Solid-state electrolyte material, preparation method, electrolyte layer, and lithium ion battery

Abstract

The present invention relates to the file of solid-state electrolyte materials of lithium ion batteries, and in particular to a solid electrolyte material, a preparation method, an electrolyte layer, and a lithium ion battery. The general chemical formula of the solid-state electrolyte material is: LiaPbCmSdOnClf, wherein 5.4≤a≤6.1, 0.9≤b≤1, 0<m≤0.1, 4.1≤d≤5, 0<n≤0.3, and 1≤f≤1.7. By co-doping an argyrodite sulfide electrolyte with two elements, i.e., O and C, an obtained solid-state electrolyte material maintains original high ionic conductivity, good mechanical strength, and excellent negative electrode stability and other excellent properties, and in addition, the air stability and positive electrode stability of the electrolyte are effectively improved, thereby significantly enhancing the overall performance and practical value of the electrolyte.

Description

Solid electrolyte material, preparation method, electrolyte layer and lithium ion battery

[0001] Cross-references

[0002] This application is based on the Chinese patent application with application number 202311740704.8 and application date December 18, 2023, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into this application as a reference. Technical Field

[0003] The present invention relates to the field of solid electrolyte materials for lithium ion batteries, and in particular to a solid electrolyte material, a preparation method, an electrolyte layer and a lithium ion battery. Background Art

[0004] In recent years, sales of new energy vehicles in my country have increased year by year, but safety accidents involving power batteries have occurred frequently. How to improve the safety of power batteries has become a key focus of the power battery industry. Currently, commercial lithium-ion power batteries use organic liquid electrolytes as lithium-ion transmission media. Their inherent high volatility and flammability pose safety risks during the battery charging and discharging process. Compared with liquid batteries, all-solid-state batteries use non-flammable solid electrolytes to replace liquid electrolytes, have higher safety and energy density, and are considered to be the most promising new generation of power battery technology. Sulfide solid electrolytes have good mechanical ductility and high ionic conductivity comparable to liquid electrolytes. They are one of the solid electrolyte materials with the most application potential in the field of all-solid-state batteries.

[0005] Among different types of sulfide electrolytes, argyrodite-type sulfide solid electrolytes such as Li6PS5Cl have attracted widespread attention from academia and industry due to their high room-temperature ionic conductivity, excellent mechanical properties, and good negative electrode interface stability. However, argyrodite-type electrolytes still have disadvantages such as poor air stability and poor compatibility with oxide positive electrodes, which affect their practical application. On the one hand, argyrodite-type electrolytes are extremely susceptible to the effects of moisture in the air. Even in a dry room with extremely low water content or an inert gas glove box, they will still react with trace amounts of moisture in the environment and cause performance degradation, resulting in their preparation and use conditions being too harsh and unable to meet the needs of industrial mass production. On the other hand, their poor compatibility with oxide positive electrode materials leads to insufficient battery cycle stability when paired with oxide positive electrodes. This is mainly related to the low oxidation stability potential of the sulfide itself, which is easily continuously oxidized by the positive electrode during the electrochemical cycle.

[0006] Summary of the Invention

[0007] (1) Purpose of the invention

[0008] The purpose of the present invention is to provide a solid electrolyte material, a preparation method, an electrolyte layer and a lithium ion battery that improve air stability and matching stability with an oxide positive electrode.

[0009] (2) Technical solution

[0010] In order to solve the above problems, the present invention provides a sulfide solid electrolyte material, the chemical formula of which is Li a P b C m S d O n Cl f , among which 5.4≤a≤6.1, 0.9≤b≤1, 0<m≤0.1, 4.1≤d≤5, 0<n≤0.3, 1≤f≤1.7.

[0011] In another aspect of the present invention, preferably, 0.01≤m≤0.05, 0.05≤n≤0.2.

[0012] In another aspect of the present invention, preferably, 5.4≤a≤5.6, 0.95≤b≤1, 4.3≤d≤4.6, and 1.4≤f≤1.6.

[0013] In another aspect of the present invention, preferably, the ionic conductivity of the sulfide solid electrolyte material is ≥5×10 -3 S / cm, electronic conductivity <10×10 -9 S / cm, and the ion conductivity retention rate after being placed in a dew point of -45°C for 24 hours is greater than 50%.

[0014] In another aspect of the present invention, preferably, a method for preparing the sulfide solid electrolyte material as described above comprises the following steps:

[0015] Step 100: mixing raw materials for forming a sulfide solid electrolyte material and grinding and mixing to obtain a first reactant;

[0016] Step 200: placing the first reactant in a quartz tube, vacuum-sealing it, calcining it, and grinding it to obtain a second reactant;

[0017] Step 300: heating the second reactant under the protection of an inert gas and introducing a carbon-containing gas to obtain a sulfide solid electrolyte material.

[0018] In another aspect of the present invention, preferably, the raw materials of the sulfide solid electrolyte material include: Li2S, P2S5, LiCl and Li2O.

[0019] In another aspect of the present invention, preferably, step 200: placing the first reactant in a quartz tube for vacuum packaging, calcining, and grinding to obtain a second reactant comprises:

[0020] The vacuum degree of the vacuum packaging is ≤50Pa;

[0021] The calcination is carried out by heating the temperature from room temperature to 400-600°C over 30-120 minutes and keeping the temperature for a preset time.

[0022] In another aspect of the present invention, preferably, the carbon-containing gas comprises at least one of CS2 or CCl4, and the flow rate of the carbon-containing gas is 1 to 20 L / min.

[0023] In another aspect of the present invention, preferably, an electrolyte layer comprises the sulfide solid electrolyte material as described above or the sulfide solid electrolyte material prepared by the preparation method as described above, and the electrolyte layer is formed by pressing the sulfide solid electrolyte material.

[0024] In another aspect of the present invention, preferably, a lithium-ion battery comprises a positive electrode layer, a negative electrode layer and a solid electrolyte layer between the positive and negative electrodes, characterized in that the solid electrolyte layer comprises the sulfide solid electrolyte material as described above, the sulfide solid electrolyte material prepared by the preparation method as described above, or the electrolyte layer as described above. (3) Beneficial effects

[0025] The above technical solution of the present invention has the following beneficial technical effects:

[0026] The present invention co-dopes an argyrodite-type sulfide electrolyte with O and C to obtain a solid electrolyte material that maintains the original excellent properties of the electrolyte material, such as high ionic conductivity, good mechanical strength, and excellent negative electrode stability, while effectively improving the air stability and positive electrode stability of the electrolyte, thereby significantly enhancing its overall performance and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a diagram of Li in Example 1 provided by the present invention. 5.54 P 0.96 C 0.04 S 4.4 O 0.1 Cl 1.5 X-ray diffraction pattern of the electrolyte.

[0028] FIG2 is a diagram of Li in Example 1 provided by the present invention. 5.54 P 0.96 C 0.04 S 4.4 O 0.1 Cl 1.5Electrochemical impedance spectroscopy of the electrolyte. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0030] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] In the description of the present invention, it should be noted that the terms "first", "second" and "third" are only used for descriptive purposes and should not be understood as indicating or implying relative importance.

[0032] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Example

[0034] A sulfide solid electrolyte material with the general chemical formula Li a P b C m S d O n Cl f , among which 5.4≤a≤6.1, 0.9≤b≤1, 0<m≤0.1, 4.1≤d≤5, 0<n≤0.3, 1≤f≤1.7.

[0035] The sulfide solid electrolyte provided by the present invention is obtained by co-doping O and C elements into a Li6PS5Cl-based argyrodite-type sulfide solid electrolyte.

[0036] It is an existing technology to improve the air stability of Li6PS5Cl-based argyrodite-type sulfide solid electrolytes by O doping. The main principle is to replace S with part of O to form a more stable PO bond in the crystal structure to replace the easily hydrolyzed PS bond, thereby improving the air stability of the electrolyte. However, while forming the PO bond, the Li-S bond, which originally had a weaker bond energy and was conducive to lithium ion transmission, will also be partially replaced by a Li-O bond with a stronger bond energy and not conducive to lithium ion transmission, resulting in a decrease in the electrolyte ion conductivity. As shown in a comparative example of the present invention, the room temperature ionic conductivity retention rate of a sulfide electrolyte doped with a small amount of O after exposure to a dew point environment of -45°C for 24 hours is increased from 36.6% when undoped to 48.7%, but its initial room temperature ionic conductivity is increased from 5.4×10 -3 S / cm decreased to 4.6×10 -3 S / cm.

[0037] In this embodiment, the ionic conductivity of the sulfide electrolyte is improved by doping the P site with C. Since the atomic radius of C is smaller than that of P atoms, a wider lithium ion transmission channel will be formed in the crystal structure after element substitution, thereby compensating for the adverse effect of O doping on ionic conductivity. The existing technology generally uses Al, Ga, In, Si, Ge, Sn, As, Sb and other ions to dope P. It is more difficult to dope with C. The main reason is that the atomic radius of C is too small and the difference with P is too large, making it difficult to incorporate into the crystal lattice. Once it cannot be effectively incorporated into the crystal lattice and exists in the form of impurities, the electronic conductivity of the electrolyte will increase, thereby seriously affecting the performance of the electrolyte in the battery, especially inducing lithium dendrites and causing battery failure.

[0038] In this embodiment, CS2 or CCl4 is used as a carbon source, and the sulfide electrolyte is annealed in a CS2 or CCl4 atmosphere to achieve trace carbon lattice doping. Analysis of the doped electrolyte reveals that the electrolyte contains considerable carbon, with a mass fraction of up to 0.5%. However, the X-ray diffraction (XRD) pattern of the electrolyte shows no impurities, and the electronic conductivity can be maintained at less than 10×10 -9 Low levels of S / cm.

[0039] The sulfide electrolyte co-doped with O and C has good air stability and room temperature ionic conductivity. As shown in one embodiment of the present invention, the sulfide electrolyte co-doped with O and C has an ionic conductivity retention rate of 81.2% after exposure to a -45°C dew point environment for 24 hours, and the initial ionic conductivity can reach 8.5×10 -3 High levels of S / cm.

[0040] Although C doping alone can improve the ionic conductivity of the sulfide electrolyte, it cannot improve its air stability. As shown in another comparative example of the present invention, the initial ionic conductivity of the sulfide electrolyte doped with C alone is 6.1×10 -3 S / cm, but its ionic conductivity retention rate after exposure to a -45°C dew point environment for 24 h was only 32.1%.

[0041] Whether doped alone or co-doped, the doping amounts of O and C are very limited. For example, when doping with O alone, if the doping amount is too high, a Li2O impurity phase will appear in the XRD pattern of the electrolyte. When co-doping with O and C, if the doping amount is too high, a Li2CO3 impurity phase will appear in the XRD pattern of the electrolyte. When doping with C alone, whether annealing is performed in a CS2 or CCl4 atmosphere, there is an upper limit to the C incorporation amount, which does not exceed 0.5%. This indicates that the reaction between CS2 and CCl4 and the electrolyte powder may be limited to the surface of the electrolyte particles. When a C content exceeding 0.5% is detected in the electrolyte, the electronic conductivity of the electrolyte will also increase significantly, indicating that the C at this time no longer exists in a compound state doped into the crystal lattice, but exists as a single substance or other highly conductive impurity.

[0042] Unexpectedly, the stability of the sulfide electrolyte obtained by co-doping with O and C and the oxide positive electrode has also been significantly improved. As shown in another set of embodiments and comparative examples of the present invention, the all-solid-state demonstration battery prepared by matching the O and C co-doped sulfide electrolyte with the NCM532 positive electrode still has a capacity retention rate of more than 71.2% after 250 cycles at a current density of 0.3C, which is much higher than the data obtained by using undoped electrolytes and separate O and C doped electrolytes (60.8%, 63.4%, and 53.1%, respectively). In-depth research found that the Li2CO3 phase was observed at the electrolyte interface after cycling. Since there is no Li2CO3 impurity phase in the initial electrolyte, the Li2CO3 phase is likely to be formed during the electrochemical cycle. Based on this, it is speculated that the scientific mechanism by which O and C co-doping improves the stability of the electrolyte and the positive electrode is that the trace amount of O and C in the electrolyte forms a stable Li2CO3 intermediate layer at the interface between the positive electrode and the electrolyte particles during the battery cycle. This intermediate layer prevents the continuous oxidation of the sulfide electrolyte during the cycle, thereby greatly improving the cycle stability.

[0043] In one embodiment of the present invention, further, Li a P b C m S d O n Cl fThe preferred composition of the sulfide solid electrolyte material is: 0.01≤m≤0.05, 0.05≤n≤0.2; 5.4≤a≤5.6, 0.95≤b≤1, 4.3≤d≤4.6, 1.4≤f≤1.6.

[0044] Within this range, the electrolyte has higher ionic conductivity and better overall performance.

[0045] In one embodiment of the present invention, further, the ionic conductivity of the sulfide solid electrolyte material is ≥5×10 -3 S / cm, electronic conductivity <10×10 -9 S / cm, and the ionic conductivity retention rate after being placed in a dew point of -45°C for 24 hours is greater than 50%. Furthermore, the ionic conductivity of the sulfide solid electrolyte material is ≥6×10 -3 S / cm.

[0046] The following will further illustrate the implementation of the sulfide electrolyte material and the preparation method thereof in conjunction with specific examples of the present invention. Unless otherwise specified, the raw materials used in each example are commercially available products, and the process conditions are conventional operating conditions unless otherwise specified.

[0047] A method for preparing the sulfide solid electrolyte material as described above comprises the following steps:

[0048] Step 100: Mixing and grinding raw materials for forming a sulfide solid electrolyte material to obtain a first reactant; the raw materials for the sulfide solid electrolyte material include: Li2S, P2S5, LiCl and Li2O;

[0049] Step 200: placing the first reactant in a quartz tube, performing vacuum packaging, calcining, and grinding to obtain a second reactant; the vacuum degree of the vacuum packaging is ≤50Pa;

[0050] Calcination is carried out by heating from room temperature to 400-600℃ over 30-120min and keeping the temperature for the preset time;

[0051] Step 300: heating the second reactant under the protection of an inert gas and introducing a carbon-containing gas to obtain a sulfide solid electrolyte material; the carbon-containing gas includes at least one of CS2 or CCl4, and the flow rate of the carbon-containing gas is 1 to 20 L / min.

[0052] An electrolyte layer comprises the sulfide solid electrolyte material as described above or the sulfide solid electrolyte material prepared by the preparation method as described above, wherein the electrolyte layer is formed by pressing the sulfide solid electrolyte material.

[0053] A lithium-ion battery comprises a positive electrode layer, a negative electrode layer and a solid electrolyte layer between the positive and negative electrodes, wherein the solid electrolyte layer comprises the sulfide solid electrolyte material described above, the sulfide solid electrolyte material prepared by the preparation method described above, or the electrolyte layer described above.

[0054] Example 1:

[0055] In an inert gas glove box, according to the chemical formula Li 5.54 P 0.96 C 0.04 S 4.4 O 0.1 Cl 1.5 8.83g Li2S, 10.67g P2S5, 6.36g LiCl, and 0.3g Li2O powders were weighed in a mass ratio and evenly ground in an agate mortar. The raw materials were then poured into a 250ml sealed ball mill and evenly ground with zirconia balls. The ball mill speed was set to 300rpm and ball milled for 12 hours to obtain the first reactant. The ground first reactant was placed in a quartz tube and vacuum packaged, maintaining the vacuum at 5Pa. The packaged quartz tube was then placed in a muffle furnace and calcined. The calcination process was carried out by heating from room temperature to 500°C over 60 minutes and keeping it at this temperature for 15 hours. The temperature was then cooled to 50°C over 8 hours to obtain the second reactant. The second reactant in the quartz tube was taken out from the glove box, ground with an agate mortar, and transferred to an atmosphere tube furnace. The second reactant was heated to 300 ° C under the protection of inert gas, and then CS2 gas was introduced into the tube furnace at a flow rate of 2 L / min. After keeping the temperature for 10 minutes, the CS2 gas was stopped, and the reactant was taken out after normal cooling and crushed to obtain Li 5.54 P 0.96 C 0.04 S 4.4 O 0.1 Cl 1.5 Solid electrolyte material, FIG1 shows the Li in Example 1 provided by the present invention 5.54 P 0.96 C 0.04 S 4.4 O 0.1 Cl 1.5 X-ray diffraction pattern of electrolyte; Figure 2 shows the Li 5.54 P 0.96 C 0.04 S 4.4 O 0.1 Cl 1.5 The electrochemical impedance spectroscopy of the electrolyte is shown in FIG1 and FIG2 . The solid electrolyte material of this embodiment does not contain any impurities and has good electrochemical performance.

[0056] Example 2:

[0057] In an inert gas glove box, according to the chemical formula Li 5.55 P 0.95 C 0.05 S 4.3 O 0.2 Cl 1.5 8.4g Li2S, 10.56g P2S5, 6.36g LiCl, and 0.6g Li2O powders were weighed in a mass ratio and evenly ground in an agate mortar. The raw materials were then poured into a 250ml sealed ball mill and evenly ground using zirconia balls. The ball mill speed was set to 300rpm and ball milled for 12 hours to obtain the first reactant. The ground first reactant was placed in a quartz tube and vacuum packaged, maintaining the vacuum at 1Pa. The packaged quartz tube was then placed in a muffle furnace and calcined. The calcination process was carried out by heating from room temperature to 600°C over 90 minutes, maintaining the temperature at this temperature for 15 hours, and then cooling to 50°C over 8 hours to obtain the second reactant. The second reactant in the quartz tube was taken out from the glove box, ground with an agate mortar, and transferred to an atmosphere tube furnace. The second reactant was heated to 300 ° C under the protection of inert gas, and then CS2 gas was introduced into the tube furnace at a flow rate of 10 L / min. After keeping the temperature for 10 minutes, the CS2 gas was stopped, and the reactant was taken out after normal cooling and crushed to obtain Li 5.55 P 0.95 C 0.05 S 4.3 O 0.2 Cl 1.5 solid electrolyte materials.

[0058] Example 3:

[0059] In an inert gas glove box, according to the chemical formula Li 5.51 P 0.99 C 0.01 S 4.44 O 0.06 Cl 1.58.95g Li2S, 11g P2S5, 6.36g LiCl, and 0.18g Li2O powders were weighed in a mass ratio and evenly ground in an agate mortar. The raw materials were then poured into a 250ml sealed ball mill and evenly ground with zirconia balls. The ball mill speed was set to 300rpm and ball milled for 12 hours to obtain the first reactant. The ground first reactant was placed in a quartz tube and vacuum packaged, maintaining the vacuum at 20Pa. The packaged quartz tube was then placed in a muffle furnace and calcined. The calcination process was carried out by heating from room temperature to 450°C over 120 minutes, maintaining the temperature at this temperature for 15 hours, and then cooling to 50°C over 8 hours to obtain the second reactant. The second reactant in the quartz tube was taken out from the glove box, ground in an agate mortar, and transferred to an atmosphere tube furnace. The second reactant was heated to 300 ° C under the protection of inert gas, and then CS2 gas was introduced into the tube furnace at a flow rate of 1 L / min. After keeping warm for 10 minutes, the CS2 gas was stopped, and the reactant was taken out after normal cooling and crushed to obtain Li 5.51 P 0.99 C 0.01 S 4.44 O 0.06 Cl 1.5 solid electrolyte materials.

[0060] Example 4

[0061] In an inert gas glove box, according to the chemical formula Li 5.64 P 0.96 C 0.04 S 4.5 O 0.1 Cl 1.4 9.66g Li2S, 10.67g P2S5, 5.26g LiCl, and 0.30g Li2O powder raw materials were weighed in a mass ratio and evenly ground and mixed using an agate mortar. The raw materials were then poured into a 250ml sealed ball mill and evenly ground using zirconia balls. The ball mill speed was set to 300rpm and ball milled for 12 hours to obtain the first reactant. The ground first reactant was placed in a quartz tube for vacuum packaging, maintaining the vacuum degree at 50Pa. The packaged quartz tube was then placed in a muffle furnace for calcination. The calcination was carried out by heating from room temperature to 400°C over 30 minutes and keeping it at this temperature for 15 hours. The temperature was then cooled to 50°C over 8 hours to obtain the second reactant. The second reactant in the quartz tube was taken out from the glove box, ground with an agate mortar to obtain the second reactant, and then transferred to an atmosphere tube furnace. The second reactant was heated to 300 ° C under the protection of inert gas, and then CCl4 gas was introduced into the tube furnace for reaction. The flow rate of CCl4 gas was 20 L / min. After keeping warm for 10 minutes, the CCl4 gas was stopped. After cooling normally, the reactant was taken out and crushed to obtain Li5.64 P 0.96 C 0.04 S 4.5 O 0.1 Cl 1.4 solid electrolyte materials.

[0062] Example 5-32

[0063] In an inert gas glove box, according to the chemical formula Li a P b C m S d O n X f Li2S, P2S5, LiCl, Li2O and other powder raw materials were weighed in different mass proportions and evenly ground and mixed using an agate mortar. Except for the different proportions of elements in the chemical formula, other synthesis conditions were the same as those in Example 1.

[0064] Comparative Example 1

[0065] In an inert gas glove box, according to the chemical formula Li 5.5 PS 4.5 Cl 1.5 9.2gLi2S, 11.12gP2S5, and 6.36gLiCl powder raw materials were weighed in a ratio, and the above raw materials were evenly ground and mixed with an agate mortar, and then poured into a 250ml sealed ball mill jar and evenly ground with zirconia balls. The ball mill speed was set to 300rpm and ball milled for 12h. The ground mixed powder was placed in a quartz tube for vacuum packaging, and the vacuum degree was maintained within 50Pa. The packaged quartz tube was then placed in a muffle furnace for calcination. The calcination procedure was to heat from room temperature to 500℃ over 120min, keep warm at this temperature for 15h, and then cool to 50℃ after 8 hours. After taking out the sample from the quartz tube from the glove box, it was ground with an agate mortar to obtain Li 5.5 PS 4.5 Cl 1.5 solid electrolyte materials.

[0066] Comparative Example 2

[0067] In an inert gas glove box, according to the chemical formula Li 5.5 PS 4.4 O 0.1 Cl 1.5 The mass ratio of 8.74gLi2S, 11.12gP2S5, 6.36gLiCl, and 0.3gLi2O powder raw materials was weighed, and the other synthesis conditions were the same as those in Comparative Example 1. Finally, Li 5.5 PS 4.4 O 0.1 Cl 1.5solid electrolyte materials.

[0068] Comparative Example 3:

[0069] In an inert gas glove box, according to the chemical formula Li 5.54 P 0.96 C 0.04 S 4.42 Cl 1.5 9.29gLi2S, 10.67gP2S5, and 6.36gLiCl powder raw materials were weighed in a ratio, and the above raw materials were evenly ground and mixed with an agate mortar. Then they were poured into a 250ml sealed ball mill and evenly ground with zirconia balls. The ball mill speed was set to 300rpm and ball milled for 12h. The ground mixed powder was placed in a quartz tube for vacuum packaging, and the vacuum degree was kept within 50Pa. The packaged quartz tube was then placed in a muffle furnace for calcination. The calcination procedure was to heat from room temperature to 500℃ over 120min, keep it at this temperature for 15h, and then cool it to 50℃ after 8 hours. After taking the sample out of the quartz tube in the glove box, the sample was ground with an agate mortar and transferred to an atmosphere tube furnace. The sample was heated to 300°C under inert gas protection, and then CS2 gas was introduced into the tube furnace. After keeping the temperature for 10 minutes, the CS2 gas was stopped. After normal cooling, the sample was taken out and crushed to obtain Li 5.54 P 0.96 C 0.04 S 4.42 Cl 1.5 solid electrolyte materials.

[0070] The general test method for sulfide electrolytes uses the following three methods:

[0071] 1. Ionic conductivity test:

[0072] The electrolyte powder was pressed into a tablet within a molded cell at a pressure of 250 MPa. The thickness of the electrolyte layer was measured, recorded as L. A symmetrical blocked electrode cell (steel column / electrolyte / steel column) was then assembled within the molded cell. The AC impedance of this cell under open-circuit conditions was measured, recorded as R. This impedance was calculated using the formula σ = L / (R·S), where σ is the ionic conductivity, L is the thickness of the electrolyte layer, R is the impedance value, and S is the electrode area of ​​the electrolyte sheet. The ionic conductivity measured at room temperature (25°C) is the ionic conductivity of the electrolyte powder.

[0073] 2. Electronic conductivity test:

[0074] The same ionic conductivity measurement method is used to measure the average current of a symmetrical barrier electrode cell at 3.5V until equilibrium. The average current value is recorded as I and calculated using the formula λ = L / (S*V / I), where λ is the electronic conductivity, L is the electrolyte layer thickness, S is the electrolyte layer area, V is the equilibrium voltage of 3.5V, and I is the equilibrium current (the average current value over 1700s-1800s). The electronic conductivity measured at room temperature (25°C) is the electronic conductivity of the electrolyte powder.

[0075] 3. Ionic conductivity retention test:

[0076] The electrolyte powder with ionic conductivity of σ0 is placed in a -45℃ dew point test chamber for 24 hours, and the ionic conductivity after placement is measured as σ t , with σ t / σ0×100% is recorded as the ionic conductivity retention rate.

[0077] The test results of the chemical composition, ionic conductivity, electronic conductivity, ionic conductivity after being placed at a dew point of -45°C for 24 hours, and ionic conductivity retention of the sulfide solid electrolytes of Examples 1-32 and Comparative Examples 1-3 are shown in Table 1.

[0078] Table 1 Test results of sulfide solid electrolytes of Examples 1-32 and Comparative Examples 1-3

[0079] Solid electrolyte cycle stability test:

[0080] The solid electrolyte is loaded into the inner liner of a circular battery mold with a diameter of 10 mm, and a pressure of 300 MPa is applied to the inner liner and the pressure is maintained for 90 seconds to form a solid electrolyte layer. Then, the solid electrolyte, NCM523 positive electrode, and conductive carbon black are weighed and evenly mixed in a ratio of 40:55:5 to form a positive electrode mixture. The inner liner of the above-mentioned battery mold is opened, and the obtained positive electrode mixture is poured into one side of the pressed electrolyte layer. A pressure of 300 MPa is applied to the inner liner and the pressure is maintained for 90 seconds to form a solid-state battery positive electrode layer. The inner liner of the above-mentioned battery mold is opened again, and a lithium-indium alloy sheet is loaded into the other side of the electrolyte layer. A pressure of 150 MPa is applied to the inner liner and the pressure is maintained for 90 seconds to form a solid-state battery negative electrode layer. Finally, an all-solid-state lithium secondary battery is formed.

[0081] The assembled all-solid-state battery pack was placed in a 25°C constant temperature box to test the battery cycle performance. The test conditions were to use a current density of 0.3C to test the first week charge and discharge performance and cycle charge and discharge performance of the solid-state battery. The voltage range during the test was set at 1.9-3.7V (Li + / Li).

[0082] The battery cycle performance test results of all-solid-state batteries prepared from the electrolytes synthesized in Examples 1-32 and Comparative Examples 1-3 are shown in Table 2.

[0083] Table 2 Battery cycle performance test results of Examples 1-32 and Comparative Examples 1-3

[0084] In summary, the sulfide solid electrolyte material obtained by the present invention improves the stability of the electrolyte and the positive electrode due to the co-doping of O and C therein. The scientific mechanism is that the trace O and C in the electrolyte form a stable Li2CO3 intermediate layer at the interface between the positive electrode and the electrolyte particles during the battery cycle. The intermediate layer prevents the continuous oxidation of the sulfide electrolyte during the cycle, thereby greatly improving the cycle stability. It also has a higher ionic conductivity. When the content of O and C is co-doped in this embodiment, no impurities will appear in the XRD spectrum of the electrolyte. The cycle stability of the oxide positive electrode is good during the charge and discharge process of the solid-state battery, and the comprehensive performance is significantly better than that of conventional undoped or single-doped sulfide solid electrolytes. At the same time, it has the characteristics of simple production method and scalable preparation, providing a good foundation for the large-scale application of solid-state electrolyte materials in all-solid-state batteries.

[0085] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

[0086] The present invention has been described above with reference to the embodiments thereof. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims and their equivalents. Those skilled in the art may make various substitutions and modifications without departing from the scope of the present invention, and such substitutions and modifications are intended to fall within the scope of the present invention.

[0087] Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.

[0088] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A sulfide solid electrolyte material, characterized in that: Its chemical formula is Li a P b C m S d O n Cl f , where 5.4≤a≤6.1, 0.9≤b≤1, 0<m≤0.1, 4.1≤d≤5, 0<n≤0.3, 1≤f≤1.

7.

2. The sulfide solid electrolyte material according to claim 1, characterized in that 0.01≤m≤0.05, 0.05≤n≤0.

2.

3. The sulfide solid electrolyte material according to claim 1, characterized in that 5.4≤a≤5.6, 0.95≤b≤1, 4.3≤d≤4.6, 1.4≤f≤1.

6.

4. The sulfide solid electrolyte material according to any one of claims 1 to 3, characterized in that: The ionic conductivity of the sulfide solid electrolyte material is ≥5×10 -3 S / cm, electronic conductivity <10×10 -9 S / cm, the ion conductivity retention rate after being placed in a dew point of -45°C for 24 hours is >50%.

5. A method for preparing the sulfide solid electrolyte material according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 100: mixing raw materials for forming a sulfide solid electrolyte material and grinding and mixing them to obtain a first reactant; Step 200: placing the first reactant in a quartz tube for vacuum packaging, calcining, and grinding to obtain a second reactant; Step 300: heating the second reactant under the protection of an inert gas, and introducing a carbon-containing gas to obtain a sulfide solid electrolyte material.

6. The preparation method according to claim 5, characterized in that: The raw materials of the sulfide solid electrolyte material include: Li2S, P2S5, LiCl and Li2O.

7. The preparation method according to claim 5, characterized in that: The step 200: placing the first reactant in a quartz tube for vacuum packaging, calcining, and grinding to obtain a second reactant, comprises: The vacuum degree of the vacuum packaging is ≤50Pa; The calcination is carried out by heating from room temperature to 400-600°C over 30-120 minutes and keeping the temperature for a preset time.

8. The preparation method according to claim 5, characterized in that: The carbon-containing gas includes at least one of CS2 and CCl4, and the flow rate of the carbon-containing gas is 1 to 20 L / min.

9. An electrolyte layer, characterized in that It comprises the sulfide solid electrolyte material according to any one of claims 1 to 4 or the sulfide solid electrolyte material prepared by the preparation method according to any one of claims 5 to 8, and the electrolyte layer is formed by pressing the sulfide solid electrolyte material.

10. A lithium ion battery comprising a positive electrode layer, a negative electrode layer and a solid electrolyte layer between the positive and negative electrodes, characterized in that: The solid electrolyte layer comprises the sulfide solid electrolyte material according to any one of claims 1 to 4, the sulfide solid electrolyte material prepared by the preparation method according to any one of claims 5 to 8, or the electrolyte layer according to claim 9.

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