Lithium-rich high-temperature sulfide electrolyte

Abstract

The present invention provides a high-temperature resistant sulfide solid electrolyte rich in lithium, which contains at least the elements of lithium (Li), phosphorus (P), and sulfur (S). The material structure factor Δ is 781 ± 1 to 1300 ± 1, where Δ = {N(Li) × 312.5 + N(P) × 346} × 4. In the formula, N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, and N(Li) ≥ 0.25. The sulfide solid electrolyte of the present invention has high thermal stability and gradually improved stability towards metallic lithium, and can form a stable interfacial layer with the metallic lithium anode, which is helpful for the long-term cycling of the metallic lithium all-solid-state battery. By increasing the content of Li, a sulfide solid electrolyte rich in lithium is formed, further improving the electrochemical stability of the sulfide solid electrolyte.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, relates to solid electrolytes, and particularly relates to a lithium-rich high-temperature-resistant sulfide solid electrolyte material. On this basis, the lithium-rich high-temperature-resistant sulfide solid electrolyte and its solid-state battery are further described. Background Art

[0002] With the rapid development of science and technology and human society, lithium-ion batteries are widely used in fields such as consumer electronics, medical electronics, electric vehicles, rail transit, mobile energy storage, smart grid, aerospace, and national defense due to their superior performance. However, these fields have put forward higher requirements for the energy density, power density, and safety of batteries. The energy density of conventional lithium-ion batteries has reached a "bottleneck". Scientists in China, the United States, Japan, etc. unanimously believe that the energy density of scalable lithium-ion batteries cannot exceed 350 W·h / Kg, and during the process of increasing their energy density, the volatile and flammable organic liquid electrolyte is extremely likely to induce safety accidents.

[0003] Since the commercially available lithium-ion batteries currently use electrolytes containing flammable organic solvents, it is necessary to install safety devices to suppress the temperature rise during short circuits or to improve the structure and materials for preventing short circuits. Solid-state batteries using non-volatile and non-flammable solid electrolytes to replace organic liquid electrolytes are one of the main solutions to solve the "bottleneck" problem of existing lithium-ion batteries, which can simplify the safety devices and have excellent manufacturing costs or productivity. Among them, sulfide solid electrolytes with high ionic conductivity and their solid electrolytes are the main development directions.

[0004] Although these sulfide solid electrolytes are non-volatile and non-flammable, they are not completely thermally safe at high temperatures. Phase transitions, thermal decomposition, and component volatilization can occur, which can have a huge impact on the ionic conductivity of the material and seriously affect its performance. More importantly, the heated sulfide solid electrolyte will still release flammable sulfur, which will produce flammable and highly toxic gases such as hydrogen sulfide in the air. Especially when there is a lithium metal negative electrode, it will pose a huge safety risk. On the other hand, the electrochemical stability of sulfide solid electrolytes is poor. From the perspective of theoretical calculations, the voltage stability range of the Li-Ge-P-S-based crystal solid electrolyte system (ionic conductivity reaches 12 mS / cm) is only 1.71 - 2.14 V (vs. Li / Li+), and redox decomposition reactions will occur outside this voltage range. Thus, sulfide solid electrolytes are extremely unstable towards lithium metal. For example, the reduction decomposition reaction of the Li-Ge-P-S-based crystal solid electrolyte system starts at 1.71 V, and LGPS is lithiated to form Li4GeS4, P, and Li2S; as the potential further decreases, multiple thermodynamic voltage platforms appear, corresponding to Li-P and Li-Ge alloys, and the reduction products at 0 V are Li2S, Li15Ge4, and Li3P, and this reaction will continue. Therefore, the demand for developing a sulfide solid electrolyte with high thermal stability, high ionic conductivity, and high electrochemical stability is extremely urgent. Summary of the Invention

[0005] Due to the urgent requirements for high thermal safety and high energy density of electrochemical energy storage devices, and at the same time, it is necessary to meet the excellent electrochemical performance of the battery at high temperatures and the safe use of high-energy-density negative electrode materials such as lithium metal. Therefore, the present invention provides a lithium-rich sulfide solid electrolyte, which simultaneously has ultra-high thermal stability, high ionic conductivity, and high electrochemical stability. Through material selection and design of the sulfide solid electrolyte, and analysis of the "material-structure-performance" of the solid electrolyte material, it is summarized that by optimizing the composition, target materials with good thermal stability can be quickly designed and screened, which are not easily decomposed, not easily sulfur-separated, and simultaneously have good ionic conductivity and ultra-high thermal stability performance.

[0006] The present invention first provides a lithium-rich high-temperature-resistant sulfide solid electrolyte, which contains at least the elements of lithium Li, phosphorus P, and sulfur S, and the material structure factor Δ is 781 ± 1 to 1300 ± 1, where Δ = {N(Li) × 312.5 + N(P) × 346} × 4. In the formula, N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, and N(Li) ≥ 0.25.

[0007] Among them, the composition of the lithium-rich high-temperature-resistant sulfide solid electrolyte is Li-P-S-M, and the content of each component is: 0.25 ≤ N(Li) ≤ 1, 0 < N(P) ≤ 0.375, 0 < N(S) ≤ 0.375, 0 ≤ N(M) ≤ 0.2. In the formula, N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, N(S) represents the atomic percentage of S, and N(M) represents the atomic percentage of the doping element M. The sum of each element is 100%. The thermal decomposition temperature of the material within this range is ≥ 400 °C.

[0008] Preferably, the structure factor Δ of the lithium-rich high-temperature-resistant sulfide solid electrolyte is 1000 ± 1 to 1300 ± 1, where Δ = {N(Li) × 312.5 + N(P) × 346} × 4. In the formula, N(Li) represents the atomic percentage of Li, and N(P) represents the atomic percentage of P. The composition of the lithium-rich high-temperature-resistant sulfide solid electrolyte is Li-P-S-M, and the content of each component is: 0.417 ≤ N(Li) ≤ 0.909, 0.08 ≤ N(P) ≤ 0.375, 0 < N(S) ≤ 0.208, 0 ≤ N(M) ≤ 0.2. In the formula, N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, N(S) represents the atomic percentage of S, and N(M) represents the atomic percentage of the doping element M. The sum of each element is 100%. The thermal decomposition temperature of the material within this range is ≥ 700 °C.

[0009] Among them, the doping element M of the lithium-rich high-temperature-resistant sulfide solid electrolyte is at least one of non-metallic elements such as oxygen O, selenium Se, fluorine F, chlorine Cl, bromine Br, iodine I or metal elements such as magnesium Mg, calcium Ca, strontium Sr, zinc Zn, scandium Sc, antimony Sb, silicon Si, germanium Ge, tin Sn, boron B, aluminum Al, gallium Ga, indium In, titanium Ti, zirconium Zr, vanadium V, niobium Nb, copper Cu, nickel Ni, manganese Mn, chromium Cr, silver Ag, lanthanum La, cerium Ce, terbium Tb, tellurium Te, lead Pb, arsenic As, bismuth Bi, etc.

[0010] Among them, the lithium-rich high-temperature-resistant sulfide solid electrolyte is stable to metallic lithium. After contacting with the metal, it can form a stable interfacial layer Li2S. In the powder X-ray diffraction using CuKα rays, characteristic peaks appear at 2θ = 26.9 ± 0.5 deg, 31.3 ± 0.5 deg, 44.78 ± 0.5 deg, and 53.06 ± 0.5 deg.

[0011] Among them, the lithium-rich sulfide electrolyte within the scope of the present invention does not show an exothermic peak below 450 °C.

[0012] Among them, for the lithium-rich sulfide electrolyte within the scope of the present invention, in X-ray diffraction, there is a strong diffraction main peak before 2θ = 34.5 ± 0.5 deg, and the presented crystallization main peak will not appear after 2θ = 34.5 ± 0.5 deg.

[0013] Among them, for the lithium-rich sulfide electrolyte within the scope of the present invention, in X-ray diffraction above 500 °C, a crystallization peak of crystalline phase A will appear near 2θ = 27 ± 0.5 deg.

[0014] Among them, for the lithium-rich sulfide electrolyte within the scope of the present invention, the ionic conductivity is not less than 1 mS / cm, and the electronic ionic conductivity is not greater than 1×10 -10 S / cm.

[0015] Among them, for the lithium-rich sulfide electrolyte within the scope of the present invention, the brightness L* value in the L*a*b* colorimetric system is 60.0 - 90.0.

[0016] Among them, for the lithium-rich sulfide electrolyte within the scope of the present invention, the density is 1.7 - 3.2 g / cm 3 .

[0017] The present invention provides a battery containing the above-mentioned lithium-rich sulfide electrolyte.

[0018] The beneficial effects produced by the present invention are as follows: Based on the composition of traditional sulfide solid electrolytes, instead of using expensive and low-reserve rare elements, inexpensive and abundant conventional elements are used. Through the corresponding design of the correlation between the structure factor Δ and the thermal stability performance of the material, as the basis for optimizing the proportion of constituent elements, a selection method and a regional scope of new materials different from traditional sulfide solid electrolytes can be obtained. The materials within the selected region have high thermal stability, do not decompose and do not precipitate sulfur at high temperatures, and moreover show good ionic conductivity and higher safety. At the same time, as the Li content increases, the stability of the sulfide solid electrolyte to metallic lithium gradually increases, and a stable interfacial layer can be formed with the metallic lithium negative electrode, which helps the long-term cycling of the metallic lithium all-solid-state battery. By increasing the Li content, a lithium-rich sulfide solid electrolyte is formed, further improving the electrochemical stability of the sulfide solid electrolyte. Description of the Drawings

[0019] The technical solutions of the embodiments of the present invention will be further described in detail below through the drawings and embodiments.

[0020] Figure 1 It is a relationship diagram between the structure factor Δ and the thermal decomposition temperature of lithium-rich sulfide solid electrolytes with different atomic ratios.

[0021] Figure 2It is the LiPS ternary composition diagram of the lithium-rich high-temperature sulfide solid electrolyte of the present invention.

[0022] Figure 3 It is the XRD test pattern of the sulfide solid electrolyte in Example 6.

[0023] Figure 4 It is the XRD test pattern of the sulfide solid electrolyte after being treated at a high temperature of 700 °C in Example 6.

[0024] Figure 5 It is the XRD test pattern of the sulfide solid electrolyte after being contacted with metallic lithium in Example 6.

[0025] Figure 6 It is the DSC test pattern of the sulfide solid electrolyte in Example 6.

[0026] Figure 7 It is the symmetrical battery composed of the sulfide solid electrolyte and metallic lithium in Example 6.

[0027] Figure 8 It is the XRD test pattern of the sulfide solid electrolyte in Example 7.

[0028] Figure 9 It is the XRD test pattern of the sulfide solid electrolyte after being treated at a high temperature of 800 °C in Example 7.

[0029] Figure 10 It is the XRD test pattern of the sulfide solid electrolyte after being contacted with metallic lithium in Example 7.

[0030] Figure 11 It is the DSC test pattern of the sulfide solid electrolyte in Example 7.

[0031] Figure 12 It is the symmetrical battery composed of the sulfide solid electrolyte and metallic lithium in Example 7.

[0032] Figure 13 It is the distribution diagram of different examples in Table 2 in the LiPS ternary projection composition diagram.

[0033] Figure 14 It is the distribution diagram of different preferred examples in Table 2 in the LiPS ternary projection composition diagram.

[0034] Figure 15 It is the charge-discharge curve of the all-solid-state battery prepared in Example 58 of this embodiment.

[0035] Figure 16 It is the cycle curve of the all-solid-state battery prepared in Example 58 of this embodiment. Detailed implementation manners

[0036] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, it should be understood that these embodiments are only for more detailed description and should not be construed as limiting the present invention in any way, that is, it is not intended to limit the protection scope of the present invention.

[0037] In the microstructure of the Li-P-S-M sulfide solid electrolyte, it can be considered to be composed of a corresponding number of [Li-S] bonds, [P-S] bonds, and chemical bonds of the doping element M, and these bonds form corresponding polyhedra and further form the macroscopic electrolyte material. The material decomposition process (physically measuring the decomposition temperature) is closely related to the essential structure of the material, that is, closely related to the number of corresponding polyhedra and the number of bonds that make up the electrolyte material.

[0038] Therefore, we define the structure factor δ of the sulfide solid electrolyte, which reflects the energy possessed by all polyhedra in the sulfide solid electrolyte, or the sum of the energies of all chemical bonds (Equation 1 and Equation 2).

[0039] δ = E{Li x P y S z M m} = ∑{E[Li-S]} + ∑{E[P-S]} + ∑{E[M]} (1)

[0040] δ = E{Li x P y S z M m} = ∑{E[LiS 4} + ∑{E[PS 3 + ∑{E[PS 4 + ∑{E[P 2 S 7 + ∑{E[P 2 S 6} + ∑{E[M]} (2)

[0042] In Equation 1 and Equation 2, E{Li x P y S z M m} represents the energy value possessed by Li x P y S z M m , E[Li-S] represents the energy contained in the [Li-S] bond, E[P-S] represents the energy contained in the [P-S] bond, E[M] represents the energy contained in the chemical bonds formed by the doping element M, E[LiS 4 , E[PS 3, E[PS 4 , E[P 2 S 7 , E[P 2 S 6 represent the energies contained in the [LiS4], [PS3], [P2S7], [PS4], and [P2S6] polyhedra respectively.

[0043] Since the purpose of introducing the doping element M is to improve the ionic conductivity, without destroying the overall ratio as much as possible and having less impact on the overall energy of the material, the energy part E[M] can be ignored in subsequent calculations to facilitate simplifying the model. Further, the number of [Li - S] bonds and [P - S] bonds can be estimated through polyhedra, simplifying Equation 2 to:

[0044]

[0045] For comparison, taking one mole as a benchmark for normalization. We define the structure factor Δ of the normalized sulfide solid electrolyte. The structure factor Δ is obtained by normalizing δ in unit measurement, reflecting the energy of all polyhedra or the total energy of all chemical bonds in the sulfide solid electrolyte under unit measurement

[0046] In Equations 3 and 4, N[LiS4], N[PS3], N[P2S7], N[PS4], and N[P2S6] represent the numbers of [LiS4], [PS3], [P2S7], [PS4], and [P2S6] polyhedra respectively, and E[LiS 4 , E[PS 3 , E[PS 4 , E[P 2 S 7 , E[P 2 S 6 represent the energies contained in the [LiS4], [PS3], [P2S7], [PS4], and [P2S6] polyhedra respectively. N Total refers to the total number of atoms in the unit cell and is used as a normalization coefficient to enable fair comparison between various systems with different unit cell sizes. To further simplify the calculation, during the calculation process, the number of atoms of the doping element M can be ignored, and N Total is recorded as the sum of the numbers of Li, S, and P atoms.

[0047] The amounts of N[LiS4], N[PS3], N[P2S7], N[PS4], and N[P2S6] can be represented by the number of central atoms therein. For example, N[LiS4] is closely related to the number of central atom Li, and N[PS3] is closely related to the number of central atom P. Based on the crystal structure of the sulfide electrolyte, it can be known that [P2S7], [PS3], and [P2S6] can all be equivalent to different connection modes of two [PS4], and quantitatively can be equivalent to the structure of [PS4]. Therefore, Equation 4 can be further simplified. By multiplying the number of central atoms by the number of bonds included in the polyhedron derived from the central atoms, Equation 5 is obtained. Equation 5 is conducive to quickly calculating the results without the aid of computer assistance, improving practicality.

[0048] Δ = {N(Li) × E[Li - S] + N(P) × E[P - S]} × 4 (5)

[0049] Where N(Li) represents the atomic percentage of the central atom Li, N(P) represents the atomic percentage of the central atom P, E[Li - S] represents the energy contained in the [Li - S] bond, and E[P - S] represents the energy contained in the [P - S] bond.

[0050] E[Li - S] and E[P - S] can be obtained from the "Handbook of Chemistry and Physics". In this way, Equation 5 can be further simplified to Equation 6.

[0051] Δ = {N(Li) × 312.5 + N(P) × 346} × 4 (6)

[0052] Where N(Li) represents the atomic percentage of the central atom Li, and N(P) represents the atomic percentage of the central atom P.

[0053] Thus, we define the structure factor Δ (Equation 6) of the normalized sulfide solid electrolyte. The structure factor Δ represents the simplified calculation of the total energy of all Li - S bonds and all P - S bonds inside the sulfide solid electrolyte, reflecting the thermal stability performance in terms of the material structure. Since this structure factor Δ is a simplified result obtained by analyzing and summarizing the "material - structure - performance" three dimensions of the sulfide solid electrolyte, and this result is uniquely related to the composition of Li - P - S - M, it is expected that by optimizing the composition ratio of Li - P - S - M in the sulfide solid electrolyte, the thermal stability of the sulfide solid electrolyte can be effectively improved, enabling the sulfide solid electrolyte to stably exist at high temperatures without obvious thermal decomposition process and sulfur evolution process, and having good ionic conductivity.

[0054] Among them, in the Li-P-S-M sulfide solid electrolyte, the element M is at least one of non-metallic elements such as oxygen O, selenium Se, fluorine F, chlorine Cl, bromine Br, iodine I, or metallic elements such as magnesium Mg, calcium Ca, strontium Sr, zinc Zn, scandium Sc, antimony Sb, silicon Si, germanium Ge, tin Sn, boron B, aluminum Al, gallium Ga, indium In, titanium Ti, zirconium Zr, vanadium V, niobium Nb, copper Cu, nickel Ni, manganese Mn, chromium Cr, silver Ag, lanthanum La, cerium Ce, terbium Tb, tellurium Te, lead Pb, arsenic As, bismuth Bi, etc.

[0055] According to the derivation process of the above Equation 6, the above Equation 6 is also applicable to the Li-P-S sulfide solid electrolyte without the doping element M, which is equivalent to an M content of 0.

[0056] To verify the relationship between the structure factor Δ and the thermal stability, we selected a series of lithium-rich sulfide solid electrolyte materials with different compositions containing lithium Li, phosphorus P, sulfur S, and other elements M. The sulfide solid electrolytes with different atomic numbers are summarized in Table 1. Through ICP testing, the accurate Li and P atomic ratios of the sulfide solid electrolyte can be obtained, and then the structure factor Δ of the device can be calculated. Electrochemical impedance spectroscopy tests (the test instrument is Zahner Zennium Pro) were carried out on the new sulfide solid electrolyte, and the ionic conductivities of the new sulfide solid electrolyte are also summarized in Table 1. During the calculation of the structure factor Δ, when calculating the atomic percentages (N(P) and N(Li)), the total number of atoms (N Total ) does not include the atomic number of the doping element.

[0057] The sulfide solid electrolyte in Table 1 was placed in a muffle furnace for heat treatment, and then the heat-treated sulfide solid electrolyte was tested and analyzed by powder X-ray diffraction with CuKα rays to obtain the phase decomposition temperature of the sulfide solid electrolyte. The structure factor Δ and their thermal decomposition temperatures of the above lithium-rich sulfide solid electrolytes with different atomic ratios are summarized in Figure 1 .

[0058] From the experimental results, the structure factor Δ changes synchronously with the thermal decomposition temperature of the sulfide solid electrolyte. The structure factor Δ of the present invention is positively correlated with the thermal decomposition temperature (thermal stability) of the sulfide solid electrolyte and can be used as an important parameter to measure the thermal stability performance of the sulfide solid electrolyte.

[0059] Table 1 Summary table of ionic conductivities and structure factor Δ of lithium-rich sulfide solid electrolytes with different atomic ratios

[0060] Chemical formula Ionic conductivity / (mS / cm) Structure factor Δ Thermal decomposition temperature / °C Example 1 Li5.2P0.48S2.32 5.1 895.54 763 Example 2 Li5.04P1.12S1.84 4.9 981.26 837 Example 3 Li4.88P1.52S1.6 5.1 1025.46 874 Example 4 Li4.72P1.84S1.44 6.2 1055.82 900 Example 5 Li4.56P2.08S1.36 6.8 1072.34 915

[0061] According to the mutual variation of the composition ratio relationship of the Li-P-S sulfide solid electrolyte, we established a ternary composition diagram of LiPS ( Figure 2 ), and combined with experiments, a lithium-rich region (the light shaded part in the figure) with a relatively high structural factor Δ in the ternary composition diagram was selected. For the doping element M, since its content is very small, it can be regarded as the doping element replacing part of P and / or S in the ternary composition, and the energy fluctuation effect brought by the doping element M is also ignored in the calculation of the structural factor Δ. Therefore, the content of LiPS in the quaternary composition containing the doping element M can be regarded as the same as that of LiPS in the ternary composition without considering the doping element M, and the range of the lithium-rich region of LiPS in the quaternary composition can be regarded as consistent with the above shaded part.

[0062] Specifically, in this region, the structural factor Δ is 781±1 to 1300±1, and the thermal decomposition temperature of the materials in this region is greater than 400 °C. Specifically, the composition of the LiPSM material in this region is 0.25≤N(Li)≤1, 0<N(P)≤0.375, 0<N(S)≤0.375, 0≤N(M)≤0.2, where N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, N(S) represents the atomic percentage of S, and N(M) represents the atomic percentage of the doping element M, and the sum of the elements is 100%. Among them, when N(M)=0, it is the LiPS ternary composition material.

[0063] Furthermore, within the above region range, region II (the dark shaded part) with a higher structural factor Δ in the composition diagram was also selected in combination with experiments. In this region, the structural factor Δ is 1000±1 to 1300±1, and through verification (specifically see the following series of examples), the materials in this region exhibit higher thermal stability and thermal decomposition temperature, and the decomposition temperature is greater than 700 °C. Specifically, the composition of the materials in this region is 0.417≤N(Li)≤0.909, 0.08≤N(P)≤0.375, 0<N(S)≤0.208, 0≤N(M)≤0.2, where N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, N(S) represents the atomic percentage of S, and N(M) represents the atomic percentage of the doping element M, and the sum of the elements is 100%.

[0064] Next, the relationship between the selected structural factor Δ region and the thermal stability of the lithium-rich material of the present invention is further verified through a series of examples.

[0065] Example 6

[0066] The present invention provides a lithium-rich sulfide solid electrolyte, which has high ionic conductivity, high thermal stability, and high electrochemical stability, can stably match with a lithium metal anode, and is used to manufacture a lithium metal all-solid-state battery with a long service life.

[0067] The preferably lithium-rich sulfide solid electrolyte in this embodiment is a sulfide solid electrolyte containing lithium (Li), phosphorus (P), and sulfur (S). The sulfide solid electrolyte material has the following atomic numbers, where the atomic numbers are N(Li)=0.608, N(P)=0.025, and N(S)=0.367. It is equivalently calculated and experimented with the chemical formula Li4.864P0.2S2.936, and it can be known that the structure factor Δ of this sulfide solid electrolyte is 794.6.

[0068] Preparation method: In this embodiment, the synthesis method adopts the solid-phase sintering method, which is mainly divided into two steps. Among them, the raw material mixing process: Using a raw material composition containing the constituent components of the sulfide solid electrolyte material, through mechanical grinding or mixing under the action of a liquid-phase solvent, a precursor material is synthesized; the heat treatment crystallization process: By heating the precursor material, the novel high-temperature-resistant sulfide solid electrolyte material is obtained. Lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), and other lithium sources and sulfur sources are used as starting materials. These powders are weighed according to the above composition in a glove box under an Ar atmosphere (dew point -70°C) and mixed in an agate mortar to obtain a raw material precursor. Then, the obtained raw material precursor is put into a 45 ml zirconia pot, and further zirconia balls (φ10 mm, 15 - 20 pieces) are put in, and the pot is completely sealed (Ar atmosphere). The pot is installed in a planetary ball mill and mechanically ground at a table rotation speed of 350 rpm for 30 hours to obtain a precursor of the novel sulfide solid electrolyte. By heating the precursor material, the heating temperature is 400 - 600°C, and the heat treatment time is 10 - 30 h, to obtain the lithium-rich sulfide solid electrolyte material. Figure 3 The XRD test pattern of the sulfide solid electrolyte powder obtained by this synthesis method is shown.

[0069] ICP Test: The sulfide solid electrolyte of the test sample was ground into a fine powder in a mortar, transferred into a crucible, placed in an oven at 105 °C for 1 hour, and then cooled in a desiccator. Weigh 0.1 g of the sample (accurate to 0.1 mg) and place it in a 100 mL beaker. Add 5 mL of the standard digestion solution and heat it on a hot plate (70 °C) until the sample is completely dissolved. Cool it to room temperature. Transfer the sample solution into a 250 mL volumetric flask, make up the volume with ultrapure water, and mix well. Then take 5 mL of the volumetric sample solution and dilute it to 50 mL, that is, dilute it 10 times. Transfer the sample solution and the diluted solution into the test instrument Thermofisher iCAP 7200 for testing. The carrier gas is N2, the gas flow rate is 0.5 L / min, the nebulizer pressure is 0.19 Mpa, and the high-frequency power is 1150 W. Through ICP testing, the accurate Li and P atomic ratios of the sulfide solid electrolyte can be obtained, and then the structure factor Δ is calculated to be 794.6.

[0070] XRD Diffraction Test: XRD measured the sample in a sealed test sample stage without contacting the air. The 2θ positions of the diffraction peaks were determined by the centroid method using the XRD analysis program JADE. The test was carried out under conventional test conditions using a powder X-ray diffractometer from Purkinje General Electric (other brands are also acceptable). Since there are differences in test parameters for different instruments, the following takes the setting parameters of the powder X-ray diffractometer from Purkinje General Electric as an example: tube voltage: 36 kV; tube current: 20 mA; X-ray wavelength: Cu-Kα ray; detector: scintillation counter; measurement range: 2θ = 10 - 80 deg; step width, scanning speed: 0.02 deg, 1 deg / min; during the process of analyzing the peak positions for confirming the existence of the crystal structure based on the measurement results, the XRD analysis program JADE was used to draw the baseline by fitting with a cubic equation, so as to obtain the peak positions. Figure 3 The XRD test pattern of the sulfide solid electrolyte in this example is shown. There is a strong diffraction main peak before 2θ = 34 deg, and the presented crystallization main peak does not appear after 2θ = 34 deg. Heat-treat the novel sulfide solid electrolyte in a muffle furnace to 700 °C, and then conduct test analysis by powder X-ray diffraction of CuKα ray. Figure 4The XRD test pattern of the sulfide solid electrolyte after being treated at a high temperature of 700 °C in the present embodiment is shown. It is found that a crystallization peak appears near 2θ = 27.3 deg, which belongs to the crystalline phase A, and the main phase is Li2S. The above-mentioned lithium-rich sulfide solid electrolyte powder is pressed into a sulfide solid electrolyte sheet under a pressure of 300 Mpa. Then, after the sulfide solid electrolyte sheet is closely attached to the lithium metal anode and kept for more than 20 h to fully carry out an interfacial reaction with the lithium metal, the lithium metal foil is removed, and then the powder scraped from the interfacial layer on the surface of the sulfide solid electrolyte sheet after the reaction is subjected to XRD testing. The sample was measured using a sealed test sample stage for XRD in a manner that does not contact air. Figure 5 It is the XRD test pattern of the powder of the reaction product of the sulfide solid electrolyte and lithium metal in the present embodiment; it is found that characteristic peaks appear at 2θ = 27 deg, 31.3 deg, 44.5 deg, and 53 deg, and these characteristic peaks belong to the crystalline phase A, Li2S, indicating that the sulfide solid electrolyte and lithium metal react to form a stable crystalline phase Li2S, which prevents further reaction.

[0071] DSC test: In order to accurately obtain the thermal stability parameters of this new sulfide solid electrolyte, differential scanning calorimetry was used for accurate testing and evaluation in the present embodiment. 5 mg of the sulfide solid electrolyte to be measured was added to a stainless-steel container for DSC (differential scanning calorimeter) and sealed. The sealed container was placed in a DSC device (NETZSCH DSC214) and measured. For the reference, 5 mg of Al2O3 was used, the heating rate was set at 5 °C / minute, and the termination temperature was set at 450 °C. According to the DSC results, the onset temperature of heat generation and the peak temperature of heat generation were obtained. It should be noted that the onset temperature of heat generation refers to the temperature at which the heat flow rises, and the peak temperature of heat generation refers to the peak temperature (the peak temperature of heat generation) at the lowest (highest) point of the heat flow. Figure 6 It is the DSC test pattern of the sulfide solid electrolyte in the present embodiment; no phase transition peak that does not appear at 210 - 350 °C was found in the sulfide solid electrolyte, and no exothermic peak of phase decomposition appeared. This shows that the sulfide solid electrolyte has a high thermal stability value, and the starting temperature of the thermal decomposition reaction exceeds 400 °C and remains stable within the test range.

[0072] Battery construction: A symmetric battery was constructed in the form of lithium metal - sulfide solid electrolyte - lithium metal, and long-term cyclic testing was carried out on a charge and discharge instrument to evaluate its electrochemical stability to lithium metal. Figure 7 It is the symmetric battery composed of the sulfide solid electrolyte and lithium metal in the present embodiment. It can be known from the test results that the sulfide solid electrolyte in the present embodiment can work stably for more than 2500 h.

[0073] Ionic conductivity test: Electrochemical impedance spectroscopy was performed on the novel sulfide solid electrolyte. The test instrument was a Zahner Zennium Pro. The novel sulfide solid electrolyte obtained in the examples was pressed into a sheet (500 MPa) to obtain a sheet with a thickness of approximately 1.24 mm and a diameter of φ10 mm. At room temperature, the alternating current impedance was measured by the two-terminal method to calculate the ionic conductivity. The measurement frequency range was from 100 mHz to 8 MHz, and the amplitude was 5 mV. The ionic conductivity of the novel sulfide solid electrolyte was measured to be 8.5 mS / cm. Similarly, the direct current polarization measurement by the two-terminal method was used to calculate the electronic conductivity. The polarization voltage was 500 mV, and the electronic conductivity of the novel sulfide solid electrolyte was measured to be 0.56×10 -10 S / cm.

[0074] Density test: The powder density of the novel sulfide solid electrolyte was measured. The test instrument was a true density meter, and its density was obtained as 1.79 g / cm 3 .

[0075] Chromaticity test: The whiteness of the novel sulfide solid electrolyte was measured. The test instrument was a powder whiteness meter. The powder to be measured was placed in the test chamber, and the sample to be measured was placed at the reflection test port of the instrument. Enter the measurement interface, press the measurement button briefly to start the measurement. The buzzer makes a "beep" sound, and at the same time, the LED indicator flashes until the flashing stops. The buzzer makes a "beep" sound again to complete the chromaticity measurement of the sulfide solid electrolyte. The brightness L* value in the L*a*b* chromaticity system is preferably 80.0.

[0076] Thermal decomposition experiment: The sulfide solid electrolyte was sealed in a quartz tube, and the quartz tube was placed in the central position of a muffle furnace. This part was heated, and at the same time, the morphological changes of the sulfide solid electrolyte during the heating process were observed. By cooling one end of the quartz tube sealed with the sulfide solid electrolyte, the sulfur precipitation situation could be obtained to observe the sulfur evolution reaction of the sulfide solid electrolyte. Through the whole-process thermal decomposition experiment on the novel lithium-rich sulfide solid electrolyte, the results showed that the morphology and state of the sulfide solid electrolyte remained stable within 600 °C, and the sulfur evolution temperature was 677 °C. Further, it was shown that when the ambient temperature exceeded 677 °C, the sulfide solid electrolyte would undergo a sulfur evolution reaction process and partial decomposition.

[0077] Example 7

[0078] A lithium-rich sulfide solid electrolyte provided by the present invention has high ionic conductivity, high thermal stability, and high electrochemical stability, can stably match with a metallic lithium negative electrode, and is used to manufacture a metallic lithium all-solid-state battery with a long service life.

[0079] The preferred lithium-rich sulfide solid electrolyte in this embodiment is a sulfide solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), and chlorine (Cl). The sulfide solid electrolyte material has the following atomic numbers, where the atomic numbers are N(Li)=0.705, N(P)=0.0242, N(S)=0.2708, N(Cl)=0.016. Calculation experiments are carried out with the chemical formula Li5.64P0.1936S2.1664Cl0.128, and it can be known that the structure factor Δ of this sulfide solid electrolyte is 914.74.

[0080] Preparation method: In this embodiment, the synthesis method adopts the solid-phase sintering method, which is mainly divided into two steps. Among them, the raw material mixing process: Using a raw material composition containing the constituent components of the sulfide solid electrolyte material, through mechanical grinding or mixing under the action of a liquid-phase solvent, a precursor material is synthesized; the heat treatment crystallization process: By heating the precursor material, the novel high-temperature-resistant sulfide solid electrolyte material is obtained. Lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), and other lithium sources and sulfur sources are used as starting materials. These powders are weighed according to the above composition in a glove box under an Ar atmosphere (dew point -70°C) and mixed in an agate mortar to obtain a raw material precursor. Then, the obtained raw material precursor is put into a 45 ml zirconia pot, and further zirconia balls (φ10 mm, 15 - 20 pieces) are put in, and the pot is completely sealed (Ar atmosphere). The pot is installed in a planetary ball mill and mechanically ground for 30 hours at a table rotation speed of 350 rpm to obtain the precursor of the novel sulfide solid electrolyte. By heating the precursor material, the heating temperature is 400 - 600 °C, and the heat treatment time is 10 - 30 h, to obtain the lithium-rich sulfide solid electrolyte material. Figure 8 The XRD test pattern of the sulfide solid electrolyte powder obtained by this synthesis method is shown.

[0081] ICP test: The test sample, the sulfide solid electrolyte, is ground into a fine powder in a mortar, transferred to a crucible, placed in an oven at 105 °C for 1 hour, and then transferred to a desiccator to cool. Weigh 0.1 g of the sample (accurate to 0.1 mg) and place it in a 100 mL beaker, add 5 mL of the standard digestion solution, heat it on a hot plate (70 °C) until the sample is completely dissolved, and cool it to room temperature. Transfer the sample solution to a 250 mL volumetric flask, make up the volume with ultrapure water, and mix well. Then take 5 mL of the volumetric sample solution and dilute it to 50 mL, that is, dilute it 10 times. The sample solution and the diluted solution are transferred to a test instrument, Thermofisher iCAP7200, for testing. The carrier gas is N2, the gas flow is 0.5 L / min, the nebulizer pressure is 0.19 Mpa, and the high-frequency power is 1150 W. Through the ICP test, the accurate Li and P atomic ratios of this sulfide solid electrolyte can be known, and further calculation shows that its structure factor Δ is 914.74.

[0082] XRD Diffraction Test: The XRD used a sealed test sample stage to measure the sample without contacting air. The 2θ position of the diffraction peak was determined by the centroid method using the XRD analysis program JADE. The powder X-ray diffraction of Purkinje General (other brands are also acceptable) was used for testing under conventional test conditions. Since there are differences in test parameters for different instruments, the following takes the setting parameters of the powder X-ray diffraction of Purkinje General as an example: tube voltage: 36 kV; tube current: 20 mA; X-ray wavelength: Cu-Kα ray; detector: scintillation counter; measurement range: 2θ = 10 - 80 deg; step width, scanning speed: 0.02 deg, 1 deg / min; during the process of analyzing the peak position for confirming the existence of the crystal structure based on the measurement results, the XRD analysis program JADE was used to draw the baseline by fitting with a cubic equation to obtain the peak position. Figure 8 The XRD test pattern of the sulfide solid electrolyte in this embodiment is shown. There is a strong diffraction main peak before 2θ = 34 deg, and the presented crystallization main peak does not appear after 2θ = 34 deg. The novel sulfide solid electrolyte was placed in a muffle furnace for heat treatment, heated to 800 °C, and then tested and analyzed by powder X-ray diffraction with CuKα ray. Figure 9 The XRD test pattern of the sulfide solid electrolyte in this embodiment after being treated at 800 °C is shown. It is found that a crystallization peak appears near 2θ = 27.3 deg, belonging to the crystalline phase A, and the main phase is Li2S. The above-mentioned lithium-rich sulfide solid electrolyte powder was pressed into a sulfide solid electrolyte sheet under a pressure of 300 Mpa. Then, after the sulfide solid electrolyte sheet was closely attached to the metal lithium negative electrode and kept for more than 20 h to allow it to fully react with the metal lithium at the interface, the metal lithium foil was removed. Then, the powder scraped from the reaction interface layer on the surface of the sulfide solid electrolyte sheet was subjected to XRD test. The XRD used a sealed test sample stage to measure the sample without contacting air. Figure 10 It is the XRD test pattern of the sulfide solid electrolyte after being in contact with the metal lithium in this embodiment; it is found that the characteristic peaks appearing at 2θ = 27 deg and 31.3 deg belong to the crystalline phase A, Li2S, indicating that the sulfide solid electrolyte and the metal lithium react to form stable Li2S, preventing further reaction.

[0083] DSC Test: To accurately obtain the thermal stability parameters of this new sulfide solid electrolyte, differential scanning calorimetry was used for accurate testing and evaluation in this example. 5 mg of the sulfide solid electrolyte to be tested was added to a stainless-steel container for DSC (differential scanning calorimeter) and sealed. The sealed container was placed in a DSC device (NETZSCH DSC 214) and measured. For the reference, 5 mg of Al2O3 was used, the heating rate was set at 5 °C / minute, and the end temperature was set at 450 °C. According to the DSC results, the heat generation start temperature and the heat generation peak temperature were obtained. It should be noted that the heat generation start temperature refers to the temperature when the heat flow rises, and the heat generation peak temperature refers to the peak temperature (heat generation peak temperature) at the lowest (highest) point of the heat flow. Figure 11 is the DSC test spectrum of the sulfide solid electrolyte in this example; no phase transition peak that does not appear at 210 - 350 °C was found in the sulfide solid electrolyte, and no exothermic peak of phase decomposition appeared. This shows that the sulfide solid electrolyte has a high thermal stability value, the starting temperature of the thermal decomposition reaction exceeds 400 °C, and it remains stable within the test range.

[0084] Stability experiment with metallic lithium: A symmetric battery was constructed in the form of metallic lithium - sulfide solid electrolyte - metallic lithium, and long-term cyclic tests were carried out on a charge-discharge instrument to evaluate its electrochemical stability towards metallic lithium. Figure 12 is the symmetric battery composed of the sulfide solid electrolyte and metallic lithium in this example. It can be known from the test results that the sulfide solid electrolyte in this example can work stably for more than 2500 h.

[0085] Ionic conductivity test: Electrochemical impedance spectroscopy was used to test the new sulfide solid electrolyte. The test instrument was Zahner Zennium Pro. The new sulfide solid electrolyte obtained in the example was pressed into a sheet (500 MPa) to obtain a sheet with a thickness of about 1.24 mm and a diameter of φ10 mm. At room temperature, the two-terminal method was used for AC impedance measurement to calculate the ionic conductivity. The measurement frequency range was 100 mHz to 8 MHz, and the amplitude was 5 mV. The ionic conductivity of the new sulfide solid electrolyte was measured to be 12.5 mS / cm. Similarly, the two-terminal method was used for DC polarization measurement to calculate the electronic conductivity. The polarization voltage was 500 mV, and the electronic conductivity of the new sulfide solid electrolyte was measured to be 0.79×10 -10 S / cm.

[0086] Density test: The powder density of the new sulfide solid electrolyte was tested using a true density meter, and its density was obtained as 1.89 g / cm 3 .

[0087] Chromaticity Test: The whiteness of the novel sulfide solid electrolyte was tested using a powder whiteness meter. The powder to be tested was placed in the test chamber, and the sample to be measured was placed at the reflection test port of the instrument. Enter the measurement interface, press the measurement button briefly to start the measurement. The buzzer emits a "beep" sound, and at the same time, the LED indicator flashes until the flashing stops. Then the buzzer emits a "beep" sound again to complete the chromaticity measurement of the sulfide solid electrolyte. In the L*a*b* chromaticity system, the preferred value of the brightness L* is 70.0.

[0088] Thermal Decomposition Experiment: The sulfide solid electrolyte was sealed in a quartz tube, and the quartz tube was placed in the central position of a muffle furnace for heat treatment. At the same time, the morphological changes of the sulfide solid electrolyte during heating were observed. By cooling one end of the quartz tube sealed with the sulfide solid electrolyte, the sulfur precipitation situation could be obtained to observe the sulfur evolution reaction of the sulfide solid electrolyte. Through the whole-process thermal decomposition experiment of the novel lithium-rich sulfide solid electrolyte, the results showed that the morphology and state of the sulfide solid electrolyte remained stable within 700 °C, and the sulfur evolution temperature was 780 °C. Further, it was shown that when the ambient temperature exceeded 780 °C, the sulfide solid electrolyte would undergo a sulfur evolution reaction process and partial decomposition.

[0089] To further verify the thermal decomposition temperature of the materials within the above-selected region, we provided a summary of Examples 8 - 57 within the region in Table 2. It can be seen that the thermal decomposition temperatures of the selected structure factors in each example within the region of 781 ± 1 to 1300 ± 1 ( Figure 13 ) are all greater than 400 °C. And for each example 41 - 57 within the region where the structure factor Δ is 1000 ± 1 to 1300 ± 1, the material composition is 0.417 ≤ N(Li) ≤ 0.909, 0.08 ≤ N(P) ≤ 0.375, 0 < N(S) ≤ 0.208, 0 ≤ N(M) ≤ 0.2 ( Figure 14 ) the thermal decomposition temperatures are all greater than 700 °C.

[0090] Table 2 Summary Table of Ionic Conductivity and Structure Factor Δ of Lithium-Rich Sulfide Solid Electrolytes with Different Atomic Ratios

[0091]

[0092]

[0093] Example 58

[0094] The novel high-temperature-resistant sulfide solid electrolyte can be used as a solid electrolyte layer in all-solid-state lithium secondary batteries or all-solid-state lithium batteries, or as a solid electrolyte mixed in the positive / negative electrode binders. By forming a layer composed of the above solid electrolyte between the positive electrode, the negative electrode, and the positive and negative electrodes, an all-solid-state battery can be constructed. Here, the layer composed of the novel high-temperature-resistant sulfide solid electrolyte can be fabricated by the following methods: for example, dropping a slurry composed of a sulfide solid electrolyte, a binder, and a solvent onto a substrate and leveling it with a doctor blade or the like; a method of cutting it with a gas knife after the slurry contacts; a screen printing method; and so on. Alternatively, for the powder of the sulfide solid electrolyte, a compact can be fabricated by pressing or the like and then appropriately processed. As the positive electrode material, a positive electrode material used as a positive electrode active material for a lithium ion battery can be appropriately used. Regarding the negative electrode material, a negative electrode material used as a negative electrode active material for a lithium ion battery can also be appropriately used. In this embodiment, the positive electrode active material is LiCoO 2 as the main body, the negative electrode is natural graphite as the main body, and the solid electrolyte is the lithium-rich high-temperature-resistant sulfide solid electrolyte of Example 7 of the present invention. Figure 15 Shown are the charge-discharge curves of the all-solid-state battery prepared with the lithium-rich high-temperature-resistant sulfide solid electrolyte as the material in this embodiment. The battery capacity performs normally, the discharge capacity reaches 170 mAh / g, and the initial efficiency reaches over 98%. Figure 16 Shown is the cycle curve of the all-solid-state battery prepared with the lithium-rich high-temperature-resistant sulfide solid electrolyte as the material in this embodiment. After 800 cycles, the capacity retention rate is above 80%, and the all-solid-state metal lithium battery has an extremely long cycle life.

[0095] It can be verified through the accumulation of the above experiments that the structure factor Δ varies synchronously with the thermal decomposition temperature of the sulfide solid electrolyte and shows a positive correlation, and can be used as an important parameter to measure the thermal stability performance of the sulfide solid electrolyte. By optimizing the composition ratio of Li-P-S in the sulfide solid electrolyte, the thermal stability of the sulfide solid electrolyte can be effectively improved, enabling the sulfide solid electrolyte to stably exist at high temperatures without obvious thermal decomposition and sulfur evolution processes, and having good ionic conductivity. By optimizing the material composition ratio in the lithium-rich region and selecting the optimized composition material rich in lithium under the condition of satisfying the structure factor Δ, a set of sulfide solid electrolyte materials with ultra-high temperature stability is obtained, and due to the enrichment of Li in the materials, they also have the ability to form a stable interfacial layer with the lithium metal negative electrode, effectively optimizing and enhancing the cycle performance.

[0096] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-temperature resistant sulfide electrolyte rich in lithium, containing at least lithium (Li), phosphorus (P), and sulfur (S) elements, with the material structure factor Δ being 1000 - 1300, wherein, Δ = {N(Li)×312.5 + N(P)×346}×4, where N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P. During the calculation of the structure factor Δ, when calculating the atomic percentages (N(P) and N(Li)), the total number of atoms N(Total) does not include the atomic quantity of the doping element; the composition of the high-temperature resistant sulfide solid electrolyte rich in lithium is Li - P - S - M, and the content of each component is: 0.417 ≤ N(Li) ≤ 0.909, 0.08 ≤ N(P) ≤ 0.375, 0 < N(S) ≤ 0.208, 0 ≤ N(M) ≤ 0.2, where N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, N(S) represents the atomic percentage of S, and N(M) represents the atomic percentage of the doping element M, and the sum of each element is 100%; the thermal decomposition temperature of the material within the element composition range is ≥ 700°C.

2. The high-temperature resistant sulfide electrolyte rich in lithium according to claim 1, characterized in that, the doping element M is at least one of non-metal elements such as oxygen (O), selenium (Se), fluorine (F), chlorine (Cl), bromine (Br), iodine (I) or metal elements such as magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), scandium (Sc), antimony (Sb), silicon (Si), germanium (Ge), tin (Sn), boron (B), aluminum (Al), gallium (Ga), indium (In), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), copper (Cu), nickel (Ni), manganese (Mn), chromium (Cr), silver (Ag), lanthanum (La), cerium (Ce), terbium (Tb), tellurium (Te), lead (Pb), arsenic (As), bismuth (Bi).

3. The high-temperature resistant sulfide electrolyte rich in lithium according to claim 1, characterized in that, the high-temperature resistant sulfide solid electrolyte rich in lithium is stable to metallic lithium and can form a stable interfacial layer Li2S after contacting with the metal; in the powder X-ray diffraction using CuKα radiation, characteristic peaks appear at 2θ = 26.9 ± 0.5 deg, 31.3 ± 0.5 deg, 44.78 ± 0.5 deg, 53.06 ± 0.5 deg.

4. The high-temperature resistant sulfide electrolyte rich in lithium according to claim 1, characterized in that, the sulfide electrolyte rich in lithium does not show an exothermic peak below 450°C.

5. The high-temperature resistant sulfide electrolyte rich in lithium according to claim 1, characterized in that, in the X-ray diffraction of the sulfide electrolyte rich in lithium, there is a diffraction main peak before 2θ = 34.5, and the presented crystallization main peak does not appear after 2θ = 34.5; in the X-ray diffraction above 500°C, a crystallization peak of crystalline phase A appears at 2θ = 27 ± 0.5 deg.

6. The high-temperature resistant sulfide electrolyte rich in lithium according to claim 1, characterized in that, The lithium-rich sulfide electrolyte has an ionic conductivity of not less than 1 mS / cm and an electronic ionic conductivity of not more than 1×10 -10 S / cm.

7. The high-temperature resistant sulfide electrolyte rich in lithium according to claim 1, characterized in that, The lithium-rich sulfide electrolyte has a lightness L* value in the L*a*b* colorimetric system of 60.0 to 90.0; The lithium-rich sulfide electrolyte has a density of 1.7 to 3.2 g / cm 3 .

8. A battery comprising the lithium-rich sulfide electrolyte according to any one of claims 1 to 7.

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