A sulfide solid-state electrolyte based on gradient hot-pressing reaction and a preparation method thereof

Abstract

The application relates to the technical field of solid electrolytes, and particularly discloses a sulfide solid electrolyte based on gradient hot-pressing reaction and a preparation method thereof. The preparation method of the sulfide solid electrolyte comprises the following steps: S1, under the protection of an inert atmosphere, LiCl, Li2S and P2S5 are mixed and ball milled according to a stoichiometric ratio of a target product to obtain a precursor powder; S2, a sulfur slow-release agent is added to the precursor powder to form a precursor compound; S3, the precursor compound is placed in a reaction container, the reaction container comprises an inner cavity and an outer cavity, the precursor compound is placed in the inner cavity, and a vapor-selective-permeation structure is arranged between the outer cavity and the inner cavity of the reaction container; S4, gradient hot-pressing reaction is carried out; S5, cooling is carried out to obtain the sulfide solid electrolyte. Through the gradient hot-pressing reaction, the sulfur compensation amount and the crystal phase growth kinetics can be accurately controlled.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid electrolyte, in particular to a sulfide solid electrolyte based on gradient hot-pressing reaction and a preparation method thereof. BACKGROUND

[0002] Sulfide solid electrolyte is considered as the core material of the next generation of high energy density batteries due to its ultra-high ionic conductivity (>5 mS / cm) and excellent interface compatibility. However, its synthesis process has the following technical bottlenecks:

[0003] 1. Dynamic loss of sulfur element: In the traditional process, sulfide raw materials (such as Li2S, P2S5) continuously volatilize sulfur (S) due to its low boiling point (444.6℃) during high-temperature reaction (>600℃), resulting in deviation of the product from the stoichiometric ratio of LiPSX, and a 30%-50% decrease in conductivity.

[0004] 2. Exogenous sulfur compensation defects: Existing technologies (such as CN113582365A) compensate for sulfur by externally introducing S vapor or mixed gas, but there are problems such as complex equipment, uneven sulfur distribution, and high cost.

[0005] 3. Poor reaction uniformity: The temperature gradient in the traditional reaction device is large, which easily leads to local overburning or unreacted areas, and the product grain boundary resistance increases.

[0006] Therefore, it is urgent to develop a controllable synthesis process with low sulfur loss rate and high product purity. SUMMARY

[0007] In view of this, the present application provides a sulfide solid electrolyte and a preparation method thereof. The present application uses in-situ sulfur compensation technology to release S vapor by decomposing sodium thiosulfate (Na2S2O3) and dynamically supplementing the volatilized sulfur, without the need for external sulfur supply equipment.

[0008] The technical scheme provided by the present application is as follows:

[0009] First aspect: a preparation method of a sulfide solid electrolyte, comprising the following steps:

[0010] S1. Under the protection of an inert atmosphere, LiCl, Li2S, and P2S5 are mixed and ball milled according to the stoichiometric ratio of the target product to obtain a precursor powder;

[0011] S2. A sulfur slow-release agent is added to the precursor powder to form a precursor composite;

[0012] S3. The precursor composite is placed in a reaction container, the reaction container comprising an inner cavity and an outer cavity; the precursor composite is placed in the inner cavity; and a vapor-selective permeation structure is arranged between the outer cavity and the inner cavity of the reaction container;

[0013] S4, performing gradient hot-pressing reaction, comprising the following steps:

[0014] a, sulfur vapor releasing stage: the reaction container is heated to above the thermal decomposition temperature of the sulfur release agent, and the pressure is controlled to generate and diffuse sulfur vapor to the outer cavity; b, directional permeation synthesis stage: under constant temperature, the sulfur vapor is guided to be directionally transmitted to the inner cavity through the vapor selective permeation structure, and permeates to the inner cavity to react with the precursor complex;

[0015] c, gradient pressure relief and impurity removal stage: the temperature is lowered to the target temperature interval, and the pressure is simultaneously adjusted to be lower than the sulfur vapor saturation pressure to discharge the unreacted residual sulfur;

[0016] S5, cooling to obtain the sulfide solid-state electrolyte.

[0017] In the preparation method, the sulfur vapor first diffuses to the outer cavity and then returns to the inner cavity. The core role is that if the sulfur vapor generated by the decomposition of the sulfur release agent directly reacts in the inner cavity, it is easy to cause the local sulfur concentration to be too high, forming sulfur elemental agglomeration or non-uniform crystallization. Through the diffusion process in the outer cavity, the vapor selective permeation structure can be used to screen and buffer the sulfur vapor, so that the proportion of the sulfur vapor molecules (such as S2 and S4) returning to the inner cavity is more in line with the stoichiometric requirement of the target product. The proportion of S4 molecules is increased at high temperature, and the higher reactivity of S4 molecules helps to promote the formation of the crystal phase of the sulfide electrolyte.

[0018] The key of the gradient hot-pressing reaction is to discharge the low-boiling-point impurities (such as unreacted Li2S decomposition products) in the precursor complex together with the sulfur vapor through the pressure difference between the outer cavity and the inner cavity (the pressure is controlled in step a of S4 to diffuse the sulfur vapor outward). In the subsequent temperature lowering stage (step c of S4), the unreacted sulfur vapor is preferentially discharged from the outer cavity by reducing the pressure in the inner cavity, so as to avoid the impurities remaining in the electrolyte to cause the decrease of the ionic conductivity.

[0019] In step S2, the sulfur release agent is selected from at least one of thiosulfate, thiocyanate and thiourea, and the addition amount is 1%-15% of the total mass of the precursor powder.

[0020] In step S3, the reaction container is a porous ceramic membrane reactor; the material of the vapor selective permeation structure is an Al2O3, ZrO2 or SiO2 film, the pore size is 0.1-5 μm, and the thickness is 0.1-3 mm.

[0021] The sulfur vapor releasing stage meets the following conditions: the heating rate is 5-20℃ / min; and the controlled pressure is 0.5-3 atm.

[0022] The directional permeation synthesis stage meets the following conditions: the constant temperature is 600-750℃; and the constant temperature time is 1-10 hours.

[0023] The gradient pressure relief and impurity removal stage meets the following conditions: programmed cooling at a rate of 0.1-1 ℃ / min to 300-500 ℃; and simultaneously adjusting the system pressure to 0.2-1 atm.

[0024] The ball milling conditions in step S1 are as follows: ball milling time 0.5-5 hours, ball-to-material ratio 5:1-20:1, and ball milling rotation speed 300-500 rmp.

[0025] The sulfide solid electrolyte is Li6PS5Cl.

[0026] The sulfide solid electrolyte prepared by the preparation method described above also belongs to the protection scope of the present application.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] 1. Precise control of sulfur release and reaction: Through the in-situ sulfur compensation technology, sodium thiosulfate (Na2S2O3) is used to release S vapor and dynamically supplement the volatile sulfur, without the need for external sulfur supply equipment. The synchronization of sulfur release rate and reaction consumption is achieved, which enables precise compensation of the dynamic loss of sulfur element in the reaction, effectively avoiding the product composition imbalance problem caused by the inability to precisely compensate for the dynamic loss of sulfur element in high-temperature reactions, thereby improving product quality and stability.

[0029] 2. Small product sulfur content deviation: The three-stage temperature control (heating-constant temperature-gradient cooling) combined with the pressure feedback system optimizes the sulfur vapor diffusion path, significantly reduces the product sulfur content deviation, and reduces the grain boundary resistance, which helps to improve the electrical performance and other related indicators of the product, and improves the product quality.

[0030] 3. Improve sulfur distribution uniformity: The inner layer of the reaction cavity is loaded with precursors, and the outer layer is permeated with sulfur vapor to achieve in-situ release and uniform distribution of sulfur vapor. Combined with the gradient temperature and pressure program, the sulfur compensation amount and crystal phase growth kinetics are precisely controlled.

[0031] Improve the electrical conductivity, which is conducive to improving the uniformity of the overall reaction and the consistency of product performance, and has important significance in the production of products related to sulfur reactions, and can improve the comprehensive performance and production efficiency of the products. BRIEF DESCRIPTION OF DRAWINGS

[0032] Other features, objects, and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings:

[0033] Figure 1 The grain boundary resistance column chart (a) and the ionic conductivity column chart (b) of Examples 1-2 and Comparative Examples 1-5 are shown in the following table:

[0034] Figure 2 Morphology of Li6PS5Cl for Example 1;

[0035] Figure 3 Sulfur element concentration distribution for Example 1. DETAILED DESCRIPTION

[0036] The application will be described in detail below with reference to examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the application. These are within the scope of protection of the application.

[0037] Example 1

[0038] (1) LiCl, Li2S, P2S5 were weighed according to the stoichiometric ratio of Li6PS5Cl, and ball-milled for 2 h (zirconia balls, ball-to-material ratio 10:1, rotation speed 300 rpm, Ar protection); a uniform precursor powder was obtained.

[0039] (2) Sulfur slow-release agent Na2S2O3 (5% of the total mass of the precursor) was added to the precursor powder, and mixed uniformly to obtain a precursor composite;

[0040] (3) Separate cavity loading: a porous ceramic membrane reactor (Hefei Shijie Membrane Engineering Co., Ltd. ceramic composite membrane tube, channel number 7)

[0041] Inner cavity: loading the precursor composite;

[0042] Outer cavity: prepositioning a porous Al2O3 membrane (pore size 0.5 μm, thickness 1 mm), which means prepositioning a porous alumina Al2O3 membrane in the outer cavity of the porous ceramic membrane reactor; its main role is to form a transmission channel for sulfur vapor, allowing the sulfur vapor generated in the sulfur permeation synthesis stage to pass through, and at the same time it may play a role in filtering or controlling the vapor transmission rate to promote the growth of Li6PS5Cl crystal phase.

[0043] (4) Gradient temperature control reaction;

[0044] Sulfur vapor release stage: heating to 650℃ at a rate of 15℃ / min, pressure maintained at 1 atm, Na2S2O3 decomposed to release S vapor (reaction: Na2S2O3→ Na2SO3+ S↑);

[0045] Sulfur permeation synthesis stage: constant temperature 650℃ for 3 h, pressure increased to 2 atm to promote the permeation of sulfur vapor through the Al2O3 membrane; Li6PS5Cl crystal phase growth was completed.

[0046] Gradient temperature reduction and sulfur removal stage: gradient temperature reduction to 400℃ at 0.5℃ / min, and synchronous pressure reduction to 0.5 atm, to remove unreacted residual sulfur;

[0047] (5) Post-processing; after cooling to room temperature, the product was taken out, ground and sieved (particle size <10 μm), and packaged and stored in an Ar glove box.

[0048] The morphology of Li6PS5Cl prepared in this example is as shown in Figure 2 , and the concentration distribution of sulfur element is as shown in Figure 3 .

[0049] Example 2

[0050] (1) LiCl, Li2S and P2S5 were weighed according to the stoichiometric ratio of Li6PS5Cl, and ball-milled (zirconia ball, ball-to-material ratio 10:1, rotation speed 300 rpm, Ar protection) for 2 h; a uniform precursor powder was obtained.

[0051] (2) Sulfur slow-release agent Na2S2O3 (8% of the total mass of the precursor) was added to the precursor powder, and mixed uniformly to obtain a precursor mixture.

[0052] (3) Separate-chamber loading: a porous ceramic membrane reactor

[0053] Inner chamber: loading the precursor mixture;

[0054] Outer chamber: pre-installing a porous Al2O3 membrane (pore size 0.5 μm, thickness 1 mm) to form a sulfur vapor transmission channel.

[0055] (4) Gradient temperature control reaction;

[0056] Sulfur vapor release stage: heating to 650℃ at 15℃ / min, pressure maintained at 1 atm, Na2S2O3 decomposed to release S vapor (reaction formula: Na2S2O3→ Na2SO3+ S↑);

[0057] Sulfur permeation synthesis stage: constant temperature 650℃ for 4 h, pressure increased to 2 atm to promote the permeation of sulfur vapor through the Al2O3 membrane; Li6PS5Cl crystal phase growth was completed;

[0058] Gradient temperature reduction and sulfur removal stage: gradient temperature reduction to 400℃ at 0.5℃ / min, and synchronous pressure reduction to 0.5 atm, to remove unreacted residual sulfur.

[0059] (5) Post-processing; after cooling to room temperature, the product was taken out, ground and sieved (particle size <10 μm), and packaged and stored in an Ar glove box.

[0060] Comparative Example 1

[0061] Comparative Example 1 differs from Example 1 in that no sulfur release agent Na2S2O3 is added.

[0062] Comparative Example 2

[0063] Comparative Example 2 differs from Example 1 in that the sulfur release agent Na2S2O3 is replaced by sublimed sulfur.

[0064] Comparative Example 3

[0065] Comparative Example 3 differs from Example 1 in that the sulfur release agent Na2S2O3 is replaced by ammonium thiosulfate ((NH4)2S2O3), which results in the release of sulfur along with SO2 (a corrosive gas) and NH3, which requires complex tail gas treatment; and the sulfur release rate is fast, but the byproduct SO2 reacts with lithium salts to form Li2SO3 impurities.

[0066] Comparative Example 4

[0067] Comparative Example 4 differs from Example 1 in that the sulfur release agent Na2S2O3 is replaced by sodium sulfate (Na2SO4).

[0068] Result: The introduction of oxygen elements causes the sulfide electrolyte to oxidize (e.g., to form Li3PO4); the sulfur utilization rate is approximately 0% (Li6PS5Cl cannot be formed), and the product is a mixture of oxide impurities.

[0069] Comparative Example 5: Traditional solid-phase sintering method

[0070] Raw material mixing: LiCl, Li2S, P2S5, and sulfur powder (total sulfur amount is the same as in Example 1) were weighed according to the stoichiometric ratio of Li6PS5Cl and ball-milled for 2 hours under argon protection (ball-to-material ratio of 10:1, rotation speed of 300 rpm);

[0071] Direct sintering: The mixed powder was placed in a single-cavity reaction furnace and heated to 650°C at a rate of 15°C / min, and then held at atmospheric pressure (1 atm) for 3 hours;

[0072] Natural cooling: The furnace was cooled to room temperature, and the product was ground and sieved (particle size <10 μm).

[0073] Performance testing

[0074] Performance testing was performed on Examples 1-2 and Comparative Examples 1-5.

[0075] Test method:

[0076] The AC impedance method is to input small amplitude sinusoidal wave voltage (or current) AC signal into the measured system under equilibrium state, analyze the frequency spectrum signal of the response of the measured system, and then obtain the impedance of the system at different frequencies to form a map. This method is widely used in the measurement of lithium ion solid electrolyte ionic conductivity. According to the blocking electrode metal Li / electrolyte material Li6PS5Cl prepared in the examples and comparative examples, the blocking electrode metal Li is constructed into a symmetrical battery, then the impedance spectrum of the battery is measured by using an electrochemical impedance spectrum device, the total impedance contributed by the electrolyte itself is determined by analyzing the spectrum data, finally the lithium ion conductivity value of the sample is calculated combined with the size of the measured electrolyte sample, and the ionic conductivity σ is calculated according to the following formula: σ = d / R×S, wherein d is the thickness (cm) of the measured sample; R is the bulk impedance (ohm) of the measured sample; S is the effective area of the electrode (cm 2 ), and the measured value is 0.785 cm 2 . The results are shown in Table 1:

[0077] Table 1

[0078]

[0079] Figure 1 The results are shown in Table 1:

[0080] The above describes the specific embodiments of the present application. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various modifications or modifications within the scope of the claims, which does not affect the essential content of the present application.

Claims

1. A method for producing a sulfide solid electrolyte based on a gradient hot-pressing reaction, characterized by, The method comprises the following steps: S1. Under the protection of an inert atmosphere, LiCl, Li2S, and P2S5 are mixed and ball milled according to the stoichiometric ratio of the target product to obtain a precursor powder; S2. A sulfur release agent is added to the precursor powder to form a precursor composite; the sulfur release agent is sodium thiosulfate; S3. The precursor composite is placed in a reaction container, which comprises an inner cavity and an outer cavity; the precursor composite is placed in the inner cavity; and a vapor-selective permeation structure is arranged between the outer cavity and the inner cavity of the reaction container; S4. A gradient hot-pressing reaction is performed, comprising the following steps: a. a sulfur vapor release stage: the reaction container is heated to a temperature above the thermal decomposition temperature of the sulfur release agent, and the pressure is controlled to generate sulfur vapor and diffuse it to the outer cavity; b. a directional permeation synthesis stage: at a constant temperature, the sulfur vapor is guided to the inner cavity through the vapor-selective permeation structure, permeates into the inner cavity, and reacts with the precursor composite; c. a gradient pressure relief and impurity removal stage: the temperature is lowered to a target temperature range, and the pressure is simultaneously adjusted to be lower than the sulfur vapor saturation pressure to remove the unreacted residual sulfur; S5. Cooling to obtain the sulfide solid-state electrolyte.

2. The production method according to claim 1, characterized by, In step S2, the amount of sodium thiosulfate added is 1%-15% of the total mass of the precursor powder.

3. The preparation method according to claim 1, characterized in that, In step S3, the vapor-selective permeation structure is a porous ceramic membrane; the material of the porous ceramic membrane is Al2O3, ZrO2, or SiO2, the pore size is 0.1-5 μm, and the thickness is 0.1-3 mm.

4. The method of claim 1, wherein, The sulfur vapor release stage satisfies the following conditions: the heating rate is 5-20℃ / min; and the controlled pressure is 0.5-3 atm.

5. The preparation method according to claim 1, characterized in that, The directional permeation synthesis stage satisfies the following conditions: the constant temperature is 600-750℃; and the constant temperature time is 1-10 hours.

6. The method of claim 1, wherein, The gradient pressure relief and impurity removal stage satisfies the following conditions: the temperature is lowered at a rate of 0.1-1℃ / min to 300-500℃; and the system pressure is simultaneously adjusted to 0.2-1 atm.

7. The preparation method according to claim 1, characterized in that, In step S1, the ball milling conditions are as follows: the ball milling time is 0.5-5 hours, the ball-to-material ratio is 5:1-20:1, and the ball milling speed is 300-500 rmp.

8. The method of claim 1, wherein, The sulfide solid-state electrolyte is Li6PS5Cl.

9. A sulfide solid-state electrolyte based on a gradient hot-pressing reaction obtained by the preparation method according to any one of claims 1-8.

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