An organic cathode material applicable to sulfide all-solid-state lithium metal batteries

Abstract

This invention discloses an organic cathode material suitable for sulfide-based all-solid-state lithium metal batteries. The organic cathode material is Li4C8H2O6@C, where C is a C-conductive agent with a diameter of 5-250 nm and an aspect ratio greater than 1 × 10⁻⁶. 3 The C-type conductive agent with ultra-high aspect ratio can form a good cross-linked conductive network in the composite cathode, allowing the conductive agent, organic cathode material and sulfide solid electrolyte to share more interfaces, which is beneficial for the transport of ions and electrons, thereby improving the utilization rate and rate performance of the active material of the composite cathode.

Description

Technical Field

[0001] This invention relates to the field of manufacturing sulfide all-solid-state lithium metal batteries, specifically to a high aspect ratio cathode material, which is particularly suitable for sulfide all-solid-state lithium metal batteries. Background Technology

[0002] With the development and improvement of energy storage batteries, compared with the relatively widely used inorganic materials, organic materials have a wide range of raw material sources, are not limited by mineral resources, have adjustable electrode potential, and have the characteristics of recyclability, reusability, designability, and low pollution, showing great potential in future battery materials. Among them, Li4C8H2O6 organic material has high specific capacity and thermal stability, minimal structural changes during charge and discharge, and a simple synthesis process, but its electronic conductivity is low.

[0003] Lithium-ion battery technology continues to advance, striving for higher performance and safety. Solid-state batteries align with this technological trend and may become the next generation of lithium-ion batteries. Solid-state electrolytes possess characteristics such as non-flammability, non-corrosiveness, and non-volatility, making them far safer than liquid batteries. Solid-state lithium-ion batteries significantly improve safety while also offering high energy density and high power density. Among these, sulfide solid-state electrolytes, due to their highest ionic conductivity, good mechanical ductility, and excellent interfacial contact with electrodes, represent the most promising technology. However, sulfide solid-state electrolytes suffer from poor electrochemical stability and are prone to electrochemical decomposition.

[0004] In recent years, several types of organic cathode materials have been developed and studied for sulfide all-solid-state batteries. However, it has been found that organic cathodes have poor conductivity and low density, resulting in low utilization of active materials in sulfide all-solid-state batteries. Some researchers have attempted to construct an electron permeation network using conductive agents to allow the conductive agents, organic cathode materials, and sulfide all-solid-state electrolytes to share more interfaces. However, the results were unexpected: the conductive agents not only affected the capacity of the organic cathode materials but also the interfacial stability of the sulfide solid electrolyte. Summary of the Invention

[0005] This invention addresses the problems in the prior art by disclosing an organic cathode material applicable to sulfide all-solid-state lithium metal batteries. When applied to sulfide all-solid-state lithium batteries, this organic cathode material enables the composite cathode to have high capacity while effectively improving its conductivity, rate performance, and active material utilization, and reducing the decomposition of sulfide electrolytes.

[0006] Two main factors limit the application of organic cathode materials in batteries. Firstly, organic cathode materials have low electronic conductivity; secondly, their low density leads to a low mass ratio of active materials in composite cathodes. Good electron transport is essential for redox reactions within composite cathodes and is also a necessary parameter for improving the utilization rate of active materials. However, sulfide solid electrolytes typically have a narrow electrochemical window. Therefore, linear conductive additives are often used in composite cathodes to reduce the contact area between the conductive agent and the sulfide solid electrolyte, thereby reducing the electrochemical decomposition of the sulfide solid electrolyte. The aspect ratio (length:diameter) of the linear conductive agent in sulfide solid electrolyte decomposition is particularly important. A very high aspect ratio facilitates the formation of a good cross-linked electrical network within the composite cathode, allowing the conductive agent, organic cathode material, and sulfide solid electrolyte to share more interfaces. This not only improves ion transport but also allows the active material to fully utilize its electrochemical activity. Because organic lithium Li4C8H2O6 has high specific capacity and thermal stability, minimal structural changes during charge and discharge, and a simple synthesis process, we selected it as one of the active materials for the cathode in this invention. We also explored the optimized application conditions of Li4C8H2O6 in sulfide solid electrolytes. We found that when combined with a conductive agent with a high aspect ratio, it can effectively improve the conductivity, rate performance, and utilization rate of the active material in the composite cathode of sulfide all-solid-state batteries.

[0007] This invention is achieved through the following technical solution:

[0008] This invention provides an organic cathode material suitable for sulfide-based all-solid-state lithium metal batteries. The organic cathode material is Li4C8H2O6@C, where C is a carbon conductive agent (C conductive agent). The diameter of the C conductive agent is 5-250 nm, and the aspect ratio is greater than 1 × 10⁻⁶. 3 .

[0009] The aspect ratio of this invention is the ratio of the length of the C-conductive agent to the diameter of the C-conductive agent. In the above design, the C-conductive agent with this ultra-high aspect ratio can form a good cross-linked conductive network in the composite cathode, so that the conductive agent, organic cathode material and sulfide solid electrolyte share more interfaces, which is beneficial to the transport of ions and electrons, thereby improving the utilization rate and rate performance of the active material of the composite cathode. Furthermore, the composite cathode with the C-conductive agent with this ultra-high aspect ratio has high capacity.

[0010] As a further embodiment, the organic cathode material Li4C8H2O6@C is an organic cathode material in situ grown from Li4C8H2O6 on the surface of a C conductive agent. This can effectively reduce the decomposition of sulfide electrolytes while maintaining high capacity, and can effectively improve electron transport within the organic cathode particles, shortening the ion and electron transport channels, thereby better leveraging the electrochemical activity of Li4C8H2O6.

[0011] As a further embodiment, the C-conductive agent includes CNT and VGCF; as an even further embodiment, the C-conductive agent is CNT.

[0012] As a further embodiment, the organic cathode material Li4C8H2O6@C, calculated as Li4C8H2O6, accounts for 15wt.%-45wt.% of the composite cathode active material by mass; as an even further embodiment, the organic cathode material Li4C8H2O6@C, calculated as Li4C8H2O6, accounts for (20±10)wt.% of the composite cathode active material by mass. When the mass percentage of Li4C8H2O6 in the composite cathode active material is between 15wt.% and 45wt.%, the improvement effects of high aspect ratio C conductive agent combined with Li4C8H2O6 on the conductivity, rate performance, and utilization rate of active material of the composite cathode in sulfide all-solid-state batteries are different. When the mass percentage of Li4C8H2O6 in the composite cathode active material is (20±10)wt.%, the combination of high aspect ratio C conductive agent with Li4C8H2O6 and sulfide solid electrolyte has the best effect on improving the conductivity and rate performance of the composite cathode.

[0013] As a further embodiment, the mass ratio of Li4C8H2O6 to C conductive agent in the organic cathode material Li4C8H2O6@C is (3-5):1; as an even further embodiment, the mass ratio of Li4C8H2O6 to C conductive agent is (4±0.3):1.

[0014] As a further embodiment, the organic cathode material Li4C8H2O6@C exhibits characteristic diffraction peaks at 13.5°, 15.5°, 22.5°, and 27° in its X-ray powder diffraction pattern expressed at a diffraction angle of 2θ.

[0015] The present invention also provides a method for preparing organic cathode material Li4C8H2O6@C, comprising weighing 2,5-dihydroxythyroid acid and C conductive agent according to the mass ratio, dispersing the weighed material in methanol, performing ultrasonic dispersion to obtain a black dispersion, adding lithium methoxide in the corresponding molar ratio to react, centrifuging and drying the reaction product, and then heating it to obtain a dark green solid powder.

[0016] As a further embodiment, the ultrasonic dispersion time is 2 hours.

[0017] As a further option, the reaction time is 24 hours.

[0018] As a further option, the heating time is 12 hours and the heating temperature is 220℃.

[0019] The present invention also provides a composite cathode comprising the above-mentioned Li4C8H2O6@C organic cathode material, which is particularly suitable for sulfide solid electrolytes.

[0020] As a further embodiment, the composite cathode further includes a sulfide solid electrolyte, wherein the mass ratio of Li4C8H2O6: sulfide solid electrolyte: C conductive agent is (15-45):(45-75):(10).

[0021] As a further option, the sulfide solid electrolyte is Li6PS5Cl.

[0022] The present invention also provides a sulfide solid-state battery comprising the above-described composite cathode.

[0023] The features and beneficial effects of this invention are as follows: The C-conductive agent with an ultra-high aspect ratio can form a good cross-linked conductive network within the composite cathode, allowing the conductive agent, organic cathode material, and sulfide solid electrolyte to share more interfaces, which is beneficial for ion and electron transport, thereby improving the utilization rate and rate performance of the active material of the composite cathode. Furthermore, the composite cathode with this ultra-high aspect ratio C-conductive agent exhibits high capacity. When using Li4C8H2O6 to in-situ coat the C-conductive agent to form the organic cathode material Li4C8H2O6@C, the decomposition of the sulfide electrolyte can be effectively reduced while maintaining high capacity. It can also effectively improve electron transport within the organic cathode particles and shorten the ion and electron transport channels, thereby better utilizing the electrochemical activity of Li4C8H2O6. The direct growth of Li4C8H2O6 on the surface of the C-conductive agent also helps to reduce the particle size of Li4C8H2O6, thereby shortening the electron migration path and improving the electron / ion transport capability of the electrode. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some drawings of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1SEM characterization images and schematic diagrams of the Li4C8H2O6 / C composite cathode provided in embodiments of the present invention are shown. Figure 1 a, Figure 1 b and Figure 1 c shows the SEM characterization image and schematic diagram of the Li4C8H2O6 / VGCF composite cathode; Figure 1 d、 Figure 1 e and Figure 1 f represents the SEM characterization image and schematic diagram of the Li4C8H2O6 / CNT composite cathode.

[0026] Figure 2 This invention provides results for the electronic conductivity and rate performance of Li4C8H2O6 / C composite cathodes when the mass percentage of Li4C8H2O6 in the composite cathode active material varies. Figure 2 a and Figure 2 b represents the electronic conductivity of the Li4C8H2O6 / VGCF composite cathode and the Li4C8H2O6 / CNT composite cathode when the mass percentage of Li4C8H2O6 in the composite cathode active material is 20 wt.% and 40 wt.%, respectively. Figure 2 c and Figure 2 d represents the rate performance of sulfide solid-state batteries of Li4C8H2O6 / VGCF composite cathode and Li4C8H2O6 / CNT composite cathode when the mass percentage of Li4C8H2O6 in the composite cathode active material is 20 wt.% and 40 wt.%, respectively. Figure 2 e and Figure 2 f represents the charge-discharge curves of the Li4C8H2O6 / CNT composite cathode when the mass percentage of Li4C8H2O6 in the composite cathode active material is 20 wt.% and 40 wt.%, respectively.

[0027] Figure 3 This invention provides embodiments of the sulfide solid-state battery and the electrostatic voltage profile of the Li4C8H2O6 / C composite cathode at different discharge rates when using different proportions of active materials. Figure 3 a and Figure 3 b represents the cycling performance of the Li4C8H2O6 / VGCF composite cathode and the Li4C8H2O6 / CNT composite cathode at 0.1C and 1C discharge rates when the mass percentage of Li4C8H2O6 in the composite cathode active material is 20wt.%. Figure 3 c and Figure 3When d represents the mass percentage of Li4C8H2O6 in the composite cathode active material of 40wt.%, the cycling performance of the Li4C8H2O6 / VGCF composite cathode and the Li4C8H2O6 / CNT composite cathode at 0.1C and 1C discharge rates. Figure 3 e and Figure 3 f represents the charge-discharge curves of the composite cathodes Li4C8H2O6 / VGCF and Li4C8H2O6 / CNT at 0.1C and 1C discharge rates when the mass percentage of Li4C8H2O6 in the composite cathode active material is 20wt.%. Figure 3 g and Figure 3 h represents the charge-discharge curves of the Li4C8H2O6 / VGCF composite cathode and the Li4C8H2O6 / CNT composite cathode at discharge rates of 0.1C and 1C when the mass percentage of Li4C8H2O6 in the composite cathode active material is 40wt.%.

[0028] Figure 4 This invention provides SEM and XRD characterization images of the Li4C8H2O6@CNT composite cathode and the Li4C8H2O6 cathode, and their electronic conductivity, when the mass percentage of Li4C8H2O6 in the composite cathode active material is different. Figure 4 a, Figure 4 b and Figure 4 c represents the SEM characterization image and schematic diagram of the composite cathode of Li4C8H2O6@CNT; Figure 4 d and Figure 4 e is the SEM characterization image of the Li4C8H2O6 cathode; Figure 4 f represents the XRD characterization images of the composite cathode of Li4C8H2O6@CNT and the Li4C8H2O6 cathode. Figure 4 g and Figure 4 h represents the electronic conductivity of the Li4C8H2O6@CNT composite cathode and the Li4C8H2O6 / CNT composite cathode when the mass percentage of Li4C8H2O6 in the composite cathode active material is 20 wt.% and 40 wt.%, respectively. Figure 4 i represents the electronic conductivity of the composite cathodes Li4C8H2O6 / VGCF, Li4C8H2O6 / CNT, and Li4C8H2O6@CNT.

[0029] Figure 5This invention provides, for embodiments thereof, the rate performance, cycle performance, Galvanostatic voltage spectrum, and charge-discharge curves of sulfide solid-state batteries with different mass percentages of Li4C8H2O6@CNT composite cathodes in the composite cathode active material, for different proportions of Li4C8H2O6. Figure 5 a represents the rate performance of sulfide solid-state batteries with different proportions of Li4C8H2O6@CNT composite cathodes and Li4C8H2O6 / CNT composite cathodes when the mass percentage of Li4C8H2O6 in the composite cathode active material is 20wt.%. Figure 5 b represents the rate performance of sulfide solid-state batteries with a ratio of (4:1) Li4C8H2O6@CNT and Li4C8H2O6 / CNT when the mass percentage of Li4C8H2O6 in the composite cathode active material is 40wt.%. Figure 5 c represents the Galvanostatic voltage spectrum of the Li4C8H2O6@CNT(4:1) composite cathode at different discharge rates; Figure 5 d and Figure 5 e represents the cycle stability and Galvanostatic voltage spectrum of sulfide solid-state batteries of Li4C8H2O6 / CNT composite cathode and Li4C8H2O6@CNT composite cathode when the mass percentage of Li4C8H2O6 in the composite cathode active material is 20 wt.%. Figure 5 f and Figure 5 g represents the cycle stability and Galvanostatic voltage spectrum of sulfide solid-state batteries with Li4C8H2O6 / CNT composite cathode and Li4C8H2O6@CNT composite cathode, respectively, when the mass percentage of Li4C8H2O6 in the composite cathode active material is 40 wt.%.

[0030] Figure 6 This invention provides schematic diagrams and active material utilization rates for Li4C8H2O6 cathodes and Li4C8H2O6@CNT composite cathodes when the mass percentage of Li4C8H2O6 in the composite cathode active material is different. Figure 6 a is a schematic diagram of the composite cathode of Li4C8H2O6 / VGCF, the composite cathode of Li4C8H2O6@CNT, and the composite cathode of Li4C8H2O6@CNT. Figure 6 b represents the utilization rate of the active material of Li4C8H2O6 / VGCF composite cathode, Li4C8H2O6 / CNT composite cathode, and Li4C8H2O6@CNT composite cathode when the mass percentage of Li4C8H2O6 in the composite cathode active material is 20wt.%. Figure 6c represents the utilization rate of the active material of Li4C8H2O6 / VGCF composite cathode, Li4C8H2O6 / CNT composite cathode, and Li4C8H2O6@CNT composite cathode when the mass percentage of Li4C8H2O6 in the composite cathode active material is 40wt.%. Figure 6 Example d compares the utilization rate of the active material with other reported organic solid-state batteries. Detailed Implementation

[0031] To facilitate understanding of the organic cathode material Li4C8H2O6@C applicable to sulfide all-solid-state lithium metal batteries of the present invention, the preparation method of the organic cathode material Li4C8H2O6@C applicable to sulfide all-solid-state lithium metal batteries of the present invention will be described more comprehensively below, and embodiments of the present invention will be given, but this does not limit the scope of the present invention.

[0032] (1) Synthesis of Li4C8H2O6: Tetralithium 2,5-dihydroxyterephthalate (Li4C8H2O6, Li4DHTPA) was prepared by the reaction of 2,5-dihydroxythyroxine (DHTPA). In a typical synthesis, 2 mL of a MEOLI-based solution (Aldrich, 2.2 mol methanol) was added dropwise to a 15 mL methanol solution containing 198 mg DHTPA (Aldrich). After reacting for 12 hours, the prepared solid (Li4C8H2O6·CH3OH) was collected by centrifugation, repeatedly washed with high-purity methanol by shaking, and then dried overnight under vacuum at 100 °C (Li4C8H2O6·CH3OH yield: 98%). The final Li4C8H2O6 was obtained by heating at 220 °C for 24 hours. Because Li4DHTPA is sensitive to air and moisture, all operations are performed in an AR-filled glove box with O2 and H2O concentrations below 1.0 ppm. Li4C8H2O6 is also available commercially.

[0033] (2) Synthesis of Li6PS5Cl: Typically, 2.07302 g of Li2S, phosphorus pentasulfide (P2S5, 99%, Aladdin), and 0.78967 g of lithium chloride (LiCl, 99%, Aladdin) were weighed into a ball mill containing 0.78967 g of ZrO with 90 g ZrO2 balls in a molar ratio of ZrO. The mixture was ball-milled for 24 hours at 400 rpm, followed by a further milling at 600 rpm for 48 hours. The resulting powder was then annealed at 550 °C for 10 hours at a heating rate of 5 °C / min, and allowed to cool naturally to room temperature. All experiments were conducted under an Ar atmosphere. Li6PS5Cl can also be commercially available.

[0034] (3) Preparation of Li4C8H2O6 / C composite cathode (composite cathode not generated in situ): Li4C8H2O6 and Li6PS5Cl:C conductive agent were weighed according to a mass ratio of 2:7:1 and ground in slurry for 20 minutes to obtain a composite cathode in which Li4C8H2O6 accounts for 20 wt.% of the active material of the composite cathode; Li4C8H2O6 and Li6PS5Cl:C conductive agent were weighed according to a mass ratio of 4:5:1 and ground in slurry for 20 minutes to obtain a composite cathode in which Li4C8H2O6 accounts for 40 wt.% of the active material of the composite cathode.

[0035] (4) Synthesis of organic cathode material Li4C8H2O6@CNT: 2,5-dihydroxythyroid acid and CNT were weighed according to the mass ratios of Li4C8H2O6 to CNT of 3:1, 4:1, and 5:1, and dispersed in methanol. After ultrasonic dispersion for 2 hours, a black dispersion was obtained. Lithium methoxide was added to the dispersion in the corresponding molar ratio for reaction. The product was centrifuged and dried into a solid powder, and then heated at 220℃ for 12 hours to obtain a dark green solid powder.

[0036] (5) Preparation of composite cathode of Li4C8H2O6@CNT: The organic cathode materials Li4C8H2O6@CNT and Li6PS5Cl were weighed according to the mass ratio of Li4C8H2O6:Li6PS5Cl:CNT in the composite cathode of 2:7:1 or 4:5:1. Because the designed organic cathode material Li4C8H2O6@CNT has a mass ratio of Li4C8H2O6 to CNT of 3:1, 4:1 and 5:1, the mass ratio of Li4C8H2O6:Li6PS5Cl:CNT in the composite cathode cannot meet 2:7:1 or 4:5:1. In this case, it is necessary to add Li4C8H2O6 or CNT separately and put them into the mortar together with the organic cathode materials Li4C8H2O6@CNT and Li6PS5Cl for grinding for 20 minutes to obtain the composite cathode of Li4C8H2O6@CNT.

[0037] (6) Assembly of the all-solid-state battery: First, 80 mg of Li6PS5Cl powder was cold-pressed into a polycarbonate cylinder with an inner wall diameter of 10 mm and a pressure below 360 MPa to manufacture solid electrolyte particles. Next, a composite cathode was uniformly diffused onto one side of the SSE particles and cold-pressed at a pressure below 873 MPa for 1 minute. The composite cathode loading was 1 mg / cm². 2 Finally, a thin lithium foil is pressed onto the other side of the SSE particle. Current-charge / discharge tests were conducted using a land-based battery testing system at 55°C and different current densities from 1.8 to 3.2V with L1. + This can be done between / LI.

[0038] Verification Result Analysis:

[0039] In this invention, we use a VGCF with a diameter of 150 nm and an aspect ratio of 40, and a VGCF with a diameter of 15 nm and an aspect ratio of 3.33 × 10⁻⁶. 3 Taking CNT as an example, this paper discusses the significant impact of ultra-high aspect ratio on the capacity, conductivity, rate performance, and active material utilization of composite cathodes in sulfide all-solid-state batteries.

[0040] To compare the effects of VGCF and CNT with different aspect ratios on the internal electron network of the electrode, the internal microstructure of composite cathodes with different conductive agents was first studied using scanning electron microscopy (SEM). Figure 1 As can be seen from a and 1b, the diameter of commercial VGCF optical fiber is approximately 150 nm and the length is approximately 6 μm, with corresponding schematic diagrams attached. Figure 1 c). The VGCF inside the electrode has a long columnar shape, which cannot form a cross-linked conductive network. This results in VGCF, Li4C8H2O6, and Li6PS5Cl solid electrolyte sharing very few interfaces, preventing a large amount of composite cathode active material from gaining ions and electrons. This poor electronic conductivity network cannot improve the electrochemical performance of the composite cathode. In contrast, commercially available CNTs with ultra-high aspect ratios... Figure 1 d-1e), with a diameter of approximately 15 nm and a length of approximately 50 μm, the carbon nanotubes within the composite cathode are in a curved fiber shape. Figure 1 f) A well-formed cross-linked conductive network can be formed within the composite cathode. It is evident that CNTs, Li4C8H2O6, and Li6PS5Cl solid electrolytes with ultra-high aspect ratios can share more interfaces. Furthermore, CNTs can also play a role in ion transport to some extent, which is beneficial for the active materials to fully utilize their electrochemical activity. Therefore, by comparing SEM images of composite cathodes using two C conductive agents with different aspect ratios, it was found that CNTs with ultra-high aspect ratios can form a better electronic conductive network in the Li4C8H2O6 / CNT composite cathode than VGCF with low aspect ratios in the Li4C8H2O6 / VGCF composite cathode.

[0041] To verify the above inference, the aspect ratio (0.04×10) was compared. 3 VGCF and aspect ratio (3.33×10) 3The electrochemical performance of composite cathodes using CNTs as conductive agents was investigated. When the mass percentage of Li4C8H2O6 in the composite cathode active material was between 15 wt.% and 45 wt.%, the electronic conductivity of the Li4C8H2O6 / CNT (not generated in situ) composite cathode and the electronic conductivity of the Li4C8H2O6 / VGCF (not generated in situ) composite cathode were compared. Examples were used for comparison when the mass percentage of Li4C8H2O6 in the composite cathode active material was 20 wt.% and 40 wt.%. Figure 2 As shown in Figure a, when the mass percentage of Li4C8H2O6 in the composite cathode active material is 20 wt.%, the electronic conductivity of the composite cathode using Li4C8H2O6 / CNT (0.502 S / cm) is significantly higher than that of the composite cathode using Li4C8H2O6 / VGCF (0.1491 S / cm), and the electronic conductivity of the Li4C8H2O6 / CNT composite cathode is 3.3 times that of the composite cathode using Li4C8H2O6 / VGCF. When the mass percentage of Li4C8H2O6 in the composite cathode active material is 40 wt.%, the electronic conductivity of the composite cathode using Li4C8H2O6 / CNT (0.1313 S / cm) is also higher than that of the composite cathode using Li4C8H2O6 / VGCF (0.1090 S / cm). Figure 2 (As shown in b). The results show that high aspect ratio CNTs are beneficial to improving the electronic conductivity of the composite cathode. Therefore, we can consider increasing the aspect ratio of the C conductive agent to the order of magnitude of 10. 3 The above advantages facilitate the combined use of cathode materials in sulfide electrolytes, which can improve the electrochemical performance of sulfide all-solid-state batteries.

[0042] Since the study also found that the improvement effect was more significant when the mass percentage of Li4C8H2O6 in the composite cathode active material was lower, we further explored the influence of the material dosage in the composite cathode. We believe this may be because when the mass percentage of Li4C8H2O6 in the composite cathode active material is 40 wt.%, the organic cathode material dominates the electrode conductivity, and the role of the C conductive agent is weakened. The improvement in the conductivity of the composite cathode stems from the optimization of the internal electron network of the composite cathode, which will improve the utilization rate and rate capability of the active material of the composite cathode. In summary, we further selected a Li4C8H2O6 / C composite cathode with a mass percentage of (20±10) wt.% in the composite cathode active material. Figure 2 c- Figure 2The table shows that when the mass percentage of Li4C8H2O6 in the composite cathode active material is 20 wt.%, the discharge specific capacity of Li4C8H2O6 / VGCF composite cathodes and Li4C8H2O6 / CNT composite cathodes using VGCF and CNT as conductive agents are compared at different discharge rates within the voltage range of 1.8-3.2V. The discharge specific capacities of the Li4C8H2O6 / VGCF composite cathode at 0.1C, 0.5C, 2C, and 5C are 82.0 mAh / g, 70.3 mAh / g, 59.4 mAh / g, and 50.9 mAh / g, respectively. Figure 2 (as shown in c); In contrast, the discharge specific capacities of the Li4C8H2O6 / CNT composite cathode at 0.1C, 0.5C, 2C, and 5C are 151.6 mAh / g, 107.8 mAh / g, 91.0 mAh / g, and 79.8 mAh / g, respectively, significantly higher than those of the Li4C8H2O6 / VGCF composite cathode. When the mass percentage of Li4C8H2O6 in the active material of the composite cathode is 40 wt.%, compared with the Li4C8H2O6 / VGCF composite cathode, the battery discharge specific capacities of the Li4C8H2O6 / CNT composite cathode at 0.1C, 0.2C, and 0.5C are 109.5 mAh / g, 89.8 mAh / g, and 70.0 mAh / g, respectively, also significantly higher than those of the Li4C8H2O6 / VGCF composite cathode. Figure 2 d). However, the difference lies in the fact that when the mass percentage of Li4C8H2O6 in the composite cathode active material is 40 wt.%, the specific capacity of the Li4C8H2O6 / CNT composite cathode at 2C and 5C is significantly lower than that of the Li4C8H2O6 / VGCF composite cathode. This indicates that under high load and high discharge rate, electron transport is no longer the main factor limiting the charge-discharge specific capacity of Li4C8H2O6. Figure 2 e and 2f are the galvanostatic charge-discharge curves of Li4C8H2O6 / CNT composite cathodes at different rates, with Li4C8H2O6 accounting for 20 wt.% of the composite cathode active material and Li4C8H2O6 accounting for 40 wt.% of the Li4C8H2O6 / CNT composite cathode active material. This is consistent with previously reported liquid batteries.

[0043] We further investigated the differences between two composite cathodes with different aspect ratios excluding lithium. When the mass percentage of Li4C8H2O6 in the composite cathode active material was low, we compared the capacity retention of the two composite cathodes with different aspect ratios at high and low rates. Figure 3As shown in Figure a, when the mass percentage of Li4C8H2O6 in the composite cathode active material is 20 wt.%, the Li4C8H2O6 / VGCF composite cathode stabilizes at 86.6 mAh / g after 0.1C cycling, with a capacity retention of 88.3% (compared to the 5th cycle). In contrast, the Li4C8H2O6 / CNT composite cathode still exhibits a high specific capacity of 145.4 mAh / g after 100 cycles, with a retention rate as high as 94.6% at 0.1C. Furthermore, at a higher 1C rate, the specific capacity of the Li4C8H2O6 / CNT composite cathode is 92.0 mAh / g after 100 cycles, with a capacity retention of 92.8%, significantly higher than that of the Li4C8H2O6 / VGCF composite cathode. Figure 3 (As shown in b). It can be seen that CNTs with ultra-high aspect ratios and Li4C8H2O6 are more likely to form a more stable electron network contact, which can improve the cycle stability and active material utilization of the Li4C8H2O6 / CNT composite cathode. We further analyzed the reasons for the capacity decrease of the Li4C8H2O6 / CNT composite cathode when the mass percentage of Li4C8H2O6 in the composite cathode active material is high and the discharge rate is high. When the mass percentage of Li4C8H2O6 in the composite cathode active material is 40 wt.%, the cycle performance of different composite cathodes can be seen from... Figure 3 c and 3d conclude that the Li4C8H2O6 / CNT composite cathode exhibits a relatively higher specific capacity than the Li4C8H2O6 / VGCF composite cathode at 0.1C and 1C. We derived this from... Figure 3 The a-3d graphs revealed that when the mass percentage of Li4C8H2O6 in the composite cathode active material was high and the discharge rate was high, the capacity difference between the two composite electrodes, the Li4C8H2O6 / CNT composite cathode and the Li4C8H2O6 / VGCF composite cathode, decreased. This indicates that a high mass percentage of Li4C8H2O6 in the composite cathode active material and a high discharge rate weaken the high specific capacity advantage of ultra-high aspect ratio CNTs. Further investigation was conducted on the effects of two conductive agents with different aspect ratios on the Li4C8H2O6 cathode (excluding lithium). The charge-discharge curves of these two composite cathodes were compared at different rates. Figure 3 e and Figure 3 In the figure, the charge-discharge curves of the Li4C8H2O6 / CNT composite cathode and the Li4C8H2O6 / VGCF composite cathode are mainly divided into two parts: one part is above 2.3V, and the other part is below 2.3V. At 0.1C or 1C, the discharge capacity of the Li4C8H2O6 / VGCF composite cathode in both parts is significantly higher (e.g., ...). Figure 3(as shown in e and 3f). When the mass percentage of Li4C8H2O6 in the composite cathode active material is 40 wt.%, ( Figure 3 g and Figure 3 (h) At a discharge rate of 1C, the discharge capacity of the Li4C8H2O6 / CNT composite cathode is similar to that of the Li4C8H2O6 / VGCF composite cathode above 2.3V. However, below 2.3V, the discharge capacity of the Li4C8H2O6 / CNT composite cathode is higher than that of the Li4C8H2O6 / VGCF composite cathode. We believe that the increased discharge capacity of the Li4C8H2O6 / CNT composite cathode may be due to the decomposition of the sulfide solid electrolyte. The decrease in specific capacity of the Li4C8H2O6 / CNT composite cathode can be attributed to the electrochemical decomposition of the sulfide solid electrolyte caused by CNTs and the corresponding large interfacial resistance. In short, the ultra-high aspect ratio CNTs form a good conductive network and promote the utilization rate of the electrochemically active material Li4C8H2O6, but they also promote the decomposition of sulfide solid electrolytes, which leads to a decrease in specific capacity when Li4C8H2O6 has a high mass ratio in the composite cathode active material and at high discharge rates.

[0044] It can be seen that when the mass percentage of Li4C8H2O6 in the composite cathode active material is 40 wt.%, the conductive network of CNTs cannot play a role in improving the electrochemical activity of the Li4C8H2O6 cathode. Therefore, an in-situ coating method was adopted in the synthesis process to directly grow Li4C8H2O6 on the surface of CNTs (Li4C8H2O6@CNT), thereby improving the interfacial contact between Li4C8H2O6 and CNTs and reducing the contact area between CNTs and the sulfide solid electrolyte. Figure 4 The microstructure and electronic conductivity of the Li4C8H2O6@CNT composite cathode were characterized, among which... Figure 4 a and Figure 4 b. The morphology of the composite cathode Li4C8H2O6@CNT was revealed using an in-situ coating strategy. It can be observed that the elongated and curved CNTs form an organic cathode material Li4C8H2O6@CNT with Li4C8H2O6. S Li4C8H2O6 intertwines to form a network, such as Figure 4 As shown in c, from Figure 4 As shown in Figure c, this structure can effectively improve the internal electron transport of Li4C8H2O6, shorten the transport channels for ions and electrons, and thus better exert the electrochemical activity of Li4C8H2O6. In addition, the direct growth of Li4C8H2O6 on the CNT surface is also beneficial to reduce the particle size of Li4C8H2O6, thereby shortening the electron migration path and improving the electron / ion transport capability of the electrode. Figure 4 d and Figure 4 The image shows only the morphology of Li4C8H2O6. Clearly, the particle size of Li4C8H2O6@CNT is significantly smaller than that of pure Li4C8H2O6, verifying that the growth of Li4C8H2O6 on CNTs is beneficial for reducing the particle size of Li4C8H2O6. Figure 4 The XRD patterns of Li4C8H2O6@CNT and Li4C8H2O6 are shown in f, confirming that the in-situ loading process does not change the chemical structure of Li4C8H2O6. Furthermore, it is easy to observe that the half-width at half-maximum (FWHM) of the diffraction peaks of Li4C8H2O6@CNT increases significantly at 27°, demonstrating that Li4C8H2O6 in CNTs… S In-situ growth on the surface leads to a reduction in grain size, which corresponds well with the SEM results. When the mass percentage of Li4C8H2O6 in the composite cathode active material is 20 wt.% and 40 wt.%, the electronic conductivity of the Li4C8H2O6@CNT (4:1) composite cathode and the Li4C8H2O6 / CNT composite cathode are as follows: Figure 4 g and Figure 4 The results showed that the electronic conductivity of the Li4C8H2O6@CNT (4:1) composite cathode was higher than that of the Li4C8H2O6 / CNT composite cathode. In the Li4C8H2O6@CNT composite cathode, the ratio of Li4C8H2O6@CNT to CNT was adjusted to ensure that the mass ratio of Li4C8H2O6:CNT:sulfide solid electrolyte in the Li4C8H2O6@CNT composite cathode was 2:7:1 or 4:5:1. Figure 4 The results show that, regardless of the mass percentage of Li4C8H2O6 in the composite cathode active material, the electronic conductivity of the Li4C8H2O6@CNT composite cathode with ultra-high aspect ratio CNTs is superior to that of the Li4C8H2O6 / VGCF composite cathode with low aspect ratio VGCF. This advantage is particularly pronounced when the mass percentage of Li4C8H2O6 in the composite cathode active material is low. When the mass percentage of Li4C8H2O6 in the composite cathode active material is high, the electronic conductivity of the Li4C8H2O6@CNT composite cathode is higher than that of the Li4C8H2O6 / CNT composite cathode. This demonstrates that in-situ generation of Li4C8H2O6 on the CNT surface enhances the advantages of ultra-high aspect ratio CNTs. This not only allows the composite cathode to maintain high specific capacity but also reduces the electrochemical decomposition of sulfide solid electrolytes, improving the electronic conductivity of the composite cathode and the contact area between the active material and the CNTs.

[0045] In Li4C8H2O6@CNT, the mass ratio of Li4C8H2O6 to CNTs is (3-5):1. To explore the optimal ratio for in-situ growth of Li4C8H2O6 on CNTs, the following three different ratios were compared and analyzed in examples: Li4C8H2O6@CNT (3:1), Li4C8H2O6@CNT (4:1), and Li4C8H2O6@CNT (5:1). The mass ratio of Li4C8H2O6:Li6PS5Cl:CNT in the composite cathode was maintained at 2:7:1, and the rate performance at these three ratios was tested. Figure 5 As shown in Figure a, the rate performance of these three Li4C8H2O6@CNT composite cathodes is superior to that of the Li4C8H2O6 / CNT composite cathode. Among them, the Li4C8H2O6@CNT (4:1) composite cathode exhibits the best rate performance, with discharge capacities of 201.4 mAh / g, 165.5 mAh / g, and 131.4 mAh / g at 0.1C, 0.5C, and 2C, respectively. We further selected the optimal mass ratio of Li4C8H2O6@CNT as (4 ± 0.3):1. This is because when the in-situ loading ratio is relatively low (e.g., 3:1), Li4C8H2O6 encapsulates a large number of CNTs, preventing the CNTs from forming a good conductive network and hindering electron transport to some extent. When the in-situ loading ratio is relatively high (e.g., 5:1), the CNT content in the composite cathode is relatively low, thus the Li4C8H2O6 and CNT content is relatively high. S The contact between them is poor. When the in-situ loading ratio is maintained at 4:1, the contact range between Li4C8H2O6 and CNTs can be improved for the optimal CNT conductive network. When the mass percentage of Li4C8H2O6 in the composite cathode active material is 40 wt.%, Figure 5 As shown in b), the rate capability of the Li4C8H2O6@CNT (4:1) composite cathode is significantly superior to that of the unmodified Li4C8H2O6 / CNT composite cathode, exhibiting discharge capacities of 95.5 mAh / g, 82.1 mAh / g, and 43.0 mAh / g at 0.5C, 1C, and 5C, respectively, which are significantly higher than those of the Li4C8H2O6 / CNT composite cathode. Figure 5c demonstrated the charge-discharge curves of the Li4C8H2O6@CNT (4:1) composite cathode when Li4C8H2O6 constituted 40 wt.% of the composite cathode active material. The charge-discharge plateau of this composite cathode was consistent with that of the Li4C8H2O6 / CNT composite cathode, indicating that the Li4C8H2O6@CNT (4:1) composite cathode exhibits the same stable discharge time as the Li4C8H2O6 / CNT composite cathode. We further investigated the capacity retention of the Li4C8H2O6@CNT (4:1) composite cathode. Figure 5 Figure d shows that the Li4C8H2O6@CNT composite cathode (Li4C8H2O6 accounts for 20 wt.% of the composite cathode active material) exhibits a capacity of 150 mAh / g at 1C, with a capacity retention of 99.9% after 100 cycles, demonstrating a very high capacity retention. However, when the mass percentage of Li4C8H2O6 in the composite cathode active material is 40 wt.%, Figure 5 f shows that the Li4C8H2O6@CNT composite cathode exhibits a capacity of 82.0 mAh / g after 200 cycles at 1C, which is significantly higher than that of the Li4C8H2O6 / CNT composite cathode. Figure 5 e and Figure 5 The data shows that at high discharge rates (1C), the charge-discharge curves of the Li4C8H2O6@CNT (4:1) composite cathode and the Li4C8H2O6 / CNT composite cathode with different mass ratios of Li4C8H2O6 in the composite cathode active material are compared. The discharge capacity of the Li4C8H2O6 / CNT composite cathode is significantly higher than that of the Li4C8H2O6@CNT composite cathode. In summary, the in-situ generation method effectively reduces the contact between CNTs and the sulfide solid electrolyte. When the composite cathode has a high mass ratio of Li4C8H2O6 in the composite cathode active material and is loaded at a high discharge rate, it effectively improves the ion / electron transport capacity, thereby enhancing the charge / discharge capacity of the active material and the battery capacity retention.

[0046] CNTs with a high aspect ratio can form conductive networks, while VGCFs with a lower aspect ratio cannot form good conductive networks in organic cathodes. CNTs with a relatively high aspect ratio can form conductive networks, such as... Figure 6 As shown in Figure a. However, a good conductive network can also promote the decomposition of sulfide solid-state points. For in-situ loaded organic cathode material Li4C8H2O6@CNT, the CNTs are encapsulated by Li4C8H2O6, which can improve their interfacial contact and reduce the CNTs. S Contact between and sulfide solid electrolytes. Figure 6Sections b and 6c summarize the different utilization rates of cathode active materials when the mass ratio of Li4C8H2O6 in the composite cathode active material is different. The composite cathodes with ultra-high aspect ratio Li4C8H2O6 / CNT and Li4C8H2O6@CNT show the main advantages at various discharge rates. It can be seen that the good conductive network formed by CNTs with ultra-high aspect ratio can improve the utilization rate of active materials in composite cathodes. Furthermore, the composite cathode of Li4C8H2O6@CNT formed by in-situ coating of CNTs with Li4C8H2O6 can further highlight the advantages of high aspect ratio CNTs compared with the other two types of composite cathodes. Our previous research revealed that when the mass proportion of Li4C8H2O6 in the composite cathode active material is high and the discharge rate is high, the Li4C8H2O6 / CNT composite cathode, while improving the utilization rate of the active material, also promotes the decomposition of sulfide electrolytes, leading to battery capacity decay. However, the in-situ generation of Li4C8H2O6 on the surface of ultra-high aspect ratio CNTs, forming a Li4C8H2O6@CNT composite cathode, not only reduces the contact area with the sulfide electrolyte, effectively preventing its decomposition, but also maintains high utilization of the active material, thus preserving the high capacity advantage of batteries at ultra-high aspect ratios. Figure 6 At a 2C discharge rate, the Li4C8H2O6@CNT composite cathode exhibits higher active material utilization than the other two composite cathodes. Furthermore, compared to previously reported organic solid-state batteries, the Li4C8H2O6@CNT composite cathode also demonstrates higher active material utilization at higher discharge rates. Figure 6 d), this is due to the optimized microstructure in this work.

[0047] Given the low electronic conductivity of organic cathode material (Li4C8H2O6), the aspect ratio of the C-conductive agent to the organic cathode material has become a critical parameter for its use in sulfide all-solid-state electrolyte batteries. In this work, the electrochemical performance of composite cathodes was comprehensively compared. The results show that the ultra-high aspect ratio C-conductive agent combined with the organic cathode material Li4C8H2O6 significantly improves the rate performance of sulfide all-solid-state batteries. However, the excellent electronic conductivity network also exacerbates the decomposition of the sulfide solid electrolyte. At high mass ratios of Li4C8H2O6 in the composite cathode active material and at high discharge rates, the capacity of the Li4C8H2O6 / CNT composite cathode rapidly decreases. Therefore, an in-situ coating strategy of Li4C8H2O6 on the CNT surface was developed to further improve the contact between Li4C8H2O6 and CNTs, ensuring that the CNT surface is completely covered by small Li4C8H2O6 particles. More importantly, this strategy avoids direct contact between the sulfide solid electrolyte and CNTs, thereby mitigating the electrochemical decomposition of the sulfide solid electrolyte. Building on this, we further investigated composite cathodes with different ratios of Li4C8H2O6@CNT. We found that the Li4C8H2O6@CNT (4:1) composite cathode achieved an active material utilization rate of 83.4% at 0.1C and possessed a high specific capacity of 200.3 mAh / g. Furthermore, at a high discharge rate of 1C, the Li4C8H2O6@CNT composite cathode could provide a specific capacity of approximately 150 mAh / g, with a capacity retention of 99.9% after 100 cycles. In summary, the ultra-high aspect ratio C-conductive agent facilitates the formation of a well-connected electrical network within the composite cathode, allowing it to share more interfaces with Li4C8H2O6 and the sulfide solid electrolyte. This not only improves ion transport but also allows the active material to fully utilize its electrochemical activity. When the discharge rate is high and the mass ratio of Li4C8H2O6 in the composite cathode active material is high, the in-situ coating method can maintain the original advantages of the high aspect ratio C conductive agent and further enhance the advantages of the C conductive agent in sulfide all-solid-state batteries. This allows the Li4C8H2O6@CNT composite cathode, sulfide solid electrolyte and CNT to form a good cross-linked electrical network, thereby improving the utilization rate of the active material of sulfide all-solid-state batteries.

[0048] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An organic cathode material suitable for sulfide-based all-solid-state lithium metal batteries, characterized in that, The organic cathode material is Li4C8H2O6@C, where C is a C-conductive agent with a diameter of 5-250 nm and an aspect ratio greater than 1×10⁻⁶. 3 .

2. The organic cathode material according to claim 1, applicable to sulfide-based all-solid-state lithium metal batteries, characterized in that, The organic cathode material Li4C8H2O6@C is an organic cathode material in situ grown from Li4C8H2O6 on the surface of C conductive agent.

3. The organic cathode material according to claim 1, applicable to sulfide-based all-solid-state lithium metal batteries, characterized in that, The C-conductive agent includes one or more of CNT and VGCF.

4. The organic cathode material according to claim 1, applicable to sulfide-based all-solid-state lithium metal batteries, characterized in that, The organic cathode material Li4C8H2O6@C, calculated as Li4C8H2O6, accounts for 15wt.%-45wt.% of the mass percentage in the composite cathode material.

5. The organic cathode material according to claim 1, applicable to sulfide all-solid-state lithium metal batteries, characterized in that, The organic cathode material Li4C8H2O6@C, calculated as Li4C8H2O6, accounts for (20±10) wt.% of the total mass of the composite cathode active material.

6. The organic cathode material according to claim 1, applicable to sulfide all-solid-state lithium metal batteries, characterized in that, The mass ratio of Li4C8H2O6 to C conductive agent in the organic cathode material Li4C8H2O6@C is (3-5):

1.

7. The organic cathode material according to claim 1, applicable to sulfide all-solid-state lithium metal batteries, characterized in that, The mass ratio of Li4C8H2O6 to C conductive agent in the organic cathode material Li4C8H2O6@C is (4±0.3):

1.

8. The organic cathode material according to claim 1, applicable to sulfide all-solid-state lithium metal batteries, characterized in that, The organic cathode material Li4C8H2O6@C exhibits characteristic diffraction peaks at 13.5°, 15.5°, 22.5°, and 27° in its X-ray powder diffraction pattern, expressed as a diffraction angle of 2θ.

9. The method for preparing the organic cathode material according to any one of claims 1-8, characterized in that, Weigh 2,5-dihydroxythyroid acid and C conductive agent according to the mass ratio, disperse the weighed material in methanol, and perform ultrasonic dispersion to obtain a black dispersion. Add lithium methoxide in the corresponding molar ratio to react, and centrifuge and dry the product after reaction, and then heat it to obtain a dark green solid powder.

10. The preparation method according to claim 9, characterized in that, The ultrasonic dispersion time is 2 hours; The reaction time is 24 hours; The heating time is 12 hours, and the heating temperature is 220°C.

11. A composite cathode comprising the organic cathode material according to any one of claims 1-8, suitable for sulfide solid electrolytes.

12. The composite cathode according to claim 11 further includes a sulfide solid electrolyte, wherein the mass ratio of Li4C8H2O6: sulfide solid electrolyte: C conductive agent is (15-45): (45-75): (10).

13. The composite cathode according to claim 12, characterized in that, The sulfide solid electrolyte is Li6PS5Cl.

14. A sulfide solid-state battery comprising the composite cathode according to any one of claims 11-13.

Images