Lithium sulfide, a method for preparing the same, and related products of lithium sulfide

Abstract

This invention provides lithium sulfide, its preparation method, and related products, belonging to the field of all-solid-state battery technology. The lithium sulfide simultaneously meets the following conditions: (1) purity ≥ 99.5%; (2) whiteness ≥ 90%; (3) electronic conductivity ≤ 0.5 × 10⁻⁶. ‑9 S / cm; (4) Particle size D50≤4μm, particle size distribution span Span≤2.0. The lithium sulfide of this application has the advantages of high purity, low electronic conductivity, narrow particle size distribution, low carbon residue, and high whiteness. The sulfide solid electrolyte prepared from it has high ionic conductivity and excellent interfacial stability, which is beneficial to improving the electrochemical performance of all-solid-state batteries.

Description

Technical Field

[0001] This application belongs to the field of all-solid-state battery technology, and in particular relates to a lithium sulfide, its preparation method, and related lithium sulfide products. Background Technology

[0002] Lithium sulfide (Li₂S) is used to prepare sulfide solid electrolytes (such as Li₂S). 5.5 PS 4.5 Cl 1.5 Li6PS5Cl, Li 10 GeP2S 12 The purity, particle morphology, and impurity control level of key precursors (such as Li3PS4) directly affect the ionic conductivity, stability, and electrochemical performance of subsequent solid electrolytes.

[0003] Currently, the carbothermal reduction method for lithium sulfate has attracted widespread attention due to its safe and low-cost raw materials. However, existing technologies using the carbothermal reduction method to prepare lithium sulfide have long suffered from the problem of balancing "reduction sufficiency, carbon residue, and particle size uniformity": (1) To improve the sufficiency of reduction, an excess of carbon source needs to be added. However, an excess of carbon source cannot react completely, which will lead to a significant increase in carbon residue, which in turn will cause the electronic conductivity of lithium sulfide to soar, resulting in electronic leakage and consumption of active lithium during battery charging and discharging, and a significant reduction in coulombic efficiency.

[0004] (2) To reduce carbon residue, the calcination temperature needs to be increased. However, high temperature will cause lithium sulfide particles to agglomerate severely, and the particle size distribution range will increase significantly. Large lithium sulfide particles cannot fully contact other raw materials used to prepare electrolytes, which will lead to incomplete solid-phase reaction, a large amount of unreacted lithium sulfide impurities and phase separation, and ultimately a decrease in cycle stability.

[0005] (3) To control the uniformity of particle size, the calcination temperature needs to be reduced. However, low temperature will lead to insufficient reduction, residual impurities such as Li2SO4 and Li2S2O3, resulting in low product purity and a significant decrease in ionic conductivity.

[0006] The aforementioned contradictions make it difficult for existing lithium sulfide products prepared by carbothermal reduction to simultaneously meet the comprehensive performance requirements of all-solid-state batteries for high ionic conductivity, high coulombic efficiency, and excellent cycle performance. Summary of the Invention

[0007] This invention provides lithium sulfide, its preparation method, and related products, aiming to solve the technical problem that lithium sulfide prepared by the existing carbothermal reduction method cannot simultaneously meet the comprehensive performance requirements of all-solid-state batteries for high ionic conductivity, high initial coulombic efficiency, and excellent cycle stability.

[0008] In a first aspect, embodiments of the present invention provide a lithium sulfide that simultaneously satisfies the following conditions: (1) Purity ≥ 99.5%; (2) Whiteness ≥ 90%; (3) Electronic conductivity ≤ 0.5 × 10 -9 S / cm; (4) Particle size D50≤4μm, particle size distribution span Span≤2.0.

[0009] Secondly, embodiments of the present invention also provide a method for preparing lithium sulfide, comprising: Lithium sulfate was mixed with a polymer carbon source and a porous carbon source to obtain a precursor; The precursor is calcined in an inert atmosphere or vacuum to carry out a carbothermic reduction reaction to obtain lithium sulfide. The polymer carbon source includes at least one of polyacrylonitrile, polyvinyl alcohol, polybenzimidazole, and polyaniline, and the porous carbon source includes at least one of lignin, biomass-derived activated carbon, chitosan, and starch.

[0010] Thirdly, embodiments of the present invention also provide a sulfide solid electrolyte, the preparation method of which includes: mixing lithium sulfide as described above with phosphorus pentasulfide and lithium halide, and subjecting the mixture to heat treatment to obtain the sulfide solid electrolyte, wherein the ionic conductivity of the sulfide solid electrolyte is 2.7 × 10⁻⁶. -3 ~3.7×10 -3 S / cm.

[0011] Fourthly, embodiments of the present invention also provide an all-solid-state battery comprising the sulfide solid electrolyte described above.

[0012] Fifthly, embodiments of the present invention also provide an electrical device comprising the all-solid-state battery described above.

[0013] The beneficial effects of the embodiments of the present invention are as follows: The lithium sulfide of this invention is the first product on the market that simultaneously meets the following conditions: purity ≥ 99.5%, whiteness ≥ 90%, and electronic conductivity ≤ 0.5 × 10⁻⁶. -9 S / cm, particle size D50≤4μm, particle size distribution span Span≤2.0. Purity ≥99.5% indicates high reduction sufficiency, resulting in fewer obstructive sites for ion transport in the prepared sulfide solid electrolyte, thus exhibiting high ionic conductivity. Whiteness ≥90% indicates that almost all added carbon source participated in the reduction reaction, with low carbon source residue, resulting in low electronic conductivity (≤0.5×10⁻⁶). -9The product is white (black when carbon residue is high), which allows the prepared sulfide solid electrolyte to have fewer electron leakage channels and lower active lithium consumption, thus resulting in a higher coulombic efficiency for the solid-state battery. Particle size D50 ≤ 4 μm and particle size distribution span Span ≤ 2.0 indicate that particle agglomeration is effectively suppressed during the reduction process, and the lithium sulfide particles are uniform in size. This uniform particle size allows for thorough molecular-level mixing of lithium sulfide with other raw materials, ensuring complete and uniform high-temperature solid-phase reaction. This avoids the generation of unreacted impurities and phase separation, significantly improving the phase purity and interfacial stability of the sulfide solid electrolyte, ultimately leading to a substantial increase in the battery's cycle capacity retention.

[0014] Experimental data demonstrate that solid-state batteries using lithium sulfide as the sulfide solid electrolyte material of this invention can achieve an ionic conductivity of 3.7 mS / cm, a coulombic efficiency of 91.5%, and a capacity retention of 88% after 100 cycles, which can meet the comprehensive performance requirements of all-solid-state batteries for high ionic conductivity, high initial coulombic efficiency, and excellent cycle stability.

[0015] This invention uses a polymer carbon source and a porous carbon source as a composite carbon source. The long-chain polymer carbon source, with its linear long-chain structure, uniformly coats the surface of each lithium sulfate particle through intermolecular entanglement during the ball milling mixing stage. During high-temperature calcination, dehydrogenation cyclization and gradual carbonization reactions occur, transforming it into a continuous carbon shell with a certain mechanical strength. This shell remains intact throughout the entire carbothermic reduction reaction, physically isolating adjacent reaction particles. This fundamentally inhibits the migration, melting, and sintering growth of lithium sulfide particles at high temperatures, ensuring that the product particle size D50 is stable within 4 μm and the particle size distribution span is ≤2.0.

[0016] Porous carbon sources, with their naturally porous structure and abundant oxygen-containing functional groups, uniformly fill the gaps between polymer-coated lithium sulfate particles during the ball milling mixing stage. During high-temperature calcination, a pyrolysis reaction occurs, removing small molecule volatiles such as hydroxyl and methoxy groups to form a three-dimensional interconnected porous carbon framework. This provides a higher number of reactive sites and a uniform reduction environment than a single carbon source, ensuring complete reduction of lithium sulfate and achieving a product purity of ≥98.8%, with a maximum of 99.6%. Simultaneously, the gas transport channels of the porous framework can quickly exhaust the CO / CO2 gas generated in the reaction, promoting the forward carbothermic reduction reaction. This ensures that the carbon source is completely consumed and escapes in gaseous form, resulting in low carbon residue and thus obtaining lithium sulfide products with low electronic conductivity and high whiteness.

[0017] By combining polymer carbon sources and porous carbon sources, a composite carbon structure of "outer shell coating + internal porous support" can be constructed in situ around lithium sulfate particles. This structure enables lithium sulfate to achieve uniform dispersion and deep reduction during mixing and high-temperature calcination, thereby producing lithium sulfide with high purity, low carbon residue, low electronic conductivity, uniform particle size distribution, and high whiteness. Attached Figure Description

[0018] To more clearly illustrate the solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a SEM image of lithium sulfide from Example 1 of this application; Figure 2 This is the electrochemical impedance spectroscopy of the sulfide solid electrolyte of Example 1 of this application; Figure 3 This is a cycle performance diagram of the battery prepared in Example 1 of this application. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Furthermore, it should be understood that the specific embodiments described herein are only for illustration and explanation of the present invention and are not intended to limit the present invention. In the present invention, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in actual use or operation, specifically the drawing directions in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0021] To address the technical problem that lithium sulfide prepared by the existing carbothermal reduction method cannot simultaneously meet the comprehensive performance requirements of all-solid-state batteries for high ionic conductivity, high initial coulombic efficiency, and excellent cycle stability, this application provides a lithium sulfide that simultaneously satisfies the following conditions: (1) Purity ≥ 99.5%; (2) Whiteness ≥ 90%; (3) Electronic conductivity ≤ 0.5 × 10 -9 S / cm; (4) Particle size D50≤4μm, particle size distribution span Span≤2.0.

[0022] For example, the purity of lithium sulfide is ≥99.5%, ≥99.6%, or any value within the range of ≥99.5%; for instance, the purity of lithium sulfide is 99.5%, 99.6%, or any value between 99.5% and 99.6%.

[0023] For example, the whiteness of lithium sulfide is ≥90%, ≥91%, ≥92%, ≥93%, ≥94%, ≥95%, or any value within the range of ≥90%; for instance, the whiteness of lithium sulfide is 90%, 91%, 92%, 93%, 94%, 95%, 96%, or any value between 90% and 96%.

[0024] For example, lithium sulfide has an electronic conductivity of 0.1 × 10⁻⁶. -9 S / cm, 0.2×10 -9 S / cm, 0.3×10 -9 S / cm, 0.4×10 -9 S / cm, 0.5×10 -9 S / cm or ≤0.5×10 -9 Any value within the range of S / cm.

[0025] For example, the particle size D50 of lithium sulfide is ≤4μm, ≤3.5μm, ≤3.4μm, or any value within the range of ≤4μm; for example, the particle size D50 of lithium sulfide is 2.9μm, 3μm, 3.1μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, 4μm, or any value between 2.9 and 4μm.

[0026] For example, the particle size distribution span of lithium sulfide is ≤2.0, ≤1.9, ≤1.8, ≤1.7, ≤1.6, ≤1.5, or any value within the range of ≤2.0; for instance, the particle size distribution span of lithium sulfide is 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or any value between 1.2 and 2.0.

[0027] In one embodiment, the lithium sulfide further satisfies at least one of the following conditions: (1) Purity ≥ 99.6%; (2) The particle size D50 is 2.9 ~ 3.5 μm, preferably 3.2 ~ 3.4 μm; the particle size distribution span Span ≤ 1.5, preferably 1.2 ~ 1.3; (3) The electronic conductivity is 0.1 × 10⁻⁶ -9 ~ 0.5×10 -9 S / cm; (4) Whiteness is 95% ~ 96%.

[0028] In some embodiments, the lithium sulfide is prepared using the preparation method described below.

[0029] This application also provides a method for preparing lithium sulfide, comprising: Lithium sulfate was mixed with a polymer carbon source and a porous carbon source to obtain a precursor; The precursor is calcined in an inert atmosphere or vacuum to carry out a carbothermic reduction reaction to obtain lithium sulfide. The polymer carbon source includes at least one of polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polybenzimidazole (PBI), and polyaniline (PANI), and the porous carbon source includes at least one of lignin, biomass-derived activated carbon, chitosan, and starch.

[0030] In the preparation method of lithium sulfide, this application effectively avoids the formation of macroscopic agglomerates of lithium sulfide by adding polymeric carbon sources and porous carbon sources, and constructs a continuous carbon framework or porous carbon structure during the formation of lithium sulfide, which has a confining effect on the nucleation, growth or spatial distribution of lithium sulfide. Specifically, the polymeric carbon source undergoes cyclization and dehydrogenation reactions during calcination, gradually condensing to form a dense aromatic carbon layer. Its long-chain structure allows it to tightly coat the surface of lithium sulfate particles, forming a "carbon shell structure". This carbon shell effectively confines the migration and melting flow of lithium sulfate, confining the carbothermic reduction reaction to the nanoscale interface, significantly improving the completeness of the reaction. The porous carbon source undergoes pyrolysis during calcination, in which easily decomposed oxygen-containing functional groups escape in gaseous form, forming a porous carbon framework with a three-dimensional interconnected network. This porous structure provides channels for small-sized lithium sulfate particles to enter the pores, allowing the reduction reaction to proceed fully within the pores. The large number of micropores and active sites provide a high reaction area for carbothermic reduction, ensuring a uniform and thorough reduction process. The polymer carbon source provides a continuous outer coating, while the porous carbon source provides internal porous support; together, they form a complete microreaction network. The coating layer confines the reaction space and controls particle growth, while the porous framework disperses reactants and promotes mass and heat transfer. Their synergistic effect combines the advantages of a large reaction area.

[0031] In one embodiment, the weight-average molecular weight of the polymer carbon source is 5 × 10⁻⁶. 4 ~5×10 5 g / mol.

[0032] For example, the weight-average molecular weight of the polymer carbon source is 5 × 10⁻⁶. 4 g / mol, 1×10 5 g / mol, 1.5×10 5 g / mol, 2×10 5 g / mol, 2.5×105 g / mol, 3×10 5 g / mol, 3.5×10 5 g / mol, 4×10 5 g / mol, 4.5×10 5 g / mol, 5×10 5 g / mol or 5×10 4 ~5×10 5 Any value between g / mol.

[0033] In one embodiment, the porous carbon source has an average pore size of 2–50 nm and a specific surface area of ​​50–800 m². 2 / g. For example, the average pore size of the porous carbon source is 2 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or any value between 2 and 50 nm; the specific surface area of ​​the porous carbon source is 50 m². 2 / g, 100m 2 / g, 150 m 2 / g、200 m 2 / g、250 m 2 / g、300 m 2 / g、350 m 2 / g、400 m 2 / g、450 m 2 / g、500 m 2 / g、550m 2 / g、600 m 2 / g、650 m 2 / g、700 m 2 / g、750 m 2 / g、800 m 2 / g or 50-800 m 2 Any value between / g.

[0034] In one embodiment, the mass ratio of the lithium sulfate to the polymer carbon source and the porous carbon source is 1:(0.05~0.3):(0.1~1.0).

[0035] For example, the mass ratio of lithium sulfate to polymer carbon source or porous carbon source can be any value between 1:0.05:0.1, 1:0.15:0.3, 1:0.1:0.3, 1:0.2:0.3, 1:0.15:0.2, 1:0.15:0.5, 1:0.12:0.4, 1:0.18:0.25, 1:0.08:0.5, 1:0.2:0.2, 1:0.13:0.35, 1:0.05:1, 1:0.3:0.1, 1:0.3:1.0 or 1 : (0.05~0.3) : (0.1~1.0).

[0036] When the mass ratio of lithium sulfate to polymer carbon source and porous carbon source is within the above range, the reaction of lithium sulfate to lithium sulfide can be fully carried out, the free carbon residue can be minimized, and a high-performance lithium sulfide product with high purity, light color (white or light gray), and significantly reduced electronic conductivity can be obtained.

[0037] Furthermore, too low an amount of polymer carbon source will lead to discontinuous coating, while too high an amount will form a thick carbon shell that hinders mass transfer, both of which are detrimental to the reaction. Too low an amount of porous carbon source will result in insufficient porous structure, while too high an amount of porous carbon source will easily generate a large number of tiny free carbon residues, affecting the color and conductivity of the product and inducing interfacial side reactions.

[0038] In one embodiment, the mixing method is ball milling, the ball milling speed is 300-500 rpm, and the ball milling time is 2-6 h. The appropriate ball milling speed and time ensure that lithium sulfate, polymer carbon source and porous carbon source are uniformly dispersed, thereby maximizing the contact area between carbon source and lithium sulfate and avoiding insufficient reduction caused by local carbon deficiency.

[0039] For example, the ball mill rotation speed is 300 rpm, 400 rpm, 500 rpm, or any value between 300 and 500 rpm; the ball milling time is 2 h, 3 h, 4 h, 5 h, 6 h, or any value between 2 and 6 h.

[0040] In one embodiment, the calcination temperature is 700–800°C, and the calcination time is 2–5 h.

[0041] For example, the calcination temperature is 700℃, 750℃, 800℃ or any value between 700℃ and 800℃; the calcination time is 2 h, 3 h, 4 h, 5 h or any value between 2 and 5 h.

[0042] It should be noted that lithium sulfide-related products include solid electrolytes, secondary batteries, and electrical equipment, specifically sulfide solid electrolytes, all-solid-state batteries, and electrical equipment.

[0043] This application also provides a sulfide solid electrolyte, the preparation method of which includes: mixing lithium sulfide as described above with phosphorus pentasulfide and lithium halide, and subjecting the mixture to heat treatment to obtain the sulfide solid electrolyte, wherein the ionic conductivity of the sulfide solid electrolyte is 2.7 × 10⁻⁶. -3 ~3.7×10 -3 S / cm.

[0044] For example, the ionic conductivity of sulfide solid electrolytes is 2.7 × 10⁻⁶. -3 S / cm, 2.8×10 -3 S / cm, 2.9×10 -3 S / cm, 3.0×10 -3 S / cm, 3.1×10 -3 S / cm, 3.2×10 -3 S / cm, 3.3×10 -3 S / cm, 3.4×10 -3 S / cm, 3.5×10 -3 S / cm, 3.6×10 -3 S / cm, 3.7×10 -3 S / cm or 2.7×10 -3 ~3.7×10 -3 Any value between S and cm.

[0045] In some embodiments, the ionic conductivity of the sulfide solid electrolyte is 3.5 × 10⁻⁶. -3 ~3.7×10 -3 S / cm.

[0046] In some embodiments, lithium halides include at least one of lithium chloride, lithium bromide, and lithium iodide.

[0047] In some embodiments, the heat treatment is carried out in an inert atmosphere, which includes at least one of Ar and N2.

[0048] In some embodiments, the heating rate of the heat treatment is 1–5 °C / min, the temperature of the heat treatment is 450–550 °C, and the time of the heat treatment is 2–10 h.

[0049] For example, the heating rate of the heat treatment is any value between 1 ℃ / min, 2 ℃ / min, 3 ℃ / min, 4 ℃ / min, 5 ℃ / min, or 1 to 5 ℃ / min; the heat treatment temperature is any value between 450 ℃, 500 ℃, 550 ℃, or 450 to 550 ℃; and the heat treatment time is any value between 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or 2 to 10 h.

[0050] In one embodiment, the sulfide solid electrolyte is Li 5.5 PS 4.5 Cl 1.5 .

[0051] The lithium sulfide obtained in this application exhibits a dispersed structure confined by a carbon skeleton. This structural feature enables it to significantly shorten the diffusion distance of the solid-phase reaction and lower the reaction energy barrier during the subsequent reaction with phosphorus pentasulfide and lithium halide to prepare sulfide solid electrolytes. This allows the sulfidation reaction to proceed fully at lower temperatures and in a shorter time, which is beneficial for forming sulfide solid electrolytes with a more uniform composition distribution and a higher proportion of locally disordered structures. The structural features of this sulfide solid electrolyte further reduce the lithium-ion migration barrier, enabling the sulfide solid electrolyte to exhibit higher room-temperature ionic conductivity and more stable interfacial behavior under the same chemical composition and testing conditions.

[0052] It should be noted that the performance improvement of the sulfide solid electrolyte in this application is determined by the structure of lithium sulfide, and cannot be achieved by simply changing the preparation method of the sulfide solid electrolyte (such as increasing the heat treatment temperature) without using the lithium sulfide product of this application.

[0053] This application also provides an all-solid-state battery comprising the sulfide solid electrolyte described above.

[0054] This application also provides an electrical device comprising the all-solid-state battery described above.

[0055] The present application will be further described below through specific embodiments. Unless otherwise specified, the experimental materials used in the embodiments can be purchased from conventional biochemical reagent companies.

[0056] I. Preparation of Lithium Sulfide Example 1 Example 1 provides a lithium sulfide, the preparation method of which includes: Lithium sulfate and polyacrylonitrile (PAN, weight average molecular weight 1.5 × 10⁻⁶) were added. 5 g / mol) and lignin (average pore size approximately 45 nm, specific surface area 300 m² / mol) 2 Mix the ingredients (g) at a mass ratio of 1:0.15:0.3, place the mixture in a ball mill, and ball mill at 400 rpm for 4 h to obtain the precursor.

[0057] The precursor was calcined in an Ar atmosphere at a temperature of 760℃ for 3 h to carry out a carbothermic reduction reaction.

[0058] After cooling, the reaction product was crushed and passed through a 100-mesh sieve to obtain lithium sulfide.

[0059] Example 1 also provides a sulfide solid electrolyte, the preparation method of which includes: The obtained lithium sulfide was mixed with phosphorus pentasulfide (P2S5) and lithium chloride (LiCl) in a molar ratio of 4:1:3. The mixed powder was placed in a sealed quartz tube or stainless steel reaction vessel. Heat treatment was performed under Ar atmosphere at a heating rate of 5 °C / min to a temperature of 550 °C for 5 h. After heat treatment, the mixture was allowed to cool naturally to obtain Li. 5.5 PS 4.5 Cl 1.5 Sulfide solid electrolyte.

[0060] Example 2 The difference between Example 2 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.1:0.3. The rest is the same as in Example 1.

[0061] Example 3 The difference between Example 3 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.20:0.30. The rest is the same as in Example 1.

[0062] Example 4 The difference between Example 4 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.15:0.20. The rest is the same as in Example 1.

[0063] Example 5 The difference between Example 5 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.15:0.50. The rest is the same as in Example 1.

[0064] Example 6 The difference between Example 6 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.12:0.40. The rest is the same as in Example 1.

[0065] Example 7 The difference between Example 7 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.18:0.25. The rest is the same as in Example 1.

[0066] Example 8 The difference between Example 8 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.08:0.50. The rest is the same as in Example 1.

[0067] Example 9 The difference between Example 9 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.20:0.20. The rest is the same as in Example 1.

[0068] Example 10 The difference between Example 10 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.13:0.35. The rest is the same as in Example 1.

[0069] Example 11 The difference between Example 11 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.05:1. Everything else is the same as in Example 1.

[0070] Example 12 The difference between Example 12 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.3:0.1. Everything else is the same as in Example 1.

[0071] Example 13 The difference between Example 13 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.04:1. Everything else is the same as in Example 1.

[0072] Example 14 The difference between Example 14 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.31:0.1. Everything else is the same as in Example 1.

[0073] Example 15 The difference between Example 15 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.3:0.09. Everything else is the same as in Example 1.

[0074] Example 16 The difference between Example 16 and Example 1 is that the mass ratio of lithium sulfate to polyacrylonitrile and lignin is 1:0.05:1.01. Everything else is the same as in Example 1.

[0075] Example 17 The difference between Example 17 and Example 1 is that the weight-average molecular weight of polyacrylonitrile is 1.0 × 10⁻⁶. 5 g / mol. The rest is the same as in Example 1.

[0076] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that polyacrylonitrile was not added, and the mass ratio of lithium sulfate to lignin was 1:0.45. The rest was the same as in Example 1.

[0077] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that lignin is not added, and the mass ratio of lithium sulfate to polyacrylonitrile is 1:0.3. The rest is the same as in Example 1.

[0078] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that lignin is not added, and the mass ratio of lithium sulfate to polyacrylonitrile is 1:0.45. The rest is the same as Example 1.

[0079] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that polyacrylonitrile was not added, and the mass ratio of lithium sulfate to lignin was 1:0.8. The rest was the same as in Example 1.

[0080] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that lignin is not added, and the mass ratio of lithium sulfate to polyacrylonitrile is 1:0.15. The rest is the same as Example 1.

[0081] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that lignin is not added, and the mass ratio of lithium sulfate to polyacrylonitrile is 1:0.6. The rest is the same as Example 1.

[0082] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that polyacrylonitrile was not added, and the mass ratio of lithium sulfate to lignin was 1:0.3. The rest was the same as in Example 1.

[0083] Comparative Example 8 The difference between Comparative Example 8 and Example 1 is that: no polyacrylonitrile and lignin are added, and carbon black is added to replace the polyacrylonitrile and lignin in Example 1. The mass of carbon black is equal to the total mass of polyacrylonitrile and lignin in Example 1. Everything else is the same as Example 1.

[0084] Comparative Example 9 The difference between Comparative Example 9 and Example 1 is that: no polyacrylonitrile and lignin were added, and graphite was added to replace the polyacrylonitrile and lignin in Example 1. The mass of graphite was equal to the total mass of polyacrylonitrile and lignin in Example 1. The rest was the same as Example 1.

[0085] Comparative Example 10 The lithium sulfide in Comparative Example 10 was commercial lithium sulfide, purchased from Aladdin Company, model L166537-10g.

[0086] The lithium sulfide prepared in the examples and comparative examples was subjected to performance tests under the same conditions, specifically including: 1. Electronic conductivity test: Sample preparation: Lithium sulfide is pressed into dense discs (10 mm in diameter, 0.5-2 mm thick) in a glove box, placed in a test mold, and used to form a symmetrical cell (electrode|electrolyte|electrode) with a blocking electrode. The entire process is protected under an inert atmosphere.

[0087] Instrument connection: Connect the mold to the electrochemical workstation and place it in a shielded box.

[0088] Apply bias voltage: Apply a constant small DC voltage (e.g., 30 mV).

[0089] Data recording: Record the curve of current decay over time for an extended period (usually several hours to tens of hours) until the current stabilizes.

[0090] Calculate: Take the steady-state current (I) from the steady-state region ss ).

[0091] Calculate the electronic resistance using Ohm's law: R e = V / I ss .

[0092] Calculate electronic conductivity: σ e = (thickness / (area × R)) e )).

[0093] 2. Whiteness test steps: Sample preparation: In a glove box, press the powdered sample into a white standard sample cup, smooth the surface to form a flat, matte test surface. Immediately seal with a transparent glass plate or a special cover.

[0094] Instrument calibration: Calibrate using the standard whiteboard and blackboard provided with the instrument.

[0095] Test: Quickly remove the sealed sample cup, place it at the instrument's measuring port, and test immediately. Record the L*, a*, and b* values, and calculate the whiteness index (WI) according to the CIE Whiteness (Ganz formula) or Hunter Whiteness formula. The higher the value, the whiter the sample.

[0096] 3. D50 and SPAN testing procedures: Use a laser particle size analyzer, such as the Malvern Mastersizer 3000 or an equivalent device.

[0097] Sample dispersion method: Take the sample (about 0.1–0.5 g), add the dispersion medium: anhydrous ethanol or isopropanol, and add a small amount of dispersant (such as PVP or surfactant), and sonicate for 3–5 min to avoid agglomeration.

[0098] Test conditions: Test mode: wet test; refractive index: lithium sulfide set to 1.65; absorbance: 0.01; the test was repeated 3 times and the average value was taken.

[0099] D50 Definition: D50 is the particle size (median particle size) that corresponds to a cumulative volume fraction of 50% in the volume distribution.

[0100] Span calculation formula: Span = (D(90)-D(10)) / D(50).

[0101] The performance test data of lithium sulfide in the examples and comparative examples are shown in Table 1.

[0102] Table 1. Performance Comparison of Lithium Sulfide in Examples and Comparative Examples

[0103] Testing the ionic conductivity of an electrolyte involves the following steps: Sample preparation: Electrolyte powder is pressed into dense discs (10 mm in diameter, 0.5-2 mm thick) in a glove box, placed in a test mold, and used to form a symmetrical cell (electrode|electrolyte|electrode) with a blocking electrode. The entire process is protected under an inert atmosphere.

[0104] Test settings: Set the frequency scan range and amplitude, then start the test.

[0105] Data Analysis: On the Nyquist plot (-Z'' vs Z'), the semicircles (or portions of semicircles) appearing in the high-frequency region typically correspond to bulk phase and / or grain boundary impedance.

[0106] Fitting is performed using an equivalent circuit (e.g., (R1CPE1)(R2CPE2)), where R1 is typically the bulk resistance (R...). β ).

[0107] The diagonal lines in the low-frequency region represent the polarization behavior of the electrode / electrolyte interface.

[0108] calculate: The volume resistance R was obtained from the fitting. β .

[0109] Calculate ionic conductivity: σ i = (thickness / (area × R)) β )).

[0110] Assembling sulfide solid electrolytes into all-solid-state batteries specifically includes: (a) The all-solid-state battery has a sandwich structure, including: a positive electrode layer, a sulfide solid electrolyte layer and a negative electrode layer.

[0111] (ii) Composition of positive electrode material: The mass ratio of positive electrode active material (NCM) to sulfide solid electrolyte (prepared by the above method) and conductive agent (Super P, VGCF) is 70:25:5.

[0112] The above materials were weighed in an inert atmosphere and mixed by grinding in a mortar and pestle for 2 hours to obtain positive electrode composite powder.

[0113] (III) Preparation of sulfide electrolyte layer The sulfide solid electrolyte powder was loaded into a mold and cold-pressed under a pressure of 300 MPa to obtain a dense electrolyte sheet with a thickness of 80 μm.

[0114] (iv) Negative electrode: Lithium alloy (Li–In).

[0115] (v) Assembling all-solid-state batteries: 1. Place the electrolyte sheet in a mold; 2. Lay the positive electrode composite material on one side of the electrolyte sheet; 3. Lay the negative electrode material on the other side; 4. Pressurize and form under 350 MPa pressure; 5. Obtain an all-solid-state battery cell.

[0116] The assembled all-solid-state batteries were subjected to electrochemical performance tests under the same conditions, namely: Test temperature: 25 ℃, voltage window: 2.6~4.2 V; charge / discharge rate: 0.1C~2C.

[0117] Solid electrolyte system: Li 5.5 PS 4.5 Cl 1.5 (LPSCl); Applied pressure: approximately 200 MPa. At least 3 batteries were tested per sample group, and the average result was taken.

[0118] The ionic conductivity and all-solid-state battery performance test results of the sulfide solid electrolytes prepared in each embodiment and comparative example are shown in Table 2.

[0119] Table 2 Performance Comparison of Examples and Comparative Examples

[0120] From Table 1, Table 2, Figure 2 and Figure 3 It can be seen that the lithium sulfide in Examples 1-17 simultaneously exhibits high purity, high whiteness, low electronic conductivity, and narrow particle size distribution (SPAN), demonstrating superior overall performance compared to Comparative Examples 1-10. The sulfide solid electrolytes in Examples 1-17 possess high ionic conductivity, and the all-solid-state batteries assembled from them exhibit high coulombic efficiency and excellent cycle stability, demonstrating superior overall performance compared to Comparative Examples 1-10.

[0121] By comparing Examples 1-17 (polymer carbon source-porous carbon source synergistic system) with Comparative Examples 1, 4, and 7 (porous carbon source system only), it can be found that the performance of lithium sulfide, sulfide solid electrolyte, and all-solid-state battery in Comparative Examples 1, 4, and 7 is inferior to that in Examples 1-17. The possible reason is that Comparative Examples 1, 4, and 7 only added a porous carbon source (lignin) during the preparation of lithium sulfide, which easily produces uncontrollable carbon residues, forming local conductive pathways and inducing interfacial side reactions; while Examples 1-17 added both polymer carbon source and porous carbon source. The introduction of polymer carbon source (PAN) can form a confined coating structure, thereby effectively suppressing electron leakage and improving interfacial stability.

[0122] By comparing Examples 1-17 (polymer carbon source-porous carbon source synergistic system) with Comparative Examples 2, 3, 5, and 6 (polymer carbon source system only), it can be found that the performance of lithium sulfide, sulfide solid electrolyte, and all-solid-state battery in Comparative Examples 2, 3, 5, and 6 is inferior to that of Examples 1-17. The possible reason is that when polymer carbon source (PAN) is used alone, it is easy to form a dense carbon layer, which hinders the diffusion of substances during the reaction process, resulting in insufficient conversion of lithium sulfate. However, in Examples 1-17, polymer carbon source and porous carbon source are added. The introduction of porous carbon source (lignin) provides a porous structure, which improves the reaction kinetics and carbon distribution uniformity.

[0123] By comparing Example 1 and Comparative Example 8, it can be found that the performance of lithium sulfide, sulfide solid electrolyte and all-solid-state battery in Comparative Example 8 is inferior to that in Example 1. The possible reason is that in the process of preparing lithium sulfide in Comparative Example 8, carbon black was added to replace the polymer carbon source and porous carbon source of this application. Carbon in the carbon black system is easy to agglomerate and the interface is not uniform, which leads to the performance degradation.

[0124] By comparing Example 1 and Comparative Example 9, it can be found that the performance of lithium sulfide, sulfide solid electrolyte and all-solid-state battery in Comparative Example 9 is inferior to that in Example 1. The possible reason is that in the process of preparing lithium sulfide, graphite was added to replace the polymer carbon source and porous carbon source of this application. Graphite has low reactivity, resulting in insufficient conversion.

[0125] By comparing Example 1 and Comparative Example 10, it can be found that the performance of the lithium sulfide, sulfide solid electrolyte, and all-solid-state battery in Comparative Example 10 is inferior to that in Example 1. The possible reasons are as follows: Comparative Example 10 uses commercial lithium sulfide. In the process of preparing the sulfide solid electrolyte, the solid-phase diffusion distance between lithium sulfide and phosphorus pentasulfide is significantly increased, the reaction kinetics are restricted, and the sulfidation reaction is prone to incomplete. As a result, local lithium-rich or sulfur-rich regions and coarse grains are generated in the obtained sulfide solid electrolyte. XRD shows that its purity is not high and there are impurities such as LiCl and Li2S. The above-mentioned structural defects further cause discontinuous lithium-ion transport channels, high interfacial impedance, and accelerated impedance growth during cycling. As a result, the obtained sulfide solid electrolyte exhibits lower room temperature ionic conductivity and poorer electrochemical cycling performance under the same test conditions.

[0126] By comparing Examples 1-12 with Examples 13-14, it can be found that the performance of lithium sulfide, sulfide solid electrolyte, and all-solid-state battery in Examples 1-12 is better than that in Examples 13-14. This may be because the mass ratio of lithium sulfate to polymer carbon source and porous carbon source in Examples 13 and 14 is not in the range of 1:(0.05~0.3):(0.1~1.0). The amount of polymer carbon source (PAN) added in Example 13 is too small, and the amount of polymer carbon source (PAN) added in Example 14 is too large. This indicates that the preferred mass ratio of lithium sulfate to polymer carbon source and porous carbon source is 1:(0.05~0.3):(0.1~1.0).

[0127] By comparing Examples 1-12 with Examples 15-16, it can be found that the performance of lithium sulfide, sulfide solid electrolyte, and all-solid-state battery in Examples 1-12 is better than that in Examples 15-16. This may be because the mass ratio of lithium sulfate to polymer carbon source and porous carbon source in Examples 15 and 16 is not in the range of 1:(0.05~0.3):(0.1~1.0). The amount of porous carbon source (lignin) added in Example 15 is too small, while the amount of porous carbon source (lignin) added in Example 16 is too large. This indicates that the preferred mass ratio of lithium sulfate to polymer carbon source and porous carbon source is 1:(0.05~0.3):(0.1~1.0).

[0128] By comparing Example 1 (PAN molecular weight 1.5 × 10⁻⁶) 5 (g / mol) and Example 17 (PAN molecular weight 1.0 × 10⁻⁶ g / mol) 5 As can be seen from the g / mol, the molecular weight of PAN was reduced in Example 17, and the SPAN of Example 17 was slightly increased, while the ionic conductivity and cycling performance were slightly decreased. This may be because the molecular weight of PAN affects the continuity and controllability of the carbonization structure, and a higher molecular weight helps to form a more uniform carbon skeleton structure.

[0129] In summary, this invention simultaneously incorporates a polymeric carbon source (PAN) and a porous carbon source (lignin) during the preparation of lithium sulfide, controlling their amounts within an appropriate range. This enables the formation of a composite carbon skeleton at the microscopic level characterized by "uniform dispersion + moderate coating + porous conductivity," achieving a strong coupling relationship between structural parameters (SPAN, whiteness) and electrochemical performance. This results in the following synergistic effects during carbothermic reduction: ensuring full conversion of lithium sulfate and improving product purity; inhibiting the formation of a continuous conductive carbon network and reducing electronic conductivity; controlling the morphology of residual carbon, maintaining a light color and high whiteness; limiting abnormal particle growth and concentrating particle size distribution; reducing side reaction impurities, thereby giving the sulfide solid electrolyte high ionic conductivity and the all-solid-state battery high coulombic efficiency and excellent cycle performance. When the content of each raw material is outside the preferred range of this application, problems such as uncontrolled carbon residue, widened particle distribution, and decreased whiteness may occur, leading to enhanced electronic conductivity, intensified side reactions, and deteriorated battery performance.

[0130] The embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A lithium sulfide, characterized in that, The lithium sulfide simultaneously meets the following conditions: (1) Purity ≥ 99.5%; (2) Whiteness ≥ 90%; (3) Electronic conductivity ≤ 0.5 × 10 -9 S / cm; (4) Particle size D50≤4μm, particle size distribution span Span≤2.

0.

2. The lithium sulfide according to claim 1, characterized in that, The lithium sulfide also satisfies at least one of the following conditions: (1) Purity ≥ 99.6%; (2) The particle size D50 is 2.9 ~ 3.5 μm, preferably 3.2 ~ 3.4 μm; the particle size distribution span Span ≤ 1.5, preferably 1.2 ~ 1.3; (3) The electronic conductivity is 0.1 × 10⁻⁶ -9 ~ 0.5×10 -9 S / cm; (4) Whiteness is 95% ~ 96%.

3. A method for preparing lithium sulfide, characterized in that, include: Lithium sulfate was mixed with a polymer carbon source and a porous carbon source to obtain a precursor; The precursor is calcined in an inert atmosphere or vacuum to carry out a carbothermic reduction reaction to obtain lithium sulfide. The polymer carbon source includes at least one of polyacrylonitrile, polyvinyl alcohol, polybenzimidazole, and polyaniline, and the porous carbon source includes at least one of lignin, biomass-derived activated carbon, chitosan, and starch.

4. The method for preparing lithium sulfide according to claim 3, characterized in that, The weight-average molecular weight of the polymer carbon source is 5 × 10⁻⁶. 4 ~5×10 5 g / mol.

5. The method for preparing lithium sulfide according to claim 3, characterized in that, The porous carbon source has an average pore size of 2–50 nm and a specific surface area of ​​50–800 m². 2 / g.

6. The method for preparing lithium sulfide according to any one of claims 3-5, characterized in that, The mass ratio of the lithium sulfate to the polymer carbon source and the porous carbon source is 1 : (0.05~0.3) : (0.1~1.0).

7. The method for preparing lithium sulfide according to any one of claims 3-5, characterized in that, The mixing method is ball milling, the ball milling speed is 300-500 rpm, and the ball milling time is 2-6 h.

8. The method for preparing lithium sulfide according to any one of claims 3-5, characterized in that, The calcination temperature is 700–800℃, and the calcination time is 2–5 h.

9. A sulfide solid electrolyte, characterized in that, The method for preparing the sulfide solid electrolyte comprises: mixing lithium sulfide as described in claim 1 or 2, or lithium sulfide prepared by any one of claims 3-8, with phosphorus pentasulfide and lithium halide, and subjecting the mixture to heat treatment to obtain a sulfide solid electrolyte, wherein the ionic conductivity of the sulfide solid electrolyte is 2.7 × 10⁻⁶. -3 ~3.7×10 -3 S / cm.

10. The sulfide solid electrolyte according to claim 9, characterized in that, The ionic conductivity of the sulfide solid electrolyte is 3.5 × 10⁻⁶. -3 ~3.7×10 -3 S / cm.

11. An all-solid-state battery, characterized in that, The all-solid-state battery comprises the sulfide solid electrolyte as described in claim 9 or 10.

12. An electrical appliance, characterized in that, The electrical device comprises the all-solid-state battery as described in claim 11.

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