A carbon-sulfur battery and its preparation method

Abstract

This invention discloses a carbon-sulfur battery and its preparation method. A sulfur-carbon compound containing C-S and S-S (sulfur atom number ≤ 4) structural units is used as the positive electrode active material. In-situ pre-lithiation is performed inside the battery package to prepare the positive electrode, and a carbon-based material is used as the negative electrode active material to prepare the negative electrode. The resulting carbon-sulfur battery with the above positive and negative electrode system is further assembled. This battery utilizes the lithium fusion reaction of the sulfur-carbon compound positive electrode material and the intercalation or alloying lithium fusion reaction of the carbon-based negative electrode to achieve an electrochemical redox reaction between the positive and negative electrode systems, thereby converting chemical energy into electrical energy. The sulfur-carbon compound positive electrode material exhibits high structural stability during the lithium fusion reaction. Compared to the loss of positive electrode active material caused by soluble lithium polysulfides during the discharge of elemental sulfur positive electrodes, a positive electrode with high cycle stability can be obtained. Furthermore, by utilizing the reversible lithium intercalation / deintercalation or alloying reaction of carbon-based materials to replace the unstable and highly active metallic lithium negative electrode, high cycle stability of the negative electrode can be achieved.

Description

Technical Field

[0001] This invention relates to a carbon-sulfur battery and its preparation method, belonging to the field of new energy battery technology. The carbon-sulfur battery developed by this invention has a higher specific energy than lithium iron phosphate batteries, reaching 280Wh / kg. Furthermore, the sulfur-carbon compound cathode material used in this carbon-sulfur battery has significant advantages such as low cost and simple preparation method. It can be used as a chemical power source for large-scale energy storage. Background Technology

[0002] The rapid development of my country's new energy industry, including new energy electric vehicles, high-altitude drones, energy storage power stations, and various portable power supplies, has placed higher technical demands on energy storage batteries. Therefore, there is an urgent need to develop new battery systems with high energy density. Among these, lithium-sulfur batteries, due to their high specific capacity of electrode materials and high specific energy of the battery system, have become a hot research area.

[0003] Conventional lithium-sulfur secondary batteries use elemental sulfur as the positive electrode active material and metallic lithium as the negative electrode active material. Lithium metal possesses a theoretical specific capacity as high as 3860 mAh / g and also exhibits the most negative electrode potential, enabling lithium-sulfur batteries to achieve higher specific energy. However, lithium metal also has the following prominent problems:

[0004] (1) Lithium metal is chemically reactive. Its high chemical reactivity and low melting point make it prone to catching fire under conditions of thermal abuse, posing a danger.

[0005] (2) Formation of lithium dendrites in lithium anode. During high-rate charging and discharging of lithium-sulfur batteries, uneven deposition of lithium can lead to the formation of lithium dendrites, which can easily penetrate the separator, causing internal short circuits and safety issues.

[0006] (3) Corrosion and pulverization of lithium anode. During cycling, lithium polysulfides dissolved in the electrolyte react with active lithium metal, causing lithium corrosion and pulverization, which seriously affects the cycle stability of lithium-sulfur batteries.

[0007] While the elemental sulfur cathode in conventional lithium-sulfur batteries boasts a high specific capacity of 1650 mAh / g, it also faces some prominent challenges:

[0008] (1) During the discharge process, elemental sulfur undergoes a ring-opening process, reducing it to long-chain sulfur molecules, which react with lithium ions to form lithium polysulfides, and are eventually reduced to Li2S. The discharge plateau is 2.1V. The dissolution of lithium polysulfides causes the loss of sulfur cathode active material.

[0009] (2) Dissolved polysulfides pass through the separator, causing corrosion and pulverization of the lithium anode, which seriously affects the cycle stability of lithium-sulfur batteries.

[0010] (3) The volume expansion during sulfur discharge seriously affects the structural stability of the sulfur cathode.

[0011] Therefore, to take advantage of the high specific capacity of sulfur-based cathode active materials, it is necessary to develop novel electrochemical reaction systems for lithium-sulfur batteries, avoid the dissolution and deposition reaction mechanisms of conventional lithium-sulfur batteries, prevent sulfur dissolution and loss, and improve the cycle stability of lithium-sulfur batteries.

[0012] This invention patent innovatively designs the positive and negative electrode materials and electrode structure, proposing a novel carbon-sulfur battery based on a carbon-sulfur compound positive electrode and a carbon group negative electrode, which can undergo charge-discharge reactions in various electrolyte systems. The carbon-sulfur compound positive electrode proposed in this invention avoids the traditional dissolution and deposition reaction mechanism of elemental sulfur, effectively improving the cycle stability of lithium-sulfur batteries. Simultaneously, the use of a carbon group negative electrode reduces the cost of lithium anodes and improves the safety of lithium anodes during charge-discharge processes, effectively enhancing the safety of lithium-sulfur batteries and reducing the cost of lithium anodes. Summary of the Invention

[0013] The purpose of this invention is to provide a carbon-sulfur battery and its preparation method.

[0014] The preparation process of carbon-sulfur batteries includes:

[0015] (1) The positive electrode of the carbon-sulfur battery is a positive electrode film made by rolling a sulfur-carbon compound positive electrode material with conductive carbon and binder. The positive electrode film made by rolling a sulfur-carbon compound material with conductive carbon and binder is rolled onto one or both sides of a porous aluminum foil, and then a porous lithium metal layer is rolled onto the film surface to prepare a composite positive electrode.

[0016] (2) The negative electrode of the carbon-sulfur battery is made of carbon-based material supported by copper foil.

[0017] (3) The positive and negative electrodes are separated by a separator to prepare a soft-pack, wound or aluminum-cased battery.

[0018] (4) Inject electrolyte into the above battery structure.

[0019] (5) The discharge voltage of the carbon-sulfur battery is 1.75~1.90V, and the charge and discharge voltage range is 0.8V~3.0V.

[0020] The sulfur-carbon compound cathode material is a sulfur-carbon compound prepared from a sulfurized organic oligomer containing a furan ring structure, and its electrochemically active groups are SS and CS bond structures. The mass percentage of sulfur in the sulfur-carbon compound is 20%~85%.

[0021] The oligomer precursor containing a furan ring structure for preparing the cathode material includes one or more of the following: furanol, furanethanol, furandiethanol, furanpropanol, furan-5-ol, etc., or one or more of dextran, glucose, deoxyascorbic acid, sucrose, and xylose (a pentose sugar). These precursors are prepared by hydrothermal carbonization, washing, and drying. The hydrothermal carbonization temperature is 150℃~200℃, and the solution used in the hydrothermal reaction is deionized water, ethanol, or a mixture thereof; the mass concentration of the precursor in the solution is 5%~30%.

[0022] The positive electrode film contains 80-90 wt% sulfur and carbon compounds, 10-5% conductive carbon, and 10-5% binder. The thickness of the positive electrode film is 20-200 μm, and the lithium film rolled onto both sides of the positive electrode layer is a 5-30 μm porous metallic lithium.

[0023] The negative electrode sheet is prepared by mixing carbonaceous materials, a binder, and conductive carbon to prepare a slurry, coating it onto copper foil, and drying it to form the electrode sheet. The carbonaceous materials used are one or a mixture of two of porous hard carbon, carbon-coated graphite, and silicon-carbon composites.

[0024] The electrolyte composition includes one or more of lithium hexafluorophosphate (LiPF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium tetrafluoroborate (LiBF4), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); the solvent is one or a mixture of several of dimethyl carbonate (DMC), diethyl carbonate (DC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me-THF), 1,3-dioxolane (1,3~DOL), dimethyl ether (DME), dimethyl phthalate (DMP), dimethyl sulfoxide (DMSO), sulfolane, ethyl isopropyl sulfone (EIS), and ethyl vinyl sulfone (EVS).

[0025] The advantages of this invention compared to existing technologies are:

[0026] This invention utilizes sulfur-carbon compounds containing C~S and S~S (sulfur atom number ≤ 4) structural units as the positive electrode active material. In-situ pre-lithiation is performed inside the battery package to prepare the positive electrode, and carbon group materials are used as the negative electrode active material to prepare the negative electrode. The resulting carbon-sulfur battery with the above positive and negative electrode system is further assembled. This battery utilizes the lithium fusion reaction of the sulfur-carbon compound positive electrode material and the intercalation or alloying lithium fusion reaction of the carbon group negative electrode to achieve an electrochemical redox reaction between the positive and negative electrode systems, thereby converting chemical energy into electrical energy. The sulfur-carbon compound positive electrode material exhibits high structural stability during the lithium fusion reaction. Compared to the loss of positive electrode active material caused by soluble lithium polysulfides during the discharge of elemental sulfur positive electrodes, a positive electrode with high cycle stability can be obtained. Furthermore, by utilizing the reversible lithium intercalation / deintercalation or alloying reaction of carbon group materials to replace the unstable and highly active metallic lithium negative electrode, high cycle stability of the negative electrode can be achieved.

[0027] 1. This invention proposes a cathode structure design based on a solid sulfur-carbon compound cathode and its lithiation layer. The sulfur-carbon compound cathode prepared by this invention avoids the dissolution and deposition reaction path of traditional elemental sulfur cathodes, thus preventing the decline in the cycle performance of lithium-sulfur batteries caused by the loss of polysulfides.

[0028] 2. Replacing the existing lithium metal anode with a carbon group anode improves the safety performance of the anode and reduces the raw material cost of lithium-sulfur battery anodes.

[0029] 3. The carbon-sulfur battery prepared using the positive and negative electrodes of the present invention can be charged and discharged in various types of electrolytes, which can effectively improve the safety performance and cycle stability of lithium-sulfur batteries under different operating ambient temperatures. Attached Figure Description

[0030] Figure 1 Example 1: First charge and second and 139th discharge curves of the carbon-sulfur battery;

[0031] Figure 2 Cyclic stability curves of carbon-sulfur batteries in Example 1. Detailed Implementation

[0032] The following embodiments are intended to enable those skilled in the art to more fully understand the present invention, but are not intended to limit the invention in any way.

[0033] The following example uses the sulfurization of oligomers prepared by hydrothermal treatment of glucose to prepare sulfur-carbon compounds: Glucose was prepared into an aqueous solution of 0.07 g / ml, subjected to hydrothermal treatment at 180°C for 4 h, the product was filtered and dried at 60°C, the dried polymer was mixed with elemental sulfur at a mass ratio of 1:2, and the mixture was placed in a nitrogen atmosphere and heat-treated at 250°C for 10 h to obtain carbon-sulfur compounds.

[0034] The preparation methods for the remaining carbon-sulfur compounds are the same as described above, except that glucose is replaced with other selected raw materials to prepare the carbon-sulfur compounds. Carbon-sulfur batteries are prepared by operating according to the methods of each embodiment.

[0035] Example 1

[0036] A sulfur-carbon compound, prepared by sulfidation of oligomers derived from glucose via hydrothermal processing, was used as the cathode material. The sulfur content in the sulfur-carbon compound cathode was 55% by mass. A cathode gel material (acetylene black as the conductive agent and PTFE as the binder, with a total solids content of approximately 50%) was prepared using NMP as a dispersion solution according to a cathode active material: conductive agent: binder ratio of 8:1:1. A cathode film with a thickness of 150 μm was prepared by rolling. The cathode film was then rolled onto a porous aluminum foil (porosity 15%, pore size 300 μm, thickness 15 μm). A 20 μm thick porous lithium foil with a porosity of 15% and a pore size of 35 μm was rolled onto both sides of the prepared cathode film to prepare the cathode for a carbon-sulfur battery. A silicon-carbon composite material (commercially available CSi-500, with a silicon content of 10%) was used as the negative electrode active material. A negative electrode slurry (acetylene black as the conductive agent and LA132 as the binder) was prepared according to a mass ratio of negative electrode active material: conductive agent: binder = 9:0.5:0.5. This slurry was coated onto a 6μm copper foil (coating thickness of 100μm) to prepare the negative electrode for a carbon-sulfur battery. The above positive and negative electrodes and a separator (polypropylene PP) were then wound together to prepare a 5Ah soft-pack carbon-sulfur battery. 10ml of electrolyte (1M LiPF6 EC:MC:EMC = 1:1:1 (volume ratio)) was injected, and after venting and sealing, the carbon-sulfur battery was prepared. The charge-discharge performance and cycle stability of the carbon-sulfur battery in the voltage range of 0.8V~3V were tested at 0.01C. Specific test results are attached. Figure 1 and attached Figure 2 .

[0037] Example 2

[0038] A sulfur-carbon compound, prepared by sulfidation of oligomers derived from glucose and sucrose via hydrothermal processing, was used as the cathode material. The sulfur content in the sulfur-carbon compound cathode was 45% by mass. A cathode slurry was prepared using NMP as the dispersion medium (acetylene black as the conductive agent and PTFE as the binder) at a ratio of 8:1:1 for the cathode active material, conductive agent, and binder. A cathode film with a thickness of 120 μm was prepared using a rolling mill method. The cathode film was then rolled onto a porous aluminum foil (20% porosity, 300 μm pore size, and 20 μm thickness). A porous lithium foil with a porosity of 20%, a pore size of 35 μm, and a thickness of 15 μm was rolled onto both sides of the prepared cathode film to prepare the cathode for a carbon-sulfur battery. A silicon-carbon composite material (commercially available CSi-500, with a silicon content of 10%) was used as the negative electrode active material. A negative electrode slurry was prepared at a ratio of negative electrode active material: conductive agent: binder = 9:0.5:0.5 (acetylene black as the conductive agent and LA132 as the binder), and coated onto an 8 μm copper foil (coating thickness of 110 μm) to prepare the negative electrode for a carbon-sulfur battery. The above positive and negative electrodes and a separator (polypropylene PP) were then wound together to prepare a 5Ah soft-pack carbon-sulfur battery. 10 ml of electrolyte (1M LiPF6 EC:MC:EMC = 1:1:1 (volume ratio)) was injected, and after venting and sealing, the carbon-sulfur battery was successfully manufactured.

[0039] Example 3

[0040] A sulfur-carbon compound, prepared by sulfidation of oligomers produced by hydrothermal synthesis under furan-5-ol catalysis, was used as the cathode material. The sulfur content in the sulfur-carbon compound cathode was 55% by mass. A cathode slurry (acetylene black as the conductive agent and PTFE as the binder; total solids content in the slurry was approximately 50%) was prepared using NMP as the dispersion medium according to a cathode active material: conductive agent: binder ratio of 8:1:1. A cathode film with a thickness of 100 μm was prepared by rolling. The cathode film was then rolled onto a porous aluminum foil (porosity 20%, pore size 300 μm, thickness 20 μm). A 15 μm thick porous lithium foil with a porosity of 15% and a pore size of 30 μm was rolled onto both sides of the prepared cathode film to prepare the cathode of the carbon-sulfur battery. A silicon-carbon composite material (commercially available CSi-500, with a silicon content of 10%) was used as the negative electrode active material. A negative electrode slurry was prepared at a ratio of negative electrode active material: conductive agent: binder = 9:0.5:0.5 (acetylene black as the conductive agent and LA132 as the binder), and coated onto a 15μm copper foil (coating thickness 120μm) to prepare the negative electrode for a carbon-sulfur battery. The above positive and negative electrodes and a separator (polypropylene PP) were then wound together to prepare a 5Ah soft-pack carbon-sulfur battery. 10ml of electrolyte (1M LiPF6 EC:MC:EMC = 1:1:1 (volume ratio)) was injected, and after venting and sealing, the carbon-sulfur battery was successfully manufactured.

[0041] Example 4

[0042] A sulfur-carbon compound, prepared by sulfidation of oligomers derived from furanol and glucose via hydrothermal processing, was used as the cathode material. The sulfur content in the sulfur-carbon compound cathode was 55% by mass. A cathode slurry (acetylene black as the conductive agent and PTFE as the binder; total solids content in the slurry approximately 50%) was prepared using NMP as the dispersion solution, with a cathode active material: conductive agent: binder ratio of 8:1:1. A cathode film with a thickness of 150 μm was prepared by rolling. The cathode film was then rolled onto a porous aluminum foil (porosity 20%, pore size 350 μm, thickness 25 μm). A 5 μm thick porous lithium foil with a porosity of 15% and a pore size of 50 μm was rolled onto both sides of the prepared cathode film to prepare the cathode for the carbon-sulfur battery. Hard carbon material was used as the negative electrode active material. A negative electrode slurry was prepared according to the ratio of negative electrode active material: conductive agent: binder = 9:0.5:0.5 (acetylene black as the conductive agent and LA132 as the binder), and coated onto a 6 μm copper foil (coating thickness of 120 μm) to prepare the negative electrode for a carbon-sulfur battery. The above positive and negative electrodes and separator (polypropylene PP) were then wound to prepare a 5Ah soft-pack carbon-sulfur battery. 10 ml of electrolyte (EC:MC:EMC = 1:1:1 (volume ratio) of 1M LiPF6 was injected, and after degassing and sealing, the carbon-sulfur battery was prepared.

[0043] Example 5

[0044] A sulfur-carbon compound, prepared by sulfidation of oligomers derived from glucose via hydrothermal processing, was used as the cathode material. The sulfur content in the sulfur-carbon compound cathode was 55% by mass. A cathode slurry (acetylene black as the conductive agent and PTFE as the binder; total solids content in the slurry approximately 50%) was prepared using NMP as the dispersion solution, with a cathode active material: conductive agent: binder ratio of 8:1:1. A cathode film with a thickness of 150 μm was prepared by rolling. The cathode film was then rolled onto a porous aluminum foil (porosity 15%, pore size 350 μm, thickness 25 μm). A 10 μm thick porous lithium foil with a porosity of 15% and a pore size of 300 μm was rolled onto both sides of the prepared cathode film to prepare the cathode for a carbon-sulfur battery. Hard carbon material was used as the negative electrode active material. A negative electrode slurry was prepared according to the ratio of negative electrode active material: conductive agent: binder = 9:0.5:0.5 (acetylene black as the conductive agent and LA132 as the binder), and coated onto a 10μm copper foil (coating thickness of 120μm) to prepare the negative electrode for a carbon-sulfur battery. The above positive and negative electrodes and separator (polypropylene PP) were then wound to prepare a 5Ah soft-pack carbon-sulfur battery. 10ml of electrolyte (EC:MC:EMC = 1:1:1 (volume ratio) of 1M LiPF6 was injected, and after degassing and sealing, the carbon-sulfur battery was prepared.

Claims

1. A carbon-sulfur battery, characterized by, The product includes a sulfur-carbon compound-lithium metal composite positive electrode, a carbon-based negative electrode and a separator, and an electrolyte; the sulfur-carbon compound is a sulfur-carbon compound material prepared by dehydrogenation sulfidation reaction of an oligomer containing a furan ring structure and sulfur free radicals under nitrogen protection at 200~300℃ for 2h~10h. The method for preparing the carbon-sulfur battery includes the following steps: (1) Preparation of sulfur-carbon compounds: Sulfur-carbon compound materials are prepared by hydrothermal carbonization of oligomers containing furan ring structure, followed by dehydrogenation sulfidation reaction with sulfur free radicals at 200~300℃ for 2h~10h under nitrogen protection. (2) Preparation of composite positive electrode: The sulfur carbon compound material in step (1) is mixed with conductive carbon and binder and rolled to prepare a positive electrode film. The positive electrode film is rolled onto one or both sides of a porous aluminum foil, and then a porous lithium metal layer is rolled onto the film surface to prepare a composite positive electrode. (3) The negative electrode of the carbon-sulfur battery is made of carbon-based material supported by copper foil; (4) The positive and negative electrodes are separated by a separator to prepare a soft-pack, wound, or aluminum-cased battery; (5) Inject electrolyte into the above battery structure.

2. A method of producing a carbon-sulfur battery as claimed in claim 1, characterized by, Includes the following steps: (1) Preparation of sulfur-carbon compounds: Sulfur-carbon compound materials are prepared by hydrothermal carbonization of oligomers containing furan ring structure, followed by dehydrogenation sulfidation reaction with sulfur free radicals at 200~300℃ for 2h~10h under nitrogen protection. (2) Preparation of composite positive electrode: The sulfur carbon compound material in step (1) is mixed with conductive carbon and binder and rolled to prepare a positive electrode film. The positive electrode film is rolled onto one or both sides of a porous aluminum foil, and then a porous lithium metal layer is rolled onto the film surface to prepare a composite positive electrode. (3) The negative electrode of the carbon-sulfur battery is made of carbon-based material supported by copper foil; (4) The positive and negative electrodes are separated by a separator to prepare a soft-pack, wound, or aluminum-cased battery; (5) Inject electrolyte into the above battery structure.

3. The carbon-sulfur battery or preparation method according to claim 1 or 2, characterized in that, The sulfur-carbon compound contains 20% to 85% sulfur by mass.

4. The carbon-sulfur battery or preparation method according to claim 3, characterized in that, The sulfur-carbon compound contains 40% to 65% sulfur by mass.

5. The carbon-sulfur battery or its preparation method according to claim 1 or 2, characterized in that, The precursor containing the furan ring structure oligomer includes one or more of the following: furanol, furanethanol, furandiethanol, furanpropanol, furan-5-ol, dextran, glucose, deoxyascorbic acid, sucrose, and xylose, which are prepared by hydrothermal carbonization, water washing, and drying.

6. The method for preparing a carbon-sulfur battery according to claim 2 or 4, characterized in that, The hydrothermal carbonization temperature is 150℃~200℃, and the time is 4~12 hours; the solution used in the hydrothermal reaction is deionized water, ethanol, or a mixture thereof; the mass concentration of the furan ring structure oligomer precursor in the solution is 5%~30%.

7. The method for preparing a carbon-sulfur battery according to claim 2, characterized in that: The positive electrode film in step (2) has a sulfur-carbon compound mass percentage of 80-90 wt%, conductive carbon of 10-5%, and binder of 10-5%.

8. The method for preparing a carbon-sulfur battery according to claim 2, characterized in that: In step (2), the thickness of the positive electrode film is 20~200μm, and the porous lithium metal layer rolled on both sides of the positive electrode layer has a thickness of 5~30μm. The porosity of the lithium metal is 20%~30%, the pore size is 30~50μm, and the thickness is 5~30μm. The porous aluminum foil has a pore size of 300~500μm, a porosity of 15%~20%, and a thickness of 15~30μm.

9. The method for preparing a carbon-sulfur battery according to claim 2, characterized in that: The method for preparing the negative electrode sheet in step (3) is to mix carbon-based materials, binders, and conductive carbon in a mass ratio of 80~90:5~10:5~10 to prepare a slurry, coat it on a copper foil and dry it to prepare an electrode sheet, with the copper foil having a thickness of 6~10μm; The carbon-based material used is one or a mixture of two of the following: porous hard carbon, carbon-coated graphite, and silicon-carbon composite.

10. The method for preparing a carbon-sulfur battery according to claim 2, 7, or 9, characterized in that: The binder is any one of PVFD, LA133, LA132, and CMC; the conductive carbon is one or a mixture of two or more of acetylene black, BP2000, and KB300.

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