Sulfide solid electrolyte, preparation method thereof and all-solid-state battery

Abstract

The invention discloses a sulfide solid electrolyte, a preparation method thereof and an all-solid-state battery. The sulfide solid electrolyte comprises Li, P, S, halogen and a soft acid element, and further comprises a sulfydryl group; the soft acid element comprises at least one of titanium, erbium, bismuth, tin, cadmium, iridium, osmium, indium or antimony. The sulfide solid electrolyte provided by the invention has high ionic conductivity, low sensitivity to water and good air stability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a sulfide solid electrolyte, a preparation method thereof, and an all-solid-state battery. Background Art

[0002] Since the electrolyte used in traditional lithium-ion batteries is an organic flammable liquid electrolyte, the safety performance of lithium-ion batteries needs to be further improved. To address this problem, more and more researchers are promoting all-solid-state batteries because the electrolyte used in all-solid-state batteries is solid, which greatly improves its safety compared to organic flammable liquid electrolytes.

[0003] One of the key components of all-solid-state batteries is the solid electrolyte. Sulfide solid electrolytes have attracted much attention because their conductivity is close to that of liquid electrolytes. In addition, the Young's modulus of sulfide solid electrolytes is lower than that of oxide solid electrolytes, which can withstand a certain amount of mechanical pressure during battery manufacturing. However, sulfide solid electrolytes easily react with water to produce H2S gas, which causes the electrolyte's ionic conductivity to drop sharply. Therefore, they need to be used in extremely low dew point environments (e.g., <-50°C) or in an inert gas glove box. This places extremely high demands on battery manufacturing facilities, sharply increases costs, and is not conducive to industrial production and promotion.

[0004] Some studies have found that lithium sulfide silver germanium sulfide electrolyte Li 12-x-m M m+ S 6-x X x The degree of hydrolysis (M = P, As, Si, Ge or Sn, X = Cl, Br or I) depends on the cation M m+ and halogen components. For example, in the hydrolysis process of Li6PS5Cl1, H2O easily reacts with PS bond to form PO bond, destroying PS4 3- Thus releasing H2S gas, however, PS4 3- It is crucial for the high conductivity of the electrolyte to destroy the PS4 3- This results in a decrease in the conductivity of the electrolyte.

[0005] At present, there are two common ways to improve it. The first method is to introduce oxides (such as Li2O, ZnO, Fe2O3 or Bi2O3) to replace M m+ 、S 2- sites, forming more stable sulfides to inhibit the generation of H2S. The second method is to coat a layer of ion conductor on the surface of the electrolyte to form a core-shell structure.

[0006] For example, CN114899480A discloses a sulfide solid electrolyte doped with group VB elements and oxygen elements, and its preparation method and application. The general formula of the doped sulfide solid electrolyte is: Li7P 1-a M a S 6-b O b , where M is one or more of group VB elements, 0 < a < 1, 0 < b < 2.5, and M is one or more of Nb, Ta, and V in group VB elements. Its preparation method includes the following steps: Step 1, mix the Li source, S source, P source, group VB elements, and O oxygen element source and perform ball milling to obtain a solid electrolyte powder; Step 2, press the solid electrolyte powder obtained in Step 1 at 300 - 900 MPa to obtain a solid electrolyte sheet; Step 3, calcine the solid electrolyte sheet obtained in Step 2, the calcination temperature is 350 - 650 °C, and the calcination time is 7 - 48 h to obtain the sulfide solid electrolyte doped with group VB elements and oxygen elements.

[0007] CN115763956A discloses a preparation method and material of a lithium ion conductor LiAlO2-coated solid electrolyte. The lithium ion conductor LiAlO2-coated solid electrolyte material has a core-shell structure, the inner core is a solid electrolyte, and the outer layer is a closely arranged nano-LiAlO2 coating layer; the particle size of the lithium ion conductor LiAlO2-coated solid electrolyte material is 10 nm - 10 μm, and the mass content of the nano-LiAlO2 coating layer is 0.1% - 5%. The solid electrolyte includes at least one of garnet-type solid electrolyte, sulfide solid electrolyte, NASICON-type solid electrolyte, LiPON-type electrolyte, and perovskite-type solid electrolyte.

[0008] However, both of the above two methods are at the cost of sacrificing conductivity and interfacial stability to lithium metal.

[0009] Therefore, providing a solid electrolyte that has high ionic conductivity and low sensitivity to water, thereby facilitating the application of all-solid-state batteries, is a technical problem that亟待解决的技术问题. Summary of the Invention

[0010] In view of the above technical problems existing in the prior art, the object of the present invention is to propose a sulfide solid electrolyte, its preparation method, and an all-solid-state battery.

[0011] To achieve the above object, the present invention adopts the following technical solutions:

[0012] In the first aspect, the present invention provides a sulfide solid electrolyte, which includes Li, P, S, halogen, and soft acid elements, and the sulfide solid electrolyte further includes a mercapto group;

[0013] The soft acid element includes at least one of titanium, erbium, bismuth, tin, cadmium, iridium, osmium, indium or antimony.

[0014] The sulfide solid electrolyte provided by the present invention has high ionic conductivity, low sensitivity to water and good air stability.

[0015] In the present invention, the performance of the sulfide solid electrolyte can be improved by the synergistic combination of mercapto groups, soft acid elements and halogens. Specifically:

[0016] First, the electrolyte contains thiol groups, which can effectively reduce the sensitivity of sulfides to moisture in the air and improve air stability without sacrificing ionic conductivity.

[0017] Second, the effects of soft acid elements are as follows: ① Due to their polarity matching, they form stronger covalent bonds with the soft base element sulfur, which can inhibit the reductive decomposition of sulfur, avoid the formation of H2S, and improve the chemical / electrochemical stability of the electrolyte to lithium metal. ② The introduction of soft acid elements can increase the mechanical strength of the electrolyte and reduce the risk of lithium dendrite penetration. ③ The introduction of soft acid elements can change the structure of the sulfide skeleton, reduce the activation energy of lithium ion migration, expand the lithium ion transmission channel, and improve ionic conductivity. ④ Soft acid elements can promote dense sintering and reduce grain boundary resistance. ⑤ Soft acid elements can increase the oxidation potential of the electrolyte, widen the electrochemical window, inhibit oxidative decomposition, and adapt to high-voltage positive electrodes. ⑥ Soft acid elements form a buffer layer at the interface, reducing side reactions, lowering interfacial impedance, improving interfacial compatibility, and stabilizing the electrode / electrolyte interface. ⑦ The larger ionic radius of soft acid elements can relieve local stress during lithium ion migration, reduce lattice distortion, and improve cycling stability.

[0018] Third, the effects of halogens are: ① The radius of halogen ions is large and their polarizability is strong, which can expand the lithium ion transmission channel or form a looser lattice structure, reduce the lithium ion migration energy barrier, and improve ionic conductivity. ② The introduction of halogens optimizes the arrangement of [PS4]3-tetrahedrons and increases the Li+ diffusion rate. ③ Halogens can passivate the interface between the electrolyte and the electrode (such as the high-voltage positive electrode) and reduce the side reaction between the sulfide and the positive electrode. ④ Halogens can form a stable passivation layer at the interface to prevent the decomposition of the electrolyte. ⑤ Halogens can widen the electrochemical window and improve oxidation stability. ⑥ Halogen doping can improve the deformability of the electrolyte, promote close contact with the electrode, and reduce the interface impedance. ⑦ Halogens can lower the melting point of sulfides, promote low-temperature sintering, and reduce grain boundary resistance.

[0019] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0020] Preferably, the halogen comprises at least one of F, Cl, Br or I.

[0021] Preferably, the soft acid element is erbium or bismuth.

[0022] Preferably, the molar ratio of each element in the sulfide solid electrolyte satisfies the following relationship:

[0023] Li: P: S: halogen: soft acid element = (1-15): 1: (0.5-10): (0.5-15): (0.001-0.5). The selection range of Li element is "1-15", for example, it can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 6.5, 7, 7.5, 8, 9, 9.5, 10, 11, 12, 12.5, 13, 14 or 15; the selection range of S element is "0.5-10", for example, it can be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 6.5, 7, 7.5, 8, 9, 9.5 or 10; the selection range of halogen is "0.5-15", for example, it can be 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5 or 15, etc.; the selection range of the soft acid element is "0.001-0.5", for example, it can be 0.001, 0.003, 0.005, 0.008, 0.01, 0.03, 0.06, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5, etc.

[0024] In a second aspect, the present invention provides a method for preparing the sulfide solid electrolyte as described in the first aspect, the preparation method comprising the following steps:

[0025] Mixing raw materials including Li, a soft acid element, P, S, and a halogen and a solvent having a structure represented by formula (I), ball milling, and then heat-treating the mixture at a temperature lower than the decomposition temperature of the mercapto group to obtain the sulfide solid electrolyte;

[0026] R1-(CH2) n -R2, formula (Ⅰ);

[0027] Wherein, 2≤n≤11, and at least one of R1 and R2 is a thiol group.

[0028] In the present invention, n can be, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, preferably 2 ≤ n ≤ 9. The carbon chain length should not be too long, otherwise the carbon content in the resulting sulfide solid electrolyte will be too high, which will reduce the specific capacity of the battery when used in the positive electrode.

[0029] The present invention utilizes a solvent method to synthesize a sulfide solid electrolyte containing a mercapto group. Even if an organic solvent (i.e., a solvent having a structure represented by formula (I)) remains, it will not affect the conductivity of the electrolyte. Instead, it will counteract the sensitivity of the sulfide electrolyte to water and oxygen, thereby improving the air stability of the sulfide solid electrolyte.

[0030] The method of the present invention does not specifically limit the types of raw materials containing Li, soft acid elements, P, S and halogens. The same element can be derived from only one substance or from multiple substances at the same time. Those skilled in the art can make a selection according to their needs.

[0031] Preferably, the solvent having the structure represented by formula (I) is at least one selected from 1-octanethiol, 1-undecanethiol, nonanethiol, heptanethiol, hexanethiol, pentanethiol, octanethiol and hexanethiol.

[0032] Preferably, the mixing method is to first physically mix the raw materials comprising Li, a soft acid element, P, S, and a halogen, and then add a solvent having the structure represented by formula (I). The advantages of adopting this mixing method are: ① Premixing can initially uniformly disperse the raw materials, avoiding stratification or localized compositional inhomogeneities caused by density or particle size differences during ball milling, improving mixing uniformity, and reducing component segregation. ② It can pre-optimize the distribution of each phase, providing a more uniform starting state for subsequent ball milling. ③ It reduces the problem of particle agglomeration that must be overcome during the initial ball milling process, allowing the ball milling energy to be more focused on particle refinement rather than mixing, thereby improving ball milling efficiency and shortening process time. ④ Because this method can achieve a uniform initial distribution, it can reduce the impact wear of localized hard particles on the ball milling jar or grinding balls, thereby protecting the ball milling media. ⑤ It can avoid amorphization or impurity phases caused by localized component excess (such as lithium salt enrichment) during ball milling, thereby improving the ionic conductivity of the sintered solid electrolyte. ⑥ Premixing ensures sufficient contact between the reactants, promoting reaction activity and making it easier to form a homogeneous product during ball milling. ⑦ This mixing method helps ensure consistent initial conditions for each ball milling, improves material reproducibility, improves process controllability, and reduces batch variability. ⑧ The adhesion of the raw materials is reduced after mixing, reducing contamination caused by material sticking to the wall or residue during the ball milling process.

[0033] The present invention does not specifically limit the physical mixing method, including but not limited to manual stirring, ball milling, magnetic stirring or stirring with a blender. The above methods can achieve the purpose of uniformly mixing the materials.

[0034] In one embodiment, physical mixing is used to open the chemical bonds of the raw materials (in this case, a mixture is obtained after physical mixing, rather than a solid electrolyte obtained by reaction), which is beneficial to the subsequent preparation of a sulfide solid electrolyte.

[0035] Preferably, the mass of the solvent having the structure shown in formula (I) is m1, and the total mass of the raw materials containing Li, soft acid elements, P, S and halogens is m2, m1:m2=(0.5~3):(7~10), wherein the selection range of m1 is "0.5~3", for example, it can be 0.5, 1, 1.5, 2, 2.5 or 3, etc.; the selection range of m2 is "7~10", for example, it can be 7, 7.5, 8, 8.5, 9, 9.5 or 10, etc.

[0036] Preferably, the rotation speed of the ball mill is 200 rpm to 800 rpm, for example, it can be 200 rpm, 220 rpm, 240 rpm, 260 rpm, 280 rpm, 300 rpm, 325 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm, 400 rpm, 415 rpm, 430 rpm, 440 rpm, 450 rpm, 460 rpm, 470 rpm, 480 rpm, 500 rpm, 515 rpm, 530 rpm, 550 rpm, 560 rpm , 580rpm, 600rpm, 630rpm, 660rpm, 680rpm, 700rpm, 725rpm, 750rpm, 775rpm or 800rpm, etc.; the time of high energy ball milling is 6h to 36h, for example, it can be 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h, 25h, 26h, 28h, 30h, 31h, 32h, 33h, 34h, 35h or 36h, etc.

[0037] Preferably, the atmosphere of the heat treatment is an inert atmosphere.

[0038] Preferably, the temperature of the heat treatment is 150°C to 300°C, for example, it can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 280°C or 300°C.

[0039] Preferably, the heat treatment time is 4h to 36h, for example, it can be 4h, 5h, 6h, 7h, 7.5h, 8h, 8.5h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 24h, 25h, 26h, 28h, 30h, 31h, 32h, 33h, 34h, 35h or 36h.

[0040] Preferably, the heating rate of the heat treatment is 0.2°C / min to 5°C / min, for example, it can be 0.2°C / min, 0.3°C / min, 0.4°C / min, 0.5°C / min, 0.6°C / min, 0.7°C / min, 0.8°C / min, 0.9°C / min, 1°C / min, 1.2°C / min, 1.5°C / min, 1.7°C / min, 1.8°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min or 5°C / min, etc.

[0041] Preferably, the cooling rate of the heat treatment is 0.5°C / min to 5°C / min, for example, it can be 0.5°C / min, 1°C / min, 1.2°C / min, 1.3°C / min, 1.5°C / min, 1.6°C / min, 1.8°C / min, 2°C / min, 2.3°C / min, 2.6°C / min, 2.8°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min or 5°C / min, etc.

[0042] In a third aspect, the present invention provides an all-solid-state battery, comprising a positive electrode, a negative electrode, and an all-solid-state electrolyte layer located between the positive electrode and the negative electrode, wherein the all-solid-state electrolyte layer comprises a first solid electrolyte, and the positive electrode comprises a positive electrode active material and a second solid electrolyte;

[0043] The first solid electrolyte and the second solid electrolyte are the sulfide solid electrolyte described in the first aspect.

[0044] By introducing the sulfide solid electrolyte described in the first aspect into the positive electrode, the conductivity of the positive electrode can be improved. Moreover, since the sulfide electrolyte layer also contains the sulfide solid electrolyte described in the first aspect, the interface compatibility between the positive electrode and the solid electrolyte layer is good, which is conducive to improving the performance of the all-solid-state battery.

[0045] Preferably, the mass ratio of the positive electrode active material to the second solid electrolyte is (80-90):(10-20). Among them, the selection range of the positive electrode active material is "80-90", for example, it can be 80, 81, 82, 83, 84, 85, 86, 87, 88, 89 or 90, etc.; the selection range of the second solid electrolyte is "10-20", for example, it can be 10, 10.5, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20, etc.

[0046] Preferably, the positive electrode active material includes a layered oxide positive electrode material and a halogen oxide coating the layered oxide positive electrode material, and the positive electrode active material is obtained by reacting a fluoride raw material with residual alkali on the surface of the layered oxide positive electrode material.

[0047] Layered oxide positive electrode materials (such as LiCoO2 or LiNi x Co y Mn 1-x-y O2, 0<x<1, 0<y<1) have the advantages of high voltage and high discharge specific capacity, but also face the following problems: First, 1. Due to the low antioxidant ability of sulfides (such as 1.5V-2.5V), an interfacial reaction will occur between the positive electrode prepared with the layered oxide positive electrode material and the sulfide electrolyte, resulting in the generation and accumulation of by-products, inhibiting ion transport; Second, the chemical potential of the sulfide solid electrolyte does not match that of the layered oxide positive electrode material, resulting in Li + depletion at the interface under the action of the charging effect; Third, during the production process and material storage of the layered oxide positive electrode material (especially the high-nickel positive electrode material), residual alkali (generally LiOH and / or Li2CO3) will be generated. This is because: during the production process, lithium salts are generally in excess, and residual alkali is generated after high-temperature calcination; during storage, certain ions (such as nickel ions) react with moisture and carbon dioxide in the air to form surface residual alkali, and this situation is more serious for high-nickel positive electrode materials. Fourth, if the sulfide solid electrolyte directly contacts the residual alkali on the surface of the positive electrode material, it will affect the performance of the sulfide solid electrolyte. The above problems will cause the performance of the battery to decline, such as the rapid decline of the cycle performance and battery capacity.

[0048] To solve this problem, in the present invention, a halogen oxide is formed by reacting a fluoride raw material with residual alkali on the surface of the layered oxide positive electrode material, which not only reduces the residual alkali, but also forms a halogen oxide coating layer in-situ on the surface of the layered oxide positive electrode material, which can effectively improve the stability of the positive electrode material at high voltage; in addition, the high ionic conductivity of the halogen oxide solid electrolyte is beneficial to improving the interfacial kinetic performance and the electrical performance of the battery.

[0049] Preferably, the fluoride raw material includes at least one of tantalum fluoride, titanium fluoride, indium fluoride, aluminum fluoride, lanthanum fluoride, hafnium fluoride, neodymium fluoride, europium fluoride, cobalt fluoride, erbium fluoride, lutetium fluoride, cerium fluoride, niobium fluoride, gadolinium fluoride, chromium fluoride, chromium fluoride, yttrium fluoride, cesium fluoride, magnesium fluoride, zinc fluoride, ytterbium fluoride, rhenium fluoride, cerium fluoride, antimony pentafluoride, tellurium hexafluoride, iridium pentafluoride, bromine pentafluoride, molybdenum hexafluoride, bismuth trifluoride, germanium tetrafluoride, tin tetrafluoride and bismuth pentafluoride.

[0050] In one embodiment, the negative electrode in the all-solid-state battery is a lithium negative electrode, and the lithium negative electrode includes lithium as a single substance. Compared with the graphite negative electrode, the lithium negative electrode has the following advantages: the theoretical specific capacity of the lithium negative electrode is as high as 3860mAh / g, which is more than 10 times that of the graphite negative electrode, which enables the lithium battery to store more charge, thereby providing a higher energy density. In addition, the lithium insertion potential of lithium is about 0.3V, which is lower than that of most alloy-type negative electrodes, which helps to achieve higher energy density. At the same time, the lithium negative electrode also has better conductivity.

[0051] In the all-solid-state battery of the present invention, the problem of battery performance degradation caused by the high reaction activity of the oxyhalides on the surface of the positive electrode material and lithium metal can be solved by introducing a sulfide solid electrolyte into the positive electrode. This is because: the oxyhalides easily undergo reduction reactions with lithium, resulting in a degradation of battery performance. To address this problem, by introducing the above-mentioned sulfide solid electrolyte containing mercapto groups, it reacts with the oxyhalides to produce LiCl, Li2S, Li2O and Li3P components, constructing a kinetically stable interface, limiting side reactions, achieving interface passivation, and improving the electrochemical performance of the all-solid-state battery. For example, the battery has good cycle stability. Preferably, the preparation method of the positive electrode active material comprises the following steps:

[0052] (1) Testing the residual alkali content on the surface of the layered oxide positive electrode material to confirm the formula amount of the fluoride raw material and the layered oxide positive electrode material;

[0053] (2) After mixing the formulated amount of fluoride raw material and layered oxide positive electrode material, calcining them in an inert atmosphere to obtain the positive electrode active material.

[0054] The present invention does not limit the test method for the residual alkali content on the surface of the layered oxide positive electrode material, and it can be, for example, a potentiometric titration method.

[0055] In one embodiment, the formulated amount of the fluoride raw material means that the mass of the fluoride raw material accounts for a% of the mass of the layered oxide positive electrode material, and a% is the same as the total content of residual alkali.

[0056] Preferably, in step (2), the mixing method is stirring, and the stirring speed is 100r / min to 500r / min, for example, 100r / min, 120r / min, 130r / min, 150r / min, 160r / min, 180r / min, 200r / min, 215r / min, 230r / min, 240r / min, 260r / min, 280r / min, 300r / min, 325r / min, 350r / min, 360r / min, 370r / min, 380r / min, 390r / min, 400r / min, 410r / min, 420r / min, 430r / min, 440r / min, 450r / min, 460r / min, 470r / min, 480r / min, 490r / min, 500r / min, 510r / min, 520r / min, 530r / min, 540r / min, 550r / min, 560r / min, 570r / min, 580r / min, 590r / min, 600r / min, 610r / min, 620r / min, 630r / min, 640r / min, 650r / min, 660r / min, 670r / min, 680r / min, 700r / min, 710r / min, 720r / min, 730r / min, 740r / min the stirring time is 0.5h to 15h, for example, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 7h, 8h, 9h, 10h, 11h, 11.5h, 12h, 13h, 13.5h, 14h or 15h, etc.

[0057] Preferably, in step (2), the calcination temperature is 100°C to 400°C, for example, it can be 100°C, 120°C, 130°C, 150°C, 160°C, 170°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 325°C, 350°C, 360°C, 370°C, 380°C or 400°C; the calcination time is 2h to 18h, for example, it can be 2h, 3h, 5h, 6h, 8h, 10h, 12h, 14h, 15h, 16h or 18h, etc.

[0058] The present invention does not limit the specific type of gas in the inert atmosphere. For example, it can be one gas or a combination of multiple gases selected from nitrogen, helium, neon or argon.

[0059] The numerical range described in the present invention includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values included in the range.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] (1) The present invention introduces halogen, soft acid element and mercapto group into the sulfide solid electrolyte, which can make the sulfide solid electrolyte have high ionic conductivity and low sensitivity to water. The conductivity of the sulfide solid electrolyte is 4.3 / ms*cm -1 Above, the air stability is above 82.9%.

[0062] (2) In the all-solid-state battery of the present invention, the conductivity of the positive electrode can be improved by introducing the sulfide solid electrolyte described in the first aspect into the positive electrode. Moreover, since the sulfide electrolyte layer also contains the sulfide solid electrolyte described in the first aspect, the interface compatibility between the positive electrode and the solid electrolyte layer is good, which is conducive to improving the performance of the all-solid-state battery.

[0063] (3) The present invention forms oxyhalides by reacting the fluoride raw material with the residual alkali on the surface of the layered oxide positive electrode material, which not only reduces the residual alkali, but also the oxyhalide coating layer generated in situ on the surface of the layered oxide positive electrode material can effectively improve the stability of the positive electrode material under high voltage; in addition, the high ionic conductivity of the oxyhalide solid electrolyte is conducive to improving the interfacial kinetics and improving the electrical performance of the battery.

[0064] (4) In the all-solid-state battery of the present invention, the problem of battery performance degradation caused by the high reaction activity of the oxyhalide on the surface of the positive electrode material and lithium metal can be solved by introducing a sulfide solid electrolyte into the positive electrode. DETAILED DESCRIPTION

[0065] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the 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.

[0066] Example 1

[0067] This embodiment provides a sulfide solid electrolyte, which includes Li, P, S, halogens (Cl and I) and soft acid elements (Ti), and also includes a thiol group.

[0068] In the sulfide solid electrolyte, Li:P:S:halogen:soft acid element=5.95:1:5:1.05:0.05.

[0069] This embodiment also provides a method for preparing the above-mentioned sulfide solid electrolyte, comprising the following steps:

[0070] According to the molecular formula of the sulfide solid electrolyte, the raw materials Li2S, P2S5, LiCl, and TiCl2 are physically mixed in a certain molar ratio of 2.5:0.5:0.95:0.05 to obtain powder raw materials, and then nonanethiol is added, and the ratio of the mass of the nonanethiol to the total mass of the powder raw materials is 0.5:9.5; high-energy ball milling is performed, the speed of the high-energy ball mill is 380 rpm, and the high-energy ball milling time is 12 hours; finally, heat treatment is performed under inert atmosphere (argon) conditions, and the heat treatment conditions are: temperature 155°C, time 20 hours, heating rate 4.5°C / min, and cooling rate 5°C / min to obtain the sulfide solid electrolyte.

[0071] Example 2

[0072] This embodiment provides a sulfide solid electrolyte, which includes Li, P, S, halogen (Cl) and soft acid element (Er), and also includes a thiol group.

[0073] In the sulfide solid electrolyte, Li:P:S:halogen:soft acid element=13.5:1:7:6:0.5.

[0074] This embodiment also provides a method for preparing the above-mentioned sulfide solid electrolyte, comprising the following steps:

[0075] According to the molecular formula of the sulfide solid electrolyte, the raw materials Li2S, P2S5, LiCl, and InCl3 are physically mixed in a certain molar ratio of 4.5:0.5:4.5:0.5 to obtain a powder raw material, and then 1-undecanethiol is added, and the ratio of the mass of the 1-undecanethiol to the total mass of the powder raw materials is 1.0:9.0; high-energy ball milling is performed, the speed of the high-energy ball milling is 550 rpm, and the high-energy ball milling time is 8.5 h; finally, heat treatment is performed under inert atmosphere (argon) conditions, and the heat treatment conditions are: temperature 250 ° C, time 7 h, heating rate 0.7 ° C / min, and cooling rate 0.5 ° C / min to obtain the sulfide solid electrolyte.

[0076] Example 3

[0077] This embodiment provides a sulfide solid electrolyte, which includes Li, P, S, halogens (Cl and I) and soft acid elements (Ti), and also includes a thiol group.

[0078] In the sulfide solid electrolyte, Li:P:S:halogen:soft acid element=5.45:1:4.55:2.35:0.25.

[0079] This embodiment also provides a method for preparing the above-mentioned sulfide solid electrolyte, comprising the following steps:

[0080] According to the molecular formula of the sulfide solid electrolyte, the raw materials Li2S, P2S5, LiI, and SnCl4 are physically mixed in a certain molar ratio of 2.05:0.5:1.35:0.25 to obtain a powder raw material, and then nonanethiol is added, and the ratio of the mass of the nonanethiol to the total mass of the powder raw materials is 2.5:7.5; high-energy ball milling is performed, the speed of the high-energy ball milling is 360 rpm, and the high-energy ball milling time is 14 hours; finally, heat treatment is performed under inert atmosphere (argon) conditions, and the heat treatment conditions are: temperature 155°C, time 12.5 hours, heating rate 0.3°C / min, and cooling rate 1.5°C / min to obtain the sulfide solid electrolyte.

[0081] Example 4

[0082] A sulfide solid electrolyte is provided, which differs from Example 1 in that the soft acid element Ti is replaced by Er.

[0083] Example 5

[0084] A sulfide solid electrolyte is provided, which differs from Example 1 in that the soft acid element Ti is replaced by Bi.

[0085] Example 6

[0086] A sulfide solid electrolyte is provided. The difference from Example 1 is that in the sulfide solid electrolyte, the content of the thiol group is changed, the contents of other elements remain unchanged, and the ratio of the mass of nonanethiol to the total mass of the powdered raw material is 0.5:10.5.

[0087] Example 7

[0088] A sulfide solid electrolyte is provided, which differs from Example 1 in that, in the sulfide solid electrolyte, Li:P:S:halogen:soft acid element=5.95:1:5:2.15:0.6.

[0089] Example 8

[0090] A sulfide solid electrolyte is provided. The difference from Example 1 is that in the sulfide solid electrolyte, Li:P:S:halogen:soft acid element=5.2:1:5:0.3:0.05.

[0091] Example 9

[0092] A sulfide solid electrolyte is provided. The difference from Example 1 is that in the sulfide solid electrolyte, Li:P:S:halogen:soft acid element=20:1:5:15.1:0.05.

[0093] Comparative Example 1

[0094] A sulfide solid electrolyte is provided, which differs from Example 1 in that nonanethiol is not added in the preparation method, and the rest is the same as Example 1.

[0095] Comparative Example 2

[0096] A sulfide solid electrolyte is provided, which differs from Example 1 in that no soft acid element is added in the preparation method, and the rest is the same as Example 1.

[0097] Comparative Example 3

[0098] A sulfide solid electrolyte is provided, which differs from Example 1 in that no halogen is added in the preparation method, and the rest is the same as Example 1.

[0099] Performance test of sulfide solid electrolyte:

[0100] (1) Ionic conductivity test of sulfide solid electrolyte:

[0101] (1) Weigh 100 mg of sulfide solid electrolyte powder and place it in a mold (10 mm diameter). Press it into an electrolyte sheet using a press (parameter: 400 MPa). Stainless steel blocking electrodes are placed at both ends of the electrolyte sheet to assemble into a blocked symmetrical cell.

[0102] (2) Using an electrochemical workstation to measure the sample impedance using electrochemical impedance spectroscopy (ECI) to obtain the resistance value R (unit: Ω) of the solid electrolyte. The test frequency is 0.01 Hz to 1 MHz, the test disturbance voltage is 5 mV, and the test temperature is the temperature inside the glove box.

[0103] (3) Take out the electrolyte sheet and measure the thickness L (in cm) of the solid electrolyte sheet using a micrometer;

[0104] (4) Then the ionic conductivity of the solid electrolyte at the temperature inside the glove box is calculated by the formula,

[0105] The formula is: σLi + =L / (R*S);

[0106] Where σLi + ——Ionic conductivity of solid electrolyte (S cm -1 );

[0107] L - thickness of solid electrolyte (cm);

[0108] R——intrinsic resistance of solid electrolyte (Ω);

[0109] S——cross-sectional area of solid electrolyte (cm 2 ).

[0110] (2) Air stability test of sulfide solid electrolyte:

[0111] (1) Turn on the dehumidifier and wait for the dew point to stabilize below -45°C for at least half an hour; Electrolyte exposure: Spread the dried weighing paper on the test bench; Take 0.5±0.03g of solid electrolyte and spread it on the weighing paper, use a medicine spoon to spread it to a thickness of 1±0.3mm, let it stand for 4.5h, and then collect the material;

[0112] (2) Weigh 120 mg of sulfide solid electrolyte powder and place it in a mold (10 mm diameter). Press it into an electrolyte sheet using a press (parameter: 400 MPa), and match stainless steel blocking electrodes at both ends of the electrolyte sheet.

[0113] (3) Using an electrochemical workstation to measure the impedance of the sample by electrochemical AC impedance spectroscopy, the resistance value R (unit: Ω) of the solid electrolyte is obtained. The test frequency is 0.01 MHz to 1 MHz, the test disturbance voltage is 5 mV, and the test is carried out in a glove box.

[0114] (4) Take out the electrolyte sheet and use a micrometer to measure the thickness L (in cm) of the solid electrolyte; then calculate the ionic conductivity σ of the solid electrolyte at the temperature inside the glove box using the formula, σ = L / (R·S);

[0115] Where, σ is the ionic conductivity of the solid electrolyte (S cm -1 );

[0116] L - thickness of solid electrolyte (cm);

[0117] R——intrinsic resistance of solid electrolyte (Ω);

[0118] S——cross-sectional area of solid electrolyte (cm 2 ).

[0119] (5) According to the process of steps (3) to (6), the conductivity of the solid electrolyte before and after exposure is tested respectively, and the air stability of the solid electrolyte is calculated by the formula: air stability = ionic conductivity after exposure / ionic conductivity before exposure × 100%.

[0120] See Table 1 for the results.

[0121] Table 1

[0122]

[0123] As can be seen from Table 1, the sulfide solid electrolyte of the present invention has high ionic conductivity and low sensitivity to water. The conductivity of the sulfide solid electrolyte is 4.3 / ms*cm -1Above, the air stability is above 82.9%.

[0124] By comparing Example 1 with Examples 4-5, it can be seen that the type of soft acid element is more preferably Er or Bi.

[0125] By comparing Example 1 with Example 6 and Comparative Example 1, it can be seen that if no thiol group is added (Comparative Example 1) or too much thiol group is introduced (Example 6), the conductivity and air stability will decrease.

[0126] By comparing Example 1 with Example 7 and Comparative Example 2, it can be seen that if no soft acid element is added or the content of the soft acid element is too high, the electrical conductivity and air stability will decrease.

[0127] By comparing Example 1 with Examples 8-9 and Comparative Example 3, it can be seen that if the halogen content is too low (Example 8), no halogen is added (Comparative Example 3), or the halogen content is too high (Example 9), the conductivity and air stability will decrease.

[0128] Preparation Example 1

[0129] Provided is a positive electrode material, the preparation method of which comprises:

[0130] (1) First, the layered oxide positive electrode material (lithium nickel cobalt manganese oxide ternary material, chemical formula LiNi 0.9 Co 0.1 Mn 0.1 The residual alkali content on the surface of O2) was tested. The types of residual alkali were Li2CO3 and LiOH, and the residual alkali content was: Li2CO3 0.85wt%, LiOH 0.45wt%.

[0131] (2) A fluoride raw material (bismuth pentafluoride) was prepared, with the fluoride raw material accounting for 1.3 wt% of the mass of the layered oxide positive electrode material. The layered oxide positive electrode material and the fluoride raw material were stirred at a speed of 250 r / min for 10.5 hours to ensure thorough mixing. Finally, the mixture was calcined at 200°C for 8 hours under an inert gas atmosphere (helium) to obtain an oxyhalide-coated positive electrode material.

[0132] In this preparation example, the residual alkali was tested by potentiometric titration, with reference to the contents disclosed in GB / T 9725-2007 "General Rules for Potentiometric Titration".

[0133] Comparative Example 1

[0134] Provide a positive electrode material, which is different from Preparation Example 1 in that the positive electrode material is a ternary material of lithium nickel cobalt manganese oxide, with a chemical formula of LiNi 0.9 Co 0.1 Mn 0.1O2, the types of residual alkali are Li2CO3 and LiOH, and the residual alkali content is: Li2CO3 0.85wt%, LiOH 0.45wt%. No treatment is done.

[0135] The antioxidant window of the positive electrode materials of Preparation Example 1 and Comparative Example 1 was tested using the following test method:

[0136] (1) Weigh 100 mg of the total material at a mass ratio of SP: positive electrode material = 5:5, place it in a mortar and grind it by hand for 10 minutes, and mix it evenly to obtain a mixture;

[0137] (2) Weigh 100 mg of sulfide solid electrolyte powder and place it in a mold liner (10 mm diameter) and press it into an electrolyte sheet using a press (parameter: 400 MPa);

[0138] (3) Spread 25 mg of the mixture in step (1) on one end of the electrolyte sheet, flatten it with a mold, and compact it with a press (parameter: 400 MPa), and introduce the Li sheet on the other end;

[0139] (4) An LSV test was performed using an electrochemical workstation, with an open circuit voltage of 5 V and a scan rate of 0.1 mV / s, to observe the oxidation current peak: the point where the current sharply increases corresponds to the material decomposition potential (the upper limit of the antioxidant window), and the oxidation window (unit: V) was obtained.

[0140] The results showed that the oxidation window of the oxyhalide-coated cathode material of Preparation Example 1 was 4.60 V, while that of the cathode material of Comparative Example 1 was 4.35 V. This indicates that the present invention, through the reaction of the fluoride raw material with the residual alkali on the surface of the layered oxide cathode material to form an oxyhalide, not only reduces the residual alkali, but also the in-situ generated oxyhalide coating on the surface of the layered oxide cathode material can effectively improve the stability of the cathode material under high voltage.

[0141] Application Examples 1-9 and Comparative Application Examples 1-4

[0142] The solid electrolytes of Examples 1-9 and Comparative Examples 1-3, and the positive electrode materials of Preparation Example 1 and Control Example 1 are used to assemble an all-solid-state battery. The preparation method includes:

[0143] (1) Weigh 100 mg of the sulfide solid electrolyte prepared above and place it in the inner liner of an alumina ceramic mold (diameter 10 mm). Press it into an electrolyte sheet using a press (parameters: 100 MPa, 30 s). Use an ear bulb to remove excess solid electrolyte powder.

[0144] (2) The prepared cathode material and the prepared sulfide solid electrolyte were mixed in a mass ratio of 85:15 and ground in a mortar for 15 min to obtain 100 mg of the mixture;

[0145] (3) Weigh 25 mg of the above mixture powder and spread it flat on the electrolyte sheet. Rotate the stainless steel electrode indenter to the bottom of the mold and rotate the indenter to spread the powder flat.

[0146] (4) Remove the indenter and place a piece of carbon-coated aluminum foil (10 mm thick) on top of the powder. Use a press to maintain pressure at 400 MPa for 2 min. Use an ear bulb to remove excess cathode powder. Then weigh it again to obtain the actual cathode material loading.

[0147] (5) Place a 100 μm thick indium foil on the other side of the electrolyte sheet, and then place a 50 μm thick lithium-copper composite tape (where the lithium layer side of the lithium-copper composite tape contacts the indium foil), both with a diameter of 10 mm;

[0148] (6) Fasten the mold and the pressing head and tighten the nut to obtain a solid-state battery.

[0149] See Table 2 for examples or comparative examples of sulfide solid electrolytes and positive electrode materials used in solid-state batteries.

[0150] Using Blue Power to test the performance of all-solid-state batteries:

[0151] (1) Test method for first-cycle discharge specific capacity: At 35±3°C, charge the battery to 3.7V at a constant current of 0.1C and charge it to a cutoff current of 0.05C at a constant voltage of 3.7V to obtain the first-cycle charge capacity A1; then discharge the battery to 2.0V at a constant current of 0.1C to obtain the first-cycle discharge capacity B1. First efficiency = B1 / A1*100%.

[0152] (2) Test method for 1C discharge capacity and capacity retention rate: At 35±3℃, charge at 1C constant current to 3.7V, charge at 3.7V constant voltage to a cut-off current of 0.05C; then discharge at 1C constant current to 2.0V, and obtain 1C discharge capacity D1. Repeat the charge and discharge steps for 100 cycles, and the discharge capacity obtained at the 100th cycle is recorded as D 100 , calculate the 100th cycle capacity retention rate based on the first cycle discharge capacity and the 100th cycle discharge capacity, the 100th cycle capacity retention rate = (D 100 / D1)×100%.

[0153] (3) Test method for rate performance: At 35±3°C, charge the battery to 3.7V at a constant current of 1C, charge it to a cutoff current of 0.05C at a constant voltage of 3.7V, and discharge it to 2.0V at a constant current of 1C. The 1C discharge capacity is recorded as D1. After five cycles, the 1C discharge capacity is calculated to obtain the average value M; charge the battery to 3.7V at a constant current of 1C, charge it to a cutoff current of 0.05C at a constant voltage of 3.7V, and discharge it to 3.7V at a constant current of 5C. The 5C discharge capacity is recorded as D2. After five cycles, the 5C discharge capacity is calculated to obtain the average value N; 5C / 1C capacity retention rate = N / M×100%.

[0154] See Table 2 for test results.

[0155] Table 2

[0156]

[0157] As shown in Table 2, the sulfide solid electrolyte of the present invention, when used in all-solid-state batteries, can improve the performance of the all-solid-state batteries due to its high ionic conductivity. However, the sulfide solid electrolytes in the all-solid-state batteries of Comparative Examples 2-4 do not contain mercapto groups, soft acid elements, or halogens, all of which can lead to decreased performance of the all-solid-state batteries.

[0158] At the same time, by comparing Application Example 1 with Application Comparative Example 1, it can be seen that the fluoride raw material reacts with the residual alkali on the surface of the layered oxide positive electrode material to form a halide oxide. The high ionic conductivity of the halide oxide solid electrolyte is beneficial to improving the interfacial kinetics and improving the electrical performance of the battery.

[0159] Of course, those skilled in the art should realize that the above embodiments are only used to illustrate the present invention and are not used to limit the present invention. As long as they are within the scope of the essential spirit of the present invention, any changes and modifications to the above embodiments will fall within the scope of the claims of the present invention.

[0160] The applicant states that the present invention is intended to illustrate the detailed methods of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed methods, that is, it does not mean that the present invention must rely on the above-described detailed methods in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A sulfide solid electrolyte, characterized in that: The sulfide solid electrolyte includes Li, P, S, halogen and soft acid elements, and the sulfide solid electrolyte also includes a thiol group; The soft acid element includes at least one of titanium, erbium, bismuth, tin, cadmium, iridium, osmium, indium or antimony.

2. The sulfide solid electrolyte according to claim 1, characterized in that The halogen includes at least one of F, Cl, Br or I; and / or, The soft acid element is erbium or bismuth; and / or, In the sulfide solid electrolyte, the molar ratio of each element satisfies the following relationship: Li:P:S:halogen:soft acid element=(1~15):1:(0.5~10):(0.5~15):(0.001~0.5).

3. A method for preparing the sulfide solid electrolyte according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: Mixing raw materials including Li, a soft acid element, P, S, and a halogen and a solvent having a structure represented by formula (I), ball milling, and then heat-treating the mixture at a temperature lower than the decomposition temperature of the mercapto group to obtain the sulfide solid electrolyte; R1-(CH2) n -R2, formula (Ⅰ); Wherein, 2≤n≤11, and at least one of R1 and R2 is a thiol group.

4. The method for preparing a sulfide solid electrolyte according to claim 3, wherein: The solvent having the structure represented by formula (I) is at least one selected from 1-octanethiol, 1-undecanethiol, nonanethiol, heptanethiol, hexanethiol, pentanethiol, octanethiol and hexanethiol; and / or, 2≤n≤9; and / or, the mixing method is: first physically mixing the raw materials containing Li, soft acid elements, P, S and halogen, and then adding a solvent having a structure represented by formula (I); and / or, The mass of the solvent having the structure represented by formula (I) is m1, the total mass of the powdered raw materials comprising Li, soft acid elements, P, S and halogen is m2, m1:m2=(0.5-3):(7-10); and / or, The ball milling speed is 200 rpm to 800 rpm, and the high-energy ball milling time is 6 h to 36 h; and / or, The atmosphere of the heat treatment is an inert atmosphere; and / or, The heat treatment temperature is 150°C to 300°C; and / or, The heat treatment time is 4h to 36h; and / or, The heating rate of the heat treatment is 0.2°C / min to 5°C / min; and / or, The cooling rate of the heat treatment is 0.5°C / min to 5°C / min.

5. An all-solid-state battery comprising a positive electrode, a negative electrode, and an all-solid-state electrolyte layer located between the positive electrode and the negative electrode, characterized in that: The all-solid-state electrolyte layer includes a first solid-state electrolyte, and the positive electrode includes a positive electrode active material and a second solid-state electrolyte; The first solid electrolyte and the second solid electrolyte are the sulfide solid electrolyte according to claim 1 or 2.

6. The all-solid-state battery according to claim 5, characterized in that The mass ratio of the positive electrode active material to the second solid electrolyte is (80-90):(10-20).

7. The all-solid-state battery according to claim 5, characterized in that The positive electrode active material comprises a layered oxide positive electrode material and a halide oxide coating the layered oxide positive electrode material. The positive electrode active material is obtained by reacting a fluoride raw material with residual alkali on the surface of the layered oxide positive electrode material.

8. The all-solid-state battery according to claim 7, characterized in that: The fluoride raw material includes at least one of tantalum fluoride, titanium fluoride, indium fluoride, aluminum fluoride, lanthanum fluoride, hafnium fluoride, neodymium fluoride, europium fluoride, cobalt fluoride, erbium fluoride, lutetium fluoride, cerium fluoride, niobium fluoride, gadolinium fluoride, chromium fluoride, chromium fluoride, yttrium fluoride, cesium fluoride, magnesium fluoride, zinc fluoride, ytterbium fluoride, rhenium fluoride, cerium fluoride, antimony pentafluoride, tellurium hexafluoride, iridium pentafluoride, bromine pentafluoride, molybdenum hexafluoride, bismuth trifluoride, germanium tetrafluoride, tin tetrafluoride and bismuth pentafluoride.

9. The all-solid-state battery according to claim 7, characterized in that: The method for preparing the positive electrode active material comprises the following steps: (1) Testing the residual alkali content on the surface of the layered oxide positive electrode material to confirm the formula amount of the fluoride raw material and the layered oxide positive electrode material; (2) After mixing the formulated amount of fluoride raw material and layered oxide positive electrode material, calcining them in an inert atmosphere to obtain the positive electrode active material.

10. The all-solid-state battery according to claim 9, characterized in that: In step (2), the mixing method is stirring, the stirring speed is 100 r / min to 500 r / min, and the stirring time is 0.5 h to 15 h; and / or, In step (2), the calcination temperature is 100° C. to 400° C., and the calcination time is 2 h to 18 h.

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