A full-solid lithium-selenium battery composite positive electrode material and a preparation method and application thereof

Abstract

The application relates to the technical field of solid-state batteries, and discloses a full-solid-state lithium-selenium battery composite positive electrode material and a preparation method and application thereof, wherein the composite positive electrode material comprises elemental selenium, silver iodide, conductive carbon and a sulfide solid-state electrolyte; according to the total mass percentage of the elemental selenium, the silver iodide, the conductive carbon and the sulfide solid-state electrolyte, the elemental selenium accounts for 25-35%, the conductive carbon accounts for 10-20%, the molar ratio of the elemental selenium to the silver iodide is 8-32:1, and the balance is the sulfide solid-state electrolyte; and the charge-discharge voltage window of the composite positive electrode material is 0.8-1.8 V. The elemental selenium positive electrode is modified by AgI, in-situ reaction of elemental silver nanoparticles and lithium iodide phases can be generated under the charge-discharge voltage window, the electron and ion collaborative transmission channel is greatly widened, the solid-solid interface impedance is reduced, the volume shrinkage and expansion are effectively relieved, and therefore the composite positive electrode material exhibits good rate performance and long cycle stability.

Description

Technical Field

[0001] This invention relates to the technical field of solid-state batteries, and in particular to an all-solid-state lithium selenide battery composite cathode material, its preparation method, and its application. Background Technology

[0002] Solid-state lithium batteries, by using non-flammable inorganic solid electrolytes instead of traditional flammable organic liquid electrolytes, fundamentally eliminate the safety hazard of battery thermal runaway, becoming an important development direction for next-generation high-safety energy storage technology. Among many cathode material systems, elemental selenium, as a conversion-type cathode material, exhibits unique intrinsic advantages in improving battery reaction kinetics and increasing the utilization rate of active materials due to its electronic conductivity being nearly 25 orders of magnitude higher than that of elemental sulfur in the same group. For example, patent CN111834625B discloses a selenium composite cathode material, its preparation method, and its all-solid-state lithium selenium battery. This selenium composite cathode material includes: nano-selenium, conductive carbon, and nano-sulfide solid electrolyte. The preparation method is as follows: first, elemental selenium and sulfide electrolyte are dissolved in two solvents respectively; then, the two solutions are sequentially added dropwise to conductive carbon and ultrasonically dispersed; after vacuum drying, a mixed powder is obtained; finally, the mixed powder is annealed in an inert gas atmosphere to obtain the selenium composite cathode material.

[0003] However, the practical application of lithium selenide batteries in all-solid-state electrolyte systems still faces extremely severe electrochemical obstacles. First, due to the lack of the wetting fluidity of liquid electrolytes, the all-solid-state system relies entirely on solid-solid point contacts between the active material, conductive agent, and solid electrolyte. These point contacts easily lead to localized charge transport obstruction and increased reaction polarization. Second, during the complete lithiation of elemental selenium into Li₂Se, a massive lattice volume expansion of up to approximately 97% occurs. In the dense solid-state battery structure, repeated and severe volumetric polarization during cycling causes mechanical delamination of the active particles from the solid electrolyte and conductive carbon, resulting in rapid degradation of the solid-solid interface contact and fragmentation of the internal conductive network of the electrode. Furthermore, due to the limited electrochemical stability window of solid electrolytes, the cathode interface is prone to irreversible oxidative decomposition at high charging voltages or localized high current densities, leading to a continuous surge in the impedance of the passivation layer, limiting the battery's rate capability and cycle life. Therefore, how to fundamentally optimize the kinetic characteristics of the solid-solid interface while maintaining the proportion of highly active materials, and effectively buffer the severe volume effect of the selenium cathode, is a technical bottleneck that urgently needs to be solved in the field of solid-state lithium selenium batteries. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an all-solid-state lithium selenide battery composite cathode material, its preparation method, and its application. The method utilizes silver iodide (AgI), a transition metal halide, to modify the elemental selenium cathode. Under the charge / discharge voltage window, it can react in situ to generate elemental silver nanoparticles with ultra-high electronic conductivity and a lithium iodide (LiI) phase with excellent interfacial wettability and high chemical stability. This significantly broadens the electron-ion co-transport channels within the electrode, reduces solid-solid interface impedance, and effectively alleviates the volume shrinkage and expansion of elemental selenium during lithium insertion / extraction, thus exhibiting excellent rate performance and long-cycle stability.

[0005] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a composite cathode material for an all-solid-state lithium selenide battery, the composite cathode material comprising elemental selenium, silver iodide, conductive carbon, and a sulfide solid electrolyte; based on a total mass percentage of 100% for elemental selenium, silver iodide, conductive carbon, and sulfide solid electrolyte, elemental selenium accounts for 25-35%, conductive carbon accounts for 10-20%, the molar ratio of elemental selenium to silver iodide is 8-32:1, and the remainder is sulfide solid electrolyte; the charge / discharge voltage window of the composite cathode material is 0.8-1.8V.

[0006] In traditional solid-state lithium selenide batteries, the solid-solid interface between the active material elemental selenium and the solid electrolyte lacks an elastic wetting phase, resulting in extremely high polarization. This invention introduces AgI, a transition metal halide with specific reactivity, which can undergo in-situ conversion within a charge / discharge voltage window of 0.8-1.8 V. This voltage window is limited because discharging below 1.8 V ensures sufficient in-situ reduction of AgI, while limiting the charging cutoff voltage to 1.8 V effectively prevents irreversible oxidative decomposition of the sulfide solid electrolyte at high potentials, thus maintaining the long-term stability of the solid-solid interface. In the cyclic voltammetry (CV) characteristic curves, this modified composite cathode material exhibits distinct reduction and oxidation peaks, corresponding to the reduction conversion of AgI to elemental silver during discharge and the reversible oxidation regeneration of elemental silver to AgI during charging, respectively. High-resolution X-ray photoelectron spectroscopy (XPS) analysis also confirms the excellent electrochemical reversibility of the AgI within the cathode. After being discharged to a low potential, the characteristic binding energy peaks originally belonging to the AgI lattice changed, replaced by significant characteristic peaks of elemental silver, proving that AgI underwent in-situ reduction and transformation. Upon charging to a high potential, the spectrum reverted to the original AgI characteristic peaks, confirming that elemental silver underwent a reverse reaction under charging conditions and regenerated AgI. This highly reversible transformation reaction constructs a dynamic electron conduction network, ensuring the structural stability of the modified component throughout its entire life cycle.

[0007] During discharge, the in-situ conversion reaction of AgI generates elemental silver nanoparticles with ultra-high electronic conductivity and a lithium iodide (LiI) phase with excellent interfacial wettability and high chemical stability. By adjusting the molar ratio of elemental selenium to silver iodide, the relative volume fractions of the in-situ generated conductive phase and interfacial buffer phase in the system are changed. Metallic silver has excellent conductivity and is distributed in nanoscale at the solid-solid interface between selenium and the solid electrolyte, eliminating the local space charge layer effect and greatly enhancing the overall electronic conductivity inside the positive electrode. At the same time, the generated LiI can act as an interfacial lubricant and induce the formation of a highly stable iodine-rich protective layer, which can act as a channel for interfacial ions, greatly optimizing the ion migration rate at the solid-solid interface, and reducing the charge transfer resistance of the modified electrode compared to the unmodified electrode.

[0008] Meanwhile, during the volume shrinkage and expansion of elemental selenium caused by charging and discharging, the in-situ generated soft LiI phase and conductive carbon network exhibit a mechanical buffering effect. This acts as a buffer layer, dynamically absorbing and mitigating the massive stress generated during lithium insertion / extraction of elemental selenium. This maintains a tight solid-solid contact between the cathode and the solid electrolyte throughout the entire lifespan, suppressing active material stripping failure. Furthermore, the in-situ reconstruction of a three-dimensional continuous electron / ion dual-conductivity network also improves the utilization rate of active materials, thereby comprehensively enhancing the rate kinetics and long-cycle reliability of the all-solid-state lithium selenium battery.

[0009] Preferably, the sulfide solid electrolyte includes Li6PS5Cl and Li6PS5Cl. 0.5 Br 0.5 At least one of Li7PS3.

[0010] Preferably, the conductive carbon includes at least one of Ketjen Black, Super P, acetylene black, and carbon nanotubes.

[0011] As a preferred embodiment, based on a total mass percentage of 100% for elemental selenium, silver iodide, conductive carbon, and sulfide solid electrolyte, elemental selenium accounts for 25-35%, conductive carbon accounts for 10-20%, the molar ratio of elemental selenium to silver iodide is 16-32:1, and the remainder is sulfide solid electrolyte.

[0012] As a preferred embodiment, based on a total mass percentage of 100% for elemental selenium, silver iodide, conductive carbon, and sulfide solid electrolyte, elemental selenium accounts for 30%, conductive carbon accounts for 15%, the molar ratio of elemental selenium to silver iodide is 16-32:1, and the remainder is sulfide solid electrolyte.

[0013] Secondly, the present invention also provides a method for preparing a composite cathode material for an all-solid-state lithium selenide battery, comprising the following steps: premixing and grinding elemental selenium with silver iodide, then sequentially adding conductive carbon and sulfide solid electrolyte and grinding them separately; then, ball milling the resulting mixture to obtain the composite cathode material.

[0014] By premixing and grinding elemental selenium and silver iodide, the initial formation of a two-phase solid solution or a tightly encapsulated surface structure is promoted, resulting in a two-phase mixed powder. Then, conductive carbon is added to the two-phase mixed powder and ground, allowing ultrafine conductive carbon particles with high specific surface area to be uniformly adsorbed on the surface of the selenium and silver iodide micro / nano particles, reconstructing the electron transport precursor network and obtaining a three-phase mixed powder. A sulfide solid electrolyte is then added to the three-phase mixed powder and ground, allowing fast-ion conductors to be uniformly encapsulated in the network voids of the electron-conducting network, forming a dense four-phase mixed powder. Finally, ball milling is performed to improve dispersibility, obtaining a powdered composite cathode material with both amorphous characteristics and high interfacial activity.

[0015] Preferably, the grinding time is 10-30 minutes.

[0016] Preferably, the parameters for the ball milling process are set as follows: the mass ratio of milling beads to the mixture is 30-50:1, the milling speed is 500-800 rpm, and the milling time is 3-8 h.

[0017] Preferably, both the grinding and ball milling are carried out under an argon atmosphere, with the water content and oxygen content in the environment controlled to be below 0.01 ppm and below 0.01 ppm, respectively.

[0018] To avoid the hydrolysis and decomposition of sulfide solid electrolytes and the impairment of the electrochemical activity of elemental selenium.

[0019] Thirdly, the present invention also provides an application of composite cathode material in all-solid-state lithium selenide batteries.

[0020] Preferably, the all-solid-state lithium selenide battery includes a positive electrode, a negative electrode, and a sulfide solid electrolyte disposed between the positive and negative electrodes; the positive electrode is made of a composite positive electrode material; and the negative electrode is made of a lithium indium alloy.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) Under voltage window conditions, AgI is converted in situ into nano-sized metallic silver particles and fast ion heterogeneous component LiI. The generated metallic silver has excellent conductivity and is distributed in the contact blind zone of the reaction three-phase interface at the nanoscale, eliminating the local space charge layer effect and greatly enhancing the overall electronic conductivity inside the positive electrode. At the same time, the generated LiI has solid ionic conductivity and can act as a channel for interfacial ions, which reduces the charge transfer resistance of the modified electrode compared with the unmodified electrode.

[0022] (2) During the volume contraction and expansion caused by charging and discharging, the soft LiI phase generated in situ and the conductive carbon network exhibit a mechanical buffering effect. This synergistic micro-nano structure can dynamically absorb and release the micro-shear stress accumulated inside the cathode particles, maintain a tight solid-solid contact between the cathode and the solid electrolyte throughout the entire life cycle, suppress the failure of active material stripping, and ensure good cycle stability.

[0023] (3) Because the three-dimensional continuous electron / ion dual conduction network is reconstructed in situ, it is beneficial for the elemental selenium particles inside the composite cathode material to be deeply activated, thereby improving the utilization rate of active materials and capacity retention rate, and no micro short circuits or severe internal self-discharge behavior caused by excessive addition of halides have occurred. Attached Figure Description

[0024] Figure 1 This is Embodiment 1 of the present invention (Se) 16 Example 2 (Se8AgI), Example 3 (Se8AgI), Example 4 (Se8AgI), Example 5 (Se8AgI), Example 6 (Se8AgI), Example 7 (Se8AgI), Example 8 (Se8AgI), Example 9 (Se8AgI), Example 1 ... 32 Comparison curves of electrochemical rate performance of all-solid-state lithium selenide batteries (AgI) and Comparative Example 1 (pure Se) in the voltage range of 0.8-1.8 V.

[0025] Figure 2 This is Embodiment 1 of the present invention (Se) 16 High-resolution X-ray photoelectron spectroscopy (XPS) characteristic analysis of composite cathode materials in AgI before charge-discharge cycles.

[0026] Figure 3 This is Embodiment 1 of the present invention (Se) 16 High-resolution X-ray photoelectron spectroscopy (XPS) characteristic analysis of composite cathode materials in AgI after discharge within a voltage window of 0.8–1.8 V.

[0027] Figure 4 This is Embodiment 1 of the present invention (Se) 16 High-resolution X-ray photoelectron spectroscopy (XPS) characteristic analysis of composite cathode materials in AgI after charging in the 0.8-1.8 V voltage window.

[0028] Figure 5 This is Embodiment 1 of the present invention (Se)16 Comparison of isothermal cyclic voltammetry (CV) curves of composite cathode materials in all-solid-state lithium selenide battery systems (AgI) and Comparative Example 1 (pure Se).

[0029] Figure 6 This is Embodiment 1 of the present invention (Se) 16 A comparison of the long cycle life of the composite cathode materials in Example 1 (pure Se) and Example 2 (AgI) under constant current charge-discharge conditions at a high current rate of 0.3C and a voltage window of 0.8-1.8 V, and the comparison of Example 1 (Se) with that of Comparative Example 2 (pure Se). 16 Charge-discharge curves of AgI at different numbers of cycles.

[0030] Figure 7 The image shown is Se in Example 1. 16 Scanning electron microscope (SEM) image of the surface morphology of AgI composite cathode material after cold pressing. Detailed Implementation

[0031] The technical solution of the present invention will be illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0032] All processes in this invention, including raw material weighing, step-by-step manual grinding, high-energy ball mill jar packaging, and all-solid-state battery assembly, are completed inside an argon glove box that maintains an ultra-pure inert gas circulation system. Water and oxygen sensor readings within the glove box are monitored in real time to strictly ensure that the water content in the environment is less than 0.01 ppm and the oxygen content is less than 0.01 ppm.

[0033] Example 1 (Se) 16 AgI composite cathode material) (1) Weighing was performed based on the fact that elemental selenium accounted for 30 wt% in the final composite cathode material. 120.0 mg of elemental selenium powder was accurately weighed, and 22.3 mg of silver iodide (AgI) powder was accurately weighed based on the molar ratio of elemental selenium to silver iodide of 16:1. Both components were placed in a clean and dry agate mortar and ground continuously for 10 min with a pestle to obtain a two-phase mixed powder.

[0034] (2) Weigh the conductive carbon according to the proportion of 15 wt% in the final composite cathode material. Accurately add 60 mg of Ketjen Black conductive carbon powder to the above agate mortar and continue grinding for 10 min to obtain a three-phase mixed powder.

[0035] (3) Weigh the material based on the fact that the remainder in the final composite cathode material is sulfide solid electrolyte. Add 197.7 mg of sulfide solid electrolyte powder (Li6PS5Cl) to the mortar and continue grinding for 10 min to obtain a four-phase mixed powder.

[0036] (4) Transfer 400.0 mg of the four-phase mixed powder to a stainless steel ball mill jar. Based on a ball-to-powder ratio of 40:1, add 16.0 g of zirconia grinding beads to the jar. Place the sealed ball mill jar onto a planetary high-energy ball mill, set the operating speed to 500 rpm, and start the alternating forward and reverse continuous ball milling mode. Set the total mechanical ball milling time to 5 h. After ball milling, Se was obtained. 16 AgI composite cathode material.

[0037] Se 16 AgI composite cathode material is cold-pressed together with an LPSCl (Li6PS5Cl) solid electrolyte layer, and a lithium indium (LiIn) alloy anode is used. The assembly is performed within a solid-state battery mold to form a standard 2032-type all-solid-state lithium selenide battery. Electrochemical tests were conducted within a voltage window of 0.8–1.8 V.

[0038] Example 2 (Se8AgI composite cathode material) (1) Weighing was performed based on the fact that elemental selenium accounted for 30 wt% in the final composite cathode material. 120.0 mg of elemental selenium powder was accurately weighed, and 44.6 mg of silver iodide (AgI) powder was accurately weighed based on the molar ratio of elemental selenium to silver iodide of 8:1. Both components were placed in a clean and dry agate mortar and ground continuously for 10 min with a pestle to obtain a two-phase mixed powder.

[0039] (2) Weigh the conductive carbon according to the proportion of 15 wt% in the final composite cathode material. Accurately add 60 mg of Ketjen Black conductive carbon powder to the above agate mortar and continue grinding for 10 min to obtain a three-phase mixed powder.

[0040] (3) Weigh the material based on the fact that the remainder in the final composite cathode material is sulfide solid electrolyte. Add 175.4 mg of sulfide solid electrolyte powder (Li6PS5Cl) to the mortar and continue grinding for 10 min to obtain a four-phase mixed powder.

[0041] (4) Transfer 400.0 mg of the four-phase mixed powder to a stainless steel ball mill jar. Add 16.0 g of zirconia grinding beads to the jar according to a ball-to-powder ratio of 40:1. Mount the sealed ball mill jar onto a planetary high-energy ball mill, set the operating speed to 500 rpm, and start the alternating forward and reverse continuous ball milling mode. Set the total mechanical ball milling time to 5 h. After ball milling, the Se8AgI composite cathode material is obtained.

[0042] The Se8AgI composite cathode material was cold-pressed together with an LPSCl (Li6PS5Cl) solid electrolyte layer, and a lithium indium (LiIn) alloy anode was used. The assembly was performed within a solid-state battery mold to form a standard 2032-type all-solid-state lithium selenide battery. Electrochemical tests were conducted within a voltage window of 0.8–1.8 V.

[0043] Example 3 (Se) 32 AgI composite cathode material) (1) Weighing was performed based on the fact that elemental selenium accounted for 30 wt% in the final composite cathode material. 120.0 mg of elemental selenium powder was accurately weighed, and 11.1 mg of silver iodide (AgI) powder was accurately weighed based on the molar ratio of elemental selenium to silver iodide of 32:1. Both components were placed in a clean and dry agate mortar and continuously ground with a pestle for 10 min to obtain a two-phase mixed powder.

[0044] (2) Weigh the conductive carbon according to the proportion of 15 wt% in the final composite cathode material. Accurately add 60 mg of Ketjen Black conductive carbon powder to the above agate mortar and continue grinding for 10 min to obtain a three-phase mixed powder.

[0045] (3) Weigh the material based on the fact that the remainder in the final composite cathode material is sulfide solid electrolyte. Add 208.9 mg of sulfide solid electrolyte powder (Li6PS5Cl) to the mortar and continue grinding for 10 min to obtain a four-phase mixed powder.

[0046] (4) Transfer 400.0 mg of the four-phase mixed powder to a stainless steel ball mill jar. Based on a ball-to-powder ratio of 40:1, add 16.0 g of zirconia grinding beads to the jar. Place the sealed ball mill jar onto a planetary high-energy ball mill, set the operating speed to 500 rpm, and start the alternating forward and reverse continuous ball milling mode. Set the total mechanical ball milling time to 5 h. After ball milling, Se was obtained. 32 AgI composite cathode material.

[0047] Se 32 AgI composite cathode material is cold-pressed together with an LPSCl (Li6PS5Cl) solid electrolyte layer, and a lithium indium (LiIn) alloy anode is used. The assembly is performed within a solid-state battery mold to form a standard 2032-type all-solid-state lithium selenide battery. Electrochemical tests were conducted within a voltage window of 0.8–1.8 V.

[0048] Comparative Example 1 (Pure Se composite cathode material) (1) The composition of the final composite cathode material was determined based on the following: elemental selenium accounted for 30 wt%, conductive carbon accounted for 15 wt%, and the remainder was sulfide solid electrolyte. 120.0 mg of elemental selenium powder, 60.0 mg of Ketjen Black conductive carbon powder, and 220.0 mg of sulfide solid electrolyte powder (Li6PS5Cl) were accurately weighed and placed in a clean and dry agate mortar. The mixture was continuously ground for 30 min using a pestle to obtain a three-phase mixed powder.

[0049] (2) Transfer 400.0 mg of the three-phase mixed powder to a stainless steel ball mill jar. Add 16.0 g of zirconia grinding beads to the jar according to a ball-to-powder ratio of 40:1. Mount the sealed ball mill jar onto a planetary high-energy ball mill, set the operating speed to 500 rpm, and start the alternating forward and reverse continuous ball milling mode. Set the total mechanical ball milling time to 5 h. After ball milling, pure Se composite cathode material is obtained.

[0050] Pure Se composite cathode material was cold-pressed together with an LPSCl (Li6PS5Cl) solid electrolyte layer, and a lithium indium (LiIn) alloy anode was used. The assembly was performed within a solid-state battery mold to form a standard 2032-type all-solid-state lithium selenide battery. Electrochemical tests were conducted within a voltage window of 0.8–1.8 V.

[0051] like Figure 1 The electrochemical rate performance comparison curves shown indicate that within the voltage window of 0.8-1.8 V, Comparative Example 1 (pure Se composite cathode material) exhibits a sharp increase in polarization and a significant decrease in specific capacity due to the lack of a highly conductive phase buffer at the solid-solid interface. At medium-low current densities of 0.1C to 0.5C, Example 1 (Se... 16 AgI composite cathode material exhibits the highest actual discharge specific capacity and the most stable voltage plateau. The underlying mechanism lies in the sufficient charge / discharge time at low to medium rates, resulting in a deep conversion reaction of elemental selenium and significant volume expansion. 16 The appropriate AgI content in the AgI configuration enables the formation of a perfectly distributed silver nano-conductive network and a LiI protective layer of suitable thickness in situ at the reaction interface. This soft LiI phase and conductive network of suitable thickness not only provide excellent mechanical buffering and suppress the huge lattice strain failure generated during deep lithium insertion, but also ensure sufficient electron transfer, thereby enabling elemental selenium to achieve extremely high utilization of active materials at this rate and giving it a capacity output advantage.

[0052] When the test current density suddenly increases to extremely high rates such as 1C or even 2C, Example 3 (Se) 32The AgI composite cathode material exhibited superior fast charge-discharge kinetics and capacity retention compared to Example 1, due to the limitation of ion diffusion kinetics at the solid-solid interface in the all-solid system. Under high-rate, high-current impact, the diffusion mass transfer rate of lithium ions in the interface passivation layer becomes the rate-determining step of the entire electrochemical reaction. 32 Due to the low AgI content, the in-situ converted LiI interface passivation layer is extremely thin. This thin interface layer, while ensuring basic wettability, greatly shortens the solid-phase diffusion path of lithium ions and significantly reduces the interface diffusion barrier. Furthermore, the fewer inactive inert byproducts also reduce geometric blockage of ion transport channels under high current. In Example 1 (Se... 16 In the AgI composite cathode material, the relatively thick LiI layer creates a steric hindrance effect on the rapid passage of high-flux ions within a very short reaction time, resulting in slightly inferior high-rate capacity. In contrast, Example 2 (Se8AgI composite cathode material), with its higher AgI content, exhibits the worst performance due to excessively high LiI concentration generated by local conversion during cycling, which triggers polyiodide shuttle and interfacial micro-short circuits, leading to high-frequency fluctuations in the voltage curve.

[0053] Despite Se 32 While AgI achieves a slight advantage in mass transfer kinetics at higher rates due to its ultra-thin interface layer, composite cathode materials with lower AgI content (a molar ratio of elemental selenium to silver iodide greater than 32:1) actually perform worse in the long-term service life of actual all-solid-state batteries. This is because the extremely thin interface layer and the relatively sparse silver conductive network cannot provide sufficient mechanical toughness to continuously withstand the repeated volumetric strain of elemental selenium (up to 97%) during long-term deep charge-discharge cycles (especially low-rate long cycles under normal operating conditions). This makes them prone to interfacial microcracks and solid-solid contact delamination in the later stages of cycling, leading to irreversible capacity decay. Taking into account the absolute capacity output at normal operating rates, the stability of the interface structure during long-term service, the ability to suppress chemical side reactions, and the control of polarization resistance, limiting the molar ratio of elemental selenium to silver iodide to 16-32:1 can better balance the rapid ion conduction at the interface and the buffering of macroscopic mechanical stress, maximizing the balance between high specific energy output, long life, and high safety and reliability of all-solid-state lithium indium batteries under normal application conditions.

[0054] like Figure 2 The example shown is Example 1 (Se) 16High-resolution X-ray photoelectron spectroscopy (XPS) analysis of the AgI composite cathode material before charge-discharge cycling (pristine state). The figure shows that in the pristine state without electrochemical cycling, the spectrum of silver (Ag 3d) in the composite cathode material exhibits a clear characteristic double peak at a specific binding energy, corresponding to the lattice binding energy characteristics of standard silver iodide (AgI); simultaneously, the spectrum of iodine (I 3d) corresponds to the stable iodide ion (I₂). - Characteristic peaks. This result shows that, through the stepwise grinding and high-energy ball milling process of the present invention, the introduced transition metal halide AgI was successfully and uniformly composited in the cathode matrix in an amorphous or highly dispersed state, and no early decomposition or harmful side reactions occurred with elemental selenium, sulfide solid electrolyte and conductive carbon during the preparation process, ensuring the integrity of the modified precursor structure.

[0055] like Figure 3 The example shown is Example 1 (Se) 16 High-resolution X-ray photoelectron spectroscopy (XPS) characteristic analysis of AgI composite cathode material during its first discharge to a low potential (discharge state) within a voltage window of 0.8–1.8 V. Combined with… Figure 5 The significant reduction peak observed in cyclic voltammetry (CV) tests at 1.1–1.3 V (vs. LiIn) indicates that when the all-solid-state lithium selenide battery discharges to the reduction operating window, the AgI inside the cathode undergoes an in-situ reduction conversion reaction. This is reflected in the XPS spectra by a significant shift and weakening of the characteristic binding energy peaks originally belonging to the AgI lattice, replaced by prominent metallic silver (Ag) peaks. 0 Characteristic peaks. This in-situ conversion reaction generates nanoscale metallic silver particles in the contact blind zone of the three-phase interface, eliminating the local space charge layer effect and greatly enhancing the overall electronic conductivity inside the cathode. At the same time, the in-situ associated iodine-rich phase (such as LiI) acts as an interface lubricant, dynamically reconstructing the ion migration path of the solid-solid interface, providing mechanical stress buffer for volume changes, and exhibiting excellent electrochemical activation characteristics.

[0056] like Figure 4 The example shown is Example 1 (Se) 16 High-resolution X-ray photoelectron spectroscopy (XPS) characteristic analysis of AgI composite cathode material after initial discharge and charging to a high potential (charged state). Combined with... Figure 5The oxidation peak observed at 1.4–1.6 V (vs. LiIn) in the cyclic voltammetry (CV) test indicates that when the all-solid-state lithium selenide battery is charged to a high potential, the internal modified components undergo a reverse reaction. The characteristic peaks of metallic silver in the XPS spectrum significantly weaken or disappear, and revert to the original AgI lattice characteristic peaks. This strongly demonstrates that the AgI exhibits excellent electrochemical reversible regeneration characteristics within the reduction / oxidation working window. More importantly, comparing the electrochemical full-cycle spectra of the pristine, discharged, and charged states, the iodine (I3d) signal remains consistently stable at the iodide ion (I3d) level. - The binding energy state of the iodine ions did not shift towards higher binding energies, indicating that they were not further oxidized to elemental iodine (I2). This shows that iodine ions do not participate in initiating additional redox couples, thereby suppressing interfacial chemical side reactions and internal self-discharge behavior caused by the generation of elemental iodine from the source. This allows the stable iodine-rich phase to function purely as a low-impedance fast lithium-ion transport channel, achieving long-term stable operation of the electron / ion dual-conductivity network.

[0057] like Figure 5 The example shown is Example 1 (Se) 16 A comparison of the isothermal cyclic voltammetry (CV) curves of Example 1 (AgI composite cathode material) and Comparative Example 1 (pure Se composite cathode material) in a battery system. Within a test voltage window of 0.8–1.8 V, Example 1 (Se... 16 The AgI composite cathode material exhibits a larger CV curve area and a larger redox peak current, with a smaller potential difference (polarization) between the oxidation and reduction peaks. This result directly demonstrates that the in-situ generated metallic silver nano-conductive network and the LiI interface lubricating layer reduce the charge transfer barrier at the solid-solid interface, thereby accelerating the reversible insertion / extraction diffusion kinetics of lithium ions.

[0058] like Figure 6 The example shown is Example 1 (Se) 16 The constant current charge-discharge long-cycle lifetime and charge-discharge curves at different cycle numbers of the AgI composite cathode material and Comparative Example 1 (pure Se composite cathode material) under a current rate of 0.3C are shown in the experimental data. It is clear from the experimental data that, during long-cycle operation, the discharge specific capacity of Comparative Example 1 (without AgI modification) continuously decreases due to the exfoliation of the solid-solid interface caused by the large lattice volume expansion of elemental selenium. In contrast, the Se composite cathode material prepared in Example 1... 16 The AgI-modified composite cathode, after undergoing long cycling at 0.3C within a 0.8-1.8 V window, exhibited a remarkably stable discharge capacity curve and demonstrated higher capacity retention compared to the unmodified pure selenium cathode. Furthermore, Example 1 maintained a near 100% coulombic efficiency throughout the entire cycle. Figure 6The charge-discharge curves shown in the figure below reveal a characteristic voltage plateau formed by the conversion reaction between AgI and Ag. This plateau remains stable across different cycle numbers, indicating that the reversible electrochemical reaction proceeds steadily. This fully demonstrates that the in-situ converted soft metal composite network provides excellent mechanical stress buffering for elemental selenium at the nanoscale, maintaining a tight, continuous, and highly stable solid-solid contact interface between the conductive network inside the cathode material and the LPSCl electrolyte layer during long-term cycling. This demonstrates significant technological potential for large-scale industrial application and commercialization.

[0059] like Figure 7 The image shown is Se in Example 1. 16 Scanning electron microscopy (SEM) images of the surface morphology of the AgI composite cathode material after cold pressing (original electrode). Microstructural observation shows that the phase components are continuously distributed, with no obvious phase separation or component segregation. The overall structure exhibits high uniformity and density, without significant large-sized pores, cracks, or macroscopic defects. This dense and uniform microstructure is conducive to building a continuous ion transport network, improving the contact stability of the electrode / electrolyte interface, and helping to suppress local current concentration, thereby enhancing the structural integrity and electrochemical reliability of the all-solid-state battery during cycling.

[0060] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A composite cathode material for all-solid-state lithium selenide batteries, characterized in that, The composite cathode material comprises elemental selenium, silver iodide, conductive carbon, and a sulfide solid electrolyte; based on a total mass percentage of 100% for elemental selenium, silver iodide, conductive carbon, and sulfide solid electrolyte, elemental selenium accounts for 25-35%, conductive carbon accounts for 10-20%, the molar ratio of elemental selenium to silver iodide is 16-32:1, and the balance is sulfide solid electrolyte; the charge / discharge voltage window of the composite cathode material is 0.8-1.8V.

2. The all-solid-state lithium selenide battery composite cathode material according to claim 1, characterized in that, The sulfide solid electrolyte includes Li6PS5Cl and Li6PS5Cl. 0.5 Br 0.5 At least one of Li7PS3.

3. The all-solid-state lithium selenide battery composite cathode material according to claim 1 or 2, characterized in that, The conductive carbon includes at least one of Ketjen Black, Super P, acetylene black, and carbon nanotubes.

4. A method for preparing the all-solid-state lithium selenide battery composite cathode material as described in any one of claims 1-3, characterized in that, The process includes the following steps: premixing and grinding elemental selenium and silver iodide, then adding conductive carbon and sulfide solid electrolyte in sequence and grinding them separately; then, ball milling the resulting mixture to obtain a composite cathode material.

5. The preparation method of the all-solid-state lithium selenide battery composite cathode material according to claim 4, characterized in that, The grinding time is 10-30 minutes.

6. The method for preparing the all-solid-state lithium selenide battery composite cathode material according to claim 4, characterized in that, The parameters for the ball milling process are set as follows: the mass ratio of milling beads to the mixture is 30-50:1, the milling speed is 500-800 rpm, and the milling time is 3-8 h.

7. The method for preparing the all-solid-state lithium selenide battery composite cathode material according to claim 4, 5, or 6, characterized in that, Both grinding and ball milling were carried out under an argon atmosphere, with the water content and oxygen content in the environment controlled to be below 0.01 ppm and below 0.01 ppm, respectively.

8. The application of a composite cathode material as described in any one of claims 1-3 or a composite cathode material prepared by the preparation method as described in any one of claims 4-7 in an all-solid-state lithium selenide battery.

9. The application according to claim 8, characterized in that, The all-solid-state lithium selenide battery includes a positive electrode, a negative electrode, and a sulfide solid electrolyte disposed between the positive and negative electrodes; the positive electrode is made of a composite positive electrode material; and the negative electrode is made of a lithium indium alloy.

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