High-purity lithium sulfide material, sulfide solid electrolyte and preparation method and application thereof

Abstract

The invention discloses a high-purity lithium sulfide material, a sulfide solid electrolyte and a preparation method and application thereof. The preparation method comprises the following steps: mixing a sulfur source, a lithium source and a composite reducing agent, and carrying out low-temperature pre-reaction and high-temperature reduction reaction to prepare the 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 ultra-pure lithium sulfide (gt, 99.9%) is directly prepared through a double-carbon-source synergistic reaction, aftertreatment loss is avoided, the yield is increased to 95% or above, meanwhile, the prepared lithium sulfide adapts to various sulfide electrolyte systems, and the cycle life and safety of the solid-state battery are remarkably better than those of a traditional liquid-state battery.

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 their preparation methods and applications. Background Art

[0002] High-purity (>99.9%) lithium sulfide materials are widely used in solid electrolytes and secondary batteries. Recently, there are various methods for preparing lithium sulfide, but there is no simple method for preparing lithium sulfide. For example, the lithium sulfide prepared by carbon reduction now is very easy to have residual carbon and needs further purification, which is time-consuming and laborious. Even if there is a method to purify and wrap the carbon in lithium sulfate to prepare high-purity lithium sulfide, this method is complex and the stability cannot be well guaranteed.

[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, interfacial stability, etc.). At present, the preparation methods of high-purity lithium sulfide mainly include carbothermal reduction method, gas-phase displacement method, solid-phase ball milling method, etc., but these methods still have the following defects: (1) The carbothermal reduction method (mainstream method) has serious residual carbon problems: when using carbon (such as graphite, carbon black) or a carbon source as a reducing agent, free carbon is easily left after the reaction and needs to be removed by additional pickling or high-temperature treatment, increasing the process complexity and cost; the purification difficulty is large: the residual carbon may wrap the lithium sulfide particles, resulting in low efficiency of subsequent purification steps (such as vacuum distillation) and affecting the product purity (usually only reaching about 99%); the batch stability is poor: it is difficult to control the mixing uniformity of carbon and lithium sources (such as lithium carbonate, lithium hydroxide), resulting in incomplete reactions or local over-reduction (generating impurities such as lithium oxide). (2) The gas-phase displacement method (preparing lithium sulfide from hydrogen sulfide and a lithium source) has high safety risks: hydrogen sulfide is prone to explosion, requires strict equipment requirements, and has high industrial production costs. (3) The solid-phase ball milling method (ball milling reaction of lithium and sulfur) has great corrosion to the ball milling tank, and the raw material lithium is expensive, which is a great challenge to the low cost of lithium sulfide; the safety is relatively high and it is not conducive to large-scale preparation. The existing methods generally have problems such as complex processes (multiple-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 further 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 their preparation methods and applications to overcome the deficiencies of the prior art.

[0005] To achieve the foregoing invention purpose, the technical solutions adopted by the present invention include: 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.

[0006] An embodiment of the present invention also provides a high-purity lithium sulfide material prepared by the foregoing preparation method.

[0007] An embodiment of the present invention also provides a sulfide solid electrolyte, which is prepared by using the foregoing high-purity lithium sulfide material.

[0008] An embodiment of the present invention also provides the use of the foregoing high-purity lithium sulfide material or sulfide solid electrolyte in the preparation of secondary batteries.

[0009] An embodiment of the present invention also provides a all-solid-state secondary battery, which includes the foregoing high-purity lithium sulfide material or sulfide solid electrolyte.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Through the synergistic reaction of dual carbon sources in the present invention, the high specific surface area carbon provides chemical activity and a conductive network, and the high expansion carbon provides a gas release channel and buffers thermal stress, so that ultra-high purity lithium sulfide can be directly prepared, avoiding post-treatment loss, and the yield is increased to more than 95%; (2) The raw material cost of the preparation method provided by the present invention is reduced, the process flow is simplified, it is compatible with the existing lithium battery production line equipment, and the mass production cycle is shortened; (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 the solid-state battery are significantly better than those of traditional liquid batteries. Description of the Drawings

[0011] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0012] Figure 1 It is the SEM diagram of lithium sulfide in Example 1 of the present invention; Figure 2 It is the XRD diagram of lithium sulfide in Example 1 of the present invention; Figure 3 It is the XRD diagram of the synthesis of a sulfide solid electrolyte from lithium sulfide in Example 1 of the present invention. Detailed Embodiments

[0013] In view of the deficiencies of the prior art, the inventors of this case have, through long-term research and a large number of practices, been able to propose the technical solution of the present invention. The present invention uses the simplest dual-carbon (high-expansion carbon source and high-specific-surface-area activated carbon) mixed in proportion, and mixed with an S source and calcined to prepare high-purity lithium sulfide. This is conducive to reducing the cost of lithium sulfide and facilitating subsequent large-scale preparation, providing a guarantee for reducing the cost of sulfide solid electrolytes in the future.

[0014] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0015] Specifically, as an 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.

[0016] In some preferred embodiments, the high-specific-surface-area carbon source includes any one or a combination of activated carbon, porous carbon, carbon aerogel, and is not limited thereto.

[0017] In some preferred embodiments, the specific surface area of the high-specific-surface-area carbon source ≥ 1500 m² / g.

[0018] In some preferred embodiments, the high-expansion carbon source includes any one or a combination of sucrose, expanded graphite, graphene, and is not limited thereto.

[0019] In some preferred embodiments, the high-expansion carbon source is a carbon source with a volume expansion multiple ≥ 50 times.

[0020] In some preferred embodiments, the sulfur source includes any one or a combination of lithium sulfate, pyrite, sublimed sulfur, and is not limited thereto.

[0021] In some preferred embodiments, the lithium source includes any one or a combination of lithium sulfate, lithium carbonate, lithium hydroxide, and is not limited thereto.

[0022] 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; In some preferred embodiments, the molar ratio of the sulfur source to the lithium source is 1:2.

[0023] 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.

[0024] In some preferred embodiments, the preparation method specifically includes: Mixing the sulfur source, lithium source and composite reducing agent by ball milling in an inert atmosphere to obtain a mixed material; And subjecting the obtained mixed material to a low-temperature pre-reaction at 200-300 °C first, then to a high-temperature reduction reaction at 800-900 °C, and finally cooling to room temperature in an inert atmosphere to obtain a high-purity lithium sulfide material.

[0025] In some preferred embodiments, the preparation method specifically includes: in an inert atmosphere, heating the obtained mixed material to 200-300 °C at a heating rate of 5-10 °C / min for low-temperature pre-reaction, and then continuing to heat to 800-900 °C at a heating rate of 10-20 °C / min for high-temperature reduction reaction, and finally cooling to room temperature in an inert atmosphere to obtain a high-purity lithium sulfide material.

[0026] Further, the time of the low-temperature pre-reaction is 1-5 h.

[0027] Further, the time of the high-temperature reduction reaction is 2-6 h.

[0028] In some more specific embodiments, the high-purity lithium sulfide material and its preparation method, and further applying it to sulfide solid electrolytes and all-solid-state secondary batteries are as follows: (1) Optimization of raw material ratio Synergistic reduction of dual carbon sources: Mixing activated carbon (high specific surface area) and sucrose (high-expansion carbon source) in a specific ratio (such as 1:5-1:10) as a composite reducing agent.

[0029] Selection of sulfur source: Preferably, a lithium sulfide precursor (such as lithium sulfate) is uniformly mixed with a lithium source (such as lithium carbonate, lithium hydroxide).

[0030] (2) Innovation of calcination process Gradient heating control: The first stage (200-300 °C): Low-temperature pre-reaction, carbonization of sucrose, and reduction of sulfur volatilization loss; The second stage (800-900 °C): High-temperature reduction, activated carbon preferentially reacts to generate carbon dioxide to avoid residual carbon; The third stage (cooling in an inert atmosphere): Inhibiting the oxidation of lithium sulfide.

[0031] One-step synthesis: By matching the ratio of dual carbon sources with temperature, high-purity lithium sulfide is directly generated without post-treatment purification.

[0032] (3) Product application expansion Preparation of solid electrolyte: Lithium sulfide and sulfides such as phosphorus pentasulfide are ball-milled in proportion to form a sulfide solid electrolyte with a high ionic conductivity (>1× S / cm).

[0033] Integration of all-solid-state battery: It is paired with a lithium metal negative electrode and a high-nickel positive electrode (such as NCM9 series) to achieve an initial efficiency of 84%.

[0034] Another aspect of the embodiments of the present invention also provides a high-purity lithium sulfide material prepared by the foregoing preparation method.

[0035] Further, the purity of the high-purity lithium sulfide material >99.9%.

[0036] Another aspect of the embodiments of the present invention also provides a sulfide solid electrolyte, which is prepared by using the foregoing high-purity lithium sulfide material.

[0037] Another aspect of the embodiments of the present invention also provides the use of the foregoing high-purity lithium sulfide material or sulfide solid electrolyte in the preparation of secondary batteries.

[0038] Another aspect of the embodiments of the present invention also provides an all-solid-state secondary battery, which includes the foregoing high-purity lithium sulfide material or sulfide solid electrolyte.

[0039] The technical solutions of the present invention will be further described in detail below in conjunction with several preferred embodiments. These embodiments are implemented on the premise of the technical solutions of the invention, and the detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0040] The experimental materials used in the following embodiments can be obtained from conventional biochemical reagent companies without special instructions.

[0041] Example 1 I. Preparation of high-purity lithium sulfide (1) Raw material composition and ratio: Sulfur source and lithium source: Lithium sulfate (purity ≥99.5%); Composite carbon source: Activated carbon (specific surface area 1500 m² / g) and sucrose (purity ≥99.5%) are mixed in a mass ratio of 1:8. The molar ratio of lithium sulfate to sucrose is 1:3; (2) Preparation steps: Mixing: Lithium sulfate and the composite carbon source are ball-milled and mixed in an argon glove box for 2 hours (rotation speed 300 rpm, ball-to-material ratio 10:1); Calcination: First stage: Heat up to 250 °C at a rate of 5 °C / min and hold for 1 hour (in a nitrogen atmosphere); Second stage: Heat up to 820 °C at a rate of 10 °C / min and hold for 3 hours (in a nitrogen atmosphere); Third stage: Cool down to room temperature in the furnace (under nitrogen protection throughout the process).

[0042] (3)Product characteristics Morphology: White powder. The SEM image is as shown in Figure 1 and the XRD pattern is as shown in Figure 2 ; Crystal form: Cubic lithium sulfide (no impurity peaks in the XRD pattern).

[0043] II. Preparation of sulfide solid electrolyte (1)Raw material ratio: Lithium sulfide (product of Example 1): 1.3787 g; Phosphorus pentasulfide (purity ≥ 99%): 1.6674 g; LiCl (purity ≥ 99.9%): 0.9539 g.

[0044] (2)Preparation steps: Ball milling: The raw materials are dry ball milled in a planetary ball mill for 20 hours (rotation speed 500 r / min, zirconia grinding balls); Heat treatment: Heat up to 550 °C at a rate of 5 °C / min and anneal for 5 hours (in an Ar atmosphere) to obtain the sulfide solid electrolyte. The XRD pattern of the sulfide solid electrolyte is as shown in Figure 3 ;

[0045] (3)Product characteristics: Ionic conductivity: 8.5× S / cm (at 25 °C, by AC impedance method); III. Assembly and testing of all-solid-state battery Weigh 65 mg of LPSCl (purity 99.9%, conductivity 8.5× S / cm) and cold press it into a tablet in a 10 mm diameter PTFE mold under a pressure of 150 MPa for 1 minute. Add 40 mg of Li3InCl6 on one side under a pressure of 150 MPa for 1 minute. Then add 10 mg of the composite cathode material on the Li3InCl6 side under a pressure of 350 MPa for 3 minutes. Subsequently, add a 6 mm diameter LiIn foil with a lithium mass fraction of 2% on the LPSCl side and apply a pressure of 100 MPa for 0.5 minute. Fasten the positive and negative electrodes to form an all-solid-state lithium-ion battery.

[0046] Example 2 The method is the same as that of Example 1, except that: the mass ratio of activated carbon to sucrose is 1:5.

[0047] Example 3 The method is the same as that of Example 1, except that: the mass ratio of activated carbon to sucrose is 1:10.

[0048] Example 4 The method is the same as that of Example 1, except that: The first stage: heat up to 200 °C at a rate of 5 °C / min and hold for 1 hour (nitrogen atmosphere); The second stage: heat up to 800 °C at a rate of 10 °C / min and hold for 3 hours (nitrogen atmosphere); The third stage: cool down to room temperature in the furnace (nitrogen protection throughout the process).

[0049] Example 5 The method is the same as that of Example 1, except that: The first stage: heat up to 300 °C at a rate of 5 °C / min and hold for 1 hour (nitrogen atmosphere); The second stage: heat up to 900 °C at a rate of 10 °C / min and hold for 3 hours (nitrogen atmosphere); The third stage: cool down to room temperature in the furnace (nitrogen protection throughout the process).

[0050] Comparative Example 1 The method is the same as that of Example 1, except that: only sucrose is used as the carbon source.

[0051] Comparative Example 2 The method is the same as that of Example 1, except that: only activated carbon is used as the carbon source.

[0052] Comparative Example 3 The method is the same as that of Example 1, except that: there is no gradient heating, that is: in the calcination, directly heat up to 820 °C in the first stage and the second stage and treat for 4 h.

[0053] Comparative Example 4 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.

[0054] Comparative Example 5 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.

[0055] Comparative Example 6 The method is the same as that of Example 1, except that: gradient heating, first reach 190 °C and then reach 820 °C.

[0056] Comparative Example 7 The method is the same as that of Example 1, except that: gradient heating, first reach 310 °C and then reach 820 °C.

[0057] Comparative Example 8 The method is the same as that of Example 1, except that: the temperature is increased in a gradient manner, first reaching 250 °C and then 750 °C.

[0058] Comparative Example 9 The method is the same as that of Example 1, except that: the temperature is increased in a gradient manner, first reaching 250 °C and then 950 °C.

[0059] 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 for details.

[0060] Table 1 XRD purity of lithium sulfide, sulfide solid electrolyte in Examples 1-5 and Comparative Examples 1-9, ionic conductivity,

[0061] It can be seen from the above results that although sucrose is a source of pyrolytic "soft carbon", its specific surface area is extremely low, and the reduction efficiency is far lower than that of activated carbon. If the proportion of activated carbon is too low, the reduction is insufficient or uneven, the structural support is poor, and the phenomena of lithium sulfide agglomeration, carbon coating, and impurity inclusion are more serious. When the temperature is increased in a gradient manner, the temperature in the first stage activates the carbon structure change (for example, the expanded carbon expands fully at 300-400 °C); whether the temperature in the second stage is high enough for complete reduction (>700 °C); if the first-stage platform is too low or too short, it cannot play a role in structural reorganization / activation; if it is too high, there is a risk of agglomeration.

[0062] In addition, the inventors of this case also referred to the foregoing examples, and conducted tests with other raw materials, process operations, and process conditions described in this specification, and all obtained relatively ideal results.

[0063] It should be understood that the technical solutions of the present invention are not limited to the limitations of the above specific implementation cases. Any technical deformation made according to the technical solutions of the present invention without departing from the spirit of the present invention and the scope protected by the claims falls within the protection scope of the present invention.

Claims

1. A method for preparing a high-purity lithium sulfide material, characterized in that, Including: 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.

2. The preparation method according to claim 1, characterized in that: The high specific surface area carbon source includes any one or a combination of activated carbon, porous carbon, carbon aerogel, etc.; And / or, the specific surface area of the high specific surface area carbon source is ≥1500 m² / g; And / or, the high-expansion carbon source includes any one or a combination of sucrose, expanded graphite, graphene, etc.; And / or, the high-expansion carbon source is a carbon source with a volume expansion multiple ≥50 times; And / or, the sulfur source includes any one or a combination of lithium sulfate, pyrite, sublimed sulfur, etc.; And / or, the lithium source includes any one or a combination of lithium sulfate, lithium carbonate, lithium hydroxide, etc.

3. The preparation method according to claim 1, wherein: 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; And / or, the molar ratio of the sulfur source to the lithium source is 1:2; And / or, 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.

4. The preparation method according to claim 1, characterized in that, Specifically including: Ball-milling and mixing the sulfur source, the lithium source and the composite reducing agent in an inert atmosphere to obtain a mixed material; And, pre-reacting the obtained mixed material at 200-300 °C, then performing a high-temperature reduction reaction at 800-900 °C, and finally cooling to room temperature in an inert atmosphere to obtain a high-purity lithium sulfide material.

5. The preparation method according to claim 4, wherein Specifically including: In an inert atmosphere, heating the obtained mixed material to 200-300 °C at a heating rate of 5-10 °C / min for low-temperature pre-reaction, and then continuing to heat to 800-900 °C at a heating rate of 10-20 °C / min for high-temperature reduction reaction, and finally cooling to room temperature in an inert atmosphere to obtain a high-purity lithium sulfide material.

6. The preparation method according to claim 5, characterized in that: The time of the low-temperature pre-reaction is 1-5 h; And / or, the time of the high-temperature reduction reaction is 2-6 h.

7. A high-purity lithium sulfide material prepared by the preparation method according to any one of claims 1-6.

8. A sulfide solid electrolyte, characterized in that: The sulfide solid electrolyte is prepared from the high-purity lithium sulfide material according to claim 7.

9. Use of the high-purity lithium sulfide material according to claim 7 or the sulfide solid electrolyte according to claim 8 in the preparation of secondary batteries.

10. A all-solid-state secondary battery, characterized in that, Including the high-purity lithium sulfide material according to claim 7 or the sulfide solid electrolyte according to claim 8.

Images