Preparation method of sulfurized polyacrylonitrile for positive electrode material of lithium-sulfur battery

Abstract

The invention discloses a preparation method of sulfurized polyacrylonitrile for a positive electrode material of a lithium-sulfur battery, which comprises the following steps: (1) mixing polyacrylonitrile with excessive oxygen-containing sulfide, reacting at high temperature, and removing the excessive oxygen-containing sulfide after the reaction; and (2) putting the product obtained after the excessive oxygen-containing sulfide is removed in the step (1) into inert gas, and calcining at high temperature to obtain the vulcanized polyacrylonitrile. The sulfurized polyacrylonitrile prepared by the method disclosed by the invention is low in hydrogen content and contains oxygen atoms, so that the coulombic efficiency and the discharge voltage of the lithium-sulfur battery assembled by taking the sulfurized polyacrylonitrile as the positive electrode material are obviously improved; therefore, the problems of low discharge voltage and low first charge-discharge efficiency of the lithium-sulfur battery assembled by taking the sulfurized polyacrylonitrile synthesized by the existing method as the positive electrode material are solved.

Description

Technical Field

[0001] The present invention relates to a preparation method of sulfurized polyacrylonitrile for a cathode material of a lithium-sulfur battery. Background Art

[0002] The theoretical energy density of a lithium-sulfur battery can reach 2600 Wh / kg, far exceeding that of a lithium-ion battery (about 250 Wh / kg), and is suitable for applications with high energy density requirements, such as electric vehicles and drones. Moreover, sulfur resources are abundant, inexpensive, and environmentally friendly, unlike lithium-ion batteries that rely on expensive cobalt and nickel. Therefore, the lithium-sulfur battery is one of the most concerned battery systems in modern research.

[0003] However, when using elemental sulfur as the cathode material of a lithium-sulfur battery, a shuttle effect will occur, that is, polysulfides will be formed during the charge and discharge process, and the polysulfides are easily dissolved in the electrolyte, resulting in battery capacity decay. And during the charge and discharge process of the elemental sulfur cathode, lithium dendrites are easily formed on the lithium anode, posing a safety hazard. Therefore, a sulfur-containing composite material is needed to replace elemental sulfur as the cathode material of a lithium-sulfur battery. Existing sulfurized polyacrylonitrile exhibits good stability and conductivity when replacing elemental sulfur as the cathode material of a lithium-sulfur battery, and sulfurized polyacrylonitrile can inhibit the shuttle effect and improve the charge and discharge efficiency. Therefore, sulfurized polyacrylonitrile is considered to be able to replace elemental sulfur as the cathode material of a lithium-sulfur battery.

[0004] The traditional method for preparing sulfurized polyacrylonitrile (SPAN) is to use a one-pot method of mixing elemental sulfur (S) and polyacrylonitrile (PAN). The sulfurized polyacrylonitrile (SPAN-S) prepared by this method has a low initial charge-discharge efficiency and a high hydrogen content (mass percentage content > 1) when assembled into a battery as a cathode material. Research shows that the mass percentage of hydrogen in theoretical sulfurized polyacrylonitrile should be 0, while the mass percentage content of hydrogen in sulfurized polyacrylonitrile synthesized using elemental sulfur is > 1, and existing research shows that too high hydrogen content in sulfurized polyacrylonitrile will cause the formation of H 2 S gas volatilization during the charge and discharge process of the lithium-sulfur battery composed of it, resulting in sulfur loss, thereby greatly reducing the initial charge-discharge efficiency of the lithium-sulfur battery. And when using the SPAN-S prepared by the existing method as the cathode material of a lithium-sulfur battery, there is also the disadvantage of a low battery discharge voltage (the discharge voltage is about 1.7 V). Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to provide a preparation method of sulfurized polyacrylonitrile for a cathode material of a lithium-sulfur battery. The sulfurized polyacrylonitrile prepared by this method has a low hydrogen content and contains oxygen atoms. When it is used as the cathode material of a lithium-sulfur battery, the lithium-sulfur battery has a high discharge voltage and a high Coulomb efficiency.

[0006] Technical Solution: The preparation method of sulfurized polyacrylonitrile according to the present invention includes the following steps:

[0007] (1) Mix polyacrylonitrile (PAN) with an excessive amount of oxygen-containing sulfide, react at a high temperature, and remove the excess oxygen-containing sulfide after the reaction.

[0008] (2) Place the product obtained from step (1) in an inert gas and calcine at a high temperature to obtain sulfurized polyacrylonitrile.

[0009] Among them, in step (1), the oxygen-containing sulfide is at least one of thionyl chloride, hyposulfurous acid, sulfurous acid, dithionous acid, pyrosulfuric acid, thiosulfuric acid, dithionous acid, sodium sulfate, sodium persulfate, sodium thiosulfate, sodium dithionite, sodium metabisulfite, sodium pyrosulfate or sodium persulfate.

[0010] Among them, in step (1), the molar ratio of polyacrylonitrile (PAN) to the oxygen-containing sulfide added is 1:6 - 12.

[0011] Among them, in step (1), the reaction temperature is 230 - 270 °C and the reaction time is 10 - 12.

[0012] Among them, in step (1), the excess oxygen-containing sulfide is removed at a high temperature.

[0013] Among them, in step (2), the calcination temperature is 300 - 350 °C and the calcination time is 5 - 6 h.

[0014] Among them, in step (2), the structural formula of the sulfurized polyacrylonitrile is as follows:

[0015]

[0016] Among them, in the sulfurized polyacrylonitrile, the hydrogen content is 0.17 - 0.45 wt.%; the oxygen content is 10.46 - 15.84 wt.%.

[0017] The present invention uses oxygen-containing sulfide as a sulfur source to prepare sulfurized polyacrylonitrile, and can utilize the oxygen in the oxygen-containing sulfide to react with the hydrogen in polyacrylonitrile (since the oxidizing property of O is higher than that of S, thus being able to more effectively oxidize the hydrogen in polyacrylonitrile), thereby reducing the hydrogen content in the product sulfurized polyacrylonitrile.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: The sulfurized polyacrylonitrile prepared by the method of the present invention has a low hydrogen content (significantly lower than that of the sulfurized polyacrylonitrile synthesized by using elemental sulfur conventionally) and contains oxygen atoms, so that the Coulomb efficiency (first charge-discharge efficiency) and discharge voltage of the lithium-sulfur battery assembled with it as the positive electrode material are both significantly improved, thereby solving the problems of low discharge voltage and low first charge-discharge efficiency existing in the lithium-sulfur battery assembled with the sulfurized polyacrylonitrile synthesized by the existing method as the positive electrode material. Description of the Drawings

[0019] Figure 1 X-ray diffractometer pattern of the sulfurized polyacrylonitrile prepared in Example 1;

[0020] Figure 2 Charge-discharge curve of the lithium-sulfur battery assembled with the sulfurized polyacrylonitrile prepared in Example 1 as the cathode material;

[0021] Figure 3 X-ray diffractometer pattern of the sulfurized polyacrylonitrile prepared in Example 2;

[0022] Figure 4 Charge-discharge curve of the lithium-sulfur battery assembled with the sulfurized polyacrylonitrile prepared in Example 2 as the cathode material;

[0023] Figure 5 X-ray diffractometer pattern of the sulfurized polyacrylonitrile prepared in Example 3;

[0024] Figure 6 Charge-discharge curve of the lithium-sulfur battery assembled with the sulfurized polyacrylonitrile prepared in Example 3 as the cathode material;

[0025] Figure 7 X-ray diffractometer pattern of the sulfurized polyacrylonitrile prepared in Example 4;

[0026] Figure 8 Charge-discharge curve of the lithium-sulfur battery assembled with the sulfurized polyacrylonitrile prepared in Example 4 as the cathode material;

[0027] Figure 9 X-ray diffractometer pattern of the sulfurized polyacrylonitrile prepared in Example 5;

[0028] Figure 10 Charge-discharge curve of the lithium-sulfur battery assembled with the sulfurized polyacrylonitrile prepared in Example 5 as the cathode material;

[0029] Figure 11 X-ray diffractometer pattern of the sulfurized polyacrylonitrile prepared in Comparative Example 1;

[0030] Figure 12 Charge-discharge curve of the lithium-sulfur battery assembled with the sulfurized polyacrylonitrile prepared in Comparative Example 1 as the cathode material;

[0031] Figure 13 X-ray diffractometer comparison pattern of the sulfurized polyacrylonitrile prepared in Example 1 and Comparative Example 1;

[0032] Figure 14 X-ray diffractometer comparison pattern of the sulfurized polyacrylonitrile prepared in Example 2 and Comparative Example 1;

[0033] Figure 15X-ray diffractometer comparison spectra of the vulcanized polyacrylonitrile prepared in Example 3 and Comparative Example 1;

[0034] Figure 16 X-ray diffractometer comparison spectra of the vulcanized polyacrylonitrile prepared in Example 4 and Comparative Example 1;

[0035] Figure 17 X-ray diffractometer comparison spectra of the vulcanized polyacrylonitrile prepared in Example 5 and Comparative Example 1. Detailed implementation manners

[0036] Example 1

[0037] The preparation method of the vulcanized polyacrylonitrile of the present invention uses thionyl chloride (SOCl 2 ) to synthesize vulcanized polyacrylonitrile with polyacrylonitrile (PAN), and specifically includes the following steps:

[0038] (1) Mix polyacrylonitrile (PAN) and thionyl chloride (SOCl 2 ) at a molar ratio of 1:12, and after stirring thoroughly, load them into a reaction kettle;

[0039] (2) Heat the reaction kettle to 270 °C and react for 10 hours;

[0040] (3) Put the reaction product into an oven to remove the excess thionyl chloride;

[0041] (4) Collect the solid product, grind it and put it into a nitrogen tube furnace, and calcine it at 300 °C for 5 h to obtain a vulcanized polyacrylonitrile solid material.

[0042] The reaction formula in the reaction process of the present invention is: C 6 H 6 N 2 +3SOCl 2 →C 6 O 2 N 2 S 3 +6HCl+[O]

[0043] Mix the vulcanized polyacrylonitrile obtained in Example 1 with polyacrylic acid (PAA) and conductive carbon (Super P) at a mass ratio of 8:1:1, and grind them thoroughly in a mortar; prepare a battery positive electrode slurry with water as the solvent, and uniformly coat it on aluminum foil; dry it in a 60 °C oven with air blowing for 5 h; cut the dried slurry together with the aluminum foil to obtain a battery positive electrode plate with a diameter of 12 mm; transfer the positive electrode plate to a glove box filled with argon (water and oxygen content <0.01 ppm), and assemble a 2032-type lithium-sulfur battery with 1MLiPF6-EC / DMC as the electrolyte. After assembly, use a Blue Power CT2001A battery test system to test the battery performance.

[0044] The structure of the prepared polyacrylonitrile was characterized by XRD. Figure 1 As shown, it can be seen that there is an obvious characteristic peak of sulfur diffraction at 26°, indicating that the prepared sample contains rich sulfur. Further elemental analysis (elemental analyzer) (as shown in Table 1) shows that the sulfur content in the sample is 22.47%, the hydrogen content is 0.17%, and the oxygen content is 12.50%. Compared with the polyacrylonitrile raw material, the hydrogen content is significantly reduced. Through battery testing (as shown in Table 1), it can be seen that the sulfur content in the sample is 22.47%, the hydrogen content is 0.17%, and the oxygen content is 12.50%. Figure 2 As shown in the figure, using the prepared sulfurized polyacrylonitrile as the positive electrode material, the first three cycle discharge voltages of the lithium-sulfur battery are 2.5V, 2.3V, and 2.3V respectively. The efficiency of the first charge and discharge is 59.41%.

[0045] Table 1 is a comparison of elemental analysis of Example 1 and polyacrylonitrile

[0046]

[0047] Example 2

[0048] The method for preparing the sulfurized polyacrylonitrile of the present invention comprises using pyrosulfuric acid (H 2 S 2 O 7 ) and polyacrylonitrile (PAN) to synthesize vulcanized polyacrylonitrile, specifically comprising the following steps:

[0049] (1) Polyacrylonitrile (PAN) and pyrosulfuric acid (H 2 S 2 O 7 ) are mixed in a molar ratio of 1:6, stirred thoroughly and then loaded into a reactor;

[0050] (2) heating the reactor to 230° C. and reacting for 10 hours;

[0051] (3) placing the reaction product in an oven to remove excess pyrosulfuric acid;

[0052] (4) The solid product was collected, ground, placed in a nitrogen tube furnace, and calcined at 300° C. for 5 h to obtain a sulfide polyacrylonitrile solid material.

[0053] The sulfurized polyacrylonitrile prepared in Example 2 was mixed with polyacrylic acid (PAA) and conductive carbon (Super P) at a mass ratio of 8:1:1 and ground thoroughly in a mortar; a battery positive electrode slurry was prepared using water as a solvent, and it was evenly coated on aluminum foil; it was dried in a 60 °C oven with air blowing for 5 h; after drying, the slurry together with the aluminum foil was cut into pieces to obtain a battery positive electrode sheet with a diameter of 12 mm; the positive electrode sheet was transferred to a glove box filled with argon (water and oxygen content < 0.01 ppm), and a 2032-type lithium-sulfur battery was assembled using 1 M LiPF6-EC / DMC as the electrolyte. After assembly, a BlueTEC CT2001A battery test system was used to test the battery performance.

[0054] The structure of the prepared sulfurized polyacrylonitrile was characterized by XRD, and the results are as Figure 3 shown. It can be seen that there is an obvious diffraction characteristic peak of sulfur element at 26°, indicating that the prepared sample contains abundant sulfur element. Through elemental analysis, it is known that the content of hydrogen element in the sulfurized polyacrylonitrile prepared in Example 2 is 0.34%, and the content of oxygen element is 14.33%. Through battery tests (as Figure 4 shown), using the prepared sulfurized polyacrylonitrile as the positive electrode material, the first three cycle discharge voltages of the lithium-sulfur battery are 2.5 V, 2.4 V, and 2.3 V respectively. The efficiency of the first charge and discharge is 56.37%.

[0055] Table 2 shows the comparison of elemental analysis between Example 2 and polyacrylonitrile

[0056]

[0057] Example 3

[0058] The preparation method of the sulfurized polyacrylonitrile of the present invention uses sodium persulfate (NaS 2 O 8 ) and polyacrylonitrile (PAN) to synthesize sulfurized polyacrylonitrile, which specifically includes the following steps:

[0059] (1) Mix polyacrylonitrile (PAN) and sodium persulfate (NaS 2 O 8 ) at a molar ratio of 1:6, and after stirring thoroughly, load them into a reaction kettle;

[0060] (2) Heat the reaction kettle to 230 °C and react for 10 hours;

[0061] (3) Then heat the muffle furnace to 300 °C and react for 5 h to remove the excess sodium persulfate;

[0062] (4) Collect the solid product, wash it with water, and dry it; then grind it and put it into a nitrogen tube furnace, and calcine it at 350 °C for 5 h to obtain a sulfurized polyacrylonitrile solid material.

[0063] The sulfurized polyacrylonitrile prepared in Example 3 was mixed with polyacrylic acid (PAA) and conductive carbon (Super P) at a mass ratio of 8:1:1 and ground thoroughly in a mortar; a battery positive electrode slurry was prepared with water as the solvent, and it was evenly coated on aluminum foil; it was dried in a 60 °C oven with air blowing for 5 h; after drying, the slurry together with the aluminum foil was cut into pieces to obtain a battery positive electrode plate with a diameter of 12 mm; the positive electrode plate was transferred to a glove box filled with argon (water and oxygen content < 0.01 ppm), and a 2032-type lithium-sulfur battery was assembled with 1 M LiPF6-EC / DMC as the electrolyte. After assembly, a battery performance test was carried out using a BlueTEC CT2001A battery test system.

[0064] The structure of the prepared sulfurized polyacrylonitrile was characterized by XRD, and the results are as Figure 5 shown. It can be seen that there is an obvious diffraction characteristic peak of sulfur element at 26°, indicating that the prepared sample contains abundant sulfur element. Through elemental analysis, it is known that the content of hydrogen element in the sulfurized polyacrylonitrile prepared in Example 3 is 0.45%, and the content of oxygen element is 15.84%. Through battery testing (as Figure 6 shown), using the prepared sulfurized polyacrylonitrile as the positive electrode material, the cycle discharge voltages of the lithium-sulfur battery for the first three times are 2.4 V, 2.4 V, and 2.4 V respectively. The efficiency of the first charge and discharge is 56.35%.

[0065] Table 3 is a comparison of the elemental analysis between Example 3 and polyacrylonitrile

[0066]

[0067] Example 4

[0068] The preparation method of the sulfurized polyacrylonitrile of the present invention uses sodium pyrosulfate (Na 2 S 2 O 5 ) and polyacrylonitrile (PAN) to synthesize sulfurized polyacrylonitrile, which specifically includes the following steps:

[0069] (1) Mix polyacrylonitrile (PAN) and sodium pyrosulfate (Na 2 S 2 O 5 ) at a molar ratio of 1:6, stir thoroughly and then load it into a reaction kettle;

[0070] (2) Heat the reaction kettle to 230 °C and react for 10 hours;

[0071] (3) Then heat the muffle furnace to 300 °C and react for 5 h to remove the excess sodium persulfate;

[0072] (4) Collecting the solid product, washing it with water, and drying it; then grinding it, placing it in a nitrogen tube furnace, and calcining it at 350° C. for 5 h to obtain a sulfide polyacrylonitrile solid material.

[0073] The sulfide polyacrylonitrile prepared in Example 4 was mixed with polyacrylic acid (PAA) and conductive carbon (Super P) in a mass ratio of 8:1:1, and ground thoroughly in a mortar; water was used as a solvent to prepare a positive electrode slurry for the battery, which was evenly coated on an aluminum foil; the slurry was dried in an oven at 60°C for 5 hours; the dried slurry was cut together with the aluminum foil to obtain a positive electrode sheet of the battery with a diameter of 12 mm; the positive electrode sheet was transferred to a glove box filled with argon (water and oxygen content <0.01ppm), and a 2032-type lithium-sulfur battery was assembled with 1MLiPF6-EC / DMC as the electrolyte. After assembly, the battery performance was tested using the Blue Electric CT2001A battery test system.

[0074] The structure of the prepared polyacrylonitrile was characterized by XRD. Figure 7 As shown, it can be seen that there is an obvious characteristic peak of sulfur diffraction at 26°, indicating that the prepared sample contains rich sulfur. Through elemental analysis, it can be seen that the hydrogen content of the sulfide polyacrylonitrile prepared in Example 4 is 0.21%, and the oxygen content is 10.46%. Through battery testing (such as Figure 8 As shown in FIG. 1 , using the prepared sulfide polyacrylonitrile as the positive electrode material, the first three cycle discharge voltages of the lithium-sulfur battery are 2.5 V, 2.4 V, and 2.4 V, respectively. The efficiency of the first charge and discharge is 56.92%.

[0075] Table 4 is a comparison of elemental analysis of Example 4 and polyacrylonitrile

[0076]

[0077] Example 5

[0078] The preparation method of the sulfurized polyacrylonitrile of the present invention uses sodium thiosulfate (Na 2 S 2 O 3 ) and polyacrylonitrile (PAN) to synthesize vulcanized polyacrylonitrile, specifically comprising the following steps:

[0079] (1) Polyacrylonitrile (PAN) and sodium thiosulfate (Na 2 S 2 O 3 ) are mixed in a molar ratio of 1:6, stirred thoroughly and then loaded into a reactor;

[0080] (2) heating the reactor to 230° C. and reacting for 10 hours;

[0081] (3) The temperature of the muffle furnace was raised to 350°C and the reaction was carried out for 5 hours to remove excess sodium persulfate;

[0082] (4) Collecting the solid product, washing it with water, and drying it; then grinding it, placing it in a nitrogen tube furnace, and calcining it at 350° C. for 5 h to obtain a sulfide polyacrylonitrile solid material.

[0083] The sulfide polyacrylonitrile prepared in Example 5 was mixed with polyacrylic acid (PAA) and conductive carbon (Super P) in a mass ratio of 8:1:1, and ground thoroughly in a mortar; water was used as a solvent to prepare a positive electrode slurry for the battery, which was evenly coated on an aluminum foil; the slurry was dried in an oven at 60°C for 5 hours; the dried slurry was cut together with the aluminum foil to obtain a positive electrode sheet of the battery with a diameter of 12 mm; the positive electrode sheet was transferred to a glove box filled with argon (water and oxygen content <0.01ppm), and a 2032-type lithium-sulfur battery was assembled with 1MLiPF6-EC / DMC as the electrolyte. After assembly, the battery performance was tested using the Blue Electric CT2001A battery test system.

[0084] The structure of the prepared polyacrylonitrile was characterized by XRD. Figure 9 As shown, it can be seen that there is an obvious characteristic peak of sulfur diffraction at 26°, indicating that the prepared sample contains rich sulfur. Through elemental analysis, it can be seen that the hydrogen content of the sulfide polyacrylonitrile prepared in Example 5 is 0.36%, and the oxygen content is 10.60%. Through battery testing (such as Figure 10 As shown in FIG. 1 , using the prepared sulfide polyacrylonitrile as the positive electrode material, the first three cycle discharge voltages of the lithium-sulfur battery are 2.4 V, 2.4 V, and 2.3 V, respectively. The efficiency of the first charge and discharge is 58.57%.

[0085] Table 5 is a comparison of elemental analysis of Example 5 and polyacrylonitrile

[0086]

[0087] Comparative Example 1

[0088] A method for synthesizing thiopolyacrylonitrile, comprising the following steps:

[0089] (1) Polyacrylonitrile (PAN) and elemental sulfur (S) were mixed uniformly by ball milling at a molar ratio of 1:6;

[0090] (2) The solid mixture was collected, placed in a nitrogen tube furnace, and calcined at 300° C. for 5 h to obtain a sulfide polyacrylonitrile solid material.

[0091] The sulfurized polyacrylonitrile prepared in Comparative Example 1 was mixed with polyacrylic acid (PAA) and conductive carbon (Super P) at a mass ratio of 8:1:1 and ground thoroughly in a mortar; a battery positive electrode slurry was prepared using water as a solvent, and it was evenly coated on aluminum foil; it was dried in a 60 °C oven with air blowing for 5 h; after drying, the slurry together with the aluminum foil was cut into pieces to obtain a battery positive electrode sheet with a diameter of 12 mm; the positive electrode sheet was transferred to a glove box filled with argon (water and oxygen content < 0.01 ppm), and a 2032-type lithium-sulfur battery was assembled using 1 M LiPF6-EC / DMC as the electrolyte. After assembly, a Blue Electric CT2001A battery test system was used to test the battery performance.

[0092] The structure of the sulfurized polyacrylonitrile prepared in Comparative Example 1 was characterized by XRD, and the results are as Figure 11 shown. It can be seen that there is an obvious diffraction characteristic peak of sulfur element at 26°, indicating that the prepared sample contains abundant sulfur element. Further, through elemental analysis (as shown in Table 2), it is known that the sulfur element content in the sample is 36.72%, and the hydrogen element content is 1.30%. Through battery tests (as Figure 12 shown), using the prepared sulfurized polyacrylonitrile as the positive electrode material of the lithium-sulfur battery, the first three cycle discharge voltages of the lithium-sulfur battery are 1.7 V, 2.1 V, and 2.1 V respectively. The efficiency of the first charge and discharge is 44.23%.

[0093] Table 6 is a comparison of the elemental analysis between Comparative Example 1 and polyacrylonitrile

[0094]

[0095] By comparing Tables 1 - 6, it can be seen that the hydrogen atom content in the sulfurized polyacrylonitrile prepared in Example 1, Example 2, Example 3, Example 4, and Example 5 is much lower than that in Comparative Example 1. After charging and discharging the lithium-sulfur batteries assembled using the sulfurized polyacrylonitrile prepared in Example 1, Example 2, Example 3, Example 4, Example 5 and Comparative Example 1 as the positive electrode material for 100 cycles, the sulfurized polyacrylonitrile materials prepared in Example 1, Example 2, Example 3, Example 4, Example 5 and Comparative Example 1 were taken for elemental analysis tests, and it was found that the sulfur content in Example 1, Example 2, Example 3, Example 4, and Example 5 remained unchanged, while the sulfur content in Comparative Example 1 decreased to 31.20%. Therefore, the lower hydrogen content in Example 1, Example 2, Example 3, Example 4, and Example 5 can ensure a 100% retention rate of sulfur content.

[0096] Through Figure 2 and Figure 12Comparing the charge-discharge curves of Example 1 and Comparative Example 1, it can be seen that the first discharge voltage of Example 1 is approximately 2.5 V, while the first discharge voltage of Comparative Example 1 is approximately 1.7 V. The discharge voltage of Example 1 is about 0.8 V higher than that of Comparative Example 1. The second and third discharge voltages of Example 1 are above 2.3 V, while the second and third discharge voltages of Comparative Example 1 are around 2.1 V, indicating that the discharge voltage of Example 1 is always higher than that of Comparative Example 1. The lower hydrogen content in Example 1 will hardly generate H 2 S gas during the charge-discharge process, reducing the occurrence of side reactions, thereby weakening the polarization effect of the battery, and then leading to an increase in the battery voltage. The increase in the battery voltage will also improve its energy density and increase its output power; at the same time, due to the relatively high electronegativity of oxygen atoms, they are prone to attracting electrons, thus forming stable oxides. In the battery, oxygen atoms can participate more effectively in the redox reaction, enhancing the oxidation ability of the electrode material, and then increasing the discharge voltage of the battery.

[0097] It can be seen through Figures 13 to 17 that there are obvious diffraction characteristic peaks of sulfur elements at 26° in Example 1, Example 2, Example 3, Example 4, Example 5 and Comparative Example 1, indicating that the prepared samples all contain abundant sulfur elements.

Claims

1. A method for preparing sulfurized polyacrylonitrile for lithium-sulfur battery positive electrode material, characterized in that: The steps include: (1) mixing polyacrylonitrile with an excess of oxygen-containing sulfide, reacting at a high temperature, and removing the excess oxygen-containing sulfide after the reaction; (2) placing the product after removing excess oxygen-containing sulfide in step (1) in an inert gas and calcining at a high temperature to obtain sulfided polyacrylonitrile.

2. The preparation method according to claim 1, characterized in that: In step (1), the oxygen-containing sulfide is at least one of thionyl chloride, sulfurous acid, sulfurous acid, dithionous acid, pyrosulfuric acid, thiosulfuric acid, dithionous acid, sodium sulfate, sodium persulfate, sodium thiosulfate, sodium dithionite, sodium pyrosulfite, sodium pyrosulfite or sodium persulfate.

3. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of polyacrylonitrile to oxygen-containing sulfide is 1:6-12.

4. The preparation method according to claim 1, characterized in that: In step (1), the reaction temperature is 230-270° C. and the reaction time is 10-12.

5. The preparation method according to claim 1, characterized in that: In step (1), excess oxygen-containing sulfides are removed at high temperature.

6. The preparation method according to claim 1, characterized in that: In step (2), the calcination temperature is 300-350° C. and the calcination time is 5-6 hours.

7. The preparation method according to claim 1, characterized in that: In step (2), the structural formula of the sulfided polyacrylonitrile is as follows:

8. The preparation method according to claim 7, characterized in that: The sulfided polyacrylonitrile has a hydrogen content of 0.17 to 0.45 wt. % and an oxygen content of 10.46 to 15.84 wt. %.

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