Composite solid electrolyte, method for preparing the same, and all-solid-state battery

Abstract

The application relates to the technical field of all-solid-state batteries, in particular to a composite solid electrolyte, a preparation method thereof and an all-solid-state battery. The preparation method comprises the following steps: placing a sulfide solid electrolyte in a molecular layer deposition reaction chamber, and circulating a precursor and an inert purge gas to perform molecular layer deposition; the precursor comprises a metal-dithiocarbamate, and the general formula of the metal-dithiocarbamate is M(S2CNR2) n , M comprises at least one of Ni, Cu, Fe, Co and Mo; when M is Cu or Fe, a dithio bond is spontaneously formed in the process of molecular layer deposition, thereby generating an organic-inorganic polymer coating layer containing a dithio bond and an -N-CS2 group; when M is Ni, Co or Mo, the preparation method further comprises the following step: performing a sulfuration reaction on the material obtained after the molecular layer deposition, thereby generating a metal sulfide coating layer containing a dithio bond and having a cubic crystal structure. The method can improve the interface stability and cycle life of the composite solid electrolyte.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of all-solid-state batteries, in particular to a composite solid electrolyte, a preparation method thereof and an all-solid-state battery. BACKGROUND

[0002] Sulfide solid electrolytes (SSE) are considered as the ideal choice for the next generation of high-energy-density all-solid-state batteries due to their ultra-high room-temperature ionic conductivity (close to or even better than liquid electrolytes).

[0003] However, sulfide solid electrolytes face severe environmental stability and interface failure problems: first, extreme environmental sensitivity is its biggest weakness, and trace amounts of water vapor in the air can cause severe decomposition, produce highly toxic and flammable H2S gas and cause the electrolyte to powder and fail, which imposes strict requirements on the battery production and storage environment (pain point one: environmental sensitivity). Second, the solid-solid interface problem is prominent: on the one hand, the physical contact between the electrode material and the SSE is poor, forming a high interface impedance (pain point two: interface impedance); on the other hand, in the cycle process, the volume change of the electrode (especially the lithium metal negative electrode) will produce a large stress, which will cause microcracks in the interface and even cause lithium dendrite penetration (pain point three: dendrite penetration), and stress accumulation itself will also damage the interface contact and accelerate battery failure.

[0004] Traditional coating or doping modification methods often have to give up one to get the other, and it is difficult to solve the three major problems at the same time.

[0005] Therefore, the present application is proposed. SUMMARY

[0006] The first object of the present application is to provide a preparation method of a composite solid electrolyte, which can solve the three major problems of interface impedance, dendrite penetration and environmental sensitivity of the existing sulfide solid electrolyte at the same time by depositing metal-dithiocarbamate on the surface of the sulfide solid electrolyte through molecular layer deposition technology: first, the dithio bond (-S-S-) forms a strong covalent bridge with the sulfur atoms on the surface of the sulfide solid electrolyte, building a molecular-level sealing barrier and completely blocking the penetration of water molecules; second, the reversible breaking / recombination characteristics of the dithio bond give the coating layer dynamic self-repairing ability, which can absorb mechanical strain and repair cracks in real time, improving the critical strain tolerance; third, the special crystal structure can provide efficient Li + channels, combined with the flexible adaptation ability of the organic chain segment, providing a ultimate protection scheme of "passivation-conduction-repair" for the sulfide electrolyte, thereby effectively improving the interface stability and cycle life of the composite solid electrolyte.

[0007] The second object of the present application is to provide a composite solid electrolyte, which can improve the interface stability and cycle performance of the battery.

[0008] The third object of the present application is to provide an all-solid-state battery with high capacity, good safety performance, excellent cycle performance and the like.

[0009] In order to achieve the above object of the present application, the following technical solutions are adopted:

[0010] The present application first provides a preparation method of a composite solid-state electrolyte, comprising the following steps: placing a sulfide solid-state electrolyte in a molecular layer deposition reaction chamber, and sequentially circulating a precursor and an inert purge gas into the reaction chamber to perform molecular layer deposition; wherein the precursor comprises a metal-dithiocarbamate, and the general formula of the metal-dithiocarbamate is M(S2CNR2) n wherein M comprises at least one of Ni, Cu, Fe, Co and Mo elements, R comprises -CH3, -C2H5 or -CH(CH3)2, and n is a coordination number matching the valence state of M.

[0011] When M is Cu or Fe, a dithio bond is spontaneously formed during the molecular layer deposition, generating an organic-inorganic polymer coating layer containing a dithio bond and a -N-CS2 group.

[0012] When M is Ni, Co or Mo, the preparation method of the composite solid-state electrolyte further comprises: placing the material obtained after the molecular layer deposition in a mixed atmosphere of H2S and Ar to perform a sulfidation reaction, generating a metal sulfide coating layer containing a dithio bond and having a cubic crystal structure.

[0013] Further, the thickness of the organic-inorganic polymer coating layer is 1-10 nm.

[0014] Further, the thickness of the metal sulfide coating layer is 1-10 nm.

[0015] Further, the metal sulfide coating layer contains Ni-S-S-Ni bridging units, Co-S-S-Co bridging units or Mo-S-S-Mo bridging units.

[0016] Further, n is 2 or 3.

[0017] Further, the pressure of the molecular layer deposition is 0.1-5 Torr.

[0018] Further, the temperature of the molecular layer deposition is 150-200℃.

[0019] Further, the number of cycles is 20-50.

[0020] Further, the deposition rate of the precursor is 0.05-0.2 Å / cycle.

[0021] Further, the pulse time of the precursor in each cycle is 0.5-2.0s.

[0022] Further, the inert purge gas comprises at least one of argon, helium and nitrogen.

[0023] Further, the flow rate of the inert purge gas is 50-200sccm.

[0024] Further, the time of the inert purge gas in each cycle is 30-90s.

[0025] Further, the flow rate of the mixed gas of H2S and Ar is 100-200sccm.

[0026] Further, the volume fraction of H2S in the mixed gas of H2S and Ar is 5%-10%.

[0027] Further, the reaction temperature of the sulfidation reaction is 200-250℃.

[0028] Further, the holding time of the sulfidation reaction is 1-2h.

[0029] Further, the sulfide solid electrolyte comprises at least one of argyrodite sulfide solid electrolyte, Thio-LiSICON sulfide solid electrolyte and Li2S-P2S5 system sulfide solid electrolyte.

[0030] Further, the particle size D50 of the sulfide solid electrolyte is 2-40μm.

[0031] Further, before the deposition of the molecular layer, the sulfide solid electrolyte is subjected to clean pretreatment, and the method of the clean pretreatment comprises: using inert gas to jet and purge the surface of the sulfide solid electrolyte; or using organic solvent to ultrasonically clean the sulfide solid electrolyte; or drying the sulfide solid electrolyte in vacuum.

[0032] The application further provides a composite solid electrolyte prepared by the above preparation method of composite solid electrolyte.

[0033] The application further provides a full solid-state battery comprising the above composite solid electrolyte.

[0034] Compared with the prior art, the application has the following beneficial effects:

[0035] (1) The preparation method of the composite solid-state electrolyte provided by the present application can deposit metal-dithiocarbamate on the surface of the sulfide solid-state electrolyte through molecular layer deposition technology, which can solve the three major pain points of the existing sulfide solid-state electrolyte, namely interface impedance, dendrite penetration, and environmental sensitivity: first, the strong covalent bridge formed by the disulfide bond (-S-S-) and the sulfur atoms on the surface of the sulfide solid-state electrolyte can build a molecular-level sealing barrier to completely block the penetration of water molecules; second, the reversible breaking / recombination characteristics of the disulfide bond can provide dynamic self-repairing ability to the coating layer, which can absorb mechanical strain and repair cracks in real time, thereby improving the critical strain tolerance; third, the special crystal structure can provide efficient Li + channels, and the flexibility of the organic chain segment can provide the sulfide electrolyte with an ultimate protection scheme integrating passivation, conduction, and repair, thereby effectively improving the interface stability and cycle life.

[0036] (2) The preparation method of the composite solid-state electrolyte provided by the present application can control the thickness of the formed coating layer at the nanometer level through MLD technology, thereby forming an ultrathin coating layer.

[0037] (3) The preparation method of the composite solid-state electrolyte provided by the present application can realize the deposition of a nanometer-thick film through MLD technology, and perfectly integrate and produce synergistic effects of the three functions of passivation, conduction, and repair, which not only simultaneously solves the three major core pain points of the sulfide electrolyte, namely environmental sensitivity, high interface impedance, and dendrite penetration / mechanical failure, but also has the characteristics of ultrathin (nanometer level), firm combination with the sulfide solid-state electrolyte (chemical bonding), and good process compatibility (MLD). This “trinity” protective layer (coating layer) provides the sulfide solid-state electrolyte with an unprecedented “ultimate armor”, which significantly improves the interface stability, safety, and long cycle life of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the specific embodiments or the prior art description will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0039] Figure 1 The Raman spectrum of the composite solid-state electrolyte prepared in Example 1 provided by the present application;

[0040] Figure 2 The TEM image of the composite solid-state electrolyte prepared in Example 6 provided by the present application. DETAILED DESCRIPTION

[0041] The technical solutions of the present application will be described clearly and completely below in combination with the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. The specific conditions are not specified in the embodiments, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0042] In a first aspect, the present application provides a preparation method of a composite solid-state electrolyte, or a method for improving the cycle stability of a solid-state electrolyte, comprising the following steps:

[0043] The sulfide solid-state electrolyte is placed in a molecular layer deposition reaction chamber, and a precursor and an inert purge gas are circulated into the chamber in sequence to perform molecular layer deposition (MLD), and after several cycles, an ultra-thin coating layer is formed on the surface of the sulfide solid-state electrolyte.

[0044] The precursor comprises a metal-dithiocarbamate (metal dithiocarbamate, MDTC for short). Metal dithiocarbamate is a class of compounds formed by the combination of dithiocarbamate and metal ions.

[0045] The general formula of the metal-dithiocarbamate is M(S2CNR2) n , wherein M includes at least one of Ni, Cu, Fe, Co and Mo elements, R includes -CH3, -C2H5 or -CH(CH3)2, and n is the coordination number matching the valence state of M.

[0046] That is, the metal-dithiocarbamate includes at least one of Ni(S2CNR2)2, Cu(S2CNR2)2, Fe(S2CNR2)3, Co(S2CNR2)2 and Mo(S2CNR2)3.

[0047] When M is Cu or Fe, a disulfide bond is spontaneously formed during the molecular layer deposition process, generating an organic-inorganic polymer coating layer containing a disulfide bond and a -N-CS2 group.

[0048] When M is Ni, Co or Mo, the preparation method of the composite solid-state electrolyte further comprises: placing the material obtained after the molecular layer deposition in a mixed gas atmosphere of H2S and Ar to perform a sulfidation reaction, generating a metal sulfide coating layer containing a disulfide bond and having a cubic crystal structure (which contains M-S-S-M bridging units).

[0049] wherein MDTC has tunable metal center (e.g. Ni, Cu, Fe, Co, etc.), and the reducible metal center (e.g. Ni, Co, etc.) can be sulfurized to construct cubic Li + Oxidative MDTC (e.g. Cu(S2CNR2)2, Fe(S2CNR2)3, etc.) can spontaneously form disulfide bond during coating process. Specifically, during the heating process of MLD coating, there are protonated sulfur groups (from P-S-H structure formed by the exposure of sulfide solid-state electrolyte to air) on the surface of sulfide solid-state electrolyte, and the precursor can transfer protons to the protonated sulfur groups. Two adsorbed intermediates can form disulfide bond (S-S covalent bond between sulfur atom in MDTC and sulfur atom on the surface of sulfide solid-state electrolyte) through intramolecular oxidation-reduction under heating, and generate sulfurized metal (organic-inorganic polymerized material) containing -S-S- and -NCS2 groups. Reducible MDTC (e.g. Ni(S2CNR2)2, Co(S2CNR2)2, Mo(S2CNR2)3, etc.) can be sulfurized by sulfurized gas blowing, and in-situ generate metal sulfide containing disulfide bond and having cubic structure. The material with such structure has good lithium ion permeability, and can significantly improve the ionic conductivity of the overall electrolyte to ensure the battery performance. The dynamic network of disulfide bond (-S-S-) has a bond energy of 150±10 kJ / mol, and provides self-repairing ability. The cubic metal sulfide channel has a space group of Fm-3m or Fd-3m, and Li+ conductivity is ≥10 -6 S / cm.

[0050] The preparation method of the composite solid-state electrolyte provided by the application innovatively uses molecular layer deposition (MLD) technology to deposit metal-dithiocarbamate (MDTC) on the surface of the sulfide solid-state electrolyte, and realizes revolutionary improvement of the electrochemical performance of the solid-state electrolyte through a triple synergistic mechanism: (1) forming a molecular-level sealing passivation: disulfide bond (-S-S-) forms a strong covalent bridge with the sulfur atom on the surface of the sulfide solid-state electrolyte, constructs a molecular-level sealing barrier, completely blocks the penetration of water molecules (H2S inhibition rate > 99%), fundamentally overcomes the environmental sensitivity of sulfide, and greatly improves the air stability and operation safety. (2) Dynamic self-repairing damage resistance: the abundant disulfide bond has a moderate bond energy (about 150 kJ / mol), and can reversibly break and recombine under the mechanical stress generated during battery cycling, like a "molecular spring". This property endows the coating layer with excellent energy dissipation and real-time self-repairing ability (critical strain tolerance > 8%), which can effectively absorb the interface strain caused by the volume change of the electrode, repair micro-cracks in real time, significantly relieve stress concentration, strongly inhibit dendrite growth and interface contact failure, and greatly improve the cycle life of the battery. (3) The special crystal structure (cubic structure) can provide efficient Li + channels (σ is about 10 -6The flexibility of the organic segment combined with the adaptability of the metal sulfide segment provides a "passivation-conduction-repair" integrated protection solution for the sulfide electrolyte, which can effectively improve the interface stability and the cycle life of the battery.

[0051] In addition, the thickness of the formed coating layer can be controlled at the nanometer level by using the MLD technology, and an ultra-thin coating layer is formed.

[0052] The present application utilizes the unique chemical structure (especially the rich disulfide bond-S-S-) and the controllable metal center (such as Ni, Cu, Fe, Co, etc.) to realize the integration of the "passivation-conduction-repair" triple synergistic function through the atomic level precision control of MLD. This ultra-thin, dense and chemically bonded coating layer film with the sulfide solid electrolyte provides a new way to solve the inherent defects of the sulfide electrolyte, significantly improves the interface stability, safety and long cycle life (>300 stable cycles) of the battery, and greatly promotes the process of sulfide-based all-solid-state batteries from the laboratory to practical application.

[0053] In some specific embodiments, the thickness of the organic-inorganic polymer coating layer is 1-10 nm, including but not limited to any one of 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or a range value between any two of them; preferably 2-5 nm. To balance the protection and ion transmission performance.

[0054] In some specific embodiments, the thickness of the metal sulfide coating layer is 1-10 nm, including but not limited to any one of 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or a range value between any two of them; preferably 2-5 nm. To balance the protection and ion transmission performance. If the coating layer is too thick, it will cause the ionic conductivity of the electrolyte to be too low, thereby affecting the battery performance.

[0055] In some specific embodiments, the metal sulfide coating layer contains Ni-S-S-Ni bridging units, Co-S-S-Co bridging units or Mo-S-S-Mo bridging units, and has an ion channel microstructure.

[0056] In some specific embodiments, the bond length of the cubic crystal metal sulfide in the metal sulfide coating layer is 2.00-2.05 Å, the interlayer spacing is ≥6.0 Å, and the Li + The diffusion barrier is ≤0.2 eV.

[0057] In some specific embodiments, the construction of the disulfide bond dynamic network satisfies: the disulfide bond density is ≥10 21 bonds / cm 3; reversible breaking / recombination occurs during charge and discharge, critical strain tolerance > 8%, self-repair response time < 10s, and dynamic self-repair mechanism.

[0058] In some embodiments, n is 2 or 3.

[0059] In some embodiments, the pressure of the molecular layer deposition is 0.1-5 Torr, including but not limited to any one of 0.1 Torr, 0.5 Torr, 1 Torr, 2 Torr, 3 Torr, 4 Torr, 5 Torr or a range value between any two of them. The pressure of the molecular layer deposition affects the mean free path and surface mobility of the precursor molecules, thereby determining the compactness, uniformity, crystallinity of the coating layer and its final electrochemical performance.

[0060] In some embodiments, the temperature of the molecular layer deposition is 150-200°C, including but not limited to any one of 150°C, 160°C, 170°C, 180°C, 190°C, 200°C or a range value between any two of them. The temperature of the molecular layer deposition is one of the core parameters for controlling the decomposition path of the precursor, reaction kinetics and final coating layer chemical structure. Different temperatures directly affect the composition, crystallinity, self-repair ability and ion conduction performance of the coating layer by regulating the thermodynamic and kinetic processes.

[0061] In some embodiments, the number of cycles is 20-50, including but not limited to any one of 20, 25, 30, 35, 40, 45, 50 or a range value between any two of them. The number of cycles determines the final thickness of the coating layer, which in turn determines the core functions of the coating layer and the overall performance of the final battery through the influence on ion migration path, interface stress, mechanical protection strength and raw material cost.

[0062] In some embodiments, the deposition rate of the precursor is 0.05-0.2 Å / cycle, including but not limited to any one of 0.05 Å / cycle, 0.1 Å / cycle, 0.15 Å / cycle, 0.2 Å / cycle or a range value between any two of them. The deposition rate is a core index for measuring surface reaction kinetics and film growth quality, which determines the compactness, defect density and final electrochemical performance of the coating layer.

[0063] In some embodiments, the pulse time of the precursor is 0.5-2.0 s, including but not limited to any one of 0.5 s, 0.8 s, 1 s, 1.2 s, 1.5 s, 1.8 s, 2.0 s, or a range between any two of them. The pulse time affects the compactness, uniformity, chemical composition of the coating layer, and the final electrochemical performance.

[0064] In some embodiments, the inert purge gas includes at least one of argon, helium, and nitrogen, preferably argon with a purity of more than 99%.

[0065] In some embodiments, the flow rate of the inert purge gas is 50-200 sccm, including but not limited to any one of 50 sccm, 80 sccm, 100 sccm, 120 sccm, 150 sccm, 180 sccm, 200 sccm, or a range between any two of them.

[0066] In some embodiments, the time of the inert purge gas (i.e., the purge time) is 30-90 s, including but not limited to any one of 30 s, 35 s, 40 s, 45 s, 50 s, 55 s, 60 s, 70 s, 80 s, 90 s, or a range between any two of them.

[0067] In some embodiments, the flow rate of the H2S and Ar mixture is 100-200 sccm, including but not limited to any one of 100 sccm, 120 sccm, 150 sccm, 180 sccm, 200 sccm, or a range between any two of them. The flow rate of the H2S and Ar mixture affects the integrity of the conduction channel and the final electrochemical performance. +

[0068] In some embodiments, the volume fraction of H2S in the H2S and Ar mixture is 5%-10%, including but not limited to any one of 5%, 6%, 7%, 8%, 9%, 10%, or a range between any two of them. The volume fraction of H2S in the H2S and Ar mixture determines the final valence state of the metal center, the type of sulfide product, and the integrity of the conduction channel. +

[0069] ​​In some embodiments, the reaction temperature of the sulfidation reaction is 200-250°C, including but not limited to any one of 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, or a range between any two of them. + electrical conductivity.

[0070] In some embodiments, the holding time of the sulfidation reaction is 1-2h, including but not limited to any one of 1h, 1.5h, 2h, or a range between any two of them.

[0071] In some embodiments, the heating rate of the sulfidation reaction is 1-5°C / min, preferably 2-3°C / min.

[0072] In some embodiments, the sulfidation reaction is carried out in a tube furnace reactor.

[0073] In some embodiments, the ratio of the mixed gas of H2S and Ar to the time of each pulse of the precursor is 1:5-20.

[0074] In some embodiments, the sulfide solid-state electrolyte includes at least one of argyrodite sulfide solid-state electrolyte (such as Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 , Li6PS5Br, etc., but not limited thereto), Thio-LiSICON sulfide solid-state electrolyte (such as Li3PS4, Li 10 GeP2S 12 , Li 10 SnP2S 12 , etc., but not limited thereto), and Li2S-P2S5 system sulfide solid-state electrolyte (including its doped variants).

[0075] In some embodiments, the particle size D50 of the sulfide solid-state electrolyte is 2-40μm, including but not limited to any one of 2μm, 3μm, 5μm, 8μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, or a range between any two of them; preferably 5-10μm, to match the particle size requirement of the sulfide electrolyte in the electrolyte layer in the battery cell.

[0076] In some embodiments, the sulfide solid-state electrolyte is subjected to clean pretreatment to obtain a clean-surface sulfide solid-state electrolyte before the deposition of the molecular layer.

[0077] The cleaning pretreatment method is that inert gas (such as argon or nitrogen, pressure 0.2-0.5 MPa) is sprayed to the surface of the sulfide solid electrolyte to remove impurities.

[0078] Alternatively, the cleaning pretreatment method is that the sulfide solid electrolyte is ultrasonically cleaned in an ultrasonic cleaning tank (power, for example, 100 W, frequency, for example, 40 kHz) by using an organic solvent, wherein the organic solvent includes acetonitrile, tetrahydrofuran or cyclohexane, and the ultrasonic cleaning time can be 10-15 min, but is not limited thereto.

[0079] Alternatively, the cleaning pretreatment method is that the sulfide solid electrolyte is dried in a vacuum oven (for example, temperature 80-100 ℃, vacuum degree ≤10 -3 Pa) for 2-3 h.

[0080] In some specific embodiments, the molecular layer deposition reaction chamber is a stainless steel cavity, and the inner lining is polytetrafluoroethylene (H2S corrosion resistant).

[0081] In some specific embodiments, the molecular layer deposition reaction chamber is equipped with a multi-channel gas delivery system, and the precursors, H2S and inert purge gas are independently controlled.

[0082] In some specific embodiments, the vacuum system of the molecular layer deposition reaction chamber includes a mechanical pump and a molecular pump, and the base vacuum is maintained to be less than 1×10 -6 Torr, and the deposition pressure is 0.1-5 Torr.

[0083] In a second aspect, the present application provides a composite solid electrolyte prepared by the above-mentioned preparation method of the composite solid electrolyte.

[0084] The composite solid electrolyte includes a sulfide solid electrolyte and a coating layer coated on the surface of the sulfide solid electrolyte, wherein the coating layer is an organic-inorganic polymer coating layer containing a disulfide bond and an -N-CS2 group, or a metal sulfide coating layer containing a disulfide bond and having a cubic crystal structure.

[0085] The composite solid electrolyte can simultaneously solve the three major pain points of interface impedance, dendrite penetration and environmental sensitivity of the existing sulfide solid electrolyte, and a battery made of the composite solid electrolyte can improve the interface stability, safety and cycle performance of the battery.

[0086] In a third aspect, the present application provides a full solid-state battery including the above-mentioned composite solid electrolyte.

[0087] The full solid-state battery has the advantages of high capacity, good cycle performance, excellent safety performance and the like.

[0088] In some specific embodiments, the composite solid-state electrolyte is used in a composite cathode (including but not limited to a sulfur composite cathode) of the all-solid-state battery. Specifically, the all-solid-state battery comprises a composite cathode containing a cathode active material (including but not limited to NCM) and the composite solid-state electrolyte.

[0089] In some specific embodiments, the composite solid-state electrolyte is used in an electrolyte layer.

[0090] In some specific embodiments, the anode layer of the all-solid-state battery comprises metal lithium, a silicon-carbon composite anode, etc., but is not limited thereto.

[0091] Embodiments of the present application will be described in detail below with reference to examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If no specific conditions are specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If no manufacturer of the reagent or instrument is specified, it is a conventional product that can be obtained by purchase on the market.

[0092] Example 1

[0093] The preparation method of the composite solid-state electrolyte provided in this example comprises the following steps:

[0094] (1) Li 5.5 PS 4.5 Cl 1.5 The sulfide solid-state electrolyte powder (particle size D50 of 6 μm) was dried in a vacuum oven at 80°C for 2 h for clean pretreatment to obtain the pretreated electrolyte material.

[0095] (2) The pretreated electrolyte material was placed in an MLD reaction cavity (background vacuum degree ≤10 -4 Pa), and copper diethyl dithiocarbamate (Cu 10 H 20 CuN2S4, i.e., Cu[S2CN(C2H5)2]2, was introduced into the reaction cavity, and ultra-high-purity inert purge gas (argon with a purity of ≥99.999%) was introduced after each cycle for molecular layer deposition. During the molecular layer deposition process, a disulfide bond was spontaneously formed. The above steps were repeated for 30 cycles to form an organic-inorganic polymer coating layer containing a disulfide bond and a -N-CS2 group. The thickness of the coating layer was 3.2 nm, and the coating layer was coated on the surface of the sulfide solid-state electrolyte. The temperature for the molecular layer deposition was 170°C, the pressure for the molecular layer deposition was 2 Torr, the deposition rate of the precursor was 0.1 Å / cycle, the pulse time of the precursor was 1.0 s during each cycle, and the flow rate of the inert purge gas was 200 sccm, and the introduction time of the inert purge gas was 90 s during each cycle.

[0096] The organic-inorganic polymer coating layer prepared in this embodiment is not a simple physical adsorption layer, but a copper-sulfur dynamic (dynamic refers to the breakage and recombination of disulfide bonds) network containing disulfide bonds formed through interfacial chemical reaction and thermal induction recombination. The coating layer includes: disulfide bonds (-S-S-) covalently bridged with the surface sulfur atoms of the sulfide solid electrolyte, N-ethyl dithiocarbamic acid (C3H7NS2), and copper sulfide (CuS2) embedded in the network.

[0097] Figure 1 The Raman spectrum of the composite solid electrolyte prepared in this embodiment is as follows: Figure 1 It can be seen that the composite solid electrolyte contains disulfide bonds.

[0098] Example 2

[0099] The preparation method of the composite solid electrolyte provided in this embodiment is basically the same as that of Example 1, except that the sulfide solid electrolyte powder is replaced by Li6PS5Cl.

[0100] Example 3

[0101] The preparation method of the composite solid electrolyte provided in this embodiment is basically the same as that of Example 1, except that the sulfide solid electrolyte powder is replaced by Li3PS4.

[0102] Example 4

[0103] The preparation method of the composite solid electrolyte provided in this embodiment is basically the same as that of Example 1, except that the cobalt diethyl dithiocarbamate precursor is replaced by iron diethyl dithiocarbamate (chemical formula is C 15 H 30 FeN3S6, i.e., Fe[S2CN(C2H5)2]3) precursor.

[0104] Example 5

[0105] The preparation method of the composite solid electrolyte provided in this embodiment includes the following steps:

[0106] (1) The Li 5.5 PS 4.5 Cl 1.5 The sulfide solid electrolyte powder (particle size D50 is 30 μm) is placed in a vacuum oven at 80°C for 2h for cleaning pretreatment to obtain the pretreated electrolyte material.

[0107] (2) The pretreated electrolyte material is placed in an MLD reaction cavity (background vacuum degree ≤10 -4 Pa), and the cobalt diethyl dithiocarbamate (chemical formula is (C5H10 NS2)3Co, i.e. a precursor with a general formula of Co[S2CN(C2H5)2]3, a high-purity inert purge gas (pure argon with a purity of 99%) is introduced after each cycle for molecular layer deposition, and the above steps are repeated for 40 cycles. In the molecular layer deposition, the temperature is 180°C, the pressure is 4 Torr, the deposition rate of the precursor is 0.2 Å / cycle, the pulse time of the precursor in each cycle is 2.0 s, the flow rate of the inert purge gas is 100 sccm, and the introduction time of the inert purge gas in each cycle is 40 s.

[0108] (3) The material obtained after the molecular layer deposition is placed in a mixed gas atmosphere of H2S and Ar for a sulfidation reaction, the flow rate of the mixed gas of H2S and Ar is 100 sccm, the volume fraction of H2S in the mixed gas of H2S and Ar is 8%, the sulfidation reaction temperature is 220°C, the sulfidation reaction time is 2 h, a metal sulfide coating layer Co9S8 (containing a Co-S-S-Co bridging structure) containing a disulfide bond and having a cubic crystal structure is generated, the thickness of the coating layer is 4.6 nm, and the coating layer is coated on the surface of the sulfide solid electrolyte.

[0109] Example 6

[0110] The preparation method of the composite solid electrolyte provided in this example is basically the same as that in Example 5, except that the cobalt diethyldithiocarbamate precursor is replaced by a nickel diethyldithiocarbamate precursor with a chemical formula of C 10 H 20 N2NiS4, i.e. a precursor with a general formula of Ni[S2CN(C2H5)2]2, and the flow rate of the mixed gas of H2S and Ar is replaced by 200 sccm, the volume fraction of H2S in the mixed gas of H2S and Ar is replaced by 10%, the sulfidation reaction temperature is replaced by 230°C, and the sulfidation reaction time is replaced by 1.5 h.

[0111] The metal sulfide coating layer containing a disulfide bond and having a cubic crystal structure formed in this example is Ni3S4 (space group Fm-3m) containing a Ni-S-S-Ni bridging structure.

[0112] Figure 2 The TEM test diagram of the composite solid electrolyte prepared in this example can be observed to have crystal lattice fringes, and the crystal lattice spacing of the 311 crystal plane of cubic Ni3S4 can be clearly seen.

[0113] Example 7

[0114] The preparation method of the composite solid-state electrolyte provided in this example is basically the same as that in Embodiment 6, except that the sulfidation reaction is performed in two steps. Specifically, the flow rate of the mixed gas of H2S and Ar is controlled to be 150 sccm, the volume fraction of H2S in the mixed gas of H2S and Ar is 3%, and the amorphous sulfide layer is generated by sulfidation at 180°C for 30 min. Then, the flow rate of the mixed gas of H2S and Ar is controlled to be 150 sccm, the volume fraction of H2S in the mixed gas of H2S and Ar is 10%, and the crystallization is performed by sulfidation at 230°C for 1 h.

[0115] The metal sulfide coating layer containing disulfide bonds and having a cubic crystal structure formed in this example has a thickness of 5.2 nm, which includes a cubic Ni3S4 phase (ion channel) on the outer surface and an amorphous buffer layer in the middle.

[0116] Embodiment 8

[0117] The preparation method of the composite solid-state electrolyte provided in this example is basically the same as that in Embodiment 5, except that the cobalt diethyldithiocarbamate precursor is replaced by a molybdenum dimethyl dithiocarbamate precursor (chemical formula: C9H 18 N3S6Mo, i.e., Mo[S2CN(CH3)2]3), and the volume fraction of H2S in the mixed gas of H2S and Ar is replaced by 10%, the sulfidation temperature is replaced by 240°C, and the sulfidation time is replaced by 1.5 h.

[0118] The metal sulfide coating layer containing disulfide bonds and having a cubic crystal structure formed in this example is cubic 3R-MoS2 (space group R3m) and contains Mo-S-S-Mo bridging structures.

[0119] Comparative Example 1

[0120] LiPS with a particle size D50 of 10 μm is used. 5.5 PS 4.5 Cl 1.5 Sulfide solid-state electrolyte powder.

[0121] Comparative Example 2

[0122] The preparation method of the composite solid-state electrolyte provided in this example is basically the same as that in Embodiment 1, except that the copper diethyldithiocarbamate precursor is replaced by a tetramethylammonium dithiocarbamate salt (chemical formula: (CH3)4N +- SC(S)N(CH3)2) (without a metal center).

[0123] Comparative Example 3

[0124] The preparation method of the composite solid electrolyte provided by the present comparative example is basically the same as that of Example 1, except that the number of cycles is replaced by 100 times.

[0125] The thickness of the coating layer prepared in the present comparative example is 126 nm.

[0126] Comparative Example 4

[0127] The preparation method of the composite solid electrolyte provided by the present comparative example is basically the same as that of Example 5, except that step (3) is not performed, i.e., no vulcanization reaction occurs.

[0128] Experimental Example

[0129] The composite solid electrolytes prepared in each of the examples and comparative examples were respectively subjected to ion conductivity and air stability (i.e., ion conductivity after exposure) tests, and the test results are shown in Table 1.

[0130] Among them, the ion conductivity test method is as follows: (1) weigh 200 mg of the composite solid electrolyte, pour it into a mold, manually rotate it to be uniform and flat, pressurize to 108 MPa, and keep pressure for 1 min; (2) measure the thickness of the pressed sheet electrolyte with a micrometer and record the data; (3) place the small mold into a metal sleeve, pressurize to 216 MPa, and tighten the 3 knobs on the sleeve; (4) test the impedance of the mold cell with an electrochemical workstation, and record the electrolyte resistance; (5) calculate the ion conductivity of the film at 25°C temperature by the formula σ = L / R x S, wherein σ is the ion conductivity (S / cm), L is the thickness of the pressed composite solid electrolyte (cm), R is the resistance perpendicular to the surface of the electrolyte powder (Ω), and S is the effective electrolyte area (cm 2 ).

[0131] The air stability test method is as follows: 0.2 g of the composite solid electrolyte is spread flat on a 2x2 cm plane, exposed in a -45°C drying room for 1 h, and then its ion conductivity is tested.

[0132] Further, the full solid-state batteries were prepared by using the composite solid-state electrolytes prepared in each example and each comparative example, and 1C specific capacity and cycle capacity retention rate tests were performed, and the specific steps were as follows: (1) according to the mass ratio of positive active material: LPSC solid-state electrolyte (particle size D50 = 1.5 μm): VGCF (vapor grown carbon fiber) = 85: 13: 2, each material was added to a mortar and ground for 10 min as a composite positive electrode material; (2) 100 mg of the composite solid-state electrolyte was weighed and poured into a mold, and manually rotated to be uniform and flat, and pressurized to 108 MPa for 1 min; (3) 20 mg of the above composite positive electrode material was weighed and poured into a mold, and manually rotated to be uniform and flat, and pressurized to 324 MPa for 1 min; (4) an indium sheet (diameter of 10 mm) and a lithium sheet (diameter of 3 mm) were added to the negative electrode side, and pressurized to 36 MPa for 30 s; (5) the small mold was placed in a metal sleeve, and pressurized to 216 MPa, and the three knobs on the sleeve were tightened; (6) first, 3 charge-discharge cycles were performed at 0.1C, and then 200 charge-discharge cycles were performed at 1C. The test results are shown in Table 1.

[0133] Table 1: Performance test results

[0134]

[0135] As can be seen from Table 1, Examples 1-2 and Examples 4-8 all exhibit high discharge capacity and cycle retention rate; although Example 3 has lower discharge capacity, it has higher cycle retention rate, which proves that the method of coating the sulfide electrolyte by MLD improves the interface stability of the electrolyte, effectively alleviating the stress concentration during the charge-discharge process.

[0136] When Comparative Example 1 is not coated, the air stability of the sulfide electrolyte is poor, and the cycle retention rate decreases.

[0137] In Comparative Example 2, the initial ionic conductivity is slightly low due to the coating of the organic matter, and the cycle stability is significantly poor due to the poor ionic conductivity.

[0138] In Comparative Example 3, the coating layer is too thick due to the excessive number of cycles of molecular layer deposition, resulting in low initial ionic conductivity, although the air stability is good, but the electrochemical performance is significantly poor due to the extremely low ionic conductivity.

[0139] In Comparative Example 4, the coating layer is an organic metal film ((diethyldithiocarbamic acid) cobalt, chemical formula (C5H 10 NS2)3Co), which is an ionic insulator, and the ionic conductivity of the sulfide solid-state electrolyte after coating is extremely low, which cannot be applied to solid-state batteries.

[0140] In summary, the application can solve the three major problems of interface impedance, dendrite penetration and environmental sensitivity of the existing sulfide solid electrolyte by depositing metal-dithiocarbamate on the surface of the sulfide solid electrolyte through the molecular layer deposition technology, and effectively improve the interface stability and cycle life of the composite solid electrolyte.

[0141] Although the present application has been illustrated and described with reference to specific embodiments, it is realized that the above-mentioned embodiments are only used to illustrate the technical solutions of the present application, and are not limiting thereof; it should be understood by those skilled in the art that the technical solutions recorded in the above-mentioned embodiments can be modified, or some or all of the technical features can be replaced equivalently without departing from the spirit and scope of the present application; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application; therefore, this means that all these replacements and modifications within the scope of the present application are included in the appended claims.

Claims

1. A method for preparing a composite solid-state electrolyte, characterized by, The method comprises the following steps: placing the sulfide solid electrolyte in a molecular layer deposition reaction chamber, and sequentially circulating a precursor and an inert purge gas into the chamber to perform molecular layer deposition; The precursor comprises a metal-dithiocarbamate salt, and a general formula of the metal-dithiocarbamate salt is M(S2CNR2) n wherein M comprises at least one of Ni, Cu, Fe, Co and Mo elements, R comprises -CH3, -C2H5 or -CH(CH3)2, and n is a coordination number matching a valence state of M. when the M is Cu or Fe, a disulfide bond is spontaneously formed during the molecular layer deposition to generate an organic-inorganic polymer coating layer containing a disulfide bond and an -N-CS2 group; when the M is Ni, Co or Mo, the method further comprises: placing the material obtained after the molecular layer deposition in a mixed atmosphere of H2S and Ar to perform a sulfidation reaction, thereby generating a metal sulfide coating layer containing a disulfide bond and having a cubic crystal structure.

2. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, The thickness of the organic-inorganic polymer coating layer is 1-10 nm. And / or, the thickness of the metal sulfide coating layer is 1-10 nm.

3. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, The metal sulfide coating layer contains Ni-S-S-Ni bridging units, Co-S-S-Co bridging units or Mo-S-S-Mo bridging units.

4. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, The n is 2 or 3.

5. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, At least one of the following conditions is met: (1) the pressure of the molecular layer deposition is 0.1-5 Torr; (2) the temperature of the molecular layer deposition is 150-200℃; (3) the number of cycles is 20-50; (4) the deposition rate of the precursor is 0.05-0.2 Å / cycle; (5) the pulse time of the precursor in each cycle is 0.5-2.0 s.

6. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, At least one of the following conditions is met: (1) the inert purge gas comprises at least one of argon, helium and nitrogen; (2) the flow rate of the inert purge gas is 50-200 sccm; (3) the introduction time of the inert purge gas in each cycle is 30-90 s.

7. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, At least one of the following conditions is met: (1) the flow rate of the mixed gas of H2S and Ar is 100-200 sccm; (2) the volume fraction of H2S in the mixed gas of H2S and Ar is 5%-10%; (3) the reaction temperature of the sulfidation reaction is 200-250℃; (4) the holding time of the sulfidation reaction is 1-2 h.

8. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, At least one of the following conditions is met: (1) the sulfide solid electrolyte comprises at least one of argyrodite-type sulfide solid electrolyte, Thio-LiSICON-type sulfide solid electrolyte and Li2S-P2S5 system sulfide solid electrolyte; (2) the particle size D50 of the sulfide solid electrolyte is 2-40 μm; (3) before the molecular layer deposition, the sulfide solid electrolyte is subjected to clean pretreatment, and the clean pretreatment method comprises: using an inert gas to jet and purge the surface of the sulfide solid electrolyte; or using an organic solvent to ultrasonically clean the sulfide solid electrolyte; or drying the sulfide solid electrolyte in a vacuum.

9. A composite solid-state electrolyte, characterized by, The composite solid electrolyte is prepared by the method of any one of claims 1-8.

10. An all-solid battery, characterized by, The composite solid electrolyte comprises the composite solid electrolyte of claim 9.

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