nm was added to the aqueous suspension of GNS. The mixed suspension is further sonicated and then dried by a spray drying process to remove water. Consequently, spherical secondary particles containing GNS and acrylonitrile-styrene copolymer and having a particle size range of 1-20 μm are obtained.

(24) 8 g sulfur is mixed with the obtained secondary particles by pestle-milling. The collected mixture is heated at 300° C. in an argon atmosphere for 5 h to get the target spherical cathode material particles with a particle size of 1-20 μm, as shown in FIG. 3.

(25) The spherical ternary composite has 50 wt % dehydrogenized acrylonitrile-styrene copolymer, 47 wt % sulfur and 3 wt % GNS.

(26) FIG. 6 shows the cycling stability of the Li—S batteries comprising the cathode made of the cathode material obtained from Example 2 . As shown in FIG. 6, the Li—S battery comprising the cathode made of the cathode material obtained from Example 2 demonstrates a first discharge capacity of 895 mAh/g and a reversible capacity of 655 mAh/g, utilization of active material higher than 83%, cycle life estimated up to 200 (80% retention).

(27) It should be noted that the aforesaid embodiments are illustrative of this invention instead of restricting it, substitute embodiments may be designed by those skilled in the art without departing from the scope of the claims below. The wordings such as “contain”, “containing”, “comprise” and “comprising” do not exclude elements or steps which are present but not listed in the description and the claims.