Surface oxygen-enriched sulfide solid electrolyte material and preparation method and application thereof

Abstract

The application belongs to the technical field of lithium batteries, and particularly relates to a surface oxygen-rich sulfide solid electrolyte material and a preparation method and application thereof. The sulfide solid electrolyte material contains lithium ions and anions containing at least a sulfur element, and further contains oxygen elements. The oxygen elements are unevenly distributed, so that the oxygen elements are substantially enriched on the outer surface of the sulfide solid electrolyte material. Compared with the prior art, the surface oxygen-rich sulfide solid electrolyte material can greatly reduce the doping amount, improve the air stability and the stability to oxide positive electrodes by using oxygen doping, and does not affect the ion conductivity.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a surface oxygen-rich sulfide solid electrolyte material and its preparation method and application. Background Technology

[0002] Since their commercialization in the early 1990s, lithium-ion rechargeable batteries have experienced rapid development due to their advantages such as high energy density and long lifespan. However, currently widely used lithium-ion batteries are liquid-phase batteries, containing flammable organic electrolytes, thus posing serious safety hazards. Frequent safety incidents involving liquid-phase lithium-ion power batteries in recent years have significantly limited the further use of this system. Using non-flammable inorganic solid materials as the electrolyte for lithium-ion batteries can not only eliminate the safety hazards caused by organic electrolyte leakage and internal thermal runaway during battery use, but also allow for use under extreme conditions such as high and low temperatures. This further enhances the value of lithium rechargeable batteries and expands their application areas. Therefore, developing solid-state electrolyte materials with high stability and high ionic conductivity is a key aspect of promoting the commercialization of solid-state batteries.

[0003] Among solid electrolytes, sulfide-based solid electrolytes have attracted much attention due to their extremely high lithium-ion conductivity. Various P-S groups are widely present in sulfide solid electrolytes. When exposed to air, these P-S groups react with H₂O to produce toxic H₂S gas, which simultaneously reduces the ionic conductivity of the solid electrolyte. Non-patent literature shows (J. SolidState Electrochem., 2013, 17, 2551-2557.) that O doping can effectively reduce the amount of H₂S gas produced. Another problem with sulfide solid electrolytes is their poor compatibility with oxide cathodes. O-doped sulfide solid electrolytes have better compatibility with oxide cathodes because they can confine the space charge layer. Non-patent literature shows (J. Alloys Compd., 2014, 591, 247-250.) that the drawback of this method is that when the substitution amount reaches a certain level, bridging O hinders Li₂O. + O migration reduces the conductivity of the electrolyte, which is detrimental to the practical application of sulfide solid electrolytes. Therefore, in order to improve the performance of sulfide solid electrolytes without reducing their ionic conductivity, the amount of O doping must be controlled.

[0004] Traditional O-doped sulfide solid electrolyte materials have the following shortcomings: 1) O element is uniformly distributed inside the electrolyte, and the O element concentration on the surface of the electrolyte particles is the same as that inside, making it difficult to reduce the doping amount; 2) Although coating the surface with an O-containing layer reduces the overall O element concentration, the preparation method is complicated, the control is difficult, and the surface coating layer is prone to "shedding" during use.

[0005] Chinese patent CN201910534210.1 reports a sulfide solid electrolyte containing [PS3O] units, which improves both ionic conductivity and stability. The amount of oxidant added is as high as 0.1wt% to 5wt%. Since the O element is distributed throughout the solid electrolyte, there is room for further optimization of the O element concentration. Meanwhile, elements other than O in the solid oxidant have an adverse effect on the performance of the solid electrolyte.

[0006] Chinese patent CN201910648164.8 reports a three-layer core-shell structured sulfide solid electrolyte. The structure of this material is too complex to be industrially applied. The addition of P2S5 and O2 significantly reduces the ionic conductivity of the original material. This may be because the preparation method makes it difficult to control the complete reaction of the two reactants, resulting in the presence of impurity phases with low ionic conductivity in the electrolyte material.

[0007] Chinese patent CN201811018312.X reports a sulfide solid electrolyte material with an oxide layer on its surface. The oxide layer contains lithium, phosphorus, halogens, and oxygen-containing oxides. This approach essentially involves surface oxide doping, but the oxygen element does not enter the crystal lattice of the sulfide solid electrolyte. The added oxides lead to a decrease in the ionic conductivity of the solid electrolyte, and the core-shell structure is very difficult to prepare. Furthermore, there is a risk of "shell detachment" during charge-discharge cycling.

[0008] Chinese patent CN201980004437.3 improves rate and cycle performance by increasing the oxygen concentration and decreasing the halogen concentration on the surface of solid electrolyte particles, thereby enhancing the contact between the solid electrolyte and the positive or negative electrode active material particles. However, this method suffers from a significant decrease in the ionic conductivity of the sulfide solid electrolyte (3.0→1.5 mS / cm, 2.7→1.5 mS / cm, 5.7→1.9 mS / cm). This is because the method involves exposing the original sulfide solid electrolyte to humid air for surface enrichment oxidation, essentially resulting in hydrolysis and failure of the electrolyte surface particles. Another drawback is the difficulty in controlling the extent and depth of the hydrolysis reaction within the electrolyte particles, and the generation of toxic hydrogen sulfide gas, which poses a hazard to the environment and operators. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a highly stable, highly ion-conducting surface-oxygen-rich sulfide solid electrolyte material, its preparation method, and the application of the obtained material in solid-state lithium secondary batteries.

[0010] This surface-enriched oxygen-sulfide solid electrolyte material contains oxygen only at a certain depth on the surface of the electrolyte particles. Surface oxygen doping improves the air stability and stability of the sulfide solid electrolyte material to the oxide cathode. Surface oxygen doping also reduces the overall oxygen concentration in the electrolyte, avoiding a decrease in ionic conductivity; that is, it utilizes the effect of oxygen doping without affecting ionic conductivity. Furthermore, the preparation method of this surface-enriched oxygen-sulfide solid electrolyte material is simple and effective, and combined with the electrolyte material crushing process, the production cost is low. Therefore, the surface-enriched oxygen-sulfide solid electrolyte material and its preparation method provided by this invention are expected to solve the problem of large-scale application of sulfide solid electrolyte materials.

[0011] Specifically, the present invention first provides a sulfide solid electrolyte material with oxygen-rich surface, wherein the sulfide solid electrolyte material contains lithium ions and anions containing at least sulfur.

[0012] The sulfide solid electrolyte material also contains oxygen, which is present in a non-uniform distribution so that the oxygen is substantially concentrated on the outer surface of the sulfide solid electrolyte material.

[0013] This invention has found that surface oxygen enrichment can greatly improve the air stability and stability of sulfide solid electrolyte materials to oxide cathodes, while also significantly reducing the overall oxygen concentration in the electrolyte and preventing a decrease in ion conductivity.

[0014] The term “the oxygen element is substantially enriched in the outer surface layer of the sulfide solid electrolyte material” as used herein means that more than 90% of the oxygen element is substantially enriched in the outer surface layer of the sulfide solid electrolyte material, more preferably more than 95%.

[0015] Preferably, L / D ≤ ​​10%, where L represents the thickness of the oxygen-rich layer on the outer surface of the sulfide solid electrolyte material, and D represents the particle diameter of the sulfide solid electrolyte material.

[0016] Further preferably, 1% ≤ L / D ≤ ​​5%, and L ≥ 5 nm. Under the above conditions, the oxygen element is enriched within a certain depth on the outer surface of the electrolyte particles (i.e., the thickness of the oxygen-rich layer), which can take into account both excellent air stability and stability to the oxide cathode, and further reduce the amount of oxygen doping.

[0017] This invention also provides a method for preparing a surface-enriched oxygen-sulfide solid electrolyte material. This method is simple and effective, and combined with the electrolyte material crushing process, it is suitable for large-scale production with low production costs. Specifically, it includes the following steps:

[0018] 1) Provide a sulfide solid electrolyte material that is substantially free of oxygen; the term “sulfide solid electrolyte material that is substantially free of oxygen” as used herein means that the oxygen content in the sulfide solid electrolyte material is less than 100 ppm, more preferably less than 50 ppm.

[0019] 2) The sulfide solid electrolyte material from step 1) is crushed in an oxygen-free medium;

[0020] 3) The sulfide solid electrolyte material treated in step 2) is crushed in an oxygen-containing medium;

[0021] 4) Heat-treat the sulfide solid electrolyte material after step 3).

[0022] The method for providing a sulfide solid electrolyte material that is substantially free of oxygen according to the present invention is arbitrary. It can be purchased or manufactured. Here, an example of a method for manufacturing the raw material solid electrolyte particles is described. However, the method for manufacturing the raw material solid electrolyte particles is arbitrary.

[0023] For example, Li2S, LiCl, and P2S5 can be weighed, mixed, and heat-treated in proportion to obtain oxygen-free sulfide solid electrolyte materials.

[0024] Preferably, the oxygen-free medium in step 2) is an oxygen-free inert gas, more preferably nitrogen, argon, or a nitrogen / argon mixture. The purpose of the crushing process under the above atmosphere is to activate the electrolyte material, thereby enhancing its reactivity with oxygen in subsequent steps.

[0025] Preferably, the crushing process in step 2) is ball milling, with a rotation speed of 200-500 rpm and a time of 5-24 h.

[0026] Preferably, the oxygen-containing medium in step 3) is an inert gas containing oxygen, and more preferably it is nitrogen, argon or a nitrogen / argon mixture containing oxygen.

[0027] Preferably, the oxygen concentration in the oxygen-containing medium in step 3) is 100–5000 ppm, and more preferably, the oxygen concentration is 3000–5000 ppm. Ball milling at the above oxygen concentration results in a sulfide solid electrolyte material that better balances high air stability, stability to the oxide cathode, and ion conductivity.

[0028] Preferably, the crushing process in step 3) is ball milling at a speed of 100–300 rpm for 2–12 hours; more preferably, the speed is 150–250 rpm for 8–12 hours. Under the above ball milling conditions, the resulting sulfide solid electrolyte material can better balance high air stability, stability to the oxide cathode, and ion conductivity.

[0029] Preferably, the heat treatment temperature in step 4) is 250℃-350℃, the heat treatment time is 3-48h, and the protective gas for the heat treatment is an inert gas.

[0030] This invention also provides the application of surface oxygen-rich sulfide solid electrolyte materials in the preparation of solid-state lithium secondary batteries.

[0031] Specifically, the present invention provides a positive electrode layer for a solid-state battery, which is prepared by the above-mentioned surface oxygen-rich sulfide solid electrolyte material or the surface oxygen-rich sulfide solid electrolyte material prepared by the above-mentioned preparation method, together with a positive electrode material and a conductive agent.

[0032] This invention provides an electrolyte layer for a solid-state battery, which is prepared from the above-described surface oxygen-rich sulfide solid electrolyte material or the surface oxygen-rich sulfide solid electrolyte material prepared by the above-described preparation method. This invention further provides a solid-state lithium secondary battery, comprising a positive electrode layer, an electrolyte layer, and a negative electrode layer, wherein the positive electrode layer is the solid-state battery positive electrode layer provided in the above-described scheme, and the electrolyte layer is the solid-state battery electrolyte layer provided in the above-described scheme.

[0033] This invention provides a surface-enriched oxygen-sulfide solid electrolyte material. Compared with existing technologies, this electrolyte material significantly reduces doping levels due to the presence of oxygen (O) at a certain depth on the surface of the electrolyte particles. O doping enhances its air stability and stability against oxide cathodes without affecting ion conductivity. Furthermore, this invention provides a simple and efficient preparation method. This type of material is easy to prepare and has low production costs; the obtained surface-enriched oxygen-sulfide solid electrolyte material exhibits controllable ion conductivity and excellent performance as an electrolyte material in all-solid-state lithium batteries.

[0034] The beneficial effects of this invention are as follows:

[0035] 1) The oxygen-rich sulfide solid electrolyte material and its preparation method provided by the present invention can greatly reduce the O element concentration by controlling the O doping within a certain depth range on the electrolyte surface, thereby reducing the adverse effects of O doping on the ion conductance of the sulfide solid electrolyte.

[0036] 2) The oxygen-rich sulfide solid electrolyte material and its preparation method provided by the present invention can be realized during the crushing process of the sintered electrolyte without additional steps and equipment, and the impact on cost during large-scale production is negligible. Attached Figure Description

[0037] Figure 1 The XPS peaks of surface O1s for the oxygen-rich sulfide electrolyte obtained in Example 1 and the oxygen-free sulfide electrolyte obtained in Comparative Example 1 are shown.

[0038] Figure 2 The XPS peaks of O1s at different depths from the surface of the oxygen-rich sulfide electrolyte obtained in Example 1 are shown.

[0039] Figure 3 The XRD patterns are those of the oxygen-rich sulfide electrolyte material obtained in Example 1 and the oxygen-free sulfide electrolyte obtained in Comparative Example 1. Detailed Implementation

[0040] The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the examples, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased from legitimate channels.

[0041] Preparation of raw material solid electrolyte

[0042] In a glove box, weigh out each raw material according to the proportions in Table 1, keeping the total weight of all raw materials constant at 5g. Place them in a 50ml zirconia ball mill jar, and add 50g of zirconia balls with a diameter of 5mm. Place the sealed ball mill jar on a ball mill, set the speed to 400rpm, and mill for 12 hours. Collect the milled sample and seal it in a vacuum quartz tube for calcination. The calcination temperature is controlled by a programmed temperature rise. After sintering, allow it to cool naturally to 50℃ to obtain the raw material solid electrolyte.

[0043] in:

[0044] Examples 1-5, Comparative Example 1: Li2S, P2S5, and LiCl were weighed according to the elemental ratio in Li6PS5Cl;

[0045] Example 6, Comparative Example 2: According to Li 5.5 PS 4.5 Cl 1.5 The elemental ratios in the sample are Li₂S, P₂S₅, and LiCl.

[0046] Example 7, Comparative Example 3: Li2S and P2S5 were weighed according to the elemental ratio in 70Li2S-30P2S5;

[0047] Example 8, Comparative Example 4: According to Li 10 GeP2S 12 The elemental ratios in the sample are Li2S, P2S5, and GeS2.

[0048] Example 9, Comparative Example 5: According to Li 9.54 Si 1.74 P 1.44 S 11.7 I 0.3 The elemental proportions in the sample are Li₂S, P₂S₅, SiS₂, and LiI.

[0049] Comparative Examples 6, 7, and 8: respectively according to Li6PS 4.95 O 0.05 Cl, Li6PS 4.9 O 0.1 The elemental ratio in Cl is determined as Li2S, P2S5, LiCl, Li2O.

[0050] Raw material solid electrolyte crushing

[0051] In the glove box, collect the raw solid electrolyte and place it in a 50ml zirconia ball mill jar, adding 50g of zirconia balls with a diameter of 5mm. Place the sealed ball mill jar on the ball mill, set the rotation speed according to ball milling speed 1 in Table 1, and set the ball milling time according to ball milling time 1 to crush the raw solid electrolyte.

[0052] Surface enrichment treatment

[0053] In the ball mill jar after crushing, N2 containing O2 is introduced according to the requirements in Table 1, and the rotation speed is set according to ball milling speed 2 and the time is set according to ball milling time 2 to perform surface enrichment oxidation treatment on the solid electrolyte.

[0054] Heat treatment

[0055] The electrolyte material with rich oxide surface was subjected to heat treatment. The heating rate was set to 3℃ / min, the temperature was raised to 320℃, and held for 10h. The protective gas was N2.

[0056] Air stability testing of solid electrolyte materials

[0057] The surface oxygen-enriched solid electrolyte materials obtained in Examples 1-9 and Comparative Examples 1-8 were subjected to air stability tests. In a glove box, 300 mg of the solid electrolyte material was weighed and placed into a 5 ml open glass bottle. The bottle was then placed in a reaction chamber with a specific humidity airflow and allowed to stand at room temperature for 24 hours. The relative humidity of the dry air was 10%, and the air flow rate was 100 ml / min. After standing, the sample was removed for ion conductivity testing.

[0058] Simulated battery assembly

[0059] The surface oxygen-rich sulfide solid electrolyte materials obtained in Examples 1-9 and Comparative Examples 1-8 were used as cathode materials (LiNi). 0.6 Co 0.2 Mn 0.2 The electrolyte material and acetylene carbon were mixed in a ratio of 70:30:1 (mass ratio). Three materials were weighed and ground in a glove box using a mortar and pestle for 20 minutes to ensure uniform mixing. Using this mixture as the positive electrode powder, a Li metal sheet as the negative electrode, and the electrolyte materials prepared in Examples 1-9 and Comparative Examples 1-8 as the electrolyte layer, an all-solid-state secondary battery was assembled.

[0060] Figure 1 The figures show the XPS peaks of O1s on the surfaces of the oxygen-rich sulfide electrolyte obtained in Example 1 and the oxygen-free sulfide electrolyte obtained in Comparative Example 1. As can be seen from the figures, the oxygen-rich sulfide electrolyte obtained in Example 1 has a significant O signal peak, indicating that O doping has been successfully performed on its surface. In contrast, the sulfide electrolyte obtained in Comparative Example 1 has almost no observable O signal peak, indicating that O doping is not present on its surface.

[0061] Figure 2 The figures show the XPS peaks of O1s at different depths from the surface of the oxygen-rich sulfide electrolyte obtained in Example 1. As can be seen from the figures, the oxygen-rich sulfide electrolyte obtained in Example 1 exhibits strong O signal peaks at distances of 0 nm and 10 nm from the surface, indicating that the electrolyte has been successfully doped with O to a certain depth. However, almost no O signal peak is observed at a distance of 50 nm from the surface, indicating that the electrolyte has only undergone O doping in the surface layer.

[0062] Figure 3The figures show the XRD patterns of the oxygen-rich sulfide electrolyte material obtained in Example 1 and the oxygen-free sulfide electrolyte obtained in Comparative Example 1. As can be seen from the figures, the XRD patterns of the oxygen-rich sulfide electrolyte obtained in Example 1 and the sulfide electrolyte obtained in Comparative Example 1 show no significant difference, and their crystal structures both conform to the JCPDS standard (34-0688, Li7PS6), indicating that surface O doping did not affect the crystal structure of the electrolyte material.

[0063] Table 1 summarizes the initial ion conductance, ion conductance after exposure, and specific discharge capacity of the electrolyte materials in Examples 1-9 and Comparative Examples 1-8, as well as the specific discharge capacity after 100 cycles of the simulated battery. The experimental results show that the surface oxygen-rich sulfide solid electrolyte material provided by the present invention has high ion conductance, high stability, and good stability against oxide cathode materials.

[0064] Table 1 Compacted density and stability data of Examples 1-9 and Comparative Examples 1-8

[0065]

[0066]

[0067] The surface oxygen-enriched sulfide solid electrolyte material and its preparation method are simple in composition, have readily available raw materials, are easy to prepare, have low production costs, and also have good stability. They are expected to solve the problem of large-scale application of sulfide solid electrolyte materials.

[0068] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a surface-oxygen-rich sulfide solid electrolyte material, characterized in that, Includes the following steps: 1) Provide sulfide solid electrolyte materials that are essentially free of oxygen; 2) The sulfide solid electrolyte material from step 1) is crushed in an oxygen-free medium; 3) The sulfide solid electrolyte material treated in step 2) is crushed in an oxygen-containing medium; 4) The sulfide solid electrolyte material treated in step 3) is subjected to heat treatment. The protective gas used in the treatment is an inert gas; The crushing process described in step 2) is ball milling at a speed of 300 rpm for 10 hours; The oxygen concentration in the oxygen-containing medium described in step 3) is 4000 ppm; The crushing process described in step 3) is ball milling at a speed of 200 rpm for 10 hours; The sulfide solid electrolyte material prepared by the method has a content of 1% ≤ L / D ≤ ​​5%, and L ≥ 5 nm, where L represents the thickness of the oxygen-rich layer on the outer surface of the sulfide solid electrolyte material, and D represents the particle diameter of the sulfide solid electrolyte material.

2. The preparation method according to claim 1, characterized in that, The oxygen-free medium mentioned in step 2) is an inert gas that does not contain oxygen.

3. The preparation method according to claim 2, characterized in that, The oxygen-free medium mentioned in step 2) is nitrogen, argon, or a nitrogen / argon mixture.

4. The preparation method according to claim 1, characterized in that, The oxygen-containing medium mentioned in step 3) is an inert gas containing oxygen.

5. The preparation method according to claim 4, characterized in that, The oxygen-containing medium mentioned in step 3) is nitrogen, argon, or a nitrogen / argon mixture containing oxygen.

6. The preparation method according to any one of claims 1 or 2, characterized in that, The heat treatment temperature in step 4) is 250℃-350℃, the heat treatment time is 3-48h, and the protective gas is an inert gas.

7. The surface-enriched oxygen-rich sulfide solid electrolyte material prepared by the preparation method according to any one of claims 1-6, characterized in that, The sulfide solid electrolyte material contains lithium ions and anions containing at least sulfur, characterized in that the sulfide solid electrolyte material also contains oxygen, which is present in a non-uniform distribution such that the oxygen is substantially enriched on the outer surface of the sulfide solid electrolyte material.

8. A positive electrode layer for a solid-state battery, characterized in that, The material is prepared by combining a positive electrode material and a conductive agent with the oxygen-rich sulfide solid electrolyte material of claim 7 or the preparation method of any one of claims 1-6.

9. An electrolyte layer for a solid-state battery, characterized in that, It is prepared from the surface oxygen-enriched sulfide solid electrolyte material of claim 7, or the surface oxygen-enriched sulfide solid electrolyte material prepared by the preparation method of any one of claims 1-6.

10. A solid-state lithium secondary battery, comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, characterized in that, The positive electrode layer is the positive electrode layer according to claim 8, and the solid electrolyte layer is the electrolyte layer according to claim 9.

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