Positive electrode material and preparation method therefor, positive electrode sheet, and lithium-sulfur battery

Abstract

The present application provides a positive electrode material and a preparation method therefor, a positive electrode sheet, and a lithium-sulfur battery. The positive electrode material comprises the following raw materials in parts by weight: 10 parts of a porous carbon conductive agent, 7-14 parts of an additive, 38-44 parts of an active substance, and 32-40 parts of a solid-state electrolyte, wherein the active substance comprises sulfur powder, and the additive comprises one or two of phosphorus pentasulfide and diphosphorus trisulfide. Lithium sulfide generated by elemental sulfur and lithium ions during battery discharge can in situ react with the additive to form a lithium-phosphorus-sulfur solid-state electrolyte; the lithium-phosphorus-sulfur solid-state electrolyte can enable most of active substances to participate in charge-discharge cycles, improving the utilization rate of the active substances, forming an ion-conducting network, and allowing for fast conduction of lithium ions; and in addition, the lithium-phosphorus-sulfur solid-state electrolyte can improve the ionic conductivity of the positive electrode material, such that under a high areal loading, an assembled all-solid-state battery ensures cycle stability while improving the specific capacity of the lithium-sulfur battery.

Description

Positive electrode materials and their preparation methods, positive electrode sheets and lithium-sulfur batteries

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202410961403.6, filed on July 17, 2024, entitled “Positive electrode material and preparation method thereof, positive electrode sheet and lithium-sulfur battery”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of electrochemical technology, specifically to a cathode material and its preparation method, a cathode electrode sheet, and a lithium-sulfur battery. Background Technology

[0004] Among the many new lithium-ion battery systems, lithium-sulfur batteries have recently become a hot research topic. Compared to traditional transition metal oxide systems, lithium-sulfur batteries have a significantly higher specific capacity, reaching as high as 1675 mAh / g, making them far superior to other lithium-ion battery systems. Although their average discharge voltage is relatively low, their energy density remains at a high level. Furthermore, all-solid-state lithium-sulfur battery systems avoid many problems associated with traditional liquid lithium-sulfur batteries, including the shuttle effect and lithium metal pulverization.

[0005] Existing all-solid-state lithium-sulfur battery cathode systems mostly employ complex materials and processes for preparation, and their performance is poor under high loading, failing to fully utilize the properties of sulfur as an active material. Therefore, it is necessary to provide a cathode material that can ensure the cycle stability of the battery. Summary of the Invention

[0006] This application provides a cathode material and its preparation method, a cathode electrode sheet, and a lithium-sulfur battery, with the aim of improving the problems of poor ionic conductivity and low specific capacity in lithium-sulfur batteries.

[0007] The first aspect of this application provides a positive electrode material comprising the following raw materials in parts by weight: 10 parts of porous carbon conductive agent, 7-14 parts of additives, 38-44 parts of active material, and 32-40 parts of solid electrolyte; wherein the active material includes sulfur powder; and the additives include one or two of phosphorus pentasulfide and phosphorus trisulfide.

[0008] The elemental sulfur in this application reacts with lithium ions to form lithium sulfide during battery discharge, which can then be combined with additives to form a lithium phosphorus sulfide (Li3PS4) solid electrolyte in situ. This lithium phosphorus sulfide solid electrolyte allows most of the active materials to participate in the charge-discharge cycle, improving the utilization rate of the active materials and forming an ion-conducting network, enabling lithium ions to conduct more quickly. It also improves the ionic conductivity of the cathode material, thus ensuring cycle stability while increasing the specific capacity of the assembled all-solid-state battery under high areal loading.

[0009] In some embodiments, the porous carbon conductive agent includes one or more of Ketjen black, acetylene black, carbon black, graphite, carbon fiber, and activated carbon.

[0010] Using porous carbon conductive agents helps phosphorus pentasulfide adhere better to the surface and allows active substances to penetrate the pores more effectively.

[0011] In some embodiments, the solid electrolyte includes one or more of lithium phosphorus-sulfur-chloride, lithium phosphorus-sulfur, lithium germanium-phosphorus-sulfur, and lithium lanthanum-zirconium-oxygen.

[0012] The second aspect of this application provides a method for preparing the above-mentioned cathode material, comprising: ball milling and mixing a porous carbon conductive agent and an additive, followed by a first sintering treatment to obtain a first intermediate product; ball milling and mixing the first intermediate product and an active material, followed by a second sintering treatment to obtain a second intermediate product; and ball milling and mixing the second intermediate product and a solid electrolyte to obtain the cathode material.

[0013] In some embodiments, the temperature of the first sintering treatment is 300°C to 420°C.

[0014] In some embodiments, the temperature of the first sintering treatment is 380°C to 400°C.

[0015] In some embodiments, the first sintering treatment takes 4 to 5 hours.

[0016] In some embodiments, the temperature of the second sintering process is 150°C to 160°C.

[0017] In some embodiments, the second sintering process takes 10 to 12 hours.

[0018] In some embodiments, the ball milling mixing time is 3 to 7 hours.

[0019] A third aspect of this application provides a positive electrode sheet, comprising the positive electrode material of the first aspect or the positive electrode material prepared according to the method of the second aspect.

[0020] The fourth aspect of this application provides a lithium-sulfur battery, including the positive electrode sheet of the third aspect. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0022] Figure 1 is an X-ray photoelectron spectroscopy analysis diagram of the first intermediate product provided in Example 1 of this application.

[0023] Figure 2 is an X-ray photoelectron spectroscopy analysis diagram of the second intermediate product provided in Example 1 of this application.

[0024] Figure 3 is an X-ray photoelectron spectroscopy analysis diagram of the cathode material provided in Embodiment 1 of this application.

[0025] Figure 4 shows the lithium-sulfur battery of Example 1 and the lithium-sulfur battery of Comparative Example 1 at a rate of 0.1C and an active material areal loading of 4 mg / cm². 2 The following is a comparison chart of specific capacities.

[0026] Figure 5 shows the lithium-sulfur battery of Example 1 and the lithium-sulfur battery of Comparative Example 1 at different rates and with an active material areal loading of 4 mg / cm². 2 The following is a comparison chart of specific capacities. Detailed Implementation

[0027] To make the inventive objectives, technical solutions, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of this application.

[0028] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0029] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "multiple (items)" in "one or more" or "one or more" means two or more.

[0030] Lithium metal anodes boast the lowest voltage (-3.04V) and extremely high specific capacity (3860mAh / g), making them a promising technology. However, due to safety concerns, most commercially available lithium-ion batteries currently use graphite anodes. Meanwhile, cathode materials typically utilize transition metal oxides, which, based on intercalation reactions, have reached their specific capacity limits, leaving very little room for improvement. The high cost of transition metal oxides, particularly due to expensive elements like cobalt, further restricts the large-scale application of lithium-ion batteries. Finally, the safety of lithium-ion batteries is increasingly concerning, with frequent spontaneous combustion incidents in electric vehicles and safety issues in mobile phone batteries proving unsatisfactory.

[0031] Traditional solid-state lithium-sulfur batteries, which combine sulfur and carbon, suffer from low specific capacity due to the low ionic conductivity of elemental sulfur and the discharge product lithium sulfide. This means that sulfur does not fully participate in the battery cycle. Furthermore, the low ionic conductivity of elemental sulfur and lithium sulfide also results in low ionic conductivity of the conventional cathode. Under high charge loading conditions, this prevents some active materials from fully participating in charge and discharge, leading to a low specific capacity.

[0032] Therefore, there is a need to provide a solid-state lithium-sulfur battery cathode material with high quality ratio, high loading capacity, and the ability to improve specific capacity.

[0033] The first aspect of this application provides a positive electrode material comprising the following raw materials in parts by weight: 10 parts of porous carbon conductive agent, 7-14 parts of additives, 38-44 parts of active material, and 32-40 parts of solid electrolyte; wherein the active material includes sulfur powder; and the additives include one or two of phosphorus pentasulfide and phosphorus trisulfide.

[0034] In this embodiment, the elemental sulfur reacts with lithium ions to form lithium sulfide during battery discharge, which can then be combined with additives to form a lithium phosphorus sulfide (Li3PS4) solid electrolyte in situ. This lithium phosphorus sulfide solid electrolyte allows most of the active materials to participate in the charge-discharge cycle, improving the utilization rate of the active materials and forming an ion-conducting network, enabling lithium ions to conduct more quickly. It also improves the ionic conductivity of the cathode material, ensuring the stability of the cycle while increasing the specific capacity of the assembled all-solid-state battery under high areal loading.

[0035] The additive can be phosphorus pentasulfide, which can work with porous carbon conductive agents to improve the specific capacity of the cathode material, thereby further improving the specific capacity of lithium-sulfur batteries.

[0036] The additive is present in parts by weight of 7 to 14, for example, 7, 8, 9, 10, 11, 12, 13, 14, or any combination of the above values. 10-12 parts may be selected.

[0037] The active substance is present in parts by weight of 38 to 44, for example, 38, 39, 40, 41, 42, 43, 44, or any combination of the above values. 40-42 parts is an option.

[0038] The solid electrolyte is present in parts by weight of 32 to 40, for example, 32, 33, 34, 35, 36, 7, 8, 39, 40, or any combination of the above values. 38-40 parts may also be selected.

[0039] In some embodiments, the porous carbon conductive agent includes one or more of Ketjen black, acetylene black, denka black, thermal cracking carbon black, channel black, graphite, carbon fiber, and activated carbon. It may be one or both of Ketjen black and activated carbon.

[0040] Using Ketjen black and activated carbon as porous carbon conductive agents helps the additives adhere better to the surface of the porous carbon conductive agent, allowing the active material to penetrate the pores better and thus improving the battery's conductivity.

[0041] In some embodiments, the solid electrolyte includes one or more of lithium phosphorus-sulfur-chloride, lithium phosphorus-sulfide, lithium germanium-phosphorus-sulfide, and lithium lanthanum-zirconium-oxygen. Lithium phosphorus-sulfur-chloride is a preferred choice; selecting it as the solid electrolyte allows most of the active material to participate in charge-discharge cycles more effectively, thus improving the overall ionic conductivity of the cathode material.

[0042] The second aspect of this application provides a method for preparing the above-mentioned cathode material, including:

[0043] S10, after ball milling and mixing the porous carbon conductive agent and additives, the first sintering treatment is carried out to obtain the first intermediate product.

[0044] S20, the first intermediate product and the active material are ball-milled and mixed, and then subjected to a second sintering treatment to obtain the second intermediate product;

[0045] S30, the second intermediate product and the solid electrolyte are ball-milled and mixed to obtain the cathode material.

[0046] As those skilled in the art will understand, ball milling utilizes the impact of falling grinding media and the grinding action between the grinding media and the inner wall of the ball mill to pulverize and mix materials. When the ball mill rotates, the friction between the grinding media and the inner wall of the ball mill carries the raw material up in the direction of rotation and then it falls back down, continuously pulverizing it. Operating conditions are good; pulverization takes place in a closed machine, eliminating dust; operation is reliable; grinding media are inexpensive and easy to replace; it can be operated intermittently or continuously. Choosing to perform ball milling in three stages allows for better mixing of the two substances during each milling process, resulting in better and more uniform mixing in subsequent milling stages; additives can achieve their target effect during the first milling stage, better adsorbing onto the surface of the porous carbon conductive agent. Multiple sintering stages allow for effective temperature control; when additives need to reach a molten state, increasing the temperature allows for controlled adsorption of active materials at lower temperatures, resulting in batteries with higher specific capacity.

[0047] In some embodiments, the temperature of the first sintering treatment is 300°C to 420°C, for example, it can be 300°C, 310°C, 320°C, 340°C, 350°C, 360°C, 380°C, 400°C, 420°C or any range of the above values. 380°C to 400°C is an option.

[0048] In some embodiments, the first sintering treatment time is 4 hours to 5.2 hours, for example, it can be 4 hours, 4.1 hours, 4.2 hours, 4.5 hours, 4.6 hours, 4.8 hours, 5 hours, or any range of the above values. It can be selected as 4.5 hours to 5 hours.

[0049] The first sintering process, conducted at the aforementioned temperature, allows the additives to reach a molten state, enabling better adsorption onto the surface of the porous carbon conductive agent.

[0050] In some embodiments, the temperature of the first sintering treatment is 380°C to 400°C.

[0051] In some embodiments, the ball milling speed is 400 rpm to 500 rpm.

[0052] In some embodiments, the temperature of the second sintering process is 150°C to 160°C, for example, it can be 150°C, 151°C, 152°C, 155°C, 156°C, 158°C, 160°C, or any range of the above values. 152°C to 155°C is an option.

[0053] In some embodiments, the second sintering treatment time is 10h to 14h, for example, it can be 10h, 10.5h, 11h, 11.5h, 12h, or any range of the above values. It can be selected as 11h to 12h.

[0054] The second sintering treatment is carried out at a temperature of 152°C to 155°C for 11 to 12 hours, which allows the active material to better form an ion-conducting network as the additives enter the pores of the porous carbon conductive agent, thereby increasing the specific capacity of the battery.

[0055] In some embodiments, the ball milling mixing time is 3 to 8 hours, for example, it can be 6 hours, 6.2 hours, 6.4 hours, 6.5 hours, 6.6 hours, 6.8 hours, 7 hours, 8 hours, or any range of the above values. A time of 6.5 to 7 hours is preferable, as it allows for more uniform mixing, ensuring the particle size reaches the target range, which is beneficial for subsequent sintering.

[0056] A third aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive electrode material of the first aspect or a positive electrode material prepared by the method of the second aspect coated on the positive current collector.

[0057] The fourth aspect of this application provides a lithium-sulfur battery, including a battery casing and a positive electrode, a negative electrode, a separator, and an electrolyte located within the battery casing.

[0058] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0059] Comparative Example 1

[0060] S10, 10 parts of Ketjen Black EC600-JD were added to a ball mill jar and ball-milled at 500 rpm for 4 hours. Then the mixture was transferred to a stainless steel reactor and sintered at 400°C for 5 hours to obtain the first intermediate product.

[0061] S20, the first intermediate product and 40 parts of sulfur powder were added to a ball mill jar and ball milled at 500 rpm for 5 hours. Then, the mixture was transferred to a stainless steel reactor and sintered at 155°C for 12 hours to obtain the second intermediate product.

[0062] S30, the second intermediate product and 40 parts of lithium phosphorus sulfur chloride were added to a ball mill jar and ball milled at 500 rpm for 7 hours to obtain the cathode material.

[0063] Comparative Example 2

[0064] S10: 10 parts Ketjen Black EC600-JD and 10 parts potassium iodide were added to a ball mill jar and ball-milled at 500 rpm for 4 hours. The mixture was then transferred to a stainless steel reactor and sintered at 400°C for 5 hours to obtain the first intermediate product.

[0065] S20, the first intermediate product and 40 parts of sulfur powder were added to a ball mill jar and ball milled at 500 rpm for 5 hours. Then, the mixture was transferred to a stainless steel reactor and sintered at 155°C for 12 hours to obtain the second intermediate product.

[0066] S30, the second intermediate product and 40 parts of lithium phosphorus sulfur chloride were added to a ball mill jar and ball milled at 500 rpm for 7 hours to obtain the cathode material.

[0067] Example 1

[0068] S10: 10 parts of Ketjen Black EC600-JD and 10 parts of phosphorus pentasulfide were added to a ball mill jar and ball-milled at 500 rpm for 4 hours. The mixture was then transferred to a stainless steel reactor and sintered at 400°C for 5 hours to obtain the first intermediate product.

[0069] S20, the first intermediate product and 40 parts of sulfur powder were added to a ball mill jar and ball milled at 500 rpm for 5 hours. Then, the mixture was transferred to a stainless steel reactor and sintered at 155°C for 12 hours to obtain the second intermediate product.

[0070] S30, the second intermediate product and 40 parts of lithium phosphorus sulfur chloride were added to a ball mill jar and ball milled at 500 rpm for 7 hours to obtain the cathode material.

[0071] The X-ray photoelectron spectroscopy (XPS) analysis of the first intermediate product prepared in Example 1 is shown in Figure 1. It can be seen that the first intermediate product has two characteristic peaks and a split double peak, with characteristic peaks of 163.9 eV and 162.3 eV, which are consistent with the two characteristic peaks of phosphorus pentasulfide.

[0072] The XPS spectrum of the second intermediate product prepared in Example 1 is shown in Figure 2. It can be seen that the second intermediate product contains both the characteristic peaks of phosphorus pentasulfide and the characteristic peak of elemental sulfur at 164.0 eV and its split double peak. Furthermore, the intensity of the characteristic peak of sulfur is significantly higher than that of phosphorus pentasulfide.

[0073] The XPS curve of the cathode material prepared in Example 1 is shown in Figure 3. It can be seen that the cathode material contains all the above-mentioned peaks, as well as the characteristic peak of lithium phosphorus sulfur chlorine at 161.1 eV, indicating that the cathode material is a composite of the second intermediate product and lithium phosphorus sulfur chlorine.

[0074] Assembly of lithium-sulfur batteries:

[0075] In a PEEK mold with an outer diameter of 40 mm and an inner diameter of 10 mm, 100 mg of lithium phosphorus sulfur chloride (solid electrolyte) was pressed into a sheet under a pressure of 300 MPa. Then, 7.85 mg of the positive electrode material powder provided in Example 1 (with a sulfur areal loading of 4 mg / cm²) was added to one side of the electrolyte layer. 2 On the other side, lithium indium alloy negative electrodes are assembled at a molar ratio of 0.5:1. After the entire battery is assembled, an external frame is used to apply a pressure of 60 MPa to the battery, and electrochemical tests are conducted at 30°C.

[0076] The lithium-sulfur battery prepared in Example 1 and the lithium-sulfur battery prepared using the materials in Comparative Example 1 show similarities at a 0.1C rate and an active material areal loading of 4 mg / cm². 2 The specific capacity comparison chart is shown in Figure 4.

[0077] The lithium-sulfur battery prepared in Example 1 and the lithium-sulfur battery prepared using the materials in Comparative Example 1 were compared at different rates and with an active material areal loading of 4 mg / cm². 2 The specific capacity comparison is shown in Figure 5, with 1C being 1675 mA / g.

[0078] Example 2

[0079] The only difference between this embodiment and Embodiment 1 is that the weight of phosphorus pentasulfide is 7 parts.

[0080] Example 3

[0081] The only difference between this embodiment and Example 1 is that the weight of phosphorus pentasulfide is 14 parts.

[0082] Example 4

[0083] The only difference between this embodiment and Embodiment 1 is that the sulfur powder is in the form of 50 parts by weight.

[0084] Example 5

[0085] The only difference between this embodiment and Embodiment 1 is that the weight parts of lithium, phosphorus, sulfur, and chlorine are 30 parts.

[0086] Example 6

[0087] The only difference between this embodiment and Embodiment 1 is that the temperature of the first sintering treatment is 320°C and the time of the first sintering treatment is 4 hours.

[0088] Example 7

[0089] The only difference between this embodiment and Embodiment 1 is that the temperature of the first sintering treatment is 400°C and the time of the first sintering treatment is 2 hours.

[0090] The performance of the lithium-sulfur batteries provided in Examples 1-9 and Comparative Examples 1-2 was tested, and the results are shown in Table 1:

[0091] Table 1

[0092] After conducting experiments with different parameters, it was found that the performance of the cathode material decreased to varying degrees after changing the material, sintering temperature, and sintering time. Therefore, in summary, the current processing method can obtain the cathode with the best performance.

[0093] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A positive electrode material, wherein, The positive electrode material comprises the following raw materials by weight: 10 parts of a porous carbon conductive agent, 7-14 parts of an additive, 38-44 parts of an active material, and 32-40 parts of a solid electrolyte. The active material comprises sulfur powder. The additive comprises one or both of phosphorus pentasulfide and phosphorus trisulfide.

2. The positive electrode material of claim 1, wherein, The porous carbon conductive agent comprises one or more of ketjen black, acetylene black, carbon black, graphite, carbon fiber, and activated carbon.

3. The positive electrode material of claim 1, wherein, The solid electrolyte comprises one or more of lithium phosphorus sulfur chloride, lithium phosphorus sulfur, lithium germanium phosphorus sulfur, and lithium lanthanum zirconium oxide.

4. A method for producing the positive electrode material as claimed in any one of claims 1 to 3, wherein The method comprises the following steps: The porous carbon conductive agent and the additive are ball-mixed and then subjected to a first sintering treatment to obtain a first intermediate product; The first intermediate product and the active material are ball-mixed and then subjected to a second sintering treatment to obtain a second intermediate product; The second intermediate product and the solid electrolyte are ball-mixed to obtain the positive electrode material.

5. The method of claim 4, wherein, The first sintering treatment is performed at a temperature of 300-420°C; and / or The first sintering treatment is performed for a time of 4-5.2 hours.

6. The method of claim 5, wherein, The first sintering treatment is performed at a temperature of 380-400°C.

7. The method of claim 4, wherein, The second sintering treatment is performed at a temperature of 150-160°C; and / or The second sintering treatment is performed for a time of 10-14 hours.

8. The method of claim 4, wherein, The ball-mixing is performed for a time of 3-8 hours.

9. A positive electrode sheet, wherein, The positive electrode material of any one of claims 1-3 or prepared according to the method of any one of claims 4-8.

10. A lithium-sulfur battery, wherein, The positive electrode sheet according to claim 9.

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