A sulfide solid-state electrolyte and a preparation method and application thereof

Abstract

The application discloses a sulfide solid electrolyte Li 6+a+5b‑c‑bɛ P 1‑a‑b Sn a M b S 5‑c‑d X 1+c O d , formula (I); wherein M is one or more of Ge, Cu, Bi, Sb, Zr, Cd, V and Cr, ɛ is the average valence of M, X is one or more of F, Cl, Br and I, 0.01<=a+b<1, 0.1<=c<=0.75, 0.001<=d<=1; a preparation method comprises dry mixing raw materials according to the stoichiometric ratio of formula (I) under the conditions of inert protective atmosphere and waterless and oxygenless, then heat treating at 400-600 DEG C for 3-30 hours, and finally cooling to obtain a sulfide electrolyte; the application further discloses application of the sulfide solid electrolyte in a full solid battery; the sulfide solid electrolyte with a argyrodite crystal structure obtained by the application can be stably stored under air conditions without any coating layer or additive protection, and meanwhile, high room temperature ionic conductivity and low activation energy are ensured.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a sulfide solid electrolyte, its preparation method, and its application. Background Technology

[0002] Since the introduction of the first commercial lithium-ion battery in 1991, lithium-ion batteries have been widely used in various electronic devices due to their high energy density, good cycle performance, and rate performance. However, most commercial lithium-ion batteries currently use organic liquid electrolytes, which have a series of safety problems such as electrolyte leakage and lithium dendrite growth piercing the separator, leading to short circuits or even explosions, thus limiting the development and progress of lithium-ion batteries.

[0003] Solid-state batteries utilize inorganic solid electrolytes, which possess excellent thermal stability, thereby reducing the risk of battery fire and explosion and effectively improving battery safety and operating temperature range. Among the many types of solid electrolytes, sulfide electrolytes have the highest room-temperature ionic conductivity, closest to that of liquid electrolytes, and hold promise as a potential replacement for liquid electrolytes. However, their poor air stability makes them prone to reacting with water and oxygen in the air, leading to performance degradation.

[0004] To address the poor air stability of sulfide electrolytes, there are currently two main solutions. One is to improve it through the introduction of additives and surface protective layers (CN106887638A), and the other is to introduce elements such as O or N into the sulfide electrolyte (CN109970083A, CN111430808A), thereby enabling its mass use in air-conditioned environments / dry indoor environments. However, regardless of the method used, the reported work currently struggles to simultaneously achieve good air stability and high room temperature ionic conductivity.

[0005] Based on the above, it is necessary to provide a sulfide solid electrolyte that combines excellent chemical stability and high room temperature ionic conductivity in order to promote the practical commercial application of all-solid-state batteries. Summary of the Invention

[0006] Based on the hard and soft acid-base theory, current strategies for doping with soft acid metals or non-metallic elements such as O, N, and Se can effectively improve the air stability of electrolytes, but usually at the cost of reducing the room temperature ionic conductivity or increasing its activation energy (Chinese Patent CN108493479A). This invention provides a novel method for multi-element substitution to simultaneously improve the air stability and room temperature ionic conductivity of sulfide electrolytes. The resulting sulfide solid electrolyte with a sulfide-germanium sulfide crystal structure can be stably stored in air without any coating or additive protection.

[0007] One objective of this invention is to provide a multi-element co-doped silver-germanium sulfide electrolyte. By optimizing the doping amount and ratio of each element, the chemical properties of the material are controlled, thereby improving the air stability of the electrolyte material. Furthermore, by increasing the configurational entropy of the system through a multi-element co-doping strategy, the high room temperature ionic conductivity and low activation energy of the sulfide electrolyte are maintained while improving its air stability.

[0008] Specifically, by simultaneously replacing part of the P element with multiple elements from Sn, Ge, Cu, Bi, Sb, Zr, Cd, V, and Cr, and replacing part of the S element with O element, and by adjusting the ratio between the doping amount of the two doping elements and the halogen content, a sulfide solid electrolyte with higher air stability and room temperature ionic conductivity can be obtained.

[0009] Specifically, the present invention provides a sulfide solid electrolyte, as shown in formula (I): Li 6+a+5b-c-bɛ P 1-a-b Sn a M b S 5-c-d X 1+c O d (I); Where M is one or more of Ge, Cu, Bi, Sb, Zr, Cd, V, and Cr, ɛ is the average valence of M, X is one or more of F, Cl, Br, and I, 0.01≤a+b<1, 0.1≤c≤0.75, and 0.001≤d≤1.

[0010] Furthermore, the three strong characteristic peaks in the XRD diffraction pattern of the sulfide electrolyte are located at 25.5±0.5°, 30.1±0.5°, and 31.5±0.5°.

[0011] Furthermore, the sulfide electrolyte particles have a size of 200 nm-5 μm and a room temperature ionic conductivity of (6.0-12.0) mS·cm. -1 The activation energy is (0.20-0.36) eV.

[0012] A second objective of this invention is to provide a method for preparing the aforementioned multi-element doped sulfide solid electrolyte, comprising the following steps: Under a protective atmosphere (such as argon or nitrogen) and in an anhydrous and oxygen-free environment, the raw materials are dry-mixed according to a certain stoichiometric ratio, followed by high-temperature heat treatment, and finally cooled to obtain sulfide electrolyte.

[0013] As a preferred option, the raw material compound for doping element M is a sulfide or a halide, and the raw material compounds for doping elements X and O are lithium compounds or compounds doped with metals.

[0014] As a more preferred option, the raw material compound for doping element M is a sulfide, and the raw material compounds for doping elements X and O are lithium compounds.

[0015] Specifically, the raw material compound for doping element M is one or more of GeS2, Cu2S, Bi2S3, Sb2S5, ZrS2, CdS, V2S5, and CrS3; the raw material compound for doping element X is one or more of LiF, LiCl, LiBr, and LiI; and the raw material compound for doping element O is Li2O.

[0016] Furthermore, the rotation speed during dry mixing is 100-20000 rpm, preferably 10000-15000 rpm, and the dry mixing time is 3 minutes to 2 hours, preferably 5-10 minutes.

[0017] Furthermore, the heat treatment temperature is 400-600℃, preferably 480-550℃.

[0018] Furthermore, the heat treatment time is 3-30 hours, preferably 6-10 hours.

[0019] This invention employs multiple metal elements to co-dope the P-site, while using oxygen to replace part of the sulfur element. This results in a sulfide electrolyte with high room temperature ionic conductivity, good air stability, and low activation energy. Solid-state lithium-ion batteries assembled based on this electrolyte exhibit high discharge specific capacity and good cycle stability.

[0020] The third objective of this invention is to provide the application of the above-mentioned sulfide solid electrolyte in all-solid-state batteries.

[0021] Furthermore, the specific application process is as follows: the prepared sulfide electrolyte or its mixture with the binder is pressed into a sheet, and then the positive electrode, negative electrode and current collector are prepared on the upper and lower surfaces of the obtained electrolyte sheet, respectively.

[0022] Furthermore, the mass percentage content of the sulfide solid electrolyte in the mixture of sulfide solid electrolyte and binder is not less than 80%.

[0023] Furthermore, the adhesive is selected from at least one of polytetrafluoroethylene (PTFE) and polyamide (TPA).

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) A multi-element co-doped oxygen-containing sulfide electrolyte was developed, which effectively improves air stability while ensuring high room temperature ionic conductivity and low activation energy.

[0025] (2) By adjusting and optimizing the doping amount and doping ratio of various metal / oxygen elements with different valence states, the overall performance of the electrolyte was improved.

[0026] (3) The entire process is relatively simple, does not involve high-pressure reaction conditions and expensive large-scale chemical equipment, and has the advantages of high output value and suitability for large-scale preparation. The performance of the sulfide electrolyte and solid lithium-ion battery prepared according to the method of this invention is significantly improved, which helps to accelerate the commercialization and application of all-solid-state lithium-ion batteries. Attached Figure Description

[0027] Figure 1 SEM images of the solid electrolytes prepared in Examples 1-3 and Comparative Examples 1-3.

[0028] Figure 2 The XRD patterns are of the solid electrolytes prepared in Examples 1-3 and Comparative Examples 1-3.

[0029] Figure 3 This is a comparison chart of air exposure time and hydrogen sulfide production for the solid electrolytes prepared in Examples 1-3 and Comparative Examples 1-3.

[0030] Figure 4 The images show the AC impedance spectra of the solid electrolytes prepared in Examples 1-3 and Comparative Examples 1-3.

[0031] Figure 5 This is a comparison chart of the cycle performance of all-solid-state lithium batteries assembled using the solid electrolytes prepared in Example 3 and Comparative Example 1.

[0032] Figure 6 The battery cycle performance diagram is for Application Example 1.

[0033] Figure 7 The battery cycle performance diagram is for Application Example 2. Detailed Implementation

[0034] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0035] Example 1 Li 5.6 P 0.9 Sn 0.05 Ge 0.05 S 4.47 Cl 1.5 O 0.03 A method for preparing sulfide electrolytes, comprising the following steps: (1) At 10000 rpm, Li2O, LiCl, Li2S, P2S5, SnS2 and GeS2 were dry-mixed for 3 minutes in a molar ratio of 0.03 : 1.5 : 2.02 : 0.45 : 0.05 : 0.05 to obtain a mixture; (2) The mixture was heat-treated at 500°C for 8 hours to obtain Li. 5.6 P 0.9 Sn 0.05 Ge 0.05 S 4.47 Cl 1. 5O 0.03 Sulfide electrolytes.

[0036] Example 2 Li 5.6 P 0.9 Sn 0.04 Bi 0.03 Sb 0.03 S 4.46 Cl 1.5 O 0.04 A method for preparing sulfide electrolytes, comprising the following steps: (1) At 10000 rpm, Li2O, LiCl, Li2S, P2S5, SnS2, Bi2S3, and Sb2S5 were dry-mixed for 3 minutes in a molar ratio of 0.04:1.5:2.01:0.45:0.04:0.015:0.015 to obtain a mixture; (2) The mixture was heat-treated at 500°C for 8 hours to obtain Li. 5.6 P 0.9 Sn 0.04 Bi 0.03 Sb 0.03 S 4.4 6Cl 1.5 O 0.04 Sulfide electrolytes.

[0037] Example 3 Li 5.63 P 0.9 Sn 0.03 Ge 0.02 Cu 0.01 Bi 0.02 Sb 0.02 S 4.45 Cl 1.5 O 0.05 A method for preparing sulfide electrolytes, comprising the following steps: (1) At 10000 rpm, Li2O, LiCl, Li2S, P2S5, SnS2, GeS2, Cu2S, Bi2S3, and Sb2S5 were dry-mixed for 3 minutes in a molar ratio of 0.05 : 1.5 : 2.015 : 0.45 : 0.03 : 0.02 : 0.005 : 0.01 : 0.01 to obtain a mixture; (2) The mixture was heat-treated at 500°C for 8 hours to obtain Li. 5.63 P 0.9 Sn 0.03 Ge 0.02 Cu 0.01 Bi 0.02 Sb 0.02 S 4.45 Cl 1.5 O 0.05 Sulfide electrolytes.

[0038] Comparative Example 1 Li 5.5 PS 4.5 Cl 1.5 A method for preparing sulfide electrolytes, comprising the following steps: (1) At 10000 rpm, LiCl, Li2S and P2S5 were dry-mixed for 3 minutes in a molar ratio of 1.5:2:0.5 to obtain a mixture; (2) The mixture was heat-treated at 500°C for 8 hours to obtain Li. 5.5 PS 4.5 Cl 1.5 Sulfide electrolytes.

[0039] Comparative Example 2 Li 5.6 P 0.9 Sn 0.1 S 4.5 Cl 1.5 A method for preparing sulfide electrolytes, comprising the following steps: (1) At 10000 rpm, LiCl, Li2S, P2S5 and SnS2 were dry-mixed for 3 minutes in a molar ratio of 1.5:2.05:0.45:0.1 to obtain a mixture; (2) The mixture was heat-treated at 500°C for 8 hours to obtain Li. 5.6 P 0.9 Sn 0.1 S 4.5 Cl 1.5 Sulfide electrolytes.

[0040] Comparative Example 3 Li 5.6 P 0.9 Sn 0.1 S 4.4 Cl 1.5 O 0.1 A method for preparing sulfide electrolytes, comprising the following steps: (1) At 10000 rpm, Li2O, LiCl, Li2S, P2S5 and SnS2 were dry-mixed for 3 minutes in a molar ratio of 0.1 : 1.5 : 1.95 : 0.45 : 0.1 to obtain a mixture; (2) The mixture was heat-treated at 500°C for 8 hours to obtain Li. 5.6 P 0.9 Sn 0.1 S 4.4 Cl 1.5 O 0.1 Sulfide electrolytes.

[0041] To fully understand the structure and chemical properties of the sulfide electrolytes prepared in Examples 1-3 and Comparative Examples 1-3, samples were taken and tested, as follows: (1) Scanning electron microscopy (SEM) test Figure 1 The images show SEM comparisons of the solid-state electrolytes prepared in Examples 1-3 and Comparative Examples 1-3. As can be seen from the images, the electrolyte particle size distribution in Example 1 is approximately 500 nm to 6 μm, in Example 2 it is approximately 300 nm to 5 μm, in Example 3 it is approximately 200 nm to 3 μm, in Comparative Example 1 it is approximately 2 μm to 10 μm, in Comparative Example 2 it is approximately 1 μm to 6 μm, and in Comparative Example 3 it is approximately 1 μm to 5 μm. That is, the average size of the products from the examples is less than the average size of the products from the comparative examples. This also explains the difference in performance between the all-solid-state batteries assembled using the examples and the comparative examples.

[0042] (2) X-ray diffraction (XRD) test Figure 2 The XRD patterns of the solid electrolytes prepared in Examples 1-3 and Comparative Examples 1-3 are shown. As can be seen from the figures, the sulfide electrolytes prepared in the examples and comparative examples each have a characteristic peak at 25.5±0.5°, 30.1±0.5°, and 31.5±0.5°, and there are no diffraction peaks from other raw materials, indicating that the prepared sulfide electrolyte samples are pure phases. The relative intensities of the diffraction peaks differ to some extent, but all satisfy (I1+I3) / I2=1.80±0.20.

[0043] (3) Air stability (H2S production under air exposure) test Figure 3 This is a comparison graph showing the air exposure time-hydrogen sulfide yield of the solid electrolytes prepared in Examples 1-3 and Comparative Examples 1-3. 100 mg of sulfide electrolyte powder was pressed into 10 mm particles at 150 MPa; the particles were then subjected to an air exposure time of 40000 cm⁻¹. 3 The container was exposed to moist nitrogen gas (40% relative humidity) containing water vapor for 30 minutes. The amount or content of H2S gas produced was calculated by measuring the H2S concentration using an H2S gas sensor.

[0044] (4) Temperature-dependent impedance test Samples were taken for variable-temperature AC impedance spectroscopy (ACIS) testing. The specific testing procedure is as follows: 0.1 g of electrolyte powder sample was weighed and pressed into a sheet at 150 MPa. Stainless steel was attached to both sides of the resulting electrolyte sheet as current collectors. AC impedance spectroscopy was performed on the electrolyte ceramic sheet using an electrochemical workstation (ZAHNER, Zennium Pro) in the frequency range of 8 MHz to 1 Hz to obtain its impedance. Test conditions: amplitude of 10 mV, data collected every 10 °C within the temperature range of 10-60 °C. Impedance data at 25 °C was used to calculate the room temperature ionic conductivity.

[0045] Based on the temperature-dependent impedance testing results, the ionic conductivity of each electrolyte sample at different temperatures was calculated, including the room temperature ionic conductivity. The formula for calculating the ionic conductivity is: σ = L / RS L is the thickness of the electrolyte sheet, R is the impedance of the electrolyte, and S is the contact area.

[0046] Based on the ionic conductivity of each sample at different temperatures, the activation energy E of each electrolyte sample was calculated using the following Arrhenius equation. a :

[0047] Where T is the absolute temperature, A is the exponential factor, and k is the absolute temperature. B It is the Boltzmann constant.

[0048] The AC impedance test results of the electrolyte samples prepared in Examples 1-3 and Comparative Examples 1-3 before and after exposure to air are as follows: Figure 4-5 As shown in Table 1, the ionic conductivity retention rate and temperature-dependent impedance test results obtained from this calculation are presented in Table 1.

[0049] Table 1

[0050] Depend on Figure 4-5As shown in Table 1, sulfide electrolytes with more element doping exhibit superior air stability, higher room temperature ionic conductivity, and lower activation energy.

[0051] Application Example 1 Weigh 100 mg of the sulfide electrolyte powder prepared in Example 3 or Comparative Example 1, pour it into a 10 mm diameter PEEK mold, and press it into an electrolyte layer under 150 MPa. Add the single-crystal nickel-cobalt-manganese ternary cathode material LiNi according to a weight ratio of 70:30:3. 0.9 Co 0.05 Mn 0.05 O2 (NCM90), the sulfide electrolyte powder prepared in Example 3 or Comparative Example 1, and carbon nanotubes (CNTs) were mixed. The resulting mixture was manually ground for 1 hour to obtain a composite cathode powder. A certain amount of the composite cathode powder was weighed and uniformly spin-coated onto one side of the sulfide electrolyte layer. The composite cathode layer was then pressed at 50 MPa. On the other side of the electrolyte layer, a lithium sheet with a diameter of 4 mm and a thickness of 10 μm and an indium sheet with a diameter of 8 mm and a thickness of 50 μm were sequentially attached. The negative electrode layer was then pressed at 100 MPa. Finally, the assembled battery was placed in a Schweilock battery mold and cold-pressed at 150 MPa. Stainless steel gaskets were added to both sides of the battery as current collectors, thus completing the assembly of the all-solid-state battery.

[0052] At 1C rate and current density of 1.78 mA·cm -2 Active substance loading: 8.65 mg / cm³ -2 And under 30℃ conditions, charge-discharge cycle tests were conducted on two groups of all-solid-state batteries, and the results are as follows: Figure 6 As shown. During the test, the coulombic efficiency of the battery group in Example 3 was greater than 75% in the first cycle (0.1C), and it could release 191 mAh·g. -1 The specific capacity is high, and it can still release more than 160 mAh·g after 100 cycles at 1C rate. -1 The specific capacity of the first group of batteries was significantly higher than that of the first group (0.1C), while the coulombic efficiency of the first group of batteries was only 68%, and the specific capacity decreased from 130 mAh·g after 100 cycles at 1C. -1 Reduced to 120mAh·g -1 The discharge specific capacity and cycle stability of the following batteries are lower than those of the batteries in Example 3.

[0053] Application Example 2 A certain mass of the sulfide electrolyte powder prepared in Example 3 was weighed and mixed with polytetrafluoroethylene (PTFE) at a weight ratio of 98.5:1.5, followed by hot rolling to obtain Li. 5.68 P 0.9 Sn 0.02 Ge 0.02 Cu 0.02Bi 0.02 Sb 0.02 S4Cl 1.5 O0 .5 -PTFE composite electrolyte film. Single-crystal nickel-cobalt-manganese ternary cathode material LiNi was mixed at a weight ratio of 70:30:3. 0.9 Co 0.05 Mn 0.05 O2 (NCM90), the sulfide electrolyte powder prepared in Example 3, and carbon nanotubes (CNTs) were mixed and manually ground for 1 hour to obtain a composite cathode powder. A certain amount of the composite cathode powder was weighed and uniformly spin-coated onto one side of the composite electrolyte membrane, and pressed at 50 MPa to obtain a composite cathode layer. Subsequently, a lithium sheet with a diameter of 4 mm and a thickness of 10 μm and an indium sheet with a diameter of 8 mm and a thickness of 50 μm were sequentially attached to the other side of the composite electrolyte membrane, and pressed at 100 MPa to obtain a negative electrode layer. Finally, the assembled battery was cold-pressed at 150 MPa for 3 minutes, and stainless steel gaskets were added to both sides of the battery as current collectors, thus completing the assembly of the all-solid-state battery.

[0054] At 1C rate and current density of 1.78 mA·cm -2 Active substance loading: 8.65 mg / cm³ -2 And under 30°C, the above-mentioned all-solid-state battery was subjected to charge-discharge cycle tests, and the results are as follows: Figure 7 As shown. During the test, the battery's coulombic efficiency was greater than 80% in the first cycle (0.1C), and it could release more than 100 mAh·g after 50 cycles at 1C. -1 Specific capacity.

Claims

1. A sulfide solid electrolyte, characterized in that... The composition is as follows: Li 5.63 P 0.9 Sn 0.03 Ge 0.02 Cu 0.01 Bi 0.02 Sb 0.0 2S 4.45 Cl 1.5 O 0.05 ; The three strong characteristic peaks in the XRD diffraction pattern of the sulfide solid electrolyte are located at 25.5±0.5°, 30.1±0.5°, and 31.5±0.5°. The sulfide solid electrolyte particles have a size of 200 nm to 5 μm and an ionic conductivity of 6.0 to 12.0 mS·cm at room temperature. -1 The activation energy is 0.20-0.36 eV.

2. The method for preparing the sulfide solid electrolyte according to claim 1, characterized in that... Includes the following steps: Under an inert protective atmosphere and in an anhydrous and oxygen-free environment, according to the chemical formula Li 5.63 P 0.9 Sn 0.03 Ge 0.02 Cu 0.01 Bi 0.02 Sb 0.0 2S 4.45 Cl 1.5 O 0.05 The raw materials are dry-mixed according to the stoichiometric ratio, then heat-treated at 400-600℃ for 3-30 hours, and finally cooled to obtain sulfide electrolyte.

3. The method for preparing the sulfide solid electrolyte as described in claim 2, characterized in that... The dry mixing speed is 100-20000 rpm, and the dry mixing time is 3 minutes to 2 hours.

4. The method for preparing the sulfide solid electrolyte as described in claim 2, characterized in that... The heat treatment temperature is 480-550℃; the heat treatment time is 6-10 hours.

5. The application of the sulfide solid electrolyte of claim 1 in all-solid-state batteries, characterized in that... The process includes pressing the sulfide solid electrolyte or a mixture thereof with a binder into a sheet, and then preparing a positive electrode, a negative electrode, and a current collector on the upper and lower surfaces of the resulting electrolyte sheet, respectively.

6. The application of the sulfide solid electrolyte as described in claim 5 in all-solid-state batteries, characterized in that... The sulfide solid electrolyte and binder mixture contains at least 80% sulfide solid electrolyte by mass percentage; the binder is selected from at least one of polytetrafluoroethylene and polyamide.

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