High-purity lithium sulfide materials, sulfide solid electrolytes, and their preparation and applications

Abstract

The present invention discloses a high-purity lithium sulfide material, a sulfide solid electrolyte, and its preparation and application. The preparation method comprises: mixing a sulfur source, a lithium source, and a composite reducing agent, and performing a low-temperature pre-reaction and a high-temperature reduction reaction to produce a high-purity lithium sulfide material; wherein the composite reducing agent comprises a high-specific surface area carbon source and a high-expansion carbon source. The present invention directly prepares ultra-high-purity lithium sulfide (>99.9%) through a synergistic reaction of two carbon sources, avoiding post-processing losses and increasing the yield to over 95%. The prepared lithium sulfide is compatible with a variety of sulfide electrolyte systems, and the cycle life and safety of solid-state batteries are significantly superior to those of traditional liquid batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium sulfide, and specifically relates to a high-purity lithium sulfide material, a sulfide solid electrolyte, and a preparation method and application thereof. Background Art

[0002] High-purity (>99.9%) lithium sulfide is widely used in solid-state electrolytes and secondary batteries. While various methods have been developed for preparing lithium sulfide, none have been simple. For example, current methods for preparing lithium sulfide using carbon reduction methods often contain residual carbon, requiring further purification, which is time-consuming and labor-intensive. Even if methods exist to purify lithium sulfide by encapsulating carbon in lithium sulfate to produce high-purity lithium sulfide, these methods are complex and lack stability.

[0003] Lithium sulfide ( ) As a key raw material for sulfide solid electrolytes, its purity (>99.9%) directly affects the performance of solid-state batteries (such as ionic conductivity, interface stability, etc.). At present, the preparation methods of high-purity lithium sulfide mainly include carbon thermal reduction, gas phase replacement, solid phase ball milling, etc., but these methods still have the following defects: (1) The carbon thermal reduction method (mainstream method) has a serious problem of residual carbon: when carbon (such as graphite, carbon black) or carbon source is used as a reducing agent, free carbon is easily left after the reaction, and additional acid washing or high-temperature treatment is required to remove it, increasing the complexity and cost of the process; purification is difficult: residual carbon may wrap lithium sulfide particles, resulting in low efficiency of subsequent purification steps (such as vacuum distillation), affecting the purity of the product (usually only about 99%); poor batch stability: the mixing uniformity of carbon and lithium source (such as lithium carbonate, lithium hydroxide) is difficult to control, resulting in incomplete reaction or local over-reduction (generating impurities such as lithium oxide). (2) The gas phase replacement method (preparing lithium sulfide from hydrogen sulfide and lithium source) has high safety risks: hydrogen sulfide is prone to explosion, has strict equipment requirements, and has high industrial production costs. (3) The solid phase ball milling method (ball milling reaction of lithium and sulfur) is highly corrosive to the ball milling tank, and the raw material lithium is expensive, which poses a great challenge to the low cost of lithium sulfide; it is also highly unsafe and not conducive to large-scale preparation. Existing methods generally have problems such as complex processes (multi-step purification), high costs (high energy consumption / equipment requirements), and insufficient product purity (residual carbon / impurities), which restrict the large-scale application of lithium sulfide and thus affect the cost reduction and commercialization process of sulfide solid electrolytes. Summary of the Invention

[0004] The main purpose of the present invention is to provide a high-purity lithium sulfide material, a sulfide solid electrolyte and its preparation method and application, so as to overcome the shortcomings of the existing technology.

[0005] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0006] An embodiment of the present invention provides a method for preparing a high-purity lithium sulfide material, which includes: mixing a sulfur source, a lithium source and a composite reducing agent and performing a low-temperature pre-reaction and a high-temperature reduction reaction to obtain a high-purity lithium sulfide material; wherein the composite reducing agent includes a high specific surface area carbon source and a high expansion carbon source.

[0007] The embodiment of the present invention also provides a high-purity lithium sulfide material prepared by the aforementioned preparation method.

[0008] An embodiment of the present invention further provides a sulfide solid electrolyte, which is made from the aforementioned high-purity lithium sulfide material.

[0009] The embodiments of the present invention also provide the use of the aforementioned high-purity lithium sulfide material or sulfide solid electrolyte in the preparation of a secondary battery.

[0010] An embodiment of the present invention further provides an all-solid-state secondary battery, which includes the aforementioned high-purity lithium sulfide material or sulfide solid electrolyte.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] (1) The present invention uses a dual carbon source synergistic reaction, where high surface area carbon provides chemical activity and a conductive network, and high expansion carbon provides a gas release channel and buffers thermal stress, thereby directly preparing ultra-high purity lithium sulfide, avoiding post-processing losses, and increasing the yield to over 95%;

[0013] (2) The preparation method provided by the present invention reduces the cost of raw materials, simplifies the process flow, is compatible with existing lithium battery production line equipment, and shortens the mass production cycle;

[0014] (3) The lithium sulfide prepared by the present invention can be adapted to a variety of sulfide electrolyte systems, and the cycle life and safety of solid-state batteries are significantly better than those of traditional liquid batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 is a SEM image of lithium sulfide in Example 1 of the present invention;

[0017] Figure 2 is the XRD pattern of lithium sulfide in Example 1 of the present invention;

[0018] Figure 3This is the XRD pattern of the sulfide solid electrolyte synthesized from lithium sulfide in Example 1 of the present invention. DETAILED DESCRIPTION

[0019] In light of the shortcomings of existing technologies, the inventors of this case, after extensive research and extensive practice, have come up with the technical solution of the present invention. This invention utilizes the simplest dual carbon (a high-expansion carbon source and a high-specific surface area activated carbon) mixed in proportion and then calcined with a sulfur source to produce high-purity lithium sulfide. This helps reduce the cost of lithium sulfide and facilitates subsequent large-scale production, providing a guarantee for cost reduction in the future development of sulfide solid electrolytes.

[0020] The technical solution of the present invention will be described clearly and completely below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Specifically, as one aspect of the technical solution of the present invention, a method for preparing a high-purity lithium sulfide material involves: mixing a sulfur source, a lithium source and a composite reducing agent and performing a low-temperature pre-reaction and a high-temperature reduction reaction to obtain a high-purity lithium sulfide material; wherein the composite reducing agent includes a high specific surface area carbon source and a high expansion carbon source.

[0022] In some preferred embodiments, the high specific surface area carbon source includes any one or more combinations of activated carbon, porous carbon, and carbon aerogel, but is not limited thereto.

[0023] In some preferred embodiments, the high specific surface area carbon source has a specific surface area of ​​≥1500 m² / g.

[0024] In some preferred embodiments, the high-expanding carbon source includes any one or more combinations of sucrose, expanded graphite, and graphene, but is not limited thereto.

[0025] In some preferred embodiments, the high-expansion carbon source is a carbon source with a volume expansion multiple of ≥50 times.

[0026] In some preferred embodiments, the sulfur source includes any one or more combinations of lithium sulfate, pyrite, and sublimed sulfur, but is not limited thereto.

[0027] In some preferred embodiments, the lithium source includes any one or more combinations of lithium sulfate, lithium carbonate, and lithium hydroxide, but is not limited thereto.

[0028] In some preferred embodiments, the mass ratio of the high specific surface area carbon source to the high expansion carbon source in the composite reducing agent is 1:5 to 1:10;

[0029] In some preferred embodiments, the molar ratio of the sulfur source to the lithium source is 1:2.

[0030] In some preferred embodiments, the molar ratio of the sulfur source to the high-expansion carbon source in the composite reducing agent is 1:2 to 1:4.4.

[0031] In some preferred embodiments, the preparation method specifically comprises:

[0032] The sulfur source, the lithium source and the composite reducing agent are mixed by ball milling in an inert atmosphere to obtain a mixed material;

[0033] Furthermore, the obtained mixed material is first subjected to a low-temperature pre-reaction at 200-300°C, then subjected to a high-temperature reduction reaction at 800-900°C, and finally cooled to room temperature in an inert atmosphere to obtain a high-purity lithium sulfide material.

[0034] In some preferred embodiments, the preparation method specifically includes: in an inert atmosphere, heating the mixture to 200~300°C at a heating rate of 5~10°C / min to perform a low-temperature pre-reaction on the obtained mixture, then continuing to heat the mixture to 800~900°C at a heating rate of 10~20°C / min for a high-temperature reduction reaction, and finally cooling the mixture to room temperature in an inert atmosphere to obtain a high-purity lithium sulfide material.

[0035] Furthermore, the low-temperature pre-reaction time is 1 to 5 hours.

[0036] Furthermore, the high temperature reduction reaction time is 2 to 6 hours.

[0037] In some more specific embodiments, the high-purity lithium sulfide material and its preparation method are further applied to sulfide solid electrolytes and all-solid-state secondary batteries, as follows:

[0038] (1) Optimization of raw material ratio

[0039] Dual carbon source synergistic reduction: Activated carbon (high specific surface area) and sucrose (high expansion carbon source) are mixed in a specific ratio (such as 1:5~1:10) as a composite reducing agent.

[0040] Sulfur source selection: preferably lithium sulfide precursor (such as lithium sulfate) and evenly mixed with lithium source (such as lithium carbonate, lithium hydroxide).

[0041] (2) Calcination process innovation

[0042] Gradient temperature control:

[0043] The first stage (200-300°C): low-temperature pre-reaction, carbonization of sucrose, and reduction of sulfur volatilization loss;

[0044] The second stage (800-900°C): high temperature reduction, activated carbon preferentially reacts to produce carbon dioxide, avoiding carbon residue;

[0045] The third stage (inert atmosphere cooling): inhibits the oxidation of lithium sulfide.

[0046] One-step synthesis: High-purity lithium sulfide is directly generated by matching the dual carbon source ratio with the temperature, without the need for post-processing and purification.

[0047] (3) Product application expansion

[0048] Preparation of solid electrolyte: Lithium sulfide and sulfide such as phosphorus pentasulfide are ball-milled in proportion to form a high ionic conductivity (>1× S / cm) of sulfide solid electrolyte.

[0049] All-solid-state battery integration: Paired with a lithium metal negative electrode and a high-nickel positive electrode (such as the NCM9 series), it achieves an initial efficiency of 84%.

[0050] Another aspect of the embodiments of the present invention further provides a high-purity lithium sulfide material prepared by the aforementioned preparation method.

[0051] Furthermore, the purity of the high-purity lithium sulfide material is >99.9%.

[0052] Another aspect of the embodiments of the present invention further provides a sulfide solid electrolyte, which is made from the aforementioned high-purity lithium sulfide material.

[0053] Another aspect of the embodiments of the present invention further provides use of the aforementioned high-purity lithium sulfide material or sulfide solid electrolyte in the preparation of a secondary battery.

[0054] Another aspect of an embodiment of the present invention further provides an all-solid-state secondary battery, which includes the aforementioned high-purity lithium sulfide material or sulfide solid electrolyte.

[0055] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments. This embodiment is implemented on the premise of the technical solution of the invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0056] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0057] Example 1

[0058] 1. Preparation of high-purity lithium sulfide

[0059] (1) Raw material composition and ratio:

[0060] Sulfur and lithium sources: lithium sulfate (purity ≥99.5%);

[0061] Composite carbon source: activated carbon (specific surface area 1500 m² / g) and sucrose (purity ≥99.5%) mixed in a mass ratio of 1:8. The molar ratio of lithium sulfate to sucrose is 1:3.

[0062] (2) Preparation steps:

[0063] Mixing: Lithium sulfate and composite carbon source were ball-milled in an argon glove box for 2 h (speed 300 rpm, ball-to-material ratio 10:1);

[0064] Calcination:

[0065] Stage 1: heating to 250°C at 5°C / min and holding for 1 hour (nitrogen atmosphere);

[0066] Stage 2: heating to 820°C at 10°C / min and holding for 3 hours (nitrogen atmosphere);

[0067] The third stage: cooling to room temperature with the furnace (nitrogen protection throughout the process).

[0068] (3) Product characteristics

[0069] Appearance: white powder, SEM image as shown Figure 1 As shown, the XRD pattern is Figure 2 As shown;

[0070] Crystal form: cubic lithium sulfide (XRD pattern without impurity peaks).

[0071] 2. Preparation of sulfide solid electrolyte

[0072] (1) Raw material ratio:

[0073] Lithium sulfide (product of Example 1): 1.3787 g;

[0074] Phosphorus pentasulfide (purity ≥99%): 1.6674g;

[0075] LiCl (purity ≥99.9%): 0.9539 g.

[0076] (2) Preparation steps:

[0077] Ball milling: The raw materials were dry milled in a planetary ball mill for 20 h (speed 500 r / min, zirconia grinding balls);

[0078] Heat treatment: heating to 550℃ at 5℃ / min, annealing for 5 hours (Ar atmosphere) to obtain sulfide solid electrolyte. The XRD pattern of sulfide solid electrolyte is as follows: Figure 3 shown.

[0079] (3) Product characteristics:

[0080] Ionic conductivity: 8.5× S / cm (25°C, AC impedance method);

[0081] 3. Full battery assembly and testing

[0082] Weigh 65 mg LPSCl (purity 99.9%, conductivity 8.5× S / cm) were cold-pressed in a 10mm diameter PTFE mold at a pressure of 150 MPa for 1 minute. 40mg of Li3InCl6 was added to one side, at a pressure of 150 MPa, for 1 minute. 10mg of the composite cathode material was then added to the Li3InCl6 side, at a pressure of 350 MPa, for 3 minutes. A 6mm diameter LiIn foil with a lithium mass fraction of 2% was then added to the LPSCl side, at a pressure of 100 MPa, for 0.5 minutes. The positive and negative electrodes were then fastened together to form an all-solid-state lithium-ion battery.

[0083] Example 2

[0084] The method is the same as that of Example 1, except that the mass ratio of activated carbon to sucrose is 1:5.

[0085] Example 3

[0086] The method is the same as that of Example 1, except that the mass ratio of activated carbon to sucrose is 1:10.

[0087] Example 4

[0088] The method is the same as in Example 1, except that:

[0089] Stage 1: heating to 200°C at 5°C / min and holding for 1 hour (nitrogen atmosphere);

[0090] Stage 2: heating to 800°C at 10°C / min and holding for 3 hours (nitrogen atmosphere);

[0091] The third stage: cooling to room temperature with the furnace (nitrogen protection throughout the process).

[0092] Example 5

[0093] The method is the same as in Example 1, except that:

[0094] Stage 1: heating to 300°C at 5°C / min and holding for 1 hour (nitrogen atmosphere);

[0095] Stage 2: heating to 900°C at 10°C / min and holding for 3 hours (nitrogen atmosphere);

[0096] The third stage: cooling to room temperature with the furnace (nitrogen protection throughout the process).

[0097] Comparative Example 1

[0098] The method is the same as that of Example 1, except that only sucrose is used as the carbon source.

[0099] Comparative Example 2

[0100] The method is the same as that of Example 1, except that only activated carbon is used as the carbon source.

[0101] Comparative Example 3

[0102] The method is the same as that of Example 1, except that there is no gradient temperature increase, that is, the temperature in the first and second stages of calcination is directly increased to 820°C for 4 hours.

[0103] Comparative Example 4

[0104] The method is the same as that of Example 1, except that the ratio of activated carbon to sucrose in the carbon source is 1:11.

[0105] Comparative Example 5

[0106] The method is the same as that of Example 1, except that the ratio of activated carbon to sucrose in the carbon source is 1:4.

[0107] Comparative Example 6

[0108] The method is the same as that of Example 1, except that the temperature is increased gradually, first to 190° C. and then to 820° C.

[0109] Comparative Example 7

[0110] The method is the same as that of Example 1, except that the temperature is increased gradually, first to 310°C and then to 820°C.

[0111] Comparative Example 8

[0112] The method is the same as that of Example 1, except that the temperature is increased gradually, first to 250°C and then to 750°C.

[0113] Comparative Example 9

[0114] The method is the same as that of Example 1, except that the temperature is increased gradually from 250°C to 950°C.

[0115] The XRD purity of lithium sulfide, the ionic conductivity of the sulfide solid electrolyte, and the capacity retention rate of the battery cell after 100 cycles in Examples 1-5 and Comparative Examples 1-9 were characterized, as shown in Table 1.

[0116] Table 1 XRD purity of lithium sulfide and sulfide solid electrolyte in Examples 1-5 and Comparative Examples 1-9

[0117] Ionic conductivity, battery capacity retention after 100 cycles

[0118]

[0119] The above results demonstrate that while sucrose is a source of pyrolytically derived "soft carbon," its specific surface area is extremely low, and its reduction efficiency is far inferior to that of activated carbon. A low activated carbon ratio results in insufficient or uneven reduction, poor structural support, and increased lithium sulfide agglomeration, carbon coating, and impurity inclusion. In a gradient heating process, the initial temperature activates carbon structural changes (e.g., 300-400°C for full expansion of expanded carbon); the subsequent temperature is high enough for complete reduction (>700°C). A low or short initial plateau prevents structural reformation / activation; a high plateau increases the risk of agglomeration.

[0120] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0121] It should be understood that the technical solution of the present invention is not limited to the above-mentioned specific implementation cases. Any technical variations made according to the technical solution of the present invention without departing from the scope of protection of the purpose of the present invention and the claims shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity lithium sulfide material, characterized in that: include: The sulfur source, the lithium source and the composite reducing agent are mixed by ball milling in an inert atmosphere to obtain a mixed material; Furthermore, the obtained mixed material is first subjected to a low-temperature pre-reaction at 200-300° C., then subjected to a high-temperature reduction reaction at 800-900° C., and finally cooled to room temperature in an inert atmosphere to obtain a high-purity lithium sulfide material; Among them, the composite reducing agent includes a high specific surface area carbon source and a high expansion carbon source; the mass ratio of the high specific surface area carbon source to the high expansion carbon source in the composite reducing agent is 1:5~1:10; the high specific surface area carbon source includes any one or more combinations of activated carbon, porous carbon, and carbon aerogel; and the high expansion carbon source is sucrose.

2. The preparation method according to claim 1, wherein: The specific surface area of ​​the high specific surface area carbon source is ≥1500 m² / g.

3. The preparation method according to claim 1, wherein: The high expansion carbon source is a carbon source with a volume expansion multiple of ≥50 times.

4. The preparation method according to claim 1, wherein: The sulfur source includes any one or more combinations of lithium sulfate, pyrite, and sublimed sulfur.

5. The preparation method according to claim 1, wherein: The lithium source includes any one or more combinations of lithium sulfate, lithium carbonate, and lithium hydroxide.

6. The preparation method according to claim 1, wherein: The molar ratio of the sulfur source to the lithium source is 1:

2.

7. The preparation method according to claim 1, wherein: The molar ratio of the sulfur source to the high-expansion carbon source in the composite reducing agent is 1:2-1:4.

4.

8. The preparation method according to claim 1, characterized in that Specifically include: In an inert atmosphere, the mixture is heated to 200-300°C at a heating rate of 5-10°C / min for a low-temperature pre-reaction, and then the temperature is further increased to 800-900°C at a heating rate of 10-20°C / min for a high-temperature reduction reaction. Finally, the mixture is cooled to room temperature in an inert atmosphere to obtain a high-purity lithium sulfide material.

9. The preparation method according to claim 8, characterized in that: The time of the low-temperature pre-reaction is 1 to 5 hours.

10. The preparation method according to claim 8, characterized in that: The high temperature reduction reaction time is 2 to 6 hours.

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